Vb

CAa

b

a

ARRAA

KBFHAIV

1

c(piacf

fbtetotIg

a

0h

Journal of Biotechnology 164 (2013) 433– 440

Contents lists available at SciVerse ScienceDirect

Journal of Biotechnology

jou rn al hom epage: www.elsev ier .com/ locate / jb io tec

anadium phosphate catalysts for biodiesel production from acid industrialy-products

arina Dominguesa, M. Joana Neiva Correiaa, Renato Carvalhob, Carlos Henriquesa, João Bordadoa,na Paula Soares Diasa,∗

CPQ & IBB & ICEMS, Instituto Superior Técnico, Technical University of Lisbon, Av. Rovisco Pais, s/n, 1049-001 Lisboa, PortugalIberol – Sociedade Ibérica de Biocombustíveis e Oleaginosas, S.A., Technological Development Department, Quinta da Hortinha – Alhandra, 2601-908 Vila Franca de Xira, Portugal

r t i c l e i n f o

rticle history:eceived 13 March 2012eceived in revised form 18 June 2012ccepted 24 July 2012vailable online 9 August 2012

eywords:

a b s t r a c t

Biodiesel production from high acidity industrial by-products was studied using heterogeneous acid cat-alysts. These by-products contain 26–39% of free fatty acids, 45–66% of fatty acids methyl esters and0.6–1.1% of water and are consequently inadequate for direct basic catalyzed transesterification. Macro-porous vanadyl phosphate catalysts with V/P = 1 (atomic ratio) prepared via sol–gel like technique wasused as catalyst and it was possible to produce in one reaction batch a biodiesel contain 87% and 94% ofFAME, depending on the by-product used as raw material. The initial FAME content in the by-products

iodieselAMEeterogeneous catalystscid oils

ndustrial by-productsanadium phosphate

had a beneficial effect on the reactions because they act as a co-solvent, thus improving the miscibilityof the reaction mixture components. The water formed during esterification process seems to hinderthe esters formation, possibly due to competitive adsorption with methanol and to the promotion ofthe FAME hydrolysis reaction.The observed catalyst deactivation seems to be related to the reductionof vanadium species. However, spent catalysts can be regenerated, even partially, by reoxidation of thereduced vanadium species with air.

. Introduction

Energy is a crucial component of modern life. Sources of energyan be classified into three groups: fossil, renewable and nuclearDemirbas, 2009). Nowadays, fossil fuels account over 80.3% of therimary energy consumed in the world and 57.7% of that amount

s used in transportation sector (Lam et al., 2010). Road, sea andir transportation are the major consumer of fossil energy thusonstituting one of the economic sectors with the highest carbonootprint (Piecyk and McKinnon, 2010).

Biofuels are pointed out as feasible substitutes of fossil fuelsor the transportation sector (Demirbas, 2007). As produced fromiomass, they are expected to provide a renewable and sus-ainable source of energy with lower GHG emissions (Lapuertat al., 2008; Jørgensen et al., 2012). Among these, first genera-ion biodiesel, a mixture of long chain fatty acids methyl (FAME)r ethyl esters (FAEE), present combustion characteristics similar

o those of petroleum diesel thus being an alternative to fossil fuel.t can be used as pure or mixed with petroleum diesel. Europeanovernments aim the incorporation of 10% of biofuels, for the global

∗ Corresponding author. Tel.: +351 218417873; fax: +351 218499242.E-mail addresses: renatocarvalho@iberol.com.pt (R. Carvalho),

psoares@ist.utl.pt (A.P.S. Dias).

168-1656/$ – see front matter © 2012 Elsevier B.V. All rights reserved.ttp://dx.doi.org/10.1016/j.jbiotec.2012.07.009

© 2012 Elsevier B.V. All rights reserved.

target of 20% of renewable energy by 2020 (Directive 2009/28/EC,2009).

Today’s commercial production of biodiesel is based on homo-geneous catalysts. The cost of biodiesel production is high, i.e.,1.5–3 times more expensive than conventional diesel (Endalewet al., 2011). According to Di Serio et al. (2008), the replacementof the homogeneous catalysts by heterogeneous catalysts couldreduce the production costs, thus making biodiesel competitivewith petroleum diesel from an economic point of view. Acid, basicand enzyme solid catalysts are referred to alternative as active forbiodiesel production (Zabeti et al., 2009).

Vegetable oils used for first generation biodiesel are expensive.Thus it is important to be able to use low costs feedstocks to pro-duce biodiesel, such as high acidity oils that do not allow the useof the conventional basic catalysts (Marchetti and Errazu, 2008). Ina recent review, Lam et al. (2010) pointed out the advantages anddisadvantages of different catalytic systems (homogeneous, het-erogeneous and enzymatic) to convert low grade oils into biodieselIn this case, heterogeneous acid catalysts have the unique advan-tage related to the fact that they can simultaneously promoteesterification and transesterification reactions, allowing the use of

high acidity oils as feedstock for biodiesel production thus con-tributing to economic viability of biodiesel (Sharma et al., 2011).

