Process for separating catalysts from organic solutions, by means of semipermeable membranes

An ultrafiltration process for separating catalyst(s) from an organic solution in which the catalyst or catalysts are dissolved, the catalyst(s) consisting essentially of phosphotungstates or arsenotungstates as an anionic portion and ammonium or phosphonium salts as a counter-ion having surfactant characteristics, which process comprises the step of passing the catalyst-containing organic solution through an ultrafiltration membrane having an exclusion molecular weight sufficient to retain some of the catalyst(s) and to form, as a permeate, an organic solution containing a reduced concentration of the dissolved catalyst(s) and, as a retenate, an organic solution having an increased concentration of the dissolved catalyst(s).