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Synthesis of glycerol carbonate from glycerol and dimethyl carbonate catalyzedby NaOH/γ-Al2O3

Rongxian Bai a,b, Yi Wang a, Shu Wang a, Fuming Mei a, Tao Li b, Guangxing Li a,b,⁎a School of Chemistry and Chemical Engineering, Huazhong University of Science and Technology, Hubei, Wuhan 430074, Chinab Hubei Key Laboratory of Material Chemistry and Service Failure, Huazhong University of Science and Technology, Wuhan 430074, China

⁎ Corresponding author at: School of Chemistry and ChUniversity of Science and Technology, Hubei, Wuhan 4387544532.

E-mail address: [email protected] (G. Li).

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Please cite this article as: R. Bai, et al., SynthProcess. Technol. (2012), http://dx.doi.org/

a b s t r a c t
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Article history:Received 9 October 2011Received in revised form 15 July 2012Accepted 24 July 2012Available online xxxx

Keywords:Glycerol carbonateGlycerolDimethyl carbonateNaOH/γ-Al2O3

The NaOH/γ-Al2O3 as catalyst for the synthesis of glycerol carbonate via transesterification of glycerol with di-methyl carbonate (DMC) has been developed in this work. Itwas found that NaOH/γ-Al2O3was a highly efficientheterogeneous catalyst for the synthesis of glycerol carbonate and the catalyst can be easily recovered andrecycled. Under the conditions of DMC/glycerol molar ratio of 2, catalyst/glycerol weight ratio of 3%, reactiontimeof 1 h, and reaction temperature of 78 °C, the conversion of glycerol and the selectivity to glycerol carbonatereached 97.9% and 99.0%, respectively. The catalytic performance of 80 wt.% NaOH/γ-Al2O3 is much better thanthat of K2CO3. A plausible reaction mechanism about this catalytic reaction was also proposed.

© 2012 Published by Elsevier B.V.

1. Introduction

Nowadays, biodiesel is being produced in great quantities. What ismore, its production continues to grow at a steady rate. However, thedevelopment of biodiesel industry frombiomass resource leads to a sur-plus of glycerol. As a renewable and cheap raw chemical, researches onthe conversion of glycerol to valuable chemicals have attracted consid-erable attention [1–6]. Glycerol carbonate (GC), one of the most attrac-tive derivatives of glycerol, can be used as chemical intermediates forpharmaceuticals, safe and environmentally friendly solvent [7,8]. GCcan be synthesized from different pathways according to involvingchemicals such as CO/H2, organic carbonate, urea or carbon dioxide[5,9–14]. Among these pathways, transesterification of glycerol with di-methyl carbonate (DMC) is one of the most important methods to pro-duce GC [9–11].

The key in the transesterification reaction is to seek highly efficientcatalysts. For the synthesis of GC via transesterification of DMC and glyc-erol, homogeneous catalysts such as 1-n-butyl-3-methylimidazolium-2-carboxylate, p-toluenesulfonic acid, H2SO4, and K2CO3, have beenreported [10,11,15]. The homogenous catalysts possess high catalyticactivity for the synthesis of GC, but it is required to separate from theproduct which is complicated and inconvenient in the industrial pro-cess. Therefore, the development of heterogeneous catalyst is necessary

emical Engineering, Huazhong0074, China. Tel./fax: +86 27

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esis of glycerol carbonate fro10.1016/j.fuproc.2012.07.027

in view of the demerit of homogeneous catalysts [15–17]. For example,Ochoa-Gómez et al. screened different basic and acidic homogeneousand heterogeneous catalysts for the synthesis of GC from glycerol andDMC. It was found that the best heterogeneous catalyst was CaOand the yield of GC reached about 95% under optimum reaction con-ditions [15]. However, this catalyst was apt to deactivate in the pres-ence of water. Takagaki et al. found that hydrotalcite showed a goodcatalytic activity for the synthesis of GC from glycerol and DMC.However, the yield of GC reached merely 82% without DMF as a sol-vent [17].

Generally, γ-Al2O3 is commonly used as a heterogeneous catalyst orsupport due to its textural properties and good availability [18–20]. Asreported previously, γ-Al2O3 loaded with other active componentscan also be used as a solid base catalyst to catalyze the synthesis oforganic carbonate via transesterification andClaisen Schmidt condensa-tion reaction [21–26]. Especially, Kim and Arzamendi found thatNa/NaOH/γ-Al2O3 and NaOH/γ-Al2O3 were efficient solid base catalystsfor the synthesis of biodiesel via transesterification from fatty acidmethy1 esters and methanol [27,28]. Therefore, it would be reasonableto expect that transesterification of glycerol with DMC can also beconducted in the presence of NaOH/γ-Al2O3.

