Distillation method with good energy efficiency for changing inflow amount

Abstract

To provide an improvement method that can accommodate even fluctuations in component ratios in raffinate second stream in a method for distilling raffinate second stream as a supply flow in at least two distillation towers.SOLUTION: Provided is a method for distilling raffinate second stream as a supply flow in at least two distillation towers DK1, DK2, in which there are at least two different inlets for the supply flow in at least the distillation tower DK1. Before introduction of the supply flow, composition thereof is analyzed, and one of at least two inlets for supply of the supply flow is selected according to the composition of the supply flow.SELECTED DRAWING: None

Description

Technical Field

[0001] The present 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. It is a feature of the method that the composition is analyzed before the feed stream is introduced and at least one of the two inlets for the supply of 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 mixtures of substances. Therefore, the distillation process is essential for the production of many chemical substances in the chemical industry. These examples are the distillation of a feed stream to remove low-boiling or high-boiling components before a chemical reaction, or the distillation of a crude product mixture to remove reactants and low-boiling and / or high-boiling by-products.

[0003] Hydrocarbon streams used in distillation generally undergo natural variations in composition and / or production-related variations. This means that the ratios of the components in the hydrocarbon stream become larger or smaller, new components are introduced, and / or other components disappear. These include, for example, the flow of substances in petrochemical production plants. The hydrocarbon stream is in particular a C4 hydrocarbon stream from a steam cracker, an FCC C4 stream, a product stream from MTBE synthesis (MTBE = methyl tert-butyl ether), a raffinate 2 stream, or a product stream from oligomerization.

[0004] The C4 hydrocarbon stream consists essentially of butadiene, isobutene, 1-butene, two 2-butenes, isobutane and n-butane. The common post-treatment method practiced worldwide for said C4 hydrocarbon stream involves the following steps: first removing most of the butadiene. In both cases, in addition to the saturated hydrocarbons n-butane and isobutane, a hydrocarbon mixture containing the olefins isobutene, 1-butene and 2-butene remains, which is called raffinate 1. Isobutene can be removed by reacting this mixture with methanol to form MTBE. Thereby, saturated hydrocarbons, linear butenes and, in some cases, residual amounts of isobutene remain. The mixture obtained after separation of butadiene and isobutene is called raffinate 2.

[0005] In a composition where the ratio of the individual components in the hydrocarbon stream, especially in raffinate 2, fluctuates, the separation operation can no longer be achieved sufficiently or higher energy has to be used to achieve the separation operation.

Summary of the Invention

Problems to be Solved by the Invention

[0006] Therefore, the problem addressed by the present invention was to improve the known distillation method. Compositions in which the ratio of the components in raffinate 2 fluctuates are absorbed with a minimum of complexity, while the separation operation is achieved in a very substantially uniform manner.

Means for Solving the Problems

[0007] The 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 distilling a raffinate 2 stream as a feed stream in a separation unit comprising at least two distillation columns DK1 and DK2, wherein each of said DK1 and DK2 includes a top at the upper end of the column and a bottom at the lower end of the column, and in each case a vapor stream is obtained at the top and a bottom stream is obtained at the bottom, and a part of the vapor stream from said DK2 is supplied to said DK2, At least partially condensing the vapor streams from the DK1 and DK2 and using the condensation energy obtained from at least one of the vapor streams from the DK1 or DK2 for heating at least one of the DK1 and DK2 by vapor compression or a heat pump; At least the DK1 has at least two different inlets for the feed stream, where the inlets are arranged one below the other when viewed from the top of the distillation column; The composition of the feed stream is analyzed before being introduced, and One of at least two inlets for the supply of the feed stream is selected according to the composition of the feed stream, including. The advantage of the method according to the invention is that by selecting the appropriate inlet to the distillation column, the separation of the hydrocarbon stream and the raffinate 2 stream used is optimized while energy is saved.

[0008] The feed stream supplied to the distillation according to the invention is a hydrocarbon stream. The feed stream used in 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 be later used for the removal of 1-butene in an integrated petrochemical process. In this case, 1-butene is separated from the raffinate 2 by distillation to obtain a raffinate 3. The removal of this 1-butene is preferably carried out by the distillation method according to the invention. The removal of 1-butene is incidental and generally not carried out completely. Therefore, 1-butene may remain in the raffinate 3. The hydrocarbon stream used in the distillation method according to the invention is a raffinate 2 stream containing at least 1-butene, 2-butene, n-butane and isobutane. 1-butene is at least partially separated from the raffinate 2 stream in the distillation.

