疏水杂多酸催化生物基脂肪酸水相脱水酯化反应的研究

Fatty acid ester is one of the important chemical products. Because of the environmental problems and shortage of fossil resources, the route from biobased fatty acid to ester derivatives is becoming an international research hot spot. However, the concentration of products by bioconversion is much lower than that through chemical methods and only the 5 g/L level could be obtained. On the other side, the procedure for the isolation and purification of biobased compounds from water solvent is tedious and high cost, which is one of the key restraining factors for the industrialization process. Based on our previous study on the esterification of C16-fatty acid to produce the biodiesel in water solvent, the project will continue to design and prepare the hydrophobic heteropolyacid catalysts, which aim at the selective adoption of substrate and water molecules, make the contact between fatty acid with alcohol at the active centers, and remove the water by-product from the catalytic center. Besides, we will also analyze the tertiary structure of heteropoly acid, the surface and pore size distribution of carrier material, the loading efficiency of heteropoly acid and the hydrophobicity of catalyst. Based on the relationship between the catalyst structure and the reaction activity, the improvement of catalyst will be studied and the esterification of fatty acid in the fermentation solution will be realized finally. These studies will provide a scientific basis for the hydrophobic heterogeneous system, a new alternate route for the transformation of fatty acid into high value-added esters and guidance for the dehydration reaction in water solvent. The new method would make the combination of fermentation and separation easy to get, achieve the natural separation of ester from water and lower production costs.

脂肪酸酯是重要的化工产品，迫于化石资源短缺及环境压力，以生物基脂肪酸为原料制备脂肪酸酯衍生物已成为国际上的研究热点。然而，基于生物转化手段的脂肪酸产物浓度仅为5 g/L，远低于化学手段的百克每升级别，产物分离、提纯困难；高衍生成本一直是制约生物基脂肪酸酯产业化的重要因素。在前期C16脂肪酸水相酯化合成生物柴油的研究基础上，本项目将继续设计合成新型疏水杂多酸催化剂，通过材料疏水功能化实现催化剂对底物分子及溶剂水分子的选择性通过，并最终实现低链及中链生物基脂肪酸水相高效酯化。此外，通过催化剂表征并关联反应效率、效果，明确最佳杂多酸活性中心三级结构、负载率、疏水性等关键参数，建立构效关系，指导催化剂优化调变；并在阻断发酵液内主要杂质干扰机制的前提下，最终实现发酵液内脂肪酸的原位酯化。该研究有望实现发酵与分离技术耦合，酯化产物自然分离，降低衍生成本，对醚化、酯化聚合等其它水相脱水反应均有借鉴意义。

迫于化石资源短缺及环境压力，以生物基脂肪酸为原料制备脂肪酸酯衍生物已成为国际上的研究热点。然而，基于生物转化手段的脂肪酸产物浓度仅为5 g/L，高衍生成本一直是制约生物基脂肪酸酯产业化的重要因素。本课题通过水热法和溶胶-凝胶法分别合成了MCM-41负载磷钨杂多酸、多孔配位聚合物封装磷钨杂多酸 (PCP(Cr)-PTA)，通过离子液体对分子筛孔道填充，获得了疏水功能化MCM-41负载磷钨杂多酸（OTS-PTA-MCM-41）。通过沉淀法一步获得疏水磷钨杂多酸季铵盐这一反胶束催化剂。所得催化剂分别使用透射电子显微镜分析（TEM）、扫描电子显微镜分析（SEM）、氮气吸附脱附分析（N2-TPD）对其形貌、孔结构进行了分析；通过傅里叶红外光谱（FT-IR）、X射线衍射分析（XRD）对其组分进行了确定；通过化学吸附分析（NH3-TPD）对其酸强进行了对比筛选；并通过热重分析（TG）明确了催化剂的热稳定性。.三类催化剂成功应用于水相脂肪酸脱水酯化制备脂肪酸酯的反应中。首先，通过七种不同模板剂得到孔径依次增大的疏水OTS-PTA-MCM-41催化剂，考察了载体孔径对反应传质的影响效果，得出了n-2规律的选择性，针对C16脂肪酸以C14为模板剂所得催化剂OTS-PTA-MCM-41(C14)具备最佳催化效果（收率93%），其最佳反应条件为150 ℃，反应3小时。应用于发酵液内混合脂肪酸酯化月桂酸甲酯、肉豆蔻酸甲酯、棕榈酸甲酯的产率分别为91.1%、87.9%和90.7%。其次，明确了PCP(Cr)-PTA在水相催化棕榈酸植被生物柴油的最佳反应条件为醇水比1:9，反应温度130 ℃，反应时间3小时，催化剂质量分数为5%，棕榈酸甲酯的产率达到84.7%；通过PCP(Cr)封装PTA活性中心具备良好的稳定性，重复五个反应周期，棕榈酸产率波动在4.6%以内，催化活性稳定性较好。最后，通过一锅法合成得到疏水CTAB/HPW季铵盐类催化剂的酯化收率为81.4%，确定了OTS-PTA-MCM-41(C14)为最佳水相生物基脂肪酸脱水酯化催化剂。此外，所研PCP(Cr)-PTA催化剂，在水相成功催化糖脱水制备环烯烃类化合物，为生物基平台化合物水相脱水制备高附件值产品提供了实验支撑。项目已发表SCI论文2篇（1区1篇），核心期刊1篇，在审SCI 1篇，申请专利3项（授权1项）。