Thermal Decomposition Of Polyethylene Research Articles

Thermal decomposition of polyolefins under different oxygen content. Composition of products and thermal effects

The thermal decomposition of polyethylene and polypropylene was studied under conditions of different oxygen contents in the carrier gas in the temperature range of 200–600 °C. The effect of adding an oxidizing agent to the carrier gas was studied at (O2/N2)mol ratios of 0/100; 1/99; 2/98; 4/96; 6/94; 10/90; 21/79. Combined TG-FTIR and TG-DSC techniques were used in the studies. Based on FTIR spectra, a quantitative and qualitative analysis of the process gaseous products was performed. The study showed that the thermal degradation of polyolefins can lead to mixtures of saturated and unsaturated hydrocarbons, which are an attractive substitute for natural gas for hydrogen production. The molar ratio of saturated/unsaturated hydrocarbons for PE and PP is 3/2. The composition of the gas product mixture as well as the heat balance of the process can be controlled by adjusting the oxygen concentration in the carrier gas. With a content of 3%O2 in the carrier gas for PE and 4%O2 for PP, autothermal conditions of the thermal processing of polyolefins are achieved. The addition of oxygen accelerates the transformation of polyolefins and thus lowers the optimal process temperature. The CxHyO and CO mixture, coexisting with the hydrocarbon mixture in some process variants, can be converted by the water shift reaction into a mixture of H2 and CO2.

Evaluation of the reactive molecular dynamics method for Research on flame retardants: ATH-filled polyethylene

We carried out reactive molecular dynamics simulations based on the ReaxFF reactive force field to study the effect of aluminium (tri)hydroxide on the thermal decomposition of polyethylene. The simulations reproduced the endothermic decomposition of aluminium (tri)hydroxide into alumina and water. Other known mechanisms of flame retardancy, such as heat absorption by the filler and its residue, were reproduced with reasonable accuracy. The simulations also revealed a chemical interaction between polyethylene and aluminium (tri)hydroxide, in which hydroxyl radicals released by the aluminium (tri)hydroxide abstracted hydrogen from the surrounding polyethylene, resulting in enhanced water production and enhanced charring of polyethylene. Based on our results, we consider reactive molecular dynamics simulations a promising tool for investigating existing and emerging flame retardant concepts, and the pyrolysis chemistry of flame retardant polymer systems.

Quantum-Chemical Study of Stressed Polyethylene and Butadiene Rubber Chain Scission

The thermal decomposition of polyethylene and butadiene rubber chains in the presence of a tensile force acting along the axis of the molecule was simulated. The reaction of an isolated chain was considered. The chain models were the octane and 2,6-octadiene molecules. A deformation was introduced in the problem by fixing nonequilibrium distances between the terminal carbon atoms. The reaction coordinate (the middle C–C bond length R) was scanned at a fixed length of the molecule (L). That is, the potential energy surface section of the reaction was constructed at L = const. The reaction sensitivity to deformation was evaluated by B3LYP, LC-ωPBE, CCSD(T), CASSCF, and MP2 quantum-chemical calculations. All these calculations showed that the molecule elongated by ~1 A for polyethylene, but shortened by 0.3–0.5 A for 2,6-octadiene during chain scission. This means that the tensile deformation accelerates the decomposition of polyethylene, but decelerates the decomposition of butadiene rubber.

Thermal conversion of polyolefins/polystyrene ternary mixtures: Kinetics and pyrolysis on a laboratory and commercial scales

The thermal treatment of the three-component mixtures of polyethylene, polypropylene and polystyrene has been investigated. Thermal reactions have been described and the kinetics of thermal decomposition using the Friedmańs differential isoconversional method have been evaluated; slow pyrolysis on a laboratory scale and the pyrolysis of a contaminated waste mixture on a commercial scale have been carried out. The obtained results show that polystyrene radicals promote the decomposition of polyolefins, as a result of which the thermal decomposition of polyethylene and polypropylene proceeds faster and the yields of the gas and oil obtained during pyrolysis are quite high: 4–6wt.% of gas and 88–90wt.% of oil in the case of laboratory-scale pyrolysis and 15wt.% of gas and losses and 80wt.% of oil in the case of commercial-scale pyrolysis. TG-FTIR and TG-MS analyses have proved that the composition of volatile pyrolysis products varies. In the case of the ternary mixture with prevailing polyethylene (and polypropylene and polystyrene being in minority), the volatiles contained mainly aliphatic hydrocarbons and substituted benzenes; in the case of the ternary mixture with prevailing polypropylene, a significantly higher amount of substituted alicyclic compounds was found. This was confirmed by the GC–MS analysis of the oils obtained. Considering the quite high HHV and LHV of oils (46–48MJ/kg and 43–45MJ/kg, resp., in the case of laboratory-scale pyrolysis and 43 and 41MJ/kg, resp., in the case of commercial-scale pyrolysis) as well as the very low content of sulfur and nitrogen, the oils can be used as a clean liquid fuel; because of their composition, they can also serve as a source of chemicals and solvents.

Assessing the effect of molecular weight on the kinetics of backbone scission reactions in polyethylene using Reactive Molecular Dynamics

Kinetics of polymer bond scission, the initial step in thermal decomposition of polyethylene and other vinyl polymers, was investigated as a function of the number of repeat units using an improved Reactive Molecular Dynamics (RMD) approach, which is introduced here. The rate of scission per bond is shown to depend on the degree of polymerization, an effect not captured by the conventional practice of modeling polymer decomposition with small-molecule Arrhenius parameters. In the new approach, implemented in an open-source C++ code RxnMD, well-behaved reactive force fields are generated using switching functions that activate and attenuate terms obtained from a conventional, non-reactive force field. In this way, predefined reaction types are modeled accurately by interpolating smoothly between non-reactive potential energy terms describing reactants, transition states, and products.

Study on the pyrolysis of polyethylene in the presence of iron and copper chlorides

Pyrolysis experiments were conducted to elucidate the effects of metal chlorides on the thermal degradation of low-density polyethylene on a continuous pyrolysis temperature range of 600 °C to 1100 °C. The present work focusses on the ratio of aromatics generated on increasing the pyrolysis temperature in the presence of metal salts, iron(II), iron(III) and copper(II) chlorides. It was observed that beside α,ω-dienes, α-olefins and n-alkanes which are usually observed during the thermal decomposition of polyethylene, the level of aromatics noticeably increases with the addition of metal salts. At high temperatures, the formation of these aromatics took place in such a way that they become the major products when polyethylene is pyrolyzed in presence of FeCl 3 and CuCl 2. Quantification of the effect of metal salts has been tempted comparing the variation of the ratio of aromatics with pyrolysis temperatures. Mechanisms responsible for the formation of these aromatics in presence of metal salts have been tentatively investigated. They are proposed to result from cyclization/dehydrogenation reactions similar to those observed during the thermal decomposition of polyethylene, but with an increased efficiency due to the metal salts.

Thermogravimetric studies on the thermal decomposition of polyethylene

The thermal decomposition of polyethylene was analyzed by dynamic and isothermal experiments. Dynamic runs with different heating rates, exposed surface and initial mass were carried out. Isothermal runs of different initial mass were also carried out. Several kinetic models were tested and the best fit to the experimental thermogravimetry curves was obtained with a model involving a surface zero-order reaction.

Effect of Atmosphere and Added Materials on Recovery of Liquid Products by Thermal Decomposition of Polyethylene

Effect of Atmosphere and Added Materials on Recovery of Liquid Products by Thermal Decomposition of Polyethylene