The catalytic hydrotreatment process is generally divided into two main reaction steps : (1) conversion to straight chain alkanes by saturation of double bonds plus removal of hetero atoms and (2) isomerization.
In the first step, unsaturated fatty acids and TAGs are saturated by catalytic hydrogenation. The saturated fatty acids are converted to straight chain alkanes by hydrodeoxygenation and decarboxylation, co-producing propane, water, CO and CO2. The early-developed catalysts employed for this step were noble metals supported onto zeolites or oxides. This later shifted to other transition metals (Ni, Mo, Co, Mo) or their supported bimetallic composites due to catalyst deactivation by poisoning, production of cracking species and process costs.
In the second step, the deoxygenated, straight chain paraffins are selectively hydrocracked and isomerized yielding highly branched alkanes or isoparaffins. The resulted organic product is a mixture of straight and branched paraffines that can be perfectly used as drop-in liquid fuel.
There is a vast experience in hydrotreating triglycerides to produce green fuels and the hydroprocessing process of crude based products is exploited in petroleum refineries for many decades. At commercial level, the hydroprocessing of lipids derived from fats and vegetable oils can be carried out using the same catalyst, reactor type and separation facilities with those that are used in the vacuum gas oil hydrotreating. Some strategies have been proposed for the downstream processing of lipids after the production process, i.e. in situ trans/esterification using lipases, or an integrated process with cell-surface display of lipases to break down triglycerides to free fatty acids and production of FAME, coupled to simultaneous regeneration of in situ carbon source (glycerol) for yeast utilization.
Within BioSFerA project, the hydrotreatment of a new type of microbial oil, derived from a 2-step biological route using renewable Hydrogen for the catalytic hydrotreating reactions, is explored. The main challenge is to develop a proper reaction process using commercial catalysts, where the desired bioliquids products (jet-like and bunker-like fuels) are produced under certain operating conditions. Due to the novelty of this venture, the hydroprocessing step need to be tested and optimized at lab scale (TRL3). The production of large volumes of lipids (>400 kg of purified lipids) offers the opportunity to validate the process at pilot scale (TRL5).