Biodiesel production from algae by using heterogeneous catalysts: A critical review

lable at ScienceDirect

Energy xxx (2014) 1e12

Contents lists avai

Energy

journal homepage: www.elsevier .com/locate/energy

Biodiesel production from algae by using heterogeneous catalysts:A critical review

Ahmad Galadima a, Oki Muraza a, b, *

a Center of Research Excellence in Nanotechnology, King Fahd University of Petroleum & Minerals, Dhahran, Saudi Arabiab Chemical Engineering Department, King Fahd University of Petroleum & Minerals, Dhahran, Saudi Arabia

a r t i c l e i n f o

Article history:Received 6 November 2013Received in revised form3 June 2014Accepted 6 June 2014Available online xxx

Keywords:Biodiesel productionEdible oilsAlgae oilsHeterogeneous catalystsGlycerol

* Corresponding author. Chemical Engineering Depaof Petroleum & Minerals, Dhahran, Saudi Arabia.

E-mail addresses: [email protected], o.mura

http://dx.doi.org/10.1016/j.energy.2014.06.0180360-5442/© 2014 Elsevier Ltd. All rights reserved.

Please cite this article in press as: GaladimaEnergy (2014), http://dx.doi.org/10.1016/j.en

a b s t r a c t

The numerous challenges associated with declining fossil fuel reserves as energy sources, have accountedfor a shift to biofuels as alternatives. However, transesterification of animal fats and edible vegetable oilsusing homogeneous acids and bases for biodiesel production is recently considered unsustainable byindustries, particularly due to food versus fuel competition, and economic and environmental challengesassociated with the feedstocks and catalyst systems, respectively. The paper therefore presents a criticalreview on the prospects of non-edible oil (i.e. algae oil) for biodiesel production via heterogeneouscatalysis. It covers the advantages of algae oil exploitation over edible oil feedstocks, progress made inthe oil extraction, available heterogeneous catalyst systems and reaction mechanisms, optimum trans-esterification conditions and the way forward. As the economic feasibility of biodiesel production fromalgae is supported by the valorization of glycerol as by-product, we have also highlighted key availableheterogeneous catalysts to upgrade glycerol into more useful industrial products.

© 2014 Elsevier Ltd. All rights reserved.

1. Introduction

Since its early commercialization as a substitute for petroleum-diesel for nearly a decade now, biodiesel have remained a goodglobal fuel for running automobile engines. Many interesting fac-tors have been attributed to this success. Among others, biodiesel ischemically non-toxic in nature, biodegradable and can simply beprepared via transesterification under mild conditions [1]. Inaddition to insignificant contribution to CO2 and other particulatematter emissions, it could be employed directly in conventionalpetroleum-diesel engines given optimal performance, particularlydue to very low sulfur and aromatic contents and compatible flash,cloud and pour points [1e3]. However, although the global demandfor biodiesel has been projected to either doubled or tripled inmany regions by 2020 and beyond and relevant researches fullyintensified, a number of factors have not been critically addressed.Conversion of the triglyceride esters in oils to the mono-alkyl esters(biodiesel) requires a reaction of the former with monohydricalcohol. Many researchers have recommended lower monohydric-alcohols (i.e. methanol to propanol), with no clear justification ofwhich provides the best viscosity requirements in line with

rtment, King Fahd University

[email protected] (O. Muraza).

A, Muraza O, Biodiesel produergy.2014.06.018

specifications by ASTM (American Society of Testing and Materials)or related international agencies [4,5]. The predicted sudden rise inthe prices of edible vegetable oils coupled with hunger threats aswell as soil degradation associated with large scale biodiesel pro-duction have on the other hand forced many agencies, particularlyfood and agricultural organizations and economic modelers toconsider the option as unviable [6,7]. So far emphasis was given tocanola, soybean, rapeseed and sunflower oils and in some instancesprocessed or used animals fat. The choice of most appropriatecatalyst and reaction conditions is similarly a great challenge toindustries. Initially hydroxides and alkoxides (methoxides andethoxides) of group IA and IIA like NaOH, KOH, NaOCH3, KOCH3,Ca(OH)2, Mg(OH)2, LiOH, NaOCH2CH3, KOCH2CH3 etc were themaintransesterification catalysts [4,8e10]. These homogeneous mate-rials are however, associatedwith great problemsmilitating againsttheir continuous application. Although faster biodiesel productioncould be attained in basically moderate reaction time, the catalystcannot be recovered at the end of the transesterification process.Therefore must be carefully neutralized leading to production oflarge quantity of wastes. Catalysts are commercially expensive andare generally affected by fatty acid concentrations even in tracequantities. The homogeneous acids like H2SO4, HCl, H3PO4 andorganic sulfuric acids of the type RSO3H (R¼ alkyl or aryl) have alsobeen classified as unreliable due to much slower reaction rates,difficult temperature requirements, high reactants (oil to alcohol)

ction from algae by using heterogeneous catalysts: A critical review,

Delta:1_given name

Delta:1_surname

mailto:[email protected]

mailto:[email protected]

www.sciencedirect.com/science/journal/03605442

http://www.elsevier.com/locate/energy

http://dx.doi.org/10.1016/j.energy.2014.06.018



Fig. 1. Yield of biodiesel per acre for some crops compared to algae.

A. Galadima, O. Muraza / Energy xxx (2014) 1e122

ratios, concentrations of catalysts, and severe corrosion problems[8,10].

The numerous problems identified have stimulated researchersat university and industry to explore better options, with greatemphasis on the flexibility of feedstock, greener catalyst systemsand conversion of the waste glycerol into more useful industrialproducts. Recently, many groups promoted a shift to algae as bio-diesel feedstock and a wide range of heterogeneous materials[11e16] as green catalyst. We have therefore documented herein acritical survey of the relevant literature on the progress made inthis regard. The paper also discusses issues of interest associatedwith heterogeneous upgrading of the glycerol produced asbyproduct from transesterification process.

2. Prospects of algae as biodiesel feedstock

Among SCO (Single Cell Organisms), algae are as promising asyeast and bacteria. A number of interesting factors have beenattributed to this fact. They are widely available and can be grownanywhere with practical consistencies, thereby limiting anycompetition with edible vegetable oils. Unlike many energy crops,algae can have up to 100 times more oil content. Theoretically,depending on the strength, algae species can produce up to a yieldof 20,000 gallons of feedstock per acre of land [17]. Table 1 presentsa short time projection of fuels from algae. By 2014, lower than 3%of the global conventional fuels production will be substituted bybiofuels of traditional origin. This percentage represents a marketsize of over $120 billions. Biofuels from algae feedstock willpotentially replace a higher percentage of fossil fuels used asautomobile fuels than the other sources. The estimated market sizefor algae is $425 billions, which is more than twice the expectedmarket size for other traditional biofuels. Thus, the algae optionsstand a market worthing hundreds of billions of dollars. Similarly,there are possibilities that these prospects would even escalate inthe long term. For example, Fig. 1 shows a comparable biodieselyield per acre of farmland for different crops, with algae as themostpromising feedstock. While the yields of most common vegetableoils is below 1000 gallons per acre, the yield from algae feedstockreaches 5000 gallons per acre, indicating tremendously a muchhigher prospect. Low land mass is required to produce hugeamount of oil for industrial biodiesel production. For example, arecent study projected the algae biodiesel to be capable of meetingthe US diesel demand with only 2e5% of the cropland exploited forthis purpose [18]. This has strong tendency to eliminate the prob-lems of food shortage and related price hike that are usuallyassociated with large scale exploitation of agricultural land forbiofuels production.

While biodiesel is considered the main obtainable fuel-produced from algae, other important fuels can similarly be pro-duced, thus enhancing their exploitation potentials. Fuels such as

Table 1Short term projection of biofuels from algae.

Short term potentials, 2014 Billion gallonsAssumed 1 gallonof oil ¼ $3.0

Total oil consumptionTotal projected supply of traditional biofuelsTotal ethanol productionTotal biodiesel production

1500412615

Share of traditional biofuels in total oil consumptionProjected market size for traditional biofuelsShare from algaeEstimated market size for algae

2.73%$123 billions9.2%$425 billions

Source:[17]. Authors' modified.

Please cite this article in press as: Galadima A, Muraza O, Biodiesel produEnergy (2014), http://dx.doi.org/10.1016/j.energy.2014.06.018

methane, hydrogen, ethanol and biogasoline can be generated fromalgae. The biomass-residues are applicable as sustainable feedstockfor combustion. Other important areas of applications for algaeinclude environmental management and production of otherproducts. Algae derivatives have excellent bioremediation proper-ties and therefore suitable for treating waste and sewage waterthrough the removal of toxins and nutrients. Pigments, nutra-ceuticals and even fertilizers can successfully be produced fromalgae.

It could be seen that, producing oil from algae and subsequentlybiodiesel as well as other products is considered highly efficient bymany authors [19e21]. The processes of cultivation, oil extractionand final conversion into biodiesel are basically comparable tothose of other edible crops such as soy, sunflower and palm. Thesefacts could be attributed to important factors leading to the esca-lated growth-rates for the algae species around many places in theworld [22e25]. It is particularly important to note that, unlike othercrops, algae can be cultivated even in harsh conditions, includingsalty and sewage receiving areas. During their growth, the algaespecies require considerable amount of atmospheric carbon diox-ide [26e28]. This factor implies that, they can be used for cheapermode of CO2 sequestration from stationary sources like oil and gasfacilities and related industrial power plants [22,27]. In fact, algaecultivation can be considered multi-beneficial [24,29]. However,there are certain difficulties hindering algae exploitation comparedto other crops. These include situation awareness (i.e. lack of fullknowledge of their prospects, especially in the developing worldwhere research is limited), poor knowledge of the most cost-feasible cultivation method and difficulty in identifying the mostaffordable algae strain with higher oil content, having fastestgrowth rate with no harvesting challenges. Other challenges are;algae production requires huge land mass and water and cold flowproblems with the net biodiesel. Some macro blueegreen algaespecies are also hazardous to human beings, especially whenexposed through recreational activities or drinking contaminatedwater. If these issues are fully addressed, algae market wouldsimply be at the forefront.

