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Phosphorus-assisted biomass thermal conversion: reducing carbon loss and improving biochar stability.

Zhao L, Cao X, Zheng W, Kan Y - PLoS ONE (2014)

Bottom Line: Carbon loss during pyrolysis was reduced from 51.7% to 35.5%-47.7%.Thermogravimetric analysis curves showed that the additives had no effect on thermal stability of biochar but did enhance its oxidative stability.Microbial mineralization was obviously reduced in the modified biochar, especially in the TSP-BC, in which the total CO2 emission during 60-d incubation was reduced by 67.8%, compared to the unmodified biochar.

View Article: PubMed Central - PubMed

Affiliation: School of Environmental Science and Engineering, Shanghai Jiao Tong University, Shanghai 200240, China; Illinois Sustainable Technology Center, University of Illinois at Urbana-Champaign, Champaign, Illinois 61820, United States of America.

ABSTRACT
There is often over 50% carbon loss during the thermal conversion of biomass into biochar, leading to it controversy for the biochar formation as a carbon sequestration strategy. Sometimes the biochar also seems not to be stable enough due to physical, chemical, and biological reactions in soils. In this study, three phosphorus-bearing materials, H3PO4, phosphate rock tailing (PRT), and triple superphosphate (TSP), were used as additives to wheat straw with a ratio of 1: 0.4-0.8 for biochar production at 500°C, aiming to alleviate carbon loss during pyrolysis and to increase biochar-C stabilization. All these additives remarkably increased the biochar yield from 31.7% (unmodified biochar) to 46.9%-56.9% (modified biochars). Carbon loss during pyrolysis was reduced from 51.7% to 35.5%-47.7%. Thermogravimetric analysis curves showed that the additives had no effect on thermal stability of biochar but did enhance its oxidative stability. Microbial mineralization was obviously reduced in the modified biochar, especially in the TSP-BC, in which the total CO2 emission during 60-d incubation was reduced by 67.8%, compared to the unmodified biochar. Enhancement of carbon retention and biochar stability was probably due to the formation of meta-phosphate or C-O-PO3, which could either form a physical layer to hinder the contact of C with O2 and bacteria, or occupy the active sites of the C band. Our results indicate that pre-treating biomass with phosphors-bearing materials is effective for reducing carbon loss during pyrolysis and for increasing biochar stabilization, which provides a novel method by which biochar can be designed to improve the carbon sequestration capacity.

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X-ray diffraction (XRD) patterns of the unmodified and modified biochars.
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pone-0115373-g005: X-ray diffraction (XRD) patterns of the unmodified and modified biochars.

Mentions: A P 2p peak around 135.0 eV is generally assigned to metaphosphate or C-O-PO3 type groups [34], [35]. Addition of chemicals, especially H3PO4, increased the P 2p peak from 133.8 eV in unmodified BC to about 135 eV, indicative of the P-C compounds formation. This observation agrees with previous findings that H3PO4 addition mainly resulted in the formation of oxygen-containing phosphorus groups which may include metaphosphates, C–O–PO3 groups, or C–PO3 groups [34], [35]. These groups are suggested to act as a physical barrier against carbon decomposition, as well as to block the active carbon sites [22], [18], resulting in reduced oxidation and mineralization of biochar. Formation of P-C compounds was further evidenced by X-ray diffraction (XRD) analysis (Fig. 5). Compared to the unmodified BC, a new peak at 2θ0 = 26.6, most likely corresponding to the P-C compounds was observed in the H3PO4-BC and TSP-BC. Although PRT is also rich in P, it is less soluble, allowing it behave differently from soluble TSP and H3PO4. A weak peak of P-C compounds was observed at 2θ0 = 26.6 in the PRT-BC (Fig. 5). Qian et al. (2014) pointed out that the P-containing radicals react with the aromatic rings produced by the pyrolysis of lignin to form P-containing species, which is an important factor influencing the distribution and stabilization of P in char [36]. Uchimiya and Hiradate (2014) indicated that orthophosphate such as CH3−O−PO32− and phenyl−O−PO32− formed in pyrolysis were stable [37]. Klupfel et al. (2014) also proposed that biochar has redox properties and acts as electron-donating [38]. This indicated that P has potential to react with the carbon in biochar. Overall, all three P-bearing additives induced the formation of P-C compounds.


