Note: Descriptions are shown in the official language in which they were submitted.
~ `
12248~1
COS 488 ~-
3/1/83
POLYMERIZATION INHIBITION PROCESS FOR VINYL AROMATIC
___ __ _____
COMPOUNDS
Background of the Invention
The present invention relates to a polymer
inhibiting composition and to a process for inhibiting the
polymerization of a readily polymerizable vinyl aromatic
compound. F
It is well known that vinyl aromatic compounds F
such as monomeric styrene, lower alkylated styrene such as
alpha-methylstyrene and the like, polymerize readily and
furthermore, that the rate of polymeriæation increases with
increasing temperature. Inasmuch as vinyl aromatic
10 compounds produced by common industrial methods contain L
impurities, these compounds must be subjected to separation
and purification processes in order to be suitable for most ~-~
types of further industrial use. Such separation and
purification are generally accomplished by distillation. r_
In order to prevent polymerization during
storage of vinyl aromatic compounds, various types of known
polymerization inhibitors have been employed usually under
refrigerated conditions. For example, common inhibitors
useful for inhibiting the polymerization of vinyl aromatic
compounds during storage conditions include
4-tert-butylcatechol (TBC) and hydroquinone.
F
. ~ ~
~; ~
2 ~224811
Sulfur, on the other hand, has been widely
employed as a polymerization inhibitor during the
distillation of various vinyl aromatic compounds. However,
while sulfur provides a reasonably effective inhibitor, its
use in such distillation processes results in a highly
significant disadvantage namely, there is formed in the
reboiler bottom of the distillation column a valueless
waste material highly contaminated with sulfur. This waste
material, furthermore represents a significant problem of
pollution and/or waste removal.
Although many compounds are effective for
inhibiting the polymerization of vinyl aromatic compounds
under differing conditions such as storage, only some of
these compounds have proved to be of any real utility for
inhibiting vinyl aromatic polymerization under distillation
conditions. One compound found effective for
polymerization inhibition is 2, 6-dinitro-p-cresol (DNPC)
disclosed in U.S. Patent No. 4,105,506 by Watson. In
addition, it has been found that previously known
polymerization inhibitors may be combined to achieve an
inhibitory effect greater than either inhibitor alone. The
synergistic effect of combining two known inhibitors was ~-
disclosed in U.S. Patent No. 4,061,545 by Watson, wherein
phenothiazine and tert-butylcatechol (TBC) were used
together in the presence of oxygen as a polymerization
inhibitor. The synergistic effect of
N-nitrosodiphenylamine combined with DNPC in inhibiting the
polymerization of vinyl toluene under vacuum conditions was
disclosed in U.S. Patent No. 4,341,600 by Watson. It has
been found, however, that as the distillation temperature
3 ~2248~1
~.
increases, the eEfectiveness of these inhibitors
decreases.
During distillation of vinyl aromatic compounds,
higher distillation temperatures are preferred in a
distillation apparatus in order to achieve a higher
throughput and a more energy efficient distillation. These
higher temperatures, however, also result in an increased
rate of polymerization which leads to unacceptable levels
of polymer in the distillation apparatus. Accordingly,
therefore, there exists a strong need for a polymerization
inhibitor which will effectively prevent the polymerization
of vinyl aromatic compounds during distillation at higher
temperatures.
Summary of the Invention
It is therefore an object of the present
invention to provide both a polymer inhibiting composition
and a process for inhibiting the polymerization of vinyl
aromatic compounds.
Another object of the invention is to provide
both a polymer inhibiting composition and a process for !~;
inhibiting the polymerization of vinyl aromatic compounds
at higher temperatures resulting in a higher recovery of
high purity, unsaturated vinyl aromatic compounds and in
the production of less undesirable by-products.
A still further object of the invention resides
in the provision of both a polymer inhibiting composition
and a process for inhibiting the polymerization of vinyl
aromatic compounds which permits the distillation apparatus
to be operated at a higher temperature and an increased
- ~224811
,~
rate of throughput without a reduction in efficiency.
