Method and plant for the hydrogenation of aldehydes

Abstract

A method for hydrogenating an aldehyde comprises: a) mixing a recirculated intermediate hydrogenation effluent with fresh aldehyde to obtain a hydrogenation feed stream; b) passing the hydrogenation feed stream over at least one bed of a primary hydrogenation catalyst in the presence of a hydrogen-containing gas to obtain an intermediate hydrogenation effluent as the recirculated intermediate hydrogenation effluent to step a); c) passing the intermediate hydrogenation effluent past an intercooler and recirculating the intermediate hydrogenation effluent as the recirculated intermediate hydrogenation effluent to step a); d) withdrawing from the recirculated intermediate hydrogenation effluent a post-cooler stream from a location downstream of the intercooler and withdrawing a pre-cooler stream from a location upstream of the intercooler; e) merging the post-cooler stream and the pre-cooler stream to provide a post-hydrogenation feed stream; f) adjusting a relative proportion between the post-cooler stream and the pre-cooler stream; and g) passing the post-hydrogenation feed stream over at least one bed of a post-hydrogenation catalyst in the presence of a hydrogen-containing gas. A plant for hydrogenating an aldehyde is adapted to the method.

Description

[0001] 241150W001 1

[0002] Method and Plant for the Hydrogenation of Aldehydes

[0003] The present invention relates to a method and a plant for hydrogenating an aldehyde.

[0004] Methods for the hydrogenation of aldehydes are of central importance in the chemical industry. Catalytic hydrogenations over heterogeneous catalysts are in many cases carried out using fixed bed reactors in order to obtain the advantages of a continuous process. For a substantially complete conversion, relatively high reaction volumes may become necessary resulting in low space-time-yields. Hydrogenation of aldehydes is an exothermic reaction and the amounts of heat which are released can cause problems with regard to heat removal in straight pass through a fixed bed reactor. Thus, to reduce the amounts of heat obtained, if appropriate, the conversion has to be limited and / or the reactor effluent has to be partially recycled. However, recycling the reactor effluent may lead to undesired effects of backmixing. In particular, there is not much economic sense in driving the conversion to completion and then to dilute a partial stream with fresh aldehyde to provide a hydrogenation feed.

[0005] Typically, large-scale hydrogenation of aldehydes takes place in a reactor arrangement in which the two or more reactors are arranged in series. This arrangement has the advantage that if the catalyst in the first reactor is deactivated, said catalyst can be changed without having to change the catalyst in the other reactors of the series.

[0006] CN 104557456 discloses a method for generating butanol via butyraldehyde liquid phase hydrogenation. The reaction device consists of a first-stage hydrogenation reactor and a second-stage hydrogenation reactor which are connected in series. The butyraldehyde conversion rate of the first-stage hydrogenation is 80 to 95% and the butyraldehyde conversion rate of the second-stage hydrogenation reactor is 95 to 99.8%.

[0007] WO 2019 / 008561 discloses a process for hydrogenating aromatic compounds over a solid catalyst in the presence of a hydrogen-containing gas comprising a first reactor operated in loop mode and a second reactor operated in straight pass, wherein at least a part of the output of the first reactor is supplied to the second reactor. The first reactor is operated in trickle bed mode, and the second reactor is operated such that the catalyst present therein is partially flooded.

[0008] All hydrogenation catalysts used in industrial production processes are subject to an aging-related performance decline during normal operation, and they need to be exchanged periodically. The aging manifests itself by a reduction in the activity of the catalyst and may also manifest itself by a reduction in efficiency. In a multistage hydrogenation process, the declining activity of the final stage catalyst must be particularly accounted for in order to achieve substantially full conversion in the hydrogenation, as the total conversion is attained only in the final stage.

[0009] Therefore, it was object of the present invention to provide an improved method for the multistage hydrogenation of aldehydes that accounts for a declining activity of the final stage hydrogenation catalyst.241150W001 2

[0010] The invention provides a method for hydrogenating an aldehyde, comprising:

[0011] a) mixing a recirculated intermediate hydrogenation effluent with fresh aldehyde to obtain a hydrogenation feed stream;

[0012] b) passing the hydrogenation feed stream over at least one bed of a primary hydrogenation catalyst in the presence of a hydrogen-containing gas to obtain an intermediate hydrogenation effluent; c) passing the intermediate hydrogenation effluent past an intercooler and recirculating the intermediate hydrogenation effluent as the recirculated intermediate hydrogenation effluent to step a);

[0013] d) withdrawing from the recirculated intermediate hydrogenation effluent a post-cooler stream from a location downstream of the intercooler and withdrawing a pre-cooler stream from a location upstream of the intercooler;

[0014] e) merging the post-cooler stream and the pre-cooler stream to provide a post-hydrogenation feed stream;

[0015] f) adjusting a relative proportion between the post-cooler stream and the pre-cooler stream; and g) passing the post-hydrogenation feed stream over at least one bed of a post-hydrogenation catalyst in the presence of a hydrogen-containing gas.

[0016] Usually, when a decline in catalyst activity occurs, the reaction temperature is increased in order to compensate for the declining catalyst activity. The reaction temperature may be increased until it reaches the design limit or becomes undesirably high, or the efficiency may become undesirably low, at which point in time the catalyst is deemed to be at the end of its lifetime and would need to be exchanged or regenerated.

[0017] The invention further relates to a plant for hydrogenating an aldehyde, comprising:

[0018] I) at least one bed of a primary hydrogenation catalyst;

[0019] ii) means for mixing a recirculated intermediate hydrogenation effluent with fresh aldehyde to obtain a hydrogenation feed stream;

[0020] ill) means for passing the hydrogenation feed stream over the at least one bed of primary hydrogenation catalyst in the presence of a hydrogen-containing gas;

[0021] iv) an intercooler and means for passing the intermediate hydrogenation effluent past the intercooler and recirculating the intermediate hydrogenation effluent to a);

[0022] v) means for withdrawing from the recirculated intermediate hydrogenation effluent a post-cooler stream from a location downstream of the intercooler and withdrawing a pre-cooler stream from a location upstream of the intercooler;

[0023] vi) means for merging the post-cooler stream and the pre-cooler stream to provide a post-hydrogenation feed stream;

[0024] vii) means for adjusting a relative proportion between the post-cooler stream and the pre-cooler stream; viii) at least one bed of a post-hydrogenation catalyst; and

[0025] ix) means for passing the post-hydrogenation feed stream over the at least one bed of post-hydrogenation catalyst in the presence of a hydrogen-containing gas.241150W001 3

[0026] The inventive method provides a convenient method for adjusting the temperature of the post-hydrogenation feed stream and allows to maintain a substantially full conversion in the hydrogenation. Further provided is a plant adapted to the method.

