Thermal Characteristics and Kinetic Calculation of Castor Oil Pyrolysis

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Available online at www.sciencedirect.com Procedia Engineering 00 (2017) 000–000

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Procedia Engineering 205 (2017) 3711–3716

10th International Symposium on Heating, Ventilation and Air Conditioning, ISHVAC2017, 1922 October 2017, Jinan, China

Thermal Characteristics and Kinetic Calculation of Castor Oil Pyrolysis Hui Lia,b, Shengli Niub,*, Chunmei Lub b

a School of Thermal Engineering, Shandong Jianzhu University, Jinan, 250101 China School of Energy and Power Engineering, Shandong University, Jinan, 250061, China

Abstract To investigate the thermal characteristics of castor oil pyrolysis, the fatty acid composition was firstly analyzed via gas chromatograph (GC). Then, the thermal characteristics was evaluated through the thermogravimetric analysis-derivative thermogravimetry (TGA-DTG) under nitrogen atmosphere at 5, 10, 15, and 20 K min-1 from 298.2 K to 873.2 K. Based on the iso-conversional method, pyrolysis kinetic parameter of the activation energy was calculated by the free model approaches of Kissinger-Akahira-Sunose method (KAS) and Flynn-Wall-Ozawa method (FWO). In addition, the reaction order was calculated through Avrami theory. The average activation energy values were calculated as 202.88 kJ mol-1 and 203.66 kJ mol-1 for KAS method and FWO method, respectively. And the average value of reaction order is 1.02. © 2017 The Authors. Published by Elsevier Ltd. © 2017 The Authors. Published by Elsevier Ltd. Peer-review under responsibility of the scientific committee of the 10th International Symposium on Heating, Ventilation and Air Peer-review under responsibility of the scientific committee of the 10th International Symposium on Heating, Ventilation and Conditioning. Air Conditioning. Keywords: castor oil; pyrolysis; TGA-DTG; kinetic calculation

1. Introduction The concerns of depleting petroleum reservoir, rising fuel prices and intensifying environmental risks have led to the driving force for renewable and alternative fuels to substitute fossil fuels. Biomass, a potential carbon neutral energy source called as sunshine fuel, has been extensively investigated [1-5]. Lipid is one of the most important biomass for its abundant availability and environmental friendly [6-8]. Especially, castor oil, obtained from extracting or pressing the Ricinus communis seed, is a promising alternative energy due to its inexpensive, non*

Corresponding author. Tel.: +86 531 88392414; fax: +86 531 88392414. E-mail address: [email protected]

1877-7058 © 2017 The Authors. Published by Elsevier Ltd. Peer-review under responsibility of the scientific committee of the 10th International Symposium on Heating, Ventilation and Air Conditioning.

1877-7058 © 2017 The Authors. Published by Elsevier Ltd. Peer-review under responsibility of the scientific committee of the 10th International Symposium on Heating, Ventilation and Air Conditioning. 10.1016/j.proeng.2017.10.297

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Hui Li et al. / Procedia Engineering 205 (2017) 3711–3716 Hui Li et al./ Procedia Engineering 00 (2017) 000–000

