A review of the enzymatic hydroesterification process for biodiesel production

Renewable and Sustainable Energy Reviews 61 (2016) 245–257

Contents lists available at ScienceDirect

Renewable and Sustainable Energy Reviews journal homepage: www.elsevier.com/locate/rser

A review of the enzymatic hydroesterification process for biodiesel production Hamed Pourzolfaghar, Faisal Abnisa, Wan Mohd Ashri Wan Daud n, Mohamed Kheireddine Aroua Chemical Engineering Department, Faculty of Engineering, University Malaya, 50603 Kuala Lumpur, Malaysia

art ic l e i nf o

a b s t r a c t

Article history: Received 1 December 2014 Received in revised form 20 December 2015 Accepted 17 March 2016

Enzymatic hydroesterification has recently attracted research interest because of the high-value products created during biodiesel production. The use of this process overcomes problems related to conventional methods for biodiesel production, such as slow reaction rate and soap formation. The method comprises two basic processes to produce fatty acid alkyl esters from triacylglycerols, namely, enzymatic hydrolysis and enzymatic esterification. Although enzymatic hydroesterification for biodiesel production has many advantages, such as lower energy consumption and converting low-quality feedstock, it has not been used on an industrial scale mainly because of some impediments, including enzyme cost and conversion efficiency. This review presents a comprehensive evaluation of recent investigations on enzymatic hydrolysis and enzymatic esterification to lower process costs and increase yields. & 2016 Published by Elsevier Ltd.

Keywords: Enzymatic hydroesterification Biodiesel Enzymatic hydrolysis Enzymatic esterification

Contents 1. 2.

Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 245 Enzymatic biodiesel production . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 246 2.1. Key factors on enzymatic biodiesel production . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 246 2.1.1. Lipase . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 247 2.1.2. Substrate . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 247 2.1.3. Acyl acceptor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 248 2.1.4. Bioreactor design . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 249 3. Hydroesterification . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 249 3.1. Enzymatic hydrolysis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 250 3.2. Enzymatic esterification . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 250 4. Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 252 Acknowledgment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 254 References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 254

1. Introduction Issues of impending supply crisis, mounting carcinogenic emission problems, and global warming are associated with the use of petroleum-based products and are the main reasons for the n

Corresponding author. Tel.: þ 60 3 79675297; fax: þ 60 3 79675319. E-mail addresses: [email protected] (H. Pourzolfaghar), [email protected] (F. Abnisa), [email protected] (W.M.A.W. Daud), [email protected] (M.K. Aroua). http://dx.doi.org/10.1016/j.rser.2016.03.048 1364-0321/& 2016 Published by Elsevier Ltd.

development of renewable biofuel sources [1–3]. Under current conditions, biodiesel (fatty acid alkyl ester), an alternative cleanburning fuel for diesel engines, has gained the most attention among biofuels because of its similarity with conventional diesel in energy content and chemical structure [3,4]. Moreover, biodiesel reduces carcinogenic compound emissions by approximately 85% compared with diesel fuel and is essentially free of sulfur, metals, and polycyclic aromatic hydrocarbons [5]. Global worriment about the use of edible oils as substrates in biodiesel production because of the potential competition with

246

H. Pourzolfaghar et al. / Renewable and Sustainable Energy Reviews 61 (2016) 245–257

food consumption and high cost of edible oil [6] (60–75% of the total cost of biodiesel production) has encouraged researchers to examine low-cost raw materials for this process [7,8]. Secondgeneration biodiesel feedstocks, such as nonedible oils, waste edible oils, and animal fats, can remarkably reduce biodiesel production costs and ensure the economic feasibility of the process [9]. However, substrates containing high levels of free fatty acids (FFAs) are undesirable in common methods of biodiesel synthesis (alkali-catalyzed alcoholysis) [10]. Transesterification of triacylglycerol (TAG) using methanol in the presence of alkaline catalyst-like sodium hydroxide, potassium hydroxide, or methoxide process is most commonly employed in industrial-scale biodiesel production [11]. The major drawback of this alkaline process is its sensitivity to FFAs in oils (42.5%), which results in soap formation, thereby reducing the yield and complicating the separation process [8,12,13]. Acid catalyst processes can be applied to substrates with high FFAs, but they have a lower reaction rate and can cause technical problems with glycerol byproducts and the purification and separation of biodiesel from the catalyst [12,14,15]. Subcritical and supercritical reactions, as non-catalytic processes, can produce a high rate of conversion over a short period of time. Nonetheless, the operating temperatures and pressures are quite high (200–400 °C and 10–25 MPa respectively) and not economical for biodiesel production [16]. The aforementioned problems have led to the development of an enzyme-catalyzed route for biodiesel production that is characterized by certain environmental and economical advantages over conventional chemical methods [17]. The enzyme catalyst process diminishes inherent problems associated with the use of an alkali/acid for producing fatty acid methyl ester (FAME) or fatty acid ethyl ester (FAEE) from substrates with either low or high FFAs. Lipase is the most prevalent enzyme used in this process [18]. The advantages of enzymatic biodiesel production include (1) no soap formation, (2) higher purity of glycerol byproducts, (3) simplified production process, (4) low-energy consumption, (5) easy enzyme recycling, and (6) easy separation of lipase from the products [19,20]. However, low reaction rate, high cost of lipase, and inhibition of enzyme activity by using organic solvents, such as n-hexane, are drawbacks of applying enzymes as catalysts for biodiesel production [5]. As a result, most current investigations in this field focus on eliminating the drawbacks of enzymatic biodiesel production, such as developing an enzymatic route with a higher reaction rate, lowering enzyme cost, and creating a more environmentally friendly process [21]. This review examines state-of-the-art process technologies for enzymatic biodiesel production, with emphasis on the two-step hydroesterification method. Recent investigations and developments on enzymatic hydrolysis and esterification of various feedstocks have also been reviewed in depth. This review also aims to present the advantages and disadvantages of using enzymes in biodiesel production from different substrates, as well as the factors influencing enzymatic biodiesel production. The results of this work may provide a reliable reference for future enzymatic hydrolysis operations and clarify the enzymatic esterification mechanism for screening proper enzymes, reactants, and operating conditions in further investigations.

2. Enzymatic biodiesel production Enzymatic biodiesel production using lipase (TAG acylhydrolase) has long been considered an environmentally friendly and energyefficient consumption route for the production of FAAE from vegetable oils [22,23]. Owing to several drawbacks in this process, it has not been used on a large scale despite its advantages, such as converting low-quality (high FFA) feedstock, lower energy consumption, and food-grade glycerol production [24]. The main

hurdles impeding the industrial application of enzymes for biodiesel production are enzyme cost and conversion efficiency [25– 27]. Reducing enzyme (lipase) cost and improving overall process economics for large-scale enzymatic biodiesel production have been the major challenges of recent research investigations [28]. Enzymatic biodiesel production can be performed through three reaction mechanisms: transesterification, interesterification, and esterification [5,29]. According to lipid chemistry, transesterification is the catalytic route of replacing the alkoxy group of an ester with an acyl acceptor (methanol, ethanol) that converts TAG in oils to glycerol and FAAE. The advantages of biodiesel production through enzyme-catalyzed transesterification include little or no byproduct generation, mild reaction conditions, reuse of the catalyst, and insensitivity to high-FFA oils [30–33]. Ester production can be achieved through synthesis with FFAs and alcohols in a process called esterification [34,35]. Esterification reactions catalyzed with lipase are among the most important, industrially relevant biochemical and chemical processes [36–38]. In enzymatic esterification of oils with high FFAs, biodiesel is directly produced through the reaction of FFAs with alcohol in the presence of an enzyme, which results in FAAE and water as byproducts [39]. The use of short-chain alcohols such as methanol in biodiesel production has drawbacks, including the inhibition of lipase activity and the undesirable combination of water and FFAs. As a result of fast deactivation and the short lifespan of enzymes during repeated experiments, a considerable amount of enzymes are required for biodiesel production, ultimately increasing the cost of biodiesel production [40]. To prevent problems with the use of short-chain alcohols and increase efficiency, enzymatic interesterification (using alternative acyl acceptors such as methyl acetate, dimethyl carbonate, and ethyl acetate) can be used in biodiesel production. Enzymatic interesterification is the transformation of TAG to biodiesel in the presence of both an acyl acceptor (like methyl acetate) and an enzyme, which results in the formation of another TAG, rather than glycerol, as the byproduct [41]. Previously mentioned biodiesel production processes have not yet been implemented on an industrial scale because of several constraints, such as slow reaction rate, alcohol inhibition, exhaustion of enzymatic activity, and high cost of enzymes [33]. Nonetheless, considerable efforts have been made by researchers to increase reaction efficiency and high-quality biodiesel production to meet the stringent quality requirements of international standards, such as ASTM 6751-03 [42–44]. Recent investigations on biodiesel production systems can be categorized into the following approaches: co-solvent systems, two-step methods, lipase combinations, value-added byproducts, ionic liquid technology, microwave usage, and ultrasonic technology [28,45,46]. Table 1 illustrates the latest developments for each system mentioned above. Among the mentioned developments for enzymatic biodiesel production, the two-step process has attracted considerable attention in the production of second-generation biodiesel given its application in a wide range of FFAs and water in feedstocks, high reaction rate, high quality of byproducts, and minimized deactivation of lipases by an acyl acceptor (such as methanol). In Section 3, hydroesterification, a two-step process for biodiesel production, is reviewed in depth. All examined conditions for oil hydrolysis and fatty acid esterification are collected to create a complementary reference aimed at lowering enzymatic hydroesterification costs and increasing efficiency at each step of the biodiesel production process. 2.1. Key factors on enzymatic biodiesel production Crucial factors affecting economic viability, yield, and conversion efficiency of enzymatic biodiesel production processes include enzymes (type and preparation method), substrates, acyl acceptors, and bioreactor design [61,62].

H. Pourzolfaghar et al. / Renewable and Sustainable Energy Reviews 61 (2016) 245–257

247

Table 1 Latest development systems for enzymatic biodiesel production. Production system

Enzyme

Advantages

Co-solvent

Novozym 435

 Using t-butanol as a co-solvent caused no inhibition of the enzyme at high 2014 480

C. antarctica

  

Two-step

Y. lipolytica Novozym 435

    

Combination of lipases

Thermomyces Lanuginosus (TLL) Novozym 435 Novozym 435Lipozyme TLIM LLPL-2

Value added by-products Novozym 435

        

Novozym 435 Ionic liquid

PEL

CAL-B

     

Ultrasound

CAL-B



Microwave

B. cepacia

  

Year

Yield (%) Ref.

methanol concentrations Enzyme was used over 7 reaction cycles The enzyme may be reused over 40 times with little reduction in enzymatic 2014 99.1 activity t-butanol improved the solubility of plant oils and minimized the inhibitory effect of methanol during the process 2011 82 No contamination of glycerol with ethanol High efficiency for biodiesel production of oil in a solvent-free method and short 2010 98 reaction time Reuse of the enzyme Suitable to feedstocks with wide range of water and contents of FFA High quality of products 2015 92.4

Continuous reuse of the lipases for 20 cycles without any loss of activity Decreased catalyst cost and increased ester yield High conversion in short reaction time Good reduction of phosphorus (P o5ppm) Complete transformation of oil to Fatty acid methyl ester Avoidance of the acid treatment required for gum removal Require mild reaction temperature Reduction in the cost of biodiesel production Generating higher-value byproducts (glycerol carbonate) in producing biodiesel from oil

[48]

[49] [50]

[51]

2015 80 2010 497

[52] [53]

495

[54]

2014

2013 96.4 92.1 2011 84.9 92 2014 94.7

Decreasing catalyst cost High conversion yield Desirable alternatives for volatile, flammable, and toxic organic solvents Reuse of the enzyme for 5 cycles 2011 100 Reuse of the enzyme for 9 cycles Use of the ionic liquid resulted in a three-phase system. This allowed a selective extraction of products. Improvement of physical, biological, and chemical processes, especially in extre- 2014 81 mely immiscible and viscous reaction system Environmentally friendly method Clean, efficient, and convenient energy source for rapid heating 2014 100 Accelerates the initial velocity of reactions

