Method for separating 1-butene from hydrocarbon stream excellent in energy efficiency

Abstract

To provide a method for separating 1-butene from a hydrocarbon stream, which saves energy cost and reduces CO2 emission.SOLUTION: A separation unit including at least two distillation columns of a first distillation column DK1 and a second distillation column DK2 separates 1-butene from a hydrocarbon flow containing at least 1-butene, 2-butene, n-butane and isobutane. One advantage of the method is double heat integration through compressed flows VB1 and VB2, which transmits energy to each flow in reboilers SV1a and SV1b, and sends the energy to column bottoms. As a result of the energy transmission in the reboilers SV1a and SV1b of the first distillation tower DK1, an amount of heated steam to be used for heating of the distillation column DK1, if any, becomes small. Accordingly, complete electrification of an energy aggregation type process can be achieved, to make green power applicable.SELECTED DRAWING: Figure 3

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 comprising at least two distillation columns DK1 and DK2, which method can utilize the heat of condensation in order to save energy costs and reduce CO 2 emissions.

Background Art

[0002] 1-Butene can be obtained in large quantities from industrial C4 hydrocarbon streams, such as the C4 cut from steam crackers or FCC units. The C4 hydrocarbon stream consists essentially of butadiene, the monoolefin isobutene, 1-butene and the two 2-butenes (cis and trans-2-butene), as well as the saturated hydrocarbons isobutane and n-butane. Due to the small differences in the boiling points of the components, their small separation factors and the formation of azeotropes, the post-treatment of the C4 hydrocarbon stream by distillation alone is difficult and uneconomical. Thus, generally, butadiene is first separated by extractive distillation or selectively hydrogenated to butene. In each case, a C4 hydrocarbon stream (referred to as raffinate 1) remains which contains not only the saturated hydrocarbons n-butane and isobutane, but also the olefins isobutene, 1-butene and 2-butene, and in which butadiene is present only in small amounts. Since the boiling points of 1-butene and isobutene are close to each other, generally 1-butene cannot be separated economically from the corresponding C4 hydrocarbon stream by simple distillation. Thus, isobutene is removed as much as possible, for example via MTBE synthesis or ETBE synthesis. Removal of isobutene gives a C4 hydrocarbon stream (referred to as raffinate 2) containing linear butenes (1-butene and 2-butene) as well as the saturated hydrocarbons isobutane and n-butane. 1-Butene can be separated from a C4 hydrocarbon stream or the like and is used in the chemical industry. The separation is carried out in a distillation unit including at least two distillation columns. Isobutane and 1-butene are obtained at the top of the first distillation column and sent to the second distillation column. Thereafter, isobutane and 1-butene are separated from each other in the second distillation column. The method is disclosed, for example, in Patent Document 1. In a known method, the energy required for separating a C4 hydrocarbon stream is usually sent to the bottoms of two distillation columns via heating steam. Heating steam can generally be utilized at a chemical production site. The cost factor cannot be underestimated when using heating steam in the volume required for the separation operation in question. Furthermore, when recycling the used heating steam, it is not always simple from a logistic point of view because the steam can only be returned within specific conditions (pressure, temperature, etc.). Furthermore, a large amount of CO 2 is generated when heating steam is generated.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] Therefore, an object of the present invention was to provide a method capable of reducing energy and CO 2 emissions as compared with known methods and capable of being incorporated into existing apparatuses.

Means for Solving the Problems

[0005] This problem is solved by the embodiments of the method proposed in claim 1 of the present application. Preferred embodiments are described in the dependent claims. The method according to the invention is a method for separating 1-butene from a hydrocarbon stream containing at least 1-butene, 2-butene, n-butane and isobutane in a separation unit comprising a first distillation column DK1 and a second distillation column DK2 of at least two distillation columns, comprising the following: The DK1 has at least two reboilers SV1a and SV1b, and the second distillation column DK2 has at least one reboiler SV2a, The reboilers SV1a and SV1b are each withdrawn at the lower end of the DK1, and a stream that is returned to the DK1 after passing through each reboiler is supplied, The reboiler SV2a is withdrawn at the lower end of the DK2, and a stream that is returned to the DK2 after passing through each reboiler is supplied, and the method comprises, here, the following: (a) Sending a raffinate 2 stream to the DK1, and in the DK1, separating it into at least one vapor stream BS1 containing at least 1-butene and isobutane and taken out at the top of the DK1, and at least one bottom stream containing at least 1-butene and 2-butene and taken out at the bottom of the DK1, (b) Separating the vapor stream BS1 into at least two sub-streams BS1a and BS1b, (c) Compressing the BS1a, which is a part of the first vapor stream of the vapor stream BS1, to produce a compressed stream VB1 for the BS1a, (d) Transferring energy from the compressed stream VB1 to the stream in the reboiler SV1a, (e) Sending the BS1b, which is the part of the vapor stream BS1 other than the BS1a, to the reboiler SV2a to transfer energy from the BS1b to the stream in the reboiler SV2a, (f) Send at least part of the compressed stream VB1 and the BS1b to the DK2, where at least isobutane is contained, and separate it into at least one vapor stream BS2 taken out at the top of the DK2 and at least one product stream containing at least 1-butene and taken out at the bottom of the DK2; (g) At least partially compress the vapor stream BS2 to produce a compressed stream VB2 for the vapor stream BS2; and (h) Transfer energy from the compressed stream VB2 to the stream in the reboiler SV1b.

