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混合溶剂萃取洗脱5分子筛吸附正构烷烃的方法在单体碳同位素分析研究中已得到了应用。由于5分子筛在长时间加热条件下可能对有机分子的氢交换反应具有一定的催化作用,因此对于该方法能否用于正构烷烃的单体氢同位素分析需要做进一步研究。本文以两种不同类型原油的饱和烃和正构烷烃混合标准样品为对象,采用环己烷-正戊烷溶剂和氢氟酸溶解-正戊烷溶剂洗脱5分子筛吸附的正构烷烃,对比分析两种萃取方式的分离效果,并分别测定了正构烷烃的单体氢同位素比值。结果表明:两种萃取方式都得到了纯化效果良好的正构烷烃组分,氢同位素测定结果的差值总体上小于4‰,在仪器分析误差范围内。经过三次环己烷-正戊烷洗脱方式获得正构烷烃回收率平均值为58%,氢氟酸溶解-正戊烷洗脱方式经过多次萃取操作获得正构烷烃回收率平均值为68%。尽管环己烷-正戊烷洗脱方式提取正构烷烃的效率较低,并且涉及在分子筛条件下多次较长时间的加热过程,但这两个因素没有导致氢同位素发生明显的分馏或交换过程,适合用于正构烷烃分离、纯化以及单体氢同位素测定。
Mixed solvent extraction eluting 5 molecular sieve n-alkane adsorption method has been applied in the study of carbon isotope analysis. Since 5 molecular sieve may have a catalytic effect on the hydrogen exchange reaction of organic molecules under long-term heating conditions, further research on whether this method can be applied to the monomeric hydrogen isotope analysis of n-alkanes is needed. In this paper, two different types of crude oil saturated hydrocarbons and n-alkanes mixed standard samples as the object, the use of cyclohexane - n-pentane solvent and hydrofluoric acid dissolved - n-pentane solvent elution 5 molecular sieve adsorption n-alkanes contrast The separation efficiencies of the two extraction methods were analyzed and the hydrogen isotope ratios of n-alkanes were determined. The results show that the two methods have good purification results of normal paraffin components, hydrogen isotope determination of the difference is generally less than 4 ‰, within the instrumental analysis error. After three times of cyclohexane - n-pentane elution obtained n-alkanes recovery average of 58%, hydrofluoric acid dissolved - n-pentane elution obtained after multiple extraction n-alkanes recovery average 68 %. Although the cyclohexane-n-pentane elution is less efficient at extracting normal paraffins and involves several longer heating cycles under molecular sieve conditions, these two factors do not result in significant fractionation or exchange of hydrogen isotopes Process, suitable for n-alkanes separation, purification, and hydrogen isotope determination.