Biodiesel Production Using Homogeneous, Heterogeneous, and Enzyme Catalysts via Transesterification and Esterification Reactions: a Critical Review.

A kinetic model for a single step biodiesel production from a high free fatty acid (FFA) biodiesel feedstock over a solid heteropolyacid catalyst

A review on the waste biomass derived catalysts for biodiesel production

Biodiesel is a green fuel, because it is biodegradable and reduces the emission of greenhouse gases. In the first generation of biofuels, the biodiesel is produced from edible oils. However, due to the high cost of biodiesel production and social problems, the use of ‘waste cooking oils’ (WCO) can improve the economics of first generation biodiesel. Traditionally, biodiesel production has been performed using homogeneous catalysts (NaOH, KOH). However, these homogenous catalysts have some disadvantages, such as difficulty in separation from reaction products and corrosiveness. The use of heterogenous catalysts can be a solution to the problems associated with homogeneous catalysts. These catalysts have some advantages such as easy separation from the reaction mixture and the material can be reused and regenerated. The aim of this chapter is to review biodiesel production from second generation WCO in the presence of heterogeneous solid acid catalysts. Biodiesel production from WCO is done using zeolites, polymers, heteropolyacids, activated carbons, metal oxides, and composite catalysts.

Biodiesel obtained from vegetable oils and animal fats, is a more environmentally friendly alternative to conventional fossil fuels. Biodiesel production through esterification and transesterification processes with an emphasis on the role of catalysts in increasing efficiency. The use of homogeneous and heterogeneous catalysts, as well as the advantages and disadvantages of each. Homogeneous catalysts, such as NaOH and KOH, are effective in increasing the reaction, but face challenges in product separation and soap formation that can reduce biodiesel yields. In contrast, heterogeneous catalysts such as CaO and zeolites offer advantages in terms of reuse and waste reduction, although with slightly lower efficiency. In addition, important factors such as catalyst concentration, alcohol to oil ratio, and reaction temperature are also reviewed to maximize biodiesel yields. Optimal catalyst concentration is essential to increase conversion efficiency, as inappropriate concentrations can slow down the reaction. The importance of choosing the right catalyst and process conditions in producing biodiesel efficiently, while considering the environmental impact of using raw materials, especially palm oilContribution to Sustainable Development Goals (SDGs):SDG 6: Clean Water and SanitationSDG 11: Sustainable Cities and CommunitiesSDG 13: Climate ActionSDG 15: Life on Land

The need for fossil fuels and the emissions generated from these fuels are increasing daily. Researchers are concerned with global warming as well as climate change; and energy sustainability and material usages are important issues today. Waste cooking oil (WCO) can be processed into biodiesel as an alternative fuel to replace diesel. Production of biodiesel using WCO as the feedstock has been of growing interest for the last two decades. A number of research papers related to the improvements in production, raw materials and catalyst selection have been published. This paper reviews the various types of heterogeneous solid catalyst in the production of biodiesel via the transesterification of WCO. The catalysts used can be classified according to their state presence in the transesterification reaction as homogeneous or heterogeneous catalysts. Homogeneous catalysts act in the same liquid phase as the reaction mixture, whereas heterogeneous catalysts act in a solid phase with the reaction mixture. Heterogeneous catalysts are non-corrosive, a green process and environmentally friendly. They can be recycled and used several times, thus offering a more economic pathway for biodiesel production. The advantages and drawbacks of these heterogeneous catalysts are presented. Future work focuses on the application of economically and environmentally friendly solid catalysts in the production of biodiesel using WCO as the raw material.

The present review primarily focuses on the perspectives and state-of-the-art of heterogeneous catalysts, nanocatalysts, biocatalysts, bifunctional catalysts, metal-organic frameworks (MOF), and covalent organic frameworks (COF) for biodiesel production. The environmental concern associated with nonrenewable fossil fuels has led to finding alternative energy sources that can be used to meet global energy demands. Biofuels such as biodiesel are one of the energy sources that could replace fossil fuels. The homogeneous acid and base catalysts are generally used for commercial biodiesel production. However, homogeneous catalysts have downsides such as toxicity, corrosion, soap formation, high wastewater output, and non-reusability. Consequently, heterogeneous acid and base catalysts have been introduced that are less sensitive to moisture and free fatty acids (FFAs), easily separated and recovered, and reusable. Recently, novel catalysts such as waste biomass-derived mesoporous heterogeneous catalysts, chemically synthesized heterogeneous catalysts, metal ion-doped heterogeneous catalysts, bifunctional acid-base catalysts, and carbonaceous char-supported hetero catalysts, nanocatalysts, MOF and COF catalysts have potential to replace homogeneous base catalysts, aid in sustainable and cost-effective biodiesel production. This review provides insights into the recent advancement of various catalysts, catalyst preparation and operations, type of catalysts and suitability, catalyst efficiency, life cycle assessment, catalyst-associated challenges, and prospects for sustainable biodiesel production.

