Biodiesel: introduction

What is biodiesel?

Biodiesel is a fuel for conventional diesel engines made from plant (or animal) oils or fats that have been chemically transformed into alkyl esters. Its properties are similar to mineral diesel, but it doesn’t have to be drilled from the ground. Any plant oil can be made into biodiesel, including algae. In fact one of Rudolf Diesel’s first engines was exhibited at the Paris exhibition of 1902 running on pure peanut oil. It can be made perfectly well from waste cooking oil too.

A sample of finished home-brew biodiesel

Sample of finished home-brew biodiesel.

Plant oil is too viscous to be used directly in a diesel engine, so one of two things needs to happen:

  1. the vehicle is converted to run on straight veg oil, or
  2. the veg oil is modified to be used in a normal diesel engine

This second method is biodiesel production. The oil is modified by making the gylcerine drop out with a chemical reaction and heat, so that it’s no longer too viscous, and can be used in any vehicle with a diesel engine, either neat, or mixed with mineral diesel. It can also be used in generators, boats, or as a heating fuel.

Biodiesel processor

Biodiesel processor.

We only support the use of biodiesel made from used cooking oil. We don’t think it’s a good idea to take up more land to grow crops for vehicles when there are so many people who don’t have enough food, and there is so much pressure on natural habitats. Large corporations are producing it from palm oil grown in huge plantations in West Africa and South-east Asia. We think that biodiesel from these sources is more environmentally-damaging than mineral diesel. See here for more information.

This means that we’re not advocating a wholesale change to biodiesel for all the world’s diesel vehicles, as there’s nowhere near enough waste cooking oil. But it’s something that can be done on a small scale, using a local waste product. Ultimately, we need to find ways to reduce our fuel use – more energy-efficient vehicles, car sharing, cycling, public transport, working from home and holidaying without flying.



What are the benefits of biodiesel?

  • climate change: the most important greenhouse gas is carbon dioxide (CO2), which is emitted by the burning of fossil fuels. Burning biodiesel also emits CO2, but this is offset by the fact that it comes from plants, and plants use CO2 from the atmosphere to grow
  • emissions: tests have shown that it is cleaner burning than normal diesel with only a very slight loss in range (how far a vehicle can go on a full tank) of 3-5%. Alkanes, carbon monoxide (CO) and particulates are reduced; only nitrous oxides may stay the same or increase, but can be reduced with a catalytic converter, and / or by altering the engine timing. Sulphur is almost completely eliminated. As well as being good for the atmosphere, this can increase operator safety on vehicles such as waste collection trucks, and the smell is much more pleasant than with conventional diesel vehicles
  • spills: it reduces the risk of spills from oil tankers; small spills and leaks from vehicles are harmless
  • waste reduction: it can reduce waste by recycling used oil. (the UK produces 100-400,000 tonnes of waste cooking each year)
Mixing a small batch of oil, alcohol and lye

Mixing a small batch of oil, alcohol and lye.

  • energy balance: biodiesel has an energy balance of 3:1, i.e. it provides 3 times the amount of energy used to produce it. (compared to not much more than 1:1 for mineral diesel)
  • it is more lubricating than mineral diesel, and so can extend engine life
  • being able to drive past a petrol station and knowing that you don’t have to give money to giant oil companies

What can I do?

You can buy biodiesel, or make your own. We recommend 100% biodiesel in the summer and a 50:50 blend of biodiesel and mineral diesel in the winter – biodiesel is more viscous at lower temperatures, so the fuel pump has to work harder with a cold start.

Glycerine and biodiesel separated after a small-batch reaction

Glycerine and biodiesel separated after a small-batch reaction.

As biodiesel is a strong solvent, you need to change your fuel filter after the first 500-1000 miles, as it could remove material from the walls of your fuel tank and deposit it in the fuel filter. This should only happen once though.

Check your vehicle’s warranty to see if it covers the use of biodiesel. Many do, but many don’t, so you’d be taking a risk. Obviously it’s fine after the warranty has run out.

There is a question mark over whether to use it in common-rail diesels and modern, computer-controlled engines. There is a risk that the more precise fuel injectors may become clogged by the slightly more viscous biodiesel, or that the computer may be confused by the oxygen in it into thinking that water is present, and various ‘safety’ features may kick in. The complexity of modern vehicles seems tailor-made to prevent people from tinkering with their vehicles and their fuel – but plenty still do. On forums many state that they’re using 100% biodiesel with modern engines. Maybe a B30 (a blend of 30% biodiesel, 70% mineral diesel) would be better. There’s no such risk with older vehicles.

Some producers will deliver biodiesel in bulk containers (IBCs)

Some producers will deliver biodiesel in bulk containers (IBCs).

Buying biodiesel

Biodiesel is available at some petrol stations, or it can be delivered in IBCs (100-litre bulk containers). See here for places to buy it.

Biodiesel processors

You’ll need a processor to make biodiesel. You can buy one, or if you’re handy, you can make one with a couple of oil drums, a pump, filter, copper pipe and plumbing fittings. It might be a cheaper (and more fun) to get together with friends to make or buy a processor. Check forums for reviews of commercial processors. See books or websites for details of how to build them.

titrating the oil to calculate the amount of catalyst to use

Titrating the oil to calculate the amount of catalyst to use.

Raw materials

You can buy used cooking oil cheaply (or maybe get it for free from local restaurants) as well as the other chemicals that are needed. See our links page.

Making biodiesel

Extreme care must be taken when making it, as it requires the use of potentially hazardous materials – the area must be well-ventilated, no naked flames, use goggles and gloves. Any good recipe book or website will include a list of safety precautions. Here’s an overview of the process:

  1. remove excess water from the oil by evaporation or heating and drawing off the bottom when it settles
  2. filter the oil
  3. ‘titrate’ a sample of oil to work out the quantity of catalyst to use in the reaction: this is a little school-chemistry-lab-type project involving isopropyl alcohol and a pH indicator
  4. mix and heat the oil with alcohol (usually methanol) and a catalyst (‘lye’ – sodium or potassium hydroxide) in a processor
  5. when the mixture settles, draw off the glycerine from the bottom (which can be used to make soap and other useful products – after recovering excess methanol from it)
  6. ‘wash’ your biodiesel with water to remove impurities
  7. filter again and de-water to produce finished biodiesel
you can build your own processor if you have the necessary plumbing skills

You can build your own processor if you have the necessary plumbing skills.

This is a basic method, and there are variations / other methods. See our step-by-step guide, plus books and websites for quantities and detailed instructions.

Testing, regulations & duty

If you buy biodiesel, duty is already paid, but if you make it, contact HM Revenue & Customs to ask about current rates of duty payable (which is constantly changing), and the Environment Agency about what permissions you need (although you probably won’t need any permits for domestic-scale production). There are companies that can test the quality of your biodiesel. See here for more details on testing, regulations & duty.

We'd love to hear your comments, tips and advice on this topic, and if you post a query, we'll try to get a specialist in our network to answer it for you.