Energy-efficient process for separating 1-butene from a hydrocarbon stream with a low driving temperature difference

Abstract

The invention relates to a process for separating 1-butene from a hydrocarbon stream containing at least 1-butene, 2-butene, n-butane and isobutane, in a separation unit comprising at least two distillation columns DK1 and DK2, wherein the heat of condensation is utilized in order to reduce energy costs and to decrease CO2 emissions.

Description

[0001] 202400211

[0002] 1

[0003] Energy-efficient process for separating 1-butene from a hydrocarbon stream with a low driving temperature difference

[0004] 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 comprising at least two distillation columns DK1 and DK2, wherein the heat of condensation is utilized to save energy costs and reduce CO2 emissions.

[0005] 1-Butene can be recovered in large quantities from technical C4 hydrocarbon streams, such as the C4 section from steamer fields or FCC units. These C4 hydrocarbon streams consist primarily of butadiene, the monoolefins 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 differences in boiling points among the constituents, their low separation factors, and the formation of azeotropes, the purely distillation-based processing of C4 hydrocarbon streams is difficult and uneconomical.

[0006] Therefore, butadiene is usually first separated by extractive distillation or selectively hydrogenated to butenes. What remains is a C4 hydrocarbon stream (so-called raffinate 1) which, in addition to the saturated hydrocarbons n-butane and isobutane, contains the olefins isobutene, 1-butene, and 2-butene, while butadiene is present only in very small amounts.

[0007] Since the boiling points of 1-butene and isobutene are very close, 1-butene cannot usually be economically separated from corresponding C4 hydrocarbon streams by simple distillation. Therefore, the isobutene is removed as completely as possible, for example via MTBE or ETBE synthesis. The removal of isobutene results in a C4 hydrocarbon stream (so-called raffinate 2) containing the linear butenes (1- and 2-butenes) and the saturated hydrocarbons isobutane and n-butane.

[0008] The separation of 1-butene from such C4 hydrocarbon streams is possible and is used in the chemical industry. The separation takes place in a distillation unit comprising at least two distillation columns. In the first distillation column, isobutane and 1-butene are collected at the top and transferred to the second distillation column. In the second distillation column, isobutane and 1-butene are then separated from each other. Such a process is disclosed, for example, in DE 102005062700 A1.

[0009] In known processes, the energy required for separating the C4 hydrocarbon stream is typically supplied to the bottom of the two distillation columns via heating steam. While heating steam is generally available at chemical production sites, the quantities required for the separation tasks represent a significant cost factor. Furthermore, the recirculation of the used heating steam is logistically challenging.

[0010] 2

[0011] It's always simple, since the steam can only be reduced within certain specifications (pressure, temperature, etc.). Furthermore, a large amount of CO2 is produced during the generation of heating steam.

[0012] Therefore, processes for separating 1-butene have already been proposed that incorporate energy recovery measures, such as the use of a heat pump and / or vapor compression. This allows the use of heating steam to be reduced or even eliminated entirely. Complete power generation is possible. By using green electricity, the process can thus be operated in a CO2-neutral manner with regard to energy input.

[0013] One problem with known methods for separating 1-butene is the high amount of energy required for distillation. Against this background, there remains a continuous need in the prior art for methods that can improve known processes, for example, by reducing the amount of energy used.

[0014] The object of the present invention was therefore to mitigate the disadvantages associated with the prior art described above. In particular, one object of the present invention is to reduce the amount of energy used. At the same time, this should enable a

[0015] Cost reduction can be achieved.

[0016] A first aspect of the present invention is a method for separating 1-butene from a hydrocarbon stream in a separation unit comprising at least two distillation columns DK1 and DK2, wherein the driving temperature difference in bottom evaporators of the distillation columns is reduced to a value between 1 and 10 K.

[0017] A second aspect of the present invention is a method for separating 1-butene from a hydrocarbon stream in a separation unit comprising at least two distillation columns DK1 and DK2, wherein the bottom evaporators of the distillation columns comprise structured heat exchanger tubes with at least one structured area.

[0018] It goes without saying that any embodiments, designs, advantages and the like, which are listed below for the purpose of avoiding repetition only with regard to one aspect of the invention, naturally also apply to the other aspects of the invention without the need for separate mention.

[0019] Furthermore, it goes without saying that the following specifications of values, numbers, and ranges are not to be understood as limiting; it is self-evident to those skilled in the art that deviations from the specified range or specifications are possible in individual cases or depending on the application, without departing from the scope of the present invention. 202400211

[0020] 3

[0021] Furthermore, it should be noted that all values ​​or parameters mentioned below, or the like, can generally be determined using standardized or explicitly specified determination methods, or using determination methods that are generally familiar to those skilled in the field.

[0022] Furthermore, it should be noted that for all relative or percentage-based quantity specifications mentioned below, especially those related to weight, these specifications must be selected or combined by a person skilled in the art in such a way that the total always results in 100% or 100% by weight, possibly including further components, ingredients, additives, or constituents, particularly as defined below. This is self-evident to a person skilled in the art.

[0023] Furthermore, for the purposes of describing the present invention, the features of the present invention cited in connection with specific embodiments, configurations, advantages, examples, or the like are also considered disclosed in combination. Thus, higher-order combinations of individual or multiple features cited for specific embodiments, configurations, application examples, or the like are also considered disclosed.

[0024] In particular, it also applies to the features characterizing the invention that any combination of these features shall be deemed disclosed, with embodiments of equal preference for the different features in their combination being preferred.

