水热条件下费托型合成反应氢同位素分馏研究  

Hydrogen isotopic fractionations during Fischer-Tropsch type synthesis under hydrothermal conditions

作　　者：赵忠峰 卢鸿[1,2] 李亢 彭平安[1,2] ZHAO Zhongfeng;LU Hong;LI Kang;PENG Ping’an(State Key Laboratory of Organic geochemistry,Guangzhou Institute of Geochemistry,Chinese Academy of Sciences,Guangzhou 510640,Guangdong,China;CAS Center for Excellence in Deep Earth Science,Chinese Academy of Sciences,Guangzhou 510640,Guangdong,China;University of Chinese Academy of Sciences,Beijing 100049,China)

机构地区：[1]中国科学院广州地球化学研究所,有机地球化学国家重点实验室,广东广州510640 [2]中国科学院深地科学卓越创新中心,广东广州510640 [3]中国科学院大学,北京100049

出　　处：《地球化学》2023年第3期271-280,共10页Geochimica

基　　金：国家重点研发计划“深地资源勘查开采”重点专项(2017YFC0603102);中国科学院战略性先导科技专项A类(XDA14010102);国家重点研发项目(2019YFC0605502);国家自然科学基金项目(41973069、41673045)联合资助

摘　　要：费托型合成(F-TT)反应是地下烃类的三大成因之一,H同位素组成研究对其生烃过程和成因识别具有重要意义。本研究分别以无机CO和CO_(2)为碳源,水为氢源,研究在370℃和50 MPa的水热条件下,F-TT反应生烃过程中H同位素分馏情况。结果显示,不管是CO参与的经典F-T反应,还是CO_(2)参与的F-TT反应,烃类产物H同位素均呈正序分布(δD(C_(1))<δD(C_(2))<δD(C_(3))<δD(C_(4))<δD(C_(5))<δD(C_(6))),符合前人有关地下非生物成因烃的H同位素正序分布特征。本研究分别根据CO和CO_(2)为碳源的亚烷基机理和羰基插入机理,从反应原理、链增长机制和分馏过程,对2种生烃过程中的H同位素呈正序分布这一规律进行了详细机理阐述。由于热成因气H同位素也呈正序分布,所以烃类气体的H同位素分布特征不能够作为无机烃类来源的判识标志。但是,通过数据对比发现,按照甲烷的H同位素值可以把热成因气(δD(C_(1))>−270‰)和前寒武纪地盾无机成因气(δD(C_(1))<−320‰)简单地区分开来。Fischer-Tropsch type(F-TT)reaction is one of the three major causes of hydrocarbon generation on earth.The study on stable hydrogen isotopic compositions of abiogenic hydrocarbons is highly significant in investigating the hydrocarbon generation process and identifying its origin.In this study,CO and CO_(2) were used as the inorganic carbon sources,and water served as the hydrogen source.The experiments were applied to study the hydrogen isotopic fractionations under hydrothermal conditions of 370℃and 50 MPa.The results revealed that hydrogen isotopes of hydrocarbon gases with a positive trend(δD(C_(1))<δD(C_(2))<δD(C_(3))<δD(C_(4))<δD(C_(5))<δD(C_(6)))occurred in the classic F-T reaction(CO as carbon source)and the F-TT reaction(CO_(2) as carbon source),which were consistent with the reported positive distributions of hydrogen isotopes of abiogenic hydrocarbons underground.Based on the alkylene mechanism and carbonyl insertion mechanism with CO and CO_(2) as carbon sources,respectively,the positive trend of hydrogen isotopes in the two series was described in detail in terms of reaction principles,chain growth mechanisms,and hydrogen isotope fractionation process.Considering that the hydrogen isotope distribution of thermogenic gases is also in positive order,it can not be used as an identification marker for the source of inorganic hydrocarbons.However,according to theδD(C_(1))values,the thermogenic gases(δD(C_(1))>−270‰)and the abiogenic gases(δD(C_(1))<−320‰)in the Precambrian shield can simply be distinguished.

关 键 词：无机生烃 费托型合成反应 氢同位素分馏 水热条件 

分 类 号：P593[天文地球—地球化学]