Abstract: For selectively removing nitrogen oxides from a carrier gas that contains hydrocarbons, the nitrogen oxides are removed by chemisorption on metal oxides, without the occurrence of undesirable secondary reactions. The metal oxides are preferably formed from metals of the 6th to 8th subgroups, whereby manganese dioxide (MnO.sub.2,) is especially preferred as a metal oxide. The process can be conducted with one or more reactor beds, which preferably operate at 10 to 40.degree. C. and are regenerated with nitrogen at a temperature of 130 to 170.degree. C.By removing nitrogen oxides from an olefin-rich gas, for example from the waste gas of an FCC unit, the resultant gas can then be fed to a cryogenic olefin extraction stage without danger of explosion.Such a waste gas contains unsaturated hydrocarbons, hydrogen, carbon monoxide, and oxygen, the oxygen having a concentration preferably between 100 and 5000 mol ppm.

Abstract: An apparatus for the cooling of a cracking-gas stream comprises a vertical pipe through which the cracking-gas stream is conducted and opening into a larger pipe section which surrounds the first-mentioned pipe across an annular gap. A plurality of inlets open tangentially into this gap, upstream of the mouth of the first pipe to distribute cooling oil along the wall of the second pipe. The cooling oil film is found to be uniform and coherent and prevents contact of the cracking gas with the wall of this pipe. A further pipe opening axially into the surrounding pipe or pipe section sprays an additional quantity of cooling oil into the cracking-gas stream downstream of the mouth of the inlet pipe.

Abstract: Crude gas, such as cracking gas, is subjected after quenching to a two stage cooling system wherein water is employed in the first stage as both a direct contact coolant and scrubbing agent to remove condensed out hydrocarbons and solids from the gas. The scrubbing liquid in the first stage is subjected to a rough decanting step to separate hydrocarbons from water which is to be recycled; however, no indirect heat exchangers are used for recycle water, thereby avoiding clogging. The gas recovered from the first cooling stage is at about the water dew point of the gas, and is then cooled in a second stage in direct contact with refrigerated water, but because the fouling substances of the gas are removed in the first stage, there is no clogging problem when the recycle water is cooled in an indirect heat exchanger with an external refrigerant.