@article{venica_chen_gratzl_2008, title={Soda-AQ delignification of poplar wood. Part 1: Reaction mechanism and pulp properties}, volume={62}, ISSN={["1437-434X"]}, DOI={10.1515/HF.2008.118}, abstractNote={Abstract Soda and soda-anthraquinone (AQ) pulpings of poplar (Populus deltoides) wood performed in a flow-through reactor gives rise to the formation of coniferyl alcohol (1) sinapyl alcohol (2) and other low molecular weight (LMW) compounds in different stages of delignification. During the heating-up period, the formation of these compounds increases until the maximum pulping temperature (t max, 170°C) is reached. Afterward, their concentration in the spent liquor decreases sharply. This effect is accompanied by solubilization of high molecular weight (HMW) lignin fractions. Compared with soda pulping, the soda-AQ pulping shows a higher production of LMW compounds because of the presence of AQ-anthrahydroquinone (AHQ) redox system. During the heating-up period, the formation of 1 and 2 – apparently originated from non-etherified β-aryl-ether moieties in the lignin – is accompanied by solubilization of lignin fragments with relative LMW. Lignin cores, having β-aryl-ether bonds as major hydrolyzable inter-unit linkages, remain in the fiber, and they give rise to solubilized lignin fragments with HMW at later delignification stages. The dissolved fragments, in particular those formed during heating-up period, undergo further degradation in the liquor. The degradation occurs via oligomers at the end of the pulping, while the residual lignin cores are more resistant. Pulps with low kappa number can be produced by maintaining higher alkali concentrations than the usual in the last delignification phase. When the pulping liquor is replaced in this stage with liquors of higher alkali concentration, extended delignification will be the result. As a consequence, less degraded lignin fragments will be deposited on fibers.}, number={6}, journal={HOLZFORSCHUNG}, author={Venica, Alberto D. and Chen, Chen-Loung and Gratzl, Josef S.}, year={2008}, month={Nov}, pages={627–636} }
 @article{venica_chen_gratzl_2008, title={Soda-AQ delignification of poplar wood. Part 2: Further degradation of initially dissolved lignins}, volume={62}, ISSN={["1437-434X"]}, DOI={10.1515/HF.2008.119}, abstractNote={Abstract Degraded lignin fragments dissolved in pulping liquor during the soda AQ pulping of poplar (Populus deltoides) wood with a flow through reactor were divided in two fractions. The first one (LF-1) was collected during the heating-up period (100°C until the final temperature t max=170°C); the second one (LF-2) was collected at t max with 60 min cooking time. These two liquors were then treated at 170°C for 70 min (leading to a liquor LF-1A) and 10 min (leading to a liquor LF-2A). By these post-treatments, pulping liquors of batch pulpings were simulated. From the four liquors, lignins were isolated and after purification the chemical and physical properties were characterized by Gel Permeation Chromatography (GPC: to obtain their molecular weight distribution), nitrobenzene oxidation, permanganate oxidation, and 13C NMR spectroscopy. By these means, the reaction mechanisms of dissolved and degraded lignin fragments in pulping liquors was elucidated and insight was gained concerning the effectiveness of the anthraquinone-anthrahydroquinone (AQ-AHQ) redox system using the corresponding batch lignin preparation as reference. The simulated batch fractions LF-1A, LF-2A, and true batch lignin preparations are similar. They have a high content of condensed arylpropane units. Among them, syringylpropane units are most severely degraded, in particular, etherified β-aryl ether bonds are cleaved to a great extent after dissolution in pulping liquor. The structure of the remaining degraded lignin fragments was changed seriously, particularly on their side chains. Oxidation and disproportionation reactions are typical. In the presence of fibers, xylans tend preferentially to simple deposition on fibers instead of grafting with the degraded lignin fragments. Dissolution of carbohydrates is not affected by higher alkali concentration at the end of the pulping, and the yield losses are caused by a better lignin removal.}, number={6}, journal={HOLZFORSCHUNG}, author={Venica, Albert D. and Chen, Chen-Loung and Gratzl, Josef S.}, year={2008}, month={Nov}, pages={637–644} }
 @article{capanema_balakshin_chen_gratzl_2006, title={Oxidative ammonolysis of technical lignins. Part 4. Effects of the ammonium hydroxide concentration and pH}, volume={26}, ISSN={["0277-3813"]}, DOI={10.1080/02773810600582350}, abstractNote={Abstract The effects of ammonium hydroxide concentration and pH on the kinetics and reaction mechanism of oxidative ammonolysis of Repap organosolv lignin were studied. The reactions were carried out at 100°C with an oxygen pressure of 8 bar (116 psi) and 0.4–1.6 M [NH4OH] and 9–12.7 pH. The resulting N‐modified lignins were analyzed for elemental composition and methoxyl group content. An increase in ammonium hydroxide concentration increased the rate of nitrogen incorporation, oxygen consumption, CO2 formation, and lignin dissolution. The rate of nitrogen incorporation was 0.5 order with respect to NH4OH concentration. The amount of oxygen consumed, oxygen incorporated into the lignin, CO2 formed, and OMe groups eliminated per mole of nitrogen incorporated decreased with increasing ammonium hydroxide concentration indicating that the increase in [NH4OH] accelerated nitrogen incorporation more than lignin oxidation. The dependence of the rate of nitrogen incorporation on the reaction pH went through a maximum leading to the conclusion that HO− competes with ammonia in reactions with electrophilic lignin centers resulting in interruption of nitrogen incorporation into the lignin.}, number={1}, journal={JOURNAL OF WOOD CHEMISTRY AND TECHNOLOGY}, author={Capanema, EA and Balakshin, MY and Chen, CL and Gratzl, JS}, year={2006}, pages={95–109} }
