INTEGRATION OF A HEAT PUMP CIRCUIT INTO A DISTILLATION PLANT FOR POLYMERIZABLE SUBSTANCES

Description

[0001] The present invention relates to a distillation plant for polymerizable substances comprising a rectification column with a bottom evaporator and a vapor condenser, wherein a heat pump circuit with a compressor fluidically connects both the bottom evaporator and the vapor condenser, and is designed such that during operation of the distillation plant the bottom evaporator is heated by the heat pump circuit and the vapor condenser is cooled by the heat pump circuit, wherein water serves as the working medium of the heat pump circuit.

[0002] Distillation plants for polymerizable substances, especially (meth)acrylates, generally suffer from the problem that excessively high temperatures of the polymerizable substances during operation can lead to strong polymerization within the distillation plant. Frequently, the bottom evaporators of these plants are affected by severe polymerization and / or significant fouling due to their high heating temperatures. This can result in substantial deposits forming on the inner walls of the bottom evaporator's flow channels. Consequently, the flow channels for the polymerizable substances can become clogged during operation, rendering the bottom evaporator inoperable.

[0003] Due to the energy-intensive process of operating such a distillation plant, a heat pump is generally a suitable option to at least partially recover the energy content of the vapor stream for use in the distillation plant.

[0004] JPS 60125201 A discloses a distillation plant for polymerizable substances in which a heat pump circuit with a compressor fluidically connects both a bottom evaporator and a vapor condenser. The bottom evaporator is heated by the heat pump circuit, and the vapor condenser is cooled by the heat pump circuit. Water is used as the working fluid in the heat pump circuit. However, this disclosure has the disadvantage that when the working fluid is compressed by the compressor, its temperature can also rise too high, causing the downstream bottom evaporator to become too hot for the polymerizable substances flowing through it.

[0005] EP 0965373 A1 discloses a distillation plant for polymerizable substances with a replaceable heat pump. The distillation plant comprises a column and a heat pump operating between a bottom evaporator and a vapor condenser of the column. The heat pump can be replaced by devices that can be connected to the bottom evaporator and the vapor condenser as needed. These replacement devices include equipment for generating steam or providing a coolant. However, when the heat pump is operated, the disadvantage arises that the working fluid's temperature can also rise excessively during compression by the compressor, causing the downstream bottom evaporator to become too hot for the polymerizable substances flowing through it.

[0006] EP 3 769 830 A1 discloses a distillation plant with a heat pump circuit.

[0007] The challenge therefore arose to ensure that the permissible temperature range for the polymerizable substances in the bottom evaporator was maintained during operation of the distillation plant. A further challenge was to be able to set the optimal temperature of the working fluid in the bottom evaporator within the distillation plant more quickly, stably, and precisely for the prevailing operating conditions.

[0008] These problems are solved according to the present invention by a distillation apparatus according to claim 1, by a method for producing a (meth)acrylate according to claim 9, by the use of a distillation apparatus according to claim 15, and by a method for operating the distillation apparatus according to claim 16. Furthermore, the invention relates to preferred embodiments of the distillation apparatus according to claims 2 to 8 and preferred embodiments of the method for producing a (meth)acrylate according to claims 10 to 14.

[0009] According to the invention, the distillation plant for polymerizable substances comprises a rectification column with a bottom evaporator and a vapor condenser, wherein a heat pump circuit with a compressor fluidically connects both the bottom evaporator and the vapor condenser, and is designed such that during operation of the distillation plant the bottom evaporator is heated by the heat pump circuit and the vapor condenser is cooled by the heat pump circuit, wherein water serves as the working fluid for the heat pump circuit, wherein a mixing element is arranged between the compressor and the downstream bottom evaporator, wherein the mixing element is configured such that cooling water is added to cool the working fluid during operation of the distillation plant.

[0010] The cooling water is added in such a quantity to cool the working fluid that a temperature of the working fluid in the range of 80 to 200 °C, preferably 100 to 160 °C, and in particular 110 to 160 °C, can be set or is set or is present at the inlet of the sump evaporator.

[0011] Adding cooling water to the working fluid between the compressor and the downstream evaporator offers the advantage of allowing for rapid, stable, and precise temperature control of the working fluid at the evaporator inlet. This prevents temperature spikes caused by the cooling water before they reach the evaporator. As a result, the permissible temperature range for the polymerizable substances in the evaporator is maintained during operation of the distillation system.

[0012] In this document, the term "rectification column" is used as a general term for apparatus in which vapors are generated by the application of heat. These vapors rise and come into contact with the outflowing liquid phase. Rectification columns are known in their general design and feature the usual components, such as an evaporator at the bottom, an evaporator in the heavy-boiler outlet, or a condenser in the light-boiler outlet, with the heavy-boiler components preferably located in the bottom and the light-boiler components preferably in the top of the rectification column. Typically, a portion of the mass flow from the heavy-boiler outlet is recycled to the bottom of the rectification column. However, it is also possible, in principle, to heat the bottom via, for example, external wall heating of the column and / or to integrate an evaporator in the bottom.Typically, a vapor stream is drawn off at the top of the rectification column and fed to a condenser. This vapor stream is also commonly referred to as the effluent. A portion of the vapor stream condensed in the condenser is returned to the rectification column, while the remainder is removed as distillate. The reflux ratio describes the ratio between the condensed vapor stream returned to the column and the condensed vapor stream removed as distillate. A reflux ratio in the range of 10 to 200% is generally used. In principle, all common internals can be used for the rectification column, such as trays, packings, and / or bulk granules.Preferred tray types include bubble-cap trays, sieve trays, valve trays, Thormann trays, and / or dual-flow trays; preferred packing materials include those with rings, coils, saddles, or braids. The rectification column may also include other standard control components, such as pressure reducers, flow regulators, or sensors. In principle, several rectification columns can be connected in series or parallel, and together they can function as a single "rectification column."

[0013] In this document, the term "reaction zone" refers to a zone where a chemical reaction can take place. This zone may be located, for example, in a reactor, in the bottom of a rectification column, or in a reactive distillation column. Preferably, if the reaction zone is located in a reactor, the reactor may have a column mounted on top of it. In the case of esterification processes taking place in the reactor, the column preferably separates water by distillation. The column itself is generally a distillation column or a rectification column with internal components. Such components include trays, such as bubble-cap trays, perforated trays, particularly dual-flow trays, packed beds, or the like. Furthermore, the reactor may be integrated into the rectification column, allowing the reaction to take place in the bottom of the rectification column.

[0014] In this document, the term "bottom evaporator" refers to a general heating element for a rectification column. The bottom evaporator typically heats a bottom mixture from the rectification column by allowing a discharge from the bottom to flow through the bottom evaporator and then be returned to the column's bottom. The bottom evaporator may also include other standard components, such as control valves, pressure reducers, flow regulators, or sensors. The evaporator can therefore also incorporate a control system. Generally, the term "bottom evaporator" can also refer to multiple evaporators connected in series or parallel. Examples of suitable bottom evaporators include thin-film, Robert, falling-film, natural circulation, and forced circulation evaporators. The evaporators can be designed as shell-and-tube heat exchangers or plate heat exchangers.Suitable evaporators are known to those skilled in the art and are described, among other places, in: SPX, Evaporator Handbook, APV Americas, Engineered Systems, Separation Technologies, 4th edition, available at https: / / userpages.umbc.edu / ~dfrey1 / ench445 / apv evap.pdf (accessed on May 20, 2022). In the heat pump circuit, the sump evaporator functions as a condenser, which at least partially, and preferably completely, condenses the working fluid through the sump discharge.

