Method for separating 1-butene from hydrocarbon stream using heat transfer medium excellent in energy efficiency

Abstract

To provide a method for separating 1-butene from a C4 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 C4 hydrocarbon flow containing at least 1-butene, 2-butene, n-butane and isobutane. One advantage of the process is heat integration through at least one heat transfer medium, which transmits energy to each flow existing in a reboiler SV1, and sends the energy to a tower bottom. As a result of the energy transmission in the reboiler SV1 of the first distillation tower DK1, an amount of heated steam to be used for heating of the DK1, if any, becomes small. A reboiler SV2 can be operated even in a part of the steam, thereby, capable of achieving complete electrification of an energy aggregation type process.SELECTED DRAWING: Figure 4

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 including a first distillation column DK1 and a second distillation column DK2 of at least two distillation columns. The present invention provides a method for utilizing the condensation heat by a heat transfer medium W 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 C4 cuts 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), and the saturated hydrocarbons isobutane and n-butane. Due to the small difference in the boiling points of the components, their small separation factors and the formation of azeotropic mixtures, the post-treatment of the C4 hydrocarbon stream by distillation alone is difficult and uneconomical. Therefore, usually, butadiene is first separated by extractive distillation or selectively hydrogenated to butene. In each case, a C4 hydrocarbon stream (referred to as raffinate 1) containing not only the saturated hydrocarbons n-butane and isobutane but also the olefins isobutene, 1-butene and 2-butene remains, and the amount of butadiene present is small. Since the boiling points of 1-butene and isobutene are close to each other, generally, 1-butene cannot be economically separated from the corresponding C4 hydrocarbon stream by simple distillation. Therefore, isobutene is removed as much as possible, for example, via MTBE synthesis or ETBE synthesis. The removal of isobutene results in a C4 hydrocarbon stream (referred to as raffinate 2) containing linear butenes (1-butene and 2-butene) and 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 known methods, the energy required for the separation of a C4 hydrocarbon stream is usually sent to the bottoms of the 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, when heating steam is generated, a large amount of CO 2 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 an embodiment 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 raffinate 2 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 one reboiler SV1, and the DK2 has at least one reboiler SV2a, the SV1 is withdrawn at the lower end of the DK1 and a stream that is returned to the DK1 after passing through the reboiler is supplied, the 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 the following: (a) Sending the 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 BS1 into at least two sub-streams BS1a and BS1b, (c) Transferring energy from the BS1a to a liquid or gaseous heat transfer medium W to produce a heat transfer medium W1, (d) Transferring energy from the BS1b, which is the part of the BS1 other than the BS1a, to the stream in the SV2 by sending the BS1b to the SV2, (e) Sending the VB1 and the BS1b at least partially to the DK2, and in the DK2, separating them into at least one vapor stream BS2 containing at least isobutane and 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, (f) Transferring the energy from the BS2 to the W to produce a heat transfer medium W2, (g) Compressing at least a portion of said W2 to produce a compressed heat transfer medium W2.1 at a higher pressure than said W2, (h) Mixing said W1 with said W2.1 to produce a mixed heat transfer medium W3, (i) Compressing at least a portion of said W3 to produce a compressed heat transfer medium W3.1 at a higher pressure than said W3, and (j) Transferring said energy from said W3.1 to the flow in said SV1. Relates to a method comprising.

[0006] One advantage of the process according to the invention is the heat integration via at least one heat transfer medium, whereby energy is transferred to each flow present in the reboiler SV1 and the energy is sent to the bottom of the column. As a result of the energy transfer in the reboiler SV1 of the first distillation column DK1, even if there was heating steam to be used for heating DK1, it would be less. Since the reboiler SV2 can also operate with a portion of the steam, (almost) complete electrification of the energy-intensive process can be achieved, whereby green power can be used. This results in a significant saving in energy costs and CO 2 emissions.