[0025] Having said that, the present invention will now be explained in detail below:

[0026] The present invention thus relates to a method for separating 1-butene from a Raffln at-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

[0027] the first distillation column DK1 has at least two bottom evaporators SV1a and SV1b and the second distillation column DK2 has at least one bottom evaporator SV2a;

[0028] The sump evaporators SV1 a and SV1 b are each supplied with a current that is taken from the lower end of the DK1 and, after passing through the respective sump evaporator, is returned to the DK1;

[0029] the sump evaporator SV2a is supplied with a current that is taken from the lower end of the DK2 and, after passing through the sump evaporator, is returned to the DK2; wherein the method comprises the following steps202400211

[0030] 4

[0031] (a) the raffinate 2 stream is directed to the first distillation column DK1 and is separated in DK1 into at least one vapor stream BS1 comprising at least 1-butene and isobutane, which is taken from the top of DK1, and into at least one bottom stream comprising at least 1-butene, n-butane and 2-butene, which is taken from the bottom of DK1;

[0032] (b) the vapor stream is split into at least two partial streams BS1a and BS1b;

[0033] (c) a first part BS1a of the vapor stream BS1 is compressed, resulting in a more compressed stream VB1 compared to the vapor stream BS1a;

[0034] (d) Energy is transferred from the compressed stream VB1 to the stream in the sump evaporator SV1a;

[0035] (e) a part BS1 b of the vapor stream BS1 other than BS1 a is directed to the sump evaporator SV2a and energy is transferred from BS1 b to the stream in the sump evaporator SV2a;

[0036] (f) the streams VB1 and BS1 b are directed at least partially to the second distillation column DK2 and are separated in DK2 into at least one vapor stream BS2, comprising at least isobutane and taken from the top of DK2, and into at least one product stream, comprising at least 1-butene and taken from the bottom of DK2;

[0037] (g) at least part of the vapor stream BS2 is compressed, resulting in a more compressed stream VB2 compared to the vapor stream BS2; and

[0038] (h) Energy is transferred from the compressed stream VB2 to the stream in the sump evaporator SV1 b, characterized in that

[0039] the driving temperature difference in the sump evaporators SV1a and SV1b is 1 to 10 K, preferably 2 to 9 K, particularly preferably 3 to 8 K.

[0040] Within the scope of the present invention, the driving temperature difference is understood to be the temperature difference between the heating and cooling medium at the inlet and outlet of the heat exchanger.

[0041] The advantage of the method according to the invention arises from the comparatively small driving temperature difference. This means that the vapor streams BS1a and BS2 need to be compressed to a lower temperature level. This results in savings in compressor power and thus in electrical energy (electricity costs).

[0042] In a further or alternative aspect of the present invention, an object is a method for separating 1-butene from a raffinate-2 stream containing at least 1-butene, 2-butene, n-butane and 202400211

[0043] 5

[0044] containing isobutane, in a separation unit comprising at least two distillation columns DK1 and DK2, wherein

[0045] the first distillation column DK1 has at least two bottom evaporators SV1a and SV1b and the second distillation column DK2 has at least one bottom evaporator SV2a;

[0046] The sump evaporators SV1 a and SV1 b are each supplied with a current that is taken from the lower end of the DK1 and, after passing through the respective sump evaporator, is returned to the DK1;

[0047] the sump evaporator SV2a is supplied with a current that is taken from the lower end of the DK2 and, after passing through the sump evaporator, is returned to the DK2; the method comprising the following steps

[0048] (a) the raffinate 2 stream is directed to the first distillation column DK1 and is separated in DK1 into at least one vapor stream BS1 comprising at least 1-butene and isobutane, which is taken from the top of DK1, and into at least one bottom stream comprising at least 1-butene, n-butane and 2-butene, which is taken from the bottom of DK1;

[0049] (b) the vapor stream is split into at least two partial streams BS1a and BS1b;

[0050] (c) a first part BS1a of the vapor stream BS1 is compressed, resulting in a more compressed stream VB1 compared to the vapor stream BS1a;

[0051] (d) Energy is transferred from the compressed stream VB1 to the stream in the sump evaporator SV1a;

[0052] (e) a part BS1 b of the vapor stream BS1 other than BS1 a is directed to the sump evaporator SV2a and energy is transferred from BS1 b to the stream in the sump evaporator SV2a;

[0053] (f) the streams VB1 and BS1 b are directed at least partially to the second distillation column DK2 and are separated in DK2 into at least one vapor stream BS2, comprising at least isobutane and taken from the top of DK2, and into at least one product stream, comprising at least 1-butene and taken from the bottom of DK2;

[0054] (g) at least part of the vapor stream BS2 is compressed, resulting in a more compressed stream VB2 compared to the vapor stream BS2; and

[0055] (h) Energy is transferred from the compressed stream VB2 to the stream in the sump evaporator SV1b, characterized in that the two sump evaporators SV1a and SV1b each comprise structured heat exchanger tubes with at least one structured section. 202400211

[0056] 6

[0057] Structured heat exchanger tubes within the scope of the present invention are to be understood as tubes comprising at least one structured area. A structured area is characterized by a repeating pattern. Examples of this are fins or channels. Corresponding tubes are known to those skilled in the art, for example, from EP 1 312885 A2, EP 1 830 151 A1, WO 2017 / 207091 A1 or WO 2022 / 106045 A1.

[0058] The structured heat exchanger tubes preferably have more than one, i.e., several, structured areas. If several structured areas are present, it is preferred that the structured heat exchanger tubes have the structured areas on the inside and / or outside of the tube. Preferably, at least one structured area is present on both the inside and the outside of the tube. In a particularly preferred embodiment of the present invention, the structured areas comprise continuously or discontinuously extending axially parallel or helically circumferential ribs.

