Energy efficient process for separation of 1-butene from hydrocarbon stream with optimized vapor compression

Abstract

The present invention relates to an energy efficient process for separating 1-butene from a hydrocarbon stream with optimized vapor compression. The subject of the invention is a process for separating 1-butene from a hydrocarbon stream containing at least 1-butene, 2-butene, n-butane and iso-butane in a separation unit comprising at least two distillation columns DK1 and DK2, wherein the heat of condensation is recycled into the process by optimized vapor compression in order to save energy costs and CO2 emissions.

Description

FIELD OF THE INVENTION

[0001] The present invention relates to a process for separating 1-butene from a hydrocarbon stream containing at least 1-butene, 2-butene, n-butane and isobutane in a separation unit comprising at least two distillation columns DK1 and DK2, wherein the condensation heat is recycled into the process by optimized vapor compression to save energy costs and CO 2 emissions. BACKGROUND OF THE INVENTION

[0002] 1-Butene can be obtained in large quantities from industrial C4 hydrocarbon streams, such as the C4 fraction from steam crackers or FCC units. These C4 hydrocarbon streams consist essentially of butadiene, the monoolefin isobutene, 1-butene and the two 2-butenes (cis- and trans-2-butene), as well as the saturated hydrocarbons isobutane and n-butane. Due to the small boiling point differences between the components, their low separation factors and the formation of azeotropes, it is difficult and uneconomical to post-treat the C4 hydrocarbon stream by distillation alone.

[0003] Therefore, butadiene is usually first separated by extractive distillation or selectively hydrogenated to form butenes. In each case, what remains is a C4 hydrocarbon stream (usually referred to as raffinate-1), which contains not only the saturated hydrocarbons n-butane and isobutane, but also the olefins isobutene, 1-butene and 2-butene, and butadiene is present at most in small amounts.

[0004] Since the boiling points of 1-butene and isobutene are very close to each other, it is usually not possible to economically separate 1-butene from the corresponding C4 hydrocarbon stream by simple distillation. Therefore, isobutene is removed as completely as possible, for example, by etherification with an alcohol (such as methanol or ethanol) to obtain MTBE or ETBE. Most of the reactive removal of isobutene produces a C4 hydrocarbon stream containing linear butenes (1- and 2-butene) as well as the saturated hydrocarbons isobutane and n-butane (what is known as raffinate 2).

[0005] It is possible to separate 1-butene from such a C4 hydrocarbon stream and it is used in the chemical industry. This separation is carried out in a distillation unit comprising at least two distillation columns. Isobutane and 1-butene are obtained at the top of the first distillation column and are led to the second distillation column. Then isobutane and 1-butene are separated from each other in the second distillation column. Such a process is disclosed, for example, in DE 102005062700A1.

[0006] In the known processes, the energy required to separate the C4 hydrocarbon stream is usually introduced at the bottom of the two distillation columns by heating steam (Heizdampf). Heating steam is usually available at a chemical production site. In the amounts required for the separation tasks under discussion, the use of heating steam represents a cost factor that cannot be underestimated. In addition, the generation of heating steam produces a large amount of CO 2 . SUMMARY OF THE INVENTION

[0007] Accordingly, an object of the present invention is to provide a method by which energy and CO 2 emissions can be saved compared to known methods, and which can be integrated into existing equipment.

[0008] This object is achieved by an embodiment of the method according to claim 1. Preferred embodiments are given in the dependent claims. The method according to the invention is a method for separating 1-butene from a raffinate-2 stream containing at least 1-butene, 2-butene, n-butane, isobutene and isobutane in a separation unit comprising at least two distillation columns DK1 and DK2, wherein

[0009] the first distillation column DK1 has at least one reboiler SV1, and the second distillation column DK2 has at least one reboiler SV2;

[0010] a stream taken out at the lower end of DK1 is fed to the reboiler SV1, and the stream is guided back to DK1 after passing through the corresponding reboiler;

[0011] a stream taken out at the lower end of DK2 is fed to the reboiler SV2, and the stream is guided back to DK2 after passing through the corresponding reboiler; wherein the method comprises the following steps:

[0012] (a) guiding the raffinate-2 stream to the first distillation column DK1 and separating it in DK1 into at least one vapor stream BS1 and at least one bottom stream, the vapor stream BS1 containing at least 1-butene and isobutane and taken out at the top of DK1, and the bottom stream containing at least 1-butene, n-butane and 2-butene and taken out at the bottom of DK1;

[0013] (b) compressing at least a part of the vapor stream BS1, thereby generating a compressed stream VB1 relative to the vapor stream BS1;

[0014] (c) transferring energy from the compressed stream VB1 to the stream in the reboiler SV1;

[0015] (d) guiding at least part of the stream VB1 to the second distillation column DK2 and separating it in DK2 into at least one vapor stream BS2 and at least one bottom stream, the vapor stream BS2 containing at least isobutane and taken out at the top of DK2, and the bottom stream containing at least 1-butene and taken out at the bottom of DK2;

[0016] (e) at least partially compressing the vapor stream BS2, thereby generating a compressed stream VB2 relative to the vapor stream BS2; and

[0017] (f) transferring energy from the compressed stream VB2 to the stream in the reboiler SV2.

[0018] One advantage of the method according to the invention is that the vapour streams BS1 and BS2 obtained in the two columns DK1 and DK2 are compressed, thus upgraded and used in the reboilers SV1 and SV2, and energy is thereby introduced into the respective bottoms. The result of the energy transfer in the reboilers SV1 and SV2 is that significantly less or even no heating steam has to be used to heat the distillation columns DK1 and DK2. This enables (almost) complete electrification of the energy-intensive process, which in turn enables the use of green electricity. This saves energy costs and CO 2 emissions.

[0019] According to the invention, the starting stream from which 1-butene is to be separated is a raffinate 2 stream containing at least 1-butene, 2-butene, n-butane and isobutane. The corresponding stream is commercially available, for example as a C4 fraction from a steam cracker or an FCC unit. As already mentioned in the introduction, raffinate 2 is formed by removing polyunsaturated C4 hydrocarbons (especially butadiene) and isobutene from the stream. Due to economic and technical reasons, it is not possible to completely remove them in many cases. However, the amounts of polyunsaturated C4 hydrocarbons (especially butadiene) and isobutene should be as low as possible.

