Process for producing acrolein or products derived therefrom

Abstract

A process for producing acrolein or products derived therefrom comprises the steps of: a) evaporating a C3- alcohol selected from 1-propanol, 2-propanol and mixtures thereof, to obtain a gaseous alcohol stream, b) subjecting the gaseous alcohol stream to dehydration in the presence of a solid dehydration catalyst, to obtain an olefin-containing stream comprising at least propylene and water, and c) subjecting the olefin- containing stream to oxidation with molecular oxygen in the presence of a catalyst for oxidizing propylene to produce acrolein, to obtain an acrolein-containing stream. The process allows for subjecting the dehydration reaction mixture without further purification to the following catalytic oxidation step c) without negatively influencing step c) in terms of catalyst performance and selectivity towards the target reaction product.

Description

[0001] Process for Producing Acrolein or Products Derived Therefrom

[0002] The present invention relates to a process for producing acrolein or products derived therefrom, in particular acrylic acid.

[0003] Acrylic acid is an important starting material in the formation of polymers. Its uses include plastics, coatings, adhesives, elastomers, paints, and polishes. Additionally, acrylic acid is used in the production of hygienic medical products, detergents, and wastewater treatment chemicals. Acrolein can serve as starting material in the industrial synthesis of acrylic acid.

[0004] Typically, propylene is oxidized to acrolein, and the obtained acrolein can be further oxidized in a second step to acrylic acid. Such two-stage processes are known per se and described, for example, in WO 2002 / 081422 A1 and the publications cited therein. In a first step, propylene is oxidized using an oxidant, e.g. air, to produce acrolein by catalytic oxidation. The produced acrolein undergoes a second oxidation step to produce acrylic acid.

[0005] Propylene is typically obtained in industrial amounts by cracking propane, or heavier paraffins or naphthas with steam at high temperature. Cracking is an endothermal process requiring high temperatures of 700 to 900 °C. Such high temperature heating is commonly achieved through natural gas firing which is inherently accompanied by CO2 emissions. Thus, propylene obtained by cracking is associated with CO2 emissions which are unavoidable or at least difficult to avoid or reduce.

[0006] The movement towards environmental sustainability has provided an impetus for the development of manufacturing processes utilizing as much raw material from renewable sources as possible. In times of climate change and significantly increasing energy prices, it is therefore an ongoing task to provide suitable alternative starting materials to propylene for preparing acrolein or acrylic acid. Possible suitable alternative starting materials are Ca-alcohols such as 1 -propanol and 2-propanol. Such Ca-alcohols can be obtained from biomass, e.g., by fermentation.

[0007] One way to achieve increased renewably-sourced carbon content is the development of alternative synthesis routes based on bio-feedstocks. This approach comes with certain drawbacks. In many cases, the synthesis route deviates significantly from the well-established fossil-based manufacturing route. Thus, the existing production facilities cannot be used, but new ones would have to be built which is economically, environmentally, and technically challenging. Moreover, the chemical industry, currently using naphtha and methane as its major carbon sources, would have to change to an economy that is based on a variety of different feedstocks, increasing the complexity of chemical production.The gradual shift from fossil to renewable carbon sources is made easier when well established manufacturing routes can continue to be used to a certain extent.

[0008] WO 2022 / 187291 A1 describes producing acrolein by selectively oxidizing 2-propanol (iso-propanol) over a first mixed metal oxide catalyst comprising oxides of molybdenum and bismuth in the presence of oxygen in the vapor phase. Acrylic acid is produced by selectively oxidizing the acrolein over a second mixed metal oxide catalyst in the presence of oxygen in the vapor phase.

[0009] JP 2015 / 160807 A describes a method for producing acrylic acid comprising (1) a step of obtaining isopropanol by a fermentation method, and (2) a step of heating the isopropanol in the presence of oxygen and partially oxidizing the isopropanol by using a partial oxidation catalyst to obtain acrylic acid or acrolein.

[0010] JP2024084492 A described a method for producing acrolein and acrylic acid including contacting a reaction gas with molecular oxygen in the presence of a catalyst. The reaction gas contains 1 to 10 mol-% of propylene and 0.01 to 8 mol-% of 2-propanol.

[0011] EP 1 090684 A1 describes a catalyst for oxidation reactions, e.g. for the gas phase oxidation of isopropanol to acrolein and of isopropanol to acrylic acid.

[0012] However, the known methods from the prior art that involve a one-step oxidation of C3 alcohols to acrolein have the drawback of low yields towards acrylic acid.

[0013] Dehydration of alcohols to form olefins is one of the oldest catalytic reactions, and numerous oxides are suitable catalysts for this reaction. In the dehydration reaction of an alcohol, a stoichiometric amount of water is generated as a by-product, and other by-products such as ethers or aldehydes may also be formed. Ethers or aldehydes, however, may act as catalyst poisons for down-stream catalytic reactions. While it is of course possible to recover the olefins from the dehydration effluent and purify the olefins to a degree comparable to that of fossil-based olefins, the effort and cost may render the process economically unattractive.

[0014] It is therefore an object of the present invention to provide a process for preparing acrolein or products derived therefrom, e.g. acrylic acid, starting from a suitable alternative starting material, i.e. a starting material other than propylene, which overcomes the mentioned drawbacks, i.e. which allows for obtaining acrolein or products derived therefrom, e.g. acrylic acid, in high yield and selectivity.This object is solved by a process for producing acrolein or products derived therefrom, e.g. acrylic acid, the process comprising the steps of:

[0015] a) evaporating a Ca-alcohol selected from 1 -propanol, 2-propanol and mixtures thereof, to obtain a gaseous alcohol stream,

[0016] b) subjecting the gaseous alcohol stream to dehydration in the presence of a solid dehydration catalyst, to obtain an olefin-containing stream comprising at least propylene and water, and

[0017] c) subjecting the olefin-containing stream to oxidation with molecular oxygen in the presence of a catalyst for oxidizing propylene to produce acrolein, to obtain an acrolein-containing stream.

[0018] A typical product derived from acrolein is acrylic acid.

[0019] The process may further comprise d) subjecting the acrolein-containing stream to oxidation with molecular oxygen in the presence of a catalyst for oxidizing acrolein to produce acrylic acid, to obtain an acrylic acidcontaining stream. In this case, the process is a process for producing acrylic acid.

[0020] Typically, acrylic acid is produced in a two-stage process starting from propylene. The inventive process involves the production of acrylic acid in three consecutive reactions steps, namely a) dehydration of 1 -propanol and / or 2-propanol to obtain propylene, b) catalytic oxidation of the propylene to acrolein, and c) catalytic oxidation of the acrolein to acrylic acid. Thus, a first advantage of the inventive process is that carrying out the inventive process is devoid of excessive investment cost, as existing acrylic acid production sites can be used which solely have to be supplemented by an upstream dehydration reactor.

[0021] It is generally known that dehydrating a Ca-alcohol yields, besides the targeted propylene, quantitative amounts of water, and can yield side products such as aldehydes and ketones (propionaldehyde for 1 -propanol as C3-alcohol, or acetone for 2-propanol as Ca-alcohol) and / or ethers. Such side products would generally be expected to be potential catalyst poisons in the following catalytic oxidation steps c) and d). As a consequence, crude dehydration reaction mixtures would be expected to require purification steps for removing the above-mentioned side products before subjecting a purified dehydration reaction mixture to the following catalytic oxidation steps c) and d) in order to avoid catalyst poisoning.

[0022] It has surprisingly been found that the process of the present invention advantageously allows for subjecting the dehydration reaction mixture as it is, i.e. without further purification, to the following catalytic oxidation step c) or to steps c) and d) without negatively influencing the steps c) and d) in terms of catalyst performance and selectivity towards the target reaction products.241172WC01 4

[0023] Step a)

[0024] Step a) involves evaporating a Cs-alcohol selected from 1 -propanol, 2-propanol and mixtures thereof in any ratios, to obtain a gaseous alcohol stream. Preferably, the Cs-alcohol is 2-propanol.