volatile and non-drying characters [9, 10] and it has been broadly used in biodiesel, lubricants, polyurethane, etc. [11-13]. The production of castor seeds in the world wide is around 1 million tons per year and China is the 2nd largest producer of castor oil [14]. Pyrolysis, a thermal decomposition of materials in the absence of oxygen, is a promising technology for biomass utilization, which converts the biomass to oil, char and gas depending on the pyrolysis condition [15, 16]. Lappi et al. [17] reported that the saponified castor oil was pyrolyzed at 1025 K for 20 s and the ketone and the aldehyde compounds accounted for the predominant released gases. Thermogravimetric analysis (TGA) is the most common method for quantifying thermal decomposition [18] due to the fast and repeatable data which enable the in-depth analysis of the mass loss segments and the determination of the kinetic parameters. Vecchio et al. [19] studied the thermal oxidation of 12 varieties of extra virgin olive oils by simultaneous TG-DSC in air atmosphere at heating rates of 2.5, 5, 7.5 and 10 K min-1 and the kinetic parameters were calculated by Kissinger equation. Studies on the oxidative kinetics of soybean oil/anhydrous milk fat blends by DSC at heating rate of 2.5, 5, 7.5, 10, and 12.5 K min-1 were done by Thurgood et al. [20]. Arrhenius parameters were calculated by using Flynn-Wall-Ozawa method and it was reported that the activation energy varied from 58.5 to 117.4 kJ kg-1. From the literatures stated above, in regard to the kinetics calculation, attentions are mainly paid to the activation energy and pre-exponential factor. Whereas, to the best knowledge of authors, the calculation of reaction order during the pyrolysis of castor oil has not been investigated, which is necessary for designment, operation and controlling of the thermochemical conversion units of gasification and pyrolysis. 2. Methods. 2.1 Materials The castor oil used in this study is purchased from the local market and its composition is determined by gas chromatograph (GC) equipped with DB-INNOWAX capillary column and a flame ionization detector (FID) on GC2010 system (Shimadzu, Co., Ltd, Japan). 2.2 TGA-DTG experiments The thermal characteristics of castor oil pyrolysis are conducted on a TGA/SDTA 851e (Mettler-Toledo, Co., Ltd, Switzerland). To avoid the possible temperature gradient in the sample and ensure the kinetic control of the process, the sample is weight to (10±0.2) mg in an aluminum oxide ceramic crucible of 5 mm of depth and 5 mm of diameter. TGA experiments are conducted from 298.2 K to 873.2 K at the linear temperature heating rates of 5, 10, 15, 20 K min-1, where the sweep gas of nitrogen (99.999% purity) is at a flow rate of 50 mL min-1. 3. Results and Discussion 3.1 Analysis of castor oil Castor oil is composed of various long carbon chain triglycerides, which includes: palmitic acid (C16:0, 2.19 %), stearic acid (C18:0, 2.47 %), oleic acid (C18:1, 6.75 %), linoleic acid (C18:2, 8.99 %), linolenic acid (C18:3, 0.77 %), ricinolic acid (C18 O3:1, 77.93 %), arachidonic acid (C20:1, 0.90 %). 3.2 TGA-DTG analysis TGA and DTG curves of castor oil pyrolysis at the temperature heating rates of 5, 10, 15, 20 K min-1 are shown in Fig. 1, where a distinct weight loss step emerges under the four experimental conditions. Meanwhile, as shown in Fig. 1(a), the initial weight loss temperature is shifted from 617.2 K at 5 K min-1 to 639.8 K at 20 K min-1. In the temperature range of 790.5 K-808.3 K, the pyrolysis process ends up with the carbon residue of 4.04%-5.03% and no distinct weight loss is observed with any further increment of temperature, where the TGA curves become almost flat till the end. Similarly, the DTG curves (Fig. 1(b)) show the clear single peak during the whole process and with



Hui Li et al. / Procedia Engineering 205 (2017) 3711–3716 Hui Li et al./ Procedia Engineering 00 (2017) 000–000

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the increment of heating rate, the maximum mass loss rate gets increased rapidly, which is heightened from 1.23×103 -1 s at 5 K min-1 to 3.56×10-3 s-1 at 20 K min-1. And at the same time the corresponding temperature of the maximum mass loss rate is moved from 670.5 K to 698.5 K. This phenomenon is normally ascribed to the heat transfer limitation at the higher temperature heating rate. Heating rate is a crucial factor affecting the decomposition results. The higher heating rate may decrease the distribution of the heat in the castor oil molecules and makes the thermal decomposition start at a higher temperature, which is consistent with the results reported by [21]. (a)

(b)

0

100

-5 -1

-10

4

,Mass loss rate×10 /s

Mass percentage/%

80

60

40

-1

5K min -1 10K min -1 15K min -1 20K min

20

-15 -20 -1

5K min -1 10K min -1 15K min -1 20K min

-25 -30 -35

0 300

400

500

600

700

Temperature/K

800

-40

300

400

500

600

Temperature/K

700

800

Fig. 1. TGA (a) and DTG (b) curves of castor oil at 5, 10, 15, and 20 K min-1

3.3 Kinetic parameters calculation of castor oil pyrolysis Iso-conversional methods, also called the model free approach, have been successfully used for studying the kinetics of different substances, which are derived with the assumption of reaction rate dependency on temperature and conversion degree only without making any assumptions about the reaction function and reaction order avoiding the risk of obtaining wrong kinetic parameters. Kinetic parameters of castor oil pyrolysis are studied through the isoconversional method, and seven conversion values from 10% to 70% with an increment of 10% are used for the kinetic calculation. Especially, Kissinger-Akahira-Sunose method (KAS) and Flynn-Wall-Ozawa method (FWO) are widely demonstrated to be proper for model free approach [22, 23]. Generally, kinetics equation under the linear heating rate is expressed as: dα dα E ) ⋅ f (α ) = k (T ) ⋅ f (α ) → β ⋅ = A ⋅ exp( − dt dT RT

