Production of light aromatics from the fast pyrolysis of lignin catalyzed by metal-modified H-ZSM-5 zeolites
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摘要: 采用浸渍法制备Zn、Ga和Mg金属改性的H-ZSM-5双功能催化剂,考察了金属种类(Zn、Ga和Mg)和磨木木质素种类(杉木针叶材磨木木质素(CF-MWL)、杨木阔叶材磨木木质素(P-MWL)和玉米秸秆草本植物磨木木质素(CS-MWL))对木质素催化热解过程中轻质芳烃产率的影响。结果表明,在三种磨木木质素中,杉木磨木木质素(CF-MWL)具有最高的碳含量(59.90%,质量分数)和高位热值(23.05 MJ/ kg),而玉米秸秆磨木木质素(CS-MWL)中的氢含量(6.51%,质量分数)和有效氢碳比(0.43)最高。催化热解结果显示,与未改性的H-ZSM-5相比,Ga/H-ZSM-5和Zn/H-ZSM-5促进了轻质芳烃的形成,而Mg/H-ZSM-5则抑制轻质芳烃生成;其中,Zn/H-ZSM-5对三种MWL催化热解制取轻质芳烃的产率最高,分别达到3.122 × 109 a.u./mg (CF-MWL)、2.916 × 109 a.u./mg(P-MWL)和2.865 × 109 a.u./mg(CS-MWL);在三种MWL中,杉木磨木木质素(CF-MWL)催化热解制备BTX的选择性产率最高,达到65.02%。催化剂表面的积炭分析结果显示,催化热解过程中生成的积炭优先占据H-ZSM-5的强酸位点,并且大部分集中于H-ZSM-5的外部。Abstract: A series of metal (Zn, Ga and Mg) modified H-ZSM-5 bifunctional catalysts were prepared by impregnation method. Three types of milled wood lignin (MWL), isolated from softwood (Chinese Fir, CF), hardwood (Poplar, P) and herbaceous plant (Corn Straw, CS), were served as starting material to produce light aromatics via the catalytic fast pyrolysis (CFP). The effect of metal modifying and lignin source on the component of bio-oil derived from the lignin CFP was investigated. The results indicate that: Among three types of MWL, CF-MWL has the highest carbon content (59.90%) and calorific value (23.05 MJ/kg), whereas CS-MWL has the highest hydrogen content (6.51%) and effective hydrocarbon ratio (0.43); Compared to H-ZSM-5, Ga/H-ZSM-5 and Zn/H-ZSM-5 can promote the production of light aromatics, whereas Mg/H-ZSM-5 inhibits the formation of light aromatics. Zn/H-ZSM-5 as a catalyst in the lignin CFP displays the highest yield of light aromatics, with 3.122 × 109 a.u./mg for CF-MWL, 2.916 × 109 a.u./mg for P-MWL, and 2.865 × 109 a.u./mg for CS-MWL. Among three types of MWLs, the CFP of CF-MWL gives highest selectivity of 65.02% to BTX. The coke is mainly deposited on the outside surface of zeolite catalyst during the pyrolysis, leading to a great decrease in the number of strong acid sites.
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Key words:
- lignin /
- catalytic fast pyrolysis /
- metal modified zeolite /
- bio-oil /
- light hydrocarbon aromatics /
- BTX
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表 1 三种磨木木质素的元素分析和高位热值
Table 1 Ultimate analysis and the higher heating value of three types of milled wood lignin
Lignin
speciesUltimate analysis w/% QHHV/
(MJ·kg−1)Hydrogen-to-carbon effective ratio C H O N S CF-MWL 59.90 6.32 33.78 0.00 0.00 23.05 0.42 P-MWL 59.62 6.09 34.27 0.00 0.02 22.77 0.36 CS-MWL 57.91 6.51 35.44 0.00 0.14 22.63 0.43 表 2 三种木质素的分子量分布
Table 2 Molecular weight distribution of three types of milled wood lignin
Lignin species Mw/Da Mn /Da Polydispersity index(PDI) CF-MWL 2160 893 2.42 P-MWL 2778 1267 2.19 CS-MWL 2665 1324 2.01 表 3 金属改性前后HZSM-5催化剂的孔结构特征
Table 3 Pore structural characteristics of the parent and metal modified HZSM-5 catalysts
Catalyst SBET/
(m2·g−1)vtotal/
(cm3·g−1)vmeso/
(cm3·g−1)vmicro/
(cm3·g−1)dpore/
nmHZSM-5 393.67 0.213 0.052 0.133 2.16 Zn/HZSM-5 382.48 0.203 0.047 0.132 2.17 Ga/HZSM-5 356.96 0.187 0.042 0.129 2.19 Mg/HZSM-5 363.78 0.183 0.06 0.112 2.18 表 4 金属改性前后HZSM-5催化剂的酸量
Table 4 Acid amount of the parent and metal modified HZSM-5 catalysts
Catalyst Acid amount/(mmol·g−1) weak acid strong acid total acid HZSM-5 0.477 0.67 1.147 Zn/HZSM-5 0.435 0.631 1.066 Ga/HZSM-5 0.427 0.656 1.083 Mg/HZSM-5 0.427 0.608 1.035 表 5 使用后Zn/HZSM-5催化剂的积炭分析
Table 5 Coke formation analysis of the spent Zn/HZSM-5 catalyst
Catalyst WMIC/ ($ {\rm{m}}{{\rm{g}}_{{\rm{coke}}}} \cdot {\rm{g}}_{{\rm{cat}}}^{ - 1} $) WEC/ ($ {\rm{m}}{{\rm{g}}_{{\rm{coke}}}} \cdot {\rm{g}}_{{\rm{cat}}}^{ - 1} $) WTC/ ($ {\rm{m}}{{\rm{g}}_{{\rm{coke}}}} \cdot {\rm{g}}_{{\rm{cat}}}^{ - 1} $) Spent Zn/HZSM-5 40.25 115.99 156.25 表 6 使用前后Zn/HZSM-5催化剂的孔结构特征
Table 6 Pore structural characteristics of the parent and spent Zn/HZSM-5
Catalyst SBET/
(m2·g−1)vtotal/
(cm3·g−1)vmeso/
(cm3·g−1)vmicro/
(cm3·g−1)dpore/
nmParent Zn/HZSM-5 382.48 0.203 0.047 0.132 2.17 Spent Zn/HZSM-5 325.17 0.122 0.034 0.088 2.09 表 7 使用前后Zn/HZSM-5催化剂的酸量
Table 7 Acidity of the parent and spent Zn/HZSM-5 catalysts
Catalyst Acide amount/(mmol·g−1) weak acid strong acid total acid Parent Zn/HZSM-5 0.435 0.631 1.066 Spent Zn/HZSM-5 0.408 0.109 0.517 -
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