CAS OpenIR
生物质与低密度聚乙烯两步法催化共热解制芳烃实验研究
于冬雪
Thesis Advisor李松庚
2020-07-01
Degree Grantor中国科学院大学
Degree Name博士
Degree Discipline化学工程
Keyword生物质,塑料,(催化)共热解,两步法,芳烃
Abstract

生物质作为唯一具有碳源的可再生能源,是广具前景的化石资源替代品,废塑料污染是全球关注的环境问题。以生物质和塑料为原料,采用催化共热解技术制备高品质富芳烃热解油,可以同时实现资源回收与能源转化,具有重要的研究价值和意义。本课题针对传统生物质与塑料催化共热解研究存在的原料间相互作用低、目标产物产率低、操作参数可调变性差(如一步法)等系列共性关键问题,提出了生物质与塑料两步法催化共热解(TSCCP)制备芳烃工艺。基于生物质典型组分的热解特征温度将共热解转化过程分解为低温和高温两步反应,能够有效缓解转化过程热解产物的二次裂解,同时对木质素形成低温活化,实现了反应物的高效转化;并通过反应原料的复合成型处理强化了原料间的相互作用,实现了芳烃的高产率、高选择性制备。本文以核桃壳和LDPE作为主要研究对象,开展了生物质与塑料两步法催化共热解(TSCCP)制备芳烃研究,重点考察了反应物热解行为、产物形成规律、工艺参数影响及优化,并对TSCCP工艺反应机理进行了深入分析。主要研究内容及结果如下:(1)首先开展了生物质典型组分与LDPE催化共热解实验。基于生物质典型组分与LDPE的热解特性(TG-DTG)及共热解实验(Py-GC/MS)研究,明确了三组共热解体系在热解行为及产物特性上存在的显著差异;根据反应物热解特性及产物随温度变化的分布特性,建立了将反应过程分解为低温段(第一步)和高温段(第二步)的TSCCP工艺;并进一步对核桃壳与LDPE单独两步法催化热解(TSCP)反应和TSCCP反应的热解产物进行对比分析,初步结果表明了生物质与塑料TSCCP工艺在促进目标产物芳烃形成、提升热解油品质方面的优势。(2)进一步针对核桃壳与LDPE利用Py-GC/MS开展了TSCCP反应条件影响规律研究。重点考察了原料配比、反应温度、停留时间等工艺参数对热解产物的影响规律,掌握了产物调控机制;并通过参数优化实验确定了TSCCP最佳反应条件。在优化条件下热解油中含氧组分选择性降至1%以下,芳烃选择性高达82.5%,芳烃中高价值BTX组分含量高于60%,同时热解油产率及目标产物芳烃的产率和选择性均显著高于传统TSCP工艺和一步法催化共热解(OSCCP)工艺,进一步验证了TSCCP制备芳烃显著优势。(3)针对生物质与LDPE共热解存在的原料混合不均及固固接触影响传质、传热等问题,提出原料的复合成型预处理,并采用固定床反应装置开展了复合成型与机械混合原料催化共热解对比研究。结果表明,复合成型处理能够实现物料的均质化,显著强化了二者间的相互接触,在快速催化共热解反应过程中通过增强二者热解中间产物间的协同作用,促进了热解油和目标产物芳烃的生成;进一步开展了复合成型原料的TSCCP反应温度、催化剂用量、停留时间等工艺参数优化实验,获得优化工艺参数;优化条件下的TSCCP与传统TSCP和OSCCP工艺的热解产物对比结果表明,复合成型原料的TSCCP工艺显著提高了目标产物芳烃的产率及选择性,降低了热解油中含氧组分的选择性,提升了产物品质。(4)对TSCCP反应机理进行了深入分析。首先基于小分子模型化合物研究了生物质与LDPE共热解转化过程目标产物芳烃的生成路径;采用TG-DTG、SEM、Raman、FTIR等系列测试手段对分步转化过程热解半焦等中间产物进行分析表征,从宏观及微观层面上对反应物的衍化行为进行了解析;在此基础上对TSCCP制芳烃反应机理进行了阐释。结果表明,生物质衍生呋喃类、醇醛酸酮类、酚类三组主要含氧组分与LDPE衍生烯烃之间均存在积极的协同作用,显著促进了芳烃的生成;基于热解特征温度建立的分步热解方式有效避免了纤维素和半纤维素组分与LDPE共热解芳烃产物在第二步高温环境的不利二次反应;第一步木质素组分发生活化促进了其与LDPE协同共转化生成芳烃。;Biomass, as the only renewable energy with organic carbon, can partially substitute fossil resources. The pollution of waste plastic has been a global environmental problem. Catalytic co-pyrolysis of biomass and plastic to produce high-quality aromatic-rich oil is a promising technology. However, there are some issues in conventional processes, such as weak interaction between the two feedstocks, low yield of target products, and poor variability of operation parameters (such as one-step catalytic co-pyrolysis, OSCCP for short). In this dissertation, a novel two-step catalytic co-pyrolysis (TSCCP) process was proposed to solve the above key scientific and technology problems. Based on pyrolysis characteristic temperatures of the three typical biomass components (cellulose, hemicellulose, lignin) and plastic, the catalytic co-pyrolysis of biomass and plastic was divided into two steps including reactions at low temperature and reactions at high temperature. The TSCCP process could effectively alleviate secondary reactions of pyrolysis products derived from cellulose, hemicellulose and plastic, meanwhile activation of lignin was formed at low temperature, thus realizing the efficient conversion of feedstocks toward target aromatics. Moreover, the yield and selectivity of aromatics were further improved through composite molding of biomass and plastic due to interaction enhancement between them. Walnut shell (WNS) and LDPE were used as model compounds of biomass and plastic. The pyrolysis behavior of feedstocks, the generation characteristic of products, the influence and optimization of process parameters were systematically investigated, and the reaction mechanism was analyzed in depth. The major contents and results are listed as follows:(1) Catalytic pyrolysis of biomass components and LDPE was carried out. TG-DTG analyses and Py-GC/MS pyrolysis experiments on biomass components and LDPE reveal that, the system of cellulose, hemicellulose with LDPE and the system of lignin with LDPE had different thermal behaviors and product characteristics. Based on the pyrolysis characteristic of reactants and the products distribution along with temperature, the TSCCP process was established to decompose biomass and plastic at a low temperature (Step 1) firstly and then at a high temperature (Step 2). Pyrolysis products of WNS and LDPE by two-step catalytic pyrolysis (TSCP) and TSCCP were compared and analyzed, thereby the advantages of TSCCP in promoting the production of aromatics and in improving the quality of pyrolytic oil were preliminarily proved.