WO2013121066A1

WO2013121066A1 - Process for the production of hydrogen by means of catalytic hydrolysis in a continuous reactor that is used to perform the method

Info

Publication number: WO2013121066A1
Application number: PCT/ES2013/070083
Authority: WO
Inventors: Gisela Mariana Arzac de Calvo; Dirk HUFSCHMIDT; Enrique Jimenez Roca; Asunción FERNANDEZ CAMACHO; Mª Angeles JIMENEZ DOMINGUEZ; Sarika TYAGI; Mª del Mar JIMENEZ VEGA; Belén SARMIENTO MARRON
Original assignee: Abengoa Hidrogeno, S.A.
Priority date: 2012-02-14
Filing date: 2013-02-12
Publication date: 2013-08-22
Also published as: ES2419506A1; ES2419506B1

Abstract

The invention relates to a process for the controlled production of a continuous flow of hydrogen, characterised in that it comprises at least the following steps: (a) a step in which a fuel solution is added to a reactor at a constant rate, said solution comprising between 9% and 19% p/p of at least one complex hydride stabilised in a hydroxide, on a catalyst of cobalt and boron (Co-B) supported on a stainless steel monolith, in which the catalyst is located inside the reactor in an excess quantity of between 37 mg and 240 mg; (b) a step comprising the catalytic hydrolysis of the complex hydride, generating a continuous flow of hydrogen; and (c) a step comprising the continuous removal of the products of the catalytic hydrolysis in the form of molten salt. The invention also relates to the unit used to carry out said method.

Description

HYDROGEN PRODUCTION PROCESS THROUGH HYDROLYSIS

CATALITICS IN A CONTINUOUS REACTOR TO CARRY OUT SAID

PROCESS

DESCRIPTION

TECHNICAL FIELD OF THE INVENTION

The present invention is framed in the field of the generation of hydrogen-rich gas streams by hydrolysis, particularly of hydrides, and more particularly of complex hydrides, which can be used in hydrogen production plants, combustion engines and especially as fuel in fuel cell systems where optimal results are obtained, more specifically in PEM type fuel cells.

BACKGROUND OF THE INVENTION

It is known that carbon monoxide-free hydrogen can be obtained by alkaline hydrolysis of sodium borohydride (BHS) in the presence of catalysts according to the following equation:

NaBH4 + 2H20 4H2 + NaB02 + Q (equation 1)

Very recent bibliographical reviews include a wide bibliography referring to the study of the reaction (equation 1), both from a fundamental point of view, and from a practical point of view, such as hydrogen generation for portable applications (BH Liu, ZP Li , J. Power Sources, 2009, 187, 527-534; UB Demirci, at al., Fuel Cells 2010, 3, 335-350; SS Muir, X. Yao, Int J. Hydrogen Energy, 36, 2011, 5983- 5997).

Among the most used catalysts with the best cost / efficiency ratio are those based on cobalt and boron (Co-B). For an extension of the ways of preparing these Co-B catalysts both in powder and supported form, the following bibliography should be used: UB Demirci, P.Miele, Phys. Chem. Chem. Phys. , 2010, 12, 14665-14651 and UB Demirci, et al., 2010, 53, 1870-1879. For any design capable of producing hydrogen based on the catalyzed hydrolysis of a complex hydride, such as preferably sodium borohydride, which wants to adapt to a fuel cell, it is essential to ensure a hydrogen production at a constant speed, at a value that will depend of the conditions of the same (power and voltage). Given the exothermic nature of the reaction (equation 1) the constancy in velocity requires that the medium in which the reaction proceeds be as isothermal as possible (BH Liu, ZP Li, S. Suda, J. Alloys and Compd. 468, 2009 , 493-493). Temperature control can be achieved with a suitable system / reactor design. Said design can vary from a simple external cooling of the reactor, a design that involves the continuous addition of reagents (semicontinuous reactor, GM Arzac, et al., Journal of Power Sources, 2011, 196, 4388-4395), to a reactor that operate by continuous flow of reagents and products, which also allows the heat released by the reaction to be continuously eliminated (SJ Kim, et al., J. Power Sources 170, 2007, 412-418). Any device that can generate hydrogen for portable applications must include a reactor that can meet the following requirements:

^• The reactor volume must be minimal;

^• The catalyst based on Cobalt and Boron (Co-B) must be supported on a support that is cheap, that allows great adhesion (since the formation of hydrogen bubbles tends to release it from its support) and that allows it to be dispersed highly;

