DE1025143B - Process for polymerizing olefins and apparatus for carrying out the process - Google Patents

Description

GERMAN

For the application of the low-pressure process for polymerizing olefins according to Ziegler on an industrial scale As is well known, there are two particular difficulties with the scale. When polymerizing will be considerable amounts of heat are released (e.g. with polyethylene 900 kcal / kg polyethylene), which are difficult to get out of the system can be discharged. However, effective heat dissipation is important because at Temperatures above 80 ° destroy the catalysts used in the polymerization. To change it is very difficult to constantly stir the reaction mixture thoroughly in a large reaction vessel. In this polymerization, however, good stirring is precisely necessary because a contact component is made there is a precipitate which must be very finely distributed. That must also be attached to this contact polymerizing olefin in finest distribution. So far, one has to achieve this effect Blade stirrer applied. With these agitators, however, sufficient agitation can only be achieved in vessels up to a certain size can be achieved. With larger vessels, the stirrer shafts are too large and there are special storage required. The necessary rotational speeds can also be at large reaction vessels cannot be achieved. Finally, this occurs very often with low-boiling solvents Difficulties with the stuffing boxes.

To circumvent the first problem, it has already been proposed to use a solvent whose boiling point is in the range of the permitted polymerization temperature. By evaporating the Solvent, the heat of reaction generated during the polymerization is then essentially used up. However, this method has the disadvantage that because of the dependence on the boiling point in the Choice of suitable solvents is very limited. You can also get by boiling at different levels a fluctuating and too weak ethylene concentration, because the ethylene is released by the solvent vapor is diluted. As a result, the quality of the products suffers.

It has now been found that all of these difficulties can be avoided in a simple manner if one circulates a large excess of the olefin to be polymerized through the reaction system. Included the solvent is removed by the gas stream according to its vapor pressure; so it becomes the Dissipation of the heat of reaction exploited the evaporation of the solvent below the boiling point. Using the vapor pressure curve, for example of cyclohexane, it is possible to calculate exactly what amount of gas, for example ethylene, at a predetermined reaction temperature in the unit of time through the reaction vessel must be directed so that the

Method of polymerizing

of olefins and device

to carry out the procedure

Applicant:

Mining Company Hibernia
Aktiengesellschaft, Herne

Dr. Günther Keller, Dr. Bruno Schaeler, Wanne-Eickel,

and Dr. Oswald Wolff, Marl (district of Reddinghausen),

have been named as inventors

Unit released heat of polymerization is dissipated. By changing the amount of gas, it can then be done in a simpler way Way, any temperature in the reaction vessel can be guaranteed.

If a quantity of gas determined in this way and required for cooling is passed through the reaction vessel, then a considerable stirring effect is also achieved. If you increase the amount of gas, the agitation can can be significantly improved, and it reaches an optimal value with appropriate dosage, the one Exceeds the effect that can be achieved by stirring the leaves in small vessels. Be that way the two difficulties mentioned at the beginning were resolved at the same time.

In general, in the case of low-boiling solvents (up to 100 °), the amount of gas required for stirring is greater than that which is required for heat dissipation. So that there is still not too much solvent in the The reaction vessel evaporates and the temperature is too low as a result, according to the invention the The solvent dimension of the incoming gas is increased so that there is only that amount of solvent takes from the reaction vessel, which is just necessary to dissipate the heat of polymerization. This can be can be achieved once by not completely cooling the gas emerging from the reaction vessel, but only so far that there is just enough solvent in terms of tension when it is passed through the reaction vessel takes along than is necessary to dissipate the heat of reaction. But you can also use the gas completely cool down and thereby condense the solvent out again; The gas is then passed through a template with solvent immediately in front of the reaction vessel sent, which you can heat up as much as you want,

709 907/441

so that this gives the gas the desired solvent tension. The latter option has the Advantage that the solvent cannot condense out within the pipe and pump system.

