Mercury-free Catalysts For Synthesis Of Vinyl Chloride Via Acetylene Hydrochlorination

The vinyl chloride monomer industry in China currently still relies on supported HgCl2 as catalysts, which are highly toxic and volatile, inevitably causing sever environmental problems. Therefore, there are wide efforts exploring non-mercury catalysts. In the study of the replacement of mercuric chloride catalysts, metal-free catalysis is one promising approach due to the fact that nonmetal materials are usually low on cost. In this work, we synthesized a series of metal free catalysts including nitrogen-doped carbon and porous boron nitride, and both exhibited good catalytic performance. We carried out some preliminary study on the scale-up of nitrogen doped carbon materials, studied their activation and deactivation mechanism, and proposed regeneration methods. The main results are summarized as the following:1. The development of N-doped carbon catalysts (NGCS700 catalyst). Using glucose as a carbon source, we apply hydrothermal reaction process and high temperature treatment under ammonia atmosphere for the synthesis of the catalyst. The resulting catalysts possess a high micro-porosity and nitrogen content (over 10 wt. %). The catalyst shows good performance in acetylene hydrochlorination reaction. The conversion of acetylene can reach over 80%-90%, with the VCM selectivity around 95%. The catalyst is stable over 300 h at 200?, and as the reaction time reaches 600 hours, the conversion drops to 85%. The deactivation of catalyst is due to coke formation, which can be burnt off at 300? in air and subsequently in ammonia atmosphere at 450?. Thus, the deactivated catalyst (acetylene conversion below 10%) can be regenerated. After regeneration, the initial conversion can reach around 80%.2. Performance of the catalyst under industrial reaction condition. By increasing the catalyst loading, the linear velocity is increased and catalyst performance is enhanced, which makes it possible to apply the catalyst under lower reaction temperature without loss of activity. A lower reaction temperature decrease the rate of coke formation and hence increase the catalyst's stability. By decrease the reaction temperature to 180oC, the stability increase to 900 h without obvious loss of activity.3. The development of porous boron nitride as metal free catalyst. (1) Material synthesis and structure. Using boric acid and melamine, we synthesize a porous boron nitride material. The material exhibits a typical hexagonal boron nitride structure with high specific surface area and high porosity of both micro and meso pores, rendering it high on defects and edges. (2) Catalytic performance. The optimized reaction temperature is 280?, under which the 1 g loaded catalyst can exhibit 99% conversion and 99% selectivity. In a near 1000 hour test on stream, the conversion dropped from 99% to 95%, suggesting a better overall performance than nitrogen doped carbon materials. (3) Reaction and deactivation mechanism and the development of regeneration methods. Studies show that the major deactivation cause is coke formation, which can be burnt off at mild condition in air. After burning off the coke, the sample should be activated in ammonia atmosphere, after which the deactivated sample can be regenerated. DFT calculation along with experiment results suggest that armchair edge sites are the possible activation sites,and the reaction may follow an Eley-Rideal mechanism, with acetylene molecules being activated on the surface of the catalysts. A possible reaction route is developed according to kinetic modelling, which includes the formation of a carbocation like intermediate.