DE1520227B2 - - Google Patents

Description

The invention relates to a process for the copolymerization of ethylene and vinyl acetate in a tubular reactor at temperatures of up to 300 ^° C. and high pressure in the presence of a catalyst.

It is known that ethylene copolymerizes with vinyl acetate can be, where high pressure and elevated temperature are used and the Polymerization is carried out in the presence of a catalyst (see French patents 1161217, 213 540 and 1226 382).

There is also a process for the continuous polymerization of ethylene at a temperature between 70 and 225 "C and a pressure of about to 2100 atmospheres in the presence of a non-polymerizable liquid medium, which serves as a dilution modifier, in the presence of a Polymerisationskalysators known, wherein the temperature of the exothermic polymerization reaction by injecting at least a portion of said dilution-modifying agent in the _essential: loan was j cooled to below the reaction temperature is controlled at present at a distance from each other ■ Set, wherein the injecting inde- 'pendent from the introduction This homopolymerization of ethylene by the so-called high pressure polymerization process can be carried out in an elongated tube

ίο Ethylene are, however, subject to certain restrictions. This is generally the case with the high pressure polymerization of ethylene in tubular reactors necessary to use chain transfer agents to control the molecular weight of the polyethylene.

This limits the applicability of the process to some extent, making it impossible to achieve high conversions since the effective concentration of the chain transfer agent increases as the ethylene polymerizes, resulting in the formation of a polymer of different molecular weight in the rear of the reactor tube than in its front parts leads. The concentration . _t can indeed to some extent be controlled by the introduction of \ of additional reaction components, but this is associated with an additional operation and is also not always satisfactory. Furthermore, if the concentration of the polymer component in the reaction stream becomes very high, the ethylene polymerization tends to clog the reactor. On the basis of the above observations and taking into account the quality of the polymer, limited conversions of about 1 to 20% in general and, using special procedures, 20 to 25% are obtained in high pressure polymerization in tubular reactors.

The object of the invention is therefore to create a Process for the copolymerization of ethylene and vinyl acetate, with achieving very high levels Conversions a copolymer of good quality and of a narrow molecular weight distribution is achieved.

The process for the copolymerization of ethylene and vinyl acetate in a tubular reactor k at temperatures of about 200 to 300 ⁰ C and higher; Pressure in the presence of a catalyst according to the \ invention is characterized in that introducing the catalyst in the polymerization without a transmission means at at least two different locations.

According to the method according to the invention, it is possible in the copolymerization of ethylene and vinyl acetate very high conversions with the achievement of a copolymer of good quality and to obtain narrow molecular weight distribution. The polymer composition is included almost independent of the conversion, i. i.e. that produced in the last part of the tubular reactor Copolymer is that produced in an upstream part of the tubular reactor Copolymer almost equivalent in terms of its properties. The advantages stated above are in the method according to the invention in particular by the specified type of cata- ■■ gate introduction achieved through which the occurrence of two or more polymerization reactions in Succession is brought about.

A particular advantage of the method according to

Invention is based on the fact that no material that acts as a transfer agent, must be present because the vinyl acetate itself takes on this function and, moreover, vinyl acetate under suitable conditions in the copolymer enters approximately at the same rate as the ethylene, the concentration of vinyl acetate remains essentially constant. This fact is added in an advantageous manner exploited by an additional catalyst to continue the copolymerization. The ethylene-vinyl acetate copolymer Melts a little lower than polyethylene, and the use of proportionately high reaction temperatures allows sufficient flowability in the reaction stream, even if it contains a high proportion of polymer.

According to one embodiment of the method according to the invention, vinyl acetate is used in an amount from 7 to 20 percent by weight of the monomers applied and the polymerization in the presence of 5 up to 30 parts per million oxygen based on the weight of the monomers carried out, and additional Oxygen is introduced in the same amount range downstream of the peak temperatures, the reactor temperature being kept above 200 ° C.

According to a further embodiment of the process according to the invention, the catalyst is introduced into an ethylene-vinyl acetate interpolymerization stream containing at least 35% by weight of the interpolymer, and the interpolymerization is continued at temperatures above 200 ° C in order to achieve high conversions. The catalyst can also be introduced into the Mischpolymerisationsstrom after a copolymerization has taken place to any substantial degree, that is, after an approximately 15 to 20 ° / ₀ by weight conversion to copolymer, wherein the copolymerization is continued under achieving high conversions. According to the process according to the invention, conversions to a high quality copolymer of greater than 50% can be obtained.

The ease with which high conversions to high quality copolymers after the process according to the invention for the copolymerization of ethylene and vinyl acetate, are obtained in marked contrast to results obtained with various other high pressure polymerizations or interpolymerizations. For example, many monomers occur when using Ethylene are copolymerized into the copolymer at a rate that so is very different from that of ethylene in that the monomeric composition of the resulting Copolymer, as the polymerization proceeds, changes significantly, making it extraordinary difficult, if not impossible, to obtain a product of constant composition when high conversion is desired in a continuous process.

In the method according to the invention, a temperature cross-section of an operating tubular reactor, which relates to the mean temperatures at various points in the reactor, generally has temperature peaks and troughs, the z. B. with reference to FIG. 3 will be described below. The process according to the invention can be carried out using a smaller amount of vinyl acetate in a suitable manner by adding catalyst at those points of the reactor at which the mean temperature is not higher than 250 ^° C., whereby an excessive temperature rise is avoided, and usually the catalyst is added at appropriate times to the average temperature during the polymerization at least at a height of about 200 ° C, preferably at least about 220 ⁰ C, at all points, in particular when oxygen is used as a catalyst to maintain.

