Modification of vermiculite by polymerization and carbonization of glycerol to

8/7/2019 Modification of vermiculite by polymerization and carbonization of glycerol to

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Modification of vermiculite by polymerization and carbonization of glycerol toproduce highly efficient materials for oil removal

Miguel de Arajo Medeiros, Maria T.C. Sansiviero, Maria Helena Arajo, Rochel Montero Lago Departamento de Qumica, ICEx, UFMG, Campus-Pampulha, 31270-901 Belo Horizonte, MG, Brazil

a b s t r a c ta r t i c l e i n f o

Article history:

Received 18 February 2009

Received in revised form 18 May 2009Accepted 8 June 2009Available online 13 June 2009

Keywords:

VermiculiteGlycerolPolymerizationCarbonization

Impregnation and reaction of glycerol (Gly) on the surface of expanded vermiculite (EV) was used to producea highly efficient absorbent to remove water spilled oils. The vermiculite was impregnated by glycerolcontaining 1, 2 and 4 mol% of H2SO4 at EV/Gly ratios, i.e.1/1, 1/2 and 1/3, and heated to 380, 580 and 750 C.SEM, TG, BET specific surface area, and Raman analyses indicated that glycerol at 380 C forms a polymerlayer. At higher temperatures, the polymer decomposed to form porous carbon covering the EV surface.These materials were investigated for the removal of three different oils, i.e. diesel, soybean and engine oilspilled on water. The obtained results showed a remarkable increase on oil removal of 600% compared to thenon-modified EV.

2009 Published by Elsevier B.V.

1. Introduction

Vermiculite canbe expanded or exfoliated to producea material witha highly porous structure (Santos, 1975; Santos and Navajas,1976; De laCalle andSuquet,1988; Bergaya et al., 2006). This vermiculite (EV) floatson the water surface(Santos,1975) andshows greatpotential to removespilled oil due to the strong capillary action of the slit shaped pores(Martins, 1990; Leo et al., 1996; Machado, 2000). Nevertheless, thehydrophilic nature of the EV surface leads a low oil removal. Severalmethods to producemorehydrophobicEV with higheroil adsorption arebased on polymer coating (Folke and Karlsson, 1995; Hluchan, 2002;Machadoet al., 2006a,b), carnaubawaxcoating(Mysore et al., 2004)andsurface modification (Martins,1990; Martins, 2005; Bergaya et al., 2006;Machado et al., 2006a,b).

In this study, glycerol polymerization and carbonization was usedto modify the EV surface. Glycerol is a co-product of the biodieselprocess with an estimated production of 100ML in 2015, only in Brazil(Klepacova et al., 2003; Dasari et al., 2005; Karinen and Krause, 2006;Behr et al., 2008; ANP, 2009). Due to economical and environmentalissues related to this large amount of glycerol produced, novelapplications are strategically important for the biodiesel program allover the world.

Glycerol can be condensed in the presence of acidic and basiccatalysts to produce ether type oligomers with two up to five units

(Seiden and Martin, 1976; Jakobson et al., 1988; Eshuis et al., 1994;Roberts etal.,1995; Jeromin etal.1998; Barraultetal., 2001; Clacens etal.,

2002; Lemke, 2003; Kraft, 2003; Barrault et al., 2004, 2005; Behr et al.2008; Medeiros et al., in press). Recent work in our laboratories showedthat glycerol can be further polymerized to a hydrophobic, crosslinked,highly resistantthermofixresin(Medeiros et al., 2008). Thispolyglycerolresin can be pyrolyzed to produce porous carbon.

Wedescribethe behaviorof EV covered with polyglycerol (PG) andEV covered with a porous carbon layer (Fig. 1).

2. Experimental

Glycerol P.A. (272816 mmol), H2SO4 (2.7210.88 mmol) and 5 gof exfoliated vermiculite (EV) were mixed in a glass reactor of 200 mLequipped with a cold trap to collect the volatiles. The system washeated in an oven at 30 C min1 up to 380, 580 or 750 C.

The vermiculite was obtained from Catalo (Brazil). The granulo-metric fraction used was 0.30.6 cm. The approximate compositionobtained by SEM/EDS microprobe was: (Al0.30Ti0.04Fe0.63Mg2.00)(Si3.21Al0.79)(O10(OH)2Mg0.13Na0.02K0.10(H2O)n). The exfoliation wascarried out by introducing the vermiculite in a quartz tube at 800 Cfor 60 s.

The modified vermiculites were prepared with EV/glycerol (gly)ratio of 1/1 and were prepared using glycerol containing 1, 2 and4 mol% H2SO4. These EV/gly samples were heated to 580 C for 1 hunder N2 and named hereon as G1S1-580, G1S2-580 and G1S4-580(where G1= glycerol/EV mass ratio 1/1, S1 sulfuric acid 1 mol%heated to 580 C). All the obtained samples were black in colorsuggesting the formation of carbonaceous materials.