To the best of our knowledge, there is no report to date in the applica-tion of the solid base catalyst of NaOH loaded onγ-Al2O3 for the synthesisof GC from glycerol and DMC. In this work, a series of NaOH/γ-Al2O3

catalysts with various NaOH loading amounts were prepared andemployed in the synthesis of GC from glycerol and DMC. It wasfound that NaOH/γ-Al2O3 was a highly efficient heterogeneous cata-lyst for the synthesis of GC and the catalyst can be easily recovered andrecycled.

m glycerol and dimethyl carbonate catalyzed by NaOH/γ-Al2O3, Fuel

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10 20 30 40 50 60 70 80

NaAlO2

Al2O

3

b

c

d

a

Inte

nsity

/ a.

u.

2θ / Degree

Fig. 1. XRD pattern of NaOH/Al2O3 (a) γ-Al2O3, (b) 5% NaOH/γ-Al2O3, (c) 40% NaOH/γ-Al2O3, and (d) 80% NaOH/γ-Al2O3.

2 R. Bai et al. / Fuel Processing Technology xxx (2012) xxx–xxx

2. Experimental procedure

2.1. Materials

Glycerol, NaOH, DMC, tetraethylene glycol and γ-Al2O3 werepurchased from Sinopharm Chemical Reagent Co., Ltd., TianjinFengchuan Chemical Reagent Science And Technology Co., Ltd.,Dongying Hi-tech Spring Chemical Industrial Co., Ltd., Fluka, andNanjing Chemical Industry Corporation Chemical Plant, respective-ly. All other chemicals were of analytical reagent grade and wereused directly without further purification except DMC (99.5%, in-dustrial grade). Glycerol carbonate (95%) for gas chromatographyanalysis was purchased from Tokyo Kasei Kogyo Co., Ltd.

2.2. Catalyst preparation

NaOH/γ-Al2O3 catalyst was prepared through a wet impregnationmethod. In a typical synthesis, 1 g of γ-Al2O3 was added into a mod-erate amount of solutions containing NaOH. The mixture was stirredat 30 °C for 2 h, and the resulting slurry was heated at 98 °C until dry-ness. Obtained sample was further dried at 110 °C for 12 h and cal-cined under air at 500 °C for 4 h. Finally, the catalyst was crushedinto particles with a diameter less than 60 μm. For convenience, thecatalysts obtained with various NaOH loading amounts of 5, 10, 20,40, 60, and 80 wt.% were designed as 5% NaOH/Al2O3 to 80% NaOH/Al2O3, respectively.

2.3. Catalytic activity test

The transesterification reaction was carried out in a two-neckround-bottomed flask equipped with a magnetic stirring bar, athermometer and a fractionating column connected to a liquid di-viding head. In a typical experiment, 0.1 mol of glycerol, 0.2 molof DMC and 3 wt.% catalysts (based on the amount of glycerol used)were mixed together in the reactor and kept under stirring at the tem-perature of 78 °C for 1 h. After the reaction, the mixture was taken out,and then the catalyst was separated by filtration, washed with metha-nol and dried at 110 °C for 5 h. The catalyst was collected and reusedfor the next run.

2.4. Procedure for recycling of the catalyst

The used dry catalyst was mixed with a new charge of reactants inthe flask and then subjected to the next run of transesterification re-action. The same procedure was employed for all reused catalysts, asdescribed in Section 2.3.

2.5. Product analysis

Reaction mixture after separation of catalyst was analyzed by gaschromatograph (Fuli 9790) using KB-Wax (30 m×0.25 mm×0.25 μm)capillary column and aflame ionization detector (FID) [29]. Tetraethyleneglycol was used as an internal standard for the GC quantitative analysisaccording to the reportedmethod [16]. Injector and detector temperaturewere kept at 250 and 280 °C, respectively. The oven temperature startedat 70 °C andwas increased at a rate of 15 °C/min until 230 °C and kept for17 min.

2.6. Catalyst characterization

The catalyst samples (diluted by KBr at the ratio of 1:200) werecharacterized by infrared (IR) analysis using Equinox 55 spectrometer(Bruker) with a resolution of 0.4 cm−1.

