Energy-efficient process for the distillation of ATBE-containing streams

Abstract

The invention relates to a process for the distillation of a stream containing at least n-butene, n-butane, isobutene, and an alkyl tert-butyl ether (ATBE) having a C1 to C5 alkyl group, in particular methyl tert-butyl ether (MTBE) or ethyl tert-butyl ether (ETBE), and an alcohol ROH where R = C1 to C5 alkyl, in particular methanol and ethanol, wherein the energy used for the distillation of the stream is made utilizable by means of heat integration.

Description

[0001] 202300139 Foreign Filing

[0002] 1

[0003] Energy-efficient process for the distillation of ATBE-containing streams

[0004] The present invention relates to a process for distilling a stream containing at least n-butene, n-butane, isobutene and an alkyl tert-butyl ether (ATBE) with a C1 to C5 alkyl, in particular methyl tert-butyl ether (MTBE) or ethyl tert-butyl ether (ETBE), and an alcohol ROH with R = C1 to C5 alkyl, in particular methanol and ethanol, wherein the energy used for distilling the stream is utilized by means of heat integration.

[0005] ATBE can be obtained from C4 hydrocarbon mixtures, for example, C4 sections from steamer assemblies or FCC units. Prior to the production of ATBE, particularly MTBE or ETBE, butadiene is separated from the C4 olefin mixtures, yielding a so-called raffinate I. In the petrochemical industry, ATBE synthesis, especially MTBE or ETBE synthesis, is primarily used to remove isobutene from the aforementioned C4 hydrocarbon mixtures. Isobutene is a branched olefin and can cause problems in subsequent reactions when linear products are desired.

[0006] In ATBE synthesis, isobutene is reacted with an alcohol ROH where R = C1- to C5-alkyl to form the corresponding alkyl tert-butyl ethers. If MTBE or ETBE are to be produced, the isobutene is reacted with methanol (to MTBE) or ethanol (to ETBE). Unlike isobutene, ATBE, especially MTBE and ETBE, can be separated relatively easily by distillation. After the removal of the isobutene, a so-called raffinate II remains, i.e., a C4 olefin mixture containing saturated hydrocarbons, linear butenes, and at most trace amounts of butadiene and isobutene.

[0007] Methods for producing ATBE, in particular MTBE or ETBE, are well known to those skilled in the art. One such known method was described, for example, in DE 102006 057 856 A1.

[0008] In order to achieve the highest possible isobutene conversion in the production of ATBE, especially MTBE or ETBE, the reaction of isobutene-containing C4 hydrocarbon mixtures can be carried out in several reaction stages, with the ATBE formed being separated after each reaction stage, and / or using a reactive distillation column.

[0009] The separation of ATBE is therefore mainly achieved by distillation or reactive distillation. Distillative separation processes have high energy requirements to ensure sufficient separation. The energy is mainly supplied via steam, which, due to the large steam volumes, incurs considerable costs and simultaneously generates high CO2 emissions. The task was therefore to develop a process for distilling an ATBE-containing feedstream, in particular MTBE or ETBE feedstream, in which the energy required for separation or...

[0010] The amount of steam required for distillation can be reduced, thereby saving costs and reducing CO2 emissions. 202300139 Foreign Filing

[0011] 2

[0012] The problem can be solved by the method according to claim 1 of the invention. Preferred embodiments are specified in the dependent claims.

[0013] The process according to the invention is a process for distilling a feed stream containing at least n-butene, n-butane, isobutene, an alkyl tert-butyl ether (ATBE) with a C1 to C5 alkyl group, and an alcohol ROH with R = C1 to C5 alkyl group, preferably methyl tert-butyl ether (MTBE) and methanol or ethyl tert-butyl ether (ETBE) and ethanol, in a reactive distillation column having at least one reaction zone and at least one distillation zone, wherein the distillation zone is arranged below the reaction zone and wherein the reaction zone contains an acidic catalyst, wherein the feed stream is passed via a preheater to the reaction distillation column and in the reaction distillation column is divided into an overhead stream containing at least n-butene, n-butane, the alcohol, in particular the methanol or the ethanol, and a maximum of 1000 ppm, preferably a maximum of 500 ppm, isobutene, and into a Swamp stream containing at least the ATBE;In the reaction zone of the reactive distillation column, at least a portion of the isobutene reacts with the alcohol ROH, in particular methanol or ethanol, over the acidic catalyst to form ATBE, in particular MTBE or ETBE; the bottom stream is taken off at a lower part of the reactive distillation column; the reactive distillation column has at least one bottom evaporator SV, which is fed with a stream taken off at the bottom of the reactive distillation column and, after passing through the bottom evaporator, is returned to the reactive distillation column; the overhead stream is at least partially used for heat integration, which comprises at least the following steps;

[0014] (a) At least partial condensation of at least a part of the overhead stream, the heat of condensation being used by transferring energy from at least a part of the overhead stream to a liquid or gaseous heat transfer medium W, thereby creating a heat transfer medium W1;

[0015] (b) Compressing at least a part of the heat transfer medium W1, preferably the entire heat transfer medium W1, thereby producing a compressed heat transfer medium W2 which has a higher pressure than the heat transfer medium W1, wherein the compression of the heat transfer medium W1 is carried out in multiple stages; and

[0016] (c) Transfer of energy from the compressed heat transfer fluid W2 to the current in the sump evaporator SV. 202300139 Foreign Filing

[0017] 3

[0018] An advantage of the process according to the invention is the heat integration via at least one heat transfer medium, from which energy in the bottom evaporator SV is transferred to the electricity present there, and thus energy is introduced into the bottom of the reactive distillation column. The energy transfer in the bottom evaporator SV means that less or even no heating steam is required to heat the reaction distillation column. This allows for (almost) complete power generation of the energy-intensive process, which in turn enables the use of green electricity. This results in significant savings in energy costs and CO2 emissions. In some cases, complete power generation of the process is even possible.

