Note: Descriptions are shown in the official language in which they were submitted.
Background of` the Invention
Field of the Invention
This invention relates to a method for 'he separation
of valuable components from a mixture of aromatic compounds and
more particularly to a novel process for recovering substantially
pure meta-xylene and ortho-xylene from a mixture ^ontaining
these components together with ethyl benzene and ?ara-xylene.
., ' ' ~.
1059928
Description of the Prior Art
Aromatic compounds and particular'y para-xylene, meta-
xylene, ortho-xylene and ethylbenzene are well known as very
useful materials in the chemical industry but are generally found
only in admixture with each other. For example, they are found
in substantial quantities in coke oven light oil and certain
virgin and reformed petroleum naphthas. Over the years many
processes have been attempting to obtain a satisfactory separation
of the several components and recover the desired components
but none of these processes has been entirely successful. Here-
_ tofore, the practice of separating these isomers has been to
use che~ical methods or to effect distillation between the isomers.
Distillation, however, is difficult because of the very close
boiling points of the components. In addition, various methods
have been devised utilizing one or more of the steps of crystal-
lization, distillation and adsorption but in general, none of
these prior processes have been able to provide a procedure for
the substantially complete isolation of all the components in
i high purity. While a number of the processes are suitable to
provide the para-xylene component in good recovery they have not
been able to provide the meta-xylene and ortho-xylene in a form
free from the para xylene and ethylbenzene.
The process of the present invention provides a unique
procedure which overcomes the disadvantages of the prior art and
provides a method for the rapid separation of the valuable compon-
ents contained in the Cg+ aromatic mixtures.
1059928
It ls accordingly one ob~ect of the present invention
to provlde a process for the separatlon of a C8~ aromatics
mlxture which contains xylene isomers and ethylbenzene
which overcomes or otherwise mitigates the problems of the
prior art.
SUMMARY OF THE INVENTION
According to this invention, a novel method is
provided for the separation and recovery of aromatic
isomers contained ln an aromatic mixture comprising
para-xylene, meta-xylene, ortho-xylene and ethylbenzene
to separate this mixture into one stream comprislng meta-
xylene-and ortho-xylene and a second stream comprising
para-xylene and ethylbenzene. The mixture is contacted
with a ZSM-5 zeolite adsorbent whereby para-xylene and
ethylbenzene are adsorbed and meta-xylene~jand ortho-xylene
are not adsorbed. The novel procedure comprises contacting
said mixture with sald ZSM-5 zeolite adsorbent maintained -
in at least two separate reactors disposed in parallel
relationship whereby when adsorption is complete in one
reactor and the ortho-xylene and meta-xylene removed,
desorption is started while simultaneously beginning
adsorption in the second reactor and desorbing the second
reactor after adsorption while simultaneously beginning
adsorption in the first reactor, recovering the para-
xylene and ethylbenzene from the desorption steps and the
meta-xylene and ortho-xylene from the adsorption steps.
1059928
Brief Description of the Drawing
Reference now made to the drawing aocompanying this
application in which there are illustrated schematic diagrams
of processes for practicing the invention, and in which like
reference numerals represent like parts, and wherein Figure 1
is a schematic diagram of one adsorption/desorption procedure
for the basic separation process; and Figure 2 represents a
schematic diagram of the basic separation process included in
an integrated continuous process for the recovery of the para-
xylene, ortho-xylene, meta-xylene and ethylbenzene.
- Description of Preferred Embodiments
The process of the present invention is concerned
with a new procedure for treatment of C8 and higher carbon-
containing aromatic mixtures for the recovery of the valuable
components contained therein. More particularly, this process
is concerned with obtaining a rapid separation and recovery of
meta-xylene, ortho-xylene, para-xylene and ethylb~nzene when
contained in a mixture thereof. Generally, mixture of this
type as obtained from most sources will contain these components
in the following concentrations.
COMPONENTS AMOUNTS
Para-xylene 15-40 wt. %
Ethylbenzene 0-15 wt. %
~ Ortho-xylene 0-25 wt. %
2~ Meta-xylene 40-60 wt. %
_ 4 --
105~928
This mixture will also generally contain other C8 and
Cg and higher paraffinic materials which are mostly aromatic in
nature and must also be separated from the above components,
although many procedures have been tried, separation of these
components by methods such as distlllation with fractionation are
unsatisfactory because the boiling points of the components are
nearly the same.
According to the process of this invention, a unique
method is provided for conducting the separation of the components
1 10 contained in a typical aromatic feed stock whi-ch serves to over-
come at least one of the primary obstacles preventing commercial-
ization of a process of the type described hereinabove.
AS pointed out previously, while the use of the ZSM-5
materials may be used to effectively obtain a good separation
between the close-boiling para-, meta-, and ortho-xylenes and
ehtylbenzene, the slowness and thus, inefficiency of the chroma-
tographic column used has been a ma~or problem. In the present
invention it is proposed to overcome this problem by adsorption
followed immediately by desorption which has been found to sub-
stantially speed up the process. One embodiment of the inventioninvolves the use of two or more columns operated in a parallel
manner so that when adsorption is being conducted in one column,
desorption can be conducted in a parallel column under such con-
ditions as to ob~ain a continuously operating process with faster
results than with use of a single column alone. Accordingly, the
basic process of this invention comprises a method for contacting
an aromatlc mixture containing para-xylene, ethylbenzene, ortho-
xylene and meta-xylene in at least one chromatographic column to
effect a separatlon thereo~, and in which system, two or more
10599;Z8
columns are preferably operated in parallel relationship.
Briefly, in this process, the aromatics mixture is
contacted with a zeolite which serves to adsorb the para-xylene and
ethylbenzene while the meta-xylene and ortho-xylene pass through
the column rather uninhibited. Immediately, on removal of the
ma~or amount-of ortho-xylene and meta-xylene, this mixture is sent
to further processing to effect separation thereof as by distil-
lation to provide excellent recovery of these components. In the
meantime, the column containing the adsorbed para-xylene and ethyl-
benzene is desorbed by methods described hereinafter for prompt
_ removal of these components from the column and this mixture is
then tr~nsported to means for desorbent recovery and recovery and
separation of the ethylbenzene and para-x~rlene as by crystallization
and distillation. Thus rapid adsorption/desorption is achieved.