3. Heterogeneous transesterification catalysts

To mitigate the various challenges encountered with the use ofhomogeneous bases and liquid acids as alcoholysis catalysts,numerous studies were reported to explore the activities of a widerange of heterogeneous materials [30e43]. Table 2 presents a list ofnumerous solid acids and bases documented as catalyst for thebiodiesel production. The solid acids comprised mainly of zeolitematerials, heteropoly acids, pure or modified oxides of transitionmetals like zirconium and molybdenum, silica and alumina


Scheme 1. Chemical equation illustrating biodiesel production.

Table 2A summary of heterogeneous transesterification catalysts reported in the literature[14e43].

Solid acids Solid bases

� Zeolitic materials such as HeY, H-Beta, ZSM-5, H-MOR, ETS-10, andETS-4.

� Sulfated zirconia (SO42�eZrO2)

supported with Al2O3 or sometimes SiO2.

� Sulfated zirconia mixed withother transitional metal oxides.e.g. SO4

2�eZrO2/WO3, SO42�eZrO2/

MO3.� Free sulfated tin oxide or sup-

ported usually over alumina orsilica (SO4

2�eSnO2/Al2O3, SO42�

eSnO2/SiO2).� Acetates of zinc or copper sup-

ported over silica� Heteropoly acids and their de-

rivatives. e.g. H3PW12O40,H4SiW12O40

� Supported organosulphonicacids. The support is mostlymesoporous silica and some timealumina.

� Nafion

� Oxides of group IIA elements:CaO, MgO, SrO, BaO.

� Carbonates of group IIA ele-ments: CaCO3, MgCO3, SrCO3,BaCO3

� Carbonates of group IA elements:K2CO3.

� Free andmixed transitional metaloxides. e.g. ZnO, CuO, CaLaO3,CaCeO3, CaZrO3, CaMnO3, CaTiO3,

etc.� Basic zeolites.� Cs-exchanged sepiolite.� Hydrotalcites (MgeAl)� Quanidine anchored cellulose or

other polymers.� Aluminates of Zinc.� Metal generated salts of primary

amino acids.� Li-promoted oxides of group IIA

elements.

Scheme 2. Mechanism of base catalyzed transesterification.

A. Galadima, O. Muraza / Energy xxx (2014) 1e12 3

catalysts [14e43]. These materials are characterized by having bothBrønsted and Lewis acid sites, that determines their activitiesduring transesterification reactions. Activities of zeolites and het-eropoly acids may also be affected by shape selectivities. Materialshaving multi-dimensional pore structure should be more favorablefor the formation of alkyl esters without cracking. Solid bases onthe other hand, comprised of basic zeolites, carbonates and com-mon oxides. The basic sites formed the main reaction centers forthese materials during biodiesel synthesis.

In the heterogeneous catalysis a good number of factors mustbe appropriately considered depending on whether the catalyst isa solid acid or base. The factors include transesterification tem-perature, the amount of catalyst, on stream reaction time, degreeof mixing or stirring, alcohol/oil content and purity index of thefeedstock. Anderson et al. [14] reported the dispersion of the activematerial over the support considerably influences the alcoholysisactivity of a BaO/Al2O3, with higher dispersions being more active.The selected temperature should be close to the monohydric-alcohol boiling point to avoid handling difficulties. Adequate re-action time should be provided (e.g. 1e3 h) in order to ensurecomplete conversion. The extent by which the catalyst interactswith the reactants is very important and thus moderate mixingwould be very important. At lowmixing rate the reaction would bevery slow, whereas high degree of mixing causes side reactionsand difficulty in handling the reaction system. The key impuritiesin most oils are free fatty acids; therefore those with very lowpercentage of free fatty acids (e.g. algae oils < 1%) would bedesirable.

Transesterification is an equilibrium derived process, via whichtriglyceride ester and monohydric-alcohol reacts in the ratio of 1:3to produce an equivalent amount of mono-alkyl esters (biodiesel)and a mole of glycerol (glycerine) as byproduct (Scheme 1). Thereaction is believed to proceed in three consecutive steps, eachinvolving the formation of mono-alkyl ester and introducing alco-holic eOH group into the triglyceride ester chain. Therefore, glyc-erol would be finally produced at the last step of the reaction.Accelerating the reaction to produce more biodiesel in shorter timerequires the monohydric-alcohol/oil content in between 4:1 and12:1 [10e15]. At values below this ratio, the yield of biodiesel


would generally be low and the reaction can shift backward,creating further negative effect on the total biodiesel yield. How-ever, at higher ratios, removal of excess alcohol may pose a greatchallenge. Factors such as reaction temperature and degree ofstirring are also very critical. Adequate stirring is required to ensuresufficient interaction between catalyst particles and the reactants[10e15]. The temperature must be close to the boiling point of themonohydric alcohol. Lower temperatures favor slow reaction,whereas much higher temperatures create handling difficulties.

3.1. Transesterification with solid bases

Reaction involving heterogeneous bases proceeds by reaction ofeither the Lewis or the Brønsted basic sites of the catalyst with amonohydric alcohol (usually ethanol or methanol). The generatedalkoxide mixture interacts with triglyceride ester in the oil to yieldbiodiesel and glycerol in the subsequent steps (Scheme 2). Themechanism is EleyeRideal type, but the strength of the basicitysignificantly influences how fast the reaction can proceed. The basicsites preferentially interacts with alcohol and remove Hþ, formingan alkoxide group (RO�), which is the main active component thatattacks the triglyceride ester at the intermediate stages. Thestronger the basic sites the more favorable the formation of thealkoxide species. Similarly, strong basicity favors subsequentcleavage and glycerol formation, and consequently the overall re-action rate would be enhanced.

Solid basic catalysts such as zeolites, oxides of first row transi-tion metals like ZnO, CuO, basic polymers and compounds of groupIIA elements (Table 2), especially the oxides and carbonates such asCaO, MgO, SrO, BaO, CaCO3, MgCO3, SrCO3 and BaCO3, have



attracted attention as heterogeneous transesterification catalysts.The latter being the most prominent. Their basicity is associatedwith metal-oxygen ion pairs (i.e. M2þeO2�) and varies in the orderBa > Sr > Ca > Mg for the oxides. These materials are easily pre-parable, less expensive, and showed low corrosion properties. Theseverity of calcination step is a very important factor that de-termines the transesterification activity of these heterogeneousbase catalysts. At high calcination temperatures, the conversiongets low due to decrease in active catalyst surface. For instance, asample of MgO calcined at 600 �C yields only 18% conversion after8 h reaction time. Whereas high conversion up to 92% was obtainedat optimum conditions; lower calcination temperatures, themethanol/oil content being 12:1 and 5.0 wt.% catalyst [15]. Similartrend was observed over CaO. However, the latter catalyst causedreusability problems after repeated cycles of applications. Thesupported carbonates of group IIA are also good alcoholysis mate-rials but these materials will be partially dissolved in the presenceof water and fatty acid impurities. The carbonates are not verystable under very high calcination temperatures (Table 3).

Mixed oxides of Ca and transition elements like Fe, Ce, Zr and Lahave also been evaluated in transesterification. Up to 95% biodieselyield had been recorded. However, high methanol to oil ratio ofabout 6:1 may be required in order to sufficiently shift the equi-librium position forward. Adequate transesterification time (maybe up to 10 h) is also needed with these materials. For example, aCaTiO3 yields 79% of biodiesel in 10 h reaction time, whereasCaCeO3 and CaZrO3 yields between 70 and 95% of biodiesel in 10 husing 1:6 (oil to methanol) ratio at 60

�C. Among the support ma-

terials Al2O3 shows higher activity, specifically due to sufficientstability and dispersion properties. It also allows enhanced surfacereactants interaction [13e15,24].

Basic zeolites and hydrotalcites are increasingly gaining atten-tion. Materials such as oxides containing zeolites, ETS-10 and fau-jasites possess basic cations that could be generated via thermaldecomposition of their supported salts. Ion exchange with highlyelectropositive cations is also very critical to the enhanced trans-esterification activity. The hydrotalcites (MgeAl) possess good ba-sicity but dissolution problems require that the materials arecarefully prepared. Preparation by co-precipitation method has sofar shown reliable stability.

3.2. Transesterification with solid acids

Catalysts in this category are more environmentally benign andsustainable than their homogeneous counterparts and have so farshown very limited corrosion and recycling problems. However, highporosity systems are required to obtain better performance. Theporosity allows appropriate adsorption-desorption and diffusion ofthe reactants andproducts. Thus, acidic zeolites (seeTable 2)wouldbepreferable here than the metal oxides or carbonates. Their structuraland acidity properties can always be modified to address diffusionallimitations and thus enhance the production of larger biodiesel yields[44e47]. However, a challenging issue with zeolites is selecting themost appropriate silicaealumina ratio as well as the modifier

Table 3Role of calcination temperature on the activity of WO3 modified ZrO2 [49].

Samplecode

Calcinationtemperature [�C]

Conversion (%),5 wt.% WO3/ZrO2

Conversion (%),15 wt.% WO3/ZrO2

A 400 93 78B 500 95 81C 600 10 20D 700 5 25E 900 5 17


concentration.Withoxides,high loading causes ablockage to theporesystems whereas free metals like Pd or Pt causes hydrogenolysis andsubsequent dehydrogenation, thus limiting biodiesel yield.

