Acid hydrolysis of cellulose. part ii: Stochastic simulation using a monte carlo technique

A Monte Carlo procedure was developed to simulate cellulose acid hydrolysis at high temperatures. Both the kinetic information related to the model compound cellobiose and the morphological aspect of cellulose including crystalline, semi-amorphous and amorphous zones were estimated from experimental data and introduced in a FORTRAN program. In our model of cellulose acid hydrolysis, the cleavage of a glycosidic bond and the degradation of glucose are considered as two irreversible reactions in series. For all the temperatures, the overall glucose disappearance rate constant used in our model, was higher than the experimental constant obtained from the degradation of pure glucose. The changes related to the effects of milling on the cellulose acid hydrolysis were successfully considered in the procedure. Finally, the observed good agreement between the simulated and the experimental data of glucose yield versus time proved that Monte Carlo simulation associated with a Markov chain is a flexible connection between cellobiose (model compound) and cellulose conversion reactions.     

Supercritical hydrolysis of cellulose for oligosaccharide production in combined technology

A combined supercritical/subcritical technology was used as a pre-treatment and hydrolysis method for ethanol production from cellulose/lignocelluloses. In a batch study for supercritical hydrolysis, which is the primary step of the combined technology, 60 mg of microcrystalline cellulose in 2.5 ml deionized water was loaded into each reactor and heated in a salt bath at a selected temperature for a specified reaction time. Cellulose was quickly hydrolyzed to oligosaccharides, hexoses and other small molecular products at temperatures above the critical point of water. Temperature and reaction time were the two key parameters that determined the products of cellulose hydrolysis. The highest yield of oligosaccharides (approximately 40%) was obtained at optimum conditions of 380 °C and a reaction time of 16 s. The corresponding yield of hexoses was 24%, giving a maximum yield of hydrolysis products of approximately 63%. A complete decomposition of hydrolysis products occurred at higher temperatures and/or longer reaction times. A kinetic analysis was performed to explain the reaction of cellulose in supercritical water. The results presented here provide a rigid framework for the use of combined supercritical/subcritical technology in subsequent research.     

The heterogeneous character of the dilute acid hydrolysis of crystalline cellulose

The end-attack model proposed by Sharples [Trans. Faraday Soc., 53 , 1003 (1957)] for the dilute acid hydrolysis of crystalline cellulose was tested using the results from the size-exclusion chromatographic analysis of samples of crystalline cellulose I and cellulose II hydrolyzed in 6.1N HCl at 107°C. The differential number distribution of the molecular weight of hydrolyzed cellulose was found to be approximately exponential, a result which is consistent with the end-attack model. Differences in the rates of hydrolysis of cellulosic materials appear to arise from differences in both the degree of polymerization and the microstructure of hydrolyzed cellulose. Evidence is also presented which suggests that the recrystallization upon hydrolysis results in part from the lateral accretion of chains which are cleaved during the hydrolysis of amorphous regions in the cellulose microfibrils.     

反应器操作方式对酶动力学拆分立体选择性的影响

描述了在批式反应器和连续流搅拌反应器（ＣＳＴＲ）中酶动力学拆分对映异构体的不同之处，从宏观反应器平衡角度，推导出了在ＣＳＴＲ反应器中不同于在批式反应器中的一定酶立体选择性（Ｅ）下，底物或产物的对映体过量值与反应的转化率之间关系的定量关系式。并通过商品脂肪酶及芽胞杆菌Ｅ－５３脂肪酶催化的萘普生甲酯的不对称水解反应得到了证实。分别在批式反应器和ＣＳＴＲ反应器中进行萘普生的酶法拆分，在一定转化率下，批式     

Specific surface to evaluate the efficiencies of milling and pretreatment of wood for enzymatic saccharification

