Energy-saving distillation process with altered inflow

Abstract

The invention relates to an energy efficient distillation process with altered inflow. The invention relates to a method for distilling a raffinate 2 stream as a feed stream in at least two distillation columns DK1 and DK2, wherein at least the distillation column DK1 has two different inlets for the feed stream. The method is characterized in that the composition of the feed stream is analyzed prior to introduction; and selecting one of the at least two inlets for feeding the feed stream according to the composition of the feed stream.

Description

Field of the Invention

[0001] The invention relates to a method for distilling a raffinate 2 stream as a feed stream in at least two distillation columns DK1 and DK2, wherein at least the distillation column DK1 has two different inlets for the feed stream. The method is characterized in that the composition of the feed stream is analyzed before introduction; and one of at least two inlets for feeding the feed stream is selected according to the composition of the feed stream. Background Art

[0002] The distillation of hydrocarbon streams is a proven technique for separating substances from a mixture of substances. Distillation methods are thus indispensable in the chemical industry for the production of many chemicals. Examples of these methods are distilling a feed stream before a chemical reaction to remove low-boiling or high-boiling components, or distilling a crude product mixture to remove reactants and low-boiling and / or high-boiling by-products.

[0003] Hydrocarbon streams used in distillation usually undergo natural and / or production-related compositional fluctuations. This means that the proportion of components in the hydrocarbon stream becomes larger or smaller, new components are introduced and / or some other components disappear. These include, for example, the material streams in petrochemical production facilities. These hydrocarbon streams are especially C4 hydrocarbon streams from steam crackers, FCC C4 streams, product streams from MTBE synthesis (MTBE = methyl tert-butyl ether), raffinate 2 streams or product streams from oligomerization reactions.

[0004] C4 hydrocarbon streams mainly consist of butadiene, isobutene, 1-butene, two 2-butenes, isobutane and n-butane. For such C4 hydrocarbon streams, the treatment methods commonly implemented worldwide include the following steps: First, most of the butadiene is removed. In both cases, this leaves a hydrocarbon mixture that contains, in addition to the saturated hydrocarbons n-butane and isobutane, the olefins isobutene, 1-butene and 2-butene and is called raffinate 1. A possible method for removing isobutene from this mixture is to react it with methanol to obtain MTBE. This leaves saturated hydrocarbons, linear butenes and an optional residual amount of isobutene. The mixture obtained after removing butadiene and isobutene is called raffinate 2.

[0005] Fluctuations in the composition of the proportions of the various components in a hydrocarbon stream, especially in raffinate 2, can lead to: the separation task can no longer be fully completed, or more energy must be used to complete the separation task. Summary of the Invention

[0006] The task achieved by the present invention is thus to improve the known distillation method. The fluctuating composition of the proportions of the components in raffinate 2 should be processed with as little input as possible, while the separation task should be completed in as basically uniform a manner as possible.

[0007] This task is achieved by an embodiment of the method claimed in claim 1. Preferred embodiments are described in the dependent claims. The method according to the invention is a method for distilling a raffinate 2 stream as a feed stream in a separation unit comprising at least two distillation columns DK1 and DK2, wherein

[0008] each of the distillation columns DK1 and DK2 comprises a top at the upper end of the column and a bottom at the lower end of the column, wherein in each case a vapor stream is obtained at the top and a bottoms stream is obtained in each case at the bottom, and wherein a part of the vapor stream from DK2 is used to feed the distillation column DK2;

[0009] the vapor streams from DK1 and DK2 are at least partially condensed, and the condensation energy obtained from at least one of the vapor streams from DK1 or DK2 is used to heat at least one of the distillation columns DK1 or DK2 by means of vapor compression or by means of a heat pump;

[0010] at least the distillation column DK1 has at least two different inlets for the feed stream, wherein, when viewed from the top of the distillation column, the inlets are arranged one above the other;

[0011] the composition of the feed stream is analyzed before introduction; and

[0012] one of the at least two inlets for feeding the feed stream is selected according to the composition of the feed stream.

[0013] One advantage of the method according to the invention is that an as-optimized-as-possible separation of the hydrocarbon feed stream and the raffinate 2 stream used can be obtained by selecting a suitable inlet into the distillation column, and energy can be saved at the same time.

