典型生物质分级选择性溶剂解制备高附加值化学品研究

The shift of fossil resource to biomass is inevitable for the sustainable development of chemical industry. The present project aims at the full and effective utilization of raw biomass, especially the effective utilization of the naturally formed bonds and building units is highly considered. The following steps are taken. At first, the selective solvation of either hemicellulose or lignin avoiding significant alteration of the other two main components of the raw biomass is studied based on the chemical bonding nature between the components or within the component. The selective solvation of both hemicellulose and lignin or both cellulose and hemicellulose avoiding significant alteration of the other is also considered. Then, subsequent selective solvation of one of the remained components is studied. Thus the solid raw biomass is transferred to liquid state, which ameliorates the mass transfer and heat transfer as well as the action of catalyst for further conversion. By treating the obtained liquids with different kinds of catalysts with corresponding processes, especially those for the catalytic conversion of oligomers formed from the solvation of one of the components (hemicellulose, lignin or cellulose), value-added chemicals and energy materials could be obtained. The interactions between the molecules of solvents, biomass derived monomers and oligomers as well as the catalysts are being studied. The understanding of the control, the synergy effects of the following complex reaction network, including dehydration, decarboxylation, hydration, isomerization, hydrogenation and degradation, is expected to facilitate the promotion, the inhibition and the utilization of their synergy effects in order to obtain high selectivity to target products. The mass and heat transfer in the above system are studied for the improvement of process efficiency. The results will be meaningful for the effective use of raw biomass materials, the development of bio-refinery, as well as the improvement of agriculture economy.

化工原料由化石资源向生物质转变，是化工可持续发展的必由之路。本项目根据生物质中组分间和组分内化学键的特点，以尽可能多利用其天然形成的化学键和结构单元、完全有效利用生物质主要组分为目标，研究低温下使生物质中单一或者两种组分优先溶剂解分离的溶剂体系，将复杂固体原料转化为组成、结构更简单的流体体系，优化传热传质过程并使催化剂易于发生作用；研究由生物质溶剂解所得单体、寡聚体等进一步转化为高附加值化学品的新催化剂和工艺；研究溶剂、单体、寡聚物与催化剂的相互作用规律及其对产物选择性的影响；研究复杂体系中脱水、脱羰、水合、异构化、加氢、降解等反应的调控与协同机制，研究如何通过对上述反应网络中部分反应的促进、协同及抑制，从而提高目标产物的选择性。由此发展高选择性体系，将毛竹、玉米秸秆、桑枝等典型生物质的三大组分完全转化为附加值更高的小分子化合物，对发展节能新型生物炼制业、促进农业发展具有十分重要的意义。

优化获得了从生物质中优先选择性溶解转化其三大组分的溶剂体系，初步认识了选择性溶解转化规律，揭示了溶剂、助剂及催化剂对选择性破坏生物质组分间和组分内化学键的作用机制。发展的AlCl3、水/马来酸体系可选择性溶解毛竹中的半纤维素，发现水主要促进半纤维素溶解，催化剂高效破坏半纤维素和木质素之间的链接键。H2O-GBL、H2O-THF、H2O-正丁醇体系可高选择性溶解木质素，发现H2O破坏非晶态纤维素与木质素之间C6-O-H组分间化学键，有机溶剂促进木质素组分内β-O-4键的断裂。优化获得了同时溶解转化半纤维素和木质素的溶剂体系，阐明了GVL和H2O的协同作用有利于H2O与木质素-OCH3基团形成氢键并解聚生成β-O-4’和β-β’型寡聚物的机制。NaCl促进H+在纤维素表面的吸附，Cl-与纤维素葡萄糖端羟基形成新的氢键，使得纤维素被逐层剥落溶解。发现了溶解转化所得流体进一步转化的复杂反应网络，通过溶剂和催化剂对网络中部分反应促进、协同及抑制，调控反应网络，提高目标产物的选择性。Na2CO3、Ni/HZSM-5可促进木质素和纤维素间酯键、醚键和氢键在较低温度下断裂，并促进木质素侧链Cα-Cβ和β-O-4中C-O键断裂，高选择性生成4-乙基酚类产物。醇原位供氢-Pt/C催化体系可高选择性获得4-丙基愈创木酚和4-丙基紫丁香酚。马来酸可抑制木糖进一步脱水生成糠醛，定向生成木糖；NaCl中Cl-可有效断裂木聚糖中的氢键，延长α、β-吡喃两种构型木糖之间的平衡时间，有利于稳定α-吡喃木糖。调控纤维素溶剂解所得六碳糖单体进一步转化的反应网络，发展了AlCl3-NaCl-H2O/THF双相体系、CO2-H2O-THF三相溶剂体系，使六碳糖单体进一步定向转化为高值化学品5-羟甲基糠醛。发展了由生物质选择性转化制备D-乳酸的催化体系，揭示了D-乳酸手性中心的形成机制，初步明晰了催化剂结构对形成不同手性乳酸的调控机制。发现YCl3与丙酮醛的不同作用方式导致反应过渡态的变形能不同，从而由木糖催化转化生成D-过量乳酸；D-乳酸可与MgO结合，形成具有手性口袋的复合物，催化丙酮醛转化为D-乳酸。形成的由糖制备HMF新技术已转让给企业，走向工业化。