Energy efficient process for separation of 1-butene from hydrocarbon stream

Abstract

The present invention relates to an energy efficient process for separating 1-butene from a hydrocarbon stream. Specifically, the subject of the present 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 utilized to save energy costs and reduce CO2 emissions.

Description

TECHNICAL FIELD

[0001] The present invention relates to a method 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 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 (such as 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 butene. 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, while 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 (usually called raffinate 2) is produced.

[0005] It is feasible to separate 1-butene from such a C4 hydrocarbon stream and 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 method is disclosed, for example, in DE 102005062700A1.

[0006] In the known methods, 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 the 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 two reboilers SV1a and SV1b, and the second distillation column DK2 has at least one reboiler SV2a;

[0010] A stream taken out at the lower end of DK1 is fed to each of the reboilers SV1a and SV1b, 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 SV2a, 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 and 2-butene and taken out at the bottom of DK1;

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

[0014] (c) compressing a first part BS1a of the vapor stream BS1, thereby producing a compressed stream VB1 relative to the vapor stream BS1a;

[0015] (d) transferring energy from the compressed stream VB1 to the stream in the reboiler SV1a;

[0016] (e) guiding the part BS1b of the vapor stream BS1 other than BS1a to the reboiler SV2a, and transferring energy from BS1b to the stream in the reboiler SV2a here;

[0017] (f) At least partially direct the stream VB1 and the stream BS1b to a second distillation column DK2 and separate them in DK2 into at least one vapor stream BS2 and at least one product stream, where the vapor stream BS2 contains at least isobutane and is withdrawn at the top of DK2, and the product stream contains at least 1-butene and is withdrawn at the bottom of DK2;

[0018] (g) At least partially compress the vapor stream BS2, thereby producing a compressed stream VB2 relative to the vapor stream BS2; and

[0019] (h) Transfer energy from the compressed stream VB2 to the stream in the reboiler SV1b.

[0020] One advantage of the method according to the invention is the realization of double heat integration by compressing the streams VB1 and VB2. In this way, energy is transferred to the corresponding streams in the reboilers SV1a and SV1b, thereby introducing energy to the bottom. The result of the energy transfer in the reboilers SV1a and SV1b in the first distillation column DK1 is that only a smaller amount or even no heating steam is required to heat the distillation column DK1. Therefore, (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.

[0021] 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 impossible to completely remove them in many cases. However, the amounts of polyunsaturated C4 hydrocarbons (especially butadiene) and isobutene should be as low as possible.

[0022] The raffinate 2 used preferably contains less than 1000 ppm, preferably less than 500 ppm of isobutene. If a relatively high 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 to react isobutene 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 the 1-butene.

[0023] Further preferably, the raffinate 2 used in the process of the present 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 in advance, in which butadiene is converted to butene and / or butane. For a person skilled in the art, the corresponding process is described, for example, in EP 3680224 A1.

[0024] 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 process described herein. The water will be enriched in the corresponding 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 below 100 ppm, particularly preferably below 5 ppm.

[0025] 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 two reboilers SV1a and SV1b. DK2 is the second distillation column and has at least one reboiler SV2a. In a preferred embodiment, the distillation column has only two reboilers SV1a and SV1b. Furthermore, the distillation column DK2 preferably has only one reboiler SV2a. The pressures in the two distillation columns DK1 and DK2 should in particular be chosen such that heat can be transferred in the reboilers. 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.

[0026] The energy required for the separation task is introduced into the first distillation column DK1 via the reboilers SV1a and SV1b. A stream taken out at the lower end of DK1 is fed to each of the reboilers SV1a and SV1b, and the stream is then guided back to DK1 after passing through the respective reboiler. The corresponding stream is heated when passing through the reboiler SV1a or SV1b. The two streams can be taken out independently of each other, i.e., at two different positions at the bottom of DK1. Alternatively, only one stream can be taken out and then separated into two streams, optionally using a splitting controller, by means of which the mass flows of the two streams are adjusted according to predetermined parameters. The feed of the two streams from the two reboilers SV1a and SV1b is especially at different positions at the bottom, which means that the two streams do not mix before entering DK2 after passing through the reboilers.

