KINECT AND THERMOGRAVIMETRIC EVALUATION OF THE WASTE COOKING OIL BIODIESEL WITH BASIL OIL LIKE ANTIOXIDANT ADDITIVE

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IX Congresso Brasileiro de Análise Térmica e Calorimetria 09 a 12 de novembro de 2014 – Serra Negra – SP - Brasil

KINECT AND THERMOGRAVIMETRIC EVALUATION OF THE WASTE COOKING OIL BIODIESEL WITH BASIL OIL LIKE ANTIOXIDANT ADDITIVE

Manoel Barbosa Dantas1, Francisco Eduardo Arruda Rodrigues1, Tathilene Bezerra Mota Gomes

Arruda2, Natália de Sousa Ribeiro1, Hermesson Jales Dantas1,Marco Aurélio Rodrigues de Melo3,

Antonio Gouveia de Souza3.

1. Instituto Federal da Paraíba - IFPB, Curso de Licenciatura em Química, Campus Sousa, CEP 58800-970, Sousa-PB, Brasil.

2. Universidade Federal do Ceará - UFC, Departamento de Química Orgânica e Inorgânica, Campus do Pici, Bl – 940, CEP 60455-760, Fortaleza-CE, Brasil.

3. Universidade Federal da Paraíba, Departamento de Química, Centro de Ciências Exatas e da Natureza (CCEN), Campus I, 58059-900, João Pessoa-PB, Brasil.

ABSTRACT

The use of antioxidant additives gives to biodiesel a higher thermal stability. In this work is discussed the utilization of the basil essential oil like additive to biodiesel from waste cooking oil (WCO). The thermograms were obtained in three different heat rates (10, 20 and 30°C/min) in oxidative atmosphere. The analyses were performed to the WCO biodiesel without the addition of the basil essential oil (BF100) and to the WCO biodiesel with 2wt% of the basil essential oil in relation to the weight of the biodiesel (BFManj2). It was observed that the decomposition of the samples occurred in only one step. The thermogravimetric data allowed the determination of the apparent kinetic parameters like activation energy and pre-exponential factor. The kinetic study was performed by the application of the equations propose by Coats-Redfern, Madhusudanan and Tang.

INTRODUCTION

With the increase of the global energy demand and a rising concern with the environmental questions, the alternative energy resources instead the fossil resources are increasingly requested. Together to this scenario, an increasing in an interest of the use of the biodiesel is noticed in the last decade. The biodiesel is a mixture of ester of fatty acid, these last obtained from animals or vegetables resources. There are three generations of the biodiesel: the first generation corresponding to the biodiesel obtained by the transesterification of edible oils; the second generation corresponding to biodiesel obtained by the transesterification of non-edible oils. The third and latest generation, correspond to the biodiesel obtained by the processing of the microalgae [4]. Thus, the utilization of the waste cooking oil (WCO) like feedstock for the production of the biodiesel is a solution environmentally correct for the disposition of this residue, besides to offer a way for your reutilization. Countries like Japan, China and United State already adopt specific measures for the collecting of WCO, with structured logistics [5], it showing the possibility of the use of this resource for the production of the biodiesel in a large scale. The production potential for the biodiesel in the Mexico and the carbon dioxide emission associated to your use like a fuel are also reported in the literature, and suggestions of a WCO collecting politic to avoid the illegal commerce were given [6]. Despite the necessity of the pretreatment for the processing and a high concentration of the free fatty acid, the WCO can be considered a promising feedstock for the obtaining biodiesel [7]. For this, methods like the use of the immobilized enzyme [8], transesterification by the direct sonication [9] and conversion using ferric sulfate and supercritical methanol process [10] are reported, besides the transesterification conventional methods.

The antioxidant substances can be used for to give a higher thermal stability for the biodiesel. These antioxidant substances can be natural or synthetic. The basil (Ocimum basilicum L.) is a natural alternative of antioxidant substance. The use of the basil extract in different solvents like an antioxidant component in sunflower oil is reported [11]. The essential oil is also used like antioxidant and the

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method of the determination of the iron reduction power and bactericidal activity is described for Teixeira et al [12]. Stevic et al conducted the antifungal evaluation of the basil essential oil [13] and the mathematical model for the extraction system was described for Cassel et al [14].

In this work, it was studied the behavior of the basil’s essential oil like antioxidant additive as well as the thermal stability of the biodiesel obtained by the transesterification of the waste of the cooking oil with ethyl alcohol. The determination of the kinetics parameters was done by analysis of the thermogravimetric data.

EXPERIMENTAL METHOD

The waste cooking oil was obtained by the collecting realized by the students of the degree course in chemistry of the Federal Institute of the Paraíba, Campus Sousa. Due to the high concentration of the free fatty acids caused for the thermal stress, the waste cooking oil was neutralized by washing with calcium hydroxide solution 10% (Synth). After the neutralization, it was conducted the transesterification by basic homogeneous catalysis. The reaction conditions used in the process were: ethyl alcohol 30wt% (Synth) and potassium hydroxide 2wt% (Synth) like catalyst, both in relations of the weight of the oil. The reaction system was maintained at ambient temperature and continuous agitation for two hours.

The basil essential oil was obtained by hydrodistillation of the dry leaves in system modified by Gottlieb. The extraction time was one hour and a half.

Thermogravimetric data (TG/DTG) were obtained by simultaneous analysis in equipment TGA Q50, V20.13 model, in synthetic air atmosphere, and temperature range of 30 to 600°C, and using 10 mg of sample.

