| Mercuric chloride(HgCl2)is used as a catalyst for the formation of vinyl chloride(VCM)in acetylene hydrochlorination(AHR),which accounts for more than 50%of China's mercury use.During the reaction,mercury will enter the downstream products and environment with the industrial waste,affecting product quality,harming the environment and personnel health.Searching of non-mercury catalysts is the fundamental way to solve the problems,which contributes to greener and more clean production of PVC.Now the gold catalyst is expected to replace industry mercury catalyst because of its high activity,electivity and stability.However,further improving the catalytic efficiency and stability of the gold catalyst simultaneously reducing the cost of the catalyst are prerequisites for realizing the industrial application of the gold catalyst.AuI/AC catalyst developed by our research group is an Au+-based catalyst.Its catalytic activity is higher than the Au3+ based catalyst disclosed in 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.Firstly,we study the kinetic of the AuI/AC catalyst to better guide the industrial application of the 0.1 AuI/AC catalyst.Secondly,we introduce sulfuric acid/ammonium persulfate system to modify the activated carbon to prepare better performance AuI/AC catalyst.Third,we study on the change of active components of the catalyst under different pretreatment and reaction conditions before and after modification in order to explain the deactivation mechanism of the catalyst.The main research contents and results are as follows:(1)The kinetics of acetylene hydrochlorination of AuI/AC catalysts was investigated.The kinetic experiments showed that when the catalyst with a size duing 60-80 mesh,space-time(W/FA)<30 g·h·mol-1,and a reaction temperature during 150-200?,the activation energy for hydrochlorination of acetylene was 129.6 kJ/mol.reaction rate constant k=1.66 × 10I4exp(-1.29 × 1 04/RT),product VCM didn't affect the speed of the reaction.By investigating the contact time limit and the reaction conditions,the suitable reaction conditions of AuI/AC catalyst were shown as follow:the temperature was 423?453 K,raw gas molar ratio HC1:C2H2=1.10?1.15,and the air speed of acetylene was 12.4?37.3 h-1.(2)Catalytic performance of Aul/AC catalysts under different modification systems was investigated by using activated carbon modification as an entry point.On this basis,the optimization method of introducing sulfuric acid/ammonium persulfate modified system as AuI/AC was proposed.Meanwhile,the optimal activated carbon modification process and the ratio of sulfuric acid/ammonium persulfate were established.At last,we successfully promoted the activity of AuI/AC catalyst by about 8 percent,and the stability got a little bit higher.(3)The valence and dispersibility of the active components of Aul/AC catalyst and AuI/AC-APS catalyst modified by ammonium persulfate(APS)under heating,HCl and C2H2 were studied systematically.The change of the catalyst revealed the characteristics and variation of the active components of the catalyst,and proposed the deactivation mechanism of the catalyst.1)The activity of the AuI/AC catalyst was contributed by Au3+-Au+-Au0.2)There was a dynamic cycle among the Au3+-Au+-Au0,Au+disproportionated to form Au3+and Au0,hydrogen chloride oxidized Au0 to Au?+,and C2H2 reduced Au?+ to form Au0.All this reaction were happening at the same time.3)The low tarman temperature of gold leaded Au0 sintering and reuniting to form large gold particles,which were unable to join the loop again. |
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