^• The catalyst with its support must cover / fill the maximum volume of the reactor, so as to take full advantage of the entire volume of the reactor and avoid preferential paths of the reagents, so that conversion is maximized;

^• The catalyst with its support must allow both the flow of stabilized complex hydride solution (BHS) and the flow of reaction products (hydrogen and borates); ^• The complete design (reactor and supported catalyst) must produce a stable flow of hydrogen, without sudden increases or decreases in its production speed;

^• The catalyst must be stable throughout the operation of the system. This means that it should not be deactivated, nor reduce its ability to accelerate the reaction, nor its efficiency, during the established operating time;

^• Once the operation of the system is finished, the catalyst must be able to be reused in an experience similar to the initial one or in different conditions, without loss of its efficiency, that is, without reducing the speed of hydrogen production. It is highly desirable that the catalyst be reused as many times as possible without loss of efficiency or deactivation;

^• If there is a deactivation of the catalyst, it is desirable that it could be reactivated by some simple, fast and safe method;

^• For the system to be efficient, the reactor should operate at high temperatures, preferably above the melting temperature of borates (60 ° C) and preferably in a continuous elimination regime, so that they do not remain in the reactor, blocking the catalyst and therefore reducing its efficiency (EY Marrero-Alfonso, et al., Int. J. Hydrogen Energy 32, 2007, 4723-4730; BH Liu, ZP Li, S. Suda, J. Alloys and Compd., 468, 2009, 493-493).

A large number of supports have been reported in the literature for catalysts based on cobalt and boron (Co-B), from the group of metal supports. Nickel foam is highlighted first, which is undoubtedly the most reported support (SJ Kim, et al., J. Power Sources 170, 2007, 412-418; HB Daim, et al., J. Power Sources, 177, 2008, 17-23; P. Krishnan, SG Advani, AK Prasad, App. Cat. B. Environmental, 86, 2009, 137-144), clays (H.Tian, Q. Guo, D.Xu, J. Power Sources, 195, 2010, 2136-2142), vulcan carbon (J. Zhao, H .Mua, J. Chen, Int. J. Hydrogen Energy, 32, 2007, 4711-4716), zeolites (M. Rakap, S. Ozkar, Appl. Catal. B. 91, 2009, 21-29), etc. In no case has the catalyst based on cobalt and boron in stainless steel been prepared as a support. Nor has it been reported, for the catalyst based on cobalt and boron, any treatment strategy on the stainless steel support to increase adhesion.

On the other hand, there is no system reported in the literature that includes a reactor that operates in continuous flow of reagents and products for catalyzed hydrolysis of complex hydrides, in which the contact between the solution and the catalyst is maximized, and stabilized hydrogen production, without rises or falls in the rate of hydrogen production.

For the catalyzed hydrolysis of sodium borohydride, there is a large number of bibliographic reports in which new catalysts are designed that are increasingly efficient, but very scarce, in which their durability and stability are studied throughout an experiment. long-term (SS Muir, X. Yao, Int J. Hydrogen Energy, 36, 2011, 5983-5997, and references included there). Very recently, a study of the durability of a Cobalt (Co) -based catalyst for the hydrolysis reaction of sodium borohydride has been reported, under conditions of generation of 100 ml.min-1 of hydrogen for a maximum of 5 minutes (O. Akdim, UB Demirci, P. Miele, Int. J. Hydrogen Energy, 36, 2011, 13669-137575). In no case has the durability of a catalyst based on cobalt and boron (Co-B) been studied, nor has the durability of any catalyst operating on a hydrogen production scale between 0.8 and 1.2 l.min-1 been studied during periods covering hours, which is of interest to the present invention (BH Liu, ZP Li, J. Power Sources, 2009, 187, 527-534; UB Demirci, et al., Fuel Cells 2010, 3, 335-350, SS Muir, X. Yao, Int J. Hydrogen Energy, 36, 2011, 5983-5997 and references included therein).

To solve these problems detected in the field, the present invention proposes a continuous hydrogen production process at constant speed and temperature, based on adding a source of hydrogen, such as a complex hydride that acts as a fuel, preferably sodium borohydride, stabilized in a hydroxide solution, which is preferably sodium hydroxide, on a catalyst based on Cobalt and Boron (Co-B), preferably supported on a previously oxidized stainless steel monolith. To adapt the already known synthesis techniques of Co-B on metal supports to the support used herein, modifications have been made therein which are part of this invention.

