Continuous process for obtaining 2-ethylhexyl acrylate

Abstract

The present invention relates to a continuous process for obtaining 2-ethylhexyl acrylate (2-EHA) from a mixture (1) which is liquid under an absolute pressure in the range of 0.5 to 100 bar and has a temperature in the range of 0 to 300° C. and comprises 2-EHA, at least one high-boiling substance, at least one homogeneous catalyst and at least one low-boiling substance, in which the mixture (1) is reduced in pressure to an absolute pressure level in the range of 0.1 to 10 bar by a pressure maintaining device (3) and the resulting two-phase gas-liquid mixture (16) is continuously fed to a spiral tube evaporator (4) in which, at a temperature in the range of 50 to 300° C., the 2-EHA content of the liquid phase of the two-phase gas-liquid mixture is reduced by partial evaporation, which is accompanied in parallel by an increase in the 2-EHA content of the gas phase of the two-phase gas-liquid mixture, and the two phases are discharged in the form of a resulting two-phase gas-liquid output stream (17).

Description

[Technical Field]

[0001] The present invention relates to a continuous process for obtaining 2-ethylhexyl acrylate (2-EHA) from a mixture (1) that is liquid under an absolute pressure ranging from 0.5 to 100 bar, has a temperature ranging from 0 to 300°C, and comprises 2-EHA, at least one high-boiling substance, at least one homogeneous catalyst, and at least one low-boiling substance. [Background technology]

[0002] The preparation of 2-EHA is disclosed, for example, in DE 10246869 A1 (BASF AG).

[0003] The production of (meth)acrylic esters here also induces the by-product 2-EHA. In the process according to D1, the acid-catalyzed esterification of acrylic acid with 2-ethylhexanol is carried out in a homogeneous liquid phase, and the esterification is carried out in a reaction zone equipped with at least one distillation unit, through which the water formed in the esterification is removed together with 2-ethylhexene, 2-ethylhexanol, and 2-EHA, which condense and separate into an aqueous phase and an organic phase.

[0004] German Patent Application Publication No. 10246869 (BASF AG) further discloses that 2-EHA can be obtained by thermally treating the residue produced from the distillation of the residue. The thermal treatment is carried out by a discontinuous process in a stirred tank, also known as a "batch process." More specifically, the thermal treatment is carried out in a stirred device, preferably at 140 to 200°C and an absolute pressure of 20 to 300 mbar. This thermal treatment leads to an undesirable cleavage reaction. The cleavage residue produced during the cleavage reaction, primarily useful products of 2-EHA, 2-ethylhexanol, acrylic acid, and a 2-ethylhexene isomer mixture, is continuously separated, condensed, and returned to the esterification process for the 2-EHA production. The still pumpable cleavage residue is, for example, discarded and incinerated in this process. These cleavage residues typically contain 25 to 35% esterification catalyst, 20 to 30% useful 2-EHA product, 10 to 20% oxyester, 2 to 3% inhibitor, and 25 to 30% high-boiling materials. If desired, the cleavage residues can be partially recycled to the process, to an extent of 0 to 80%. To improve pumpability, the cleavage residues are typically mixed with a solvent such as Oxo oil and then utilized, for example, thermally. However, this approach involves more work and higher costs due to the additional resources required. A drawback of this process is that, despite possible optimization, due to the high concentration of homogeneous catalyst during the cleavage of the high-boiling materials, toward the end of the batch process, the product formed is no longer useful 2-EHA product, but instead a mixture of 2-ethylhexene isomers. These low-boiling materials are no longer usable in the process and must be disposed of. Furthermore, long residence times in batch processes result in the further formation of polymer that can no longer undergo cleavage, resulting in a rapid increase in the viscosity of the residue. The solvent required for dilution results in additional work and increased costs, as well as increased amounts of residue.

[0005] There are no known more efficient processes for obtaining or isolating 2-EHA.

[0006] Another process for obtaining a different useful product, namely cyclododecatriene (CDT), is disclosed in EP 1907342 (BASF SE), which describes a continuous process based on a pressure-maintaining device and a spiral tube evaporator. The short residence time of the solution in the spiral tube evaporator significantly reduces the amount of undesirable cleavage residues in the solution, which contains CDT, high-boiling substances, and other polymers. The liquid and gas are separated from each other by a downstream gravity separator. The useful CDT product is then found in large amounts in the condensate.

[0007] Spiral tube evaporators are well known and are described, for example, in German Patent Application No. DE 19600630 (Bayer AG). This discloses an evaporator device in which the mechanical force required to keep the heat exchange surface transparent is provided by flow forces, not by internal rotation. The evaporator device consists of a single externally heated spiral tube. The single-tube evaporator is operated in this case such that a solution or suspension is fed into the device in an overheated state under absolute pressure, and some of the volatile components of the solution evaporate immediately upon entering the device. This vapor serves to transport the increasingly viscous solution or suspension through the device, ensuring that the heat transfer surface remains transparent.

[0008] The objective was to provide a new, more efficient process for evaporating the useful product 2-EHA from the mixture (1) produced as a reaction effluent in the production of (meth)acrylic acid esters, for example, by the acid-catalyzed esterification of acrylic acid with 2-ethylhexanol. The production of (meth)acrylic acid esters can be achieved, for example, by a process according to DE 10246869 (BASF AG). At the same time, the new, more efficient process should also minimize capital costs and expenditures for the construction of facilities and equipment.

