Process for purifying linear alpha olefins

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 at least one impurity to a distillation column having a plurality of stacked stages; withdrawing a side stream from at least one of the plurality of stacked stages; feeding the side stream to a reactor comprising an isomerization catalyst that converts at least a portion of the at least one impurity from a first isomer to a second isomer to produce a reactor product stream having a reduced content of the first isomer; returning the reactor product stream to the stages of the distillation column; and withdrawing an overhead stream from the distillation column comprising the linear alpha olefin product and having a reduced content of the at least one impurity.

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 feedstocks in the petrochemical industry, and among these linear alpha olefins, unbranched olefins in which the double bond is located at the end 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 then be oxidized to obtain synthetic fatty acids useful in the manufacture of lubricants, especially those with odd carbon numbers. Linear alpha olefins are also used in the manufacture of detergents, such as linear alkylbenzene sulfonates, which are prepared by the Friedel-Crafts reaction of benzene with linear olefins followed by sulfonation. Another important use of linear alpha olefins involves the production of linear low density polyethylene (LLDPE) by catalytic copolymerization with ethylene.

[0003] The preparation of alpha-olefins is mainly based on the oligomerization of ethylene, which has the corollary that the alpha-olefins produced have an even number of carbon atoms. The ethylene oligomerization process mainly utilizes organoaluminum compounds or transition metals as catalysts. The oligomerization process is typically carried out in the presence of a catalyst that includes a zirconium component, such as zirconium tetraisobutyrate, and an aluminum component, such as ethylaluminum sesquichloride, as an activator. 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.

[0004] It is desirable to purify the alpha-olefin products of oligomerization reactions to very high purity levels, for example, purity levels greater than 99.5 mole %. Achieving such high purity using conventional separation methods can be difficult due to the presence of impurities with boiling points very close to that of the target alpha-olefin products. There remains a need in the art for improvements in separation methods for such products. Summary of the Invention [Means for solving the problem]

[0005] Summary of the Invention An exemplary implementation of the present disclosure is directed to a method for purifying a linear alpha olefin product stream. In particular, the method of the present invention involves the use of at least one side reactor arranged to receive at least a portion of the flow through a distillation column, the side reactor containing an isomerization catalyst capable of converting at least one impurity from a first isomer to a second isomer, the second isomer being more easily separated from the target linear alpha olefin. In this manner, the side reactor can improve the separation efficiency of the distillation column, allowing the target linear alpha olefin to be purified to a very high purity level.

[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 at least one impurity to a distillation column having a plurality of stacked stages; withdrawing a side stream from at least one of the plurality of stacked stages; feeding the front end stream to a reactor comprising an isomerization catalyst that converts at least a portion of the at least one impurity from a first isomer to a second isomer to produce a reactor product stream having a reduced content of the first isomer; returning the reactor product stream to a stage of the distillation column; and withdrawing an overhead stream from the distillation column comprising the linear alpha olefin product and having a reduced content of the at least one impurity.

[0008] Embodiment 2: The method of embodiment 1, wherein the at least one impurity is a branched olefin.

[0009] Embodiment 3: The method of embodiment 1 or 2, wherein the linear alpha olefin product is 1-hexene and the at least one impurity is 2-ethyl-1-butene or an isomer thereof.

[0010] Embodiment 4: The method of any one of embodiments 1 to 3, wherein the first isomer is 2-ethyl-1-butene and the second isomer is cis- or trans-3-methyl-2-pentene.

[0011]

[0023] Embodiment 5: The method of any one of embodiments 1-4, wherein the overhead stream comprises at least about 99.5 mole % 1-hexene.

[0012]

[0023] Embodiment 6: The method of any one of embodiments 1-5, wherein the overhead stream comprises about 200 ppm or less of n-hexane.

[0013]

[0023] Embodiment 7: The process of any one of embodiments 1-6, wherein the overhead stream comprises about 0.15 mol % or less of 2-ethyl-1-butene or an isomer thereof.

[0014]

[0023] Embodiment 8: The isomerization catalyst is heated at a pressure of about 1 to 10 bar, a temperature of about 45 to 100°C, and for about 0.5 to 8.5 hours. -1 8. The method of any one of the preceding claims, wherein at a liquid hourly space velocity of about 1000 rpm, about 80 mol % or more of 2-ethyl-1-butene can be converted to said second isomer in about 1 hour.

