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。     

椰壳酸水解制备木糖的反应动力学

本文研究了椰壳经酸水解制备木糖的反应温度、反应时间和酸浓度对水解液中木糖浓度的影响，探讨了椰壳酸水解反应的机理，建立了木聚糖降解与木糖分解的均相不可逆连串水解反应动力学模型，求出了反应活化能Ea，木糖生成与分解反应速率常数k_1、k₂，建立了k₁ 与酸浓度C和反应温度T的关系式，分析了提高k₁与k₁/k₂比值的酸水解条件，其规律可供实现工业化生产借鉴。     

A kinetic study of xylose recovery from a hemicellulose-rich biomass for xylitol fermentative production

Hemicellulose in the complex structure of lignocellulosic substances is mainly composed of xylan which is a polymer based on monosaccharide xylose. Using acidic or enzymatic hydrolysis, hemicellulose can be depolymerized into its constituent monomer. The kinetics of hemicellulose depolymerization and decomposition in oat hull was investigated under moderate pressures with catalyst (H₂SO₄) concentration up to 0.55?N and temperatures of up to 130?°C for a total residence time of 150?min. Different trends of recovery or generation and kinetic mechanisms obtained for the components in the hydrolysate which could be described by different kinetic models, that is, a single-phase kinetic mechanism with product decomposition (two-step sequential reaction) could describe xylose generation. However, generation of arabinose, furfural, and acetic acid followed a single-phase mechanism with no decomposition (one-step reaction). Generation of glucose in the hydrolysate followed a biphasic mechanism due to the fast- and slow-releasing fractions into the liquid phase which was apparently with no decomposition. A pentose recovery of almost 80% was achieved under optimal conditions. Parameters of xylitol bioproduction indicated that a xylitol/xylose conversion yield of 0.80?g/g is achievable from the concentrated hydrolysate with no complementary treatment proving its low toxicity compared to other hemicellulose resources.     

Kinetic studies of xylan hydrolysis of corn stover in a dilute acid cycle spray flow-through reactor

Xylan of corn stover was pretreated with 1%, 2% and 3% (w/w) sulfuric acid at relatively low temperatures (90°C, 95°C and 100°C) in a dilute acid cycle spray flow-through reactor (DCF). The hydrolysis of xylan to its monomeric xylose was modeled by a series of first-order reactions. Both biphasic and Saeman hydrolysis models were applied to fit the experimental data. The results confirmed that the kinetic data of xylan hydrolysis fitted a first-order irreversible reaction model and the experimental data. The reaction rates of xylose monomer formation and degradation were sensitive to catalyst concentration and temperature. Higher catalyst concentration and lower reaction temperature result in high xylose yield. The activation energy for xylose formation and degradation were determined to be 112.9 and 101.0 kJ·mol^-1, respectively. Over 90% theoretical xylose obtained from corn stover can be used to produce ethanol, xylitol and fumaric acid by fermentation.     

小麦秸秆水热预处理半纤维素降解动力学研究

水热预处理是木质纤维素原料高效能源转化的主要工艺流程之一，但是以小麦秸秆为原料的水热预处理的反应路径与反应机理仍有研究不足之处, 制约该预处理过程的优化及实际生产应用。本文以小麦秸秆为研究对象，实验研究了木质纤维素水热预处理过程反应动力学。研究发现，在水热预处理过程中，小麦秸秆的主要降解过程是半纤维素降解产生低聚木糖、木糖以及糠醛的过程，半纤维素在水热过程中几乎完全降解。随着预处理温度的升高，水解液中低聚木糖和木糖的浓度降低，而糠醛的浓度增加；随着保温时间的延长，低聚木糖与木糖的浓度先增加后减小，糠醛的浓度会趋于稳定。根据实验结果提出反应路径并拟合获得动力学速率常数和反应活化能，所获的动力学模型可以很好地解释反应物浓度的变化，与实验数据吻合良好。该模型可以为小麦秸秆水解预处理系统的设计提供参考。     

Epoxidation of karanja (Pongamia glabra) oil catalysed by acidic ion exchange resin

