Buijs Wim, Hussein Ibnelwaleed A, Mahmoud Mohamed, Onawole Abdulmujeeb T, Saad Mohammed A, Berdiyorov Golibjon R
Engineering Thermodynamics, Process & Energy Department, Delft University of Technology, Leeghwaterstraat 39, 2628 CB Delft, The Netherlands.
Gas Processing Center, College of Engineering, Qatar University, P.O. Box 2713, Doha, Qatar.
Ind Eng Chem Res. 2018 Aug 8;57(31):10095-10104. doi: 10.1021/acs.iecr.8b01928. Epub 2018 Jul 5.
A common problem that faces the oil and gas industry is the formation of iron sulfide scale in various stages of production. Recently an effective chemical formulation was proposed to remove all types of iron sulfide scales (including pyrite), consisting of a chelating agent diethylenetriaminepentaacetic acid (DTPA) at high pH using potassium carbonate (KCO). The aim of this molecular modeling study is to develop insight into the thermodynamics and kinetics of the chemical reactions during scale removal. A cluster approach was chosen to mimic the overall system. Standard density functional theory (B3LYP/6-31G*) was used for all calculations. Low spin KFe(II)(SH) and KFe(II)(SH) clusters were derived from the crystal structure of pyrite and used as mimics for surface scale FeS. In addition, KDTPA was used as a starting material too. High spin KFe(II)DTPA, and KS were considered as products. A series of K Fe(II)(SH) complexes ( = -2, = 5-0) with various carboxylate and glycinate ligands was used to establish the most plausible reaction pathway. Some ligand exchange reactions were investigated on even simpler Fe(II) complexes in various spin states. It was found that the dissolution of iron sulfide scale with DTPA under basic conditions is thermodynamically favored and not limited by ligand exchange kinetics as the activation barriers for these reactions are very low. Singlet-quintet spin crossover and aqueous solvation of the products almost equally contribute to the overall reaction energy. Furthermore, seven-coordination to Fe(II) was observed in both high spin KFe(II)DTPA and KFe(II)(EDTA)(HO) albeit in a slightly different manner.
石油和天然气行业面临的一个常见问题是在生产的各个阶段形成硫化铁垢。最近，有人提出了一种有效的化学配方来去除所有类型的硫化铁垢（包括黄铁矿），该配方由螯合剂二乙烯三胺五乙酸（DTPA）在高pH值下与碳酸钾（KCO）组成。这项分子建模研究的目的是深入了解除垢过程中化学反应的热力学和动力学。选择了一种簇方法来模拟整个系统。所有计算均使用标准密度泛函理论（B3LYP/6-31G*）。低自旋KFe(II)(SH)和KFe(II)(SH)簇是从黄铁矿的晶体结构中推导出来的，并用作表面垢FeS的模拟物。此外，KDTPA也用作起始原料。高自旋KFe(II)DTPA和KS被视为产物。一系列具有各种羧酸盐和甘氨酸盐配体的K Fe(II)(SH) 配合物（ = -2， = 5-0）被用来确定最合理的反应途径。在各种自旋态的更简单的Fe(II)配合物上研究了一些配体交换反应。研究发现，在碱性条件下用DTPA溶解硫化铁垢在热力学上是有利的，并且不受配体交换动力学的限制，因为这些反应的活化能垒非常低。单重态-五重态自旋交叉和产物的水合作用对总反应能量的贡献几乎相等。此外，在高自旋KFe(II)DTPA和KFe(II)(EDTA)(HO)中都观察到了与Fe(II)的七配位，尽管方式略有不同。
