Determination of optimum conditions for thermal regeneration and characterization of a spent bleaching earth

Journal Pre-proof DETERMINATION OF OPTIMUM CONDITIONS FOR THERMAL REGENERATION AND CHARACTERIZATION OF A SPENT BLEACHING EARTH ´ Suyanne Angie Lunelli Bachmann, Rita de Cassia Siqueira Curto Valle, Atilano Antonio Vegini, Lorena Benathar Ballod Tavares

PII:

S2213-3437(19)30626-8

DOI:

https://doi.org/10.1016/j.jece.2019.103503

Reference:

JECE 103503

To appear in:

Journal of Environmental Chemical Engineering

Received Date:

29 July 2019

Revised Date:

30 September 2019

Accepted Date:

24 October 2019

Please cite this article as: Bachmann SAL, Valle RdCSC, Vegini AA, Tavares LBB, DETERMINATION OF OPTIMUM CONDITIONS FOR THERMAL REGENERATION AND CHARACTERIZATION OF A SPENT BLEACHING EARTH, Journal of Environmental Chemical Engineering (2019), doi: https://doi.org/10.1016/j.jece.2019.103503

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DETERMINATION OF OPTIMUM CONDITIONS FOR THERMAL REGENERATION AND CHARACTERIZATION OF A SPENT BLEACHING EARTH

Suyanne Angie Lunelli Bachmanna*1, Rita de Cássia Siqueira Curto Valleb, Atilano

a

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Antonio Veginia, Lorena Benathar Ballod Tavaresc

Departamento de Engenharia Química, Universidade Regional de Blumenau, 89030-

000 Blumenau, SC, Brasil ([email protected]; [email protected])

Departamento de Engenharias, Universidade Federal de Santa Catarina, 89065-300

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Blumenau, SC, Brasil ([email protected])

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Centro de Ciências Tecnológicas, Programa de Pós-Graduação em Engenharia

Ambiental. Universidade Regional de Blumenau, 89030-000 Blumenau, SC, Brasil

Corresponding Author: [email protected]

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*

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([email protected])

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Instituto Federal de Educação, Ciência e Tecnologia do Rio Grande do Sul, 95770-000 Feliz, RS, Brasil

Graphical Abstract

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The bleaching performance is dependent of the temperature. Temperatures equal to 800 °C had a negative effect on the bleaching performance. The type of treatment does not significantly influence on the bleaching performance. The optimal conditions suggested by model were 108 min at 587 °C. A good fit was obtained with this model (R² = 97.88 %).

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Highlights

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Abstract

In this study, the optimal conditions of the thermal regeneration, for a spent bleaching earth (SBE) used to bleaching of soybean oil was evaluated. In order to determine the optimal conditions, it was used the response surface method (RSM). The UV-VIS spectrophotometry assays were performed in the soybean oil to determine the bleaching

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performance. The similarities and differences between the activated bleaching earth (ABE), the spent bleaching earth (SBE) and the regenerated spent bleaching earth (RSBE) (only best regeneration result obtained) samples were evaluated by means of atomic absorption spectrophotometry (AAS), scanning electron microscopy (SEM), differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA). The bleaching performance of the regenerated spent bleaching earth (RSBE) ranged between 47.62-100 %, with the best result being obtained for assay at 600 °C during 90 min. The

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optimal conditions for the thermal regeneration suggested by model were 108 min at 587 °C (103 %). The characteristics of the regenerated spent bleaching earth were

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similar to the activated bleaching earth (ABE).

Keywords: spent bleaching earth, optimization, thermal regeneration, response surface

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method, characterization

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1 INTRODUCTION

Activated clay is a commercial material obtained from natural montmorillonites.