[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 not possible. However, the amount of polyunsaturated C4 hydrocarbons, especially butadiene, and isobutene should be minimal. The raffinate 2 used preferably contains less than 1000 ppm, preferably less than 500 ppm of isobutene. 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. Thus, 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 less than 4% by mass of polyunsaturated C4 hydrocarbons. 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. A corresponding method is described for those skilled in the art, for example, in European Patent Application Publication No. 3680224. The raffinate 2 stream used may further contain a predetermined amount of water, particularly in an amount of 150 - 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 a pipe in the distillate container of the distillation column DK1 and / or DK2. The bottom products of the distillation columns DK1 and DK2 are characterized in that the contents of butadiene and water are extremely low, 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 one reboiler SV1. The distillation column DK2 is the second distillation column and has at least one reboiler SV2. In a preferred embodiment, there is only the reboiler SV1 in the distillation column. Also, it is preferred that there is only the reboiler SV2 in the distillation column DK2. The pressures in the two distillation columns DK1 and DK2 must be selected in particular such that heat can be transferred to the reboiler. 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 reboiler SV1. The reboiler SV1 is supplied with the stream withdrawn at the lower end of the distillation column DK1 and returned to DK1 after passing through each reboiler. The stream is heated when passing through the reboiler SV1. This situation is comparable to the reboiler SV2 of the second distillation column DK2, whereby the energy required for the separation operation is sent. Therefore, the reboiler SV2 is supplied with the 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 SV2 and at least partially evaporates.

[0009] In the present invention, the "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, especially heat, from one stream to another, it is a heat transfer body. The stream to be evaporated is withdrawn from the bottom of the distillation column via the extraction section and supplied to the reboiler. The evaporated stream is returned to each distillation column in the region of the bottom via at least one supply section, regardless of the presence of the 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 evaporator known to those skilled in the art and suitable for use in a distillation column may be alternatively used.

[0010] The raffinate 2 sent to the first distillation column DK1 is separated in the distillation column DK1 into at least two streams, namely at least one vapor stream BS1 taken out at the top of the distillation column DK1 containing at least 1-butene and isobutane, and at least one bottom stream taken out at the bottom of the distillation column DK1 containing at least 1-butene and 2-butene. This bottom stream can introduce oligomerization. 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. 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. The raffinate 2 stream can, in principle, be sent to the first distillation column DK1 via 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 invention in which 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 taken out from the distillation column DK1. The pressure of the vapor stream BS1 is in the range of particularly 6 to 15 bar (absolute pressure), preferably 7.5 to 13 bar (absolute pressure). The temperature of the vapor stream BS1 is in the range of particularly 45 °C to 120 °C, preferably 48 °C to 100 °C, more preferably 50 °C to 90 °C, even more preferably 55 °C to 80 °C, and most preferably 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 with fixed valves or movable valves, tunnel cap trays or slot trays. Unstructured packings are generally beds of random packings. The random packings used are usually Raschig rings, Pall rings, Berl saddles, Super-Rings / Super-Rings Plus or Intalox (registered trademark) saddles. Structured packings are sold, for example, under the trade name Mellapack (registered trademark) by Sulzer. The above internal structures and further suitable internal structures are known to those skilled in the art and can be used similarly. The specific pressure drop per theoretical stage of the preferred internal structures is low. The pressure drop per theoretical stage of structured packings and random packings is, for example, significantly lower in terms of pressure loss per theoretical stage than that of trays. 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. 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 a side draw above the internal structure of the distillation column DK1. 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 bottom tray of the distillation column DK1.

