Method for producing a copolymer proceeding from at least one aromatic vinyl compound

Abstract

The invention relates to a method for producing a copolymer (CP) proceeding from at least one aromatic vinyl compound (A), in particular styrene and / or alpha-methylstyrene, and at least one further monomer (M) from the group consisting of acrylonitrile and methacrylate, the method comprising the following steps: a) polymerisation, b) separation of volatile components, wherein a vapour flow (B) is obtained, c) condensation of at least parts of the vapour flow (B), wherein a first condensate (KS1) and / or a second condensate (KS2) are / is recycled. The invention further relates to a device for performing the method.

Description

[0001] Process for producing a copolymer starting from at least one aromatic vinyl compound

[0002] Description

[0003] The invention relates to a process for producing a copolymer starting from at least one aromatic compound, in particular styrene and / or alpha-methylstyrene, and at least one further monomer from the group consisting of acrylonitrile and methacrylate. The process comprises the polymerization of the at least one aromatic vinyl compound and the at least one further monomer in at least one reactor in the presence of at least one organic solvent, the separation of volatile components to obtain a vapor stream, and the condensation of at least portions of the vapor stream. Furthermore, the invention relates to an apparatus for carrying out the process.

[0004] In process engineering, the term "vapor" describes volatile, gaseous products that arise during chemical reactions, the distillation of liquid mixtures, evaporation, degassing, or drying. The volatile components of vapors can include aromatic vinyl monomers such as styrene or alpha-methylstyrene, vinyl cyanide monomers such as acrylonitrile, methacrylate monomers such as methyl methacrylate (MMA), and / or organic solvents such as ethylbenzene, but also water vapor, especially in small amounts.

[0005] According to the process of the invention, several steps of condensing the separated volatile components are carried out using heat exchangers such as condensers. This allows the amount of monomers such as styrene, alpha-methylstyrene, methyl methacrylate, and / or organic solvents such as ethylbenzene to be reduced.

[0006] The resulting copolymers, such as styrene-acrylonitrile copolymers (SAN copolymers), particularly alpha-methylstyrene-acrylonitrile copolymers (AMSAN copolymers) and / or styrene-methyl methacrylate copolymers (SMMA copolymers), exhibit excellent formability, rigidity, and durability, even when exposed to weathering. These copolymers can be used in a variety of applications, including the manufacture of automobiles, computers, printers, copiers, household appliances, audio systems, and electrical components.

[0007] A copolymer of an aromatic vinyl compound and a vinyl cyanide compound and / or methacrylate is typically produced by reacting the monomers in an organic solvent. The polymerization product initially contains unreacted monomers and organic solvent, which must preferably be removed in an environmentally safe manner. The copolymerization can be carried out in one or more reactors. The resulting polymerization product is transferred to an evaporation tank, which can also be referred to as a degassing vessel, and volatile components such as residual monomers and organic solvent are separated. The condensation of the separated volatile components takes place using condensers. Purification is also carried out to obtain the final copolymer product in the highest possible yield.

[0008] EP 3 689 923 B1 describes a process for producing a polymer from an aromatic vinyl compound and a vinyl cyanide compound. A freshly added organic solvent is sprayed onto separated volatile components. The separation of volatile components from the product mixture, which contains polymer, residual monomers, and organic solvent, is carried out using an evaporation tank and by condensing the separated volatile components in one or two condensers connected in series. Improved condensation can be achieved by increasing the pressure and reducing the cooling temperature.

[0009] The disadvantage of increasing the pressure is the associated undesirable increase in the proportion of volatile organic components remaining in the polymer.

[0010] Furthermore, EP 3 689 923 B1 lists installation limitations as limits for lowering the temperature of a feed refrigerant in the condensation, which leads to the expulsion of uncondensed volatile components from the process. Furthermore, condensation efficiency is reduced when the amount of low-boiling-point vinyl cyanide monomers is increased.

[0011] A further disadvantage of the method described in the prior art is the spraying of solvent, as there is a risk of the additional solvent accumulating in the entire system. In this case, a corresponding portion of the condensate must be removed from the system and disposed of.

[0012] Uncondensed volatile components are released into the environment or atmosphere through a wastewater treatment system using a water-driven liquid ring pump. The more the amount of uncondensed volatile components can be reduced, the lower the wastewater treatment effort and the amount of emissions. US 4,555,384 discloses a process and apparatus for the continuous bulk polymerization of styrene and alkenyl nitrile monomers. Vapor containing monomers is withdrawn directly from the polymerization reactor and fed to a condenser.

[0013] EP 3 689 919 A1 relates to the preparation of a polymer from an aromatic vinyl compound and a vinyl cyanide compound, wherein an evaporated part of the reaction mixture is also led from the reactor into a condenser.

[0014] The task is to provide an energy-efficient and low-emission process and a corresponding device in which, in particular, the separation and disposal of condensed vapors and, if applicable, wastewater can be avoided.

