Process for hydrogenating substrates

Abstract

The present invention provides a process for obtaining a liquid product by hydrogenating a substrate in a hydrogenation reactor, comprising: (a) supplying the following to the hydrogenation reactor: (i) a fresh substrate, (ii) fresh hydrogen gas, (ii) recirculated liquid product, and (iii) recirculated hydrogen gas; (c) recovering the liquid product in the liquid product stream from the outlet of the hydrogenation reactor; (d) recovering the liquid product in the recirculated liquid product stream and returning at least a portion of it to the hydrogenation reactor as recirculated liquid product; and (e) recovering hydrogen gas from the outlet of the hydrogenation reactor as a hydrogen gas recirculation stream and returning at least a portion of it to the hydrogenation reactor as recirculated hydrogen gas, wherein the hydrogen gas recirculation stream passes through an eductator before being returned to the hydrogenation reactor, and the driving fluid in the eductator is either a fresh substrate, a recirculated liquid product stream, a combination of a fresh substrate and a recirculated liquid product stream, or the driving fluid is fresh hydrogen gas.

Description

Technical Field

[0001] The present invention relates to a process and an apparatus for hydrogenating a substrate. More particularly, the present invention relates to a process for hydrogenating an aldehyde, which may be unsaturated, to obtain a saturated alcohol.

Background Art

[0002] Conventional liquid-phase hydrogenation reactors, such as those described in U.S. Patent No. 4,148,830 and U.S. Patent No. 5,087,763, which are used to hydrogenate aldehydes formed by hydroformylation of alkenes and optionally perform aldol condensation to produce so-called "oxo" alcohols, are operated with only a slight excess of hydrogen gas in order to minimize vent losses of hydrogen.

[0003] Such reactors are also operated with a large amount of liquid recirculation in order to minimize the adiabatic temperature rise of the reactor.

[0004] Operation with such a slightly excessive amount of hydrogen makes the hydrogenation reactor prone to local hydrogen depletion, which is accompanied by subsequent degradation of catalyst performance and an increase in by-product formation. The reactor is also more likely to degrade in performance if there is insufficient complete mixing of the liquid recirculate and the fresh aldehyde feed.

[0005] The present invention seeks to address the problem of achieving an effective balance between hydrogen loss and optimal reactor performance without significantly increasing the cost and maintenance requirements of the plant.

Summary of the Invention

[0006] The inventors have found that by using a large volume of liquid recirculation flow as the driving fluid in the eductor to circulate hydrogen to the hydrogenation reactor, the availability of hydrogen in the reactor is increased, which is supported by an improvement in substrate conversion rate and a reduction in byproduct formation. Therefore, the reactor performance can be improved in terms of increased substrate conversion rate and reduced byproduct formation without increasing the amount of hydrogen supplied to the reactor, and consequently without increasing hydrogen vent losses. This is achieved without increasing the cost and maintenance requirements of a dedicated recirculation compressor for hydrogen recirculation.

[0007] Therefore, the present invention relates to a process for obtaining a liquid product by hydrogenating a substrate in a hydrogenation reactor, (a) The hydrogenation reactor must include the following: (i) Fresh substrate, (ii) Fresh hydrogen gas, (ii) Recirculated liquid products, (iii) supplying recycled hydrogen gas, (b) To recover the liquid product in the liquid product stream from the outlet of the hydrogenation reactor, (c) Recovering the liquid product in the recirculated liquid product stream and returning at least a portion, preferably substantially all, of it to the hydrogenation reactor as recirculated liquid product, (d) recovering hydrogen gas as a hydrogen gas recirculation stream from the outlet of the hydrogenation reactor and returning at least a portion, preferably substantially all, of it to the hydrogenation reactor as recirculated hydrogen gas, The hydrogen gas recirculation flow passes through the eductor before being returned to the hydrogenation reactor. The present invention provides a process in which the driving fluid in the eductor is a fresh substrate, a recirculating liquid product flow, or a combination of a fresh substrate and a recirculating liquid product flow, or the driving fluid is fresh hydrogen gas.

[0008] Furthermore, it is a device for hydrogenating a substrate, (a) A hydrogenation reactor configured to hydrogenate a substrate to obtain a liquid product, (b) means for supplying fresh substrate to the hydrogenation reactor, (c) Means for supplying fresh hydrogen gas to the hydrogenation reactor, (d) Means for recovering the liquid product flow from the outlet of the hydrogenation reactor, (e) Means for recovering the liquid product as a liquid product recirculation flow, (e) Means for returning the liquid product recirculation flow to the hydrogenation reactor, (f) Means for recovering hydrogen gas from the outlet of the hydrogenation reactor as a hydrogen gas recirculation flow, (g) Means for returning the hydrogen gas recirculation flow to the hydrogenation reactor, (f) comprising an eductor configured to receive the hydrogen gas recirculation flow before the hydrogen gas recirculation flow is returned to the hydrogenation reactor, Also provided is an apparatus in which the eductor is configured to use a fresh substrate, a recirculating liquid product flow, or a combination of a fresh substrate and a recirculating liquid product flow as the driving fluid.

