(653b) Compositional Analysis and Advanced Distillation Curves for Mixed Alcohols Produced Via Syngas On a K-Comosx Catalyst

Hensley, J., National Renewable Energy Laboratory
Lovestead, T., National Institute of Standards and Technology
Christensen, E., National Renewable Energy Laboratory
Dutta, A., National Renewable Energy Laboratory
Bruno, T., National Institute of Standards and Technology
McCormick, R., National Renewable Energy Laboratory

The distillation behavior of mixed alcohols was studied by use of the Advanced Distillation Curve (ADC) methodology. Crude mixed alcohols (oxygenates) were generated from syngas over a potassium-promoted cobalt-molybdenum-sulfide catalyst and assayed for major and minor products. Distillation (boiling) curves were generated for the crude mixed oxygenate products and composition channel data were collected. The crude mixed alcohols consisted primarily of methanol with significant quantities of ethanol, 1-propanol, 1-butanol, methyl acetate, and ethyl acetate. These 6 species constitute 93.7 % – 95.8 % (mass/mass) of the total product.  Ester, ether, and aldehyde impurities were identified, as well as thiols and organic sulfides.  Considering just the alcohol products without impurities, these can be blended into gasoline at 8.5 % (vol/vol) and meet the requirements of the Octamix waiver if an appropriate corrosion inhibitor were also included (blend would contain 3.0 % – 3.4 % methanol, more than 2.5 % higher alcohols (vol/vol) and a total oxygen content of 3.7 % (mass/mass)). Distillation targeted at 50% methanol removal increased the volume of product that could be blended to over 9 % (vol/vol). Methanol, aldehydes, and dimethyl sulfide were the first to vaporize from the mixture, and all C4+ alcohols remained within the last 20 % of the distilled volume. Other products, including ethanol, propanols, esters, and organic sulfur species distilled over a range of boiling temperatures. ADCs suggest the presence of one or more azeotropes in the distillate, consistent with a large number of known binary azeotropes between components found in the mixed oxygenate product. Enthalpies of combustion were calculated for multiple distilled fractions and ranged from 890 kJ·mol-1 in the first drop of distillate to 1150 kJ·mol-1 in the first drop collected after distilling 80 % of the original liquid volume. This energy density is low compared to 91 octane gasoline at 3700 and 4940 kJ·mol-1 in the first drop and at 80 %, respectively. Comparisons of fractional distillation of the mixed oxygenate products showed directional agreement between experiment and simulation with Aspen Plus.  This study provides useful insights into mixed oxygenate products derived from a sulfided catalyst, including considerations for process recycle, product constituents and their blending, and the applicability of distillation information from process simulators.