Sieving methods have been almost exclusively used for feedstock size-reduction characterization in the biomass refining literature. This study demonstrates a methodology to properly characterize specific surface of biomass substrates through two dimensional measurement of each fiber of the substrate using a wet imaging technique. The methodology provides more information than sieving methods about biomass substrate. The measured dimensions of individual fibers were used to estimate the substrate external surface based on a cylinder model. The substrate specific surface and mechanical milling energy consumption were then correlated to enzymatic hydrolysis glucose yield. Results indicated that the developed methodology is effective in differentiating various size-reduction and chemical pretreatment processes in terms of cellulose to glucose conversion efficiency and size-reduction energy consumption. Thermomechanical disk milling (DM-I), exposing cellulose, is more effective than a high pressure thermomechanical disk milling (DM-II), exposing lignin, in subsequent enzymatic hydrolysis. However, DM-I is more energy intensive than DM-II. Both DMs that produce fibers are more efficient in enzymatic hydrolysis than hammer milling that produces fiber bundles. Chemical pretreatment not only increased cellulose conversion, but also reduced mechanical milling energy consumption. The present methodology identified the sulfite pretreatment C as the most efficient pretreatment in terms of glucose yield and milling energy consumption.     

Hydrolysis of Penicillin G by Penicillin G Acylase Immobilized on Chitosan Microbeads in Different Reactor Systems

The kinetic parameters for penicillin G hydrolysis in systems with penicillin G acylase from Escherichia coli (free and immobilized on activated chitosan microbeads produced by electrostatic extrusion) were determined. The obtained kinetic results indicated that both systems (free and immobilized) are inhibited by high concentrations of the substrate (penicillin G) as well as by products of the reaction (6‐aminopenicillanic acid and phenylacetic acid). The microbeads appeared convenient for penicillin G acylase immobilization reducing negative inhibitory effects. The hydrolysis was also investigated in a packed bed reactor. The derived kinetic model predicted good hydrolysis rates in the reactor while the system with recirculation of the reaction mixture proved to be a potentially favorable solution providing operation at low shear stresses and possibly higher hydrolysis rates than in the packed bed reactor alone.     

Acid hydrolysis of cellulose. part i. experimental kinetic analysis

The main objective of this investigation is to obtain experimental data for the sulfuric acid hydrolysis of cotton and mechanically pretreated cotton fibres. These data indicate that some glycosidic bonds of cellulose have very high accessibility to catalytic ions. It was also shown that milling increases the accessibility of some glycosidic bonds of cellulose and decreases the volume of the crystalline regions of cotton. From the glucose yield versus time data, it was found that the effect of milling on the rate of cellulose depolymerization depends on the reactivity and accessibility of the glycon rings of cellulose. It was also found that at 1OO°C, the rate of cellulose depolymerization was not affected by the extraction of cotton wax and this was related to a rolling up process of cotton wax caused by melting. The kinetic constants of glucose degradation and cellobiose hydrolysis have been determined for the stochastic simulation of cellulose depolymerization which is the subject of the second part of this work.     

Study on the enzymatic hydrolysis of racemic methyl ibuprofen ester

The hydrolysis of racemic methyl ibuprofen ester in the presence of lipase from Candida rugosa was investigated in shake flasks. Experiments were performed to study the effect of temperature, pH and shaking speed on the reaction rate. Different hydrophobic co‐solvents were screened for the highest reaction rate and the presence of enzyme inhibition by substrate and products was examined. A kinetic expression was then proposed to describe the reaction. Kinetic parameters were determined for the optimum operating conditions and the proposed model was verified with the experimental results. Next, this reaction was scaled up to a fed batch stirred tank reactor. Batch reactor and fed batch reactor configurations were compared for better conversions. The effects of aqueous phase hold‐up, substrate concentration and feed flow rate on the conversion of the reaction were also studied. Higher conversions were obtained in a fed batch reactor when compared with the batch reactor. In the fed batch reactor, increased conversions were observed with lower feed flowrates and high aqueous phase hold‐up. © 2001 Society of Chemical Industry     

Thermodynamic properties of the enzymatic hydrolysis of sunflower oil in high-pressure reactors

