An apparatus and a process for working up a mixture containing easily polymerizable components and decomposable components

Abstract

The invention relates to an apparatus for working up a mixture containing easily polymerizable components and decomposable components, the apparatus (101) comprising a tank reactor (103) and a heat exchanger (109) being connected to the bottom (113) of the tank reactor (103) by a recirculation line (111) so that liquid phase can be withdrawn from the tank reactor (103), flow through the heat exchanger (109) and be returned into the tank reactor (103), wherein a feed line (123) for a reactant opens into the recirculation line (111) upstream the heat exchanger (109). The invention further relates to a process for working up a mixture containing easily polymerizable components and decomposable components in such an apparatus.

Description

[0001] 230162W001

[0002] 1

[0003] An apparatus and a process for working up a mixture containing easily polymerizable components and decomposable components

[0004] Description

[0005] The invention relates to an apparatus for working up a mixture containing easily polymerizable components and decomposable components, comprising a tank reactor. The invention further relates to a process for working up a mixture containing easily polymerizable components and decomposable components.

[0006] In many chemical processes undesired by-products are formed. These by-products generally must be separated from the intended product and usually are deposited. However, these by-products usually reduce the yield and deteriorate the product quality. Further, as in most cases the by-products are not valuable products but must be disposed, the disposal costs increase.

[0007] For this purpose, it is advantageous, if at least a part of the by-products can be decomposed into the desired product and / or into the reactants, which then can be separated off and recycled into the reaction.

[0008] It is particularly known from processes for producing esters by reacting (meth)acrylic acid and an alkanol to separate off an oxyesters containing bottom product. The bottom product is heated in the presence of an acid to decompose the oxyesters. The resulting decomposition product directly evaporates by the reaction heat and can be separated off. Such processes are described for example in DE-A 19536 191, DE-A 19547459, DE-A 19547485, and DE-A 19851 984.

[0009] In each of the known processes, the decomposition of the bottom product is carried out in a tank reactor with a column being connected to a gas space of the tank reactor. For supplying the required reaction heat and the heat for evaporating the decomposition product, the tank reactor comprises heating means, for example a double jacket or heating coils attached to the wall of the tank reactor, through which a heating medium flows. Alternatively, heating means are used which are placed inside the reactor.

[0010] Due to the small heat exchange surface based on the amount of liquid in the tank reactor, the evaporation capacity is low, which results in long dwell time of generally several hours and / or high wall temperature. The high wall temperature and the long dwell time have the disadvantage that the formation of high boilers, particularly polymers, is promoted. These polymers may form layers on the inner walls of the tank reactor, resulting in a poorer performance and further the high boilers are undesired by-products that have to be removed and, generally, deposited.

[0011] Therefore, it is an object of the present invention to provide an apparatus and a process for working up a mixture containing easily polymerizable components and decomposable components, in which the decomposition reaction230162W001

[0012] 2

[0013] can be carried out with shorter dwell time and / or lower wall temperature and in which the formation of high boilers and fouling at the surfaces can be minimized or even avoided.

[0014] This object is achieved with an apparatus for working up a mixture containing easily polymerizable components and decomposable components for recovery of reactants and desired reaction product by reaction and rectification, the apparatus comprising a tank reactor and a heat exchanger being connected to the bottom of the tank reactor by a recirculation line so that liquid phase can be withdrawn from the tank reactor, flow through the heat exchanger and be returned into the tank reactor, wherein a feed line for a reactant opens into the recirculation line upstream the heat exchanger and the heat exchanger is part of a forced circulation flash evaporator.

[0015] The object further is achieved by a process for working up a mixture containing easily polymerizable components and decomposable components for recovery of reactants and desired reaction product by reaction and rectification in such an apparatus, comprising:

[0016] (a) feeding the mixture into the tank reactor, in which the decomposable components are decomposed into decomposition products, wherein a liquid phase and a gas phase containing decomposition products are obtained;

[0017] (c) withdrawing a top stream containing decomposition products from a gas space of the tank reactor;

[0018] wherein liquid phase is withdrawn from the tank reactor, heated in the heat exchanger and returned into the tank reactor, wherein the liquid phase at least partly evaporates by flash evaporation and wherein the average flow velocity of the liquid phase is larger than 1 m / s in a heat exchange section of the heat exchanger.

