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煤热解是“富煤少油”国家应对能源、化学品需求的有效手段，然而现有煤热解工艺获得的焦油中重质组分（沸点高于360℃的馏分）含量高，造成热解工艺系统难以稳定运行。多数煤热解技术均处于中试或工业示范阶段，尚未实现工业化稳定运行，寻找低成本、制备流程简单、储量丰富的高效催化剂催化煤热解产物，降低焦油中重质组分含量是解决该问题的关键。本文针对上述技术难题，提出将大宗固体废弃物赤泥（RM）的综合利用、烷基化装置废弃硫酸无害化处置与催化煤热解产物提高热解油气品质工艺进行耦合，以赤泥基催化剂制备过程中催化剂物化性质的变化、烷基化废酸制备碳基催化剂的自组装过程的探究、赤泥酸解产物高值化利用为主线，通过采用单段固定床或两段固定床反应器实现不同种类催化剂原位或非原位催化煤热解，考察了不同类型催化剂、不同催化提质方式的催化提质效果，以实现提高煤热解焦油品质、定向调控煤热解挥发物二次反应的目的，为煤热解过程的催化调控和废弃物的资源化利用提供理论支撑。论文的主要研究内容和结果如下：1. 赤泥基催化剂原位催化煤热解的研究对赤泥进行酸碱处理，制备了不同钠含量的系列赤泥基催化剂，通过催化剂中钠含量的调控、酸溶剂的选择可实现定向调节催化剂的酸性、孔道特征的目的，建立了酸碱处理定向调变赤泥基催化剂物化性质的方法。在固定床反应器中考察了赤泥基催化剂原位催化煤热解的效果，结果表明：600℃条件下，煤单独热解焦油、轻质焦油（沸点小于360℃的馏分）产率达到最大值，分别为11.1 wt.%和6.6 wt.%，轻质组分含量为60.0%；与单独煤热解相比，当添加煤量4.0 wt.%的3.2%Na/RM时，轻质焦油产率为7.7 wt.%，焦油中轻质组分含量达到74.0%，分别增加了16.7%和23.3%。与水洗催化剂样品相比，酸碱处理后催化剂的强酸位点降低或消失，弱酸强度增加，催化剂上积碳减少，焦油中轻质焦油的含量提高，酸碱处理是改变赤泥催化剂材料物化性质提高催化提质性能的有效手段。赤泥基催化剂中氧化铁可以提供晶格氧，促进C-C键的断裂，增加CO和CO2产率；碱金属与碱土金属组分可以促进重质焦油组分的裂解，抑制催化剂积碳，但却增加了气体产率；二氧化钛组分有利于焦油中轻质组分含量的提高。2. 赤泥基催化剂对煤热解挥发物的催化提质研究在两段固定床反应器中考察了不同酸（硝酸、盐酸、硫酸）、碱处理赤泥基催化剂对煤热解挥发物的催化提质效果，结果表明，当采用煤样10 wt.%的硝酸处理样品（NC，钠含量为4.9 wt.%）作为催化剂、裂解温度为500℃时，轻质焦油产率为7.4 wt.%，焦油中轻质焦油含量为80.0%，与单纯煤热解相比分别增加了12.1%和33.3%。为进一步降低赤泥基催化剂中钠的含量，在酸碱处理制备赤泥催化剂过程中，通过多次水洗制备了低钠含量（钠含量0.4~1.3 wt.%）的催化剂，并考察了其对煤热解挥发物的催化提质作用。当采用煤样10 wt.%的硫酸处理后多次水洗样品（SCWM，钠含量为1.1 wt.%）作为催化剂、裂解温度为500℃时，轻质焦油产率为7.0 wt.%，焦油中轻质焦油含量为80.0%，与单纯煤热解相比分别增加了6.1%和33.3%。结果表明，赤泥基催化剂制备过程中增多过滤水洗的次数，可有效降低赤泥基催化剂中的钠含量，但同时增大了催化剂的比表面积，进一步加大了煤热解挥发分中焦油组分的裂解和催化剂孔道内的积碳，降低了催化提质性能。3. 表面功能化炭材料（红油炭材料）对煤热解挥发物的催化提质研究采用一步聚合的方法，将烷基化废酸中有机物与浓硫酸分离，制备了磺化的聚炭材料（PCMs），高温热解聚炭材料后制备得到红油炭材料（RDCMs）。对RDCMs的自组装过程进行了详细的探讨，并将其用作催化提质煤热解挥发分的催化剂。结果表明，烷基化废酸中的烯烃化合物在浓硫酸的作用下，发生加成、环化、芳构化等一系列反应，生成了具有多孔结构、硫掺杂的炭材料；当采用煤样10 wt.%的RDCMs作为催化剂、裂解温度为500℃时，轻质焦油产率达到7.8 wt.%，焦油中轻质焦油含量为80.0%，与单纯煤热解相比提高了19.6%和33.3%。RDCMs的催化性能优于活性炭（AC）和半焦，与AC和半焦相比，RDCMs在其自组装过程中形成了丰富的孔道结构，具有较大的比表面积，并且硫掺杂碳骨架形成了较多的缺陷位点。另外，硫的掺杂提高了催化剂活化热解水的能力，有效促进了煤热解挥发分的氧化、加氢反应和重质组分的裂解。4. 赤泥高值化与煤热解工艺耦合研究将赤泥改性半焦（RMMC）、赤泥酸解后的含铁废液分别用作非原位、原位催化煤热解的催化剂，用以解决赤泥原位催化煤热解后催化剂难以回收，以及原位催化煤热解工艺对廉价金属溶液需求的两方面难题。研究结果表明，与单纯煤热解相比，当采用煤样10 wt.%的RMMC、裂解温度为450℃时，轻质焦油产率达到6.9 wt.%，焦油中轻质焦油含量为77.0%，分别提高了4.5%和28.3%，超过45%的重质组分被裂解，其催化提质性能优于普通半焦。与半焦相比，RMMC比表面积明显增加、具有丰富的金属活性组分，重质组分裂解能力明显增加。当向煤喷淋煤量0.25 wt.%的含铁废液时，轻质焦油产率为7.6 wt.%，焦油中轻质组分含量达到73.0%，分别增加了15.2%和21.7%。含铁废液中的Fe、Al活性组分促进了煤热解挥发分的氧化反应和重质组分的裂解，提高了焦油中轻质组分的比例。5. HZSM-5对煤热解挥发物的催化提质研究不同硅铝比的HZSM-5被用作煤热解挥发物的催化提质催化剂，用以考察催化剂酸性特征对催化煤热解过程中焦油品质、积碳的影响。结果表明，当HZSM-5硅铝比为23增长到310时，催化剂上积碳从120.1 mg/g-catalyst降到23.9 mg/g-catalyst，随着硅铝比的增加，强酸和弱酸量降低，催化剂积碳量逐渐降低；HZSM-5中强酸与弱酸位点的比值与焦油品质具有一定的联系，当比值越高时，越利于提高焦油中轻质焦油的含量；另外，随着硅铝比的增加，焦油中芳烃组分含量逐渐降低，这表明HZSM-5的酸性强弱与挥发分的氢转移、环化、芳构化反应相关，硅铝比低时，HZSM-5酸性强，可通过烯烃的低聚-环化-脱氢反应，生成更多的芳烃组分。;Coal pyrolysis was an effect way to meet the demand of energy and chemicals for the oil-poor but coal-rich countries. However, high content of heavy components (boiling point over 360 °C) in tar would cause unstable operation of the whole system, resulting in the failure of industrialization of coal pyrolysis process. The key to solve these problems is to decrease the content of heavy component in tar through catalytic upgrading using catalysts with low-cost, simple preparation process, high-efficiency, and high-reserves during coal pyrolysis process. This study proposed the integrated process coupling comprehensive utilization of solid waste red mud (RM), harmless disposal of waste sulfuric acid from alkylation process, and catalytic upgrading of coal pyrolysis