Multi-stage oxidative dehydrogenation process with inter-stage cooling
View Patent ↗A method of oxidatively dehydrogenating a dehydrogenation reactant includes providing a first gaseous feed stream to a first adiabatic, catalytic reaction zone with less than a stoichiometric amount of oxygen and superheated steam, oxidatively dehydrogenating dehydrogenation reactant in said first adiabatic, catalytic reaction zone and subsequently cooling the effluent, adding additional oxygen and reacting the effluent stream in at least one subsequent adiabatic reaction zone. The dehydrogenation system enables higher conversion and yield per pass and in some cases greatly reduces steam usage and energy costs. In a preferred integrated process, ethylene is converted to n-butene which is then oxidatively dehydrogenated to butadiene.
1. A method of oxidatively dehydrogenating a dehydrogenation reactant comprising:
(a) providing a first gaseous feed stream to a first adiabatic, catalytic reaction zone at a first-stage inlet temperature, the first feed stream including a dehydrogenation reactant, oxygen and superheated steam, wherein the molar ratio of superheated steam to dehydrogenation reactant is from 0.5:1 to 7.5:1;
(b) oxidatively dehydrogenating dehydrogenation reactant in said first adiabatic, catalytic reaction zone to provide a first-stage effluent stream enriched in said dehydrogenated product at a first-stage effluent temperature above said first-stage inlet temperature;
(c) cooling the first-stage effluent stream in a first heat transfer zone to a second-stage inlet temperature lower than said first-stage effluent temperature to provide a second gaseous feed stream comprising superheated steam, dehydrogenation reactant and dehydrogenated product, wherein the cooling of the first stage effluent stream is carried out (i) by indirect heat exchange with a heat exchanger or (ii) by direct heat exchange by way of atomizing water into said stream;
(d) feeding said second gaseous feed stream at said second-stage inlet temperature to a second adiabatic, catalytic reaction zone along with additional oxygen;
(e) oxidatively dehydrogenating dehydrogenation reactant in said second adiabatic, catalytic reaction zone to provide a second stage effluent stream further enriched in said dehydrogenated product at a second stage effluent temperature above said second-stage inlet temperature; and
(f) recovering said dehydrogenated product,
wherein the temperature delta between the first stage inlet temperature and the first stage effluent temperature is from 200° F. to 600° F. and the temperature delta between the second stage inlet temperature and the second stage effluent temperature is from 200° F. to 600° F.
2. The method according to claim 1 , wherein the molar ratio of superheated steam to dehydrogenation reactant in said first gaseous feed stream is from 3:1 to 7:1.
3. The method according to claim 1 , wherein the molar ratio of oxygen to dehydrogenation reactant in said first gaseous feed stream is from 0.1:1 to 0.85:1.
4. The method according to claim 1 , wherein the molar ratio of oxygen to dehydrogenation reactant in said first gaseous feed stream is from 0.1:1 to 0.4:1.
5. The method according to claim 1 , wherein additional oxygen is added to said second gaseous feed stream such that feed to the second adiabatic reaction zone has a molar ratio of oxygen:dehydrogenation reactant of from 0.1:1 to 0.85:1.
6. The method according to claim 1 , wherein additional oxygen is added to said second gaseous feed stream such that feed to the second adiabatic reaction zone has a molar ratio of oxygen:dehydrogenation reactant of from 0.1:1 to 0.4:1.
7. The method according to claim 1 , wherein the temperature delta between the first-stage inlet temperature and the first-stage effluent temperature is at least 250° F.
8. The method according to claim 1 , wherein the temperature delta between the second stage inlet temperature and the second stage effluent temperature is at least 250° F.
9. The method according claim 1 , wherein said dehydrogenation reactant comprises butenes and said dehydrogenated product comprises butadiene.
10. The method according to claim 1 , wherein said step of cooling said first stage effluent stream comprises indirect heat transfer.
11. The method according to claim 1 , wherein said step of cooling said first stage effluent stream comprises direct heat transfer utilizing a tube and shell heat exchanger or a plate and frame heat exchanger.
