Whole-cell biocatalysts for biodiesel fuel production

Biodiesel fuel (BDF), which refers to fatty acid alkyl esters, has attracted considerable attention as an environmentally friendly alternative fuel for diesel engines. Alkali catalysis is widely applied for the commercial production of BDF. However, enzymatic transesterification offers considerable advantages, including reducing process operations in biodiesel fuel production and an easy separation of the glycerol byproduct. The high cost of the lipase enzyme is the main obstacle for a commercially feasible enzymatic production of biodiesel fuels. To reduce enzyme associated process costs, the immobilization of fungal mycelium within biomass support particles (BSPs) as well as expression of the lipase enzyme on the surface of yeast cells has been developed to generate whole-cell biocatalysts for industrial applications.     

Biodiesel production with special emphasis on lipase-catalyzed transesterification

The production of biodiesel by transesterification employing acid or base catalyst has been industrially accepted for its high conversion and reaction rates. Downstream processing costs and environmental problems associated with biodiesel production and byproducts recovery have led to the search for alternative production methods. Recently, enzymatic transesterification involving lipases has attracted attention for biodiesel production as it produces high purity product and enables easy separation from the byproduct, glycerol. The use of immobilized lipases and immobilized whole cells may lower the overall cost, while presenting less downstream processing problems, to biodiesel production. The present review gives an overview on biodiesel production technology and analyzes the factors/methods of enzymatic approach reported in the literature and also suggests suitable method on the basis of evidence for industrial production of biodiesel.     

Biotechnological production of biodiesel fuel using biocatalysed transesterification: A review

Biotechnological production of biodiesel has attracted considerable attention during the past decade compared to chemical-catalysed production since biocatalysis-mediated transesterification has many advantages. Currently, there are extensive reports on enzyme-catalysed transesterification for biodiesel production; the related research can be classified into immobilised-extracellular and immobilised-intracellular biocatalysis and this review focusses on these forms of biocatalyst for biodiesel production. The optimisation of the most important operating conditions affecting lipase-catalysed transesterification and the yield of alkyl esters, such as the type and form of lipase, the type of alcohol, the presence of organic solvents, the content of water in the oil, temperature and the presence of glycerol, are discussed. However, there is still a need to optimise lipase-catalysed transesterification and reduce the cost of lipase production before it is applied commercially. Optimisation research of lipase-catalysed transesterification could include development of new reactor systems with immobilised biocatalysts, the use of lipases tolerant to organic solvents, intracellular lipases (whole microbial cells) and genetically modified microorganisms (intelligent yeasts). Biodiesel fuel is expensive in comparison with petroleum-based fuel and 60–70% of the cost is associated with feedstock oil and enzyme. Therefore ways of reducing the cost of biodiesel with respect to enzyme and substrate oils reported in literature are also presented.     

Enzymatic transesterification for biodiesel production

Biodiesel consists monoalkyl esters of long chain fatty acids. It is produced from vegetable oils or fats either by chemical transesterification or by lipase-catalyzed transesterification with methanol or ethanol. Biodiesel is a green fuel and can be used as a blend with diesel or alone. Either way, it does not require any modification in engine design or storage facilities. The enzymatic process offers several advantages over the chemical routes. The handicap of increase in process cost because of the cost of the enzyme can be overcome by using efficient production process for enzyme and using reusable derivatives of enzymes, such as immobilized enzyme. Numerous strategies available in the area of non-aqueous enzymology can be exploited during the enzymatic alcoholysis for biodiesel production. Some of the technical challenges and their possible solutions are also discussed.     

Kinetics and mechanism of the cutinase-catalyzed transesterification of oils in AOT reversed micellar system

The kinetics of the enzymatic transesterification between a mixture of triglycerides (oils) and methanol for biodiesel production in a bis(2-ethylhexyl) sodium sulfosuccinate (AOT)/isooctane reversed micellar system, using recombinant cutinase from Fusarium solani pisi as a catalyst, was investigated. In order to describe the results that were obtained, a mechanistic scheme was proposed, based on the literature and on the experimental data. This scheme includes the following reaction steps: the formation of the active enzyme–substrate complex, the addition of an alcohol molecule to the complex followed by the separation of a molecule of the fatty acid alkyl ester and a glycerol moiety, and release of the active enzyme. Enzyme inhibition and deactivation effects due to methanol and glycerol were incorporated in the model. This kinetic model was fitted to the concentration profiles of the fatty acid methyl esters (the components of biodiesel), tri-, di- and monoglycerides, obtained for a 24 h transesterification reaction performed in a stirred batch reactor under different reaction conditions of enzyme and initial substrates concentration.     