In accomplishing the foregoing and other objects,
there has been provided in accordance with the present
invention a composition for inhibiting the distillation of
a readily polymerizable vinyl aromatic compound in the
presence of oxygen when subject to elevated temperature
such as in a distillation process, the composition
comprising an effective amount of 2,6-dinitro-p-cresol and
an effective amount of a phenylene diamine having the
formula
R~ - N~ 2
wherein R1 and R2 are alkyl, aryl or hydrogen.
In an alternate embodiment, the inhibitor
composition comprises an effective amount of
2,6-dinitro-p-cresol and 4-tert-butylcatechol.
The vinyl aromatic compounds covered in the
present invention include styrene, substituted styrene,
divinylbenzene, vinyltoluene, vinyl naphthalene and the
polyvinylbenzenes. This group is also understood to
include all structural isomers thereof.
Also, in accomplishing the foregoing other
objects, there is provided in accordance with the present
invention, a process for inhibiting the polymerization of a
readily polymerizable vinyl aromatic compound comprising
subjecting the vinyl aromatic compound to heating
30 conditions, such as distillation, in the presence of ~-
effective amounts of 2,6-dinitro-p-cresol and the
, . _
~224811
.~
aforementioned phenylenediamine derivatives or
4-tert-butylcatechol respectively, and oxygen.
According to the present process, the amount of
polymerization occurring within the distillation apparatus
5 at temperatures as high as 150C is significantly reduced
in comparison with conventionally employed methods. In ~;
addition, the distillation apparatus may be operated at a
higher temperature and pressure than when using
conventional inhibitors thereby allowing a higher rate of
10 distillation throughput.
Further objects, features, and advantages of the
invention will become apparent from the detailed c
description which follows and from the claims.
15 Brief-Description of the Drawings
Fig. 1 is a schematic diagram of one embodiment
of the process of the present invention utilizing a three
column distillation train, and
Fig. 2 is a schematic diagram of another
20 embodiment of the process of the present invention ~T
utilizing direct injection of the vinyl aromatic feed into
the recycle column. r
~;:
Detailed Desc_ ptlon of the Preferred Embodiment
_ _ _ ~ _
The present invention employs
2,6-dinitro-p-cresol, hereinafter referred to as DNPC, and
a phenylenediamine derivative in the presence of oxygen, as
a polymerization co-inhibitor composition during the
heating of vinyl aromatic compounds.
The phenylenediamine of the present invention has
, ~
l224all
the formula: -
R1 - N - ~ - N - R2
wherein R1 is an alkyl group, aryl group or hydrogen, and
R2 is an alkyl group, aryl group, or hydrogen. It is ~-
preferred that the allcyl groups of R1 and R2
respectively contain from 1 to 12 carbons inclusive.
Examples of such preferred p'nenylenediamine derivatives
include p-phenylenediamine, N, N'dimethyl phenylenediamine,
N, N'-diethylphenylenediamine, N, N'-Bis~1,4-dimethylpentyl)
-p-phenylenediamine, and N-4-methyl-2-pentyl-N'-phenyl-p- ~K'
phenylenediamine.
It should be noted that N, N'-Bis (1,
4-dimethylpentyl)-p-phenylenediamine and
N-4-methyl-2-pentyl-N'-phenyl-p-phenylenediamine are
particularly preferred; however, N, N'-Bis (1,
4-dimethylpentyl)-p-phenylenediamine is the most preferred.
The distillation techniques of the present
20 invention are suitable for use in virtually any type of
separation of a readily polymerizable vinyl aromatic
compound from a mixture where the compound is subjected to ~-
temperatures above room temperature. By polymerization
inhibitor it is meant that unwanted polymerization of the
vinyl aromatic monomer is prevented at elevated
temperatures such as in a distillative apparatus. .'
Increasing the temperature in the apparatus has the -
advantages of a higher distillation rate, however, this
increased temperature can cause a higher rate of
polymerization which is counterbalanced by the introduction
~2248~1 -
'~
of the inhibitor of the present invention. In its most
useful application, the composition is applied to a
distillation mixture of vinyl aromatic compounds selected
from the group consisting of styrene, substituted styrene
5 such as alpha-methyl styrene, divinylbenzene, vinyl
toluene, vinyl naphthalene, and the polyvinylbenzenes.