[0009] Such mixture (1) comprises 2-EHA, at least one high-boiling material, at least one homogeneous catalyst, and at least one low-boiling material.

[0010] Preferred and exemplary compositions of the mass fractions of components present in mixture (1) are given below in weight percent, where the sum of 2-EHA, high boilers, homogeneous catalyst, low boilers, and additional components adds up to 100% by weight. The additional components have only a negligible effect on the process according to the invention, and therefore are not of industrial relevance to the process according to the invention.

[0011] The preferred composition of the individual components of mixture (1) and their mass fractions based on mixture (1) expressed in weight percent are as follows: ·2-EHA:≧10.0wt% ·High boiling point substances: ≧0.3% by weight Polymer: 0.1 to 10.0 wt% o 2-Ethylhexyl 3-(2-ethylhexoxy)-propionate: ≥ 0.1 wt% o 2-Ethylhexyl 2-diacrylate: 0.1 to 12.0% by weight · Homogeneous catalyst: 0.1~15.0% by weight · Low boiling point substances: 0.1~20.0% by weight o Water: 0~15.0% by weight o Acrylic acid: 0 to 15.0% by weight o 2-Ethylhexanol: 0 to 15.0% by weight o 2-Ethylhexene isomer: 0 to 15.0% by weight Additional ingredients: 0 to 10.0% by weight

[0012] In a particularly preferred configuration, the preferred configuration of the individual components of mixture (1) and their mass fractions based on mixture (1) stated in weight percent is as follows: · 2-EHA:20.0~80.0wt% · High boiling point substances: 0.3~60% by weight Polymer: 0.1 to 6.0% by weight o 2-Ethylhexyl 3-(2-ethylhexoxy)-propionate: 0.1 to 45.0% by weight o 2-Ethylhexyl 2-diacrylate: 0.1 to 10.0% by weight · Homogeneous catalyst: 0.1~15.0% by weight · Low boiling point substances: 0.1~15.0% by weight o Water: 0~10.0% by weight o Acrylic acid: 0 to 10.0% by weight o 2-Ethylhexanol: 0 to 10.0% by weight o 2-Ethylhexene isomer: 0 to 10.0% by weight Additional ingredients: 0-6.0% by weight

[0013] In an exemplary configuration, the preferred configuration of the individual components of mixture (1) and their mass fractions based on mixture (1) stated in weight percent are as follows: Water 0.2% by weight 2-Ethylhexene isomer 0.3% by weight Acrylic acid 0.6% by weight 2-ethylhexanol 0.4% by weight 2-Ethylhexyl acrylate (2-EHA) 84.5% by weight 2-Ethylhexyl 3-(2-ethylhexoxy)-propionate 4.0% by weight 2-Ethylhexyl 2-diacrylate 4.4% by weight Polymer 4.3% by weight p-Toluenesulfonic acid as a homogeneous catalyst: 1.1 wt% Additional ingredients 0.2% by weight

[0014] In a further exemplary configuration, preferred configurations of the individual components of mixture (1) and their mass fractions based on mixture (1) expressed in weight percent are as follows: Water 4.0% by weight 2-Ethylhexene isomer 4.5% by weight Acrylic acid 4.1% by weight 2-Ethylhexanol 6.0% by weight 2-Ethylhexyl acrylate (2-EHA) 10.7% by weight 2-Ethylhexyl 3-(2-ethylhexoxy)-propionate 50.0% by weight 2-Ethylhexyl 2-diacrylate 10.0% by weight Polymer 10.0% by weight p-Toluenesulfonic acid 0.5 wt% as homogeneous catalyst Additional ingredients 0.2% by weight

[0015] In a further exemplary configuration, preferred configurations of the individual components of mixture (1) and their mass fractions based on mixture (1) expressed in weight percent are as follows: Water 0.7% by weight 2-Ethylhexene isomer 1.1% by weight Acrylic acid 0.4% by weight 2-ethylhexanol 0.5% by weight 2-Ethylhexyl acrylate (2-EHA) 12.4% by weight 2-Ethylhexyl 3-(2-ethylhexoxy)-propionate 79.8% by weight 2-Ethylhexyl 2-diacrylate 3.0% by weight Polymer 1.0% by weight p-Toluenesulfonic acid 0.8 wt% as homogeneous catalyst Additional ingredients 0.3% by weight

[0016] In a further exemplary configuration, preferred configurations of the individual components of mixture (1) and their mass fractions based on mixture (1) expressed in weight percent are as follows: Water 0.8% by weight 2-Ethylhexene isomer 1.0% by weight Acrylic acid 0.5% by weight 2-ethylhexanol 0.4% by weight 2-Ethylhexyl acrylate (2-EHA) 60.3% by weight 2-Ethylhexyl 3-(2-ethylhexoxy)-propionate 11.0% by weight 2-Ethylhexyl 2-diacrylate 0.4% by weight Polymer 1.6% by weight p-Toluenesulfonic acid as a homogeneous catalyst 15.0 wt% Additional ingredients 9.0% by weight

[0017] In a further exemplary configuration, preferred configurations of the individual components of mixture (1) and their mass fractions based on mixture (1) expressed in weight percent are as follows: Water 0.4% by weight 2-Ethylhexene isomer 0.1% by weight Acrylic acid 0.4% by weight 2-Ethylhexanol 0.9% by weight 2-Ethylhexyl acrylate (2-EHA) 52.5% by weight 2-Ethylhexyl 3-(2-ethylhexoxy)-propionate 28.8% by weight 2-Ethylhexyl 2-diacrylate 5.8% by weight Polymer 3.0% by weight p-Toluenesulfonic acid 4.1 wt% as homogeneous catalyst Additional ingredients 4.0% by weight

[0018] At the same pressure, eg, standard pressure, a low boiling substance has a lower boiling point than 2-EHA, and a high boiling substance has a higher boiling point than 2-EHA.

