@article{ahmed_abdelaziz_roberts_2016, title={Preparation of Al2O3/AlF3-supported ruthenium catalysts for the hydrogenolysis of biodiesel-derived crude glycerol}, volume={55}, number={19}, journal={Industrial & Engineering Chemistry Research}, author={Ahmed, T. S. and Abdelaziz, O. Y. and Roberts, G. W.}, year={2016}, pages={5536–5544} }
 @article{hussain_liu_roberts_2012, title={Synthesis of cross-linked, partially neutralized poly(acrylic acid) by suspension polymerization in supercritical carbon dioxide}, volume={51}, number={35}, journal={Industrial & Engineering Chemistry Research}, author={Hussain, Y. A. and Liu, T. and Roberts, G. W.}, year={2012}, pages={11401–11408} }
 @article{zhang_li_cao_shi_liu_yuan_roberts_2011, title={Improved kinetic model of crystallization for isotactic polypropylene induced by supercritical CO(2): Introducing pressure and temperature dependence into the Avrami equation}, volume={50}, number={18}, journal={Industrial & Engineering Chemistry Research}, author={Zhang, R. H. and Li, X. K. and Cao, G. P. and Shi, Y. H. and Liu, H. L. and Yuan, W. K. and Roberts, G. W.}, year={2011}, pages={10509–10515} }
 @article{cain_roberts_kiserow_carbonell_2011, title={Modeling the thermodynamic and transport properties of decahydronaphthalene/propane mixtures: Phase equilibria, density, and viscosity}, volume={305}, ISSN={["0378-3812"]}, DOI={10.1016/j.fluid.2011.02.009}, abstractNote={Abstract The density and viscosity of propane mixed with 66/34 trans/cis -decahydronaphthalene were measured over a wide range of temperatures (323–423 K), pressures (2.5–208 bar), and compositions (0–65 mol% propane). For conditions giving two phases, the composition of the dense phase was measured in addition to the density and viscosity. The modified Sanchez-Lacombe Equation of State (MSLEOS) was used with a single linearly temperature-dependent pseudo-binary interaction parameter to correlate the phase compositions and densities. The compositions and densities of the mixtures were captured well with absolute average deviations between the model and the data of 5.3% and 2.3%, respectively. The mixture viscosities were computed from a free volume model (FVM) by using a single constant binary interaction parameter. Density predictions from the MSLEOS were used as input mixture density values required for the FVM. The FVM was found to correlate well with the mixture viscosity data with an absolute average deviation between the model and the data of 5.7%.}, number={1}, journal={FLUID PHASE EQUILIBRIA}, author={Cain, Nathaniel and Roberts, George and Kiserow, Douglas and Carbonell, Ruben}, year={2011}, month={Jun}, pages={25–33} }
 @article{cain_haywood_roberts_kiserow_carbonell_2011, title={Polystyrene/Decahydronaphthalene/Propane Phase Equilibria and Polymer Conformation Properties from Intrinsic Viscosities}, volume={49}, ISSN={["0887-6266"]}, DOI={10.1002/polb.22282}, abstractNote={Abstract}, number={15}, journal={JOURNAL OF POLYMER SCIENCE PART B-POLYMER PHYSICS}, author={Cain, Nathaniel and Haywood, Alexander and Roberts, George and Kiserow, Douglas and Carbonell, Ruben}, year={2011}, month={Aug}, pages={1093–1100} }
 @article{ahmed_desimone_roberts_2010, title={Continuous precipitation polymerization of vinylidene fluoride in supercritical carbon dioxide: A model for understanding the molecular-weight distribution}, volume={65}, ISSN={["1873-4405"]}, DOI={10.1016/j.ces.2009.08.039}, abstractNote={Abstract Poly(vinylidene fluoride) (PVDF) that is synthesized by precipitation polymerization in supercritical carbon dioxide (scCO2) has a bimodal molecular weight distribution (MWD) and a very broad polydispersity index (PDI) under certain reaction conditions. Different models have been formulated to account for this behavior. This paper presents a homogenous model for a continuous stirred-tank reactor (CSTR) that includes the change of the termination reaction from kinetic control to diffusion control as the chain length of the polymeric radicals increases, and accounts for the change in the termination rate constant with macroradical chain length in the diffusion-controlled region. The model also includes the chain transfer to polymer reaction. Comparison of the model output with experimental data demonstrates that changes of the MWD, including the development of a bimodal distribution, with such reaction conditions as monomer concentration and average residence time are successfully predicted. In addition, the model can capture the occurrence of gelation, which appears to be responsible for a region of inoperability that was observed in the polymerization experiments. The success of this homogeneous model is consistent with recent research demonstrating that the CO2-rich phase is the main locus of polymerization for the precipitation polymerization of vinylidene fluoride and vinylidene fluoride/hexafluoropropylene mixtures in scCO2, at the conditions that have been studied to date.}, number={2}, journal={CHEMICAL ENGINEERING SCIENCE}, author={Ahmed, Tamer S. and DeSimone, Joseph M. and Roberts, George W.}, year={2010}, month={Jan}, pages={651–659} }
 @article{dong_turgman-cohen_roberts_kiserow_2010, title={Effect of Polymer Size on Heterogeneous Catalytic Polystyrene Hydrogenation}, volume={49}, ISSN={["0888-5885"]}, DOI={10.1021/ie1011905}, abstractNote={The effect of polymer coil size on the rate of polystyrene (PS) hydrogenation was studied in a slurry reactor with mixtures of decahydronaphthalene (DHN) and carbon dioxide (CO2) as the solvent for the polymer. The PS coil size was changed by varying the polymer molecular weight from 9300 g/mol to 357 000 g/mol and by varying the CO2 concentration. Using a 5% Pd/5% Ru/SiO2 catalyst, the rate of aromatic ring hydrogenation at 150 °C was found to be strongly dependent on the size of a polymer coil relative to the average pore diameter of the catalyst. Significant pore diffusion limitations, as indicated by values of the Weisz modulus, were observed with increasing polymer molecular weight. Increasing the concentration of CO2 resulted in increased reaction rates, with an improvement of nearly 2 orders of magnitude at the highest PS molecular weight.}, number={22}, journal={INDUSTRIAL & ENGINEERING CHEMISTRY RESEARCH}, author={Dong, Laura Beth and Turgman-Cohen, Salomon and Roberts, George W. and Kiserow, Douglas J.}, year={2010}, month={Nov}, pages={11280–11286} }
 @article{cao_liu_roberts_2010, title={Predicting the Effect of Dissolved Carbon Dioxide on the Glass Transition Temperature of Poly(acrylic acid)}, volume={115}, ISSN={["1097-4628"]}, DOI={10.1002/app.31278}, abstractNote={Abstract}, number={4}, journal={JOURNAL OF APPLIED POLYMER SCIENCE}, author={Cao, Gui-Ping and Liu, Tao and Roberts, George W.}, year={2010}, month={Feb}, pages={2136–2143} }
 @article{kim_kim_kim_ahmed_dong_roberts_oh_2010, title={The effect of prepolymer crystallinity on solid-state polymerization of poly(bisphenol A carbonate)}, volume={51}, number={12}, journal={Polymer}, author={Kim, J. and Kim, Y. J. and Kim, J. D. and Ahmed, T. S. and Dong, L. B. and Roberts, G. W. and Oh, S. G.}, year={2010}, pages={2520–2526} }
 @book{roberts_2009, title={Chemical reactions and chemical reactors}, publisher={Hoboken, NJ: John Wiley & Sons}, author={Roberts, George W.}, year={2009} }
 @article{kim_dong_kiserow_roberts_2009, title={Complex Effects of the Sweep Fluid on Solid-State Polymerization: Poly(bisphenol A carbonate) in Supercritical Carbon Dioxide}, volume={42}, ISSN={["1520-5835"]}, DOI={10.1021/ma802193q}, abstractNote={The effects of the sweep fluid on solid-state polymerization (SSP) of poly(bisphenol A carbonate) (BPA-PC) were investigated. Prepolymers with two different number-average molecular weights, PCP6C (Mn = 3800 g/mol) and PCP9C (Mn = 2400 g/mol), were synthesized using melt transesterification. Solid-state polymerization of these prepolymers was carried out at temperatures in the range of 150−190 °C with supercritical carbon dioxide (scCO2) and N2 as the sweep fluids. It was found that scCO2 at 207 bar could either increase or decrease the rate of SSP relative to the rate in atmospheric N2, depending on the prepolymer molecular weight. At 190 °C, the molecular weights of the polymers synthesized from the higher-molecular-weight prepolymer (PCP6C) were higher with scCO2 as the sweep fluid compared to those of the polymers synthesized with N2. In contrast, at the same temperature of 190 °C, the molecular weights of the polymers synthesized from the lower-molecular-weight prepolymer (PCP9C) were lower with scCO...}, number={7}, journal={MACROMOLECULES}, author={Kim, Jaehoon and Dong, Laura Beth and Kiserow, Douglas J. and Roberts, George W.}, year={2009}, month={Apr}, pages={2472–2479} }
 @article{dong_carbonell_roberts_kiserow_2009, title={Determination of polystyrene-carbon dioxide-decahydronaphthalene solution properties by high pressure dynamic light scattering}, volume={50}, ISSN={["1873-2291"]}, DOI={10.1016/j.polymer.2009.09.069}, abstractNote={The diffusion coefficients of polystyrene (PS) in decahydronaphthalene (DHN) and in solutions of carbon dioxide (CO2) and DHN were measured for dilute PS solutions over a range of temperatures and CO2–DHN ratios using high pressure dynamic light scattering. Infinite dilution diffusion coefficients (D0) of PS and dynamic second virial coefficients (kD) were determined for essentially monodisperse 308 kDa PS. At a system pressure of 20.7 MPa, PS diffusion coefficients increased by a factor of 2.5, and the activation energy of diffusion decreased by approximately 16% when DHN was “expanded” with 44 mol% CO2. However, the hydrodynamic radius of PS at a given temperature was not particularly sensitive to the CO2 concentration. Solvent quality, as measured by kD, decreased at higher CO2 concentrations. The addition of CO2 to polymer solutions may offer a way to “tune” the properties of the solution to facilitate the heterogeneous catalytic hydrogenation of polymers.}, number={24}, journal={POLYMER}, author={Dong, Laura Beth and Carbonell, Ruben G. and Roberts, George W. and Kiserow, Douglas J.}, year={2009}, month={Nov}, pages={5728–5732} }
 @misc{du_kelly_roberts_desimone_2009, title={Fluoropolymer synthesis in supercritical carbon dioxide}, volume={47}, ISSN={["1872-8162"]}, DOI={10.1016/j.supflu.2008.11.011}, abstractNote={Herein we review the environmentally friendly synthesis of fluorinated polymers in supercritical carbon dioxide (scCO2). Historically, many high-performance fluorinated materials are commercially synthesized in aqueous media using fluorinated surfactants or in non-aqueous conditions using fluorinated solvents. Our group has pioneered both the homogeneous and heterogeneous polymerization of fluorinated monomers in scCO2. This review includes discussions on the synthesis of main-chain and side-chain fluoropolymers conducted via a chain-growth or continuous process. Specific materials consist of acrylate- and styrene-based systems, poly(vinyl ether)s, tetrafluoroethylene- and vinylidenefluoride-based, as well as novel fluorinated elastomers and thermoplastics.}, number={3}, journal={JOURNAL OF SUPERCRITICAL FLUIDS}, author={Du, Libin and Kelly, Jennifer Y. and Roberts, George W. and DeSimone, Joseph M.}, year={2009}, month={Jan}, pages={447–457} }