[0013] The distillation column DK1 is preferably operated in reflux. "Reflux" means that at least part of the vapor stream BS1 withdrawn at the upper end of the distillation column DK1 is fed back to the distillation column DK1. The reflux ratio when establishing the reflux is preferably from 2 to 30, more preferably from 5 to 20, and particularly preferably from 8 to 15. 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, and in the context of the present invention, the reflux ratio means the ratio of the mass flow rate (kg / h) withdrawn from the column that is 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 withdrawn, 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 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 (c) above, energy is transferred from the partial stream BS1a to the liquid or gaseous heat transfer medium W, resulting in the heat transfer medium W1. The energy transferred in this case is preferably heat, and as a result, the heat transfer medium W1 is heated. The transfer of energy to the heat transfer medium W reduces the energy content of BS1a, i.e., the stream is cooled and / or condensed. The heat transfer medium W used may be any working medium known to those skilled in the art. The heat transfer medium W is preferably selected from the group consisting of water; alcohol; alcohol-water mixtures; aqueous salt solutions; ammonia; mineral oils such as diesel oil; heat oils such as silicone oil; bio-oils such as limonene; and aromatic or aliphatic hydrocarbons such as dibenzyltoluene, more preferably water, methanol, ethanol, propanol, n-pentane, n-butane, n-hexane, n-propane or ammonia, and even more preferably water. When the heat transfer medium W is used in the liquid phase, i.e., as the liquid heat transfer medium W, in step (c), and energy, preferably heat, is supplied thereto in step (c), the heat transfer medium W evaporates at least partially, and a gaseous heat transfer medium W1 is obtained. When the heat transfer medium W is used in the gas phase, i.e., as the gaseous heat transfer medium W, in step (c), and energy, preferably heat, is supplied thereto in step (c), a gaseous heat transfer medium W1 is likewise obtained.

[0015] The term "liquid heat transfer medium" in the context of the present invention means that, with respect to the total mass of the heat transfer medium used in step (c), the mass of the heat transfer medium used in step (c) is in the liquid state of matter in excess of 50%, more preferably in excess of 55%, even more preferably in excess of 75%, even more preferably in excess of 90%, and still more preferably in excess of 99%. The term "gaseous heat transfer medium" in the context of the present invention means, respectively, that, with respect to the total mass of the heat transfer medium used in step (c), it is in the gaseous state of matter in excess of 30% by mass, more preferably in excess of 50% by mass, even more preferably in excess of 75% by mass, even more preferably in excess of 90% by mass, and still more preferably in excess of 99% by mass of the heat transfer medium used in step (c). The transfer of energy in step (c) can be carried out by a process known to those skilled in the art or by a heat exchanger known to those skilled in the art, such as the above-mentioned evaporator. The heat exchanger in this case may be a condenser for the condensation of BS1a. This has the advantage that no additional condenser needs to be installed.

[0016] After the energy transfer described in (c) above, the heat transfer medium W1 preferably has an increased temperature and / or an increased pressure compared to the heat transfer medium W. In a preferred embodiment of the present invention, W1 preferably has a temperature in the range of 30 to 80 °C. The pressure of W1 is preferably in the range of 1 to 20 bar, preferably 3 to 12 bar. The heat transfer medium W1 corresponds to the heat transfer medium W, but it is obvious that W and W1 differ only in their pressure and / or temperature, and in some cases, when W is used in liquid form, they also differ in the state of matter.

[0017] In step (d) of the method according to the present invention, at least a portion BS1b of the vapor stream BS1 other than BS1a is sent to the reboiler SV2, and energy is transferred in the reboiler SV2 from BS1b to the stream existing within the reboiler SV2. As a result of the reduction in the energy of BS1b in step (d), BS1b is preferably at least partially condensed. The transfer of energy from BS1b to the stream within the reboiler SV2, preferably the heating of the stream within the reboiler SV2 by BS1b, is preferably direct. By direct transfer, it means that BS1b and the stream within SV2 do not come into direct contact, but energy, particularly heat, is transferred from BS1b to the stream within SV2 without the need for an additional heat transfer medium. The reboiler SV2 used may be a heat exchanger or a heat exchanger known to those skilled in the art, particularly an evaporator. After the streams BS1a and BS1b transfer energy to the heat transfer medium W or energy is transferred to each stream by passing through the reboiler SV2, the streams BS1a and BS1b are then at least partially sent to the second distillation column DK2 in step (e), and then the separation of isobutane and 1-butene is carried out to obtain a 1-butene stream with maximum purity. In the distillation column DK2, at least one vapor stream BS2 containing at least isobutane and drawn from the top of the distillation column DK2 and at least one product stream containing at least 1-butene and drawn from the bottom of the distillation column DK2 are separated. The two streams BS1a and BS1b may be sent to the second distillation column DK2 independently as separate feed streams or collectively. Before the stream is sent to the second distillation column by (e), in a preferred embodiment, streams BS1a and BS1b are sent to a flash vessel where they are expanded to obtain the liquid phase FP1 of streams BS1a and BS1b. The flash vessel may further include a condenser to condense the obtained vapor phase portion.

