Process for preparing a copolymer proceeding from at least one aromatic vinyl compound

Abstract

The invention relates to a process for preparing 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 process comprising the following steps: a) polymerization, b) removal of volatile components to obtain a vapour stream (B), c) condensation of at least portions of the vapour stream (B), wherein a negative pressure is generated by means of a vacuum system (VA) and the vacuum system (VA) comprises at least one pump (P) which is designed as a liquid-ring pump system and is operated with a liquid (F), which on the pressure side of the pump (P) is separated by means of a liquid separator (FA) from a discharge gas withdrawn from the pump (P) and is supplied to the pump (P). The invention further relates to an apparatus for carrying out the process.

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 styrene 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, the condensation of at least portions of the vapor stream, and the generation of a vacuum. 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. The amount of monomers such as styrene, alpha-methylstyrene, methyl methacrylate, and / or organic solvents such as ethylbenzene discharged from the process can be reduced by using liquid ring pumps to create a vacuum, which are filled with organic liquids containing the monomers and solvents used in the reaction.

[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, retaining these even under the influence of weathering. These copolymers can be used in various fields, including the manufacture of automobiles, computers, printers, copiers, household appliances, audio systems, and electrical components. A copolymer of an aromatic vinyl compound and a vinyl cyanide compound and / or methacrylate is typically prepared 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 called a degassing vessel, and volatile components such as residual monomers and organic solvent are removed under vacuum. Condensation of the separated volatile components takes place using condensers. Purification is then carried out to obtain the final copolymer product in the highest possible yield.

[0007] 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.

[0008] The disadvantage of increasing the pressure is the associated undesirable increase in the proportion of volatile organic components remaining in the polymer.

[0009] 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.

[0010] 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.

[0011] EP 3 689 919 A1 relates to the production of a polymer from an aromatic vinyl compound and a vinyl cyanide compound, wherein a vaporized portion of the reaction mixture is also fed from the reactor to a condenser. Liquid ring pumps are known for generating a vacuum. Condensable components in the inlet stream to the vacuum pump can condense in the liquid ring. If water is used as the liquid in the liquid ring, it is typically contaminated, especially if the drawn-in gas contains organic components. This results in wastewater that must be discarded and purified. Accordingly, emissions into the environment arise, which must be minimized.Furthermore, the use of water in a liquid ring pump limits the temperature ranges for heat exchangers to cool the liquid in the liquid ring pump system, since undesirable ice formation can occur at temperatures below 0°C.

[0012] The task is to provide an energy-efficient and low-emission process and a corresponding device that avoids the separation and disposal of wastewater and any condensed vapors.

[0013] 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, in particular of 10 to 100 mbar,absolute 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, whereby a vapor stream is obtained which contains the volatile components, c) condensation of at least parts of the vapor stream obtained in step b) in at least one further heat exchanger, whereby at least one condensate is obtained, d) optionally recycling of the at least one condensate to the reactor of step a), wherein the negative pressure in the degassing vessel is generated by means of a vacuum system which is arranged in particular downstream of the at least one further heat exchanger, and the vacuum system comprises at least one pump which is designed as a liquid ring pump system and is operated with a liquid which is obtained on the pressure side of the pump from an exhaust gas which is taken from the pump,separated by a liquid separator and fed to the pump.

[0014] The invention further 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 and a vacuum system, wherein these are connected in series downstream in the specified order, the third heat exchanger has an inlet space, in particular a headspace, and a collection space, in particular a sump space, and is preferably arranged vertically and the vacuum system is fluidically connected to the collection space of the third heat exchanger, the vacuum system has at least one pump which is designed as a liquid ring pump system,an overflow and a pump heat exchanger, and the pump heat exchanger is arranged downstream on the high-pressure side of the pump and is connected to the low-pressure side of the pump via a return line. Preferably, a supply line is arranged between the overflow and the pump heat exchanger, via which the liquid is added to the vacuum system, in particular the liquid ring pump system.

