DE2220617A1 - METHOD FOR PRODUCTION OF HYDROGEN - Google Patents

Description

METALLGESELLSCHAFT '6 Frankfurt / Main, April 20

Aktiengesellschaft DrWer / GSch

Prov. No. 6982 LT

Process for the production of hydrogen

Hydrogen is used in many branches of chemical engineering, however, the quantities required in each individual case are very different. They range from a few cubic meters per hour z. B. in special factories of the pharmaceutical industry up to over one hundred thousand cubic meters per hour, for example in the synthesis of ammonia.

Numerous processes are available for the production of hydrogen. If the required quantities are large, most of the raw materials used today are natural gas, crude oil or crude oil fractions. By reacting with steam and optionally oxygen, gaseous and liquid hydrocarbons can be converted at high temperatures, usually above 700 ° C., sometimes up to 1400 ° C., to a gas mixture consisting essentially of hydrogen and the oxides of carbon and unreacted water vapor. These gases are converted, if necessary after purification and the addition of further water vapor, at lower temperatures over catalysts, which convert the carbon monoxide with water vapor to carbon dioxide and hydrogen. The CO content of the gas can be reduced very far, so that a very concentrated hydrogen is obtained _{after the CO 0 has been washed out.} In two-

German *

stage processes can be achieved by using copper-containing catalysis

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* · Ct -

gates at temperatures around 200 C in the second stage in this shift reaction Residual concentrations of CO of less than 0.5 vol. ' can be achieved. Where the remaining low CO concentrations of a few tenths of a percent when using the hydrogen, e.g. B. interfere as catalyst poisons, they can be known to Methanation catalysts are hydrogenated to methane, whereby the CO content in pure hydrogen to a few ppm (parts per million) can be lowered.

These processes are suitable for producing small amounts of hydrogen less well. Nevertheless, hydrogen is obtained in small quantities of a few hundred cubic meters per hour, for example by reacting liquid gas with steam over nickel-containing catalysts in externally heated reaction tubes and then Further processing of the generated cracked gas in practically the same way as in the production of large quantities. However, you have to considerable disadvantages are accepted. When splitting liquid hydrocarbons with water vapor in a tube furnace A practically methane-free gas is only obtained when this steam reforming at high temperatures, if possible above 800 C, with a high excess of water vapor and about atmospheric pressure will. In the large-scale industrial hydrogen production the methane content in the product gas is reduced by using a two-stage procedure that the steam reforming at A relatively small excess of steam is carried out at about 800 ° and high pressure, and that the methane-containing primary gas generated in this process in a second stage known as the secondary reformer at higher temperatures, which can considerably exceed 1000 C with an addition of oxygen, with the cleavage of the methane

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is set. This is a two-stage way of working for smaller systems practically not feasible, so that only single-stage steam reforming would remain, with methane-free hydrogen only with Atmospheric pressure can be generated.

The possible use of the at various points in large systems of the process accumulating heat in waste heat boilers and war- ■ meaustauschern and the associated increase in profitability is not or only very imperfectly in the smaller systems possible because the outlay on equipment is too great. Furthermore, the catalysts operating at high temperatures are in their Service life severely damaged if the systems are switched off and on again frequently and at short intervals. Such However, the mode of operation is often necessary, or at least at least, in those areas of technology in which only small amounts of hydrogen are required he wishes. An uninterrupted operation for several months is in contrast to the large systems mentioned at the beginning rarely found. A further disadvantage is therefore that systems of the type mentioned need a relatively long time until they deliver hydrogen in the desired amount. With frequent interruptions This disadvantage has a particular effect on operation, as the hydrogen system often already several hours before the consuming one Systems must be approached. Similar difficulties arise when production is terminated or interrupted.