 @article{wang_chen_gratzl_2005, title={Dechlorination of chlorophenols found in pulp bleach plant E-1 effluents by advanced oxidation processes}, volume={96}, ISSN={["1873-2976"]}, DOI={10.1016/j.biortech.2004.08.011}, abstractNote={Studies were conducted on the response of 2,4,6-trichlorophenol (1), 2,3,4,5-tetrachloro-phenol (2) and 4,5-dichloroguaiacol (3) toward advanced oxidation processes, such as UV-, O2/UV-, H2O2/UV-, O3/UV- and O3-H2O2/UV-photolyses with irradiation of 254 nm photons. The compounds 1-3 are among the chlorophenols found in the Kraft-pulp bleach plant E-1 effluents. The studies were extended to treatment of these compounds with ozonation and O3-H2O2 oxidation systems in alkaline aqueous solution. Except for the O2/UV-photolysis of 1 and H2O2/UV-photolysis of 2, the dechlorination of 1-3 by O2/UV- and H2O2/UV-potolyses were less effective than the corresponding N2UV-potolysis of 1-3. Guaiacol-type chlorophenols were more readily able to undergo dechlorination than non-guaiacol type chlorophenols by N2/UV-, O2/UV- and H2O2/UV-potolyses. In addition, the efficiency for the dechlorination of 1-3 by N2/UV-, O2/UV- and H2O2/UV-potolyses appeared to be dependent upon the inductive and resonance effects of substituents as well as number and position of chlorine substituent in the aromatic ring of the compounds. The dechlorination of 2 by treatment with O3 alone is slightly more effective than the corresponding the O3/UV-photlysis, whereas the dechlorination of 2 by treatment with the combination of O3 and H2O2 was slightly less effective than the corresponding O3-H2O2/UV-photolysis. In contrast, the dechlorination of 3 on treatment with O3 alone was slightly less effective than the corresponding the O3/UV-photolysis, whereas the dechlorination of 3 on treatment with the combination of O3 and H2O2 was slightly more effective than the corresponding the O3-H2O2/UV-photolysis. In the dechlorination of 2 and 3, chemical species derived from ozone and hydrogen peroxide in alkaline solution were dominant reactions in the O3/UV- and O3-H2O2/UV-photolysis systems as in the O3 and O3-H2O2 oxidation systems. Possible dechlorination mechanisms involved were discussed on the basis of kinetic data.}, number={8}, journal={BIORESOURCE TECHNOLOGY}, author={Wang, R and Chen, CL and Gratzl, JS}, year={2005}, month={May}, pages={897–906} }
 @article{xie_chen_gratzl_2005, title={Dechlorination of pulp bleaching plant E-1 effluent by ArF* and KrF* excirner laser photolysis. Part 1. Dechlorination of chlorophenols identified in E-1 effluent}, volume={172}, ISSN={["1010-6030"]}, DOI={10.1016/j.jphotochem.2004.10.021}, abstractNote={Among the chlorophenols identified in the bleaching plant E-1 effluent, 4,5-chloroguaiacol (2), 3,4,5,6-tetrachloroguaiacol (3), 2,4,6-trichlorophenol (4) and 2,3,4,5-chlorophenol (5) were selected as model compounds for dechlorination at pH 7 and 10.5 in nitrogen- and oxygen-saturated aqueous solutions at 20 °C by ArF* (193 nm) and KrF* (248 nm) excimer laser photolyses. The ArF* (193 nm) excimer laser photolysis was more effective than the KrF* (248 nm) excimer laser photolysis in dechlorinating 2–5. The dechlorinations of 2–5 were determined to be first order reactions; first order with respect to total organically bound chlorine of substrate, first order overall. The efficiency of dechlorination was found to depend on the initial pH of reaction mixture, substituent pattern of 2–5, and the wavelength of excimer laser radiation. The dechlorination rates of chlorinated guaiacols 2 and 3 were faster than the chlorinated phenols 4 and 5 under the same reaction condition while rate of 3 was faster than that of 2. Furthermore, the dechlorination rate of a substrate increased with increasing initial pH. The dechlorination rates of chlorophenols investigated were almost the same in N2- and O2-saturated solutions. However, when 2% H2O2 per substrate was added to the initial reaction mixture of 5 in the ArF* (193 nm) excimer laser photolysis, the dechlorination rate increased considerably. Quantum yields (Φ) for the generation of chloride ions were determined for the ArF* (193 nm) and KrF* (248 nm) excimer laser photolyses of 2–5 in both N2- and O2-saturated solutions. In general, the quantum yields in O2-saturated solutions were slightly higher than the corresponding values in N2-saturated solutions and was increased appreciably with addition of 2% H2O2.}, number={3}, journal={JOURNAL OF PHOTOCHEMISTRY AND PHOTOBIOLOGY A-CHEMISTRY}, author={Xie, TY and Chen, CL and Gratzl, JS}, year={2005}, month={Jun}, pages={222–230} }
 @article{xie_chen_gratzl_2005, title={Dechlorination of pulp bleaching plant E-1 effluent by ArF* and KrF* excirner laser photolysis. Part 2. Dechlorination of polychlorinated oxylignins}, volume={172}, ISSN={["1010-6030"]}, DOI={10.1016/j.jphotochem.2004.11.018}, abstractNote={Abstract The E-1 effluent from bleaching of pine kraft pulp was fractionated by ultrafiltration to obtain polychlorinated oxylignin fractions, PCOL-1, PCOL-2, PCOL-3 and POCL-4 with relative molecular mass ( M r ) of 6500, 6000, 5500 and 3500, respectively. These PCOLs were characterized by elemental and functional group analyses, and gel permeation chromatography. The PCOLs were decolorized and dechlorinated in the presence of H 2 O 2 in O 2 -saturated solution at 20 °C by ArF * (193 nm) excimer photolysis. The results showed that both the decolorization and dechlorination were dependent on both the initial pH and concentration of H 2 O 2 per substrate in the reaction mixture. In general, the decolorization increases with increasing pH and concentration of added H 2 O 2 . At pH 10.5 with 8% H 2 O 2 per substrate to the initial reaction mixture, approximately 70% of chromophoric structures were degraded within the initial 60 min irradiation of ArF * (193 nm) laser radiation, then leveled off. The dechlorination reactions followed first order reaction law; first order with respect to total organically bound chlorine; first order overall. The dechlorination rates increase with increasing both pH and concentration of H 2 O 2 per substrate. The quantum yields ( Φ ) for the generation of chloride ions from PCOLs in the presence of 2% H 2 O 2 were appreciably lower than the values observed for the monomeric chlorophenols, in the range of approximately 0.03 versus 0.9. The ArF * excimer laser photolysis of PCOLs were also monitored by gel permeation chromatography. PCOL-2 was degraded into fragments with relative molecular mass ( M r ) of approximately 1500. Similarly, PCOL-3 and PCOL-4 were degraded into fragments with M r of approximately 4000 and 3000, respectively. In contrast, the M r of PCOL-1 was increased to approximately 6500, indicating the occurrence of condensation among the degraded fragments.