Different types of heterogeneous acid catalysts have beentested in the biodiesel production. In the literature, the catalytic

4 f Biote

plvS(faoCceiit

t1fn1es2to

btfTavyf

cpa

2

2

vaa2

ouVpasrsArdwpd2

34 C. Domingues et al. / Journal o

erformances for resins, tungstated and sulfated zirconia, polyani-ine sulfate, heteropolyacids, metal complexes, sulfated tin oxide,anadium phosphate and zeolites, among others, are described (Dierio et al., 2007, 2008; Melero et al., 2009). Kiss and Rothenberg2006) reported that acid catalyst must have a hydrophobic sur-ace, with multi Brönsted acid sites, in order to avoid both waterdsorption and the adsorption of the hydrophobic carbon chainf the fatty acids that occur when isolated sites are available.hen et al. (2007) studied the methanolysis reaction over acidatalysts (sulfated materials) and concluded that Brönsted sitesxhibit an important role on catalytic performances. Recent find-ngs (Shi et al., 2012) showed that Brönsted sites are activen esterification, whereas Lewis acid sites are more active inransesterification.

Vanadium phosphorus oxides (VPOs) are known as catalysts forhe mild oxidation of hydrocarbons and alcohols (Ennaciri et al.,999) and they are industrially used to produce maleic anhydriderom n-butane (O’Mahony et al., 2004). They possesses simulta-eously Brönsted (P OH) and Lewis acid sites (V O) (Busca et al.,989), so they can promote simultaneously esterification and trans-sterification reactions. The strength and the nature, of the acidites strongly depend on the preparation procedure (Kamiya et al.,003). The existence of strong Brönsted acid sites was proven byhe large amounts of dimethyl ether obtained during methanolxidation (Ennaciri et al., 1999).

Excellent performances of vanadium phosphorus catalysts foriodiesel production were reported by Di Serio et al. (2007), despiteheir low specific surface. Lately, Behera and Parida (2012) success-ully used analogous catalysts for the esterification of oleic acid.hey also studied the esterification of acetic acid with the VPO cat-lysts (Parida and Behera, 2010). Published results indicate thatanadium phosphorus oxides will be able to catalyze the methanol-sis of acid raw oils, which contain simultaneously triglycerides andatty acids.

The present research work reports the catalytic behavior of VPOatalysts for biodiesel production from high acidity industrial by-roducts. Additionally, data for rapeseed oil and oleic acid werelso presented, for comparison purposes.

. Experimental

.1. Preparation of the catalysts

Several methods are available in the literature to prepareanadyl phosphate catalysts. The most common procedures usu-lly involve long contact times, under reflux, between powder V2O5nd an aqueous solution of o-phosphoric acid (Parida and Behera,010).

A novel method involving a sol–gel like procedure, basedn the Pechini method (Pechini, 1967; Dias et al., 2010) wassed. Batches of 20 g of vanadium phosphorus catalysts with/P = 1 (atomic ratios) were prepared. All the used chemicals werero analysis grade. Briefly aqueous solutions (100 mL each) ofmmonium vanadate and ammonium phosphate were preparedeparately adding citric acid as complexation agent (molar ratio cit-ic acid/ammonium salt = 1). The hot solution of phosphate salt waslowly added to the vanadium hot solution under vigorous stirring.fter this step the liquid mixture, intense blue, was slowly evapo-ated at ≈80 ◦C under stirring and the resulting viscous xerogel wasried overnight at 120 ◦C. The dried material was, low density foam

ith green shade, was crushed in a Pyrex mortar and the obtainedowder was calcined in a muffle during 5 h at 500–700 ◦C. Moreetails on the preparation procedure are given elsewhere (Dias,012).

chnology 164 (2013) 433– 440

2.2. Characterization of the catalysts

The BET surface areas were obtained by N2 physisorption usingASAP 2010 Micromeritics equipment. The particles size distribu-tions, for fresh catalysts, were assessed by laser diffraction (blueradiation, 455 nm) based on Lorenz Mie law. Malvern Mastersizer2000 equipment was used. The morphology of fresh and postreaction samples was examined using a JOEL JSM7001F FEG-SEMmicroscope with an Oxford energy dispersive X-ray high vacuumdetector (E = 20 kV) for elemental microanalysis. X-ray diffractionpatterns were recorded with a Rigaku Geigerflex diffractometerwith Cu K� radiation at 40 kV and 40 mA (2◦/min).

The diffuse reflectance UV–vis spectra, of fresh catalysts, werecollected using a Cary 5000 Varian equipment with a DRA 2500diffuse reflectance accessory (integration sphere). The spectra weredeconvoluted using symmetric Gaussian shape lines.

The reactivation procedure was studied by thermogravimetryusing a TG-DTA-DSC LabSys, from Setaram, equipment. The cata-lyst reactivation temperature was selected from TG mass loss/gainprofile.

2.3. Raw materials

The rapeseed oil, the industrial by-products and the methanolwere supplied by Iberol S.A., a Portuguese biodiesel producer. Thecommercial oleic acid (p.a. grade) was used as raw material, forcomparison purposes. The two acidic raw materials used in thiswork, identified as P1 and P2, are produced in the plant of Iberol bymixing the glycerol phases obtained after the two reaction batcheswith the washing waters of the biodiesel purification step. Thismixture contains methanol, glycerol, catalyst, soaps, water and theentrained oil and biodiesel and the by-products were producedafter methanol and glycerol recovery, by acidulation of the soapsto free fatty acids (soap splitting). Thus, after water removal, theproducts used in the experiments have a high content of free fattyacids and methyl esters as shown in Table 2. Additionally, the initialcontent of glycerides (GL) in these two products may be estimatedby a mass balance giving a content of 7.8% for P1 and 15.1% for P2.

