【作者】 张军；

【导师】 王勇；

【作者基本信息】 中国石油大学 ， 化工过程机械， 2008， 博士

【摘要】 腐蚀是困扰油气工业发展的一个极为突出的问题。在众多的防腐蚀方法中,缓蚀剂因具有经济、高效、适应性强等优点,目前被广泛应用在石油石化领域,发挥着极其重要的作用。近年来,随着人们环保意识的增强,研发新型高效、环境友好的绿色缓蚀剂越来越受到重视;然而传统的缓蚀剂设计与评价是建立在猜测和大量探索性实验基础之上,成本高,周期长,工作带有一定的盲目性,因此设计开发新型缓蚀剂迫切需要理论指导。本论文以8种不同烷基链长的1-(2-氨乙基)-2-烷基-咪唑啉缓蚀剂((NH2)C2H4-C3H4N2-CH2(CH2)nCH3,n=5,7,9,11,13,15,17,19)为研究对象,采用量子化学计算、分子力学和分子动力学模拟相结合的分子模拟方法,对其抑制碳钢CO2腐蚀的缓蚀机理开展了多尺度模拟研究,分析了缓蚀剂分子的反应活性,考察了烷基链长对缓蚀剂缓蚀性能的影响规律,探索了溶剂化效应对缓蚀剂吸附成膜的作用机制,研究了缓蚀剂膜阻碍腐蚀粒子扩散的动力学过程。通过研究和分析,取得了如下研究成果:8种咪唑啉分子的反应活性区域均分布在分子的咪唑环及其极性官能团上。咪唑环和极性官能团上的3个N原子为亲电反应中心,可提供电子与金属表面形成配位键;咪唑环上成双键结构的C、N两原子为亲核反应中心,可接受金属表面提供的电子形成反馈键。烷基链长对分子的整体反应活性和活性区域分布基本不产生影响。吸附发生时,咪唑啉分子极性的头部因具有较强的电荷转移作用而优先吸附于金属表面,非极性的烷基长链则背离金属表面并以一定的倾角自组装成密排结构的疏水膜。随烷基链长的增加,缓蚀剂膜自身的稳定性以及膜与基体的结合强度逐步增强,因此链长增加有利于其缓蚀效率的提高。对于Fe和FeCO3两种表面,当烷基链长分别大于13和15时,缓蚀剂方可形成高覆盖度、致密的缓蚀剂膜,能有效阻碍腐蚀介质向Fe表面扩散,抑制Fe表面的阴阳极反应。但依此真空条件下的简单模型,8种缓蚀剂缓蚀性能的理论评价结果与文献中液相腐蚀体系的实验结果并不完全相符。液相条件下,烷基链长在7-15范围内时,缓蚀剂分子与Fe和FeCO3表面的结合强度随链长的增加而增大,并在链长为15时达到最大;随链长(17-21)的进一步增加,缓蚀剂分子的吸附稳定性则逐渐下降,这主要是由于水分子强烈的溶剂化作用导致长链缓蚀剂分子严重扭曲变形,进而影响其与表面的作用方式和强度所致。液相中的自组装成膜过程显示,链长为15的咪唑啉分子具有良好的团聚效应,长链间相互交织形成高度致密的疏水膜,能有效覆盖Fe和FeCO3表面,因而具有最好的缓蚀性能;而当分子烷基碳链较短或较长时,链间大部呈离散状态,膜疏松多孔,不能有效抑制腐蚀的进程,缓蚀性能较差。同种缓蚀剂在FeCO3表面比其在Fe表面的吸附更加稳定。考虑溶剂效应的计算模型能较准确地描述缓蚀剂在金属表面的吸附成膜行为,缓蚀性能的理论评价结果与文献实验结果基本吻合。自由体积、粒子与膜的相互作用以及膜的自扩散性能是影响缓蚀剂膜抑制腐蚀粒子扩散能力的三个决定性因素。同种缓蚀剂膜对正负离子(H3O+、Cl-和HCO3-)比对H2O分子具有更强的扩散抑制能力。短链缓蚀剂分子具有较强的刚性,成膜时分子链间交织并不明显,彼此间制约能力差,此时缓蚀剂膜不仅具有较强的自扩散性能,而且因存在相对较大的自由体积,腐蚀粒子与膜的相互作用也较弱,因此腐蚀粒子在短链分子膜中具有较强的扩散迁移能力;随链长的增加,分子的柔性增强,烷基链易卷曲形变而相互交织,造成膜的自扩散能力降低,自由体积减小,膜对粒子的包覆以及粒子与膜的相互作用增强,从而较好地阻碍腐蚀粒子在膜中扩散。因此,相对于短链分子,长链分子膜对腐蚀粒子具有更好的扩散抑制能力,但当链长大于15时,这种抑制能力不再明显增加。缓蚀性能的理论评价结果在链长为7-15范围内与文献实验结果一致。更多还原