[0019] "Working up” in the context of the present invention means that side products formed in the reactor, i.e. the decomposable components, are decomposed back into the reactants and the desired reaction product using heat, time and catalyst, for example sulfuric acid. The reactants and the desired reaction product are recovered from the waste stream by suitable methods, usually by rectification, and the reactants may be recycled into step (a).

[0020] By using the heat exchanger and withdrawing liquid phase from the reactor, pass it through the heat exchanger, heat it in the heat exchanger and return it into the tank reactor, it is possible to use a larger heat transfer surface based on the amount of liquid in the tank reactor and, thus, reduce the necessary dwell time and / or the wall temperature for evaporating and separating off the low boilers, particularly the decomposition product. Further, since the liquid phase flows through the heat exchanger, the contact time of the liquid phase with heated walls can be reduced and thus the formation of fouling also can be reduced. A further reduction of the formation of fouling can be achieved by setting the flow rate and the flow velocity of the liquid phase in the heat exchanger.230162W001

[0021] 3

[0022] By setting the flow rate such that the flow velocity in the heat exchange section of the heat exchanger is larger than 1 m / s, more preferred in a range of 1 to 5 m / s, more preferred in a range from 1 to 3 m / s and particularly in a range from 1.5 to 2.5 m / s, fouling on the heat exchange surfaces of the heat exchanger can be avoided.

[0023] The heat exchanger is part of a forced circulation flash evaporator and may be any heat exchanger, in which the liquid phase passing the heat exchanger can be heated, and which is known to a skilled person. Suitable heat exchangers for example are shell-and-tube heat exchangers, plate heat exchangers or spiral heat exchangers.

[0024] The heat exchange section means that part of the heat exchanger, in which heat is transferred from a heating medium to the liquid phase. If the heat exchanger is a shell-and-tube heat exchanger, the heat transfer section is the section in which the tubes are arranged, so that the velocity in the heat exchange section means the velocity in the tubes of the heat exchanger, if the liquid phase flows through the tubes, or, when the heating medium flows through the tubes, the velocity of the liquid phase in the space surrounding the tubes. Accordingly, if the heat exchanger is a plate heat exchanger, the flow velocity in the heat exchange section is the velocity in the space between the plates and in a spiral heat exchanger, the flow velocity in the heat exchange section is the velocity in the spiral.

[0025] If the forced circulation flash evaporator comprises a heat exchanger and a flash apparatus, the liquid phase is heated in the heat exchanger to a temperature below boiling temperature and subsequently fed into the flash apparatus. The pressure in the flash apparatus is below the pressure in the heat exchanger, so that the heated liquid phase expands and due to expansion, a part of the liquid phase evaporates. Subsequently, the liquid phase and the gas phase formed in the flash apparatus are returned into the tank reactor. Alternatively and preferably, the flash evaporator comprises only a heat exchanger. In this case, the liquid phase is heated in the heat exchanger to a temperature below the boiling point so that the liquid phase does not start to evaporate. The heated liquid phase then is returned into the tank reactor in which the pressure is below the pressure in the heat exchanger. Due to expansion when entering the tank reactor, at least a part of the liquid phase evaporates.

[0026] The part of the liquid phase that evaporates by flash evaporation preferably is in a range from 2 to 15 wt.-%, more preferred in a range from 3 to 10 wt.-%, and particularly in a range from 4 to 8 wt.-%.

[0027] For heating the liquid phase in the heat exchanger and subsequently expand the liquid phase for partial evaporation, the liquid phase is compressed before being fed into the heat exchanger. For compression, any suitable pump known to a skilled person can be used. In this case, the pump not only promotes the forced circulation but simultaneously compresses the liquid phase.

[0028] Using the heat exchanger has the additional advantage that the liquid phase in the tank reactor is mixed by the fluid flow and precipitation of components is avoided and that it is possible to omit an additional stirrer in the tank reactor. However, to assist mixing in the tank reactor, the tank reactor may comprise a stirrer.230162W001

[0029] 4

[0030] The stirrer may be of any type known to a skilled person. Preferably, the stirrer comprises stirrer blades scraping along the inner walls of the tank reactor. By scraping along the inner walls of the tank reactor, deposits that may form on the inner walls is removed and mixed into the liquid phase.