(1)

Where α refers to reaction conversion, α=(M0-Mt)/(M0-Mf) (M0 refers to initial mass; Mt refers to the sample mass at time t; Mf refers to the final mass), f(α) refers to the reaction mechanism model, k(T) refers to the reaction rate constant described by Arrhennius equation, namely, k (T)=A·exp (-E/RT) (A refers to the pre-exponential factor; E refers to the activation energy; R refers to the gas constant.), T is temperature, β refers to the linear heating rate (β=dT/dt=constant). Eq. (1) can be integrated into,



α

0

T dα E = g (α ) = Aβ −1  exp(− )dT 0 f (α ) RT

(2)

For KAS method, Coats-Redfern approximation is applied for the temperature integration as shown in Eq. (3), g (α ) =

A RT 2 E ⋅ exp(− ) β E RT

(3)

The following equation is obtained by rearrangement and taking the natural logarithm of Eq. (3), ln(

β T2

 AE  E ) = ln  −  Rg (α )  RT

(4)

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As for FWO method, Doyle's approximation is used for temperature integration, g (α ) =

A

β

0.00484 exp( −1.052

E ) RT

(5)

By taking the natural logarithm and rearrangement of Eq. (5), Eq. (6) is obtained,  AE  E (6) ln( β ) = ln   − 5.331 − 1.052 RT  Rg (α )  The regression lines of ln(β/T2) versus 1/T for KAS method and ln(β) versus 1/T for FWO method, based on the same conversion at different temperature heating rates, give the activation energy obtained from the slope. In this study, the TGA is conducted under the four temperature heating rates of 5, 10, 15, 20 K min-1 and the regression lines based on KAS method and FWO method are presented in Fig. 2(a)(b), respectively. It can be observed from these figures that the regression lines are parallel indicating the activation energy at the different conversions follows a single mechanism or unification of multiple reaction mechanisms. The slope, the activation energy (E) and the correlation coefficient (R) are listed in Table 1. (a) -9.6

2

-1

2.7 -1

-10.5

10% 20% 30% 40% 50% 60% 70%

3.0

lnβ/K s

-1

-10.2

ln(β//T )/K s

(b) 3.3

10% 20% 30% 40% 50% 60% 70%

-9.9

-10.8

2.4 2.1

-11.1

1.8

-11.4

1.5

-11.7 1.41

1.44

1.47

1.50

1.53

1.56

1.41

3

1.44

1.47

T×10 /K

1.50

1.53

1.56

3

T×10 /K

Fig. 2. Regression lines to pyrolysis of castor oil based on KAS (a) method and FWO (b) method at 5, 10, 15, 20 K min-1

As data illustrated in Table 1, it is interesting to note there is no significant difference in the activation energy obtained between the two different methods and the relative error (ζ) is less than 0.8%, which lies within the kinetic equation errors. It is demonstrated that not only one mathematical method could be used to calculate the activation energy as long as they are properly selected, though the value varies to a certain degree. It may be found that the activation energy for castor oil pyrolysis is in the range of 182.97-233.44 kJ mol-1 with varying conversion (10% ≤ α ≤ 70%). The average value is observed as 202.88 kJ mol-1 and 203.66 kJ mol-1 for KAS method and FWO method, respectively. With the pyrolysis proceeded, the activation energy gets increased slowly, but no more than 5% before 50% conversion. Yet, as the conversion is shifted from 50% to 60%, the corresponding activation energy is changed from 205.98 kJ mol-1 to 233.44 kJ mol-1 for KAS method and 206.65 kJ mol-1 to 232.85 kJ mol-1 for FWO method, which is respectively increased by 13.33% and 12.67%. Then, the activation energy begins to decrease when the conversion value exceeds 60%. At the conversion of 70%, the activation energies separately drop to 223.19 kJ mol-1 for KAS and 223.67 kJ mol-1 for FWO. Table 1. Slope, E and R deduced from KAS method and FWO method α/%

