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Патент USA US3078650

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United States Patent O?tice
3,078,641
Patented Feta. 26, 1963
1
2
Zeolite X exhibits adsorptive properties that are unique
3,078,641
among known adsorbents. The common adsorbents, like
SEPARATKQN @F SULFUR CQOMPGUND§
FRGM ‘VAPGR MlXTUlisEd
chorcoal and silica gel, show adsorption selectivities based
primarily on the boiling point or critical temperature
of the adsorbate. Activated zeolite X, on the other hand,
exhibits a selectivity based on the size and shape of the
adsorbate molecule. Among those adsorbate molecules
Robert M. Milton, Buffalo, N.Y., assignor to Union
‘Carbide Corporation, a corporation of New Yuri:
No Drawing. Filed Dec. 31, 1959, Ser. No. 863,104
8 Claims. (til. 55--73)
whose size and shape are such as to permit adsorption
This invention relates to a method for adsorbing ?uids
by zeolite X, a very strong preference is exhibited toward
and separating a mixture of ?uids into its component 10 those that are polar, polarizable, and unsaturated. An
parts. More particularly, the invention relates to a
other property of zeolite X that contributes to its unique
method of separating hydrogen sul?de from a vapor
mixture thereof with hydrogen and/or alkanes contain
position among adsorbents is that of adsorbing large
quantities of adsorbate at either very low pressures, at
ing less than six carbons per molecule. Still more par
very low partial pressures, or at very low concentrations.
ticularly, the invention relates to a method for preferen 15 One or a combination of one or more of these adsorption
tially adsorbing hydrogen sulfide from fuel gases.
characteristics or others can make zeolite X useful for
This application is a continuation-in-part of copending
numerous gas or liquid separation processes where adsorb
‘patent application Serial No. 400,386, ?led December
ents are not now employed.
24, 1953, now abandoned.
' Illustrating the utility of this invention, it may, for
example, be desirable to remove hydrogen sul?de from
mits more ef?cient and more economical operation of
numerous processes now employing other absorbents.
fuel gases such as natural gas. Hydrogen sul?de is a
common undesirable impurity in such fuels which con
‘exhibit any appreciable molecular sieve action, whereas
sist primarily of alkanes and hydrogen. Such fuel gases
may be “sweetened,” i.e., have the undesirable hydrogen
sul?de removed therefrom, by the present adsorption
In the tables which follow, the term “Weight %
adsorbed” refers to the percentage increase in the weight
The use of zeolite X per
Common adsorbents like silica gel and charcoal do not
the various forms of zeolite X do.
of the adsorbent. The adsorbent was activated by heat
process.
ing it at a reduced pressure to remove adsorbed mate
Broadly, the invention comprises mixing molecules,
rials.
Throughout the speci?cation the activation tem
in a fluid state, of the materials to be adsorbed or sepa
perature for zeolite X was 350° C., and the pressure at
rated with a crystalline synthetic dehydrated zeolite X, 30 which it was ‘heated was less than about 0.1 millimeter
and effecting the adsorption of the adsorbate by the
of mercury absolute unless otherwise speci?ed. Like
zeolite.
wise, the pressure given for each adsorption is the pres
Zeolite X, and the methods for making zeolite X,
sure of the adsorbate under the adsorption conditions
are described in detail and claimed in US. patent appli
unless the contrary is speci?ed.
cation Serial No. 400,389, ?led December 24, 1953, now 35
The present process for separating hydrogen sul?de
U.S. Patent No. 2,882,244, issued April 14, 1959, in the
from certain vapor mixtures depends upon the selectivity
name of R. M. Milton.
of the internal surfaces of the zeolite X crystal towards
It is the principal object of the present invention to
this strongly polar compound as compared with the al
provide a process for the selective adsorption of mole
kanes and hydrogen. Zeolite X is capable of adsorbing
cules from ?uids. A further object of the invention is 40 all of these compounds based on a consideration of the
to provide a method whereby certain molecules may be
zeolite X pore size and critical molecular dimensions of
adsorbed and separated by crystalline synthetic zeolite
the compounds. For example, the pores of zeolite X'are
X from ?uid mixtures of these molecules and other 31 sufficiently large and in fact do receive methane, octane
molecules.
and hydrogen molecules.
