Note: Descriptions are shown in the official language in which they were submitted.
20~040~
''~UPOM~TOGRAPHIC ~EPARATION PROCE8~
FOR RECOVERING EITHBR 2,6-DET OR 3,5-DET
FROM A MIXTURB THEREOF WITH AN~-n~K DET I80MER"
BACKGROUND OF THE I-Nv~N-llON
The field of art to which this invention
pertains is the solid bed adsorptive separation of
isomeric mixtures of diethyltoluene (DET). More
specifically, the invention relates to a process for
separating particular isomers of DET--specifically, 2,6-
and 3,5-diethyltoluene from other diethyltoluene isomers
by employing a solid bed adsorption system.
BACKGROUND OF THE I~v~NllON
Both 2,6- and 3,5-diethyltoluene isomers are
important starting materials for making diethyltoluene
diamines, from which polyureas and polyurethanes are
derived. Also, 2,6- and 3,5-diethyltoluene find
application as a desorbent material in certain adsorptive
chromatographic separations, e.g., p-xylene from its
isomers and p-xylene from mixtures of C8 and Cg aromatics.
It is well known in the separation art that
certain crystalline aluminosilicates can be used to
separate hydrocarbon types from mixtures thereof.
Furthermore, X and Y zeolites have been employed in a
number of processes to separate individual hydrocarbon
isomers. However, no previously published adsorptive
chromatographic separation processes have come to light
for separating diethyltoluene isomers.
It is, however, known that crystalline
aluminosilicates, or zeolites, used in other adsorptive or
chromatographic separations of various mixtures, can be
made in the form of agglomerates having high physical
strength and attrition resistance. Methods for forming
the crystalline powders into such agglomerates include the
: 2
addition of an inorganic binder, generally a clay
comprising a silicon dioxide and aluminum oxide, to the
high purity zeolite powder in wet mixture. The blended
clay zeolite mixture is extruded into cylindrical type
pellets or formed into beads which are subsequently
calcined in order to convert the clay to an amorphous
binder of considerable mechanical strength. As binders,
clays of the kaolin type, water permeable organic polymers
or silica are generally used.
The invention herein involves using such
agglomerates as adsorbent in a chromatographic proceRs
which can be practiced in fixed or moving adsorbent bed
systems. The preferred system for this separation is a
countercurrent simulated moving bed system, such as
described in Broughton U.S. Patent 2,985,589.
Cyclic advancement of the input and
output streams can be accomplished by a manifolding
system, which are also known, e.g., by rotary disc valves
shown in U.S. Patents 3,040,777 and 3,422,848. Equipment
20 utilizing these principles are familiar, in sizes ranging
from pilot plant scale (deRosset U.S. Patent 3,706,812) to
commercial scale in flow rates from a few ml per hour to
many thousands of cubic meters per hour.
Also, in some cases illustrated herein, it is
25 necessary to remove components of the feed in three
product streams in order to remove undesired components of
the feed in an intermediate stream from the extract and
raffinate streams. This intermediate stream can be termed
a second raffinate stream, as in U.S. Patent 4,313,015 or
30 a second extract stream, as in U.S. Patent 3,723,302.
This case pertains when
a contaminating component in the feed is more strongly
adsorbed than the desired product or when two product
streams are desired and additional material in the feed
can be removed in an intermediate stream. In the latter
case, if it is desired to keep the concentration of the
-.:
"
3 ~ 4 ~
contaminating component in the product as low as possible,
a first extract is taken off, high in concentration of the
desired component and lower in the contaminating product
followed by a second extract withdrawn at a point in the
extract zone between the desorbent inlet and the first
extract point, containing a high concentration of the
contaminant and a lower concentration of the desired
product. It may not be necessary to use a second
- desorbent if the desorbent is able to first desorb the
lightly held product and then desorb the remaining more
strongly held contaminants.
Some separations cases discussed herein may
require a two-stage process, wherein a first stage
separation is operated in the rejective mode to obtain a
highly purified raffinate product, e.g., 3,5-DET, and the
extract from the first stage is reprocessed in the same or
a different column with the same adsorbent/desorbent
combination to separate the most strongly adsorbed
component, the extract product, e.g., 2,6-DET, from the
intermediately-held components of the feed. The
separations may also be reversed with the first stage
separation operation to obtain a highly purified extract
product, e.g., 2,6-DET and contacting a second adsorbent
with the first stage raffinate in rejective mode to obtain
a highly purified second stage raffinate product, e.g.,
3,5-DET. The latter modification is similar to that
disclosed in deRosset U.S. Patent 4,213,913 and will be
understood therefrom.
The invention may also be practiced in a
cocurrent, pulsed batch or continuous process, like those
described in U.S. Patents 4,159,284 and 4,402,832,
respectively. The continuous process described in
4,402,832 is also capable of operating so as to obtain
three product streams as mentioned above.
