Study On Mercury-Free Catalysts Of Non-Noble Metal For Acetylene Hydrochlorination

Vinyl chloride is an important chemical monomer (VCM). Because the reality of energy structure in China, most of VCM have been obtained from the acetylene hydrochlorination based on coal chemical processes. So far, mercuric chloride (HgCl2) is a widely used catalyst in commercial plants. However, the capacity of the commercial processes is restricted because of the Hg residue problems, HgCl2with highly toxic and volatile properties, and other safety aspects. Due to a growing awareness of environmental issues, efforts are directed towards looking for a new mercury-free catalyst to realize the clean production of VCM.Non-noble metal are the developing research direction of mercury-free catalysts. In this paper, molecular sieve, oxide, activated carbon, and immobilized ionic liquid have been used as the component of catalysts to study. We have also investigated the effects of carrier, active component, cocatalyst, carrier pre-treatment, catalyst composition, and preparation process on the acetylene hydrochlorination.We found the optimal conditions to prepare non-noble metal mercury-free solid catalysts. The mass ratio of the active component SnCl2and another was2:1. The active component/supporter and stabilizer/active component were1:4,0.05:1, respectively. Ultrasound assisted, concentrated hydrochloric acid, secondary immersion, and calcination treatment could obviously improve the catalytic activity. Meanwhile, ultrasound assisted, calcination treatment, and trace amounts of rare earth compounds could stable the catalytic activity for a long time. Using the concentrated hydrochloric acid to dissolve active components could make catalysts earlier access to the state of activity. Under the reaction conditions (reaction temperature=140℃, acetylene space velocity>300h-1, and VHCl: VC2H2=1.10), the solid catalyst SnCl2-CuCl-Tb4O7/C which prepared by the above preparation methods could continuously catalyze the acetylene hydrochlorination27h. The selectivity of vinyl chloride was around98%. The conversion of acetylene was maintained at77%within6h, and it fluctuated around60%after20h. According to the catalyst characterization and analysis (BET, XRD, TG/DTG, SEM, FT-IR), three reasons lead to the deactivation of solid catalysts. The first reason would attribute to the loss of unstable stannous chloride, another one was the reunion of active component, and the last one was the carbon deposition.We have synthesized a series ionic liquid (IL). The ionic liquid was loaded on the activated carbon, and then the IL/C system was used as a catalyst. The ionic liquid which consisted of triethylamine hydrochloride, stannous chloride and zinc chloride has good catalytic activity to the acetylene hydrochlorination. When the mass ratio of SnCl2to ZnCl2was2:1, the catalyst had the best activity. For this [Et3NH]Cl-SnCl2/ZnCl2/C catalyst, the acetylene conversion was more than30%and the selectivity of vinyl chloride over95%. When the [Et3NH]Cl-SnCl2/ZnCl2contained CuCl, the acetylene conversion of the IL/C catalyst could also be more than25%. According to the results of catalytic performance and the SEM analysis, we considered that there was an interaction between metal chlorides and the carrier; meanwhile, the reactant C2H2/HCl dissolved in the IL was likely to react with metal chlorides on carrier surface. Acetylene hydrochlorination in the pure IL would not overreact, which illustrated the IL could limit the degree of the catalytic reaction. From the TG/DTG and FT-IR, we also found that immobilized IL catalysts had the carbon deposition as the same as solid catalysts.