[0006] The advantage of the method according to the present invention is the double heat integration via the compressed streams VB1 and VB2, whereby energy is transferred to each stream in the reboilers SV1a and SV1b and the energy is sent to the bottom of the column. As a result of the energy transfer in the reboilers SV1a and SV1b of the first distillation column DK1, even if there is heating steam to be used for heating the distillation column DK1, it will be less. Therefore, (almost) complete electrification of the energy-intensive process can be achieved, whereby green power can be used. Thereby, a significant amount of energy cost and CO 2 emissions are saved.

[0007] In the present invention, the starting stream from which 1-butene is separated is a raffinate 2 stream containing at least 1-butene, 2-butene, n-butane and isobutane. The corresponding stream can be obtained, for example, as a C4 cut from a steam cracker or an FCC unit. As described above, raffinate 2 is formed by the removal of polyunsaturated C4 hydrocarbons, especially butadiene and isobutene, from the stream. For economic and technical reasons, complete removal is often impossible. However, the amount of polyunsaturated C4 hydrocarbons, especially butadiene, and isobutene should be minimized. The raffinate 2 used preferably contains isobutene of less than 1000 ppm, preferably less than 500 ppm. When more isobutene is present in the starting stream, MTBE synthesis or ETBE synthesis (methyl-tert-butyl ether = MTBE / ethyl-tert-butyl ether = ETBE) is carried out between the two distillation columns DK1 and DK2, and after reacting isobutene with methanol (in the case of MTBE) or ethanol (ETBE), MTBE or ETBE can be separated. Therefore, the concentration of isobutene upstream of the second distillation column DK2 can be significantly reduced. This is because isobutene can be obtained from the bottom of the second distillation column, that is, from 1-butene. More preferably, the raffinate 2 used in the method of the present invention contains polyunsaturated C4 hydrocarbons of less than 4% by mass. In a particularly preferred embodiment, the concentration of polyunsaturated C4 hydrocarbons should be less than 500 ppm. When the stream contains a larger amount of butadiene, selective hydrogenation to convert butadiene to butene and / or butane can be carried out in advance. Corresponding methods are described, for example, in European Patent Application Publication No. 3680224 for those skilled in the art. The raffinate 2 stream used may further contain a predetermined amount of water, particularly in an amount of 150 to 4000 ppm. The water is preferably at least partially separated by the method described herein. The water accumulates in the vapor streams BS1 and BS2 respectively in each of the two distillation columns DK1 and DK2, and is obtained as a second liquid phase after condensation, which can be separated through the pipes in the distillate containers of the distillation columns DK1 and / or DK2. The bottom products of the distillation columns DK1 and DK2 are characterized by extremely low contents of butadiene and water, preferably less than 100 ppm each, more preferably less than 5 ppm each.

