17.2.1 Introduction

As discussed in the introduction alcohols are produced via the synthesis gas route. The crucial step here is not the synthesis gas production via gasification but the conversion of synthesis gas into alcohols. For methanol this is a common practice although this is not straightforward: high pressure (50-100 bars), the right composition and purity of CO and H2 is necessary. For ethanol a number of synthesis routes have been proposed. Table 17.1 shows possible routes for ethanol production based on synthesis gas routes. Two routes can be distinguished: direct and indirect synthesis via intermediate products. The direct route would be the most interesting route from a molecular efficiency point of view, but the present catalytic systems (Cu-Zn-Co oxides/halides, Rh(CO)12 on La2O3) only produce ethanol with relatively low yields (28-49 wt%). This is why the indirect route for ethanol production is still the most used one. Of this last method there are again different kind of options among which are homologation (= chain extention) and a sequence of carbonylation, esterification and hydrogenation.

17.2.2 Hydrocarbonylation van methanol to ethanol

The hydrocarbonylation is a synthesis gas based route via which extention of the alcohol with a CH2 group is carried out; in this case the extension of methanol to ethanol:

CH3OH + CO + 2 H2 « C2H5OH + H2O

By carrying out the reaction in tetrahydrofuran as solvent, good yields can be achieved (89%). The catalysts used in this process are based on metals like Cu, Fe and Ni.