Effects of potassium and CO atmosphere on properties of biomass chars from flash pyrolysis
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摘要: 利用固定床反应器、红外光谱仪、吸附仪、X射线衍射仪、电感耦合等离子原子发射光谱仪、偏光显微镜等对比研究了原生生物质（原生物质）及水洗脱钾生物质（脱钾生物质）在N2及富一氧化碳（CO）气氛下所得半焦的产率、官能团及其他物化结构的变化规律。研究表明，与脱钾生物质相比，热解温度低于750℃时，原生物质的半焦产率降低、比表面积增大、芳环结构减少而烷基、脂肪族结构等增加；与N2相比，富CO气氛下所得半焦产率降低、比表面积增大，芳香结构、脂肪族结构、烷基减小。而热解温度高于750℃时，生物质中的钾和热解气氛中的CO均使生物质半焦产率增加、官能团数量和比表面积减少。利用偏光显微镜对生物质半焦表面矿物质的研究表明，热解温度低于750℃时，所得半焦表面矿物组分较少且高度分散；热解温度高于750℃时，所得半焦表面矿物组分较多，分布密集且熔融团聚现象随温度升高而增多。而对于半焦石墨化程度的研究表明，半焦石墨化程度随温度升高而增加，但低热解温度所得半焦的石墨化程度较差。温度高于750℃时，CO气氛使石墨化程度增加，而钾使石墨化程度降低。Abstract: Raw biomass and its de-potassium sample washed by water were pyrolyzed in a fixed bed reactor under pure N2 and CO-rich atmosphere at different temperatures. The obtained biomass chars were characterized by Fourier transform infrared spectroscopy (FT-IR), surface area analyzer, inductively coupled plasma emission spectroscopy and polarizing microscope. The yields of char, functional groups and other physicochemical structure were also studied and their evolution behaviors were examined. The results show that below 750 ℃, the BET surface areas and the amounts of alkyl and aliphatic functional groups in the chars derived from raw biomass are higher than those of de-potassium ones, but the char yields and the amounts of aromatic functional groups in the chars of raw biomass are lower than that of de-potassium samples. As to the effect of CO atmosphere, the yields of char and the amounts of all functional group in the chars derived from CO-rich atmosphere are less than that of N2 atmosphere, But the surface areas is higher than that of N2 atmosphere. Above 750 ℃, both potassium and CO can help to increase the char yields but decrease the amount of functional group and BET surface areas. In addition, the minerals are highly scattered and theirs amount on the surface of chars (raw biomass char, N2 atmosphere) is less when the pyrolysis temperature is lower than 750 ℃; while above 750 ℃, those are higher and the clusters of fusion mineral components increases with increasing pyrolysis temperature. As for the graphitization degree of biomass chars, it increases with increasing pyrolysis temperature but poor graphitization was obtained when the pyrolysis temperature is lower than 750 ℃. Moreover, CO can help to increase while K decreases the graphitization degree above 750 ℃.
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Key words:
- biomass char /
- potassium /
- pyrolysis atmosphere
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图 1 不同热解条件下的半焦产率变化
Figure 1 Yield of char at different pyrolysis conditions
●: D at N2 atmosphere; ○: D at CO:N2=1:1 atmosphere; ■: R at N2 atmosphere; □: R at CO:N2=1:1 atmosphere
图 2 N2气氛下原生物质半焦表面矿物质附着分布图
Figure 2 Distribution of mineral matter on surface of biomass chars obtained under N2atmosphere
(a): 550 ℃; (b): 650 ℃; (c): 750 ℃; (d): 850 ℃; (e): 950 ℃; (f): 950 ℃ A-biomass char
图 3 不同热解条件下K对热解半焦官能团的影响
Figure 3 Effects of K on functional groups of char at different pyrolysis conditions
(a): 550 ℃ N2 atmosphere; (b): 550 ℃ CO:N2=1:1 atmosphere; (c): 950 ℃ N2 atmosphere; (d): 950 ℃ CO:N2=1:1 atmosphere
图 4 不同热解条件下CO对热解半焦官能团的影响
Figure 4 Effects of CO on functional groups of char at different pyrolysis conditions
(a): 550 ℃ R-biomass char; (b): 550 ℃ D-biomass char; (c): 950 ℃ R-biomass char; (d): 950 ℃ D-biomass char
图 5 富CO气氛下不同热解温度的原生物质半焦XRD谱图
Figure 5 XRD spectra of different R-biomass char under CO:N2=1:1 atmosphere
图 6 富CO气氛下原生物质950 ℃热解半焦Gaussian拟合曲线
Figure 6 Gaussian fitting curves for 002 peak of R-biomass 950 ℃ char under CO:N2=1:1 atmosphere
表 1 松木屑的工业分析和元素分析
Table 1 Proximate and ultimate analyses of biomass
表 2 松木屑灰成分分析
Table 2 Ash composition of biomass
表 3 不同半焦的比表面积
Table 3 BET surface area of different chars
表 4 富CO气氛下原生物质950 ℃热解半焦晶体结构参数
Table 4 Crystal structure parameters of R-biomass 950 ℃char under CO:N2=1:1 atmosphere
表 5 不同热解半焦的部分晶体结构参数
Table 5 Part of crystal structure parameters of different chars
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