Inert gases, e.g. nitrogen, methane, can also be added to the circulating gas. This has particular advantages the polymerization of higher olefins, such as propylene, butylene, carried out at high pressures and relatively low polymerization temperatures are either already liquid or in the solvent solve in significant amount.

The products obtained according to the process of the invention are more uniform and qualitatively better than that previously known because, on the one hand, a constant temperature is guaranteed and overheating are no longer possible and, on the other hand, a high and always constant olefin concentration is achieved.

The drawing shows an expedient embodiment of a device for carrying out the method shown.

In the reaction vessel 1 is the solvent with the contact. The circulating gas is by means of the pump 3 is pumped through the heated solvent reservoir 6 below into the reaction vessel and exits again at the top, then goes through the cooler 4, the entrained solvent condensing and separates from the gas in the condensation pot 5. The condensate is then either in the reaction vessel or returned to the template 6 in order to maintain the old solvent level. Through line 2 fresh gas can be fed to the system, through line 7 if the inerts are too enriched Circulating gas can be discharged.

example 1

In a large, according to the method of patent application B 37789 IV b / 39 c continuously charged reaction vessel, which is essentially an upright cylinder of about 800 mm diameter, there are 2 m ^{3 of} cyclohexane with the corresponding Ziegler contacts. The solvent throughput should be 1 m ⁸ / h and the polymer yield should be 100 kg / h. In this case 90,000 kcal per hour have to be removed, for which 1050 kg of cyclohexane have to be evaporated. If you want to polymerize under an ethylene pressure of 2 atmospheres, 450 m ^{3 of} ethylene are required, provided the temperature in the reaction vessel is kept at 70 ° and in the cooler at 25 °. To produce a good stirring effect, 500 to 700 m ³ / h of circulating gas are required. In order to keep the reaction vessel at 70 ° anyway, either the gas only has to be cooled down to about 35 instead of 25 °, or it is cooled down to 25 ° and reheated to 35 ° in front of the reaction vessel in the template 6. ^{84 m 3 of} 98% ethylene per hour are introduced through line 2, and ^{10 m 3 of} 82% ethylene are withdrawn from line 7 every hour.

Example 2

In a reaction vessel as in Example 1, in which propylene is to be polymerized discontinuously at a pressure of 10 atm, there are 2 m ^{3 of} n-hexane with the corresponding amount of Ziegler contact. A mixture of propylene and nitrogen is used as the circulating gas, and fresh propylene is always pumped into the system through line 2. The gas circulation is kept so high that a temperature of below 40 ° is maintained in the reaction vessel. This gives the resulting polypropylene particularly good physical and mechanical properties.

Claims (4)

Patent claims: 1. Process for polymerizing olefins in the presence of known ones dissolved in solvents or suspended catalysts according to Ziegler, characterized in that it is used in excess used olefin to be polymerized, to which inert gases can be added, in such an amount in the circuit that the stirring effect necessary for the polymerization is brought about, wherein at the same time so much solvent is evaporated below its boiling point by the circulating gas that as a result, the heat of reaction is dissipated and the polymerization temperature is kept as constant as possible will. 2. The method according to claim 1, characterized in that a larger amount of gas is circulated leaves than is necessary for heat dissipation, the gas emerging from the reaction vessel only is cooled to such an extent that when it is reintroduced into the reaction vessel it provides the heat dissipation required Takes the amount of solvent with you. 3. The method according to claim 1 and 2, characterized in that that one cools the circulating olefin completely and immediately before the reaction vessel again loaded with solvent to such an extent that the necessary heat dissipation in the reaction vessel Amount of solvent is entrained by the gas stream. 4. Device for performing the method according to claims 1 to 3, characterized by a circulatory system consisting of a reaction vessel (1), a pump (3) for the circulation of the Olefins, a solvent template (6), a cooler (4) and a condenser (5). 1 sheet of drawings © 709 907/441 2.58