The numerous separation and environmental challenges asso-ciated with sulfuric acid have triggered the evaluation of sulfatedzirconias and organosulphonic acids as transesterification catalysts.With unsupported systems, the SO4

2� may easily be lost in the re-action medium and thus the catalyst deactivation by acidity decay.Therefore the incorporation of porous silica or alumina as supportmaterial is necessary to solve this problem. Zirconia normally existsas monoclinic, tetragonal and cubic phases. It has been establishedthat, the tetragonal phase exerts much higher transesterificationactivity than the other phases, especially when doped withappropriate quantity of amorphous WO3. In some cases, sulfatedzirconia can be replaced with sulfated tin oxide or tungstated-zirconia supported over alumina to obtain comparable activity[49]. In addition to the phase properties, the loading of WO3 andcalcinations temperature influence the activity of ZrO2 (Table 3).Calcination at 500 �C ensures optimum ester yields, especially withthe lower loadings. Higher calcination temperatures sintered thecatalyst, with significant resistance associated with higher WO3

loadings [49].Heteropoly acids and their derivative salts are also good mate-

rials for alcoholysis. Especially due to their water tolerance poten-tials, which significantly limit deactivation by hindering theconversion of Lewis to Brønsted acid sites. Their super acidityproperties coupled with structural networks promote their degreeof transesterification, compared with homogeneous hydroxidesand acids. They can easily be recycled and reused, thus reducingproduction cost and environmental inconsistencies. However, theirspecific mechanism of action has not yet been established [48e53].Recently, Alsalme et al. [52] heterogeneously esterified hexanoicacid and transesterified the corresponding ester as a model studywith a range of heteropoly acids (H3PW12O40, Cs2.5H0.5PW12O40,H4SiW12O40, H3PW12O40/Nb2O5, H3PW12O40/ZrO2, and H3PW12O40/TiO2) and high methanol concentration (1:20) at 60 �C and atmo-spheric pressure. The results when compared with some homo-geneous and solid acid catalysts such as sulfuric acid, Amberlyst-15,HeYand H-Beta zeolites indicated the heteropoly acids to be bettermaterials due to higher yield and catalyst stability. Kineticmodeling by Talebian-Kiakalaieh et al. [51] has also shown thesematerials to offer significant resistance to fatty acid interferenceduring the conversion of used cooking oil. Good activity of 88.6%conversion was achieved under optimal parameters; at 65 �C,methanol/oil content of 70:1 and 10 wt.% catalyst. This implies thematerials to have considerable prospects for the transesterificationof macro-algae (i.e. those with high fatty acid concentrations).

In acid catalysis, both the homogeneous and heterogeneousmethods proceed via basically a similar reaction mechanism, withthe Brønsted option being preferential. The acidity should be of theBrønsted type, production of water and glycerol during the trans-esterification process have previously been reported to significantlydeactivate the Lewis acid sites. Initially, a carbonyl group is pro-tonated in order to enhance its electrophilicity thereby making itmore ready for nucleophilic attack (Scheme 3). The rate of attackbetween free alcohol and the Brønsted sites adsorbed carboxylicacid is usually the rate determining step with most solid acids.Thus, the mechanism is of the EleyeRideal type. However, whereLewis sites participate, their strength determines the slowest step.

4. Heterogeneous transesterification of algae oil

Oil extraction is basically the initial and critical step in biodieselproduction from plants after harvesting (Fig 2). An attractive pro-cedure is one that ensures reduced extraction cost but high oil yield


Table 4Data for biodiesel production over solid catalysts (including zeolites) from algae andsome common oils.

Feedstock Catalysts Biodiesel yield/Conversion (%)

Soybean Zirconia, titania [73] 88.10Corn oil Zirconia, titania [73] 88.30Algae oil Zirconia, titania [73] 90.20Algae oil 4% NiO, 18% MoO3/

alumina [79]99.00

Algae oil 0.75% Pt-SAPO-11 [79] 83.00Algae oil 4% NiO, 18% MoO3/H-

ZSM-5 [79]98.00

Algae oil Microporous titania[79]

94.70

Algae oil (HY-340) niobiumoxide [79]

94.27

Algae oil Hierarchical H-Betazeolites [79]

99.50

Algae oil Amberlyst-15 [78] >98Microalgal's lipid Modified alumina [71] 97.5Fresh water microalgae oil Modified titania [15] >95Fresh water microalgae lipids Porous titania

microsphere [15]>95

Groundnut oil BaO/Al2O3 [14] 80Cotton seed oil

(fatty acid ¼ 4.34%)BaO/Al2O3 [14] 80

Sunflower oil ZrO2/La2O3 [16] 84.9Yellow horn Cs2.5H0.5PW12O40 [16] 96.22Waste cooking oil MgO/TiO2 [16] 91.6Palm oil CaO/Al2O3 [16] 98.64Jatropha curcas oil CaO/Fe3O4 [30] 95Soybean oil Li/MgO [30] 93.9Chinese tallow seed oil KF/CaO [30] 96.8Croton megalocarpus oil sulfated SnO2eZrO2

[30]95

Waste cooking oil Zeolite Y (Y756) [31] 85Waste cooking oil H3PW12O40.6H2O [31] 87Waste cooking oil K3PO4 [31] 97.3Mutton fat MgO/KOH [35] 98Sunflower oil NaeX zeolite [45] 83.53

Scheme 3. Mechanism of transesterification via acid catalysis.


[18,46]. The two fundamental methods available for algae today arethe mechanical and chemical methods. The mechanical method ismainly expeller press or ultrasound-assisted whereas hexane sol-vent, soxhlet and supercritical fluid extractions are the availablechemical methods. The mechanical method requires algae drying,thus making it energy intensive whereas health and safety issuesare critical for the chemical option [18,46]. Adopting supercriticalextraction process involved the used of expensive high pressureequipment that is also energy intensive. Industrially, a single stepprocess by OriginOil Company is used in wide application. Themethod involved sequential steps of harvesting, concentration, andextraction oil from algae. It separate oil, biomass and water in asingle step (mostly in less than 1 h). No chemicals or heavyequipment is needed and the process requires no initial dewateringof the fresh algae. Another novel method is that of CavitationTechnologies Inc. The company's Nano-based reactor is employedto generate cavity bubbles in the solvent [54]. Collapsing of thebubbles close to the cell walls generates pulses that break the cellwalls to produce oils into the extraction solvent. The Catilin'smethod, which is under research and development stage, would beof great interest to the Nano-technologists. Specially developedmesoporous nanoparticles would be employed to preferentiallyextract and sequester specific fuel-based compounds in the algal

Fig. 2. Flowsheet representation of biodiesel production from algae.


lipid feed. The free fatty acids and triglycerides rich balanced algaloil would be transesterified into biodiesel using the T300 catalystdeveloped by the company. A key important issue here is that, thetechnology is potentially very efficient and involved heterogeneouscatalyst, thereby ensuring environmental sustainability, costreduction, catalyst reusability and high purity biodiesel and glyc-erol [54]. Other methods of oil extraction that are under investi-gation include enzymatic extraction and osmotic shock, with theformer being considered much more expensive than the hexaneextraction method. The process utilizes specific molecules of en-zymes to break the cell walls with a common solvent, therebymaking fractionating the oil easier.

Demirbas and Demirbas [55] recently reported an estimate of upto 80,000 liters per acre of algae oil. This figure exceeds 30 times thequantity obtainable from other feedstocks like palm oil. Theyshowed common algae species such as Botryococcus brauni andSchizochytrium sp. to yield up to 77% oil based on dry matter. Amodel by the same authors revealed 100,000 L of oil per hectare foralgae species compared to only 446 and 952 L per hectare for soyand sunflower plants, respectively. Vazhappilly and Chen [56],Volkman et al. [57] and Yaguchi et al. [58] have reported closertrends. Algae oils are also known to be rich in fatty acids of theunsaturated class. They include omega-3's, omega-6, docosahex-anoic and ecosapentanoic acids. These compounds could be iso-lated and employed for other industrial applications, consequentlyfavoring economic exploitability [59,60].

After the successful oil extraction, the next step is the trans-esterification of the oil into biodiesel. Algae oils are basically



converted using similar methods adopted for other vegetable oils[55,61e63]. Xu et al. [61] employed Chlorella protothecoides (analgae specie) for biodiesel synthesis. Cells removal was achieved byagitation coupled with distilled water-washing before drying usinga freeze dryer process. Oil was obtained through pulverization ofpowdered cells using mortar followed by extractionwith n-hexane.The optimum parameters include equivalent catalyst concentration(i.e. according to oil weight), methanol/oil ratio (56:1) at temper-ature of 30 �C, which reduces product density from 0.912 to 0.864during 4 h on stream. There are evidences that, homogeneouscatalysts were given emphasis to the production process in therecent time [64e70]. However, the sensitivity of these materials tofatty acids of the algae oil feed and production of low qualityglycerol suggested the need for a shift to the heterogeneous ma-terials. Both materials can be employed in line with Fig 2. With thelatter catalysts, limited energy is required for soap and glycerineremoval (i.e. during purification). Catalyst is also easily removedand recycled during the separation process. The heterogeneousmethod will greatly replace the currently used homogeneousprocess in the near future. Heteropoly acids such as H3PW12O40,Cs2.5H0.5PW12O40, H4SiW12O40, H3PW12O40/Nb2O5, H3PW12O40/ZrO2, and H3PW12O40/TiO2 have shown desirable tolerance to highfree fatty acid concentrations, yielding high conversions of bio-diesel at ordinary conditions for vegetable oils [50e53]. This novelopportunity could be extended to algae oils with much greaterpotential. Acidic zeolites such as H-Beta, H-ZSM-5, H-MOR, H-ETS-10, H-ETS-4 with moderate acidity properties and sufficientporosity allow faster transesterification with limited side reactionsinterference for the vegetable oils under controlled conditions[44e47]. This is another great opportunity for the algae oils. Ma-terials based on WO3/ZrO2 should be employed at appropriateloadings and calcinations. The 15 wt.%WO3/ZrO2 calcined at 500 �Cused for oil yields 95% conversion for other oils (see Table 3). Thus,similar preparations have potentials for much higher yields withalgae oil under comparably constant reaction conditions. Hetero-geneous bases are also prospecting materials (see Table 4). Oxidesof Ca, Sr and Mg, mixed oxides with transition metals, and sup-ported over silica or aluminawere extensively studied for other oilswith their properties fully evaluated. These materials could simi-larly be fully exploited for the algae oils, with the hope that, chal-lenges such as dissolution, sintering, thermal instability andrecyclability problems encountered could be mitigated throughappropriate choice of parameters.