[0009] Preferably, the substrate is an aldehyde or acrolein, which is hydrogenated to an alcohol. In a preferred embodiment, the driving fluid in the eductor is fresh substrate, a recirculating liquid product flow, or a combination of fresh substrate and a recirculating liquid product flow. Most preferably, the driving fluid in the eductor contains a recirculating liquid product flow. Preferably, the ratio of the recirculating liquid product flow to the fresh substrate (i.e., mass flow rate of the recirculating liquid product flow: mass flow rate of the fresh substrate) is at least 10:1, preferably at least 20:1. In such embodiments, the hydrogen flow through the hydrogenation reactor is preferably at least 120%, more preferably at least 130%, of the stoichiometric hydrogen flow required to hydrogenate the substrate flow through the hydrogenation reactor. Such a flow rate is also called a 20%, preferably 30%, excess hydrogen. Using such excess hydrogen in the hydrogenation reactor without recirculating it would involve costly purging of unreacted hydrogen. However, compressing such excess hydrogen during recirculation using a compressor can be uneconomical. Advantageously, the present invention uses a large liquid product recirculation flow, which is advantageous in terms of heat removal, to drive hydrogen gas recirculation, providing a significant hydrogen excess in an economical manner. This advantageously reduces the risk of hydrogen deficiency in the hydrogenation reactor. This advantageous combination of large liquid product recirculation and large hydrogen gas recirculation, enabled by an eductor driven by large liquid product recirculation, can be particularly advantageous in the hydrogenation of aldehydes or acroleins to alcohols as part of an oxo alcohol process. In some embodiments, the process further includes a purification reactor, which may be a separate reactor or a separate catalyst bed within the same reactor. The liquid product flow from the hydrogenation reactor is supplied to the purification reactor, preferably together with a hydrogen flow containing fresh hydrogen. A hydrogen excess is also desirable in the purification reactor, for example, to result in a high conversion rate, and the hydrogen flow through the purification reactor is preferably at least 105%, more preferably at least 110%, of the stoichiometric hydrogen flow required to hydrogenate the substrate flow through the reactor.This may represent further loss of unreacted hydrogen, but according to the present invention, the hydrogen gas exiting the purification reactor is preferably combined with the hydrogen gas recovered from the hydrogenation reactor to form part of the hydrogen gas recirculation flow received by the eductor. In this way, the recirculation of large amounts of liquid products in the hydrogenation reactor is conveniently used not only to drive excess hydrogen gas through the hydrogenation reactor but also to drive excess hydrogen gas through the purification reactor. [Brief explanation of the drawing]

[0010] [Figure 1] This is a schematic diagram of a conventional liquid hydrogenation process. [Figure 2] This is a schematic diagram of the process according to the present invention. [Figure 3] This is a schematic diagram of a further process according to the present invention. [Figure 4] This is a schematic diagram of an emitter used in the process according to the present invention. [Figure 5] This table shows the relationship between the amount of hydrogen passing through the reactor, catalytic activity (with respect to aldehyde slip), and the amount of by-products produced in the hydrogenation of butyraldehyde. [Modes for carrying out the invention]

[0011] Hydrogenation of a substrate means adding molecular hydrogen to one or more double bonds in a molecule to give a corresponding single bond. The properties of the double bond are not particularly limited; examples include hydrogenating a carbon-carbon double bond to give a carbon-carbon single bond, and hydrogenating a carbon-oxygen double bond to give a carbon-oxygen single bond.

[0012] The substrate may be any substrate containing a double bond that can be hydrogenated using gaseous hydrogen in liquid-phase hydrogenation to produce a liquid hydrogenation product. More specifically, it is a substrate such that the hydrogenation reaction requires a large amount of liquid recirculation to minimize the adiabatic temperature rise of the reactor. Suitablely, the substrate may be an aldehyde and the product may be an alcohol. The aldehyde may typically be a straight-chain saturated aldehyde and the product may be a corresponding saturated alcohol. Alternatively, the aldehyde may be an α,β-unsaturated aldehyde, such as a 2-alkylalkenal, and the product may be a corresponding saturated alcohol, such as a 2-alkylalkanol. Saturated aldehydes are typically C3-C 20 Preferably C3~C 15 Unsaturated aldehydes are typically C4-C 20 Preferably C4~C 15 Examples of aldehyde substrates and alcohol products include butyraldehyde and butanol, 2-ethylhexa-2-enal and 2-ethylhexanol, 2-propylhept-2-enal and 2-propylheptanol, and isononylaldehyde and isononyl alcohol. Fresh substrate is supplied to the system as a liquid stream and may enter directly into the eductor, directly into the hydrogenation reactor, or initially combined with a liquid product recirculation stream upstream or downstream of the eductor. The point of supply of fresh substrate depends largely on the driving fluid used in the eductor.

