【作者】 王雪；

【导师】 王睿坤；

【作者基本信息】 华北电力大学 ， 动力工程及工程热物理， 2025， 硕士

【摘要】 燃煤烟气中CO₂的排放是温室气体主要来源之一,因此开发经济高效的碳捕集技术对于加速碳中和进程和推动可持续发展具有重要的战略意义。生物炭因其原料来源广泛、结构可调、吸附性能优异以及经济环保等特点,已成为CO₂捕集与污染治理领域的研究热点。然而大多数炭材料缺乏固定的元素组成和内部结构,使用传统炭模型进行研究存在一定的局限性,为此,本研究构建了一种能够精确表征生物炭内部结构和表面性质的分子模型,并采用分子模拟方法研究了生物炭在不同物化性质及外界条件下CO₂的吸附性能和吸附行为。从微观层面深入阐明了吸附质与吸附剂之间的相互关系,弥补了实验研究中对CO₂微观吸附机制未能充分探讨的不足。本研究首先探讨了具有不同孔径分布的生物炭对CO₂的吸附机理。研究结果表明,孔径结构和外界条件对CO₂的吸附性能均有显著影响。微孔（孔径范围为2～20（?））和微孔/介孔（孔径范围为2～30（?））生物炭均能有效吸附CO₂,并且随着压力的增大,吸附量也随之增加。在相同温度下,微孔生物炭对CO₂的吸附表现更为有利,最大吸附量可达7.69 mmol/g,较微孔/介孔生物炭高出192.4%。所有类型的生物炭吸附量均随着温度升高而减小,吸附规律与实验结果一致。特别地,温度对微孔生物炭的吸附影响较小,因为微孔内具有较强的分子间作用力,使CO₂的吸附较为稳定,难以扩散或脱附。以上证实了孔隙结构对CO₂吸附稳定性的调控作用,微孔结构更有利于CO₂的吸附。为了进一步研究表面修饰对生物炭吸附性能的影响,在上述模型的基础上构建了氮氧官能团修饰模型。研究结果表明,不同官能团的引入对吸附性能影响不同,羧基修饰生物炭表现出最强的吸附能力,吸附量比未修饰生物炭增加了10.46 mmol/g。修饰后的生物炭吸附过程中的系统相互作用能显著增加,且静电相互作用能占据主导地位。静电相互作用能越强,生物炭的吸附性能越优越。尤其是吡咯氮和羧基修饰生物炭,其静电相互作用能分别占比53%以上和62%以上,显著的提升吸附效果。研究还发现,官能团的引入显著改变了CO₂的吸附位置,CO₂优先吸附在官能团邻近区域,表明官能团的引入增加了生物炭的活性位点,从而促进了CO₂向孔径结构内部的吸附。研究结果为调节生物炭的孔径结构和表面性质提供了重要的理论指导。本研究还探讨了典型烟气碳捕集工况下,无水烟气和含水烟气中其他气体对CO₂吸附的影响,并考察了水含量对吸附性能的影响。在微孔生物炭中,单组分吸附能力的顺序为H₂O>CO₂>O₂>N₂;而在微孔/介孔生物炭中,更有利于除CO₂外其他气体的吸附。H₂O和CO₂的吸附同时受到静电相互作用力和范德华力的影响,而N₂和O₂的吸附则主要由范德华力主导。在无水烟气中,各气体最大吸附量依次为:CO₂（1.25 mmol/g）、N₂（0.24 mmol/g）和O₂（0.02mmol/g）,且CO2/N2、CO2/O2选择性系数(S_CO2/N2、S_CO2/O2)始终大于1,表明CO₂在与N₂和O₂竞争时具有优势。在含水烟气中,H₂O由于其较强的极性和易形成水分子簇的特性,优先占据孔隙空间,导致CO₂的吸附量随着水含量的增加显著下降,尤其是在孔结构较大的生物炭中更为明显。同时,CO₂/H₂O选择性系数(S_CO2/H2O)小于1,表明水是限制含水烟气中CO2捕集效率的关键因素。该研究阐明了烟气组分的竞争吸附机制,为优化生物炭材料在无水烟气和含水烟气中的碳捕集性能提供了理论依据。更多还原

