A desiccant regeneration system is disclosed which employs polymerization
diluent as regeneration medium for monomer recycle desiccant driers
in ethylene-alpha olefin copolymerizations and utilizes existing
diluent purification systems (i.e., systems employed in polymerization
processes for diluent recycle), thereby avoiding separate regeneration
facilities, providing high purity regeneration fluid and allowing
regeneration at relatively mild temperatures.
What is claimed is:
1. A method for regenerating a desiccant drier deactivated by the
dehydration of a higher alpha olefin, said alpha olefin being used
in a process comprising copolymerization of ethylene and said higher
alpha olefin and employing Ziegler-type catalysis which comprises
the steps of:
a. contacting said drier with a portion of dry recycle polymerization
diluent for a period of time sufficient to remove substantially
all adsorbed water therefrom and reactivate the desiccant in said
b. passing the diluent used in regeneration from said drier to
a polymerization diluent purification system employed for recycle
of diluent in the copolymerization process.
2. The method of claim 1 wherein the dry polymerization diluent
used in regeneration of said drier is heated to a vaporous state
prior to contact with said drier and which method additionally comprises
the subsequent step of contacting said drier after reactivation
of said desiccant with a portion of dry liquid recycle polymerization
diluent for a period of time sufficient to cool said desiccant to
a temperature suitable for dehydration of said alpha olefin.
3. The method of claim 2 wherein said diluent is hexane.
4. The method of claim 2 wherein the desiccant is cooled to a temperature
in the range of from about 60.degree.C. to about 20.degree.C.
5. The method of claim 1 wherein said copolymerization process
is a terpolymerization process and the termonomer is a nonconjugated
6. The method of claim 1 wherein said desiccant drier is an alumina
7. The method of claim 1 wherein said higher alpha olefin is propylene.
8. A method of regenerating a desiccant drier deactivated by the
dehydration of liquid propylene, said propylene being subsequently
used in a process comprising the terpolymerization of ethylene,
propylene, and a nonconjugated diene and employing Ziegler-type
catalysis which comprises the steps of:
a. flushing said drier with propylene vapors to remove liquid propylene
b. contacting said drier with a portion of dry, heated, vaporous
recycle polymerization diluent for a period of time sufficient to
remove substantially all adsorbed water therefrom and reactivate
the desiccant in said drier, said vaporous diluent passing downwardly
through said drier;
c. passing a portion of dry liquid recycle polymerization diluent
upwardly through said drier after reactivation of said desiccant
for a period of time sufficient to cool said desiccant to a temperature
suitable for dehydration of liquid propylene; and
d. passing the vaporous diluent of step (b) and the liquid diluent
of step (c), after passage of each through said drier, to a polymerizaion
diluent purification system for recycle of diluent in the terpolymerization
9. The method of claim 8 wherein the diluent is hexane.
10. The method of claim 8 wherein the desiccant is cooled to a
temperature in the range of from about 60.degree.C. to about 20.degree.C.
11. The method of claim 10 wherein the desiccant is alumina.
BACKGROUND OF THE INVENTION
The novel regeneration scheme disclosed herein is employed in ethylene-higher
alpha olefin copolymerizations. Typically, the alpha olefin will
have the general formula: R -- CH = CH.sub.2 where R is a C.sub.1
to C.sub.8 alkyl radical, preferably a C.sub.1 to C.sub.4 alkyl
radical. The alpha olefin may be linear or branched and, while a
single alpha olefin is preferred, mixtures may be employed. Illustrative
examples include propylene; 1-butene; 1-heptene; 1-decene; 4-methyl-1-pentene;
44'-dimethyl-1-hexene; 566-trimethyl-1heptene, etc.; particularly
preferred herein is propylene.
The copolymers may be a terpolymer wherein the third monomer is
a nonconjugated diene preferably having 6 to 15 carbon atoms. These
types of terpolymers are known as ethylene-propylene-diene terpolymers,
i.e., EPDMs. Representative useful dienes include 5-methylene-2-norbornene,
5-ethylidene-2-norbornene, 5vinyl-2-norbornene, 2-ethyl-norbornadiene,
14-hexadiene, dicyclopentadiene, 4789-tetrahydroindene, etc.
