U.S. patent application number 10/685633 was filed with the patent office on 2005-04-21 for method for improved production of cyclohexenyl and alkenyl aromatic compounds.
This patent application is currently assigned to Fina Technology, Inc.. Invention is credited to Butler, James R., Merrill, James.
Application Number | 20050085677 10/685633 |
Document ID | / |
Family ID | 34520646 |
Filed Date | 2005-04-21 |
United States Patent
Application |
20050085677 |
Kind Code |
A1 |
Butler, James R. ; et
al. |
April 21, 2005 |
Method for improved production of cyclohexenyl and alkenyl aromatic
compounds
Abstract
Disclosed is an improvement in a process of preparing
cyclohexenyl and alkenyl aromatic compounds, such as styrene, that
enables economical and convenient removal of nitrogen compounds.
The nitrogen compounds can be stabilizers or neutralizers or
derived from stabilizers or neutralizers added to prevent styrene
homopolymerization. The nitrogen compounds are removed from, in the
case of styrene production, the benzene fraction that results from
dehydrogenation of ethylbenzene. Because of the preferential
solubility of nitrogen compounds in water, a majority of such
compounds can be removed by intimately contacting the benzene
fraction with sufficient water, at an appropriate point in the
process, and then removing most or all of the water with the
entrained nitrogen compounds.
Inventors: |
Butler, James R.;
(Friendswood, TX) ; Merrill, James; (Katy,
TX) |
Correspondence
Address: |
FINA TECHNOLOGY INC
PO BOX 674412
HOUSTON
TX
77267-4412
US
|
Assignee: |
Fina Technology, Inc.
Houston
TX
|
Family ID: |
34520646 |
Appl. No.: |
10/685633 |
Filed: |
October 15, 2003 |
Current U.S.
Class: |
585/323 |
Current CPC
Class: |
C07C 15/46 20130101;
C07C 15/44 20130101; C07C 13/28 20130101; C07C 2601/16
20170501 |
Class at
Publication: |
585/323 |
International
Class: |
C07C 002/00 |
Claims
What is claimed is:
1. A process for preparing cyclohexenyl or alkenyl aromatic
compounds comprising alkylation of a cyclohexane or aromatic
compound; dehydrogenation of the alkylated cyclohexane or aromatic
compound to form a process stream including a cyclohexenyl or
alkenyl aromatic compound; and separating the process stream into a
cyclohexenyl or alkenyl aromatic compound rich fraction and a
cyclohexane or aromatic compound rich fraction, wherein the process
further comprises adding nitrogen-containing compounds at one point
in the process and using water to extract the nitrogen-containing
compounds or, break down products of the nitrogen-containing
compounds, from the cyclohexane or aromatic compound rich fraction
at another point in the process.
2. A process for preparing styrene comprising alkylating benzene to
form ethylbenzene, dehydrogenating ethylbenzene to form a process
stream containing styrene, unreacted ethylbenzene, benzene and
toluene products, separating the process streams into styrene,
benzene and toluene fractions, and recycling the benzene fraction
back into the process wherein the process further comprises adding
a nitrogen-containing compound at one point in the process and
using water to extract the nitrogen-containing compounds, or break
down products of the nitrogen-containing compounds, from the
benzene fraction at another point in the process.
3. The process of claim 2 wherein the nitrogen-containing
compounds, or break down products of the nitrogen-containing
compounds, are extracted by intimately contacting the benzene
fraction with water in an amount of from about 0.1 percent to about
10 percent by weight of benzene.
4. The process of claim 3 further comprising removing the water
containing nitrogen compounds, or break down products of the
nitrogen-containing compounds, from the benzene fraction such that
no more than about 900 ppm water remains, prior to or after mixing
the recycled benzene fraction with fresh benzene prior to
alkylation.
5. The process of claim 2 wherein the benzene fraction is contacted
with water in an amount of from about 0.5 percent to about 4
percent by weight of benzene.
6. The method of claim 2 wherein the water is introduced
immediately after separation of the benzene, styrene and toluene
fractions.
7. The method of claim 2 wherein the water is introduced into the
system as water entrained in feedstocks to the process.
8. The process of claim 6 wherein the water is removed as a liquid
via drying or distillation.
9. The process of claim 7 wherein the water is removed as a liquid
via drying or distillation.
10. The process of claim 2 wherein the water is introduced
concurrent with the mixing of fresh and recycled benzene and the
water is removed after alkylation in a drying column.
11. The process of claim 2 wherein the nitrogen-containing
compounds are stabilizers or neutralizers or break down products of
these compounds.