 @article{ahmed_desimone_roberts_2009, title={Kinetics of the Homopolymerization of Vinylidene Fluoride and Its Copolymerization with Hexafluoropropylene in Supercritical Carbon Dioxide: The Locus of Polymerization}, volume={42}, ISSN={0024-9297 1520-5835}, url={http://dx.doi.org/10.1021/ma801911j}, DOI={10.1021/ma801911j}, abstractNote={In previous studies, the continuous polymerization of vinylidene fluoride (VF2) and mixtures of VF2 with hexafluoropropylene (HFP) was carried out in supercritical carbon dioxide (scCO2) using a continuous stirred-tank reactor (CSTR). Most of the polymerizations were heterogeneous; i.e., polymer particles precipitated during the reaction. However, some were homogeneous, especially at higher HFP concentrations. In this study, the data from the earlier experiments have been tested against three kinetic models to determine the primary locus of the heterogeneous polymerizations. The first model, the “solution polymerization” model, is based on the assumption that all of the polymerization reactions take place in the continuous, CO2-rich phase, with no reaction in the polymer phase. In the second model, the “surface polymerization” model, chain initiation occurs in the continuous phase, while chain propagation and termination occur in a thin zone on the surface of the polymer particles. The third model, the “i...}, number={1}, journal={Macromolecules}, publisher={American Chemical Society (ACS)}, author={Ahmed, Tamer S. and DeSimone, Joseph M. and Roberts, George W.}, year={2009}, month={Jan}, pages={148–155} }
 @article{kelly_kim_roberts_lamb_2008, title={Characterization of Pd/gamma-Al2O3 Catalysts Prepared Using [Pd(hfac)(2)] in Liquid CO2}, volume={49}, ISSN={["1572-9028"]}, DOI={10.1007/s11244-008-9075-2}, number={3-4}, journal={TOPICS IN CATALYSIS}, author={Kelly, M. Jason and Kim, Jaehoon and Roberts, George W. and Lamb, H. Henry}, year={2008}, month={Aug}, pages={178–186} }
 @article{kim_kelly_lamb_roberts_kiserow_2008, title={Characterization of palladium (Pd) on alumina catalysts prepared using liquid carbon dioxide}, volume={112}, ISSN={["1932-7447"]}, DOI={10.1021/jp711495n}, abstractNote={Palladium (II) hexafluoroacetylacetonate (Pd(hfac)2) dissolved in liquid carbon dioxide (L-CO2) was used to deposit Pd nanoparticles onto low-surface-area α-alumina (13 m2/g) and high-surface-area γ-alumina (207 m2/g). These nanoparticles were prepared by contacting Pd(hfac)2 dissolved in L-CO2 with the alumina at 6.9 MPa and 28.5 °C and then slowly venting gaseous CO2 until L-CO2 was completely evaporated. After depressurization to remove the CO2 and unabsorbed Pd(hfac)2, the impregnated Pd(hfac)2 was reduced in hydrogen at a relatively low temperature of 75 °C. The adsorption isotherm of Pd(hfac)2 on γ-alumina suggests a weak interaction between the organometallic compound and the support. The average Pd particle size on the low-surface-area α-alumina, measured by scanning electron microscopy, increased from 13.1 ± 3.5 to 59.9 ± 11.3 nm, and the metal dispersion, measured by pulsed CO chemisorption, decreased from 11 to 3%, as the Pd loading on the alumina was increased from 0.15 to 1.54 wt %. With the ...}, number={28}, journal={JOURNAL OF PHYSICAL CHEMISTRY C}, author={Kim, Jaehoon and Kelly, M. Jason and Lamb, H. Henry and Roberts, George W. and Kiserow, Douglas J.}, year={2008}, month={Jul}, pages={10446–10452} }
 @article{ahmed_desimone_roberts_2008, title={Continuous copolymerization of vinylidene fluoride with hexafluoropropylene in Supercritical carbon dioxide: High-hexafluoropropylene-content amorphous copolymers}, volume={41}, ISSN={["0024-9297"]}, DOI={10.1021/ma702526u}, abstractNote={Copolymerization of vinylidene fluoride (VF2) and hexafluoropropylene (HFP) was carried out in supercritical carbon dioxide using a continuous stirred tank reactor. Three different HFP/VF2 molar feed ratios were studied, 59:41, 66:34, and 73:27, giving rise to amorphous copolymers containing about 23, 26, and 30 mol % HFP, respectively. The experiments were carried out at 40 °C with pressures in the range of 207–400 bar using perfluorobutyryl peroxide as the free radical initiator. Depending on the copolymer composition, the molecular weight, and the reaction pressure, either a homogeneous (solution) or a heterogeneous (precipitation) polymerization was observed. The effects of feed monomer concentration and reaction pressure were explored at otherwise constant conditions. The rate of polymerization (Rp) and the number-average molecular weight (Mn) increased linearly with the total monomer concentration, independent of the mode of polymerization, i.e., homogeneous or heterogeneous. Both Rp and Mn increase...}, number={9}, journal={MACROMOLECULES}, author={Ahmed, Tamer S. and DeSimone, Joseph M. and Roberts, George W.}, year={2008}, month={May}, pages={3086–3097} }
 @article{spivey_wilcox_roberts_2008, title={Direct utilization of carbon dioxide in chemical synthesis: Vinyl acetate via methane carboxylation}, volume={9}, ISSN={["1566-7367"]}, DOI={10.1016/j.catcom.2007.08.023}, abstractNote={The use of CO2 as a reactant for chemical synthesis generally is limited by the unfavorable equilibrium that results from the large, negative free energy of formation of CO2. Here, we report the direct catalytic synthesis of vinyl acetate from an equimolar gaseous mixture of CO2 + CH4 + C2H2 at 1 atm and temperatures between 200 and 400 °C. We are not aware of any previous reports of this reaction, which appears to proceed in two steps: (1) acetic acid is formed by the reaction of CO2 and CH4; (2) acetic acid then reacts with acetylene to form vinyl acetate. The formation of acetic acid from CO2 and CH4 is very unfavorable thermodynamically. However, the reaction of acetic acid with acetylene shifts the overall equilibrium to the right. Although 5% Pt/Al2O3 catalyzes the formation of vinyl acetate from the mixture of CO2 + CH4 + C2H2, the most effective catalyst system is an admixture of 5% Pt/Al2O3, which has been shown to catalyze the direct formation of acetic acid from CH4 + CO2, and Zn acetate/carbon, which is known to catalyze the formation of vinyl acetate from acetic acid and acetylene.}, number={5}, journal={CATALYSIS COMMUNICATIONS}, author={Spivey, James J. and Wilcox, Esther M. and Roberts, George W.}, year={2008}, month={Mar}, pages={685–689} }
 @article{kim_roberts_kiserow_2008, title={Effect of prepolymer molecular weight on solid state polymerization of poly(bisphenol a carbonate) with nitrogen as a sweep fluid}, volume={46}, ISSN={["0887-624X"]}, DOI={10.1002/pola.22819}, abstractNote={Abstract}, number={15}, journal={JOURNAL OF POLYMER SCIENCE PART A-POLYMER CHEMISTRY}, author={Kim, Jaehoon and Roberts, George W. and Kiserow, Douglas J.}, year={2008}, month={Aug}, pages={4959–4969} }
 @article{kim_gracz_roberts_kiserow_2008, title={Spectroscopic analysis of poly(bisphenol A carbonate) using high resolution C-13 and H-1 NMR}, volume={49}, ISSN={["0032-3861"]}, DOI={10.1016/j.polymer.2007.11.046}, abstractNote={Quantitative structural and end-group analysis of poly(bisphenol A carbonate) (BPA-PC) was carried out and number average molecular weights (Mn) were determined using 125.76 MHz 13C and 500.13 MHz 1H nuclear magnetic resonance (NMR) spectroscopy. BPA-PC with a wide range of end-group ratios (0.26–2.83) and number average molecular weights (1500–9000 g/mol) was synthesized using melt transesterification by changing the initial monomer (bisphenol A and diphenyl carbonate) ratios and reaction conditions. Results of the NMR analysis for the melt-polymerized samples were compared with those of a commercial BPA-PC with a Mn of 16,000 g/mol. It was demonstrated that NMR spectroscopy is a very selective and accurate method not only for quantification of both phenolic and phenyl chain end-groups but also in the structural analysis of main chain groups. Extremely small concentrations of end-groups (∼0.02 per repeating unit) were analyzed. In addition, NMR spectroscopy was found to be an excellent tool for detecting residual monomer and the presence of the reaction byproduct (phenol). The molecular weights that were determined using NMR end-group quantification agreed well with the molecular weights measured by gel-permeation chromatography (GPC).}, number={2}, journal={POLYMER}, author={Kim, Jaehoon and Gracz, Hanna S. and Roberts, George W. and Kiserow, Douglas J.}, year={2008}, month={Jan}, pages={394–404} }
 @article{ahmed_desimone_roberts_2007, title={Continuous copolymerization of vinylidene fluoride with hexafluoropropylene in Supercritical carbon dioxide: Low hexafluoropropylene content semicrystalline copolymers}, volume={40}, ISSN={["0024-9297"]}, DOI={10.1021/ma0713613}, abstractNote={The copolymerization of vinylidene fluoride with hexafluoropropylene (HFP) was carried out in supercritical carbon dioxide by precipitation polymerization using a continuous stirred tank reactor. Copolymers with ca. 10 mol % HFP were synthesized at 40 °C and pressures in the range of 207−400 bar using perfluorobutyryl peroxide as the free radical initiator. The effects of feed monomer concentration and reaction pressure were both explored at otherwise constant conditions. The rate of polymerization (Rp) and the number-average molecular weight (Mn) increased linearly with the total monomer concentration up to about 6 M, the highest concentration investigated. The Rp and the Mn were strongly influenced by the reaction pressure. An 80% increase in both Rp and Mn was observed when the reaction pressure rose from 207 to 400 bar. The molecular weight distributions of the synthesized copolymer showed a long tail that increased to become a broad shoulder with increasing total monomer concentration. This tail incr...}, number={26}, journal={MACROMOLECULES}, author={Ahmed, Tamer S. and DeSimone, Joseph M. and Roberts, George W.}, year={2007}, month={Dec}, pages={9322–9331} }
 @article{mahammad_roberts_khan_2007, title={Cyclodextrin - hydrophobe complexation in associative polymers}, volume={3}, ISSN={["1744-683X"]}, DOI={10.1039/b700167c}, abstractNote={We develop a new rheology-based method to study the complexation of cyclodextrins with hydrophobes in hydrophobically modified associative polymer solutions. The associative polymers have comb-like structure with hydrophobic groups randomly attached to the polymer backbone. Intermolecular interactions between the hydrophobic groups form a transient network resulting in thickening of the polymer solutions. On addition of cyclodextrins (CD) to the solution, the hydrophobes are encapsulated within the hydrophobic cavity of the cyclodextrins. This reduces viscoelastic properties of the polymer solution by several orders of magnitude. We exploit the existence of a dynamic equilibrium between CD adsorbed to the hydrophobes and free CD in the solution, to develop a rheology-based Langmuir-type adsorption isotherm for estimating the binding constant for molecular complexation. The model is based on the assumption that the amount of CD adsorbed is proportional to the reduction in elastic modulus of the polymer solution due to the encapsulation of the network junctions by CD. The effects of temperature on binding constant are studied to estimate the enthalpy and entropy of complexation. Experiments are conducted with both α-and β-CD at different polymer concentrations and temperatures to estimate the relative strength of binding of the CDs. At a given temperature and a polymer concentration, α-CD has a lower binding constant compared to that of β-CD, indicating higher affinity of α-CD to adsorb onto the hydrophobes. Since α-CDs have a smaller ring size, they can snugly fit to the hydrophobes and the association leads to higher enthalpy and entropy change.}, number={9}, journal={SOFT MATTER}, author={Mahammad, Shamsheer and Roberts, George W. and Khan, Saad A.}, year={2007}, pages={1185–1193} }