[0008] The method according to the invention is carried out in a separation unit comprising at least two distillation columns DK1 and DK2. The distillation column DK1 is the first distillation column and has at least two reboilers SV1a and SV1b. The distillation column 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. Also, it is preferred that the distillation column DK2 has only one reboiler SV2a. The pressures in the two distillation columns DK1 and DK2 must be selected in particular such that heat can be transferred to the reboilers. The terms "first distillation column", "distillation column DK1" and "DK1" should be considered synonymous in the context of the present invention. The terms "second distillation column", "distillation column DK2" and "DK2" should likewise be considered synonymous in the context of the present invention. The energy required for the separation operation is sent to the first distillation column DK1 via the reboilers SV1a and SV1b. Each of the reboilers SV1a and SV1b is supplied with a stream withdrawn at the lower end of the distillation column DK1 and returned to the distillation column DK1 after passing through each reboiler. The streams are each heated when passing through the reboiler SV1a or SV1b. One option is to take out the two streams independently, i.e., at two different locations at the bottom of the distillation column DK1. Alternatively, after taking out only one stream, it can be separated into two streams, optionally using a splitting control device that adjusts the mass flow rates of the two streams with respect to a predetermined parameter. The supply of the two streams from the two reboilers SV1a and SV1b is carried out in particular at different points at the bottom, which means that the two streams are not mixed after passing through the reboilers and before entering the distillation column DK2. This situation is comparable to the reboiler SV2a of the second distillation column DK2, whereby the energy required for the separation operation is sent. Therefore, the reboiler SV2a is supplied with a stream withdrawn at the lower end of the distillation column DK2 and returned to the distillation column DK2 after passing through each reboiler. The stream is heated when passing through the reboiler SV2a and at least partially evaporated.

[0009] In the present invention, a "reboiler" refers to an evaporator that heats the bottom of each distillation column. The reboiler is usually arranged outside each distillation column. Since the reboiler transfers energy, particularly heat, from one stream to another, it is a heat transfer medium. The stream to be evaporated is withdrawn from the bottom of the distillation column through an extraction section and supplied to the reboiler. The evaporated stream is returned to each distillation column in the bottom region through at least one supply section, regardless of the presence or absence of a liquid residue. Suitable evaporators that can be used as reboilers are, for example, natural circulation evaporators, forced circulation evaporators, forced circulation flash evaporators, kettle evaporators, falling film evaporators or thin film evaporators. Heat exchangers for evaporators commonly used in the case of natural circulation evaporators and forced circulation evaporators are shell and tube or plate devices. In addition to the above, any other design of evaporators known to those skilled in the art and suitable for use in distillation columns may be used.

[0010] The raffinate 2 sent to the first distillation column DK1 contains at least two streams in the distillation column DK1, namely at least 1-butene and isobutane, and is separated into at least one vapor stream BS1 taken out at the top of the distillation column DK1 and at least one bottom stream containing at least 1-butene and 2-butene and taken out at the bottom of the distillation column DK1. This bottom stream can introduce oligomerization (not shown). The vapor stream BS1 may be taken out at the top of the distillation column in the form of a plurality of sub-streams BS1n (n is an integer and equal to the number of sub-streams). The same applies to the bottom stream. The bottom temperature of the first distillation column DK1 is preferably in the range of 40 to 110 °C, preferably 50 to 100 °C. In principle, the raffinate 2 stream can be sent to the first distillation column DK1 through one or more supply points. If there are a plurality of supply points for the raffinate 2 stream, a plurality of separate streams are directed to the distillation column accordingly. In an embodiment of the present invention where the raffinate 2 stream is sent to the distillation column DK1 as two or more separate streams, it is advantageous if the supply points of the individual streams are at essentially the same height on the distillation column DK1.

[0011] The pressure and temperature of the vapor stream BS1 are specified below. This relates in particular to the pressure and temperature of at least one vapor stream BS1 when at least one vapor stream BS1 is withdrawn from the distillation column DK1. The pressure of the vapor stream BS1 is in the range of in particular 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 in the range of in particular 45°C to 120°C, preferably in the range of 48°C to 100°C, more preferably in the range of 50°C to 90°C, still more preferably in the range of 55°C to 80°C, and even more preferably in the range of 60°C to 80°C. The distillation column DK1 used for the separation of the raffinate 2 stream can be any distillation column known to those skilled in the art. The distillation column DK1 preferably includes internal structures. Suitable internal structures are, for example, trays, unstructured packings (random packings) or structured packings. The trays used are usually bubble cap trays, sieve trays, valve trays, tunnel cap trays or slot trays. The unstructured packing is generally a bed of random packing. The random packing used is usually a Raschig ring, Pall ring, Berl saddle or Intalox (registered trademark) saddle. The structured packing is sold, for example, under the trade name Sulzer Mellapack (registered trademark). The above internal structures and further suitable internal structures are known to those skilled in the art and can be used similarly. The pressure drop per theoretical stage of the preferred internal structures is low. The pressure drop per theoretical stage of regular and irregular packings is significantly lower than that of trays, for example. This has the advantage that the pressure drop in the distillation column DK1 is kept as low as possible, so that the mechanical output of the compressor and the temperature of the raffinate 2 stream to be evaporated are kept low.