【Abstract】 CO₂ emission from coal-fired flue gas is one of the main sources of greenhouse gases,so the development of cost-effective carbon capture technology is of strategic importance to accelerate the process of carbon neutrality and promote sustainable development.Biochar has become a research hotspot in the field of CO ₂ capture and pollution control due to its wide source of raw materials,adjustable structure,excellent adsorption performance,and economic and environmental protection.However,most of the carbon materials lack fixed elemental composition and internal structure,and there are some limitations in using the traditional carbon model for the study.Therefore,in this study,a molecular model that can accurately characterize the internal structure and surface properties of biochar was constructed,and molecular simulation methods were used to investigate the adsorption performance and adsorption behaviour of CO₂ under different physical and chemical properties and external conditions.The interrelationship between adsorbent and adsorbent was elucidated at the microscopic level,which makes up for the inadequacy of the CO₂ adsorption mechanism that has not been fully explored in experimental studies.In this study,the adsorption mechanism of CO₂ by biochar with different pore size distributions was firstly investigated.The results showed that both the pore size structure and external conditions had a significant effect on the CO ₂ adsorption performance.Both microporous（pore size range of 2～20（?））and microporous/mesoporous（pore size range of 2～30（?））biochars were able to adsorb CO₂ efficiently,and the adsorption amount increased with the increase of pressure.At the same temperature,the microporous biochar showed a more favourable performance for CO₂ adsorption,with the maximum adsorption up to 7.69 mmol/g,which was 192.4%higher than that of the microporous/mesoporous biochar.The adsorption amount of all types of biochar decreased with increasing temperature,and the adsorption pattern was consistent with the experimental results.Particularly,the temperature had less effect on the adsorption of microporous biochar because of the strong intermolecular forces within the micropores,which made the adsorption of CO₂ more stable and difficult to diffuse or desorb.The above confirms that the pore structure regulates the stability of CO₂ adsorption,and the microporous structure is more favourable for CO₂ adsorption.In order to further investigate the effect of surface modification on the adsorption performance of biochar,a nitrogen-doped and oxygen-doped group modification model was constructed on the basis of the above model.The results showed that the introduction of different functional groups had different effects on the adsorption performance,and the carboxyl group-modified biochar showed the strongest adsorption capacity,with the adsorption amount increasing by 10.46mmol/g compared with that of the unmodified biochar.The systemic interaction energy in the adsorption process of the modified biochar was significantly increased,and the electrostatic interaction energy dominated the adsorption process.The stronger the electrostatic interaction energy,the more superior the adsorption performance of biochar.Especially,the electrostatic interaction energy of pyrrole pyrrole-N and carboxyl group modified biochar accounted for more than 53%and62%,respectively,which significantly enhanced the adsorption effect.It was also found that the introduction of functional groups significantly changed the adsorption location of CO₂,with CO₂ preferentially adsorbed in the region adjacent to the functional groups,indicating that the introduction of functional groups increased the active sites of the biochar,thereby promoting the adsorption of CO ₂ to the interior of the pore structure.The results provide important theoretical guidance for regulating the pore structure and surface properties of biochar.In this study,the effects of other gases on CO₂ adsorption in anhydrous flue gas and flue gas containing water under typical flue gas carbon capture conditions were also investigated,and the effects of water content on the adsorption performance were examined.In microporous biochar,the order of single-component adsorption capacity was H₂O>CO₂>O₂>N₂;while in microporous/mesoporous biochar,it was more favourable for the adsorption of other gases except CO₂.The adsorption of H₂O and CO₂ was affected by both electrostatic interaction forces and van der Waals forces,whereas the adsorption of N₂ and O₂ was mainly dominated by van der Waals forces.In anhydrous flue gas,the maximum adsorption amounts of each gas were,in order,CO₂（1.25 mmol/g）,N₂（0.24 mmol/g）and O₂（0.02 mmol/g）,and the CO₂/N₂,CO₂/O₂ selectivity coefficient(S_CO2/N2,S_CO2/O2)was always greater than 1,suggesting that CO2 has an advantage in competing with N₂ and O₂.In the water-containing flue gas,H₂O preferentially occupied the pore space due to its strong polarity and easy formation of water molecule clusters,resulting in a significant decrease in CO ₂ adsorption with the increase of water content,especially in the biochar with large pore structure.Meanwhile,the CO2/H2O selectivity coefficient(S_CO2/H2O)was less than 1,indicating that water was the key factor limiting the CO₂ capture efficiency in water-containing flue gas.This study elucidated the competitive adsorption mechanism of flue gas components and provided a theoretical basis for optimising the carbon capture performance of biochar materials in anhydrous and aqueous flue gas.更多还原