Note: Descriptions are shown in the official language in which they were submitted.
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PREPARATION OF CHLORINATE~ POLYOLEFINS
The present invention relates to the pre-
paration of chlorinated polyolefins. More particularly,
the invention relates to an improved method for chlori-
nating polyethylene and polypropylene in aqueous suspension.
The patent and journal literature is repletewith descriptions of various methods for preparing
chlorinated polyolefins. In generall however, the
description merely states th~t the polyolefin is chlor-
inated in aqueous suspension by introducing a stream ofchlorine gas beneath the liguid level of the suspension.
In the absence of a method for efficiently dispersing
the chlorine gas in the suspension, the chlorination is
not as efficient nor the product as uniform as it would
be if the chlorine were better dispersed. The present
invention provides an improved method for the introduction
of chlorine gas into an aqueous suspension of a polyolefin.
The present invention is a method ~or
preparing a chlorinated polyolefin, comprising the
steps of:
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(a) suspending a particulate mass of a polyolefin
or chlorinated polyolefin in an aqueous medium;
and
(b) injecting a submerged jet of chlorine gas
traveling at a linear velocity of at least 18.3
meters per second (m/s) into the suspension,
thereby atomizing the chlorine, and
chlorinating the polyolefin or chlorinated
polyolefin.
In general, the present invention provides a
met'hod and suitable apparatus for the more efficient
chlorination of a particulate polyolefin or chlorinated
polyolefin suspended in an aqueous medium. The method
comprises subjecting the suspension of the polyolefin
or chlorinated polyolefin to a submerged jet of
chlorine gas traveling at a velocity sufficient to
atomize the chlorine into extremely finely-divided
bubbles intimately mixed with the aqueous suspension.
In general, a linear velocity of at least 18.3 meters
per second (m/s) or about sixty feet per second is
required~ The upper practical limit of the gas
velocity is the sonic velocity. After the desired
degr0e of chlorination has been achieved, the product
may be separated and dried by any of several well-known
m2ans. The term "atomize" as used herein means to
disperse the stream of chlorine gas into such minute
bubbles that the gas is intimately mixed with the
aqueous suspension, forming in effect a separate phase
near the point of introduction of the gas. The term
"submerged" means below the liquid level of the
suspension.
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The present invention also is an apparatus for
contacting a particulate polyolefin or chlorinated
polyolefin solid suspended in a liquid with a gas,
comprising: a vessel defining an interior space and
including an agitator for keeping the solid suspended
in the liquid; inlet means located in a bottom wall of
said vessel for introducing chlorine gas into said
vessel, said inlet means including a tubular member
attached at one end to said bottom wall and extending
outwardly and away from the bottom wall, jet-forming
means disposed in the tubular member for forming a jet
of chlorine gas introduced into the vessel, said jet-
forming means including a plug disposed within the
tubular member, said plug having an internal passageway
through which the chlorine gas is introduced into the
vessel, the plug having an end defining a surface which
is tapered and extends into the interior space of the
vessel rom an inner surface of the bottom wall, with
the tapered surface of the end of the plug defining
with the inner surface of the bottom wall an angle of
between about 120 degrees to about 150 degrees; and
means for connecting the tubular member to a chlorine
gas delivery line.
Suitable apparatus for the practice of the
present invention includes a vessel equipped with an
agitator for keeping a particulate solid suspended in a
liquid. In the vessel a port extends outwardly from
the interior of the vessel for introducing chlorine gas
into the vessel. Means for forming the high velocity
jet of chlorine introduced into the vessel through the
port is also included in the apparatus. This means
should provide the jet of gas at sufficient linear
velocity to atomize the gas in the aqueous suspension.
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Figure 1 is a cross sectional elevation view of
a portion of an apparatus according to the present
invention.
Figure 2 is a graph showing improved
temperature-pressure conditions achieved for the
chlorinat;on of polyethylene with the method and
apparatus of the present invention.
More specifically, Figure 1 shows a small
section of a chlorination reactor 1 made according to
the present invention. The reactor 1 includes a vessel
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wall 2, only a small portion of which is shown in the
drawing. The reactor 1 is equipped with means (not
shown) for keeping a particulate mass of solids suspen-
ded in a liguid. Suspension means for this purpose are
well-known in the art, and include for example mechanical
and electrical agitators or mixers. A port 3 extends
through and outwardly from the interior of the vessel
wall 2. Disposed within the port 3 is an internal plug
.~ 4 with an internal passageway 5. The plug 4 forms a
gas tight seal with the port 3 and with a gas-delivery
line 6. .One end Sa of the passageway 5 widens and
forms a continuation of the enlarged end 6a of the
gas-delivery line 6. The other end of the passageway 5
opens into the interior of the reactor 1. The exit end
4b of the plug 4 extends obliquely a short distance
into the interior of the reactor 1. By a short dis-
tance is meant a distance that is small compared with
the total length of the plug 4 and passageway 5. The
exit end 4b of the plug 4 defines an angle ~ of between
2.1 radians ~120 degrees) and 2.6 radians (150 degrees)
with the interior surface 2a of the vessel wall 2.