[0020] The raffinate 2 used preferably contains less than 2500 ppm, preferably less than 1000 ppm, more preferably less than 500 ppm of isobutene. If a higher amount of isobutene is present in the starting stream, MTBE or ETBE synthesis (methyl tert-butyl ether = MTBE / ethyl tert-butyl ether = ETBE) can be carried out between the two distillation columns DK1 and DK2 so that isobutene reacts with methanol (to give MTBE) or ethanol (to give ETBE), and the MTBE or ETBE is then separated off (see EP 1806330 A1 or EP1813588 A1). This can greatly reduce the isobutene concentration upstream of the second distillation column DK2. This is because isobutene will be obtained in the bottom of the second distillation column and thus in the 1-butene.

[0021] Further preferably, the raffinate 2 used in the method according to the invention contains less than 4% by weight of polyunsaturated C4 hydrocarbons. In a particularly preferred embodiment, the concentration of polyunsaturated C4 hydrocarbons should be less than 500 ppm. If the stream should contain a higher amount of butadiene, selective hydrogenation can be carried out beforehand, in which butadiene is converted to butene and / or butane. Corresponding methods are known to the person skilled in the art, for example from EP 3680224 A1.

[0022] The raffinate-2 stream used may additionally contain a certain amount of water, especially in an amount of 150 to 4000 ppm. The water is preferably at least partially separated by the method described herein. The water will be enriched in the respective vapor streams BS1 and BS2 in each of the two distillation columns DK1 and DK2 and obtained as a second liquid phase after condensation, which can be separated out by the nipples (Euter) in the distillation vessels of DK1 and / or DK2. The bottom products of DK1 and DK2 are characterized by very low butadiene and water contents, preferably each less than 100 ppm, particularly preferably less than 5 ppm.

[0023] The process according to the invention is carried out in a separation unit comprising at least two distillation columns DK1 and DK2. DK1 is the first distillation column and has at least one reboiler SV1. DK2 is the second distillation column and has at least one reboiler SV2. In a preferred embodiment, the distillation column has only one reboiler SV1. In addition, the distillation column DK2 preferably has only one reboiler SV2. The pressures in the two distillation columns DK1 and DK2 should be chosen in particular such that the separation task is made easier by influencing the relative volatility, but the compression of the volumetric streams BS1 and BS2 does not become too energy-consuming. The terms "first distillation column", "distillation column DK1" and "DK1" should be regarded as synonymous in the context of the present invention. The terms "second distillation column", "distillation column DK2" and "DK2" should likewise be regarded as synonymous in the context of the present invention.

[0024] The energy required for the separation task is introduced into the first distillation column DK1 via the reboiler SV1. A stream taken from the lower end of DK1 is fed to the reboiler SV1, and after passing through the respective reboiler, the stream is then guided back into DK1. The stream is heated during its passage through the reboiler SV1.

[0025] The situation is similar for the reboiler SV2 of the second distillation column DK2, by means of which the energy required for the separation task is introduced. For this purpose, a stream taken from the lower end of DK2 is fed to the reboiler SV2, and after passing through the respective reboiler, the stream is then guided back into DK2. The stream is heated during its passage through the reboiler SV2 and at least partially evaporated in the process.

[0026] According to the invention, a "reboiler" means an evaporator that heats the bottom of the respective distillation column. Such reboilers are usually arranged outside the respective distillation column. Since energy (especially heat) is transferred from one stream to another in the reboiler, they are heat exchangers. The stream to be evaporated is taken from the bottom of the distillation column through an outlet (Abzug) and fed to the reboiler. The evaporated stream (optionally with a liquid residue part) is returned through at least one inlet to the bottom region of the respective distillation column.

[0027] Suitable evaporators that can be used as reboilers are, for example, natural circulation evaporators, forced circulation evaporators, forced circulation evaporators with expansion (Entspannung), kettle evaporators, falling film evaporators or thin film evaporators. The heat exchangers of the evaporators commonly used in the case of natural circulation evaporators and forced circulation evaporators are shell-and-tube or plate-type devices. In addition to the above-mentioned devices, any other evaporator design known to those skilled in the art and suitable for distillation columns can alternatively be used.

[0028] The raffinate 2 led to the first distillation column DK1 is separated in the distillation column DK1 into at least two streams, namely at least one vapor stream BS1 and at least one bottom stream. The vapor stream BS1 contains at least 1-butene and isobutane and is taken off at the top of DK1, and the bottom stream contains at least 1-butene and 2-butene and is taken off at the bottom of DK1. This bottom stream can be led to an oligomerization reaction (not shown). The vapor stream BS1 can also be taken off at the top of the distillation column in the form of a plurality of sub-streams BS1n, where n is an integer and equal to the number of sub-streams. The same applies to the bottom stream. The temperature at the bottom of the first distillation column DK1 is preferably in the range of 40 to 110 °C, preferably 50 to 100 °C.

[0029] In principle, the raffinate 2 stream can be introduced into the first distillation column DK1 via one or more feed points. If strong fluctuations in the feed concentration are expected, it may be meaningful to provide a plurality of different feed points. For example, their optimal positions can be found by simulation through minimization of the energy requirement. If a plurality of feed streams with different compositions are to be processed, the optimal feed points can be determined analogously for each feed. In principle, the raffinate 2 stream can also be pre-divided into a plurality of sub-streams, even in the case of the same or constant composition. In this case, the raffinate 2 stream is introduced into the distillation column DK1 in the form of two or more separate streams. It is advantageous here when the feed points of the respective streams are substantially at the same height on the distillation column DK1.