[0015] It is known that using a higher coolant temperature is more economical than using a lower coolant temperature. Therefore, it is desirable to condense as much vapor as possible at a higher coolant temperature. If the process allows for the addition of coolant at a higher inlet temperature in at least one condensation step, river water or cooling water produced by cooling with river water can be used. This eliminates the need to provide cooling water or brine using refrigeration systems.

[0016] A higher coolant temperature can be compensated for by a larger heat transfer surface. This can be achieved by using larger heat exchangers, or by injecting evaporating liquids to improve condensation efficiency.

[0017] Furthermore, reducing the temperature can prevent system clogging due to polymerization of the resulting condensate, especially if it does not contain an inhibitor, since polymerization generally occurs more rapidly at higher temperatures. Accordingly, a lower system temperature is advantageous with regard to clogging. This is achieved by recirculating the condensate and the associated early cooling of the vapor stream.

[0018] The invention relates to a process for producing a copolymer starting from at least one aromatic vinyl compound, in particular styrene and / or alpha-methylstyrene, and at least one further monomer from the group consisting of acrylonitrile and methacrylate, the process comprising the following steps: a) polymerization of the at least one aromatic vinyl compound and the at least one further monomer in at least one reactor in the presence of at least one organic solvent, whereby a polymerization product is obtained which contains the copolymer, residual monomers, at least one organic solvent and optionally oligomers, b) separation of volatile components from the polymerization product obtained in step a), wherein the separation is carried out in a degassing vessel at a negative pressure of 1 to 150 mbar absolute, in particular of 10 to 100 mbar absolute,takes place and the polymerization product is heated in a first heat exchanger and the first heat exchanger is operated at a first media inlet temperature of more than 200°C, in particular in a range from 220°C to 340°C, and wherein a vapor stream is obtained which contains the volatile components, c) condensation of at least parts of the vapor stream obtained in step b), wherein the vapor stream is cooled in at least a second heat exchanger and a third heat exchanger, a first condensate exits at the second heat exchanger and a second condensate exits at the third heat exchanger, wherein the second heat exchanger is operated at a second media inlet temperature in a range from 10°C to 40°C, in particular from 15°C to 30°C, and the third heat exchanger is operated at a third media inlet temperature in a range from -10°C to 30°C, in particular from -10°C to 15°C,is operated and the second media inlet temperature is at least 10°C higher than the third media inlet temperature, and wherein the first condensate and / or the second condensate are recirculated and brought into contact with the vapor stream at at least one point upstream of the second heat exchanger and / or at a further point in the third heat exchanger, in particular injected into the vapor stream, and d) optionally recirculating the first condensate and / or the second condensate into the reactor of step a).

[0019] The invention also relates to an apparatus for carrying out the process according to the invention, comprising a reactor, a first heat exchanger, a degassing vessel, optionally a column with a column headspace, a second heat exchanger with a gas outlet and a liquid outlet, a third heat exchanger, these being connected in series downstream in the specified order, the third heat exchanger having an inlet space and a collecting space and preferably being arranged vertically, the liquid outlet of the second heat exchanger and / or the collecting space of the third heat exchanger being connected to the inlet space of the third heat exchanger via a first condensate line,optionally, the liquid outlet of the second heat exchanger and / or the collecting space of the third heat exchanger are connected to the column headspace of the column via a second condensate line and optionally, the liquid outlet of the second heat exchanger and / or the collecting space of the third heat exchanger are connected to a vapor line connecting the degassing vessel to the column via a third condensate line.

[0020] The process and apparatus according to the invention allow the condensation of the vapor stream, i.e., the volatile components from the polymerization product, to be carried out more economically and with lower emissions. Furthermore, if a column is used, fewer monomers and solvents are discharged via the oligomers obtained and separated during the condensation. The amount of monomers and solvent discharged can be further reduced by at least partially recirculating the condensate.

[0021] The process according to the invention comprises a multi-stage condensation. At least two heat exchangers, namely the second heat exchanger and the third heat exchanger, are used to condense the vapor stream. The third media inlet temperature is preferably lower than the second media inlet temperature. Accordingly, the second heat exchanger is preferably operated at a higher temperature than the third heat exchanger. In the downstream third heat exchanger, which is preferably operated at a lower coolant temperature than the upstream second heat exchanger, only the volatile components still remaining in the vapor after the second heat exchanger are condensed. Therefore, the coolant, with a particularly lower temperature in the third heat exchanger, is only required for some of the volatile components.For the condensation of the part of the volatile components that has already been condensed in the second heat exchanger, a coolant with a higher temperature is sufficient, which is energetically advantageous.

[0022] By recirculating the condensate, the condensation effect is improved, so that the proportion of vapors that can already be condensed in the second heat exchanger is increased.

[0023] It has been found that by recycling the condensate to support the condensation of the volatile components, which takes place at at least one location and / or the further location, the additional supply of solvents can be dispensed with, so that the accumulation of solvents in the overall system is avoided.

[0024] By recirculating the condensate, which in turn evaporates through contact with the hot volatile components, the volatile components are cooled before the actual condensation takes place, so that the cooling capacity still to be provided by the heat exchangers is reduced and at the same time the condensation efficiency is increased.