[0015] In this document, the term "water separator" refers to a device that can, for example, separate water droplets from a gas stream. Typical examples of water separators include a demister, especially a wire mesh demister, a centrifugal droplet separator, or a lamella separator. The water separator may be located in a water collection tank or be a standalone unit.

[0016] In this document, the term "vapor condenser" refers to an apparatus that cools and condenses a vapor stream from a distillation plant. Typical examples of vapor condensers are shell-and-tube heat exchangers, jacketed tube heat exchangers, or plate heat exchangers. To prevent polymer formation, the heat exchanger may be equipped with nozzles for injecting a solution containing polymerization inhibitor(s). In a heat pump circuit, the vapor condenser functions as an evaporator, at least partially, and preferably completely, vaporizing the working fluid through the heat-supplying vapor stream.

[0017] In this document, the term "mixing element" refers to a device that mixes a liquid stream with another liquid stream. The mixing element is, in particular, a component separate from the compressor. Furthermore, the mixing element is preferably arranged downstream of the compressor. Typical examples of a mixing element are a steam jet, a Venturi mixer, one or more mixing nozzles, or a long pipe serving as the mixing section. In the case of a pipe several meters long, mixing nozzles are arranged individually within the pipe. Alternatively, the mixing nozzles are formed by openings in the partition wall of a coaxially designed pipe.

[0018] In this document, the term "compressor" refers to a machine that compresses gases. A geared turbo compressor is an example of a suitable compressor. This type of compressor typically features multiple compression stages and intermediate stages, with each intermediate stage equipped with an intercooling device.

[0019] In this document, the term "working medium" generally refers to the fluid that flows through the heat pump circuit and, in particular, can add or remove heat through its local phase changes.

[0020] In this document, a "heat pump" is generally understood to be a machine that, by expending technical work, absorbs thermal energy from a lower-temperature reservoir and, together with the drive energy, transfers it as usable heat to a system at a higher temperature to be heated. The system to be heated could, for example, be a sump evaporator, and the lower-temperature reservoir could, for example, be a vapor condenser.

[0021] In this document, the term "heat pump circuit" generally refers to a circuit through which a working fluid circulates. The heat pump circuit includes a compressor, a condenser, and an evaporator, each connected to the circuit in a fluid-tight manner. Within the heat pump circuit, the sump evaporator acts as the condenser, and the vapor condenser acts as the evaporator.

[0022] In this document, the term "cooling water" refers to water used to cool the working fluid in the compressor or at a point between the compressor and the downstream sump evaporator in the heat pump circuit. Cooling water can generally be added to the working fluid from outside the heat pump circuit via a line leading into the heat pump circuit. According to the invention, the cooling water is provided by branching off a partial flow of the working fluid at a point in the heat pump circuit located between the sump evaporator and a downstream vapor condenser.

[0023] In this document, the term "fluidically connected" means that, generally, two or more components through which a fluid can flow, such as several flow pipes, are connected in such a way that a fluid can flow through these connected components. As a rule, sufficient technical tightness should be ensured when a fluid flows through the components.

[0024] In a preferred embodiment of the distillation plant, the mixing element is configured such that, during operation of the distillation plant, cooling water with a temperature in the range of 1 to 160 °C, more preferably 105 to 150 °C, and particularly 110 to 140 °C, is added to the working fluid to cool it, wherein the cooling water has a mass flow rate in the range of 3 to 10% relative to the mass flow rate of the working fluid. This offers the advantage that the optimal temperature of the working fluid at the inlet of the bottom evaporator can be set quickly, stably, and precisely.

[0025] The distillation plant is configured such that, during operation, the working fluid partially serves as cooling water. This cooling water is drawn from a section of the heat pump circuit extending from the bottom evaporator to the vapor condenser in the main flow direction of the working fluid. Specifically, the distillation plant features a return line that fluidically connects the outlet of the bottom evaporator in the heat pump circuit to the mixing element. This return line is located in the section of the heat pump circuit extending from the bottom evaporator to the vapor condenser in the main flow direction of the working fluid. Preferably, the cooling water is drawn from and returned at an absolute pressure in the range of 2 to 8 bar, and more preferably from 4 to 6 bar.The working fluid used as cooling water is preferably extracted or returned at a temperature in the range of 105 to 150 °C, more preferably from 110 to 140 °C.

[0026] It was surprisingly discovered that the refrigerant cooled by the sump evaporator can be partially used as cooling water. This technical implementation offers the advantage that no additional external cooling water is required and the heat pump cycle is not disrupted by external cooling water, unless an exceptional case occurs. An exceptional case would arise, for example, if the refrigerant leaks from the heat pump cycle or if the refrigerant needs to be partially replaced with fresh refrigerant. Complex safety devices such as pressure relief valves or elaborate pressure damping systems become redundant. Furthermore, the efficiency of the heat pump is increased compared to cooling with a cooling medium outside the heat pump cycle.

[0027] In a preferred embodiment of the distillation plant, the vapor condenser is a vertical shell-and-tube heat exchanger. This saves space in the distillation plant and makes the injection of a solution containing polymerization inhibitor(s) technically easy to implement.

[0028] In a preferred embodiment of the distillation plant, the bottom evaporator has a downstream condensate tank in the heat pump circuit, and both the condensate tank and the mixing element are designed such that, during operation of the distillation plant, some of the working fluid flows from the condensate tank to the mixing element as auxiliary cooling water. Collecting the working fluid in a condensate tank after the bottom evaporator offers the advantage that, even if the mass flow rate of the working fluid is reduced, sufficient working fluid is available as auxiliary cooling water.

[0029] In a preferred embodiment of the distillation plant, both the condensate tank and the compressor are arranged such that, during operation of the distillation plant, the working fluid partially flows from the condensate tank to the compressor as auxiliary cooling water. This offers the advantage that the compressor is also cooled without having to rely on other fluids. The condensate tank allows for intermediate storage of the working fluid, ensuring that sufficient working fluid is always available as auxiliary cooling water for both cooling the compressor and cooling the working fluid between the compressor and the downstream sump evaporator.

[0030] In a preferred embodiment of the distillation plant, the compressor includes one or more compression stages, and the distillation plant is configured such that, during operation, the cooling water is at least partially added to the working fluid by an intermediate mixing element for each compression stage. Each intermediate mixing element is located between adjacent compression stages of the compressor. Preferably, each intermediate mixing element is fluidically connected to the outlet of the sump evaporator in the heat pump circuit via the return line. With multiple compression stages, the advantage is that the working fluid is cooled between the stages without the need to use other fluids.

[0031] In a preferred embodiment of the distillation plant, a liquid droplet separator or a pipe with a length-to-diameter ratio of at least 10 is connected downstream of each intermediate stage mixing element. This protects the downstream compression stage from droplets that could damage the compressor.