[0027] Generally, the inventive method proceeds in a hydrogenation system comprising one or more primary hydrogenation reactors (in the following, collectively referred to as the primary hydrogenation reactor) accommodating the at least one bed of a primary hydrogenation catalyst and one or more posthydrogenation reactors (in the following, collectively referred to as the post-hydrogenation reactor) accommodating the at least one bed of a post-hydrogenation catalyst.

[0028] In the primary hydrogenation reactor, the majority of the aldehyde is hydrogenated. Preferably, passing the hydrogenation feed stream over the at least one bed of primary hydrogenation catalyst yields a partial hydrogenation conversion; and passing the post-hydrogenation feed stream over the at least one bed of post-hydrogenation catalyst yields a total hydrogenation conversion; wherein the partial hydrogenation conversion contributes 75 to 98 percentage points to the total hydrogenation conversion.

[0029] The method comprises a) mixing a generally liquid recirculated intermediate hydrogenation effluent with fresh aldehyde to obtain a hydrogenation feed stream.

[0030] The hydrogenation feed stream supplied to the bed of a primary hydrogenation catalyst contains the aldehyde dissolved in the hydrogenation product which has been recycled via the recirculated intermediate hydrogenation effluent. The hydrogenation product acts as a compatible diluent for the aldehyde. The purpose of the diluent is to act as a heat sink; to limit the temperature rise within the hydrogenation zone to acceptable limits. The diluent further acts to compensate for a fluctuating load of the hydrogenation system; and also to provide an appropriate volumetric flow into the catalyst bed, such that a desired liquid superficial velocity is achieved along with the desired product conversion and temperature rise. The concentration of aldehyde in the hydrogenation feed stream is accordingly preferably selected in dependence of the expected acceptable temperature rise across the hydrogenation zone and / or the desired liquid superficial velocity. Preferably, the method comprises mixing the recirculated intermediate hydrogenation effluent stream and the fresh aldehyde at a volume ratio of 1 : 1 to 20: 1 , preferably 2:1 to 12: 1 , more preferably 3: 1 to 10: 1.

[0031] The fresh aldehyde may be injected, e.g., via T-piece, into a passage through which the recirculated intermediate hydrogenation effluent is passed. It is desirable that the recirculated intermediate hydrogenation effluent is mixed with fresh aldehyde so as to obtain a blend which is as homogeneous as possible. Any measures known in the prior art as suitable for achieving this effect may be used. Generally, the means for mixing the recirculated intermediate hydrogenation effluent with fresh aldehyde may be a junction where a pipe or tubing containing the recirculated intermediate hydrogenation effluent intersects with a pipe or tubing containing the fresh aldehyde. In one embodiment, a static mixer may be employed. Introduction of static mixers in pipes provides a simple solution to mixing fluids. The mixers cause continuous breakdown of the stream flowing in the pipe, causing turbulence and a quick stirring of the individual threads of the stream.241150W001 4

[0032] Aldehydes

[0033] Aldehydes are known to the person skilled in the art as organic compounds with a terminal carbonyl group (R-C(=O)-H). The substituent R of the aldehyde may be cyclic or acyclic. The substituent R of the aldehyde may be saturated or unsaturated. The cyclic substituent R of the aldehyde may be aliphatic or aromatic. The acyclic substituent R of the aldehyde may be linear or branched.

[0034] Such aldehydes generally contain from 2 to about 20 carbon atoms and may in the case of those aldehydes containing 3 or more carbon atoms include one or more unsaturated carbon-carbon bonds. Thus, as used herein the term "aldehyde" includes both saturated and unsaturated aldehydes, including aldehydes wherein the only hydrogenatable group is the aldehyde group, and aldehydes which contain further hydrogenatable groups such as olefinic groups, >C=C<, in addition to the aldehyde group.

[0035] In addition to carbon atoms, the substituent R of the aldehyde may incorporate hetero atoms, giving rise to, e.g., a heterocyclic or heteroaromatic group, or being present as functional groups selected from hydroxy, carboxyl, ester, or ether groups. Such heteroatoms may be selected from oxygen, nitrogen and sulfur, preferably oxygen.

[0036] Typical aldehydes include acetaldehyde, propionaldehyde, n- and iso-butyraldehydes, n-pentanal, n-hexanal, 2-methylbutanal, 2-ethylhex-2-enal, 2-ethylhexanal, 2-methylpentanal, 3-methylpentanal, 4-methyl-pentanal, glyoxal, 4-t-butoxybutyraldehyde, hydroxypivaldehyde, Cg-Oxo-aldehydes, undecanal, dodecanal, tridecanal, crotonaldehyde, benzaldehyde, p-methoxybenzaldehyde, p-methylbenzaldehyde, phenylacetaldehyde, (p-methoxyphenyl)acetaldehyde, (3,4-dimethoxy-phenyl)acetaldehyde, furfural, 4-formyltetrahydropyran, 3-formyltetrahydrofuran, 5-formylvaleronitrile, hydroformylated polyisobutene (poly isobutene aldehyde, PI BA), hydroformylated oligomers obtained by metathesis of 1 -pentene and cyclopentene, as well as mixtures of two or more thereof.

[0037] Aldehydes and mixtures of aldehydes can be produced by hydroformylation of an olefin or mixed olefins in the presence of a cobalt catalyst or a rhodium complex catalyst. The result may be a mixture of isomers. The ratio of the n-aldehyde to the iso-aldehyde in the product depends to a certain extent on the selected hydroformylation conditions and upon the nature of the hydroformylation catalyst used.

