Method for separation of carbon monoxide by highly dispersed cuprous compositions

The present invention is directed to active compositions, such as adsorbents and catalysts, which comprise cuprous compounds dispersed on amorphous oxide or carbon macroporous supports. The compositions are prepared by impregnating cupric compounds on pretreated supports with the aid of an aqueous solution of an ammonium salt of a di- or polycarboxylic acid dispersant, such as ammonium citrate, followed by activation of the cupric compound or reduction of the cupric compound to the corresponding cuprous compound. Methods of synthesis and processes utilizing the compositions are also disclosed.

FIELD OF THE INVENTION 
The present invention is directed to active composite copper-containing 
compositions for adsorption and catalysis produced by impregnation of a 
support with cupric compounds using nitrogen-containing dispersants. More 
specifically, the present invention is directed to copper-containing 
compositions as adsorbents, selective for carbon monoxide or olefins, 
containing highly dispersed cupric/cuprous compounds, which are dispersed 
by the use of pretreatment of the support and impregnation of cupric 
compound precursors with nitrogen-containing dispersants for subsequent 
activation of the cupric compound and/or reduction to the cuprous ion 
state. 
BRIEF DESCRIPTION OF THE PRIOR ART 
Both carbon monoxide and hydrogen are gases widely used in the chemical 
industry. The current technique used to produce both pure hydrogen and 
carbon monoxide is to steam reform methane, remove carbon dioxide by 
scrubbing with amine solutions and finally cryogenic separation of carbon 
monoxide and hydrogen. However, there is considerable interest in 
developing an adsorption process that is capable of separating carbon 
monoxide and hydrogen. The key advantages of an adsorption system over 
cryogenic separations are low energy requirements, capability of producing 
higher purity hydrogen and absence of any needs for liquid cryogens. The 
principle technical hurdle in developing an adsorption system to produce 
high purity carbon monoxide is identifying an adsorbent that is capable of 
separating dilute, unreacted methane in the steam methane reformation 
off-gas from bulk carbon monoxide. The carbon monoxide over methane 
selectivity of an adsorbent must be high to produce a high purity carbon 
monoxide stream. Chemical users of carbon monoxide are requiring higher 
and higher product purity to eliminate unwanted side reaction during 
carbon monoxide use and the synthesis of engineering plastics and 
polyurethane foams. Current methane purity specification in carbon 
monoxide for many applications is nearing 25 PPM or less. Thus, an 
adsorbent capable of producing carbon monoxide of this purity must 
demonstrate high carbon monoxide selectivity. In addition to high carbon 
monoxide selectivity, an adsorbent for this process must also exhibit a 
large carbon monoxide working capacity. The larger the carbon monoxide 
working capacity, the smaller the adsorption beds and lower capital costs 
for such an adsorptive separation. 
U.S. Pat. No. 3,789,106 discloses the use of zeolites and mordenites that 
have their sodium ions ion-exchanged with copper as well as other metals 
to adsorb carbon monoxide. The main objective is to remove trace amounts 
of carbon monoxide from gas mixtures. In the case of this patent, the 
copper ion becomes a cation replacing sodium in the zeolitic or mordenitic 
molecular sieve structure. 
U.S. Pat. No. 4,019,879 discloses the adsorptive separation of carbon 
monoxide using zeolitic molecular sieves which are ion exchanged to 
introduce cations of cuprous valences into the structure. Cupric ions may 
first be impregnated in the zeolitic structure followed by reduction of 
the cupric ions to cuprous ions in the ion exchange procedure. 
U.S. Pat. No. 4,470,829 discloses an adsorbent for selective adsorption of 
carbon monoxide comprising a copper halide, an aluminum halide and a 
polystyrene or its derivative as one embodiment or a copper halide and 
aluminum halide and activated carbon or graphite as a second embodiment. 
The adsorbent is produced by mixing together the three components in a 
hydrocarbon solvent and then driving off the solvent. 
U.S. Pat. No. 4,587,114 discloses the production of a carbon monoxide 
adsorbent using cuprous or cupric compounds impregnated on a carbon 
support using solvents which are removed after the impregnation. The 
solvents include water, aqueous hydrochloric acid or ammonium formate, 
primary or secondary alcohol having 1 to 7 carbon atoms, acetone, 
ethylacetate, formic acid, acetic acid, benzene, toluene, propionitrile, 
acetonitrile and aqueous ammonica. 
