CA2015069A1 - Process and adsorbent for separating co from a mixture thereof with hydrocarbon - Google Patents

Abstract

"PROCESS AND ADSORBENT FOR SEPARATING CO2 FROM A MIXTURE THEREOF WITH HYDROCARBON"

ABSTRACT

Clinoptilolites, including both natural clinoptilolites and those which have been ion-exchanged with metal cations such as lithium, sodium, potassium, calcium, magnesium, barium, strontium, zinc, copper, cobalt, iron and manganese, are useful as selective adsorbents for the removal of traces of carbon dioxide from streams of hydrocarbons having kinetic diameters of not more than about 5 Angstroms.
Also disclosed is a modified clinoptilolite adsorbent containing sodium cations and non-sodium cation produced by a two step ion-exchange process wherein the first step exchanges sodium cations and the second step exchanges the non-sodium cation.

Description

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"PROCESS AND ADSORBENT FOR SEP~RATING CO~
FROM A MIXTURE THEREOF WITH HYDROCAR~ON' FIELD OF THE INVENTTON

This invention relates to a process for the purification of hydrocarbons contaminated with CO2. More specifically, this invention relates to a process for the removal of carbon dioxide and, optionally, water from hydrocarbons using clinoptilolites adsorbent. The clinoptilolites used may be either natural clinoptilolites or clinoptilolites which have been modified by ion-exchange with one or more o~ a number of metal cations.

BACKGROUND OF THE INVENTION

It is known that mixtures of molecules havingdiffering sizes and shapes can be separated by contacting the mixture with a molecular sieve into which one compo-nent of the mixture to be separated is more strongly adsorbed by the molecular sieve than the other. The strongly adsorbed component is preferentially adsorbed by the molecular sieve and leaves behind outside the molecu-lar sieve a mixture ~hereinafter re~erred to as the "firstproduct mixture") which is enriched in the weakly or non-adsorbed component as compared with the original mixture.
The first product mixture is separated ~rom the molecular sieve and the conditions of the molecular sieve varied (typically either the temperature of or the pressure upon the molecular sieve is altered), so that the adsorbed 2 ~ g ~aterlal ~esomes desorbea, thereby prsduc~ng ~ ~econd ~ix~ure ~hich i~ enric~ed in She adsorbed component ~s c~mpared with the original mixture.
Whatever ~he exact details of the apparatus and process steps used ln ~uch a process, cr~tical factors include the capacity of the molecular sieYe for the more adsorbable components and the selactivity of the molecular sieve (iOe., th~ ratio in which the . components to be separated are adsorbed). In many ~uch processes, z~olites are the preferred ~dsorbents because o~ their high adsorption capacity and, when chosen so that their pores are of an appropriate size, their high selectivity.
Most prior art attempts to use zeolites in the separation ~f gaseous mixtures have bean made with synthetic zeolitesO Although natural zeolites are readily available ~t low cost, hitherto the natural zeoli~es have not been favored as adsorbents b~cause it has been felt that the natural zeolites are not sufficiently consistent in compos~tion to be useful as adsorbents $n such processes. However, there are relatively ~ew ~ynthetic zeolites with pore sizes in the range of a~out 3 to 4 A, which Ls the pore size range of ~nterest for ~ number of potentially important gaseous separations t for example ~aparation of carbon diox~de ~rom ~ethane and other hydrocarbons, including ethylene 2 ~

~nd propylen~, ha~lng kinetic diameter~ not gre~t~r tha~
about 5 A.
As a result o~ th~ lack o~ zeol~te~ havlng pore sizes ~n the range of 3 to 4 A, certain ~mportant industrial separations are conducted rather inefficiently. For exampl2, in the manufacture of polyethylene, so-called ~thylene streams are produced which contain ethylene, ethane and propane, together with traces (typically of the order of 10 parts per million) of carbon dioxide. It is necessary to lower the already ~mall proportion of carbon dioxide further before the ethylene ~tream reaches th~ polymerization reactor, because the presence of even a few paxts per : million of carbon dioxide poisons commercial ethylene lS polymerization catalysts. At present, carbon dioxide removal is usually effected by passing the ethylene stream through a bed of calcium zeolite A. Although calcium A zeoli.~e is an efficient adsorber of carbon dioxide, it ~lco adsorbs relatively large guan~itie~ of ethylene, and given the much greater partial pressure of ~thylene in th~ ethylene ~tream, the quantity of ethylene adsorbed is much greater than that of carbon dioxide. ~hus, relatively large guantities of ethylene ~re wa~ted in the removal o~ the traces of car~on dioxide. Similar problems are encounter~d in the propylene ~tream used to manufacture polypropyle~e.

