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Statistical modelling of acid activation on cotton oil bleaching by Turkish bentonite
Journal of Food Engineering 75 (2006) 137–141 www.elsevier.com/locate/jfoodeng
Statistical modelling of acid activation on cotton oil bleaching by Turkish bentonite E. Gu¨lsßah Kirali, Oral Lac¸in
*
Atatu¨rk University, Department of Chemical Engineering, Centrum, 25240 Erzurum,Turkey Received 13 February 2005; accepted 5 June 2005 Available online 8 August 2005
Abstract The aim of the study was to determine the highest bleaching capacity and derive a model for acid activation of a Turkish bentonite using a full factorial design. The selected factors were contact time, solid to liquid ratio, acid concentration and moisture of bentonite. A first-order model is obtained by using 24 full factorial design. Auxiliary experiments for the second-order model were conducted according to an orthogonal central composite design. An experimental test carried out using a factorial design 24 indicated that contact time, solid to liquid ratio and moisture of bentonite have a positive effect, whereas acid concentration has a negative effect. Furthermore, the highest bleaching capacity was found to be 74.2%. Ó 2005 Elsevier Ltd. All rights reserved. Keywords: Bleaching; Activated bentonite; Factorial design; Neutralized cotton oil
1. Introduction In crude edible oil refining, the bleaching treatment is a critical step. After its degumming and neutralization during the refining process, crude edible oil still contains undesirable impurities such as phospholipids, soap, trace metals, carotenoids, xanthophylls, chlorophyll, tocopherols and gossypol. These impurities not only degrade quality of the oil by alteration of its taste and color, but also effect its market value by giving it a color that will not be appreciated by the consumer. The removal of these impurities improves the sensory quality and oxidative stability of the deodorized oil (Boukerrouı & Ouali, 2002). Bleaching clays are by far the most common adsorbents for decolourization of edible oils. They consist of hydrated aluminium silicates. Starting material for *
Corresponding author. Tel.: +90 4422314554; fax: +90 2360957. E-mail addresses: [email protected], [email protected] (O. Lac¸in). 0260-8774/$ - see front matter Ó 2005 Elsevier Ltd. All rights reserved. doi:10.1016/j.jfoodeng.2005.06.010
the production of bleaching clay is the clay rock called bentonite (Rossi, Gianazza, Almprese, & Stanga, 2003; Srasra & Trabelsi-Ayedi, 2000; Taylor, Jenkins, & Ungermann, 1989). Bentonite consists predominately of smectite a 2:1 clay mineral containing an octahedral sheet between two tetrahedral sheets. Smectite crystals are negatively charged due to the substitution of the trivalent aluminium ions by bivalent ions like Mg2+ and Fe2+ and substitution of tetrahedral Si4+ by AI3+ (Study group, 2001). Bentonites are highly valued for their properties, which stem from their high surface area and their tendency to absorb water in the interlayer sites. These properties are enhanced with acid activation (Christidis, Scott, & Dunham, 1997). If the natural bentonite is treated with acid, the cations between the layers of the montmorillonite crystal are replaced by protons of the mineral acids (Study group, 2001) and the structure is partially destroyed (Christidis et al., 1997). Ca-bentonite + 2Hþ $H-bentonite + Ca2þ
138
E.G. Kirali, O. Lac¸in / Journal of Food Engineering 75 (2006) 137–141
Some studies on the performance of acid activated clay and the factorial design method in this study were found in the literature. Gannouni, Bellagi, and Bagane (1999) examined the optimum conditions for acid activation of a clay using an orthogonal central composite design in order to bleach olive oil. The selected variables were temperature, reaction time, initial acid concentration and liquid/solid weight ratio. The results obtained from the experiments showed that the last is the most significant factor in the activation process followed in the decreasing order of importance, by time, temperature and initial acid concentration. Chegrouche and Bensmaili (2002) investigated the removal of Ga(III) from the aqueous solution by adsorption on activated bentonite using a factorial design 23 and it was determined that pH and mass of bentonite have a positive effect, whereas temperature