SUNFLOWER OIL BLEACHING BY ACID-ACTIVATED BENTONITE

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1 Rcv. rcr. Quim. lng. Quim. Vol. O N 2, Pags. S - SUNFLOWER OIL BLEACHING BY ACID-ACTIVATED BENTONITE Edson Luiz Foletto, Sérgío Luiz Jahn, Cristina Volzone 2, Luismar Marques Porto3 Department o Chemical Engineering, Federal University o Santa Maria (UFSM), Brazil. z center o Technology o Mineral Resources and Ceramic, CETMIC (CIC-CONICET), Buenos Aires, Argentina. 3 Department o Chemical and Food Engineering, Federal University o Santa Catarina (UFSC), Brazil. Abstract Two bentonite clays with diieren! mineralogical compositions rom Mendoza, Argentine, were activated with H.SO, solutions o 4 and$ N at 90ºC or 3.5 hours. This treatment aected clay structural properties as was shown by the~ogravimetry, inrared spectrometry and chemical analysis. Bleaching eiciency or sunlower oíl was strongly dependen! on acid concentraton used or clay activation. The samples have bleaching capacity comparable to the standard. The mineralogical cornposition oí natural clays has inluenced the properties o activated clays. i i Keywords: Acid-treated clays, bentonile, oil bleaching l. INTRODUCTION Acid activated bentonites have been used as salid acid catalysts and catalyst supports or a number o organic applications that requires an extreme degree o reaction control o considerable industrial interest. -4 lt has also been used in the oodstus industry, sulphur production, orest and water conservation, in chemical industry, environmental protection, the paper industry 5 6 as well as or bleaching o vegetable oils. - 9 The bleaching o edible vegetable oils involves the removal o a variety o impurities wich include phosphatides, atty acids, gums, trace metals, etc. ollowed by decolorization. The bleaching capacity o bentonites is greatly increased by activation treatment. While sorne o these clays are naturally bleaching, sorne have to be treated with mineral acids. 0-3 Bentonite consists predominately o smectite a 2: clay mineral containing an octahedral sheet between two tetrahedral sheets. Smectite crystals are negatively charged due to the substitution o the trivalent aluminium ions by bivalent ions like Mg 2 + and Fe+ and substitution o tetrahedral s by Al3. 4 Activation proceeds with partía! dissolution o smectite and includes an initial replacement o the interlayer cations by H, ollowed by dissolution o the octahedra! and tetrahedral sheets with subsequent release o structural cations. This attack aiters the structure, chemical composition and physical properties o the clay while increasing the adsorption capacity. 5 Christidis et al. 8 examined the bleaching capacity and acid activation o bentonites rom Aegean, Greece. observing in a ive-old increase o the surace area o raw materials. The activated samples have been rendered suitable or bleaching o rapeseed oíl lt was determined that the optimum bleaching capacity in not associated with maximum surace area and the optimum conditions or activation are obtained using a variety o combinations o acid stregth and residence time. Despite numerous studies, no deinite relationship exists between the perormance o the acid-activated clay and the composition or properties o the original clay. Hence, each clay has to be speciically activated and tested or its perormance. 6 The preparation o acidactivated bentonite must be controlled in arder to obtain maximum bleaching capacity. 4 The present study deals with the acid activation o Argentine bentonites and testing o their bleaching capacity or sunlower oíl, in comparison with the bleaching capacity o a standard commercial bleaching clay. IL EXPERIMENTAL Two natural bentonites (named as K and W) rom two dierent deposits o the Mendoza province, Argentine, were used as the starting 5

