ES2366218A1 - Hydrogen production through a thermoquimic water dissociation cycle using redox oxides (Machine-translation by Google Translate, not legally binding) - Google Patents

Abstract

Production of hydrogen through a thermochemical water dissociation cycle using redox oxides. The present invention relates to a process for the production of hydrogen by thermochemical cycles comprising the use of active oxides, such as the modified cerium oxides. These systems allow the production of pure hydrogen at low temperature, cyclically, by using a simple and easy to operate system. Being a process for the production of hydrogen in a renewable form and outside the carbon cycle. (Machine-translation by Google Translate, not legally binding)

Description

Hydrogen production through a cycle Thermochemical water dissociation using redox oxides.

The present invention relates to a hydrogen production process through a cycle thermochemical that includes the use of active oxides. Therefore, the The present invention can be framed within the field of energy production, specifically the production of hydrogen.

Prior art

Currently 86% of the hydrogen produced It comes from the refurbished hydrocarbons, however this route does not offers a solution to the problem derived from dependence on fossil fuels, as well as reducing emissions of CO2. Therefore, to build a hydrogen economy truly sustainable it is necessary that it be produced at from sources and renewable elements.

Within this framework, one of the alternatives is hydrogen production from water and solar energy concentrated. It is possible to make a direct break of the molecule of water, however this process has disadvantages such as high required temperature (2227 ° C) or the need to separate the hydrogen from the oxygen produced. For this reason, the break indirectly of the water molecule by thermochemical cycles not only eliminates the need to separate hydrogen and oxygen if not that also the temperature required to carry out the reaction It is smaller. Also the conversion of heat directly into hydrogen by thermochemical cycles it is much more efficient than transforming heat into electricity or performing electrolysis of Water.

Within the two-stage cycles, those based on redox metal oxides have been studied extensively for being the simplest and most efficient systems in production Cyclic hydrogen from water. The two stage cycle using redox metal oxides proceeds through a first endothermic thermal reduction stage where the oxide loses partially oxygen of its structure (Ec 1) followed by a second exothermic stage (Ec 2) corresponding to the hydrolysis of the oxide partially reduced anterior to form H2 and regenerate the metal oxide (Ec 2).

The net reaction is H2O + thermal energy ? H 2 + ½ O 2.

one

This cycle was originally proposed by Nakamura in Solar Energy 1977, 19, 467 using the redox pair Fe 3 O 4 /
Ugly. Subsequently, the ZnO / Zn redox pair has also been considered as a potential candidate to carry out water rupture in two-stage thermochemical cycles taking into account its potential transformation efficiency as indicated in J. Chem. Eng. Sci 1998, 53 (14), 2503 . However, the high reduction temperature of the ZnO / Zn (> 1962 ° C) and Fe 3 O 4 / FeO (> 2227 ° C) redox pairs implies severe sintering, melting and vaporization of materials that decrease efficiency and durability in Cyclic operation Additionally, in the cycles using these redox pairs, the separation of the reduction products (FeO or Zn) is necessary to avoid reoxidation, a fact that introduces irreversibilities and complexity in large-scale operation.

To reduce the temperature of reduction of Fe 3 O 4 to FeO, materials based on solid solutions between Fe 3 O 4 and other oxides forming ferrites with spinel structure MFe 2 O 4 have been examined } Co spinels have been tested, as indicated in Int. J. Hydrogen Energy, 2002, 27 (6), 611 , Ni as shown in Solar Energy 2008; 82, 73, of Zn as indicated in Solar Energy 2004, 76, 317 , of Ni-Zn as shown in Solar Energy 2005, 79, 409 and Ni-Mn as presented in Energy, 1995, 20 (4) 325 . These ferrites are thermally reduced at temperatures below that of the case of pure Fe 3 O 4. However, the thermal reduction of these ferrites is close to their melting points and therefore the reduced ferrites sinter after reduction by decreasing the production of H2 in the subsequent hydrolysis cycle. To prevent sintering of ferrites during thermal reduction, it has been proposed to support them in monoclinic ZrO2 or in cubic ZrO2 stabilized with yttrium due to their good thermal properties against sintering in the temperature range from 1000 to 1400 ° C as indicated in the articles published in Sol. Energy 2005, 78, 623; Solar Energy 2008, 82, 73 and J. Solar Energy Eng. 2008 130 (1) , 1. This type of supported ferrites has hydrogen productions and stability in cycles superior to unsupported ferrites. However, although with these approximations, more moderate reduction temperatures are achieved than those required by the Fe_ {O} {{4} / FeO) pair, the hydrogen production achieved is low, which still leads to the search for alternatives.

