Process for hydrogenation of 1,3-butadiene

Abstract

A method for improving the selectivity of selective hydrogenation of residual 1,3-butadiene in a C4 fraction of a hydrocarbon raffinate stream in a fixed bed reactor is described. The method may include co-feeding a competitive chemical that increases the mechanical selectivity to 1-butene and 2-butene while increasing the isomerization selectivity to 2-butene in the product stream. The hydrogenation reactor and competitive chemical conditions may be adjusted to selectively produce butenes relative to butane or isobutane, wherein the butenes include 1-butene and / or 2-butene.

Description

[0001] Existing related technology applications

[0002] This application is filed under the Patent Cooperation Treaty and claims priority to U.S. Provisional Application No. 62 / 841,063, filed on April 30, 2019, which is hereby incorporated by reference in its entirety.

[0003] Federally Sponsored Research Statement

[0004] not applicable.

[0005] References to microfilm

[0006] not applicable. Technical Field

[0007] The present invention relates generally to the field of chemistry. More specifically, the present invention generally relates to a process for the selective hydrogenation of dienes in a mixed stream of olefins. Specifically, the present invention relates to the selective hydrogenation of 1,3-butadiene. Background Art

[0008] Light olefins such as ethylene, propylene and butenes can be produced using various processes such as steam cracking, fluid catalytic cracking, methanol conversion to olefins, paraffin dehydrogenation, alcohol dehydration, methane coupling and Fischer-Tropsch reactions. However, these processes can produce different levels of acetylenic and / or diene by-products. These by-products are removed from the light olefin stream because they can act as poisons for downstream processing catalysts.

[0009] One such problematic by-product that interferes with downstream processing is 1,3-butadiene (BD). BD can account for about 40% of the C4 fraction of the initial raffinate stream leaving the steam cracker. BD has commercial uses, primarily as a component in synthetic rubber polymers. Therefore, extraction methods can be used to remove BD from the initial raffinate stream leaving the cracker. However, the recovery is not 100%, with 0.1-2 wt% of BD remaining in the raffinate stream (Raffinate 1) that continues down the process line. Although at much smaller concentrations, this residual BD can still poison the catalyst and react with acidic components required for reactions occurring down the process line (e.g., in an alkylation or metathesis unit).

[0010] Hydrogenation in one or more fixed bed reactors can be used to reduce the amount of residual BD in the raffinate stream. During this reaction, the raffinate stream containing BD is reacted with hydrogen over a Group VIII metal catalyst such as palladium or platinum. Nickel can be used for applications where full saturation is required. The main product of the hydrogenation reaction is 1-butene. However, depending on the nature of the co-catalyst, the hydrogen partial pressure, and the temperature of the reactor, 1-butene can be isomerized to 2-butene. As the butadiene concentration approaches even lower values ​​(<0.5%), full saturation of butene isomers to butanes becomes more significant compared to the selective hydrogenation of BD to 1-butene or 2-butene.

[0011] Some methods for controlling the hydrogenation of BD involve preventing complete saturation to butanes by incorporating promoters in / on the catalyst that prevent complete saturation of BD. Other methods involve preferentially forming one specific butene isomer while suppressing butane formation by feeding bystander species that bind to the catalyst surface and do not participate in the reaction.

[0012] Therefore, there is a need for a method for increasing product selectivity during the hydrogenation of 1,3-butadiene. Ideally, the method could be performed in-line without the need for additional reactors and could be rapidly adjusted on-the-fly to target the formation of specific hydrogenation products. Summary of the invention

[0013] Described herein is an improved process for the selective hydrogenation of 1,3-butadiene (BD) present in a mixed olefin stream to butenes using a liquid or gas phase fixed bed reactor unit. In particular, the hydrogen stream is co-fed with a gas stream containing at least one competing chemical that competes with the hydrogen for active sites on the catalyst for the hydrogenation process. When the mixed olefin stream containing BD is introduced into the hydrogenation reactor unit, the competition between the hydrogen and the competing chemical results in the preferential formation of butenes over butanes. The amount of the competing chemical as well as the reactor conditions can be adjusted to increase the selectivity for the formation of 2-butene relative to 1-butene, or vice versa. One aspect of the improved process is the ability of the competing chemical to adjust the selectivity for 1-butene and 2-butene without hindering the nearly complete (>99.9%) conversion of BD.

[0014] In more detail, the competing chemical is a molecule that competes with hydrogen for the active site on the catalyst responsible for butane formation. The competing chemical is not consumed during the reaction, but is a spectator species and only occupies the active site. This allows one of the double bonds in BD to be selectively saturated to produce 1-butene or 2-butene without forming a fully saturated butane or isobutane molecule.

