CIESC Journal ›› 2022, Vol. 73 ›› Issue (11): 5251-5262.DOI: 10.11949/0438-1157.20221000

• Special column for Thermalchemical conversion of biomass and organic solid wastes • Previous Articles     Next Articles

Study on the steam gasification mechanism of waste PP plastics based on ReaxFF-MD and DFT methods

Weiwei XUAN1,2(), Yanwu DONG1, Hailun WANG1   

  1. 1.School of Energy and Environmental Engineering, University of Science and Technology Beijing, Beijing 100083, China
    2.Key Laboratory for Thermal Science and Power Engineering of Ministry of Education, Tsinghua University, Beijing 100084, China
  • Received:2022-07-15 Revised:2022-09-29 Online:2022-12-06 Published:2022-11-05
  • Contact: Weiwei XUAN

基于ReaxFF-MD和DFT的废旧PP塑料水蒸气气化机理研究

玄伟伟1,2(), 董彦吾1, 王海轮1   

  1. 1.北京科技大学能源与环境工程学院,北京 100083
    2.清华大学热科学与动力工程教育部重点实验室,北京 100084
  • 通讯作者: 玄伟伟
  • 作者简介:玄伟伟(1988—),女,博士,副教授,xww@ustb.edu.cn
  • 基金资助:
    热科学与动力工程教育部重点实验室开放基金和基本科研业务费项目(FRF-TP-19-008A3)

Abstract:

Gasification technology is an important method for treating the increasing amount of waste plastics and producing H2-rich syngas. ReaxFF-MD and DFT methods were used to study the reaction mechanism of water vapor gasification of polypropylene (PP) plastics and the generation path of each product gas, and the effects of temperature and water content on the product distribution of syngas were further explored. The results show that the main reaction process in the early stage of steam gasification of PP plastics is the breaking of monomer bond with small dissociation energy at the places where the propylene (CH3—CH̿    CH2) monomer are formed. Subsequently, the monomer continue to dissociate into smaller C1—C2 hydrocarbon molecules, ·H, CH3· and other free radical fragments. In the steam reforming reaction stage, there are many ways to generate H2, but the collision of free ·H radicals generated from the C-containing structure in the early stage with H2O molecular is the main way, accounting for 70% of the total H2. At the same time, the accompanying generated ·OH radical is the main way of generating CO through the process of combining with small molecules and removing H. Increasing the temperature and water content can promote the steam reforming reaction of hydrocarbons, so as to improve the yield of H2 and CO, but the improvement effect is gradually weakened. The above results can be a guide to master the plastic gasification process and select proper experimental parameters.

Key words: molecular simulation, gasification, waste plastics, syngas, chemical reaction

摘要:

气化技术是处理日益增多的废旧塑料并生产富H2合成气的重要方法。利用ReaxFF-MD与DFT方法相结合研究了聚丙烯(PP)塑料水蒸气气化的反应机理及各产物气的生成路径,进一步探究了温度、水含量对合成气产物分布的影响。研究结果表明:PP塑料的水蒸气气化前期以解离能较小处的单体连接键断裂形成丙烯(CH3—CH̿    CH2)单体为主要反应过程。随后,单体继续解离生成更小的C1~C2烃类分子及·H、CH3·等自由基片段。在水蒸气重整反应阶段,H2的生成有多种路径,但由前期含C结构上脱掉的游离·H自由基与H2O的结合是H2的最主要生成路径,占据了H2生成量的70%。同时伴随产生的·OH自由基通过与小分子结合,脱H等过程,是CO的主要生成方式。提高温度和含水量可促进烃类的水蒸气重整反应,从而提高H2和CO合成气产率,但改善效果逐渐减弱。以上结果对于掌握塑料水蒸气反应进程,以及实验参数调整有重要指导意义。

关键词: 分子模拟, 气化, 废旧塑料, 合成气, 化学反应

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