KAS method slope

R

E/kJ mol

10

22.00

0.99

182.97

20

22.47

0.99

186.79

FWO method -1

ζ/%

R

E/kJ mol-1

23.32

0.99

184.28

0.71

23.80

0.99

188.10

0.69

slope



Hui Li et al. / Procedia Engineering 205 (2017) 3711–3716 Hui Li et al./ Procedia Engineering 00 (2017) 000–000 30

23.04

0.99

191.56

24.39

0.99

192.75

0.62

40

23.60

0.99

196.23

24.96

0.99

197.30

0.54

50

24.77

0.99

205.98

26.15

0.99

206.65

0.32

60

28.08

0.99

233.44

29.46

0.99

232.85

0.25

70

26.85

0.99

223.19

28.30

0.99

223.67

0.21

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Besides the activation energy, the reaction order is also an important factor to illustrate pyrolysis process and calculated through Avrami theory [24] as described in Eq. (7),

α = 1 − exp

− k (T )

(7)

βn

By taking double natural logarithm and rearrangement, Eq. (7) is transformed into, ln(− ln(1 − α )) = ln A −

E − n ln β RT

(8)

Thus, plots of ln(-ln(1-α)) versus lnβ is established under the same temperature and the slope of the regression line, n, is the reaction order. Just like the calculation of the activation energy, six temperature points distributed in the conversion range from 10% to 70% are selected at heating rates of 5, 10, 15, 20 K min-1. The correlation coefficient (R) and the calculated reaction order are presented in Table 2. From the value of R in Table 2, it is found that the Avrami theory is fitted well to estimate the reaction order for pyrolysis of castor oil. The reaction order varies indistinctively at the different temperatures which further illustrates the castor oil pyrolysis is composed of many parallel and sequential pyrolysis reactions corresponding with TGADTG results. It is also should be noted that though the reaction order exhibits a slight change, the average value is 1.02 which is close to 1.00, indicating the pyrolysis of castor oil can be practically treated as the first order during the whole process. Table 2. Reaction order deduced from Avrami theory for castor oil pyrolysis at six temperature points. Temperature/K

R

n

667

0.99

1.10

670

0.99

1.08

673

0.99

1.05

677

0.99

1.02

681

0.99

0.96

684

0.99

0.90

4. Conclusion In this study, the thermal characteristics of and kinetic parameters calculation of castor oil pyrolysis were evaluated through TGA–DTG. According to the results, the castor oil pyrolysis exhibits a distinct weight loss step. And the initial weight loss temperatures as well as the maximum value of the mass loss rate are shifted to higher temperature region as the increment of temperature heating rate. Two representative model free approaches, KAS method and FWO method, are selected to calculate the activation energy and the average values deduced from two methods are 202.88 kJ mol–1 and 203.66 kJ mol–1, respectively. The maximum activation energy is achieved at 60% conversion. The average reaction order determined by Avrami theory is 1.02 which is close to 1.00, suggesting the pyrolysis of castor oil practically follows the first order during the whole process. This study is expected to support

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Hui Li et al. / Procedia Engineering 205 (2017) 3711–3716 Hui Li et al./ Procedia Engineering 00 (2017) 000–000

