Promoted zinc chromite catalyst for higher alcohol synthesis in a slurry reactor

The motivation for this research was the desire to synthesize higher (C₂–C₄) alcohols in a slurry reactor from a mixture of carbon monoxide (CO) and hydrogen (H₂), so called “synthesis gas”.; Unpromoted “zinc chromite” catalyst and the same catalyst promoted with 6 wt% cesium (Cs) were evaluated in a continuous slurry reactor with decahydronaphthalene (DHN) and tetrahydroquinoline (THQ) as slurry liquids. The conditions were: Temperature—375°C and 400°C; Pressure—13.6 MPa (2000 psig); Gas Hourly Space Velocity (GHSV)—5000 standard liters/kg(cat)-hr; and H₂/CO feed ratio—0.5,1.0 and 2.0 mole/mole. The experiments lasted for 8–12 days of continuous operation. In, DHN, upon adding Cs, promoted catalyst obtained greater higher alcohol (HA) selectivity. However, this catalyst showed more sensitive to the change of operating conditions than the unpromoted one. Liquid medium affected catalyst activity and selectivity by the competitive adsorption and interaction(s) between liquid and adsorbed species on the catalyst surface. The selectivity of HA and DME, and CO conversion observed in THQ appeared to be lower compared with DHN. Methane selectivity was higher when using THQ as slurry liquid.; In contrast to DHN, THQ was extensively alkyalted to methyl THQs during the experiment. The alkylation rate was faster with unpromoted catalyst than with the Cs-promoted catalyst. A variety of analyses were carried out to identify the major components of the “spent” THQ. Silica gel liquid chromatography and HPLC (high performance liquid chromatography) were used to fractionate the “spent” THQ, while GC/MS (gas chromatography/mass spectroscopy), FTIR (Fourier transform infrared) spectroscopy and NMR (nuclear magnetic resonance) were applied to identify the major compounds. Methyl-, dimethyl-, and trimethyl-THQ comprised more than 80% of the “spent” liquid. The balance was various methylated indoles. A methyl group always was attached to the N atom in the ring structure. To explain the liquid medium effect on apparent catalyst activity and selectivity, mechanisms have been proposed.