[0019] Provision of the feed stream

[0020] The feedstream used in the process according to the invention contains at least n-butene, n-butane, isobutene, an alkyl tert-butyl ether (ATBE) with a C1 to C5 alkyl group, and an alcohol ROH with R = C1 to C5 alkyl group. Preferably, the feedstream contains at least n-butene, n-butane, isobutene, methyl tert-butyl ether (MTBE), and methanol, or the feedstream contains at least n-butene, n-butane, isobutene, ethyl tert-butyl ether (ETBE), and ethanol.

[0021] The feed stream is therefore derived from a previous ABTE synthesis, preferably an MTBE or ETBE synthesis. In the corresponding synthesis, the C1 to C5 alcohol, preferably methanol or ethanol, and the C4 hydrocarbon mixture, comprising at least isobutene, n-butane, and 1-butene, are reacted in one or more reactors such that the isobutene and the alcohol react to form the corresponding ATBE, preferably MTBE or ETBE. The reactor(s) for the ATBE synthesis, in particular the MTBE or ETBE synthesis, can be conventional fixed-bed reactors (tube bundle reactors, adiabatic fixed-bed reactors, recirculating reactors, etc.), stirred tank reactors, or combinations of these reactor types.

[0022] The ATBE synthesis, in particular the MTBE or ETBE synthesis, is preferably carried out at temperatures in the range of 30 to 150 °C, more preferably from 40 to 110 °C. The pressure during the ATBE synthesis, in particular the MTBE or ETBE synthesis, is preferably 5 to 30 bar (absolute bar), more preferably 7 to 22 bar, and most preferably 8 to 13 bar. The molar ratio of alcohol to isobutene used in the ATBE synthesis, in particular the MTBE or ETBE synthesis, is preferably 3:1 to 0.9:1, more preferably 2:1 to 1:1, and most preferably 1.2:1 to 1:1. The ratio can be adjusted by adding a corresponding amount of alcohol to the first or each of the reactors.

[0023] In a preferred embodiment, the ATBE synthesis, in particular the MTBE or ETBE synthesis, is carried out in at least two reactors, wherein the first reactor is designed as an adiabatic fixed-bed reactor with recirculation (circulating reactor) and the second and each optionally subsequent reactor are designed as fixed-bed reactors without recirculation. The ratio of recirculated quantity to fresh feed (referring to the quantities of C4 hydrocarbon mixture and alcohol, respectively) 202300139 Foreign Filing

[0024] 4 is preferably located in the recirculating reactor at 0.5 to 15 t / t, particularly preferably at 1 to 5 t / t and most preferably at 2 to 3 t / t.

[0025] ATBE synthesis, and in particular MTBE or ETBE synthesis, is preferably carried out in the presence of a solid catalyst. The catalyst used in the process according to the invention preferably has acidic centers on its surface.

[0026] For the synthesis of ATBE, and in particular MTBE or ETBE, solid catalysts such as zeolites, acid-activated bentonites and / or aluminas, sulfonated zirconium oxides, montmorillonites, or acidic ion exchange resins can be used. Acidic ion exchange resins are particularly preferred as acidic catalysts.

[0027] A preferred group of acidic catalysts are solid ion exchange resins, particularly those containing sulfonic acid groups. Suitable ion exchange resins can be, for example, those produced by the sulfonation of phenol / aldehyde condensates or of cooligomers of aromatic vinyl compounds. Examples of aromatic vinyl compounds used to prepare the cooligomers include styrene, vinyltoluene, vinylnaphthalene, vinylethylbenzene, methylstyrene, vinylchlorobenzene, vinylxylene, and divinylbenzene. In particular, the cooligomers formed by reacting styrene with divinylbenzene are used as precursors for the preparation of ion exchange resins containing sulfonic acid groups. The resins can be produced in gel, macroporous, or sponge form.

[0028] Dielon exchange resins are preferably used in their H-form, with the option of exchanging some of the H-ions for other cations, particularly metal cations. Strongly acidic resins of the styrene-divinylbenzene type are sold under, among others, the following trade names: Duolite C20, Duolite C26, Amberlyst 15, Amberlyst 35, Amberlite IR-120, Amberlite 200, Dowex 50, Lewatit SPC 118, Lewatit SPC 108, K2611, K2621, OC 1501.

[0029] The reaction mixture obtained from the ATBE synthesis, in particular the MTBE or ETBE synthesis, is then fed to the reactive distillation column and thus to the process according to the invention.

[0030] Reactive distillation

[0031] The reaction mixture from the ATBE synthesis, in particular the MTBE or ETBE synthesis, is further processed in a reactive distillation. There, the feed stream is divided into an overhead stream containing at least n-butene, n-butane, the alcohol, in particular methanol or ethanol, and a maximum of 1000 ppm, preferably a maximum of 500 ppm, isobutene, and into a bottom stream containing at least the ATBE; 202300139 Foreign Filing

[0032] 5

[0033] Reactive distillation is carried out in a reactive distillation column, which has at least one reaction zone and at least one distillation zone. The reaction zone contains an acidic catalyst, which is why both the reaction of isobutene with the alcohol ROH, in particular methanol or ethanol, and distillation take place in the reaction zone.

