PARTIAL DEHYDROGENATION OF ORGANIC LIQUIDS

Abstract

The present invention concerns a process for producing hydrogen by partial dehydrogenation of an organic liquid, said process comprising a step of supplying at least one organic liquid having a Degree of Hydrogenation DHplus, a step of partially dehydrogenating said liquid, a step of recovering firstly gaseous hydrogen and secondly said organic liquid having a Degree of Hydrogenation DHminus, and wherein the ratio DHplus/DHminus is between 1 and 25, endpoints excluded.

The invention likewise concerns a hydrogenation/dehydrogenation cycle comprising at least the process of the invention for producing hydrogen by partial dehydrogenation of an organic liquid and at least one hydrogenation reaction of said organic liquid.

Claims

1-11. (canceled)

12. A process for producing hydrogen by partial dehydrogenation of an organic liquid, said process comprising: a step of supplying at least one organic liquid having a Degree of Hydrogenation DH.sub.plus, a step of partially dehydrogenating said liquid, a step of recovering firstly gaseous hydrogen and secondly said organic liquid having a Degree of Hydrogenation DH.sub.minus, the ratio DH.sub.plus/DH.sub.minus being between 1 and 25, endpoints excluded.

13. The process as claimed in claim 12, wherein the partial dehydrogenation step is carried out by implementing one or more of the following means, individually or in a combination of two or more thereof: blocking of the reaction before a 100% dehydrogenation yield is obtained, reaction temperature lower than the temperature commonly used for the dehydrogenation reaction, reaction pressure lower than the pressure commonly used for the dehydrogenation reaction, low-selectivity dehydrogenation catalyst, and any other means for regulating the dehydrogenation reaction kinetics.

14. The process as claimed in claim 12, wherein the organic liquid is liquid at ambient temperature and pressure.

15. The process as claimed in claim 12, wherein the organic liquid is a mixture of two or more organic liquids which may have identical or different Degrees of Hydrogenation.

16. The process as claimed in claim 12, wherein the organic liquid possesses at least one aromatic ring, which is optionally partially dehydrogenated.

17. The process as claimed in claim 12, wherein the organic liquid corresponds to the general formula (1):
(A−X).sub.n−B  (1) in which: A and B, which are identical or different, represent, independently of one another, an aromatic ring optionally partially dehydrogenated and optionally substituted by one or more saturated or partially or completely unsaturated hydrocarbon radicals comprising from 1 to 20 carbon atoms, X represents a spacer group, selected from the group consisting of a single bond, an oxygen atom, a sulfur atom, the divalent radical —(CRR′).sub.m—, the divalent radical >C═CRR′, and the divalent radical —NR″—, R and R′, which are identical or different, are selected, independently of one another, from hydrogen and a saturated or partially or completely unsaturated hydrocarbon radical comprising from 1 to 6 carbon atoms, R″ represents a saturated or partially or completely unsaturated hydrocarbon radical comprising from 1 to 6 carbon atoms, m represents an integer of between 1 and 4, endpoints included, and n can be equal to 0 or represents an integer equal to 1, 2 or 3, with the restriction that, when n is equal to 0, B is substituted by one or more hydrocarbon radicals, as defined above.

18. The process as claimed in claim 12, wherein the organic liquid is selected from the group consisting of benzyltoluene (BT), dibenzyltoluene (DBT), their partially dehydrogenated homologs, and mixtures thereof in any proportions.

19. The process as claimed in claim 12, wherein the organic liquid has a Degree of Hydrogenation DH.sub.plus conforming to the inequation 0.6≤DH.sub.plus<1.

20. The process as claimed in claim 12, wherein the organic liquid has a Degree of Hydrogenation DH.sub.minus conforming to the inequation 0<DH.sub.minus≤0.6.

21. A hydrogenation/dehydrogenation cycle comprising at least the process as claimed in claim 12 for producing hydrogen by partial dehydrogenation of an organic liquid and at least one hydrogenation reaction of said organic liquid.

22. The cycle as claimed in claim 21, comprising one or more dehydrogenation processes including at least one which is a process of partial dehydrogenation as claimed in claim 12, prior to and/or consecutively with one or more hydrogenation reactions of an organic liquid capable of storing, transporting and releasing hydrogen.

23. The process of claim 12, wherein the ratio DH.sub.plus/DH.sub.minus is between 1.1 and 20, endpoints included.

Description

EXAMPLES

Example 1

[0090] The examples which follow correspond to partial dehydrogenation tests carried out on an organic liquid, namely DiBenzylToluene (DBT), from Arkema.

[0091] A 100 mL three-neck flask fitted with a condenser is charged with 0.1 mol of H18-DBT and 0.15 mol % of a platinum-on-alumina (0.5% by weight) catalyst. The assembly is purged by nitrogen flushing to remove any trace of ambient air from the reactor. After calibration of the thermal conductivity analyzer (FTC200, version 1.05, Wagner) at ambient temperature, the mixture is heated to 300° C. using a heating jacket. The hydrogen released is collected by virtue of the constant nitrogen stream and the amount of hydrogen produced is monitored continuously using the thermal conductivity analyzer (FTC200, version 1.05, Wagner).

