Acid hydrolysis of glycosidic bonds in oat β‐glucan and development of a structured kinetic model

Homogeneous acid‐catalyzed hydrolysis of oat β‐glucan, which contains β‐(1,4) and β‐(1,3) glycosidic bonds in a nonrandom order, was studied at 353 K using HCl and H₂SO₄. A new structured kinetic model was developed that takes into account the difference in the reactivity of β‐(1,4) and β‐(1,3) glycosidic bonds as well as their positions in the polysaccharide chain. To minimize the correlation of adjustable parameters in the new model, the reactivities of these bonds were studied independently (T = 313…363 K; c_H+ = 0.1…2 mol/L) using cellobiose and laminaribiose. The difference in kinetic parameters (e.g., T = 338 K: k_β‐(1,4) = 0.693 × 10^?3 L/mol/min, k_β‐(1,3) = 1.027 × 10^?3 L/mol/min) was found to be statistically significant (P < 0.0001), which emphasizes the need for the structured model for oat β‐glucan hydrolysis. The simulation of β‐glucan hydrolysis with the new model was in good agreement with the experimental data and shows improvement over existing nonstructured models. © 2018 American Institute of Chemical Engineers AIChE J, 64: 2570–2580, 2018     

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.     

半纤维素稀酸循环喷淋冲滤水解动力学

采用稀酸循环喷淋冲滤（dilute acid cycle spray flow-through,DCF）反应器在温和的条件下水解玉米秸秆半纤维素,分析了半纤维素稀酸水解产物组分,研究不同温度、硫酸浓度和时间对主要产物木糖浓度的影响。探讨了其水解反应机理并以酸催化反应机理为基础,把玉米秸秆半纤维素及其水解产物按化学组成和性质进行集总划分,并对反应网络进行合理简化,提出了一种半纤维素稀酸水解反应的简化集总动力学模型。通过参数估计求取动力学参数,建立集总动力学模型以预测半纤维素主要水解产物。结果表明,喷淋作用加快了半纤维素的连续解聚过程,从而使得木糖得率超过90%,而其降解产物糠醛等较少。得到的模型能较好预测不同条件下主要产物含量。通过改进的Arrhenius方程确定木糖生成和降解的活化能分别为107.1 kJ·mol^-1和102.2 kJ·mol^-1。     

Auto-Catalyzed Hydrolytic Depolymerization of Poly(Butylene Terephthalate) Waste at High Temperature

Auto-catalyzed hydrolytic depolymerization of poly(butylene terephthalate) (PBT) waste in neutral water was carried out in an autoclave at 200°, 215°, 230°, and 245°C under autogenously pressure. The effects of particle size, agitator speed, charge ratio, and reaction time on PBT hydrolyses were studied. Reaction products were terephthalic acid (TPA) and 1,4-butanediol (BD) that were recovered, analyzed, and confirmed. Yields of TPA and BD were almost equal to PBT conversion. Analyses of PBT waste samples were also undertaken. A kinetic model for PBT hydrolysis was fitted with the experimental data. Moreover, a noncatalytic PBT hydrolysis was studied to understand the effect of auto-catalyzed action during reaction. Various kinetic parameters (i.e., hydrolysis rate constant, equilibrium constant, backward rate constant, Gibbs free energy, enthalpy, and entropy) of reaction were calculated. The transfer of laboratory data is required during process commercialization through pilot plant. The dependence of the rate constant on the reaction temperature was correlated by the Arrhenius plot giving activation energy of 87 kJ/mol and the corresponding Arrhenius constant of 5.56 × 10⁹[(g ET/mol)^1.5 min^?1] for PBT hydrolysis.     

Photo-induced radicals in glucose and cellobiose

Photo-induced radicals in glucose and cellobiose, the model compounds of cellulose molecule, were studied by ESR spectrometry. Very poor formation of radicals in glucose as compared to those in cellobiose was observed. However, a spectrum showing a singlet line was easily produced by the use of light involving shorter wavelengths. It was estimated to be due to the radical formed at the reducing C₁ position of glucose molecule. By paper chromatography, the photo-irradiated cellobiose was confirmed to split into glucose through scission of glucosidic bonds in the molecule. The ESR spectrum of the acid-hydrolyzed cellulose similar to that of the unhydrolyzed sample was a seven-line spectrum, but the relative signal intensity was here markedly low. This phenomenon seems to be caused by the reduction of amorphous portion in the samples due to acid hydrolysis. It was concluded that the glucosidic bonds in cellobiose and cellulose molecules are very active toward light and play an important role in the radical formation in photo-irradiated samples.     