It has been found that conducti~g a process of this type
-in combination with a second identical and parallel column provides
many advantages in a system designed to ultimately recover- all the
valuable components. In this system the two columns are maintained
; in parallel relationship and the feed is introduced into one column
at a time by use of, for example, a three-way valve mechanism which
will be more fully described in the drawings accompanying the appli-
cation. In the system disclosed herein, the feed is introduced into
one column wherein the adsorption procedure outlined above is
effected and for maximum efficiency, when the meta-xylene and
ortho-xylene have passed through the column, desorption is begun
immediately and the feed into the system is diverted to the
parallel column.
-- 6 --
~059928
Thus, while desorption is occurring in one column, adsorption
is taking place in the second column. At the end of the cycle
in each column the systems are then reversed so that a continuous
adsorption/desorption can be carried out in the parallel columns
by the use of the valve mechanisms attached thereto.
This system is illustrated in its simplest embodiment
` for example in Figure 1 wherein two columns I and II are shown
disposed in parallel relationship to effect the adsorption/
desorption technique which comprises the basic process of the
invention. As shown in Figure 1, the aromatic-feed enters through
line 1 into the three-way^valve 2. To begin the separation process
the valve is manipulated so that the feed passes into line 3 and
thus into column 5 which-contains the zeolite adsorption material
and sufficient time is allowed for adsorption to occur in the
column. In Figure 1, it will be seen that the components pass
u? through the column and the unadsorbed materials comprising
the ma~or amount of ortho-xylene and meta-xylene are passed
out via line 6 to further separation procedures. 'As soon as
; the ortho-xylene and meta-xylene are substantially removed
through line 6, desorption is started with the introduction of
the desorbent from line 7 through valve 8 with introduction into
the column by line 9. As soon as desorption is started in column
I or simultaneously therewith, the feed coming through valve 2
is diverted to line 4 so that adsorption can begin in column 12.
Thus, at this point adsorption is taking place in column II and
desorption is occurring in column I.
- - 1059928
The adsorption is conducked in column 12 as in column
5 with the effluent taken off at line 11 and passed to line 6
for further separation as by distillation. The adsorption is
conducted over a zeolite adsorbent as in column 5 and as described
in more detail hereinafter.
In operating the system with the two columns, optimum
' efficiency would be obtained by adjustment of feed rates and other
conditlons such that as feed is introduced into one column to
begin adsorption, desorption can begin in the second column.
Conversely, when adsorption is completed in the first column and
desorption in the second eolumn, the feed streams can be reversed
to obtain desorption in the first column and adsorption in the
second column. If the feed streams are accurately ad~usted, a
continuous adsorption/desorption operation can be carried out
to achieve continuous separation of ~he feed stream.
~After desorption occurs in either of columns I or II
the éffluent from these desorptions which includes the desorbent
as well as para-xylene, ethylbenzene and perhaps minor amounts
of ortho-xylene and meta-xylene, is taken from column I by line
13 and column II by line 13' into line 14 and passed to desorbent
recovery station 16. At this station the desorbent is recovered
by conventional means and removed from the system by line 16 for
recycle if desired. Then the ethylbenzene, para-xylene mixture
is removed by line 18 for separation and/or recovery by any of
various procedures such as crystallization and distillation.
From the above described techniques for use of the
parallel columns and effecting the separations, it is to be
1~599Z8
appreciated that a prompt and efficient separatlon between the
two most difficult to separate component mixtures is achieved.
Moreover, this separation is effected in an efficient manner for
maximum recovery of all the components contained in this mixture.
It is to be appreciated, of course, that more than one set of
parallel separatory columns can be used and this invention is
considered to include such multiple parallel columns.
This basic separation process is shown in Figure 2
when integrated into one type of a complete and continuous system
for recovery of all the components contained in an arornatlc
_ mixture so that maximum recovery of all desirable components is obta-ined.
Referring now to Figure 2 in detail where like compo-
nents contain the same reference numerals as in Figure l, it will be
seen that the feed enters the system thro~gh line l directly or
may be combined with a later`recycle from column 29 and is
introuduced into columns I and II as described hereinabove-for
Figure l. Columns I and II are operated as in Figure l, that i~,
; by the parallel adsorption/desorption procedures so that ultimately
there is recovered from line 6 a mixture containing most of the
ortho-xylene and meta-xylene in the original feed. This feed
stream is passed to a xylene-splitter column where the meta-xylene
and the ortho-xylene are separated by distillation with most of
the meta-xylene being removed through line l9. The resulting
bottoms, comprising ortho-xylene and any other C8 and Cg aromatics,
are taken through line 20 to column 21 for further distillation.
_ 9 _
105992~3 :
In this column heavier boiling Cg+ components are removed through
line 23 for discard. The distillate comprising prlmarily ortho-
xylene with perhaps some meta-xylene is taken from line 22 and
passed to isomerization station 27. At this station any type of
isomerization reaction may be conducted but it is highly preferable
to conduct a low temperature isomerization reaction with toluene
dilution, as more fully described hereinafter to form additional
amounts of the xylenes which are taken off through line 28,
recycled and introduced into feed line 1 for additional conversion
and recovery in accordance with the process. ~
In the meantime, the para-xylene/ethylbenzene mixture
removed~from columns I and II with the desorbent in line 14, is
sent to a desorbent recovery station where the desorbent is re-
moved conventionally via line 17. The remaining mixture in line
18 is forwarded for further processing for the separation of the
para-xylene/ethylbenzene. Conventionally a good separation
between these two components at the para-xylene recovery station
24 is by a technique such as crystallization which is, of course,
well-known to the art and is carried out so that the para-xylene
in substantially pure form is recovered through line 25. ~he
resulting product comprising primarily ethylbenzene is recycled
by line 26 for mixing with the feed in line 1 and introduced into
the system. In an alternative procedure the feed in line l
and the recycled mixture in line 26 are distilled in column 29
to recover at least a portion of the ethylbenzene from line 30 and
the resulting mixture of xylenes fed by line l to the system.