The amount of vinyl acetate in the polymerization stream has a significant impact on that in the process results obtained according to the invention. It is essential that there be sufficient vinyl acetate to to significantly lower the melting point and / or the solubility of the resulting copolymer to increase significantly in the polymerization stream. In general, it is desirable to keep the melting point around 5 ° C or more below that of polyethylene, which has a proportionally much greater influence on the Polymerization properties caused. The range of about 7 to 20 or 25 percent by weight vinyl acetate, based on the copolymer, is of particular interest. Less than 7 weight percent vinyl acetate usually do not give polymerization properties significantly different from those that can be obtained when ethylene is polymerized alone.

The process according to the invention is also directed to an improved process for the production of rubber-like Ethylene vinyl acetate copolymers directed. In this embodiment of the invention Ethylene-vinyl acetate copolymers are high quality with a vinyl acetate content of, for example 35 to 75 weight percent in high conversions by polymerization in a tubular Reactor under high pressure at more moderate temperatures, not significantly above 200 up to 225 ° C, through repeated introduction of the polymerization catalysts, which are moderate with such Temperatures are effective.

In the method according to the invention, the working pressure is of essential importance. At pressures of 1055 or 1406 to 2812 kg / cm ² or higher, the vinyl acetate and ethylene enter the copolymer at about the same rate at suitable working temperatures. At pressures that are significantly below 1055 kg / cm ² , for example 703 kg / cm ² or less, the mixed monomers obviously do not polymerize at the same rate, which causes a change in the concentration of the vinyl acetate and the molecular weight of the product and, as a result, polyvinyl acetate is formed; one of the most significant effects of this is the reduction in molecular weight. The use of at least 7 to 10 percent by weight vinyl acetate in the process according to the invention significantly improves the internal temperature properties of the polymerization; If enough vinyl acetate is used, the temperature at a given point in the reactor tube is subject to only very small periodic temperature changes, for example _: 15 "C or less, as observed for short time intervals, for example 1 hour (although the temperature tends to increase in the course of the polymerization within periods of 20 to 40 hours or more to a greater extent from / u-

soft). In addition, the improved flow properties of the polymerization mixture are evident from the lower pressure drop across the reactor. When the required proportion of vinyl acetate is used at the appropriate polymerization temperatures, the pressure drop between the inlet end and the discharge end of the reactor (measured at the moment the outlet valve is wide open) is no more than about one ninth to one fifth of the working pressure or about 281 and 492 kg / cm ^2, respectively, for the reactor used in Examples 1 and 4 when the working pressure is about 2461 kg / cm ² . The pressure drop is expected to increase somewhat at higher conversions due to the longer effective reactor tube required to achieve higher conversions. However, when operating according to the preferred conditions described here, in particular at sufficiently high temperatures, even if higher conversions than those described here are achieved, the pressure drop across the reactor exceeds about 0.25 to 0.5% of the working pressure for per 1% of the monomers converted into ethylene-vinyl acetate copolymer not, and generally 4 to 8% of the working pressure for each of the catalyzed reaction taking place in the reactor, ie for each addition or introduction of catalyst, is not exceeded.

As can be seen from the temperature cross-section of the reactions shown in FIGS. 3 and 4 are illustrated and as will be described below, the polymerization process according to the invention can as a series operation of two or more individual ethylene-vinyl acetate copolymerization reactions being represented. The concentration of catalyst contemplated for each such reaction is generally about the amount that is necessary to obtain comparable results for a single reaction, whereby the total amount of catalyst in the process according to the invention is about / i times that Is the amount used in a single reaction when /; the number of reactions (or catalyst introductions) of the method according to the invention indicates: provided, of course, that an adequate small number of responses is provided. The total amount of the in the method according to the Invention used catalyst would if the entire amount at once or at a single Addition point would cause a carbonization, but is in the process according to the invention, despite the use of such large amounts of catalyst, no substantial decomposition of the Copolymer observed.

The total amount of catalyst used in the process according to the invention is general in the range of about 15 to 30 parts per million (molar basis) of the monomer charge.

The time between catalyst introductions is usually sufficient to allow the reaction to occur reaches a peak temperature and then cools down to a temperature low enough to ensure that a further introduction of the catalyst does not increase to an undesirable one causes high temperature. The time span of the individual reactions changes considerably Extent with the dimensions and heat transfer properties of the reactor. While the catalyst is usually introduced below 250 "C and below 150 ° C if a higher proportion of Vinyl acetate is used, it can be introduced at higher temperatures if it is in sufficient quantities small amounts, although it should be noted that the amount of catalyst also affects the molecular weight of the product affects what is to be considered.

The amount of catalyst introduced is generally equal to about 5 to 20 parts per million parts (monomeric Basis) of the monomer feed, e.g. at least about 5 parts by weight per million However, oxygen based on the weight of the monomer charge is not high enough to be below the High temperature polymerization conditions to cause carbonization. In some reactors it is however, it is not feasible to use more than 20 parts per million oxygen for each introduction, and it is generally necessary to use less than 30 parts per million oxygen with each introduction.

Amounts of oxygen on the order of 10 to 15 parts per million by weight based on the monomers Charge, are suitably introduced, and it is often convenient to be the same with each introduction Amount to use.

Generally, the catalyst will be diluted considerably prior to introduction to an appropriate level and can be diluted with either gases or liquids. It is useful in admixture with the monomer mixture of the reactor charge in concentrations of 100 to 1000 parts imported per million; the addition of a fairly large amount of cool monomers, along with the catalyst causes a slight drop in the internal temperature at the point of addition in the reactor, but which is usually not harmful. If the catalyst is in the form of a solution in such Hydrocarbons, such as n-pentane, η-hexane, etc .. is added, the catalyst is generally in Concentrations of 0.5 to 2 percent by weight or more of the hydrocarbon are used. The catalyst is usually fed continuously at the introduction points, but it can be cyclic, be added intermittently, etc.

