from glycerol as the by-product of biodiesel production to value-added monoacetin by continuous and...

Journal of Industrial and Engineering Chemistry xxx (2014) xxx–xxx

G Model

JIEC-2013; No. of Pages 6

From glycerol as the by-product of biodiesel production tovalue-added monoacetin by continuous and selectiveesterification in acetic acid

Hajar Rastegari, Hassan S. Ghaziaskar *

Department of Chemistry, Isfahan University of Technology (IUT), Isfahan, 84156-83111, Islamic Republic of Iran

A R T I C L E I N F O

Article history:

Received 19 January 2014

Received in revised form 19 April 2014

Accepted 20 April 2014

Available online xxx

Keywords:

Continuous glycerol esterification

Selective glycerol esterification

Monoacetin

Acetic acid

Biodiesel by-product

A B S T R A C T

A continuous and selective method for monoacetin synthesis was developed. Effects of the process

parameters including reaction temperatures (100–140 8C), acetic acid to glycerol mol ratios (1–3), feed

flow rates (0.2–0.6 mL min�1), and pressures (1–160 bar) on the glycerol conversion and the monoacetin

selectivity were studied. At the optimum conditions of 100 8C, acetic acid to glycerol mol ratio of 1, feed

flow rate of 0.6 mL min�1, and 1 bar, the glycerol conversion and monoacetin selectivity was,

respectively, 53% and 93%. The effect of water amount in the feed (3–15%)was also studied at the

optimum conditions.

� 2014 The Korean Society of Industrial and Engineering Chemistry. Published by Elsevier B.V. All rights

reserved.

Contents lists available at ScienceDirect

Journal of Industrial and Engineering Chemistry

jou r n al h o mep ag e: w ww .e lsev ier . co m / loc ate / j iec

Introduction

The development of renewable fuels has become important overthe last few years due to the depletion of petroleum reserves andincreased environmental concerns. Biodiesel is a renewable fueltraditionally produced via transesterification of triglycerides withmethanol. Two phases are produced in this process. The upper phasecontains the main biodiesel product, and the lower phase which isproduced with an approximate amount of 10% of the total biodieselby weight, is called crude glycerol [1]. This phase consists of glyceroland many other chemicals including nonreacted methanol, salts,water, and nonglycerol organic materials [2]. The composition of thisphase depends on the method of transesterification and also postprocesses to purify the crude glycerol. However the glycerol andwater concentrations are in the range of 50–88% and 3–15%,respectively [2]. The traditional applications of glycerol are incosmetics, food industries and pharmaceuticals [3]. For thesecommercial applications the quality of glycerol must be improveduntil it has an acceptable purity (>98%) that is completely differentfrom those obtained in biodiesel plants [4]. So many expensive postprocesses must be used to purify the crude glycerol [5]. According to

* Corresponding author. Tel.: +98 311 3913260/+98 913 111 8276;

fax: +98 311 3912350.

E-mail address: [email protected] (H.S. Ghaziaskar).

Please cite this article in press as: H. Rastegari, H.S. Ghaziaskar, J. Ind

http://dx.doi.org/10.1016/j.jiec.2014.04.023

1226-086X/� 2014 The Korean Society of Industrial and Engineering Chemistry. Publis

Oil World’s estimate, the world market for biodiesel is expected toreach 37 billion gallons per year by 2016. As a result around 4 billiongallons of crude glycerol will be produced at that year [6]. But theconventional applications of glycerol cannot accommodate thislarge volume of glycerol coming from biodiesel production whichneeds further costly purification steps. Therefore, it is necessary todevelop processes which generate value added products. Moreover,proper utilization of glycerol can reduce the costs of biodieselproduction up to 6.5% [7].

One of the glycerol promising applications is its chemicaltransformation. Glycerol is a biodegradable triol and up to its threehydroxyl groups can be functionalized. In this context, one optionis glycerol esterification with acetic acid to obtain mono-, di-, andtri-esters of glycerol acetates. Monoacetin (MA) and diacetin (DA)are building blocks of polyesters and cryogenics, and triacetin (TA)is used as fuel additive and in cosmetics as moisturizer [4,8].