[0015] 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 with lower emissions. By using a liquid for the liquid ring pump that contains condensable components of the vapor, the generation of wastewater is eliminated.

[0016] The formation of wastewater can be prevented by operating the liquid ring pump system with a liquid taken from the discharge side of the pump, thus recirculating the condensate from the process, and using it as a liquid ring. Accordingly, an organic liquid is used in the vacuum system, the components of which are contained in the gas drawn in by the pump. By separating the liquid from the exhaust gas on the discharge side of the pump, it is also possible, particularly via the overflow, to return condensed organic components of the exhaust gas to the reactor for further conversion, if necessary via an evaporative cooler.

[0017] 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.

[0018] The liquid comprises in particular an organic mixture and preferably consists 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 that can be achieved, is determined by the vapor pressure of the liquid used. The presence of styrene and / or alpha-methylstyrene in the liquid can reduce the vapor pressure compared to acrylonitrile, for example.The higher the proportion of styrene and / or alpha-methylstyrene in the liquid, the lower the achievable minimum absolute pressure.

[0019] Particularly during the degassing of polymers made from aromatic vinyl compounds, such as acrylonitrile and / or methacrylate, small amounts of gaseous monomers and / or solvents may remain in the exhaust stream of the vacuum system. Optionally, these volatile components can be condensed in the exhaust stream of the vacuum system via a heat exchanger.

[0020] 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.

[0021] The media inlet temperature refers to the temperature in 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. At least one additional heat exchanger serves for cooling; a coolant is supplied to each of them.

[0022] 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.

[0023] Preferably, the first heat exchanger is 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.

[0024] The vacuum system, which is preferably arranged downstream of the degassing vessel, more preferably downstream of the at least one further 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 removed. A gaseous phase containing the volatile components and is referred to as vapor or vapor stream, is removed from the degassing vessel, in particular above the phase containing the copolymer. The vapor stream is in particular gaseous.

[0025] 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.

[0026] The produced copolymer preferably comprises SAN copolymers, AMSAN copolymers, and / or SMMA copolymers. The vapor stream is preferably condensed in several stages. More preferably, the vapor stream is condensed first in a second heat exchanger and then in a third heat exchanger. The vapor stream is further cooled in the third heat exchanger, which also counteracts polymerization and thus blockage of the pipeline, and in particular, achieves the most complete condensation possible.

[0027] 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.

[0028] Preferably, the at least one aromatic vinyl compound A is added to the liquid of the liquid ring pump system, in particular in a mixture with the inhibitor. Further preferably, at least portions of the at least one condensate are added to the liquid F.

[0029] Preferably, the liquid outlet of the second heat exchanger and / or the collecting space of the third heat exchanger are 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. 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.

[0030] The aromatic vinyl compound is preferably fed at the liquid separator and / or between the liquid separator and the fourth heat exchanger.

[0031] By adding the aromatic vinyl compound or by recirculating the condensate, blockage of the vacuum system and the overflow lines due to polymerization is avoided.

[0032] By returning the condensate, which contains components of the vapor stream, to the vapor stream, the condensation efficiency can be slightly reduced and the amount of uncondensed vapor at the inlet of the vacuum system increased compared to adding solvent to the vapor stream, according to EP 3 689 923 B1. This is compensated for by using a liquid in the liquid ring pump system that contains at least one aromatic vinyl compound. The uncondensed vapors can be condensed in the vacuum system and returned to the reactor. However, particularly with efficient condensation of the vapor stream, few monomers and / or solvents remain in the exhaust gas and correspondingly fewer organic components are condensed in the vacuum system. Therefore, the exchange rate of the liquid ring pump liquid is low, as is the amount of liquid flowing off via the overflow of the liquid separator.Due to the low exchange rate in the condensate with low overflow, the liquid has a relatively long residence time in the vacuum system, which can lead to polymerization and clogging. The additional addition of the aromatic vinyl compound A reduces the liquid's residence time in the vacuum system and thus prevents polymerization.