Preferred herein is 5-ethylidene-2-norbornene.
The monomeric reactants are typically present in the following
amounts, measured per 100 parts of polymerization solvent: about
0.1 to about 10.0 preferably 1.0-6.0 (e.g., 2.75) parts ethylene;
about 0.1 to about 20.0 preferably 1.0-15.0 (e.g., 12.5) parts
alpha olefin (e.g., propylene); from 0.0 to about 2.0 preferably
0.0-1.0 (e.g., 0.22), parts diene (e.g., 5-ethylidene-2-norbornene).
Here, as elsewhere in this specification, all parts given are parts
by weight unless otherwise specifically stated.
The catalyst composition preferably employed in making these polymers
is a Ziegler-type catalyst and may include a compound of a transition
metal (preferably a halide such as titanium tetrachloride or vanadium
tetrachloride) together with, as cocatalyst, an organometal compound
(e.g., an organoaluminum compound such as diethylaluminum chloride).
The mole ratio of cocatalyst to catalyst is generally in the range
of 1:1 to 16:1 preferably 1.5:1 to 7:1. The total catalyst composition
used in polymerization may vary depending upon the particular components
used, but is generally in the range of about 0.01 to about 0.1 parts,
preferably 0.05 parts, per 100 parts of diluent.
The polymerization diluent is a nonreactive medium, typically an
aromatic hydrocarbon such as toluene, a saturated aliphatic hydrocarbon
such as heptane, pentane or hexane, or a chlorohydrocarbon such
as tetrachloroethylene. Hexane is preferred.
Reaction temperatures for polymerization are in the range of about
10.degree. to about 75.degree.C., preferably about 25.degree. to
about 40.degree.C. (e.g., 30.degree.C.). Reactor pressures should
be above the vapor pressure of the reacting medium at reactor temperature.
Normally pressures are in the range of about 0 to about 70 atmospheres,
preferably about 4 to about 10 atmospheres (e.g., 6 atm.). All steps
in the reaction should be carried out in the absence of oxygen,
moisture, CO.sub.2 or other harmful materials. Therefore, all components
of the reaction mixture should be pure and dry and blanketed with
inert gas such as nitrogen or methane.
After reaction, the reactor effluent, as withdrawn, normally contains
unreacted light monomer (e.g., ethylene and propylene), unreacted
termonomer when employed, and copolymer, this being dissolved in
diluent to form a solution containing about 3 to about 15 typically
5 parts copolymer per 100 parts diluent, i.e., polymer cement. This
effluent is withdrawn at a temperature of about -10.degree.C. to
about 70.degree.C., typically 30.degree.C., and a pressure of about
4 to about 10 atmospheres, typically 6 atmospheres.
The reactor effluent is then subjected to flashing at reduced pressures
in order to separate as overhead substantially all unreacted ethylene.
Flashing conditions are in the range of about 10.degree. to about
50.degree.C., typically 20.degree.C., and about 1.0 to about 2.0
atmospheres, typically 1.2 atmospheres. Under these conditions some
unreacted higher alpha olefin (e.g., propylene) and some diluent
may also be withdrawn as overhead. This overhead may be directly
The flash bottoms, containing polymer cement, diluent, unreacted
higher alpha olefin, some active and some spent catalyst is then
subjected to catalyst quench and deashing (i.e., catalyst residue
removal) by contact with water which may contain small amounts of
alcohols such as methanol and/or acids such as sulfuric or hydrochloric
acid as deashing aids.
After deashing the polymer effluent is subjected to steam stripping
to remove as overhead substantially all diluent, steam, substantially
all remaining higher alpha olefin and unreacted diene if employed;
and, as bottoms, a copolymer slurry in water. This stripping operation
is conducted at a temperature in the range of about 60.degree. to
about 130.degree.C., typically 110.degree.C., and a pressure of
from about 0.5 to about 3 atmospheres, typically 2 atmospheres.
The overhead is fractionated in vaporous form to remove heavy impurities
from the polymerization diluent and is then subjected to partial
condensation at a temperature of about 20.degree. to about 50.degree.
C., typically 30.degree. C., and a pressure of about 1.0 to about
2.0 atmospheres, typically 1.4 atmospheres, in order to condense
and liquefy substantially all diluent (e.g., hexane) and steam.