2.1.1. Lipase Lipases (carboxylesterases) are enzymes that can be classified as animal, plant, or microbial based on their origin. They catalytically convert triglycerides into fatty acids, glycerol, and di- and monoglycerides [63,64]. Lipases can also catalyze interesterification, transesterification, and esterification reactions in organic solvents and sub/supercritical media—typically for biodiesel production— because they are serine hydrolases [65,66]. Lipases of microbial origin are more stable than plant and animal lipases and are available in bulk at lower cost [67–69]. The structural properties of lipases from different sources can exhibit different activities on different substrates; therefore, any process should be optimized based on the selected enzyme and substrate [70]. The choice of a particular lipase to modify a lipid is dependent on the type of desired modification and may be reformed via straightforward synthesis and transesterification, hydrolysis reformation, fatty acidspecific reformation, or site-specific reformation of TAG [24]. Lipases may be classified into three groups depending on their specificities to substrates: fatty acid-specific; 1,3-specific; and nonspecific [70–72]. However, for optimal biodiesel production, lipases should be able to convert all three forms of glycerides (nonspecific enzymes) to biodiesel [73]. The cost of lipase production is one of the major hurdles in the industrial application of lipases. This obstacle can be eliminated through lipase immobilization [74]. Immobilization involves physically binding the enzymes to a solid support so that the substrate can pass over the enzyme support and be converted into the product [75]. Enzyme immobilization is increasingly being used because prolonged enzyme–substrate

[47]

[55] [56] [57]

[58]

[59]

[60]

contact results in decreased redundant byproducts and purification steps; it also enables recycling of the enzyme, thereby lowering costs. Binding the enzyme to a support can also result in enzyme stabilization and prevent the contamination of both the product and the enzyme. Immobilization technologies can be classified into three categories: cross-linking, carrier binding, and entrapment [76]. Carriers used for lipase immobilization include Sepabeads, cellulosic nanofibers, polyurethane foam, activated carbon, and silica [77]. Selecting the proper technology and carrier for immobilization strictly depends on the source of the lipase, the reaction system (two-phase, organic solvent, or aqueous), and the conditions of the process, such as pressure, temperature, and pH. The most frequently used method for immobilization is the adsorption of lipase on a carrier. It is the simplest method, and it constitutes the formation of reversible surface reactions between the enzymes and the carrier. The method is simple, fast, inexpensive, and reversible; in addition, no chemical changes to the support or the enzymes are needed [78,79]. 2.1.2. Substrate Selecting an appropriate biodiesel feedstock highly depends on the chemistry process, the chemical and physical properties of the oil, the economy of the process, and the geographical position, agricultural potential, and climate conditions of the production area [80–82]. The input materials employed in biodiesel production are classified into three specific categories: plant-derived oils (edible and non-edible oils), waste oils (animal fats, waste cooking oils, yellow grease, and lard) [83], and oleaginous microorganisms

248

H. Pourzolfaghar et al. / Renewable and Sustainable Energy Reviews 61 (2016) 245–257

Table 2 Review of some oil sources for biodiesel production [87–91]. Category

Source

Oil content (Wt%)

Main fatty acids

Major Producer countries

Plant derived Oils

Canola Castor Coconut Corn Cotton seed Desert date Hemp seed Jatropha Jojoba Karanja Linseed (Flaxseed) Mahua Mustard seed Neem Olive Palm Palm Kernel Peanut Polanga (Undi) Pumpkin seed Rapeseed Rice bran Rubber seed Safflower seed Sesame seed Soybean seed Sunflower Tobacco seed Tung Beef Tallow Chicken fats Fish fats Porklard Waste salmon Waste cooking oil Microalgae Bacteria Fungi Yeast

40–45 45–50 65–68 3.1–5.7 18–20 45–50 22–38 50–60 45–50 30–40 35–45 35–40 33 20–30 15–35 40–45 44–53 45–50 65 31.5 40–45 15–23 40–60 35 50 18–20 25–30 30–43 16–18 – – – – – – 30–70 – – –

Oleic, Linoleic, Linolenic Ricinoleic, Linoleic, Oleic Linoleic, Palmitic Linoleic, Oleic, Palmitic Linoleic, Palmitic, Oleic Linoleic, Oleic, Stearic Linoleic, Oleic Oleic, Linoleic, Palmitic Gondoic, Erucic, Oleic Oleic, Linoleic, Palmitic Linolenic, Linoleic, Oleic Oleic, Palmitic, Linoleic Erucic, Linolenic, Linoleic Oleic, Linoleic, Stearic Oleic, Linoleic, Palmitic Oleic, Palmitic, Linoleic Lauric, Myristic, Palmitic Oleic, Linoleic, Palmitic Linoleic, Oleic, Linolenic Linoleic, Oleic, Palmitic Oleic, Linoleic, Linolenic Linoleic, Oleic, Palmitic Oleic, Linoleic, Linolenic Linoleic, Oleic, Palmitic Linoleic, Oleic, Palmitic Linoleic, Oleic, Palmitic Linoleic, Oleic, Palmitic Linoleic, Oleic, Palmitic Eleostrearic, Oleic, Linoleic Oleic, Palmitic, Stearic Oleic, Palmitic, Linoelaidic – – Oleic, Palmitic, Docosahexaenoic Oleic, Palmitic, Stearic – – – –

Canada, China, India Mediterranean, Eastern Africa, India Filipinas, Indonesia, India USA, Mexico, Russia China, India, Pakistan, USA Middle east,North Africa France, China Indonesia, Ghana, Madagascar Southwestern North America East Indies, Philippines, India China, Belgium, USA, Germany India, Bengal Canada, Hungary, Great Britain, India India, Burma, Thailand, Iran Spain, Italy, Greece Indonesia, Malaysia, Thailand Indonesia, Malaysia, Nigeria China, India, Nigeria India, Indonesia, Bangal China, India, Russia Canada, China, Germany China, India, Indonesia India, Sri Lanka, Indonesia, Malaysia India, USA, Mexico Myanmar, India, China China, USA, Brazil Ukraine, Russia, Argentina China, India, Brazil Western and southern China USA, all countries All countries All countries China, USA Norway, Chile, UK All countries USA, Europe, India USA,UK USA USA

Waste Oils

Oleaginous Microorganisms

(microalgae, bacteria, fungi, and yeast) [84–86]. Table 2 illustrates useful information (oil content, composition, and major producers) on several oil sources from each category. According to the table, coconut, microalgae, jatropha, and polanga have the highest oil content (65–68%, 30–70%, 50–60%, and 65%, respectively). Biodiesel production can also be classified into three generations, namely, first, second, and third generation, on the basis of various factors, including type of feedstock, type of processing technology, and their level of development. In first-generation biodiesel, feedstocks generally consist of edible vegetable oils, such as sunflower oil in Ukraine, soybean oil in China, South America, and the USA, rapeseed oil in Europe, and palm oil in tropical countries [92]. Given the drawbacks in using edible oils, such as limited sources, high cost, and competition with food consumption, second-generation biodiesel feedstocks (e.g., waste cooking oils and non-edible oils) are used to reduce the production costs of biodiesel and increase food security [4,83,93,94]. Using waste oils and animal fats as feedstock also addresses the problem of waste oil disposal [95–97]. However, the need for large areas of land with moist soil is a disadvantage for many second-generation feedstocks. This problem could be completely addressed with thirdgeneration biodiesel, which is derived from oleaginous microorganisms. This generation can produce 15–300 times more oil for biodiesel production than conventional crops on an area basis. Additionally, compared with traditional crop plants commonly harvested once or twice a year, oleaginous microorganisms have a very short harvesting cycle (1–10 days), allowing for multiple or continuous harvests with considerably increased yields [98].

2.1.3. Acyl acceptor Alcohols such as methanol are the most frequently used acyl acceptors for biodiesel production [73,99]. However, the inactivation of lipases caused by adding methanol (e.g., adding a 1.2 M equivalent) is a major hurdle in enzymatic biodiesel production [20,48], leading researchers to seek an alternative alcohol or process condition to increase biodiesel production. Several alcohols (e.g., isopropanol, tert-butanol, propanol, butanol, branched alcohol, and octanol), as well as solvent engineering and stepwise alcohol additions, have been tested. To date, using ethanol as an alternative alcohol and a stepwise alcohol addition are promising strategies for surmounting this obstacle [100]. As an alternative alcohol for biodiesel production, ethanol is inexpensive and less toxic than methanol; it is considered a renewable source because it can be simply produced from renewable sources [101]. Regarding their characteristics as fuels, FAME and FAEE only have minor differences. As an example, FAEEs possess somewhat lower cloud and pour points and moderately larger viscosities than FAMEs [102,103]. Hernandez-Martin and Otero [104] compared enzyme-catalyzed transesterification of sunflower oil with two alcohols, including methanol and ethanol, in identical processing conditions. They found that enzyme deactivation was greater with methanol than in ethanol. In addition, the ethanolysis of sunflower oil through Novozym 435 was much faster than through methanolysis (100% conversion to FAAE, compared with 85% FAME production at 25 °C for 24 h). The stepwise addition of alcohol, which was initially presented and performed by Shimada et al. [105] and Watanabe et al. [106], is

H. Pourzolfaghar et al. / Renewable and Sustainable Energy Reviews 61 (2016) 245–257

another solution to minimize enzyme inhibition in biodiesel production. In this method, alcohol is added to the reactor in several steps over time. The type of enzyme and substrate strictly determines alcohol/substrate molar ratio in each alcohol addition step [107]. In Nie et al. [108], the effects of the frequency of adding methanol to the mixture (2 g salad oil, 10 wt% water, 5 mL hexane, and 20 wt% lipase) were investigated by performing the addition of methanol from 1 to 10 times. The study results demonstrated that conversion could not be increased any further when the amount of methanol added stepwise exceeds three times the amount of methanol. 2.1.4. Bioreactor design Many bioreactor configurations, including batch-stirred tank reactors (STRs) [109,110], packed bed reactors (PBRs) [20,108,111], fluid beds, expanding beds, recirculation membrane reactors, and static mixers, have been examined for enzymatic biodiesel production [73]. Batch-STRs and PBRs are the most widely studied bioreactors in this field. STR is the simplest bioreactor type, consisting of a propeller that mechanically stirs reactant mixtures. The major disadvantage of a batch-STR is its low level of productivity because of the need to empty, wash, and reload the reactor for each new batch. However, this problem can be eliminated by using a continuous STR [77]. To reduce operational costs, enzymatic production of biodiesel must be carried out in a mode of continuous operation. Numerous studies have reported the successful use of PBRs for enzymatic production of biodiesel under various setups, including nine PBRs operated serially with hydrocyclone set next to the PBRs to split the glycerol, three PBRs operated serially with intermediate removal of glycerol and the addition of methanol, single recirculating PBR, and single PBR with stepwise methanol addition [19,30,112,113]. Some advantages of continuously using PBRs include ease of assembly, low cost, high production efficiency, ease of maintenance and operation, and automated quality control [114,115]. The optimization of PBRs for use in enzymatic biodiesel production processes is the primary focus of recent research efforts [116,117]. Yoshida et al. [118] tested a PBR for enzymatic biodiesel production using the alcoholysis of Shirashima oil catalyzed with an Aspergillus oryzae biocatalyst. An oil to ME conversion of 96.1% was attained under optimized conditions that included 140 min per pass residence time and a stepwise methanol addition of 4.25 M equivalents to oil for 6 passes. In a study by Chen et al. [119], a PBR for continuous biodiesel production was examined using the alcoholysis of oil (soybean) catalyzed with Novozym 435. Under optimized conditions that included a flow rate of 0.1 ml/min at 52 °C and an oil/ methanol molar ratio of 1:4, a molar conversion of 83% was achieved without any loss in lipase activity for 30 d in continuous operation. Shaw et al. [120] tested a PBR for producing biodiesel from soybean oil with Novozym 435 as catalyst and n-hexane, tert-butanol as a cosolvent and achieved a conversion of 75%.