[0025] In step a), the at least one aromatic vinyl compound and the at least one further monomer are present in the at least one organic solvent and are polymerized in the at least one reactor to form the polymerization product. Continuous bulk polymerization or solvent polymerization preferably takes place in the at least one reactor. The polymerization product contains the copolymer, residual monomers, the at least one organic solvent, and optionally oligomers. To separate volatile components from the polymerization product, it is fed to the degassing vessel via the first heat exchanger, in which the polymerization product is heated.

[0026] The media temperature refers to the temperature at the inlet of the heating or cooling medium of the respective heat exchanger. In the first heat exchanger, the polymerization product is heated by a heating medium. The first, second, and third heat exchangers serve for cooling; each is supplied with a coolant.

[0027] In the first heat exchanger, the volatile components such as unreacted monomers, solvents, or oligomers are preferably partially evaporated, so that the first heat exchanger can also be referred to as a partial evaporator. In the reactor, the polymerization product is preferably present at a reactor temperature in a range from 105°C to 180°C, more preferably in a range from 105°C to 125°C or in a range from 140°C to 180°C. The polymerization product is preferably heated in the first heat exchanger to a temperature in a range from 180°C to 270°C.

[0028] The first heat exchanger is preferably arranged on the degassing vessel and, in particular, forms a structural unit with the degassing vessel. Alternatively, the first heat exchanger can be arranged separately from the degassing vessel. A vacuum system, which is preferably arranged downstream of the degassing vessel, more preferably downstream of the third heat exchanger, preferably creates a negative pressure in the system, in particular in the degassing vessel into which the polymerization product, including the volatile components, enters from the first heat exchanger. Here, the copolymer is separated from the volatile components. A phase containing the copolymer, which forms the lower phase in the degassing vessel, is discharged. A gaseous phase containing the volatile components and is referred to as vapor or vapor stream, is discharged from the degassing vessel, in particular above the phase containing the copolymer.The vapor stream is primarily gaseous. The third media inlet temperature at the third heat exchanger can be used to control the amount of gaseous vapor reaching the vacuum system.

[0029] The vapor stream preferably contains the aromatic vinyl compound, in particular aromatic vinyl monomer such as styrene and / or alpha-methylstyrene, at least one further monomer, in particular vinyl cyanide monomer such as acrylonitrile, methacrylate monomer such as MMA, oligomers and / or organic solvent such as ethylbenzene, toluene and / or methyl ethyl ketone (MEK), and optionally water, in particular steam. A solution fed to the first heat exchanger and from which the vapor stream is formed preferably contains 1 to 5,000 ppm of water. The stream, referred to as vapor stream B in the context of the invention, varies in quantity and composition over the course of the described process steps.

[0030] The copolymer produced preferably comprises SAN copolymers, AMSAN copolymers and / or SMMA copolymers.

[0031] The vapor stream is condensed in several stages. Preferably, the vapor stream is condensed first 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 and thus clogging of the pipes, and, in particular, achieves the most complete condensation possible.

[0032] Preferably, the vapor stream is passed through a separation unit, in particular a column, upstream of the second heat exchanger, in which the vapor stream is brought into contact with the first condensate and / or the second condensate, oligomers being removed from the vapor stream.

[0033] In a preferred embodiment, a column, which may have internals, is arranged upstream of the second heat exchanger. The first condensate and / or the second condensate are preferably fed into the upper part, in particular at the top, of the column. The bottom of the column is preferably heated, in particular to a temperature in a range from 150°C to 280°C. Oligomers which have been condensed out of the vapor stream are preferably collected in the bottom. The remaining vapor stream is preferably withdrawn at the top of the column and fed to the second heat exchanger. Liquid from the bottom of the column can be recycled, in particular for further depletion of monomers and solvent, and in particular can be fed to the first point together with the first condensate and / or the second condensate.

[0034] The wording “before” with regard to the spatial arrangement of apparatuses is understood in the context of the present invention to mean that a first element such as a heat exchanger or a column is arranged upstream with respect to the conveying direction of a second element such as another heat exchanger, so that the vapor stream first reaches the first element and then to the second element, for example from the column into the second heat exchanger.

[0035] A first condensate is formed in the second heat exchanger, while the remaining gaseous vapor stream is fed to the third heat exchanger, where a second condensate is formed. The first condensate and / or the second condensate are 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 vapor stream.

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

[0037] The negative pressure in the degassing vessel is preferably generated by means of a vacuum system, which is arranged in particular downstream of the at least one further heat exchanger. The vacuum system is preferably designed as a liquid ring pump system and is more preferably operated with a liquid, wherein the liquid in particular comprises an organic mixture, preferably consisting of the organic mixture, and in particular the liquid contains 10 to 90 wt. % of the at least one aromatic vinyl compound, in particular styrene and / or alpha-methylstyrene, 5 to 50 wt. % of the at least one further monomer and 0.5 to 50 wt. % of the organic solvent, in particular ethylbenzene, based on the total liquid in the vacuum system. Styrene and / or alpha-methylstyrene is preferably added to the liquid.The vacuum achievable via the liquid ring pump system, i.e., the minimum absolute pressure, is determined by the vapor pressure of the liquid used. The presence of styrene and / or alpha-methylstyrene in the liquid, for example, can lower the vapor pressure compared to acrylonitrile. The higher the proportion of styrene and / or alpha-methylstyrene in the liquid, the lower the achievable minimum absolute pressure.