U.S. Pat. No. 4,713,090 discloses a carbon monoxide adsorbent comprising a 
composite support of silica and/or alumina and activated carbonized 
material carrying a copper compound impregnated with the assistance of a 
solvent including aqueous solutions of ammonical formic acid, ammonia 
water and nitrogen-containing solvents selected from the group of 
propionitrile, acetonitrile, diethyl amine, dimethyl formamide and 
N-methyl pyrrolidone. 
U.S. Pat. No. 4,914,076 discloses an adsorbent for selective adsorption of 
carbon monoxide comprising a support of alumina or silica-alumina 
impregnated with a cupric salt carried by a solvent incorporating a 
reducing agent, after which the solvent is removed and the cupric salt is 
reduced to a cuprous salt. The solvent utilized to deposit the cupric 
compound was water containing a reducing agent. Other solvents identified 
include formalin, formic acid, alcohol and the like. The reducing agent 
includes low valence metal salts of iron, tin, titanium and chromium and 
organic compounds in low degree of oxidation including aldehydes, 
saccharides, formic acid, oxallic acid and so on. 
U.S. Pat. No. 4,917,711 discloses a carbon monoxide selective adsorbent 
produced from mixing in solid form or through solvent intermixing a 
support from the group of zeolites, alumina, silica gel, alumino silicate, 
alumino phosphate and combinations with a cuprous compound, wherein the 
cuprous compound can be derived from a cupric compound deposited on the 
support from a solvent selected from the group of water, hydrochloric 
acid-containing aqueous solution, primary or secondary alcohols having 1 
to 7 carbon atoms, acetone, ethylacetate, hydrocarbons having 4 to 7 
carbon atoms, propionitrile and acetonitrile. 
All of these prior art patent attempts to produce a carbon monoxide 
selective adsorbent fail to provide sufficiently high dispersions of 
cuprous ions on a macroporous support to effectively adsorb bulk 
quantities of carbon monoxide from gas mixtures additionally containing 
methane, wherein the adsorbent has sufficiently high selectivity for 
carbon monoxide over methane, so as to permit carbon monoxide purities 
with less than 25 ppm of methane. The present invention overcomes these 
drawbacks by providing a novel adsorbent, having unexpectedly high 
dispersions of cuprous ion on the macroporous support as will be described 
in greater detail below. 
BRIEF SUMMARY OF THE INVENTION 
The present invention is an active composite copper-containing composition 
comprising a high surface area support of amorphous oxide or carbon and a 
dispersed cuprous compound prepared by impregnating the support with a 
cupric compound in an aqueous solvent having an ammonium salt of a di- or 
polycarboxylic acid dispersant, removing the solvent and activating the 
composite composition by heating to an elevated temperature. 
Preferably, the composition is an adsorbent. 
Alternatively, the composition is a catalyst. 
More preferably, the absorbent is selective for carbon monoxide or olefins. 
Preferably, the amorphous oxide support is pretreated to activate the 
support by heating to an elevated temperature in the range of 
approximately 100.degree. to 500.degree. C. 
Preferably, the carbon support is pretreated to activate the support by 
oxidation. 
Preferably, the ammonium salt of a di- or polycarboxylic acid dispersant is 
selected from the group of ammonium citrate, ammonium tartrate, ammonium 
succinate, ammonium phthalate, ammonium adipate, ammonium 
(ethylenedinitrilo)tetraacetate, and mixtures thereof. 
Preferably, the activation or reduction elevated temperature is in the 
range of approximately 200.degree. to 400.degree. C. 
Preferably, the cupric compound is selected from the group consisting of 
cupric halides, cupric carboxylates, cupric oxygen acids, cupric amine 
complexes and mixtures thereof. 
Preferably, the loading of copper on the support is in the range of 
approximately 3 to 40 wt. %. 
Preferably, the present invention is an adsorbent selective for carbon 
monoxide or olefins comprising an active, composite, copper-containing 
composition comprising a high surface area support of amorphous oxide or 
carbon and a dispersed cuprous compound prepared by impregnating the 
support with a cupric compound in an aqueous solvent having an ammonium 
salt of a di- or polycarboxylic acid dispersant, removing the solvent and 
reducing the cupric compound to a cuprous compound on the support by 
heating to an elevated temperature. 
Alternatively, the present invention is a catalyst comprising an active 
composite copper containing composition comprising a high surface area 
support of amorphous oxide or carbon and a dispersed cuprous compound 
prepared by impregnating the support with a cupric compound in an aqueous 
solvent having an ammonium salt of a di- or polycarboxylic acid 
dispersant, removing the solvent and reducing the cupric compound to a 
cuprous compound on the support by heating to an elevated temperature. 
