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.     

Model for Continual Depolymerization of Biomass Catalyzed by Dilute Sulfuric Acid

Ethanol fuel from biomass is conventionally produced via the hydrolysis of biomass catalyzed by acid. In this paper, it is understood that the degree of polymerization of cellulose is randomly distributed and that the rupture of β‐1,4‐glucosidic bonds during acidic hydrolysis of cellulose is a process of continual depolymerization. From this perception, a model is established for the continual depolymerization of cellulose catalyzed by acid. Meanwhile, analog computation resulted in the activation energy and the reaction rate constant related to the rupture of β‐1,4‐glucosidic bonds. The established model is highly validated by test runs and thus assumed as a model that can be used to describe the depolymerization route taken in acidic hydrolysis of cellulose. The calculated activation energy and rate constant for the rupture of β‐1,4‐glucosidic bonds correspond to the rule of acidic hydrolysis of cellulose. Investigation of the model is of great significance in further studies on the hydrolysis mechanism of cellulose.     

水热条件下CO_2催化棉纤维水解制糖过程动力学

以脱脂棉为纤维素模型化合物,研究了水热条件下CO2催化棉纤维水解制糖过程动力学特性,考察了温度和CO2压力的影响。结果表明:高温有利于棉纤维水解生成糖,同时会加速糖的分解;升高CO2压力可以明显加快棉纤维的水解速度。通过对实验数据关联,建立了棉纤维在水热条件下CO2催化水解的等压动力学模型和等温动力学模型。与实验数据相比,模型的相对标准偏差都在±15%之内。模型分析表明,适当提高反应温度对于提高棉纤维生成糖的选择性是有利的。     

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     

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.     

用反应量热仪研究棉短绒纤维素的乙酰化反应

用反应量热仪(RCle)对棉短绒纤维素的乙酰化反应进行了研究。研究发现:该反应放热速率图基本由3～4个放热峰构成;初期第一或第二个放热峰的峰值较大,主要为醋酐的水解反应;往后峰值依次变小,直至缓慢放热,主要为纤维素乙酰化反应。研究中还测量了不同反应温度及水分含量对反应放热速率的影响,并与木浆粕的反应过程进行了对比。结果表明,棉短绒纤维素乙酰化过程具有非均相表面反应的特点。放热速率随温度的升高而加快。提高水分含量,使醋酐水解放热量变大,并能破坏反应区结构,提高反应速率,缩短总反应时间。与木浆粕相比,棉短绒纤维素具有结晶度高及α-纤维素含量高的特点,反应放热表现为:初期放热速率低,中后期高,总体反应时间较长。     

Hydrothermal pretreatment for deconstruction of plant cell wall: Part II. Effect on cellulose structure and bioconversion

Influences of both ultrastructural modification of cellulose after hydrothermal pretreatment and products derived from lignin‐carbohydrate complex (LCC) on the subsequent enzymatic digestibility and fermentation were studied in this study. Under hydrothermal conditions, it was found that the rearrangement of hydrogen bonding pattern in cellulose via allomorph and conformational changes which was mainly severity‐dependent increased the numbers of water‐exposed glycosidic bond and the formation of “amorphous‐like” cellulose fibril facilitated enzymatic hydrolysis. Pseudo lignin, soluble xylo‐oligomers, phenols and degradation products from high severity impeded enzymatic digestion. LCC and phenols which were rich in pH‐controlled prehydrolyzate did not sufficiently inhibit yeast while furans and some aromatics which were rich in high‐severity prehydrolyzate might be potential inhibitors. Trade‐off phenomenon was solved by pH‐controlled operation and high yields in both glucose (83–93%) and xylose (75–80%) were simultaneously obtained. The final ethanol yield from cellulose to ethanol reached as high as 84–93%. © 2018 American Institute of Chemical Engineers AIChE J, 64: 1954–1964, 2018     

硫酸水解对再生纤维素纤维葡萄糖转化率的影响

用浓硫酸水解竹浆、棉浆、木浆三种再生纤维素纤维,通过改变反应温度和时间,找出再生纤维素纤维水解葡萄糖得率最优的反应条件,并对不同种类的纤维素纤维水解液进行高效液相色谱分析。结果表明:当反应温度为50℃、反应时间为120 min时,竹浆再生纤维素纤维的葡萄糖转化率可达75%;在高效液相色谱中,竹浆再生纤维素纤维在7 min的位置有较明显的出峰,在12.5～14.5 min的位置有一个双峰,有别于木浆、棉浆再生纤维素纤维。     

Crosslinking cotton cellulose with ethyleneurea derivatives having varying hydrogen-bonding capabilities. II. Accessibility determinations

In a continuation of previously reported work of the effect on cotton cellulose of ethyleneurea crosslinking agents modified with ring substituents of varying hydrogen-bonding capabilities, accessibilities of the cellulosic hydroxylic protons to exchange with deuterium oxide vapor were determined by means of infrared spectroscopy. In analyzing these values with respect to previously reported data on physical properties of the treated fabrics, it was found that accessibility to deuterium oxide did not correlate with moisture regain of the resin-treated samples as has been reported for physically modified celluloses. It appears that the different resins did have some effect on the structure of water adsorbed by the fiber and also that the solvent affected the manner in which the resins attached themselves to the cellulose and eliminated water from the structure. Values of accessibility were not found to correlate well with crease recovery, although a weak trend was indicated. Accessibility was found to decrease as the infrared band for ring stretching decreased.     