[0033] The remaining vapor stream drawn into the vacuum system contains, in particular, the less condensable low-boiling components. The higher the proportion of low-boiling components in the liquid ring system, i.e., the liquid, the lower the achievable vacuum, and thus the higher the absolute pressure. The aromatic vinyl compound, in comparison, is a high-boiling component, so a better vacuum, i.e., a lower absolute pressure, can be achieved when the aromatic vinyl compound is added to the liquid. A lower pressure can result in a lower residual monomer content in the degassed copolymer.

[0034] 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.

[0035] 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 a mixture with an inhibitor, and the amount of aromatic vinyl compounds 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.

[0036] The added aromatic vinyl compound preferably contains an inhibitor, in particular in a concentration of more than 1 ppm, based on the amount of aromatic vinyl compound added. The inhibitor content, in particular dissolved in the at least one aromatic vinyl compound, is preferably 1 to 50 ppm, based on the mixture of aromatic vinyl compound and inhibitor in the vacuum system.

[0037] By adding the inhibitor, blockages in the area of ​​the liquid ring pump and in the connecting line from the overflow to the container can be minimized or avoided.

[0038] Preferably, the vapor stream is cooled in at least a second heat exchanger and a third heat exchanger, wherein the second heat exchanger 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 is operated at a third media inlet temperature T3 in a range from -10° to 30°C, in particular from -10°C to 15°C, and wherein in particular the second media inlet temperature T2 is at least 10°C higher than the third media inlet temperature T3. The amount of gaseous vapor that reaches the vacuum system can be controlled via the third media inlet temperature T3 at the third heat exchanger.

[0039] At least two heat exchangers, namely the second heat exchanger and the third heat exchanger, are preferably used to condense the vapor stream. The third media inlet temperature is preferably lower than the second media inlet temperature. Accordingly, the heat exchanger is preferably operated at a higher temperature than the first 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. The coolant with the lower temperature in the third heat exchanger is therefore only required for a portion of the volatile components. A coolant with a higher temperature is therefore sufficient for the condensation of the portion of the volatile components that has already been condensed in the second heat exchanger, which is energetically advantageous.

[0040] By recirculating the condensate, the condensation effect can be improved, so that the proportion of vapors that can already be condensed in the second heat exchanger is increased.

[0041] Preferably, the liquid is cooled in a pump heat exchanger, which can also be referred to as a fourth heat exchanger. Preferably, the 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 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.

[0042] 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, a 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.In the second heat exchanger, not all components necessarily have to be condensed, so that the second heat exchanger can be operated with a warmer coolant such as river water.

[0043] In particular, the exhaust gas heat exchanger is subjected to a higher pressure than the one upstream of the vacuum system. This allows for better condensation and thus the removal of organic components, particularly acrylonitrile, from the exhaust gas of the vacuum system, especially the pump.

[0044] The vacuum system, in particular, has a liquid ring pump fluid circuit with the liquid separator and the 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 the overflow, the fourth heat exchanger, and the exhaust gas heat exchanger.

[0045] Preferably, the vapor stream, in particular upstream of the at least one further heat exchanger, in particular upstream of the second heat exchanger and the third heat exchanger, is passed through a separation unit, in particular a column, in which the vapor stream is brought into contact with the at least one condensate, in particular with the first condensate and / or the second condensate, oligomers being removed from the vapor stream, and the at least one condensate, preferably the first condensate and / or the second condensate, is fed in particular at the top of the column. In a preferred embodiment, a column, which may have internals, is connected upstream of the second heat exchanger. Preferably, the first condensate and / or the second condensate are fed in the upper part, in particular at the top, of the column.

[0046] The bottom of the column is preferably heated, in particular to a temperature in a range from 150°C to 280°C. Oligomers condensed from 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 at least one further heat exchanger, in particular the second heat exchanger. A liquid phase from the bottom of the column can be recycled, in particular for further depletion of monomers and solvent, and in particular fed upstream of the column, in particular at a first point, together with the at least one condensate, in particular with the first condensate and / or the second condensate.