[0012] In a particularly preferred embodiment of the present invention, the distillation column DK1 includes a large number of trays, preferably 150 to 300 trays, more preferably 170 to 220 trays. In the context of the present invention, taking out at least one vapor stream BS1 containing at least 1-butene and isobutane at the top of the distillation column DK1 means, in particular, that at least one vapor stream BS1 is taken out as a top stream or as a side draw above the internal structure of the distillation column DK1. In the context of the present invention, taking out at least one vapor stream containing at least 1-butene and 2-butene at the bottom of the distillation column DK1 means, in particular, that at least one bottom stream is taken out directly at the bottom or the lower trays of the distillation column DK1.

[0013] The distillation column DK1 is still, preferably, operated under reflux. "Reflux" means that the vapor stream BS1 withdrawn at the upper end of the distillation column DK1 is at least partially fed back to the distillation column DK1. The reflux ratio when the reflux is established is preferably 2 to 30, more preferably 5 to 20, and particularly preferably 8 to 15. The reflux can be established by attaching a condenser to the top of the distillation column DK1. The vapor stream BS1 is partially condensed in the condenser and fed back to the distillation column DK1. The vapor stream or a portion thereof can be applied as reflux to the distillation column only after compression and expansion. Generally, in the context of the present invention, the reflux ratio means the ratio of the mass flow rate (kg / h) taken out from the column returned to the column in liquid form (reflux) to the ratio of the mass flow rate (kg / h) discharged from each column in liquid or gaseous form. After the vapor stream BS1 is taken out, the vapor stream BS1 is separated into at least two sub-streams BS1a and BS1b in (b) above. The separation can in principle be carried out by known methods, for example, a splitter (with closed-loop control using a compressor and / or a control valve). Another option that can be envisaged is closed-loop control that adjusts the mass flow rates of BS1a and BS1b as a function of specific parameters.

[0014] Thereafter, in the above (c), the first part BS1a of the vapor stream BS1 is compressed, resulting in a compressed stream VB1 for the vapor sub-stream BS1a. The pressure of the stream BS1a is generally the same as that of the stream BS1 when withdrawn from the distillation column DK1. It may be advantageous to heat the stream BS1a before compression so that a two-phase mixture is not formed during compression. The heating may be carried out by an internal heat source (see WT-1 in FIGS. 3 and 4 of the present application) or an external heat source. The pressure of VB1 after compression is higher than the pressure of BS1a. The exact value of the pressure of VB1 can be set by a person skilled in the art according to the requirements in subsequent energy transfer as long as the condition that the pressure VB1 > the pressure BS1a is satisfied. The value of the pressure VB1 / the pressure BS1a (pressures in absolute bar respectively) 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. The temperature of the sub-stream VB1 is preferably higher than the temperature of the vapor sub-stream BS1a, and the value of the temperature VB1 / the temperature BS1a (temperatures in K respectively) is preferably in the range of 1.03 to 10, more preferably 1.04 to 9, more preferably 1.05 to 8, more preferably 1.06 to 7, more preferably 1.07 to 6, and most preferably 1.08 to 5.

[0015] At least a portion of the vapor sub-stream BS1a can be compressed in the above (c) by any desired method known to those skilled in the art. For example, the compression can be carried out mechanically and in one or multiple stages. In this case, "one stage" means that the compression is carried out from one pressure level to another pressure level. "Multiple stages" means that the compression is first carried out to the pressure level X and then from X to the pressure level Y. In multi-stage compression, two or more compressors of the same type or different types of compressors may be used. The multi-stage compression may be carried out using one or more compressors. Whether one-stage compression or multi-stage compression is used depends on the compression ratio and thus on the pressure at which the vapor sub-stream BS1a is compressed. In the method according to the invention, a compressor particularly suitable for compressing the vapor stream BS1a into VB1 is any compressor known to those skilled in the art capable of compressing a gas stream, preferably a mechanical compressor. Suitable compressors are, for example, single-stage or multi-stage geared turbocompressors, piston compressors, screw compressors, centrifugal compressors or axial flow compressors.