3. Hydroesterification Hydroesterification is an integrated process combining two essential processes, esterification and hydrolysis, in successive reactions to generate biodiesel. This process can be performed through (1) catalyst-free hydroesterification (sub/supercritical hydrolysis and esterification), (2) enzymatic/chemical hydroesterification, and (3) enzymatic hydroesterification [121]. Hydroesterification was recently established as a means to address problems related to conventional biodiesel production methods using second-generation feedstocks containing high percentages of FFA and water, such as animal fats, non-edible oils, and waste cooking oils [122,123]. Some disadvantages of conventional approaches include slow reaction rates, soap formation, difficulties in catalyst purification, and contamination of glycerol byproduct both with methanol and salt produced from neutralization of the employed

249

catalyst, thus resulting in low-value glycerol [124]. Conversely, the advantage of hydroesterification as a method for producing biodiesel is the creation of glycerol without interaction with methanol; the resulting byproduct is a higher-value food-grade glycerol. Another major advantage of this method is that it allows the use of raw material fats and oils with high amounts of water and high concentrations of FFAs, which have a low market price [125]. One of the leading investigations regarding enzymatic hydroesterification occurred in 2007 [126]. Watanabe et al. [126] converted acid oil into FAME by means of esterification of FFA to FAME via Candida antarctica lipase following the hydrolysis of acylglycerols using Candida rugosa lipase. They obtained a high degree of esterification (98%), eliminated the inhibition of glycerol on the immobilized lipase, and completed more than 40 cycles of reused lipase. Other investigations performed by different researchers found various process routes to increase efficiency of the process while decreasing reaction time and cost. Wei-Jia Ting et al. [127] used an enzymatic/acid-catalyzed hydroesterification method to increase the efficiency of the esterification step to 99% by examining different acids as the catalyst (sulfuric, hydrochloric, nitric, phosphoric, and acetic acid). Furthermore, by using a binary method to immobilize the enzyme, they achieved a high degree of hydrolysis in approximately 5 h (88%). In another study, De Sousa et al. [128] characterized and applied a low-cost plant enzyme for producing biodiesel (97% hydrolysis conversion) through enzyme/chemical hydroesterification from different types of substrates. According to their report, the produced biodiesel was of excellent quality, with a viscosity of 5.5 mm2/s, ester content of 97.1%, total glycerol content of 0.09% w/w, maximum methanol content of 0.05% w/w, and CFPP of 0 °C. The application of a hydroesterification process to different types of feedstocks has also been researched. Almarales et al. [129] studied biodiesel production by using microalgae Nannochloropsis oculata as raw material. They used an Al2O3-supported Nb2O5 catalyst and achieved 92.3% and 92.24% conversion rates for the hydrolysis and esterification processes respectively. Enzymatic hydroesterification has gained the most attention from researchers in this field. Fig. 1 represents a schematic flow diagram of the enzymatic hydroesterification process. From the figure, biodiesel production by enzymatic hydroesterification method occurs in two consecutive steps: enzymatic hydrolysis and enzymatic esterification. In the first step, all glycerides (mono-, di-, and triglycerides) are converted into FFAs and high-purity glyceride using enzyme as catalyst in the presence of water. Then, the separated FFAs are esterified with an alcohol in the company of an enzyme as catalyst to produce pure FAAE (biodiesel). Water, a byproduct of the second step, is reused in the hydrolysis step in a continuous method. Identifying low-cost lipases with higher conversion efficiencies and optimizing process conditions have been the major subjects of recent investigations. Talukder et al. [50] employed Novozym 435 and C. rugosa lipases as biocatalysts for the esterification of FA and hydrolysis of crude palm oil (CPO) respectively. They reported that the complete conversion of CPO to FA could be achieved in 4 h under optimized conditions by using C. rugosa, and a 98% conversion rate of FA to FAME could be achieved in 2 h by applying Novozym 435 as a catalyst. In another survey, Meng et al. [49] used Yarrowia lipolytica lipase for the hydrolysis of soybean oil to FA and used immobilized Y. lipolytica for the esterification step. They achieved a higher conversion efficiency (hydrolysis 92.5%; esterification 85%) with a lower loading of enzymes into the process with less reaction time compared with the aforementioned study by Watanabe et al. [126]. In another study, Adachi et al. [130] studied the direct use of lipaseproducing cells as whole-cell biocatalysts in the hydroesterification process for producing biodiesel from soybean and palm oils. They applied C. rugosa lipase and immobilized r-CALB in the hydrolysis and esterification steps respectively. Their results revealed that obstacles in the lipase purification steps could be overcome by

250

H. Pourzolfaghar et al. / Renewable and Sustainable Energy Reviews 61 (2016) 245–257

Fig. 1. Schematic flow diagram of the enzymatic hydroesterification process.

applying r-CALB as a catalyst in the esterification step, considering that lipase developed methyl ester content of about 90% after 6 h without any stepwise additions of methanol. Furthermore, they were able to limit the water content to maintain the catalyst during esterification. In 2015, Paula et al. [131] studied the enzymatic synthesis of alkyl esters by a two-step hydrolysis/esterification process using unrefined macaw palm oil as feedstock. Thermomyces Lanuginosus (TLL) immobilized on poly-hydroxybutyrate (PHB) was used as a biocatalyst. Under optimum experimental conditions, complete hydrolysis was reached after 110 min along with 92.4% ester conversion in only 15 min. The results showed a highly efficient process for enzymatic biodiesel production. 3.1. Enzymatic hydrolysis Fats and oils (TAG) have a common molecular structure consisting of a mole of glycerol (or glycerin) and three ester functional groups. One of the reactions of TAGs is the hydrolysis of the ester groups, resulting in fatty acids and glycerol, as shown schematically in Fig. 2 [36,132–134]. Products of this reaction (i.e., fatty acids and glycerol) are used extensively as raw materials in cosmetics, food, pharmaceutical products [135–137], biofuel, soap, and synthetic detergents [138]. This reaction may be catalyzed using lipase, base, or acid, despite the fact that it also progresses as a non-catalyzed reaction between the water dissolved in the fat phase and the fat itself under appropriate pressure and temperature conditions [139]. The traditional hydrolysis of TAG process (colgate-emery process) demands a temperature of 250 °C or higher, and pressure of nearly 4.82 MPa to achieve high conversion (98%). However, this process is remarkably energy intensive [140]. To reduce energy consumption and decrease thermal degradation of products, a number of researchers developed an alternative enzyme-catalyzed hydrolysis that occurs at room temperature. Enzymatic reactions can occur under milder temperature and pH conditions, reduce energy costs, consume less solvent, and provide cleaner products with a reduced danger of undesirable side reactions [141–143]. Enzyme-catalyzed hydrolysis reaction may be defined with a Michaelis–Menten mechanism when a lipase is the catalyst in multiphase systems [144]. A variety of models of this kinetic mechanism have been suggested [133]. Ideally in the two-dimensional (2-D) Michaelis–Menten catalytic mechanism (Fig. 2), the reaction progresses via adsorption of soluble lipase on an aqueous–organic interface. Then, this adsorbed lipase binds with the substrate molecule and produces an enzyme–substrate complex. Subsequent to a number of chemical steps, the soluble products diffuse into the water layer (P1 and P2). In Fig. 2, E¼lipase, E*¼lipase on an aqueous/organic surface,

Fig. 2. 2-D four-step reaction for lipase-catalyzed hydrolysis of substrate at the mixture interface [35].

E*S¼the enzyme–substrate complex, P1*¼ Product 1 on the interface, P2*¼ Product 2 on the interface, P1 ¼Product 1 diffused in the water layer, and P2 ¼ Product 2 diffused in water. The rate constants, kp and kd, are related to the adsorption-desorption of enzymes between the aqueous and lipid–water interface [36]. Studying the kinetics of enzymatic hydrolysis helps improve both the quality and yield of the processed products (fatty acids and glycerol) and the process conditions (temperature, pH, type and concentration of enzyme, and oil-to-buffer ratio). Depending on feedstock compositions, various hydrolysis procedures with certain process conditions have been developed to date. To select the proper method for enzymatic hydrolysis, recent procedures in existing literature have been outlined in Table 3. 3.2. Enzymatic esterification The next step in the hydroesterification route for biodiesel production is the esterification of fatty acids produced in the hydrolysis step into FAAE. In the current stage, FA is esterified with an acyl acceptor in the presence of a catalyst to generate FAAE and water as byproducts [158,159]. The applied catalysts for this process can be categorized into biological (enzymes) and chemical (bases and/or acids) agents [132,159]. Enzymatic esterification was developed a number of decades earlier [160], and various lipases have been employed in conjunction with organic solvents, free solvent systems, and primary or secondary alcohols. More recently, biotechnology and chemical industries have expressed interest in this research because of the growing organic ester applications and the significance of the derived products [161]. Numerous mechanisms have been suggested for enzymatic esterification processes [162]. Depending on the solvent system and the applied lipase, a ping-pong bi–bi mechanism or a Michaelis–Menten model can be used to incorporate kinetics of lipase-catalyzed esterification reactions, besides factors influencing reaction rate [36]. (Eqs. (1) and 2) represent the general reaction mechanism for fatty acid esterification with alcohol. Based on these

Table 3 Review of enzymatic hydrolysis of various feedstocks under different reaction conditions. Enzyme

Substrate

Reaction conditions Oil/buffer

T (°C)

Time (hrs.) pH

Yield (%) 480

–

35

–

6.8

C. rugosa type VII Jatropha curcas L.

2:1 (w/w) 10% (w/v)

40 40

5 2

8 8

C. rugose

Soybean Oil Refined palm oil Crude palm oil Olive oil Physic nut oil Castor oil Biodiesel waste Animal tallow Babassu Palm oil Soybean oil Waste cooking oil

15.9 (m/m) 15.9 (m/m) 44.1 (m/m) 1:1 (v/v)

43.5 43.5 37 30

60 min 70 min 80 min 10

88 87 95 99 98 24 75 75 4.5 55 72 32 6.8–7.4 100

Lipozyme

Macauba kernel oil

2:1 (w/w)

55

6

8

82

Soy deodorizer distillate Acid oil

40% (w/w)

45

3

–

71

60% (w/w)

30

24

–

66

Canola oil

30 wt%

37.5

2

4.5

100

Babassu oil Palm oil

1:5 0.1 g/ml

40 45

3 90 min

8 7.5

88 97

Soybean oil Palm oil Soybean oil

2:1 (w/w)

30 50 60

24

7

48

8

92 89 89

1:1 (v/v) 200 g oil/120 ml water 50% (v/v)

30 40

4 48

7 –

100 92.5

30

6

4

99.6

40

15

–

–

40

90 min

6

100

35–40 40

12

7 9.5

42.5 –

Ambient temperature 40

1

7

40

24

7.5

78

35

72

7

480

33–39

110 min

4.5

100

Ricinus communis

RM IM

C. rugose C. rugose Ricinus Communis L. B-22 C. Rugosa type VII C. rugose Thermomyces lanuginosus C. rugose Y. lipolytica

Crude palm oil Soybean oil

50% (v/v)

Ricinus Communis L. Candida sp. 99–125

Acid oil

Lipase-SP398

Palm oil

A. oryzae Pancreatic lipase

Castor oil Olive oil

200 g oil/240 g water 25 g oil/ 1 lit water 3/1 50% (v/v)

A. oryzae

Castor oil

4/1

C. rugose

Jatrohpa Curcas oil

Mucor circinelloides

Waste sardine oil

10 g oil/ 5 g water –

Thermomyces

MPPO

35% m/m

Waste cooking oil

It was found that in using R. oryzae lipase, a two-step reaction mechanism for the enzymatic conversion of triolein occurs that includes consecutive hydrolysis and esterification. The enzyme was immobilized onto chitosan beads using the binary method. Economic and efficient enzyme that could be used for different carbon-chain substrates.