[0009] The raffinate 2 used preferably contains less than 2500 ppm, preferably less than 1000 ppm, particularly preferably less than 500 ppm of isobutene. More preferably, the raffinate 2 used in the process 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. If the stream contains a high content of butadiene, selective hydrogenation to convert butadiene to butene and / or butane may be carried out in advance. The corresponding methods are known to those skilled in the art. The raffinate 2 stream used may further contain a predetermined amount of water, particularly in an amount of 150 to 4000 ppm. The water is preferably at least partially removed by distillation. The water accumulates in the vapor stream obtained in the distillation column, is obtained as a second liquid phase after condensation, and can be separated through a pipe in the distillate container of the distillation column. The bottom product from the distillation column is 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.

[0010] 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 each configured to include 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 through which the feed stream used, i.e., the raffinate 2, can be fed into the distillation column DK1. The at least two inlets are arranged vertically when viewed from the top of the column, i.e., from the upper end of the column. Thus, the at least two inlets are arranged at different heights rather than at the same height when viewed spatially and from the bottom. The distillation column DK2 has at least two different inlets through which the stream from DK1 can be fed into the distillation column DK2. The distillation column DK1 or DK2 for the process according to the invention may have more than two, i.e., three, four, five or more inlets, and it is obvious that the streams are each fed into the distillation column according to their composition through the inlets.

[0011] The thermal energy required for the separation operation is usually sent to the distillation column via at least one reboiler. In this case, preferably, this stream flows through the reboiler and is withdrawn into or at the bottom of the lower end of the distillation column, and then returned to the distillation column after passing through the reboiler. The stream is heated when passing through the reboiler. The term "reboiler" as used in the present invention refers to an evaporator that heats the bottom of each distillation column. The reboiler is usually arranged outside each distillation column. The reboiler is a heat transfer body that transfers energy, particularly heat, from one stream to another. The stream to be evaporated is withdrawn (at least partially) from the bottom of the distillation column through the extraction section and supplied to the reboiler. The evaporated stream is returned to each distillation column in the bottom region via at least one supply section, with or without a liquid residue ratio. 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. The heat exchangers for evaporators typically used in the case of natural circulation evaporators and forced circulation evaporators are shell and tube or plate devices. As described above, any other design of evaporators suitable for use in distillation columns known to those skilled in the art can be alternatively used.

[0012] At least two distillation columns also preferably have a number of internal structures, such as random packings, structured packings or trays. These internal structures ensure sufficient contact between the vapor rising in the distillation column and the liquid flowing down, thereby reliably improving mass transfer and heat transfer. The trays used are typically bubble cap trays, sieve trays, valve trays with fixed or movable valves, tunnel cap trays or slot trays. Unstructured packings generally consist of beds of random packings. The random packings used are typically 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. These and other suitable internal structures are known to those skilled in the art and can be used similarly. The preferred internal structures have a low specific pressure drop per theoretical stage. The pressure drop per theoretical stage of structured and random packings is significantly lower than that of trays, for example. This has the advantage that the pressure drop in the distillation column(s) 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.

[0013] In a particularly preferred embodiment of the present invention, the distillation column DK1 comprises internal structures, preferably 2 to 300 internal structures, more preferably 2 to 250 internal structures, even more preferably 2 to 220 internal structures. The internal structures are arranged vertically in the distillation column DK1 when viewed from the top of the distillation column. In a preferred embodiment of the present invention, the inlets are each at the height of at least one of the internal structures. Since the inlets are arranged vertically, the inlets may, in principle, be arranged at different heights relative to one of the internal structures. However, it is particularly preferred that at least two inlets are at the height 1 of different internal structures.

[0014] In an even more particularly preferred embodiment of the present invention, the distillation column DK2 includes internal structures, preferably 2 to 300 internal structures, more preferably 2 to 250 internal structures, and even more preferably 2 to 220 internal structures. The internal structures are arranged vertically in the distillation column DK2 as viewed from the top of the distillation column. In a preferred embodiment of the present invention, each of the inlets is at the height of at least one of the internal structures. Since the inlets are arranged vertically, the inlets may, in principle, be arranged at different heights relative to one of the internal structures. However, it is particularly preferred that at least two inlets are at the height 1 of different internal structures.