[0019] The boiling point of 2-EHA at standard pressure is 218°C. At standard pressure, low boiling materials generally range from 50 to 215°C, and high boiling materials range from 220 to 400°C. [Prior art documents] [Patent documents]

[0020] [Patent Document 1] DE 10246869 [Patent Document 2] European Patent No. 1907342 [Patent Document 3] DE 19600630 Summary of the Invention [Problem to be solved by the invention]

[0021] The new process should avoid or at least significantly reduce the formation of cleavage residues and polymer formation, since these phenomena lead to excessively high viscosities in the residues, thereby making the process much more difficult.

[0022] Furthermore, the process should produce a similar output per kilogram of 2-EHA from the reaction as a batch process, such as that described in German Patent Application Publication No. 10246869 (BASF AG), with the same or improved quality in terms of color, color stability, odor, and / or purity. Furthermore, the loss of useful 2-EHA product due to the formation of residues in the bottoms and low-boiling substances (e.g., 2-ethylhexene isomers) and high-boiling substances (e.g., polymers) should also be minimized. This also reduces the energy consumption of the process. [Means for solving the problem]

[0023] These objects are achieved according to the invention by a continuous process for obtaining 2-ethylhexyl acrylate (2-EHA) from a mixture (1) that is liquid under an absolute pressure in the range of 0.5 to 100 bar and has a temperature in the range of 0 to 300°C, and that comprises 2-EHA, at least one high-boiling substance, at least one homogeneous catalyst, and at least one low-boiling substance, characterized in that the mixture (1) is depressurized to an absolute pressure level in the range of 0.1 to 10 bar by a pressure-maintaining device (3), and the resulting two-phase gas-liquid mixture (16) is continuously fed to a spiral tube evaporator (4), in which, at a temperature in the range of 50 to 300°C, the 2-EHA content of the liquid phase of the two-phase gas-liquid mixture is reduced by partial evaporation, which is accompanied by a concomitant increase in the 2-EHA content of the gas phase of the two-phase gas-liquid mixture, and the two phases are discharged in the form of a resulting two-phase gas-liquid output stream (17).

[0024] The invention further relates to preferred configurations of the process according to claims 2 to 18.

[0025] It has been found that short residence times, such as in the range of 0.3 to 10 minutes, in a continuous process can significantly prevent the formation of low-boiling materials and high-boiling polymers from the 2-ethylhexene isomers, which means that cleavage residues can be prevented or at least significantly reduced.

[0026] It has also been found that the process according to the invention should not only be carried out with the shortest possible residence time, but also at low temperatures as well as low absolute pressures.

[0027] This can therefore be achieved using thin film or short path evaporators, optionally in combination with an upstream falling film, forced circulation or forced circulation flash evaporator. Thin film or short path evaporators are described, inter alia, on pages 44-46 of the article cited below:

[0028] M. Dippel, Faculty of Mechanical Engineering of the Ruhr University Bochum, 2016.

[0029] However, due to the equipment used for this purpose, the process has proven to be technically complex. Further disadvantages of this equipment concept include the relatively high investment costs of the combined falling-film and thin-film evaporators, and the high variable costs of operating the thin-film evaporators. Furthermore, the use of evaporator types such as falling-film evaporators, forced-circulation evaporators, and forced-circulation flash evaporators entails significant process risks, as high-boiling components present in the feed stream and potential decomposition products during evaporation tend to form deposits on hot surfaces. Furthermore, deposits can also form within the thin-film evaporator, for example on the internal wiper system, which can lead to system shutdowns.

[0030] According to the present invention, it has been found that in a device of relatively simple construction, namely a spiral tube evaporator (4), high boiling point substances can be removed without the addition of an external liquid film and avoiding the formation of deposits on the heated walls. This would not have been expected by a person skilled in the art, since spiral tube evaporators have a significantly higher heat flow density compared to conventional thin film evaporators and consequently operate at significantly higher temperature differences, which typically leads to increased formation of polymers and deposits.

[0031] Although the process according to the invention produces little or no useful 2-EHA addition products, overall process integration indicates that the process according to the invention provides yields of 2-EHA similar to those of batch processes such as the batch process according to DE 10246869 (BASF AG).

[0032] Due to the prevention of the formation of high boiling point materials in the process according to the invention, the resulting residue (10) remains pumpable even in the absence of diluent.

[0033] In the process according to the invention, the short residence time of the two-phase gas-liquid mixture (16) in the spiral tube evaporator (4) means that polymer formation due to excessive thermal stress is effectively prevented or at least significantly reduced compared to the batch process described above. The temperature in the spiral tube evaporator (4) here is in the range of 50 to 300°C, preferably in the range of 100 to 200°C, more preferably in the range of 140 to 160°C.