[0032] In a preferred embodiment of the distillation plant, the distillation plant is configured such that, during operation, cooling water with a temperature in the range of 1 to 160 °C, more preferably 105 to 150 °C, and particularly 110 to 140 °C, is added to the working fluid through the intermediate mixing element in such a quantity that a temperature difference between the temperature of the working fluid and the temperature at which the working fluid exists as saturated vapor under the existing absolute pressure can be set at the inlet of the downstream compression stage in the range of 2 to 50 °C, preferably in the range of 5 to 20 °C. Preferably, in this embodiment, the cooling water is added through the intermediate mixing element at a mass flow rate in the range of 3 to 10% of the mass flow rate of the working fluid at the compressor inlet.This has the advantage that the cooling water is added to the working fluid between the compression stages in an energy-efficient manner, so that only as much cooling water as necessary is added.

[0033] In a preferred embodiment of the distillation plant, the mixing element and / or the intermediate-stage mixing element is a mixing nozzle, a steam jet, or a Venturi pump. These variants result in an energy-efficient, robust, and economical technical implementation.

[0034] In a preferred embodiment of the distillation plant, the distillation plant is configured such that, during operation, a further vapor condenser is included downstream of the vapor condenser, and this further vapor condenser comprises a downstream phase separator. The phase separator is designed such that both an aqueous and an organic phase can form during operation of the distillation plant. Preferably, one of these two phases is at least partially recycled to the rectification column, and most preferably, both phases are each at least partially recycled separately to the rectification column via two separate recycling loops. This offers the advantage that the amount of aqueous phase can be recycled to the rectification column independently of the amount of organic phase, and vice versa.

[0035] In a preferred embodiment of the distillation plant, the vapor condenser and the further vapor condenser are vertical shell-and-tube heat exchangers. A vertical shell-and-tube heat exchanger offers the advantage that the preferred addition of a solution containing polymerization inhibitor(s) can be more easily implemented in the inlet region of the shell-and-tube heat exchanger.

[0036] In a preferred embodiment of the distillation plant, a phase separator is connected downstream of the vapor condenser. The phase separator is designed such that both an aqueous and an organic phase form in the phase separator during operation of the distillation plant, and these two phases are at least partially recycled to the rectification column. Preferably, the two phases are recycled separately to the rectification column via two separate recirculation channels. This offers the advantage of achieving optimal separation in the rectification column for processes involving polymerizable substances.

[0037] In a preferred embodiment of the distillation plant, the distillation plant is configured such that, during operation, the bottoms evaporator is designed such that its walls, which are exposed to the bottoms mixture from the rectification column during operation, are made of a stainless and acid-resistant material selected from the group consisting of zirconium, stainless steels, and nickel-based alloys. This virtually or even completely prevents corrosion processes on the walls.

[0038] In a preferred embodiment of the distillation system, a water separator is included in the heat pump circuit. The water separator is fluidically connected to the vapor condenser in such a way that, during operation of the distillation system, the working fluid flows from the water separator into the vapor condenser and subsequently back from the vapor condenser into the water separator. The water separator serves as a collection reservoir for the working fluid, ensuring that, even with a reduction in the working fluid mass flow rate, sufficient working fluid is available both for cooling the vapor condenser and for the compressor. Furthermore, the water separator dampens potential pressure fluctuations in the heat pump circuit. A demister is preferably integrated into the water separator to protect the downstream compressor from damage caused by liquid droplets.

[0039] In a preferred embodiment of the distillation plant, the distillation plant is configured such that, during operation of the distillation plant, cooling water with a temperature in the range of 1 to 160 °C, more preferably 105 to 150 °C, and in particular 110 to 140 °C, is added to the working medium by the mixing element in such a quantity that a temperature difference between the temperature of the working medium and the temperature at which the working medium exists as saturated vapor under the existing absolute pressure can be set at the inlet of the bottom evaporator in the range of 5 to 50 °C, more preferably 5 to 20 °C, wherein the existing absolute pressure is preferably in the range of 2 to 8 bar, and particularly preferably in the range of 4 to 6 bar.In this embodiment, the cooling water is preferably added through the mixing element at a mass flow rate in the range of 3 to 10% of the working fluid mass flow rate. This offers the advantage of energy-efficient addition of the cooling water to the working fluid between the compressor and the downstream sump evaporator. Only the necessary amount of cooling water is added, ensuring that the working fluid transfers sufficient heat to the sump evaporator while also preventing the working fluid temperature from becoming excessively high.

[0040] A further aspect of the invention is the use of a distillation apparatus according to the invention, wherein the distillation apparatus is used in chemical processes, in particular in processes for the production of (meth)acrylates, preferably n-butyl(meth)acrylates, or in processes in which (meth)acrylates, preferably n-butyl(meth)acrylates, are present. The use of a distillation apparatus according to the invention in such chemical processes offers the advantage that polymer formation in the heat pump circuit is avoided.

[0041] Another object of the invention is a method for operating the distillation plant according to the invention.

[0042] According to the invention, in the process for operating the distillation plant according to the invention, a liquid mixture is fed into the rectification column, wherein during the distillative separation a vapor stream with a temperature in the range of 35 to 120 °C, in particular 50 to 100 °C, is formed at the inlet of the vapor condenser and a bottom product with a temperature in the range of 80 to 160 °C, in particular 80 to 130 °C, is formed in the bottom of the rectification column, and the working fluid is fed at least partially from the bottom evaporator to the vapor condenser to be cooled, whereby the working fluid heats up in the vapor condenser, wherein the working fluid at the outlet of the vapor condenser has a temperature in the range of 35 to 120 °C, in particular 50 to 100 °C, and an absolute pressure in the range of 0.1 to 0.9 bar, preferably 0.3 to 0.7 bar. and then the working fluid is compressed by the compressor,The working fluid at the compressor outlet has a temperature in the range of 100 to 300 °C, preferably 150 to 250 °C, and an absolute pressure in the range of 1 to 10 bar. Cooling water is then added to the working fluid via the mixing element in such a quantity that a temperature at the inlet of the sump evaporator is set in the range of 80 to 200 °C, preferably in the range of 100 to 160 °C, and more preferably in the range of 110 to 160 °C.

[0043] Adding cooling water to the working fluid between the compressor and the downstream evaporator offers the advantage of rapid, stable, and precise temperature control of the working fluid at the evaporator inlet. This allows temperature spikes to be mitigated by the cooling water before they reach the evaporator. As a result, the permissible temperature range for the polymerizable substances in the evaporator is maintained during operation of the distillation system.

[0044] Preferably, in the process for operating the distillation plant, the cooling water at a temperature in the range of 1 to 160 °C, more preferably from 105 to 150 °C, in particular from 110 to 140 °C, is added to the working medium through the mixing element, wherein the cooling water has a mass flow rate in relation to the mass flow rate of the working medium in the range of 3 to 10%.

[0045] Further preferred embodiments of the method for operating the distillation plant are given in accordance with the above preferred embodiments of the distillation plant according to the invention.