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Clinoptilolit~s are ~ Xnown cl~ss o~
natur~l zeolites which have not hitherto been u~2d ~xtensi~ely ~or separation o~ gaseous mixtures, nlthough a few such sPparat~ons are described in the literature.
For example, ~uropean Patent Application No. 84850131.8 (Publication No. ~32 239) describes a procesC for the separation of oxygen and argon using as the adsorbent raw clinoptilolite (i.e., clinopt~lolite which has not been sub~ectsd to any ion-exchange~.
Industrial Gas Separation (published by the American Chemical Society), Chapter 11, Franki2wicz and Donnell, ~ethane/Nitrogen Gas Separation over the Zeolite Clinoptilolite by the Selecti~e Adsorptio~ of Nitrogen (1983) describes separ tion of gaseous ~ixtures of me~hane and nitrogen using both raw clinoptilolitP
and clinoptilolite which had been ion-exchanged with calcium.
It is known that the adsorption properties of many zeolites, and hence their ability to separate gaseous mixtures, can be varied by incorporating various metal cations into ~he ~eolite , typically by ion-exchange or impregnation. For exa~ple, U.S. Patent No. 2,882,243 to Milton describe~ the use of zeolite A
having a silica/alumina ratio o~ 1~85 ~ 0~5 and containing hydrogen, amm~nium, alkali ~etal, alkaline earth m~tal or transition metal cations. Ihe patent 2 ~ 9 ~tates ~hat R A 2eolite adsorbs w~ter and exclude~
hydrocarbon~ and alcohol~, while Ca A zeolite adsorb3 ~tra~ght-chain hydrocarbons but excludes branched-ehain ~nd aromatic hydrocarbons.
In most cases, the changes in the adsorption properties of zeolites ~ollowing ion-exchange are consistent with a physic~l blocking of the pore opening by the cation introduced; in general, in any given zeolite, the larger the radius o~ the ion introduced, the s~aller the pore diameter of the treated zeolite (for ~xample, the pore diameter of ~ A zeolite is ~maller than that of Na ~ zeolite), as measured by the size of the molecules which can be adsorbed into the zeolite.
It has now been discovered that clinoptilolites (both natural clinoptilolites and clinoptilolites which have been ion-exchanged with any one or more of a n~mber of metal cations) exhibit adsorption properties which are use~ul in the separation of carbon dioxide ~rom hydrocarbons. In contrast to mo~t prior art zeolites ~odified by ion-excha~ge, ~h~
pore sizes, and hence the adsorption properties, of ion-~xchangsd clinoptilolites are not ~ ple function of the ioJlic radius of the ~xchanged cations.

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SUMMARY OF THE INVENTION
This ~nvention provides a process for carbon dioxide from a mixture thereof with a hydrocarbon having a kinetic diameter of not more than about 5 Angstroms, which process comprises contacting the mi~ture with an adsorbent containing clinoptilolite at C02 adsorption conditions, thereby causing the carbon dioxide to be selectively adsorbed into the clinoptilolite. If the hydrocarbon also contains water as an impurity, contacting the hydrocarbon with the clinoptilolite will normally remove the water as well as the carbon dioxide.
Desirably, the hydrocarbon contains from 1 to 5, preferably 1 to 4, carbon atoms and is an acyclic hydrocarbon.
This invention also provides a modified clinoptilolite adsorbent wherein at least about 40 percent of the ion-exchangeable cations originally present in the natural clinoptilolite are replaced by sodium and a cation selected from sodium, potassium, calcium, magnesium, barium, strontium, zinc, copper, cobalt, iron, manganese and mixtures thereof, the modified clinoptilolite adsorbent being produced by a process comprising subjecting a natural clinoptilolite to a first ion-exchange step with a solution containing sodium cations until at least about ~0 percent of the ion-exchangeable non-sodium cations in the natural clinoptilolite have been replaced by sodium cations, thereby producing a sodium clinoptilolite, and thereafter subjecting the resulting sodium clinoptilolite to a second ion-exchange step with a _7~ 6 9 solution containing any one or more of lithium, sodium, potassium, calcium, magnesium, barium, strontium, zinc, copper, cobalt, iron and manganese cations until the desired degree of ion-exchange with the non-sodium cation is attained.
DETAILED DESCRIPTION OF THE INVENTION
This invention provides a process for separating a minor proportion of carbon dioxide from a mixture thereof with a hydrocarbon having a kinetic diameter of not more than about 5 Angstroms, which process comprises contacting the carbon-dioxide-containing hydrocarbon with a clinoptilolit adsorbent at CO2 adsorption conditions.
The clinoptilolites used in the process of the present invention may be natural clinoptilolites. However, being natural materials, clinoptilolites are variable in composition; chemical analysis shows that the cations in clinoptilolite samples from various mines vary widely.
Moreover, natural clinoptilolites frequently contain substantial amounts of impurities, especially soluble silicates, which may cause difficulties in the aggregation or pelletization of the clinoptilolite (discussed in more detail below), or may cause undesirable side-effects which would inhibit practicing this invention.
Accordingly, before being used in the process of the present invention, it is preferred that the clinoptilolites be modified by ion-exchange with at - 2 ~
-B-lea~t one ~etal cation. A~ong ~he cation~ ~hlch c~n u3e~ully be ion-exchanged lnto clinoptilolite~ are lithiu~, sodium, potass~u~, ~agnesiu~t calc~um, strontium, bariu~, z~nc, ~opper, cobalt, iron and manganese cations. Desirably, the lon-exchange i5 continued until at least about 40 percent of the cations in the natural clinoptilolite have been replaced by one or more of these cat~ons. The pre~erred metal cations for treatment of the clinoptilolites used in the process of the present invention are lithium, ~odiu~, calcium, magnesium, barium and strontium cations, with sodium being especially preferred. When 60dium is used as the ion-exchange metal cat~on, it is preferred that the ion-exchange b~ continued until at least about 50 percent of the total cations in the clinoptilolite ~re replaced by sodium cations.
Since clinoptilolite is a natural ~aterial, the particle sizes o~ the commercial product varies, and the particle size of the clinoptilolite may ~fect the speed and completeness of the ion-exchange react~on. In general, it ~s recomme~ded that th p~rticle size of the clinopt1101ite used in the ion-exchange reaction be not great~r than about 2.38 mm in diameter (8 U.S. Mesh).
Although the particle sizes of many commercial clinoptilolites axe greater, their particle sizes are readily reduced by grinding or - 2 ~
_9_ other techn~qu~s wh~ch ~ill be ~a~lliar to those ~k~ d in the lon-exchange o~ ~olecular sieves.
~echn$gues ~or the ion-exchange of zeol1tes ~uch as clinoptilolite are well-known to those ~killed in the molecular sieve art, and hence will not be described in detail herein. In the lon-exchange, the cation is conveniently present in the eolution in the form of a soluble salt--typically it is chloride. It is desirable that the ion-exchange be continued until at least about 40 percent, and preferably 60 percent, of the cations in the original clinoptilolite have been replaced, and in most cases it is convenient to continue the ion-exchange until no further amount of the desired cation can easily be introduced into the clinoptilolite. To secure maxi~um replacement o~ the original j clinoptilolite cations, it is recommended that the ion-! exchange be conducted using a ~olution containing a guantity of the cation to be introduced which is ~rom a~out 2 to ~bsut 100 ti~es the ion-exchange capacity of the clinoptilolite. Typically the ion-exchange s~lution will contain ~rom abouk 0.1 to about 5 moles per liter of the cation, and will be contacted with the original clinoptilolite for at least about 1 hour~ The ion-exchange ~ay be conduGted at ambient temperature~ -although in ~any cases carrying out the ~on-exchange at r~