}, number={3}, journal={JOURNAL OF PHOTOCHEMISTRY AND PHOTOBIOLOGY A-CHEMISTRY}, author={Xie, TY and Chen, CL and Gratzl, JS}, year={2005}, month={Jun}, pages={231–240} }
 @article{wang_chen_gratzl_2004, title={Dechlorination and decolorization of chloro-organics, in pulp bleach plant E-1 effluents, by advanced oxidation processes}, volume={94}, DOI={10.1016/j.biotech.2004.01.005}, number={3}, journal={Bioresource Technology}, author={Wang, R. and Chen, C. L. and Gratzl, J. S.}, year={2004}, pages={267–274} }
 @article{wang_chen_gratzl_2004, title={Ozonation of pine kraft lignin in alkaline solution. Part 1: Ozonation, characterization of kraft lignin and its ozonated preparations}, volume={58}, ISSN={["1437-434X"]}, DOI={10.1515/HF.2004.116}, abstractNote={Abstract Pine kraft lignin was purified to obtain a kraft lignin preparation (KL) with weight average molecular mass (Mw) of 5500. The KL was then ozonated with an ozone-air stream containing 2–2.5% of ozone in 0.1 M sodium hydroxide solution to prepare ozonated kraft lignin preparations with ozone consumption of 10, 25, 30 and 40% per KL; Oz-10-KL, Oz-25-KL, Oz-30-KL and Oz-40-KL, respectively. The pH of reaction mixture was decreased with increasing ozone consumption, while the carboxylic acid content and the Mw of resulting ozonated lignins increase with increasing ozone consumption. The KL and its ozonated preparations were then characterized by elemental composition, functional group analysis, molecular mass distribution and nitrobenzene-K4MnO4 oxidation. The results showed that the KL extensively undergoes oxidative cleavage of both side chains and aromatic moieties without decrease in the Mw as well as dehydrogenationive coupling of phenolic degraded fragments by active oxygen radical species, such as hydroperoxyl and hydroxyl radicals. The formation of these active oxygen radical species are produced by way of a series of reactions initiated by the reaction of ozone with hydroxide anions at pH range of 12.4–10.5, producing superoxide (-O2•) and hydroperoxyl (HOO•) radicals.}, number={6}, journal={HOLZFORSCHUNG}, author={Wang, R and Chen, CL and Gratzl, JS}, year={2004}, pages={622–630} }
 @article{wang_chen_gratzl_2004, title={Ozonation of pine kraft lignin in alkaline solution. Part 2: Surface active properties of the ozonated kraft lignins}, volume={58}, ISSN={["1437-434X"]}, DOI={10.1515/HF.2004.117}, abstractNote={Abstract The surface tension and interfacial tension of the F-1000, F-1800, F-5000 and F-15000 fractions obtained by ultrafiltration of the Oz-25-KL, Oz-30-KL and Oz-40-KL preparations (ozonated kraft lignin, KL, preparations with ozone consumption of 25, 30 and 40% per KL) were determined with the concentration range of 1–30 g l-1 at pH of 6, 9 and 11. The surface tension of these ozonated KL preparations decreased with increasing concentration and pH according to the simplified Gibbs adsorption equation for dilute aqueous solution, ∂γ= -RTΓ∂(ln C). The results were discussed in term of functional group contents and weight average molecular mass (Mw) of the ozonated KL preparations. The surface tension of the ozonated KL preparations decreased with increasing carboxylic acid content and, to some extent, phenolic hydroxyl content, but increased with increasing Mw. The synergistic effect of the ozonated KL preparations with a commercial surfactant was then investigated. The oil-water interfacial tension was determined in the ozonated KL preparations in an aqueous solution containing 1.5% Petrostep B-120R and 1.5% sodium chloride with hexane as oil phase by spinning drop technique. The interfacial tension of the system also decreased with increasing the concentration of ozonated KL preparations in the range of 1–16 g l-1 according to the simplified Gibbs adsorption equation. Thus, the addition of a small amount of ozonated KL preparations to the aqueous solution containing 1.5% Petrostep B-120R and 1.5% sodium chloride showed a remarkable synergistic effect on reducing the interfacial tension.}, number={6}, journal={HOLZFORSCHUNG}, author={Wang, R and Chen, CL and Gratzl, JS}, year={2004}, pages={631–639} }
 @article{alves_capanema_chen_gratzl_2003, title={Comparative studies on oxidation of lignin model compounds with hydrogen peroxide using Mn(IV)-Me(3)TACN and Mn(IV)-Me4DTNE as catalyst}, volume={206}, ISSN={["1381-1169"]}, DOI={10.1016/S1381-1169(03)00448-5}, abstractNote={Comparative studies are conducted on the kinetics and reaction mechanism for the oxidation of lignin model compounds, 1-(3,4-dimethoxyphenyl)ethanol (1), 1-(3,4-dimethoxyphenyl)-1-propene (2) and E-1,2-diphenylethene (3) with hydrogen peroxide at reaction temperatures below 80 °C using [LMn(IV)(μ-O)3Mn(IV)L](PF6)2 (C-1) and [L′Mn(IV)(μ-O)3Mn(IV)](ClO4)2 (C-2) as catalyst. The disappearance rate of 1 and 2 in the first phase of C-1-catalyzed oxidation increases up to the temperature range of 50–60 °C then decreases with increasing reaction temperature. The cause for the slow down of the disappearance rate is not known. Based on the kinetic data and reaction products identified, C-1 is found to be more effective as catalyst in the oxidation of 1 and 