The relevance of heterogeneous catalysis in biodiesel production cannot be overemphasized, as heterogeneous catalysts have eliminated the demerits associated with a homogeneous catalysts. Some heterogeneous catalysts experience drawbacks such as partial recoverability and reusability, energy and waste conservation issues during biodiesel processing and leaching of active catalyst sites. This paper highlights and summarizes several heterogeneous catalysts used in biodiesel production. The catalyst preparation, reaction conditions, feedstock, and biodiesel yield for the heterogeneous base and acid catalysts were emphasized. The inability of heterogeneous base catalysts to trans-esterify low-grade oil with high free fatty acid (FFA) is a primary concern; the cost of processing low-grade oil with high FFA using heterogeneous acid catalysts is also a big issue. Nano-doped heterogeneous catalysts with unique properties were recommended because they can process oil with high FFA transesterification, improve reaction efficiency, simplify production, reduce the leaching of active sites, enable better biodiesel yield by minimizing energy and waste, and increase catalyst recoverability, activity, selectivity and durability.

Homogeneous, heterogeneous and enzymatic catalysis for transesterification of high free fatty acid oil (waste cooking oil) to biodiesel: A review

Homogeneous base catalyst has wide acceptability in biodiesel production because of their fast reaction rates. However, postproduction costs incurred from aqueous quenching, wastewater and loss of catalysts led to the search for alternatives. Heterogeneous base catalyst is developed to cater these problems. The advantages of heterogeneous catalyst are their high basicity and non-toxicity. This work compared the production of biodiesel using two different kind of catalysts that is homogeneous catalyst (sodium hydroxide, NaOH and potassium hydroxide, KOH) and heterogeneous catalysts (calcium, oxide, CaO catalyst derived from chicken and ostrich eggshells). Transesterification of waste cooking oil (WCO) and methanol in the presence of heterogeneous base catalyst was conducted at an optimal reaction condition (calcination temperature for catalyst: 1000 °C; catalyst loading amount: 1.5 wt%; methanol/oil molar ratio: 10:1; reaction temperature: 65 °C; reaction time: 2 hours) with 97% biodiesel yield was obtained. While, the homogeneous base catalyst gave higher biodiesel yield of 98% at optimum operating condition (catalyst concentration: 0.75 wt%; methanol/oil molar ratio: 6:1; reaction temperature: 65 °C; reaction time: 1 hours). The slight difference in the biodiesel yield was due to the stronger basic strength in the homogeneous catalyst and were not statistically not different (p=0.05). However, despite these advances, the ultimate aim of producing biodiesel at affordable low cost and minimal-environmental-impact is yet to be realized.

Biodiesel is a renewable, clean-burning, and biodegradable fuel which can be synthesized from readily available domestic and natural sources, such as edible, non-edible and waste cooking oils, which may serve as a substitute to petro-diesel. It is produced by catalytic transesterification of fats and oils. A number of researches has been devoted to discovering a benign catalyst, especially heterogeneous acid catalyst that could convert non-edible and waste cooking oils with high free fatty acid into biodiesel, in an attempt to reduce the cost of production. The cost of production of biodiesel is still far higher than that of conventional petro-diesel, owing to the cost of edible oil currently being used, processes involved, and cost of conventional heterogeneous catalysts employed. This study assessed the role of various catalysts; homogeneous, heterogenous and enzyme-catalyzed transesterification reactions, in terms of their advantages and disadvantages in biodiesel production in order to establish very promising catalysts. Some methods of heterogeneous acid catalysts were also highlighted. Amongst the common heterogeneous catalyst, carbon-based solid acid catalysts were recommended as very promising solid acid catalyst that can utilize the non-edible oils in biodiesel production. The advantages of carbon-based solid acid catalysts include cheap readily available raw materials for their synthesis, easier production processes, relative stability, high reusability and potential for utilizing waste and non-edible oils for biodiesel production. 
 Nnaji, J. C. | Department of Chemistry, Michael Okpara University of Agriculture, Umudike, Abia State, Nigeria

