Process for preparing copolymers from at least one aromatic vinyl compound

Abstract

The invention relates to a method for producing a copolymer (CP) made of at least one aromatic vinyl compound (A), in particular styrene and / or alpha-methylstyrene, and at least one further monomer (M) of the group consisting of acrylonitrile and methacrylic acid esters, comprising the following steps: a) polymerizing, b) separating the volatile components, c) separating the volatile components, and d) separating the volatile components. Wherein a vapor stream (B) is obtained, c) condensing at least part of the vapor stream (B), and wherein the first condensate (KS1) and / or the second condensate (KS2) is recovered. The invention also relates to a device for carrying out the method.

Description

manual

[0001] The present invention relates to a process for preparing a copolymer from at least one aromatic compound, in particular styrene and / or alpha-methylstyrene, and at least one other monomer from the group consisting of acrylonitrile and methyl acrylate, wherein the process comprises polymerizing at least one aromatic vinyl compound and at least one other monomer in at least one reactor in the presence of at least one organic solvent, removing volatile components to obtain a vapor stream, and condensing at least part of the vapor stream. The invention also relates to an apparatus for carrying out the process.

[0002] In process engineering, the term "vapor" describes volatile gaseous products formed in chemical reactions and in the distillation, evaporation, degassing or drying of liquid mixtures. The vapor may contain, as volatile components, for example aromatic vinyl monomers (e.g. styrene or α-methylstyrene), vinyl cyanide monomers (e.g. acrylonitrile), methyl acrylate monomers (e.g. methyl methacrylate MMA) and / or organic solvents (e.g. ethylbenzene), but may also contain water vapor (especially small amounts of water vapor).

[0003] In the process of the invention, the removed volatile components are subjected to several condensation steps using heat exchangers (such as condensers, for example). Here, the amount of monomers discharged from the process, such as styrene, α-methylstyrene, methyl methacrylate and / or organic solvents (such as ethylbenzene) can be reduced.

[0004] The obtained copolymers, such as styrene-acrylonitrile copolymers (SAN copolymers), in particular α-methylstyrene-acrylonitrile copolymers (AMSAN copolymers) and / or styrene-methyl methacrylate copolymers (SMMA copolymers), have excellent formability, stiffness and durability, and can maintain these properties even under weathering. The copolymers can be used in various fields, including the manufacture of automobiles, computers, printers, copiers, household appliances, audio systems and electrical components.

[0005] Copolymers of aromatic vinyl compounds and vinyl cyanide compounds and / or methacrylates are usually prepared by reacting monomers in an organic solvent. The polymer product first contains unconverted monomers and organic solvents, which must be removed in an environmentally friendly manner. The copolymerization can be carried out in one or more reactors. The obtained polymer product is transferred to an evaporation tank (also referred to as a degassing vessel) and volatile components (such as residual monomers and organic solvents) are separated. The removed volatile components are condensed using a cooler. In addition, purification is performed to obtain the copolymer end product in maximum yield.

[0006] EP3689923B1 describes a method for preparing a polymer from an aromatic vinyl compound and a vinyl cyanide compound. Freshly added organic solvent is sprayed on the separated volatile components. The volatile components are separated from the product mixture containing polymer, residual monomers and organic solvent using an evaporator and by condensing the separated volatile components in one or two condensers in series. Better condensation can be achieved by increasing the pressure and reducing the cooling temperature.

[0007] A disadvantage of increasing the pressure is that it leads to an undesirable increase in the proportion of residual volatile organic components in the polymer.

[0008] Furthermore, EP3689923B1 specifies the installation limit, i.e., reducing the temperature of the coolant input in the condensation, which results in uncondensed volatile components being discharged from the process. Furthermore, as the amount of low-boiling vinyl cyanide monomer increases, the condensation efficiency decreases.

[0009] Another disadvantage of the methods described in the prior art is solvent spraying, since the additionally added solvent is likely to accumulate in the entire system. In this case, an appropriate portion of the condensate must be removed from the system and disposed of.

[0010] The uncondensed volatile components are discharged to the environment or atmosphere through the wastewater treatment system using a water driven liquid ring pump. The greater the reduction of uncondensed volatile components, the lower the wastewater treatment complexity and / or emissions.

[0011] US 4,555,384 discloses a method and apparatus for continuous bulk polymerization of styrene monomer and alkenyl nitrile monomer. Steam containing monomers is directly withdrawn from the polymerization reactor and sent to a condenser.

[0012] EP 3689919 A1 relates to the preparation of polymers from aromatic vinyl compounds and vinyl cyanide compounds, wherein the evaporated part of the reaction mixture is likewise conducted from the reactor into a condenser.

[0013] The object is to provide an energy-saving and low-emission method and a corresponding device, in which in particular the separation and treatment of condensed steam and possible waste water can be avoided.

[0014] It is known that it is more economical to use a higher coolant temperature than a lower coolant temperature. It is therefore desirable to condense as high a proportion of the steam as possible at a relatively high coolant temperature. If the process allows the supply of a coolant with a relatively high feed temperature in at least one condensation step, river water or cooling water produced by cooling with river water can be used. Here, the provision of cooling water or brine by means of a refrigeration system can be dispensed with.

[0015] The higher temperature of the coolant can be compensated by a larger heat transfer surface area. To this end, a larger heat exchanger can be used first, or the condensation efficiency can be improved or replaced by injecting an evaporating liquid.