2 than C-2, but less effective in the oxidation of 3. In the C-1- and C-2-catalyzed oxidation, 1 is oxidized to the corresponding α-carbonyl derivative 4, while 2 readily undergoes epoxidation of the conjugated double bond to produce the corresponding epoxides 5 and 6. The anti-Markovnikov nucleophilic addition of hydroxide and hydroperoxide anions on 5 and 6 then produced α,β-diol 7 and benzaldehyde derivative 8, which are non-catalytic reactions and rate determining steps. The compound 3 also undergoes epoxidation of conjugated aliphatic double bond producing the corresponding epoxide 9. However, none of the corresponding α,β-diol and benzaldehyde derivative is detected in the reaction mixture. In addition, 2 is more susceptible to expoxidation than 3. On the basis of the kinetics and reaction mechanism of the reactions, the catalytic cycles of the C-1- and C-2-catalyzed oxidation of 1–3 are postulated.}, number={1-2}, journal={JOURNAL OF MOLECULAR CATALYSIS A-CHEMICAL}, author={Alves, V and Capanema, E and Chen, CL and Gratzl, J}, year={2003}, month={Oct}, pages={37–51} }
 @article{capanema_balakshin_chen_gratzl_kirkman_2002, title={Oxidative ammonolysis of technical lignins - Part 3. Effect of temperature on the reaction rate}, volume={56}, ISSN={["0018-3830"]}, DOI={10.1515/HF.2002.063}, abstractNote={Summary The effect of the reaction temperature on the kinetics and the reaction mechanism of oxidative ammonolysis of Repap organosolv lignin have been studied. The reaction was conducted in 0.8 M Nh4oh solution under oxygen pressure of 12 bar and at three different temperatures, 70 °C, 100 °C and 130 °C. The resulting N-modified lignins were analyzed by elemental and methoxyl group. About 20–25% of maximum nitrogen content is incorporated into the lignin very fast, in 1–2 min of the reaction. The reaction kinetics then follows a pseudo-first order reaction law and consists of two phases. The activation energies for nitrogen incorporation and lignin solubilization are rather low, in the range of 33–34 kJ/mol. Linear correlation between nitrogen incorporated into the lignin and molecular oxygen uptake, oxygen incorporation, CO2 formation, O-demethylation and total carbon loss was analyzed at the different reaction temperatures. On the basis of kinetic data obtained so far, we have postulated that the reaction temperature affects the reaction rate, but not the reaction pathways. The reaction temperature also affects the ratios between different reaction pathways, though the effect is not very strong. The results obtained are discussed in the terms of competitive reactions of lignin oxidation followed by nitrogen incorporation and lignin deactivation involving nitrogen}, number={4}, journal={HOLZFORSCHUNG}, author={Capanema, EA and Balakshin, MY and Chen, CL and Gratzl, JS and Kirkman, AG}, year={2002}, pages={402–415} }
 @article{balakshin_chen_gratzl_kirkman_jakob_2001, title={Biobleaching of pulp with dioxygen in laccase-mediator system - effect of variables on the reaction kinetics}, volume={16}, ISSN={["1873-3158"]}, DOI={10.1016/S1381-1177(01)00062-5}, abstractNote={Comparative studies were carried out on the kinetics and mechanism of pulp biobleaching with laccase-mediator system (LMS) with two different mediators, 1-hydroxybenzotriazole (HOBT) and N-hydroxyacetanilide (NHAA). The optimal NHAA and laccase charge was found to be 0.1 mmol and 10 U per gram of pulp with pulp consistency of 10%, at the reaction temperature of 40 °C for 8 h under atmospheric pressure, respectively. The kinetic studies on Kappa number reduction and dioxygen uptake suggest that a very fast rate of delignification with NHAA at the beginning of the process is the result of fast formation of the oxidized mediator species. However, a very slow delignification rate after the initial phase (0.5–1 h) could be caused by low stability of the mediator species. After the reaction time of 2 h, the degree of delignification is higher when HOBT is used as mediator. In contrast to the delignification with NHAA, the formation of the oxidized mediator species is the rate-determining step of the pulp biobleaching with dioxygen in the LMS using HOBT as mediator. Increase in temperature increases the rate of chemical reactions, but decreases the laccase stability. The optimal temperature for pulp biobleaching with HOBT and laccase from Coriolus versicolor is 40 °C. Increasing oxygen pressure improves the efficiency of delignification due to better penetration of the reagents, but does not affect the rate of chemical reactions. The reaction mechanism is discussed based on the kinetic data.}, number={3-4}, journal={JOURNAL OF MOLECULAR CATALYSIS B-ENZYMATIC}, author={Balakshin, M and Chen, CL and Gratzl, JS and Kirkman, AG and Jakob, H}, year={2001}, month={Dec}, pages={205–215} }
 @article{balakshin_capanema_chen_gratzl_kirkman_gracz_2001, title={Biobleaching of pulp with dioxygen in the laccase-mediator system - reaction mechanisms for degradation of residual lignin}, volume={13}, ISSN={["1873-3158"]}, DOI={10.1016/S1381-1177(00)00225-3}, abstractNote={Pine Kraft-AQ pulp was biobleached with pressurized dioxygen at 40°C in laccase-mediator system (LMS), i.e. in acetate buffer (pH 4.5) containing Coriolus-laccase and 1-hydroxy-benzotriazole (HOBT), the latter being as a mediator. The LMS-treatment was followed by alkaline extraction (E) under standard conditions. The structures of the residual lignins before and after the biobleaching did not differ appreciably. This indicates that only a part of the residual lignin in the pulp undergoes oxidative degradation in the LMS treatment. In contrast, the treatment resulted in strong changes in the structure of the lignin isolated from E-effluents. The 2D HMQC (1H13C correlation) spectra showed the disappearance of β-O-4′, β-β′ and β-5′ bonds in the structure of the alkaline soluble lignin (ASL) from E-effluents, which are present in the 2D spectrum of the original residual lignin (RKL). In addition, the spectra exhibited new signals that are assigned to ArCOOH in biphenyl (5-5′) moieties. This implies that oxidative cleavage of side chains plays an important role in the delignification of pulp. The NMR studies also indicated that intensive degradation of aromatic ring has occurred in the biobleaching. However, premethylation of neither benzyl alcohol nor phenolic hydroxyl groups of the residual lignin in pulp before the biobleaching affected the rate of delignification. The latter indicates that phenolic moieties participate not only in oxidative degradation but also dehydrogenative polymerization reactions in the biobleaching. This is consistent with an appreciable increase in the proportion of fractions with higher molecular mass in lignin isolated from E-effluents.