[0031] Since a part of the contents in the tank reactor remain in the liquid phase, it is necessary to remove the liquid phase. For removal of the liquid phase, a withdrawal line is provided. Particularly if the tank reactor is operated in a semi-continuous mode, i.e. fresh material is fed into the tank reactor during operation, it is necessary to remove a part of the contents during operation. For this purpose, it is preferred that the withdrawal line branches off the recirculation line. The withdrawal line may branch off at any position of the recirculation line. However, it is preferred that the withdrawal line branches off upstream the heat exchanger.

[0032] By arranging the withdrawal line such that it branches off the recirculation line upstream the heat exchanger, the amount of the liquid phase withdrawn from the process does not flow through the heat exchanger and is not heated. Further, to reduce equipment, it may be further preferred that the withdrawal line branches off the recirculation line between the pump and the heat exchanger. By such an arrangement, no additional pump is required for withdrawing the part of the liquid phase. Particularly, if a forced circulation flash evaporator is used and the pressure is increased in the pump, the increased pressure is sufficient for inducing a flow to the part of the liquid phase withdrawn from the process, so that the part of the liquid phase withdrawn from the process will flow by pressure difference between the pressure induced by the pump and the pressure at a target destination, for example a collecting tank, which usually has ambient pressure.

[0033] Depending on the process carried out in the apparatus, it may be necessary to add additional components into the tank reactor. For this purpose, a feed line for a reactant is provided. According to the invention, the feed line for the reactant opens into the recirculation line upstream the heat exchanger. If the withdrawal line branches off the recirculation line upstream the heat exchanger, it is further preferred that the feed line for the reactant opens into the recirculation line between the withdrawal line and the heat exchanger. By this arrangement it is ensured that no reactant is withdrawn with the part of the liquid phase withdrawn from the process. It is a further advantage of feeding the additional components upstream the heat exchanger, that non-reacted components comprised in the liquid phase may react in the heat exchanger, thereby forming product, so that the formation of by-products can be reduced and the yield of product can be increased.

[0034] The apparatus may be used in any process in which a mixture containing easily polymerizable components and decomposable components is obtained. In this context, "easily polymerizable components” means components that start to polymerize at process conditions without adding additional reactants and / or catalysts and without supplying additional energy.

[0035] "Decomposable components” are any components that can be decomposed into the desired reaction product and / or into reactants used in the initial reaction for producing the desired reaction product.230162W001

[0036] 5

[0037] In the tank reactor, the decomposable components are decomposed into decomposition products. For separating the decomposition products from the mixture containing the easily polymerizable components and the decomposable components, low boilers including the decomposition products evaporate and form the gas phase.

[0038] Preferably, the gas phase rises and enters the column that is connected to a gas space of the tank reactor. In one embodiment, the column is a demister. In this case, to avoid or at least reduce the formation of polymers, reflow is necessary to keep the internals in the column wet. Additionally, it is preferred that the liquid phase that is recycled into the column contains stabilizer to avoid the formation of polymers. In an alternative embodiment, the column is a rectification column. In the rectification column, the temperature decreases from bottom to top and such the gaseous components start to condense depending on their boiling temperature. The design of the rectification column may be any design common for rectification columns.

[0039] The column contains internals, for example trays and / or packings. If the column contains packings, the packings may be structured packings or a packed bed. The packing material may be for example saddles, rings, like Raschig®-rings, Pal l®-rings. If trays are used as internals, the trays may be for example dual flow trays, sieve trays, bubble trays, valve trays, or tunnel trays. Particularly preferably, the internals used in the column are dual flow trays or packed beds comprising rings. Using dual flow trays or rings allows for an easy cleaning to remove blockings which may be caused by polymerization.

[0040] At the top of the column, a gaseous top stream containing decomposition products is withdrawn.

[0041] If the column is a rectification column, at least a part of the top stream containing decomposition products is passed through a condenser and returned into the rectification column for setting the temperature at the top of the rectification column. In the condenser, the top stream is cooled and at least a part of the components contained in the top stream condenses, so that a liquid stream or a two phase stream, containing a liquid portion and a gaseous portion is returned into the rectification column.

[0042] If the column is a demister, which is preferred, a part of the top stream containing decomposition products is passed through a condenser and returned into the column for keeping the internals wet. This is necessary to reduce the formation of fouling on the internals. Besides condensing a part of the top stream, it is also possible to feed a liquid stream from the process onto the internals of the demister for keeping them wet. Independently of condensing and returning a part of the top stream or feeding a liquid stream from the process onto the internals of the demister, it is preferred to add a stabilizer to further reduce fouling and to avoid undesired polymerization.