2 " Rcv. Pcr. Quím. lng. Quím. Vol. O N Pags. 5 - materials. A commercial product, Tonsil, was used or the evaluation o the bleaching capacity o the experiments. Alkali-reined sunlower oil was gently donated by Bunge Alimentos S.A (Gaspar-SC, Brazil). The bentonite sample (40g) was treated with 400ml o 4 N or 8 N sulphuric acid (analytical grade) at 90ºC or 3.5h in an instantaneously stirred at a glass reaction vessel with relux. Ater the acid treatment, the sample was iltered and washed with distilled water until it would be ree o SO 4,_. The samples were dried at 60ºC or 2h and ground to pass through a 0.074mm sieve. Activated samples were designate~ as K4, K8, W4 and W8, where the numerical value indicates the concentration o acid solution used or the treatment. Bleaching experiments were conducted in a procedure analogous to that o the American oíl Chemical Society (AOCS) Oicial Method Ce 8a-52. The bleaching process was carried out under a vacuum o 450 mmhg at the constant temperature o OOºC with a contact time o 30min. Stirring and heating were carried out by means o on electric heating band wrapped and a mechanic stirrer. The ratio o the mass o clay to the vol u me o acid solution was : O (w/v). During the bleaching, a stream o N 2 was maintained above the oil surace. The hot oil and clay mixture was iltered under vacuum and the color o the bleached oil was measured spectrophotometrically (WFJ525-W UV-visible spectrophotometer). The bleaching capacity percentage (BC) o the clays was determined rom the equation 7 : [(A 0 -A)/A 0 ] X 00 where "A " 0 and "A" are the absorbance o neutral oíl and bleached oil, respectively, at the maximum absorbance o the neutral oil (at wavelength 420nm). The structural changes o the Argentinean acid bentonites were examined by means o thermogravimetric (TGA) and inrared spectrometric (IR) anaiyses and chemical analysis (XRF). TGA was perormed with a Netzsch STA 409 thermal anayzer at a heating rate o OºC.min under a low o atmospheric air o 35ml min-, in the temperature range 25- OOOºC. IR spectra were recorded in the region cm i with a Perkin-Elmer 6 PC spectrophotometer, using the KBr pellet technique. Chemical compositions o the samples were determined by X-ray luorescence technique with a Philips PW 2400 spectrometer.. RESULTS ANO DISCUSSION The mineralogical compositions o two clay samples were determined by Foletto et al. 8 Smectite is the main clay mineral in both samples (35% in K and 4 7% in W). The K bentonite contains quartz and eldspar as impurities, whereas W bentonite contains also gypsum and kaolinite. Table N shows the chemical analysis o the bentonites ater treatments with suluric acid. The interlayer cations o the bentonites were removed. The residual Ca 2, Na+ and K are dueto the presence o impurities such as micas and eldspars, which are insoluble in acid medium. 9 Part o the Mg 2, Fe 2 3 and Al 3 + was removed rom the octahedral sheet. Ti 4... cations remain were insoluble. The increase o Si 4 and the reduction o the octahedral cations, which were originated by an increase o the acid concentration resulted in an increase o the Si/(AI+ Mg +Fe) ratio. The loss o weight by dehydroxylation (%) o the samples was obtained rom TGA curves in the range ºC (Figure N ); the TGA curves were used ar the evaluation o the attack o the octahedral sheets ater acid treatment (Table N 2). The octahedral sheet destruction was calculated as a relative reduction percentage ot the weight loss, with respect to the original sample. The activated K samples showed 4 to 9% o destruction o the octahedral sheet, while the activated W samples showed 2 to 5% o destruction. These results showed that even at high acid concentration (i.e., concentration o 8 N), the structures o smectites were not totally destroyed. Figure Nº 2 shows the inrared spectra o the original and the acid treated bentonites. No important changes were observed, although the bands Si-O-Al (525 cm- ) and Si-O-Si (465cm ) were modiied. The intensity ratios o both bands are shown in Table Nº 3. Table Nº 3 presents the results o the characterizations o the natural and activated samples and bleaching o the sunlower oil. Figures Nº 3, 4 and 5 show the relation between the structural changes and bleaching capacity o the bentonites. The results o the analyses indicate that an increase o the acid concentration causes a greater attack on the bentonite structure, and consequently improves the bleaching capacity. The level o clay attack was bigger or the K that the W sample. 52

3 Rcv. Pcr. Quim. lng. Quim. Vol. O J\ 2, Pags. 5 - Table Nº. Results o XRF analysis, expressed as oxides (%). Sample Si0 2 Alp 3 Fe MgO Ca O Na 2 0 K 2 0 Ti0 2 MnO r K K K w W W r: 5 - / (AJ3 + Mg2-+Fe 2 -"-) ratio. { t. [ í.a loe i I" rn-o-2"00_ 3.,.0_0_4_,or-o-5,...00_6.,.0_0_70.-o_a, ,00-w- ooo ~ Temperature ( C) Figure N. TGA curves o the natural and activated samples. Table N 2. Results obtained o TGA curves. Sample Weight loss range Octahedral sheet e destruction (%) K 2.69 O.DO K K w 3.28 O.DO W W Wavenumber (cm Figure N 2. lnrared spectra o natural and activated samples. Table N 3. Slruclural changes and oíl bleaching capacity o natural and activated samples. Sam ple IR!I CAC 2 TGC3 BC (%) Sunlower K 0...: K K8 O w W W () Si-O-Al/S-0-Si ratio (obtained rom IR spectra, Figure Nº 2). (2) Si/(Al+Mg+Fe) ratio (obtained rom chemical analysis, Table N ). (3) Octahedral sheet destruction (%) (obtained rom TGA curves, Table Nº 2). (4) Bleaching capacity (BC) in sunlower oil. The acid activated K bentonites showed a slightly superior bleaching capacity than the acid W bentonites and this behavior could be attributed to the higher acid attack o the K smectite structure when compared to the W smectite. Comparing the mineralogical compositions, the sample K presents more MgO content than sample W. lt has been observed that smectites with greater MgO contents in their structure are more activated by mineral acids than!hose smectites with minor MgO content. 20 An optimization in the experimental conditions o acid treatment o the W bentonite probably would cause a higher attack in its structure and consequently would lead to a better adsorptive capacity, because this sample has higher clay content than K bentonite. 8 53