 @article{chin_roberts_ollis_2007, title={Kinetic Modeling of photocatalyzed soot oxidation on titanium dioxide thin films}, volume={46}, ISSN={["0888-5885"]}, DOI={10.1021/ie070083t}, abstractNote={Recent research [Mills et al. Chemosphere 2006, 64, 1032−1035; Lee and Choi J. Phys. Chem. B 2002, 106, 11818−11822] has demonstrated photocatalytic oxidation of “soot” by titanium dioxide thin films. However, little attention has been paid to developing kinetic models of photocatalyzed soot destruction. We develop here a series/parallel kinetic model for soot oxidation and use it to analyze the CO2 data of Mills et al. and the mass loss data of Lee and Choi. The model assumes two oxidation pathways:  a single step yielding CO2 directly and a serial sequence through a solid intermediate species, which is subsequently oxidized to CO2. We extend this simple model to include variable O2 partial pressure, which is used to evaluate the initial CO2 data of Lee and Choi. These models fit the experimental CO2 data of Mills et al. and Lee and Choi well. The simple kinetic model also describes the mass loss data of Lee and Choi for the front mode of sample irradiation.}, number={23}, journal={INDUSTRIAL & ENGINEERING CHEMISTRY RESEARCH}, author={Chin, Paul and Roberts, George W. and Ollis, David F.}, year={2007}, month={Nov}, pages={7598–7604} }
 @misc{royer_roberts_2006, title={Continuous method and apparatus for separating polymer from a high pressure carbon dioxide fluid stream}, volume={7,063,839}, publisher={Washington, DC: U.S. Patent and Trademark Office}, author={Royer, J. R. and Roberts, G. W.}, year={2006} }
 @article{ahmed_desimone_roberts_2006, title={Copolymerization of vinylidene fluoride with hexafluoropropylene in supercritical carbon dioxide}, volume={39}, ISSN={["1520-5835"]}, DOI={10.1021/ma051268j}, abstractNote={Vinylidene fluoride (VDF) and hexafluoropropylene (HFP) were copolymerized in supercritical carbon dioxide (scCO2) by a free radical mechanism with and without the use of a fluorinated graft poly(methyl vinly ether-alt-maleic anhydride) copolymer (F-g-PMVE-MA) stabilizer. A series of VDF−HFP copolymers, with composition varying from 1.46 to 25.62 mol % (HFP in copolymer), were synthesized with yields in the range 25−54 wt %. The reactivity ratios of VDF and HFP in CO2 were estimated as rVDF = 5.13 and rHFP ≈ 0. The weight-average molecular weights of copolymers, relative to narrow standard poly(methyl methacrylate), were between 35 and 188 kg/mol, and the polydispersity was between 1.4 and 3.1. A solubility study demonstrated that VDF−HFP copolymers were more soluble in CO2 than in VDF or HFP. In addition, F-g-PMVE-MA was found to act as a stabilizer for the copolymerization of VDF and HFP in scCO2, leading to products with higher molecular weight and improved morphology.}, number={1}, journal={MACROMOLECULES}, author={Ahmed, TS and DeSimone, JM and Roberts, GW}, year={2006}, month={Jan}, pages={15–18} }
 @article{liu_desimone_roberts_2006, title={Cross-linking polymerization of acrylic acid in supercritical carbon dioxide}, volume={47}, ISSN={["0032-3861"]}, DOI={10.1016/j.polymer.2006.03.103}, abstractNote={Cross-linking polymerization of acrylic acid in supercritical carbon dioxide (scCO2) was studied in a batch reactor at 50 °C and 207 bar with either triallyl pentaerythritol ether or tetraallyl pentaerythritol ether as the cross-linker and with 2,2′-azobis(2,4-dimethyl-valeronitrile) as the free radical initiator. All polymers were white, dry, fine powders. Scanning electron microscopy showed that the morphology of the polymer particles was not affected by cross-linking. As the cross-linker concentration was increased, the polymer glass transition temperature first decreased, then increased. Water-soluble and water-insoluble polymers were synthesized by adjusting the cross-linker concentration. Viscosity measurements showed that the polymer thickening effect strongly depended on the degree of cross-linking. Finally, cross-linking polymerization of acrylic acid in scCO2 was carried out in a continuous stirred tank reactor. The use of cross-linker decreased the monomer conversion in this system.}, number={12}, journal={POLYMER}, author={Liu, Tao and DeSimone, Joseph M. and Roberts, George W.}, year={2006}, month={May}, pages={4276–4281} }
 @article{mahammad_prud'homme_roberts_khan_2006, title={Kinetics of enzymatic depolymerization of guar galactomannan}, volume={7}, ISSN={["1525-7797"]}, DOI={10.1021/bm060333+}, abstractNote={A new mathematical model based on Michaelis Menten (MM) kinetics is developed to predict the changes in molecular weight distribution (MWD) during the enzymatic depolymerization of guar galactomannan. The model accounts for the effect of branching by considering the guar molecule as a substrate having three types of bonds with different MM kinetic parameters. The overall kinetics of the enzymatic reactions then can be represented in terms of composite kinetic parameters that are functions of the MM parameters for the individual bonds. The depolymerization is assumed to follow a random scission mechanism, in which an enzyme randomly attacks the substrate molecule at any one of the three types of bonds, and leaves the substrate on cleavage of the bond. Expressions for the variation in molecular weights during depolymerization are developed by applying moment generating techniques to the kinetic model. The model is evaluated against the complete MWD obtained using gel permeation chromatography. During the initial stages of depolymerization, the enzymatic reaction is in the zero-order regime of MM kinetics and the polydispersity index (PDI) increases with time. Subsequently, the PDI decreases as the depolymerization tends to follow first order kinetics. We also show that for a zero-order, random or nonrandom scission, the variation of PDI with time can exhibit a maximum. These analyses confirm that an increase in PDI during the depolymerization is not necessarily due to nonrandom scission, as previously concluded.}, number={9}, journal={BIOMACROMOLECULES}, author={Mahammad, Shamsheer and Prud'homme, Robert K. and Roberts, George W. and Khan, Saad A.}, year={2006}, month={Sep}, pages={2583–2590} }
 @article{liu_desimone_roberts_2006, title={Kinetics of the precipitation polymerization of acrylic acid in supercritical carbon dioxide: The locus of polymerization}, volume={61}, ISSN={["1873-4405"]}, DOI={10.1016/j.ces.2005.11.052}, abstractNote={The precipitation polymerization of acrylic acid (AA) has been carried out at 50 and 70∘C in supercritical carbon dioxide (scCO2), using a continuous stirred-tank reactor. Three kinetic models are compared with experimental data on the rate of polymerization and the viscosity-average molecular weight. The first model, the “solution polymerization” model, is based on the assumption that all reactions: initiation, propagation, and termination, take place in the fluid phase; no reaction takes place in the polymer phase. In the second model, the “surface polymerization” model, chain initiation is assumed to occur in the fluid phase, whereas chain propagation and termination occur in a thin zone on the surface of the polymer particles. The third model, the “interior polymerization” model, is similar to the “surface polymerization” model, except that chain propagation and chain termination take place uniformly throughout each polymer particle. Monomer is assumed to be in phase equilibrium between the supercritical fluid and the polymerization zone. The surface polymerization and interior polymerization models both provide a much better description of the experimental data than the solution polymerization model. This suggests that a significant portion of AA polymerization takes place in the polymer phase, when scCO2 is the reaction medium. However, the data do not support a choice between the surface and interior polymerization models.}, number={10}, journal={CHEMICAL ENGINEERING SCIENCE}, author={Liu, T and DeSimone, JM and Roberts, GW}, year={2006}, month={May}, pages={3129–3139} }
 @article{liu_garner_desimone_roberts_bothun_2006, title={Particle formation in precipitation polymerization: Continuous precipitation polymerization of acrylic acid in supercritical carbon dioxide}, volume={39}, ISSN={["0024-9297"]}, DOI={10.1021/ma061260p}, abstractNote={The morphology of the polymer produced during continuous precipitation polymerization of acrylic acid in supercritical carbon dioxide (scCO2) varied significantly with reaction conditions. Three different morphologies were observed:  a coagulum of primary particles with diameters of 100−200 nm, irregular particles with diameters of 5−20 μm, and spheres with diameters of 10−100 μm. To explore the variables that control particle morphology, the glass transition temperature (Tg) of poly(acrylic acid) (PAA) was measured at several CO2 pressures using high-pressure differential scanning calorimetry. Sorption of scCO2 into PAA also was measured at various temperatures and pressures with a quartz crystal microbalance. Chow's equation described the Tg reduction by CO2 quite accurately. Formation of large spherical particles of PAA was favored when the polymer molecular weight was relatively low and when the polymerization temperature was well above Tg.}, number={19}, journal={MACROMOLECULES}, author={Liu, Tao and Garner, Pamela and DeSimone, Joseph M. and Roberts, George W. and Bothun, Geoffrey D.}, year={2006}, month={Sep}, pages={6489–6494} }