[0046] The distillation apparatus according to the invention is particularly suitable for the production of a (meth)acrylate. A further object of the invention is a process for the production of a (meth)acrylate by reacting (meth)acrylic acid with an alcohol corresponding to the (meth)acrylate in the presence of an acidic catalyst and a polymerization inhibitor, comprising the steps of: Providing a rectification column with a bottom evaporator and a vapor condenser, wherein a heat pump circuit with a compressor fluidically connects both the bottom evaporator and the vapor condenser, and water serves as the working fluid for the heat pump circuit; carrying out an esterification within a reaction zone, wherein the components (meth)acrylic acid and alcohol are used in a molar ratio in the range of 1.0 : 1.0 to 1.0 : 2.0, preferably in the range of 1.0 : 1.1 to 1.0 : 1.5, and wherein the esterification takes place at a temperature in the range of 80 to 150 °C, preferably in the range of 100 to 130 °C, and at an absolute pressure in the range of 0.2 to 5.0 bar, preferably in the range of 0.4 to 1.5 bar, thereby obtaining a resulting reaction mixture; separating the water of esterification formed during the esterification from the reaction mixture within the rectification column,wherein the sump evaporator is heated by the working fluid flowing through it in the heat pump circuit, a gaseous vapor stream enriched by the esterification water is discharged at the top of the rectification column, the vapor stream is condensed in the vapor condenser to form an organic phase and an aqueous phase, the vapor condenser being cooled by the working fluid flowing through it in the heat pump circuit and the working fluid having a temperature in the range of 35 to 120 °C, preferably 50 to 100 °C, at the outlet of the vapor condenser, and the working fluid being supplied from the outlet of the vapor condenser to the compressor, wherein the working fluid is compressed within the compressor and has a temperature in the range of 100 to 300 °C, preferably 150 to 250 °C, and an absolute pressure in the range of 1 to 10 bar at the outlet of the compressor.wherein a mixing element is arranged in the heat pump circuit between the compressor and the downstream sump evaporator and cooling water with a temperature in the range of 1 to 160 °C, preferably 105 to 150 °C, particularly 110 to 140 °C, is added to the working fluid by the mixing element in such a quantity that the working fluid at the inlet of the sump evaporator has a temperature in the range of 80 to 200 °C, preferably 100 to 160 °C, more preferably 110 to 160 °C.

[0047] Adding cooling water to the working fluid between the compressor and the downstream evaporator offers the advantage of allowing for rapid, stable, and precise temperature control of the working fluid at the evaporator inlet. This prevents temperature spikes caused by the cooling water before they reach the evaporator. As a result, the permissible temperature range for the polymerizable substances containing (meth)acrylates in the evaporator is maintained during operation of the distillation system.

[0048] In the process for producing a (meth)acrylate, the working fluid cooled by the sump evaporator is partially used as cooling water. This technical implementation offers the advantage that no additional cooling water is required and the heat pump circuit is not disrupted by external cooling water, unless an exceptional case occurs. An exceptional case would be, for example, if the working fluid leaks from the heat pump circuit or if the working fluid needs to be partially replaced with fresh working fluid. This eliminates the need for complex safety devices such as pressure relief valves or elaborate pressure damping systems. Furthermore, it was surprisingly found that the cooling water ensures that the required temperature range of the working fluid is always maintained, thus preventing polymerization, fouling, and / or deposits on the inner walls of the flow channels of the sump evaporator.

[0049] In the process for producing a (meth)acrylate, the cooling water is preferably added at a mass flow rate of 3 to 10% relative to the mass flow rate of the working fluid. In a preferred embodiment of the process for producing a (meth)acrylate, the cooling water is added at a temperature of 1 to 160 °C, more preferably 105 to 150 °C, and particularly 110 to 140 °C, at a mass flow rate of 3 to 10% relative to the mass flow rate of the working fluid. This offers the advantage that the cooling water is added to the working fluid between the compressor and the downstream sump evaporator in an energy-efficient manner. Only the necessary amount of cooling water is added, ensuring that the working fluid transfers sufficient heat to the sump evaporator and that the temperature of the working fluid is not excessively high.

[0050] In the process for producing a (meth)acrylate, the working fluid partially serves as cooling water. This cooling water is drawn from a section of the heat pump circuit extending from the bottom evaporator to the vapor condenser in the main flow direction of the working fluid. In particular, a working fluid condensate formed in the bottom evaporator is used as cooling water. Preferably, the cooling water is drawn at an absolute pressure in the range of 2 to 8 bar, more preferably from 4 to 6 bar, or, more specifically, returned to the mixing element. The cooling water is preferably drawn at a temperature in the range of 105 to 150 °C, more preferably from 110 to 140 °C, or, more specifically, returned to the mixing element.

[0051] In a preferred embodiment of the process for producing a (meth)acrylate, the sump evaporator has a downstream condensate tank in the heat pump circuit and the working fluid flows partially from the condensate tank to the mixing element as cooling water.

[0052] In a preferred embodiment of the process for producing a (meth)acrylate, the working fluid flows partially from the condensate container to the compressor as cooling water.

[0053] In a preferred embodiment of the method for producing a (meth)acrylate, the compressor includes one or more compression stages, and in the case of multiple compression stages, the cooling water is added at least partially to the working fluid by means of an intermediate mixing element for each compression stage, wherein the respective intermediate mixing element is located between the adjacent compression stages of the compressor.

[0054] In a preferred embodiment of the process for producing a (meth)acrylate, a liquid droplet separator is connected downstream of the respective intermediate mixing element between the adjacent compression stages.

[0055] In a preferred embodiment of the process for producing a (meth)acrylate, cooling water with a temperature in the range of 1 to 160 °C, more preferably 105 to 150 °C, and particularly 110 to 140 °C, is added to the working fluid through the intermediate mixing element in such a quantity that a temperature difference between the temperature of the working fluid and the temperature at which the working fluid exists as saturated steam under the existing absolute pressure is established at the inlet of the downstream compression stage in the range of 2 to 50 °C, preferably in the range of 5 to 20 °C. Preferably, in this embodiment of the process, the cooling water is added through the intermediate mixing element at a mass flow rate in the range of 3 to 10% of the mass flow rate of the working fluid at the compressor inlet.This has the advantage that the cooling water is added to the working fluid between the compression stages in an energy-efficient manner, so that only as much cooling water as necessary is added.

[0056] In a preferred embodiment of the process for producing a (meth)acrylate, the mixing element used and / or the intermediate mixing element is a mixing nozzle, a steam jet or a Venturi pump.

[0057] In a preferred embodiment of the process for producing a (meth)acrylate, a phase separator is connected downstream of the vapor condenser, wherein both an aqueous and an organic phase are formed in the phase separator and these two phases are at least partially returned to the rectification column, wherein the two phases are preferably returned separately to the rectification column by two separate recirculations.

[0058] In a preferred embodiment of the process for producing a (meth)acrylate, a further vapor condenser is included downstream of the vapor condenser, and this further vapor condenser comprises a downstream phase separator, wherein both an aqueous and an organic phase are formed in the phase separator. Preferably, one of these two phases is at least partially recycled to the rectification column. Most preferably, both phases are each at least partially recycled separately to the rectification column via two separate recycling loops.

[0059] In a preferred embodiment of the process for producing a (meth)acrylate, the walls of the bottom evaporator, which are exposed to the bottom mixture from the rectification column during operation of the distillation plant, are made of a stainless and acid-resistant material selected from the group consisting of zirconium, stainless steels and nickel-based alloys.

[0060] In a preferred embodiment of the method for producing a (meth)acrylate, a water separator is included in the heat pump circuit, wherein the working fluid flows from the water separator into the vapor condenser and subsequently the working fluid flows back from the vapor condenser into the water separator.

[0061] In a preferred embodiment of the process for producing a (meth)acrylate, cooling water with a temperature in the range of 1 to 160 °C, more preferably 105 to 150 °C, and particularly 110 to 140 °C, is added to the working fluid through the mixing element in such a quantity that a temperature difference between the temperature of the working fluid and the temperature at which the working fluid exists as saturated steam under the existing absolute pressure can be set or is set at the inlet of the bottom evaporator in the range of 5 to 50 °C, more preferably 5 to 20 °C, wherein the existing absolute pressure is preferably in the range of 2 to 8 bar, and particularly preferably in the range of 4 to 6 bar. In particular, in this preferred embodiment, the cooling water is added through the mixing element at a mass flow rate in the range of 3 to 10% of the mass flow rate of the working fluid.

