Energy efficient process for separation of 1-butene from hydrocarbon stream using heat transfer medium

Abstract

The present invention relates to an energy efficient process for separating 1-butene from a hydrocarbon stream using a heat transfer medium. Specifically, the subject of the invention is a process for separating 1-butene from a C4 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, in which the heat of condensation is made available by means of a heat transfer medium W in order to save energy costs and reduce CO2 emissions.

Description

FIELD OF THE INVENTION

[0001] The present invention relates to a process for separating 1-butene from a C4 hydrocarbon stream containing at least 1-butene, 2-butene, n-butane and isobutane in a separation unit, said separation unit comprising at least two distillation columns DK1 and DK2, wherein the condensation heat can be utilized by means of a heat-carrying medium to save energy costs and reduce CO 2 emissions. BACKGROUND OF THE INVENTION

[0002] 1-Butene can be obtained in large quantities from industrial C4 hydrocarbon streams (e.g. C4 fractions from steam crackers or FCC units). These C4 hydrocarbon streams basically consist 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 only by distillation.

[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 called 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 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 much as possible, for example by MTBE or ETBE synthesis. By removing isobutene, a C4 hydrocarbon stream containing linear butenes (1- and 2-butene) as well as the saturated hydrocarbons isobutane and n-butane is produced (usually called 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. This method is disclosed, for example, in DE 102005062700A1.

[0006] In the known processes, the energy required for separating 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, using heating steam means a cost factor that cannot be underestimated. In addition, in terms of logistics, the recycling of waste heating steam is not always simple, because the steam can only be returned within certain conditions (pressure, temperature, etc.). In addition, the generation of heating steam produces a large amount of CO2 . SUMMARY OF THE INVENTION

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

[0008] This object is achieved by an embodiment of the method set forth in 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 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 withdrawn at the lower end of DK1 is fed to the reboiler SV1, and the stream is returned to DK1 after passing through the corresponding reboiler;

[0011] a stream withdrawn at the lower end of DK2 is fed to the reboiler SV2, and the stream is returned 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 being withdrawn at the top of DK1, and the bottom stream containing at least 1-butene and 2-butene and being withdrawn at the bottom of DK1;

[0013] (b) separating the vapor stream into at least two sub-streams BS1a and BS1b;

[0014] (c) transferring energy from BS1a to a liquid or gaseous heat carrier medium W to produce a heat carrier medium W1;

[0015] (d) guiding the part BS1b of the vapor stream BS1 other than BS1a to the reboiler SV2, and transferring energy from BS1b to the stream in the reboiler SV2 here;

[0016] (e) guiding the stream BS1a and the stream BS1b at least partially to the second distillation column DK2 and separating them in DK2 into at least one vapor stream BS2 and at least one product stream, the vapor stream BS2 containing at least isobutane and being withdrawn at the top of DK2, and the product stream containing at least 1-butene and being withdrawn at the bottom of DK2;

[0017] (f) Energy is transferred from BS2 to a liquid or gaseous heat transfer medium W, thereby generating a heat transfer medium W2;

[0018] (g) At least a portion of the heat transfer medium W2 is compressed, thereby generating a compressed heat transfer medium W2.1 having a higher pressure than the heat transfer medium W2;

[0019] (h) The heat transfer medium W1 is mixed with the compressed heat transfer medium W2.1, thereby generating a mixed heat transfer medium W3;

[0020] (i) At least a portion of the mixed heat transfer medium W3 is compressed, thereby generating a compressed heat transfer medium W3.1 having a higher pressure than the mixed heat transfer medium W3;

[0021] (j) Energy is transferred from the compressed heat transfer medium W3.1 to the stream in the reboiler SV1.

[0022] An advantage of the method according to the invention is the thermal integration by means of at least one heat transfer medium, through which energy is transferred to the stream present therein in the reboiler SV1, so that energy is introduced at the bottom. As a result of the energy transfer in the reboiler SV1 in the first distillation column DK1, less heating steam, or even no heating steam at all, is required to heat the distillation column DK1. Since the reboiler SV2 can also be operated with a portion of the vapor, (almost) complete electrification of the energy-intensive process can be achieved, which in turn enables the use of green electricity. This saves a considerable amount of energy costs and CO 2 emissions.

[0023] 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. Corresponding streams are 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.

[0024] The raffinate 2 used preferably contains less than 1000 ppm, preferably less than 500 ppm of isobutene. If a higher amount of isobutene is present in the starting feed 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 (for MTBE) or ethanol (ETBE), and then MTBE or ETBE is separated out. Thus, the isobutene concentration upstream of the second distillation column DK2 can be greatly reduced. This is because isobutene will be produced at the bottom of the second distillation column and thus in 1-butene.

[0025] Further preferably, the raffinate 2 used in the process 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 processes are known to those skilled in the art, for example from EP 3680224 A1.