This chapter presents one method to obtain the renewable “biodiesel” energy source thru animal fats transesterification with high free fatty acid content. The authors tested different methods to produce biodiesel from waste animal fats. The purpose of research was to use the byproduct from the meat industry, the wastes in form of fats with high free fatty acid contend (FFA), fats that cannot be used in other sectors, like supplement in animal food, due to high contamination and FFA content. The research underlines a correlation between social-economic development and air quality in an urban area. We also intend to improve the knowledge in the field of alternative fuels, field not well covered in Romania, especially if the waste management and potential are in sight. The relevance of this research theme in the knowledge development is related to the fact that studies regarding environment protection are not an objective but a dynamic process that requires adequate instruments and concrete actions in the frame of a coherent legislative frame. (Popescu, 2009) The chapter will follow three directions: first will describe the research conducted in order to obtain an “receipt” to produce the biodiesel from waste animal fats; second will describe the pilot installation constructed to improve the biodiesel production receipt and third will describe some research conducted in order to prove (or validate) the positive impact on the urban environment if the biodiesel in used in stead of regular diesel. In a broad sense, energy conversion is the capacity to promote changes and/or actions (heating, motion, etc.), and biomass includes all kinds of materials that were directly or indirectly derived not too long ago from contemporary photosynthesis reactions, such as vegetal matter and its derivatives: wood fuel, wood-derived fuels, fuel crops, agricultural and agro-industrial by-products, and animal by-products. Bioenergy is the word used for energy associated to biomass, and biofuel is the bioenergy carrier, transporting solar energy stored as chemical energy. (Ionel, 2008) Biofuels can be considered a renewable source of energy as long as they are based on sustainable biomass production. The style will adjust your fonts and line spacing. Improving the efficiency of the existing power-plants using fossil fuels, the use of renewable fuels and renewable energy sources and the increased use of nuclear power are all considered to be important means of reducing greenhouse-gas emissions. One possibility to reduce greenhouse-gas emissions is to substitute biomass for

Biodiesel, which is an alternative renewable fuel, is defined as mono alkyl ester of long-chain fatty acids and has properties comparable to those of fossil-based diesel. Biodiesel can be produced from vegetable oils or animal fats. The most common method used to produce biodiesel is a reversible chemical reaction called transesterification. This reaction takes place either in the presence of catalysts at lower temperature and pressure or in the absence of catalysts at higher temperature and pressure in supercritical state. Catalyzed transesterification reaction is preferred in biodiesel production because of the moderate reaction conditions. Homogeneous base catalysis can be used in transesterification when fresh vegetable oil is used as a feedstock due to its low cost, high catalytic activity, and feasibility to operate at low temperatures. Homogeneous acid catalysis is a better choice when the feedstock contains higher amounts of free fatty acids (FFAs). Heterogeneous base and acid catalysis are preferred due to their easy separation from biodiesel, hence reducing number of product purification steps. However, heterogeneous catalysis is still under development and has a promising future in biodiesel industries. In this chapter, various acid- and base-catalyzed esterification and transesterification reactions are discussed, and recent trend in catalyst development is highlighted. It is recommended that a proper selection of catalyst is made in a transesterification reaction, depending largely on the type of feedstock.

Biodiesel fuel has shown great promise as an alternative to petro-diesel fuel. Biodiesel production is widely conducted through esterification and transesterification reaction, catalyzed by homogeneous or heterogeneous catalysts. In the present endeavour, sulphated zirconia has been prepared using microwave method and characterized by using XRD, FT-IR, BET surface area, SEM and acidity measurement. The utility of synthesized catalyst is demonstrated in catalytic biodiesel production from acid oil feed stock. The influence of different parameters such as the catalyst concentration, oil: methanol ratio, operation time on the yield and properties of the produced biodiesel were studied. The produced biodiesel was characterized by using gas chromatography-mass spectroscopy (GC-MS) and NMR. Keywords: Heterogeneous acid catalyst, sulfated zirconia, acid oil, biodiesel

The world is gradually moving toward a severe energy crisis due to depletion of fossil fuels. Biodiesel is one of the technically and economically feasible options to solve the aforesaid problem. However, the overall costs of biodiesel production associated with the increasing market price of its feedstock clearly influence the profitability of the process. Therefore, biodiesel production has been directed toward waste materials as feedstock such as waste cooking oil (WCO). On the other hands, WCO is dealing with high free fatty acids (FFA) contents which gives a significant effect to the transesterification reaction, resulting in a lower biodiesel production. Therefore, a viable catalyst is needed for wide industrial usage in biodiesel synthesis from WCO. CaO is one of the promising heterogeneous catalyst for the transesterification reaction. However, CaO is deals with some limitations that need to overcome. This research paper deals with the synthesis of heterogeneous calcium titanate (CT) catalyst from calcium oxide (CaO) and titanium precursor by a sol-gel method for pilot evaluation in biodiesel production. CT catalyst was produced under different calcination temperature (200 °C, 400 °C, 600°C, 800 °C). The synthesized catalysts were evaluated for performance in transesterification reaction of methanol with WCO. BET surface area, XRD, and SEM were measured to correlate the activity with the structural features of the catalysts. The results exhibited that the calcination temperature of 400 °C is more preferable in terms of technical and economic feasibility. A biodiesel yield of 80.0 % was observed with a methanol to oil molar ratio of 15:1 and 1 wt. % of CT catalyst loading amount in 1 h at 65 °C which is comparative with commercial CaO catalyst calcined at 400 °C (60.0 % of biodiesel yield) at the same reaction conditions.

A review of breakthroughs in biodiesel production with transition and non-transition metal-doped CaO nano-catalysts