Thermochemical cycles based on CeO 2 / Ce 2 O 3 as shown in Solar Energy 80, 1611 , in SnO 2 / SnO as indicated in Int. J. of Hyd. Energy 2008, 33, 6021 and GeO2 / GeO as shown in Int. J. of Hyd. Energy 2009, 34, 4283 , have been the last reported metal oxides that have reduction temperatures lower than Fe 3 O 4 and ZnO. Among them, the CeO_ {2} / Ce_ {2} {3} pair is the most interesting due to the possibility it offers for its thermal reduction at temperatures below 1800 K as indicated in Energy 2007 32, 656 . To improve the low temperature reducibility of cerium oxide, materials based on CeO2 doped with different elements (M = Mn, Fe, Ni and Cu) have been studied as redox oxides to carry out the thermochemical cycle of rupture of water in two stages as shown in the works published in Energy 2007 32, 656; J. Mater. Sci 2008 43, 3153 and J. Phys. Chem. Sol. 2009, 70, 1008 . In these systems, an improvement in hydrogen production is observed (cm 3 H 2 / g at 1773 K: 0.97 for Cu-CeO 2, 1.9 for Fe-CeO 2, 2 , 6 for Ni-CeO 2 and 3.77 for Mn-CeO 2) compared to pure CeO 2 (0.7 cm 3 H 2 / g) or supported ferrites in ZrO 2 (1.77 cm 3 H 2 / g). Despite these improvements, the main problem associated with cerium oxide as a redox material in high temperature thermal cycles derives from its low thermal stability, which implies sintering with loss of surface area during high temperature treatments.

Of the redox metal oxides of the state of technique described above, there are desirable improvements to the development of materials that have a lower temperature of thermal reduction, high thermal stability and high capacity for the production of hydrogen by thermochemical cycles at from water.

Description of the invention

The present invention provides a process for the production of hydrogen by cycles thermochemicals using modified cerium oxides. These systems allow the production of pure hydrogen at low temperature, of cyclically, by using a simple system and easy operation Being a procedure for the production of hydrogen in a renewable way and outside the carbon cycle.

The present invention relates to a procedure for the production of H2 by dissociation of water by a thermochemical cycle that includes the use of oxides modified cerium, as catalysts, supported or not supported on a support. The present invention also provides a catalyst of modified cerium oxide on a support, as well as its procurement procedure

A first aspect of the present invention is refers to a process for obtaining hydrogen, (from now method of the invention), which comprises the steps:

to)

reduction of a catalyst by thermal energy at a temperature higher than 820 ° C, and

b)

oxidation of the catalyst obtained in stage (a) with water vapor,

where the catalyst is a cerium oxide modified with at least one cation that is selected from the list that comprises: Ti 4+, Sr 2+, Hf 4+, La 3+, Ba 2+, Gd 3+, Y 3+, Pr 4+, Ca 2+ and any of its combinations, where percentage of cerium cation replacement is from 0.01 to 49%.

In a preferred embodiment the cation is select from La 3+, Zr 4+, Pr 4+ or any of your combinations

The cerium oxides used in the procedure of the invention exhibit a good behavior in terms of activity and stability, maintaining a surface area greater than 5 m 2 / g and high mobility of oxygen ions in Cerium oxide network at high temperature.

\hbox{entiende en la presente invención a un material altamente
resistente a la degradación térmica.}

The modified cerium oxide may be deposited on a support. In a preferred embodiment, the support is selected from metallic, metal oxide, metal alloy, high thermal stability support or any combination thereof. By "metallic support" in the present invention is meant that substance that acts as a support and is of metallic composition, with metallic elements that are selected from alkaline earth, transition metal, rare earths or metalloids. By "metallic alloy" in the present invention is meant a solid mixture comprising two or more metals uniformly distributed within the solid material. By "support of high thermal stability"

 \ hbox {understands in the present invention a highly material
resistant to thermal degradation.} 

In a more preferred embodiment the support Metallic is selected from Pt, Ni, Ru, Rh, Co or Pd.

