Natural gas conversion to higher hydrocarbons using plasma interactions with surfaces. Final report

摘要

Experiments are reported in which a methane plasma is created, and the methyl ions and hydrogen ions are accelerated within a microchannel array so that they interact with neutral methane molecules on the inside surfaces of the microchannels. No catalysts are used, and the device operates at room temperature. Impact energies of the ions are in the range of 10 eV to greater than 100 eV, and the energy delivered in the interaction at the surfaces causes the production of larger hydrocarbon molecules, such as C(sub 2)H(sub 2), C(sub 2)H(sub 4), and C(sub 2)H(sub 6), along with C(sub 3), C(sub 4), C(sub 5)m C(sub 6), C(sub 7)m and C(sub 8) molecules. There is a decreasing percentage of larger molecules produced, in comparison with the C(sub 2) and C(sub 3) types. Conversion effectiveness is greater at higher pressure, due to the increased ionic activity. The yield of the higher hydrocarbons depends upon the external voltage used, and voltage can be used as a control parameter to adjust the output mixture proportions. A conversion energy of 2.59 kilowatt hours/killogram of output has been demonstrated, and a reduction of this by a factor of 10 is possible using known techniques. In batch experiments, the selectivity for C(sub 2) has varied from 47% to 88%, and selectivity for C(sub 6) has ranged from 0% to 12.8%. Other hydrocarbon selectivities also span a wide and useful range. The estimated costs for hydrocarbons produced with this technology are in the range of $200 per tonne, in production quantities, depending upon natural gas costs. Pilot production experiments are recommended to make these estimates more precise, and to address strategies for scaling the technology up to production levels. Applications are discussed.