Blending vegetable oil with solvents

Introduction to Blended Biofuels Diesel (BBD)

Blended Biofuels Diesel (BBD) is the process of making a fuel blend of oils with solvents. The purpose of making a biofuels blend diesel is to thin the resulting blended fuel to near the viscosity of diesel fuel, to improve the blend’s burn characteristics, and reduce its gel-point. The resulting solution should be a uniform solution without precipitates.

The common method of Blending Biofuels Diesel

The most common method of blending is to blend a petroleum distillate with a vegetable oil to thin it out to near the viscosity of diesel fuel. The most common petroleum distillates used in blending are gasoline (petrol), kerosene (paraffin) and/or diesel fuel. Note: kerosene (paraffin) is not a street-legal fuel in some nations, so there might be heavy fines resulting in their use.

Other commonly used solvents

Other solvents successfully used in making blended biofuels for diesel engines are: Acetone, Methyl Ethel Ketone (MEK), Pure Gum Turpentine (PGT), Xylene, Toluene, lacquer thinner, citrus oils, mineral spirits, paint thinner. Note: some of these solvents are not street-legal, so there might be heavy fines resulting in their use. They may also be hard on hoses and seals.

Theory behind Blending Biofuels Diesel

A solvent is used to reduce the viscosity of the source oil, because the viscosity of vegetable oils varies from plant oil to plant oil; however, the average is about 12 times as viscous as diesel fuel. Viscosity is also a function of temperature, thus blend ratio is also a function of operating temperature.

Commonly used solvents in Blending Biofuels Diesel

Since the viscosity of diesel fuel is twice that of gasoline (petrol), then one needs to use twice as much diesel fuel as gasoline (petrol) for the same thinning effect. And, the viscosity of kerosene (paraffin) is halfway between that of diesel fuel and gasoline (petrol), so half again as much kerosene (paraffin) is needed as gasoline (petrol) to produce a functional vegetable oil-based road fuel for diesel engines.

There are other factors in choosing a solvent for blending. The most common other factor is the gel-point of the resulting solution. The gel-point of oils and solvents is the point at which a substance begins to solidify.

Gel-point of Blended Biofuels Diesel

Vegetable oils tend to gel at about 32F (0c). Diesel fuel gels at about -22F (-30c). Kerosene (paraffin) gels at about -60F (-51c). And, gasoline (petrol) gels at about -131F (-90c).

However, a blend gels at a point between the gel points of its components, and is a function of the volumetric relationship between those components.

The typical functional blend ratios and useful temperature ranges

50% diesel fuel to 50% vegetable oil will run fine in a heated fuel line up to 212F (100c), and down to 28F (-2c) operating temperature.

30% kerosene (paraffin) to 70% vegetable oil will run fine in a heated fuel line up to 212F (100c), and down to 15F (-10c)operating temperature.

20% gasoline (petrol) to 80% vegetable oil will run fine in a heated fuel line up to 120F (50c) and down to 0F (-18c)operating temperature.

Blends of more than one solvent can be used

Some people prefer blending diesel fuel, vegetable oil and gasoline (petrol). Here are some functional relationships between the three components:

5% gasoline (petrol), to 40% diesel fuel, to 55% vegetable oil.

10% gasoline (petrol), to 30% diesel fuel, to 60% vegetable oil.

15% gasoline (petrol), to 20% diesel fuel, to 65% vegetable oil.

20% gasoline (petrol), to 10% diesel fuel, to 70% vegetable oil.

25% gasoline (petrol), to 0% diesel fuel, to 75% vegetable oil.

Blends with biodiesel

It is also common practice to blend solvents into biodiesel to prevent it from gelling at cold temperatures.

Gasoline (petrol), to Biodiesel blend ratios:

5% gasoline (petrol), to 95% biodiesel 28F (-2c) operating temperature.

10% gasoline (petrol), to 90% biodiesel 20F (-7c) operating temperature.

15% gasoline (petrol), to 85% biodiesel 10F (-12c) operating temperature.

20% gasoline (petrol), to 80% biodiesel 0F (-18c) operating temperature.

25% gasoline (petrol), to 75% biodiesel -10F (-23c) operating temperature.

Note: not all biodiesel gels at the same temperature, so biodiesel made from high melting point esters (HMPE) amy require higher levels of gasoline (petrol) added to it to prevent gelling.

The Blending Method

Blending methods vary; however, the most common method of making Blended Biofuels Diesel (BBD) is to blend the solvent with the source vegetable oil prior to settling, de-watering and filtering, because blending solvents with vegetable oils has three basic functions. Blending reduces the viscosity of the source oil, reduces its gel-point, and tends to force water, and other contaminants, out of solution. This means that thinned oil will drop its contaminant load much more quickly than the more viscous source oil. Where it is common for Straight Vegetable Oil users will settle their oil for weeks, blenders find they can settle their blend for as little as a few hours to a few days.

Thinned vegetable oils will also pass through a filter more quickly than the more viscous source oil. Where Straight Vegetable Oil users may gravity feed their SVO through a filter taking days, thinned vegetable oils will also pass through a filter in minutes.

Blended oils will also remain liquid at lower temperatures, so that filtering can take place at much colder temperatures than the source oil will allow.

A solvent that is readily soluble in vegetable oils, such as petroleum distillates, do not require a great deal of agitation to dissolve into the source vegetable oil, and will remain in solution indefinitely. Thus, most blenders fill a settling drum to about 75% full with the source oil, then pour on top of that oil their solvent, such as gasoline (petrol), then rock the drum a little, or swirl a paddle a few times around in the solution.

Settling

Settling Blended Biofuels Diesel (BBD) prior to filtering is simply allowing the blend to remain undisturbed in its settling drum for anywhere from 3 hours to 3 days.

After an adequate settling period most blenders will drain off the precipitates that settle to the bottom of the settling drum. To facilitate drain off the precipitates blenders will tend to have a cone-shaped, or bell-shaped bottom on their settling drum, and will have a valve at the bottom for draining off those precipitates.

Precipitates

The precipitates that settle out from a blend will begin to settle out within minutes after agitation ceases. Those precipitates are primarily particulates and liquids. The particulates precipitates are mostly particles of dust, free-carbon and food particles. The liquid precipitate is mostly water, but there can also be animal fat and lacquers. The water precipitate can contain dissolved components which are common in the commercial kitchen, such as: salt, sugar and spices. Animal fat is problematic because of its high melting point. Lacquer is naturally occurring in vegetable oils.

Filters and Filtering

Cartridge and bag filters that are deigned for filtering drinking water are commonly used for filtering Blended Biofuels Diesel (BBD). They are very effective for filtering these fuel blend; however, one must keep in mind that some nations blend alcohol at various percentages into gasoline (petrol) fuel stocks. The alcohol content in gasoline (petrol) can cause deterioration of fuel hoses, seals and filter seals, so if one blends with gasoline (petrol), then one should be aware of the alcohol content in this fuel. Or, filter with bag filters which are not affected by alcohol content in the fluid stream being filtered.

--Jhananda 19:49, 9 April 2011 (BST)