Synthetic methods in phase equilibria: A new apparatus and error analysis of the method

• A new apparatus for studying high-pressure phase equilibria is described.
• The apparatus was tested through the study of known systems.
• The agreement of the results with literature confirms the quality of the apparatus.
• The influence of error sources associated to this experimental method is analysed.
• Experimental conditions are recommended for minimisation of experimental errors.

A new apparatus for the study of high-pressure phase equilibria using a synthetic method is described. The apparatus was especially developed for the study of solubilities of gases in condensed phases, at temperatures ranging from 243 K to 353 K and pressures up to 20 MPa. The quality of the equipment was confirmed through several tests, including measurements along the three phase co-existence line for the system ethane + methanol, the study of the solubility of methane in water, and of carbon dioxide in water.An analysis regarding the application of the synthetic isothermal method in the study of gas solubilities was performed, in order to evaluate the influence of common assumptions and of various experimental aspects on the final solubility results. The analysis revealed that the largest influence on the precision of the solubility results is related to the ratio between the volumes of the two phases in equilibrium. Experiments with small volume of the vapour phase are less susceptible to the influence of other sources of errors, resulting in a higher precision of the final results.

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