Method for purifying linear alpha-olefins using a step-heating distillation column.

Abstract

The present disclosure provides a method for purifying a linear alpha olefin product, the method comprising the steps of: feeding a linear alpha olefin feed stream comprising a linear alpha olefin product and ethylene to a feed stage of a distillation column, the distillation column having a plurality of stacked stages disposed between an overhead outlet and a bottom reboiler, the stacked stages comprising a stripping section and a rectification section; feeding an aliphatic paraffin hydrocarbon solvent to the rectification section of the distillation column to absorb the linear alpha olefins; adding heat to at least one of the plurality of stacked stages in the stripping section of the distillation column between the feed stage and the bottom reboiler; withdrawing an overhead stream comprising ethylene from the overhead outlet; and withdrawing a bottoms stream comprising the linear alpha olefin product from the distillation column.

Description

[Technical Field]

[0001] This disclosure relates to a method for purifying a stream of linear alpha-olefin products from an oligomerization reaction. [Background technology]

[0002] Linear olefins are a class of hydrocarbons useful as raw materials in the petrochemical industry, and among these linear alpha-olefins, unbranched olefins, in which their double bonds are located at the ends of the chain, form an important subclass. Linear alpha-olefins can be converted to linear primary alcohols by hydroformylation. Hydroformylation can also be used to prepare aldehydes, i.e., they can be oxidized to provide synthetic fatty acids, particularly those with an odd number of carbon atoms, which are useful in the production of lubricants. Linear alpha-olefins are also used in the production of detergents such as linear alkylbenzene sulfonates, which are prepared by the Fiedel-Crafts reaction and subsequent sulfonation of benzene and linear olefins. Another important application of linear alpha-olefins relates to the production of linear low-density polyethylene (LLDPE) through catalytic copolymerization with ethylene.

[0003] The preparation of alpha-olefins is largely based on the oligomerization of ethylene, which inevitably results in the alpha-olefin having an even number of carbon atoms. The oligomerization process for ethylene mainly utilizes organoaluminum compounds or transition metals as catalysts. The oligomerization method is typically carried out in the presence of a catalyst containing a zirconium component, such as zirconium tetraisobutyrate, and an aluminum component as an activator, such as ethylaluminum sesquichloride. Typically, the effluent from the reactor used to produce linear alpha-olefins is directed to one or more distillation columns to separate the various fractions of linear alpha-olefins. [Overview of the Initiative] [Problems that the invention aims to solve]

[0004] It is desirable to purify the alpha-olefin product from oligomerization reactions to a very high purity level, such as above 99.5 mol%. Achieving such high purity can be challenging when using conventional separation processes due to the presence of reactor effluent containing components with a wide range of boiling points. This wide range of boiling points results in a large sensible heat load in conventional distillation columns, where the temperature changes dramatically in the column's stripping section, making it difficult to design an efficient distillation column. Improvements to the separation process for such products remain a need in the art. [Means for solving the problem]

[0005] (Summary of the invention) Illustrative realizations of the present disclosure relate to processes and systems for purifying linear alpha-olephon product streams, particularly linear alpha-olefin product streams (e.g., streams containing C2-C10+ components) which are mixtures of components with widely different boiling points. In particular, the processes and systems of the present disclosure utilize a step-heated distillation column that applies heat directly to specific stages of the column so that all the sensible heat required in the column is not needed from a reboiler. Thus, efficient distillation column design and stable operation are possible without dramatically changing the column diameter in the stripping section to account for steep liquid / vapor flow gradients. Furthermore, in certain embodiments, an aliphatic paraffinic hydrocarbon solvent is added to the rectification section of the distillation column to absorb linear alpha-olefins, preventing or reducing the loss of desired products in the top product stream of the column, thereby improving column performance and avoiding the need for an expensive refrigeration system that may be required when a conventional top condenser with reflux is used. The selected solvent is typically the same solvent used in the upstream oligomerization process to produce linear alpha-olefins, and the solvent flow into the column is typically recycled from the downstream separation process, where the solvent is recovered for reuse in the reactor.

[0006] This disclosure includes, but is not limited to, the following embodiments.

[0007] Embodiment 1: A method for purifying a linear alphaolefin product, comprising: feeding a linear alphaolefin feed stream containing a linear alphaolefin product and ethylene into a feed stage of a distillation column, wherein the distillation column has a plurality of stacked stages located between the top outlet and the bottom reboiler, the stacked stages comprising a stripping section of the distillation column between the feed stage and the bottom reboiler, and a rectification section between the feed stage and the top outlet; feeding an aliphatic paraffinic hydrocarbon solvent (e.g., n-heptane) into the rectification section of the distillation column to absorb the linear alphaolefin; adding heat to at least one of the plurality of stacked stages in the stripping section of the distillation column located between the feed stage and the bottom reboiler; withdrawing the top stream containing ethylene from the top outlet; and withdrawing the bottom stream containing a linear alphaolefin product (e.g., 1-hexene) from the distillation column.

