자동차용 폐윤활유의 열분해 반응 속도

김승수, 전병희, 윤왕래*, 김성현

고려대학교 화학공학과, 한국에너지기술연구소 전환공정연구팀*

Pyrolysis Kinetics of Waste Automobile Lubricating Oil

Seung-Soo Kim, Byung-Hee Chun, Wang Lai Yun*,Sung Hyun Kim

Dept. of Chem. Eng., Korea University. Seoul, Korea

Energy Conversion Team, Korea Institute of Energy Research, Taejon, Korea*

Introduction

The amount of domestic waste automobile lubricating oil was 343,335 kL in 1997[1]. Some studies to elucidate the mechanism of the degradation of organic materials have been reported. Paolo et al. proposed that the thermal degradation of polystyrene followed first-order kinetics in the initial part of the reaction[2]. Maria et al. and Ryoichi et al. researched the thermal cracking of coal residues[3-4]. Their lump model was proposed the lump model which considers parallel reactions for oil + gas and coke formation. Levent et al. and Prakash et al. developed for the pyrolysis of petroleum waste a combined parallel and series reaction scheme[5-6]. Though the extensive knowledge has been accumulated about lumped kinetics, no attempt has been made so far the kinetic model for the waste automobile lubricating oil. This study is important, because it will give more insight into the waste automobile lubricating oil re-refined process. The reason for the increase in the yields of pyrolysis liquid can be explained from the values of the kinetic rate parameters.

The main purpose of this work is to propose a reaction pathway for the pyrolysis of waste automobile lubricating oil and to develop a kinetic model for the pyrolysis. Kinetic parameters in these equations were evaluated by nonlinear least-squares regression of the experimental data to the numerical solutions of the differential equations. The effects of reaction temperature and residence time were analyzed.

Experimental Section

The pyrolysis reaction for the waste automobile lubricating oil was conducted in a microscale tubing reactor. The volume of tubing reactor was 39-cm3. A sample mass of 5g was charged into the tubing reactors for all experimental runs. The pyrolysis experiments were carried out at different temperatures(420, 430, and 440 ℃) and reaction times(5, 10, 15, 20, 30, 40, and 50 min). Gas yield was obtained by weighing the tubing reactor before and after venting gases from the tubing reactor. Other pyrolyzed products were separated into oil (hexane soluble) and coke (hexane insoluble) by forward sequential extraction procedure.

The liquid products were analyzed for simulating boiling point distribution (ASTM D-2887)[17]. Capillary column a HP-1 (0.53mm i.d., 5m length) was employed with programmed temperature from 50 to 350 ℃. The peaks were identified by comparing retention times with those of known reference compounds.

Kinetic Model Development

In this work, the kinetic study of the formation C5∼C25 was limited to the product of the reaction. To simplify the kinetic treatment of the experimental data, the volatile products were lumped in two groups, C5∼C11 and C12∼C25.

The pyrolysis of waste automobile lubricating oil mechanism assumed for the kinetic model development in this study is shown below.

1. All the reactions are irreversible.

2. The reactions are first order.

3. Products of the pyrolysis of waste automobile lubricating oil include gas,     oils, and coke.

4. The kinetic study limits to the produced oils.

C1(C5∼C11)

k3

A(>C25)                B(C12∼C25)                 C2(C5∼C11)     ( 1 )

k1                         k2

Based on these assumptions the rate of formation/depletion of various components can be written as follows:

[eqn: ~~~{dC_A over dt} ~=~-{(`k_1 ~-~ k_3`)}`C_A ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~(2)]

where CA is the concentration of >C25, k1 is the kinetic constant for C12∼C25  formation.

The rate of C12∼C25 formation is expressed by:

[eqn: ~~~{dC_B over dt} ~=~{ k_1 `C_A ~-~ k_2 `C_B } ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~(3)]

where CB is the concentration of C12∼C25 , k2 is the kinetic constant for    C5∼C11  formation.

C1 and C2 are the same component among the components of produced oil. Thus, the rate of C5∼C11 formation is expressed by:

[eqn: ~~~{dC_C over dt} ~=~{ k_1 `C_A ~+~ k_2 `C_B } ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~(4)]

where CC is the concentration of C5∼C11 , k3 is the kinetic constant for C5∼C11 formation from the >C25 and C12∼C25.

Results and Discussion

In Figure 1, 2, and 3 represent the yields to the two groups of products and reactant as functions of time at the temperature of 420, 430, and 440 ℃. The yield of C5∼C11 and C12∼C25 shows increase depending on time at which the yield of >C25 gradually decrease. The parameter estimation problem can be mathematically formulated into the constrained nonlinear optimization program(Levenberg-Marquardt method). The estimated reaction rate constants are shown in Table 1. The reaction kinetic constants indicate the selectivity of products. The reaction rate constant k1 was increased with the temperature of pyrolysis increasing from 420 ℃ to 430 ℃. It has been appeared the similar reaction rate constant at the temperature of 430 ℃ and 440 ℃. The temperatures were increasing, k2 was smaller and the k3 was higher. It means that the pyrolysis of waste automobile lubricating oil become predominant reaction pathway from >C25 to C5∼C11 formation comparing with from C12∼C25 to C5∼C11 formation.

Conclusion

1. A lumped kinetic model was proposed to represent the pyrolysis reaction of automobile lubricating oil in tubing reactor, where C5∼C11 and C12∼C25 were separately taken into account as products. The proposed kinetic model was found to well represent the experimental results.

2. The reaction rate constants k1 and k3 were increased in which the reaction temperatures were increasing. However, the temperatures were increasing, the reaction rate constant k2 was smaller. Thus, the formations of products increasing with temperature >C25 to C12∼C25 and >C25 to C5∼C11 are preferred the formation of C12∼C25 to C5∼C11.

Acknowledgement

This research was supported by the Korea Institute of Energy Research.

Reference

1. Korea Lubricating Oil Industries Association Bulletin, Vol.3, No.86, 1998.

2. Paolo Carniti et al., Ind. Eng. Chem. Res. 30, 1624-1629, 1991.

3. Maria T. Martinex et al., Fuel, 76, 9, 871-877, 1997.

4. Ryoichi Yoshida et al., Fuel, 55, October, 337-340, 1976.

5 Levent Ballice et al., Fuel, 76, 5, 375-380, 1997.

6 Prakash et al., Fuel Processing Technology, 51, 83-100, 1997.

Figure 1. Product distribution on      Figure 2. Product distribution on

Waste automobile lubricating oil       Waste automobile lubricating oil

at 420 ℃                           at 430 ℃

Temperature(℃)	Rate constant(min-1)
	k1	k2	k3
420	0.0375	0.0151	0.0134
430	0.0536	0.0096	0.0198
440	0.0519	0.0051	0.0285

Figure 1. Product distribution on     Table 1. Reaction rate constant(min-1)

Waste automobile lubricating oil      Waste automobile lubricating oil

at 420 ℃