This group is understood to include all structural isomers
of the aforementioned compounds. The preferred application
of the present invention relates to the distillation of
10 crude styrene.
The amounts of polymerization inhibitor added may
vary over a wide range depending upon the conditions of b~;
distillation. Generally, the degree of stabilization is r
proportional to the amount of inhibitor added. In
15 accordance with the present invention, it has been found,
based on vinyl aromatic feed to the B-T column 10 or the
recycle column 90, that a phenylenediamine concentration
generally between about 50 ppm and 2000 ppm and a DNPC
concentration between about 100 ppm and 2000 ppm have
20 generally produced suitable results, depending primarily r-
upon the temperature of the distillative mixture and the
degree of inhibition desired. Preferably however, the r-
phenylenediamine lnhibitor o~ the present invention is used
in concentration from about 50 ppm to about 1000 ppm and
the DNPC concentration is from about 250 ppm to about 1000
ppm. The preferred ppm ratio of phenylenediamine to DNPC
is 2:3. There is no particular order for mixing the
compounds of the present invention. In one particular
embodiment tl-ey are added together at atmospheric
30 temperature and pressure outside the distillation train and r
8 ~Z;~481~
injected therein. The distillation technique of the
present invention is suitable for use in virtually any type
of distillative separation of a readily polymerizable vinyl
aromatic compound from a mixture wherein the vinyl aromatic
compound is subject to temperatures above room
temperature.
Oxygen must be added to the system in order for
the phenylenediamine co-inhibitor to work properly. Oxygen
is added separately into the system to achieve a greater
concentration of oxygen in the required area. The oxygen
employed in the present invention may be in the form of
oxygen or an oxygen-containing gas. If an
oxygen-containing gas is employed, the remaining F-
constituents of the gas must be inert to the vinyl aromatic
compound under the distillation conditions. The most
useful and least expensive source of oxygen is air, which
is preferred for the present invention. The amount of
oxygen may vary widely, but generally it is desirable to
use that amount found in air.
Referring to the drawings, FIG. 1 illustrates a
conventional styrene distillation train comprising a
benzene-toluene fractionation column 10, referred to in the r
industry as a B-T column, an ethylbenzene or recycle column
12, and a styrene or finishing column 14. It should be
25 ~oted that the operational principles of the present
distillation method are highly suitable for use, with minor
modifications, with other distillation equipment used in
the purification of other vinyl aromatic compounds. As
shown in FIG. 1, a crude styrene feed is introduced into
30 the intermediate portion of B-T column 10 through feedline r
9 1224811
~,
16. B-T column lO may be of any suitable design known to
one skilled in the art and may contain any suitable number
of vapor-liquid contacting devices, such as bubble cap
trays, perforated trays, etc. Usually, however, column 10
5 contains less than forty distillation trays. Column 10 is
also equipped with a suitable reboiler 18 for supplying
heat thereto. Temperature of reboiler 18-is generally from
about 190F to about 250F.
W'nile most of the polymer is formed in the
10 ethylbenzene or recycle column 12, a small but significant
amount of the total polymer formed during distillation is
formed in the B-T column 10. Accordingly, a polymerization
inhibitor is desirable within this column. To prevent
polymerization in the B-T column 10, 2, 6-dinitro-p-cresol
15 hereinafter referred to as DNPC, is introduced into the B-T
column 10 as a separate stream through line 20, or it may
be incorporated into the crude styrene feed flowing through
line 16. To facilitate the process, the phenylenediamine
inhibitor may also be introduced into the B-T column 10
20 through line 20 or it may be incorporated into the crude ~-
styrene feed flowing through line 16. Although the ?
phenylenediamine inhibitor provides little or no inhibition ~'
in B-T column 10 due to lack of oxygen, it is transported
with the B-T bottoms through line 24 to the recycle column
25 12 where it acts as the primary inhibitor therein. When
the DNPC and/or phenylenediamine polymerization inhibitor
are added to the B-T column 10 as a separate stream they -
are preferably dissolved in a volatile aromatic hydrocarbon
diluent such as ethylbenzene. The position of the
30 inhibitor feedline 20 will normally be intermediate to B-T
' ~22481~
column 10 in order to achieve an inhibitor distribution
which is nearly coincident with the distribution of the
readily polymerizable vinyl aromatic compound within the
column 10.