[0062] In a particularly preferred embodiment of the process for producing a (meth)acrylate, the (meth)acrylate is an n-butyl(meth)acrylate.

[0063] The particularly preferred process for the preparation of an n-butyl(meth)acrylate is based on the starting materials n-butanol and (meth)acrylic acid. In this document, (meth)acrylic acid refers to a grade of (meth)acrylic acid that preferably contains at least 98 wt.%, and more preferably at least 99.5 wt.%, (meth)acrylic acid, and preferably also a maximum of 0.2 wt.% water, and preferably a maximum of 0.03 wt.% each of acetic acid, propionic acid, and isobutyric acid. Preferably, an n-butanol grade is used that contains at least 99.5 wt.% n-butanol, a maximum of 0.05% n-butanal, a maximum of 0.02% dibutyl ether, a maximum of 0.1% other alcohols, and a maximum of 0.05% water. The color number is preferably a maximum of APHA 5, and the acid number a maximum of 0.03 mg KOH / g.

[0064] Suitable polymerization inhibitors for the production of (meth)acrylate, which act as stabilizers, can be, for example, N-oxides (nitroxyl or N-oxyl radicals, i.e., compounds that have at least one NO group), such as... B. 4-Hydroxy-2,2,6,6-tetramethylpiperidine-N-oxyl (HO-TEMPO), 4-Oxo-2,2,6,6-tetramethyl-piperidine-N-oxyl, 4-Acetoxy-2,2,6,6-tetramethyl-piperidine-N-oxyl, 2,2,6,6-Tetra-methylpiperidine-N-oxyl, Bis(1-oxyl-2,2,6,6-tetramethyl-piperidine-4-yl)sebacate, 4,4',4"-Tris(2,2,6,6-tetramethyl-piperidine-N-oxyl)-phosphite or 3-Oxo-2,2,5,5-tetramethyl-pyrrolidine-N-oxyl; mono- or polyhydric phenols, which may have one or more alkyl groups, such as alkylphenols, for example o-, m- or p- Cresol (methylphenol), 2-tert-butylphenol, 4-tert-butylphenol, 2,4-di-tert-butylphenol, 2-methyl-4-tert-butylphenol, 2-tert-butyl-4-methylphenol, 2,6-tert-butyl-4-methylphenol, 4-tert-butyl-2,6-dimethylphenol or 6- tert.-Butyl-2,4-dimethylphenol; quinones, such as hydroquinone, hydroquinone monomethyl ether, 2-methylhydroquinone, or 2,5-di-tert-butylhydroquinone; hydroxyphenols, such as catechol (1,2-dihydroxybenzene) or benzoquinone; aminophenols, such as p-aminophenol; nitrosophenols, such as p-nitrosophenol; alkoxyphenols, such as 2-methoxyphenol (guaiacol, catechol monomethyl ether), 2-ethoxyphenol, 2-isopropoxyphenol, 4-methoxyphenol (hydroquinone monomethyl ether), mono- or ditert-butyl-4-methoxyphenol; tocopherols, such as... B. α-Tocopherol and 2,3-Dihydro-2,2-dimethyl-7-hydroxybenzofuran (2,2-Dimethyl-7-hydroxycoumaran), aromatic amines, such as N,N-diphenylamine or N-nitrosodiphenylamine; phenylenediamines, such as N,N'-dialkyl-p-phenylenediamine, wherein the alkyl groups may be the same or different and each independently consist of 1 to 4 carbon atoms and may be straight-chain or branched, such asN,N'-Dimethyl-p-phenylenediamine or N,N'-Diethyl-p-phenylenediamine, hydroxylamines, such as N,N-diethylhydroxylamine, imines, such as methylethylimine or methylene violet, sulfonamides, such as N-methyl-4-toluenesulfonamide or N-tert-butyl-4-toluenesulfonamide, oximes, such as aldoximes, ketoximes or amidoximes, such as diethylketoxime, methylethylketoxime or salicyladoxime, phosphorus-containing compounds, such as triphenylphosphine, triphenylphosphite, triethylphosphite, hypophosphorous acid or alkyl esters of phosphorous acids; sulfur-containing compounds, such as diphenyl sulfide or phenothiazine; Metal salts, such as copper or manganese, cerium, nickel, chromium salts, for example -chlorides, -sulfates, -salicylates, -tosylates, -acrylates or -acetates, such as copper acetate, copper(II) chloride, copper salicylate, cerium(III) acetate or cerium(III) ethylhexanoate, or mixtures thereof.

[0065] In the production of (meth)acrylate, at least one compound from the group consisting of hydroquinone, hydroquinone monomethyl ether, phenothiazine, 4-hydroxy-2,2,6,6-tetramethylpiperidine-N-oxyl, 4-oxo-2,2,6,6-tetramethylpiperidine-N-oxyl, bis(1-oxyl-2,2,6,6-tetramethyl-piperidine-4-yl)sebacate, 2-tert-butylphenol, 4-tert-butylphenol, 2,4-di-tert-butylphenol, 2-tert-butyl-4-methylphenol, 6-tert-butyl-2,4-dimethylphenol, 2,6-di-tert-butyl-4-methylphenol, 2-methyl-4-tert-butylphenol, and hypophosphoric acid is preferably used as a polymerization inhibitor or polymerization inhibitor mixture. Copper(II) acetate, copper(I) chloride, copper(II) chloride, copper(II) salicylate and cerium(III) acetate are used.

[0066] Phenothiazine (PTZ) and / or hydroquinone monomethyl ether (MEHQ) and / or HO-Tempo are particularly preferred as polymerization inhibitors in the production of n-butyl(meth)acrylate.

[0067] Preferably, in the production of n-butyl(meth)acrylate, the polymerization inhibitor is dissolved in one or more liquid organic compounds. The organic compound is preferably 2-butanol and / or n-butyl(meth)acrylate in the production of n-butyl(meth)acrylate.

[0068] The usual mineral acids and sulfonic acids are suitable as esterification catalysts in the production of (meth)acrylate, preferably sulfuric acid, phosphoric acid, alkylsulfonic acids (e.g. methanesulfonic acid, trifluoromethanesulfonic acid) and arylsulfonic acids (e.g. benzenesulfonic, p-toluene or dodecylbenzenesulfonic acid) or mixtures thereof, but acidic ion exchangers or zeolites can also be used.

[0069] Sulfuric acid, methanesulfonic acid, p-toluenesulfonic acid, m-toluenesulfonic acid, o-toluenesulfonic acid or mixtures thereof are particularly preferred in the production of (meth)acrylate.

[0070] p-Toluenesulfonic acid is particularly preferred as an esterification catalyst in the production of n-butyl(meth)acrylate. In the reaction zone, which is preferably located within the reactor, its content, based on the reaction mixture contained therein, is advantageously 0.1–10.0 wt.%, preferably 0.1–6.0 wt.%. Other organic sulfonic acids such as methanesulfonic acid, benzenesulfonic acid, dodecylbenzenesulfonic acid, and / or sulfuric acid can also be used. Their quantity is equimolar to that of para-toluenesulfonic acid. Corresponding mixtures are also possible. The content of catalytically active acid in the bottom of the rectification column, based on the mixture contained therein, can advantageously be between 2.5 and 50.0 wt.% para-toluenesulfonic acid or an equimolar amount of other organic sulfonic acid and / or sulfuric acid.