A
The functions and properties of adsorbents and
desorbents in the chromatographic separation of liquid
components are well-known, see
Zinnen et al U.S. Patent 4,6~2,397.
Although numerous uses for isomers of DET or
mixtures thereof are known, e.g., as precursors of
reactants, e.g., curing agents or isocyanates for making
polyurethanes, e.g., diethyltoluene diamine and diethyl-
toluene diisocyanate, they have recently been found to be
a highly advantageous heavy desorbent for a
chromatographic process for separating para-xylene from
mixtures of xylene isomers. DET isomer desorbents are
preferred especially for separating xylene mixtures which
also contain Cg aromatics, the latter of which are
difficult to separate from p-diethylbenzene, (p-DEB), a
frequently taught desorbent for use in this application.
Currently, mixtures of DET isomers are used in
the preparation of polyurethane precursors, but it would
be highly desirable to make the precursors from highly
pure individual isomers of DET in order to obtain higher
yields of the desired reactant. Additionally, the yield
of individual DET isomers can be increased by isomerizing,
at isomerization conditions, the raffinate isomer mixture
with an isomerization catalyst selected for a particular
isomer, for example, zeolites containing trace metals, as
is known in the art, and recycling the raffinate with
increased concentration in one of the isomers with the
feed to the instant process.
SUMMARY OF THE INVENTION
In brief summary, the invention is in one
embodiment a chromatographic process for separating 2,6-or
3,5-DET from a mixture thereof with at least one other DET
isomer of diethyltoluene. The process comprises
contacting the DET isomer mixture at adsorption conditions
A
with an adsorbent selected from the following Groups: A)
X zeolite exchanged with a potassium cation; B) X zeolite
exchanged with sodium or copper or Y zeolite exchanged
with copper, sodium, barium or calcium; and C) X zeolite
exchanged with barium or lithium or with potassium and
barium or Y zeolite exchanged with potassium, sodium,
barium or calcium, thereby selectively adsorbing one of
the DET isomers contained in the feed; thereby
selectively adsorbing one of the DET isomers contained in
the feed thereon and removing, or eluting at least one
relatively non-adsorbed DET isomer from contact with the
adsorbent to form a raffinate stream. An extract stream
containing the adsorbed DET isomer is thereafter recovered
by subjecting the rich adsorbent to desorption conditions
with a desorbent material comprising monocyclic alkyl-
substituted aromatic hydrocarbon, e.g., p-xylene,
p-diethylbenzene, m-diethylbenzene or toluene.
In a preferred embodiment, the invention is as
described above in the first embodiment except that the
feed contains 3,5-DET, the adsorbent is limited to those
recited in Group A, the adsorbed isomer is 3,5-DET, the
extract stream is rich in 3,5-DET and the raffinate stream
is depleted in 3,5 DET relative to the feed.
In a second preferred embodiment, the invention
is as described above in the first embodiment except that
the feed contains 2,6-DET, the adsorbent is limited to
those specified in Group B, the adsorbed isomer is 2,6-
DET, the extract stream is rich in 2,6-DET and the
raffinate stream is depleted in 2,6-DET relative to the
feed.
In a third preferred embodiment, the invention
is as described above in the first embodiment except that
the feed contains 3,5-DET, the adsorbent is limited to
those set forth in Group C, the non-adsorbed isomer is
3,5-DET, the extract stream is depleted in 3,5-DET and the
2~20~
raffinate stream is enriched in 3,5-DET relative to the
feed.
With an adsorbent such as those listed above in
Group C, which in combination with a desorbent liquid
mixture will selectively adsorb all the DET isomers except
3,5-DET, which is relatively non-adsorbed and which elutes
near the void volume, 3,5-DET is eluted as raffinate and
other components are adsorbed and eluted as extract by
desorption with the desorbent. This so-called rejective
separation mode is particularly desirable where the 3,5-
DET is the major component, since utilities are lower and
adsorbent capacity requirement is lower per unit of output
product.
One group of adsorbents, on which 2,6-DET is
selectively adsorbed most strongly consists of those
adsorbents that we listed above in Group B and in this
case 2,6-DET is recovered in the extract and the other DET
isomers in the raffinate.
Another group of adsorbents, which least
strongly adsorb 3,5-DET, consists of Y zeolites, cation
exchanged with sodium, calcium or barium. With this group
of adsorbents, the preferred desorbents, are toluene, p-
DEB and m-DEB. It has now been established that these
adsorbents will alter the selectivity pattern such that
2,6-DET is the most strongly adsorbed isomer and 3,5-DET
is the least strongly adsorbed, or rejected, isomer.
Other embodiments of our invention encompass
details about feed mixtures, adsorbents, desorbent
materials and operating conditions, all of which are
hereinafter disclosed in the following discussion of each
of the facets of the present invention.
BRIEF DESCRIPTION OF THE DRAWINGS
Figure 1 is a chromatograph trace of the
separation of 2,6-DET from a mixture of DET isomers with
NaX zeolite adsorbent and a desorbent comprising 30 vol
p-DEB and 70 vol ~ i~ooctane.