[0027] The situation of the reboiler SV2a of the second distillation column DK2 is similar. The energy required for the separation task is introduced by means of this reboiler. For this purpose, the feed to the reboiler SV2a is a 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 the process of passing through the reboiler SV2a and is at least partially evaporated during this process.

[0028] According to the present invention, a "reboiler" refers to 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 to the reboiler. The evaporated stream (optionally with a liquid residue part) is returned to the bottom region of the corresponding distillation column through at least one inlet.

[0029] 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-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 also be used alternatively.

[0030] 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 taken out at the top of DK1. The bottom stream contains at least 1-butene and 2-butene and is taken out at the bottom of DK1. This bottom stream can be guided to an oligomerization reaction (not shown). The vapor stream BS1 can also be taken out 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. This also 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.

[0031] In principle, the raffinate-2 stream can be guided to the first distillation column DK1 through one or more feed points. If there are multiple feed points for the raffinate-2 stream, then correspondingly multiple separate streams are guided to the distillation column. In an embodiment of the present invention in which the raffinate-2 stream is guided 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.

[0032] 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 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 more preferably in the range of 60 °C to 80 °C.

[0033] 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, 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 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.

[0034] 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 the mechanical power of the compressor and the temperature of the raffinate-2 stream to be evaporated remain low.

[0035] In a particularly preferred embodiment of the invention, the distillation column DK1 comprises a plurality of trays, preferably 150 to 300 trays, further preferably 170 to 220 trays.

[0036] 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 especially means that at least one vapor stream BS1 is taken out in the distillation column DK1 as a top stream or as a side stream above the internals.

[0037] 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 especially means that at least one bottom stream is taken out directly at the bottom of the distillation column DK1 or at the lower trays.

[0038] The distillation column DK1 also operates in a reflux mode, preferably 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.

[0039] 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 refers to 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.

[0040] 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 (where a compressor and / or a regulating valve are used for control (Regelung)). Also conceivable here would be a control method by which the mass flow rates of BS1a and BS1b are adjusted with the change of specific parameters.

[0041] Subsequently, in step (c), the first part BS1a of the vapor stream BS1 is compressed, thereby generating a compressed stream VB1 relative to the vapor sub-stream BS1a. The stream BS1a generally has the same pressure as the stream BS1 when it is taken out from the distillation column DK1. It may be advantageous to heat the stream BS1a 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-1 in the present application Figure 3 and 4 or an external heat source. The pressure of VB1 after compression is higher than the pressure of BS1a. A person skilled in the art can set the exact value of the pressure of VB1 according to the requirements of subsequent energy transfer, provided that the condition that the pressure of VB1 > the pressure of BS1a is satisfied. The quotient of the pressure of VB1 / the pressure of BS1a (the pressures are each in bar absolute pressure) is preferably in the range of 1.1 to 10, more preferably in the range of 1.2 to 8, more preferably in the range of 1.25 to 7, and most preferably in the range of 1.3 to 6.

[0042] The temperature of the sub-stream VB1 is preferably higher than the temperature of the vapor sub-stream BS1a, and the quotient of the temperature VB1 / temperature BS1a (with the temperature in K in each case) is preferably in the range from 1.03 to 10, more preferably in the range from 1.04 to 9, more preferably in the range from 1.05 to 8, more preferably in the range from 1.06 to 7, more preferably in the range from 1.07 to 6, and most preferably in the range from 1.08 to 5.

[0043] In step (c), at least a part of the vapor sub-stream BS1a can be compressed in any desired manner known to the person skilled in the art. For example, the compression can be carried out mechanically and in single-stage or multi-stage compression. In this case, the meaning of "single-stage" means that the compression proceeds from one pressure level to another pressure level. The meaning of "multi-stage" means that the compression is first carried out 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. The multi-stage compression can be carried out with one or more compressors. The use of single-stage or multi-stage compression depends on the compression ratio and thus on the pressure to which the vapor sub-stream BS1a is to be compressed.

[0044] In the process according to the invention, suitable compressors, in particular compressors for compressing the vapor stream BS1a to VB1, are any compressors known to the person skilled in the art, preferably mechanical compressors, with which a gaseous stream can be compressed. Suitable compressors are, for example, single-stage or multi-stage gear turbo compressors, piston compressors, screw compressors, centrifugal compressors or axial flow compressors.

