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We have evaluated the vapor–liquid equilibriumand heat of absorption of CO2 over water-lean mixturesof the amines diisopropylamine and N,N-diethylethanolamine （DEEA）. This extends our previous research onwater-lean solvents containing ethanolamine. The organic diluents N-methyl-2-pyrrolidone （NMP） and ethylene glycol （MEG） havebeen employed for solvent formulation. Since both diisopropylamine（a hindered amine） and N,N-diethylethanolamine（a tertiary amine） react with CO2 to form mainly bicarbonatein aqueous solutions, their behavior in nonaqueous mixtures is quitedifferent from that of monoethanolamine. While MEG seems to maintainthe reactivity of both diisopropylamine and DEEA even in nonaqueousmixtures, nonaqueous solvents with NMP act essentially as physicalabsorbents. This is an important indication that MEG is able to takepart in the reaction mechanism between these amines and CO2, perhaps through alkylcarbonate formation, a fact that can be tracedback to its relatively low autoprotolysis constant （pKS）. This study represents a departure from our previoustreatment on loss of CO2 solubility in water-lean solventswith monoethanolamine based on solvation phenomena alone, as it hasbecome clear that the shift in equilibria in solvents with hinderedand tertiary amines must account for Le Chatelier’s principle.
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