[0008] Embodiment 2: The method according to Embodiment 1, further comprising the step of applying heat to multiple stacked stages of the stripping section of a distillation column, such as applying heat to at least two stages and up to six stages.

[0009] Embodiment 3: The method according to Embodiment 1 or 2, wherein the step of applying heat includes applying heat through a heat exchanger located either inside or outside the distillation column, and optionally the amount of heat applied to the stripping section above the reboiler is about 50 to about 75% of the total heat load applied to the stripping section of the distillation column.

[0010] Embodiment 4: The method according to any one of Embodiments 1 to 3, wherein the heating step includes: drawing a liquid by-stream from at least one of the plurality of stacked stages of the stripping section of a distillation column; feeding the by-stream into a secondary reboiler adapted to at least partially vaporize the by-stream to produce a vapor-containing effluent; and returning the vapor-containing effluent from the secondary reboiler to the stages of the stripping section of the distillation column.

[0011] Embodiment 5: The method according to any one of Embodiments 1 to 4, further comprising the steps of (i) drawing, (ii) supplying, and (iii) returning, performed in multiple stages of the stripping section of a distillation column using multiple auxiliary reboilers.

[0012] Embodiment 6: The method according to any one of Embodiments 1 to 5, wherein the stage of the distillation column has a first diameter of the rectification section of the distillation column and a second diameter of the stripping section, the second diameter being larger than the first diameter, for example, the second diameter being 5 times or less the first diameter.

[0013] Embodiment 7: The method according to any one of Embodiments 1 to 6, wherein the average interstage change in vapor flow rate in the bottom five stages of the stripping section of the distillation column is about 12% or less, and / or the average interstage change in liquid flow rate in the bottom five stages of the stripping section of the distillation column is about 20% or less.

[0014] Embodiment 8: The method according to any one of Embodiments 1 to 7, wherein the top flow of the column contains about 90% by weight or more of ethylene, for example, about 95% by weight or more of ethylene, and / or the mass ratio of the aliphatic paraffinic hydrocarbon solvent added to the distillation column to ethylene in the top flow is about 0.15 to about 0.5, and / or the top flow passes through a compressor.

[0015] Embodiment 9: The method according to any one of Embodiments 1 to 8, wherein the linear alpha-olefin feed stream comprises an aliphatic paraffinic hydrocarbon solvent, such as n-heptane and 1-hexene.

[0016] Embodiment 10: The method according to any one of Embodiments 1 to 9, wherein the linear alpha-olefin feed stream contains hydrocarbons other than C5 or lower ethylene at about 3 wt% or less.

[0017] Embodiment 11: A system for preparing and purifying a linear alpha-olefin product, comprising: an ethylene oligomerization reactor that generates an effluent containing a linear alpha-olefin product and ethylene; a distillation column in fluid communication with the effluent of the ethylene oligomerization reactor at a feed stage, the distillation column having a plurality of stacked stages disposed between a top outlet and a bottom reboiler and including a stripping section of the distillation column between the feed stage and the bottom reboiler and a rectification section between the feed stage and the top outlet; an aliphatic paraffin hydrocarbon solvent source in fluid communication with the rectification section of the distillation column; and at least one heating device disposed to apply heat to at least one stage of the stripping section of the distillation column between the feed stage and the bottom reboiler.

[0018] Embodiment 12: The system according to Embodiment 11, wherein the heating device includes one or more sub-reboilers, and each reboiler is operably arranged to receive a liquid sidestream from a different stage of the stripping section of the distillation column and at least partially vaporize it, and to return the vapor-containing effluent to the stripping section of the distillation column.

[0019] Embodiment 13: The system according to Embodiment 11 or Embodiment 12, wherein the number of sub-reboilers is 2 to 6.

[0020] Embodiment 14: The system according to any one of Embodiments 11 to 13, wherein the stages of the distillation column have a first diameter in the rectification section of the distillation column and a second diameter in the stripping section, and the second diameter is larger than the first diameter, for example, the second diameter is 5 times or less the first diameter.

[0021] Embodiment 15: The overhead stream from the distillation column contains ethylene at about 90 wt% or more, for example ethylene at about 95 wt% or more; and / or the effluent from the ethylene oligomerization reactor contains an aliphatic paraffin hydrocarbon solvent and 1 - hexene; and / or the effluent from the ethylene oligomerization reactor contains hydrocarbons other than C5 or lower ethylene at about 3 wt% or less, the system according to any one of Embodiments 11 - 14.