[0026] The raffinate-2 stream used can 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 nipple (Euter) in the distillation vessel of DK1 and / or DK2. The bottom products of DK1 and DK2 are characterized by having a very low butadiene and water content, preferably each less than 100 ppm, particularly preferably less than 5 ppm.

[0027] 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 the 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 in particular be selected such that heat can be transferred in the reboiler. 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.

[0028] The energy required for the separation task is introduced into the first distillation column DK1 via the reboiler SV1. The feed to the reboiler SV1 is the stream withdrawn from the lower end of DK1, and after passing through the corresponding reboiler, this stream is then guided back to DK1. The stream is heated during its passage through the reboiler SV1.

[0029] 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, the feed to the reboiler SV2 is the stream withdrawn from the lower end of DK2, and after passing through the corresponding reboiler, this stream is then guided back to DK2. The stream is heated during its passage through the reboiler SV2 and is at least partially evaporated during this process.

[0030] According to the present invention, a "reboiler" means an evaporator that heats the bottom of the corresponding distillation column. Such reboilers are usually arranged outside the corresponding 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 withdrawn from the bottom of the distillation column through an outlet and fed into the reboiler. The evaporated stream (optionally with a liquid residue portion) is returned through at least one inlet to the bottom region of the corresponding distillation column.

[0031] Suitable evaporators that can be used as reboilers are, for example, natural circulation evaporators, forced circulation evaporators, forced circulation evaporators with expansion, 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 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 also be used alternatively.

[0032] The raffinate 2 guided 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 withdrawn at the top of DK1, and the bottom stream contains at least 1-butene and 2-butene and is withdrawn at the bottom of DK1. This bottom stream can be guided to an oligomerization reaction. The vapor stream BS1 can also be withdrawn 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, more preferably 50 to 100 °C.

[0033] In principle, the raffinate-2 stream can be directed to the first distillation column DK1 via one or more feed points. If there are multiple feed points for the raffinate-2 stream, then multiple separate streams are accordingly directed to the distillation column. In an embodiment of the present invention in which the raffinate-2 stream is directed to the distillation column DK1 as two or more separate streams, it is advantageous when the feed points of the individual streams are substantially at the same height on the distillation column DK1.

[0034] The pressure and temperature of the vapor stream BS1 are given below. This particularly relates to the pressure and temperature of at least one vapor stream BS1 when withdrawn 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, more preferably in the range of 60°C to 80°C.

[0035] 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 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 also known to those skilled in the art and can equally be used.

[0036] 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.

[0037] In a particularly preferred embodiment of the present invention, the distillation column DK1 comprises a plurality of trays, preferably 150 to 300 trays, further preferably 170 to 220 trays.

[0038] In the context of the present invention, the meaning of taking out at least one vapor stream BS1 containing at least 1-butene and isobutane at the top of the distillation column DK1 in particular means that at least one vapor stream BS1 is taken out as a top stream or as a side fraction above an internal component in the distillation column DK1.

[0039] In the context of the present invention, the meaning of taking out at least one bottom stream containing at least 1-butene and 2-butene at the bottom of the distillation column DK1 in particular means that at least one bottom stream is taken out directly at the bottom of the distillation column DK1 or at the lower trays.

[0040] The distillation column DK1 is preferably operated in a reflux mode. The meaning of "reflux" means that at least part of the vapor stream BS1 taken out at the top of the distillation column DK1 is re-fed into the distillation column DK1. In the case of establishing such a reflux, the reflux ratio is preferably from 2 to 30, more preferably from 5 to 20, and particularly preferably from 8 to 15.

[0041] The reflux can be established by installing a condenser at the top of the distillation column DK1. The vapor stream BS1 is partially condensed in the condenser and re-fed into the distillation column DK1. The vapor stream or a part thereof can also be used as the reflux back to the distillation column only after compression and expansion. Generally speaking and in the context of the present invention, the reflux ratio means the ratio of the part of the mass flow rate (kg / h) taken out from the column that is returned (refluxed) to the column in liquid form to the part of the mass flow rate (kg / h) that is discharged from the corresponding column in liquid or gaseous form.

[0042] After taking out the vapor stream BS1, the vapor stream BS1 is separated into at least two sub-streams BS1a and BS1b in step (b). The separation can in principle be carried out in a known manner, for example by means of a splitter (wherein a compressor and / or a regulating valve are used for control (Regelung)). Also conceivable here is a control method by which the mass flow rates of BS1a and BS1b are adjusted with the change of specific parameters.

[0043] Subsequently, in step (c), energy is transferred from the sub-stream BS1a to a liquid or gaseous heat carrier medium W, generating a heat carrier medium W1. In this case, the energy to be transferred is preferably heat, and a heated heat carrier medium W1 is generated. By transferring energy to the heat carrier medium W, the energy content of BS1a is reduced, that is, the stream will be cooled and / or condensed.