Chemical Recycling and Kinetics of Aqueous Alkaline Depolymerization of Poly(Butylene Terephthalate) Waste

Depolymerization reactions of poly(butylene terephthalate) (PBT) waste in aqueous sodium hydroxide solution were carried out in a batch reactor at 80–140 °C at atmospheric pressure by varying PBT particle size in the range of 50–512.5 μm. Reaction time was also varied from 10–110 min to understand the influence of PBT particle size and reaction time on the batch reactor performance. Agitator speed, particle size of PBT and reaction time required were optimized. Disodium terephthalate (salt) and 1,4‐butanediol (BD) remain in the liquid phase. BD was recovered by the salting‐out method. Disodium terephthalate was separated by acidification to obtain solid terephthalic acid (TPA). The produced monomeric products (TPA and BD) and PBT were analyzed. The yields of TPA and BD were in agreement with PBT conversion. The depolymerization reaction rate was first order to PBT concentration as well as first order to sodium hydroxide concentration. The acid value of TPA changes with the reaction time as well as particle size of PBT. This indicates that PBT molecules get fragmented and hydrolyze simultaneously with aqueous sodium hydroxide to produce BD and disodium terephthalate. Activation energy, Arrhenius constant, equilibrium constant, Gibbs free energy, enthalpy and entropy were determined. The dependence of the hydrolysis rate constant on reaction temperature was correlated by the Arrhenius plot, which shows an activation energy of 25 kJ/mol and an Arrhenius constant of 438 L/min/cm².     

Effect of ultrasound on sulfuric acid-catalysed hydrolysis of starch

The influence of ultrasound on the hydrolysis of starch was investigated at moderate temperature range (90-100°C) and in the dilute sulfuric acid (1-5 wt%). Enhancements of the reaction rate by ultrasound was observed. The degree of the relative enhancement depended on the reaction temperature. The model reaction by maltose showed that the acid hydrolysis of glucosidic linkages was first order with respect to the substance concentration and the hydrogen ion concentration, respectively. And the activation energies of the control and the ultrasound-aided hydrolysis of maltose were 30.2 and 23.4 kcal/mol, respectively. Enhancement was thus expressed as the alleviation of activation energy by ultrasound irradiation.     

Effect of degree of deacetylation of chitosan on the kinetics of ultrasonic degradation of chitosan

The objective of the study was to explore the effect of the degree of deacetylation (DD) of the chitosan used on the degradation rate and rate constant during ultrasonic degradation. Chitin was extracted from red shrimp process waste. Four different DD chitosans were prepared from chitin by alkali deacetylation. Those chitosans were degraded by ultrasonic radiation to different molecular weights. Changes of the molecular weight were determined by light scattering, and data of molecular weight changes were used to calculate the degradation rate and rate constant. The results were as follows: The molecular weight of chitosans decreased with an increasing ultrasonication time. The curves of the molecular weight versus the ultrasonication time were broken at 1‐h treatment. The degradation rate and rate constant of sonolysis decreased with an increasing ultrasonication time. This may be because the chances of being attacked by the cavitation energy increased with an increasing molecular weight species and may be because smaller molecular weight species have shorter relaxation times and, thus, can alleviate the sonication stress easier. However, the degradation rate and rate constant of sonolysis increased with an increasing DD of the chitosan used. This may be because the flexibilitier molecules of higher DD chitosans are more susceptible to the shear force of elongation flow generated by the cavitation field or due to the bond energy difference of acetamido and β‐1,4‐glucoside linkage or hydrogen bonds. Breakage of the β‐1,4‐glucoside linkage will result in lower molecular weight and an increasing reaction rate and rate constant. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 90: 3526–3531, 2003     