[0092] The number of moles of hydrogen released can be correlated with the Degree of Hydrogenation DH.sub.minus at the end of the dehydrogenation step. For each test, a determination is made of the molar percentage of DBT degraded (number of moles remaining/number of moles introduced).

[0093] The results are presented in table 1 below:

TABLE-US-00001 TABLE 1 DH.sub.minus % degradation DBT 0 5 0.15 1 0.33 0.01 0.67 0.008 1 0.002

[0094] The results above show clearly that total dehydrogenation (DH.sub.minus=0) leads to 5% degradation of the DBT. With a partial dehydrogenation step (DH.sub.minus>0), the degradation of the DBT is considerably diminished, becoming negligible or virtually negligible for a DH.sub.minus greater than 0.15.

[0095] It is possible accordingly to envisage, for example, a succession of partial dehydrogenation reactions, each leading to a release of hydrogen and a remaining fraction of DBT (undegraded DBT) which is low, even with a DH.sub.minus of 0.33 (remaining fraction of DBT of 0.99%). After n partial dehydrogenation reactions, and therefore n hydrogen release reactions, the degradation of the DBT will be contained within entirely reasonable limits, with degradation equivalent to 0.99n at the end of the n.sup.th dehydrogenation reaction.

Example 2

[0096] This example is carried out starting from H12-BT, a hydrogenated form of benzyltoluene (BT) prepared by Arkema.

[0097] A 100 mL three-neck flask fitted with a condenser is charged with 0.1 mol of H12-BT, characterized by a DH.sub.plus=0.95, and 0.15 mol % of a platinum-on-alumina (0.5% by weight) catalyst. The assembly is purged by nitrogen flushing to remove any trace of ambient air from the reactor. The mixture is heated to variable temperatures using a heating jacket. The hydrogen released is collected by virtue of the constant nitrogen stream and the amount of hydrogen produced is monitored continuously using the thermal conductivity analyzer (FTC200, version 1.05, Wagner).

[0098] The number of moles of hydrogen released can be correlated with the Degree of Hydrogenation DH.sub.minus at the end of the dehydrogenation step. For each test, a determination is made of the molar percentage of BT degraded (number of moles remaining/number of moles introduced in the form of H12-BT).

[0099] The results are presented in table 2 below:

TABLE-US-00002 TABLE 2 Dehydrogenation % reaction degradation Test temperature DH.sub.minus DH.sub.plus/DH.sub.minus BT 2-01 285° C. 0.02 47.5 2 2-02 270° C. 0.05 19.0 0.5 2-03 250° C. 0.23 4.1 0.3

Example 3

[0100] This example is carried out starting from H12-BT, a hydrogenated form of benzyltoluene (BT) prepared by Arkema, and describes the change in the carrier molecule (termed LOHC) over 200 successive hydrogenation/dehydrogenation cycles. Each dehydrogenation step is carried out according to the procedure described in example 2, and each hydrogenation step is carried out in a stainless steel batch autoclave with a volume of 300 mL. The hydrogenated or partially hydrogenated form of the LOHC molecule is introduced simultaneously with the Ru/Al.sub.2O.sub.3 catalyst in a molar ratio of 400:1. The reaction is conducted at 150° C. and the hydrogen pressure applied is 50 bar (5 MPa) and the reaction time is one hour.

[0101] For each test, a determination is made of the molar percentage of residual BT (number of moles remaining/number of moles introduced in the form of H12-BT) at the end of the 200 cycles. “Residual BT” means any molecule which is neither BT nor partially or totally hydrogenated BT. The residual BT can be easily analyzed and quantified (in moles) by any appropriate analytical means, and in particular by GC-MS analysis. More specifically, in the context of the present invention, the degradation is measured by fluid analysis at the end of the cycles by coupled gas chromatography/mass spectrometry (GC/MS), in electron ionization and quadrupole analyzer mode.

[0102] Test 3.01 corresponds to a succession of total hydrogenation and dehydrogenation reactions, executed at 280° C. Test 3.02 corresponds to a succession of partial hydrogenation and dehydrogenation reactions executed at 250° C.

[0103] The results are presented in table 3 below. The values of DH.sub.plus and DH.sub.minus presented in table 3 are the average values calculated from the values of DH.sub.plus and DH.sub.minus in each cycle.

TABLE-US-00003 TABLE 3 Dehydrogenation % residual BT reaction Number of DH.sub.plus before DH.sub.minus after at the end of 200 Test temperature cycles dehydrogenation dehydrogenation cycles performed 3-01 280° C. 200 1 0 65 3-02 250° C. 200 0.95 0.15 98.5

[0104] These results show that when the cycles are conducted under conditions where the hydrogenation and dehydrogenation reactions are complete, the percentage of residual BT is low, hence indicating substantial degradation of the LOHC compound. Conversely, when the hydrogenation and dehydrogenation reactions are partial, the LOHC compound is markedly less degraded.