不同形态钠对伊敏褐煤碳黑生成特性的影响

Effects of different forms of sodium on the formation characteristics of Yimin lignite soot

摘要:

为揭示褐煤的碳黑生成特性与Na在煤衍生碳黑形成过程中的作用,采用电感耦合等离子体发射光谱仪、X射线光电子能谱仪和傅里叶变换红外吸收光谱仪研究分别担载了空白、物理吸附态Na (ANa)与离子可交换态Na (INa)的酸洗伊敏褐煤在沉降炉中不同停留时间下热解所产生碳黑的产率、表面与整体化学特性. 结果表明:在表面增长阶段,褐煤的碳黑产率增幅远超焦油产率降幅；当停留时间足够长时,碳黑产率有所降低,含氧官能团含量升高；担载Na可以降低碳黑产率,但INa对碳黑的抑制作用比ANa强得多,且INa可以使热解气溶胶中醚与砜的含量升高. 这些现象说明:在褐煤二次热解过程中,小分子芳香化合物、脂肪族物质与轻质气体也会通过表面增长提高碳黑产率. 褐煤热解气中含氧物质可以在停留时间足够长时表现出对碳黑的氧化作用. INa可以保持与焦炭或挥发分之间有机结合状态,在一次热解过程减少初级焦油释放,在二次热解过程中促进挥发分与含氧物质结合；而ANa在一次热解过程中作用不明显. 在二次热解过程中,气化的ANa与INa抑制碳黑形成的作用机制相同.

Abstract:

To reveal the soot formation characteristics of lignite and the role of Na in coal-derived soot formation, inductively coupled plasma emission spectrometer, X-ray photoelectron spectroscopy, fourier transform infrared absorption spectrometer and other methods were used to study the yield, surface and overall chemical properties of soot produced by the pyrolysis of acid-washed Yimin lignite loaded with blank, physically adsorbed Na (ANa) and ion-exchangeable Na (INa) under different residence time in a drop-tube reactor. The results show that during the surface growth stage of lignite derived soot, the increase of soot yield is far more than the decrease of tar yield. When the residence time is long enough, soot yield decreases and oxygen-containing functional groups content increases. Loading Na can reduce soot yield, but INa has much stronger inhibitory effect on soot than ANa, and INa also can increase ether and sulfone content in pyrolysis aerosol. These phenomena indicate that during lignite secondary pyrolysis, small molecular aromatic compounds, aliphatic substances and light gases would also increase soot yield through surface growth. Oxygen-containing substances in lignite pyrolysis gas can exhibit oxidation of soot when the residence time is long enough. INa can maintain the organic binding state with char or volatiles, reduce primary tar release in primary pyrolysis, and promote the combination of volatiles and oxygen-containing substances in secondary pyrolysis. But ANa has no obvious effect in primary pyrolysis. In the second pyrolysis, gasified ANa and INa have the same mechanism of inhibiting soot formation.