Formation of HNCO, HCN, and NH3 from the pyrolysis of bark and nitrogen-containing model compounds

Abstract

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.

Measurement of HONO, HNCO, and other inorganic acids by negative-ion proton-transfer chemical-ionization mass spectrometry (NI-PT-CIMS): application to biomass burning emissions

“…8c where HNCO is correlated with CO measurements (interpolated to a 1-s timeline). The HNCO/CO flaming stage slope is 0.28% in this experiment, and is likely related to the C/N pyrolysis chemistry that takes place in biomass burning (Hansson et al, 2004). The only compound that can be compared between the inorganic acids measured by the NI-PT-CIMS and the instack FTIR instrument is HONO.…”

“…While cyanate salts, such as sodium cyanate (NaOCN), are known to be stable, they evolve HNCO vapor upon acidification (Fischer et al, 2002), and HNCO has been shown to be the most thermodynamically stable of the possible CHNO isomers (Mladenovic and Lewerenz, 2008). There are several studies of the pyrolysis of biomass, coal, and polyamides, that have unambiguously identified HNCO as a major product by infrared spectroscopy (Hansson et al, 2004;Nelson et al, 1996). As a result of these studies and the above chemical considerations, the signal at mass 42 is assigned to HNCO.…”

“…The methods include FTIR which is rapid and specific (Hansson et al, 2004), sample condensation and derivatization with a reagent containing an HO-or HNR-group (Karlsson et al, 2001), and selective hydrolysis and detection as NH 3 (Krocher et al, 2005). All of these methods are limited either by low inherent sensitivity, or require significant sample collection times.…”

A Review of Thermal Co-Conversion of Coal and Biomass/Waste

“…Quaternary forms of nitrogen are also present, especially in low-rank coals. Amine functionalities are observed in low-rank coals [160], while they are present in biomass in diverse forms: proteins [161,162] (polymer of amino acids), alkaloids (heterocyclic nitrogen compounds), non-protein amino acids, nucleic acids, inorganic nitrogen and chlorophyll [163]. Chlorophyll, the green coloring matter in leaves and green stems, contains N in a magnesium-containing pyrrole derivative.…”

“…Ren and Zhao [175] studied the pyrolysis and O 2 and CO 2 gasification behavior of phenylalanine, aspartic acid and glutamic acid in a TGA at temperatures ranging from 0 K to1073 K. The distinct structures of these amino acids cause them to behave slightly differently under argon pyrolysis as well as O 2 and CO 2 gasification. Ren et al [176] found that the structure of the amino acids, the mineral matter content of biomass [178,179], the pyrolysis/gasification condition and the particle size [161,180] affects significantly the fate of nitrogen during pyrolysis of biomass. The thermal decomposition of amino acids and proteins proceeds mainly through dehydration with formation of cyclic amides, with diketopiperazine (DKP) being the common one [172][173][174]177].…”