微波辐射-亚临界CO2调变催化纤维素制乙酰丙酸机理研究

A new strategy of levulinic acid production from direct conversion of cellulose was proposed by using a microwave radiation method associated with the subcritical CO2 system in this project so as to solve the difficult technical problems such as uncontrollable transformation of cellulose, low yield and instability of levulinic acid. Herein, cellulose feedstock was firstly pretreated by microwave radiation technology to improve the accessibility and reactivity in the aqueous phase, and then transformed into levulinic acid under the subcritical CO2 system, following by investigating the kinetics of carbonic acid formation according to the reaction between CO2 and H2O as well as the modulation of organic acid, and therefore exhibiting a promising substitute for the use of traditional hydrochloric acid, sulfuric acid, inorganic acid or solid acid catalyst in the transformation of cellulose by the adjustment of the key intermediates of the coupling reaction between CO2 and organic acids. Meanwhile, the molecular mechanism of cellulose conversion would be elucidated in the process of hydrolysis, dehydration and hydrolysis, and then the nature of adjusted cellulose conversion and controlled product would be revealed by the combination of the establishment of a related dynamic model. In addition, taking account of the water-gas shift reaction between H2O and CO derived from the decomposition of HCOOH byproduct, the desirable CO2 could be realized recycle in such a system, achieving technology breakthroughs on the green conversion of cellulose into levulinic acid in the aqueous phase, and therefore providing directive theory and technical data for the promising production of chemicals and liquid fuel from lignocellulosic biomass in a biorefinery.

针对纤维素水相转化合成化学品乙酰丙酸中目标产物收率低、不稳定及难调控等技术瓶颈，提出微波辐射-亚临界CO2联用体系中纤维素定向转化与产物可控的构思。采用微波辐射技术对纤维素预处理改性，提高纤维素的可及性与反应活性，并通过CO2与H2O耦合形成碳酸的动力学研究，结合有机多元酸的调变特性，构建中间关键产物的CO2与有机酸调变控制耦合反应，取代传统盐酸、硫酸等无机酸或固体酸催化剂，研究纤维素在反应体系中水解-脱水-再水解的分子历程与作用机制，并建立相关动力学模型，揭示纤维素定向转化与产物可控规律，在此基础上，利用水气变换转化，实现CO2的体系内循环，获得纤维素水相定向绿色转化乙酰丙酸技术新突破，为纤维素类生物质绿色转化成化学品及高品位液体燃料等领域的规模化利用提供理论依据和技术支撑。

针对纤维素由葡萄糖聚合的特点，提出亚临界CO2耦合弱酸催化降解纤维素制取乙酰丙酸的技术思路。本项目首先以葡萄糖模型化合物为研究对象，探索了CO2亚临界体系中葡萄糖转化为5-羟甲基糠醛和乙酰丙酸的反应工艺及变化规律，发现了CO2的添加可以增加反应体系的酸性，促进葡萄糖的转化，并研究了有机多元酸和路易斯酸耦合对葡萄糖的酸脱水影响，明确了最佳的反应工艺，追踪分析了产物的生成规律，得出有机多元酸对产物中5-羟甲基糠醛或乙酰丙酸的生成影响不大，但在铝盐和钨盐等路易斯酸存在下，葡萄糖在CO2亚临界体系中可完全转化，脱水产物中乙酰丙酸的收率明显增加。此外，由于果糖脱水制取5-羟甲基糠醛或乙酰丙酸收率要比葡萄糖大很多，实验中开展了葡萄糖异构转变成果糖的实验，合成了MgO/NaY和凹土催化剂，考察了反应温度、反应压力和反应时间等参数对葡萄糖异构性能的影响，利用谱学手段研究了催化剂微观结构，建立了催化剂结构与性能之间的构效关联。在此基础上，开展了纤维素结构的微波改性和CO2体系中的催化降解行为，讨论了多元酸和路易斯酸对乙酰丙酸生成的转化规律，利用催化加氢技术研究和拓宽了纤维素的高值化利用。. 项目执行期间，共发表/接收论文7篇，其中SCI论文5篇，EI论文2篇，参加国际会议1人次，申请国家发明专利2件。