Karanja oil with an iodine value of 89 g/100 g was epoxidised in situ with aqueous hydrogen peroxide and acetic acid in the presence of Amberlite IR‐120 acidic ion exchange resin as catalyst. The effect of the operating variables on the oxirane oxygen content, as well as on the oxirane ring stability and the iodine value of the epoxidised karanja oil, were determined. The variables studied were stirring speed, hydrogen peroxide‐to‐ethylenic unsaturation molar ratio, acetic acid‐to‐ethylenic unsaturation molar ratio, temperature, and catalyst loading. The effects of these parameters on the conversion to the epoxidised oil were studied and the optimum conditions for the maximum oxirane content were established. The proposed kinetic model takes into consideration the two side reactions, namely, epoxy ring opening involving the formation of hydroxy acetate and hydroxyl groups, and the reaction between the peroxyacid and the epoxy group. The kinetic and adsorption constants of the rate equations were estimated by the best fit using Marquardt's algorithm. Good agreement between experimental and predicted data validates the proposed kinetic model. From the estimated kinetic constants, the apparent activation energy for the epoxidation reaction was found to be 11 kcal/mol.     

Influence of pretreatment conditions on composition of liquid hydrolysate and subsequent enzymatic saccharification of remaining solids

In the present work, the effect of dilute acid pretreatment was studied on the composition of liquid hydrolysate obtained after pretreatment by employing different combinations of process variables (temperature, time and acid concentration). The effect of pretreatment was also studied on subsequent enzymatic saccharification of remaining solids to obtain maximum yield of sugars. The efficiency of pretreatment was measured in terms of high‐xylose and low‐glucose yields, which was found most suitable at pretreatment conditions of 120°C, 120 min and 2% (v/v) acid concentration. With increased severity of pretreatment, xylose yield decreased with concomitant increase in glucose yield. The decrease in xylose yield was attributed to conversion into degradation products such as 5‐hydroxylmethyl furfural (HMF) and acetic acid. The percentage of enzymatic saccharification increased with increased pretreatment severity. Saccharification of biomass pretreated at 180°C, 7 min and 0.5% (v/v) acid concentration produced the maximum glucose yield of saccharification of 352 g/kg dry matter, compared to just 97 g glucose/kg dry matter in the case of untreated biomass. The same pretreatment conditions resulted in maximum total sugar yield of pretreatment and saccharification of 459 g/kg dry matter, which was more than 67% of the total potential sugars in biomass. © 2012 Canadian Society for Chemical Engineering     

玉米芯水解制备木糖的研究

文章对玉米芯酸性水解制备木糖的工艺条件进行了研究。以硫酸作为催化剂,考察了不同的反应温度、酸浓度、反应时间、固液物料比及浓缩次数对木糖产率的影响。得出最佳的制备木糖的工艺条件为:酸浓度为3%、反应时间3小时、物料比1∶8、沸腾浓缩3次,该条件下木糖收率可达49.74%。     

玉米秸秆半纤维素制备木糖醇的研究

首先采用无污染的碱性过氧化氢法研究了半纤维素的分离与提取,然后对提取的半纤维素分别进行化学水解和酶水解比较,最后研究了水解液发酵制备木糖醇。结果表明,半纤维素分离提取的优化参数为:2%过氧化氢,2%氢氧化钠,加热时间4 h,反应温度75℃。使用CF3COOH水解半纤维素所得木糖含量为67%~73%,水解率为76%~84%,稀盐酸预处理半纤维素再化学水解所得木糖含量高达88%,水解率上升至大约90%。半纤维素的酶水解实验表明,木聚糖酶的水解专一性高于半纤维素酶,木聚糖酶水解率为38%~60%。在水解液发酵实验中,酶水解液的木糖醇转化率高于化学水解液。另外,通过浓缩半纤维素水解液,提高发酵液的木糖初始浓度,有利于菌株生长,可以提高木糖醇转化率。研究对于玉米秸秆半纤维素制备化学品具有一定的指导意义。     