[0015] Embodiment 9: The method of any one of embodiments 1-8, wherein no more than about 3 mol % of 1-hexene is converted to a different isomer under the same reaction conditions.

[0016] Embodiment 10: The method of any one of embodiments 1 to 9, wherein the isomerization catalyst comprises an alumina material, a zeolite material, or an ion exchange resin, such as a zeolite material having a silica to alumina molar ratio in the range of 5 to 1000, or in the range of 25 to 300.

[0017]

[0031] Embodiment 11: The method of any one of embodiments 1 to 10, wherein the distillation column is substantially free of catalytic material.

[0018]

[0023] Embodiment 12: The method of any one of embodiments 1 to 11, wherein the distillation column comprises no more than about 150 stages.

[0019] Embodiment 13: The method of any one of embodiments 1 to 12, wherein the operating temperature of the reactor is from about 45° C. to about 100° C.

[0020] Embodiment 14: The method of any one of embodiments 1 to 13, wherein the distillation column includes an overhead condenser that generates a reflux stream that is returned to the distillation column, and the reflux ratio is from about 4 to about 20, for example, from about 7 to about 15.

[0021] Embodiment 15: The method of any one of embodiments 1 to 14, wherein the step of providing the side stream in the reactor comprises providing the side stream to a first reactor of a pair of a first reactor and a second reactor arranged in parallel, such that the second reactor is available for regenerating the isomerization catalyst while the first reactor is in use.

[0022] These and other features, aspects and advantages of the present disclosure will become apparent from reading the following detailed description 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 this 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 present disclosure should be considered 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 summary is provided only for the purpose of summarizing some exemplary implementations in order to provide a basic understanding of some aspects of the present disclosure. It is therefore understood that the exemplary implementations described above are merely examples and should not be construed in any way to narrow the scope or spirit of the present disclosure. 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 thus described aspects of the present disclosure in general terms above, reference is now made to the accompanying figures, which are not necessarily drawn to scale. [Brief description 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. [Diagram 2] FIG. 1 is a schematic diagram of an exemplary embodiment of a distillation column with two side reactors according to the present disclosure. [Diagram 3] FIG. 1 is a schematic diagram of an exemplary embodiment of a distillation column with one side reactor according to the present disclosure. [Figure 4]FIG. 1 is a schematic diagram of an exemplary embodiment of a distillation column with two side reactors arranged in parallel according to the present disclosure. [Diagram 5] FIG. 1 is a schematic diagram of an exemplary embodiment of a distillation column with a single side reactor used for Aspen Plus simulations in accordance with the present disclosure. [Figure 6] 5A-5C are graphical illustrations of the results of a simulation of the system layout of FIG. 5 to determine the optimal location of the side reactor according to one embodiment. [Figure 7] 5A-5C are graphs showing the results of a simulation of the system configuration of FIG. 5 to determine the effect of reflux ratio on product purity. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0026] Hereinafter, some implementations of the present disclosure will be described more fully with reference to the attached 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 being 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 numerals refer to like elements throughout.

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

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

[0029] As used herein, unless otherwise specified or clear from the context, "or" of a set of operands is an "inclusive or," whereby it is true if and only if one or more of the operands are true, as opposed to an "exclusive or," which is false when all 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. Additionally, the articles "a" and "an" mean "one or more," unless otherwise specified or clear from the context to be intended in the singular form.