[0038] Further aldehydes can be obtained by condensation reactions; for example, 2-ethy lhex-2-enal can be made by condensation of 2 moles of n-butyraldehyde and 2-propylhept-2-enal by condensation of 2 moles of n-valeraldehyde. Examples of aldehyde hydrogenation reactions are the production of n-butanol from n-butyraldehyde, of 2-ethyl hexanol from 2-ethylhex-2-enal, or 2-propylheptanol from 2-propylhept-2-enal, of undecanol from undecanal, of neopentyl glycol from hydroxypivaldehyde, and of 4-t-butoxybutanol from 4-t-butoxybutyraldehyde.

[0039] The invention is used to special advantage for hydrogenation of aldehydes containing from about 3 to about 15 carbon atoms to the corresponding alkanols.

[0040] The method comprises b) passing the hydrogenation feed stream over at least one bed of a primary hydrogenation catalyst, preferably one bed of a primary hydrogenation catalyst, in the presence of a241150W001 5

[0041] hydrogen-containing gas to obtain an intermediate hydrogenation effluent. Suitable means for passing the hydrogenation feed stream over the at least one bed of primary hydrogenation catalyst include a pumping circuit generally comprised of piping and a pump.

[0042] Generally, the hydrogenation feed stream is passed over the bed of primary hydrogenation catalyst term in trickle bed mode. The liquid trickles over the packing in essentially a laminar film or in rivulets, and the gas flows continuously through the voids in the bed. This is sometimes termed the gas continuous region. The recycle of an intermediate hydrogenation effluent acts to warrant even wetting of all parts of the catalyst bed by the use of high superficial liquid velocity through the catalyst bed. Uneven wetting may result in the formation of "dry pockets" in the catalyst bed, which can create hotspots in the catalyst bed, leading to one or more pockets of shortened catalyst life. In addition, an uneven flow of liquid can create channelling through the bed.

[0043] Preferably, the method comprises passing the hydrogenation feed stream over the at least one bed of primary hydrogenation catalyst at a superficial velocity of 40 m / h or more, preferably 45 m / h or more, such as 40 to 70 m / h or 45 to 60 m / h. In a preferred embodiment, the method comprises passing the hydrogenation feed stream over the at least one bed of primary hydrogenation catalyst at a superficial velocity of 40 m / h or more, preferably 45 m / h or more, such as 40 to 70 m / h or 45 to 60 m / h, wherein the ratio of the length to the diameter of the at least one first bed of hydrogenation catalyst is 2:1 or more, preferably 4:1 or more. "Superficial velocity” is defined as volume flow (in m3 / h) divided by the cross-section (in m2) of the catalyst bed.

[0044] To achieve a desired conversion, it may be necessary to use an elongated bed of hydrogenation catalyst. Although the cross-section of the catalyst bed may have any shape, for example a square or elliptical shape, cylindrical beds are generally used. Preferably, the ratio of the length to the diameter of the at least one first bed of hydrogenation catalyst is 2:1 or more, preferably 4:1 or more. The ratio of the length to the diameter of the at least one first bed of hydrogenation catalyst may in particular be in the range of 2.5:1 to 50:1, preferably 4:1 to 40:1, more preferably 3:1 to 30:1. Instead of a single elongated catalyst bed having the l / d ratio specified above, two or more catalyst beds may be connected in series, these beds having a smaller l / d ratio than the said elongated bed but producing a similar effect. The number of series-connected reactor beds used is usually from 2 to 10. Series-connected reactor beds may be contained in one reactor or in reactors connected in series, e.g., each catalyst bed in a separate reactor. When a cascade of 2 or more series-connected catalyst beds is implemented, catalyst poisons which may be comprised in the hydrogenation feed stream, such as sodium, tend to poison only the catalyst in the first catalyst bed, whereas the catalyst in subsequent catalyst beds remains unpoisoned. In one embodiment, a cascade of at least 3 series-connected catalyst beds is used.

[0045] Generally, the hydrogenation feed stream is passed over the at least one bed of a primary hydrogenation catalyst at an inlet temperature of 60 to 170 °C, preferably 100 to 150 °C.

[0046] Hydrogen-Containing Gas

[0047] The primary hydrogenation and post-hydrogenation are accomplished in the presence of a hydrogencontaining gas. A hydrogen-containing gas may be supplied at several points of the primary hydrogenation241150W001 6

[0048] and post-hydrogenation reactors, for example, hydrogen-containing gas may be supplied to the primary hydrogenation and a makeup of hydrogen-containing gas may be supplied to the post-hydrogenation reactor. It is however preferred that the hydrogen-containing gas is supplied only to the primary hydrogenation reactor. Unconsumed hydrogen-containing gas from the primary hydrogenation is directed to the post-hydrogenation.

[0049] The hydrogen-containing gas may be flowed through the bed of primary hydrogenation catalyst concurrently or countercurrently to the hydrogenation feed, preferably concurrently downward.

[0050] The hydrogen-containing gas may be flowed through the bed of post hydrogenation catalyst concurrently or countercurrently to the post-hydrogenation feed stream, preferably concurrently downward.

[0051] The hydrogen-containing gas supplied to the hydrogenation preferably contains a major amount of hydrogen and at most a minor amount of one or more inert gases, such as nitrogen, methane, other low molecular weight hydrocarbons, such as ethane, propane, n-butane and iso-butane, carbon oxides, argon or the like. Preferred hydrogen-containing gases are accordingly gases containing at least about 70 mol-% up to about 95 mol-% or more, e.g. about 99 mol-%, of hydrogen. The balance may be one or more of N2, CO, CO2, Ar, Ne, CH4 and other low molecular weight saturated hydrocarbons. In some cases, for example when using nickel hydrogenation catalysts, the presence of CO and CO2 cannot be tolerated and the total carbon oxides concentration should not, in this case, be more than about 5 to 10 ppm by volume. Such hydrogen-containing gases can be obtained in conventional manner from synthesis gas and other usual sources of hydrogencontaining gases, followed, if necessary, by appropriate pretreatment to remove impurities, such as sulfurous impurities, e.g. H2S, COS, CH3SH, CH3SCH3, and CH3SSCH3, and halogen-containing impurities, e.g. HOI and CH3CI, which may exert a deleterious influence on catalytic activity, i.e. catalyst inhibition, poisoning or deactivation, as well as by the removal of the carbon oxides. Preparation of suitable hydrogencontaining gases will accordingly be effected according to usual production techniques.

