translate English to French: Finally, the heavy residues may be subjected to hydrogenation, i.e., hydrogen is added under conditions of high temperature and pressure, in the presence of catalysts, to convert heavy compounds of high carbon/hydrogen ratio to lighter, more valuable compounds of higher hydrogen content.
Au cours du procédé, on peut éliminer, du moins en partie, des contaminants comme le soufre, l’azote, les halogènes et les métaux.