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Alternative TitleCandidate Generation and Screening for Guanidine and Amidine CO2 Absorbents
Thesis Advisor温浩
Degree Grantor中国科学院研究生院
Degree Discipline应用化学
KeywordCo2吸收 胍类和脒类化合物 产品工程 量子化学 反应机理
Abstract在制氢及合成氨工业的气体净化流程中,脱除CO2是关键步骤,因此CO2的吸收已成为化工、能源和环境等领域的重要研究课题之一。脒类、胍类化合物相对于传统的醇胺类吸收剂具有对设备腐蚀性小、CO2解吸能耗低等特点,有潜力成为新型的CO2吸收剂。 本文采用产品工程的思路,提出了一套设计开发新型CO2吸收剂的方案:首先以吸收CO2的活性基团作为提问结构在数据库中进行子结构检索,并以化合物的物理化学性质作为约束条件对检索结果进行初步筛选,得到候选化合物;然后采用量化计算的方法,分析候选化合物的化学反应特性,剔除与CO2反应活性较低的化合物;最后通过实验手段验证剩余化合物吸收CO2的实际效果,最终选定合适的CO2吸收剂。 根据上述设计方案,首先以含氮基团为提问子结构,以溶解度和摩尔质量为约束条件,从化学主题数据库中检索出候选化合物;采用量子化学计算的方法对10种胍类化合物与CO2的反应做了系统的理论研究;在此基础上结合热力学分析方法,筛选出合适的胍类化合物,并总结出影响胍类碳酸氢盐产物稳定性的初步规律。研究结果表明: 当胍与CO2以1:1的摩尔比反应时生成的产物最稳定。在胍结构中,酮亚胺基N原子是亲核反应的活性位点,反应活性远超过伯氨基N原子。在胍的碳酸氢盐产物结构中,碳酸氢根离子中的两个O原子能够与相邻胍阳离子中的两个H原子形成两条作用很强的O…H–N氢键。动力学分析结果表明,胍分子直接与CO2生成氨基甲酸盐的反应遵循酮亚胺基N原子亲核进攻CO2的机理;氨基甲酸盐在碱性环境中的水解反应遵循OH-亲核进攻羧酸根中心C原子的机理。 链状氨基取代和含有双胍基结构的胍类化合物可以作为CO2的吸收剂,而含有羧基的链状和环状胍类化合物一般不适合作为CO2的吸收剂。影响胍类化合物吸收CO2反应ΔG的主要因素是官能团的种类,而不是构型和碳链的长短。 此外,针对脒类化合物,以DBU(1,8-二氮杂双环[5.4.0]-7-十一烯)为例展开了CO2吸收反应的热力学分析。结果表明,DBU与C3~C6各烷基醇吸收CO2反应的ΔG基本相当。进而以DBU与正丙醇吸收CO2的反应为例,提出了四种反应机理,并通过热力学及动力学分析的方法逐一验证其合理性。结果表明,两种双分子两步反应机理被否定,第三种双分子反应机理有一定的合理性,三分子一步反应的机理最为合理。 本文关于胍类和脒类CO2吸收剂的研究思路和结果将为今后新型CO2吸收剂的开发和优选提供方法参考和理论基础。
Other AbstractIn the gas purification process of hydrogen production and synthetic ammonia industries, CO2 capture is the necessary procedure, and it is getting more important in the research of chemical industry, energy and environment. Compared with traditional aqueous CO2 absorbents such as alcohol amine, the amidine and guanidine bases are arguably potential absorbing agent because of the weaker corrosiveness to equipment and lower energy consumption of CO2 desorption. Based on the perspective of product engineering, a solution of CO2 absorbents development was proposed. At first, the absorbents candidates could be retrieved from the database by taking active groups as query substructures and taking physicochemical characteristics as constraint conditions. Then the quantum chemical studies on the reactions between CO2 and absorbents would be carried out in order to screen out the less reactive candidates. Finally the suitable CO2 absorbents can be selected by the experimental verification. According to above solution, the absorbents candidates were firstly retrieved from the Chemical Database by taking nitrogenous groups as query substructures and taking solubility and molar mass as constraint conditions. Then the CO2 capture reaction employing guanidine was conducted through the quantum chemical studies, and the proper guanidine candidates were chosen based on the thermodynamic analyses. Meanwhile the influence rules of the stabilities of the bicarbonate guanidinium products were summarized. The main conclusions are as follows: The product is more stable when the mole ratio of the reactants, guanidine and CO2, is 1:1. N atoms in the ketimine groups are the most reactive sites of the protonation in the molecules. In the guanidinium cation, strong hydrogen bonds exist between the O atoms in the bicarbonate anion and their adjacent H atoms. The mechanism studies indicate that in the direct reaction between guanidine and CO2 molecules, the N atom in the ketimine group nucleophilicly attacks the CO2 molecule, and in the hydrolysis of carbaminate, the OH- nucleophilicly attacks the C atom in the carboxyl anion. The guanidine with chain amino group or double guanidine groups may be the proper candidates, but the chain or cyclic guanidine with carboxyl is inappropriate. The main influencing factor of the ΔG of the CO2 capture reaction is the kind of the functional group in the absorbents, instead of the structure and the length of the carbochain. In addition, the quantum chemical studies on the reaction of binding CO2 by amidine base DBU (1,8-Diazabicyclo[5.4.0]undec-7-ene) and propanol were carried out, and four imaginary mechanisms were suggested. The thermodynamic and kinetic analyses indicate that the possible reaction mechanisms can be a two-step bimolecular reaction and a one-step trimolecular reaction. In the bimolecular mechanism, the intermediate is formed by DBU and CO2 and then propanol nucleophilicly attacks the intermediate. In the trimolecular mechanism, O and H atoms of hydroxyl in propanol form O–C bond with CO2 and form H–N bond with DBU, respectively. The trimolecular mechanism seems more reasonable because of the consideration of kinetic parameters. The research thoughts and results about guanidine and amidine CO2 absorbents in this dissertation may provide reference for the development and optimization of new kinds of CO2 absorbing agents.
Document Type学位论文
Recommended Citation
GB/T 7714
王亦秋. 胍类和脒类CO2吸收剂候选结构的生成与筛选研究[D]. 中国科学院研究生院,2013.
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