[0059] Structured heat exchanger tubes offer the advantage of improved heat transfer between the media within the heat exchanger. This improved heat transfer allows for lower temperature differentials and enables the structured tubes to be made smaller compared to standard tubes. The use of structured heat exchanger tubes also results in reduced compressor power consumption and thus lower electricity costs. The structured sections facilitate improved heat exchange between the media in the sump evaporators.

[0060] It is understood that the two aspects of the present invention can be present both individually and in combination, i.e., the claimed driving temperature difference and / or the use of structured heat exchanger tubes.

[0061] According to the present invention, the output stream from which the 1-butene is to be separated is a raffinate 2 stream containing at least 1-butene, 2-butene, n-butane, and isobutane. Such streams are commercially available, for example, as C4 fraction from steamer fields or FCC units. As mentioned in the introduction, raffinate 2 is produced by removing polyunsaturated C4 hydrocarbons, particularly butadiene, and isobutene from the stream. Complete removal is often not possible for economic and technical reasons. However, the amounts of polyunsaturated C4 hydrocarbons, especially butadiene, and isobutene should be kept as low as possible.

[0062] Preferably, the raffinate 2 used contains less than 1000 ppm, preferably less than 500 ppm, isobutene. If higher amounts of isobutene are present in the feed stream, MTBE or ETBE synthesis (methyl tert-butyl ether = MTBE / ethyl tert-butyl ether = ETBE) could be carried out between the two distillation columns DK1 and DK2 to react the isobutene with methanol (for MTBE) or ethanol (for ETBE) and then separate the MTBE or ETBE. This allows the 202400211

[0063] 7

[0064] The concentration of isobutene before the second distillation column DK2 is significantly reduced. Isobutene would otherwise accumulate in the bottom of the second distillation column, forming the 1-butene solution.

[0065] Furthermore, the raffinate 2 used in the process of the present invention preferably contains less than 4 wt.% polyunsaturated C4 hydrocarbons. In a particularly preferred embodiment, the concentration of the polyunsaturated C4 hydrocarbons should be less than 500 ppm. Should the streams contain higher amounts of butadiene, selective hydrogenation could be carried out beforehand, in which the butadiene is converted to butenes and / or butanes. Corresponding processes are described, for example, in EP 3680224 A1.

[0066] The raffinate-2 stream used may also contain certain amounts of water, particularly in the range of 150 to 4000 ppm. It is preferred that the water be at least partially removed by the process described here. The water will accumulate in each of the two distillation columns DK1 and DK2 in the respective vapor streams BS1 and BS2 and, after condensation, will form a second liquid phase, which can be separated via condensers in the distillate vessels of DK1 and / or DK2. The bottoms products of DK1 and DK2 are characterized by very low butadiene and water contents, preferably below 100 ppm each, and particularly preferably below 5 ppm.

[0067] 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 bottom evaporators, SV1a and SV1b. DK2 is the second distillation column and has at least one bottom evaporator, SV2a. In a preferred embodiment, the distillation column has only the two bottom evaporators, SV1a and SV1b. It is also preferred that distillation column DK2 has only the single bottom evaporator, SV2a. The pressures in the two distillation columns, DK1 and DK2, should be selected such that heat can be transferred in the bottom evaporators. Within the scope of the present invention, the terms "first distillation column," "distillation column DK1," and "DK1" are to be understood as synonymous.Likewise, the terms “second distillation column”, “distillation column DK2” and “DK2” are to be understood as synonymous within the scope of the present invention.

[0068] The energy required for the separation process is supplied to the first distillation column DK1 via the bottom evaporators SV1a and SV1b. Each bottom evaporator SV1a and SV1b is fed with a stream drawn from the bottom of DK1 and returned to DK1 after passing through the respective bottom evaporator. The respective stream is heated as it passes through the bottom evaporator SV1a or SV1b. The two streams can be drawn independently of each other, i.e., from two different points in the bottom of DK1. Alternatively, only one stream can be drawn, which is then split into the two streams, possibly using a split control system to adjust the mass flow rates of the two streams based on a predefined parameter. The feeds for the two streams from the two bottom evaporators SV1a and SV1b are located at different points in the bottom of DK1.

[0069] 8

[0070] The two streams are not mixed after passing through the sump evaporator before entering the DK2.

[0071] A similar process applies to the bottom evaporator SV2a of the second distillation column DK2, through which the energy required for the separation process is supplied. The bottom evaporator SV2a is supplied with a current drawn from the lower end of DK2 and returned to DK2 after passing through the bottom evaporator. As the current passes through the bottom evaporator SV2a, it is heated and at least partially evaporates.

[0072] According to the invention, evaporators that heat the bottom of the respective distillation column are referred to as "bottom evaporators." Such a bottom evaporator is typically arranged outside the respective distillation column. Since energy, in particular heat, is transferred from one stream to another in bottom evaporators, they are heat exchangers. The stream to be evaporated is drawn off from the bottom of the distillation column via a draw-off and fed to the bottom evaporator. The evaporated stream, optionally with a residual liquid, is returned to the respective distillation column in the bottom region via at least one inlet.

[0073] Suitable evaporators that can be used as bottom evaporators include, for example, natural circulation evaporators, forced circulation evaporators, forced circulation evaporators with expansion, boiler evaporators, falling film evaporators, and thin-film evaporators. A tube bundle or plate heat exchanger is typically used as the heat exchanger for the evaporator in natural and forced circulation evaporators. However, any other evaporator design known to those skilled in the art and suitable for use with a distillation column can also be used. In all of the types mentioned, structured heat exchanger tubes or, alternatively, structured surfaces, such as structured plates, can be used.

