Degradation Products Of Polyethylene Research Articles

Striking influence of chain structure of polyethylene on the formation of cup-stacked carbon nanotubes/carbon nanofibers under the combined catalysis of CuBr and NiO

A one-pot approach was used to convert polyethylene (PE) with different chain structures into carbon nanomaterials (CNMs) under the combined catalysis of CuBr and NiO at 700°C, including linear low density polyethylene (LLDPE), low density polyethylene (LDPE) and high density polyethylene (HDPE). The effect of chain structure of PE on the yield, morphology, microstructure, phase structure and thermal stability of CNMs, including cup-stacked carbon nanotubes (CS-CNTs) and carbon nanofibers (CNFs), were investigated by scanning electron microscope, transmission electron microscope (TEM), high-resolution TEM, X-ray diffraction, Raman spectroscopy and thermal gravimetric analysis. In addition, the degradation products from different chain structures of PE under the catalysis of CuBr were analyzed by gas chromatography and gas chromatography–mass spectrometry. It was demonstrated that the branched structure played an important effect in the degradation products of PE. The dehydrogenation and aromatization of LLDPE were remarkably promoted by Br radicals from the decomposition of CuBr to form a large amount of light hydrocarbons and a relatively small amount of aromatics, favoring the formation of long and straight CS-CNTs. However, the degradation of LDPE was not obviously influenced by Br radicals due to its high extent of branched structure, while the random cleavage of HDPE was accelerated with the formation of a lot of olefins with long chains, resulting in the formation of short and winding CNFs. This work will contribute to the conversion of mixed waste polyolefin into high value-added CNMs.

Catalytic degradation of polyethylene over solid acid catalysts

In this study we investigated the catalytic degradation of polyethylene (PE) in a fixed-bed reactor composed of a melter and a catalytic cracking bed. Solid acid catalysts, silica–alumina and zeolites [HZSM-5, natural zeolite (NZ), Y zeolite, etc.] were screened for polyethylene degradation in the range of 450–500°C. The degradation products of PE, especially a liquid fraction, formed over solid acid catalysts, were analyzed by gas chromatography–mass spectroscopy (GC–MS). Compared with those obtained by thermal degradation, the catalytic degradation products are distributed in a narrow range of carbon numbers. The liquid fraction contained large amounts of iso-paraffins and aromatics, as are present in the gasoline fraction of petroleum. The NZ catalyst (clinoptilolite structure, occurring in the Youngil area of Korea) was an efficient catalyst for the PE degradation. The acidity and characteristic pore structure of zeolites appear to be responsible for the good performance. The effects of temperature, contact time, and the presence of nickel metal on the product distribution in PE degradation are also discussed in this work.

Gas chromatographic determination of the products of degradation of polyethylene over a silica—alumina catalyst

The degradation products of polyethylene, especially a liquid fraction, formed over a silica-alumina catalyst were analyzed by glass capillary column gas chromatography. The liquid fraction contains large amounts of the same isoalkanes and aromatics as are present in the gasoline fraction of petroleum. Most of the isoalkanes are monobranched with a methyl group at the 2- or 3-position. The aromatics consist mainly of those with one or more methyl groups and are produced highly selectively at carbon numbers higher than 7. The degradation products are distributed in a narrow range of carbon number compared with those obtained by thermal degradation. The relative yield Of C 3C- 5 fractions was greater than 70 wt. % at the initial stage of the reaction. Isomerization, aromatization and hydrogen transfer reactions seem to play an important rôle in the secondary degradation of the primary products of polyethylene.

Differential heats of adsorption and isotherms of some alkanes and naphthenes on silica gel

The degradation products of polyethylene, especially a liquid fraction, formed over a silica-alumina catalyst were analyzed by glass capillary column gas chromatography. The liquid fraction contains large amounts of the same isoalkanes and aromatics as are present in the gasoline fraction of petroleum. Most of the isoalkanes are monobranched with a methyl group at the 2- or 3-position. The aromatics consist mainly of those with one or more methyl groups and are produced highly selectively at carbon numbers higher than 7. The degradation products are distributed in a narrow range of carbon number compared with those obtained by thermal degradation. The relative yield Of C3C-5 fractions was greater than 70 wt. % at the initial stage of the reaction. Isomerization, aromatization and hydrogen transfer reactions seem to play an important rôle in the secondary degradation of the primary products of polyethylene.