Destructive Hydrogenation

the processing of hydrogen-poor low-grade fuels (coal, shale, coal tar, and mazut) to convert them to hydrogen-enriched fuels and oils or into raw material suitable for further processing. Destructive hydrogenation is performed at 400°-560° C and an H₂ pressure of 20-70 meganewtons per sq m (MN/m²), or 200-700 kilograms-force per sq cm (kgf/cm²), using catalysts containing iron, molybdenum, nickel, or tungsten in two or three stages, depending on the nature of the raw material being processed. The main reactions in this process are hydrogenation (the addition of hydrogen to aromatic and unsaturated hydrocarbons and heterocyclic compounds) and destructive hydrogenation (a reaction of splitting of molecules of the raw material, with addition of hydrogen to them). This leads to formation of products that are more volatile and have a greater hydrogen content than the initial raw material.

Destructive hydrogenation was first used in such a form in Germany at the beginning of the 20th century (F. Bergius) for treating coal. In view of the high hydrogen consumption and complex technological layout of the process, this version of destructive hydrogenation was not developed in the postwar period. At present another form of destructive hydrogenation, so-called hydrocracking, is being used extensively. Hydrogen is used at a pressure of 3-10 MN/m² (30-100 kgf/cm²) in the presence of catalysts that provide sufficiently thorough conversion of the raw material with low hydrogen consumption (1-3 percent of the amount of raw material). The importance of destructive hydrogenation increased in connection with the refining of heavy, tarry crude with a high sulfur content.

A variant of the destructive hydrogenation process is hydrogenolysis, which is used to make unsubstituted aromatic hydrocarbons from alkyl-substituted aromatic hydrocarbons —for example, benzene from toluene—and is performed at 800° C (without a catalyst) or at 620°-650° C (with a catalyst) at an H₂ pressure of 6.5-10 MN/m² (65-100 kgf/cm²). An intermediate process between destructive and nondestructive hydrogenation is the hydrogénation refining of fuels—hydrofining.