Dimethyl ether (DME) can be produced much more ef ciently in a single-stage, liquidphase process from natural gas-based syngas as compared to the conventional process via dehydration of methanol. This process, based on dual catalysts slurried in inert oil, alleviates the chemical equilibrium limitation governing the methanol synthesis reaction and concurrently improves per-pass syngas conversion and reactor productivity. The potential, therefore, for production of methyl acetate via dimethyl ether carbonylation is of industrial importance. In the present study, conversion of dimethyl ether and carbon monoxide to methyl acetate is investigated over a variety of group VIII metal-substituted phosphotungstic acid salts. Experimental results of this catalytic reaction using rhodium, iridium, ruthenium, and palladium catalysts are evaluated and compared in terms of selectivity toward methyl acetate. The effects of active metal, support types, multiple metal loading, and feed conditions on carbonylation activity of DME are examined. Iridium metal substituted phosphotungstic acid supported on Davisil type 643 (pore size 150 A, surface area 279 m 2 /g, mesh size 230-425) silica gel shows the highest activity for DME carbonylation.

The conversion of dimethyl ether (DME) to hydrocarbons is the latter step in the conversion of syngas to hydrocarbons via DME. The shape-selective ZSM-5 zeolite catalyst plays an instrumental part in this reaction in limiting the higher end of the product spectrum. This process, being of an exothermic nature, results in atemperature rise across the catalyst bed causing some hydrocarbons to be deposited on the catalyst as coke. The presence of water as a byproduct in the catalyst environment also enhances the catalyst deactivation.Deactivation of the ZSM-5 catalyst is studied in detail in terms of catalyst performance and life over a period of time. The conversion of DME and the hydrocarbon product distribution are studied as a function of time-on-stream. The Si0 2 / Ah03 molar ratio of the ZSM-5 catalyst is regarded to be important in determining the degree of coke formation as well as the product distribution of the final hydrocarbon product. Catalysts used in aging experiments were studied as to determine the quantity and structure of the deposited coke. Extracted coke from the catalyst was analyzed using gas chromatography/mass spectrometry methods. The coked catalyst was also analyzed using infra-red as well as x-ray diffraction techniques.

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