Esterification is an acid catalyzed reaction which traditionally iscarried out over mineral acids. The problem here is that thesecatalysts are non-reusable, corrosive, toxic, and often hard toremove from the products [9]. These problems can be overcome bythe use of solid acid catalysts. The scientific literature containsmany reports on the use of heterogeneous acid catalysts forglycerol esterification such as ion-exchange resins [10–12],heteropolyacids [13], Zeolites [10], and others.

Many of these heterogeneous acid catalysts have some draw-backs. For example ion-exchange resins and heteropolyacids

. Eng. Chem. (2014), http://dx.doi.org/10.1016/j.jiec.2014.04.023

hed by Elsevier B.V. All rights reserved.


mailto:[email protected]


http://www.sciencedirect.com/science/journal/1226086X

www.elsevier.com/locate/jiec


Fig. 1. The schematic diagram of the setup used for the esterification reaction; (1)

nitrogen cylinder; (2) feedstock reservoir; (3) HPLC pump; (4) 3 way valve; (5) air

oven; (6) preheating coil; (7) reactor; (8) cooling jacket; (9) back pressure regulator;

(10) collection vessel.

H. Rastegari, H.S. Ghaziaskar / Journal of Industrial and Engineering Chemistry xxx (2014) xxx–xxx2

G Model


exhibit poor thermal stability, poor regeneration ability, lowturnover numbers, and low specific surface area [14,15]. Supportedheteropolyacids have high surface area and better thermal stabilitybut are limited by accessibility and efficiency of the catalyst [16]and Zeolites are less active compared to the ion-exchange resins[17]. So the major problem in using heterogeneous acids instead ofhomogeneous mineral acids lies in the lack of a solid acid that isactive, stable, and inexpensive as much as mineral acids. Therefore,it is industrially important to design a continuous system for MAsynthesis from glycerol without using any solid acid catalyst.

Chemical reactions can be performed under sub/supercriticalconditions to benefit the effect of pressure and temperature uponthe thermophysical properties of the reaction, such as dielectricconstant, viscosity, and polarity [18]. The most importantadvantages of these conditions compared to normal chemicalreactions using catalysts are that no catalyst is needed in thereaction and also the conversion rate is usually higher because ofsome properties of these fluids [18]. So the continuous productioncan be more feasible under sub/supercritical conditions.

Saka et al., developed a two step process for converting oils andfats to fatty acids and TA by subcritical acetic acid (Tc = 317 8C;Pc = 58 bar) followed by the fatty acids conversion to fatty acidmethyl esters by supercritical methanol (Tc = 239 8C; Pc = 81 bar)[19]. TA was hardly observed even after 40 min at reactiontemperature of 250 8C, 200 bar, and acetic acid to oil mol ratio of54, while the maximum yield was observed at 300 8C after 30 minand they achieved the TA yield of 85% by weight. Wei et al. usedsupercritical methanol, carbon dioxide, and acetic acid to producebiodiesel from soybean oil [20]. Acetic acid was added to consumethe glycerol byproduct and also to increase the hydrolysis of fattyacids. At the optimum conditions of 280 8C, 200 bar, methanol tooil mol ratio of 60, and acetic acid to oil mol ratio of 3, 30% of theproduced glycerol from transesterification was converted toacetins, after 90 min. The aims of these works were consumptionof glycerol byproduct of biodiesel at the reaction conditions thatare severe.

Herein, the continuous esterification of glycerol with acetic acidwithout using any solid acid catalyst under milder conditions wasstudied. Response surface methodology (RSM) was used to assessthe reaction parameters of temperature, acetic acid to glycerol molratio, feed flow rate, and pressure to achieve the best results interms of glycerol conversion and MA selectivity. Then at theoptimum conditions the effect of the feed water content wasinvestigated. Finally, the noncatalyzed reaction was comparedwith catalyzed reaction. H-beta Zeolite (HBZ) was selected to do acatalyzed reaction because of its water resistance and hydrophobicsurface.