[0074] The raffinate 2, which is fed to the first distillation column DK1, is separated in the distillation column DK1 into at least two streams, i.e., into at least one vapor stream BS1, comprising at least 1-butene and isobutane, which is withdrawn from the top of DK1, and into at least one bottom stream, comprising at least 1-butene, n-butane, and 2-butene, which is withdrawn from the bottom of DK1. This bottom stream can be subjected to oligomerization (not shown). The vapor stream BS1 can also be withdrawn from the top of the distillation column in the form of several partial streams BS1n, where n is an integer equal to the number of partial streams. The same applies to the bottom stream. The temperature in the bottom of the first distillation column DK1 is preferably in the range of 40 to 110 °C, more preferably 50 to 100 °C.

[0075] In principle, the Raffinate-2 stream can be fed into the first distillation column DK1 via one or more inlets. If several inlets for the Raffinate-2 stream are present, several separate streams are fed into the distillation column. In the embodiments of the present invention, in which the Raffinate-2 stream is fed into the distillation column DK1 as two or more separate streams, it is advantageous to

[0076] 9

[0077] when the inlets of the individual streams are essentially at the same height on the distillation column DK1.

[0078] The pressure and temperature of the vapor stream BS1 are specified below. This refers in particular to the pressure and temperature of the at least one vapor stream BS1 when it is taken from the distillation column DK1. The pressure of the vapor stream BS1 is preferably in the range of 8.5 to 12.5 bar absolute, and more preferably in the range of 9 to 10.5 bar absolute. This also corresponds to the top pressure of DK1. The temperature of the vapor stream BS1 is preferably in the range of 35 °C to 105 °C, more preferably in the range of 48 °C to 100 °C, more preferably in the range of 50 °C to 90 °C, more preferably in the range of 55 °C to 80 °C, and most preferably in the range of 60 °C to 80 °C.

[0079] Any distillation column known to those skilled in the art can be used as distillation column DK1 for separating the raffinate-2 stream. Preferably, distillation column DK1 contains internals. Suitable internals include, for example, trays, unstructured packings, or structured packings. Bubble-cap trays, sieve trays, valve trays, tunnel trays, or slotted trays are commonly used as trays. Unstructured packings are generally packed beds. Raschig rings, Pall rings, Berl saddles, or Intalox® saddles are commonly used as packings. Structured packings are marketed, for example, under the trade name Mellapack® by Sulzer. In addition to the internals mentioned, other suitable internals are known to those skilled in the art and can also be used.

[0080] Preferred internals exhibit a low specific pressure drop per theoretical separation stage. Structured packings and fills, for example, have a significantly lower pressure drop per theoretical separation stage than trays. This has the advantage that the pressure drop in distillation column DK1 remains as low as possible, thus keeping the mechanical power consumption of the compressor and the temperature of the raffinate-2 stream to be evaporated low.

[0081] In a particularly preferred embodiment of the present invention, the distillation column DK1 comprises a plurality of trays, preferably between 150 and 300 trays, more preferably between 170 and 220 trays.

[0082] Within the scope of the present invention, the withdrawal of at least one vapor stream BS1, comprising at least 1-butene and isobutane, at the head of the distillation column DK1 means in particular that the at least one vapor stream BS1 is withdrawn as a head stream or as a side draw above the internals in the distillation column DK1.

[0083] Within the scope of the present invention, the withdrawal of the at least one bottom stream, comprising at least 1-butene, n-butane and 2-butene, from the bottom of distillation column DK1 means in particular that the at least one bottom stream is withdrawn directly from the bottom or the lower plate of distillation column DK1.

[0084] 10

[0085] Distillation column DK1 is preferably operated with reflux. Reflux means that the vapor stream BS1 withdrawn at the top of distillation column DK1 is at least partially returned to distillation column DK1. In cases where such reflux is implemented, the reflux ratio is preferably 2 to 30, more preferably 5 to 20, and particularly preferably 8 to 15.

[0086] A reflux can be established by installing a condenser at the top of the distillation column DK1. In the condenser, the vapor stream BS1 is partially condensed and returned to the distillation column DK1. Alternatively, the vapor stream, or a portion thereof, can be returned to the distillation column as reflux only after compression and expansion. Generally, and for the purposes of this invention, the reflux ratio is understood to be the ratio of the proportion of the mass flow (kg / h) withdrawn from the column that is returned to the column in liquid form (reflux) to the proportion of this mass flow (kg / h) that is discharged from the respective column in liquid or gaseous form.

[0087] After the extraction of the vapor stream BS1, the vapor stream BS1 is split in step (b) into at least two partial streams BS1a and BS1b. This splitting can be carried out in a known manner, for example by a splitter (control at a compressor and / or a control valve). Alternatively, a control system could be used to adjust the mass flow rates of BS1a and BS1b depending on a specific parameter.

[0088] Subsequently, in step (c), a first portion BS1a of the vapor stream BS1 is compressed, resulting in a stream VB1 that is more compressed than the vapor stream BS1a. The stream BS1a typically has the same pressure as the stream BS1 when it is drawn from the distillation column DK1. It can be advantageous to heat the stream BS1a before compression to prevent the formation of a two-phase mixture during compression. Heating can be carried out using internal or external heat sources. After compression, the pressure of VB1 is higher than the pressure of BS1a. The exact value for the pressure of VB1 can be adjusted by a person skilled in the art, depending on the requirements of the subsequent energy transfer, as long as the condition pressure VB1 > pressure BS1a is met. The ratio of pressure VB1 / pressure BS1a (pressures in bar abs.) is preferably in the range of 1.05 to 10, more preferably 1.1 to 8, more preferably 1.15 to 5, most preferably 1.2 to 3.

[0089] The temperature of the partial flow VB1 is preferably higher than the temperature of the vapor partial flow BS1a, and results from the relationship between pressure and temperature from the pressure increase of the partial flow VB1 and the conditions prevailing at the beginning of the compression.