The present invention is also directed to a method for synthesis of an 
active, composite, copper-containing composition having a high surface 
area support of amorphous oxide or carbon and a dispersed cuprous compound 
comprising contacting such support with an aqueous solvent containing a 
cupric compound in an ammonium salt of a di- or polycarboxylic acid 
dispersant to impregnate the support with cupric compound, removing the 
solvent from the support and activating the composite compound by heating 
to an elevated temperature. 
Preferably, the support is pretreated prior to impregnation with the cupric 
compound to render the support more susceptible to the impregnation. More 
preferably, the pretreatment is performed on a carbon support by 
oxidation, such as acid washing. Alternatively, the pretreatment is 
performed on an amorphous oxide support by heating to a temperature in the 
range of approximately 100.degree. to 500.degree. C., optionally in an 
inert atmosphere. 
Preferably, the activation and/or reduction elevated temperature is in the 
range of approximately 200.degree. to 400.degree. C. 
Preferably, the cupric compound is selected from the group of cupric 
halides, cupric carboxylates, cupric oxygen acids, cupric amine complexes, 
cupric hydroxide and mixtures thereof. 
The present invention is also directed to a process of selectively 
separating carbon monoxide from a gas mixture containing carbon monoxide 
and at least one other gas selected from the group of carbon dioxide, 
methane, nitrogen, hydrogen, argon, helium, ethane and propane, 
comprising: contacting the gas mixture with a copper containing adsorbent 
comprising a high surface area support of amorphous oxide or carbon and 
dispersed cuprous compound prepared by impregnating the support with a 
cupric compound in an aqueous solvent having an ammonium salt of a di- or 
polycarboxylic acid dispersant, removing the solvent and reducing the 
cupric compound to a cuprous compound on the support by heating to an 
elevated temperature, selectively adsorbing carbon monoxide on the 
adsorbent and separately desorbing the carbon monoxide from the adsorbent 
to recover the carbon monoxide. 
Preferably, the gas mixture is passed through one or more beds of the 
adsorbent in a sequence of steps, comprising: adsorbing carbon monoxide 
from a gas mixture in a bed of such adsorbent, desorbing the bed of 
adsorbent after adsorption, purging the bed of adsorbent with carbon 
monoxide, evacuating the bed of adsorbent to recover the carbon monoxide 
and repressurizing the bed of adsorbent to the pressure of adsorption by 
passing a non-adsorbed gas into the bed of adsorbent. 
The present invention also is a process of catalyzing the reaction of 
reaction media in a reaction selected from the group of oxidation, 
water-gas shift, methanol synthesis, and oxychlorination, comprising: 
contacting the reaction media under appropriate conditions of reaction 
with a copper-containing catalyst, comprising a high surface area support 
of amorphous oxide or carbon and a dispersed cuprous compound prepared by 
impregnating the support with a cupric compound in an aqueous solvent 
having an ammonium salt of a di- or polycarboxylic acid dispersant, 
removing the solvent and reducing the cupric compound to a cuprous 
compound on the support by heating to an elevated temperature. 
More preferably, the present invention is an adsorbent selective for carbon 
monoxide preferentially over carbon dioxide, methane and nitrogen, 
comprising an active, composite, copper-containing composition, comprising 
a high surface area support of macroporous alumina, pretreated by heating 
at an elevated temperature in an inert gas and a dispersed cuprous 
compound prepared by impregnating the alumina support with copper 
chloride, dissolved in water with an ammonium citrate dispersant, removing 
the water and reducing the copper chloride to a cuprous compound on the 
alumina support by heating to an elevated temperature in the range of 
approximately 200.degree. to 400.degree. C.

EXAMPLE 1 
Sixteen pounds of LaRoche activated alumina grade 201 was heat treated in 
air at 200.degree. C. for 16 hours. The alumina was then impregnated with 
3.6 liters of an aqueous solution containing 5.0 pounds of CuCl.sub.2 
.multidot.2H.sub.2 O and 0.6 pounds of ammonium citrate. The material was 
then air dried at 250.degree. F. for 16 hours and then activated at 
200.degree. C. in nitrogen for another 16 hours. 