~levated temperatur~, u~ually 1~5~ than lOO-C, accel~rates the ~on-exchange proce~.
Since clinoptilolite 15 ~ natur~l ~aterial of variable composit~on, the cations present ~n the raw clinoptilolite vary, although typically the cations include a major proportion of alkali ~etals. It is typically found that, even after the most exhaustive ion-exchan~, a proportion of the original . clinoptilolite cations can not be replaced by oth~r cations. However, the presence of this ~mall proportion o~ the original clinoptilolit~ cations does not interfere with the use o~ the ion-exchanged clinoptilolites in the process o~ the present invention.
Any of the modified ~linoptilolites of the present invention can be prepared directly by ion-exchange of natural clinoptilolite with the ', appropriate cation. ~owever, in practice such direct ion-exchange may not be the ~ost economical or practical technique. Being natural ~inerals, clinoptilolites ~re variable in composition and requently contain substantial amounts o~ impurities, especially ~olubl~
silicates. ~o ensure as complete an ion-exchange as possible, and al o to remove impurities, it is desirable to ef~ect th~ ion-sxchanye of the clinoptilolite usi~g a large excess of the cation which it is deslred to ~ntroduce. How~ver; if, for example, a large exces~ of 2 ~
barium is used in such an ion-exchange, the disposal and/or recovery of barium from the used ion-exchange solution presents a difficult environmental problem, in view of the limitations on release of poisonous barium salts into the environment. Furthermore, some impurities, including some silicates, which are removed in a sodium ion-exchange are not removed in a barium ion-exchange because the relevant barium compounds are much less soluble than their sodium counterparts.
In addition, when the modified clinoptilolites of the present invention are to be used in industrial adsorbers, it is preferred to aggregate (pelletize) the modified clinoptilolite to control the macropore diffusion to increase the crush strength of the resulting adsorber material and to minimize pressure drop in the adsorber. If the binderless clinoptilolite is used as the adsorbent, the clinoptilolite may compact, thereby blocking, or at lPast significantly reducing flow through, the column. Those skilled in molecular sieve technology are aware of conventional techniques for aggregating molecular sieves; such techniques ~sually involve mixing the molecular sieve with a binder, which is typically a clay, forming the mixture into an aggregate, typically by extrusion or bead formation, and heating the formed molecular sieve/clay mixture to a temperature of about 600-700C to convert the green aggregate into one which is resistant to crushing.