[72]

[127] [128]

Short reaction time is required for hydrolysis of oils.

The enzyme has no need for any purification and immobilization step and might be considered as an economic biocatalyst for the production of concentrated fatty acid triglycerides. The enzyme was used in more than five cycles without any pretreatment and with a slight decrease in FA production. The conversion yields obtained for use of Lipozyme RM IM where higher than those obtained from Lipozyme TL IM and Lipozyme 435. The addition of salts and surfactants did not promote increased production of FFAs, while adding n-hexane and heptane as a buffer to the reaction medium led to an increased reaction rate. High-pressure carbon dioxide (SC-CO2) has been used for hydrolysis process.

[145]

Powder enzyme was used for hydrolysis and almost low conversion of acylglycerol to FA was achieved. Economic lipase that was extracted from dormant castor bean seeds showed satisfactory results on production of free fatty acids from triglyceride. The used enzyme has a preference for substrate of short to medium chain length. The low oil/buffer ratio for the hydrolysis process makes it an expensive route for producing FA from oils. –

[126]

[130]

The enzyme has low-rate conversion of triglycerides to FA.

[152]

The applied enzyme could be reused for more than 10 cycles with average FA yield of 92%. Although the oil/water ratio is high in comparison with other studies, the reaction time is high and cannot be considered as a suitable condition for hydrolysis process. High efficiency reached with high oil concentration (50% v/v) and without organic solvent and emulsifier. –

[50] [49]

Experimental outcomes revealed that the interfacial area between the aqueous phase containing the enzyme and the oil drops controls the hydrolysis rate. Additives such as salts and isooctane have no or negative effect on the rate of hydrolysis. Biphasic enzyme membrane reactor (EMR) was used for the hydrolysis of olive oil to fatty acids. The hydrolysis process was carried out in oil in water emulsions that resulted in optimizing the usage of enzyme. The effect of agitation was studied in order to maximize the hydrolysis efficiency.

[136]

[146] [147]

[148]

[149] [150] [151]

[121] [153]

[154] [155] [156] [157]

Analytical results were revealed an increase in omega-3 (EPA and DHA) content as much [51] as 12.56% compared to the crude oil. [131]

251

Triolein

Ref.

H. Pourzolfaghar et al. / Renewable and Sustainable Energy Reviews 61 (2016) 245–257

R. oryzae

Remarks

H. Pourzolfaghar et al. / Renewable and Sustainable Energy Reviews 61 (2016) 245–257

T (°C) Oil/buffer Lanuginosus (TLL)

Enzyme

Table 3 (continued )

Substrate

Reaction conditions

Time (hrs.) pH

Yield (%)

Remarks

Response surface methodology was used to study all variables affecting enzymatic Hydrolysis.

Ref.

252

equations, fatty acid [B] forms a connection with the enzyme and produces enzyme-acyl intermediate [EB] with liberation of water as the first product. Then, alcohol [A] binds to the enzyme-acyl, thereby leading to liberation of the second product [P], and the enzyme restores its original form [162]. Enzyme þ Acid 2 Enzyme Acyl 2 Ester þEnzyme

ð1Þ

Eþ ½B2½EB þ ½A2½EBA-E þ P

ð2Þ

Water=↑

Alcohol=↓

The incorporating factors that affect enzymatic esterification reactions to determine the best conditions for maximum ester yield were recently studied. Among the important factors that influence the efficiency of enzymatic esterification are the enzymes (type, preparation method, and concentration), time, temperature, and pH of the reaction; molar ratio of the substrates; and the type of alcohol, mixing rate, presence of impurities, and water content in the reaction medium [163]. Table 4 shows a comprehensive list of recent investigations for enzymatic esterification from various feedstocks and under different reaction conditions. The list will facilitate comparison and convenient selection of substrates in future studies.

4. Conclusion An alkali-catalyzed process is the current dominant method in the large-scale production of biodiesel from virgin vegetable oils. However, because of intrinsic drawbacks, such as saponification difficulties, energy intensity, high production costs, and difficulties in glycerol separation, this process is not the best option for biodiesel production from low-cost feedstocks (waste cooking oils, nonedible oils, fats, etc.) in terms of yield and quality. Alternative chemical methods, such as acid-catalyzed processes, cannot offer any characteristic advantages in producing biodiesel from feedstocks with high levels of FFA and water. The enzyme-catalyzed process offers many environmental and economic benefits over the chemical method, including low-temperature reaction conditions, reuse of enzymes, highly pure products, lower alcohol-to-oil ratios, avoidance of side reactions, easier product separation and recovery, biodegradability, and environmental acceptance. However, enzymatic biodiesel production has some major obstacles, such as high cost of enzymes and inhibition of enzymes by alcohol. The development of enzymatic biodiesel production has focused on cost-effective and environmentally friendly processes with highquality products in a short reaction time. Some recent production systems have been introduced and compared in this paper, and the two-step process is concluded as the most promising approach in this field. Enzymatic hydroesterification is a two-step approach in biodiesel production from feedstocks with high FFA and water content. Applying this process can dramatically reduce difficulties associated with using biocatalysts for producing biodiesel. This methodology integrates two essential processes in consecutive reactions for biodiesel production, namely, enzymatic hydrolysis and enzymatic esterification. Therefore, most of the recent investigations for the two essential processes have been thoroughly surveyed in this paper. The following particular conclusions are based on the review from these recent investigations: 1. Enzymatic hydroesterification is the most suitable process for biodiesel production from low-cost feedstocks. 2. Depending on geographical position, a specific feedstock is appropriate for biodiesel production. 3. Each feedstock or enzyme needs unique process conditions that should be optimized in laboratory scales.

Table 4 Review of enzymatic esterification of various feedstocks under different reaction conditions Enzyme

Substrate

Reaction conditions Oil/Alc

Yield (%) T (°C) Time (hrs.)

Alcohol

Remarks

Ref.

The lipase showed high operational stability in product yield even after eight successive batch cycles. Using fermented solids resulted in lower production cost of biodiesel with enzymes. The applied lipase showed much higher conversion than solid acid catalyst for the same reaction time. High-pressure carbon dioxide (SC-CO2) was used for esterification process. This method has higher efficiency and lower reaction time in comparison with shake flask method (88%, 7 h). The FA esterification was carried out in two subsequent steps. More than 98% of the total esterification was preserved, albeit the first and second esterification reactions were iterated every 24 h for 40 days. By optimizing the esterification conditions, more than 19 reuses of the lipase were achieved with esterification rates above 80%. Different kinetic models have been examined for esterification of FA with alcohol and Prazeres et al.'s model proved to be the most appropriate for this reaction. It showed that the esterification reaction complied with second-order product inhibition. The stability of the enzyme was tested in more than 15 consecutive cycles and the biodiesel yield could maintain at 88.6%. The ability to reuse the lipase was tested, revealing that the immobilized lipase could be reused six times with a conversion up to 90%. The lipase showed higher catalytic activity on unsaturated fatty acids (such as Oleic acid) rather that saturated ones.

[164]

The lipase was reused for more than 50 cycles without significant loss of its activity.

[50]

PFAD

1:4

81.4

50

6

Ethanol

B. Cepacia Novozym 435

Soybean SODD

2:1 (w/w) 1:1

92 83.5

50 50

31 90 min

Ethanol Ethanol

Lipozyme IM

soybean deodorizer distillate Acid oil

–

95

36

3

Butanol

–

99

30

24

Methanol

1:1

480

30

24

Ethanol

1:2

76.2

35

24

Butanol

Candida sp. 99–125 Oleic acid

1:2

95.8

30

24

Ethanol

Candida sp. 99–125 Soybean oil Safflower oil Linseed oil Corn oil Palm oil Novozym 435 Crude palm oil

1:3

91 91.8 90.8 91.2 88.5 98

40

30

Methanol

40

3

Methanol

85

30

3

Ethanol

C. antarctica

Candida sp. 99–125 Acid oil R.oryzae

Tuna fish oil fatty acids

Soybean oil

NS81006

Oleic acid

1:4.5

90

45

3

Candida sp. 99–125 Waste cooking oil

1:2

96

40

8

Lipozyme IM

Castor oil

1: 3

98

65

8

Lipozyme IM Lipozyme IM

SODD Crude Jatropha oil

1: 2.3 –

89 86

46 60

2 10

Rhizomucor miehei Macauba pulp acid oil

1:2

91

40

8

Novozym 435 C. antarctica Candida sp. 99–125 C. rugosa Novozym 435 CL-PCMC-LIP/Gly

Soybean fatty acids Oleic acid Waste cooking oil SODD PFAD Palmitic acid

1:6 1:1 – 1:4 1:2 1:4

 100 490 98.9 93 94.6 495

65 32 40 29 45 50

6 24 40 18 8 1

Novozym 435

Microalgal FFAs

1:1.5

92.6

25

4

Novozym 435

Waste cooking oil

1:6

89.5

40

24

Thermomyces Lanuginosus(TLL) Lipozyme RM IM

MPPO

1:1

92.4

32.5

15 min

Crude rapeseed oil

–

90

50

22

Different steps for the addition of ethanol to the reaction mixture were examined and three stepwise additions of the alcohol showed the best results. Ethanol Reuse of the free lipase could be achieved either by natural gravity force or by centrifugation while maintaining a high level of lipase operational stability. Methanol It was found that the initial water content of the substrate has no significant effect on the production of biodiesel. Ethanol The applied enzyme showed higher conversion efficiency in comparison with Lipozyme 435 (81.4%). Ethanol – Methanol The results revealed that enzymatic esterification follows multisubstrate ping pong mechanism with competitive inhibition by the alcohol. Ethanol The fermented solid showed a fair conversion rate and reusability in enzymatic esterification process. Ethanol The used ultrasonic irradiation had little influence on the conversion efficiency of the process. Ethanol The enzyme was reused up to ten cycles and the conversion efficiency was almost constant. Methanol The CFPP of the mixture decreased from 5 °C to  3 °C. Methanol – Methanol The enzyme was reused up to 13 cycles and the conversion efficiency was higher than 90%. Methanol Kinetic results such as maximum velocity of the reaction, inhibition constant of alcohol, Michaelis-Menten's constants and others were reported which are important basis for further up-scaling studies. Methanol Similar esterification degrees were obtained during several experimental scales (from 4 to 40 g FFAs). Ethanol The analysis of CCD results was confirmed the good fit of experimental data to the quadratic model. Hexanol The results revealed that biocatalyst prepared by physical adsorption of TLL on PHB particles is extremely favorable to catalyze esterification reactions at high reactant concentrations. Monoacylglycerol (MAG) The effect of many influential factors on the esterification yield was surveyed in this study.

[148] [126]

[167] [162]

[168] [169]

[49] [170] [171] [172] [173] [174] [121] [175] [39] [153] [176] [177] [178]

[179] [52] [131] [180] 253

Y. lipolytica

1:1.2 (m/ m) 1:2

[165] [166]

H. Pourzolfaghar et al. / Renewable and Sustainable Energy Reviews 61 (2016) 245–257

CL-PCMC

254

H. Pourzolfaghar et al. / Renewable and Sustainable Energy Reviews 61 (2016) 245–257

4. The range of temperature and pH in enzymatic hydrolysis are 30–60 °C and 4.5–9.5 respectively. 5. Candida rugosa (C. rugosa) is the most common enzyme used in enzymatic hydrolysis. 6. The range of temperature in enzymatic esterification is 25– 65 °C. 7. The enzymatic esterification of high FFA feedstock by ethanol and methanol has shown that it is currently the best method. 8. Novozym 435 (C. rugosa) is the most common enzyme used in enzymatic esterification.