[0034] Thus, in contrast to previous experience with conventional evaporator concepts, 2-EHA losses due to polymer formation in the evaporator system remain extremely low, in favorable cases less than 1 wt. % relative to mixture (1).

[0035] Thus, a novel solution is provided for obtaining 2-EHA in an efficient process, which allows for a long service life and low operating costs in addition to low expenditure on equipment.

[0036] In an advantageous embodiment of the process, a preheater (2) upstream of the pressure maintenance device (3) heats the liquid mixture (1) to a temperature in the range of 100 to 200°C if the mixture (1) is not already at a temperature of at least 100°C.

[0037] This avoids effects such as smearing and / or caking, since the mixture (1) has a high temperature from the start and therefore a lower viscosity.

[0038] In a preferred embodiment, the spiral tube evaporator (4) is operated at an absolute pressure in the range of 1 to 2000 mbar.

[0039] In a more preferred configuration, the proportion of 2-EHA in the liquid phase is reduced to a 2-EHA content of less than 20% by weight in one pass through the spiral tube evaporator (4).

[0040] In a particularly preferred configuration, the proportion of 2-EHA in the liquid phase was reduced to a 2-EHA content of less than 10% by weight in one pass through the spiral tube evaporator (4).

[0041] This is made possible by the inventive use of a spiral tube evaporator (4) and by process parameters such as the temperature of the mixture (1) upon exiting the preheater (2), which results in an efficient process in which losses of 2-EHA in the residue (10) are largely avoided.

[0042] In a preferred embodiment, the formation of 2-ethylhexene isomers in the process is less than 2% by weight based on mixture (1), which is made possible, inter alia, by the short residence time and / or low temperature in the spiral tube evaporator.

[0043] Preferably, a portion of the liquid phase of the two-phase vapor-liquid output stream (17) withdrawn from the spiral tube evaporator (4) can be returned to the spiral tube evaporator (4) for further partial evaporation, thereby further improving the purification of the distillate (9).

[0044] Depending on the costs involved and the composition of the mixture, it is also possible to achieve nearly complete separation of 2-EHA from mixture (1).

[0045] In a further embodiment, a stripping gas (7) can be added to the two-phase gas-liquid mixture (16) downstream of the pressure maintenance device (3), for example via a feed conduit, so that the partial evaporation in the spiral tube evaporator (4) is carried out in the presence of the stripping gas (7). The stripping gas (7) can be preferably steam or an inert gas, preferably nitrogen, or a mixture of different gases that reduces the partial pressure of the vaporizable components in the mixture (1) and increases the gas velocity.

[0046] Preferably, the stripping gas (7) is fed to the spiral tube evaporator (4) to achieve a desired flow pattern and / or to adjust the residence time of the two-phase gas-liquid mixture (16) therein. Furthermore, residual low-boiling substances can be removed from the gas-liquid mixture (16) by stripping. The amount of stripping gas fed to the spiral tube evaporator (4) is preferably in the range of more than 0% to 50% by weight, particularly preferably in the range of more than 0% to 20% by weight, and very particularly preferably in the range of more than 0% to 5% by weight, in each case based on the mixture (1). The term "total feed stream" therefore includes the mixture (1) and the stripping gas (7).

[0047] The stripping gas (7) can also be preferably filled with low boiling substances, which allows for better separation of the low boiling substances in the spiral tube evaporator.

[0048] The residence time can generally be determined by the flow rate and geometry of the spiral tube evaporator (4) with the spiral tube (5). The residence time in the spiral tube evaporator (4) and associated piping system is preferably set in the range of 0.3 to 10 minutes, more preferably in the range of 0.5 to 2 minutes. In particular, this reduces or even completely avoids thermal decomposition (cleavage reaction) of the target product and polymer formation.

[0049] The process is generally carried out continuously, although the separation principle can also be carried out as a continuous batch process.

[0050] Under certain circumstances, it may be desirable to fin the helical tubes (5) in the helical tube evaporator (4) internally and / or externally. This is understood to mean the attachment of fins to the inside or outside of the helical tubes (5). These fins improve the performance of the helical tubes (5). This improvement comes about both by providing a larger heat transfer surface area and by generating additional turbulence. The inside of the helical tubes (5) may be fully or partially equipped with a wire knit. This is understood to mean the introduction of a wire knit into the helical tubes (5), improving heat and mass transfer.

[0051] In a further embodiment, instead of a single spiral tube evaporator (4), two or more spiral tube evaporators (4) are connected in series to form an evaporator cascade, and the gas-liquid mixture (16) entering the evaporator cascade gradually reduces the 2-EHA content of its liquid phase through partial evaporation of the liquid phase.

[0052] In this variant, it may be advantageous to operate the individual spiral tube evaporators of the evaporator cascade at different pressures, preferably in the range of 1 to 2000 mbar, more preferably in the range of 5 to 200 mbar, or at the same pressure.

[0053] In a further embodiment, instead of a single spiral tube evaporator (4), two or more spiral tube evaporators (4) can be connected in parallel to form an evaporator cascade, in which the liquid-vapor mixture (16) entering the evaporator cascade undergoes partial evaporation of the liquid phase to reduce the 2-EHA content of the liquid phase, i.e., separation between the two evaporators.