[0045] In step (d) of the process according to the invention, energy is transferred from the compressed stream VB1 to the stream in the reboiler SV1a. Step (d) reduces the energy of VB1 such that VB1 is at least partially condensed, in particular. According to the invention, the expression "energy transfer" particularly means heating, i.e. the transfer of energy in the form of heat.

[0046] The transfer of energy from VB1 to the stream in the reboiler SV1a is preferably effected by VB1 heating the stream in the reboiler SV1a, preferably directly. The meaning of direct transfer is that, although the streams in VB1 and SV1a do not come into direct contact, the energy, in particular heat, is transferred from VB1 to the stream in SV1a in the absence of any additional heat transfer medium. The reboiler SV1a used can be a heat exchanger or heat exchanger known to the person skilled in the art, in particular an evaporator.

[0047] In a preferred embodiment, step (d) of the method according to the invention can bring about particular benefits. The residual energy obtained when compressing the vapor stream BS1a to the compressed vapor stream VB1 (which is dissipated) is not left unused here, but is used for the distillation DK2. This is done by first compressing the BS1a to VB1 to such an extent that the degree of compression of the VB1 exceeds that required for the SV1a. The heat of condensation obtained in the additional compression can be fed into the column DK2 via the stream VB1. The additional compressor power required is generally less than the heating steam power saved thereby.

[0048] In step (e) of the method according to the invention, at least a part BS1b of the vapor stream BS1 other than BS1a is directed to the reboiler SV2a, where energy is transferred from the BS1b to the stream present in the reboiler in the reboiler SV2a. By step (e), the energy of the BS1b is reduced, such that the BS1b is at least partially condensed, in particular.

[0049] The transfer of energy from the BS1b to the stream in the reboiler SV2a is preferably direct by heating the stream in the reboiler SV2a with the BS1b. The meaning of direct transfer is that, although the BS1b and the stream in the SV2a do not come into direct contact, the energy, in particular heat, is transferred from the BS1b to the stream in the SV2a in the absence of an additional heat transfer medium. The reboiler SV2a used can be a heat transfer device or heat exchanger familiar to those skilled in the art, in particular an evaporator.

[0050] After the streams VB1 and BS1b have passed through the reboiler SV1a or SV2a and transferred energy to the respective streams, then in step (f), these streams VB1 and BS1b are at least partially directed to the second distillation column DK2, where the separation between isobutane and 1-butene is then carried out to obtain a 1-butene stream of the highest possible purity. The two streams VB1 and BS1b can be directed to the second distillation column DK2 separately from each other as different feed streams, or together to the second distillation column DK2.

[0051] Before directing the streams to the second distillation column in step (f), according to a preferred embodiment, the streams VB1 and BS1b are directed to a flash vessel and expanded therein to obtain the liquid phase FP1 of the streams VB1 and BS1b. The flash vessel can additionally include a condenser in order to condense a part of the obtained gas phase.

[0052] In a preferred embodiment of the present invention, the streams VB1 and BS1b are jointly directed to a second distillation column. For this purpose, in particular, the two streams are given the same pressure and the same temperature. If the streams VB1 and BS1b are to be jointly directed to a distillation column, it is preferred to combine the streams VB1 and BS1b in a flash vessel and obtain a common liquid phase FP1.

[0053] Then, at least a part FP1a of the liquid phase FP1 is directed to the distillation column DK2 according to step (f). 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.

[0054] It is further preferred to return a part FP1b of the liquid phase FP1 other than FP1a as reflux to the first distillation column DK1. It is particularly preferred to transfer energy 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 familiar to those skilled in the art can be used.

[0055] In the second distillation column DK2, a stream that contains at least isobutane and 1-butene is separated into at least one vapor stream BS2 that contains at least isobutane and is taken off at the top of DK2, and at least one product stream that contains at least 1-butene and is taken off at the bottom of DK2.

[0056] The distillation column DK2 for separating the two streams VB1 and BS1b can be any distillation column known to those skilled in the art. The distillation column DK2 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, 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 or saddle packings. Structured packings are sold, for example, by Sulzer under the 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.