[0016] In addition, by lowering the temperature it is also possible to avoid blockages in the system due to polymerization of the condensate obtained, especially when it does not contain any inhibitors, since generally polymerization occurs more rapidly at higher temperatures. Therefore, lower temperatures in the system are favorable for blockages. This is achieved by early cooling of the circulating condensate and the associated steam flow.

[0017] The present invention relates to a process for preparing a copolymer made from at least one aromatic vinyl compound, in particular styrene and / or α-methylstyrene, and at least one other monomer from the group consisting of acrylonitrile and methacrylate, wherein the process comprises the following steps: a) polymerizing at least one aromatic vinyl compound and at least one other monomer in at least one reactor in the presence of at least one organic solvent to obtain a polymer product comprising a copolymer, residual monomers, at least one organic solvent and oligomers, if any, b) separating volatile components from the polymerization product obtained in step a), wherein the separation is carried out in a degassing vessel under reduced pressure of 1 to 150 mbar absolute, in particular 10 to 100 mbar absolute, and The polymer product is heated in a first heat exchanger, and the first heat exchanger is at a temperature greater than 200° C., in particular at 220° C. to 340° C. Operating at the first medium feed temperature within the range, to obtain a vapor stream comprising volatile components, c) condensing at least a portion of the steam stream obtained in step b), wherein the steam stream is cooled in at least one second heat exchanger and a third heat exchanger, a first condensate flowing out of the second heat exchanger and a second condensate flowing out of the third heat exchanger, wherein the second heat exchanger is operated at a second medium feed temperature in the range of 10°C to 40°C, in particular 15°C to 30°C, and The third heat exchanger is operated at a third medium feed temperature in the range of -10°C to 30°C, in particular -10°C to 15°C, and The second medium feed temperature is at least 10°C higher than the third medium feed temperature, and wherein the first condensate and / or the second condensate is returned at at least one location upstream of the second heat exchanger and / or at another location in the third heat exchanger and contacted with the steam flow, in particular injected into the steam flow, and d) optionally recycling the first condensate and / or the second condensate to the reactor of step a).

[0018] The present invention also relates to an apparatus for implementing the method of the present invention, comprising a reactor, a first heat exchanger, a degassing vessel, an optional tower having a tower top space, a second heat exchanger having a gas outlet and a liquid outlet, and a third heat exchanger, wherein these heat exchangers are connected to the downstream in sequence in a specified order, the third heat exchanger has a feed space and a collecting space and is preferably arranged vertically, the liquid outlet of the second heat exchanger and / or the collecting space of the third heat exchanger are connected to the feed space of the third heat exchanger via a first condensation pipe, the liquid outlet of the second heat exchanger and / or the collecting space of the third heat exchanger are optionally connected to the tower top space via a second condensation pipe, and the liquid outlet of the second heat exchanger and / or the collecting space of the third heat exchanger are optionally connected to the steam pipe connecting the degassing vessel to the tower via a third condensation pipe.

[0019] The process according to the invention or the device according to the invention allows the condensation of the vapor stream, i.e. the volatile components from the polymerization product, to be carried out more economically and with reduced emissions. Furthermore, if such a column is used, the oligomers obtained and separated by condensation discharge less monomers and solvents. By at least partially recycling the condensate, the amount of discharged monomers and solvents can be further reduced.

[0020] The method of the present invention includes multi-stage condensation. At least two heat exchangers, namely the second heat exchanger and the third heat exchanger, are used to condense the steam flow. The third medium feed temperature is preferably lower than the second medium feed temperature. Therefore, the second heat exchanger is preferably operated at a higher temperature than the third heat exchanger. In the downstream third heat exchanger, it is preferably operated at a lower coolant temperature than the second heat exchanger upstream thereof, and only the volatile components still remaining in the steam downstream of the second heat exchanger are condensed. Therefore, in the third heat exchanger for only a part of the volatile components, a coolant with a lower temperature is particularly required. Therefore, for the condensation of the volatile component part that has been condensed in the second heat exchanger, a coolant with a higher temperature is sufficient, which is energetically advantageous.

[0021] The recovery of the condensate improves the condensation effect, so that the proportion of the steam that can be condensed in the second heat exchanger is increased.

[0022] It has been found that recycling the condensate to assist in condensing the volatile components at at least one location and / or another location allows for the allocation of additional solvent supply, thereby avoiding solvent accumulation throughout the system.

[0023] The recovery of the condensate, which in turn evaporates by contact with the hot volatile components, cools the volatile components even before the condensation is actually carried out, so that the cooling capacity that still needs to be provided by the heat exchanger is reduced and the condensation efficiency is increased.

[0024] The at least one aromatic vinyl compound and the at least one other monomer are present in at least one organic solvent in step a) and polymerized in at least one reactor to form a polymer product. Preferably, continuous bulk polymerization or solvent polymerization is carried out in at least one reactor. The polymer product comprises copolymers, residual monomers, at least one organic solvent and any oligomers. In order to separate volatile components from the polymer product, the polymer product is sent to a degassing vessel through a first heat exchanger, where the polymer product is heated.

[0025] The medium temperature refers to the temperature in the feed of the heating or cooling medium of each heat exchanger. In the first heat exchanger, the polymer product is heated by the heating medium. The first heat exchanger, the second heat exchanger and the third heat exchanger are used for cooling, and each heat exchanger is supplied with a coolant.

