Process for separating C.sub.6 olefin hydrocarbons

A process for separating a normal C.sub.6 olefin hydrocarbon from a mixture of the same with a C.sub.6 olefin branched chain and/or cyclic hydrocarbon. The process comprises contacting the mixture at separation conditions with a molecular sieve comprising a crystalline silica. The normal C.sub.6 olefin hydrocarbon is selectively retained and will be recovered from the molecular sieve by displacement with a displacement material comprising pentene-1 or butene-1. The process preferably employs a simulated moving bed.

BACKGROUND OF THE INVENTION 
The field of art to which this invention pertains is hydrocarbon 
separation. Specifically, this invention relates to a process which 
utilizes a crystalline silica composition as a molecular sieve and a 
displacement material to separate a normal C.sub.6 olefin hydrocarbon from 
a feed mixture of the same with a C.sub.6 branched chain and/or cyclic 
olefinic hydrocarbons. 
BACKGROUND INFORMATION 
There is an abundance of prior art in the separation field, especially art 
relating to countercurrent fixed bed type operations, which deal with the 
separation of normal paraffins from other classes of hydrocarbons using a 
solid adsorbent. Examples of such art are U.S. Pat. Nos. 2,957,927 to 
Broughton et al; 3,239,455 to Lickus et al; 3,405,057 to Neuzil et al; 
4,000,059 to Wanless and 4,006,197 to Bieser. The most common adsorbents 
used throughout the prior art processes for the above separations are the 
crystalline aluminosilicates, the best known of which are the zeolites. 
The crystalline aluminosilicates function as "molecular sieves", that is, 
they contain pores having cross-sectional diameters which will accept 
certain molecules in a mixture of molecules of specific size and shape, 
i.e., normal olefins; while rejecting others, i.e., branched chain and 
cyclic, thereby separating the accepted molecules from the mixture. 
There is recent art that teaches the utility of crystalline silica as an 
adsorbent in separating hydrocarbons. Silicalite is a crystalline silica 
disclosed and claimed in U.S. Pat. Nos. 4,061,724 and 4,104,294 to Grose 
et al. The separation process utilizing silicalite contemplated by the 
Grose et al patents comprises, in general terms, the separation of an 
organic compound from an aqueous solution. U.S. Pat. No. 4,309,281 to 
Dessau discloses the ability of pure crystalline silica or high 
silica/alumina crystalline silica to effect the separation of linear 
olefins from branched chain and cyclic olefins. Dessau, however, does not 
discuss desorbents that might be used in that separation. 
The present invention relates to a process for separating a normal C.sub.6 
olefin from a mixture of the same with C.sub.6 branched chain and cyclic 
olefins using crystalline silica and specific desorbents found to be 
uniquely suitable. 
SUMMARY OF THE INVENTION 
In brief summary, the invention is, in a broadest embodiment, a process for 
separating a normal C.sub.6 olefin hydrocarbon from a mixture of the same 
with a branched chain and/or cyclic C.sub.6 olefinic hydrocarbon. The 
process comprises contacting the mixture at separation conditions with a 
molecular sieve comprising crystalline silica having a silica to alumina 
mole ratio of at least 12 to effect the selective retention of the normal 
C.sub.6 olefin hydrocarbon by the molecular sieve. The components of the 
mixture not retained are removed from contact with the molecular sieve, 
and the normal C.sub.6 olefin hydrocarbon is recovered by displacement at 
displacement conditions with a displacement material comprising butene-1 
or pentene-1. 