[0014] The feed stream fed to the distillation according to the invention is a hydrocarbon stream. The feed stream for the distillation method according to the invention is a raffinate 2 stream. The raffinate 2 stream contains at least 1-butene, 2-butene, n-butane and isobutane. The raffinate 2 stream can undergo 1-butene separation in other processes of the petrochemical process network. This includes separating 1-butene from the raffinate 2 by distillation to obtain a raffinate 3. This 1-butene separation is preferably carried out by the distillation method according to the invention. Incidentally, the 1-butene separation is usually not carried out completely. Thus, 1-butene may still remain in the raffinate 3.

[0015] The hydrocarbon stream for the distillation method according to the invention is a raffinate 2 stream containing at least 1-butene, 2-butene, n-butane and isobutane. In the distillation, 1-butene will be at least partially separated from the raffinate 2 stream.

[0016] The raffinate 2 used preferably contains less than 2500 ppm, preferably less than 1000 ppm, particularly preferably less than 500 ppm of isobutene. Further preferably, the raffinate 2 used in the process according to the invention contains less than 4% by weight of polyunsaturated C4 hydrocarbons. In a particularly preferred embodiment, the concentration of polyunsaturated C4 hydrocarbons should be less than 500 ppm. If the stream is to contain a higher amount of butadiene, selective hydrogenation can be carried out beforehand, in which butadiene is converted to butene and / or butane. Corresponding processes are known to those skilled in the art.

[0017] The raffinate 2 stream used can additionally contain a certain amount of water, in particular in an amount of 150 to 4000 ppm. The water is preferably removed at least partially by distillation. The water will be enriched in the vapor stream obtained in the distillation column and obtained as a second liquid phase after condensation, which can be separated out via the nipple (Euter) in the distillation vessel of the distillation column. The bottom product from the distillation column is characterized by a very low content of butadiene and water, preferably each less than 100 ppm, more preferably less than 5 ppm.

[0018] The process according to the invention is carried out in a separation unit comprising at least two distillation columns DK1 and DK2. The distillation columns can be any known distillation columns suitable for the corresponding separation process. The distillation columns DK1 and DK2 are constructed such that they each comprise a top at the upper end of the column and a bottom at the lower end of the column. At least the distillation column DK1 has at least two different inlets via which the feed stream used (i.e., the raffinate 2) can enter the distillation column DK1. Viewed from the top of the column, i.e., from the upper end of the column, the at least two inlets are arranged one above the other. Spatially and viewed from the bottom, the at least two inlets are thus not arranged at the same height but at different heights. The distillation column DK2 can also have at least two different inlets via which the stream from DK1 can enter the distillation column DK2.

[0019] Obviously, the distillation column DK1 or DK2 used in the process according to the invention can also have more than two, i.e., three, four, five or more inlets via which the respective streams are introduced into the distillation column according to its composition.

[0020] The heat energy required for the separation task is usually introduced into the distillation column via at least one reboiler. The stream withdrawn at the lower end, i.e., in or at the bottom of the distillation column, preferably flows through the reboiler here and returns to the distillation column after passing through the reboiler. The stream is heated when passing through the reboiler.

[0021] According to the present invention, a "reboiler" refers to an evaporator that heats the bottom of the corresponding distillation column. Such reboilers are typically provided outside the corresponding distillation column. Since energy (especially heat) is transferred from one stream to another in the reboiler, they are heat exchangers. The stream to be evaporated is (at least partially) withdrawn from the bottom of the distillation column through an outlet (Abzug) and fed into the reboiler. The evaporated stream (optionally with a liquid residue portion) is returned through at least one inlet to the bottom region of the corresponding distillation column.

[0022] Suitable evaporators that can be used as reboilers are, for example, natural circulation evaporators, forced circulation evaporators, forced circulation evaporators with expansion (Entspannung), kettle evaporators, falling film evaporators or thin film evaporators. The heat exchangers of the evaporators commonly used in the case of natural circulation evaporators and forced circulation evaporators are shell-and-tube or plate-type devices. In addition to the above devices, any other evaporator design known to those skilled in the art and suitable for distillation columns can also be used alternatively.

[0023] The at least two distillation columns preferably also have a plurality of internal components, such as bulk packing beds, (structured) packings or trays. These internal components ensure sufficient contact between the vapor rising in the distillation column and the liquid flowing downward and improve mass transfer and heat transfer. The trays used are typically bubble-cap trays, sieve trays, valve trays with fixed or movable valves, channel trays or slotted trays. The non-structured packings are usually bulk packing beds. The bulk packings used are typically Raschig rings, Pall rings, Berl saddles, SuperRinge / SuperRinge Plus or saddle packings. Structured packings are sold, for example, by Sulzer under the trade name These and other suitable internal components are known to those skilled in the art and can equally be used.