has negative effect. Christidis et al. (1997) examined the bleaching capacity and acid activation of bentonites from the islands of Milos and Chios, Aegean, Greece, consisting of chambers and Tatatilla-type and Otay-type montmorillonite, respectively, resulted in a four- to five-fold increase of the surface area of the raw materials. The activated materials have been rendered suitable for bleaching of rapeseed oil through removal of b-carotene. It was determined that the optimum bleaching capacity is not associated with maximum surface area and the optimum conditions for activation are obtained using a variety of combinations of acid strength and residence time. Despite numerous studies, no definite relationship exists between the performance of acid activated clay and the composition or other properties of the original clay. Hence, each clay has to be specifically activated and tested for its performance (Hymore, 1996). Although Turkey has rich bentonite reserves which is used in activated clay production, the studies on activated clay production have not reached the desired level yet. With this purpose, the utilization of bentonite obtained from Arguvan–Malatya region was investigated for bleaching of neutralized cotton oil. The aim was to determine the highest bleaching capacity and derive a model for acid activation of a Turkish bentonite using a full factorial design.
2. Experimental 2.1. Design of experiments Factorial design is widely used in statistical planning of experiments to obtain empirical linear models relating process response to process factors (Pradymna, Nail, & Das, 2000; S ß ayan & Bayramog˘lu, 2004). 2n factorial design, where each variable runs at two levels, is often used
to obtain first-order models. If the variance analysis indicates that overall curvature is significant, auxiliary experiments are carried out to develop a second-order model. Among the various second-order designs, the orthogonal central composite design is widely used as it only requires 2n additional runs (Myers, 1971). A full factorial design was selected to study the influence of the different factors (e.g. contact time, solid to liquid ratio, acid concentration and moisture of bentonite) on the bleaching efficiency of bentonites. 2.2. Materials The natural bentonite originated from Arguvan (Malatya–Tu¨rkiye). It was crushed using a jaw crusher and ground to pass through a 75 lm sieve (200 mesh ASTM) using a porcelain mill. The chemical composition of the Turkish bentonite was determined by XRay fluorescence spectroscopy (XRF, ARL 9800 XP) as follows: (wt.%); SiO2: 45.48, Al2O3: 17.70, Fe2O3: 8.22, CaO: 6.05, MgO: 4.01, Na2O: 3.84, K2O: 2.51 and loss on ignition (LOI): 10.95. X-ray diffraction patterns of Turkish bentonite was obtained using a Rigaku 2000 JCPDS DMAX (29– 1490) diffractometer (XRD) with CuKa radiation (30 kV and 30 mA and automatic monochromator) at a scanning rate 2h of 2° min1. The diffraction patterns of Turkish bentonite before and after activation, which are obtained at the highest bleaching capacity, are given in Fig. 1. The specific surface area of Turkish bentonite before and after activation, which are obtained at the highest bleaching capacity before and after activation was measured by using the BET-N2 method. The specific surface areas before and after activation were found to be 15.64 and 38.32 m2 g1, respectively. The neutralized cotton oil was provided by Doyasan Oil Comp. in Erzurum (Tu¨rkiye). All chemicals used were analytical grade. 2.3. Methods 2.3.1. Acid activation The experimental set up consists of a rotary evaporator, round-bottom three-necked flask, mechanic stirrer, vacuum pump, thermometer and a constant temperature circulator. Activation was carried out in HCI concentrations varying from 1 to 5 N at the temperature of 95 °C ± 1 °C and solid to liquid ratio of 0.1–0.5 g mL1. Contact time was 2–6 h and the moisture of bentonite was 4–12%. The suspension was cooled in air and filtered off and then washed several times with distilled water to remove excess Cl ions and dried in constant weight at 100 °C. These acid activated bentonites were used to bleach the neutralized cotton oil. The chemical
E.G. Kirali, O. Lac¸in / Journal of Food Engineering 75 (2006) 137–141
139
Fig. 1. The diffraction patterns of Turkish bentonite obtained the highest bleaching capacity before and after activation.
