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NIRE Annual Report
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 1999

Continuous-Distribution Kinetics for Macromolecular Conversion for Degradataion of Plastics

Hydrocarbon Research Division
Energy Resources Department
Objectives
For the development of effective methods to utilize organic resources, it is required to evaluate "rate" of the conversion of heavy oil conversion and chemical recycling of waste. Recently we have reported liquid-phase cracking of phenolic resin resulting regeneration of phenols1). Continuous-distribution kinetics is the convenient method to analyze rate of degradation for macromolecules, in which the molecular-weight distribution (MWD) continuously spans the wide range of molecular weights. Rate of degradation can be defined by time differentials of molar concentration of a polymer as well as reaction rate of chemicals of a few components. MWDs of a polymer and its reaction mixtures at some reaction times under some temperatures give changes of molar concentration. Constructing a mathematical model based on simple reaction schemes and comparing the mathematical results with experimental results give the rate of degradation. We have examined such kinetic models for phenolic resin (novolac) degradation to obtain the apparent kinetic parameters.
Results
A continuous-flow apparatus equipped with a tubular reactor was used to obtain the apparent rate of novolac resin degradation. Different from polyethylene degradation2), substituted phenol linked with each other by methylene group is the major component depicted as A in liquid-phase cracking of novolac solution. Scheme A represents radical formation and radical coupling, scheme B is pseudo first order representation of radical stabilization with tetralin, and scheme C is radical recombination/fragmentation. Behavior of a radical, especially, reaction of a radical with tetralin, is so important that the scheme of radical stabilization is included.
Material balance equations with assumptions like ks >> kc and kf a(0) >> kF give
a(0) (t) = kq ao(0) exp(kst)/{kq+2 ao(0) kf [exp(ks t)-1]} (1)
a(0) (0) = ao(0) and a(0) (t®¥,= kq /2 kf)
where a(0) (t) is the molar concentration of novolac polymer, A(x), at the reaction time
 t and ao(0) is the initial molar concentration of the polymer.
This model agreed to the experimental results shown in Fig. 1 except the plots later than 50 min at 370 and 390°C, where monomeric species was not detected due to analytical difficulty. Arrhenius plot based on the data at the first 10 min at 310-390°C; gave the linear relation of ln(rate) to 1/T.
Fig. 1. a(0)(t) versus time

Selected Publications
1) Sato, Y., Kodera, Y., Kamo, T., Energy & Fuels, 13, 364, 1999.
2) Kodera, Y., McCoy, B. J., AIChE J., 43, 3205, 1997.

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