2.4. Catalytic tests

The methanolysis reactions were carried out at temperatureshigher than the refluxing temperature of the methanol using a highpressure stainless steel reactor equipped with mechanical stirrer(600 rpm). The standard procedure for each catalytic test involvesthe mixture of 100 g of oil with 5% (w/w) of powder catalyst andwith methanol (0.55 g/1 g oil that, for the soybean or rapeseed oilscorresponds to a molar ratio of methanol:oil of 15/1). After 6 h, at125 ◦C, the reactor was cooled down and the catalyst was removedby vacuum filtration and the liquid mixture was transferred into adecantation funnel. After phase separation, the methyl ester layerwas washed with water, centrifuged and dried at 80–90 ◦C undervacuum (0.05 bar) with a rotary evaporator (RE-111, Büchi). Addi-tionally, several experiments were carried out with the industrialby-product P2 to test other reaction conditions such as the use ofa different temperature (60 ◦C and 150 ◦C), smaller catalyst con-centration (2.5% and 1.25%), reaction time (3 h) and weight ratio ofmethanol to by-product (0.30 g/g). In order to evaluate the deac-tivation of catalysts several reaction batches were performed withthe same catalyst sample, with and without intermediate activationstep consisting in recalcination in a muffle (as described above).

The FAME content of the purified crude biodiesel samples wasevaluated using near infrared spectroscopy (NIR), against previ-ously developed calibration (Baptista et al., 2008). The spectra, ofthe liquid samples, were acquired using an ABB BOMEM MB160

C. Domingues et al. / Journal of Biotechnology 164 (2013) 433– 440 435

-0.3

-0.2

-0.1

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

10.80.60.40.20

Ad

sorb

ed a

mou

nt

(mm

ol/

g)

P/Po

625ºC

Fig. 1. N2 adsorption/desorption isotherms for sample calcined at 625 ◦C.

FM

eS

st

3

3

ioiaMapoathtsdt

Table 1Typical EDS elemental analysis of catalysts.

Element Apparent conc. (%) Intensity correction wt.% at.%

C 13.8 0.5049 11.7 19.9O 62.7 0.5812 45.9 58.9P 51.9 1.4101 15.7 10.4

at 10 after the reactions with pure oleic acid and with the by-

ig. 2. Effect of the calcination temperature on the external (laser diffraction-alvern) and BET surface areas.

quipment with a InGaAs detector and a transflectance probe fromOLVIAS (Basel, Switzerland).

The acidity of all samples was determined by titration with KOHolution, whereas water content was measured by Karl-Fisher titra-ion (Felizardo et al., 2007).

. Results and discussion

.1. Characterization of the catalysts

The powder catalysts showed yellow-green shades depend-ng on the calcination temperature. The N2 adsorption isothermsf powders, before reaction, display type II (Fig. 1) adsorptionsotherms characteristics of macroporous materials (IUPAC, 1994),s expected for the sol–gel like preparation technique (Frenzer andaier, 2006). All the characterized samples displayed BET surface

reas lower than 10 m2/g, which is considerable lower than theublished value for the catalyst obtained by contacting V2O5 with-phosphoric acid (Rownaghi et al., 2009). Likely, the BET surfacerea decreases with the raise of the calcination temperature dueo sinterization. However, the sample calcined at 700 ◦C presentsigher surface area than the sample calcined at 625 ◦C possibly dueo a vanadium pyrophosphate phase formation. Also, data in Fig. 2

how that the BET and the external surface based on the particleiameter become indistinguishable with the rise of the calcinationemperature, thus indicating a drop of the catalyst porosity.

V 52.0 0.8286 26.7 10.8

Total 100.0

The macroporosity of fresh catalysts was also confirmed by SEMimages (Fig. 3). As shown, the sample calcined at 700 ◦C exhibiteda different morphology with visible lamellae whereas for lowercalcination temperatures the morphology corresponds to sinteredmaterials. As mentioned elsewhere (Rownaghi et al., 2009), thelamellae like morphology is typical of VPO materials prepared byreflux method. The post reaction catalysts also showed a lamel-lar morphology ascribable to vanadyl hydrogen phosphate phases(O’Mahony et al., 2003, 2004). The elemental analysis by EDS,performed during SEM micrographs acquisition, showed uniformcomposition for all the fresh and post reaction samples. Typical datain Table 1 confirm the equimolar V/P ratio used in preparation step.EDS analysis also shows that none of the elements (P or V) is selec-tively leached in the reaction medium as post reaction samples alsopresented equimolar V/P composition.

The XRD patterns of fresh samples, in Fig. 4, show, forsamples calcined at temperatures higher than 500 ◦C, patternsbelonging to well crystallized vanadium phosphorus oxide (JCPDS01-071-0859). Also, the diffractogram of the sample calcinedat 500 ◦C shows lower crystallinity and the lines belonging tovanadium phosphorus oxide are overlapped with the lines ascrib-able to hydrated phases: VOPO4·2H2O (main line at 12.03◦) andVOHPO4·4H2O (main line at 11.95◦) (Guliants et al., 1996). Fig. 4 alsoshows that the XRD patterns of the post reaction samples are simi-lar to the pattern of the fresh sample calcined at 500 ◦C and presentlines ascribable to hydrated phases: VOHPO4 (JCPDS 00-048-1158)and V(PO4)(H2O) (JCPDS 01-088-1244). Only the sample calcinedat 700 ◦C preserves, after reaction batch #1, the lines belongingto initial VOPO4 phase showing that higher calcination tempera-ture enhances the catalyst stability. Additionally, the broad line ataround 10◦ observed for all the samples after reaction batch #1 iseventually ascribable to the formation of intercalated species in thelayered structure of hydrated VOPO4 (Melánová et al., 2007).