[0015] The interior of a distillation column is defined by the theoretical plates it produces. Distillation columns are generally designed by the number of theoretical plates. In the case of trays as internal structures, the number of theoretical plates is determined by multiplying the tray efficiency (number of theoretical plates = number of trays × tray efficiency). In the case of random packings or structured packings, the number of theoretical plates is obtained by multiplying the HETP value (height corresponding to one theoretical plate) by the height of the packing bed of the random packing or structured packing used (number of theoretical plates = HETP value × height of the packing bed of the random packing or structured packing). The HETP value can be determined with reference to the substance mixture to be separated and the random packing or structured packing used. Usually, a plurality of theoretical plates result from a random packing or structured packing, i.e., one of the internal structures.

[0016] The separation unit may clearly include one or more additional distillation columns. Whether one or more additional distillation columns are present in the separation unit depends on the separation operation to be achieved. If fluctuations in the feed composition are also expected in the flow to the additional distillation column(s), fluctuations in the selected inlets may also be applied with respect to the composition of each flow. One or more distillation columns may likewise be configured like known distillation columns, i.e., they may have a bottom and a top, may utilize a reboiler for the introduction of thermal energy, and may include a number of internal structures such as random packings, structured packings or trays.

[0017] The first step of the method according to the invention is to analyze the composition of the feed stream, i.e., raffinate 2, before introducing it. This means that at least the (percentage) ratio, concentration or amount of the components of the raffinate 2 stream relevant to the selection of the inlet for the supply of the hydrocarbon stream is determined. In a preferred embodiment, the components of the separation characteristic of each case are determined, in which case it is preferred to determine the n-butane content and / or isobutane content for using the raffinate 2 stream. The composition analysis can be carried out by any known analysis method. Preferred analysis methods for the method according to the invention are Raman spectroscopy and gas chromatography. The composition of the raffinate 2 stream can in principle be analyzed online, i.e., such that the measurement is carried out within the process. On the other hand, the measurement may be carried out such that a sample is taken at an appropriate point and then this sample is analyzed outside the process.

[0018] Depending on the composition of the raffinate 2 stream or the stream fed to DK2, one of at least two inlets for supplying each stream is selected. This means that based on at least two inlets, either the higher or the lower of the at least two inlets functions as the feed for the distillation column, through which each stream, i.e., for example, the raffinate 2 stream, is sent to the distillation column. This also applies if there are more than two inlets, but it is not necessary that the highest or the lowest inlet is selected, and an intermediate inlet can also be selected. In the pipelines to at least two inlets of the distillation column in the distillation according to the invention, there are separate closing devices, preferably the pipelines to each inlet can be opened and closed independently. The corresponding closing devices are known to those skilled in the art and are, for example, valves of a suitable type. The method according to the invention may in principle be operated continuously or batchwise. The method according to the invention is preferably operated continuously. Whether the method is operated continuously or discontinuously, the composition of the streams used can vary between methods. The material streams used industrially, i.e., raffinate 2, usually undergo some fluctuations. This change in composition is not necessarily large enough to affect the distillation process in question. However, during the method according to the invention, the composition of each stream can change and thus it may not be possible to switch to other inlets. This means that, depending on the composition of the streams used, the process is analyzed continuously at predetermined time intervals not only once but throughout the process. The separation between two analytical measurements can vary depending on the type of hydrocarbon stream used. In principle, the time between two analytical measurements can be 10 - 59 seconds, 1 - 59 minutes, 1 - 23 hours, or 1 - several days.

[0019] If a switch from one of at least two inlets to another inlet is necessary, the switch of each stream to the other inlet can be automatic or manual. For the switch, one inlet and / or the conduit to the inlet is closed and the other inlet and / or the conduit to the inlet is opened. If the switch to the other inlet is automatic, the switch can be made such that the analysis results are evaluated by a control unit, for example a computer, and the switch to the other inlet is made when the value exceeds or falls below the limits of the composition of each stream. This automation using computer-aided evaluation is extremely easy to implement since it is a comparison of a limit value with a measured value. Also, human errors can be avoided as much as possible and the switch can be made more quickly. Suitable limits are all measurable parameters related to the composition of the stream or its components, i.e., for example, the already mentioned (percentage) ratios, concentrations or amounts of the components in the stream.