The control of the temperature and the speed of hydrogen production in this process are based on the control of the rate of addition or aggregation of the fuel solution on the supported catalyst.

Based on practical considerations, the system includes a continuous reactor in which not only the fuel solution is added continuously on the catalyst, but the reaction products are continuously removed from the medium so that they do not accumulate blocking the catalyst . The design of the continuous reactor also allows to reduce its volume to the maximum and, mainly, autonomy is no longer limited by its size, as in the case of the semicontinuous reactor previously reported (GM Arzac, et al., Journal of Power Sources, 2011, 196, 4388-4395).

DESCRIPTION OF THE INVENTION

The main object of the present invention is a process for the controlled production of hydrogen from the catalyzed hydrolysis of at least one complex hydride, preferably sodium borohydride (according to equation (1) set forth in the previous section), in a wide range of speeds and with control of the flow of hydrogen production on demand.

Another object of the present invention is the design of an installation for the production of hydrogen under constant flow conditions, in accordance with the aforementioned procedure, which is characterized in that it comprises a reactor of minimum volume (preferably around 11 mi) It works on a continuous basis of reagent input and output of products, which does not require refrigeration, and which has a potentially unlimited autonomy. In addition, said reactor is characterized by presenting a simple design, being able to be constructed with light and transparent materials such as PMMA (polymethylmethacrylate). The transparency of the reactor allows observing the production of hydrogen, having greater control over what happens in the system.

In this way, the developed device is chemically stable and safe before, during and after the operation.

The hydrogen obtained could feed a hydrogen production plant or a combustion engine, although the hydrogen production process of the present invention is preferably designed to feed a fuel cell, preferably PEM type, to produce electrical energy.

Also, the present invention encompasses the development of a method for machining stainless steel monoliths that will support the catalyst, a heat treatment on mechanized monoliths to improve the adhesion of the Co-B catalyst (based on cobalt and boron) and a technique of synthesis of the catalysts on the oxidized monolith.

The present invention also encompasses the use of a novel in situ reactivation method and an ex situ method that allows the reuse of catalysts supported on stainless steel monoliths. The reactivation method is based on the first of the cases in the aggregate of an aliquot of combustible solution on the catalyst before starting the continuous aggregate, and in the addition of a diluted acid, preferably hydrochloric acid (HC1), in the second case. Thanks to the catalyst's in situ reactivation method, it is possible to maintain its initial activity up to 6 cycles, before the complete deactivation occurs. On the other hand, the ex situ reactivation of the catalyst which, used 6 cycles, has been completely deactivated, allows recovering part of the initial activity due to a cumulative or memory effect.

DESCRIPTION OF THE FIGURES

In order to contribute to a better understanding of the invention, and in accordance with a practical embodiment thereof, an integral part of this description is accompanied by a series of figures where, with an illustrative and never limiting nature of the invention, it has been represented the next:

Figure 1A Diagram of the hydrogen production facility by means of the process described herein, comprising the following elements:

a storage tank (1) of the fuel solution comprising the complex hydride stabilized by a hydroxide;

dispensing means (2) of the constant flow fuel solution within the continuous reactor (3);

a continuous reactor (3) without refrigeration;

a hydrogen separator tank of the hydrolysis products (4);

hydrogen stream drying medium (5);

means for dispensing hydrogen stream to the fuel cell (6);

an optional thermocouple (10).

Figure IB Scheme of the continuous reactor (3) of Figure 1A comprising the following elements: a cylindrical body (7);

a lid with opening and closing (8), which allows the entry of combustible liquid;

an output device (9) of the hydrogen stream and hydrolysis products;

Figure 2A Representation of the winding procedure of the stainless steel sheet to produce the monolith that acts as a catalyst support.

Figure 2B Photograph of bare stainless steel monolith.

Figure 2C Photograph of the monolith covered with catalyst based on cobalt and boron (Co-B).

Figure 3. Scanning electron microscopy micrographs of bare stainless steel (Figure 3A) and treated stainless steel at 900 ° C for 2h (Figure 3B).

Figure 4. Graphical representation of hydrogen production speed and temperature as a function of time, for one hour (Figure 4A) and hydrogen production speed as a function of time for 9 hours (Figure 4B).