In another embodiment the present invention is the process of the above 
broadest embodiment employing the steps of: (a) maintaining net fluid flow 
through a column of the molecular sieve in a single direction, which 
column contains at least three zones having separate operational functions 
occurring therein and being serially interconnected with the terminal 
zones of the column connected to provide a continuous connection of the 
zones; (b) maintaining a retention zone in the column, the zone defined by 
the molecular sieve located between a feed input stream at an upstream 
boundary of the zone and a raffinate output stream at a downstream 
boundary of the zone; (c) maintaining a purification zone immediately 
upstream from the retention zone, the purification zone defined by the 
molecular sieve located between an extract output stream at an upstream 
boundary of the purification zone and the feed input stream at a 
downstream boundary of the purification zone; (d) maintaining a 
displacement zone immediately upstream from the purification zone, the 
displacement zone defined by the molecular sieve located between a 
displacement fluid input stream at an upstream boundary of the zone and 
the extract output stream at a downstream boundary of the zone; (e) 
passing the feed mixture into the retention zone at separation conditions 
to effect the selective retention of the normal C.sub.6 olefin hydrocarbon 
by the molecular sieve in the retention zone and withdrawing a raffinate 
output stream from the retention zone; (f) passing a displacement fluid 
into the displacement zone at displacement conditions to effect the 
displacement of the normal C.sub.6 olefin hydrocarbon from the molecular 
sieve in the displacement zone; (g) withdrawing an extract output stream 
comprising the normal C.sub.6 olefin hydrocarbon and displacement fluid 
from the displacement zone; (h) withdrawing a raffinate output stream 
comprising the C.sub.6 olefin branched chain and/or cyclic hydrocarbons 
from the displacement zone; and (i) periodically advancing through the 
column of molecular sieve in a downstream direction with respect to fluid 
flow in the retention zone, the feed input stream, raffinate output 
stream, displacement fluid input stream, and extract output stream to 
effect the shifting of zones through the molecular sieve and the 
production of extract output and raffinate output streams. 
Other embodiments of the present invention encompass details about feed 
mixtures, molecular sieves, displacement fluids and operating conditions, 
all of which are hereinafter disclosed in the following discussion of each 
of the facets of the present invention.

DESCRIPTION OF THE INVENTION 
In order to gain a better understanding of the process of this invention, 
the following definitions of terms that are used throughout this 
specification are given. 
The term "feed stream" indicates a stream in the process through which feed 
material passes to the molecular sieve. A feed material comprises one or 
more extract components and one or more raffinate components. An "extract 
component" is a compound or type of compound that is more selectively 
retained by the molecular sieve while a "raffinate component" is a 
compound or type of compound that is less selectively retained. In this 
process normal C.sub.6 olefin hydrocarbons from the feed stream are 
extract components while feed stream C.sub.6 branched chain and cyclic 
olefin hydrocarbons are raffinate components. Usually the term "extract 
component" as used herein refers to a more selectively retained compound 
or type of compound which is to be the desired product, such as normal 
C.sub.6 olefin hydrocarbons in this process. The term "displacement fluid" 
shall mean generally a material capable of displacing an extract 
component. The term "displacement fluid" or "displacement fluid input 
stream" indicates the stream through which displacement fluid passes to 
the molecular sieve. The term "raffinate output stream" means a stream 
through which most of the raffinate components are removed from the 
molecular sieve. The composition of the raffinate stream can vary from 
about 100 % displacement fluid to essentially 100% raffinate components. 
The term "extract stream" or "extract output stream" shall mean a stream 
through which an extract material which has been displaced by a 
displacement fluid is removed from the molecular sieve. The composition of 
the extract stream can also vary from about 100% displacement fluid to 
essentially 100% extract components. 
Although it is possible by the process of this invention to produce high 
purity (99+%) normal C.sub.6 olefin hydrocarbons at high recoveries (90% 
or higher), it will be appreciated that an extract component is never 
completely retained by the molecular sieve, nor is a raffinate component 
completely non-retained by the molecular sieve. 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 raffinate component appearing in the particular 
stream. More specifically, the ratio of the concentration of the retained 
normal C.sub.6 olefin hydrocarbons to that of the non-retained components 
will be lowest in the raffinate stream, next highest in the feed mixture, 
and the highest in the extract stream. Likewise, the ratio of the 
concentration of the non-retained components to that of the retained 
normal C.sub.6 olefin hydrocarbons will be highest in the raffinate 
stream, next highest in the feed mixture, and the lowest in the extract 
stream. 
The term "selective pore volume" of the molecular sieve is defined as the 
volume of the molecular sieve which selectively retains extract components 
from the feed stock. The term "non-selective void volume" of the molecular 
sieve is the volume of the molecular sieve which does not selectively 
retain extract components from the feed stock. This volume includes the 
cavities of the molecular sieve which are capable of retaining raffinate 
components and the interstitial void spaces between molecular sieve 
particles. The selective pore volume and the non-selective void volume are 
generally expressed in volumetric quantities and are of importance in 
determining the proper flow rates of fluid required to be passed into an 
operational zone for efficient operations to take place for a given 
quantity of molecular sieve. 