12. In a process for preparing cyclohexenyl or alkenyl aromatic
compounds, wherein the process includes an alkylation of a
cyclohexane or aromatic compound; a dehydrogenation of the
alkylated cyclohexane or aromatic compound to form a process
stream; and a separation of the process stream into a cyclohexenyl
or alkenyl aromatic compound rich component and a cyclohexane or
aromatic compound rich component; and the process also includes the
use of nitrogen-containing compounds, the improvement comprising
using water to extract the nitrogen-containing compounds from the
cyclohexane or aromatic compound rich component.
13. The process of claim 12 wherein the nitrogen-containing
compounds, or break down products of the nitrogen-containing
compounds, are extracted by intimately contacting the cyclohexane
or aromatic compound rich component with water in an amount of from
about 0.1 percent to about 10 percent by weight of the cyclohexane
or aromatic compound rich component.
14. The process of claim 13 wherein the cyclohexane or aromatic
compound rich component is contacted with water in an amount of
from about 0.5 percent to about 4 percent by weight of the
cyclohexane or aromatic compound rich component.
15. The process of claim 13 further comprising removing the water
containing nitrogen compounds, or break down products of the
nitrogen-containing compounds, from the benzene fraction such that
no more than about 900 ppm water remains, prior to or after mixing
the recycled benzene fraction with fresh benzene prior to
alkylation.
16. The process of claim 12 wherein the cyclohexenyl or alkenyl
aromatic compound is styrene.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] This invention relates to the preparation of cyclohexenyl
and alkenyl aromatic compounds. In particular, the invention
relates to the preparation of styrene.
[0003] 2. Background of the Art
[0004] Among the cyclohexenyl and alkenyl aromatic compounds
finding the most extensive use around the world is styrene. Styrene
is utilized widely in the plastics industry for the manufacture of
plastics, rubber-modified impact polystyrene,
acrylonitrile-butadiene-styrene terpolymer, styrene acrylonitrile
copolymer, styrene-butadiene type synthetic rubber, and a host of
other copolymers, terpolymers, and the like. While a wide variety
of methods of producing styrene are now known, one of the simplest
and most economical methods involves using a benzene feed which is
converted, via alkylation, to ethylbenzene and then, via continuous
dehydrogenation, to a process stream comprising styrene, toluene
and benzene products. The dehydrogenation may be done catalytically
in an adiabatic or isothermal reactor. Primary products are
styrene, unreacted ethylbenzene, and smaller amounts of toluene and
benzene. The process stream components are then separated via a
distillation columns, with the styrene and toluene being recovered
as products, and the benzene being recycled to begin the alkylation
phase again.
[0005] A problem that is encountered during this process is that
additives such as amines for neutralization of carbonic acid in
process water and inhibitors to decrease styrene polymerization are
added. Common stabilizers and neutralizers include amine compounds,
which effectively inhibit the styrene homopolymerization and
neutralize the carbonic acid but unfortunately byproducts are then
retained with the benzene fraction. Such nitrogen compounds are
undesirable in the benzene fraction because they tend to interfere
with the alkylation and/or hydrogenation catalysts when the benzene
is recycled in the process. Generally the nitrogen compounds
therefore require an additional filtration step of the benzene
through a clay or zeolitic bed to absorb them. This bed must be
appropriately maintained to ensure continued efficacy in removing
the nitrogen compounds.
SUMMARY OF THE INVENTION
[0006] In one aspect, the present invention is a process for
preparing cyclohexenyl or alkenyl aromatic compounds. The process
includes alkylation of a cyclohexane or aromatic compound;
dehydrogenation of the alkylated cyclohexane or aromatic compound
to form a process stream including a cyclohexenyl or alkenyl
aromatic compound; and separating the process stream into a
cyclohexenyl or alkenyl aromatic compound rich fraction and a
cyclohexane or aromatic compound rich fraction. The process also
includes adding nitrogen-containing compounds at one point in the
process and using water to extract the nitrogen-containing
compounds, or the break down products of the nitrogen-containing
compounds, from the cyclohexane or aromatic compound rich fraction
at another point in the process.
[0007] In another aspect, the present invention is a process for
preparing styrene. The process includes alkylating benzene to form
ethylbenzene, dehydrogenating ethylbenzene to form a process stream
containing styrene, unreacted ethylbenzene, benzene and toluene
products, separating the process streams into styrene, benzene and
toluene fractions, and recycling the benzene fraction back into the
process. The process also includes adding a nitrogen-containing
compound at one point in the process and using water to extract the
nitrogen-containing compounds, or the break down products of the
nitrogen-containing compounds, from the benzene fraction at another
point in the process.