}, number={1-3}, journal={JOURNAL OF MOLECULAR CATALYSIS B-ENZYMATIC}, author={Balakshin, M and Capanema, E and Chen, CL and Gratzl, J and Kirkman, A and Gracz, H}, year={2001}, month={Apr}, pages={1–16} }
 @article{capanema_balakshin_chen_gratzl_kirkman_2001, title={Oxidative ammonolysis of technical lignins - Part 1. Kinetics of the reaction under isothermal condition at 130 degrees C}, volume={55}, ISSN={["0018-3830"]}, DOI={10.1515/HF.2001.066}, abstractNote={Summary Investigations were conducted on the oxidative ammonolysis of REPAP organosolv lignin at 130 °C in 0.8M NH4OH solution under oxygen pressure of 12 bar. The lignin was completely solubilized at the reaction time of 165 min. The kinetics of the nitrogen incorporation consists of two phases. The first phase is up to the reaction time of approximately 35 min including 15 min heating up period. The rate of nitrogen incorporation in the first phase is 2.3 times higher than that in the second phase: κ1 = 4.58 × 10−4 s−1 versus κ2 = 1.90 × 10−4 s−1. The oxygen uptake and CO2 formation in the reaction is rather high. When the nitrogen incorporation was ceased after reaction for 255 minutes, more than 4 moles of oxygen/C9-unit of lignin were consumed and approximately 1.5 moles of carbon dioxide/C9-unit of lignin were released. In addition, extensive O-demethylation of methoxyl groups occurred. The molar ratio of the nitrogen incorporation to the methoxyl group eliminated is approximately 1.4 and 0.7 for the soluble and insoluble N-modified lignins, respectively. Structural analyses of the soluble N-modified lignins by FTIR and 1H NMR spectroscopic techniques showed only quantitative differences in the spectra obtained at different reaction times. This indicates that the reaction pathways do not change in the course of the oxidative ammonolysis. Possible reaction mechanisms of the oxidative ammonolysis are discussed on the basis of the experimental data.}, number={4}, journal={HOLZFORSCHUNG}, author={Capanema, EA and Balakshin, MY and Chen, CL and Gratzl, JS and Kirkman, AG}, year={2001}, pages={397–404} }
 @article{capanema_balakshin_chen_gratzl_kirkman_2001, title={Oxidative ammonolysis of technical lignins - Part 2. Effect of oxygen pressure}, volume={55}, ISSN={["0018-3830"]}, DOI={10.1515/HF.2001.067}, abstractNote={Summary Investigations were conducted on the effects of oxygen pressure on the oxidative ammonolysis of REPAP organosolv lignin at 130 °C under oxygen pressure of 5, 8 and 12 bar. The rates of reactions monitored, such as nitrogen incorporation, lignin solubilization, oxygen uptake and CO2 formation, increase with increasing oxygen pressure. Kinetics of nitrogen incorporation under different oxygen pressure consists of two phases and follows a first order law in each phase. Linear correlation between the rate of nitrogen incorporation and oxygen pressure implies that the reaction is first order with respect to oxygen concentration. This indicates that oxygen participates directly in the rate-determining step of nitrogen incorporation. The rate of lignin solubilization also linearly increases with increasing oxygen pressure, implying that the rate of lignin degradation directly depends on oxygen pressure. The nitrogen incorporation is linearly correlated with the oxygen uptake, CO2 formation, oxygen incorporation into lignin, loss of carbon and methoxyl group content under all values of oxygen pressure and during the entire reaction period. This suggests that the reactions in the oxidative ammonolysis of lignin proceed via the same pathways in the different kinetic phases. In addition, the changes in the oxygen pressure were found to have only minor effect upon the coefficients of these linear correlations. This is in good agreement with the structures of N-modified lignin elucidated from FTIR and indicates that oxygen pressure affects only the reaction rate, but not the reaction mechanism.}, number={4}, journal={HOLZFORSCHUNG}, author={Capanema, EA and Balakshin, MY and Chen, CL and Gratzl, JS and Kirkman, AG}, year={2001}, pages={405–412} }
 @article{capanema_balakshin_chen_gratzl_gracz_2001, title={Structural analysis of residual and technical lignins by H-1-C-13 correlation 2D NMR-spectroscopy}, volume={55}, ISSN={["1437-434X"]}, DOI={10.1515/HF.2001.050}, abstractNote={Summary Structural analysis was conducted on residual lignin from pine Kraft AQ pulp, Eucalyptus Kraft lignin from Eucalyptus globulus and Repap Organosolv lignin by 2D 13C-1H correlation NMR spectroscopic techniques such as HMQC sequence. These lignins contain a rather wide variety of saturated aliphatic groups. The HMQC NMR spectra of the lignins do not verify the presence of diarylmethane moieties in any lignin investigated. The type and amount of other condensed structures depend on the nature of lignin preparation. All the lignins investigated still contained β-O-4′, pino- and syringayresinol (β-β′) and phenylcoumarane (β-5′) structures. Stilbene structures were also identified. Vinyl ether structures were present only in Eucalyptus Kraft lignin. All the lignins contain α-carbonyl groups conjugated to aromatic moieties as terminal side chains rather than involving β-O-4′ structures. No coniferyl alcohol and coniferyl aldehyde type structures are detected in the lignins after pulping. The spectra of kraft lignins show some new signals, the origin of which is discussed.}, number={3}, journal={HOLZFORSCHUNG}, author={Capanema, EA and Balakshin, MY and Chen, CL and Gratzl, JS and Gracz, H}, year={2001}, pages={302–308} }
