(487w) Stability of Metal Polymer Composite Membranes for Partial Hydrogenation of Soybean Oil

Partial hydrogenation of vegetable oils is an important reaction in the food industry, used for the production of base stocks for margarines and shortenings. In the U.S. alone, the annual production of margarines and shortenings was around 8 billion pounds in 2007. Partial hydrogenation of vegetable oil is a three phase (gas-liquid-solid) reaction with hydrogen as a gas, oil as a liquid and the catalyst as a solid. Partial hydrogenation of vegetable in a traditional three phase slurry reactor leads to low concentration of hydrogen at the surface of the catalyst thus producing high amounts of trans fatty acids (TFAs). Dietary TFAs are associated with increased risk of ischemic heart disease, colon cancer, type-2 diabetes and allergic diseases in children. FDA regulations require listing of the TFA content on food labels. So the design of a commercial hydrogenation process/technology that produces minimum amounts of TFA becomes essential.

Here we investigate the use of metal polymer composite membranes to allow the gaseous and the liquid phase to come in direct contact with each other at the catalyst surface, without the need for the dispersion of one phase into other as is practiced traditionally. A membrane capable of selectively transporting hydrogen while acting to prevent any loss of liquid phase is incorporated in the reactor housing. Oil is pumped on one surface of the membrane where it comes into contact with the catalytic metal surface supported on the polymeric membrane support. The metal catalyst has a high hydrogen coverage that has diffused through the membrane due to an imposed chemical potential driving force. High concentrations of hydrogen on the catalyst surface, and the resulting decrease in temperature, promote the hydrogenation reaction at the expense of the cis to trans isomerization.

At an iodine value of 100 the (70C, 3.4 atm H2) metal polymer composite membranes produced less than 2 wt% TFA while the conventional system produced nearly 10 wt% TFA (Pt catalyst). Successive hydrogenation runs were performed to evaluate the stability of composite membranes as a function of number of batches of oil treated. A decrease in hydrogenation rate was observed with successive hydrogenation runs without any change in hydrogenation selectivity and cis-trans isomerization. The presentation will discuss the concept, the effect of repeated hydrogenation runs on the performance, and the possible causes of activity loss.