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Review

Bio-Derived Catalysts: A Current Trend of Catalysts Used in Biodiesel Production

by
Hoang Chinh Nguyen
1,*,†,
My-Linh Nguyen
2,3,†,
Chia-Hung Su
3,*,
Hwai Chyuan Ong
4,*,
Horng-Yi Juan
3 and
Shao-Jung Wu
3
1
Faculty of Applied Sciences, Ton Duc Thang University, Ho Chi Minh City 700000, Vietnam
2
Graduate Institute of Applied Science and Technology, National Taiwan University of Science and Technology, Taipei City 106335, Taiwan
3
Department of Chemical Engineering, Ming Chi University of Technology, New Taipei City 243303, Taiwan
4
Centre for Green Technology, Faculty of Engineering and Information Technology, University of Technology Sydney, Ultimo, NSW 2007, Australia
*
Authors to whom correspondence should be addressed.
†
These authors contributed equally to this work.
Catalysts 2021, 11(7), 812; https://doi.org/10.3390/catal11070812
Submission received: 3 June 2021 / Revised: 29 June 2021 / Accepted: 29 June 2021 / Published: 1 July 2021
(This article belongs to the Special Issue Catalysts for Biofuel and Bioenergy Production)
Versions Notes

Abstract

:
Biodiesel is a promising alternative to fossil fuels and mainly produced from oils/fat through the (trans)esterification process. To enhance the reaction efficiency and simplify the production process, various catalysts have been introduced for biodiesel synthesis. Recently, the use of bio-derived catalysts has attracted more interest due to their high catalytic activity and ecofriendly properties. These catalysts include alkali catalysts, acid catalysts, and enzymes (biocatalysts), which are (bio)synthesized from various natural sources. This review summarizes the latest findings on these bio-derived catalysts, as well as their source and catalytic activity. The advantages and disadvantages of these catalysts are also discussed. These bio-based catalysts show a promising future and can be further used as a renewable catalyst for sustainable biodiesel production.

1. Introduction

Global industrialization leads to the extensive use of fuel-based energy for transportation, which consequently causes the depletion of fossil fuels and global warming. Therefore, renewable fuels are considered an alternative energy to solve the problem of fuel depletion and environmental pollution. Biodiesel, a biomass-derived fuel, is a promising bioenergy, which is increasingly produced worldwide to replace fossil fuels because of its combustion efficiency, compatibility with diesel engines, and low carbon dioxide emissions [1,2]. As a result, studies have been focusing on developing an efficient approach for biodiesel production.
Biodiesel is mainly synthesized from oils/fat (derived from plants, animals, and microorganisms) through the (trans)esterification process [3,4]. The efficiency of this process is mainly affected by several factors including the quality of feedstock (level of free fatty acids), the type of acyl acceptor (e.g., alcohols or methyl acetate), and the type of reactions (e.g., noncatalytic reaction, chemical-catalyzed reaction, and enzymatic reaction) [5,6]. To enhance the reaction efficiency, most studies focused on developing efficient catalysts for the (trans)esterification reaction. Consequently, different types of catalysts, such as alkali catalysts, acid catalysts, and enzymes have been studied [7,8]. Commonly, chemical catalysts (such as KOH, NaOH, H2SO4, and HCl) are used for biodiesel production processes [9]. Although these chemical catalysts efficiently catalyze the reaction, they retain several limitations regarding their reusability, negative effect on the environment, and complicated purification steps in the downstream process [2]. Therefore, studies have shifted to using bio-derived catalysts for biodiesel production.
Bio-based catalysts have increasingly attracted attention for biodiesel production due to their availability and environmentally friendly nature [8]. Those catalysts are derived from natural sources and divided into 3 types: alkali catalysts, acid catalysts, and biocatalysts (enzymes). Each type of catalyst has its advantages and disadvantages for biodiesel production. To synthesize these catalysts, various biomass materials and synthesis methods have been reported [8]. Catalysts derived from different sources possess different catalytic activity. This review aims to summarize the bio-derived catalysts for biodiesel production. The natural sources used for catalyst synthesis are reported. The advantages and disadvantages of each type of catalyst are also discussed in this review.