The choice of appropriate reaction conditions and supportmaterials is very important in heterogeneous algae trans-esterification [25,69,71e77]. Umdu et al. [71] studied the proper-ties of Al2O3 doped MgO and CaO during the conversion of amarine microalgae, by monitoring the methanol concentrationand the amount of active materials at 323 K. They observed thatunsupported CaO and MgO showed negligible activity, whereasCaO/Al2O3 system yields the most promising activity, due to higherbasic sites concentration and basic strengths. Dacus et al. [72]tested pure metal and metal oxide catalysts in order to develop aheterogeneous method using algae as feedstock. It was concludedthat like other vegetable oils, algae can be successfully convertedto biodiesel using these heterogeneous materials at low trans-esterification temperature. Similarly, no unwanted products thatrequire purification were produced. The catalysts also producedbiodiesel at low temperatures for a number of edible vegetable oilscontaining common impurities like free fatty acids. This impliesthe materials to have strong potentials for algae oils. McNeff et al.[73] incorporated a new fixed-bed continuous reactor system,employing porous titania, zirconia and alumina (with their mixedoxides) as heterogeneous alcoholysis catalysts under high pressure(2500 psi) and temperatures of 300e450 �C, with a number of


feedstocks (algae, corn, tall and soybean oils). The catalysts provedvery efficient, especially with the algae oil (Table 4). Percentagebiodiesel yields of 90.2, 88.3 and 88.1% were obtained from algae,corn and soybean oils, respectively under constant conditions.Similarly, the economics of the process indicated much more costeffectiveness than with conventional homogeneous options.Limited interference due to fatty acids was encountered. Thethermal stability of the catalysts is also very interesting for reus-ability purpose. Some authors [78], have recently developed a twosteps in situ process, with potentials to reduce the fatty acidsinterference encountered with some heterogeneous base catalystsand increase biodiesel yield. The method involved a pre-esterification of the algae oil before the base-catalyzed trans-esterification. It can allow biodiesel recovery up to 98%, greaterthan values obtainable by a single-step catalytic in situ process.Dong et al. [78] shows that, the heterogeneous material,Amberlyst-15, was employed without activity decay for eightrepeated times. Catalyst loading causes increased in ester yield upto 30 wt.%, beyond which its concentration has no any effect on thetransesterification activity. On the contrary, increasing methanolto algae oil ratio shows the negative effect on biodiesel yield, withoptimal value obtained at a yield of 20%. The technology canpotentially play a good role as more environmentally sustainablecost-reduced method due to the optimal biodiesel yield andcatalyst reusability. Recently, Sani et al. [79] have also reported arange of heterogeneous solid acids such as NiOeMoO3/Al2O3, Pt-SAPO-11, NiOeMoO3/H-ZSM-5 and microporous titania to besuccessfully employed for microalgae oil. The conversions weregenerally between 83 and 99% (see Table 4), catalysts were verystable, no corrosion or recycling problems encountered and thematerials showed potentials for reduced industrial productioncosts in comparison to homogeneous systems. Generally, manyauthors [25,46,80e98] have the great opinion that biodiesel pro-duction from algae or comparable non-edible feedstock via het-erogeneous catalysis would be the best method for the future.However, research should be intensified to identify what thetechnical and economical feasibility by integrating economic as-pects with science, technology and policy issues.

Another interesting issue is that, algae oil can similarly beemployed for production of gasoline and or diesel range hydro-carbons [99e102], animal feeds and fine chemicals [25] and evenHVO (Hydrogenated Vegetable Oil). Solid acid catalysts are the keyheterogeneous materials exploited in this respect. The generalconversion processes include cracking, hydrotreating and hydro-deoxygenation [99,103,104]. Among the solid catalysts Al2O3, AlCl3and oxides of Ca and Mg, SAPO-5, SAPO-11 [99], HZSM5, HBEA andUSY [99,104] have been evaluated as goodmaterials for the crackingreactions. Heterogeneous systems such as NieMo/g-Al2O3, sul-phides of NiMo and CoMo and their silica-alumina supports aregood candidates for hydrotreating of bio-oils even at low temper-atures, with limited stability challenges. They have shown goodthermal stability with resistances to catalyst poisons in the reactionfeed. Alumina, zeolites and silica supported Ni and/or noble metalcatalysts are primary deoxygenation materials and could be used toconvert fatty acids in the algae oil to liquid hydrocarbons of mostlydiesel range.

Recently, Hu et al. [105] pyrolyzed oil obtained from oil-richedblue-green algae (microcystis species) at temperatures rangingbetween 300 and 700 �C in a fixed bed reactor. The liquid bio-oilproduced was found to be rich in gasoline and diesel range hy-drocarbons, especially at the optimal temperature of 500 �C. Ben-zene, phenols, methylphenols and heterocyclic amines like pyrrole,indole, pyridine and substituted pyrazines were similarly detectedto significant concentrations. Similar observations were reportedby other authors using different species [63,106e112].


http://www.sciencedirect.com/science/article/pii/S0196890410002761

Table 5A summary of key industrial derivatives from glycerol [110e125].

Product Uses Production process

1,3-Propanediol Formulation of solvents, co-polyesters, powder,UV-cured coatings etc.

Clostridium butyricum method.

1,2-Propanediol Industrial commodity/raw-material. Raney Nickel method, Pt on NaeY zeolite.Dihydroxyacetone In cosmetic industry as a tanning agent. Catalytic oxidation of aqueous glycerol using Pt

catalysts.Succinic Acid Manufacture of synthetic resins, biodegradable

polymers etc.Fermentation process.

Hydrogen Next generation renewable fuel, hydrogenationreactions etc.

Heterogeneously catalytic steam reforming atmoderate temperatures, aqueous reformingover tin promoted Raney nickel catalysts.

Polyglycerols Anti-fogging, lubricants, antistatic additives,plasticizers etc.

Selective etherification of glycerol.

Polyesters Polymer applications. The reaction of glycerol with adipic acid usingSn based catalysts, catalytic reaction of citricacid with glycerol at different mole ratios.

Liquid hydrocarbons e.g. diesel, light naptha Fuels applications. Low temperature catalytic synthesis followedby FischereTropsch synthesis.

Polyhydroxyalkanoates Polymer applications. Fermentation process.Syngas, methane Fuel for energy. Catalytic supercritical water gasification

(CSCWG) method.Oleifins Polymer feedstock, fuel additives. Catalytic conversion using zeolites like ZSM-5,

zeolite Beta, and zeolite Y.Others e.g. allyl alcohol, methanol, and formaldehyde Industrial raw-materials, solvents, etc. Catalytic supercritical water gasification

(CSCWG) method.

Fig. 3. Conversion of glycerol to gaseous and intermediate liquid products via com-bined gasification and pyrolysis process.


5. Glycerol conversion

Glycerol (propan-1,2,3-triol) is a simple trihydric-alcohol withother names as alcohol glyc�erin�e, glicerol, glucerite, glycerin,glycerine, glyc�erine, vegetable glycerin etc. It both occurs naturallyand can be synthesized industrially or in the laboratories. Thecompound forms the triester backbone of triglycerides (see Scheme1) and phospholipids. Glycerol is colorless, odorless compoundwidely employed as raw-material in some key industries. The threehydroxyl groups account for considerable water solubility.

Glycerol is the key waste product produced (up to 1 kg per 10 kgof algae oil) from biodiesel production, that has in the past beenconsidered a great challenge to industries [14e16,68e70,113].However, there are progresses that the compound could be purifiedand successfully converted to a number of useful industrial raw-materials (Table 5). Initially, homogeneous catalysis was mainlyemployed, but series of problems similar to those of biodieselsynthesis have accounted for a shift to the heterogeneous method.

Hirai et al. [114] has carried out gaseous phase steam reformingof glycerol with a range of transitionmetals usingMgO, Y2O3, Al2O3,ZrO2, SiO2, CeO2 and LaO3 as support materials, prepared byemploying the conventional impregnation method and reactionsmonitored under atmospheric conditions. Best and promisingresult was obtained with 3 wt.% Ru supported on Y2O3 at 500 �C,due to significant resistance to deactivation by carbon deposition.Tapah et al. [115] employed mixed Fe2O3 and Cr2O3 as catalyst andglycerol concentrations of 2e30 wt.% at flow rates from [10e65 ml/min] for a CSCWG (catalytic supercritical water gasification) con-version of glycerol. The results showed high temperature and lowglycerol concentrations to increased the yield and selectivity to-ward H2 production. Similarly, syngas of about 64 mol % was pro-duced with minimum 4:1 mol ratio of H2:CO. Other volatilehydrocarbons (methane and ethylene) were obtained to significantyields. This promotes the optional use of the technology for turbineoperations. Nearly 100% conversion of glycerol was successful athigh temperature of 550 �C. Also a maximum of 11 wt.% of meth-anol, allyl alcohol and formaldehyde were obtained at 400 �Ctemperature. Catalyst stability was also studied and was found toreach relative stability for up to 9 h of reactions. The choice of


reaction conditions influences the key reaction products from thegasification process. For example, Markocic et al. [116], Long andFang [117] and Peterson et al. [118] reported high pressures, lowtemperatures, upgraded feeds and acid catalyst systems to producemainly liquid products. Whereas opposite conditions producedmainly hydrogen, syngas and other gaseous hydrocarbons. Guoet al. [119] showed that, depending on reaction conditions, anumber of liquid products (including methanol and formaldehyde)could be generated as intermediates during the CSCWG process(see Fig. 3).

