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Industrial Crops and Products 49 (2013) 299– 303

Contents lists available at SciVerse ScienceDirect

Industrial Crops and Products

journa l h om epage: www.elsev ier .com/ locate / indcrop

ynthesis of maleated-castor oil glycerides from biodiesel-derivedrude glycerol

avid A. Echeverri, William A. Perez, Luis A. Rios ∗

rupo Procesos Fisicoquímicos Aplicados, Universidad de Antioquia, Sede de Investigación Universitaria, Cra. 53 # 61 - 30 Medellín, Colombia

a r t i c l e i n f o

rticle history:eceived 6 March 2013eceived in revised form 4 May 2013ccepted 7 May 2013

a b s t r a c t

Castor oil glycerides were obtained from the glycerolysis of castor oil or its methyl esters with alkaline-crude glycerol. High monoglyceride yields were obtained between 20–30 min and 180–200 ◦C with bothsubstrates. The glycerolysis of castor oil afforded highest yield of products at 180 ◦C and 30 min (50.4 ofmonoglycerides and 35% of diglycerides). However, the glycerolysis of methyl esters was more selectivetoward the formation of monoglycerides. Castor oil glycerides were further esterified with maleic anhy-

eywords:aleated glyceridesonoglycerides

rude glycerolastor oilaleic anhydride

dride without catalyst. Reaction was followed by acid value and 1H NMR. ca. 87% conversion of hydroxylgroups was obtained at 90 ◦C. The final product contained 2.6 maleate groups per glyceride molecule.

© 2013 Elsevier B.V. All rights reserved.

iodiesel

. Introduction

Industrial uses of vegetable oils in last years have increased dueo concerns about depletion of fossil fuels and environmental issuesBiermann et al., 2011). The use of non-edible oils such as castor oilnd jatropha oil in chemical purposes can reduce the consumptionf edible oils for these applications (Biermann et al., 2011; Rios et al.,013). Castor oil is one of the most valuable oils due to its high con-ent of ricinoleic acid (ca. 90%). Ricinoleic acid has a double bondlose to a hydroxyl group, which confers it special physical andhemical properties. Castor oil is a raw material with wide appli-ation in many chemical industries such as paints, coatings, inks,ubricants and a variety of other products (Dix et al., 1995).

An interesting strategy to obtain vegetable oil-based monomersonsists of the attachment of readily polymerizable func-ional groups to the triglyceride structure forming vegetable oil

acromonomers. Attachment of these functionalities can be donehrough unsaturations, allylic carbons, ester groups, hydroxylroups and � carbons to carbonyl groups (Mazo et al., 2012;onda et al., 2011). Hydroxylated and non hydroxylated oils suchs castor oil, jatropha oil or soybean oil can be converted to

ydroxyl derivatives through alcoholysis (transesterification) orpoxidation-hydroxylation (Can et al., 2001, 2006a; Echeverri et al.,

∗ Corresponding author. Tel.: +57 4 2196589; fax: +57 4 2196543.E-mail addresses: larios@udea.edu.co, daleza212@gmail.com,

ariospfa@gmail.com (L.A. Rios).

926-6690/$ – see front matter © 2013 Elsevier B.V. All rights reserved.ttp://dx.doi.org/10.1016/j.indcrop.2013.05.008

2010; Rios et al., 2011, 2013). The main advantage of the alcoholysisroute is that it produces principally primary hydroxyl moieties.

Alcoholysis of vegetable oils can be accomplished with severalpolyols like glycerol, pentaerythritol and bisphenol-A propoxylate.However, considering the price of raw materials it is more conve-nient the use of glycerol. Price of glycerol has diminished due tothe glut of crude glycerol from biodiesel production (Yang et al.,2012). Biodiesel-derived crude glycerol possesses very low valuedue to the impurities. Therefore, value-added uses of crude glycerolare convenient in order to improve economics of biodiesel. Use ofalkaline crude glycerol in the production of mono- and diglyceridesthrough glycerolysis of oils and their methyl esters is a promis-sory application because impurities in crude glycerol are catalystsof the reaction. A few works regarding to the glycerolysis of fatsand methyl esters with alkaline crude glycerol has been reported(Chetpattananondh and Tongurai, 2008; Noureddini et al., 2004;Noureddini and Medikonduru, 1997; Echeverri et al., 2010, 2012).

