RU216707U1 - Hydrogen production device - Google Patents

Abstract

The utility model relates to a device for producing pure hydrogen from oxygen-containing organic compounds of C1 chemistry, such as methanol or dimethyl ether. A device for producing pure hydrogen is proposed, consisting of a fuel processor for the catalytic conversion of oxygenates into a hydrogen-containing gas at a temperature of 320-350°C and atmospheric pressure and a hydrogen pump with a polymeric proton-conducting membrane based on polybenzimidazole. The technical result is hydrogen with a purity of 99.97 vol.%. 1 ill., 2 tab.

Description

The utility model relates to devices for producing pure hydrogen from oxygen-containing organic compounds of C1 chemistry, such as methanol and dimethyl ether.

Recently, hydrogen has been considered as an alternative and environmentally friendly energy carrier. Traditional methods of hydrogen production - catalytic transformations of hydrocarbons - are usually accompanied by the formation of such products as CO, CO ₂ , CH ₄ and (N ₂ - in the case of partial oxidation with air). Therefore, an efficient hydrogen purification technology is an urgent task for both the industrial and energy sectors. The following hydrogen separation technologies are known from the state of the art: cryogenic, adsorption, and membrane technologies, and devices for their implementation. These methods are very energy intensive, expensive to operate, and require complex maintenance.

The method of electrochemical purification of hydrogen in a device called "hydrogen pump" was first proposed 50 years ago (US 3475302 A, C01B 3/50, 10/28/1969; US 3489670 A H01M 8/06, 01/13/1970). The principle of operation of a hydrogen pump is that a hydrogen-containing mixture is supplied to the anode space of an electrochemical device - a fuel cell or an electrolyzer operating in an electrolytic mode. An external DC power supply is required to run the device. Hydrogen molecules are oxidized at the anode to protons, which migrate through the proton-conducting polymer membrane to the cathode. The electrons pass through the outer circuit to the cathode and recombine with protons, forming pure hydrogen.

One of the first works (J.M. Sedlak, J.F. Austin, A.B. LaConti // Int. J. Hydrogen Energy. 1981. V.6 P.45) demonstrated the use of a fuel cell with a proton-exchange membrane of the Nafion type for electrochemical pumping of hydrogen from low to high pressure and hydrogen extraction from an inert gas to obtain high purity hydrogen. This scheme allows hydrogen to be concentrated from the exhaust gases at the outlet of the fuel cell for recycling or subsequent storage.

The hydrogen pump can also concentrate hydrogen downstream of the fuel processor for delivery to the fuel cell. The main disadvantages of fuel cells with a low-temperature Nafion-based proton-conducting membrane as a hydrogen pump are their low resistance to impurities, such as carbon monoxide CO, and the need to humidify the supplied gas mixture. For example, at operating temperatures of a hydrogen pump < 100°C, platinum electrodes are already poisoned at a CO content of 2–100 ppm due to its strong adsorption on the catalyst surface.

The high thermal stability and chemical resistance of the proton-conducting membrane based on polybenzimidazole (PBI) at high operating temperatures up to 200°C suggest significant advantages for use in a hydrogen pump, namely: provide an increased resistance of the electrode to gaseous impurities containing CO (up to 5 vol.% ); fast electrode kinetics for both anodic and cathodic reactions (US 9806365, С01B 3/503, С25B 1/04, B01D 53/32, 10/31/2017).

In recent years, devices for producing hydrogen have been intensively studied in connection with the development of compact fuel processors - devices for producing hydrogen. The production of hydrogen from hydrocarbons (natural gas, diesel fuel, etc.) is carried out in reactors at high temperatures (above 700°C), and the resulting gas mixture contains a significant amount of CO, more than 10 vol.%. To reduce the concentration of CO and increase the concentration of hydrogen, a CO steam reforming reactor (CO + H ₂ O = CO ₂ + H ₂ ) is usually used at the 2nd stage. Industrial copper-containing catalysts Cu-Zn-Al-O _x provide a reduction in CO concentration to ~2 vol.%.

A gas mixture similar in composition can be obtained in one stage by steam reforming of oxygenates (for example, methanol or dimethyl ether). This is due to the high activity and selectivity of bifunctional copper-containing catalysts, the low temperature of the process of steam reforming of oxygenates compared to traditional hydrocarbons, and the absence of impurities of sulfur compounds in the feedstock, which are poisonous for most catalysts, and the resulting gas mixture contains no more than 2 vol. CO.

As noted above, a mixture with this amount of carbon monoxide is suitable for supply to a hydrogen pump in order to purify hydrogen from impurities. Thus, the combination of a fuel processor for producing hydrogen from oxygenates and a hydrogen pump will make it possible to create a fairly compact device for producing pure hydrogen.

Depending on the conversion method (steam, air, steam-air), the choice of initial reagents, process conditions (temperature, pressure, flow characteristics), the composition of the obtained reformate, the presence or absence of a catalyst, the fuel processor consists of different systems, blocks, elements, components . Typically, a fuel processor based on liquid fuels includes a starting device, reagent supply systems, an evaporator, a steam heater, and a catalytic reactor.

