Density and speed of sound in CO2 mixtures

21GRD06 MetCCUS Paper on the measurement of the thermophysical properties of CO2 mixtures for CCUS (with target uncertainties: for density better than 0.1 %, for specific heat capacity better than 1 %, for viscosity less than 3 %, for speed of sound in liquid better than 0.05 %, for gas phase at high temperature 0.03 %) submitted to an open access peerreviewed journal D7 - A4.1.5 Organisation name of the lead participant for the deliverable: Istituto Nazionale di Ricerca Metrologica and S. Lago (INRiM), P. A Giuliano Albo (INRiM) and A. Quattrone (INRiM), A. Moreau (UVa), X. Peredes (UVa), F. Vélez (UVa), Due date of the deliverable: 01.04.2025 Actual submission date of the deliverable: 23.10.2025 Confidentiality Status: PU - Public, fully open (remember to deposit public deliverables in a trusted repository) Deliverable Cover Sheet Funded by the European Union. Views and opinions expressed are however those of the author(s) only and do not necessarily reflect those of the European Union or EURAMET. Neither the European Union nor the granting authority can be held responsible for them. The project has received funding from the European Partnership on Metrology, co-financed from the European Union’s Horizon Europe Research and Innovation Programme and by the Participating States. 1 of 5 Thermodynamic properties of carbon dioxide and amine 1 binary mixtures for CCUS 2 S. Lago a , A. Moreau b , A. Quattrone a , X. Paredes b , F. Vélez b , P. A. Giuliano 3 Albo a 4 a Istituto Nazionale di Ricerca Metrologica (INRiM), Strada delle Cacce 91, 10135 Torino, 5 Italy 6 b TermoCal Research Group, Bioeconomy Research Institute BioEcoUVa, University of 7 Valladolid, Paseo del Cauce 59, 47011 Valladolid, Spain. 8 Abstract 9 Accurate knowledge of the thermophysical properties of CO 2 -rich systems is 10 crucial for ensuring the successful deployment of CCUS technologies across Eu11 rope. Understanding the thermophysical properties of carbon dioxide mixtures 12 with a range of potential impurities reveals gaps between the experimental data 13 required for the systems design and operation. 14 In this context, important experimental properties were measured for CO 2 + 15 monoethanolamine and CO 2 + diethanolamine binary mixtures, supporting the 16 development of more rened and accurate formulations of dedicated equations 17 of state. 18 1. Materials for CCUS 19 Monoethanolamine (MEA) and diethanolamine (DEA) are, among the most 20 common alkanolamines, used in sour gas absorption technology. Their abil21 ity to chemically absorb carbon dioxide via exothermic reactions makes them 22 vital components in carbon capture, utilization, and storage (CCUS) technolo23 gies. Furthermore, MEA and DEA serve as benchmarks in evaluating new 24 CO 2 absorbent materials. Their established performance, combined with well25 documented limitations, make them reference points for thermodynamic mod26 elling and optimization of next-generation solvents. Current research in CCUS 27 aims to discover or develop alternative solvents with improved thermal sta28 bility, reduced regeneration energy, and lower corrosiveness, while maintaining 29 comparable absorption capacities. In this context, a deeper thermodynamic un30 Email address: [email protected] (S. Lago) Preprint submitted to Elsevier November 21, 2025 derstanding of these substances contributes to the ongoing eort to optimize 31 CCUS technologies and transition toward more sustainable industrial practices. 32 2. Density measurements 33 For density ρ measurements, a vibrating tube densimeter was used. The 34 working principle is based on the electromagnetic excitation of a U-shaped 35 Hastelloy tube which contains a uid inside, where the fundamental oscilla36 tion period is function of the total mass of the system related with the uid 37 density. The periods were measured using a Keysight 53220A universal fre38 quency counter, with 10−6 ms standard uncertainty over periods around 4 ms. 39 In Fig. 1 it is possible to see an example to experimental results of density as 40 function of pressure for MEA + CO 2 mixtures with α=0.15 mol CO2 /mol MEA 41 Figure 1: Experimental density as function of pressure for MEA + CO 2 mixtures: α=0.15 mol CO2 /mol MEA ; at temperatures: ( Ö ) 293.15 K; ( ▲ ) 313.15 K; ( ⬩ ) 333.15 K; ( • ) 353.15 K; ( ∆ ) 373.15 K; ( ◦ ) 393.15 K. Lines represent the calculated values using modied TammannTait equation. Mixtures uncertainty analysis showed an expanded relative uncertainty bet42 ter than 0.3 % for a 95.5 % level of condence. 43 Density measurements of pure MEA, pure DEA, binary systems MEA + CO 2 44 and binary systems DEA + CO 2 were performed at pressures from 0.1 MPa to 45 70 MPa, six temperatures ranging from (293.15 K  393.15 K) for MEA binary 46 mixtures and four temperatures ranging from (313.15 K  373.15 K) for DEA 47 2 binary mixtures. In all cases, densities were measured at three CO 2 loadings 48 α = (0.15, 0.2 and 0.3) mol CO2 /mol amine . 49 3. Speed of sound measurements 50 Speed of sound was measured using the traditional double pulse-echo method. 51 This technique is based on a direct measurement of the transit time of a pulse 52 signal, propagating over an independently known distance within the uid. 53 This work presents speed of sound experimental results in samples of pure 54 monoethanolamine, and in mixtures of MEA + CO 2 in three dierent con55 centrations, with α = (0.15, 0.20 and 0.30) mol CO2 /mol MEA ; besides of pure 56 diethanolamine, and in two binary mixtures composed of DEA + CO 2 , with 57 α=(0.15 and 0.20) mol CO2 /mol DEA . Measurements were carried out in the 58 temperature range between 293.15 and 393.15 K and for several pressures up to 59 60 MPa, depending from the mixtures or pure uid. In Fig. 2 it is possible to 60 see the experimental speed of sound results as function of pressure for MEA + 61 CO 2 mixture with α=0.15 mol CO2 /mol MEA . 62 Figure 2: Experimental speed of sound as function of pressure for MEA + CO 2 mixture with α=0.15 mol CO2 /mol MEA ; (  ) 313.15 K; ( ◦ ) 333.15 K; ( ▲ ) 353.15; ( ▽ ) 373.15 K. The uncertainty of the speed of sound measurements was 0.33 % as maximum 63 value, obtained combining the contributions of the uncertainties of the quantities 64 used to determine it. 65 3 4. Conclusion 66 The present work, part of a European Project Metrology Support for Car67 bon Capture Utilisation and Storage MetCCUS, aims to provide validated ref68 erence measurements and ensure the traceability of the results for thermophys69 ical parameters of binary mixtures of carbon dioxide and amines. The authors 70 are condent that these results will be useful for developing a more rened and 71 accurate formulation of a dedicated equations of state. 72 5. Acknowledgements 73 The research leading to these results has received funding from the European 74 Union on the basis of Decision No. 912/2009/EC in the frame of the EPM 75 Metrology Support for Carbon Capture Utilisation and Storage MetCCUS 76 (21GRD06 MetCCUS). 77 4