 @article{chin_sun_roberts_spivey_2006, title={Preferential oxidation of carbon monoxide with iron-promoted platinum catalysts supported on metal foams}, volume={302}, ISSN={["1873-3875"]}, DOI={10.1016/j.apcata.2005.11.030}, abstractNote={A series of 5 wt% Pt/0.5 wt% Fe/γ-Al2O3 catalysts supported on metal foams of different geometries were synthesized and tested for preferential oxidation of a low CO concentration in the presence of a high H2 concentration. The catalysts were tested in a fixed bed adiabatic reactor at a total pressure of 0.2 MPa (absolute) to simulate fuel processor operating pressure. The inlet temperature was varied from 80 °C to 170 °C, and the gas hourly space velocity ranged from 5000 h−1 to 45,000 h−1. The inlet gas composition to the reactor reproduced that of the effluent stream from the water-gas-shift reactor in a typical fuel processor: H2 42%, CO2 9%, H2O 12%, CO 1.0%, O2 0.5–1.0%, and N2 35–35.5%. The geometry of a foam is characterized by the volume fraction of solid material (cell density) and by the number of pores per inch. The catalysts with lower cell densities generally exhibited higher CO conversions and selectivities. Under most operating conditions, the CO conversion and selectivity of the best metal foam catalysts were comparable to those of a 400 cells per square inch, ceramic straight-channel monolith with the same nominal catalyst loading. Both the reverse water-gas-shift (r-WGS) reaction and transport resistances affected the performance of these catalysts. Under adiabatic conditions, the r-WGS reaction made it impossible to achieve low outlet CO concentrations. The effects of space velocity and linear velocity were studied independently using various catalyst lengths and volumetric gas flow rates. At a constant space velocity, the CO conversion increased with higher linear velocities, suggesting a significant mass transfer resistance between the bulk gas and the catalyst surface.}, number={1}, journal={APPLIED CATALYSIS A-GENERAL}, author={Chin, P and Sun, XL and Roberts, GW and Spivey, JJ}, year={2006}, month={Mar}, pages={22–31} }
 @article{kim_roberts_kiserow_2006, title={Supported Pd catalyst preparation using liquid carbon dioxide}, volume={18}, ISSN={["0897-4756"]}, DOI={10.1021/cm061440d}, abstractNote={Uniform Pd crystallites were formed on native silicon oxide by depositing Pd(hfac)2 from liquid carbon dioxide and subsequently reducing in hydrogen at a relatively low temperature of 150 °C.}, number={20}, journal={CHEMISTRY OF MATERIALS}, author={Kim, Jaehoon and Roberts, George W. and Kiserow, Douglas J.}, year={2006}, month={Oct}, pages={4710–4712} }
 @article{whittier_xu_zanten_kiserow_roberts_2006, title={Viscosity of polystyrene solutions expanded with carbon dioxide}, volume={99}, ISSN={["1097-4628"]}, DOI={10.1002/app.22483}, abstractNote={Abstract}, number={2}, journal={JOURNAL OF APPLIED POLYMER SCIENCE}, author={Whittier, RE and Xu, DW and Zanten, JH and Kiserow, DJ and Roberts, GW}, year={2006}, month={Jan}, pages={540–549} }
 @article{cotugno_di maio_mensitieri_iannace_roberts_carbonell_hopfenberg_2005, title={Characterization of microcellular biodegradable polymeric foams produced from supercritical carbon dioxide solutions}, volume={44}, ISSN={["0888-5885"]}, DOI={10.1021/ie049445c}, abstractNote={The formation of foams of biodegradable poly(e-caprolactone) (PCL) from CO2 solutions in molten PCL was investigated. This study included characterization of the CO2 diffusion and equilibrium solubility in molten PCL in contact with supercritical CO2 (scCO2). Experiments were performed at 70, 80, and 90 °C at CO2 pressures up to 25 MPa. The effective mutual diffusivity of CO2 in molten PCL was measured as a function of the CO2 pressure. The data revealed a dramatic increase in apparent effective diffusivity at elevated pressure, likely related to the formation of fluid bubbles, phase-separated from the previously homogeneous, molten PCL solution of CO2. Microcellular PCL foams were produced by starting from an equilibrium CO2−PCL solution at 70 °C over a wide range of initial pressures (from 6.9 to 32 MPa) by quenching down to foaming temperatures (from 24 to 30 °C) followed by rapid depressurization to atmospheric pressure. Foam structures were characterized by scanning electron microscopy, and cell size...}, number={6}, journal={INDUSTRIAL & ENGINEERING CHEMISTRY RESEARCH}, author={Cotugno, S and Di Maio, E and Mensitieri, G and Iannace, S and Roberts, GW and Carbonell, RG and Hopfenberg, HB}, year={2005}, month={Mar}, pages={1795–1803} }
 @article{liu_desimone_roberts_2005, title={Continuous precipitation polymerization of acrylic acid in swercritical carbon dioxide: The polymerization rate and the polymer molecular weight}, volume={43}, ISSN={["1099-0518"]}, DOI={10.1002/pola.20728}, abstractNote={Abstract}, number={12}, journal={JOURNAL OF POLYMER SCIENCE PART A-POLYMER CHEMISTRY}, author={Liu, T and Desimone, JM and Roberts, GW}, year={2005}, month={Jun}, pages={2546–2555} }
 @article{sirijaruphan_goodwin_rice_wei_butcher_roberts_spivey_2005, title={Effect of metal foam supports on the selective oxidation of CO on Fe-promoted Pt/gamma-Al2O3}, volume={281}, number={02-Jan}, journal={Applied Catalysis. A, General}, author={Sirijaruphan, A. and Goodwin, J. G. and Rice, R. W. and Wei, D. G. and Butcher, K. R. and Roberts, G. W. and Spivey, J. J.}, year={2005}, pages={18-} }
 @article{kennedy_roberts_desimone_2005, title={Heterogeneous polymerization of fluoroolefins in supercritical carbon dioxide}, volume={175}, ISBN={["3-540-22923-X"]}, ISSN={["1436-5030"]}, DOI={10.1007/b100114}, abstractNote={In recent years, carbon dioxide has been investigated for its potential to replace the aqueous and organic solvents used in polymerization processes. Carbon dioxide has several benefits, including being environmentally benign, a tunable solvent, resistant to chain transfer, and of low viscosity which facilitates high initiator efficiencies and fluid handling. Homo- and copolymerization of fluoroolefins such as tetrafluoroethylene (TFE), vinylidene fluoride (VF2), hexafluoropropylene (HFP), and perfluorinated vinyl ethers in carbon dioxide are particularly interesting because of the significant waste reduction and the elimination of potentially harmful processing agents. This review focuses on recent developments in polymerizing fluoroolefins via heterogeneous polymerization in carbon dioxide. At least one CO2-based polymerization process has recently been commercialized, and additional research is underway to understand the kinetics associated with polymerizing fluoroolefins in carbon dioxide. As researchers improve their understanding of CO2-based polymerizations, and as industry continues to look for more economically and environmentally-sound alternatives to existing processes, it will become more and more common to employ carbon dioxide as a polymerization medium.}, journal={POLYMER PARTICLES}, author={Kennedy, KA and Roberts, GW and DeSimone, JM}, year={2005}, pages={329–346} }
 @article{xu_carbonell_kiserow_roberts_2005, title={Hydrogenation of polystyrene in CO2-expanded solvents: Catalyst poisoning}, volume={44}, ISSN={["0888-5885"]}, DOI={10.1021/ie040243q}, abstractNote={Organic solvents expanded with supercritical carbon dioxide can be excellent media for hydrogenation reactions. However, catalyst poisoning by CO formed via the reverse water-gas-shift reaction occurs during many hydrogenations in the presence of CO2. In this research, the hydrogenation of polystyrene in CO2-expanded decahydronaphthalene was studied in a batch reactor using two hydrogenation catalysts, 5%Pd/BaSO4 and 65%Ni/Al2O3/SiO2. The 5%Pd/BaSO4 catalyst deactivated at 150 °C and CO2 pressures of 250−2250 psig (1.8−15.6 MPa). Approximately 50 ppm CO was present in the CO2-rich light phase after about 10 h at 150 °C, 750 psig H2 pressure, and 2250 psig CO2 pressure. A model that incorporates CO poisoning was developed to describe deactivation of the Pd/BaSO4 catalyst. The 65%Ni/Al2O3/SiO2 catalyst was more active for ring hydrogenation than 5%Pd/BaSO4, and very little CO was formed in the presence of CO2. The Ni catalyst deactivated in the presence of CO2 at 180 °C, possibly due to H2O formed in a meth...}, number={16}, journal={INDUSTRIAL & ENGINEERING CHEMISTRY RESEARCH}, author={Xu, DW and Carbonell, RG and Kiserow, DJ and Roberts, GW}, year={2005}, month={Aug}, pages={6164–6170} }
 @article{sirijaruphan_goodwin_rice_wei_butcher_roberts_spivey_2005, title={Metal foam supported Pt catalysts for the selective oxidation of CO in hydrogen}, volume={281}, number={02-Jan}, journal={Applied Catalysis. A, General}, author={Sirijaruphan, A. and Goodwin, J. G. and Rice, R. W. and Wei, D. G. and Butcher, K. R. and Roberts, G. W. and Spivey, J. J.}, year={2005}, pages={09-} }
 @article{kiserow_shi_roberts_gross_desimone_2005, title={Solid-state polymerization of poly(bisphenol A carbonate) facilitated by supercritical carbon dioxide}, volume={898}, ISBN={["0-8412-3887-1"]}, ISSN={["0097-6156"]}, DOI={10.1021/bk-2005-0898.ch007}, abstractNote={During the solid state polymerization (SSP) of poly(bisphenol A carbonate), both the forward reaction rate constant and the phenol diffusion coefficient inside the polymer particle were significantly higher when SSP was carried out in supercritical carbon dioxide (scCO 2 ) compared to in atmospheric N 2 . These enhancements depended on the reaction conditions, and can be understood in terms of the CO 2 concentrations in the polymer. Polymer with a M w as high as 78100 has been synthesized by SSP with scCO 2 as the sweep fluid.}, journal={ADVANCES IN POLYCARBONATES}, author={Kiserow, DJ and Shi, CM and Roberts, GW and Gross, SM and DeSimone, JM}, year={2005}, pages={86–94} }
 @misc{royer_roberts_2004, title={Continuous method and apparatus for separating polymer from a high pressure carbon dioxide fluid stream}, volume={6,806,332}, number={2004 Oct. 19}, publisher={Washington, DC: U.S. Patent and Trademark Office}, author={Royer, J. R. and Roberts, G. W.}, year={2004} }
 @article{ahmed_desimone_roberts_2004, title={Continuous precipitation polymerization of vinylidene fluoride in supercritical carbon dioxide: modeling the molecular weight distribution}, volume={59}, number={22-23}, journal={Chemical Engineering Science}, author={Ahmed, T. S. and Desimone, J. M. and Roberts, G. W.}, year={2004}, pages={5139–5144} }
 @misc{desimone_roberts_charpentier_2004, title={Multimodal fluoropolymers and methods of making the same}, volume={6,716,945}, number={2004 Apr. 6}, publisher={Washington, DC: U.S. Patent and Trademark Office}, author={DeSimone, J. M. and Roberts, G. W. and Charpentier, P. A.}, year={2004}, month={Apr} }
 @article{wilcox_roberts_spivey_2003, title={Direct catalytic formation of acetic acid from CO2 and methane}, volume={88}, ISSN={["1873-4308"]}, DOI={10.1016/j.cattod.2003.08.007}, abstractNote={The direct synthesis of acetic acid from methane and carbon dioxide was investigated. Diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) experiments showed the formation of an adsorbed acetate on both a 5% Pd/carbon and a 5% Pt/alumina catalyst when the catalyst was exposed to a mixture of methane and carbon dioxide at a temperature of about 400 °C. Temperature programmed reaction (TPR) experiments showed the formation of gas phase acetic acid from carbon dioxide and methane at about 400 °C over a 5% Pt/alumina catalyst.}, number={1-2}, journal={CATALYSIS TODAY}, author={Wilcox, EM and Roberts, GW and Spivey, JJ}, year={2003}, month={Dec}, pages={83–90} }
 @article{shi_roberts_kiserow_2003, title={Effect of supercritical carbon dioxide on the diffusion coefficient of phenol in poly(bisphenol A carbonate)}, volume={41}, ISSN={["1099-0488"]}, DOI={10.1002/polb.10459}, abstractNote={Abstract}, number={11}, journal={JOURNAL OF POLYMER SCIENCE PART B-POLYMER PHYSICS}, author={Shi, CM and Roberts, GW and Kiserow, DJ}, year={2003}, month={Jun}, pages={1143–1156} }