-- 10- --
1059928
It will be seen from a study of the reaction systems of Figure 2
that a completely integrated and continuous process is provided
for the recovery of all the v~luable components contained in the
mlxture. Moreover, because of the use of the parallel columns to
effect the adsorptionidesorption procedures in the initial step
a highly efficlent process is provided.
In the above system of Figure 2 the various distillations,
isomerizations and crystallizations may be conducted by means
that are well-known to the art or as described herein. Since these
are well-known in the art, no necessity is se~n for the purposes
of this disclosure to pro~ide further details of such known
processes except to point out that the essential novelty herein
resides in the adsorption/desorption technique of the initial step
and its combination with the other steps in an integrated and cyclic
process.
It is reiterated that a basic novelty of this invention
resides in the use of the parallel columns with simultaneous
adsorption and desorption. Exemplified herein is the basic process
of Figure 1 wherein two streams are recovered, one stream comprising
ethylbenzene and para-xylene and the other stream comprising
essentially the meta-xylene and ortho-xylene. After this initial
separation is achieved various procedures may be utilized for
operating the process in a continuous manner with many variations
available for the recovery of any one of the components in greater
excess. Figure 2 as described herein provides a process which is
particularly valuable for the production of para-xylene, meta-xylene
and ethylbenzene. On the other hand, the process may be incor-
por2ted into a system wherein the predominate prodùct desired is
lOS9928
,
meta-xylene or the predominate product desired is ortho-
xylene.
As pointed out above, the adsorption and desorption
procedures conducted herein represent the basic novelty of
the present invention. In the adsorption process, the
feed is introduced into the column or othe~ vessel containing
-, the zeolite adsorbent at a temperature preferably
about 50-500F. and more-preferably about 100-400~.
The feed is passed through a vessel such as a column con-
taining the adsorbent or over a porous bed of the same
_ in a conventional manner and in either the liquid or gas
phase. -`As the feed passes over the adsorbent, the para-
xylene and ethylbenzene are adsorbed within the pores of
the zeolite whereas the meta-xylene and ortho-xylene pass
through the vessel or over the bed withou~`being adsorbed
to any substantial degree.
After the meta-xylene and ortho-xylene have left the
reactor, the para-xylene and ethylbenzene are then desorbed
from the adsorbent. The desorption may be carried out, for
example by heating the adsorbent, reducing the partial pressure
of the sorbed material in the vapor surrounding the adsorbent,
lowering the total pressure of the system or purging ~ith a
suitable inert desorbent gas such as steam, he'ium, nitrogen,
aromatic hydrocarbons (e.g. toluene or benzene) or other
organic or inorganic compounds. As a result of these de-
sorption techniques, the paraxylene and ethylbenzene are eluted
in this order in the vapor operation and in reverse order'in
the li~uid phase operation. The desorption can be conducted
in either the li~1uid or vapor phase or alternatively may
be conducted by reduced pressure and/or increased temperature
- - 12 -
..
- 1059928
.
in the absence of a desorbent material. If a desorbent is
used the resul~ing mixture o~ para-xylene and ethylbenzene
. .
and desorbent is then passed to a conventional system for
desorbent recovery and the desorbent may then be reused in
,' the system.
In the description of Figure 2, an isiomerization
step is conducted to convert at least a portion of the mixture
to para-xylene, a preferred product. The isomerization step
may be conducted in any desired manner for conducting such
isomerization as known in the art, but is preferably con-
ducted under relatively low temperature with tolene dilution.
It is highly preferred that this isomerization step be conducted
as a low temperature isomerization with tolene dilution
wherein tolene diluent is added to the systems. This type of
isomerization is called LTI herein. ,While LTI is the
nreferred,manner of conducting the isomerization, it is to be
understood that any of the well-known isomerization techniques
can be used in this step so long as ethylbenzene is not
produced.
When using the low temperature isomerization stage
with tolene dilution it may be carried out in any desired
manner but is preferably conducted employing about 5 to 30%
by'weight, preferably 10 to 20% by weight of added tolene,
based on the amount of material charged to the isomerization
stage, as a diluent to increase selectively in the isomeri-
zation of the meta-xylene and ortho-xylene and the formation of,
para-xylene. This isomerization reaction may be carried out
over any desired catalyst but is preferably carrièd out in
the presence of a crystalline alu,minosilicate catalyst which
,has a pore size of greater than 5 Angstrom units such as
-- 3
.
10599Z8
zeolites, X, Y, mordenite, and ZSM-4. Because members of
the family of zeolites designated as ZSM-4 possess extraordinary
selectivity, such materials are especially preferred.
The low temperature isomerization may be carried
out at temperatures between about 250F. and 1000F. and at
pressures ranging from ambient pressures or less up to about
2000 psig. In general, the isomerizatlon reaction is
` preferably carrled out at temperatures ranging from about
~50F. to 650F. Within these limits the conditions of
temperature and pressure may vary considerably depending upon
equilibrium considerations and reaction
- 14 -
-
lOS~39Z8
conditions. Quite obvlously optimum conditions are those in whichmaximum y~elds of desired isomer products are obtained and hence
considerations of temperature and pressure may vary within a
range of conversion levels designed to provide the highest
selectivity and maximum yield. However, in a preferred operation
using the ZSM-4 catalyst, it has been found that controlled
isomerizations can be effectively achieved at temperatures below
about 600F and a llquid phase operation usin~ sufflcient
pressure to maintain the material in a liquid phase. The liquid
- 10 phase operation is especially advantageous since high levels of
activity and selectivity can be maintained for an extended period
of time.
