Chapter 7 Classical and Non-Classical Routes for Alcohol Synthesis

Abstract

This chapter discusses the older established routes used for the industrial synthesis of particular chemical grade alcohols from hydrogen-rich synthesis gas, as well as recently developed catalysts and processes that have commercial potential for producing mixtures of fuel-grade alcohols from synthesis gas derived from sources such as coal or biomass. Methanol synthesis is a well-developed process that occurs as one of the most active (up to 2 kg methanol/kg catalyst/hr) and selective heterogeneous catalytic reactions used in an industrial process. It can be carried out as a high temperature and high pressure process over catalysts such as ZnO/Cr 2 O 3 or as a low temperature and moderature pressure (5–10 MPa) process over copper-based catalysts. While this method of catalyst modification has long been known, it is notable that the addition of alkali to these three classes of catalysts can result in the suppression of the formation of hydrocarbons, enhancement of the alcohol yields, and shifting of the selectivity toward C 2 -C 4 alcohols from H 2 -poor gas synthesis gas. Other catalyst systems are being probed for their potential in converting synthesis gas to alcohols, and these include Pd-based catalysts, such as Pd/SiO 2 ; other noble metal catalysts, such as supported Rh and Ni-based catalysts. Pathways that have been proposed for higher alcohol synthesis include CO insertion to form a C-C bond, followed by hydrogenation; homologation of methanol by CO via a symmetric intermediate and condensation of two alcohol molecules via dehydration.