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Bark pellets have been pyrolyzed in a fluidized bed reactor at temperatures between 700 and 1000 • C. Identified nitrogen-containing species were hydrogen cyanide (HCN), ammonia (NH 3 ), and isocyanic acid (HNCO). Quantification of HCN and to some extent of NH 3 was unreliable at 700 and 800 • C due to low concentrations. HNCO could not be quantified with any accuracy at any temperature for bark, due to the low concentrations found. Since most of the nitrogen in biomass is bound in proteins, various protein-rich model compounds were pyrolyzed with the aim of finding features that are protein-specific, making conclusions regarding the model compounds applicable for biomass fuels in general. The model compounds used were a whey protein isolate, soya beans, yellow peas, and shea nut meal. The split between HCN and NH 3 depends on the compound and temperature. It was found that the HCN/NH 3 ratio is very sensitive to temperature and increases with increasing temperature for all compounds, including bark. Comparing the ratio for the different compounds at a fixed temperature, the ratio was found to decrease with decreasing release of volatile nitrogen. The temperature dependence implies that heating rate and thereby particle size affect the split between HCN and NH 3 . For whey, soya beans, and yellow peas, HNCO was also quantified. It is suggested that most HCN and HNCO are produced from cracking of cyclic amides formed as primary pyrolysis products. The dependence of the HNCO/HCN ratio on the compound is fairly small, but the temperature dependence of the ratio is substantial, decreasing with increasing temperature. The release of nitrogen-containing species does not seem to be greatly affected by the other constituents of the fuel, and proteins appear to be suitable model compounds for the nitrogen in biomass.

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The conversion of fuel nitrogen to NO and N2O have been determined in a small-scale fluidized bed. Small batches of coal particles were used, permitting the separation of the formation reactions within individual particles from subsequent destruction or re-formation on other particles. From time-resolved measurements of the concentrations of NO, N2O, CO2, CO, and CH4, the instantaneous fractional conversions of coal nitrogen to NO and N2O as a function of fractional char burnout were obtained for bed temperatures between 975 and 1148 K. The conversion to N2O decreases with increasing temperature, whereas that to NO exhibits a maximum between 1023 and 1095 K. As a particle burns out, the instantaneous conversion to N2O decreases, whereas the reversed trend is seen for NO. The cumulative fuel nitrogen conversion to NO is in the range of 0.18-0.46, whereas the conversion to N2O is in the range of 0.04-0.18. The NO and N2O emissions can be explained by a model in which the nitrogen bound in the char is converted to NO and N2O on oxidation within pores. The split between the NO and N2O depend on the local NO concentration and the temperature. The NO and N2O formed are subsequently reduced as they diffuse out of the pores. This model explains the increase in fractional conversion to NO and decrease in fractional conversion to N2O with increasing carbon conversion. The temperature dependence is a function of the activation energies of the governing reactions.

Citation for the published paper: Hansson, K. ; Samuelsson, J. ; Åmand, L. et al. (2003) "The temperature's inuence on the selectivity between HNCO and HCN from pyrolysis of 2,5-diketopiperazine and 2-pyridone". Fuel, vol. 82 pp. 2163Fuel, vol. 82 pp. -2172 Downloaded from: http://publications.lib.chalmers.se/publication/239164 Notice: Changes introduced as a result of publishing processes such as copy-editing and formatting may not be reflected in this document. For a definitive version of this work, please refer to the published source. Please note that access to the published version might require a subscription.Chalmers Publication Library (CPL) offers the possibility of retrieving research publications produced at Chalmers University of Technology. It covers all types of publications: articles, dissertations, licentiate theses, masters theses, conference papers, reports etc. Since 2006 it is the official tool for Chalmers official publication statistics. To ensure that Chalmers research results are disseminated as widely as possible, an Open Access Policy has been adopted. The CPL service is administrated and maintained by Chalmers Library.(article starts on next page)The temperature's influence on the selectivity between HNCO and HCN from pyrolysis of 2,5-diketopiperazine and 2-pyridone AbstractTwo cyclic amides, 2-pyridone and 2,5-diketopiperazine (DKP), were pyrolysed at temperatures ranging from 700 to 1100 8C. Pyridone is the only one of the four main nitrogen functionalities found in coal that is likely to form HNCO under pyrolysis. DKP is a primary pyrolysis product from proteins, which are the main nitrogen source in biomass. The formation of HNCO from biomass has been suggested to originate from DKP and other cyclic amides. The aromatic 2-pyridone was thermally more stable than the non-aromatic DKP. Both amides formed HCN, HNCO and NH 3 . The NH 3 yields, about 3 -4% for 2-pyridone and 10% for DKP, were almost independent of temperature. The HCN yield on the other hand showed strong temperature dependence and increased with temperature for both of the cyclic amides. The HNCO yield decreased with increasing temperature for DKP over the whole temperature interval. For 2-pyridone, the pyrolysis was incomplete at the lowest temperature in the investigation. Between 900 and 1100 8C, the pyrolysis of 2-pyridone was complete and the HNCO yield decreased with increasing temperature. The HNCO/HCN ratio for both of the cyclic amides decreased with increasing temperature over the whole investigated temperature range. The finding in literature that the HNCO formation from cracking of coal tars produced a maximum HNCO yield at an intermediate temperature, is explained by the thermal stability of pyridone at low temperatures and the selectivity towards HCN at high temperatures. q