DE2128134B2 - Process for the continuous polymerization of ethylene and a reactor for its implementation - Google Patents

Description

The invention relates to a method for continuous Polymerization of ethylene or A-Jjylen im Mixture with one or more comonomers at pressures of at least 300 at and temperatures of maximum 400 ° C in the presence of catalytic amounts of oxygen or of one or more Free radical initiators and from 0-20 mol% of a moderator, the flow rate being of the polymerization mixture is approximately constant over the entire length of the reactor and the reactor with a heating 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 is provided, and a tubular reactor for carrying out such a process.

The homo- and copolymerization of ethylene in the presence of oxygen or other radical-forming substances It is known that substances at high pressures are carried out in Kbsselautoklavcn or in tubular reactors.

The previous π tr-shaped reactors exist in generally from a very elongated tube of uniform diameter with a heating and Cooling jacket and a relief valve at the reactor outlet. Although such a reactor manufacture Permitted by ethylene polymers, its performance corresponds both in terms of sales and the operational safety as well as the achievable polymer quality do not meet today's high requirements. In particular, the conversion is limited, otherwise the frciwcrdcndc heat of polymerization increases would lead to the decomposition temperature of the reaction mixture being exceeded. Local, operational safety However, dangerous temperature peaks cannot be avoided. These temperature maxima also lead to an extremely heterogeneous polymer in terms of polymer structure and length, which in particularly unfavorable cases contaminates with carbon formed by partial decomposition is.

From DE-AS 12 39 855 a method for controlling the Rcaktionsablaufcs in the production of high pressure polyethylene from ethylene gas finally is known in which the current flowing through a reactor Mengcnsfrom Dtirchfitißdrtickimpiihe are superimposed and the Rcaktionsprodiikt introduced via a Knlspannungsvcntil in a high pressure separator and from this the polyethylene and unconverted ethylengas are withdrawn, the pressure being measured at the inlet of the reactor and the actual pressure (after suitable conversion) being fed as an actual value to a hat controller, which reacts to the oil voltage valve of the reactor

Furthermore, there is a targeted temperature control in the reactor, but this process is still in need of improvement, since it does not solve the problems described above to the desired extent. The same applies to the process according to DE-AS 12 98 271, according to which a tubular Ethylene high-pressure polymerization system is provided at the reaction tube outlet with a second valve connected to a separate separation system, which automatically comes into operation when the main outlet valve is closed when the measured temperatures exceed a certain maximum value.

The invention is based on the object of the generic method described at the beginning to train that it is the production of homo- and copolymers of ethylene of improved quality and in increased yield with greater operational reliability under the exclusion of dangerous temperature peaks. In addition, the invention is intended to be a Implementation of this procedure is particularly suitable Propose device.

The invention solves this problem by the characterizing features of the patent claims.

Should once during the continuous operation of the polymerization reactor according to the invention Despite the large number of control units, the measured along the reactor for uncontrollable reasons Temperatures and / or pressures exceed a certain maximum value or the measured jo If the pressure falls below a certain minimum value, the previously mentioned valve is automatically activated Reactor outlet closed and 'per reaction mixture so long by a second, with one separate polymer-monomer-Absciv 'desystem ver η tied valve until the temperature and pressure conditions in the reactor return to normal Ensure the course of the polymerization.

, The reactor of the invention made possible by its special design and by the variety of measuring and control units, as opposed to the usual tubular reactors compliance with well-defined preset, narrowly defined Polymerisalionsbedingungen and thus the production of polyethylene or Äthylcn copolymers especially v> homogeneous, ie high quality. In particular, there are no specks whatsoever. which both the mechanical and άπ. strongly deteriorate optical polymer properties ?.

According to the present invention, not only the homopolymers 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 Connections. v>

As stated above, a pressure valve is arranged in the front part of the reactor according to the invention. Further pressure measuring points are provided along the reactor. The pressure values determined at these further pressure measuring points are also taken into account to determine a uniform pressure level and temperature profile. According to a preferred embodiment of the invention, ethylene in a mixture with initiators, moderators and / or comonomers is fed into the devices distributed over the length of the regulator. Furthermore, it can be advantageous to provide one or more initiator injection devices distributed over the entire length of the reactor.

