NOVELTY - Cryogenic separation by washing with nitrogen to produce mixture of hydrogen and nitrogen with less than 1% methane and/or less than 1% carbon monoxide, comprises: e.g. cooling synthesis gas (1) containing hydrogen, nitrogen, methane and less than 5% of carbon monoxide and partially condensed to produce hydrogen enriched gas (9) and methane enriched first liquid (7); partially condensing hydrogen enriched gas to produce vapor (11) enriched in hydrogen and second liquid (13) enriched in methane; and passing at least a portion of hydrogen enriched vapor and liquid nitrogen to washing column.    USE - The process is useful for cryogenic separation by washing with nitrogen to produce a mixture of hydrogen and nitrogen containing less than 1% methane and/or less than 1% carbon monoxide.    ADVANTAGE - The process: provides mixture of hydrogen and nitrogen containing less than 1% of methane and/or less than 1% of carbon monoxide (claimed); utilizes less amount of nitrogen, thus reduces the cost of synthesis gas generation unit and consumes less energy to heat the methane rich fluid; provides separation of fluid rich in methane with high recovery rate and with high purity, thus increases the yield of synthesis gas and reduces the cost of gasification unit.    DETAILED DESCRIPTION - Cryogenic separation by washing with nitrogen to produce a mixture of hydrogen and nitrogen containing less than 1% methane and/or less than 1% carbon monoxide, comprises: cooling a synthesis gas (1) containing hydrogen, nitrogen, methane and less than 5% of carbon monoxide in a heat exchanger and partially condensed to produce a hydrogen enriched gas (9) and methane enriched first liquid (7); partially condensing the hydrogen enriched gas to produce a vapor (11) enriched in hydrogen and a second liquid (13) enriched in methane; passing at least a portion of the hydrogen enriched vapor to a washing column; passing liquid nitrogen at the top of the washing column; withdrawing hydrogen and nitrogen mixture at the top of the washing column; and mixing the first and second liquid enriched in methane, warming at least a portion of the mixture in heat exchanger to form gas rich in methane. An INDEPENDENT CLAIM is also included for an apparatus for cryogenic separation by washing with nitrogen to produce a mixture of hydrogen and nitrogen containing less than 1% methane and/or less than 1 % carbon monoxide, comprising a heat exchanger, means for feeding the synthesis gas to cool and partially condense in a first separator pot, means for sending the partially condensed fluid in the heat exchanger to the first pot to produce the hydrogen-enriched gas and the first liquid, means for partially condensing the enriched gas hydrogen to produce a hydrogen-enriched vapor and the second methane-enriched liquid, a second separator pot to separate the steam and the second liquid, a washing column, means for sending at least a portion of the hydrogen-enriched vapor from the second separator pot to the washing column, means for sending liquid nitrogen at the top of the wash column, means for withdrawing the mixture of hydrogen and nitrogen at the top of the wash column, means for mixing the first and second liquid enriched with methane, means for expanding the mixture or liquids to be mixed, and means for sending at least part of the expanded liquid mixture or relaxed in the heat exchanger to form a gas rich in methane.    DESCRIPTION OF DRAWING(S) - The figure shows the process of cryogenic separation by washing with nitrogen to produce mixture of hydrogen and nitrogen.    Synthesis gas (1)    Methane enriched first liquid (7)    Hydrogen enriched gas (9)    Vapor enriched in hydrogen (11)    Second liquid enriched in methane (13)