龚桐荻, 蔡勤杰, 张素平. 木屑与低密度聚乙烯两段式共热解制备液体芳烃研究[J]. 燃料化学学报(中英文). DOI: 10.3724/2097-213X.2024.JFCT.0006
引用本文: 龚桐荻, 蔡勤杰, 张素平. 木屑与低密度聚乙烯两段式共热解制备液体芳烃研究[J]. 燃料化学学报(中英文). DOI: 10.3724/2097-213X.2024.JFCT.0006
GONG Tongdi, CAI Qinjie, ZHANG Suping. Production of liquid aromatics by two-stage co-pyrolysis of sawdust and low-density polyethylene[J]. Journal of Fuel Chemistry and Technology. DOI: 10.3724/2097-213X.2024.JFCT.0006
Citation: GONG Tongdi, CAI Qinjie, ZHANG Suping. Production of liquid aromatics by two-stage co-pyrolysis of sawdust and low-density polyethylene[J]. Journal of Fuel Chemistry and Technology. DOI: 10.3724/2097-213X.2024.JFCT.0006

木屑与低密度聚乙烯两段式共热解制备液体芳烃研究

Production of liquid aromatics by two-stage co-pyrolysis of sawdust and low-density polyethylene

  • 摘要: 本研究设计了两段式的热解过程,以松木木屑和低密度聚乙烯(LDPE)协同转化制备液体芳烃。催化热解过程所得液体产物自然分层为有机相和水相,当使用两段式热解体系时,其有机相产率比传统单段热解提高11.4%。通过木屑与LDPE单独热解与共热解对比发现,木屑与LDPE共热解过程中存在基于氢转移的协同作用,能够促进液体芳烃的形成,且该协同作用在两段式过程中更显著。原料中LDPE所占比例会影响协同效应强度;在木屑和LDPE质量比为1∶1时协同效应最显著,所得有机相产率达到47.2%,其中,芳烃含量为93.8%。提高两段温度可以促进木屑和LDPE挥发分的析出并强化芳构化反应,但过高的温度会促进气体生成;当初步热解段温度在600 ℃,协同转化段温度在500 ℃时,共热解芳烃产率最高。碱性氧化物MgO可以促进木屑与LDPE的初步热解,使用MgO作为初步热解段催化剂对比ZrO2有机相产率提高5.2%,对协同转化段HZSM-5催化剂通过Ga2O3进行负载能够进一步提升协同转化效果,最终有机相产率达到51.5%,其中,芳烃含量达到98.9%。

     

    Abstract: Biomass can be converted into light aromatic hydrocarbons (such as benzene, toluene, and xylene) through catalytic pyrolysis to produce high-value chemicals, enabling its efficient utilization. However, biomass possesses the characteristic of being “rich in oxygen and deficient in hydrogen,” resulting in the generation of a large amount of oxygen-containing compounds during the pyrolysis process. This leads to easy oxidation, high acidity, and viscosity, as well as poor quality of the liquid products, with low aromatic hydrocarbon content, necessitating further modification and upgrading for utilization. Co-pyrolysis of plastics and biomass holds promise for improving the quality of biomass pyrolysis liquid products by utilizing the hydrogen-rich properties of plastics, reducing the oxygen content in the pyrolysis liquid products, and increasing the yield of aromatic hydrocarbons. In this study, a two-stage pyrolysis process, consisting of a preliminary pyrolysis stage and a synergistic conversion stage, was designed to synergistically convert pine wood sawdust and low-density polyethylene (LDPE) into liquid aromatic hydrocarbons. The liquid products obtained from the catalytic pyrolysis process naturally separate into an organic phase and an aqueous phase. When using the two-stage pyrolysis system, the organic phase yield was 11.4% higher than that of traditional single-stage pyrolysis. By comparing the separate pyrolysis and co-pyrolysis of sawdust and LDPE, it was found that there was a synergistic effect based on hydrogen transfer during the co-pyrolysis process, which promoted the effective deoxygenation of oxygen-containing compounds generated during the initial pyrolysis of sawdust into aromatic hydrocarbons, thereby increasing the yield of the target product, aromatic hydrocarbons, and this synergistic effect was more significant in the two-stage process. The proportion of LDPE in the feedstock influenced the strength of the synergistic effect during co-pyrolysis; when the mass ratio of sawdust to LDPE was 1∶1, the hydrogen supply from LDPE during the pyrolysis process was more balanced with the hydrogen demand of the sawdust pyrolysis products. At this ratio, the synergistic effect during co-pyrolysis was most significant, with an organic phase yield of 47.2% and an aromatic hydrocarbon content of 93.8%. Increasing the temperatures in the preliminary pyrolysis stage and the synergistic conversion stage can promote the volatilization of sawdust and LDPE and enhance the aromatization reaction, but excessively high reaction temperatures can lead to excessive cracking of intermediate products and promote gas generation; the highest yield of aromatic hydrocarbons from co-pyrolysis was achieved when the temperature in the preliminary pyrolysis stage was set at 600 ℃ and in the synergistic conversion stage at 500 ℃. The alkaline oxide MgO can enhance the preliminary pyrolysis of sawdust and LDPE, producing higher-quality intermediate products for subsequent synergistic conversion processes, thereby increasing the yield of aromatic hydrocarbons. Using MgO as the catalyst in the preliminary pyrolysis stage resulted in a 5.2% increase in the organic phase yield compared to the acidic oxide ZrO2; further enhancing the synergistic conversion effect, co-loading the HZSM-5 catalyst in the synergistic conversion stage with Ga2O3 using the incipient wetness impregnation method led to an organic phase yield of 51.5%, with an aromatic hydrocarbon content of 98.9%

     

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