Biodiesel production using heterogeneous catalysts

The production and use of biodiesel has seen a quantum jump in the recent past due to benefits associated with its ability to mitigate greenhouse gas (GHG). There are large number of commercial plants producing biodiesel by transesterification of vegetable oils and fats based on base catalyzed (caustic) homogeneous transesterification of oils. However, homogeneous process needs steps of glycerol separation, washings, very stringent and extremely low limits of Na, K, glycerides and moisture limits in biodiesel. Heterogeneous catalyzed production of biodiesel has emerged as a preferred route as it is environmentally benign needs no water washing and product separation is much easier. The present report is review of the progress made in development of heterogeneous catalysts suitable for biodiesel production. This review shall help in selection of suitable catalysts and the optimum conditions for biodiesel production.     

Production of Biodiesel Using Immobilized Lipase—A Critical Review

Increase in volume of biodiesel production in the world scenario proves that biodiesel is accepted as an alternative to conventional fuel. Production of biodiesel using alkaline catalyst has been commercially implemented due to its high conversion and low production time. For the product and process development of biodiesel, enzymatic transesterification has been suggested to produce a high purity product with an economic, environment friendly process at mild reaction conditions. The enzyme cost being the main hurdle can be overcome by immobilization. Immobilized enzyme, which has been successfully used in various fields over the soluble counterpart, could be employed in biodiesel production with the aim of reducing the production cost by reusing the enzyme. This review attempts to provide an updated compilation of the studies reported on biodiesel production by using lipase immobilized through various techniques and the parameters, which affect their functionality.     

Biodiesel production through lipase catalyzed transesterification: An overview

Recently, with the global shortage of fossil fuels, excessive increase in the price of crude oil and increased environmental concerns have resulted in the rapid growth in biodiesel production. The central reaction in the biodiesel production is the transesterification reaction which could be catalyzed either chemically or enzymatically. Enzymatic transesterification has certain advantages over the chemical catalysis of transesterification, as it is less energy intensive, allows easy recovery of glycerol and the transesterification of glycerides with high free fatty acid contents. Limitations of the enzyme catalyzed reactions include high cost of enzyme, low yield, high reaction time and the amount of water and organic solvents in the reaction mixture. Researchers have been trying to overcome these limitations in the enzyme catalyzed transesterification reaction. This paper is meant to review the latest development in the field of lipase catalyzed transesterification of biologically derived oil to produce biodiesel.     

Optimization of a Novel Two-step Process Comprising Re-esterification and Transesterification in a Single Reactor for Biodiesel Production Using Waste Cooking Oil

Waste cooking oil (WCO) has attracted attention as a non-edible feedstock for biodiesel. Although an alkali catalyst has several advantages over an acid catalyst in biodiesel production, biodiesel conversion from WCO is only 5.2% when using an alkali catalyst (NaOH), owing to its high free fatty acid (FFA) content of 4.2%. In this study, a novel two-step process in a single reactor, comprised of re-esterification of the FFAs with crude glycerol, using a Tin (II) chloride (SnCl₂) catalyst, and subsequent transesterification with methanol, using an alkali catalyst, was adopted, and each step was optimized. This study revealed that the FFA content after re-esterification should be approximately 1.5%, not only to save glycerol and the catalyst involved in the re-esterification, but also to achieve high biodiesel conversion during the transesterification. An alkaline catalyst was successfully used to produce biodiesel in the second step, and a 92.8% conversion to biodiesel was achieved under the optimized conditions (0.6% catalyst relative to WCO, 0.2mL-methanol/WCO, 70ºC, 3 h). Overall, this novel two-step process achieved highly enhanced biodiesel conversion (4.0% to 92.8%) with significantly reduced reaction time (12 h to 4 h) and methanol requirements (15 mL/g-WCO to 0.2 mL/g-WCO).     

Biodiesel production by transesterification using immobilized lipase

Biodiesel can be produced by transesterification of vegetable or waste oil catalysed by lipases. Biodiesel is an alternative energy source to conventional fuel. It combines environmental friendliness with biodegradability, low toxicity and renewability. Biodiesel transesterification reactions can be broadly classified into two categories: chemical and enzymatic. The production of biodiesel using the enzymatic route eliminates the reactions catalysed under acid or alkali conditions by yielding product of very high purity. The modification of lipases can improve their stability, activity and tolerance to alcohol. The cost of lipases and the relatively slower reaction rate remain the major obstacles for enzymatic production of biodiesel. However, this problem can be solved by immobilizing the enzyme on a suitable matrix or support, which increases the chances of re-usability. The main factors affecting biodiesel production are composition of fatty acids, catalyst, solvents, molar ratio of alcohol and oil, temperature, water content, type of alcohol and reactor configuration. Optimization of these parameters is necessary to reduce the cost of biodiesel production.     