[0054] In this variant, it may be advantageous to operate the individual spiral tube evaporators of the evaporator cascade at different pressures, preferably in the range of 1 to 2000 mbar, more preferably in the range of 5 to 200 mbar, or at the same pressure.

[0055] In a further embodiment, the evaporator stages of the evaporator cascade (each stage in each case representing an individual spiral tube evaporator) can also optionally be operated at least in part by heat integration. For example, the heat integration of two spiral tube evaporators (4) can be preferably designed as follows:

[0056] The first spiral tube evaporator (4) is operated at a product-side absolute pressure of 200 mbar and heated with heating steam (approximately 204°C) at 17 bar (absolute pressure). The steam condensate that accumulates in the first spiral tube evaporator (4) at a temperature of, for example, 150°C is used to heat the second spiral tube evaporator (4), which is operated at 50 mbar. This has the advantage of low steam consumption.

[0057] By properly setting the operating point of the spiral tube evaporator, very high area specific performance can be achieved at short residence times.

[0058] Thus, in laboratory tests, up to 5 kg / h of 2-EHA-containing solution could be flowed through a spiral tube with an internal diameter of 6 mm without any problems.

[0059] In a further embodiment, the two-phase vapor-liquid output stream (17) from the spiral tube evaporator (4) is fed to a downstream separator (6), which is preferably a gravity separator.

[0060] The gravity separator here is preferably operated at a pressure in the range from 1 to 2000 mbar absolute, preferably in the range from 5 to 200 mbar absolute, more preferably in the range from 15 to 50 mbar absolute.

[0061] In principle, instead of a gravity separator, a centrifugal droplet separator or a separator with a demister can also be used, both of which have the function of separating liquid from vapor / gas.

[0062] The evaporation rate is understood to mean the ratio of the amount of distillate to the feed rate. The evaporation rate can be determined, for example, by experiment.

[0063] The evaporation rate of the two-phase vapor-liquid mixture (16) in the spiral tube evaporator (4) also determines the concentration of useful 2-EHA product in the bottom product, which is the product that collects in the bottom region of the downstream separator (6), which is preferably a gravity separator.

[0064] The heating temperature and pressure settings in the spiral tube evaporator (4) determine the evaporation rate of the two-phase gas-liquid mixture (16).

[0065] The absolute pressure downstream of the pressure maintenance device (3) can vary greatly during operation and, in the process according to the invention, is in the range of 0.1 to 10 bar. The absolute pressure establishes itself according to the operating parameters. The absolute pressure in the separator (6) is set in the range of 1 to 2000 mbar, preferably in the range of 5 to 200 mbar, more preferably in the range of 15 to 50 mbar.

[0066] The pressure downstream of the pressure maintenance device (3) depends, among other things, on the following parameters: Absolute pressure in the separator (6) Length and diameter of the spiral tube (5) Material properties such as density or viscosity of the liquid mixture (1) -Temperature downstream of preheater (2) Mass flow rate and volume flow rate through the spiral tube (5) of the spiral tube evaporator (4)

[0067] In a preferred embodiment, the polymer formation in the spiral tube evaporator (4) and the separator (6) is less than 5% by weight combined, based on the mixture (1). This is made possible, inter alia, by the short residence time and / or low temperature in the spiral tube evaporator (4).

[0068] In a preferred embodiment, the gas fraction of the two-phase vapor-liquid output stream (17) fed to the separator (6) is fed from the separator (6) to a condenser (12) where it is condensed to form a distillate (9), also referred to as a vapor stream.

[0069] The vapor stream can be condensed to a distillate (9) in a conventional condenser (12), such as a shell-and-tube apparatus or a quench condenser.

[0070] The resulting condensate, which essentially contains the useful 2-EHA product, can be worked up in a conventional distillation unit or further used directly. The concentration of 2-EHA in the distillate (9) is typically 30% to 90% by weight.

[0071] The bottom stream from separator (6) essentially contains the high boiling point materials and catalyst fraction formed during the reaction. Depending on the operating mode, the content of useful 2-EHA products in the bottom stream is less than 30% by weight, preferably less than 10% by weight, more preferably less than 5% by weight. In specific embodiments, it is even possible to achieve a residual proportion of 2-EHA of less than 1% by weight.

[0072] In a further embodiment, the absolute pressure in the vapor stream is from 1 to 10 4 mbar, preferably 1 to 10 3 In a further preferred embodiment, the steam flow is at an absolute pressure in the range of 1 to 100 mbar.

[0073] By appropriately designing the geometry of the spiral tube evaporator (4) and its spiral tubes (5), in a preferred embodiment, it is possible to establish a wavy film flow in the piping, in the sense of turbulence, depending on the overall volumetric flow rate, the gas fraction, the required absolute pressure in the separator (6), etc. This achieves intensive heat and mass transfer. High throughput results in high wall shear stresses, which effectively prevent the accumulation of solidified deposits on the heated walls.

[0074] The spiral tube evaporator (4) can be heated, for example, by condensing steam or by means of a thermostatic oil circuit. Electrical heating is also possible.

[0075] The preferred geometry of the spiral tube evaporator (4) is shown in Figure 1. In the figure, the parameter d i is the inner diameter of the tube, D is the curvature diameter of the helical tube (5) (also called the diameter of the helical coil), and h is the pitch of the helical tube (5).