[0043] For obtaining the decomposition products as product, the part of the top stream not being returned into the column is removed. If the top stream contains several components, the top stream removed from the column can be worked-up further, for example by distillation or other separation processes. Alternatively and preferred, the decomposition230162W001

[0044] 6

[0045] products may be recycled into the tank reactor to form the easily polymerizable components as product or may be recycled into a separation apparatus in which product is separated from reactants or into the esterification section of the process.

[0046] If the column is a rectification column and trays are used as internals, it is further possible to remove medium boiling components via side outlets from the rectification column. This allows for obtaining several product stream, each containing different components. Depending on the purity of the product streams, further purification may be carried out.

[0047] The mixture containing easily polymerizable components and decomposable components may be for example a bottom stream obtained by working up a crude product stream of an esterification reaction. Preferably, the esterification reaction is an esterification reaction of (meth)acrylic acid and an alkanol, thereby obtaining a (meth)acrylate.

[0048] For producing the (meth)acrylate, (meth)acrylic acid and an alkanol react in the presence of a catalyst. The main side reactions are the formation of oxyesters, diacrylic esters and diacrylic acid. Unreacted starting compounds and the (meth)acrylate to be formed are separated by distillation and an oxyester containing bottom product is formed. This bottom product is the mixture containing the easily polymerizable components and decomposable components formed in the side reactions.

[0049] Suitable processes for producing (meth)acrylate are described for example in DE-A 19536 191, DE-A 19547459, DE-A 19547485, and DE-A 19851 984.

[0050] The alkanol may be any suitable alkanol, generally, the alkanol is a Ci to Ci2-alkanol, preferably a C3- to Cs-alkanol and particularly n-butanol.

[0051] Depending on the alkanol, the (meth)acrylate may be for example butyl acrylate, 2-ethylhexyl acrylate, methyl acrylate, ethyl acrylate, tert-butyl acrylate or 2-octyl acrylate. Particularly, the (meth)acrylate is butyl acrylate.

[0052] The reaction generally is carried out in the presence of an acid as catalyst. For this purpose, it is preferred to feed additionally an acid into the tank reactor. The acid preferably is fed into the mixture containing easily polymerizable components and decomposable components before entering the tank reactor.

[0053] The acid preferably is selected from the group consisting of mineral acids like sulfuric acid or phosphoric acid, and organic acids like alkyl sulfonic acids, aryl sulfonic acids, for example methanesulfonic acid or p-toluene sulfonic acid. Preferably, the acid is a sulfonic acid, more preferred an alkyl sulfonic acid and particularly methanesulfonic acid, p-toluenesulfonic acid or dodecylbenzene sulfonic acid or a mixture thereof.

[0054] For reducing the formation of undesired by-products, particularly ethers, like n-dibutyl ether in a process for producing butyl acrylate, it is preferred to feed (meth)acrylic acid into the tank reactor. The theoretical ratio of alkanol to230162W001

[0055] 7

[0056] (meth)acry lie acid obtainable by decomposition of the decomposable components of the mixture containing easily polymerizable components and decomposable components, preferably is in a range from 0.3 to 12, more preferred in a range from 1.5 to 5. If the acrylate is butyl acrylate, the theoretical ratio of alkanol to (meth)acrylic acid preferably is in a range from 0.3 to 5, particularly in a range from 1.5 to 5. If the theoretical ratio of alkanol to (meth)acrylic acid exceeds 1, it is preferred to add (meth)acrylic acid. The (meth)acrylic acid preferably is fed into the recirculation line upstream the heat exchanger. Feeding the (meth)acrylic acid upstream the heat exchanger has the advantage that the (meth)acrylic acid is heated to the desired temperature before being fed into the tank reactor. This has the additional advantage that the content in the tank reactor is not cooled by the additional (meth)acrylic acid.

[0057] To withdraw a part of the liquid phase from the tank reactor, a withdrawal line is connected to the bottom of the tank reactor. Preferably, the withdrawal line is connected to the recirculation line upstream the point for feeding the (meth)acrylic acid. By connecting the withdrawal line to the recirculation line, only one line is connected to the bottom of the tank reactor. Further, by connecting the withdrawal line upstream the point for feeding the (meth)acrylic acid, it is avoided, that some of the freshly added (meth)acrylic acid is withdrawn with the liquid phase.