The formula for zeolite X may be Written as follows: 45
Based on these considerations, one skilled in the
art would logically conclude that zeolite X would not
possess any particular‘ selectivity for hydrogen sul?de in
D.
In this formula “1* ” represents a metal, "11” its valence,
and “Y” may be any value up to 8 depending on the
’ , preference to the other constituents of the present vapor
mixture. Contrary to these expectations, it has been discovered that zeolite X possesses an extremely strong
selectivity for hydrogen sul?de to the substantial exclu
sion of alkanes and hydrogen. One reason for this
identity of the metal and the degree of hydration of the
crystal. X-ray diffraction data may be employed to de
selectivity is the highly polar nature of hydrogen sul?de
?ne the crystal structure of zeolite X. Such information
as compared with the other possible constituents of the
and processes for synthesizing zeolite X, are provided in 55 vapor mixture. Since the lower molecular Weight al- p
U.S. Patent No. 2,882,244.
kanes and hydrogen are the major components of fuel
The adsorbents contemplated herein include not only
‘gases such as natural gas, an adsorption process utilizing
the sodium form of zeolite X which is a common form
zeolite X as the adsorbent is quite effective for the
produced, but also crystalline materials obtained from
sweetening of such fuel gases. Table I contains data
such a zeolite by partial or complete replacement of the 60 showing the percent of the various gases adsorbed by
sodium ion with other cations. Sodium cations can
zeolite X. In Table I, all of the adsorptions were car~
be replaced, in part or entirely, by other ions. For ex
ried out at 25° C.
ample, this may be accomplished by ion exchange tech
An important characteristic of zeolite X is its property
niques.
of adsorbing large amounts of adsorbates at low adsorb
3,078,641
A.
3
ate pressures, partial pressures, or concentrations.
drated zeolite X.
This
The ?ow is stopped as soon as hydro
gen sul?de is detected in the etlluent. At this point, the
property makes zeolite X useful in the removal of adsorb~
etlluent is substantially free of hydrogen sul?de contami~
able impurities from gas and liquid mixtures, since it has
nation. If large amounts are tolerable, the adsorption
a relatively high adsorption capacity even when the mate
rial being adsorbed from a mixture is present in very low 5 can be continued until the hydrogen sul?de level reaches
the predetermined value.
concentrations. E?icient recovery of minor components
of mixtures is also possible. High degrees of adsorption
Example 11
at low pressures on zeolite X is also illustrated in Table I.
TABLE I
Adsorhatc
111$ ...................... ._
Adsorbent
NaiX ..... ..
Pressure
Wt. percent
mm. Hg
adsorbed
0.5
11.5
11
400
22. 6
35. 0
(EN; ...................... .-
N?zX _____ _.
500
Less than 1
CQI'IG _____________________ N
NBQX _____ ._
5
O. 2
25
300
700
0. 8
8. 3
10. 2
1
0. 8
5
4
25
3. l
2. G
ll. 1
700
14. 6
700
17. 3
710
729
17. (i
17. 6
C515 ..................... ._
NnzX ..... __
Xl-Cqllm ................... _-
NZMX ..... _.
i-Cqll’w ___________________ __
N?gX _____ ..
11-05111: ___________________ _.
B43511" ................... ..
Xl~CaH1z ___________________ __
t
Natural gas, containing principally methane, ethane,
10 propane, hydrogen and lesser amounts of the butanes,
0.2
2.4:
5. 5
400
11. 5
18. 4
205
18. 4
224
19. 3
O. 18
4. 8
0. 22
20
20
20
20
20
20
10. 2
19. 2
18. 3
15. 8
17. 9
l9. 2
16. l
11.0
30
2. 3
5. 0
2. 3
20. 8
20. 8
14. 2
5. 0
14. 2
An advantage that may be taken of this high adsorp
tion capacity at low pressures is the operation of adsorp—
pentanes and hexanes, together with sulfur impurities,
chie?y hydrogen sul?de and the lower boiling mercaptans,
particularly methyl mercaptan, is passed through a bed
of dehydrated sodium zeolite X. The ef?uent is sub
15 stantially depleted in hydrogen sul?de and the mercap
tans.
