Investigation On Continuous Crystallization Process Of Chloroacetic Acid

Chloroacetic acid is an important organic chemical raw material and widely used in pesticide,carboxymethyl cellulose,medicine,dye and other fields.The intermittent crystallization process has been used since the production of chloroacetic acid and the crystallization temperature is controlled by experience.Some drawbacks such as difficult process control,difficult to automation and high energy consumption have been found,the crystal products with small crystal,wide particle size distribution and low purity and quality can not satisfy the market demand for the high-grade chloroacetic acid,so every year in our country still needs to pay higher price to import a certain amount of high-grade chloroacetic acid,and the imports show the tendency of increase year by year.Therefore,it is very important to improve the existing crystallization process to produce products with large and homogeneous particles and high quality.Nowadays,the study on the continuous crystallization process of chloroacetic acid has not been reported.So,in this paper the process was investigated.The crystallization thermodynamics of chloroacetic acid was studied.The crystallization interface stability zone width was obtained and the specific heat capacity of chloroacetic acid mother liquor and crystallization heat of chloroacetic acid were also got,and they were 2.04kJ/(kg? oC)and 174.67kJ/kg respectively.The effects of crystallization temperature,residence time and stirring speed on the product size distribution and quality of chloroacetic acid were studied by small test experiment.The result showed that the continuous crystallization process of chloroacetic acid was feasible and the optimal crystallization conditions which were crystallization temperature 28?,residence time 30 h and the stirring speed 40r/min were selected.The crystal obtained had large and uniform particles and high quality and chloroacetic acid was 98.39%,dichloroacetic acid was 0.70%.A pilot scale experimental equipment was designed and installed on the basis of the small test experiment,and by debugging and improving the equipments to make the experiments run smoothly.The process conditions were further researched and provided technical parameters for industrial design.The results showed that the crystallization temperature was 28?,residence time was 40 h and the stirring speed was 40r/min.The continuous crystallization process of chloroacetic acid with the annual output of 1000 tons was designed.Firstly,the type of crystallizer was selected and it was Oslo cooling crystallizer.And then the process was determined according to the properties of Oslo crystallizer and chloroacetic acid.Based on the above,the process calculation was carried out.The Oslo crystallizer was designed and the selection of major equipments was made based on the process design requirements and calculation results.The flow chart of the process and the equipments layout were given according to the requirement of design.Through the researching on the continuous crystallization process of chloroacetic acid,the thermodynamics and optimal crystallization conditions were got,and then the process was designed.All of the above studies lay the foundation for the industrialization.