analysis of the bentonite obtained at the highest bleaching capacity was (wt.%); SiO2: 69.99 Al2O3: 12.53, Fe2O3: 2.16, CaO: 1.94, MgO: 0.22, Na2O: 4.44, K2O: 2.70 and LOI: 4.40. 2.3.2. Bleaching Bleaching experiments were performed in a roundbottom three-necked flask equipped with a stirring rod. The acid-activated bentonite was added to the oil for 20 min at about 80 °C (under reduced pressure). The acid activated bentonites/oil ratio was 2 (wt.%) (these values are used in factory processing). As soon as bleaching was finished, the bleached oil was separated by filtration at 50 °C. Care must be taken that the filtrate be clean of solid particles. The samples were kept in coloured bottles. The colour changes in the treated oils were determined spectrophotometrically at the best wavelength of 408 nm (Shimadzu UV160A). Results were calculated as b-carotene equivalents after comparison against a calibration curve prepared with 0–20 mg L1b-carotene solutions in petroleum ether. For this purpose, the bleaching capacity of the activated clays was determined from the following equation: The readings from spectrums were repeated three times and then the average was taken. C0 C Bleaching capacity ð%Þ ¼ 100 C0 where C0 is the concentration (mg L1) of b-carotene in the neutralized cotton oil at a wavelength of 408 nm and C is concentration (mg L1) of b-carotene in the neutralized cotton oil at a wavelength of 408 nm.
3. Results and discussion In order to determine the optimum conditions and derive a model for acid activation of a Turkish bentonite, a full factorial of the type 24 has been used. Contact time (X1), solid to liquid ratio (X2), acid concentration (X3) and moisture of bentonite (X4), were chosen as independent variables to model. Factor levels are shown in Table 1. The matrix for four variables is varied at two levels (+1 and 1). The higher level of variable was designed as ‘‘+’’ and the lower level was designed as ‘‘’’. Initially, the 24 full factorial design was used to obtain first-order model with interaction terms. As usual, the experiments were performed in random order to avoid systematic error. In addition, three central replicates were also added to the experimental design to calculate pure experimental error. The bleaching capacity (%) is given in Table 2. A first model with interaction terms was chosen to fit the experimental data Y ¼ b0 þ b1 X 1 þ b2 X 2 þ b3 X 3 þ b4 X 4 þ b5 X 1 X 2 þ b6 X 1 X 3 þ b7 X 2 X 3 þ b8 X 2 X 4 þ b 9 X 1 X 2 X 3
ð1Þ
Table 1 Factor levels used in the full factorial design Factors
Low level ()
High level (+)
Medium level (0)
Contact time (h) (X1) Solid to liquid ratio (g mL1) (X2) Acid concentration (N) (X3) Moisture of bentonite (%) (X4)
2 0.1 1 4
6 0.5 5 12
4 0.3 3 8
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Table 2 Experimental design and bleaching capacity of activated bentonite Experiment no.
X1
X2
X3
X4
% Bleaching capacity
6 7 12 9 1 8 13 4 5 10 16 2 11 14 3 15 10 20 30
+ + + + + + + + 0 0 0
+ + + + + + + + 0 0 0
+ + + + + + + + 0 0 0
+ + + + + + + + 0 0 0
28.2 26.3 28.4 73.7 41.7 23.6 42.0 43.5 28.8 24.7 40.6 42.9 20.3 13.0 74.2 53.9 30.3 31.3 29.7
Table 4 Experimental design for second-order model and bleaching capacity of activated bentonite Experiment no.