Unsaturated monomers can be obtained by the attachmentof maleate groups (maleinization) to hydroxyl functionalities oftriglycerides or their derivatives. For instance, maleated castoroil has been obtained in high yields by catalyzed and thermalmaleinization of castor oil by several authors (Can et al., 2006a;Wang et al., 2007). In addition, thermal and microwave assistedmaleinization of castor oil were studied recently in our group(Mazo et al., 2012). It was observed that the reaction was com-

plete within 7 h at 80 ◦C and within 3 h at 100 ◦C, regardless of theheating method used. Besides castor oil, ricinoleic acid has beenesterified with maleic anhydride at 90 ◦C using toluene as solvent,as reported by Teomim et al. (1999). Catalyzed maleinization of

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ydroxyl-derivatives of soybean oil and castor oil has been con-ucted by Can et al. (2006a). Thus, maleated soybean oil glyceridesere obtained at 100 ◦C using several catalysts such as sodiumydroxide, sulphuric acid, 2-methyl imidazole and p-toluene sul-honic acid. According to the results, the best catalyst was 2-methyl

midazole, which afforded a yield of 93% in 5 h. Likewise, cas-or oil derivatives of glycerol, pentaerythritol and bisphenol-Aropoxylate were esterified with maleic anhydride at 98 ◦C, using,N-dimethyl benzylamine as catalyst. These monomers wereopolymerized with styrene affording hard rigid plastics (Can et al.,006a). Properties of polymers were comparable to those of high-erformance unsaturated polyester resins.

Previous works related with the use of biodiesel-derived crudelycerol and the residual catalyst in the glycerolysis of oils haveeen conducted only with soybean oil or palm. To the best ofur knowledge, glycerolysis of castor oil or its methyl esters hasot been evaluated before with crude glycerol, using alkaline

mpurities as the catalyst. On the other hand, the maleiniza-ion of castor-oil glycerides obtained from biodiesel-derived crudelycerol as well as data at different temperatures and reactionimes have not been reported before. Moreover, the uncatalyzed

aleinization of mono- and diglycerides of castor oil below 100 ◦Cs not found in the literature.

In this work, the glycerolysis of castor oil and methyl esterserivate thereof were accomplished with crude glycerol, obtainedrom biodiesel production. Effects of the temperature and reactionime were evaluated. Reactions were followed by gas chromatog-aphy in order to determine influence of reaction conditions ononoglyceride and diglyceride content. In addition, these glyce-

ides were esterified with maleic anhydride without catalyst. Theffect of the temperature on the acid values as a function of the reac-ion time was analyzed. Conversions of hydroxyl groups as well as

aleate and fumarate yields were analyzed by 1H NMR.

. Material and methods

.1. Materials

Sodium hydroxide (>99%), methanol (≥99.8%), and maleic anhy-ride (≥98%) were obtained from Sigma–Aldrich (Sigma Aldrich, Stouis, MO). Refined soybean oil (acid value, 0.17 mg KOH/g) andechnical grade castor oil (acid value, 1.96 mg KOH/g; hydroxylalue, 160 mg KOH/g) were purchased from a local distributorFig. 1).

.2. Synthesis of castor oil glycerides (COG)

COG were obtained from the glycerolysis of castor oil and methylsters derived thereof. Castor oil glycerolysis was conducted in

250-mL round-bottom flask, equipped with a nitrogen inlet,echanical stirring and heating mantle. Castor oil (150.0 g) was

eated to the reaction temperature (180–220 ◦C) and then crudelycerol (42.35 g) was added in a 2.5/1 molar ratio of pure glyc-rol to oil according to the purity obtained by gas chromatography88.1%). Once the reaction was completed, 2.0 mL of H2SO4 solu-ion in water (50%, w/w) was added to neutralize the catalyst. The

ixture was allowed to cool to 100 ◦C to separate the neutralizedatalyst and the most of the excess glycerol in the bottom of theask.

Glycerolysis of castor oil methyl esters was carried out in a sim-lar assembly as describe above, but in addition, a Dean-Stark-type

ondenser was connected to collect the methanol generated in theeaction. Molar ratio of glycerol to methyl esters was 1.25/1. Tem-erature ranged from 160–200 ◦C. The same procedure describedor castor oil glycerolysis was followed, except that for a batch of

nd Products 49 (2013) 299– 303

150.0 g of methyl esters and 63.25 g of crude glycerol, 3.0 mL ofH2SO4 solution in water (50%, w/w) were added.