volatiles. Aiming at catalytic upgrading coal pyrolysis volatiles via in-situ and ex-situ catalytic process using red mud-based catalyst and surface functionalized carbon-based catalyst, this study investigated the property changes of red mud during acid-alkali treatment, the self-assembly process of alkylation waste sulfuric acid, and the high value utilization of byproduct from red mud acidization process. In the fixed-bed or two-stage fixed-bed reactor, different kinds of catalysts were investigated to improve tar quality during catalytic coal pyrolysis. This study will contribute to coal pyrolysis reaction control and resource utilization of solid and liquid wastes by providing feasible methods and theoretical support.1. In-situ catalytic coal pyrolysis over red mud-based catalyst. Red mud-based catalyst (RMC) with different sodium content were prepared by using acid-alkali treatment. It was found that changing sodium content could modify the characteristics of RMC. Moreover, the effects of composition and structure of catalyst on catalytic upgrading performance of RMC was investigated in a fixed-bed reactor by mix shaping of coal and RMC with different sodium contents. After adding 4wt.% RMC with sodium content of 3.2 wt.% into coal, the yield of light tar (boiling point < 360°C) increased to 7.7 wt.% and the light fraction in tar was as high as 74.0%, which were much higher than those from coal pyrolysis without catalyst. The content of sodium in the RMC had a great influence on product distribution of coal catalytic pyrolysis. The low-content sodium with high concentration acids contributed to the formation of coke. Whereas, with the increase of sodium content in RMC, coking was suppressed but more gaseous products were produced. The iron oxide in RMC was reduced via providing lattice oxygen during catalytic coal pyrolysis, thus prompting C-C bond cleavage and yield of CO2 and CO. The titanium species in RMC improved the light tar fraction. The acid-alkali treatment could prepare the RMC with desired ability for catalytic coal pyrolysis via composition and structure modification of raw red mud. 2. Ex-situ catalytic coal pyrolysis over red mud-based catalyst. RMC was used as catalyst for upgrading coal pyrolysis volatiles in a two-stage fixed-bed reactor. The results showed that the yield and fraction of light tar after catalytic upgrading using nitric acid and alkali treated RMC (NC) with sodium content of 4.9 wt.% (10 wt.% of the tested coal) at 500 oC were 7.4 wt.% and 80.0%, respectively, which increased by 12.1 % and 33.3% in comparison with that from coal pyrolysis without catalyst. Moreover, the SCWN with low-content of sodium (0.4-1.3 wt.%) was prepared by further water washing after sulfuric acid and alkali treatment. The best catalytic performance of these catalysts was 7.0 wt.% and 80.0% of light tar yield and fraction at 500 oC over 10 wt.% SCWM with sodium content of 1.1 wt.