[0026] In the first heat exchanger, volatile components such as unconverted monomers, solvents or oligomers are preferably partially evaporated, so the first heat exchanger can also be referred to as a partial evaporator. In the reactor, the reactor temperature of the polymer product is preferably in the range of 105° C. to 180° C., further preferably in the range of 105° C. to 125° C. or in the range of 140° C. to 180° C. The polymer product is preferably heated to a temperature in the range of 180° C. to 270° C. in the first heat exchanger.

[0027] The first heat exchanger is preferably arranged at the top of the degassing container and in particular forms a construction unit together with the degassing container. Alternatively, the first heat exchanger can be arranged separately from the degassing container. With the help of a vacuum system preferably arranged downstream of the degassing container, further preferably arranged downstream of the third heat exchanger, preferably there is a reduced pressure in the system, in particular in the degassing container, wherein the polymerization product including the volatile components from the first heat exchanger enters the degassing container. The copolymer is separated from the volatile components here. The phase containing the copolymer that forms the lower phase in the degassing container is discharged. The gas phase containing volatile components and referred to as steam or steam flow is discharged from the degassing container, in particular above the phase containing the copolymer. In particular, the steam flow is gaseous. The third medium feed temperature in the third heat exchanger can be used to control the amount of gaseous steam reaching the vacuum system.

[0028] The vapor stream preferably comprises an aromatic vinyl compound (in particular an aromatic vinyl monomer, such as styrene and / or α-methylstyrene), at least one other monomer (in particular a vinyl cyanide monomer, such as acrylonitrile), an acrylic monomer (for example MMA), an oligomer and / or an organic solvent (for example ethylbenzene, toluene and / or methyl ethyl ketone (MEK)), and optionally water (in particular water vapor). The solution supplied to the first heat exchanger and from which the vapor stream is formed preferably comprises 1 to 5000 ppm of water. The stream referred to in the context of the present invention as vapor stream B varies in volume and composition as the process steps are carried out.

[0029] The copolymers prepared preferably include SAN copolymers, AMSAN copolymers and / or SMMA copolymers.

[0030] The vapor stream is condensed in multiple stages. Preferably, the vapor stream is first condensed in the second heat exchanger and then in the third heat exchanger. In the third heat exchanger, the vapor stream is further cooled, which also counteracts polymerization, thereby preventing pipe blockages and, in particular, achieving complete condensation in the ideal case.

[0031] Preferably, the vapor stream upstream of the second heat exchanger is conducted through a separation unit, in particular a column, wherein the vapor stream is contacted with the first condensate and / or the second condensate, and oligomers are removed from the vapor stream.

[0032] In a preferred embodiment, the second heat exchanger has a column connected upstream, which column may have internals. The first condensate and / or the second condensate is preferably sent to the upper part of the column, in particular the top.

[0033] The bottom of the column is preferably heated, in particular to a temperature in the range of 150° C. to 280° C. The oligomers condensed out of the vapor stream are preferably collected at the bottom. The remaining vapor stream is preferably withdrawn from the top of the column and fed to a second heat exchanger. The liquid at the bottom of the column can be returned, in particular for further depletion of monomers and solvent, in particular fed together with the first condensate and / or the second condensate at the first location.

[0034] The expression "upstream" with respect to the spatial arrangement of the device is understood in the context of the present invention to mean that a first element (e.g. a heat exchanger or a tower) is located upstream relative to the conveying direction of a second element (e.g. another heat exchanger), so that the steam flow first reaches the first element and then reaches the second element, for example flowing from a tower to a second heat exchanger.

[0035] In the second heat exchanger, a first condensate is formed, while the remaining gaseous steam flow is fed to a third heat exchanger, in which a second condensate is formed. The first condensate and / or the second condensate is returned at least to the third heat exchanger and additionally or alternatively, in particular additionally, further upstream of the second heat exchanger and brought into contact with the steam flow.

[0036] Preferably, in particular when the column is connected upstream of the second heat exchanger, the first condensate and / or the second condensate is recycled, in particular injected, into the column and / or into the steam line between the degassing vessel and the column.

[0037] The reduced pressure is preferably generated in the degassing container by a vacuum system, which is particularly arranged downstream of at least one further heat exchanger. The vacuum system is preferably designed as a liquid ring pump system, and is further preferably operated with a liquid, wherein the liquid particularly comprises an organic mixture, preferably consists of an organic mixture, and the liquid particularly comprises 10% to 90% by weight of at least one aromatic vinyl compound, particularly styrene and / or α-methylstyrene, 5% to 50% by weight of at least one other monomer and 0.5% to 50% by weight of an organic solvent, particularly ethylbenzene, based on the total amount of liquid in the vacuum system. Styrene and / or α-methylstyrene are preferably added to the liquid. The reduced pressure that can be achieved by the liquid ring pump system, that is, the minimum absolute pressure that can be achieved, comes from the vapor pressure of the liquid used. The presence of styrene and / or α-methylstyrene in the liquid, for example, can reduce the vapor pressure compared to acrylonitrile. The higher the content of styrene and / or α-methylstyrene in the liquid, the lower the minimum absolute pressure that can be achieved.

[0038] Specifically, the vacuum system has a liquid ring pump liquid circuit with a liquid separator and an overflow pipe. The vacuum system preferably comprises a liquid ring pump system, a jet pump, a liquid ring pump liquid circuit with a liquid separator and an overflow pipe, a fourth heat exchanger and an exhaust gas heat exchanger.