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~ he binder~ u~ed t~ aggreg~te ~he clinoptilolites ~y in~lude clay~ ailicas, aluminas, Detal oxides ~nd m~xtures thereof. In add~tion, the cl~noptilolites m~y be formed with material~ such as silica, alumina, silica-alum$na, silica-magnesia, 6ilica-zirconia, 6ilica-thoria, silica-berylia, and silica-titania, as well as ternary composltions, such as 6ilica-alumina-thoria, silica-alumina~zirconia and clays present as binders. The relative proportions oP the above materials and the clinoptilolltes may vary widely with the clinoptilolite conten~ ranging between 1 and 99 percent by weight of the composite with 70 to 95 percent typlcally being preferred. Where the clinoptilolite is to be formed into aggregates prior to use, such aggregates are desirably about 1 to about 4 mm. in diameter.
! Although the iOn-exchanye(s) needed to produce the modified clinoptilolites of this invention may be cond~cted either before or after aggregation, it i~
often lnadvisable to subject raw clinoptilolite to the process of conver ion to the aggregate, 6ince variaus impuriti~s ~ay be affected by the heat required ~or aggregation and may interfer~ with the formation of aggregates. However, in ~ome cases, ~t may also be desir~ble to avoid Fub~cting 60me ~odified cl~noptilolites of the invention to the heat reguired ~or aggregatlon, ~ince certain of these ~odi~ied 2 ~ 9 -13~
cl~nopt~lol~tes ~re a~ected by heat, ~ discuss~d in more d~tall below.
To ~oid the aforementioned di~iculti~, it ts generally preferred to produce modifiQd S clinoptilolites of t~e present invention other than ~odium clinoptilolite by first sub~ecting raw clinoptilolite to ~ sodium ion-exchange, aggregating the ~odium clinoptilolite thus produced, and then effecting a second ion-exchange on t~e aggregat2d material to introduc~ the desir~d non-sodium c~tions. ~hen ~ 60dium clinoptilolite itself is to be used, it is in general not necessary to carry out a second sodium ion-exchange a~ter aggregation; the aggregated 80~ium clinoptilolite may be used without urther processing and ~ives satisfactory results, which do not appear to be æigni~icantly improved by a sec~nd ion-exchange.
Before being used in the processes of the present invention, the clinoptilolites need to be activated by heating. If the clinoptilolite is aggregated as discussed abov~, ths heat required ~or aggregation will normally be ~u~ficient to e~fect activation ~l~o, 80 ~hat no furt~er hea~ing is reguired.
I~, however, ~he clinoptilolite is not to bs aggregated, ~ ~eparate activation ~tep will usually be reguira~.
2~ ~odium clinoptilolite can be activated by heating ~n air or vacuum to approximately 350-C for about 9 hour~ The temperature needed ~or activati9n o~ ~ny ~peci~en o~
el~noptllolit¢ is easily determined by routine ~mpiri~al tests which pose no d~fficulty to those ~k~lla~ ln molecular sieve technology.
If the modified clinoptilolites are produced by the preferred double exchange process di~cussed above, in which a raw clinoptilolite is ~irst ~odium ? ion-exchanged, the resultant sodium clinoptilolite aggregated, and finally the aggregated ~od~um clinoptilolite is ion-exchanged with the desired non-sodium cation, it is normally necessary to effect a second activation of the final product; however, the activation temperature required is not as high as that required ~or aggregation, and consequently one avoids exposing the clinoptilolite product of the second ion-exchange step to aggregation temperatures. In some cases, it is desirable i to limit the temperatures to which some o~ the twice exchanged clinoptilolites of the present invention are exposed ~ince exposure of the modified ~linoptilolit~ to excessive temperat~res may cau~e ~tructural damage o~
the clinoptilolite which may rend~r it less ef~ective in the process of the present in~ention.
The process o~ the present invention is primarily intQnded for re~oval of traces of car~on 2S ~ioxide ~rom hydrocar~ons, especially ethylene ~treams (comprising mai~ly ethylene and ~thane) sur~ as those 2 ~

u~ed in ~e produc:tion Or poly~thylene ~and th¢
corre~ponaing propylene stream~, comprising malnly propylene and propane, such as those u~ed ~n the manufacture o~ polypropylene), where the presence of e~en a few parts per million of carbon dioxide causes ~evere poisoning of the polymerization catalyst. In such streams, the carbon dioxide content of the gas i8 normally not greater than about 200 vol. parts per million, and the carbon dioxide partial pressure not greater ~han about 20 Torr. (0.026 atmospheres or 2.67 kPa). As alread~
mentioned, sodium clinoptilolite is the preferred material for this process. The same process will remove any water which ~ay be present in the hydrocarbon stream, and this removal of water is also desirable ~ince water, even in very small amounts, is active as a polymerizatio~
! catalyst p~ison.
I The present process ~ay also be use~ul for the ~eparation o~ carbon dioxide ~rom methane or other hydrocarbons for use in ~ process such ag ~te~m reforming. The present invention ~ay ~lso be used to separate carbon dioxide ~rom butanes and butenes~ or even larger hydrocarbons (for example n-h~xane) which have kinetic diameters not greater than about 5 ~.
Since these types o~ processes involve th~
6eparation Or minor amounts o~ carbon dioxid~ (and optionally water) impurity ~rom ~uch larger amounts of 2 ~ ~ r~ ~3 ~ 9 hydrocarbons, they may be effected in the conventional manner by simply passing the hydrocarbon stream through a bed of the clinoptilolite maintained at CO2 adsorption conditions including a temperature in the range of -15 to 60C and a pressure selected to achieve the target flow rate of the input stream through the bed. The bed is normally in aggregate form. As the operation of the process continues, there develops in the bed a so-called "front" between the clinoptilolite loaded with carbon dioxide and clinoptilolite not so loaded, and this front moves through the bed in the direction of gas flow. Before the front reaches the downstream end of the bed (which would allow impure hydrocarbon gas to leave the bed), the bed is regenerated by cutting off the flow of the feed hydrocarhon gas mixture and passing through the bed a purge gas which causes desorption of the carbon dioxide ~and water, if any i5 present) from the bed. In industrial practice, the purge gas is typically nitrogen or natural gas heated to a temperature in the range of 50 to 350C, and such a purge gas is also satisfactory int he processes of the present invention.
A nitrogen purge operation leaves the bed loaded with nitrogen. To remove this nitrogen, it is only necessary to pass one or two bed volumes of the hydrocarbon stream through the bed; the resultant gas leaving the bed is mixed with nitrogen and should normally be discarded. The loss of gas resulting from such discarding is negligible, since the purging and subse~uent removal of nitrogen only require to be J

