Influence of p-Xylene (PX) Accumulation on the Operation of Pure Terephthalic Acid (PTA) Solvent Dehydratic Distillation Column

In the production of pure terephthalic acid, a tiny amount of reactant p-xylene may enter into the acetic acid dehydration distillation column through the feed stream. In normal operation, p-xylene will not leave the column from the top or bottom product. It will be accumulated in the top of dehydration distillation column and decanter. With the accumulation of p-xylene, the operation cost will be increased gradually, to ensure the purity specifications of the top and bottom products. To reduce the operation cost. it is necessary to cut down the concentration of p-xylene by draining some organic reflux and make up the pure entrainer intermittent. In this paper, reboiler duties at different concentrations of p-xylene in the reflux were analyzed. The optimal operation condition-that the concentration of p-xylene is decreased by draining some organic reflux when the mass fraction of p-xylene accumulation exceeds 0.15-had been suggested. Finally, the residue curves diagram of three key components in the top of the column was used to interpret the draining place of p-xylene.