2013 1(12)

MASS-SPECTROMETRY OF IONIZED ARGON, METHANE AND ARGON-METHANE SUPERSONIC JETS.

Zarvin A.E., Khodakov M.D., Korobeyshchikov N.G., Kalyada V.V.

Novosibirsk State University, Novosibirsk, Russia

Introduction

Interest in studying the processes of methane chemical transformations, its conversion into heavy and, first of all, liquid hydrocarbons or oxygenates right at gas mining sites is conditioned by technological needs and remains strong for years. Unfortunately, synthesis of heavy hydrocarbons from natural oil gas using plasma-chemical methods, when the source material is affected by the self-maintained or the non-self-maintained discharge has not yet been conducted. Considerable success has only been achieved in the sphere of destruction processes, e.g. when producing hydrogen from methane.

Purpose

Obtain high-intensity methane cluster flows.

Method

Experiments were conducted using the gas-dynamic complex LEMPUS.

Results

Experiments were conducted using the gas-dynamic complex LEMPUS. In order to test the equipment and methodically check the truthfulness of the obtained results a series of Ar_n⁺ peaks (where n=1-7) in order of decreasing intensity was detected.

As the estimates show, methane is condensed slightly better than argon, so it would be natural to expect analogous mass spectre like argon. However, the detected mass spectre showed the presence of Ñ₁⁺ and Ñ₂⁺. The absence of methane oligomers in the mass spectre can be caused by destruction of clusters to monomers.

Experimental data on argon-methane mixtures obtained for three mixtures with three different concentrations (2.5%, 5%, 10%) of methane in argon within a broad stagnation pressure range is of our principal interest here. Since small amounts of methane are contained in argon, methane gas dynamics will be analogous to those of a monoatomic gas. Mass peaks which correspond to masses of methane and are steadily detected along the whole examined range. One more characteristic of the mixture mass spectres is the presence of protonated ions from one of methane molecules that build up the cluster. After normalizing methane mass peak amplitudes according to the analogous sum for argon it was confirmed that when switching to the developed condensation mode, starting approximately with P_o = 90 kPa, within a relatively narrow range of stagnation pressures methane concentration on the molecular beam axis rises drastically compared to the initial value; besides, an almost eight-fold increase occurs for all three mixtures, after which this new ratio of partial concentrations for mixture components remains constant.

It has been ascertained that large-size clusters in a supersonic jet of methane are not detected by mass spectrometry of oligomeric pieces, which can be conditioned by their fragmentation into monomers. At the same time, in the mass spectre of argon mixtures containing small amounts of methane, both methane oligomers and mixed argon-methane clusters are apparently detected. It has been demonstrated that it is reasonable to use specially selected gas mixtures for obtaining high-intensity methane cluster flows.

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