In another more preferred embodiment the support of Metal alloy is selected from Pt-Rh, Ru-Pt or Pt-Ni.

In another more preferred embodiment the support of metal oxide is selected from nickel oxide, oxide Ruthenium or iridium oxide.

In another more preferred embodiment the support of High thermal stability is selected from metal mesh, silicon carbide, aluminum oxide, zirconium oxide, cordierite or any of its combinations.

The deposit of modified oxides on supports of high thermal resistance improves its activity and thermal stability in high temperature cycles.

The process of the invention is based on a cycle that includes two coupled processes, based on reduction and successive oxidation of modified cerium oxides acting as effective way in the dissociation of water. In that cycle, the first process or step as indicated above cerium oxide modified is partially reduced at temperatures greater than 820 ° C, and in the next stage the partially reduced cerium oxide is oxidizes with water capturing the oxygen of this molecule and releasing simultaneously hydrogen (H2) gas.

The thermal energy used in step (a) it can be any source of heat that provides a temperature greater than 1100 ° C, preferably the thermal energy used in the Stage (a) is solar thermal energy.

The oxidation stage can be performed with a gaseous stream comprising water vapor with a purity of 5 to 100%. More preferably the purity of the water vapor is 20 to 100%.

The process of the invention can be carried out. carried out in each of the two stages, independently, to temperatures below 1600 ° C.

It is desirable to apply the lowest possible temperature to maximize cycle performance and durability of modified cerium oxides.

In a preferred embodiment the process of the invention is carried out in a reactor that is selected from between fixed bed reactor, fluidized bed reactor, mobile bed or dragged bed reactor.

Where in a more preferred embodiment reactor is selected from among fluidized bed reactor, bed reactor mobile or in dragged bed reactor.

The process of the invention allows the heat conversion directly into hydrogen more efficient than transforming heat into electricity and performing the conventional electrolysis of water.

The present invention therefore relates to a simple hydrogen production process from renewable and abundant substances in nature such as the solar radiation and water. A prominent advantage of the procedure of the invention is the greatest theoretical efficiency of this process regarding the electrolysis of water coupled with a system of solar electricity generation due to energy efficiency of the invention is not limited by the conversion of heat into electricity.

In a second aspect, the present invention is refers to a compound, (hereafter compound of the invention), comprising a cerium oxide modified with at least a cation that is selected from the list comprising: Ti 4+, Sr 2+, Hf 4+, La 3+, Ba 2+, Gd 3+, Y 3+, Pr 4+, Ca 2+ and any combination thereof, where Cerium cation replacement percentage is 0.01 to 49%, where The modified cerium oxide is deposited on a support.

In a preferred embodiment the cation is select from La 3+, Zr 4+, Pr 4+ or any of your combinations

In a preferred embodiment the support is select from metallic, metallic oxide, metallic alloy, high thermal stability support or any of its combinations, as described above.

In a more preferred embodiment the support Metallic is selected from Pt, Ni, Ru, Rh, Co or Pd.

In another preferred embodiment the support of Metal alloy is selected from Pt-Rh, Ru-Pt or Pt-Ni.

In another more preferred embodiment the support of metal oxide is selected from nickel oxide, oxide Ruthenium or iridium oxide.

In another more preferred embodiment the support of high thermal stability is selected from a mesh metallic, silicon carbide, aluminum oxide, zirconium oxide, Cordierite or any of its combinations.

Preferably the support has a percentage by weight between 0.01% and 5% with respect to cerium oxide modified. And more preferably the weight percentage of between 0.1 and 2% with respect to modified cerium oxide.

A third aspect of the present invention is refers to the use of the compound of the invention as a catalyst.

In a preferred embodiment the compound of the invention is used as a catalyst for the production of hydrogen.

In another preferred embodiment the production of Hydrogen is made from water vapor.