Under the distillation conditions imposed in
column 10, an overhead stream comprising benzene and
toluene is removed via line 22. These low boiling aromatic
hydrocarbons are subsequently condensed and passed to
storage for further use. The bottoms product in the B-T
column comprising styrene, ethylbenzene, inhibitor and tar,
serves as a charge to the recycle or ethylbenzene column
12. The bottoms product is introduced into the
intermediate portion of ethylbenzene column 12 by means of
line 24 and pump 26. The recycle column 12 may be of any
suitable design known to those skilled in the art and may
contain from 40 to 100 trays. Preferably, however, the
recycle column is of the parallel path design.
Additionally, it is also preferable that the recycle column
contain a large number of trays, as many as 72, in order to
achieve a proper separation between the similar boiling
styrene and ethylbenzene. The B-T bottoms are preferably
introduced into the intermediate portion of the recycle
column 12.
A certain amount of inhibitor protection within
the ethylbenzene column 12 is provided by the
phenylenediamine composition introduced intermediate to
column 12 through line 2~, together with the B-T bottoms
fraction through line 30, or with the DNPC into the B-T
column through line 20. It is necessary to add air only to
30 recycle column 12 due to DNPC protection in the rest of the ~r~
1 1
- 1224811
.
distillation train. In the recycle column 12 a more
effective polymerization inhibitor is necessary due to the
high temperatures up to 150C therein which are desirable
in that column for a more energy efficient distillation.
5 By obtaining temperatures of at least 118C and preferably
130C or more, low pressure steam may bè recovered from an
overhead condensor (not shown) on recycle column 12.
Oxygen is introduced into reboilers 32 through
air purge lines 36 and 38 respectively. Alternatively,
10 oxygen may be introduced into reboilers 32 through sump or
boot 40 via line 42 if there is sufficient air
pressure/volume to reach the reboilers through line 43.
For the phenylenediamine to be effective, an equilibrium
amount of oxygen is dissolved in the liquid phase of the
15 column 12; however, the amount of oxygen introduced should
not exceed that amount which could cause explosion therein.
The oxygen is dispersed throughout the column 12 where it
works in conjunction with the phenylenediamine to inhibit
polymerization therein. The amount of oxygen necessary
20 will depend on the number and spacing of oxygen inlets
around column 12, and how efficiently oxygen and liquid
hydrocarbon are mixed therein. Therefore in practical
application, the oxygen flow is increased as long as
polymer yields are reduced, limited by the amount of oxygen
25 which would yield an explosive mixture. Complete
dispersion of air throughout column 12 does not generally ;~
occur, therefore the presence of DNPC therein works as a r
co-inhibitor at those locations where the effectiveness of
the phenylenediamine is diminished due to the absence of
30 air. Therefore, the DNPC continues providing
12
~224~
.
-~..
polymerization inhibition in those areas of recycle column
12 where there is an absence of air thereby providing an
overall higher polymerization inhibition effectiveness than
would have been achieved if only phenylenediamine had been
present by itself or in combination with other oxygen
- activated inhibitors.
Surprisingly, it has been found that not only is
DNPC compatible with the phenylenediamine, DNPC also works
as a polymerization inhibitor in the presence of air as
10 well as in its ~bsence. DNPC therefore also provides
inhibitor protection in addition to that provided by
phenylenediamine in those areas of the recycle column where
there is effective air dispersion. It has been found,
however, that when DNPC alone is used as an inhibitor in
15 the presence of air, the DNPC is exhausted more rapidly.
This may be due to the fact that more polymer free radicals
are generated in the presence of air. Therefore, to
maintain effective DNPC/oxygen polymerization inhibition f
over an extended period of time it is necessa~y to add more
20 DNPC inhibitor. Additional DNPC and phenylenediamine
protection may be obtained by the recycle of tar conl:~ining
DNPC/phenylenediamine back into recycle column 12 as
explained in U.S. Patent No. 4,272,344.
Alternatively, the phenylenediamine inhibitor may
25 be introduced with the DNPC inhibitor into the B-T column
10 through line 20 as a DNPC/phenylenediamine mixture.
