Effect of Potassium on the Mechanisms of Biomass Pyrolysis Studied using Complementary Analytical Techniques

Abstract

Complementary analytical methods have been usedto study the effect of potassium on the primary pyrolysis mechanisms of cellulose and miscanthus. Thermogravimetry, calorimetry, high temperature 1 H NMR (in-situ and real time analysis of the fluid phase formed during pyrolysis) and water extraction of quenched char followed by SEC/MS-ELSD (size exclusion chromatography coupled with mass spectrometry and evaporative light scattering detector have been combined). Pyrolysis was conducted under fixed bed conditions to impose similar mass transfer conditions as TGA/DSC and 1 H NMR to produce charfor SEC/MS. Potassium impregnated in cellulose suppresses the formation of anhydro-sugars measuredby SEC/MS, reduces the formation of mobile protons as observed by in-situ 1 H NMR and gives rise to a mainly exothermic signal (by calorimetry). Interestingly, the evolution of mobile protons formed from Kimpregnated cellulose follows with a very similar pattern the evolution of the mass loss rate with the mobile protons are formed before mass loss commences during pure cellulose pyrolysis. This methodology has been also applied to miscanthus, demineralised miscanthus, potassium re-impregnated miscanthus after demineralization, raw oak and douglas fir. We discuss the mechanism of primary pyrolysis of biomass and notably highlight the importance of the intermediate liquid phase.

Synergistic Effects of Catalyst Mixtures on Biomass Catalytic Pyrolysis

“…Potassium was shown to prevent the production of acids, anhydrosugars, acetol, and xylose, while K 3 PO 4 promotes hemicellulose char, gas, and H 2 O (Bulushev and Ross, 2011;Le Brech et al, 2016;Zhang et al, 2017), which is in line with the present study. Furthermore, K 3 PO 4 mostly inhibited the primary hemicellulose oxygenates but mostly catalyzed lignin, as confirmed by the considerable increase in phenolic derivatives (Lu et al, 2013;Le Brech et al, 2016;Zhang et al, 2017).…”

“…Clinoptilolite has been reported to catalyze the decomposition of lignin, yielding a bio-oil rich in phenolic compounds, and the amount of alkylphenols, pyrocatechols, and BTEXs (benzene, toluene, ethylbenzene and xylenes) generated from lignin decomposition also increased by clinoptilolite (Lee et al, 2016). Potassium was shown to prevent the production of acids, anhydrosugars, acetol, and xylose, while K 3 PO 4 promotes hemicellulose char, gas, and H 2 O (Bulushev and Ross, 2011;Le Brech et al, 2016;Zhang et al, 2017), which is in line with the present study. Furthermore, K 3 PO 4 mostly inhibited the primary hemicellulose oxygenates but mostly catalyzed lignin, as confirmed by the considerable increase in phenolic derivatives (Lu et al, 2013;Le Brech et al, 2016;Zhang et al, 2017).…”

Thermal Investigation and Kinetic Modeling of Lignocellulosic Biomass Combustion for Energy Production and Other Applications

“…with heating rates of 10, 20 and 30 °C min -1 , respectively. These results are in a line with the work reported by Brech et al 50 and a distinguishing lignin pyrolysis peak at around 700 °C was described by Yang et al 48 . Alvarez et al studied the combustion of twenty-eight common biomass types, including miscanthus and they reported that miscanthus showed two temperature ranges of combustion of 240-340 and 450-550 °C using the DTG data 51 .…”

Potassium doping increases biochar carbon sequestration potential by 45%, facilitating decoupling of carbon sequestration from soil improvement

“…The increased stability of carbon can be explained by the catalytic effect of AMs on biomass pyrolysis, such as enhanced cross-linking reactions (e.g., dehydration forming C=C or C-O-C) resulting in a highly cross-linked biochar, compared to biochar from untreated biomass 34,35 .…”