Applied Clay Science 45 (2009) 213219

Corresponding author. Departamento de Qumica, Universidade Federal de MinasGerais, Belo Horizonte, MG, 31270-901, Brazil. Tel.: +55 31 34095719; fax: +55 3134095700.

E-mail address: [email protected] (R.M. Lago).

0169-1317/$ see front matter 2009 Published by Elsevier B.V.

doi:10.1016/j.clay.2009.06.008

Contents lists available at ScienceDirect

Applied Clay Science

j o u r n a l h o m e p a g e : w w w. e l s ev i e r. c o m / l o c a t e / c l a y
mailto:[email protected]://dx.doi.org/10.1016/j.clay.2009.06.008http://www.sciencedirect.com/science/journal/01691317http://www.sciencedirect.com/science/journal/01691317http://dx.doi.org/10.1016/j.clay.2009.06.008mailto:[email protected]


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The modified vermiculites were characterized by: (a) BET specificsurface area (22 cycles N2 adsorption/desorption in an Autosorb 1Quantachome); (b) powder XRD (Rigaku, model Geigerflex, with Nifiltered Cu-K =1.54184 , 4 min1); (c) thermogravimetricanalyses (Shimadzu TGA60 simultaneous DTATG), under air and N2atmosphere with heating rate of 10 C min1; (d) scanning electronmicroscopy (SEM) in a Jeol-84A with Au sputtering coated samples

fixed in a carbon tape; (e) Fourier transform infrared (FT-IR) spectros-copy, using a Perkin Elmer Spectrum GX FT-IR System and (f) Ramanspectroscopy using a Renishaw INVIA, with lens 50 and opening of0.55. The mercury porosimetry measurements were performed in aQuantachrome type PoreMaster 60 porosimeter.

The sorption experiments were carried simulating an oil spillingsituation using 15 mL of contaminant, i.e., diesel, soybean andengineoil,in 100 mL water understirring.Amounts of 0.5 gof modified vermiculitewere added to thesuspension. After 3 minthe modified vermiculitewasremoved and the excess of the contaminant present on the modifiedvermiculite surface wasremovedin a sieve.The sorbedoil wasmeasuredby weighting. All the sorption tests were carried out in triplicate.

3. Results and discussion

ESI-MS (electrospray ionization mass spectrometry) showed thatat 280 C oligomerization to di, tri and tetraglycerol and polymeriza-tion to larger molecules took place during the first hours of reaction(Fig. 2).

The reaction formed a highly resistant thermofix resin composedof a crosslinked polyether (Scheme 1).

At 300400 C small amounts of carbon were formed. At highertemperatures polyglycerol decomposed to porous carbon (Scheme 1).

Pure EV showed flat layers with small fragments on the edges(Fig. 3). G1S1-580 and G1S2-580 (Fig. 3bd) had irregular deposits onthe surface with 0.54.0 m long needle-like structures.

SEMimages of G1S2-580 andG2S2-580(Fig.4b andc) were similarto those displayed in Fig. 3. However, a porous structure completelycovered the EV layers of G3S2-580 (Fig. 4c and d).

SEM images of G1S1 showed that the needle shaped structurespresent at 380 and 580 C (Fig. 5ac) were completely destroyed at750 C (Fig. 5d).

The specific surface area BET measurements, to samples EV, G1S1-380, G1S1-580, G1S1-750, G1S2-580, G1S4-580, G2S2-580 and G3S2-580, indicated that the carbon deposits did not affect significantly thespecific surface area (ca. 3, 2, 4, 4, 4, 5, 3 and 3 m2.g-1, respectively),especially micro and mesopores. On the other hand, a significantincrease on the macroporosity was observed by mercury porosimetryfor G1S1-580 and G1S1-750 which increased from 1.2 cm3g1 for EVto 1.7 and 1.9 cm3g1. In fact, visual inspection of the samples afterreaction with glycerol showed further expansion to almost twice theoriginal volume.

EV showed above 400 C a small mass gain probably associatedwith some oxide formation followed by a mass loss likely related tothe dehydroxylation and carbonate decomposition (Fig. 6).

G1S1-380 showed a mass loss of ca. 10% up to ca. 620 C likely dueto the decomposition/oxidation of the polyglycerol and mainly to theoxidation of carbon deposits. Carbon contents estimated from the TGanalyses for the different samples are shown in Fig. 7.

The G1S1 series showed a decrease on the carbon content from 10to 4% between 380 and 750 C. The higher temperature should lead toa further decomposition of polyglycerol to volatile compounds. Asexpected, the carbon content decreased from ca. 17 to 4%, when theGly/EV ratio decreased from 3:1 to 1:1.

In the XRD diagrams (Fig. 8) the main EV reflection at 25.8(d=0.354 nm) remained present in all samples. Thus, the modifica-tion of vermiculitedid notaffect significantly the vermiculite structure.In general, reflection intensities after modification decreased. Somesmall reflections disappeared likely due to the carbon layer.

