Methyl isobutyl ketone (MIBK) is a valuable solvent and a possible precursor to branched alkanes that can be used as octane boosters. Acetone produced by the fermentation of glucose can be converted to MIBK in two steps. The first involves the condensation of acetone to form diacetone alcohol (DAA), a rapid and reversible reaction, which is then followed by the slower dehydration of DAA to form mesityl oxide (MO). These reactions are catalyzed by hydroxyapatite (HAP). Since the conversion of acetone to MO is not favored thermodynamically, MO must be hydrogenated to MIBK, the latter reaction being catalyzed by Pd/SiO2. The rate of DAA dehydrogenation to MO is sensitive to the basicity of O atoms present on the surface of hydroxyapatite. This property can be controlled by cation exchange of Ca2+ for other divalent cations. It is observed that as the electronegativity of the cation decreases the activity of HAP increases and reaches a maximum for Sr2+; however, progressing to Ba2+ results in a decrease in activity. DFT calculations of the free energy Lewis acid and Brønsted base sites and shows why an optimum in DAA dehydration activity is attained with decreasing electronegativity of the divalent cation present at the surface of HAP.

The mechanism and kinetics of acetone condensation to methyl isobutyl ketone

255th National Meeting (2018)

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