 @article{xu_carbonell_kiserow_roberts_2003, title={Kinetic and transport processes in the heterogeneous catalytic hydrogenation of polystyrene}, volume={42}, ISSN={["0888-5885"]}, DOI={10.1021/ie0301841}, abstractNote={The heterogeneous catalytic hydrogenation of polystyrene (PS) dissolved in decahydronaphthalene was studied in a batch reactor using 5% Pd/BaSO4 as the catalyst. The effects of temperature and H2 partial pressure were investigated over the ranges from 90 to 180 °C and 1.72 to 6.89 MPa. The PS concentration ranged from 1 to 9 wt %. The rate of ring hydrogenation was approximately first-order with respect to PS, with an apparent activation energy of 59.6 kJ/mol. The hydrogenation rate depended on the agitation rate up to a threshold value, which increased with the concentration of PS in the solution. The possible influence of three mass-transfer steps (H2 transport from the gas into the polystyrene solution, PS transport to the surface of the catalyst particles, and PS diffusion in the pores of the catalyst) is analyzed. The last two steps do not appear to be kinetically important at the conditions of this study.}, number={15}, journal={INDUSTRIAL & ENGINEERING CHEMISTRY RESEARCH}, author={Xu, DW and Carbonell, RG and Kiserow, DJ and Roberts, GW}, year={2003}, month={Jul}, pages={3509–3515} }
 @article{roberts_chin_sun_spivey_2003, title={Preferential oxidation of carbon monoxide with Pt/Fe monolithic catalysts: interactions between external transport and the reverse water-gas-shift reaction}, volume={46}, ISSN={["1873-3883"]}, DOI={10.1016/j.apcatb.2003.07.002}, abstractNote={A series of Pt/Al2O3 catalysts, promoted with Fe and supported on 400 cpsi (cells per square inch) (62 cells/cm2) ceramic straight-channel monoliths, was synthesized and evaluated for preferential oxidation (PROX) of a low concentration of CO in the presence of a high concentration of H2. These catalysts were evaluated in an adiabatic reactor at a total pressure of 0.20 mPa inlet temperatures of 80–170 °C, and a space velocity of 30,000 h−1. The inlet gas composition was—H2: 42%, CO2: 9%, H2O: 12%, CO: 0–1.0%, O2: 0–1.0%, with N2 as the balance. For a catalyst containing 5 wt.% Pt in the washcoat, the carbon monoxide and oxygen conversions increased as the iron concentration in the washcoat was increased up to about 0.5 wt.% Fe. The reverse water-gas-shift (r-WGS) reaction played an important role in determining the outlet CO concentration. A catalyst with 1.6 g/in.3 (0.098 g/cm3) of an alumina washcoat containing 5 wt.% Pt/Al2O3 promoted with 0.5 wt.% Fe was selected for detailed investigation. The effects of both space velocity and linear velocity were studied. External transport was a significant resistance with this catalyst, at the above experimental conditions. The external resistances to heat and mass transfer, coupled with the effect of the r-WGS reaction, reduced the observed CO conversion and selectivity.}, number={3}, journal={APPLIED CATALYSIS B-ENVIRONMENTAL}, author={Roberts, GW and Chin, P and Sun, XL and Spivey, JJ}, year={2003}, month={Nov}, pages={601–611} }
 @article{sun_roberts_2003, title={Synthesis of higher alcohols in a slurry reactor with cesium-promoted zinc chromite catalyst in decahydronaphthalene}, volume={247}, ISSN={["0926-860X"]}, DOI={10.1016/S0926-860X(03)00093-0}, abstractNote={The synthesis of higher alcohols from H2/CO mixtures was studied in a continuous slurry reactor using unpromoted “zinc chromite” catalyst and the same catalyst promoted with 6 wt.% cesium (Cs). Decahydronaphthalene (DHN) was used as the slurry liquid. Two temperatures 375 and 400 °C, and three H2/CO feed ratios 0.5, 1.0, and 2.0 (mol/mol), were explored. The pressure, 13.6 MPa (2000 psig), and the gas hourly space velocity (GHSV), 5000 standard l/(kg (cat) h), were constant. Compared with unpromoted zinc chromite, the Cs-promoted catalyst shifted the product distribution away from methanol towards higher alcohols, although methanol was still the major product. The higher alcohols were primarily ethanol, 1-propanol and isobutanol. Higher temperature favored higher alcohol synthesis (HAS), and a higher H2/CO ratio led to lower oxygenate selectivity and higher hydrocarbon selectivity. These trends were more pronounced with the Cs-promoted catalyst than with the unpromoted catalyst. The performance of both catalysts was comparable to that of similar catalysts in fixed-bed reactors operating at approximately the same conditions.}, number={1}, journal={APPLIED CATALYSIS A-GENERAL}, author={Sun, XL and Roberts, GW}, year={2003}, month={Jul}, pages={133–142} }
 @article{kennedy_desimone_roberts_2002, title={A commentary on "Carbon dioxide-poly(vinylidene fluoride) interactions at high pressure"}, volume={40}, ISSN={["0887-6266"]}, DOI={10.1002/polb.10103}, abstractNote={Journal of Polymer Science Part B: Polymer PhysicsVolume 40, Issue 6 p. 602-604 Rapid Communication A commentary on “Carbon Dioxide–Poly(vinylidene Fluoride) Interactions at High Pressure” Karen A. Kennedy, Karen A. Kennedy Department of Chemical Engineering, North Carolina State University, Raleigh, North Carolina 27695-7905Search for more papers by this authorJoseph M. Desimone, Joseph M. Desimone Department of Chemical Engineering, North Carolina State University, Raleigh, North Carolina 27695-7905 Department of Chemistry, CB 3290, Venable and Kenan Laboratories, University of North Carolina at Chapel Hill, Chapel Hill, North Carolina 27599-3290Search for more papers by this authorGeorge W. Roberts, Corresponding Author George W. Roberts groberts@eos.ncsu.edu Department of Chemical Engineering, North Carolina State University, Raleigh, North Carolina 27695-7905Department of Chemical Engineering, North Carolina State University, Raleigh, North Carolina 27695-7905Search for more papers by this author Karen A. Kennedy, Karen A. Kennedy Department of Chemical Engineering, North Carolina State University, Raleigh, North Carolina 27695-7905Search for more papers by this authorJoseph M. Desimone, Joseph M. Desimone Department of Chemical Engineering, North Carolina State University, Raleigh, North Carolina 27695-7905 Department of Chemistry, CB 3290, Venable and Kenan Laboratories, University of North Carolina at Chapel Hill, Chapel Hill, North Carolina 27599-3290Search for more papers by this authorGeorge W. Roberts, Corresponding Author George W. Roberts groberts@eos.ncsu.edu Department of Chemical Engineering, North Carolina State University, Raleigh, North Carolina 27695-7905Department of Chemical Engineering, North Carolina State University, Raleigh, North Carolina 27695-7905Search for more papers by this author First published: 01 February 2002 https://doi.org/10.1002/polb.10103Citations: 1Read the full textAboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinked InRedditWechat Citing Literature Volume40, Issue615 March 2002Pages 602-604 RelatedInformation}, number={6}, journal={JOURNAL OF POLYMER SCIENCE PART B-POLYMER PHYSICS}, author={Kennedy, KA and Desimone, JM and Roberts, GW}, year={2002}, month={Mar}, pages={602–604} }
 @article{saraf_gerard_wojcinski_charpentier_desimone_roberts_2002, title={Continuous precipitation polymerization of vinylidene fluoride in supercritical carbon dioxide: Formation of polymers with bimodal molecular weight distributions}, volume={35}, ISSN={["1520-5835"]}, DOI={10.1021/ma0203602}, abstractNote={The polymerization of vinylidene fluoride in supercritical carbon dioxide was studied in a continuous stirred tank reactor using diethylperoxydicarbonate as the free radical initiator. Experiments were carried out to investigate the effect of inlet monomer concentration, temperature, average residence time, and agitation on the polymerization rate, the average molecular weights, and the molecular weight distribution of the poly(vinylidene fluoride). A homogeneous kinetic model that includes inhibition due to chain transfer to monomer predicted the polymerization rates reasonably well. However, imperfect mixing, rather than a chemical effect, may have caused the apparent inhibition observed at high monomer concentrations. At inlet monomer concentrations greater than about 1.5 M, broad and bimodal molecular weight distributions were observed. An extended homogeneous kinetic model that includes chain transfer to polymer predicted the polydispersities reasonably well. This model also predicted a region of ino...}, number={21}, journal={MACROMOLECULES}, author={Saraf, MK and Gerard, S and Wojcinski, LM and Charpentier, PA and DeSimone, JM and Roberts, GW}, year={2002}, month={Oct}, pages={7976–7985} }
 @article{saraf_wojcinski_kennedy_gerard_charpentier_desimone_roberts_2002, title={Continuous precipitation polymerization of vinylidene fluoride in supercritical carbon dioxide: Molecular weight distribution}, volume={182}, ISSN={["1521-3900"]}, DOI={10.1002/1521-3900(200206)182:1<119::AID-MASY119>3.0.CO;2-P}, abstractNote={The surfactant-free precipitation polymerization of vinylidene fluoride (VF2) in supercritical carbon dioxide was studied in a continuous stirred autoclave. The polymerization temperature ranged from 65 to 85°C, the average residence time in the reactor varied from 10 to 50 min., and the pressure was between 210 and 305 bar. Diethyl peroxydicarbonate was used as the initiator. The fractional conversion of monomer varied from 7 to 26%, the number-average molecular weight of the polymer was between about 14,000 and 79,000, and the weight-average molecular weight was between about 21,000 and 700,000. In many cases, the polymer exhibited a bimodal molecular-weight distribution, especially at high monomer concentrations.}, journal={MACROMOLECULAR SYMPOSIA}, author={Saraf, MK and Wojcinski, LM and Kennedy, KA and Gerard, S and Charpentier, PA and DeSimone, J and Roberts, GW}, year={2002}, month={Jun}, pages={119–129} }
 @article{gross_bunyard_erford_roberts_kiserow_desimone_2002, title={Determination of the equilibrium constant for the reaction between bisphenol A and diphenyl carbonate}, volume={40}, ISSN={["1099-0518"]}, DOI={10.1002/pola.10098}, abstractNote={Abstract}, number={1}, journal={JOURNAL OF POLYMER SCIENCE PART A-POLYMER CHEMISTRY}, author={Gross, SM and Bunyard, WC and Erford, K and Roberts, GW and Kiserow, DJ and DeSimone, JM}, year={2002}, month={Jan}, pages={171–178} }