[0039] The vacuum system is preferably fluidically connected to the collecting space of the third heat exchanger. The vacuum system preferably comprises at least one pump designed as a liquid ring pump system, an overflow pipe and a pump heat exchanger, the pump heat exchanger being preferably arranged downstream of the high-pressure side of the pump and connected to the low-pressure side of the pump via a return pipe. Preferably, a feed pipe is arranged between the overflow pipe and the pump heat exchanger, the feed pipe being used to add liquid from the vacuum system, in particular the liquid ring pump system.

[0040] The vacuum system is preferably arranged downstream of the third heat exchanger. The vacuum system provides a reduced pressure in particular in the first heat exchanger, the degassing vessel, if appropriate in the column, the second heat exchanger and the third heat exchanger.

[0041] Preferably, the reduced pressure is produced in the degassing container by a vacuum system, which is in particular arranged downstream of the second heat exchanger and the third heat exchanger. The vacuum system preferably comprises at least one pump which is designed as a liquid ring pump system and operates with a liquid which is separated from the waste gas drawn off by the pump on the pump pressure side by a liquid separator and fed to the pump.

[0042] This pump, also called a vacuum pump, can have an upstream ejector pump, also called an ejector, in order to be able to further reduce the pressure in the plant section up to the degassing vessel.

[0043] Preferably, at least a portion of the first condensate and / or the second condensate is fed into the liquid in the liquid ring pump system. Further preferably, at least one aromatic vinyl compound A is added to the liquid.

[0044] According to EP3689923B1, recycling condensate containing components of the steam stream into the steam stream can slightly reduce the condensation efficiency compared to adding solvent to the steam stream, thereby increasing the amount of uncondensed steam at the inlet of the vacuum system. This can be compensated by using a liquid containing at least one aromatic vinyl compound in the liquid ring pump system. Uncondensed steam can still be condensed in the vacuum system and returned to the reactor.

[0045] Optionally, the uncondensed volatile components in the liquid can be condensed by the exhaust gas heat exchanger of the vacuum system and returned to the reactor. The exhaust gas heat exchanger is preferably operated at a higher pressure than the second heat exchanger and / or the third heat exchanger. Specifically, the exhaust gas heat exchanger is operated at a pressure of more than 900 mbar. Therefore, the condensation efficiency of the exhaust gas heat exchanger is high, so that almost no gaseous steam escapes into the exhaust gas.

[0046] The liquid separator preferably has an overflow. Further preferably, the liquid passing through the overflow is removed from the vacuum system and in particular returned to the reactor.

[0047] Preferably, a portion of the at least one aromatic vinyl compound is added to the liquid, wherein the at least one aromatic vinyl compound is present in particular in admixture with an inhibitor, and the amount of the aromatic vinyl compound added to the liquid is at least 10% by weight, further preferably at least 20% by weight, of the gaseous part of the vapor flow supplied to the vacuum system.

[0048] The content of the inhibitor, particularly the content of the inhibitor dissolved in at least one aromatic vinyl compound, is preferably 1 to 50 ppm based on the mixture of the aromatic vinyl compound and the inhibitor in the vacuum system.

[0049] The liquid is preferably cooled in a pump heat exchanger, which is also referred to as a fourth heat exchanger. Further preferably, a portion of the at least one aromatic vinyl compound is added to the liquid upstream of the pump heat exchanger. The pump heat exchanger is preferably operated at a fourth medium feed temperature T4. Further preferably, the fourth medium feed temperature T4 is lower than the second medium feed temperature T2 of the second heat exchanger. Specifically, the difference between the second medium feed temperature T2 and the fourth medium feed temperature T4 is at least 10°C.

[0050] The exhaust gas of the vacuum system is preferably at least partially condensed in an exhaust gas heat exchanger, which is also referred to as the fifth heat exchanger, further preferably at ambient pressure, in particular at a pressure greater than 900 mbar. The exhaust gas heat exchanger is preferably operated at a fifth medium feed temperature T5; further preferably, the fifth medium feed temperature T5 is lower than the second medium feed temperature T2 of the second heat exchanger. Specifically, the difference between the second medium feed temperature T2 and the fifth medium feed temperature T5 is at least 10°C. Due to the lower temperature in the exhaust gas heat exchanger, components that are still in a gaseous state when leaving the second heat exchanger may condense downstream of the second heat exchanger. Therefore, it is not necessary for all components to have condensed in the second heat exchanger, so the second heat exchanger can be operated using a hotter coolant (e.g. river water).

[0051] Preferably, the first condensate and / or the second condensate are contacted co-currently with the steam flow at a first position upstream of the tower, the first condensate and the second condensate are contacted counter-currently with the steam flow at a second position in the tower, and / or the first condensate and / or the second condensate are contacted co-currently with the steam flow at a third position in the third heat exchanger.

[0052] Recovering the first condensate and / or the second condensate at a first location, in particular upstream of the column, results in cooling of the vapour stream before entering the column, resulting in lower levels of deposits, ie lower polymerisation, in the column.

[0053] Feeding the first condensate and / or the second condensate at the second location results in further separation of oligomers from the condensate.

[0054] Recovering the first condensate and / or the second condensate at the third location is particularly used for cooling the condensate from the first buffer container.

[0055] The vapour stream is preferably cooled by feeding the first condensate and / or the second condensate at a first location wherein the temperature difference between the vapour stream upstream and downstream of the first location is at least 25°C and the temperature of the vapour stream downstream of the first location is at least 120°C.

[0056] Furthermore, it is preferred that the vapor stream is cooled by feeding the first condensate and / or the second condensate at the second location, wherein the temperature of the vapor stream downstream of the second location is further preferably in the range of 65°C to 190°C.

