Note: Descriptions are shown in the official language in which they were submitted.
i48;~
It is well known in the separation art tnat cer-
tain crystalline aluminosilicates can be used to se?arate
hydrocarbon species from mix-tures thereof. In particular,
the separation of normal paraEfins from branched chained
parafins can be accomplished by using the type ~ zeolites
which have pore openinys from 3 to 5 Angstroms. Such a
separation process is disclosed for example in U.S. Patents
2,985,589 and 3,201,491. ~hese adsorben-ts allow a separa-
tion based on the physical size differences in the molecules
by allowing the smaller or normal hydrocarbons to be passed
in-to the cavities within the crystalline aluminosilicate
adsorbent, while excluding the larger or branched chain ;~
molecules.
U.S. Patents 3,265,750 and 3,510,423, for example,
disclose processes in which larger pore diameter ~eolites
such as the type X or type Y structured zeolites can be
; used to separate olefinic hydrocarbons. ;~
. ~ ~
In addition to separating hydrocarbon t~ es, the
type X or type Y zeolite have also been employed in processes
to separate individual hydrocarbon isomers. In the process
¦ described in U.S. Patents 3,668,730; 3,668,732; 3,626,020,
and 3,686,342, for example, they are used to separate
desired xylene isomers; in U.S. Patent 3,668,267 they are
.
used to separate particular alkyl substitu-ted naphthalenes.
The present invention relates to a process ~or
the separation of lr3-butadiene from a ~eed mixture compris-
ing L,3-butadiene and at least one other C4 unsaturate with
a particular crystalline aluminosilicate adsorbent.
- -2-
: . ` ~ .
.' ' ~
1~ 32~
I have found that an adsorben-t comprisiny a
crystalline aluminosilicate zeolite selected from the group
consisting of type X structured and type Y structured zeo-
lites containing one or more selected cations a-t excha~seable
. 5 cationic sites exhibi-ts selectivity for 1,3-butadiene with
:............... respect to other hydrocarbons present in a feed mixture
.. comprising 1,3-butadiene thereby making separation of 1,3-
butadiene by so!id-bed selective adsorption possible.
In brief summary, my inven-tion is, in one embodi-
~ 10 ment, a process for separating 1,3-butad.iene from a feed
i mixture comprising 1,3-butadiene and at least one other
., C4 unsaturate which process comprises contacting a-t ad-
sorption conditions said mix-ture with an adsorbent compris- ;~
iny a crystalline aluminosilicate selected from t~pe X `
'--:
structured and type Y structured zeolites containing at
¦ least one cation selected from lithium, sodium, potassi~,
} rubidium, cesium, and barium at the exchangeable cationic
sites thereby selectively~ adsorbing 1,3-butadiene from said
:
: mixture.
-~ 20 Other embodiments and objects of the present
. invention encompass details about feed mixtures, adsor-
~ - bents, desorbents, and operating conditions all OL which
.-
are hereinafter disclosed in the following discussion of
: each of these facets of the present invention.
;:~ 25 The process of this invention provides a.superior :~
.. ~ - alternative to such methods of concentrating or separating
-~ 1,3-butadiene as: extractive distillation with selective
solvents; selective adsorption with cuprous salt solutions;
: -3-
.. . ' ' `.
,.
, .,
.. ~ ,.
. , . . , . , :.
~4829
azeotropic distillation ~ith ammoni.a; and sulfone fo~ma-
tion. Of these methods, only the first two have achieved
commercial prominence.
Butadiene, industrially the most important diole- .
fin, is used to produce polymer components used, for example,
in synthetic rubber and is also used as a chemical inter-
mediate for a great variety of compounds.
Adsorbents which can be used ln the process of
this invention are generally referred to as crystalline
aluminosilicates or molecular sie~es and can comprise both
the natural and synthetic aluminosilicates. ~-
- The type X structured and type Y structured .`: ~
zeolites as used in this specification shall include. ~j
; crystalline aluminosilicates having a three dimensional
interconnected cage structure and can specifically be ~ -
defined in U.S. Patents 2,882,244 and 3,130,007. The
terms "type X structured" and "type Y structured" zeolites
as used herein shall lnclude all zeolites which have a
general structure as represented in the above two cited
: -20 patents and additionally, shall specifically include those
crystalline aluminosilicates produced from either of the
zeolites described in U.S. Patent 2,882,244 and 3,130,007
,' as starting materials by various ion-exchange techniques
or thermal treatments or combinations thereof to modify ~
the properties (such as pore diameter or cell size) of the .. ;. .
type X or type Y zeolite starting material. As an example, .
the modified type Y zeolite produced by the thermal treat-
men-t of an ammonium-exchanged type Y zeolite in the presence
.
;:
,~
~'.~ .,
:,~ . ~ , . . :
o~ water vapor as described in U.S. Paten-t 3,506,400 s~all
be included within the term "t:ype Y struc-tured zeolite"
as shall any zeolite produced by subseq4en-t ion-exchang2
of the modified type Y zeolite so produced. In the most
limiting sense only these terms refer to type X and type
Y zeolites.
The type X structured zeoli-tes can be represented
;l in terms of mole oxides as represented in formula 2 belo.~:
Formula 2
( 9--2)M2/n:A123:(2-5+0.5)siO2:y~20 ; ..
¦ where "M" represents at least one cation having a valence
of not more than 3, "n" represen-ts the valence of "M",
and "y" is a value up to about 9 depending upon the iden_ity
; of "M" and the degree of hydration of the crystalline
: 15 structure.