The powder X-ray diffraction (XRD) patterns were recorded on anXRD diffract-meter (X'pert pro), using Ni-filtered Cu Kα radiation. The

Please cite this article as: R. Bai, et al., Synthesis of glycerol carbonate froProcess. Technol. (2012), http://dx.doi.org/10.1016/j.fuproc.2012.07.027

working voltage and current were 40 kV and 40 mA, respectively. The2θ range used was from 10° to 80° with a scanning speed of 2°/min.

The BET surface area of the catalysts was measured using nitrogenadsorption at 77.3 K on a volumetric adsorption apparatus (Autosorb-1,Quantachrome). High purity nitrogen (99.99%)was used in this analysis.

The basic strength and basicity of the solid catalysts were deter-mined by Hammett indicator method. In this experiment, the followingHammett indicators were used: bromthymol blue (H_=7.2), phenol-phthalein (H_=9.8), 2,4-dinitroaniline (H_=15.0) and 4-nitroaniline(H_=18.4). The basic strength is defined as being stronger than theweakest indicator andweaker than the strongest indicator. The basicityvalues (expressed as: mmol/g) of the catalysts were measured by theHammett indicator–benzene carboxylic acid (0.02 mol/L anhydrousethanol solution) titration, based on the procedure described in the lit-eratures [22,23,30].

The sodium content in the reactionmixture wasmeasured by atom-ic absorption spectrometry method (Perkin-Elmer 2380). The sodiumcontent can be used to estimate the leaching of the NaOH from theNaOH/γ-Al2O3 in the reaction.

3. Results and discussion

3.1. Characterization

The XRD patterns of γ-Al2O3 and NaOH/γ-Al2O3 with differentNaOH loading amounts were measured, and the results are shownin Fig. 1. The peak positions of γ-Al2O3 are in good agreement withthe JCPDS (00-47-1308). As shown, the diffraction peaks obtainedfor γ-Al2O3 (Fig. 1a) and 5% NaOH/γ-Al2O3 (Fig. 1b) do not showany observable differences. For the 40% NaOH/γ-Al2O3 catalyst thediffraction peaks related to the NaAlO2 were detected (JCPDS01-083-0316) and their intensities increased with an increasingloading amount of NaOH up to 80 wt.%. The XRD patterns did notshow any peaks related to the NaOH and other crystalline species.These results agree well with that reported by Noiroj et al. for KOH/Al2O3 catalyst [31]. The KOH was well dispersed on Al2O3 at lowKOH loading, and if there is a further increase in KOH loading toover 25 wt.%, the new phase of Al–O–K compound is being observed[31].

The XRD patterns for reused 80% NaOH/γ-Al2O3 catalyst arepresented in Fig. 2. It can be seen that the patterns showmainly the dif-fraction peaks corresponding to the Na2Al2O4 (JCPDS 00-029-1165).Furthermore, it was certain that the crystalline phase kept unchangedafter reusing the catalyst in the transesterification reaction, because



10 20 30 40 50 60 70 80

Na2Al

2O

4

Al2O

3

d

b

c

a

Inte

nsity

/ a.

u.

2θ / Degree

Fig. 2. XRD pattern of γ-Al2O3 and 80% NaOH/γ-Al2O3 (a) γ-Al2O3, (b) first reusedNaOH/γ-Al2O3, (c) second reused NaOH/γ-Al2O3, and (d) third reused NaOH/γ-Al2O3.

Table 1Basic properties with different loading amounts of NaOH/Al2O3.

Entry Loading amount of NaOH (wt.%) Basic strength (H_) Basicity (mmol/g)

1 0 b7.2 /2 5 15.0–18.4a 0.533 10 15.0–18.4a 0.844 20 15.0–18.4 1.635 40 15.0–18.4 1.196 60 15.0–18.4a 0.567 80 9.8–15.0 0.508 100 ≥18.4 /

a The color of solution is slight mauve.

3R. Bai et al. / Fuel Processing Technology xxx (2012) xxx–xxx

the intensities of diffraction peaks varied very little after the third timeof reuse (Fig. 2a, b, and c).

Fig. 3 shows the FTIR spectra of γ-Al2O3 and NaOH/γ-Al2O3 withdifferent NaOH loading amounts. The peak at 1640 cm−1 was attrib-uted to the bending mode of \OH group of physically adsorbedwater, while the peak at 1450 cm−1 denotes the carbonate [32].The peak at around 3500 cm−1 corresponds to the stretching vibra-tion of Al–O–Na group and becomes broader with increasing loadingamount of NaOH [22].

