Gas chromatography-mass spectrometry and high-performance liquid chromatographic analyses of thermal degradation products of common plastics

Thermal degradation of waste plastics under non-sweeping atmosphere: Part 2: Effect of process temperature on product characteristics and their future applications

The current energy demand and diminishing conventional fuels have forced researchers to find an alternative source of energy. Waste to energy is the current trend for converting waste materials (plastic waste) into valuable fuels. This article mainly discussed the detailed characterization of the pyrolytic products, their comparative analysis and the reaction mechanism at varying operating temperature. This article is a successor of part 1, which primarily focused on the characterization of different waste plastics, their TG analysis, the effect of reactor temperature on yield analysis in a batch reactor and their detailed degradation mechanism. Furthermore, the results presented in this article report the characterization of products at three processing temperatures of 450, 500 and 550 °C. The pyrolytic oils from all wastes excluding PS show a very low density ranging from 0.71 to 0.76 kg/m³, whereas PS pyrolytic density is reported between 0.86 and 0.88 kg/m³. The viscosity of oils increases with an increase in the processing temperature and is similar to the conventional fuels. The FTIR analysis of the products (oil & gases) obtained from HDPE, PP and mixed plastic waste (MIX) shows a large presence of alkanes and a higher presence of aromatics. PS analysis reported a large presence of aromatics (~75%). The GC-MS analysis of all pyrolytic oils from waste plastics, simulated wastes (virgin plastics) and distilled fraction of MIX pyrolysis oil is compared. The GC analysis of non-condensable gases at all processing temperature reports that MIX produce the maximum H₂; HDPE, PS and MIX produces a high amounts of CH₄ too. The formation of lower hydrocarbons (C₅-C₁₂) in pyrolysis oil shows a trend as MIX > PP > PS > HDPE, while for the heavier hydrocarbons (>C₁₉) it is HDPE > PP > PS > MIX. The potential of the utilization of these products has been discussed in different sectors for future research.

The Chemistry and Kinetics of Polyethylene Pyrolysis: A Process to Produce Fuels and Chemicals

The annual global production of plastics reached 335 million metric tons in 2016. Most waste plastics are landfilled or enter the natural environment in an uncontrolled manner. Pyrolysis can convert waste plastics, such as polyethylene (PE), to smaller hydrocarbons that can be used as fuels or chemicals. In this work, pyrolysis of PE was studied by thermogravimetric analysis (TGA) and in a fluidized-bed reactor. A kinetic model based on two parallel first-order random-scission steps was developed on the basis of the TGA results. PE was pyrolyzed in a fluidized-bed reactor over the temperature range of 500-600 °C and at residence times of 12.4-20.4 s. The yield of gas-phase products increased from 8.2 to 56.8 wt %, and the yield of liquid-phase products decreased from 81.2 to 28.5 wt % as the temperature increased from 500 to 600 °C. Detailed analysis of the gas- and liquid-phase products revealed their potential as precursors for production of fuels and chemicals. Gas-phase products included hydrogen, C₁ -C₄ paraffins, C₂ -C₄ olefins, and 1,3-butadiene. The major liquid-phase products were mono-olefins and cycloalkanes/alkadienes with smaller amounts of n-paraffins, isoparaffins, and aromatics. The carbon-number distribution of the fluidized-bed pyrolysis products suggested contributions of nonrandom reactions of random-scission fragments at low conversion.

The pollution characteristics of odor, volatile organochlorinated compounds and polycyclic aromatic hydrocarbons emitted from plastic waste recycling plants

Plastic waste treatment trends toward recycling in many countries; however, the melting process in the facilities which adopt material recycling method for treating plastic waste may emit toxicants and cause sensory annoyance. The objectives of this study were to analyze the pollution characteristics of the emissions from the plastic waste recycling plants, particularly in harmful volatile organochlorinated compounds, polycyclic aromatic hydrocarbons (PAHs), odor levels and critical odorants. Ten large recycling plants were selected for analysis of odor concentration (OC), volatile organic compounds (VOCs) and PAHs inside and outside the plants using olfactometry, gas chromatography-mass spectrometry and high performance liquid chromatography-fluorescence detector, respectively. The olfactometric results showed that the melting processes used for treating polyethylene/polypropylene (PE/PP) and polyvinyl chloride (PVC) plastic waste significantly produced malodor, and the odor levels at downwind boundaries were 100-229 OC, which all exceeded Taiwan's EPA standard of 50 OC. Toluene, ethylbenzene, 4-methyl-2-pentanone, methyl methacrylate and acrolein accounted for most odors compared to numerous VOCs. Sixteen organochlorinated compounds were measured in the ambient air emitted from the PVC plastic waste recycling plant and total concentrations were 245-553 microg m(-3); most were vinyl chloride, chloroform and trichloroethylene. Concentrations of PAHs inside the PE/PP plant were 8.97-252.16 ng m(-3), in which the maximum level were 20-fold higher than the levels detected from boundaries. Most of these recycling plants simply used filter to treat the melting fumes, and this could not efficiently eliminate the gaseous compounds and malodor. Improved exhaust air pollution control were strongly recommended in these industries.

Characterization of semi-volatile organic compounds emitted during heating of nitrogen-containing plastics at low temperature

Because of recent volume increases, appropriate management of plastic recycling, which generates various organic compounds, is required to ensure the chemical safety of the processes. The processing temperature and resin type are the important factors determining both the efficiency of the processes and the emission of chemicals. Therefore, we studied the thermal degradation of various plastics at various temperatures from 70 to 300 degrees C under oxygen-present conditions to identify the semi-volatile organic compounds (SVOCs) emitted and to understand their thermal behaviors. The plastics examined were nitrogen-containing resins, such as polyamide 6, polyurethane, melamine formaldehyde, urea formaldehyde and acrylonitrile-butadiene-styrene. Major commodity plastics were also investigated for comparison. In total, more than 500 SVOCs were detected as emissions from plastics. While various nitrogen-containing SVOCs were detected from nitrogen-containing resins, the major commodity plastics released only these, which possibly were included as additives. These results indicate that the nitrogen atoms in the SVOCs emitted originated from the resins and additives, and not from ambient air at low temperature. As a result of the detection of raw materials, degradation chemicals and by-products of the polymers in the emissions, we found that the variation in chemical species is dependent on the resins. Additives were also emitted from all the resins, meaning that these chemicals were also released to the environment at the temperature examined. In most cases, the numbers and concentrations of SVOCs increased with increasing heating temperature. The variation of thermal behaviors of SVOCs was related to the origins and chemical species of SVOCs.

A brush fire forensic case

In Italy, every summer forest fires attract public attention due to the number of victims, the intensity of the fires, the areas devastated, the environmental damage and the loss of property. Excluding some fires by natural causes, other causes are related to the social, economic, and productive profile of the territory. The erroneous expectation is that wooded areas destroyed by fire can then be used for private interests. Often, a fire, started to clear a small area, can completely change the expected result, producing disaster, loss of property, destruction of entire forests and resident fauna, and kill innocent people. In this case report, the reconstruction of an arson scene, the analytical techniques and the results obtained are illustrated in this paper, with the aim of sharing with other research laboratories the current knowledge on forest fire.