 @article{sun_jones_gesick_xu_roberts_2002, title={Liquid/catalyst interactions in slurry reactors: changes in tetrahydroquinoline composition during methanol synthesis over zinc chromite}, volume={231}, ISSN={["1873-3875"]}, DOI={10.1016/S0926-860X(02)00069-8}, abstractNote={The excellent thermal stability of tetrahydroquinoline (THQ) under reducing conditions [1] has led to its use as a slurry liquid for several catalytic reactions: the synthesis of methanol over “zinc chromite” catalyst [2], the synthesis of higher alcohols over promoted “zinc chromite” [3], and the dehydrogenation of methanol to formaldehyde over various copper-containing catalysts [4], [5]. However, the rate and selectivity of alcohol synthesis over zinc chromite catalyst was much different with THQ as the slurry liquid than with several similar compounds. It also was found that THQ was alkylated during both alcohol synthesis and methanol dehydrogenation. To understand the behavior of THQ-derived slurry liquids, various analyses were carried out on a sample of this liquid that was obtained after 240 h of continuous operation under methanol synthesis conditions. Silica gel liquid chromatography (LC) and high performance LC (HPLC) were used to fractionate the “spent” slurry liquid, while gas chromatography/mass spectroscopy (GC/MS), Fourier transform infrared (FT-IR) spectroscopy and nuclear magnetic resonance (NMR) spectroscopy were applied to identify the major compounds. Methyl-, dimethyl-, and trimethyl-THQ comprised more than 80% of the “spent” slurry liquid. The balance primarily was various methylated indoles. A methyl group always was attached to the N atom in the ring structure. There was no evidence of further alkylation of methyl groups. These results appear to eliminate the possibility that the observed differences between THQ and similar hydrocarbon slurry liquids result from the nucleophilicity of secondary amines in the liquid. They also suggest that alkylation of THQ will eventually stop as the ring positions in THQ become saturated. A mechanism for the alkylation of THQ is proposed.}, number={1-2}, journal={APPLIED CATALYSIS A-GENERAL}, author={Sun, XL and Jones, NW and Gesick, JC and Xu, LL and Roberts, GW}, year={2002}, month={May}, pages={269–280} }
 @misc{wilcox_roberts_spivey_2002, title={Thermodynamics of light alkane carboxylation}, volume={226}, number={1-2}, journal={Applied Catalysis. A, General}, author={Wilcox, E. M. and Roberts, G. W. and Spivey, J. J.}, year={2002}, pages={317–318} }
 @article{goodner_gross_desimone_roberts_kiserow_2001, title={Broadening of molecular-weight distribution in solid-state polymerization resulting from condensate diffusion}, volume={79}, ISSN={["0021-8995"]}, DOI={10.1002/1097-4628(20010131)79:5<928::AID-APP170>3.0.CO;2-X}, abstractNote={A kinetic model for the solid-state polymerization of poly(bisphenol A carbonate) in a single particle has been developed and used to investigate the broadening of molecular-weight distribution as a result of slow condensate diffusion. The model is based on melt-phase transesterification kinetics and Fickian diffusion of phenol, the condensate, in the amorphous regions of the semicrystalline particle. Model predictions compare favorably to experimental data. When diffusion is slow compared to reaction, a condensate concentration gradient is established. This gradient induces a molecular-weight gradient, which results in a broadened overall molecular-weight distribution with an overall polydispersity above the theoretical limit for homogenous step-growth polymerization. As the mass transfer resistance inside the particle is decreased, the average molecular weight increases faster with time, and the overall polydispersity decreases. A stoichiometric imbalance of end groups decreases the obtainable molecular weight but mitigates the deleterious effects of slow condensate diffusion. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 79: 928–943, 2001}, number={5}, journal={JOURNAL OF APPLIED POLYMER SCIENCE}, author={Goodner, MD and Gross, SM and Desimone, JM and Roberts, GW and Kiserow, DJ}, year={2001}, month={Jan}, pages={928–943} }
 @article{frankel_jang_spivey_roberts_2001, title={Deactivation of hydrodechlorination catalysts I. Experiments with 1.1.1-trichloroethane}, volume={205}, ISSN={["0926-860X"]}, DOI={10.1016/S0926-860X(00)00577-9}, abstractNote={In order to understand the cause(s) of catalyst deactivation, microreactor studies were carried out on the catalytic hydrodechlorination (HDC) of 1,1,1-trichloroethane (111-TCA) using a fixed-bed reactor divided into three segments. The catalysts studied were: ηδ-alumina, α-alumina, Pt/α-alumina, Pt/η-alumina, and Pt/ηδ-alumina. Experiments were carried out at atmospheric pressure over a temperature range of 423–623 K and at H2/111-TCA molar ratios between 10 and 99. Only the Pt-containing catalysts were able to remove all three Cl atoms from 111-TCA. However, increasing amounts of partially-dechlorinated compounds were formed as the Pt/ηδ-alumina and the Pt/η-alumina catalysts deactivated. The only product with ηδ-alumina was 1,1-dichloroethylene (11-DCE). The conversion of 111-TCA decreased more rapidly with time for Pt/ηδ-alumina than for ηδ-alumina without Pt. Much larger quantities of coke were formed on the Pt/ηδ-alumina than on the ηδ-alumina, at similar conditions. The ηδ-alumina was essentially completely regenerated by heating in flowing He at 773 K. The Pt/η-alumina was only partially regenerated by this technique. The apparent stability of the Pt/ηδ-alumina catalysts increased with increasing Pt concentration. Poisoning by hydrochloric acid, a reaction product, did not cause significant deactivation of either the ηδ-alumina or the Pt/ηδ-alumina catalysts.}, number={1-2}, journal={APPLIED CATALYSIS A-GENERAL}, author={Frankel, KA and Jang, BWL and Spivey, JJ and Roberts, GW}, year={2001}, month={Jan}, pages={263–278} }
 @article{frankel_jang_roberts_spivey_2001, title={Deactivation of hydrodechlorination catalysts II - Experiments with 1,1-dichloroethylene and 1,1-dichloroethane}, volume={209}, ISSN={["0926-860X"]}, DOI={10.1016/S0926-860X(00)00784-5}, abstractNote={In an earlier paper [K.A. Frankel, B.W.-L. Jang, J.J. Spivey, G.W. Roberts, Appl. Catal. A, in press], it was shown that certain alumina and Pt/alumina catalysts deactivated rapidly during the hydrodechlorination (HDC) of 1,1,1-trichloroethane (111-TCA) at temperatures between 423 and 623 K. Large quantities of coke were formed on these catalysts at some conditions. In the present research, the deactivation associated with four intermediates in the HDC of 111-TCA; 1,1-dichloroethylene (11-DCE), 1,1-dichloroethane (11-DCA), chloroethane, and ethylene, was investigated. Experiments were carried out with ηδ-alumina and 3% Pt/η-alumina at 423 and 523 K, atmospheric pressure, and at a H2/chlorinated hydrocarbon/He ratio of 10/1/89. The ηδ-alumina, without Pt, catalyzed the removal of one molecule of HCl from each of the saturated chlorocarbons. Deactivation of the ηδ-alumina was rapid with 111-TCA and 11-DCA, and relatively slow with chloroethane. There was no reaction over ηδ-alumina when 11-DCE was fed. The fresh Pt/η-alumina catalyst was able to remove all of the Cl from the chlorocarbons. This catalyst deactivated with 111-TCA and 11-DCA, but no deactivation was observed with 11-DCE and chloroethane. At comparable conditions, much more coke was deposited on the Pt/η-alumina catalyst with 111-TCA than with any of the other compounds. Hydrochloric acid did not appear to cause deactivation. A reaction scheme is proposed to summarize the major reaction pathways and to identify potential causes of catalyst deactivation.}, number={1-2}, journal={APPLIED CATALYSIS A-GENERAL}, author={Frankel, KA and Jang, BWL and Roberts, GW and Spivey, JJ}, year={2001}, month={Feb}, pages={401–413} }
 @article{frankel_spivey_roberts_2001, title={Mathematical model of the deactivation of Pt/alumina catalyst during the hydrodechlorination of 1,1,1-trichloroethane}, volume={139}, journal={Catalyst deactivation 2001: Proceedings of the 9th international symposium, Lexington, KY, USA, 7-10 October 2001 (Studies in surface science and catalysis;  139)}, publisher={Amsterdam; New York: Elsevier}, author={Frankel, K. A. and Spivey, J. J. and Roberts, G. W.}, editor={J. J. Spivey, G. W. Roberts and Davis, B. H.Editors}, year={2001}, pages={439–446} }
 @misc{roberts_kilpatrick_2001, title={Methods and apparatus for separating Fischer-Tropsch catalysts from liquid hydrocarbon product}, volume={6,217,830}, number={2001 April 17}, publisher={Washington, DC: U.S. Patent and Trademark Office}, author={Roberts, G. W. and Kilpatrick, P. K.}, year={2001} }
 @article{shi_desimone_kiserow_roberts_2001, title={Reaction Kinetics of the Solid-State Polymerization of Poly(bisphenol A carbonate) Facilitated by Supercritical Carbon Dioxide}, volume={34}, ISSN={0024-9297 1520-5835}, url={http://dx.doi.org/10.1021/ma011068h}, DOI={10.1021/ma011068h}, abstractNote={The kinetics of solid-state polymerization (SSP) of poly(bisphenol A carbonate) was investigated with supercritical CO2 (scCO2) as the sweep fluid. The CO2 flow rate and polymer particle size were chosen to ensure that the kinetics was controlled by the rate of the forward transesterification reaction, i.e., so that both external and internal phenol diffusion limitations were negligible. The forward reaction rate constants were determined between 90 and 135 °C, at CO2 pressures of 138, 207, and 345 bar. At a given temperature, the reaction rate was higher with scCO2 as the sweep fluid than with N2, especially at lower temperatures. The rate constant for the forward transesterification reaction increased with increasing CO2 pressure up to about 207 bar, at which point the rate constant was no longer sensitive to CO2 pressure. The activation energy decreased from 23.9 kcal/mol in N2 to 15.5, 11.6, and 11.4 kcal/mol at CO2 pressures of 138, 207, and 345 bar, respectively. The effect of scCO2 on the rate of p...}, number={22}, journal={Macromolecules}, publisher={American Chemical Society (ACS)}, author={Shi, Chunmei and DeSimone, Joseph M. and Kiserow, Douglas J. and Roberts, George W.}, year={2001}, month={Oct}, pages={7744–7750} }
 @article{shi_gross_desimone_kiserow_roberts_2001, title={Reaction kinetics of the solid state polymerization of poly(bisphenol A carbonate)}, volume={34}, ISSN={["0024-9297"]}, DOI={10.1021/ma001942r}, abstractNote={The kinetics of solid-state polymerization (SSP) of poly(bisphenol A carbonate) was investigated with N2 as the sweep gas. The N2 flow rate and prepolymer particle size were chosen to eliminate the influence of both external and internal phenol diffusion, and to ensure that the kinetics was controlled by the rate of the forward transesterification reaction. The forward reaction rate constants were evaluated at different temperatures between 120 and 165 °C, and the activation energy for SSP of poly(bisphenol A carbonate) with N2 as the sweep gas was determined to be 99.6 kJ/mol. At each temperature, the polymer molecular weight increased with time, eventually reaching an asymptotic value. The asymptotic molecular weight increased with temperature. The glass transition temperature (Tg) of the polymer increased as the molecular weight increased. At lower reaction temperatures, Tg approaches the reaction temperature as the polymerization proceeds, and the achievable molecular weight appears to be limited by d...}, number={7}, journal={MACROMOLECULES}, author={Shi, CM and Gross, SM and DeSimone, JM and Kiserow, DJ and Roberts, GW}, year={2001}, month={Mar}, pages={2060–2064} }
 @article{gross_roberts_kiserov_desimone_2001, title={Synthesis of high molecular weight polycarbonate by solid-state polymerization}, volume={34}, ISSN={["1520-5835"]}, DOI={10.1021/ma001958h}, abstractNote={The solid-state polymerization (SSP) of small particles (20 μm) of poly(bisphenol A carbonate) resulted in high molecular weight material (Mw of 36 000 g/mol). Molecular weight distribution broaden...}, number={12}, journal={MACROMOLECULES}, author={Gross, SM and Roberts, GW and Kiserov, DJ and DeSimone, JM}, year={2001}, month={Jun}, pages={3916–3920} }