[0020] Within the scope of the method of the present invention, it is preferable that at least one of the two distillation columns DK1 and DK2 is operated under reflux, and preferably both distillation columns DK1 and DK2 are operated under reflux. "Reflux" means that the vapor stream withdrawn at the upper end of the distillation column is at least partially returned to at least one distillation column. The reflux can be established by attaching a condenser to the top of each distillation column. The vapor stream is at least partially condensed in the condenser and returned to the distillation column. When the reflux is established, the reflux ratio is preferably from less than 1 to 100, more preferably from 1 to 50, and particularly preferably from 1 to 30. Generally, in the context of the present invention, the reflux ratio is understood to mean the ratio of the mass flow rate (kg / h) withdrawn from the column that is recycled to the column in liquid form (reflux) to the ratio of this mass flow rate (kg / h) discharged from each column in liquid or gaseous form.

[0021] The temperature and pressure in at least one distillation column are determined by the desired separation operation and thus in relation to the hydrocarbon stream used. Finding the exact temperature and the exact pressure is not so much of a problem for those skilled in the art. Those skilled in the art can very easily determine the temperature and pressure from the relative volatility or with reference to the separation operation to be achieved.

[0022] The distillation process is generally a very energy-intensive process in which thermal energy is introduced through the bottom to achieve the separation operation. At the same time, the removed vapor is cooled to at least partially condense. In the method according to the present invention, it is advantageous to employ heat integration means in order to recover the energy within the system and make use of it. Suitable means for heat integration are the use of vapor compression and heat pumps. One possible means for thermal integration is vapor compression. This involves at least partial compression of the vapor stream withdrawn at the top. This increases the pressure of the vapor stream. Compression introduces additional energy into the system. Compression of at least part of the vapor stream can be carried out by any method known to those skilled in the art. For example, compression can be carried out mechanically and in one or multiple stages. Here, "one stage" means that the compression is carried out from one pressure level to another. "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 can be used. Multi-stage compression can preferably be carried out using one compressor or a plurality of 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 compressed. A suitable compressor for use in the method according to the invention, in particular for the compression of the vapor stream, is any compressor known to those skilled in the art, preferably a mechanical compressor, with which a gas stream can be compressed. Suitable compressors include, for example, single-stage or multi-stage geared turbo compressors, piston compressors, screw compressors, centrifugal compressors or axial flow compressors.

[0023] After compression, the compressed vapor stream is sent to a heat exchanger to transfer thermal energy to another stream. For example, the distillation column can be heated by transferring thermal energy to the stream in the reboiler. The term "energy transfer (movement)" in the present invention means, in particular, heating, i.e., the transfer of energy in the form of heat. Another means for thermal integration is the use of a heat pump. The vapor stream withdrawn at the top of at least one distillation column is here used to transfer thermal energy to a heat medium. After the energy transfer, the heat transfer medium is preferably at a high temperature and / or high pressure. 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 flash evaporators, kettle evaporators, falling film evaporators or thin film evaporators. Similarly to the above, any other design of evaporators suitable for use in distillation columns known to those skilled in the art can be alternatively used. The heat exchanger in this case may be a condenser for condensing the vapor stream. This has the advantage that there is no need to install an additional condenser. The heat medium used may be any working medium known to those skilled in the art. The heat transfer medium 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, particularly preferably water.

[0024] After the above energy transfer, the heat transfer medium is at least partially compressed, resulting in a heat transfer medium compressed at a higher pressure than the heat transfer medium before compression. At least partial compression of the heat medium may be carried out by any method known to those skilled in the art. For example, as defined above, the compression can be carried out mechanically and in one or multiple stages. In the method according to the invention, a suitable compressor is any compressor known to those skilled in the art that can compress a gas stream, preferably a mechanical compressor. Suitable compressors are, for example, single-stage or multi-stage geared turbo compressors, piston compressors, screw compressors, centrifugal compressors or axial flow compressors.

