Experimental Research On Aging And Reactive Precipitation Of CTA

Terephthalic acid is an important raw material for the manufacture of polyester fiber and plastics. In industrial process PX is oxidized into crude terephthalic acid (CTA),using air as oxidant ,acetic acid as solvent, cobalt/manganese/bromide as catalyst, then CTA is purified by aging. In this paper, research of CTA aging and PX reaction precipitation is discussed. First, factors that may affect aging such as temperature, agitation, water content are investigated experimentally. The experiments show that during aging the average size of CTA increases remarkably, and temperature is the only factor that affects crystal growing. The concentration of 4-CBA in TA decreases faster by increasing temperature, the rate of TA purification also accelerates by decreasing water content unless the water content is lower than its critical value. Secondly, preliminary research of PX reaction precipitation is carried out, in which the effect of PX feed rate, temperature, water content and oxygen concentration in off gas are taken into consideration. It is shown that during the reaction the average size of TA and the concentration of intermediates in liquid phase and impurities in solid phase are getting larger and larger. The growing rate of TA crystals increases along with PX feed rate and water content. The concentration of intermediates in liquid phase and impurities in solid phase accumulate faster when PX feed rate increases, temperature decreases, water content increases or oxygen concentration in off gas decreases. Increase of temperature or decrease of PX feed rate could aggravate the HAc burning reaction while water content has little effect on that. A new intermediate in liquid phase( α -Bromo-p-toluic acid) is discovered, the concentration of which decreases slowly during the reaction.