活性炭基疏水性固体酸催化剂的制备及其在乙醇酯化中的性能

Preparation of Activated Carbon-Based Hydrophobic Solid Acid Catalyst and Its Performance in Esterification of Ethanol

通过椰壳基活性炭(AC)来负载硫酸锆(ZS),制备得到催化剂ZS-AC,然后用硅烷对其进行疏水改性,制备得到疏水性的酯化反应催化剂。实验发现烷基链长度对催化剂的疏水性能影响较大,液固接触角由小到大依次为ZS-AC(40.5°)<ZS-AC-C4(94.7°)<ZS-AC-C7(121.2°)<ZS-AC-C8(136°)。在105℃反应温度下考察了上述4种催化剂的反应活性和重复使用性能。结果显示,随着烷基链长度的增加,催化活性也随之增加,其中经C7H16O2Si改性过的ZS-AC-C7具有最高的催化活性和稳定性。当酸醇物质的量之比为4∶1,催化剂与醇的质量比为12%,反应时间为4.5h时,乙醇达到最大转化率98.8%,乙酸乙酯的收率达到97.2%,接近化学平衡。经过疏水处理过的催化剂重复使用4次后依然可以保持较高的催化活性。

Water produced in the synthesis of ethyl acetate from acetic acid and ethanol can combine with the solid acid catalyst,which results in the loss of active components and reduction of the catalytic activity.Zirconium sulfate(ZS)is a kind of solid acid catalyst with excellent esterification catalytic activity and selectivity.In order to improve the stability of ZS,ZS-AC was prepared by loading ZS over the surface of coconut shell-based activated carbon(AC),and then ZS-AC was modified with silane groups to prepare the hydrophobic solid acid catalyst ZS-AC-C n,where n was the alkyl chain carbon atom numbers.The Fourier transform infrared(FT-IR)spectra revealed that the solid acid catalysts were successfully grafted with silane group,and the alkyl chain length had a great influence on the hydrophobicity of the catalyst.The liquid-solid contact angles increased in the following order:ZS-AC(40.5°)<ZS-AC-C 4(94.7°)<ZS-AC-C 7(121.2°)<ZS-AC-C 8(136°).The reactivity and reusability of these four types of catalysts were investigated at a reaction temperature of 105℃.The results showed that the catalytic activity increased with the increasing of the alkyl chain length,and the catalyst treated with C 7H 16 O 2Si had the highest activity and stability.Thermogravimetric analysis(TG)showed that the hydrophobic catalyst had a better thermal stability compared to the hydrophilic catalyst.When the molar ratio of acetic acid to alcohol was 4∶1,the mass ratio of catalyst to alcohol was 12%,and the reaction time was 4.5 h,the maximum conversion of ethanol reached 98.8%and the yield of ethyl acetate reached 97.2%.At this point,the esterification reaction approached the chemical equilibrium.Moreover,the hydrophobic catalyst was stable in the presence of water which showed the conversion of ethanol was about 92%after repeated use for 4 times.