Under these partial condensation conditions the higher alpha olefin
remains gaseous and is readily separated from the condensed components.
However, significant amounts of water vapor may also remain uncondensed;
therefore the alpha olefin must be dried prior to recycle to the
polymerization reactors. For this purpose driers containing adsorbent
materials such as activated alumina are preferred. After a time
such materials will, of course, become saturated and must be replaced
THE PRIOR ART
It is known to employ light petroleum solvents (e.g., n-butane)
to regenerate adsorbent materials and to recycle the desorbing fluid
a number of times until saturated with adsorbate (see U.S. Pat.
No. 3208157). It is also known to employ polymerization diluent
(e.g., toluene) for the regeneration of an adsorbent deactivated
by dehydration of a hydrocarbon (e.g., a conjugated diene). However,
this latter process (disclosed in U.S. Pat. No. 3117095) requires
use of a regeneration system separate from the polymerization process
(i.e., a "closed loop" system), and employs "wet"
diluent as regenerating medium. That is, on "heat up",
the diluent employed is simply separated from the water layer by
extraction and heated to the desired temperature. No drying step
for the diluent is employed. Therefore, the regeneration must necessarily
be run at fairly high temperatures due to known water-solvent equilibrium
factors in order to obtain acceptable results.
THE PRESENT INVENTION
It has now been discovered that by integration of the monomer drier
regeneration system within the overall polymerization process, it
is possible to regenerate adsorbent bed driers using polymerization
diluent at lower temperatures and/or shorter times than previously
possible while, at the same time, attaining improved drying at significant
cost savings since a separate "closed loop" regeneration
system is avoided and existing process equipment is employed.
The preferred embodiment of the present invention may best be described
by reference to the FIGURE. As stated previously, the steam stripper
overhead in the copolymerization process is fractionated directly
to remove heavy impurities (and diene if employed) from the polymerization
diluent. The fractionated overhead vapors are subsequently separated
into two streams by partial condensation. One stream, line 41 contains
wet vaporous higher alpha olefin. This stream is compressed, cooled
and condensed; any water formed as a separate water layer is withdrawn
by extraction leaving a wet liquid alpha olefin stream, line 1.
(It will become obvious to those skilled in the art that this novel
process is equally applicable to regenerating adsorbent bed driers
wherein the stream to be dried is in the vapor phase rather than
liquid phase as discussed hereafter). The liquid phase formed by
the aforementioned partial condensate contains diluent, water, and
minor amounts of unreacted alpha olefin. The separate water layer
is withdrawn by extraction leaving a wet liquid diluent stream,
In order to recycle diluent this second stream must necessarily
be treated to remove all contaminants, leaving pure, dry liquid
diluent. It is a novel feature of this invention that the processing
steps which must be employed in order to prepare pure dry diluent
are also incorporated in the regeneration process for regeneration
of adsorbent bed driers used in the alpha olefin recycle system.
This results in considerable cost savings as well as improved drier
regeneration since the use of pure dry diluent as regenerating medium
allows regeneration at lower temperatures and/or shorter times than
The adsorbent bed driers for alpha olefin, as shown in the FIGURE,
are indicated by numerals 5 and 13. It should be understood that
in commerical operation these driers may be, and preferably are,
operated in lead/guard position or a number of driers may be operably
connected to be on stream in series or in parallel while others
may be in the process of being regenerated. For simplicity, however,
drier 5 will be described as on stream while drier 13 is being regenerated.
Also for simplicity, the adsorbent described will be activated alumina,
the alpha olefin described will be propylene, and the alpha olefin
will be in the liquid phase.
Prior to the regeneration step, wet liquid propylene in line 1
is passed through line 2 valve 3 and line 4 to drier 13 wherein
moisture is removed by the alumina bed with liquid propylene being
passed upwardly therethrough. With driers in lead/guard position,
liquid propylene exits drier 13 through line 6 valve 7 and lines
8 and 9 from whence the dried propylene enters guard drier 5 through
line 10 valve 11 and line 12. Propylene passes upwardly through
drier 5 and exits through line 14 valve 15 and lines 16 and 17
from whence the dried propylene may be recycled to the polymerization
After a period of time the alumina beds of drier 13 become substantially
ineffective because of adsorbed moisture and must be regenerated.
