Chemical looping
This invention relates to a method of chemical looping using non-stoichiometric materials with a variable degree of non-stoichiometry. One application of these methods is in the water gas shift reaction for H 2 production. The methods of the invention can overcome limitations, e.g. those associated with chemical equilibria, which prevent chemical processes from proceeding with complete conversion of starting materials to products.
1. A method of carrying out a chemical reaction which involves the transfer of an element or group X from one chemical species to another, the method comprising sequentially:
A) passing a chemical species P through a fixed bed reactor, the chemical species P flowing from a first position of the fixed bed reactor to a second position of the fixed bed reactor, and extracting the resulting chemical species PX y from the second position of the fixed bed reactor; and then
B) passing a chemical species QX z through the fixed bed reactor, the chemical species QX z flowing from the second position of the fixed bed reactor to the first position of the fixed bed reactor, and extracting the resulting chemical species Q from the first position of the fixed bed reactor;
C) optionally repeating steps A) and B) in sequence at least once;
wherein P and Q are chemical species which are selected such that both P and Q can accept the element or group X and both PX y and QX z can donate the element or group X; y and z are integers; and wherein the fixed bed reactor comprises at least one non-stoichiometric material which has the formula M n X p(1-q) where n and p are integers required for stoichiometric bonding between M and X and 0<q<1 or 0>q>−1; wherein the material is able to adopt a range of values of q; and wherein M represents a single element or a mixture of more than one element.
2. A method of claim 1 , wherein greater than 50% of both QX z and P are converted to Q and PX y respectively.
3. A method of claim 1 , wherein the non-stoichiometric material is a solid.
4. A method of claim 1 , wherein P is passed through the reactor in step A) as a mixture with other components.
5. A method of claim 1 , wherein QX z is passed through the reactor in step B) as a mixture with other components.
6. A method of claim 1 , wherein P, PX y , Q and QX z are all gases within the temperature range of the reaction.
7. A method of claim 1 , wherein X is an element.
8. A method of claim 7 , wherein X is a non-metal.
9. A method of claim 8 , wherein X is oxygen.
10. A method of claim 9 , wherein Q is H 2 and QX z is H 2 O.
11. A method of claim 10 , wherein P is selected from: CO, H 2 , at least one organic molecule or a mixture thereof.
12. A method of claim 1 , wherein P is CO, PX y is CO 2 , Q is H 2 and QX z is H 2 O.
13. A method of claim 1 , wherein P is a mixture of H 2 and CO, PX y is a mixture of H 2 O and CO 2 , Q is H 2 and QX z is H 2 O.
14. A method of claim 13 , the method comprising a step F before step A, step F comprising forming the mixture of H 2 and CO by reforming a hydrocarbon.
15. A method of claim 1 , wherein P is at least one organic molecule , PX y is a mixture of CO and H 2 , Q is H 2 and QX z is H 2 O.
16. A method of claim 15 , wherein the mixture of H 2 and CO obtained in step A is subsequently further oxidised to CO 2 or H 2 O and the heat which is generated during said oxidation is extracted and transferred to the fixed bed reactor.
17. A method of claim 15 , further comprising, after step B and before step A, passing O 2 through the reactor bed, the O 2 flowing from the second position of the fixed bed reactor to the first position of the fixed bed reactor.
18. A method of claim 1 , wherein 0<q<1.
19. A method of claim 1 , wherein the material M n X p(1-q) is a perovskite.
20. A method of claim 1 , wherein the perovskite comprises lanthanum, strontium, iron, oxygen and optionally aluminium.
21. A method of claim 19 , wherein the material M n X p(1-q) is La 0.7 Sr 0.3 FeO 3-δ (LSF).
22. A method of claim 10 , wherein the reactor is at a temperature of from 500° C. to 1200° C.