[0025] The Ca-alcohol used in step a) is preferably a biomass-derived Cs-alcohol. Using biomass-derived Ca-alcohols is advantageous in terms of environmental protection. Herein, biomass-derived Ca-alcohols denote Ca-alcohols purified from an organic compound obtained through a fermentation process with fermentable sugar of biomass, or Ca-alcohols obtained by a process including a catalytic chemical conversion and thermochemical conversion of biomass. Biomass is roughly classified to those derived from resource crops and those derived from waste. Examples of biomass derived from resource crops include edible crops, wood, and grass and flowers, and unutilized portions of these crops can also be used. Examples of biomass derived from waste include food waste, sludge such as sewage, livestock manure, and waste paper.

[0026] In an embodiment, the gaseous alcohol stream comprises a diluent gas. A diluent gas is a gas that is inert under the conditions encountered in the inventive process, in particular does not take part in dehydration of step b), oxidation of step c) and oxidation of step d), and does not give rise to side reactions. Using a gaseous alcohol stream comprising the diluent gas also is favorable due to safety reasons, i.e. for preventing formation of an explosive gas mixture. Preferably, the diluent gas comprises nitrogen. A gaseous alcohol stream comprising nitrogen as the diluent gas may be a mixture of the Cs-alcohol and air. Preferably, a ratio of air to the Cs-alcohol in the gaseous alcohol stream is in the range of 10:1 to 1:10, preferably 5:1 to 1:5, more preferably 3:1 to 1:1 (vol / vol).

[0027] In an embodiment, step a) comprises sparging a gaseous stream comprising diluent gas through liquid C3-alcohol, or injecting liquid Cs-alcohol into a gaseous stream comprising diluent gas, or a combination thereof, to obtain the gaseous alcohol stream.

[0028] Typically, sparging the gaseous stream comprising diluent gas through liquid Cs-alcohol involves providing the Cs-alcohol, e.g. in a reservoir, and introducing the gaseous stream comprising diluent gas into the Cs-alcohol, e.g. via a tube immersed into the Cs-alcohol. The gaseous stream comprising diluent gas and / or the liquid Cs-alcohol in the reservoir may be pre-heated to faciliate loading of the gaseous stream with the Cs-alcohol during the passage of the gaseous stream through liquid Cs-alcohol. For example, a concetration of 25.5 vol.-% may be obtained by setting the saturation temperature to 70 °C for 1-propanol and to 52 °C for 2-propanol, respectively.

[0029] Typically, injecting liquid Cs-alcohol into a gaseous stream comprising diluent gas involves raising the pressure of the liquid Cs-alcohol, e.g. by pump and releasing or ejecting the pressurized liquid Cs-alcohol through a small orifice. By passing the pressurized liquid Cs-alcohol through a small orifice, high hydraulic pressures are inducedand the liquid Ca-alcohol is evaporated. The gaseous stream comprising diluent gas may be pre-heated to faciliate instantaneous evaporation of the injected liquid alcohol.

[0030] The small orifice may be a nozzle. The diameter of the nozzle is not particularly limited. The diameter of the nozzle is selected such that a desired pressure buildup is maintained at a given flow rate. Generally, the nozzle is manufactured from a metal, e.g. brass, stainless steel etc. The surface of the nozzle which is in contact with the pressurized liquid stream may preferably be protected, e.g. coated, in order to avoid or even to prevent abrasion of said surface which would disadvantageously lead to damage or destruction of the nozzle.

[0031] Step b)

[0032] Step b) comprises subjecting the gaseous alcohol stream as obtained in step a) to dehydration in the presence of a solid dehydration catalyst, to obtain an olefin-containing stream comprising at least propylene and water.

[0033] In certain embodiments, further components may be added to the gaseous stream, in particular gases such as oxygen or an oxygen-containing gaseous mixture such as air.

[0034] In an embodiment, the solid dehydration catalyst comprises an acidic solid catalyst, e.g. a Bronsted acidic solid catalyst. The solid dehydration catalyst is preferably selected from alumina, aluminosilicates, aluminophosphate, silica aluminophosphate, zeolite, solid phosphoric acid, zirconia, and mixtures thereof.

[0035] Preferably, the solid dehydration catalyst comprises alumina. The content rate of alumina, based on the total weight of the solid dehydration catalyst, is preferably at least 90 wt.-%, more preferably at least 95 wt.-%, more preferably at least 97 wt.-%, more preferably at least 98 wt.-%, more preferably at least 99 wt.-%, more preferably at least 99.5 wt.-%. The content rate of alumina in the solid dehydration catalyst can suitably be determined by ICP emission spectrometric analysis. ICP emission spectrometric analysis can be performed with, for example, an Optima 8300 ICP-OES Spectrometer (manufactured by Perkin Elmer).

[0036] In case the solid dehydration catalyst contains alumina, the crystal form of alumina is not particularly limited, and various types of alumina, such as a-alumina, p-alumina, y-alumina, cr-alumina, 0-alumina, 6-alumina, alumina hydrate, and combinations thereof, can be used. Preferably, the solid dehydration catalyst comprises Y-alumina due to its generally higher activity.

[0037] The solid dehydration catalyst typically forms a catalyst bed of dehydration catalyst particles. The gaseous alcohol stream is passed through the catalyst bed in step b).

[0038] Preferably, at least 90 wt.-% of the solid dehydration catalyst have a particle size in the range of 700 to 10000 pm, such as 800 to 9500 pm, or 1000 to 9000 pm. The solid dehydration catalyst may be, if necessary,molded, and when the shape of the catalyst is any other shape than a spherical shape, the length in a direction at which the maximum length is observed is defined as the particle size.

[0039] The solid dehydration catalyst may have a BET surface area in the range of 30 to 1000 m2 / g, such as 40 to 800 m2 / g, or 60 to 500 m2 / g or 80 to 300 m2 / g. The BET surface area of the solid dehydration catalyst is a value calculated from an N2 adsorption / desorption isotherm, and can be measured with, for example, TriStar 3000 (manufactured by Shimadzu Corporation).

[0040] The form of the solid dehydration catalyst is not particularly limited. The solid dehydration catalyst may be in the form of a shaped particle such as a sphere, a pill, an extrudate or chips. Preferably, the solid dehydration catalyst is in the form of an extrudate. Extrudates may be in the forms of rings, cylinders, trilobes, quadralobes, and asymmetric quadralobes.

[0041] In an embodiment, the process comprises carrying out step b) at a temperature in the range of 280 to 400 °C, preferably 280 to 350 °C.

[0042] In an embodiment, the process comprises carrying out step b) at an operating pressure in the range of 1 to 10 bara (bar absolute).

[0043] In an embodiment, the process comprises carrying out step b) at a gas residence time in the range of 0.2 to 2 s, based on the volume of the bed of dehydration catalyst (gas hourly space velocity GHSV of 2500 to 20000 IT1).

[0044] In an embodiment, the process comprises carrying out step b) at a propanol conversion in the range of 90 to 100%, preferably 95 to 100%, more preferably 99 to 100%, most preferably 99.5 to 100%, in particular 99.7 to 100%.

[0045] In an embodiment, the process comprises carrying out step b) at a selectivity to propylene in the range of 95 to 100 mol-%, preferably 97 to 100 mol-%, more preferably 98 to 100 mol-%, most preferably 99 to 100 mol-%.

[0046] In an embodiment, the process comprises carrying out step b) at a selectivity to propionaldehyde in the range of 0 to 4 mol-%, preferably 0 to 3 mol-%, more preferably 0 to 2 mol-%, most preferably 0 to 1 mol-%.

[0047] In an embodiment, the process comprises carrying out step b) at a selectivity to acetone in the range of 0 to 2 mol-%, preferably 0 to 1 mol-%, more preferably 0 to 0.5 mol-%, most preferably 0 to 0.2 mol-%.Step c)

[0048] Step c) comprises subjecting the olefin-containing stream to oxidation with molecular oxygen in the presence of a catalyst for oxidizing propylene to produce acrolein, to obtain an acrolein-containing stream.

[0049] The gaseous alcohol stream as obtained in step a) is generally used without prior purification. This does not preclude filter operations to remove solids, e.g., due to catalyst abrasion, from the gaseous stream. Also, components may be added to the gaseous stream, in particular gases such as oxygen or oxygen-containing gaseous mixtures such as air.

