AU576599B2

AU576599B2 - Preparation of chlorinate olefins

Info

Publication number: AU576599B2
Application number: AU44970/85A
Authority: AU
Inventors: James B. Akers Jr.; Douglas E. Leng; Randall J. Normand
Original assignee: Dow Chemical Co
Current assignee: Dow Chemical Co
Priority date: 1985-06-10
Filing date: 1985-06-10
Publication date: 1988-09-01
Anticipated expiration: 2005-06-10
Also published as: AU4497085A

Description

PREPARATION OF CHLORINATED 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 replete with descriptions of various methods for preparing chlorinated polyolefins. In general, however, the description merely states that the polyolefin is chlor- inated in aqueous suspension by introducing a stream of chlorine gas beneath the liquid 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 for preparing a chlorinated polyolefin, comprising the steps of: (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 sus¬ pension of jthe polyolefin or chlorinated polyolefin, thereby atomizing the chlorine, and chlorinating the polyolefin or chlori- nated polyolefin.

In general, the present invention provides a method and a 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 chlo¬ rine 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 degree of chlorination has been achieved, the product may .be separated and dried by any of several well-known means. 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. The present invention also is an apparatus for contacting a particulate solid suspended in a liquid with a gas, comprising: a vessel including an agitator for keeping the solids suspended in the liquid, and a port extending outwardly from the interior of the vessel for introducing gas into the vessel; and means disposed in the port for forming a jet of gas introduced into the vessel through the port, said high velocity ^" jet of gas having sufficient linear velocity to atomize in the aqueous suspension.

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.

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 temper- " ature-pressure conditions achieved for the chlorination 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 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 liquid. 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 ah internal passageway 5. The plug 4 forms a gas-tight seal with the port 3 and with a gas-delivery line 6. One end 5a 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 φ 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 φ 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 entrance end 4a of the^" plug 4 tapers outwardly to conform to the enlarged end 6a of the gas-delivery line 6, thereby forming a gas-tight seal when the flanges 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 gas injected beneath the surface of the suspension from the passageway 5 at a rate sufficient to atomize the chlorine and form an intimate mixture of the chlorine and the suspension. In order to atomize 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 g'as 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 result that any objects protruding into the reactor 1 beyond the vessel wall 2 below the liquid level are subjected to intense mechanical wear. By extending the exit end 4b of the plug 4 into the interior of the reactor 1 and by inclining the exit end 4b of the plug 4 away from the inside surface 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 three phases are intimately mixed.

The temperature at which the reaction is carried out is generally between 93 and 149°C (about 200° and about 300°F). Preferably, the reaction is initiated 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. 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.

The 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 experiment illustra¬ ting the invention, and showing the improved results obtained with the invention.

Experiment ϊ 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 (kg> 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 li_ hours, with the reactor temperature rising over that period of time from an initial value of 99°C (210°F) to a final value of about 138°C (280°F). The composition _ 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 product, " 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 reactor. Instead of chlori- nating the polyethylene at the same flow rate and a lower 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 required to produce the chlorinated polyethylene. Other ways of utilizing the improvements inherent in the present invention, including for example the prepa¬ ration of a more uniformly substituted, product, will be apparent to those skilled in the art.

Claims

WHAT IS CLAIMED IS:

1. A method for preparing a chlorinated polyolefin, comprising the steps of:

(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 sus¬ pension of the polyolefin or chlorinated polyolefin, thereby atomizing the chlorine, and chlorinating the polyolefin or chlori¬ nated polyolefin.

2. The method of Claim 1,^" wherein the linear velocity of the chlorine gas is. between 30.5 and 91.4 m/s.

3. The method of Claim 2, wherein the temperature of the suspension is between 93° and 149°C.

4. The method of Claim 1, wherein the polyolefin is polyethylene or polypropylene.

5. The method of Claim 2, wherein the polyolefin is polyethylene or polypropylene.

6. The method of Claim 3, wherein the polyolefin is polyethylene or polypropylene.

7. The method of Claim 1 including the step of separating and recovering the chlorinated polyolefin product.

8. An apparatus for contacting a particulate solid suspended in a liquid with a gas, comprising: a vessel including an agitator for keeping the solids suspended in the liquid, and a port extending outwardly from the interior of the vessel for introducing gas into the vessel; and means disposed in the port for forming a jet of gas introduced into the vessel through the port, said high velocity jet of^"gas having sufficient linear velocity to atomize in the aqueous suspension.

9. The apparatus of Claim 8, wherein the particulate solid is a polyolefin and the liquid is an aqueous medium.

•10. The apparatus of Claim 8, wherein the^" gas is chlorine.