Abstract
The depletion of fossil fuel reserves and increased environmental concerns related to fossil fuel production and combustion has forced the global communities to search for renewable fuels. In this regard, microalgae-based biodiesel has been considered as one of the interesting alternatives. Biodiesel production from the cultivation of microalgae is eco-friendly and sustainable. Moreover, microalgae have several advantages over other bioenergy sources, including their good photosynthetic capacity and faster growth rates. The productivity of microalgae per unit land area is also significantly higher than that of terrestrial plants. The produced microalgae biomass is rich with high quality lipids, which can be converted into biodiesel by transesterification reactions. Generally, the transesterification reactions are carried out in the presence of a homogeneous or heterogeneous catalyst. The homogeneous catalysts have many disadvantages, including their single use, slow reaction rate and saponification issues due to the presence of fatty acids in the feedstock. The acidic nature of the homogeneous catalysts also causes equipment corrosion. On the other hand, the heterogeneous catalysts offer several advantages, including their reusability, higher reaction rate and selectivity, easy product/catalyst separation and low cost. Due to these facts, the development of solid phase transesterification catalysts have been receiving growing interest. The present review is focused on the use of heterogeneous catalysts for biodiesel production from microalgal oil as a reliable feedstock with a comparison to other available feedstocks. It also highlights optimal reaction conditions for maximum biodiesel yields, reusability of the solid catalysts, cost, and environmental impact. The superior lipid content of microalgae and the efficient concurrent esterification and transesterification of the solid acid−base catalysts can offer new advancements in biodiesel production.
Highlights
Current worldwide energy resources are mostly based on non-renewable fossil fuels which are the major source of greenhouse gas CO2 emissions [1,2]
The present review focuses on the use of solid base, acid, acid−base and biocatalysts for biodiesel production from microalgal oil as the reliable feedstock with comparison to other available feedstock
Microalgal lipid is mostly triacylglyceride that can be transformed into biodiesel as fatty acid methyl esters via transesterification
Summary
Current worldwide energy resources are mostly based on non-renewable fossil fuels which are the major source of greenhouse gas CO2 emissions [1,2]. Catalysts 2020, 10, 1025 different challenges related to renewable energy sources, biodiesel is a promising alternative for petroleum-based diesel fuel [13]. CO2 is soap the carbon resource for the growth of homogeneous catalytic transesterification, the postseparation treatment between the end-product microalgae [44], (6) biodiesel produced from algal lipid is nonhazardous and highly eco-friendly [44], biodiesel and glycerol needs lengthy increases production the cost of the endcustomary products [28,29,30]. The microalgae have superior lipid production yields, which have catalytic transesterification, including separation of biodiesel from glycerol, catalyst recycling/reuse, been noticed between 58,000. Viriya-empikul et al (2012) investigated Ca-based solid catalysts derived from industrial waste for biodiesel production from palm oil [38]. This review highlights the suitable heterogeneous catalysts for biodiesel production from microalgae in terms of the yield of biodiesel, optimal reaction conditions, reusability of the catalyst, cost and environmental sustainability [39]
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