[0071] The invention is explained in more detail below with reference to the drawing. The drawing is to be understood as a schematic representation. It does not represent any limitation of the invention, for example with regard to specific dimensions or embodiments. It shows: Fig. 1 : A schematic process flow diagram of an exemplary distillation plant according to the invention for the production of a (meth)acrylate using a heat pump.

[0072] List of reference symbols used: B-Line for supplying the polymerization inhibitor D-Line for removing an organic phase from a phase separator E-Line for removing an aqueous phase from a phase separator F-Line for supplying an aqueous phase from a phase separator to a rectification column G-Line for supplying an organic phase from a phase separator to a rectification column P-Line for supplying working fluid from a compressor to a mixing element Q-Line for supplying working fluid from a mixing element to a sump evaporator S-Line for supplying working fluid from a condensate tank to a water separator T-Line for supplying working fluid from a condensate tank to a mixing element U-Line for supplying working fluid from a condensate tank to an intermediate mixing element V-Line for supplying external working fluid X-Line for removing working fluid from the heat pump circuit Y-Line toSupply of external working fluid Z Line for supplying a mixture of substances resulting from a reactor 1 Rectification column 2 Sump evaporator 3 First vapor condenser 4 Second vapor condenser 5 Phase separator 6 Water separator 7 Compressor 8 Mixing element 9 Condensate tank 10 Intermediate mixing element between two compression stages 11 Liquid droplet separator between two compression stages 12 Second compression stage of a compressor 13 Pump for conveying the working fluid from the water separator to the vapor condenser 14 Pump for conveying the working fluid from the condensate tank to the water separator 15 First compression stage of the compressor 16 Expansion valve

[0073] Fig. 1Figure 1 schematically shows a process flow diagram of an exemplary process according to the invention for the production of polymerizable substances, preferably for the production of a (meth)acrylate, in which a mixture of substances resulting from a reaction zone is conveyed through a line Z into a rectification column 1.

[0074] A vapor stream is discharged at the top of the rectification column 1. In a downstream vapor condenser 3, the vapor stream is partially condensed, forming an organic phase and an aqueous phase. The vapor condenser 3 is a vertical shell-and-tube heat exchanger 3, in which one or more polymerization inhibitor(s) contained in a solution are added via a line B in the inlet region of the shell-and-tube heat exchanger 3. Furthermore, the shell-and-tube heat exchanger 3 is equipped with spray nozzles connected to line B. The spray nozzles distribute the polymerization inhibitor(s) contained in the solution onto the inside of the tubes of the shell-and-tube heat exchanger 3.

[0075] This stabilizes the vapor flow directly during condensation, thus efficiently preventing polymer formation.

[0076] A further vapor capacitor 4 connected downstream of vapor capacitor 3 condenses the low-boiling elements remaining in the vapor stream, thereby completely condensing the vapor stream in vapor capacitor 4.

[0077] The condensate is then fed to a phase separator 5. The organic phase is at least partially recycled to the rectification column 1 via line G, while the remaining portion of the organic phase is discharged from the distillation unit via line D. The aqueous phase is at least partially recycled to the rectification column 1 via a separate line F, while the remaining portion of the aqueous phase is discharged from the distillation unit via line E.

[0078] A bottom evaporator 2 heats the bottom of the rectification column 1 by allowing at least a portion of the bottom discharge to flow through the bottom evaporator 2 and then be returned to the bottom. The remaining portion of the bottom discharge is discharged from the distillation unit.

[0079] The first vapor condenser 3 is cooled by the working fluid flowing through it in the heat pump circuit. The working fluid flows from the outlet of the vapor condenser 3 via a water separator 6 to a compressor 7, the water separator 6 comprising a demister.

[0080] Compressor 7 contains a first compression stage 15 and a second compression stage 12. Compressor 7 compresses the working fluid. The working fluid then flows through a line P from the outlet of compressor 7 into a mixing element 8. From the mixing element 8, the working fluid flows through a line Q to the inlet of the sump evaporator 2. The working fluid then flows from the outlet of the sump evaporator 2 into a condensate tank 9. A pump 14 delivers a partial flow of the working fluid, which serves as cooling water, to the mixing element 8 in a line T. The mixing element 8 then adds the working fluid, which serves as cooling water, to the working fluid flowing from compressor 7.

[0081] By means of pump 14, a further partial flow of the working fluid, which serves as cooling water, is conveyed from the condensate tank 9 to the intermediate mixing element 10 via a line U. A liquid droplet separator 11 downstream of the intermediate mixing element 10, which preferably contains a wire mesh, protects the second compression stage 12 from liquid droplets.

[0082] By means of pump 14, a further partial flow of the working fluid is conveyed through a line S from the outlet of the condensate tank 9 to the inlet of the water separator 6, wherein the working fluid is expanded by an expansion valve 16 before or preferably at the inlet to the water separator 6. Subsequently, the working fluid is conveyed by pump 13 from the water separator 6 to the vapor condenser 3.

[0083] In exceptional cases, external steam can also be added to line Q via line V as a working fluid to increase the temperature of the working fluid at the inlet of the sump evaporator 2. In exceptional cases, external water can also be added to the water separator 6 via line Y as a working fluid.

[0084] The working fluid can be discharged from the heat pump circuit at any time via a line X, for example if excessive pressure builds up in the heat pump circuit or if the working fluid needs to be replaced. Examples

[0085] The following examples of the process for the production of n-butyl acrylate are represented by thermodynamic simulations. The software Aspen Plus® (Aspen), available at https: / / www.aspentech.com, was used for this purpose. Aspen is a comprehensive simulation software used for modeling, simulating, and optimizing chemical processes and plants in industry. Aspen features extensive model databases for modeling basic operations as well as substance databases for the properties of many different substances. Example 1

[0086] A thermodynamic simulation of an embodiment of the process according to the invention for the production of n-butyl acrylate using a distillation apparatus according to Fig. 1was carried out in Aspen and yielded the following results: A mixture of substances resulting from a reactor is fed through a line Z to a rectification column 1 at a mass flow rate of 30010 kg / h and at a temperature of 105 °C, the mixture having the following composition in weight fractions: Butanol 0,079 n-Butyl acrylate 0,650 Acrylic acid 0,070 Water 0,003 n-Butoxypropionic acid n-butyl ester 0,098 rest 0,100

[0087] A vapor stream at a temperature of 88 °C is discharged from the top of rectification column 1. The mass flow rate of the vapor stream is 37,350 kg / h, with the following composition by weight: Water 0,381 Butanol 0,086 n-Butyl acrylate 0,526 rest 0,007

[0088] The vapor stream is then condensed in a vertical shell-and-tube heat exchanger (vapor condenser 3) and in a further, downstream vertical shell-and-tube heat exchanger (vapor condenser 4), forming an organic phase and an aqueous phase. The condensate has a temperature of 32 °C and an absolute pressure of 0.8 bar. Vapor condenser 3 is equipped with spray nozzles in the inlet area, which distribute a solution containing one or more polymerization inhibitors onto the inside of the tubes of the shell-and-tube heat exchanger. The mass flow rate of the solution is 90 kg / h. This directly stabilizes the condensate during its formation and consequently prevents polymerization.