[0030] <Ethylene oligomerization method and system> Linear alpha olefins (LAOs) have the chemical formula C x H 2x Linear alpha olefins are olefins having the formula: C 1-(2-(2-phenylene)-1-propene, C 2-(2-phenylene)-1-propene, C 3-(2-phenylene)-1-propene, C 4-(2-phenylene)-1-propene, C 5-(2-phenylene)-1-propene, C 6-(2-phenylene)-1-propene, C 7-(2-phenylene)-1-propene, C 8-(2-phenylene)-1-propene, C 9-(2-phenylene)-1-propene, C 10-(2-phenylene)-1-propene, C 11-(2-phenylene)-1-propene, C 12-(2-phenylene)-1-propene, C 13-(2-phenylene)-1-propene, C 14-(2-phenylene)-1-propene, C 15-(2-phenylene)-1-propene, C 16-(2-phenylene)-1-propene, C 17-(2-phenylene)-1-propene, C 18-(2-phenylene)-1-propene, C 19-(2-phenylene)-1-propene, C 20-(2-phenylene)-1-propene, C 21-(2-phenylene)-1-propene, C 22-(2-phenylene)-1-propene, C 23-(2-phenylene)-1-propene, C 24-(2-phenylene)-1-propene, C 25-(2-phenylene)-1-propene, C 26-(2-phenylene)-1-propene, C 27-(2-phenylene)-1-propene, C 28-(2-phenylene)-1-propene, C 29-(2-phenylene)-1-propene, C 30-(2-phenyl 20 ~C 24 , C 24 ~C 30 and C 20 ~C 30 Linear alpha olefins constitute a class of commercially important alpha olefins, including higher 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 methods for the production of 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 may occur at a temperature of 10-200°C, such as 20-100°C, such as 50-90°C, such as 55-80°C, such as 60-70°C. The operating pressure may be 1-5 megapascals (MPa), such as 2-4 MPa. The process may be continuous and the average residence time may be 10 minutes to 20 hours, such as 30 minutes to 4 hours, such as 1-2 hours. The residence time may be selected to achieve the desired conversion with high selectivity.

[0033] The method can be carried out in solution using an inert solvent that is advantageously non-reactive with the catalyst composition.Examples of suitable organic solvents can include, but are not limited to, aromatic hydrocarbon solvents that may be unsubstituted or substituted with halogen, such as toluene, benzene, xylene, monochlorobenzene, dichlorobenzene, chlorotoluene; aliphatic paraffinic hydrocarbons such as pentane, hexane, heptane, octane, nonane, decane; alicyclic hydrocarbon compounds such as cyclohexane, decahydronaphthalene; and halogenated alkanes such as dichloroethane and dichlorobutane.

[0034] The process can be carried out in any reactor, for example 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 gases leaving the top of the reactor can be cooled using a series of external coolers and condensers. The gas phase can be recycled after further cooling.

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

[0036] The organic phase, after passing through the catalyst 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 recycle loop while the product is fed to an intermediate vessel and then 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] As shown in Figure 1, system 10 can include a reactor 12, a toluene (or other solvent) source 14, and a separation train 16. In a typical production mode, reactants 18, such as ethylene, a solvent, and a catalyst, can be fed to reactor 12 to produce linear alpha olefins and various impurities, such as branched olefins and polymeric materials. After reaction, a bleed stream 20 can be directed to separation train 16, where the bleed stream is separated from the unreacted reactants, the produced linear alpha olefins, such as C 4 ~C 20+ The separation train 16 may include olefins, a solvent, a catalyst, and various impurities. The separation train 16 may be configured to separate the linear alpha olefins from the solvent, the catalyst, various impurities, and any unreacted ethylene. The separation train 16 may separate each linear alpha olefin, for example, C 4 Flow, C 6 Flow, C 8 Separation train 16 separates linear alpha olefins into specific fractions, e.g., C 4 ~C 10 Fraction, C 11 ~C 17 Fraction, C 18 ~C 20 Fraction, C 20+The fractions may also be separated into fractions or any other desired fractions.

[0038] The linear alpha olefin products may be isolated using a procedure that includes an aqueous caustic catalytic quench followed by washing with water and final product recovery by distillation. For example, a liquid product comprising a solvent (e.g., toluene) in which ethylene is dissolved may be fed to the separation train 16 described above. In the first column, unconsumed ethylene may be separated from the linear alpha olefin products and the solvent. The ethylene may be recycled back to the reactor. The heavier fraction may be sent to a subsequent separation section where it may be separated into different linear alpha olefin fractions (e.g., C8, C10, >C12). The solvent may be recovered and recycled back to the reactor.

[0039] Polymer fouling in the reactor may occur during the oligomerization reaction process. Such fouling is typically detected, for example, by a decrease in the discharge flow rate, a decrease in the internal condenser performance, an increase in the differential pressure at various locations in the reactor, etc. Such fouling may be treated by flushing the reactor with toluene or another solvent to remove the polymeric material by-product. The flushed toluene containing the polymeric material may be directed to a separation train containing the linear alpha olefin reaction product. The polymeric material is soluble in at least one linear alpha olefin, so the flushed toluene may exit the separation train essentially free of polymeric material and may be recycled back to the toluene source for subsequent reactor flushing.

