USRE19733E - Process for the production of - Google Patents

Description

Reissued Oct. 22, 1935 UNITED STATES 19,733 PROCESS FOR THE PRODUCTION OF HYDROGEN Fritz Hansgirg, Badenthein, Carlnthia. Austria,

assignor to American poration, Pittsburgh, Pa.,

Mme-lam Metals Cora corporation of Delaware No Drawing. No. 1,836,919, dated Dcoember 15, 1931, Serial No. 451,500, May 29,

1930. Application tor reissue Serial No. 715,378

Claim.

2C+2HzO=2CO+2H:-57.2 kilogram cals. (I)

1 At lower temperatures, below 1,000 0., C01 is formed, in addition to C0, in accordance with the equation C+2m0=COa+2H:-l8.0 kilogram cals. (11) A state of equilibrium, dependent on the temperature, is established between C0 and CO2, which is displaced, in favor of the CO, at high temperature. Since theoretically, the formation of hydrogen according to Equation 11 leads to a gaseous mixture tree irom carbon monoxide and, in addition requires a far smaller expenditure of heat, it would be e! advantage to conduct the drogen process in accordance with that equat on. The gaseous mixture obtained at lower temperature would also be the most suitable for the technical recovery of hydrogen, since the precipitation 01' carbon dioxide is far simpler, in practice than the elimination 01 carbon monoxide. The dlfliculty, however, arises that the reaction velocity. which becomes progressively smaller as the temperature falls, is far too slow for practical working at those temperatures at which the equilibrium is established in iavor of Equation 11.

Formerly, attempts were frequently made to overcome this inconvenience, especially in order to make possible the direct recovery of hydrogen, almost free from carbon monoxide, by conducting the process in accordance with Equation 11. In order to increase the velocity of the reaction, ithasbeen proposed, inter alia, to employ hydrates or carbonates oi the aikalis, or the corresponding water-soluble compounds, of the alkaline earths as catalysts. According to this known process. materials containing carbon, impregnated with the said water-soluble compounds, were to be exposed, in an incandescent state, to the action of ordinary or superheated steam.

The proposal advanced in this direction, however, did not prove successful, and consequently, for the technical recovery of hydrogen from water gas, the water gas process was allowed to proseed at high temperature, the carbon monoxide MII'OII 13, 1934,

being then removed from the resulting gaseous mixture in a separate working operation.

This result was secured, in addition to liquefaction, chiefly by oxidizing the carbon monoxide to carbon dioxide by the aid of steam and with the agency oi catalysts. This process is economical, it the oxidation 0! the carbon monoxide be carried out under high pressure, but, in its really valuable methods or procedure, it is by no means simple, and at the same time, furnishes a mixture of hydrogen and carbon dioxide, which still always contains carbon monoxide, even though in small amounts, so that a chemical purification (such as washing the gas with solutions of cuprous salts) is still necessary in order to obtain pure hydrogen.

Another process for the recovery 01 pure hydrogen from water gas containing carbon monoxide, has recourse, in the oxidation of the carbon monoxide by means 01' steam, to fixing the carbon dioxide by substances capable of absorbing same, lime in particular, for accelerating the reaction. By the continuous removal of the carbon dioxide from the reaction mixture, the equilibrium associated with the reaction CO+H2O=H2+CO2 is displaced in favor of the carbon dioxide. in carrying out this process, the water gas is passed, together with an excess of steam, over lime which is heated, in a retort, to a temperature below the decomposition temperature of calcium carbonate. An addition 01. catalytic substances has been found to facilitate the reaction. As carbon dioxide-absorbing substance lump lime is preterably employed, which is rapidly transformed into calcium carbonate, even in the interior, during the passage of the water gas. From this carbonate, quick lime is recovered by calcining, and is again brought into reaction with water gas. Further proposals have been made, in order to improve this process, the employment of steam in exactly, or approximately, stoichiometric proportions being particularly recommended.

The present invention solves, in the first place, the problem of the direct production cl 9. mixture of hydrogen and carbon dioxide, low in, or tree 5 from, carbon monoxide, by the action 01 steam on carbon (or substances containing carbon), in the presence of additions which accelerate the reaction, and under conditions substantially approximating Equation 11 o! the water gas process. According to me invention, the process is conducted with the employment of magnesia, magnesium carbonate or magnesium hydroxide, as catalysts, at a temperature which, though, above the decomposition temperature 01 magnesium g carbonate, does not substantially exceed 750 C. The invention is based upon the fact that the equilibrla associated with the reaction ZCOF C-i-C are of decisive importance for the production of hydrogen free from carbon monoxide. From this point of view, the temperature of 500 most favorable temperature for the reaction, in that, at this temperature, the equilibrium is practically completely displaced, in favor of carbon dioxide. Above 500 C., CO: in the presence of J is reconverted into C0 to an increasing extent as the temperature rises, so that, for the forma tion of a gaseous mixture low in carbon monoxide, the range of temperature above 750 C., is not longer to be considered. Below 700- 750 0., however, the reaction veiocity of the hydrogen process is already retarded to such an extent that the reaction cannot be carried out on a technical scale. The problem therefore arose of finding an eflective and insensitive contact mass which will enable the reaction velocity of the formation of hydrogen to be suillciently increased in the range of temperature below 750 C. A mixture of carbon with magnesium carbonate has been found admirably suited tor the purpose. This is based on the relatively low decomposition temperature of magnesium carbonate, which can be reduced to even below 500 C. by diluting the gas phase with steam, and thereby lowering the partial pressure of the carbon dioxide.