[0044] The heat-carrying medium W used can be any working medium familiar to those skilled in the art. The heat-carrying medium W is preferably selected from water; alcohols; alcohol-water mixtures; salt solutions; ammonia; mineral oils such as diesel oil; heat transfer oils such as silicone oil; bio-oils such as limonene; and aromatic or aliphatic hydrocarbons such as dibenzyltoluene, more preferably water, methanol, ethanol, propanol, n-pentane, n-butane, n-hexane, n-propane or ammonia, and particularly preferably water.

[0045] If the heat-carrying medium W is used in the liquid phase in step (c), i.e., the liquid heat-carrying medium W, and energy, preferably heat, is supplied to it in step (c), the heat-carrying medium W will at least partially evaporate, and thus a gaseous heat-carrying medium W1 will be obtained. If the heat-carrying medium W is used in the gas phase in step (c), i.e., the gaseous heat-carrying medium W, and energy, preferably heat, is supplied to it in step (c), the gaseous heat-carrying medium W1 will likewise be obtained.

[0046] In the context of the present invention, the expression "liquid heat-carrying medium" means that > 50% by weight, more preferably > 55% by weight, more preferably > 75% by weight, more preferably > 90% by weight, and particularly preferably > 99% by weight of the heat-carrying medium used in step (c) is in the liquid state, in each case based on the total weight of the heat-carrying medium used in step (c).

[0047] In the context of the present invention, the expression "gaseous heat-carrying medium" means that > 30% by weight, more preferably > 50% by weight, more preferably > 75% by weight, more preferably > 90% by weight, and particularly preferably > 99% by weight of the heat-carrying medium used in step (c) is in the gaseous state, in each case based on the total weight of the heat-carrying medium used in step (c).

[0048] The energy transfer in step (c) can be carried out by methods known to those skilled in the art or by heat exchangers known to those skilled in the art, such as the evaporator already mentioned. In this case, the heat exchanger can also be a condenser for condensing BS1a. The advantage of this is that no additional condenser needs to be installed.

[0049] After the energy transfer described in step (c), the heat-carrying medium W1 preferably has an elevated temperature and / or an elevated pressure compared to the heat-carrying medium W. In a preferred embodiment of the present invention, W1 has a temperature in the range of 30 °C to 80 °C. The pressure of W1 is preferably in the range of 1 bar to 20 bar, preferably 3 bar to 12 bar.

[0050] It is readily understood that the heat-carrying medium W1 corresponds to the heat-carrying medium W, and the difference between W and W1 lies only in their respective pressures and / or temperatures, and, depending on the circumstances, when W has been used in liquid form, in the state of matter.

[0051] In step (d) of the method according to the invention, at least a part of BS1b other than BS1a in the vapor stream BS1 is guided to the reboiler SV2, where energy is transferred from BS1b to the stream present in the reboiler. By step (d), the energy of BS1b is reduced such that BS1b is preferably at least partially condensed.

[0052] The transfer of energy from BS1b to the stream in the reboiler SV2 preferably occurs by BS1b heating the stream in the reboiler SV2 and is preferably direct. By

[0053] "direct transfer" means that BS1b and the stream in SV2 do not come into direct contact, but rather energy, in particular heat, is transferred from BS1b to the stream in SV2 without an additional heat transfer medium. The reboiler SV2 used can be a heat transfer device or heat exchanger familiar to those skilled in the art, in particular the evaporator already mentioned above.

[0054] After the streams BS1a and BS1b have transferred energy to the heat-carrying medium W or have passed through the reboiler SV2 and transferred energy to the respective streams, in step (e), these streams BS1a and BS1b are at least partially guided to the second distillation column DK2, and then the separation between isobutane and 1-butene is carried out in the second distillation column DK2 to obtain as pure a 1-butene stream as possible. The separation in DK2 is carried out to separate into at least one vapor stream BS2 and at least one product stream. The vapor stream BS2 contains at least isobutane and is taken out at the top of DK2, and the product stream contains at least 1-butene and is taken out at the bottom of DK2. The two streams BS1a and BS1b can be guided to the second distillation column DK2 independently of each other as different feed streams or together.

[0055] Before guiding the streams to the second distillation column in step (e), according to a preferred embodiment, the streams BS1a and BS1b are guided to a flash vessel and expanded therein to obtain the liquid phases FP1 of the streams BS1a and BS1b. The flash vessel can additionally include a condenser in order to condense a part of the obtained gas phase.

[0056] In a preferred embodiment of the invention, the streams BS1a and BS1b are guided to the second distillation column together. For this purpose, in particular, the two streams are made to have the same pressure and the same temperature. If the streams BS1a and BS1b are to be guided to the distillation column together, it is preferred to combine the streams BS1a and BS1b in the flash vessel and obtain them as a common liquid phase FP1.

[0057] Then, at least a part FP1a of the liquid phase FP1 is guided to the distillation column DK2 according to step (e). For this purpose, in a particularly preferred embodiment, a pump is used. Pumps known to those skilled in the art can be used here. Suitable pumps are, for example, chemical standard pumps.

