5-7 OCTOBER

ISFR

2011

51

TOLEDO (SPAIN)

MODELING OF TUBE REACTOR FOR PYROLYSIS OF POLYETHYLENE
J.M.N. Van Kasteren1, Q. Zhou1
1 Eindhoven University of Technology, Eindhoven Energy Institute, PO Box 513, 5600 MB Eindhoven, The Netherlands

e-mail:j.m.n.v.kasteren@tue.nl

Abstract
A Mathematical model of a tubular reactor is used to describe the pyrolysis process of poylethylene with which it is possible
to investigate the effects of tube reactor geometrical dimensions on pyrolysis behaviors of polyethylene, which is beneficial toscaling up the reaction system. The temperature and PE concentration profiles in the tube reactor are obtained using thismodel. By adjusting variants such as PE flow velocity, reactor diameter and length, the optimal parameters to realize theoptimal process design for pyrolysis can be obtained.

Keywords: Modeling; Tube reactor; Pyrolysis; Waste polymers; Recycling

1. Introduction
Dutch government is planning to increase the plastic
recycling by 42% by 2012. Pyrolysis of polymers is often
regarded as the most promising technology for resource
recovery from waste polymer materials. Quite a lot ofresearch work on the pyrolysis of individual and mixed
plastics into liquid products has been reported[1].Especially, developing pyrolysis reactors is of special
interest to realize industrial application. Among thevaious reactors, tube reactor possesses the advantagesof simplicity and ability to conduct continuous process [2].
In this paper, mathematical model of the tubular reactor
is developed to investigate the effects of tube reactor
geometrical dimensions on pyrolysis behaviors ofpolyethylene.

2. Materials and Methods
Scheme of the tube reactor were shown in Fig.1.
Flow inrr=R

Heat conduction through the wall is neglected;
Heat conduction in axial direction is neglected.
Assumptions were made for pyrolysis reaction ofpolyethylene:
Reactions are first order;
Reactions are irreversible;
No mass transfer resistances;
The temperature dependence of the rate
constants is described by the Arrhenius
equation.
The model was calculated with Borland Delphi 7 byadjusting the programming code Adinra.pas, whichsolves concentration and temperature profiles in the tube
reactor based on an alternating direction implicit method.

3. Results and Discussion
Equations of continuity and energy based on theassumptions for the mathematical model are as follows:

Flow outr=0z

Equation of continuity (equation 1):

C PEzvz r

Fig.1 Scheme of the tube reactor
Assumptions were made to describe the heat transfer
model in the tube reactor:
Steady state;
Heat transfer is in radial and axial directions;
No velocity in r and θ directions;
Velocity profile is parabolic (laminar flow);
Viscosity is constant;
No shear stress;
Feed is 1000 kg/h (~5000 t/y);
T0 = 195°C, Twall = 450°C;

interiores libro.indd 51DPECr PPEEr rrkC PPE ((1))

Equation of energy (equation 2):vz rTzrr(rT)
rkC PEECpH r (2)Polyethylene pyrolysis is a well known process [3]. Table
1 listed related data for the model.
The pyrolysis reaction rate constants are summed up inTable 2. Where
k1 describes the reaction Polyethylene → heavy oils;
k2: Polyethylene → light oils;
k3: Polyethylene → gas;

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6th International Symposium on Feedstock Recycling of Polymeric Materials

k4: Polyethylene → polymer of lower molecular weight.
Table 1. The constants used for the modeling

By adjusting the variants such as PE flow velocity,
reactor diameter and length, optimal parameters forpyrolysis can be obtained.

Parameter

Constant

References

Tr=R (Temperature of the reactor wall,oC)

450

Molecular weight of the polyethylene (Da)

200000[1] J.Scheirs, W.Kaminsky. Feedstock Recycling andPyrolysis of Waste Plastics: Converting Waste Plastics
into Diesel and Other Fuels. Hoboken, NJ. 2006. Wiley &Sons.
[2] A. Angyal, N. Miskolczi, L. Bartha and I. Valkai.
Catalytic cracking of polyethylene waste in horizontal
tube reactor. Polymer Degradation and Stability 94(2009) 1678-1683.
[3] P.A. Costa, F.J. Pinto, A.M. Ramos, I.K. Gulyurtlu, I.A.
Cabrita, M.S. Bernardo, Kinetic evaluation of thepyrolysis of polyethylene waste, Energy&Fuels, 21(2007)
2489 – 2498.

Cp (Heat capacity, J/(kg·K))

49

Thermal conductivity (W/(m·K)

0.25

Density, kg/m3

920

Viscosity, Pa·s

2478

CPE,z=0 (Initial concentration of PE, mol/m3)

5H r (Enthalpy of the reaction, KJ/kg)-1300

Table 2 The reaction rate constants for pyrolysis ofpolyethylene depending on temperature [3]T [°C]
K[s-1]

400

420

450

470

k1

0.02750.10060.02930.0332k2

0.00210.06040.23150.4488k3

0.00000.00030.00000.0000k4

0.07770.11990.06930.1678

According to the mathematical model, a 3 D temperature
profile along the tube reactor depending on the diameterand length were obtained (Fig.2)

Fig. 2 3D temperature profile for the tube reactor(Diameter: 0.03m; Length: 1m)

4. Conclusions
In summary, mathematical model of a tubular reactor isused to describe the pyrolysis system of PE. The
temperature and PE concentration profiles during
pyrolysis in the tube reactor were obtained.

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