Conventional Pyrolysis Method Research Articles

Iron–Nitrogen Coordination in Modified Graphene Catalyzes a Four‐Electron‐Transfer Oxygen Reduction Reaction

AbstractIt is shown that iron–nitrogen (Fe/N) coordination in an Fe/N‐modified graphene (Fe/N‐graphene) electrocatalyst catalyzes a four‐electron transfer oxygen reduction reaction (ORR). The Fe/N‐graphene is synthesized by heat‐treating graphene oxides in the presence of an Fe/N complex at 900 °C for just 45 s. When the heat‐treatment period is increased, the Fe/N coordination bonds are broken and the number of electrons involved in the ORR decreases. Extended X‐ray absorption fine structure analysis and X‐ray absorption spectroscopy (XAS) show that both a complete sp2 graphitic structure and a high density of Fe/N coordination structures exist in the Fe/N‐graphene material, which is in contrast to the carbon‐based catalyst prepared by using the conventional pyrolysis method. XAS analysis also reveals that back‐donation from Fe atoms coordinated with N to an O antibonding π* orbital occurrs, promoting the four‐electron transfer ORR.

FINITE ELEMENT MODELING OF SELECTIVE HEATING IN MICROWAVE PYROLYSIS OF LIGNOCELLULOSIC BIOMASS

Microwave pyrolysis overcomes the disadvantages of conventional pyrolysis methods by efficiently improving the quality of final pyrolysis products. Biochar, one of the end products of this process is considered an efficient vector for sequestering carbon to offset atmospheric carbon dioxide. The dielectric properties of the doping agents (i.e., char and graphite) were assessed over the range of 25◦– 400◦C and used to develop a finite element model (FEM). This model served to couple electromagnetic heating, combustion, and heat and mass transfer phenomena and evaluated the advantages of selective heating of woody biomass during microwave pyrolysis. The dielectric properties of the doping agents were a function of temperature and decreased up to 100◦C and thereafter remained constant. Regression analysis indicated that char would be a better doping substance than graphite. The simulation study found that doping helped to provide a more efficient heat transfer within the biomass compared to non-doped samples. Char doping yielded better heat transfer compared to graphite doping, as it resulted in optimal temperatures for maximization of biochar production. The model was then validated through experimental trials in a custom-built microwave pyrolysis unit which confirmed that char doping would be better suited for maximization of biochar. Received 25 August 2013, Accepted 16 October 2013, Scheduled 22 October 2013 * Corresponding author: Baishali Dutta (baishali.dutta85@gmail.com). 2 Dutta, Dev, and Raghavan

Recycling of poly(ethylene terephthalate) waste through methanolic pyrolysis in a microwave reactor

In this study, the methanolic pyrolysis (methanolysis) of poly(ethylene terephthalate) (PET) taken from waste soft-drink bottles, under microwave irradiation, is proposed as a recycling method with substantial energy saving. The reaction was carried out with methanol with and without the use of zinc acetate as catalyst in a sealed microwave reactor in which the pressure and temperature were controlled and recorded. Experiments under constant temperature or microwave power were carried out at several time intervals. The main product dimethyl-terephthalate was analyzed and identified by FTIR and DSC measurements. It was found that PET depolymerization, is favored by increasing temperature, time and microwave power. High degrees of depolymerization were measured at temperatures near 180°C and at microwave power higher than 150W. Most of the degradation was found to occur during the initial 5–10min. Compared to conventional pyrolysis methods, microwave irradiation during methanolic pyrolysis of PET certainly results in shorter reaction times supporting thus the conclusion that this method is a very beneficial one for the recycling of PET wastes.

Microwave pyrolysis of corn stalk bale: A promising method for direct utilization of large-sized biomass and syngas production

The microwave pyrolysis technology, which can overcome the disadvantages of conventional pyrolysis methods such as heating slow and necessity of feedstock shredding, has been used to pyrolyze the corn stalk bale. The experiments were carried out with respect to the time-resolved temperature distribution, mass loss and product properties. In order to get a deeper understanding, the traditional pyrolysis using electric heating method was also performed. The comparison results indicated that microwave pyrolysis had obvious advantages over electric heating pyrolysis, such as heating rapid and uniform, more valuable products obtained. The content of H 2 attained the highest value of 35 vol.% and syngas (H 2 and CO) was greater than 50 vol.%. Material properties, heat and mass transport mechanisms, as well as chemical reactions had significant influences on the microwave pyrolytic characteristics. Data and information obtained are useful for the design and operation of pyrolysis of large-sized biomass via microwave heating technology.

Competing Channels in the Thermal Decomposition of Azidoacetone Studied by Pyrolysis in Combination with Molecular Beam Mass Spectrometric Techniques

The thermal decomposition of azidoacetone (CH3COCH2N3) was studied using a combined experimental and computational approach. Flash pyrolysis at a range of temperatures (296-1250 K) was used to induce thermal decomposition, and the resulting products were expanded into a molecular beam and subsequently analyzed using electron bombardment ionization coupled to a quadrupole mass spectrometer. The advantages of this technique are that the parent molecules spend a very short time in the pyrolysis zone (20-30 mus) and that the subsequent expansion permits the stabilization of thermal products that are not observable using conventional pyrolysis methods. A detailed analysis of the mass spectra as a function of pyrolysis temperature revealed the participation of five thermal decomposition channels. Ab initio calculations on the stable structures and transition states of the azidoacetone system in combination with an analysis of the dissociative ionization pattern of each channel allowed the identity and mechanism of each channel to be elucidated. At low temperatures (296-800 K) the azide decomposes principally by the loss of N2 to yield the imine (CH3COCHNH), which can further decompose to CH3CO and CHNH. At low and intermediate temperatures a process involving the loss of N2 to yield CH3CHO and HCN is also open. Finally, at high temperatures (800-1250 K) a channel in which the azide decomposes to a stable cyclic amine (CO(CH2)2NH) (after loss of N2) is active. The last channel involves subsequent thermal decomposition of this cyclic amine to ketene (H2CCO) and methanimine (H2CNH).