[0034] The same catalysts can be used in the reaction zone of the reactive distillation column as disclosed in the previous section for ATBE synthesis, in particular MTBE or ETBE synthesis. These include zeolites, acid-activated bentonites and / or aluminas, sulfonated zirconium oxides, montmorillonites, or acidic ion exchange resins. Acidic ion exchange resins are particularly preferred as acidic catalysts. In the reactive distillation column, the catalyst can either be integrated into a packing, for example KataMax® or KataPak®, or polymerized onto shaped bodies.

[0035] The reactive distillation column used can have one or more reaction zones, with a distillation zone preferably located above the uppermost and another below the lowermost reaction zone. Particularly preferably, the reactive distillation column has one reaction zone with a pure distillation zone located above and below it.

[0036] The reaction zone preferably has a separation efficiency of 5 to 130, preferably 20 to 60 theoretical separation stages. Structured or unstructured packings, in which the acidic catalyst is integrated, are preferably used as separation stages. Unstructured packings are generally packed beds. Common packing materials include Raschig rings, Pall rings, Berl saddles, SuperRings / SuperRings Plus, or Intalox® saddles. Structured packings are marketed, for example, under the trade name Mellapak® by Sulzer.

[0037] The distillation zone located below the lowest reaction zone preferably has a separation efficiency of 10 to 40, more preferably 15 to 35, and most preferably 15 to 25 theoretical separation stages. If a distillation zone is present above the uppermost reaction zone, it preferably has 2 to 20, more preferably 5 to 15, and most preferably 5 to 10 theoretical separation stages. Trays are particularly suitable as separation stages for the distillation zone. Bubble-cap trays, sieve trays, valve trays with fixed or movable valves, tunnel trays, or slotted trays are commonly used.

[0038] The feed stream to the reactive distillation column preferably enters the distillation zone located below the lowest reaction zone. Particularly preferably, the feed is introduced 5 to 20 theoretical separation stages below the reaction zone. The temperature of the feed stream is controlled by the preheater and is preferably in the range of 40 °C to 90 °C, and particularly preferably between 50 °C and 85 °C.

[0039] The reaction of isobutene with alcohol to form ATBE, in particular MTBE or ETBE, takes place in the reaction zone of the reactive distillation column, depending on the pressure, preferably in the 202300139 Foreign Filing

[0040] 6

[0041] The temperature range is from 40 °C to 120 °C, preferably from 60 °C to 90 °C, and particularly preferably from 65 °C to 85 °C. The temperature in the bottom of the reactive distillation column is preferably significantly higher than in the reaction zone; more preferably, the temperature in the bottom of the reactive distillation column is in the range of 100 °C to 160 °C, and particularly preferably in the range of 120 °C to 145 °C. The pressure in the reactive distillation column, measured at the top of the column, is preferably from 3 to 13 bar (absolute bar), more preferably from 5 to 11 bar, and particularly preferably from 6 to 10 bar.

[0042] In the process according to the invention, it can be advantageous if the reactive distillation column is operated with a reflux ratio of less than 1.5, preferably in the range of 0.2 to 1.2, more preferably in the range of 0.25 and 1.1 and particularly preferably in the range of 0.5 to 1.

[0043] The bottoms product is drawn off as a bottoms stream from a lower section of the reactive distillation column. The bottoms product of the reactive distillation is a mixture containing preferably at least 90 wt% and particularly preferably at least 95 wt% ATBE, especially MTBE or ETBE. It also contains a portion of the excess alcohol, especially methanol or ethanol. This mixture can be used as a component for gasoline. If desired, this mixture can be further processed to ATBE, especially MTBE or ETBE, with a higher purity.

[0044] In a preferred embodiment of the present invention, the bottom stream from the reactive distillation column is used to heat the feed stream in the preheater, whereby energy in the form of heat is transferred from the bottom stream to the feed stream. In this case, known heat exchangers can be used as preheaters, enabling the desired energy transfer from the bottom stream to the feed stream.

[0045] The reactive distillation column is heated via the bottom evaporator (SV). The energy required for distillation and / or reaction is supplied to the reactive distillation column via this evaporator. The bottom evaporator (SV) is fed with a current drawn from the bottom of the reactive distillation column. After passing through the bottom evaporator and being heated there, the current is returned to the reactive distillation column. Suitable evaporators that can be used as bottom evaporators (SV) include natural circulation evaporators, forced circulation evaporators, forced circulation evaporators with expansion, boiler evaporators, falling film evaporators, and thin-film evaporators. A tube bundle or plate heat exchanger is typically used as the heat exchanger for the evaporator in both natural and forced circulation evaporators.In addition to those mentioned, any other type of evaporator known to experts and suitable for use on a distillation column can also be used.

[0046] In a preferred embodiment, the sump evaporator SV comprises structured

[0047] Heat exchanger tubes with at least one structured area. Structured heat exchanger tubes 202300139 Foreign Filing

[0048] 7 within the scope of the present invention are to be understood as tubes comprising at least one structured area. A structured area is characterized by a repeating pattern. Examples of this are ribs or channels. Corresponding tubes are known to those skilled in the art, for example, from EP 1 312 885 A2, EP 1 830 151 A1, WO 2017 / 207091 A1 or WO 2022 / 106045 A1.

