Abstract.

The value which may be added to natural gas, by its direct conversion to olefins, has prompted the low-density plasma approach. A geometry was chosen in which conversion takes place in a large-surface-area electrode assembly, where methane ions combine with methane neutrals to produce C2+ gases. Bench-level experiments are reported on the direct, one-step conversion of methane to ethylene, propylene, and other light hydrocarbons, in a low-pressure plasma glowdischarge. Relative percentages of useful higher hydrocarbons in the output mixture range up to 42% for ethylene, to 68% for ethane, and to 48% for acetylene. The relative proportions depend upon the pressure, the current, and the voltage across the plasma discharge. Conditions have been established which favor the formation of one or two of these desirable compounds, at the expense of the other light hydrocarbon products. The production operations for which this technology is intended would include a separation of the methane component in the output mixture, and its recycling in a feedback loop, to extinction, if no other uses were planned. Results are presented relating the yields of the preferred gases to the pressure and the electrical conditions. compounds. They also showed that the

INTRODUCTION

statistical nature of plasma interations at surfaces leads invariably to a mixture of Production of ethylene and propylene products in the output stream, with some from the methane component of natural gas by control over the relative proportions which can thermally-driven methods has been very be attributed to choices of operating pressure difficult, as methane is the most stable and ion energy. hydrocarbon. It has been used primarily for heating fuel, for production of electric power, SURFACE INTERACTIONS OF IONS and for methanol or fertilizer production. It AND NEUTRALS has been priced accordingly, whenever it is connected to a gas pipeline network, and has a In a plasma discharge, the presence of an very low wellhead price when the gas is in a electric field accelerates available electrons to location remote from a pipeline network. an average energy which is sufficient to cause The possibility of direct conversion to ionization of any neutral molecules with which high-value manufactured gases, such as light they collide, causing the production of olefins, could add significant value to natural additional electrons along with the positive gas which would otherwise remain ions. A methane gas is ionized in this way to undeveloped. This has prompted experiments form methyl ions, of several types, the most using low-density plasmas, in which the ion common being CH3, and also

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