There is no preferred order of mixing these together. A
random order of mixing at ambient temperature and pressure
will achieve suitable results. A portion of the
13 1224811
DNPC/phenylenediamine inhibitor travels through the B-T
column to the recycle column 12 together with the B-T
bottoms product.
The bottoms portion from recycle column 12
comprisinq styrene inhibitor and tar is withdrawn from the
reboiler area of recycle column 12 through line 60. The
recycle bottoms is then fed by pump 62 into the
intermediate portion of the styrene or finishing column 14
through line 64. Optionally, the bottoms material may be
introduced into the lower portion of the styrene column 14
through line 66.
The finishing column 14 may be of any suitable ~;
design known to those skilled in the art. A typical column
will contain for example, about 24 distillation trays.
Reboilers 68 are connected to sump 76 through line 78 and
pump 80. Reboiler 68 is generally operated at a
temperature from about 82C to about 121C. Generally,
inhibitor protection is adequately provided in this column
by the DNPC and phenylenediamine inhibitor present in the
20 bottoms feed. A portion of the tar from column 14 may be r-
recycled at least back into the ethylbenzene column 12
through line 88 in order to further supplement the DNPC
within the system. ?`
The high purity styrene overhead product is
withdrawn through line 74 from styrene column 14. The
styrene column bottoms product, composed of polystyrene,
undistilled styrene, heavy by-products and the DNPC/
phenylenediamine co-inhibitor, is withdrawn off the
reboiler recirculating line 78 and directed to a flash pot
30 54 via line 85 for further processing. In the flash pot 84 r
14
~224811
,~,
residual styrene is removed from the bottoms of the styrene
column and recycled back thereto through line 86. The tar
produced in the flash pot 84 is withdrawn from the system
on a continuous bas-s through line 83 or recycled back to
the recycle column 12 or B-T column 10 through line 88.
FIG. 2 illustrates the application of the
distillation method of the present invention to another
typical distillation train. A styrene feed is introduced
through line 91 into the intermediate portion of recycle
10 column 90, which is preferably of the parallel distillation
path design. Line 92 supplies the phenylenediamine
inhibitor to the recycle column 90. Heat is supplied to
the bottoms of column 90 by means of reboilers 94. Oxygen r
is introduced into reboilers 94 through air purge lines 96
15 and 98. Oxygen may be introduced directly into reboilers
94 through sump or boot 100 and line 101 if there is
sufficient oxygen pressure and volume to reach the ~-
reboilers through lines 97. In B-T column 122, benzene and
toluene are withdrawn as an overhead fraction through line
20 123 and are subsequently condensed for further use. An
ethylbenzene bottoms product is withdrawn through line 124 i,
and is recycled for further use. Reboiler 126 provides B-T rb
column 122 with the necessary heat for distillation.
The recycle bottoms product comprising
25 polystyrene, undistilled styrene, heavy by-products,
phenylenediamine and DNPC is withdrawn from recycle column 1-
90 through line 128. The impure styrene fraction is then
charged to the upper portion of the styrene column 130 by
means of pump 132 and line 133. Optionally, impure styrene
30 may be introduced into the lower region of styrene column ~:
12~481~
100 through line 134. A reboiler circuit comprising
reboiler 136 and pump 138 is attached to the styrene or
finishing column 130 for supplying the necessary heat
thereto. DNPC is preferably introduced with the
5 phenylenediamine into recycle column 90 through line 92.
The purified styrene overhead product is withdrawn through
line 144.
Reboilers 148 are connected to finishing column
sump 136 through recirculating line 145 and pump 150. The
10 finishing column bottoms produce is withdrawn off reboiler
recirculating line 145 for further processing in flash pot
146. Flash pot 146 recycles back into finishing column 14 ~;
through line 149. The tar produced during the distillation r
process is withdrawn through line 152 or recycled back to
15 the distillation train through line 154.
