Process for purifying linear alpha olefins by staged 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] The present disclosure relates to a process for purifying a linear alpha olefin product stream from an oligomerization reaction. [Background technology]

[0002] Linear olefins are a class of hydrocarbons useful as raw materials in the petrochemical industry. Among these linear alpha olefins, unbranched olefins, whose 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, which can be oxidized to provide synthetic fatty acids, particularly those with odd carbon numbers, 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 of benzene with linear olefins followed by sulfonation. Another important use 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 olefins produced having an even number of carbon atoms. The oligomerization process for ethylene primarily utilizes organoaluminum compounds or transition metals as catalysts. The oligomerization process 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 various fractions of linear alpha olefins. Summary of the Invention [Problem to be solved by the invention]

[0004] It is desirable to purify the alpha olefins from an oligomerization reaction to very high purity levels, such as levels greater than 99.5 mol%. Achieving such high purity can be challenging using conventional separation processes due to the presence of reactor effluents containing components with widely varying boiling points. Due to this wide range of boiling points, in conventional distillation columns, temperatures vary dramatically in the stripping section of the column, resulting in a large sensible heat load that makes the design of an efficient distillation column challenging. There remains a need in the art for improved separation processes for such products. [Means for solving the problem]

[0005] (Summary of the Invention) Exemplary implementations of the present disclosure are directed to processes and systems for purifying linear alpha olefin product streams, particularly those that are mixtures of components with widely differing boiling points (e.g., streams containing C2-C10+ components). In particular, the disclosed processes and systems utilize a staged heating distillation column that adds heat directly to certain stages of the column so that all of the sensible heat required by the column is not required from a reboiler. In this manner, 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 paraffin hydrocarbon solvent is added to the rectification section of the distillation column to absorb the linear alpha olefins and prevent or reduce loss of desired products in the column overhead product stream, which improves column performance and avoids the need for costly refrigeration systems that may be required when a conventional overhead condenser with reflux is used. The solvent selected is typically the same solvent used in the upstream oligomerization process to produce linear alpha olefins, and the solvent stream to the column is typically recycled from a downstream separation process that recovers the solvent for reuse in the reactor.

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

[0007] Embodiment 1: A method for purifying a linear alpha olefin product, comprising: 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 including a stripping section of the distillation column between the feed stage and a bottom reboiler and a rectification section between the feed stage and an overhead outlet; feeding an aliphatic paraffin hydrocarbon solvent (e.g., n-heptane) 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 bottom stream comprising the linear alpha olefin product (e.g., 1-hexene) from the distillation column.

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

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

[0010] Embodiment 4: The method of any one of embodiments 1-3, wherein the step of applying heat comprises withdrawing a liquid side stream from at least one of the plurality of stacked stages of a stripping section of the distillation column; feeding the side stream into a secondary reboiler adapted to at least partially vaporize the side stream to produce a vapor-containing effluent; and returning the vapor-containing effluent from the secondary reboiler to a stage of the stripping section of the distillation column.

[0011] Embodiment 5: The method of any one of embodiments 1-4, further comprising performing the (i) withdrawing, (ii) feeding, and (iii) returning steps at multiple stages in the stripping section of the distillation column using multiple secondary reboilers.

[0012] Embodiment 6: The method of any one of embodiments 1-5, wherein the distillation column trays have a first diameter in a rectifying section of the distillation column and a second diameter in a stripping section of the distillation column, the second diameter being larger than the first diameter, e.g., the second diameter being no greater than 5 times the first diameter.

[0013] Embodiment 7: The method of any one of embodiments 1 to 6, wherein the average stage-to-stage variation of the 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 stage-to-stage variation of the 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 of any one of embodiments 1 to 7, wherein the overhead stream comprises about 90% by weight or more ethylene, for example about 95% by weight or more ethylene, and / or the mass ratio of the aliphatic paraffinic hydrocarbon solvent added to the distillation column to the ethylene in the overhead stream is about 0.15 to about 0.5, and / or the overhead stream passes through a compressor.

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

[0016] Embodiment 10: The process of any one of embodiments 1-9, wherein the linear alpha olefin feed stream comprises about 3 wt. % or less of C5 or lower hydrocarbons other than ethylene.

