ИСТИНА

Accurate knowledge of the thermodynamic properties of carbon dioxide (CO₂), especially the position of the phase line (pressure and transition temperature), is critically important for many technological processes: from supercritical fluid extraction to carbon capture and storage (CCS) technologies. The presence of even small amounts of non-condensing impurities can significantly shift the phase transition point, which leads to errors in the design and operation of equipment. Microfluidic chips provide a unique opportunity for high-precision and high-speed screening of such effects with small volumes of reagents.The purpose of this work is to quantify the effect of hydrogen (H₂) and helium (He) impurities with a concentration of 1% on the pressure of the liquid-gas phase transition of pure CO₂ in the temperature range from -10°C to +30°C using a microfluidic installation.For each system under study (pure CO₂, CO₂+H₂, CO₂+He), the pressure of the appearance/disappearance of the meniscus (phase boundary) was recorded visually (using a digital microscope) at five fixed temperatures: -10, 0, 10, 20 and 30°C. Pressure measurements were carried out using two calibrated absolute pressure sensors.Transition pressure values were obtained for pure CO₂, which are in good agreement with the literature data, which confirms the reliability of the microfluidic technique used. However, during a series of experiments on a microfluidic chip, an unexpected and significant effect of small (1%) impurities on the phase behavior of carbon dioxide was revealed. Contrary to the possible assumption that such small concentrations are insignificant, the results clearly showed 28 that even minor additions of hydrogen and helium contribute to a statistically significant decrease in the pressure of the liquid-gas phase transition point at all five temperature points studied (-10°C, 0°C, 10°C, 20°C, 30°C).The data obtained may indicate that the presence of light non-condensing impurities (H₂, He) disrupts the molecular interaction in the liquid phase of CO₂. A likely explanation for the observed effect is that hydrogen and helium molecules, having high volatility and low boiling point, act as "leavening agents" of the structure of liquid carbon dioxide. Their presence between the CO₂ molecules facilitates the transition from the liquid to the gaseous phase, which now requires less external pressure at the same temperature.