Chapter 10 - The Indirect and Direct Conversion of CO2 into Higher Carbon Fuels

Abstract

This review examines the concept of transforming CO2 ultimately into high hydrocarbon fuels as a means of closing the carbon cycle. It is noted that this in effect is two challenges and must address not only the environmental impact, but also the need for clean renewable energy. It describes the two potential routes; Indirect routes which covers the generation of syngas via the Dry Methane Reforming process and the subsequent conversion of syngas into hydrocarbons via the Fischer-Tropsch process. Examination of the concept of methanol to hydrocarbons is also dealt with; while this is a more convoluted process compared to Fischer-Tropsch it allows production of gasoline range hydrocarbons with octane number enhancement properties. Direct routes are also described briefly and examine the concept of the chemical transformation of CO2 into fuels, in this section the limitations of such a process of demonstrated, with specific emphasis on the reduction of catalyst choice, due to reduced activity towards CO2 compared to CO. As such to overcome these limitations specific additives may be employed. The chapter concludes with a critical examination of the future perspectives for such processes and with specific emphasis upon potential areas of research to improve the viability of widespread application. In particular it is commented that perhaps the biggest and most difficult challenge for closing the carbon cycle arises from the need for a clean, cheap and most importantly renewable source of H2.