[0052] The hydrogen-containing gas supplied to the hydrogenation may be, for example, a hydrogen stream produced by steam reforming of natural gas followed by the water gas shift reaction, then by CO2 removal. Purified hydrogen streams obtained by the pressure swing adsorption treatment of hydrogen admixed with CO, CO2 and light hydrocarbon gases may be used. Substantially pure hydrogen from an electrolysis plant is also envisaged as hydrogen-containing gas.

[0053] Hydrogen is relatively poorly soluble in organic liquids, and thus the dissolution of hydrogen in the organic phase and its subsequent migration through the liquid phase to the catalyst surface may be rate limiting steps in liquid phase hydrogenation. For this reason, the use of high partial pressures of hydrogen is often necessary. Generally, a balance has to be struck between additional process efficiency and the additional capital and running costs associated with use of high pressures. Preferably, the method comprises passing the hydrogenation feed stream over the at least one bed of primary hydrogenation catalyst at a pressure of 10 to 40 bar(a). Herein, pressures indicated by bar(a) refer to absolute pressures.

[0054] The primary hydrogenation catalyst may be any of the hydrogenation catalysts commonly used for the hydrogenation of aldehydes. Aldehyde hydrogenation catalysts include cobalt compounds; nickel or copper compounds which may contain small amounts of chromium or another promoter like manganese,241150W001 7

[0055] molybdenum, or zinc; mixtures of copper and nickel and / or chromium; and other Group VIII metal catalysts, such as Pt, Pd, Rh, Ru and mixtures thereof, on supports, such as carbon, silica, alumina and silica-alumina or other oxidic materials.

[0056] Preferably, the at least one bed of primary hydrogenation catalyst comprises a copper hydrogenation catalyst, in particular a nickel-copper-manganese hydrogenation catalyst or a cobalt-copper-manganese hydrogenation catalyst. Such catalysts are described in EP 3878831 and DE 2321 101.

[0057] The nickel-copper-manganese hydrogenation catalyst preferably has an active mass comprising from 40 to 80% by weight of nickel, from 10 to 50% by weight of copper and from 2 to 10% by weight of manganese referred to the total mass of nickel, copper and manganese in the catalyst.

[0058] The cobalt-copper-manganese hydrogenation catalyst preferably comprises cobalt, copper and manganese, more preferably comprises cobalt, copper, manganese and molybdenum.

[0059] The catalyst particles substantially all have a particle diameter in the range of from 1 to 10 mm, preferably in the range of 1.5 mm to 5 mm, as measured by a conventional sieve analysis technique. "Substantially all" is intended to mean that at least 90% of particles have a diameter within the range indicated. The catalyst particles may be of any desired shape, such as cylindrical or spherical, but are conveniently cylindrical. In the case of spherical or granular catalyst particles, the particle size is essentially equivalent to particle diameter, whereas in the case of cylindrical catalyst particles or particles of more complex shape the particle size is typically in the range of 1 to 20 mm, preferably in the range of 1.5 to 10 mm.

[0060] In one embodiment, the catalyst particles have a multilobal cross-sectional shape, such as a trilobal shape. These have a cross-sectional shape consisting of a plurality of essentially symmetrical lobes located about a central point. In particular, the catalyst particles may have a trilobal shape wherein the cross-section of the trilobal shape is defined by three convex curves, each of which is in contact with a circle of diameter d circumscribing the cross-section and having three intersection points within the circle, wherein the distance a between any two intersection points is from 0.45 to 0.65 times the diameter d of the circle circumscribing the cross-section. Suitable catalyst particles having a trilobal shape are described, e.g., in EP 4433207 A1.

[0061] The hydrogenation feed suitably enters the primary hydrogenation reactor near its top and is uniformly distributed over the cross-section of the catalyst bed. In one embodiment, this is achieved by injecting the hydrogenation feed through a nozzle arranged over a perforated plate. The liquid drips through the holes of the perforated plate and onto the catalyst bed below. In other embodiments, commercially available liquid distributor trays may be used which are configured to achieve a uniform distribution of the liquid over the cross-section of the catalyst bed. Such liquid distributor trays may also be arranged between catalyst beds within the reactor to reestablish uniform distribution of the liquid.

[0062] Within the hydrogenation reactor, the catalyst particles are supported by a support plate to prevent catalyst migration downstream. The support plate is designed to achieve the necessary mechanical strength for retaining the bed of hydrogenation catalyst. Despite the requirement for mechanical strength, the free crosssection of the reactor should not be reduced. Grid-type packing supports which are flat necessarily reduce the available free cross-section due to the area occupied by the grid bars.241150W001 8

[0063] Therefore, it is preferred to use support plates that offer an open area equivalent to 100% or more of the cross-sectional area of the reactor.

[0064] Preferred support plates are so-called multi-beam packing supports or Norton trays. These comprise a slotted or perforated plate that is corrugated. The corrugations may adopt, e.g., a trapezoidal profile. The multi-beam packing supports have a high percentage of open area so as to allow the unrestricted flow of both liquid and gas through the supports. A series of slotted or perforated beams allow the liquid and the gas to flow through openings which are small enough so as to hold back the catalyst particles.

[0065] Alternatively, the support plate has a central, cylindrical elevation, where the periphery of the cylinder is slotted or perforated. Liquid may flow radially from the catalyst bed outside the cylinder into the interior of the cylinder. The catalyst may also be supported by a "bottom basket”, i.e., a support plate having a central, cylindrical elevation, where the periphery of the cylinder is slotted or perforated, placed in the bottom outlet of the reactor.