The isomerization reaction can be carried out over a
wide range of licuid hourly space velocities (LHSV) within the
`i i5 ~ range of 0.05 to 40. Good selectivity is-obtained within these
limits.
As pointed out above, the initial separation is
carried out in a chromatographic manner utilizing an adsorbent
which will adsorb only the para-xylene and ethylbenzene but not
the other materials of the mixture. The preferred materials to
effect these separations are certain crystalline aluminosilicate
zeolite molecular sieves which have the desired properties. Pre-
ferred zeolites are the ZSM-5 zeolites described below.
More preferred are ZSM-5 zeolites which have been
reacted with certain silanes as described hereinafter.
1059928
. .
The temperature at which the separations are carried
out is also lmportant; thus, temperatures ranging ~rom about
100C. to about 250C. should be used. It should be noted
that a wider temperature range can be employed but because of
the possibllity of catalytic conversion in the zeolite-containlng
column, 250C appears to be a suitable upper llmit. A more
preferred temperature range is between about 100C to 200C.
Generally, these zeolltic materials allow selective
separations to be achieved depending on either the size, shape
or polarity of the sorbate molecules. This class of novel
crystalline aluminosilicates can generally be stated to have
intermediate shape-selective sorption properties. The unique
nature,of this novel class of zeolites is characterized by the
presence of uniform pore openings which are apparently elliptical
,' rather than circula~r in nature. The effective pore openlngs of
this unique class of zeolites have both a ma~or and a minor axes,
and it is for this reason that the unusual and novel molecular
sieving effect~-are achleved. The unique type of molecular
sieving produced has generally been referred to as a "keyhole"
molecular sieving action. From their dynamic molecular sieving
properties it would appear that the ma~or and minor axes of the
elliptical pore in this family of zeolites have effective sizes
o . O
~ of about 7.0 + 0.7A and 5.0 + 0.5A, respectively.
,
' 16 -
1059928
.
This general family of zeolites are described as ZSM-5
type compositions. In general, they have the characteristic ~-ray
diffraction pattern set forth in Table I hereinbelow. ZSM-5
compositions can al80 be identified, in terms of mole ratios of
oxides, as follows:
0.9 + 0.2 M20 : W203 : 5-100 Y2 Z H20
wherein M is a cation, n is the ~alence of said cation, W is
selected from the group consisting of aluminum and gallium, Y is
selected from the group consisting of silicon and germanium, and
Z is from 0 to 40. In a more preferred synthesized form, the
zeolite has a formula, in terms of mole ratios of oxides, as
follows:
0.9 + 0.2 M20 : A1203 : 5-100 SiO2 : z H20
n
. and M is selected from the group consisting-uf a mixture of
- 15 alkali metal cations, especially sodium, and tetraalkylammonium
cations, the a-lkyl groups of which preferably ~ontain 2-5 carbon
atoms.
; In a preferred embodiment of ZSM-5, W is aluminum, Y
ls silicon and the silica/alumina mole ratio is at least 10 and
; 20 ranges up to about ~0.
Members of the family of ZSM-5 zeolites possess a
definite distinguishing crystalline structure whose X-ray diffrac-
tion pattern shows the significant lines set forth in Table I
following: -
1059928
. .
TABLE I
Interplanar Spacing d(A) Relative Intensity
11.1 + 0.2 S
10.0 + 0.2 S
7.4 + 0.15 W
7.1 + 0~15 W
6.3 + 0.1 W
6.04 + 0.1 W
5.97 + 0.1 W
5.56 + 0.1 W
5.01 + 0.1 W
4.60 + 0.08 W
~ 4.25 + o.o8 W
3.85 + 0.07 VS
3.71 +~0.05 . --S
-- 3.64 + 0.05 M
3.04 + 0.03 W
2.g9 + 0.02 W
~ 2.94 + 0.02 W
m ese values as well as all other X-ray data were determined by
standard techniques. The radiation was the K-alpha doublet of
copper, and a scintillation counter spectrometer with a strip
~ .
chart pen recorder was used. The peak heights, I, and the
positions as a function o~ 2 times~theta, where theta is the
Bragg angle, were read from the spectrometer chart. From the-se,
the relative intensitles, 100 I/I, where I is the intensity of
- 18 -
1059928
the strongest line or peak, and d (obs.), the interplanar spacing
in A, corresponding to the recorded lines, were calculated. In
Table I the relatlve intensities are given in terms of the
symbols S = strong, M = medium, W = weak and VS = very strong.
It should be understood that this X-ray diffraction pattern is
characteristic of all the species of ZSM-5 compositions. Ion
, exchange of the sodium ion with other cations reveals substantially
the same pattern with some minor shifts in interplanar spacing
and variation in relative intensity. Other minor ~ariations can
occur depending on the silicon to aluminum ratio of the particular
sample, as well as if it had been sub~ected to thermal treatment.
Various cation exchanged forms of ZSM-5 have ~een prepared. X-
ray powd~r diffraction patterns o~ several of these forms are set
forth below in Table II. The ZSM-5 forms set forth below are all
aluminosilicates.
TABLE II
~ X-ray Diffraction
ZS~-5 Powder in Cation Exchanged Forms
d SDacin~s Observed
.
As
Made HCL NaCL CaC12 REC13 AgNO3
11.15 11.16 - 11.19 11.19 11.19 11.19
10.01 10.03 10.05 10.01 10.06 10.01
9.74 9.78 9.80 9.74 9.79 9.77
-- -- 9.01 9.02 -- 8.99
8.o6 -- -- -- __ __
7.44 7.46 7.46 7.46 7.40 7.46
7.08 7.07 7.09 7.11 -- 7.09
6.70 6.72 6.73 6.70 6.73 6.73
6.36 6.38 6.38 6.37 6.39 6.37
5.99 6.00 6.01- 5.99 6.02 6.01
- 5.70 5.71 5.73 5.70 5.72 5.72
5.56 5.58 ~ 5.58 5.57 5.59 -5.58
5.37 -- 5.38 5.37 5.38 5.37
-- 19 --
~ ~c
: . ... . . . ... . .
lOS99Z8
. .