When molecular sieve "passes" into an operational zone (hereinafter defined 
and described) its non-selective void volume together with its selective 
pore volume carries fluid into that zone. The non-selective void volume is 
utilized in determining the amount of fluid which should pass into the 
same zone to displace the fluid present in the non-selective void volume. 
If the fluid flow rate passing into a zone is smaller than the 
non-selective void volume rate of molecular sieve material passing into 
that zone, there is a net entrainment of liquid into the zone by the 
molecular sieve. Since this net entrainment is a fluid present in 
non-selective void volume of the molecular sieve, it in most instances 
comprises less selectively retained feed components. 
Displacement fluids or desorbent materials used in various prior art 
adsorptive or molecular sieve separation processes vary depending upon 
such factors as the type of operation employed. In the swing bed system in 
which the selectively retained feed component is removed from the 
molecular sieve by a purge stream, displacement fluid selection is not as 
critical and displacement fluid comprising gaseous hydrocarbons such as 
methane, ethane, etc., or other types of gases such as nitrogen or 
hydrogen may be used at elevated temperatures or reduced pressures or both 
to effectively purge the retained feed component from the molecular sieve. 
However, in molecular sieve separation processes which are generally 
operated continuously at substantially constant pressures and temperatures 
to ensure liquid phase, the displacement fluid must be judiciously 
selected to satisfy many criteria. First, the displacement fluid should 
displace an extract component from the molecular sieve with reasonable 
mass flow rates without itself being retained. Secondly, displacement 
fluid must be compatible with the particular molecular sieve and the 
particular feed mixture. More specifically, they must not reduce or 
destroy the critical ability of the molecular sieve to retain an extract 
component and reject a raffinate component. Displacement fluids should 
additionally be substances which are easily separable from the feed 
mixture that is passed into the process. Both the raffinate stream and the 
extract stream are removed from the molecular sieve in admixture with 
displacement fluid and without a method of separating at least a portion 
of the displacement fluid, the purity of the extract product and the 
raffinate product would not be very high, nor would the displacement fluid 
be available for reuse in the process. It is therefore contemplated that 
any displacement fluid used in this process will preferably have a 
substantially different average boiling point than that of the feed 
mixture to allow separation of at least a portion of displacement fluid 
from feed components in the extract and raffinate streams by simple 
fractional distillation, thereby permitting reuse of displacement fluid in 
the process. The term "substantially different" as used herein shall mean 
that the difference between the average boiling points between the 
displacement fluid and the feed mixture shall be at least about 5.degree. 
C. The boiling range of the displacement fluid may be higher or lower than 
that of the feed mixture. Finally, displacement fluid should also be 
materials which are readily available and therefore reasonable in cost. In 
the preferred isothermal, isobaric, liquid-phase operation of the process 
of this invention, it has been found that displacement fluids comprising 
butene-1 or pentene-1 meet these requirements and are surprisingly 
effective. A particularly preferred mixture for displacement material is 
iso-octane and butene-1 or pentene-1. The iso-octane functions as a 
carrier and diluent for the olefin which effects the actual displacement, 
and also serves to flush the void spaces of the molecular sieve. 
The molecular sieve to be used in the process of this invention comprises a 
crystalline silica having a silica to alumina mole ratio of at least 12 
such as the silicalite of Grose et al as previously mentioned. Silicalite 
is a hydrophobic crystalline silica molecular sieve. Due to its 
aluminum-free structure, silicalite does not show ion-exchange behavior 
and is hydrophobic and organophilic. A more detailed discussion of 
silicalite may be found in the article "Silicalite, A New Hydrophobic 
Crystalline Silica Molecular Sieve"; Nature, Vol. 271, 9 February 1978, 
incorporated herein by reference. 
Crystalline silica is uniquely suitable for the separation process of this 
invention for the presumed reason that its pores are of a size and shape 
(about 6 angstrom units in diameter) that enable the crystalline silica to 
function as a molecular sieve, i.e., accept the molecules of C.sub.6 
normal olefin into its channels or internal structure, while rejecting the 
molecules of C.sub.6 olefin hydrocarbons of other structural classes. 
Examples of other crystalline silicas suitable for use in the present 
invention are those having the trademark designation "ZSM" and 
silica/alumina mole ratios of at least 12. The ZSM adsorbents are as 
described in U.S. Pat. No. 4,309,281 to Dessau, incorporated herein by 
reference. 