Figure 5. (Figure 5A) Hydrogen production rate and temperature as a function of time for a fuel solution aggregate rate of 19% w / w between 5 and 0.8 ml / minute; (Figure 5B) Hydrogen production rate as a function of the rate of aggregate of fuel solution (fuel) at 19% w / w; (Figure 5C) Hydrogen production rate and temperature as a function of time for a fuel solution aggregate rate of 9% w / w between 10 and 1.6 ml / minute; (Figure 5D) Hydrogen production rate as a function of the rate of aggregate of fuel solution at 9% w / w.

Figure 6. Average hydrogen production rate (VH2) divided by the hydrogen production rate of the first use cycle (initial VH2) as a function of the number of use cycles. DETAILED DESCRIPTION OF THE INVENTION

The present invention relates to a process for the production of a continuous flow of hydrogen by catalyzed hydrolysis of at least one complex hydride, which comprises at least the step of adding at a constant speed to a reactor a combustible solution comprising a complex hydride. stabilized in hydroxide, on a Co-B catalyst that is supported on a stainless steel monolith, in an excess amount inside the reactor (Figures 1 and 2).

Also object of the present invention is an installation for producing a stream of hydrogen according to the process described. Said installation comprises at least the elements that have been presented in Figure 1A to better illustrate an embodiment of the invention, without supposing said figure a limitation thereof in its most generic form.

Thus, the installation comprises at least the following elements: a storage tank (1) of the fuel solution comprising the stabilized complex hydride; dispensing means (2) of the constant flow fuel solution within the reactor; a continuous reactor (3) without refrigeration; a hydrogen separator tank of the hydrolysis products (4); a means for drying the hydrogen stream (5) and means for dispensing the hydrogen stream to the fuel cell system (6).

The reactor is comprised at least of a cylindrical body (7), a lid with opening and closing (8), which allows the entry of combustible liquid and an outlet device (9) of the hydrogen flow and hydrolysis products (Figures 1A and IB).

Both the storage tank (1) and the continuous reactor can be constructed with plastic materials, thus minimizing the weight according to the operating conditions of the system (flow of hydrogen, time or concentration of the fuel solution).

Optionally, said continuous reactor (3) may comprise a thermocouple (10) for simultaneous temperature measurement. The greatest singularities of the continuous reactor described here are:

^• Does not require external cooling;

^• The continuous elimination of hydrolysis products can minimize their size, and prevent deactivation until cycle number 6;

^• The autonomy is not limited by the reactor, but by the feeding and storage tanks of waste.

The support of the catalyst is essential in this type of continuous reactor because the stabilized solution of complex hydride that feeds it must produce a conversion of the complex hydride into hydrogen with a speed preferably between 1.66 and 0.3 1 / min (in the case of a reactor of around 11 ml capacity and a catalyst size appropriate to said capacity), which implies a continuous and violent gas production, which must take place without the catalyst being dragged. Since the reaction products are constantly removed from the reactor and directed to the separator tank, the joint entrainment of catalyst particles would gradually lead to a loss of efficiency and conversion of the process until its complete stop. On the other hand, the operating times required in the case of long-term experiments (9 hours) and / or the need to reuse the same supported catalyst in successive experiments without loss of efficiency, require that the supported catalyst be stable and Be well attached to the support. The support must also ensure adequate dispersion of the catalyst on it and also inside the reactor, filling it completely, which avoids sudden ups and downs of the hydrogen production rate. The support can consist of commercial 316 stainless steel, in the form of a plate with hexagonal holes, honeycomb type. The preferred choice of this type of support is due to its low cost and its ease of machining (Figure 2A). Since the reactor is cylindrical, the monoliths are constructed by winding the plate to give a cylinder that is filled with a second smaller cylinder obtained in the same way (Figure 2B). The monolith thus constructed is subjected to an oxidation in oxygen atmosphere, at a temperature of 900 ° C for 2 hours, to produce an oxide layer thereon. This oxide layer gives it a greater roughness that causes the catalyst to adhere more to it, reducing losses (Figure 3).

Preferably, in order to achieve the generation of a continuous flow of hydrogen into the reactor, the excess amount of catalyst is between 37 and 240 mg. In this way the main objective of this invention is achieved, which is to produce a continuous flow at a constant and controlled rate of hydrogen. This hydrogen flow can serve as a source of fuel to other devices, such as a combustion engine, but preferably to a fuel cell, since in this case the continuous supply of a hydrogen flow is essential for its operation.

Also preferably the concentration of complex hydride in the fuel solution is between 9% and 19% w / w. In the case of the 19% w / w borohydride solution, said solution being added on the catalyst at a rate preferably between 0.8 and 5 ml / min, the temperature is between 82.4 ° C and 103.9 ° C, achieving a flow continuous and constant hydrogen between 1.66 and 0.30 1 / minute.

