Ways to reduce the high viscosity of Vegetable Oils

Different ways have been considered to reduce the high viscosity of vegetable oils:

1. Dilution of 25 parts of vegetable oil with 75 parts of diesel fuel.

2. Microemulsions with short chain alcohols such as ethanol or methanol.

3. Transesterification with ethanol or methanol, which produces biodiesel.

4. Pyrolysis and catalytic cracking, which produces alkanes, cycloalkanes, alkenes,

and alkylbenzenes.

1. Dilution of oils with solvents and microemulsions of vegetable oils lowers the viscosity, some engine performance problems, such as injector coking and more carbon deposits, etc. To dilute vegetable oils the addition of 4% ethanol increases the brake thermal efficiency, brake torque, and brake power, while decreasing brake specific fuel consumption. Since the boiling point of ethanol is less than those of vegetable oils the development of the combustion process may be assisted through unburned blend spray. The viscosity of oil can be lowered by blending with pure ethanol. 25 parts vegetable oil and 75 parts diesel have been blended as diesel fuel. This mixture is not suitable for long-term use in a direct injection engine.

2. Another way to reduce of the high viscosity of vegetable oils, microemulsions with immiscible liquids such as methanol, ethanol, and ionic or non-ionic amphiphiles. Short engine performances of both ionic and non-ionic microemulsions of ethanol in soybean oil were nearly as good as that of No. 2 diesel fuel.. All microemulsions with butanol, hexanol, and octanol met the maximum viscosity requirement for No. 2 diesel fuel. The 2-octanol is an effective amphiphile in the micellar solubilization of methanol in triolein and soybean oil. Lower viscosities and better spray patterns (more even) could be achieved with an increase of butanol. All microemulsions with butanol, hexanol, and octanol meet the maximum viscosity requirement for No. 2 diesel. The 2-octanol is an effective amphiphile in the micellar solubilization of methanol in triolein and soybean oil. Methanol is often used due to its economic advantage over ethanol.

3. Among all these alternatives, transesterification seems to be the best choice, as the physical characteristics of fatty acid esters (biodiesel) are very close to those of diesel fuel, and the process is relatively simple. In the esterification of an acid, an alcohol acts as a nucleophilic reagent; in hydrolysis of an ester, an alcohol is displaced by a nucleophilic reagent. Transesterified vegetable oils have proven to be a viable alternative diesel engine fuel with characteristics similar to those of diesel fuel. The transesterification reaction proceeds with a catalyst or any unused catalyst by using primary or secondary monohydric aliphatic alcohols having 1–8 carbon atoms as follows. Transesterification is catalyzed by a base (usually alkoxide ion) or acid (H2SO4 or dry HCl). The transesterification is an equilibrium reaction. To shift the equilibrium to the right, it is necessary to use a large excess of the alcohol or else to remove one of the products from the reaction mixture. Furthermore, the methyl or ethyl esters of fatty acids can be burned directly in unmodified diesel engines, with very low deposit formation. Although short-term tests using neat vegetable oil show promising results, longer tests lead to injector coking, more engine deposits, ring sticking, and thickening of the engine lubricant. These experiences lead to the use of modified vegetable oil as a fuel. Technical properties of biodiesel, such as the physical and chemical characteristics of methyl esters related are close to, such as physical and chemical characteristics of methyl esters related to its performance in compression ignition engines are close to petroleum diesel fuel. Compared with transesterification, the pyrolysis process has more advantages. The liquid fuel produced from pyrolysis has similar chemical components to conventional petroleum diesel fuel.

4. Pyrolysis utilizes biomass to produce a product that is used both as an energy source and a feedstock for chemical production. Compared with transesterification, the pyrolysis process has more advantages. The liquid fuel produced from pyrolysis has similar chemical components to conventional petroleum diesel fuel. Vegetable oils can be converted to a maximum of liquid and gaseous hydrocarbons by pyrolysis, decarboxylation, deoxygenation, and catalytic cracking processes.