In another embodiment of the present invention,
an effective amount of 4-tert-butylcatechol is introduced
into the aforementioned distillation trains through recycle
columns 12, 90 in place of the phenylenediamine to act as a
20 co-inhibitor with DNPC. It has been found that DNPC and
4-tert-butylcatechol, hereinafter referred to as TBC, is an
efficient co-inhibitor system in the presence of air at 2
temperatures up to 140C. An effective amount of TBC,
based on vinyl aromatic feed to the B-T column 10 or the
recycle column 90, is from about 50 ppm to about 2000 ppm;
a preferred amount of TBC is from about 200 ppm to about
1000 ppm. The preferred ppm ratio of TBC to DNPC iS 2 to 3.
Use of the compositions and methods of the
present invention enables a distillation apparatus to operate
, . .
r
:.:
16
12Z4811
,~,
with an increased throughput rate as opposed to conventional
prior art processes since higher temperatures are permitted
in the recycle column due to introduction of effective
amounts of DNPC/phenylenediamine or DNPC/TBC inhibitor
composition. In addition, the DNPC inhibitor may be used in
the remaining fractionation columns to insure effective
polymerization inhibition where lower temperatures and
absence of air are encountered. Therefore, higher
distillation temperatures and higher pressure may be utilized
without the formation of objectionable amounts of
polymer. In this manner, the rate of distillation may be
increased without increasing the amount of polymerization --
which was previously experienced in the conventional
distillation procedures.
In addition by optimizing the distribution of
the DNPC/phenylenediamine or DNPC/TBC inhibitor within the
recycle column and by optimizing the distribution of DNPC
inhibitor in the remaining fractionation columns of the ~~
distillation train, greater temperatures may be achieved in
the recycle column than in conventional distillation
procedures to permit more efficient energy recovery
therefrom. ,-
In order to more fully describe the present
invention, the following examples are presented which are
intended to be illustrative and not in any sense limitative
of the invention.
Example 1
Two 100 ml reaction flasks were prepared. A
30 first (1) was charged with 25 grams styrene to which was i~-
17
12248~
added lO0 ppm DNPC and 50 ppm Flexone 4L, (a trademark of
Uniroyal Chemical, Flexone 4L having the chemical formula
N, N'-Bis (1,4-dimethylpentyl)-p-phenylenediamine as
discussed in the Uniroyal Material Safety Sheet covering
Flexone 4L). A second
(2) flask was charged with 25 grams styrene to which was
added 200 ppm DNPC. The flasks were fitted with magnetic
stirrers and septum closures and heated in a stirred oil
bath to 138C plus or minus 2C. The first flask was
purged with approximately 3 ml/min air run beneath the
liquid surface during the period of distillation. The
second flask was run under a nitrogen blanket. After two
hours the samples were tested for the degree of styrene
polymerization as a check, by measuring the changes in
refractive index. As a check, occasionally the monomer was
stripped off and the remaining polymer weighed. A final
polymer yield of 14.94% resulted in the first flask, ~~
whereas a final polymer yield of 18.24% resulted in Flask
2, indicating the superior inhibitory effectiveness at high
temperature of the phenylenediamine/DNPC co-inhibitor
system over the DNPC alone.
Example 2
A 100 ml reaction flask was charged with 25 grams
styrene to which was added 100 ppm DNPC and 90 ppm TBC.
The flask was fitted with a magnetic stirrer and septum ,;
closure and heated in a stirred oil bath to 1t8C plus or
minus 2C. The flask was purged with 1-2 ml/minute of air
run beneath the liquid surface during the period of
30 heating. The following results were obtained: ~
r
t
, ",,
1~
12Z4811 -
~.'
time (minutes) % polymerization
_______
O O
0.34
120 0.42
5 150 0.58
180 0.75
210 1.23 -
Comparison Exampl'e 2A
__ __ _
10A 100 ml flask was charged with 25 grams styrene
to which was added 100 ppm DNl?C. The procedure of Example
2 was followed and the following results were obtained:
time (minutes) % polymerization
O O
1560 0.50
120 12.52 (DNPC
consumed) ~,.
Comparison Example 2B
20A 100 ml flask was charged with 25 grams styrene ,~.
to which was added 90 ppm TBC. The procedure of Example 2 ~:-
was followed and the following results were obt~ained:
time (minutes) _polymerization
O O
2560 1.15
120 1.71 ,~
150 1.71
1~30 2.60
210 9.29
30 The results of Example 2 and Comparison Examples 2A and 2B
l9
:~224811
indicate the increased effectiveness of the DNPC/TBC
co-inhibitor composition at lower temperatures over DNPC or
TBC alone.
