Steep hikes of petroleum prices and rising demand of petroleum products compels the scientific society to think for the renewable alternative fuels like biodiesel. Biodiesel production is generally carried out through the process of transesterification reaction. The reaction is facilitated with a suitable catalyst either homogeneous or heterogeneous. The selection of appropriate catalyst depends on the amount of free fatty acids in the oil. Heterogeneous catalyst provides high activity, high selectivity, high water tolerance properties and these properties depend on the amount and strengths of active acid or basic sites. Basic catalyst can be subdivided based on the type of metal oxides and their derivatives. Similarly, acidic catalyst can be subdivided depending upon their active acidic sites. New varieties of mixed catalyst are also available in literatures. Catalyst generated from bio-waste and other biocatalysts which are heterogeneous in nature and extensively reported in literature are also reviewed. This review focused about the recent invention and use of the heterogeneous acid, base and biocatalysts for biodiesel production and their suitability for industrial application.

Modern heterogeneous catalysts for biodiesel production: A comprehensive review

Biodiesel is gaining acceptance in the market as fuel and lubricant. It is expected that biodiesel industries will rapidly grow worldwide in the coming years and information on biodiesel feedstock, production, and characteristics will be crucial than ever especially for those using vegetable oils as feedstock as these are currently the major sources for making biodiesel. In the present paper, a comprehensive review is reported on feedstock, production technologies, and characteristics of biodiesel. More specifically, selected available vegetable oils are explored as feedstock for biodiesel production. Production technologies including latest catalyst developments are discussed. Finally, biodiesel characteristics and parameters influencing the corresponding properties are revealed. Since this paper covers a wide range in biodiesel area, it serves as a general public education medium as well as a research reference for biodiesel production from vegetable oils.

Biodiesel from vegetable oils

Biodiesel, which could be derived from plant oils and animal fats, is considered as a promising substitute for petroleum diesel fuel because of its advantages, such as renewability, biodegradability, less environmental toxicity, and superior combustion efficiency. The feedstock used for biodiesel production primarily include edible oils, non-edible oils, waste oils, and animal fats. Consistent scientific investigations are performed to locate innovative oil resources and minimize the utilization of expensive food-grade oils for biodiesel production. The extensive research information is available on the determination of physico-chemical properties of different plant oils. This review will present a general information related to the existing varieties of oil feedstocks, their lipid content, and fatty acid composition. This article further discusses different methods employed to enable the usage of plant oils as biofuel, such as its direct use, blending, thermal cracking, microemulsion, and alcoholysis process. Among the possible methodologies for biodiesel production, alcoholysis process, in the presence or absence of a catalytic material, have been frequently employed. The benefits and limitations of using homogeneous, heterogeneous, enzyme catalysts, and supercritical method for the alcoholysis process are comprehensively discussed. In the current article, efforts have been made to review the recent inventions in homogeneous and heterogeneous catalytic materials utilized for biodiesel production. The present study shall provide a tool for the selection of an optimal catalyst for a large-scale biodiesel production.

A review on recent advancement in catalytic materials for biodiesel production.

Biodiesel production is worthy of continued study and optimization of production procedures due to its environmentally beneficial attributes and its renewable nature. Heterogeneous transesterification is considered to be a green process. The process requires neither catalyst recovery nor aqueous treatment steps and very high yields of methyl esters can be obtained, close to the theoretical value. However, heterogeneously catalyzed transesterification generally requires more severe operating conditions, and the performance of heterogeneous catalysts is generally lower than that of the commonly used homogeneous catalysts. Heterogeneous catalysis for biodiesel production has been extensively investigated in the last few years. Many metal oxides have been studied for the transesterification process of oils; these include alkali earth metal oxides, transition metal oxides, mixed metal oxides and supported metal oxides. The use of solid metal oxides as catalysts in oil transesterification is well established, accordingly, researchers’ attempts are now focused on how to attain the highest catalyst activity. Catalyst activity is a function of its specific surface area, base strength and base site concentration. High specific surface area, strong base strength and high concentration of base sites are characteristics of an active transesterification catalyst. This review provides a brief overview of the different metal oxides frequently used in the process of transesterification of oils for the production of biodiesel with special reference to the various methods of catalyst preparation and catalyst characterization. Reaction conditions and catalyst leaching analysis are also highlighted. Finally, concluding remarks regarding catalyst selection and catalyst preparation steps are provided.

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Zhiyong Wang

Papers

Transesterification of sunflower oil to biodiesel on zro2 supported la2o3 catalyst