Alcohols as alternative fuels: An overview

Due to the phase out of lead in all gasoline grades and the adverse health and environmental effects of MTBE, the synthesis of higher alcohols, particularly ethanol, from synthesis gas has drawn considerable interest. Low molecular weight alcohols such as ethanol have replaced other additives as octane boosters in automotive fuels. Adding alcohols to petroleum products allows the fuel to combust more completely due to the presence of oxygen, which increases the combustion efficiency and reduces air pollution. The presence of alcohols in fuel causes corrosion to metallic fuel system components. In order to make the best use of alcohols as alternative fuels; one can redesign the engine or the vehicle can be redesign or one can blend in one or more additives to the ethanol or methanol to improve its characteristics. Catalytic conversion of synthesis gas to alcohols is advantageous, as this uses various renewable and non-renewable carbon resources. Different catalytic systems can be used for synthesizing higher alcohols from synthesis gas. Depending on the process conditions and the catalyst used, the reaction mechanism varies and the products include primary and secondary alcohols of both normal and branched carbon chains. The present paper includes an overview of the processes and catalysts used depending on the production of specific alcohols, as well as, the reaction mechanisms currently accepted. Transition metal-promoted alkali-modified molybdenum sulphide catalysts are considered to be more attractive to improve CO hydrogenation and for the production of linear alcohols.

Graphical abstractFigure optionsDownload full-size imageDownload high-quality image (109 K)Download as PowerPoint slideHighlights► Ethanol replaced other additives as octane boosters in automotive fuels. ► Syngas obtained from carbon resources can be catalytically converted to alcohols. ► Alkali-modified molybdenum-based catalysts are more attractive for alcohols synthesis.