[0013] The hydrogenation reactor can be operated under any suitable conditions. Generally, a catalyst is used. Any suitable catalyst can be used. Generally, especially in the case of aldehydes including α,β-unsaturated aldehydes, the active component of the catalyst is based on metals of Groups VI to XI. Suitable examples include copper, nickel, manganese, zinc, cobalt, palladium, ruthenium and iron. The catalyst may be supported. Any suitable carrier can be used. Suitable carriers include alumina, silica, aluminosilicate, titania, zirconia or diatomaceous earth. A particularly suitable catalyst can be a supported copper chromite or copper-alumina catalyst, especially in the case of aldehydes including α,β-unsaturated aldehydes. The catalyst may also contain, for example, a promoter to improve selectivity.

[0014] Hydrogenation can be carried out in the liquid phase. Any suitable configuration can be used and the reactor can be operated under any suitable conditions. The specific conditions selected depend on the catalyst selected. For example, especially in the case of aldehydes including α,β-unsaturated aldehydes, hydrogenation can be carried out at a temperature of about 100°C to about 200°C and a pressure from atmospheric pressure to about 15 MPa. In one configuration, hydrogenation can be carried out as a co-current flow in a packed catalyst bed.

[0015] When a nickel catalyst is used in a liquid-phase reaction, especially in the case of aldehydes including α,β-unsaturated aldehydes, the temperature can be less than about 150°C and the pressure can be about 1 to about 3 MPa. When a copper chromite catalyst is used in a liquid-phase reaction, especially in the case of aldehydes including α,β-unsaturated aldehydes, the temperature can be about 50°C to about 200°C and the pressure can be about 0.1 MPa to about 5 MPa, for example about 0.5 MPa to about 5 MPa.

[0016] The recirculation of the liquid product is carried out to remove the reaction heat. As understood by those skilled in the art, the heat release during the reaction depends on the substrate. For example, in the case of an aldehyde substrate, the higher the number of carbon atoms in the aldehyde, the lower the heat release per unit mass. Typically, the temperature rise is maintained below about 50 °C. The recirculation ratio of the liquid product to the fresh substrate is typically about 2:1 to about 60:1, preferably about 5:1 to about 40:1, on a mass basis. In some embodiments, the recirculation ratio of the liquid product to the fresh substrate is, on a mass basis, preferably from about 10:1, or more preferably from about 20:1, to about 100:1, or more preferably to about 60:1, or even more preferably to about 40:1. Typically, the liquid product recirculation stream passes through a cooler before the recycled liquid product is returned to the hydrogenation reactor. The cooler may be, for example, a heat exchanger where the removed heat is utilized to raise steam. The liquid product recirculation stream typically passes through a recirculation pump before passing through an eductor. When combining the liquid product recirculation stream with the fresh substrate to obtain a driving fluid, the liquid product recirculation stream typically passes through a recirculation pump before being combined with the fresh substrate.

[0017] As is generally known, an eductor is a pump that uses the Venturi effect to pump fluid in a closed line using a driving fluid. The driving fluid provides pumping energy. After entering the eductor, the driving fluid flows through a convergence section into a narrow throat, where its velocity increases and its pressure decreases. After leaving the throat, the driving fluid enters a diverging section, i.e., a nozzle, where its velocity decreases and its pressure increases, creating a low-pressure region used to draw in and pump other fluids. The driving fluid and other fluids exit the eductor through the nozzle as a single flow. In detail, the present invention typically uses a large volume of liquid product recirculation flow in liquid-phase hydrogenation to pump hydrogen gas recirculation and make more effective use of hydrogen in the system. Therefore, the driving fluid is preferably a liquid product recirculation flow, or a combination of fresh substrate and liquid product recirculation flow. However, the fresh substrate feed may be large enough to act effectively as a driving fluid on its own, and therefore, in an alternative way, the fresh substrate feed can be used as a driving fluid. Alternatively, in some examples, fresh hydrogen gas can also be used as a driving fluid. This can be advantageous when a hydrogen feedstock with relatively high pressure is used, and therefore, a noticeable drop in pressure can be tolerated before the drive fluid is supplied to the reactor.