Farther, the diffractograms of the catalyst used to process theacid industrial by-products (Fig. 5), keep the lines belonging toVOPO4 whereas the same catalyst after processing the rapeseedoil is totally reduced to vanadyl hydrogen phosphate. This resultmay be related to the presence in the reaction mixture of thewater produced in the esterification reaction of FFA (Reaction 1below), which led to a decrease of the catalyst activity. However,the spent catalyst can be regenerated by recalcination (Di Serioet al., 2007). In fact, the XRD data for recalcined sample (625 ◦C)show that this thermal treatment is effective to reverse the crys-tallographic changes suffered during reaction and in this sampleonly small lines of VOPO4·2H2O (main line at 12.03 (Guliants et al.,1996)) are observed. Actually, the effect of the reactivation of thecatalyst by calcination at 625 ◦C for 5 h on its activity is remarkablebecause the FAME yield obtained in the second reaction batch withthe reactivated sample increased from 64% up to 91%.

Fig. 6 presents the XRD patterns of the catalysts used in theexperiments carried out with rapeseed oil, the by-product P2 andoleic acid. As shown, the catalyst does not display the broad line

◦

product P2, thus indicating the absence of intercalated species. Thefact that the main difference between these experiments and thosethat allowed the formation of intercalated species appears to be

436 C. Domingues et al. / Journal of Biotechnology 164 (2013) 433– 440

nd post reaction (rapeseed oil) catalyst.

ttpiatg

ciatttlatttifd

Uoaetcrhco

Table 2Acidity, water and FAME content of oil raw materials.

FFA Water FAME

wt.%

P1 25.7 0.60 65.9P2 39.3 1.10 44.5Rapeseed oil 0.12 0.03 0

Fig. 3. SEM micrographs of fresh a

he content of glycerol in the reaction mixture allows to speculatehat the glycerol formed during reaction is the intercalated com-ound. It is important to note that despite the high FAME content

n the sample obtained after reaction with the by-product P2, themount of glycerol produced due to the transesterification reac-ion was low because this sample contains a low initial content oflycerides (<15% as estimated by mass balance).

The thermogravimetry profile (TG) for post reaction (batch #1)atalyst (Fig. 7), which is similar to the ones of all the character-zed samples, also shows that reoxidation begins (weight gain) atround 400 ◦C. Since no bulk reduced phases were observed by XRD,he later process should be related to the oxidation of species onhe surface of the catalyst. Furthermore, the weight loss suffered byhe samples at lower temperature confirms the presence of interca-ated compounds (Datta et al., 2010). According to Fig. 7, the catalystfter batch #2 begins to reoxidize at a temperature of 50 ◦C higherhan the sample after batch #1, eventually due to its higher reduc-ion degree. The contribution of surface adsorbed organic specieso the TG profile, of post reaction catalysts, was discarded tack-ng into account the infrared spectra of post reaction catalysts. Inact, spectra obtained by reflectance do not exhibited (unpublishedata) bands attributable to such adsorbed species.

The fresh catalysts (yellowish-green) were characterized byV–vis using diffuse reflectance. The spectra in Fig. 8 show anal-gous features for all the samples with a main absorption bandround 300 nm attributable to the O2− V4+ charge transfer (Wangt al., 2010). This result seems to indicate that fresh catalyst con-ains vanadium reduced species in surface. In addition to the bandentered at 300 nm, all the spectra present a broad band in the

ange 400–500 nm. The maximum of this band is displaced towardigh wave lengths raising the calcination temperature. This bandan be deconvoluted into two bands one centered at 500 nm andther centered at 380 nm ascribable to charge transfer of O2− V5+

Note: Glycerides (GL) content assessed by mass balance(GL = 100 − (FFA + H2O + FAME)): P1 – 7.8%; P2 – 15.1%.

(Guliants et al., 1996). Curilla et al. (1988) and Di Serio et al. (2007)established that the band at 500 nm belongs to V3+ species of VPOcatalysts whereas Wang et al. (2010) attributed the same band toV5+ in octahedral environment. Since the citrate route usually pro-duces catalysts with reduced surfaces, the attribution of the bandaround 500 nm to V3+ species seems plausible for the character-ized catalysts. The post reaction samples show an intense band inthe range 200–300 nm and broad and low intensity band around680 nm that can be due to V4+ species (Cavani et al., 2010). Such V4+

species seems to be responsible for the catalysts deactivation. Thereactivated catalyst (recalcined at 625 ◦C) presents a UV–vis spec-trum with the main band around 300 nm, (V4+ species), overlappedwith a band centered at 380 nm (V5+ species), thus indicating thatthe reoxidation was only partial.

3.2. Catalytic tests

The catalytic performances of the prepared VPO materials were

assessed by methanolysis of the different lipid raw materialscharacterized in Table 2. As mentioned above, the methyl esterscontent of the liquid samples was assessed by NIR spectroscopyand the spectra of one of the industrial by-products before and after

C. Domingues et al. / Journal of Biotechnology 164 (2013) 433– 440 437

45403530252015105

Inte

nsit

y (a

.u.)

2θθ(o)

570ºC

625ºC

700ºC

VPO5 JCPS 01 -071-0859

500ºC

fresh

45403530252015105

Inte

nsit

y (a

.u.)