Continuous biodiesel production using in situ glycerol separation by membrane bioreactor system

Biodiesel is one of the most promising renewable fuel sources. Candida antarctica lipase B (CalB) has been used for biodiesel production because of its high activity and stability. However, CalB can only be utilized in industrial biodiesel production if the enzyme deactivation by methanol and the negative effects of glycerol can be mitigated. Methanol inhibition can be avoided by utilizing a stepwise addition of methanol, but there is no suitable method to reduce the glycerol effect. This study aims to use a membrane bioreactor system to remove glycerol during biodiesel production. In addition, methanol inhibition can be reduced by continuously feeding methanol through the membrane system. This continuous membrane bioreactor system can be used for efficient biodiesel production.     

Biocatalysis: Towards ever greener biodiesel production

The cost of lipases and the relatively slower reaction rate remain as the major obstacles for enzymatic production of biodiesel as opposed to the conventional chemical processes. This paper reviews the starting oils usually employed in biodiesel production, the processes for transforming them to biodiesel placing particular emphasis on enzymatic transesterification. The pros and cons of the lipase-based process, the key operational variables and the technological alternatives for attenuating lipase deactivation are also discussed. Finally, suggestions are made for future studies, paying particular attention to the use of whole cell immobilization in the production process, as this methodology may reduce both the cost of the biocatalyst and dependence on lipase manufacturers.     

Improvement of enzymatic biodiesel production by controlled substrate feeding using silica gel in solvent free system

A silica gel-based substrate feeding system was developed to prevent methanol inhibiting the catalyst during enzymatic biodiesel synthesis. In the system, silica gel swelled upon methanol addition and subsequently released it in a controlled manner to prevent excess methanol affecting the enzyme. Biodiesel was synthesized by the enzymatic transesterification of canola oil with methanol. For this reaction, enzyme loading, methanol/oil molar ratio, silica gel dosage, glycerol content, and methanol feeding method were tested using commercial immobilized enzymes (Novozym 435 and Lipozyme RM IM from Novozymes). The results showed that conversion was highest with controlled substrate feeding rather than direct methanol addition, suggesting that the method developed here can easily prevent enzyme inhibition by limiting methanol concentration to an acceptable level.     

An overview on the recent advances in the transesterification of vegetable oils for biodiesel production using chemical and biocatalysts

Biodiesel, chemically defined as monoalkyl esters of long chain fatty acids, are derived from renewable feed stocks like vegetable oils and animal fats. It is produced by both batch and continuous transesterification processes in which, oil or fat is reacted with a monohydric alcohol in the presence of a catalyst. The conventional method of producing biodiesel involves acid and base catalysts to form fatty acid alkyl esters. Downstream processing costs and environmental problems associated with biodiesel production and byproducts recovery have led to the search for alternative production methods and alternative substrates. Enzymatic reactions involving lipases can be an excellent alternative to produce biodiesel through a process commonly referred to as alcoholysis, a form of transesterification reaction or through an interesterification reaction. In order to increase the cost effectiveness of the process, the enzymes are immobilized using a suitable matrix. The use of immobilized lipases and whole cells may lower the overall cost, while presenting less downstream processing problems. Main focus of this paper is to discuss the important parameters that affect the biodiesel yield, various immobilization techniques employed, mechanisms and kinetics of transesterification reaction and the recent advances in continuous transesterification processes.     

Biodiesel production—current state of the art and challenges

Biodiesel is a clean-burning fuel produced from grease, vegetable oils, or animal fats. Biodiesel is produced by transesterification of oils with short-chain alcohols or by the esterification of fatty acids. The transesterification reaction consists of transforming triglycerides into fatty acid alkyl esters, in the presence of an alcohol, such as methanol or ethanol, and a catalyst, such as an alkali or acid, with glycerol as a byproduct. Because of diminishing petroleum reserves and the deleterious environmental consequences of exhaust gases from petroleum diesel, biodiesel has attracted attention during the past few years as a renewable and environmentally friendly fuel. Since biodiesel is made entirely from vegetable oil or animal fats, it is renewable and biodegradable. The majority of biodiesel today is produced by alkali-catalyzed transesterification with methanol, which results in a relatively short reaction time. However, the vegetable oil and alcohol must be substantially anhydrous and have a low free fatty acid content, because the presence of water or free fatty acid or both promotes soap formation. In this article, we examine different biodiesel sources (edible and nonedible), virgin oil versus waste oil, algae-based biodiesel that is gaining increasing importance, role of different catalysts including enzyme catalysts, and the current state-of-the-art in biodiesel production. JIMB 2008: BioEnergy—special issue.     