2. Bio-Derived Alkali Catalysts for Biodiesel Production

Biodiesel is commonly produced through transesterification of vegetable oil or animal fat with short-chain alcohols (e.g., methanol and ethanol) in the presence of liquid/homogenous alkali catalysts (e.g., NaOH, KOH). The homogenous alkali catalyst-catalyzed transesterifications achieve high biodiesel yield within a short reaction time (30–45 min) and proceed at atmospheric pressure [10]. However, emulsification, difficulty in separation of the catalyst after reaction, and generation of excess wastewater are major problems associated with those catalysts [11]. To address these issues, heterogeneous alkali catalysts have been increasingly developed as alternative catalysts for biodiesel production. The use of heterogeneous alkali catalysts for biodiesel production simplifies the operation, easily removes and recovers catalysts from the reaction mixture, results in better biodiesel refining, and lowers environmental problems as compared to homogenous catalysts [10]. Furthermore, heterogeneous alkali catalysts can be synthesized from various cheap materials, thus reducing the production cost [12]. However, heterogeneous catalytic reactions are typically time-consuming and require a higher reaction temperature than the homogenous alkali catalyst-catalyzed transesterification due to diffusion problems owing to the formation of three phases of the reactants (methanol–oil–solid catalyst) [8]. Therefore, studies have focused on developing solid catalysts with high catalytic activity to produce biodiesel under mild reaction conditions and short reaction time [13].
Alkali catalysts derived from biomass have attracted considerable interest in biodiesel production due to their ecofriendly nature, low cost, and the availability of biomass as a material for the synthesis of catalysts. Moreover, the use of biomass for catalyst synthesis can solve the environmental problems caused by surplus biomass waste. Therefore, various types of bio-derived alkali catalysts have been studied for transesterification reactions. Biomass-derived calcium oxide (CaO) is one of the most promising solid alkali catalysts used for biodiesel production [14]. The availability of CaO has been recorded in different types of waste/low-cost materials, mainly from animal-derived biomass, including eggshell [15], Turbo jourdani shell [16], oyster shell [17], Pomacea canaliculata shell [18], Turbonilla striatula shell [19], crap shell [20], mussel (Perna varidis) shell [21], Grooved razor shell [22], conch shell [23], Malleus malleus shells [24], and animal bone [25]. The catalytic activities of the synthesized CaO catalysts vary, depending on the materials used and the synthesis method. Among the materials used, eggshell seems to be one of the most suitable materials and attracted extensive investigations for the synthesis of CaO catalyst since it contains a high level of CaCO3 and is easy to obtain [26]. Yaşar [26] reported the synthesis of a CaO catalyst from waste eggshell. The transesterification reaction catalyzed by eggshell-derived CaO resulted in 96.81% biodiesel yield, compared to 95.12% biodiesel produced by commercial CaO, under the reaction conditions of 4% catalysts, 1 h reaction time, and 60 °C reaction temperature [26]. The synthesis method also seems to affect the catalytic activity of the catalyst; therefore, catalysts are derived from the same materials, but they exhibit various catalytic activities (yielding 90–97% biodiesel) [26,27]. For example, Gollakota et al. [28] used eggshell-supported pyrolysis residue as a solid alkali catalyst for transesterification of waste cooking oil (WCO). This study also compared the catalytic activity of unsupported eggshell catalysts and the supported catalyst. Results revealed that the biodiesel yield reached over 95% at 65 °C using 10% supported catalyst with a methanol to oil molar ratio of 12:1 in 3 h. In comparison with unsupported eggshell catalysts, the synthesized catalyst shows improved surface area and catalytic activity [28]. Goli et al. [29] reported biodiesel production from soybean oil using a CaO catalyst that was derived from chicken eggshell waste, yielding 93% biodiesel, whereas Kirubakaran et al. [27] also used a waste chicken eggshell-derived CaO catalyst for biodiesel production and reported 90.41% biodiesel yield under optimal reaction conditions.
In addition to CaO, other calcium (Ca)-based catalysts synthesized from biomass have been reported as potential alkali catalysts for biodiesel production [15,30]. Gupta et al. [15] synthesized eggshell-CaDG catalyst for biodiesel production. The transesterification of WCO was conducted to compare the catalytic activity of eggshell-CaOC-H-D and eggshell-CaDG. Under optimized reaction conditions (catalyst loading of 1.5%, reaction time of 50 min, methanol:oil molar ratio of 10:1, temperature of 60 °C, and agitation speed of 300 rpm), the eggshell-CaDG catalyzed reaction provided 96.07% biodiesel. The eggshell-CaDG demonstrated higher catalytic activity than eggshell-CaOC-H-D (93.10% biodiesel yield under the optimal reaction conditions of temperature of 65 °C, catalyst loading of 3%, methanol:oil molar ratio of 12:1, 400 rpm, and reaction time of 90 min) [15]. Both catalysts (eggshell-CaOC-H-D and eggshell-CaDG) could be reused for up to five cycles for biodiesel production [15]. In addition, alkali catalyst obtained from the plant materials through calcination method such as calcined Musa acuminata peduncle [30], calcined waste cupuaçu (Theobroma grandiflorum) seeds [31], calcined banana peel [32], calcined elephant-ear tree pod husk [33], calcined kola nut husk pod [34], calcined Brassica nigra plant [35], ZrO2-supported bamboo leaf ash [36], calcined Sesamum indicum ash [37], calcined Tectona grandis leaves [38], calcined fig (Ficus carica) leaves [39], calcined ginger (Zingiber officinale) leaves [40], calcinated Carica Papaya stem [41], and calcined Musa balbisiana Colla peel [42], also efficiently converted oil into biodiesel with conversion rates of higher than 95.1% (Table 1).
Activated carbon-based and biochar catalysts derived from biomass are another type of alkali catalyst, which shows promise for biodiesel production. These catalysts are mainly synthesized from plant materials through the carbonization process. Recently, Naeem et al. [43] reported the use of KOH/corn cob activated carbon catalyst for biodiesel production with a biodiesel yield of 97.8%, whereas the nano-bifunctional catalyst from rice husk resulted in 98.6% biodiesel yield [44]. Due to their high catalytic activity, the synthesis of these bio-based activated carbon catalysts and other bio-based alkali catalysts is still an objective of investigation for biodiesel production.