Zeolite systems like HeY, H-ZSM-5, H-Beta etc could similarly beemployed to convert glycerol into olefins (usually ethene, propeneand n-butene) under controlled conditions, the choice of whichdepends on the zeolite and/or desired reaction products. Liquidhydrocarbons of diesel and naphtha range could similarly be ob-tained. Zakaria et al. [120] reported an integrated route to diesel and


Fig. 4. Integrated routes for the conversion of glycerol, a byproduct in biodiesel plant, to fuels.


light naphtha production coupling low temperature catalytic con-version of glycerol with WGS (wateregas shift) technology andFischereTropsch synthesis (Fig. 4). They have also reported anumber of authors have successfully converted glycerol into olefinsusing USY, ZSM-5, H-MOR, macroporous NieW system, Y-zeolite,BETA and silica and alumina supports at temperatures between 300and 650 �C, yielding nearly 100% glycerol conversion and up to 60%olefins production. Zakaria et al. [121] showed the activity of Ca, Cu,Li, Mg and Ni doped ZSM-5 zeolites characterized by FTIR, XRD andNH3 desorption, to depends on the catalyst structureeacidityproperties during oleifins and paraffins production from glycerol.Metal loadings improved HZSM-5 acidity and glycerol conversion.Recently, Van de Vyver et al. [122], Possato et al. [123], Serafin et al.[124], Gonzalez et al. [125] andKimet al. [126] showed the activityofzeolites in glycerol conversion to diols and olefins, to be dependenton the structural, acidity and active metal properties. Zeolites withlow porosity produced light gaseous products, acidity enhancesconversion and metals loading promotes acidity and texturalproperties thereby enhancing glycerol conversion. Table 6 presentsa further detail of various literature reports on the conversion of

Table 6A literature report of glycerol conversions into various products over zeolites and some

Method/process Catalyst syst

Glycerol to olefins (high olefins selectivity) CuZSM-5Glycerol to ethane and propane (high selectivity) H-ZSM-5 (29Glycerol to fuel H-ZSM-5 (29Glycerol to propane Macropore NGlycerol to olefins USYGlycerol to paraffins, light olefins, CO, CO2 and hydrogen

(variable selectivities)Cu/ZSM-5, C

Glycerol dehydration to acrolein and acetol (high selectivityto acrolein)

MFI-15, MFI

Glycerol conversion to 1,2-propanediol (higher selectivityto 1,2-propanediol than ethanol or propanol)

Pt/NaY

Glycerol etherification with t-butanol (Higher selectivity toglycerol monoethers, i.e. 64e100%)

Amberlyst-1

Glycerol conversion to hydrogen by steam reforming(nearly 90% selectivity to hydrogen)

Ru/Y2O3, Ru

Glycerol reforming in supercritical water ZnSO4, WO3


glycerol to different products over a range of zeolites and other solidacid catalysts. The selectivity to the desired reaction product(s) hasshowndependenceon the catalyst compositions and the conversionmethod adopted. An important issue is that glycerol has clear po-tentials as industrial raw-material for the generation of many reli-able products and/or feedstock. However, full realization of itsnumerous benefits requires improved studies [127e132], involvingeconomic, policy, science and engineering issues. Integratingappropriate environmental designs (giving emphasis to catalyst andreactor design and experimental conditions) with life cycle assess-ment and economic implications would be a great deal in this re-gard. Another important area of vital importance that should befurther explored is the conversion of glycerol to glycerol carbonateand relevant alcohols like 1,3-ditert-butoxypropan-2-ol, that is acompound with excellent properties as combustion improver fordiesel fuel [133e141]. Al-Lal et al. [133] showed the reaction ofglycerol with hydrochloric acid to produced epichlorohydrin, whichcan subsequently be converted to 1,3-ditert-butoxypropan-2-ol viareactionwith tert-butanol. Catalytic conversion and selectivitywere100 and 48.9%, respectively. At constant conditions, the activity is

other solid acids.

em Conversion (%)

100 [120]) 35.70e80.20 [120]) 91e95 [120]ieW 100 [120]

100 [120]r/ZSM-5, Ni/ZSM-5, Li/ZSM-5 100 [120]

-40 and Al2O3 95, 78 and 78, respectively [123]

18.1e18.4 [122]

5, mordenite, Beta and ZSM-5 81, 10, 83 and 58, respectively [125]

/Al2O3 and Ru/ZrO2 100, 80 and 100, respectively [114]

/TiO2 and Ru/TiO2 80, 100 and 100, respectively [116]



catalyst dependent. For example HClO4 and BF3/Et2O both yieldconversion of 100%, but with selectivities of 25.8 and 52.6%,respectively whereas KOH produced only 56.5 and 6.7% for con-version and selectivity, respectively. It is particularly important thatthe net CO2 emission for the feedstock combustionwas found to bevery negligible. Ellis [142] on the other hand, indicated eSO3modification to influence the acidic and catalytic properties of a lowtemperature etherification carbon catalyst. Sulfonation createsacidity up to 4 mmol/g and only mono- and d-glyceryl ethers wereproduced to very high selectivities. However, catalyst decomposi-tion was noticed at temperatures exceeding 236 �C. Pico et al. [143]showed benzyl alcohol etherification of glycerol to produceddibenzyl ether as themost selective reactionproduct at temperatureclose to 100 �C. Mechanistically, the reaction obeys EleyeRidealscheme. Among the heterogeneous materials gaining attention forthe etherification process, group IIA oxides (e.g. CaO and modifiedcatalysts), zeolites like basic mesoporous MCM-41, acidic BETA, ionexchange resins like Amberlysts and metal modified heteropolyacids are widely considered [130,144e150]. Some recent studies[151e160] have also shown catalysts such as tungstated zirconia, Cu/Al2O3, La modified Ni/Al2O3, Ni/CeZrO, oxides of W and V, Ru on Ir-ReOx/SiO2, Na, K, Li and Cs modified alumina and K-zeolites as goodsystems for catalytic conversion of glycerol to polyols, poly-urethanes, glycerol carbonates, oxygenated fuel additives and co-rich hydrogen gas. However, a major issue is that the most favor-able reaction conditions for achieving higher yields and the mech-anisms of action of most materials are still being soughted. Furtherstudies should therefore be carried out with the aim of identifyingthe most appropriate catalysts preparation methods, favorabletemperature, pressure and space velocity. Reaction mechanismsmust be fully followed to understand the actual chemistry involved.These are required for extending the laboratory findings to indus-trial applications. Large quantities of glycerol are produced frombiodiesel production daily [161,162]. Therefore, understanding theoverall reaction design for glycerol conversion would be veryeconomical for the industry.

6. Conclusions

The numerous studies indicated the continuous exploitation ofedible oils, either from plants or animals, as biodiesel feedstock tobe seriously associated with hunger threats and food prices.However, algae species that can produce high grade biodiesel arewidely abundant and can also be cultivated with limited environ-mental challenges. The methods of cultivation, oil extraction andtransesterification are basically comparable to those of regular-edible crops. Algae can be cultivated even in salty environments.They are known for CO2 consumption during their growth period,therefore dually suitable for environmental management. Theseand many other stated factors would certainly eclipse their pros-pects as sustainable feedstocks. Transesterification using hetero-geneous catalysts from oxides, zeolites and their derivatives willcontinue to attract industrial attention. Solid acid and solid basecatalysts are potentially cheaper and can be recovered, recycled andreused after the transesterification process. They show very lesssensitivity to free fatty acids in the feed, if appropriately designed,and therefore produce high purity biodiesel, with propertiesmeeting international standards. However, the actual reactionmechanisms and ways of optimizing the triglyceride esters con-version with many of these catalysts must be fully investigated.Taking into account the nature of the support or the active phase,well dispersed catalyst particles and moderate temperature arepotential approaches to enhance the adsorption-desorption of thereactants and to improve product yield. Zeolite catalysts should betailored such that the frameworks possess desirable porosity and


acidity/basicity properties.Where dopedwithmetals or oxides caremust be taken to avoid pore blockage that can result to competitivetransesterification versus cracking process. Heteropoly acids arealso promising, especially due to free fatty acid tolerance, howeverextensive studies are required to fully establish their mode of ac-tions for improved performance. Exploitation of algae for biodieseland other industrial raw-material production is certainly a multi-functional option. However, a number of issues must beaddressed to ensure full benefits. The most cost effective algaecultivation and oil extraction methods must be identified. Afford-able algae species with high oil contents and fast-growth rates inspecific environments should be fully examined.

On the other hand, the high purity glycerol from the heteroge-neous transesterification of algae oil has strong potentials to reduceindustrial dependence on non-renewable petrochemicals as raw-materials. However, the research must be intensified to identifythe most appropriate heterogeneous catalysts, their mode of action(s) and optimal reaction conditions. Oxides and zeolites haveindicated strong potentials in the formulation of many liquid andgaseous products such as formaldehyde, diols, allyl alcohols, olei-fins, methane and hydrogen fuel, as well as other liquid hydrocar-bons like diesel and light naphtha. Other important products areglycerol carbonate and derived alcohols like 1,3-ditert-butox-ypropan-2-ol, that are compounds with excellent properties ascombustion improver for diesel fuel. Attention can therefore bedirected toward their improved performance.

Acknowledgments

The authors would like to acknowledge the support provided byKing Abdul-Aziz City for Science and Technology (KACST) throughthe Science& Technology Unit at King Fahd University of Petroleum& Minerals (KFUPM) for funding this work through project 10-NAN1392-04 as part of the National Science, Technology andInnovation Plan.

References

[1] Pachauri R, Reisinger A. IPCC fourth assessment report. Geneva: IPCC; 2007.[2] Alamu O, Waheed M, Jekayinfa S. Manuscript EE 07 00 9. Alkali-catalysed

laboratory production and testing of biodiesel fuel from Nigerian palmkernel oil, vol. IX; July, 2007.

[3] Galadima A, Garba Z. Catalytic synthesis of ethyl ester from some commonoils. Sci World J 2009;4(4):1e5.

[4] Vicente G, Martınez M, Aracil J. Integrated biodiesel production: a compar-ison of different homogeneous catalysts systems. Bioresour Technol2004;92(3):297e305.

[5] Schuchardt U, Sercheli R, Vargas RM. Transesterification of vegetable oils: areview. J Braz Chem Soc 1998;9(3):199e210.

[6] Estevez E, Janowski T. Electronic governance for sustainable development econceptual framework and state of research. Gov Inf Q 2013;30(Suppl. 1):S94e109.

[7] Galadima A, Garba ZN, Ibrahim BM, Almustapha MN, Leke L, Adam IK. Bio-fuels production in Nigeria: the policy and public opinions. J Sustain Dev2011;4(4). p. 22.

[8] Freedman B, Butterfield RO, Pryde EH. Transesterification kinetics of soybeanoil 1. J Am Oil Chem Soc 1986;63(10):1375e80.

[9] Narasimharao K, Lee A, Wilson K. Catalysts in production of biodiesel: areview. J Biobased Mater Bioenergy 2007;1(1):19e30.

[10] Lotero E, Liu Y, Lopez DE, Suwannakarn K, Bruce DA, Goodwin JG. Synthesisof biodiesel via acid catalysis. Ind Eng Chem Res 2005;44(14):5353e63.

[11] Liu X, He H, Wang Y, Zhu S. Transesterification of soybean oil to biodieselusing SrO as a solid base catalyst. Catal Commun 2007;8(7):1107e11.