曲霉产壳聚糖酶的水解作用模式

从曲霉CJ22-326发酵培养液中分离纯化得到2种壳聚糖酶组分(ChiB, ChiA),通过测定酶解液体系粘度和对酶解产物进行TLC和HPLC分析,对其水解模式的研究结果表明,酶ChiB是一种内切壳聚糖酶,以随机进攻方式作用于壳聚糖分子链内部,从而使体系粘度快速下降. 以低聚糖为底物的水解产物分析表明,它作用于GlcN?GlcN糖苷键,不能作用于GlcNAc?GlcNAc糖苷键,不水解壳四糖及以下聚合度的甲壳低聚糖,壳五糖被水解成壳二糖和壳三糖,壳六糖主要被水解成壳三糖. 酶ChiA是一种外切氨基葡萄糖苷酶,主要从壳聚糖分子或甲壳低聚糖分子一端依次切下氨基葡萄糖残基,它只作用于GlcN?GlcN和GlcN?GlcNAc糖苷键.     

New lignocellulose pretreatments using cellulose solvents: a review

Non‐food lignocellulosic biomass is the most abundant renewable bioresource as a collectable, transportable, and storable chemical energy that is far from fully utilized. The goal of biomass pretreatment is to improve the enzymatic digestibility of pretreated lignocellulosic biomass. Many substrate factors, such as substrate accessibility, lignin content, particle size and so on, contribute to its recalcitrance. Cellulose accessibility to hydrolytic enzymes is believed to be the most important substrate characteristic limiting enzymatic hydrolysis. Cellulose solvents effectively break linkages among cellulose, hemicellulose and lignin, and also dissolve highly‐ordered hydrogen bonds in cellulose fibers accompanied with great increases in substrate accessibility. Here the history and recent advances in cellulose solvent‐based biomass pretreatment are reviewed and perspectives provided for addressing remaining challenges. The use of cellulose solvents, new and existing, provides opportunities for emerging biorefineries to produce a few precursors (e.g. monosaccharides, oligosaccharides, and lignin) for the production of low‐value biofuels and value‐added biochemicals. © 2012 Society of Chemical Industry     

秸秆中木质素对其超低酸水解过程的影响

以湖北稻草秸秆为研究对象,研究了超低酸水解木质纤维素的适宜条件,测定了适宜条件下的超低酸法水解15种不同种类秸秆的纤维素及半纤维素的转化率、还原糖得率及结晶度的变化。实验结果表明:秸秆投料量3 g、硫酸投料量45 mL(硫酸质量分数0.05%)、搅拌转速500 r/min、反应温度210 ℃、反应时间10 min为适宜的水解条件。对15种不同种类秸秆的水解结果统计得到,随着秸秆中木质素含量的增大,纤维素和半纤维素的转化率都逐渐降低,还原糖得率逐渐降低;通过SEM和X衍射分析水解前后的木质纤维素结构,得到了木质素影响水解过程的方式:1)木质素含量越大,纤维素的结晶度越大,纤维素的非晶化越困难,从而影响了纤维素的水解;2)原木质素不溶于反应体系且在酸性条件下相对稳定,富木质素层的木质素阻碍反应物与产物扩散,使富木质素层内的纤维素、半纤维素水解速率降低;3)木质素含量越高,木质纤维素的富木质素层越厚、强度越大,水解时难以从颗粒表面脱落,进一步降低水解速率。     

Degradation Kinetics of Xylose and Glucose in Hydrolysate Containing Dilute Sulfuric Acid

In preparation of fuel alcohol from biomass as feedstock, hydrolysis with dilute acid as catalyst is one way to produce fermentable saccharide, xylose and glucose. However, the acid is also the catalyst in degradation of xylose and glucose and the yield of sacchride is dependent on the kinetic behaviors of saccharide. The degradation kinetics of xylose and glucose in the hydrolysate was investigated under the conventional process conditions of hydrogen ion concentration from 0.05 to 0.2 mol/L and temperature from 150 to 200℃. With a numerical calculation method, the kinetic parameters were estimated, and the activation energy of xylose and glucose in the degradation reaction was obtained. The kinetic equations correlating the effect of hydrogen ion concentration on the rate constants of degradation reaction were established. Comparison between the calculated results from the equations and experimental ones proved that the established kinetic model could satisfactorily predict the degradation behavior of xylose and glucose in the acidic hydrolysate.     