[0058] Embodiments of the invention are shown in the figures and explained in more detail in the following description.

[0059] In the figures:

[0060] Figure 1 shows an apparatus for working up a mixture containing easily polymerizable components and decomposable components according to the state of the art,

[0061] Figure 2 shows an apparatus for working up a mixture containing easily polymerizable components and decomposable components according to the invention,

[0062] An apparatus for working up a mixture containing easily polymerizable components and decomposable components according to the state of the art is shown in figure 1.

[0063] An apparatus 1 for working up a mixture containing easily polymerizable components and decomposable components according to the state of the art comprises a tank reactor 3 and a column 5 being connected to a gas space 7 of the tank reactor 3. The column 5 usually is a demister. For heating the contents in the tank reactor 3, the tank reactor 3 comprises a double jacket 9 or heating coils attached to the outer wall of the tank reactor 3. The double jacket 9 comprises an inlet 11 and an outlet 13 for a heat transfer medium. The heat transfer medium may be any suitable heat transfer medium for heating the contents in the tank reactor 3. Preferably, the heat transfer medium is steam.

[0064] The mixture containing easily polymerizable components and decomposable components to be worked up in the apparatus 1 is fed into the tank reactor 3 via a first feed line 15. Additional components, for example a catalyst or further reactants may be fed into the tank reactor via a second feed line 17 and a third feed line 19. The second feed line 17230162W001

[0065] 8

[0066] and the third feed line 19 may enter directly into the tank reactor 3 or, preferably, as shown here, into the first feed line 15, so that the different components fed into the tank reactor 3 via the first, second and third feed lines 15, 17, 19 are mixed before entering the tank reactor 3.

[0067] Besides arranging the feed lines 15, 17, 19 as shown in figure 1, it is also possible to arrange the feed lines 15, 17, 19 such that all feed lines directly enter into the tank reactor 3. Further, it is for example possible that two feed lines open separately into the tank reactor and at least one feed line opens into one of the feed lines that open into the reactor for premixing two components before being fed into the tank reactor 3.

[0068] The tank reactor 3 contains the gas space 7 and a liquid phase 21. The liquid phase preferably is stirred by using a stirrer 23. The stirrer 23 particularly comprises blades that scrape along the inner wall of the tank reactor 3 to avoid formation of deposits and to remove deposits that may have formed.

[0069] The liquid phase 21 contained in the tank reactor 3 may be removed via a withdrawal line 25, which is connected to the bottom of the tank reactor 3. Connecting the withdrawal line 25 to the bottom of the tank reactor 3 has the advantage that the complete liquid phase easily can be withdrawn from the tank reactor 3, if necessary.

[0070] The gas phase formed in the tank reactor 3 enters the column 5. The column 5 may be a rectification column in which the gas phase is separated into higher boiling components and lower boiling components. This is achieved by setting the temperature such that it decreases from bottom to top of the column 5. However, usually, the column 5 is a demister for separating off liquid components from the top stream, for example aerosols or droplets that are entrained with the gas stream.

[0071] The lower temperature at the top of the rectification column may be achieved by removing gas phase at the top of the rectification column via a gas withdrawal line 27 and feeding a condensed return flow via a recirculation line 29 at the top of the rectification column 5. If the column is a demister, the recirculation line 29 is used to feed liquid that preferably contains stabilizer into the column 5 for keeping internals wet and thereby minimizing the formation of polymer.

[0072] For returning liquid into the column 5, independently of whether the column is used as a demister or a rectification column, at least a part of the gas phase withdrawn via the gas withdrawal line 27 is condensed in a suitable condenser and recycled into the column 5 via the recirculation line 29. For this purpose, the recirculation line 29 branches off the gas withdrawal line 27 and the condenser is arranged in the recirculation line 29 or, if it is intended to condense the complete gas stream withdrawn from the rectification column 5 in the gas withdrawal line 27.