Table
Table 1. Several bio-derived alkali catalysts for biodiesel production.
Table 1. Several bio-derived alkali catalysts for biodiesel production.
CatalystFeedstockReaction ConditionsConversion/Biodiesel Yield (%)Time of Reuse/Corresponding Biodiesel Yield (%)Ref.
Catalyst Loading (%)Alcohol: Fatty Acid Molar RatioTime (min)Temp. (°C)
Eggshell-derived CaORapeseed oil49:1606095.123/93.24[12]
Chicken eggshell-derived CaOWCO1.510:1506096.075/81.15[15]
Chicken eggshell-derived CaOChicken fat8.513:130057.590.415/85[27]
Chicken eggshell-derived CaOWCO1012:11806595-[28]
Chicken eggshell-derived CaOSoybean oil710:118057.5934/75[29]
Eggshell-derived CaOPhoenix dactylifera L. seed oil512:1906593.56/>80[45]
Eggshell-derived CaO/SiO2 WCO814:160609110/>85[46]
Chicken eggshell-derived CaOJatropha curcas oil26:11209098-[47]
Chicken eggshell-derived CaOChlorella vulgaris biomass1.3910:11807092.033/>85.2[48]
Fe3O4 nanoparticles impregnated eggshellPongamia pinnata oil212:112065987/98[49]
Chicken eggshell-derived CaOTerminalia belleric seed oil2.259:19062.597.98-[50]
Chicken eggshell-derived CaOPalm kernel oil410:1605097.15/>90[51]
Al2O3 impregnated on calcined eggshellsRubber seed oil312:12406598.9-[52]
Chicken eggshell-derived CaORubber seed oil59:12406597.84-[53]
Eggshell-derived CaO supported on a fly ash-based zeolitic materialSunflower oil66:1306099.25/97.9[54]
Chicken eggshell-derived CaOWCO59:11656587.8-[55]
Palm mill fly ash-supported CaO derived from eggshells (CaO/PMFA)Palm oil610:11807086.25/70[56]
KOH impregnated eggshellReutealis trisperma oil512:1606094-[57]
Eggshell-derived CaO supported W-Mo mixed oxideWCO215:11207096.25/90[58]
KF/eggshell-Fe3O4Neem oil615:112065975/>75[59]
Chicken eggshell-derived CaOSunflower oil511:11806083.24/>80[60]
La2O3/CaO derived from eggshellPalm oil1012:12506092.3-[61]
Ostrich eggshell-derived CaO WCO1.5711:11146597.54-[62]
Chicken eggshell-derived CaOWCO1.6111.4:11146594.7-[62]
Fe3O4/CaO derived from eggshellPalm oil 610:11207090-[63]
Chicken eggshell-derived CaOWCO1.477.85:11444390.133/73.3[64]
Eggshells-derived CaO Rubber seed oil412:11806599.67/86.4[65]
Chicken eggshell-derived CaOSoybean oil39:12406594.2-[66]
Quail eggshell-derived CaOSoybean oil39:12406594.8-[66]
CaO@MgO nanocatalyst derived from chicken eggshellWaste edible oil4.57116.7:1424.869.3798.37-[67]
SrO/CaO derived from eggshell Jatropha oil4.7727.6:189.86599.715/>60%[68]
Na-K doped CaO derived from calcined eggshell (Na₁K₁/CaO)Canola oil39:11805097.64/66.0[69]
Egg shell-derived nano-CaOChlorella pyrenoidosa oil2.0630:11806093.446/85.2[70]
Duck eggshell-derived CaOMomordica charantia oil10 806596.8-[71]
Na impregnated calcined eggshellMadhuca indica oil59:1606081.565/>70[72]
Zn doped eggshell-derived CaO WCO520:12406596.745/64.5[73]
Zn doped eggshell-derived CaOEucalyptus oil56:11506593.85/>88[74]
Chicken eggshell-derived CaOWCO1.510:12105091.425/48[75]
Chicken bone-derived CaOAlgal oil59:118065954/>80[75]
Chicken eggshell-derived CaOAlgal oil59:118065944/70[76]
Chicken manure-derived catalystAlgal oil59:118065854/>60[76]
Chicken eggshell-derived Ca-based catalystsWaste cooking palm oil315:11808090.13/>70[77]
Turbo jourdani shell-derived CaOPalm oil103:14208099.338/>75[16]
Oyster shell-derived CaOWCO69:11806587.3-[17]
Pomacea canaliculata shell-derived CaOPalm oil0.812:13606595.24/90.7[18]
Activated carbon supported CaO from Turbonilla striatula shellWCO1140:1420120965/96[19]
Crap shell-derived CaOWaste fish oil2.512:1906596.65/80[20]
NaOH impregnated activated carbon/CaO derived Perna varidis shellPalm oil7.50.5:11806595.12-[21]
Grooved razor shell-derived CaOWCO515:118065945/87[22]
Conch shell-derived CaOMoringa oleifera oil8.0228.662:11306597.06-[23]
Malleus malleus shells derived CaOWCO7.511.85:186.256593.81-[24]
Calcined sheep bone impregnated fly ash catalystMustard oil105.5:13606590.47/80.3[25]
Snail shell-derived CaO nanocatalystScum oil0.8912.4:1145.1561.698.935/>90[78]
Hydnocarpus wightiana oil0.8712.7:1119.6858.696.93-
Snail shell-derived CaOSoybean oil69:121065905/80[79]
KOH impregnated snail shell Soybean oil69:121065965/90[79]
Snail shell-derived CaOSoybean oil36:142028988/90[80]
Quail eggshell-derived CaOSunflower oil210.5:112060993/78.26[81]
CaO-based catalyst derived from eggshell-snail shell-wood ash mixedMixture of Irvingia gabonensis, Pentaclethra macrophylla, and Elais guineensis oil 4.58:164.7161.61985/79[82]
Ram bone supported Cr catalystUsed frying mustard oil48:1306096.855/95.56[83]
Lithium based chicken bone compositeCanola oil418:11806096.65/82[84]
Lithium/zinc supported on chicken bone catalystWaste canola oil418:121060987/>96[85]
Goat bone-derived nano-CaOScenedesmus algal oil211:11806092-[86]
KOH impregnated CaO derived from goat boneWCO69:13006584-[87]
Chicken and fish bone-derived CaOWCO1.9810:1926589.55/<50[88]
Struthio camelus bone-derived CaOWCO515:12406090.565/>80[89]
Poly- glycidylmethacrylate grafted flax fibersCottonseed oil2.533:11206088.63/72.5[90]
Calcined cupuaçu (Theobroma grandiflorum) seedsSoybean oil10%10:14808098.363/>20[31]
K2O-KCl derived from calcined banana peelSoybean oil1.515:1606595.14/75.5[32]
Calcined husk of Enterolobium cyclocarpum podsOil blend2.9611.44:15.886598.774/74.68[33]
Calcined kola nut husk podHevea brasiliensis seed oil3.56:1756596.97-[34]
Calcined Brassica nigra plantSoybean oil712:1256598.793/>96[35]
ZrO2 supported on bamboo leaf ash Soybean oil1215:1305092.75-[36]
Calcined Sesamum indicum ashSunflower oil712:1406598.93/94.2[37]
Calcined Tectona grandis leavesWCO2.56:1180RT1004/>80[38]
Calcined Ficus carica leavesWCO16:11206090.75-[39]
Calcined ginger (Zingiber officinale) leaves activated by KOHSunflower oil1.66:1906093.83-[40]
Calcined Carica papaya stemWCO29:11806095.236/85.4[41]
Calcined banana peel WCO26:1180601003/66.66[42]
KOH/corncob-derived activated carbonWCO118:1604597.82/35[43]
Supermagnetic catalyst derived from rice husk doped with K2O and FeWCO412:12407598.65/>80[44]
CaO/zeolite-based catalyst derived from chicken eggshell and coal fly ashSunflower oil66:1306097.8-[54]
Orange peel ash Soybean oil76:1420RT985/85[91]
Rice husk biochar supported CaOPalm oil89:11806593.410/85[92]
Silica impregnated CaO derived from eggshellVirgin cooking palm oil320:11206087.56/>80[93]
Sugarcane leaf ashCalophyllum inophyllum oil519:1180649710/74[94]
SiO2-rich sugarcane bagasse ash Palm oil620:11806593.85/70.3[95]
Calcined barnacles shellAglaia korthalsii seed oil4.712.2:11806597.124/95.83[96]
Calcined banana peduncleCeiba pentandra oil1.9789.2:1606598.69-[97]
Silica-supported CaO derived from goat boneWCO615:112060947/40[98]
Calcined quail beaksRapeseed oil712:12406596.76/>90[99]
Calcined walnut shell Sunflower oil512:11060984/>95[100]
RT: room temperature.