[12] Liu X, He H, Wang Y, Zhu S, Piao X. Transesterification of soybean oil tobiodiesel using CaO as a solid base catalyst. Fuel 2008;87(2):216e21.

[13] Ma H, Li S, Wang B, Wang R, Tian S. Transesterification of rapeseed oil forsynthesizing biodiesel by K/KOH/g-Al2O3 as heterogeneous base catalyst. JAm Oil Chem Soc 2008;85(3):263e70.

[14] Anderson JA, Beaton A, Galadima A, Wells RPK. Role of Baria dispersion inBaO/Al2O3 catalysts for transesterification. Catal Lett 2009;131(1e2):213e8.

[15] Chouhan A, Sarma A. Modern heterogeneous catalysts for biodiesel pro-duction: a comprehensive review. Renew Sustain Energy Rev 2011;15(9):4378e99.


http://refhub.elsevier.com/S0360-5442(14)00716-6/sref1






















































[16] Ramachandran K, Suganya T, Nagendra Gandhi N, Renganathan S. Recentdevelopments for biodiesel production by ultrasonic assist trans-esterification using different heterogeneous catalyst: a review. Renew Sus-tain Energy Rev 2013;22:410e8.

[17] Promotion, C.f.J., algae biodiesel: commercialization, research & businessplatform; 2014. URL: http://www.jatrophaworld.org/global_algae_biodiesel_world_2012_93.html [accessed April, 2014].

[18] Martín Mariano. I.E.G; 2014. URL: http://egon.cheme.cmu.edu/Papers/MartinGrossmannBiodiesel%20production%20algae.pdf [accessed June,2014].

[19] Azadi P, Brownbridge G, Mosbach S, Smallbone A, Bhave A, Inderwildi O. Thecarbon footprint and non-renewable energy demand of algae-derived bio-diesel. Appl Energy 2014;113:1632e44.

[20] Pfromm PH, Amanor-Boadu V, Nelson R. Sustainability of algae derivedbiodiesel: a mass balance approach. Bioresour Technol 2011;102(2):1185e93.

[21] Singh J, Gu S. Commercialization potential of microalgae for biofuels pro-duction. Renew Sustain Energy Rev 2010;14(9):2596e610.

[22] Gallagher BJ. The economics of producing biodiesel from algae. Renew En-ergy 2011;36(1):158e62.

[23] Chisti Y. Biodiesel from microalgae. Biotechnol Adv 2007;25(3):294e306.[24] Schenk PM, Thomas-Hall SR, Stephens E, Marx UC, Mussgnug JH, Posten C.

Second generation biofuels: high-efficiency microalgae for biodiesel pro-duction. Bioenergy Res 2008;1(1):20e43.

[25] Mata TM, Martins AA, Caetano NS. Microalgae for biodiesel production andother applications: a review. Renew Sustain Energy Rev 2010;14(1):217e32.

[26] Packer M. Algal capture of carbon dioxide; biomass generation as a tool forgreenhouse gas mitigation with reference to New Zealand energy strategyand policy. Energy Policy 2009;37(9):3428e37.

[27] Zhao B, Su Y. Process effect of microalgal-carbon dioxide fixation andbiomass production: a review. Renew Sustain Energy Rev 2014;31:121e32.

[28] Powell E, Hill G. Carbon dioxide neutral, integrated biofuel facility. Energy2010;35(12):4582e6.

[29] Patil V, Tran K-Q, Giselrød HR. Towards sustainable production of biofuelsfrom microalgae. Int J Mol Sci 2008;9(7):1188e95.

[30] Borges M, Díaz L. Recent developments on heterogeneous catalysts for bio-diesel production by oil esterification and transesterification reactions: areview. Renew Sustain Energy Rev 2012;16(5):2839e49.

[31] LamMK, Lee KT, Mohamed AR. Homogeneous, heterogeneous and enzymaticcatalysis for transesterification of high free fatty acid oil (waste cooking oil)to biodiesel: a review. Biotechnol Adv 2010;28(4):500e18.

[32] Roschat W, et al. Biodiesel production based on heterogeneous processcatalyzed by solid waste coral fragment. Fuel 2012;98:194e202.

[33] Agarwal M, Chauhan G, Chaurasia SP, Singh K. Study of catalytic behavior ofKOH as homogeneous and heterogeneous catalyst for biodiesel production. JTaiwan Inst Chem Eng 2012;43(1):89e94.

[34] Kiss FE, Jovanovi�c M, Bo�skovi&cacute GC. Economic and ecological aspects ofbiodiesel production over homogeneous and heterogeneous catalysts. FuelProcess Technol 2010;91(10):1316e20.

[35] Mutreja V, Singh S, Ali A. Biodiesel from mutton fat using KOH impregnatedMgO as heterogeneous catalysts. Renew Energy 2011;36(8):2253e8.

[36] Dias JM, Alvim-Ferraz M, Almeida MF, M�endez Díaz JD, Polo MS, Utrilla JR.Selection of heterogeneous catalysts for biodiesel production from animalfat. Fuel 2012;94:418e25.

[37] Choudhury HA, Chakma S, Moholkar VS. Mechanistic insight into sono-chemical biodiesel synthesis using heterogeneous base catalyst. UltrasonSonochem 2014;21.

[38] Endalew AK, Kiros Y, Zanzi R. Inorganic heterogeneous catalysts for bio-diesel production from vegetable oils. Biomass Bioenergy 2011;35(9):3787e809.

[39] Kazemian H, Turowec B, Siddiquee MN, Rohani S. Biodiesel production usingcesium modified mesoporous ordered silica as heterogeneous base catalyst.Fuel 2013;103:719e24.

[40] Boey P-L, Maniam GP, Hamid SA. Performance of calcium oxide as a het-erogeneous catalyst in biodiesel production: a review. Chem Eng J2011;168(1):15e22.

[41] Birla A, et al. Kinetics studies of synthesis of biodiesel from waste frying oilusing a heterogeneous catalyst derived from snail shell. Bioresour Technol2012;106:95e100.

[42] Farooq M, Ramli A, Subbarao D. Biodiesel production from wastecooking oil using bifunctional heterogeneous solid catalysts. J Clean Prod2013;59:131e40.

[43] Sakai T, Kawashima A, Koshikawa T. Economic assessment of batch biodieselproduction processes using homogeneous and heterogeneous alkali cata-lysts. Bioresour Technol 2009;100(13):3268e76.

[44] Macario A, Moliner M, Diaz U, Jorda JL, Corma A, Giordano G. Biodieselproduction by immobilized lipase on zeolites and related materials. Stud SurfSci Catal 2008;174:1011e6.

[45] Babajide O, Musyoka N, Petrik L, Ameer F. Novel zeolite Na-X synthesizedfrom fly ash as a heterogeneous catalyst in biodiesel production. Catal Today2012;190(1):54e60.

[46] Carrero A, Vicente G, Rodríguez R, Linares M, Del Peso GL. Hierarchical ze-olites as catalysts for biodiesel production from Nannochloropsis microalgaoil. Catal Today 2011;167(1):148e53.


[47] Borges LD, Moura NN, Costa AA, Braga PR, Dias JA, Dias SC. Investigationof biodiesel production by HUSY and Ce/HUSY zeolites: Influenceof structural and acidity parameters. Appl Catal A: General 2013;450:114e9.

[48] Zou C, Zhao P, Shi L, Huang S, Luo P. Biodiesel fuel production from wastecooking oil by the inclusion complex of heteropoly acid with bridged bis-cyclodextrin. Bioresour Technol 2013 Oct;146:785e8.

[49] Jothiramalingam R, Wang MK. Review of recent developments in solid acid,base, and enzyme catalysts (heterogeneous) for biodiesel production viatransesterification. Ind Eng Chem Res 2009;48(13):6162e72.

[50] Katada N, Hatanaka T, Ota M, Yamada K, Okumura K, Niwa M. Biodieselproduction using heteropoly acid-derived solid acid catalystH4PNbW11O40/WO3/Nb2O5. Appl Catal A General 2009;363(1):164e8.

[51] Talebian-Kiakalaieh A, Amin NAS, Zarei A, Noshadi I. Transesterification ofwaste cooking oil by heteropoly acid (HPA) catalyst: optimization and kineticmodel. Appl Energy 2013;102:283e92.

[52] Alsalme A, Kozhevnikova EF, Kozhevnikov IV. Heteropoly acids as catalystsfor liquid-phase esterification and transesterification. Appl Catal A General2008;349(1):170e6.

[53] Tsigdinos GA. Heteropoly compounds of molybdenum and tungsten, intopics in current chemistry. Springer; 1978. pp. 1e64.

[54] Oilgae, algae oil extraction; 2014. http://www.oilgae.com/algae/oil/extract/extract.html [accessed June, 2014].

[55] Demirbas A, Fatih Demirbas M. Importance of algae oil as a source of bio-diesel. Energy Convers Manag 2011;52(1):163e70.

[56] Vazhappilly R, Chen F. Heterotrophic production potential of omega-3polyunsaturated fatty acids by microalgae and algae-like microorganisms.Bot Mar 1998;41(1e6):553e8.

[57] Volkman JK, Jeffrey SW, Nichols PD, Rogers GI, Garland CD. Fatty acid andlipid composition of 10 species of microalgae used in mariculture. J Exp MarBiol Ecol 1989;128(3):219e40.

[58] Yaguchi T, Tanaka S, Yokochi T, Nakahara T, Higashihara T. Production ofhigh yields of docosahexaenoic acid by Schizochytrium sp. strain SR21. J AmOil Chem Soc 1997;74(11):1431e4.

[59] Wen Z-Y, Chen F. Heterotrophic production of eicosapentaenoic acid bymicroalgae. Biotechnol Adv 2003;21(4):273e94.

[60] Grobbelaar J. Physiological and technological considerations for optimisingmass algal cultures. J Appl Phycol 2000;12(3e5):201e6.

[61] Xu H, Miao X, Wu Q. High quality biodiesel production from a microalgaChlorella protothecoides by heterotrophic growth in fermenters. J Biotechnol2006;126(4):499e507.