The amount of catalyst and the polymerization temperature influence the molecular weight of the resulting copolymer in the opposite way, ie. higher catalyst concentrations and higher temperatures cause a decrease in molecular weight. Altering the catalyst concentrations and temperatures within the required ranges is essential to achieve the desired molecular weights, which are usually within the melt index range of about 0.5 to 20 decigrams min. (-D 1238 ASTM) lie at 19O ⁰ C, made. In some cases it may be desirable to run the later reactions at higher temperatures than the first, but to use lower amounts of catalyst in order to obtain a high molecular weight product and still take advantage of the beneficial effect of the high temperature on the mobility of the polymerization stream contains a high proportion of polymer to have. In general, the complete polymerization to maintain the temperature of the oil jacket to at least 170 ° C and often about 20O ⁰ C in Examples 1 to 3 carried out at a relatively high temperature, and it is usually desirable.

The polymerization process according to the invention

1 52-P ... 2.27

^{7 8}

requires a longer period of time and a greater length of pressure-flow pulses are preferably achieved by a given tubular reactor than by operating the drain valve at the outlet end of a polymerization reaction occurring in a single reaction tube. It should be noted that the reaction is carried out. In a reactor tube usual flow system compressors, pumps of given dimensions and heat transfer 5 and / or pressure boosters to the ethylene reaction properties, in which, for example, the catalyst component on the extraordinarily high reaction gate to /? Bodies introduced amount to both pressure to bring a device to thorough the time as the pipe length measured from the start of the poly- mixing the selected amounts of combined catamerization to the end (until it stops) lyser and vinyl acetate with the ethylene, a Equipment (measured for example from the time io tion to pass the mixture of them and from the initiation of the reaction which causes a temperature ethylene through the tubular reactor, a preliminary increase to a certain value, up to the heater which is used first and / or going back below a given value where the front part of the reaction tube, which stops as a preheater reaction), is times the values used for one, and a drain valve at the outlet end comprises simple polymerization in the same reactor tube 15 of the reaction tube through soft the end under the same conditions. reaction mixture of ethylene and vinyl acetate plus The process according to the invention can be carried out in each polymer in a polymer separation zone with a low-tubular reactor which flows to carry out the lower pressure. The pressure on the final reaction continuous polymerization of ethylene suitable mixture can be relieved and will be carried out. However, in order to achieve 20, it is usually very much a remarkable improvement in the conversion at this outlet valve - desirable, for example, from the standard lung and often a practical necessity - reaction pressure within the range of about keit, the reaction flow pressure-flow impulses 1055 kg / cm ² or preferably about 1758 to, and this can most suitably be ^{effected in a 3515 kg / cm 2} absolute in the reaction tube on a reactor capable of automatic cyclic pressure of 35 to 387 kg / cm ² in the separation zone. See operation of its drain valve at the end of the reac- As stated above, the flow stop tube is set up. It is often necessary for the flow impulses to bring about considerable flow release valves, advantageously by suitable handling of the flowing reaction mixture. On the basis of pulses at certain time intervals of such this description, a person skilled in the art is easily able to give different frequency and size that the pipe of 3o working conditions of this valve indicate to clogging accumulations of polymer on the reaction system the desired pressure flows inner walls essentially kept free to issue mungs impulses. In all cases in which, while a suitable mean temperature is imposed by operating or manipulating the valve Im through indirect heat exchange within the reaction, the valve may be wide open during a dwell time, which is the time 35 to one rapid pressure drop in the reaction tube during which the polymerization is proceeding, not to cause essential. This of course causes a corresponding exceeding to be maintained. The frequency corresponding increase in the pressure drop over that of the imposed stream impulses, the duration of the parts of the pipe in which the current is most restricted by the various phases of a single circuit and the accumulation of merisate, and the size of the impulses are of course one for the different 40 Increase in the flow rate of the reaction systems and conditions somewhat different- reaction mixture through these parts and so through the, however, they become through a suitable series of all parts of the tube. After this has taken place in a counter-checked manner, the valve is then immediately partially or completely closed to the extent that the pressure drop and the flow rate are changed, which causes the polymer to build up. As soon as the pressure in the reaction tube was up, prevent. In most cases, this should restore the previous pressure, which is the Stan frequency at least once every 2 minutes and the previous operating pressure of the process, or a little preferably once every fraction of a minute, such as once below, the drain valve is suddenly again 45 seconds to once per second. Once opened as wide as it was first, and a new one starts every few seconds, e.g. B. once every 3 to 10 seconds, 50 cycle. The described mode of operation can be continued in accordance with this as desired, and by far the preferred frequency. The time taken by a given embodiment and giving more superior results one part of the cycle to the same part of the next than that obtained when the frequency cycle elapses is considered to be the frequency of the cycle once every 20 seconds. This is how a frequency running process is called.

less than 20 seconds preferred. Advantageous for everyone who is less than 55, but can be entirely permissible

Flow impulse is intended to increase the resulting increased impulse by maintaining an equal-

Rate of reaction mixture through the moderate outlet stream from the reaction tube and

Pipe 2 to 10 times or multiple the standard change in inlet flow conditions, such as

be operating speed. Preferably, the by suitable handling of the pumps, which the

Flow impulses from corresponding pressure impulses ⁶ ° lead reaction mixture into the pipe, imposed

accompanied, they can be as Druckström- in this case.