3. Bio-Derived Acid Catalysts for Biodiesel Production

Alkali-catalyzed transesterification is efficient for producing biodiesel from refined oils (containing a low level of free fatty acids (FFA)). However, the biodiesel yield is significantly reduced when the oil contains a high level of FFA (>1%, w/w) because alkali catalysts cannot convert FFA into biodiesel and the liquid alkali catalysts can react with FFA to form soap [2]. Therefore, acid-catalyzed esterification/transesterification is commonly proposed to produce biodiesel from high FFA-containing oils. Acid catalysts simultaneously catalyze the esterification of FAA and transesterification of oil (triglyceride) into biodiesel; therefore, they are insensitive to the quality of the raw material. In addition, the use of the acid catalysts for biodiesel production prevents the saponification reaction, which is commonly found in the homogenous alkali-catalyzed transesterification reaction. Homogenous acid catalysts (such as HCl, H2SO4, H3PO4) are widespread in biodiesel production because they efficiently convert FFA and triglyceride into biodiesel [9,10]. However, there are lots of associated problems in the downstream process, which is costly and requires complicated steps for product purification and separation of the catalyst. In addition, the use of these homogenous acid catalysts causes corrosive damage to the equipment and negatively affects the environment. These liquid catalysts are also difficult recover and reuse. To address these obstacles, heterogenous/solid acid catalysts have been increasingly considered as promising alternative catalysts to facilitate a cleaner, safer, simpler, and cheaper process for biodiesel production [101,102].
In recent years, biomass-derived acid catalysts have gained much interest in biodiesel production due to their ecofriendly properties, potential reusability, and the availability and low cost of materials used for catalyst synthesis. Recently, several forms of heterogeneous acid carbon-based catalysts have been developed for biodiesel production from high-FFA oils. The carbonization followed by sulfonation method is commonly used to synthesize various solid acid catalysts such as sulfonated carbon from corn cobs [103], sulfonated starch [104], sulfonated carbon from vegetable oil asphalt [105], sulfonated carbon from cacao shell [106], sulfonated rice husk [107], sulfonated bamboo [108], sulfonated sugarcane bagasse [109], sulfonated biochar derived from cassava peel [110], and sulfonated biochar derived from sugarcane bagasse, corncob, coconut shell, and peanut shell [111]. Different materials result in different catalytic activities of the synthesized catalysts. The catalysts prepared from these materials demonstrated good catalytic efficiency towards esterification of high-FFA oils, with FFA conversions ranging from 71% to 98% [109,110]. Among the materials used, waste shells, such as cacao shell [106], wing shell [112], and coconut shell [113], show promise for the synthesis of solid acid catalysts. More acid catalysts used for biodiesel production are shown in Table 2. In comparison with alkali catalysts, the bio-based acid-catalyzed reaction commonly requires a longer reaction time and higher temperature for biodiesel production. Therefore, the acid-catalyzed reaction is only suggested for producing biodiesel from feedstock containing a high level of FFA.

