Online pervaporation was applied to control the oxidation reaction of primary alcohols, n-propanol and n-butanol, to the aldehyde formation. Polydimethylsiloxane (PDMS) was used as the pervaporation membrane. The swelling extent of the PDMS membrane with the different liquids involved in the oxidation reaction (reactants and products) was assessed. The permeate flux and the weight fraction of aldehyde were examined as a function of the following parameters: reaction temperature, reaction time, and crosslinking extent of the membrane. The optimal conditions were found as follows: temperatures of 60 and 70 degreesC for the oxidation of n-propanol and n-butanol, respectively, reaction time of 70 min, and 4% of crosslinking agent. The mass flux rate of the permeate was found to vary with temperature according to a linear Arrhenius-type relationship with activation energy of 2.40 and 2.66 kcal/mol for n-propanol and n-butanol, respectively. Under these conditions, the formation of ester, a product of a further oxidation of aldehyde, did not occur. (C) 2003 Elsevier B.V. All rights reserved.