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

[0018] Embodiment 12: The system of embodiment 11, wherein the heating device includes one or more secondary reboilers, each operatively arranged to receive and at least partially vaporize a liquid side stream from a different stage of the stripping section of the distillation column, and to return a vapor-containing effluent to the stripping section of the distillation column.

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

[0020] Embodiment 14: The system of any one of embodiments 11-13, 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, the second diameter being larger than the first diameter, e.g., the second diameter being no greater than 5 times the first diameter.

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

[0022] These and other features, aspects, and advantages of the present disclosure will become apparent from the following detailed description read in conjunction with the accompanying figures, which are briefly described below. The present disclosure includes any combination of two, three, four, or more features or elements described in the present disclosure, regardless of whether such features or elements are explicitly combined or otherwise recited in a specific exemplary implementation described herein. The present disclosure is intended to be read holistically such that any separable features or elements of the disclosure are to be viewed as combinable in any of its aspects and exemplary implementations, unless the context of the disclosure clearly dictates otherwise.

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

[0024] Having described aspects of the present disclosure in general terms above, reference is now made to the accompanying drawings, which are not necessarily drawn to scale. [Brief explanation of the drawings]

[0025] [Figure 1]FIG. 1 is a block diagram of an ethylene oligomerization system according to an exemplary implementation of the present disclosure. [Figure 2] 1 is a schematic diagram of an exemplary embodiment of a staged heating distillation column according to the present disclosure. [Figure 3] 10 graphically illustrates simulation results of the temperature profile of an exemplary embodiment of a staged heating distillation column from the experimental section. [Figure 4] 10 graphically illustrates the results of a simulation of the temperature profile of a conventional distillation column from the experimental section. [Figure 5] 10 graphically illustrates simulation results of vapor and liquid flow profiles for an exemplary embodiment of a staged heating distillation column from the experimental section. [Figure 6] 10 graphically illustrates the results of a simulation of vapor and liquid flow profiles for a conventional distillation column from an experimental section. DETAILED DESCRIPTION OF THE INVENTION

[0026] Certain implementations of the present disclosure will now be described more fully below with reference to the accompanying figures, in which some, but not all, implementations of the present disclosure are shown. Indeed, various implementations of the present disclosure may be embodied in many different forms and should not be construed as limited to the implementations set forth herein; rather, these exemplary implementations are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the disclosure to those skilled in the art. Like reference characters refer to like elements throughout.

[0027] Unless otherwise specified or clear from the context, references to first, second, or the like should not be construed to imply a particular order. A feature described as being above another feature (unless otherwise specified or clear from the context) may instead be below, and vice versa; similarly, a feature described as being to the left of another feature may instead be to the right, and vice versa. Reference may also be made herein to quantitative measures, values, geometric relationships, or the like, and unless otherwise noted, any one or more, if not all, of these may be absolute or approximate to account for acceptable variations that may occur, such as those due to engineering tolerances or the like.

[0028] All ranges disclosed herein are inclusive of the endpoints, and the endpoints are independently combinable with each other (e.g., a range of "up to 25 wt.%, or more specifically, 5 wt.% to 20 wt.%" includes the endpoints of the range "5 wt.% to 25 wt.%," and all intermediate values, etc.). "Combinations" are inclusive of blends, mixtures, alloys, reaction products, and the like.

[0029] As used herein, unless otherwise specified or clear from context, "or" of a set of operands is an "inclusive disjunction," whereby it is true if and only if one or more of the operands is true, as opposed to an "exclusive or," which is false when all of its 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 clear from context that the singular form is referred to.

