Kohshiroh Yokota

Supercritical phase Fischer-Tropsch synthesis reaction

Abstract A Fischer-Tropsch synthesis reaction was conducted in a supercritical fluid medium using a fixed bed reactor. Although the rate of reaction and the diffusion of reactants and products were slightly lower than those in the gas phase reaction, the removal of reaction heat and waxy product from the catalyst surface were much more effective than those in the gas phase reaction. The supercritical phase reaction produced more higher carbon compounds (> C 25 ) than reactions in either liquid or gas phase.

Supercritical phase Fischer—Tropsch synthesis reaction: 3. Extraction capability of supercritical fluids

Abstract A Fischer-Tropsch (FT) synthesis reaction was conducted in supercritical fluid media using conventional FT catalysts such as cobalt, ruthenium and iron catalysts. Waxy products were effectively extracted in situ from the catalyst bed. Among several supercritical solvents, n-hexane gave the highest extraction capability and the highest reaction rate. It was found that only 2 wt% of the total hydrocarbon product remained on the catalyst in the supercritical phase reaction, while 10–25 wt% of the product remained in the gas phase reaction. The partial pressure of the solvents could be reduced to one-third of the critical pressure while maintaining effective extraction capability for wax in the case of n-hexane solvent. It was also found that the olefin content in the hydrocarbon was highest for supercritical phase reaction in three reaction phases (gas, liquid and supercritical). This was attributed to the well-balanced extraction of primary product olefins from the catalyst and their quick diffusion.

Supercritical phase fischer-tropsch synthesis

Abstract Fischer-Tropsch synthesis reaction was conducted in a supercritical fluid medium using a fixed bed reactor. Although the rate of the reaction and the diffusion of reactants were slightly lower than those in the gas phase reaction, the removal of reaction heat and waxy products from the catalyst surface were much more effective than those in the gas phase reaction. The olefin content of the product hydrocarbon was much higher in the supercritical phase reaction than in the liquid phase reaction or in the gas phase reaction. This was attributed to the shortest apparent residence time of the product in the catalyst bed for the supercritical phase, which was caused by the well-balanced desorption and diffusion of products.

Mechanistic study on the alcohol synthesis over molybdenum catalysts: Addition of probe molecules to COH2

The addition of probe molecules, such as ethylene, propylene, methanol, ethanol, and acetaldehyde, to COH2 feed was studied over the KCl-promoted and the unpromoted MoSiO2 catalyst under synthetic conditions, in order to clarify the reaction paths for the formation of hydrocarbons and alcohols. The results of olefin addition study suggest that the alcohol formation from COH2 proceeds by a mechanism including steps identical with those in the hydrocarbonylation of olefins and that KCl suppresses the simple hydrogenation of olefins. Both of the Mo catalysts demonstrate a poor catalytic activity for the homologation of methanol to ethanol. Alcohol homologation seems to be only a minor process in the formation of C+2 alcohols. No significant activity of Mo catalysts for incorporation of acetaldehyde into C3 oxygenated compounds may exclude the intermediacy of aldehydes for the chain growth of alcohols. Hydrogenation of acetaldehyde to ethanol is the fast and predominant reaction, in agreement with the fact that alcohols compose more than 90% of the organic oxygenates produced from COH2. Aldol condensation is apparently unimportant for the chain growth. The contribution of alcohol dehydration to hydrocarbon formation may be insignificant over the KCl-promoted catalyst with KMo = 0.4. Consequently, a mechanism including CO insertion into the alkyl-metal bond is proposed for the main reaction path for the higher alcohol formation from COH2. The role of K is supposed to slow the hydrogenation of surface alkyl species to form alkanes as well as to increase the active sites for alcohol formation by retarding the reduction of Mo.

Characterization of mass transfer in supercritical-phase Fischer-Tropsch synthesis reaction

Mass transfer, which includes the diffusion of either reactant or hydrocarbon products in the supercritical-phase Fischer-Tropsch synthesis reaction, was studied experimentally as well as by numerical simulations. On the diffusion of the reactant gas, the relationship between catalyst effectiveness factor and the catalyst particle size or reaction temperature was studied in supercritical phase, gas phase and liquid phase, respectively. The lowest apparent Arrhenius activation energy appearing in the liquid-phase reaction could be attributed to the lowest catalyst effectiveness factor shown in this reaction phase, which was caused by the slowest diffusion of reactant in the liquid-filled catalyst pores. The higher carbon-chain growth probability achieved on the catalyst calcined at high temperature is attributed partly to the quick diffusion of CO inside the catalyst pellets as well as to the quick transportation of the primary α-olefin products. Secondary reaction and diffusion behavior of the primary α-olefins were studied in the various reaction phases. The effect of catalyst pellet size or contact time is also discussed.

Oxidative dehydrogenation of lower paraffins with ZSM-5 zeolite catalysts

Abstract It was found that the oxidative dehydro-aromatization of lower paraffins was effectively catalysed by either a protonic or metal ion-exchanged ZSM-5 zeolite at temperatures from 450 to 550°C. Oxygen reacted selectively with surface hydrogen to promote its removal as water, to decrease its surface concentration, and, thus, to enhance the formation of aromatic hydrocarbons.

Supercritical Phase Fischer-Tropsch Synthesis Reaction

Summary Characteristic features of Fischer-Tropsch synthesis reaction which was operated in the supercritical n-hexane media were summarized in three points, (1) quick diffusion of reactants (2) effective removal of reaction heat and (3) effective wax extraction, α-olefins and water, which was the primary product and by-product of F-T synthesis, extracted from the catalyst bed most effectively in the supercritical phase reaction to suppress its secondary hydrogenation to paraffins. Extraction capability of the fluid was intensively studied and was found to be defined as the conbination of desorption from the catalyst surface and diffusion inside the catalyst pores.

Active Species and Mechanism for Mixed Alcohol Synthesis Over Silica-Supported Molybdenum Catalysts

Abstract The presence of metallic Mo and MoO 2 on SiO 2 was found to be a prerequisite to the development of activity and selectivity for alcohol synthesis from CO-H 2 . The gradual increase in alcohol production during the reaction is ascribed to the formation of CO-reduction induced defects on MoO 2 . Experiments performed by adding olefins to CO-H 2 revealed that CO insertion into a metal-alkyl like bond constitutes the reaction pathway to alcohols. The role of K and Cl in the promotion of alcohol production is discussed.

Effects of Sulfur-containing Compounds on Methanol to Conversion over ZSM-5 Cataiyst

Methanethiol was completely decomposed to form hydrocarbons and hydrogen sulfide (H2S)during the MTG (Methanol To Gasoline) reaction on H-ZSM-5 under pressurized conditions. Sulfur-containing compounds in the feed suppressed the gas formation and promoted the C4+ aliphatics while keeping the aromatics formation constant.Although the pulse treatment of the H-ZSM-5 with H2 showed no effect on the products distribution under atmospheric conditions, the low concentration of hydrogen sulfide (105ppm)in the feed promoted the olefin contents in lower hydrocarbons while keeping the selectivities of C-C3 hydrocarbons, C4+ aliphatics, and aromatics unchanged. Hydrogen sulfide was assumed to suppress the transfer hydrogenation of olefins by surface hydrogen which was produced during the aromatization of olefins.