4. Enzyme

With an increasing demand for environmental protection, green processes have been rapidly developed for chemical production. Consequently, various ecofriendly processes have been proposed for producing biodiesel to reduce the adverse environmental effects [5,149]. Particularly, the enzyme-catalyzed reaction is one of the most promising processes for biodiesel production due to the ecofriendly and reusable nature of the enzyme. Notably, the enzymatic process proceeds at mild reaction temperature and pressure, thus lowering the energy consumption [150]. For this approach, biodiesel can be produced via lipase-catalyzed transesterification or lipase-catalyzed hydroesterification processes (hydrolysis of oils into FFA followed by esterification of the produced FFA with short-chain alcohols). The lipase catalyzes the esterification and transesterification simultaneously; therefore, the enzymatic process is insensitive to high-FFA oil [150]. Because of such benefits, enzymatic processes have been widely developed for biodiesel production from various feedstocks [150].
The efficiency of the enzymatic process mainly depends on the activity of lipases. Therefore, a great effort has been made to use lipase from different sources (microorganisms, plants, animals) for biodiesel production [151,152] (Table 3). The most common source of the lipase is microorganisms such as Candida antarctica [153,154], Thermomyces lanuginosu [155,156], Rhizomucor miehei [157,158], Pseudomonas cepacia [159,160], Candida rugosa [161,162], Aspergillus oryzae [163], Burkholderia cepacia [164,165], Adansonia grandidieri [166], Rhizopus oryzae [167], Pseudomonas fluorescens [168], Lactobacillus plantarum [169], and Aspergillus terreus [170]. Lipases from microorganisms are mainly used for biodiesel production due to the availability of sources and rapid growth rate of microorganisms for enzyme production [171]. Lipase activity depends not only on the source of the enzyme, but also the type of enzyme used (immobilized form or liquid form) [171]. Immobilizing lipase on the support material can enhance the stability of the enzyme, making the enzyme less susceptible to the pH, temperature, and impurities of reactants [171]. Notably, the supports and/or immobilization protocols can greatly modulate the specific activity of lipase, affecting biodiesel yield. Tacias-Pascacio et al. [172] immobilized different lipases on different supports and used them for biodiesel production. They found that the specific activity of lipases and biodiesel yield greatly depended on the support, solvent used, and media [172]. In addition, the immobilized enzyme is easy to reuse. Consequently, lipase immobilized on various supporting materials has been studied for biodiesel production. Recently, Iuliano et al. [173] reported that lipase from C. rugosa was physically attached to Mg modified Fe2O4 nanoparticles and used to turn brewers’ spent grains into biodiesel. After 48 h at 45 °C, a remarkable yield of 98% was achieved using a 1:4 oil/methanol molar ratio. In addition, lipases were immobilized on other materials such as graphene oxide [174], polyhydroxyalkanoate [175], alginate-polyvinyl alcohol (PVA) [167], polydopamine coated iron oxide (Fe3O4_PDA_lipase) [170], modified polyporous magnetic cellulose support [153], Co2+-chelated magnetic nanoparticles [168], core-shell structured Fe3O4@MIL-100(Fe) composites [162], Fe3O4/Au nanoparticles [176], waste-derived activated carbon support [177], genipin cross-linked chitosan [178], and other materials [160]. Several immobilized lipases have been commercialized and used for biodiesel production such as Novozym® 435 (lipase B from C. antarctica) [179,180,181] and Lipozyme TL IM (lipase from T. lanuginosus) [182]. Nevertheless, the immobilized lipase-catalyzed reaction rate is relatively low due to the mass transfer limitation between the substrate and enzyme [183]. Notably, the immobilized lipases are expensive, thus limiting their industrial applications.
Liquid lipase formulations or free lipases have been considered as a substitute for immobilized lipase for biodiesel production due to their high catalytic activity and significantly low cost (30 to 50 times lower) as compared to immobilized lipase [183,210]. Recent studies have demonstrated a promising use of several liquid lipases for biodiesel production such as C. antarctica lipase A [154] and liquid lipase formulations from T. lanuginosus (Eversa® Transform, Eversa® Transform 2.0, and NS-40116) [195,205,211]. The use of liquid lipase facilitates the homogenous reaction, thus overcoming the mass transfer limitation presented in the immobilized lipase-catalyzed reaction. However, liquid lipase is sensitive to the reaction environment. Studies have reported that high water content (from the feedstock and/or generated from the esterification of alcohol and fatty acid) not only promotes the reverse reaction but also negatively affects the lipase activity (including the formation of lipase-lipase aggregates in aqueous media), thus reducing the biodiesel production efficiency [183]. To address this obstacle, several adsorbents such as superabsorbent polymer, silica gel, alumina, and molecular sieve have been used to remove the water from the reaction mixture, enhancing the reaction efficiency [183,212,213].
Similarly, the type of acyl acceptor used also affects the lipase-catalyzed reaction. Studies have reported that lipase is deactivated using a high amount of methanol or ethanol, lowering the biodiesel yield [181,185]. In addition, the use of methanol or ethanol as an acyl acceptor for biodiesel production resulted in the formation of by-product glycerol [181]. This by-product also inhibits the activity of lipases, especially immobilized lipases because it can easily accumulate on the surface of immobilized lipases [181]. To address this obstacle, methyl acetate is proposed as another alternative acyl acceptor for biodiesel production [185]. The use of methyl acetate prevents the inhibition of lipase caused by methanol/ethanol and by-product glycerol (no glycerol produced in the reaction), thus enhancing the reaction rate [185]. Besides this method, ultrasounds [214,215] or very hydrophobic supports [216,217] can be used as another approach to lower the negative effect of glycerol on the enzyme. Studies have reported that ultrasounds can stir the enzyme particles from the inside and avoid the formation of the glycerin/water phase [215,218].
Another concern for each specific lipase in biodiesel production is associated with the oil source [218]. Fats/oils are a very heterogenous substrate, which are mainly comprised of triglycerides, low levels of mono and diglycerides, and some FFA [218]. Therefore, enzyme specificity affects the enzyme activity over each substrate [218]. To address this issue, the combination of different lipases (combi-lipase) has been proposed for biodiesel production [190,219]. There are several types of combi-lipase, which include co-immobilized lipases (different lipases immobilized on the same support), a mixture of individually immobilized lipases, and a mixture of free lipases [218]. Guan et al. [219] firstly reported the use of R. miehei lipase and P. cyclopium lipase mixture (in a liquid form) for biodiesel production from soybean oil. The result showed that the R. miehei lipase (individual enzyme) resulted in 68.5% biodiesel yield, but the yield increased to 95% when using the mixture of R. miehei and P. cyclopium lipases [219]. This was due to the use of lipases with different specificities [218,219]. In another study, the individual use of R. oryzae lipase and C. rugosa lipase resulted in 94.36% biodiesel yield at a reaction time of 9 h and 92.63% biodiesel yield at a reaction time of 30 h, respectively [220]. However, the biodiesel yield reached 98.16% (at a reaction time of 6 h) by using the mixture of both enzymes [220]. Similarly, various combi-lipases such as lipase cocktail (67% C. antarctica lipase B and 33% R. miehei lipase) [190]; immobilized C. rugosa and R. miehei lipases [175,202], co-immobilized R. miehei lipase and C. antarctica lipase B [193]; a mixture of 10% T. lanuginosus lipase, 75% C. antarctica lipase B, and 15% R. miehei lipase [221]; a mixture of lipases from porcine and T. lanuginosus (in both liquid and immobilized forms) [222]; a mixture of immobilized C. rugosa and R. oryzae lipases [223], and co-immobilized C. rugosa and R. oryzae lipases [224,225] were also tested for biodiesel production. These combi-lipases showed a higher biodiesel yield than the individual enzymes [175,190,193]. Mixtures of the same enzyme immobilized using different protocols/support materials also affect the biodiesel yield. Toro et al. [226] immobilized the same lipase (T. lanuginosus lipase) on two different supports (Purolite®ECR1604 and Lewatit®VPOC1600) and used them for biodiesel production from palm olein. The biodiesel yield reached 70.3% (for lipase immobilized on Purolite®ECR1604) and 78.2% (for lipase immobilized on Lewatit®VPOC1600). Notably, the biodiesel yielded increased to 86.1% when the mixture of the two individually immobilized lipases was used [226]. This could be explained by the fact that the enzyme features (flexibility of their active site and their mechanism of action) can be modulated by changes in the immobilization protocol [172]. Consequently, the changes in the support feature influence the stability, activity, and specificity of the lipase [172,218].
Generally, although both immobilized and liquid lipases (individual lipases or combi-lipases) show effectiveness for converting oil into biodiesel, their industrial application is still limited due to the high cost of the enzyme as compared to chemical catalyst [227,228]. Therefore, further studies on lipase-catalyzed biodiesel production are still required to improve the efficiency and economic feasibility of the process.