EXAMPLE 2 
Sixteen pounds of granular Darco activated carbon from American Norit was 
heat treated in wet (207% relative humidity) air at 250.degree. F. for 
sixteen hours. Following this treatment, the carbon was impregnated with a 
7.3 liter aqueous solution containing 11.2 pounds of CuCl.sub.2 
.multidot.2H.sub.2 O and 0.8 pounds of ammonium citrate dibasic and dried 
in nitrogen at 250.degree. F. for sixteen hours. The adsorbent was then 
activated in nitrogen at 200.degree. C. 
The results of static and dynamic testing of the adsorbents prepared in 
Examples 1 and 2 are shown in Tables 1 and 2 below. 
TABLE 1 
__________________________________________________________________________ 
(mmole/g/atm) 
(mmole/g/atm) 
(mmole/g) 
Adsorbent K.sub.H CO at 30.degree. C. 
K.sub.H CH.sub.4 at 30.degree. C. 
S.sub.H 
N CO, 2 atm, 30.degree. C. 
__________________________________________________________________________ 
Linde 5A 6.6 1.1 6.0 
1.3 
Cu(II) on alumina (Ex. 1) 
34.5 0.035 985.7 
1.0 
Cu(II) on Darco (Ex. 2) 
7.5 0.048 156.3 
1.2 
Cu(II) on alumina 
17.1 0.042 407.1 
0.8 
(no pretreat) 
__________________________________________________________________________ 
TABLE 2 
__________________________________________________________________________ 
Adsorbent S.sub.T 
(mmole/g) O.sub.e 
(mmole/g) O.sub.LPP 
(mmole/g) O.sub.P 
O.sub.LPP /O.sub.e 
__________________________________________________________________________ 
Linde 5A 1.8 
0.87 0.57 0.30 66% 
Cu(II) on alumina (Ex. 1) 
7.2 
0.66 0.22 0.44 33% 
Cu(II) on Darco (Ex. 2) 
5.3 
0.84 0.28 0.56 33% 
__________________________________________________________________________ 
The results in Table 1 were obtained in a standard volumetric adsorption 
apparatus for measurement of equilibrium adsorption isotherms. The results 
in Table 2 were obtained in the single column unit, 2 inches in diameter 
and four feet in length. The sequence of steps followed to obtain the 
results presented in Table 2 are as follows: 
1. Presaturation of the bed with 10% carbon monoxide and 90% hydrogen at 5 
psig; 
2. Countercurrent repressurization with hydrogen to 200 psig; 
3. Cocurrent adsorption of a feed mixture containing 25% carbon monoxide, 
2% methane, 1% nitrogen and 72% hydrogen at 200 psig; 
4. Cocurrent depressurization of the column to 5 psig; 
5. Cocurrent purge with carbon monoxide at 5 psig. 
The results in Table 2 were obtained at 24.degree. C. 
The results presented in Table 1 include the Henry's Law Constant for 
carbon monoxide and methane adsorption, K.sub.H CO and CH.sub.4, 
respectively, the Henry's Law selectivity S.sub.H and the carbon monoxide 
capacity of the adsorbents at 30.degree. C. and 2 atmospheres pressure. 
Table 1 shows that the adsorbents produced following Examples 1 and 2 have 
a much greater CO/CH.sub.4 then conventional zeolitic adsorbents. The 
carbon monoxide and methane adsorption characteristics for 5A zeolite are 
given in Table 1 for comparison purposes. The Henry's Law selectivity of 
5A zeolite for carbon monoxide over methane is about 6, while the value 
for adsorbents produced by techniques described in the disclosure vary 
from 150 to 1,000. A high CO/CH.sub.4 selectivity is required of 
adsorbents for this application to produce high purity carbon monoxide. 
The other primary adsorbent requirement for this application is a large 
carbon monoxide capacity. Table 1 also gives carbon monoxide capacities of 
the various adsorbents at 30.degree. C. and 2 atmospheres of carbon 
monoxide pressure. The results show that the carbon monoxide capacity of 
the adsorbents produced with techniques described in this disclosure have 
capacity about equal or greater than those of 5A zeolite. Thus, 
equilibrium single component adsorption isotherms indicate that the 
adsorbents produced using techniques described in the present invention, 
have the necessary adsorbent requirements of high CO/CH.sub.4 selectivity 
and high carbon monoxide capacity. 