[0050] As outlined above, this is both surprising and advantageous: It is generally known that dehydrating a Ca-alcohol yields, besides the targeted propylene, quantitative amounts of water, and can yield side products such as aldehydes (propionaldehyde for 1 -propanol as Cs-alcohol, or acetone for 2-propanol as Ca-alcohol) and / or ethers. Such side products would generally be expected to be potential catalyst poisons in the following catalytic oxidation steps c) and d). As a consequence, crude dehydration reaction mixtures would be expected to require purification steps for removing the above-mentioned side products before subjecting a purified dehydration reaction mixture to the following catalytic oxidation steps c) and d) in order to avoid catalyst poisoning. As outlined above, it has surprisingly been found that the process of the present invention advantageously allows for subjecting the crude dehydration reaction mixtures as it is, i.e. without further purification, to the following catalytic oxidation steps c) and d) without negatively influencing the steps c) and d) in terms of catalyst performance and selectivity towards the target reaction products.

[0051] Step c) involves oxidation with molecular oxygen. Suitably, an external source of molecular oxygen is supplied, such as oxygen, synthetic air and air. Air is particularly preferred.

[0052] In an embodiment, the catalyst for oxidizing propylene to produce acrolein comprises a molybdenum-containing catalyst. The catalyst for oxidizing propylene to produce acrolein may be in the form of a multimetal oxide of molybdenum. Such catalysts are known per se.

[0053] In an embodiment, the multimetal oxide has a stoichiometry of the general formula (I)

[0054] Moi2BiaFebX1cX2dX3eX4fOn

[0055] (I)

[0056] wherein

[0057] X1= nickel and / or cobalt,

[0058] X2= thallium, samarium, an alkali metal and / or an alkaline earth metal,X3= zinc, phosphorus, arsenic, boron, antimony, tin, cerium, lead, vanadium, chromium, niobium and / or tungsten,

[0059] X4= silicon, aluminum, titanium and / or zirconium,

[0060] a = 0.2 to 5,

[0061] b = 0.01 to 5,

[0062] c = 0 to 10,

[0063] d = 0 to 2,

[0064] e = 0 to 8,

[0065] f = 0 to 10, and

[0066] n is a number determined by the valence and frequency of the elements in (I) except oxygen.

[0067] In preferred embodiments, the stoichiometric coefficients are as follows:

[0068] a = 0.4 to 2,

[0069] b = 2 to 4,

[0070] c = 3 to 10,

[0071] d = 0.02 to 2,

[0072] e = 0 to 5, and

[0073] f = 0.5 or 1 to 10.

[0074] X1is preferably cobalt, X2is preferably K, Cs and / or Sr, more preferably K, X3is preferably tungsten, zinc and / or phosphorus, and X4is preferably Si. Particularly preferably, the variables X1to X4simultaneously have the above definitions. It is even more preferred that all stoichiometric coefficients a to f and all variables X1to X4simultaneously have the above-mentioned advantageous definitions.

[0075] In one embodiment, the catalytically active multimetal oxide has a stoichiometry of the general formula (II)

[0076] [Y1a'Y2b,OX']p[Y3c'Y4d,Y5e'Y6f'Y7g'Y8h'Oy']q

[0077] (II)

[0078] wherein

[0079] Y1= only bismuth or bismuth and at least one of the elements tellurium, antimony, tin and copper,

[0080] Y2= molybdenum and / or tungsten,

[0081] Y3= an alkali metal, thallium and / or samarium,

[0082] Y4= an alkaline earth metal, nickel, cobalt, copper, manganese, zinc, tin, cadmium and / or mercury,

[0083] Y5= iron or iron and at least one of the elements vanadium, chromium and cerium,

[0084] Y6= phosphorus, arsenic, boron and / or antimony,

[0085] Y7= a rare earth metal, titanium, zirconium, niobium, tantalum, rhenium, ruthenium, rhodium, silver, gold, aluminum, gallium, indium, silicon, germanium, lead, thorium and / or uranium,Y8= molybdenum and / or tungsten,

[0086] a' = 0.01 to 8,

[0087] b' = 0.1 to 30,

[0088] o' = 0 to 4,

[0089] d' = 0 to 20,

[0090] e' >0 to 20,

[0091] f = 0 to 6,

[0092] g' = 0 to 15,

[0093] h' = 8 to 16,

[0094] x', y' are numbers determined by the valence and frequency of the elements in (II) except oxygen, and p, q are numbers whose p / q ratio is between 0.1 and 10.

[0095] Particularly advantageous catalytically active multimetal oxides of stoichiometry (II) are those in which Y1is only bismuth.

[0096] Catalytically active multimetal oxides of stoichiometry (II) comprise three-dimensional regions of the chemical composition Y1aY2bOx', which are dispersed in a matrix phase of the chemical composition Y3cY4dY5e'Y6fY7g'Y8h'Oy'.

[0097] The production of such catalysts is described in detail in DE 4407020 A1, EP 0575897 A1, DE 3338380 A1 and EP 2 114562 A1.

[0098] Within the stoichiometries of the general formula (II), preference is given to those which correspond to the general formula (Ila)

[0099] [Bia"Z2b"OX"]p"[Z8i2Z3C"Z4d"Fee"Z5rZ6g"Z7h"Oy"]q"

[0100] (Ha)

[0101] wherein

[0102] Z2= molybdenum and / or tungsten,

[0103] Z3= nickel and / or cobalt,

[0104] Z4= thallium, an alkali metal and / or an alkaline earth metal, preferably K, Cs and / or Sr,

[0105] Z5= phosphorus, arsenic, boron, antimony, tin, cerium, vanadium, chromium and / or Bi,

[0106] Z6= silicon, aluminum, titanium and / or zirconium, preferably Si,

[0107] Z7= copper, silver and / or gold,

[0108] Z8= molybdenum and / or tungsten,

[0109] a" = 0.1 to 1,

[0110] b" = 0.2 to 2,c" = 3 to 10,

[0111] d" = 0.02 to 2,

[0112] e" = 0.01 to 5, preferably 0.1 to 3,

[0113] f" = 0 to 5,

[0114] g" = 0 to 10, preferably >0 to 10, more preferably 0.2 to 10 and most preferably 0.4 to 3,

[0115] h" = 0 to 1,

[0116] x", y" are numbers determined by the valence and frequency of the elements in (Ila) except oxygen, and p", q" are numbers whose p" / q" ratio is between 0.1 and 5, preferably between 0.5 and 2.

[0117] Within the catalytically active multimetal oxides of stoichiometry (Ila), preference is given to those in which Z2b" = (tungsten)b" and Z812 = (molybdenum)^.

[0118] The catalyst for oxidizing propylene to produce acrolein may be in the form of, for example, pellets, beads or rings with a through-hole produced by a tableting machine or an extrusion machine. Otherwise, it can be similarly effectively used in a form with catalytic components deposited on a refractory support.

[0119] The catalyst for oxidizing propylene to produce acrolein and its production is described in detail in US 8,232,425 B2, for example.

[0120] In an embodiment, the process comprises carrying out step c) at a temperature in the range of 300 to 450 °C.

[0121] In an embodiment, the process comprises carrying out step c) at an operating pressure in the range of 1 to 10 bara (bar absolute).

[0122] In an embodiment, the process comprises carrying out step c) at a concentration of propylene in the olefin-containing stream in the range of 3 to 9 vol.-%, preferably 4 to 8 vol.-%, most preferably 4.5 to 7.5 vol.-%.

[0123] In an embodiment, the process comprises carrying out step c) at a molar ratio of molecular oxygen to propylene in the olefin-containing stream in the range of 1:1 to 3:1, preferably 1.4:1 to 2.5:1, most preferably 1.5:1 to 2:1.

[0124] In an embodiment, the process comprises carrying out step c) at a gas residence time in the range of 0.5 to 6 s, based on the volume of the bed of catalyst for oxidizing propylene to produce acrolein and the total volumetric gas feed rate at the standard temperature and pressure (STP: 0 °C and 101.325 kPa) (gas hourly space velocity GHSV of 600 to 7200 h1).Step d)

[0125] Step d) comprises subjecting the acrolein-containing stream obtained in step c) to oxidation with molecular oxygen in the presence of a catalyst for oxidizing acrolein to produce acrylic acid, to obtain an acrylic acidcontaining stream.

