水热条件下棉纤维的结构演变特性

为了研究棉纤维的水热行为,以微晶纤维素和葡萄糖为模型化合物,探讨水热条件下棉纤维的碳化过程及结构演变特性。分别利用HPLC、SEM、XRD、FTIR、XPS及EA对水热液相主要产物和水热焦炭的结构及性质进行了表征分析。结果表明,棉纤维可在水热条件下碳化形成炭微球,碳化产物与微晶纤维素和葡萄糖的水热碳化产物具有类似的晶体结构和含氧官能团,但产物形貌结构与性能较差;葡萄糖是棉纤维水解碳化成球的重要中间产物;棉纤维水解为葡萄糖的收率较低,只有部分棉纤维水解为单糖,进而产生两种不同的碳化路径,主要产物形貌为不规则颗粒物。     

水热条件下棉纤维的结构演变特性

为了研究棉纤维的水热行为,以微晶纤维素和葡萄糖为模型化合物,探讨水热条件下棉纤维的碳化过程及结构演变特性。分别利用HPLC和SEM、XRD、FT-IR、XPS及EA等手段对水热液相主要产物和水热焦炭的结构及性质进行了表征分析。结果表明,棉纤维可在水热条件下碳化形成炭微球,碳化产物与微晶纤维素和葡萄糖的水热碳化产物具有类似的晶体结构和含氧官能团,但产物形貌结构与性能较差;葡萄糖是棉纤维水解碳化成球的重要中间产物;棉纤维水解为葡萄糖的收率较低,只有部分棉纤维水解为单糖,进而产生两种不同的碳化路径,主要产物形貌为不规则颗粒物。     

流化床内生物质合成气制取甲烷的实验与宏观动力学

为了研究低温低压下流化床反应器中生物合成气催化制取甲烷过程,制备了Ni基甲烷化催化剂,对其进行表面形态分析,并考察了该催化剂催化合成气制备甲烷反应中操作条件对甲烷化过程的影响。实验结果表明,在低温低压的条件下,合成气甲烷化过程受到操作参数(反应温度、压力、空速和氢碳比等)的影响较大。较高的反应压力和氢碳比有利于甲烷的生成,反应温度存在最佳值,空速则有一折中值。根据实验结果,考虑到温度对甲烷生成的影响,引入了基于甲烷化反应温度的修正系数,建立了低温低压下合成气制备甲烷的宏观动力学模型。实验数据与模拟数据比较符合,验证了所建宏观动力学模型的正确性,从而为准确描述低温低压下合成气催化制取甲烷的过程奠定基础。     

焦炉气非催化部分氧化制合成气数值模拟

基于Curran反应机理,采用Chemkin软件对贫氧条件下的焦炉气非催化部分氧化过程进行了模拟,并考察了反应温度、反应压力和氧气与焦炉气物质的量之比对焦炉气非催化部分氧化制合成气反应的影响。结果表明:该模型能较好地模拟工业操作条件下的焦炉气非催化部分氧化反应;焦炉气非催化部分氧化动力学时间尺度为毫秒级;反应温度越高,动力学时间越短,当温度提高至1373 K后,动力学时间未见明显缩短;反应压力越大,动力学时间越短,当压力提高至3.0MPa后,动力学时间未见明显缩短;氧气和焦炉气物质的量之比越大,动力学时间越短,但得到的合成气摩尔分数以及H_2和CO物质的量之比也相应降低:当氧气和焦炉气物质的量之比增大至0.262后,合成气中H2和CO物质的量之比维持在2.0~2.5。     

草酸水解甜高粱秸秆渣的Saeman动力学模型

利用草酸作为催化剂水解甜高粱秸秆渣制备木糖,测定了不同温度下的木糖收率和副产物糠醛产量;依据半纤维素水解的Saeman模型,计算得到了木聚糖水解和木糖降解的动力学数据,其活化能分别为5.89×104,1.38×104J/mol。分析结果表明:木聚糖水解反应速度快,但是生成的木糖容易发生降解;模型最优化反应条件为125℃和77min,实验得到的木糖收率为52.11%。草酸作为一种有机酸,能够用于催化半纤维素水解制备木糖,副产物糠醛的产率较低。     

Ru/CNT催化纤维二糖加氢制备山梨醇的机理及动力学

针对纤维素的转化,研究了以钌碳纳米管(Ru/CNT)为催化剂,纤维素模型分子纤维二糖催化加氢制备山梨醇的反应。通过对反应产物的分析,考察了纤维二糖转化生成山梨醇的反应机理,建立了纤维二糖催化加氢的动力学模型。并根据实验数据,拟合得到纤维二糖催化加氢反应各步的反应数率常数和表观活化能,其中,纤维二糖水解活化能为147.1 KJ·mol^-1;纤维二糖部分加氢活化能为73.8 KJ·mol^-1。纤维二糖催化加氢反应模型的建立,为纤维素资源的高效利用提供了重要的基础数据。     

CO2置换CH4水合物中CH4的实验和动力学

在自行设计的反应装置中考察了2.8 MPa和3.25 MPa压力下，温度271.2、273.2和276.0 K时CO2气体置换十二烷基硫酸钠（SDS）体系CH4水合物中CH4的置换过程。实验数据表明，在反应的前50 h，CH4水合物的分解速率较快，其后分解速率变慢。冰点以上CH4水合物的分解速率较快。基于动力学数据，建立了SDS体系置换反应过程中CH4水合物的分解动力学模型和CO2水合物的生成动力学模型。计算得到CH4-CO2置换反应过程中CH4水合物的分解活化能为28.81 kJ·mol-1，CO2水合物的生成活化能为68.40 kJ·mol-1。数据表明，CH4水合物的分解可能受置换反应过程中水分子的重排控制，而CO2水合物的生成可能受CO2气体在水合物中的扩散控制。     

