催化学报 ›› 2017, Vol. 38 ›› Issue (5): 862-871.DOI: 10.1016/S1872-2067(17)62819-5

• 论文 • 上一篇    下一篇

固载型季铵盐离子液体催化合成环状碳酸酯:烷基链长及羟基的影响

焉晓明a,b, 丁璇a, 潘昱a, 许小伟a, 郝策a, 郑文姬a, 贺高红a,b   

  1. a. 大连理工大学石油与化学工程学院, 精细化工国家重点实验室, 辽宁盘锦 124221;
    b. 大连理工大学化工学院, 精细化工国家重点实验室, 辽宁大连 116024
  • 收稿日期:2017-02-14 修回日期:2017-03-16 出版日期:2017-05-18 发布日期:2017-05-10
  • 通讯作者: Gaohong He
  • 基金资助:

    国家自然科学基金(21406031,21476044,U1663223);长江学者奖励计划(T2012049);精细化工国家重点实验室(KF1507);大连市高层次人才创新支持计划(2015R056);辽宁省教育厅(LT2015007);中央高校基本科研业务费专项资金(DUT16TD19).

Quaternary-ammonium-immobilized polystyrenes as efficient and reusable heterogeneous catalysts for synthesis of cyclic carbonate: Effects of linking chains and pendent hydroxyl group

Xiaoming Yana,b, Xuan Dinga, Yu Pana, Xiaowei Xua, Ce Haoa, Wenji Zhenga, Gaohong Hea,b   

  1. a. State Key Laboratory of Fine Chemicals, Research and Development Center of Membrane Science and Technology, School of Petroleum and Chemical Engineering, Dalian University of Technology, Panjin 124221, Liaoning, China;
    b. State Key Laboratory of Fine Chemicals, School of Chemical Engineering, Dalian University of Technology, Dalian 116024, Liaoning, China
  • Received:2017-02-14 Revised:2017-03-16 Online:2017-05-18 Published:2017-05-10
  • Supported by:

    This work was supported by the National Natural Science Foundation of China (21406031, 21476044, U1663223), the Changjiang Scholars Program (T2012049), the State Key Laboratory of Fine Chemicals (KF1507), Dalian High-Level Talent Support Program (2015R056), Education Department of the Liaoning Province of China (LT2015007), and Fundamental Research Funds for the Central Universities (DUT16TD19).

摘要:

CO2是造成温室效应的主要原因,同时又是地球上储量最为丰富的可再生C1能源.因此,CO2资源化受到了广泛关注.CO2与环氧化物反应可合成环状碳酸酯,后者广泛用作极性溶剂、锂离子电池的电解液和聚碳酸酯中间体等.但是,由于CO2的化学惰性,其反应需要高活性的催化剂.近年来,碱性金属、金属配合物及离子液体等均相催化剂被用于催化CO2与环氧化物加成反应.其中,离子液体具有高热稳定性、低挥发性和结构可调性,得到了广泛研究.季铵盐、咪唑盐和季鏻盐等离子液体已经被证实具有较高的催化活性.然而,均相催化剂回收困难,而且产物需要进一步纯化.将离子液体固载化制备成非均相催化剂,可以实现简单的固/液分离.聚合物、SiO2、SBA-15、氧化石墨烯和羧甲基纤维素等固载化催化剂已经广泛用于CO2和环氧化物的环加成反应.虽然非均相催化剂显示了潜在的优势,但是催化活性较低的问题仍然亟待解决,尤其是在较温和的反应条件下.因此,通过催化剂分子结构设计以提高催化性能,成为目前的研究热点.
本文提出在催化活性基团和载体之间引入长烷基链,增加催化活性位点与反应物的接触面积,同时引入助催化的羟基,通过长链与羟基的协同作用,提高非均相催化剂活性.本文合成了羟基功能化长柔性链季铵化聚苯乙烯微球非均相催化剂([AHTAPC-PS]X,X=Cl,Br,I),用于催化CO2与环氧化物的环加成反应,并与不含羟基的长烷基链季铵盐离子液体非均相催化剂([TAPB-PS]Br)及短烷基链季铵盐离子液体非均相催化剂([TMA-PS]X)的催化性能进行了对比.考察了固载后的离子液体烷基链长及侧链羟基对催化性能的影响,并通过实验和密度泛函理论计算研究了催化机理.红外光谱、扫描电镜和能量散射谱结果充分证明了季铵盐非均相催化剂的成功合成;热重测试表明,此类催化剂具有可以满足反应需求的热稳定性.密度泛函理论计算结果显示,与短烷基链非均相催化剂相比,长烷基链非均相催化剂的阴离子负电性更强,同时羟基与环氧化合物的氧原子之间存在强的氢键作用.羟基形成的氢键可以增加环氧化物的C–O键长,同时强负电的阴离子更加容易攻击β-碳原子,促进环氧化物开环.另外,长烷基链结构使得卤素阴离子具有与反应物更大的接触范围,因此提高了反应活性.当采用短烷基链季铵盐非均相催化剂时,环氧丙烷(PO)与CO2环加成反应生成碳酸丙烯酯(PC)的产率仅为70.9%,而采用长烷基链季铵盐非均相催化剂时产率可达91.4%(135℃,1.5 MPa,3 h),进一步加入助催化的羟基,则PC产率可提高到98.5%.此外,含羟基的长烷基季铵盐非均相催化剂在温和条件下也具有较高的催化活性(100℃,1.5 MPa,3 h,PC产率78.4%),该催化剂同时具有较高的循环稳定性(10次循环后,PC产率≥ 96%,选择性≥ 99%).综上所述,该催化剂具有优异的综合性能,展现了良好的工业应用前景.

关键词: 环加成反应, 季铵盐, 长烷基链, 羟基, 非均相催化

Abstract:

Spherical polystyrene-supported ammonium salts containing different linking chains between the support and ammonium groups were prepared as efficient and easily reusable heterogeneous catalysts for the cycloadditions of CO2 and epoxides. The effects of the length of the linking chains and a hydroxyl group pendent on the linking chain on the catalytic performance of ionic liquid immobilized catalysts and their mechanisms were studied through experiments and density functional theory calculations. It was found that, compared with a short linking chain, a long chain can make the halogen anion more negative and provide a larger contact area of the catalysts with the reactants, thus enhancing the reaction kinetics. The hydroxyl group can stretch the C–O bonds of the epoxides, promoting the reaction thermodynamics. As a result, for the cycloaddition of propylene oxide, the yield of propylene carbonate is much higher for the catalyst with a long linking chain (yield: 91.4%) compared with the yield for that with a short chain (yield: 70.9%), and is further increased in the presence of pendent hydroxyl groups (yield: 98.5%). The catalyst also shows a high catalytic activity even at mild temperature and good reusability (yield: ≥ 96% for 10 cycles), and the selectivity is always above 99%.

Key words: Cycloaddition, Ammonium, Long alkyl chain, Hydroxyl group, Heterogeneous catalyst