Abstract: A liquid product (4) leaving a furnace (2) is introduced into a series of cyclone separators (5, 6, 7). The liquid product to be vaporized is introduced tangentially into the top portion (5a, 6a, 7a) of each cyclone to place the product into contact with a side wall (5b, 6b, 7b) of the cyclone. A gaseous phase (11, 12, 13) formed in each cyclone is collected in the central zone (8, 9, 10) of the cyclone and is then introduced into a vacuum distillation column (3). The liquid phase obtained in each cyclone is collected at the bottom (5c, 6c, 7c) of the cyclone and then is introduced tangentially into the top (6a, 7a) of the following cyclone or, in the case of the last cyclone, is introduced directly into the vacuum distillation column (3). The side wall (5b, 6b, 7b) of each cyclone (5, 6, 7) is heated to a temperature near the maximum temperature allowable for avoiding all thermal deterioration of the product.