. The -type Y structured zeolites can be represen ed -~
¦ in terms of the mole oxides for the sodium form as repre~
sented by Formula 3 below:
~3 Formula 3
(o~g*0~2)Na2O:A12O3:WSiO2 yH2o
~ where "w" is a value of greater than about 3.up to 8, and
: "y" may be any value up to abou-t 9. -
. Adsorbents contemplated herein include not only .
the sodium form of the type X and type Y zeolites but also ~.
. 25 crystalline materials obtained from such a zeolite by
. partial or complete replacement of sodium cations at the
. exchangeable cationic sites with other individual cations.
or group of cations. The term "exchangeable cationic
-5-
,.,i,
;
;: , , - - ,
~. .: .. ~ : :
~:16~8z~
sites" generally reEers -to -the sites occupied by sodium
cations present in the type X and ~ype Y zeoli-tes as in-
dicated in Formula 2 and Formula 3 above. Sodium cations
originally present a-t these si.tes can b~ replaced or ex-
changed with o-ther cations.
Cationic or base exchange methods are generally
known to those familiar wi-th the field of crystalline alu-
minosilicate production. They are generally per~ormed by
contacting the zeolite with an aqueous solution of the
i 10 soluble salt of the cations desired to be placed upon the
zeolite. The desired degree of exchange takes plac~ be-
fore the sieves are removed from the aqueous solu,ion,
washed and dried to a desired water content. It is con-
templated that cation exchange operations may take place
using individual solutions of desired cations placed on
the zeolite or using an exchange solution containing a
mixture of cations, where two or more desired cations are
placed on the zeolite. ;
.
The cations which can be placed upon the zeolite
¦ 20 adsorbent include those of Group I-A, Group II-A, GroupVIII-A, and the Group I-s metals of the Periodic Table of
lemen-ts. -
Eor the purposes of this invention, cations to
be used on the adsorbent shall include cations selected
from the above-mentioned groups and with the limi-ation
that the cation or cations to be used be selective towards ~,
1,3-butadiene from the other feed stock components. Pref- -
- erably the zeolite adsorbent will contain at least one `
: . ~, .
~ -6- ~
., . ~ .
::
. ::
1~164!3~9
cation selected from the group consisting of lithium,
sodium, potassium, rubidium, cesium, and ~arium at the
; exchangeable cationic sites. More preEerably the z201ite
absorbent will contain at least one cation selected from
the group consisting of sodium, potassium, and b~rium
since cations from this group selectively adsorb 1,3-
butadiene from other feèd mixture componen-ts in a highly
selective manner.
When singular cations are base exchanyed upon a
zeolite, the singular cations can comprise anywhere from
~ 5 up to 75 wt. % on a relative volatile free basis of the! zeolite depending upon the molecular weight of the material
exchanged upon the zeolite. I-t is con-templated that when
single ions are placed upon the zeolite that they may be
on the zeolite in concentrations of from about 1~ to about ~;
100~ of the original cations present (ge-nerally sodlum~
upon the zeolite prior to its being ion-exchanged. By
knowin~ the empirical formula, including the silica to
~ alumina ratio of the zeolite used, its water content~ and¦ 20 the percentage of binder used if any, it is possible to ~-
calculate the percentage of ion exchange that has taken
- place.
When two or more cations are placed upon the
zeolite, there are two parameters in which one can operate
- 25 in order to effecti~ely produce a zeolite having tne maxi-
mum selective properties. One of the parameters is the
extent of the zeolite ion exchange which is determined ~`~
by the length of time, temperature, and cation concentra-
. '' '
.
. ,
. .
. .
. .~ ,;; . - . , . . , , -' ; . ' ' . ' ,
~L~648Z~
tion. The other par~meter is the ratio of individual,
cations placed on the zeolite. In lnstances in which
the cation pairs comprise a Group I-A metal and a Group
II-A metal, the weight ratio of these two respective com-
ponents ~pon the zeolite can vary anywhere from about less
than one up to about one hundred depending upon the molecu-
lar weiyht of the Group I-A or Group II-A metal. -
Because of the reactive nature of 1,3-butadiene,
it is very importan-t that the adsorbent possess little ~ ;
or no catalytic activity toward polymerization or isomer-
ization which would either degrade the product quality,
! reduce the overall yield of desired produc-t or possibly
degrade adsorbent performance. We have found that for
the separation of 1,3-butadiene the polymerization effects
of the adsorbent are of primary concern. Unless the
adsorbent possesses little or no polymerization activity,
¦ 1,3-butadiene will rapidly polymerize. It is thought that
such activity is due primarily to the presence o~5 hydrogen
1 cations within the zeolite or the binder used to pro~uce
¦ 20 the adsorben-t particles. I have discovered that ion-
! exchanginy a starting material comprlsing a type X or
type Y structured zeolite with a dilute aqueous solution ~-
¦ of sodium or potassium hydroxide elimina-tes such acid sites
! and produces a finished adsorbent with little or no cata-
lytic activity. This ion-exchange step is then followed
by subsequent ion-exchanges with the desired cation or
cations. During these subsequent ion-exchange steps and
washes, it is important that the pH of the exchange medium
_~
~ .
. .
: .. ~. .
4~
be maintained at or above 7 to avoid recreatin~ acid
sites.
Butadiene is syn-thesized commercially in the
United States by four methods: 1) by catalytic dehydro-
genation of concentrated n-butylenes; 2) by catalytic
dehydrogenation of n-butane; 3) as a by-product, in rather
- low yield, from severe high-temperature cracking of liquld
hydrocarbons for production of unsaturates; and 4) frorn
- ethyl alcohol by a combination of catalytic dehydrogenation
and dehydration. The first two methods are the most fr~
quently used methods.