[0049] The structured heat exchanger tubes preferably have more than one, i.e., several, structured areas. If several structured areas are present, it is preferred that the structured heat exchanger tubes have the structured areas on the inside and / or outside of the tube. Preferably, at least one structured area is present on both the inside and the outside of the tube. In a particularly preferred embodiment of the present invention, the structured areas comprise continuously or discontinuously extending axially parallel or helically circumferential ribs.

[0050] The use of structured heat exchanger tubes has the advantage of saving additional compressor power and thus electrical energy (electricity costs). The structured sections improve heat exchange between the media in the sump evaporators.

[0051] It is understood that the two aspects of the present invention can be present both individually and in combination, i.e., the claimed logarithmic temperature difference and / or the use of structured heat exchanger tubes.

[0052] The overhead product of the reactive distillation column is an alcoholic distillate, particularly one containing ethanol, which contains at least n-butene, n-butane, and a maximum of 1000 ppm, preferably a maximum of 500 ppm, isobutene. The alcohol, especially methanol or ethanol, can be separated from the overhead product, for example, by an extraction step, particularly by extraction with water. Traces of butadiene can be removed from the product thus obtained, which is often also referred to as Raffinate II, by selective hydrogenation (SHP). Raffinate II can then be subjected to a further process step, for example, 1-butene separation or butene oligomerization.

[0053] Before the overhead stream is removed from the process, at least part of it is used for heat integration. The remaining portion can also be used for heat integration by applying the energy at another point in a reaction sequence, for example, the distillation of C4 streams. The heat integration according to the present invention comprises at least the following steps:

[0054] Step (a)

[0055] In step (a) at least a part of the head current is at least partially condensed, whereby the

[0056] Condensation heat is utilized by transferring energy from at least part of the headstream to 202300139 Foreign Filing

[0057] 8 a liquid or gaseous heat transfer medium W is transferred, resulting in a heat transfer medium W1.

[0058] Any working medium familiar to those skilled in the art can be used as the heat transfer medium W. The heat transfer medium W is preferably selected from the group consisting of water; alcohols; alcohol-water mixtures; salt-water solutions; ammonia; mineral oils, such as diesel oils; thermal oils, such as silicone oils; biological oils, such as limonene; and aromatic or aliphatic hydrocarbons, such as dibenzyltoluene. Water, methanol, ethanol, propanol, n-pentane, n-butane, n-hexane, n-propane, or ammonia are further preferred, with n-pentane and / or water being particularly preferred.

[0059] If the heat transfer medium W is used in step (a) in its liquid phase, i.e., as a liquid heat transfer medium W, and energy, preferably heat, is supplied to it in step (a), the heat transfer medium W is at least partially vaporized, resulting in a gaseous heat transfer medium W1. If the heat transfer medium W is used in step (a) in its gaseous phase, i.e., as a gaseous heat transfer medium W, and energy, preferably heat, is supplied to it in step (a), a gaseous heat transfer medium W1 is also obtained.

[0060] In the context of the present invention, the term "liquid heat transfer medium" means that > ​​50 wt.%, more preferably > 55 wt.%, more preferably > 75 wt.%, more preferably > 90 wt.% and particularly preferably > 99 wt.% of the heat transfer medium used in step (a) is in the liquid state, in each case based on the total weight of the heat transfer medium used in step (a).

[0061] In the context of the present invention, the term "gaseous heat transfer medium" means that > ​​30 wt.%, more preferably > 50 wt.%, more preferably > 75 wt.%, more preferably > 90 wt.% and particularly preferably > 99 wt.% of the heat transfer medium used in step (a) is in the gaseous state, in each case based on the total weight of the heat transfer medium used in step (a).

[0062] The energy transfer in step (a) can be carried out using methods or heat exchangers known to those skilled in the art, such as evaporators. Suitable evaporators that can be used as bottom evaporators include, for example, natural circulation evaporators, forced circulation evaporators, forced circulation evaporators with expansion, boiler evaporators, falling film evaporators, or thin-film evaporators. A tube bundle or plate heat exchanger is typically used as the heat exchanger for the evaporator in natural circulation and forced circulation evaporators. However, in addition to those mentioned, any other evaporator design known to those skilled in the art that is suitable for use on a distillation column can also be used.

[0063] In this case, the heat exchanger can also serve as the condenser for condensing BS1a. This has the advantage that no additional condenser needs to be installed. 202300139 Foreign Filing

[0064] 9

[0065] Following the energy transfer described in step (a), the heat transfer medium W1 preferably has a higher temperature and / or a higher pressure than the heat transfer medium W. In a preferred embodiment of the present invention, W1 has a temperature in the range of 30 °C to 85 °C. The pressure of W1 is preferably in the range of 1 bar to 20 bar, more preferably 3 bar to 12 bar.

[0066] It goes without saying that the heat transfer medium W1 corresponds to the heat transfer medium W and that W and W1 differ only in their respective pressure and / or temperature and, if applicable, if W was used as a liquid, in their state of matter.

[0067] In a preferred embodiment of the present invention, the overhead stream of the reactive distillation column is separated prior to the heat integration according to the invention, and only a portion of the overhead stream is used for heat integration. The remaining portion of the overhead stream can be cooled by means of a condenser and at least partially condensed. The condensation energy generated in this process can be used elsewhere in the process or at the production site.

