U.S. patent application number 13/497267 was filed with the patent office on 2012-11-08 for single column stripping and drying process.
Invention is credited to Walter C. Moore, Kevin C. Seavey, Carlos M. Villa, John W. Weston.
Application Number | 20120279082 13/497267 |
Document ID | / |
Family ID | 43530676 |
Filed Date | 2012-11-08 |
United States Patent
Application |
20120279082 |
Kind Code |
A1 |
Seavey; Kevin C. ; et
al. |
November 8, 2012 |
Single Column Stripping and Drying Process
Abstract
Organic materials are stripped and dried in a single column
having two contact zones. A stripping gas is introduced into an
upper contact zone and flows through the organic material in that
zone. A drying gas is introduced into a lower contact zone. The
drying gas contacts the organic material in both the upper and
lower contact zones, and is removed from the top of the column
together with the stripping gas. This process permits very
efficiently removal of volatile organic compounds as well as
efficient drying, while requiring on low levels of the stripping
and drying gasses.
Inventors: |
Seavey; Kevin C.; (Clute,
TX) ; Moore; Walter C.; (Lake Jackson, TX) ;
Weston; John W.; (Sugar Land, TX) ; Villa; Carlos
M.; (Lake Jackson, TX) |
Family ID: |
43530676 |
Appl. No.: |
13/497267 |
Filed: |
September 21, 2010 |
PCT Filed: |
September 21, 2010 |
PCT NO: |
PCT/US10/49567 |
371 Date: |
March 21, 2012 |
Related U.S. Patent Documents
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
|
|
61246654 |
Sep 29, 2009 |
|
|
|
Current U.S.
Class: |
34/505 |
Current CPC
Class: |
B01D 3/38 20130101; B01D
3/26 20130101; B01D 3/143 20130101; B01D 3/343 20130101; C08G 65/30
20130101 |
Class at
Publication: |
34/505 |
International
Class: |
F26B 7/00 20060101
F26B007/00 |
Claims
1. A process for stripping and drying a starting organic material,
comprising: a) introducing the starting organic material into an
upper contact zone of a column that has an upper contact zone and a
lower contact zone, and allowing the starting organic material to
travel downwardly through the column, through the upper contact
zone and then through the lower contact zone to a bottom section of
the column; b) introducing a stripping gas into the upper contact
zone of the column and above the lower contact zone of the column
such that the stripping gas moves upwardly through the upper
contact zone, where it contacts the starting organic material and
removes impurities therefrom, and then to a top section of the
column; c) introducing a drying gas into the lower contact zone of
the column such that the drying gas moves upwardly through the
lower contact zone where it contacts a portion of the organic
material and removes moisture from therefrom, then moves upwardly
through the upper contact zone where it contacts another portion of
organic material, and then moves to a top section of the column; d)
removing the stripping gas and the drying gas from the top section
of the column above the upper contact zone; and e) removing the
stripped and dried organic material from the bottom section of the
column below the lower contact zone, wherein the starting organic
material is a liquid polyether having a molecular weight of from
500 to 10,000 or crude polymer polyol, the starting organic
material contains from 50 to 5,000 ppm of volatile organic
impurities and up to 50,000 ppm of water, and the stripped and
dried organic material contains up to 10 ppm of volatile organic
compounds and up to 200 ppm of water.
2. The process of claim 1 wherein the stripping gas is superheated
steam.
3. The process of claim 1 wherein the drying gas contains no more
than 50 ppm moisture.
4. The process of claim 3, wherein from 0.002 to 0.03 parts by
weight of stripping gas are passed through the column per part by
weight of the organic material.
5. The process of claim 4, wherein from 0.0001 to 0.1 parts by
weight of drying gas are passed through the column per part by
weight of the organic material.
6. The process of claim 5, wherein the column is operated at a
pressure of from 5 to 100 mbar.
7. The process of claim 6, wherein the column is operated at a
temperature of from 90 to 150.degree. C.
8-10. (canceled)
Description
[0001] The present invention relates to a process for stripping
impurities from organic compounds and organic polymers such as
poly(alkylene oxide) polymers.