[0016] In step (d) of the method according to the invention, energy is transferred from the compressed stream VB1 to the stream in the reboiler SV1a. As a result of the energy reduction of VB1 in step (d), VB1 is at least partially condensed, in particular. In the present invention, the term "energy transfer" particularly means heating, i.e., energy transfer in the form of heat. The transfer of energy from VB1 to the stream in the reboiler SV1a, preferably the heating of the stream in the reboiler SV1a by VB1, is preferably direct. By direct transfer is meant that although there is no direct contact between VB1 and the stream in SV1a, energy, in particular heat, is transferred from VB1 to the stream in SV1a without the presence of an additional heat transfer medium. As the reboiler SV1a, a heat exchanger known to those skilled in the art or a heat exchanger, in particular an evaporator, may be used.

[0017] In a preferred embodiment, step (d) of the method according to the invention can bring about certain advantages. The surplus energy obtained when compressing the vapor stream BS1a into the compressed vapor stream VB1 is not dissipated without being utilized, but is used in the distillation column DK2. This is because BS1a is first compressed into VB1, and VB1 is compressed to an extent exceeding the required level in SV1a. The heat of condensation obtained by further compression can be supplied to the distillation column DK2 via the stream VB1. The additional compressor output required is generally smaller than the heating steam power saved. In step (e) of the method according to the invention, at least a portion BS1b of the vapor stream BS1 other than BS1a is sent to the reboiler SV2a, where energy is transferred from BS1b to the stream present in the reboiler in SV2a. As a result of the energy reduction of BS1b in step (e), BS1b is at least partially condensed, in particular. The transfer of energy from BS1b to the flow in reboiler SV2a, preferably the heating of the flow in reboiler SV2a by BS1b, is preferably direct. By direct transfer is meant that there is no direct contact between BS1b and the flow in SV2a, but energy, particularly heat, is transferred from BS1b to the flow in SV2a without an additional heat transfer medium. As the reboiler SV2a, a heat exchanger or heat exchanger known to those skilled in the art, particularly an evaporator, may be used. After the flows VB1 and BS1b pass through the reboiler SV1a or SV2a to transfer energy to each flow, the flows VB1 and BS1b are at least partially sent to the second distillation column DK2 in (f) above, and then the separation of isobutane and 1-butene is carried out to obtain a 1-butene stream of maximum purity. The two flows VB1 and BS1b may be sent to the second distillation column DK2 independently as separate feed streams or together. Before the flow by (f) to the second distillation column is sent to the second distillation column, in a preferred embodiment, the flows VB1 and BS1b are sent to a flash vessel where they are expanded to obtain the liquid phase FP1 of the flows VB1 and BS1b. The flash vessel may further include a condenser to condense the obtained gaseous phase portion.

[0018] In a preferred embodiment of the present invention, the flows VB1 and BS1b are sent to the second distillation column collectively. For this reason, the two flows are brought to the same pressure and the same temperature in particular. Therefore, when the flows VB1 and BS1b are sent to the distillation column collectively, it is preferable that the flows VB1 and BS1b are merged in the flash vessel and obtained as a common liquid phase FP1. Thereafter, at least a portion FP1a of the liquid phase FP1 is sent to the distillation column DK2 in (f) above. For this reason, a pump is used in a particularly preferred embodiment. Here, a pump known to those skilled in the art may be used. A suitable pump is, for example, a standard chemical pump. Furthermore, it is more preferable to reflux the flow FP1b of other parts of the liquid phase FP1 other than FP1a to the first distillation column DK1. Before the raffinate 2 stream is sent to the first distillation column DK1, it is particularly preferable to transfer energy from the flow FP1b of other parts to the raffinate 2 stream. Thereby, the raffinate 2 stream is preheated. This is energetically advantageous because less energy is sent for the separation operation via the reboiler. The transfer of energy from FP1b to the raffinate 2 stream, preferably the heating of the raffinate 2 stream by FP1b, is preferably direct, that is, without using an additional heat transfer medium. For this purpose, a heat transfer device or a heat exchanger known to those skilled in the art may be used.

[0019] 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 taken out at the top of the distillation column DK2, which contains at least isobutane, and at least one product stream taken out at the bottom of the distillation column DK2, which contains at least 1-butene. The distillation column DK2 used for the separation of the two streams VB1 and BS1b may be any distillation column known to those skilled in the art. The distillation column DK2 preferably includes internal structures. Suitable internal structures are, for example, trays, unstructured packings (random packings) or structured packings. The trays used are usually bubble cap trays, sieve trays, valve trays, tunnel cap trays or slot trays. Unstructured packings are generally beds of random packings. The random packing elements used are usually Raschig rings, Pall rings, Berl saddles or Intalox (registered trademark) saddles. Structured packings are sold, for example, under the trade name Sulzer Mellapack (registered trademark). The above internal structures and further suitable internal structures are known to those skilled in the art and can be used similarly. The theoretical stage-by-stage specific pressure drop of the preferred internal structure is low. The theoretical stage-by-stage pressure drop of structured packings and random packings is significantly lower than that of trays, for example. This has the advantage that the pressure loss in the distillation column in distillation column DK2 is kept as low as possible, and thus the mechanical output of the compressor and the temperatures of the two streams VB1 and BS1b to be evaporated are kept low.