The results presented in Table 2 demonstrate dynamic adsorbent performance 
by measurement of breakthrough curves. The data presented in Table 1 are 
results of single component measurements, while the data in Table 2 is 
from adsorbent testing with multi-component gas mixtures. The results 
depicted in Table 2 include the thermodynamic selectivity of the adsorbent 
under feed conditions, S.sub.T, the evacuated carbon monoxide capacity 
between 0.1 and I atmosphere, Q.sub.e,the amount of low pressure carbon 
monoxide purge needed to clean the bed free of methane, Q.sub.LPP, the 
carbon monoxide productivity of the adsorbent, Q.sub.p, which is equal to 
Q.sub.e -Q.sub.LPP and the percentage of the evacuation quantity required 
for low pressure carbon monoxide purge. Clearly, the thermodynamic 
selectivity of the adsorbents of the present invention are superior to 
that of 5A zeolite. This improved selectivity corresponds to improved 
carbon monoxide and methane separation during the feed step. In addition 
to improved CO/CH.sub.4 separation, which is needed to produce high purity 
carbon monoxide, the adsorbents disclosed herein demonstrate higher carbon 
monoxide productivity than 5 A zeolite. This means smaller bed sizes are 
required for the new materials. Finally, all the new adsorbents require 
less low pressure carbon monoxide purge than 5A zeolite. The process 
employed to produce high purity carbon monoxide, which is more thoroughly 
described below, requires that the effluent gas from the low pressure 
purge is recycled to the feed of the bed to keep the carbon monoxide 
recovery high. The low pressure purge effluent, which is at about 
atmospheric pressure, must be recompressed to feed pressure (approximately 
200 psig). This puts a severe power penalty on the process. Hence, the 
lower the low pressure purge requirement, the lower the power requirements 
for the process. Thus, single column testing of the new adsorbents show 
that compared to conventional adsorbents, the materials of the present 
invention have (1) improved CO/CH.sub.4 selectivity and therefore improved 
CO/CH.sub.4 separation, (2) improved carbon monoxide productivity and 
therefore reduced bed sizes, and (3) reduced low pressure purge 
requirements and therefore lower process power requirement. 
The utility of the adsorbents produced by the present invention was also 
tested in a pilot development unit to obtain process design parameters. 
The unit consists of four beds, 12 feet in length and 2 inches in 
diameter. Two of the beds were filled with the adsorbent described herein, 
while two of the other beds contained 5A zeolite for hydrogen purification 
recovery. Only the cycle for the two beds used for carbon monoxide 
recovery will be described. The steps include (1) pressurization with pure 
hydrogen countercurrent to the direction of feed to superambient pressure 
(200 psig), (2) feed with a gas mixture containing carbon monoxide, 
methane, hydrogen and nitrogen at 200 psig, (3) cocurrent depressurization 
of the column to 25 psig. (This depressurization effluent is recycled to 
the feed end of the bed to insure high carbon monoxide recovery), (4) 
cocurrent purge with product carbon monoxide at 0 to 5 psig and (5) 
evacuation of pure carbon monoxide product at vacuum levels of 80 torr. 
Then the cyclic process is continued from steps 1 through 5. The important 
process parameters obtained from these experiments include the evacuated 
carbon monoxide product Q.sub.e,the amount of carbon monoxide low pressure 
purge required, Q.sub.LPP and the carbon monoxide productivity of the 
adsorbent, Q.sub.p, which is given by Q.sub.e -Q.sub.LPP. From a process 
point of view, it is desirable to increase the values of Q.sub.p while 
minimizing Q.sub.LPP quantities. Clearly, as Q.sub.p increases, the bed 
size for a given size carbon monoxide plant decreases which reduces the 
capital costs of the plant. Also, it is desired to minimize Q.sub.LPP , 
since the low pressure purge effluent must be repressurized from about 
ambient pressure to feed pressure. Thus, the recycle of the low pressure 
purge effluent is an energy intensive step which is the principle power 
contribution to the process. The results of the pilot development unit 
testing on the adsorbent of Example 1 is shown in Table 3. In all cases, 
adsorption was carried out at 200 psig with a gas composition of 25% 
carbon monoxide/2% methane/1% nitrogen and 72% hydrogen. These results 
show that the compositions of the present invention have higher carbon 
monoxide productivity, higher carbon monoxide recovery and require less 
low pressure purge than 5A zeolite. Therefore, these adsorbents are much 
improved materials for the production of carbon monoxide in this process 
scheme. 
TABLE 3 
__________________________________________________________________________ 
(mmole/cycle) 
(mmole/cycle) 
(mmole/cycle) CH.sub.4 in 
Adsorbent 
(.degree.C.) T ads 
O.sub.e O.sub.LPP 
O.sub.P CO Recovery 
CO Product 
__________________________________________________________________________ 
Linde 5A 24 9.17 6.97 2.20 60% 500 ppm 
Cu(II) on alumina 
50 5.88 1.22 4.65 85% 32 ppm 
__________________________________________________________________________ 
It has already been mentioned that an important step in the production of 
improved carbon monoxide adsorbents is the pretreatment step. Basically 
the pretreatment step allows for higher copper dispersion on the support. 