[0024] The preferred internal components have a low specific pressure drop per theoretical plate. Structured packings and bulk packings have, for example, a significantly lower pressure drop per theoretical plate than trays. The advantage is that the pressure drop in the (one or more) distillation columns remains as low as possible, so that the mechanical power of the compressor and the temperature of the raffinate 2 stream to be evaporated remain low.

[0025] In a particularly preferred embodiment of the present invention, the distillation column DK1 comprises internals, preferably 2 to 300 internals, more preferably 2 to 250 internals, particularly preferably 2 to 220 internals. Viewed from the top of the distillation column, the internals are arranged one above the other within the distillation column DK1. In a preferred embodiment of the present invention, the inlets are each at the height of at least one internal component. Since the inlets are arranged one above the other, the inlets can in principle also be arranged at different heights based on one of the internal components. However, particularly preferably, at least two inlets are located at the heights of different internal components.

[0026] In another particularly preferred embodiment of the present invention, the distillation column DK2 comprises internals, preferably 2 to 300 internals, more preferably 2 to 250 internals, particularly preferably 2 to 220 internals. Viewed from the top of the distillation column, the internals are arranged one above the other within the distillation column DK2. In a preferred embodiment of the present invention, the inlets are each at the height of at least one internal component. Since the inlets are arranged one above the other, the inlets can in principle also be arranged at different heights based on one of the internal components. However, particularly preferably, at least two inlets are located at the heights of different internal components.

[0027] The internals of the distillation column are defined by the theoretical plates they generate. Distillation columns are typically designed via the number of theoretical plates. In the case of trays as internals, the number of theoretical plates is obtained by multiplying the number of trays by the tray efficiency (number of theoretical plates = number of trays * tray efficiency). In the case of a packed bed of random packing or (structured) packing, the number of theoretical plates is obtained by multiplying the HETP value (the equivalent height of one theoretical plate) by the height of the packed bed of random packing or (structured) packing used (number of theoretical plates = HETP value * height of the packed bed of random packing or (structured) packing). The HETP value can be determined with reference to the substance mixture to be separated and the packed bed of random packing or (structured) packing used. Typically, a plurality of theoretical plates are generated by the packed bed of random packing or (structured) packing, i.e., one of the internals.

[0028] It should be clear that the separation unit can comprise one or more additional distillation columns. Whether one or more additional distillation columns are present in the separation unit depends on the separation task to be accomplished. If fluctuations in the feed composition are also expected in the feed stream entering the additional distillation column(s), changing the selected inlets according to the composition of the corresponding feed stream also applies here. The distillation column(s) can be constructed similarly to the distillation column already described, i.e., having a bottom and a top, using a reboiler to introduce thermal energy, and can include a plurality of internals such as a packed bed of random packing, (structured) packing, or trays.

[0029] The first step in the method according to the invention is to analyze the feed stream before introduction, i.e., the composition of the raffinate 2. This means determining at least the (percentage) ratio, concentration, or amount of the (one or more) components of the raffinate 2 stream relevant to the selection of the inlet for feeding the hydrocarbon stream. In a preferred embodiment, in each case, the characteristic separated components are determined; in the case of the present invention, for the use of the raffinate 2 stream, it is preferred to measure the n-butane content and / or the isobutane content. The analysis of the composition can be carried out by any known analytical method. Preferred analytical methods for the method according to the invention are Raman spectroscopy and gas chromatography. In principle, the composition of the raffinate 2 stream can be analyzed online, i.e., such that the measurement is carried out in the method. On the other hand, the measurement can also be carried out such that a sample is taken at a suitable point and subsequently analyzed outside the method.

[0030] Depending on the composition of the raffinate 2 stream or the stream fed to DK2, one of at least two inlets for feeding the corresponding stream is selected. This means that the higher or lower inlet of at least two inlets (based on at least two inlets) serves as the feed inlet of the distillation column, and the corresponding stream - i.e., for example, the raffinate 2 stream - is introduced into the distillation column via this feed inlet. If there are more than two inlets, this applies accordingly, where it is not necessarily required to select the highest or lowest inlet, but one or more intermediate inlets can be selected.

[0031] In the distillation according to the invention, the pipelines leading to at least two inlets of the distillation column preferably have suitable closing devices so that the pipelines leading to each inlet can be closed and opened independently of each other. The corresponding closing devices are well known to those skilled in the art, such as valves of a suitable type.