[0047] 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.

[0048] In a preferred embodiment, 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 preferably recycled 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.

[0049] Preferably, in particular when the column is connected upstream of the second heat exchanger, the at least one condensate, in particular the first condensate and / or the second condensate, is returned, in particular injected, into the column and / or into a vapor line between the degassing vessel and the column.

[0050] The vacuum system is preferably arranged downstream of the last of the at least one further heat exchanger, in particular the third heat exchanger. The vacuum system provides the negative pressure, in particular in the first heat exchanger, the degassing vessel, optionally the column, the at least one further heat exchanger, in particular the second heat exchanger, and the third heat exchanger. Preferably, the first condensate and / or the second condensate are recirculated into vapor stream B.

[0051] Preferably, a first condensate exits the second heat exchanger and a second condensate exits the third heat exchanger. Further preferably, the first condensate and / or the second condensate are recirculated and brought into contact with the vapor stream B at at least one point upstream of the second heat exchanger and / or at another point in the third heat exchanger, in particular injected into the vapor stream.

[0052] By recirculating at least part of the condensate, the condensation of the vapor stream, i.e., the volatile components from the polymerization product, can be carried out more effectively and with lower emissions. Furthermore, the oligomers obtained from the condensation have a higher purity.

[0053] 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.

[0054] By returning the condensate to the vapor stream to support the condensation of the volatile components, an additional supply of solvents for cooling can be dispensed with, thus preventing an accumulation of solvents in the overall system.

[0055] 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, in particular by injection into a vapor line. Additionally or alternatively, the first condensate and / or the second condensate are brought into contact with the vapor stream in cocurrent at a second point in the column. Additionally or alternatively, 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.

[0056] By recirculating the first condensate and / or the second condensate at the first point, especially upstream of the column, the vapor stream is cooled before entering the column, resulting in fewer deposits and thus a lower degree of polymerization in the column. Feeding the first condensate and / or the second condensate at the second point leads to further separation of oligomers from the condensate.

[0057] The return of the first condensate and / or the second condensate at the third location serves in particular to cool condensate from the first buffer tank.

[0058] Preferably, the third heat exchanger is arranged vertically; more preferably, the first condensate and / or the second condensate are fed into an inlet chamber of the third heat exchanger.

[0059] 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.

[0060] 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 first point.

[0061] At least one buffer tank, which can also be referred to as a storage tank, can be arranged downstream of the at least one further heat exchanger, in particular 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 at least one condensate, in particular the first condensate and / or the second condensate, is collected in one or more buffer tanks, with water, in particular from the at least one 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.

[0062] Preferably, the vapor stream when removed from the degassing vessel contains 10 to 90% by weight, in particular 25 to 65% by weight, of the at least one aromatic vinyl compound, in particular styrene and / or alpha-methylstyrene, 5 to 60% by weight, in particular 10 to 40% by weight, of the at least one further monomer, in particular acrylonitrile, and 0.5 to 50% by weight, in particular 25 to 45% by weight, of the organic solvent, in particular ethylbenzene, toluene and / or MEK, in each case based on the total vapor stream.

[0063] In addition or alternatively to adding an inhibitor to the vacuum system, an inhibitor can be added upstream of the vacuum system. An 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 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.

[0064] 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).

[0065] Preferably, the sum of the amounts of the at least one condensate, in particular of the first condensate and the second condensate, which is recycled at the at least one point and the further point, in particular at the first point, the second point and the third point, is at least 50 wt.%, based on the vapor stream which is withdrawn from the degassing vessel.

[0066] Preferably, the at least one condensate, in particular the first condensate and / or the second condensate, is fed to the first point in a total amount of up to 40 wt. %, based on the vapor stream withdrawn from the degassing vessel. Furthermore, the at least one condensate, in particular the first condensate and / or the second condensate, is 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 recycled, the condensate is recirculated multiple times.