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It exhibits moderate superficial negative charge, high cation exchange capacity and large specific surface area, being able to adsorb substances into its structure. The low

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cost and abundance of this group of minerals in the environment explains its large-scale use in the bleaching of vegetable oils 0,0. The main use of activated clay is in the

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removal of impurities related to color the oils without changing the chemical properties of the product 0,0. In the bleaching process, other undesirable compounds such as soap, heavy metals and phosphorus compounds 0. After being used in the processing of vegetable oils, the spent bleaching clay or spent bleaching earth contains unsaturated oil which makes the waste unstable and limits the disposal options 0,0. Generally, the residue is disposed on landfill without any

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treatment 0. It is estimated that 1.2–1.6 kg of spent bleaching earth is generated per metric ton of edible oil produced 0 and in 2016/17, vegetable oil production amounted about 189.2 million metric tons worldwide 0. This shows the waste relevance in relation to the environment. Several spent bleaching earth regeneration processes have been reported in the literature. The most usually being chemical, thermal or thermochemical regeneration processes 0,0. Some process less commons also reported, such as regeneration by

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heating in aqueous medium, by wet oxidation under pressure 0,0 and by the action of gaseous stream (air and CO2) 0. Thermal regeneration processes can also be associated

with previous extraction using organic solvents 0,0,0. However, literature shows that the

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regeneration only through thermal treatment presents a higher bleaching performance

than the regeneration and thermal treatment with previous extraction making the use of

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solvent 0,00.

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After removing the pollutants from SBE, there claimed clay can be reactivated and reused in the polymer–clay composite material 0, clay products 0, as substitute of coal in the boiler plant 0, such as bio active materials 0 and carbon nanocomposites for

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wastewater treatment 0, or as adsorbent of organic compounds, such as drugs and reactive dyes 0,0 and heavy metal ions 0.

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The recovery of spent bleaching earth by applying heat treatment has proved to

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be an important technology in relation to processes where activated bleaching earths are used as filtering auxiliaries or adsorbents. However, it is necessary to investigate the application of this regeneration process on an industrial scale. Thus, the parameters that most influence the earth regeneration process need to be properly adjusted in order to obtain the maximum performance of regeneration associated with economy in terms of energy, reagents and regeneration time. Although there is recycling optimization of

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spent earth utilized to bleach spent lubricating oil, there is no particular case mentioned for the soybean oil 0.

2 EXPERIMENTAL In this paper, the unused clay samples are referred to activated bleaching earth (ABE), the spent clay previously used for the bleaching of soybean oil as spent bleaching earth (SBE), and the thermally regenerated clay as regenerated spent

for the bleaching soybean oil were from the same batch.

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2.1 Thermal regeneration and adsorption essays

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bleaching earth (RSBE), in order to simplify future references. The SBE samples used

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Samples of ABE, SBE and neutral soybean oil were supplied by Bunge (Brazil S/A).

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Thermal regeneration was conducted according to an adapted methodology 0. For the thermal regeneration without the extraction of the residual oil, 3.0 g of the SBE

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sample was weighed in a porcelain crucible and were placed in a muffle furnace (EDGCON 3P) and the regeneration time was considered to begin after the stabilization

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of the tested temperatures. The regeneration process was conducted in laboratorial scale with the presence of atmospheric air, i.e. inert atmosphere was not used.

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Although the studies recommend that regeneration occurs by preliminary acid activation followed by heat treatment 0, acid activated clays can cause corrosion in industrial bleaching tanks 0. Alternatively, in this work, was proposed a preliminary washed with hot distilled water and a preliminary extraction with a solvent (n-hexane). Some SBE samples were previously washed in hot distilled water in order to partially remove the residual oil, according to adapted methodology (Huang et al.,

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2007). In this procedure, a 0.10 g/mL (10 % mass/volume) aqueous solution of SBE was prepared. The solution was heated to 100 °C in a water bath and kept under stirring for 20 min. The solution was decanted and vacuum filtered. Then the SBE trapped by the filter was weighed and immediately transfer to a muffle furnace to conduct the thermal regeneration process described previously. The thermal regeneration of the SBE sample was also carried out after the preliminary extraction of the residual oil using a solvent (n-hexane). The oily extracts

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were obtained by solid-liquid extraction according to a previously proposed methodology 0. After the extraction, the sample was washed with distilled water and transferred to a muffle furnace to conduct the regeneration process. The oil was

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separated from the solvent in a rotary evaporator at a temperature of 60 °C. The

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percentage of oil adsorbed (%) was calculated using Equation (1):

and

are initial and final mass of sample, respectively.