-a7-per~or~d af~er the pas~age o~ hun~reds or thousand~ of bed volumes of impure hydrocarbon.
I~ the process o~ the pres~nt ~nvsntion is to be u~ed ~o Beparate carbon dioxide ~rom hydrocarbons containing larger amounts of carbon dioxide (of the order of 10 percent), other conventionzl pressure swing adsorption and temperatur~ ~wing adsorption techniques may be used inlieu of or in combination with the instant process. Such techniques are well known to tho~e skilled in lO molecular sieve technology; see, for example, U.S. Patents Nos.:
3,430,418 3,738,~8~
3,986,849 4,398,926 4, S89, 888 and 4,723,966, ! and British Patent No. 1,536,995.
It should be noted that the change in pore eize of the cl~noptilolite after ion-exchange is ot a simple function of the ~onic radiuc of th~ cation ~ntroduced. It has been determin~d empirically, by measuring the adsorption of variou~ly ~ized gas molecules into ~on-exchanged clinoptilolites, tha~ the order o~ pore sizes in such ~linoptilolites ~:
CaClino ~ NaCl~no ~ ~iClino < ~gClino ~ Zn~lino < XClino ~ Sr~lino < BaClino 2 ~ ' fl wh~re ~Clino" r~presents the cllnopt$101it~ lattice ~ra~Qwork. Since calciu~ and ~a~nesium catlons have ~onic radii smaller than 6trontium and barium ~ations, and ~ince sodium and lith~um cations hav2 ioni~ radii smaller than potassium cations, increase in radiuu of ~on-exchanged cation does not always correlate with decrease in pore size of th~ clinoptilolite, and thus, unlike many other zeolites, the change in pore ~ze of . ion-exchanged clinoptilolites cannot be a simple matter o~ pore blocking.
Although ion-exchange of clinoptilol~te does produce a modified clinoptilolite having a consistent pore size, the exact pore size depends not only upon the metal cation(s) exchanged but also upon the ther~al treatment of the product following ion-exchange. In general, there is a t~ndency for the pore size of the ~odified clinoptilolites of this in~ention to decrease with exposure to increasing temperatura. Accordingly, in selecting an activation temperature for the ~odi~ied clinoptilolites, care should be taken not to heat modified clinoptilolites to temperatures which cause reductions in pore size o s~vere as to adversely affect the performance of the modified clinoptilolite in the process of the present invention.
Although the behavior of khe modified clinoptilolites on exposure to heat does limit ~he 2~ ~a~s --19~
activation temper~tures ~h~ch can ~e e~ployed, ~he ther~al reduction ~n pore ~ize ~oe~ o~f~r the po~sibillty of ~ e tuning~ the pore size Or ~ modified clinoptilolite to opti~ze its performancQ in the process of the present invention.
~ he following Examples are given, though by way o~ illustration only, to show preferred processes of the present invention. All adsorption measurements are . at 23'C unless otherwise stated. ~urthermore, all separation factors given in the form "Separation factor X/Y"
are calcul~ted by:
Separation factor X/Y e p~ /Px . ~
where Px and Py are the partial pressures of components X and Y
in the feed gas respectively and Lx and Ly are the corresponding loadings of X and Y in the adsorbent expressed as millimoles per gram of adsorbent.
EX~MPLES
Example 1: Natural Clinoptilolites Seven different samples of commercially available natural or raw clinoptilolites were used in these experimen~s and as starting materials for the preparation of some of the modified clinoptilolites prepared in the later Examples. The chemical analyses of these natural clinoptilolites are shown in Table 1 below, while carbon dioxide and ethane separation data are shown in Table 2.

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For coDIp~ri~on~ Tal: lQ 2 include~ dat~ for zeolit~ 5A, comm~rcial ~nat~ri~l u~ed ~or gas separat~ons.

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Ç ~ ç;~ elinoptilslite ~wt. percentL ~ E E G
~oss on 12.6 15,2 13.2 11.6 13.6 13.8 13.3 ignition Al2O3 14.188 12.618 12.903 12.670 13.426 13.573 13.379 (anhydrous) sio 72.883 75.236 76.152 75.924 75.9~4 74.710 75.779 (a ~ydrous) Na20 3.547 2.252 4.090 3.801 3.831 3.840 3.656 (anhydrous) X~o 1.796 2.170 4.078 4.355 2.280 2.541 1.984 ~anhydrous) MgV 1.796 2.123 0.325 0.575 0.714 1.044 0.734 (anhydrous) CaO 3.3~1 2.724 1.039 1.403 1.887 2.390 2.434 (anhydrous) SrO 0.049 0.018 - 0.032 0.345 0.563 0.406 (anhydrous~
BaO 0.135 0.051 - 0.376 0.071 0.246 0.248 (anhydrous) Fe2O3 2.208 3.054 0.919 0.989 1.262 1.508 1.292 tanhydrous) ~ABLE 2 linoptilol~te Adsorption lwt. percent) A ~ C ~ ~ ~ G 5A
Co , 5 ~orr, 5.1 5.6 6.8 6.1 5.8 ~.9 ~.4 8.
3 ~ours C2H4, 0.981 2.177 0.990 ~.904 1.453 1.098 2.222 7.700 700 Torr 3 hour~
Separation 463 229 612 601 356 398 257 95 ~actor C02/C2H~