[0018] In a preferred embodiment of the present invention, streams BS1a and BS1b are collectively sent to the second distillation column. For this reason, the two streams are brought to the same pressure and the same temperature in particular. Therefore, when streams BS1a and BS1b are collectively sent to the distillation column, it is preferred that streams BS1a 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 (e). 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 preferred to reflux the stream FP1b of the other portion other than FP1a of the liquid phase FP1 to the first distillation column DK1. It is particularly preferred to transfer energy from the stream FP1b of the other portion to the raffinate 2 stream before the raffinate 2 stream is sent to the first distillation column DK1. Thereby, the raffinate 2 stream is preheated. This is energy - 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, i.e., without using an additional heat transfer medium. For this reason, as described above, 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, a stream containing at least isobutane and 1 - butene each is separated in (e) into at least one vapor stream BS2 containing at least isobutane and taken out at the top of the distillation column DK2 and at least one product stream containing at least 1 - butene and taken out at the bottom of the distillation column DK2. The distillation column DK2 used for the separation of the two streams VB1 and BS1b or FP1a can 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 with fixed valves or movable valves, tunnel cap trays or slot trays. Unstructured packings are generally beds of random packings. The random packings used are usually Raschig rings, Pall rings, Berl saddles, Super-Rings / Super-Rings Plus or Intalox (registered trademark) saddles. Structured packings are sold, for example, under the trade name Mellapack (registered trademark) by Sulzer. The above internal structures and further suitable internal structures are known to those skilled in the art and can be used similarly. The specific pressure drop per theoretical stage of the preferred internal structure is low. The pressure drop per theoretical stage of structured packings and random packings is, for example, significantly lower than that of trays. This has the advantage that the pressure loss in the distillation column in the distillation column DK2 is kept as low as possible, and thus the mechanical output of the compressor and the temperatures of the two streams BS1a and BS1b or FP1a to be evaporated are kept low.

[0020] In a particularly preferred embodiment of the present invention, the second distillation column DK2 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 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. 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 according to the invention, and thus the product stream is 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 the separation in the first distillation column DK1 ultimately determines the purity of 1-butene in the product stream taken out from the second distillation column DK2. This is because butane is likewise obtained as a high-boiling substance in the distillation column DK2, i.e., together with 1-butene. This contaminates the 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, the butane contained in the stream (1a, FP1a) sent to the distillation column DK2 is preferably 500 to 900 ppm or less based on the total amount of the stream. Through the process according to the invention, the temperature at the bottom of the second distillation column DK2 is preferably in the range of 30 to 100 °C, preferably 45 to 80 °C. 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 the reflux is established is preferably 10 to 80, particularly preferably 30 to 50. Reflux can be established by attaching a condenser to the top of distillation column DK2. Vapor stream BS2 is partially condensed in the condenser and fed back to distillation column DK2. Generally, and in the context of the present invention, the reflux ratio means the ratio of the mass flow rate (kg / h) withdrawn from the column and 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. The vapor stream BS2 obtained in distillation column DK2 is used for heat integration. In (f) above, energy is transferred from BS2 to a liquid or gaseous heat transfer medium W, resulting in heat transfer medium W2. The energy transferred in this case is preferably heat, and as a result, heat transfer medium W2 is heated. The transfer of energy to heat transfer medium W reduces the energy content of BS2, i.e., the stream is cooled and / or condensed. The heat transfer medium W used can be any working medium known to those skilled in the art. Heat transfer medium W is preferably selected from the group consisting of water; alcohol; alcohol-water mixture; aqueous salt solution; ammonia; mineral oil, such as diesel oil; heat transfer oil, such as silicone oil; bio-oil, such as limonene; and aromatic or aliphatic hydrocarbons, such as dibenzyltoluene, more preferably water, methanol, ethanol, propanol, n-pentane, n-butane, n-hexane, n-propane or ammonia, and even more preferably water. It is preferred that the heat transfer medium W used in (c) and (f) is the same. It is particularly preferred that there is a heat transfer medium circuit through which heat transfer medium W passes through (c) and (f) to (j). When heat transfer medium W is used in (f) as a liquid phase, i.e., liquid heat transfer medium W, and energy, preferably heat, is supplied to it in (f), heat transfer medium W evaporates at least partially, and gaseous heat transfer medium W2 is obtained. When heat transfer medium W is used in (f) as a gas phase, i.e., gaseous heat transfer medium W, and energy, preferably heat, is supplied to it in (f), gaseous heat transfer medium W2 is likewise obtained.