[0090] The compression of at least part of the vapor stream BS1a in step (c) can be carried out in any manner known to those 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, single-stage means that a202400211

[0091] 11

[0092] Compression from one pressure level to another takes place. Multi-stage means that compression first occurs to pressure level X and then from X to pressure level Y. In multi-stage compression, several compressors of the same design or compressors of different designs can be used. Multi-stage compression can be carried out with one or more compressor units. The use of single-stage or multi-stage compression depends on the compression ratio and thus on the pressure to which the vapor stream BS1a is to be compressed.

[0093] Any compressor known to those skilled in the art, preferably a mechanical compressor capable of compressing gas flows, is suitable as a compressor in the method according to the invention, particularly for compressing the vapor streams BS1a to VB1. Suitable compressors include, for example, single- or multi-stage geared turbo compressors, piston compressors, screw compressors, centrifugal compressors, or axial compressors.

[0094] In step (d) of the process according to the invention, energy is transferred from the compressed stream VB1 to the stream in the sump evaporator SV1a. Through step (d), the energy of VB1 decreases, so that VB1, in particular, condenses at least partially. According to the invention, the phrase "transfer of energy" means, in particular, heating, i.e., the transfer of energy in the form of heat to the stream in the sump evaporator.

[0095] The transfer of energy from VB1 to the current in the sump evaporator SV1a, preferably the heating of the current in the sump evaporator SV1a by VB1, preferably occurs directly. Direct transfer means that VB1 and the current in SV1a do not come into direct contact, but that energy, in particular heat, is transferred from VB1 to the current in SV1a without the presence of an additional heat transfer medium. Heat exchangers or heat transfer devices familiar to those skilled in the art, in particular evaporators, can be used as the sump evaporator SV1a.

[0096] Step (d) of the process according to the invention can lead to a particular advantage in a preferred embodiment. The excess energy obtained during the compression of the vapor stream BS1a to the compressed vapor stream VB1 is not dissipated unused, but is employed in distillation DK2. This is achieved by first compressing BS1a to VB1 to a degree exceeding that required in SV1a. The heat of condensation obtained during this additional compression can be fed into column DK2 via the VB1 stream. The required additional compressor power is generally less than the heating steam power saved as a result.

[0097] In step (e) of the process according to the invention, at least a portion BS1b of the vapor stream BS1, different from BS1a, is directed to the sump evaporator SV2a, where energy from BS1b is transferred to the stream present in the sump evaporator SV2a. Step (e) reduces the energy of BS1b, causing BS1b to condense, at least partially.

[0098] 12

[0099] The transfer of energy from BS1b to the current in the sump evaporator SV2a, preferably the heating of the current in the sump evaporator SV2a by BS1b, preferably occurs directly. Direct transfer means that BS1b and the current in SV2a do not come into direct contact, but that energy, in particular heat, is transferred from BS1b to the current in SV2a without the need for an additional heat transfer medium. Heat exchangers or heat transfer devices familiar to those skilled in the art, especially evaporators, can be used as the sump evaporator SV2a.

[0100] After streams VB1 and BS1b have passed through the bottom evaporators SV1a and SV2a respectively, transferring energy to the respective streams, these streams are at least partially directed to the second distillation column DK2 in step (f). There, the separation of isobutane and 1-butene takes place to obtain the purest possible 1-butene stream. The two streams, VB1 and BS1b, can be fed to the second distillation column DK2 independently as separate feed streams or together.

[0101] Before the streams are directed to the second distillation column in step (f), in a preferred embodiment, the streams VB1 and BS1b are directed to a flash vessel and expanded there, resulting in a liquid phase FP1 of the streams VB1 and BS1b in addition to a gaseous phase. The flash vessel may additionally include a condenser to condense a portion of the gaseous phase.

[0102] In a preferred embodiment of the present invention, the streams VB1 and BS1b are fed together to the second distillation column. For this purpose, the two streams are brought to the same pressure and temperature. Therefore, if the streams VB1 and BS1b are to be fed together to the distillation column, it is preferred that the streams VB1 and BS1b are combined in the flash vessel and form a common liquid phase FP1.

[0103] At least a portion of the liquid phase FP1a is subsequently directed to the distillation column DK2 according to step (f). In a particularly preferred embodiment, a pump is used for this purpose. Pumps known to those skilled in the art can be used here. Suitable pumps include, for example, standard chemical pumps.

[0104] It is further preferred that a portion FP1b of the liquid phase FP1, different from FP1a, is returned as reflux to the first distillation column DK1. It is particularly preferred that energy is transferred from the FP1b stream to the Raffinate-2 stream before the Raffinate-2 stream is introduced into the first distillation column DK1. This preheats the Raffinate-2 stream. Another possibility is to use the bottoms stream of the first distillation column DK1 to preheat the Raffinate-2 stream.

[0105] This is energetically advantageous because less energy needs to be supplied to the separation process via the bottom evaporators. The transfer of energy from FP1 b or from the bottom stream of DK1 to the raffinate-2 stream, preferably the heating of the raffinate-2 stream by FP1 b or by the 202400211

[0106] 13

[0107] The sump flow of DK1 preferably occurs directly, i.e., without the use of an (additional) heat transfer medium. Heat exchangers or heat transfer devices familiar to those skilled in the art can be used for this purpose.

[0108] In the second distillation column DK2, the streams, each containing at least isobutane and 1-butene, are separated into at least one vapor stream BS2, which contains at least isobutane and is taken from the top of DK2, and at least one product stream, which contains at least 1-butene and is taken from the bottom of DK2.

