Near infrared spectroscopy applied for high-pressure phase behavior measurements

• Synthetic method was modified by an insertion of NIR probe.
• Pressure and type of phase transitions were clearly identified by NIR.
• Proposed methodology is robust for phase behavior investigations at high pressures.

This work presents a new technique for phase behavior monitoring at high-pressure conditions. The consolidated synthetic method was modified by insertion of a near infrared probe inside the high-pressure variable-volume view cell. A system composed by carbon dioxide and a distilled petroleum fraction was used to validate the proposed methodology. The experiments were performed in the temperature range of 293–333 K, carbon dioxide mass fraction of 0.350–0.900 and pressures up to 20 MPa. The phase transitions pressures visually observed were compared with those detected by the spectrophotometer and good correlations were obtained with global mean deviation of 1.4%. Besides, it was possible to identify the type of vapor-liquid phase transitions (bubble or dew points) and the position at diagram (before or after the critical concentration) for the liquid–liquid equilibrium. The proposed methodology is promptly extended to several others systems.

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