[0030] The pressure and temperature of the vapor stream BS1 will be given below. This particularly relates to the pressure and temperature of at least one vapor stream BS1 when taken out from the distillation column DK1. The pressure of the vapor stream BS1 is especially in the range of 6 to 15 bar absolute pressure, preferably in the range of 7.5 to 13 bar absolute pressure. The temperature of the vapor stream BS1 is especially in the range of 45 °C to 120 °C, preferably in the range of 48 °C to 100 °C, further preferably in the range of 50 °C to 90 °C, further preferably in the range of 55 °C to 80 °C, and particularly preferably in the range of 60 °C to 80 °C.

[0031] The distillation column DK1 for separating the raffinate-2 stream can be any distillation column known to those skilled in the art. The distillation column DK1 preferably contains internals. Suitable internals are, for example, trays, random packings (bulk packings) or structured packings. The trays used are usually bubble-cap trays, sieve trays, valve trays with fixed or movable valves, channel-cap trays or slotted trays. Random packings are usually beds of bulk packing. The bulk packing used is usually Raschig rings, Pall rings, arc saddles, SuperRinge / SuperRinge Plus or saddle packings. Structured packings are sold, for example, by Sulzer under a trade name. In addition to the internals mentioned, other suitable internals are also known to those skilled in the art and can equally be used.

[0032] The preferred internals have a low pressure drop per theoretical plate. For example, the pressure drop per theoretical plate of structured packings and bulk packings is significantly lower than that of trays. The advantage of this is that the pressure drop in the distillation column DK1 remains as low as possible, so that the mechanical power of the compressor and the temperature of the raffinate 2 stream to be evaporated remain low.

[0033] In a particularly preferred embodiment of the invention, the distillation column DK1 comprises a plurality of trays, preferably 150 to 300 trays, more preferably 170 to 220 trays.

[0034] In the context of the present invention, the meaning of withdrawing at least one vapor stream BS1 containing at least 1-butene and isobutane at the top of the distillation column DK1 is in particular that at least one vapor stream BS1 is withdrawn in the distillation column DK1 as a top stream or as a side stream above an internal component.

[0035] In the context of the present invention, the meaning of withdrawing at least one bottom stream containing at least 1-butene and 2-butene at the bottom of the distillation column DK1 is in particular that at least one bottom stream is withdrawn directly at the bottom of the distillation column DK1 or at the lower trays.

[0036] The distillation column DK1 is preferably operated in reflux mode. The meaning of "reflux" is that at least part of the vapor stream BS1 withdrawn at the top of the distillation column DK1 is re-fed into the distillation column DK1. In establishing such reflux, the reflux ratio is preferably 2 to 30, more preferably 5 to 20, and particularly preferably 8 to 15.

[0037] Reflux can be established by installing a condenser at the top of distillation column DK1. Vapor stream BS1 is partially condensed in the condenser and re-fed to distillation column DK1. The vapor stream can also be used as reflux to the distillation column after compression and expansion. Generally and in the context of the present invention, the reflux ratio refers to the ratio of the portion of the mass flow rate (kg / h) withdrawn from the column that is returned (refluxed) to the column in liquid form to the portion of the mass flow rate (kg / h) that is discharged from the corresponding column in liquid or gaseous form.

[0038] After withdrawing vapor stream BS1, vapor stream BS1 is compressed, thereby generating a compressed stream VB1 relative to vapor stream BS1. It may be advantageous to heat stream BS1 before compression so as not to form a two-phase mixture during compression. The heating can be carried out by an internal (see WT1 in the present application Figure 6 and 7 or an external heat source. The pressure of VB1 after compression is higher than the pressure of BS1. As long as the condition that pressure VB1 > pressure BS1 is satisfied, the exact value of the pressure of VB1 can be set by a person skilled in the art according to the requirements in the subsequent energy transfer. The quotient of pressure VB1 / pressure BS1 (pressures in bar absolute pressure respectively) is preferably from 1.1 to 10, more preferably from 1.2 to 8, more preferably from 1.25 to 7, and most preferably from 1.3 to 6.

[0039] The temperature of sub-stream VB1 is preferably higher than the temperature of vapor stream BS1, and the quotient of temperature VB1 / temperature BS1 (temperature in K in each case) is preferably from 1.03 to 10, more preferably from 1.04 to 9, more preferably from 1.05 to 8, more preferably from 1.06 to 7, more preferably from 1.07 to 6, and most preferably from 1.08 to 5.

[0040] At least a portion of vapor stream BS1 can be compressed in step (b) in any desired manner known to a person skilled in the art. For example, the compression can be carried out mechanically and can be carried out in single-stage or multi-stage compression. In this regard, "single-stage" means compression from one pressure level to another pressure level. "Multi-stage" means first compressing to pressure level X and then from X to pressure level Y. In multi-stage compression, multiple compressors of the same type or different types can be used. Multi-stage compression can preferably be achieved with one or more compression machines. The use of single-stage or multi-stage compression depends on the compression ratio and thus on the pressure to which vapor stream BS1 is to be compressed.

[0041] Suitable compressors in the process according to the invention, in particular compressors for compressing the vapor stream BS1 to VB1, are any compressors known to the person skilled in the art, preferably mechanical compressors, with which a gas stream can be compressed. Suitable compressors are, for example, single-stage or multi-stage gear-driven turbo compressors, piston compressors, screw compressors, centrifugal compressors or axial compressors.

[0042] In step (c) of the process according to the invention, energy is transferred from the compressed stream VB1 to the stream in the reboiler SV1. By step (c), the energy of VB1 is reduced such that VB1 can be partially condensed. According to the invention, the phrase "energy transfer" in particular means "heating", i.e. the transfer of energy in the form of heat.

[0043] The energy transfer from VB1 to the stream in the reboiler SV1, preferably by heating the stream in the reboiler SV1 with VB1, is preferably direct. Direct transfer means that the streams in VB1 and SV1 do not come into direct contact, but that energy, in particular heat, is transferred from VB1 to the stream in SV1 in the absence of an additional heat transfer medium. The reboiler SV1 used can be a heat exchanger or heat exchanger known to the person skilled in the art, in particular an evaporator.

