Kinetics of Aqueous-Phase Hydrogenation of Organic Acids and Their Mixtures over Carbon Supported Ruthenium Catalyst

Abstract

Aqueous-phase hydrogenation of lactic acid (2-hydroxypropanoic acid) and propionic (propanoic) acid over 5 wt % Ru/C catalyst was performed in a three-phase stirred batch reactor. Kinetic data were collected for reactions at 343−423 K, 3.4−10.3 MPa hydrogen pressure, and 0.05−5 M acid feed concentrations. Adsorption and reaction of individual acids, acid mixtures, and combinations of acids with their alcohol products were investigated to characterize relative hydrogenation rates of the two acids and the extent to which the presence of one species influences the reactivity of another. Mass transfer analysis showed that acid conversion rates were not limited by mass transport resistances over the reaction conditions studied. A two-site Langmuir−Hinshelwood (L−H) kinetic model with a single set of rate and adsorption constants fits the conversion kinetics of both individual and mixed acid hydrogenations. Competitive adsorption of acids and their alcohol products strongly affects hydrogenation rates.