~ All of the conversion processes yield products
-¦ in which 1,3-butadiene is mixed with other closely boiling
¦ hydrocarbons. For example, when concentrated 2-butene and
l-butene are catalytically dehydrogenated to produce 1,3-
~ butadiene the stabilized effluent from this operation con-
``¦ tains, in addition to 1,3-butadiene, unreacted isomeric
n-butenes, some n-butane, isobutane, isobutylene, appre-
ciable concentration of C3 components, and small concen-
¦ 20 trations of components heavier than C4 hydrocarbons.
Table 1 below lists the hydrocarbons frequently
found in crude butadiene fractions from such sources.
The relative amounts of these hydrocarbons present in crude
butadiene vary considerably, depending upon the type o,
~:
hydrocarbon conversion process employed. Other C~ unsat-
urates, primarily mono-olefins, are always presen, in major
~ amoun-ts. Non-conjugated diolefins and acetylenes are minor
;¦ constituents, but they generally increase with lncreasing
.,' ,,
~648'~
tempera-ture cluring hydrocarbon conversion. For the most
part, however, they are hiyhly objectionable contaminants
in purified butadiene and hence their concentrations in
the latter must be carefully controlled.
Ordinarily fractionation alone is incapable OL
separating 1,3-butadiene of the desired purity (ordinarily
98 wt. % or higher) from these mixtures. Commercially
butadiene is separated from olefins and paraffins primarily
by extractive distillation with selective solvents and by
~ 10 selective adsorption with cuprous salt solutions.
j A polar solvent is employed in extractive dis-. tillation processes to increase the volatility of some
componen-ts in the mixture relative to other components in
. the mixture with the resul-t that separation of the desired
15 component by distillation is made possible. Polar solvents
such as acetonitrile, acetone, furfural, dimethyl_ormamide,
dioxane, phenol, and N-methylpyrrolidone, and their corres~
. ponding aqueous admixtures have been used in extractive
distillation processes for 1,3-butadiene separation.
.
. ~''
. ' ' ~
~ . :
.
`".'''
. ''~' '.
: , -10- ' ;' '
. ' .
.
, , ~ .
~L~648Z~
TABLI~ 1
COMPOUNDS IN A TYPICAL CRUDE BUTADIENE
FRACTIONS AND T~IEIR NO~AL BOILING POINTS
Compound B.p., C.
Paraffins:
_
Propane -42.1
Isobutane -11.72 .
n-Butane - 0.55
. Mono-olefins: ~:
Propylene (propene) -47.6
Isobutylene (methylpropene) - 6.93
Butene - 6.32
trans-2-butene 0.86
: cis-2-butene 3.64 ~ - :
3-Methyl-l-butene 18.8
i Diolefins
¦ Propadiene (allene) -34.3
1,3-Butadiene - 4,54
1,2-Butadiene 10.3
1,4-Pentadiene 26.12
¦ Acetylenes:
¦ ~ Methylacetylene -23.2
:~ Vinylacetylene 5.0
.~ Ethylace-tylene 8.6 ;;
. 25 Butadiyne (biacetylene) 10.3
. Dimethylacetylene 27.1
`. ~'
, ~'
~ j
,.' . , ~.
:~
.
1~6~1~Z5~ ~
In the conventional extract~ve distillation pro-
cesses, the butanes and butenes e~hibit an enhanc~d vola-
tility relative ~o the diolefinic and acotylenic materi~ls
and are recnvered as an o~erhead product from the extrac-
tlve distillation zoneO The less volat~le hydrocarbons,
e.g., the diolefins and higher acetylenes,are separ~ted ~ -~
. .
together ~ith the polar solvent as the bottoms produc~ from
- the extractive distillation zone. The butadiene product
is reco~ered directly from ehe bottsms product in a strip-
ping zone at ele~ated temperature~ The energy requlred to
effect the separation ln the extractive distillation zone
and in the stripping ~one is supplied by reboilers attached
to each zone.
The extractive distiLlation method suffers from
:. :
several disadvantag~s. One disadvanta~e is that relatively `~;
large amo~nts of energy are required to reboil both ths
-~ extracti~e distillation zone~ which is typically a 100
plate colum~ and the stripping %one~ Another disadvan~
::.., ~
- tage islbhat solvent losses occur in several ways during
extractive dis~illation. Physical losses occur from leak~
age and from carryover in the raffinate. Other losses
occur ro~ chemical reactlvity or thermal degradation of
the solvent. In the case o phenol for lnseance~ a hi8h
boiling iaactive sludge forms from reaction with traces of i
., . ,~ ~dienes present in ehe hydrocarbon fesd~ Furfural is sens~
tive to elevated temperatures in the presPnce of oxygen,
water~ or unsaturated hydrocarbons resulting in polymeriza-
tion. ~hus~ contiNuous redistillation of a portion of the -
: . ~
.. , ;
i .
~ ~12-
1~364~
circulating solvent or intermittent redistillation of
the -total solvent inven-tory is usually required to rernove
such solvent impurities. Acldi-tionally, control o~ the
extractive distillation is usually difEicul-t. The tempera-
ture gradient in the tower does not correlate with the ac-
tual separation being carried out. Control is usually
by material balance supplemen-ted by frequent produce SaM-
ples and analyses and in some cases spectroscopic or chro-
matographic instruments have been employed for continuous
analysis to aid in tower operation.