Figure 2 is a similar chromatographic trace to
illustrate the separation of 3,5-DET by a rejective
separation process, using a BaY adsorbent and 30 vol.%
p-DEB/70 vol.% n-heptane desorbent. This figure also
illustrates an embodiment of the invention in which 2,6-
DET is the most strongly adsorbed isomer, therefore
permitting recovery of 3,5-DET and 2,6-DET in purified
form in the same process.
Figure 3 is a chromatographic trace to
illustrate the separation of 3,5-DET by a rejective
separation process using a Ba-exchanged X faujasite
adsorbent and a mixture of 30 vol % p-xylene and 70 vol %
n-heptane as desorbent.
Figures 4 and 5 are chromatographic traces
similar to Figure 2 in that both 2,6-DET and 3,5-DET can
be separated and separately recovered in the extract and
raffinate, respectively, in Figure 4 with a NaY zeolite
adsorbent and p-DEB desorbent and in Figure 5 with a CaY
zeolite adsorbent and 30% m-DEB in n-heptane as desorbent.
Figure 6 is a chromatographic trace of the
separation of 3,5-diethyltoluene from a mixture of DET
isomers with KX zeolite adsorbent and a desorbent
comprising 30% p-DEB and 70% isooctane.
Figure 7 is a chromatographic trace similar to
Figure 1, except that the desorbent is 100% p-cymene.
DETAILED DESCRIPTION OF THE INVENTION
Adsorbents used in the process of this invention
comprise specific crystalline aluminosilicates or
molecular sieves, namely, X and Y zeolites. The zeolites
have known cage structures in which the alumina and silica
tetrahedra are intimately connected in an open three-
dimensional network to form cage-like structures with
.~".
s
2~040~
window-like pores. The tetrahedra are cross-linked by the
sharing of oxygen atoms with spaces between the tetrahedra
occupied by water molecules prior to partial or total
dehydration of this zeolite. The dehydration of the
zeolite results in crystals interlaced with cells having
molecular dimensions and thus the separation which they
effect is dependent essentially upon differences between
the sizes of the feed molecules as, for instance, when
smaller normal paraffin molecules are separated from
larger isoparaffin molecules by using a particular
molecular sieve. In the process of this invention,
however, the term "molecular sieves", although widely
used, is not strictly suitable since the separation of
specific aromatic isomers is apparently dependent on
differences in electrochemical attraction between the
different isomers and the adsorbent rather than on pure
physical size differences between the isomer molecules.
In hydrated form, the crystalline
aluminosilicates encompass type X zeolites which are
represented by Formula 1 below in terms of moles of
oxides:
Formula 1
25 (o.9po.2)M2/no:Al2o3:(2.5po.5)sio2:yH2o
where "M" is a cation having a valence of not more than 3
which balances the electrovalence of the tetrahedra and is
generally referred to as an exchangeable cation, "n"
represents the valence of the cation, and "y", which
represents the moles of water, is a value up to about 9
depending upon the identity of "M" and the degree of
hydration of the crystal. As noted from Formula 1, the
SiO2/A1203 mole ratio is 2.5pO.5. As the X zeolite is
initially prepared, the cation "M" is usually
predominately sodium, that is, the major cation at the
exchangeable cationic sites is sodium and the zeolite is
therefore referred to as a sodium-X zeolite. Depending
upon the purity of the reactants used to make the zeolite,
other cations mentioned above may be present, however, as
impurities.
In one embodiment of the invention, in which
3,5-DET is substantially non-adsorbed and recovered as a
raffinate product, operative adsorbents are formed when
the sodium cation of an X zeolite, as prepared, is
substantially completely cation exchanged by barium,
lithium or mixtures of barium and potassium. In another
embodiment, in which 2,6-DET is selectively adsorbed by
the adsorbent, operative adsorbents are formed when the
cation of an X zeolite is exchanged with copper or sodium
(i.e., original form as prepared). In yet another
embodiment wherein 3,5-DET is selectively adsorbed, the
preferred adsorbent is X zeolite exchanged with potassium.
The type Y structured zeolite, in the hydrated
or partially hydrated form, can be similarly represented
in terms of moles of oxides as in Formula 2 below:
Formula 2
(0.9+0.2) M2/no:Al2o3:wsio2 yH2o
where "M", "n" and "y" are the same as above and "w" is a
value greater than about 3 up to about 6. The SiO2/A1203
mole ratio for type Y structured zeolites can thus be from
about 3 to about 6. For both zeolites, the cation "M" may
be one or more of a variety of cations but, as the Y type
zeolites are initially prepared, the cation "M" is also
usually predominately sodium. The type Y zeolite
containing predominately sodium cations at the
exchangeable cationic sites is, therefore, referred to as
a sodium-exchanged type-Y, or NaY, zeolite. Depending
upon the purity of the reactants used to make the zeolite,
~, "~
202~ ~Q~
other cations mentioned above may be present, however, as
impurities.