Modeling and optimization of dilute nitric acid hydrolysis on corn stover

BACKGROUND: Because of its high cost, nitric acid has not been widely employed as the catalyst for hydrolysis of lignocellulosic biomass to obtain fermentable sugars. However, recently more and more research results have reported that nitric acid was more effective than other acids for the hydrolysis of lignocellulose. Therefore, it is necessary to find an optimum condition for nitric acid pretreatment and a means of reducing the cost. RESULTS: In this work, low concentrations of nitric acid and short reaction times were considered to optimize the pretreatment process. The kinetic parameters of models to predict the concentrations of xylose, glucose, arabinose, acetic acid and furfural in the hydrolysates were obtained. Applying the kinetic models, the optimum conditions were: 150 °C, 0.6% HNO₃ and 1 min, which yielded a solution containing up to 22.01 g L^?1 xylose, 1.91 g L^?1 glucose, 2.90 g L^?1 arabinose, 2.42 g L^?1 acetic acid and 0.21 g L^?1 furfural, which were consistent with the predicted values. The influence of temperature was also studied using the Arrhenius equation. CONCLUSIONS: A combination of experimental data and model analysis suggested that 96% xylose yield can be achieved by using low concentration nitric acid for a short reaction time, which could greatly reduce the pretreatment cost. Therefore, dilute nitric acid could be considered a good choice for the hydrolysis of corn stover. Copyright © 2010 Society of Chemical Industry     

Kinetics of epoxidation of jatropha oil with peroxyacetic and peroxyformic acid catalysed by acidic ion exchange resin

The kinetics of epoxidation of jatropha oil by peroxyacetic/peroxyformic acid, formed in situ by the reaction of aqueous hydrogen peroxide and acetic/formic acid, in the presence of an acidic ion exchange resin as catalyst in or without toluene, was studied. The presence of an inert solvent in the reaction mixture appeared to stabilise the epoxidation product and minimise the side reaction such as the opening of the oxirane ring. The effect of several reaction parameters such as stirring speed, hydrogen peroxide-to-ethylenic unsaturation molar ratio, acetic/formic acid-to-ethylenic unsaturation molar ratio, temperature, and catalyst loading on the epoxidation rate as well as on the oxirane ring stability and iodine value of the epoxidised jatropha oil were examined. The multiphase process consists of a consecutive reaction, acidic ion exchange resin catalysed peroxyacid formation followed by epoxidation. The catalytic reaction of peroxyacetic/peroxyformic acid formation was found to be characterised by adsorption of only acetic (or formic) acid and peroxyacetic/peroxyformic acid on the active catalyst sites, and the irreversible surface reaction was the overall rate determining step. The proposed kinetic model takes into consideration two side reactions, namely, epoxy ring opening involving the formation of hydroxy acetate and hydroxyl groups and the reaction of the peroxyacid and epoxy group. The kinetic and adsorption constants of the rate equations were estimated by the best fit using nonlinear regression method. Good agreement between experimental and predicted data validated the proposed kinetic model. From the estimated kinetic constants, the apparent activation energy for epoxidation reaction was found to be 53.6 kJ/mol. This value compares well with those reported by other investigators for the same reaction over similar catalysts.     

葡萄糖高温降解生产乙酰丙酸的动力学研究

Levulinic acid is a kind of new green platform chemical with wide application. The kinetics of levulinic acid formation from glucose decomposition at high temperature was investigated. Glucose containing 1%, 3% or 5% H2SO4 was treated at 170℃ or 190℃. For the various experimental conditions assayed, the time-courses of glucose and glucose degradation products （including 5-hydroxymethylfurfural and levulinic acid） were established. These variables were correlated with the reaction time based on the equations derived from a pseudo-homogeneous, first-order kinetic model, which provided a satisfactory interpretation of the experimental results. The set of kinetic parameters from regression of experimental data provided useful information for understanding the levulinic acid formation mechanism.     

木质纤维素超临界水解糖化产物分析的研究

在超临界条件下水解桉木,探讨了反应时间对液体产物分布的影响。结果表明:反应时间对葡萄糖、纤维二糖、木糖、5-羟甲基糠醛(5-HMF)的产率影响明显,最大分别为17.17%、2.58%、6.82%、12.70%。同时,低聚糖的种类会随着反应时间的延长而变化。水解液的主要组分为:低聚糖、纤维二糖、葡萄糖、木糖、5-HMF、糠醛、酚类物质,以及呋喃、酮、醛、醇、有机酸、芳香族和脂肪类化合物等,且产物种类和浓度受反应时间的影响。在超临界水中,桉木的水解和热解反应同时发生。另外,木质素的存在影响桉木超临界水解的产率。     

氯化铁催化木糖降解制备糠醛反应动力学

研究了温度在443.15～483.15K时0.1mol/L氯化铁催化木糖降解生成糠醛的反应动力学过程。首先建立并验证了反应的动力学模型,根据模型得到了木糖降解、糠醛降解和缩合反应的速率常数。由阿伦尼乌斯方程拟合得到其表观活化能分别为107.94kJ/mol、65.86 kJ/mol和26.36kJ/mol。结果表明,高温和较短反应时间有利于糠醛收率的提高,在反应温度483.15K、60min条件下,最大糠醛收率可达78%。     