[0018] The flow used as the driving fluid must be at a sufficiently high pressure to allow for at least a noticeable pressure drop across the eductor. The pressure drop of the driving fluid across the eductor is not particularly limited and depends on the nature and quantity of the driving fluid and the specific reactor design. A typical pressure drop when the recirculating fluid is fresh substrate, a recirculating liquid product flow, or a combination of fresh substrate and a recirculating liquid product flow may be in the range of about 0.02 to about 1.0 MPa, preferably about 0.05 to about 0.40 MPa. The flow rate of the liquid driving fluid depends on the nature and scale of the hydrogenation reaction and the reactor design.

[0019] The hydrogen gas recirculation flow is typically about 0.1 to 5 times the stoichiometric requirement of hydrogen, preferably about 0.2 to 1 time. A vent is also provided in the hydrogenation reactor to maintain a desired partial pressure of hydrogen in the reactor and to purge inert substances from the system. This vent can be taken directly from the reactor or from the hydrogen gas recirculation flow. This vent has no greater flow rate than the vent from a hydrogenation reactor that does not use hydrogen gas recirculation according to the present invention. Typical hydrogen vent purging may be about 1% to 30% of the stoichiometric requirement of hydrogen, but is not particularly limited and may be affected by impurities in the hydrogen gas feed and the generation of by-product gases. One of the advantages of the present invention is that higher catalytic activity and less by-product generation can be achieved without increasing the amount of hydrogen supplied to the reactor (which would necessitate venting and thus increase the amount of hydrogen lost from the system). Typically, the volume ratio of liquid to gas leaving the reactor is less than 20:1, preferably less than 10:1, and more preferably less than 5:1. The volume ratio is typically greater than 0.5:1. Gas leaving the reactor means that which passes through all outlets, including the vent and recirculation flow. Liquid leaving the reactor means that which passes through all outlets, including the product outlet and recirculation flow. The majority of gas leaving the reactor is, of course, due to the recirculation flow, which brings about the advantages of the present invention without increasing hydrogen venting.

[0020] Fresh substrate, recirculated liquid products, and recirculated hydrogen gas are typically supplied to the hydrogenation reactor as a single flow from a single inlet. However, alternative supply methods are also conceivable. For example, if the driving fluid is a combination of fresh substrate and recirculated liquid product flows, a flow containing fresh substrate, recirculated liquid product flows, and recirculated hydrogen gas exits the eductor. This flow may be supplied directly to the reactor, or it may pass through a disengagement pot that separates the hydrogen gas from the flow and supplies the elementary gas to the hydrogenation reactor from a separate inlet. If only one of the fresh substrate or recirculated liquid product flows is the driving fluid, the other flow may be combined with a flow that exits the eductor before being supplied to the hydrogenation reactor, or it may be supplied through a separate inlet. The present invention is realized by a hydrogen gas recirculation flow and a driving fluid as defined herein passing through an eductor, supplying fresh substrate, recirculated liquid products, and recirculated hydrogen gas to the hydrogenation reactor. Fresh hydrogen gas is typically supplied to the hydrogenation reactor from a separate inlet.

[0021] In the process of the present invention, when the substrate is an α,β-unsaturated aldehyde, most of the α,β-unsaturated aldehyde is hydrogenated. However, some partially hydrogenated products are also produced. For example, when hydrogenating a 2-alkylalkenal to obtain a 2-alkylalkanol, partially hydrogenated products such as 2-alkylalcanal and 2-alkylalkenol may be produced. Also, heavier substances, i.e., substances with a higher molecular weight and / or boiling point than the desired product alcohol, may be produced. Therefore, the process of the present invention may include further distillation and purification steps to obtain the desired product in high purity, for example, as disclosed in International Publication 2018 / 069714 in the case of the production of 2-alkylalkanols, or in International Publication 2019 / 197831 in the case of the simultaneous production of alcohols such as butanol and 2-alkylalkanols.