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

[0039] The vacuum system is preferably fluidically connected to the collecting chamber of the third heat exchanger. The vacuum system preferably comprises at least one pump, designed as a liquid ring pump system, an overflow, and a pump heat exchanger. The pump heat exchanger is preferably arranged downstream on the high-pressure side of the pump and connected to the low-pressure side of the pump via a return line. A supply line, via which the liquid is added to the vacuum system, in particular the liquid ring pump system, is preferably arranged between the overflow and the pump heat exchanger.

[0040] The vacuum system is preferably located downstream of the third heat exchanger. The vacuum system provides the negative pressure, in particular, in the first heat exchanger, the degassing vessel, possibly the column, the second heat exchanger, and the third heat exchanger.

[0041] Preferably, the negative pressure in the degassing vessel is generated by means of a vacuum system, which is arranged in particular 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 is operated with a liquid that is separated from an exhaust gas taken from the pump by means of a liquid separator on the pressure side of the pump and fed to the pump.

[0042] The pump, which is also called a vacuum pump, can be preceded by a jet pump, which is also called an ejector, in order to enable a further reduction of the pressure in the system part up to the degassing vessel.

[0043] Preferably, at least portions of the first condensate and / or the second condensate are fed to the liquid of the liquid ring pump system. More preferably, the at least one aromatic vinyl compound A is fed to the liquid. By returning the condensate, which contains components of the vapor stream, to the vapor stream, the condensation efficiency can be slightly reduced compared to the addition of solvent to the vapor stream according to EP 3 689 923 B1, and thus the amount of uncondensed vapor at the inlet of the vacuum system can be increased. This can be compensated for by using a liquid in the liquid ring pump system which contains at least one aromatic vinyl compound. The uncondensed vapors can be condensed in the vacuum system and returned to the reactor.

[0044] Optionally, volatile components that have not been condensed in the liquid can be condensed via an exhaust heat exchanger in the vacuum system and returned to the reactor. The exhaust heat exchanger is preferably operated at a higher pressure than the second heat exchanger and / or the third heat exchanger. In particular, the exhaust heat exchanger is operated at a pressure of more than 900 mbar. Therefore, the condensation efficiency of the exhaust heat exchanger is high, so that almost no gaseous vapors escape into the exhaust gas.

[0045] The liquid separator preferably has an overflow. Further preferably, liquid passing through the overflow is removed from the vacuum system and, in particular, returned to the reactor.

[0046] 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 a mixture with an inhibitor, and the amount of aromatic vinyl compound added to the liquid is at least 10% by weight, more preferably at least 20% by weight of a gaseous portion of the vapor stream which is fed to the vacuum system.

[0047] Preferably, the content of inhibitor, in particular dissolved in the at least one aromatic vinyl compound, is 1 to 50 ppm, based on the mixture of aromatic vinyl compound and inhibitor in the vacuum system.

[0048] Preferably, the liquid is cooled in a pump heat exchanger, which is also referred to as the fourth heat exchanger. More preferably, the portion of the at least one aromatic vinyl compound is added to the liquid upstream of the pump heat exchanger. Preferably, the pump heat exchanger is operated at a fourth media inlet temperature T4. More preferably, the fourth media inlet temperature T4 is lower than the second media inlet temperature T2 of the second heat exchanger. In particular, a difference between the second media inlet temperature T2 and the fourth media inlet temperature T4 is at least 10°C. Preferably, the exhaust gas from the vacuum system is at least partially condensed in the exhaust gas heat exchanger, which is also referred to as the fifth heat exchanger, more preferably at ambient pressure, in particular at a pressure of more than 900 mbar.Preferably, the exhaust gas heat exchanger is operated with a fifth media inlet temperature T5; more preferably, the fifth media inlet temperature T5 is lower than the second media inlet temperature T2 of the second heat exchanger. In particular, the difference between the second media inlet temperature T2 and the fifth media inlet temperature T5 is at least 10°C. Due to the lower temperature at the exhaust gas heat exchanger, components that left the second heat exchanger in a gaseous state can still be condensed downstream of the second heat exchanger. Therefore, not all components necessarily have to be condensed in the second heat exchanger, so the second heat exchanger can be operated with a warmer coolant, such as river water.

[0049] Preferably, the first condensate and / or the second condensate are brought into contact with the vapor stream in cocurrent at a first point upstream of the column, the first condensate and the second condensate are brought into contact with the vapor stream in countercurrent at a second point in the column and / or the first condensate and / or the second condensate are brought into contact with the vapor stream in cocurrent at a third point in the third heat exchanger.

[0050] By recirculating the first condensate and / or the second condensate at the first point, especially before the column, the vapor stream is cooled before entering the column, so that fewer deposits, and therefore a lower degree of polymerization, occur in the column.

[0051] The addition of the first condensate and / or the second condensate at the second point leads to further separation of oligomers from the condensate.