The base sites over heterogeneous catalysts are active centers fortransesterification reaction [33,34]. Thus, it is important to under-stand the effects of basic strength and basicity of the catalysts onthe catalytic performance. The basic strength and the basicity of a se-ries of NaOH/γ-Al2O3 catalysts were measured by using a Hammettindicator, and the results were collected in Table 1. The parentγ-Al2O3 was acidic and could not convert the color of bromthymolblue. The basic strength was improved by introducing NaOH ontoγ-Al2O3 samples, the catalysts were proved to be capable of changingquickly the color of 2,4-dinitroaniline (H_=15.0) from yellow tomauve. But the catalysts, excepting 80%NaOH/γ-Al2O3, failed to convert4-nitroaniline (H_=18.4) to its conjugate base form. The resultsindicated that their base strength can be denoted as 15bH_b18.4.According to the definition of Tanabe, these samples can be regarded

4000 3500 3000 2500 2000 1500 1000 500

Wave number (cm-1)

Tra

nsm

itan

ce (

a.u.

)

d

c

b

a

Fig. 3. FTIR spectra of γ-Al2O3 and NaOH/γ-Al2O3 (a) γ-Al2O3, (b) 5% NaOH/γ-Al2O3,(c) 40% NaOH/γ-Al2O3, and (d) 80% NaOH/γ-Al2O3.


as strong bases [30]. However, in the case of 80% NaOH/Al2O3 catalyst,it only works for converting the color of phenolphthalein (H_=9.8)but is unable to convert 2,4-dinitroaniline (H_=15.0) to its conjugatebase form. Thus, its base strength can be denoted as 9.8bH_b15.

Furthermore, the basicity of the catalyst increased with increasingthe loading amount of NaOH and the maximum basicity (1.63 mmol)was achieved for 20% NaOH/γ-Al2O3. Increasing the loading amount ofNaOH led to the decrease of the basicity, suggesting that the excessNaOH could react with the γ-Al2O3 or cover the active sites on thecomposite surface [24]. This consists with the results reported by Wanget al. for KF/MgO catalyst [32].

The results for measured BET surface area and pore volume areshown in Table 2. It can be seen that the BET surface area and the porevolume decrease with the increase of the loading amount of NaOH, par-ticularly this tendency becomes quite appreciable when the alumina isloaded with 80% NaOH. The results indicated that introducing NaOHonto the support can damage the textural property of the support,which results in a decrease of surface area and pore volume. Further-more, the formation of sodium aluminate from the interaction of the al-kali metal compounds with the support is also responsible for thediminishing of surface area [28]. This phenomenon is in agreementwith that obtained from the XRD pattern.

3.2. Effect of loading amount of NaOH on the synthesis

The acid/base properties ofγ-Al2O3 can bemodified by loading othercompounds based on its textural properties, such as surface area, porevolume and pore-size distribution [18]. For example, γ-Al2O3 loadedwith KF, CexO andKNO3 has often beenused as solid base catalyst to cat-alyze the transesterification reaction [21–25]. In the present work,γ-Al2O3 loaded with various amounts of NaOH was prepared andstudied for the synthesis of GC from glycerol and DMC.

Itwas found that the catalytic performance ofγ-Al2O3was influencedby the loading amount of NaOH, results are shown in Table 3 aswell as inFig. 4. The neat γ-Al2O3 employed in the reaction leads to the conversionof glycerol at the level of 4.7%. The use of γ-Al2O3 loading with NaOHimproved the conversion of glycerol and the selectivity to GC. Further-more, it was found that the conversion of glycerol did not depend onthe loading amount of NaOH, while the loading amount of NaOH hada significant influence on the selectivity to GC. Especially, in the caseof 80% NaOH/γ-Al2O3, the selectivity to GC reached 99.0%.

Furthermore, the effect of catalyst amount on the conversion hasalso been investigated and the results are collected in Table 3. Theconversion of glycerol was depended on the applied amount of thecatalyst, whereas the selectivity to GC was almost retained stable at

Table 2BET surface area and pore volume.

Catalysts BET area (m2/g) Pore volume (cm3/g)

γ-Al2O3 194.5 0.48435% NaOH/Al2O3 181.8 0.469080% NaOH/Al2O3 21.7 0.1030



Table 3Effect of different catalysts on the synthesis.