[0076] The dimensionless curvature ratio a is the inner diameter d i is the ratio of the radius of curvature to the diameter of curvature D, and is expressed by the following formula. a=d i / D

[0077] The dimensionless pitch b is the ratio of the pitch of the helical tube h to the curvature diameter D, and is expressed by the following formula: b=h / D

[0078] The dimensionless curvature ratio a is in the range of 0.01 to 0.5, preferably in the range of 0.01 to 0.4, more preferably in the range of 0.02 to 0.2, and most preferably in the range of 0.02 to 0.1.

[0079] The dimensionless pitch b is in the range of 0.01 to 1.0, preferably in the range of 0.02 to 0.8, more preferably in the range of 0.05 to 0.5, and most preferably in the range of 0.06 to 0.18.

[0080] The dimensionless pitch b is set here independently of the dimensionless curvature ratio a.

[0081] Thus, the helical tubes (5) in the helical tube evaporator (4), or each individual helical tube of the helical tube evaporator in the case of an evaporator cascade, should independently have a dimensionless curvature ratio a in the range of 0.01 to 0.5 and a dimensionless pitch b in the range of 0.01 to 1.0.

[0082] Preferably, the helical tubes (5) in the helical tube evaporator (4), or each individual helical tube of the helical tube evaporator in the case of an evaporator cascade, should independently have a dimensionless curvature ratio a in the range of 0.01 to 0.4 and a dimensionless pitch b in the range of 0.02 to 0.8.

[0083] Particularly preferably, the helical tubes (5) in the helical tube evaporator (4), or each individual helical tube of the helical tube evaporator in the case of an evaporator cascade, should independently have a dimensionless curvature ratio a in the range of 0.02 to 0.1 and a dimensionless pitch b in the range of 0.06 to 0.18.

[0084] In the case of an evaporator cascade, the design of the spiral tubes, determined inter alia by the curvature ratio a or the dimensionless pitch b, applies to all spiral tube evaporators. The parameters of the individual spiral tubes can be set independently for each individual spiral tube evaporator.

[0085] The invention will be discussed in more detail below with reference to the drawings, which should be understood as schematic representations and which do not constitute limitations of the invention, for example with regard to specific dimensions or design variations. [Brief explanation of the drawings]

[0086] [Figure 1] 1 shows a sketch of the geometry of the helical tube (5) in the helical tube evaporator (4), with the pitch h, inner diameter di, and diameter (curvature) D of the helical tube (5) shown. [Figure 2] 1 is a diagram of a continuous process according to the present invention for obtaining 2-EHA, in which separation of, inter alia, high-boiling substances is carried out in a continuous spiral tube evaporator system. A liquid mixture (1) is fed to a preheater (2), then depressurized via a pressure-maintaining device (3), and fed to a spiral tube evaporator (4) in the form of a two-phase gas-liquid mixture (16). A distillate (9), which is to be condensed via a condenser (12), is separated from the residue (10) by a separator (6). Optionally, the distillate (9) can be fed to the mixture (1) upstream of the preheater (2) to concentrate the target product 2-EHA. [Figure 3]1 shows a discontinuous prior art process for obtaining 2-EHA. The mixture (1) is fed to a discontinuously operated stirred tank (13). Separation of, inter alia, high-boiling substances takes place in the stirred tank (13) with external heating, which may be carried out by means of heated steam (14), and the resulting condensate (15) is discharged from the stirred tank (13). The residue (10) is discharged from the stirred tank (13). A vapor stream is sent from the stirred tank (13) to a condenser (12), where it condenses. The distillate (9) containing the target product 2-EHA can optionally be recycled to the process. DETAILED DESCRIPTION OF THE INVENTION

[0087] Example Example 1 Example 1 discloses a continuous process configuration according to the present invention as shown in Figure 2. In this configuration, high boiling point materials are separated in a continuous spiral tube evaporator system. The helical tube (5) in this example had the following dimensions: Inner diameter: d i =7 mm Curvature diameter: D=250 mm Pitch: h=40 mm Dimensionless pitch: b=0.028 Dimensionless curvature ratio: a=0.16

[0088] The solution to be worked up, which had a 2-EHA concentration of 52.5% by weight and contained high-boiling substances such as polymers and catalysts, was fed to and heated in a preheater (2) operated by a Marlotherm SH. Preheating was carried out at 130 °C. The heated solution was discharged from the preheater via a conduit. The absolute pressure in the preheater was regulated to 1.5 bar by a downstream pressure-maintaining device (3) designed as a shut-off valve with an internal diameter of 10 mm. 0.1 m 2 A conventional shell-and-tube apparatus with a heat transfer surface area of ​​1000 psi served as the preheater. Downstream of the pressure maintenance device (3), the heated solution was reduced in pressure to 0.5 bar absolute and fed to the spiral tube evaporator (5) at a temperature of 120°C.

