Distn. appts. for sepg. close-boiling light hydrocarbons chosen from ethylene/ethane, propylene/propane or 1-butylene/n-butane mixts., comprises (a) a high pressure section at subcritical pressure having high and low temp. stages; (b) a bottoms product zone at superatmos. pressure; (c) an intermediate section having one or more intermediate zones of successively lower pressure from the high pressure section to the bottoms product zone; (d) high and low temp. stages in each of the intermediate zones; (e) a feed zone in fluid communication with at least one of the sections for receiving a mixt. of hydrocarbons including light and heavy components; (f) an overhead condensing zone adjacent the low temp. stage of the high pressure section for condensing the light component at a condensation temp.; (g) several cooling loops each including an expansion valve for flashing fluid from a high temp. stage into a coolant supply line below the condensation temp. through the condensing zone and into coolant return lines for introducing fluid of similar pressure into the low pressure stage of each intermediate zone and the bottoms product zone, in which at least one of the cooling loops flashes fluid from the high temp. stage of one of the intermediate zones; (h) several compression loops for compressing fluid from the bottoms product zone and the low temp. stage of each intermediate zone, and discharging the compressed fluid to a high temp. stage of similar pressure; (i) a line for taking off light-component product of reduced heavy component content from adjacent the condensing zone; (j) a line for taking off heavy-component product of reduced light-component content from the bottoms product zone. Also claimed is a method for sepg. such close-boiling light hydrocarbons.    USE -   Thermo-mechanically integrated distillation of close-boiling light hydrocarbons.    ADVANTAGE -   Integrated distn. of close-boiling hydrocarbons e.g. ethylene from ethane; where no column section operates above min. internal reflux, achieving high thermodynamic efficiency with low operating and capital costs.