Date of Award
Doctor of Philosophy
Chemical and Biological Engineering
Richard C. Seagrave
The purpose of this work was to develop an optimum chemical process philosophy for the manufacture of [beta]-hydroxy-[beta]-methyl-butyrate (HMB), using existing synthesis and purification schemes as a starting point. Process analysis and improvement were performed as a means to increase overall efficiency and to address environmental concerns;A protein breakdown suppresser, HMB is used as a nutritional supplement or as a feed additive. The current process which employs reaction of diacetone alcohol and sodium hypochlorite, separation of the product by batch extraction, and crystallization, displays very low efficiency and has to deal with waste disposal issues. Currently, the high costs of this process negatively infringe on the price of the product on the human market and constitute the main obstacle in fully exploiting the animal market;The first two steps, reaction and extraction, were studied in detail, as they are of crucial importance for the outcome and profit of the entire operation. Reaction kinetics and equilibrium were investigated experimentally in an effort to identify operating conditions such as temperature, reactant ratio, species concentration, solvent and salt effects that will result in an increased molar yield. A kinetic model is proposed and a computer simulation was performed that led to estimating the rate constant in the formation of HMB, which is necessary for reactor design. The current extraction technology was evaluated and it was concluded that its poor performance, with low product recovery and high solvent usage, can be attributed to both the batch and cross-current mode of operation and to the limitations of ethyl acetate as an extractant for HMB. A series of screening experiments was performed to identify solvents capable of providing superior partition coefficients and selectivities. Several physical extractants, such as methyl-ethyl ketone, hexanol and reactive extractants, such as methyl-ethyl ketone solutions of tertiary fatty amines and chloroform solutions of tri-octyl phosphine oxide, were found to display excellent HMB separation capacities;The results of this work demonstrate that the bleach/diacetone alcohol synthesis of HMB can be significantly improved by a combination of changes in both chemistry and equipment. Reaction yield can be increased from 50% to 72% in a tubular reactor operated at sub-ambient temperatures, at a NaOCl/substrate initial ratio of 3.7 and in the presence of chloride ions. By using a continuous, counter-current column and a reactive extractant, extraction efficiency can be enhanced by 19% and solvent consumption can be reduced to a half. Overall, product yield can be increased by 70%, material costs are reduced by 24% for the reaction and by 60% for extraction. Operating costs can be substantially diminished.
Digital Repository @ Iowa State University, http://lib.dr.iastate.edu/
Barac, George, "Process analysis and yield enhancement for the production of beta-hydroxy-beta-methyl-butyrate (HMB) " (1998). Retrospective Theses and Dissertations. 11594.