[0022] The present invention may be particularly advantageous in the process of producing oxo alcohols. Accordingly, in a particularly preferred embodiment of the present invention, the process of producing oxo alcohols comprises: hydroformylation of a mixture of olefin and synthesis gas in the presence of a hydroformylation catalyst to produce an aldehyde; separation of the aldehyde from the catalyst by evaporating the aldehyde from the catalyst; and hydrogenation of the aldehyde to an alcohol, wherein the hydrogenation involves (a) supplying a hydrogenation reactor with (i) an aldehyde, (ii) fresh hydrogen gas, (iii) a recycled liquid product containing alcohol, and (iv) recycled hydrogen gas; and (b) recovering the liquid product containing alcohol from the liquid product stream at the outlet of the hydrogenation reactor. The present invention provides a process comprising: (c) recovering the alcohol-containing liquid product in the liquid product recirculation stream and returning at least a portion of it to the hydrogenation reactor as recirculated liquid product; and (d) recovering hydrogen gas from the outlet of the hydrogenation reactor as a hydrogen gas recirculation stream and returning at least a portion of it to the hydrogenation reactor as recirculated hydrogen gas, wherein the hydrogen gas recirculation stream passes through an eductor before being returned to the hydrogenation reactor, and the driving fluid in the eductor is an aldehyde, the liquid product recirculation stream, or a combination of an aldehyde and the liquid product recirculation stream, or the driving fluid is fresh hydrogen gas, most preferably the driving fluid includes the liquid product recirculation stream.In a more particularly preferred embodiment of the present invention, a process for producing an oxo alcohol comprises: hydroformylation of a mixture of an olefin and synthesis gas in the presence of a hydroformylation catalyst to produce an aldehyde; separation of the aldehyde from the catalyst by evaporating the aldehyde from the catalyst; purification of the aldehyde by aldolization to produce acrolein; and hydrogenation of the acrolein to an alcohol, wherein the hydrogenation involves (a) supplying to a hydrogenation reactor (i) acrolein, (ii) fresh hydrogen gas, (iii) a recycled liquid product containing alcohol, and (iv) recycled hydrogen gas from the outlet of the hydrogenation reactor The present invention provides a process comprising: (c) recovering the alcohol-containing liquid product from the liquid product stream; (d) recovering the alcohol-containing liquid product from the liquid product recirculation stream and returning at least a portion of it to the hydrogenation reactor as recirculated liquid product; and (e) recovering hydrogen gas from the outlet of the hydrogenation reactor as a hydrogen gas recirculation stream and returning at least a portion of it to the hydrogenation reactor as recirculated hydrogen gas, wherein the hydrogen gas recirculation stream passes through an eductor before being returned to the hydrogenation reactor, and the driving fluid in the eductor is acrolein, the liquid product recirculation stream, or a combination of acrolein and the liquid product recirculation stream, or the driving fluid is fresh hydrogen gas. In any of the particularly preferred embodiments, the olefin can be obtained from a Fischer-Tropsch reaction, a methanol-to-olefin process, a refinery, a sustainable source, or any other olefin source. The synthesis gas can be obtained, for example, from the reforming or gasification (of coal, natural gas, or any other suitable feedstock). Synthesis gas can also be obtained from sustainable feedstocks. One example involves capturing carbon dioxide, generating hydrogen through electrolysis or from another source, and then converting the carbon dioxide and hydrogen into synthesis gas using a reverse water-gas shift reaction. If olefins and / or impurities are present in the synthesis gas, they can be removed in the feedstock purification section.

[0023] Hydroformylation is a reaction between carbon monoxide and olefins, producing an aldehyde. An aldehyde has one more carbon atom than an olefin. Hydroformylation is typically represented by U.S. Patents 4,769,498, 4,885,401, 5,113,022, 5,202,297, 5,235,113, 4,668,651, 4,748,261, 5,254,741, 5,391,801, 5,059,710, 3,527,809, and 5,391,801. The reaction is carried out using a homogeneous rhodium catalyst having an organophosphorus ligand, such as those described in Publications No. 4283562, No. 4400548, No. 4482749, No. 4599206, No. 4716250, No. 4717775, No. 4731486, No. 4737588, or International Publication No. 8001690. Typically, the hydroformylation reaction is carried out in two or more reactors. The aldehyde product and the rhodium catalyst are sent from the reactor to a catalyst recovery unit, where the aldehyde product is separated from the rhodium catalyst and its solvent. The solvent may typically be the aldehyde, a heavy product produced during the reaction, or any other suitable solvent. Examples of methods for separating or stabilizing rhodium catalysts can be found in U.S. Patents No. 4,774,361, No. 5,874,640, No. 5,892,119, No. 6,090,987, No. S6294,700, No. S6100,432, No. S5114,473, No. S4148,830 and No. S4247,486.

[0024] Aldehydes include mixtures of n-aldehydes and isoaldehydes. Aldehydes may be hydrogenated to both n-alcohols and iso-alcohols, or they may be aldolized and hydrogenated to form mixtures of branched alcohols, such as C10 alcohols in the form of a mixture of 2-propylheptanol isomers. However, aldehydes are preferably sent to a distillation column to be substantially separated into n-aldehydes and isoaldehydes.

[0025] Downstream of the distillation column, n-aldehydes such as n-butyraldehyde are preferably then hydrogenated to n-alcohols such as n-butanol or sent to the aldolization section. Isoaldehydes may be used as products, or, in some cases, such as when 2-propylheptanol is produced, they may be passed through the aldolization section together with some or all of the n-aldehydes.