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where,

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Equation (1)

The efficiency of the thermal regeneration of the SBE was verified by adsorption

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essays using neutral soybean oil, according to an adapted methodology 0,0. A mass of neutral oil equivalent to 0.98 g/g (98 % mass) of the sample composition was weighed

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into a round-bottom flask. The previously weighed oil was then heated to 100 °C in a heating mantle, under stirring in a relative vacuum (360 mmHg) in order to avoid/minimize the oxidation of the oil. After stabilization of the temperature of the system, the vacuum was interrupted and added 0.02 g/g (2 % mass) of ABE/RSBE and then immediately restarted. The experiment was held under these conditions for 30 min, and the oil was separated from the SBE by vacuum filtration.

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Although the free fatty acids (FFA) content, saponification value and iodine value (SV and IV) are three quality parameters used to evaluate bleaching earth 0, several works evaluated the bleaching earth performance by the color 0,0,0,0, because it is the most important factor for the commercial value of this oil 0. The soybean oil is usually graded on a Lovibond color scale 0,0. However, it was not used because this equipment was not available. Then, the oil samples were analyzed by UV-VIS spectrophotometry (Shimadzu, model UV-1650 PC) in a wavelength of 450 ηm, as

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indicated in literature, because it is the wavelength detects the oil pigments, such as chlorophyll and carotenes 0,0. The bleaching performance was calculated using

is absorbance of oil prior to bleaching and

is absorbance of clarified oil.

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where,

Equation (2)

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Equation (2) 0.

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2.2 Experimental design and optimization

The experiments were performed in two steps. Firstly was used a factorial design

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2^2^3 was used to verify the variables that are significant influencing on the bleaching performance. Researchers have recommended regeneration clays at temperatures

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between 300 and 800 °C for 30-180 min 0,0. Thus, it was tested two levels of time and temperature (-1 and +1), and three types of pre-treatment (-1, 0 and +1). On second moment, after knew the each factor effects, the response surface method, through of central composite design (CCD) was performed to analyzed and optimized the influence on operational conditions on bleaching performance. In present study, two parameters

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were time and temperature (-α, -1, 0, +1, +α). Table 1 shows the factors evaluated with the respective variations.

Table 1. Factors evaluated and the levels of variation in the thermal regeneration tests Levels Variables

Symbols -α

-1

0

1

α

x1

559

600

700

800

841

Time (min)

x2

18

30

60

90

102

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Temperature (°C)

Washing Without oil Pre-treatment

x3

-

-

With oil

with hot extraction

extraction

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water

The central composite design (CCD) was used to obtain a quadratic model,

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consisting of factorial trials and starting points to estimate quadratic effects and central points to estimate the variability in bleaching performance as the responses (Y). Use of

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CCD enabled to study the most efficient parameters affecting the process and cooperated in evaluating the possible interactions between the two parameters during

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the process. Additionally, the central composite design is “flexible and efficient in furnishing sufficient data on impact of various parameters with minimum number of

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experimental runs” 0.

The central composite design experimental, as well factorial design, data were

employed using Statistica version 7.0 (StatSoft, USA) and then interpreted. Behavior of the system is explained by the following second-order polynomial equation (Montgomery and Runger, 2010):

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Equation (3)

where Y is the dependent variable, xi and xj are the independent variables, β0, βi, βii and βij are the regression coefficients of model and e is the model’s error. An analysis of variance (ANOVA) and R2 statistic were performed to evaluate

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significant differences between factors and check the adequacy of variables studied.