Table 4 shows the effect of pretreatment on the water adsorption capacity 
of the support for copper loading and copper dispersion on both carbon and 
alumina based materials. The results show that the pretreatment step 
increases both the copper dispersion on the adsorbents and the water 
adsorption capacity of the support at 20% relative humidity. It follows 
that techniques that enhance the water adsorption capacity of the support 
will help increase the dispersion of copper. The enhanced copper 
dispersion, which was measured by carbon monoxide adsorption, results in 
increased carbon adsorption capacities. 
TABLE 4 
______________________________________ 
(wgt %) 
Adsorbent H.sub.2 O Capacity at 20% r.h. 
Cu dispersion 
______________________________________ 
Cu(II) on alumina 
10.8% 53% 
(pretreated) 
Cu(II) on alumina 
5.7% 38% 
(not pretreated) 
Cu(II) on Darco 
5.1% 46% 
(pretreated) 
Cu(II) on Darco 
0.8% 28% 
(not pretreated) 
______________________________________ 
Adsorbents capable of producing high purity carbon monoxide from gas 
streams containing methane must have a high selectivity for carbon 
monoxide over methane. It is well known that monovalent copper ions can 
very selectively reversibly bind carbon monoxide. However, it is difficult 
to get highly dispersed monovalent copper ions on porous supports. This is 
primarily because monovalent copper ions are unstable and monovalent 
copper salts are insoluble. In terms of the stability of monovalent copper 
ions in oxidizing atmospheres, monovalent copper ions are readily oxidized 
to bivalent copper ions, while under reducing conditions (such as gas 
streams containing carbon monoxide) monovalent copper ions are reduced to 
copper metal. Thus keeping monovalent copper ions stabilized on porous 
supports is a difficult task. In addition, monovalent copper salts are 
quite insoluble. In order to get monovalent copper in solution, treatment 
with either strong acid or base is necessary. Even with these solvents, 
the solubility of monovalent copper is so low that loading of large weight 
percents of monovalent copper on porous supports requires many 
impregnations. Thus, in order to make an adsorbent capable of very 
selective and reversible carbon monoxide adsorption, there must be a large 
number of highly dispersed monovalent copper ions on the porous support to 
maximize available monovalent copper per unit volume of adsorbent bed. 
This is difficult to do because of the instability and insolubility of 
monovalent copper. The dispersants of the present invention are effective 
to achieve the high dispersion of the monovalent copper that is required 
to selectively adsorb bulk quantities of carbon monoxide at high purity 
from mixed gas streams. Table 5 shows a comparison of examples of the 
ammonium salts of di- and polycarboxylic acid dispersants of the present 
invention in contrast to other ammonium compounds and carboxylic acids 
that could be contemplated as dispersants or reducing agents for copper 
loaded adsorbents for carbon monoxide. 
TABLE 5 
______________________________________ 
(mmole/g) 
Agent Delta n CO 
Cu Dispersion 
______________________________________ 
None 0.03 3% 
Citric Acid 0.26 43% 
NH.sub.4 Citrate 
0.45 56% 
Dextrose 0.26 29% 
NH.sub.4 Carbonate 
0.10 12% 
NH.sub.4 Chloride 
0.08 10% 
NH.sub.4 Formate 
0.21 24% 
______________________________________ 
(Delta n CO is isothermal working capacity at 30.degree. C. between 0.1 
and 1 atm.) 
It is apparent that the ammonium salts of di- and polycarboxylic acids give 
the best dispersions in comparison to other oxy compounds and other 
ammonium compounds. The present invention preferably achieves copper 
dispersions sufficient to selectively adsorb bulk quantities of carbon 
monoxide from carbon monoxide and methane-containing gas streams so as to 
produce a carbon monoxide product gas having less than 25 ppm of methane, 
more preferably the copper dispersion is in the approximate order of 
magnitude of 30 to 80%. Dispersion is defined as the moles of copper on 
the surface of the composition divided by the total moles of copper in the 
composition. Although not wishing to be held to any particular theory, it 
is believed that the ammonium salts of di- and polycarboxylic acid salts 
work best as dispersants because the copper ion-exchanges with the 
ammonium in solution before actual deposition on the support to disperse 
the copper to a greater degree than mere solute dissolution in a solvent 
so that when the impregnation occurs and the solvent is removed, the 
copper is in a much more highly dispersed condition than mere dissolution 
of a solute in a solvent would provide. It is also apparent that the 
ammonium salts of acids give higher CO working capacities than the other 
oxy compounds and ammonium compounds. As a result, the compositions of the 
present invention provide better adsorbents than the prior art adsorbents 
that do not use such dispersants. 