Acknowledgment The authors gratefully acknowledge the financial support from GSP-MOHE (mo008-2015), University of Malaya, Malaysia.

References [1] Aransiola EF, Ojumu TV, Oyekola OO, Madzimbamuto TF, Ikhu-Omoregbe DIO. A review of current technology for biodiesel production: state of the art. Biomass Bioenergy 2014;61:276–97. http://dx.doi.org/10.1016/j.biombioe.2013.11.014. [2] Ma F, Hanna MA. Biodiesel production: a review. Bioresour Technol 1999;70:1–15. http://dx.doi.org/10.1016/S0960-8524(99)00025-5. [3] Atabani AE, Silitonga AS, Badruddin IA, Mahlia TMI, Masjuki HH, Mekhilef S. A comprehensive review on biodiesel as an alternative energy resource and its characteristics. Renew Sustain Energy Rev 2012;16:2070–93. http://dx. doi.org/10.1016/j.rser.2012.01.003. [4] Zhang Y, Dube MA, McLean DD, Kates M. Biodiesel production from waste cooking oil: 1. Process design and technological assessment. Bioresour Technol 2003;89:1–16. http://dx.doi.org/10.1016/S0960-8524(03)00040-3. [5] Christopher LP, Zambare VP. Enzymatic biodiesel: challenges and opportunities. Appl Energy 2014;119:497–520. http://dx.doi.org/10.1016/j. apenergy.2014.01.017. [6] Haas MJ, McAloon AJ, Yee WC, Foglia T a. A process model to estimate biodiesel production costs. Bioresour Technol 2006;97:671–8. http://dx.doi.org/ 10.1016/j.biortech.2005.03.039. [7] Aranda DAG, da Silva C, Detoni C. Current processes in brazilian biodiesel production. Int Rev Chem Eng 2009;1:603–8. [8] Nasaruddin RR, Alam MZ, Jami MS. Evaluation of solvent system for the enzymatic synthesis of ethanol-based biodiesel from sludge palm oil (SPO). Bioresour Technol 2014;154:155–61. http://dx.doi.org/10.1016/j.biortech.2013.11.095. [9] Atadashi IM, Aroua MK, Abdul Aziz AR, Sulaiman NMN. Production of biodiesel using high free fatty acid feedstocks. Renew Sustain Energy Rev 2012;16:3275–85. http://dx.doi.org/10.1016/j.rser.2012.02.063. [10] Guimarães Freire DM, de Sousa JS, Cavalcanti-Oliveira ED. A. biotechnological methods to produce biodiesel. In: Pandey A, Larroche C, Ricke SC, Dussap CG, Gnansounou E, editors. Biofuels-alternative feedstocks and conversion processes. Amsterdam: Academic Press; 2011. p. 315–37. [11] Sharma Y, Singh B, Upadhyay S. Advancements in development and characterization of biodiesel: a review. Fuel 2008;87:2355–73. http://dx.doi.org/ 10.1016/j.fuel.2008.01.014. [12] Patel A, Brahmkhatri V, Singh N. Biodiesel production by esterification of free fatty acid over sulfated zirconia. Renew Energy 2013;51:227–33. http://dx. doi.org/10.1016/j.renene.2012.09.040. [13] Ghaly A, Dave D, Brooks MS, Budge S. Production of biodiesel by enzymatic transesterification: review. Am J Biochem Biotechnol 2010;6:54–76. [14] Hayyan A, Alam MZ, Mirghani MES, Kabbashi NA, Hakimi NINM, Siran YM. Sludge palm oil as a renewable raw material for biodiesel production by twostep processes. Bioresour Technol 2010;101:7804–11. http://dx.doi.org/ 10.1016/j.biortech.2010.05.045. [15] Yang F, Hanna M a, Sun R. Value-added uses for crude glycerol: a byproduct of biodiesel production. Biotechnol Biofuels 2012;5:13. http://dx.doi.org/ 10.1186/1754-6834-5-13. [16] Rathore V, Madras G. Synthesis of biodiesel from edible and non-edible oils in supercritical alcohols and enzymatic synthesis in supercritical carbon dioxide. Fuel 2007;86:2650–9. http://dx.doi.org/10.1016/j.fuel.2007.03.014. [17] Stamenkovic OS, Velickovic AV, Veljkovic VB. The production of biodiesel from vegetable oils by ethanolysis: current state and perspectives. Fuel 2011;90:3141–55. http://dx.doi.org/10.1016/j.fuel.2011.06.049. [18] Jin G, Bierma TJ, Hamaker CG, Rhykerd R, a Loftus L. Producing biodiesel using whole-cell biocatalysts in separate hydrolysis and methanolysis reactions. J Environ Sci Health A: Tox Hazard Subst Environ Eng 2008;43:589–95. http://dx.doi.org/10.1080/10934520801893576. [19] Watanabe Y, Shimada Y, Sugihara A, Tominaga Y. Enzymatic conversion of waste edible oil to biodiesel fuel in a fixed-bed bioreactor. J Am Oil Chem Soc 2001;78:703–7.

[20] Shimada Y, Watanabe Y, Sugihara A, Tominaga Y. Enzymatic alcoholysis for biodiesel fuel production and application of the reaction to oil processing. J Mol Catal B: Enzym 2002;17:133–42. [21] Lam MK, Lee KT, Mohamed AR. Homogeneous, heterogeneous and enzymatic catalysis for transesterification of high free fatty acid oil (waste cooking oil) to biodiesel: a review. Biotechnol Adv 2010;28:500–18. http: //dx.doi.org/10.1016/j.biotechadv.2010.03.002. [22] Ranganathan SV, Narasimhan SL, Muthukumar K. An overview of enzymatic production of biodiesel. Bioresour Technol 2008;99:3975–81. http://dx.doi. org/10.1016/j.biortech.2007.04.060. [23] Noraini MY, Hwai CO, Badrul MJ, Chong WT. A review on potential enzymatic reaction for biofuel production from algae. Renew Sustain Energy Rev 2014;39:24–34. http://dx.doi.org/10.1016/j.rser.2014.07.089. [24] Bisen PS, Sanodiya BS, Thakur GS, Baghel RK, Prasad GBKS. Biodiesel production with special emphasis on lipase-catalyzed transesterification. Biotechnol Lett 2010;32:1019–30. http://dx.doi.org/10.1007/s10529-010-0275-z. [25] Yun H, Wang M, Feng W, Tan T. Process simulation and energy optimization of the enzyme-catalyzed biodiesel production. Energy 2013;54:84–96. http: //dx.doi.org/10.1016/j.energy.2013.01.002. [26] Iso M, Chen B, Eguchi M, Kudo T, Shrestha S. Production of biodiesel fuel from triglycerides and alcohol using immobilized lipase. J Mol Catal B: Enzym 2001;16:53–8. [27] Marchetti JM, Miguel VU, Errazu AF. Possible methods for biodiesel production. Renew Sustain Energy Rev 2007;11:1300–11. http://dx.doi.org/ 10.1016/j.rser.2005.08.006. [28] Hama S, Kondo A. Enzymatic biodiesel production: an overview of potential feedstocks and process development. Bioresour Technol 2013;135:386–95. http://dx.doi.org/10.1016/j.biortech.2012.08.014. [29] Shah S, Sharma S, Gupta M. Biodiesel preparation by lipase-catalyzed transesterification of Jatropha oil. Energy Fuel 2004:154–9. http://dx.doi. org/10.1021/ef030075z. [30] Gog A, Roman M, Toşa M, Paizs C, Irimie FD. Biodiesel production using enzymatic transesterification – current state and perspectives. Renew Energy 2012;39:10–6. http://dx.doi.org/10.1016/j.renene.2011.08.007. [31] Ciftci ON, Temelli F. Enzymatic conversion of corn oil into biodiesel in a batch supercritical carbon dioxide reactor and kinetic modeling. J Supercrit Fluids 2013;75:172–80. http://dx.doi.org/10.1016/j.supflu.2012.12.029. [32] Tupufia SC, Jeon YJ, Marquis C, Adesina AA, Rogers PL. Enzymatic conversion of coconut oil for biodiesel production. Fuel Process Technol 2013;106:721– 6. http://dx.doi.org/10.1016/j.fuproc.2012.10.007. [33] Akoh CC, Chang S, Lee G, Shaw JF. Enzymatic approach to biodiesel production. J Agric Food Chem 2007;55:8995–9005. http://dx.doi.org/10.1021/ jf071724y. [34] Liu W, Yin P, Zhang J, Tang Q, Qu R. Biodiesel production from esterification of free fatty acid over PA/NaY solid catalyst. Energy Convers Manag 2014;82:83–91. http://dx.doi.org/10.1016/j.enconman.2014.02.062. [35] Borges M, Díaz L. Recent developments on heterogeneous catalysts for biodiesel production by oil esterification and transesterification reactions: a review. Renew Sustain Energy Rev 2012;16:2839–49. http://dx.doi.org/ 10.1016/j.rser.2012.01.071. [36] Stergiou P, Foukis A, Filippou M, Koukouritaki M, Parapouli M, Theodorou LG. Advances in lipase-catalyzed esterification reactions. Biotechnol Adv 2013;31:1846–59. http://dx.doi.org/10.1016/j.biotechadv.2013.08.006. [37] Aschenbrenner EM, Weiss CK, Landfester K. Enzymatic esterification in aqueous miniemulsions. Chemistry 2009;15:2434–44. http://dx.doi.org/ 10.1002/chem.200801691. [38] Lortie G. Enzyme catalyzed esterification. Biotechnol Adv 1997;15:1–15. http://dx.doi.org/10.1016/S0734-9750(96)00046-8. [39] Rosset I, Cavalheiro M, Assaf E, Porto A. Enzymatic esterification of oleic acid with aliphatic alcohols for the biodiesel production by candida antarctica lipase. Catal Lett 2013:863–72. http://dx.doi.org/10.1007/s10562-013-1044-0. [40] Jeong GT, Park DH. Synthesis of rapeseed biodiesel using short-chained alkyl acetates as acyl acceptor. Appl Biochem Biotechnol 2010;161:195–208. http: //dx.doi.org/10.1007/s12010-009-8777-7. [41] Kim SJ, Jung S, Park Y, Park K. Lipase catalyzed transesterification of soybean oil using ethyl acetate, an alternative acyl acceptor. Biotechnol Bioprocess Eng 2007;12:441–5. [42] Kumaran P, Mazlini N, Hussein I, Nazrain M, Khairul M. Technical feasibility studies for Langkawi WCO (waste cooking oil) derived-biodiesel. Energy 2011;36:1386–93. http://dx.doi.org/10.1016/j.energy.2011.02.002. [43] Vasudevan P, Briggs M. Biodiesel production—current state of the art and challenges. J Ind Microb Biotechnol 2008;35:421–30. http://dx.doi.org/ 10.1007/s10295-008-0312-2. [44] Yusuf N, Kamarudin SK, Yaakub Z. Overview on the current trends in biodiesel production. Energy Convers Manag 2011;52:2741–51. http://dx.doi. org/10.1016/j.enconman.2010.12.004. [45] Teixeira CB, Madeira Junior JV, Macedo GA. Biocatalysis combined with physical technologies for development of a green biodiesel process. Renew Sustain Energy Rev 2014;33:333–43. http://dx.doi.org/10.1016/j.rser.2014.01.072. [46] Mazubert A, Poux M, Aubin J. Intensified processes for FAME production from waste cooking oil: a technological review. Chem Eng J 2013;233:201– 23. http://dx.doi.org/10.1016/j.cej.2013.07.063. [47] Azócar L, Navia R, Beroiz L, Jeison D, Ciudad G. Enzymatic biodiesel production kinetics using co-solvent and an anhydrous medium: a strategy to improve lipase performance in a semi-continuous reactor. New Biotechnol 2014;31:422–9. http://dx.doi.org/10.1016/j.nbt.2014.04.006.