[0020] In a particularly preferred embodiment of the present invention, the second distillation column DK2 comprises a large number of trays, preferably 150 to 300 trays, more preferably 170 to 220 trays. In the context of the present invention, taking out at least one vapor stream BS2 containing at least isobutane at the top of the distillation column DK2 means in particular that at least one vapor stream BS2 is taken out as a top stream or as a side draw above the interior of the distillation column DK2. In the context of the present invention, taking out at least one product stream containing at least 1-butene at the bottom of the distillation column DK2 means in particular that at least one product stream is taken out directly at the bottom of the distillation column DK2 or at a tray below. The product stream preferably contains at least 99% by mass of 1-butene, more preferably at least 99.5% by mass of 1-butene, even more preferably at least 99.6% by mass of 1-butene. 1-Butene is the target product of the process of the present invention and is thus discharged from the process. 1-Butene may be used, for example, as a comonomer in the production of polyethylene.

[0021] Here, it should be noted that the purification degree of separation in the first distillation column DK1 finally determines the purity of 1-butene in the product stream taken out from the second distillation column DK2. This is because butane is similarly obtained as a high-boiling component in the distillation column DK2, that is, together with 1-butene. This contaminates 1-butene. Therefore, the separation of the raffinate 2 stream in the distillation column DK1 should be ensured so that butane hardly reaches the distillation column DK2 as much as possible. Therefore, it is preferable that the butane contained in the stream (1a, FP1a) sent to the distillation column DK2 is 500 to 900 ppm or less with respect to the total amount of the stream. Through the method according to the present invention, the temperature at the bottom of the second distillation column DK2 is preferably in the range of 30 to 100 °C, preferably 45 to 80 °C. More 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).

[0022] The distillation column DK2 can operate under reflux. Reflux means that the vapor stream BS2 taken out at the upper end of the distillation column DK2 is at least partially returned to the distillation column DK2. The reflux ratio when establishing the reflux is preferably 10 to 80, particularly preferably 30 to 50. Reflux can be established by attaching a condenser to the top of the distillation column DK2. The vapor stream BS2 is partially condensed in the condenser and fed back to the distillation column DK2. Generally, in the context of the present invention, the reflux ratio means the ratio of the mass flow rate (kg / h) taken out from the column returned to the column in liquid form (reflux) to the ratio of the mass flow rate (kg / h) discharged from each column in liquid form or gaseous form. Thereafter, in (g) above, the vapor stream BS2 is at least partially compressed, resulting in a compressed stream VB2 for the vapor stream BS2. The pressure of VB2 after compression is higher than the pressure of BS2. The exact value of the pressure of VB2 can be set by those skilled in the art according to the requirements in subsequent energy transfer as long as the condition that the pressure of VB2 > the pressure of BS2 is satisfied. The quotient of the pressure of VB2 / the pressure of BS2 (the pressure in each case is absolute pressure in bar) is preferably in the range of 1.1 to 10, more preferably 1.2 to 8, still 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 that a two-phase mixture is not formed during compression. The heating may be carried out by an internal heat source (refer to WT-2 in FIGS. 3 and 4 of the present application) or an external heat source. The temperature of the secondary stream VB2 is preferably higher than the temperature of the vapor stream BS2, and the quotient of the temperature of VB2 / the temperature of BS2 (the temperature is in each case K) is preferably in the range of 1.03 to 10, more preferably 1.04 to 9, still more preferably 1.05 to 8, still more preferably 1.06 to 7, still more preferably 1.07 to 6, and most preferably 1.08 to 5.

[0023] At least a portion of the vapor secondary stream BS2 can be compressed in any desired manner known to those skilled in the art in (c) above. For example, the compression can be carried out mechanically and in one or multiple stages. In multi-stage compression, two or more compressors of the same type or different types of compressors may be used. Multi-stage compression may be carried out using one or more compressors. Whether one-stage compression or multi-stage compression is used depends on the compression ratio and thus on the pressure at which the vapor secondary stream BS2 is compressed. In the method according to the present invention, a compressor particularly suitable for compressing the vapor secondary stream B2 into VB2 is any compressor known to those skilled in the art that can compress a gas stream, preferably a mechanical compressor. Suitable compressors are, for example, one-stage or multi-stage geared turbo compressors, piston compressors, screw compressors, centrifugal compressors, or axial flow compressors.

