Experimental abiotic synthesis of methanol in seafloor hydrothermal systems during diking events

The abiotic synthesis of organic compounds in seafloor hydrothermal systems is one mechanism through which the subsurface environment could be supplie d with reduced carbon. A flow-through, fixed-bed laboratory reactor vessel, the Catalytic Reactor Vessel (CRV) system, has been developed to investiga te mineral-surface promoted organic synthesis at temperatures up to 400 deg reesC and pressures up to 30 MPa, conditions relevant to seafloor hydrother mal systems. Here we present evidence that metastable methanol can be direc tly synthesized from a gas-rich CO2-H-2-H2O mixture in the presence of a mi neral substrate. Experiments have been performed without a substrate, with quartz, and with a mixture of quartz and magnetite. Temperatures and pressu res in the experiments ranged from 200 degreesC to 350 degreesC and from 15 to 18 MPa, respectively. Maximum conversion of 5.8 X 10(-4)% CO2 to CH3OH per hour was measured using a mixture of magnetite and quartz in the reacto r. After passivation of the stainless steel reactor vessel, experiments dem onstrate that methanol is formed at temperatures up to 350 degreesC in the presence of magnetite, and that the formation rate decreases over time. The experiments also show a loss of surface reactivity at 310 degreesC and a r egeneration of surface reactivity with increased temperature up to 350 degr eesC. Concentrations of CO, and H, used in the experiments simulate periodi c, localized and dynamic conditions occurring within the seafloor during an d immediately following magmatic diking events. High concentrations of CO, and H, may be generated by dike injection accompanied by exsolution of CO2 and reaction of dissolved H2O with Feo in the magma to form H-2. The experi ments described here examine how the ephemeral formation of an H-2-CO2-rich vapor phase within seafloor hydrothermal systems may supply reactants for abiotic organic synthesis reactions. These experiments show that the presen ce of specific minerals can promote the abiotic synthesis of simple organic molecules from common inorganic reactants such H2O, CO2 and H-2 Under geol ogically realistic conditions. (C) 2001 Elsevier Science B.V. All rights re served.