[0052] The return of the first condensate and / or the second condensate at the third point serves in particular to cool condensate from the first buffer tank.

[0053] Preferably, the vapor stream is cooled by supplying the first condensate and / or the second condensate at the first point, wherein the temperature difference in the vapor stream before and after the first point is at least 25°C and the vapor stream after the first point has a temperature of at least 120°C.

[0054] Furthermore, the vapor stream is preferably cooled by the supply of the first condensate and / or the second condensate at the second point, wherein the vapor stream more preferably has a temperature in a range of 65°C to 190°C after the second point.

[0055] At least one buffer tank, which can also be referred to as a storage tank, can be arranged downstream of the second heat exchanger and / or the third heat exchanger, i.e., downstream of the second heat exchanger and / or the third heat exchanger. Preferably, the first condensate and / or the second condensate are collected in one or more buffer tanks, with water, in particular from the first condensate and / or the second condensate, optionally being separated in at least one buffer tank. At least one of the one or more buffer tanks preferably comprises a water separator.

[0056] Preferably, the vapor stream when removed from the degassing vessel contains 10 to 90 wt.%, in particular 25 to 65 wt.%, of the at least one aromatic vinyl compound, in particular styrene, 5 to 60 wt.%, in particular 10 to 40 wt.%, of the at least one further monomer, in particular acrylonitrile, and 0.5 to 50 wt.%, in particular 25 to 45 wt.%, of the organic solvent, in particular ethylbenzene, toluene and / or MEK, in each case based on the total vapor stream.

[0057] Additionally, an inhibitor can be added. Preferably, an inhibitor is added to the first condensate and / or the second condensate, in particular upstream of the third heat exchanger. The inhibitor is preferably fed to the third heat exchanger together with the first condensate and / or the second condensate. The inhibitor, in particular dissolved in the at least one aromatic vinyl compound, is preferably added in an amount of 1 to 20 ppm, based on the vapor stream withdrawn from the degassing vessel.

[0058] The inhibitor preferably contains or consists of 4-tert-butylcatechol (TBC), alkoxyphenol such as 4-methoxyphenol (MEHQ) and / or, in particular sterically hindered, thiophenol such as 4-hydroxy-2,2,6,6-tetramethylpiperidinyloxyl (4-hydroxy-TEMPO).

[0059] Preferably, the sum of the amounts of the first condensate and the second condensate which are recycled at the at least one location and the further location, in particular at the first location, the second location and the third location, is at least 50 wt.%, based on the vapor stream which is withdrawn from the degassing vessel.

[0060] Preferably, the first condensate and / or the second condensate are fed at the first point in a total amount of up to 40 wt.%, 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 at the second point, in a total amount of up to 150 wt.%, based on the vapor stream withdrawn from the degassing vessel. If more than 100 wt.% is recirculated, the condensate is recirculated multiple times.

[0061] Preferably, the first condensate and / or the second condensate are injected into a vapor line at at least one point, in particular upstream of the column.

[0062] The first heat exchanger, the second heat exchanger, and the third heat exchanger are preferably designed as tube-bundle 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.

[0063] A vertical arrangement is understood to mean that, in the direction of gravity, there is first an inlet chamber, then a heat exchange surface, in particular a tube bundle, and then a collecting chamber. The inlet chamber is preferably a head chamber, and the collecting chamber is preferably a sump chamber. In particular, 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 of the second heat exchanger, are arranged perpendicular to the direction of gravity.

[0064] The first condensate and / or the second condensate are preferably injected into the head region of the third heat exchanger, in particular in the flow direction of the vapor stream.

[0065] Water is preferably used as the medium in the second heat exchanger. The medium used in the third heat exchanger is preferably brine and / or water containing 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 with river water or a coolant provided by cooling with river water. The river water is preferably used in a secondary circuit.

[0066] The medium in the first heat exchanger is, in particular, a heating medium. Diphyl steam such as Therminol VP1 or a heating fluid, in particular a heating oil, is preferably used as the medium in the first heat exchanger. The heating oil is preferably selected from mineral oils or synthetic oils known to those skilled in the art, for example, as Therminol T66, T62, T55, T72, or Melatherm SH.

[0067] Brief description of the drawings Embodiments of the invention are illustrated in the drawings and are explained in more detail in the following description.

[0068] They show:

[0069] Figure 1 is a schematic representation of a first embodiment of the invention,

[0070] Figure 2 is a schematic representation of a second embodiment of the invention and

[0071] Figure 3 is a schematic representation of a third embodiment of the invention.

[0072] Figure 1 shows a schematic representation of a first embodiment of the invention.

[0073] An aromatic vinyl compound A, at least one further monomer M and an organic solvent L are fed to a reactor R. In the reactor R, a polymerization product PP is formed which comprises a copolymer CP and the organic solvent L.

[0074] The polymerization product PP is first fed to a first heat exchanger WT1, where it is heated with a heating medium having a first medium inlet temperature T1. The heated polymerization product PP passes from the first heat exchanger WT1 into a degassing vessel EB, from which the copolymer CP and a gaseous vapor stream B containing volatile components are withdrawn.

