【作者】 陈文明；

【导师】 陈明强； 王君；

【作者基本信息】 安徽理工大学 ， 化学工艺， 2007， 硕士

【摘要】 目前工业糠醛主要是通过矿物酸（主要是硫酸）催化五碳糖或半纤维素在200℃～250℃下脱水得到。在这种条件下,生成糠醛的选择性不超过70%,而且矿物酸具有腐蚀性,容易造成污染。采用固体催化剂制备糠醛有可能提高选择性,并且使工艺过程绿色化。本文考察了三种固体催化剂催化木糖脱水制备糠醛的工艺过程。分别以ZSM-5、斜发沸石和固体磷酸钙为催化剂进行实验,考察了催化剂、溶剂甲苯用量、反应时间、反应温度和搅拌速率各种不同因素对糠醛产率的影响;当反应物木糖为5g时,以糠醛产率为目标函数确定了最佳工艺参数;并对以固体磷酸钙为催化剂时的反应动力学进行了研究。以ZSM-5为催化剂进行木糖脱水制备糠醛的实验中,得到最佳工艺条件为:在木糖5.0g、甲苯100.0ml、蒸馏水50.0ml、分子筛（Si/AL=59）2.0g、转速n=700r/min,设定反应温度T=170℃,反应时间t=4h。在此条件下最大产率为29.2%。由实验结果分析可知在本实验体系中催化剂ZSM-5对糠醛的选择性较高,但木糖转化率较低。以斜发沸石催化剂进行木糖脱水制备糠醛的实验中,得到最佳工艺条件为:木糖定量为5g,则斜发沸石催化剂为1.5g、蒸馏水50ml、甲苯125ml、反应时间为4小时、反应温度为170℃、搅拌速率为700r/min。在此条件下最大产率为66%。由实验结果分析可知在本实验体系中斜发沸石催化剂的选择性很高。由ZSM-5、斜发沸石分子筛催化剂的实验结果对比可知,硅铝比小的斜发沸石比较适合本实验体系,在实验中酸性较强的催化剂对糠醛的选择性较低,因此在木糖脱水制备糠醛的实验中采用硅铝比小的分子筛催化剂效果比较好。以磷酸钙催化剂进行木糖脱水制备糠醛的实验中,得到最佳工艺条件为:木糖定量为5g,则斜发沸石催化剂为1.0g、蒸馏水50ml、甲苯100ml、反应时间为5小时、反应温度为180℃、搅拌速率为700r/min。在此条件下最大产率为65.3%。由实验结果分析可知在本实验体系中磷酸钙催化剂的选择性很高;根据实验数据对木糖脱水制备糠醛的反应动力学进行了研究,通过分析计算得出:反应级数为一级,即反应为本征动力学控制的一级反应;反应活化能E_α=50.39kJ/mol,指前因子A=1.587×10⁵ s^-1;并确定了反应速率方程,其方程表达式为:r=1.587×10⁵e^{-5.039×104/RT}C_木糖。更多还原

【Abstract】 At present primary method producing furfural is dehydration of C₅-sugar or hemicellulose on 200℃～250℃using mineral acid as catalyst. Under this condition, selectivity of preparing furfural is no t higher than 70% and that mineral acid has causticity, so it actually brings environment pollution. The selectivity of the process may be increased and the process can also be more cleaner. Three kinds solid catalysts have been investigated for dehydration of xylose to produce furfural.Different reagents were used for catalyst, such as molecular sieve （5A）, clinoptilolite and calcium orthophosphate. Effects of various factors （the amount of catalyst and solvent, reaction time and temperature, stirring speed） on yield of furfural were discussed. The optimal conditions were determined using yield of furfural as an objective function. Reaction kinetics of dehydration of xylose were also studied using calcium orthophosphate as catalyst.As for preparing furfural from xylose dehydration using molecular sieve （5A） as catalyst, the optimized conditions are determined as follows: the amount of xylose 5g, the amount of molecular sieve （5A） catalyst 2.0g, water（as a solvent for xylsoe） 50ml, toluene（as furfural extract） 100ml, reaction time 4h, reaction temperature 170℃. The yield of furfural reaches 29.2% under this condition. The results showed that the selectivity of molecular sieve （5A） to furfural is high while the fractional conversion of xylose is low.As for preparing furfural from xylose dehydration using clinoptilolite as catalyst, the optimized conditions are determined as follows: the optimized conditions are determined as follows: the amount of xylose 5g, the amount of clinoptilolite catalyst 1.5g, water（as a solvent for xylsoe） 50ml, toluene（as furfural extract） 125ml, reaction time 4h, reaction temperature 170℃.The yield of furfural reaches 66% under the optimal condition. The selectivity of clinoptilolite to furfural is high.Clinoptiolite of little silica-alumina rata is propitious to experiment system according to experiment result of two molecular sieve catalysts. Catalyst of strong acidity has lower selectivity to furfural. Molecular sieve catalyst of little silica-alumina rata has good effect under this experiment system. As for preparing furfural from xylose dehydration using Calcium orthophosphate as catalyst, the optimized conditions are determined as follows: the optimized conditions are determined as follows: the amount of xylose 5g, the amount of Calcium orthophosphate catalyst 1.0g, water（as a solvent for xylsoe） 50ml, toluene（as furfural extract） 100ml, reaction time 5h, reaction temperature 180℃.The yield of furfural reaches 65.3% under the optimal condition. The selectivity of Calcium orthophosphate to furfural is high. Dehydration kinetics using calcium orthophosphate as catalyst was studied. The results show that the dehydration is a first order reaction of intrinsic kinetics and activation energy is 50.39kJ/mol, pre-exponential factor is 1.587×10⁵s^-1.Reaction rate equation is determined as follows: r = 1.587×10⁵ e ^{-5.039×104/RT} C_xylose更多还原