[0023] The term "liquid heat transfer medium" in the present invention means that, for each of them, with respect to the total mass of the heat transfer medium used in (f) above, the mass of the heat transfer medium used in (f) exceeds 50%, more preferably exceeds 55%, still more preferably exceeds 75%, still more preferably exceeds 90%, and even more preferably exceeds 99% and is in the liquid state of the substance. The term "gaseous heat transfer medium" in the context of the present invention means that, for each of them, with respect to the total mass of the heat transfer medium used in (f) above, it exceeds 30% by mass, more preferably exceeds 50% by mass, still more preferably exceeds 75% by mass, still more preferably exceeds 90% by mass, and even more preferably exceeds 99% by mass of the heat transfer medium used in (f) and is a gaseous substance. The transfer of energy in (f) above can be carried out by a process known to those skilled in the art or by a heat exchanger known to those skilled in the art, such as the evaporator mentioned above. The heat exchanger in this case may be a condenser for the condensation of BS2. This has the advantage that no additional condenser needs to be installed. After the transfer of energy described in (f) above, the heat transfer medium W2 preferably has an increased temperature and / or pressure compared to the heat transfer medium W. In a preferred embodiment of the present invention, W1 preferably has a temperature in the range of 30 to 80 °C. The pressure of W2 is preferably in the range of 1 to 20 bar, preferably 2 to 8 bar. In a preferred embodiment of the present invention, the pressure and / or temperature of the heat transfer medium W2 is lower than the pressure and / or temperature of the heat transfer medium W1. When energy is transferred from the vapor stream BS2 to the heat transfer medium in (f) above, BS2 can be discharged from the process as an isobutane stream IB1. However, in a preferred embodiment of the present invention, before being removed from the process as BS2IB1, the stream VB2 is sent to a flash vessel where it is expanded to obtain a liquid phase FP2. The flash vessel may further include a condenser to condense the obtained gaseous phase portion. Subsequently, at least a portion FP2a of the liquid phase FP2 may be discharged from the process as an isobutane stream IB1. For this purpose, a pump is preferably used in particularly preferred embodiments. In certain situations, a pump may not be necessary if a sufficient pressure ratio is provided. When using a pump, a pump known to those skilled in the art may be used. A suitable pump is, for example, a standard chemical pump. Further preferably, a portion FP2b of the liquid phase FP1 other than FP2a is returned to the first distillation column DK2 as reflux.

[0024] In the subsequent step (g), at least a portion of the heat transfer medium W2 is compressed, compressed with respect to W2, and a heat transfer medium W2.1 at a higher pressure than the heat transfer medium W2 is produced. The pressure of W2.1 after compression is preferably in the range of 1 to 20 bar, preferably 3 to 12 bar. More preferably, the pressures of the compressed heat transfer medium W2.1 and the heat transfer medium W1 are the same or at most the change is ±10%.

[0025] At least a portion of the heat transfer medium W2 can be compressed in any desired manner known to those skilled in the art in step (g). 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 pressure level X and then from X to pressure level Y. 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 heat transfer medium W2 is compressed.

