Purification Of Terephthaloyl Chloride By Melt Crystallization

High purity terephthaloyl chloride is an important material of para-aramid fiber.However,the domestic output and quality of terephthaloyl chloride can't meet demand.Therefore,the research and development of terephthaloyl chloride represents the general trend.This article aims at making a best process program to purify terephthaloyl chloride,in order to meet the production of para-aramid fiber.The paper used terephthalic acid as the starting material and 4 equiv of thionyl chloride as the acyl chloride reagent.The reaction was carried out under reflux temperature for 6h with 5%benzyltriethylammonium chloride as catalyst to yield a raw product of 96%purity.This paper outlines the concept,principle and research progress of melt crystallization.It also presents the properties,application,security,transportation,research and production status of terephthaloyl chloride.The analysis,characterization and purification of the terephthaloyl chloride are discussed as well.Raw terephthaloyl dichloride is filtered from the reaction mixture and rinsed with dimethyl sulfoxide to get a product with a purity not less than 96%.The impurities in the product are mainly p-phthalic acid(TPA),benzyltriethylamine chloride(BTEAC)and threphthalic acid monochloride(TPMC).TPA.BTEAC or TPMC has a melting point of above 200?,much higher than that of TPC,and hence can be removed through melt crystallization.The impurities of the lower melting point are discharged as sweat while thoses of the higher melting point are drained off by the sweat as tiny powder.The final crystal left in the melting pipe is therefore purer TPC.The sweat and uncrystallized mold can be circulated with crude product for further purification.The product terephthaloyl chloride could be characteried by infrared spectra,mass spectrometry,1H NMR and melting point.For detecting the purity of terephthaloyl chloride,it is firstly transformed to dimethyl terephthalate and then analysed by HPLC using SGE-C18AC column and methanol-water(4:1)as mobile phase.The result is an average of 6 parallel 20pL injections.A standard curve is prepared from 5 groups of different concentrations of dimethyl terephthalate.A regression equation y=240347761x+80743 is gotten by Microsoft Office Excel,where y is the UV absorption peak area at 242nm,x is the concentration of terephthaloyl chloride.The correlation coefficient of it is R2=0.99997.The best processing conditions for melt crystallization of terephthaloyl dichloride are as follows:heating rate of 0.1 ?/min to a final temperature of 77? for sweating,the cooling rate was 0.05?/min to a final temperature of 64?.A product of more than 99.9%purity is yield from a crude terephthaloyl dichloride of 96%purity under this optimized condition,which meets the requirements of para-aramid fiber production.The melt crystallization,which doesn't need solvents and can be carried out at ordinary pressure and low temperature with simple equipments,is a green process.