As the molecules included in the various types of liquid biomass can be relatively large and complicated, cracking reactions are desired to convert them into molecules of the size and boiling point range of conventional fuels, mainly gasoline, kerosene and diesel. A characteristic reaction that occurs during catalytic hydrotreating of oils / fats is the cracking of tri­glycerides into its consisting fatty acids (carboxylic acids) and propane as shown in Scheme 1 [5][6]. This reaction is critical as it converts the initial large triglycerides molecules of boiling point over 600°C into mid­distillate range molecules (naphtha, kerosene and diesel).

Other cracking reactions may take place however such as those de­scribed in Schemes 2 and 3, depending on the type of molecules pres­ent in the feedstock. For example Scheme 2 is a cracking reaction which may occur during catalytic hydrotreatment of pyrolysis oil which includes polyaromatic and aromatic compounds. Alternatively Scheme 3 may fol­low deoxygenation of carboxylic acids on the produced long chain paraf­finic molecules, leading to smaller chain paraffins, during the upgrading of Fischer-Tropsch wax.

R-R’ + H2 — ► R-H + R‘-H

SCHEME 3.