[0015] The ratio of competitive chemicals to hydrogen must be maintained during the hydrogenation process to prevent competition between competitive chemicals and BD. If too many competitive chemicals are used, they may occupy too many active sites, which reduces the hydrogenation rate of BD. However, the molar ratio between competitive chemicals and hydrogen is a process condition that can be changed to improve the selectivity of specific butenes. In some embodiments, the molar ratio of competitive chemicals to hydrogen is between about 0.0001:1 and 0.02:1. Alternatively, the molar ratio may be between about 0.0002:1 and about 0.0005:1. In yet another alternative, the molar ratio may be between about 0.00025:1 and about 0.00075:1. In some embodiments, the molar ratio may be between about 0.0001:1 and 0.001:1. In other embodiments, the molar ratio may be between about 0.001:1 and 0.008:1. In other embodiments, the molar ratio may be between about 0.005:1 and 0.01:1. In other embodiments, the molar ratio may be between about 0.0005:1 and 0.005:1.

[0016] Competitive chemicals can be co-fed with the hydrogen stream and / or the mixed olefin stream into a single selective hydrogenation reactor unit, or if a series of reactors is used, fed into the lead and / or tail reactors. Competitive chemicals fed into the lead reactor can increase the mechanical selectivity for butene formation, while competitive chemicals fed into the tail reactor can increase the thermodynamic selectivity for butene formation.

[0017] In some embodiments, the competing chemical is CO. Alternatively, the competing chemical is carbon dioxide (CO2), or a mixture of CO and CO2.

[0018] While improvements in selectivity are achieved by using competing chemistries under conventional reactor conditions, the pressure and temperature of the reactor during the hydrogenation process can be varied to further shift the hydrogenation reaction toward specific products. Thus, this approach can be used to increase the selectivity of BD to 1-butene and 2-butene, particularly when the reactor is operated at high hydrogen partial pressures and BD is nearly fully converted.

[0019] The method includes any of the following embodiments, in any combination of one or more thereof:

[0020] A method for selectively hydrogenating 1,3-diene (BD) comprises combining a hydrogen gas stream with a gas stream containing at least one competing chemical, wherein the molar ratio of the competing chemical to the hydrogen in the combined stream is between 0.0001:1 and 0.02:1. The combined stream is then co-fed with a mixed olefin stream containing BD to a hydrogenation reactor unit filled with a heterogeneous hydrogenation catalyst and operated in a liquid phase or a gas phase. The stream can then be reacted in the presence of a heterogeneous hydrogenation catalyst to convert BD to n-butane and at least one butene. The molar ratio of butene to n-butane product is between 40:1 and 80:1.

[0021] A method for selectively hydrogenating 1,3-butadiene (BD) comprises combining a hydrogen gas stream with a gas stream containing at least one competing chemical, wherein in the initial combined stream, the molar ratio of the competing chemical to the hydrogen is between 0.0001:1 and 0.001:1. The combined stream can then be co-fed with a mixed olefin stream containing BD into a hydrogenation reactor unit. The hydrogenation reactor unit is filled with a heterogeneous hydrogenation catalyst and operates in a liquid phase or a gas phase. The stream reacts with the heterogeneous hydrogenation catalyst to convert BD into n-butane and at least one butene, wherein the molar ratio of butene to n-butane product is between 40:1 and 80:1.

[0022] In any of the above methods, the competitive chemical may be carbon monoxide, carbon dioxide, or both. In any of the above methods, the molar ratio of the competitive chemical to hydrogen may be between 0.0001:1 and about 0.001:1. In some embodiments, the molar ratio is between about 0.0001:1 and 0.02:1. Alternatively, the molar ratio may be between about 0.0002:1 and about 0.0005:1. In yet another alternative, the molar ratio may be between about 0.00025:1 and about 0.00075:1. In other embodiments, the molar ratio may be between about 0.001:1 and 0.008:1. In other embodiments, the molar ratio may be between about 0.005:1 and 0.01:1. In other embodiments, the molar ratio may be between about 0.0005:1 and 0.005:1.

[0023] In any of the above methods, the amount of BD in the mixed olefin stream may be between greater than 0 and 5 wt%. In some embodiments, the amount of BD in the mixed olefin stream may be between greater than 0 and 3 wt%. In some embodiments, the amount of BD in the mixed olefin stream may be between about 1.1 and about 3 wt%. In some embodiments, the amount of BD in the mixed olefin stream may be between about 2 and about 4 wt%. Alternatively, the mixed olefin stream may be a raffinate 2 stream (as defined below).

