The Spent Catalyst Ammonia Extraction By Zinc And Preparation Of Ultrafine Zinc Oxide To Expand The Pilot Study

Vinyl acetate is one of the organic chemicals with the highest output all over the world. Producing vinyl acetate is mainly by means of synthesizing acetylene, and activated carbon carrying Zn(Ac)₂ is used as the main catalyst in vinyl acetate industry. However, the catalyst easily loses its activity after being used a period of time, resulting in the abandonment of a great deal of materials. The exhausted catalyst contains about 25% Zn(Ac)2, so those discarded exhausted catalyst not only wastes the resource seriously, but also pollutes the environment severely if they can not be used.To solve this problem, in this paper, the investigation of an expanded experiment of preparing ultra-fine zinc oxide using zinc extracted from exhausted catalyst being used to synthesize vinyl acetate by the method of ammonia leaching was carried out. The ultra-fine zinc oxide products which are widely used in many fields were obtained, suggesting that the comprehensive utilization of exhausted catalyst is achieved. Moreover, the manufactural process accomplishes clean production and circulating economy mode.By using exhausted catalyst as material, the expanded experiment of the exhausted catalyst pre-treated under microwave radiation and leached by ammonia water was performed on the basis of the present conditions of the utilization of exhausted catalysts. The optimum conditions were obtained through experiments and a specially designed microwave equipment for the expanded experiment was researched and developed. This device uses automated control and achieves to go in and come out materials continuously. Proved by the experiment, this device is stable and consistently dependable, which provides guarantees for the forward expanded experiment.By using the orthogonal test method, the experiment to deal with 1kg exhausted catalyst pre-treated by microwave heating and leached zinc by the mixed liquor of ammonia hydrocarbonate and ammonia water was performed. The factors that affect the leaching ratio, such as the pre-treating temperature of microwave, the ratio of solid to liquor, leaching time and the dose of leaching liquor were investigated. The optimal process conditions of leaching zinc are as follows: the operating temperature of microwave radiation is 950℃; the ratio of solid to liquor is 1:2; the leaching process is performed at room temperature for 3 hours; the dose of leaching liquor is: adding 900ml ammonia water and 388g ammonia hydrocarbonate every kilogram exhausted catalyst. Under these conditions, the zinc leaching ratio is up to 96.68%. The result shows that the process of using ammonia water to leach exhausted catalyst is stable and feasible, and it can be used to proceed the further expanded experiment.On the basis of the experiment dealing with 1kg exhausted catalyst, the expanded experiment of 8kg materials was carried out by using the 60kw horizontal microwave oven as pre-treatment device. The optimal process conditions of medium experiment are as follows: the rotation speed is 50v/min; the output of material is 0.4 kg/min; the vapor pressure is 0.005 Pa. The optimum conditions of leaching experiment are as follows: the leaching liquor is the mixture of ammonia hydrocarbonate and ammonia water; the ratio of liquor to solid is 2:1; leaching at room temperature and atmospheric pressure; the dose of leaching liquor is that 1kg exhausted catalyst add 900ml ammonia water and 388g ammonia hydrocarbonate; the leaching time is 3h; washing three times.After heating the leaching ammonia through steam, the precursor of zinc oxide, that is zinc hydroxide carbonate, was obtained, and the well-distributed ultra-fine active zinc oxide was obtained through the processes of filtrating, washing, drying and calcining. The gas received in the processe of evaporating ammonia retraced to prepare leaching liquor after condensation. The influence of the time of evaporating ammonia and the flux of steam on the yield of precursor was investigated. The optimum conditions are as follows: the time of evaporating ammonia is 2h, the flux of steam is 40g/min. Under these conditions, the yield of the precursor is up to 99.99%. The structures of the precursor were characterized by scan electronic microscope (SEM) under the conditions of 110-130℃and drying for 2-3h. The result shows that the zinc hydroxide carbonate particle is uniformly sized, small, well-distributed and less-conglomerated.In calcining experiment, the factors of calcining temperature and the calcining time that affect the properties of products were also studied. The optimum conditions are as follows: the calcining temperature is 550℃, the calcining time is 3h. Under these conditions, the small, well-distributed and less-conglomerated zinc oxide powder can be obtained, and the purity of zinc oxide powder exceeds 99.5%.The process of ammonia leaching method is simple and easy to operate. The producing process achieves the closed circulation of material, and the received ammonia can retrace to the leaching system to recycle. Furthermore, the exhausted catalyst can be regenerated. Therefore, this pollution-free technology is of great practical significance and broad application prospects.