Closest to the proposed technical solution is a device for the implementation of steam catalytic conversion of methanol, and/or dimethyl ether, and/or dimethoxymethane (RU 138423, B01J 7/00, 03/20/2014), which contains a catalytic reactor for conversion, a unit for preparing the initial mixture , consisting of an evaporator, a superheater and a mixer of the reacting initial mixture, a heating device with a built-in afterburner for anode gases resulting from the operation of fuel cells. The disadvantage of the claimed device is the composition of course gas containing 59-61% hydrogen and impurities.

The task to be solved by this utility model is the creation of a compact device for producing high-purity hydrogen from oxygenates (methanol or dimethyl ether).

The technical result is hydrogen with a purity of 99.97 vol.%.

The most suitable solution for creating a compact hydrogen production device is the use of a fuel processor (reformer), in which dimethyl ether or methanol is steam reformed on a catalyst that is copper, cerium and aluminum oxides deposited on a heat-conducting metal carrier, such as fechral (CuO /CeO ₂ /Al ₂ O ₃ /FeCrAl). The use of this catalyst, due to its high catalytic activity and selectivity, makes it possible to obtain a hydrogen-enriched gas mixture with a low content of carbon monoxide (<2 vol.%). It should be noted that a gas mixture of this composition can be used further for the electrochemical purification of hydrogen from impurities using a hydrogen pump with a polymeric proton-conducting membrane based on polybenzimidazole.

The problem is solved by a device for obtaining pure hydrogen, which is a fuel processor and a hydrogen pump connected in series with a polymeric proton-conducting membrane. The device includes a fuel processor for producing hydrogen-containing gas by catalytic conversion of oxygen-containing organic compounds C1 (oxygenates). In this case, dimethyl ether (DME) or methanol is used as oxygenates, and the steam reforming of oxygenates is carried out at atmospheric pressure and a temperature of 320-350°C using a block catalyst containing, for example, oxides of aluminum, cerium and copper, sequentially deposited on the surface of the block made of fechral mesh. The fulfillment of the above requirements ensures the complete conversion of the raw material into a hydrogen-enriched gas mixture (reformate) with a low CO content (less than 5 vol.%). The resulting reformate is sent to a hydrogen pump with a polymeric proton-conducting membrane. The hydrogen pump uses a polymer proton-conducting membrane based on polybenzimidazole, operating at a temperature of ~170°C.

The composition of the block structured catalyst includes copper up to 5 wt.%, cerium oxide - up to 5 wt.%, aluminum oxide - 10 wt.%, the rest is Fechral.

The proposed device is schematically presented in the Figure, where 1 - evaporator / mixer, 2 - catalytic reactor, 3 - reformate, 4 - anode space, 5 - polymeric proton-conducting membrane based on polybenzimidazole, 6 - cathode space, 7 - purified hydrogen, 8 - source direct current.

The device works as follows.

In the fuel processor, consisting of a flow tubular reactor (2) with a block structured catalyst CuO/CeO ₂ /Al ₂ O ₃ /FeCrAl weighing 1.5 g, heated to 320-350°C, using systems for the preparation and supply of reagents (1 ) a mixture of oxygenate with water is fed at a rate of 2 l/(g _cat h) at atmospheric pressure. The catalyst has a composition, wt.%: copper oxide - 2, CeO ₂ - 4, Al ₂ O ₃ - 6, the rest - fechral. The catalyst ensures the complete conversion of the raw material into a hydrogen-containing gas (reformate) with a concentration of H ₂ ~ 70 vol.% and CO less than 2 vol.%.

The reformate (3) after the fuel processor is fed into the anode space (4) of the hydrogen pump. Hydrogen molecules are oxidized at the anode to protons, which migrate through the proton-conducting polymer membrane (5) based on polybenzimidazole (ZBT GmbH, Germany) towards the cathode space (6). The electrons pass through the external circuit to the cathode and recombine with protons, forming pure hydrogen (7). An external DC power supply (8) is required to start the device.

The results of experiments on the production of hydrogen in the proposed device are shown in tables 1 and 2. As oxygenates, a mixture of methyl alcohol and water is used at a ratio of CH ₃ OH:H ₂ O=47:53 vol.% and a temperature in the reactor of 320°C (table 1 ) or a mixture of DME and water at a ratio of CH ₃ OCH ₃ :H ₂ O = 24:76 vol.% and a temperature in the reactor of 350°C (table 2). The concentration of H ₂ after electrochemical purification in a hydrogen pump with a membrane based on polybenzimidazole is 99.97 vol.%.

Table 1 Initial mixture, vol.% Composition of the Reformed, vol. % The concentration of H ₂ after the hydrogen pump, vol.% _{H2 CO2} CO _H2O CH ₃ OH: H ₂ O = 47:53 71 22.6 1.6 4.5 99.97

table 2 Initial mixture, vol.% Composition of the Reformed, vol. % The concentration of H ₂ after the hydrogen pump, vol.% _{H2 CO2} CO DME _H2O CH ₃ OCH ₃ : H ₂ O \u003d 24:76 70 22.4 2 0.5 4.5 99.97

Claims (1)

A device for producing pure hydrogen, which is a fuel processor connected in series, designed to carry out the catalytic conversion of oxygen-containing organic compounds, such as dimethyl ether or methanol, into hydrogen-containing gas at a temperature of 320-350 ° C and atmospheric pressure using a block catalyst containing aluminum oxides , cerium, and copper, sequentially deposited on the surface of a block made of a fechral mesh, and a hydrogen pump with a polymeric proton-conducting membrane based on polybenzimidazole.

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