H. Pourzolfaghar et al. / Renewable and Sustainable Energy Reviews 61 (2016) 245–257

[48] Wang Y, Liu J, Gerken H, Zhang C, Hu Q, Li Y. Highly-efficient enzymatic conversion of crude algal oils into biodiesel. Bioresour Technol 2014;172:143–9. http://dx.doi.org/10.1016/j.biortech.2014.09.003. [49] Meng Y, Wang G, Yang N, Zhou Z, Li Y, Liang X. Two-step synthesis of fatty acid ethyl ester from soybean oil catalyzed by Yarrowia lipolytica lipase. Biotechnol Biofuels 2011;4:6. http://dx.doi.org/10.1186/1754-6834-4-6. [50] Talukder MMR, Wu JC, Fen NM, Melissa YLS. Two-step lipase catalysis for production of biodiesel. Biochem Eng J 2010;49:207–12. http://dx.doi.org/ 10.1016/j.bej.2009.12.015. [51] Purwanto MG, Maretha MV, Wahyudi M, Goeltom MT. Whole cell hydrolysis of sardine (Sardinella lemuru) oil waste using mucor circinelloides NRRL 1405 immobilized in poly-urethane foam. Procedia Chem 2015;14:256–62. http://dx.doi.org/10.1016/j.proche.2015.03.036. [52] Kochepka DM, Dill LP, Couto GH, Krieger N, Ramos LP. Production of fatty acid ethyl esters from waste cooking oil using Novozym 435 in a solvent-free system. Energ Fuel 2015. http://dx.doi.org/10.1021/acs.energyfuels.5b02116. [53] Huang Y, Zheng H, Yan Y. Optimization of lipase-catalyzed transesterification of lard for biodiesel production using response surface methodology. Appl Biochem Biotechnol 2010;160:504–15. http://dx.doi.org/10.1007/ s12010-008-8377-y. [54] Cesarini S, Haller RF, Diaz P, Nielsen PM. Combining phospholipases and a liquid lipase for one-step biodiesel production using crude oils. Biotechnol Biofuels 2014;7:29. http://dx.doi.org/10.1186/1754-6834-7-29. [55] Go AR, Lee Y, Kim YH, Park S, Choi J, Lee J. Enzymatic coproduction of biodiesel and glycerol carbonate from soybean oil in solvent-free system. Enzyme Microb Technol 2013;53:154–8. http://dx.doi.org/10.1016/j.enzmictec.2013.02.016. [56] Seong P-J, Jeon BW, Lee M, Cho DH, Kim D-K, Jung KS. Enzymatic coproduction of biodiesel and glycerol carbonate from soybean oil and dimethyl carbonate. Enzyme Microb Technol 2011;48:505–9. http://dx.doi.org/ 10.1016/j.enzmictec.2011.02.009. [57] Huang ZL, Yang TX, Huang JZ, Yang Z. Enzymatic production of biodiesel from Millettia pinnata seed oil in ionic liquids. Bio Energy Res 2014. http://dx.doi. org/10.1007/s12155-014-9489-6. [58] De Diego T, Manjón A, Lozano P, Iborra JL. A recyclable enzymatic biodiesel production process in ionic liquids. Bioresour Technol 2011;102:6336–9. http://dx.doi.org/10.1016/j.biortech.2011.02.071. [59] Santin CMT, Scherer RP, Nyari NLD, Rosa CD, Dallago RM, de Oliveira D, et al. Batch esterification of fatty acids charges under ultrasound irradiation using candida antarctica B immobilized in polyurethane foam. Biocatal Agric Biotechnol 2014;3:90–4. http://dx.doi.org/10.1016/j.bcab.2014.02.005. [60] Da Rós PCM, Silva WCE, Grabauskas D, Perez VH, de Castro HF. Biodiesel from babassu oil: Characterization of the product obtained by enzymatic route accelerated by microwave irradiation. Ind Crops Prod 2014;52:313–20. http: //dx.doi.org/10.1016/j.indcrop.2013.11.013. [61] Antczak MS, Kubiak A, Antczak T, Bielecki S. Enzymatic biodiesel synthesis – key factors affecting efficiency of the process. Renew Energy 2009;34:1185– 94. http://dx.doi.org/10.1016/j.renene.2008.11.013. [62] Yan Y, Li X, Wang G, Gui X, Li G, Su F. Biotechnological preparation of biodiesel and its high-valued derivatives: a review. Appl Energy 2014;113:1614– 31. http://dx.doi.org/10.1016/j.apenergy.2013.09.029. [63] Jaeger KE, Reetz MT. Microbial lipases form versatile tools for biotechnology. Trends Biotechnol 1998;16:396–403. http://dx.doi.org/10.1016/S0167-7799 (98)01195-0. [64] Hasan F, Shah AA, Hameed A. Methods for detection and characterization of lipases: a comprehensive review. Biotechnol Adv 2009;27:782–98. http://dx. doi.org/10.1016/j.biotechadv.2009.06.001. [65] Feng X, Patterson DA, Balaban M, Emanuelsson EAC. Characterization of tributyrin hydrolysis by immobilized lipase on woolen cloth using conventional batch and novel spinning cloth disc reactors. Chem Eng Res Des 2013;91:1684–92. http://dx.doi.org/10.1016/j.cherd.2013.06.009. [66] Gupta R, Gupta N, Rathi P. Bacterial lipases: an overview of production, purification and biochemical properties. Appl Microbiol Biotechnol 2004;64:763–81. http://dx.doi.org/10.1007/s00253-004-1568-8. [67] Aarthy M, Saravanan P, Gowthaman MK, Rose C, Kamini NR. Enzymatic transesterification for production of biodiesel using yeast lipases: an overview. Chem Eng Res Des 2014:1–11. http://dx.doi.org/10.1016/j.cherd.2014.04.008. [68] Aguieiras ECG, Cavalcanti-Oliveira ED, Freire DMG. Current status and new developments of biodiesel production using fungal lipases. Fuel 2015;159:52–67. http://dx.doi.org/10.1016/j.fuel.2015.06.064. [69] Bajaj A, Lohan P, Jha PN, Mehrotra R. Biodiesel production through lipase catalyzed transesterification: an overview. J Mol Catal B: Enzym 2010;62:9– 14. http://dx.doi.org/10.1016/j.molcatb.2009.09.018. [70] Hayes D. Enzyme-catalyzed modification of oilseed materials to produce eco-friendly products. J Am Oil Chem Soc 2004;81:1077–103. http://dx.doi. org/10.1007/s11746-004-1024-2. [71] Ribeiro B, Castro A, Coelho M, Freire D. Production and use of lipases in bioenergy: a review from the feedstocks to biodiesel production. Enzyme Res 2011;2011:615803. http://dx.doi.org/10.4061/2011/615803. [72] Li W, Li R, Li Q, Du W, Liu D. Acyl migration and kinetics study of 1 (3)positional specific lipase of Rhizopus oryzae-catalyzed methanolysis of triglyceride for biodiesel production. Process Biochem 2010;45:1888–93. http: //dx.doi.org/10.1016/j.procbio.2010.03.034. [73] Fjerbaek L, Christensen KV, Norddahl B. A review of the current state of biodiesel production using enzymatic transesterification. Biotechnol Bioeng 2009;102:1298–315. http://dx.doi.org/10.1002/bit.22256.

255

[74] Narwal SK, Gupta R. Biodiesel production by transesterification using immobilized lipase. Biotechnol Lett 2013;35:479–90. http://dx.doi.org/ 10.1007/s10529-012-1116-z. [75] Zhang B, Weng Y, Xu H, Mao Z. Enzyme immobilization for biodiesel production. Appl Microbiol Biotechnol 2012;93:61–70. http://dx.doi.org/ 10.1007/s00253-011-3672-x. [76] Abdulla R, Ravindra P. Dev Sustain Chem Bioprocess Technol 2013:197–202. http://dx.doi.org/10.1007/978-1-4614-6208-8. [77] Nigam S, Mehrotra S, Vani B, Mehrotra R. Lipase immobilization techniques for biodiesel production: an overview. Int J Renew Energy Biofuels 2014;2014:1–16. http://dx.doi.org/10.5171/2014.664708. [78] Murty V, Bhat J, Muniswaran P. Hydrolysis of oils by using immobilized lipase enzyme: a review. Biotechnol Bioprocess Eng 2002;7:57–66. [79] Tan T, Lu J, Nie K, Deng L, Wang F. Biodiesel production with immobilized lipase: a review. Biotechnol Adv 2010;28:628–34. http://dx.doi.org/10.1016/j. biotechadv.2010.05.012. [80] Yaakob Z, Mohammad M, Alherbawi M, Alam Z, Sopian K. Overview of the production of biodiesel from waste cooking oil. Renew Sustain Energy Rev 2013;18:184–93. http://dx.doi.org/10.1016/j.rser.2012.10.016. [81] de Araújo CDM, de Andrade CC, de Souza e Silva E, Dupas FA. Biodiesel production from used cooking oil: a review. Renew Sustain Energy Rev 2013;27:445–52. http://dx.doi.org/10.1016/j.rser.2013.06.014. [82] Math MC, Kumar SP, Chetty SV. Technologies for biodiesel production from used cooking oil – a review. Energy Sustain Dev 2010;14:339–45. http://dx. doi.org/10.1016/j.esd.2010.08.001. [83] Talebian-Kiakalaieh A, Amin N, Mazaheri H. A review on novel processes of biodiesel production from waste cooking oil. Appl Energy 2013;104:683–710. http://dx.doi.org/10.1016/j.apenergy.2012.11.061. [84] Feofilova EP, Sergeeva YE, Ivashechkin AA. Biodiesel-fuel: content, production, producers, contemporary biotechnology (review). Appl Biochem Microbiol 2010;46:369–78. http://dx.doi.org/10.1134/S0003683810040010. [85] Kawentar WA, Budiman A. Synthesis of biodiesel from second-used cooking oil. Energy Procedia 2013;32:190–9. http://dx.doi.org/10.1016/j.egypro.2013.05.025. [86] Bart JCJ, Palmeri N. Stefano Cavallaro, 5-Feedstocks for biodiesel production. In: Woodhead Publishing Series in Energy; 2010. p. 130–225. [87] Galadima A, Muraza O. Biodiesel production from algae by using heterogeneous catalysts: a critical review. Energy 2014;78:72–83. http://dx.doi.org/ 10.1016/j.energy.2014.06.018. [88] Marchetti JM. A summary of the available technologies for biodiesel production based on a comparison of different feedstock's properties. Process Saf Environ Prot 2012;90:157–63. http://dx.doi.org/10.1016/j.psep.2011.06.010. [89] Avhad MR, Marchetti JM. A review on recent advancement in catalytic materials for biodiesel production. Renew Sustain Energy Rev 2015;50:696– 718. http://dx.doi.org/10.1016/j.rser.2015.05.038. [90] Vicentini KV, Vicentini A, Gomes da Rosa R, Aranda DAG, Cruz YR. Potential of biodiesel production from palm oil at Brazilian Amazon. Renew Sustain Energy Rev 2015;50:1013–20. http://dx.doi.org/10.1016/j.rser.2015.05.055. [91] Baskar G, Aiswarya R. Trends in catalytic production of biodiesel from various feedstocks. Renew Sustain Energy Rev 2016;57:496–504. http://dx.doi.org/ 10.1016/j.rser.2015.12.101. [92] Rosillo-Calle F. A global overview of vegetable oils, with reference to biodiesel. A Report for the IEA Bioenergy; 2009. [93] Gnanaprakasam A, Sivakumar VM, Surendhar A, Thirumarimurugan M, Kannadasan T. Recent strategy of biodiesel production from waste cooking oil and process influencing parameters: a review. J Energy 2013;2013:1–10. http://dx.doi.org/10.1155/2013/926392. [94] Kulkarni MG, Dalai AK. Waste cooking oil an economical source for biodiesel: a review. Ind Eng Chem Res 2006:2901–13. http://dx.doi.org/10.1021/ ie0510526. [95] Enweremadu CC, Mbarawa MM. Technical aspects of production and analysis of biodiesel from used cooking oil – a review. Renew Sustain Energy Rev 2009;13:2205–24. http://dx.doi.org/10.1016/j.rser.2009.06.007. [96] Chen Y, Xiao B, Chang J, Fu Y, Lv P, Wang X. Synthesis of biodiesel from waste cooking oil using immobilized lipase in fixed bed reactor. Energy Convers Manag 2009;50:668–73. http://dx.doi.org/10.1016/j.enconman.2008.10.011. [97] Hama S, Yoshida A, Tamadani N, Noda H, Kondo A. Enzymatic production of biodiesel from waste cooking oil in a packed-bed reactor: an engineering approach to separation of hydrophilic impurities. Bioresour Technol 2013;135:417–21. http://dx.doi.org/10.1016/j.biortech.2012.06.059. [98] Firoz A, Mobin S, Chowdhury H. Third generation biofuel from algae. Procedia Eng 2015;105:763–8. http://dx.doi.org/10.1016/j.proeng.2015.05.068. [99] Zhao T, No DS, Kim Y, Kim YS, Kim I-H. Novel strategy for lipase-catalyzed synthesis of biodiesel using blended alcohol as an acyl acceptor. J Mol Catal B: Enzym 2014;107:17–22. http://dx.doi.org/10.1016/j.molcatb.2014.05.002. [100] Robles-Medina A, González-Moreno PA, Esteban-Cerdán L, Molina-Grima E. Biocatalysis: towards ever greener biodiesel production. Biotechnol Adv 2009;27:398–408. http://dx.doi.org/10.1016/j.biotechadv.2008.10.008. [101] Li Q, Xu J, Du W, Li Y, Liu D. Ethanol as the acyl acceptor for biodiesel production. Renew Sustain Energy Rev 2013;25:742–8. http://dx.doi.org/ 10.1016/j.rser.2013.05.043. [102] Bozbas K. Biodiesel as an alternative motor fuel: production and policies in the European Union. Renew Sustain Energy Rev 2008;12:542–52. http://dx. doi.org/10.1016/j.rser.2005.06.001. [103] Verma P, Singh V. Assessment of diesel engine performance using cotton seed biodiesel. Integr Res Adv 2014;1:1–4.