[0067] Preferably, the at least one condensate, in particular the first condensate and / or the second condensate, is injected into the vapor line upstream of the column, in particular at the at least one point.

[0068] The first heat exchanger and the at least one further heat exchanger, in particular 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. A vertical arrangement is understood to mean that in the direction of gravity there is first an inlet space, in particular a head space, then a heat exchange surface, in particular a tube bundle, and then a collection space, in particular a sump space. The inlet space is preferably a head space and the collection space is preferably a sump space. 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, especially those of the second heat exchanger, are arranged perpendicular to the direction of gravity.

[0069] The at least one condensate, in particular the first condensate and / or the second condensate, are preferably injected into the head space of the third heat exchanger, in particular in the flow direction of the vapor stream.

[0070] 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.

[0071] 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.

[0072] Short description of the drawings

[0073] Embodiments of the invention are illustrated in the drawings and are explained in more detail in the following description.

[0074] They show:

[0075] Figure 1 is a schematic representation of a process overview and

[0076] Figure 2 is a schematic representation of an embodiment of the method according to the invention.

[0077] Figure 1 shows a schematic representation of a process overview. 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. The polymerization product PP is first fed to a first heat exchanger WT1, where the polymerization product PP is heated using a heating medium having a first media 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.

[0078] 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.

[0079] 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.

[0080] A vacuum system VA is also connected to the sump chamber SR of the third heat exchanger WT3. This vacuum system is operated with a 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 a fourth heat exchanger WT4. Flue gas AG from the vacuum system VA is condensed in a fifth heat exchanger WT5 to reduce gaseous emissions from the process. Buffer gas is stored in the third buffer tank PB3 to compensate for throughput fluctuations. 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 cooled before it enters the column K.

[0081] 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.

[0082] 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.

[0083] 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.

[0084] Figure 2 shows a schematic representation of an embodiment of the method according to the invention.

[0085] The aromatic vinyl compound A and the further monomer M are reacted in the reactor R in the solvent L to form the copolymer CP. The polymerization product PP is transferred to the degassing vessel EB, which has a first heat exchanger WT1, in which the copolymer CP is separated from a vapor stream B.

[0086] The vapor stream B undergoes multi-stage condensation using a second heat exchanger WT2 and a third heat exchanger WT3. This produces a first condensate KS1 and a second condensate KS2, which are temporarily stored in a buffer tank PB and at least partially returned to the reactor R. The remaining gaseous vapor stream B from the condensation enters a vacuum system VA, which includes a liquid ring pump system. A liquid separator FA is connected downstream of the vacuum system VA, in which a liquid F is separated, which drives the liquid ring pump system.

[0087] Aromatic vinyl compound A mixed with inhibitor is added to the liquid F separated by the liquid separator FA via a feed line ZL, and the liquid stream is fed to a fourth heat exchanger WT4 before the liquid F and the added aromatic vinyl compound A are returned to the vacuum system VA. An exhaust gas AG from the liquid separator FA is further cooled in an exhaust gas heat exchanger WT5 to remove condensable components from the exhaust gas AG.

[0088] The fourth heat exchanger WT4 is operated with a fourth media inlet temperature T4 and the exhaust gas heat exchanger WT5 is operated with a fifth media inlet temperature T5.

[0089] The invention is not limited to the embodiments described here. Rather, numerous modifications are possible within the scope defined by the claims.

[0090] Examples

[0091] The method was carried out according to the embodiment shown in Figure 1.

