Method for olefins production
View Patent ↗Disclosed is a process for the catalytic dehydrogenation of alkanes so as to form the corresponding olefins. The reaction mixture is subjected to membrane separation of hydrogen, in a separate unit. Preferably a plurality of alternating reaction and separation units is used. The process of the invention serves the purpose of reducing coke formation on the catalyst, and also of achieving a higher alkane conversion without a similar increase in coke formation. The process can also be used for the production of hydrogen.
1. A method for producing an alkene by dehydrogenation of a corresponding alkane to the alkene, comprising the steps of:
(i) providing a hydrocarbon source comprising at least one alkane;
(ii) dehydrogenating the hydrocarbon source in the presence of a dehydrogenation catalyst to form a reaction mixture comprising hydrogen and an alkene corresponding to the at least one alkane
(iii) separating the reaction mixture in a metal membrane to form a permeate comprising hydrogen and a retentate comprising unconverted alkane and the alkene corresponding to the at least one alkane;
(iv) purifying the alkene from the retentate comprising the alkene and the unconverted alkane;
(v) recycling the unconverted alkane in (iv);
wherein the dehydrogenation reaction and the membrane separation are conducted in separate units,
wherein the dehydrogenation in (ii) is conducted at a temperature of 500-650° C. and the separation in (iii) is conducted at a lower temperature of 420-490° C., and
wherein said method comprises a plurality of dehydrogenation steps (ii) and a plurality of separation steps (iii), wherein each dehydrogenation step is followed by a separation step, and wherein the retentate from each separation step is subjected to a subsequent dehydrogenation step such that said dehydrogenation steps and said separation steps are alternating.
2. The method according to claim 1 , wherein the recycled unconverted alkane is pre-heated to 500-650° C. prior to conducting the subsequent dehydrogenation step.
3. The method according to claim 1 , comprising 3 or 4 dehydrogenation steps and 3 or 4 membrane separation steps.
4. The method according to claim 1 , wherein the alkane to be dehydrogenated is selected from the group consisting of ethane, propane, butane and mixtures thereof.
5. The method according to claim 1 , wherein the separation in (iii) and (vi) comprises providing a permeate side of the membrane with a sweeping steam so as to reduce a partial pressure of hydrogen.
6. The method of claim 1 , which further comprises separating the hydrogen from the permeate.
7. The method according to claim 6 , wherein the separation in (iii) comprises sending a sweeping steam to a permeate side of the metal membrane to reduce a partial pressure of hydrogen and produce a permeate comprising hydrogen and steam, and separating the hydrogen by allowing the steam to condence.
8. The method of claim 1 wherein the membrane comprises palladium.
9. A method for producing an alkene by dehydrogenation of a corresponding alkane to the alkene, comprising the steps of:
(i) providing a hydrocarbon source comprising at least one alkane;
(ii) dehydrogenating the hydrocarbon source at a temperature of 500-650° C. in the presence of a dehydrogenation catalyst in a first dehydrogenation reactor to form a first reaction mixture comprising hydrogen and an alkene corresponding to the at least one alkane;
(iii) separating the first reaction mixture in a first metal membrane, located in a separate unit from the first dehydrogenation reactor, at a temperature of 420-490° C. to form a first permeate comprising hydrogen and a first retentate comprising unconverted alkane and the alkene corresponding to the at least one alkane;
(iv) heating the first retentate to a temperature of 500° C.-550° C.;
(v) dehydrogenating the first retentate in a second dehydrogenation reactor in the presence of the dehydrogenation catalyst to form a second reaction mixture comprising hydrogen and the alkene corresponding to the at least one alkane;
(vi) separating the second reaction mixture in a second metal membrane, located in a separate unit from the second dehydrogenation reactor, to form a second permeate comprising hydrogen and a second retentate comprising unconverted alkane and the alkene corresponding to the at least one alkane;
(vii) optionally repeating steps (iv) to (vi) one or more times with the second retentate and one or more subsequent retentate formed from said repetition of steps;
(viii) purifying the alkene from a last retentate comprising the alkene and the unconverted alkane;
(ix) recycling the unconverted alkane in (viii).
10. The method according to claim 9 , wherein the alkane to be dehydrogenated is selected from the group consisting of ethane, propane, butane and mixtures thereof.
11. The method according to claim 9 , wherein the separation in (iii) and (vi) comprises sending a sweeping steam to a permeate side of the metal membrane to reduce a partial pressure of hydrogen.
12. The method of claim 9 wherein the temperature in (ii) is 500-550° C.