Figure 2 shows the hydrogenation rate of four ketones: 2-propanone (acetone), 2-butanone, 2-pentanone, and 3-pentanone (18). From typical VFA compositions in the fermentor, these four ketones comprise about 90% of the expected product. The hydrogenation was performed at 1 atm total pressure and near-ambient temperature. The reaction rates are expressed as moles of alcohol product per minute per gram of Raney nickel catalyst. The right-most data points of each figure indicate the hydrogenation rate of pure ketone. The data points to the left indicate the hydrogenation rate of ketone mixed with 2-propanol, the dominant product in the MixAlco Process.

Comparing the hydrogenation rates of the four ketones at 40°C (the only temperature that is common to all), they are all very similar and differ at most by a factor of two. At a catalyst concentration of 50 g Raney nickel/L, a temperature of 40°C, and a total pressure of 1 atm, the time required to hydrogenate 99% of

Table IV. Thermal Conversion of VFA Salts to Ketones Calcium Acetate* Calcium Propionate* Calcium Butyrate* Activation energy (kJ/mol) 642.6 ± 28.0 b2327 ±162 c691.7 ± 73.3 386.5 ±15.8 Frequency factor (min1) 109.4 ±0.4 b414.7 ± 0.4 c121.1+0.2 66.12 ±0.22 Time required for 90% conversion at 440°C (min) 0.817 0.0283 0.915 Yield (g actual liquid/g theoretical liquid) 93.1 ±0.9 87.5+0.7 94.4 ±0.9 Maximum temperature studied (°С) 455 475 508 2-Propanone (acetone) (%) 91.5 ±4.3 Isophorone (%) 2.78 ±2.6 2,4-Dimethyl phenol (%) 3-Pentanone (%) 0.30 ±0.63 96.9 ±0.9 2-Butanone (%) 1.06 ±0.37 5-Methyl-2-hexanone (%) 4-Heptanone (%) 0.49 ±0.13 94.9 ±3.46 2-Pentanone (%) 2.84 ±1.7 3-Heptanone (%) 0.44 ±0.07 3-Hexanone (%) 0.39 ±0.26 Other (%) 5.43 ±1.71 1.57 ±0.85 1.44 ±1.79 a Error band represent ± two standard deviations. b398°C and below ‘above 398°C

2-propanone is 4.4 h. The reaction rate increases linearly with hydrogen pressure (18), so the reaction time could be reduced to under one hour using a moderate pressure. Alternatively, the catalyst concentration could be increased.

The hydrogen would likely be derived from reformed natural gas, an abundant domestic energy source. In large-scale production, hydrogen costs about the same as gasoline per unit of energy (Appleby, J., Texas A&M University, personal communication, 1996), so there are no economic penalties associated with its use. The ketone may be viewed as a hydrogen carrier which avoids the need for high — pressure tanks to store gaseous hydrogen.