[0044] Before introducing the stream VB1 into the second distillation column in step (d), in a preferred embodiment, the stream VB1 is introduced into a flash vessel and expanded therein to obtain a liquid phase FP1. The flash vessel can additionally contain a condenser to condense a part of the obtained gas phase.

[0045] Then at least a part FP1a of the liquid phase FP1 is guided to the distillation column DK2 according to step (d). For this purpose, in a particularly preferred embodiment, a pump is used. Pumps known to the person skilled in the art can be used here. Suitable pumps are, for example, chemical standard pumps.

[0046] Further preferably, the part FP1b of the liquid phase FP1 other than FP1a is returned as reflux to the first distillation column DK1. Particularly preferably, energy is transferred from the stream FP1b to the raffinate 2 stream before introducing the raffinate 2 stream into the first distillation column DK1. Thereby, the raffinate 2 stream is preheated. This is energetically advantageous because less energy needs to be introduced for the separation task carried out by the reboiler. The transfer of energy from FP1b to the raffinate 2 stream, preferably by heating the raffinate 2 stream with FP1b, is preferably direct, i.e. without using (additional) heat transfer media. For this purpose, heat exchangers or heat exchangers known to the person skilled in the art can be used.

[0047] The material flow VB1 or FP1a is also guided to the second distillation column DK2. If the amount of isobutene in the material flow VB1 or the material flow FP1a is too high to meet the specifications of the 1-butene product from DK2, as described above, additional MTBE or ETBE synthesis can be provided between the distillation columns DK1 and DK2. For this purpose, the material flow VB1 or the material flow FP1a is guided to the MTBE or ETBE synthesis, and at least part of the isobutene present is converted into MTBE or ETBE.

[0048] MTBE or ETBE synthesis is generally known to those skilled in the art. To prepare MTBE or ETBE from a material flow containing isobutene, an acidic ion exchange resin (sulfonic acid group) can be used in particular as a heterogeneous catalyst. MTBE or ETBE synthesis can be carried out in one or more reactors connected in series. The catalyst is preferably used in the form of a fixed bed catalyst. Since the formation of MTBE or ETBE is an equilibrium reaction, it may be expedient to use at least one reactive distillation column in which the reaction and the removal of MTBE or ETBE take place simultaneously. In reactive distillation, the pressure should be 3 to 15 bar and the temperature in the reaction zone should be 55 to 75 °C.

[0049] After the synthesis, MTBE or ETBE is preferably separated from the material flow VB1 or FP1a by distillation. This method is also known to those skilled in the art. Only then is VB1 or FP1a guided to the distillation column DK2.

[0050] In the second distillation column DK2, the material flows each containing at least isobutane and 1-butene are separated according to step (d) into at least one vapor material flow BS2 containing at least isobutane and taken off at the top of DK2, and at least one product material flow containing at least 1-butene and taken off at the bottom of DK2.

[0051] The distillation column DK2 for separating the raffinate 2 material flow can be any distillation column known to those skilled in the art. The distillation column DK2 preferably includes internals. Suitable internals are, for example, trays, random packings (bulk packings) or structured packings. The trays used are usually bubble-cap trays, sieve trays, valve trays with fixed or movable valves, channel-cap trays or slotted trays. Random packings are usually bulk packing beds. The bulk packings used are usually Raschig rings, Pall rings, arc saddles, SuperRinge / SuperRinge Plus or saddle packings. Structured packings are sold, for example, by Sulzer under a trade name. In addition to the internals mentioned, other suitable internals are known to those skilled in the art and can equally be used.

[0052] Preferred internals have a low pressure drop per theoretical plate. For example, structured packings and random packings have a significantly lower pressure drop per theoretical plate than trays. The advantage of this is that the pressure drop in distillation column DK2 remains as low as possible, so that the mechanical power of the compressor and the temperature of the stream to be evaporated remain low.

[0053] In a particularly preferred embodiment of the invention, the second distillation column DK2 comprises a plurality of trays, preferably 150 to 300 trays, more preferably 170 to 220 trays.

[0054] In the context of the present invention, the meaning of withdrawing at least one vapor stream BS2 containing at least isobutane at the top of the distillation column DK2 in particular means that at least one vapor stream BS2 is withdrawn in the distillation column DK2 as a top stream or as a side cut above an internal component.

[0055] In the context of the present invention, the meaning of withdrawing at least one product stream containing at least 1-butene at the bottom of the distillation column DK2 in particular means that at least one product stream is withdrawn directly at the bottom of the distillation column DK2 or at the lower trays. The product stream preferably contains at least 99 wt% of 1-butene, more preferably at least 99.5 wt% of 1-butene, particularly preferably at least 99.6 wt% of 1-butene. 1-Butene is the target product of the process, so the product stream is discharged from the process. 1-Butene can be used, for example, as a comonomer in the production of polyethylene.

[0056] It should be noted here that the separation sharpness in the first distillation column DK1 ultimately determines the purity of 1-butene in the product stream withdrawn from the second distillation column DK2. This is because n-butane and 2-butene are also obtained as high boilers in DK2 and are thus obtained together with 1-butene. This will contaminate the 1-butene. It should therefore be ensured that the raffinate 2 stream in DK1 is separated as far as possible so that hardly any n-butane reaches DK2. It is therefore preferred that the stream (1a, VB1 or FP1a) fed to DK2 contains less than 1500 ppm, preferably less than 1200 ppm, particularly preferably less than 900 ppm of n-butane, based on the total amount of the stream.

[0057] During the process according to the invention, the temperature at the bottom of the second distillation column DK2 is preferably in the range from 30 to 100 °C, preferably from 45 to 80 °C. Further preferably, the pressure at the top of the second distillation column DK2 is in the range from 3 to 12 bar absolute pressure, preferably from 5 to 10 bar absolute pressure.

[0058] The distillation column DK2 can also be operated in reflux. The meaning of "reflux" means that at least part of the vapor stream BS2 taken from the top of the distillation column DK2 is re-fed back into the distillation column DK2. In the case of establishing such reflux, the reflux ratio is preferably from 10 to 100, more preferably from 30 to 50.