[0030] Ethylene oligomerization process and system Linear alpha olefins (LAOs) have the chemical formula C x H 2xLinear alpha olefins are olefins with a molecular formula of 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44, 45, 46, 47, 48, 49, 50, 51, 52, 53, 54, 55, 56, 57, 58, 59, 60, 61, 62, 63, 64, 65, 66, 67, 68, 69, 70, 71, 72, 73, 74, 75, 76, 77, 78, 79, 80, 81, 82, 83, 84, 85, 86, 87, 88, 89, 90, 91, 92, 93, 94, 95, 96, 97, 98, 99, 100, 101, 102, 103, 104, 105, 106, 107, 108, 109, 110, 111, 112, 113, 114, 115, 116, 117, 118, 119, 120, 12 20 ~C 24 , C 24 ~C 30 and C 20 ~C 30 It comprises the industrially important class of alpha-olefins, including higher blends of olefins. Linear alpha-olefins are useful intermediates for producing 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 Ziegler-Natta type catalysts or non-Ziegler-Natta type catalysts.

[0032] The oligomerization can occur at a temperature of 10 to 200°C, such as 20 to 100°C, such as 50 to 90°C, such as 55 to 80°C, such as 60 to 70°C. The operating pressure can be 1 to 5 megapascals (MPa), such as 2 to 4 MPa. The process can be continuous, with an average residence time of 10 minutes to 20 hours, such as 30 minutes to 4 hours, such as 1 to 2 hours. The residence time can be selected to achieve the desired conversion with high selectivity.

[0033] The process can be carried out in solution using an inert solvent system, which can be composed of one or more solvents that are advantageously unreactive with the catalyst composition. Examples of suitable organic solvents include, but are not limited to, unsubstituted or halogen-substituted aromatic hydrocarbon solvents, such as toluene, benzene, xylene, monochlorobenzene, dichlorobenzene, chlorotoluene; aliphatic paraffin hydrocarbons, such as pentane, hexane, heptane, octane, nonane, decane; alicyclic hydrocarbon compounds, such as cyclohexane, decahydronaphthalene; and halogenated alkanes, such as dichloroethane and dichlorobutane, and 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. The oligomerization of ethylene is an exothermic reaction that can be cooled by an excess stream of ethylene. The gas leaving the top of the reactor can be cooled using a series of external coolers and condensers. The gas phase, after further cooling, can be recycled.

[0035] The bottoms stream leaving the bottom of the oligomerization reactor may contain active catalyst and unreacted ethylene. The reaction may be terminated to avoid undesirable side reactions by removing the catalyst components from the organic phase through extraction with a caustic aqueous phase. Contact with the caustic aqueous phase may result in the formation of unreacted inorganics corresponding to the catalyst components.

[0036] After passing through a catalyst removal system, the organic phase can be passed through a molecular sieve absorption bed and then fed to a distillation column to recover dissolved ethylene. The recovered ethylene can be recycled through an ethylene recycle loop, with the product being fed to an intermediate tank, after which the product can be fed to a separation section. In certain embodiments, linear alpha olefins produced from the reactor can be directed to a separation train.

[0037] 1, system 10 may include a reactor 12, a solvent supply 14, and a separation train 16. In a typical production mode, reactants 18, such as ethylene, a solvent, and a catalyst may be fed into reactor 12 to produce linear alpha olefins and various impurities, such as branched olefins and polymeric materials. After reaction, a bleed stream 20 may be directed into separation train 16, which may contain unreacted reactants, the produced linear alpha olefins, e.g., C4-C6, and the like. 20+ The linear alpha olefins may include olefins, a solvent, a catalyst, and various impurities. Separation train 16 may be configured to separate the linear alpha olefins from the solvent, catalyst, various impurities, and any unreacted ethylene. Separation train 16 may separate each linear alpha olefin, resulting in, for example, a C4 stream, a C6 stream, a C8 stream, etc. Separation train 16 may separate the linear alpha olefins into specific fractions, for example, C4-C 10 Distillate, C 11 ~C 17 Distillate, C 18 ~C 20 Distillate, C 20+ It may also be separated into fractions, or any other desired fractions.