[0040] <Integrated distillation column and side reactor> In accordance with the present disclosure, separation train 16 includes at least one distillation column with at least one side reactor connected thereto. The type of distillation column may vary, examples of which include columns equipped with bubble cap trays, valve trays, or sieve trays.

[0041] The side reactor contains an isomerization catalyst adapted to convert at least one impurity, such as branched olefins, entering the distillation column from a first isomer to a second isomer. It is advantageous for the boiling point of the second isomer to be further away from the boiling point of the desired alpha-olefin product compared to the first isomer. Thus, the second isomer is more easily separated from the desired alpha-olefin product by the distillation column compared to the first isomer.

[0042] When the desired alpha olefin product is 1-hexene, which has a boiling point of 63.48° C., one example of a problematic impurity (i.e., the first isomer) is 2-ethyl-1-butene, which has a boiling point of 64.67° C. However, 2-ethyl-1-butene can be converted to a higher boiling isomer (i.e., the second isomer), such as cis- / trans-3-methyl-2-pentene, using an isomerization catalyst. This equilibrium-limiting reaction is shown below:

[0043] [ka]

[0044] Exemplary isomerization catalysts include alumina materials, zeolite materials, or ion exchange resins. Suitable catalysts typically include acidic functional groups. Alumina catalysts are available, for example, under the trade name SELEXSORB® (e.g., SELEXSORB® CD or CDL) from BASF Corporation or third party suppliers. Ion exchange resin catalysts are available, for example, under the trade name AMBERLYST® (e.g., AMBERLYST® 15) from Dow Chemical Company or third party suppliers.

[0045] The zeolite catalyst material can be of various types, in some embodiments, the zeolite is selected from the group consisting of ABW, ACO, AEI, AEL, AEN, AET, AFI, AFN, AFO, AFR, AFS, AFT, AFX, AFY, AHT, APC, APD, ASV, ATN, ATO, ATS, ATT, ATV, AVL, AWO, AWW, BCT, BEA, BEC, BIK, BOF, BOG, BOZ, BPH, BRE, BSV, CAN, CAS, CDO, CFI, CGF, CGS, CHA, CHI, CLO, CON, CZP, DAC, DDR, DFO, DFT, DON, EAB, EDI, EEI, EMT, EON, EPI, ERI, ESV, ETR, EUO, EZT, FAU, FER, GIS, GME, GON, GOO, HEU, IFR, I FY, IHW, IMF, IRN, ISV, ITE, ITG, ITH, ITW, IWR, IWS, IWV, IWW, JBW, JRY, JSR, JST, KFI, LAU, LEV, LOV, LTA, LTF, LTL, LTN, MAZ , MEI, MEL, MER, MFI, MFS, MON, MOR, MOZ, MRE, MSE, MTF, MTT, MVY, MTW, MWF, MWW, NAB, NAT, NES, NPO, NPT, NSI, OBW, OFF, OKO, OSI, OSO, OWE, PAR, PAU, PCR, PHI, PON, PUN, RHO, RON, RRO, RSN, RTE, RTH, RWR, RWY, SAF, SAO, SAS, SAT, SAV, SBE, SBS, SBT, SC O, SEW, SFE, SFF, SFG, SFH, SFN, SFO, SFS, SFW, SGF, SIV, SOF, SOS, SSF, SSY, STF, STI, STO, STT, STW, SVR, SZR, TER, THO, TON, TSC, TUN, UEI, UFI, UOS, USI, UTL, UWY, VET, VFI, VNI, VSV, WIE, WEN, YUG, ZON, and mixtures or intergrowths thereof. In some embodiments, the zeolite comprises a framework type selected from the group consisting of AEI, BEA (beta zeolite), CHA (chabazite), FAU (zeolite Y), FER (magnesium oxide), MFI (ZSM-5), and MOR (mordenite).Non-limiting examples of zeolites having these structures include chabazite, faujasite, zeolite Y, ultrastable zeolite Y, beta zeolite, mordenite, silicalite, zeolite X, and ZSM-5.

