(DE3716898-A)      He is recovered from a gas mixt. contg. N2, CH4 and opt. other gases using known absorbers filled with zeolitic material. The process involves apart from an absorption step (A) a press build up phase comprising 3 press building steps, (B) a press relief phase comprising 4 press relief steps and opt. (C) a press equalisation phase comprising 2 press equalisation steps. A prefilter is pref. arranged upstream, filled with activated C to absorb higher hydrocarbons and other impurities. The gas mixt. contains less than 10, esp. 2-8 vol.% He and the final prod. contains at least 95 vol.% He.    USE/ADVANTAGE -   To treat a gas mixt. recovered from oil wells; an intermediate enrichment in a cooling plant is no longer required.    (12pp)    (US5089048-A)      Helium enrichment uses pressure swing adsorption from a gas mixt. comprising helium, nitrogen and methane, which are passed through carbon molecular sieves which adsorb nitrogen and methane. Gas mixt. is fed cyclically to four adsorber vessels arranged in parallel order. Mixt. passes successively through a pressure build-up, an adsorptive and a pressure relief phase, both brought about by pressure compensation where (a) pressure build-up phases comprises (1) pressure increase from a final vacuum pressure (P1) to a medium pressure (P3), (2) pressure increase from medium (Pe) to higher (P4), and (3) increased pressure from high (P4) to highest pressure level (P5); (b) pressure relief phase comprises (1) pressure relief from highest level (P5) down to (P4), (2) pressure relief down from (P4) down to (P3), (3) pressure relief down from (P3) to (P2); and (4) pressure relief down from (P2) to (P1); (c) pressure compensation is in two steps, first step takes place between outlet of a second adsorber where the second pressure build-up step occurs and second step takes place between outlet of first adsorber where second pressure relief step occurs; and (d) third and fourth pressure relief steps are affected by counter-flow where a waste gas low in helium is yielded.    Pref. pressure steps are P1 = 50m.bar, P2 = 1 bar, P3 = 4 bar, P4 = 11.7 bar, P5 = 20 bar.    USE/ADVANTAGE -   Produces a high deg. of purity. Used for refrigerationplants, shielding gas, space technology and as a carrier gas in chromatography.    (SU1816229-A3)      A gas mixt. of He, N2, CH4, etc. is passed through C molecular sieves, which adsorb N2, CH4, etc. cyclically using four parallel-connected adsorbers in each of which successive pressure build-up, adsorption and pressure relief phases are carried out.    The pressure build-up phase comprises (i) increase from a final vacuum pressure (P1) to a medium pressure (P3), (ii) increase from (P3) to a high pressure (P4) and (iii) increase from (P4) to the max. pressure (P5), i.e. the adsorption pressure. The pressure relief phase comprises (i) redn. from (P5) to (P4), (ii) redn. from (P4) to (P3), (iii) redn. from (P3) to atmos. pressure (P2) and (iv) redn. from (P2) to (P1). Pressure equalisation comprises (i) a first stage from the outlet of a first adsorber, carrying out pressure relief from P5 to P4, to the inlet of a second adsorber, carrying out pressure increase from P3 to P4, and (ii) a second stage from the outlet of the first adsorber, carrying out relief from P4 to P3, to the inlet of a third adsorber, carrying out increase from P1 to P3. Pressure reliefs from P3 to P2 and from P2 to P1 are carried out in countercurrent, producing a low He content off-gas, and pressure build-up from P4 to P5 is carried out with prod. gas.    ADVANTAGE -   Process allows the enrichment in natural gas with low He content to obtain high yields of crude He-contg. more than 50% He without intermediate cryogenic enrichments.    (JP96032549-B2)      A gas mixt. of He, N2, CH4, etc. is passed through C molecular sieves, which adsorb N2, CH4, etc. cyclically using four parallel-connected adsorbers in each of which successive pressure build-up, adsorption and pressure relief phases are carried out.    The pressure build-up phase comprises (i) increase from a final vacuum pressure (P1) to a medium pressure (P3), (ii) increase from (P3) to a high pressure (P4) and (iii) increase from (P4) to the max. pressure (P5), i.e. the adsorption pressure. The pressure relief phase comprises (i) redn. from (P5) to (P4), (ii) redn. from (P4) to (P3), (iii) redn. from (P3) to atmos. pressure (P2) and (iv) redn. from (P2) to (P1). Pressure equalisation comprises (i) a first stage from the outlet of a first adsorber, carrying out pressure relief from P5 to P4, to the inlet of a second adsorber, carrying out pressure increase from P3 to P4, and (ii) a second stage from the outlet of the first adsorber, carrying out relief from P4 to P3, to the inlet of a third adsorber, carrying out increase from P1 to P3. Pressure reliefs from P3 to P2 and from P2 to P1 are carried out in countercurrent, producing a low He content off-gas, and pressure build-up from P4 to P5 is carried out with prod. gas.    ADVANTAGE -   Process allows the enrichment in natural gas with low He content to obtain high yields of crude He-contg. more than 50% He without intermediate cryogenic enrichments.