ZSM-5@ZrO2复合催化剂核壳结构构造及甲醇和硫化氢吸附转化行为

Since the disadvantages of low methanethiol yield and short catalyst lifetime in the thiolation of methanol with H2S, the design and fabrication of a ZSM-5@ZrO2 composite with a core-shell and hierarchical structure is proposed as a manner to solve the problems that simultaneous enhancements for methanol conversion and methanethiol selectivity require completely different activity sites of catalyst and reaction temperature, by the formation of synergistic catalytic effect of L-B acid sites combined with unique reaction route of core(weak acid sites)-shell(mostly base sites). Impacts of procedures including tune processing of surface charge property of core phases, impregnation operation of ZrO2 seeds and secondary growth of shell crystals on core-shell structures, physicochemical characteristics and adsorption conversion properties are taken into account in this project, aiming for that an obtained novel composite catalyst with a core-shell structure exhibits the synergistic catalytic effect, considerably enhancing the methanol conversion, restraining the formation of dimethyl sulfide, hydrocarbon, carbon oxides and etc. and alleviating the deactivation rate of the catalyst. It is expected that a highly economical methanethiol synthesis technology with low energy consumption could be developed by exploring the interactions of preparation conditions and structure properties, structure properties and adsorption conversion behaviors of methanol and hydrogen sulfide, establishing the structure-activity relationships, and revealing the competition reaction mechanisms between methanol dehydration and methanethiol synthesis and deactivation behavior of the catalyst. Finally, our research achievements would provide the reference for other similar heterogeneous catalysis, exhibiting important scientific significance and application prospects.

针对硫化氢-甲醇法合成甲硫醇工艺存在产品收率低、催化剂寿命短等问题，项目提出构造基于微-介孔体系的ZSM-5@ZrO2催化剂核壳结构，形成L-B酸活性中心和核（弱酸）-壳（碱性为主）特殊反应路径的协同催化环境，以解决同时提高甲醇转化率和甲硫醇选择性要求不同酸碱中心和不同反应温度的瓶颈问题。系统研究核相表面电荷性质调变、晶种浸渍播种、壳相晶粒二次生长等制备工艺条件对催化剂核壳结构、物化性质及吸附转化特性的影响，使催化剂在较低反应温度下能提供有效增强甲醇转化率、抑制甲硫醚、碳氢及碳氧等副产物生成和缓解失活速率的协同环境。掌握催化剂制备条件与结构性质、结构性质与甲醇和硫化氢分子吸附转化行为的影响规律，建立催化剂构效关系，揭示甲醇脱水与甲硫醇合成竞争反应机制和催化剂失活行为，最终形成低能耗、高效经济性甲硫醇合成技术。研究成果将为我国同类多相酸碱催化技术提供借鉴，具有重要科学意义和应用前景。

甲硫醇（CH3SH）属重要精细化工中间体，因其在硫醇有机物中相对分子质量最小，性质活泼，可广泛应用于食品及饲料添加剂、农药、医药等工业。我国甲硫醇市场供需矛盾十分突出，甲硫醇年产量不到2万吨，而年需求量达数十万吨。基于贵州特色煤资源的碳硫分子转化利用工业发展背景，项目采用硫化氢甲醇法工艺合成甲硫醇，针对该工艺存在产品收率低和催化剂寿命短等问题，现有催化剂改性制备主要基于浸渍负载原理调变催化剂表面酸碱种类和比例，但该法会覆盖催化剂部分活性中心和堵塞孔道致使催化效率提升不明显。项目提出构造ZSM-5@ZrO2催化剂核壳结构，构建不仅有利于增强甲醇较低温度下解离吸附的L-B酸协同催化中心，还能提供有效抑制甲硫醚、碳氢及碳氧等副产物生成、增强甲硫醇选择性及缓解失活速率的微-介孔层级结构协同催化核壳反应路径，以解决提高甲醇转化率和甲硫醇选择性要求不同活性中心和不同反应温度的技术瓶颈问题。.采用水热包覆技术，借助原位光谱分析手段和表面反应技术，开展了ZSM-5@ZrO2核壳结构催化剂制备、构效关系、吸附转化行为及积碳失活行为等方面的研究工作。借助聚电解质层层组装的方法制备了以t-ZrO2为壳相的ZSM-5@t-ZrO2包覆复合材料，通过壳层上碱位分布的约束作用，提高了甲硫醇的选择性。以PDDA+/PSS-/PDDA+顺序进行聚电解质改性得到的全包覆复合材料，在反应温度370℃、反应压力1.0MPa、原料进料空速1.5h-1、H2S/CH3OH摩尔比2:1、N2流量90ml·min-1反应条件下，甲硫醇的选择性高达95%，甲醇转化率接近90%，催化寿命达20h，与未改性复合材料相比提高了20%。理论上，建立了催化剂构效关系，获得了催化剂失活行为规律；技术上，在较低反应温度下获得较高产品收率的同时又大幅度延长催化剂寿命，最终形成了低能耗、高效经济性甲硫醇合成技术。项目研究成果将为我国同类多相酸碱催化技术提供借鉴，同时也可助推甲硫醇合成工业化进程，缓解我国甲硫醇供需矛盾。