[0057] At least one buffer container (also referred to as storage container) can be arranged downstream of the second heat exchanger and / or the third heat exchanger. The first condensate and / or the second condensate are preferably collected in one or more buffer containers, wherein, in the at least one buffer container, water is optionally separated, in particular from the first condensate and / or the second condensate. At least one of the one or more buffer containers preferably comprises a water separator.

[0058] The vapor stream drawn off from the degassing vessel preferably comprises 10 to 90% by weight, in particular 25 to 65% by weight, of at least one aromatic vinyl compound, in particular styrene, 5 to 60% by weight, in particular 10 to 40% by weight, of at least one further monomer, in particular acrylonitrile, and 0.5 to 50% by weight, in particular 25 to 45% by weight, of organic solvent, in particular ethylbenzene, toluene and / or MEK, the above percentages by weight being in each case based on the total vapor stream.

[0059] In addition, an inhibitor may be added. The inhibitor is preferably added to the first condensate and / or the second condensate, in particular upstream of the third heat exchanger. The inhibitor is preferably supplied to the third heat exchanger together with the first condensate and / or the second condensate. The amount of inhibitor added, in particular an inhibitor dissolved in at least one aromatic vinyl compound, is preferably 1 to 20 ppm, based on the steam flow extracted from the degassing vessel.

[0060] The inhibitor preferably comprises or consists of 4-tert-butylcatechol (TBC), an alkoxyphenol such as 4-methoxyphenol (MEHQ) and / or a thiophenol, in particular a sterically hindered thiophenol such as 4-hydroxy-2,2,6,6-tetramethylpiperidinyloxy (4-hydroxy-TEMPO).

[0061] The total amount of the first condensate and the second condensate returned at the at least one location and the further location, in particular at the first location, the second location and the third location, is preferably at least 50% by weight, based on the vapor stream withdrawn from the degassing vessel.

[0062] The first condensate and / or the second condensate are preferably fed to the first location in a total amount of up to 40% by weight, based on the vapor stream withdrawn from the degassing vessel. Furthermore, the first condensate and / or the second condensate are preferably fed to the column, in particular to the second location, in a total amount of up to 150% by weight, based on the vapor stream withdrawn from the degassing vessel. In the case of a recovery amount of more than 100% by weight, the condensate is repeatedly recycled.

[0063] The first condensate and / or the second condensate is preferably injected into the vapor line at at least one point, in particular upstream of the column.

[0064] The first heat exchanger, the second heat exchanger and the third heat exchanger are preferably designed as shell and tube heat exchangers. The first heat exchanger is preferably arranged vertically. The second heat exchanger is preferably arranged horizontally. The third heat exchanger is preferably arranged vertically.

[0065] A vertical arrangement means that, in the direction of gravity, first the feed space, then the heat exchange surface, in particular the tube bundle, and then the collecting space. The feed space is preferably the top space and the collecting space is preferably the bottom space. In particular, the tubes of the first heat exchanger and / or the third heat exchanger are aligned in the direction of gravity. In a horizontal arrangement, the tubes, in particular the tubes of the second heat exchanger, are arranged perpendicular to the direction of gravity.

[0066] The first condensate and / or the second condensate is preferably injected into the head space of the third heat exchanger, in particular in the flow direction of the steam flow.

[0067] The medium used in the second heat exchanger is preferably water. The medium used in the third heat exchanger is preferably brine and / or water containing ethylene glycol. The medium in the second heat exchanger and the third heat exchanger is preferably a cooling medium. The second heat exchanger is preferably operated using river water or by cooling the coolant provided with river water. River water is preferably used for the secondary circuit.

[0068] The medium in the first heat exchanger is in particular a heating medium. The medium used in the first heat exchanger is preferably Diphyl steam, such as Therminol VP1 or a heating liquid, in particular a heating oil. The heating oil is preferably selected from mineral oils or synthetic oils known to those skilled in the art, such as Therminol T66, T62, T55, T72 or Melatherm SH. BRIEF DESCRIPTION OF THE DRAWINGS

[0069] A working example of the invention is shown in the drawings and is explained in detail in the following description.

[0070] The figure shows:

[0071] Figure 1 is a schematic diagram of a first embodiment of the present invention,

[0072] Figure 2 is a schematic diagram of a second embodiment of the present invention, and

[0073] Figure 3 FIG. 4 is a schematic diagram of a third embodiment of the present invention.

[0074] Figure 1 FIG. 1 shows a schematic diagram of a first embodiment of the present invention.

[0075] An aromatic vinyl compound A, at least one further monomer M and an organic solvent L are added to a reactor R. In the reactor R a polymer product PP comprising a copolymer CP and an organic solvent L is formed.

[0076] First, the polymer product PP is fed to the first heat exchanger WT1, where it is heated with a heating medium at a first medium feed temperature T1. The heated polymer product PP is transferred from the first heat exchanger WT1 to a degassing vessel EB, from which the copolymer CP is first extracted, and then a gaseous vapor stream B containing volatile components is extracted.

[0077] From the degassing vessel EB, a vapor stream B is fed via a vapor line BL into a column K with a head space KKR and internals E. Oligomers OL are withdrawn from the bottom of the column K, which is heated by means of a heating jacket H. From the top of the column K, the remaining vapor stream B is transferred onwards into a second heat exchanger WT2, where it is partially condensed with a coolant having a second medium feed temperature T2, whereby a first condensate KS1 is withdrawn from the second heat exchanger WT2 at a liquid outlet FLA. The first condensate KS1 is temporarily stored in a first buffer vessel PB1.