[0024] In any of the above methods, the at least one butene can be a combination of 1-butene and 2-butene. In any of the above methods, the molar ratio of 2-butene to 1-butene can be greater than 1. Alternatively, the molar ratio of 2-butene to 1-butene can be from 1 to 3.5.

[0025] In any of the above methods, the hydrogenation reactor unit can be an independent fixed bed reactor or a series of fixed bed reactors. Alternatively, the hydrogenation reactor unit can be a series of fixed bed reactors, wherein the co-feeding of the combined hydrogen stream and the gas stream and the mixed olefin stream containing BD occurs at the lead reactor, the tail reactor or both reactors in the hydrogenation reactor unit.

[0026] In any of the above methods, during the co-feeding step, the temperature of the hydrogenation reactor unit can be maintained between 70°F and 180°F. Alternatively, during the co-feeding step, the pressure of the hydrogenation reactor unit can be maintained between 300 and 50 psig. In yet another alternative, during the co-feeding step, the temperature of the hydrogenation reactor unit can be maintained between 70°F and 180°F, and the pressure can be maintained between 300 and 50 psig.

[0027] In any of the above methods, the reaction results in 100% conversion of BD, wherein at least 95% of BD is converted to at least one butene. Alternatively, the reaction results in 100% conversion of BD, wherein at least 95% of BD is converted to a combination of 1-butene and 2-butene. In yet another alternative, the reaction results in 100% conversion of BD, wherein at least 99% of BD is converted to at least one butene or a combination of 1-butene and 2-butene.

[0028] In any of the above methods, the molar ratio of butene to the n-butane product may be between 40:1 and 60:1. In some embodiments, the molar ratio of butene to the n-butane product is between 40:1 and 70:1. In some embodiments, the molar ratio of butene to the n-butane product is between 50:1 and 70:1. In some embodiments, the molar ratio of butene to the n-butane product is between 50:1 and 80:1. In some embodiments, the molar ratio of butene to the n-butane product is between 60:1 and 80:1.

[0029] A method for selectively hydrogenating 1,3-butadiene (BD) comprising combining a hydrogen gas stream and a gas stream containing at least one competing chemical species, and then co-feeding the combined stream with a mixed olefin stream containing BD into a hydrogenation reactor unit filled with a heterogeneous hydrogenation catalyst and operating in a liquid phase or a gas phase. The stream is then reacted with a heterogeneous hydrogenation catalyst to convert BD into n-butane and at least one butene, wherein the reaction results in 100% conversion of BD, wherein at least 95% of BD is converted to a combination of 1-butene and 2-butene. The resulting butene to n-butane product may have a molar ratio of between 40:1 and 80:1. The molar ratio of the competing chemical species to hydrogen in the initial combined stream may be between 0.0001:1 and 0.02:1, wherein the competing chemical species is carbon monoxide, carbon dioxide, or both. The hydrogenation reactor unit can be a stand-alone fixed bed reactor or a series of fixed bed reactors, wherein the temperature of the hydrogenation reactor unit is maintained between 70°F and 180°F during the co-feed step and / or the pressure of the hydrogenation reactor unit is maintained between 300 psig and 50 psig during the co-feed step.

[0030] This Summary is provided to introduce a selection of concepts that are further described below in the Detailed Description. This Summary is not intended to identify key features or essential features of the described subject matter, nor is it intended to be used as an aid in limiting the scope of the described subject matter. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1 The effect of CO on the instantaneous butene selectivity at various liquid hourly space velocities (LHSV) is shown.

[0032] Figure 2 The effect of co-feeding CO2 into the lead or tail reactor on the overall butene selectivity is shown.

[0033] Figure 3 The effect of the 2-butene / 1-butene ratio is shown, where CO2 is co-fed into the lead or tail reactor. DETAILED DESCRIPTION

[0034] definition

[0035] As used herein, the term "raffinate" refers to the olefin residual stream obtained after the removal of desired chemicals / materials. In the cracking / crude oil refining process, the C4 raffinate stream refers to the mixed olefin stream recovered from the cracker / fluid catalytic cracking (FCC) unit. Raffinate 1 refers to the C4 residual olefin stream obtained after separation of BD from the C4 raffinate stream. Raffinate 2 refers to the C4 residual olefin stream obtained after separation of both BD and isobutylene from the C4 raffinate stream. Since the extraction efficiency of conventional BD recovery units is less than 100%, about 0.1-2 wt. % of BD remains in the raffinate 1 and 2 streams.