Integrated production for biodiesel and 1,3-propanediol with lipase-catalyzed transesterification and fermentation

Biodiesel, a renewable alternative to fossil energy, has shown great prospects for global proliferation in the past decade. Lipase catalyzed transesterification for biodiesel production, as a biological process with many advantages has drawn increasing attention. As a by-product, glycerol accounts for about 10% w/w of biodiesel during the process of biodiesel production. As a result, the conversion of glycerol has become a common problem which has to be resolved if considering large amount of biodiesel production. Glycerol can be fermented into 1,3-propanediol, a high value added chemical with a promising future in the polymers, for example, polytrimethylene terephthalate, and also fermentation approaches for 1,3-propanediol production which have drawn more and more attention due to advantages such as relatively low investment, mild reaction conditions and using renewable sources as the starting materials. Based on the latest technology advancements in lipase-mediated transformation for biodiesel production, the aerobic fermentation technology and genetic engineering for 1,3-propanediol production, and the integrated production of 1,3-propanediol from crude glycerol could be a promising way to improve the profit of the whole process during biodiesel production.     

Glycerol extracting dealcoholization for the biodiesel separation process

By means of utilizing sunflower oil and Jatropha oil as raw oil respectively, the biodiesel transesterification production and the multi-stage extracting separation were carried out experimentally. Results indicate that dealcoholized crude glycerol can be utilized as the extracting agent to achieve effective separation of methanol from the methyl ester phase, and the glycerol content in the dealcoholized methyl esters is as low as 0.02 wt.%. For the biodiesel separation process utilizing glycerol extracting dealcoholization, its technical and equipment information were acquired through the rigorous process simulation in contrast to the traditional biodiesel distillation separation process, and results show that its energy consumption decrease about 35% in contrast to that of the distillation separation process. The glycerol extracting dealcoholization has sufficient feasibility and superiority for the biodiesel separation process.     

Esterification using a liquid lipase to remove residual free fatty acids in biodiesel

Lately, the price of liquid formulated lipase enzymes, usable in biodiesel production, has been significantly reduced. This enables one-time use of these enzymes for transesterification, and the process is used industrially. However, the process suffers a drawback by leaving 2−3 % free fatty acids in the crude biodiesel, which reduces the profitability. This article discusses a novel enzymatic FFA esterification reaction utilizing liquid lipase B from Candida antarctica (CALB) along with glycerol at low water concentrations to eliminate the residual FFA. The reaction setup was found able to reduce the free fatty acid concentration to within biodiesel specifications of < 0.25 wt.% FFA. Additionally, two alternative process setups are proposed, which were both found viable through a combination of experiments and simulations, and can be developed into full-scale processes. The resulting two-step enzymatic biodiesel process - transesterification followed by esterification - provides a potential process layout for the industrial production of biodiesel.     

Biodiesel fuel production via transesterification of oils using lipase biocatalyst

Biodiesel has gained widespread importance in recent years as an alternative, renewable liquid transportation fuel. It is derived from natural triglycerides in the presence of an alcohol and an alkali catalyst via a transesterification reaction. To date, transesterification based on the use of chemical catalysts has been predominant for biodiesel production at the industrial scale due to its high conversion efficiency at reasonable cost. Recently, biocatalytic transesterification has received considerable attention due to its favorable conversion rate and relatively simple downstream processing demands for the recovery of by-products and purification of biodiesel. Biocatalysis of the transesterification reaction using commercially purified lipase represents a major cost constraint. However, more cost-effective techniques based on the immobilization of both extracellular and intracellular lipases on support materials facilitate the reusability of the catalyst. Other variables, including the presence of alcohol, glycerol and the activity of water can profoundly affect lipase activity and stability during the reaction. This review evaluates the current status for lipase biocatalyst-mediated production of biodiesel, and identifies the key parameters affecting lipase activity and stability. Pioneer studies on reactor-based lipase conversion of triglycerides are presented.     

Process design and evaluation of value-added chemicals production from biomass

Three different biodiesel production processes were simulated using the SuperPro Designer program. The process for producing biodiesel from soybean oil and methanol was designed using commercial chemical catalysts. This chemical process was compared with the biological process catalyzed by immobilized enzymes. In addition, a hybrid process consisting of catalytic biodiesel production and enzymatic glycerol carbonate production was designed and simulated for the conversion of waste glycerol to value-added chemical. Finally, the economics and productivity of these processes were evaluated to determine economic feasibility.