[0068] The two at least partially condensed partial streams of the overhead stream are, according to a preferred embodiment, directed to a flash container after their respective condensation and expanded there, resulting in a liquid phase FP1 of the two partial streams. The flash container can additionally include a condenser to condense a portion of the resulting gaseous phase. It is preferred that the two partial streams of the overhead stream are combined in the flash container and form a common liquid phase FP1.

[0069] At least a portion FP1a of the liquid phase FP1 is subsequently removed from the process as the overhead product. In a particularly preferred embodiment, a pump is used for this purpose. Pumps known to those skilled in the art can be used here. Suitable pumps include, for example, standard chemical pumps. It is further preferred that a portion FP1b of the liquid phase FP1, different from FP1a, is returned to the reactive distillation column as reflux.

[0070] Step (b)

[0071] In the subsequent step (b), at least a portion of the heat transfer fluid W1, preferably the entire heat transfer fluid W1, is compressed, resulting in a heat transfer fluid W2 that is more compressed than W1 and has a higher pressure than heat transfer fluid W1. After compression, the pressure of W2 is preferably in the range of 1 bar to 20 bar, more preferably 3 bar to 12 bar.

[0072] The compression of at least one part of the heat transfer medium W1 in step (b) can be carried out in any manner known to a person skilled in the art. For example, the compression can be carried out mechanically and in one or more stages. In this context, single-stage means that compression takes place from one pressure level to another. Multi-stage means that compression is first carried out to a 202300139 Foreign Filing

[0073] 10

[0074] The fluid is compressed from pressure level X to pressure level Y. In multi-stage compression, several compressors of the same design or compressors of different designs can be used. Multi-stage compression can be performed with one or more compressor units. The choice between single-stage and multi-stage compression depends on the compression ratio and thus on the desired pressure of the heat transfer fluid W1.

[0075] Any compressor known to those skilled in the art, preferably a mechanical compressor capable of compressing gas flows, is suitable as a compressor in the method according to the invention, particularly for compressing the heat transfer medium W1. Suitable compressors include, for example, single- or multi-stage geared turbo compressors, piston compressors, screw compressors, centrifugal compressors, or axial compressors.

[0076] The compression of the heat transfer fluid W1 takes place in multiple stages, i.e., in at least two stages. In a preferred embodiment of the present invention, the heat transfer fluid W1 is compressed in a single, preferably multi-stage, compressor. The number of stages required depends on the desired compression ratio.

[0077] Step (c)

[0078] In step (c) of the process according to the invention, energy is transferred from the compressed heat transfer medium W2 to the current in the sump evaporator SV. Step (c) reduces the energy of W2, so that W2 preferably condenses at least partially. According to the invention, the phrase "transfer of energy" means, in particular, heating, i.e., the transfer of energy in the form of heat.

[0079] The transfer of energy from W2 to the current in the sump evaporator SV, preferably the heating of the current in the sump evaporator SV by W2, preferably occurs directly. Direct transfer means that W2 and the current in SV do not come into direct contact, but that energy, in particular heat, is transferred from W2 to the current in SV without the presence of an additional heat transfer medium. Heat exchangers or heat transfer devices familiar to those skilled in the art, especially evaporators, can be used as the sump evaporator SV.

[0080] The energy transfer in step (c) can be carried out using methods or heat exchangers known to those skilled in the art. Suitable evaporators that can be used as heat exchangers include, for example, natural circulation evaporators, forced circulation evaporators, forced circulation evaporators with expansion, boiler evaporators, falling film evaporators, or thin-film evaporators. In addition to those mentioned, any other evaporator design known to those skilled in the art that is suitable for use on a distillation column can also be used. Preferably, the evaporator comprises structured heat exchanger tubes with at least one structured section. This has already been mentioned. 202300139 Foreign Filing

[0081] 11

[0082] The heat transfer medium is preferably circulated. This means that the heat transfer medium W2 is returned after energy transfer in step (c) and used again in step (a).

[0083] The heat integration achieved through the heat pump described here could also be combined with other heat integration measures. It would be possible to incorporate one or more vapor compression systems.

[0084] In a preferred embodiment of the present invention, the compression in step (b) is carried out in two stages. This means that the heat transfer medium W1 is compressed twice, with the first compression producing a compressed heat transfer medium W1.1, which has a higher pressure than W1, and the second compression producing the compressed heat transfer medium W2, which has a higher pressure than both W1.1 and W1. The twice-compressed heat transfer medium W2 is then used for energy transfer in step (c).

[0085] It has already been mentioned that the heat transfer medium W2 at least partially condenses during energy transfer in step (c). In the case of the two-stage compression in step (b), this makes it possible to utilize some of the energy present in the heat transfer medium W2 after the energy transfer in step (c). For this purpose, it is preferred if the at least partially condensed heat transfer medium W2 is fed into a flash vessel operated at the pressure level between the two compression stages. A gaseous phase and a liquid phase are formed in the flash vessel. The gaseous phase (flash fraction) in the flash vessel is fed between the two compression stages. The flash fraction is thus mixed with the compressed heat transfer medium W1, subjected to the second compression, and used for energy transfer in step (c).

[0086] The liquid portion from the flash container is fed to step (a) as heat transfer fluid W. It is further preferred if the liquid portion is used to preheat the heat transfer fluid W1 before compression, whereby energy is transferred from the liquid portion to the heat transfer fluid W1. This superheats the heat transfer fluid W1 and reduces the energy required for compression.