5. Catalyst Reusability

For biodiesel conversion, the catalyst’s effectiveness is not only determined by its catalytic activity but also its recoverability and reusability. Since homogenous catalysts cannot be reused for the next batch of production, heterogeneous catalysts play an important role in reducing production costs. Their recyclability not only lowers production costs but also maximizes environmental protection [229]. As compared to homogenous catalysts, one of the benefits of heterogeneous catalysts is that they can be reused several times. Furthermore, these catalysts may be regenerated or used for other purposes after losing their catalytic activity, such as construction materials, soil stabilizers, cement industries, and phosphate adsorbents [230].
Most of the bio-derived acid and alkali catalysts can be reused 4–7 times to yield biodiesel of 65–85% (Table 1 and Table 2). da Luz Corrêa et al. [122] prepared sulfonated carbon-based catalysts from murumuru kernel shell and used them for FFA conversion. The first use of the catalyst resulted in 95.1%, but the FFA conversion was reduced to 84.5% and 66.3% after the second and third catalyst reuses, respectively. The reusability of a solid base oxide catalyst derived from chicken eggshell was investigated by performing transesterification using the same catalyst for 10 cycles, and the yield was found to be marginally reduced after the seventh cycle, which may be due to catalyst pores being blocked, reducing reactant adsorption and desorption [49]. Kirubakaran and Arul [27] also investigated the reusability of a heterogeneous catalyst derived from eggshell. The catalyst could be reused five times to yield 85% biodiesel. After that, the biodiesel yield reduced significantly, suggesting that the catalyst’s stability had deteriorated. This is due to the presence of active Ca(OH)2 phases which reacted partially with the homogenous mixture in the transesterification reaction. In comparison with solid bio-based acid and alkali catalysts, several immobilized lipases show better reusability. Several immobilized lipases can be reused for up to 20 cycles without loss of enzyme activity [181,185]. However, the use of immobilized lipase for biodiesel production is still under lab-scale investigation because of the high cost of the enzyme. Therefore, to be used for industrial biodiesel production, further studies are still required to improve the catalytic activity, stability, and reusability of bio-based catalysts. In addition, a pilot-scale investigation is also needed to evaluate the potential use of these catalysts for biodiesel production before being used for industrial applications.

6. Environmental and Economic Evaluation

Catalyst selection is one of the crucial issues in biodiesel production with the aim to minimize energy consumption, waste generation and treatment, and reduce production costs [185]. The use of bio-based catalysts (alkali catalysts, acid catalysts, and enzymes) lowers the environmental effect since these catalysts are derived from natural sources (plants, animals, or microorganisms). These catalysts are also easy to separate from the reaction mixture and reuse, reducing the generation of wastewater and chemical residues in the downstream process, especially the purification step. Consequently, the fee for the purification step and waste treatment can be reduced, lowering the production cost.
Several studies have also evaluated the economic feasibility of different biodiesel production processes [231,232]. The bio-derived alkali- and bio-derived acid-catalyzed processes are more economically feasible than the conventional process (H2SO4- or KOH-catalyzed process) for biodiesel production since the cost of those catalysts (and total biodiesel production cost) is considered lower than that of conventional chemical catalysts (KOH or H2SO4) [232,233,234]. Among these two processes, the alkali-catalyzed transesterification seems to be superior to the acid-catalyzed process because the former proceeds at a lower temperature, has a shorter reaction time, and requires a lower molar ratio of alcohol to oil as compared to the latter, as shown in Table 1 and Table 2 [232,235]. In addition, the bio-based alkali and bio-based acid catalysts can be synthesized from the same natural source, but the synthesis of bio-based acid catalyst commonly requires one more step (sulfonation) [232]. Consequently, in some cases, the cost of bio-derived acid catalysts can be higher than that of bio-derived alkali catalysts. However, the cost of each specific catalyst depends on various factors including the source, synthesis method, and its reusability [232]. Therefore, it is difficult to compare the cost of all different types of catalysts. Different from bio-derived acid and alkali catalysts, the enzyme is expensive, especially the immobilized enzyme, making the lipase-catalyzed biodiesel production less competitive [236,237]. To reduce the enzyme cost, free lipase (or liquid lipase formulation) has been proposed for biodiesel production [183]. However, the reusability of liquid lipases is limited [183]. Therefore, the enzymatic process is still under investigation to improve its industrial application. Generally, among the three processes, the bio-derived alkali- and bio-derived acid-catalyzed processes are more economically feasible than the enzymatic process [236]. However, no individual studies have been conducted to compare the economic feasibility of the bio-derived acid-, bio-derived alkali-, and enzyme-catalyzed biodiesel production processes. Therefore, more studies are still required to evaluate and compare the economic feasibility of these processes.

7. Future Prospects and Conclusions

The use of biomass-derived catalysts has become a recent interest to make biodiesel production more sustainable. In addition, the use of these catalysts is promising to reduce the current high cost of biodiesel production, making biodiesel competitive with petro-diesel fuels. Research is therefore aimed to develop environmentally friendly, cost-effective, and efficient biomass-derived catalysts for biodiesel production. Consequently, different natural sources (animals, plants, microorganisms) have been used for synthesizing bio-based catalysts including acid catalysts, alkali catalysts, and enzymes. The catalytic activity of these catalysts varies among them. The use of acid or alkali catalysts depends on the quality of the feedstock. Besides, enzymes can be used as an alternative to both acid and alkali catalysts for biodiesel production. These catalysts show their advantages and disadvantages when they are used for biodiesel production. These catalysts show promise for biodiesel production, but these investigations have been stopped at lab-scale investigations. More investigations on these catalysts are therefore needed, especially large-scale investigations to prove the potential use of these catalysts for industrial biodiesel production.