A fourth aspect of the present invention is refers to a procedure for obtaining the compound of the invention, comprising the steps:

to)

cationic replacement of cerium, in the cerium oxide, by a method that is selected from: chemical coprecipitation, evaporation, solid state reaction, combustion, sol-gel synthesis or hydrothermal synthesis, Y

b)

Modified Cerium Oxide Deposit obtained in step (a) on at least one support by a method that is selected from impregnation, coprecipitation-deposit, ion exchange, immersion-evaporation, microemulsion, dip-coating, spraying, electrospray or Any of your combinations.

The cationic substitution, that is, the introduction of cations in the cerium oxide structure is you can perform using any of the known methodologies in the state of the art and known to any expert in the matter, which give rise to solids of high surface area. In a preferred embodiment the cationic step replacement method (a) is selected from chemical coprecipitation, synthesis sol-gel or hydrothermal synthesis.

Moreover, the deposit can be made by impregnation or by precipitation-deposit.

The use of supports on the surface of modified oxides of cerium improves its activity in the production of hydrogen in the hydrolysis stage (step (b)) of the process of the invention, like the cationic substitution methods of deposition can be any of the methodologies known for any subject matter expert that will give rise to distributions homogeneous, with low agglomeration and good dispersion of metal particles or oxides.

In the case of being high supports thermal stability, what is deposited are cerium oxides modified on the support, depositing in quantities between 0.05 and 1 g / cm2, more preferably between 0.05 and 0.20 g / cm2.

Throughout the description and the claims the word "comprises" and its variants not they intend to exclude other technical characteristics, additives, components or steps. For those skilled in the art, other objects, advantages and features of the invention will be partly detached of the description and in part of the practice of the invention. The The following examples are provided by way of illustration, and are not It is intended to be limiting of the present invention.

Examples

The invention will be illustrated below through tests carried out by the inventors, which puts manifest the specificity and effectiveness of the procedure of hydrogen production through the use of a catalyst modified cerium oxide.

Example one

This example illustrates the preparation of an oxide of modified cerium active and stable in hydrogen production according to the present invention, based on a cerium oxide modified with cations of different nature (M n + = Ti 4+, Sr 2+, Zr 4+, Hf 4+, La 3+, Tb 3+, Ba 2+, Gd 3+, Y 3+ or Pr 4+). The coprecipitation of the Ce 4+ and M n + ions using as precipitating agent NH4OH generated from hydrolysis urea controlled. The solids obtained were air dried and subsequently treated in air at 650 ° C for 10 h to calcine them

Example 2

This example illustrates the preparation of an oxide of modified cerium active and stable in hydrogen production according to the present invention, based on the deposit of metals (Ru, Co, Rh, Pd, Pt, Ni, Pt-Rh, Ru-Pt or Pt-Ni) on the surface of the modified cerium oxides prepared according to example 1. The deposit of metals on the surface of oxides Modified cerium is performed by wet impregnation of the modified cerium oxides with solutions containing ions metallic After impregnation the solids obtained were dried in air and were subsequently treated in air at different temperatures to calcine them and ensure adhesion of metals to rust modified cerium.

Example 3

This example illustrates the preparation of an active and stable modified cerium oxide in the production of hydrogen according to the present invention, based on a modified cerium oxide with cations of different nature (M n + = Ti 4+ , Sr 2+, Zr 4+, Hf 4+, La 3+, Tb 3+, Ba 2+, Gd 3+ , Y 3+ or Pr 4+) and deposited on a substrate of high thermal stability (shaped metals, SiC, aluminum oxides, cordierite or zirconium oxides). Coprecipitation of the Ce 4+ and M n + ions is carried out in situ on the substrate using as a precipitating agent NH 4 OH generated from the controlled hydrolysis of urea. The solids obtained were dried and subsequently treated in air at 650 ° C for 10 h to calcine them and ensure adhesion of the modified oxide layer of cerium to the support.

Example 4

This example illustrates the redox oxide behavior in the thermochemical cycle of water dissociation of a modified cerium oxide representative of the present patent in the production of hydrogen by thermochemical water dissociation reaction. This example also illustrates the comparative behavior against redox oxides belonging to the state of the art claimed for the production of hydrogen by thermochemical dissociation reaction of water (CeO 2 according to Solar Energy 80.1611 ).

