Measurements and modeling of high-pressure excess molar enthalpies and isothermal vapor–liquid equilibria of the carbon dioxide + N,N-dimethylformamide system

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• 作者：Fouad Zahran ; Concepció ; n P ; o ; Albertina Cabañ ; as ; Juan A.R. Renuncio
• 关键词：Supercritical carbon dioxide ; N ; N-dimethylformamide ; Excess molar enthalpies ; Vapor– ; liquid equilibria ; Equation of state
• 刊名：The Journal of Supercritical Fluids
• 出版年：2010
• 出版时间：December 2010
• 年：2010
• 卷：55
• 期：2
• 页码：566-572
• 全文大小：250 K

文摘

Mixtures of supercritical CO₂ and N,N-dimethylformamide (DMF) are very often involved in supercritical fluid applications and their thermodynamic properties are required to understand and design these processes. Excess molar enthalpies () for CO₂ + DMF mixtures were measured using an isothermal high-pressure flow calorimeter under conditions of temperature and pressure typically used in supercritical processes: 313.15 and 323.15 K at 9.00, 12.00, 15.00 and 18.00 MPa and 333.15 K at 9.00 and 15.00 MPa. The Peng–Robinson and the Soave–Redlich–Kwong equations of state were used in conjunction with the classical mixing rules to model the literature vapor–liquid equilibrium and critical data and the excess enthalpy data. In most cases, CO₂ + DMF mixtures showed very exothermic mixing and excess molar enthalpies exhibited a minimum in the CO₂-rich region. The lowest value (−4526 J mol⁻¹) was observed for a CO₂ mole fraction value of 0.713 at 9.00 MPa and 333.15 K. On the other hand, at 9.00 MPa and 323.15 and 333.15 K varies linearly with CO₂ mole fraction in the two-phase region where a gaseous and a liquid mixture of fixed composition are in equilibrium. The effects of pressure and temperature on the excess molar enthalpy are large. For a given mole fraction, mixtures become less exothermic as pressure increases or temperature decreases. These excess enthalpy data were analyzed in terms of molecular interactions, phase equilibria, density and critical parameters previously reported for CO₂ + DMF. All throughout this paper, the key concepts and modeling tools originate from the work of van der Waals: the paper is intended as a small piece of recognition of van der Waals overwhelming contributions to thermodynamics.