In the case of the 9% w / w borohydride solution, said solution being added to the catalyst at a rate preferably between 1.6 and 10 ml / min, the temperature is between 85.2 and 78.6 ° C, achieving a continuous and constant flow of hydrogen between 1.43 and 0.30 1 / minute.

Preferably, in any of the cases or variants mentioned herein, the complex hydride is sodium borohydride. It has been found that the optimum values of hydrogen production are achieved with sodium borohydride (BHS) as a source of hydrogen, following equation (1) set forth in the "Background of the invention" section.

Also preferably, the solution that acts as a fuel with which the complex hydride is stabilized is sodium hydroxide. More preferably, the solution is 4.5% w / w sodium hydroxide (in percent by weight of the solution).

As for the catalyst based on cobalt and boron (Co-B), it is preferably supported on previously oxidized stainless steel monoliths.

As described, with the continuous addition of the fuel solution to the reactor it is possible to control the speed and temperature of hydrogen production (Figure 4A), thus being able to dispense with the installation of additional reactor heating and / or cooling systems and of agitation methods, since the latter is achieved by the fuel itself added directly on the catalyst and the formation of the bubbles during the reaction.

In one of the most preferred embodiments of the invention, the hydrogen production process by hydrolysis, comprises adding in a continuous reactor, a solution comprising 4.5% w / w sodium borohydride on a cobalt and boron-based catalyst (Co -B) supported on previously oxidized stainless steel monoliths.

Of all the embodiments that this invention comprises, the most preferred would be a process for the production of a continuous flow by catalyzed hydrolysis of a complex hydride, which comprises at least the step of adding continuously and at a constant speed to a continuous reactor a fuel solution comprising sodium borohydride in a concentration between 9 and 19% w / w, stabilized with sodium hydroxide at a percentage of 4.5% by weight of solution on a catalyst based on cobalt and boron (Co-B), wherein said The catalyst is supported on a previously oxidized stainless steel monolith that is added in an amount between 37 and 240 mg.

By carrying out an addition of the fuel solution at a constant speed, hydrogen production is obtained at a constant speed and also at a constant temperature. The fuel solution is added at a speed between 5 and 0.8 ml / min, in the case of the BHS solution 19% w / w. In the case of the 9% w / w BHS solution, the speed is between 10 and 1.6 ml / min. The temperature is controlled at a constant value by the constant rate addition of a stabilized solution of complex hydride, which is preferably BHS.

Under conditions of constant flow of stabilized complex hydride solution, a constant hydrogen production is achieved at a rate that is related to the flow of complex hydride solution as shown in Figure 5.

The continuous flow of stabilized solution of complex hydride on the supported catalyst and the continuous flow of reaction products, hydrogen and the hydrolysis product (NaB02XH20, equation (1)) ensure the elimination of possible blockers of catalyst activity. Since the continuous flow of stabilized solution over the catalyst allows the reactor to work at temperatures that range from 70 to 120 ° C, the hydrolysis product remains a molten salt. Continuous removal of this molten salt from this reaction medium ensures the stability of the catalyst in long-term hydrogen release experiments that range from 1 to 6 hours without loss of efficiency and conversion (Figure 6). At times greater than 6 hours a small deactivation of the catalyst occurs which reduces its activity to 90% with respect to the initial one. The continuous feeding of the reactor with stabilized solution of complex hydride on the catalyst and the continuous elimination of the hydrolysis product in the form of molten salt make the catalyst can be reused for 6 cycles without complete deactivation, although with a loss of efficiency of 10%. Deactivation after 6 cycles occurs in this case due to memory or cumulative effect.

In a particular embodiment of the described invention that can encompass any of the preferences described above, the process further comprises, prior to the aggregation of the fuel solution on the catalyst:

stabilize the complex hydride in the fuel solution comprising the hydroxide.

In another particular embodiment, which encompasses any of the above, the process comprises:

extract the hydrogen stream obtained by hydrolysis from the reactor and direct it to washing means.

Washing the hydrogen stream or not, a particular embodiment of the process further comprises directing the hydrogen stream continuously and at a constant speed to a fuel cell, preferably the fuel cell is PEM.