% of tested coal. The characterization of the RMC showed that further water washing lowered the sodium content but elevated the specific surface area of RMC, resulting in more catalytic cracking reaction, coke formation, and lower tar yield.3. Ex-situ catalytic coal pyrolysis over sulfated carbon-based catalysts, red oil-derived carbon materials (RDCMs). Surface functionalized carbon-based catalysts, RDCMs were prepared by the self-assembly process from waste red oil (RO) produced in industrial alkylation process. The characterization results showed that the alkene in the RO formed the carbon-based materials with doped sulfur and high specific surface area through reactions of addition, cyclization, aromatization, et al. The performance of carbon-based catalysts on upgrading of coal pyrolysis volatiles was investigated in a two-stage fixed-bed reactor. Compared with activated carbon (AC) or char, RDCMs exhibited better performance in increasing the yield and fraction of light tar. The higher specific surface areas and relatively more defects of RDCMs promoted the conversion of more heavy tar into light tar. The high-content doped sulfur in RDCMs contributed to more oxidation reaction in the secondary reaction for producing gaseous products. The pyrolysis water could be activated on the sulfur functional group to form ?H and ?OH radicals, which were able to stabilize the larger radical fragments from cracking of larger molecular in tar forming more oxygenated organic compounds. The light tar yield and fraction of catalytic upgrading over RDCMs (10 wt.% of the tested coal) at 500 oC were 7.9 wt.% and 80.0%, respectively, which increased by 19.6 % and 33.3% in comparison with that from coal pyrolysis without catalyst.4. Ex-situ catalytic coal pyrolysis over red mud modified char (RMMC) and in-situ catalytic coal pyrolysis using discard solution from red mud acidification process. In order to solve the problems of recovery of RMMC after in-situ catalytic coal pyrolysis and high demand of metal solution for in-situ catalytic coal pyrolysis, the RMMC and discard solution from red mud acidification process were used to ex-situ and in-situ catalytic coal pyrolysis, respectively. The light tar yield and fraction of catalytic upgrading over RMMC (10 wt.% of the tested coal) at 450 oC were 6.9 wt.% and 77.0%, which increased by 4.5% and 28.3%, respectively, in comparison with that from coal pyrolysis without catalyst. Compared with that of char, the specific surface area, metal content of RMMC increased dramatically, resulting in better ability of catalytic heavy component cracking. After adding 0.25 wt.% discard solution containing iron and aluminum species into coal, the light tar yield and fraction were 7.7 wt.% and 74.0%, which increased by 15.2 % and 21.7%, respectively, in comparison with that from coal pyrolysis without catalyst. The metal component in the discard solution could promote the catalytic oxidation reaction and cracking reaction, thus elevating the light tar yield and fraction. 5. Ex-situ catalytic coal pyrolysis over HZSM-5 with different SiO2/Al2O3 ratios. The effect of SiO2/Al2O3 ratio of HZSM-5 on the tar quality and coke formation during catalytic coal pyrolysis was investigated. The results showed that the carbon deposition amount reached to 120.1 mg/g-catalyst over H23. Moreover, the carbon deposition decreased with the increase of the SiO2/Al2O3 ratio. The tar quality was related with the ratio of strong and weak acid amount. The higher ratio benefited light tar fraction. Additionally, with the increase of SiO2/Al2O3 ratio, the aromatics content in the tars decreased, indicating the stronger acid sites promoted oligomerization, cyclization, dehydrogenation reaction of olefins, thus causing higher yield of aromatics during catalytic coal pyrolysis.
|王德亮. 低变质煤热解油气催化提质研究[D]. 中国科学院大学,2019.|
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