Hwai Chyuan Ong

Enzymatic transesterification for biodiesel production: a comprehensive review

Biodiesel is a type of renewable fuel and a potential alternative for continuously consumed fossil resources. Currently, the method applied for biodiesel production is transesterification which is divided into non-catalyzed reaction, chemical-catalyzed reaction and enzymatic reaction. Enzymatic reaction is more advantageous than the other methods because of its mild reaction conditions, easy product recovery, no wastewater generation, no saponification and higher quality of products. The main component in this reaction is an enzyme called lipase which can catalyze wide variety of substrate including free fatty acids. Two other main raw materials for biodiesel synthesis are oil and acyl acceptor such as alcohol. Biodiesel catalyzed by enzyme is affected by many factors such as lipase specificity, lipase immobilization, oil composition and purity, oil to acyl acceptor molar ratio, acyl acceptors, temperature, and water content. Many methods have been tested to manipulate these factors and improve the enzymatic reaction for biodiesel production. These methods include combination of lipases, enzyme pretreatment, enzyme post treatment, methanol addition technique, use of solvent and silica gel, and reactor design. This paper will critically discuss the three major components of enzymatic production of biodiesel and the methods used to improve enzymatic reaction, as well as a review on its economic evaluation and industrial scale production.

Recent developments on algal biochar production and characterization

Algal biomass is known as a promising sustainable feedstock for the production of biofuels and other valuable products. However, since last decade, massive amount of interests have turned to converting algal biomass into biochar. Due to their high nutrient content and ion-exchange capacity, algal biochars can be used as soil amendment for agriculture purposes or adsorbents in wastewater treatment for the removal of organic or inorganic pollutants. This review describes the conventional (e.g., slow and microwave-assisted pyrolysis) and newly developed (e.g., hydrothermal carbonization and torrefaction) methods used for the synthesis of algae-based biochars. The characterization of algal biochar and a comparison between algal biochar with biochar produced from other feedstocks are also presented. This review aims to provide updated information on the development of algal biochar in terms of the production methods and the characterization of its physical and chemical properties to justify and to expand their potential applications.

Synthesis, characteristics and sonocatalytic activities of calcined γ-Fe2O3 and TiO2 nanotubes/γ-Fe2O3 magnetic catalysts in the degradation of Orange G

In this work, γ-Fe2O3 and TiO2 NTs/γ-Fe2O3 composites with good magnetism and sonocatalytic activity were prepared by a facile polyol method and utilize the principle of isoelectric point method, respectively. The structural and magnetic features of the prepared calcined γ-Fe2O3 and composite catalysts were investigated by transmission electron microscopy (TEM), powder X-ray diffraction (XRD), surface analysis, UV-Vis diffuse reflectance spectra (UV-Vis DRS), vibrating sample magnetometry (VSM) and zeta potential analysis. The effects of calcination temperature on γ-Fe2O3 phase variation, physical properties and sonocatalytic properties were investigated. The porosity, specific surface area, band gap energy and sonocatalytic activity of γ-Fe2O3 were gradually decreased with calcination temperature increased. TiO2 NTs/γ-Fe2O3 with appropriate composition and specific structural features possess synergetic effects such as efficient separation of charge carriers and hydroxyl radicals produced by heterogeneous fenton and fenton-like reactions. This enhanced the sonocatalytic activity for the degradation of Orange G under ultrasonic irradiation. The sonocatalytic reactions obeyed pseudo first-order kinetics. All these information provide insight into the design and development of high-efficiency catalyst for wastewater treatment.

A perspective on bioethanol production from biomass as alternative fuel for spark ignition engine

The increasing consumption of fossil fuels has led to the development of alternative fuels for the future. Domestic biofuel production and the utilization of alternative fuels can decrease dependency on petroleum oil, reduce trade deficits, reduce air pollution and reduce carbon dioxide emission. Bioethanol is a renewable fuel produced by the fermentation of sugar which is derived from plants such as sugarcane or beet, maize, or cassava etc. However, bioethanol consumption in an engine is approximately 51% higher than gasoline since the energy per unit volume of ethanol is 34% lower than for gasoline. Bioethanol is an oxygenated fuel that contains 35% oxygen, which can reduce particulate matter and NOx emissions caused by combustion of the fuel. Therefore, bioethanol–gasoline blends can significantly reduce petroleum use and GHG emission. In addition, utilization of lignocellulosic materials in bioethanol production is the most viable pathway from an environmental point of view. This paper reviews the current status and technologies involved in bioethanol production and the properties and engine performance from various biomass feedstocks which are the recommended sustainable alternative fuel in the future.

Biodiesel production from Calophyllum inophyllum−palm mixed oil

ABSTRACT The objective of this study is to investigate the biodiesel production from Calophyllum inophyllum −palm mixed oil. The C. inophyllum–palm biodiesel (C. inophyllum palm oil methyl ester, CPME) is first produced by mixing the crude oils at an equal ratio of 50:50 vol%, followed by degumming, acid-catalyzed esterification, purification, and, last, alkaline-catalyzed transesterification. With this systematic procedure, the acid value of the CPME is 0.4 mg KOH/g, resulting in a significant enhancement of oxidation stability (114.21 h). The results indicate that the fatty acid methyl ester composition of the CPME may be the reason for its larger higher heating value (39.4 MJ/kg) and lower kinematic viscosity (4.15 mm2/s). In short, CPME satisfied the ASTM D6751 and EN 14214 standards as a promising alternative fuel in the future.