TABLE II ( cont . )
As
Made HCl NaCl CaC12 REC13 AgN03
5.13 5.11 5.14 5.12 5.14 __
4.99 5.01 5.D1 5.01 5.01 5.01
- - _ - 4 74 __ __ __
4.61 4.62 4 62 4.61 4.63 4.62
-- -- 4.46 4.46 -- 4.46
4.36 4.37 4.37 4.36 4.37 4.37
4.~'26 4.27 4.27 4.26 4.27 4.27
4.08 -- 4.09 4.09 4.09 4.09
4.00 4.01 4.01 4.00 4.01 4.01
3.84 3.85 3.85 3.85 3.86 3.86
3.82 3.82 3.82 3.82 3.83 3.82
3.75 3.75 3.75 3.76 3.76 3.75
3.72 3.72 3.72 3.72 3.72 3.72
3.64 3.65 3.65 3.65 3.65 3.65
__ 3.60 3.60 3.60 3.61 3.60
3.48 3.49 3.49 3.48 3.49 3.49
3.44 3.45 3.45 3.44 3.45 3.45
3.34 3~5 3.36 3.35 3.35 3.35
-3.31- 3.31 3.32 3.31 3.32 3.32
3.25 3.25 3.26 3.25 3.25 3.26
3.17 -_ __ 3.17 3.18 __
3.13 3.14 3.14 3.14 3.15 3.14
3.05 3.05 - 3.o5 3.04 3.06 3.05
~2.98 2.98 2.99 2.98 2.99 2.99
__ __ __ - - 2.97 - -
__ 2.95 2.95 2.94 2.95 2.95
2.86 2.8I 2.87 2.87 2.87 2.87
2.80 - - - - - - - - - - -
2.78 __- __ 2.78 -- 2.78
2.73 2.74 2.74 2.73 2.74 2.74
2.67 - - - - 2.68 - - - -
2.66 - - - - 2.65 - - - -
2.60 2.61 2.61 2.61 2.61 2.61
__ 2.59 2.59 - - - -
2.57 -- 2.57 2.56 -- 2.57
2.50 2.52 - 2.52 2.52 2.52 --
2.49 2.49 2.49 2.49 2.49 2.49
4 - - 2.45
2.41 2.42 2.42 2.42 2.42 --
2.39 2.40 2.40-~ 2.39 2.40 2.40
__ __ - - -2.38 2.35 2.38
__ 2.33 ~~ 2.33 2.32 2.33
- - 2.30 - - __ __ _
- - 2.24 2.23 2.23
-- 2.20 2.21- 2.20 2.20 --
- - 2.18 ~ 2.18 - - - - - -
2.17 2.17 - - - -
_ 20 -
1OS9~2 8
TABLE II (cont.)
As
Made HCl NaCl CaC12 REC13 AgN03
- - 2.13 - - 2.13 - - - -
- - 2.11 2.11 - - 2.11 - -
- - - - - - 2.10 2.10 - -
-- 2. o8 2. o8 -- 2. o8 2. o8
__ _ 2.07 2.07 - - - -
_ __ 2.04
.01 2.01 2.01 2.01 2.01 2.
1.99 2.00 1.99 1.99 1.99 1.99
- - - - - - 1.97 1.96 - -
.95 1.95 1.95 1.95 1.95 --
__ _ __ -- _ 1.94 - -
-- 1.92 1.92 1.92 1.92 1.92
1 9l - - - - - - 1.9l - -
- - 1.88
.87 1.87 1.87 1.87 1.87 1.87
- - 1.86 - - ~
1.84 1.84 -- -- 1.84 1.84
1.83 1.83 1.83 1.83 1.83 _
.82 - - 1.81 - - 1.82 - -
1.77 1.77 1.79 1.78 -- 1.77
- 1.76 1.76 1.76 1.76 1.76 1.76
1.75 1.75
_ 1.74 1.74 1.73 _
.71 1.72 1.72 - 1.71 -~ -- 1.70
1.67 1.67 1.67 -- 1.67 1.67
- 1.66 1.66 -- 1.66 1.66 1.66
_ _ 1.65 1.65 - - - _
- - - - 1.64 1.64 - - _
-- 1.6~ 1.63 1.63 1.63 1.62
-- 1.61 1.61 1.61 -- 1.6
.58 - - __ __ _
_ 1.57 1.57 -~ 1.57 1.57
-- -- 1.56 1.56 1.56 --
Zeolite ZSM-5 can be suitably prepared by preparing a
solution containing tetrapropyl ammonium hydroxide, sodium oxide,
- an oxide of aluminum or gallium, an oxide of silica or germanium,
and-water and having a composition, in terms of mole ratios of
40 oxides, ~alling within the following ranges:
- 21 -
.
~059928
TABLE III
Particular1y
~road Preferred Preferred
OH/SiO 0.07-1.0 0.1-0.8 0.2-0.75
R4N~/(R4N + +Na~) 0.2-0.95 0.3-0.9 -4-0-9
5H2O/OH 10-300 10-300 10-300
~ Y2/W23 5-100 10-60 10-40
`~ - wherein R is propyl, W is aluminum or gallium and Y is sillcon
or germanium, maintaining the mixture until crystals of the
zeolite are formed. Thereafter, the crystals are separated from
the liquid and recovered. Typical reaction conditions consist
- of heating the foregoing reaction mixture to a temperature of
from about 90C. to 200C. for a period of time of from about six
hours to 60 days. A more preferred temperature range is from
about 100 to 175C. wlth the amount of time at a temperature in
such range being from about 12 hours to ~ days.
~ The digestion of the gel particles is carried out until
crystals form. The solid product is separated from the reaction
; medium, as by cooling the whole to room temperature, filtering,
and water washing.
