The　chlorine　(Cl-2)　drying　technology　using　ionic　liquids　(ILs)　as　absorbents　was　proposed　for　the　first　time　and　systematically　investigated　from　the　molecular　level　scaled　up　to　the　industrial　level.　The　hygroscopic　IL　[EMIM]　[CH3SO3]　was　screened　as　a　suitable　absorbent　from　238　potential　IL　candidates　consisting　of　14　cations　and　17　anions,　by　calculating　the　Cl-2　and　H2O　solubility　and　separation　selectivity　of　Cl-2　to　H2O　in　different　Its　based　on　the　COSMO-RS　model.　The　microscopic　atomic　and　molecular　insights　into　the　separation　mechanisms　were　deeply　revealed　by　using　COSMO-RS　model　analyses　(i.e.,　sigma-profiles,　sigma-potentials,　excess　enthalpies,　entropies,　and　Gibbs　free　energies)　and　quantum　chemistry　calculation　(binding　energies　and　weak　interaction　analyses).　The　Cl-2　solubility　in　pure　IL　and　H2O　+　IL　systems　were　predicted　by　the　COSMO-RS　model,　and　the　results　agree　with　the　microscopic　mechanism　identification.　Moreover,　the　strict　equilibrium　stage　model　employed　with　the　COSMO-RS　model　parameters　was　built　to　perform　the　process　simulation,　and　continuous　Cl-2　drying　with　ILs　was　conceptually　designed　and　optimized　at　industrial　scale.　It　was　confirmed　that　[EMIM][CH3SO3]　is　a　very　promising　absorbent　leading　to　a　less　IL　amount,　a　much　lower　energy　consumption　than　the　other　IL　[EMIM][BF4],　which　has　a　very　bright　industrialization　potential　used　for　Cl-2　drying　technology.　(C)　2020,　Institute　of　Process　Engineering,　Chinese　Academy　of　Sciences.　Publishing　services　by　Elsevier　B.V.　on　behalf　of　KeAi　Communications　Co.,　Ltd.