Membrane contactors operating in mild conditions for liquid phase partial oxidation of methane

Abstract

An integrated catalytic membrane system for liquid phase partial oxidation of light hydrocarbons such as methane in mild operating conditions has been studied and tested. On the basis of tests on methane solubility and chemical stability of some candidate solvents, water was chosen as the reaction medium. The low methane solubility in water was enhanced by working under moderate pressure (0.4 MPa) and then integrating the catalytic system with a gas–liquid membrane contactor. Catalytic tests, using the Fenton reagent (Fe 2+, H 2O 2), were carried out in a batch system to study the influence of some operating conditions on system performance. Best results were obtained under the following operating conditions: [Fe 2+] = 2.70 mmol L −1; [H 2O 2] = 54 mmol L −1; T = 25 °C; pH = 2.98. GC–MS analyses evidenced production of dimethyl peroxide (DMP), that can be potentially converted to methanol (two moles per mole of DMP). Then results obtained in the batch system were applied carrying out some catalytic tests in the integrated membrane system. It was evidenced the influence of inside membrane diameter and material type on system performance and the positive effect of the membrane contactor to disperse methane in the liquid phase. Among three tested membranes the ceramic tubular membrane (0.2 μm pore size) gave the best performance avoiding problems related to membrane degradation, plugging and fouling. It was pointed out that integration of the catalytic system with a membrane contactor enhanced system performance decreasing H 2O 2 consumption, thanks to a lower oxidation of methane to CO 2, thus resulting in an increase of system selectivity.