Review on technologies for conversion of natural gas to methanol

Abstract

Continuous flaring of natural gas remains a great environmental threatening practice going on in most upstream hydrocarbon production industry across the globe. About 150 billion m³ of natural gas are flared annually, producing approximately 400 million tons of carbon dioxide alone among other greenhouse gases. A search into a viable method for natural gas conversion to methanol becomes imperative not only to save the soul of the ever-changing climate but also to bring an end to wastage of valuable resources by converting hitherto wasted natural gas to wealth. Currently the technologies of conversion of natural gas to methanol could be categorized into the conventional and the innovative technologies. The conventional technology is sub-divided into the indirect method also called the Fischer-Tropsch Synthesis (FTS) method and the direct method. The major commercial technology currently in use for production of methanol from methane is the FTS method which involves basically two steps which are the steam reforming and the syngas hydrogenation steps. The FTS method is highly energy intensive and this is a factor responsible for its low energetic efficiency. The direct conversion of methane to methanol is a one-step partial oxidation and lower temperature method having higher energetic efficiency advantage over the FTS method. The direct method occurs at temperature range of 380–470 °C and pressure range of 1–5 MPa while the FTS occurs at temperature range of 700–1100 °C and atmospheric pressure. Both methods are carried out under effect of metallic oxide catalysts such as Mo, V, Cr, Bi, Cu, Zn, etc. The innovative methods which include electrochemical, solar and plasma irradiation methods can be described as an approach to either of the two conventional methods in an innovative way while the biological method is a natural process driven by methane monooxygenase (MMO) enzyme released by methanotrophic bacteria. The aim of this study is to review the current state of the technology for conversion of methane to methanol so as to make abreast the recent advances and challenges in the area.