Determination of CO2 Solubility in Water by NIR Spectroscopy under Different Temperature and Pressure Conditions

Sep 29, 2026

Monitoring the solubility of carbon dioxide (CO2) in water under high-pressure and temperature conditions is essential for industrial operations. This work develops a noninvasive near-infrared (NIR) spectroscopy method to monitor CO2 dissolution in ultrapure water in real time. An NIR spectrophotometer is coupled to an apparatus like the static synthetic method. Spectral preprocessing and partial least-squares (PLS) regression correlate spectra with solubility. The model is calibrated using thermodynamic values from Peng–Robinson EOS with NRTL, achieving R2 > 0.99 and 9.91% average external prediction error, enabling robust estimation from spectral data for environmental and industrial monitoring.

LanguageEnglish

CategoryResearch & Report

FormatPDF

Pages10

Reading Time25 min

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Abstract

1. Introduction

This article is licensed under CC-BY 4.0 [http://pubs.acs.org/journal/acsodf](http://pubs.acs.org/journal/acsodf) Article Determination of CO2 Solubility in Water by NIR Spectroscopy under Different Temperature and Pressure Conditions Lorena Armando da Silveira, Lorena Mariah Oliveira Lima, Thiago Rodrigues da Cunha, Fabiane Santos Serpa, Ranyere Lucena Souza, Rosane Alves Fontes, Giselle Maria Lopes Leite da Silva, M̂onica Teixeira da Silva, Jussara de Mello Silva, Tiago Cavalcante Freitas, Luiz Alexandre Sacorague, Claudio Dariva, Marcos Ĺucio Corazza, and Elton Franceschi * Cite This: ACS Omega 2025, 10, 58714−58723 Read Online | | | | | | | | --- | --- | --- | --- | --- | --- | | ACCESS | Metrics & More | | Article Recommendations | | *sı Supporting Information | ABSTRACT: Monitoring the solubility of carbon dioxide (CO2) in water under high-pressure and-temperature conditions is critical for industrial processes. Although the solubility behavior of CO2 is well-established in the literature, most conventional methods rely on offline, invasive, or indirect measurements. In this study, a methodology was developed to monitor CO2 solubility in water using near-infrared (NIR) spectroscopy due to its sensitivity to molecular interactions and ability to detect structural changes in the aqueous matrix in real time. The experimental system consisted of an apparatus similar to the static synthetic method coupled with an NIR spectrophotometer, enabling noninvasive spectral data acquisition during the dissolution of CO2 in ultrapure water under varying temperature (40 to 60 °C) and pressure (0.15 to 2.35 MPa) conditions. Spectral data were preprocessed and correlated with CO2 solubility using partial least-squares (PLS) regression. The PLS model was calibrated using solubility values obtained from a thermodynamic model based on the Peng−Robinson equation of state (PR-EoS) and the NRTL activity coefficient model, which was parametrized using experimental data from the literature. The developed model showed high predictive performance (R2 > 0.99) with an average external prediction error of 9.91%. In comparison, the thermodynamic model yielded a mean absolute deviation of 0.073% in pressure predictions. The results demonstrate that NIR spectroscopy is sensitive to spectral variations associated with molecular interactions between CO2 and water, enabling the construction of robust predictive models. This integrated approach provides a reliable and real-time method for indirectly estimating CO2 solubility from spectral data. It thus represents an alternative tool for industrial and environmental monitoring of dissolved gases. 1. INTRODUCTION The solubility of gases in liquids has been extensively investigated over the past decades due to its broad relevance in industrial and environmental applications, such as enhanced oil recovery (EOR), gas absorption, and the mitigation of phenomena like scaling and corrosion. 1−3 Among the systems of greatest practical interest is the dissolution of CO2 in water, which plays a key role in processes involving gas−liquid mass transfer.1,2,4−12 It is well-known that the solubility of CO2 in water increases with increasing pressure and decreases with increasing temperature, and its behavior has been extensively characterized under equilibrium conditions. The methods traditionally employed to determine CO2 solubility include the synthetic method, the volumetric method, and offline analytical techniques such as chromatography and titration. Although widely used, these approaches present limitations, such as their invasive nature, the requirement of sample withdrawal, low temporal resolution, and restrictions under conditions of low solubility. Fouriertransform infrared (FTIR) spectroscopy, in turn, enables the direct detection of CO2 via its asymmetric stretching band at approximately 2340 cm−1 and bending mode at 660 cm−1 . However, its application in pressurized a

FAQs

Why is monitoring CO2 solubility in water under varying pressure and temperature important?

It is critical for industrial processes involving gas–liquid mass transfer and also for environmental control where dissolved gases affect outcomes such as scaling and corrosion.

How does the proposed method use NIR spectroscopy to estimate CO2 solubility?

NIR spectra are collected during CO2 dissolution, and spectral changes are correlated with CO2 solubility using preprocessing and partial least-squares (PLS) regression based on calibration data.

What performance did the developed PLS model achieve compared with the thermodynamic model?

The PLS model showed high predictive performance with R2 greater than 0.99 and an average external prediction error of 9.91%, while the thermodynamic model produced a mean absolute deviation of 0.073% in pressure predictions.

Sep 29, 2026

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