[0026] In aldolation, aldehydes react to form acrolein (also known as alkenal), which is preferably subsequently hydrogenated to an alcohol. Examples include aldolating n-butyraldehyde to produce ethyl-propyl-acrolein (also known as 2-ethylhexenal), which is then hydrogenated to 2-ethylhexanol, or aldolating baleraldehyde to produce propyl-butyl-acrolein (also known as 2-propylheptenal), which is then hydrogenated to 2-propylheptanol.

[0027] The hydrogenation reactor preferably comprises: a primary catalyst bed having an inlet and an outlet end, regardless of whether it is for n-aldehydes or isoaldehydes from a distillation column, or for acrolein from aldolization; means for supplying a primary feed stream containing fresh feed and recycled liquid products to the inlet end of the primary catalyst bed; a secondary catalyst bed having an inlet and an outlet end, extending substantially vertically through the primary catalyst bed; means for supplying a secondary feed stream containing recycled liquid products to the inlet end of the secondary catalyst bed; means for recovering liquid products from the outlet end of the primary catalyst bed and recirculating at least a portion of the liquid products as recycled liquid products to the inlet ends of the primary and secondary catalyst beds; a partition wall between the primary and secondary catalyst beds; means for supplying a primary gas stream containing fresh hydrogen gas and / or recycled hydrogen gas only to the inlet end of the primary catalyst bed; and means for supplying a secondary gas stream containing fresh hydrogen gas and / or recycled hydrogen gas only to the inlet end of the secondary catalyst bed. In such a reactor, the primary catalyst bed may be a hydrogenation reactor as described herein, and the secondary catalyst bed may be a purification reactor as described herein.

[0028] The product alcohol is preferably purified in one or more distillation columns to obtain the desired purity. Examples of possible purification schemes are disclosed in International Publications 2018 / 069714 and 2019 / 197831.

[0029] The present invention may be particularly advantageous in the production of 2-alkyl alkanols, such as 2-ethylhexanol or 2-propylheptanol, preferably 2-ethylhexanol. Thus, olefins and synthesis gas can be reacted by hydroformylation to produce n-aldehydes and isoaldehydes, which can then be separated in a distillation column. The n-aldehydes are preferably aldolized to produce 2-alkyl alkenals, which are preferably hydrogenated to 2-alkyl alkanols using the above process. Isoaldehydes are typically hydrogenated to isoalkanols using the above process or sold as isoaldehydes. In some processes, only a portion of the n-aldehydes are used to produce 2-alkyl alkanols, and the portion of the n-aldehydes is hydrogenated to n-alkanols using the above process. As a specific example, propene and synthesis gas can be hydroformylated to form a mixture of isobutyraldehyde and n-butyraldehyde. Following the separation of isobutyraldehyde and n-butyraldehyde in a distillation column, at least a portion of the n-butyraldehyde is aldolized to 2-ethylhexenal, which is then hydrogenated to 2-ethylhexanol. The isobutyraldehyde may be hydrogenated to isobutanol or sold as isobutyraldehyde. A portion of the n-butyraldehyde may be hydrogenated to n-butanol. The present invention will now be described with reference to the attached drawings as an example. The drawings are schematic, and it will be understood by those skilled in the art that commercial plants may require further equipment items such as temperature sensors, pressure relief valves, control valves, flow controllers, and level controllers. Providing such equipment accessories does not constitute part of the present invention and follows conventional chemical engineering practices.

[0030] Figure 1 shows a conventional hydrogenation process using liquid recirculation, for example, to hydrogenate an aldehyde. Fresh hydrogen gas is supplied as flow 5 to a hydrogenation reactor 7 containing a suitable hydrogenation catalyst, which may be a copper catalyst in the case of an aldehyde. The reactor 7 is also supplied with a combination of fresh substrate from flow 1 and liquid recirculation 17 via a single flow 3. A liquid flow 11 containing the liquid product, which is the corresponding alcohol in the case of an aldehyde substrate, is withdrawn from the outlet at the bottom of the reactor. The liquid recirculation flow 17 is also withdrawn from the bottom of the reactor. The liquid recirculation flow passes through a recirculation pump 13 and a heat exchanger 15 containing a coolant that removes reaction heat from the system. After cooling, the liquid recirculation flow is combined with the fresh substrate flow 1. A gas purge 9 containing inert material and excess hydrogen is also withdrawn from the reactor 7. This is typically sent to a vent. The vent flow is sufficient to maintain an appropriate partial pressure of hydrogen in the reactor so that approximately stoichiometric amounts of hydrogen are present and no hydrogen is wasted (i.e., the hydrogen flow in the vent is only a small proportion of the stoichiometric amount of hydrogen required). For example, the volume ratio of liquid leaving the reactor to gas leaving through vent flow 9 may be greater than, for example, 50:1. However, as mentioned above, such levels of hydrogen in the reactor can lead to performance degradation in terms of lower catalytic activity and higher byproduct production.