Degradation of Organic Pollutants by the Advanced Oxidation Processes

A kinetic model hss been developed for the degradation of organic pollutants concerning with hydroperoxide ion as the initial step for generation of hydroxyl radical and its subsequent reac-tion mechanisms. Rate equstions were derived for depletion of ozone and pollutants in the peroxone oxidation process using ozone and hydrogen peroxide as combined oxidants. Kinetic data obtained experimentally form the hydrogen peroxide-ozone reaction and peroxone oxidstion of nitrohenzene were analyzed by using the proponse rate equations.     

硫代硫胺氧化反应动力学研究

探讨了双氧水氧化硫代硫胺反应的机理，建立了描述氢离子浓度和双氧水浓度变化的氧化动力学方程，与实验结果吻合良好。研究表明，该反应是酸的自动催化反应，氢离子初始浓度的增加可以加速反应进程，由此为实际工业生产中氧化前的加酸工序提供了原理性的指导依据。     

纤维素水解液中木糖发酵制丁醇

对实验室菌种进行筛选后,得到一株能利用纤维素水解液木糖发酵生产丁醇的菌株。研究发现,该菌株不仅能利用水解液中的葡萄糖,还可以利用水解液中的木糖。对菌种生长特性探索,批式发酵中碳源、氮源以及CaCO3等条件优化后,得到最佳种子培养时间为20～24 h,并确定了木糖浓度为20 g/L的纤维素水解液用于15 L发酵罐实验,在37 ℃静置培养84 h,丁醇产量10.95 g/L,总溶剂16.78 g/L（丙酮、乙醇、丁醇三者之和）,木糖利用率达到70%以上,总溶剂转化率为39.4%。解决了纤维素水解液中木糖不能被利用而造成的经济损失问题。     

甲酸催化玉米芯水解生成木糖的动力学

玉米芯是一种价格低廉、可再生的资源,其可以被用来生产高附加值的化工产品。本文主要研究在甲酸质量分数3%、液固比为10mL/g、反应温度（120～150℃）、反应时间（0～240min）条件下玉米芯中半纤维素水解过程。采用两相模型对玉米芯水解过程中木糖浓度进行拟合并得到反应过程的动力学参数。木糖降解反应的活化能大于其生成反应的活化能,这表明高温不利于木糖的生产。对得到动力学方程进行分析,获得最佳的反应条件：甲酸质量分数3%、液固比10mL/g、反应温度140℃、反应时间180min。最佳反应条件下得到的木糖浓度为26.9 g/L。     

酯化-酯交换两步法制备生物柴油的动力学

以潲水油（WCO）为原料,探讨了酯化-酯交换两步法制备生物柴油的反应动力学。以活性炭负载硫酸铁［Fe₂(SO₄)₃/AC］为负载型催化剂,通过测定不同反应温度、不同甲醇/脂肪酸（FFA）摩尔比条件下WCO中游离脂肪酸的转化率,以此确定酯化反应的动力学控制步骤及动力学方程中的待定参数,从而建立了在实验温度范围内酯化反应的动力学方程,并根据碱催化酯交换反应机理,在简化的动力学模型基础上,推导出了WCO中甘油三酯（TG）与甲醇发生酯交换反应的宏观动力学方程。结果表明,酯化反应和酯交换反应的动力学方程在实验条件范围内都能较好地描述各自的反应过程。     

麦草酸水解及水解液木糖发酵的研究

采用甲酸/盐酸水解体系水解麦草,发现 65℃ 水解 0.5 h 可实现麦草中半纤维素的充分水解。选用热带假丝酵母发酵麦草甲酸水解液制取木糖醇。分别研究了在不同浓度甲酸及甲酸根条件下D-木糖的发酵效果,发现在 2 g/L 的甲酸及 5 g/L 的甲酸根条件下,D-木糖实现发酵并得到最大产率的木糖醇,高浓度的甲酸及甲酸根都会抑制D-木糖的发酵。采用D311型阴离子交换树脂脱除甲酸根,实现了麦草水解液的发酵,木糖醇最高得率为 16.88%(木糖醇/木糖)。