Development of Catalysts for Polymer Degradation and Their Application to Plastics Recycling and Hydrogen Production

研究了氢氟硅酸盐、FSM-16负载氧化镓和氢硼硅酸盐作为聚烯烃化学回收的催化剂，将其降解为有用的石油化工原料。在低密度和高密度聚乙烯和聚丙烯的降解过程中，低聚硅酸盐对氢和芳香烃（主要是苯、甲苯和二甲苯）的共产具有较高的活性。氢气和BTX的产率随反应温度的升高而增加，在500℃时分别达到3%和55%以上。待降解聚烯烃的结构对产物分布影响不大。这可以通过分解碎片的频繁骨架异构化机制来解释。用Ga/FSM-16作催化剂时，虽然芳烃在催化剂表面转化为碳质物质而降低了产率，但其产氢率高达4.5 wt%，相当于聚烯烃中含氢量的32%。硼硅酸氢可以将聚烯烃分解成低分子量烯烃。丙烯和丁烯为主要产物，其产率随反应温度的升高而增加，石蜡和芳烃的产率有限。从这三种聚烯烃的降解过程中观察到几乎相同的产物分布。这些结果表明，利用镓和硼催化剂开发的技术是聚烯烃化学回收的新选择。

H-gallosilicate, gallium oxide supported on FSM-16, and H-borosilicate have been developed as catalysts for chemical recycling of polyolefins by degradation into useful petrochemical feedstocks.The gallosilicate showed a high activity for the coproduction of hydrogen and aromatic hydrocarbons, mostly benzene, toluene, and xylenes (BTX), from the degradation of low- and high-density polyethylene and polypropylene. The hydrogen and BTX yields increased with reaction temperature and went up to over 3 and 55 wt% at 500 ℃, respectively. The product distribution was influenced little by the structure of the polyolefins to be degraded. This can be explained by a mechanism involving frequent skeletal isomerization of the decomposed fragments.A high hydrogen yield of 4.5 wt%, the value of which corresponds to 32 % of the moles of hydrogen being contained in the polyolefins, was obtained when Ga/FSM-16 was used as a catalyst, although the yield of aromatics was reduced because of their transformation into carbonaceous materials on the catalyst surface.H-borosilicate was found to be a catalyst that can break down polyolefins into lower molecular weight olefins. Propylene and butenes were the main products and their yields increased with reaction temperature, while paraffins and aromatics were obtained in limited amounts. Almost the same product distributions were observed from the degradation of the three polyolefins.These results indicate that the developed technologies using gallium and boron catalysts are highly promising as new options for chemical recycling of polyolefins.