The Modeling and Optimization of the Catalytic Hydrogenation of Butyric Acid to Butanol

Butanol production has become an increasingly important process because of its direct impact on fuel cost savings and furthermore the economy. Using algae as a feedstock for butanol production has proven to be an effective method and consists of two main steps: fermentation of algae to form butyric acid and conversion of butyric acid to butanol. A catalytic hydrotreater is currently being used for the second part of the process and is executed by adding hydrogen to the butyric acid to make butanol. In order to make butyric acid for this process, algal solution that was formed from the hydrolysis of algae is left to react in a fermentation broth and then filtered. Carbon dioxide and hydrogen are both removed from the fermentation broth in this process. This research focuses on the optimization of the hydrogenation process i.e. the optimal  operating conditions to achieve high butanol yield using plug flow reactor kinetics. The main reactions occurring during the hydrogenation are (i) conversion of butyric to butyric acid to butanol (desired reaction) and (ii) the conversion of butanol to butane (undesired reaction). This study investigates this problem by using reaction kinetics, mathematical modeling in Matlab® and Excel as well as process simulation in Aspen. The data fit the model best when the reaction was first order in butyric acid and zero order in hydrogen. Arrhenius activation energies, frequency factors were obtained and used to calculate equilibrium constants which were then compared to the experimental values. The data suggests that highest butanol yield occurs at and shorter residence times and that the reaction rate for the desired reaction increases with increasing temperature.