Method for purifying a gas rich in hydrocarbons

Process for purifying a gas (1) rich in hydrocarbons and comprising at least 10 ppm by volume of hydrocarbons having at least six carbon atoms, comprising the following steps: Step a) Cooling said gas to a temperature between -20°C and -60°C by heat exchange with at least one coolant (3) in a heat exchanger (2); Step b) Scrubbing of compounds containing at least six carbon atoms from the gas partially liquefied in step a) in a washing column (5) containing a column (5) overhead (8) in its highest end and a column (5) bottom (7) in its lowest end in order to form, as washing column (5) overhead (8), a gas stream (9) containing less than 5 ppm by volume of compounds containing at least six carbon atoms and, as washing column (5) bottoms (7), a liquid stream (6) enriched in compounds containing at least five carbon atoms; Step c) At least partial condensation of said gas stream (9) resulting from step b) in a heat exchanger (10, 2) in order to form a two-phase stream (15); Step d) Separating said two-phase stream (15) resulting from step c) in a phase separator pot (16) at a temperature between -60°C and -80°C in order to form a gas stream (17) as pot overhead and a liquid stream (18) as pot bottoms (16); Step e) Use of the liquid stream (18) resulting from step d) as washing column (5) overhead (8) reflux; Step f) Condensation of the gas stream (17) resulting from step d) by heat exchange in a heat exchanger (20, 2) at a temperature below -100°C in order to form a liquefied gas (21) containing less than 5 ppm by volume of compounds containing at least six carbon atoms.