In additional embodiments of the invention, 2,6-
DET is selectively adsorbed by a Y zeolite exchanged with
barium or copper or 3,5-DET can be recovered in a
rejective separation with a Y zeolite in the sodium form
or exchanged with barium or potassium.
In further embodiments, in which the
exchangeable cation sites are exchanged with certain
cations, the selectivity order is unexpectedly altered
such that 2,6-DET is the most strongly adsorbed DET isomer
while 3,5-DET is the rejected, or least strongly adsorbed,
DET isomer. In other words, both species can be isolated
with a chromatographic process using the same adsorbent
and it is further possible to recover both rejected and
most strongly adsorbed isomers in a single process. The
adsorbents, in which it has been discovered that the
selectivity order is as above described, are Y zeolites,
cation exchanged with sodium (i.e., in the initial form,
or as prepared), calcium or barium cations. In the case
of barium-exchanged Y zeolite, the separation of 2,6-DET
from the 2,3-DET isomer in the extract is considered
somewhat marginal, although operative, but if a feed were
used in which little or no 2,3-DET is present, the
separation is quite viable. Feed preparation could
include either removal of 2,3-DET prior to separation, or
isomerization to convert 2,3-DET to another isomer or
modification of reaction conditions, e.g., selection of
the catalyst, to minimize the formation of 2,3-DET. In
some cases, it might be acceptable to produce a 2,6-DET
extract containing considerable amounts of 2,3-DET and/or
2,5-DET, for example, as a preferred mixture for use as a
desorbent in separating p-xylene from its isomers and
ethylbenzene.
Typically, adsorbents used in separative
processes contain the crystalline zeolite material
11 2~2~
dispersed in an amorphous matrix or binder, having
channels and cavities therein which enable liquid access
to the crystalline material. Silica, alumina, clay or
mixtures thereof are inorganic substances typical of such
matrix materials. Organic materials, such as polymers of
styrene/divinyl-benzene, are also used as a matrix. The
binder aids in forming or agglomerating the crystalline
particles which otherwise would comprise a fine powder.
The adsorbent may thus be in the form of particles such as
extrudates, aggregates, tablets, macrospheres or granules
having a desired particle range, preferably from about 16
to about 60 mesh (Standard U.S. Mesh) which corresponds to
a nominal apperture of 0.25 to 1.19 mm.
Feed mixtures which can be utilized in the
process of this invention will comprise at least one of
the isomers, 3,5-DET or 2,6-DET, and may additionally
contains at least one other DET aromatic isomer. Crude
hydrocarbon streams containing substantial quantities of
Cll aromatic isomers are produced by alkylation and
isomerization processes, which are well known to the
refining and petrochemical arts. Cll aromatics other than
DET isomers, such as butyltoluenes and cymenes, may be
formed which may necessitate their removal by other means,
such as fractionation, or isomerization to DET isomers.
Otherwise, they may be coextracted with the product DET
isomer or be eluted with the raffinate (non-adsorbed)
product, and, of course, reduce the purity of the desired
DET isomer product.
In a rejective mode of operation designed to
separate the 3,5-DET from a feed mixture containing 3,5-
DET and at least one other DET aromatic, the mixture is
contacted with an adsorbent, selected from the group
aforementioned, on which 3,5-DET is least strongly
adsorbed, consisting of X zeolites, cation exchanged with
barium, mixtures of barium and potassium or lithium and Y
zeolites, cation exchanged with barium, potassium or
2 ~ J\ ~
12
sodium (i.e., in the original form as prepared), at
adsorption conditions whereby the 3,5-DET is the least
selectively adsorbed isomer. The other isomers are
adsorbed and retained by the adsorbent while the 3,5-DET
is relatively unadsorbed and is eluted from the
interstitial void spaces between the particles of
adsorbent and from the surface of the adsorbent. The
adsorbent containing the more selectively adsorbed isomer
is referred to as a "rich" adsorbent. The other isomers,
which may include 2,6-DET and other DET isomers in the
feed are then recovered from the rich adsorbent by
contacting the rich adsorbent with a desorbent material at
desorption conditions. As aforementioned, the relatively
more strongly adsorbed isomers of DET, referred to as the
extract, can be isomerized to increase the concentration
of one or more of said isomers and can be recycled to the
separation process to increase the recovery of 3,5-DET.
The general flow scheme for such a rejective
adsorptive separation involves recovering the less
adsorbed feed component(s) from the non-selective void
volume and weakly adsorbing volume before the more
strongly adsorbed component(s); the relatively unadsorbed
component(s) is thereby recovered in the raffinate. A
particular advantage of such a system lies where the
unadsorbed fraction or component is large in relation to
the other fraction or components, since substantially less
adsorbent and smaller sized equipment is required for a
given feed throughout than if the large fraction is
selectively adsorbed on the adsorbent.