[0089] The absolute pressure in the separator (6) was 20 mbar. The feed rate of the mixture (1) was 3 kg / h. The temperature in the separator (6) was 150°C. The evaporation rate achieved during the experiment was 68%. The composition of the liquid mixture (1) flowing into the spiral tube evaporator (4) was the same as in Comparative Example 1. Water 0.4% by weight 2-Ethylhexene isomer 0.1% by weight Acrylic acid 0.4% by weight 2-Ethylhexanol 0.9% by weight 2-Ethylhexyl acrylate 52.5% by weight 2-Ethylhexyl 3-(2-ethylhexoxy)-propionate 28.8% by weight 2-Ethylhexyl 2-diacrylate 5.8% by weight p-Toluenesulfonic acid 4.1% by weight Additional ingredients and polymers 7.0 wt.%

[0090] The 2.04 kg / h distillate (9) had the following composition: Water 0.2% by weight 2-Ethylhexene isomer 2.6% by weight Acrylic acid 0.2% by weight 2-Ethylhexanol 2.0% by weight 2-Ethylhexyl acrylate 70.2% by weight 2-Ethylhexyl 3-(2-ethylhexoxy)-propionate 17.2% by weight 2-Ethylhexyl 2-diacrylate 5.2% by weight p-Toluenesulfonic acid 2.0% by weight Additional ingredients and polymers 0.4% by weight

[0091] The residue (10) of 0.96 kg / h had the following composition: Water 0.1% by weight 2-Ethylhexene isomer 0.1% by weight Acrylic acid 0.3% by weight 2-Ethylhexanol 0.9% by weight 2-Ethylhexyl acrylate 8.0% by weight 2-Ethylhexyl 3-(2-ethylhexoxy)-propionate 40.0% by weight 2-Ethylhexyl 2-diacrylate 5.0% by weight p-Toluenesulfonic acid 25.0% by weight Additional ingredients and polymers 20.6 wt.%

[0092] Compared to the existing work-up process from the prior art described in Example 2, the process according to the invention using a spiral tube evaporator made it possible to reduce the amount of residue (10) from 0.42 kg per kg of feed to 0.32 kg per kg of feed.

[0093] Furthermore, in Example 2, the cleavage occurring in the existing down-treatment process resulted in the formation of a larger amount of the 2-ethylhexene isomer.

[0094] Compared to existing post-treatment processes, the process according to the invention using a spiral tube evaporator made it possible to reduce the amount of 2-ethylhexene isomer from 0.12 kg / kg of feed to 0.02 kg / kg of feed.

[0095] No irreversible coating of the heated surfaces of the helical tube evaporator was observed even after several days of operation.

[0096] Comparative Example 1 Comparative Example 1 illustrates a prior art discontinuous process configuration and is described in more detail below with reference to FIG.

[0097] The separation of high boiling materials, e.g. polymers, was carried out in a stirred tank (13) operated discontinuously with external heating provided via heating steam (14). The volume of the stirred tank was 8 m 3The amount of mixture (1) as feedstock was 6 tons at a temperature of 120°C. The absolute pressure in the stirred tank (12) was set at 40 mbar. The temperature in the bottom area of ​​the stirred tank (12) was 145°C.

[0098] Heating of the stirred tank was stopped after 10 hours.

[0099] The steam flow from the stirred tank is 100 m 2 The condensed water was condensed in a condenser (12) designed as a conventional shell-and-tube heat exchanger with a heat exchange surface area of ​​1.0 MPa.

[0100] The distillate (9) was recycled back into the process, where the undesired 2-ethylhexene isomers obtained as low boiling materials were subsequently removed and incinerated.

[0101] The composition of the mixture (1) entering the stirred tank was the same as in Example 1: Water 0.4% by weight 2-Ethylhexene isomer 0.1% by weight Acrylic acid 0.4% by weight 2-Ethylhexanol 0.9% by weight 2-Ethylhexyl acrylate 52.5% by weight 2-Ethylhexyl 3-(2-ethylhexoxy)-propionate 28.8% by weight 2-Ethylhexyl 2-diacrylate 5.8% by weight p-Toluenesulfonic acid 4.1% by weight Additional ingredients and polymers 7.0 wt.%

[0102] 4400 kg of distillate (9) had the following composition: Water 0.7% by weight 2-Ethylhexene isomer 16.0% by weight Acrylic acid 1.3% by weight 2-Ethylhexanol 14.0% by weight 2-Ethylhexyl acrylate 70.0% by weight 2-Ethylhexyl 3-(2-ethylhexoxy)-propionate 2.3% by weight 2-Ethylhexyl 2-diacrylate 0.7% by weight p-Toluenesulfonic acid 0.1% by weight Additional ingredients and polymers 0.9% by weight

[0103] The cleavage resulted in the formation of 704 kg of 2-ethylhexene isomers per batch process.

[0104] Based on the feed rate, the amount of 2-ethylhexene isomer formed was 0.12 kg per kg of feed.

[0105] The 1600 kg residue (10) had the following composition: Water 0.1% by weight 2-Ethylhexene isomer 0.1% by weight Acrylic acid 0.3% by weight 2-Ethylhexanol 0.9% by weight 2-Ethylhexyl acrylate 21.0% by weight 2-Ethylhexyl 3-(2-ethylhexoxy)-propionate 20.0% by weight 2-Ethylhexyl 2-diacrylate 5.0% by weight p-Toluenesulfonic acid 24.0% by weight Additional ingredients and polymers 28.6 wt.%

[0106] To improve the pumpability of the residue (10), the residue (10) was mixed with 900 kg of Oxo oil 9N and then subjected to thermal utilization.

[0107] The total amount of residue was 2500 kg and based on the feed, the amount of residue was 0.42 kg / kg.