Crude glycerol was obtained from the transesterification of soy-bean oil with methanol (methanol/oil molar ratio of 6/1), at 65 ◦Cand catalyzed with 0.37% of NaOH respect to the oil, according tothe procedure of Echeverri et al. (2010). No further purification stepapart from methanol removal was accomplished for crude glycerol.The same procedure was followed for the transesterification of cas-tor oil with methanol. Crude methyl ester phase was washed withhot-water until elimination of alkaline components (confirmed bytitration with HCl) followed by heating at 100 ◦C under vacuum toremove water. The purity of castor oil methyl esters obtained bygas chromatography was 93%.

1H NMR spectra of the glycerolysis products showed the follow-ing signals:

1H NMR [CDCl3, ı (ppm)]: 5.54 (m, CH CH CH2 CH(OH)), 5.37 (m, CH CH CH2 CH(OH) ), 5.08 (m, CH(OC O) ),

4.25–4.05 (m, CH2(OC O) ), 3.98–3.84 (m, CH OH), 3.76–3.52(m, CH2OH), 2.34 (t, CH2(C O)O ), 2.20 (m, CH CH2 CH(OH) ),2.02 (m, CH2 CH CH ), 1.58 (t, CH2 CH2 (C O)O ), 1.45 (m,

CH2 CH2 CH(OH) ), 1.42–1.14 (m, nCH2 ), 0.85 (t, CH3 ).

2.3. Synthesis of maleated castor oil glycerides (MACOG) (Fig. 1)

Reaction was carried out in test tubes closed with rubberstoppers, according to the time intervals to be evaluated. 10-mLmagnetically stirred test tubes was used. COG (0.2 g) was mixedwith maleic anhydride (0.3 g) in each test tube. The tubes werestirred in a heating bath at the reaction temperature (80, 90 and100 ◦C). The tubes were withdrawn from the heating bath at 10,30, 45, 60 and 120 min and cooled in a water container to stop thereaction quickly before the chemical characterization.

1H NMR spectrum of the maleinization products showed thefollowing signals:

1H NMR [CDCl3, ı (ppm)]: 6.89 (m, CH CH , from fumaratemoieties, 0.1 H), 6.32 (m, CH CH from maleate moieties,5.2 H), 5.48 (m, CH(OC O) , 1.6 H), 5.30 (m, CH CH, fromfatty acid chain, 1.8 H), 5.02 (q, CH2 CH(OC O) CH2, 0.8 H),4.50–4.05 (m, CH2(OCO) , 4 H), 2.34 (m, CH2(C O)O , 5 H),2.01 (m, CH2 CH CH , 2.9 H), 1.58 (t, CH2 CH2(C O)O , 5.5H), 1.41–1.14 (m, CH2 , 22.3 H), 0.85 (t, CH3 , 4.3 H).

2.4. Characterization

Glycerol in crude glycerol as well as diglycerides and mono-glycerides in the glycerolysis products were determined by astandardized method (Brüschweiler and Dieffenbacher, 1991).Methyl esters in glycerolysis products were determined by gaschromatography according to BS EN14103 method. An Agilent7890A with flame ionization detector was used. A DB5-HT witha length of 15 m, an inner diameter of 0.32 mm and a film thick-ness of 0.1 �m was used. Tetradecane was employed as internalstandard for the quantification of products. Helium was used as car-rier. Contents of NaOH and soap in crude glycerol were determinedby modified AOCS method Cc 17-79 (Van Gerpen et al., 2004).

Reactions were followed by acid value titration and 1H NMR. Forthe determination of acid value of the maleinization samples, sameprocedure of Wang et al. (2007) was followed. This procedure con-sists in hydrolysis of excess of maleic anhydride and titration withKOH ethanol solution. 1H NMR.(300 MHz) spectra were obtainedusing a Bruker AMX400 spectrometer with Fourier transform and

CDCl3 as solvent.

Data plotted in the accompanying figures correspond to themeans of triplicate experiments with a relative standard devia-tion < 5% in all cases.

D.A. Echeverri et al. / Industrial Crops and Products 49 (2013) 299– 303 301

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the other hand, at 160 ◦C more than 60 min was required to reachequilibrium.