[0066] The hydrogenation catalyst may rest directly on the support plate. However, it is preferred that at least one layer of an inert filler is arranged between the support plate and the hydrogenation catalyst bed. The inert filler may be comprised, e.g., of inert refractory materials such as alumina. The inert filler may be of an arbitrary shape and are preferably spheres. To minimize pressure drop and reduce the tendency of fouling, at least the inert filler in the layer adjacent to the support plate has a significantly larger diameter than the catalyst particles. For example, the inert filler in the layer adjacent to the support plate has a weight average particle diameter of at least 4 times the weight average particle diameter of the catalyst particles. Between the inert filler layer adjacent to the support plate and the catalyst particles, a further inert filler layer may be arranged. The weight average particle diameter of the inert filler in the further layer is preferably smaller than the weight average particle diameter of inert filler in the layer adjacent to the support plate.

[0067] Instead of a single elongated catalyst bed, two or more catalyst beds may be connected in series. In one embodiment, at least one layer of an inert filler is arranged between at least two of the catalyst beds connected in series. In another embodiment, distributing devices may be located between two consecutive catalytic beds or in interbed zones. Distributing devices may comprise an intermediate tray configured so as to allow for a redistribution of the feed across the cross-section of the subsequent catalyst bed. When such an intermediate tray is implemented, it is preferred that at least one layer of an inert filler is arranged between the intermediate tray and the subsequent catalyst layer, wherein the height of the inert layer is suitably in the range of 5% to 10% of the subsequent catalyst layer.

[0068] Catalyst activity gradually decreases and after a certain operation time, the catalyst needs to be replaced. In order to facilitate the removal of spent catalyst from the reactor, in one embodiment, the reactor comprises a side opening for discharging spent catalyst or a plurality of catalyst dropout openings around the periphery of the reactor for discharging spent catalyst.

[0069] The method comprises c) passing the intermediate hydrogenation effluent past an intercooler and recirculating the intermediate hydrogenation effluent to step a) as the recirculated intermediate hydrogenation effluent. To this end, the intermediate hydrogenation effluent is passed via an external loop through a suitable intercooler to extract and dissipate heat from the intermediate hydrogenation effluent.241150W001 9

[0070] Suitable means for passing the intermediate hydrogenation effluent past the intercooler and recirculating the intermediate hydrogenation effluent include a recirculation circuit incorporating a pump. The recirculation circuit may comprise a pipeline for guiding the intermediate hydrogenation effluent, a pump for passing the intermediate hydrogenation effluent past the intercooler, and a pipeline for recirculating the intermediate hydrogenation effluent. It should be appreciated that the pumping circuit for passing the hydrogenation feed stream over the at least one bed of primary hydrogenation catalyst may coincide with the recirculation circuit.

[0071] The intercooler may be implemented as any heat exchanger, e.g., a shell and tube heat exchanger which may be configured for either parallel or counter-flow, or other suitable heat exchanger, such as a double pipe heat exchanger, any suitable variant of a plate heat exchanger. Secondary cooling water, sea water or any other suitable liquid may be used as the coolant in the heat exchanger, preferably secondary cooling water. In some embodiments, a gas to liquid heat exchanger may be used, and in some such embodiments air or other readily available gas may be used as be the coolant. The intermediate hydrogenation effluent may be heat integrated via the coolant of the intercooler with other process steps such as aldehyde distillation, for example in accordance with EP 2822921 A1.

[0072] The method comprises d) withdrawing from the recirculated intermediate hydrogenation effluent stream a post-cooler stream from a location downstream of the intercooler and withdrawing a pre-cooler stream from a location upstream of the intercooler; and e) merging the post-cooler stream and the pre-cooler stream to provide a post-hydrogenation feed stream. This means that the intermediate hydrogenation effluent stream is divided into three streams: a post-cooler stream, a pre-cooler stream and a recycle stream which is recirculated to step a), wherein the post-cooler stream and the pre-cooler stream are merged to provide a post-hydrogenation feed stream that is directed to post-hydrogenation.

[0073] Suitable means for withdrawing from the recirculated intermediate hydrogenation effluent the post-cooler stream and pre-cooler stream include a branch line from a recirculation circuit carrying the recirculated intermediate hydrogenation effluent, which branch line is operated by a valve configured to open the branch line.

[0074] Temperature Control

[0075] At startup of the hydrogenation, the temperature of the post-hydrogenation feed stream should be as low as possible. The catalyst activity of the post-hydrogenation catalysts decreases steadily. In order to essentially maintain a desired conversion in the post-hydrogenation, the decrease of catalyst activity can be counteracted by a temperature increase of the post-hydrogenation feed.

[0076] Hence, the method comprises d) withdrawing from the recirculated intermediate hydrogenation effluent a post-cooler stream from a location downstream of the intercooler and withdrawing a pre-cooler stream from a location upstream of the intercooler, e) merging the post-cooler stream and the pre-cooler stream to provide a post-hydrogenation feed stream, and f) adjusting a relative proportion between the post-cooler stream and the pre-cooler stream. It is understood that the pre-cooler stream is hotter than the post-cooler stream. Thus, the relative proportion between the post-cooler stream and the pre-cooler stream may be adjusted to adjust the temperature of the post-hydrogenation feed stream to a pre-determined value. In241150W001 10

[0077] particular, the pre-determined value may be increased as the activity of the post-hydrogenation catalyst decreases.

[0078] It should be appreciated that the method encompasses situations in which the post-hydrogenation feed stream consists only of the post-cooler stream or the pre-cooler stream, i.e., the proportion of the post-cooler stream or the pre-cooler stream is 100%.

[0079] Suitable means for merging the post-cooler stream and the pre-cooler stream to provide a posthydrogenation feed stream may be a junction where a pipe or tubing containing the post-cooler stream intersects with a pipe or tubing containing the pre-cooler stream.