Commercially available molecular sieves heretofore used in the separation 
of the present invention have some entrance diameters less than 6 
angstroms, examples of which are chabazite, Type A (both sodium and 
calcium forms), faujasite, mordenite, etc. A serious problem with these 
adsorbents is the low exchange rate for displacement of feed straight 
chain hydrocarbons with displacement fluid molecules and thus the long and 
inefficient cycle times required to effect displacement. The discovery 
leading to the present invention is that crystalline silica, which has 
some entrance diameters of 6 angstroms, does not exhibit such low exchange 
rate particularly when the displacement material employed is butene-1 or 
pentene-1. 
The molecular sieve may be employed in the form of a dense compact fixed 
bed which is alternatively contacted with the feed mixture and 
displacement fluid materials. In the simplest embodiment of the invention, 
the molecular sieve is employed in the form of a single static bed in 
which case the process is only semi-continuous. In another embodiment, a 
set of two or more static beds may be employed in fixed bed contacting 
with appropriate valving so that the feed mixture is passed through one or 
more molecular sieve beds while the displacement fluid materials can be 
passed through one or more of the other beds in the set. The flow of feed 
mixture and displacement fluid materials may be either up or down through 
the molecular sieve. Any of the conventional apparatus employed in static 
bed fluid-solid contacting may be used. The particles of silicalite 
molecular sieve will preferably have a particle size range of about 16-60 
mesh (Standard U.S. Mesh). 
Simulated moving bed flow systems have a much greater separation efficiency 
than fixed molecular sieve bed systems and are therefore preferred. In the 
moving bed or simulated moving bed processes the retention and 
displacement operations are continuously taking place which allows both 
continuous production of an extract and a raffinate stream and the 
continual use of feed and displacement fluid streams. One preferred 
embodiment of this process utilizes what is known in the art as the 
simulated moving bed countercurrent flow system. The operating principles 
and sequence of such flow system are described in U.S. Pat. No. 2,985,589, 
incorporated herein by reference. In such a system it is the progressive 
movement of multiple liquid access points down a molecular sieve chamber 
that simulates the upward movement of molecular sieve contained in the 
chamber. Only four of the access lines are active at any one time: the 
feed input stream, displacement fluid inlet stream, raffinate outlet 
stream, and extract outlet stream access lines. Coincident with this 
simulated upward movement of the solid molecular sieve is the movement of 
the liquid occupying the void volume of the packed bed of molecular sieve. 
So that counter-current contact is maintained, a liquid flow down the 
molecular sieve chamber may be provided by a pump. As an active liquid 
access point moves through a cycle, that is, from the top of the chamber 
to the bottom, the chamber circulation pump moves through different zones 
which require different flow rates. A programmed flow controller may be 
provided to set and regulate these flow rates. 
The active liquid access points effectively divide the molecular sieve 
chamber into separate zones, each of which has a different function. In 
this embodiment of the process, it is generally necessary that three 
separate operational zones be present in order for the process to take 
place, although in some instances an optional fourth zone may be used. 
The retention zone, zone 1, is defined as the molecular sieve located 
between the feed inlet stream and the raffinate outlet stream. In this 
zone, the feedstock contacts the molecular sieve, an extract component is 
retained, and a raffinate stream is withdrawn. Since the general flow 
through zone 1 is from the feed stream which passes into the zone to the 
raffinate stream which passes out of the zone, the flow in this zone is 
considered to be a downstream direction when proceeding from the feed 
inlet to the raffinate outlet streams. 
Immediately upstream with respect to fluid flow in zone 1 is the 
purification zone, zone 2. The purification zone is defined as the 
molecular sieve between the extract outlet stream and the feed inlet 
stream. The basic operations taking place in zone 2 are the displacement 
from the non-selective void volume of the molecular sieve of any raffinate 
material carried into zone 2 by the shifting of molecular sieve into this 
zone and the displacement of any raffinate material retained within the 
selective pore volume of the molecular sieve. Purification is achieved by 
passing a portion of extract stream material leaving zone 3 into zone 2 at 
zone 2's upstream boundary, the extract outlet stream to effect the 
displacement of raffinate material. The flow of material in zone 2 is in a 
downstream direction from the extract outlet stream to the feed inlet 
stream. 