The EV showed no Raman signal while all modified vermiculitesexhibited a band at ca. 1587 cm1 (Fig. 9). As the samples were black,this band, termed G band related to tangential vibration modes,suggests the formation of graphitic structures (Reich and Thomsen,

2004). A band at ca. 1386 cm1

is likely related to defect carbonstructures, such as amorphous carbon termed band D (Reich andThomsen, 2004; Tuinstra and Koenig, 1970; Wang et al., 1990). As thetemperature increased to 580 and 750 C the intensity of both bandsincreased due to enhanced formation of carbon. Although the carbonformation mechanism is not clear, it is likely related to the thermaldecomposition of polyglycerol. Typical Raman bands of glycerol and

Fig. 1. Modification of vermiculite by catalytic polymerization of glycerol and carbonization.

Fig. 2. Polymerization of glycerol at 280 C in the presence of 1 mol% H2SO4 monitoredby ESI-MS (detail: glycerol consumption during the reaction).

Scheme 1. Formation of carbon by thermal decomposition of polyglycerol.

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Fig. 3. SEM images: (a) EV; (b) G1S1-580; (c) G1S2-580; (d) G1S4-580.

215M. de Arajo Medeiros et al. / Applied Clay Science 45 (2009) 213 219


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Fig. 4. SEM images: (a) EV, (b) G1S2-580; (c) G2S2-580; (d) G3S2-580.



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Fig. 5. SEM images: (a) EV; (b) G1S1-380; (c) G1S1-580; (d) G1S1-750.



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polyglycerol, between 1000 and 1500 cm1, corresponding, i.e. thebond vibration CCO (1054 and 1115 cm1) and vibration of OHprimary groups (1149 and 1109 cm1) (Mudalige and Pemberton,2007; Mendelovici et al., 2000) were not observed. These resultssuggest that most of the polyglycerol decomposed.

The results of oil sorption experiments are shown in Fig. 10.EV absorbed similar amounts of the different oils with approxi-

mately 0.81.2 goil/gEV. When EV was impregnated with glycerol (Gly/EV=1/1) and heated at 380 C, the oil sorption capacity increasedalmost twice to ca. 2 goil/gEV. As the temperature was increased to 580and 750 C oil sorption reached 45 goil/gEV. Soybean oil sorption canbe used to compare this efficiency with previous data published. Somecare must be taken in comparing different vermiculites and differentexpansion procedures. Nevertheless, the modified EV showed higheroil sorptioncomparedwith several EV based materialsin the literature.For example, soybean sorption has been reported as 2.2 goil/gEV(Machado et al., 2006a,b), 3.1 goil/gEV (Martins, 1990, commerciallyavailable) and 4.1 goil/gEV (Mysore et al., 2004).

This increase in oil removal (25 goil/gEV) is likely related to theextensive carbonization of the polyglycerol at 750 C which produced

a much more hydrophobic carbon surface.As the H2SO4 concentration was increased from 1 to 2 and 4 mol%,

no significant differenceof soybean oilsorptionwas observed (Fig.11).Apparently, the carbonizationwas not stronglyaffected by the amountof catalyst when exceeding 1 mol%. Without H2SO4 no reaction tookplace and the glycerol was completely lost by evaporation.

As larger amounts of glycerol were impregnated on EV (sampleG2S2-580 and G3S2-580) only a small increase on the oil sorption wasobserved. These results clearly indicate that the sorption capacity did

Fig6. TG curves in air for EV, G1S1-380, G1S1-580,G1S1-750,G1S2-580,G2S2-580, andG3S2-580 (in detail DTA).

Fig. 7. Carbon contents determined from TG data.

Fig. 8. XRD diffractograms of EV-580, G1S2-580, G2S2-580, G3S2-580 and G1S1-750.

Fig. 9. Raman spectra of pure EV and G1S1-380, G1S1-580 and G1S1-750.

Fig. 10. Effect of temperature on the sorption of soybean, diesel and engine oil.



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not depend strongly on the glycerol content above the ratio 1/1.Probably, the sorption capacity depends on the formation of a carbonlayer covering the EV surface and this layer is already formed for theGly/EV ratio 1/1.

4. Conclusion

Glycerol in the presence of H2SO4 as catalyst was polymerized ontheexpanded vermiculitesurface at 380, 580 and 750 C. This reactionproduced a polymeric layer at lower temperatures which carbonizedat higher temperature. The products showed remarkable oil sorptioncapacity of ca. 500% for soybean, engine and diesel, especially afterheating to 750 C (sample G1S1-750) due to the formation of ahydrophobic carbon layer.

Acknowledgements

The authors are grateful to CNPq, CAPES, FAPEMIG and UFMG for

the research funds.

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Fig. 11. Effect of H2SO4 concentration and Gly/EV ratio on the sorption of soybean oil.


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