[0126] Step d) involves oxidation with molecular oxygen. Suitably, an external source of molecular oxygen is supplied, such as oxygen, synthetic air and air. Air is particularly preferred.

[0127] As outlined above, the catalyst for oxidizing acrolein to produce acrylic acid may comprises a molybdenum-containing catalyst. The catalyst for oxidizing acrolein to produce acrylic acid may be in the form of a multimetal oxide of molybdenum. Such catalysts are known per se.

[0128] In one embodiment, the multimetal oxide has a stoichiometry of the general formula (III)

[0129] MOl2VaX1bX2cX3dX4eX5fX6gOn

[0130] (HI)

[0131] wherein

[0132] X1= W, Nb, Ta, Cr and / or Ce,

[0133] X2= Cu, N I, Co, Fe, Mn and / or Zn,

[0134] X3= Sb and / or Bi,

[0135] X4= one or more alkali metals (Li, Na, K, Rb, Cs) and / or H,

[0136] X5= one or more alkaline earth metals (Mg, Ca, Sr, Ba),

[0137] X6= Si, Al, Ti and / or Zr,

[0138] a = 1 to 6,

[0139] b = 0.2 to 4,

[0140] c = 0 to 18, preferably 0.5 to 18,

[0141] d = 0 to 40,

[0142] e = 0 to 2,

[0143] f = 0 to 4,

[0144] g = 0 to 40, and

[0145] n is a number determined by the valence and frequency of the elements in (III) except oxygen.

[0146] Preferably, the variables are to be selected within the specified ranges with the proviso that the molar proportion of the element Mo, based on the total amount of all elements except oxygen in the multimetal oxide material (III), is 20 to 80 mol-%, the molar ratio of Mo contained in the catalytically active multimetal oxide material (III) to V, Mo / V contained in the catalytically active multimetal oxide material (III), is 15:1 to 1:1, and the241172WC01 12

[0147] corresponding molar ratio of Mo / (total amount of W and Nb) is 80:1 to 1 :4 (and the corresponding molar ratio of Mo / Cu is 30:1 to 1:3 when the multimetal oxide material contains Cu).

[0148] Preferred multimetal oxide catalysts (III) are those in which

[0149] X1= W, Nb and / or Cr,

[0150] X2= Cu, Ni, Co and / or Fe,

[0151] X3= Sb,

[0152] X4= Na and / or K,

[0153] X5= Ca, Sr and / or Ba,

[0154] X6= Si, Al and / or Ti,

[0155] a = 2.5 to 5,

[0156] b = 0.5 to 2,

[0157] c = 0.5 to 3,

[0158] d = 0 to 2,

[0159] e = 0 to 0.2,

[0160] f = 0 to 1,

[0161] g = 0 to 15, and

[0162] n is a number determined by the valence and frequency of the elements in (III) except oxygen.

[0163] Preferred multimetal oxide catalysts correspond to the following general stoichiometry (Illa)

[0164] MOl2VaX1bX2cX5fX6gOn

[0165] (Hla)

[0166] wherein

[0167] X1= W and / or Nb,

[0168] X2= Cu and / or Ni,

[0169] X5= Co and / or Sr,

[0170] X6= Si and / or Al,

[0171] a = 3 to 4.5,

[0172] b = 1 to 1.5,

[0173] c = 0.75 to 2.5,

[0174] f = 0 to 0.5,

[0175] g = 0 to 8, and

[0176] n is a number determined by the valence and frequency of the elements in (Illa) except oxygen.

[0177] In (Illa), Mo / Cu is preferably between 30:1 and 1:3, and the corresponding molar ratio Mo / (total amount of W and Nb) is between 80:1 and 1:4.Preferably, the variables within the specified ranges are to be selected with the proviso that the molar proportion of the element Mo, based on the total amount of all elements except oxygen in the catalytically active multimetal oxide material (Illa), is 20 to 80 mol-%, the molar ratio of Mo contained in the catalytically active multimetal oxide material (Illa) to V, Mo / V contained in the catalytically active multimetal oxide material (Illa) is 15:1 to 1:1, the corresponding molar ratio Mo / Cu 30:1 to 1 :3, and the corresponding molar ratio Mo / (total amount of W and Nb) 80:1 to 1 :4.

[0178] The catalyst for oxidizing acrolein to produce acrylic acid may be in the form of, for example, pellets, beads or rings with a through-hole produced by a tableting machine or an extrusion machine. Otherwise, it can be similarly effectively used in a form with catalytic components deposited on a refractory support.

[0179] The catalyst for oxidizing acrolein to produce acrylic acid and its production is described in detail in US 8,232,425 B2, for example.

[0180] In an embodiment, the process comprises carrying out step d) at a temperature in the range of 240 to 360 °C.

[0181] In an embodiment, the process comprises carrying out step d) at an operating pressure in the range of 1 to 10 bara (bar absolute).

[0182] In an embodiment, the process comprises carrying out step d) at a concentration of acrolein in the acrolein-containing stream in the range of 3 to 9 vol-%, preferably 3.5 to 7 vol-%, most preferably 4 to 7 vol-%.

[0183] In an embodiment, the process comprises carrying out step d) at a molar ratio of molecular oxygen to acrolein in the acrolein-containing stream in the range of 0.5:1 to 2:1, preferably 0.7:1 to 1.8:1, most preferably 0.8:1 to 1.5:1.

[0184] In an embodiment, the process comprises carrying out step d) at a gas residence time in the range of 0.5 to 15 s, based on the volume of the bed of catalyst for oxidizing acrolein to produce acrylic acid and the total volumetric gas feed rate at the standard temperature and pressure (STP: 0 °C and 101.325 kPa) (gas hourly space velocity GHSV of 240 to 7200 IT1).

[0185] Further process steps

[0186] Acrolein can be the product of the process described above. In this case, a step of acrolein purification is suitably carried out. Alternatively, products derived from acrolein, in particular acrylic acid, can be the product of the process. In this case, the process is preferably devoid of a step of acrolein purification, and the product derived from acrolein, in particular acrylic acid, can be obtained as described in detail below.The acrolein-containing stream obtained in step c) comprises acrolein, and may further comprise unreacted propylene and / or water and / or the diluent gas and / or side products such as carbon dioxide, carbon monoxide, aldehydes, ethers etc. The recovery of acrolein from the acrolein-containing stream typically involves scrubbing the acrolein-containing stream with water or a water-solvent mixture in a separation device to remove the side products. The resulting stream may then be passed to an absorber, where an aqueous solution of acrolein is obtained by absorbing the gas into cold water. The aqueous acrolein solution is typically sent to a desorption column, where the solution is stripped to give acrolein.

[0187] In case step d) is carried out, an acrylic acid-containing stream is obtained. The acrylic acid-containing stream comprises acrylic acid, and further comprises unreacted propylene and / or unreacted acrolein and / or water and / or the diluent gas and / or side products such as carbon dioxide, carbon monoxide, aldehydes, ethers etc. In an embodiment, the process additionally comprises

[0188] - cooling the acrylic acid-containing stream, to condense condensable constituents out of the acrylic acidcontaining stream, and

[0189] - separating the condensed constituents from gaseous uncondensable constituents.

[0190] Suitably, the acrylic acid-containing stream is cooled to a temperature in the range of 100 to 180 °C.

[0191] Herein, the term „ gaseous uncondensable constituents” denotes any constituents contained in the acrylic acidcontaining stream which are not condensed under the conditions prevailing in the steps of cooling and separating mentioned above. For example, the uncondensable constituents may comprise the diluent gas and carbon oxides. In an embodiment, the process additionally comprises returning a part of the gaseous uncondensable constituents as the diluent gas to step a). Suitably, a part of the gaseous uncondensable constituents is vented and, e.g., directed to incineration (as "purge gas”). Removing a part of the gaseous uncondensable constituents is suitably carried out in order to avoid accumulation of side products such as, e.g., carbon dioxide and carbon monoxide etc. (also known as "purging”), and / or of excess diluent gas such as, e.g., nitrogen if air is added as oxygen-containing gaseous mixture.

[0192] In an embodiment, the process comprises

[0193] - introducing the acrylic acid-containing stream into a column having a plurality of separatory trays, - withdrawing crude acrylic acid from the column via a sidedraw,

[0194] - withdrawing water from the column via a sidedraw, and

[0195] - withdrawing gaseous uncondensable constituents from the top of the column.