X1
X2
X3
X4
% Bleaching capacity
19 17 23 20 18 22 24 21
+1.547 1.547 0 0 0 0 0 0
0 0 +1.547 1.547 0 0 0 0
0 0 0 0 +1.547 1.547 0 0
0 0 0 0 0 0 +1.547 1.547
5.0 10.6 54.3 54.7 22.0 46.6 49.8 10.8
ratio, contact time for 6 h, 1 N HCI concentration and 4% moisture. The lowest bleaching capacity was also obtained for activated bentonite at 0.1 solid to liquid ratio, contact time for 2 h, 1 N HCI concentration and 4% moisture of bentonite.
where Y is the bleaching capacity (%), b0–b9 are the interaction coefficients and X1–X4 are dimensionless coded factors for the variables. The first-order model obtained by variance analysis conducted at 95% confidence interval is as follows: Y ¼ 36.69 þ 0.63X 1 þ 8.70X 2 2.28X 3 þ 1.95X 4 þ 3.41X 1 X 2 9.59X 1 X 3 9.74X 2 X 3 1.74X 2 X 4 1.75X 1 X 2 X 3
ð2Þ
The analysis of variance revealed that the overall curvature effect was significant; therefore, the orthogonal central composite design was used to estimate quadratic terms separately. New factor levels are given in Table 3. The design matrix and results of the auxiliary runs are given in Table 4. The second-order model tested at 95% confidence level is as follows: Y ¼ 28.34 þ 0.06X 1 þ 6.67X 2 3.58X 3 þ 4.40X 4 7.77X 21 þ 11.7X 22 þ 3.31X 23 þ 1.64X 24
4. Conclusions The highest bleaching capacity and a model for acid activation of a Turkish bentonite was investigated by means of full factorial design in order to bleach neutralized cotton oil. The bleaching capacity of the bentonite was determined with respect to solid to liquid ratio, contact time, concentration and moisture of bentonite by means of factorial design. Initially, the 24 full factorial design was used to obtain first-order model with interaction terms. Based on the results of analysis of variance, it was necessary to conduct auxiliary experiments, using an orthogonal central composite design, to obtain second-order model relating bleaching capacity to the experimental variables. The highest bleaching capacity obtained was 74.2%. It is believed that the model obtained for bleaching capacity of oils may provide a background for pilot and industrial scale applications.
þ 3.41X 1 X 2 9.59X 1 X 3 0.66X 1 X 4 9.74X 2 X 3 1.74X 2 X 4 1.75X 1 X 2 X 3
ð3Þ
As shown in Table 2, the highest bleaching capacity was obtained for bentonite activated at 0.5 solid to liquid
Table 3 Auxiliary factor levels used in the central composite design Parameters
Low level (a)
High level (+a)
Medium level (0)
Contact time (h) (X1) Solid to liquid ratio (g mL1) (X2) Acid concentration (N) (X3) Moisture of bentonite (%) (X4)
0.91 0.01 0.01 1.81
7.09 0.59 5.99 14.19
4 0.3 3 8
References Boukerrouı, A., & Ouali, M.-S. (2002). Edible oil bleaching with a bentonite activated by micro wave irradiation. Annales Chimie— Science des Materiaux, 27, 73–81. Chegrouche, S., & Bensmaili, A. (2002). Removal of Ga (III) from aqueous solution by adsorption on activated bentonite using a factorial design. Water Research, 36, 2898–2904. Christidis, G. E., Scott, P. W., & Dunham, A. C. (1997). Acid activation and bleaching capacity of bentonites from the islands of Milos and Chios, Agean, Greece. Applied Clay Science, 12, 329–347. Gannouni, A., Bellagi, A., & Bagane, M. (1999). Pre´paration dÕune argile active´e pour la de´coloration de lÕhuile dÕolive. Annales Chimie—Science des Materiaux, 24, 407–416.