[0073] An apparatus for working up a mixture containing easily polymerizable components and decomposable components according to the invention is shown in figure 2.230162W001

[0074] 9

[0075] An inventive apparatus 101 for working up a mixture containing easily polymerizable components and decomposable components comprises a tank reactor 103 and a column 105 being connected to a gas space 107 of the tank reactor 103. In contrast to the apparatus 1 according to the state of the art, the tank reactor 103 according to the invention comprises a heat exchanger 109 for heating the liquid phase.

[0076] The heat exchanger 109 is connected to the tank reactor 103 by a recirculation line 111. The recirculation line 111 branches off at the bottom 113 of the tank reactor 103 and enters into the gas space 107 in the tank reactor 103 during normal operation.

[0077] For generating a liquid flow through the recirculation line 111, a pump 115 is provided. For evaporating at least a part of the liquid phase by flash evaporation, the pump 115 also is used for compressing the liquid phase.

[0078] For expanding the liquid phase for flash evaporation, an expanding device 117, for example a throttle is provided in the recirculation line 111. However, if the at least part of the liquid phase is to be evaporated by flash evaporation, it is preferred that the liquid phase heated in the heat exchanger 109 expands when entering the tank reactor 109. In this case, the expanding device 117 is placed at the entrance into the tank reactor 109.

[0079] The mixture containing easily polymerizable components and decomposable components to be worked up in the apparatus 101 is fed into the tank reactor 103 via a first feed line 119. Additional components, for example a catalyst or further reactants may be fed into the tank reactor via a second feed line 121. The second feed line 121 may enter directly into the tank reactor 103 or, preferably, as shown here, into the first feed line 119, so that the different components fed into the tank reactor 103 via the first feed line 119 and the second feed line 121 are mixed before entering the tank reactor 103.

[0080] Further components, particularly acrylic acid if the apparatus 101 is used for working up a crude reaction product of an esterification reaction of (meth)acrylic acid and an alkanol, may be fed into the tank reactor via a third feed line 123. The third feed 123 line enters into the recirculation line 111 upstream the heat exchanger 109.

[0081] The tank reactor 103 contains the gas space 107 and a liquid phase 125. The liquid phase 125 may be stirred by using a stirrer 127. If a stirrer is used, the stirrer 127 particularly comprises blades that scrape along the inner wall of the tank reactor 103 to avoid formation of deposits and to remove deposits that may have formed. However, as the liquid phase is mixed by recirculation through the recirculation line 111, an additional stirrer 127 is not necessary and, preferably, is omitted.

[0082] The liquid phase 125 contained in the tank reactor 103 may be removed via a withdrawal line 131, which is connected to the recirculation line 111. The withdrawal line preferably is arranged at a position upstream the third feed line 123 to avoid that components fed into the process via the third feed line 123 are removed through the withdrawal line 131.230162W001

[0083] 10

[0084] The gas phase formed in the tank reactor 103 enters the column 105. The column 105 may be a rectification column, in which the gas phase is separated into higher boiling components and lower boiling components. This is achieved by setting the temperature such that it decreases from bottom to top of the rectification column 105. However, preferably the column 105 is a demister.

[0085] The lower temperature at the top of the rectification column is achieved by removing gas phase at the top of the rectification column via a gas withdrawal line 133 and feeding a condensed return flow via a second recirculation line 135 at the top of the rectification column 105.

[0086] If the column 105 is a demister, it is preferred that a part of the top stream is condensed and recycled into the column 105 to keep internals contained in the column 105 wet for minimizing the polymer formation. For this purpose, it is further preferred, that stabilizer is added to the part of the top stream that is returned into the column 105.

[0087] Generally, at least a part of the gas phase withdrawn via the gas withdrawal line 133 is condensed in a suitable condenser and recycled into the column 105 via the second recirculation line 135. For this purpose, the second recirculation line 135 branches off the gas withdrawal line 133 and the condenser is arranged in the second recirculation line 135 or, if it is intended to condense the complete gas stream withdrawn from the rectification column 105, in the gas withdrawal line 133.

[0088] Besides arranging a column 105 on top of the tank reactor 103, it is also possible to provide a separate column that is connected by a connecting pipe with the gas space of the reactor. In this case, the connecting pipe preferably branches off at the top of the tank reactor 103 and enters at the bottom into the column 105. If a separate column 105 is used, it is particularly preferred to arrange the column above the tank reactor 103, so that the gas phase can flow upwards and the liquid phase can flow back into the reactor without using a conveying equipment, for example a pump for feeding the gas into the column and the liquid back into the tank reactor.230162W001

[0089] 11

[0090] Examples:

[0091] In all of the following streams, the remainder missing to 100 wt-% contains unspecified components.