[0046] The silica-to-alumina molar ratio ("SAR") of the zeolite can vary over a wide range. For example, the zeolite can have a SAR of about 1 to about 1000. In one or more embodiments, the zeolite has a SAR molar ratio ranging from about 1, about 2, about 5, about 8, about 10, about 15, about 20, or about 25 to about 30, about 35, about 40, about 45, about 50, about 60, about 70, about 80, about 90, about 100, about 150, about 200, about 260, about 300, about 400, about 500, about 750, or about 1000 (e.g., about 10 to about 150 or about 20 to about 80). In certain embodiments, the zeolitic material has a silica-to-alumina molar ratio ranging from 5 to 1000 or from 25 to 300.

[0047] In certain embodiments, an isomerization catalyst can be characterized based on how much of an undesired first isomer is converted to a second isomer. For example, in certain embodiments, an isomerization catalyst can be characterized based on how much of an undesired first isomer is converted to a second isomer at a pressure of about 1-10 bar, a temperature of about 45-100° C., and a reaction time of about 0.5-8.5 h. -1 At a liquid hourly space velocity of 1000 rpm, about 80 mol % or more of the 2-ethyl-1-butene (e.g., about 85 mol % or more, or about 90 mol % or more, or about 95 mol % or more) can be converted to the second isomer in about 1 hour. In some embodiments, about 3 mol % or less of the 1-hexene (e.g., about 2 mol % or less, or about 1 mol % or less) is converted to a different isomer under the same reaction conditions described above.

[0048] The side reactor or reactors can be operated, for example, as either a plug flow reactor (otherwise known as a tubular reactor) or a continuous stirred tank reactor (CSTR), and can be operated at temperatures and pressures independent of the operating temperature and pressure of the distillation column. The impure 1-hexene feed can be fed to the tubular reactor in either upflow or downflow mode. In some embodiments, the feed stream is fed in upflow mode.

[0049] The external side reactor is extremely useful when the catalyst reaction conditions (e.g., temperature and pressure) do not match the desired distillation conditions. This process configuration is also extremely useful when slow reactions that require large amounts of catalyst must be carried out. Conventional reactive distillation columns can typically hold catalyst in only 20-40% of the column volume. Placing the catalyst in the side reactor circumvents this limitation with reactive distillation processes. Typical operating temperatures for the side reactor range from about 40 to about 100° C., e.g., from about 50 to about 70° C. The amount of catalyst in the side reactor can vary. In certain embodiments, the catalyst charge is from about 3,000 to about 6,000 kg catalyst per side reactor, e.g., from about 4,000 to about 5,000 kg.

[0050] Because the catalyst is located outside the distillation column, regeneration of the catalyst can be accomplished more easily compared to a reactive distillation column. It may be advantageous to use two external side reactors configured in parallel so that one reactor can be operated while the other reactor is undergoing regeneration. An exemplary regeneration method includes passing hot nitrogen gas, for example, nitrogen at about 200°C or higher, or about 250°C or higher, or about 280°C or higher (e.g., about 250 to about 300°C), through the catalyst bed.

[0051] Given the advantages of having the isomerization catalyst outside the distillation column, in certain embodiments, the distillation column utilized in this disclosure may be described as being substantially or completely free of catalytic material, meaning that the distillation column contains less than 1% by volume of catalyst, or less than 0.5% by volume of catalyst, or 0% by volume of catalyst within the column.

[0052] An exemplary implementation of a distillation column with an integrated side reactor is shown in FIG. 2. As shown, the separation train can include a distillation column 30, which typically includes a condenser 32 as an upper stage and a reboiler 34 as a lower stage. A distillate stream 36 exits the top of the column as a product stream. A bottoms stream 38 also exits the column. A feed stream 40 enters the column at a desired feed stage, which can vary. The feed stream 40 typically includes an alpha olefin product that requires further purification along with one or more impurities, such as branched olefins. The reflux ratio of the distillation column can vary, with exemplary ranges being from about 4 to about 20, such as from about 7 to about 15.

[0053] The number of side reactors in fluid communication with distillation column 30 can vary. Various embodiments have from 1 to 10 side reactors. In Figure 2, two side reactors 44 and 46 are shown. As shown, each of side reactors 44 and 46 is arranged to remove liquid from a stage of distillation column 30 using pumps 48 and 50, which can be controlled using respective controllers 52 and 54, such as level indicating controllers.