E.G. Kirali, O. Lac¸in / Journal of Food Engineering 75 (2006) 137–141 Hymore, F. K. (1996). Effects of some additives on the performance of acid-activated clays in the bleaching of palm oil. Applied Clay Science, 10, 379–385. Myers, R. H. (1971). Responce surface methodology. Allyn and Bacon, 126. Pradymna, K., Nail, L. B. S., & Das, S. C. (2000). Aqueous SO2 leaching studies on nishikhal manganese ore through factorial experiment. Hydrometallurgy, 54, 217–228. Rossi, M., Gianazza, M., Almprese, C., & Stanga, F. (2003). The role of bleaching clays and synthetic silica in palm oil physical refining. Food Chemistry, 82, 291–296.
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Srasra, E., & Trabelsi-Ayedi, M. (2000). Textural properties of acid activated glauconite. Applied Clay Science, 17, 71–84. Study group (2001). Bleaching of edible fats and oils. European Journal of Lipid Science and Technology, 103, 505–551. S ß ayan, E., & Bayramog˘lu, M. (2004). Statistical modeling and optimization of ultrasound-assisted sulfuric acid leaching of TiO2 from red mud. Hydrometallurgy, 71, 397–401. Taylor, D. R., Jenkins, D. B., & Ungermann, C. B. (1989). Bleaching with alternative layered minerals: a comparison with acid activated Montmorillonite for bleaching Soybean oil. JAOCS, 66, 334– 341.
Statistical modelling of acid activation on cotton oil bleaching by Turkish bentonite E. Gu¨lsßah Kirali, Oral Lac¸in
*
Atatu¨rk University, Department of Chemical Engineering, Centrum, 25240 Erzurum,Turkey Received 13 February 2005; accepted 5 June 2005 Available online 8 August 2005
Abstract The aim of the study was to determine the highest bleaching capacity and derive a model for acid activation of a Turkish bentonite using a full factorial design. The selected factors were contact time, solid to liquid ratio, acid concentration and moisture of bentonite. A first-order model is obtained by using 24 full factorial design. Auxiliary experiments for the second-order model were conducted according to an orthogonal central composite design. An experimental test carried out using a factorial design 24 indicated that contact time, solid to liquid ratio and moisture of bentonite have a positive effect, whereas acid concentration has a negative effect. Furthermore, the highest bleaching capacity was found to be 74.2%. Ó 2005 Elsevier Ltd. All rights reserved. Keywords: Bleaching; Activated bentonite; Factorial design; Neutralized cotton oil
1. Introduction In crude edible oil refining, the bleaching treatment is a critical step. After its degumming and neutralization during the refining process, crude edible oil still contains undesirable impurities such as phospholipids, soap, trace metals, carotenoids, xanthophylls, chlorophyll, tocopherols and gossypol. These impurities not only degrade quality of the oil by alteration of its taste and color, but also effect its market value by giving it a color that will not be appreciated by the consumer. The removal of these impurities improves the sensory quality and oxidative stability of the deodorized oil (Boukerrouı & Ouali, 2002). Bleaching clays are by far the most common adsorbents for decolourization of edible oils. They consist of hydrated aluminium silicates. Starting material for *
Corresponding author. Tel.: +90 4422314554; fax: +90 2360957. E-mail addresses: [email protected], [email protected] (O. Lac¸in). 0260-8774/$ - see front matter Ó 2005 Elsevier Ltd. All rights reserved. doi:10.1016/j.jfoodeng.2005.06.010
the production of bleaching clay is the clay rock called bentonite (Rossi, Gianazza, Almprese, & Stanga, 2003; Srasra & Trabelsi-Ayedi, 2000; Taylor, Jenkins, & Ungermann, 1989). Bentonite consists predominately of smectite a 2:1 clay mineral containing an octahedral sheet between two tetrahedral sheets. Smectite crystals are negatively charged due to the substitution of the trivalent aluminium ions by bivalent ions like Mg2+ and Fe2+ and substitution of tetrahedral Si4+ by AI3+ (Study group, 2001). Bentonites are highly valued for their properties, which stem from their high surface area and their tendency to absorb water in the interlayer sites. These properties are enhanced with acid activation (Christidis, Scott, & Dunham, 1997). If the natural bentonite is treated with acid, the cations between the layers of the montmorillonite crystal are replaced by protons of the mineral acids (Study group, 2001) and the structure is partially destroyed (Christidis et al., 1997). Ca-bentonite + 2Hþ $H-bentonite + Ca2þ