[0080] Suitable means for adjusting the relative proportion may be at least one valve. One or more valves may be coupled to the passages for the post-cooler stream and the pre-cooler stream to control their relative flow rates directed to the post-hydrogenation. In one embodiment, the passage for the pre-cooler stream may include a first valve for adjusting a flow rate of pre-cooler stream while the passage for the post-cooler stream may or may not include a second valve for adjusting the flow rate of post-cooler stream. One or both of the first and second valves may be continuously variable valves wherein a position of the valve is continuously variable from a fully closed position to a fully open position. For example, the valve(s) may be shifted from a default, partially open position towards a fully open position. By adjusting the valve(s) to adjust a flow rate of the post-cooler stream and the pre-cooler stream, a temperature-controlled mixture may be provided at the post-hydrogenation inlet. In an alternate embodiment, flow rates of the post-cooler stream and the pre-cooler stream may be controlled by a common valve. Preferably, the common valve is a controlled proportioning valve that is configured to adjust a flow rate from the post-cooler stream and the pre-cooler stream to provide a temperature-controlled mixture at the post-hydrogenation inlet. It should be appreciated that the valve for adjusting the relative proportion may coincide with the valve operating a branch line for withdrawing from the recirculated intermediate hydrogenation effluent the post-cooler stream and pre-cooler stream.

[0081] Liquid Level

[0082] The control of flow rate of the post-hydrogenation feed stream passed to post-hydrogenation is not especially limited and may be a constant flow.

[0083] In a preferred embodiment however, the method comprises retaining the intermediate hydrogenation effluent in a holding zone, withdrawing from the holding zone intermediate hydrogenation effluent to be passed past the intercooler and recirculated to step a), monitoring a liquid level in the holding zone, and adjusting the flow rate of the post-hydrogenation feed stream based on the monitored liquid level. The holding zone may be arranged within or outside of the primary hydrogenation reactor. Conveniently, the holding zone may be the bottoms of the primary hydrogenation reactor.

[0084] The liquid level of intermediate hydrogenation effluent in the holding zone may be controlled by withdrawing a controlled amount of the intermediate hydrogenation effluent and passing the intermediate hydrogenation effluent through a valve responsive to a liquid level sensing device in communication with the holding zone. The operation is simply that as the liquid level in the holding zone falls below the desired level, the sensing241150W001 11

[0085] device actuates the valve to restrict the flow of intermediate hydrogenation effluent until the desired level is reestablished; whereas when the liquid level rises above the desired level the sensing device actuates the valve to permit increased flow of intermediate hydrogenation effluent therethrough until the desired level is reestablished.

[0086] Post-Hydrogenation

[0087] The method further comprises g) passing the post-hydrogenation feed stream over at least one bed of a post-hydrogenation catalyst, preferably one bed of a post-hydrogenation catalyst, in the presence of a hydrogen-containing gas.

[0088] Suitable means for passing the post-hydrogenation feed stream over the at least one bed of posthydrogenation catalyst in the presence of a hydrogen-containing gas include piping guiding the posthydrogenation feed stream towards the post-hydrogenation catalyst bed.

[0089] The superficial velocity at which the post-hydrogenation feed stream is passed over the at least one bed of post-hydrogenation catalyst may be controlled independently from the superficial velocity at which the hydrogenation feed stream is passed over the at least one bed of primary hydrogenation catalyst. Hence, the superficial velocities may be the same or different. Preferably, the post-hydrogenation feed stream is passed over the at least one bed of post-hydrogenation catalyst at a superficial velocity which is less than the superficial velocity at which the hydrogenation feed stream is passed over the at least one bed of primary hydrogenation catalyst, such as at least 10% less or at least 20% less.

[0090] Preferably, the method comprises passing the post-hydrogenation feed stream over the at least one bed of post-hydrogenation catalyst at a superficial velocity of 15 m / h or more, preferably 20 m / h or more, such as 15 to 35 m / h or 20 to 30 m / h. Preferably, the ratio of the length to the diameter of the at least one bed of post-hydrogenation catalyst is 2:1 or more, preferably 4:1 or more.

[0091] In a preferred embodiment, the method comprises passing the post-hydrogenation feed stream over the at least one bed of post-hydrogenation catalyst at a superficial velocity of 15 m / h or more, preferably 20 m / h or more, such as 15 to 35 m / h or 20 to 30 m / h, wherein the ratio of the length to the diameter of the at least one bed of post-hydrogenation catalyst is 2:1 or more, preferably 4:1 or more.

[0092] Preferably, the method comprises passing the post-hydrogenation feed stream over the at least one bed of post-hydrogenation catalyst at an inlet temperature of 60 to 190 °C, preferably 100 to 160 °C.

[0093] Preferably, the method comprises passing the post-hydrogenation feed stream over the at least one bed of post-hydrogenation catalyst at a pressure of 10 to 40 bar(a).

[0094] The post-hydrogenation catalyst may be any of the hydrogenation catalysts commonly used for the hydrogenation of aldehydes and may be selected from those catalysts discussed above with respect to the primary hydrogenation catalyst.241150W001 12

[0095] Preferably, the at least one bed of post-hydrogenation catalyst comprises a copper hydrogenation catalyst, in particular a nickel-copper-manganese hydrogenation catalyst or a cobalt-copper-manganese hydrogenation catalyst as discussed above.

[0096] Preferably, the at least one bed of primary hydrogenation catalyst and the at least one bed of posthydrogenation catalyst comprise the same catalyst.

[0097] Preferably, the method comprises passing the post-hydrogenation feed stream over the at least one bed of post-hydrogenation catalyst in single-pass mode under essentially adiabatic conditions. The adiabatic temperature rise across the at least one bed of the post-hydrogenation catalyst can be accepted in view of the limited degree of conversion which occurs in this bed.

[0098] The embodiments regarding the structure of primary hydrogenation reactor as discussed above, in particular with regard to liquid distribution and catalyst support plate, are likewise applicable to the post-hydrogenation reactor. Generally, the post-hydrogenation feed stream is passed over the bed of post-hydrogenation catalyst term in trickle bed mode.

[0099] Safety Concept

[0100] In one embodiment, the method comprises a safety scheme, which comprises measuring the temperature increase AT of the post-hydrogenation feed stream over the at least one bed of post-hydrogenation catalyst, and shutting down the plant when the temperature increase AT exceeds a predetermined threshold.