12. The method according to claim 1 , wherein said step of cooling said first stage effluent stream comprises providing a water spray into said heat transfer zone.
13. The method according to claim 1 , further comprising cooling the second-stage effluent stream and providing the cooled second-stage effluent stream along with additional oxygen to a third adiabatic reaction zone and dehydrogenating dehydrogenation reactant in said third adiabatic reaction zone.
14. The method according to claim 1 , further comprising providing at least one of the reaction zones with an acetylene removal catalyst.
15. The method according to claim 14 , wherein the acetylene removal catalyst comprises Ni, Fe, an alkali metal, and optionally an alkaline earth element.
16. The method according to claim 1 , carried out in an apparatus for oxidatively dehydrogenating a dehydrogenation reactant comprising:
(a) a first adiabatic reaction zone having a fixed bed of ferrite dehydrogenation catalyst adapted for receiving a gaseous feed stream comprising a dehydrogenation reactant, oxygen and superheated steam and providing an effluent stream enriched in dehydrogenated product at an effluent temperature higher than the temperature of the feed stream to the first adiabatic reaction zone;
(b) a heat exchanger for receiving said effluent stream and cooling said effluent stream to a temperature lower than said effluent temperature to provide a second gaseous feed stream;
(c) a second adiabatic reaction zone having a fixed bed of ferrite dehydrogenation catalyst adapted for receiving said second gaseous feed stream; and
(d) an oxygen feed for supplying additional oxygen to said second reaction zone,
wherein a bed of acetylene and aldehyde removal catalyst is interposed between said first and second adiabatic reaction zones.
17. The method according to claim 1 , carried out in an apparatus for oxidatively dehydrogenating a dehydrogenation reactant comprising:
(a) a first adiabatic reaction zone having a fixed bed of ferrite dehydrogenation catalyst adapted for receiving a gaseous feed stream comprising a dehydrogenation reactant, oxygen and superheated steam and providing an effluent stream enriched in dehydrogenated product at an effluent temperature higher than the temperature of the feed stream to the first adiabatic reaction zone;
(b) a heat exchanger for receiving said effluent stream and cooling said effluent stream to a temperature lower than said effluent temperature to provide a second gaseous feed stream;
(c) a second adiabatic reaction zone having a fixed bed of ferrite dehydrogenation catalyst adapted for receiving said second gaseous feed stream; and
(d) an oxygen feed for supplying additional oxygen to said second reaction zone,
wherein a bed of acetylene and aldehyde removal catalyst is provided immediately downstream of each adiabatic reaction zone.
18. In a method of making butadiene by way of oxidative dehydrogenation, the improvement comprising:
(a) dimerizing ethylene to n-butene in a homogeneous catalytic reaction medium to provide an n-butene rich stream;
(b) mixing the n-butene rich stream with steam and an oxygen rich gas to provide a gaseous feed stream;
(c) providing the gaseous feed stream to a plurality of adiabatic, catalytic reaction zones arranged in series, the feed stream including n-butene, oxygen and superheated steam, wherein the molar ratio of superheated steam to n-butene is from 0.5:1 to 7.5:1;
(d) oxidatively dehydrogenating n-butene reactant in said plurality of adiabatic, catalytic reaction zones to provide a plurality of effluent streams enriched in butadiene as compared with the gaseous feed stream;
(e) cooling the effluent stream(s) in one or more heat transfer zones to a temperature lower than its effluent temperature, wherein the cooling of an effluent stream is carried out (i) by indirect heat exchange with a heat exchanger or (ii) by direct heat exchange by way of atomizing water into said stream and injecting additional oxygen into the effluent stream(s) prior to feeding the effluent stream to a subsequent oxidative dehydrogenation reaction zone; and
(f) recovering said butadiene,
wherein the temperature delta between a first stage inlet temperature and a first stage effluent temperature is from 200° to 600° F. and the temperature delta between a second stage inlet temperature and a second stage effluent temperature is from 200° to 600° F.