[0002] Many organic compounds and polymers are manufactured using
processes that leave them with some level of impurities and/or
moisture. It is often necessary to remove those impurities and that
moisture to very low levels, so that the product is suitable for
use in some downstream operation. There are many instances of this
in the chemical industry. One prominent example is in manufacturing
poly(alkylene oxide) polymers; the crude polyols often contain
significant amounts of volatile aldehyde impurities which, among
other things, impart a noxious odor to the polyols and to products
such as polyurethane foam that are made from the polyols. In
addition, the polyether polyols often contain up to 5% or so by
weight of water, which needs to be reduced to much lower levels
before the polyols can be used in polyurethane manufacturing. A
related manufacturing process is the production of so-called
polymer polyols by the polymerization of monomers such as styrene
and/or acrylonitrile in the presence of a poly(alkylene oxide)
polyol. The polymer polyol products generally contain significant
quantities of volatile organic impurities, especially unreacted
monomers, which need to be removed from the product before it can
be used.
[0003] Stripping methods are commonly used to remove volatile
impurities from organic compounds to very low levels. One common
approach to stripping is to pass the organic compound downwardly
through a stripping column, which is often operated at
subatmospheric pressures. A stripping gas, usually steam, is passed
upwardly through the column, countercurrent to the organic
compound, and carries volatile organic impurities with it out of
the top of the column.
[0004] Stripping processes for removing volatile impurities from
polyether polyols are described, for example, in U.S. Pat. No.
6,060,627 and US Published Patent Application Nos. 2008/0033139 and
2008/0033214. In U.S. Pat. No. 6,060,627, a propoxylated glycerin
containing water, allyl alcohol and propylene glycol allyl ethers
is sent to a reboiler evaporator to remove the bulk of the water,
and then vacuum stripped with steam as the stripping gas. The
weight ratio of steam to polyether polyol mixture being treated is
about 0.0287:1. In US 2008/0033139, a two-column stripping
apparatus is described for stripping residual monomers from a
polymer polyol product. The working examples of that application
describe very high steam to polyol ratios (0.2:1 by weight). These
high levels of steam are described as reducing the levels of
residual monomer and isopropanol from around 12,000 to 13,000 ppm
to as low as 1 ppm each, but more typical results are in the range
of 10 to 20 parts per million. In addition, a specific impurity, a
"recombination product" remains in the polyol at the level of
hundreds of parts per million, and water content is not reduced or
is even increased.
[0005] US 2008/0033214 describes a stripping process for polyether
polyols which, prior to treatment, are said to have at most 100
parts per million volatile organic compounds. The stripping process
removes these only to the 20 ppm level, which is said to be enough
to reduce odor but is nonetheless a significant loading. The weight
ratio of stripping gas to polyol is said to be from 0.01 to 0.05.
The example describes stripping using nitrogen as a stripping
agent.
[0006] Drying also can be performed in a column, by passing a
drying gas through the column countercurrent to the flow of the
organic material.
[0007] It is desirable to develop a stripping and drying process
which effectively removes volatile organic impurities to very low
levels, such as 10 ppm or below, and which also removes water to
low levels, such as to 200 ppm or below, and which does so
efficiently and inexpensively.
[0008] This invention is such a process. This invention is a
process for stripping and drying a starting organic material,
comprising:
[0009] a) introducing the starting organic material into an upper
contact zone of a column that has an upper contact zone and a lower
contact zone, and allowing the starting organic material to travel
downwardly through the column, through the upper contact zone and
then through the lower contact zone to a bottom section of the
column;
[0010] b) introducing a stripping gas into the upper contact zone
of the column and above the lower contact zone of the column such
that the stripping gas moves upwardly through the upper contact
zone, where it contacts the starting organic material and removes
impurities therefrom, and then to a top section of the column;
[0011] c) introducing a drying gas into the lower contact zone of
the column such that the drying gas moves upwardly through the
lower contact zone wherein contacts a portion of the organic
material and removes moisture from therefrom, then moves upwardly
through the upper contact zone where it contacts another portion of
organic material, and then moves to a top section of the
column;
[0012] d) removing the stripping gas and the drying gas from the
top section of the column above the upper contact zone; and
[0013] e) removing the stripped and dried organic material from the
bottom section of the column below the lower contact zone.