[0196] Suitably, the column is a condensation tower. The column may have 75 to 80 separatory trays.Preferably, the acrylic acid-containing stream is introduced into the bottom of the column or as a sidefeed, preferably as a sidefeed. Suitably, the crude acrylic acid is withdrawn from the column at a position located below the position from which the water is withdrawn from the column.

[0197] The water withdrawn from the column typically has a pH value in the range of 1.5 to 4.5, i.e., is acidic water. The acidic water may be subjected to incineration.

[0198] Purification of crude acrylic acid

[0199] In an embodiment, the process additionally comprises purifying the crude acrylic acid by absorption, crystallization, distillation, or a combination thereof.

[0200] Usually, the absorption of acrylic acid takes place in an absorption liquid suitable for the absorption of acrylic acid, such as diphenyl, diphenyl ether, dimethyl phthalate, ethylhexanoic acid, N-methylpyrrolidone, kerosene fractions or mixtures thereof; oligomeric acrylic acids, such as mixtures containing di-, tri- and tetraacrylic acid, or water. For his purpose, the absorption liquid is brought into contact with the crude acrylic acid in an absorption column in countercurrent flow, e.g. after cooling by means of a heat exchanger at a temperature in the range of 100 to 180 °C.

[0201] In an embodiment, the acrylic acid-containing stream obtained in step d) is cooled by means of a quench system. For example, such quench systems are described in US 6,498,272 B1. For this purpose, the hot acrylic acid-containing stream is suitably brought into contact with a quench liquid in a quench vessel to obtain an acrylic acid-containing stream as a mixture of gaseous and liquid components which are fed to absorption columns. The quench liquid can be condensed acrylic acid-containing stream, i.e., condensed acrylic acidcontaining stream can be brought into contact with the hot acrylic acid-containing stream for direct cooling of the hot acrylic acid-containing stream. A part of the condensed acrylic acid-containing stream is removed as a purge from the circulation and can be fed to the absorption columns.

[0202] Suitable absorption columns include packed columns, packed tray columns, valve tray columns or bubble cap columns. The absorption liquid loaded with acrylic acid usually contains volatile impurities such as water, acrolein, formaldehyde, formic acid and / or acetic acid. These can be at least partially removed by stripping with a stripping gas, e.g. nitrogen or air, in a countercurrent desorption column. The acrylic acid is usually recovered by rectificative separation at reduced pressure, e.g. at a pressure in the range of 0.04 to 0.1 bara, e.g. in a packed or tray column. The acrylic acid can be removed as an overhead product or via a sidedraw in the upper section of the desorption column, whereby the absorption liquid is conveniently recycled and reused for absorption. If water is used as the absorption liquid, the acrylic acid is isolated from the aqueous acrylic acid solution by extraction in an extraction column in countercurrent with an extraction agent, such as ethyl acetate, butyl acetate, ethyl acrylate, 2-butanone or mixtures thereof, and subsequent distillation of the extract.The crystallization of the crude acrylic acid not particularly limited. The crystallization can be continuous or discontinuous, be carried out in one or more stages. For example, fractional crystallization may be carried out. In the case of multi-stage process crystallization, after each crystallization stage, the crystals are separated from the mother liquor, and the mother liquor may be subjected another crystallization, or be returned to the condensation tower, if applicable. Suitable crystallization temperatures are in the range of 0 to 15 °C.

[0203] For fractional condensation (distillation), the crude acrylic acid is suitably cooled to 100 to 180 °C and conveniently introduced into the lower section of a column with separating internals. As the gas stream rises within the column, a middle boiling fraction can be removed as a crude acrylic acid fraction via a suitably installed collecting tray.

[0204] Oxygen feeding

[0205] Steps c) and d) require the presence of molecular oxygen for the oxidation reactions to take place. In order to convert propylene as completely as possible to acrylic acid, a sufficient amount of molecular oxygen, i.e. at least 1.5 equivalents of molecular oxygen are needed. Molecular oxygen or a gas mixture containing molecular oxygen may be fed to the gaseous stream at one or more of several points. In an embodiment, the process comprises feeding molecular oxygen to the diluent gas prior to step a), to the gaseous alcohol stream prior to step b) and / or to the olefin-containing stream prior to step c).

[0206] For this purpose, enough molecular oxygen for both oxidation steps (at least two equivalents of molecular oxygen), i.e. for the oxidation of propylene to acrolein and for the oxidation of acrolein to acrylic acid, can be fed to the diluent gas prior to dehydration step a).

[0207] This finding is surprising as it is generally known that adding oxygen to a non-oxidative reaction, i.e. a reaction in which no oxygen is consumed, can result in coking or in the formation of unwanted by-products. Possible byproducts of the inventive process may be aldehydes (propionaldehyde for 1 -propanol as Cs-alcohol, or acetone for 2-propanol as Ca-alcohol) and / or ethers. In other words, it would be expected that a reaction mixture subjected to a dehydration reaction should preferably contain only very small amounts of oxygen or even be essentially free of oxygen. In the context of the present invention, the dehydration step b) does not consume oxygen, whereas the oxidation steps c) and d) do consume oxygen. It has surprisingly been found that the process of the present invention advantageously allows for adding oxygen already in the dehydration step. This is advantageous as the inventive process can be devoid of a dedicated oxygen addition between steps b) and / or c) which reduces plant and operational complexity.

[0208] Additionally or alternatively, according to an embodiment, the process may comprise feeding molecular oxygen to the gaseous alcohol stream prior to step b) and / or to the olefin-containing stream prior to step c), herein alsoreferred to "intermediary molecular oxygen feeding”. In this case(s), (fresh) molecular oxygen is fed to the gaseous alcohol stream and / or to the olefin-containing stream prior to step c) and / or step d), respectively.

[0209] Reactors

[0210] Step b), i.e. the dehydration of the gaseous alcohol stream to obtain the olefin-containing stream, can be carried out in any reactor suitable for gas-phase reactions. For example, step b) is carried out in a dehydration reactor which may be selected from a fixed bed reactor or a fluid bed reactor.

[0211] Suitably, for carrying out step b), a layer of the solid dehydration catalyst is filled into the dehydration reactor, and the gaseous alcohol stream is allowed to pass through the dehydration reactor, thereby performing the dehydration reaction of step b).

[0212] In case a fixed bed reactor or a fluid bed reactor is used, the location of the layer of the solid dehydration catalyst in the reactor, the proportion of the layer of the solid dehydration catalyst in the reactor, and the like are not particularly limited, and any form commonly used can be applied.

[0213] Step c), i.e. the oxidation of the olefin-containing stream to obtain the acrolein-containing stream, can be carried out in any reactor suitable for gas-phase reactions. For example, step c) is carried out in a shell-and-tube reactor. In this case, step c) typically comprises the following steps:

[0214] - providing a shell-and-tube reactor comprising a plurality of reaction tubes, the reaction tubes comprising a bed of the catalyst for oxidizing propylene to produce acrolein,

[0215] - introducing of the olefin-containing stream into the reaction tubes,

[0216] - subjecting the olefin-containing stream to oxidation as outlined in step c),

[0217] - cooling a hot acrolein-containing stream to obtain the acrolein-containing stream, and

[0218] - withdrawing the acrolein-containing stream from the shell-and-tube reactor.

[0219] Step d), i.e. the oxidation of the acrolein-containing stream to obtain the acrylic acid-containing stream, typically comprises the following steps:

[0220] - providing a shell-and-tube reactor comprising a plurality of reaction tubes, the reaction tubes comprising a bed of the catalyst for oxidizing acrolein to produce acrylic acid,

[0221] - introducing of the acrolein-containing stream obtained as described above into the reaction tubes, - subjecting the acrolein-containing stream to oxidation as outlined in step d),

[0222] - cooling a hot acrylic acid-containing stream to obtain the acrylic acid-containing stream, and

[0223] - withdrawing the acrylic acid-containing stream from the shell-and-tube reactor.

[0224] The following embodiments apply for both the shell-and-tube reactor for carrying out step c) and for the shell-and-tube reactor for carrying out step d), unless noted otherwise.The shell-and-tube reactor may be any shel l-and-tube reactor suitable for gas phase oxidations such as a fixed bed tube bundle heat exchange reactor. Conducting the reaction in a fixed bed tube bundle heat exchange reactor allows for uniform heat removal and good heat exchange.