[0031] Figure 2 shows the process according to the present invention in which a hydrogen gas recirculation flow 19 is withdrawn from the reactor 7. The recirculation flow 19 passes through a liquid-driven eductor 21, in which case the driving fluid flow 25 is a combination of fresh substrate feed 1 and liquid recirculation flow 17. The combination of fresh substrate, liquid recirculation flow, and hydrogen gas recirculation exiting the eductor 21 is supplied to the reactor 7 as flow 3. This system effectively utilizes the driving force from a liquid recirculation pump 13, which is typically required for the large volume of liquid recirculation (e.g., about 20:1 by mass in the case of aldehyde hydrogenation) required in such a system, in order to pump the hydrogen gas recirculation by the action of the eductor. A vent 9 is also provided to purge inert material from the system, and some hydrogen is released to maintain the desired partial pressure of hydrogen in the reactor. In this system, the volume ratio of liquid exiting the reactor to gas exiting through vent flow 9 is less than or equal to the volume ratio in the system shown in Figure 1. However, catalytic performance is enhanced primarily by a higher utilization rate of hydrogen in the reactor, which is achieved without the addition of a recirculation compressor.

[0032] Figure 3 shows the process according to the present invention. In this process, the driving fluid in the eductor is only the liquid recirculation flow 17. Therefore, fresh substrate enters the reactor 7 independently by flow 1, and the combination of liquid recirculation 17 and hydrogen gas recirculation 19 enters the reactor 7 by flow 23.

[0033] Figure 4 shows an example of an eductator 21 that can be used in the present invention. The driving fluid 25 passes through the convergence section 29 and enters the throat 31, which causes an increase in velocity and a decrease in pressure. After leaving the throat 31, the driving fluid enters the diverging nozzle 33, which reduces the velocity and increases the pressure, creating a low-pressure region that draws the hydrogen recirculation flow 19 into the eductator. The combination of the driving fluid and the hydrogen recirculation flow exits the eductator as a single flow 3. [Examples]

[0034] The hydrogenation of butyraldehyde for the production of n-butanol was carried out using an alumina-supported copper hydrogenation catalyst in a test-scale apparatus configuration corresponding to the system shown in Figure 1. The hydrogenation was carried out over 252 hours. Specific conditions, products, selectivity, and the conversion rate of butyraldehyde are shown in the table in Figure 5. In summary, the reaction was carried out at a feed rate of 100 g / h, a liquid recirculation to feed ratio of 18:1, and a liquid space velocity of 1.0 (LHSV, h). -1 The experiment was conducted with a catalyst bed outlet temperature of 160°C, a pressure of 290 or 319 psig, and vent flow rates of 1, 3, 4, 5, and 10 normal liters per hour (NLPH), while inlet nitrogen gas flow rates of 0 and 3 NLPH were used. The nitrogen gas flow serves to dilute the amount of hydrogen gas in the system, thereby recreating lower hydrogen concentrations in the reactor. The volume ratio of liquid to gas leaving the reactor is given for the run time during which pure hydrogen is used as the gas feed, and this indicates the large amount of hydrogen vent required to achieve a low volume ratio of liquid to gas leaving the reactor without hydrogen gas recirculation.

[0035] The data in the table in Figure 5 shows that increasing the hydrogen flow rate improves selectivity, even when the partial pressure of hydrogen leaving the reactor is nominally the same. This is particularly evident from the comparison of data from 86 hours of operation and 116 hours of operation. When the vent is only 1 NLPH and close to the stoichiometric level of hydrogen in the reactor, the amount of aldehyde slip and byproduct formation increases compared to when the vent is 10 NLPH and there is a much higher amount of hydrogen in the reactor than the stoichiometric level, resulting in a larger amount of available hydrogen in the reactor. Therefore, when operating an industrial reactor with nearly stoichiometric levels of hydrogen to minimize hydrogen loss (e.g., under the 116-hour condition with a vent flow of 1 NLPH), the volume ratio of liquid to gas leaving the reactor is typically about 40:1, and the efficiency of the hydrogenation reaction can be affected. At the additional data points at 131, 181, 220, and 252 hours, nitrogen is used in the gas to simulate further hydrogen depletion in the reactor. A decrease in the level of available hydrogen in the reactor is found to lead to even greater aldehyde slip and byproduct formation. The effects of extremely small outlet gas volume are expected to be greater in industrial plants with larger diameters compared to laboratory units, for example, because it can cause uneven flow rather than uniform distribution of all bubbles.