 @article{goodner_desimone_kiserow_roberts_2000, title={An equilibrium model for diffusion-limited solid-state polycondensation}, volume={39}, ISSN={["0888-5885"]}, DOI={10.1021/ie990648o}, abstractNote={A model for unsteady-state solid-state polycondensation (SSP) is developed and is applied to the polymerization of poly(bisphenol A carbonate) and poly(ethylene terephthalate) (PET). The model assumes that diffusion of the reaction condensate in the solid polymer is the rate-limiting step in the overall polymerization kinetics. Therefore, the reversible polycondensation reaction is at local equilibrium throughout the polymer particle at all times. The model is applicable to the three general types of step-growth polymerization:  AB, A2, and A2 + B2 polycondensation. Through comparison with the predictions of a full kinetic model for polycarbonate synthesis, it is demonstrated that the equilibrium model provides an upper bound on molecular weight and its rate of increase. Model predictions are also compared to experimental data for PET SSP. These comparisons show that the equilibrium model provides a useful tool for understanding the effects of temperature and particle size as well as for establishing a lo...}, number={8}, journal={INDUSTRIAL & ENGINEERING CHEMISTRY RESEARCH}, author={Goodner, MD and DeSimone, JM and Kiserow, DJ and Roberts, GW}, year={2000}, month={Aug}, pages={2797–2806} }
 @article{charpentier_desimone_roberts_2000, title={Continuous precipitation polymerization of vinylidene fluoride in supercritical carbon dioxide: Modeling the rate of polymerization}, volume={39}, ISSN={["0888-5885"]}, DOI={10.1021/ie000354z}, abstractNote={The kinetics of the surfactant-free precipitation polymerization of vinylidene fluoride (VF2) in supercritical carbon dioxide have been studied in a continuous stirred autoclave. Diethyl peroxydicarbonate was used as the free-radical initiator. The stirring rate and agitator design had no effect on the rate of polymerization (Rp) or on the weight-average molecular weight (Mw) of the formed poly(vinylidene fluoride) (PVDF). The fractional conversion of VF2 ranged from 7 to 26%, and Rp was as high as 27 × 10-5 mol/L·s at 75 °C and at a VF2 feed concentration of 2.5 mol/L. The PVDF polymer was collected as a dry, “free-flowing” powder and had Mw's up to 150 kg/mol and melt flow indices as low as 3.0 at 230 °C. Homogeneous, free-radical kinetics provided a reasonable basis for describing the rate of polymerization, despite the heterogeneous nature of the system. The order of the reaction with respect to the monomer was found to be 1.0, and the order with respect to the initiator was 0.5. The experimental data...}, number={12}, journal={INDUSTRIAL & ENGINEERING CHEMISTRY RESEARCH}, author={Charpentier, PA and DeSimone, JM and Roberts, GW}, year={2000}, month={Dec}, pages={4588–4596} }
 @article{gross_roberts_kiserow_desimone_2000, title={Crystallization and solid-state polymerization of poly(bisphenol A carbonate) facilitated by supercritical CO2}, volume={33}, ISSN={["1520-5835"]}, DOI={10.1021/ma990901w}, abstractNote={Poly(bisphenol A carbonate) was synthesized by solid-state polymerization (SSP) using supercritical CO2 to induce crystallinity in low molecular weight polycarbonate beads. The CO2-induced crystallization was studied as a function of time, temperature, molecular weight, and pressure. There was an optimum temperature for crystallization which depended on the molecular weight of the polymer. The molecular weight and percent crystallinity of the polymer produced by SSP were determined as a function of time and radial position in the bead. The molecular weight and percent crystallinity were strong functions of the particle radius, probably because of the slow diffusion of phenol out of the polymer particles. Nitrogen and supercritical CO2 were used as sweep fluids for the SSP process. The polymerization rate was always higher in supercritical CO2 at otherwise comparable conditions. We hypothesize that supercritical CO2 plasticizes the amorphous regions of the polymer, thereby increasing chain mobility and the...}, number={1}, journal={MACROMOLECULES}, author={Gross, SM and Roberts, GW and Kiserow, DJ and DeSimone, JM}, year={2000}, month={Jan}, pages={40–45} }
 @article{roberts_carbonell_saez_2000, title={Gas-lift reactors for rapid reactions with appreciable gas consumption}, volume={23}, DOI={10.1002/(sici)1521-4125(200001)23:1<80::aid-ceat80>3.0.co;2-m}, abstractNote={Gas-lift reactors offer important advantages for a number of gas/liquid and gas/liquid/solid reactions. However, the design and operation of these reactors can be complex when there is a substantial change in the molar gas flow rate along the length of the reactor, e.g., when a gaseous reactant is converted into a liquid product. In this situation, there is a strong coupling between reactor hydrodynamics and reaction kinetics, which arises from the fact that the rate of liquid circulation through the reactor and the longitudinal profile of gas holdup in the riser are mutually dependent. Several one-dimensional models have been developed to describe kinetic/hydrodynamic coupling in gas-lift reactors. These models offer useful insights into the parameters that affect reactor performance. The models can also be used to explore different approaches to scale-up.}, number={1}, journal={Chemical Engineering & Technology}, author={Roberts, G. W. and Carbonell, R. G. and Saez, A. E.}, year={2000}, pages={80–87} }
 @article{shreiber_roberts_2000, title={Methanol dehydrogenation in a slurry reactor: evaluation of copper chromite and iron/titanium catalysts}, volume={26}, ISSN={["0926-3373"]}, DOI={10.1016/S0926-3373(00)00114-4}, abstractNote={The dehydrogenation of methanol to formaldehyde is a cornerstone in the concept of environmentally-benign synthesis through in situ generation of formaldehyde. This reaction was studied in a slurry reactor at temperatures between 598 and 673 K over four different catalysts: Raney copper, copper chromite, 3% Mn/copper chromite and iron/titanium (FeTi) alloy. The three copper-based catalysts were effective at promoting methanol dehydrogenation, and the differences in activity and selectivity between these catalysts were relatively small at 598 K, 2.75 MPa, 10/1 N2/methanol feed ratio, and 12,000 sL/kg-hr space velocity. At these conditions, methyl formate was the primary product with the copper catalysts, and the formaldehyde concentration was near chemical equilibrium with Raney copper and 3% Mn/copper chromite. The FeTi catalyst was ineffective on a weight basis, although its activity was comparable to the copper catalysts on a surface area basis. Deactivation of the copper chromite catalyst was relatively slow at 673 K, after an initial period of stabilization. The slurry liquid, 1,2,3,4-tetrahydroquinoline (THQ), was dehydrogenated and alkylated to some extent during the reaction.}, number={2}, journal={APPLIED CATALYSIS B-ENVIRONMENTAL}, author={Shreiber, EH and Roberts, GW}, year={2000}, month={Apr}, pages={119–129} }
 @misc{roberts_kilpatrick_2000, title={Methods and apparatus for separating Fischer-Tropsch catalysts from liquid hydrocarbon product}, volume={6,114,399}, number={2000 Sept. 5}, publisher={Washington, DC: U.S. Patent and Trademark Office}, author={Roberts, G. W. and Kilpatrick, P. K.}, year={2000} }
 @article{charpentier_kennedy_desimone_roberts_1999, title={Continuous Polymerizations in Supercritical Carbon Dioxide:  Chain-Growth Precipitation Polymerizations}, volume={32}, ISSN={0024-9297 1520-5835}, url={http://dx.doi.org/10.1021/ma990377t}, DOI={10.1021/ma990377t}, abstractNote={ADVERTISEMENT RETURN TO ISSUEPREVCommunication to the...Communication to the EditorNEXTContinuous Polymerizations in Supercritical Carbon Dioxide: Chain-Growth Precipitation PolymerizationsP. A. Charpentier, K. A. Kennedy, J. M. DeSimone, and G. W. RobertsView Author Information Department of Chemical Engineering, North Carolina State University, Box #7095, Raleigh, North Carolina 27695-7905, and Department of Chemistry, University of North CarolinaChapel Hill, Venable and Kenan Laboratories, CB#3290, Chapel Hill, North Carolina 27599 Cite this: Macromolecules 1999, 32, 18, 5973–5975Publication Date (Web):August 12, 1999Publication History Received12 March 1999Published online12 August 1999Published inissue 1 September 1999https://doi.org/10.1021/ma990377tCopyright © 1999 American Chemical SocietyRIGHTS & PERMISSIONSArticle Views357Altmetric-Citations65LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit Read OnlinePDF (46 KB) Get e-AlertscloseSUBJECTS:Gel permeation chromatography,Monomers,Polymerization,Polymers,Precipitation Get e-Alerts}, number={18}, journal={Macromolecules}, publisher={American Chemical Society (ACS)}, author={Charpentier, P. A. and Kennedy, K. A. and DeSimone, J. M. and Roberts, G. W.}, year={1999}, month={Sep}, pages={5973–5975} }
 @article{marquez_saez_carbonell_roberts_1999, title={Coupling of hydrodynamics and chemical reaction in gas-lift reactors}, volume={45}, DOI={10.1002/aic.690450220}, abstractNote={Abstract}, number={2}, journal={AIChE Journal}, author={Marquez, H. A. and Saez, A. E. and Carbonell, R. G. and Roberts, G. W.}, year={1999}, pages={410–423} }
 @article{see_roberts_saez_1999, title={Effect of drag and frictional losses on the hydrodynamics of gas-lift reactors}, volume={45}, ISSN={["1547-5905"]}, DOI={10.1002/aic.690451121}, abstractNote={The purpose of this communication is to examine several assumptions concerning the drag and frictional losses in gas-lift reactors that are common to the Saez et al. (1998) and Marquez et al. (1999) models, and to some other published models. These assumptions are as follows. (1) The friction factor in the downcomer must be adjusted upward with respect to correlations for fully developed, single-phase flow in pipes in order to account for developing flow. (2) Mechanical energy losses in the gas/liquid separator and the straightening vanes can be neglected. (3) Frictional losses in the riser are adequately described by the correlation of Akita et al. (1988), which explicitly accounts for two-phase flow.}, number={11}, journal={AICHE JOURNAL}, author={See, KH and Roberts, GW and Saez, EA}, year={1999}, month={Nov}, pages={2467–2471} }
