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I N D U S T R I A L A N D ENGINEERING CHEMISTRY
Vol. 22, No. 4
Absorption of Carbon Monoxide by Cuprous Ammonium Salts' William Gump and Ilse Ernst DRESDEX,GERMANY
H E separation of water gas into hydrogen and carbon monium chloride, and 7.5 parts of water is able to absorb monoxide is an important technical problem, par- carbon monoxide to the amount of nineteen times its own ticularly in the preparation of pure hydrogen for the volume a t 0" C. and of thirteen times at 10" C. A higher synthesis of ammonia. This separation can be accomplished concentration of cuprous ions increases the absorption power by refrigeration (Linde system), where the carbon monoxide in a proportional ratio. A solution with 3 parts of cuprous is liquefied under high pressure. However, the installation chloride will absorb more than fifteen times its own volume cost of the Linde apparatus is high compared with that a t 10" C., but here there is danger that the carbon monoxide necessary for the removal of carbon monoxide by chemical addition compound, being less soluble, might be precipitated methods of absorption. below 10" C. Solutions of cuprous amThe experimental determonium salts are generally mination of the absorption A search for a new absorbent for carbon monoxide used to absorb the carbon power of these solutions was for use in the separation of water gas into carbon monoxide and they are realways made with water gas monoxide and hydrogen is described. Various mixtures generated by heating. This c o n t a i n i n g about 40 per containing cuprous ammonium salts were studied and absorption of carbon moncent carbon monoxide. A found to be unsatisfactory, and then a large number oxide b y cuprous amnioc e r t a i n amount of water of organic acids and phenols as substitutes for the nium salts mas thoroughly gas (usually 10 liters) was carbonate in the cuprous oxide-ammonium carbonates t u d i e d b y t h e writers, passed for 4 5 minutes ammonia mixture were investigated. Cuprous amthrough several wash bottles particularly f r o m a t e c 11 monium lactate was found to have the most favorable nical standpoint, and has filled w i t h t h e c u p r o u s properties as an absorbent for carbon monoxide. This chloride-ammonium c h l o led to an improved absorbabsorbent has also been tried with success on a semiride or any other absorpent for carbon monoxide. plant scale. tion solutioii and cooled to Their interest was espet h e d e s i r e d temDerature. c i a l l y in the preparation The saturated solition was of p u r e ,carbon monoxide from water gas, but this new absorption solution will be then heated to 100" C., and the evolved gas was received quite as useful where pure hydrogen for the synthesis of am- in a small, calibrated gas tank. Its volume and content of monia is desired. Most of the carbon monoxide in the mater- carbon monoxide were determined and the found volume gas mixture is first oxidized catalytically to carbon dioxide Tyas reduced to 0" C. and 760 mm. preqsure. Although this cuprous chloride-ammonium chloride mixand the latter is removed by scrubbing it out Tyith water under pressure. The small amounts of carbon monoxide ture is an excellent absorbent for carbon monoxide, it was remaining in the gas produced, being poisonous to the catalyst, found to be unsatisfactory for technical use on account of are then completely eliminated by ammoniacal cuprous difficulties in getting a resistant metallic material. Iron and all iron-containing alloys shorn a strong tendency toward solutions. The absorption of carbon monoxide by cuprous chloride deposition of copper and the iron gradually goes into soluhas been known since 1850 (9) and was thoroughly studied tion. If iron is replaced by copper or other metals which do by Berthelot ( 2 ) several years later. Since the introduction not precipitate the copper from the absorption mixture, these of this method for the determination of carbon monoxide metals or alloys are also quickly corroded. The writers have tested almost all available metals and alloys without success. many papers on this subject have appeared (.5). Two different absorption mixtures containing cuprous The experiments were carried out in