On the basis of our previous results, where optimal conditions for the lipase-catalyzed hydrolysis of sunflower oil in a high-pressure batch stirred tank reactor were determined, some thermodynamic and kinetic properties of lipase preparation Lipolase 100T (Aspergillus niger lipase) were established. Activation energy (32.7 kJ/mol) was determined from an Arrhenius plot. Activity of the Lipolase 100T increased between 35 and 50°C, but with further temperature increase thermal deactivation occurred. The thermal deactivation rate constant was 0.40, and the deactivation enthalpy was 123.0 kJ/mol. Because of the desirability of continuous applications of enzyme-catalyzed reactions, a high-pressure continuous flat-shape membrane reactor (HP CFSMR) was designed. Hydrolysis of sunflower oil in this reactor was performed. Maximal conversion in the HP CFSMR was achieved after 1 h. A polysulfone membrane was successfully used as a separation unit, and the highest conversion of FFA was determined at 50°C, 200 bar, and a flow rate for substrates of 0.1 mL/min (each).     

Fatty acid selectivity of microbial lipase and lipolytic enzymes from salmonid fish intestines toward astaxanthin diesters

The objective of the work described in this paper was to study a possible FA selectivity of digestive lipolytic enzymes isolated from salmon and trout intestines toward astaxanthin diesters of various FA composition and compare it with the FA selectivity of microbial lipase. Astaxanthin diesters of varying FA composition were prepared in excellent yields (>90%) by chemical esterification using a carbodiimide coupling aget. The astaxanthin diesters were screened in a hydrolysis reaction by various commercially available lipases. The highest conversion rates were observed with the Candida rugosa lipase, which discriminated against n−3 PUFA. The rate of hydrolysis was determined by HPLC. Digestive lipolytic enzymes isolated from salmon and rainbow trout intestines displayed reversed FA selectivity. Thus, astaxanthin diesters highly enriched with n−3 PUFA including EPA and DHA were observed to be hydrolyzed at a considerably higher rate than the more saturated esters. Similar trends in FA selectivity were observed in the hydrolysis of fish oil TAG by the digestive lipolytic enzyme mixtures.     

Effects of ball milling on structural changes and hydrolysis of lignocellulosic biomass in liquid hot-water compressed carbon dioxide

Mechanical activation is an effective method for destroying the crystalline structure. Biomass, especially its hemicellulose, can be degraded in the green solvent of liquid hot-water compressed carbon dioxide. To improve the degradation of crystalline cellulose in liquid hot-water compressed carbon dioxide, pretreatment of camphorwood sawdust by mechanical activation with a stirring ball mill was studied. Ball milling parameters and their effects on structure were determined by SEM, XRD and FT-IR. The influence of milling parameters on cellulose conversion can be ranked as follows: ball milling speed>activation time>the mass ratio of ball to biomass. The optimum milling condition was obtained at ball milling speed of 450 rpm and mass ratio of 30: 1 of ball to biomass for 2 h. In this condition, cellulose crystallinity of sawdust decreased from 60.93% to 21.40%. The cellulose conversion was 37.8%, which was nearly four times of raw material (10.2%). The glucose yield in the hydrolysate was 1.49 g·L^?1, which was nearly three times of that of raw material. It showed mechanical activation can destroy the crystalline structure of cellulose to promote degradation and the damage of lignocellulosic internal structure caused by ball milling is irreversible.     

Hydrolysis of birch wood by simultaneous ball milling,dilute citric acid,and fungus Penicillium simplicissimum treatment at room temperature

In this study, birch wood chips were treated in one‐step ball milling (BM) hydrolysis with dilute citric acid and fungus Penicillium simplicissimum at room temperature and atmospheric pressure. An efficient conversion process for the production of fermentable sugars from woody biomasses using wet BM system was developed, in which wood lignocellulose was hydrolyzed into reducing sugars with the total yield of 245.3 mg/g wood. The concentrations of several major substances in the hydrolyzate were discussed in detail. The yields of the monomeric sugars were notably increased in the presence of fungus P. simplicissimum. Corresponding structure transformations before and after milling were analyzed by X‐ray diffraction, UV spectroscopy, transmission Fourier transform infrared spectroscopy, and environmental scanning electron microscopy clearly indicated that this combined treatment could be attributed to the crystalline and chemical structure changes of wood lignocellulose during BM. When compared with traditional method of BM, this work showed a more simple, novel, and environmental friendly way in mechanochemical treatment of lignocellulosic biomass, especially woody biomass. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