[0032] The method according to the invention can in principle be operated continuously or batchwise. The method according to the invention is preferably a continuously operated method.

[0033] In the case of a continuously operated method and a method operated batchwise, the composition of the streams used may change during the course of the method. The material streams used industrially (here the raffinate 2) often suffer from certain fluctuations. Such changes in composition are not always large enough to affect the relevant distillation process. However, during the course of the method according to the invention, the composition of the corresponding stream may also change and thus it is necessary to switch to another inlet. This means that the composition of the stream used in each case is not analyzed only once throughout the method, but continuously at predetermined time intervals. The interval between two analytical measurements can vary depending on the type of hydrocarbon stream used. In principle, the interval between two analytical measurements can be from 10 to 59 seconds, 1 to 59 minutes, 1 to 23 hours, or 1 to several days.

[0034] If a conversion from one of at least two inlets to another is required, the conversion of the corresponding material flow to the other inlet can be carried out automatically or manually. During the conversion, one inlet and / or the pipe leading to the inlet is closed, while the other inlet and / or the pipe leading to the inlet is opened.

[0035] If the conversion to the other inlet is automatic, the conversion can be carried out as follows: with the aid of a control unit, for example a computer, the analysis results are evaluated, and in the case of a value above or below the boundary value of the corresponding material flow composition, the conversion to the other inlet is carried out. Such automation with the aid of computer-aided evaluation is very easy to implement because it is a comparison between the boundary value and the measured value. In addition, human errors are avoided as much as possible, and the conversion can be carried out more quickly. Suitable boundary values are all measurable parameters related to the composition of the material flow or its components, i.e. for example the (percentage) proportion, concentration or amount of the (one or more) components in the material flow already mentioned.

[0036] In the context of the method according to the invention, at least one of the two distillation columns DK1 and DK2 is preferably operated with reflux; preferably, both distillation columns DK1 and DK2 are operated with reflux. "Reflux" means that at least part of the vapor material flow taken out at the top of the distillation column is guided back into at least one distillation column. The reflux can be established by installing a condenser at the top of the corresponding distillation column. The vapor material flow is at least partially condensed in the condenser and then returned to the distillation column. In the case of forming such a reflux, the reflux ratio is preferably less than 1 to 100, more preferably 1 to 50, and particularly preferably 1 to 30. Generally and in the context of the present invention, the reflux ratio refers to the ratio of the part (reflux) that is returned to the column in liquid form to the part that is discharged from the corresponding column in liquid or gaseous form in the mass flow rate (kg / h) taken out of the column.

[0037] The temperature and pressure in at least one distillation column are determined by the required separation task and are therefore based on the hydrocarbon material flow used. Finding the correct temperature and the correct pressure is not a problem for a person skilled in the art. A person skilled in the art will be able to determine the temperature and pressure quite easily based on the relative volatility or the separation task to be completed.

[0038] The distillation method is generally a rather energy-consuming method, in which heat energy is introduced via the bottom to complete the separation task. At the same time, the separated vapor is cooled to at least partially condense it. In the method according to the invention, it is advantageous to take heat integration measures to recover the energy within the system and make it available. Suitable measures for heat integration are vapor compression and the use of a heat pump.

[0039] One possible measure for heat integration is vapor compression. This involves at least partially compressing the vapor stream withdrawn from the top. This increases the pressure of the vapor stream. Additional energy is introduced into the system by compression. At least a portion of the vapor stream can be compressed in any manner known to those skilled in the art. For example, compression can be carried out mechanically and in single-stage or multi-stage compression. At this point, "single-stage" means compression from one pressure level to another. "Multi-stage" means first compressing to pressure level X and subsequently from X to pressure level Y. In multi-stage compression, multiple compressors of the same type or different types can be used. Multi-stage compression can preferably be achieved with one compressor or multiple compressors. The use of single-stage or multi-stage compression depends on the compression ratio and thus on the pressure to which the vapor sub-stream is to be compressed.

[0040] Compressors suitable in the method according to the invention, in particular for compressing vapor streams, are any compressors known to those skilled in the art, preferably mechanical compressors, with which a gas stream can be compressed. Suitable compressors are, for example, single-stage or multi-stage gear-driven turbo compressors, piston compressors, screw compressors, centrifugal compressors or axial compressors.