Experimental

Materials

Acetic acid (purity >99.85%) was purchased from FanavaranPetrochemical Co. (Iran). Glycerol (purity >99.9%) was purchasedfrom USP (Malaysia). TA (purity >99%) and DA (purity = 50%verified by GC-FID) were purchased from Fluka (Germany). MAwas synthesized via a previously reported method (purity >95%)[21]. Absolute ethanol (purity >99.9%) and 2-ethylhexanoic acid(purity >99%) were purchased from Bidestan Co. (Iran) and TatChemical Co. (Iran), respectively. HBZ (cp814c) was purchasedfrom Zeolyst1 Co.

Procedure

Schematic diagram of the apparatus used to do the reaction isshown in Fig. 1. The major components were an HPLC pump


(model PU-980, JASCO Co.), a tubular reactor (i.d. = 0.84 cm,length = 23 cm) from 316 stainless steel, placed in an air ovenwith a temperature control of �1 8C throughout the experiment, acooling jacket, back pressure regulator (model BP 1580-81, JASCOCo.), and a collection vial immersed in a cold trap.

Before the reaction, the system was purged with nitrogen. Aftertemperature stabilization, the feed was pumped in to the system ata predetermined flow rate and the pressure was adjusted via thebackpressure regulator. At each operating condition, eight sampleswere collected at different time intervals with collection efficiencyof higher than 95%. In all experiments the tubular reactor was filledwith crushed Pyrex glass (CPG). For further studies, selected CPGhad a mesh range of 16–40.

Analytical method

Identification of the products was carried out by GC-MS (model6890N, Agilent technologies). TA, DA and MA were the onlyproducts and no side products were observed. The retention timesof these products were 5.6, 6.1 and 6.4 min, respectively. Analysisof the samples was carried out using a GC-FID (model 3420,BEIFEN, China). The carrier gas was nitrogen and a SGE capillarycolumn of BP-20 (i.d. = 0.25 mm, length = 30 m, film thick-ness = 0.25 mm) was used for separations. All injections weremade in the split mode (split ratio of 1:30) with the followingtemperature program: 100 8C ramped to 260 8C at 30 8C min�1

where it was held for 3 min. The injector and the detectortemperature were set at 260 8C and 280 8C, respectively. Quantifi-cation was performed by injecting some standard solutionscontaining 2-ethylhexanoic acid as an internal standard andintegrating the peak areas to draw the calibration curves. Theglycerol conversion, each product selectivity and yield werecalculated as follows:

Conversion ð%Þ ¼ Moles o f glycerol reacted

Moles o f glycerol fed to the reactor� 100 (1)

Selectivity ð%Þ ¼ Moles o f each product

Moles o f glycerol reacted� 100 (2)

Yield ð%Þ ¼ Moles o f each product

Moles o f glycerol fed to the reactor� 100 (3)

Characterization

FT-IR spectra were recorded on a JASCO FT-IR-680 plusspectrometer in KBr pellets. 5 mg of each sample were mixedwith 100 mg of dried KBr. Spectra were recorded from 400 to4000 cm�1 with 32 scans and a resolution of 4 cm�1.



Table 1Experimental glycerol conversion and MA selectivity according to the experimental matrix design for a three-level-four factors CCD.

Run no. Variables Conversion (%) Selectivity (%)

