Paul M. Mathias

Improving the regeneration of CO2-binding organic liquids with a polarity change

This paper describes a solvent regeneration method unique to CO2-binding organic liquids (CO2BOLs) and other switchable ionic liquids: utilizing changes in polarity to shift the free energy of the system. The degree of CO2 loading in CO2BOLs is known to control the polarity of the solvent; conversely, polarity can be exploited as a means to control CO2 loading. In this process, a chemically inert nonpolar “antisolvent” (AS) such as hexadecane (C16) is added to aid in de-complexing CO2 from a CO2-rich CO2BOL. The addition of this polarity assist reduces the temperature required for regeneration of our most recent CO2BOL, 1-((1,3-dimethylimidazolidin-2-ylidene)amino)propan-2-ol by as much as 73 °C. The lower regeneration temperatures realized with this polarity change allow reduced solvent attrition and thermal degradation. Furthermore, the polarity assist shows considerable promise for reducing the regeneration energy of CO2BOL solvents, and separation of the CO2BOL from the AS is as simple as a cooling the mixture to promote phase separation. Based on vapor–liquid and liquid–liquid equilibrium measurements of a candidate CO2BOL with CO2, with and without an AS, we present the evidence and impacts of a polarity change on a CO2BOL. Equilibrium thermodynamic models and analysis of the system were constructed using Aspen Plus®, and forecasts of preliminary process configurations and feasibility are also presented. Lastly, projections of solvent performance for removing CO2 from a subcritical coal-fired power plant (total net power and parasitic load) are presented with and without this polarity assist and compared to the U.S. Department of Energys Case 10 monoethanolamine baseline.

The role of experimental data in chemical process technology

Experimental data have served two critical roles in chemical process technology: (1) by providing the definitive quantitative basis to evaluate competing processes, to optimize designs, and ultimately to guarantee plant performance; and (2) by guiding the form and structure of applied-thermodynamics correlations. This paper first presents two representative applications to highlight the role of thermodynamic and transport properties in chemical process technology: ammonia recovery from syngas using water as solvent, and design of a caustic-guard system to eliminate small residual concentrations of SO2 from a gas stream. These applications illustrate the first role of experimental data. The paper next studies the second role by examining the historical contribution of experimental data—over two centuries—in guiding the development of key concepts and correlations, such as Henry’s law (1802), group-contribution methods (Kopp, 1842), Raoult’s law (1878), second-virial-coefficient correlation (Berthelot, 1907), surface-tension correlation (Macleod, 1923), the use of one property to estimate another (Othmer, 1940), cubic equations of state (Redlich and Kwong, 1949), electrolyte systems (van Krevelen, 1949), acentric factor (Pitzer, 1955), and highly accurate equations of state (Span and Wagner, 2003). The analysis reveals that careful, accurate, and wide-ranging experimental data have identified the patterns of the underlying phenomena.

Modified Trouton’s Rule for the Estimation, Correlation, and Evaluation of Pure-Component Vapor Pressure

Insights from the venerable Trouton’s Rule have been used to guide the development of an applied-thermodynamic method for the estimation, correlation, and evaluation of pure-component vapor pressure. Trouton’s Rule very simply and succinctly states that the entropy of vaporization of fluids at their normal boiling point is a constant (≈10.5 times the gas constant). Detailed evaluation of the data for many families of chemical compounds reveals the subtle patterns of departures from the rule, and facilitates the development of a useful new correlation. Several examples are presented to demonstrate the value of the new correlation to estimate, correlate, extrapolate, and evaluate vapor-pressure data, and to understand the patterns of vapor-pressure behavior. The methodology provides a guide for the development of thermodynamic correlations, and the resulting correlations are expected to be useful for the practice of applied thermodynamics.