2.3 Characterization of bleaching earths

In order to evaluate the color alteration of the RSBE in comparison to ABE, the

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sample iron content was determined by atomic absorption spectroscopy (Varian, model SpectrAA 220F).

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The morphology of the ABE, SBE and RSBE samples, was evaluated by scanning

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electron microscopy (SEM). The technical procedure consists in analyzing samples covered with a conducting layer of gold ions using a sample metalizer (Quorum Q150R

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ES) and after observed in an electron microscope (Tescan VEGA 3 SEM) with acceleration tension of 10 kV.

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Thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC) were performed according to a methodology adapted in 0, using Shimadzu DTG-60 and

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DSC-60 systems, respectively. This procedure was performed to monitor the clay transformations with temperatures varying from 40-1000 °C for the TGA. Samples for the TGA tests were packed in platinum capsules at 40-600 °C. For the DSC analysis, the samples were encapsulated in aluminum material at 10 °C.min-1 with a nitrogen flow of 100 mL.min-1.

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It is relevant to consider that, as the objective of this study was to determine the optimal conditions to the thermal regeneration, the previously mentioned analysis were applied for ABE, SBE and RSBE (only best results).

3 RESULTS AND DISCUSSION 3.1 Bleaching tests and regeneration efficiency The average percentage of retained oil obtained was 17.83 % ± 0.79. Previous

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studies have reported a percentage of residual oil of 20-30 % 0,0. Studies also indicate that recovering the oil extracted from the SBE with different solvents (methanol,

ethanol, petroleum ether, pentane, hexane, and heptane) produces low quality oils for

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reuse 0. In this study, however, the extraction was applied to remove some of the organic matter represented by the oil and some of the organic pigments, with the

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chlorophyll and carotene 0,0, as well as to reduce the risk of combustion before

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subjecting the SBE to heat treatment 0. It is important to notice that the percentage of residual oil could have been influenced by the presence of organic compounds that may have been removed by the organic solvent used in the extraction process. From the point

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of view of the removal potential of soybean oil pigments, the choice of the most efficient thermal treatment was based on bleaching tests carried out on the neutral oil.

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The results of the experimental design proposed in order to verify which

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variables influence the bleaching performance are shown in Table 2.

Table 2. Bleaching performance results obtained from tests on the thermal regeneration of the SBE (factorial design 2x2x3) Temperature

Time

Pre-treatment

Bleaching performance

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(min)

(%)

600

30

Without oil extraction

99.2

600

30

Washing with hot water

96.5

600

30

With oil extraction

95.9

600

90

Without oil extraction

100.0

600

90

Washing with hot water

99.5

600

90

With oil extraction

97.0

800

30

Without oil extraction

77.9

800

30

Washing with hot water

800

30

With oil extraction

800

90

Without oil extraction

800

90

Washing with hot water

43.7

800

90

With oil extraction

73.6

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(°C)

57.7 83.4

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53.0

Adsorption essays performed at moderate temperatures (600 °C) without previous extraction of the residual oil showed bleaching performance higher than 99 %.

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Also observed the bleaching performance was higher than 73 % to for the SBE with previous oil extraction. It is occurs due to the interaction of the solvent with the organic

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substances adsorbed on the earth, such as carotenes. The main type of carotene found in

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vegetable oils is β-carotene (tetraterpene – C40H56), which is a non-polar and very soluble, especially at high temperatures 0, which may be favorable to the interaction with non-polar solvent (n-hexane). Due to the protonated clay surface 00, the organic compounds, especially the chlorophyll, can react with the Bronsted and Lewis acid sites, which increase after heat treatment 0,0. Some compounds derived from chlorophyll, especially pheophytin have,