Valves 3 7 and 11 are then closed and valve 18 is opened, thereby
permitting wet liquid propylene to pass through line 2 valve 18
and line 12 to drier 5. Propylene passes upwardly through drier
5 moisture is adsorbed by the alumina beds in said drier, and exits
as dry propylene for recycle through line 14 valve 15 and lines
16 and 17. Drier 13 is now ready for regeneration.
The first step in the regeneration process requires removal of
liquid propylene remaining in drier 13. Conventionally, inert gases
have been employed for this procedure. However, these gases present
the possibility of external contaminants being introduced. Therefore,
it is preferred to flush the drier with dry propylene vapors (or
even dry liquid diluent) easily obtained from the polymerization
process. The propylene vapors are introduced through line 19 and
valve 20 and passed downwardly through line 6 to drier 13. The flushed
liquid propylene exits the drier through line 4 line 21 valve
22 lines 23 and 24 and valve 25 from whence it may be recycled
to line 1 by means not shown. After all liquid propylene has been
flushed from the drier, valves 20 and 25 are closed and the drier
is depressured by opening valves 22 and 26 and releasing propylene
vapors through lines 4 21 and 23 into line 27.
At this point the alumina bed is regenerated by passing downwardly
therethrough pure, dry diluent, preferably in vaporous form, which
is obtained from the diluent recycle system as more fully described
hereafter. The diluent is introduced to drier 13 through line 28
and valve 29 and passed downwardly through line 6.
Temperature of regeneration, since pure, dry diluent is employed
as regenerating medium, may be as low as about 100.degree.C., and,
in fact, it is not even necessary in order to achieve good regeneration
that the diluent be vaporous. Thus, it is possible to avoid the
later step of "cool down" entirely if desired. Of course,
at low temperatures, equilibria between the water in the alumina
bed and that adsorbed by the diluent are reached more slowly. Consequently,
it is desirable to maintain regeneration temperatures in the range
of about 150.degree. to about 200.degree.C., more preferably about
170.degree.C., although temperatures as high as 250.degree.C. are
acceptable. Pressures are generally in the range of about 1 to about
15 atmospheres, preferably about 1 atmosphere to about 6 atmospheres,
typically 4 atmospheres. At such temperatures and pressures the
diluent will be vaporous. Regeneration times may vary from about
5 to about 40 hours, normally from 10 to 30 hours, typically 20
The regenerating medium employed herein is "bone dry",
i.e., has less than about 1 wppm of water, as opposed to prior art
processes employing "wet" media. Thus, it can be seen
that at any given temperature, once equilibrium has been established
between the regenerating medium and the desiccant bed, the desiccant
will approach a lower water content than if wet regenerating media
were employed. As a result, the instant process allows regeneration
at significantly shorter times than previously possible at equivalent
regeneration temperatures, or allows lower regeneration temperatures
to attain similar efficiencies. Further, by adjusting conditions
it is within the skill of the art to achieve both shorter times
and lower temperatures. In addition, the novel process permits more
efficient regenerations in that the desiccant bed will contain less
residual moisture after regeneration than with prior art processes.
The diluent, after use in regeneration, contains any heavy tars,
etc., which may have formed on the desiccant bed. Diluent is recovered
from drier 13 by opening valves 22 and 26 and allowing diluent to
pass downwardly through lines 4 21 and 23 to line 27 where it
is combined with steam stripped overhead from the polymerization
process prior to treatment of said overhead vapors in the diluent
purification system, said system being necessary to allow recycling
of diluent in the polymerization process.
After regeneration, depending on the temperatures employed, it
may be desirable to decrease temperature in the drier prior to placing
said drier on stream. In the instant process this is readily accomplished
by use of dry liquid polymerization diluent. Valve 22 is closed
and pure dry liquid diluent, again from the polymerization process
as more fully described hereafter, is introduced to the drier by
opening valve 30 allowing diluent to pass upwardly through the
drier through lines 31 and 4. Cooling diluent exits drier 13 through
lines 6 and 32 and open valve 33 to line 23 through which it passes
downwardly through valve 26 to line 27 where it is combined with
steam stripped overhead prior to diluent recycle treatment.