[0036] As used herein, the term "space velocity" refers to the volume of reactants fed per hour. For example, 7 hr -1 The space velocity means that the reactor can process feed equivalent to seven reactor volumes per hour.

[0037] As used herein, the term "hydrogenation reactor unit" refers collectively to all hydrogenation reactors used for the hydrogenation reaction. Depending on the concentration of the olefin being hydrogenated, one, two, or three reactors in a single hydrogenation reactor unit may be used. In some embodiments, the reactors are all the same, but this is not required. The reactor in the hydrogenation reactor unit may be a gas phase fixed bed reactor. Alternatively, the reactor in the hydrogenation reactor unit may be a liquid phase fixed bed reactor. When more than one reactor is present in the hydrogenation reactor unit, the first reactor may be referred to as the lead reactor, and the last reactor may be referred to as the tail reactor.

[0038] The terms "butane" and "n-butane" are used interchangeably to refer to an unbranched C4H 10 Isomers.

[0039] In the claims or the specification, when used in conjunction with the term "comprising," the use of the word "a" or "an" means one or more than one, unless the context dictates otherwise.

[0040] The term "about" refers to the stated value plus or minus the margin of error for the measurement, or plus or minus 10% if no method of measurement is indicated.

[0041] The term "or" as used in the claims is intended to mean "and / or" unless explicitly stated to refer to only alternatives or the alternatives are mutually exclusive.

[0042] The terms "comprise," "have," "include," and "contain" (and their variations) are open-ended linking verbs and allow for the addition of additional elements when used in a claim.

[0043] The phrase "consisting of" is closed and excludes all additional elements.

[0044] The phrase "consisting essentially of excludes additional material elements, but permits the inclusion of non-material elements that do not substantially change the properties of the presently disclosed methods.

[0045] This article uses the following abbreviations:

[0046] abbreviation the term B1 1-Butene B2 2-Butene BD 1,3-Butadiene CO Carbon monoxide <![CDATA[CO2]]> carbon dioxide FCC Fluid Catalytic Cracking <![CDATA[H2]]> hydrogen IDLH Immediate danger to life or health LHSV Liquid Hourly Space Velocity DETAILED DESCRIPTION

[0048] The present invention provides a novel method for controlling the products formed during the hydrogenation of 1,3-butadiene (BD) in a mixed olefin or raffinate stream. Specifically, the mechanical or thermodynamic selectivity of the hydrogenation reaction is altered in situ by co-feeding a gas containing at least one competing chemical with the hydrogen stream. This competing chemical shifts the hydrogenation reaction toward the production of butenes. The selectivity of the reaction can also be altered to preferentially form 1-butene or 2-butene.

[0049] The hydrogenation reaction of the mixed olefin stream containing BD occurs in at least one liquid phase or gas phase fixed bed reactor containing a conventional selective hydrogenation catalyst. The present method does not change the olefin stream composition of the equipment setting or introduction. On the contrary, the method improves the reactor to allow the gas containing competitive chemical substances to be co-fed with the hydrogen stream at different positions on the reactor unit. Alternatively, the mixed olefin feed can also be co-fed with hydrogen and competitive chemical substance streams.

[0050] In some embodiments, the competitive chemical and the hydrogen stream are co-fed into a pre-reactor in a hydrogenation reactor unit (or a separate reactor of a single reactor unit). This allows in-situ modification of the catalyst because the competitive chemical can compete with hydrogen for active sites on the catalyst, particularly active sites responsible for the complete saturation of butenes to BD. However, the competitive chemical does not participate in the actual hydrogenation reaction. By occupying active sites on the catalyst and acting as a spectator, the competitive chemical can change the mechanical (i.e., kinetic) selectivity of the catalyst so that butane formation is suppressed and butenes are preferentially formed.

[0051] This change in mechanoselectivity has previously been difficult to achieve because the hydrogenation reaction occurs at high hydrogen partial pressures, which shift the hydrogenation reaction toward butane formation. However, by co-feeding a gas containing at least one competing chemical species capable of occupying active sites on the catalyst into the pre-reactor, the hydrogenation reaction can be tuned to preferentially produce butenes relative to butanes, as well as selectively shift the reaction to produce 1-butene or 2-butene.

