Measurement of water solubility limits in CO₂ mixtures to underpin safe pipeline transportation of CO₂

Welcome to the final blog by researchers from the University of Nottingham working on the UKCCSRC Call 2 project, Measurement of water solubility limits of CO₂ mixtures to underpin the safe pipeline transportation of CO₂.(PIs :Michael George and Martyn Poliakoff).

This UKCCSRC project has focused on the measurement of water solubility limits in CO₂ mixtures to underpin safe pipeline transportation of CO₂. The presence of any water in CO₂ rich mixtures can result in high acidity and subsequent corrosion of pipelines. The UKCCSRC’s Research and Pathways to Impact Delivery report identified understanding the water solubility limits for supercritical-phase CO₂ with N₂ and H₂ impurities, as a crucial step for the development of a viable, safe CO₂ distribution network. This research project has been split into two main objectives: (i) continue to develop robust methods for assessing common impurities in CO₂ streams and (ii) establish the effect of the common impurities on the solubility of water in CO₂ by establishing a developing bespoke equipment and methodology for assessing common impurities in CO₂ streams. The first objective of this project required the development of methods for measuring water solubility and two separate methods have been developed using custom-built equipment, relying on Karl-Fischer titration or IR spectroscopy. I have joined the team towards the end of the project

We have adapted a Karl-Fischer titrator for use with our bespoke high-pressure equilibrium cell to determine water content in gaseous mixtures. This method measures water content indirectly, consuming the water present in a chemical reaction at constant current. Application of voltage then allows water to be ‘back-calculated’. The Karl Fischer method was used to validate the spectroscopic method outlined below and saw good agreement (± 3%) versus;literature values for pure CO₂.

We have also used a spectroscopic method that directly measures water content by monitoring the ν2 infrared absorption band of water using a Fourier Transform Infra-red (FTIR) spectrometer with a custom-built high pressure IR cell. Comparison to the literature was favourable and results were validated with the above Karl Fischer method for pure CO₂. To improve reproducibility, several macro programmes were written and applied to the set-up. These programmes reduced the required amount of manual input by the operator, allowing for successive analytical runs, whilst making a much happier researcher.

“We have investigated the effect of the common impurities on the solubility of water in CO₂ and found that our methodologies are accurate to within 3% of current literature techniques and prove viable and valuable procedures for establishing the effect of impurities within CO₂ streams, crucial for safe transportation of CO₂. The data for the 5% and 10% N₂ + CO₂ mixture at 40 °C and between 8-18 MPa have been previously reported, with most of this work focused on the H₂ + CO₂ systems. The results for 10% H₂ show a further reduction in water solubility compared to that of 5% and 10% N₂, a trend which is expected based on their respective densities. One of the most significant findings of this work is that the water solubility appears to be independent of mixture composition. Preliminary results suggest that a given temperature, the water solubility appears to depend only on the density of the mixture within the pressure range of this study. If this is found to be a general finding then this may simplify future calculations regarding safety limits as mixture density is a measurable variable possibly allowing for easier prediction of water solubility