Lee Eng Oi

Abstract The increase in greenhouse gas emission due to the burning of fossil fuels since the last century has led to global warming. This has triggered numerous researches in green hydrocarbon alternatives from renewable oil. Microalgae is one of the potential sources of green hydrocarbon, which will reduce the dependency on fossil fuel. This is because microalgae have a high oil or lipid content, rapid growth rate, and high ability to sequester carbon dioxide. Besides that, their cultivation does not require arable land and will, therefore not compete with global food production. The current biofuel production is based on the transesterification of triglyceride to biodiesel which suffered from several drawbacks such as high acidity, high viscosity, and low heating value, etc . A more efficient reaction route needs to be developed to produce biofuel which possesses similar properties as the fossil-derived fuel. Therefore, this review aims to encompass the conversion of microalgae oil towards green hydrocarbons via various catalytic reactions. The fundamental chemistry and mechanisms involved in the conversion of microalgae oil to useful chemical products are also discussed in detail.

The greenhouse gases contributed by combustion of fossil fuel has urged the need for sustainable green fuel production. Deoxygenation is the most reliable process to convert bio-oil into green fuel. In this study, the deoxygenation of triolein was investigated via mesoporous TiO2 calcined at different temperature in the absence of external H2. The high conversion of fuel-liked hydrocarbons showed the in situ H2 produced from the reaction. The mesoporous TiO2 calcined at 500 °C (M500) demonstrated the highest activity, around 76.9% conversion was achieved with 78.9% selectivity to hydrocarbon. The reaction proceed through second order kinetic with a rate constant of 0.0557 g−1trioleinh−1. The major product of the reaction were diesel range saturated and unsaturated hydrocarbon (60%) further the formation of in situ H2. It is interesting to observe that higher calcination temperature improve crystallinity and remove surface hydroxyls, meanwhile increase the acid density and medium strength acid site. The conversion of triolein increased linearly with the amount of medium strength acid sites. This result suggests that medium-strength acidity of catalyst is a critical factor in determining deoxygenation activities. In addition, the presence of mesopores allow the diffusion of triolein molecules and improve the selectivity. Hence, mesoporous TiO2 with Lewis acidity is a fascinating catalyst and hydrogen donor in high-value green fuel.

H 2-Free catalytic deoxygenation of biomass-derived organic compounds is an important technology to produce green hydrocarbons without the relevant carbon footprint associated with H 2. In this work, the effects of the crystal size of zeolite Y (Y20: 20 nm, Y65: 65 nm, Y380: 380 nm and Y2750: 2.75 μm) on the deoxygenation reaction of triolein are reported. The reaction is performed under solvent-free conditions without the addition of hydrogen. As the crystal size decreases, the triolein conversion and the yield of de-oxygenated products increase. In addition, better product quality is obtained: higher hydrocarbon formation , higher diesel formation, lower formation of heavy hydrocarbons and higher diesel-to-gasoline ratio are observed. The high activity is related to the high concentration of acid sites, with accessible medium acid strength comprised of Brønsted and Lewis acid sites located on the external surface of the crystals. A linear relationship is observed between the rate constant of triolein depletion and the amount of medium strength acid sites. Further conversion of the fatty acids which are obtained from the hydrogenolysis of triolein (first rate-determining step) to deoxygenated products occurs on the surfaces of the zeolite crystals. The better accessibility of the Y20 sample with the smallest crystal size leads to improved catalytic performance. In comparison with previously reported catalysts, H 2-free deoxygenation over nanosized ze-olite Y appears to be an interesting industrial option to obtain high yields of green diesel.

The increase in greenhouse gas emission due to the burning of fossil fuels since the last century has led to global warming. This has triggered numerous researches in green hydrocarbon alternatives from renewable oil. Microalgae is one of the potential sources of green hydrocarbon, which will reduce the dependency on fossil fuel. This is because microalgae have a high oil or lipid content, rapid growth rate, and high ability to sequester carbon dioxide. Besides that, their cultivation does not require arable land and will, therefore not compete with global food production. The current biofuel production is based on the transesterification of triglyceride to biodiesel which suffered from several drawbacks such as high acidity, high viscosity, and low heating value, etc. A more efficient reaction route needs to be developed to produce biofuel which possesses similar properties as the fossil-derived fuel. Therefore, this review aims to encompass the conversion of microalgae oil towards green hydrocarbons via various catalytic reactions. The fundamental chemistry and mechanisms involved in the conversion of microalgae oil to useful chemical products are also discussed in detail.

The greenhouse gases contributed by combustion of fossil fuel has urged the need for sustainable green fuel production. Deoxygenation is the most reliable process to convert bio-oil into green fuel. In this study, the deoxygenation of triolein was investigated via mesoporous TiO2 calcined at different temperature in the absence of external H2. The high conversion of fuel-liked hydrocarbons showed the in situ H2 produced from the reaction. The mesoporous TiO2 calcined at 500 °C (M500) demonstrated the highest activity, around 76.9% conversion was achieved with 78.9% selectivity to hydrocarbon. The reaction proceed through second order kinetic with a rate constant of 0.0557 g−1trioleinh−1. The major product of the reaction were diesel range saturated and unsaturated hydrocarbon (60%) further the formation of in situ H2. It is interesting to observe that higher calcination temperature improve crystallinity and remove surface hydroxyls, meanwhile increase the acid density and medium strength acid site. The conversion of triolein increased linearly with the amount of medium strength acid sites. This result suggests that medium-strength acidity of catalyst is a critical factor in determining deoxygenation activities. In addition, the presence of mesopores allow the diffusion of triolein molecules and improve the selectivity. Hence, mesoporous TiO2 with Lewis acidity is a fascinating catalyst and hydrogen donor in high-value green fuel.

Titanium dioxide (TiO 2) has become increasingly popular as a catalyst. Although many applications of TiO 2 involve photocatalysis and photoelectrochemical reactions, there are numerous interesting discoveries of TiO 2 for other reactions. This review focuses on the recent development of TiO 2 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 TiO 2 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 TiO 2 .