[0025] In the next step, energy is transferred from the compressed heat transfer medium to a stream heated within the system, preferably within a reboiler, to heat the distillation column. In contrast to vapor compression where the vapor obtained at the top of the distillation column is compressed and used for heat energy transfer, when a heat pump is used, an intervening heat transfer medium exists. However, the principle is the same, and energy is collected at one point in the process and used in other steps of the process.

[0026] The method of the present invention is used for the separation of the raffinate 2 stream. Here, the separation unit preferably consists of at least two distillation columns DK1 and DK2, and at least two different inlets for the hydrocarbon stream are in the first distillation column DK1. The raffinate 2 sent to the first distillation column DK1 contains at least two streams in the distillation column DK1, namely at least 1-butene and isobutane, and is separated into at least one vapor stream BS1 taken out at the top of DK1 and at least one bottom stream containing at least 1-butene and 2-butene and taken out at the bottom of DK1. The vapor stream BS1 may be taken out at the top of the distillation column in the form of a plurality of sub-streams BS1(n) (n is an integer and equal to the number of sub-streams). The same applies to the bottom stream. The bottom temperature of the first distillation column DK1 is preferably in the range of 40 to 110 °C, preferably 50 to 100 °C. 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 particular 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 in particular in the range of 45 °C to 120 °C, preferably in the range of 48 °C to 100 °C, more preferably in the range of 50 °C to 90 °C, still more preferably in the range of 55 °C to 80 °C, and even more preferably in the range of 60 °C to 80 °C. In the context of the present invention, taking out at least one vapor stream BS1 containing at least 1-butene and isobutane at the top of the distillation column DK1 means in particular that at least one vapor stream BS1 is taken out as the top stream or as a side draw above the internal structure of the distillation column DK1. In the context of the present invention, taking out at least one vapor stream containing at least 1-butene and 2-butene at the bottom of distillation column DK1 means, in particular, that at least one bottom stream is taken out directly at the bottom or the lower trays of distillation column DK1.

[0027] Distillation column DK1 is preferably operated with reflux. "Reflux" means that the vapor stream BS1 withdrawn at the upper end of distillation column DK1 is at least partially fed back to 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.

[0028] The vapor stream from the first distillation column DK1 is sent to the second distillation column DK2. Here, it may be heat integration means using vapor compression or a heat pump, and the energy can be collected by at least partial condensation of the vapor stream BS1 and used for heating DK1 and / or DK2. If the amount of isobutene in the stream fed to distillation column DK2 is too high to meet the specification for the 1-butene product from DK2, further MTBE synthesis or ETBE synthesis can be carried out between distillation columns DK1 and DK2. For this purpose, the stream is fed to MTBE synthesis or ETBE synthesis, at least partially converting the isobutene present to MTBE or ETBE, and then separating the MTBE or ETBE formed. The synthesis of MTBE or ETBE is generally known to those skilled in the art. To produce MTBE or ETBE from an isobutene-containing stream, acidic ion exchange resins (sulfonic groups) can be used as heterogeneous catalysts in particular. 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 appropriate to use at least one reactive distillation column in which the reaction and the removal of MTBE or ETBE occur simultaneously. The pressure in the reactive distillation ranges from 3 to 15 bar, and the temperature in the reaction zone should be between 55 and 75 °C. After synthesis, MTBE or ETBE is preferably separated by distillation. This method is also known to those skilled in the art. Subsequently, the stream with a lower isobutene content obtained can be fed to distillation column DK2.

[0029] In the second distillation column DK2, the hydrocarbon stream supplied, the vapor stream from DK1 containing at least isobutane and 1-butene is separated into at least one vapor stream BS2 containing at least isobutane and taken out at the top of DK2 and at least one product stream containing at least 1-butene and taken out at the bottom of DK2. The distillation column DK2 may have at least two different inlets for the hydrocarbon stream supplied from DK1, and the inlets are arranged one above the other when viewed from the top of the distillation column DK2.

[0030] The distillation column DK2 used for the separation of the raffinate 2 stream may be any distillation column known to those skilled in the art. The distillation column DK2 preferably includes internal structures. Suitable internal structures are, for example, trays, unstructured packings (random packings) or structured packings. The trays used are usually bubble cap trays, sieve trays, valve trays 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.