[0022] These and other features, aspects, and advantages of the present disclosure will become apparent from the following detailed description when read in conjunction with the accompanying drawings which are briefly described below. The present disclosure encompasses any combination of two, three, four, or more features or elements described herein, whether or not such features or elements are explicitly combined or are recited in the specific exemplary implementations described herein. The present disclosure is intended to be read as a whole such that any separable feature or element of the present disclosure should be considered combinable in any of its aspects and exemplary implementations, unless the context of the present disclosure clearly indicates otherwise.

[0023] Therefore, it is understood that this brief summary is provided only for the purpose of summarizing some exemplary implementations to provide a basic understanding of some aspects of the present disclosure. Thus, the above-described exemplary implementations are merely examples and should not be construed as in any way narrowing the scope or spirit of the present disclosure. Other exemplary implementations, aspects, and advantages will become apparent from the following detailed description when interpreted in conjunction with the accompanying drawings which illustrate the principles of some of the described exemplary implementations by way of example.

[0024] Having described aspects of the present disclosure in the foregoing general terms, reference is now made to the accompanying drawings, which are not necessarily drawn to scale. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] [Figure 1]This is a block diagram of an ethylene oligomerization system according to an exemplary implementation of the present disclosure. [Figure 2] This is a schematic diagram of an exemplary embodiment of the step-heated distillation column according to the present disclosure. [Figure 3] The graph shows the simulation results of the temperature profile of an exemplary embodiment of a step-heated distillation column from the experimental section. [Figure 4] The results of the temperature profile simulation for a conventional distillation column from the experimental section are shown in graph form. [Figure 5] The results of simulations of vapor and liquid flow profiles for an exemplary embodiment of a step-heated distillation column from the experimental section are shown graphically. [Figure 6] The results of simulations of the vapor and liquid flow profiles of a conventional distillation column from the experimental section are shown in graph form. [Modes for carrying out the invention]

[0026] Next, some examples of implementations of this disclosure will be described more fully below, with reference to the accompanying drawings, which show some, though not all, examples of implementations of this disclosure. In fact, various examples of implementations of this disclosure may be embodied in many different forms and should not be construed as being limited to the examples described herein; rather, these exemplary examples are provided so as to make this disclosure thoroughly complete and so as to convey the scope of this disclosure to those skilled in the art. Similar reference numerals refer to similar elements throughout.

[0027] Unless otherwise specified or evident from the context, the first, second, or similar references should not be interpreted as suggesting a particular order. A form described as being above another form (unless otherwise specified or evident from the context) may instead be below it, and vice versa; similarly, a form described as being to the left of another form may instead be to its right, and vice versa. Quantitative measures, values, geometric relationships, or similar may also be referred to herein, but unless otherwise specified, one or more of these may be absolute or approximate in order to describe any acceptable variation that may occur, such as that resulting from engineering tolerances or similar.

[0028] All ranges disclosed herein also include endpoints, which are independently combinable (for example, the range “up to 25% by weight, or more specifically 5% to 20% by weight” includes the endpoints of the range “5% to 25% by weight” and all intermediate values, etc.). “Combination” includes blends, mixtures, alloys, reaction products, and the like.

[0029] As used herein, unless otherwise specified or it is clear from the context, the "or" in a pair of operands is an "inclusive disjunction," meaning true only if one or more of the operands are true, in contrast to the "exclusive OR," which is false when all of the operands are true. Thus, for example, "[A] or [B]" is true if [A] is true or if [B] is true, or if both [A] and [B] are true. Furthermore, the articles "a" and "an" mean "one or more" unless otherwise specified or it is clear from the context that they refer to the singular form.

[0030] Ethylene oligomerization process and system Linear alpha-olefins (LAOs) are chemically formulated with C x H 2xThese are olefins having a linear hydrocarbon chain and are distinguished from other monoolefins with similar molecular formulas by the linearity of the hydrocarbon chain and the position of the double bond at the 1st or alphath position. Linear alpha olefins include 1-butene, 1-hexene, 1-octene, 1-decene, 1-dodecene, 1-tetradecene, 1-hexadecene, 1-octadecene, and C 20 ~C 24 , C 24 ~C 30 and C 20 ~C 30 This includes industrially important classes of alpha-olefins, including higher-grade blends of olefins. Linear alpha-olefins are useful intermediates in the manufacture of detergents, synthetic lubricants, copolymers, plasticizers, and many other important products.

[0031] Existing processes for producing linear alpha-olefins typically rely on the oligomerization of ethylene. For example, linear alpha-olefins can be prepared by catalytic oligomerization of ethylene in the presence of a Ziegler-Natta type catalyst or a non-Ziegler-Natta type catalyst.

