Integration of a fused silica capillary and in-situ Raman spectroscopy for investigating CO2 solubility in n-dodecane at near-critical and supercritical conditions of CO2

To determine the solubility of CO 2 in n-dodecane at T  = 303.15–353.15 K, P  ≤ 11.00 MPa, an integrated fused silica capillary and in-situ Raman spectroscopy system was built. The Raman peak intensity ratio ( I CO 2 / I C - H ) $(I_{{\text{CO}}_2}/I_{\text{C}-\text{H}})$ between the upper band of CO 2 Fermi diad ( I CO 2 $I_{{\text{CO}}_2}$ ) and the C–H stretching band of n-dodecane ( I C - H ) $\left(I_{\text{C}-\text{H}}\right)$ was employed to determine the solubility of CO 2 in n-dodecane based on the calibrated correlation equation between the known CO 2 molality in n-dodecane and the I CO 2 / I C - H $I_{{\text{CO}}_2}/I_{\text{C}-\text{H}}$ ratio with R 2  = 0.9998. The results indicated that the solubility of CO 2 decreased with increasing temperature and increased with increasing pressure. The maximum CO 2 molality (30.7314 mol/kg) was obtained at 303.15 K and 7.00 MPa. Finally, a solubility prediction model ( ln S = ( P − A ) / B $\text{ln}S=(P-A)/B$ ) based on the relationship with temperature ( T in K) and pressure ( P in MPa) was developed, where S is CO 2 molality, A = − 8 × 10 − 6 T 2 + 0.0354 T − 8.1605 $A=-8\times {10}^{-6}{T}^2+0.0354T-8.1605$ , and B = 0.0405 T − 10.756 $B=0.0405T-10.756$ . The results indicated that the solubilities of CO 2 derived from this model were in good agreement with the experimental data.