Extractive　distillation　processes　enable　the　separation　of　non-ideal　mixtures,　including　minimum　or　maximum　boiling　azeotropes　and　low　relative　volatility　mixtures.　Unlike　azeotropic　distillation,　the　entrainer　fed　at　another　location　than　the　main　mixture　induces　an　extractive　section　within　the　column.　A　general　feasibility　criterion　shows　that　intermediate　and　light　entrainers　and　heterogeneous　entrainers　are　suitable　along　common　heavy　entrainers.　Entrainer　selection　rules　rely　upon　selectivity　ratios　and　residue　curve　map　(rcm)　topology　including　univolatility　curves.　For　each　type　of　entrainer,　we　define　extractive　separation　classes　that　summarize　feasibility　regions,　achievable　products　and　entrainer　-　feed　flow　rate　ratio　limits.　Case　studies　are　listed　as　Supplementary　materials.　Depending　on　the　separation　class,　a　direct　or　an　indirect　split　column　configuration　will　allow　to　obtain　a　distillate　product　or　a　bottom　product,　which　is　usually　a　saddle　point　of　rcm.　Batch　and　continuous　process　operations　differ　mainly　by　the　feasible　ranges　for　the　entrainer　-　feed　flow　rate　ratio　and　reflux　ratio.　The　batch　process　is　feasible　under　total　reflux　and　can　orient　the　still　path　by　changing　the　reflux　policy.　Optimisation　of　the　extractive　process　must　systematically　consider　the　extractive　column　along　with　the　entrainer　regeneration　column　that　requires　energy　and　may　limit　the　product　purity　in　the　extractive　column　through　recycle.　For　the　sake　of　reducing　the　energy　cost　and　the　total　cost,　pressure　change　can　be　beneficial　as　it　affects　volatility,　or　new　process　structures　can　be　devised,　namely　heat　integrated　extractive　distillation,　extractive　divided　wall　column　or　processes　with　preconcentrator.　(C)　2018　Institution　of　Chemical　Engineers.　Published　by　Elsevier　B.V.　All　rights　reserved.