(2) The effects of process parameters on TSCCP were studied by Py-GC/MS using WNS and LDPE. The influences of feedstock ratio, reaction temperature and residence time on products distribution were systematically investigated. The regulation mechanisms of products were analyzed, and the optimal experimental conditions were obtained. Under the optimum conditions, the selectivity of oxygenates in pyrolytic oil was reduced to less than 1%, but the selectivity of aromatics was as high as 82.5%, and the content of high-value BTX components in aromatics was over 60%. Results show that the yield of pyrolytic oil, the yield and selectivity of aromatics were all significantly improved by TSCCP compared with the conventional TSCP and OSCCP.(3) Pretreatment of feedstocks by composite molding was proposed, against the problems in conventional mechanical mixing feeding mode, such as uneven mixing of feedstocks and limitation of heat and mass transfer caused by solid-solid contact model. Catalytic co-pyrolysis experiments on feedstocks from composite molding and mechanical mixing were performed respectively using a fixed-bed reactor. Results show that, in comparison, the composite molding pretreatment significantly contributed to the production of pyrolytic-oil and target aromatics, owing to the homogenization of feedstocks, the enhancement of contact, and the improvement of synergistic effect. The process parameters optimization was studied systematically by TSCCP using the prepared composite molding feedstocks further, including experiments on reaction temperature, catalyst dosage and residence time. Results show that, under the optimal conditions using the composite molding feedstocks, compared with the conventional TSCP and OSCCP, TSCCP has increased the yield and selectivity of aromatics significantly, meanwhile has reduced the content of oxygen compounds, thus dramatically improving the quality of pyrolytic oil. (4) The reaction mechanism of TSCCP was explored in depth. The generation pathway of aromatics was studied through catalytic pyrolysis of small molecular model compounds. The evolution pathway of feedstocks during TSCCP was investigated macroscopically and microscopically through characterizing of chars produced at different temperatures along the pyrolysis procedure, using TG-DTG, Van Krevelen curves, SEM, Raman, FTIR, etc.. Finally, the reaction mechanism for TSCCP was concluded. Results reveal that: a) positive synergistic effect was generated between oxygenates (including furans, alcohols, acids, aldehydes, ketones, and phenols) derived from cellulose, hemicellulose and lignin components in biomass and olefins derived from LDPE; b) since the stepwise pyrolysis process was developed based on pyrolysis characteristic temperatures of reactants, the secondary reactions occurred at high temperature in Step 2 for co-pyrolysis products of cellulose, hemicellulose and LDPE were inhibited; c) lignin activation was occurred at low temperature in Step 1; thus the formation of aromatics was significantly promoted under the combined effects of the above three factors. 

Language中文
Document Type学位论文
Identifierhttp://ir.ipe.ac.cn/handle/122111/49696
Collection中国科学院过程工程研究所
Recommended Citation
GB/T 7714
于冬雪. 生物质与低密度聚乙烯两步法催化共热解制芳烃实验研究[D]. 中国科学院大学,2020.
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