Catalyzed hydrolysis of polyethylene terephthalate melts

The effect of zinc catalysts on the hydrolytic depolymerization of polyethylene terephthalate (PET) melts in excess water was studied using a 2-L stirred pressure reactor at temperatures of 250, 265, and 280°C. The main products of the reaction were found to be terephthalic acid, ethylene glycol, and diethylene glycol. Rate constants were calculated from initial rate data at each temperature and found to be about 20% greater than the corresponding rate constants for uncatalyzed hydrolysis. The catalytic effect of zinc, as well as sodium, salts is attributed to the electrolytic destabilization of the polymer-water interface during hydrolysis. The depolymerization rate data at 265°C were found to fit a kinetic model proposed earlier for the uncatalysed hydrolysis of PET. The effect of zinc and sodium salts on the activation energy of hydrolysis, or on the formation of ethylene glycol monomer is unclear. © 1994 John Wiley & Sons, Inc.     

强酸性树脂催化下六元糖降解反应动力学

开展了以固体酸替代无机酸降解模型物质六元糖的研究。利用小型高压反应釜测定了在130～160℃范围内Amberlyst 35W和36W树脂催化下葡萄糖和果糖的降解反应动力学,结果表明35W树脂的加入对葡萄糖异构化成果糖的速率影响较小,但可提高果糖脱水生成中间产物5-羟甲基糠醛以及5-羟甲基糠醛脱羧生成乙酰丙酸的速率,从而提高产物乙酰丙酸的收率;在0.2 g 35W树脂催化下,葡萄糖和果糖的降解反应活化能分别为111、97.0 kJ·mol^-1。Amberlyst 36W与35W具有相似的催化活性,同时Amberlyst 35W和36W在实验条件下可以重复使用。该研究结果证实了用耐水型强酸性树脂替代现有的无机酸催化制备乙酰丙酸的可能性。     

Pyridine-catalyzed depolymerization of cellulose during carbanilation with phenylisocyanate in dimethylsulfoxide

Carbanilation reactions of cellulose samples (bleached cotton linters and Avicel) with phenylisocyanate in dimethylsulfoxide (DMSO) were carried out at 60°C in the presence of various pyridine derivatives. The molecular weight distributions of the resulting cellulose tricarbanilates (CTCs) were measured by high-performance size exclusion chromatography. When pyridine or its derivatives were included in the reactions, the CTCs had reduced degree of polymerization (DP) values compared to those of CTCs prepared without the additives. The cellulose depolymerization was promoted by pyridines with electron-donating substituents and was not favored by pyridines with electron-withdrawing substituents nor with groups at positions ortho to the pyridine ring nitrogen atom. For the 3-, 4-, and 3,4- substituted pyridines, there was a linear relationship between log (weight-average CTC DP) and the pK_a (in water) of the pyridine derivative. For 2- and 2,6-substituted pyridines, the DP–pK_a relationships were different, probably because of steric effects of the different substituents ortho to the pyridine nitrogen atom. The optimum DMSO : pyridine solvent ratio for cellulose depolymerization during carbanilation in DMSO : pyridine mixtures was 3 : 1. All three components, phenylisocyanate, pyridine or its derivatives, and DMSO, are required for the depolymerization reaction. It is suggested that the depolymerization may be a consequence of cellulose oxidation by DMSO and/or cleavage of glucosidic bonds of partially carbanilated cellulose by reactions promoted by an enhanced solvent effect of DMSO.     

The influence of pH upon the hydrolysis of carboxymethylcellulose with cellulases from Trichoderma reesei

We have studied the enzymatic hydrolysis of carboxymethylcellulose (CMC) with Celluclast, a commercial preparation of cellulases deriving from Trichoderma reesei, by monitoring the variation in the concentrations of glucose and reducing sugars at a constant temperature of 50°C and different pH values. We determined both glucose and overall yield, concluding that the production of glucose directly by endoglucanase is higher than that coming from the hydrolysis of cellobiose by β‐1,4‐glucosidase and that the rate at which cellobiose is formed can be calculated via kinetic parameters that are due in the end mainly to exoglucanase activity. We observed the effect of pH upon the kinetic parameters and found that the ideal value for the hydrolysis of CMC is one of pH 4.9.     

