Production of renewable aromatics and olefins by catalytic co-cracking of fatty acid methyl esters and methanol
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摘要: 甘油三酸酯及其衍生物(如脂肪酸甲酯,FAMEs)催化裂化是制备可再生芳烃和烯烃的潜在途径,但该路径严重受限于HZSM-5分子筛催化剂的积炭失活。为调控FAMEs裂化产物分布并减缓催化剂的失活速率,本研究发展了FAMEs和甲醇催化共裂化的反应策略。结果表明,FAMEs和甲醇催化共裂化能够提高烯烃的选择性并降低芳烃的选择性,在原料中甲醇含量为60%时芳烃和烯烃的总选择性高达70.9%。甲醇的引入不仅能够提高烯烃的收率,而且有助于抑制单环芳烃持续脱氢形成多环芳烃,进而减少积炭的生成并延长HZSM-5/Al2O3催化剂的使用寿命。在温度为450 ℃、压力为0.16 MPa、FAMEs空速为4 h−1和反应时长为12 h的条件下,引入与FAMEs等质量的甲醇能够将催化剂的积炭量从17.8%降低为10.1%。此外,FAMEs和甲醇共裂化反应中部分失活的HZSM-5/Al2O3可以通过简单焙烧进行再生,再生催化剂的结构、酸性和反应活性与新鲜催化剂相比无明显改变。Abstract: Catalytic cracking of triglycerides and their derivatives (e.g., fatty acid methyl esters, FAMEs) by HZSM-5 zeolite offers a promising route to produce renewable aromatics and olefins, but it is primarily hindered by the rapid catalyst deactivation caused by coke. In this work, the co-cracking of FAMEs and methanol over HZSM-5/Al2O3 composites was developed to regulate the product distribution and slower the catalyst deactivation. Co-feeding methanol with FAMEs enhanced the olefin selectivity at the expense of aromatics, and the total selectivities of aromatics and olefins added up to 70.9% with an optimized methanol content of 60%. The co-feeding of methanol not only promoted the olefin yield but also retarded the consecutive H-elimination of aromatics to polycyclic aromatics, thus reducing the coke formation and prolonging the catalyst lifespan. Under the conditions of 450 °C, 0.16 MPa and a space velocity of FAMEs at 4 h−1, increasing the methanol blending ratio in FAMEs from zero to 50% reduced coke from 17.8% to 10.1% after reaction for 12 h. Besides, the spent catalyst for the co-cracking reaction could be easily regenerated by coke combustion, yielding similar structure, acidity and activity to those of the fresh one.
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Key words:
- catalytic cracking /
- fatty acid methyl ester /
- methanol /
- aromatic /
- olefin
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Table 1 Physicochemical properties of HZSM-5/Al2O3 catalysts
HZSM-5/Al2O3 (Si/Al)f Specific surface area /(m2·g−1) Pore volume /(mL·g−1) internal external total micropore mesopore total Calcined 23 303 42 345 0.163 0.271 0.434 Steam-treated 31 261 44 305 0.128 0.283 0.411 Used 32 127 35 162 0.060 0.180 0.240 Reactivated 32 219 113 332 0.111 0.312 0.423 Table 2 Amount of Brønsted (B) and Lewis (L) acid sites determined by Py-FTIR on HZSM-5/Al2O3 catalysts
HZSM-5/Al2O3 Total acid /(mmol·g−1, 200 °C) Medium & strong acid /(mmol·g−1, 350 °C) B L B+L B/L B L B+L B/L Fresh 0.35 0.067 0.42 5.3 0.21 0.044 0.26 4.8 Steam-treated 0.17 0.091 0.26 1.8 0.14 0.049 0.19 2.8 Reactivated 0.20 0.047 0.25 4.2 0.16 0.041 0.20 3.9 -
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