[0014] The stripping process of this invention offers several
potential advantages over previous approaches in which the
stripping and drying steps are conducted separately. Costs for
equipment are lower, because the stripping and drying are conducted
in a single column instead of multiple columns. Volatile organic
impurities often can be reduced to very low levels using
surprisingly small amounts of stripping gas. This results in
reduced costs for those materials and fewer costs associated with
handling the larger volumes of gases. When the stripping gas is
steam, as is preferred, the invention also offers advantages in
energy costs (because less steam needs to be produced) and in
wastewater treatment costs (for example, to dispose of condensed
steam and volatile organic compounds entrained therein). Because
the drying gas passes through the upper contact zone and contacts
the organic material there, it contributes to the stripping that
occurs in the upper contact zone and thus reduces the amount of
stripping gas that is needed. This reduces the size and cost of the
vacuum system required to operate the column at reduced
pressure.
[0015] The process is well-adapted for continuous operation, which
again reduces costs and eliminates in some cases the need for
storing the organic material prior to the stripping and drying
process. Eliminating or reducing the storage of the material can in
some instances, as in the case when the organic material is a
polyether, reduce or eliminate the need to add stabilizers such as
antioxidants, or to make pH adjustments to the material, or to
conduct other pretreatments of the material.
[0016] The FIGURE is a schematic drawing of the process of the
invention.
[0017] Turning to the FIGURE, stripping column 9 includes liquid
inlet 1, through which the starting organic polymer or compound
containing volatile organic impurities is introduced into column 9.
The starting organic material, upon entering column 9, flows
downwardly through upper contact zone 2 of column 9. Stripping gas
is introduced into upper contact zone 2 column 9 through stripping
gas inlet 5. Stripping gas inlet 5 is below liquid inlet 1, where
the starting organic material is introduced into the column, and
above lower contact zone 3. Generally, the location of stripping
gas inlet 5 will demark the division between upper contact zone 2
and lower contact zone 3 of column 9.
[0018] Stripping gas introduced into column 9 travels upwardly,
passing through upper contact zone 2 where it contacts starting
organic compound or polymer and at least partially strips volatile
(relative to the organic material) impurities from organic
material.
[0019] The stripping gas with entrained impurities then passes
upwardly to top section 10 of column 9, where it exits column 9
through gas outlet 4. Top section 10 is generally the portion of
column 9 above liquid inlet 1, where the gasses can accumulate to
be removed from column 9 through gas outlet 4.
[0020] The organic material, having passed downwardly through upper
contact zone 2, then enters lower contact zone 3 of column 9. A
drying gas is introduced via drying gas inlet 6 into lower contact
zone 3, where it contacts the organic material and removes moisture
therefrom. Generally, the location of drying gas inlet 6 will
demark the division between lower contact zone 3 and bottom section
8 of column 9. The dried organic material then flows to a bottom
section 8 of column 9 where it collects below drying gas inlet 6
and from where it is removed from column 9 via outlet 7. After
passing through lower contact zone 3, the drying gas passes
upwardly through column 9 into upper contact zone 2, where it
contacts more of the organic material, at the same time as the
organic material contacts the stripping gas. The drying gas is
believed to contribute to the stripping operation that occurs in
upper contact zone 2. The drying gas then passes into top section
10 and is removed together with the stripping gas through gas
outlet 4.
[0021] Apart from having the specific features described above
(i.e., the various inlets and outlets and upper and lower contact
zones), stripping column 9 does not need to have any special
construction or design. It may be constructed of any suitable
material, taking into account the operating conditions (mainly
temperature and pressure), the particular organic material, the
particular stripping gas and the particular drying gas. Various
grades of steel or aluminum are generally suitable.
[0022] Stripping column 9 will generally contain a packing in at
least upper contact zone 2 and lower contact zone 3. The packing
serves the purposes of distributing the organic material more
uniformly across the cross-section of the column, increasing the
residence time of the organic material within the column,
increasing the surface area of the organic material to facilitate
better contact with the stripping and drying gases, and of
facilitating heat transfer if needed. A wide variety of porous
materials are suitable as the packing, including meshes, wools,
fibers, a series of porous plates, beads or other particulates,
various types of structured packings, trays and the like. As
before, the material of construction is not considered to be
critical and will be selected taking the operating conditions and
the particular organic material, stripping gas and drying gas into
account. Metal and ceramic packings are generally preferred. If
metal packings are used, the metal should be resistant to chemical
attack from water and/or other chemical species.
[0023] Stripping column 9 may also contain one or more supports for
holding the packing material in place within the column.
[0024] The packing in stripping column 9 may have a specific
surface area of from 150 to 500 m.sup.2 per cubic meter. A
preferred specific surface area is from 230 to 450
m.sup.2/m.sup.3.