[0089] The condensate is then fed to a phase separator 5. The resulting organic phase is recycled at a mass flow rate of 8062 kg / h through line G of the rectification column 1 and discharged from the distillation unit at a mass flow rate of 15250 kg / h through line D. The resulting aqueous phase is recycled at a mass flow rate of 15590 kg / h through line F of the rectification column 1 and discharged separately from the distillation unit at a mass flow rate of 1855 kg / h through line E.

[0090] A bottoms discharge with a mass flow rate of 377,400 kg / h and a temperature of 95 °C is drawn from the bottom of rectification column 1, heated to a temperature of 95 °C by a bottoms evaporator 2, and returned to rectification column 1. A further bottoms discharge with a mass flow rate of 16,330 kg / h and a temperature of 95 °C is discharged from the distillation unit.

[0091] The mixture in the sump of rectification column 1 has the following composition by weight: Water 0.356 Acrylic acid 0.130 n-Butoxypropionic acid-n-butyl ester 0.195 Acryloxy ester 0.096 High boiling point 0.098 Remainder 0.147

[0092] The vapor condenser 3 is cooled by the working fluid flowing through it in the heat pump circuit. The mass flow rate of the working fluid is 78,250 kg / h, and the working fluid has a temperature of 80 °C and an absolute pressure of 0.47 bar at the outlet of the vapor condenser 3. In the simulation, water is used as the working fluid.

[0093] The working fluid flows at a mass flow rate of 17250 kg / h from the outlet of the vapor condenser 3 via a liquid droplet separator 6 to a compressor 7.

[0094] At the inlet of compressor 7, the working fluid has a temperature of 80 °C and an absolute pressure of 0.47 bar. Compressor 7 contains two compression stages 15 and 12 and is a two-stage geared turbo compressor. Compressor 7 compresses the working fluid such that it has an absolute pressure of 2.8 bar and a temperature of 206 °C at the outlet of compressor 7.

[0095] The working fluid then flows from the outlet of compressor 7 through a line P to a steam-jet nozzle, which acts as a mixing element 8. Subsequently, the working fluid flows through a line Q from the steam-jet nozzle to the inlet of the sump evaporator 2. A cooling fluid is added to the working fluid via the intermediate steam-jet nozzle, so that the working fluid at the inlet of the sump evaporator 2, which is designed as a shell-and-tube evaporator, has a temperature of 140 °C, an absolute pressure of 2.8 bar, and a mass flow rate of 19,980 kg / h. This is achieved by pumping a partial flow of the working fluid as cooling water from the outlet of the condensate tank 9 through a line T to the steam-jet nozzle at a mass flow rate of 1,085 kg / h and a temperature of 131 °C.The steam-jet nozzle then adds the working fluid, which serves as cooling water, to the working fluid flowing in from compressor 7.

[0096] Pump 14 conveys a further partial flow of the working fluid at a mass flow rate of 1644 kg / h and a temperature of 131 °C through line U from the outlet of the condensate tank 9 to another steam jet nozzle. This second steam jet nozzle acts as an intermediate mixing element 10 and is located between the first compression stage 15 and the second compression stage 12. The second steam jet nozzle adds the working fluid, which serves as cooling water, to the working fluid flowing from the first compression stage 15. A liquid droplet separator 11 downstream of the second steam jet nozzle protects the subsequent compression stage 12 from liquid droplets. The temperature difference between the temperature of the working fluid at the inlet to the subsequent compression stage 12 and the saturated steam temperature of the working fluid is 10 °C at the given pressure.

[0097] A further partial flow of the working fluid is pumped by pump 14 at a mass flow rate of 17250 kg / h and a temperature of 131 °C through a line S from the outlet of the condensate tank 9 to the inlet of the liquid droplet separator 6, whereby the working fluid is expanded by an expansion valve 16 before entering the liquid droplet separator 6. Immediately before the working fluid flows through the expansion valve 16, the temperature of the working fluid is 131 °C and the absolute pressure of the working fluid is 4 bar.

[0098] Subsequently, a pump 13 conveys the working fluid at a temperature of 80 °C and an absolute pressure of 1 bar from the liquid droplet separator 6 to the vapor condenser 3. Comparative example 1

[0099] With the exception of the features mentioned below, this comparison example 1 is structured in the same way as example 1. Here too, a thermodynamic simulation was carried out using the Aspen software.

[0100] The working fluid is not cooled by a mixing element 8 after exiting compressor 7. As a result, the working fluid has a temperature of 206 °C at the inlet of the bottom evaporator 2, instead of the 140 °C found in Example 1. The mass flow rate of the working fluid in line P is 18,890 kg / h in this comparative example, instead of the 19,980 kg / h found in Example 1. The higher temperature of the working fluid also results in higher temperatures in the bottom evaporator 2. Due to the dynamic behavior of the distillation system, this also leads to higher temperature peaks, which can overheat the bottom mixture flowing through the bottom evaporator 2. In practice, this can lead to fouling and / or polymer formation in the bottom evaporator 2. The system would then have to be shut down for cleaning at shorter intervals. Comparative example 2

[0101] With the exception of the features mentioned, this comparison example 2 is structured in the same way as example 1. Here too, a thermodynamic simulation was carried out using the Aspen software.

[0102] In contrast to Example 1, no working fluid serving as cooling water is added to either the mixing element 8 or the intermediate mixing element 10. Instead, in this comparative example 2, the working fluid is cooled at these two points by means of corresponding heat exchangers. The use of the heat exchangers reduces both the mass flow rate of the working fluid exiting compressor 7 from 18,890 kg / h to 17,250 kg / h and the mass flow rate of the working fluid entering sump evaporator 2 from 19,980 kg / h to 17,250 kg / h.

[0103] Under these conditions, a total of 1569 kW of heat is extracted from the heat pump circuit by the two heat exchangers. Due to the reduced flow rate of working fluid through the sump evaporator 2, less heat is transferred to the sump mixture flowing through it. Instead, an external heat transfer medium, such as heating steam, must be added to the sump evaporator 2. This also reduces the efficiency of the heat pump circuit.

Claims

1. A distillation plant for polymerizable substances, comprising a rectification column (1) having a reboiler (2) and a vapor condenser (3), wherein a heat pump circuit having a compressor (7) fluidically connects both the reboiler (2) and the vapor condenser (3), and is designed such that, during the operation of the distillation plant, the reboiler (2) is heated by the heat pump circuit and the vapor condenser (3) is cooled by the heat pump circuit, wherein the working medium used in the heat pump circuit is water, wherein a mixing element (8) is disposed between the compressor (7) and the downstream reboiler (2), wherein the mixing element (8) is configured such that, during the operation of the distillation plant, the working medium is cooled by adding a cooling water in such an amount that, at the inlet of the reboiler (2), a temperature of the working medium in the range from 80 to 200°C can be established, and wherein the distillation plant is configured such that, during the operation of the distillation plant, the working medium serves partly as cooling water, wherein the working medium that serves as cooling water is taken from a subregion of the heat pump circuit that extends from the reboiler (2) as far as the vapor condenser (3) in the main flow direction of the working medium.