T (C) X (mol ratio) F (mL min�1) P (bar) MA DA TA

1 120 2 0.4 80 77 75 24 1

2 100 1 0.6 1 53 93 7 0

3 100 3 0.2 1 80 73 25 2

4 100 1 0.2 1 59 89 11 0

5 120 2 0.4 80 78 75 23 2

6 120 2 0.6 80 74 78 20 2

7 140 3 0.2 160 87 59 38 3

8 140 1 0.2 160 61 84 14 2

9 100 1 0.6 160 53 92 8 0

10 140 3 0.6 1 85 66 33 1

11 140 2 0.4 80 80 72 27 1

12 120 2 0.4 1 78 75 23 2

13 120 2 0.2 80 77 73 26 1

14 120 2 0.4 80 78 76 22 2

15 120 2 0.4 160 79 77 21 2

16 100 3 0.6 1 55 91 9 0

17 100 3 0.6 160 58 90 10 0

18 100 3 0.2 160 81 74 24 2

19 120 2 0.4 80 78 75 24 1

20 120 2 0.4 80 78 75 24 1

21 140 3 0.6 160 84 66 33 1

22 100 2 0.4 80 67 86 10 4

23 140 1 0.2 1 62 83 15 2

24 140 1 0.6 160 62 85 13 2

25 120 1 0.4 80 57 89 11 0

26 100 1 0.2 160 57 90 10 0

27 140 3 0.2 1 85 60 38 2

28 120 2 0.4 80 78 76 23 1

29 140 1 0.6 1 61 85 13 2

30 100 2 0.4 80 73 81 18 2

31 100 3 0.4 80 67 72 24 4

H. Rastegari, H.S. Ghaziaskar / Journal of Industrial and Engineering Chemistry xxx (2014) xxx–xxx 3

G Model


Experimental design

Design of experiment was used to investigate the processparameters in the esterification reaction. The experimental designwas carried out by Central Composite Design (CCD), consisting offour independent variables (temperature, T, acetic acid to glycerolmol ratio, X, feed flow rate, F, and pressure, P) at three coded levels(�1, 0, 1). The selection of these ranges was based on some initialexperiments. The experiments were then conducted based on thedesign matrix shown in Table 1. Upon completion of all theexperimental runs, the responses obtained (glycerol conversionand MA selectivity) were then analyzed by RSM using a quadraticpolynomial equation as shown below:

Y ¼ b0 þXn

i¼1

biXi þXn

i¼1

biiX2i þ

Xn

i¼1

Xn

j > 1

bi jXiX j (4)

where Y is the response, b0, bi, bii, bij are intercept, linear, quadratic,and interaction coefficients, respectively; n is the number ofvariables studied and optimized in the experiments; and Xi and Xj

are the coded independent variables. All the experimental datawere statistically analyzed by Minitab software, version 14. Thequality of the developed model was determined by the value ofcorrelation (R2) while analysis of variance (ANOVA) was used toevaluate the statistical significance of the model.

Results and discussions

Model fitting and ANOVA

The significance of each parameter was determined by T-value(Table 2). The null hypothesis states that the value of the parametercoefficient is zero, if the T-value for each parameter is greater thanthe critical T-value, therefore, the null hypothesis is rejected. The


P-value is the probability that a parameter coefficient can be zero. Ifit is greater than 0.05, the parameter has no significant effect in themodel (at confidence level of 95%) and can be eliminated.

The model ANOVA confirmed the validity of the models. The P-values of the models for both the glycerol conversion and MAselectivity were 0.000 describing that the regressions at theconfidence level of 95% (P < 0.05) are significant. There is no lack offit at the confidence level of 95% (calculated Flack of fit are less thanthe critical values). The adjusted correlation coefficients (R2

adj) of0.913, and 0.967 obtained for the glycerol conversion, and MAselectivity, respectively, which indicates good performance of themodels in predicting the data trends (Fig. 2).

Effects of process parameters

Effect of acetic acid to glycerol mol ratio

Considering the influence of the variables through thecoefficients shown in Table 2, it is remarkable that the aceticacid to glycerol mol ratio is the most influenced variable on theglycerol conversion and MA selectivity. This factor has positive andnegative effect on the conversion and MA selectivity as indicatedby the positive and negative values of the regression coefficients(Table 2), respectively. These results are consistent with thosereported in the literature in which higher mol ratio of acetic acid toglycerol will shift the reversible esterification reaction forward,resulting in increase in the conversion. As shown in Fig. 4 an aceticacid to glycerol mol ratio of 1, is the most favorable for the selectivesynthesis of MA. According to stoichiometric ratios (Scheme 1)higher mol ratios will shift the esterification reaction to the 2ndand 3rd steps, so MA selectivity decreases.

Effect of temperature

An increase in the reaction temperature increases the rate ofreaction leading to an increase in the conversion (Fig. 3) while it



Table 2Regression coefficients, T-value, and P-value for the model estimated by Minitab software for the conversion, and MA selectivity of the esterification reaction.