To separate 2,6-DET from a feed mixture
containing 2,6-DET and at least one other DET isomer, the
mixture is contacted with an adsorbent selected from the
group mentioned above, on which 2,6-DET is most strongly
adsorbed, consisting of X zeolites, cation exchanged with
sodium (as prepared) or copper and Y zeolites, cation
2 ~
13
exchanged with sodium (as prepared), calcium, copper or
barium.
In the present invention, it is generally
preferred to operate continuously at substantially
- 5 constant pressures and temperatures to ensure liquid phase
and thus the desorbent material relied upon must be
judiciously selected to satisfy several criteria. First,
the desorbent material should displace an extract
component from the adsorbent with reasonable mass flow
rates without itself being so strongly adsorbed as to
unduly prevent the extract component from displacing the
desorbent material in a following adsorption cycle.
Secondly, the desorbent material must be compatible with
the particular adsorbent and the particular feed mixture.
More specifically, it must not reduce or destroy the
critical selectivity of the adsorbent for an extract
component with respect to the raffinate component or react
chemically with the feed components. The desorbent
material should additionally be easily separable from the
feed mixture that is passed into the process. Both the
raffinate components and the extract components are
typically removed from the adsorbent in admixture with
desorbent material, and without a method of separating at
least a portion of desorbent material, the purity of the
extract product and the raffinate product would not be
very high nor would the desorbent material be available
for reuse in the process. It is, therefore, contemplated
that any desorbent material used in this process will have
a substantially different average boiling point than that
of the feed mixture or any of its components, i.e., more
than about 5~C difference, to allow separation of at least
a portion of the desorbent material from feed components
in the extract and raffinate streams by simple fractional
distillation, thereby permitting reuse of desorbent
material in the process.
14 2~P403
Finally, desorbent materials should be readily
available and reasonable in cost. However, a suitable
desorbent or desorbents for a particular separation with
specific adsorbent are not always predictable. In the
preferred isothermal, isobaric, liquid-phase operation of
the process of this invention, it has now been determined
that desorbent materials comprising monocyclic alkyl-
substituted aromatic hydrocarbons, such as p-DEB, m-DEB,
toluene, p-cymene or p-xylene, must be selected with
regard to the specific separation in order to effectively
desorb the extract from the adsorbent. In well-known
manner, the desorbent can be separated from the extract
product by distillation. Diluents for the desorbent may
also be used in some instances to modify the desorbent
strength to achieve better separation, resolution and
desorption rates. Examples of such dilution agents
include normal paraffins, isoparaffins, ethers, and
halogenated hydrocarbons.
Adsorption conditions will include a temperature
range of from about 20 to 250~C with about 60 to about
200~C being more preferred and a pressure just sufficient
to maintain liquid phase, which may be from about
atmospheric to 4240 kPa. Desorption conditions will
include the same range of temperatures and pressure as
used for adsorption conditions.
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.
A dynamic testing apparatus is employed to test
various adsorbents and desorbent material with a
3S particular feed mixture to measure the adsorbent
characteristics of adsorptive capacity and exchange rate.
2 ~ Q ~
The apparatus consists of a helical adsorbent chamber of
approximately 70-75 ml 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 equipment, such as
refractomers, polarimeters, chromatographs, etc., can be
attached to the outlet line of the chamber and used to
analyze, "on-stream", the effluent stream leaving the
adsorbent chamber.
A pulse test, performed using this apparatus and
the following general procedure, is used to determine
data, e.g., selectivities, for various adsorbent systems.
The adsorbent in the chamber is filled to equilibrium with
a particular desorbent by passing the desorbent material
through the adsorbent chamber. At a convenient time, a
pulse of feed containing known concentrations of a tracer
and of a particular extract component or of a raffinate
component, or both, normally diluted in desorbent material
is injected for a duration of several minutes. Desorbent
flow is resumed, and the tracer and the extract and
raffinate components are eluted as in a liquid-solid
chromatographic operations. The effluent can be analyzed
by on-stream chromatographic equipment and traces of the
envelopes of corresponding component peaks developed.
Alternatively, effluent samples can be collected
periodically and later analyzed separately by gas
chromatography.
From information derived from the test,
adsorbent performance can be rated in terms of void
volume, retention volume for an extract or a raffinate
component, and the rate of desorption of an extract
component from the adsorbent and selectivity. Void volume
3s is the non-selective volume of the adsorbent, which is
expressed by the amount of desorbent pumped during the
2~2~
16
interval from the initial flow to the center of the peak
envelope of the tracer. The net retention volume (NRV) of
an extract or a raffinate component may be characterized
by the distance between the center of the peak envelope
(gross retention volume) of the extract or raffinate
component and the center of the peak envelope (void
volume) of the tracer component or some other known
reference point. It is expressed in terms of the volume
in cubic centimeters of desorbent material pumped during
this time interval, represented by the distance between
the peak envelopes. The rate of exchange or desorption
rate of an extract component with the desorbent material
can generally be characterized by the width of the peak
envelopes 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 an
extract component which has just been desorbed. This
distance is again the volume of desorbent material pumped
during this time interval. Selectivity, ~, is determined
by the ratio of the net retention volumes (NRV) of the
more strongly adsorbed component to each of the other
components.