2. The distillation plant according to claim 1, wherein the reboiler (2) has a downstream condensate vessel (9) in the heat pump circuit, and both the condensate vessel (9) and the mixing element (8) are set up such that, during the operation of the distillation plant, the working medium flows partly from the condensate vessel (9) to the mixing element (8), serving as cooling water.

3. The distillation plant according to claim 2, wherein both the condensate vessel (9) and the compressor (7) are set up such that, during the operation of the distillation plant, the working medium flows partly from the condensate vessel (9) to the compressor (7), serving as cooling water.

4. The distillation plant according to any of claims 1 to 3, wherein the compressor (7) comprises one compression stage (15) or two or more compression stages (15, 12), and the distillation plant is set up such that, during the operation of the distillation plant, the cooling water in the case of two or more compression stages (15, 12) is added at least partly to the working medium via one intermediate-stage mixing element (10) for each compression stage, wherein the respective intermediate-stage mixing element (10) is between the respectively adjacent compression stages (15, 12) of the compressor (7).

5. The distillation plant according to claim 4, wherein, in the case of two or more compression stages (15, 12), one liquid droplet separator (11) is connected downstream of each intermediate-stage mixing element (10) between the respectively adjacent compression stages (15, 12).

6. The distillation plant according to any of claims 1 to 5, wherein the mixing element (8) and / or each intermediate-stage mixing element (10) present in the case of two or more compression stages (15, 12) is a mixing nozzle, a steam jet or a Venturi pump.

7. The distillation plant according to any of claims 1 to 6, wherein a phase separator (5) is connected downstream of the vapor condenser (3), wherein the phase separator (5) is designed such that, during the operation of the distillation plant, both an aqueous phase and an organic phase are formed in the phase separator (5), and these two phases are at least partly recycled to the rectification column (1), wherein the two phases are preferably recycled separately to the rectification column (1) via two separate recycling conduits.

8. The distillation plant according to any of claims 1 to 7, wherein a water separator (6) is present in the heat pump circuit, wherein the water separator (6) is fluidically connected to the vapor condenser (3) in such a way that, during the operation of the distillation plant, the working medium flows from the water separator (6) into the vapor condenser (3), and then the working medium flows back from the vapor condenser (3) into the water separator (6).

9. A process for preparing a (meth)acrylate by reacting (meth)acrylic acid with an alcohol corresponding to the (meth)acrylate in the presence of an acidic catalyst and a polymerization inhibitor, comprising the steps of: • providing a rectification column (1) having a reboiler (2) and a vapor condenser (3), wherein a heat pump circuit having a compressor (7) fluidically connects both the reboiler (2) and the vapor condenser (3), and the working medium used in the heat pump circuit is water, • performing an esterification within a reaction zone, where the (meth)acrylic acid and alcohol components are used in a molar ratio in the range from 1.0 : 1.0 to 1.0 : 2.0, preferably in the range from 1.0 : 1.1 to 1.0 : 1.5, and where the esterification takes place at a temperature in the range from 80 to 150°C, preferably in the range from 100 to 130°C, and at an absolute pressure in the range from 0.2 to 5.0 bar, preferably in the range from 0.4 to 1.5 bar, as a result of which a resultant reaction mixture is obtained, • separating the water of esterification formed in the esterification from the reaction mixture within the rectification column (1), wherein the reboiler (2) is heated by the working medium that flows through it in the heat pump circuit, • discharging a gaseous vapor stream enriched by the water of esterification at the top of the rectification column (1), • condensing the vapor stream in the vapor condenser (3) to form an organic phase and an aqueous phase, wherein the vapor condenser (3) is cooled by the working medium flowing through it in the heat pump circuit, and the working medium at the outlet from the vapor condenser (3) is at a temperature in the range from 35 to 120°C, and • feeding the working medium from the outlet of the vapor condenser (3) to the compressor (7), wherein the working medium is compressed within the compressor (7) and the working medium at the compressor outlet is at a temperature in the range from 100 to 300°C and an absolute pressure in the range from 1 to 10 bar, wherein a mixing element (8) in the heat pump circuit is disposed between the compressor (7) and the downstream reboiler (2), wherein the working medium is cooled by adding a cooling water at a temperature in the range from 1 to 160°C to the working medium via the mixing element (8) in such an amount that, at the inlet of the reboiler (2), the working medium is at a temperature in the range from 80 to 200°C, and • the working medium serves partly as cooling water, wherein the working medium that serves as cooling water is taken from a subregion of the heat pump circuit that extends from the reboiler (2) as far as the vapor condenser (3) in the main flow direction of the working medium.

10. The process according to claim 9, wherein the cooling water is added at a temperature in the range from 1 to 160°C and with a mass flow rate relative to the mass flow rate of the working medium in the range from 3% to 10%.

11. The process according to claim 9 or 10, wherein the compressor (7) comprises one compression stage (15) or two or more compression stages (15, 12) and, in the case of two or more compression stages (15, 12), the cooling water is added at least partly to the working medium via one intermediate-stage mixing element (10) for each compression stage, wherein the respective intermediate-stage mixing element (10) is between the respectively adjacent compression stages (15, 12) of the compressor (7).

12. The process according to claim 11, wherein the working medium is cooled by adding the cooling water at a temperature in the range from 1 to 160°C to the working medium via the intermediate-stage mixing element (10) in such an amount that, at the inlet of the downstream compression stage, a temperature difference between the temperature of the working medium and the temperature at which the working medium under the existing absolute pressure takes the form of saturated steam in the range from 2 to 50°C, preferably in the range from 5 to 20°C, is established.

13. The process according to any of claims 9 to 12, wherein the working medium is cooled by adding the cooling water at a temperature in the range from 1 to 160°C to the working medium via the mixing element (8) in such an amount that, at the inlet of the reboiler (2), a temperature difference between the temperature of the working medium and the temperature at which the working medium under the existing absolute pressure takes the form of saturated steam in the range from 5 to 50°C can be established, where the existing absolute pressure is preferably in the range from 2 to 8 bar, more preferably in the range from 4 to 6 bar.

14. The process according to any of claims 9 to 13, wherein the (meth)acrylate is an n-butyl (meth)acrylate.

15. The use of a distillation plant according to any of claims 1 to 8, wherein the distillation plant is used in chemical processes, especially in processes for preparing (meth)acrylates, or in processes in which (meth)acrylates, preferably n-butyl (meth)acrylates, occur.

16. A method of operating a distillation plant according to any of claims 1 to 8, wherein a liquid mixture (Z) is conveyed into the rectification column (1), and in the distillative separation a vapor stream having a temperature in the range from 35 to 120°C is formed at the inlet of the vapor condenser (3), and a bottoms product having a temperature in the range from 80 to 160°C is formed in the bottom of the rectification column (1), and the working medium from the reboiler (2) is fed at least partly to the vapor condenser (3) to be cooled, and the working medium is heated in the vapor condenser (3), wherein the working medium at the outlet from the vapor condenser (3) is at a temperature in the range from 35 to 120°C and an absolute pressure in the range from 0.1 to 0.9 bar, preferably 0.3 to 0.7 bar, and then the working medium is compressed by the compressor (7), as a result of which the working medium at the outlet from the compressor (7) is at a temperature in the range from 100 to 300°C and an absolute pressure in the range from 1 to 10 bar, and then cooling water is added to the working medium via the mixing element (8) in such an amount that a temperature at the inlet of the reboiler (2) in the range from 80 to 200°C, preferably in the range from 100 to 160°C, is established.