Effect of hierarchical ZSM-5 zeolites on product distribution of low rank coal fast pyrolysis in a fluidized bed
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摘要: 采用晶种诱导法和碱处理法制备了不同介-微孔复合结构的多级孔ZSM-5分子筛,利用XRD、TEM、NH3-TPD、氮气物理吸附等手段对其结构性质进行了表征,并考察了其对低阶煤流化床快速热解产物分布的影响。结果表明,碱处理后不同程度上增加了分子筛催化剂的比表面积、介孔孔容和平均孔径。多级孔ZSM-5分子筛促进了热解挥发分中脂肪烃的裂解环化和酚池的解离,提高了焦油中轻质芳烃的收率。在碱浓度为0.3 mol/L时轻质芳烃收率达到最大,其中,单环芳烃和萘/甲基萘较微孔分子筛分别增加了2.7倍和0.9倍。在碱浓度达到0.4 mol/L时,由于过度脱硅造成表面塌陷,分子筛催化剂性能下降。Abstract: A series of hierarchical ZSM-5 zeolites was prepared by seed induction method and alkali-treated method, and their crystal structural, textural and acidic properties were characterized by XRD, TEM, NH3-TPD, and N2-sorption. The effect of hierarchical ZSM-5 zeolites on product distribution of low rank coal fast pyrolysis in fluidized bed was investigated. The results showed that the specific surface area, mesoporous pore volume and average pore size of the zeolites were increased to different degree after alkali treatment. Hierarchical ZSM-5 zeolites promoted the cyclization of aliphatics and the dissociation of phenol pool of volatile from coal pyrolysis, and increased the content of light aromatics. The yield of light aromatics reached the maximum at 0.3 mol NaOH. The content of mono-aromatics and naphthalene/methylnaphthalene increased by 2.7 times and 0.9 times respectively compared with microporous zeolites. The catalysts performance decreased at 0.4 mol NaOH due to excessive desilication.
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Key words:
- low rank coal /
- pyrolysis /
- fluidized bed /
- hierarchical zeolites /
- product distribution
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表 1 神东煤的工业分析与元素分析
Table 1 Proximate and ultimate analyses of the SD coal
Proximate analysis w/% Ultimate analysis wdaf/% Mad Ad Vdaf FCdaf* C H O* N S 15.32 9.53 35.61 64.39 77.84 4.47 16.26 1.04 0.39 * by difference 表 2 碱处理前后ZSM-5分子筛的相对结晶度、硅铝比和收率变化
Table 2 Relative crystallinity, Si/Al ratio and yields of ZSM-5 before and after alkali-treatment
Sample Relative crystallinity/% n(Si)/n(Al) Recovery w/% Z50 100 56 100 Z50-0.1M 99 48 74 Z50-0.2M 96 44 65 Z50-0.3M 71 41 57 Z50-0.4M 54 38 40 表 3 碱处理前后ZSM-5分子筛的孔结构参数
Table 3 Porosity properties of ZSM-5 zeolites before and after alkali-treatment
Sample SBET/(m2·g−1) Smeso/(m2·g−1) Smicro/(m2·g−1) vtotal/(cm3·g−1) vmicro/(cm3·g−1) vmeso/(cm3·g−1) daver/nm vmicro/vmeso Z50 422 28 394 0.20 0.17 0.03 1.5 5.7 Z50-0.1M 445 36 409 0.25 0.16 0.07 2.7 2.6 Z50-0.2M 462 77 385 0.29 0.16 0.12 5.3 1.4 Z50-0.3M 475 134 341 0.35 0.15 0.20 9.6 0.8 Z50-0.4M 516 205 311 0.49 0.13 0.36 11.4 0.4 表 4 碱处理前后ZSM-5分子筛的NH3-TPD计算
Table 4 NH3-TPD computed results of ZSM-5 samples before and after alkali-treatment
Sample Weak acid peak Strong acid peak Total acid content/ (mmol·g−1) desorption peak temperature/℃ acid content/ (mmol·g−1) desorption peak temperature/℃ acid content/ (mmol·g−1) Z50 211 0.194 437 0.213 0.407 Z50-0.1M 212 0.189 405 0.239 0.428 Z50-0.2M 215 0.211 410 0.263 0.474 Z50-0.3M 217 0.261 403 0.264 0.525 Z50-0.4M 221 0.328 405 0.331 0.659 -
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