The following non-limiting examples are
presented to illustrate the process of the present
invention and are not intended to unduly restrict the
scope of the claims attached hereto.
EXAMPLE 1
The previously described pulse test apparatus
was used to obtain data for this example, which
illustrates the separation of 2,6-DET, in the extract,
from the other isomers of DET. The liquid temperature was
165~ and the flow was up the column at the rate of 1.26
ml/min. The feed stream comprised 2.0 ml pulses of a
- ~ 17 ~ Q ~
solution containing 1.5 ml of a mixture of the
diethyltoluene isomers, 2,3-, 2,5-, 2,6- and 3,5-DET, and
0.3 ml of n-hexane tracer and 1.0 ml of desorbent, 30%
vol. p-diethylbenzene in 70% vol. iSooCtane. The mixture
of DET isomers was approximately 43 % (vol) 3,5-DET, 20%
2,5 DET, 23% 2,6-DET and 7% 2,3-DET with the balance
consisting of other C11 aromatics. The column was packed
with clay bound Na-X faujasite adsorbent of 20-50 mesh
particle size corresponding to an apperature size of 0.297
to 0.84 mm. The 2,6-DET isomer was selectively adsorbed
and recovered as the extract product.
The selectivity (~), as earlier described, was
calculated from the trace of the peaks generated for the
components. The results of this example are shown in the
following Table 1 and Figure 1.
TABLE 1
Component NRV BETA(~)
(ml) (ml)
n-C6 0.0 tracer
2,3-DET 22.9 2.51
3,5-DET 36.4 1.58
2,6-DET 57.4 reference
2,5-DET 29.8 1.93
In general, the above data does show that the
present invention provides a 2,6-diethyltoluene selective
system, with adequate selectivities for the commercial use
of the separation of the present invention.
EXAMPLE 2
The previously described pulse test was also
used to obtain data similar to that of Example 1, but
using a different adsorbent in place of the NaX zeolite
exemplified above. In the first test, the feed was 2.0 ml
.. . ~
~'
18 ~ ~ 2 ~
of a solution containing 1.5 ml of the DET isomer mixture
of Example 1, 0.3 ml n-hexane tracer and 1 ml of the same
desorbent, 30% p-diethylbenzene in isooctane. The
adsorbent was Cu-X. The column temperature was 165~C,
flow rate up the column was 1.14 ml per min. The results
of the pulse test, shown in Table 2 below, also indicate a
2,6-DET selective process. In a second test at 145~C and
flow rate of 1.02 cc/min, a feed, comprising 2 cc of a
solution containing 1 cc of the same mixture of DET
isomers, 1 cc desorbent and 0.3 cc n-C8, was separated in
the column filled with Y zeolite exchanged with copper
ions in exchangeable sites. The desorbent was 100%
diethylbenzene (p-DEB). The results are also shown in the
following Table 2.
TABLE 2
Test No. comPonentNRV BETA(~)
(ml)
1 n-C6 0.0 tracer
3,5-DET28.9 1.69
2,3-DET26.6 1.84
2,6-DET48.9 reference
2,5-DET26.3 1.86
2 n-C8 0.0 tracer
3,5-DET9.7 1.71
2,3-DET11.7 1.42
2,6-DET16.6 reference
2,5-DET 8.7 1.90
EXAMPLE 3
Further pulse tests were run to demonstrate a
process for selectively adsorbing the other isomers of DET
in preference to the 3,5-isomer, i.e., the relatively non-
adsorbed species, and thereby rejectively separating and
..
19 ~ 4 ~ ~
recovering 3,5-DET in the raffinate. In the tests, p-DEB
or p-xylene was the desorbent, either undiluted or diluted
to 30% with either n-heptane, n-dodecane, or iSOOCtane.
Table 3 shows the results of each of the pulse tests in
this example. NRV is the net retention volume, discussed
previously. For clarity, the Cl1 impurities are not
reported.
In Test No. 1, the adsorbent was a Y zeolite,
exchanged with barium ions at the exchangeable sites and
the desorbent was 30% p-DEB diluted with n-heptane. The
feed pulse was 2 ml of a solution containing 1.7 ml of the
DET isomer mixture of Example 1 and 0.3 ml n-Cll tracer.
