hydrogen (H 2 ) and another element or a compound, usually in the presence of a catalyst .
It may involve adding hydrogen at the sites of double or triple bonds (see bonding ) to make them single bonds (i.e., to saturate an unsaturated compound; see saturation ), or to aromatic compounds to make them cyclic hydrocarbons . Edible oils with unsaturated fatty acids are liquid at room temperature; food manufacturers use hydrogenation to convert a fraction to saturated fatty acids to make the product more solid. A second type of hydrogenation involves breaking up a compound (hydrogenolysis, or destructive hydrogenation) and is of great importance in the {{link=petroleum">petroleum industry. Numerous processes in gasoline and petrochemical manufacturing are based on it.