Author Contributions

Conceptualization, H.C.N., H.C.O. and C.-H.S.; writing—original draft preparation, M.-L.N., H.-Y.J., S.-J.W. and H.C.N.; writing—review and editing, H.C.N., H.C.O. and C.-H.S. All authors have read and agreed to the published version of the manuscript.

Funding

This research received no external funding.

Conflicts of Interest

The authors declare no conflict of interest.

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Table
Table 2. Several bio-derived acid catalysts for biodiesel production.
Table 2. Several bio-derived acid catalysts for biodiesel production.
CatalystFeedstockReaction ConditionsConversion/Biodiesel Yield (%)Time of Reuse/Corresponding Biodiesel Yield (%)Ref.
Catalyst Loading (%)Alcohol: Fatty Acid Molar RatioTime (min)Temp. (°C)
Sulfonated-carbonized bamboo Oleic acid58:1606597.315/<40[108]
Sulfated angel wing shells Palm fatty acid distillate26:115290987/>80[112]
Sulfonated-carbonized coconut shellPalm oil630:13606088.15-[113]
Sulfated-carbonized Jatropha curcas seedJaropha curcas oil7.512:1606099.134/81.03[114]
Carbonaceous solid acid magnetic catalyst from empty fruit bunchPalm fatty acid distillate416:118010098.66/79[115]
Sulfonated cow dung-derived carbon-based catalystPalm fatty acid distillate 418:1609096.57/75[116]
CaO-based calcined angel wing shell sulfated catalystPalm fatty acid distillate515:118080984/>40[117]
Sulfonated-carbonated coconut meal residueWaste palm cooking oil512:118015095.54/82[118]
Sulfonated carbon derived from coconut meal residueWaste cooking oil69:13006596-[119]
Sulfated Ce supported activated carbon derived from coconut shellChicken fat oil312:16090935/90[120]
Sulfonated and magnetic catalyst derived from palm kernel shellWaste cooking oil3.6613:11026590.24/73.63[121]
Sulfonated carbon-based catalysts from murumuru kernel shellOleic acid510:1909097.24/66.3[122]
Sulfonated carbon-based catalyst from Murumuru kernel shellJupati oil630:124013591.84/>80[123]
Sulfonated biochar derived from sawdustPongamia pinnatta oil29:11208595.64/85.7[124]
Sulfonated-carbonized Zanthoxylum bungeanum seedZanthoxylum bungeanum seed oil830:124014095.65/57/9[125]
Sulfonated-calcined kenaf seed cake Palm fatty acid distillate210:1906597.95/>90[126]
Palm biochar-based sulfated zirconiumPalm fatty acid distillate315:11807594.35/80.2[127]
Sulfonated activated carbon derived from Monk fruit seed (Siraitia grosvenorii) 4 36012098.54/84.4[128]
Sulfonated-derived tea wastePalm fatty acid distillate 49:19065975> 80[129]
Sulfonated-carbonized Hura crepitans seed podHigh-FFA vegetable oil109:1609094.814/93.37[130]
Sulfonated-carbonized cotton stalkMadhuca indica oil518:13006089.27/83.4[131]
Sulfonated activated carbon derived from Mesua ferrea shellMesua ferrea oil106:11205595.57-[132]
Sulfonated biochar derived from palm empty fruit bunchPalm fatty acid distillate2030:142011098.1-[133]
Sulfonated carbon derived from corncob residuePalm fatty acid distillate315:112070855/60[134]
Sulfonated carbon derived from coconut meal residueWaste palm oil512:172065–7092.74/>80[135]
Sulfonated-carbonized spent coffee groundsOleic acid1010:14208091.24/26.41[136]
Sulfonated pine needle-derived carbonLevulinic acid55:14808096.14/>60[137]
Sulfonated rice huskOleic acid55:1202899.83/70[138]
Sulfonated rubber de-oiled cakeWaste cooking oil8.1812.8:1606391.23/80[139]
Magnetic carbonaceous acid derived from Jatropha hullsJatropha crude oil7.518:145018095.95/94.3[140]
Sulfonated carbon derived from potato peelOleic acid512:11508097.25/68[141]
Sulfonated waste yeast residueWaste cooking oil110:13606096.26/<80[142]
Sulfonated-carbonized cacao shellOleic acid57:1144045944/<50[143]
Sulfonated coconut coir huskWaste palm oil1012:118013089.84/<80[144]
Sulfonated lignin-derived from olive cakeWaste vegetable oil1035:1360655710/75[145]
Sulfonated soaked palm seed cake derived catalystPalm fatty acid distillate (PFAD)2.59:11206097.8-[146]
Sulfonated-calcined corncobs and calcined poultryNeem seed oil2.5814.76:172.6561.9092.894/76[147]
Sulfonated brewer’s spent yeastPalm fatty acid distillate 821:11806587.8-[148]
Table
Table 3. Several lipases used for biodiesel production.
Table 3. Several lipases used for biodiesel production.
CatalystFeedstockReaction ConditionsConversion/Biodiesel Yield (%)Time of Reuse/Corresponding Biodiesel YieldRef.
Catalyst Loading (%)Alcohol: Fatty Acid Molar RatioTime (h)Temp. (°C)
C. antarctica lipase B (CALB) immobilized on modified polyporous magnetic cellulose beadsYellow horn seed oil151.6:126092.35/85[153]
C. antarctica lipase A (CALA)Palm oil5.57:1223094.6-[154]
Novozym® 435 (CALB immobilized on macroporous acrylic resin)Residual babassu oil0.14 g18:144896.810/90.96[179]
Novozyme® 435Castor oil fatty acid103:156088.64-[180]
Novozyme® 435Spirogyra oil14.5:142.53593.2-[184]
Novozym® 435Black soldier fly larvae oil17.5814.64:11239.596.9720/>95[185]
CALASoybean oil57:1263892.4-[186]