The ammonium salts of di- and polycarboxylic acid dispersants of the 
present invention also have another advantage in processing economics. 
These dispersants lead to less corrosion of process equipment during 
manufacture due to their enhanced ability to capture chlorides evolved 
during the use of cupric chloride and other chloride copper sources. HCl 
evolves during the thermal activation of the compositions. In the case of 
citric acid, ion exchange of the proton on the acid with Cu(II) ions leads 
to the formation of HCl in the solution. Upon activation of the adsorbent, 
the HCl is evolved which leads to corrosion of piping downstream of the 
activation vessel. On the other hand, in the ammonium citrate case, ion 
exchange of Cu(II) for ammonium ions takes place in solution thereby 
effectively buffering the solution. Upon thermal activation of the 
adsorbent, the majority of the chloride ion is retained on the adsorbent 
surface as NH4Cl, reducing potential corrosion problems. 
Evidence of the significance of using the ammonium salt is given in Table 
6. The aqueous impregnating solution using ammonium citrate has a higher 
pH than that using citric acid. This shows that the hydrogen ion content, 
and therefore devolatilized HCl upon activation, in the ammonium citrate 
solution is less. In addition, Table 6 shows that the Cl/Cu molar ratio of 
both unactivated samples is 2.0 as would be expected from the starting 
material CuCl.sub.2. However, after thermal treatment in N.sub.2 at 
200.degree. C., the Cl/Cu ratio on the ammonium citrate sample is 1.8, 
while that of the citric acid sample is 1.4. This clearly shows that the 
present invention's dispersants of ammonium salts of di- and 
polycarboxylic acids lead to the desirable retention of chloride on the 
support. 
TABLE 6 
______________________________________ 
Adsorbent Solution pH 
Cl/Cu Ratio 
______________________________________ 
NH.sub.4 Citrate 
2.8 2.0 
(unactivated) 
NH.sub.4 Citrate 
-- 1.8 
(activated) 
Citric Acid 1.5 2.0 
(unactivated) 
Citric Acid -- 1.4 
(activated) 
______________________________________ 
Another approach to achieving high CO/CH.sub.4 selectivity, is to minimize 
adsorption of methane. Since there are no specific forces involved in 
adsorption of methane, the extent of methane adsorption is controlled by 
the porous structure of the support. Methane adsorption is enhanced as the 
pore size of the support decreases. Thus, microporous supports like 
zeolites and gas phase carbons will exhibit significant methane adsorption 
and therefore lower CO/CH.sub.4 selectivity than macroporous supports like 
amorphous oxides, silica, alumina, silica-alumina, titania and liquid 
phase carbons. Therefore, the adsorbents produced by the techniques 
described in the present invention consist of porous, preferably 
macroporous, supports, typically having pores greater than approximately 
20 Angstroms in diameter, upon which are impregnated highly dispersed 
insoluble and unstable monovalent copper ions. These monovalent copper 
ions demonstrate selective and reversible carbon monoxide adsorption, 
which is needed for the production of high purity carbon monoxide by 
adsorption, while the macroporous characteristics of the support preclude 
any contemporaneous adsorption of methane which would diminish the overall 
adsorbent selectivity. 
The compositions of the present invention are also useful as adsorbents for 
selectively adsorbing olefins, such as ethylene, from mixed gases. In 
tests comparable to the tests run to obtain the data for Table 1 above, 
runs were also undertaken to selectively adsorb ethylene from a gas 
mixture using a prior art adsorbent (5A zeolite) and an example of the 
present invention. This is reported in Table 7 below wherein K values are 
of comparable or analogous measurements as recited for Table 1 above. 
TABLE 7 
__________________________________________________________________________ 
(mmole/g/atm) 
(mmole/g/atm) 
(mmole/g/atm) 
Adsorbent 
K.sub.H C.sub.2 H.sub.4 at 30.degree. C. 
K.sub.H C.sub.2 H.sub.6 at 30.degree. C. 
S.sub.H 
N C.sub.2 H.sub.4, 2 atm, 30.degree. 
