Carbon isotope analysis method for series of hydrocarbon compounds in natural gas

Abstract

The invention belongs to the technical field of analysis methods for natural gas and especially relates to a carbon isotope analysis method for a series of hydrocarbon compounds in natural gas. The method comprises the following steps: step A, carrying out solid-phase micro-extraction enrichment on a series of hydrocarbon compounds in natural gas; step B, separating the hydrocarbon compounds and carrying out qualitative analysis on unknown hydrocarbon compounds; and step C, carrying out carbon isotope determination on the hydrocarbon compounds. According to the invention, solid-phase micro-extraction technology is introduced into a natural gas isotope analysis method and combined with a GC-IRMS analysis system, influence of factors like equilibrium time and equilibrium temperature on difference of adsorption capability of the hydrocarbon compounds and on carbon isotope values are analyzed, and operation conditions are optimized, so effective enrichment and carbon isotope composition analysis of the series of hydrocarbon compounds in natural gas are realized. The method provided by the invention can realize rapid and effective enrichment and carbon isotope composition analysis of the series of hydrocarbon compounds in natural gas.

Description

technical field [0001] The invention relates to the technical field of analysis methods for natural gas, in particular to a method for analyzing carbon isotopes of a series of hydrocarbon compounds in natural gas. Background technique [0002] The stable isotopic composition of specific compounds has gradually developed into an important tracer tool and plays an important role in many disciplines such as earth science, environmental science, and ecology. This technology has been realized since the 1980s with the successful docking of Gas Chromatography (GC) and Isotope Ratio Mass Spectrometry (IRMS). 13 C / 12 C. 2 H / 1 H. 15 N / 14 N. 18 O / 16 Isotopic composition analysis of elements such as O. Due to the special status of carbon isotopes in nature, its isotopic composition has been widely used in oil and gas geochemistry, environmental geochemistry, biogeochemistry and other fields. For example: in the field of oil and gas geochemistry, the CH in natural gas can be...

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Problems solved by technology

[0004] As early as the early 1990s, an on-line analysis method for carbon isotopes of conventionally contained hydrocarbons in natural gas had been established. However, due to the relatively low sensitivity of the GC-IRMS system, for carbon, it takes an average of 5 nmol for a single compound to reach the normal range of the instrument. However, the concentration of trace hydrocarbons in natural gas generally decreases significantly with the increase of carbon number, and its content generally ranges from mg / L to μg / L. Therefore, sample pretreatment is difficult, and corresponding analysis methods have not been established. Therefore, relevant geochemical research has not made substantial progress, and there are only reports on the application of carbon isotopes in individual related compounds.

However, using traditional gas enrichment methods, such as: purge and trap method, its operation process is complicated, and it is easy to cause isotope fractionation

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