[0032] Oligomerization can be induced at temperatures ranging from 10 to 200°C, e.g., 20 to 100°C, 50 to 90°C, 55 to 80°C, or 60 to 70°C. The operating pressure can be 1 to 5 megapascals (MPa), e.g., 2 to 4 MPa. The process can be continuous, and the average residence time can be 10 minutes to 20 hours, e.g., 30 minutes to 4 hours, or 1 to 2 hours. The residence time can be selected to achieve the desired conversion rate with high selectivity.

[0033] The process can be carried out in a solution using an inert solvent system which may consist of one or more solvents that are advantageously unreactive to the catalyst composition. Examples of desired organic solvents include, but are not limited to, unsubstituted or halogenated aromatic hydrocarbon solvents, e.g., toluene, benzene, xylene, monochlorobenzene, dichlorobenzene, chlorotoluene; aliphatic paraffinic hydrocarbons, e.g., pentane, hexane, heptane, octane, nonane, decane; alicyclic hydrocarbon compounds, e.g., cyclohexane, decahydronaphthalene; and halogenated alkanes, e.g., dichloroethane and dichlorobutane, as well as combinations thereof.

[0034] The process can be carried out in any reactor, such as a loop reactor, a plug-flow reactor, or a bubble column reactor. Ethylene oligomerization is an exothermic reaction that can be cooled by the excess flow of ethylene. The gas escaping from the top of the reactor can be cooled using a series of external coolers and condensers. The gas phase after further cooling can be recirculated.

[0035] The bottom flow away from the bottom of the oligomerization reactor may contain the activated catalyst and unreacted ethylene. The reaction can be terminated to avoid undesirable side reactions by removing the catalyst component from the organic phase through extraction with the caustic aqueous phase. Contact with the caustic aqueous phase may result in the formation of unreacted inorganic substances corresponding to the catalyst component.

[0036] The organic phase, after passing through a catalytic removal system, can pass through a molecular sieve absorption bed and then be fed to a distillation column to recover dissolved ethylene. The recovered ethylene can be recycled through an ethylene recirculation loop, along with the product, which is fed to an intermediate tank, and then to a separation section. In certain embodiments, the linear alpha-olefin produced from the reactor can be directed to the separation column.

[0037] As shown in FIG. 1, system 10 may include reactor 12, solvent source 14, and separation train 16. In a normal production mode, reactants 18 such as ethylene, a solvent, and a catalyst are fed into reactor 12 to produce linear alpha olefins and various impurities such as branched olefins and polymer materials. After the reaction, the effluent stream 20 can be directed into separation train 16, which may include unreacted reactants, the produced linear alpha olefins, for example C4-C 20+ olefins, solvent, catalyst, and various impurities. Separation train 16 can be configured to separate the linear alpha olefins from the solvent, catalyst, various impurities, and any unreacted ethylene. Separation train 16 can separate each linear alpha olefin, resulting in, for example, a C4 stream, a C6 stream, a C8 stream, etc. Separation train 16 can also separate the linear alpha olefins into a particular fraction, for example C4-C 10 fraction, C 11 -C 17 fraction, C 18 -C 20 fraction, C 20+ fraction, or any other desired fraction.

[0038] The linear alpha olefin product can be isolated using procedures that include an aqueous caustic catalyst quench, followed by a water wash, and recovery of the final product by distillation. For example, a liquid product containing a solvent that includes dissolved ethylene can be fed to separation train 16 as described above. In a first column, unconsumed ethylene can be separated from the linear alpha olefin product and the solvent. The ethylene can be recycled to the original reactor. The heavy fraction can be passed through a subsequent separation section where the heavy fraction can be split into various linear alpha olefin fractions (e.g., C8, C 10 , >C 12 ). The solvent can also be recovered and recycled to the original reactor.

[0039] Polymer fouling in the reactor can occur during the oligomerization reaction process. Such fouling is typically detected by, for example, reduced effluent flow rate, reduced internal condenser performance, or increased differential pressure at various points within the reactor. Such fouling can be treated by flushing the reactor with a solvent to remove polymer material byproducts. The flushed solvent, containing the polymer material, can be directed into a separation column containing linear alpha-olefin reaction products. Since the polymer material is soluble in at least one of the linear alpha-olefins, the flushed solvent can exit through a separation column that is essentially free of polymer material and be recycled back to the original solvent source for subsequent reactor flushing.

[0040] In certain embodiments, the choice of solvent system for the ethylene oligomerization reaction can increase the selectivity for a particular desired linear alpha-olefin. For example, it has been found that a combination of a first paraffinic solvent and a second aromatic solvent may be favorable for selective oligomerization. In certain embodiments adapted for the selective production of 1-hexene, n-heptane is used as the first (paraffinic) solvent to increase the selectivity of 1-hexene, and xylene is optionally used as the second (aromatic) solvent for catalyst dissolution and reactor cleaning.

