In-situ catalytic upgrading of tar from integrated process of coal pyrolysis with steam reforming of methane over carbon based Ni catalyst
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摘要: 本研究采用Ni/KD-9催化剂,对CP-SRM过程焦油进行原位催化提质研究。结果表明,在650 ℃热解温度下,CP-SRM在5Ni/KD-9催化作用下的焦油产率为24.4%,略低于不进行催化提质的焦油产率,而轻质焦油产率(18.9%)是未提质时的1.4倍。相比未提质焦油,用5Ni/KD-9提质后焦油中的C2、C3和C4烷基取代苯含量分别增加0.5、0.6和4.0倍;酚和萘的含量也明显提高。采用同位素示踪方法结合典型组分质谱图,探究了催化提质过程的反应机理。结果表明,5Ni/KD-9可以同时催化焦油裂解和甲烷蒸汽重整(SRM),SRM过程产生的小分子自由基,如·CHx,·H和·OH可以与焦油裂解产生的自由基结合,从而避免焦油的过度裂解。Abstract: In order to improve the tar quality by decreasing the heavy tar content and ensuring high tar yield, in-situ catalytic upgrading of tar from the integrated process of coal pyrolysis coupled with steam reforming of methane was conducted over carbon (KD-9) based Ni catalyst. The results show that at 650 °C, the tar yield of CP-SRM over 5Ni/KD-9 is 24.4%, which is a little lower than that of without catalyst, while the light tar yield (i.e.,18.9%) is 1.4 times higher than that of without catalyst, and the content of C2, C3 and C4 alkyl used as a substitute for benzene significantly increases tar yields by 0.5, 0.6 and 4.0 times, respectively. The content of phenols and naphthalenes in tar also increases dramatically after upgrading. Isotope tracer approach combined with the mass spectra of typical components was employed in exploring the mechanism of the upgrading process. The results show that 5Ni/KD-9 catalyzes coal tar cracking and SRM at the same time. Small free radicals such as ·CHx, ·H and ·OH generated by SRM can combine with free radicals from tar cracking, thus avoiding excessive cracking of tar.
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Key words:
- coal pyrolysis /
- catalytic upgrading /
- tar /
- steam reforming of methane /
- isotope tracer
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Table 1 Proximate and ultimate analyses of PS coal and KD-9
Sample Proximate analysis w/% Ultimate analysis wdaf/% Mad Ad Vdaf C H N S O* PS coal 1.26 23.52 42.65 78.42 5.08 1.38 0.77 14.35 KD-9 3.86 1.22 14.19 94.08 1.11 0.32 4.16 0.33 * : by difference Table 2 Textural properties of the fresh and spent xNi/KD-9 catalysts
Sample SBET/(m2·g−1) Smic/(m2·g−1) vt/(cm3·g−1) dave/nm Ni grain size /nm* KD-9 530 463 0.504 3.8 – 2Ni/KD-9 526 449 0.502 3.8 – 5Ni/KD-9 521 455 0.503 3.9 26.5 10Ni/KD-9 516 449 0.512 4.0 27.1 15Ni/KD-9 506 435 0.491 3.9 28.1 KD-9-S 90 30 0.273 12.1 – 2Ni/KD-9-S 92 32 0.247 10.7 – 5Ni/KD-9-S 118 54 0.248 8.4 29.2 10Ni/KD-9-S 143 80 0.265 7.4 30.6 15Ni/KD-9-S 193 126 0.274 5.7 29.8 * : Calculated by Scherrer formula from XRD patterns Table 3 Proton distribution of tars from CP-S&M with or without 5Ni/KD-9 (%)
Proton type Assignments Without catalyst 5Ni/KD-9 Har (6.3–9.3) aromatic protons 22.36 27.51 Hu (6.3–7.2) uncondensed Har 63.42 42.73 Hc (7.2–9.3) condensed Har 36.58 57.27 Hal (0.5–6.3) aliphatic protons 77.64 72.49 Hγ (0.5–1.2) protons of CH3 in the γ position or further away from aromatic rings; protons of alkanes 24.07 15.18 Hβ (1.2–2.1) protons of CH2 or CH in β position or further away from aromatic rings; protons of CH3 in the β position of aromatic rings 38.17 33.24 Hα (2.1–4.3) protons of CH, CH2 or CH3 in the α position to aromatic rings 33.10 37.26 Ho (4.3–6.3) protons of OH, OCHx and alkenyl of aromatic rings; protons of alkenes 4.66 14.32 Har/Hal 0.29 0.38 Hu/Hc 1.73 0.75 Table 4 Carbon distribution of tars from CP-S&M with or without 5Ni/KD-9 (%)
Carbon type Assignments Without catalyst 5Ni/KD-9 Car (108–160) aromatic carbons 53.55 47.08 Car1 (130–160) aromatic carbons connected to aliphatic chains, heteroatomic or aromatic substituents, and condensed aromatic rings shared by two rings 10.17 8.11 Car2 (108–130) condensed aromatic rings shared by three rings and protonated aromatic carbons 89.83 91.89 Cal (10–41) aliphatic carbons 46.45 52.92 CH+CH2 (23–41) aliphatic carbons CH2+CH 59.58 53.67 CH3 (10–23) aliphatic carbons CH3 40.42 46.33 fa=Car/Ctotal 0.54 0.47 Table 5 Deuterium distribution of tar by using CD4 and D2O as tracer (%) with 5Ni/KD-9
Deuterium type Assignments CH4+D2O CD4+H2O DAr (6.0–10.0) total aromatic deuterium 61.73 41.73 DUar (6.0–8.0) uncondensed aromatic D 96.43 96.83 DCar (8.0–10.0) condensed aromatic D 3.57 3.17 DAl (0.2–4.5) total aliphatic deuterium 38.27 58.27 Dγ (0.2–1.5) γ or further sites of aromatic rings and CH3 alkyl 19.83 53.76 Dβ (1.5–2.0) β sites of aromatic rings 10.77 40.43 Dα (2.0–3.2) α sites of aromatic rings 69.20 5.81 Dδ (3.2–4.5) deuterium associated with heteroatom functionality 0.20 0.00 -
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