Sustainable bioethanol production from microalgae through ionic liquid as a potential catalyst: Review

Abstract

The trend of fuel consumption is very high, while the source of petroleum fuel that is used today is getting thinner. This requires another alternative fuel source that can be used as a substitute for petroleum. It is estimated that in 2030, the world will need more than 60% of the current energy supply. British Petroleum (BP), in 2005, also stated that 47.5% of Indonesia's energy needs were met by fuel oil. At present, Indonesia's petroleum reserves are only 1 percent of the world's total oil reserves. Meanwhile, according to BP Migas, Indonesia has been a full importer of oil (net oil importer) since July 2004. Therefore, new energy sources that have high economic value are needed from renewable materials or commonly called biofuels. Production of biofuels comes from the trans-esterification reaction of fatty acid which, produces methyl ester. Vegetables, animals, and microalgae can be used for fatty acid sources by their oil. Microalgae have a more beneficial prospect compared to vegetables and animals. Microalgae have a fast grow-rate, high oil productivity, low production cost, and not having a competition with food industries. Microalgae are photosynthetic microorganisms that can use sunlight and carbon dioxide to produce biomass. This biomass contains high levels of fat to be used as biofuel. Among microalgae, Botryococcus braunii is the one with high oil quantity inside their cells (25 - 75%). The process of converting microalgae biomass into bioethanol consists of delignification (separation of lignin), hydrolysis, fermentation (conversion of sugar monomers to alcohol), and product purification. Optimizing biofuels as a renewable energy source through the development of catalysts for trans-esterification reactions of fatty acids into methyl esters and conversion of biomass to ethanol. The ionic liquid is currently in the spotlight as a potential catalyst in various chemical reactions. Delignification process using ionic liquid can be performed at low temperature and pressure (below 100°C and atmospheric pressure), and almost all the lignin can be separated from the fiber. Solvent separation by adding anti-solvent. The boiling temperature of the ionic liquid is above 300°C. That is why the vapor pressure would be shallow, and almost all the solvent can be reused. Developments of advanced microalgae bioethanol production technologies are crucial in order to improve the cost-effectiveness in implementing a strategy for utilizing biomass as potential renewable energy.