256

H. Pourzolfaghar et al. / Renewable and Sustainable Energy Reviews 61 (2016) 245–257

[104] Hernández-Martín E, Otero C. Different enzyme requirements for the synthesis of biodiesel: Novozym 435 and Lipozyme TL IM. Bioresour Technol 2008;99:277–86. http://dx.doi.org/10.1016/j.biortech.2006.12.024. [105] Shimada Y, Watanabe Y, Samukawa T, Sugihara A, Noda H, Fukuda H. Conversion of vegetable oil to biodiesel using immobilized Candida antarctica lipase. J Am Oil Chem Soc 1999;76:789–93. http://dx.doi.org/10.1007/ s11746-999-0067-6. [106] Watanabe Y, Shimada Y, Sugihara A, Tominaga Y. Stepwise ethanolysis of tuna oil using immobilized Candida antarctica lipase. J Biosci Bioeng 1999;88:622–6. http://dx.doi.org/10.1016/S1389-1723(00)87090-5. [107] Mounguengui RWM, Brunschwig C, Baréa B, Villeneuve P, Blin J. Are plant lipases a promising alternative to catalyze transesterification for biodiesel production? Prog Energy Combust Sci 2013;39:441–56. http://dx.doi.org/ 10.1016/j.pecs.2013.05.003. [108] Nie K, Xie F, Wang F, Tan T. Lipase catalyzed methanolysis to produce biodiesel: optimization of the biodiesel production. J Mol Catal B: Enzym 2006;43:142–7. http://dx.doi.org/10.1016/j.molcatb.2006.07.016. [109] Osterberg E, Blomstrom AC, Holmberg K. Lipase catalyzed transesterification of unsaturated lipids in a microemulsion. J Am Oil Chem Soc 1989;66:1330– 3. http://dx.doi.org/10.1007/BF03022757. [110] Freedman B, Pryde EH, Mounts TL. Variables affecting the yields of fatty esters from transesterified vegetable oils. J Am Oil Chem Soc 1984;61:1638– 43. http://dx.doi.org/10.1007/BF02541649. [111] Watanabe Y, Shimada Y, Sugihara A, Noda H, Fukuda H, Tominaga Y. Continuous production of biodiesel fuel from vegetable oil using immobilized Candida antarctica lipase. J Am Oil Chem Soc 2000;77:355–60. http://dx.doi. org/10.1007/s11746-000-0058-9. [112] Banapurmath NR, Tewari PG, Hosmath RS. Performance and emission characteristics of a DI compression ignition engine operated on Honge, Jatropha and sesame oil methyl esters. Renew Energy 2008;33:1982–8. http://dx.doi. org/10.1016/j.renene.2007.11.012. [113] Lang DA, Mannesse ML, de Haas GH, Verheij HM, Dijkstra BW. Structural basis of the chiral selectivity of Pseudomonas cepacia lipase. Eur J Biochem 1998;254:333–40. [114] Nielsen PM, Brask J, Fjerbaek L. Enzymatic biodiesel production: technical and economical considerations. Eur J Lipid Sci Technol 2008;110:692–700. http://dx.doi.org/10.1002/ejlt.200800064. [115] Royon D, Daz M, Ellenrieder G, Locatelli S. Enzymatic production of biodiesel from cotton seed oil using t-butanol as a solvent. Bioresour Technol 2007;98:648–53. http://dx.doi.org/10.1016/j.biortech.2006.02.021. [116] Hama S, Tamalampudi S, Yoshida A, Tamadani N, Kuratani N, Noda H. Process engineering and optimization of glycerol separation in a packed-bed reactor for enzymatic biodiesel production. Bioresour Technol 2011;102:10419–24. http://dx.doi.org/10.1016/j.biortech.2011.08.073. [117] Hama S, Tamalampudi S, Yoshida A, Tamadani N, Kuratani N, Noda H. Enzymatic packed-bed reactor integrated with glycerol-separating system for solvent-free production of biodiesel fuel. Biochem Eng J 2011;55:66–71. http: //dx.doi.org/10.1016/j.bej.2011.03.008. [118] Yoshida A, Hama S, Tamadani N, Fukuda H, Kondo A. Improved performance of a packed-bed reactor for biodiesel production through whole-cell biocatalysis employing a high-lipase-expression system. Biochem Eng J 2012;63:76–80. http://dx.doi.org/10.1016/j.bej.2011.11.003. [119] Chen HC, Ju HY, Wu TT, Liu YC, Lee CC, Chang C. Continuous production of lipase-catalyzed biodiesel in a packed-bed reactor: optimization and enzyme reuse study. J Biomed Biotechnol 2011. http://dx.doi.org/10.1155/2011/950725. [120] Shaw JF, Chang S, Lin SC, Wu TT. Continuous enzymatic synthesis of biodiesel with Novozym 435. Energ Fuel 2008;22:840–4. http://dx.doi.org/10.1021/ ef7005047. [121] Aguieiras ECG, Cavalcanti-Oliveira ED, de Castro AM, Langone MAP, Freire DMG. Biodiesel production from Acrocomia aculeata acid oil by (enzyme/ enzyme) hydroesterification process: use of vegetable lipase and fermented solid as low-cost biocatalysts. Fuel 2014;135:315–21. http://dx.doi.org/ 10.1016/j.fuel.2014.06.069. [122] Ngaosuwan K, Lotero E, Suwannakarn K, Jr JGG, Praserthdam P. Hydrolysis of triglycerides using solid acid catalysts. Ind Eng Chem Res 2009;48:4757–67. [123] Minami E, Saka S. Kinetics of hydrolysis and methyl esterification for biodiesel production in two-step supercritical methanol process. Fuel 2006;85:2479–83. http://dx.doi.org/10.1016/j.fuel.2006.04.017. [124] Meher L, Vidyasagar D, Naik S. Technical aspects of biodiesel production by transesterification-a review. Renew Sustain Energy Rev 2006;10:248–68. http://dx.doi.org/10.1016/j.rser.2004.09.002. [125] Manco I. Experimental evaluation of the hydroesterification process: production of biodiesel from Canola oil. Sci Acta 2009;11:8–11. [126] Watanabe Y, Nagao T, Nishida Y, Takagi Y, Shimada Y. Enzymatic production of fatty acid methyl esters by hydrolysis of acid oil followed by esterification. J Am Oil Chem Soc 2007;84:1015–21. http://dx.doi.org/10.1007/ s11746-007-1143-4. [127] Ting WJ, Huang CM, Giridhar N, Wu WT. An enzymatic/acid-catalyzed hybrid process for biodiesel production from soybean oil. J Chin Inst Chem Eng 2008;39:203–10. http://dx.doi.org/10.1016/j.jcice.2008.01.004. [128] de Sousa JS, Cavalcanti-Oliveira ED, Aranda DAG, Freire DMG. Application of lipase from the physic nut (Jatropha curcas L.) to a new hybrid (enzyme/ chemical) hydroesterification process for biodiesel production. J Mol Catal B: Enzym 2010;65:133–7. http://dx.doi.org/10.1016/j.molcatb.2010.01.003.

