DE2128134A1 - Process for polymerisation and polymerisation reactor for its implementation - Google Patents

Description

4-7 720 T

Bnhico AG-, Zurich, and Prof. Dr. Dr. K.-H. Imhausen

Polymerization process and polymerization reactor

for its implementation

The homo- and copolymerization of ethylene in the presence of Oxygen or other radical-forming substances at high Pressing is known to take place in kettle autoclaves or in tubular reactors.

The "previous tubular reactors" generally exist from a very elongated tube of uniform diameter with a heating and cooling jacket and an expansion valve at the reactor outlet. Although such a reactor manufacture Permitted by ethylene polymers, its performance corresponds both in terms of turnover and operational safety as well as with regard to the achievable polymer quality not today's high demands. In particular, the turnover is limited, otherwise the one that is released Heat of polymerization would lead to the decomposition temperature of the reaction mixture being exceeded. Local that Nevertheless, temperature peaks that endanger operational safety cannot be avoided. These temperature maxima also lead to an extremely heterogeneous polymer in terms of polymer structure and chain length, which is particularly unfavorable Cases is contaminated with carbon formed by partial decomposition.

(It has now been found that these disadvantages are in the; - 2 -

108807/1871

Avoid continuous polymerization of ethylene when using a specially designed reactor according to the invention is used.

G-UBJECT of the present invention is a process for the continuous polymerization of ethylene "at pressures of at least 3oo and maximum temperatures of 4oo ° C forming in the presence of catalytic amounts of oxygen or of one or several en radical initiators, such as azo peroxygen and Compounds, and from o-2o mol .- $ of a moderator, such as lower alkanes, cycloaliphatics, aromatics, chlorinated hydrocarbons, alcohols, ketones and aldehydes, the process according to the invention being characterized in that the internal diameter of the reactor is so "dimensioned that the flow rate of the polymerization mixture over the entire length of the reactor is approximately 'constant, and that the reactor with an irritant and cooling jacket divided into several independent segments and with several optionally operated devices for feeding in ethylene distributed over the entire length of the reactor, optionally in G-emic with initiators, moderator en and optionally comonomers and optionally with one or more initiator injection devices distributed over the entire length of the reactor and with several temperature measuring points distributed over the entire length of the reactor as well as a pressure measuring point in the front part of the reactor and with a valve at the reactor outlet, which is provided depending on the measured temperatures and pressures is set by means of suitable regulating and actuating elements so that a uniform pressure level and temperature profile is maintained in the reactor, and which, depending on the speed of the changes in the measured temperatures and pressures suddenly briefly by a certain amount until a given pressure

109887 / 1-871

is, and that the reactor with a second, with a separate one Polymer-monomer separation system connected valve is provided at the reactor outlet, which automatically punctures occurs "while the first valve is closed when the measured Temperatures and pressures exceed a certain maximum value or if the measured pressures exceed a certain value Fall below the minimum value. ·

The mode of operation of the reactor according to the invention goes out the following, but in no way limiting example:

Example ;

5 · 5οο kg / h of a mixture of ethylene, 8.0 ° / o propane and 18 ppm oxygen, compressed to 2,450 atm, are fed to the reactor according to the invention at the inlet and in the front zone of the reactor by indirect heating to about 155 ° C heated. At this temperature, the polymerization reaction begins, whereby the temperature of the reaction mixture increases. Part of the heat of polymerization is removed by indirect cooling of this zone of the reactor. At the point in the reactor at which the temperature of the reaction mixture is expected to reach 28o ° C., a further 1200 kg / h of the above-mentioned ethylene mixture are introduced, the cross-section of the reactor being expanded from now on in such a way that the flow rate in the reactor remains almost constant. In the downward flow direction, at the points at which the temperature of the reaction mixture again reaches 280 ° G as expected despite indirect cooling, a further 1,5oo kg / h or 1,800 kg / h of the ethylene mixture are fed in, the cross-section of the reactor is expanded in each case from the feed points on in such a way that the flow rate remains almost constant over the entire length of the reactor.

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The setting of the pressure level and temperature profile iin The reactor takes place via a valve on the which is controlled as a function of the temperatures and pressures measured along the length of the reactor Reactor output, which also depends on the speed changes in the measured temperatures and pressures suddenly briefly by a certain amount up to is opened to reach a predetermined pressure.

After leaving the reactor, the polymerization mixture is worked up in the usual way. That with a turnover of Obtained polyethylene with a seawater index of 7.2 and a density of ο.927 is excellent for laminates and process hollow bodies.

