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215. Distribution of PAH generated in fluidized bed combustion and pyrolysis experiments

Author

Tobías, Aurelio, García, Roberto, Holdenb, K.M.L., Mitchell, Stuart C., Pis, José J., McRae, Carole, Snape, Colin E., Moinelo, Sabino R., Tobías, Aurelio, García, Roberto, Holdenb, K.M.L., Mitchell, Stuart C., Pis, José J., McRae, Carole, Snape, Colin E., and Moinelo, Sabino R.

Abstract

This chapter discusses the distribution of Polycyclic aromatic hydrocarbons (PAH) generated in fluidized-bed combustion and pyrolysis experiments. PAH is quantified following the extraction of samples recovered from fluidized-bed combustion (FBC) tests on Spanish lignite (Aragon) at various combustion temperatures and air/fuel ratios in a pilot plant scale FBC unit. A selection of the results are detailed and discussed with respect to the sampling, extraction, and analysis procedures. FBC conditions markedly affect the amount of PAHs produced and emitted into the atmosphere. Maximum PAH concentrations occur at low temperatures, when combustion is less efficient, and at high air excesses. In the PAH recovery from the materials of the different sampling points, supercritical fluid extraction (SFE) provides a more reliable method for high molecular weight compounds than Soxhlet extraction. Observations are made under fluidized-bed pyrolysis conditions, where condensation reactions predominate at higher temperatures.

Published
1995

221. The efficiency of charcoal decontamination for radiocarbon dating by three pre-treatments – ABOX, ABA and hypy.

Author

Bird, Michael I., Levchenko, Vladimir, Ascough, Philippa L., Meredith, Will, Wurster, Christopher M., Williams, Alan, Tilston, Emma L., Snape, Colin E., and Apperley, David C.

Subjects
CHARCOAL, DECONTAMINATION (From gases, chemicals, etc.), RADIOCARBON dating, COMPARATIVE studies, TEMPERATURE effect, PYROLYSIS
Abstract

Here we report results of a direct inter-comparison of the ability of three radiocarbon pre-treatment techniques to remove radiocarbon contamination introduced by exposing known-radiocarbon-free charcoal made at three different temperatures (300, 400 and 500 °C) to environmental contamination on a rainforest floor for one to three years. The initial charcoal had no measureable radiocarbon, but 14C activity increased after environmental exposure to ∼1 pMC after one year (apparent age of ∼40,000 yrs BP) and ∼5 pMC after three years (apparent age of ∼25,000 years). For the 400 and 500 °C samples, all techniques were able to reduce contamination by >90%. Acid–base oxidation (ABOX) provided the most reliable decontamination, reducing the radiocarbon activity of the one year samples to background, and reducing the radiocarbon activity of the three year samples to 0.04 ± 0.02 pMC or less (apparent age >56,900 yrs BP). The performance of ABOX was superior to that of both acid–base–acid (ABA) and hydrogen pyrolysis (hypy) treatments, with ABA performing better than hypy in most cases. No technique was able to fully remove decontamination from the 300 °C charcoal (although ABOX again removed the most contamination), likely due to the incompletely pyrolized nature of the charcoal which is dominated by aromatic clusters of small ring size. All the techniques rely on removing contaminant carbon faster than indigenous carbon and this condition is not met in the case of charcoal produced at temperatures below ∼350 °C. While all pre-treatments are useful for routine sample processing, the results suggest that ABOX is the only technique that can provide reliable decontamination of charcoal of an age close to the dating limit of the radiocarbon dating technique. [ABSTRACT FROM AUTHOR]

Published
2014
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222. Nitrogen-enriched and hierarchically porous carbon macro-spheres -- ideal for large-scale CO[sub 2] capture.

Author

Bingjun Zhu, Kaixi Li, Jingjing Liu, Hao Liu, Chenggong Sun, Snape, Colin E., and Zhengxiao Guo

Abstract

A facile and efficient "spheridization" method is developed to produce nitrogen-enriched hierarchically porous carbon spheres of millimeters in diameter, with intricate micro-, meso- and macro-structural features. Such spheres not only show exceptional working capacity for CO2 sorption, but also satisfy practical requirements for dynamic flow in post-combustion CO2 capture. Those were achieved using co-polymerized acrylonitrile and acrylamide as the N-enriched carbon precursor, a solvent-exchange process to create hierarchically porous macro-sphere preforms, oxidization to induce cyclization of the polymer chains, and carbonization with concurrent chemical activation by KOH. The resulting carbon spheres show a relatively high CO2 uptake of 16.7 wt% under 1 bar of CO2 and, particularly, an exceptional uptake of 9.3 wt% under a CO2 partial pressure of 0.15 bar at 25 °C. Subsequent structural and chemical analyses suggest that the outstanding properties are due to highly developed microporous structures and the relatively high \pyridinic nitrogen content inherited from the co-polymer precursor, incorporated within the hierarchical porous structures. [ABSTRACT FROM AUTHOR]

Published
2014
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223. The Properties of Individual Carbon Residuals and Their Influence on The Deactivation of Ni-CaO-ZrO2 Catalysts in CH4 Dry Reforming.

Author

Wang, Changzhen, Sun, Nannan, Zhao, Ning, Wei, Wei, Zhang, Jun, Zhao, Tiejun, Sun, Yuhan, Sun, Chenggong, Liu, Hao, and Snape, Colin E.

Subjects
METHANE, ELECTRON microscopy, THERMOGRAVIMETRY, X-ray diffraction, CATALYSTS, CATALYST poisoning, CARBON
Abstract

Ni-CaO-ZrO2 catalysts with different properties were prepared and tested for CO2 reforming of methane. The catalysts were characterized by means of transmission electron microscopy, thermogravimetric analysis, Raman spectroscopy, X-ray photoelectron spectroscopy, and X-ray diffraction to reveal their distinct properties and carbon deposition behaviors in the reforming reaction. It was found that the catalyst prepared by a coprecipitation method and ageing by heating to reflux exhibited a nanocrystalline structure with strong metal-support interaction, which was responsible for both high activity and stability, but it also exhibited the highest carbon formation rate among the tested catalysts. This result suggests that catalyst deactivation might not necessarily correlate with the amount of formed carbon, and the individual properties of carbon residuals could play a more decisive role. Carbon residuals on different catalysts were identified as amorphous carbon, encapsulating carbon, whisker carbon, and graphite, which had different influence on the deactivation. On the surface of the most active and stable catalyst, the carbon species mainly consisted of amorphous and whisker carbon, suggesting that the formation of such carbon species does not necessarily lead to catalyst deactivation. In contrast, the deactivation was found to be closely related to the formation of encapsulating carbon and graphite, which could coat the catalyst surface. The accumulation of different carbon residuals was proven to follow a formation-diffusion/elimination scenario, which was significantly influenced by the Ni particle size and Ni-ZrO2 interactions. [ABSTRACT FROM AUTHOR]

Published
2014
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248. Book and software reviews

Author

Hill, Steve, primary, Forbes, S., additional, Newbery, J. E., additional, MacMahon, Desmond, additional, Snape, Colin E., additional, Lewis, Ivor, additional, Burgess, C., additional, and Sadler, Peter J., additional

Published
1996
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