[62] Campbell MN. Biodiesel: algae as a renewable source for liquid fuel. GuelphEng J 2008;1:2e7.

[63] Miao X, Wu Q, Yang C. Fast pyrolysis of microalgae to produce renewablefuels. J Anal Appl Pyrol 2004;71(2):855e63.

[64] Wen B, Zhang JP, Wen G. Continuous flow fixed-bed biodiesel productionfrom algae oil; 2009.

[65] Hu Q, Sommerfeld M, Jarvis E, Ghirardi M, Posewitz M, Seibert M, Darzins A.Microalgal triacylglycerols as feedstocks for biofuel production: perspectivesand advances. Plant J 2008;54(4):621e39.

[66] Plata V, Kafarov V, Moreno N. Optimization of third generation biofuelsproduction: biodiesel from microalgae oil by homogeneous trans-esterification. Chem Eng Trans 2010;21:1201e6.

[67] Plata V, Kafarov V, Moreno N. Optimization of third generation biofuelsproduction: biodiesel from microalgae oil by homogeneous trans-esterification; 2010.

[68] Martín M, Grossmann IE. Optimal engineered algae composition for the in-tegrated simultaneous production of bioethanol and biodiesel. AIChE J2013;59(8):2872e83.

[69] Santacesaria E, Vicente GM, Di Serio M, Tesser R. Main technologies in bio-diesel production: state of the art and future challenges. Catal Today2012;195(1):2e13.

[70] Martín M, Grossmann IE. Simultaneous optimization and heat integration forbiodiesel production from cooking oil and algae. Ind Eng Chem Res2012;51(23):7998e8014.

[71] Umdu ES, Tuncer M, Seker E. Transesterification of Nannochloropsis oculatamicroalga's lipid to biodiesel on Al2O3 supported CaO and MgO catalysts.Bioresour Technol 2009;100(11):2828e31.

[72] Dacus Iii RW, Mebane RC, Jones FJ. A kinetic study of the production ofbiodiesel from algae; 2009.

[73] McNeff CV, McNeff LC, Yan B, Nowlan DT, Rasmussen M, Gyberg AE. Acontinuous catalytic system for biodiesel production. Appl Catal A General2008;343(1e2):39e48.

[74] Severson K, Martín M, Grossmann IE. Simultaneous optimization and heatintegration for the production of algae based biodiesel using bioethanol;2012.

[75] Helwani Z, Othman MR, Aziz N, Kim J, Fernando WJN. Solid heterogeneouscatalysts for transesterification of triglycerides with methanol: a review.Appl Catal A General 2009;363(1e2):1e10.

[76] Krohn BJ, McNeff CV, Yan B, Nowlan D. Production of algae-based biodieselusing the continuous catalytic Mcgyan® process. Bioresour Technol2011;102(1):94e100.

[77] Vasudevan PT, Briggs M. Biodiesel productiondcurrent state of the art andchallenges. J Ind Microbiol Biotechnol 2008;35(5):421e30.










































































































































































































































[78] Dong T, Wang J, Miao C, Zheng Y, Chen S. Two-step in situ biodiesel pro-duction from microalgae with high free fatty acid content. Bioresour Technol2013;136:8e15.

[79] Sani YM, Daud WMAW, Aziz A. Solid acid-catalyzed biodieselproduction from microalgal oilethe dual advantage. J Environ Chem Eng2013;1(3):113e41.

[80] Rathore V, Madras G. Synthesis of biodiesel from edible and non-edible oilsin supercritical alcohols and enzymatic synthesis in supercritical carbon di-oxide. Fuel 2007;86(17):2650e9.

[81] Sharma YC, Singh B, Korstad J. Latest developments on application ofheterogenous basic catalysts for an efficient and eco friendly synthesis ofbiodiesel: a review. Fuel 2011;90(4):1309e24.

[82] Giannakopoulou K, et al. Conversion of rapeseed cake into bio-fuel in a batchreactor: effect of catalytic vapor upgrading. Microporous Mesoporous Mater2010;128(1):126e35.

[83] Boey PL, Ganesan S, Maniam GP, Khairuddean M, Efendi J. A new hetero-geneous acid catalyst for esterification: optimization using response surfacemethodology. Energy Convers Manag 2013;65:392e6.

[84] Macario A, Giordano G. Catalytic conversion of renewable sources for bio-diesel production: a comparison between biocatalysts and inorganic cata-lysts. Catal Lett 2013;143(2):159e68.

[85] Perego C, Millini R. Porous materials in catalysis: challenges for mesoporousmaterials. Chem Soc Rev 2013;42:3956e76.

[86] Serrano D, Pizarro P. Synthesis strategies in the search for hierarchical zeo-lites. Chem Soc Rev 2013;42:4004e35.

[87] Verma D, Kumar R, Rana BS, Sinha AK. Aviation fuel production from lipidsby a single-step route using hierarchical mesoporous zeolites. Energy Envi-ron Sci 2011;4(5):1667e71.

[88] Cejka J, Van Bekkum H, Corma A, Schueth F. Introduction to zeolite molecularsieves, vol. 168. Elsevier; 2007.

[89] Hara M. Biomass conversion by a solid acid catalyst. Energy Environ Sci2010;3(5):601e7.

[90] Rinaldi R, Schüth F. Design of solid catalysts for the conversion of biomass.Energy Environ Sci 2009;2(6):610e26.

[91] Huber GW, Iborra S, Corma A. Synthesis of transportation fuels frombiomass: chemistry, catalysts, and engineering. Chem Rev 2006;106(9):4044e98.

[92] Iliopoulou EF, Antonakou EV, Karakoulia SA, Vasalos IA, Lappas AA,Triantafyllidis KS. Catalytic conversion of biomass pyrolysis products bymesoporous materials: effect of steam stability and acidity of Al-MCM-41catalysts. Chem Eng J 2007;134(1):51e7.

[93] Demirbas A. Progress and recent trends in biodiesel fuels. Energy ConversManag 2009;50(1):14e34.

[94] Demirbas A. Progress and recent trends in biofuels. Prog Energy Combust Sci2007;33(1):1e18.

[95] Demirbas M, Balat M. Recent advances on the production and utilizationtrends of bio-fuels: a global perspective. Energy Convers Manag2006;47(15):2371e81.

[96] Yusuf N, Kamarudin S, Yaakub Z. Overview on the current trends in biodieselproduction. Energy Convers Manag 2011;52(7):2741e51.

[97] Lim S, Teong LK. Recent trends, opportunities and challenges of biodiesel inMalaysia: an overview. Renew Sustain Energy Rev 2010;14(3):938e54.

[98] Kiss AA, Dimian AC, Rothenberg G. Solid acid catalysts for biodiesel Pro-ductioneTowards sustainable Energy. Adv Synth Catal 2006;348(1e2):75e81.

[99] Lercher JA, Zhao C, Brueck T. Catalytic deoxygenation of microalgae oil togreen hydrocarbons. Green Chem 2013;15:1720e39.

[100] Tran NH, Bartlett JR, Kannangara GSK, Milev AS, Volk H, Wilson MA. Catalyticupgrading of biorefinery oil from micro-algae. Fuel 2010;89(2):265e74.

[101] Thangalazhy-Gopakumar S, Adhikari S, Chattanathan SA, Gupta RB. Catalyticpyrolysis of green algae for hydrocarbon production using H-ZSM-5 catalyst.Bioresour Technol 2012;118:150e7.

[102] Harman-Ware AE, Morgan T, Wilson M, Crocker M, Zhang J, Liu K. Microalgaeas a renewable fuel source: fast pyrolysis of Scenedesmus sp. Renew Energy2013;60(0):625e32.

[103] Duan P, Savage PE. Hydrothermal liquefaction of a microalga with hetero-geneous catalysts. Ind Eng Chem Res 2010;50(1):52e61.

[104] Milne TA, Evans RJ, Nagle N. Catalytic conversion of microalgae and vege-table oils to premium gasoline, with shape-selective zeolites. Biomass1990;21(3):219e32.

[105] Hu Z, Zheng Y, Yan F, Xiao B, Liu S. Bio-oil production through pyrolysis ofblue-green algae blooms (BGAB): product distribution and bio-oil charac-terization. Energy 2013;52:119e25.

[106] Choi HS, Choi YS, Park HC. Fast pyrolysis characteristics of lignocellulosicbiomass with varying reaction conditions. Renew Energy 2012;42:131e5.

[107] Yaman S. Pyrolysis of biomass to produce fuels and chemical feedstocks.Energy Convers Manag 2004;45(5):651e71.

[108] Czernik S, Bridgwater A. Overview of applications of biomass fast pyrolysisoil. Energy Fuels 2004;18(2):590e8.

[109] Carlson TR, Vispute TP, Huber GW. Green gasoline by catalytic fast pyrolysisof solid biomass derived compounds. ChemSusChem 2008;1(5):397e400.

[110] Melligan F, Auccaise R, Novotny EH, Leahy JJ, Hayes MHB, Kwapinski W.Pressurised pyrolysis of Miscanthus using a fixed bed reactor. BioresourTechnol 2011;102(3):3466e70.


[111] Bae YJ, Ryu C, Jeon JK, Park J, Suh DJ, Suh YW. The characteristics of bio-oilproduced from the pyrolysis of three marine macroalgae. Bioresour Technol2011;102(3):3512e20.

[112] Park HJ, Park KH, Jeon JK, Kim J, Ryoo R, Jeong KE. Production of phenolicsand aromatics by pyrolysis of miscanthus. Fuel 2012;97:379e84.

[113] Pachauri N, He B. Value-added utilization of crude glycerol from biodieselproduction: a survey of current research activities. In: Proceedings of theASABE Annual International Meeting; 2006.

[114] Hirai T, Ikenaga NO, Miyake T, Suzuki T. Production of hydrogen by steamreforming of glycerin on ruthenium catalyst. Energy Fuels 2005;19(4):1761e2.

[115] Tapah BF, Santos RCD, Leeke GA. Processing of glycerol under sub and su-percritical water conditions. Renew Energy 2014;62:353e61.

[116] Marko�ci�c E, Kramberger B, van Bennekom JG, Jan Heeres H, Vos J, Knez �Z.Glycerol reforming in supercritical water: a short review. Renew SustainEnergy Rev 2013;23:40e8.