[0058] 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 the raffinate-2 stream is introduced 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 evaporators known to those skilled in the art can be used, as described above.

[0059] In the second distillation column DK2, the streams each containing at least isobutane and 1-butene are separated according to step (e) into at least one vapor stream BS2 containing at least isobutane and taken off at the top of DK2, and at least one product stream containing at least 1-butene and taken off at the bottom of DK2.

[0060] The distillation column DK2 for separating the two streams BS1a and BS1b or FP1a 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 beds of bulk packings. 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 the trademark name. In addition to the mentioned internals, other suitable internals are also known to those skilled in the art and can equally be used.

[0061] Preferred internals have a low pressure drop per theoretical plate. For example, structured packings and bulk packings have a significantly lower pressure drop per theoretical plate than trays. The advantage of this is that the pressure drop in the distillation column DK2 remains as low as possible, so the mechanical power of the compressor and the temperature of the two streams BS1a and BS1b or FP1a to be evaporated remain low.

[0062] In a particularly preferred embodiment of the present invention, the second distillation column DK2 comprises a plurality of trays, preferably 150 to 300 trays, more preferably 170 to 220 trays.

[0063] In the context of the present invention, the meaning of taking out 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 taken out as a top stream or as a side stream above an internal component in the distillation column DK2.

[0064] In the context of the present invention, the meaning of taking out 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 taken out 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, and particularly preferably at least 99.6 wt% of 1-butene. 1-Butene is the target product of this process, and thus the product stream is discharged from the process. 1-Butene can be used, for example, as a comonomer in the production of polyethylene.

[0065] 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 taken out from the second distillation column DK2. This is because butane is also obtained as a high boiler in DK2 and thus together with 1-butene. This contaminates the 1-butene. Therefore, it should be ensured that the raffinate-2 stream separation in DK1 operates in such a way that almost no butane enters DK2. Thus, the streams led to DK2 (BS1a and BS1b or FP1a) preferably contain at most 500 to 900 ppm of butane, based on the total amount of the stream.

[0066] During the process according to the present invention, the temperature at the bottom of the second distillation column DK2 is preferably in the range of 30 to 100 °C, preferably 45 to 80 °C. Further preferably, the pressure at the top of the second distillation column DK2 is in the range of 3 to 12 bar absolute pressure, preferably 5 to 10 bar absolute pressure.

[0067] The distillation column DK2 can also be operated with reflux. The meaning of "reflux" means that at least part of the vapor stream BS2 taken out from the top of the distillation column DK2 is re-fed back into the distillation column DK2. In the case of establishing such a reflux, the reflux ratio is preferably 10 to 80, particularly preferably 30 to 50.

[0068] Reflux can be established by installing a condenser at the top of distillation column DK2. Vapor stream BS2 is partially condensed in the condenser and re-fed back into distillation column DK2. 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 respective column in liquid or gaseous form.

[0069] The vapor stream BS2 obtained in distillation column DK2 is used for heat integration. In step (f), energy is transferred from vapor stream BS2 to a liquid or gaseous heat transfer medium W, thereby producing heat transfer medium W2. In this case, the energy to be transferred is preferably heat, and a heated heat transfer medium W2 is produced. Transferring the energy to heat transfer medium W will reduce the energy content of BS2, i.e., the stream is cooled and / or condensed.

[0070] The heat transfer medium W employed can be any working medium familiar to those skilled in the art. Heat transfer medium W is preferably selected from water; alcohols; alcohol-water mixtures; aqueous salt solutions; ammonia; mineral oils such as diesel oil; heat transfer oils such as silicone oil; bio-oils such as limonene; and aromatic or aliphatic hydrocarbons such as dibenzyltoluene, more preferably water, methanol, ethanol, propanol, n-pentane, n-butane, n-hexane, n-propane or ammonia, and particularly preferably water. The heat transfer medium W used in steps (c) and (f) is preferably the same. Particularly preferably, there is a heat transfer medium circuit in which heat transfer medium W passes through steps (c) and (f) to (j).

[0071] If the heat transfer medium W is used in liquid phase in step (f), i.e., liquid heat transfer medium W, and energy, preferably heat, is supplied to it in step (f), then the heat transfer medium W will at least partially evaporate, and thus a gaseous heat transfer medium W2 will be obtained. If the heat transfer medium W is used in gas phase in step (f), i.e., gaseous heat transfer medium W, and energy, preferably heat, is supplied to it in step (f), then a gaseous heat transfer medium W2 will also be obtained.

[0072] In the context of the present invention, the expression "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 (f) is in the liquid state, in each case based on the total weight of the heat transfer medium used in step (f).

[0073] In the context of the present invention, the expression "gaseous heat - carrying medium" means that more than 30% by weight, further preferably more than 50% by weight, further preferably more than 75% by weight, further preferably more than 90% by weight, and particularly preferably more than 99% by weight of the heat - carrying medium used in step (f) is in the gaseous state of matter, in each case based on the total weight of the heat - carrying medium used in step (f).