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in their structure, bivalent protonated ions that facilitate the electrostatic interaction with the ABE active sites during bleaching 0. In this case, in addition to the physical adsorption process chemisorption occurs 0, therefore, these organic compounds are more strongly attached to the ABE. The desorption of these compounds is facilitated by the action of the solvent, which is capable of interacting with these organic substances. The organic compounds are removed previously to the heat treatment due to low polarity of the solvent and it improves the ABE bleaching performance. It was verified

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that the regeneration temperature exerts a significant influence (p-value = 0.00069 and F value = 33.148) on the bleaching performance when compared to the other factors

studied. On the other hand, the time variable had little or no significant effect on the

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response (p-value = 0.2685 and F value = 1.444). This corroborate with results

presented in Table 2. It is possible observed that time higher than 30 min associated

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with temperature of the 800 °C presented bleaching performance lower than 73.6 %. Therefore, this variable was disregarded in order to evaluate the effects of pre-

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to the type of treatment.

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treatment. Figure 1 (a) shows the Pareto’s chart and a plot of the mean values according

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>>Insert Figure 1 <<

Temperatures equal to 800 °C had a negative effect on the response, as shown in

Figure 1 (a), that is, the higher the temperature used in the treatment, the lower the bleaching performance obtained. This is because the clay is dehydroxylated, modifying its structure, as it will be demonstrated later through the analysis of TGA and DSC. According to the data reported in Figure 1 (b) can verified that it was possible to

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achieve a higher bleaching performance applying moderate temperatures in the SBE regeneration (600 °C). Thus, since it is not necessary to operate the process at high temperatures, savings can be made in terms of energy consumption.

3.2 Optimization of the regeneration process In this study, a central composite design (CCD) was performed in order to optimize the process and verify the possibility of non-linearity in the bleaching

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performance values as a function of the variables studied. Considering the feasibility for industrial application, as well as the simplicity of the thermal regeneration process, the additional points were only included for tests without pre-treatment due to the fact of

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the type of treatment does not significantly influence the bleaching performance (p-

value = 0.3202 and F value = 1.144). It is also believed that the absence of pre-treatment

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could make the thermal regeneration process more attractive for industry because the

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use of organic solvents would be dispensable, thus avoiding unnecessary costs with solvent recovery. Moreover, the use of hot water would also result in a liquid effluent to be treated. Therefore, it was not apply these points to the other pre-treatments studied.

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The results are shown in Table 3.

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Table 3. Axial and central points of the central composite rotational design to

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investigate the bleaching performance (x1, temperature; x2, time)

Essay

x1

x2

Bleaching Performance (%)

1

-1

-1

99.2

2

-1

1

100.0

3

1

-1

77.9

14

1

1

53.0

5

0

0

95.0

6

0

0

97.1

7

0

0

96.8

8

-1.4142

0

98.5

9

1.4142

0

47.6

10

0

-1.4142

95.7

11

0

1.4142

94.1

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The experimental data obtained in the adsorptions essays carried out with the

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RSBE at 600 °C for 90 min, without previous extraction of the residual oil, showed a

higher bleaching performance (100 %). This indicates that the SBE regenerated under

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these conditions had the same bleaching potential as the ABE. The analysis of variance

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of the CCD showed that the time and temperature variables have significant effects on the response (significance level of 5 %). The effect of the interaction between these

(Table 4).

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variables also exerts a significant influence on the bleaching performance (p < 0.05)

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Table 4. Analysis of variance (ANOVA) of the central composite rotational design for

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the bleaching performance Factor

a

b

(1) Temperature (°C)

2460.34

(2) Time (min) (3) with (2) a

SQ

DF

F value

p value

1

1835.209

0.00054

97.46

1

72.697

0.01348

145.20

1

108.309

0.00910

SQ Sum of squares, bDF degrees of freedom.

