Study On Regeneration Of Bismuth-based Non-mercury Catalysts With Steam Method For Acetylene Hydrochlorination

In this study, we forcus on the mercury pollution problem of polyvinyl chloride(PVC) industry, which is the urgent need to solve. At present, in China, PVC production is mainly depending on the calcium carbide acetylene hydrochlorination. Due to the use of mercury catalyst, PVC industry is facing the challenge of environmental problems. Therefore, environment friendly acetylene hydrochlorination mercury-free catalyst has attracted many attentions of the society and is becoming a hot spot of current research.At present, non mercury catalyst consists of precious metal catalysts and non noble metal catalysts. This research is related to the non noble metal catalyst due to cost reasons. The catalytic properties of non noble metal catalysts(activity and selectivity of catalyst with mercury) are almost approach the level of industry in the domestic and foreign research data.. But due to the formation carbon deposition in the process, the life of catalyst is short. Therefore, mercury-free catalyst has not been effective for replacing mercury catalyst and needs to be studied further. In order to improve the mercury-free catalyst performance and usage, the steam regeneration method was used to regenerate non-noble metal bismuth based mercury free catalyst for acetylene hydrochlorination deactivation and discussed the regeneration mechanism; Conditions of steam flow, activation temperature, and activation time were optimized. The surface morphology, structure and related physical and chemical properties of the support and catalysts before and after use were characterized, as well as the regenerated catalyst. Under the optimal process conditions, regeneration was take place many times and the catalyst regeneration was evaluated in fixed bed. The results showed as below.(1) In coal activated carbon as the carrier with concentration of 25% Bi Cl3 acid for pickling liquid impregnated activated carbon carrier and prepared the type of Bismuth base catalyst in acetylene hydrochlorination. Then, the water vapor treatment was adopted after deactivation of the catalyst. Catalytic performance tests show the water vapor treatment exhibits good deactivation catalyst regeneration ability. Using orthogonal design method to investigate the catalyst regeneration performance, the factor were water vapor in different regeneration temperature, water vapor velocity and regeneration time on the influence of catalyst regeneration, which indicates that the catalyst regeneration time is the main factor of catalyst regeneration efficiency. The temperature of 600 oC, vapor velocity of 30 cm3/min and the regeneration time of 120 min are the optimal conditions, which the highest activity of regenerated catalyst was even higher than the fresh catalyst. Furthermore, the best effect can be achieved 112.5% of the initial activity of the fresh catalyst after catalyst regeneration.(2) Through the results of BET, SEM, EDS, TEM, XRD, FT-IR and TG to the catalyst samples analyze, it demonstrated that the main reason of catalyst deactivation is the active component covering with the reaction process of carbon and the loss of active component. After steam activation treatment, the active component of catalyst is being exposed recover certain catalytic properties. Compared to the deactivation of catalyst, the surface morphology of catalyst regeneration exhibits some changes, which produced more holes and showed species formation on the surface of crystal type, straw cocooning. Bi on the surface of the catalyst in the form of bismuth oxychloride and may produce a new active species of bismuth oxychloride(compared with the X- ray diffraction PDF standard card), bismuth oxychloride in the catalyst surface would be the active center of the catalyst, which can ineffectively inhibit the loss of active components and restore the activity and live of the catalyst.(3) Compared to traditional method, solvent washing method, charcoal burning regeneration air, the introduction of steam recycling regeneration can delay the loss rate of catalyst active component effectively. After 5 times of steam regeneration, the regeneration of the catalyst activity reached 52.4% of the initial activity, which can improve the service life of the catalyst effectively.