[0038] The linear alpha olefin products can be isolated using a procedure including an aqueous caustic catalyst quench treatment followed by a water wash and recovery of the final product by distillation. For example, the liquid product comprising the solvent with dissolved ethylene can be fed to separation train 16 as described above. In the first column, unconsumed ethylene can be separated from the linear alpha olefin products and solvent. The ethylene can be recycled to the original reactor. The heavy fraction can be routed through a subsequent separation section where the heavy fraction is separated into various linear alpha olefin fractions (e.g., C8, C9, C10, C12, C14, C16, C18 ... 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, increased differential pressure at various locations within the reactor, etc. Such fouling can be treated by flushing the reactor with a solvent to remove the polymeric by-product. The flushed solvent containing the polymeric by-product can be directed into a separation train containing the linear alpha-olefin reaction product. The polymeric by-product is soluble in at least one linear alpha-olefin, and therefore the flushed solvent can exit the separation train essentially free of polymeric by-product and be recycled to the original solvent source for subsequent reactor flushing.

[0040] In certain embodiments, the choice of solvent system for an ethylene oligomerization reaction can increase selectivity to certain desired linear alpha-olefins. For example, it has been discovered that the combination of a first paraffinic solvent and a second aromatic solvent can be advantageous 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 1-hexene selectivity, and optionally xylene is used as the second (aromatic) solvent for catalyst dissolution and reactor cleanup.

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

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

[0043] Staged heating distillation column According to the present disclosure, separation train 16 includes a first stage-heated distillation column adapted to recover unreacted ethylene from the reactor effluent. The type of distillation column may vary, examples of which include columns equipped with trays (bubble cap trays, valve trays, sieve trays, etc.) or random or structured packing. Stage-heated distillation columns are characterized by the addition of heat at one or more stages in the stripping section of the column to augment the heat provided by the reboiler. The heat addition is typically achieved using a heat exchanger or other heating device positioned either internally or externally to the distillation column. The number of stages to which heat is added can vary but is typically between one and six stages.

[0044] An exemplary implementation of a staged distillation column 30 is shown in Figure 2. The distillation column 30 is in fluid communication with the effluent of the reactor 12 of Figure 1, shown as feed stream 32 entering the column at a feed stage, the location of which may vary. The staged distillation column 30 is adapted to separate the reactor effluent into an ethylene stream 34 suitable for recycle to the reactor 12 and a bottoms product stream 36 containing the remainder of the reactor effluent, including the desired linear alpha-olefins and solvent. The bottoms product stream 36 can be further processed if desired to separate the remaining components of the reactor effluent. The bottoms product stream 36 is withdrawn from a reboiler 56, which also produces a boiling stream 44 that is returned to the column 30.

[0045] In some embodiments of the present disclosure, a conventional overhead condenser that generates a reflux stream is very costly and complicated to implement. Typical overhead streams are primarily ethylene, which means that the overhead condenser may require a refrigeration system to generate reflux for return to the column. To overcome this problem, in certain embodiments of the present disclosure, a solvent stream is fed to the rectification section to adsorb the heavy components, as described more fully below. Thus, in certain embodiments, the systems and methods of the present disclosure can be characterized by the absence of an overhead condenser that returns reflux to column 30.

[0046] In certain embodiments, the overhead from distillation column 30 is compressed in compressor 38, which can be a multi-stage compressor having, for example, 2 to 6 or 2 to 4 stages, before being recycled to the original reactor. To improve the efficiency of the compression and remove condensables, the overhead is optionally cooled in heat exchanger 60 and passed through vapor-liquid separator 40 upstream of compressor 38. Optionally, the compressed overhead stream is also cooled after compression in heat exchanger 62 and also passed through a second vapor-liquid separator 40′ to remove condensables before being recycled. The combined condensate from the two vapor-liquid separators 40 and 40′ can be returned to column 30 as a minor reflux stream 42. Exemplary vapor-liquid separators include a flash drum, a knock-out drum, a knock-out pot, a compressor suction drum, and the like.

[0047] In an embodiment of the present disclosure, staged heated distillation column 30 includes a rectification section 46 above 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 entry point where ethylene is removed from the reactor effluent. In certain embodiments, at least a portion of rectification section 46 also includes an absorption section in which 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 as used in reactor 12 of FIG. 1, thereby reducing or eliminating linear alpha-olefin product left overhead and destroyed within the reactor. This absorption is obtained from the addition of an aliphatic paraffinic hydrocarbon solvent (e.g., n-heptane) stream 50 to column 30 near the top of the column. The stage to which the aliphatic paraffinic hydrocarbon solvent is added can vary, but is typically one of the top five stages of column 30. The aliphatic paraffinic hydrocarbon solvent stream 50 is typically obtained by recycling from a downstream portion of the separation train 16 .