ming pulses are designated, and the size The dimensions of the tubular reactors, in

can, as indicated, by the increase in which the method according to the invention is carried out

speed and / or the change in pressure can change to a significant extent,

(as measured at the inlet end of the reactor tube 65 Theoretical Considerations show that to achieve

will be measured and should be measured for each print, practical reaction speeds and product

Flow impulse approx. 5 to 25% of the standard speed, the reaction mixture continues

Operating pressure. passed through an elongated pipe

should be, which a rapid removal of the heat caused by the highly exothermic copolymerization of Ethylene is set free with vinyl acetate, allows. Heat transfer considerations that in connection with the fact that the polymerization reaction is a highly exothermic Reaction is and must be carefully controlled, make it desirable that the reaction tube one has a comparatively small diameter, and this is especially so when the conversion is per passage is very high. It is therefore desirable that the ratio of the length of the reaction tube to the inner diameter of the reaction tube is very high, for example at least about 300: 1 to 500: 1 and often up to to 1000: 1 and higher. For example, tubes with inner diameters of about 25 mm or larger up to about 3 mm and a length of about 240 m and longer up to about 12 m can be used.

The invention is explained in more detail below with reference to the drawing, for example. In the Drawing represents

F i g. 1 shows schematically an apparatus which is used for practicing the method according to FIG Invention is suitable;

F i g. Figure 2 is a flow sheet showing the reactor, feed lines, catalyst introduction pumps and illustrates the recirculation system;

F i g. 3 is a graph of the temperatures obtained at various points in the reactor plotted as reaction temperature versus residence time. Line A represents the temperatures in the multiple feed run of Example 1, while line B is a graph of the temperatures of a single feed run for comparison purposes;

F i g. 4 is a graph of temperatures which are obtained at various points in the reactor, plotted as the reaction temperature against time.

In Fig. 1 is a polymerization reaction tube with 10 designated. This tube is shown in a coiled shape, but it can also be another shape have, for example, be straight. A vertical position of the tube supports the flow of polymer. It should be noted that this is high pressure equipment and uses appropriate steels and construction conditions Need to become. The reaction tube 10 is shown surrounded by three successive jackets; a heat exchange means is passed through each of these jackets by means of the inlet and outlet locations shown directed. The first jacket with the reference number 12, the second jacket with the reference number 14 and the third jacket with the reference numeral 16 can be used as an optional arrangement of three consecutive Zones of the reactor are considered. Usually the heat exchange medium that passes through the jacket 12 is passed, hotter than the monomers entering the reaction tube 10 while the heat exchange medium which is passed through the jackets 14 and 16 is cooler than the reaction mixture in the corresponding zones of the reaction tube 10, so that exothermic heat of reaction is removed will.

The monomer mixture is withdrawn from a source via line 18 into which a small amount of catalyst is introduced (if catalyst is added prior to heating). The mixture is then brought to reaction pressure by any suitable means such as pressure boosters shown schematically by reference numeral 22. These can e.g. B. consist of two or more cylinders which are phase shifted by 180 ° with respect to the suction and compression, which takes place by means of pistons located therein. The mixture thus pressurized is then fed through line 24 to the preheater 26, in which the temperature, e.g. B. to 75 to 150 ⁰ C,

ίο is increased. The reaction mixture is then through the line 28 passed through a regulating valve 30 to the inlet of the reaction tube 10. The valve 30 is in suitably formed, and its actuation is with the actuation of the pressure intensifiers 22 in Aligned so that a fairly constant pressure of the reaction mixture entering the valve is maintained. This constant pressure is sufficient to overcome the pressure drop across the valve and also the standard working pressure in the reaction tube 10 during those parts of the circuit, in which the relief or relief valve 32 is closed or modulated to this standard working pressure maintain, provide. Other methods of delivering the reaction mixture ^ at the inlet of the reaction tube 10 at the desired speed and pressure are of course available, such as the omission of the valve 30 and only a control the speed of the pumps 22 to maintain a constant flow rate of the mass create. The drain or relief valve 32 is arranged at the outlet end of the reaction tube 10 to the To lower the pressure of the final reaction mixture of unreacted monomers and polymer and their To regulate the flow in the separator 34. The polymer is separated from the monomers in the separator 34, which is preferably kept above the temperature of the melting point of the polymer is, leaving a mass of molten ethylene vinyl acetate product is obtained by injection through valve 36 and line 38. The separator 34 is shown schematically and can have any suitable construction. It goes without saying that the drawing is not to scale and that the separator 34 is large enough to hold a 'substantial amount of the molten polymer to keep. The separated monomer is recovered through valve 40 and line 42.

The drain or relief valve 32 can be operated by hand. For technical production over However, the valve should be extended for long periods of time by suitable means, which are designated by 44, operated and regulated automatically. While the various mechanical and electrical arrangements, those used to achieve the desired cyclic actuation of the relief valve 32 can be, are numerous and can be appropriately chosen by those skilled in the art, becomes one simple and preferred arrangement schematically in FIG. 1, the actuation of the valve 32 in response to the pressure at the inlet end of the reactor 10 by an appropriate or pneumatic one Control line 46 takes place. The valve actuation "mechanism 44 is set in such a way that it maintains a constant pressure at the Pressure regulating point at the inlet end of the reactor tube 10 maintains. In other words, if the pressure at the pressure control point via the

11 12

agreed and previously set standard working pressure curve for multiple introduction very similar to that

increases, the valve 32 opens automatically a little, so the single tip of the curve for a single introduction

that in this way every further increase in pressure is reduced.