[0024] 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. As a result of the reduction in the energy of VB2 in step (d), VB2 is at least partially condensed, in particular. In the context of the present invention, the term "energy transfer" means in particular heating, i.e. energy transfer in the form of heat. The transfer of energy from VB2 to the stream in the reboiler SV1b, preferably the heating of the stream in the reboiler SV1b by VB2, is preferably direct. By direct transfer is meant that there is no direct contact between VB2 and the stream in SV1b, but energy, in particular heat, is transferred from VB2 to the stream in SV1b without the presence of an additional heat transfer medium. As the reboiler SV1b, a heat exchanger or heat exchanger known to the person skilled in the art, in particular an evaporator, may be used.

[0025] After the stream VB2 has passed through the reboiler SV1b and transferred energy to the stream present therein, VB2 may be discharged from the process as the isobutane stream IB1. However, before VB2 is removed from the process as IB1, in a preferred embodiment of the present invention, the stream VB2 is sent to a flash vessel where it is expanded to obtain the liquid phase FP2. The flash vessel may further include a condenser to condense the gaseous phase portion obtained. Thereafter, at least a portion FP2a of the liquid phase FP2 may be discharged from the process as the isobutane stream IB1. For this purpose, a pump is preferably used in a particularly preferred embodiment. In certain situations, a pump may not be necessary if a sufficient pressure ratio is provided. If a pump is used, a pump known to the person skilled in the art may be used. A suitable pump is, for example, a standard chemical pump. It is further preferred to return the portion FP2b of the liquid phase FP1 other than FP2a to the second distillation column DK2 as reflux.

[0026] In the basic configuration 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 by a single, preferably multi-stage compressor. The number of stages required depends on the target compression ratio. The heat integration by vapor compression described in this specification may be combined with other means for heat integration. Here, one or more heat pumps may be provided. The present invention will be described below with reference to the drawings. The drawings are for illustrative purposes only and should not be construed as limiting.

Brief Description of the Drawings

[0027]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Embodiments for Carrying out the Invention

[0028] For all of the following examples, a raffinate 2 stream of 55 t / h was used. The composition of the raffinate 2 stream was as follows: 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. The amount of energy required for the operation of the plant described in the example for separating 1-butene from raffinate 2 was calculated by simulation using Aspen V10. The physical data was verified by operating data and operating tests.

Example

[0029] [Example 1 (not of the present invention)] In the embodiment according to FIG. 1, only the one in which direct heat integration was performed between the tower DK1 and the distillation tower DK2 (as disclosed in Patent Document 1) was carried out. In this case, the tower DK1 was operated at a top pressure of 11 bar, and the distillation tower DK2 was operated at a top pressure of 7 bar. Therefore, using a part of the vapor stream BS1b, heat can be transferred to the distillation tower DK2 via the reboiler SV2a. The amount of heat required for a 1-butene volume of 10.3 t / h with 1-butene of 99.6% purity is 10.3 MW in the distillation tower DK2. For this reason, the distillation tower DK2 is heated using a vapor stream of 125.5 t / h from the distillation tower DK1. Nevertheless, it is necessary to introduce 15.9 MW into the distillation tower DK1 via an external heat source / media (for example, heating steam).

[0030] [Example 2 (not of the present invention)] In this embodiment, direct heat integration between distillation columns DK1 and DK2 is carried out (as disclosed in German Patent Application Publication No. 10 2005 062 700) and complemented using vapor compression (see FIG. 2). In Example 1, the 4.0 MW of condensation heat from distillation column DK1 that is not used for heat integration between distillation columns DK1 and DK2 is utilized by single-stage vapor compression by compressor V1 and sent to distillation column DK1 via secondary reboiler SV1a. By vapor compression via reboiler SV1a, a total of 4.4 MW can be transferred. Accordingly, the external heat demand in distillation column DK1 decreases from 15.9 MW (Example 1) to 11.5 MW. In order to compress the vapor from 11 bar to 16.9 bar and thereby generate a driving temperature difference of K in SV1a, a total of 382 kW of electric power must be consumed in compressor V1.