[0092] Comparative Example

[0093] 1134 kg / h of a crude reaction stream obtained in a process for esterifying n-butyl acrylate, which contains 22 wt-% n-butyl acrylate, 68.5 wt-% butoxy ester, 8.6 wt-% diacrylic ester was fed through the first feed line 15 into the tank reactor 3 of the apparatus 1 according to figure 1.

[0094] Via the second feed line 17 131 kg / h acrylic acid and via the third feed line 1938 kg / h dodecylbenzene sulfonic acid were fed into the tank reactor 3.

[0095] In the tank reactor 3 high boilers were decomposed at a temperature of 166 °C and a pressure of 1 bar(abs). For setting the temperature in the tank reactor 3, steam was flowing through the double jacket 9 of the tank reactor 3.

[0096] The liquid stream withdrawn at the bottom of the tank reactor 3 was set such that an average dwell time of 48 h in the tank reactor was achieved. In the tank reactor, 537 kg / h butoxy ester were decomposed and 13 kg / h n-dibutyl ether were formed, which corresponds to a specific formation rate of 24 kg n-dibutyl ether per ton butoxyester.

[0097] At the bottom of the tank reactor 155 kg / h of the liquid phase were withdrawn. The liquid phase contained 0.4 wt-% n-butanol, 0.2 wt-% n-dibutyl ether, 16.4 wt-% n-butylacrylate, 1.4 wt-% acrylic acid, 56.4 wt-% butoxy ester, 6.6 wt-% diacrylic ester and 12.9 wt% dodecylbenzene sulfonic acid.

[0098] At the top of the rectification column 1236 kg / h of a gas stream were withdrawn. The gas stream had a temperature of 152 °C and contained 4.7 wt-% n-butanol, 1.1 wt-% n-dibutyl ether, 70.6 wt-% n-butyl acrylate, 5.8 wt-% acrylic acid, 12.9 wt-% butoxy ester and 0.9 wt-% dicarylic ester.

[0099] At a temperature of 25 °C, the liquid phase withdrawn at the bottom contained solid particles and still was good pumpable.

[0100] After a runtime of 500 h the formation of deposits on the inner walls of the tank reactor 3 could be observed.230162W001

[0101] 12

[0102] Example

[0103] 446 g / h of a crude reaction stream containing 53.2 wt-% n-butyl acrylate, 40 wt-% butoxy ester, and 4.6 wt-% diacrylic ester was fed through the first feed line 119 into the tank reactor 103 of the apparatus 101 according to figure 2.

[0104] Via the third feed line 12350 g / h acrylic acid and via the second feed line 121 4 g / h dodecylbenzene sulfonic acid were fed.

[0105] In the tank reactor 103 high boilers were decomposed at a temperature of 180 °C and a pressure of 0.9 bar(abs). For setting the temperature in the tank reactor 103, 300 kg / h of the liquid phase were recirculated through the heat exchanger 109 which is operated with steam for heating the liquid phase. Before entering the heat exchanger 109 the liquid phase is compressed to a pressure of 3.2 bar(g) and about 20 wt-% of the liquid phase evaporate by flash evaporation when the liquid phase is returned into the tank reactor 103.

[0106] 31 g / h of the liquid phase were withdrawn via withdrawal line 131. Thus, an average dwell time of 60 h in the tank reactor was achieved. In the tank reactor, 113 g / h butoxy ester were decomposed and 2.4 g / h n-dibutyl ether were formed, which corresponds to a specific formation rate of 21 g n-dibutyl ether per kg butoxyester.

[0107] The liquid phase withdrawn via withdrawal line 131 contained 0.4 wt-% n-butanol, 0.1 wt-% n-dibutyl ether, 30.7 wt-% n-butylacrylate, 3.6 wt-% acrylic acid, 46.7 wt-% butoxy ester, 5.1 wt-% diacrylic ester and 12.0 wt% dodecylbenzene sulfonic acid.

[0108] At the top of the rectification column 480 g / h of a gas stream were withdrawn. The gas stream had a temperature of 176 °C and contained 3.2 wt-% n-butanol, 0.51 wt-% n-dibutyl ether, 74.0 wt-% n-butyl acrylate, 7.4 wt-% acrylic acid, 10.9 wt-% butoxy ester and 0.7 wt-% dicarylic ester.