[0078] The still remaining gaseous steam flow B enters the third heat exchanger WT3 from the gas outlet GA of the second heat exchanger WT2, where it is further condensed by another coolant having a third medium feed temperature T3. The second heat exchanger WT2 is arranged horizontally, while the third heat exchanger WT3 is arranged vertically. The second condensate KS2 is drawn off from the bottom space SR of the third heat exchanger WT3 and sent to the second buffer container PB2. Water W is separated in the second buffer container PB2. The second buffer container PB2 is filled hydraulically; the upper phase flows into the third buffer container PB3 through the top of the second buffer container PB2.

[0079] The vacuum system VA is also connected to the bottom space SR of the third heat exchanger WT3 and operates with liquid F and comprises a vacuum pump VP and a liquid separator FA with an overflow U. The vacuum pump VP is designed as a liquid ring pump. The liquid F is cooled in the fourth heat exchanger WT4. The waste gas AG from the vacuum system VA is condensed in the fifth heat exchanger WT5 to reduce gas emissions in the process. The buffer is stored in the third buffer container PB3 to compensate for fluctuations in production volume.

[0080] The first condensate KS1 from the heat exchanger WT2 is injected into the steam stream B at a first point ED1 in the steam line BL upstream of the column K. By evaporating the first condensate KS1 at the first point ED1 , the steam stream B is already cooled before entering the column K.

[0081] Furthermore, the first condensate KS1 from the second heat exchanger WT2 is introduced at a second point ED2 into the top of the column K and is contacted there with the vapor stream B to separate the oligomers OL.

[0082] Furthermore, the first condensate KS1 is injected at a third position ED3 in the head space KR of the third heat exchanger WT3 to further cool the steam flow B and obtain a second condensate KS2.

[0083] The second condensate KS2 and the mixture from the third buffer container PB3 can be partially added to the first condensate KS1 for recovery at the first location ED1, the second location ED2 or the third location ED3. In addition, the mixture collected in the third buffer container PB3 is returned to the reactor R by a pump and, if necessary, to the reactor R through another buffer container in order to convert the remaining unconverted monomers into copolymers CP. The pump P is used to convey the condensates KS1, KS2.

[0084] Figure 2 FIG. 2 shows a schematic diagram showing a second embodiment of the present invention.

[0085] In the illustrative second embodiment, in contrast to the first embodiment, the vapor stream B is supplied directly from the degassing vessel EB to the second heat exchanger WT2, so that there is no column K. The first condensate KS1 is injected from the second heat exchanger WT2 into the head space KR of the third heat exchanger WT3 in order to cool the condensate as much as possible, and the second condensate KS2 is returned to the reactor R via a further buffer vessel if necessary. Inhibitors can be added in the case of recycling to the third heat exchanger WT3.

[0086] Figure 3 A schematic diagram of a third embodiment of the present invention is shown. A vapor stream B is fed through a tower K into a second heat exchanger WT2 and from there onwards directed to a third heat exchanger WT3. In this illustrative embodiment, the second and third heat exchangers WT2 and WT3 are arranged horizontally.

[0087] The first condensate KS1 from the second heat exchanger WT2 and the second condensate KS2 from the third heat exchanger WT3 are mixed in the second buffer vessel PB2 and fed partly at a first position ED1 into the steam stream B in the steam line BL upstream of the column K and partly at a second position ED2 at the top of the column K. The hotter first condensate KS1 is mixed with the cold second condensate KS2 in the second buffer vessel PB2.

[0088] The invention is not limited to the working examples described herein. Instead, several modifications are possible within the scope of the claims.

[0089] Examples

[0090] The process follows Figure 1 The first example is carried out to produce a SAN copolymer.

[0091] The total flow rate fed into the reactor was 4.3 t / h. First, 2.47 t / h of copolymer was withdrawn from the degassing vessel, and then 1.83 t / h of steam was withdrawn from the degassing vessel. The polymer contained 1.6 to 2 t / h of styrene and 0.47 to 0.87 t / h of acrylonitrile. In each case, a polymer containing 65% by weight of styrene and 35% by weight of acrylonitrile was produced.

[0092] Example 1

[0093] A vapor stream was withdrawn from the degassing vessel at a temperature of 260° C. Upstream of the column, the vapor stream was contacted with 200 l / h of first condensate and the mixture was injected into the vapor line so that the total temperature of the feed stream entering the column was 225° C. The temperature at the bottom of the K column was controlled at 250° C.

[0094] At the top of the column, 2.2 t / h of the first condensate were fed in. The recovery at this feed point was therefore 120%.

[0095] The pressure at the top of the column is 53 mbar. A vapor stream is withdrawn from the top of the column at a temperature of 160°C and fed to a second heat exchanger, where it is partially condensed by a coolant having a second medium feed temperature T2 of 19 to 25°C. When leaving the second heat exchanger, the second medium temperature is 30°C. 2.86 t / h of first condensate are withdrawn from the second heat exchanger, and the remaining vapor stream is fed to a third heat exchanger at a temperature of 30°C. The temperature of the first condensate is 47°C.

[0096] At the third position, 0.46 t / h of the first condensate was sprayed into the head space of the third heat exchanger. The third medium feed temperature in the third heat exchanger was 7°C.

[0097] Downstream of the third heat exchanger, 0.85 t / h of styrene were fed in and the mixture was returned to the reactor.