[0074] The energy transfer in step (f) can be carried out by methods known to those skilled in the art or by heat exchangers known to those skilled in the art (such as the evaporator already mentioned). In this case, the heat exchanger can also be a condenser for condensing BS2. The advantage of this is that no additional condenser needs to be installed.

[0075] After the energy transfer described in step (f), the heat - carrying medium W2 preferably has an elevated temperature and / or an elevated pressure compared to the heat - carrying medium W. In a preferred embodiment of the present invention, W1 preferably has a temperature in the range of 30 °C to 80 °C. The pressure of W2 is preferably in the range of 1 bar to 20 bar, preferably 2 bar to 8 bar. In a preferred embodiment of the present invention, the pressure and / or temperature of the heat - carrying medium W2 is less than the pressure and / or temperature of the heat - carrying medium W1.

[0076] After the energy has been transferred from the vapor stream BS2 to the heat - carrying medium in step (f), BS2 can be discharged from the process as an isobutane stream IB1. However, before removing BS2 as IB1 from the process, in a preferred embodiment of the present 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 part of the obtained gas phase.

[0077] Then, at least a part FP2a of the liquid phase FP2 can be discharged from the process as an isobutane stream IB1. For this purpose, in a particularly preferred embodiment, a pump is used. In some cases, and given a sufficient pressure ratio, it will also be possible not to use a pump. If a pump is used, pumps known to those skilled in the art can be used. Suitable pumps are, for example, chemical standard pumps. Further preferably, a part FP2b of the liquid phase FP1 other than FP2a is returned as a reflux to the second distillation column DK2.

[0078] In the subsequent step (g), at least a part of the heat - carrying medium W2 is compressed, thereby producing a heat - carrying medium W2.1 which has been compressed relative to W2 and is at a higher pressure than the heat - carrying medium W2. The pressure of the compressed W2.1 is preferably in the range of 1 bar to 20 bar, preferably 3 bar to 12 bar. Further preferably, the pressure of the compressed heat - carrying medium W2.1 is the same as or differs by at most ± 10% from the pressure of the heat - carrying medium W1.

[0079] In step (g), at least a part of the heat-carrying medium W2 can be compressed in any manner known to a person skilled in the art. For example, the compression can be carried out mechanically and in a single stage or in multiple stages. In this context, the meaning of "single stage" means that the compression is carried out from one pressure level to another pressure level. The meaning of "multiple stages" means that the compression is first carried out to pressure level X and then from X to pressure level Y. In a multi-stage compression, compressors of the same construction type or different construction types can be used. The multi-stage compression can be achieved with one or more compressors. The use of single-stage compression or multi-stage compression depends on the compression ratio and thus on the pressure to which the heat-carrying medium W2 is to be compressed.

[0080] The heat-carrying medium W1 in step c) is preferably at a higher pressure than the heat-carrying medium W2 in step f). The heat-carrying medium W2 is brought to the same or a similar pressure compared to W1 by the compression in step (g). In this context, the expression "similar pressure" means that the pressure of W1 and the pressure of the compressed heat-carrying medium W2.1 differ from each other by less than 5%, preferably by less than 1%.

[0081] In the method according to the invention, suitable compressors, in particular compressors for compressing the heat-carrying medium W2, are any compressors known to a 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 turbine compressors, piston compressors, screw compressors, centrifugal compressors or axial compressors.

[0082] In the subsequent step (h), the compressed heat-carrying medium W2.1 is mixed with the heat-carrying medium W1, thereby producing a mixed heat-carrying medium W3. The mixing can be simply achieved by joining two pipelines without special internal components. This is basically familiar to a person skilled in the art. The mixing of the two heat-carrying media W2.1 and W1 has the following advantage: the superheating of the heat-carrying medium W1 can contribute to the superheating of the heat-carrying medium W2.1. Therefore, no other heat exchanger needs to be present before the mixed heat-carrying medium W3 is compressed in the subsequent step (i).

[0083] In the step (i) already mentioned, at least a part of the heat-carrying medium W3 is compressed, thereby producing a heat-carrying medium W3.1 which has been compressed relative to W3 and has a higher pressure than the heat-carrying medium W3. The pressure of W3.1 after compression is preferably within the range of 5 bar to 30 bar, preferably in the range of 10 bar to 20 bar.

[0084] In step (i), at least a portion of the heat transfer medium W3 can be compressed in any 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 this regard, "single stage" means that the compression is carried out from one pressure level to another pressure level. "Multiple stages" means that the compression is first carried out to pressure level X and then from X to pressure level Y. In a multi-stage compression, multiple compressors of the same construction type or different construction types can be used. The multi-stage compression can be achieved with one or more compressors. The use of single-stage compression or multi-stage compression depends on the compression ratio and thus on the pressure to which the heat transfer medium W3 is to be compressed.

