An exploratory study of phosphorus release from biomass by carbothermic reduction reactions

Review of Phosphorus Chemistry in the Thermal Conversion of Biomass: Progress and Perspectives

“…Carbothermic reduction is a process in which carbon is used to reduce another compound. For phosphates, a carbothermic reduction can be generalized as: − P 2 O 5 false( normals , normall false) + 5 C false( normals false) → P 2 false( normalg false) + 5 CO false( normalg false) where P 2 O 5 represents the phosphorus oxide part of a phosphate. This kind of reaction has long been used to produce elemental phosphorus from phosphate rock through the overall reaction R45: ,, Ca 3 ( PO 4 ) 2 false( normals false) + 3 SiO 2 false( normals false) + 5 C false( normals false) → 3 CaSiO 3 false( normals false) + P 2 false( normalg false) + 5 CO false( normalg false) The reaction is performed at high temperatures (1200–1500 °C).…”

“…Whereas the reduction of phosphate rock was studied extensively due to its relevance in industry, the reduction of other phosphates relevant for conversion of biomass was investigated to a lesser extent. Compared to Ca 3 (PO 4 ) 2 , other phosphates of common ash-forming elements are more easily reduced . Hence, the reduction of phosphates may be important for the release of phosphorus in certain thermal conversion processes.…”

“…When heated at a rate of about 10 °C/min, CO(g) was released in one major peak from around 850 to 1050 °C in quantities corresponding to all oxygen leaving the sample as CO(g), which would suggest the alkali is present as M(g) rather than M 2 O(g), as desccibed by the overall reaction: 2 MPO 3 false( normall false) + 6 C false( normals false) → 2 M false( normalg false) + 0.5 P 4 false( normalg false) + 6 CO false( normalg false) Reaction R51 is reasonable considering the reducing conditions in the carbon bed and that M 2 O(g) may not be very stable. The authors also investigated the reduction of alkali pyro- and orthophosphates . These alkali phosphates did also not undergo the same sequence as the Mg- and Ca-phosphates (meta → pyro → ortho → oxide) .…”

“…Where no symbols are indicated, the data are based on continuous measurements using either CO+CO 2 analysis or TGA. a The data were adapted from Lidman Olsson et al A C/P molar ratio of 25 was used . Activated carbon was used as carbon source .…”

“…a The data were adapted from Lidman Olsson et al A C/P molar ratio of 25 was used . Activated carbon was used as carbon source . The data for alkaline earth phosphates are based on CO + CO 2 measurements, whereas the data for alkali phosphates are based on TGA analysis .…”