[0098] The fourth heat exchanger WT4 and the fifth heat exchanger WT5 were operated at a coolant feed temperature of 7° C. Only trace amounts of monomers or solvents were detected in the exhaust gas of the fifth heat exchanger WT5. ​​No waste water required treatment.

[0099] Example 2

[0100] based on Figure 3Another exemplary embodiment is described below, in which about 500 kg / h of the first and second condensate mixture is injected into the steam pipe at the first position, where the recovery rate is about 95%. This results in a temperature of the total flow at the inlet into the tower of 158°C. The temperature at the bottom of the tower is controlled at 162°C. 400 kg / h of the mixture of the first condensate and the second condensate are sent to the top space of the tower. The temperature of the steam flow leaving the tower at the top is 79.5°C. The temperature of the second medium when leaving the second heat exchanger is 24°C, so the temperature of the remaining steam flow is 35°C and is directed to the third heat exchanger.

[0101] In the third heat exchanger the third medium feed temperature T3 is 1.5°C which results in a gas flow temperature of 21°C leaving the third heat exchanger WT3.

[0102] In this case, there is no wastewater to be sent to wastewater treatment. Only trace amounts of monomer or solvent can be detected in the exhaust gas from the vacuum pump.

[0103] While in Example 1 almost complete recovery of all monomers and solvents was achieved through multiple condensate addition points and no significant contamination in the waste water or exhaust gas was observed, in Example 2 this was achieved by more significantly reducing the steam temperature upstream of the second heat exchanger WT2.

[0104] Comparative Example 1

[0105] The process was carried out in essentially the same manner as in Example 1, with the difference that the vapor stream was contacted upstream of the column with 200 l / h of ethylbenzene (as organic solvent L) instead of the first condensate. This resulted in an increase in the liquid level in the buffer vessel upstream of the reactor, so that about 6 tons of the mixture had to be separated and processed after 12 hours. Reference numerals list CP Copolymer A Aromatic vinyl compounds M Other monomers R Reactor L Organic solvents PP polymer products EB Degassing Vessel T1 First medium feed temperature B Steam flow BL Steam Pipe WT1 First heat exchanger WT2 Second heat exchanger WT3 Third Heat Exchanger WT4 Fourth heat exchanger WT5 Fifth Heat Exchanger GA Gas outlet FLA Liquid Outlet KS1 First Condensate KS2 Second Condensate T2 Second medium feed temperature T3 Third medium feed temperature ED1 1st position ED2 2nd position ED3 Third position I inhibitors VA Vacuum System F Liquid FA Liquid Separator U Overflow PB1 First buffer container PB2 Second buffer container PB3 Third buffer container P Pump E Internal components H Heating Jacket K Tower OL oligomer SR Bottom Space W Water VP Vacuum Pumps AG Exhaust KR Headspace

Claims

1. A process for preparing a copolymer (CP) made from at least one aromatic vinyl compound (A), in particular styrene and / or α-methylstyrene, and at least one other monomer (M) from the group consisting of acrylonitrile and methacrylate, wherein the process comprises the following steps: a) polymerizing at least one aromatic vinyl compound (A) and at least one other monomer (M) in at least one reactor (R) in the presence of at least one organic solvent (L), to obtain a polymer product (PP) comprising a copolymer (CP), residual monomers, at least one organic solvent (L) and possibly oligomers, b) separating volatile components from the polymer product (PP) obtained in step a), wherein the separation is carried out in a degassing vessel (EB) under reduced pressure of 1 to 150 mbar absolute, in particular 10 to 100 mbar absolute, and the polymer product (PP) is heated in a first heat exchanger (WT1), and the first heat exchanger (WT1) is operated at a first medium feed temperature (T1) of more than 200° C., in particular in the range of 220° C. to 340° C., to obtain a vapor stream (B) comprising volatile components, c) condensing at least a portion of the steam stream (B) obtained in step b), wherein the steam stream (B) is cooled in at least one second heat exchanger (WT2) and a third heat exchanger (WT3), a first condensate (KS1) flowing out of the second heat exchanger (WT2) and a second condensate (KS2) flowing out of the third heat exchanger (WT3), wherein the second heat exchanger (WT2) is operated at a second medium feed temperature (T2) in the range of 10°C to 40°C, in particular 15°C to 30°C, and The third heat exchanger (WT3) is operated at a third medium feed temperature (T3) in the range of -10°C to 30°C, in particular -10°C to 15°C, and the second medium feed temperature (T2) is at least 10°C higher than the third medium feed temperature (T3), and wherein the first condensate (KS1) and / or the second condensate (KS2) is returned at at least one point (ED1, ED2) upstream of the second heat exchanger (WT2) and / or at another point (ED3) in the third heat exchanger (WT3) and is contacted with the steam flow (B), in particular injected into the steam flow (B), and d) optionally recycling the first condensate (KS1) and / or the second condensate (KS2) into the reactor (R) of step a).

2. The method according to claim 1, characterized in that The vapor stream (B) upstream of the second heat exchanger (WT2) is guided through a separation device, in particular a column (K), wherein the vapor stream (B) is contacted with the first condensate (KS1) and / or the second condensate (KS2) in order to remove oligomers from the vapor stream (B).

3. The method according to claim 2, characterized in that the first condensate (KS1) and / or the second condensate (KS2) is contacted co-currently with the steam stream (B) at a first location (ED1) upstream of the column (K), The first condensate (KS1) and / or the second condensate (KS2) is contacted with the steam stream (B) in countercurrent at a second location (ED2) in the column (K) and / or The first condensate (KS1) and / or the second condensate (KS2) is contacted co-currently with the steam flow (B) at a third location (ED3) in the third heat exchanger (WT3).