Fig. 1. Synt

. Results and discussion

.1. Glycerolysis of triglycerides and methyl esters of castor oil

Glycerolysis of triglycerides and methyl esters of castor oil wasonducted with alkaline-crude glycerol obtained from biodieselroduction. The purity of crude glycerol, obtained by gas chro-atography, was 88.1%. Contents of NaOH and soap were 1.7 and

.4% (w/w) respectively. The remaining 2.8% corresponds mainlyo methyl esters, glycerides and water. Since glycerolysis is a base-atalyzed reaction, no further catalyst was added to the reactionixture.The effect of the temperature on the glycerolysis of castor oil and

ts methyl esters was evaluated, as shown in Figs. 1 and 2. In the casef the castor oil glycerolysis (Fig. 2) high concentrations of productsere obtained from the beginning of the reaction for all the tem-eratures evaluated. Highest concentrations of products (around0.4% of monoglycerides and 34% of diglycerides) were obtained at80 ◦C and 30 min. Once equilibrium was reached, concentrationsf product tended to decrease with the time. This behavior wasore marked at 220 ◦C. This trend can be explained by the rever-

ion of the reaction represented in Eq. (1), which is favored withhe temperature and the catalyst concentration (Sonntag, 1982).

riglyceride + Glycerol � Monoglyceride + Diglyceride (1)

In the case of the glycerolysis of methyl esters (Fig. 3) the highestoncentrations of monoglycerides (around 45 wt%) were attainedt 180 ◦C and 20 min or 200 ◦C and 5 min. At 180 ◦C, once the maxi-um value of monoglycerides was reached, this value remained

of MACOG.

almost stable through the time. However, at 200 ◦C, once equi-librium was reached, products tended to decrease with time. On

Fig. 2. Effect of the temperature on the glycerolysis of castor oil. Solid lines, MG.Dashed lines, DG.

302 D.A. Echeverri et al. / Industrial Crops and Products 49 (2013) 299– 303

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ig. 3. Effect of the temperature on the glycerolysis of castor oil methyl esters. Solidines, MG. Dashed lines, DG.

Monoglyceride/diglyceride ratios (MDR) were calculated for theata of Figs. 2 and 3 as shown in Fig. 4. MDR were lower for thelycerolysis of triglycerides in comparison with the glycerolysis ofethyl esters at 160 and 180 ◦C. These results suggest that the glyc-

rolysis of methyl esters tended to be more selective toward theormation of monoglycerides at low temperatures. This is because,ccording to Eq. (2), diglycerides are not formed in the early stagesf the glycerolysis of methyl esters, in contrast with the glyc-rolysis of triglycerides (Eq. (1)). At 200 ◦C, MDR were similar foroth substrates since decomposition of monoglycerides throughhe equilibriums represented by Eq. (3) or Eq. (1) increases withhe temperature (Noureddini and Medikonduru, 1997).

ethyl ester + Glycerol � Monoglyceride + Methanol (2)

Monoglyceride � Diglyceride + Glycerol (3)

According to above results, castor oil glycerolysis afforded high-st content of monoglycerides (50.4 wt%) at 180 ◦C and 30 min inomparison with methyl ester glycerolysis. This mixture was usedor the synthesis of MACOG after neutralization of the catalyst with

ig. 4. Monoglyceride/diglyceride ratios for the glycerolysis of triglycerides (dashedines) and methyl esters of castor oil (solid lines) at several temperatures.

Fig. 5. Acid values as a function of the reaction time at different temperatures forthe maleinization of COG.

H2SO4. The catalyst must be neutralized at the end of the reactionbefore cooling to prevent reversion of the reaction (Sonntag, 1982).After cooling, part of glycerol was settled and removed from themixture. The final composition of the mixture was 53.5, 36.0 and3.2% of monoglycerides, diglycerides and glycerol, respectively. Thedifference to 100 in the mixture is: castor oil triglycerides plus thefatty acids formed during neutralization step.

3.2. Synthesis of MACOG

Maleinization of COG was followed by acid number as shownin Fig. 5. Decreasing of acid number indicates the consumptionof maleic anhydride. It should be mentioned that during the acidvalue measurement all the remaining maleic anhydride is con-verted to maleic acid. In spite of no catalyst was added, the acidvalues decreased rapidly in the first minutes for all the tem-peratures. Highest acid values were attained at 80 ◦C, indicatingrelatively incomplete reaction. Increasing of the temperature at90 ◦C improved the rate of consumption of maleic anhydride. How-ever, at 100 ◦C the increase in sublimation rate of maleic anhydridewith the temperature could have hindered the reaction of maleicanhydride. Theoretical final acid value of the samples taking intoaccount the initial composition of the mixtures and consideringcomplete reaction is 476. However, the lowest value obtained was553 at 90 ◦C. Possible explanations for these results are the subli-mation of maleic anhydride and secondary reactions of hydroxylgroups, as it will be shown later.