Another object of the present invention is the reactivation and reuse of the catalyst based on Cobalt and Boron (Co-B) because, after each 1-hour experiment, a slight deactivation of the catalyst occurs due to deposition of borates on the surface thereof and oxidation of cobalt. The method consists of adding on the supported catalyst deposited in the reactor, a small amount of stabilized solution of complex hydride for a few seconds and wait for the temperature to reach 60 ° C and then turn on the pump that feeds the catalyst with stabilized solution of complex hydride This causes the catalyst to reactivate in situ and convert complex hydride efficiently again. This reactivation process in situ can be repeated a maximum of 6 times (Figure 6), since then the memory effect (cumulative effect) completely deactivates the catalyst.

After the reactivation in situ described above, the reactor begins to release hydrogen and, once it enters the regime (induction time), it does so in a stable and safe way during the time that the fuel aggregate lasts. In a particular embodiment of the invention, as shown in Figure 4B, the elapsed time has been a maximum of 9 hours.

After complete deactivation it is possible to at least partially reverse this effect by adding diluted acid, in what constitutes an ex situ reactivation. The borates that are deposited on the surface of the catalyst are soluble in acid medium whereby, in a preferred embodiment of the invention, the monolith is immersed with catalyst supported in 10-4 M hydrochloric acid (HC1 10-4 moles / liter) at least 15 minutes This monolith is washed with distilled water and reused in the same continuous reactor system. The efficiency of the catalyst is recovered but does not completely return to that prior to the reactivation step (Figure 6).

EXAMPLES OF EMBODIMENT OF THE INVENTION

A series of examples are described below by way of illustration of the invention. In these examples, the system has been tested under conditions of producing between 0.15 and 1.5 1 / min of hydrogen at constant speed, operating at a constant temperature of between 90 and 120 ° C, depending on the conditions, during times ranging from lh to 9h The possibility of reusing the same catalyst in successive 1-hour experiments has been tested for 10 cycles. The possibility of using the in situ reactivation step proposed by this invention between each experiment has been studied. In cases where the catalyst has been completely deactivated, the possibility of carrying out an ex situ reactivation of the catalyst, previously reported in (O. Akdim, UB Demirci, P. Miele, Int. J. Hydrogen Energy, 36, 2011, 13669-13675), but only tested under working conditions that include the production of 100 ml / min of hydrogen for a maximum 5 minutes, on a catalyst that is based only on cobalt and not on cobalt-boron like the one presented in the present invention.

Example 1. Manufacture of stainless steel monolith that will work as a support for the catalyst.

The monolith that is subsequently used as a catalyst support is manufactured using a commercial 316 stainless steel sheet, with hexagonal perforations of 6 mm side and a porosity of 79% (See Figure 2A). A piece of the 6.3 cm side blade is cut and rolled until a hollow cylinder approximately 1.3 cm in diameter is obtained (see figure 2A). That cylinder is filled with a piece of 6.3 cm sheet of rolled side on itself up to 3 times obtaining an approximately solid cylinder. The first hollow cylinder is filled with the solid cylinder, obtaining a single cylinder that functions as a catalyst support, filling the reactor total (See figure 2B).

Example 2. Oxidation of stainless steel monolith to increase catalyst adhesion.

To increase the surface roughness of the stainless steel monolith shown in example 1, a calcination is carried out in static air at 900 ° C for 2h. Prior to calcination, a wash in purified water is carried out undergoing the ultrasound action for 30 min. Then, the same washing is done but using acetone. The heating is done with a speed of 5 ° C / minute. After heating for 2 hours, let it cool until it reaches room temperature. The oxidized monolith thus obtained is coated with an oxide layer that makes its surface more rough than that of the bare metal (See Figure 3). The monoliths thus oxidized are those that are used as support for the subsequent preparation of the catalysts. Example 3. Preparation of a catalyst based on Cobalt and Boron (Co-B) supported on previously oxidized stainless steel monolith.

The catalyst based on Cobalt and Boron (Co-B) supported on the previously oxidized monolith is prepared by reduction of an ethanolic solution of CoC126H20 by an aqueous solution of sodium borohydride stabilized in NaOH. The ethanolic solution of the cobalt precursor (CoC126H20) is prepared using ethanol and the concentration is 30% w / v. The previously oxidized monolith is immersed in the ethanolic solution of the cobalt precursor for 5 minutes. Subsequently, it is removed from the solution and dried under a stream of nitrogen. Once dried, it is immersed in the 19% w / w BHS solution stabilized in 1% w / w NaOH for one minute. The monolith is removed from the solution and washed with purified water, ethanol and acetone and dried under a stream of nitrogen. The process described above is repeated about 12 times.