acid, neutral, and alkachloride are applied ( 3 ): (1) cuprous chloride, hydrochloric line (all t o litmus) cuprous chloride-ammonium chlorideacid, and water; and (2) cuprous chloride, ammoniuiii (ammonia) solutions. As could be expected, the metals, with the exception of copper, show greatest stability in the chloride, ammonia, and water. The hydrochloric acid solutioii is not practical for tecli- alkaline medium, but none is resistant enough for technical nical purposes and furthermore its absorption power is loner purposes. Non-metallic materials, such as rubber or stonethan that of the ammoniacal mixture ( I O ) . The present ware, could not be considered on account of their iiisufficient work was therefore limited to the investigation of the am- heat conductivity. It was surprising that copper goes into solution very rapidly. moniacal system. It was first believed that the copper is dissolved on reducing Mixtures Containing Cuprous Chloride the cupric salt formed by the air in the absorption vessel or The ordinary solution of cuprous chloride and ainiiioniuin by the small amounts of oxygen in the water gas. But much chloride in ammonia liquor ( 3 )was used first, but it was soon more copper went into solution than would be needed for the found that a mixture which has no free ammonia and which reduction of cupric salt and the copper was not resistant reacts acid t o litmus absorbs better than the ammoniacal nhen either oxygen or cupric ion was carefully excluded. Cuprous oxide-ammonium chloride and cuprous chloridesolution. Furthermore, no ammonia is lost by evaporation during the heating period of regeneration. A solution of, ammonium sulfate mixtures, with and without ammonia, for instance, 2.0 parts of cuprous chloride, 2.5 parts of am- were also investigated, but without success. Either the absorption power or the resistance toward metals was inPresented before t h e Division of Gas and 1 Received April 11, 1929 sufficient. Fuel Chemistry at t h e 77th Meeting of t h e American Chemical Society, Kanziier ( 7 ) adds copper sulfate, ammonium sulfate, or Columbus, Ohio, April 29 t o May 3, 1929.
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I S D C S T R I A L A S D E T G I S E E R I S G CHEMISTRY
April, 1930
another sulfate to the ammoniacal cuprous chloride solution in order to protect the iron of the apparatus. The present writers did not see any value in this addition of a sulfate. Damiens ( 4 ) proposed a new absorbent, cuprous sulfate ,in the presence of concentrated sulfuric acid. This mixture shows good absorption power, but the writers did not like to apply it for technical use on account of the sulfuric acid. Absorbents Containing Ammonium Carbonate or Formate
If the ammonium chloride of a cuprous oxide-ammonium cliloride-ammonia solution is replaced by ammonium carbonate or ammonium formate, absorbents are obtained where the tendency toward deposition of the copper by the iron of the apparatus is greatly reduced. These cuprous ammonium carbonate and ammonium formate-ammonia mixtures were first mentioned in a German patent ( I ) of the Radische Anilin und Soda Fabrik in 1914, and were thoroughly studied by Hainsworth and Titus (6) and by Larson and Teitsworth (8) in this country. However, tlie use of ammonium carbonate is not recommended because it decomposes into ammonia and cdrbon dioxide a t temperatures above 80" C. and because, in the presence of carbon monoxide, copper is precipitated a t higher temperatures (above GO" C.) according to the equation: C U ~ ( N H ~ ) . $ C OCO ~ 2H20 ---+2(NHa)zCO3 ~ C U This reaction also takes place with ammonium formate, but' to a much less degree. Larson and Teitsworth could find ammonium carbonate in a cuprous ammonium formate solution after carbon monoxide had passed through. The present writers were able to confirin this observation. The reaction of forming ammonium carbonate and of precipitating copper proceeds more rapidly a t higher temperatures, with increased concentration of cuprous salt, and with higher pressures of the carbon monoxide. I n order to expel 90 per cent of the absorbed carbon monoxide, the absorption solution has to be heated t,o about 80" C., a temperature a t n-hich too much copper is precipitated over a long period.