Structural features of native cellulose gels and films from their susceptibility to enzymic attack

The reaction of enzymic hydrolysis has been used as a probe to evidence the different structural features of bacterial native cellulose gels and films synthesized from different carbon sources. The gels were found to be more hydrolyzable than were the films, both in terms of reaction extent and of initial reaction rate, by factors increasing with temperature. For instance, a cellulose gel synthesized from glucose showed at 50°C a hydrolysis yield twice as much as that of the corresponding film, thus revealing, in the former case, a higher level of substrate accessibility and enzyme penetrability. It has been suggested that the increase of gel accessibility with temperature can be associated with a corresponding lowering of the amount of structured water close to the polymer chains in the gel. The significant decrease of susceptibility to enzymic attack observed in going from the cellulose film obtained from glucose to that obtained from xylose has been related to the markedly lower value of specific surface area estimated in the latter case. Likely, in the film obtained from xylose, densely packed microfibrils occur that are scarcely accessible to enzyme. In some cases, the reaction progress has been followed by SEM analysis. Microcrystalline cellulose has been also considered for comparison.     

AlCl3对纤维素高温液态水中水解反应的影响

以微晶纤维素为模型化合物,研究了AlCl3对其在高温液态水(HTLW)中的水解反应的影响.液相产品分析显示,AlCl3能够促进纤维素水解,降低水解反应温度,并在短时间内提高葡萄糖的收率.在T=260℃,P=5.2±0.2 MPa,t=1 min,体系中加入0.01%(质量百分浓度)的AlCl3可以将纤维素的转化率提高至...     

木质素对蔗渣酶水解的影响

采用机械活化方法对蔗渣进行处理,研究在原料可及性变化时木质素对蔗渣酶解的影响,用牛血清蛋白（BSA）预先使原料中木质素吸附饱和的方法来测定木质素对酶的吸附情况、用X-射线衍射和扫描电镜来测定蔗渣结晶结构、表面形态来表征原料可及性,从而分析影响的可能机制。结果表明木质素对蔗渣酶水解的影响与蔗渣可及性有关,原料可及性越高,影响越小。当蔗渣可及性相对较低时,此时木质素影响蔗渣酶水解转化率的两种方式（木质素与纤维素、半纤维素组成的致密结构限制纤维素对酶的可及性及木质素对纤维素酶的无效吸附作用）同时存在。当原料的可及性增加到一定程度后（如机械活化2h的蔗渣）,木质素对纤维素酶的吸附作用几乎消除,木质素对蔗渣酶水解的影响主要表现为对酶的可及性的限制。     

A study of the fine structure of cellulosic fibers by level-off degree of polymerization measurements

The crystallization of disordered and partly disordered cellulose on hydrolysis with boiling dilute mineral acid was studied and the level-off degree of polymerization (LODP) of cotton after treatment with inter-or intracrystalline swelling agents was determined. The LODP, of cotton and of cotton which had been swollen in morpholine were similar, indicating that the LODP of cotton cellulose was not affected by this intercrystalline swelling agent. It appears that the aggregates of cellulose chains present in cotton which has been treated with aqueous NaOH of mercerizing strength and then washed with water are not uniformly accessible to hydrolyzing acid and that the accessibility to the acid is not changed when the cellulose is dried. The LODP of samples of mercerized, ethanol-washed, never-dried cotton that had been acetylated was obtained and the results are discussed in terms of current views on the fine structure of cotton.     

Structural changes and enhanced accessibility of natural cellulose pretreated by mechanical activation

A kind of natural cellulose, bleached pine pulp (BPP), was pretreated by mechanical activation (MA) using a self-designed stirring ball milling. The effect of MA pretreatment on the dissolving capacity and molecular chain structure of BPP were investigated by the determination of alkaline solubility (Sa) and degree of polymerization (DP). In addition, the changes in crystal structure of MA-pretreated BPP with different milling times were qualitatively and quantitatively measured by X-ray diffraction and Fourier transform infrared spectroscopy, and the morphology modification was observed by scanning electron microscopy. It was found that MA significantly increased the Sa and reduced the DP of BPP, contributing to the destruction of inter- and intramolecular hydrogen bonds and macromolecular chains in cellulose. The stable crystal structure of BPP was also remarkably damaged during MA processing, resulting in the variation of surface morphology, the increase of amorphous region ratio and hydrogen bond energy, and the decrease in crystallinity and crystalline size, which efficiently increased the accessibility of natural cellulose and would have positive effects on subsequent treatments. The crystalline form of natural cellulose was not changed by MA, and no new functional groups generated during milling.     