[0059] The pressure ranges for the top pressure were defined in the foregoing paragraphs, namely the pressures at the tops of the distillation columns DK1 and DK2. In principle, accordingly, the two columns can be operated in a dual-pressure connection, i.e., at different pressures. In addition to the vapor compression described here, energy can also be transferred from the high-pressure column to the low-pressure column. However, according to the present invention, it is preferred that the distillation columns DK1 and DK2 be operated at the same top pressure or at a similar top pressure, where in the case of a similar top pressure, the top pressures differ by at most 20%, preferably at most 15%. In addition to the lower equipment complexity, a lower energy input is advantageous. Finally, the relative volatility will decrease with increasing pressure, and the amount of energy required to complete the separation task will become much larger, at least in the high-pressure column.

[0060] Subsequently, in step (e), at least part of the vapor stream BS2 is compressed, thereby producing a compressed stream VB2 relative to the vapor stream BS2. The pressure of the compressed VB2 is higher than the pressure of BS2. A person skilled in the art can set the exact value of the pressure of VB2 according to the requirements of subsequent energy transfer, provided that the condition that the pressure of VB2 > the pressure of BS2 is satisfied. The quotient of the pressure of VB2 / the pressure of BS2 (the pressures are each in bar absolute pressure) is preferably in the range of 1.1 to 10, more preferably 1.2 to 8, more preferably 1.25 to 7, and most preferably 1.3 to 6. It may be advantageous to heat the stream BS2 before compression so as not to form a two-phase mixture during compression. The heating can be carried out by means of an internal (see WT-2 in the present application Figure 6 and Figure 7 in the application) or an external heat source.

[0061] The temperature of the sub-stream VB2 is especially higher than the temperature of the vapor stream BS2, and the quotient of the temperature of VB2 / the temperature of BS2 (the temperature in each case is in K) is preferably in the range of 1.03 to 10, more preferably in the range of 1.04 to 9, more preferably in the range of 1.05 to 8, more preferably in the range of 1.06 to 7, more preferably in the range of 1.07 to 6, and most preferably in the range of 1.08 to 5.

[0062] In step (e), at least a portion of the vapor stream BS2 can be compressed in any desired manner known to those skilled in the art. For example, the compression can be mechanical and carried out in a single stage or multiple stages. In multi-stage compression, multiple compressors of the same type or different types can be used. Multi-stage compression can be carried out with one or more compression machines. The use of single-stage or multi-stage compression depends on the compression ratio and thus on the pressure to which the vapor stream BS2 is to be compressed.

[0063] Any compressor known to those skilled in the art, particularly a compressor suitable for compressing the vapor stream BS2 to VB2, preferably a mechanical compressor, can be used to compress the gas stream. Suitable compressors are, for example, single-stage or multi-stage turbines, piston compressors, screw compressors, centrifugal compressors or axial compressors.

[0064] In step (f) of the method according to the invention, energy is transferred from the compressed stream VB2 to the stream in the reboiler SV2. By step (f), the energy of VB2 is reduced such that VB2 can be at least partially condensed. According to the invention, the phrase "energy transfer" particularly means "heating", i.e., transferring energy in the form of heat.

[0065] The transfer of energy from VB2 to the stream in the reboiler SV2, preferably by heating the stream in the reboiler SV2 with VB2, is preferably direct. The meaning of direct transfer is that VB2 and the stream in SV2 do not come into contact, but energy, especially heat, is transferred from VB2 to the stream in SV2 in the absence of an additional heat transfer medium. The reboiler SV2 used can be a heat transfer device or heat exchanger known to those skilled in the art, particularly an evaporator.

[0066] After the stream VB2 has passed through the reboiler SV2 and transferred energy to the stream present therein, VB2 can be discharged from the process as an isobutane stream IB1. However, before removing VB2 as IB1 from the process, in a preferred embodiment of the invention, the stream VB2 is directed to a flash vessel and expanded therein to obtain a liquid phase FP2. The flash vessel can additionally include a condenser in order to condense a portion of the obtained gas phase.

[0067] Then, at least a portion FP2a of the liquid phase FP2 can be discharged from the process as an isobutane stream IB1. For this purpose, a pump is used in a particularly preferred embodiment. In certain cases and given a sufficient pressure ratio, a pump may not be necessary. If a pump is used, a pump known to those skilled in the art can be used. Suitable pumps are, for example, chemical standard pumps. Further preferably, the portion FP2b of the liquid phase FP1 other than FP2a is returned as reflux to the first distillation column DK2.

[0068] In a basic embodiment of the present invention, the two streams BS1 and BS2 are each compressed by a single compressor. In a preferred embodiment of the present invention, the two streams BS1 and BS2 are preferably compressed in a multi-stage manner in a single compression machine. The number of required stages depends on the target compression ratio to be achieved for the respective vapor streams BS1 and BS2.

[0069] The thermal integration of vapor compression described here can also be combined with other thermal integration measures. One or more heat pumps can also be provided here. BRIEF DESCRIPTION OF THE DRAWINGS

[0070] The present invention will be described below with reference to the drawings. The drawings are for illustrative purposes and should not be considered restrictive.

[0071] Figure 1 An embodiment without thermal integration according to the prior art and not according to the present invention is shown. The raffinate 2 stream (1) is introduced into the first distillation column DK1, where it is separated into a vapor stream BS1 that contains at least 1-butene and isobutane and is taken out at the top of DK1, and a bottoms stream (2) that contains at least 1-butene and 2-butene and is taken out at the bottom of DK1. The stream (2) can be directed to an oligomerization reaction (not shown). The energy input to the distillation column DK1 is achieved by transferring energy to the stream in the reboiler SV1. The vapor stream BS1 is at least partially condensed by a cooling device (K1), such as an air cooler or a heat exchanger operating with cooling water, and is sent to a storage container, where a liquid phase FP1 and FP1w can be produced. The organic liquid phase (FP1) is separated into two streams, FP1a (which is introduced into the second distillation column DK2) and FP1b (which is led back as reflux to the first distillation column). In addition, a heavy aqueous phase (5) can be separated out. In the distillation column DK2, it is separated into a vapor stream BS2 that contains at least isobutane and is taken out at the top of DK2, and a product stream (3) that contains at least 1-butene and is taken out at the bottom of DK2. The energy input to the distillation column DK2 is achieved by transferring energy to the stream in the reboiler SV2. This transfer is achieved with heating steam.