~' Selective absorption with cuprous salt solutions
is also co~mercially used to purify butadiene from crude
fractions derived from both thermal cracking and catalytic
dehydrogenation processes. The solubility of a hydrocarbon
:
¦ 15 in solutions of this type generally increases wi-th the de- ;
- gree of unsaturation, butadiene being many times more solu-
.: . ~.
ble than the closely-boiling butenes. Essentially three
processing s-teps are involved in this purification opera-
tion, an absorption stage in which butadiene, along with a
portion of the mono-olefins and other unsaturates, is dis- ;
solved in the solvent; an enrichment stage, generally ;
- effected by a combination of heating and stripping with
~¦ enrlched butadiene, in which essentially all of the dis-
solved hydrocarbons except butadiene are stripped from the
solvent; and a desorption sta~e in which purified butadiene
is stripped from the enriched solvent. By appropriate re-
cycling of steams between these stages, high recoveries
'
~ -13-
~: ~.~
. ', ' ' .
..
'~
,':
: ;
~.'.' .. - - , :,
i.: . .
.. . . .
of butadiene can be obtained. Like extr~ctive distilla- ;
tion, however, this process also has rather high energy
re~uirements c~nd has the same attendant problems of circu-
lating-solvent life and con-tamination of degradation.
- The process of my invention avoids the problems
associated with reactive circulating solvents and provides
- a process less difficult in operation by which high purity
butadiene can be produced at operating costs at least
competitive with those of existing processes.
To separate 1,3-butadiene from a feed mixture
containing 1,3-butadiene and at least one -ot~her=l-~ C4 unsat-
urate by the process of our invention, the mixture is con-
tacted with a particular adsorbent and the butadiene is -~ .
. :.
more selectively adsorbed and retained by the adsorbent
while the less selectively adsorbed obher C4 unsaturate is
removed from the interstitial void spaces between the par-
ticles of adsorbent and the surface of the adsorbent. The
adsorbent containing the more selectively adsorbed 1,3- ~
. .,~- , .
butadiene is referred as a "rich" adsorbent -- rich in the
more selectively adsorbed 1,3-butadiene.
; The more selectively adsorbed feed component is
commonly referred to as the extract component of the feed
-: : :: ~ ., .
mixture, while the less selectively adsorbed component is `~ -
referred to as the raffinate component. Fluid streams ;~
leaving the adsorbent comprising an extract component and ` ~ -
comprising a raffinate component are referred to, respec-
tively, as the extract stream and the raffinate stream. As ~;~
previously mentioned, the crude butadiene feed mixtures `~
, , '
'' ` '` ,"
~64~;~9
will ~Isually contain many components -- primarily C3's
and C~'s -- and it will therefore be recognized that all of
the components presen-t in the -feed mixture, other -than
1,3-butadiene, will be less selectively adsorbed by the
adsor~ent with respect to 1,3-butadiene. Thus, the raf-
finate stream will contain as raffinate components all of
the feed componen-ts besides 1,3-bu-tadiene and the extract
stream will contain 1,3-butadiene as the extract component.
Although it is possible by the process of this
invention to produce high purity (98~ or greater), 1,3-
butadiene at high recoveries, it will be appreciated that
an extract component is never completely adsorbed by the
adsorbent, nor is a raffinate component completely non-
adsorbed by the adsorbent. Therefore, small amounts of a
raffinate component can appear in the extract stream, and,
likewise, small amounts of an extract component can appear
in the raffinate stream. The extract and raffinate streams
then are further distinguished from each other and from -
the feed mixture by the ratio of the concentrations of an
extract component and a specific raffinate ~omponent, both
appearing in the particular stream. For example, the ratio
ofconcentration of the more selectively adsorbed l,3-buta-
diene to the concentration of less selectively adsorbed
butene-l will be highest in the extract stream, next high-
est in the feed mix-ture, and lo~est in the raEfinate stream.
Likewise, the ratio of the less selectively adsorbed butene-l
to the more selectively adsorbed l,3-butadiene ~ill be high-
est in the raffinate stream, next highest in the feed mix-
ture, and the lowest in the extract stream.
--15-- ' ':
- -: ~: . -i:: . : -.
. -, . .. . .
~641~Z~
;
The adsorbent c~n be contalned in one or more
cha~bers where through progra~med flow i~to and out of the
chambers separation of the diene is effected. The adsor-
bent may be contacted wlth a desorbent material which i~
capable of displacing the adsorb~d 193-butadiene fro~ the
adsorbent. Alternati~ely, the 1,3-butadiene could bs
removed fr~ the adsorbent by purging or by increasin~ the
temperature of the adsorbent or by decreasing ~he pressure
of the cha~ber o~ ves~el coneaining the adsorbent or by a
coDbination of these means.
The adsorbent may be e~ployed in the form of a
dense compact fixed bed which is alternatively contac~ed
with the eed mixture and ~ desorbent material (hereinafter - -
described). In the simplest embodiment of the invention
the adsorbent is employed in the form of a single static
bed in which case the process is only semi~continuous.
A set of two or ~ore static beds ~ay be employed in fixed- i,
bPd coneacting with appropriate valving so that the feed ~ ~
~ixtur~ is passed throu~h one or more adsorbent beds ~hile - ~ ~ ;
the desorbent material is passed through one or more of the
other beds in the set. The flow of ~eed mi~ture and de- -
sorbent ma~erial may be either up or down through the ad- -
sorbent. Any of the conventional apparatus employed in
static bed fluld-solid contacting may be used.
Movlng bed or simula~ed moving-bed systems, how-
ever, have a ~uch 8reater separation efficiency than fi~ed
adsorben~ bed systems and are therefore preferred.
