Methanation is a highly exothermic reaction. It should beavoided because heat dissipation is a problem at industrial scaleduring higher-alcohols synthesis.6 Methane is the most thermodynamically favored product of CO hydrogenation. Figure 5shows that when methane is allowed as a product, the equilibriumyield of ethanol is essentially zero at all conditions of interest.Another important side reaction is the water gas shift (WGS)reaction (eq 4) because it can affect the H2/CO ratio, since itproduces H2 along with CO2.