Phosphorus-assisted biomass thermal conversion: reducing carbon loss and improving biochar stability.

Zhao L, Cao X, Zheng W, Kan Y - PLoS ONE (2014)

X-ray diffraction (XRD) patterns of the unmodified and modified biochars.
© Copyright Policy
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4274024&req=5

pone-0115373-g005: X-ray diffraction (XRD) patterns of the unmodified and modified biochars.
Mentions: A P 2p peak around 135.0 eV is generally assigned to metaphosphate or C-O-PO3 type groups [34], [35]. Addition of chemicals, especially H3PO4, increased the P 2p peak from 133.8 eV in unmodified BC to about 135 eV, indicative of the P-C compounds formation. This observation agrees with previous findings that H3PO4 addition mainly resulted in the formation of oxygen-containing phosphorus groups which may include metaphosphates, C–O–PO3 groups, or C–PO3 groups [34], [35]. These groups are suggested to act as a physical barrier against carbon decomposition, as well as to block the active carbon sites [22], [18], resulting in reduced oxidation and mineralization of biochar. Formation of P-C compounds was further evidenced by X-ray diffraction (XRD) analysis (Fig. 5). Compared to the unmodified BC, a new peak at 2θ0 = 26.6, most likely corresponding to the P-C compounds was observed in the H3PO4-BC and TSP-BC. Although PRT is also rich in P, it is less soluble, allowing it behave differently from soluble TSP and H3PO4. A weak peak of P-C compounds was observed at 2θ0 = 26.6 in the PRT-BC (Fig. 5). Qian et al. (2014) pointed out that the P-containing radicals react with the aromatic rings produced by the pyrolysis of lignin to form P-containing species, which is an important factor influencing the distribution and stabilization of P in char [36]. Uchimiya and Hiradate (2014) indicated that orthophosphate such as CH3−O−PO32− and phenyl−O−PO32− formed in pyrolysis were stable [37]. Klupfel et al. (2014) also proposed that biochar has redox properties and acts as electron-donating [38]. This indicated that P has potential to react with the carbon in biochar. Overall, all three P-bearing additives induced the formation of P-C compounds.

Bottom Line: Carbon loss during pyrolysis was reduced from 51.7% to 35.5%-47.7%.Thermogravimetric analysis curves showed that the additives had no effect on thermal stability of biochar but did enhance its oxidative stability.Microbial mineralization was obviously reduced in the modified biochar, especially in the TSP-BC, in which the total CO2 emission during 60-d incubation was reduced by 67.8%, compared to the unmodified biochar.

View Article: PubMed Central - PubMed

Affiliation: School of Environmental Science and Engineering, Shanghai Jiao Tong University, Shanghai 200240, China; Illinois Sustainable Technology Center, University of Illinois at Urbana-Champaign, Champaign, Illinois 61820, United States of America.

ABSTRACT
There is often over 50% carbon loss during the thermal conversion of biomass into biochar, leading to it controversy for the biochar formation as a carbon sequestration strategy. Sometimes the biochar also seems not to be stable enough due to physical, chemical, and biological reactions in soils. In this study, three phosphorus-bearing materials, H3PO4, phosphate rock tailing (PRT), and triple superphosphate (TSP), were used as additives to wheat straw with a ratio of 1: 0.4-0.8 for biochar production at 500°C, aiming to alleviate carbon loss during pyrolysis and to increase biochar-C stabilization. All these additives remarkably increased the biochar yield from 31.7% (unmodified biochar) to 46.9%-56.9% (modified biochars). Carbon loss during pyrolysis was reduced from 51.7% to 35.5%-47.7%. Thermogravimetric analysis curves showed that the additives had no effect on thermal stability of biochar but did enhance its oxidative stability. Microbial mineralization was obviously reduced in the modified biochar, especially in the TSP-BC, in which the total CO2 emission during 60-d incubation was reduced by 67.8%, compared to the unmodified biochar. Enhancement of carbon retention and biochar stability was probably due to the formation of meta-phosphate or C-O-PO3, which could either form a physical layer to hinder the contact of C with O2 and bacteria, or occupy the active sites of the C band. Our results indicate that pre-treating biomass with phosphors-bearing materials is effective for reducing carbon loss during pyrolysis and for increasing biochar stabilization, which provides a novel method by which biochar can be designed to improve the carbon sequestration capacity.

Show MeSH