[0085] In the method according to the invention, suitable compressors, in particular compressors for compressing the heat transfer medium W3, are any compressors known to those 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 turbine compressors, piston compressors, screw compressors, centrifugal compressors or axial compressors.

[0086] In step (j) of the method according to the invention, energy is transferred from the compressed heat transfer medium W3.1 to the stream in the reboiler SV1. Step (j) reduces the energy of W3.1 such that W3.1 is preferably at least partially condensed. According to the invention, the phrase "energy transfer" particularly means "heating", i.e., transferring energy in the form of heat.

[0087] The transfer of energy from W3.1 to the stream in the reboiler SV1 is preferably effected by heating the stream in the reboiler SV1 with W3.1, preferably directly. The meaning of direct transfer is that, although the streams of W3.1 and in SV1 do not come into direct contact, the energy, in particular heat, is transferred from W3.1 to the stream in SV1 without an additional heat transfer medium. The reboiler SV1 used can be a heat transfer device or heat exchanger known to those skilled in the art, in particular an evaporator.

[0088] The energy transfer in step (j) can be effected by methods known to those skilled in the art or by heat exchangers known to those skilled in the art. Suitable evaporators that can be used as heat exchangers are, for example, natural circulation evaporators, forced circulation evaporators, forced circulation evaporators with expansion, kettle evaporators, falling film evaporators or thin film evaporators. In addition to the above-mentioned evaporators, any other evaporator design known to those skilled in the art and suitable for a distillation column can alternatively be used.

[0089] In a basic embodiment of the invention, the two streams W2 and W3 are each compressed with a single compressor. In a preferred embodiment of the invention, the two streams W2 and W3 are compressed in a single compressor (preferably a multi-stage compressor). The number of stages required depends on the target compression ratio.

[0090] As described above, it is preferred to convey the heat-carrying medium in a circuit. This means that after the energy is transferred in step (j), the heat-carrying medium W3.1 is returned and used again in steps (c) and (f). For this purpose, in a preferred embodiment of the present invention, only a single heat-carrying medium is used throughout the process. Thus, the heat-carrying medium W used in steps (c) and (f) is the same. The heat-carrying medium W3.1 can also be cooled before being partially guided as the heat-carrying medium W to step (c) and partially to step (f). The reason for this is that the heat-carrying medium W, which absorbs the heat energy of condensation from the vapor streams BS1 and BS2, should preferably be at a specific pressure and temperature level in order to be able to absorb the required amount of heat energy in the heat exchanger. For this purpose, it may be necessary to cool the heat-carrying medium W3.1 after the energy is transferred in the reboiler. In order to utilize this energy, the cooling can be carried out in a heat exchanger through which the heat-carrying medium W2 is preheated. This in turn can result in less energy being required to be introduced by the compressor(s).

[0091] After the energy transfer in step (j) of the method according to the invention, the heat-carrying medium W3.1 can be used to preheat the raffinate-2 stream, which is then guided to the first distillation column. Subsequently, the heat-carrying medium W3.1 will return after preheating and be partially guided as the heat-carrying medium W to step (c) and partially to step (f). If there is no preheating, the heat-carrying medium W3.1 returns without this additional step and is partially guided as the heat-carrying medium W to step (c) and partially to step (f).

[0092] The heat integration carried out with the heat pump described herein can also be combined with other heat integration measures. One or more vapor compressions can also be provided herein. Description of the Drawings

[0093] The present invention will be described below with reference to the accompanying drawings. The drawings are for illustrative purposes only and should not be construed as restrictive.

[0094] Figure 1shows an embodiment according to the prior art, namely a conventional dual-pressure circuit (see Example 1). The raffinate-2 stream (1) is led to the first distillation column DK1, in which it is separated into a vapor stream BS1 and a bottoms stream (2). The vapor stream BS1 contains at least 1-butene and isobutane and is taken from the top of DK1, and the bottoms stream (2) contains at least 1-butene and 2-butene and is taken from the bottom of DK1. The stream (2) can be led to an oligomerization reaction (not shown). The bottom of column DK1 is heated in a reboiler SV1 with, for example, heating steam. The vapor stream BS1 is separated into two vapor streams BS1a and BS1b. A part BS1b of the vapor stream is led to the reboiler SV2, without additional compression, where it transfers energy to the stream present therein. The stream is heated after coming out from the bottom and then returns again. BS1a is cooled by a heat exchanger WT-1. The two streams BS1a and BS1b are sent to a flash vessel, in which expansion generates a liquid phase FP1. The liquid phase is separated into two streams FP1a and FP1b. FP1a is led to the second distillation column DK2, and FP1b is led as reflux to the first distillation column. In distillation column 2, the stream is separated into a vapor stream BS2 and a product stream (3). The vapor stream BS2 contains at least isobutane and is taken from the top of DK2, and the product stream (3) contains at least 1-butene and is taken from the bottom of DK2. The vapor stream BS2 is cooled in a heat exchanger WT-2 and sent to a flash vessel, in which expansion generates a liquid phase FP2. A part FP2a of the FP2 phase will leave the process as an isobutane stream (4), and another part FP2b will return as reflux to the second distillation column.