ENZYMATIC HYDROLYSIS OF CELLULOSE: DETERMINATION OF KINETIC PARAMETERS

The effects of cellulose substrate concentration, cellulase enzyme concentration, and product concentration on the kinetic parameters involved in the enzymatic hydrolysis of cellulose have been studied. The Michaelis constant showed a decreasing trend with a decreasing crystallinity of cellulose substrate while the maximum reaction rate showed an increasing trend. These kinetic parameters were found to be significantly larger when the enzyme concentration was increased. The adsorption kinetic parameters showed an increasing trend as the crystallinity is decreased. It was found that the optimal enzyme loading should be determined by the source, concentration, and crystallinity of cellulose substrate and the initial specific rate of cellulose hydrolysis which is, in large part, influenced by the degree of crystallinity of cellulose substrate. The inhibition constant for cellulase-by cellobiose and that for cellobiase were also determined. These kinetic parameters determined experimentally can be applied to kinetic modeling and simulation of cellulose hydrolysis.     

CONCENTRATED ACID CONVERSION OF PINE SAWDUST TO SUGARS. PART II: HIGH-TEMPERATURE BATCH REACTOR KINETICS OF PRETREATED PINE SAWDUST

A study of high-temperature, concentrated-acid hydrolysis kinetics was undertaken for pretreated pine utilizing a corotating twin-screw extruder reactor. Five different acid concentrations were prepared ranging from 5 to 30 wt.% acid. These solutions were subjected to high-temperature acid hydrolysis at 110°, 120°, and 130°C using a custom-fabricated zirconium batch reactor. A number of nonlinear and linear regression analyses were undertaken so that the concentration of less resistant cellulose, resistant cellulose, glucose, and decomposition products could be obtained as a function of time, temperature, and acid concentration. Application of the kinetic rate constants obtained from the static batch reactor hydrolysis studies demonstrates that more than 50% of the theoretical glucose available in the pine sawdust can be obtained in roughly 25 minutes and 41% of the theoretical glucose available can be achieved in as little as 3 minutes. Further analysis highlights the importance of the pretreatment technique in achieving significant quantities of theoretical glucose in a short high-temperature reaction time.     

CONCENTRATED ACID CONVERSION OF PINE SAWDUST TO SUGARS. PART II: HIGH-TEMPERATURE BATCH REACTOR KINETICS OF PRETREATED PINE SAWDUST

A study of high-temperature, concentrated-acid hydrolysis kinetics was undertaken for pretreated pine utilizing a corotating twin-screw extruder reactor. Five different acid concentrations were prepared ranging from 5 to 30 wt.% acid. These solutions were subjected to high-temperature acid hydrolysis at 110°, 120°, and 130°C using a custom-fabricated zirconium batch reactor. A number of nonlinear and linear regression analyses were undertaken so that the concentration of less resistant cellulose, resistant cellulose, glucose, and decomposition products could be obtained as a function of time, temperature, and acid concentration. Application of the kinetic rate constants obtained from the static batch reactor hydrolysis studies demonstrates that more than 50% of the theoretical glucose available in the pine sawdust can be obtained in roughly 25 minutes and 41% of the theoretical glucose available can be achieved in as little as 3 minutes. Further analysis highlights the importance of the pretreatment technique in achieving significant quantities of theoretical glucose in a short high-temperature reaction time.     

泰勒流反应器的流动及反应特性

利用由静态混合器、喷嘴和分气盒组成的新型布气装置在搅拌釜式反应器中诱导生成泰勒流,对反应器流动特性及反应特性进行了实验研究。结果表明,与常规搅拌釜式反应器相比,泰勒流反应器内物料流动更加接近于平推流流型,泰勒流的生成在反应器内构建出局部平推流区域,降低了物料返混程度。反应器反应性能因流动特性改变而得以增强,相同实验条件下,在泰勒流反应器中进行的蔗糖水解反应转化率比在常规搅拌釜式反应器中高出26.7%。在一定操作范围内,局部平推流区域和反应转化率均随搅拌转速或进气量的增加而增大。泰勒流反应器可简化为平推流区和全混流区并联的流动模型,推导出了反应转化率与平推流区域占反应器总体积比率之间的关联关系。     