[0054] FIG. 3 provides a more detailed view of one exemplary embodiment of a side reactor 60 integrated with a distillation column 62, shown in partial cross-section. As shown, a sump holding pot 64 can be used to hold liquid exiting the distillation column upstream of a pump 66 used to pump the liquid through the side reactor 60. A vapor pressure equalization line 68 can extend from the top of the holding pot 64 to the vapor headspace of a distillation column tray 70, which is shown as a bubble cap tray for illustrative purposes only. Optionally, the system can include a preheater 72 upstream of the side reactor 60 and a cooler 74 downstream from the side reactor. Although not shown, any desired heating / cooling of the streams entering or exiting the side reactor can be accomplished by heat exchange with the column feed stream to increase the thermal efficiency of the process.

[0055] The flow rate into the side reactor can vary, and in particular can be any percentage of the flow of liquid in the column. Additionally, the relative positions of the stage from which liquid is withdrawn to feed the side reactor and the stage to which the discharge from the side reactor is returned can vary. The liquid can be withdrawn and returned to the same stage or to an adjacent stage or a stage further away from the stage from which it was withdrawn. Thus, the number of stages between the stage from which it is withdrawn and the stage from which it is returned can be 0 or any number from 1 to 100 or more. Liquid can be withdrawn from multiple stages and fed to the same reactor or to multiple reactors.

[0056] As mentioned above, two side reactors in parallel can be integrated with a distillation column. An example of such an embodiment is shown in FIG. 4, where a 1-hexene feed stream enters a distillation column with two side reactors in parallel, labeled R. The use of parallel reactors allows one reactor to be shut down for regeneration when the isomerization catalyst becomes fouled or otherwise deactivated, without interrupting operation of the distillation column. Purified 1-hexene exits the top of the column, and the majority of the impurities exit as a bottom stream.

[0057] The feed stream to the column can vary in composition, but is typically at least 96 mol % or at least 98 mol % 1-hexene (e.g., from about 96 mol % to about 98.5 mol % or from about 98 mol % to about 98.5 mol %) and at least 0.5 mol % or at least 0.8 mol % 2-ethyl-1-butene (e.g., from about 0.5 mol % to about 1.5 mol % or from about 0.8 mol % to about 1.2 mol %).

[0058] The use of a side reactor as contemplated herein allows for purification of 1-hexene or other linear alpha olefins in the overhead stream of the distillation column to a purity of about 99.5 mol % or greater. In certain embodiments, the overhead product stream from the distillation column is characterized by a very low impurity content, for example, about 0.3 mol % or less, or about 0.2 mol % or less, or about 0.15 mol % or less of branched olefins, such as 2-ethyl-1-butene. When the target linear alpha olefin is 1-hexene, in certain embodiments, the overhead product stream is also characterized by a very low n-hexane content, for example, about 200 ppm or less, or about 150 ppm or less of n-hexane.

[0059] The use of a side reactor as contemplated in this disclosure can reduce the number of stages that might otherwise be required to achieve very high purity of a particular linear alpha olefin, such as 1-hexene. For example, in certain embodiments, the number of distillation stages required to achieve high purity of linear alpha olefins (e.g., about 99.5 mole % or greater) is about 150 or less, or about 120 or less (e.g., about 80 to about 150 stages).

[0060] This technique is broadly applicable to the isomerization reactions of C6 compounds described herein, but may also be applied to other reactions that are equilibrium limited, including, for example, the isomerization of other linear alpha olefins, the metathesis of C2-C12 olefins, the etherification of C4 and C5 olefins with alcohols (e.g., methanol, ethanol, or isoamyl alcohol) to form gasoline additives that increase the octane number of fuels, esterification, acetalization, etc.

[0061] experiment EXAMPLES

[0062] [Example 1] A series of laboratory reactor tests were conducted using a tubular reactor with various isomerization catalysts to determine the feasibility of using isomerization catalysts to convert 2-ethyl-1-butene (2E1B) to different isomers, such as cis- or trans-3-methyl-2-pentene. Conversions (mol %) were determined for both 2E1B and 1-hexene (1H) under the test conditions shown in Table 1 for pressure (P), temperature (T), liquid hourly space velocity (LHSV) and residence time (TOS). The catalysts tested included various zeolites, alumina materials and one ion exchange resin.

[0063] [Table 1]

[0064] The results are also shown in Table 1. All of the catalysts tested were able to convert at least a portion of the 2E1B to the more desirable isomers. However, some catalysts were not particularly selective for the conversion of 2E1B and also converted significant amounts of 1-hexene to the undesirable different isomers. The highest performing catalysts include, for example, ZSM-5 zeolites (especially the larger SAR), SELEXSORB CD and the ion exchange resin AMBERLYST-15.

