Key Takeaways & Executive Findings
- •• • Dual-site 10%K–N%P@bamboo powder raised dry-basis char yield from 49.7% to 53.1% at 553 K for 15 min, a 3.4 percentage-point gain, while the air-dried high heating value of the char remained essentially unchanged; this directly improves solid carbon productivity without sacrificing fuel quality. • • Single-site 15%K2CO3@bamboo powder reduced dry-basis char yield to 30.3% and raised char heating value to 26.67 MJ/kg, i.e., a 39% yield loss and 14.1% heating value gain versus raw bamboo powder; this confirms that alkali-only loading is unsuitable for carbonization processes targeting char as the primary product. • • Ash content of bamboo char increased only from 0.86% to 0.96% with the dual-site material, a 0.10 percentage-point increment, indicating that the additive does not materially degrade char quality or combustion behavior. • • The carbon-fixation mechanism is attributed to a three-dimensional network formed by P and K species on the bamboo surface that promotes secondary cracking of pyrolysis volatiles; this surface-confined architecture allows lower additive loadings than conventional solid additives, reducing separation and cost penalties.
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Abstract
A supported carbon-fixation material was prepared by rotary evaporation using K2CO3 and P2O5 as active components and bamboo powder as the carrier, and its effect on bamboo powder pyrolysis was investigated. Under identical pyrolysis conditions, the dual-site supported carbon-fixation material increased the dry-basis char yield of bamboo powder from 49.7% to 53.1%, while the air-dried high heating value of the corresponding char remained essentially unchanged. Characterization indicated that the carbon-fixation effect originates from a three-dimensional network structure formed by P and K active components on the bamboo powder surface, which effectively promotes secondary cracking of pyrolysis gas at the surface and enhances char yield. The addition of the dual-site supported carbon-fixation material increased the ash content of bamboo char from 0.86% to 0.96%, with no significant influence on the combustion characteristics of the char. In contrast, single-site K2CO3-loaded materials promoted pyrolysis but reduced char yield: at 15% K2CO3 loading, the dry-basis char yield decreased to 30.3% and the char heating value increased to 26.67 MJ/kg, representing a 39% decrease in char yield and a 14.1% increase in heating value relative to raw bamboo powder. The dual-site formulation therefore resolves the trade-off between catalytic activity and carbon retention, providing a low-cost route for biomass pyrolysis carbonization.
1. Introduction
Biomass pyrolysis carbonization operates under slow heating, low temperature, and oxygen-limited conditions, producing gas, liquid, and solid products in comparable proportions. Industrial deployment has been constrained by low process economics and small production scale. Existing solid additives, including K salts, CaCl2, Fe salts, HZSM-5, and MCM-41, act predominantly through solid-solid reactions with limited contact area, necessitating high additive loadings. After reaction, the additive remains mixed with the char and is difficult to separate, making additive cost a decisive barrier to commercial use.
The present work analogizes the industrial catalyst architecture of carrier plus active center. K2CO3 serves as the metal-ion activation component and P2O5 as the non-metal carbon-fixation component, both supported on low-cost bamboo powder via rotary evaporation. This supported configuration is intended to increase active-component utilization and lower material cost. Single-site K2CO3 materials were first evaluated and found to promote pyrolysis while reducing char yield, which is counterproductive when char is the target product. The dual-site K–P formulation was therefore developed to retain carbon while preserving heating value, and its performance was benchmarked against raw bamboo powder under identical pyrolysis conditions.
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ZHANG Zhitao, ZHANG Shuanglin, LI Wen, YANG Shuquan (2026). Effect of Dual-Site Supported Carbon-Fixation Materials on the Char Yield of Bamboo Powder Pyrolysis. Acta Energiae Solaris Sinica. https://doi.org/10.19912/j.0254-0096.tynxb.202608_9657
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Frequently Asked Questions
What is the quantitative trade-off between char yield and heating value when switching from single-site K2CO3 to the dual-site K–P material?
Raw bamboo powder at 553 K for 15 min gives 49.7% dry-basis char yield and 23.38 MJ/kg air-dried high heating value. Single-site 15%K2CO3@bamboo powder gives 30.3% yield and 26.67 MJ/kg, i.e., 39% lower yield and 14.1% higher heating value. The dual-site material restores yield to 53.1% while keeping heating value essentially unchanged, eliminating the yield penalty that disqualifies single-site K2CO3 for char-targeted carbonization.
Does the dual-site additive degrade char quality through ash enrichment, and what is the measured penalty?
Ash content rises from 0.86% to 0.96%, a 0.10 percentage-point increase. The paper reports no significant influence on combustion characteristics. For combustion or co-firing applications this ash increment is minor, though it must be accounted for in ash disposal and slagging assessments at scale.
What is the proposed mechanism for carbon retention, and what characterization supports it?
P and K active components form a three-dimensional network structure on the bamboo powder surface. This surface architecture promotes secondary cracking of pyrolysis gas at the surface, converting volatiles into solid carbon and raising char yield. The mechanism is supported by SEM surface morphology and composition contrast analysis, thermogravimetric-differential thermal analysis, bomb calorimetry, and proximate analysis.
What are the operational boundaries of the reported pyrolysis protocol?
Reactions were conducted in a fixed-bed quartz reactor under 100 mL/min N2 purge for at least 30 min, heated from room temperature at 10 K/min to a final temperature between 523 and 573 K, held for 30 min, then cooled naturally under N2. The reported yield and heating value data correspond to 553 K for 15 min. Scale-up must verify that the 10 K/min ramp and 30 min hold are achievable in larger reactors without internal temperature gradients.
What is the industrial case for the supported material versus conventional solid additives?
Conventional solid additives rely on solid-solid contact, require high loadings to provide sufficient contact area, and remain mixed with char after reaction, making separation impractical and additive cost prohibitive. The supported configuration disperses active components on a cheap bamboo carrier via rotary evaporation, increasing active-site utilization and lowering material cost. The dual-site material achieves a 53.1% char yield with only a 0.10 percentage-point ash increase, addressing both the yield and cost bottlenecks that have stalled additive-based biomass carbonization.
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