[0072] Figure 2 An embodiment not according to the present invention is also shown, in which heat recovery is only carried out in the distillation column DK1. And Figure 1Different from the embodiments shown, the vapor stream BS1 is currently brought to a higher pressure with compressor V1 and then led as stream VB1 to reboiler SV1. Energy is transferred in reboiler SV1 to the stream present there, the stream from the bottom is heated and then returns again to introduce the energy required for separation. Then VB1 is led to a flash vessel where the liquid phase FP1 is obtained, which returns as reflux FP1b to the uppermost tray of the column and as FP1a is fed as feed to DK2. In addition, a heavy aqueous phase (5) can be separated off.

[0073] Figure 3 Embodiments which are not according to the invention are also shown, in which the heat integration takes place only in distillation column DK2. Different from Figure 1 the embodiments shown, the vapor stream BS2 is currently brought to a higher pressure with compressor V2 and then led as stream VB2 to reboiler SV2. Energy is transferred in reboiler SV2 to the stream present there, the stream from the bottom is heated and then returns again to introduce the energy required for separation. Stream VB2 is fed into a flash vessel where the liquid phase FP2 is generated by expansion. This liquid phase (FP2) is separated into two streams FP2b (which returns as reflux to the second distillation column DK2) and an isobutane stream (4) (which is discharged from the process). In addition, a heavy aqueous phase (5) can be separated off.

[0074] Figure 4Shows a basic embodiment of the present invention. The raffinate 2 stream (1) is introduced into the first distillation column DK1, where it is separated into a vapor stream BS1 that contains at least 1-butene and isobutane and is taken off at the top of DK1, and a bottom stream (2) that contains at least 1-butene and 2-butene and is taken off at the bottom of DK1. The stream (2) can be directed to an oligomerization reaction (not shown). The vapor stream BS1 is brought to a higher pressure with a compressor V1 and then directed as stream VB1 to a reboiler SV1, where it transfers energy to the stream present there, the stream from the bottom is heated and then returns again. Then the stream VB1 is fed into a flash vessel, where a liquid phase FP1 is generated by expansion. This liquid phase (FP1) is separated into two streams FP1a (which is directed to the second distillation column DK2) and FP1b (which returns as reflux to the first distillation column DK1). In the distillation column DK2, it is separated into a vapor stream BS2 that contains at least isobutane and is taken off at the top of DK2, and a product stream (3) that contains at least 1-butene and is taken off at the bottom of DK2. The vapor stream BS2 is brought to a higher pressure with a compressor V2 and then directed as stream VB2 to transfer energy to the stream in the reboiler SV2. Subsequently, the stream VB2 is fed into a flash vessel, where a liquid phase FP2 is generated by expansion. This liquid phase (FP2) is separated into two streams FP2b (which returns as reflux to the second distillation column DK2) and an isobutane stream (4) (which is discharged from the process). If the feed to DK1 contains trace amounts of water, it can be separated as a heavy aqueous phase (5) from the flash vessels of DK1 and DK2. Thereby, the water content of the product streams 2 and 3 can be minimized.

[0075] Figure 5 Shows another embodiment according to the present invention. Different from Figure 4 is that the stream FP1a is not directly directed to the distillation column DK2. Instead, this stream still contains a certain amount of isobutene, which will be obtained in the product stream (3) during the separation in DK2 and will contaminate the product stream (3). Therefore, the stream FP1a is fed into an MTBE or ETBE unit, where the isobutene first reacts with methanol to obtain MTBE or with ethanol to obtain ETBE, and then is separated from MTBE, for example, with the participation of a reactive distillation column. The stream FP1c obtained from the MTBE unit contains almost no MTBE and is separated in the distillation column DK2 as Figure 4 described.

[0076] Figure 6 Shows another embodiment according to the present invention. Different from Figure 4The difference first lies in the presence of two additional heat exchangers (WT1, WT2), through which energy is transferred from the feed streams VB1 (in WT1) and VB2 (in WT2) to superheat the feed streams BS1 (in WT1) and BS2 (in WT2). This can prevent the vapor feed stream from entering the two-phase region during compression and ensure that no liquid droplets are formed that could damage the compressor. Additionally, the feed streams VB1 and VB2 in the heat exchangers VW1 and VW2 can additionally release energy to the feed streams of DK1 and DK2, thereby reducing the energy requirements of the reboilers SV1 and SV2 and thus the drive power of the compressors V1 and V2. Compared with Figure 4 Another difference is that condensers (KO1, KO2) for pressure control are installed in each of the two flash vessels. Additionally, this condenser can also be used for the startup process.

[0077] Figure 7 shows another embodiment of the present invention. Compared with Figure 6 the difference is that the feed stream FP1a is not directly led to the distillation column DK2. Instead, this feed stream still contains a certain amount of isobutene, which will be obtained in the product stream (3) during the separation in DK2 and will contaminate this product stream (3). Therefore, the feed stream FP1a is made to enter the MTBE or ETBE unit, where the isobutene first reacts with methanol to obtain MTBE or with ethanol to obtain ETBE, and then is separated from the MTBE, for example, with the participation of a reactive distillation column. The feed stream FP1c obtained from the MTBE unit contains almost no MTBE and is separated in the distillation column DK2 as described above.

[0078] Figure 8 shows another embodiment of the present invention. Compared with Figure 4 the difference is that here a compressor (V3) with multiple compression machines is used. For example, the compression of BS1 and BS2 can occur independently of each other in one compressor. Additionally, here the heavy aqueous phase (5) is separated with the help of a nipple (which is represented by a protrusion).