[0052] Alternatively, some embodiments of the method of the present invention feed competitive chemicals and hydrogen gas streams to the tail reactor in the hydrogenation reactor unit to increase the thermodynamic selectivity of forming butenes. This change of introducing competitive chemicals and hydrogen gas streams will preferentially move the hydrogenation product toward the production direction of thermodynamically stable 2-butene.

[0053] Specifically, the tail reactor is a "finishing reactor" in which the concentration of BD is relatively small. This allows more butenes to compete for active sites on the catalyst, thereby reducing the BD conversion rate. In order to limit butene competition, the operator feeds excess hydrogen. This results in complete conversion of BD and formation of butanes at a faster rate than the first or front reactor. Feeding at least one competing chemical with the hydrogen stream allows the competing chemical to compete with the excess hydrogen while reducing the rate of butane formation. Complete conversion of BD is not affected.

[0054] Alternatively, some embodiments of the present process feed the competing chemical species and the hydrogen stream to both the pre-reactor and the post-reactor.

[0055] The ratio of competing chemicals to hydrogen must be maintained during the reaction to prevent competition with the BD for active sites. Too much competing chemicals causes the BD to be blocked by the catalyst, resulting in a reduction in the amount of butene produced. This also reduces the conversion percentage of the BD and increases the risk of the BD interfering with reactions occurring downstream. Although too high a concentration of competing chemicals may also poison the hydrogenation catalyst, a reduction in the selectivity and conversion of the BD may occur before the catalyst is poisoned.

[0056] In some embodiments, the molar ratio of the competitive chemical to hydrogen at the feed point is between about 0.0001:1 and about 0.02:1. Alternatively, the molar ratio may be between about 0.0002:1 and about 0.0005:1. In yet another alternative, the molar ratio may be between about 0.00025:1 and about 0.00075:1. In yet another alternative, the molar ratio may be between about 0.0001:1 and 0.001:1. These ratios apply to the front and / or rear feed points.

[0057] In yet another embodiment, the competing chemical species and hydrogen stream are fed to the lead reactor and the tail reactor.This multi-point feeding scheme allows to utilize both mechanical and thermodynamic selectivity to fine tune the hydrogenation of BD to obtain the desired products.

[0058] Regardless of the location of the feed point, the competing chemical can be any gaseous compound that can occupy the active sites on the hydrogenation catalyst to prevent certain hydrogenation reactions. In addition, the competing chemical is a bystander substance and does not undergo a reaction itself. In addition, the competing chemical can be easily flushed out of the reactor by conventional cleaning methods. In some embodiments, the competing chemical is carbon monoxide. Alternatively, the competing chemical can be carbon dioxide.

[0059] Any catalyst conventionally used for BD hydrogenation can be used with the presently described methods. The hydrogenation catalyst can comprise a Group VIII metal. In some hydrogenation catalysts, the Group VIII metal can include palladium, platinum, and / or nickel. The active metal can also be disposed on an inert support material, such as alpha alumina, silica, and the like.

[0060] In the process of the present invention, when the competitive chemical and hydrogen stream are co-fed, the reactor pressure can be maintained between about 50 and 300 psig. Alternatively, the pressure during the co-feeding process can be between about 100 and 250 psi. The reactor temperature is maintained between about 70°F and 180°F. Alternatively, the reactor temperature can be between about 90 and 180°F.

[0061] The reactor can be operated at a H2 / BD molar ratio of about 0.9:1 to about 5:1. Alternatively, the ratio can be about 1:1 to about 4:1, or about 1:1 to about 3:1. In yet another alternative, the ratio is 1.45:1.

[0062] The process of the present invention is capable of hydrogenating at least 99% of BD in an olefin stream. In some embodiments, 100% conversion is possible. By controlling the pressure and temperature settings of the reactor and adding competitive chemicals at a carefully controlled ratio with hydrogen, the process described herein can selectively convert BD into at least 95% butene. Alternatively, at least 97% of BD is converted to butene, and the remaining BD is fully saturated with n-butane. In some embodiments, the butene and butane formed are present in a molar ratio of butene to n-butane between about 40:1 and 80:1.

[0063] In addition to preventing the formation of butane, the method can also be adjusted to selectively form 1-butene or 2-butene. In some embodiments, the ideal molar ratio of 2-butene to 1-butene is between about 1: 1 and 3: 1, and is achieved by utilizing a competitive chemical substance to hydrogen molar ratio of about 0.0002: 1 to about 0.001: 1. In some embodiments, the molar ratio of 2-butene to 1-butene is greater than 1. When 1-butene is the desired product, a smaller amount of competitive chemical substances is required. This is because 1-butene is a kinetically controlled product in the hydrogenation reaction. However, reducing the amount of competitive chemical substances also increases the amount of saturation because fewer active sites responsible for saturation are occupied.

