The variation of the phase-equilibrium behavior of chemisorbed gases with solvent concentration in mixed-solvent systems and resulting effects on the design of split-loop chemisorption processes are studied. Split-loop absorption as currently practiced is thermodynamically inefficient due to variations in solvent concentration during stripping. Adding equipment to enable better control of solvent composition results in improved process economics relative to single-loop absorption. Examination of concentration-enthalpy plots identifies the supply of stripping vapor as the main thermodynamic bottleneck of absorption-stripping processes. This suggests an alternative split-loop flow sheet in which the solvent for gas polishing is regenerated using a small fraction of the clean processed gas. This novel recycle arrangement has lower energy and capital costs and can be further integrated with other gas-processing technology. The new processes are illustrated with the example of hydrogen sulfide (H2S) and carbon dioxide (CO2) removal from hydrocarbons using aqueous methyldiethanolamine. Ultrahigh separation of H2S at much-reduced energy use is possible, either selectively or nonselectively with respect to CO2.