138
E.G. Kirali, O. Lac¸in / Journal of Food Engineering 75 (2006) 137–141
Some studies on the performance of acid activated clay and the factorial design method in this study were found in the literature. Gannouni, Bellagi, and Bagane (1999) examined the optimum conditions for acid activation of a clay using an orthogonal central composite design in order to bleach olive oil. The selected variables were temperature, reaction time, initial acid concentration and liquid/solid weight ratio. The results obtained from the experiments showed that the last is the most significant factor in the activation process followed in the decreasing order of importance, by time, temperature and initial acid concentration. Chegrouche and Bensmaili (2002) investigated the removal of Ga(III) from the aqueous solution by adsorption on activated bentonite using a factorial design 23 and it was determined that pH and mass of bentonite have a positive effect, whereas temperature has negative effect. Christidis et al. (1997) examined the bleaching capacity and acid activation of bentonites from the islands of Milos and Chios, Aegean, Greece, consisting of chambers and Tatatilla-type and Otay-type montmorillonite, respectively, resulted in a four- to five-fold increase of the surface area of the raw materials. The activated materials have been rendered suitable for bleaching of rapeseed oil through removal of b-carotene. It was determined that the optimum bleaching capacity is not associated with maximum surface area and the optimum conditions for activation are obtained using a variety of combinations of acid strength and residence time. Despite numerous studies, no definite relationship exists between the performance of acid activated clay and the composition or other properties of the original clay. Hence, each clay has to be specifically activated and tested for its performance (Hymore, 1996). Although Turkey has rich bentonite reserves which is used in activated clay production, the studies on activated clay production have not reached the desired level yet. With this purpose, the utilization of bentonite obtained from Arguvan–Malatya region was investigated for bleaching of neutralized cotton oil. The aim was to determine the highest bleaching capacity and derive a model for acid activation of a Turkish bentonite using a full factorial design.
2. Experimental 2.1. Design of experiments Factorial design is widely used in statistical planning of experiments to obtain empirical linear models relating process response to process factors (Pradymna, Nail, & Das, 2000; S ß ayan & Bayramog˘lu, 2004). 2n factorial design, where each variable runs at two levels, is often used
to obtain first-order models. If the variance analysis indicates that overall curvature is significant, auxiliary experiments are carried out to develop a second-order model. Among the various second-order designs, the orthogonal central composite design is widely used as it only requires 2n additional runs (Myers, 1971). A full factorial design was selected to study the influence of the different factors (e.g. contact time, solid to liquid ratio, acid concentration and moisture of bentonite) on the bleaching efficiency of bentonites. 2.2. Materials The natural bentonite originated from Arguvan (Malatya–Tu¨rkiye). It was crushed using a jaw crusher and ground to pass through a 75 lm sieve (200 mesh ASTM) using a porcelain mill. The chemical composition of the Turkish bentonite was determined by XRay fluorescence spectroscopy (XRF, ARL 9800 XP) as follows: (wt.%); SiO2: 45.48, Al2O3: 17.70, Fe2O3: 8.22, CaO: 6.05, MgO: 4.01, Na2O: 3.84, K2O: 2.51 and loss on ignition (LOI): 10.95. X-ray diffraction patterns of Turkish bentonite was obtained using a Rigaku 2000 JCPDS DMAX (29– 1490) diffractometer (XRD) with CuKa radiation (30 kV and 30 mA and automatic monochromator) at a scanning rate 2h of 2° min1. The diffraction patterns of Turkish bentonite before and after activation, which are obtained at the highest bleaching capacity, are given in Fig. 1. The specific surface area of Turkish bentonite before and after activation, which are obtained at the highest bleaching capacity before and after activation was measured by using the BET-N2 method. The specific surface areas before and after activation were found to be 15.64 and 38.32 m2 g1, respectively. The neutralized cotton oil was provided by Doyasan Oil Comp. in Erzurum (Tu¨rkiye). All chemicals used were analytical grade. 