Solvent heat of vaporization

The liquid solvent added to a pharmaceutical material generally exists in a variety of states. Some will condense or be pulled by capillary forces into macroscopic pores and fissures or into the interstitial spaces between particles. A state of local equilibrium can be assumed to exist at the interface between the liquid and vapor phases of solvent so situated. As a result, the temperature and vapor pressure exerted by the condensed solvent will not be independent of one another. Fig. 4 shows the equilibrium vapor pressure vs. temperature relationship for a number of common solvents. Heats of vaporization are shown parenthetically. Among common solvents, acetone has the highest vapor pressure and water the lowest. Water requires three-five times the energy of the common organic solvents to vaporize. 

Fig. 4 Vapor pressure curves for common solvents. Heats of vaporization are shown parenthetically. (From Refs. . )...

In principle, aU these aspects related with the solvent selection will have an impact on the outcome of the LCA metrics of the various alternatives. Fig. 13.2 presents a generic flowsheet for the solvent-based postcombustion CO2 capture processes, illustrating also the main concerns from an LCA point of view. If the LCA scope is to screen solvents for postcombustion CO2 capture without performing process simulations (i.e., in a very early phase of process design, where perhaps the number of solvent molecules to be screened is immense, for instance, in computer-aided molecular design [CAMD] of solvent molecules [68]), the potential solvents should be characterized based on properties that would indicate their expected performance in the capture process (e.g., the standard flowsheet of Fig. 13.2). These properties can be thermodynamic in nature (e.g., solubility parameters between CO2 and the solvent, solvent heat of vaporization. 

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