The foregoing product is dried, e.g. at 230F., for
from about 8 to 2~ hours. Of course, milder conditions may be
employed if desired, e.g., room temperature under ~acuum.
~SM-5 is preferably formed as` an aluminosilicate.
The composition can be prepared utilizing materials which supply
the appropriate oxide. Such compositions include for an alumino-
silicate, sodium aluminate, alumina, sodium silicate, silica
- 22 -
10599Z8
hydrosol, silica gel, silicic acid, sodium hydroxide and tetra-
propylammonium hydroxide. It will be understood that each oxide
component utilized in the reaction mixture for preparing a member
of the ZSM-5 family can be supplled by one or more initial
reactants and they can be mixed together in any order. For
; example, soaium oxide can be supplied by an aqueous solution of
sodium hydroxide, or by an aqueous solutlon of sodium silicate;
tetrapropylammonium cation can be supplied by the bromlde salt.
The reaction mixture can be prepared either batchwise or con-
t~nuously. Crystal size and crystallization tlme of the ZSM-5
composition will vary with the nature of the reaction mixture
employed. The family of ZSM-5 zeolites is disclosed and clalmed
in U.S. Patent No. 3,702,886.
The zeolites used in the instant invention can have the
original cations associated therewith replaced by a wide variety
of other cations according to techniques well-known in the art.
Typical replacing cations would include hydrogen, ammonium and
metal cations ~ncluding mixtures of the same.
Typical ion exchange techniques would be to contact
the particular zeolite with a salt o~ the desired replacing
cation or catlons. Although a wide variety of salts can be
; employed, particular preference is given to chlorides, nitrates
. and sulfates.
. - .
1059928
.
Representative ion exchange techniques are disclosed in
a wide variety o~ patents including United States 3,140,249,
- United States 3,140,251 and United States 3~140,253.
Following contact with the salt solution of the desired
replaclng catlon, the zeolites are then preferably washed with
water and dried at a temperature ranging ~rom 150F. to about
- 600F. and thereafter calcined in air or other inert gas at tem-peratures ranging from about 500F. to 1500~. for periods o~ time
ranging from 1 to 48 hours or more.
Prior to use, the zeolites should be dehydrated at
least partially. This can be done by heating to a temperature
in the range of 200 to 600C. in an atmosphere, such as air,
nitrogen, etc. and at atmospheric or subatmospheric pressures for
between 1 and 48 hours. Dehydration can also be performed at
- lower temperatures merely by using a vacù~m,-but a longer time 1s
required to obtain a sufficient amount of dehydration.
In practicing the aprocess, it ma~ b~ desired to
....
incorporate the zeollte with another material resistant to the
temperatures and other conditions employed in the separation
processes. Such matrix materials include synthetic or naturally
occurring substances as well as inorganic materials such as
clay, silica and/or metal oxides. The latter may be elther
naturally occurring or in the form of gelatinous precipitates
or gels including mixtures of silica and metal oxides.
Naturally occurring clays which can be composited
- with the zeolites~include the montmorillonite and kaolin
family, which families include the sub-bentonites, and the
- 24 -
..
- 105~Z8
kao'ins commonly known as Dixie McNamee-Georgia and Florida
cla-.s or others in which the main mineral constituent is halloy-
site, kaolinite, dickite, nacrite, or anauxite. Such clays can
be used in the raw state as originally mined or initially sub-
~ec~ed to calcination, acid treatment or chemical modlfication.
In addition to the foregoing materials, the ZSM-5 type
zeolites can be composited with a porous matrix material such as
sil~ca-alumina, sillca-magnesia, silica-zirconia, silica-thoria,
sil~ca-beryllia, sillca-titania as well as ternary compositions
such as silica-alumina-thoria, silica-alumina-zirconia, silica-
_ alu~ina-magnesia and sllica-magnesia-zirconia. The matrix can
be ~n the~form of a cogel. The relative proportions of finely
div~ded crystalline aluminosilicate ZSM-5 and inorganic oxide gel
mat~ix vary widely with the crystalllne aluminosilicate content
- 15 ran~ing from about 1 to about 99 p-ercent b-~ weight and more
usually, particularly when the composite is prepared in the form
of beads in the range of about 40 to about 90 percent by weight
of the composite.
Another embodiment of thls invention resides in sub-
~ecting the zeolite ZSM-5 type to a mild steam treatment carried
out at ele~ated temperatures of 800F. to 1500F. and preferably
at temperatures of about 1000F. to 1400F. The treatment may
be ~ccomplished in an atmosphere of 100 percent steam or in
atmosphere consisting of steam and a gas which is substantially
inert to the aluminosilicate. The steam treatment apparently
pro~ides beneficial properties in the aluminosilicate compositions
ar.d can be conducted before, after or in place of the calcination
treatment .
1059928
Even more highly preferred adsorbents are ZSM-5
zeolites which have been treated or contacted with a silane
co~pound as superior results are achieved using these products
as adsorbents. The organlc substituted silanes deemed useful in
5 5 the process of the present invention are those of the following
general formula:
. R
R~;i , R
Rl
wherein, in the above formula, R is an organic radical as de-
scrlbed hereinafter and each Rl is also an organic radical such
.,, ~
3 10 as those defined below for the group R, a hydrogen atom or a
halogen atom such as chlorlne or bromine. Organic radicals which
may be ~ or Rl include alkyl of 1 and more preferably up to about
40 carbon atoms, alkyl or aryl carboxylic acid acyl whereln the
organic portion of said acyl group contains about 1 to 30 carbon
atoms and said aryl group contains about 6 to 24 carbon atoms,
aryl groups-o1~ about 6 to 24 carbons, which may also be further
substituted, alkaryl and aralkyl groups contalning about 7 up to
about 30 carbon atoms. Highly preferred compounds falling within
the above structure are those wherein R is alkyl of about 12 to 24
~20 c2rbon atoms, i.e., the long chained alkyl groups, and each R
is hydrogen or chlorine. Highly preferred silanes are octa-
decyltrichlorosilane and dodecyltrichlorosilane. Organic silanes
o~ the type useful in the process of the present invention are
known in the art and may be prepared by known methods.