-16-
1064BZ~
Speclfically~ the more preferred processlng flow
sche~es which can be utilized to effect the process of this
invention are those known in the art as simulated moving-
bed countercurrent syseems. One such system incl~des the
flow scheme described in U.S.Patent ~,985,589 issued to
D. B. Broughton. Thls patent generally described the
processing sequence involYed in a particular simula~ed
moving-bed countercurrent solid~fluid contacting process.
In fact, the processing sequence generally descrihed in ~ ;
that patent is the preferred mode of operating the separa-
tion process disclosed herein.
~ith thst processing sequence therefore9 ~n~ -
embodiment of my invention is a process for separating
173-butadiene frvm a feed mixture comprising 1~3-butadiene
and ae least one other C4 unsaturate which process comprises
the steps of: contacting said mixture at adsorption condi~
tions with a particular ~eolitic adsorbent to effect ehe
selective adsorption of 1,3-butadisne; withdra~ing fro~ the ` ~-~
adsorbent a stream ccmprising the less seleceively ~dsorbed
other C4 unsaturate; contac~ing the adsorbent at desorp-
tion condi~ions with a desorbent m~terial to effect the -`
removal of the selectively adsorbed 1~3-butadiene from the --
adsorbent; and, withdrawing fro~ the adsorbent ~ stream
... . . .
co~prising tesorbent ~aterial and 1~3-butadiene.
Preferred operating conditions for both adsorp~
tion ~nd desorption of this particular embodiment of my
inven~ion include a temperature within the range of from
~ .
:
~ -17~
. . . . . ~ .. . .
10648Z9
21 to 232C. and a pressure within the range of fro~ .
about 1 to 35 atmospheres. E'urthermore, both adsorption
and desorption are preferably affected at conditions
selected to maintain liquid phase throu~hout the process ~_
operation.
Adsorption and desorption could, of course, be
conducted both in the vapor phase or liquid phase or one ~
operation may be conducted in the vapor phase and the other ~ '
in the liquid phase. Operating pressures and temperatures
for adsorption and desorption migh-t be the same or different.
The desorbent materials which can be used in the ~ .
various processing schemes employing this adsorbent will
vary depending on the type of operation employed. The ~ `
term "desorbent material" as used herein means any fluid
substance capable of removing a selectively adsorbed feed
component from the adsorbent. In the swing-bed system in
which the selectively adsorbed feed component is removed ~;
from the adsorbent by a purge stream, gaseous hydrocarbons
such as methane, ethane, etc , or other types of gases such
as nitrogen or hydrogen may be used at elevated tempera-
tures or reduced pressure or both to effecti~ely purge the
adsorbed feed component from the adsorbent. i
However, in processes which are generally operated ~ ;
at substantially constant pressures and temperatures to
insure liquid phase, the desorbent material relied upon
must be judiciously selected in order that it may displace
the adsorbed feed component from the adsorbent with rea-
sonable mass flow rates and also without unduly pre~enting
-18-
~.
. ~ : , :.,: :
iO~'Z~ .
the extract component from displacincJ the desorbent i~ a
following adsorption cycle.
Desorben-t materials which can be used in the
process of this invention should additionally be substances
which are easily separable from the feed mixture that is
, passed into the process. In desorbing the preferentially
¦ adsorbed component of -the Eeed, ~oth desorbent material
and the extract component are removed from the adsorbent
j in admixture. Withou-t a method of separation of these
two materials, the purity of the ex-tract component of the
feed stock would not be very high since it would be dilu_ed
¦ with desorbent. It is conternplated tha-t any desorbent
¦ material used in this process will have a substantially
j different average boiling point than that of the feed
mixture. More specifically, "substantially di~ferent"
shall mean that the difference between the average boiling ~-
points shall be at least about 20F. The boiling range of
the desorbent material could be higher or lower than tha~
of the feed mixture. The use of a desorbent material ha~ing -~
a substantially different average boiling point than ~a-
of the feed allows separation of desorbent material from
feed components in the extract and raffinate streams by
simple fractionation or other methods thereby permitting
reuse of desorbent material in -the process.
~5 Desorbent materials which can be used in the
process of this invention include paraffins, olefins,
aromatics, ethers, alcohols, cyclic dienes, and ketones.
In -the preferred isothermal, isobaric, liquid-phase
.
,
: ~ : : , . . ~, . i
operation of` the process of my invention, I have found
that desorbent materials compris:ing olefins, aromatics or
mixtures of o]efins and aromatics are particularly effec-
-tive. Speci~ically, desorbent materials comprising linear
olefins, such as octene-l for example J and aromatics such
as benzene and toluene all of wh:ich are easily separable
from 1,3-butadiene by conventional distillation are espe-
cially preferred for this type of operation. Mixtures of
olefins or aromatics, or olefins and aromatics with paraf-
fins have, additionally, been found -to be effective desor-
bent materials. The paraffins can include straight or
branched chain paraffins or cycloparaffins having a boil-
ing point substantially different from the feed to allow
separation from feed components. Typical concentrations of
an olefin or an aromatic or an olefin and an aromatic~ when
used in admixtures with a paraffin can be from a few volume
percent'up to near 100 vol. % of~theltotal desorkent mate-
rial and preferably will be within the range of from about
25 vol. % to about 100 vol. ~0 with an even more preferred
20 range being from about 50 vol. % to about 100 vol. % of the
total desorbent material.
With the types and some operating features of
processes employing adsorbents to separate 1,3-butadiene
by selective adsorption now in mind, one can appreciate
that certain characteristics of adsorbents are highly de-
sirable, if not absolutely necessary, to the successful -~
operation of a selective adsorption process. Among such
characteristics are: adsorptive capacity for some volume -
" :~
.