[0026] The pressure of the heat transfer medium W1 in step (c) is preferably higher than that of the heat transfer medium W2 in step (f). Due to the compression in step (g), the pressure of the heat transfer medium W2 becomes the same or similar compared to W1. Here, "the pressures are similar" means that the difference between the pressure of W1 and the pressure of the compressed heat transfer medium W2 after compression is less than 5%, preferably less than 1%. In the method according to the invention, a compressor particularly suitable for compressing the heat transfer medium W2 is any compressor known to those skilled in the art that is capable of compressing a gas stream, preferably a mechanical compressor. Suitable compressors are, for example, single-stage or multi-stage geared turbo compressors, piston compressors, screw compressors, centrifugal compressors or axial flow compressors.

[0027] The compressed heat transfer medium W1 is then mixed with the heat transfer medium W1 in (h) above to produce a mixed heat transfer medium W3. The mixing can be done by simply merging two pipelines without any special internal structure. This is basic and known to those skilled in the art. The mixing of the two heat transfer media W2.1 and W1 has the advantage that the superheat of the heat transfer medium W1 can contribute to the superheat of the heat transfer medium W2.1. As a result, no other heat exchanger is required before the mixed heat transfer medium W3 is compressed in (i) below. In (i) above, at least a portion of the heat transfer medium W3 is compressed, compressed with respect to the heat transfer medium W3, and a heat transfer medium W3.1 at a higher pressure than the heat transfer medium W3 is produced. The pressure of W3.1 after compression is preferably in the range of 5 to 30 bar, preferably 10 to 20 bar. The compression of at least a portion of the heat transfer medium W3 can be carried out in any manner known to those skilled in the art in (i) above. For example, the compression can be carried out mechanically and in single-stage or multi-stage compression. In this case, "single-stage" means that the compression is carried out from one pressure level to another pressure level. "Multi-stage" means that the compression is first carried out to pressure level X and then from X to pressure level Y. In multi-stage compression, two or more compressors of the same type or different types of compressors can be used. Multi-stage compression can be carried out using one or more compressors. Whether single-stage compression or multi-stage compression is used depends on the compression ratio and thus on the pressure at which the heat transfer medium W3 is compressed. In the method according to the invention, a compressor particularly suitable for compressing the heat transfer medium W3 is any compressor known to those skilled in the art that is capable of compressing a gas stream, preferably a mechanical compressor. Suitable compressors are, for example, single-stage or multi-stage geared turbo compressors, piston compressors, screw compressors, centrifugal compressors or axial flow compressors.

[0028] In step (j) of the method according to the invention, energy is transferred from the compressed heat transfer medium W3.1 to the flow in the reboiler SV1. In step (j), the energy of W3.1 can be reduced, preferably at least partially condensing W3.1. The term "energy transfer (movement)" in the present invention particularly means heating, i.e., energy transfer in the form of heat. The transfer of energy from W3.1 to the flow in the reboiler SV1, preferably the heating of the flow in the reboiler SV1 by W3.1, is preferably direct. Direct transfer means that W3.1 and the flow in SV1 do not come into direct contact, but energy, particularly heat, is transferred from W3.1 to the flow in SV1 without the presence of an additional heat transfer medium. As the reboiler SV1, a heat exchanger or heat exchangers known to those skilled in the art, particularly an evaporator, may be used. The energy transfer in step (j) can be carried out by a process known to those skilled in the art or by using a heat exchanger known to those skilled in the art. Suitable evaporators that can be used as heat exchangers are, for example, natural circulation evaporators, forced circulation evaporators, forced circulation flash evaporators, kettle evaporators, falling film evaporators or thin film evaporators. Similarly as above, any other design of evaporators known to those skilled in the art and suitable for use in distillation columns may be alternatively used.