and the pressure is dropped somewhat. According to a further feature, the invention comprises once the pressure at the pressure control point under the 5 training the use of a circulation system in a If the standard working pressure falls, valve 32, ethylene-vinyl acetate copolymerization, closes automatically by a small amount sufficient to provide essential conditions for effective use return the pressure to the preselected value. such a system. It can easily be seen that This modulation process is known to the person skilled in the art. Even at moderate pressures, vinyl acetate tends to knows. For example, a working pressure of io at elevated temperatures in the presence of Kataly-13 600 kg can be preselected, and the system can polymerize and free radicals have sufficient sensitivity to prevent such polymerization Maintain pressure within 45.3 kg. According to one of the circulating systems, it is a significant problem Working method to bring about poses. However, it has been found that such Flow pulses in the process according to the 15 polymerization can be avoided in that Invention, the control of the drive equipment is sufficient time and the polymerization flow device 44 for the drain valve 32 in response to reactor space can be reduced to about 230 ° C or below to cool the pressure signals passed through line 46 before being discharged from the reactor anticipating by a timing device, and further by having a drain vessel subject. The timer is set to 20 used to select the polymer product from the not that they separate at the beginning of the cycle to the response of the reacted monomer. As a result of that Motor 44 to the taking place via line 46 enough cooling space against the discharge end of the Pressure display is running ahead or a response to the reactor is provided, is not only prevented and causes the drain valve 32 to cool the materials well, rather than it will is opened. At the end of the previously set time, there is enough reaction time left to last which usually take less than 1 second for the catalyst to tolerate substantially, timer 48 causes valve 32 to be consumed; any residue of catalyst will is closed immediately or at least in a throttle - obviously with the polymeric product in the position goes. The valve 32 is held until the drainage vessel is disconnected, thereby eliminating the monopressure within the reaction system, 30 mers return to the cycle in a catalyst-free state has returned to the standard working pressure. That can be let through the circulation system. It is also Time switch system can be designed in such a way that a desired, sufficiently small amounts of catalyst new circuit then immediately with another opening at the last introduction or the last injection of valve 32 is started to use a sudden so that it is essentially in the kata pressure drop and pressure-flow impulse to give 35 lysator is consumed (one suitable for dispensing or the circuit cannot be closed at this point - maximum temperature is around 250 ° C). Habits rather, it can be a normal loan, the last point of introduction before the abbot of the drain valve for a short period of time giving end of the pipe to a temperature drop be approved before the end of the cycle. If from 40 to 60 ° C or more to allow in the pipe, the latter is the case as soon as the standard 4 ° after the peak temperature is reached. Man working pressure has been reached at the pressure regulating point, further cooling within the pipe could occur line 46 is to allow the signal to motor 44, but this would not be the most effective dodge the valve 32 begins to modulate to represent the use of the reactor space. Moreover is To maintain standard working pressure, and this it is essential to maintain a certain minimum temperature continued until the timer to maintain the circuit 45 right to a mobility of the one lets start again. containing high proportion of polymer product

In Fig. 2, the designations of the flowing stream must be ensured. The polymer separation vessel

no further explanation. The illustrated or drainage vessel in which the product ends up

Circulation system works effectively despite the fact that the reactor is collected is generally available

that one might expect the vinyl acetate in the 50 to be under a pressure that is between atmospheric

unpolymerized monomers polymerized and one at the beginning of a polymerization run to 70

Creates contamination in the return pipe. or 141 kg / cm ² during the run, the vessel

However, the lines from the catalyst introduction or will expediently at a pressure of about

Injection pumps can be operated in suitable places at the 105 kg / cm ² , and the temperature in the

The reactor must be connected, and part of the catalyzer drainage vessel is high enough to allow easy ejection

Sators can of course also allow at any point in the polymer from him and is in

the feed line to the reactor either before or generally in the range of 180 to 200 ° C.

introduced or introduced after the compression stage

be injected. Examples explained in more detail.

In Fig. 3, line A illustrates the temperature 60.
temperature peaks and valleys of the method according to Bei- B e 1 s ρ ι e 1 1
Game 1, while line B is a comparable process. A polymerization was carried out in a reactor with a single introduction carried out in the same as that of FIG. 1 is similar, but five reactor tubes at 2461 kg / cm ² and using different oil jacket zones and a facility of 12 to 14 parts per million oxygen as a catalyst for feeding the catalyst to different sator to achieve a conversion of 13.5 ° / ₀ points along the course of the reaction tube. illustrated. A comparison of lines A and B The reaction tube had an inner diameter clearly shows that the various tips of 7.9 mm and a length of 58.5 m, oxygen

was mixed with the monomers before heating and the reaction tube in two different places fed. The following values illustrate the conditions and results of the experiment:

Total flow, kg / hr 18.2

Oxygen concentration

Inlet flow, parts by weight per million .... 8 Introduction at "Λ". Parts by weight each

Million 15

Introductory run at "ß", parts by weight per million " 15

Internal temperatures

Peak temperature after inlet, "C 250

Temperature at <> A « 215

Mushroom temperature according to "A" 240

Temperature at »ß« 200

Mushroom temperature after »ß« 280

Oil jacket temperature, C

Zone 1
Zone 2
Zone 3
Zone 4
Zone 5

1.8 m
1.5 m
1.5 m
1.5 in
1.5 m

215 190 180 185 180

Pressure drop across the reactor, kg'cm ² ... 211

Conversion. % 57.5

Vinyl acetate. Weight percent of the mono-

feeding 10.0

Polymer properties

Density, g ml 0.9270

Tensile strength wedge at break, kg.cm- 128

Elongation at break. "" 670

Melt index. Decigram min. At 190C 3.7

The product was qualitatively comparable to that obtained by feeding at a single point under the same conditions. The entry point ". ·!" Was about 23.4 m from the inlet end of the pipe and the point "ß" about 43.8 m from the inlet end. The feed points were 12.1 to 15.2 m below the points of the peak temperature. The last feed point was about 15.2 m from the end of the tube, so that the reaction temperature remained about 6.0 m before it left the reaction tube. The polymerization was carried out at a pulse frequency of 5 seconds and a pulse intensity pressure drop of 105 kg cm ² at the inlet of the reaction tube.