2θ(o)

pos t reac�on : batch#1

VOHPO4 JCPD S 00 -048 -1158VOPO4 JCPD S 01 -071 -0859

V(PO4)(H2 JCPDS 01 -088 -1244O)

Cal. 500ºC

Cal. 570ºC

Cal. 625ºC

Cal. 700ºC FAME - 72%

FAME - 80%

FAME - 85%

FAME - 60%

FW

rr5t

mcaaSitiglc

m

Fig. 5. XRD patterns of fresh (625 ◦C) post reaction and recalcined catalyst (productP2 as raw material; Wcat./Woil = 5%; methanol/oil weight ratio = 0.55 g/g; 125 ◦C; 6 h):(a) fresh catalyst calcined at 625 ◦C; (b) batch #1; (c) batch #2; (d) batch #1 calcinedat 625 ◦C; (e) batch #2 of catalyst (d).

ig. 4. XRD patterns for fresh and post reaction (batch #1) catalysts (rapeseed oil;cat./Woil = 5%; methanol/oil = 15; 125 ◦C; 6 h; without intermediate regeneration).

eaction is presented in Fig. 9. As shown, the spectrum of the post-eaction sample reveals the disappearance of the peak at around200 cm−1, which is characteristic of water (Felizardo et al., 2007)hat was removed during the drying step.

Catalysts calcined at 500 ◦C up to 700 ◦C were tested in theethanolysis of rapeseed oil, using 5% of catalyst (weight ratio of

atalyst/oil). In view of the experimental errors, data in Fig. 10 shown almost null effect of the calcination temperature on the catalystctivity. This result apparently disagrees with the findings of Dierio et al. (2007). They reported an increase of the catalytic activ-ty raising the calcination temperature. These authors stated thathe thermal treatment remove the hydration of water thus increas-ng the Lewis acidity related with coordinatively unsaturated VOroups. In the present work the samples were prepared by sol–gel

ike technique hence, the heat released by the burning of the carbonompounds (citrates) masks the reported calcination effect.

Data for the second reaction batch, performed without the inter-ediate regeneration of the catalyst, confirm the beneficial effect

Fig. 6. XRD patterns for fresh catalyst (calcined at 625 ◦C) and samples after reactionwith P2 oil, rapeseed oil and oleic acid.

on the catalyst stability of using higher calcination temperatures.In fact, the sample calcined at 700 ◦C only loses 27% of the activ-ity between batches #1 and #2, whereas for the sample calcinedat 570 ◦C the conversions drops 40%. In the same figure, a replicaof the catalytic test performed with catalyst calcined at 625 ◦C ispresented showing good reproducibility. Also the second batch forrecalcined catalyst revealed that deactivated samples can be par-

tially regenerated by a simple calcination procedure.

Main results obtained for the catalytic behavior of VPO usingacid oils, as raw material, are depicted in Table 3. The yieldsof the esterification reaction and of the FAME production were

438 C. Domingues et al. / Journal of Biotechnology 164 (2013) 433– 440

Table 3Transesterification and esterification conversions obtained with acid raw materials. (Calcination temperature – 625 ◦C; Wcat./Woil = 5%; CH3OH/Oil weight ratio = 0.55 g/g, 6 h,125 ◦C.)

FFA FAME Conversion (%)

Oil phase, w/w (%) Esterification Transterification

P1 2.8 95.2 89.1 85.9P2 7.2 87.0 81.7 76.6Oleic acid 12.4 79.0 79.0 –

-15

-13

-11

-9

-7

-5

-3

-1

7006005004003002001000

Wei

ght l

oss

(%)

T (ºC)

batch#2calcine d at 625ºC

reoxida�on

Batch#1

F#

cbeis3(cO47ttats6PTtok

tFrTait2ioIa

t

0

2

4

6

8

10

12

14

16

800700600500400300200

Ku

bel

ka-M

un

k

Wavelenght (nm)

500ºC570ºC625ºC700ºC

0

1

2

3

4

5

6

7

8

800700600500400300200

Ku

bel

ka-M

un

k

Wavelenght (nm)

625ºC, freshpost reac�onreac�vate d at 625ºC

Fig. 8. UV–vis DRS spectra of fresh post reaction (batch #1) and reactivated catalysts(calcined at 625 ◦C).

ig. 7. TG profile of post reaction catalyst (calcined at 625 ◦C) after reaction batch1 and after batch #2.

alculated for each test as the ratio between the actual conversiony the maximum possible value to be obtained (which for P2, forxample, are: FFA – 39.3% and FAME – 55.5%). From data in Table 3t can be concluded that in only one reaction batch there was aignificant decrease of the FFA content of the products (≈26% and9% for P1 and P2, respectively). Thus, as founded by other authorsMelánová et al., 2007), there is no doubt that vanadium phosphateatalysts are able to catalyze the esterification reaction of the FFA.n the other hand, the FAME content increased by about 29% and3% for P1 and P2, which led to a global FAME yield of 85.9% and6.6%, respectively. Therefore, since the decrease of the FFA con-ent is lower than the increase of the FAME content, it is possibleo conclude that the transesterification reaction of the glycerideslso occurred. Furthermore, assuming that glycerides content inhe reaction product is also estimated by a mass balance, it is pos-ible to calculate that for P2 about 82% of the initial FFA and about2% of the initial GL reacted in only one reaction stage, whereas for1 these values were slightly higher (89% and 82%, respectively).he difference between the yields of the esterification and transes-erification reactions may be explained by the lower initial contentf GL, when compared to the content of FFA and also by the fasterinetics of the esterification reaction (López et al., 2008).