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Figure 2 shows the response surface (a) and the contour curve (b), respectively, obtained from the experimental data on the bleaching performance. >>Insert Figure 2<< The response surface method showed a trend towards an optimum region (point of maximum) for the bleaching performance (Figure 2 (b)). The experimental data obtained from CCD were fitted to a second-order polynomial model (Equation (4)), since it was defined that the linear, quadratic and interaction components have a

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significant effect on the response.

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Equation (4)

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A good fit was obtained with this model. The coefficient of determination, R², was 97.88 %, which represent very well the behavior of the factors at the levels studied

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on the response. The maximum point of the function was obtained by partial derivation of the regression model equation. Moreover, the optimum conditions indicated by the

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model for thermal regeneration process of the SBE were 108 min at 587 °C. Under these conditions, the value predicted by the model for the bleaching performance was 103 %.

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The literature shows that thermochemical regeneration of SBE, with solvent at temperature up 500 to 600 °C yield bleaching performances above 90 % 0. However, as

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the study was carried out with a view towards industrial application, the use of solvents were not of interest, because it increases the cost regeneration process due to the need for solvent recovery. Thus, the regeneration carried out at 600 °C for 90 min was considered satisfactory, since it provided a bleaching performance of 100 % within a shorter time than that predicted by the model.

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3.3 Clay Characterization The RSBE samples had a reddish brown color (Figure 3). >>Insert Figure 3<< Clay minerals naturally contain iron impurities, which impart a reddish coloration 0,0 and the hematite (Fe2O3) is the main iron compound present in red colored clays 00,0. Quantitative iron analysis was investigated on ABE, SBE and RSBE samples. For the evaluation of the RSBE, the treatment with the best bleaching

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performances (100 %) was selected. The ABE and the RSBE presented an iron content of 1.61 % and 2.30 %, respectively. Iron content of 1.59-3.49 % for bentonite clay of

bleaching was reported in the literature 0. However, the RSBE had a higher iron content

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than the other samples, which could be due to the incorporation of iron from the vegetable oil during the bleaching process. The literature indicates that iron

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incorporation does not significantly influence pore volume 0, thus it is believe that the

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presence of iron up to 2.30 % in RSBE has no significant influence on bleaching performance.

Scanning electron microscopy (SEM) was performed in order to observe the

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characteristics of the ABE, SBE and RSBE. The results are showed in Figure 4.

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>>Insert Figure 4<<

In the samples of ABE (Figure 4 (a)) and RSBE (Figure 4 (b)), it was observed

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aggregates and compact regions, generally smaller than 10 μm. This is the characteristic of highly fragmented clays, adsorbents or carbonized materials 0 and/or submitted to acid treatment 0. This is occurs due to the acid reaction with the clay surface and the heating temperature which cause the dissolution of retained impurities, thus influencing the surface proprieties of the adsorbent 0. Although the highly fragmented appearance, previous results showed that it was not observed alteration in RSBE bleaching

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performance. The samples showed a morphology characteristic of montmorillonite-type clay minerals 0,0. The SBE (Figure 4 (b)) showed an aggregate morphology with irregular appearance. This aspect occurs after the bleaching soybean oil process, becoming saturated ABE (Thair et al., 2013). Additionally, SBE also presented larger agglomerates when compared to ABE and RSBE. On the other hand, the morphological characteristics for the RSBE were more similar to the ABE than SBE. This similarity

compounds present in the SBE and the dehydration 0,0.

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can be attributed to the regeneration process that involves the vaporization of organic

Thermal analysis of the samples was carried out in order to evaluate the changes

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in the physical properties of the material as a function of time and temperature. The DSC/TGA curves obtained for the ABE are typical of montmorillonite, as seen in

>>Insert Figure 5<<

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typical of regenerated earths.