[0109] At a temperature of 25 °C, the liquid phase withdrawn at the bottom did not contain solid particles and was good pumpable.

[0110] After a runtime of 500 h no formation of solids on the inner walls of the tank reactor 3 could be observed.

[0111] Although the temperature and the dwell time in the reactor in the example which was carried out in a laboratory scale were higher, which usually would result in an increased formation of high boilers and an increased fouling compared to the conditions of the comparative example, it can be seen that by using the external heat exchanger formation of solids on the inner walls of the tank reactor could be avoided.

Claims

230162W00113Claims1. An apparatus for working up a mixture containing easily polymerizable components and decomposable components for recovery of reactants and desired reaction product by reaction and rectification, the apparatus (101) comprising a tank reactor (103) and a heat exchanger (109) being connected to the bottom (113) of the tank reactor (103) by a recirculation line (111) so that liquid phase can be withdrawn from the tank reactor (103), flow through the heat exchanger (109) and be returned into the tank reactor (103), wherein a feed line (123) for a reactant opens into the recirculation line (111) upstream the heat exchanger (109) and the heat exchanger (109) is part of a forced circulation flash evaporator.

2. The apparatus according to claim 1, wherein a column (105) is connected to a gas space (107) of the tank reactor (103), the column (105) preferably being a demister.

3. The apparatus according to claim 1 or 2, wherein a pump is arranged upstream the heat exchanger (109) and an expansion device is arranged downstream the heat exchanger (109), so that liquid phase being heated in the heat exchanger (109) evaporates at least partly after having passed the expansion device.

4. The apparatus according to any of claims 1 to 3, wherein the tank reactor (103) comprises a stirrer (127).

5. The apparatus according to any of claims 1 to 4, wherein a withdrawal line (131) branches off the recirculation line (111) upstream the heat exchanger (109), wherein the feed line (123) for a reactant preferably opens into the recirculation line (111) between the withdrawal line (131) and the heat exchanger (109).

6. A process for working up a mixture containing easily polymerizable components and decomposable components for recovery of reactants and desired reaction product by reaction and rectification in an apparatus according to any of claims 1 to 5, comprising:(a) feeding the mixture into the tank reactor (103), in which the decomposable components are decomposed into decomposition products, wherein a liquid phase and a gas phase containing decomposition products are obtained;(b) withdrawing a top stream containing decomposition products from a gas space of the tank reactor (103);wherein liquid phase is withdrawn from the tank reactor (103), heated in the heat exchanger (109) and returned into the tank reactor (103), wherein the liquid phase at least partly evaporates by flash evaporation and230162W00114wherein the average flow velocity of the liquid phase is larger than 1 m / s in a heat exchange section of the heat exchanger (109).

7. The process according to claim 6, wherein the top stream containing decomposition products passes a demister for removing liquid components.

8. The process according to claim 6 or 7, wherein the column (105) is a rectification column and at least a part of the top stream containing decomposition products is passed through a condenser and returned into the rectification column.

9. The process according to claim 6 to 8, wherein the mixture containing easily polymerizable components and decomposable components is a bottom stream obtained by working up a crude product stream of an esterification reaction.

10. The process according to claim 9, wherein the esterification reaction is a esterification reaction of (meth)acrylic acid and an alkanol, thereby obtaining a (meth)acrylate.

11. The process according to claim 10, wherein the (meth)acrylate is butyl acrylate, 2-ethylhexyl acrylate, methyl acrylate, ethyl acrylate, tert-butyl acrylate or 2-octyl acrylate.

12. The process according to claim 10 or 11, wherein additionally an acid is fed into the tank reactor (103).

13. The process according to claim 12, wherein the acid is sulfuric acid, p-toluenesulfonic acid, 4-dodecylbenzene sulfonic acid phosphoric acid or a sulfonic acid.

14. The process according to any of claims 10 to 13, wherein (meth)acrylic acid is fed into the recirculation line (111) upstream the heat exchanger (109).

15. The process according to any of claims 10 to 14, wherein a withdrawal line (131) is connected to the recirculation line (111) upstream the point for feeding the (meth)acrylic acid for withdrawing a part of the liquid phase.

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