Immediately upstream of zone 2 with respect to the fluid flowing in zone 2 
is the displacement zone or zone 3. The displacement zone is defined as 
the molecular sieve between the displacement fluid inlet and the extract 
outlet streams. The function of the displacement zone is to allow a 
displacement fluid which passes into this zone to displace the extract 
component which was retained in the molecular sieve during a previous 
contact with feed in zone 1 in a prior cycle of operation. The flow of 
fluid in zone 3 is essentially in the same direction as that of zones 1 
and 2. 
In some instances, an optional buffer zone, zone 4 may be utilized. This 
zone, defined as the molecular sieve between the raffinate outlet stream 
and the displacement fluid inlet stream, if used, is located immediately 
upstream with respect to the fluid flow to zone 3. Zone 4 would be 
utilized to conserve the amount of displacement fluid utilized in the 
displacement step since a portion of the raffinate stream which is removed 
from zone 1 can be passed into zone 4 to displace displacement fluid 
present in that zone out of the zone into the displacement zone. Zone 4 
will contain enough displacement fluid so that raffinate material present 
in the raffinate stream passing out of zone 1 and into zone 4 can be 
prevented from passing into zone 3 thereby contaminating extract stream 
removed from zone 3. In the instances in which the fourth operational zone 
is not utilized, the raffinate stream passed from zone 1 to zone 4 must be 
carefully monitored in order that the flow directly from zone 1 to zone 3 
can be stopped when there is an appreciable quantity of raffinate material 
present in the raffinate stream passing from zone 1 into zone 3 so that 
the extract outlet stream is not contaminated. 
A cyclic advancement of the input and output streams through the fixed bed 
of molecular sieve can be accomplished by utilizing a manifold system in 
which the valves in the manifold are operated in a sequential manner to 
effect the shifting of the input and output streams thereby allowing a 
flow of fluid with respect to solid molecular sieve in a countercurrent 
manner. Another mode of operation which can effect the countercurrent flow 
of solid molecular sieve with respect to fluid involves the use of a 
rotating disc valve in which the input and output streams are connected to 
the valve and the lines through which feed input, extract output, 
displacement fluid input and raffinate output streams pass are advanced in 
the same direction through the molecular sieve bed. Both the manifold 
arrangement and disc valve are known in the art. Specifically, rotary disc 
valves which can be utilized in this operation can be found in U.S. Pat. 
Nos. 3,040,777 and 3,422,848, incorporated herein by reference. Both of 
the aforementioned patents disclose a rotary type connection valve in 
which the suitable advancement of the various input and output streams 
from fixed sources can be achieved without difficulty. 
In many instances, one operational zone will contain a much larger quantity 
of molecular sieve than some other operational zone. For instance, in some 
operations the buffer zone can contain a minor amount of molecular sieve 
as compared to the molecular sieve required for the retention and 
purification zones. It can also be seen that in instances in which 
displacement fluid is used which can easily displace extract material from 
the molecular sieve that a relatively small amount of molecular sieve will 
be needed in a displacement zone as compared to the molecular sieve needed 
in the buffer zone or retention zone or purification zone or all of them. 
Since it is not required that the molecular sieve be located in a single 
column, the use of multiple chambers or a series of columns is within the 
scope of the invention. 
It is not necessary that all of the input or output streams be 
simultaneously used, and in fact, in many instances some of the streams 
can be shut off while others effect an input or output of material. The 
apparatus which can be utilized to effect the process of this invention 
can also contain a series of individual beds connected by connecting 
conduits upon which are placed input or output taps to which the various 
input or output streams can be attached and alternately and periodically 
shifted to effect continuous operation. In some instances, the connecting 
conduits can be connected to transfer taps which during the normal 
operations do not function as a conduit through which material passes into 
or out of the process. 
It is contemplated that at least a portion of the extract output stream 
will pass into a separation means wherein at least a portion of the 
displacement fluid can be separated to produce an extract product 
containing a reduced concentration of displacement fluid. Preferably, but 
not necessary to the operation of the process, at least a portion of the 
raffinate output stream will also be passed to a separation means wherein 
at least a portion of the displacement fluid can be separated to produce a 
displacement fluid stream which can be reused in the process and a 
raffinate product containing a reduced concentration of displacement 
fluid. The separation means will typically be a fractionation column, the 
design and operation of which is well known to the separation art. 