RESULTS AND DISCUSSION

The thermograms obtained from BF100 and BFManj2 showed degradation in a single step. This step is correlated to the pyrolysis of the ethyl esters and it was confirmed by the presence of the only peak in the DTG of the samples (Fig. 1, 2 and 3). The initial degradation temperature of the samples occurred in a value higher than 100°C and the possibility of water presence was excluded. The increase of the initial temperature degradation for the biodiesel with basil’s essential oil it was observed in the thermogram when the heat rate was low, in the case, 10°C/min. On the other hand, the addition of the basil’s essential oil decreased the initial degradation temperature when the heat rate of the thermogravimetric experiment was higher than 10°C/min. The temperature range and the temperature peak observed in the DTG are compiled in the Table 1.

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Fig. 2 TGA and DTG for BF100 and BFManj2 in the 10°C/min heat rate and oxidative atmosphere

Fig. 3 TGA and DTG for BF100 and BFManj2 in the 30°C/min heat rate and oxidative atmosphere

Table 1 Representative data for TG for BF100 and BFManj2

Heating rate 10°C/min 20°C/min 30°C/min

Temperature range (°C) Tpeak (°C) Temperature range (°C) Tpeak (°C) Temperature range (°C) Tpeak (°C) BF100 117 - 224 198.47 131 - 264 236.91 138 - 253 240.71 BFManj2 125 - 233 213.80 124 - 235 212.75 131 - 263 226.91

The kinetic analysis was realized for the only step of the samples degradation. Important kinetics parameters like the apparent energy activation (Ea) and the apparent pre-exponential factor (A) was determined. The values were called apparent because your determination was based in methods developed for samples in a solid state. But these concepts were extended for samples in liquid state, in special liquid fuels, with great advantage [15-19]. The methods were based in the resolution of the Arrhenius equation for the non-isothermal process and without the supposition of the specific kinetic. Several models were tested and it was chosen the model that gave the linear correlation (R2) most close to the unit. After the choice of the kinetic model, the kinetic parameters were calculated by the application of the Coats-Redfern, Madhusudanan and Tang equations.

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The value of the apparent activation energy did not change significantly for BFManj2 in comparison with BF100 when the heating rate applied in the experiment was 10°C/min. The apparent activation energy range was 71.8 to 72.3 KJ/mol. When the heating rate was increased to 20°C/min, the value of the apparent activation energy for BFManj2 was lower than BF100. But, when the heating rate was increased to 30°C/min, the value of the apparent activation energy to BFManj2 was higher than BF100. The difference between the values of the apparent activation energy was 3 KJ/mol when the heating rate was 20°C/min and 2 KJ/mol for the 30°C/min. The value of the linear relation coefficient for all the methods and heating rates employed in the analysis was higher than 0.99. The methods suggest for the both samples a pseudo-kinetic R2, which is based in bidimensional nuclear geometrical model. For the R2 model, the nucleation and diffusion occurs in a fast step and the process is controlled by the limitrophe phase. The apparent energy activation values obtained by each method were agreed among themselves. The Coats-Redfern method did not provide a reliable value to pre-exponential factor.

Table 2 Kinetic data for the samples.

BF100 BFManj2%

10°C/min 20°C/min 30°C/min 10°C/min 20°C/min 30°C/min

CR Ea (KJ/mol) 71.76 66.01 71.57 71.87 69.16 67.83 A (s-1) 5.54 x 10 -2 6.36 x 10-3 1.72 x 10-2 1,75 x 10-2 5.24 x 10-3 2.56 x 10-3 R2 0.9994 0.9995 0.9995 0.9928 0.9989 0.9995 MD Ea (KJ/mol) 71.98 65.89 70.23 72.17 69.46 68.13 A (s-1) 4.54 x 10 6 2.46 x 106 1.37 x 106 1.52 x 106 4.24 x 105 2.00 x 105 R2 0.9994 0.9995 0.9995 0.9929 0.9989 0.9995 TG Ea (KJ/mol) 72.29 66.36 71.97 72.17 69.47 68.15 A (s-1) 1.08 x 10 6 1.01 x 105 3.34 x 105 1.56 x 106 4.36 x 105 2.06 x 105 R2 0.9994 0.9995 0.9995 0.9929 0.9989 0.9995 Conclusion

The thermogravimetric behavior of the biodiesel from waste cooking oil with basil essential oil was evaluated. The initial temperature of degradation of the biodiesel from waste cooking oil was lower than the sample with basil essential oil additive when the heating rate was 10°C/min. When the heating rate was increased, the value for the initial temperature degradation was higher for the sample without the additive. It was concluded that the use of the basil essential oil did not favor the thermal stability when the heating rate is higher than 10°C/min. Correlation between the apparent activation energy and the heating rate was not observed: for 10°C/min, the value of the apparent activation energy was the same for the samples, when the heating rate was 20°C/min the value of the apparent activation energy for BF100 was lower than BFManj2 and when the heating rate was 30°C/min the value of the apparent activation energy for BF100 was higher than BFManj2. The integral methods suggest as an apparent mechanism for the only step of the degradation the model R2. There was concordance between the activation energy values obtained from Coats-Redfern, Madhusudanan and Tang methods. These values

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were approximately equivalents to values found for other kinds of the biodiesel reported in the literature [15, 17, 20], as well as to the biodiesel obtained by the heterogeneous catalytic transesterification of the waste cooking oil [21].

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