[0057] Preferred internals have a low pressure drop per theoretical plate. For example, the pressure drop per theoretical plate of structured packings and random packings is significantly lower than that of trays. This is advantageous in that the pressure drop in distillation column DK2 remains as low as possible, so that the mechanical power of the compressor and the temperatures of the two feed streams VB1 and BS1b to be evaporated remain low.

[0058] 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.

[0059] 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 the internals. 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, 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.

[0060] 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 butane is also obtained as a high boiler in DK2 and thus is obtained 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 hardly any butane enters DK2. Therefore, the stream(s) fed to DK2 (VB1 or FP1a) preferably contain at most 500 to 900 ppm of butane, based on the total amount of the stream(s).

[0061] During the process according to the 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.

[0062] The distillation column DK2 can also be operated with reflux. The meaning of "reflux" means that at least part of the vapor stream BS2 withdrawn 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 10 to 80, particularly preferably 30 to 50.

[0063] Reflux can be established by installing a condenser at the top of distillation column DK2. The 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 (reflux) that is returned to the column in liquid form to the portion of the mass flow rate (kg / h) withdrawn from the column that is discharged from the corresponding column in liquid or gaseous form.

[0064] Subsequently, in step (g), the vapor stream BS2 is at least partially compressed, thereby generating 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 of pressure VB2 > pressure BS2 is satisfied. The quotient of pressure VB2 / pressure 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 3 and Figure 4 or an external heat source.

[0065] The temperature of the sub-stream VB2 is preferably higher than the temperature of the vapor stream BS2, and the quotient of temperature VB2 / temperature BS2 (the temperatures in each case are 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.

[0066] In step (c), at least a part of the vapor stream BS2 can be compressed in any desired manner known to a person skilled in the art. For example, the compression can be carried out mechanically and in single-stage or multi-stage compression. In multi-stage compression, multiple compressors of the same type or different types can be used. The multi-stage compression can be carried out 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 vapor stream BS2 is to be compressed.

[0067] Suitable compressors in the method according to the present invention, especially for compressing the vapor stream BS2 into VB2, are any compressors known to a person skilled in the art, preferably mechanical compressors, by means of which a gas stream can be compressed. Suitable compressors are, for example, single-stage or multi-stage turbines, piston compressors, screw compressors, centrifugal compressors or axial compressors.

[0068] In step (h) of the method according to the invention, energy is transferred from the compressed stream VB2 to the stream in the reboiler SV1b. By step (h), the energy of VB2 is reduced such that VB2 is at least partially condensed, in particular. According to the invention, the expression "energy transfer" particularly refers to heating, i.e., the transfer of energy in the form of heat.

[0069] The transfer of energy from VB2 to the stream in the reboiler SV1b is preferably effected by heating the stream in the reboiler SV1b with VB2, preferably directly. The meaning of direct transfer is that, although the streams in VB2 and SV1b do not come into direct contact, energy, in particular heat, is transferred from VB2 to the stream in SV1b in the absence of an additional heat transfer medium. The reboiler SV1b used can be a heat transfer device or heat exchanger familiar to those skilled in the art, in particular an evaporator.

[0070] After the stream VB2 has passed through the reboiler SV1b and transferred energy to the stream present therein, VB2 can be discharged from the method as an isobutane stream IB1. However, before removing VB2 as IB1 from the method, in a preferred embodiment of the invention, the stream VB2 is guided 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.

[0071] Then, at least a part FP2a of the liquid phase FP2 can be discharged from the method 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 can also be dispensed with. 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, the part FP2b of the liquid phase FP1 other than FP2a is returned as reflux to the first distillation column DK2.

[0072] In the basic embodiment of the invention, the two streams BS1a and BS2 are each compressed with a single compressor. In a preferred embodiment of the invention, the two streams BS1a and BS2 are compressed in a single compressor (preferably a multi-stage compressor). The number of stages required depends on the target compression ratio.

[0073] The thermal integration by means of vapor compression described here can also be combined with other thermal integration measures. One or more heat pumps can also be provided here. Description of the Drawings

[0074] The invention will be explained below with reference to the drawings. The drawings are for illustrative purposes only and should not be construed as restrictive.