- 26 -
,.
~059928
For example, the tetrachloro substituted silane, SiC14, may be
prepared by the reaction of chlorine and silica and the resulting
product may then be reacted with the desired number of moles of
a metal salt of the organic compound containing the radical for
R or Rl desired, by heating. Other silanes employed in the
process of the present inventlon may be prepared by slmilar
procedures, all of which are well known in the art.
The desired silane is then contacted wlth a zeollte
of the type described hereinbefore, one requirement of the zeolite
belng that lt have an available hydrogen for reaction. The
_ silane should be selected so that steric hindrance problems are
avoided. Thus in the above formula, R and only two Rl should
be organlc radlcals which means that at least one Rl should be
hydrogen.
The selected silane and the crystalline alumlnoslllcate
- zeollte are contacted in the preferred procedure at an elevated
temperature. Preferably, the silane and zeollte ;are contacted on
a welght basls of about 1:5 to 5:1, preferably about 1:2 to 1:1,
respectively. It is also preferable that a blnder for the zeollte
be employed such as, for example, bentonite. For good contact
between the reactants~ it is also preferable to employ a reaction
medlum. Satlsfactory reaction media lnclude the ethers, aliphatlc
hydrocarbohs and halo-substituted aliphatic hydrocarbons of 5 to
about 8 carbon atoms, (e.g., n-heptalne), the aromatlc,
halo-substltuted aromatic hydrocarbons and nltrogen containlng
compounds such as heterocycllcs. A particularly pre~erred medla
ls pyrldine.
- 27 -
.
' -
- lOS99Z8
The following examples are presented to illustrate the
invention but it is not to be considered as limited thereto. In
the examples and throughout the specification parts are by weight
unless otherwise indicated.
EXAMPLES 1-4
~` Typical preparations of ZSM-5 type zeolites are shown
in these examples. Examples 1-3 show the preparation of the
hydrogen form ZSM-5 and they involve the use of tetrapropyl-
ammonium hydroxide (TPAOH) or bromide (TPABr). Example 4 shows
a typical preparation of the hydrogen ~orm ZSM-8 using tetraethyl-
ammonium hydroxide (TEAOH). Reaction conditions and results
are shown in Table V.
- 28 -
. , .. . ~ ... . . ~ . . . . . .
1059928
.
., . o~
O E-~ K
~1 0
0~0 ~ ~O ~CO
C~O ~ . . . I
Z 3 ~ 1 ~J L~O ~ ~ O~ O
.. ,~ o~ ~ 1 o ~1 o~ ~1 `' a~ u~
bO ~ bl~ 1 O
~0 0 0
,~ O O O
~7 ~r) o
C~
O
~ hm~10 Ooc~u~
td m ~ o . . . ~
æ 1 ~ 0 ~ .~ 0 ~ ~O o ~ o ~o ~ ~:
. a E~ z ~ O N ~ X ~ O ~1 O~ ~1 O~ Cq
R ~ Q ~ ~ O
o
O O''
. . - . - - O
O 3 IS~ ~D 3 N O
O
-,l cq
~ ~ S~
S
O ~D
U~ '
~`J N ~)1-~
. . I
~ m oa~ ~ 0 o~r o o O N Lr~ ~E
~U R 'C O~ ~ O ~I K ~1 0 N O
Ph ~ ~1~ rl o N
WO E~
. -' ' ~ ~ ~ ~
¢00 ~ C~
E-~~1 ~ .,
c~ ~ ~1
0 3
~ I , .
O N
N E-~
~1 0 ~ q:~
- ¢ ~ N ~ - O ~ O~
rl . . I
Z ~1 N O Ct) h L~ O ~ ~1:) 0 J O Lr~ 0 3
15~ ~ C~J ~ X ~ O r~
I ~I O N 1
~1 ~1
O O ~ Q~
tY~ N N S
~0 Cq
, . ~1
o
_~
O ~ O
~rl
1~ ^ ^ ff rl
o a~ ~ S o ~ o
o a~ o ~ 3 0 U~ ) ~ O
`' S C) ~ ~ ~ ~ ,
O . 0 a) X C) ~a ~ r-l ~1 ~ ~ O O N~d
rl Ei ~ ~ O O ~O h
~ Z ~: u~ X
s ~--
m ~, .
-
-- 29 - .
.. . .
-- ... y .~ .. ~ .. ~. ..
105992~3
EXAMPLE 5
In this example 30 parts of a ZSM-5 crystalline
aluminosilicate zeolite of the type prepared in Examples 1-3
comprising 80 parts ZSM-5 and 20 parts bentonite binder, were
refluxed with octadecyltrichlorosilane in a weight ratio of
1:1 in 200 cc normal-heptane solvent for a period of four hours.
- Thereafter the resulting solid product was recovered by decanta-
~ tion, the solid washed first with chloroform, t~en with normal-
pentane and then dried at a temperature of 125C. for four hours.
EXAMPLE 6
The aromatic mixture employed as the feedstock in
this example was 100 grams of a mixture containing 12 weight
percent ethylbenzene, 25 weight percent para-xylene, 45 weight
percent meta-xylene, 15 weight percent ortho-xylene and 3 weight
percent of Cg and higher aromatic paraffi~. Thls mixture was
initially heated to 350F. and ~hen passed through parallel
columns containing ZSM-5 zeolite as the adsorbent. The adsorbent
was of the type prepared in Examples 1-3. A stream of steam
passed over the mixture at 350F. served as the desorbent.
By use of the apparatus of Figure 1, two parallel
columns were operated. By us of the three-wa~ valves the ~eed
was first lntroduced into Column I at 350F. As the last of the
para-xylene and ortho-xylene left the column, steam desorbent gas
was_introduced. Simultaneously feed was started into Column II.
After three passes, rates o~ feed and carrier gas desorbent were
adjusted so that as adsorption was completed in each column,
desorption could be started and vice-versa.