[0108] After a few days of operation, the stirred tank had to be cleaned due to fouling. The polymer that formed contaminated the inner wall of the stirred tank, which also served as a heat transfer surface, meaning that the heat transfer required for evaporation was no longer possible. [Explanation of symbols]

[0109] 1 mixture 2 Preheater 3 Pressure Maintenance Device 4. Spiral tube evaporator 5 Spiral tube 6 separator 7 Stripping Gas 8 heating oil 9 Distillate 10 Residue 12 Condenser 13 Mixing tank 14. Heating steam 15 Condensate 16 Two-phase gas-liquid mixture 17 Output Current

Claims

1. 1. A continuous process for obtaining 2-ethylhexyl acrylate (2-EHA) from a mixture (1) that is liquid under an absolute pressure in the range of 0.5 to 100 bar and has a temperature in the range of 0 to 300°C, and that comprises 2-EHA, at least one high-boiling substance, at least one homogeneous catalyst, and at least one low-boiling substance, characterized in that the mixture (1) is reduced in pressure to an absolute pressure level in the range of 0.1 to 10 bar by a pressure-maintaining device (3), and the resulting two-phase gas-liquid mixture (16) is continuously fed to a spiral-tube evaporator (4), in which, at a temperature in the range of 50 to 300°C, the 2-EHA content of the liquid phase of the two-phase gas-liquid mixture is reduced by partial evaporation, which is accompanied by a concomitant increase in the 2-EHA content of the gas phase of the two-phase gas-liquid mixture, and the two phases are discharged in the form of a resulting two-phase gas-liquid output stream (17).

2. 2. The process according to claim 1, characterized in that the preheater (2) upstream of the pressure maintenance device (3) heats the liquid mixture (1) to a temperature in the range of 100 to 200°C if the mixture (1) is not already at a temperature of at least 100°C.

3. 3. A process according to claim 1 or 2, characterized in that the spiral tube evaporator (4) is operated at an absolute pressure in the range of 1 to 2000 mbar.

4. 4. The process according to claim 1, wherein the proportion of 2-EHA in the liquid phase is reduced to a 2-EHA content of less than 20% by weight in one pass through the spiral tube evaporator (4).

5. 4. The process according to claim 1, wherein the proportion of 2-EHA in the liquid phase is reduced to a 2-EHA content of less than 10% by weight in one pass through the spiral tube evaporator (4).

6. 6. The process according to claim 1, wherein the formation of 2-ethylhexene isomer in the process is less than 2% by weight, based on the mixture (1).

7. 7. The process according to any one of claims 1 to 6, characterized in that part of the liquid phase of the two-phase vapor-liquid output stream (17) withdrawn from the spiral tube evaporator (4) is returned to the spiral tube evaporator (4) for further partial evaporation.

8. 8. The process according to claim 1, wherein a stripping gas (7) is added to the two-phase gas-liquid mixture (16) downstream of the pressure maintenance device (3), whereby the partial evaporation in the spiral tube evaporator (4) is carried out in the presence of a stripping gas (7).

9. 9. The process according to any one of claims 1 to 8, characterized in that instead of a single spiral tube evaporator (4), two or more spiral tube evaporators (4) are connected in series to form an evaporator cascade, and the gas-liquid mixture (16) entering the evaporator cascade gradually reduces the 2-EHA content of the liquid phase through partial evaporation of the liquid phase.

10. 9. The process according to any one of claims 1 to 8, characterized in that instead of a single spiral tube evaporator, two or more spiral tube evaporators (4) are connected in parallel to form an evaporator cascade, and the gas-liquid mixture (16) entering the evaporator cascade undergoes partial evaporation of the liquid phase to reduce the 2-EHA content of the liquid phase, i.e., separation between two evaporators.

11. 11. The process according to claim 9 or 10, characterized in that the individual spiral tube evaporators of the evaporator cascade are operated at different pressures in the range of 1 to 2000 mbar or at the same pressure.

12. 12. The process according to claim 11, characterized in that the individual spiral tube evaporators of the evaporator cascade are at least partly operated by heat integration.

13. 13. The process according to any one of claims 1 to 12, characterized in that the two-phase vapor-liquid output stream (17) from the spiral tube evaporator (4) is fed to a downstream separator (6) operated at an absolute pressure in the range of 1 to 2000 mbar.

14. 13. The process according to any one of claims 1 to 12, characterized in that the two-phase vapor-liquid output stream (17) from the spiral tube evaporator (4) is fed to a downstream separator (6) operated at an absolute pressure in the range of 5 to 200 mbar.

15. 15. A process according to claim 13 or 14, characterized in that the downstream separator (6) is a gravity separator.

16. 16. The process according to any one of claims 13 to 15, characterized in that the formation of polymer in the spiral tube evaporator (4) and the separator (6) is less than 5% by weight combined, based on the mixture (1).

17. 17. The process according to any one of claims 13 to 16, characterized in that the gas fraction of the two-phase gas-liquid output stream (17) fed to the separator (6) is fed from the separator (6) to a condenser (12) where it is condensed to form a distillate (9).

18. 18. The process according to any one of claims 1 to 17, characterized in that the helical tubes (5) in the helical tube evaporator (4), or each individual helical tube of a helical tube evaporator in the case of an evaporator cascade, independently have a dimensionless curvature ratio a in the range of 0.01 to 0.5 and a dimensionless pitch b in the range of 0.01 to 1.0.

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