The results of the pulse test are shown in Fig. 2 and
Table 3 below. As can also be seen in Fig. 2, 2,6-DET was
most strongly adsorbed onto the BaY zeolite and therefore
illustrates one adsorbent which can be employed to
separate either or both 2,6- and 3,5-DET isomers in a
single process. In Test No. 2, the adsorbent was X
zeolite exchanged with a mixture of barium and potassium
ions and the desorbent was 30~ p-DEB in n-heptane. The
feed pulse was the same as in Test No. 1. In Test No. 3,
the adsorbent was X zeolite, exchanged with lithium ions
and the desorbent was 30% p-DEB in i~ooctane. The feed
pulse was the same as in Example 1. In Test No. 4, the
adsorbent was Y zeolite exchanged with barium at the
exchangeable sites and the desorbent was 30% toluene in n-
heptane. The feed pulse was the same as in Test No. 1.
In Test No. 5, the adsorbent was KY and the desorbent was
30% p-xylene in n-heptane. The feed pulse was 5 cc of a
solution containing 1.5 cc of the DET isomer mixture of
Example 1, 0.29 cc n-Cg tracer, and 3 cc desorbent. In
Test No. 6, the adsorbent was X faujasite, exchanged with
barium cations, and the desorbent was 30~ p-xylene in n-
heptane. The feed pulse was 2 cc of a solution containing
1.7 cc of the DET isomer mixture of Example 1 and 0.3 cc
n-C12. As can be seen in Figure 3, 3,5-DET was the least
- 2~2~5~
strongly adsorbed isomer, illustrating a separating system
which can be employed to separate 3,5-DET in a rejective
process.
~ D20 ~3B
21
TABLE 3 ~
Test No. ComponentNRV BETA(~)
(ml)
1 n-Cll 0.0 tracer
BaY 3,5-DET8.0 3.69
Temp: 120~C 2,3-DET22.6 1.30
Flow Rate: 2,6-DET29.4 1.00
1.26 cc/min 2,5-DET 16.2 1.81
2 n-Cll 0.0 tracer
BaKX 3,5-DET3.9 reference
Temp: 145~C 2,3-DET5.8 0.67
Flow Rate: 2,6-DET7.0 0.56
1.32 cc/min 2,5-DET 8.5 0.46
3 n-C6 0.0 tracer
LiX 3,5-DET30.2 reference
Temp: 165~C 2,3-DET51.5 0.59
Flow Rate: 2,6-DET49.6 0.61
1.17cc/min 2,5-DET34.0 0.89
4 n-Cll 0.0 tracer
BaY 3,5-DET3.1 reference
Temp: 125~C 2,3-DET15.9 0.19
Flow Rate: 2,6-DET15.2 0.20
1.02 cc/min 2,5-DET 12.8 0.24
n-Nonane0.0 tracer
KY 3,5-DET20.6 reference
Temp: 150~C 2,3-DET26.6 0.77
Flow Rate: 2,6-DET28.1 0.73
1.22 cc/min 2,5-DET 29.8 0.69
~20~0~
22
Test No. Component NRV BETA(B)
(ml)
6 n-C12 0.0 tracer
S BaX 3,5 DET 5.9 reference
Temp: 200~C 2,3-DET 16.5 0.36
Flow Rate: 2,6-DET 14.4 0.41
1.23 cc/min 2,5-DET 16.9 0.35
DET * 12.7 0.46
DET * 12.1 0.49
* Undetermined isomer
EXAMPLE 4
Further pulse tests were run to demonstrate an
additional adsorbent whereby 2,6-DET and 3,5-DET can be
recovered as the extract product and/or the raffinate
product, respectively, in a single stage, if desired, or
in a two-stage process, as aforementioned. In a single
stage, a third, intermediate product stream is required,
but both isomers can be separately recovered in purified
form in a two-stage process, where the 2,6-DET extract is
the product in the first stage and the raffinate, 3,5-DET,
is the product in the second stage, which is a rejective
process as described above. The adsorbent and desorbent
can be the same in both stages, resulting in lower capital
costs, or a different combination may be used. Also, the
sequence of the stages, as set forth above, can be
reversed. In Test No. 1, the feed pulse was 2 cc of a
solution containing 1 cc of the DET isomer mixture of
Example 1, 1 cc of the desorbent and 0.3 cc n-C8. The
desorbent was 100% p-DEB. In Test No. 2, the feed pulse
was 5 cc of a solution containing 1 cc desorbent, 0.3 cc
n-C10 tracer, and 4 cc of a DET isomer mixture with the
following composition: 41.2 vol % 3,5-DET, 5.4% 2,3-DET,
2 ~
23
14.3% 2,6-DET, and 9.2% 2,5-DET, with the balance
consisting of other Cll aromatics such as butyl toluene
isomers and p-cymene. The desorbent in this test was 50%
p-DEB in n-heptane. In Test No. 3, at 200~C and column
flow of 1.21 cc/min, the feed pulse was 2 cc of the same
solution as Test 1. The desorbent was 30% m-diethyl-
benzene (m-DEB) diluent with n-heptane. The adsorbent in
each of the preceding tests was Y zeolite, with sodium
ions in the cation-exchangeable sites. In Test No. 4, at
200~C and column flow rate of 1.23 cc/min., the feed pulse
was 2 cc of the same solution as Test 1. The adsorbent in
this test was Y zeolite with calcium ions in the cation-
exchangeable sites. The desorbent in this test was 30% m-
DEB in n-heptane. The results of the experiments are
shown in Table 4 below. Pulse Test No. 1 is illustrated
in the chromatograph of Figure 4; Pulse Test No. 4 is
illustrated in the chromatograph of Figure 5. It is noted
from Test No. 2 that even in the presence of Cll
impurities such as p-cymene and butyltoluenes, 2,6-DET and
3,5-DET can be recovered in purified form, since they are
the most strongly adsorbed and least strongly adsorbed
species, respectively.