[0031] Example 3 (the present invention) In this embodiment, direct heat integration between distillation columns DK1 and DK2 is carried out (as disclosed in German Patent Application Publication No. 10 2005 062 700) and complemented using multi-stage vapor compression according to the present invention (see FIG. 3). The embodiment described in Example 2 is complemented by further vapor compression. Since 9.9 MW of condensation heat from distillation column DK2 can be utilized in distillation column DK1, the vapor in distillation column DK2 is compressed. The condensation heat increased by compressor V2 is transferred via a further reboiler SV1b. For this purpose, the vapor flow in the second distillation column DK2 is compressed from 7 bar to 21 bar. 2.6 MW of electric power is required. A total of 11.5 MW can be transferred via SV1b, and as a result, no external heat source for steady-state operation is required. Accordingly, the energy-intensive process of 1-butene distillation is fully electrified. The results of Examples 1 to 3 are summarized in Table 1 below. Table 1: Summary of Examples

[0032]

Table 1

Claims

1. 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, a first distillation column DK1 and a second distillation column DK2, the process comprising the steps of: DK1 has at least two reboilers SV1a and SV1b, and DK2 has at least one reboiler SV2a; The SV1a and SV1b are each supplied with a stream extracted from the lower end of the DK1 and returned to the DK1 after passing through each of the reboilers; The SV2a is withdrawn at the bottom end of the DK2 and is supplied with a stream that is returned to the DK2 after passing through each of the reboilers, wherein: (a) sending said raffinate 2 stream to said DK1 and separating it in said DK1 into at least one vapor stream BS1 comprising at least 1-butene and isobutane, which is withdrawn at the top of said DK1, and at least one bottom stream comprising at least 1-butene and 2-butene, which is withdrawn at the bottom of said DK1; (b) separating said BS1 into at least two substreams BS1a and BS1b; (c) compressing the BS1a, a portion of the first vapor stream of the BS1, to produce a compressed stream VB1 relative to the BS1a; (d) transferring energy from said VB1 to a flow in said SV1a; (e) transmitting the BS1b, which is a portion of the BS1 other than the BS1a, to the SV2a, thereby transferring energy from the BS1b to a flow in the SV2a; (f) at least partially sending said VB1 and said BS1b to said DK2 and separating them in said DK2 into at least one vapor stream BS2 comprising at least isobutane, which is withdrawn at the top of said DK2, and at least one product stream comprising at least 1-butene, which is withdrawn at the bottom of said DK2; (g) at least partially compressing the BS2 to produce a compressed flow VB2 relative to the BS2; and (h) transferring energy from said VB2 to a flow in said SV1b; A method comprising:

2. 2. The method of claim 1, wherein the VB1 and the BS1b are sent to a flash vessel where they are expanded to provide a liquid phase FP1 of the BS1a and the BS1b.

3. 3. The method of claim 2, wherein said VB1 and said BS1b are combined in a flash vessel to obtain a common liquid phase FP1.

4. 4. The method according to claim 3, wherein at least a portion FP1a of the liquid phase FP1 is fed to said DK2, preferably by means of a pump.

5. 5. The method according to claim 3 or 4, wherein the other part of the liquid phase FP1, stream FP1b, is returned to said DK1 as reflux.

6. 6. The method according to claim 5, wherein energy is transferred from another portion of stream FP1b to the raffinate 2 stream before the raffinate 2 stream is sent to said DK1.

7. The process according to any one of claims 1 to 5, wherein the temperature of the bottom of DK1 is in the range of 40 to 110 ° C. or 50 to 100 ° C.

8. The process according to any one of claims 1 to 6, wherein the temperature of the bottom of DK2 is in the range of 30 to 100 ° C. or 45 to 80 ° C.

9. The method of any one of claims 1 to 5, wherein said DK1 has between 150 and 300 plates.

10. The method according to any one of claims 1 to 5, wherein said DK2 has between 150 and 300 plates.

11. Method according to any one of claims 1 to 10, wherein for compression of the BS1a and the BS2 only a single compressor is used.

12. The process of any one of claims 1 to 5, wherein the VB2 is expanded in a flash vessel to obtain liquid phase FP2.

13. 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. 14. The method according to claim 13, wherein the other part of the liquid phase FP2, stream FP2b, is returned to said DK2 as reflux.

15. The process of any one of claims 1 to 6, wherein the product stream comprises at least 99% by weight 1-butene, at least 99.5% by weight 1-butene, or at least 99.6% by weight 1-butene.

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