[0064] With respect to the following examples, the process of the present invention is illustrated using a single fixed bed reactor and a mixed olefin feed stream similar to the raffinate 2 stream. However, these examples are merely exemplary, and the process can be broadly applied to any hydrogenation reactor unit that allows co-feeding of competing chemical species gases with a hydrogen stream, and any olefin feed containing BD.

[0065] Example

[0066] The following examples are included to illustrate embodiments of the appended claims. These examples are illustrative only and are not intended to unduly limit the scope of the appended claims. Those skilled in the art will appreciate that many changes may be made to the specific embodiments disclosed and still achieve the same or similar results without departing from the spirit and scope disclosed herein. The following embodiments should in no way be construed as limiting or defining the scope of the appended claims.

[0067] Olefin Feed: The composition of the olefin feed used in the following embodiments is provided in Table 1.

[0068]

[0069] The composition has a BD concentration similar to that of the raffinate 1 or 2 stream after extraction of BD.

[0070] Unless otherwise stated, a constant H2 / BD ratio of 1.45:1 was maintained in each example so that the effects of competing chemicals on the hydrogenation process could be more easily observed.

[0071] Reactor: A single liquid phase fixed bed reactor with a commercially available catalyst was used in the following examples. Competing chemicals and a hydrogen stream were co-fed into the "front" reactor to mechanically alter the selectivity for butene formation. Reactor pressures were maintained at 150 psig and 250 psig. Unless otherwise stated, reactor temperature was maintained at 120°F.

[0072] Embodiment 1:

[0073] In this example, various molar ratios and space velocities of carbon monoxide (CO) to hydrogen in a fixed bed reactor were used to selectively form butenes during the hydrogenation process.

[0074] A CO / H2 molar ratio of about 0:1 to 0.0013:1 was introduced into the fixed bed reactor together with a mixed olefin stream containing a small amount of BD. This was done to increase the mechanical selectivity of butenes during the hydrogenation reaction. The effect of residence time in the hydrogenation reactor on selectivity was observed by using relatively slow, medium and fast space velocities. The results of Example 1 are shown in Figure 1 middle.

[0075] For slow and medium space velocities up to 0.0005:1 molar ratio, a significant increase in selectivity is observed, with a peak before a decrease. This decrease above 0.0005:1 molar ratio is attributed to a decrease in BD converted when the active sites on the catalyst are occupied by increasing amounts of CO. However, since the amount of CO is very low, the catalyst is not considered to be poisoned at this time.

[0076] At faster space velocities, selectivity does increase slightly at higher mole ratios, however this improvement in selectivity is inconsistent and not as great as at slower space velocities.

[0077] This suggests that competing chemicals such as CO can be used to influence the selectivity of the butadiene hydrogenation reaction. However, too much competing chemical leads to reduced selectivity because the competing chemical begins to oversaturate the active sites, preventing the BD reaction.

[0078] In addition, the space velocity can also be adjusted to increase the selectivity of the hydrogenation reaction.

[0079] Embodiment 2:

[0080] The ability of carbon dioxide to improve the selective hydrogenation of BD was also tested. Like CO, it is believed that CO2 competes with H2 for active sites on the catalyst. However, CO2 is different from CO as a competing chemical. First, CO2 has a much higher direct danger to life or health (IDLH) value than CO (40,000 ppm vs. 1,200 ppm). This means that CO2 is a safer chemical and accidental exposure is unlikely to escalate to life-threatening levels. Second, CO2 can be provided internally at some sites. CO2 is a by-product of the steam cracking process, so the CO2 used in the method of the present invention can be derived from an olefin cracking unit. In addition, a petrochemical plant may have a CO2 capture unit, which can be the source of the CO2 required for the method currently described.

[0081] To understand the effect of CO2 on the selectivity of butene formation, various changes were made to the CO2 concentration and reactor conditions. These effects were compared to the baseline results of 100% BD conversion under conventional reactor conditions without competing chemicals and to the baseline results of 100% BD conversion under conventional reactor conditions with CO2 as the competing chemical.

[0082] This example used a single fixed bed reactor with a hydrogenation catalyst obtained from a commercial supplier, as described in Example 1. The hydrogenation catalyst was pretreated by first mixing it with a silicon carbide competitive chemical at a mass ratio of 1:5. The catalyst was then reduced under H2 for 24 hours before contacting with the olefin stream.

