Partial hydrogenation of sunflower oil was carried out in a membrane reactor in pore-flow-through mode in n-heptane as solvent. The membrane reactor consisted of a porous alpha-Al2O3 membrane impregnated with Pd or Pt as the active catalyst and was constructed as a loop of saturation vessel and membrane module. Hydrogenation experiments were performed at different temperatures, hydrogen pressures and noble metals as catalysts. The experiments in the membrane reactor were compared with experiments in a slurry reactor with a powder catalyst for benchmarking. The stearic acid content at an iodine value (IV) of about 80 was 10-15% in the membrane reactor and 45% in the slurry reactor, respectively. The selectivity for the monoene fatty acids could be improved with decreasing hydrogen pressures. The content of trans fatty acids at IV approximate to 80 was 30-45% in the membrane reactor, whereas in the slurry reactor 12% were obtained. For the trans-isomer formation, the influence of hydrogen pressure and temperature in the membrane reactor was rather low. Pd showed a higher activity and selectivity compared to Pt, but promoted the trans-isomerization to a greater extent. (C) 2007 Elsevier B.V. All rights reserved.