~ -20-
~.,
:10~48~9
oE an extract component per volume o~ adsorbenti the selec-
tive adsorption of an extract component with res~ect to
a raE~inate component and the desorbent material; suffi~
~ ciently fast rates of adsorption and desorption of the
¦ 5 extrac-t component to and from the adsorbent; an~, little or
no catalytic activity Eor undesired reactions such as
polymeri~ation and isomerization.
Capacity of the adsorben-t for adsorbing a spe-
cific volume of an extract component is, of course, a
necessityi without such capacity the adsorbent is useless
for adsorptive separa-tion. Furthermore, the hi~her the
adsorbent's capacity for an extract component, the better
is the adsorbent. Inereased capacity of a partieular
adsorbent makes it possible to reduee the amount of adsor-
bent needed to separate the extract componen-t contained in
a particular charge rate of feed mixture. A reduction in
the amount of adsorbent required Eor a specific adsorptive
separation reduces the cost of the separation process.
It is important that the good initial capacity of the ad- -
sorbent be maintained during ac-tual use in the separation
process over some economieally desirable life.
The second neeessary adsorbent eharacteristic
is the ability of the adsorbent to separate components of -
the feed; or, in other words, that the adsorbent possess
adsorptive selectivi-ty, (B), for one component as compared
to another component. Selectivity can be express'2d not
only for one feed mixture component as compared to another
but can also be expressed between any feed mixture co~ponent
. -~,
-21- ;
. ~ '
,
'`~ ~
-.- :: .- , . . .: -
; . - , ' , ~, , .
i~48~9
and the desorbent. The selectivity, (B), as used through-
out this specification is defined as the ratio of -the two
components of the adsorbed phase over the ratio of the same
two components in -the unadsorbecl phase at equilibrium con- ;~
ditions.
Selectivity is shown as Equation 1 below:
Equation 1
Selectivity = (B) , Eol. ~ercent C/vol. ercen_ ~ A
ol. percent C/vol. p~e~rcent ~3U
where C and D are two components of the feed represented
in volume percent and the subscripts A and U represent the
adsorbed and unadsorbed phases respectively. The equilibrium
conditions as defined here were determined when the feed
passing over a bed of adsorbent did no-t change composition
after contacting the bed of adsorbent. In other words,
there was no new transfer of material occurring between the
unadsorbed and adsorbed phases.
As can be seen where the selectivity of two com-
ponents approaches 1.0 there is no preferential adsorption
of one component by the adsorbent. As the (B) becomes less
than or greater than 1.0 there is a preferential selectivity
by the adsorbent of one component. When comparing the selec-
tivity by the adsorbent of one component C over component D,
-
a (B) larger than 1.0 indicates preferential adsorp-tion of
component C within the adsorbent. A (B) less tha~ l.U would
,~
indicate that component D is preferentially adsorbed leaving
an unadsorbed phase richer in componen* C and an adsorbed
`' ;
~ .
-22-
~i .
.
. . . .. .. ..
1~69~!3Z9
phase richer in component D. Desorben-ts ideally ~Jould
have a selectivity equal to about 1 or slightly less than
1. ~
The third.important characteristic is the rate
: 5 of exchange of the extract component of the feed mlxture
material or, in other words, the relative rate of desorp-
tion o the extract component. This characteristic relates .,~.
to the amoun-t of desorbent material -that must be employed ~ .
i in the process to recover the extract component ~rom the
¦ 10 adsorbent; faster rates of exchange reduce the amount of
desorbent material needed to remove the extract component,
It is also necessary that the adsorbent possess .
little or no catalytic activity toward polymerization or
isomerization of any of the feed components. Such activity :
might effect adsorbent capacity or selec-tivity or product ~-
yields or all of these. Polymerizati.on tends primarily to
degrade the adsorbent in addition to reducing yields some-
what. Polymerization effects are generally considered to
be primarily physical impediments which can prevent the
adsorption of the extract component by obstructing the :
surface of the adsorbent and the pores present in the struc~
ture of the adsorbent. This shortens the useful life of ~:
the adsorbent and makes necessary frequent regeneration :
treatments to restore the adsorptive properties o the
adsorbent. Isomerization activity tends primarily to de-
crease the yield of a desired feed component. It is the `
elimination of polymerization activity which we have found
to be of primary concern rather than isomerization activity ~ :
-23- ~ :
. , ` ..
.~
'~
1 -
~6~ :
in the process of my inventlon. It is, therefore~ exeremely
important that the catalytic activity be substantially
rèduced or preferably totally eliml~ated by proper methods
of ~anufacture of a selected adsorbent.
Whlle reducing the temperature of the operations
of the adsorption process in which ehe catalytic activity
is present ~ill substantially reduce ~he catalytiç ac~ivity
because of the associated reduction in the rate of reaction,
this procedure in adsorptiYe separation processes employing
molecular sieves is generally not desirable because the ;~
reduction in temperature also reduces ehe rates of adsorp- -
tion and desorption of the ex~ract componen~.