[0075] The vapor stream B is led from the degassing vessel EB via a vapor line BL into a column K with a column headspace KKR, which has internals E. Oligomers OL are withdrawn from the bottom of column K, which is heated by a heating jacket H. From the top of column K, the remaining vapor stream B is further transferred to a second heat exchanger WT2, where the vapor stream B is partially condensed with a coolant having a second media inlet temperature T2, so that 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 tank PB1.

[0076] The remaining gaseous vapor stream B passes from the second heat exchanger WT2 via a gas outlet GA into a third heat exchanger WT3, where it is further condensed using an additional coolant with a third media inlet temperature T3. The second heat exchanger WT2 is arranged horizontally, while the third heat exchanger WT3 is arranged vertically. A second condensate KS2 is taken from the third heat exchanger WT3 from a sump chamber SR and fed to a second buffer tank PB2. Water W is separated in the second buffer tank PB2. The second buffer tank PB2 is hydraulically filled; an upper phase flows over the top of the second buffer tank PB2 into a third buffer tank PB3.

[0077] A vacuum system VA, operated with a liquid F and comprising a vacuum pump VP and a liquid separator FA with an overflow U, is also connected to the sump chamber SR of the third heat exchanger WT3. The vacuum pump VP is designed as a liquid ring pump. The liquid F is cooled in a fourth heat exchanger WT4. An exhaust gas AG from the vacuum system VA is condensed in a fifth heat exchanger WT5 to reduce gaseous emissions from the process. Buffer is stored in the third buffer tank PB3 to compensate for throughput fluctuations.

[0078] The first condensate KS1 from the heat exchanger WT2 is injected into the vapor stream B at a first point ED1 in the vapor line BL upstream of the column K. By evaporating the first condensate KS1 at the first point ED1, the vapor stream B is already cooled before it enters the column K.

[0079] Furthermore, the first condensate KS1 from the second heat exchanger WT2 is introduced into the top of the column K at a second point ED2 and brought into contact with the vapor stream B in order to separate the oligomers OL.

[0080] In addition, the first condensate KS1 is injected at a third point ED3 in a headspace KR of the third heat exchanger WT3 in order to further cool the vapor stream B and obtain the second condensate KS2.

[0081] The second condensate KS2 and the mixture from the third buffer tank PB3 can be partially added to the first condensate KS1 for recirculation at the first point ED1, the second point ED2, or the third point ED3, respectively. Furthermore, the mixture collected in the third buffer tank PB3 is recirculated to the reactor R by a pump and, if necessary, through another buffer tank to convert remaining unreacted monomers into the copolymer CP. Pumps P are used to convey the condensates KS1 and KS2.

[0082] Figure 2 schematically shows a second embodiment of the invention. In the exemplary second embodiment, in contrast to the first embodiment, the vapor stream B is fed to the second heat exchanger WT2 directly from the degassing vessel EB; thus, there is no column K. The first condensate KS1 is injected from the second heat exchanger WT2 into the headspace KR of the third heat exchanger WT3 to cool the condensate as much as possible, and the second condensate KS2 is optionally returned to the reactor R via another buffer vessel. Inhibitor can be added during the return to the third heat exchanger WT3.

[0083] Figure 3 shows a schematic representation of a third embodiment of the invention. The vapor stream B is fed to the second heat exchanger WT2 via a column K and from the second heat exchanger WT2 into a third heat exchanger WT3. The second heat exchanger WT2 and the third heat exchanger WT3 are arranged horizontally in this exemplary embodiment.

[0084] The first condensate KS1 from the second heat exchanger WT2 and the second condensate KS2 from the third heat exchanger WT3 are mixed in a second buffer tank PB2 and partially fed at a first point ED1 into the vapor stream B in the vapor line BL upstream of the column K and at a second point ED2 at the top of the column K. The warmer first condensate KS1 is mixed with the cold second condensate KS2 in the second buffer tank PB2.

[0085] The invention is not limited to the embodiments described here. Rather, numerous modifications are possible within the scope defined by the claims.

[0086] Examples

[0087] The process was carried out according to the first embodiment shown in Figure 1, producing a SAN copolymer.

[0088] A total feed stream of 4.3 t / h was fed to the reactor. At the degassing vessel, 2.47 t / h of copolymer and 1.83 t / h of vapor were removed. 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 wt.% styrene and 35 wt.% acrylonitrile was produced.

[0089] Example 1

[0090] The vapor stream was taken from the degassing vessel at a temperature of 260°C. Upstream of the column, the vapor stream was contacted with 200 l / h of the first condensate, with the mixture being injected into the vapor line so that the total feed stream to the column had a temperature of 225°C. The bottom of column K was heated to 250°C.

[0091] At the top of the column, 2.2 t / h of the first condensate were fed in. This feed point resulted in a recycling rate of 120%.