S Example 3
A 12" diameter pilot plant fractionation column
packed with Norton Intalox Packing was utilized to distill
a 1:1 mixture of ethylbenzene and styrene. The column had
a continuous feed and overhead draw to simulate a
10 conventional recycle column. 300 ppm of DNPC (based on
styrene content) and 200 ppm of Flexzone 4L (based on
styrene content) was introduced into the column. Air was S
introduced into the column at a rate of 1.2 liters/minute.
The reboiler temperature was maintained at 118C. sOttoms
15 were drawn off every 30 to 60 minutes to maintain a
constant reboiler level. At hourly intervals, the feed
rate, overhead rate, column temperature profile, reflux
ratio and overhead pressure were recorded. At 2 hour
intervals, bottom and overhead samples were collected. At
20 6 to 8 hour intervals, aldehyde and peroxide content in the
overhead were determined. The percent polymer in the fL~
bottoms was determined by vacuum evaporating a portion of
the bottoms to dryness, placing a portion of tne bottoms
product in a flask, heating the flask to drive off the
25 monomer, and then weighing the remaining amount which
comprises polymer.
The following results were obtained:
Polymer Yield: 0-0.21%
Aldehydes: 181-427 ppm
Peroxides: 13-25 ppm
i224811
As a further test, the oxygen rate was decreased
from 0.50 to 0.25 liters/minutes, then to 0.10
liters/minutes; the polymer yield ranged from 0.24 to
0.36%.
. 5 P:
Rxample 4
_
The procedure of Example 3 was followed utilizing
300 ppm DNPC and 200 ppm TBC. The reboiler temperature was
maintained at 118C.
The following results were obtained:
Polymer Yield: 0.80-1.22%
Aldehydes: 220-420 ppm
Peroxides: 25-141 ppm
As a further test, the oxygen flow rate was
15 decreased from 0.50 to 0.25 liter/min then to 0.10
liter/min; the polymer yield steadily increased from 1.29
to 2.09%. E
.~
Comparison Example 3/4
___ . . ...
The procedure oE Example 3 was followed except no
air was introduced to the column and 500 ppm DNPC alone was
utilized as an inhibitor. The reboiler was maintained at
118C. The polymer yield ranged from 3.97 to 4.25%.
Example 5
The procedure of Example 3 was followed utilizing
300 ppm DNPC and 200 ppm Flexzone 4L (the same
concentrations used at 118C in Example 3). The reboiler
temperature was maintained at 132C.
The following results were obtained:
` 21 i224811
Polymer Yield: 0.80-1.22%
Aldehydes: 280-346 ppm
Peroxides: 48-80 ppm
As a further test, the oxygen flow rate was
decreased from 0.50 to 0.25 liter/min, then to 0.10
liter/min; as a result the polymer yield increased slightly
from 1.24 to 1.47%.
Example 6
._
The procedure of Example 3 was followed utilizing
600 ppm DNPC and 400 ppm TBC. (Double the concentrations
used at 118C in Example 4.) Reboiler temperature was ~
maintained at 132C. r
The following results were obtained:
Polymer Yield: 1.01-1.36~
Aldehydes: 310-440 ppm
Peroxides: 107-167 ppm
As a further test, the oxygen flow rate was
decreased from 0.50 to 0.25 liter/min, then to 0.10
20 liter/min; as a result the polymer yield steadily increased .
from 1.57 to 2.92%.
;.
Comparison Example 5/6
________
The procedure of Example 3 was followed utilizing
1000 ppm DNPC alone as an inhibitor. (Double the
concentration of DNPC used at 118C in Comparison Example
3/4.)
The following results were obtained:
Polymer Yield: 2.70-3.00%
r
22
1224811
.~,
Aldehydes: 220-260 ppm
Peroxides: 49-96 ppm
While the present invention has been described in
various preferred embodiments and illustrated by numerous
examples, a skilled artist will appreciate that various
modifications, substitutions, omissions and changes may be
made without departing from the spirit thereof.