Example 2

An experiment was conducted approximately under the conditions of Example 1 with the exception that a little lower temperatures were used at the oxygen supply points and the vinyl acetate 15 percent by weight of the monomer feed. The conversion was 46%. and the The mixed polymer had a density of 0.9317. The unreacted monomers can, as from the The flow diagram of FIG. 2 can be found. be fed back into the circulation with good results.

Example 3

A batch was made with 10 weight percent vinyl acetate in the monomer charge and no oxygen in the monomer inlet stream, but with an introduction of oxygen at four points along the reaction tube. It became a 46% conversion achieved.

One of the advantages of the method according to the invention is the fact that the need for the presence of some external chain transfer agent and, consequently, the adverse results and necessity of different concentrations thereof to regulate the concentrations should be avoided. However, it can in special cases

ίο be desired, means of transmission from different Reasons to introduce, and such chain transfer agents as low saturated hydrocarbons, in particular those that contain at least 3 carbon atoms, and acetone can be used in minor Use amounts or higher amounts, such as 0.3 to 15 mol percent by weight, based on the ethylene! will. The method according to the invention is mainly based on a dry method or a Process directed without solvents, and although small amounts of solvents or water may occasionally be present, obviously does not require the method according to the invention the large amounts of benzene or other solvents or water required for various polymerization reactions characteristics are such as amounts greater than 10 percent by weight of the ethylene feed.

The above examples illustrate the

Improvements in oxygen catalyzed

High pressure interpolymerization of ethylene and vinyl acetate, however, the invention is also based on improvements in interpolymerization of ethylene and vinyl acetate, which are used by any other free radical catalysts, as usual in high pressure polymerization of ethylene, particularly those peroxy oxygen compounds which have decomposition temperatures in the Environment of about 160 ³ C, at which oxygen initiates the ethylene polymerizations. Examples of peroxy compounds which are often used in such polymerizations are 2,4-dichlorobenzoyl peroxide. Caprylic peroxide, lauroyl peroxide, t-butyl peroxyisobutyrate, benzoyl peroxide, p-chlorobenzoyl peroxide, di-t-butyl diperphthalate, t-butyl peracetate, t-butyl perbenzoate. Dicumyl peroxide, t-butyl peroxide (technical), methyl ethyl ketone peroxide, di-t-butyl peroxide. p-menthane peroxide, pinene peroxide, cumene peroxide and 2,5-dimethylhexane-2,5-dihydroperoxide. The catalysts are generally used in amounts such as to give polymerization effects equal to those obtained in the above-described ranges of oxygen amounts, which in most cases are molar percentages equal to those in which oxygen is used.

While Examples 1 to 3 relate to improvements in interpolymerization, which are lower Amounts such as about 10 to 20 percent vinyl acetate based on total monomer charge, is the multiple introduction in interpolymerizations. which higher proportions of vinyl acetate, such as 25 to 75 weight percent of the monomer charge. use, usable, although there is a Number of special cases is necessary to change the reaction conditions. For example, it is due to the Chain transfer effect of the high vinyl acetate concentration necessary at low temperatures to work to obtain a product with a sufficiently high molecular weight, and the use

15 16

such lower temperatures continues its use apart from its effect on the properties

The vinyl acetate content also has a sufficiently low decomposition rate of the polymers from catalysts

temperatures, as they arise from the aforementioned direct influence on the polymerisation to be used

Can be selected in advance. conditions to achieve high molecular weights

The invention also acts on this tendency to obtain high conversions together. There Reduction of the molecular weight counteracts by both high polymerization temperatures as well The catalysts are added in proportions to encourage the production of polymers A fairly high conversion without high temperatures and low molecular weight has been found to obtain temperature peaks that have usually been present that it is necessary to have means of erecting, if, in order to achieve high conversion, relatively low levels of polymerization are maintained Catalyst is added all at once. to find temperatures in the invention, at which The polymerization stream has been found to have vinyl acetate levels in the range of 35 to for continuous polymerization in a tubular- 75 percent by weight.

A major advantage of the multiple catalyst flowable is sufficient for the small diameter reactor remains, even if it has a high level of solids, its effectiveness lies in its effectiveness when used in accordance with content from the high conversion and the invention for producing improved Umrelativ moderate temperatures are used. Conversions of ethylene-vinyl acetate copolymers

The mixed polymerisation mixture is even used for sat rubber. Thus, an absence of solvents or the like is sufficient to implement the invention in adding additional catalyst to add the polymerization in a flowing analyzer and to provide the correct ambient temperature mixture at conversions of 35% and above to allow additional polymerization for, even if only moderate polymerisation-high conversions are allowed. At a particular temperature in the range from 150 to 200 ⁰ C exist. It should be noted that the aforementioned temperatures are added to the polymerization stream after 20% lower than those generally converted into a bulk polymerization of ethylene or ethylene interpolymer at 25 or more of the monomer therein are,
which contains small amounts of vinyl acetate as in Example 1. According to this embodiment of the process, one and 3 will lead to considerable conversions into free radical-containing polymerization catalyst in a tubular reactor. It is necessary to be used for low temperatures. It is important to avoid high polymerisation temperatures if you notice that the expression "low temperature high proportions of vinyl acetate are used here" relative to the polymerisation catalysts, a copolymer of usable high motors is used to produce catalysts which have the molecular weight to obtain. In general, it is desirable to polymerize in the range from about 100 or 120 to the polymerization to form interpolymer 160 ' ³ C, rather than characterizing it in higher temperature ranges with average molecular weights (such as those governing 35. In addition, high polydes will be determined by osmotic procedures). to carry out in the merization temperatures by adding the Kata range from 20,000 to 30,000. In the case of lysators in separate portions, in order to regulate the exothermic temperature resulting from the polymerization, which is much above 200 to 250 ° C, in the presence of large amounts of vinyl acetate rise, avoided.

