Reactor for catalytic dehydrogenation of hydrocarbons with selec

Details Reactor for catalytic dehydrogenation of hydrocarbons with selec Reactor for catalytic dehydrogenation of hydrocarbons with selec

1997-08-05

1999-12-07

McMahon, Timothy

Chemical apparatus and process disinfecting, deodorizing, preser

Chemical reactor

Including heat exchanger for reaction chamber or reactants...

422191, 422220, B01J 0804, B01J 1000, B01J 802, B01J 3502

Patent

active

059978260

DESCRIPTION:

BRIEF SUMMARY
FIELD OF INVENTION

The present invention relates to a reactor for catalytic dehydrogenation of dehydrogenatable hydrocarbons, in particular C.sub.3 and/or C.sub.4 hydrocarbons, to more unsaturated hydrocarbons, with selective oxidation of hydrogen.


BACKGROUND OF THE INVENTION

Catalytic dehydrogenation of hydrocarbons is a well known and commercially important process. The reaction is strongly endothermic. At adiabatic conditions this will result in a lowering of the temperature in the reaction mixture and a consequent lowering of the reaction velocity. Therefore, existing catalytic dehydrogenation processes are dependent on external heat supply to uphold the reaction temperature. Besides, dehydrogenation reactions are subject to equilibrium limitations at typical process conditions.
The above-mentioned limitations have led to the development of autothermal dehydrogenation processes wherein the dehydrogenation is effected in combination with an oxidation of formed hydrogen to water with an oxygen-containing gas. At typical reaction conditions, the exothermic heat generated by the combustion of about half of the formed hydrogen will compensate for the heat loss resulting from the endothermic dehydrogenation reaction. In addition to achieving a desired heat balance, the consumption of hydrogen in the combustion reaction will shift the equilibrium of the desired dehydrogenation reaction in the direction of a higher conversion to dehydrogenated hydrocarbons.
It is strongly desired in such an autothermal dehydrogenation of hydrocarbons that a selective oxidation of hydrogen takes place without any substantial oxidation of hydrocarbons to carbon oxides, as oxidation of hydrocarbons will reduce the efficiency of the dehydrogenation process, due to a direct loss of product and also due to the formation of carbon monoxide. Carbon monoxide may have a deleterious effect on the performance of the dehydrogenation catalyst and thus indirectly reduce the yield of the desired dehydrogenated hydrocarbon.
U.S. Pat. No. 4,914,249 describes a process for autothermal dehydrogenation of a dehydrogenatable hydrocarbon, comprising two dehydrogenation stages and an intermediate oxidation stage for a selective oxidition of hydrogen to water. In this previously known process, the effluent stream from the first dehydrogenation stage, comprising a mixture of dehydrogenated hydrocarbon, unconverted hydrocarbon, hydrogen and steam, is subjected to a selective oxidation of hydrogen on a separate oxidation catalyst in a separate oxidation zone, to which zone the oxygen-containing gas required for the combustion is fed, preferably at a position adjacent to the bed of oxidation catalyst. The effluent from this separate oxidation zone is then subjected to the next dehydrogenation step. Said patent does not specify the flow conditions at which the oxygen-containing gas is introduced into the oxidation zone and mixed with the effluent stream from the first dehydrogenation stage.
U.S. Pat. No. 4,739,124 discloses another autothermal dehydrogenation process. Here, a hydrocarbon represented by ethane is dehydrogenated catalytically in a reactor comprising at least two separate beds of a dehydrogenation catalyst. A feed stream comprising ethane is passed into the first bed of dehydrogenation catalyst maintained at dehydrogenation conditions comprising temperatures in the range of 538.degree. C. to 750.degree. C. The effluent stream from this bed, comprising ethane, ethylene formed as a product and hydrogen formed as a by-product, is cooled and then mixed with an oxygen-containing gas, whereupon the obtained mixture is fed to a separate bed of a selective hydrogen oxidation catalyst maintained at oxidation promoting conditions. The effluent stream from said oxidation bed, which has been heated as a result of the hydrogen combustion, is passed to a second bed of dehydrogenation catalyst similar to the first bed of dehydrogenation catalyst.
The purpose of cooling the effluent stream from the first bed of dehydrogenation catalyst in the process of

REFERENCES:
patent: 3502737 (1970-03-01), Ghublikian
patent: 3855330 (1974-12-01), Mendelsohn
patent: 4778941 (1988-10-01), Tagamolila
patent: 4806624 (1989-02-01), Herber et al.
patent: 4891464 (1990-01-01), Staggs
patent: 5043500 (1991-08-01), Tagamolila

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