A comparative study of biodiesel production methods for Reutealis trisperma biodiesel

ABSTRACT In this study, three types of biodiesel production methods are compared in order to maximize Reutealis trisperma biodiesel yields and it is found that the best method is esterification-neutralization-transesterification. The optimum methanol to oil molar ratio, catalyst concentration, reaction temperature, and reaction time are also determined from laboratory experiments and modeling using response surface methodology. There is excellent agreement between the predicted and experimental Reutealis trisperma biodiesel yields under optimum process conditions, with a value of 99.23 and 98.72%, respectively. The physicochemical properties of the Reutealis trisperma biodiesel also fulfill the fuel specifications of the ASTM D6751 standard.

Recent advances of titanium dioxide (TiO2) for green organic synthesis

Titanium dioxide (TiO2) has become increasingly popular as a catalyst. Although many applications of TiO2 involve photocatalysis and photoelectrochemical reactions, there are numerous interesting discoveries of TiO2 for other reactions. This review focuses on the recent development of TiO2 as a catalyst in green organic synthesis including in hydrodeoxygenation, hydrogenation, esterification/transesterification, the water–gas shift reaction, and visible light-induced organic transformation owing to its strong metal-support interaction (SMSI), high chemical stability, acidity, and high redox reaction at low temperature. The relationship between the catalytic performance and different metal or metal oxide dopants, and different polymorphs of TiO2 are discussed in detail. It is interesting to note that the reduction temperature and addition of promoters have a significant effect on the catalytic performance of TiO2.

Optimization of extraction of lipid from Isochrysis galbana microalgae species for biodiesel synthesis

ABSTRACT Microalgae are promising alternative plant sources for biodiesel production because of the significant increase in lipid yield through heterotrophic cultivation and genetic engineering approaches. This study aims to evaluate the extraction and conversion of lipids from Isochrysis galbana. Response surface methodology (RSM) was used to optimize lipid extraction and thereby obtain high yields from the four microalgae species. The optimal lipid yields for Isochrysis galbana is 8.41 wt%. Moreover, the dominant lipid composition found from Isochrysis galbana extractions was palmitic acid (C16:0) at 22.3%. The high saturated acid of Isochrysis galbana contributed to the improved biodiesel properties because biodiesel quality is influenced by the lipid composition of microalgae species. The study employed the two-step esterification–transesterification process to convert the microalgae oil into biodiesel, glycerol, and water. The FAME content is 99.7% under the methanol to oil molar mass of 12:1, 1 wt%, 65°C, and 800 rpm. Furthermore, the main biodiesel properties, such as viscosity, higher heating value, and iodine value, were measured according to ASTM D6751 and EN 14124. Results show that microalgae oil can potentially be used as biofuel in future applications.

A comparative study of ultrasound and infrared transesterification of Sterculia foetida oil for biodiesel production

ABSTRACT In this study, biodiesel production using ultrasound and infrared techniques is introduced. The ultrasound and infrared techniques are more efficient for biodiesel production since they improve the mass transfer between the immiscible reactants, increase chemical reactions, and decrease the reaction time and energy consumption. The effect of the reaction time on the acid value of the esterified Sterculia feotida oil is also investigated and it is found that the acid value is 0.76 and 0.85 mg KOH/g for the ultrasound and infrared technique, respectively, at a reaction time of 60 min. In addition, it is found that the biodiesel yield obtained from the ultrasound technique is higher (99.41%) compared to the infrared technique (98.55%) at a reaction time of 60 min. The KOH catalyst is analyzed for both of these techniques and it is found that the ultrasound technique gives faster absorbed reaction compared to the infrared technique. Hence, it can be concluded that the ultrasound and infrared transesterification techniques are promising techniques for biodiesel production.

A review on the engine performance and exhaust emission characteristics of diesel engines fueled with biodiesel blends

Biodiesels have gained much popularity because they are cleaner alternative fuels and they can be used directly in diesel engines without modifications. In this paper, a brief review of the key studies pertaining to the engine performance and exhaust emission characteristics of diesel engines fueled with biodiesel blends, exhaust aftertreatment systems, and low-temperature combustion technology is presented. In general, most biodiesel blends result in a significant decrease in carbon monoxide and total unburned hydrocarbon emissions. There is also a decrease in carbon monoxide, nitrogen oxide, and total unburned hydrocarbon emissions while the engine performance increases for diesel engines fueled with biodiesels blended with nano-additives. The development of automotive technologies, such as exhaust gas recirculation systems and low-temperature combustion technology, also improves the thermal efficiency of diesel engines and reduces nitrogen oxide and particulate matter emissions.