[0087] In a further preferred embodiment of the present invention, the reactive distillation column has a side evaporator STV, which is fed with a side stream ST taken from above the bottom of the reactive distillation column and returned to the reactive distillation column after passing through the side evaporator STV. The use of a side evaporator reduces the overall power requirement during compression in step (b).

[0088] The side stream ST, which feeds the side evaporator STV, is preferably taken from below the feed stream inlet, more preferably from 2 to 7 trays below the feed stream inlet, and particularly preferably from 2 to 4 trays below the feed stream inlet. The stream returned from the side evaporator to the reactive distillation column is preferably 202300139 Foreign Filing

[0089] 12 at least partially introduced into the reactive distillation column on the same floor or separation stage as the feed to the reactive distillation column.

[0090] The side evaporator is heated by the heat transfer fluid from the previously mentioned heat integration process. The compression in step (b) must also take place in at least two stages. Energy from a portion of the heat transfer fluid W1.1 is transferred to the side stream ST in the side evaporator STV, whereby at least a portion of the heat transfer fluid W1.1 condenses, at least partially, during the energy transfer.

[0091] The side evaporator STV may be a well-known type of evaporator. Suitable evaporators that can be used as heat exchangers include, for example, natural circulation evaporators, forced circulation evaporators, forced circulation evaporators with expansion, boiler evaporators, falling film evaporators, or thin-film evaporators.

[0092] In a preferred embodiment, the side evaporator STV comprises structured heat exchanger tubes with at least one structured region. Structured heat exchanger tubes within the scope of the present invention are to be understood as tubes comprising at least one structured region. A structured region is characterized by a repeating pattern. Examples include fins or channels. Such tubes are known to those skilled in the art, for example, from EP 1 312 885 A2, EP 1 830 151 A1, WO 2017 / 207091 A1, or WO 2022 / 106045 A1.

[0093] The structured heat exchanger tubes preferably have more than one, i.e., several, structured areas. If several structured areas are present, it is preferred that the structured heat exchanger tubes have the structured areas on the inside and / or outside of the tube. Preferably, at least one structured area is present on both the inside and the outside of the tube. In a particularly preferred embodiment of the present invention, the structured areas comprise continuously or discontinuously extending axially parallel or helically circumferential ribs.

[0094] The use of structured heat exchanger tubes has the advantage of saving additional compressor power and thus electrical energy (electricity costs). The structured sections improve heat exchange between the media in the sump evaporators.

[0095] It is understood that the two aspects of the present invention can be present both individually and in combination, i.e., the claimed logarithmic temperature difference and / or the use of structured heat exchanger tubes.

[0096] The side stream ST is preferably not completely evaporated in the side evaporator STV. The side evaporator is preferably not a total evaporator, but can serve as a further separation stage 202300139 Foreign Filing

[0097] 13. The side stream is considered to be outside the reactive distillation column. Therefore, a liquid phase and a gaseous phase of the side stream preferably accumulate in the side evaporator. The gaseous phase is preferably introduced into the reactive distillation column onto the same tray or separation stage as the feed to the reactive distillation column. The liquid phase of the side stream is introduced into the reactive distillation column onto one or more trays below the feed for the gaseous phase of the side stream.

[0098] The heat transfer fluid W1 will at least partially condense during heat transfer in the side evaporator. The heat transfer fluid can then be returned to step (a) as heat transfer fluid W1 to be used again as heat transfer fluid W1. When returning the at least partially condensed heat transfer fluid to step (a), preheating of the heat transfer fluid W1 before compression can also be provided to save compressor power due to the superheating of W1.

[0099] In this embodiment with side evaporator STV, the bottom evaporator SV of the reactive distillation column is also heated with the heat transfer fluid W2. After energy transfer in step (c), the at least partially condensed heat transfer fluid W2 is returned to step (a) and used there as heat transfer fluid W. It is further preferred if, after energy transfer in step (c), the heat transfer fluid W2 is used to preheat the heat transfer fluid W1.1 before the second compression, whereby energy is transferred from the heat transfer fluid W2 to the heat transfer fluid W1.1. An embodiment with a flash tank would also be possible, in which the gaseous phase is returned between the two compressor stages and the liquid phase is returned to step (a) as heat transfer fluid W.

[0100] In a further preferred embodiment, the two at least partially condensed streams of the heat transfer medium from the sump evaporator SV and the side evaporator STV are mixed together and then returned to step (a).

[0101] The present invention is explained below with reference to the illustrations. The illustrations serve for clarification purposes only and are not to be understood as limiting.

[0102] Fig. 1 shows an exemplary, non-inventive configuration of the reactive distillation column for MTBE synthesis. The feed stream (A) is preheated using the preheater (1) and fed into the reactive distillation column (2). The vapor is taken off as the overhead stream (3) and condensed in the heat exchanger (3) using, for example, cooling water. A portion of the overhead stream is returned to the reactive distillation column (2) as reflux via a distillate receiver (4) and a reflux pump (5). The remaining portion is discharged as a stream depleted of isobutene, i.e., raffinate II (C). The heat energy required for the separation process is supplied to the reactive distillation column (2) via the bottom evaporator (6), which is operated with purchased heating steam. The sump flow (B) undergoes heat integration via a pressure booster pump (7) to preheat the feed flow (A) in the preheater (1) and is then discharged. 202300139 Foreign Filing

[0103] 14

[0104] Fig. 2 shows an exemplary configuration of the reactive distillation column for MTBE synthesis according to the invention, based on the configuration described in Fig. 1. In this example, the heat of condensation is partially used to supply the heat energy required for the separation process to the column (2). In this embodiment, a portion of the overhead stream is condensed at the heat exchanger (8) to heat the heat transfer fluid W1. The heat transfer fluid W1 is then further heated in the preheater (9). Subsequently, the heat transfer fluid W1 is compressed to a higher pressure level by a multi-stage compression process (10⁻¹, 10⁻²), resulting in the compressed heat transfer fluid W2. The compressed heat transfer fluid W2 is used to heat the bottom evaporator (6). After energy transfer in the bottom evaporator (6), the heat transfer fluid is returned to the heat exchanger (8) and reused as heat transfer fluid W1.