Also surprisingly, taking into account the fact that esterifica-ion is much faster than transesterification (López et al., 2008), theAME yield obtained using oleic acid (79%) was lower than the valueeached for rapeseed oil in the same experimental conditions (87%).his low activity can be due to the formation of water that candsorb competitively with methanol, thus reducing the availabil-ty of the active sites. Additionally, the presence of water favorshe reverse hydrolysis reaction of the methyl esters (Oliveira et al.,010), thus decreasing the FAME yield. On the other hand, the high

nitial content of FAME in the by-products increases the miscibilityf the reaction mixture thus reducing the mass transfer limitations.

n fact, the pre-existent FAME acts as co-solvent (Qiu et al., 2011)nd favors both transesterification and esterification reactions.

In spite of the good results presented in Table 3, the final con-ent of FFA in the products after batch #1 are higher than the

Fig. 9. NIR spectra used for FAME quantification of P3 acid oil before and afterreaction.

C. Domingues et al. / Journal of Biotechnology 164 (2013) 433– 440 439

Table 4Catalytic tests with by-product P2 (Wcat./Woil = 5%; CH3OH/oil weight ratio = 0.55 g/g; 125 ◦C; 6 h).

Catalyst (calc. 625 ◦C) Oil Reaction batch FFA (wt.%) FAME (%)

Initial Final Initial Final

Fresh P2 #1 39.2 7.2 44.5 87.0Fresh P2 after batch #1

(washed and dried)7.2 2.3 87.0 94.0

Post batch #1 without regeneration P2 #2Post batch #1 regenerated P2 #2

Fu

m(tbaeiwitsFsist

rabmlf

TC

ig. 10. Effect of the catalysts calcination temperature on the catalytic behaviorsing rapeseed oil (Wcat./Woil = 5%; methanol/oil = 15 molar; 125 ◦C; 6 h).

aximum value allowed by the European Standard for biodiesel0.5 mg KOH/g or ≈0.25% FFA), and the FAME contents are lowerhan 96.5% imposed by EN 14214. Therefore, a second reactionatch using the fresh catalyst and the product obtained (washednd dried) in the batch #1 of P2 was carried out in the standardxperimental conditions. As shown in Table 4, with this proceduret was possible to decrease the content of FFA from 7.2% to 2.3%,

hile the content of FAME increased from 87.0% to 94.0%, whichs close to the minimum value imposed by EN 14214. Even withhe use of fresh catalyst, the small increase of the fame yield in thisecond batch may be explained by the small amounts of FFA andAME in the product obtained after batch #1, which contribute to alow rate of the transesterification and esterification reactions dur-ng this second batch. However, as for the first batch and due to theame reasons, the increase of the FAME content is mainly due tohe esterification of the FFA.

The reutilization of the prepared catalysts, with and withoutegeneration, was evaluated using the by-product P2 and the cat-lyst calcined at 625 ◦C. Data in Table 4 show that the catalyst can

e reused without regeneration but with worst catalytic perfor-ances. In fact, between two consecutives batches the catalyst

oosed around 23% of its activity in terms of FAME yield, whereasor rapeseed this reduction was around 40%. However, it was

able 5atalytic behavior for by-product P2 (catalyst calcination temperature – 625 ◦C).

Wcat/Woil (%) CH3OH/oil (w/w) T (◦C) Reaction time (

5 0.55 125 6

2.5 0.55 125 6

1.25 0.55 125 6

5 0.30 125 6

5 0.55 60 6

5 0.55 150 6

5 0.55 125 3

39.2 25.7 44.5 64.039.2 4.9 44.5 91.0

possible to reactivate the catalyst by calcination, whereas for rape-seed oil the regeneration was only partial (Fig. 10). This difference inthe catalysts behavior may be related to the fact that after process-ing the acid oils the catalyst maintained the XRD lines belongingto the VOPO4 phase, whereas after processing rapeseed oil onlythe vanadyl hydrogen phosphate lines seems to be present in thediffractogram (Fig. 4).

To evaluate the influence of the main variables on the final prop-erties of biodiesel produced from P2, several experiments werecarried out, which are presented in Table 5. The presented dataallow to conclude that decreasing the ratio Wcat./Woil increases theFFA content and decrease the FAME content of biodiesel. However,the decrease of the catalyst concentration from 5% to 1.25% affectsmore the GL reaction than the FFA esterification.

In what concerns the concentration of methanol, the decreaseof the weight ratio of methanol:P2 from 0.55 g/g to 0.30 g/g wasinvestigated. It is worth noting that because this by-product alreadycontains 44.5% of FAME, the latter value correspond to an excess ofmethanol of about 400% versus the amount of methanol necessaryto carry out the esterification of the FFA and the transesterificationof the GL. This value is similar to the one used when the transes-terification reaction of soybean or rapeseed oil is carried out witha molar ratio of methanol:oil of 15.

Thus, Table 5 shows that the reduction of the methanol excessto values similar to the ones used for virgin oils has a negative effecton the results. In fact, the concentration of the FFA increased by 2.3times, whereas the FAME content decreased from 87% to 73%. Thisresult is a clear indication that due to the high initial FAME contentin P2 it is necessary to use a larger excess of methanol in order toshift the esterification and transesterification reactions to the rightto produce more FAMEs.