[0048] The amount of aliphatic paraffinic hydrocarbon solvent added to column 30 depends in part on 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, e.g., 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 added solvent to the ethylene in the overhead effluent from the column. An exemplary range for the mass ratio of solvent to ethylene is about 0.15 to about 0.5, e.g., about 0.2 to about 0.4. In certain embodiments, the mass ratio is about 0.15 or greater, or about 0.2 or greater, or about 0.25 or greater, or about 0.3 or greater.

[0049] In certain embodiments of the present disclosure, recycled ethylene stream 34 contains about 90 wt% or more ethylene, for example, about 95 wt% or more ethylene (e.g., about 97-99 wt% ethylene), which may be compressed and returned to reactor 12. A small purge stream of the recycled ethylene stream (not shown) may be sent to a flare system to prevent the buildup of lighter components, such as nitrogen, in the process. Bottoms product stream 36 typically contains very little ethylene, for example, 1-3 wt% ethylene.

[0050] The staged heating distillation column 30 adds heat directly to certain stages in the column's stripping section 48 so that all of the sensible heat required for the column is not required from the reboiler 56. As noted above, this heat can be added through heat exchange that occurs either internal to the column 30 or external to the column. In this manner, efficient distillation column designs are possible without many drastic changes in the column diameter.

[0051] For illustrative purposes only, FIG. 2 illustrates external heat addition using heat exchangers 52, 52′ and pumps 54, 54′. As shown, liquid can be withdrawn from a stage within the stripping section 48 of distillation column 30 using pumps 54, 54′ and passed through heat exchangers 52, 52′ adapted to introduce heat into the liquid withdrawn from the column, typically resulting in at least partial vaporization of the liquid. The vapor-containing effluent from the heat exchange is returned to column 30. The location of the stage from which the liquid is withdrawn can vary. The vapor-containing effluent from heat exchangers 52, 52′ can be returned to the same stage from which the liquid was withdrawn, or can be returned to another stage in the stripping section 48 of column 30. While FIG. 2 illustrates two heat exchangers 52, 52′ drawing from two different stages of column 30, as previously discussed, the exact number of stages to which heat is added can vary.

[0052] The amount of heat added to augment the reboiler heat duty can vary. The amount of heat added in the stripping section of column 30 above the reboiler can be characterized as a percentage of the total heat duty added to the column (including any secondary reboilers and the main bottom reboiler). In certain embodiments, the percentage of heat added above the bottom reboiler (through the secondary reboiler) is about 50 to about 75% of the total heat duty added, e.g., about 55 to about 70%. For example, if the total heat duty is about 6,500 to about 7,500 kW, the amount of heat added above the bottom reboiler is typically about 3,250 to about 5,625 kW, e.g., about 3,575 to about 5,250 kW.

[0053] Due to the addition of heat in the stripping section to augment the reboiler, an efficient distillation column 30 can be designed, and in certain embodiments, only one tray diameter varies throughout the column length. For example, the trays of the distillation column can have a first diameter in the rectification section and a second diameter in the stripping section, the second diameter being larger than the first diameter, e.g., no more than five times the first diameter, 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 (e.g., 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, distillation column 30 can be characterized by stage-to-stage stability with respect to temperature profile and 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 stage-to-stage temperature variation of about 2.5° C. or less, or about 2.0° C. or less.