Sample A corresponds to CeO_ {2} representative of the state of the art consisting of the oxide without modify and prepared according to the procedure described in the example 1. The modified cerium oxides B and C were prepared according to procedure described in example 1 varying the nature of the cation introduced into the cerium oxide structure (sample B: Zr in a 20% molar concentration and shows C: Ca in a 20% molar concentration).

The oxides were tested in the cycles of thermal reduction and hydrolysis in a test system at scale of laboratory. The thermal reduction of the oxides was carried out under gas inert at 1500 ° C while the hydrolysis stage on the oxides partially reduced was carried out under a stream of H2O (31% vol) in inert at 1000 ° C. The gases generated in the thermal reduction (O 2) and in hydrolysis (H 2) were analyzed in a Gas chromatograph coupled to the test system. The results of hydrogen production obtained in the hydrolysis stage is summary in Table 1.

Comparative activity trials put manifestly the improvement in the production of hydrogen on the oxide "B" prepared according to the invention with respect to cerium oxide claimed in the state of the art as an asset for the reaction of thermochemical water dissociation.

TABLE 1 Comparative study of oxides activity modified cerium used in dissociation water thermochemistry to obtain hydrogen

2

The modified cerium oxide "C" illustrative of the introduction of a cation not included in this invention has a lower level of hydrogen production with respect to the oxide containing a cation, Zr oxide B, collected in the invention. This result illustrates the fundamental role played by the selection of the cation introduced into the cerium oxide network to hydrogen production by thermochemical dissociation of water using redox cycles.

Example 5

This example is illustrative of the behavior of modified cerium oxides representative of the present invention with different concentration of the cation introduced in the cerium oxide network. The modified cerium oxides B and D are prepared according to the procedure described in example 1 varying the amount of cation introduced into the oxide network (sample B: Zr in a 20% molar concentration and shows D: Zr in a concentration 30% molar).

The oxides were tested as redox oxides using the system and test conditions described in the Previous example. The test results are summarized in the Table 2.

TABLE 2 Comparative study of oxides activity modified cerium used in dissociation water thermochemistry to obtain hydrogen

3

Comparative activity trials teach the influence that the cation concentration introduced into the network of cerium oxide has in production and performance in generation of hydrogen achieved with the use of the oxides described in the patent.

Example 6

This example is illustrative of the behavior of modified cerium oxides representative of the present invention based on the deposit of metals on the surface of modified oxides of cerium. The modified cerium oxide E is prepared according to the procedure described in example 2 (containing Pt with a concentration 1% by weight).

The oxides were tested as redox oxides using the system and test conditions described in the Previous example. The test results are summarized in the Table 3.

TABLE 3 Comparative study of oxides activity modified cerium used in dissociation water thermochemistry to obtain hydrogen

4

Comparative activity trials teach the remarkable influence of the presence of metal on the surface of modified cerium oxide on production and yield in the generation of hydrogen achieved with the use of oxides described in the patent.

Example 7

This example is illustrative of the behavior of cerium oxides modified and deposited on a substrate of high thermal stability representative of the present invention. The modified cerium oxide F corresponds to the D oxide supported on monoclinic ZrO2 (25% by weight of D on ZrO2) prepared according to the procedure described in the example 3.

The oxides were tested as redox oxides using the system and test conditions described in the Previous example. The test results are summarized in the Table 4

TABLE 4 Comparative study of oxides activity modified cerium used in dissociation water thermochemistry to obtain hydrogen

5

Comparative activity trials teach the remarkable influence of depositing cerium oxides modified on suitable supports on production and hydrogen generation efficiency with the use of oxides described in the patent.