The above-mentioned advantages that can be achieved with the invention are based on careful coordination and integration of all units, regulating and actuating elements. This is the only way to guarantee trouble-free operation. It must be rated as surprising that the arrangement of further pressure measuring points along the reactor opens up the possibility of any changes along the reactor (e.g. the formation of polymer plugs) immediately during their formation and, thanks to the control system, such changes extremely quickly and extremely effectively Eliminate the disturbance.

The invention is further illustrated by the following example are explained in more detail.

example

5500 kg / h of a mixture of ethylene, 8.0% propane and 18 ppm oxygen, compressed to 2450 atm, are fed to the reactor according to the invention at the inlet and heated to about 155 ° C. in the front zone of the reactor by indirect heating A polymerization reaction, whereby the temperature of the reaction mixture rises. Part of the heat of polymerization is removed by indirect cooling of this zone of the reactor. At the point in the reactor where the temperature of the reaction mixture is expected to reach 280 ° C., a further 1200 kg / h of the above-mentioned ethylene mixture are introduced, the cross-section of the reactor from now on being widened so that the flow rate in the reactor is almost constant remain. In the flow direction downwards are the points at which the temperature of the fteaktionsmischung reached again, as expected 280 ⁰ C in spite of indirect cooling, additional 1500 kg / h and 1800 kg / h of ethylene mixture fed, wherein the cross section of the reactor, each of the feed points is expanded in such a way that the flow rate remains almost constant over the entire length of the reactor.

The setting of the pressure level and temperature profile in the reactor takes place via a depending on the Measured along the reactor temperatures and pressures controlled valve at the reactor outlet, which in addition, depending on the speed of the 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 customary manner. That at a conversion of 21.2% obtained polyethylene with a melt index of 7.2 and a density of 0.927 can be processed excellently into laminates and hollow bodies.

Claims (2)

Patent claims: 20th 2 ^r > so I, a process for the continuous polymerization of ethylene or ethylene in admixture with a or more comonomers at pressures of at least 300 atm and temperatures of at most 400 ° C in the presence of catalytic amounts of oxygen or of one or more radicals forming initiators and from 0-20 mol% of a moderator, the flow rate being of the polymerization mixture is approximately constant over the entire length of the reactor and the Reactor with a heating and cooling jacket divided into several independent segments and with a plurality of optionally operated devices distributed over the entire length of the reactor Feeding of ethylene is provided thereby characterized in that the reactor with several distributed over the entire length of the reactor Temperature measuring points and a pressure measuring point in the front part of the reactor, further pressure measuring points is provided along the reactor and with a valve at the reactor outlet, which depends on of the measured temperatures and pressures by means of suitable regulating and actuating elements is adjusted so that a uniform pressure level and temperature profile are maintained in the reactor is, and which depending on the speed of changes in the measured Temperatures and pressures suddenly drop by a certain amount until they reach a predetermined pressure is opened, and that the reactor with a second, with a separate Polymer-monomer separation system connected valve is provided at the reactor outlet, which c> 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 Press below a certain minimum value. 2. Tubular reactor for the continuous polymerization of ethylene or ethylene in a mixture with one or more comonomers at pressures of at least 300 at and temperatures of a maximum of 400 ⁰ C in the presence of catalytic amounts of oxygen or of one or more radical-forming initiators and from 0-20 mole% of a moderator, wherein the flow rate of the polymerization rates ^r * i-mix is over the entire reactor length approximately constant and the reactor with a split in several independent segments Ke: z and cooling jacket and having a plurality of via total reactor length distributed, optionally betric- v <driven equipment is provided for feeding ethylene, characterized in that the reactor with a plurality of distributed over the entire Rcakiorlänge Temperaturmcßslellen and a Druckmeßsicile in the front part of the reactor, "> further Druckmeßsiellen along the Keakior * and is provided with a valve aiii Rcaktoraiisgang, 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 suddenly depends on the speed of changes in the measured temperatures and pressures for a short time is opened 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 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.