[0055] Furthermore, in certain embodiments, the average stage-to-stage change in vapor flow rate in the bottom five stages of the stripping section of the distillation column is about 12% or less (e.g., 10% or less, or about 8% or less). This is calculated by determining the absolute percentage change in flow rate (whether increasing or decreasing) between each of the bottom five stages and averaging the total. In certain embodiments, the average stage-to-stage change in vapor flow rate in the bottom five stages of the stripping section of the distillation column is about 8,000 kg / hr or less. In some embodiments, the average stage-to-stage change in liquid flow rate in the bottom five stages of the stripping section of the distillation column is about 20% or less (e.g., 18% or less, or about 16% or less). This is calculated by determining the absolute percentage change in flow rate (whether increasing or decreasing) between each of the bottom five stages and averaging the total. In certain embodiments, the average stage-to-stage change in liquid flow rate in the bottom five stages of the stripping section of the distillation column is about 20,000 kg / hr or less. [Example]

[0056] experiment A process simulation study was conducted using Aspen Plus. The simulation compared two distillation column designs: (1) a conventional distillation column with 30 trays and all heat added to the reboiler (stage 30); and (2) a staged heating distillation column of the present invention with 30 trays and heat added to the reboiler plus stages 19, 21, 24, and 27. In both cases, stage 18 is the feed stage, and recycled n-heptane solvent is added at stage 3. The simulation used the same feed stream and the same target effluent flow rate for each column design. The characteristics of the feed stream are set forth in Table 1 below, and the characteristics of the recycled n-heptane solvent are set forth in Table 2 below.

[0057] [Table 1]

[0058] [Table 2]

[0059] Aspen Plus designed the most efficient column for each design case to achieve an overhead flow of at least 90 wt. % ethylene. For conventional columns with reboilers, the Aspen Plus design included significant stage diameter variations throughout the column to account for varying vapor and liquid flows, particularly in the stripping section. The simulated conventional column had three different diameters throughout the column: approximately 0.5 meters in the rectification section (stages 1-17) and two different diameters in the stripping section. From stages 18-21, the required stage diameter was approximately 1.2 meters, and from stages 22-29, the required diameter was approximately 3 meters. Thus, conventional column designs are inevitably complicated by significant diameter variations and at least three different sections.

[0060] In contrast, the simulations revealed that the design of a column in which additional heat is added in four stages of the stripping section can be less complex, with the rectifying section having a diameter of about 0.5 meters (stages 1 to 17) and the stripping section being optimized to a single diameter of about 1.8 to 2.2 meters. Unlike conventional column designs, stage-heated columns could be designed with only one diameter varying throughout the column length.

[0061] The simulations also calculated temperature and vapor / liquid flow profiles for each column design. These profiles are set forth in Figures 3-6. As shown in Figure 3, for the staged heating column, the temperature profile (right-hand plot) in the stripping section of the column is more stable from stage to stage compared to the conventional column design (Figure 4). Similarly, as shown in Figure 5, for the staged heating column, the liquid (square line markers) and vapor (circular line markers) flows (right-hand plot) in the stripping section of the column are more stable from stage to stage compared to the conventional column design (Figure 6). This increased stability of temperature and flow in the stripping section of the column of the present invention allows for efficient column design and operation with only one diameter change throughout the column.

[0062] In general, the present invention may alternately comprise, consist of, or consist essentially of any suitable components disclosed herein. The present invention may additionally or alternatively be formulated to be free or substantially free of any component, material, ingredient, adjuvant, or species used in prior art compositions or that are not normally necessary to achieve the function and / or purpose of the present invention.

[0063] Many modifications and other implementations of the present disclosure will come to mind to one skilled in the art to which this disclosure pertains having the benefit of the teachings presented in the foregoing descriptions and the associated drawings. It is to be understood, therefore, that the disclosure is not limited to the particular implementations disclosed herein, and that modifications and other implementations are intended to be included within the scope of the appended claims. Although specific terms are employed herein, they are used in a generic and descriptive sense only and not for purposes of limitation.

Claims

1. 1. A method for purifying a linear alpha olefin product, comprising: (a) feeding the linear alpha olefin product and a linear alpha olefin feed stream comprising ethylene to a feed stage of a distillation column having a plurality of stacked stages disposed between the overhead outlet and the bottoms reboiler, the stacked stages including a stripping section of the distillation column between the feed stage and a bottoms reboiler, and a rectification section of the distillation column between the feed stage and an overhead outlet; (b) feeding an aliphatic paraffinic hydrocarbon solvent to the rectification section of the distillation column to absorb linear alpha olefins; (c) adding heat to at least one of a plurality of stacked stages in the stripping section of the distillation column between the feed stage and the bottoms reboiler; (d) withdrawing an overhead stream comprising ethylene through an overhead outlet; (e) withdrawing a bottoms stream from the distillation column comprising the linear alpha olefin product; A method comprising:

2. 10. The method of claim 1, comprising applying heat to a plurality of stacked stages in the stripping section of the distillation column, such as applying heat to at least two stages and up to six stages.