[0079] Figure 9Shows an alternative embodiment where two distillation columns have different pressures and the vapor compression is connected in different ways. The raffinate 2 stream (1) is introduced into the first distillation column DK1, where it is separated into a vapor stream BS1 that contains at least 1-butene and isobutane and is taken off at the top of DK1, and a bottoms stream (2) that contains at least 1-butene and 2-butene and is taken off at the bottom of DK1. The vapor stream BS1 is separated into two vapor streams BS1a and BS1b. The BS1a is brought to a higher pressure with a compressor V1 and then guided as a stream VB1 to the stream in the reboiler SV1a for energy transfer. The second part of the vapor stream BS1b is guided to the reboiler SV2a without additional compression, where it transfers energy to the stream present here, and the stream from the bottom is heated and then returned again. After the energy transfer, the two streams VB1 and BS1b are sent to a flash vessel, where a liquid phase FP1 is generated by expansion. This liquid phase is separated into two streams FP1a (which is guided to the second distillation column DK2) and FP1b (which is guided as a reflux to the first distillation column). In distillation column 2, the stream is separated into a vapor stream BS2 that contains at least isobutane and is taken off at the top of DK2, and a product stream (3) that contains at least 1-butene and is taken off at the bottom of DK2. The vapor stream BS2 is brought to a higher pressure with a compressor V2 and then guided as a stream VB2 to the stream in the reboiler SV1b for energy transfer. The VB2 then terminates in a flash vessel and is at least partially condensed into a liquid phase FP2, whereby a part FP2a of the isobutane stream (4) leaves the process, and another part FP2b is recycled as a reflux to the second distillation column. Detailed Description

[0080] Examples

[0081] For all the following examples, a raffinate 2 stream of 55 t / h is used. This raffinate 2 stream has the following composition: 1-butene 45.1% / n-butane 22.4% / trans-2-butene 15.9% / cis-2-butene 8.9% / isobutane 7.4% / isobutene 300 ppm and water 590 ppm.

[0082] By using simulations with Aspen V10, the amount of energy required for the operation of the device for separating 1-butene from raffinate 2 detailed in the examples is calculated. The substance data is verified by operating data and operating tests.

[0083] Example 1 (not according to the invention)

[0084] In Figure 1In the embodiment shown, the raffinate 2 having the above composition is fed into the distillation column DK1. The column is operated at a top pressure of 6 bar absolute pressure. The top temperature is 43 °C, and 140 theoretical trays are considered. The lean 1-butene stream (raffinate 3) is discharged via the bottom of the column. The bottom temperature is 62 °C. A pressure drop of 1000 mbar in DK1 is considered. A distillate stream of 15.2 t / h is withdrawn via the top, which contains approximately 77 wt% 1-butene and approximately 22 wt% isobutane. The distillation in DK1 requires a heating power of 15 MW, which is introduced into the column via the reboiler SV1 with heating steam.

[0085] The second distillation column DK2 is operated in a similar manner. In order to separate 1-butene from the isobutane in the distillate stream from DK1, 10.2 MW of heating power is introduced into the second column DK2 by heating steam in the reboiler SV2. At the bottom of DK2, a product stream of 11.6 t / h is discharged with a purity of 99.6 wt% 1-butene. 3.6 t / h is discharged at the top of DK2. 95% of this distillate stream consists of isobutane. The column is also operated at a top pressure of 6 bar absolute pressure and a top temperature of 40 °C. The pressure drop for 140 theoretical trays is 1000 mbar. The bottom temperature is set at 56.6 °C.

[0086] In summary, in Figure 1 the interconnection shown, 25.2 MW of externally supplied heating steam must be used.

[0087] Example 2 (not according to the invention)

[0088] Another test is carried out with the Figure 2 interconnection shown. Different from Figure 1 Example 1, vapor compression is carried out in the distillation column DK1. For this purpose, the vapor stream BS1 from DK1 is compressed by the compressor V1 to 11 bar absolute pressure. The result is the compressed vapor stream VB1, which can be condensed in the reboiler SV1. At 11 bar absolute pressure, the compressed vapor stream condenses at 73 °C. This compression operation requires 1.6 MW of electrical power. 15 MW can be transferred via SV1.

[0089] In summary, in Figure 2 the interconnection shown, 10.2 MW of externally supplied heating steam and 1.6 MW of electrical power must be used.

[0090] Example 3 (not according to the invention)

[0091] Another test is carried out with the Figure 3 interconnection shown. Different from Figure 1Different from Example 1, vapor compression is carried out in distillation column DK2. For this purpose, 1.0 MW of electrical power is required to compress vapor BS2 to a higher pressure level of 11.7 bar absolute pressure, and thus the condensation heat can be utilized in SV2. 10.2 MW can be transferred.

[0092] In summary, in Figure 3 the interconnectedness shown, 15 MW of externally supplied heating steam and 1.0 MW of electrical power are required.

[0093] Example 4 (according to the present invention)

[0094] Another test is carried out with the Figure 4 interconnectedness shown. Here, thermal integration according to the present invention is provided for the two distillation columns DK1 and DK2. For this purpose, a single compressor with at least two stages can be installed or two separate compressors can be used. The two vapor streams are compressed to the required pressure level (see Examples 2 and 3) to generate a driving temperature difference of approximately 10 K, and thus the condensation heat is recycled into the process. Thus, in the interconnectedness shown, both columns DK1 and DK2 can be fully electrified.

[0095] In Figure 4 the embodiment shown, no externally supplied heating steam needs to be used. The operation of the compressor only requires 2.6 MW of electrical power.

[0096] Example 5 (according to the present invention)

[0097] Another test is carried out with the Figure 6 interconnectedness shown, where the difference from Figure 4 is particularly that the vapor streams BS1 and BS2 and the feed streams are additionally preheated. The excess heat generated by introducing electrical power does not need to be removed via additional cooling operations, but is used to preheat the vapor streams in heat exchangers WT1 and WT2, and the feed streams in preheaters VW1 and VW2. Thus, in Example 4, the 2.6 MW of electrical power required in the compressor can be reduced to a total of 2.3 MW. Here, too, no externally supplied heating steam needs to be used.