[0109] Any distillation column known to those skilled in the art can be used as distillation column DK2 for separating the two streams VB1 and BS1b. Preferably, distillation column DK2 contains internals. Suitable internals include, for example, trays, unstructured packings, or structured packings. Commonly used trays are bubble-cap trays, sieve trays, valve trays, tunnel trays, or slotted trays. Unstructured packings are generally packed beds. Commonly used packing materials include Raschig rings, Pall rings, Berl saddles, or Intalox® saddles. Structured packings are marketed, for example, under the trade name Mellapack® by Sulzer. In addition to the internals mentioned, other suitable internals are known to those skilled in the art and can also be used.

[0110] Preferred internals exhibit a low specific pressure drop per theoretical separation stage. Structured packings and fillers, for example, have a significantly lower pressure drop per theoretical separation stage than trays.

[0111] In a particularly preferred embodiment of the present invention, the second distillation column DK2 comprises a plurality of trays, preferably between 150 and 300 trays, more preferably between 170 and 220 trays.

[0112] Within the scope of the present invention, the withdrawal of at least one vapor stream BS2, comprising at least isobutane, at the head of the distillation column DK2 means in particular that the at least one vapor stream BS2 is withdrawn as a head stream or as a side draw above the internals in the distillation column DK2.

[0113] Within the scope of the present invention, the withdrawal of the at least one product stream comprising at least 1-butene from the bottom of distillation column DK2 means, in particular, that the at least one product stream is withdrawn directly from the bottom or the lower plate of distillation column DK2. The product stream preferably contains at least 99 wt.% 1-butene, more preferably at least 99.5 wt.% 1-butene, and most preferably at least 99.6 wt.% 1-butene. The 1-butene is the target product of the present process, which is why the product stream is removed from the process. The 1-butene can, for example, be used as a co-monomer in the production of polyethylene.

[0114] 14

[0115] It is important to note that the separation efficiency in the first distillation column DK1 ultimately determines the purity of the 1-butene in the product stream taken from the second distillation column DK2. Butane, being a high-boiling compound, is also present in DK2 and therefore occurs along with the 1-butene. This would contaminate the 1-butene. Therefore, care should be taken to ensure that the separation of the raffinate 2 stream in DK1 is carried out in such a way that as little butane as possible reaches DK2. It is therefore preferable that the stream (1a, FP1a) fed to DK2 contains a maximum of between 500 and 900 ppm butane, based on the total volume of the stream.

[0116] In the sump of the second distillation column DK2, the temperature during the process according to the invention is preferably in the range of 30 to 100 °C, preferably 45 to 80 °C. Furthermore, the pressure at the top of the second distillation column DK2 is preferably in the range of 4 to 8 bar absolute, preferably 5 to 7 bar absolute.

[0117] Distillation column DK2 can continue to be operated with reflux. Reflux means that the vapor stream BS2 withdrawn at the top of distillation column DK2 is at least partially returned to distillation column DK2. In cases where such reflux is implemented, the reflux ratio is preferably 10 to 100, and particularly preferably 30 to 50.

[0118] A reflux can be established by at least partially condensing at least a portion of the vapor stream BS2 in a condenser K and returning it to the distillation column DK2. Generally, and for the purposes of this invention, a reflux ratio is understood to be the ratio of the proportion of the mass flow (kg / h) withdrawn from the column that is returned to the column in liquid form (reflux) to the proportion of this mass flow (kg / h) that is discharged from the respective column in liquid or gaseous form.

[0119] In step (g), at least a portion of the vapor stream BS2 is compressed, resulting in a more compressed stream VB2 compared to the vapor stream BS2. The pressure of VB2 after compression is higher than the pressure of BS2. The exact value for the pressure of VB2 can be adjusted by a person skilled in the art, depending on the requirements of the subsequent energy transfer, as long as the condition pressure VB2 > pressure BS2 is met. The ratio of pressure VB2 / pressure BS2 (pressures in bar abs.) is preferably in the range of 1.1 to 10, more preferably 1.2 to 8, more preferably 1.3 to 6, and most preferably 1.5 to 4. It can be advantageous to heat the stream BS2 before compression to prevent the formation of a two-phase mixture during compression. Heating can be carried out using internal (see WT-2 in Fig. 2 of the present application) or external heat sources.

[0120] The temperature of the partial flow VB2 is preferably higher than the temperature of the vapor flow BS2, and results from the relationship between pressure and temperature, specifically from the pressure increase of the partial flow VB2 and the conditions prevailing at the beginning of compression.

[0121] 15

[0122] The compression of at least one part of the vapor stream BS2 in step (g) can be carried out in any manner known to those skilled in the art. For example, the compression can be performed mechanically in a single stage or in multiple stages. In multi-stage compression, several compressors of the same design or compressors of different designs can be used. Multi-stage compression can be carried out with one or more compressor units. The choice between single-stage and multi-stage compression depends on the compression ratio and thus on the pressure to which the vapor stream BS2 is to be compressed.

[0123] Any compressor known to those skilled in the art, preferably a mechanical compressor capable of compressing gas flows, is suitable as a compressor in the method according to the invention, particularly for compressing the vapor stream BS2 to VB2. Suitable compressors include, for example, single- or multi-stage turbines, piston compressors, screw compressors, centrifugal compressors, or axial compressors.

[0124] In step (h) of the process according to the invention, energy is transferred from the compressed stream VB2 to the stream in the sump evaporator SV1 b. Through step (h), the energy of VB2 decreases, so that VB2, in particular, condenses at least partially. According to the invention, the phrase "transfer of energy" means, in particular, heating, i.e., the transfer of energy in the form of heat.

[0125] The transfer of energy from VB2 to the current in the sump evaporator SV1b, preferably the heating of the current in the sump evaporator SV1b by VB2, preferably occurs directly. Direct transfer means that VB2 and the current in SV1b do not come into direct contact, but that energy, in particular heat, is transferred from VB2 to the current in SV1b without the need for an additional heat exchanger medium. Heat exchangers familiar to those skilled in the art, especially evaporators, can be used as the sump evaporator SV1b.

