High Ethanol Selectivity Research Articles

The Effect of Rhodium Particle Size on Ethanol Synthesis by Catalytic Hydrogenation of Carbon Dioxide over Silica Supported Rhodium Catalysts.

Ethanol synthesis by CO 2 hydrogenation was carried out over Rh/SiO 2 catalyst. Several catalysts were prepared using acetate hydrate, nitrate and chloride precursors of rhodium, and the effects of the precursor on reaction behavior were investigated. The remarkable effect of Rh precursor on the ethanol selectivity as well as activity of reaction was observed. The highest ethanol selectivity was obtained over the 5 wt% Rh/SiO 2 catalyst prepared from rhodium acetate hydrate precursor. It has been suggested that the difference in Rh precursor changed the mean particle size of Rh/SiO 2 catalysts, resulting in the change in the ethanol selectivity.

Bioenergetics and end‐product regulation of Clostridium thermosaccharolyticum in response to nutrient limitation

Fermentation of xylose by Clostridium thermosaccharolyticum was studied in batch and continuous culture in which the limiting nutrient was either xylose, phosphate, or ammonia. Transient results obtained in continuous cultures with batch grown inoculum and progressively higher feed substrate concentrations exhibited ethanol selectivities (moles ethanol/moles other products) in excess of 11. The hypothesis that this high ethanol selectivity was a general response to mineral nutrient limitation was tested but could not be supported. Growth and substrate consumption were related by the equation q(s)(1 - Y(x) (c))G(ATP) = (mu/Y(ATP) (max)) + m, with q(s) the specific rate of xylose consumption (moles xylose/hour . g cells), Y(x) (c) the carbon based cell yield (g cell carbon/g substrate carbon), G(ATP) the ATP gain (moles ATP produces/mol substrate catabolized), micro the specific growth rate (1/h), Y(ATP) (max) the ATP-based cell yield (g cells/mol ATP), and m the maintenance coefficient (moles ATP/hour . g cells). Y(ATP) (max) was found to be 11.6 g cells/mol ATP, and m 9.3 mol ATP/hour . g cells for growth on defined medium. Different responses to nutrient limitation were observed depending on the mode of cultivation. Batch and immobilized cell continuous cultures decreased G(ATP) by initiating production of the secondary metabolites, propanediol, and in some cases, D-lactate; in addition, batch cultures increased the fractional allocation of ATP to maintenance and/or wastage. Nitrogen-limited continuous free-cell cultures maintained a constant cell yield, whereas phosphate-limited continuous free-cell cultures did not. In the case of phosphate limitation, the decreased ATP demand associated with the lowered cell yield was accompanied by an increased rate of ATP consumption for maintenance and/or wastage. Neither nitrogen or phosphorus-limited continuous free-cell cultures exhibited an altered G(ATP) in response to mineral nutrient limitation, and neither produced secondary metabolites.

Direct microbial conversion

Process development is reviewed for ethanol production from cellulosic biomass via direct microbial conversion (DMC). Experimental data addressing cellulase production and ethanol tolerance are also presented for the candidate DMC organismsClostridium thermocellum andClostridium thermosaccharolyticum. Two potential paths are identified for obtaining organisms for use in DMC. Path 1 involves modification of excellent ethanol producers, so that they also become good cellulase producers; Path 2 involves modification of excellent cellulase producers, so that they also become good ethanol producers. Cellulase production, ethanol tolerance, and ethanol selectivity are considered for both Path 1 and Path 2 organisms. It is concluded thatin situ cellulase production has the potential to allow cost reductions relative to state-of-the-art process designs on the order of 50¢/gal. Based on the data available, the value of cellulase production bythermocellum corresponds to 90% of this amount. However, each process path has a strategic obstacle to be overcome: high-level cellulase expression and secretion for Path 1, and high ethanol selectivity for Path 2. Ethanol tolerance is not seen as a primary factor in choosing between DMC and other ethanol process alternatives.