[0008] In still another aspect, the present invention is, in a
process for preparing cyclohexenyl or alkenyl aromatic compounds,
wherein the process includes an alkylation of a cyclohexane or
aromatic compound; a dehydrogenation of the alkylated cyclohexane
or aromatic compound to form a process stream; and a separation of
the process stream into a cyclohexenyl or alkenyl aromatic compound
rich component and a cyclohexane or aromatic compound rich
component; and the process also includes the use of
nitrogen-containing compounds, an improvement of using water to
extract the nitrogen-containing compounds from the cyclohexane or
aromatic compound rich component.
DETAILED DESCRIPTION OF THE EMBODIMENTS
[0009] The present invention is useful in a process for preparing
cyclohexenyl and alkenyl aromatic compounds, such as styrene, that
include alkylation of benzene to form ethylbenzene, followed by
dehydrogenation of ethylbenzene to form a process stream containing
styrene, benzene and toluene products, which are then separated
into styrene, unreacted ethylbenzene, benzene and toluene
fractions, and the benzene fraction is recycled. Nitrogen compounds
are employed to prevent homopolymerization of the styrene product.
Amine compounds are also injected into the process to neutralize
carbonic acid in the water phase of the process. In this process
the invention provides an improvement comprising intimately
contacting the benzene fraction with water and then removing the
water containing nitrogen compounds from the benzene fraction prior
to alkylation of the recycled benzene fraction.
[0010] The present invention thus includes many possible
embodiments, since the water can be injected at more than one
possible point during the process, and can likewise be removed at
more than one point, and via more than one means. In one
embodiment, the water is injected with the fresh benzene prior to
alkylation, which is also prior to the entry of the recycled
benzene; the fresh and recycled benzenes are thoroughly mixed; and
then they are passed through a drying column which removes the
water and the entrained nitrogen compounds and passes the now-dry
benzene on to the alkylation unit.
[0011] In accordance with the present invention, styrene is
continuously mass produced in a dehydrogenation process of
ethylbenzene in any type of reactor conventionally employed for a
continuous mass styrene production process. For example, a reactor
is charged with ethylbenzene under dehydrogenation conditions and a
styrene-, unreacted ethylbenzene-, benzene- and toluene-containing
process stream is formed. Neutralizing amines such as morpholine as
added to the stream to increase the pH of the co-existing water
phase. Stabilizing compounds that contain nitrogen, such as
2,6-dinitro-p-cresol, 4-tert-butylcatechol, 7-substituted quinone
methides, phenyldiamine, 2,6-dinitro-p-cresol,
N,N-bis(hydroxypropyl)hydr- oxylamine, and other amine compounds,
may then be added to the organic phase of the process stream to
prevent homopolymerization of the styrene and then the process
stream passes to a separation unit where the three products are
separated into fractions and removed, with the stabilizing
compounds retained primarily with the tar fraction.
[0012] The benzene fraction can include nitrogen compounds and/or
their breakdown products. It can therefore be desirable to treat
the benzene fraction in some way to remove the nitrogen compounds
prior to recycling the benzene fraction back into the process. Such
treatment may include passing through an absorbent bed that
includes as the absorbent material at least one adsorbent such as a
zeolite, activated carbon, clay, alumina, and the like. Other
possible treatments include further distillation, fractionation, or
additional separation steps. Following removal of the nitrogen
compounds, the benzene fraction is ready for recycle to the
alkylation phase of the process, where it is to be first mixed with
fresh benzene or added directly to the process as a separate
stream.
[0013] The method of the present invention finds particular use in
commercial systems where economics represent a driving factor. It
has been found that when the benzene containing the nitrogen
compounds is intimately mixed with water, the major portion of the
nitrogen compounds preferentially entrain with the water, and
therefore can be easily removed simply by removing the water. Thus,
the need for use of an absorbent bed is greatly minimized, thus
reducing maintenance and replacement requirements, and addition of
water is a relatively negligible cost. This combination makes
application of the present invention highly desirable in commercial
styrene production at most of the world's styrene production
facilities.
[0014] In applications of the present invention it can be desirable
to ensure that the contact between the nitrogen-containing benzene
fraction and the water is sufficiently intimate to maximize the
entrainment of the nitrogen compounds. Thus, a relatively high
degree of mixing is strongly preferred. This mixing can take place
at more than one point in the production process, thus presenting a
process improvement that can be adapted to some extent to fit the
configuration of the apparatuses being employed.
[0015] For example, in one embodiment water can be injected at a
point in the process that is shortly after the separation of the
dehydrogenation product fractions, styrene, toluene and benzene in
the case of styrene production. With appropriate injection and flow
line design, as will be obvious to those skilled in the art, the
water will achieve an intimate mixing with the benzene fraction.