[0031] The 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 significantly lower than that of trays, for example. 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 temperature of the stream to be evaporated are kept low. 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 inside of the distillation column DK2. In the context of the present invention, taking out at least one product stream containing at least 1-butene at the bottom of distillation column DK2 means, in particular, that at least one product stream is taken out directly at the bottom tray or a tray below the bottom tray of 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, and even more preferably at least 99.6% by mass of 1-butene. 1-Butene is the target product of the method of the present invention, and thus the product stream is discharged from the method. 1-Butene may be used, for example, as a comonomer in the production of polyethylene. Through the method according to the present invention, the temperature at the bottom of the second distillation column DK2 is preferably in the range of 30 to 100 °C, preferably 45 to 80 °C. More preferably, the pressure at the top of the second distillation column DK2 is in the range of 3 to 12 bar (absolute pressure), preferably 5 to 10 bar (absolute pressure). "Reflux" means that the vapor stream BS2 withdrawn at the upper end of the distillation column DK2 is at least partially fed back to the distillation column DK2. The distillation column DK2 may be operated under reflux. "Reflux" means that the vapor stream BS2 withdrawn at the upper end of the distillation column DK2 is at least partially returned to the distillation column DK2. The reflux ratio when establishing the reflux is preferably 10 to 100, particularly preferably 30 to 50. The present invention will be described below with reference to the drawings. The drawings are useful for illustration purposes but should not be regarded as limiting.

Brief Description of the Drawings

[0032]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Figure 8

Figure 9

Embodiments for Carrying Out the Invention

[0033] The explanation can be found in the following examples.

Examples

[0034] This example considers a column in which 1-butene and isobutane are separated from the raffinate 2 stream at the top of the column. This example considers, for example, two different compositions (Z1 and Z2) of the raffinate 2 stream that are intended to account for seasonal feedstock variations. Table 1 shows the different feed compositions. Table 1: Raffinate 2 Compositions

[0035]

Table 1

[0036]

Table 2

Claims

1. 1. A process for distilling a raffinate 2 stream as a feed stream in a separation unit comprising at least two distillation columns DK1 and DK2, DK1 and DK2 each comprise a top at the upper end of the column and a bottom at the lower end of the column, in each case a vapor stream is obtained at the top and a bottom stream is obtained at the bottom, DK2 is fed with a part of the vapor stream from DK1, At least partially 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 DK1 and DK2 by vapor compression or a heat pump; At least said DK1 has at least two different inlets for said feed streams, where said inlets are arranged one below the other when viewed from the top; the composition of said feed stream is analyzed prior to being introduced; and one of the at least two inlets for supplying the feed stream is selected in response to the composition of the feed stream; A method comprising:

2. 2. The method of claim 1, wherein the DK1 comprises 2 to 300, 2 to 250, or 2 to 220 internals, random packing, structured packing, or trays.

3. 3. The process of claim 2, wherein the internals in DK1 are arranged above and below the top of the distillation column, and wherein the at least two inlets are at different internals heights.

4. The process according to any one of claims 1 to 3, wherein during the process the composition of the raffinate 2 stream changes and has to be switched to the other said inlet.

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

6. 6. The method according to claim 5, wherein the switching is performed automatically by evaluating the analytical results by a control unit or computer and switching to the other inlet when values ​​are above or below the limits of the composition of the Raffinate 2 stream.

7. 3. The method according to claim 1 or 2, wherein the analysis of the composition of the raffinate 2 stream is carried out by Raman spectroscopy or gas chromatography.

8. The process according to any one of claims 1 to 7, which is carried out continuously or batchwise.

9. 9. The process according to any one of claims 1 to 8, wherein at least one of DK1 and DK2 is operated with reflux and the reflux ratio is from less than 1 to 100, from 1 to 50, or from 1 to 30.

10. 10. The method according to any one of claims 1 to 9, wherein the composition of the raffinate 2 stream s is continuously analysed throughout the process at predetermined time intervals.

11. 11. The method according to any one of claims 1 to 10, wherein DK2 has at least two different inlets for the hydrocarbon stream fed from DK1, said inlets being arranged one above the other when viewed from the top of DK2.

12. 12. The method of claim 11, wherein the DK2 comprises 2 to 300, 2 to 250, or 2 to 220 internals, random packing, structured packing, or trays.

13. 13. The process of claim 12, wherein the internals in DK2 are arranged above and below the top of the distillation column, and wherein at least two inlets are at different internals heights.

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