Data from catalytic behavior (Table 5) showed that the reactiontemperature is a crucial issue for biodiesel production. Actually, at60 ◦C the rate of transesterification and esterification were almostnull. Raising the temperature from 125 ◦C to 150 ◦C the yield ofboth reactions increase 10%. At 150 ◦C the FAME yield using onereaction batch (6 h) was equivalent to the FAME yield obtainedat 125 ◦C using two consecutive reaction batches (12 h). Data inTable 5 also show that at 125 ◦C the transesterification reaction is

more sensitive to the reaction time than the esterification reac-tion. This result agrees with the three steps reaction mechanismof transesterification instead one step mechanism of esterificationreaction.

h) FFA FAME Esterif. Transesterif.

w/w (%) in oil phase Conversion(%)

7.2 87.0 81.7 76.610.2 82.5 74.1 68.510.4 75.6 73.5 56.016.6 73.1 57.8 51.539.3 48.4 0.0 7.0

3.3 93.5 91.6 88.311.8 84.6 70.0 72.3

4 f Biote

4

ptettac

bo4pa

dc

R

B

B

B

C

C

C

D

D

D

D

D

DD

D

E

E

40 C. Domingues et al. / Journal o

. Conclusions

Vanadium phosphorus oxides (V/P = 1 atomic ratio) were pre-ared by sol–gel like route and showed to be active for theransesterification of vegetable oils allowing to obtain methylsters yields higher than 80%, even using mild temperature reac-ion conditions (125 ◦C). The same catalysts were successfully usedo esterify oleic acid but the water formed during reaction neg-tively affected the catalytic performances, probably due to theompetitive adsorption with methanol.

This VPO catalyst also allowed to produce, in only one reactionatch of 6 h at 125 ◦C, a mixture containing 87% of FAME and 7.2%f FFA using as raw material an industrial by-product containing4.5% of FAME and 39.2% of FFA. However, at 150 ◦C the biodieselroduced has a FFA and FAME contents of 3.3% and 93.5%, whichre close to the values imposed by EN 14214.

During the esterification/transesterification reactions the vana-ium species suffered reduction that led to the deactivation of theatalysts. However, these catalysts were reactivated by calcination.

eferences

aptista, P., Felizardo, P., Menezes, J., Correia, M.J.N., 2008. Multivariate near infraredspectroscopy models for predicting the methyl esters content in biodiesel. Ana-lytica Chimica Acta 607, 153–159.

ehera, G.C., Parida, K.M., 2012. Fascinating and challenging role of tungstate pro-moted vanadium phosphate towards solvent free esterification of oleic acid.Dalton Transactions 41, 1325–1331.

usca, G., Ramis, G., Lorenzelli, V., 1989. FT-IR study of the surface prop-erties of polycrystalline vanadia. Journal of Molecular Catalysis 50,231–240.

avani, F., De Santi, D., Luciani, S., Löfberg, A., Bordes-Richard, E., Cortelli, C., Leanza,R., 2010. Transient reactivity of vanadyl pyrophosphate, the catalyst for n-butaneoxidation to maleic anhydride, in response to in situ treatments. Applied Catal-ysis A: General 376, 66–75.

hen, H., Peng, B., Wang, D., Wang, J., 2007. Biodiesel production by the transesterifi-cation of cottonseed oil by solid acid catalysts. Frontiers of Chemical Engineeringin China 1, 11–15.

ˇurilla, J., Domansky, R., Wichterlová, B., 1988. Spectroscopic study of the vanadium-phosphate catalyst used in the selective oxidation of n-butane to maleicanhydride. Applied Catalysis 36, 119–125.

atta, A., Sakthivel, S., Kaur, M., Venezia, A.M., Pantaleo, G., Longo, A., 2010. Noveltransformations amongst mesostructured VPO phases synthesized throughsurfactant assisted organization from an exfoliated solution of VOPO4·2H2O.Microporous and Mesoporous Materials 128, 213–222.

emirbas, A., 2007. Importance of biodiesel as transportation fuel. Energy Policy 35,4661–4670.

emirbas, A., 2009. Biofuels: Securing the Planet’s Future Energy Needs. Springer-Verlag, London Limited, http://dx.doi.org/10.1007/978-1-84882-011-1.

i Serio, M., Cozzolino, M., Tesser, R., Patrono, P., Pinzari, F., Bonelli, B., Santacesaria,E., 2007. Vanadyl phosphate catalysts in biodiesel production. Applied CatalysisA: General 320, 1–7.

i Serio, M., Tesser, R., Pengmei, L., Santacesaria, E., 2008. Heterogeneous catalystsfor biodiesel production. Energy and Fuels 22, 207–217.

ias, A.P.S., Unpublished results, 2012.ias, A.P.S., Dimitrov, L.D., Oliveira, M.C.-R., Zavoianu, R., Fernandes, A., Portela, M.F.,

2010. Oxidative dehydrogenation of butane over substoichiometric magnesiumvanadate catalysts prepared by citrate route. Journal of Non-Crystalline Solids356, 1488–1497.

irective 2009/28/EC of the European Parliament and of the Council of 23 April 2009.http://eurlex.europa.eu/LexUriServ/LexUriServ.do?uri=OJ:L:2009:140:0016:0062:EN:PDF.

ndalew, A.K., Kiros, Y., Zanzi, R., 2011. Inorganic heterogeneous catalysts forbiodiesel production from vegetable oils. Biomass and Bioenergy 35, 3787–3809.

nnaciri, S.A., Malka, K., Louis, C., Barboux, P., R’Kha, C., Livage, J., 1999. Sol–gel syn-thesis and catalytic properties of vanadium phosphates. Catalysis Letters 62,79–85.

chnology 164 (2013) 433– 440

Felizardo, P., Baptista, P., Uva, M.S., Menezes, José C., Correia, M.J.N., 2007. Monitoringbiodiesel fuel quality by near infrared spectroscopy. Journal of Near InfraredSpectroscopy 15, 97–105.