Reference can be made to D. B. Broughton U.S. Pat. No. 2,985,589, and to a 
paper entitled "Continuous Adsorptive Processing--A New Separation 
Technique" by D. B. Broughton presented at the 34th Annual Meeting of the 
Society of Chemical Engineers at Tokyo, Japan on Apr. 2, 1969, both 
references incorporated herein by reference, for further explanation of 
the simulated moving bed countercurrent process flow scheme. 
Another type of simulated moving bed system is the cocurrent system set 
forth in patent application Ser. No. 407,680, filed Aug. 12, 1982, 
incorporated by reference herein in its entirety, in the name of Clarence 
G. Gerhold, entitled "High Efficiency Continuous Separation Process." 
Although both liquid and vapor phase operations can be used in many 
adsorptive separation processes, liquid-phase operation is preferred for 
this process because of the lower temperature requirements and because of 
the higher yields of extract product that can be obtained with 
liquid-phase operation over those obtained with vapor-phase operation. 
Adsorption conditions will include a temperature range of from about 
40.degree. to about 250.degree. C. and a pressure sufficient to maintain 
liquid phase. Displacement conditions will include the same range of 
temperatures and pressures as used for retention conditions. 
The size of the units which can utilize the process of this invention can 
vary anywhere from those of pilot-plant scale (see for example U.S. Pat. 
No. 3,706,812) to those of commercial scale and can range in flow rates 
from as little as a few cc an hour up to many thousands of gallons per 
hour. 
A dynamic testing apparatus is employed to test various molecular sieves 
with a particular feed mixture and displacement material to measure the 
molecular sieve characteristics of retention capacity and exchange rate. 
The apparatus consists of a molecular sieve chamber of approximately 70 cc 
volume having inlet and outlet portions at opposite ends of the chamber. 
The chamber is contained within a temperature control means and, in 
addition, pressure control equipment is used to operate the chamber at a 
constant predetermined pressure. Quantitative and qualitative analytical 
equipment such as refractometers, polarimeters and chromatographs can be 
attached to the outlet line of the chamber and used to detect 
quantitatively or determine qualitatively one or more components in the 
effluent stream leaving the molecular sieve chamber. A pulse test, 
performed using this apparatus and the following general procedure, is 
used to determine selectivities and other data for various molecular sieve 
systems. The molecular sieve is filled to equilibrium with a particular 
displacement material by passing the displacement material through the 
molecular sieve chamber. At a convenient time, a pulse of feed containing 
known concentrations of a particular extract component or of a raffinate 
component or both, all diluted in displacement fluid, is injected for a 
duration of several minutes. Displacement fluid flow is resumed, and the 
extract component or the raffinate component (or both) are eluted as in a 
liquid-solid chromatographic operation. The effluent can be analyzed 
on-stream or alternatively, effluent samples can be collected periodically 
and later analyzed separately by analytical equipment and traces of the 
envelopes or corresponding component peaks developed. 
From information derived from the test, molecular sieve performance can be 
rated in terms of void volume, retention volume for an extract or a 
raffinate component and the rate of displacement of an extract component 
by the displacement fluid. The retention volume of an extract or a 
raffinate component may be characterized by the distance between the 
center of the peak envelope of an extract or a raffinate component and the 
peak envelope of the tracer component or some other known reference point. 
It is expressed in terms of the volume in cubic centimeters of 
displacement fluid pumped during this time interval represented by the 
distance between the peak envelopes. The rate of exchange of an extract 
component with the displacement fluid can generally be characterized by 
the width of the peak envelopes at half intensity. The narrower the peak 
width, the faster the displacement rate. The displacement rate can also be 
characterized by the distance between the center of the tracer peak 
envelope and the disappearance of an extract component which has just been 
displaced. This distance is again the volume of displacement fluid pumped 
during this time interval. 
The following example is presented to further illustrate the process of 
this invention but it is not intended to limit the invention to the 
operating conditions nor the materials disclosed therein. 
EXAMPLE 
The above described pulse test apparatus was used to obtain data for this 
example. A series of five runs were made, with the differences between 
runs relating to differences in one or more of the variables comprising 
the composition of molecular sieve, displacement fluid, water content of 
the molecular sieve (substantially dry unless stated otherwise) and column 
temperature. The column was packed with alumina bound silicalite (80 wt. % 
silicalite). For each run, the flow was up the column at the rate of 1.2 
ml/min. Following is a table which comprises a tabulation of various 
details for each run as well as results derived from the elution curves 
which are shown as FIGS. 1 through 5, each figure corresponding to a 
similarly numbered run. 