2.3. Methods 2.3.1. Acid activation The experimental set up consists of a rotary evaporator, round-bottom three-necked flask, mechanic stirrer, vacuum pump, thermometer and a constant temperature circulator. Activation was carried out in HCI concentrations varying from 1 to 5 N at the temperature of 95 °C ± 1 °C and solid to liquid ratio of 0.1–0.5 g mL1. Contact time was 2–6 h and the moisture of bentonite was 4–12%. The suspension was cooled in air and filtered off and then washed several times with distilled water to remove excess Cl ions and dried in constant weight at 100 °C. These acid activated bentonites were used to bleach the neutralized cotton oil. The chemical
E.G. Kirali, O. Lac¸in / Journal of Food Engineering 75 (2006) 137–141
139
Fig. 1. The diffraction patterns of Turkish bentonite obtained the highest bleaching capacity before and after activation.
analysis of the bentonite obtained at the highest bleaching capacity was (wt.%); SiO2: 69.99 Al2O3: 12.53, Fe2O3: 2.16, CaO: 1.94, MgO: 0.22, Na2O: 4.44, K2O: 2.70 and LOI: 4.40. 2.3.2. Bleaching Bleaching experiments were performed in a roundbottom three-necked flask equipped with a stirring rod. The acid-activated bentonite was added to the oil for 20 min at about 80 °C (under reduced pressure). The acid activated bentonites/oil ratio was 2 (wt.%) (these values are used in factory processing). As soon as bleaching was finished, the bleached oil was separated by filtration at 50 °C. Care must be taken that the filtrate be clean of solid particles. The samples were kept in coloured bottles. The colour changes in the treated oils were determined spectrophotometrically at the best wavelength of 408 nm (Shimadzu UV160A). Results were calculated as b-carotene equivalents after comparison against a calibration curve prepared with 0–20 mg L1b-carotene solutions in petroleum ether. For this purpose, the bleaching capacity of the activated clays was determined from the following equation: The readings from spectrums were repeated three times and then the average was taken. C0 C Bleaching capacity ð%Þ ¼ 100 C0 where C0 is the concentration (mg L1) of b-carotene in the neutralized cotton oil at a wavelength of 408 nm and C is concentration (mg L1) of b-carotene in the neutralized cotton oil at a wavelength of 408 nm.
3. Results and discussion In order to determine the optimum conditions and derive a model for acid activation of a Turkish bentonite, a full factorial of the type 24 has been used. Contact time (X1), solid to liquid ratio (X2), acid concentration (X3) and moisture of bentonite (X4), were chosen as independent variables to model. Factor levels are shown in Table 1. The matrix for four variables is varied at two levels (+1 and 1). The higher level of variable was designed as ‘‘+’’ and the lower level was designed as ‘‘’’. Initially, the 24 full factorial design was used to obtain first-order model with interaction terms. As usual, the experiments were performed in random order to avoid systematic error. In addition, three central replicates were also added to the experimental design to calculate pure experimental error. The bleaching capacity (%) is given in Table 2. A first model with interaction terms was chosen to fit the experimental data Y ¼ b0 þ b1 X 1 þ b2 X 2 þ b3 X 3 þ b4 X 4 þ b5 X 1 X 2 þ b6 X 1 X 3 þ b7 X 2 X 3 þ b8 X 2 X 4 þ b 9 X 1 X 2 X 3
ð1Þ
Table 1 Factor levels used in the full factorial design Factors
Low level ()
High level (+)
Medium level (0)
Contact time (h) (X1) Solid to liquid ratio (g mL1) (X2) Acid concentration (N) (X3) Moisture of bentonite (%) (X4)
2 0.1 1 4
6 0.5 5 12
4 0.3 3 8
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E.G. Kirali, O. Lac¸in / Journal of Food Engineering 75 (2006) 137–141
Table 2 Experimental design and bleaching capacity of activated bentonite Experiment no.