[0041] The described oligomerization can present challenges in separating unreacted ethylene from the reactor effluent due to the broad boiling range exhibited in the effluent. For example, if the oligomerization reaction is insufficiently selective for 1-hexene, the resulting effluent will contain ethylene as well as C8+ components, making it difficult to strip the ethylene from the reactor effluent in the initial distillation column of separation column 16. The broad boiling range, associated with a lack of reactor effluent components with chain lengths between ethylene and 1-hexene, necessitates a large sensible heat load to achieve the desired ethylene stripping.

[0042] Typically, the reactor effluent consists mainly of aliphatic paraffinic hydrocarbon solvents, such as n-heptane (e.g., more than 50% by weight of aliphatic paraffinic hydrocarbon solvents), and also contains linear alpha-olefins such as 1-hexene. In certain embodiments, the reactor effluent meets the following criteria: (1) more than about 7.5% by weight of the effluent (e.g., more than about 8% by weight, or more than about 9% by weight, or more than about 10% by weight, e.g., about 7.5% to about 15% by weight) is ethylene; (2) more than about 60% by weight of the effluent (e.g., more than about 62% by weight, or more than about 65% by weight, or more than about 70% by weight, e.g., about 60% to about 80% by weight) is aliphatic paraffinic hydrocarbon solvent, such as n-heptane. (3) The effluent is more than about 7.5% by weight (for example, more than about 8% by weight, or more than about 9% by weight, or more than about 10% by weight, for example, about 7.5% to about 15%) of 1-hexene or another linear olefin; and / or (4) The effluent is less than about 3% by weight (for example, less than about 2% by weight, or less than about 1% by weight, or less than about 0.5% by weight, for example, about 0.1% to about 3%) of C5 or a hydrocarbon other than lower ethylene.

[0043] Step-heating distillation column According to this disclosure, the separation column 16 includes a first step-heated distillation column adapted to recover unreacted ethylene from the reactor effluent. The type of distillation column may vary, and examples include columns with trays (bubble cap trays, valve trays, sieve trays, etc.) or random or structured packing materials. A step-heated distillation column is characterized by the addition of heat at one or more stages in the stripping section of the column to enhance the heat provided by the reboiler. The addition of heat is typically achieved using a heat exchanger or other heating device located either inside or outside the distillation column. The number of stages to which heat is added can vary, but is typically 1 to 6 stages.

[0044] An exemplary implementation of a step-heated distillation column 30 is shown in Figure 2. The distillation column 30 is in fluid contact with the effluent from reactor 12 in Figure 1, which is shown as a feed stream 32 entering the column at a feed stage, the location of which may vary. The step-heated distillation column 30 is adapted to separate the reactor effluent into an ethylene stream 34 suitable for recirculation to reactor 12, and a bottom product stream 36 containing the remainder of the reactor effluent, including the desired linear alpha-olefin and solvent. The bottom product stream 36 can be further processed if it is desired to separate the remaining components of the reactor effluent. The bottom product stream 36 is drawn from a reboiler 56, which also generates a boiling stream 44 returning to the column 30.

[0045] In some embodiments of this disclosure, conventional top condensers that generate reflux flow are very costly and complex to implement. Typical top outflow flows are primarily ethylene, which means that the top condenser may require a refrigeration system to generate reflux material returning to the column. To overcome this problem, in certain embodiments of this disclosure, a solvent flow is supplied to a rectification section to adsorb heavy components, as will be better explained below. Thus, in certain embodiments, the systems and methods of this disclosure can be characterized by the absence of a top condenser that returns reflux material to column 30.

[0046] In certain embodiments, the top flow from the distillation column 30 is compressed in a compressor 38, which may be a multistage compressor having, for example, 2-6 or 2-4 stages, before being recycled to the original reactor. To improve compression efficiency and remove condensate, the top flow is optionally cooled in a heat exchanger 60 and passes through a vapor-liquid separator 40 upstream of the compressor 38. Optionally, the compressed top flow is also cooled after compression in a heat exchanger 62 and also passes through a second vapor-liquid separator 40' to remove condensate before being recycled. The combined condensate from the two vapor-liquid separators 40 and 40' can return to the column 30 as a less refluxed flow 42. Exemplary vapor-liquid separators include flash drums, knockout drums, knockout pots, compressor suction drums, and similar.

