Coconut Oil as Biofuel
Posted by Energy, 3rd June 2010
Coconut oil is a widely used liquid biofuel that is clean, relatively cheap, easy to extract, non-toxic and aromatic. It can also be used for cooking, in spreads, in health food products and cosmetics, and as a medication vector. The leftover coconut meal can be used to make flour, biscuits, chicken pellets and fish food while the husks and shells with their high heating value are an efficient dry fuel, making the common coconut one of the most useful nuts around.
As engine fuel, coconut oil can be used in three ways:
- As a direct substitute for petroleum diesel.
- As an additive to petroleum diesel or bio-diesel.
- As the base ingredient of bio-diesel.
Oil Extraction Process
Raw coconut oil is extracted simply by removing the husks and shells, then grating, drying and pressing the remaining coconut meat (copra). Copra can be pressed using traditional methods or the more efficient Direct Micro Expelling (DME) method invented by Kokonut Pacific. Irrespective of the method, the best quality oil is obtained from mature coconuts between 12 and 15 months old that have been processed within a few hours after opening. The yield depends on the age and species of coconut but is around 50ml per nut. An experienced group of four people with reliable equipment and a continuous supply of coconuts can comfortably produce 50-60 litres of oil per day. The extracted oil can be used in raw form or converted into biodiesel.
Download the file in the brown box at top right for a pictorial of a village operation using the DME method.
Raw Oil as Diesel Engine Fuel
Diesel engines are known as the beasts of burden of the engine world because of their high torque, robust construction and the fact that they consume almost any kind of oil. Most simple triglycerides, such as coconut oil, will burn quite readily. However, since most diesel engines are designed around the lower acid content and specific viscosities/combustion properties of refined fuels they will eventually sustain damage if raw oil is used for extended periods.
The two main causes of damage are coking and clogging. Coking is the deposition of solid carbon inside the engine due to incomplete fuel combustion, which may eventually cause the engine to seize up even with regular cleaning. Clogging occurs when the oil starts to solidify or gel inside the engine, which occurs at 22-25°C for 100% coconut oil. This is less of a problem in warmer climates. A pre-injection fuel heater can be installed to prevent the oil from gelling, although it is more common simply to use a blended fuel as this addresses most engine problems without the need for engine modifications.
NB. Manufacturer warranties are sometimes void if raw oils or other non-approved fuels are used.
Coconut Oil/Biodiesel Fuel Blends
Blended fuels are commonly used if coconut oil is to be used over long periods. A widely-used blend is 49% coconut oil, 49% biodiesel and 2% kerosene, with variations to suit local cost, availability and climate. Fuel performance will vary according to fuel/oil ratio. For single injection engines, an increase in oil concentration leads to an increase in fuel consumption and reduced engine power. This is usually measured by brake mean effective pressure (BMEP), which reduces by ~20% when 100% coconut oil is used, and brake-specific fuel consumption (BSFC), which increases by ~20% in the same scenario. The relationships between these variables are complex but can be approximated to linear for all practical purposes, which means these percentages can be used to extrapolate estimates of fuel performance characteristics for other fuel/oil ratios.
Emissions from Fuel Blends
Engine emissions are also related to the fuel/oil ratio. Smoke, NOx and CO2 emissions decrease as the percentage of coconut oil in the fuel mixture increases, reducing by ~75% for smoke, ~40% for NOx and ~15% for CO2 when 100% coconut oil is used. These relationships are linear so emissions estimates for other fuel blends can also be extrapolated from these values.
Data source: Performance and emission characteristics of a diesel engine fueled with coconut oil/diesel fuel blend
Herchel T.C. Machacon, Seiichi Shiga, Takao Karasawa, Hisao Nakamura, Biomass and Bioenergy 20 (2001) pp63-69
The cleanest way to use coconut oil in diesel engines is to convert it to biodiesel by transesterification. While best results are obtained in a refinery or a chemistry lab, this is a fairly simple process that can still yield good quality fuel in a garage or garden shed with simple household equipment. Refined biodiesel has less than 0.05% water/sediment content and less than 0.25% w/v total glycerol content but it only needs to be as clear and non-viscous as is needed by the engine for it to function. As long as the fuel lines remain unclogged the fuel filter will capture any unfiltered particulates. The fuel filter will therefore need to be replaced more often. The test of a reasonable quality DIY fuel is if it is miscible, gels at around 10°C and a glass of it is not too cloudy to see through. The tighter the transesterification and filtering technique, the better the fuel quality, the lower the noxious emissions and the better the engine performance.
Basic transesterification method:
1. Prepare methoxide by mixing methanol and hydroxide in 1L:17.5g ratio.
2. Transesterify pure coconut oil by mixing with methoxide in 5:1 ratio at 55°C heat.
3. Release biodiesel by washing mixture with water, thereby dissolving glycerine by-product.
4. Decant biodiesel carefully after mixture settles and cools, leaving glycerol solution.
5. Distill methanol at 65°C heat from remaining glycerol for re-use, or boil it off, leaving glycerine solution.
6. Evaporate water from glycerine solution and fashion leftover solids into cakes of Best Kwality Kokonut Soap.
7. Compost any remains away from water sources.
A walkthrough of the entire detailed process can be found here.
NB. Sodium Methoxide is a corrosive and dangerous chemical so appropriate safety precautions should be taken whenever it is used. There may also be local regulations and excises relating to the commercial manufacture and/or sale of biodiesel and the disposal of glycerol.
The microeconomic outlook is good for small-scale coconut oil production at the source. If manual extraction methods are used, four people can comfortably produce about 50 litres of coconut oil per day. If the Kokonut Pacific small business model is used, start-up costs for a 50L/day operation are less than A$25k for a fully installed village-style plant. Whether the oil is more profitable as fuel oil, biodiesel or cooking oil depends on the local market price of these products at the time of commerce. If coconuts are plentiful and other fuels are not under-priced, typical payback time on a $25k investment is 2-4 years.
The outlook is also promising for domestic electricity generation, although this will largely depend on the local price and availability of methanol, hydroxide and, of course, coconuts. A village house that uses 10kWh/day using a diesel generator that consumes 0.3 litres of biodiesel per kWh, will need four adults, two days labour and about 800 coconuts to produce enough biodiesel to meet their monthly requirements. Electricity from coconut oil typically costs 2-6 times that of urban grid-supplied electricity, so its economic feasibility is dependent on the comparitive cost of the grid connection and the labour cost of harvesting and processing the coconuts plus the purchase cost of a diesel generator.
More information on this topic can be found in the discussion thread at http://www.ewb.org.au/discussions/52/10523
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