## 3 Industrial Co-Processing Options
### Hydrotreating Vegetable Oils/Fats  
Hydrotreating is primarily used in petroleum refineries to remove impurities (particularly sulphur) from petroleum product streams. Hydrotreating reactors are mostly fixed catalyst beds. Typically, the catalysts are regenerated at an off-site facility after months of operation (the cycle varies from 12 months to 36 months), as replacement of the catalyst is costly. Thus, there is a considerable financial risk involved in inserting unknown biomass feedstocks that could deactivate the catalyst prematurely.  
Vegetable oils (or fats) are made up of triglycerides. A triglyceride is made up of three fatty acid chains linked to a glycerol molecule. When a fat is hydrotreated, the glycerol molecule is split from the fatty acid chains (note: waste oils and fats may contain free fatty acids which are fatty acids not connected to a glycerol). The glycerol becomes propane gas after more hydrotreating, and the fatty acid chains become liquid hydrocarbons. Both vegetable oils and fats, and animal fats are comprised principally of fatty acids with carbon chains 16 or 18 carbons long (i.e., \"C16\" and \"C18\") (although minor amounts of other fatty acids can be present) [27]. Carbon chain lengths of the aliphatic components in petrol tend to be C5 to C10, those in diesel fuels tend to be C14 to C20 and in kerosene C10 to C16 [28]. Therefore, fatty acid chains following hydrotreating will normally end up as diesel fraction molecules, or possibly kerosene, as opposed to going into other products from the refinery. However, the hydrotreating process can also accidentally \"hydro-crack\" or split some of the fatty acid chains to produce shorter hydrocarbon molecules [29]. Figure 2 presents the renewable oil deoxygenation reaction pathways.  
\begin{table}
\begin{tabular}{c c c c c c c c} \hline \hline  & **Unit** & **Vegetable** & **Used** & **Fast Pyrosis** & **Catalytic** & **HTL Bio-Oil** & **Crude Oil** \\  & & **Oils** & **Cooking Oil** & **Bio-Oil** & **(CPO)** & **(Bio-Crude)** & **Cude Oil** \\ \hline Carbon & (wt\%) & 76–79 & 72–78 & 54–68 & 62–73 & 73–78 & 83–87 \\ Oxygen & (wt\%) & 9–11 & 10–18 & 28–40 & 20–24 & 8–17 & \textless{}1 \\ Hydrogen & (wt\%) & 11–12 & 10–12 & 5–8 & 6–7 & 7–8 & 11–14 \\ Sulphur & (wt\%) & \textless{}0.0002 & & 0.05-0.2 & & & \textless{}4 \\ Nitrogen & (wt\%) & \textless{}0.002 & \textless{}0.04 & 0–0.2 & & & 0.1 \\ Energy content LHV & M\({}_{\text{LHV}}\)/kg & 36–37 & & 16–19 & 24–29 & 27–36 & 38–42 \\ \hline \hline \end{tabular} Source: [16; 17; 18; 19; 20; 21; 22; 23; 24; 25; 26].  
\end{table}
Table 1: Typical composition of biobased feedctocks used for co-processing in refineries.  
Figure 2: Renewable oil deoxygenation reaction pathways [30].  
When hydrotreating a vegetable oil, it is possible to reduce the amount of hydrogen needed by allowing some oxygen in the vegetable oil to be removed by combining it with some of the carbon within the vegetable oil itself (thus forming CO or CO\({}_{2}\)). This \"wasting\" of bio-carbon reduces the yield of co-processed fuels, but allows the refinery to co-process using lower amounts of hydrogen inputs (thus reducing their costs).  
Production of HVO from tall oil, a by-product of the pulp and paper industry, has begun to occur mainly in Finland and Sweden. Both tall oil itself and tall oil pitch are included in Annex IX of RED II as counting double towards renewable energy targets in the transport sector.