[0029] In the basic configuration of the present invention, the two flows W2 and W3 are each compressed by a single compressor. In a preferred embodiment of the present invention, the two flows W2 and W3 are compressed by a one-stage, preferably multi-stage compressor. The number of required stages depends on the target compression ratio. As described above, the heat transfer medium is preferably circulated. This means that after the heat transfer medium W3.1 transfers energy in step (j), it is fed back in steps (c) and (f) and reused. Therefore, in a preferred embodiment of the present invention, only a single heat transfer medium is used throughout the process. Accordingly, the heat transfer medium W used in steps (c) and (f) is the same. The heat transfer medium W3.1 may be cooled before partially heading towards step (c) and step (f) as the heat transfer medium W. This is preferable because if the heat transfer medium W that absorbs thermal energy from the condensation of the vapor streams BS1 and BS2 is at a specific pressure and temperature level, it can absorb a desired amount of thermal energy in the heat exchanger. For this reason, it may be necessary to cool the heat transfer medium W3.1 after transferring energy in the reboiler. This energy can be utilized by performing the cooling in a heat exchanger that preheats the heat transfer medium W2. As a result, there is an effect that less energy needs to be introduced by the compressor thereafter.

[0030] After the energy transfer in step (j) of the method according to the present invention, before the stream of raffinate 2 is sent to the first distillation column, the stream of raffinate 2 may be preheated using the heat transfer medium W3.1. Thereafter, the heat transfer medium W3.1 is recycled after preheating and is sent partially as the heat transfer medium W to step (c) and partially to step (f). If not preheated, the heat transfer medium W3.1 is recycled without going through this further step and is sent partially as the heat transfer medium W to step (c) and partially to step (f). The heat integration by the heat pump described herein may be used in combination with other means for heat integration. Here, one or more vapor compressions may be provided. The present invention will be described below with reference to the drawings. The drawings are for illustrative purposes and should not be construed as limiting.

Brief Description of the Drawings

[0031]

Figure 1

Figure 2

Figure 3

Figure 4

Embodiments for Carrying Out the Invention

[0032] For all the following examples, a raffinate 2 stream of 55 t / h was used. The composition of the raffinate 2 stream is 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.

Examples

[0033] [Example 1 (Not of the Present Invention)] In the embodiment according to FIG. 1, an exclusive direct heat integration between the column DK1 and the distillation column DK2 was carried out (as disclosed in Patent Document 1). In this case, the column DK1 was operated at a top pressure of 11 bar, and the distillation column DK2 was operated at a top pressure of 7 bar. Therefore, a part of the vapor stream BS1b can be used to transfer heat to the distillation column DK2 via the reboiler SV2. 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 column DK2. For this reason, the distillation column DK2 is heated using a vapor stream of 125.5 t / h from the distillation column DK1. Nevertheless, it is necessary to introduce 15.9 MW into the distillation column DK1 via an external heat source / media (for example, heating steam).

[0034] [Example 2 (not of the present invention)] In this embodiment, it is assumed that the unused condensation heat is utilized in the distillation column DK1 by means of interconnection. Here, only 4 MW of the condensation heat from the distillation column DK1 can be utilized via a heat pump. As in Example 1, the distillation column DK1 is operated at a top pressure of 11 bar (absolute pressure) and a maximum temperature of 72°C. Therefore, methanol can be evaporated at 1.1 bar using the condensation heat from the distillation column DK1. Thereafter, the gaseous methanol is passed through a preheater to prevent droplet formation in the downstream compressor. The methanol reaches a pressure or temperature level at which heat can be transferred via SV1. For this reason, 450 kW of electric power is required. The condensed methanol returns from SV1 to the condenser of the distillation column DK1 via preheating. Thereby, the external heating output can be reduced from 15.9 MW to 11.45 MW. A further external heating output is sent via a further evaporator SV1a.

[0035] [Example 3 (not of the present invention)] In this embodiment, it is assumed that unused condensation heat is utilized through interconnection. Here, only the condensation heat from the distillation column DK2 of 9.9 MW can be utilized via a heat pump. As in Example 1, the column distillation column DK2 is operated at a top pressure of 7 bar (absolute pressure) / maximum temperature of 50°C. As in Example 2, since methanol has to be evaporated under reduced pressure, methanol is not suitable as a heat transfer medium here. In this example, n-pentane is used as the working medium. The condensation heat from the distillation column DK2 is utilized to evaporate n-pentane at 1.4 bar (absolute pressure). The gaseous n-pentane needs to be superheated before the next compression. The n-pentane is compressed to a pressure level of 5 bar (absolute pressure) so that it can be used in the distillation column DK1. This requires 2000 kW of electric power. With the wiring according to the present invention, 11.9 MW of external heating electric power can be replaced with 2000 kW of electric power. The remaining 4 MW of external heating electric power is sent through an additional evaporator SV1a.