TABLE 
__________________________________________________________________________ 
RUN COLUMN 
MOLECULAR 
NO. TEMP. SIEVE DISPLACEMENT FLUID 
FEED HALF WIDTH 
RETENTION 
__________________________________________________________________________ 
VOLUME 
1 60.degree. C. 
Silicalite/ 
25:75 iso-C.sub.8 :1- 
40 liq. Vol. % 
4-Me--C.sub.5.sup.=2 
C.sub.6.sup.=1 = 11.3 
Al.sub.2 O.sub.3 
octene of 7:3 C.sub.6.sup.=1 to 
9.3 
4-Me--C.sub.5.sup.=2 
C.sub.6.sup.=1 = 8.0 
in Desorbent 
2 60.degree. C. 
Silicalite/ 
25:75 iso-C.sub.8 :1- 
40 liq. Vol. % 
4-Me--C.sub.5.sup.=2 
C.sub.6.sup.=1 = 7.6 
Al.sub.2 O.sub.3 + 4% H.sub.2 O 
octene of 7:3 C.sub.6.sup.=1 to 
9.4 
4-Me--C.sub.5.sup.=2 
C.sub.6.sup.=1 = 7.3 
in Desorbent 
3 80.degree. C. 
Silicalite/ 
25:75 iso-C.sub.8 :1- 
40 liq. Vol. % 
4-Me--C.sub.5.sup.=2 
C.sub.6.sup.= 1 = 8.1 
Al.sub.2 O.sub.3 
octene of 7:3 C.sub.6.sup.=1 to 
9.3 
4-Me--C.sub.5.sup.=2 
C.sub.6.sup.=1 = 8.5 
in Desorbent 
4 60.degree. C. 
Silicalite/ 
25:75 iso-C.sub.8 :1- 
40% liq. Vol. % 
4-Me--C.sub.5.sup.=2 
C.sub.6.sup.=1 = 9.9 
Al.sub.2 O.sub.3 
pentene of 7:3 C.sub.6.sup.=1 to 
10.7 
4-Me--C.sub.5.sup.=2 
C.sub.6.sup.=1 = 12.3 
in Desorbent 
5 60.degree. C. 
Silicalite/ 
71.6:28.4 iso-C.sub.8 : 
40 liq. Vol. % 
4-Me--C.sub.5.sup.=2 
C.sub.6.sup.=1 = 28.5 
Al.sub.2 O.sub.3 
1-butene of 7:3 C.sub.6.sup.=1 to 
13.8 
4-Me--C.sub.5.sup.=2 
C.sub.6.sup.=1 = 24.0 
in Desorbent 
__________________________________________________________________________ 
BRIEF DESCRIPTION OF DRAWINGS 
The figures graphically illustrate the effectiveness of the present 
invention. Some separations are better than others. For example, in those 
separations, shown in FIGS. 1, 2 and 3, which do not employ the required 
displacement material of the present invention, it appears impossible to 
completely displace the normal C.sub.6 olefin extract component. This 
would, of course, preclude commercial exploitation of the process, no 
matter how good the separation between the feed mixture extract and 
raffinate components. 
On the other hand, when pentene-1 or butene-1 are employed as displacement 
materials, as shown in FIGS. 4 and 5, respectively, displacement of the 
C.sub.6 olefin is essentially complete. The elongation of the curves in 
FIG. 5 is due to the very low concentration of butene-1 in mixture with 
iso-octane diluent, which mixture comprised the displacement material. 
Such dilution would, of course, be avoided in a commercial embodiment. 
FIGS. 1-3 using octene-1 show a large amount of tailings of hexene-1 from 
the absorbent versus the relatively clean cessation of hexene-1 eluding 
from the absorbent when pentene-1 is employed (See FIG. 4). It was 
surprising and unexpected that the octene-1 never completely displaced the 
normal C.sub.6 olefin extract component whereas the pentene-1 of FIG. 4 
resulted in essentially complete displacement. The time of linear speed 
recorded was the same for all FIGS. 1-5.