Biodiesel is an alternative biofuel that can replace diesel oil without requiring modifications to the engine and advantageously produces cleaner emissions. Biodiesel can be produced through transesterification process between oil or fat and alcohol to form esters and glycerol. The transesterification can be carried out with or without a catalyst. The catalyzed production of biodiesel can be performed by using homogeneous, heterogeneous and enzyme. Meanwhile, non-catalytic transesterification with supercritical alcohol provides a new way of producing biodiesel. Microwave and ultrasound assisted transesterification significantly can reduce reaction time as well as improve product yields. Another process, a plasma technology is promising for biodiesel synthesis from vegetable oils due to very short reaction time, no soap formation and no glycerol as a by-product. This paper reviews briefly the technologies on transesterification reaction for biodiesel production using homogeneous, heterogeneous, and enzyme catalysts, as well as advanced methods (supercritical, microwave, ultrasonic, and plasma technology). Advantages and disadvantages of each method were described comprehensively.

Biodiesel synthesis reaction routes from palm oil using plasma electro-catalysis process over Dielectric-Barrier Discharge (DBD) plasma reactor were studied. The study was focused on finding possible reaction mechanism route during plasma electro-catalysis process. The prediction was performed based on the changes of Gas Chromatography Mass Spectrometer (GC-MS) and Fourier Transform Infra Red (FT-IR) analyses to the biodiesel products with respect to time length of plasma treatment. It was found that main reaction mechanism occurred in the plasma electro-catalysis system was non-thermal pyrolysis rather than transesterification. The main reactions within the plasma treatment were due to collision between high energetic electrons (supplied from high voltage power supply through high voltage electrode) and the reaction mixtures. The high energetic electrons affected the electrons pair of covalent bonding to be excited or dissociated even ionized at higher energy. Therefore, this plasma electro-catalysis system was promising for biodiesel synthesis from vegetable oils due to only very short time reaction was needed, even no need a catalyst, no soap formation, and no glycerol by-product. This system could produce fatty acid methyl ester yield of 75.65% at 120 seconds and other possible chemicals, such as alkynes, alkanes, esters, carboxylic acid, and aldehydes. However, during the plasma process, the reaction mechanisms were still difficult to be controlled due the action of available high energetic electrons. The advanced studies on how to control the reaction mechanism selectively in the plasma electro-catalysis will be published elsewhere. © 2014 by Authors, Published by BCREC Group. This is an open access article under the CC BY-SA License (https://creativecommons.org/licenses/by-sa/4.0)

This paper was purposed for testing reusability and stability of calcium oxide-based catalyst (K2O/CaO-ZnO) over transesterification reaction of soybean oil with methanol to produce biodiesel. The K2O/CaO-ZnO catalyst was synthesized by co-precipitation method of calcium and zinc nitrates followed by impregnation of potassium nitrate. The fresh and used catalysts were tested after regeneration. The catalysts were characterized by Scanning Electron Microscopy (SEM), X-ray Diffraction (XRD), and BET Surface Area in order to compare the catalyst structure between the fresh and used catalysts. The catalyst testing in transesterification proses was carried out at following operating conditions, i.e. catalyst weight of 6 wt.%, oil to methanol mole ratio of 1:15, and temperature of 60 oC. In addition, metal oxide leaching of K2O/CaO-ZnO catalyst during reaction was also tested. From the results, the catalysts exhibited high catalytic activity (80% fatty acid methyl ester (FAME) yield after three-cycles of usage) and acceptable reusability after regeneration. The catalyst also showed acceptable stability of catalytic activity, even after three-cycles of usage.

The production of biodiesel using zeolite catalysts from geothermal solid waste has been studied. This study aims to make zeolite catalysts as catalysts in biodiesel production, assessing the effect of catalyst concentration, and temperature in the esterification–transesterification process on the biodiesel yield produced. The results showed that the synthesized zeolite catalyst was an analcime zeolite catalyst (Al_1.9Na_1.86O₁₂Si₄). The biodiesel yield of 98.299% with 100% fatty acid alkyl ester (FAAE) content was achieved at a catalyst concentration of 5%wt and a reaction temperature of 300 °C for one-hour reaction time. The yield of biodiesel decreased with repeated catalysts, which experienced morphological changes before and after three usage times. Consequently, in this case, the catalyst cannot be regenerated.

The objective of this research was to utilize microalgae Chlorella sp. and Spirulina sp., as biosorption agents for heavy metals removal available in textile waste water. The biosorption of Cu and Cr ions from textile waste water solutions by immobilized algae (Spirulina and Chlorella) were tested under laboratory conditions as a function of waste concentration (15-50% dilution) and ratio of bead and waste water (1:1-1:3). Experimental results showed that the Langmuir adsorption models were suitable for describing the short-term biosorption of by all algal species. The best ratio of bead: wastewater (v/v) for removal heavy metal in textile wastewater was 1:3. The maximum Cu removed from the waste was 89% while Cr was removed with 90% by using Chlorella sp. The algae Spirulina showed a higher removal capacity of 90%. The maximum absorption capacity of Cu was achieved at 16.2 and 13.6 mg/g by using Spirulina and Chlorella, respectively, while the maximum sorption capacity for Cr was achieved at 1.95 and 1.45 mg/g for algae Spirulina and Chlorella, respectively.

Energy demand will increase along with the increase in population. The current energy demand is dominated by non-renewable energy as it could reduce dependence on fossil energy sources; hence, it is imperative to be developed. Biodiesel with waste cooking oil as its raw material is one of the renewable energies currently being developed. Catalyst can be utilized to improve the quality of biodiesel product and process. The major content in solid waste of geothermal power plant is silica oxide, while dolomite contains magnesium oxide and calcium oxide. This study aims to test the MgO-CaO/SiO2 catalyst performance from geothermal waste and dolomite in biodiesel production. The results of catalyst characterization based on FTIR, SEM, and BET tests indicates a successful impregnation method in MgO-CaO/SiO2 catalyst production. The result shows that the best variable to produce biodiesel is at the ratio of MgO-CaO: SiO2 is 15:85. The conversion of biodiesel using this variable is 92.63%. The overall results of biodiesel obtained in this study have a good quality and is in accordance with SNI 7182-2015.