Oligomerization of methane to higher hydrocarbons using microwave heating and microwave plasmas

Date of Completion

January 2004

Keywords

Engineering, Chemical

Degree

Ph.D.

Abstract

Catalytic microwave heating and microwave plasmas processes have been used as for the oligomerization of methane to higher hydrocarbons. ^ Microwave-Induced Oligomerization (MIO) of methane to higher hydrocarbons has been the focus of very few fundamental studies. Our primary goal was to understand what factors control such MIO processes, and their effect on catalysts activities and product distribution. Optimization of reactor types, modes of operation (contact times, pulse vs. continuous), catalyst pretreatment, and addition of dielectrics have been used to optimize conversion and selectivity. Product analyses by gas chromatography mass spectrometry methods, and catalysts characterization by TPR, TPD, BET, XPS and XRD studies before and after reaction. The microwave heating oligomerization experiments have shown that nickel, iron powder, and activated carbon can act as selective catalysts for oligomerized products of methane. Oligomers ranging from C2 to C6 hydrocarbons (benzene) have been prepared in good selectivity depending on the nature of diluent, type of catalyst, catalyst pretreatment and the power levels used in the microwave reactor. The use of He as diluent gas favors the oligomerization of methane via microwave heating. Data suggest that the dielectric constant is not the most important factor in the oligomerzation of methane via microwave heating. Conversion and activities of materials we used were not proportionally related to the surface area of the catalysts. Changes in catalysts structure, composition, morphology, particle size, surface area, before and after reaction, were correlated with catalysts activity and procust distribution. Microwave plasmas were used to activate C-H bonds in methane molecules. The major products observed in these earlier reactions are C2H2, C2H4, and C2H 6. We examined the effect of pressure (1–50 Torr), flow rate, and applied power (0–120 W), presence of dielectric materials, type of cavity (Beenakker or Evenson), cavities in series or in parallel, expansion and compression effects, as well as the presence of a radical initiator (I 2, in this case) on the product distribution of methane oligomerization via microwave plasmas. The Beenakker cavity is more efficient than the Evenson cavity. The Beenakker cavity with or without He favors the formation of C 4S when using C2H4 and C2H2 as a feed. The Evenson cavity favors the formation of C4S and C 6S when using ethylene as a feed and the formation of C7S and C8S when using acetylene. (Abstract shortened by UMI.) ^

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