疏水-亲水双功能催化剂用于聚甲氧基二甲醚合成

Based on the hydrophobic-hydrophilic properties of the surface and bulk structure of the catalyst, the effect of hydrophobic- hydrophilic structure of the catalyst on the reactive system with water as the side product was investigated with the synthesis of polyoxymethylene dimethyl ethers（PODE） from methanol and formaldehyde. In a catalytic reaction, the water lowered the stability of hydrophilic catalyst and the effective amount of catalytic active center was reduced by the competitive adsorption of water on the surface of the catalyst to a certain extent..In the reaction system of polyoxymethylene dimethyl ethers from methanol and formaldehyde, there are hydrophobic materials, for example methylal or PODE with different polymer degree, and hydrophilic materials, namely methanol and formaldehyde. In the above catalytic reaction process, methanol and formaldehyde were easier catalyzed by the hydrophobic acid center while methylal and PODE with different polymer degree were easier catalyzed by the hydrophilic acid center..In this project, the hydrophobic-hydrophilic bi-functional catalyst with high stability and activity was prepared by the following steps: deposition of active ingredient on the surface of nanoporous alumina, package of the hydrophobic agent (silane) and fixation of hydrophilic active groups. The above catalyst was used in the synthesis of polyoxymethylene dimethyl ethers from methanol and formaldehyde and the preparation of the catalyst can be extended to other reaction systems with water as the side product. .PODE without the carbon-carbon bonds can be used as the diesel additive and is vital for easing the diesel exhaust pollution.

以催化剂表面和体相结构的疏水-亲水性质为基础，结合甲醇和甲醛合成聚甲氧基二甲醚（PODE）反应，研究了催化剂的疏水-亲水结构对副产水反应体系的影响。催化反应过程中，水的存在降低了亲水型催化剂的稳定性，同时水在催化剂表面的竞争吸附，一定程度上减少了有效催化活性中心的数量。甲醇和甲醛合成PODE反应体系中包括疏水性物质如甲缩醛和不同聚合度的PODE，也包括亲水性物质如甲醇、甲醛。在催化反应过程中，既需要亲水型的活性中心进行催化甲醇甲醛反应，同样也需要疏水型的活性中心催化甲缩醛、不同聚合度的PODE反应。本项目通过活性组分沉积于多孔纳米氧化铝表面、疏水剂（硅烷）包裹、亲水活性基团固定等步骤制备高稳定性、高活性的疏水-亲水双功能催化剂，用于甲醇和甲醛合成PODE反应。并将催化剂制备方法推广至其它副产水的反应体系中。PODE分子中不含碳碳键，可用作柴油添加剂，对缓解柴油车尾气污染具有重要的意义。

本项目以碳一化工（以甲醇、一氧化碳等为原料合成其他化学品的化学工业）为研究背景，旨在解决该过程中反应活化难，目标产物选择性差的问题，从而降低甲醇化工过程中生产成本和反应后续的分离成本。通过改变催化剂表面和体相结构的疏水-亲水性质，实现对甲醇化工反应过程的控制，提高活性、优化目标产物选择性。以甲醇和甲醛合成聚甲氧基二甲醚（PODE）反应为研究对象，考察了催化剂结构和性能之间的构效关系。证实了催化剂表面和体相结构的疏水-亲水性质对催化反应性能之间的强内在关系。通过调控催化剂表面的亲疏水性能可以实现对不同目标产物的选择性控制。实现了载体的性质对催化过程影响的调控能力。在催化过程中，往往关注的是活性对性能的影响，实际上，催化剂和原料及中间物质的吸附过程也是至关重要的，通过本项目的研究，揭露了吸附过程对整个反应过程的影响。为后续的催化剂设计和制备提供了新的思路和方法。为了验证该结论的普适性，将该理论应用到其他甲醇化工反应过程，包括甲醇脱水制二甲醚、合成气制低碳醇等过程，得到了类似的结论，对于副产水的反应体系中，载体（催化剂）的亲疏性能对原料物质的活化和目标产物的选择性都起到重要的作用。