[0092] Example 1

[0093] A total feed stream of 10.9 t / h was fed to the reactor. 6.9 t / h of copolymer and 4 t / h of vapor were withdrawn at the degassing vessel. The polymer contained 65 wt.% styrene and 35 wt.% ACN. A pressure of 50 mbar absolute was measured in the degassing vessel. The vapor stream was withdrawn from the degassing vessel at a temperature of 260°C. Upstream of the column, the vapor stream was contacted with 325 l / h of the first condensate. The bottom of column K was heated to 250°C. 2.2 t / h of the first condensate were fed at the top of the column. Furthermore, the pressure at the top of the column was 45 mbar. The vapor stream was taken 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 with a second media inlet temperature T2 of 23 °C. The second media temperature leaving the second heat exchanger was 30 °C.3.5 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. At the third point, 1.0 t / h of the first condensate was sprayed into the headspace of the third heat exchanger. The third media inlet temperature T3 at the third heat exchanger was 7 °C.

[0094] A quantity of 150 kg / h of gaseous vapor was fed to the liquid ring pump while generating the negative pressure. Upstream of the fourth heat exchanger WT4, 0.5 t / h of a solution containing 12 ppm TBC in styrene was added. The fourth heat exchanger WT4 and the exhaust gas heat exchanger WT5 were operated at a coolant inlet temperature, T4 and T5, of 7°C, respectively. The quantity removed at the overflow was 650 kg / h. Only traces of monomers and solvents were detectable in the exhaust gas from the exhaust gas heat exchanger WT5. ​​No wastewater requiring disposal was generated.

[0095] Even after two years of operation, no growths were found in the vacuum system or in the overflow line.

[0096] Example 2

[0097] Example 2 was essentially carried out as in Example 1, except that the styrene supply was shut off upstream of the fourth heat exchanger (WT4). Subsequently, a slow increase in pressure in the degassing tank to 55 mbar absolute was observed. After approximately 6 months of operation, growths were found at the outlet of the liquid ring pump and in the line from the liquid separator to the third buffer tank (PB3).

[0098] List of reference symbols

[0099] CP Copolymer

[0100] A Aromatic vinyl compound

[0101] M Additional monomer

[0102] R reactor

[0103] Organic solvent

[0104] PP polymerization product

[0105] EB degassing tank

[0106] T1 First media inlet temperature

[0107] B vapor stream

[0108] BL vapor line

[0109] WT1 First heat exchanger

[0110] WT2 Second heat exchanger

[0111] WT3 Third heat exchanger

[0112] WT4 pump heat exchanger

[0113] WT5 exhaust gas heat exchanger

[0114] GA gas outlet

[0115] FLA liquid outlet

[0116] KS1 First Condensate

[0117] KS2 Second condensate

[0118] T2 Second media inlet temperature

[0119] T3 Third media inlet temperature

[0120] ED1 First position

[0121] ED2 Second Position

[0122] ED3 Third Site Inhibitor

[0123] VA Vacuum system F Liquid FA Liquid separator U Overflow ZL Supply line PB1 First buffer tank PB2 Second buffer tank PB3 Third buffer tank P Pump E Internals H Heating jacket K Column