Term Conversion MA selectivity

Coefficient T-value P-value Coefficient T-value P-value

Constant* 76.000 79.845 0.000 76.195 152.041 0.000

T 5.655 7.478 0.000 �6.627 �16.645 0.000

X 8.850 11.702 0.000 �7.766 �19.505 0.000

F �3.644 �4.819 0.000 3.411 8.567 0.000

P 0.150 0.198 0.845 0.050 0.126 0.902

T2 �2.813 �0.502 0.622 1.993 1.901 0.075

X2 �9.466 �6.301 0.000 4.043 3.856 0.001

F2 1.236 0.552 0.588 �1.356 �1.293 0.214

P2 4.086 1.983 0.065 �1.006 �0.960 0.352

TX 2.656 3.311 0.004 �3.087 �7.310 0.000

TF 3.431 4.277 0.001 �1.737 �4.114 0.001

TP �0.031 �0.039 0.969 �0.075 �0.178 0.861

XF �2.543 �3.171 0.006 2.575 6.097 0.000

XP 0.493 0.616 0.547 �0.162 �0.385 0.705

FP 0.218 0.273 0.789 �0.262 �0.622 0.543

* The significant parameters are shown in bold face.


G Model


reduces the MA selectivity as shown in Fig. 4 and Table 2. Thereaction Gibbs free energies of the MA and DA formation arerelatively small (19.15 and 17.80 kJ mol�1), while for the TAformation is large (55.58 kJ mol�1) [22]. So MA formation waspredominant at lower reaction temperatures (Fig. 4), and theselectivity toward DA and TA, along with glycerol conversion

Fig. 2. Plots of the predicted (calculated by fitting the models) versus experimental

values for glycerol conversion (a) and MA selectivity (b).


increased with an increase in temperature from 100 8C to 140 8C, asshown in Table 1. These results suggest that the MA selectivityvaried with glycerol conversion too.

Effect of feed flow rate

The effect of feed flow rate was investigated within the intervalof 0.2–0.6 mL min�1. Increasing the feed flow rate reduces theresidence time of the reaction mixture in the reactor so thatglycerol conversion reduced (negative coefficient in Table 2). TheMA selectivity increased with increasing feed flow rate (positivecoefficient in Table 2). This is because the residence time reducesand there is no sufficient time for the DA and TA steps to proceedand hence the formation of DA and TA reduces (Table 1).

Effect of pressure

As is shown in Table 2 the pressure had no significant effect onthe esterification reaction in the range of 1–160 bar at theconfidence level of 95% (P-value >0.05). In this range the variationsin the pressure will not significantly change the viscosity anddiffusion coefficients of the reaction mixture and hence will notalter the residence time, so the conversion (Fig. 3) and MAselectivity (Fig. 4) were unaffected.

Process optimization

The optimum values of the selected variables were obtainedusing the response optimizer tool of Minitab software. Thepredicted optimal values to give maximum glycerol conversionand MA selectivity were a temperature of 100 8C, acetic acid toglycerol molar ratio of 1, feed flow rate of 0.6 mL min�1, andpressure of 1 bar. Under these optimum conditions the predictedmaximum conversion and selectivity were 51% and 94%, respec-tively. To verify the model predictions, the optimum responsevariables were tested under predicted optimum conditions. Theconversion and MA selectivity from the experiment were 53% and93%, respectively, which are close to the model prediction.

Scheme 1. Three consecutive reversible steps of glycerol esterification with acetic

acid.



Fig. 3. Response surface plots for the glycerol conversion in the continuous esterification of glycerol with acetic acid.

Fig. 4. Response surface plots for the MA selectivity in the continuous esterification of glycerol with acetic acid.

H. Rastegari, H.S. Ghaziaskar / Journal of Industrial and Engineering Chemistry xxx (2014) xxx–xxx 5

G Model


Effect of the reactor packing-material

To lower the dead volume of reactor, in one of the experimentsthe tubular reactor was packed with CPG and in the other with astainless steel filings. In order to investigate the effect of packingmaterial on the responses, two experiments were carried out in theoptimized reaction conditions (temperature of 100 8C, acetic acidto glycerol mol ratio of 1, feed flow rate of o.6 mL min�1, pressureof 1 bar, and the feed water of 3% by weight).

