Thermodynamic models for calculating mutual solubilities in H2O-CO2-CH4 mixtures

One of the measures for reducing global CO2 emissions is to capture CO2 and store it safely in geological formations. Safe and effective CO2 management requires reliable tools for calculate accurately the properties of both pure CO2 and CO2 in mixtures. If the default models and parameters of commercial flow sheeting tools are used when predicting the solubility of water in CO2 and CO2 in mixtures may not always result in satisfactory results. Having in mind the need for reliable operation of the processes along the CO2 capture, transport and injection chain, reliable tools are cardinal. The purpose of the present work has been to establish reliable model parameters by selecting equation of state (EOS) models for evaluation, develop a database of reliable experimental data on solubility of H2O, CO2 and CH4 based on data collected from literature, use the data to establish and suggest model parameters based on the database, and test and document the ability of the various EOS models to predict the solubility of H2O in CO2 or a mixture Of CO2 and CH4. Experimental data on solubility of H2O, CO2 and CH4 were collected from literature and compared with a model based on the rest of the experimental data in order to evaluate the quality of the data. The second order SRK-HV (SRK-Huron Vidal) model with six parameters was used as model for evaluating the experimental data. The models SRK-VdW (Soave Redlich Kwong, Van der Waals mixing rules), SRK-HV (SRK-Huron Vidal) and the CPA (Cubic Plus Association) was evaluated. Based on the data for the mutual solubilities of H2O, CO2 and CH4, new model parameters were adapted for the SRK-HV, and the CPA models. Solubility of H2O in CO2 and H2O in the CO2CH4 mixture was emphasized. The second order SRK-HV model produced acceptable results with deviation from 3% to 9% between experiments and the model. The CPA model was less accurate, producing results with deviation from 9% to 35% between experiments and the model. The SRK-VdW model gave two different binary coefficients, one for solubility of water in liquid CO2 and another for solubility Of CO2 in water. That gave same deviation as the SRK-HV model, (typically 7% for H2O in CO2 but 93% for CO2 in water, or 4% for CO2 in water but 93% for H2O in CO2 with another binary coefficient). The SRK-VdW is not indented for use of two different binary coefficients.