[0025] Stripping column 9 may have a jacket for applying a heating
or cooling medium such as steam to the outside of the column to
provide for temperature control. Other heating and cooling devices
may be present in addition to or in place of such a jacket.
Stripping column 9 will also generally contain means for
distributing the stripping gas supplied by stripping gas inlet 5
across the cross-section of the column. Therefore, stripping gas
inlet 5 will generally be in fluid communication with a stripping
gas distribution means, through which stripping gas is received
from stripping gas inlet 5 and introduced into stripping column 9.
The stripping gas distribution means preferably introduces the
stripping gas into column 9 at multiple locations across its
cross-section. The stripping gas distribution means may include,
for example, one or more distribution plates, spargers, bubbles,
jets, nozzles or similar apparatus.
[0026] Similarly, drying gas inlet 6 will also generally be in
fluid communication with means for distributing the drying gas
across the cross-section of stripping column 9. Suitable designs
for such drying gas distribution means include those mentioned
above with regard to the stripping gas distribution means.
[0027] Stripping column 9 may contain means for distributing the
organic material introduced through inlet 1 across the
cross-section of the column. Again, specific apparatus as are
mentioned above with regard to the stripping gas distribution means
are entirely suitable.
[0028] Gas outlet 4 is preferably in fluid communication with a gas
removal means for withdrawing the stripping and drying gases from
column 9, and, if column 9 is to be operated under subatmospheric
pressure, for pulling a vacuum onto column 9. The gas removal means
may be of any suitable design. Mechanical devices such as simple
fans or blowers and vacuum pumps of various designs are suitable.
If the stripping gas is steam or other easily condensable gas, the
gas removal means may consist of or include one or more condensers,
which condense the gas and thereby produce a vacuum in the system.
Combinations of these approaches can be used.
[0029] Outlet 7 also is preferably in fluid communication with a
pumping means for withdrawing the stripped and dried organic
material from the column. The pumping means is any sort of device
for moving a liquid through a conduit. Various types of pumps and
impellers are suitable. The design of the pumping means is not
considered to be critical to the invention.
[0030] The organic material is any organic compound or mixture of
organic compounds, which is a liquid under the conditions at which
the stripping column is operated. A mixture of organic compounds
may include a solution of one material in a solvent, which solvent
may be a process solvent from some upstream step, or one which is
used to dissolve or reduce the viscosity of another organic
material for processing through the stripping column. The organic
material, prior to treatment according to this invention, will
generally contain one or more impurities which are more volatile
than the organic material (and more volatile than any solvent which
is needed to maintain the organic material as a liquid through the
stripping and drying process) and which can be removed by
stripping. The organic material may contain moisture, i.e., some
small amount of water, prior to being introduced into stripping
column 9. This is the usual case when the stripping gas is
something other than steam. When steam is used as the stripping
gas, the organic material will usually absorb some moisture from
the steam in upper contact zone 2, which moisture is then removed
through contact with the drying gas in lower contact zone 3.
[0031] The organic material may include or consist of (apart from
impurities and moisture) one or more organic polymers, which may or
may not be dissolved in some solvent.
[0032] The starting organic material may contain, for example, from
10 to 20,000 parts per million by weight (ppm) of volatile organic
impurities. Greater levels of organic impurities are difficult to
remove to very low levels in a stripping process. A preferred level
of volatile organic impurities in the starting organic material is
from 50 to 5,000 ppm and a more preferred level is from 50 to 2,000
ppm. The starting organic material may contain up to 50,000 ppm of
water, up to 10,000 ppm water, up to 5,000 ppm of water, or up to
2,500 ppm of water.
[0033] A preferred organic material is a crude liquid polyether
having a molecular weight of from about 500 to 10,000, which is the
product of an alkylene oxide polymerization reaction. The alkylene
oxide may be, for example, ethylene oxide, propylene oxide,
butylenes oxide, 1,2-hexane oxide, tetrabutylene oxide, styrene
oxide, or a mixture of any two or more thereof. These oxides can be
polymerized in an anionic polymerization process in the presence of
an initiator compound and of an alkali metal hydroxide catalyst.