Preferably, the angle ~ so defined is between 2.3
radians (rad) and 2.4 rad and even more preferably it is
between 2.34 rad and 2.37 rad (134 degrees and 136
degrees). The entran~e end 4a of the plug 4 tapers
outwardiy to conform to the enlarged end 6a of the
gas-delivery line 6, thereby forming a gas-tight seal
when the f~anges 7, 8 and 9 of the plug 4, port 3 and
line 6 are fastened together as shown.
The preparation of chlorinated polyolefins is
carried out by suspending in water the polyolefin used
as reactor feed and the chlorinated polyolefin formed,
while subjecting the suspension to a jet of chlorine
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_5.
gas i~jected beneath the surface of the suspension from
the passageway 5 at a rate sufficient to atomize the
chlorine and form an intimate mixtur~ of the chlorine
and the suspension. In order to atomiæe the chlorine
it is necessary that the linear velocity of the gas
stream as it leaves the passageway 5 be at least 18.3
m/s. Preferably, the linear velocity of the gas is
between 30.5 and 91.4 m/s.
,
Besides forming a gas-tight seal between the
gas-delivery line 6 and the port 3, the plug 4 provides
needed protection of the passageway 5 from liquid
forces and from abrasion encountered in the environment
inside the reactor 1. Keeping the solids in suspension
requires that the slurry be vigorously agitated, with
the re~sult that any objects protruding into the reactor
l beyond the vessel wall 2 below the liquid level are
subjected to intense mechanical wear. By extending the
exit end 4b of the plug g into the interior of the
reactor 1 and by lnclining the exit end 4b of the plug
4 away from the insidè surf~ce 2a of the vessel wall 2,
the swirling mass of suspended solids is directed
inward into the reactor 1 and into the jet of chlorine
gas, thereby forming a combined stream of gas, liquid,
and solids in which the thxee phases are intimately
mixed.
~ he temperature at which the reactio~ is
caxried out is generally between 93 and 149C (about
200 and about 300F). Preferably, the reaction is
initiat.ed at a lower temperature, which is increased as
the reaction progresses. A trace amount of a wetting
agent may beneficially be dissolved in the water used
to suspend the particulate polyolefin and chlorinated
polyolefin.
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While the present invention is most advanta-
geously applied to the preparation of chlorinated
polyolefins, especially polyethylene and polypropylene,
it should be recognized that the invention is applicable
to any process requiring efficient contact between a
gas and a solid suspended in a liquid. Advantages of
the present invention for the chlorination of polyole-
fins include a more uniform distribution of chlorine in
,; the final chlorinated product; a drastic reduction in
frequency of chlorine feed line-plugging; and the
capability of operating the chlorination reactor at a
lower pressure, at a faster flow rate of chlorine, or
both.
T'ae invention will now be illustrated by the
following experiments. Experiment 1 is a comparative
experiment not according to the invention in which
high-density polyethylene was chlorinated using conven-
tional technology by introducing the chlorine into the
suspension at a rate less than that required to atomize
the chlorine. Experiment 2 is an expe,riment illustra-
ting the invention, and showing the improved ,results
obtained with the invention.
Experiment 1'
Chlorine was fed through a gas-delivery line
which extended below the surface of an agitated suspen-
'~ sion of high-density polyethylene powder in water, at a :
rate of 0.82 kilograms (k~) per hour per kg of polyethyl-
ene, and a linear flow velocity of 3.35 m/s ~11 feet
per second). The chlorine flow was continued for about
1~ hours, with the reactor temperature rising over that
period of time from an initial value of 99~C (210F) to
a final value of about 138C (280F). The composition
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of the chlorinated polyethylene separated and recovered
as product comprised 36 percent chlorine by weight.
The relationship between reactor temperature and pressure
is shown as the upper curve in Figure 2.
Experiment 2
Using the apparatus shown in Figure 1, a
chlorination was carried out using the same conditions
. and same temperature-time schedule used in Experiment
. 1, except the linear flow velocity of the chlorine was
changed to 54.9 m/s (180 feet per second). The final
pxoduct, after separation and drying, contained 36
percent chlorine by weight. The temperature-pressure
relationship observed in this example is shown as the
lower curve in Figure 2. Examination of the resulting
curves in Figure 2 shows that the use of the present
invention made it possible to achieve the same degree
of chlorination under otherwise identical conditions
while employing significantly lower pressures for
delivering chlorine to the reactcr. Instead of chlori-
nating the polyethylene at the same flow rate and alower pressure of chlorine, it is of course also pos-
sible to chlorinate at a faster flow rate and the same
pressure, thereby substantially decreasing the time
re~uired to produce the chlorinated polyethylene.
Other ways of utilizing the improvements inherent in
the present invention, including for example the prepa-
.ration of a mora uniformly substituted product, will beapparent to those skilled in the art.
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