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From the d~ta ~n ~ble 2, lt ~ e seen th~t all the ~even d insptilolite ~pecimens had carbon diox~de/e~hane ~2p2rat~0n ~actors ~ubstantially better than tha~ of zeol$te 5A.
~xample 2 : Sodium ~lino~tilollte 1500 Gm. (dry weight) of clinoptilolite C in Example 1 was ground to particles having a diameter of 0.3 to 0.59 mm ; (30 x 50 U.S. mesh) and placed in a jacketed glass column. The column was heated to 80C by passing oil through the jacket, and 30 liters of 1.86 N sodium chloride solution was passed through the column at a flow rate of 19 ml/minute for 16 hours.
The clinoptilolite was then washed by passing distilled water through the column, and dried in air at ambient temperature.
The ~odium ~linoptilolite thus produced was subjected to chemical analysis and its ads~rption properties were measured using a ~cBain quartz spring b~lance. Before being used in the adsorption tests, the eodium clinoptilolite was activated by heating to 375-C
under vacuum ~or one hour.
Part of the sodium clinoptilolite was then 6ubjected to a second ~odium ion-exchange. 200 Grams of the sodium clin4ptilollte were treated in th ~ame colu~n ~s before ~y passing ~ liters o~ 0.5 ~ ~odium chloride soluticn ov~r ~he clinoptilolite or 16 hours.
The chemical analysis and adsorption properties o~ the 2 ~ 9 doubly-~xchanged ~odium ~linoptilollte wQre then ~easured in the ~a~e manner a~ b~ore.
~ he chemical analyses of both ~odium clinoptilolltes ~re ~hown in Table 3 below, and their adsorption properties are shown in Table 4, along with those of 5A zeolite; in both cases, the singly-exchanged material is designated "NaClino", while the doubly-exchanged ~aterial is designated "NaNaClino". For comparative purposes, the chemical analysis and adsorption data ~or th~ clinoptilolite C ~tarting material (given in ~ables 1 and 2 above) are repeated in Tables 3 and 4.

Component (wt. percent) NaClino NaNaClino Clino C
Loss on 13.3 14.5 13.2 ignition A1203 13.033 12.982 12.903 ( anhydrOUS ) Si0 79.123 78~246 76.152 (a ~ydrous) Na20 6.332 6~199 4.090 (anhydrous) Y~O 1.465 0.750 4.07a (anhydrous) ~g~ 0.219 - 0.325 (anhydrous) CaO 0.27~ 0.199 1.039 (anhydrous) F~03 0.980 ~ 0.919 (anhydrous) 2 ~

D;a J, el~

cent~ 1~aÇll~ 1~ Çl~no~
C0 ~ ~ ~orr, ~ .8 ~.2 3 hou~s ~, 700 ~orr~ 0.1000.100 - -3 ~our#
S~pflrat~on a749 ~47 ~380 r~tDr CO2/~
l~lat~r~ 4.7 ~orr 13.4 _ ~3,~
S~para~lon 17 84 8 - 27 68 ~ac'c4r ~20~C%4 ctH6, 50 ~r~ 0.1000~100 - 3. l 3 hours aoparatlon - 23go - 132 ft.~tor ~2~ 2~
Sep~ration 36B 354 - 18 fa~tor ~02~C2H~
C2H4 S0 ~orr 0.3000.200 ~ 4.8 3 hour~
~eparatlon ~ 7 iactor HzO/C2~4, 50 To~
~epar~ti~n li5 1 ~at~)r Co2/C2H~ ~ 50 Torr ~, 7~ ~o7:~ ~ 0.507 ~.g9P 7.7 3 h~urs ~par~ on - 620~ - S
~CtQ~
HzOJC~H~,, 700 ~o~r ~a~c~on ~ 5 ~e~3E
CO2/~2Hf" 700 To~r 2 ~
-25~
Fro~ the data ln Tablo~ 3 and ~, ~t w~ e ~een that ~oth the ~ingly and doubly-exchanged ~odium clinoptilol$tes would be use~ul ~or the 6eparat~0n of carbon diox~de ~nd water ~rom hydrocarbon gas ~trea~s, S that both are superior to the untreated C11noptilolite C
~or this purpose, and that all three of the ~linoptilolites are much bett~r than 5A zeolite. The second ~odium ion-exchange does no~ appre~iably increase . the sodium content of the ~linoptilol~te, but does reduce the potassium and calc~um contents. However, since the second ~odium ion-exchange does not appreciably increase the relevant separatisn ~actors, in general a si~gl~ ~odium ion-exchange would be sufficient to provide a material 6uitable for use in the process of the present invention.
Example 3 : Potassium clinoptilolite 200 Gm. ~dry weight) of the singly-exchanged sodium clinoptilolite prepared in Example 2 was placed ~ in a iacketed glass column. The c~lumn was heated to 80-C by passing o~l through the jacket, ~nd 9 liter~ of 0.5 ~ potassium chloride solution was passed through the column at a flow ra~e of 9 mlJ~inute ~or 16 hours. The slinop~ilolite was then washed by pass~ng distilled water through the column, and dried in air at a~bient temperature.

2 ~

.~
~ he po~a~iu~ clinoptllol~S~ ~hu~ produce~ was ~ub~ected to chemical ~nalysi~ ~nd ~t~ ad~orption properties were measured u~ing a McBa~n quartz ~pring balance. Before being used i~ the adsorption test~, the potassium clinoptilolite was activated 'Qy heating to 375-C under vacuulD ~or one hour. The resul~s are shown in Tables 5 and 6 ~elow.

Component ~wt. percent! XClino L~ss cn 12 . 4 igni~ion Al203 12 982 (anhydrous~ -SiO 76. 027 ( ar~ydrous ) Na 0 0.251 ( a~hydrous ) 10 . 5~6 (anhydrous) MgO
(anhydrous) CaO 0.148 (anhydrous) 2 ~

~o~LQ~

CO2, 5 ~orr, 5.4 3 hours CH , 700 Torr, 1.1 3 ~ours Separatlon 250 factor Watert 4.7 Torr ~1.0 Separation 1324 factor C2H6, 50 Torr 2.3 3 hours Separation 85 factor H20/Cj!H6 Separation 16 factor C2H4 50 Torr 2.2 3 hours Separation 83 factor Separation 16 ~actor ~02/C~

