Equilibria in the mixed solvent system Glycol-NaOH-CO2-Water applied to corrosion modelling
Sustainable process-product development & green chemistry
Modelling, Design & Analysis of Processes with Ionic Liquids (T1-1P)
Keywords: corrosion glycol CO2 solubility activity
Gas produced in oil production is saturated in water (also known as wet gas). It contains CO2 and the water condenses at the cold pipe wall during transportation. NaOH and glycol (MEG) or methanol is injected to prevent gas hydrates and corrosion. CO2 dissolves in the water-MEG-NaOH liquid phase and the electrolytes will corrode the lower peripheral part of the pipeline. Various protective corrosion products are produced, depending on the chemical environment.
CO2 corrosion products are the focus of this study. It is known that FeCO3(s) forms as a product and behaves as a diffusion barrier of the corrosive components and prevents iron from dissolving.
The chemical environment of a typical pipeline has an ionic strength (I) of approximately 0.1 to 10 which clearly indicates high non-ideality of the liquid phase. Electrolytic diffusion processes deviate strongly from ideal conditions at ionic strengths above 1. All existing corrosion models, both simple electrochemical and mechanistic models assume ideal liquid phase. All lack the correct description of the diffusion processes, bulk activities, and surface activities/concentrations.
It is clear that an advanced electrolytic model is required, but most existing models do not produce accurate results at ionic strengths higher than 6 mol/kg. The extended UNIQUAC has proven to be able to do this.
In this work we seek to get a better understanding of the CO2 corrosion through experimental work and modelling.
The experimental work focuses on the corrosion products in the complicated CO2-NaOH-H2O-MEG-Fe system. SLE (Solid-Liquid-Equilibrium) experiments have been carried out in the mixed solvent electrolyte subsystem NaHCO3-Na2CO3-H2O-MEG.
The modelling is done through correlation of the experimental VLE (Vapour –Liquid-Equilibrium) and SLE data using the Extended UNIQUAC activity coefficient model for electrolytes.
Results will be shown of modelling the corrosion products using the activity coefficient model to predict dissolution of corrosion products and corrosion under diffusion control showing the stability of the products and the concentrations at which diffusion control may prevent pipeline corrosion.
Presented Monday 17, 13:30 to 15:00, in session Modelling, Design & Analysis of Processes with Ionic Liquids (T1-1P).