 @article{balakskin_chen_gratzl_kirkman_jakob_2000, title={Biobleaching of pulp with dioxygen in the laccase-mediator system. Part 1. Kinetics of delignification}, volume={54}, ISSN={["0018-3830"]}, DOI={10.1515/HF.2000.066}, abstractNote={Summary Kinetics of pine kraft-AQ pulp delignification with the laccase-mediator system (LMS) and the effects of variable factors on the delignification were studied. The delignification was conducted in acetate buffer solution at pH 4.5 and at 40°C under atmospheric pressure. Only a part of the residual lignin could be removed in one-stage processes. Kinetics of kappa number reduction follows a pseudo-second order rate law with pulp consistency of 10 %, mediator charge of 0.1 mmole HOBT/g pulp and laccase charage of 10 U Coriolus laccase/g pulp. Kinetics of dioxygen uptake follows a pseudo-first order rate law up to first 8 hours of the reaction and a pseudo-zero order rate law at the reaction time of 8–24 hours. The amounts of dioxygen consumed per removal of one C9-unit equivalent of residual lignin is rather high, 1.5–2.5 mole, and increases with increasing reaction time. Experimental data show that side reactions between the Laccase-Mediator System and products of oxidative degradation of lignin strongly inhibit the delignification either by chemical or physical means or both. Removal of the degraded lignin fragments by alkaline extraction effectively restores the delignification of pulp with LMS. A four-stage process consisting of consecutive treatment of pulp with dioxygen-laccase-HOBT (LMS) followed by alkaline extraction (E), (LMS-E)4, decreased kappa number of a pine kraft-AQ pulp from 21.8 to less than 5. On the basis of the kinetic data, the mechanism of the pulp delignification with LMS is discussed.}, number={4}, journal={HOLZFORSCHUNG}, author={Balakskin, M and Chen, CL and Gratzl, JS and Kirkman, AG and Jakob, H}, year={2000}, pages={390–396} }
 @article{gratzl_chen_2000, title={Chemistry of pulping: Lignin reactions}, volume={742}, journal={Lignin: Historical, biological, and materials perspectives}, publisher={Washington, DC: American Chemical Society}, author={Gratzl, J. S. and Chen, C. L.}, editor={W. G. Glasser, R. A. Northey and Schultz, T. P.Editors}, year={2000}, pages={392–421} }
 @article{potthast_rosenau_kosma_chen_gratzl_2000, title={Confirmation of the presence of formaldehyde and N-(methylene)morpholinium cations as reactive species in the cellulose/NMMO/water system by trapping reactions}, volume={54}, ISSN={["0018-3830"]}, DOI={10.1515/HF.2000.016}, abstractNote={Summary The presence of formaldehyde (4) in solutions of cellulose in N-methylmorpholine-N-oxide (NMMO, 1) has been shown by trapping formaldehyde as dimedone adduct 8 in a two-phase system. o-Dichlorobenzene was used as an inert solvent to extract the trapping product as soon as it had formed. Morpholine is a degradation product of NMMO and is always present in systems containing NMMO. Formaldehyde can react with morpholine to form an intermediate carbenium-iminium ion, N-(methylene) morpholinium (6). The occurrence of 6 in the system cellulose/NMMO was demonstrated by trapping this intermediate in a Mannich type reaction with 2-acetonaphthone (9). Both formaldehyde and N-(methylene)morpholinium cations are highly reactive species readily undergoing further reactions with nucleophiles. These processes might contribute to the observed discoloration of the reaction mixture, and might also be responsible for the decomposition of NMMO that is inducible by carbenium-iminium ions.}, number={1}, journal={HOLZFORSCHUNG}, author={Potthast, A and Rosenau, T and Kosma, P and Chen, CL and Gratzl, JS}, year={2000}, pages={101–103} }
 @article{balakshin_chen_gratzl_kirkman_jakob_2000, title={Kinetic studies on oxidation of veratryl alcohol by laccase-mediator system - Part 1. Effects of mediator concentration}, volume={54}, ISSN={["0018-3830"]}, DOI={10.1515/HF.2000.028}, abstractNote={Summary Kinetics of the laccase-catalyzed oxidation of veratryl alcohol with dioxygen in the presence of 2,2′-Azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) diamonium salt (ABTS), the mediator, were studied to elucidate the possible reaction mechanism and the role of the mediator in this reaction. The reaction follows a pseudo-first order reaction law. The first order rate constant (κ) is dependent on the Mediator/Substrate (M/S) ratio and has a maximum at M/S molar ratio of 0.15. The kinetic studies show that the mechanism of veratryl alcohol oxidation with dioxygen-laccase-ABTS is rather complex and includes different reaction pathways. The mediator is involved in competitive reactions. It has been suggested that at low mediator concentration, the veratryl alcohol is oxidized via the laccase redox cycle. The mediator acts mostly as a laccase activator at a M/S ratio lower than 0.15. With increasing ABTS concentration with respect to the substrate concentration, ABTS acts increasingly as a cosubstrate competing with the original substrate for active centers of the laccase. This results in inhibition of veratryl alcohol oxidation in the enzyme cycle and increases the role of substrate oxidation by an oxidized mediator.}, number={2}, journal={HOLZFORSCHUNG}, author={Balakshin, MY and Chen, CL and Gratzl, JS and Kirkman, AG and Jakob, H}, year={2000}, pages={165–170} }