[129] Almarales Á, Chenard G, Abdala R. Hydroesterification of Nannochloropsis oculata microalga's biomass to biodiesel on Al2O3 supported Nb2O5 catalyst. Nat Sci 2012;4:204–10. [130] Adachi D, Hama S, Nakashima K, Bogaki T, Ogino C, Kondo A. Production of biodiesel from plant oil hydrolysates using an Aspergillus oryzae whole-cell biocatalyst highly expressing Candida antarctica lipase B. Bioresour Technol 2013;135:410–6. http://dx.doi.org/10.1016/j.biortech.2012.06.092. [131] Bressani AP, Garcia KC, Hirata DB, Mendes AA. Production of alkyl esters from macaw palm oil by a sequential hydrolysis/esterification process using heterogeneous biocatalysts: optimization by response surface methodology. Bioprocess Biosyst Eng 2015;38:287–97. http://dx.doi.org/10.1007/ s00449-014-1267-5. [132] Papamichael EM, Stergiou PY, Foukis A, Kokkinou M, Theodorou LG. Effective kinetic methods and tools in investigating the mechanism of action of specific hydrolases. Med Chem Drug Des: INTECH Open Sci Croat 2012:235–74. [133] Aloulou A, Rodriguez J a, Fernandez S, van Oosterhout D, Puccinelli D, Carrière F. Exploring the specific features of interfacial enzymology based on lipase studies. Biochim Biophys Acta 1761;2006:995–1013. http://dx.doi.org/ 10.1016/j.bbalip.2006.06.009. [134] Reis P, Holmberg K, Watzke H, Leser ME, Miller R. Lipases at interfaces: a review. Adv Colloid Interface Sci 2009;147–148:237–50. http://dx.doi.org/ 10.1016/j.cis.2008.06.001. [135] Salimon J, Abdullah BM, Salih N. Hydrolysis optimization and characterization study of preparing fatty acids from Jatropha curcas seed oil. Chem Cent J 2011;5:67. http://dx.doi.org/10.1186/1752-153X-5-67. [136] Noor I, Hasan M, Ramachandran K. Effect of operating variables on the hydrolysis rate of palm oil by lipase. Process Biochem 2003;39:13–20. [137] Sun F, Chen H. Organosolv pretreatment by crude glycerol from oleochemicals industry for enzymatic hydrolysis of wheat straw. Bioresour Technol 2008;99:5474–9. http://dx.doi.org/10.1016/j.biortech.2007.11.001. [138] Papanikolaou S, Fakas S, Fick M, Chevalot I, Galiotou-Panayotou M, Komaitis M. Biotechnological valorisation of raw glycerol discharged after bio-diesel (fatty acid methyl esters) manufacturing process: production of 1,3-propanediol, citric acid and single cell oil. Biomass Bioenergy 2008;32:60–71. http: //dx.doi.org/10.1016/j.biombioe.2007.06.007. [139] Rukmini A, Raharjo S. Pattern of peroxide value changes in virgin coconut oil (VCO) due to photo-oxidation sensitized by chlorophyll. J Am Oil Chem Soc 2010;87:1407–12. http://dx.doi.org/10.1007/s11746-010-1641-7. [140] Barnebey HL, Brown AC. Continuous fat splitting plants using the colgateemery process. J Am Oil Chem Soc 1948;25:95–9. http://dx.doi.org/10.1007/ BF02579733. [141] Sharma S, Gangal S, Rauf A. Lipase mediated hydrolysis of Mimusops elengi and Parkinsonia aculeata seed oils for the determination of positional distribution of fatty acids. Ind Crops Prod 2009;30:325–8. http://dx.doi.org/ 10.1016/j.indcrop.2009.04.004. [142] Mendes AA, Oliveira PC, de Castro HF. Properties and biotechnological applications of porcine pancreatic lipase. J Mol Catal B: Enzym 2012;78:119– 34. http://dx.doi.org/10.1016/j.molcatb.2012.03.004. [143] Li SF, Wu WT. Lipase-immobilized electrospun PAN nanofibrous membranes for soybean oil hydrolysis. Biochem Eng J 2009;45:48–53. http://dx.doi.org/ 10.1016/j.bej.2009.02.004. [144] Hermansyah H, Wijanarko A, Dianursanti, Gozan M, Wulan P. kinetic model for triglyceride hydrolysis using lipase: a review. Makara J Technol 2007;11:30–5. http://dx.doi.org/10.7454/mjt.v11i1.124. [145] Santos KC, Cassimiro DMJ, Avelar MHM, Hirata DB, de Castro HF, FernándezLafuente R. Characterization of the catalytic properties of lipases from plant seeds for the production of concentrated fatty acids from different vegetable oils. Ind Crops Prod 2013;49:462–70. http://dx.doi.org/10.1016/j.indcrop.2013.05.035. [146] Talukder MMR, Wu JC, Chua LPL. Conversion of waste cooking oil to biodiesel via enzymatic hydrolysis followed by chemical esterification. Energy Fuel 2010;24:2016–9. http://dx.doi.org/10.1021/ef9011824. [147] Raspe D, Filho LC, da Silva C. Effect of additives and process variables on enzymatic hydrolysis of macauba kernel oil (Acrocomia aculeata). Int J Chem Eng 2013;2013:1–8. [148] Nagesha GK, Manohar B, Udaya Sankar K. Enzymatic esterification of free fatty acids of hydrolyzed soy deodorizer distillate in supercritical carbon dioxide. J Supercrit Fluids 2004;32:137–45. http://dx.doi.org/10.1016/j. supflu.2004.02.001. [149] Avelar MHM, Cassimiro DMJ, Santos KC, Domingues RCC, De Castro HF, Mendes AA. Hydrolysis of vegetable oils catalyzed by lipase extract powder from dormant castor bean seeds. Ind Crops Prod 2013;44:452–8. http://dx. doi.org/10.1016/j.indcrop.2012.10.011. [150] Willerding A, Neto C, da Rocha F. Hydrolytic activity of bacterial lipases in amazonian vegetable oils. Quim Nova 2012;35:1782–6. [151] Serri NA, Kamarudin AH, Rahaman SN Abdul. Preliminary studies for production of fatty acids from hydrolysis of cooking palm oil using C. rugosa Lipase. J Phys Sci 2008;19:79–88. [152] Cavalcanti-Oliveira E d’Avila, da Silva PR, Ramos AP, Aranda DAG, Freire DMG. Study of soybean oil hydrolysis catalyzed by thermomyces lanuginosus lipase and its application to biodiesel production via hydroesterification. Enzyme Res 2010. http://dx.doi.org/10.4061/2011/618692. [153] Wang M, Nie K, Liu L, Zhang X, Cao H, Deng L. Biodiesel production by combined fatty acids separation and subsequnently enzymatic esterification to improve the low temperature properties. Bioresour Technol 2014. http: //dx.doi.org/10.1016/j.biortech.2014.08.011.

H. Pourzolfaghar et al. / Renewable and Sustainable Energy Reviews 61 (2016) 245–257

[154] Rathod VK, Pandit AB. Effect of various additives on enzymatic hydrolysis of castor oil. Biochem Eng J 2009;47:93–9. http://dx.doi.org/10.1016/j. bej.2009.07.008. [155] Pugazhenthi G, Kumar A. Enzyme membrane reactor for hydrolysis of olive oil using lipase immobilized on modified PMMA composite membrane. J Membr Sci 2004;228:187–97. http://dx.doi.org/10.1016/j.memsci.2003.10.007. [156] Puthli MS, Rathod VK, Pandit AB. Enzymatic hydrolysis of castor oil: process intensification studies. Biochem Eng J 2006;31:31–41. http://dx.doi.org/ 10.1016/j.bej.2006.05.017. [157] Kabbashi NA, Mohammed NI, Alam Md Z, Mirghani MES. Hydrolysis of Jatropha curcas oil for biodiesel synthesis using immobilized Candida cylindracea lipase. J Mol Catal B: Enzym 2015;116:95–100. http://dx.doi.org/ 10.1016/j.molcatb.2015.03.009. [158] Marchetti JM, Miguel VU, Errazu AF. Techno-economic study of different alternatives for biodiesel production. Fuel Process Technol 2008;89:740–8. http://dx.doi.org/10.1016/j.fuproc.2008.01.007. [159] Pasias S, Barakos N, Alexopoulos C, Papayannakos N. Heterogeneously catalyzed esterification of FFAs in vegetable oils. Chem Eng Technol 2006;29:1365–71. http://dx.doi.org/10.1002/ceat.200600109. [160] Susumu O, Mieko I, Yoshio T. Synthesis of various kinds of esters by four microbial lipases. Biochim Biophys Acta: Lipids Lipid Metab 1979;575:156–65. [161] Torres S, Castro G. Non-aqueous biocatalysis in homogeneous solvent systems. Food Technol Biotechnol 2004;42:271–7. [162] Bhandari K, Chaurasia SP, Dalai AK, Gupta A, Singh K. Kinetic study on enzymatic esterification of tuna fish oil fatty acids with butanol. J Mol Catal B: Enzym 2013;94:104–10. http://dx.doi.org/10.1016/j.molcatb.2013.05.006. [163] Zaks A, Klibanov AM. The effect of water on enzyme action in organic media. J Biol Chem 1988;263:8017–21. [164] Raita M, Laothanachareon T, Champreda V, Laosiripojana N. Biocatalytic esterification of palm oil fatty acids for biodiesel production using glycinebased cross-linked protein coated microcrystalline lipase. J Mol Catal B: Enzym 2011;73:74–9. http://dx.doi.org/10.1016/j.molcatb.2011.07.020. [165] Soares D, Pinto AF, Goncalves AG, Mitchell DA, Krieger N. Biodiesel production from soybean soapstock acid oil by hydrolysis in subcritical water followed by lipase-catalyzed esterification using a fermented solid in a packedbed reactor. Biochem Eng J 2013;81:15–23. http://dx.doi.org/10.1016/j. bej.2013.09.017. [166] Souza MS, Aguieiras ECG, Da Silva MAP, Langone MAP. Biodiesel synthesis via esterification of feedstock with high content of free fatty acids. Appl Biochem Biotechnol 2009;154:253–67. http://dx.doi.org/10.1007/s12010-008-8444-4. [167] Li WN, Chen BQ, Tan TW. Esterification synthesis of ethyl oleate in solventfree system catalyzed by lipase membrane from fermentation broth. Appl Biochem Biotechnol 2011;163:102–11. http://dx.doi.org/10.1007/ s12010-010-9020-2. [168] Jiang Y, Liu X, Chen Y, Zhou L, He Y, Ma L. Pickering emulsion stabilized by lipase-containing periodic mesoporous organosilica particles: a robust

[169] [170]

[171]

[172]

[173]

[174]

[175]

[176]

[177]

[178]

[179]

[180]

257

biocatalyst system for biodiesel production. Bioresour Technol 2014;153:278–83. http://dx.doi.org/10.1016/j.biortech.2013.12.001. Tan T, Nie K, Wang F. Production of biodiesel by immobilized Candida sp. lipase at high water content. Appl Biochem Biotechnol 2006;128:109–16. Ren H, Li Y, Du W, Liu D. Free lipase-catalyzed esterification of oleic acid for fatty acid ethyl ester preparation with response surface optimization. J Am Oil Chem Soc 2012;90:73–9. http://dx.doi.org/10.1007/s11746-012-2146-3. Liu S, Nie K, Zhang X, Wang M, Deng L, Ye X. Kinetic study on lipase-catalyzed biodiesel production from waste cooking oil. J Mol Catal B: Enzym 2014;99:43–50. http://dx.doi.org/10.1016/j.molcatb.2013.10.009. de Oliveira D, Di Luccio M, Faccio C, Rosa C, Bender J, Lipke N. Optimization of enzymatic production of biodiesel from castor oil in organic solvent medium. Appl Biochem Biotechnol 2004;115:771–80. http://dx.doi.org/10.1385/ ABAB:115:1-3:0771. Facioli NL, Barrera-Arellano D. Optimisation of enzymatic esterification of soybean oil deodoriser distillate. J Sci Food Agric 2001;81:1193–8. http://dx. doi.org/10.1002/jsfa.928. Gofferjé G, Stäbler A, Herfellner T, Schweiggert-Weisz U, Flöter E. Kinetics of enzymatic esterification of glycerol and free fatty acids in crude Jatropha oil by immobilized lipase from Rhizomucor miehei. J Mol Catal B: Enzym 2014;107:1–7. http://dx.doi.org/10.1016/j.molcatb.2014.05.010. Trentin CM, Scherer RP, Dalla Rosa C, Treichel H, Oliveira D, Oliveira JV. Continuous lipase-catalyzed esterification of soybean fatty acids under ultrasound irradiation. Bioprocess Biosyst Eng 2013:841–7. http://dx.doi.org/ 10.1007/s00449-013-1052-x. Zhou WW, Qin DH, Qian JQ. Optimisation of enzymatic pretreatment of soybean oil deodoriser distillate for concentration of tocopherols. Int J Food Sci Technol 2009;44:1429–37. http://dx.doi.org/10.1111/j.1365-2621.2009.01975.x. Mulalee S, Srisuwan P, Phisalaphong M. Influences of operating conditions on biocatalytic activity and reusability of Novozym 435 for esterification of free fatty acids with short-chain alcohols: a case study of palm fatty acid distillate. Chin J Chem Eng 2015. http://dx.doi.org/10.1016/j.cjche.2015.08.016. Raita M, Kiatkittipong W, Laosiripojana N, Champreda V. Kinetic study on esterification of palmitic acid catalyzed by glycine-based crosslinked protein coated microcrystalline lipase. Chem Eng J 2015. http://dx.doi.org/10.1016/j. cej.2015.01.016. López BC, Cerdán LE, Medina AR, López EN, Valverde LM, Peña EH, Moreno PAG, Grima EM. Production of biodiesel from vegetable oil and microalgae by fatty acid extraction and enzymatic esterification. JBB 2015;119:706–11. http: //dx.doi.org/10.1016/j.jbiosc.2014.11.002. von der Haar D, Stäbler A, Wichmann R, Schweiggert-Weisz U. Enzymatic esterification of free fatty acids in vegetable oils utilizing different immobilized lipases. Biotechnol Lett 2015;37:169–74. http://dx.doi.org/10.1007/ s10529-014-1668-1.