Study On The Technique In Production Of Chloromethane By NH₄Cl And CH₃OH

Ammonium chloride is the main by-product in the production of soda and aminoacid. The output of ammonium chloride was more than 13 million tons in China in 2009, how to efficiently utilize so many ammonium chloride has become the bottleneck of the soda development. A new process to react ammonium chloride with methanol was proposed in this thesis to produce chloromethane and ammonia. Chloromethane is a high-value product and ammonia can be recycled to the process of soda production. Based on the review on the decomposition of ammonium chloride and the synthesis of methyl chloride, fluidized bed reactor was selected as commercial reactor type. Some catalysts for this process were prepared and the best one was selected.The reaction of ammonium chloride and methanol is consist of two-step: thermal decomposition of ammonium chloride and the further reaction between hydrogen chloride react with methanol. Based on the thermodynamics analysis, this reaction is a endothermicreaction, and reaction temperature should be controlled in 350～500℃. When the temperature is too low, ammonium chloride can not be decomposed, and the coking deactivation of catalyst would be accelerated when temperature is too high.The experimental results show that porous sphericalγ-Al2O3 is a good catalyst carrier bacause it has larger BET and there are enough active sites with weak acid. Then 4% ethyl orthosilicate was selected as the surface modification to improve the behavior of the catalyst. The experimental results with this catalyst showed that the strong acid sites were covered by ludox, and formed more B acid sites, resulting in the increase of the yield of methyl chloride to 68.59 %, which is 20 % higher than that before surface modification.8% ZnCl2 and 4%Cu(NO3)2 were furether impregnated to the above carrier in order to increase the catalyst activation. The experimental results showed that the impregnating agents can inhibit the formation of L strong acid sites, and increase the metal active sites on the catalyst surface, and the yield of methyl chloride can reach 74.22 % and 75.6 %. Respectively.The experimens were made on selecting best operation conditions. The results showed that the best conditions are: the reaction temperature, 350～370℃; molar ratio, 0.8～1.2; space velocity, 360380 min-1.The experiments on the recirculation of by-products amines to the reaction as the raw material were also done in this paper. The results indicated that the yield of methyl chloride increased obviously, it increase 11 %. Finally, the coke deposition on the catalyst Ni/b-Al is studied in this paper. TG-DTA analysis was used to studing the sites of coke deposition. The results showed that coke was formed both in the active sites and catalyst carrier, and the rate of coke formation can be reduced by improving the calcination temperature.