For the production of small amounts of hydrogen, one already has long sought other ways. For example, ammonia, which can be transported and stored in liquefied form, evaporates and over suitable catalysts at elevated temperature converted into a gas ^ the hydrogen and nitrogen in the process

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ratio 3: 1 contains. The high nitrogen content is a nuisance to the most applications do not the course of the reactions, but represents a very undesirable ballast. For example, must in a hydrogenation which has a hydrogen partial pressure of 10 Atmospheres, when using a mixture of 3 parts hydrogen and 1 part nitrogen, the pressure in the reaction space must be increased in order to reach the desired partial pressure come. If a mixture of hydrogen and nitrogen in a ratio of 1: 1 is present in the reaction space at a total pressure of 20 atmospheres should be, then gas must be continuously withdrawn from the reaction chamber, with which a third of the original ammonia generated hydrogen is lost. Despite these drawbacks, the method is widely used because of its simplicity.

Hydrogen can also be obtained by the electrolytic decomposition of water. The electrolysis is advantageous here performed under pressure, whereby .sich a compression of the generated Hydrogen is unnecessary in many cases. The production of hydrogen by electrolysis is only economical if the price of electrical energy is not too high.

It has now been found that hydrogen can be produced in a simple manner by passing a mixture of methanol vapor and water vapor over fixed catalysts at elevated temperature and normal or elevated pressure. Those catalysts which contain copper as an essential component are particularly suitable for the process according to the invention. On such catalysts, the conversion of methanol with water vapor already takes place at temperatures of 200 to 250 ° C. Theoretically, the conversion of methanol with water vapor according to the equation CHLOH + H ₀ O = CO ₀ + 3 H gives me a gas

Ö Cl Ct Ct

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CO ₀ (25% by volume) and H ₀ (75% by volume). As an accompanying reaction

Δ Δ

however, follows the reversal of the conversion reaction already mentioned several times above according to CO ₀ + H ₀ = CO + HO, so that with

Ci Ci Ct

Conversely, a certain amount of CO is always formed. Since the fiction, contemporary "method at very low temperature

doors works, but the CO content of the gas produced is in extremely low, as desired.

The conversion of methanol with water vapor to hydrogen and carbon dioxide is endothermic. The reaction mixture must therefore have heat are fed. This can be done in a number of ways. The catalytic converter can be arranged in tubes that are heated from the outside or a heating medium is passed through pipes located in a reaction chamber filled with a catalyst. One special simple operation results when the mixture of methanol and water vapor before entering the catalyst bed is heated so high that the heat content of the mixture is sufficient to provide the heat of reaction.

The pressure can be freely selected within wide limits. Only at pressures above 50 ata does the methanol conversion become noticeably incomplete.

A modification of the process is that the reaction is carried out in two stages, the conversion of the methanol with steam to a gas which still contains some CO taking place in the first stage at temperatures of 250 to 300 ° C., while in the second stage the reaction takes place at temperatures below 250 C this CO is largely converted to CO ₀ and H _{0 with water vapor}

Δ Δ

is set, the necessary cooling of the gas mixture between the two stages can be easily achieved by injecting

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liquid water can be achieved.

The advantage of this two-step procedure is that as a result the higher reaction rate, which is greater at a higher temperature, in the first stage with a high space velocity over the catalyst which means a smaller amount of catalyst and a smaller reactor for a given throughput.

The catalysts to be used for the inven tion like ate process preferably contain copper as an essential component. These copper-containing catalysts also contain zinc and / or manganese in the form of their oxides and optionally one or more of the following elements in the form of the oxides: magnesium, Calcium, aluminum, titanium, vanadium, chromium. The catalysts can be prepared in a known manner by that from a solution which contains the appropriate elements in the form of nitrates, acetates or in another form by addition of alkali or ammonia, or alkali or ammonium carbonates, a precipitate is generated, which the metals in the form of Contains hydroxides or carbonates. This precipitate is filtered off, washed, dried and, with the addition of lubricants, how graphite is pressed into tablets. Before being used for the process of the invention, the catalysts become useful activated by treatment with hydrogen at temperatures around 200 ° C. Through this treatment, the copper gets into the transferred into metallic form. However, it is also possible to carry out this reduction with the mixture of methanol and steam. The contacts treated in this way, however, show a somewhat reduced service life.