If the process is stopped as soon as sulfur com
pounds are detected in the e?iuent, the effluent will be
almost completely free of contamination.
Zeclite X may be used as an adsorbent for the purposes
20 indicated above in any suitable form. For example, a
column of powdered crystalline material has given excel
lent results as has a pelleted form obtained by pressing
into pellets a mixture of zeolite X and a suitable binding
agent such as clay.
What is claimed is:
25
1. A process ‘for the separation of hydrogen sul?de
from a vapor mixture thereof with at least one gas se
lected from the group consisting of hydrogen and alkanes
containing less than six carbon atoms which comprises
30 intimately contacting said vapor mixture with crystalline,
synthetic, at least partially dehydrated zeolite X whereby
said hydrogen sul?de is preferentially adsorbed from said
mixture, and separating the hydrogen sul?de-depleted
35
vapor mixture from said zeolite X.
2. A process in accordance with claim 1 wherein said
zeolite X is sodium zeolite X.
y
3. A process according to claim 1 in which said vapor
mixture contains hydrogen sul?de and methane.
4. A process according to claim 1 in which said vapor
mixture contains hydrogen sul?de and ethane.
,
tion processes at higher temperatures than are normally 40
5. A process according to claim 1 in which said vapor
used with common adsorbents. The adsorption power
mixture contains hydrogen sul?de and propane.
of physical adsorbents usually decreases with increasing
6. A process according to claim 1 in which said vapor
temperature, and therefore while the adsorption capacity
mixture contains hydrogen sul?de and butane.
of many adsorbents in a certain separation may be suf?
7. A process according to claim 1 in which said vapor
cient if operated at one temperature, the capacity may 45 mixture contains hydrogen sul?de and pentane.
not be suflicient to make operation feasible at a higher
8. A process according to claim 1 in which said vapor
temperature. With strongly adsorbing zeolite X, how~
ever, substantial capacity is retained at higher tempera
tures.
The present separation is preferably eifected at a
temperature below 973“ K., since the crystal structure
of zeolite X will be disrupted or damaged with conse
quent loss of adsorption capacity and reduction in pore
size. For maximum efficiency this adsorption process is
performed at temperatures less than 616° K. but higher
mixture contains hydrogen sul?de and hydrogen.
References Cited in the ?le of this patent
UNITED STATES PATENTS
2,270,058
2,882,244
Jones ________________ __ Jan. 13, 1942
Milton ______________ .._ Apr. 14, 1959
OTHER REFERENCES
than 283° K. This is for the reason that above such 55
Separation
of
Mixtures Using Zeolites as Molecular
range, the hydrocarbon constituents of the vapor feed
Sieves, Parts I, II, III, Barrer, J. Soc. Chem. Ind., vol.
stream in contact with zeolite X will tend to isomerize,
64, May 1945, pages 130—135.
hydrogenate, aromatize and polymerize, all of which‘ will
Molecular-Sieve Action of Solids, Barrer, Quarterly
clog the pores and cause loss of capacity of zeolite X
molecular sieve. Also, to employ adsorption tempera 60 Review (1949), Chem. Society, London, pages 293-320.
Crystalline Zeolites, I, The Properties of a New Syn
tures below about 283° K., a refrigerating system would
thetic Zeolite, Type A. Breck'et al., J.A.C.S., vol. 78, No.
23, Dec. 8, 1956, pages 596345971.
Examine These Ways To Use Selective Adsorption,
Example I
65 Linde Co., Petroleum Re?ner, vol. 36, No. 7, July 1957,
A mixture of propane containing about 0.1 mole frac
pages 136-140.
tion of hydrogen sul?de is passed through a bed of dehy
be required which increases the complexity and expense
of operation.
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