Frenzer, G., Maier, W.F., 2006. Amorphous porous mixed oxides: sol–gel ways toa highly versatile class of materials and catalysts. Annual Review of MaterialsResearch 36, 281–331.

Guliants, V.V., Benziger, J.B., Sundaresan, S., Wachs, I.E., Jehng, J.-M., Roberts, J.E.,1996. The effect of the phase composition of model VPO catalysts for partialoxidation of n-butane. Catalysis Today 28, 275–295.

IUPAC, 1994. Recommendations for the characterization of porous solids. Pure andApplied Chemistry 66, 1739–1758.

Jørgensen, A., Bikker, P., Herrmann, I.T., 2012. Assessing the greenhouse gasemissions from poultry fat biodiesel. Journal of Cleaner Production 24,85–91.

Kamiya, Y., Nishiyama, H., Yashiro, M., Satsuma, A., Hattori, T., 2003. The roleof Brønsted and Lewis acid sites of vanadyl pyrophosphate measured bydimethylpyridine-temperature programmed desorption in the selective oxida-tion of butane. Journal of the Japan petroleum Institute 46, 62–68.

Kiss, A.D., Rothenberg, G., 2006. Solid acid catalysts for biodiesel produc-tion – towards sustainable energy. Advanced Synthesis and Catalysis 348,75–81.

Lam, M.K., Lee, K.T., Mohamed, A.R., 2010. Homogeneous, heterogeneous and enzy-matic catalysis for transesterification of high free fatty acid oil (by-productcooking oil) to biodiesel: a review. Biotechnology Advances 28, 500–518.

Lapuerta, M., Armas, O., Rodríguez-Fernández, J., 2008. Effect of biodiesel fuelson diesel engine emissions. Progress in Energy and Combustion Science 34,198–223.

López, D.E., Goodwin Jr., J.G., Bruce, D.A., Furuta, S., 2008. Esterification and transes-terification using modified-zirconia catalysts. Applied Catalysis A: General 339,76–83.

Marchetti, J.M., Errazu, A.F., 2008. Comparison of different heterogeneous cata-lysts and different alcohols for the esterification reaction of oleic acid. Fuel 87,3477–3480.

Melánová, K., Benes, L., Svoboda, J., Zima, V., 2007. Intercalation of esters into vanadylphosphate. Journal of Physics and Chemistry of Solids 68, 765–769.

Melero, J.A., Iglesias, J., Morales, G., 2009. Heterogeneous acid catalysts forbiodiesel production: current status and future challenges. Green Chemistry 11,1285–1308.

Oliveira, J.F.G., Lucena, I.L., Alves Saboya, R.M., Rodrigues, M.L., Torres, A.E.B., Fernan-des, F.A.N., Cavalcante Jr., C.L., Parente Jr., E.J.S., 2010. Biodiesel production fromwaste coconut oil by esterification with ethanol: the effect of water removal byadsorption. Renewable Energy 35, 2581–2584.

O’Mahony, L., Henrya, J., Suttona, D., Curtina, T., Hodnetta, B.K., 2003. Time-resolvedin situ X-ray diffraction in the crystallization of VOHPO4·0.5H2O. Catalysis Let-ters 90, 171–175.

O’Mahony, L., Curtin, T., Zemlyanov, D., Mihov, M., Hodnett, B.K., 2004. Surfacespecies during the crystallization of VOHPO4·0.5H2O. Journal of Catalysis 227,270–281.

Parida, K.M., Behera, G.C., 2010. A facile synthesis of vanadium phosphate: an effi-cient catalyst for solvent free esterification of acetic acid. Catalysis Letters 190,197–204.

Pechini, M., 1967, July. Method of preparing lead and alkaline earth titanates andniobates and coating method using the same to form a capacitor. U.S. Pat. No. 3330 697.

Piecyk, M.I., McKinnon, A.C., 2010. Forecasting the carbon footprint of road freighttransport in 2020. International Journal of Production Economics 128, 31–42.

Qiu, F., Li, Y., Yang, D., Li, X., Sun, P., 2011. Biodiesel production from mixed soybeanoil and rapeseed oil. Applied Energy 88, 2050–2055.

Rownaghi, A.A., Taufiq-Yap, Y.H., Rezaei, F., 2009. High surface area vanadium phos-phate catalysts for n-butane oxidation. Industrial and Engineering ChemistryResearch 48, 7517–7528.

Sharma, Y.C., Singh, B., Korstad, J., 2011. Advancements in solid acid catalysts forecofriendly and economically viable synthesis of biodiesel Biofuels. Biofuels,Bioproducts and Biorefining 5, 69–92.

Shi, W., Zhao, J., Yuan, X., Wang, S., Wang, X., Huo, M., 2012. Effects of Brønstedand Lewis acidities on catalytic activity of heteropolyacids in transesterifi-cation and esterification reactions. Chemical Engineering and Technology 35,347–352.

Wang, F., Dubois, J.-L., Ueda, W., 2010. Catalytic performance of vanadium pyrophos-phate oxides (VPO) in the oxidative dehydration of glycerol. Applied CatalysisA: General 376, 25–32.

Zabeti, M., Daud, W.M.A.W., Aroua, M.K., 2009. Activity of solid catalysts for biodieselproduction: a review. Fuel Processing Technology 90, 770–777.