Variation of non‐isothermal crystallization behavior of isotactic polypropylene with varying β‐nucleating agent content

The non‐isothermal crystallization behavior, the crystallization kinetics, the crystallization activation energy and the morphology of isotactic polypropylene (iPP) with varying content of β‐nucleating agent were investigated using differential scanning calorimetry (DSC) and scanning electron microscopy (SEM). The DSC results showed that the Avrami equation modified by Jeziorny and a method developed by Mo and co‐workers could be successfully used to describe the non‐isothermal crystallization process of the nucleated iPPs. The values of n showed that the non‐isothermal crystallization of α‐ and β‐nucleated iPPs corresponded to a tridimensional growth with homogeneous and heterogeneous nucleation, respectively. The values of crystallization rate constant showed that the rate of crystallization decreased for iPPs with the addition of β‐nucleating agent. The crystallization activation energy increased with a small amount (less than 0.1 wt%) of β‐nucleating agent and decreased with higher concentration (more than 0.1 wt%). The changes of crystallization rate, crystallization time and crystallization activation energy of iPPs with varying contents of β‐nucleating agent were mainly determined by the ratio of the content of α‐ and β‐phase in iPP (α‐PP and β‐PP) from the DSC investigation, and the large size and many intercrossing lamellae between boundaries of β‐spherulites for iPPs with small amounts of β‐nucleating agent and the small size and few intercrossing bands among the boundaries of β‐spherulites for iPPs with large amounts of β‐nucleating agent from the SEM examination. Copyright © 2010 Society of Chemical Industry     

Kinetics of neutral hydrolytic depolymerization of PET (polyethylene terephthalate) waste at higher temperature and autogenious pressures

Neutral hydrolytic depolymerization of PET (Polyethylene terephthalate) waste was studied using 0.5‐L high pressure autoclave at the temperatures 100, 150, 200, 230, and 250°C at autogenious pressures 15, 80, 230, and 451 psi (pound per square inch) and time intervals of 60, 90, 120, and 150 min, respectively. The obtained terephthalic acid (TPA) was characterized by measuring its acid value and recording FTIR spectra. Depolymerization of the PET by neutral hydrolysis was found to be first order with velocity constant in the order of 10^?2 min^?1. Energy of activation and frequency factor were obtained by slope and intercept of Arrhenius plot, which were found to be 99.58 KJ mole^?1 and 2.9 × 10⁸ min^?1respectively. Effect of temperature on rate of depolymerization reaction was also studied and optimized: rate of reaction increased drastically on increase in temperature from 150 to 200°C. Modified shrinking core model based on acid values focused the light on depolymerization of the PET into TPA by fragmentation due to formation of pores and cracks. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

纤维素热解机理研究进展：以中间态纤维素为核心的纤维素演变

纤维素热解的机理研究对于生物质能的热利用至关重要,能够有效指导工业实际应用。基于著名的Broido-Shafizadeh模型,纤维素热解被分为两步,首先转变为活性的熔融态中间体（中间态纤维素）,然后通过解聚和开环生成左旋葡聚糖、5-羟甲基糠醛、羟基乙醛等重要的化工原料。在这两步转变中,主要涉及低温段氢键网络的断裂、中间态纤维素的生成,以及高温段的解聚和吡喃环开环反应。本文从这3个部分对前人的研究进行了综述,着重介绍了中间态纤维素的生成和表征,综述了纤维素热解几个研究方向：结晶度和结晶形态对热解的影响、纤维素解聚反应方式、吡喃环开环方式等,详细阐述了二次反应对纤维素热解的影响,并提出了部分解决方案。关于纤维素热解依然存在诸多未知和争论,需要进一步的实验研究和理论计算对其进行揭示。     

Separation and recovery of the constituents from lignocellulosic biomass by using ionic liquids and acetic acid as co-solvents for mild hydrolysis

Previously, ionic liquids were found to partially dissolve lignocellulosic biomass. Here, it is reported that the biomass itself does not dissolve directly, but that it is hydrolyzed first before the constituents (cellulose, hemicellulose and lignin) dissolve into the ionic liquid. By addition of an acidic catalyst, this hydrolysis step can take place at milder conditions. Acetic acid is chosen as a suitable acidic catalyst, because it is already present in lignocellulosic biomass in the form of acetyl groups on the hemicellulose. Here, it is shown that acetic acid also works as co-solvent, increasing the solubility of the constituents of lignocellulosic biomass in the ionic liquid. The milder conditions for hydrolysis result in a higher degree of utilization of the lignocellulosic biomass, whereby all constituents can be fully recovered and further processed and the ionic liquid can be reused.