TY - JOUR
T1 - An Exploratory Study of Phosphorus Release from Biomass by Carbothermic Reduction Reactions
AU - Lidman Olsson, Emil O.
AU - Glarborg, Peter
AU - Leion, Henrik
AU - Dam-Johansen, Kim
AU - Wu, Hao
PY - 2023
Y1 - 2023
N2 - Phosphorus (P) from biomass can cause operational problems in thermal conversion processes. In order to explore the release mechanism of P to the gas phase, carbothermic reduction of meta-, pyro-, and orthophosphates of ash elements commonly found in biomass; sodium, potassium, magnesium, and calcium
was investigated. Mixtures of each phosphate and activated carbon were
heated to 1135 °C in a laboratory-scale reactor, with the CO and CO2
evolving from the sample monitored, and the chemical composition of
selected residues analyzed to quantify the release of P. Thermal
gravimetric analysis was also performed on selected samples. The
alkaline earth phosphates were reduced in steps, following the sequence
meta → pyro → ortho → alkaline earth oxide.
However, the alkali metaphosphates appear to be reduced in one step, in
which both alkali and P are released. Alkali pyro- and orthophosphate
appear to undergo a two-step process. In the first step, mainly alkali
is released and in the second step both alkali and P. An intermediate is
produced in the first step, which has a K:P:O atomic ratio of about
2:1:2.7, indicating it might be a phosphite with the overall
stoichiometry; K4P2O5. The reduction of alkaline earth phosphates could be interpreted using available thermodynamic data, whereas thermodynamic equilibrium calculations
for the alkali phosphates did not correspond well to the experimental
observations. Kinetics were derived for the different reduction
reactions, and can be used to compare the reactivity of the phosphates.
The work suggests that carbothermic reduction reactions are important
for the release of P in the temperature range 850–1135 °C and relevant
for biomass combustion, pyrolysis and gasification.
AB - Phosphorus (P) from biomass can cause operational problems in thermal conversion processes. In order to explore the release mechanism of P to the gas phase, carbothermic reduction of meta-, pyro-, and orthophosphates of ash elements commonly found in biomass; sodium, potassium, magnesium, and calcium
was investigated. Mixtures of each phosphate and activated carbon were
heated to 1135 °C in a laboratory-scale reactor, with the CO and CO2
evolving from the sample monitored, and the chemical composition of
selected residues analyzed to quantify the release of P. Thermal
gravimetric analysis was also performed on selected samples. The
alkaline earth phosphates were reduced in steps, following the sequence
meta → pyro → ortho → alkaline earth oxide.
However, the alkali metaphosphates appear to be reduced in one step, in
which both alkali and P are released. Alkali pyro- and orthophosphate
appear to undergo a two-step process. In the first step, mainly alkali
is released and in the second step both alkali and P. An intermediate is
produced in the first step, which has a K:P:O atomic ratio of about
2:1:2.7, indicating it might be a phosphite with the overall
stoichiometry; K4P2O5. The reduction of alkaline earth phosphates could be interpreted using available thermodynamic data, whereas thermodynamic equilibrium calculations
for the alkali phosphates did not correspond well to the experimental
observations. Kinetics were derived for the different reduction
reactions, and can be used to compare the reactivity of the phosphates.
The work suggests that carbothermic reduction reactions are important
for the release of P in the temperature range 850–1135 °C and relevant
for biomass combustion, pyrolysis and gasification.
KW - Biomass
KW - Thermal conversion
KW - Phosphorus
KW - Phosphate
KW - Carbothermic reduction
U2 - 10.1016/j.proci.2022.07.087
DO - 10.1016/j.proci.2022.07.087
M3 - Journal article
SN - 1540-7489
VL - 39
SP - 3271
EP - 3281
JO - Proceedings of the Combustion Institute
JF - Proceedings of the Combustion Institute
IS - 3
ER -