To increase the adhesion of the catalyst to the support, without losing catalytic activity, it was subjected to a 2-hour heat treatment in an inert atmosphere at 300 ° C (1 ° C / minute). With this process a catalyst mass of 80 to 120 mg of Cobalt-Boron is obtained with a charge of 10-15mg catalyst / g monolith. The photograph of the finished monolith is shown in Figure 2C.

Example 4. Process according to the present invention to produce 0.8-1.2 1 / min of hydrogen for 1 h and 9 h from the hydrolysis of sodium borohydride in sodium hydroxide solution, on a catalyst as in the previous example.

To produce 0.8-1.2 1 / min of hydrogen, a stabilized BHS solution with a 19% w / w concentration thereof has been selected. Said solution is added at a constant speed of 2.8 g / min, according to the required hydrogen production rate, on the catalyst located in the reactor, which is part of the continuous system, obtaining a hydrogen production of 0.8-1.2 almost instantaneously 1 / min The hydrogen flow is stable and constant over an hour and the temperature is constant and stable during that time (Figure 4A). The average temperature value is between 90 and 120 ° C. The process thus described can be prolonged for at least 9 h, with a constant and stable production of hydrogen that is always the same during the first 6 hours and then is reduced to 90% with respect to the initial one (Figure 4B). So that during the last three hours of the process (from the 6th to the 9th hour inclusive) the activity could be recovered to 100% of the initial, it is necessary to increase the speed of adding fuel solution.

Example 5. Process according to the present invention to produce between 0.3 1 / min and 1.66 1 / min using stabilized BHS solution at 19% w / w and 9% w / w.

The system described herein is versatile in terms of the rate of hydrogen production. The continuous nature of the reactor means that the variation in the fuel flow results in a variation in the hydrogen flow with an almost instantaneous response and keeping the temperature constant, as seen in Figure 5. In this example the reactor has been fed continuous containing the catalyst based on Cobalt and Boron (Co-B) of Example 3 with:

i) a 19% w / w stabilized BHS fuel solution with a fuel aggregate rate of between 5 and 0.8 ml / minute. It has been observed that the rate of hydrogen production varies with the rate of fuel aggregate, and these data are shown in Figure 5B. The hydrogen production rate is between 0.3 1 / min and 1.66 1 / min and the temperature between 82.4 and 103.9 ° C (Figure 5A);

ii) a 9% w / w stabilized BHS fuel solution with a fuel aggregate rate of between 10 and 1.6 ml / minute. It has been observed that the rate of hydrogen production varies with the rate of fuel aggregate, and these data are shown in Figure 5D.

The hydrogen production rate is found between 0.3 1 / min and 1.43 1 / min and the temperature between 78.6 and 85.2 ° C (Figure 5C).

Example 6. Process of washing and reactivation in situ of the catalyst of example 3 by means of the reactivation protocol proposed in the present invention and its reuse in the process of example 4.

To reuse the catalyst of example 3, the monolith containing catalyst based on cobalt and boron (Co-B) is removed. It must be removed from the continuous reactor and washed with milliQ water, ethanol and then dried under a stream of nitrogen, to avoid oxidation of the support that was not covered by catalyst. The reactivation procedure is an on-site process, because it consists of putting the washed monolith back into the continuous reactor and administering a quantity of combustible solution for a few seconds until the evolution of hydrogen begins and the temperature reaches about 60 ° C. After the reactivation process in situ, the pump that feeds the continuous reactor with fuel solution is turned on, and the conditions of example 4 are repeated, to give the same results for a maximum of 5 reuses, not counting the initial one. After 6 uses, counting the initial one, the catalyst begins to deactivate significantly (See Figure 6).

Example 7. Ex situ washing and reactivation process of the catalyst of Example 6 by means of the reactivation protocol proposed in the present invention and its reuse in the process of Example 4.

As stated in example 6, the catalyst can be used as proposed in example 4 and reused a maximum of 5 times without counting the initial. After this, the catalyst is completely deactivated, and the in situ reactivation proposed in Example 6 no longer produces any positive results. It is then proposed in this example an ex situ reactivation process that includes removing the monolith that has been reused 6 times counting the initial one, washing it with purified water and immersing it in a dilute acid solution, preferably 10-4 M hydrochloric acid (HC1 10-4 mol / liter). The catalyst thus reactivated can be reused at least 3 more times with an activity that is not identical to the previous ones, but 80% (See Figure 6).