4 ,. Rcv. Pcr. Quim. lng. Quim. Vol. O N Pags. 5 - The best bleaching capacity results o the activated bentonites obtained in this paper were compared with a commercial sample, as shown in Table Nº 4. The retention o color impurities rom sunlower oíl by Tonsil (commercial sample) were similar to the bentonites treated with 8N sulphuric acid. IV. CONCLUSION Attack on the bentonite structure as a result o the suluric acid treatment is strongly dependent on the acid concentration. These treatments etects under clay structural properties were tested by thermogravimetric, inrared spectromeijc analysis and chemical analysis. The activated samples were tested in arder to veriy their bleaching capacity in sunlower oil and were compared to a standard commercial bleaching clay. Bleaching eiciency was strongly dependent on acid concentration used ar clay activation. The treated samples ha ve shown a bleaching capacity compared to the standard. The mineralogical composition o natural clays have inluenced the properties o treated clays and these properties increased its bleaching power. ~:: K!. : g_ 35-j c:3 30 j 0>25.!: 20 ~ ro , ~...,.,_J natural clays _J Q , ,..-~-.-~-,-~ 0,0 0,5 0,20 0,25 0,30 0,35 0,40 0,45 Si-O-Al I Si-O-Si ratio Figure N 3. Bleaching capacity vs. Si-O-Al I Si-O-Si ratio. ~ 50.._, ~ 45 ~ 40 g. 35 u 30 gi 25 :.e 20 (.) 2 5, W4:Jt,,,, 5i \.,_ natural clays o~~~~~~~~-.-~~~~~--< ,5 4,0 4,5 5,0 5.5 Si / Al+M +Fe ratio en 0 *. t Figure N 5. Bleaching capacity vs. Si I (Al+Mg+Fe) ratio. Table N 4. Bleaching capacities o Tonsil and prepared acid bentonites (K8 and W8). Sample BC (%) Sunlower Ton sil K \IV Acknowledgments Financial support o CAPES and CNPq, Brazilian governmental agencies ar education and research, and PIP0200-CONICET, Argentina are thankully acknowledged REFERENCES. Mokaya, R. and Jones, W. Journal o Catalysis, , Breen, C.; Zahoor, F.D.; Madejová, J. and Komadel, P. Joumal o Physical Chemistry B, 27, 5324, Volzone, C. ; Masini O.; Comelli, N. A. ; Grzona, L. M.; Ponzi, E. N. and Ponzi M. l. Applied Catalysis A: General, 2. 23, 200. l50 :::- 45 K4 WB ;~ :; 40.. ~ - - ro,,,,.., g.35 -<-* natural clays,--:;:-- w 4 -~ 25i I.-;:::.--.t= 20 ~!. -: -- ~ 5 i/.-;::- (].) ro io, 5) 54 - K8 o +~~~--.~~,--~.-~.-~-.-~-; o Octahedral sheet destruction (%) Figure N 4. Bleaching capacity vs. octahedral sheet destruction Foletto, E. L.; Valentini, A.; Probst, L. F. D. and Porto, L. M. Latin American Applied Research, 32, Clarke, G. M. Special clays. Industrial Minerals, 26, 25, 985. ODriscoll, M. Industrial Minerals, 250, 43, 988. Srasra. F.; Bergaya, H.; van Damme, H. and Ariguib, N. K. Applied Clay Science, 4, 4, 989. Christidis, G. E.: Scott, P. W and Dunham, A. C. Applied ClayScience, 2,

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