This article needs to be updated.(January 2012)
Hydrotreated vegetable oil (HVO) is a biofuel made by the hydrocracking or hydrogenation of vegetable oil. Hydrocracking breaks big molecules into smaller ones using hydrogen while hydrogenation adds hydrogen to molecules. These methods can be used to create substitutes for gasoline, diesel, propane, kerosene and other chemical feedstock. Diesel fuel produced from these sources is known as green diesel or renewable diesel.
The majority of plant and animal oils are triglycerides, suitable for refining. Refinery feedstock includes canola, algae, jatropha, salicornia, palm oil, tallow and soybeans. One type of algae, Botryococcus braunii produces a different type of oil, known as a triterpene, which is transformed into alkanes by a different process.
The production of hydrotreated vegetable oils is based on introducing hydrogen molecules into the raw fat or oil molecule. This process is associated with the reduction of the carbon compound. When hydrogen is used to react with triglycerides, different types of reactions can occur, and different resultant products are combined. The second step of the process involves converting the triglycerides/fatty acids to hydrocarbons by hydrodeoxygenation (removing oxygen as water) and/or decarboxylation (removing oxygen as carbon dioxide).
A formulaic example of this is C3H5(RCOO)3 + 12H2 -> C3H8 + 3RCH3 + 6H2O
The chemical formula for HVO Diesel is CnH2n+2
Hydrotreated oils are characterized by very good low temperature properties. The cloud point also occurs below −40 °C. Therefore, these fuels are suitable for the preparation of premium fuel with a high cetane number and excellent low temperature properties. The cold filter plugging point (CFPP) virtually corresponds to the cloud point value, which is why the value of the cloud point is significant in the case of hydrotreated oils.
Comparison to biodiesel
Both HVO diesel (green diesel) and biodiesel are made from the same vegetable oil feedstock. However the processing technologies and chemical makeup of the two fuels differ. The chemical reaction commonly used to produce biodiesel is known as transesterification.
The production of biodiesel also makes glycerol, but the production of HVO does not.
Various stages of converting renewable hydrocarbon fuels produced by hydrotreating is done throughout energy industry. Some commercial examples of vegetable oil refining are:
- Neste NExBTL
- Topsoe HydroFlex technology
- Axens Vegan technology
- H-Bio, the ConocoPhilips process
- UOP/Eni Ecofining process.
Neste is the largest manufacturer, producing 2 million tonnes annually (2013). Neste completed their first NExBTL plant in the summer 2007 and the second one in 2009. Petrobras planned to use 256 megalitres (1,610,000 bbl) of vegetable oils in the production of H-Bio fuel in 2007. ConocoPhilips is processing 42,000 US gallons per day (1,000 bbl/d) of vegetable oil. Other companies working on the commercialization and industrialization of renewable hydrocarbons and biofuels include Neste, REG Synthetic Fuels, LLC, ENI, UPM Biofuels, Diamond Green Diesel partnered with countries across the globe. Manufacturers of these renewable diesels report greenhouse gas emissions reductions of 40-90% compared to fossil diesel, as well as better cold-flow properties to work in colder climates. In addition, all of these green diesels can be introduced into any diesel engine or infrastructure without many mechanical modifications at any ratio with petroleum-based diesels.
Renewable diesel from vegetable oil is a growing substitute for petroleum. California fleets used over 200,000,000 gallons of renewable diesel in 2017. The California Air Resources Board predicts that over 2 billion gallons of fuel will be consumed in the state under its Low Carbon Fuel Standard requirements in the next ten years. Fleets operating on Renewable Diesel from various refiners and feedstocks are reported to see lower emissions, reduced maintenance costs, and nearly identical experience when driving with this fuel.
A number of issues have been raised about the sustainability of HVO, primarily concerning the sourcing of its lipid feedstocks. Waste oils such as used cooking oil are a limited resource and their use cannot be scaled up beyond a certain point. Further demand for HVO would have to be met with crop-based virgin vegetable oils, but the diversion of vegetable oils from the food market into the biofuels sector has been linked to increased global food prices, and to global agricultural expansion and intensification. This is associated with a variety of ecological and environmental implications; moreover, greenhouse gas emissions from land use change may in some circumstances negate or exceed any benefit from the displacement of fossil fuels.
A 2022 study published by the International Council on Clean Transportation found that the anticipated scale-up of renewable diesel capacity in the U.S. would quickly exhaust the available supply of waste and residual oils, and increasingly rely on domestic and imported soy oil. The report also noted that increased U.S. renewable diesel production risked indirectly driving the expansion of palm oil cultivation in Southeast Asia, where the palm oil industry is still endemically associated with deforestation and peat destruction.
- Indirect land use change impacts of biofuels
- Algae fuel
- Renewable hydrocarbon fuels via decarboxylation/decarbonylation
- Sustainable oils
- Vegetable oil fuel
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