[0105] Fig. 3 shows an exemplary configuration of the reactive distillation column for MTBE synthesis according to the invention, which is based on the configurations described in Fig. 1 and Fig. 2. The difference is that the heat transfer fluid W2 is fed into a flash vessel (11) which is operated at the pressure level between the two compression stages. A gaseous phase and a liquid phase are generated in the flash vessel. The gaseous phase (flash fraction) in the flash vessel is fed between the two compression stages (10⁻¹, 10⁻²). The liquid fraction is returned to the heat exchanger (8).

[0106] Fig. 4 shows an exemplary configuration of the reactive distillation column for MTBE synthesis according to the invention, based on the configurations described in Fig. 1. The difference lies in the inclusion of a side evaporator (12) supplied with a flow located just below the inlet. An intermediate extraction point is provided in the heat pump. At this point, the heat pump needs to provide a smaller temperature difference. Consequently, the heat transfer fluid W1.1 can be used to heat the side evaporator (12) after the first compression (10-1). After heating in the bottom evaporator (6), the heat transfer fluid is used via a further preheater (13) to further heat the heat transfer fluid W1.1.

[0107] Examples

[0108] For all subsequent examples, a raffinate I stream of 51 t / h was used. The raffinate I stream has the following composition: 44.1 wt% MTBE, 2.6 wt% MeOH, 0.6 wt% isobutene, 32.1 wt% butenes (sum of 1-butene, cis-2-butene and trans-2-butene) and 20.6 wt% butanes (sum of n-butane and isobutane).

[0109] The amount of energy required for the operation of the plants shown in the examples, for the synthesis and separation of MTBE and raffinate 2, was calculated using simulations with Aspen V12. The material properties and the kinetic model were validated by operational data and field tests.

[0110] Example 1 (not according to the invention) 202300139 Foreign Filing

[0111] 15

[0112] This example is based on Fig. 1. 51 t / h of feed (stream A) of the product mixture at a temperature of 40°C is preheated to 75°C via the preheater (1) and fed into the reactive distillation column (2). Ten trays are installed above the feed tray, where the feed is introduced. Above this, the reactive zone begins. Three packed beds are installed. Ten more trays are installed above the reactive zone. The overhead stream is condensed in the heat exchanger (3). The heat of condensation, 4.6 MW, is transferred to cooling water. The reflux, 19.8 t / h, is returned to the column via a distillate receiver (4) and a reflux pump (5). The distillate stream of 27.7 t / h is a raffinate II (C) and is further processed downstream. Ten separation stages are installed below the feed tray of the reactive distillation column (2). The evaporator power of 5.2 MW is supplied via the sump evaporator (6), which is operated with heating steam.The hot bottom product (7) 23.3 t / h MTBE with a purity of 99.6 wt% is subjected to heat integration for preheating via a booster pump. 1.4 MW are transferred to preheat the feed stream.

[0113] Example 2 (according to the invention)

[0114] Fig. 2 shows a circuit according to the invention, which is based on the circuit described in Fig. 1. In this example, the heat of condensation is partially used to provide the heating power of the column (2) with a heat pump. 1.1 MW is condensed against cooling water at the heat exchanger (3). 3.5 MW is condensed against n-pentane at the heat exchanger (8). At 55°C and 1.9 bar abs., 68 t / h of n-pentane evaporate. The evaporated n-pentane is superheated to ΔT = 40 K. Subsequently, the n-pentane stream is compressed to a higher pressure level by a multi-stage compression stage. To transfer 5.2 MW of evaporator power to the heat exchanger (6), a pressure of 13.3 bar abs. must be set on the pressure side of the multi-stage compression stage (10⁻¹ - 10⁻²). This requires an electrical power input of 1.7 MW. Therefore, the heating output can be provided with a coefficient of performance (COP) of 3.1.

[0115] Example 3 (according to the invention)

[0116] Fig. 3 shows a circuit according to the invention, which is based on the circuit described in Fig. 1 and Fig. 2. In this example, the heat of condensation is partially used to provide the heating power of the column (2) with a heat pump. 0.7 MW is condensed against cooling water at the heat exchanger (3). 3.9 MW is condensed against n-pentane at the heat exchanger (8). At 55°C and 1.9 bar abs., 42 t / h of n-pentane evaporate. The evaporated n-pentane is superheated to ΔT = 40 K. Subsequently, the n-pentane stream is brought to a higher pressure level by a multi-stage compression with intermediate expansion (11). In a first compression stage, a pressure of 5.84 bar abs. is generated. This requires 0.6 MW of compressor power. At a further compressor stage, the flash flow of 26 t / h from the intermediate expansion is also drawn in and brought up to a pressure level of 13.3. (By the 202300139 Foreign Filing)

[0117] 16

[0118] During intermediate relaxation, the total compressor power is reduced from 1.7 MW (Example 2) to 1.3 MW. Consequently, the heating power can be provided with a coefficient of performance (COP) of 4.

