Method of use of an ionic liquid for storing hydrogen

Abstract

A method releases hydrogen by forming a second ionic liquid from a first ionic liquid by releasing hydrogen from the first ionic liquid by exposing the first ionic liquid to water and a catalyst. The first ionic liquid includes a cation and an anion including a borohydride. The release of the hydrogen forms a borate, which makes up the anion of the second ionic liquid. The cation of the first ionic liquid is the same as that of the second ionic liquid. A reaction system includes the first and second ionic liquids, water and a catalyst.

Claims

1. A method of releasing hydrogen comprising: forming a second ionic liquid from a first ionic liquid by releasing hydrogen from the first ionic liquid by exposing the first ionic liquid to water and a catalyst, wherein the first ionic liquid comprises a cation and an anion comprising a borohydride, and wherein the releasing of the hydrogen forms a borate, and wherein the second ionic liquid comprises the cation and an anion comprising the borate.

2. A method according to claim 1, wherein the cation is a quaternary or protonated cation.

3. A method according to claim 2, wherein the cation comprises one to four moieties selected from the group consisting of: hydrogen, C1-C20-alkyl, C1-C20-alkenyl, C1-C20-alkinyl, C1-C20-cycloalkyl, C1-C20-cycloalkenyl, C1-C20-aryl, and C1-C20-heteroaryl.

4. A method according to claim 3, wherein the cation is selected from the group consisting of: pyridinium, pyrrolium, thiazolium, oxazolium, and quinolinium, wherein one of the one to four moieties is bound to the nitrogen atom and/or one to three of the one to four moieties are bound to carbon atoms of the carbon ring.

5. A method according to claim 3, wherein the cation is selected from the group consisting of: ammonium, phosphonium, and sulfonium.

6. A method according to claim 3, wherein the cation is selected from the group consisting of: piperidinium, pyrrolidinium, and morpholinium, wherein one or two of the one to four moieties is bound to the nitrogen atom or one to three of the one to four moieties are bound to carbon atoms of the carbon ring.

7. A method according to claim 3, wherein the cation is selected from the group consisting of: imidazolium, benzimidazolium, pyrazolium, and benzotriazolium, wherein a respective one of the one to four moieties is bound to each nitrogen atom, or one to three of the one to four moieties are bound to carbon atoms of the carbon ring.

8. A method according to claim 2, wherein the cation is selected from the group consisting of: trioctylmethylammonium, tetrahexylammonium, tetraoctylammonium, and 1-octyl-3-methylimidazolium, trihexylmethylammonium, triethylmethylammonium, tributylmethylammonium, 1-ethyl-3-methylimidazolium, 1,3-dimethylimidazolium, 1-butyl-3-methylimidazolium, 1,2,3-trimethylimidazolium, 1-ethyl-3-methylimidazolium, 1-ethyl-2,3-dimethylimidazolium, and 1-butyl-2,3-dimethylimidazolium.

9. A method according to claim 1, wherein the catalyst is a transition metal or a noble metal.

10. A method according to claim 1, wherein the first ionic liquid or the second ionic liquid has a predetermined viscosity value.

11. A method according to claim 10, wherein the viscosity level is set to the predetermined viscosity value is set by adding an additive.

12. A method according to claim 1, further comprising: adding a basic additive to the first ionic liquid or the second ionic liquid.

13. A method according to claim 12, wherein the basic additive is at least one selected from the group consisting of: alkaline metal hydroxides, alkaline earth metal hydroxides, alkaline metal carbonates, alkaline earth metal carbonates, quaternary tetraalkylammonium hydroxides, quaternary tetraalkylammonium carbonates, quaternary tetraalkylphosphonium hydroxides, quaternary tetraalkylphosphonium carbonates, and quaternary tetraalkylphosphonium alkylcarbonates.

14. A method according to claim 1, wherein the first ionic liquid releases at least three hydrogen molecules per boron atom.

15. A method according to claim 14, wherein the borohydride is selected from the group consisting of BH.sub.4.sup., B.sub.2H.sub.7.sup. and B.sub.3H.sub.8.sup..

16. A method according to claim 15, wherein the borohydride is BH.sub.4.sup..

17. A reaction system for storing and releasing hydrogen, comprising: a first ionic liquid comprising a cation and an anion comprising a borohydride; a second ionic liquid comprising the cation and an anion comprising a borate; water; and a catalyst.

18. A reaction system according to claim 17, wherein the borate is a metaborate.

19. A reaction system according to claim 17, wherein the catalyst is a transition metal or a noble metal.

20. A reaction system according to claim 17, wherein the cation comprises one to four moieties selected from the group consisting of: hydrogen, C1-C20-alkyl, C1-C20-alkenyl, C1-C20-alkinyl, C1-C20-cycloalkyl, C1-C20-cycloalkenyl, C1-C20-aryl, and C1-C20-heteroaryl.

21. A reaction system according to claim 17, further comprising a basic additive selected from the group consisting of: alkaline metal hydroxides, alkaline earth metal hydroxides, alkaline metal carbonates, alkaline earth metal carbonates, quaternary tetraalkylammonium hydroxides, quaternary tetraalkylammonium carbonates, quaternary tetraalkylphosphonium hydroxides, quaternary tetraalkylphosphonium carbonates, and quaternary tetraalkylphosphonium alkylcarbonates.

22. An ionic liquid for releasing hydrogen, comprising: a first ionic liquid comprising a cation and an anion comprising a borohydride; and optionally water.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The invention will be described in more detail hereinafter with reference to examples of embodiment but to which the invention is not limited.

(2) FIG. 1 schematically illustrates a cycle process for hydrogen storage based on an ionic liquid.