[117] Long YD, Fang Z. Hydrothermal conversion of glycerol to chemicals andhydrogen: review and perspective. Biofuels Bioprod Bioref 2012;6(6):686e702.

[118] Peterson AA, Vogel F, Lachance RP, Fr€oling M, Antal Jr MJ, Tester JW. Ther-mochemical biofuel production in hydrothermal media: a review of sub- andsupercritical water technologies. Energy Environ Sci 2008;1(1):32e65.

[119] Guo S, Guo L, Yin J, Jin H. Supercritical water gasification of glycerol: In-termediates and kinetics. J Supercrit Fluids 2013;78:95e102.

[120] Zakaria ZY, Amin NAS, Linnekoski J. A perspective on catalytic conversion ofglycerol to olefins. Biomass Bioenergy 2013;55:370e85.

[121] Zakaria ZY, Linnekoski J, Amin NAS. Catalyst screening for conversion ofglycerol to light olefins. Chem Eng J 2012;207e208:803e13.

[122] Van de Vyver S, D'Hondt E, Sels BF, Jacobs PA. Preparation of Pt on NaYzeolite catalysts for conversion of glycerol into 1, 2-propanediol. Stud SurfSci Catal 2010;175:771e4.

[123] Possato LG, Diniz RN, Garetto T, Pulcinelli SH, Santilli CV, Martins L. Acomparative study of glycerol dehydration catalyzed by micro/mesoporousMFI zeolites. J Catal 2013;300:102e12.

[124] Serafim H, Fonseca IM, Ramos AM, Vital J, Castanheiro JE. Valorization ofglycerol into fuel additives over zeolites as catalysts. Chem Eng J 2011;178:291e6.

[125] Gonz�alez MD, Cesteros Y, Salagre P. Establishing the role of Brønsted acidityand porosity for the catalytic etherification of glycerol with tert-butanol bymodifying zeolites. Appl Catal A General 2013;450:178e88.

[126] Kim YT, Jung KD, Park ED. A comparative study for gas-phase dehydration ofglycerol over H-zeolites. Appl Catal A General 2011;393(1e2):275e87.

[127] Rahmat N, Abdullah AZ, Mohamed AR. Recent progress on innovative andpotential technologies for glycerol transformation into fuel additives: acritical review. Renew Sustain Energy Rev 2010;14(3):987e1000.

[128] Luque R, Luque R, Budarin V, Clark JH, Macquarrie DJ. Glycerol trans-formations on polysaccharide derived mesoporous materials. Appl Catal BEnviron 2008;82(3):157e62.

[129] Guerrero-P�erez MO, Rosas JM, Bedia J, Rodríguez-Mirasol J, Cordero T. Recentinventions in glycerol transformations and processing. Recent Pat Chem Eng2009;2(1):11e21.

[130] Gu Y, Azzouzi A, Pouilloux Y, J�erome F, Barrault J. Heterogeneously catalyzedetherification of glycerol: new pathways for transformation of glycerol tomore valuable chemicals. Green Chem 2008;10(2):164e7.

[131] Amaral PFF, Ferreira TF, Fontes GC, Coelho MAZ. Glycerol valorization: newbiotechnological routes. Food Bioprod Process 2009;87(3):179e86.

[132] Ruiz VR, Velty A, Santos LL, Leyva-P�erez A, Sabater MJ, Iborra S. Gold catalystsand solid catalysts for biomass transformations: Valorization of glycerol andglycerolewater mixtures through formation of cyclic acetals. J Catal2010;271(2):351e7.

[133] Al-Lal A-M, García-Gonz�alez J-E, Llamas A, Monjas A, Canoira L. A new routeto synthesize tert-butyl ethers of bioglycerol. Fuel 2012;93:632e7.

[134] Yu Z, Xu L, Wei Y, Wang Y, He Y, Xia Q. A new route for the synthesis ofpropylene oxide from bio-glycerol derivated propylene glycol. Chem Com-mun 2009;26:3934e6.

[135] Kiatkittipong W, Intaracharoen P, Laosiripojana N, Chaisuk C, Praserthdam P,Assabumrungrat S. Glycerol ethers synthesis from glycerol etherificationwith tert-butyl alcohol in reactive distillation. Comput Chem Eng2011;35(10):2034e43.

[136] Izquierdo J, Montiel M, Pales I, Outon P, Galan M, Jutglar L. Fuel additivesfrom glycerol etherification with light olefins: state of the art. Renew SustainEnergy Rev 2012;16(9):6717e24.

[137] Yadav GD, Chandan PA, Gopalaswami N. Green etherification of bioglycerolwith 1-phenyl ethanol over supported heteropolyacid. Clean Technol Envi-ron Policy 2012;14(1):85e95.

[138] Viswanadham N, Saxena SK. Etherification of glycerol for improved pro-duction of oxygenates. Fuel 2013;103:980e6.

[139] Vlad E, Bildea CS, Bozga G. Design and control of glycerol-tert-butyl alcoholetherification process. Sci World J 2012:2012.

[140] Frusteri F, Cannilla C, Bonura G, Spadaro L, Mezzapica A, Beatrice C. Glycerolethers production and engine performance with diesel/ethers blend. TopCatal 2013;56(1e8):378e83.

[141] Liu J, Yang B, Yi C. Kinetic study of glycerol etherification with isobutene. IndEng Chem Res 2013;52(10):3742e51.


























































































































































































































































[142] Ellis N. Glycerol etherification by tert-butanol catalyzed by sulfonated carboncatalyst. J Appl Sci 2010;10(21):2633e7.

[143] Pico MP, Rodríguez S, Santos A, Romero A. Etherification of glycerol withbenzyl alcohol. Ind Eng Chem Res 2013;52(41):14545e55.

[144] Clacens J-M, Pouilloux Y, Barrault J. Selective etherification of glycerol topolyglycerols over impregnated basic MCM-41 type mesoporous catalysts.Appl Catal A General 2002;227(1):181e90.

[145] Ruppert AM, Meeldijk JD, Kuipers BW, Erne BH, Weckhuysen BM. Glyceroletherification over highly active CaOebased materials: new mechanisticaspects and related colloidal particle formation. Chem-A Eur J 2008;14(7):2016e24.

[146] Klep�a�cov�a K, Mravec D, Kaszonyi A, Bajus M. Etherification of glycerol andethylene glycol by isobutylene. Appl Catal A General 2007;328(1):1e13.

[147] Pariente S, Tanchoux N, Fajula F. Etherification of glycerol with ethanol oversolid acid catalysts. Green Chem 2009;11(8):1256e61.

[148] Clacens J-M, Pouilloux Y, Barrault J, Linares C, Goldwasser M. Mesoporousbasic catalysts: comparison with alkaline exchange zeolites (basicity andporosity). Application to the selective etherification of glycerol to poly-glycerols. Stud Surf Sci Catal 1998;118:895e902.

[149] Clacens J, Pouilloux Y, Barrault J. Synthesis and modification of basic meso-porous materials for the selective etherification of glycerol. Stud Surf SciCatal 2000;143:687e95.

[150] Tamura M, Amada Y, Liu S, Yuan Z, Nakagawa Y, Tomishige K. Etherificationof glycerol. Petroleum Coal 2003;45:1e2.

[151] Tamura M, Amada Y, Liu S, Yuan Z, Nakagawa Y, Tomishige K. Promotingeffect of Ru on Ir-ReOx/SiO2 catalyst in hydrogenolysis of glycerol. J MolCatal Chem 2014;388e389(0):177e87.

[152] Shen L, Yin H, Wang A, Lu X, Zhang C. Gas phase oxidehydration of glycerolto acrylic acid over Mo/V and W/V oxide catalysts. Chem Eng J 2014;244(0):168e77.


[153] Sanchez EA, Comelli RA. Hydrogen production by glycerol steam-reformingover nickel and nickel-cobalt impregnated on alumina. Int J Hydrogen En-ergy 2014;39(16):8650e5.

[154] S�anchez G, Friggieri J, Keast C, Drewery M, Dlugogorski BZ, Kennedy E. Theeffect of catalyst modification on the conversion of glycerol to allyl alcohol.Appl Catal B Environ 2014;152e153(0):117e28.

[155] Sun D, Yamada Y, Sato S. Effect of Ag loading on Cu/Al2O3 catalyst in theproduction of 1,2-propanediol from glycerol. Appl Catal A General2014;475(0):63e8.

[156] Srinivasa Rao G, Sowmya M, Pethan RN, Balla Putra K, Chary Komandur VR.Vapour phase dehydration of glycerol to acrolein over tungstated zirconiacatalysts. Appl Surf Sci 2014;309(0):153e9.

[157] Algoufi YT, Hameed BH. Synthesis of glycerol carbonate by trans-esterification of glycerol with dimethyl carbonate over K-zeolite derivedfrom coal fly ash. Fuel Process Technol 2014;126(0):5e11.

[158] Shao S, Shi A-W, Liu C-L, Yang R-Z, Dong W-S. Hydrogen production fromsteam reforming of glycerol over Ni/CeZrO catalysts. Fuel Process Technol2014;125(0):1e7.

[159] Siew KW, Lee HC, Gimbun J, Cheng CK. Production of CO-rich hydrogen gasfrom glycerol dry reforming over La-promoted Ni/Al2O3 catalyst. Int JHydrogen Energy 2014;39(13):6927e36.

[160] Hu S, Li Y. Polyols and polyurethane foams from base-catalyzed liquefactionof lignocellulosic biomass by crude glycerol: Effects of crude glycerol im-purities. Ind Crops Prod 2014;57(0):188e94.

[161] Demirbas A. Biodiesel production from vegetable oils via catalytic and non-catalytic supercritical methanol transesterification methods. Prog EnergyCombust Sci 2005;31(5e6):466e87.

[162] Meher LC, Vidya Sagar D, Naik SN. Technical aspects of biodiesel productionby transesterificationda review. Renew Sustain Energy Rev 2006;10(3):248e68.



























































































Date post:	03-Feb-2017
Category:	Documents
Upload:	oki
View:	216 times
Download:	2 times

Biodiesel production from algae by using heterogeneous catalysts: A critical review

Documents