Turning waste vegetable oil into diesel oil - a realistic proposition or a pipedream?

It is technically possible to run a diesel car or truck on straight vegetable oil (SVO). However, the oil must be preheated to reduce viscosity and surface tension. The use of SVO for fuel is not recommended as a long-term solution due to build-up of carbon deposits in the engine and accumulation of SVO in the lubricant, which causes reduced engine life.

It is more realistic to use vegetable oil as fuel by transforming it into biodiesel, which has a lower boiling point and viscosity and yields better engine performance. The chemical process by which oil or fat is converted into biodiesel is called transesterification, which involves alcohol (methanol) and a catalyst (sodium hydroxide or lye). Two gallons of cooking (vegetable) oil will make about a gallon of biodiesel.

Non-toxic and biodegradable, biodiesel is actually cleaner than petroleum diesel. Emissions from biodiesel contain less sulfur dioxide, carbon dioxide, particulate matter (or soot, which exacerbates asthma), and no carbon monoxide. Biodiesel is commonly blended with standard diesel. The B5 blend (5% biodiesel and 95% petroleum diesel) has been approved for all diesel engines.

Though worldwide availability of biodiesel is growing, it is tiny compared to the use of standard petroleum. In 2010, the market for biodiesel was approximately 2 billion gallons in the U.S. and 2.5 billion in Europe. Since biodiesel has reduced contribution to greenhouse gas, some governments tax it favorably compared to gasoline.

Every year, plants, factories and restaurants produce billions of gallons of used cooking oil. If this used oil can be recycled and converted into biodiesel, tons of waste grease would be diverted from city pipes and landfills, leading to improved air and water quality and reducing blockages in sewer pipes. Waste cooking oil can be harvested from developed areas as a so-called urban crop, instead of using virgin vegetable oil. Some restaurants can actually generate revenue by selling their used cooking oil. Some cities have private companies or public services to haul away waste grease for free.

Recycled cooking oil is primarily used in animal feed, soap manufacturing and biofuel production. The oil recycling industry is threatened by alternative biofuel production inputs, such as soybeans or sugarcane, which may be heavily government subsidized. The industry faces significant uncertainty.


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