The advantage of the production of hydrogen from methanol and water vapor according to the invention is that methanol is cheap Large chemical industry product in sufficient

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Quantities and high purity is available everywhere, and that no methane is formed in the fiction like aßen reaction of methanol with water vapor at normal or elevated pressure. This enables the production of inert gas-free hydrogen under pressure. A plant for carrying out the method according to the invention can be assembled from conventional elements of chemical process engineering. The main components of the system are evaporators and preheaters for the feedstocks methanol and steam, one or two catalytic reactors, which can be designed as adiabatic shaft reactors or as reactors with heat exchange elements, and a system for absorbing the carbon dioxide and for condensing the water vapor from the reaction product . The leaching of carbon dioxide can be used in conventional manner with an alkaline reacting, regenerable solvents · eg an aliphatic amine or alkanolamine _s example with mono- or diethanolamine, done. If absolute purity with respect to carbon monoxide is required of the hydrogen produced, a known methanation step can be provided in which residues of CO are catalytically hydrogenated to methane by the large excess of hydrogen. This methanation stage expediently follows the system for washing out carbon dioxide and for condensing the water vapor. A steam boiler is generally sufficient to supply the system with energy.

The simplicity of the system is due not least to the fact that the in catalytic processes often require very costly precautions for desulfurization of the feedstock or the primary intermediate products omitted. Since also the commercially available tiviuiisehe methanol Is offered sulfur-free, needs in the process according to the invention on the sulfur sensitivity of the catalysts

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lei to be taken into consideration.

The following examples, which relate to the preparation, may serve to explain the process according to the invention in detail judge suitable catalysts and their use in the process according to the invention.

example 1

Creation of a Kiipfer-zinc-aluminum contact.

A solution of 12 kg of sodium carbonate in 100 l of water at 90 ° C. is allowed to run 100 l of solution, likewise heated to 90 ° C., with constant stirring, which contains the following amounts of nitrates: 14.50 kg of Cu (NOg) ₂ 3 H ₂ O; 8.92 kg Zn (NOg) ₂ 6 H ₃ O and 3.75 kg Al (NOg) ₃ 9 H ₀ O. The precipitate obtained is filtered off with suction and washed with a total of 250 liters of warm water. It is then dried at 120 ° C., then heated to 300 ° C. for four hours and then pressed with the addition of 2% by weight of graphite to form tablets with a height of 5 mm and a diameter of 5 mm. The elements are in this. Catalyst in the atomic ratio Cu: Zn: Al = 6: 3: 1.

Example 2

Production of a copper-manganese-chromium contact, analogously to Example 1, a precipitate is first produced which contains copper and manganese in an atomic ratio of 1: 1. _{Cf O Q} is then incorporated into the moist filter cake in such an amount that the chromium content in the finished contact is 20 atom%. The further processing takes place as in example 1.

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Example 3

Production of hydrogen.

For the conversion of methanol with water vapor, an apparatus is used which contains ten pipes, each 50 mm in inner diameter and 2 m in length, in an outer jacket with inlet and outlet lines. The ends of the tubes are welded into a tube sheet and contain 40 l of a contact made according to Example 2 containing copper, chromium and manganese. Steam at 30 atmospheres pressure, superheated to 340, is introduced into the outer jacket. The resulting steam condensate is discharged in a known manner. A mixture of 48 kg of methanol vapor and 100 kg of water vapor is passed through the pipes under a pressure of 5 atmospheres. With the steam condensate discharged from the outer jacket of the apparatus, an evaporator is heated in which the methanol is evaporated under a pressure of 5 atmospheres. A gas emerges from the tubes filled with catalyst, which, calculated dry, contains -Λ 2 vol.% CO, 24.9 vol.% CO ₀ and 74.9 vol.% H ₀

3 ■

holds. The dry amount of gas is 135 Nm. Gets out of the gas

3 washed out the carbonic acid, 101 Nm of hydrogen are obtained mi «3 vol.% CO.