[0036] The use of a hydrogen recirculation flow, in which the recirculation energy of the liquid recirculation is effectively utilized to pump hydrogen recirculation via an eductor, reduces the volume ratio of liquid to gas leaving the reactor, increases the stoichiometric level of hydrogen in the reactor, and thus increases the amount of hydrogen available for the reaction. This thus provides the advantages shown in the data in Table 5. However, it is not necessary to increase the hydrogen flow to the reactor to increase the available hydrogen, and therefore not necessary to increase the vent flow, nor is it necessary to vent a stoichiometric excess of hydrogen and lose it from the system. In detail, this is achieved without the need for an extra compressor by utilizing the recirculation energy of the liquid product flow via an eductor. Therefore, the extra costs and maintenance requirements associated with a mechanical compressor are not required.

[0037] In an industrial process for the hydrogenation of C9 aldehydes, with an inlet pressure of 3.0 MPa, a flow rate of 550,000 kg / h, and a density of 730 kg / m³, the following conditions were met: 3 The driving fluid is a liquid recirculation system that includes a combination of a fresh aldehyde feed and liquid recirculation, with a viscosity of 0.5 mPas, a vapor pressure of 0.02 MPa, a driving pressure of 3.25 MPa, and a temperature of 150°C, and a flow rate of 1040 kg / hour and a density of 3.0 kg / m³. 3 Simulations of an eductor operating with an eductor suction pressure of 2.9 MPa and recirculating gas at a temperature of 160°C show that the ratio of outlet liquid to outlet gas in the hydrogenation reactor can be 2.2:1 on a volume basis. Without an eductor, the ratio of outlet liquid to outlet gas is approximately 80:1 on a volume basis. This indicates that a beneficial gas flow for recirculation can be extracted from the reactor with an operational pressure drop.

Claims

1. A process for obtaining a liquid product by hydrogenating a substrate in a hydrogenation reactor, (a) The hydrogenation reactor may have the following, namely: (i) Fresh substrate, (ii) Fresh hydrogen gas, (ii) Recirculated liquid products, (iii) Supplying recycled hydrogen gas, (b) To recover the liquid product in the liquid product stream from the outlet of the hydrogenation reactor, (c) Recovering the liquid product in the recirculated liquid product stream and returning at least a portion of it to the hydrogenation reactor as the recirculated liquid product, (d) recovering hydrogen gas as a hydrogen gas recirculation flow from the outlet of the hydrogenation reactor and returning at least a portion of it to the hydrogenation reactor as the recirculated hydrogen gas, The hydrogen gas recirculation flow passes through the eductor before being returned to the hydrogenation reactor. A process wherein the driving fluid in the eductor is a fresh substrate, the recirculated liquid product flow, or a combination of the fresh substrate and the recirculated liquid product flow, or the driving fluid is the fresh hydrogen gas.

2. The process according to claim 1, wherein the substrate is an aldehyde and the product is an alcohol.

3. The process according to claim 2, wherein the aldehyde is an unsaturated aldehyde and the product is a saturated alcohol.

4. The process according to any one of claims 1 to 3, wherein the driving fluid is a combination of the fresh substrate and the liquid product recirculation flow.

5. The process according to any one of claims 1 to 4, wherein the volume ratio of the liquid leaving the reactor to the gas leaving the reactor is less than 20:

1.

6. The process according to any one of claims 1 to 5, wherein the recirculation ratio of the liquid product to the fresh substrate is greater than 10:1 by mass.

7. The process according to any one of claims 1 to 6, wherein the hydrogen stream passing through the hydrogenation reactor is at least 120% of the stoichiometric hydrogen stream required to hydrogenate the substrate stream passing through the hydrogenation reactor.

8. The process according to any one of claims 1 to 7, wherein the process further includes a purification reactor, and the hydrogen gas exiting the purification reactor is combined with the hydrogen gas recovered from the hydrogenation reactor to form part of the hydrogen gas recirculation flow received by the eductor.

9. A device for hydrogenating a substrate. (a) A hydrogenation reactor configured to hydrogenate the substrate to obtain a liquid product, (b) means for supplying fresh substrate to the hydrogenation reactor, (c) means for supplying fresh hydrogen gas to the hydrogenation reactor, (d) Means for recovering the liquid product stream from the outlet of the hydrogenation reactor, (e) Means for recovering the liquid product as a liquid product recirculation flow, (e) Means for returning the recirculated liquid product flow to the hydrogenation reactor, (f) Means for recovering hydrogen gas from the outlet of the hydrogenation reactor as a hydrogen gas recirculation flow, (g) Means for returning the hydrogen gas recirculation flow to the hydrogenation reactor, (f) an eductor configured to receive the hydrogen gas recirculation flow before it is returned to the hydrogenation reactor, An apparatus wherein the emitter is configured to use the fresh substrate, the recirculated liquid product flow, or a combination of the fresh substrate and the recirculated liquid product flow as the driving fluid.

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