Claims

RE IVI DICATIONS

1. Process for the controlled production of a continuous flow of hydrogen, characterized in that it comprises at least the following stages:

(a) adding at a constant speed to a continuous reactor a combustible solution comprising between 9% and 19% w / w of at least one complex hydride stabilized in a hydroxide, on a cobalt and boron (Co-B) catalyst supported in a stainless steel monolith, wherein said catalyst is inside the reactor in an excess amount comprised between 37 mg and 240 mg;

(b) a stage of catalytic hydrolysis of the complex hydride, resulting in a continuous flow of hydrogen; Y

(c) continuously remove the products of catalytic hydrolysis in the form of molten salt.

2. Process according to claim 1, wherein when the fuel solution comprises 9% w / w of at least one complex hydride, the fuel solution is added to the reactor at a rate between 1.6 ml / minute and 10 ml / minute.

3. Process according to claim 1, wherein when the fuel solution comprises 19% w / w of at least one complex hydride, the fuel solution is added to the reactor at a rate between 0.8 ml / minute and 5 ml / minute.

4. Process according to claim 2, wherein when the addition of the fuel solution is carried out at a rate between 1.6 ml / minute and 10 ml / minute, the catalytic hydrolysis is carried out at a temperature between 78.6 ° C and 85.2 ° C.

5. Process according to claim 3, wherein when the addition of the fuel solution is carried out at a rate between 0.8 ml / minute and 5 ml / minute the Catalytic hydrolysis is carried out at a temperature between 82.4 ° C and 103.9 ° C.

6. Process according to any one of the preceding claims, wherein the complex hydride is sodium borohydride.

7. Process according to any one of the preceding claims, wherein the hydroxide is sodium hydroxide in a percentage of 4.5% by weight of the solution.

8. Process according to any one of the preceding claims, wherein the reactor operates without external cooling.

9. Process according to any one of the preceding claims, wherein the steel monolith has been previously obtained from a process comprising at least one machining and heat treatment step to improve the subsequent adhesion of the catalyst.

10. Process according to claim 9, wherein said heat treatment consists of a treatment at 900 ° C, for 2h.

11. Process according to any one of the preceding claims, characterized in that it also comprises an in situ reactivation process of the cobalt and boron catalyst supported on the steel monolith.

12. Process according to claim 11, wherein said reactivation process in situ comprises carrying out a first addition of fuel solution on the catalyst prior to the continuous addition of the fuel solution.

13. Process according to any one of the preceding claims, characterized in that once The cobalt and boron catalyst has lost its activity, the process comprises an additional ex situ reactivation process of the catalyst.

14. Process according to claim 13, wherein said ex situ reactivation process comprises adding a dilute acid on the catalyst.

15. Process according to claim 14, wherein said dilute acid is hydrochloric acid.

16. Process according to claim 14 or 15, wherein after ex situ reactivation, the reactivated catalyst is reused in the process.

17. Use of the continuous flow of hydrogen obtained from the process according to any one of claims 1 to 16 to produce energy.

18. Use according to claim 17, wherein said energy production is carried out by a fuel cell.

19. Installation for carrying out a process according to any one of claims 1 to 16, characterized in that it comprises at least:

a storage tank (1) of fuel solution;

a continuous reactor (3);

dispensing means (2) of the fuel solution within the continuous reactor (3);

a separating tank (4) of the hydrogen stream and of the hydrolysis products.

means for drying the hydrogen stream (5) separated in the separator tank (4);

20. Installation according to claim 19, characterized in that it additionally comprises means for dispensing the hydrogen stream to at least one fuel cell (6).

21. Installation according to claim 19 or 20, wherein the continuous reactor (3) comprises the following elements:

a cylindrical body (7);

a lid with opening and closing (8) to regulate the supply of fuel solution;

an output device (9) of the hydrogen stream and of the hydrolysis products.

22. Installation according to claim 21, wherein said continuous reactor (3) also comprises at least one thermocouple (10).

23. Installation according to claim 21 or 22, wherein the continuous reactor (3) is constructed of a light and transparent material consisting of polymethylmethacrylate.

24. Steel monolith suitable for use as a support for a process catalyst according to any one of claims 1 to 16, wherein said monolith is obtained from a process comprising at least one machining and heat treatment step to improve catalyst adhesion.

25. Use of a steel monolith according to claim 24 as a support for a process catalyst according to any one of claims 1 to 16.