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Absorbents Containing Other Organic Acids or Phenols
Apparently only absorbents with cuprous annnonium salts of carbonic acid and formic acid are described in the literature. The vriters decided t o investigate a hrge number of other organic acids and of phenols in order to find a morr satisfactory absorbent for carbon monoxide. The test solutions were prepared froin cuprous oxide, the organic acid or the phenol, ammonia, and water, aiid t h e absorption power was determined in the same way as w-ns described for the cuprous chloride-ammonium chloride mixtures. A small amount of cuprous oxide always reinainetl undissolved, so all tlie solutions m r e saturated with cuprour ions. Table I
.4crn
OR
Pticso:,
Formic acid Acetic acid Rlonochloroacetic acid Propionic acid n-Butyric acid Glycolic acid Lactic acid Tartaric acid Citric acid Aminoacetic acid a-Aminopropionic acid Henzenesulfonic acid Salicylic acid o-Aminobenzoic acid Phenol p-h'itrophenol m-Cresol
.&BSORPTlOS OF S O L S . A T 0'
c.
1-tilumes 6 1 6.0 7.0 14 9 10 4 17.0
15.0 Segligible 2.0 22.4 19.9 9.8 2.0
15.0 15 2 7.8 10.4
.kIJSORPTION OF CARBON ~ I O N O X I D I ;
TO 1 hIOL
Cu?o
.WOlS 0 48
0.39 0.36 0 95 0.71 0.99 0.94
0.06 1.12 1.07 0.56 0.16 0.83 0.89 0.54
0.61
I n one series the ingredients of the solutions were taken in the same proportion wit'hout considering the molecular
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weight of the acid or the phenol; in another series the ratio of cuprous oxide to acid was on a molecular basis. The amount of ammonia was always the same; there was a large excess of ammonia over the amount necessary t o form the ammonium salt of the acid. The further increase of this excess ammonia has only a slight influence on the ahsorption power. SERIESI-In the first series the solutions were prepared from 13 grams of cuprous oxide, 25 grams of acid or phenol. 85 cc. of ammonia (d, 0.910), and 100 cc. of mater. The resulk are given in Table I. The best absorption is obt,aiiieti with the aniiiio acids, but, they cannot be used as they reduce the cuprous compounds to metallic copper. The re,wlts indicate that one mol of cuprous oxide absorbs as maximum about one mol of carbon monoxide, an observation also made by previous investigators. SERIES2-The proportions of the second series were mol of cuprous oxide, 68 cc. of mol of acid or phenol, ammonia (d, 0.910), aiid 38 cc. of water. Table I1 pi\.?the results. Tahle I1 ~~
ABSORPTIONO F S O L N . A T 0" c I'olumes 10.3 13.1 13 2 8 3
SUBST.AK;CIS ProDionic acid GIg'colic acid Lactic acid Tartaric acid Citric acid Phenol
5 s
8.0
These experiments aiid others carried out with different concentrations of ammonia led t o the conclusion that cuprous ammonium lactate has the most favorable properties as ail absorbent for carbon monoxide. These cuprous ammonium lactate-ammonia mixtures do not attack iron and are absolutely stable. The absorption power remained the sanie after twenty and more regenerations where the solution was heated to 80" C. t o expel t,he carbon monoxide. Of course, the ammonia lost by evaporation must be replaced from time to time. This absorption solution is grayish brown; the reducing action of the water gas is sufficient to prevent tlie oxidation of the cuprous salt. Effect of Temperature on Absorption with Cuprous Ammonium Lactate Mixture
The influence of the temperature on absorption atid gas e\-olutioii was also studied with the new absorbent. If we take the absorption a t 0" C. as 100, v e find an a l ~ r p t i o i i of 88.9 a t 10" c'. a i d of 55.3 at, 20" C. T h r pa> e\-olutioii i. as follow-.: .kB>ORBcD CARBON h f O K O X l D E
Degrees Centigr.ide Per rent
60 80.2
i0 83.6
SO
(10
90.3
96.4
1IJO !i