the basic data for the industrial application of castor oil pyrolysis. Acknowledgements The work is supported by Shenzhen Science and Technology Research and Development Funds (JCYJ20160331184515666), the Young Scholars Program of Shandong University (YSPSDU, 2015WLJH33), the Fundamental Research Funds of Shandong University (2015JC024), and the Doctoral Fund of Shandong Jianzhu University (XNBS1603). References [1] Abnisa F, Arami–Niya A, Wan Daud WMA, Sahu JN, Noor IM. Utilization of oil palm tree residues to produce bio–oil and bio–char via pyrolysis. Energy Convers Manage. 2013;76:1073–82. [2] Li H, Niu SL, Lu CM, Liu MQ, Huo MJ. Use of lime mud from paper mill as a heterogeneous catalyst for transesterification. Sci China Tech Sci. 2014;57:438–44. [3] Gil MV, Riaza J, Álvarez L, Pevida C, Pis JJ, Rubiera F. A study of oxy–coal combustion with steam addition and biomass blending by thermogravimetric analysis. J Therm Anal Calorim. 2012;109:49–55. [4] Magdziarz A, Wilk M. Thermal characteristics of the combustion process of biomass and sewage sludge. J Therm Anal Calorim. 2013;114:519–29. [5] Li H, Niu S, Lu C, Liu M, Huo M. Transesterification catalyzed by industrial waste—Lime mud doped with potassium fluoride and the kinetic calculation. Energy Convers Manage. 2014;86:1110–7. [6] Ashraful AM, Masjuki HH, Kalam MA, Rizwanul Fattah IM, Imtenan S, Shahir SA, et al. Production and comparison of fuel properties, engine performance, and emission characteristics of biodiesel from various non–edible vegetable oils: A review. Energy Convers Manage. 2014;80:202–28. [7] Demirbaş A. Biodiesel fuels from vegetable oils via catalytic and non–catalytic supercritical alcohol transesterifications and other methods: a survey. Energy Convers Manage. 2003;44:2093–109. [8] Lehto J, Oasmaa A, Solantausta Y, Kytö M, Chiaramonti D. Review of fuel oil quality and combustion of fast pyrolysis bio–oils from lignocellulosic biomass. Appl Energy. 2014;116:178–90. [9] Dias JM, Araújo JM, Costa JF, Alvim–Ferraz MCM, Almeida MF. Biodiesel production from raw castor oil. Energy. 2013;53:58–66. [10] Ogunniyi DS. Castor oil: A vital industrial raw material. Bioresour Technol. 2006;97:1086–91. [11] Zhang L, Zhang M, Hu L, Zhou Y. Synthesis of rigid polyurethane foams with castor oil–based flame retardant polyols. Ind Crops Prod. 2014;52:380–8. [12] Zeng Q, Dong G. Influence of load and sliding speed on super–low friction of nitinol 60 alloy under castor oil lubrication. Tribol Lett. 2013;52:47–55. [13] Rodríguez–Guerrero JK, Rubens MF, Rosa PTV. Production of biodiesel from castor oil using sub and supercritical ethanol: Effect of sodium hydroxide on the ethyl ester production. J Supercrit Fluids. 2013;83:124–32. [14] Dias AN, Cerqueira MBR, Moura RRd, Kurz MHS, Clementin RM, D’Oca MGM, et al. Optimization of a method for the simultaneous determination of glycerides, free and total glycerol in biodiesel ethyl esters from castor oil using gas chromatography. Fuel. 2012;94:178–83. [15] Çepelioğullar Ö, Pütün AE. Thermal and kinetic behaviors of biomass and plastic wastes in co–pyrolysis. Energy Convers Manage. 2013;75:263–70. [16] Lim X, Sanna A, Andrésen JM. Influence of red mud impregnation on the pyrolysis of oil palm biomass–EFB. Fuel. 2014;119:259–65. [17] Lappi H, Alén R. Pyrolysis of vegetable oil soaps–Palm, olive, rapeseed and castor oils. J Anal Appl Pyrolysis. 2011;91:154–8 [18] El–Sayed SA, Mostafa ME. Pyrolysis characteristics and kinetic parameters determination of biomass fuel powders by differential thermal gravimetric analysis (TGA/DTG). Energy Convers Manage. 2014;85:165–72. [19] Vecchio S, Cerretani L, Bendini A, Chiavaro E. Thermal decomposition study of monovarietal extra virgin olive oil by simultaneous thermogravimetry/differential scanning calorimetry: relation with chemical composition. J Agric Food Chem. 2009;57:4793–800. [20] Thurgood J, Ward R, Martini S. Oxidation kinetics of soybean oil/anhydrous milk fat blends: A differential scanning calorimetry study. Food Res Int. 2007;40:1030–7. [21] Wu JL, Wang CW, Yin XL, Wu CZ, Ma LL, Zhou ZQ, Chen HP. Study on prolysis of heavy fractions of bio–oil by using TG–FTIR analysis. Acta Energiae Sol Sinica, 2010; 31: 113–7. [22] Manikandan G, Jayabharathi J, Rajarajan G, Thanikachalam V. Kinetics and vaporization of anil in nitrogen atmosphere – Non–isothermal condition. J King Saud University–Sci. 2012;24:265–70. [23] Gundogar AS, Kok MV. Thermal characterization, combustion and kinetics of different origin crude oils. Fuel. 2014;123:59–65. [24] Ruitenberg G, Woldt E, Petford–Long AK. Comparing the Johnson–Mehl–Avrami–Kolmogorov equations for isothermal and linear heating conditions. Thermochimica Acta. 2001;378:97–105.