Process and device for catalytic dehydrogenation of a C.sub.2+ paraffinic charge comprising means for inhibiting the freezing of water in the effluent

In a process of catalytic dehydrogenation of a C.sub.2+ paraffinic hydrocarbon charge, said process comprising (i) dehydrogenating said charge in gas phase optionally in the presence of hydrogen, to produce a dehydrogenation gaseous effluent comprising water, hydrogen, olefinic hydrocarbons and unconverted paraffinic hydrocarbons, (ii) cooling the effluent of (i), (iii) compressing the cooled effluent of (ii), (iv) inhibiting freezing of the water contained in the compressed effluent of (iii), (v) cooling the compressed effluent of (iii) in a heat exchanger, (vi) separating the compressed and cooled effluent of (v) in a separation zone and (ii) recovering hydrogen and hydrocarbons, for the most part olefinic, wherein at least one part of the cooled effluent is saturated with in a saturation zone by direct contact with a mixture of liquid phases containing mostly water, before or after the compression step, and wherein the improvement comprises inhibiting the freezing of water in the effluent in (iv):

• (a) by contacting in a stripping zone at least one part of the effluent that is compressed and saturated with water with a recycled liquid phase containing both water and a solvent, said solvent being a nonhydrocarbon organic compound, normally liquid, other than water, said compound being at least partially water-miscible and distillable at a temperature lower than that of the distillation of water, to obtain a gas phase charged with solvent and effluent and an aqueous liquid phase;
• (b) by introducing the gas phase that is charged with solvent and effluent into the remaining part of the effluent that is compressed and saturated with water, when the whole of the effluent that is compressed and saturated with water has not been put in contact with the recycled liquid phase;
• (c) by circulating the gas phase that is charged with solvent and effluent of (b), or of (a) when (b) is not necessary, in said heat exchanger during the cooling step;
• (d) by separating in the separation zone a decanted liquid phase containing water and solvent and
• (e) by recovering and by recycling the decanted liquid phase of (d) to said stripping column of (a).