[0041] After compression, the compressed vapor stream is directed to a heat exchanger where it transfers thermal energy to another stream. For example, thermal energy can be transferred to the stream in a reboiler and thus heat the distillation column. According to the invention, the phrase "energy transfer" particularly refers to heating, i.e., transferring energy in the form of heat.

[0042] Another measure for heat integration is the use of a heat pump. The vapor stream withdrawn from the top of at least one distillation column is used here to transfer thermal energy to a heat-carrying medium. After the energy transfer, the heat-carrying medium preferably has an elevated temperature and / or an elevated pressure.

[0043] The energy transfer can be carried out by methods known to those skilled in the art or using heat exchangers known to those skilled in the art. Suitable evaporators that can be used as heat exchangers are, for example, natural circulation evaporators, forced circulation evaporators, forced circulation evaporators with expansion, kettle evaporators, falling film evaporators or thin film evaporators. In addition to those mentioned above, any other evaporator design known to those skilled in the art and suitable for distillation columns can also be used. The heat exchanger can also be a condenser for condensing the vapor stream in this case. The advantage is that no additional condenser needs to be installed.

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

[0045] After the energy transfer mentioned, the heat-carrying medium is at least partially compressed, thereby producing a compressed heat-carrying medium at a higher pressure than the heat-carrying medium before compression.

[0046] The compression of at least a part of the heat-carrying medium can be achieved in any manner known to those skilled in the art. For example, as already defined above, the compression can be carried out mechanically and in single-stage or multi-stage compression. Suitable compressors in the method according to the invention are any compressors known to those skilled in the art, preferably mechanical compressors, with which a gas stream can be compressed. Suitable compressors are, for example, single-stage or multi-stage gear-driven turbo compressors, piston compressors, screw compressors, centrifugal compressors or axial compressors.

[0047] In the next step, energy is transferred from the compressed heat-carrying medium to the stream to be heated in the system, preferably in a reboiler, in order to heat the distillation column thereby.

[0048] Compared with vapor compression, in which the vapor obtained at the top of the distillation column is compressed and used for heat transfer, a heat-carrying medium is also inserted when using a heat pump. However, the principle is the same: energy is collected at one point in the method and used at another point in the method.

[0049] This method is used to separate the raffinate 2 stream. The separation unit preferably consists here of at least two distillation columns DK1 and DK2, where there are at least two different inlets for the hydrocarbon stream in the first distillation column DK1. The raffinate 2 introduced into 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 off at the top of DK1 and containing at least 1-butene and isobutane, and at least one bottom stream taken off at the bottom of DK1 and containing at least 1-butene and 2-butene. The vapor stream BS1 can also be taken off at the top of the distillation column in the form of a plurality of sub-streams BS1(n), where n is an integer and equal to the number of sub-streams. This also applies to the bottom stream. The temperature at the bottom of the first distillation column DK1 is preferably in the range of 40 to 110 °C, preferably 50 to 100 °C.

[0050] The pressure and temperature of the vapor stream BS1 will be given below. This particularly relates to the pressure and temperature of at least one vapor stream BS1 when taken from the distillation column DK1. The pressure of the vapor stream BS1 is particularly in the range of 6 to 15 bar absolute pressure, preferably in the range of 7.5 to 13 bar absolute pressure. The temperature of the vapor stream BS1 is particularly in the range of 45 °C to 120 °C, preferably in the range of 48 °C to 100 °C, further preferably in the range of 50 °C to 90 °C, further preferably in the range of 55 °C to 80 °C, more preferably in the range of 60 °C to 80 °C.

[0051] In the context of the present invention, the meaning of taking at least one vapor stream BS1 containing at least 1-butene and isobutane at the top of the distillation column DK1 particularly means that at least one vapor stream BS1 is taken as the top stream or as a side stream above the internal components in the distillation column DK1.

[0052] In the context of the present invention, the meaning of taking at least one bottom stream containing at least 1-butene and 2-butene at the bottom of the distillation column DK1 particularly means that at least one bottom stream is taken directly at the bottom of the distillation column DK1 or at the lower trays.

[0053] The distillation column DK1 is preferably operated in reflux mode. The meaning of "reflux" means that at least part of the vapor stream BS1 taken at the top of the distillation column DK1 is re-fed into the distillation column DK1. In the case of establishing such reflux, the reflux ratio is preferably 2 to 30, more preferably 5 to 20, and particularly preferably 8 to 15.

