No abstract

No abstract

Polymer production and utilization are currently widespread and have greatly improved people's standards of living. However, due to their stable and nonbiodegradable nature, postconsumer polymers pose challenging issues to the environment and ecosystems. Efforts are being made not only to contain the generation of polymer wastes and associated littering but, also, to find ways of utilizing them sustainably. Aside from mechanical recycling, which turns postconsumer polymers into new polymer products, and thermal recycling, which releases the thermal energy contained within waste plastics through combustion, chemical recycling converts waste polymers into feedstock for chemicals/materials/fuels production. This manuscript reviews prior work on a special application of the particular chemical recycling route that converts polymers into carbon-based nanomaterials. These materials feature extraordinary physical and chemical properties with tremendous applications potential. However, their production processes are both resourceand energy-intensive. Yet, by taking advantage of the high carbon content of waste polymers, as well as of their high energy content, a cost-effective, environmentally-friendly, and self-sustaining production of carbon nanomaterials can be achieved. V C 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014, 131, 39931.

No abstract

A fundamental investigation has been conducted on the combustion behavior of single particles (75-150 μm) of four coals of different ranks: anthracite, semi-anthracite, medium-volatile bituminous and high-volatile bituminous. A laboratory-scale transparent laminar-flow drop-tube furnace was used to burn the coals, electricallyheated to 1400 K. The experiments were performed in different combustion atmospheres: air (21%O 2 /79%N 2 ) and four simulated dry oxy-fuel conditions: 21%O 2 /79%CO 2 , 30%O 2 /70%CO 2 , 35%O 2 /65%CO 2 and 50%O 2 /50%CO 2 . The ignition and combustion of single particles was observed by means of three-color pyrometry and high-speed high-resolution cinematography to obtain temperature-time histories and record combustion behavior. On the basis of the observations made with these techniques, a comprehensive examination of the ignition and combustion behavior of these fuels was achieved. Higher rank coals (anthracite and semi-anthracite) ignited heterogeneously on the particle surface, whereas the bituminous coal particles ignited homogeneously at the gas phase. Moreover, deduced ignition temperatures increased * Corresponding author: Tel.: 001 (617) 373-3806; Fax: 001 (617) 373-2921 E-mail address: y.levendis@neu.edu 2 with increasing coal rank and decreased with increasing oxygen concentrations.Strikingly disparate combustion behaviors were observed depending on the coal rank.The combustion of bituminous coal particles took place in two phases. First, volatiles evolved, ignited and burned in luminous enveloping flames. Upon extinction of these flames, the char residues ignited and burned. In contrast, the higher rank coal particles ignited and burned heterogeneously. The replacement of the background N 2 gas of air with CO 2 (i.e., changing from air to an oxy-fuel atmosphere) at the same oxygen mole fraction impaired the intensity of combustion. It reduced the combustion temperatures and lengthened the burnout times of the particles. Increasing the oxygen mole fraction in CO 2 to 30-35% restored the intensity of combustion to that of air for all the coals studied. Volatile flame burnout times increased linearly with the volatile matter content in the coal in both air and all oxygen mole fractions in CO 2 . On the other hand, char burnout times increased linearly or quadratically versus carbon content in the coal, depending on the oxygen mole fraction in the background gas.