[0098] Example 6 (according to the present invention)

[0099] Another test is carried out with the Figure 7 interconnectedness shown, where the difference from Figure 6The difference lies in the presence of the MTBE unit. In the interconnections shown here, isobutene passes over the top of DK1 and remains at the bottom of DK2. It thus follows 1-butene and can hardly be separated from 1-butene in this interconnection. As a result, an increase in concentration occurs. If a second MTBE stage is included between DK1 and DK2, the concentration of isobutene in 1-butene can be reduced. Thus, the separation of n-butane in column DK1 no longer needs to be carried out strictly. In addition, more isobutane can be left at the bottom. In total, an additional 200 kW of electrical power can be saved thereby.

[0100] Example 7 (not according to the invention)

[0101] In this embodiment, direct heat integration is carried out between columns DK1 and DK2 (as disclosed in DE 102005062700A1) and is supplemented with multistage vapor compression according to the invention (see Figure 9 ). In this case, column DK1 is operated at a top pressure of 11 bar and column DK2 is operated at a top pressure of 7 bar. Thereby, a part of the vapor stream BS1 can be used to transfer heat via the reboiler SV2a in DK2. Via single-stage vapor compression by means of compressor V1, 4.0 MW of condensation heat from DK1 becomes available and is introduced via the second reboiler SV1a in DK1. For this purpose, 382 kW of electrical power must be applied in compressor V1. In addition, the vapor from DK2 is compressed so that 9.9 MW of condensation heat from DK2 can be used for DK1. The condensation heat boosted by compressor V2 is transferred via another reboiler SV1b. For this purpose, 2.6 MW of electrical power is required. A total of 11.5 MW can be transferred via SV1b by using 2.98 MW of electrical energy.

[0102] The results of Examples 1 - 7 are summarized in Table 1 below.

[0103] Table 1: Summary of Examples

[0104]

[0105] It has been found that the embodiments of the process according to the invention for the separation of 1-butene have the following effects: Compared to known solutions, much less external heating power needs to be used. The potential for savings is thus quite considerable. The additional electrical power required for operating the compressors is much smaller, and CO 2 -neutral operation can be achieved when using green electricity.

[0106] It has also been found that the embodiment in which the two distillation columns DK1 and DK2 are operated at different pressures is disadvantageous because it requires the use of a larger amount of electrical energy.

Claims

1. A process for separating 1-butene from a raffinate-2 stream comprising at least 1-butene, 2-butene, n-butane, isobutene and isobutane in a separation unit comprising at least two distillation columns DK1 and DK2, wherein The first distillation column DK1 has at least one reboiler SV1 and the second distillation column DK2 has at least one reboiler SV2; The reboiler SV1 is fed with the stream taken out at the lower end of DK1, and the stream is directed back to DK1 after passing through the corresponding reboiler; The reboiler SV2 is fed with a stream taken off at the lower end of DK2, and the stream is directed back to DK2 after passing through a corresponding reboiler; wherein the method comprises the following steps: (a) directing the raffinate-2 stream to a first distillation column DK1 and separating it in DK1 into at least one vapor stream BS1, wherein the vapor stream BS1 comprises at least 1-butene and isobutane and is withdrawn at the top of DK1, and at least one bottom stream comprises at least 1-butene, n-butane and 2-butene and is withdrawn at the bottom of DK1; (b) compressing at least a portion of vapor stream BS1, thereby producing a compressed stream VB1 relative to vapor stream BS1; (c) energy is transferred from the compressed stream VB1 to the stream in the reboiler SV1; (d) conducting the stream VB1 at least partially to a second distillation column DK2 and separating it in DK2 into at least one vapor stream BS2, which comprises at least isobutane and is taken off at the top of DK2, and at least one bottom stream, which comprises at least 1-butene and is taken off at the bottom of DK2; (e) at least partially compressing vapor stream BS2, thereby producing a compressed stream VB2 relative to vapor stream BS2; and (f) Energy is transferred from the compressed stream VB2 to the stream in the reboiler SV2.

2. The process according to claim 1, wherein the distillation columns DK1 and DK2 are operated at the same top pressure or at similar top pressures, wherein in the case of similar top pressures the top pressures differ by at most 20%, preferably by at most 15%.

3. The process according to claim 1 or 2, wherein an MTBE or ETBE synthesis is arranged between the distillation columns DK1 and DK2, which is fed with the stream VB1. 4 . The process according to claim 1 , wherein the stream VB1 is conducted to a flash vessel and expanded there, whereby a liquid phase FP1 of the stream VB1 is obtained. 5 . The process according to claim 4 , wherein at least a portion FP1a of the liquid phase FP1 is introduced into the distillation column DK2 , preferably by means of a pump. 6 . The process according to claim 5 , wherein a further part FP1b of the liquid phase FP1 is returned as reflux to the distillation column DK1 .

7. The process according to any of the preceding claims, wherein energy is transferred from stream FP1b to the raffinate 2 stream before it is introduced into the first distillation column DK1.

8. The process according to any of the preceding claims, wherein the temperature at the bottom of the first distillation column DK1 is in the range from 40 to 110°C, preferably from 50 to 100°C.

9. The process according to any of the preceding claims, wherein the temperature at the bottom of the second distillation column DK2 is in the range from 30 to 100°C, preferably from 45 to 80°C. 10 . The process according to claim 1 , wherein the distillation column DK1 has 150 to 300 trays. 11 . The process according to claim 1 , wherein the distillation column DK2 has 150 to 300 trays.

12. The process according to any of the preceding claims, wherein only a single compressor is used for the compression of streams BS1 and BS2.

13. The process according to claim 1, wherein the stream VB2 is expanded in a flash vessel, where a liquid phase FP2 is obtained.

14. The process according to claim 12, wherein at least a portion FP2a of the liquid phase FP2 is discharged from the process as a product stream, preferably by means of a pump.

15. The process according to claim 13, wherein a further part FP2b of the liquid phase FP2 is returned as reflux to the distillation column DK2.

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