天然气中微痕量氢同位素的在线连续分析

为实现天然气中丰度很低的氢同位素分析,自制氢气富集分离装置,利用在159和77 K温度条件下5A分子筛对不同气体组分的物理吸附性能差异,使天然气样品中微痕量氢与烃类组分分离,并进一步富集后,由载气送入色谱-同位素质谱计系统,分析其同位素组成。分析过程为在线连续流模式,与色谱同位素质谱工作站联动控制,从根本上解决了微痕量氢同位素分析的技术瓶颈。采用本方法分析了已知氢同位素组成的不同浓度人工混合样品,结果表明,本分析方法具有较高的精确度和良好线性,能够满足天然气中氢浓度低至1×10-5(V/V)样品准确分析的要求,标准偏差小于3.3‰。用此方法对不同含油气盆地6个天然气样品进行了分析检测,并对样品中氢同位素组成特征及成因进行了探讨。

On-line Continuous-Flow Microananlysis of Hydrogen in Natural Gases

A hydrogen preconcentration equipment was developed to separate and enrich the micro-hydrogen in natural gases with molecular sieve trap at 77 K and 159 K.The enriched hydrogen was carried into GC-isoto ratio mass spectrometric(IRMS) system by carrier gas to analyze the isotope composition.This on-line continuous-flow process can overcome the difficulty for the determination of micro-hydrogen in natural gases.A set of manual standard samples were analyzed by the method.The results show the method is applicable for the 1×10-5(V/V) hydrogen in the sample and has a good reproductivity and linearity,the relative standard deviation is less than 3.3‰.Using this method,the six gas samples from different oil-gas-bearing basins were analyzed.Further more,the isotope composition origin of hydrogen in natural gas was discussed.