2~4~ ~
24
TABLE 4
Test No. ComponentNRV BETA(B)
(ml)
1 n-C8 0.0 tracer
Temp: 145~C 3,S-DET8.7 2.46
Flow Rate: 2,3-DET13.3 1.61
1.02 cc/min 2,6-DET21.4 reference
2,5-DET9.9 2.16
2 n-C10 0.0 tracer
Temp: 150~C 3,5-DET8.1 3.99
Flow Rate: p-cymene16.5 1.75
1.26 cc/min 2,3-DET17.6 1.64
2,6-DET28.8 reference
2,5-DET14.2 2.02
butyl toluene isomer 19.3 1.49
butyl toluene isomer 14.2 2.03
3 n-C10 ~ ~ tracer
Temp: 200~C 3,5-DET9.4 3.21
Flow rate: 2,5-DET19.4 1.56
1.21 cc/min 2,3-DET20.5 1.47
2,6-DET30.2 reference
4 n-C10 ~ ~ tracer
Temp: 200~C 3,5-DET9.1 4.19
Flow Rate: 2,3-DET24.5 1.56
1.23 cc/min 2,5-DET24.9 1.54
2,6-DET38.2 reference
EXAMPLE 5
The liquid temperature in this pulse test was
165~C and the flow was up the column at the rate of
1.26ml/min. The feed stream comprised 2.0 ml pulses of a
solution containing 1.5 ml of a mixture of diethyltoluene
isomers, and 0.3 ml of n-hexane tracer and 1.0 ml of
desorbent, 30% vol p-diethylbenzene in 70% (vol)isooctane.
The mixture of DET isomers was approximately the same as
in Example 1. The column was pac~ed with clay bound K-X
faujasite adsorbent of 0.297 to 0.84 mm particle size.
The 3,5-DET isomer was selectively adsorbed and recovered
is the extract product.
The selectivity (~), as earlier described, was
calculated from the trace of the peaks generated for the
components. The results of this example are shown on the
following Table 5 and Figure 6.
TABLE 5
Component GRV NRV BETA(~)
(ml) (ml)
n-hexane 41.6 0.0 tracer
3,5-DET 76.4 34.8 reference
2,3-DET 69.8 28.2 1.24
2,6-DET 68.0 26.4 1.32
2,4-DET 58.0 16.4 2.13
2,5-DET 57.2 15.7 2.22
In general, the above data does show that the present
invention provides a 3,5-diethyltoluene selective system,
with adequate selectivities for the commercial use of the
separation of the present invention.
.
~ .
~; ~
2~2~
EXAMPLE 6
The previously described pulse test was also used to
obtain data similar to that of Example 5, but using a
desorbent other than exemplified above. In this case, the
feed was 2 ml of a solution containing 1 ml of the same
DET isomer mixture used in Example 1, 0.3 ml n-octane
tracer, and 1 ml of desorbent. The desorbent was p-
cymene. The column temperature was 145~C, flow rate up
the column was 1.14 ml per min. The results of the pulse
test are shown in Figure 7 and Table 6 below.
TABLE 6
15Component GRV NRV BETA(B)
(ml) (ml)
n-octane 38.9 0.0 tracer
3,5-DET 51.3 12.4 reference
2,4-DET 43.2 4.2 2.93
2,3-DET 49.0 10.1 1.23
2,6-DET 48.8 9.8 1.26
2,5-DET 43.9 4.9 2.51
EXAMPLE 7
Another pulse test was run using a 2 ml feed pulse of
a solution containing 1.3 ml of the same DET isomer
mixture of Example 1 and 0.7 ml of tracer, n-decane.
After the feed pulse, the desorbent flow, which in this
case was m-diethylbenzene (m-DEB), was resumed. Column
flow was 1.3 ml per minute and the temperature was 200~C.
Again, 3,5-DET was selectively adsorbed on the zeolite and
desorbed with desorbent as shown in the following Table 7.
2 ~ 2 0 b Q t~
27
TABLE 7
Component GRV NRV BETA B
(ml) (ml)
n-C10 38.5 0.0 tracer
3,5-DET 67.9 29.3 reference
2,4-DET 49.2 10.7 2.75
2,3-DET 64.1 26.5 1.15
10 2,6-DET 61.3 22.7 1.29
2,5-DET 52.1 13.5 2.17
