| Mercury-free catalyst is the development direction,but it is difficult to industrialize maily subject to expensive preperation cost and low catalytic activity.The low-mercury catalyst and mercury regeneration are the main means of reducing mercury emission.The treatment of chemical waste gas gradually changed from harmless to chemical resources recycling,especially the high-value utilization of resources,becoming a more advanced development direction.The use of low-mercury catalyst to convert acetylene impurity in the polyvinyl chloride(PVC)by-product hydrogen chloride waste gas into chlorinated hydrocarbons,combined with continuous rectification to remove light and heavy components impurities to prepare electronic grade hydrogen chloride(HCl),is an effective way to achieve high value utilization of chemical waste gas and reduce mercury emissions.Electronic grade hydrogen chloride gas is mainly used in semiconductor wafer epitaxial process.Controlling the HCl impurities content were the key indicator for the preparation of electronic grade HCl from the waste gas.Since acetylene(-84?)and hydrogen chloride(-85?)boiling point is very close,the conversion of acetylene to vinyl chloride(-13.9?)by catalytic reaction,and then remove impurities by distillation method is the most effective method.The high efficiency and stability of the low-mercury catalyst used is the key technology of the whole process in the abatement of acetylene impurity through catalytic reaction.The physical properties of the support activated carbon have a great influence on the distribution of the active site of the catalyst,and have a decisive effect on the performance of the catalyst.During the preparation of the activated carbon,the factors such as the ratio of brown coal(HM)and Ningxia Taixi coal(TX),the carbonization temperature,the ratio of KOH activator,the activation temperature,the activation time and the addition of auxiliary activator Fe304 were investigated in the effect on pore structure and pore size distribution of activated carbon.Studies have shown that TX is beneficial to the formation of activated carbon micropores,while HM is beneficial to the increase of mesopores.With the increase of carbonization temperature,the specific surface area of activated carbon increases first and then decreases,reaching the highest 1882 m2/g at 450?,the pore volume being the largest 1.09 cm3/g,and the proportion of mesopores reaching 59.8%.With the increase of KOH addition ratio,the specific surface area of activated carbon reaches the highest 1995 m2/g at R=2.0%,the pore volume is also the largest 1.38 cm3/g and the ratio of mesopores can reach 65.1%.When the activation temperature is T=800?,the specific surface area and pore volume can reach 1908 m2/g and 1.23 cm3/g.The mesoporosity,strength and the yield of activated carbon can also be improved.When the activation time is 40 min,the specific surface area and pore volume can reach 2054 m2/g and 1.39 cm3/g.The strength and yield of activated carbon are also superior.The addition of auxiliary activator Fe304 increases the specific surface area and mesoporosity of the activated carbon to 2195 m2/g and 72.3%,respectively,which helps to increase the mesoporosity and also enhances the strength of activated carbon.dddfIn this paper,the multi-step loading active center process is used to improve the dispersibility in the surface and pores of the support.This method has a significant effect on improving the overall performance of the catalyst.Different catalyst support studies have shown that the order of catalytic activity is K-TX-O<K-WG-O<K-S20-0<K-S40-0<K-FeO.8-O.Activated carbon support with high mesoporosity is beneficial to increase catalyst activity,and the pore structure formed by adding activator Fe304 is beneficial to enhance catalyst life.The catalyst prepared by adding the auxiliary agent KCl can "plug" the micropores and increase the dispersibility of the mercuric chloride as the active center of the catalyst.At the same time,the KC1 can form a covalent complex with HgCl2 which enhance the fix effect of mercury,also increasing the catalyst activity decrease time from 140 hours to 180 hours.Impregnation of the active center mercury chloride by multiple loadings resulted in improved dispersibility,and the content of acetylene decreased from 0.38 ppm to 0.29 ppm.Under the optimized reaction conditions,when the reaction temperature is 140?,the mass space velocity of hydrogen chloride is 0.4 h-1,and the reaction pressure is not lower than 0.5 MPa,the catalyst activity is optimal,and the acetylene content in the raw material is reduced from 2000 ppm to less than 0.1 ppm,which achives the requirements of catalytic reaction and impurity abatement.Through the in-situ IR spectroscopy study of partially deactivated catalysts and completely deactivated catalysts,the results shows that the deactivation of partially deactivated catalysts is mainly due to the accumulation of organics in the pores of the activated carbon and the coating of active centers on the support surfaces,thereby reducing the catalytic activity of the active center and degrading the performance of the catalyst.The deactivation of fully deactivated catalysts is partly due to the loss of mercury.In this paper,the high polarity characteristic of high purity hydrogen chloride was utilized to form a bond at high temperature with organic aggregates,which were taken away from the tunnel and the active center surface to restore the activity of the catalyst.The in-situ IR method was used to study the regeneration process of partially deactivated catalysts.It shows that with the progress of the regeneration process,the organics in the partially deactivated catalysts are gradually removed,the catalyst support pores are gradually released,and the catalytic activity is increased.In the investigation of parameters such as regeneration temperature,regenerated hydrogen chloride space velocity,and regeneration time,optimized regeneration conditions are temperature 220?,hydrogen chloride space velocity 500 h-1,time 60 hr.After in-situ regeneration of fully deactivated catalyst followed by in-vitro mercury recovery,it can be seen that the completely deactivated catalyst after in-vitro regeneration,its catalytic performance reaches the level of fresh catalyst,the difference between the life and fresh catalyst is about 12%,and the regeneration effect is obvious.This paper focuses on the industrial preparation devices of activated carbon support,low-mercury catalyst preparation and continuous double-tower distillation process for the preparation of micro-nano-electronic hydrogen chloride.After simulation calculation,in the optimized light conponent rectification system,the number of stages is 28,the feed temperature is 17?,the reflux feed ratio is 2.3.The economic energy consumption Y value is minimized and the system conditions are optimal.In the heavy component rectification system,when the number of stages reaches 16,the content of heavy component impurities falls below the design specification.At this time,the feed stage is optimally the 12th stage,and the reflux ratio is 0.45.The impurity components are removed below the national standard value to meet the micro-nano electronic use requirements.According to the stability analysis of continuously produced hydrogen chloride products,the Cpk values of oxygen,methane,carbon monoxide,acetylene impurities are all greater than 1.67,the nitrogen,carbon dioxide,and moisture impurities have Cpk values between 1.33 and 1.67,and the overall process is at A level.The integrated process has been successfully applied in the Zibo Wandali electronic hydrogen chloride industrial production,which has provided hundreds of tons of products for domestic and foreign electronics companies. |
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