[0054] The vapor stream from the first distillation column DK1 is led to the second distillation column DK2. Thermal integration measures such as vapor compression or using a heat pump are possible here, where energy can be collected by at least partial condensation of the vapor stream BS1 and used to heat DK1 and / or DK2. If the amount of isobutene in the stream led to the distillation column DK2 is too high to meet the specifications of the 1-butene product from DK2, an additional MTBE or ETBE synthesis can be provided between the distillation columns DK1 and DK2. For this purpose, the stream is led into the MTBE or ETBE synthesis, and the isobutene present is at least partially converted into MTBE or ETBE, and then the formed MTBE or ETBE is separated out.

[0055] The synthesis of MTBE or ETBE is in principle known to those skilled in the art. To prepare MTBE or ETBE from a feed stream containing isobutene, acidic ion exchange resins (sulfonic acid groups) can be used in particular as heterogeneous catalysts. The synthesis of MTBE or ETBE can be carried out in one or more reactors connected in series. The catalyst is preferably used in the form of a fixed bed catalyst. Since the formation of MTBE or ETBE is an equilibrium reaction, it may be expedient to use at least one reactive distillation column in which the reaction and the separation of MTBE or ETBE take place simultaneously. In reactive distillation, the pressure should be from 3 to 15 bar and the temperature in the reaction zone is from 55 to 75 °C. After synthesis, MTBE or ETBE is preferably separated by distillation. This method is also known to those skilled in the art. The resulting feed stream with less isobutene can subsequently be directed to distillation column DK2.

[0056] In the second distillation column DK2, the supplied hydrocarbon feed stream (here a vapor feed stream from DK1, which contains at least isobutane and 1-butene) is separated into at least one vapor feed stream BS2 containing at least isobutane and taken off at the top of DK2 and at least one product feed stream containing at least 1-butene and taken off at the bottom of DK2. The distillation column DK2 can likewise have at least two different inlets for the hydrocarbon feed stream from DK1, where, viewed from the top of the distillation column DK2, the inlets are arranged one above the other.

[0057] The distillation column DK2 for separating the raffinate 2 feed stream can be any distillation column known to those skilled in the art. The distillation column DK2 preferably contains internals. Suitable internals are, for example, trays, random packings (bulk packings) or structured packings. The trays used are generally bubble-cap trays, sieve trays, valve trays with fixed or movable valves, channel trays or slotted trays. Random packings are generally beds of bulk packings. The bulk packings used are generally Raschig rings, Pall rings, Berl saddles, SuperRinge / SuperRinge Plus or saddle packings. Structured packings are sold, for example, by Sulzer under the trade name . In addition to the internals mentioned, other suitable internals are known to those skilled in the art and can likewise be used.

[0058] Preferred internals have a low pressure drop per theoretical plate. For example, structured packings and bulk packings have a significantly lower pressure drop per theoretical plate than trays. The advantage of this is that the pressure drop in the distillation column DK2 remains as low as possible, so that the mechanical power of the compressor and the temperature of the feed stream to be evaporated remain low.

[0059] In a particularly preferred embodiment of the present invention, the second distillation column DK2 comprises a plurality of trays, preferably 150 to 300 trays, more preferably 170 to 220 trays.

[0060] In the context of the present invention, the meaning of withdrawing at least one vapor stream BS2 containing at least isobutane at the top of the distillation column DK2 is in particular that at least one vapor stream BS2 is withdrawn as a top stream or as a side stream above the internals in the distillation column DK2.

[0061] In the context of the present invention, the meaning of withdrawing at least one product stream containing at least 1-butene at the bottom of the distillation column DK2 is in particular that at least one product stream is withdrawn directly at the bottom of the distillation column DK2 or at the lower trays. The product stream preferably contains at least 99 wt% of 1-butene, more preferably at least 99.5 wt% of 1-butene, particularly preferably at least 99.6 wt% of 1-butene. 1-Butene is the target product of the process, and thus the product stream is discharged from the process. 1-Butene can be used, for example, as a comonomer in the production of polyethylene.

[0062] During the process according to the present invention, the temperature at the bottom of the second distillation column DK2 is preferably in the range of 30 to 100 °C, preferably 45 to 80 °C. Further preferably, the pressure at the top of the second distillation column DK2 is in the range of 3 to 12 bar absolute pressure, preferably 5 to 10 bar absolute pressure.

[0063] The distillation column DK2 can also be operated with reflux. The meaning of "reflux" is that at least part of the vapor stream BS2 withdrawn from the top of the distillation column DK2 is re-fed back into the distillation column DK2. In the case of establishing such reflux, the reflux ratio is preferably 10 to 100, particularly preferably 30 to 50. Description of the Drawings

[0064] The present invention will be described below with reference to the drawings. The drawings are for illustrative purposes and should not be considered restrictive.

