Studies On New Separation Technology Of Acephate

Acephate (O,S-dimethyl-N-acetylphoramidothioate) will probably be the main phosophororgantic pesticide as the substitute of O,S-dimethylphoramidothioate for its higher medical effect, lower toxicity and biological degradability. Acephate is on sale principally in the form of crystal in national and international markets. Acephate crystal is obtained after separation and purification technology from crude oil which is manufactured by the reaction of isomerization and acetylation successively from O,O-dimethylphoramidothioate. At the moment, the purity of crystal and the crystal yield during the process of separation and purification are both very low which resulted in the high production cost. Many manufacture apparatus of acephate in our country have been stopped production. As the synthesis technology of acephate is fairly mature, so how to improve and optimize the separation and purification technology is becoming a key problem hurry to be resolved.At present, the separation technology of acephate with the character of neutralizing crude oil by ammonia water is ordinarily adoppted by most of chemical works in our country. Because of the introduction of water phase in the neutralization by ammonia water the chemical loss of acephate is relatively high, simultaneously, a large amount of phosophororgantic waste water which is difficult to deal with is procduced. To avoid these deficiencies, a separation technology with extraction and recovery of acetic acid is developed in 1998. However, the acetic acid existing during the part of process has bad effect on some important equipments, on the other hand, it's difficult to recover the solvents as two solvents using in separation are easy to blend each other.According to the disadvantages of existing separation technology, an innovation method of neutralization of crude oil by ammonia gas is put forward, which not only keeps the advantage of no introduction of water phase and recovery of acetic acid but also has no problem of erosion. In line with the principle of high crystal yield and low separation cost we have explored a new separation technology of neutralization of crude oil by ammonia gas: firstly, crude oil and solvent are mingled, then the mixed solution is neutralized by ammonia gas directly, the crude crystal is obtained from the desolvented centrifugal filtrate by the process of crystallization, washing and drying. Acetic acid with high additional price can be recovered by the double decomposition reaction from filter cake. This technology is easy to be realized without producing phosophororgantic waste water. As a result, the purity of acephate crystal is more than 96.5% and crystal yield is "about 69% (according to O,S-dimethyl-N-acetylphoramidothioate). To further improve the yield and purity of crystal, twice crystallization and recrystallization process are added to the ameliorated technology in which the purity of crystal is more than 97% and the yield of crystal is about 80%.We have also researched on the liquid-solid equilibrium of acephate and the solvent of 1,2-dichlocoethane in this paper. The equation of λ. h is used to describe the equilibrium process. Through simulated calculation, the influence of temperature to the solubility of acephate and the variable law of the rate of dropping in temperature and crystallization are discussed, which is helpful to the design and optimization of crystallization process.