 @article{balakshin_chen_gratzl_kirkman_jakob_2000, title={Kinetic studies on oxidation of veratryl alcohol by laccase-mediator system. Part 2. The kinetics of dioxygen uptake}, volume={54}, ISSN={["0018-3830"]}, DOI={10.1515/HF.2000.029}, abstractNote={Summary The kinetics of dioxygen uptake in the laccase-catalyzed oxidation of veratryl alcohol with dioxygen in the presence of ABTS, the mediator, was studied. The kinetics of dioxygen uptake consists of two phases: (1) the initial phase up to a reaction time of one hour, and (2) the second phase, after a reaction time of one hour. In the initial phase, ABTS is mainly oxidized to the corresponding cation radical. The kinetics of dioxygen uptake follows a pseudo-zero order rate law. The dioxygen uptake under the reaction condition correlates with the initial ABTS concentration according to the stoichiometric relationship of 0.25 moles dioxygen per mole ABTS. In the second phase, veratryl alcohol is mainly oxidized to veratraldehyde. The kinetics of the dioxygen uptake follows a pseudo-first order rate law. The dioxygen uptake correlates linearly with the yield of veratraldehyde. The stoichiometric ratio between the formation of veratraldehyde and the consumption of dioxygen differs slightly at different M/S ratios. On average, however, it is 0.42 moles of dioxygen per one mole of veratraldehyde formed. The reaction mechanism is discussed on the basis of the kinetic data.}, number={2}, journal={HOLZFORSCHUNG}, author={Balakshin, MY and Chen, CL and Gratzl, JS and Kirkman, AG and Jakob, H}, year={2000}, pages={171–175} }
 @article{cui_puthson_chen_gratzl_kirkman_2000, title={Kinetic study on delignification of kraft-AQ pine pulp with hydrogen peroxide catalyzed by Mn(IV)-Me4DTNE}, volume={54}, ISSN={["1437-434X"]}, DOI={10.1515/HF.2000.069}, abstractNote={Summary The kinetics of delignification of a kraft-AQ southern pine pulp with hydrogen peroxide catalyzed by [LMn(IV)(μ-O)3Mn(IV)](ClO4)2 (1), where L = 1,2-bis(4,7-dimethyl-1,4,7-triazacyclonon-1-yl)ethane was studied. The degree of delignification was significantly improved by using the catalyst. The pulp was bleached for 2 hours at 80°C, in 10% consistency with 2% NaOH, 4% H2O2 and 60 ppm catalyst charges on pulp (O.D.). Kappa number of the pulp was reduced from 31.6 to 16.8 corresponding to a degree of delignification of approximately 4%, while GE brightness was increased from 24.2 to 44.7. At the same time, viscosity of the resulting pulp was reduced from 31.1 mPa•s to 20.1 mPa•s compared to the reduction from 31.1 mPa•s to 20.1 mPa•s in the uncatalyzed bleaching under the same reaction condition. This indicates that the degradation of the carbohydrates was moderate in the catalyzed bleaching compared to the uncatalyzed bleaching. The delignification was found to follow pseudo first order kinetics with respect to kappa number, i.e., residual lignin, in the initial phase and quickly slowed down after 30 minutes (residual phase) under all the reaction temperatures investigated. The delignification rate constants in the initial phase were 0.17, 0.18, and 0.21 min−1 at 50, 60, and 80°C, respectively. Degree of delignification at the delignification time of 30 minutes is approximately 40% at 80°C. The possible delignification mechanism was discussed on the basis of the kinetic studies and lignin model compound experiments.}, number={4}, journal={HOLZFORSCHUNG}, author={Cui, Y and Puthson, P and Chen, CL and Gratzl, JS and Kirkman, AG}, year={2000}, pages={413–419} }
 @article{chen_potthast_rosenau_gratzl_kirkman_nagai_miyakoshi_2000, title={Laccase-catalyzed oxidation of 1-(3,4-dimethoxyphenyl)-1-propene using ABTS as mediator}, volume={8}, ISSN={["1381-1177"]}, DOI={10.1016/S1381-1177(99)00059-4}, abstractNote={The fungal laccases catalyzed oxidation of 1-(3,4-dimethoxyphenyl)-1-propene (2) with dioxygen in acetate buffer (pH 4.5) producing 1-(3,4-dimethoxyphenyl)propane-1,2-diol (4) and its 1-O-acetyl and 2-O-acetyl derivatives 5 and 6, and 3,4-dimethoxybenzaldehyde (7). However, in phosphate buffer (pH 5.9), the same reaction produced only 4 and 7. When 4 was treated in the same fashion in the phosphate buffer, it was converted into 7 with more than 95 mol% yield. This, together with the formation of 5 and 6 in the acetate buffer, showed that 2 is converted into 3–5 via 1-(3,4-dimethoxyphenyl)propane-1,2-epoxide (3) in the acetate buffer in the presence of ABTS. The major reaction of fungal laccase-catalyzed oxidation of 2 with dioxygen in the presence of ABTS is epoxidation of the double bond conjugated to the aromatic ring.}, number={4-6}, journal={JOURNAL OF MOLECULAR CATALYSIS B-ENZYMATIC}, author={Chen, CL and Potthast, A and Rosenau, T and Gratzl, JS and Kirkman, AG and Nagai, D and Miyakoshi, T}, year={2000}, month={Feb}, pages={213–219} }
 @article{cui_chen_gratzl_patt_1999, title={A Mn(IV)-Me4DTNE complex catalyzed oxidation of lignin model compounds with hydrogen peroxide}, volume={144}, ISSN={["1381-1169"]}, DOI={10.1016/S1381-1169(99)00042-4}, abstractNote={1-(3,4-dimethoxyphenyl)ethanol, 1-(3,4-dimethoxyphenyl)-1-propene (mixture of E- and Z-isomers) and E-1,2-diphenylethene were chosen as model compounds to investigate the reactivity of lignin toward hydrogen peroxide catalyzed by [L′Mn(IV)(μ-O)3Mn(IV)](ClO4)2 where L′ is 1,2-bis-(4,7-dimethyl-1,4,7-triazacyclonon-1-yl)ethane. All the model compounds investigated were readily oxidized to a significant extent by hydrogen peroxide when catalyzed by this complex. The reaction products were identified by GCMS, and the reaction kinetics was studied. Based on these results, the mechanisms of the reactions have been elucidated. The catalyst preferentially epoxidates C–C double bonds conjugated with aromatic moieties. The activation energy of the reactions was determined.}, number={3}, journal={JOURNAL OF MOLECULAR CATALYSIS A-CHEMICAL}, author={Cui, Y and Chen, CL and Gratzl, JS and Patt, R}, year={1999}, month={Aug}, pages={411–417} }
 @misc{rosenau_potthast_kosma_chen_gratzl_1999, title={Autocatalytic decomposition of N-methylmorpholine N-oxide induced by Mannich intermediates}, volume={64}, number={7}, journal={Journal of Organic Chemistry}, author={Rosenau, T. and Potthast, A. and Kosma, P. and Chen, C. L. and Gratzl, J. S.}, year={1999}, pages={2166–2167} }