[0075] Figure 1Shows an embodiment according to the prior art. The raffinate-2 stream (1) is directed to a first distillation column DK1, where 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 withdrawn at the top of DK1, and the bottoms stream (2) contains at least 1-butene and 2-butene and is withdrawn at the bottom of DK1. The stream (2) can be directed to an oligomerization reaction (not shown). Optionally after pre-condensation (not shown), the vapor stream BS1 is separated into two vapor streams BS1a and BS1b. BS1a is directed as reflux to the first distillation column DK1. BS1b is directed without additional compression to the reboiler SV2a of the second distillation column, where energy is transferred to the stream present there, which is heated after coming out from the bottom and then returns again. This corresponds to a conventional double-pressure circuit, where DK1 operates at a higher pressure than DK2 (see Example 1). In the 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 withdrawn at the top of DK2, and the product stream (3) contains at least 1-butene and is withdrawn at the bottom of DK2. The vapor stream is separated into streams BS2a and BS2b after optional condensation. BS2a is returned as reflux to DK2, while BS2b is discharged from the process as an isobutane stream (4).

[0076] Figure 2 Shows an embodiment which is also not of the present invention and which corresponds substantially identically to the embodiment of Figure 1 . The only difference is that the stream BS1a is raised to a higher pressure with a compressor V1 and then directed to the reboiler SV1a for energy transfer. The two streams BS1a and BS1b are combined after energy transfer, and part of them flows as reflux to DK1 and part of them flows as feed to DK2.

[0077] Figure 3 Shows an embodiment according to the present invention, which is mostly the same as the embodiment shown in Figure 2 . The difference is that the stream compressed with the compressor V1 is called VB1. In addition, the vapor stream BS2 is compressed with another compressor V2 and directed as VB2 to the reboiler SV1b. In this way, the use of external heating steam can be completely dispensed with.

[0078] Figure 4 Shows an embodiment which is also according to the present invention and which mostly corresponds to Figure 3The difference is that after the two material streams VB1 and BS1b transfer energy in the corresponding reboilers SV1a and SV2a, they are sent to a flash vessel, where a liquid phase FP1 is generated by expansion. This liquid phase is separated into two material streams FP1a and FP1b. FP1a is guided to the second distillation column DK2, and FP1b is guided as reflux to the first distillation column. The sequence of the material stream VB2 after transferring energy in the reboiler SV1b is similar. Then, VB1 reaches the flash vessel and is at least partially condensed into the liquid phase FP2, where a part FP2a of the isobutane stream (4) leaves the process, and the other part FP2b returns as reflux to the second distillation column.

[0079] Figure 5 shows an embodiment that is mostly the same as the embodiment shown in Figure 1 and Figure 2 The difference is that there are two additional heat exchangers (WT-1, WT-2), through which energy is transferred from the material streams VB1 (in WT-1) and VB2 (in WT-2) to the material streams BS1a (in WT-1) and BS2 (in WT-2). This can save energy additionally.

[0080] Figure 6 shows an embodiment that is mostly the same as the embodiment shown in Figures 1 to 3 The difference is that condensers (7, 8) for pressure control are installed in each of the two flash vessels. In addition, the condensers can also be used for starting the process. Detailed implementation mode

[0081] Examples

[0082] All the following examples use a raffinate-2 material stream of 55 t / h. The raffinate 2 material 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.

[0083] The amount of energy required for the operation of the device for separating 1-butene from raffinate 2 detailed in the examples is calculated by simulation using Aspen V10. The substance data is verified through operation data and operation tests.

[0084] Example 1 (not of the present invention):

[0085] In accordance with Figure 1In the embodiment, direct heat integration was only implemented between columns DK1 and DK2 (as disclosed in DE102005062700 A1). In this case, column DK1 operates at a top pressure of 11 bar, while column DK2 operates at a top pressure of 7 bar. Therefore, a portion of the vapor stream BS1b can be used to transfer heat to DK2 via reboiler SV2a. For a 1-butene amount of 10.3 t / h at a 1-butene purity of 99.6% in DK2, the required heat is 10.3 MW. For this purpose, a 125.5 t / h vapor stream from DK1 is used to heat DK2. Nevertheless, 15.9 MW still needs to be introduced into DK1 via an external heat source / media (such as heating steam).