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     

木素的存在对纤维素水解反应性能及其产物结构的影响

对木素含量为0.9％—8.3％的速生杨硫酸盐浆进行了X—射线分析研究。利用多相水解方法测定了其反应性能。研究结果确定,浆中结晶纤维素含量取决于木素脱出程度并随着木素含量的降低而增加。木屑和浆中的纤维素结晶度相当高,而在脱木素过程中只呈微小变化。木素存在于多相水解反应过程中起着阻碍纤维素水解的作用,降低其反应速度常数。基于研究结果,提出了木素与纤维素结晶部分外表面联结的结论.并探讨了这种联结键的可能形式。     

木质纤维素新型预处理与顽抗特性

木质纤维素是地球上最丰富的可再生生物质资源,其中纤维类多糖的酶催化降解是木质纤维素生物精炼的关键环节之一。对木质纤维素进行预处理,破坏底物的顽抗特性,是实现木质纤维素高效酶解糖化的必要途径。为此,各国学者围绕预处理技术开发以及底物顽抗特性开展了大量研究,本文对近几年来在这两方面取得的最新成果进行了综述和分析。在预处理方面,重点介绍了组合预处理、低温预处理、绿色溶剂与电化学预处理4类新型预处理技术,并对预处理效果与技术优势进行了评价;在底物顽抗特性方面,综述了木质素、结晶度、酶可及度等不同顽抗特性对纤维素酶解的影响规律,重点总结了近年来顽抗特性研究方面的新方法、新认识与新理解。上述研究成果有助于了解当前木质纤维素预处理研究的导向以及明确制约纤维素酶解的关键因素,为设计和筛选适宜的预处理方式、深刻理解纤维素酶解机制提供基础和指导。     

Infrared spectroscopy studies of cyclic anhydrides as intermediates for ester crosslinking of cotton cellulose by polycarboxylic acids. IV. In situ free radical copolymerization of maleic acid and itaconic acid on cotton

Polycarboxylic acids have been used as crosslinking agents for cotton fabrics and paper to replace the traditional formaldehyde‐based reagents. Previously, we found that a polycarboxylic acid esterifies cotton cellulose through the formation of a five‐membered cyclic anhydride intermediate. Both maleic acid (MA) and itaconic acid (ITA) are extremely difficult to polymerize under conditions normally used for free radical polymerization. It has been reported in the literature that treatment of cotton fabric with a mixture of MA and ITA significantly improved wrinkle‐resistance of the fabric. In this research, we investigated the in situ copolymerization of MA and ITA on cotton fabric. Fourier transform‐infrared spectroscopy was used to study the anhydride carbonyl formed on the cotton fabric treated with the mixtures of MA and ITA. A redox titration technique also was applied to determine the quantity of alkene double bonds on the treated fabric. It was found that free radical copolymerization of MA and ITA does not occur on the fabric at elevated temperatures when potassium persulfate is present as an initiator. It does occur, however, when both potassium persulfate and sodium hypophosphite are present on the fabric. The in situ copolymerization on the cotton fabric probably is initiated by a reduction–oxidation system. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 75: 327–336, 2000     

Behavior of cyanoethylated cotton towards gamma radiation

Unmodified cotton fabric, cyanoethylated cottons having 0.12, 0.55, 0.77, and 1.24% N as well as cotton treated with NaOH under conditions similar to those of cyanoethylation but in absence of acrylonitrile were exposed to gamma radiation doses (3.199–31.199 Mrads). The six substrates before and after irradiation were assessed for copper number, carboxyl content, degree of polymerization, tensile strength, and elongation at break to determine the extent of degradation of these substrates. The effect of radiation dose on the nitrogen content of cyanoethylated cottons was also examined. It was found that degradation is higher the higher the radiation dose irrespective of the substrate used. Nevertheless, the extent of degradation is determined by nature of the substrate. Introduction of cyanoethyl groups in the molecular structure of cotton cellulose impart certain resistance to radiation degradation of cotton provided that these groups are present in appreciable amounts (0.55% N and above). The cyanoethyl groups seems to impede oxidation of the cellulose hydroxyls and/or glucosidic bonds against radiolysis. On the other hand, when present in smaller amounts, the cyanoethyl groups are not able to outweigh the increased accessibility of cotton cellulose brought about by the alkaline environment of the cyanoethylation reaction. Hence, substrates containing lower cyanoethyl contents are more susceptible to degradation than the modified cotton, and in this respect they are similar to alkali-treated cotton.     

微波辐射技术在淀粉水解制葡萄糖反应中的研究

对微波幅射与常规加热条件下淀粉水解制葡萄糖反应进行了对比。结果表明 ,在微波辐射条件下 ,反应速度是常规加热法的 10 0倍 ,极大地降低了能耗。同时 ,还考察了多种金属卤化物及硫酸盐对淀粉水解制葡萄糖收率和速率的影响 ,发现微波功率 80 0 W时 ,在 0 .0 5 %盐酸中 ,某些金属盐能使淀粉在 2～ 3 min内快速水解 ,而且所得产物几乎全部是葡萄糖。