These results ~ndicate that the potassi~m clinoptilolite was ~ble to separate carbon dioxide ~nd water from hydrocarbon ~treams, but that its r~levant ~eparation factors were lower than those of the natural 2~5~
~28-cllnoptllolite ~ro~ wh~ch i~ i~ der~ved or Sho~e o~ ~he ~odiu~ clinoptilol~tes prepared in Example 2 above~
Th~se ad~orption results also demonstrate that, contrary to what would be expected on the basis of the ionic radii of ~he cat~ons involved tNa4 has a Pauling ionic radius o~ O.95 A, while g~ has a Pauling ionic radius of 1.3~ A), the potassium clinoptilolite has a substantially qreater pore ~ize than the ~odium - clinoptilolite. Accordingly, the pore size of a modified clinoptilolite of this inve~tion cannot be predicted from a knowledge of the ionic radius of the cation introduced and the normal pore blocking ~echanism which is typical of the zeolites, and thus the cation ~ust affect the pore gize of the ~linoptilolite by ~ome ~echanism other than simple physical pore blocking.
, Example 4 : Separation of carbon dioxide from ethylene ! streams usin~ zeolite 5A and sodium clinoptiloli~
A colu~n 1 inch internal diameter by 5 feet was filled with zeolite 5A (a commercial product ~old by UOP) in the form of pellets 1.6 mm (1/16 inch) ir. diameter. An ethylene feed stream containing rom 1~ to 70 parts per ~illion by volume o~ carb~n dioxide was passed through the column at 3721 kPa (525 psi~.) and 90 F
at a flow rate of 1.98 m /hr. (70 standard cubic feet per hour).
~12e effluent from the column w~s initially ~r~e fro~
carhon dioxide; howeYer, after 6.9 hours of operation, 2 ~
o29 ~
carbon disxide began to ~ppear ~n ~he ef ~luen~ and z~ached a concentration of 10 perGent of its csncantration ln the ~eed . At an average carbon diox~ de concentration in the feed o~ 45 parts per milllon by volume, the eguilibrium carbon dioxide loading of the zeol~te was 0.31 weight percent.
A sodium clinoptilolite was prepared by a single ion-exchange of a clinoptilol~te with E;odium chloride.
The sodium clinoptilolite was formed into 1.6 mm (1/16 inch) diameter pellets using 5 percent by weight Avery clay binder, and tested for its ability to remove carbon dioxide from the ethylene ~eed ~tream under the ~ame conditions as described for zeolite 5A. Breakthrough o~
carbon dioxide occurred only after 43 hours of operation, and at an average carbon dioxide concentration in the feed of 46 parts per million by volume, the eguilibriu~ carbon dioxide loading of ~he clinoptilolite was 1.63 weight percent, 5.3 times the equilibrium loading o~ the 5A zeolite. Thus, the ~odium clinoptilolite was greatly ~uperior to the SA zeolite in removing carbon dioxide fro~ the ethylene feed ~tre~m.
~xamples 5 18: Adsorptio~ propertie~ of various modi~ied clinoptilolites A number of modi~ied ~linoptilolites were prepared in substant~ally the 6ame way as in E:x~mple ~
~bove, and their ~dsorption properties were determined 2 ~ 9 usi~g the ~cB~n ~pring balance, in ~ome ca~es ~ft~r p~lletization ~ith clay. The method~ of preparation ~re sum~arized in Table 7 below; in th~ column headed ~Start~ng Nateri~l", NClino Al' etc refers to the natural 5 clinopt~lolites described in Example 1 above, wh~le "NaClino" refers to the 6inaly-exchanged material produced in Example Z above. A ~_n in the column headed ~Binder" indicates that the modi~ied clinoptilolite was not pelletized before the adsorption me~surements were made. Chemical analyses of the modified clinoptilolites are given in Table 8 and adsorption data in Table 9.
All adsorption measurements were taken at 23-C. A prime (') following the Clinoptilolite letter indicates matsrial from the same deposit as the corresponding clinoptilolite in Example 1 above, but from a different lot of ore.

2 ~

--3 ~--~ ' , Sta~t~n~

Na~lino 0.4N ~Cl lOOx QXC
N~Cllno o.ZM M~C12 20x oxc~
7 ~Cl.~no 0.2SN ~12 lOx ex~es~ -8 ~Cllr~o 0. ~5M ~C12 lox ~xce~
~Cl~no o~aM ~Clz ~00~ 1~X¢05~1 -10 ~llno E' Aa 2x~ple 2 11 Cllno E~ ~.aM RCl20X ~xce~ -12 ~1 irlo E ~ lM ~5gC1~ 12X ~xoe~s 5% Av~y - cl~y 13 CllnP E ~ ~ 3M ~la~ Ox exce~ -~4 ~llno ~' 0.3M ~a~lz lOx eX~e~ S~ A~ary cl~y Cl~no A' Ae ~Sxa~ple ~ -16 Clino A~ XCl~ lO0X exc~ss 17 Cl~no B' A~ Exa~ple 2 lC Cllr~o ~ XCl, 101~ exo~

, !

, , 2 ~

o 0l o ~ o -- o o ~ -- ~

~I N ~ ~ ~ O ~ O _ ~ -- N ~ ~
~1 _ N V~ -- ' _¦ ~ N ~ N

`O O O 1~ ~ ~ N
~111 ~ H ;~ O _ O _ _ --I ~1 -- ~ o e~ o o ~
O O ~ ~ N ~ID
Nl _ ~ N N N O O --R ~ ~ ~ H N
o ~ o o o o o ~1 ~ ~ ~ ~ ~ ;~3 ~ O
l ~ r` ;~ ~ .