[0047] In embodiments of the present disclosure, the step-heated distillation column 30 includes a rectification section 46 above a feed stream 32 adapted to absorb 1-hexene or other linear alpha-olefins from the reactor effluent, and a stripping section 48 below the feed material entry point where ethylene is removed from the reactor effluent. In certain embodiments, at least a portion of the rectification section 46 also includes an absorption section, where heavier components, including 1-hexene or other linear olefins, are removed from the stripped ethylene by contact with an aliphatic paraffinic hydrocarbon solvent, typically the same solvent used in reactor 12 in Figure 1, thus reducing or eliminating linear alpha-olefin products remaining at the top of the column and broken down in the reactor. This absorption is obtained by adding a stream 50 of an aliphatic paraffinic hydrocarbon solvent (e.g., n-heptane) to the column 30 near the top of the column. The stage to which the aliphatic paraffinic hydrocarbon solvent is added can be modified, but is typically one of the top five stages of the column 30. The aliphatic paraffinic hydrocarbon solvent stream 50 is typically obtained by recirculating it from the downstream portion of the separation column 16.

[0048] The amount of aliphatic paraffinic hydrocarbon solvent added to column 30 varies in part with the number of rectification stages in the column. The amount of solvent required increases as the number of rectification stages decreases. Typically, column 30 has a total of 10 to 120 stages, more typically about 20 to about 50 stages. The rectification section of column 30 typically contains about 5 to about 30 stages, for example, about 5 to about 20 stages. The amount of solvent added to the column in the rectification section can be characterized as the mass ratio of the solvent added to the ethylene in the top effluent from the column. An exemplary range of the mass ratio of solvent to ethylene is about 0.15 to about 0.5, for example, about 0.2 to about 0.4. In certain embodiments, the mass ratio is about 0.15 or higher, or about 0.2 or higher, or about 0.25 or higher, or about 0.3 or higher.

[0049] In certain embodiments of this disclosure, the recirculated ethylene stream 34 contains about 90% by weight or more of ethylene, e.g., about 95% by weight or more of ethylene (e.g., about 97–99% by weight of ethylene), which can be compressed and returned to the reactor 12. A small purge stream of the recirculated ethylene stream (not shown) can be sent to a flare system to prevent the accumulation of lighter components such as nitrogen during the process. The bottom product stream 36 typically contains very little ethylene, e.g., 1–3% by weight of ethylene.

[0050] The stepped-heated distillation column 30 adds heat directly to a specific stage of the stripping section 48 of the column, so that all the sensible heat required for the column does not need to come from the reboiler 56. As described above, this heat can be added through heat exchange that occurs either inside or outside the column 30. In this way, an efficient distillation column design is possible without numerous radical changes in the column diameter.

[0051] For illustrative purposes only, Figure 2 shows external heat addition using heat exchangers 52, 52' and pumps 54, 54'. As illustrated, the liquid can be drawn from a stage in the stripping section 48 of the distillation column 30 using pumps 54, 54' and passed through heat exchangers 52, 52' which are adapted to introduce heat into the liquid drawn from the column, typically resulting in at least partial vaporization of the liquid. The vapor-containing effluent from the heat exchanger returns to the column 30. The stage from which the liquid is drawn can be changed. The vapor-containing effluent from the heat exchangers 52, 52' can return to the same stage from which the liquid was drawn, or to a different stage in the stripping section 48 of the column 30. Figure 2 shows two heat exchangers 52, 52' drawing from two different stages of the column 30 as described above, but the exact number of stages to which heat is added can be changed.

[0052] The amount of heat added to increase the reboiler heat load can be varied. The amount of heat added in the stripping section of the tower 30 above the reboiler can be characterized as a percentage of the total heat load added to the tower (including all auxiliary reboilers and the main tower bottom reboiler). In a particular embodiment, the percentage of heat added above the tower bottom reboiler (through the auxiliary reboilers) is about 50 to about 75% of the total heat load added, for example, about 55 to about 70%. For example, if the total heat load is about 6,500 to about 7,500 kW, the amount of heat added above the tower bottom reboiler is typically about 3,250 to about 5,625 kW, for example, about 3,575 to about 5,250 kW.

[0053] An efficient distillation column 30 can be designed by adding heat in the stripping section to enhance the reboiler, and in certain embodiments, only one tray diameter varies over the entire length of the column. For example, the trays of the distillation column may have a first diameter in the rectification section and a second diameter in the stripping section, where the second diameter is larger than the first diameter, for example, no more than five times the first diameter, or no more than four times the first diameter, or no more than three times the first diameter. In other words, the ratio of the first diameter (rectification section) to the second diameter (stripping section) is about 1:5 or less, or about 1:4 or less, or about 1:3 or less (for example, a ratio of about 1:5 to about 1:2). In certain embodiments, the entire rectification section has the same first tray diameter, and the entire stripping section has the same second tray diameter.

