The Development And Application Study Of Gold Catalysts For Acetylene Hydrochlorination

Acetylene hydrochlorination to vinyl chloride (VCM) is an important part of poly vinyl chloride (PVC) industry, supplying over 70% of polymeric monomer of PVC every year. But it uses mercury catalyst, which is harmful to environment and employees. Searching of non-mercury catalysts is the fundamental way to solve the problems, which contributes to greener and more clean production of PVC. Au catalysts are the best non-mercury catalysts so far and have biggest potential to replace Hg catalyst. However, further improvement of their catalytic efficiency and stability to lower the cost is the precondition to industrial application.MIV-Au0/AC catalyst developed by our research group is an Au0-based catalyst. Its catalytic activity is better than Au3+-based catalysts public reported. However, there are still some problems existed, such as ambiguity of the change of active centre during the reaction, poor stability. Hence, it is necessary to find out the reasons of catalyst deactivation and put forward a improved method. Based on this, we introduced thiol to develop catalyst with higher activity. In addition, the TOF of AuI/AC catalyst developed by our research group is 30.7 mol g-1 h-1, which is best in published literatures. In 270 h lab test, its rate of deactivation was only 1/5 of industrial mercury catalysts. Therefore, it is potential and valuable to further advance industrial application. Moreover, for pilot-scale study, the preparation and reaction conditions of extruded AuI/AC catalyst have been investigated. Major contents and conclusions of this article are listed below:1) We investigated the property change of active component and the reasons of deactivation of MIV-Au0/AC catalyst. The results indicated that the active component would migrate and agglomerate under the heated condition. HC1 could oxidize Au0 to Au3+, and strip Au atoms from the surface of Au NPs. π bond of C2H2 could impact on the surface of Au NPs, converting Au NPs into inactive Au0-s. C2H2 also could reduce Au3+into inactive Au0-s. They might occur at the same time. Au NPs and Auδ + contributed to the catalytic activity together, and the former was more active than the latter. Firstly, the active structure of Au NPs was damaged by dispersion or sintering of Au NPs. Secondly, Auδ+was reduced to Au0 with no active structure. They might be the main reasons of deactivation.2) According to the results above, we introduced reducing thiol to prepare Au0-based Au-Cu-SH/AC catalyst. Thiol can reduce Au3+ to Au0 species during the preparation process, and bond to the surface of Au NPs, avoiding the agglomeration during the preparation process. It also helped protecting Au NPs from structure damage, stabilizing Au NPs and keeping more active structure under the reaction ambience. Through thiol, Au0 species with a specific surface structure and grain size could exhibit better catalytic performance than Au3+. Better dispersity of Au NPs and protection of active structure was the key of high activity and stability. With better catalytic performance than Au/AC and Au-Cu/AC catalysts, the optimum molar ratio of Au/Cu/SH was 1:1:10. With a specific rate up to 13.3 mol g-1 h-1, Au1Cu1SH10/AC catalyst appeared to be 1.56 times as active as the ordinary Au/AC catalyst and over 99.9% selectivity to VCM. The rate of deactivation was only 24.4% of Au/AC and 26.3% of AulCul/AC, which means the lifetime of Au-Cu/AC catalyst could be extended.3) We transplanted Au1 active formula to industrial coal-based activated carbon successfully, getting an extruded Au1/AC catalyst with excellent catalytic performance. Through optimization of preparation method and adjustment of parameters, such as the content of KI, drying temperature, the activity of the extruded AuI/AC catalyst prepared could reach 80% of laboratorial testing catalysts. The active center of the extruded Au1/AC catalysts could be induced and converted only under the reaction temperature over 180℃, leading to good catalytic activity. However, the introduction of H2 would do harm to catalysts, resulting in rapid deactivation. Thus, the reaction temperature of 180℃ and none of H2 in feed gas are more suitable to extruded AuI/AC catalyst.