 @article{marquez_amend_carbonell_saez_roberts_1999, title={Hydrodynamics of gas-lift reactors with a fast, liquid-phase reaction}, volume={54}, ISSN={["0009-2509"]}, DOI={10.1016/S0009-2509(98)00351-0}, abstractNote={The reactive absorption of CO2 into concentrated KOH solutions was studied in an external-loop, gas-lift reactor. Three different inlet gas compositions were used: air, 50–50 vol% air–CO2, and pure CO2. The downcomer liquid velocity and the axial profile of the cross-sectionally averaged gas holdup in the riser were measured. The reaction is so fast that the CO2 is consumed appreciably along the riser, and this causes a significant reduction in the liquid circulation relative to a system with no reaction. A one-dimensional, pseudo-steady-state model has been developed to describe the interactions of hydrodynamics, mass transfer, and chemical reaction for the bubbly flow regime in the riser. The model considers mass transfer from the gas to the liquid phase and its enhancement due to the chemical reaction, and is based on the spatially averaged equations of continuity, momentum, and macroscopic mechanical energy. The rate of liquid circulation, and the axial variation of gas holdup, gas composition, pressure, and gas and liquid velocity, are predicted. The gas/liquid mass transfer coefficient and the bubble radius at the sparger, neither of which was known a priori, were used to minimize the error of the data with respect to the model.}, number={13-14}, journal={CHEMICAL ENGINEERING SCIENCE}, author={Marquez, MA and Amend, RJ and Carbonell, RG and Saez, AE and Roberts, GW}, year={1999}, month={Jul}, pages={2263–2271} }
 @article{roberts_marquez_haney_1999, title={Liquid catalyst interactions in slurry reactors: methanol synthesis over zinc chromite}, volume={183}, ISSN={["0926-860X"]}, DOI={10.1016/S0926-860X(99)00076-9}, abstractNote={The performance of a `zinc chromite' catalyst was studied in a continuous slurry reactor using three different liquids: decahydronaphthalene, tetrahydronaphthalene, and tetrahydroquinoline. The reactor feed was a mixture of hydrogen and carbon monoxide with a H2/CO ratio of either 0.5 or 2. The reactor was operated over a temperature range of 598–698 K and at a total pressure of about 14 MPa. The characteristics of the slurry liquid had a major influence on both the overall reaction rate and the product distribution. The rate of methanol synthesis was much higher when tetrahydroquinoline was used than with the other two liquids. The product distribution was shifted away from oxygenates and towards hydrocarbons when tetrahydronaphthalene was used. The slurry liquid was analyzed by GC/MS (gas chromatography/mass spectrometry) during and after the reaction. There was no evidence of significant cracking or hydrocracking of any of the liquids. However, tetrahydroquinoline was alkylated during the reaction, and tetrahydronaphthalene was dehydrogenated to some extent. Tetrahydroquinoline, and perhaps tetrahydronaphthalene, may have participated in the catalytic cycle.}, number={2}, journal={APPLIED CATALYSIS A-GENERAL}, author={Roberts, GW and Marquez, MA and Haney, CA}, year={1999}, month={Jul}, pages={395–410} }
 @article{shreiber_rhodes_roberts_1999, title={Methanol dehydrogenation with Raney copper in a slurry reactor}, volume={23}, number={1}, journal={Applied Catalysis. B, Environmental}, author={Shreiber, E. H. and Rhodes, M. D. and Roberts, G. W.}, year={1999}, pages={9–24} }
 @article{biales_di wan_kilpatrick_roberts_1999, title={Separation of Fischer-Tropsch wax from catalyst using near-critical fluid extraction: Analysis of process feasibility}, volume={13}, ISSN={["0887-0624"]}, DOI={10.1021/ef980208u}, abstractNote={The technical feasibility of a near-critical fluid extraction (NCE) process for the recovery of heavy normal paraffins from a Fischer−Tropsch slurry reactor has been analyzed. Process simulations were carried out using the ASPEN PLUS program, considering 100 individual compounds from C1 to C100. Four light solvents were evaluated:  n-pentane, n-hexane, n-heptane, and n-octane. These four compounds are major products of the F−T reaction. Most of the analysis was concentrated in two regions:  (1) high solvent/product ratios (ca. 20/1), such that product could be recovered by temperature-retrograde condensation; and, (2) low solvent/product ratios (ca. 3/1). The latter region appeared to require higher extraction temperatures and higher slurry flowrates, but had several attractive features such as lower vapor flowrates, lower solvent makeup rates, and lower energy requirements. The concentration of solvent in the product from the NCE process was never low enough for the process to be self-sufficient in solve...}, number={3}, journal={ENERGY & FUELS}, author={Biales, JM and Di Wan, Y and Kilpatrick, PK and Roberts, GW}, year={1999}, pages={667–677} }
 @article{gross_flowers_roberts_kiserow_desimone_1999, title={Solid-State Polymerization of Polycarbonates Using Supercritical CO2}, volume={32}, ISSN={0024-9297 1520-5835}, url={http://dx.doi.org/10.1021/ma981395y}, DOI={10.1021/ma981395y}, abstractNote={We report the extension of the crystallization process with supercritical CO 2 to granules or beads of low molecular weight polycarbonate in an effort to create a material that can undergo slid-state polymerization without using toxic organic solvents}, number={9}, journal={Macromolecules}, publisher={American Chemical Society (ACS)}, author={Gross, Stephen M. and Flowers, Devin and Roberts, George and Kiserow, Douglas J. and DeSimone, Joseph M.}, year={1999}, month={May}, pages={3167–3169} }
 @article{fields_lim_roberts_1998, title={Catalytic destruction of methyl tertiary butyl ether (MTBE) with a Pt/Rh monolithic automotive exhaust catalyst}, volume={15}, ISSN={["1873-3883"]}, DOI={10.1016/s0926-3373(97)00039-8}, abstractNote={Abstract The destruction of methyl tertiary butyl ether (MTBE) was studied using a Pt/Rh monolithic automotive catalyst. Inlet temperatures to the catalyst ranged from about 450 to about 775 K, and the amount of oxygen in the feed ranged from 0 to about 120% of stoichiometric. The presence of carbon dioxide, water and i -octane (2,2,4-trimethyl pentane) in the feed was also investigated. The decomposition of MTBE into methanol and i -butene (2-methyl-1-propene) was kinetically significant at these conditions. Both methanol and i -butene were present in the effluent from the catalyst at all operating conditions. Carbon dioxide and water had no significant effect on the kinetics of MTBE disappearance. The rate of MTBE destruction was faster than the oxidation of i -octane.}, number={1-2}, journal={APPLIED CATALYSIS B-ENVIRONMENTAL}, author={Fields, DL and Lim, PK and Roberts, GW}, year={1998}, month={Jan}, pages={93–105} }
 @article{saez_marquez_roberts_carbonell_1998, title={Hydrodynamic model for gas-lift reactors}, volume={44}, ISSN={["0001-1541"]}, DOI={10.1002/aic.690440619}, abstractNote={Abstract}, number={6}, journal={AICHE JOURNAL}, author={Saez, AE and Marquez, MA and Roberts, GW and Carbonell, RG}, year={1998}, month={Jun}, pages={1413–1423} }
 @article{roberts_marquez_mccutchen_1997, title={Alcohol synthesis in a high-temperature slurry reactor}, volume={36}, ISSN={["0920-5861"]}, DOI={10.1016/S0920-5861(96)00243-X}, abstractNote={Abstract A family of hydrocarbon liquids has been discovered that is stable at temperatures up to about 400°C in the presence of synthesis gas. The performance of a commercial, ‘zinc chromite’, ‘high pressure’ methanol synthesis catalyst was evaluated in a slurry reactor using two of these liquids, decahydronaphthalene and tetrahydronaphthalene, to suspend the catalyst. The evaluation covered a range of temperatures from 275° to 425°C, total pressures from 6.9 to 17.2 MPa, H2/CO ratios from 0.5 to 2.0 and space velocities from 1500 to 10 000 sl kg(catalyst)−1 h−1. Methanol was the only significant product at the lower end of this temperature range. The methanol synthesis reaction was close to equilibrium at the highest temperature, and there were significant quantities of dimethyl ether, olefins, methane and carbon dioxide in the product. Catalyst performance was sensitive to the composition of the slurry liquid, but was relatively stable in decahydronaphthalene over a long period of time.}, number={3}, journal={CATALYSIS TODAY}, author={Roberts, GW and Marquez, MA and McCutchen, MS}, year={1997}, month={Jun}, pages={255–263} }
 @article{roberts_marquez_mccutchen_haney_shin_1997, title={High-temperature slurry reactors for synthesis gas reactions .1. Liquid thermal stability}, volume={36}, ISSN={["0888-5885"]}, DOI={10.1021/ie970136e}, abstractNote={The use of slurry reactors has been limited to reactions that take place at temperatures below about 573 K because many of the liquids that have been used to suspend the solid catalyst are not stable above this temperature. The thermal stability of a number of organic liquids was evaluated at temperatures between 648 and 698 K and at H2 partial pressures of about 7 MPa. Certain saturated and partially-saturated, fused-ring compounds with no alkyl groups or bridges are quite stable at these conditions. Of the compounds tested, tetrahydronaphthalene, tetrahydroquinoline, and decahydronaphthalene were the most stable. Analysis of the liquids at the end of the thermal stability evaluation supports some speculation concerning possible degradation reactions.}, number={10}, journal={INDUSTRIAL & ENGINEERING CHEMISTRY RESEARCH}, author={Roberts, GW and Marquez, MA and McCutchen, MS and Haney, CA and Shin, ID}, year={1997}, month={Oct}, pages={4143–4154} }
 @misc{charpentier_desimone_roberts, title={Apparatus for continuous production of polymers in carbon dioxide}, volume={7,410,620}, number={2008 Aug. 12}, author={Charpentier, P. A. and DeSimone, J. M. and Roberts, G. W.} }
 @misc{khan_roberts_royer, title={CO2-assisted deploymerization, purification and recycling of step-growth polymers}, volume={6,919,383}, publisher={Washington, DC: U.S. Patent and Trademark Office}, author={Khan, S. A. and Roberts, G. W. and Royer, J. R.} }
 @article{charpentier_desimone_roberts, title={Continuous polymerizations in supercritical carbon dioxide}, volume={819}, journal={Clean solvents: Alternative media for chemical reactions and processing}, publisher={Washington, DC: American Chemical Society; New York: Distributed by Oxford University Press}, author={Charpentier, P. A. and Desimone, J. M. and Roberts, G. W.}, editor={M. A. Abraham, L. MoensEditor}, pages={113–135} }
 @misc{charpentier_desimone_roberts, title={Continuous process for making polymers in carbon dioxide}, volume={6,914,105}, publisher={Washington, DC: U.S. Patent and Trademark Office}, author={Charpentier, P. A. and DeSimone, J. M. and Roberts, G. W.} }
 @misc{roberts_xu_kiserow_carbonell, title={Hydrogenation of polymers in the presence of supercritical carbon dioxide}, volume={7,408,009}, number={2007 Apr. 11}, publisher={Washington, DC: U.S. Patent and Trademark Office}, author={Roberts, G. W. and Xu, D. and Kiserow, D. J. and Carbonell, R. G.} }
 @article{mahammad_abdala_roberts_khan, title={Manipulation of hydrophobic interactions in associative polymers using cyclodextrin and enzyme}, volume={6}, number={17}, journal={Soft Matter}, author={Mahammad, S. and Abdala, A. and Roberts, G. W. and Khan, S. A.}, pages={4237–4245} }
 @misc{royer_desimone_roberts_khan, title={Methods of CO2-assisted reactive extrusion}, volume={6,900,267}, publisher={Washington, DC: U.S. Patent and Trademark Office}, author={Royer, J. and DeSimone, J. M. and Roberts, G. W. and Khan, S. A.} }
 @article{xu_carbonell_roberts_kiserow, title={Phase equilibrium for the hydrogenation of polystyrene in CO2-swollen solvents}, volume={34}, number={1}, journal={Journal of Supercritical Fluids}, author={Xu, D. W. and Carbonell, R. G. and Roberts, G. W. and Kiserow, D. J.}, pages={09-} }