[0054] In certain embodiments, the distillation column 30 can be characterized by the stability between stages with respect to the temperature profile and the vapor and liquid flow profiles within the stripping section of the column. For example, in certain embodiments, the bottom five stages of the stripping section of the distillation column have a temperature variation between stages of about 2.5°C or less, or about 2.0°C or less.

[0055] Furthermore, in certain embodiments, the average interstage change in vapor flow rate across the bottom five stages of the stripping section of a distillation column is approximately 12% or less (e.g., 10% or less or approximately 8% or less). This is calculated by determining the absolute percentage change in flow rate between each of the five bottom stages (increase or decrease) and averaging the sum. In certain embodiments, the average interstage change in vapor flow rate across the bottom five stages of the stripping section of a distillation column is approximately 8,000 kg / hour or less. In some embodiments, the average interstage change in liquid flow rate across the bottom five stages of the stripping section of a distillation column is approximately 20% or less (e.g., 18% or less or approximately 16% or less). This is calculated by determining the absolute percentage change in flow rate between each of the five bottom stages (increase or decrease) and averaging the sum. In certain embodiments, the average interstage change in liquid flow rate across the bottom five stages of the stripping section of a distillation column is approximately 20,000 kg / hour or less. [Examples]

[0056] experiment Process simulation studies were conducted using Aspen Plus. This simulation compared two distillation column designs: (1) a conventional distillation column with 30 stages where all heat is added to the reboiler (stage 30); and (2) the present invention's step-heated distillation column with 30 stages where heat is added to stages 19, 21, 24, and 27 in addition to the reboiler. In both cases, stage 18 is the feed stage, and the recirculated n-heptane solvent is added to stage 3. The simulations used the same feed flow and target flow for each column design. The characteristics of the feed flow are described in Table 1 below, and the characteristics of the recirculated n-heptane solvent are described in Table 2 below.

[0057] [Table 1]

[0058] [Table 2]

[0059] Aspen Plus designed the most efficient tower for each design case to achieve a top flow of at least 90 wt% ethylene. In conventional towers with reboilers, the Aspen Plus design included significant stage diameter variations throughout the tower to account for the changing steam and liquid flows, particularly in the stripping section. The simulated conventional tower had three different diameters throughout the tower, with a diameter of approximately 0.5 m in the rectification section (stages 1-17) and two different diameters in the stripping section. Stages 18-21 required a stage diameter of approximately 1.2 m, and stages 22-29 required a diameter of approximately 3 m. Thus, the design of conventional towers is inevitably complicated by significant diameter variations and at least three different sections.

[0060] In contrast, simulations revealed that a tower design in which additional heat is added to four stages of the stripping section could be less complex, as the rectification section had a diameter of approximately 0.5 meters (stages 1-17), and the stripping section could be optimized to a single diameter of approximately 1.8-2.2 meters. Unlike conventional tower designs, the staged heating tower could be designed with only one diameter varying over the entire length of the tower.

[0061] The simulation also calculated temperature profiles and vapor / liquid flow profiles for each tower design. These profiles are shown in Figures 3-6. As shown in Figure 3, in the stepped-heated tower, the temperature profile in the tower's stripping section (plot on the right) is more stable per stage compared to the conventional tower design (Figure 4). Similarly, as shown in Figure 5, in the stepped-heated tower, the liquid (square line markers) and vapor (circular line markers) flows (plot on the right) in the tower's stripping section are more stable per stage compared to the conventional tower design (Figure 6). This increased stability of temperature and flow in the tower's stripping section in the present invention enables efficient tower design and operation with only one diameter change throughout the entire tower.

[0062] In general, the present invention may consist of, or be essentially composed of, any suitable components disclosed herein, alternately. The present invention may be added to or instead of any components, materials, ingredients, adjuvants, or chemical species used in prior art compositions, or any that are not ordinarily necessary to achieve the function and / or purpose of the present invention.

[0063] Many modifications and other practices of this disclosure will be conceivable to those skilled in the art to which this disclosure relates, who are of interest in the teachings presented in the foregoing description and the associated figures. Therefore, it should be understood that this disclosure is not limited to the specific practices disclosed herein, and modifications and other practices are intended to be included within the scope of the appended claims. Certain terms are used herein, but they are used only in a general and descriptive sense and are not intended to be limiting.

Claims

1. A method for purifying linear alpha-olefin products, (a) A step of supplying a linear alpha-olefin feed stream containing the linear alpha-olefin product and ethylene to a feed stage of a distillation column, wherein the distillation column has a plurality of stacked stages located between the top outlet and the bottom reboiler, the stripping section of the distillation column between the feed stage and the bottom reboiler, and the rectification section between the feed stage and the top outlet. (b) A step of supplying an aliphatic paraffinic hydrocarbon solvent to the rectification section of the distillation column to absorb a linear alpha-olefin, (c) A step of applying heat to at least one of the multiple stacked stages of the stripping section of the distillation column located between the feed stage and the bottom reboiler, (d) A step of drawing out the top flow containing ethylene from the top outlet of the column, (e) A step of drawing out the bottom flow containing the linear alphaolefin product from the distillation column. Methods that include...