(3) FIG. 2 schematically shows a catalytic converter comprising a catalyst material.

(4) FIG. 3 schematically shows a container for storing a hydrogen storage medium.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

(5) The illustration in the drawing is schematically. FIG. 1 schematically shows a cycle process or a recycling process 100 for hydrogen storage, which process is based on an ionic liquid. At the beginning of the process an ionic liquid may be manufactured from trio ctylmethylammoniummethylcarbonate

(6) ##STR00001## and sodium borohydride (NaBH.sub.4) which is schematically depicted by arrow 101 in FIG. 1. The resulting ionic liquid is trioctylmethylammonium-borohydride (TOMA-BH.sub.4)

(7) ##STR00002## wherein trioctylmethylammonium forms the cation and the borohydride forms the anion which also includes hydrogen which may be released afterwards. TOMA-BH.sub.4 is not solvable in water but may release hydrogen when brought into contact with water and a catalyst, which is schematically indicated by arrow 102.

(8) Compared to NaBH.sub.4 the use Of TOMA-BH.sub.4 may exhibit several advantages. For example, TOMA-BH.sub.4 may be stable, while NaBH.sub.4 may decompose quite fast even in alkaline environments. Furthermore, TOMA-BH.sub.4 may not react with water and may not be solved in water, i.e. may form a separate phase floating on a water phase, while NaBH.sub.4 may react with water and may be solvable in water. Additionally, TOMA-BH.sub.4 may exhibit a lower tendency to crystallize compared to NaBH.sub.4, especially at low temperatures.

(9) As a catalyst transition metals may be used, e.g. platinum or palladium. As a result of the releasing of hydrogen a second ionic liquid is formed which comprises trioctylmethylammonium as the cation while comprising metaborate as the anion and which can be written in the following form:

(10) ##STR00003##

(11) That is, trioctylmethylammonium-metaborate (TOMA-BO.sub.2) is formed, which shows a significant miscibility gap with water as well. The metaborate anion may especially at elevated temperatures partially or completely react to borate or polyborate anions; anyway, this borate or polyborate anions do not disturb the process and show nearly identical properties as the metaborate anion. So the term metaborate herein can be seen more generally to be a mixture of metaborate and/or borate and/or polyborate. In a next step of the cycle process the TOMA-BO.sub.2 may be brought into contact with aqueous solution of sodium borohydride (NaBH.sub.4) which is indicated by arrow 103 leading to the formation of TOMA-BH.sub.4 and an aqueous solution of sodium metaborate (NaBO.sub.2) wherein TOMA-BH.sub.4 and NaBO.sub.2 forms two phases of the resulting liquid. These two phases can be separated leading to recycled TOMA-BH.sub.4. It should be mentioned that small amounts of water in TOMA-BH.sub.4 may not be of negative impact since TOMA-BH.sub.4 does not react with the water in the absence of a catalyst. The NaBO.sub.2 may then be converted into NaBH.sub.4 by using common methods which NaBH.sub.4 may then be used again in the recycling process (arrow 103).

(12) FIG. 2 schematically shows a possible form of a catalytic converter comprising a catalyst material. In general the catalytic converter 200 comprises or substantially consists of a noble metal, e.g. platinum or palladium, and has a great surface to facilitate a reaction, e.g. a release of hydrogen. In particular, the catalytic converter is formed of a plurality of small balls or spheres 201 having a diameter of about 1 mm to 2 mm. These spheres are formed to a structure having a hexagonal, cubic or face-centered cubic arrangement of the spheres. In particular, the arrangement should be as dense as possible to increase the surface the catalyst and the ionic liquid come into contact. The plurality of spheres may be sintered to form the catalytic converter 200. The single spheres 201 may be formed by sintering metal powder, wherein the powder particles have a size in the micrometer or nanometer range, e.g. between 1 nm and 50 micrometer, more particular in the range of 10 nm to 5 micrometer. Due to the fact that the catalytic converter comprises a plurality of balls or spheres the catalytic converter may adopt almost any desired form, e.g. may be cut to the desired form.

(13) FIG. 3 schematically shows a container 300 for storing a hydrogen storage medium. In particular, the container 300 comprises an inlet 301, an outlet 302 and a moveable, elastic or flexible membrane 303 separating two chambers or portions of the container from each other. By using the inlet 301 a hydrogen rich ionic liquid, e.g. TOMA-BH.sub.4, may be supplied into the container filling the left chamber 304 in FIG. 3, while the outlet 302 may be used to discharge a hydrogen depleted ionic liquid, e.g. TOMA-BO.sub.2, from the right chamber 305 in FIG. 3. Furthermore, the container 300 comprises an output connection 306 arranged in the chamber 304 which is connected to an external housing 307 in which a catalytic converter is arranged. That is in the housing the hydrogen is released from the hydrogen rich ionic liquid and the hydrogen depleted ionic liquid is generated. Furthermore, the housing is connected to an input connection 308 of the container 301 which input connection is arranged in the chamber 305.

(14) Finally, it should be noted that the above-mentioned embodiments illustrate rather than limit the invention, and that those skilled in the art will be capable of designing many alternative embodiments without departing from the scope of the invention as defined by the appended claims. In the claims, any reference signs placed in parentheses shall not be construed as limiting the claims. The word comprising and comprises, and the like, does not exclude the presence of elements or steps other than those listed in any claim or the specification as a whole. The singular reference of an element does not exclude the plural reference of such elements and vice-versa. In a device claim enumerating several means, several of these means may be embodied by one and the same item of software or hardware. The mere fact that certain measures are recited in mutually different dependent claims does not indicate that a combination of these measures cannot be used to advantage.