Coconut Oil as Biofuel

Posted by Anoop Gupta to Energy, 3rd June 2010

Coconut oil is a widely used liquid biofuel. It 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.

 

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, best quality oil is obtained from mature coconuts between 12 and 15 months old that have been processed within a few hours after opening. Oil yield depends on the age and species of coconut but is approximately 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 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. As a fairly simple triglyceride, coconut oil will burn quite readily. However, since most engines are designed around the lower acid content and specific viscosities/combustion properties of refined fuels they will eventually sustain damage if straight 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, although this is less of a problem in warmer climates. In vehicles, 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 resulting from the use of straight oil.

NB. Manufacturer warranties are sometimes void if straight oils or 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 accordingly as it is largely dependent on the 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 measured by brake mean effective pressure (BMEP), which reduces by ~20% and brake-specific fuel consumption (BSFC), which increases by ~20%, both when 100% coconut oil is used. The relationships between these variables are actually quite complex but they can be approximated to linear in the real world so the quoted pecentages could be used to estimate 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 also linear. 

 

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

 

Making Coco-Biodiesel

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 yields good quality fuel in a garden shed with readily available equipment. Bowser-quality biodiesel has less than 0.05% water/sediment content and less than 0.25% w/v total glycerol content. Good quality DIY fuel should gel at around 10°C and be as clear as cooking oil. A tighter technique means a better quality fuel and lower CO2 emissions.

Basic transesterification method:

 

1. Prepare methoxide by mixing methanol and hydroxide in predetermined ratio.

2. Transesterify pure coconut oil by mixing with methoxide at low heat.

3. Release biodiesel by washing mixture with water, dissolving glycerine by-product.

4. Decant biodiesel carefully after mixture settles and cools, leaving glycerol solution.

5. Distill remaining methanol for re-use, leaving glycerine solution.

6. Evaporate water from glycerine solution and fashion leftover solids into Best Kwality Kokonut Soap.

7. Compost any remains away from water sources.

A walkthrough of the entire process can be found here.

 

NB. Methoxide is a 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.

 

Microeconomics

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 their local market price. If coconuts are plentiful and the market prices are comparable with other fuels, typical payback time is around 2-4 years.

 

The outlook is also promising for domestic electricity generation. A typical village house might use 10kWh/day using a diesel generator that consumes 0.3 litres per kWh. At this rate, a household of four adults will need two days to extract enough coconut oil to meet their monthly electricity requirement, which is feasible in most village economies. Electricity from coconut oil typically costs 2-6 times that of grid-supplied electricity. The difference is due to the labour cost of harvesting and processing the coconuts as well as the comparative costs of grid connection versus that 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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