When businesses begin looking at renewable alternatives to conventional diesel, HVO and biodiesel often appear side by side. Although the two fuels can be made from similar raw materials, they are produced differently and have distinct characteristics.
Both may begin with vegetable oils, used cooking oils or animal fats. Biodiesel is produced through a process called transesterification, which creates Fatty Acid Methyl Ester (FAME). HVO is produced through hydrotreatment, which converts the raw material into paraffinic hydrocarbons.
This difference in production changes the chemical composition of the finished fuel, affecting how it can be blended, stored and used.
What is biodiesel?
Biodiesel is a renewable fuel commonly produced from vegetable oils, used cooking oils and animal fats.
The term is sometimes used broadly, but conventional biodiesel is usually FAME. In its pure, unblended form, it may be described as B100, with the number indicating that the fuel contains 100% biodiesel.
However, most drivers and businesses encounter biodiesel as a smaller component of conventional diesel rather than as B100.
What does B7 diesel mean?
Standard road diesel supplied in the UK generally meets the BS EN 590 specification and may contain up to 7% FAME by volume.
This is where the name B7 comes from:
- The letter B indicates biodiesel
- The number 7 indicates that the fuel can contain up to 7% biodiesel
- The remaining fuel is primarily conventional fossil diesel
B7 does not necessarily contain exactly 7% FAME. The designation shows the maximum concentration permitted under the specification.
Blending biodiesel into conventional diesel increases its renewable content while allowing the finished fuel to remain suitable for most diesel vehicles.
How is biodiesel produced through transesterification?
Biodiesel is produced using a chemical process known as transesterification.
During this process, oils or fats are reacted with an alcohol, usually methanol, in the presence of a catalyst. This produces two main substances: FAME and glycerol. The FAME becomes the biodiesel.
The process changes the original oil so that it can be used as a diesel fuel. However, the resulting FAME molecules still contain oxygen. This affects how the fuel responds to air, moisture, temperature and extended storage.
These properties help explain why FAME biodiesel and HVO can behave differently, despite potentially being made from similar raw materials.
Can pure biodiesel be used in diesel engines?
Pure biodiesel, usually referred to as B100, can be used in some diesel engines and items of equipment. However, it should only be considered where the manufacturer has approved the relevant fuel specification and concentration.
An engine that can use B7 is not automatically approved for B100. Higher concentrations of FAME can introduce several practical considerations, including:
- Compatibility with seals, hoses and other fuel-system materials
- Different cold-weather performance
- Greater sensitivity to oxidation during storage
- An increased tendency to absorb and retain moisture
- A higher risk of microbial contamination where free water is present
- Deposits being loosened from older tanks and fuel systems
- Different maintenance or servicing requirements
The cold-flow characteristics of biodiesel can also vary according to the feedstock used to produce it. A B100 fuel made from one raw material may therefore behave differently at low temperatures from one made using another.
Pure biodiesel can be a viable fuel in suitable applications, but it requires the correct equipment approval, fuel quality, storage arrangements and maintenance procedures.
How is HVO produced through hydrotreatment?
HVO stands for Hydrotreated Vegetable Oil, although its name can be slightly misleading. The raw materials used to produce it are not limited to virgin vegetable oil. Waste oils and animal fats may also be used.
During hydrotreatment, the prepared feedstock reacts with hydrogen at high temperatures and pressures in the presence of a catalyst. This removes oxygen and converts the material into hydrocarbons.
Further processing, including isomerisation, can then be used to adjust properties such as cold-weather performance.
The result is a paraffinic diesel fuel rather than an ester-based biodiesel. HVO generally meets the EN 15940 specification for paraffinic diesel fuels.
Because the oxygen is removed during production, HVO has a chemical structure closer to conventional diesel than FAME biodiesel does.
Why does HVO behave differently from biodiesel?
The main difference comes back to how each fuel is produced:
- Transesterification produces oxygen-containing esters known as FAME
- Hydrotreatment removes oxygen and produces paraffinic hydrocarbons
FAME’s ester structure makes it more sensitive to certain storage conditions. It has a greater affinity for water than fossil diesel and is generally more susceptible to oxidation.
This does not mean FAME-containing diesel will inevitably deteriorate or develop microbial contamination. Tank condition, water ingress, temperature, fuel turnover and housekeeping all have an important influence. Our guide to how FAME affects diesel storage explores these factors in more detail.
HVO does not have the same ester chemistry. It is generally more resistant to oxidation, has a lower affinity for water and can offer more consistent cold-weather performance than conventional FAME biodiesel.
These characteristics can make HVO particularly relevant to businesses that store fuel for longer periods or operate seasonal machinery, backup generators and other equipment with irregular fuel turnover.
HVO must still be stored correctly. Water, dirt and existing tank contamination can affect any fuel, so switching to HVO should not replace regular tank inspection and maintenance.
Can HVO be used without blending?
HVO can be supplied as HVO100, meaning it is used in its unblended form rather than being mixed with fossil diesel.
It can also be blended with conventional diesel in different proportions. As HVO is not FAME, it does not contribute to the 7% FAME limit behind the B7 designation. However, the finished fuel must still comply with the appropriate specification for how it is sold and used.
HVO can replace conventional diesel in many compatible engines without mechanical modification. Businesses should still check the vehicle or equipment manufacturer’s approval before switching, including any requirements relating to EN 15940 or XTL fuel.
HVO or biodiesel: which is more suitable?
There is no single answer for every operation.
Biodiesel has an established role as a renewable component within standard B7 diesel. Higher blends and B100 can also be used in applications designed or approved for them, provided their compatibility, storage and maintenance requirements are properly managed.
HVO may be more suitable where a business wants to replace conventional diesel without taking on the same FAME-related storage and compatibility considerations. Its paraffinic composition gives it different performance characteristics from conventional biodiesel, despite the two fuels potentially beginning with similar raw materials.
The appropriate choice will depend on:
- Manufacturer approval
- How long the fuel will be stored
- Fuel turnover
- Operating temperatures
- Existing tanks and fuel infrastructure
- The business’s emissions and sustainability objectives
- Feedstock provenance and supporting documentation
For a broader comparison with conventional diesel, read our guide to HVO vs diesel for UK businesses.
Bulk HVO supply from Oilfast
Oilfast supplies bulk HVO to businesses across Scotland, supported by our network of local depots and experienced delivery teams.
If you are considering HVO for vehicles, machinery, generators or other diesel-powered equipment, our team can help you review your requirements and arrange a reliable supply.
Give us a call on 03302 320 104