[0092] The pressure at the top of the column was 53 mbar. The vapor stream was withdrawn from the top of the column at a temperature of 160 °C and fed to the second heat exchanger, where it was partially condensed with a coolant having a second media inlet temperature T2 of 19 to 25 °C. The second media temperature upon leaving the second heat exchanger was 30 °C. 2.86 t / h of the first condensate were withdrawn from the second heat exchanger, and the remaining vapor stream was fed to the third heat exchanger at a temperature of 30 °C. The first condensate had a temperature of 47 °C.

[0093] At the third location, 0.46 t / h of the first condensate was injected into the headspace of the third heat exchanger. The third fluid inlet temperature at the third heat exchanger was 7°C.

[0094] After the third heat exchanger, 0.85 t / h of styrene was added and the mixture was returned to the reactor.

[0095] The fourth heat exchanger (WT4) and the fifth heat exchanger (WT5) were operated at a coolant inlet temperature of 7°C. Only traces of monomers and solvents were detectable in the exhaust gas from the fifth heat exchanger (WT5). No wastewater requiring disposal was generated.

[0096] Example 2

[0097] Based on the embodiment shown in Figure 3, a further embodiment is described below, wherein approximately 500 kg / h of the mixture of first and second condensate were injected into the vapor line at the first point, with a recycling rate of approximately 95%. This resulted in a temperature of 158°C in the total stream at the inlet to the column. The bottom of the column was heated to a temperature of 162°C. 400 kg / h of the mixture of first condensate and second condensate were fed into the headspace of the column. The vapor stream leaving the top of the column had a temperature of 79.5°C. The second media temperature upon leaving the second heat exchanger was 24°C, so that the remaining vapor stream had a temperature of 35°C and was fed into the third heat exchanger.At the third heat exchanger, the third media inlet temperature T3 was 1.5 °C, resulting in a temperature of the gas stream leaving the third heat exchanger WT3 of 21 °C.

[0098] In this example, no wastewater was generated that required wastewater treatment. Only traces of monomers and solvents were detectable in the exhaust gas from the vacuum pump.

[0099] While in Example 1 a practically complete recovery of all monomers and solvents was achieved by several condensate addition points and neither wastewater was generated nor significant pollution was observed in the exhaust gas, in Example 2 this was achieved by a significantly greater reduction of the vapor temperature upstream of the second heat exchanger WT2.

[0100] Comparison example 1

[0101] The process was essentially carried out as in Example 1, except that instead of the first condensate, the vapor stream was contacted with 200 l / h of ethylbenzene as organic solvent L upstream of the column. This led to an increase in the fill level in the buffer tank upstream of the reactor, so that after 12 hours, approximately 6 t of the mixture had to be separated and disposed of.

[0102] List of reference symbols

[0103] CP Copolymer A Aromatic vinyl compound M Additional monomer R Reactor L Organic solvent PP Polymerization product EB Degassing vessel T1 First media inlet temperature B Vapor stream BL Vapor line 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 media inlet temperature T3 Third media inlet temperature ED1 First point ED2 Second point ED3 Third point I Inhibitor VA Vacuum system F Liquid FA Liquid separator U Overflow PB1 First buffer vessel PB2 Second buffer vessel PB3 Third buffer vessel P Pump E Internals H Heating jacket K Column OL Oligomers SR Bottom chamber W Water

[0104] VP vacuum pump

[0105] AG Exhaust

[0106] KR Head space

Claims

Patent claims 1. A process for producing a copolymer (CP) starting from at least one aromatic vinyl compound (A), in particular styrene and / or alpha-methylstyrene, and at least one further monomer (M) from the group consisting of acrylonitrile and methacrylate, the process comprising the following steps: a) polymerization of the at least one aromatic vinyl compound (A) and the at least one further monomer (M) in at least one reactor (R) in the presence of at least one organic solvent (L), whereby a polymerization product (PP) is obtained which contains the copolymer (CP), residual monomers, at least one organic solvent (L) and optionally oligomers, b) separation of volatile components from the polymerization product (PP) obtained in step a), wherein the separation is carried out in a degassing vessel (EB) at a negative pressure of 1 to 150 mbar absolute, in particular of 10 to 100 mbar absolute,takes place and the polymerization product (PP) is heated in a first heat exchanger (WT1) and the first heat exchanger (WT1) is operated at a first media inlet temperature (T1) of more than 200°C, in particular in a range from 220°C to 340°C, and wherein a vapor stream (B) is obtained which contains the volatile components, c) condensation of at least parts of the vapor stream (B) obtained in step b), wherein the vapor stream (B) is cooled in at least a second heat exchanger (WT2) and a third heat exchanger (WT3), a first condensate (KS1) exits at the second heat exchanger (WT2) and a second condensate (KS2) exits at the third heat exchanger (WT3), wherein the second heat exchanger (WT2) is operated at a second media inlet temperature (T2) in a range from 10°C to 40°C, in particular from 15°C to 30°C, and the third heat exchanger (WT3) with a third media inlet temperature (T3) in a range of -10°C to 30°C,especially from -10°C to 15°C, and, the second media inlet temperature (T2) is at least 10°C higher than the third media inlet temperature (T3), and wherein the first condensate (KS1) and / or the second condensate (KS2) are recirculated and are brought into contact with the vapor stream (B) at at least one point (ED1, ED2) upstream of the second heat exchanger (WT2) and / or at a further point (ED3) in the third heat exchanger (WT3), in particular are injected into the vapor stream (B), and d) optionally recirculating the first condensate (KS1) and / or the second condensate (KS2) into the reactor (R) of step a). Process according to claim 1, characterized in that the vapor stream (B) is passed upstream of the second heat exchanger (WT2) through a separation unit, in particular a column (K), in which the vapor stream (B) is brought into contact with the first condensate (KS1) and / or the second condensate (KS2), oligomers being removed from the vapor stream (B).Process according to claim 2, characterized in that the first condensate (KS1) and / or the second condensate (KS2) are brought into contact with the vapor stream (B) in cocurrent at a first point (ED1) upstream of the column (K), the first condensate (KS1) and / or the second condensate (KS2) are brought into contact with the vapor stream (B) in countercurrent at a second point (ED2) in the column (K) and / or the first condensate (KS1) and / or the second condensate (KS2) are brought into contact with the vapor stream (B) in cocurrent at a third point (ED3) in the third heat exchanger (WT3).Method according to one of claims 1 to 3, characterized in that the vapor stream (B) is cooled by the supply of the first condensate (KS1) and / or the second condensate (KS2) at the first point (ED1) and the temperature difference in the vapor stream (B) before and after the first point (ED1) is at least 25°C and the vapor stream (B) after the first point (ED1) has a temperature of at least 120°C and / or the vapor stream (B) is cooled by the supply of the first condensate (KS1) and / or the second condensate (KS2) at the second point (ED2) and the vapor stream (B) after the second point (ED2) has a temperature in a range from 65°C to 190°C.

