Mineral-assisted production of benzene under hydrothermal conditions: Insights from experimental studies on C6 cyclic hydrocarbons

Stefania Venturi, Franco Tassi, Ian Gould, Everett Shock, Hilairy Hartnett, Edward D. Lorance, Christiana Bockisch, Kristopher M. Fecteau, Francesco Capecchiacci, Orlando Vaselli

Research output: Contribution to journalArticlepeer-review

3 Scopus citations

Abstract

Volatile Organic Compounds (VOCs) are ubiquitously present at low but detectable concentrations in hydrothermal fluids from volcanic and geothermal systems. Although their behavior is strictly controlled by physical and chemical parameters, the mechanisms responsible for the production of most VOCs in natural environments are poorly understood. Among them, benzene, whose abundances were found to be relatively high in hydrothermal gases, can theoretically be originated from reversible catalytic reforming processes, i.e. multi-step dehydrogenation reactions, involving saturated hydrocarbons. However, this hypothesis and other hypotheses are difficult to definitively prove on the basis of compositional data obtained by natural gas discharges only. In this study, therefore, laboratory experiments were carried out to investigate the production of benzene from cyclic hydrocarbons at hydrothermal conditions, specifically 300. °C and 85. bar. The results of experiments carried out in the presence of water and selected powdered minerals, suggest that cyclohexane undergoes dehydrogenation to form benzene, with cyclohexene and cyclohexadiene as by-products, and also as likely reaction intermediates. This reaction is slow when carried out in water alone and competes with isomerization and hydration pathways. However, benzene formation was increased compared to these competing reactions in the presence of sulfide (sphalerite and pyrite) and iron oxide (magnetite and hematite) minerals, whereas no enhancement of any reaction products was observed in the presence of quartz. The production of thiols was observed in experiments involving sphalerite and pyrite, suggesting that sulfide minerals may act both to enhance reactivity and also as reactants after dissolution. These experiments demonstrate that benzene can be effectively produced at hydrothermal conditions through dehydrogenation of saturated cyclic organic structures and highlight the crucial role played by minerals in this process.

Original languageEnglish (US)
JournalJournal of Volcanology and Geothermal Research
DOIs
StateAccepted/In press - Aug 31 2016

Keywords

  • Benzene
  • Catalytic reforming
  • Hydrothermal gases
  • Laboratory experiments
  • Mineral catalysts
  • Organic compounds

ASJC Scopus subject areas

  • Geophysics
  • Geochemistry and Petrology

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