Continuous vinyl chloride monomer production by acetylene hydrochlorination on Hg-free bismuth catalyst: From lab-scale catalyst characterization, catalytic evaluation to a pilot-scale trial by circulating regeneration in coupled fluidized beds

This contribution proposes a novel process for VCM production. To eliminate hot spots, fluidized-bed, rather than fixed-bed, was selected as the reactor. Bi/Cu/H3PO4 series catalyst supported on silica gel was employed to replace the industrial HgCl2 catalyst, and exhibited acceptable initial activity (30% activity of HgCl2) and stability in differential reactor referring to that of HgCl2 catalyst under the condition of 200 °C and 360 h− 1 (space velocity, volume based). The coke covered on the active sites during reaction led to rapid catalyst deactivation. Therefore, several types of regeneration method were explored to burn off the coke. The two-step regeneration method in which the H2O and air were fed respectively to promote regeneration revealed good ability in recovering catalyst activity. The fluidized bed reactor (FBR) was selected to prevent formation of hot spots because of its excellent heat transfer capacity, which is tens of times to fixed bed reactor. Over 700 h industrial trial was operated in FBR, which exhibited good performance in conversion of C2H2, maintaining around 80% in former 200 h and detecting by-product no more than 100 ppm, while the loss of activity components in high temperature was still a main problem after circulating regeneration cycles. Overall, the trials present a very promising green process in replacing the previous contaminated one for PVC industry.