the tendency to form a copolymer of an undesirable 4 ° The temperature curve of a low molecular weight in operation. If a tubular reactor has, based on the medium-continuous polymerization through the use of leren temperatures, at various points of the effective coolant or heat exchange medium and reactor generally temperature mushrooms and troughs on multiple introduction of initiators for low (as e.g. in the following 4, the temperature is sufficiently controlled so that the mass 45 is shown). This execution of the process can keep the polymerization at temperatures below 2OO ' ^J C suitably by the addition of the catalyst and only a small part of the polymer points of the reactor at which the average temperature in the range of about temperature not higher than about 160 ⁰ C, and generally reaches 200 to 225 ^: C, it is possible, however, high my in places where the average temperature conversions in ethylene-vinyl acetate mixed poly-5 ° below 150 '"C, are achieved, whereby any Merisate of high molecular weight with excessive vinyl acetate temperatures of the resulting increased contents of 35 to 75 percent by weight or the like to th conversion are avoided.

The reference to the vinyl acetate content of the doors should not exceed 200 ° C, and the top polymers refers to the polymer, which is not higher than 200 to 55 temperature in the reactor the polymers present and produced from vinyl acetate 225 ^ C.

has been. In general, the vinyl acetate content is organic peroxy catalysts

in this embodiment of the invention in that preferred in this embodiment according to the invention,

Range from 35 to 75 percent by weight and leads to particularly those peroxy catalysts which one

Generation of ethylene-vinyl acetate copolymerization at temperatures not higher than 60

ten with rubber-like properties, d. H. Introduce 160 ° C again. The special temperature at

contraction after expansion and slight lead- which the catalyst is introduced depends on natural Shape change. At really low stay- borrowed to some extent from the special one Deformation properties may require their catalyst, but is generally in the range

be at least a vinyl acetate content of 40% to 65 from 100 to 150 ° C, usually at about 120 to 140 ° C.

and it may be desirable, in the range of benzoyl hydroxide, e.g. B. very good at 120 to 130 C. Stay from 40 to 60% vinyl acetate to be introduced as well. For a catalytic converter with a

best contraction properties. higher introduction temperature, for example t.-butyl-

peracetate, it may be desirable to introduce at about 160 ⁰ C. Preferably Peroxydkatalysatoren wherein the decomposition temperature is assumed to be the temperature at which the half-life is 1 minute are used which do not decompose at temperatures higher than 160 ⁰ C. These catalysts include, for example, 2,4-dichlorobenzoyl peroxide, caprylyl peroxide, lauroyl peroxide, t-butyl peroxy isobutyrate, benzoyl peroxide, p-chlorobenzoyl peroxide, di-t-butyl diperphthalate and t-butyl peracetate.

One of the advantages of using a thin-walled, elongated tubular reactor of small diameter is the rapid dissipation of the exothermic heat of reaction. The immersion of the reactor in a bath contributes to the heat distribution, the bath temperature influencing the rate of heat loss. However, the bath temperature should not be so low as to prevent or terminate the polymerization. To the polymerization to effect according to this embodiment of the invention, it is desirable to use bath temperatures in the range of 100 to 140 ⁰ C.

In Fig. 4, line C illustrates the temperature peaks and troughs of a process which includes two catalyst introductions, while line D represents a comparable process with a single introduction. The time is divided by the position of the pipe section (pipe number) in the reactor consisting of 20 pipes. The method, which is illustrated by the line C, resulted in a 32 ° / ^e o'g conversion while the illustrated by the line D method had a 13 ° / _o by weight conversion. A comparison of lines C and D shows that the peaks with multiple inserts of the single peak of a curve are very similar with a single addition.

The following examples illustrate this embodiment of the invention in more detail.

Example 4

A polymerization was carried out in one of the FIGS. 1 similar reactor carried out, but with 5 different oil jacket zones of the same length and with facilities for the introduction of the catalyst at various points along the reaction tube. The reactor was tortuous in shape and had twenty sections called "pipes" with four pipes for each of the oil jacket zones. That The reactor tube had an internal diameter of 7.9 mm and a length of 58.2 m. Benzoyl peroxide was introduced into the reaction tube at two places. The catalyst was not the monomers The inlet end of the reaction tube is added. The following values explain the conditions and results of the attempt:

Total flow, kg / hr 18.5

Benzoyl peroxide concentration, mole / mole
Monomer

Introduction to »Λ«, parts per million 12
Introduction to »ß«, parts per million 9

Internal temperatures, ⁰ C

Temperature at t> A « 125

Peak temperature according to "A" 210

Temperature at »ß« 120

Peak temperature after »ß« 200

Oil jacket temperature,

Zone No. 1

Zone No. 2

Zone No. 3

Zone No. 4

Zone No. 5

132 132 120

125 125

Dwell time ranges, seconds 150 to 300

Pressure drop across the reactor, kg / cm ² ... 281

ίο Joint size, kg / cm ² 105

Conversion,% 32

Vinyl acetate, weight percent of the monomer charge 45

The polymerization was continued continuously without interruption for more than 17 hours. The entry point "Λ" was about 7.6 m from the inlet end of the pipe and the entry point "ß" about 38 m from the inlet end. Samples of the

The ethylene-vinyl acetate copolymer had a vinyl acetate content of 45 to 46 percent by weight, a melt index (decigrams / minute at 150 ^° C.) of 13 to 15 and a density of about 0.97. The good quality and suitable high molecular weight of the interpolymer is demonstrated by the following properties of a compression molded white material:

500 ° / o module, kg / cm ² 105 to 115

Tensile strength, kg / cm ² 162 to 169

Elongation, ° / ₀ 570

Reduced permanent deformation ¹ ),% 7 to 8

^J ) Percentage of expansion not regained 10 minutes after breakage.

