Hydrotreatment to HVO

Hydrotreatment is the first part of the two-staged hydroprocessing process for the production of a range of fuels from oils and fats. The products of hydroprocessing are hydrocarbons with properties superior to conventional biodiesel and fossil diesel. Hydroprocessing can use a wide range of waste fats and oils as feedstocks, hence the synonym HEFA Hydroprocessed Esters and Fatty Acids is increasingly applied. The product is sulfur-, oxygen-, nitrogen- and aromatics-free diesel which can be used without modification in diesel engines. These diesel-type hydrocarbons, also referred to as hydrotreated vegetable oil (HVO) or renewable diesel, can even be tailored to meet aviation fuel requirements. Hydroprocessing is therefore an alternative process to esterification to produce a diesel substitute from biomass.

Hydroprocessing process

Hydroprocessing uses hydrogen to convert unsaturated compounds such as alkenes and aromatics into saturated alkanes (paraffins) and cycloalkanes, which are more stable and less reactive. The conversion is usually a two-staged process.

The first stage, the so-called hydrotreatment, takes place at reaction temperatures between 300 °C and 390 °C. First hydrogen is added to saturate the double bonds of the unsaturated vegetable oil triglycerides. Then more hydrogen is added to remove the propane backbone, hereby cleaving the saturated vegetable oil triglycerides to fatty acids. Finally, the fatty acids either undergo hydrooxygenation (by addition of more hydrogen the oxygen leaves as H₂O) or decarboxylation (oxygen leaves as CO₂ without further addition of hydrogen), or a combination of these two. The result is a mixture of straight chain, branched chain, and cyclic paraffinic hydrocarbons.

The second stage of hydroprocessing involves alkane isomerisation and cracking, bringing the biofuel to a quality that equals or surpasses specifications for conventional petroleum fuels.

Feedstock

• Common (food crop) vegetable oils from rapeseed, sunflower, soy bean as well as palm oil and others
• Alternative non-food oils such as jatropha and algae oil
• Waste fats such as animal fats or used cooking oil (UCO)

Products

HVO/HEFA are straight chain paraffinic hydrocarbons that are free of aromatics, oxygen and sulfur and have high cetane numbers. HEFA offers a number of benefits over FAME (Fatty Acid Methyl Esters), such as reduced NOx emissions, better storage stability, and better cold flow properties. Properties are similar to biomass-to-liquid (BTL) diesel fuels produced by Fischer-Tropsch (FT) synthesis, hence HEFA can typically be used in all diesel engines.

Commercial facilities/processes

The following companies established production of HVO.

• Neste Oil
• Total S.A.
• Eni
• Renewable Energy Group Inc

Details can be found here: HVO/HEFA

Sources:

The potential and challenges of drop-in biofuels,  IEA Bioenergy Task 39, 2014

Review of Heterogeneous Catalysts for Catalytically Upgrading Vegetable Oils into Hydrocarbon Biofuels, 2017

Hydrotreated Vegetable Oil (HVO) as a Renewable Diesel Fuel; Hannu Aatola et al, Seppo Mikkonen, 2008