Nitrogen Migration during Pyrolysis of Raw and Acid Leached Maize Straw

Abstract

Solid biofuel is considered as a possible substitute for coal in household heat production because of the available and sustainable raw materials, while NOx emissions from its combustion have become a serious problem. Nitrogen-containing compounds in pyrolysis products have important effects on the conversion of fuel-N into NOx-N. Understanding these converting pathways is important for the environmentally friendly use of biomass fuels. The nitrogen migration during pyrolysis of raw and acid leached maize straw at various temperatures was investigated in this study. Thermal gravimetric analysis and X-ray photoelectron spectroscopy were used to investigate the performances of thermal decomposition and pyrolysis products from samples. The main nitrogen functional groups in biomass and biochar products were N-A (amine-N/amide-N/protein-N), pyridine-N, and pyrrole-N, according to the findings. The most common gaseous NOx precursor was NH3, which was produced primarily during the conversion of N-A to pyridine-N and pyrrole-N. The formation of HCN mainly came from the secondary decomposition of heterocyclic-N at high temperatures. Before the pyrolysis temperature increased to 650 °C, more than half of the fuel-N was stored in the biochar. At the same pyrolysis temperature, acid-leached maize straw yielded more gas-N and char-N than the raw biomass. The highest char-N yield of 76.39 wt% was obtained from acid-leached maize straw (AMS) pyrolysis at 350 °C. Low pyrolysis temperature and acid-leaching treatment can help to decrease nitrogen release from stable char structure, providing support for reducing nitrogenous pollutant emissions from straw fuel.

Fast Pyrolysis of Tea Waste under a Hydrogen-Rich Atmosphere: A Study on Nitrogen Evolution and Green Ammonia Production

“…The result suggested that the introduction of H 2 strengthened the thermal cracking of more stable N–A types, which was in accordance with the results of Wang et al and Wei et al The yields of N-6 and N-5 showed a maximum value at 500 and 600 °C, respectively. This might be ascribed to the fact that N–A was converted into more N-6/N-5 through direct cyclization, dimerization, and rearrangement at lower temperatures and the secondary decomposition of N-5/N-6 was enhanced at higher temperatures. ,, At the temperatures from 600 to 800 °C, the N-5 yield decreased faster than N-6, which demonstrated that N-5 showed less thermal stability than N-6 at high temperatures . H radicals were active in the rupture of N-containing ring systems .…”

“…Besides, it was found that a H 2 -rich atmosphere produced less heterocyclic–N than an Ar atmosphere at the same temperature. This phenomenon could be explained by two possible reasons: ,,, (1) the H 2 -rich atmosphere suppressed the polymerization of amine–N into heterocyclic–N by deactivating the free radicals and (2) the combination of H 2 and high temperatures promoted the ring-opening reactions of heterocyclic–N, resulting in more NH 3 and HCN.…”

“…When the temperature was raised from 500 to 600 °C, the NH 3 –N yield increased from 6.31 to 10.7 wt % under an Ar atmosphere and from 14.31 to 22.78 wt % under a H 2 -rich atmosphere. The generation of NH 3 at low temperatures was primarily due to the direct decomposition of labile N–A in fuels and secondary cracking of amine–N in tar. , Further, the introduction of H 2 considerably aided the thermal cracking of more N–A and amine–N, thereby resulting in more NH 3 –N production . Upon raising the temperature to 800 °C, as much as 19.33 wt % existed as NH 3 –N under an Ar atmosphere.…”

“…The N 1s signal was then curve-resolved using peaks with a 70% Gaussian and 30% Lorentzian line shape and a FWHM of 1.7 eV. The peaks at 398.5 ± 0.3, 399.9 ± 0.2, 400.4 ± 0.2, 401.4 ± 0.2, and 402–405 eV corresponding to the energy positions were assigned to the nitrogen functionalities of pyridinic-N (N-6), amide/amine/protein–N (N–A), pyrrolic–N (N-5), quaternary–N (N–Q), and N–oxide (N–X), respectively. ,,, The yield of each nitrogen functionality in chars was calculated as follows Y normalC normalh normala normalr − normalN normali = m normalC normalh normala normalr − normalN m normals − normalN • A normalC normalh normala normalr − normalN normali ∑ A normalC normalh normala normalr − normalN normali where A Char–Ni is the peak area of each nitrogen functionality in the XPS spectra of char–N.…”

“…The peaks at 398.5 ± 0.3, 399.9 ± 0.2, 400.4 ± 0.2, 401.4 ± 0.2, and 402−405 eV corresponding to the energy positions were assigned to the nitrogen functionalities of pyridinic-N (N-6), amide/amine/protein−N (N−A), pyrrolic−N (N-5), quaternary−N (N−Q), and N−oxide (N−X), respectively. 19,29,41,42 The yield of each nitrogen functionality in chars was calculated as follows…”