Kinetic study of the enantioselective hydrolysis of a meso‐diester using pig liver esterase

A kinetic study of the hydrolysis of the diester dimethyl cis‐cyclohex‐4‐ene‐1,2‐dicarboxylate, to the (1S,2R)‐monoester, catalysed by the enzyme Pig Liver Esterase (PLE) was performed. The effects of the most relevant parameters that influence the enzymatic conversion were studied, such as pH, temperature and concentration of substrate and reaction products. It was concluded that the pH at which the enzyme exhibits a maximum activity is pH 7. At 25 °C PLE presents a better long‐term stability and enantioselectivity than at higher temperatures, although the reaction rate is slower. The kinetic results obtained are well described by the Michaelis–Menten equation, although a slight deviation to this model was observed for low substrate concentrations. Methanol, a co‐product of the enzymatic hydrolysis, was found to act as a non‐competitive inhibitor of the reaction. The Michaelis–Menten parameters were determined and a comprehensive kinetic model, which already accounts for methanol inhibition, is presented. © 2000 Society of Chemical Industry     

The heterogeneous character of the dilute acid hydrolysis of crystalline cellulose. III. Kinetic and X-ray data

Thirteen prehydrolyzed samples of cellulose, including native, mercerized, and regenerated materials were hydrolyzed in 1% and 1.5% sulfuric acid at 160, 170, and 180°C. Pseudo first-order rate constants and weight average degrees of polymerization were determined for each sample. For all cellulose samples, data from several experiments were used to determine the dependence of the rate of hydrolysis on sulfuric acid concentration. The results obtained in this study indicate that Sharples' end-attack model is consistent with kinetic data for the hydrolysis of cellulose II samples, but is not applicable to the hydrolysis of cellulose I samples. X-ray diffraction analyses indicated that, for native and mercerized cellulose samples, structural changes during dilute acid hydrolysis are not significant. However, data for rayon indicated that such changes may need to be taken into account in analysis of the reaction kinetics.     

An explanation of increased hydrolysis of the β-(1,4)-glycosidic linkages of grafted cellulose using molecular modeling

Grafting various groups onto cellulose is found to substantially increase acid hydrolysis of the β-(1,4)-glycosidic linkages. Molecular modeling is used to explain how various substituents such as esters and ethers cause this phenomenon. A substituent helps stabilize hydrolyzed cellulose by serving as an anchor to the end of the cleaved cellulose to which it is bonded, making it less mobile, and allowing it to have stronger interactions than those in pure hydrolyzed cellulose. Hydrolysis increases with increasing size of the substituent. Molecules sorbed but not grafted to cellulose do not increase hydrolysis. Hydrolysis mainly occurs at glucoses bonded to the substituent, and supporting experiments show that hydrolysis approaches equilibrium when no substituent remains on the cellulose fiber.     

Effect of ball milling on the hydrolysis of microcrystalline cellulose in hot‐compressed water

Ball milling leads to a considerable reduction in cellulose particle size and crystallinity, as well as a significant increase in the specific reactivity of cellulose during hydrolysis in hot‐compressed water (HCW). Cryogenic ball milling for 2 min also results in a significant size reduction but only little change in cellulose crystallinity and specific reactivity during hydrolysis. Therefore, crystallinity is the dominant factor in determining the hydrolysis reactivity of cellulose in HCW while particle size only plays a minor role. Ball milling also significantly influences the distribution of glucose oligomers in the primary liquid products of cellulose hydrolysis. It increases the selectivities of glucose oligomers at low conversions. At high conversions, the reduction in chain length plays an important role in glucose oligomer formation as cellulose samples become more crystalline. An extensive ball milling completely converts the crystalline cellulose into amorphous cellulose, substantially enhancing the formation of glucose oligomers with high degrees of polymerization. © 2010 American Institute of Chemical Engineers AIChE J, 2011