CO与亚硝酸甲酯催化偶联合成草酸二甲酯的本征动力学研究

在微型管式反应器中,采用高效的Pd/Al2O3催化剂,在388～418 K的温度范围,1∶1～3∶1的CO与MN比,50～150 mL/min的原料气流速条件下进行了CO与亚硝酸甲酯催化偶联合成草酸二甲酯的本征动力学实验;通过对反应机理的推导,动力学模型的筛选及优化,得出CO偶联合成草酸二甲酯的本征动力学模型。结果表明:CO与亚硝酸甲酯催化偶联合成草酸二甲酯是以表面羰化反应为控制步骤。     

5-羟甲基糠醛在稀硫酸催化下的降解反应动力学

5-羟甲基糠醛脱羧生成乙酰丙酸是生物质资源出发制备乙酰丙酸过程中的关键步骤之一。为了研究低硫酸浓度下水解生物质制备乙酰丙酸工艺的可行性,系统地测定了在压力5 MPa、初始浓度1～9 mg·ml^-1、硫酸浓度0.05%～0.4%（质量分数）、温度150～190℃条件下,5-羟甲基糠醛在稀硫酸催化下的降解反应动力学数据,并以主反应生成乙酰丙酸、副反应生成腐黑质的平行反应动力学模型对数据进行了拟合,拟合结果表明,在实验范围内,主、副反应对5-羟甲基糠醛均为一级反应;主反应对H⁺浓度为1.16级,反应的活化能为78.5 kJ·mol^-1;副反应对H⁺浓度为0.722级,反应的活化能为98.0 kJ·mol^-1。研究结果表明,降低温度和提高硫酸浓度有利于提高生成乙酰丙酸的选择性。     

用离子交换树脂催化水解醋酸甲酯的反应动力学研究

研究了在常压下、温度为３０８～３２８Ｋ的范围内，用阳离子交换树脂作催化剂的醋酸甲酯催化水解宏观反应动力学。建立了实验条件下的动力学模型。研究了反应温度、催化剂浓度、水酯比、催化剂装填方式及进料中含甲醇等因素对催化水解的影响。实验数据采用拟均相二级反应动力学模型进行回归，得出醋酸甲酯催化水解的正逆反应活化能为３５．５和２９．５ｋＪ／ｍｏｌ。与催化剂浓度关联的最终速率表达式为：ｋ＋＝（５．３９２７９×１０－１０Ｃ－２．０７２０５９×１０－８）ｅｘｐ（－４．２７０／Ｔ）ｋ－＝（５．９１０６６×１０－１０Ｃ－１．５１５４３×１０－８）ｅｘｐ（－３．４２８／Ｔ）     

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。     

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.     

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。     

低分压CO2在有机胺水溶液中的溶解度

建立了一套用于测定低分压CO2在有机胺水溶液中溶解度的实验装置。在298、308 K下分别测定了低分压CO2在较低浓度的乙醇胺(MEA)、二乙醇胺(DEA)水溶液中的溶解度。结果表明,在较低的溶解度下,CO2在有机胺水溶液中的平衡分压接近于0;当溶解度增大到一定程度后,平衡分压随其增加而急剧增大,同时,温度的升高和有机胺浓度的增大均能增大CO2的平衡分压。通过实验数据拟合得到的理论模型参数与实验值符合较好。     

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.     

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.     

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.     

Kinetic studies of wheat straw hydrolysis using sulphuric acid

The kinetics of cellulose and hemicellulose hydrolysis of wheat straw was studied using both isothermal and non-isothermal techniques in a batch reactor. Reactions were carried out between 100 and 210°C and product sugars were analyzed using a Bio-Rad HPX-87P liquid chromatographic column. A simple first order series reaction model was used for both cellulose and hemicellulose hydrolysis reactions and kinetic parameters were obtained for the Arrhenius rate equations for three different sulphuric acid concentrations (0.5, 1.O and 1.5%). Activation energies remained constant with acid concentration but the pre-exponential factors showed an increase with acid concentration. To minimize the amount of experimental data required and to achieve a unique solution to the kinetic parameters, the technique of combining isothermal and non-isothermal reaction data was studied.     

Chain reaction mechanism of cellulose pyrolysis

Chatterjee and Conrad¹ studied the kinetics of pyrolysis of cotton cellulose in the temperature range 270–310°C and proposed a chain reaction mechanism. Lipska and Parker⁸ studied the pyrolysis of the α-cellulose in the temperature range 250–300°C and interpreted the kinetic data differently. Both articles were published almost simultaneously. In this paper Lipska and Parker's complete data have been again analyzed and reinterpreted in light of the chain reaction mechanism. The energies of activation for initiation and propagation steps of the cellulose decomposition reaction are discussed.     

微波条件下纤维素在磷酸中的快速水解

微波条件下磷酸快速水解纤维素得到葡萄糖,而葡萄糖可替代甲醛制备新型环保PF(酚醛树脂)。以微波功率、反应时间和反应温度为试验因素,以葡萄糖产率为考核指标,采用正交试验法优选出磷酸水解纤维素的最佳工艺条件。结果表明:各因素对磷酸水解纤维素的影响依次为反应温度>反应时间>微波功率;当微波功率为240 W、反应温度为100℃和反应时间为40 s时,水解液中葡萄糖含量为80.7%,葡萄糖浓度为40.35 g/L;超声波能加快纤维素在磷酸中的溶解速率,常温时纤维素完全溶解在磷酸中需要72 h,而微波条件下纤维素完全溶解在磷酸中只需2 h。