Release of chlorine during oat straw pyrolysis doped with char and ammonium chloride

Abstract

Chlorine is one of the most undesirable elements in agricultural biomass which can cause operating problems during its thermal conversion. Even in low-temperature pyrolysis, chlorine is released in the gaseous phase. Therefore, in order to study the chlorine release during pyrolysis, the following samples were analyzed: oat straw, oat straw doped with char, oat straw doped with NH4Cl, and char doped with NH4Cl. The pyrolysis process of these feedstocks was conducted at 400, 500 and 600 °C under an inert atmosphere, with a short residence time (2 min) for a sample in the reactor. It transpired that the doping of ammonium chloride into oat straw increased the char yield. Doping oat straw with char as well as NH4Cl promoted biochar carbonization. Chlorine release was significantly inhibited when increasing the pyrolysis temperature from 400 to 600 °C for samples of oat straw, oat straw doped with char, and oat straw doped with NH4Cl. In addition, despite the increase in pyrolysis temperature, the percentage of chlorine distributed into the gas phase decreased. Doping oat straw with NH4Cl had a positive effect on increasing the share of furfural (up to 12.9% at 400 °C) in non-condensed gases identified by pyrolysis gas chromatography-mass spectrometry.