[0065] [Example 2] A process simulation study was performed using Aspen Plus. The simulated process is shown diagrammatically in FIG. 5, where F-SF3 is the 1-hexene feed stream, SF2-80 is a distillation column with 81 theoretical stages, TOP-SF3 is the overhead product stream, BOT-SF3 is the bottoms stream, and RSTO-80 is a side reactor that receives the inlet stream SIDEOUT3 from the distillation column and returns SIDEIN3 to the distillation column. A simulation study was performed to study the optimal location of one side reactor configuration, and it was observed that the optimal feed location for the side reactor was stage 47, with liquid being returned to the column at stage 48. The simulated feed stream was 98.15 mol % 1-hexene and 0.99 mol % 2E1B. The results of this study are shown in FIG. 6.

[0066] Further simulation studies were performed using a fixed catalyst charge of 4,347 kg in the side reactor and the same simulated feed stream as above to study the effect of reflux ratio on 1-hexene purity. The results are shown in Figure 7, and it can be seen that increasing the reflux ratio increases the 1-hexene purity in the product stream while simultaneously decreasing the n-hexane impurity.

[0067] In general, the present invention may alternatively 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 components, materials, ingredients, adjuvants, or species used in prior art compositions or that are otherwise not essential to the function and / or achievement of the purpose of the present invention.

[0068] 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 present disclosure is not limited to the specific implementations disclosed herein, but 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: feeding a linear alpha olefin feed stream comprising a linear alpha olefin product and at least one impurity to a distillation column having a plurality of stacked stages; removing a side stream from at least one of the plurality of stacked stages; feeding said side stream to a reactor containing an isomerization catalyst that converts at least a portion of said at least one impurity from a first isomer to a second isomer to produce a reactor product stream having a reduced content of said first isomer; returning said reactor product stream to a stage of said distillation column; removing an overhead stream from said distillation column comprising said linear alpha olefin product and having a reduced content of said at least one impurity; A method comprising:

2. 10. The method of claim 1, wherein the at least one impurity is a branched olefin.

3. 2. The process of claim 1, wherein said linear alpha olefin product is 1-hexene and said at least one impurity is 2-ethyl-1-butene or an isomer thereof.

4. 4. The method of claim 3, wherein the first isomer is 2-ethyl-1-butene and the second isomer is cis- or trans-3-methyl-2-pentene.

5. 4. The process of claim 3, wherein the overhead stream comprises at least about 99.5 mole percent 1-hexene.

6. 4. The process of claim 3, wherein the overhead stream comprises about 200 ppm or less of n-hexane.

7. 4. The process of claim 3, wherein the overhead stream comprises less than or equal to about 0.15 mole percent 2-ethyl-1-butene or an isomer thereof.

8. The isomerization catalyst is heated at a pressure of about 1 to 10 bar, a temperature of about 45 to 100° C., and for about 0.5 to 8.5 h. －１ 4. The process of claim 3, wherein at a liquid hourly space velocity of about 1000 rpm, about 80 mole percent or more of the 2-ethyl-1-butene can be converted to said second isomer in about one hour.

9. 9. The process of claim 8, wherein no more than about 3 mole percent of 1-hexene is converted to a different isomer under the same reaction conditions.

10. 2. The process of claim 1, wherein the isomerization catalyst comprises an alumina material, a zeolitic material or an ion exchange resin, for example a zeolitic material having a silica to alumina molar ratio in the range of 5 to 1000 or in the range of 25 to 300.

11. 10. The method of claim 1, wherein the distillation column is substantially free of catalytic material.

12. 10. The process of claim 1, wherein the distillation column comprises no more than about 150 stages.

13. 10. The method of claim 1, wherein the operating temperature of the reactor is from about 45°C to about 100°C.

14. 2. The process of claim 1, wherein the distillation column includes an overhead condenser that produces a reflux stream that is returned to the distillation column, the reflux ratio being from about 4 to about 20, e.g., from about 7 to about 15.

15. 2. The method of claim 1, wherein the step of supplying the side stream at the reactor comprises the step of supplying the side stream to a first reactor of a set of first and second reactors arranged in parallel, wherein the second reactor is available for regenerating the isomerization catalyst while the first reactor is in use.

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