[0065] Figure 1Shows an embodiment with two distillation columns DK1(5) and DK2(15), which have a plurality of internal components (6, 16). The internal components (6, 16) are only shown schematically; in other words, the structure may actually be different. Furthermore, in industrial practice, the quantity is usually much larger. The internal components (6, 16) are arranged vertically above and below each other from the top of the column. In this case, the internal components are trays. The raffinate 2 to be separated can be guided into the distillation column DK1(5) via pipe 1, pipe 2 or an optional additional pipe n or via the corresponding inlets. The dotted pipe n indicates that other inlets may also exist. The raffinate 2 is analyzed via the corresponding analysis unit QC(7) to determine which of these pipes should be selected. The feed of the raffinate 2 via one of the inlets (1, 2, n) is regulated by means of valves (8a, 8b, 8n). The bottom stream (4) is removed at the bottom of the column DK1(5). The vapor stream is obtained at the top and condensed in the heat exchanger (9). A part of the condensed vapor stream is introduced into the first distillation column DK1(5), and another part is introduced into the second distillation column DK2(15). Further distillation takes place here. The bottom stream (14) is removed at the bottom of the column DK2(15). The vapor stream is obtained at the top and condensed in another heat exchanger (19). A part of the condensed vapor stream is introduced into the second distillation column DK2(15), and another part is discharged. The condensation energy obtained in the heat exchangers (9, 19) is subsequently used to heat one or both bottoms of the distillation columns DK1 and DK2(5, 15), and the heat integration is not shown in the figure.

[0066] Figure 2 Shows another embodiment of the present invention, which largely corresponds to the embodiment according to Figure 1 The difference from Figure 1 is that the vapor stream from the first distillation column DK1(5) can be guided into the distillation column DK2(15) via pipe 11, pipe 12 or an optional additional pipe m or via the corresponding inlets. The dotted pipe m indicates that other inlets may exist. The raffinate 2 is analyzed via the corresponding analysis unit QC(17) to determine which of these pipes should be selected. The feed of a part of the condensed vapor stream via one of the inlets (11, 12, m) is regulated by means of valves (18a, 18b, 18m).

[0067] Figure 3 Shows another embodiment of the present invention, which largely corresponds to the embodiment according to Figure 1 The difference from Figure 1 is that the internal component (16) present in the second distillation column DK2(15) is a random packing bed or (structured) packing.

[0068] Figure 4 Shows another embodiment of the present invention, which largely corresponds to the embodiment according toFigure 2 embodiments. Different from Figure 2 is that the internals (16) present in the second distillation column DK2 (15) are a packed bed of random packing or (structured) packing.

[0069] Figure 5 shows another embodiment of the present invention, which largely corresponds to the embodiment according to Figure 4 . Different from Figure 4 is that the internals (6) present in the first distillation column DK1 (5) are also a packed bed of random packing or (structured) packing.

[0070] Figure 6 shows another embodiment of the present invention, which largely corresponds to the embodiment according to Figure 2 . Different from Figure 2 is that the analysis units (7, 17) are connected to a control unit (UC), by means of which the analysis results are evaluated, and a conversion to another inlet can be achieved by means of valves (8a, 8b, 8n, 18a, 18b, 18m).

[0071] Figure 7 shows another embodiment of the present invention, which largely corresponds to the embodiment according to Figure 6 . Different from Figure 6 is that the internals (16) present in the second distillation column DK2 (15) are a packed bed of random packing or (structured) packing.

[0072] Figure 8 shows another embodiment of the present invention, which largely corresponds to the embodiment according to Figure 4 . Different from Figure 7 is that the internals (16) present in the first distillation column DK1 (15) are also a packed bed of random packing or (structured) packing.

[0073] Figure 9 shows, for two compositions Z1 and Z2, the required evaporator power Q R plotted as a function of the trays (here the feed tray N F ). Illustrations can be found in the following examples. Detailed Description

[0074] Examples

[0075] This example considers a column by means of which 1-butene and isobutane are separated from the raffinate 2 stream at the top. Two different compositions (Z1 and Z2) of the raffinate 2 stream are considered in this example, which are intended to account for, for example, periodic raw material fluctuations. Table 1 shows the different feed compositions.

