Biomass for Fuel from Plants and Garbage
Bio-Diesel - Alternative Energy to Diesel Oil
At present we use the fossil fuel hydrocarbon crude oil which, after being refined supplies us with unleaded petrol and low sulphur diesel for use in our cars.
Before we see how biodiesel is produced, let’s recap on hydrocarbons formation, and in particular crude oil. (See my article about offshore oil and gas.)
Fossil fuels were formed over 300 million years ago during the Carboniferous period, oil and gas being formed under the seabed from the organic remains of marine animals and plankton.
Once the oil reservoir is discovered, a floating drilling rig drills a hole down through the sand and rock into the reservoir. This well is then sealed and a production platform installed over the top of the well, the supporting legs secured to the seabed by steel piles driven into the bedrock.
The well is then uncapped and pipes are used to bring the oil up from the reservoir to the production platform where it passes through different processing equipment, removing water and impurities from the oil. The semi-refined oil is now pumped ashore through sub-sea pipelines laid on the sea bed, usually directly into a refinery, or pumped through pipelines to a refinery.
Hydrocarbons such as oil and gas are not sustainable and world oil and gas supplies are due to run out before the end of this century.
The UK and Dutch Sections of the North Sea Oil Fields, and America’s oil fields are all nearing depletion and due to run out in a few decades. This leaves Europe and America dependant on their oil supply from some very unfriendly Eastern Oil States and Russia who can cut of our oil supply on a whim.
It is in all our interest therefore that we develop greener biofuels to drive not only our car and commercial transport engines, but also to fire our power stations.
One method of reducing our dependency on fossil fuels for transport is by producing biofuels. These man-made fuels and can be classed as renewable energy or CO2 neutral because they were made from plants and when they are combusted, the CO2 released is taken back in by replanted vegetation.
So, in using biofuels we will reduce transport CO2 emissions and mitigate Global Warming.
Biofuels can be classified as First and Second Generation Biofuels.
In this article we shall examine first generation biofuels and in particular the formation of biodiesel processed from plant oils.
Biodiesel is currently produced from used cooking oil, tallow and, from oil-rich crops such as rapeseed.
There are currently three different means of producing biodiesel from oil and fat,
- Base Catalysed Transesterification of oil and fats
- Formation of fatty acids from the oil
- Transesterification using Direct Acid Catalysts
In this article we shall examine the most popular method of biodiesel processing – base catalysed transesterification and to start with we shall look at the different feedstock used.
The popular feedstocks used are
- Used cooking oil – this should not be used as a direct substitute for diesel as it will carbonise the combustion components. The oil must be centrifuged to remove the food particles before being used for biodiesel processing.
- Rapeseed – grown throughout the world for cooking oil and food additives as well as for biodiesel processing, but uses large quantities of nitrogen based fertilizer in cultivation.
- Soy Beans – best cultivated in countries with hot summers, but not exceeding temps of 40º C (104º F). These are a good meat substitute, high in protein and contain a high proportion of oil. The Amazon rain forest is being exploited by deforestation due to increased soybean production for food and oil.
- Palm oil – derived from the leaves of the oil palm leaves, this oil is used as a cooking medium, as well being used in biodiesel processing.
- Tallow – oil and fat produced from animal parts, also used as a lubricant and weather proofing agent as well as in the processing of biodiesel.
Base Catalysed Transesterification
This process involves the crushing or rendering of the feedstock to produce the oil or the reuse of centrifuged cooking oil. The catalyst and alcohol (in this case we shall assume the catalyst to be sodium hydroxide, the alcohol being methanol) are agitated in a vessel where the catalyst is dissolved in the alcohol. The solution is pumped from here into a pressure vessel where the oil is added and kept at a temperature above that of the alcohol boiling point.
This brings us to the transesterification stage where the oil and fat react with the alcohol, the sodium hydroxide accelerating the reaction. Once this process is complete we are left with methyl ester biodiesel and glycerol, which require separation either by sedimentation in tanks, or speeded up by centrifuging.
The glycerol can be further treated for use in the chemical industry or sold on in the condition it was separated.
When Rapeseed oil is reacted with methanol the biodiesel produced is Rape Methyl Ester (RME)
When Used Cooking Oil is reacted with Methanol, the biodiesel produced is Used Cooking Oil Methyl Ester (UCOME)
When canola oil (a variation of rape oil) is reacted with methanol the biodiesel produced is Canola Ethyl Ester (CEE)
Advantages of Using Biofuelsl
- When used as fuel in internal combustion engines biofuels emit less CO2 to the atmosphere than conventional fossil fuels. (Between 50%-60% less CO2 emissions.)
- Using biofuels can save the motorist money; new cars are road-taxed on CO2 emissions therefore; the lower the engines CO2 emissions the less road tax to pay.
- The Overseas Development Institute (ODI) has stated it believed the production of biofuels was relieving world poverty by increased employment in this field worldwide.
Disadvantages of Using Biofuels
- Some people claim that they are not carbon neutral because of the energy input in growing and harvesting the crops.
- There is a belief that the land used for growing biomass crops should be used for growing crops to feed the indigenous people.
- There is also the debate regarding biodiversity – land that would normally be habitats to animals and plants is being used to grow biofuels. Some have cited the Brazilian Rain Forests as an example.
Web Sites Visited
Biodiesel processing and production
GlobeCore. Biodiesel equipment plant, Biodiesel reactors producer