5. Method according to one of claims 1 to 4, characterized in that the first condensate (KS1) and / or the second condensate (KS2) are collected in one or more buffer tanks (PB1, PB2), wherein water is optionally separated in at least one buffer tank (PB1, PB2).

6. Process according to one of claims 1 to 5, characterized in that the vapor stream (B) upon removal from the degassing vessel (EB) is 10 to 90 wt.% of at least one aromatic vinyl compound (A), 5 to 60 wt.% of at least one further monomer (M) and 0.5 to 50 wt.% of the organic solvent (L), in particular ethylbenzene, based on the total vapor stream (B).

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

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

10. Process according to one of claims 2 to 9, characterized in that the first condensate (KS1) and / or the second condensate (KS2) are injected into a vapor line at at least one point (ED1) upstream of the column (K). 11 . Process according to one of claims 2 to 10, characterized in that the first condensate (KS1) and / or the second condensate (KS2) are fed at the top of the column (K).

12. Method according to one of claims 1 to 11, characterized in that the first condensate (KS1) and / or the second condensate (KS2) at the further Point (ED3) in the third heat exchanger (WT3), in particular at the third point (ED3), in a total amount of up to 150 wt. %, based on the vapor stream (B) withdrawn from the degassing vessel (EB). Method according to 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) are fed into an inlet chamber of the third heat exchanger (WT3). Process according to one of claims 1 to 13, characterized in that the sum of the amounts of the first condensate (KS1) and the second condensate (KS2) which are recycled at the at least one point (ED1, ED2) and the further point (ED3), in particular at the first point (ED1), the second point (ED2) and the third point (ED3), is at least 50 wt.%, based on the vapor stream (B) which is withdrawn from the degassing vessel (EB).Method according to one of claims 1 to 14, characterized in that the second heat exchanger (WT2) is operated with river water or a coolant which is provided by cooling with river water. Method according to one of claims 1 to 15, characterized in that the negative pressure in the degassing container (EB) is generated by means of a vacuum system (VA), which is arranged in particular downstream of the at least one further heat exchanger (WT2, WT3), and the vacuum system (VA) is designed as a liquid ring pump system and is operated with a liquid (F), wherein the liquid (F) comprises an organic mixture, preferably consists of the organic mixture, and in particular the liquid (F) to. 10 to 90 wt.% of at least one aromatic vinyl compound (A), 5 to 50 wt.% of at least one further monomer (M) and 0.5 to 50 wt.% of the organic solvent (L), in particular ethylbenzene, based on the total liquid (F) in the vacuum system (VA). 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 column headspace (KKR), a second heat exchanger (WT2) with a gas outlet (GA) and a liquid outlet (FLA), and a third heat exchanger (WT3), these being connected in series downstream in the specified order. the third heat exchanger (WT3) has an inlet space and a collection space and is preferably arranged vertically, the liquid outlet of the second heat exchanger (WT2) and / or the collection space of the third heat exchanger (WT3) are connected to the inlet space of the third heat exchanger (WT3) via a first condensate line, optionally the liquid outlet of the second heat exchanger (WT2) and / or the collection space of the third heat exchanger (WT3) are connected to the column head space (KKR) of the column (K) via a second condensate line and optionally the liquid outlet of the second heat exchanger (WT2) and / or the collection space of the third heat exchanger (WT3) are connected to a vapor line which connects the degassing vessel (EB) to the column (K) via a third condensate line.

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