Study On Solvent Washing Method For Purification Of Terephthalic Acid

Purified terephthalic acid is the main material of polyester production.The key technology is mastered by several foreign companies.The drying process has high investment and energy consumption in present technology. A new process is developed to substitute for drying method in this research project.Washing solvent water and p-xylene were experimental studied respectively to remove the acetic acid and catalyst residue of crude terephthalic acid.The ways of vacuum filtration after replacement and beating and centrifuging were studied in this work.Gas chromatography was used to analyze the content of acetic acid and p-xylene in the filter cake. Catalyst residue is detected by atomic absorption spectroscopy. With water as washing solvent the acetic acid was reduced from 10% to 0.1% in proper condition in the ways of vacuum filtration. A result of 0.0827% was obtained by centrifuging method. P-xylene is a better solvent to wash crude terephthalic acid. Acetic acid residue was reduced from 0.18% to about 0.1% by centrifuging and p-xylene residue could be 8% after beating method, a better result of 4.4% was obtained by centrifuging method. Washing with p-xylene by Industrial centrifugal machine was experimental studied and a good result was obtained. After secondary washing with water the acetic acid residue of crude terephthalic acid and p-xylene residue were respectively reduced to below 0.1% and 1.7%.The removal rate of catalysts reached a high level.One dimensional model for specific resistance of filter cake was set up in this work. The relationship between slurry concentration, pressure difference and specific resistance was fitted.