Claims (28)

1. Procedure for obtaining hydrogen that It comprises the stages:

to.

reduction of a catalyst by thermal energy at a temperature higher than 820 ° C, and

b.

oxidation of the catalyst obtained in stage (a) with water vapor.

where the catalyst is a cerium oxide modified with at least one cation that is selected from the list that comprises: Ti 4+, Sr 2+, Hf 4+, La 3+, Ba 2+, Gd 3+, Y 3+, Pr 4+, Ca 2+ and any of its combinations, and where the percentage of cerium cation replacement It is from 0.01 to 49%. 2. Method according to claim 1, where the cation is selected from La 3+, Zr 4+, Pr 4+ or any combination thereof. 3. Procedure according to any of the claims 1 or 2, wherein the modified cerium oxide It is deposited on a support. 4. Method according to claim 3, where the support is selected from metallic, metallic oxide, metal alloy, high thermal stability support or Any of your combinations. 5. Method according to claim 4, where the metal support is selected from Pt, Ni, Ru, Rh, Co or Pd. 6. Method according to claim 4, where the metal alloy support is selected from Pt-Rh, Ru-Pt or Pt-Ni. 7. Method according to claim 4, where the metal oxide support is selected from among nickel, ruthenium oxide or iridium oxide. 8. Method according to claim 4, where the high thermal stability support is selected from Between metal mesh, silicon carbide, aluminum oxide, oxide of zirconium, cordierite or any of its combinations. 9. Procedure according to any of the claims 1 to 8, wherein the thermal energy used in the Stage (a) is solar. 10. Procedure according to any of the claims 1 to 9, wherein the water vapor has a purity of 5 to 100%. 11. Method according to claim 10, where the water vapor has a purity of 20 to 100%. 12. Method according to any one of claims 1 to 11, characterized in that they are carried out in each of the two stages, independently, at temperatures below 1600 ° C. 13. Procedure according to any of the claims 1 to 12, wherein obtaining hydrogen is carried to conducted in a reactor that is selected from a fixed bed reactor, fluidized bed reactor, mobile bed reactor or reactor dragged bed. 14. Method according to claim 13, where the reactor is selected from a fluidized bed reactor, mobile bed reactor or entrained bed reactor. 15. Compound comprising a cerium oxide modified with at least one cation that is selected from the list that comprises: Ti + 4, Sr 2+, Hf 4+, La 3+, Ba 2+, Gd 3+, Y 3+, Pr 4+, Ca 2+ and any of its combinations, where percentage of cerium cation replacement is 0.01 to 49%, and where the modified cerium oxide is deposited on a support. 16. Compound according to claim 15, wherein The support is selected from metallic, metal oxide, alloy metal, high thermal stability support or any of its combinations 17. Compound according to any of the claims 15 or 16, wherein the cation is selected from La 3+, Zr 4+, Pr 4+ or any of its combinations 18. Compound according to any of the claims 15 to 17, wherein the metal support is selected from between Pt, Ni, Ru, Rh, Co or Pd. 19. Compound according to any of the claims 15 to 17, wherein the metal alloy support is select from Pt-Rh, Ru-Pt or Pt-Ni. 20. Compound according to any of the claims 15 to 17, wherein the metal oxide support is selects from nickel oxide, ruthenium oxide or oxide iridium 21. Compound according to any of the claims 15 to 17, wherein the high stability support Thermal is selected from metal mesh, silicon carbide, aluminum oxide, zirconium oxide, cordierite or any of its combinations 22. Compound according to any of the claims 15 to 21, wherein the support has a percentage in weight between 0.01% and 5% with respect to cerium oxide modified. 23. Compound according to claim 22, wherein the support has a weight percentage of between 0.1 and 2% compared to to modified cerium oxide. 24. Use of the compound according to any of the claims 15 to 23, as catalyst. 25. Use of the compound according to claim 24, as a catalyst for hydrogen production. 26. Use according to claim 25, wherein the Hydrogen production is done from water vapor. 27. Procedure for obtaining the compound according to any of claims 15 to 23, comprising:

to.

The cationic replacement of cerium, in cerium oxide, by means of a method selected from: chemical coprecipitation, evaporation, solid state reaction, combustion, synthesis sol-gel or hydrothermal synthesis, and

b.

he modified cerium oxide deposit obtained in step (a) on at least one support by a method that is selected from between impregnation, coprecipitation-deposit, ion exchange, immersion-evaporation, microemulsion, dip-coating, spraying, electrospray or any combination thereof.

28. Method according to claim 27 where the cationic substitution method of step (a) is select from chemical coprecipitation, synthesis sol-gel or hydrothermal synthesis.