Methane Bubbled Through Seawater Can be Converted to Methanol With High Efficiency.

Abstract

Partial oxidation of methane (POM) is achieved by forming air-methane microbubbles in saltwater to which an alternating electric field is applied using a copper oxide foam electrode. The solubility of methane is increased by putting it in contact with water containing dissolved KCl or NaCl (3%). Being fully dispersed as microbubbles (20-40 µm in diameter), methane reacts more fully with hydroxyl radicals (OH·) at the gas-water interface. The alternating voltage (100 mV) generates two synergistic POM processes dominated by Cl^- → Cl· + e^- and O₂ + e^- → O₂ ^-• under positive and negative potentials, respectively. By tuning the frequency and amplitude, the extent and path of the POM process can be precisely controlled so that more than 90% methanol is selectively formed compared to the two byproducts, dichloromethane, and acetic acid. The methane to methanol conversion yield is estimated to be 57% at a rate of approximately 887 µM h^-1. This method appears to have potential for removing methane from air using seawater or for converting higher-concentration methane sources into value-added methanol.