[0126] After the current VB2 has passed through the sump evaporator SV1b and transferred energy to the current present there, VB2 can be used in a preheater to transfer energy to the currents BS1a and / or BS2. This superheats the currents, causing them to be in a gaseous state. This prevents the formation of droplets that could damage the compressor. Heat exchangers familiar to experts can be used as preheaters.

[0127] Afterwards, VB2 can be removed from the process as isobutane stream IB1. However, before VB2 is removed from the process as IB1, according to a preferred embodiment of the present invention, the stream VB2 is directed to a flash vessel and expanded there, resulting in a liquid phase FP2. The flash vessel can additionally include a condenser to condense a portion of the resulting gaseous phase.

[0128] At least a portion of the liquid phase FP2b can subsequently be removed from the process as an isobutane stream IB1. In a particularly preferred embodiment, a pump is used for this purpose. Under certain circumstances and with a sufficient pressure ratio, it would also be possible to operate without a pump. If a pump is used, [the following applies] known to those skilled in the art.

[0129] 16

[0130] Pumps are used. Suitable pumps include, for example, standard chemical pumps. It is further preferred that a portion FP2a of the liquid phase FP1, different from FP2b, is returned as reflux to the second distillation column DK2.

[0131] In the basic embodiment of the present invention, the two streams BS1a and BS2 are each compressed by a single compressor. In a preferred embodiment of the present invention, the two streams BS1a and BS2 are compressed in a single, preferably multi-stage, compressor. The number of stages required depends on the desired compression ratio.

[0132] The present invention is explained below with reference to the illustrations. The illustrations serve for clarification purposes only and are not to be understood as limiting.

[0133] Fig. 1 shows an embodiment of the process which, depending on the driving temperature difference, can be operated according to the invention or not. The raffinate-2 stream (1) is fed to the first distillation column DK1 and there is separated into a vapor stream BS1, which comprises at least 1-butene and isobutane and is taken from the top of DK1, and into a bottom stream (2), which comprises at least 1-butene, n-butane, and 2-butene and is taken from the bottom of DK1. This stream (2) can be directed to an oligomerization stage (not shown). The vapor stream BS1 is separated into the two vapor streams BS1a and BS1b. BS1a is pressurized to a higher pressure by the compressor V1 and then directed to the bottom evaporator SV1a for energy transfer.BS1b is fed without additional compression to the bottom evaporator SV2a of the second distillation column, where it transfers energy to the existing stream coming from the bottom, which is heated or evaporated and then returned. After energy transfer, the two streams BS1a and BS1b are combined, with some returning to DK1 and some feeding to DK2. In distillation column DK2, the streams are separated into a vapor stream BS2, which contains at least isobutane and is drawn from the top of DK2, and a product stream (3), which contains at least 1-butene and is drawn from the bottom of DK2. A portion of the vapor stream BS2 is compressed by a further compressor V2 and fed as VB2 to the bottom evaporator SV1b. Another portion of the vapor stream BS2 is condensed by condenser K.The resulting current from the condensed part of the vapor current and VB2 after energy transfer is partly fed back to DK2 and partly discharged from the process as isobutane current (4).

[0134] Fig. 2 shows another embodiment according to the invention, which largely corresponds to Fig. 1. The difference is that, after energy transfer in the respective bottom evaporators SV1a and SV2a, the two streams VB1 and BS1b are fed to a flash tank, where expansion produces a liquid and a gaseous phase. The liquid phase FP1 is separated into the two streams FP1a, which is fed to the second distillation column DK2, and FP1b, which is returned to the first distillation column. A similar process occurs with stream VB2 after energy transfer in the bottom evaporator SV1b. VB2 and the condensed part of the 202400211

[0135] 17

[0136] The vapor streams fall into a flash vessel as liquid phase FP2, a portion of which, FP2b, exits the process as isobutane stream (4), and another portion, FP2a, is returned as reflux to the second distillation column. A further difference from Fig. 1 is the presence of two additional heat exchangers (WT-1, WT-2) through which energy is transferred from streams VB1 (in WT-1) and VB2 (in WT-2) to streams BS1a (in WT-1) and BS2 (in WT-2). This allows for additional energy savings.

[0137] Examples

[0138] For all subsequent examples, a raffinate 2 stream of 55 t / h was used. The raffinate 2 stream has the following composition: 1-butene 41.4% / n-butane 24.7% / trans-2-butene 16.4% / cis-2-butene 8.2% / isobutane 8.9% / isobutene 590 ppm and water 0 ppm.

[0139] The amount of energy required to operate the plants shown in the examples for separating 1-butene from raffinate 2 was calculated using a simulation with Aspen Plus V12. The material properties were validated by operational data and field tests.

[0140] Example 1 (according to the invention):

[0141] In this embodiment, direct heat integration between columns DK1 and DK2 is carried out (as disclosed in DE 102005 062 700 A1) and, according to the invention, supplemented by multi-stage vapor compression (see Fig. 1). Furthermore, a driving temperature difference of 10 K is also present. The difference lies in the fact that the pressure in DK2 has been reduced to 6 bar absolute and in DK1 to 9.7 bar absolute. This increases the separation efficiency in the column, and the temperature in the sump of DK1 can also be lowered to 80 °C, thereby reducing the required energy input into the sump of DK1. This results in a lower required compressor power.

[0142] The vapor from column DK1 is compressed to utilize its condensation heat. The condensation heat, enhanced by compressor V1, is transferred via the bottom evaporator SV1a. For this purpose, the vapor flow from the first column DK1 is compressed from 9.7 bar to 15.9 bar. An electrical power of 0.75 MW is required.