[0101] The temperature increase AT of the post-hydrogenation feed stream over the at least one bed of posthydrogenation catalyst is a measure for the concentration of unreacted aldehyde in the post-hydrogenation feed stream (or the intermediate hydrogenation effluent) and, hence, a measure of hydrogenation conversion in the primary hydrogenation reactor. In order to avoid exceeding the design temperature of the primary hydrogenation reactor in case of, e.g., a failure of the control loops, the concentration of aldehyde in the primary hydrogenation reactor needs to be limited. The limit can be determined based on the reaction enthalpy, the inlet temperature to the primary hydrogenation reactor and the design temperature of the primary hydrogenation reactor.

[0102] In one embodiment, the safety scheme comprises measuring the temperature T2 of the post-hydrogenation effluent and shutting down the plant when the temperature T2 exceeds a predetermined threshold. This threshold is suitably below the design temperature of the post-hydrogenation reactor. Alternatively or additionally, the safety scheme comprises measuring the temperature T 1 of the intermediate hydrogenation effluent and shutting down the plant when the temperature T1 exceeds a predetermined threshold. This threshold is suitably below the design temperature of the primary hydrogenation reactor.

[0103] It is understood that shutting down the plant may comprise interrupting the fresh aldehyde stream.241150W001 13

[0104] Options for Discharge

[0105] The post-hydrogenation effluent leaving the bed of a post-hydrogenation catalyst may be separated to yield an excess gas phase and a liquid post-hydrogenation effluent. Separation can be accomplished by a separator that is located inside the post-hydrogenation reactor. This means that separation is effected at the pressure prevailing in the post-hydrogenation reactor. This option is particularly interesting if the excess gas is to be used in another reaction, that has less stringent requirements for hydrogen purity than hydrogenation and in which higher inert gas concentrations can be tolerated. An example of a reaction with less stringent requirements for hydrogen purity is hydroformylation. Hence, in an embodiment, the excess gas separated from the post-hydrogenation effluent may be directed to a hydroformylation reaction of an olefinic substrate. Alternatively, a separator may be used that is in fluid connection with post-hydrogenation reactor but located outside the post-hydrogenation reactor.

[0106] As a further alternative, the post-hydrogenation effluent may be expanded into a low-pressure separator. This embodiment involves lowest investment. This option is interesting if the hydrogen is not to be used further, but is incinerated for its calorific value. The flow of the post-hydrogenation effluent into the low-pressure separator may be controlled such that a predetermined pressure in the low-pressure separator is maintained. Flow of the post-hydrogenation effluent into the low-pressure separator should be sufficiently high so as to avoid accumulation of liquid in the catalyst bed(s) of the post-hydrogenation reactor(s). In practice, this means that the flow of the post-hydrogenation effluent into the low-pressure separator is gasliquid, preferably biphasic. This in turn implies that the vent rate of excess gas from the low-pressure separator must be high enough. An increase in the differential pressure in the post-hydrogenation reactor(s) is indicative of an accumulation of liquid in the catalyst bed(s) of the post-hydrogenation reactor(s). If such an increase is observed in the course of the process, the vent rate must be corrected accordingly.

[0107] In venting excess gas, account must be taken of the circulating inert gases, e.g. N2, Ar, CH4 and the like, which are inevitably present in the hydrogen-containing gas. In some cases, the primary hydrogenation and / or post-hydrogenation may proceed under decarbonylation of the aldehyde as an undesired side reaction. The obtained CO may accumulate in the system, in particular when recycle streams are used, and exert a deleterious influence on catalytic activity, i.e. catalyst inhibition, poisoning or deactivation. In this case, the concentration of CO should be maintained below defined thresholds. The concentration of CO may be maintained below defined thresholds by adjusting the vent rate.

[0108] In an embodiment where the post-hydrogenation feed stream and unconsumed hydrogen-containing gas are passed from the primary hydrogenation reactor to post-hydrogenation in the post-hydrogenation reactor to obtain a post-hydrogenation effluent; and excess gas is separated from the post-hydrogenation effluent, excess gas may be vented at a controlled vent rate; and the flow of hydrogen-containing gas fed to the primary hydrogenation reactor is controlled in dependence of a measured pressure in the hydrogenation system to maintain a predetermined pressure in the hydrogenation system, allowing for hydrogenating an aldehyde at a controlled pressure.

[0109] Generally, the vent rate is set to control the buildup of inert gases in the hydrogenation system. This may be accomplished by setting the vent rate to control the hydrogen content of the vented excess gas to be within a desired range, preferably from 70 to 95 % by volume, in particular 75 to 90 % by volume. The241150W001 14

[0110] hydrogen content of the vented excess gas may be determined continuously or periodically, preferably by gas chromatography or thermal conductivity detection.

[0111] The invention is further illustrated by the accompanying drawing and the following example.

[0112] Fig. 1 schematically shows a plant for the hydrogenation of aldehydes according to the invention.

[0113] According to Fig. 1, fresh aldehyde 101 is mixed into recirculated intermediate hydrogenation effluent 102. The resultant hydrogenation feed stream 103 is passed over a bed of a primary hydrogenation catalyst 104 in primary hydrogenation reactor 105. Hydrogen-containing gas is introduced via line 106. An intermediate hydrogenation effluent 107 is retained in the bottoms of primary hydrogenation reactor 105. Intermediate hydrogenation effluent is withdrawn via pump 108, and a partial stream thereof is passed through intercooler 109. A partial stream of the thus obtained cooled intermediate hydrogenation effluent constitutes recirculated intermediate hydrogenation effluent 102.

[0114] A post-cooler stream 110 is withdrawn from the intermediate hydrogenation effluent from a location downstream of the intercooler, while a pre-cooler stream 111 is withdrawn from a location upstream of the intercooler.

[0115] Post-cooler stream 110 and pre-cooler stream 111 are merged to provide post-hydrogenation feed stream 112. The liquid level of intermediate hydrogenation effluent in the bottoms is monitored by level controller LC, and the flow rate of the post-hydrogenation feed stream is adjusted by valve 113 which in turn is controlled by flow controller FC based on the monitored liquid level. Post-hydrogenation feed stream 112 is passed over a bed of a post-hydrogenation catalyst 114 in post-hydrogenation reactor 115.