Example 4

Production of hydrogen.

In a container with an internal diameter of 80 mm and a length of 1500 mm there are 6 liters of a copper produced according to Example 1, Zinc and aluminum containing catalyst. In a gas-heated evaporation apparatus, a mixture of 5 kg of methanol and 30 kg of water evaporated at a pressure of 30 ata and brought to a temperature of 340 ° C. At this temperature the mixture enters the catalyst. Through the Implementation, the temperature drops until it exits the container

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ter down to about 220 C. It flows hourly from the catalyst

14.1 Nm of a gas that contains CO and H in a ratio of 1: 3

Δ Δ

and its CO content is below 0.05% by volume.

Example 5

Production of hydrogen.

A mixture of 72 kg of methanol and 180 kg of steam, preheated to 300 ° C., is introduced under a pressure of 3 atmospheres into 40 l of a catalyst which contains copper, zinc and chromium in an atomic ratio of 3: 5: 2 and whose temperature is embedded in the layer , pipes through which flue gas flows is kept at 280 to 290 C. In the gas mixture emerging from this layer
liquid water is injected in an amount of 7 kg per hour. This causes the temperature to drop to 230 C _{11 at} this temperature
the mixture in 60 l of a copper, chromium and manganese-containing catalyst, which was prepared according to Example 2, becomes cloudy. 180 Nm of cracked gas by volume are obtained per hour. The zinc and chromium-containing catalysts known for high pressure methanol synthesis can also be used in the first stage of this procedure.

3Q9846 / 06Q9

Claims (11)

- ii PATENT CLAIMS 1) Process for the production of hydrogen, characterized in that a mixture of methanol and water is passed in vapor form at temperatures of 150 to 350 C and normal or elevated pressure over a catalyst and unconverted water vapor and carbon dioxide per se from the gas mixture formed known way removed. 2) Method according to claim 1, characterized in that catalysts are used which contain copper as an essential component. 3) Method according to claim 2 _a characterized in that catalysts are used which, in addition to copper, also contain zinc and / or manganese and optionally one or more of the following elements: magnesium, calcium, aluminum, titanium, vanadium, chromium. 4) The method according to claim 3, characterized in that all the elements contained in the catalyst are originally in the form of their oxides or carbonates and that the catalyst before using a what
is bred. generation of a hydrogen treatment at temperatures around 200 C and 5) Method according to one of claims 1 to 4, characterized in that the reaction of the methanol with water vapor takes place in an apparatus which contains the catalyst in rooms, which either from the outside through the walls or through devices embedded in the rooms on indirect Ways heat is supplied. 309846/0609 6) Method according to claim 5, characterized in that the catalyst is kept at temperatures between 180 and 300, preferably 200 to 250 ° C. 7) A method according to any one of claims 1 to 4, characterized net gekennzeich that the reaction is carried out in two stages, methanol and water vapor reacted in a first stage at temperatures of 250 to 350, preferably 260 to 300 C and then optionally after the addition of liquid water to lower the temperature in a second stage at temperatures of 180 to 250, preferably 200 to 230 C react further. 8) Method according to one of claims 1 to 4, characterized in that a mixture of methanol and water vapor on one over 300 ° C lying temperature is heated and implemented without additional heat supply on the catalyst. 9) Method according to claim 8, characterized in that the molar ratio of water to methanol is above 5. 10) Method according to one of claims 1 to 9, characterized in that the pressure during the reaction is up to 50 ata, preferably 1 to 25 ata. 11) A method according to any one of claims 1 to 10, characterized in that known from the resulting by the reaction gas mixture unreacted water and COV i * ¹ per se Ci Way removed and in the gas thus treated residues of carbon oxides in a known manner at elevated temperature hydrogenated to methane over suitable catalysts. 309846/0609