More than 10 million tons of biodiesel fuel (BDF) have been produced in the world from the transesterification of vegetable oil with methanol by using acid catalysts (sulfuric acid, H₂SO₄), alkaline catalysts (sodium hydroxide, NaOH or potassium hydroxide, KOH), solid catalysts and enzymes. Unfortunately, the price of BDF is still more expensive than that of petro diesel fuel due to the lack of a suitable raw material oil. Here, we review the best selection of BDF production systems including raw materials, catalysts and production technologies. In addition, glycerol formed as a by-product needs to be converted to useful chemicals to reduce the amount of glycerol waste. With this in mind, we have also reviewed some recent studies on the utilization of glycerol.

Various aromatic compounds, i.e., nitrobenzene, aniline, phenol, benzoic acid, salicylic acid, 2-chlorophenol, 4-chlorophenol, styrene, chlorobenzene, toluene, ethylbenzene and n-propylbenzene were decomposed under identical ultrasonic irradiation conditions. The relationships between the initial rates of degradation of these aromatic compounds and their physicochemical parameters were systematically investigated. It was revealed that some correlations between the degradation rates and parameters of volatility, Henry's law constant and vapor pressure, were observed only in the limited high range of parameters. It was suggested that the Henry's law constant and vapor pressure had influenced on the rate of degradation for some of the tested aromatic compounds. In contrast, better correlations between the initial rates of degradation and hydrophobic parameters, water solubility and LogP (water-octanol partition coefficient), were observed over the wide range of chosen parameters. These results meant that the hydrophobicity of the compounds significantly affected their accumulation at the gas-liquid interface of the bubbles and it was the most important factor for the sonochemical degradation of aromatic compounds. In particular, for the sonolysis of water-insoluble organic compounds, LogP was found to be the representative parameter for understanding the hydrophobic properties of water-insoluble compounds.

A new, homogeneous method for producing biodiesel fuel (BDF), achieving a minimum emission of waste and a low consumption of energy, was developed by adding organic solvents such as acetone to a reaction mixture of oil and methanol with an alkaline catalyst. By adding acetone and a smaller amount of catalyst at room temperature, fatty acid methyl ester (FAME) was formed within 5 min with a quality satisfying the international BDF standards, even in the coexistent of water in the raw material. The difference in the kinetic data when using isopropyl alcohol (IPA) (all compounds are in a single phase) and acetone (all compounds except glycerin are in a single phase), shows that the retardation of FAME formation in the presence of glycerin product is not due to the reverse reaction but to the removal of methanol and KOH catalyst from the reaction phase by the precipitated glycerin produced during the final stages of the reaction.