[0225] Typically, such fixed-bed tube bundle heat exchange reactors comprise a reactor shell, usually cylindrical, in which a large number (plurality) of reaction tubes (a tube bundle) are accommodated, usually in a vertical arrangement. Each of these reaction tubes contains a (fixed) bed of the catalyst as outlined above.

[0226] Typically, the reaction tubes have a wall thickness of 1 to 3 mm, an internal diameter of 20 to 30 mm and a tube length of 2 to 4 m. In terms of application technology, the number of reaction tubes may be at least 5000, preferably at least 10000. The number of reaction tubes is frequently 15000 to 35000. The reaction tubes are normally arranged homogeneously distributed within the shell-and-tube reactor, whereby the distribution is suitably selected such that the distance between the centric inner axes of the reaction tubes closest to each other is 35 to 45 mm.

[0227] Furthermore, a heat exchange medium is typically passed through the space surrounding the reaction tubes in order to dissipate the process heat. After leaving the container, the heat exchange medium is brought back to its original temperature, e.g. in external heat exchangers, before it re-enters the reactor. The use of molten salts ("salt bath”) such as potassium nitrate, potassium nitrite, sodium nitrite and / or sodium nitrate, or low-melting-point metals such as sodium, mercury and alloys of various metals is particularly favorable as heat exchange medium.

[0228] As outlined above, the reaction tubes typically comprise a bed of the above-mentioned catalyst. The reaction tubes may comprise, atop of the bed of the catalyst, a top layer of an inert material. The inert material may be a non-porous material. It suitably comprises silicon oxide, aluminum oxide, silicon carbide, zirconium oxide, titanium oxide, germanium oxide, metal silicates, organic polymers, porous metals, or mixtures or combinations thereof. For example, it may comprise a combination of silicon oxide and aluminum oxide.

[0229] Typically, in the shell-and-tube reactor is provided a headspace above the reaction tubes defined by the reactor head, and an upper tubesheet to which the entrance ends of the reaction tubes are attached, and which upper tubesheet is attached at its outer circumference to the reactor shell. Suitably, the entrance ends of the reaction tubes are sealed to the upper tubesheet in a gas-tight manner and open into the headspace. The gas stream flowing through the reaction tubes is fed into the reaction tubes via the headspace, so that each reaction tube or at least a part thereof corresponds to an elongated reaction zone.

[0230] For withdrawing a stream from the shell-and-tube reactor, usually, in the shell-and-tube reactor is provided a bottomspace below the reaction tubes defined by the reactor bottom, and a lower tubesheet to which theentrance ends of the reaction tubes opposite to the entrance ends attached to the upper tubesheet are attached. Suitably, the lower tubesheet is attached at its outer circumference to the reactor shell of the shell-and-tube reactor. Thus, withdrawing a stream from the shell-and-tube reactor typically occurs via withdrawing the stream from the bottomspace of the shell-and-tube reactor.

[0231] In all processing steps, stabilizers and / or polymerization inhibitors for acrylic acid can be added in a manner known per se. A suitable stabilizer is, for example, phenothiazine. Suitable polymerization inhibitors are, for example, hydroquinone, hydroquinone monomethyl ether, p-nitrosophenol, tert-butylphenols or mixtures thereof.

[0232] All system components that come into contact with gaseous streams in the described process are made of materials that are resistant to acetic acid, acrolein or acrylic acid under the prevailing reaction conditions.

[0233] Fig. 1 depicts a schematic illustration of a process for producing acrylic acid according to the invention.

[0234] The invention is further illustrated by the accompanied figure and the examples that follow.

[0235] Fig. 1 depicts a schematic illustration of the inventive process for producing acrylic acid. A reservoir 1 containing a Ca-alcohol 10 is provided. A gaseous stream comprising diluent gas 11 is sparged through the Ca-alcohol 10 via a tube immersed into the Ca-alcohol 10 at a pressure of 1 atm (step a)). To the obtained gaseous stream comprising the Ca-alcohol and diluent gas, oxygen or an oxygen-containing gaseous mixture 12 is added, to obtain a gaseous alcohol stream 13 comprising the Ca-alcohol, diluent gas and oxygen.

[0236] The gaseous alcohol stream 13 is subjected to an electrically heated dehydration reactor 2. In the dehydration reactor 2, the gaseous alcohol stream 13 is dehydrated in the presence of Y-AI2O3 as solid dehydration catalyst (step b)). An olefin-containing stream 14 comprising propylene, water, diluent gas and oxygen is obtained which is subjected to a first shell-and-tube reactor 3.

[0237] In the electrically heated first shell-and-tube reactor 3, the propylene contained in the olefin-containing stream 14 is oxidized with molecular oxygen in the presence of MoBIFeCoK-oxide as catalyst for oxidizing propylene to produce acrolein (step c)). An acrolein-containing stream 15 comprising acrolein, water, diluent gas and oxygen is obtained which is subjected to a second shell-and-tube reactor 4.

[0238] In the electrically heated second shell-and-tube reactor 4, the acrolein contained in the acrolein-containing stream 15 is oxidized with molecular oxygen in the presence of MoVWCuSb-oxide as catalyst for oxidizing acrolein to produce acrylic acid (step d)). An acrylic acid-containing stream 16 is obtained which can be subjected to further purification steps (not shown in Fig. 1).241172WC01 20

[0239] Examples

[0240] Abbreviations

[0241] In the context of the following examples, the following abbreviations were used:

[0242] - 1-PrOH 1 -propanol

[0243] - 2-PrOH 2-propanol

[0244] - C3= propylene

[0245] - ACR acrolein

[0246] - AA acrylic acid

[0247] - PrAI propionaldehyde

[0248] - AcAI acetaldehyde

[0249] - AcOH acetic acid

[0250] Materials

[0251] As solid dehydration catalyst, Y-AI2O3 (AI3992, available from BASF SE) was used.

[0252] As catalyst for oxidizing propylene to produce acrolein, MoBIFeCoK-oxide was used which was prepared based on a procedure described in US 6,881,702 B2 according to the following steps:

[0253] (1) Dissolve 10.59 g of ammonium heptamolybdate in 30 g of distilled water at 60 °C

[0254] (2) Prepare a solution by dissolving 2.24 g of KOH in 1.1 g of distilled water at 20 °C, add 0.033 g of the obtained solution to the solution obtained in (1). Keep the mixed solution at 60 °C

[0255] (3) Dissolve 10.19 g of cobalt nitrate pentahydrate in 7 g of distilled water at 30 °C, then add 5.93 g of iron nitrate nonahydrate to this solution and stir for 30 min at 30 °C. After stirring, keep the solution at 60 °C. (4) Dissolve 1.46 g of bismuth nitrate pentahydrate in 4 g of distilled water at 60 °C, and add mixture into the solution obtained in (3) kept at 60 °C

[0256] (5) Slowly add the resulting 60 °C mixed aqueous solution of Co, Fe, and Bi dropwise over 30 min to the 60 °C solution of (2) while stirring

[0257] (6) After addition of (5) is complete, continue stirring for 15 min while maintaining the temperature at 60 °C, then add 0.95 g of silica gel and continue stirring at 60 °C for additional 15 min

[0258] (7) Place the resulting slurry in an eggplant-shaped flask and dry at 60 °C using an evaporator

[0259] (8) Place the entire dried solid in an alumina crucible and place it in a muffle furnace without covering it. Firing is performed under the following temperature program conditions: 160 °C for 2 h — > 200 °C for 2 h — > 230 °C for 2 h — > 270 °C for 2 h 380 °C for 1 h 430 °C for 1 h 500 °C for 2 h Cool

[0260] Alternatively to step (7), step (7)' can be carried out between steps (6) and (8):

[0261] (7)' Mix 1.5 wt.-% of graphite with the entire amount of dried solid and mix thoroughly in an agate mortarAs catalyst for oxidizing acrolein to produce acrylic acid, MoVWCuSb-oxide was used which was prepared based on a procedure described in WO 2024 / 120861 A1 according to the following steps:

[0262] 171 g of ammonium paratungstate heptahydrate (W content = 70.65 wt.-%) were added to 3000 g of water in a 10 L flask at 95 °C while stirring with a paddle stirrer at 250 rpm. After addition, stirring was continued for 5 min. A clear solution with a temperature of approx. 95 °C and a pH of 6.3 was obtained. Subsequently, 1161 g of ammonium heptamolybdate tetrahydrate (Mo content = 54.3 wt.-%). After addition, stirring was continued for 5 min. A clear solution with a temperature of approx. 95°C and a pH of 6.1 was obtained. Subsequently, 192 g of ammonium metavanadate (V content = 43.56 wt.-%) was added. After addition, stirring was continued for 5 min. An orange solution with a temperature of approx. 95°C and a pH of 6.5 was obtained. Subsequently, 40 g of antimony trioxide (Sb2C>3; Sb content = 83.54 wt.-%) was added. After addition, stirring was continued for 30 min. A black suspension with a temperature of approx. 95°C and a pH of 6.6 was obtained. Subsequently, 131 g copper(ll) acetate monohydrate (Cu(CH3COO)2 ■ H2O; Cu content = 31.8 wt.-%) was added. After addition, stirring was continued for 10 min. A black suspension with a temperature of approx. 95°C and a pH of 6.2 was obtained. The resulting suspension was then fed continuously for approx. 2 h into a Mobile Minor 2000 spray tower with spray head no. F0 A1 (available from GEA Niro, Soeborg, Denmark) using a rotary atomizer at 30000 rpm. Drying was carried out in a hot air flow (9 Nm3 / h) at an inlet temperature of 310 °C and an outlet temperature of 120 °C. A powder was obtained. 1000 g of the powder was fed into a ZS1-80 kneader (available from Coperion Werner & Pfleiderer GmbH & Co. KG; Stuttgart, Germany). The powder was kneaded with 370 g of an aqueous solution of acetic acid (acetic acid content 35 wt.-%) at 15 rpm for 30 min at ambient temperature. The material was then extruded (1 to 10 cm length, 6 mm diameter). The strands were dried in a convection oven for 16 h at 120 °C under lean air flow (5 vol.-% O2 in N2, 300 NL / h). 400 g of the precursor mass removed from the circulating air drying oven was calcined discontinuously in a rotary kiln (analogous to US 9, 149,799 B2). The calcination was carried out under a gas flow of air and nitrogen (total volume of 186 NL / h) with an oxygen content of 2.3 vol.-%. The rotary kiln was heated to 400 °C within the 2 h and kept at this temperature for 1 h. The heating was then switched off and cooled down to ambient temperature while continuing to rotate. The material removed from the rotary kiln was then ground to a finely divided powder in a ZM 200 mill (available from Retsch GmbH, Haan, Germany).

[0263] Methods

[0264] General Procedure 1

[0265] The following examples were carried out in a reactor system consisting of three independently operated fixed bed reactors connected in series as shown in Fig. 1 and as described above. Helium is used as diluent gas (gaseous stream comprising diluent gas 11 in Fig. 1). A mixture of oxygen and nitrogen is use as oxygencontaining gaseous mixture (oxygen-containing gaseous mixture 12 in Fig. 1). The flow conditions are indicated for each dedicated example below.241172WC01 22

[0266] In the context of the following examples, the reactor configurations were as follows:

[0267] A glass tubular reactor (inner diameter 4 mm, length 20 mm) containing the solid dehydration catalyst fixed in the middle of the reactor was used as reactor for b) dehydration of the gaseous alcohol stream. The reactor was vertically set in an electric furnace and heated electrically. Temperatures were monitored by thermocouples outside the reactor. The gas flow line outside the reactor was kept at 90 °C to avoid condensation. The gaseous alcohol stream was flowed from the bottom to the top of the reactor through the catalyst zone.

[0268] A SUS made tubular reactor (inner diameter 10 mm, length 30 mm) containing the catalyst for oxidizing propylene to produce acrolein (MoBIFeCoK-oxide) fixed in the middle of the reactor was used as reactor for c) oxidation of the olefin-containing stream. The reactor was vertically set in an electric furnace and heated electrically. Temperatures were monitored by thermocouples outside and inside the reactor. The olefin-containing stream was flowed from the top to the bottom of the reactor. The connection SUS lines between the reactor for step c) and the reactor for step d) (see below) were maintained at 180 °C to prevent condensation.

[0269] A glass tubular reactor (inner diameter 8 mm, length 20 mm) containing the catalyst bed comprising the mixture of the catalyst for oxidizing acrolein to produce acrylic acid (MoVWCuSb-oxide) and 5 g of SiC fixed in the middle of the reactor was used as reactor for d) oxidation of the acrolein-containing stream. The reactor was vertically set in an electric furnace and heated electrically. Temperatures were monitored by thermocouples outside and inside the reactor. The acrolein-containing stream was flowed from the top to the bottom of the reactor. The connection SUS lines between the reactor for step d) and vent were maintained at 180 °C to prevent condensation.

[0270] Compositions of the olefin-containing stream, the acrolein-containing stream and the acrylic acid-containing stream were determined as follows: A ten-port valve and a six-port valve connected with the reaction gas lines was used for gas sampling of inlet and outlet at 160 °C and the thus sampled gases were injected into three different GC columns:

[0271] - MS-5A, 2 m, 65 °C for O2, N2, and CO, with TCD detector,

[0272] - Gaskuropak 54, 2 m, 90 °C for CO2, C3H6, with TCD detector, and

[0273] - Porapak QS, 1 m, 180 °C for propylene, acetaldehyde, acrolein, propanol, acetic acid, acrylic acid, with FID detector.

[0274] Quantitative analysis was conducted using N2 as the internal standard.

[0275] Example 1 - Influence of temperature on dehydration of 2-propanol

[0276] In Example 1, dehydration temperatures were investigated. For this purpose, a gaseous alcohol stream was obtained as follows: 17.4 mL / min of N2; 2.3 mL / min of O2; 4.3 mL / min of He; 1.2 mL / min of 2-propanol. Thegaseous alcohol stream was subjected to the inventive process as described in General Procedure 1. As solid dehydration catalyst, 0.1 g (0.035 mL) of Y-AI2O3 was used. Different dehydration temperatures were investigated (243 °C, 292 °C, 342 °C). For every temperature, conversion of 2-propanol in the obtained olefin-containing stream was > 99.9% with a selectivity towards propylene of > 99.9%. These results show that under the applied conditions, dehydration temperatures in a broad range are suitable.

[0277] Example 2a - Conversion of 1 -propanol

[0278] In Example 2a, conversion of 1 -propanol at different dehydration temperatures was investigated. For this purpose, a gaseous alcohol stream was obtained as follows: 16.8 mL / min of N2; 2.3 mL / min of O2; 3.5 mL / min of He; 1.2 mL / min of 1-propanol. The gaseous alcohol stream was subjected to the inventive process as described in General Procedure 1. As solid dehydration catalyst, 0.1 g (0.035 mL) of Y-AI2O3 was used. As catalyst for oxidizing propylene to produce acrolein, 1 g (0.63 mL) of MoBiFeCoK-oxide was used. As catalyst for oxidizing acrolein to produce acrylic acid, 0.15 g of MoVWCuSb-oxide mixed with 5 g of SiC (total volume 3.6 mL) was used.able 1. Conversion and selectivity calculated based on respective reaction step.