[0143] The vapor from column DK2 is also compressed to make the condensation heat from DK2 usable for DK1. The condensation heat, enhanced by compressor V2, is transferred via a further bottom evaporator SV1b. For this purpose, the vapor flow from the second column DK2 is compressed from 6 bar to 18 bar. An electrical power of 2.31 MW is required.

[0144] In total, 3.06 MW must be used in Example 2 to utilize all the condensation heat and operate the process entirely for electricity generation. 202400211

[0145] 18

[0146] Example 2 (according to the invention):

[0147] Example 2 corresponds to the procedure according to Example 1 with a lower driving temperature difference of 6 K when using structured heat exchanger tubes in the sump evaporators.

[0148] The vapor from column DK1 is compressed to utilize its condensation heat. The condensation heat, enhanced by compressor V1, is transferred via the bottom evaporator SV1a. For this purpose, the vapor flow from the first column DK1 is compressed from 9.7 bar to 14.7 bar. An electrical power of 0.60 MW is required.

[0149] The vapor from column DK2 is also compressed to make the condensation heat from DK2 usable for DK1. The condensation heat, enhanced by compressor V2, is transferred via a further bottom evaporator SV1b. For this purpose, the vapor flow from the second column DK2 is compressed from 6 bar to 16.3 bar. An electrical power of 2.05 MW is required.

[0150] In total, 2.65 MW must be used in example 2 to utilize all the condensation heat and to operate the process entirely for electricity generation.

[0151] The results of examples 1 and 2 are summarized in Table 1 below.

[0152] Table 1: Summary of Examples

[0153]

[0154] * According to the invention

[0155] It turns out that the inventive design of the method results in significantly less electrical power being required in the compressors. The potential for savings is therefore considerable.

Claims

202400211 19 Patent claims 1. 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 the first distillation column DK1 has at least two bottom evaporators SV1a and SV1b and the second distillation column DK2 has at least one bottom evaporator SV2a; The sump evaporators SV1 a and SV1 b are each supplied with a current that is taken from the lower end of the DK1 and, after passing through the respective sump evaporator, is returned to the DK1; the sump evaporator SV2a is supplied with a current that is taken from the lower end of the DK2 and, after passing through the sump evaporator, is returned to the DK2; the method comprising the following steps (a) the raffinate 2 stream is directed to the first distillation column DK1 and is separated in DK1 into at least one vapor stream BS1 comprising at least 1-butene and isobutane, which is taken from the top of DK1, and into at least one bottom stream comprising at least 1-butene, n-butane and 2-butene, which is taken from the bottom of DK1; (b) the vapor stream is split into at least two partial streams BS1a and BS1b; (c) a first part BS1a of the vapor stream BS1 is compressed, resulting in a stream VB1 that is more compressed than the vapor stream BS1a; (d) Energy is transferred from the compressed stream VB1 to the stream in the sump evaporator SV1a; (e) a part BS1b of the vapor stream BS1 other than BS1a is directed to the sump evaporator SV2a and energy is transferred from BS1b to the stream in the sump evaporator SV2a; (f) the streams VB1 and BS1 b are directed at least partially to the second distillation column DK2 and are separated in DK2 into at least one vapor stream BS2, comprising at least isobutane and taken from the top of DK2, and into at least one product stream, comprising at least 1-butene and taken from the bottom of DK2; (g) at least part of the vapor stream BS2 is compressed, resulting in a more compressed stream VB2 compared to the vapor stream BS2; and202400211 20 (h) Energy is transferred from the compressed stream VB2 to the stream in the sump evaporator SV1b, characterized in that The driving temperature difference in the sump evaporators SV1a and SV1b is 1 to 10 K.

2. Method according to claim 1, wherein the driving temperature difference in the sump evaporators SV1a and SV1b is 2 to 9 K, preferably 3 to 8 K.

3. Method according to one of the preceding claims, wherein the two sump evaporators SV1a and SV1b each comprise structured heat exchanger tubes with at least one structured area.

4. The method of claim 3, wherein the structured heat exchanger tubes have more than one structured area.

5. The method of claim 4, wherein the structured heat exchanger tubes have the structured areas on the inside and / or outside of the tube.

6. Method according to any one of claims 3 to 5, wherein the structured areas comprise continuously or discontinuously extending axially parallel or helically circumferential ribs.

7. Method according to one of the preceding claims, wherein the head pressure in the distillation column DK2 is in the range of 4 to 8 bar absolute.

8. Method according to one of the preceding claims, wherein the head pressure in the distillation column DK1 is in the range of 8.5 to 12.5 bar absolute.

9. Method according to one of the preceding claims, wherein the streams VB1 and BS1b are directed to a flash container and expanded there, resulting in a liquid phase FP1 of the vapor streams BS1a and BS1b.

10. Method according to claim 9, wherein the streams VB1 and BS1 b are combined in the flash container and are produced as a common liquid phase FP1.

11. Method according to claim 10, wherein at least a part FP1 a of the liquid phase FP1 is directed to the distillation column DK2, preferably by means of a pump.

12. The method of claim 10 or 11, wherein another part FP1b of the liquid phase FP1 is returned as reflux to the distillation column DK1. 202400211 21 13. Method according to claim 12, wherein energy is transferred from stream FP1b to the raffinate-2 stream before the raffinate-2 stream is introduced into the first distillation column DK1.

14. Method according to one of the preceding claims, wherein only a single compressor is used for the compression of the streams BS1 a and BS2.

15. Method according to any of the preceding claims, wherein the product stream contains at least 99 wt.% 1-butene, preferably at least 99.5 wt.% 1-butene, particularly preferably at least 99.6 wt.% 1-butene.

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