[0076] Table 1: Composition of Raffinate 2

[0077]

[0078] Using Aspen Version 10 and an adapted substance data model based on operationally verified substance data for calculations. Consider a column with 140 theoretical trays (200 trays with a tray efficiency of 0.7). The n-butane content at the top is kept constant at 800 ppm. Figure 5 The resulting graph is shown, in which for two compositions Z1 and Z2, the required evaporator power Q R is plotted as a function of the tray (here the feed tray N F ). The energy requirement is at its lowest at the lowest point of the corresponding curve. Table 2 shows the sensitivity analysis, which shows the correlation between the required heat (QR) in megawatts (MW) in the trays and the evaporator as a function of the composition of the feed (Z1 and Z2). In the case of a high 1-butene content (Z1) in the feed, it is advantageous to feed the feed to tray 126. The evaporator requires 0.13 MW less than when the raffinate with composition Z1 is fed to tray 119. For a high n-butane content in the feed, as in composition Z2, a greater total heat is required. In addition, the optimal trays are different. While tray 126 is energetically favorable in the case of composition Z1, tray 119 should be selected in an energetically preferred manner in the case of composition Z2. Thus, a conversion of trays results in an energy saving of 0.49 MW. These energy savings lead to CO 2 and operating cost savings.

[0079] Table 2: Results of the sensitivity analysis

[0080] Z1 Z2 Tray QR[MW] QR[MW] 119 15.15 18.87 126 15.02 19.36

Claims

1. A process for distilling a raffinate 2 stream as feed stream in a separation unit comprising at least two distillation columns DK1 and DK2, wherein The distillation columns DK1 and DK2 each comprise a top at the upper end of the column and a bottom at the lower end of the column, wherein in each case a vapor stream is obtained at the top and in each case a bottom stream is obtained at the bottom, and wherein the distillation column DK2 is fed with part of the vapor stream from DK2; at least partly condensing the vapor streams from DK1 and DK2 and using the condensation energy obtained from at least one of the vapor streams from DK1 or DK2 for heating at least one of the distillation columns DK1 or DK2 by means of vapor compression or by means of a heat pump; at least the distillation column DK1 has at least two different inlets for the feed streams, wherein the inlets are arranged one above the other, viewed from the top of the distillation column; Analyze the composition of the feed stream prior to introduction; as well as One of the at least two inlets for supplying the feed stream is selected depending on the composition of the feed stream.

2. The process according to claim 1 , wherein the distillation column DK1 comprises internals such as random packing beds, (structured) packings or trays, preferably 2 to 300 internals, further preferably 2 to 250 internals, particularly preferably 2 to 220 internals. 3 . The process according to claim 2 , wherein the internals are arranged one above the other in the distillation column DK1 , viewed from the top of the distillation column, and the at least two inlets are present at the height of different internals.

4. The process according to any one of the preceding claims, wherein during the process the composition of the raffinate 2 stream changes and has to be switched to another inlet.

5. The method according to claim 4, wherein the switching of the raffinate 2 stream to another inlet is performed automatically or manually.

6. The method according to claim 5, wherein the switchover is performed automatically by evaluating the analysis results by means of a control unit, preferably a computer, and in the event of exceeding or falling below a limit value in the composition of the raffinate 2 stream, a switchover to the other inlet is performed.

7. The process according to any one of the preceding claims, wherein the analysis of the composition of the raffinate 2 stream is performed by Raman spectroscopy and gas chromatography.

8. The process according to any one of the preceding claims, wherein the process is carried out continuously or in a batch mode, preferably continuously. 9 . The process according to claim 1 , wherein at least one of the distillation columns DK1 and DK2 is operated under reflux and the reflux ratio is from less than 1 to 100, further preferably from 1 to 50, particularly preferably from 1 to 30.

10. The process according to any one of the preceding claims, wherein the composition of the raffinate 2 stream is analyzed continuously throughout the process at predetermined time intervals.

11. The process according to claim 1, wherein the distillation column DK2 has at least two different inlets for the hydrocarbon stream fed from DK1 and the inlets are arranged one above the other, viewed from the top of the distillation column DK2.

12. The process according to claim 11, wherein the distillation column DK2 comprises internals such as random packing beds, (structured) packings or trays, preferably 2 to 300 internals, further preferably 2 to 250 internals, particularly preferably 2 to 220 internals.

13. The process according to claim 12, wherein the internals are arranged one above the other in DK2, viewed from the top of the distillation column, and the at least two inlets are present at the height of different internals.

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