[0083] The ability of CO2 to affect the BD conversion process to selectively form butenes under typical industrial conditions was measured. The reactor pressure was maintained at 150 psig and the reactor was operated at 90° F. The conversion of BD was maintained at 100%.

[0084] Before introducing CO2 into the reactor along with the olefin feed, a baseline of 100% BD conversion was first obtained. This baseline run, or a CO2 / H2 ratio of 0, is included in Table 2 below for comparison with the results of the remaining tests conducted with increasing CO2 / H2 molar ratios. In the remaining runs, CO2 was fed into the reactor along with H2 and the olefin feed at a slow space velocity.

[0085]

[0086] Similar to CO, the present results show that the selectivity of butenes over butanes increases with increasing CO2 / H2 molar ratio until about 0.00071: 1. At this point, the selectivity begins to decrease because CO2 competes with BD for active sites on the catalyst.

[0087] Additionally, an increase in the selectivity of 2-butene relative to 1-butene was observed when the CO2 / H2 molar ratio was maintained at about 0.00023:1-0.00071:1. The increase in the selectivity of 2-butene relative to 1-butene can be used to tailor the feedstock for the production of isooctane in an acid-based alkylate unit or propylene in a metathesis unit. The results indicate that the CO2 / H2 molar ratio can be adjusted to balance the selectivity of butene formation relative to butane with the desire to preferentially form 2-butene. However, the CO2 concentration can be varied to prevent this double bond isomerization reaction.

[0088] The reaction conditions were then varied to measure their effects on butene selectivity during the hydrogenation reaction.

[0089] CO2 Feed Termination: The effect of terminating the CO2 flow and the resulting reversibility (if any) was measured. In this example, the reaction was conducted while increasing the CO2 / H2 ratio from 0 (no dilution) to 0.00071:1. At the end of the experiment, CO2 was terminated to determine a) the change in butene selectivity and b) the change in BD conversion.

[0090] As before, CO2 was co-fed with H2 and olefin feed, and a constant H2 / BD ratio of 1.45:1 was maintained. Before CO2 was introduced into the reactor together with the olefin feed, a baseline result of 99.81% BD conversion was obtained for comparison. Finally, a second set of baseline results was obtained. The results show that the effect of CO2 on selectivity is reversible, i.e., after terminating CO2 at the end of the experiment, the recovered BD conversion and butene selectivity are close to the original values ​​obtained at the beginning of the experiment. The results are shown in Table 3.

[0091]

[0092] As mentioned previously, butenes are formed preferentially over butanes. However, as the CO2 / H2 molar ratio increases to 0.00071:1, the total amount of butadiene converted decreases. After an initial increase in butene selectivity, the amount of butene produced decreases slightly as the amount of CO2 increases. A decrease is also observed in the formation of n-butane.

[0093] High pressure: The effect of CO2 on the reactor under high pressure conditions is reviewed. To address the increase in pressure, a 5h -1 As before, CO2 was co-fed with H2 and olefin feed, and a constant H2 / BD ratio of 1.45:1 was maintained. Before CO2 was introduced into the reactor together with the olefin feed, a baseline run was performed at 100% BD conversion for comparison. The remaining runs were also performed at 100% BD conversion. The results are shown in Table 4.

[0094]

[0095] These results indicate that the overall selectivity for butenes at higher pressures (250 psig) is greater than the selectivity at lower pressures (150 psig), as shown in the results in Tables 2 and 4. The rate of increase in selectivity for butenes and the favorability of forming 2-butene (compared to 1-butene) at higher operating pressures is less than the rate at low pressures. However, the observation that competing chemicals increase selectivity for all butenes and 2-butenes is still observed at high pressures. These results indicate that the method is suitable for high-pressure and low-pressure reactor applications, however, as observed herein, the trend of competing chemicals to increase the overall selectivity for butenes and the overall selectivity for 2-butene is higher at low pressures.

[0096] Embodiment 3:

[0097] The effect of the feed point location of the competing chemical and hydrogen was also tested using CO2 as the competing chemical. Figure 2 The effect on the overall butene selectivity is shown. Figure 3 The effect on the 2-butene / 1-butene ratio is shown, where CO2 is fed to the lead or tail reactor.

[0098] The amount of 2-butene increases as the feed reaches the tail. This indicates that competing chemicals prevent the formation of butane by competing with hydrogen for active sites on the catalyst. Figure 2 The selectivity ratios of greater than 97% shown in support of . A similar preference for butene formation is also shown when a competing chemical is fed into the lead reactor.

