(505f) Application of Non-Dispersive Solvent Extraction in PTA Plant Wastewater Treatment

Purified Terephthalic Acid (PTA) producing process generates about 50 million m³ wastewater in China every year. PTA plant wastewater (COD 3000-5000 mg.L^-1) mainly contains intermediate p-Toluic Acid (PT), other small amount of aromatic acids and metal ions. Traditional biodegration and other physico-chemical treatment have been studied since ten yeas ago, however, PTA plant wastewater still cannot reuse at low cost nowadays.

The aim of this work is to develop a complete recycling process for simutenously reusing water and recycling PT and Benzoic Acid (BA) by implementation of Non-dispersive Solvent Extraction (NDSX).

In the first process step appropriate extractant was chosen: p-xylene is the strating material of PTA process and it is an ideal extractant for three reasons: A. The partition coefficient of PT between PX and water is more than 10 which indicates PX has high extraction efficiency. B. After extraction water can direct reuse in hydrogenation process. C. After extraction PX can direct go back to oxidation unit without further separation.

The NDSX process was experimentally studied and simulated. Microporous polypropylene hollow fiber membrane with outer-diameter of 490 μm, thichness of 50 μm, porosity of 0.45 and pore size 20 nm x 200 nm were used. The extraction experiments were conducted in single membrane extraction and a lab scale membrane contactor. PT and BA were separated from simulated wastewater and removal efficiencies were 90% and 40% at beat conditions, respectively.

The NDSX was simulated with a 2D rigrous model which taking into account the axial and radial variation in the fluid properties and an empirical model at the same time. The partition coefficients of PT and BA between PX and water were experimentally obtained. The simulation results fit well with the experiments.

Base on the experimental results the complete recycling route was validated.