4. The method according to any one of claims 1 to 3, characterized in that: The vapour stream (B) is cooled by feeding the first condensate (KS1) and / or the second condensate (KS2) at the first location (ED1), and the temperature difference between the vapour stream (B) upstream and downstream of the first location (ED1) is at least 25°C, and the temperature of the vapour stream (B) downstream of the first location (ED1) is at least 120°C, and / or The vapor stream (B) is cooled by feeding the first condensate (KS1) and / or the second condensate (KS2) at the second location (ED2), and the temperature of the vapor stream (B) downstream of the second location (ED2) is further preferably in the range of 65°C to 190°C.

5. The method according to any one of claims 1 to 4, characterized in that: The first condensate (KS1) and / or the second condensate (KS2) is collected in one or more buffer containers (PB1, PB2), wherein water is optionally separated off in at least one buffer container (PB1, PB2).

6. The method according to any one of claims 1 to 5, characterized in that The vapor stream (B) removed from the degassing vessel (EB) contains from 10 to 90% by weight, based on the total vapor stream (B), of at least one aromatic vinyl compound (A), 5 to 60% by weight of at least one other monomer (M) and 0.5 to 50% by weight of an organic solvent (L), in particular ethylbenzene.

7. The method according to any one of claims 1 to 6, characterized in that: An inhibitor (I) is added to the first condensate (KS1) and / or the second condensate (KS2) upstream of the third heat exchanger (WT3).

8. The method according to claim 7, characterized in that The inhibitor (I), in particular dissolved in at least one aromatic vinyl compound, is added in an amount of 1 to 20 ppm, based on the vapor stream (B) withdrawn from the degassing vessel (EB).

9. The method according to any one of claims 3 to 8, characterized in that feeding the first condensate (KS1) and / or the second condensate (KS2) at the first point (ED1) in a total amount of up to 40% by weight, based on the steam flow (B) withdrawn from the degassing vessel (EB), and / or The first condensate (KS1) and / or the second condensate (KS2) is fed in a total amount of up to 150% by weight, based on the vapor stream (B) withdrawn from the degassing vessel (EB), to the column (K), in particular to the second point (ED2).

10. The method according to any one of claims 2 to 9, characterized in that The first condensate (KS1) and / or the second condensate (KS2) are injected into the steam line at at least one point (ED1) upstream of the column (K).

11. The method according to any one of claims 2 to 10, characterized in that At the top of the column (K), the first condensate (KS1) and / or the second condensate (KS2) is fed.

12. The method according to any one of claims 1 to 11, characterized in that In another position (ED3), in particular the third position (ED3), of the third heat exchanger (WT3), the first condensate (KS1) and / or the second condensate (KS2) is fed in a total amount of up to 150% by weight, based on the steam flow (B) withdrawn from the degassing vessel (EB).

13. The method according to any one of claims 1 to 12, characterized in that The third heat exchanger (WT3) is arranged vertically and in particular the first condensate (KS1) and / or the second condensate (KS2) is fed into the feed space of the third heat exchanger (WT3).

14. The method according to any one of claims 1 to 13, characterized in that The sum of the amounts of the first condensate (KS1) and the second condensate (KS2) returned at at least one location (ED1, ED2) and another location (ED3), in particular at the first location (ED1), the second location (ED2) and the third location (ED3), is at least 50% by weight, based on the steam flow (B) withdrawn from the degassing vessel (EB).

15. The method according to any one of claims 1 to 14, characterized in that The second heat exchanger (WT2) is operated with river water or coolant provided by river water cooling.

16. The method according to any one of claims 1 to 15, characterized in that a reduced pressure in the degassing vessel (EB) is generated by a vacuum system (VA), which is in particular arranged downstream of at least one further heat exchanger (WT2, WT3) and which is designed as a liquid ring pump system and operates with a liquid (F), wherein the liquid (F) comprises an organic mixture, preferably consists of an organic mixture, and in particular the liquid (F) comprises from 10 to 90 wt. %, based on the total liquid (F) in the vacuum system (VA), of at least one aromatic vinyl compound (A), 5 to 50 wt. % of at least one other monomer (M) and 0.5 to 50% by weight of an organic solvent (L), in particular ethylbenzene.

17. An apparatus for carrying out the process according to any one of claims 1 to 16, comprising at least one reactor, a first heat exchanger (WT1), a degassing vessel (EB), optionally a column (K) with a head space (KKR), a second heat exchanger (WT2) with a gas outlet (GA) and a liquid outlet (FLA), a third heat exchanger (WT3), in, These devices are connected downstream in sequence in the specified order. The third heat exchanger (WT3) has a feed space and a collection space and is preferably arranged vertically. The liquid outlet of the second heat exchanger (WT2) and / or the collecting space of the third heat exchanger (WT3) is connected to the feed space of the third heat exchanger (WT3) via a first condensate conduit, The liquid outlet of the second heat exchanger (WT2) and / or the collecting space of the third heat exchanger (WT3) is optionally connected via a second condensate line to the top space (KKR) of the column (K) and The liquid outlet (WT2) of the second heat exchanger and / or the collecting space (WT3) of the third heat exchanger are optionally connected via a third condensate line to a steam line connecting the degassing vessel (EB) with the column (K).

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