Optimum cleaning-in-place conditions for stainless steel microfiltration membrane fouled by terephthalic acid solids

Terephthalic acid (TPA) is a raw material of polyester fiber and polyethylene terephthalate. When TPA is produced by catalytic air oxidation of p-xylene in the presence of acetic acid solvent, most of produced TPA exists in the form of crystalline suspended solids. A microfiltration process may be used to recover TPA, but the microfilters are subjected to fouling and therefore cleaning-in-place (CIP) regimes need to be developed. In this research, the effects of variations to CIP conditions were investigated on the flux recovery accomplished in a TiO2-sintered stainless steel microfiltration membrane (0.1 μm pore size) fouled with TPA. The extent of flux recovery was estimated as the ratio of the stabilized flux obtained during CIP to the water flux value achieved under corresponding operational conditions. Based upon batch solubility tests, sodium hydroxide (NaOH) was chosen as the major cleaning agent for the present experiment. The extent of flux recovery increased with increasing NaOH concentration over the range of 3–4% (w/v) NaOH, but decreased at NaOH concentrations above 4%. The flux recovery was favored at high cross-flow velocities, high temperatures and low transmembrane pressures. A high temperature run of cleaning did not produce any adverse effects up to 70 °C. The addition of surfactants (SDS and Tween 80) to the caustic cleaning agent led to a significant reduction in cleaning efficiency.