(492b) Aqueous-Phase Catalytic Hydrogenation of Organic Acids and Their Mixtures

Biomass-based organic acids are attractive feedstocks for chemicals production because they are available in quantity and can undergo a variety of reactions to form useful products. Hydrogenation of organic acids over metal catalysts in water produces alcohol products that are important building blocks for pharmaceuticals, foods, agriculture, and polymers. The development of low-cost, high-efficiency hydrogenation routes will open economically viable pathways from renewable resource-derived materials to today's petroleum-based chemicals. To develop an improved mechanistic understanding of the conversion of organic acids to alcohols, we seek to investigate substrate-metal interactions in aqueous solution, and then to relate those adsorption properties to efficacy for hydrogenation. The aqueous-phase hydrogenation of lactic acid, propionic acid, and 3- hydroxypropionic acid over 5 wt % Ru/carbon catalyst was performed in a three-phase stirred batch reactor. Kinetic data was collected for reactions at 363-423K, 1000psi hydrogen pressure and 0.1-5M acid feed concentration. The adsorption and reduction of individual acids, multiple acids, and combinations of acids with their alcohol products on fully reduced metals were investigated to understand the relative binding strengths of the substrates on the metal surface, and how the presence of one species at the surface influences the reactivity of another. A thorough mass-transfer analysis showed that the acids conversion rate was not limited by mass-transport resistances over the ranges of temperature and acids feed concentration investigated. A Langmuir-Hinshelwood (L-H) kinetic model was proposed to fit the acids conversion kinetics and detailed information on the competitive adsorption coefficients for the reaction species was determined. The research presented here provides insight into the catalytic reaction mechanism and forms the basis for further investigation of the aqueous-phase hydrogenation.