At 500 C. the reaction occurs to form an equilibrium, when the amounts of steam employed correspond to the stoichi ometrical proportions of Equation II, or only slightly exceed those proportions. Magnesium carbonate therefore has the capacity of rapidly absorbing, and again parting with, carbon dioxide in the hydrogen process conducted in accordance with Equation II, at the optimum temperature suitable for reliably preventing the formation of carbon monoxide. This is not the case, either with the alkali carbonates or calcium carbonate. According to the invention, the performance of the hydrogen process with the use of magnesium carbonate as catalyst, at temperatures which do not substantially exceed 500 C. enables hydrogen, practically free from carbon monoxide, to be obtained directly.

If, for example, wood charcoal be mixed with magnesium carbonate, in theproportions of parts by weight of charcoal to 5-25 parts by weight of magnesium carbonate, and such mixture be treated, at about 500 C., with the stoichiometrical amount of steam (corresponding to 2 molecules of H20 to 1 moi. of C). the reaction proceeds in practical accordance with Equation II and with quite suiflcient velocity. The process is also of importance for the production of mixtures of hydrogen and carbon dioxide. However, since, as is known, the carbon dioxide can be easily separated from this mixture, the process primarily affords a practically applicable method for the recovery of pure hydrogen.

or course, magnesium oxide or hydroxide, which are immediately converted into magnesium carbonate, can be introduced into the reaction in place of magnesium carbonate. The process can also be carried out with crude materials which contain magnesium oxide or hydroxide in sumcient amount. The catalyst remains unaltered in composition and active, without regeneration,

C.isthe so that only the gasifled carbon has to be replaced. Bince the course of the reaction for the formation of hydrogen in accordance with Equation II is slightly endothermic, the reaction temperature of approximately 500 C. can be maintained by the application of a very small amount of heat.

Claims for gasifying charcoal with steam, in the specified manner, for the direct production of a mixture of hydrogen and carbon dioxide, free 10 from carbon monoxide, are contained in Patent No. 1,926,587, issued September 12, 1933, on an application constituting a division of my original application Serial Number 457,500. The invention is, however, especially useful in eliminating, 15 or substantially eliminating, carbon monoxide from water gas, or other gaseous mixtures of similar composition, containing same, and in this aspect of the invention the gas, or gaseous mixture, containing carbon monoxide, is passed, in 20 association with steam, over a mixture of charcoal (or substances containing carbon) and magnesium oxide or hydroxide or carbonate, which is maintained at a temperature above the decomposition temperature of magnesium carbonate, but not substantially exceeding 500 C. The course of the reaction may be expressed by the following equations:

Since the reaction 2CO=C+COz is decidedly exothermic, only a very small supply of heat from outside is required also in this case, in order to 35 maintain the temperature at about 500 C. If, in this method of carrying out the process, the amount of steam added be only Just suflicient for the carbon formed in accordance with the equation 2CO=C+CO2 to combine, in the nascent 40 state, with the steam, in accordance with the Equation H of the hydrogen process, and form carbon dioxide, the catalytic material will remain entirely unaltered. The process can be carried out quietly, without any further addition of 45 carbon being needed. In any event, however, no reactivation of the catalyzer material is required, because, even in this case, the working temperature is higher than the decomposition temperature of the magnesium carbonate.

It is suificient to bring the gases, prior to their passing out of the apparatus, into contact, for 20-30 seconds, with a layer of contact material which is maintained at a temperature not substantially exceeding 500 C. With this proviso, 55 zones of the contact material which are traversed by the gases in an earlier stage, can also be heated to temperatures between 500 and 750 C., for the purpose of accelerating the reaction.

Example 1 An intimate mixture of Wood charcoal and calcined magneslte, and containing, for example, 1 part by weight of magnesium oxide for every 4 parts by weight of charcoal, is allowed to de- 65 scend through an externally heated shaft furnace in which the contact mass is maintained at about 500 C. Steam is passed, in counter flow. through the descending charge. The contact mass, low in charcoal, issuing at the lower 70 end of the shaft is again mixed with sufiicient added charcoal to restore the desired magnesium oxide-charcoal ratio, above noted, and the resulting mixture is returned into the top of the shaft furnace, thus permitting a cyclic opera- 7o conditions of the present be converted per hour. also be replaced by a rotary tube furnace, oper- Example 2 An intimate mixture is prepared from finely ground, calcined magnesite and wood charcoal, in the proportions of 1: 4 to 1: 5, and a granular mass is formed by the addition oia binding agent, such as a solution of an alkali carbonate. The contact mass is preferably introduced into externally heated tubes. The gaseous mixture to be purified is passed over the heated contact mass in association with the stoichiometric amount of steam, in the proportion 1 mol. H201 moi. C0.