X1
X2
X3
X4
% Bleaching capacity
6 7 12 9 1 8 13 4 5 10 16 2 11 14 3 15 10 20 30
+ + + + + + + + 0 0 0
+ + + + + + + + 0 0 0
+ + + + + + + + 0 0 0
+ + + + + + + + 0 0 0
28.2 26.3 28.4 73.7 41.7 23.6 42.0 43.5 28.8 24.7 40.6 42.9 20.3 13.0 74.2 53.9 30.3 31.3 29.7
Table 4 Experimental design for second-order model and bleaching capacity of activated bentonite Experiment no.
X1
X2
X3
X4
% Bleaching capacity
19 17 23 20 18 22 24 21
+1.547 1.547 0 0 0 0 0 0
0 0 +1.547 1.547 0 0 0 0
0 0 0 0 +1.547 1.547 0 0
0 0 0 0 0 0 +1.547 1.547
5.0 10.6 54.3 54.7 22.0 46.6 49.8 10.8
ratio, contact time for 6 h, 1 N HCI concentration and 4% moisture. The lowest bleaching capacity was also obtained for activated bentonite at 0.1 solid to liquid ratio, contact time for 2 h, 1 N HCI concentration and 4% moisture of bentonite.
where Y is the bleaching capacity (%), b0–b9 are the interaction coefficients and X1–X4 are dimensionless coded factors for the variables. The first-order model obtained by variance analysis conducted at 95% confidence interval is as follows: Y ¼ 36.69 þ 0.63X 1 þ 8.70X 2 2.28X 3 þ 1.95X 4 þ 3.41X 1 X 2 9.59X 1 X 3 9.74X 2 X 3 1.74X 2 X 4 1.75X 1 X 2 X 3
ð2Þ
The analysis of variance revealed that the overall curvature effect was significant; therefore, the orthogonal central composite design was used to estimate quadratic terms separately. New factor levels are given in Table 3. The design matrix and results of the auxiliary runs are given in Table 4. The second-order model tested at 95% confidence level is as follows: Y ¼ 28.34 þ 0.06X 1 þ 6.67X 2 3.58X 3 þ 4.40X 4 7.77X 21 þ 11.7X 22 þ 3.31X 23 þ 1.64X 24
4. Conclusions The highest bleaching capacity and a model for acid activation of a Turkish bentonite was investigated by means of full factorial design in order to bleach neutralized cotton oil. The bleaching capacity of the bentonite was determined with respect to solid to liquid ratio, contact time, concentration and moisture of bentonite by means of factorial design. Initially, the 24 full factorial design was used to obtain first-order model with interaction terms. Based on the results of analysis of variance, it was necessary to conduct auxiliary experiments, using an orthogonal central composite design, to obtain second-order model relating bleaching capacity to the experimental variables. The highest bleaching capacity obtained was 74.2%. It is believed that the model obtained for bleaching capacity of oils may provide a background for pilot and industrial scale applications.
þ 3.41X 1 X 2 9.59X 1 X 3 0.66X 1 X 4 9.74X 2 X 3 1.74X 2 X 4 1.75X 1 X 2 X 3
ð3Þ
As shown in Table 2, the highest bleaching capacity was obtained for bentonite activated at 0.5 solid to liquid
Table 3 Auxiliary factor levels used in the central composite design Parameters
Low level (a)
High level (+a)
Medium level (0)
Contact time (h) (X1) Solid to liquid ratio (g mL1) (X2) Acid concentration (N) (X3) Moisture of bentonite (%) (X4)
0.91 0.01 0.01 1.81
7.09 0.59 5.99 14.19
4 0.3 3 8
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