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Figure 5 (a). However, for the RSBE DSC/TGA curves, shown in Figure 5 (b), are

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In Figure 5(a) and (b) two-peaked DSC curves are shown, indicating endothermic reactions (labels A and B) representing dehydration and dehydroxylation

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of the sample, respectively 0,0,0. The amplitudes of the RSBE sample peaks were lower than the amplitudes of the ABE peaks. This may be due to the thermal treatment applied

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in the regeneration of the sample before it was submitted to DSC analysis, causing partial dehydration and dehydroxylation as well as the vaporization of the vegetable oil, pigments, and other adsorbed impurities 00. The effects of temperature on the thermal properties of the ABE and RSBE are summarized in this section. The TGA curves for both samples show two zones of weight loss in the temperature ranges of 40-180 °C and 180-600 °C. These

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transformations happen due to the removal of the adsorbed water in the interlamellar clay layer which occurs throughout the process (200-500 °C) 0. The second weight loss can also be associated to the removal of structural water from the clay 0,0. The dehydroxylation temperatures for the ABE and RSBE were 526.63 °C and 447.35 °C, respectively, and the corresponding weight losses were 17.63 % and 11.16 %. The amplitude of the DSC peaks and the weight loss of the RSBE were lower when compared to the ABE. This is possible because according with literature the ABE

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is more humid than RSBE 0, could be associated with partial dehydration and dehydroxylation 0,0. Besides that, the weight loss may be too due to carbonization, that is the vaporization of the organic compounds, color pigments and oil adsorbed in the

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clay 0,0.

The DSC curves end at 600 °C while the TGA curves continue up to 1000 °C.

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This is because the capsules used in the DSC were aluminum that have a melting point

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close to 600 °C, while those used for the TGA were platinum, with a higher melting

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point, allowing the analysis to be continued up to temperatures close to 1000 °C.

4 CONCLUSIONS

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In this study, the optimal conditions of time and temperature were determined for the thermal regeneration of the spent bleaching earth (SBE). It was observed that the

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bleaching performance is dependent of the temperature, although temperatures equal to 800 °C had a negative effect on the bleaching performance while the type of treatment does not significantly influence on the bleaching performance. The optimal conditions for the thermal regeneration suggested by model were 108 min at 587 °C (103 %). However, the bleaching performance of 100 % was obtained at 600 °C during 90 min. It was considered a good result because the necessity of a thermic treatment time higher

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than 90 min spends more energy. The thermal regeneration under suitable conditions lead to SBE regaining their bleaching performance. The bleaching performance of regenerated spent bleaching earth (RSBE) (best result) was similar to that observed for activated bleaching earth (ABE). The morphological characteristics for the RSBE were more similar to the ABE than SBE. Although the thermal regeneration caused highly fragmented bleaching earth, this did not change the RSBE’s bleaching performance. The DSC and TGA curves of the RBES and ABE presented similar behaviors. Further

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studies should be carried out to evaluate the use of RSBE in the bleaching in order to verify the quality of the soybean oil obtained. Also is necessary evaluated how many

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regeneration cycle’s is possible.

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ACKNOWLEDGEMENTS

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The authors are grateful for support from the Regional University of Blumenau and Bunge Alimentos S/A. The author L.B.B. Tavares holds a fellowship from the Brazilian

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governmental agency CNPq.

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Figure Caption Figure 1. Pareto chart with estimates of the effects of the planning variables on the bleaching performance (a) and graph of the mean values for the effect of temperature and pre-treatment on the bleaching performance (b). (L) – linear effect; (Q) – quadratic

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effect (fitting image: double column)

Figure 2. Response surface (a) and contour curve (b) for the bleaching performance as a

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1.5 column)

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function of time and temperature obtained in tests without pre-treatment (fitting image:

Figure 3. Colors of RSBE (90 min at 600 °C) ((fitting image: single column)

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Figure 4. Micrographs of bleaching earth samples. (a): ABE, (b): SBE and (c): RSBE

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(90 min at 600 °C) (fitting image: double column)

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Figure 5. DSC/TGA curves for ABE (a) and RSBE at 600 °C for 90 min (b) (fitting image: 1.5 column)

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