The obtained glycerol conversion and MA selectivity usingstainless steel filings as reactor packing material were,

Fig. 5. FT-IR spectra of the CPG before and after reaction.


respectively, 57% and 81% at the optimum reaction conditionswhich shows that the glycerol conversion has increased for 6%while the MA selectivity has been reduced for about 13%compared to the case that the reactor was filled with CPG.

FT-IR spectra of CPG before and after the reaction were given inFig. 5. The main bands centered at around 3500, 1010 and770 cm�1 could be attributed to Si–OH, Si–O–Si asymmetricstretching and Si–O–Si bending vibration, respectively. The peak at1627 cm�1 assigned to the bending vibration of H2O. The hydroxylgroups at the surface of CPG can interact with water molecules inthe reaction medium through hydrogen bonds. This might be thereason that the MA selectivity increased when CPG was used asfiller of the reactor.

Effect of water addition

In most cases crude glycerol is purified by expensive separationsteps prior to further use. Therefore, it is highly desirable to utilizecrude glycerol directly in the esterification reaction. As mentioned inthe introduction section crude glycerol contains 3–15% water byweight. Therefore, additional experiments were conducted in whichthe amount of water in the feed was 9% and 15% in order to check theinfluence of the feed water content on the glycerol conversion andMA selectivity. As shown in Table 3, the conversion of glycerol isreduced from 53% at the water content of 3% to the conversion of 20%at the water content of 15% in the feed while surprisingly the MAselectivity increased from 93% to 99%, respectively.

The overall process is a chain of three consecutive andreversible reactions and water is produced as a by-product in all



Table 3Effect of water on the glycerol conversion and MA selectivity.

Mass percent of water

in the feed (%)

Conversion (%) Selectivity (%)

MA DA TA

3 53 93 7 0

9 36 96 4 0

15 20 99 1 0

Scheme 2. Esterification reaction mechanism.


G Model


three steps. Therefore, addition of water negatively affects theequilibrium and drives back the reaction; as a result the conversionis reduced. Moreover, the presence of water does not allow thereaction proceeds to produce DA and TA and consequently the MAselectivity is increased.

Comparative study between noncatalyzed and catalyzed reaction with

HBZ

The noncatalyzed reaction was compared with catalyzedreaction in which HBZ was used. The catalyst area, Si to Al molratio and acid capacity were 710 m2 g�1, 38 and 0.54 mmol g�1,respectively. The acid capacity of the catalyst was determined byback titration with standard solution of sodium hydroxide. Beforethe reaction was performed, the catalyst was activated attemperatures of 200 8C for 2 h and then 450 8C for 4 h in nitrogenand oxygen streams [23]. The catalytic run was performed in theoptimum conditions over 3 g of HBZ with feed water content of15% by weight.

The glycerol conversion increased from 20% to 26% when HBZwas used. As shown in Scheme 2, esterification reactions needsacid catalysts [24] and the acid strength is an important factoraffecting the kinetics of the reaction. Moreover, the presence ofwater in the reaction medium either as a product of reaction or theadded-water might allow the acetic acid become dissociated andthe proton produced catalyzes the esterification reaction [19], butusing HBZ increases the reaction medium acid strength so that thereaction rate and conversion increased compared to noncatalyzedreaction. In the presence of HBZ, the MA selectivity decreasedabout 8%. The reason for this reduction is that, MA moleculesundergo further esterification reactions to produce DA. So usingsolid acids cannot be helpful in this process with the aim ofselective synthesis of MA.

Conclusions

We developed a continuous and selective process using atubular reactor filled with crushed Pyrex glass for the synthesis of


MA from glycerol and acetic acid with no extra catalyst used. Theresults showed that the most important variables were the aceticacid to glycerol mol ratio, the temperature, and the feed flow rate.The pressure had no significant effect on the esterification reactionin the range of 1–160 bar at the confidence level of 95% (P-value>0.05).