1H NMR spectrum of MACOG (obtained at 90 ◦C and 60 min) isshown in Fig. 6. Consumption of hydroxyl groups of COG was con-firmed by the disappearance of peaks corresponding to methyleneand methine protons attached to hydroxyls in COG spectrum (notshown) at 3.52–3.98 ppm. The formation of maleate half-esters ofCOG was confirmed by the signals at 6.32, 5.48 and 4.05–4.50 cor-responding respectively to maleate double bond protons as wellas methine and methylene protons attached to maleates. Furtherevidence for MACOG formation was the peak at 5.02 ppm corre-sponding to methine proton of fatty acids attached to maleategroup. Isomerization of maleate to fumarate was observed in a littleextent according to the signals of fumarate double bond protons at

6.89 ppm.

The content of fumarate and maleate in MACOG was deter-mined taking as reference the peak of methylene protons of theglycerol backbone at 4.05–4.50 ppm and the signals at 6.32 and

D.A. Echeverri et al. / Industrial Crops a

Fig. 6. 1H NMR spectrum of MACOG. 90 ◦C, 60 min.

Table 1Conversion of hydroxyl groups and maleate and fumarate yield (calculated from the1H NMR).

Temperature (◦C) Time (min) % conversion Maleatea

contentFumaratea

content

80 120 80.23 2.38 0.0190 60 86.60 2.61 0.03

100 60 86.14 2.50 0.06

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Number of maleate or fumarate groups per glyceride molecule.

.89 in 1H NMR spectra as shown in Table 1. Likewise, the conver-ions of hydroxyl groups were calculated from integration of theeak at 3.52–3.98 ppm of the 1H NMR spectra of COG. The conver-ion at 80 ◦C (80.2% at 2 h) and maleate content (2.4 maleates perlyceride molecule) were lower with respect to the higher temper-tures, with longer reaction time. These results indicate a sluggisheaction at 80 ◦C due to low temperature, as shown before for acidalue results. At 90 and 100 ◦C the conversions of hydroxyl groupsere about 86% at 1 h. This value is near to the reported by Can

t al. (85.2%) using as catalyst N,N-dimethyl benzylamine and aigher reaction time (5 h) (Can et al., 2006b). This is a remark-ble result since thermal maleinization of mono- and diglyceridesf castor oil below 100 ◦C has not been reported before. Maleateontents at 90 and 100 ◦C were 2.6 and 2.5 maleates per glycerideolecule, respectively. At reaction times higher than 60 min no sig-

ificant change in the hydroxyl conversion was observed for 90 and00 ◦C. The expected value is 3 maleates per glyceride molecule.ccording to Can et al. (2006b) the dehydration of ricinoleic acidhains and diester formation that may occur during maleinizationeaction could explain the low hydroxyl conversions and maleateield. Evidence for dehydration was not found. Dehydration leads toormation of 9,12-octadecadienoic and 9,11-octadecadienoic acids.owever, in 1H NMR spectrum of MACOG, protons of conjugatedethine groups in 9,11-octadecadienoic acid are not observed.n the other hand, 2.8 ppm peak corresponding to methyleneroup between two double bonds in 9,12-octadecadienoic acid isbserved. However, this peak was observed previously in castor oilpectrum (not shown). Presence of secondary ester linkage of oneatty acyl molecule to the alkyl backbone of another fatty acid frag-

ent is suggested by 4.87 ppm peak of 1H NMR of MACOG (Isbellnd Cermak, 2002). The sublimation of maleic anhydride could belso responsible for the observed values, as it was already explainedor the acid value results.

nd Products 49 (2013) 299– 303 303

4. Conclusions

Maleated half-esters of castor oil were obtained by glycerolysis-maleinization processes. Glycerolysis of castor oil was accom-plished with castor oil and its methyl esters using alkalinecrude glycerol. High monoglyceride yields were obtained between20–30 min and 180–200 ◦C with both substrates. The glycerolysisof castor oil afforded highest monoglyceride and diglyceride yield,50.4 and 35% respectively, at 180 ◦C and 30 min. However, the glyc-erolysis of methyl esters was more selective toward the formationof monoglycerides. Malinization of COG was conducted withoutcatalyst affording ca. 87% conversion of hydroxyl groups at 90 ◦C.The product contained 2.6 maleate groups per glyceride molecule.

Acknowledgements

Financial support of “Departamento administrativo de cien-cia y tecnología-Colciencias” and “Universidad de Antioquia” isacknowledged.

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