__________________________________________________________________________ 
C. 
Linde 5A 
180 9 20 
2.5 
Cu (II) on 
27 0.09 300 
1.0 
alumina (Ex. 1) 
__________________________________________________________________________ 
It is apparent that the olefin selective adsorbent of the present invention 
has a much higher selectivity for ethylene than the prior art adsorbent. 
Such selectivity can be translated into higher purities and reduced 
capital cost for a given quantity of gas to be separated. 
The pretreatment step for the supports of the present invention is 
important in combination with the actual procedure for dispersing copper 
on the support in achieving the loadings and extent of dispersion 
necessary for the superior selectivity and working capacity for carbon 
monoxide that adsorbents of the present invention display. The present 
invention differs from previous descriptions of copper-bearing carbon 
monoxide adsorbents by the use of pretreatment of the support in 
conjunction with dispersants for the solvent impregnation of copper to 
result in the improved compositions of the present invention. The 
pretreatment step can be achieved in a number of ways dependent on the 
nature of the support, that is taking into account whether the support is 
an amorphous oxide or carbon. Prior to impregnation of carbon supports 
with monovalent copper ions, the present invention describes a 
preoxidation step. This oxidation step, which can be accomplished by 
either gas phase oxidants such as air, oxygen, steam, or nitrogen oxides 
or liquids such as nitric acid, hydrogen peroxide and others, puts oxygen 
functional groups on the carbon surface which serve as anchors for the 
monovalent copper ions. In addition, the oxidation step produces a more 
polar support which is more readily wetted by the polar monovalent copper 
salt solutions than the untreated carbon. Both the enhanced wetting and 
the anchoring sites for monovalent copper produce an adsorbent with 
improved monovalent copper dispersion and therefore carbon monoxide 
capacity. With respect to inorganic supports, pretreatment of amorphous 
oxides supports also enhances monovalent copper dispersion. Enhancing the 
surface acidity of inorganic supports prior to liquid phase impregnation 
increases the dispersion of monovalent copper and therefore increases 
carbon monoxide adsorption capacity. Increasing the surface acidity of 
inorganic oxides can be accomplished by simple heat treatment, preferably 
in inert gases, to approximately 100.degree. to 500.degree. C. or by 
pretreatment of the support with mineral acids. 
The present invention has been described with regard to a novel combination 
of pretreatment of macroporous supports and subsequent impregnation of 
bivalent copper in an aqueous solution using ammonium salts of di- and 
polycarboxylic acid dispersants to achieve very high dispersions of the 
copper on the support. The composite composition is subsequently 
post-treated at elevated temperature in inert gas to reduce the bivalent 
copper to monovalent copper. The advantage of this technique for the 
production of carbon monoxide adsorbents is that bivalent copper salts are 
very soluble in aqueous solutions. This obviates the need for strong acid 
or base solutions as in the case of impregnating monovalent copper salts. 
Impregnation of porous supports with solutions of strong acid or base 
require pollution abatement techniques which increase the price of the 
adsorbent. In addition, the solubility of bivalent copper salts in water 
are much greater than the monovalent copper salts in acid or base 
solution, which means that the bivalent copper salts in aqueous solution 
require fewer impregnations to achieve a desired copper loading. The 
techniques described in the present invention for monovalent copper-based 
carbon monoxide adsorbents are different from those previously disclosed 
in that a pretreatment step is involved, a different impregnation 
technique is employed, ammonium salts of di- and polycarboxylic acid 
dispersants are added directly to the aqueous bivalent copper solution and 
post-treatment reduction and activation is employed. Increasing the 
acidity and water adsorption capacity of the inorganic support enhances 
the dispersion of the bivalent copper and therefore increases the carbon 
monoxide capacity. Furthermore, a preoxidation step with carbonaceous 
supports increases the dispersion of bivalent copper and increases the 
carbon monoxide capacity as well. 
Recently the purity specification for carbon monoxide have become more 
stringent, requiring very low methane impurities of the order of 25 ppm in 
the carbon monoxide product. Adsorbents produced by the techniques 
described in the present invention are capable of separating methane from 
carbon monoxide to produce high purity carbon monoxide products having 
less than 25 ppm of methane. In this way, the composite compositions of 
the present invention overcome the drawbacks and effect a solution to 
outstanding problems in the industry utilizing high purity carbon 
monoxide. 
The present invention has been set forth with regard to several preferred 
embodiments, but the full scope of the invention should be ascertained 
from the claims which follow.