[0119] Example 4 (according to the invention)

[0120] A further optimization according to the invention is shown in Example 4. Here, a multi-stage heat pump with intermediate extraction is provided. A liquid extraction point is installed two trays below the feed stage and fed to a side evaporator (12). At this point, the heat pump must provide a smaller temperature difference. Consequently, the n-pentane evaporated at 8 must be brought to a lower pressure. 3.4 MW are transferred at the side evaporator, requiring an electrical power of 0.5 MW. In the sump evaporator (6), 3 MW must be transferred compared to the previous examples. To provide this amount of heat, an electrical power of 0.6 MW must be supplied. Due to the shift in the temperature profile, or rather the boiling up of low-boiling substances by the introduction of the side evaporator, a higher total heating power must be introduced into column 2.In total, only 1.1 MW of electrical power is required to ensure the necessary heating output. This results in a COP of 5.8.

[0121] It is evident that the embodiments according to the invention replace externally purchased heating power with electrical power. When green electricity is used, this can also achieve a significant reduction in CO2 emissions.

Claims

202300139 Foreign Filing 17 Patent claims 1. A process for distilling a feed stream containing at least n-butene, n-butane, isobutene, and an alkyl tert-butyl ether (ATBE) with a C1 to C5 alkyl group and an alcohol ROH with R = C1 to C5 alkyl group, in a reactive distillation column having at least one reaction zone and at least one distillation zone, wherein the distillation zone is arranged below the reaction zone and wherein the reaction zone contains an acidic catalyst, wherein the feed stream is passed to the reaction distillation column via a preheater and in the reaction distillation column is separated into an overhead stream containing at least n-butene, n-butane, the alcohol, in particular methanol or ethanol, and a maximum of 1000 ppm, preferably a maximum of 500 ppm, isobutene, and into a bottom stream containing at least the ATBE; In the reaction zone of the reaction distillation column, at least some of the isobutene reacts with the alcohol ROH on the acidic catalyst to form ATBE;the bottom stream is taken from a lower part of the reactive distillation column; the reactive distillation column has at least one bottom evaporator SV which is fed with a stream taken from the bottom of the reactive distillation column and returned to the reactive distillation column after passing through the bottom evaporator; wherein the overhead stream is at least partially used for heat integration, which includes at least the following steps; (a) At least partial condensation of at least a part of the overhead stream, the heat of condensation being used by transferring energy from at least a part of the overhead stream to a liquid or gaseous heat transfer medium W, thereby creating a heat transfer medium W1; (b) Compressing at least a part of the heat transfer medium W1, preferably the entire heat transfer medium W1, thereby producing a compressed heat transfer medium W2 which has a higher pressure than the heat transfer medium W1, wherein the compression of the heat transfer medium W1 is carried out in multiple stages; and (c) Transfer of energy from the compressed heat transfer medium W2 to the current in the sump evaporator SV. 202300139 Foreign Filing 18 2. The method according to claim 1, wherein the headstream is split and only a portion is used for heat integration.

3. The method according to claim 2, wherein the other part of the headstream is at least partially condensed in a heat exchanger.

4. Method according to one of the preceding claims, wherein the bottom stream from the reactive distillation column is used to heat the feed stream in the preheater, wherein energy in the form of heat is transferred from the bottom stream to the feed stream.

5. Method according to claim 1, wherein the heat transfer medium W1 is compressed twice, wherein in the first compression a compressed heat transfer medium W1 .1 is formed which has a higher pressure than W1 and in the second compression the compressed heat transfer medium W2 is formed which has a higher pressure than W1.1 and than W1.

6. Method according to one of the preceding claims, wherein the heat transfer medium W2 is at least partially condensed during energy transfer in step (c).

7. Method according to claim 6, wherein the at least partially condensed heat transfer medium W2 is fed into a flash container which is operated at the pressure level which lies between the two compression stages, whereby a gaseous phase and a liquid phase are formed in the flash container.

8. Method according to claim 7, wherein the gaseous fraction (flash fraction) from the flash container is directed between the two compression stages.

9. Method according to claim 7 or 8, wherein the liquid portion from the flash container is recycled to step (a) and used there as a heat transfer medium W.

10. Method according to claim 9, wherein the liquid portion is used to preheat the heat transfer medium W1 before compression, wherein energy is transferred from the liquid portion to the heat transfer medium W1.

11. A method according to any of the preceding claims, wherein the reactive distillation column has a side evaporator STV which is fed with a side stream ST which is taken from above the bottom of the reactive distillation column and is returned to the reactive distillation column after passing through the side evaporator STV.

12. Method according to claim 11, wherein energy is transferred from a portion of the heat transfer medium W1.1 to the side stream ST in the side evaporator and the portion of the heat transfer medium W1.1 during the 202300139 Foreign Filing 19 Energy transfer is at least partially condensed, preferably returned to step (a) and used there as heat transfer medium W.

13. Method according to claim 11 or 12, wherein the heat transfer medium W2 is used after the energy transfer in step (c) to preheat the heat transfer medium W1 .1 before the second compression, wherein energy is transferred from the heat transfer medium W2 to the heat transfer medium W1 .

1.

14. Method according to claim 13, wherein the at least partially condensed heat transfer medium W2 is returned to step (a) and is used there as heat transfer medium W.

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