The press-formed mass was formed by a heat treatment of 30 minutes at 160 ⁰ C of the following composition:

Parts by weight

Ethylene-vinyl acetate copolymer .. 400

Rutile titanium dioxide 200

Precipitated silica 40

Dicumyl peroxide on calcium carbonate .. 16

B e i s ρ i e 1 5

Using the reactor described in Example 4, a polymerization was carried out as follows:

Total flow, kg / h

18.5

Benzoyl peroxide concentration, mole / mole monomer

Introduction at »Λ«, parts per million 9 to 16

Introduction at »ß«, parts per million 9 to 16

Internal temperature, ⁰ C

Temperature at »Λ« 125

Peak temperature according to "A " 215

Temperature at »ß« 130

Peak temperature according to »ß« 210

oil jacket temperature, ⁰ C

Zonel 132

G ₅ zone 2 132

Zone 3 120

Zone 4 132 to 123

Zone 5 132 to 123

19 20

Residence time range, seconds 150 to 300 molecular weights in the range of 20,000 to 30,000

Pressure drop across the reactor, kg / cm ² ... 352 (measured by osmosis) and are determined by the

Impact size, kg / cm ² 105 borne pale of any polymer with low

Conversion,% 31.6 Molecular Weight with Above Average Vinyl

Vinyl acetate, weight percent of the mono- 5 acetate content marked. For example, has a

Merger charge 45 ethylene-vinyl acetate copolymer rubber good

Quality in the range of 40 to 60% vinyl acetate

The resulting copolymer had a weight loss on extraction with methanol

Melt index (decigrams / minute at 150 ^° C.) of no more than 5%. Such a weight loss

13 to 17, a density of about 0.97 and a vinyl ίο can easily be determined by taking 0.25 g

acetate content of about 45%. If, as in the case of rubber granules, in 75 ml of methanol for 1 hour

game 4 that has been hardened or heat treated, fraud boils and then a second extraction with fresh

the tensile strength 150 kg / cm ² , the elongation 540% methanol and then dry at 110'C

and 500% modulus 125 kg / cm ² . net.

If there is a polymerization with the same mono- 15 With reference to the melt indices, it should be noted that

merenbeschickung and under approximately the same that the mixed polymer rubber types on

Conditions, however, with the introduction of the catalyst due to their different vinyl acetate contents quite

was carried out at only one point, the behavior was different. For rubber types with 40 to

Conversion only about 19%, and the effective reaction 60 percent by weight vinyl acetate, however, it is generally

extended over a much smaller space in the 20 my desired, melt indices no higher than

Reactor. 20 decigrams / minute (at 150 ° C), and

As stated above, the process yields these melt indices will usually be over 5 decades high conversions to chewing grams / minute in accordance with the invention. Furthermore, the use of chuk-like ethylene-vinyl acetate copolymers of moderate temperatures in the process seeks to have good tensile strength and other good properties of ethylene-vinyl acetate copolymers. It is desirable to carry out the polymerization in such a way that very little branching is introduced, so that when hardening occurs, as in the case of hardening, apart from that due to the acetate groups; Game 4, tensile strengths of at least 105 kg / cm ^{2 as a} result, the copolymer has properties that maintain elongations of at least 500%. The shafts consisting of highly crystallized sections, which are interrupted by acetate groups in Ab mixed polymer rubber types with suitable properties, have generally resulted in numerical averages.

For this purpose 2 sheets of drawings

Claims (6)

Patent claims: 1. A process for the copolymerization of ethylene and vinyl acetate in a tubular reactor at temperatures of 200 to 300 ⁰ C and high pressure in the presence of a catalyst, characterized in that the catalyst is introduced during the polymerization without a transfer agent at at least two different points. 2. The method according to claim 1, characterized in that vinyl acetate is used in an amount of 7 to 20 percent by weight of the monomers, the polymerization in the presence of 5 to 30 parts of oxygen per million, based on the weight of the monomers, and additional oxygen in introduces the same quantity range downstream of the peak temperatures, the reactor temperature being kept ^{above 200 ° C.} 3. The method of claim 1 or 2, characterized in that additional oxygen is introduced into the reaction stream where the temperature is in the range of 200 to 250 ⁰ C. 4. The method according to claim 1, characterized in that there is vinyl acetate in an amount of 35 to 75 percent by weight of the monomers applies, with the bulk of the polymerization takes place at temperatures not above 200 ° C. 5. The method according to claim 1 or 4, characterized in that 40 to 60 percent by weight vinyl acetate-containing monomers in the absence of solvents with a peroxygen catalyst with a decomposition temperature not above 160 ⁰ C, the flowing stream is allowed to cool and additional catalyst at temperatures not over 150 ⁰ C and in an amount of 5 to 20 molar parts per million, based on the monomer feed. 6. The method according to any one of claims 1 to 5, characterized in that the reaction is carried out at pressures above 1050 kg / cm ² .