Should once during the continuous operation of the invention Polymerization reactor despite the large number of control units for uncontrollable reasons along the Reactor measured temperatures and / or pressures exceed a certain maximum value or the measured pressures fall below a certain minimum value, the aforementioned valve at the reactor outlet is automatically closed and the reaction mixture so long through a second, connected to a separate polymer-monomer separation system Discharged the valve until the temperature and pressure conditions in the reactor ensure normal polymerization again.

The reactor according to the invention is made possible by its special design and by the large number of measuring and control units In contrast to the previously usual tubular reactors, the adherence to precisely defined, prescribed, narrowly restricted ones Polymerization conditions and thus the production of polyethylene or ethylene copolymers are particularly homogeneous, a. H. high quality. In particular, there are no specks whatsoever

10 9 8 8 7/1671

on which both the mechanical and the optical Significantly deteriorate polymer properties.

According to the present invention, not only can homopolymerization of ethylene, but also the continuous polymerization of ethylene in a mixture with one or more Comonomers such as vinyl esters, acrylic acid derivatives, alkenes or mixtures of these compounds can be carried out.

As stated above, according to the front part of the reactor the invention arranged a pressure measuring point. It can be useful to arrange further pressure measuring parts along the reactor. The pressure values determined at these further pressure measuring points are also used to maintain a uniform pressure Pressure levels and temperature profile "are taken into account.

- 6 109887/1671

Claims (1)

Patent claims: Process for the continuous polymerization of ethylene at pressures of at least 300 at and temperatures of a maximum of 400 C in the presence of catalytic Ilengen oxygen or from one or more radicals Initiators and from ο - 20 mol .-% of a moderator, characterized in that the flow rate of the polymerization mixture is approximately constant over the entire length of the reactor, and that the Reactor with a heating and cooling jacket subdivided into several independent segments and with several Optionally operated devices 2 for feeding in ethylene and with, distributed over the entire length of the reactor several temperature measuring points distributed over the entire length of the reactor as well as a pressure measuring point in the front part of the reactor and provided with a valve at the reactor outlet which depends on the measured temperatures and pressures by means of suitable regulating and actuating elements is set so that a uniform pressure level and temperature profile is maintained in the reactor, and which depending on the speed of changes in the measured temperatures and pressures suddenly briefly by a certain amount until a given pressure is reached, and that the reactor with a second valve connected to a separate polymer-monomer separation system at the reactor outlet is provided, which automatically comes into operation, while the first valve is closed when the measured Temperatures and pressures exceed a certain maximum value or if the measured pressures fall below a certain minimum value. Process according to claim 1, characterized in that ethylene in a mixture with one or more comonomers, such as vinyl esters, acrylic acid derivatives, alkenes or mixtures this connection t will ORIGINAL BATHROOM 3 · Method according to claims 1-2, characterized in that that at the facilities distributed over the length of the reactor, ethylene in a mixture with initiators, moderators and / or comonomers is fed. 4. Tubular reactor for the continuous polymerization of ethylene at pressures of at least 300 atm and temperatures of a maximum of 400 ⁰ C in the presence of catalytic! Amounts of oxygen or of one or more radical initiators and from 0 - 20 mol -.% Of a moderator, characterized in that the inner diameter dec is ■ reactor such that the flow rate of the polymerization is approximately constant over the entire reactor length, and that the reactor with a heating and cooling jacket divided into several independent segments and with several optionally operated devices distributed over the entire length of the reactor for feeding in ethylene and additives and with several temperature measuring points distributed over the entire length of the reactor as well as a pressure measuring point in the front part of the reactor and is provided with a valve at the reactor outlet, which is set as a function of the measured temperatures and pressures by means of suitable regulating and actuating elements so that a uniform pressure level and temperature profile is maintained in the reactor, and which is dependent t the rate of changes in the measured temperatures and pressures is suddenly opened briefly by a certain amount until a predetermined pressure is reached, and that the reactor is provided with a second valve connected to a separate polymer-monomer separation system at the reactor outlet, which is automatic comes into operation while the first valve is closed if the measured temperatures and pressures exceed a certain maximum value or if the measured pressures fall below a certain minimum value, 109887/1671 -8- 5. Reactor according to claim 4, characterized in that he distributed one or more over the entire length of the reactor Having initiator injectors. 6. Reactor according to claims 4-5, characterized in that that further pressure measuring points are arranged along the reactor. Dr.T / hu 10 9 8 8 7/1671