[0099] The above examples demonstrate that reactor conditions, space velocity, and concentration of new competing chemicals can be adjusted to selectively form 2-butene or 1-butene instead of butane while also maintaining high conversion of BD. This ability to selectively produce certain products is helpful because some products may be more desirable to the user than others.

[0100] The following references are incorporated herein by reference in their entirety for all purposes.

[0101] U.S. Patent No. 4,517,395A

[0102] U.S. Published Application No. US2006 / 0235255A1

Claims

1. A method for selectively hydrogenating 1,3-butadiene, comprising: a) combining a hydrogen gas stream with a gas stream containing at least one competing chemical to form a combined stream, wherein the molar ratio of the competing chemical to the hydrogen is between 0.0001:1 and 0.00075:1 and wherein the competing chemical is carbon dioxide; b) co-feeding a mixed olefin stream containing 1,3-butadiene with the combined stream into a hydrogenation reactor unit, wherein the hydrogenation reactor unit is filled with a heterogeneous hydrogenation catalyst and operates in liquid phase or gas phase, wherein the hydrogenation catalyst comprises palladium, platinum and / or nickel; c) reacting said stream in the presence of said heterogeneous hydrogenation catalyst; and, d) converting the 1,3-butadiene into n-butane and at least one butene, wherein the molar ratio of butene to n-butane is between 40:1 and 80:

1.

2. The process of claim 1, wherein the hydrogenation reactor unit is an independent fixed bed reactor or a series of fixed bed reactors.

3. The process of claim 2, wherein the hydrogenation reactor unit is a series of fixed bed reactors, and the co-feeding step occurs at the lead reactor, the tail reactor, or both reactors in the hydrogenation reactor unit.

4. The method of claim 1, wherein the molar ratio of the competing chemical species to the hydrogen is between 0.0001:1 and 0.0005:

1.

5. The method of claim 1, wherein the at least one butene is a combination of 1-butene and 2-butene.

6. The process of claim 5, wherein the molar ratio of 2-butene to 1-butene in the converting step is between 1 and 3.

5.

7. The process of claim 1, wherein said converting step results in 100% conversion of said 1,3-butadiene, wherein at least 95% of said 1,3-butadiene is converted to at least one butene.

8. The process of claim 1, wherein the converting step results in a 100% conversion of the 1,3-butadiene, wherein at least 99% of the 1,3-butadiene is converted to at least one butene.

9. The process of claim 1 wherein the temperature of the hydrogenation reactor unit is maintained between 70 and 180°F during the co-feeding step.

10. The process of claim 1 wherein the pressure of the hydrogenation reactor unit is maintained between 300 and 50 psig during the co-feeding step.

11. The process of claim 1 wherein the amount of 1,3-butadiene in the mixed olefin stream is between greater than 0 and 5 wt%.

12. A process for selectively hydrogenating 1,3-butadiene in a mixed olefin stream, comprising: a) combining a hydrogen gas stream with a gas stream containing a competing chemical to form a combined stream, wherein the ratio of the competing chemical to the hydrogen is between 0.0001:1 and 0.00075:1 and wherein the competing chemical is carbon dioxide; b) co-feeding a mixed olefin stream containing 1,3-butadiene with the combined stream into a hydrogenation reactor unit, wherein the hydrogenation reactor unit is filled with a heterogeneous catalyst and operates in liquid phase or gas phase, wherein the hydrogenation catalyst comprises palladium, platinum and / or nickel; c) reacting the stream with the heterogeneous hydrogenation catalyst; and, d) converting the 1,3-butadiene into n-butane and at least one butene, wherein the molar ratio of butene to n-butane is between 40:1 and 80:

1.

13. The process of claim 12, wherein the hydrogenation reactor unit is a stand-alone fixed bed reactor or a series of fixed bed reactors.

14. The method of claim 13, wherein the co-feeding is carried out in a front reactor, a tail reactor or two reactors.

15. The process of claim 12 wherein the temperature of the hydrogenation reactor unit is maintained between 70 and 180°F during the co-feeding step.

16. The process of claim 12, wherein the pressure of the hydrogenation reactor unit is maintained between 300 and 50 psig during the co-feeding step.

17. The method of claim 12, wherein the amount of 1,3-butadiene is between greater than 0 and 5 wt%.

18. The method of claim 12, wherein the converting step results in 100% conversion of the 1,3-butadiene, wherein at least 95% of the 1,3-butadiene is converted to a combination of 1-butene and 2-butene.

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