[0116] The relative proportion between the post-cooler stream 110 and the pre cooler stream 111 is adjusted via valve 116. Valve 116 is controlled by temperature controller TC that may receive a signal from a thermocouple that sights the bed of post-hydrogenation catalyst 114.

[0117] From the bottoms of post-hydrogenation reactor 115, a post-hydrogenation effluent 117 is withdrawn. The post-hydrogenation effluent 117 may be separated in low-pressure separator 118 to yield an excess gas phase 119 and a liquid post-hydrogenation effluent 120. The flow of post-hydrogenation effluent 117 to low-pressure separator 118 may be controlled via valve 121.

[0118] Example 1

[0119] In an industrial hydrogenation plant according to Fig. 1, n-butanal is hydrogenated to n-butanol. The hydrogenation takes place in a hydrogenation system comprising a primary hydrogenation reactor accommodating a bed of a primary hydrogenation catalyst and a post-hydrogenation reactor accommodating a bed of a post-hydrogenation catalyst. The overall reactor throughput across both reactors is 0.2 tons per cubic meter.

[0120] 7,000 kg / h of fresh n-butanal, mixed with recycled effluent from the primary reactor at a recycle ratio of 10, and 200 kg / h of hydrogen are fed into the primary hydrogenation reactor. For 110 kJ / mol reaction enthalpy,241150W001 15

[0121] the temperature of the primary hydrogenation reactor increases adiabatically by 25 °C. The superficial velocity of the hydrogenation feed in the primary hydrogenation reactor is 45 m / h. The reactor diameter of the primary hydrogenation reactor is 1.7 m, wherein the height of the catalyst bed is 13 m. The conversion of the aldehyde to the alcohol is 85% in the primary hydrogenation reactor.

[0122] At start-up of the hydrogenation plant, the post-hydrogenation feed stream consists of the post-cooler stream. After start-up of the plant, the post-cooler stream is mixed with gradually increasing amounts of the pre-cooler stream to obtain the post-hydrogenation feed stream. Towards the end of the catalyst lifetime until the shutdown of the plant, the post-hydrogenation feed stream consists of the pre-cooler stream.

[0123] In the post-hydrogenation reactor, the residual unconverted 15% of the aldehyde are converted to alcohol at an adiabatic temperature increase of 148 °C. The superficial velocity of the post-hydrogenation feed in the post-hydrogenation reactor is 25 m / h. The reactor diameter of the post-hydrogenation reactor is 0.69 m, wherein the height of the catalyst bed is 15 m.

Claims

241150W001 16Claims1. A method for hydrogenating an aldehyde, comprising:a) mixing a recirculated intermediate hydrogenation effluent with fresh aldehyde to obtain a hydrogenation feed stream;b) passing the hydrogenation feed stream over at least one bed of a primary hydrogenation catalyst in the presence of a hydrogen-containing gas to obtain an intermediate hydrogenation effluent; c) passing the intermediate hydrogenation effluent past an intercooler and recirculating the intermediate hydrogenation effluent as the recirculated intermediate hydrogenation effluent to step a);d) withdrawing from the recirculated intermediate hydrogenation effluent a post-cooler stream from a location downstream of the intercooler and withdrawing a pre-cooler stream from a location upstream of the intercooler;e) merging the post-cooler stream and the pre-cooler stream to provide a post-hydrogenation feed stream;f) adjusting a relative proportion between the post-cooler stream and the pre-cooler stream; and g) passing the post-hydrogenation feed stream over at least one bed of a post-hydrogenation catalyst in the presence of a hydrogen-containing gas.

2. Method according to claim 1, comprising adjusting a relative proportion between the post-cooler stream and the pre-cooler stream to adjust the temperature of the post-hydrogenation feed stream to a pre-determined value.

3. Method according to claim 2, wherein the pre-determined value is increased as the activity of the post- hydrogenation catalyst decreases.

4. Method according to claim 2 or 3, wherein adjusting the relative proportion is accomplished via at least one valve.

5. Method according to any one of the preceding claims, comprising retaining the intermediate hydrogenation effluent in a holding zone, withdrawing from the holding zone intermediate hydrogenation effluent to be passed past the intercooler and recirculated as the recirculated intermediate hydrogenation effluent to step a), monitoring a liquid level in the holding zone, and adjusting the flow rate of the post-hydrogenation feed stream based on the monitored liquid level.

6. Method according to any one of the preceding claims, wherein the post-hydrogenation feed stream is passed over the at least one bed of post-hydrogenation catalyst in single-pass mode under essentially adiabatic conditions.241150W001 177. Method according to any one of the preceding claims, wherein the at least one bed of primary hydrogenation catalyst and / or the at least one bed of post-hydrogenation catalyst comprise a nickel - copper-manganese hydrogenation catalyst.

8. Method according to any one of the preceding claims, wherein the at least one bed of primary hydrogenation catalyst and the at least one bed of post-hydrogenation catalyst comprise the same catalyst.

9. A plant for hydrogenating an aldehyde, comprising:I) at least one bed of a primary hydrogenation catalyst;II) means for mixing a recirculated intermediate hydrogenation effluent with fresh aldehyde to obtain a hydrogenation feed stream;ill) means for passing the hydrogenation feed stream over the at least one bed of primary hydrogenation catalyst in the presence of a hydrogen-containing gas;iv) an intercooler and means for passing the intermediate hydrogenation effluent past the intercooler and recirculating the intermediate hydrogenation effluent as the recirculated intermediate hydrogenation effluent to II);v) means for withdrawing from the recirculated intermediate hydrogenation effluent a post-cooler stream from a location downstream of the intercooler and withdrawing a pre-cooler stream from a location upstream of the intercooler;vi) means for merging the post-cooler stream and the pre-cooler stream to provide a post-hydrogenation feed stream;vii) means for adjusting a relative proportion between the post-cooler stream and the pre-cooler stream;viii) at least one bed of a post-hydrogenation catalyst; andlx) means for passing the post-hydrogenation feed stream over the at least one bed of posthydrogenation catalyst in the presence of a hydrogen-containing gas.

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