 @misc{chen_gratzl_kirkman_potthast_rosenau_1999, title={Selective enzymatic oxidation of aromatic methyl groups to aldehydes by oxygen in the presence of a laccase-mediator catalyst}, volume={5,888,787}, number={1999 Mar. 30}, publisher={Washington, DC: U.S. Patent and Trademark Office}, author={Chen, C. and Gratzl, J. S. and Kirkman, A. G. and Potthast, A. and Rosenau, T.}, year={1999} }
 @article{kadla_chang_chen_gratzl_1998, title={Reactions of lignin with cyanamide activated hydrogen peroxide Part 1. The degradation of lignin model compounds}, volume={52}, ISSN={["1437-434X"]}, DOI={10.1515/hfsg.1998.52.5.506}, abstractNote={Monomeric lignin model compounds representing various functional groups found in residual lignins were reacted with cyanamide activated hydrogen peroxide. Non-phenolic lignin model compounds failed to react even under extreme reaction conditions (90°C), while phenolic lignin model compounds underwent rapid oxidation. Reaction optimization studies reveal that these reactions are strongly dependent on pH and the cyanamide-to-peroxide ratio, while temperature is not a factor. Through the use of electron paramagnetic resonance (EPR) spectroscopy free radical involvement has been demonstrated. In contrast to previous literature, a predominately free-radical mechanism exists, and on the basis of the reactions carried out in the presence of superoxide dismutase, the presence of .O 2 - has been determined.}, number={5}, journal={HOLZFORSCHUNG}, author={Kadla, JF and Chang, PM and Chen, CL and Gratzl, JS}, year={1998}, pages={506–512} }
 @article{kadla_chang_chen_gratzl_1998, title={Reactions of lignin with cyanamide activated hydrogen peroxide Part 2. The degradation mechanism of phenolic lignin model compounds}, volume={52}, ISSN={["0018-3830"]}, DOI={10.1515/hfsg.1998.52.5.513}, abstractNote={The reactions of monomeric phenolic lignin model compounds with cyanamide activated hydrogen peroxide were studied. Analyses of the various reaction products indicate four main reactions occur : aromatic hydroxylation, demethoxylation, radical coupling and oxidative ring opening. The predominate products from apocynol and acetoguaiacone were dicarboxylic acid compounds, maleic/fumaric, oxalic and succinic acid derivatives, consistent with degradation by superoxide. In the degradation of creosol, 3-hydroxy-4-methoxy-6-methyl-N-methylaniline was the major compound isolated, providing evidence of a cyanamide radical. Finally, plausible pathways to the formation of superoxide anion and cyanamide oxidation products from alkaline hydrogen peroxide and cyanamide are proposed and their impact on delignification is discussed.}, number={5}, journal={HOLZFORSCHUNG}, author={Kadla, JF and Chang, HM and Chen, CL and Gratzl, JS}, year={1998}, pages={513–520} }
 @article{uraki_chen_gratzl_1997, title={Sonolysis of chloro-organics in bleach plant E-1 effluents}, volume={51}, ISSN={["0018-3830"]}, DOI={10.1515/hfsg.1997.51.5.452}, abstractNote={Degradation of chloro-organics in bleach plant E-1 effluents by ultrasound sonication was investigated to evaluate the effects of ultrasonic treatment on the dechlorination. On sonolysis, ca. 65mol% of 4-chlorophenol (1) at concentration of 1.0x10 -4 M in aqueous solution was decomposed and 35mol% of chlorine in the substrate was released as chloride ions (Cl) alter 80 min at room temperature under atmospheric pressure. By contrast, under the same reaction conditions, only ca. 11mol% and 3mol% of (1) were decomposed at the concentrations of 1.0x10 -3 M and 1.0x10 -2 M with the release of ca. 5 and 1mol% of Cl - , respectively. Although the kinetics for the disappearance of (1) fits a first-order law, the rate constant decreases with increasing initial concentration of the substrate. This suggests that the disappearance rate of (1) does not follow the first order law and the reaction mechanism involved is rather complex. When hydrogen peroxide was added to the solution in the molar ratio of substrate to hydrogen peroxide 1:10, both the rates of degradation and dechlorination were not affected. However, an addition of a smaller amount of hydrogen peroxide to the solution resulted in a decrease in the rate of the degradation. In the presence of hydrogen peroxide, the kinetics for the decomposition of (1) also follows the same pattern for that without hydrogen peroxide. On sonolysis, polychlorinated oxylignins (PCOLs) isolated from E-1 effluent released chloride ions. The high relative mass PCOL released larger amounts of chloride ions than the low relative mass PCOL. The sonolysis brought about a very small decrease in the relative mass of PCOLs, and no significant degradation of PCOLs except for release of chloride ions. This result suggests that an acoustic cavitation by ultrasonic treatment plays a important role in cleavage of C-Cl bonds, but not C-C bonds.}, number={5}, journal={HOLZFORSCHUNG}, author={Uraki, Y and Chen, CL and Gratzl, JS}, year={1997}, pages={452–458} }
 @misc{parthasarathy_sundaram_jameel_gratzl_klein_1991, title={Two stage process for the oxygen delignification of lignocellulosic fibers with peroxide reinforcement in the first stage}, volume={5,011,572}, number={1991 Apr. 30}, publisher={Washington, DC: U.S. Patent and Trademark Office}, author={Parthasarathy, V. R. and Sundaram, M. and Jameel, H. and Gratzl, J. S. and Klein, R. J.}, year={1991} }
 @misc{gratzl_1989, title={Process for delignification of cellulosic substances by pretreating with a complexing agent followed by peroxide prior to kraft digestion}, volume={4,826,568}, number={1989 May 2}, publisher={Washington, DC: U.S. Patent and Trademark Office}, author={Gratzl, J. S.}, year={1989} }
 @misc{gratzl_1989, title={Process for the delignification of cellulosic substances by pretreating with a complexing agent followed by hydrogen peroxide}, volume={4,826,567}, number={1989 May 2}, publisher={Washington, DC: U.S. Patent and Trademark Office}, author={Gratzl, J. S.}, year={1989} }