The water, containing the now-entrained nitrogen compounds, is then
removed via, for example, use of a simple separation unit designed
to remove water based upon differentiation of density; a
distillation unit; conventional stripping or other drying means;
and the like. The "cleaned" benzene can then be routed to the
alkylation unit where it can be, optionally, mixed with fresh
benzene, and then converted into more ethylbenzene.
[0016] In another embodiment, the nitrogen-containing benzene that
has been separated from the styrene and toluene is refluxed
directly for mixing with the fresh benzene, and water is added at
the same point. Again, assuming appropriate flow design to ensure
intimate mixing of all components, the nitrogen compounds quickly
and preferentially transport into the water phase. At this point
the benzene/water process stream can be passed through a
distillation unit, drying column, fixed adsorbent bed, or other
means to remove the water and, therefore, the nitrogen
compounds.
[0017] The proportion of water can be important in some embodiments
of the present invention, particularly where the levels of nitrogen
compounds are comparatively high. Desirably the water is employed
in an amount that is sufficient to optimize entrainment of the
undesirable nitrogen compounds, but not of such an excess that
removal of the water becomes unnecessarily problematic. In one
embodiment a proportion of water ranging from about 1 percent to
about 10 percent, based on weight of benzene, is employed, which is
equivalent to from about 10,000 ppm water to about 30,000 ppm of
water in benzene. In another embodiment the proportion of water
ranges from about 2 percent to about 4 percent, based on weight of
benzene. Most consistent performance is generally found when the
water is deionized water, boiler feed water, or steam condensate
which reduces potentially adverse side reactions accruing from the
presence of even very low amounts of conventional water treatment
compounds.
[0018] It is also desirable to ensure that contact of the water
with the nitrogen-containing benzene is of sufficient duration to
optimize removal of the nitrogen compounds without interfering with
the flow of the continuous process. Thus, design of the benzene
reflux and water-injection systems should take the flow rates into
account and should be designed to optimize this time. In one
embodiment the intimate contact is maintained for at least about 1
minute. In another embodiment the intimate contact is maintained
for at least about 5 minutes. Generally, longer times promote
increased nitrogen compound removal, with the goal being to remove
at least about 90 percent of such compounds.
[0019] Ultimately it is desirable to remove the water via the
selected drying means such that no more than about 900 ppm water
remains, which is sufficient in many cases to enable recycle of the
benzene. However, the present industry standard demands that no
more than about 50 ppm remain for optimum performance, and this
level should be easily attainable using any of the conventional
drying technologies mentioned hereinabove.
[0020] The benefits of the present invention include, in
particular, the need for less frequent regeneration of the
alkylation catalyst or catalysts, and also less frequent change-out
of the absorbent beds currently used to remove most of the nitrogen
compounds from the benzene fraction prior to recycle. While it may
still be desirable to employ such beds with the present invention,
they will thus require significantly less maintenance, and the
amount of nitrogen compounds that do ultimately reach the
alkylation catalyst in the recycled benzene will be greatly
minimized in comparison with recycled benzene which has not been
subjected to the practice of the present invention.
EXAMPLE
[0021] The following example is provided to illustrate the present
invention. It is not, however, intended to be, nor should it be
construed, as being limitative of the scope of the invention in any
way.
Example 1
[0022] The equilibrium concentration of nitrogen compounds in water
in contact with a benzene fraction that has been separated from a
stabilized styrene-, benzene-, and toluene-containing process
stream is determined using a gas chromatography method utilizing
the ANTEK 7090 SCD/NCLD with automated gas and/or liquid sampling
valves. The ANTEK 7090 SCD/NCLD is available from ANTEK Instruments
L.P. The equilibrium concentration is determined to be 18.0
ppm.
[0023] Water is injected at two different rates, 0.1 gal/min
[0.3785 l/min] and 0.2 gal/min [0.7516 l/min], into a flow line
containing the benzene fraction process stream and then recovered
and analyzed using the same method of above. The nitrogen
concentration of the sample taking during the 0.1 gal/min water
injection is 17.0 ppm. The nitrogen concentration of the sample
taking during the 0.2 gal/min water injection is 19.0 ppm.
[0024] These observations can be interpreted to mean that the
distribution of nitrogen compounds in the water phase is at
equilibrium for the distribution of these compounds between the oil
and water phases. A higher rate of water injection with equal or
greater concentration of nitrogen compounds shows that the water
injection is removing nitrogen compound from the oil phase.
[0025] It is further noted that while a part of the foregoing
disclosure is directed to some embodiments of the invention,
various modifications will be apparent to and appreciated by those
skilled in the art. It is intended that all such variations within
the scope of the claims and are embraced by the foregoing
disclosure.
* * * * *