CALB immobilized on methacrylic resinWaste animal fat1410:164087-[187]
CALB immobilized on magnetic nanoparticlesPalm fatty acid distillate 81.6:1105082.745/80.19[188]
CALB immobilized magnetic nanoparticlesMicroalgal oil110:133091.44/90[189]
67% CALB + 33% lipase from R. mieheiResidual chicken oil155:133089.95-[190]
CALBSoybean oil33:1154064.7-[191]
CALB immobilized on silica nanoflowersWaste oil 33.24 mg2.63:18.1145.9798.515/76.68[192]
CALB and Rhizomucor miehei lipase co-immobilized on epoxy functionalized silica gelPalm oil4.9 U/mg5.9:133.535.678.3-[193]
Lipozyme TL100L (T. lanuginosu lipase)Waste phoenix seed 9.74.3:16.93193.8-[155]
Lipozyme TL IM (immobilized T. lanuginosus lipase)Rapeseed oil55:152598.76-[156]
Lipozyme TL IMAnkistrodesmus sp. oil9.68:1124297.69 [194]
T. lanugionous immobilized on Fe3O4 nanoparticlesSoybean oil94:1284182.210/71.23[182]
Lipase NS 40116 (liquid lipase formulation derived from T. lanuginosus)Residual chicken oil 0.34:1363593.16-[195]
Lipozyme TL IM Rapeseed oil59:173099.89-[196]
Lipozyme TL100LPhoenix tree seed oil105:16.983098.8-[197]
Lipase NS 40116 Soybean oil0.76.3:183597.1-[198]
Lipase NS 40116Soybean oil0.54.5:1123594.35/90[199]
T. lanuginosus lipase immobilized on Immobead 150None-edible oils3.557.64:123690-[200]
T. lanuginosus lipase immobilized on Fe3O4/Au nanoparticlesTomato seeds oil206:1244598.55/68.95[176]
Liquid formulation of T. lanuginosus lipasePalm oil mill effluent2100 U4:1244097.43-[201]
Eversa Transform lipase (liquid lipase from T. lanuginosus)Oleic acid11.983.44:12.535.2596.735/<30[183]
R. miehei lipasesOleic acid202:1440854/74[157]
R. miehei lipase immobilized on magnetic nanoparticlesBabassu oil51:164081.7-[158]
C. rugosa immobilized on polyhydroxybutyrate + R. miehei immobilized on polyhydroxybutyrateWCO16:1244596.510/28.95[175]
Mixture of polyhydroxybutyrate-immobilized C. rugosa and R. miehei lipasesMixed chicken waste oil2.56:1124097.115/10[202]
P. cepacia lipase immobilized on bio-support beads.Hybrid non-edible oil106:124507812/19.5[159]
P. cepacia lipase immobilized on bio-support beadsNon-edible hybrid oil9.465.93:124.3249.784.5810/>70[160]
P. cepacia lipase immobilized on hybrid PVA/AlgNaCrude castor oil106:12450786/70[203]
C. rugosa lipases immobilized on immobead 150Acutodesmus obliquus oil153:185095.365/90.07[161]
C. rugosa lipase immobilized lipase on core-shell structured Fe3O4@MIL-100(Fe) composites Soybean oil254:1604092.35/83.6[162]
C. rugosa lipase immobilized on magnetic Fe3O4-poly (glycidyl methacrylate-co-methacrylic acid) compositeSoybean oil254:1544092.85/79.4[204]
C. rugosa immobilized on Mg modified Fe2O4 nanoparticlesBrewers’ spent grains oil304:14845984/87[173]
Eversa® Transform 2.0 (liquid lipase from T. lanuginosus)Palm oil0.24:1244097-[205]
A. oryzae ST11 lipase immobilized on polyacrylonitrile coated magnetic nanoparticlesPalm oil303:1243794.75/65[163]
B. cepacia lipase immobilized on hydroxyapatite coated magnetic nanoparticleWCO 7:14840984/82[164]
B. cepacia lipase immobilized on mesoporous silica/iron oxide magnetic core-shell nanoparticleWCO366.2:12534923/81[165]
B. cepacia lipaseSunflower oil103.4:1150>99-[206]
A. grandidieri lipaseSunflower oil252:1964095-[166]
R. oryzae lipase immobilized on alginate-polyvinyl alcoholSludge palm oil23:1 4091.315/>91[167]
P. fluorescens lipase immobilized onto Co2+-chelated magnetic nanoparticlesWCO7.54:112509510/83[168]
Immobilized L. plantarum lipaseOlive oil56:1237814/>65%[169]
Lipase immobilized on graphene oxideKaranja oil38:1242588-[174]
Oreochromis niloticus lipaseWCO30 kUnit4:1284596.5 [151]
A. terreus AH-F2 lipase immobilized on polydopamine coated iron oxide WCO106:13037925/>80[170]
Steapsin lipase immobilized on waste-derived activated carbon supportRubber seed oil36:152083.97/>77[177]
Steapsin lipase immobilized on Immobead-350WCO144:28144088.33 [207]
Proteus sp. NH 2-2 lipasesoybean oil0.54:1364091.5 [208]
Garbage lipaseNaganishia liquefaciens NITTS2 oil206.4:1163597.13 [209]
Lipase (from porcine pancreas) immobilized on genipin cross-linked chitosan beads WCO7.59:1104092.334/>80[178]
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Nguyen, H.C.; Nguyen, M.-L.; Su, C.-H.; Ong, H.C.; Juan, H.-Y.; Wu, S.-J. Bio-Derived Catalysts: A Current Trend of Catalysts Used in Biodiesel Production. Catalysts 2021, 11, 812. https://doi.org/10.3390/catal11070812

AMA Style

Nguyen HC, Nguyen M-L, Su C-H, Ong HC, Juan H-Y, Wu S-J. Bio-Derived Catalysts: A Current Trend of Catalysts Used in Biodiesel Production. Catalysts. 2021; 11(7):812. https://doi.org/10.3390/catal11070812

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Nguyen, Hoang Chinh, My-Linh Nguyen, Chia-Hung Su, Hwai Chyuan Ong, Horng-Yi Juan, and Shao-Jung Wu. 2021. "Bio-Derived Catalysts: A Current Trend of Catalysts Used in Biodiesel Production" Catalysts 11, no. 7: 812. https://doi.org/10.3390/catal11070812

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