Entry Catalyst % conversion ofglycerol

% conversiona ofglycerol

% selectivity of

GC Glycidol

1 No catalyst / / / /2 γ-Al2O3 4.7 2.1 / /3 NaOH/Al2O3 97.9 45.4 99.0 1.04 NaOH/Al2O3

b 93.7 42.7 98.6 1.45 NaOH/Al2O3

c 98.0 47.6 98.8 1.16 NaOH/Al2O3

d 73.5 40 98.7 1.37 K2CO3 94.3 45.8 95.5 4.58 NaOHe 93.8 47.1 32.3 30.2

Reaction conditions: temperature: 78 °C; the molar ratio of DMC to glycerol: 2; glycerol:0.1 mol; the amount of catalyst: 3.0 wt.% (based on glycerol); NaOH/Al2O3: 80%NaOH/Al2O3; and reaction time: 1.0 h.

a Reaction time: 20 min.b The amount of catalyst: 2.0 wt.%.c The amount of catalyst: 4.0 wt.%.d The molar ratio of DMC to glycerol: 1.e Unknown compound was detected.


99.0%. For the catalyst amounts of 2 and 4 wt.%, the conversion ofglycerol reached about 93.7% and 96.8%, respectively (entries 4 and5). For comparison, the catalytic activity of the homogeneous catalyst,K2CO3, was also examined in the model reaction (entry 7). In thiscase, the selectivity to GC reached 95.5%, which confirmed that thecatalytic performance of NaOH/γ-Al2O3 was better than that of K2CO3.

Previously, in the synthesis of biodiesel via transesterification, Xieand Baz found that a strong correlation exists between the basicityvalue of the synthesized catalysts and their activities. It was statedthat the biodiesel yield increases monotonically with increasing ba-sicity of the catalyst surface, whereas the biodiesel yield has no obvi-ous relation with the basic strength of the catalyst [22,23]. However,in the present work, we have found that the selectivity to GC isinfluenced by the basic strength of NaOH/γ-Al2O3 catalyst. It is probablyattributed to the fact that the strong bases (H_>15) led to the genera-tion of glycidol by intermolecular dehydration of glycerol, which hasbeen detected in the product mixture. Kim et al. investigated the rela-tionship between the catalytic performances of Na/NaOH/γ-Al2O3,NaOH/γ-Al2O3, and Na/γ-Al2O3 catalysts with their basic properties byusing CO2-TPD and XPS method. They found that the high catalyticperformance of Na/NaOH/γ-Al2O3 can be ascribed to its strong basicstrength [27]. Singh et al. also found the similar phenomena duringthe synthesis of biodiesel via transesterification reaction; the high yieldof biodiesel was achieved with PbO and PbO2 catalysts that had a weak

0 20 40 60 8070

80

90

100

40

60

80

100

Loading of NaOH (wt %)

Fig. 4. Effect of different loading amounts of NaOH on the synthesis. ■ conversion ofglycerol; ▼selectivity of glycerol carbonate; ● conversion of DMC. Reaction conditions:temperature: 78 °C; the molar ratio of DMC to glycerol: 2; glycerol: 0.1 mol; theamount of catalyst: 3.0 wt.% (based on glycerol); and reaction time: 1.0 h.


basic strength [35]. To confirm the above-mentioned speculation, NaOH(H_≥18.4)was adopted to test its catalytic performance for the synthesisof GC under the same reaction condition (entry 8). It was found that theselectivity to GC reached merely 32.3%.

Taking into account the results obtained from the catalyst charac-terization and activity test of NaOH/γ-Al2O3, we can conclude that thecatalytic properties of the catalysts were influenced by the basicstrength presented in the solid; the strong basic strength is not bene-ficial to the synthesis of GC.

3.3. Recycling of the reused catalyst

An important evaluating standard for the heterogeneous catalyst isits ability for recovery and reuse. The results of reused catalysts are listedin Table 4. It was found that the conversion of glycerol slowly decreasedwith the increase of reused times, the same trend for the conversion ofDMC was also obtained. However, the selectivity to GC was almost notchangedwhen the catalystwas reused for the fourth time, so the catalystshowed good recycling ability. The loss of activity might be attributed tothe leaching of ionic species (Na+, OH−) from the catalyst into productmixture as also reported with transesterification reaction [23,24].

In order to ascertain the reason for the decrease of the catalytic ac-tivity, the Na content in the liquid product mixture taken from the sec-ond run was detected by atomic absorption spectrometry method. Itwas found that the Na content in the product mixture was 12.1 ppm,which indicated the leaching of ionic species after reuse of the catalystand confirmed the influence on the slow decrease of the catalytic activ-ity of NaOH/γ-Al2O3 in the transesterification reaction.