This cool-down step is continued until the temperature of the desiccant
bed has decreased to a temperature of from about 60.degree.C. to
about 30.degree.C., preferably 40.degree.C., at a pressure of about
1.5 atmospheres. Liquid diluent is then pressured from the bed by
use of dry propylene vapor obtained through line 19 and valve 20
from downstream process equipment now shown.
The diluent exits drier 13 and passes to line 27 in the same manner
as vaporous diluent used in regeneration. Drier 13 is now ready
to be placed on steam.
As noted previously, line 27 is the conduit through which passes
diluent, alpha olefin, water, impurities, etc., in vapor form from
the aforementioned steam stripping operation. To this conduit, through
line 23 and valve 26 is added at various times during monomer drier
regeneration, vaporous and liquid diluent used in said regeneration
and containing some alpha-olefin, water, tars and other impurities
adsorbed from the drier beds. By this combination and the use of
a portion of purified recycle diluent as regeneration medium, it
is possible to utilize the diluent purification system both for
diluent recycle and as an integral part of the monomer drier regeneration
facilities, thereby avoiding completely separate regeneration facilities.
The diluent purification system may be integrated with the monomer
regeneration system, as seen by the FIGURE, as follows: After line
23 feeds into line 27 the combined steam stripped overhead and
vaporous and liquid diluent used in drier regeneration containing
diluent, water, alpha olefin and contaminants, etc., is preferably
fed to fractionating column 34.
Column 34 is operated at a temperature in the range of about 110.degree.
to about 60.degree.C., typically 75.degree.C., and a pressure of
about 3.0 to about 1.0 atmospheres, typically 1.8 atmospheres. Under
these conditions, substantially all heavy impurities and unreacted
diene are withdrawn as bottoms through line 35. As overhead, diluent,
water, and unreacted alpha olefin are withdrawn in gaseous form
through line 36 partially condensed in condenser 37 and passed
to settler drum 39 through line 38.
Condenser 37 is operated at temperatures in the range of about
20.degree. to about 50.degree.C., typically 30.degree.C., and pressures
of 1.0 to 3.0 atmospheres, typically 1.3 atmospheres. Under these
conditions unreacted alpha olefin and any light impurities will
remain gaseous, are withdrawn via line 41 and may be recycled to
the wet vaporous alpha olefin stream prior to compression, etc.,
of that stream as heretofore described. Wet alpha olefin which passes
through conduit 41 eventually enters the desiccant driers through
line 1 after suitable processing not described herein.
Water is withdrawn from drum 39 through line 40 and wet diluent
is withdrawn through line 42 by pump 43. A portion is recycled to
fractionator 34 through line 44 and the remainder is passed to drying
tower 46 via line 45.
Tower 46 is operated at a temperature in the range of about 90.degree.
to about 150.degree.C., typically 130.degree.C., and a pressure
of about 2 to about 10 atmospheres, typically 5 atmospheres. Under
these conditions, any remaining water and any remaining dissolved
unreacted alpha olefin are withdrawn as overhead through line 47
and recycled to line 36. Pure dry liquid diluent is withdrawn as
bottoms through line 48 a portion recycled to drying tower 46 through
line 50 and heat exchanger 49 and the remainder passed through
pump 51 to line 52.
The majority of this dry diluent is recycled to the polymerization
reactor. A minor portion is diverted through line 53 for use as
regeneration medium for the alumina driers. By minor portion is
meant amounts of from about 2 to 10%, typically about 5%. The temperature
of this diverted liquid diluent is normally in the range of about
90.degree. to about 150.degree.C., typically 130.degree.C.
The diluent in line 53 to be used as regenerating medium may be
passed to vaporizer 54 where the diluent may be heated to desired
temperatures for regeneration of drier 13 to which it is passed
through line 28 valve 29 and line 6 as heretofore described.
A portion of diluent in line 53 may be diverted therefrom prior
to vaporization through line 59 and cooler 60 to line 31. This liquid
diluent at 30.degree. to 50.degree.C. may be used as heretofore
described, to cool down the drier after regeneration. Further, the
liquid diluent in line 31 may also be employed to further control
the temperature of vaporized diluent in line 28 by admixture therewith
through line 55 and control valve 56.