0~1 ~ N ~ O _ C O N O 1 N ~
~ ~ d ;~ ~ - o ~ 2 ~ N ~! o ~4 ICi N N 0` N~ ~0 O O ~ ~ ~O
æ

r4 ~ ~ _ O _ ~ O O P~ _ ---:!1 3 -eo~, ~ 7~r~ 2 ~ a.6s ~.~7 S.~l ~.U ~ .n - .
Cll, ~0 7~rr, ~.~2 0.90 ~.09 l.S~ O.~ 8 0.~0 l.n 0.12 1.U
hs~
S~r~tion 7~6 ~13 1522 1~2 SW ~70 0S4 ~ 18~0 19S
t~ r C~21CN~
ibt~ .r Torr13.062 13.9l,3 12.~0 1~ ?
~pui~lenL4al ~051 105~4 1109 t-etor h2~1cN~, ~2116. 50 Torr 0.~8 0.~3 0.10 i.r6 ~ 0.4~ Z,t5 0.~7 2.59 ~ b~J,ii r~tlon 515 7~qt2~ 1l2 t~or N2~tC~N6 S~p~rd~ 1 114t~3 ~0 ~ 4 13 ~et~r Co2lc~
e2~l~, 50 ~orr ~,~19 0.8~ 0;~ S 0.55 3,1~~ hwrg tiX Z3~ ~t~ 6 f~e~l~t H~0~211 ~2~ tlsn ~ 571 ~ ~ 11 50 ~0 ~......
~e~6P
co2/~all~

,.

2~Q~

The above data show that the ~odi~ied clinoptilol~tes stronsly ~d~orb ~ar~on dioxide ~nd water but have low adsorptions o~ ~ethane, ~thylene ~nd ethane, 50 that these clinoptilolites are use~ul ~or 5 separating carbon d~oxide and water from hydrocarbon strea~s. ~he potassium and zinc clinoptilolites ~re comparable to zeolite 5A in thelr ability to effect these ~eparations ~see the data for zeolite 5A in ~able 4 above), while the other modified clinoptilolites have ~eparation factors much better than zeolite 5A, and should thus provide better selectivity îor the eparation of carbon dioxide and water from methane, ethane, and ethylene. Sodlum clinoptilolite is superior to potassium clinoptilolite independent of the source of the ore.

Claims (13)

1. A process for separating carbon dioxide from a mixture thereof with a hydrocarbon having a kinetic diameter of not more than about 5 Angstroms, which process comprises contacting the mixture with an adsorbent containing clinoptilolite at CO2 adsorption conditions, thereby causing the carbon dioxide to be selectively adsorbed into the clinoptilolite.

2. The process of Claim 1 further characterized in that the clinoptilolite used therein has been previously subjected to ion-exchange with at least one metal cation selected from the group consisting of lithium, sodium, potassium, calcium, magnesium, barium, strontium, zinc, copper, cobalt, iron, manganese and mixtures thereof until at least about 40 percent of the cations originally present in the clinoptilolite have been replaced by one or more of said metal cations.

3. The process of Claim 2 further characterized in that the ion-exchange is continued until at least about 60 percent of the total cations originally present in the clinoptilolite are replaced by the specified cations.

4. The process of Claim 1 further characterized in that the CO2 adsorption conditions include a temperature in the range of from -15 to +60°C.

5. The process of Claim 1 further characterized in that the carbon dioxide content of the mixture is not greater than about 200 vol. parts per million.

6. The process of Claim 1 further characterized in that the carbon dioxide partial pressure in the mixture is not greater than about 20 Torr (0.026 atmospheres or 2.67 kPa).

7. The process of Claim 1 further characterized in that the hydrocarbon is an acyclic hydrocarbon containing not more than 5 carbon atoms.

8. The process of Claim 7 further characterized in that the hydrocarbon comprises at least one of methane, ethylene, ethane, propylene, propane, a butane and a butene.

9. The process of Claim 1 further characterized in that after sufficient carbon dioxide has been adsorbed into the adsorbent containing clinoptilolite, the adsorption is stopped and thereafter an inert gas having a temperature of at least about 50°C is passed through the CO2-containing adsorbent, thereby causing desorption of the carbon dioxide and regeneration of the adsorbent.

10. A modified clinoptilolite adsorbent wherein at least about 40 percent of the ion-exchangeable cations originally present in a natural clinoptilolite are replaced by sodium and a cation selected from lithium, potassium, calcium, magnesium, barium, strontium, zinc, copper, cobalt, iron, manganese and mixtures thereof, the modified adsorbent being produced by a process comprising subjecting a natural clinoptilolite to a first ion-exchange step with a solution containing sodium cations until at least about 40 percent of the ion-exchangeable non-sodium cations in the natural clinoptilolite have been replaced by sodium cations, thereby producing a sodium clinoptilolite, and thereafter subjecting the resulting sodium clinoptilolite to a second ion-exchange step with a solution containing any one or more of lithium, potassium, calcium, magnesium, barium, strontium, zinc, copper, cobalt, iron and manganese cations until the desired degree of ion exchange with the non-sodium cation is attained.

11. The modified clinoptilolite adsorbent of Claim 10 further characterized in that before the second ion-exchange step the sodium clinoptilolite produced in the first ion-exchange step is admixed with a binder and heated to produce a pellet containing sodium clinoptilolite bound together by the binder and the second ion-exchange step is then performed on the pellet.

12. The process of Claim 1 further characterized in that the modified clinoptilolite adsorbent of Claim 10 or 11 is used therein.

13. The process of any one of Claims 1 to 9 and 12 wherein the mixture contains water and the water and CO2 are selectively adsorbed on the adsorbent.