Effects of Carbon Monoxide and Dimethyl Ether on the Bubble Points of CO₂ Streams from 247.15 K to Critical Conditions

The quality of CO₂ streams in carbon capture, utilization, and storage is critical, as even small amounts of impurities can significantly affect phase behavior and operational integrity. This study investigated how carbon monoxide (CO) and dimethyl ether (DME), at concentrations of 0.5–5%, impact the bubble points of CO₂ streams compared to pure CO₂ at equal temperatures. Experiments were conducted from 247.15 K to near-critical conditions using constant composition expansion methods. The measurement uncertainties were 0.14 K and 0.03 MPa for the temperatures and pressures, respectively, and the composition uncertainties were 0.0009 and 0.0011 mol/mol for CO₂–CO and CO₂–DME systems, respectively. Results showed that CO had a greater effect on the bubble points of CO₂ than DME, attributed to CO’s lower molecular weight. In contrast, DME caused a negative deviation from pure CO₂ vapor pressures due to its heavier molecular weight. Model validations using the Peng–Robinson and Multi-Fluid Helmholtz Energy Approximation equations of state revealed that both provided accurate predictions, with MFHEA outperforming PR, achieving deviations below 2.5%. These findings indicate that noncondensable gases like CO increase the risk of two-phase flow during CO₂ transport, particularly at low temperatures, emphasizing the need for careful impurity management in CCUS systems.