Release of phosphorus from thermal conversion of phosphorus-rich biomass chars – Evidence for carbothermic reduction of phosphates

Biomass can be used to generate heat, power, or biofuels in thermal conversion processes such as combustion, gasification and pyrolysis. However, some types of biomass contain high levels phosphorus, which released the gas phase cause operational environmental problems. The mechanism(s) responsible for phosphorus release has not been convincingly established. Understanding high-temperature chemistry is also important order enable efficient recovery residues from biomass. In this work, wheat bran char sunflower seed different environments (100 % N2, 1–20 O2, 10 CO2) temperatures (900–1100 °C) was studied. chars were converted a horizontal tube reactor characterized using ICP-OES, XRD, SEM-EDS, 31P NMR. ash-forming elements determined ICP-OES analysis sample residues, whereas carbon CO CO2 analysis. both chars, present primarily together with potassium magnesium, mainly pyrophosphates char, largely orthophosphates char. For increased 27 at 900 °C 71 1100 least 20 lower oxidizing atmospheres (1–20 CO2). reached maximum 55 N2. molar ratio carbon/phosphorus close 2.5, fits well theoretical value carbothermic reduction phosphates (P2O5(s, l) + 5C(s) → P2(g) 5CO(g)). At °C, sodium occurred during first min. It shown that KMgPO4, model compound, could reduced by starting 950 but remained condensed phase. work provides better understanding presents evidence showing reactions an mechanism seed- grain-based