Production, distribution and storage
Bio-/Synthetic gasoline is produced either from biomass/organic matter or by synthesis from inorganic sources (air, electricity, and water).
Production routes include MTG processes (e.g., ExxonMobil process and Haldor Topsøe’s Tigas process), Virent's BTL process, Fischer-Tropsch processes, and Refinery integrated processes.
The ExxonMobil process is in operation in New Zealand and Wesseling in Germany. TIGAS is operating in e.g. Texas.
Virent’s BTL “BioForming” process may produce a different type of hydrocarbons and oxygenates depending on selected process and depending on the technology selected, the bio-forming process can generate hydrocarbons e.g. for gasoline, jet fuel, or diesel fuel. (Huber 2006).
In one example, the main product contained C3-C6 alkanes and aromatics (Figure 1). Also low level of alkenes and oxygenates were produced. (Blommel 2008). In the batch shown in Figure 1, major parts of hydrocarbons were light C3-C6. In the gasoline pool, usage of the lightest hydrocarbons is limited. High-octane branched alkanes are generally more favorable gasoline components than low-octane straight-chain alkanes. Aromatics have generally good octane numbers, but due to environmental reasons, the aromatic content of gasoline is limited. For instance, in Europe a maximum 35 vol-% of aromatics is allowed in gasoline (Fuel Quality Directive 2009/30/EC).
There is no published data of products from Virent’s process.
Even if the Fischer-Tropsch (FT) process could be optimized for diesel fuel, gasoline would be formed to some extent. In addition, Sasol in South-Africa has a high-temperature Fischer-Tropsch process specially designed for gasoline production. The FT product is treated with e.g. alkylation, hydrotreatment and isomerization before blending of gasoline. Olefins originating from the FT process are treated with conversion of olefins to distillate (COD) process. Final product consists of alkanes, alkenes, and aromatics, and even ethanol and MTBE are used in this gasoline. Final products containing synthetic fuels must fulfill requirements for regular gasoline and diesel fuel. (Larsen et al. 2007).
Larsen et al. (2007) studied Danish gasoline, alkylate, and FT gasoline with a passenger car. The gasoline studied contained 70% of FT gasoline. Fuel properties of FT gasoline used in the study are shown in Table 2. Aromatic content of this gasoline batch was 32%.
Refinery integrated processing
Oils and fats can be used as co-feed in Fluid Catalytic Cracking (FCC) units of traditional petroleum refineries. According to Holmgren et al. (2007), research octane number of gasoline fraction from FCC unit is higher for oils and fats as feedstocks than for petroleum crude oil as feedstock. (Holmgren et al. 2007). FCC gasoline is used as normal blending component, and thus properties of final products depend on the refinery blending schemes. If pyrolysis oil is used as a feedstock for hydroprocessing unit, the product is an aromatic blending stock. (Holmgren et al. 2007). Blending of high-aromatic component in gasoline is limited.
One option to produce hydrocarbons for gasoline is to hydrotreat oils and fats. Today, hydrotreatment units are optimized to produce hydrotreated vegetable oil (HVO) diesel fuel, such as Neste Oils NExBTL renewable diesel. However, gasoline fraction is formed as a side-product in these processes. Gasoline fraction from hydrotreatment of oils and fats is paraffinic, oxygen-, aromatic-, and sulfur-free.