[0095] Figure 2 shows an embodiment that is not of the present invention, which is mostly the same as the embodiment shown in Figure 1 . The difference is that in the heat exchanger WT-1, energy is transferred from the stream BS1a to the heat transfer medium, and the heat transfer medium is compressed by a compressor V1 and then used to heat the bottom of DK1 in the reboiler SV1. An additional reboiler SV1a may be required to sufficiently heat the bottom of DK1.

[0096] Figure 3 shows an embodiment that is not of the present invention, which is mostly the same as the embodiment shown in Figure 1 . The difference is that in the heat exchanger WT-2, energy is transferred from the stream BS2 to the heat transfer medium, and the heat transfer medium is compressed by a compressor V2 and then used to heat the bottom of DK1 in the reboiler SV1. In the recirculation operation, the returned heat transfer medium is used in the heat exchanger WT-3 to preheat the heat transfer medium before compression. Here, an additional reboiler SV1a may also be required to sufficiently heat the bottom of DK1.

[0097] Figure 4 shows an embodiment of the present invention, which is mostly the same as the embodiment shown in Figures 1 to 3 . The difference is that two heat pumps from Figure 2 and Figure 3 are combined. In the heat exchanger WT-2, energy is transferred from the stream BS2 to the heat-carrying medium, and the heat-carrying medium is compressed in the compressor V2. In the heat exchanger WT-1, energy is transferred from the stream BS1a to the heat-carrying medium, and the two heat-carrying media are mixed. The mixed heat-carrying medium is then compressed in the compressor V3 and used to heat the bottom of DK1 in the reboiler SV1. In this embodiment, no additional reboiler is required in DK1. Detailed Description of the Invention

[0098] Examples

[0099] All the following examples use a raffinate-2 stream of 55 t / h. The 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 45 ppm and water 590 ppm.

[0100] The amount of energy required for the operation of the apparatus for separating 1-butene from raffinate 2 detailed in the examples was calculated by simulation using Aspen V10. The substance data was verified through operating data and operating tests.

[0101] Examples

[0102] Example 1 (not of the present invention):

[0103] In the embodiment according to Figure 1 , only direct heat integration was implemented between columns DK1 and DK2 (as disclosed in DE102005062700 A1). In this case, column DK1 was operated at a top pressure of 11 bar, while column DK2 was operated at a top pressure of 7 bar. Therefore, a part of the vapor stream BS1 could be used to transfer heat to DK2 through the reboiler SV2. For an amount of 10.3 t / h of 1-butene at a purity of 99.6% 1-butene in DK2, the heat required was 10.3 MW. For this purpose, a 125.5 t / h vapor stream from DK1 was used to heat DK2. Nevertheless, 15.9 MW still needed to be introduced into DK1 through an external heat source / media (such as heating steam).

[0104] Example 2 (not of the present invention):

[0105] The interconnection concept according to the invention makes the unused condensation heat available in DK1. Only 4 MW of the condensation heat from DK1 becomes available here via a heat pump. As in Example 1, column DK1 is operated at a top pressure of 11 bar absolute and a top temperature of 72 °C. Thus, the condensation heat from DK1 can be used to evaporate methanol at 1.1 bar. The gaseous methanol then passes through a preheater to prevent cavitation corrosion in the downstream compressor. The methanol is brought to a certain pressure or temperature level such that heat can be transferred via SV1. For this purpose, an electrical power of 450 kW is required. The condensed methanol flows back from SV1 to the condenser of DK1 via preheating. Thus, the external heating power can be reduced from 15.9 MW to 11.45 MW. The additional external heating power is introduced via an additional evaporator SV1a.

[0106] Example 3 (not according to the invention):

[0107] The interconnection concept according to the invention makes the unused condensation heat available. Only 9.9 MW of the condensation heat from DK2 becomes available here via a heat pump. As in Example 1, column DK2 is operated at a top pressure of 7 bar absolute / top temperature of 50 °C. Methanol (as in Example 2) is not suitable as a heat transfer medium here because the methanol has to be evaporated under reduced pressure. In this example, n-pentane is used as the working medium. The condensation heat from DK2 is used to evaporate n-pentane at an absolute pressure of 1.4 bar. The gaseous n-pentane has to be superheated before subsequent compression. To make the n-pentane available for DK1, it is compressed to a pressure level of 5 bar absolute pressure. This requires an electrical power of 2000 kW. Using the interconnection according to the invention, 11.9 MW of external heating power can be replaced by 2000 kW of electrical power. The still missing 4 MW of external heating power is introduced via an additional evaporator SV1a.

