Higher alcohol synthesis (HAS) from syngas over a CuCo based catalyst was investigated under supercritical hexanes conditions. The effects of hexanes/syngas molar ratio, H2/CO molar ratio, and gas hourly space velocity (GHSV) on gas‐phase HAS and supercritical hexanes‐phase HAS (SC‐HAS) were investigated. The CO conversion remained relatively constant with increases in the hexanes/syngas molar ratio, whereas the CH4 selectivity decreased. Higher alcohol productivity was found to increase monotonically with an increase in the hexanes/syngas molar ratio. Productivity of higher alcohols increased with an increase in the H2/CO ratio under the gas‐phase conditions. An opposite trend in higher alcohol productivity with H2/CO was observed in SC‐HAS. Further experiments were performed using argon as the reaction medium for comparison with the supercritical hexanes medium results. The enhanced higher alcohol productivity observed in this system can be attributed to improved extraction of alcohol products from the catalyst pores under the supercritical conditions. © 2014 American Institute of Chemical Engineers AIChE J, 60: 1786–1796, 2014

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Supercritical Fischer-Tropsch Synthesis (SC-FTS) using a potassium-promoted iron-based catalyst has been shown to produce large amounts of heavy (C10+) aldehydes and methyl ketones, while traditional gas phase FTS does not produce these compounds in significant amounts under either fixed or slurry bed operation. In order to better understand this behavior, a series of studies was undertaken to determine the effect of process conditions (H2/CO ratio, temperature, pressure, and supercritical hexanes media ratio) on the performance of iron-based SC-FTS generally, and on aldehyde formation specifically. Over the range of process conditions studied, heavy aldehyde selectivity was found to decrease with increasing temperature, while both elevated pressure and increased media ratio favored aldehyde production. Changes in the H2/CO ratio had little influence on syncrude functionality. The role of potassium promotion was also investigated by operating a potassium-free iron-based catalyst under SC-FTS conditions. In the absence of potassium promotion, no heavy aldehydes were detected.

Supercritical fluid (SCF) reaction media have been previously shown to facilitate heat removal and heavy product extraction from catalyst active sites in a variety of heterogeneous catalytic reactions, such as Fischer−Tropsch synthesis (FTS). This work explores the feasibility of using SCF media to enhance methanol-to-hydrocarbons (MTH) reaction performance relative to traditional, gas-phase operation. Conversion of methanol over H-ZSM-5 was carried out in a continuous fixed-bed reactor in the presence of supercritical isooctane. Isooctane was selected as the SCF medium primarily because of its low reactivity over H-ZSM-5. The performance of SCF-assisted MTH was compared with that of gas-phase MTH at both 300 and 370°C. Relative to gas phase operation at the same conditions, the use of supercritical isooctane resulted in improved catalyst maintenance and increased hydrocarbon productivity with increasing time on stream.