3.4. Comparison of the catalytic activity of NaOH/γ-Al2O3 with otherreported heterogeneous catalysts

The yield of GC obtained from the transesterification of glycerolwithDMCwas comparedwith that obtained for other reported catalysts, andthe results are collected in Table 5. The solid base catalysts, exceptMgO,showed reasonable GC yield under mild reaction conditions. The activ-ity of present catalyst is comparable to KF/HAP and better than otherreported heterogeneous catalysts [18,20,32]. These results indicatethat NaOH/γ-Al2O3 is a promising candidate to replace homogeneouscatalysts for the synthesis of GC from glycerol and DMC via transes-terification reaction.

3.5. The proposed mechanism for transesterification of glycerol with DMC

Kim and Taufiq-yar have reported that sodium aluminate formedduring the reaction of NaOH and alumina exerted a basic character[27,36], which was also verified by the FTIR results and XRD analysisof fresh and reused catalysts. Based on this statement, sodium alumi-nate is proposed to be responsible for the surface active species in thesynthesis of GC. Recently, several reaction models were proposed todescribe the oil transesterification on catalyst surface based on theEley–Rideal type of mechanism [37,38]. Based on these models andthe experimental results, a plausible mechanism has been proposed(Scheme 1). Firstly, the basic sites of catalyst are involved in the

Table 4Recycling of catalyst used in the transesterification.a

Entry Numbersreused

Conversion ofglycerol (%)

Conversion ofglycerol (%)b

Conversion ofDMC (%)

Selectivityof GC (%)

1 1st 97.9 45.4 49.1 99.02 2st 96.8 44.8 48.2 96.43 3st 96.0 44.5 47.5 97.04 4st 94.7 44.0 47.1 95.4

a Reaction conditions: temperature: 78 °C; themolar ratio of DMC to glycerol: 2; glycerol:0.1 mol; the amount of catalyst: 3.0 wt.% (based on glycerol); and reaction time : 1.0 h.

b Reaction time: 20 min.



Table 5Comparison of the catalytic activity of NaOH/γ-Al2O3 with other reported heteroge-neous catalysts.

Catalyst Reaction time(min)

DMC/glycerola

GC yieldb

(%)Space time yield(mol/g cat h)

Ref.

NaOH/γ-Al2O3c 60 2 97 0.35 /

KF/HAP 50 2 99 0.42 [6]Mg/Al/Zr 90 5 94 0.07 [9]CaO 90 3.5 91 0.11 [15]MgO 90 3.5 12 0.01 [15]Hydrotalcite 60 5 82 0.01 [17]HTc-Mg0.25d 300 2 82 0.01 [29]

Space time: the yield of mol of GC formed per gram of the catalyst and unit of time.a Molar ratio.b GC: glycerol carbonate.c Present work.d Ethylene carbonate.

5R. Bai et al. / Fuel Processing Technology xxx (2012) xxx–xxx

activation of glycerol to produce glyceroxide anion (C3H7O3−). Subse-

quently, Lewis acid sites on the surface of the catalyst coordinate to thecarbonyl oxygen of DMC andmake the carbonyl carbon greatly positive-ly charged. This enhances the nucleophilic attack of the glyceroxideanion to form the methyl glyceryl carbonate intermediate (MGC) and amethoxide anion, and the proton abstracted by the base transfers tomethoxide anion to create methanol. Finally, MGC undergoes a cycliza-tion reaction through a nucleophilic attack of the oxygen anion fromthe secondary hydroxyl group to the carbonyl carbon, and then the GCwas obtained.

4. Conclusions

In summary, NaOH/γ-Al2O3 was prepared and investigated as aheterogeneous catalyst for the synthesis of glycerol carbonate fromglycerol and DMC. It was found that the catalyst has merits of highconversion of glycerol and high selectivity to glycerol carbonateunder mild reaction conditions. The catalytic performance of NaOH/γ-Al2O3 was better than that of homogeneous catalyst of K2CO3, andthe catalyst can be easily recovered and recycled. Thus, NaOH/γ-Al2O3 is a promising candidate to replace homogeneous catalystsfor the synthesis of glycerol carbonate via transesterification of glyc-erol with DMC.

Scheme 1. Proposed reaction mechanism for transesterification of glycerol with di-methyl carbonate.


Acknowledgment

The authors thank the Analytical and Testing Centre, HuazhongUniversity of Science and Technology, China for the characterizationanalysis.

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