[0108] Example 4 (according to the invention):

[0109] The interconnection concept according to the invention makes the unused condensation heat available. With the aid of a multistage heat pump, a total of 13.5 MW of condensation heat from the two columns DK1 and DK2 becomes available here. As in Example 1, column DK2 is operated at a top pressure of 7 bar absolute / top temperature of 50 °C. The condensation heat from DK2 is used to evaporate n-pentane at an absolute pressure of 1.4 bar. The gaseous n-pentane has to be superheated before subsequent compression. First, the gaseous n-pentane is compressed to a pressure level of 2.1 bar absolute pressure using the first compressor stage. In addition, the condensation heat from DK1 is used to evaporate n-pentane at 2.1 bar absolute pressure. The gaseous n-pentane stream formed from the condensation heat of DK1 is sucked in together with the compressed n-pentane stream and compressed to a pressure level of 5 bar absolute pressure. A total electrical power of 3.2 MW is required for full electrification.

[0110] The results of Examples 1 to 4 are summarized in Table 1 below.

[0111] Table 1: Summary of Examples

[0112] Example 1 Example 2 Example 3 Example 4 External heating power [MW] 15.9 11.45 4 0 Electric power of the compressor [MW] 0 0.55 2 3.2

[0113] It has been found that the method embodiments of the present invention for 1-butene separation have the following effects: compared with the known technical solutions, much less external heating power needs to be used. Therefore, the potential for savings is huge. The additional electrical power required for compressor operation is much smaller, and CO 2 neutralization operation can be achieved when using green electricity.

Claims

1. A process for separating 1-butene from a raffinate-2 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 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 and 2-butene and is withdrawn at the bottom of DK1; (b) separating the vapor stream into at least two substreams BS1a and BS1b; (c) Energy is transferred from BS1a to the liquid or gaseous heat carrier medium W, thereby producing heat carrier medium W1; (d) directing a portion BS1b of the vapor stream BS1 other than BS1a to a reboiler SV2, and transferring energy therefrom from BS1b to the stream in the reboiler SV2; (e) conducting stream BS1a and stream BS1b at least partially to a second distillation column DK2 and separating 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 product stream, which comprises at least 1-butene and is taken off at the bottom of DK2; (f) energy is transferred from BS2 to the liquid or gaseous heat carrier medium W, thereby producing the heat carrier medium W2; (g) compressing at least a portion of the heat transfer medium W2, thereby producing a compressed heat transfer medium W2.1 having a higher pressure than the heat transfer medium W2; (h) mixing the heat transfer medium W1 with the heat transfer medium W2.1, thereby producing a mixed heat transfer medium W3; (i) compressing at least a portion of the mixed heat medium W3, thereby producing a compressed heat medium W3.1 having a higher pressure than the mixed heat medium W3; (j) Energy is transferred from the compressed heat transfer medium W3.1 to the stream in the reboiler SV1. 2 . The process according to claim 1 , wherein stream BS1a and stream BS1b are conducted to a flash vessel and expanded therein, thereby producing vapor stream BS1a and liquid phase FP1 of vapor stream BS1b. 3 . The process according to claim 2 , wherein the stream BS1a and the stream BS1b are combined in a flash vessel and obtained as a common liquid phase FP1 . 4 . The process according to claim 3 , wherein at least a portion FP1a of the liquid phase FP1 is conducted to a distillation column DK2 . 5 . The process according to claim 4 , wherein a further part FP1b of the liquid phase FP1 is returned as reflux to the distillation column DK1 .

6. 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.

7. 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. 8 . The process according to claim 1 , wherein the distillation column DK1 has 150 to 300 trays. 9 . The process according to claim 1 , wherein the distillation column DK2 has 150 to 300 trays.

10. The process according to any of the preceding claims, wherein the stream BS2 is expanded in a flash vessel, in which a liquid phase FP2 is obtained. 11 . The process according to claim 10 , wherein at least a portion FP2a of the liquid phase FP2 is discharged from the process as a product stream and a further portion FP2b of the liquid phase FP2 is returned as reflux to the distillation column DK2 . 12 . The process according to claim 1 , wherein the product stream comprises at least 99% by weight of 1-butene, preferably at least 99.5% by weight of 1-butene, particularly preferably at least 99.6% by weight of 1-butene.

13. The method according to any of the preceding claims, wherein only a single heat carrier medium is used throughout the method. 14 . The method according to claim 1 , wherein the heat transfer medium W 3 . 1 is recirculated after preheating and is conducted as heat transfer medium W partly to step c) and partly to step f).

15. The method according to any one of the preceding claims, wherein the heat transfer medium is selected from water; alcohol; alcohol-water mixture; brine solution; ammonia; mineral oil, such as diesel; thermal oil, For example, silicone oils; bio-oils, such as limonene; and aromatic or aliphatic hydrocarbons, such as dibenzyltoluene, Preferably water, methanol, ethanol, propanol, n-pentane, n-butane, n-hexane, n-propane or ammonia, Water is particularly preferred.

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