[0036] Example 4 (the present invention) The wiring according to the present invention is assumed to enable the utilization of unused condensation heat. Here, a total of 13.5 MW of condensation heat from the distillation columns DK1 and DK2 can be utilized by a multi-stage heat pump. As in Example 1, the distillation column DK2 is operated at a top pressure of 7 bar (absolute pressure) / maximum temperature of 50°C. The condensation heat from the distillation column DK2 is utilized to evaporate n-pentane at 1.4 bar (absolute pressure). The n-pentane gas has to be superheated before the next compression. The n-pentane gas is first compressed to a pressure level of 2.1 bar (absolute pressure) in the first compressor stage. Further, the condensation heat from the distillation column DK1 is utilized to evaporate n-pentane at 2.1 bar (absolute pressure). The n-pentane gas generated by the condensation heat from the distillation column DK1 is sucked in from the second compressor stage together with the already compressed n-pentane and compressed to a pressure level of 5 bar (absolute pressure). A total of 3.2 MW of electric power is required for complete electrification. The results of Examples 1 to 4 are summarized in Table 1.

[0037]

Table 1

Claims

1. 1. A process for separating 1-butene from a raffinate 2 stream containing at least 1-butene, 2-butene, n-butane and isobutane in a separation unit comprising at least two distillation columns, a first distillation column DK1 and a second distillation column DK2, the process comprising the steps of: DK1 has at least one reboiler SV1, and DK2 has at least one reboiler SV2a. The SV1 is withdrawn from the lower end of the DK1 and is supplied with a stream that is returned to the DK1 after passing through the reboiler; 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) transferring energy from the BS1a to a liquid or gaseous heat transfer medium W to produce a heat transfer medium W1; (d) transmitting the BS1b, which is a portion of the BS1 other than the BS1a, to the SV2, thereby transferring energy from the BS1b to a flow in the SV2; (e) sending said VB1 and said BS1b at least partially 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; (f) transferring the energy from the BS2 to the W to produce a heat transfer medium W2; (g) compressing at least a portion of W2 to produce a compressed heat transfer medium W2.1 at a higher pressure than W2; (h) mixing said W1 with said W2.1 to form a mixed heat transfer medium W3; (i) compressing at least a portion of W3 to generate a compressed heat transfer medium W3.1 having a higher pressure than W3; and (j) transferring said energy from said W3.1 to a flow in said SV1; A method comprising:

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

3. 3. The method of claim 2, wherein the BS1a and the 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 sent to said DK2.

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

6. 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.

7. 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.

8. The method of any one of claims 1 to 7, wherein said DK1 has between 150 and 300 plates.

9. The method according to any one of claims 1 to 8, wherein said DK2 has between 150 and 300 plates.

10. The process according to any one of claims 1 to 9, wherein the BS2 is expanded in a flash vessel to obtain a liquid phase FP2.

11. 11. The process according to claim 10, wherein at least a portion FP2a of the liquid phase FP2 is discharged from the process as a product stream and another portion FP2b of said FP2 is returned to said DK2 as reflux.

12. The process of any one of claims 1 to 11, 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.

13. The method according to any one of claims 1 to 12, wherein only a single heat transfer medium is used throughout the process.

14. 14. The method according to claim 1, wherein the W3.1 is recycled after preheating as the W, partly to c) and partly to f).

15. 15. The method according to any one of claims 1 to 14, wherein the heat transfer medium is selected from the group consisting of water, alcohol, alcohol water mixture, salt water solution, ammonia, mineral oil, diesel oil, thermal oil, silicone oil, biological oil, limonene, aromatic hydrocarbons, aliphatic hydrocarbons, dibenzyltoluene, methanol, ethanol, propanol, n-pentane, n-butane, n-hexane, n-propane.

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