Water addition affects the esterification rate and theequilibrium of the reaction, because water can promote esterhydrolysis, so that the conversion decreased while MA selectivityincreased to 99% by increasing the feed water content to 15% byweight. The glycerol conversion and MA selectivity of 26% and91% were achieved by using HBZ as a catalyst. This workdemonstrated that the selective esterification of glycerol to MAcould be performed with acetic acid as a substrate and probablyas a catalyst.

Acknowledgments

Authors would like to thank IUT for partial financial support.Professor M. Yalpani is acknowledged for his critical review of thework and nice suggestions.

References

[1] C.W. Chiu, M.A. Dasari, G.J. Suppes, W.R. Sutterlin, AIChE J. 52 (2006) 3543–3547.[2] Glycerol Purification, EET Corp., Available at hhttp://www.eetcorp.com/heepm/

biodiesel.pdfi.[3] B. Katryniok, S. Paul, V. Belliere-Baca, P. Rey, F. Dumeigni, Green Chem. 12 (2010)

2079–2080.[4] N. Rahmat, A.Z. Abdullah, A.R. Mohamed, Renewable Sustainable Energy Rev. 14

(2010) 987–990.[5] R.M. Banavali, R.T. Hanlon, A.K. Schultz, US Patent US 7,534,923 B2, 2009.[6] X. Fan, R. Burton, Y. Zhou, Sci. J. 3 (2010) 17–22.[7] M.P. Dorado, F. Cruz, J.M. Paloma, F.J. Lopez, Renewable Energy 31 (2006)

1231–1240.[8] P.C. Smith, Y. Ngothai, Renewable Energy 35 (2010) 1145–1150.[9] J. Lilja, J. Aumo, T.D. Salmi, Yu. Murzin, P. Maki-Arvela, M. Sundell, K. Ekman, R.

Peltonen, H. Vainio, Appl. Catal., A: Gen. 228 (2002) 253–267.[10] V.L.C. Goncalves, B.P. Pinto, J.C. Silva, C.J.A. Mota, Catal. Today 133–135 (2008)

673–677.[11] D. Rodriguez, E.M. Gaigneaux, Catal. Today 195 (2012) 14–21.[12] M. Rezayat, H.S. Ghaziaskar, Green Chem. 11 (2009) 710–715.[13] C.E. Gnocalves, L.O. Laier, A.L. Cardoso, M.J. Silva, Fuel Process. Technol. 102 (2012)

46–52.[14] S. Wang, J.A. Guin, Chem. Commun. 24 (2000) 2499–2500.[15] S. Mallick, K.M. Parida, Catal. Commun. 8 (2007) 889–893.[16] B.M. Reddy, M.K. Patil, B.T. Reddy, Catal. Lett. 125 (2008) 97–103.[17] T.A. Peters, N.E. Benes, A. Holmen, J.T.F. Keurentjs, Appl. Catal., A: Gen. 297 (2006)

182–188.[18] J. Lu, E.C. Boughner, C.L. Liotta, C.A. Eckert, Fluid Phase Equilib. 198 (2002) 37–49.[19] S. Saka, Y. Isayama, Z. Ilham, X. Jiayu, Fuel 89 (2010) 1442–1450.[20] C.Y. Wei, T.C. Huang, H.H. Chen, J. Chem. (2013) (article ID of 789594).[21] C.C. Yu, Y.S. Lee, B.S. Cheon, S.H. Lee, Bull. Korean Chem. Soc. 24 (2003) 1229–

1230.[22] X. Liao, Y. Zhu, S.G. Wang, H. Chen, Y. Li, Appl. Catal., B: Environ. 94 (2010)

64–70.[23] J.H. Ahn, R. Kolvenbach, C. Neudeck, S.S. Al-Khattaf, A. Jentys, J.A. Lercher, J. Catal.

311 (2014) 271–280.[24] M.B. Smith, J. March, March’s Advanced Organic Chemistry, Reactions, Mecha-

nisms and Structure, sixth ed., John Wiley and Sons, Inc. Publication, New Jersey,2007, pp. 1402–1403.


http://refhub.elsevier.com/S1226-086X(14)00221-4/sbref0005




































from glycerol as the by-product of biodiesel production to value-added monoacetin by continuous and...

Documents