Selective hydrogenolysis of methyl and ethyl acetate in the gas phase on copper and supported Group VIII metal catalysts

The selective hydrogenolysis of methyl and ethyl acetate to ethanol over different copper-based and supported Group VIII metal (Pd, Rh, Pt, Co, Ni) catalysts has been studied in the gas phase at 448–623 K and 0.1–6.0 MPa. Measurements of activity and selectivity show that the copper-based catalysts CuO/MgO-SiO 2, CuO/ZnO/MnO/Al 2O 3, and CuO/ZnO/Fe 2O 3 in particular exhibit very high selectivities for ethanol at nearly complete acetate conversions under moderate reaction conditions. In the case of copper-catalyzed methyl acetate hydrogenolysis kinetic measurements indicated a complex reaction network consisting of consecutive-competitive reactions due to transesterification of methyl acetate to give ethyl acetate, followed by its subsequent hydrogenolysis to ethanol. Therefore, the kinetics of selective hydrogenolysis of ethyl acetate have been studied separately. Kinetic parameters of a power rate law were determined by fitting to conversion versus space time data and made it also possible to describe satisfactorily the complex reaction network. In contrast, supported monometallic catalysts containing Pd, Rh or Ni were found to be ineffective in the hydrogenation of the acyl group due to multiple splitting of C-O and C-C bonds forming light hydrocarbons, acetic acid and carbon oxides. Addition of Zn to Pd/Al 2O 3 provides a major change towards higher ethanol selectivity. Furthermore, the catalytic properties of mono- and multimetallic Co/TiO 2 catalysts have been investigated. The use of an electropositive metal, such as Fe, for the preparation of a Co-Rh-Fe/TiO 2 catalyst promotes the formation of ethanol from ethyl acetate with substantially higher conversions.

In‐Situ recovery of ethanol from fermentation broth by hydrophobic adsorbents

AbstractThe in‐situ recovery of ethanol from fermentation by different hydrophobic adsorbents has been studied. Liquid phase experiments have demonstrated that pentasil zeolites have a high selectivity for ethanol in the low concentration range. It is shown that the contact of the fermentation broth with the zeolite NaZSM‐5 avoids the product inhibition. On the other hand, the ethanol production rate dramatically changes in dependence on the glucose‐to‐adsorbent ratio.

Ethanol production from starch in a pervaporation membrane bioreactor using Clostridium thermohydrosulfuricum

To attain both high productivity and efficient recovery of ethanol from broth, a membrane bioreactor consisting of a jar fermentor and a pervaporation system was applied to the direct production of ethanol from uncooked starch with a thermophilic anaerobic bacterium, Clostridium thermohydrosulfuricum. From four types of ethanol-selective membranes tested, microporous polytetrafluoroethylene (PTFE) membrane, the pores of which are impregnated with silicone rubber, was chosen for its large flux, high ethanol selectivity, and high stability. During fed-batch fermentation with pervaporation in the membrane bioreactor, ethanol was continuously extracted and concentrated in two traps with concentrations at 5.6%-6.2% (w/w) in trap 1 (20 degrees C) and 27%-32% (w/w) in trap 2 (liquid N(2)), while the ethanol concentration in the broth was maintained at 0.85-0.9% (w/w). Due to the low ethanol concentration in the broth, and the immobilization of bacterial cells by the membrane, the number of viable cells, and, eventually, the ethanol productivity, increased in the membrane bioreactor.

Homologation of methanol with a new cobalt phosphine carbonyl complex catalyst

A new cobalt phosphine carbonyl complex has been prepared by treating a mixture of Co 2 (CO) 8 and tri-n-butylphosphine with synthesis gas. The structure of the complex was shown to be Co(CO) 3 PBu 3 PBu 2 (O) on the basis of 1 H, 13 C and 31 P NMR, IR, and mass spectral data, molecular weight determination and elemental analysis. The complex was found to be a very effective catalyst for the homologation of methanol, exhibiting high activity and high ethanol selectivity.