2. The method according to claim 1, further comprising the step of applying heat to a plurality of stacked stages of the stripping section of the distillation column.

3. The method according to claim 2, wherein heat is applied in at least two stages and up to six stages.

4. The method according to any one of claims 1 to 3, wherein the step of applying heat includes applying heat through a heat exchanger located either inside or outside the distillation column, and optionally the amount of heat applied to the stripping section above the reboiler is 50 to 75% of the total heat load applied to the stripping section of the distillation column.

5. The aforementioned step of applying heat, i) A step of drawing a liquid sidestream from at least one of the plurality of stacked stages of the stripping section of the distillation column, ii) A step of supplying the sidestream into a secondary reboiler adapted to vaporize the sidestream at least partially to generate a steam-containing effluent, iii) A step of returning the steam-containing effluent from the auxiliary reboiler to the stripping section of the distillation column. The method according to any one of claims 1 to 3, including

6. The method of claim 5, further comprising the steps of (i) drawing out, (ii) supplying, and (iii) returning, using a plurality of auxiliary reboilers to perform the steps of a plurality of stages of the stripping section of the distillation column.

7. The method according to any one of claims 1 to 3, wherein the stage of the distillation column has a first diameter of the rectification section of the distillation column and a second diameter of the stripping section, the second diameter being larger than the first diameter.

8. The method according to claim 7, wherein the second diameter is five times or less the first diameter.

9. The method according to any one of claims 1 to 3, wherein the average interstage change in vapor flow rate at the bottom five stages of the stripping section of the distillation column is 12% or less, and / or the average interstage change in liquid flow rate at the bottom five stages of the stripping section of the distillation column is 20% or less.

10. The method according to any one of claims 1 to 3, wherein the top flow of the column contains 90% by weight or more of ethylene, and / or the mass ratio of the aliphatic paraffinic hydrocarbon solvent added to the distillation column to ethylene in the top flow of the column is 0.15 to 0.5, and / or the top flow of the column passes through a compressor.

11. The method according to claim 10, wherein the top flow of the tower contains 95% by weight or more of ethylene.

12. The method according to any one of claims 1 to 3, wherein the linear alphaolefin feed stream comprises the aliphatic paraffinic hydrocarbon solvent and 1-hexene.

13. The method according to claim 12, wherein the aliphatic paraffinic hydrocarbon solvent comprises n-heptane.

14. The method according to claim 13, wherein the linear alphaolefin feed stream contains 3% by weight or less of a hydrocarbon other than C5 or a lower ethylene.

15. A system for preparing and purifying linear alpha-olefin products, (a) an ethylene oligomerization reactor that produces the linear alpha-olefin product and effluent containing ethylene, (b) A distillation column having fluid communication with the effluent of the ethylene oligomerization reactor at the feed stage, the distillation column having a plurality of stacked stages located between the top outlet and the bottom reboiler, the stripping section of the distillation column between the feed stage and the bottom reboiler, and the rectification section between the feed stage and the top outlet. (c) A supply source of aliphatic paraffinic hydrocarbon solvent that is in fluid contact with the rectification section of the distillation column, (d) at least one heating device and positioned to apply heat to at least one stage of the stripping section of the distillation column between the feed stage and the bottom reboiler. A system that includes this.

16. The system according to claim 15, wherein the heating device includes one or more sub-reboilers, each reboiler being operable to receive and at least partially vaporize liquid by-flows from different stages of the stripping section of the distillation column, and to return vapor-containing effluent to the stripping section of the distillation column.

17. The system according to claim 16, wherein the number of auxiliary reboilers is 2 to 6.

18. The system according to claim 15, wherein the stage of the distillation column has a first diameter of the rectification section of the distillation column and a second diameter of the stripping section, the second diameter being larger than the first diameter.

19. The system according to claim 18, wherein the second diameter is five times or less the first diameter.

20. The system according to claim 15, wherein the top flow from the distillation column contains 90% by weight or more of ethylene, and / or the effluent from the ethylene oligomerization reactor contains an aliphatic paraffinic hydrocarbon solvent and 1-hexene, and / or the effluent from the ethylene oligomerization reactor contains 3% by weight or less of C5 or lower hydrocarbons other than ethylene.

21. The system according to claim 20, wherein the top flow from the distillation column contains 95% by weight or more of ethylene.

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