- 30 -
--\
1059928
The components not adsorbed in the adsorption step,
mostly ortho- and meta-xylene were sent to a column and distilled.
The adsorbed material eluted with the desorbent was processed
to remove the desorbent and the residue, cooled to effect
5 crystallization and recovered the para-xylene.
- ~ EXAMPLES 7-13
These examples will illustrate a continuous cyclic
operat~on utilizing a single column containing ZSM-5.
In these examples a mixture of 80% by weight of ZSM-5
10 and 20% by weight of bentonite were sized -30 to +60 mesh and
placed in a column having an inside diameter of 0.875 inches and
a length of 35 inches. The total weight of sorbent in the
column was 259 grams of which 80% or 207 grams was ZSM-5.
In all cases, the conditions utilized were 300F. and
15 atmospheric pressure.
The procedure in all cases involved:
~ charging the C8 aromatic mixture at a rate of
224 cc/hr until 22cc of effluent was obtained,
(2) steam was then passed through the column at 224 cc/hr
20 until 9 cc of condensed hydrocarbons were obtained, --
(3) desorption was continued at a steam rate of 224 cc/hr
until 75 grams of water and C8 aromatics were obtained; and
(4) the bed was then purged with nitrogen to remove
adsorbed water and the cycle repeated.
The results obtained as well as other operating con-
ditions are set f~rth below wherein " effluent" represents the
product from step 1 supra; " displacement " the product from step 2
and " adsorbate~'' the product from step 3. The designationCEB
refers to impurities lighter than ethylben7ene.
- 31 -
1~599;~8
.
,, oooo oooo oooo oooo oooo oooo oooo
~d ..~. .... .... .... .... .... ....
oooo oooo oooo oooo oooo oooo oooo
o - oooo oooo oooo oooo oooo oooo oooo
O ~N O ~1 ~N O ~1~N ~ r-~~N r-l N ~N ~1 ~1 ~1 ~1 ~N O ~i
rn 3
~1 ~ ~ Ir~ O O Ir~ 0 3~1 IS~ U:~ ~ ~1 1~D ~D ~'`D ~ ~ ~ ~ ~ ~) t--~D
td O X
E ~ ~: 3~ ~ ~ ~D ~D ~J~ ~D ~aa ~D ~N
Cl ~
O
a:~ Q ~
O ~ ~ ~ O ~ Ir.O r--l ~1 Ir~N ~ V~ J~--1 ~1 ~1 15~ ~1 ~1 ~ ~ ~1 ~`J ~1 ~)O X .... .... ........ .... ~1 ~ ~ O O ~1 1r~ 0 0 a~ ~1 O O~ J ~ O ~ N ~1 O ~O ~ O ~3 ~1 O N
O ~I J ~/ ~r r-l J ~ J r ~ 3 ~I J ~I -1 3
~ _
O U~
~1 ~1 O O N N 3 N 03 N ~'`D3 ~1 15~3 3 N ~ 3 ~I t--~) 3 N ~3
J~ 1~ .... ........ .... .... .... ....
~1~ O O ~) /J~ O N OO~ O O ~~ O O 0 ~ O O ~ CJ~ O O ~1 ~ O O N
h ~ 3 J ~ ~1 ~ 5
~ .
¢ d CS~D ~0 ~O ~ O3 ~D ~ ~) 3 ~ ~ N ~D N ~ O ~ O
F:1 a~ ~IS\ O ~O N 3 O Ir~ ~IN O ~ JN O 1~\3 N O J r~l N O J ~ N O J tr~
cq Y ,1
cd
S
~ J~
S-~ ~11
O~1 O ,D 0 ~ r~ ~1 ~ Ir~ 5 IS~ J3 ~ ~ r~ ~ O ~ ~ O
cd ~0 ~ I . . .I . . . I . . .I . . . I . . . I . . . I . . .
~ ,i O I 1~ N ~ I ~D ~ N I ~O N NI ~O N N I ~O N N I ~D ~ N I ~ ~) N
O~ 5~
1~ ~1 0
S N ~D ~1 ~ ~O N 1~5N ~N ~O ~1 ~ ~ O ~O ~ O
~D ~D I I I I I I I -
o a) Q) a~
~rl ~ 3 0 F ~
E h :~ r I h ~ S ~i h :~--I h ::~ ~I h :~,~1 h ~ ~I h
) ~ r-l Q. O ~ ~I Q~ O ~ ~I Q, O ~ ~1 ~ O ~ ~I Q~ O ~a ~ P. o ~ ~ P, o
¢ ~ ~ ~ ~ ~ ~ ~ ¢ ~ ~ ~ ~ ~ ~ ~ ¢ ~ ~ ~ ~:
a~
0 ~ O ~I N ~)
. t~
X
-- 32 -- -
,.
lOSg928 . ,
As can be seen from the above results, the combined
ethylbenzene and p-xylene content of the effluent was less than
0.5 weight percent. The effluent can be very easily sub~ected
to conventional distillation to recover m-xylene and orthoxylene.
The fract$on labeled "displacement" contained less
than 1% ethylbenzene and could be fed to a low temperature xylene
isomerization unit.
The adsorbate contained only about 11 weight percent of
meta- and ortho-xylene combined so that p-xylene can easily be
recovered by conventional crystallization techniques with subse-
quent recovery of ethylbenzene by fractionation.
In describing the process of this invention, the word
~'~dsorbed" has been used in a relative sense. Thus in the
speclfication and claims, the terms " adsorbed'' and "not adsorbed "
should be underst~od to mean " preferenti~lly- adsorbedt' and
- " preferentially not adsorbed'' since such adsorptions in chromato-
graphic system~ such as thls do not always occ~r to the extent
of absolutely complete adsorption.
The invention has been described herein with reference
to certain preferred embodiments, however, as obvious variations
thereon will become apparent to those skilled in the art the
invention is not to be considered as limlted thereto.
. .
- 33 -