[0086] Example 2 (not of the present invention):

[0087] In this embodiment, direct heat integration between columns DK1 and DK2 (as disclosed in DE102005062700 A1) was implemented and supplemented with vapor compression (see Figure 2 ). The 4.0 MW of condensation heat from DK1 (not used for heat integration between DK1 and DK2 in Example 1) can be made available through the first-stage vapor compression of compressor V1 and introduced via the second reboiler SV1a in DK1. A total of 4.4 MW can be transferred through vapor compression via reboiler SV1a. Therefore, the external heat requirement in column DK1 is reduced from 15.9 MW (Example 1) to 11.5 MW. To compress the vapor from 11 bar to 16.9 bar to create a driving temperature difference of 8 K in SV1a, compressor V1 requires a total of 382 kW of electrical power consumption.

[0088] Example 3 (of the present invention):

[0089] In this embodiment, direct heat integration between columns DK1 and DK2 (as disclosed in DE 102005062700 A1) was implemented and supplemented with multi-stage vapor compression according to the present invention (see Figure 3 ). The embodiment described in Example 2 was supplemented with additional vapor compression. The vapor in DK2 was compressed so that 9.9 MW of condensation heat from DK2 could be used for DK1. The elevated condensation heat with the aid of compressor V2 was transferred via another reboiler SV1b. For this purpose, the vapor stream in the second column DK2 was compressed from 7 bar to 21 bar. 2.6 MW of electrical power is required. A total of 11.5 MW can be transferred through SV1b, such that no external heat source is required for steady-state operation. Therefore, the energy-intensive 1-butene distillation process has been fully electrified.

[0090] The results of Examples 1 to 3 are summarized in Table 1 below.

[0091] Table 1: Summary of Examples

[0092] Example 1 Example 2 <![CDATA[Example 3 * <!-- 9 -->]]> External heating power [MW] 15.9 11.5 0 Compressor power [MW] 0 0.38 2.98

[0093] * The present invention

[0094] It has been found that embodiments of the method of the present invention have the following effects: compared with known technical solutions, much less external heating power needs to be used. Therefore, there is great potential for savings. The additional electrical power required for compressor operation is much smaller, and CO 2 neutral operation can be achieved when using green electricity.

Claims

1. A process for separating 1-butene from a hydrocarbon stream comprising 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 two reboilers SV1a and a reboiler SV1b, and the second distillation column DK2 has at least one reboiler SV2a; The reboiler SV1a and the reboiler SV1b are each fed with the stream taken out at the lower end of DK1, and the streams are directed back to DK1 after passing through the corresponding reboilers; The reboiler SV2a 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) compressing a first part BS1a of the vapor stream BS1, thereby generating a compressed stream VB1 relative to the vapor stream BS1a; (d) transferring energy from the compressed stream VB1 to the stream in the reboiler SV1a; (e) directing a portion BS1b of the vapor stream BS1 other than BS1a to a reboiler SV2a, wherein energy is transferred from BS1b to the stream in the reboiler SV2a; (f) conducting stream VB1 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; (g) at least partially compressing vapor stream BS2, thereby producing a compressed stream VB2 relative to vapor stream BS2; and (h) Transferring energy from the compressed stream VB2 to the stream in the reboiler SV1b. 2 . The process according to claim 1 , wherein stream VB1 and stream BS1b are conducted to a flash vessel and expanded therein, thereby producing vapor stream BS1a and a liquid phase FP1 of vapor stream BS1b. 3 . The process according to claim 2 , wherein the stream VB1 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 , preferably by means of a pump. 5 . The process according to claim 3 , wherein a further part FP1b of the liquid phase FP1 is returned as reflux to the distillation column DK1 . 6 . The process according to claim 5 , wherein energy is transferred from stream FP1 b to the raffinate-2 stream before the raffinate-2 stream is introduced into the first distillation column DK1 .

7. 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.

8. 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. 9 . The process according to claim 1 , wherein the distillation column DK1 has 150 to 300 trays. 10 . The process according to claim 1 , wherein the distillation column DK2 has 150 to 300 trays.

11. The process according to any of the preceding claims, wherein only a single compressor is used for compressing stream BS1a and stream BS2.

12. The process according to any of the preceding claims, wherein the stream VB2 is expanded in a flash vessel, in which a liquid phase FP2 is obtained.

13. 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.

14. 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.

15. The process according to any of the preceding claims, wherein the product stream contains 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.

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