【Abstract】 Corrosion is one of the prominent problems in petroleum industry. Among the numerous corrosion-prevention approaches, inhibitor has been widely applied and played a significant role in petroleum and petrochemical fields, with its characteristic of economy, high-performance, and adoptability. And recently, with the recognition of environment protection, the development of new efficient and environment-friendly green inhibitors has gained more attention. Traditionally, design and evaluation of inhibitors are based on trial-and-error experiments, and bear the shortcomings of high-cost, long-cycle, and blindness to some extent. Hence, the theoretical guidance of the R&D for the new inhibitors is in urgent need. In this paper, 8 kinds of 1-(2-aminoethyl)-2-alkylimidazolines with various alkyl chain lengths ((NH2)C2H4-C3H4N2-CH2(CH2)nCH3,n=5, 7, 9, 11, 13, 15, 17, and 19) were chosen to explore their corrosion inhibition mechanism for CO2 corrosion of carbon steel with multi-dimensional simulation by quantum chemistry calculation, molecular mechanics and molecular dynamics modeling. The reactivity of these molecules was analyzed, the influence of alkyl chain length on corrosion performance was investigated, the membrane forming mechanism of these molecules in the presence of solvent was proposed, and the diffusion dynamics of corrosion particles inhibition by inhibitor membrane was studied. The research results are as follows.The reaction active areas of these 8 inhibitor molecules are homogeneously distributed on the imidazoline ring and its polar functional groups. The 3 nitrogen atoms on imidazoline ring and polar functional groups are electrophilic reactive centers, which can donate electrons to metal surface to form coordinate bond. And carbon and nitrogen atoms on both ends of the C=N double bonds are nucleophilic centers, which can accept electrons from metal surface to from back-donating bond. Alkyl chain length generally shows no significant influence on reactivity of the whole molecule and active area distribution. When the adsorption process occurs, the head of imidazoline molecule is preferentially adsorbed on metal surface because of its strong electron transferring effect, and the non-polar alkyl chain deviates from the surface with certain inclination angle and self-assemblies into a compactly-arranged hydrophobic membrane. With the alkyl chain length increases, the stability of the inhibitor membrane and the binding strength between the membrane and the metal substrate increase gradually, which means long alkyl chain is beneficial to inhibition efficiency of the inhibitors. For two kinds of surfaces of Fe and FeCO3, when the alkyl chain length respectively exceeds 13 and 15, the inhibitor can form a high-coverage and compact membrane on metal surface to prevent the corrosion media from diffusion to metal surface and reduce both anode and cathode reactions on Fe surface. But according to this simple model under vacuum conditions, the theoretical evaluation results of inhibited efficiency of the 8 inhibitors are not completely in correspondence with experimental results in literatures.In solutions, when the range of alkyl chain length is from 7 to 15, the binding energy between inhibitor molecules and metal surface increases with the alkyl chain length, and reaches maximum when chain length is 15. With further extension of the alkyl chain from 17 to 21, the adsorption stability decreases gradually, which is mainly because of twist of inhibitor molecules ascribed to the solvent effect of water molecules and its further influence on interaction mode and strength. The formation of self-assembly membrane in solution indicates that imidazoline with alkyl chain length of 15 has good clustering effect and best inhibition performance in that the long chains interweave to form compact hydrophobic membrane, which can cover the metal surface well. When the alkyl chain is shorter or longer than 15, the alkyl chains are mostly in discrete state and the membranes are loose and porous, which results in reduced inhibition performance. Identical inhibitor is adsorbed more stable on FeCO3 surface than on Fe surface. The calculation model considering solvent effect can describe the adsorption and membrane-forming behavior of inhibitors more accurately. And the theoretical evaluation results match well with experimental results in literatures.Free volume, interaction between particles and membrane, and self-diffusion performance of membrane are the 3 critical factors influencing the performance for prevention of corrosion particles diffusion by inhibitor membrane. Identical inhibitor membrane has more prevention ability for cations and anions (H3O+, Cl-, and HCO3-) than that for H2O molecules. Molecules with shorter chain have larger rigidity, which reduces the interweaving and interactions of molecule chains. Therefore, the inhibitor membrane has larger self-diffusion capacity and weaker interaction with corrosion particles with comparatively larger free volume. So the corrosion particles have stronger diffusion ability in short chain molecule membranes. As the alkyl chain extends, the molecular flexibility increases, which makes the alkyl chains easily twist and interweave, to reduce the membrane self-diffusion ability and free volume, and enhance the particles coating by membrane and interaction between particles and membrane, which prevents the corrosion particles from diffusing in membrane. Thus, compared to short chain molecules, long chain molecular membrane has better diffusion-reducing ability, which stops enlargement when alkyl chain length is longer than 15. Theoretical evaluation results were in good accordance with experimental results in literatures when the alkyl chain length is between 7 and 15.更多还原