[0124] OL Oligomers SR Sump chamber W Water VP Vacuum pump

[0125] AG exhaust KR headspace PB buffer tank

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, in particular of 10 to 100 mbar,absolute 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, whereby 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) in at least one further heat exchanger (WT2, WT3), whereby at least one condensate (KS1, KS2) is obtained, d) optionally recycling the at least one condensate (KS1, KS2) into the reactor (R) from step a), whereby the negative pressure in the degassing vessel (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) has at least one Pump includes (P),which is designed as a liquid ring pump system and is operated with a liquid (F) which is separated on the pressure side of the pump (P) from an exhaust gas taken from the pump (P) by means of a liquid separator (FA) and fed to the pump (P). Process according to claim 1, characterized in that at least parts of the at least one condensate (KS1, KS2) are fed to the liquid (F). Process according to claim 1 or 2, characterized in that the liquid separator (FA) has an overflow (II) and liquid (F) which passes through the overflow (U) is removed from the vacuum system (VA). Process according to one of claims 1 to 3, characterized in that a part of the at least one aromatic vinyl compound (A) is added to the liquid (F), wherein the at least one aromatic vinyl compound (A) is present as a mixture with an inhibitor (I) and the amount of aromatic vinyl compound (A) added to the liquid (F) is at least 10% by weight, preferably at least 20% by weight of a gaseous portion of the vapor stream (G) which is fed to the vacuum system (VA).Process according to claim 4, characterized in that the content of inhibitor (I), in particular dissolved in the at least one aromatic vinyl compound (A), is 1 to 50 ppm, based on the mixture of aromatic vinyl compound (A) and inhibitor (I) in the vacuum system (VA). Method according to one of claims 1 to 5, characterized in that the vapor stream (B) is cooled in at least a second heat exchanger (WT2) and a 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) is operated at a third media inlet temperature (T3) in a range from -10° to 30°C, in particular from -10°C to 15°C, and wherein in particular the second media inlet temperature (T2) is at least 10°C higher than the third media inlet temperature (T3).Process according to one of claims 1 to 6, characterized in that the liquid (F) is cooled in a pump heat exchanger (WT4). Process according to one of claims 1 to 7, characterized in that the portion of the at least one aromatic vinyl compound (A) is added to the liquid (F) upstream of the pump heat exchanger (WT4).

9. The method according to claim 8, characterized in that the pump heat exchanger (WT4) is operated with a fourth media inlet temperature (T4) which is lower than the second media inlet temperature (T2) of the second heat exchanger (WT2) and a difference between the second media inlet temperature (T2) and the fourth media inlet temperature (T4) is at least 10°C.

10. Method according to one of claims 1 to 9, characterized in that the exhaust gas of the vacuum system (VA) is at least partially condensed in an exhaust gas heat exchanger (WT5), in particular at ambient pressure.

11. Method according to claim 10, characterized in that the exhaust gas heat exchanger (WT5) is operated with a fifth media inlet temperature (T5) which is lower than the second media inlet temperature (T2) of the second heat exchanger (WT2) and a difference between the second media inlet temperature (T2) and the fifth media inlet temperature (T5) is at least 10°C.

12. The process according to any one of claims 1 to 11, characterized in that the vapor stream (B), in particular upstream of the at least one further heat exchanger (WT2, WT3), is passed through a separation unit, in particular a column (K), in which the vapor stream (B) is brought into contact with the at least one condensate (KS1, KS2), oligomers being removed from the vapor stream (B) and the at least one condensate (KS1, KS2) being fed in particular at the top of the column (K).

13. The method according to any one of claims 6 to 12, characterized in that a first condensate (KS1) exits the second heat exchanger (WT2) and a second condensate (KS2) exits the third heat exchanger (WT3), 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).

14. Method according to one of claims 1 to 13, characterized in that the second heat exchanger (WT2) is operated with river water or a coolant provided by cooling with river water.

15. Method according to claim 14, characterized in that the first condensate (KS1) and / or the second condensate (KS2) is / are collected at a first location (ED1) in front of the Column (K) are brought into contact with the vapor stream (B) in cocurrent, in particular by injecting it into a vapor line, 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). Process according to one of claims 9 to 11, 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 space, in particular a head space (KR), of the third heat exchanger (WT3). Apparatus for carrying out the process according to one of claims 1 to 16, comprising a 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), a third heat exchanger (WT3) and a vacuum system (VA), wherein these are connected in series downstream in the specified order, the third heat exchanger (WT3) has an inlet space, in particular a headspace (KR), and a collection space, in particular a sump space (KR), and is preferably arranged vertically, and the vacuum system (VA) is fluidically connected to the collection space, in particular the sump space, of the third heat exchanger (WT3), the vacuum system (VA) comprises at least one pump (P), which is designed as a liquid ring pump system, an overflow (II) and a pump heat exchanger (WT4), and the pump heat exchanger (WT4) is arranged downstream on the high-pressure side of the pump (P) and is connected to the low-pressure side of the pump (P) via a return line.

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