Alternatively, the oxides can be polymerized, again in the presence
of an initiator compound, using a double metal cyanide catalyst
complex. The crude liquid polyether will generally be terminated in
hydroxyl groups, and may have, for example, from 1 to 12 hydroxyl
groups per molecule. Crude liquid polyethers manufactured in these
ways typically contain a number of organic impurities, including
unreacted oxides, various aldehyde by-products and the like, which
are more volatile than the liquid polyether and are susceptible to
being removed in a stripping process. Polyethers made using an
anionic polymerization process are often in addition treated to
neutralize and remove the catalyst residues and for that reason
often contain some amount of entrained moisture.
[0034] Another preferred organic material is a crude polymer polyol
which is obtained from a polymer polyol process in which one or
more ethylenically unsaturated monomers are polymerized in the
presence of a polyether polyol. Such crude polymer polyol products
tend to contain up to 20,000 ppm, preferably up to 10,000 of
unreacted monomers, chain transfer agents, free radical initiators
and/or decomposition residues of these.
[0035] The stripping gas is selected such that, under the
conditions used in the stripping column, it exists in the gas phase
and does not react with the organic material. The stripping gas
also preferably has low solubility in the organic material. A
preferred stripping gas is easily condensable, as this allows a
vacuum to be pulled in the stripping column by condensing the
stripping gas that has been removed from the column. Superheated
steam is an especially preferred stripping gas. By "superheated" it
is meant that the steam is at a temperature above its dew point
under the conditions at which the column is operated. Mixtures of
gases can be used, such as, for example, a mixture of superheated
steam and air, or of superheated steam and an inert gas such as
nitrogen or argon. The amount of stripping gas may range from
0.0002 to 0.1 kg or more of stripping gas per kg of organic
material. A preferred amount is from 0.0002 to 0.03 kg per kg of
organic material and a more preferred amount is from 0.0002 to 0.02
kg per kg of organic material.
[0036] The drying gas is also selected such that, under the
conditions used in the stripping column, it exists in the gas phase
and does not react with the organic material, and also preferably
has low solubility in the organic material. The drying gas should
contain no more than 100, preferably no more than 50 ppm of water.
Dry air is a useful stripping gas, but inert gasses such as argon
and especially nitrogen are preferred. The amount of drying gas may
range from 0.0001 to 0.1 kg of organic material. A preferred amount
is from 0.0001 to 0.003 kg per kg of organic material.
[0037] The temperature and pressure conditions at which the
stripping and drying process is performed will of course depend on
the particular organic material, the nature of the organic
impurities and the particular stripping and drying gases that are
used. The temperature and pressure in the stripping column are such
that the organic material (apart from volatile organic impurities
that are to be removed) remains in the liquid state as it passes
through the column, and such that the stripping and drying gases
remain in the gaseous state as they pass up through the column.
Subatmospheric pressures are preferred, to facilitate removal of
the volatile organic impurities and water from the organic
material. The pressure inside the stripping column may be, for
example, from 5 to 100 mbar or from 15 to 50 mbar. A suitable
temperature may be from 0 to 160.degree. C. A preferred
temperature, especially for stripping polyethers is from 90 to
150.degree. C., and a more preferred temperature is from 120 to
140.degree. C.
[0038] It is generally desirable to reduce the amount of organic
impurities and moisture in the treated organic material to very low
levels, such as, for example, to 10 ppm or below in the case of
organic impurities and to 200 ppm or below in the case of residual
moisture. It is more preferred to reduce the level of the volatile
organic impurities to 1 ppm or below.
[0039] The following examples are provided to illustrate the
invention, but not to limit the scope thereof. All parts and
percentages are by weight unless otherwise indicated.
EXAMPLE 1
[0040] A single stripping column designed as shown in FIG. 1 is
constructed. A crude polyol containing 6,000 ppm water and 1,000
ppm volatile organic impurities is passed through the column at
130.degree. C. The column is operated at 15 mbar. The stripping gas
is superheated steam, and the drying gas is nitrogen. Only 0.005 kg
of steam per kg of crude polyol is needed to reduce the amount of
volatile organic impurities to 0.5 ppm. The amount of nitrogen
drying gas is only 0.0004 kg per kg of crude polyol; this amount is
sufficient to reduce the water content to 100 ppm. Therefore, with
this invention, not only is steam consumption very low but the
total amount of stripping plus drying gas is also very low and the
water content is reduced dramatically in addition to the
near-complete removal of volatile organic compounds.
* * * * *