In order to test various adsorbents to me~sure
~he characteristics of adsorptive capacity and selectivlty,
a dynamic testing apparatus is employed. The apparatus
consists of an adsorbent chamber of approximately 70 cc
volume having inlet and outlet portlon at opposite ends of ~`
the chamber. The chamber Is contained within a temperature
control means, and, in addition, pressure cont~ol equipment
is used to operate the cha~ber at a cons~ant predetermined
pressure. Chromatographic analysis equipment can bc at-
tached to the outlet line of khe cha~ber and used to analyze
ehe effluent stream leaving ~he adsorbent chamberO
A pulse test, performed usin~ this apparatus and
the following general procedure3 is used to determine selec-
ti~ities and other data for ~arious adsorbent systems. An
adsorbent system comprises a particular adsorbent, feed ~;
material~ and desorbent material~ The adsorbent is filled
-2~-
. - : ~ . - . , . . ,, :
8Z~
to equllibrlum with a particular clesorb~nt ~aterial by
passing the desorbent material throu~h the adsorbent cham~
; ber. At a convenient time, a pulse of feed containing known
COnCentratiDns of a non-adsorbed paraffinic tracer ~n-
nonaDe for instance), 1~3-butadier~e, and at leas~ one other
C4 unsaturate all diluted in desorbent material ~s inJec~ed
~ into the test chamber for a duration of several minutes~
Desorbent flow is resumed, and the tracer and the other feed
components are el~ted as in a liquid-solid chromatographic
operation. The effluent can be analyzed by on-stream chro-
matographic equipment and traces of the envelopes of corres-
ponding feed component peaks developed. Alternatively,
effluent samples can be collected periodically and later
analyzed separately by gas chromatography.
From information derived from the chromatographic
traces~ adsorbent performance can be ra~ed in terms of
capacity index for an ex~ract comp~nent9 selectivity for
one ~eed co~ponent with respect to the other (osually an ~-~
extract c~mponent with respect to a raffinate component)
and the rate of desorption of extract component by the de-
sorbentO The capacity index may be charactsrized by the
distance between the cen~er of the peak envelope of the
extract component and the peak en~elope of the tracer c~m~
ponent or some other known reference pointO It is expressed
in terms of the volume in cub~c centimeters of desorbent
pumped during thisitime interval~ Selec~ivity) (~), for
the extract compcnent with respect ~o raffinate component
is characteri7-ed by the ratio of the distance between ~he
~25-
.... , , ~, . . . . .............. . . .
,. , ,,, . - . . ,. , . , . ::
.
1~6~3Z9
center oE the extract componen-t peak envelope and -the
tracer peak envelope (or other reEerence point) to -the
correspondin~ distance for the rafinate component. The
rate of exchange of the extract componen-t can ~enerally be
characterized by the width of -the extrac-t componen~ peak
envelope at half intensity. The narrower the peak width,
the faster the desorption rate. The desorption rate can
also be characterized by the distance between the center
of the tracer peak envelope and the disappearance of the
extract component which has ~ust been desorbed. This dis-
tance is again the volume of desorbent pumped during this
time interval.
To translate this type oE data into a practical
separation process requires actual testing of the best
sys-tem in a continuous countercurrent liquid-solid contact-
ing device. The general operating principles of such a ~ ~
device has been previously described and are found in i ;
Broughton U.S. Patent 2,985,589. A specific laboratory-
size apparatus utilizing these principles is described
inde Rosset et al U.S. Patent 3,706,812. The equipment com-
prises multiple adsorbent beds with a number of access
lines attached to dis-tribu-tors within the beds and terminat-
ing at a rotary distributing valve. At a given valve posi-
tion, feed and desorbent are being introduced -through two
~ 25 of the lines and raffinate and extract are being withdrawn
:
through two more. All remaining access lines are inactive
and when the position o~ the distributing valve is advanced
by one index, all active positions will be advanced by one
-26-
~, .. . . . . .
.
9 ~ :
bed. This simulates a condition ln which -the adsorbent
physically moves in a direc-tion coun-tercurrent to the liquid
flow. Additional details on the above-mentioned adsorbent
testing apparatus and adsorbent evalua-tion techniques may be
found in the paper "Separation of C8 Aroma-tics by Adsorption"
by A. J. de Rosset, R. W. Neuzil, D. J. Korous, and D. H.
Rosback presented at the American Chemical Society, Los
Angeles, Cali~ornia, March 28 through April 2, 1971.
The feasibilit~ o~ separating 1,3-butadiene from
` 10 a feed mixture comprising 1,3 butadiene and at least one
other C4 unsaturate by selective adsorption, which was
demonstrated by pulse test results, may be confirmed by
continuous -testing in the laboratory-sized apparatus de- -
scribed above.
EXA~1PLE
¦ The following example is presented to fu~her ~-~
¦ illustrate the basis and benefit of -the presen-t invention
¦ ~ and is not intended to limit the scope of the invention.
This example presents results of pulse tests
which were performed using a particular adsorbent primarily
to determine selectivities of the adsorbent Eor 1,3-buta~
- diene relative to other C4 unsaturates. The selectivity
numbers obtained illustrate the adsorbent's ability to
separate 1,3-butadiene from the o-ther C4 unsaturates.
The particular adsorbent employed was a potassium
exchanged Type X structured zeolite which contained a small
portion of binder ma-terial and which was approximately
20-40 mesh particle size.
: :
-27-
. .
~,~r - .... ....... .
~,.',.'~.. , ' . '' ' . : ~ . .
" . :' ' . ' . ': ' ' :. . ., '
lO~B2~
.
The adsorben-t ~as prepa.red Erom base material
comprising commercially available 13X zeolite in the form
of nominal 1/16 x 1/8-inch extrudate. This base material.
was ground to produce 20-40 U.S. Standard Mesh particle
size material and this ground base material was then ion-
exchanged with a dilute aqueous caustic solution (about 4 -
. wt. % NaOH) for the purpose of eliminating catalytic activity
. oE the final adsorbent. The zeolite was then ion-exchanged
with a potassium chloride solu-tion to give a volatile-free :
3 lo potassium oxide conten-t of about 9 wt % and the adsorbent
j was then dried to a water level of 1.4 wt. % before it was
3 utilized in the pulse test apparatus. The adsorbent was
placed in a 70 cc adsorbent column which was maintained at
constant temperature and at constant pressure to ensure
liquid-phase operation during the entire test procedure
for each pulse test performed. The column effluent was ~
sampled every 2.5 minutes by an automatic sampling chro- ` .-
matograph.