Under these conditions. any desired quantities of gaseous mixtures containing carbon monoxide can be converted into carbon dioxide with one and the same charge of contact material, without any increase or diminution of the initial amount of the latter, provided the amount oi steam employed to the carbon mon oxide content.

According to a heretofore proposed. metallic nickel and cobalt, deposited on pumice or other porous carriers, are employed for eliminating the carbon monoxide from water gas, by oxidizing it to carbon dioxide at a temperature of 350-450" 0. Within the scope of this process, it is also proposed. by the subsequent or simultaneous passage of steam. to utilize the carbon, deposited in accordance with the reaction 2CO==CO:+C, for the process, in accordance with equation C+2Ha=2Ha The value, as an improvement, of the present process which, by the employment of a very cheap and insensitive contact mass, solves the oi! steam to form hydrogen, low in, or free from, carbon monoxid and also enables the complete subsequent elimination oi carbon monoxide from mixtures of the same kind containing the latter, becomes particularly apparent by comparison with the said known process which merely aims to free water gas from carbon monoxide by subsequent oxidation with the aid 01' expensive and sensitive catalysts.

I use the term magnesium oxide in the following claims to include not only preformed magnesium oxide but also magnesium compounds yielding um oxide under the temperature and mixtures oi magnesium oxide with such substances.

what I claim is:

1. The process of obtaining hydrogen, including reacting a mixture carbon monoxide and steam in the presence of an intimate mixture of a carmaterlal and magnesium oxide, the steam being present in amount insuflicient to react substantially at the working temperature with the carus material.

2. The process of obtaining hydrogen, including reacting a mixture 0! carbon monoxide and steam in the presence of an intimate mixture of a carbonaceous material and magnesium oxide at a temperature of substantially 500 C., the steam :5 being present in amount insufficient to react substantially with the carbonaceous material.

3. 'me process ofobtaining hydrogen, including reacting a mixture 01 carbon monoxide and steam in the presence of a mixture of charcoal and magnesium carbonate, the steam being present in amount insumcient to react substantially at the working temperature with the carbonaceous material.

4. The process of obtaining hydrogen, in'cludi5 ing reacting a mixture of water gas and steam in the presence of a mixture of charcoal and magnesium carbonate, the steam being present in amount insuflicient to react substantially at the rezii'mking temperature with the carbonaceous ma- 2O 5. The process of obtaining hydrogen, including reacting a mixture of water gas and steam in the presence 01' a mixture comprising 100 parts of charcoal and 5 to parts of magnesium car- 25 bonate, the steam being present in amount insufficient to react substantially at the working temperature with the carbonaceous material.

6. The process of obtaining hydrogen, including presence naceous material and magnesium oxide. the steam being present in amount insuflicient to react substantially at the working temperature with the carbonaceous material.

'1. The process of obtaining hydrogen, including reacting a mixture of water gas and steam in the presence of an intimate mixture 01 a carbonaceous material and magnesium hydroxide, the steam being present in amount insumcient to re- 4 act substantially at the working temperature with the carbonaceous material.

8. The process of obtaining hydrogen, including reacting a mixture of water gas and steam in the proportion of 1 mol. HzOzi moi. CO in the 5 presence of a mixture of finely ground calcined magnesite and wood charcoal in the proportion of 1:4 to 1:5.

9. The process of obtaining hydrogen, including reacting a mixture of a carbon monoxidecontaining gas and steam in the presence oi a mixture of a carbonaceous material and magnesium oxide at a temperature of substantially 0., the steam being present in amount insuflicient to react substantially with the carbonaceous material whereby to form hydrogen and carbon dioxide according to the equation 12. 'lheprooeaotobtflnlng idmemincludreoctingamiztureotcarbommnnozldeand 13. The process of obtaining hydrogen, includingreactingamlxtureotwotergasmdatenmln the presence ofamlxtureofa 1 mnportion at lzitolzfi made terlal and magnesium oxide oontflnlng in addition alkali carbonate, the steam being present in amount insumcient to react substantially at the working temperature with the ma.- terial.

Certificate of Correction Reissue No. 19,733. October 22, 1935.

[SEAL] LESLIE FRAZER, Acting Ummidsionar f Patents.

12. 'lheprooeaotobtflnlng idmemincludreoctingamiztureotcarbommnnozldeand 13. The process of obtaining hydrogen, includingreactingamlxtureotwotergasmdatenmln the presence ofamlxtureofa 1 mnportion at lzitolzfi made terlal and magnesium oxide oontflnlng in addition alkali carbonate, the steam being present in amount insumcient to react substantially at the working temperature with the ma.- terial.

Certificate of Correction Reissue No. 19,733. October 22, 1935.

[SEAL] LESLIE FRAZER, Acting Ummidsionar f Patents.