Liquefaction of commodity polymers to oils and gases can be used to recover the energy value of these materials. This article reports liquefaction data for highdensity polyethylene (HDPE), one of the major plastics in recycled material. Thermal degradation of HDPE to oil-gas mixtures required higher temperatures (450 -490°C) than low-density polyethylene (LDPE) (430 -460°C) because of fewer chain branching points for HDPE, which are more susceptible to chain scission reactions. The addition of hydrogen (0.1-1.5 MPa) had negligible effect on product distribution. HDPE thermal degradation is consistent with a random chain scission mechanism. Product distributions for degradation at 450°C were modeled assuming random chain scission with a rate constant k( x) dependent on the molecular weight x by a power law model dependence, k( x) ϭ k b x b , where k b is the pseudo-first-order rate constant, and b is the power index of dependence on molecular weight. Degradation rates dropped rapidly after initial breakup of the chains, and 2 sets of coefficients were needed to describe the molecular weight distributions as functions of reaction time. The error in model was about 10%. This model can be used to optimize the production of oils from thermal degradation of HDPE.
Liquefaction of commodity polymers to oils and gases can be used to recover the energy value of these materials. This article reports liquefaction data for highdensity polyethylene (HDPE), one of the major plastics in recycled material. Thermal degradation of HDPE to oil-gas mixtures required higher temperatures (450 -490°C) than low-density polyethylene (LDPE) (430 -460°C) because of fewer chain branching points for HDPE, which are more susceptible to chain scission reactions. The addition of hydrogen (0.1-1.5 MPa) had negligible effect on product distribution. HDPE thermal degradation is consistent with a random chain scission mechanism. Product distributions for degradation at 450°C were modeled assuming random chain scission with a rate constant k( x) dependent on the molecular weight x by a power law model dependence, k( x) ϭ k b x b , where k b is the pseudo-first-order rate constant, and b is the power index of dependence on molecular weight. Degradation rates dropped rapidly after initial breakup of the chains, and 2 sets of coefficients were needed to describe the molecular weight distributions as functions of reaction time. The error in model was about 10%. This model can be used to optimize the production of oils from thermal degradation of HDPE.
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