The feed mixture utilized comprised 20 vol. % ;~
each of butene-l, cis-butene-2, trans-butene-2, isobutylene,
and 1,3-butadiene, to which was added a small amount of
n-butane as a "tracer" for reference purposes. The mix-`
ture was injected into the test column in pulses of 3.6
cc each. Different desorbent materials comprising octene-l
or benzene or toluene were employed for the various pulse
tests.
The effluent was analyzed by the on-stream chro-
matographic equipment and traces of the envelopes of com-
. ' ~.
-28-
.
. ' . ' .
.
::. ~ . . . , ~: :
. ~.: : : . .. ..
.: . . . - :
4~:9
ponent peaks were developed. Yrom informa-tion derive~
from the chromatographic traces, selectivities of the
adsorben-t for 1,3-bu-tadiene with respect to butene-l and
with respec-t to the o-ther C4's in the feed material were
¦ S obtained in the manner previously described. Additionally
3 the wid-ths of the butadiene peak envelopes, at half inten-
:~! sity, were measured as an indication of -the rate of exchange
I of butadiene with different desorbent materials. Results . ::
.j , .
! obtained for eleven pulse tests, A through K, are shown in ~:~
the Table 2 below.
. ' '' ::
.' ~'':'' '.
.~''' .''
''' :
.~. .
. ,
.:
. ~,`
.' '~ -
.,
.
. ': ~
; , ....
. ' ~:
' ~
: : '
-29- `
.
.
, ~
`. '' ' '' '.' ' '' '. ' . ' .' , .. ' ' ", ' , " ~
- - ~ Q~
~,
~,
q)
rl
u~ o r~ c~ r~~ o
. Q 3 ~D ~ ~ ~r ~I ~~ ~ ~1
I ~
~d
~ Q~
: o~
_
. a) c~ .'
t~ co o oo u~
~: ~ o
~:~) ~ ID C~ ~ ~ I I . . . .
a)~ ~:: ~ ~ D r~
.q Q .
~ ~ ,
tn~ a) ~.
.. -.
~ ,
a) ~
,1
, O . '
. ~ ,1 ~ . - ~,
. ~ ~ l
. ~ .S ~ r~ ~ r~
X ~ ~) .
, ~ ~
': ,
. Q ~ ~
. E~ - ~ . "~
0 . ': ~
. ~ ~ ~
.~ ~ V In In n o o o o o u~ o o
E~ o u~
: :
::S
' :
I
I I a) I Q~
u~ O o~ a~ r~
aJ ~) ~ V a~ a) a) N . N C)
E~ S~ 1 O O -1-) a) a) N r~ N 1` N i~ r~ ~
: ID Id -1~ 1 -IJ I O N ~) ~ C_) O a) ~1 ~) - O
a~ Q -l C) t) O ~; O O I . a) I a) I Q Q O I
~1 O O 0 ~-1 0-~1 0 Q s~ Q ~ ~ \ c
. ::~ U~ ~ op o~Oo\ C~O oP o~ o~ o~ o~ 0~ ~ ~ ~
J (~ ~1 o~ I ~1 ~
O ~ ~ ~ ~ O O '~ O
O O O O ~ ~1 0 0 0 0 0 0 0 :- ~ O o ~
~ o 0~ > O O ~ ~
OO OO O ~ oO oo ~U~ o o oo o
~1~ ~ r~ ~ r~) r~ r~ ~ ~ ~ ~ oo ,~
, ~ O
Ul ~
u~
g ~c m ~ a ~ C H. ~:
. ~30-
.
~C~&i48Z~
The selectivity values shown Eor -the eleven'pulse
; tests demonst,ra-te first o:E all the adsorbent's ability to
selectively adsorb 1,3-butadiene f:rom a feed stream con- ~ .
taining 1,3-butadiene and at leas-t one other C4 unsaturate, .'~ .
thereby making possible the butadiene separation process
of this invention. All selectivities were at least about
5 or yreater~
, The data also indicates the general eflects o
temperature on selectivity and on the rate of exchange o~
. 10 butadiene with the adsorbent material as measured by the ,
.
butadiene peak half width. Specifically, tests A and B
employed the same desorbènt material but were conducted
at 55C. and 95C. respec-tively. At the higher temperatures ;~
of 95C. the selectivities decreased from 6.7 and 16.8 .'~
' 15 respectively at 55C. to 5.2 and 9.0 respectively at 95C. ~'
. but at the higher temperature the rate oE exchange of buta-
diene with the de.sorbent material was faster than that at the ;
lower temperature as evidenced by the narrower butadiene .
peak width. These effects are shown again by the results
of pulse tests F and G.
Also shown by the data is the general effect of
- the concentration of the olefin or aromatic in the desorbent ,'.
material upon the rate of exchanye of butadiene.with the
desorbent material. Generally, faster exchange rates are ' ,,.;
obtained with higher olefin or aromatic concentrations as
evidenced by the narrower butadiene peak widths. Specifi-
;~ cally this is shown by comparing the results of tests A
and C, the results of tests J and K, and the results o.
tests E, F, G, and H.
-31- ~ ',
;`, ,,:
~ , '.
