【作者】 张晔；

【导师】 陈明强；

【作者基本信息】 安徽理工大学 ， 环境工程， 2014， 博士

【摘要】 随着化石资源的日益减少以及化石燃料使用过程中CO2的排放对地球气候造成的影响日益严重,如果继续依赖化石资源,人类将面临的结果是能源危机。因此,许多研究正致力于探索开发非化石碳能源。其中,以木质纤维素为原料发展生物炼制技术被认为是一种最有前途的替代方案。糠醛,一种重要的平台化合物,不仅可以通过进一步反应直接转化为生物燃料,还可以衍生出数量众多的下游产品,成为科学工作者关注的焦点。本文首先以木糖为模型化合物,在140-160℃温度范围内,考察了甲苯／水双相体系中不同金属氯化物催化木糖的转化效果。随后,在上述研究的基础上,选取AlC13·6H2O为催化剂,在单因素实验的基础上,采用响应面法考察了反应温度、反应时间、AICl3浓度及木糖浓度、固液比对木糖和玉米芯水转化制备糠醛的影响,建立预测模型；采用一级反应模型对实验数据进行动力学研究,得到相关动力学参数,建立动力学模型。最后,针对甲苯／水双相反应体系中A1C13催化玉米芯半纤维素水解制备糠醛的反应机理进行了探讨。通过以上研究,得出以下结论：(1)与未添加催化剂相比,选用的金属氯化物均具有一定的催化效果,其中两性金属氯化物AICl3及过渡金属CrCl3的催化效果较优。动力学分析结果表明,AICl3为催化剂时,糠醛生成速率常数k1与糠醛分解速率常数k2的比值大于CrCl3为催化剂时的比值,表明AICl3为催化剂时,木糖转化为糠醛的相对反应速率较快,糠醛产率高,即AICl3的催化效果优于CrCl3。(2)反应温度、反应时间及AICl3浓度是木糖脱水制备糠醛的重要影响因素。反应温度的升高及AICl3浓度的增加均能促进木糖发生转化,提高糠醛产率。响应面分析表明,当反应温度为149.71℃,反应时间为112.79min, AlC13浓度为0.10mol·L-1,木糖初始浓度为0.35mol·L-1时,木糖转化率接近100%,此时糠醛产率为46.51%。动力学分析表明：木糖脱水生成糠醛的反应活化能为110.76kJ·mol-1,而糠醛发生分解反应的活化能为158.38kJ·mol-1。(3)甲苯／水双相反应体系中,AICl3可以有效催化玉米芯半纤维素水解制备糠醛。响应面分析表明：反应温度、AICl3浓度是糠醛产率的主要影响因素。当反应温度为177℃,反应时间为78.38min, AICl3浓度为0.08mol·L-1,固液比为0.15g·mL-1时,糠醛产率为52.69%。动力学研究表明,AICl3为催化剂时,木糖转化为糠醛的活化能小于半纤维素转化为木糖的活化能,且随着AICl3浓度的增加,木糖转化为糠醛的活化能降低。当AlC13浓度分别为0.06mol·L-1、0.10mol·L-1、0.14mol·L-1时,木糖转化为糠醛的活化能分别为95.87kJ·mol-1、78.91kJ·mol-1、75.68kJ·mol-1。玉米芯水解前后XRD及SEM分析表明,AICl3能够有效破坏玉米芯致密的纤维组织结构,实现半纤维素水解。综合实验结果(1)、(2)、(3),对双相体系中AICl3催化玉米芯中半纤维水解的作用机理进行初步探讨。反应机理主要包括两方面：一方面,Al3+发生水解,形成的H+能够有效催化半纤维素水解生成木糖；另一方面,AICl3中的金属中心可以与木糖分子中的氧原子发生配位作用,促使木糖异构为木酮糖,进而脱去三分子水形成糠醛。更多还原

【Abstract】 With the accessible oil fields are becoming depleted and CO2emissions from fossil fuel are affecting the earth’s climate, the most imminent result that awaits mankind is the tremendous crisis of energy if we remain dependent on the fossil resources. Hence, much research is being devoted to exploring non-fossil carbon energy resources. Among these, the lignocellulosic refining technology with lignocellulose as raw materials is considered as a promising alternative program. Furfural, an important platform compound, which can be directly converted into biofuels or many down-stream products through further reaction, has become the focus of scientists.The effects of different metal chlorides on conversion of xylose into furfural in toluene/water system at140～160℃were studied first in this paper. Based on the above research, aluminum chloride was chosen as catalyst. The response surface methodology was used to determine the effects of independent variables, including reaction temperature, reaction time, concentration of aluminum trichloride and xylose concentration, liquid solid ratio on the conversion of xylose and corncob. Meanwhile, the first order reaction model were developed to explain the relationship between the reaction rate constants and reaction temperature and AICl3concentrations, and the kinetic parameters were obtained. Finally, the mechanism of conversion of corncob into furfural catalyzed by AICl3in biphasic system was discussed.Through the above research, the main conclusions were summarized as follows:(1) Compared with no catalyst loading, all the tested chlorides could converse xylose into furfural, the amphoteric metal chloride AICl3and transition metal chloride CrCl3had better catalytic performances. The kinetic study results showed that the ratio of rate constants beween formation and decomposition of furfural catalyzed by AICl3was greater than that catalyzed by CrCl3, which indicated that the catalytic activity of AICl3was better than that of CrCl3.(2) The independent variables including reaction temperature, reaction time and concentration of AICl3had a significant effect on dehydration of xylose into furfural. With the reaction temperature and concentration of AICl3increasing,the xylose conversion could be promoted and the furfural yield should be improved respectively. The maximum predicted furfural yield was46.51%when the temperature, reaction time, AICl3concentration and the initial xylose concentration were149.71℃,112.79min, O.lmol·L-1and0.35mol·L-1, respectively. Under these conditions, the xylose conversion was nearly100%. With the first order kinetic equation, the evaluated activation energies of formation and decomposition reaction of furfural were110.76kJ·mol-1,158.38kJ-mol"1, respectively.(3) AICl3was an effective catalyst for corncob hydrolysis into furfural in biphasic system. The surface response analysis for corncob conversion indicated that reaction temperature and AICl3concentration were highly significant term. A furfual yield of52.66%could be achieved at temperature of177℃, time of78.38min, AlC13concentration of0.08mol·L-1and the solid liquid ratio of0.15g·L-1.Kinetic study showed that the activation energy of furfural formation was less than xylose formation with AICl3as catalyst, and with increasing concentration of AICl3, the activation energy of furfural formation decreased. When the concentration of AICl3were0.06mol·L-1,0.10mol·L-1,0.14mol·L-1, the activation energies of the conversion xylose into furfural were95.87kJ·mol’1,78.91kJ·mol-1and75.68kJ·mol-1, respectively. The XRD and SEM analysis of corncob before and after hydrolysis showed that AICl3could effectively break the structure of fibrous tissue and promote the hydrolysis of corncob.(4) Above all, the mechanism of hydrolysis of corncob hemicellulose into furfural catalyzed by AICl3in biphasic system was discussed. It can be devided into two parts. On the one hand, hydrogen ions from aluminum ions hydrolysis in water, could improve the formation of xylose. On the other hand, the coordination effect between metal center of AICl3and oxygen atom of xylose molecule could isomerize xylose into xylulose, then remove three molecules of water to form furfural.更多还原