3. 3. The method of claim 1 or claim 2, wherein the step of adding heat comprises adding heat through a heat exchanger located either inside the distillation column or outside the distillation column, and optionally, the amount of heat added to the stripping section above the reboiler is about 50 to about 75% of the total heat load added to the stripping section of the distillation column.

4. the step of applying heat i) withdrawing a liquid minor stream from at least one of the plurality of stacked stages of the stripping section of the distillation column; ii) feeding the side stream into a side reboiler adapted to at least partially vaporize the side stream to produce a vapor-containing effluent; iii) returning the vapor-containing effluent from the secondary reboiler to a stage in the stripping section of the distillation column; 3. The method of claim 1 or claim 2, comprising:

5. 5. The method of claim 4, further comprising carrying out the steps of (i) withdrawing, (ii) feeding, and (iii) returning at multiple stages in the stripping section of the distillation column using multiple secondary reboilers.

6. 3. The method of claim 1 or claim 2, wherein the stages of the distillation column have a first diameter in the rectifying section of the distillation column and a second diameter in the stripping section of the distillation column, the second diameter being larger than the first diameter, e.g., the second diameter being not more than five times the first diameter.

7. 3. The method of claim 1 or claim 2, wherein the average stage-to-stage variation of the 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 stage-to-stage variation of the liquid flow rate in the bottom five stages of the stripping section of the distillation column is about 20% or less.

8. 3. The method of claim 1 or claim 2, wherein the overhead stream comprises about 90 wt. % or more ethylene, for example about 95 wt. % or more ethylene, and / or the mass ratio of aliphatic paraffin hydrocarbon solvent added to the distillation column to ethylene in the overhead stream is about 0.15 to about 0.5, and / or the overhead stream passes through a compressor.

9. 3. The process of claim 1 or claim 2, wherein the linear alpha olefin feed stream comprises the aliphatic paraffin hydrocarbon solvent, such as n-heptane and 1-hexene.

10. 10. The process of claim 9, wherein the linear alpha olefin feed stream comprises about 3 wt% or less of C5 or lower hydrocarbons other than ethylene.

11. 1. A system for preparing and purifying a linear alpha olefin product, comprising: (a) an ethylene oligomerization reactor producing an effluent comprising said linear alpha olefin product and ethylene; (b) 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 the overhead outlet and the bottoms reboiler, the distillation column including a stripping section of the distillation column between the feed stage and a bottoms reboiler, and a rectification section between the feed stage and an overhead outlet; (c) an aliphatic paraffinic hydrocarbon solvent source in fluid communication with the rectification section of the distillation column; (d) at least one heating device positioned to add heat to at least one stage of the stripping section of the distillation column between the feed stage and the bottoms reboiler; Including, the system.

12. 12. The system of claim 11, wherein the heating device comprises one or more secondary reboilers, each operatively arranged to receive and at least partially vaporize a liquid side stream from a different stage of the stripping section of the distillation column and to return a vapor-containing effluent to the stripping section of the distillation column.

13. 13. The system of claim 12, wherein the number of secondary reboilers is between 2 and 6.

14. 12. The system of claim 11, wherein the stages of the distillation column have a first diameter in the rectifying section and a second diameter in the stripping section of the distillation column, the second diameter being larger than the first diameter, e.g., the second diameter being no more than five times the first diameter.

15. 12. The system of claim 11, wherein the overhead stream from the distillation column comprises about 90 wt. % or more ethylene, e.g., about 95 wt. % or more ethylene, and / or the effluent from the ethylene oligomerization reactor comprises the aliphatic paraffin hydrocarbon solvent and 1-hexene, and / or the effluent from the ethylene oligomerization reactor comprises about 3 wt. % or less C5 or lower hydrocarbons other than ethylene.

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