[0279] Conversion [%] Selectivity [%] Y.hl [%] # Step T [°C] 1-PrOH C3= O2ACR C3= ACR AcAI AA AcOH CO CO2PrAI Ether AA b) 338 100.0 - 1.8 - 97.5 - 0.5 - - 0.2 0.4 1.4 0.0 - 1 c) 351 - 94.5 61.0 - - 86.9 0.9 5.8 0.9 2.1 3.5 - 0.0 - d) 273 - 94.0 83.0 99.7 - - tr t2] 95.9 2.4 0.4 1.2 tr P] 0.0 81.9 b) 328 100.0 - 1.5 - 97.4 - 0.5 - - 0.0 0.3 1.8 0.0 - 2 c) 351 - 95.7 60.2 - - 86.4 0.9 5.8 0.8 2.3 3.7 - 0.0 - d) 273 - 95.4 84.1 99.2 - - tr [2] 95.7 2.6 0.5 1.3 tr Pi 0.0 81.9 b) 319 99.8 - 1.1 - 97.3 - 0.5 - - 0.0 0.2 2.0 0.0 - 3 c) 351 - 95.3 60.8 - - 85.7 1.1 5.8 1.0 2.4 4.0 - 0.0 - d) 273 - 94.0 86.2 98.8 - - tr [2] 95.3 2.8 0.6 1.3 tr P] 0.0 80.0 b) 309 98.8 - 1.7 - 97.1 - 0.4 - - 0.0 0.1 2.4 tr [2] - 4 c) 351 - 94.9 63.0 - - 83.8 1.7 5.7 1.4 3.0 4.5 - tr [2] - d) 273 - 94.2 84.5 98.8 - - tr [2] 94.7 3.9 0.3 1.1 tr P] tr [2] 76.4 b) 299 95.1 - 1.0 - 96.2 - 0.3 - - 0.0 0.1 3.4 tr [2] - 5 c) 351 - 94.8 65.6 - - 78.9 3.1 5.3 2.5 4.3 5.9 - tr [2] - d) 273 - 93.0 89.8 97.9 - - tr [2] 91.2 6.8 0.7 1.3 tr P] tr [2] 65.7

[0280]

[0281] 1] Yield

[0282] 2] tr = small amount formed, no quantitative analysisUnder the conditions of Example 2a, full conversion of 1 -propanol was obtained at dehydration temperatures of > 328 °C. As can be seen from the results shown in Table 1, decreasing dehydration temperatures resulted in increasing amounts of side product acetic acid (AcOH), CO, CO2 and propionaldehyde (PrAI). The results are summarized in Table 1, entries 1 to 5.

[0283] Example 2b - Conversion of 1 -propanol

[0284] In Example 2b, conversion of 1 -propanol at different dehydration temperatures was investigated. For this purpose, a gaseous alcohol stream was obtained as follows: 16.8 mL / min of N2; 2.3 mL / min of O2; 3.5 mL / min of He; 1.2 mL / min of 1-propanol. The gaseous alcohol stream was subjected to the inventive process as described in General Procedure 1. As solid dehydration catalyst, 0.2 g (0.07 mL) of Y-AI2O3 was used. As catalyst for oxidizing propylene to produce acrolein, 1 g (0.63 mL) of MoBIFeCoK-oxide was used. As catalyst for oxidizing acrolein to produce acrylic acid, 0.15 g of MoVWCuSb-oxide mixed with 5 g of SIC (total volume 3.6 mL) was used.able 2. Conversion and selectivity calculated based on respective reaction step.

[0285] Conversion [%] Selectivity [%] Y.hl [%] # Step T [°C] 1-PrOH C3= O2ACR C3= ACR AcAI AA AcOH CO CO2PrAI Ether AA b) 340 100.0 - 5.6 - 95.6 - 1.2 - - 0.0 1.1 2.1 0.0 - 6 c) 351 - 93.2 66.6 - - 84.5 0.8 5.4 1.1 3.2 5.0 - 0.0 - d) 273 - 95.2 78.8 99.3 - - tr t2] 96.9 2.5 0.1 0.6 - 0.0 77.2 b) 330 100.0 - 4.4 - 95.5 - 1.1 - - 0.0 0.8 2.6 0.0 - 7 c) 351 - 94.7 61.6 - - 84.3 0.8 5.6 1.1 3.2 5.0 - 0.0 - d) 273 - 94.3 79.9 98.8 - - tr [2] 96.0 2.6 0.3 1.1 - 0.0 77.4 b) 320 100.0 - 3.4 - 95.8 - 0.9 - - 0.0 0.6 2.8 0.0 - 8 c) 351 - 95.0 62.2 - - 84.1 1.0 5.4 1.2 3.3 5.0 - 0.0 - d) 273 - 93.8 87.6 97.5 - - tr [2] 95.5 2.7 0.3 1.5 - 0.0 76.1 b) 311 100.0 - 2.9 - 95.7 - 0.8 - - 0.0 0.4 3.1 tr [2] - 9 c) 351 - 94.2 63.5 - - 83.2 1.4 5.4 1.4 3.4 5.1 - tr [2] - d) 273 - 93.9 82.9 98.1 - - tr [2] 95.1 3.4 0.4 1.1 - tr [2] 74.9 b) 301 100.0 - 2.7 - 95.1 - 0.6 - - 0.0 0.3 3.9 tr [2] - 10 c) 351 - 94.1 67.8 - - 80.4 2.5 5.0 2.1 4.2 5.8 - tr [2] - d) 273 - 93.6 88.1 96.8 - - tr [2] 93.5 5.4 0.2 1.0 - tr [2] 69.6

[0286]

[0287] 1] Yield

[0288] 2] tr = small amount formed, no quantitative analysisIn contrast to Example 2a, higher amounts of the solid dehydration catalyst were used in Example 2b (0.1 g vs.

[0289] 0.2 g of Y-AI2O3). As can be seen from the results shown in Table 2 (entries 6 to 10), full conversion of 1-propanol was obtained for all dehydration temperatures (301 to 340 °C) in Example 2b showing that increased amounts of the solid dehydration catalyst have a positive impact on conversion of 1 -propanol in step b).

[0290] Example 3a - Conversion of 2-propanol

[0291] In Example 3a, conversion of propylene (comparative example) and conversion of 2-propanol at different dehydration temperatures (inventive examples) was investigated. For the comparative example (see Table 3, entry 11), an olefin-containing stream was obtained as follows: 21.5 mL / min of N2; 2.3 mL / min of O2; 1.2 mL / min of propylene. For the inventive examples, a gaseous alcohol stream was obtained as follows: 16.8 mL / min of N2; 2.3 mL / min of O2; 3.5 mL / min of He; 1.2 mL / min of 2-propanol. The olefin-containing stream of the comparative example was subjected to a process as described in General Procedure 1 without the dehydration step. The gaseous alcohol stream of the inventive exampless was subjected to the process as described in General Procedure 1. As solid dehydration catalyst in the inventive examples, 0.1 g (0.035 mL) of Y-AI2O3 was used. As catalyst for oxidizing propylene to produce acrolein, 1 g (0.63 mL) of MoBiFeCoK-oxide was used (both in the comparative and inventive examples). As catalyst for oxidizing acrolein to produce acrylic acid, 0.15 g of MoVWCuSb-oxide mixed with 5 g of SiC (total volume 3.6 mL) was used (both in the comparative and inventive examples).able 3. Conversion and selectivity calculated based on respective reaction step.

[0292] Conversion [%] Selectivity [%] Yield [%] # Step T [°C] 2-PrOH C3= O2ACR C3= ACR AcAI AA AcOH CO CO2AA c) 350 - 94.5 45.3 - - 88.3 0.6 5.1 0.2 1.9 3.9 - 11*

[0293] d) 266 - - 63.6 99.2 - - tr ni 96.7 1.4 0.6 1.3 84.9 b) 340 100.0 - 0.6 - 99.9 - 0.0 - - 0.0 0.1 - 12 c) 349 - 95.8 54.3 - - 86.9 1.1 5.6 0.6 2.2 3.6 - d) 274 - 95.1 78.9 99.3 - - tr ni 95.7 2.3 0.7 1.3 84.4 b) 330 100.0 - 0.5 - 99.9 - 0.0 - - 0.0 0.1 - 13 c) 349 - 95.8 55.9 - - 87.2 1.0 5.6 0.6 2.2 3.4 - d) 274 - 95.1 76.4 99.2 - - tr ni 96.2 2.2 0.4 1.2 85.0 b) 320 100.0 - 0.2 - 100.0 - 0.0 - - 0.0 0.0 - 14 c) 349 - 95.6 58.9 - - 87.5 1.1 5.5 0.6 2.1 3.2 - d) 274 - 95.5 75.2 99.0 - - tr ni 96.3 2.3 0.2 1.1 85.1 b) 311 100.0 - 0.1 - 100.0 - 0.0 - - 0.0 0.0 - 15 c) 349 - 96.1 56.0 - - 87.5 1.0 5.7 0.5 2.0 3.2 - d) 274 - 95.3 75.9 98.6 - - tr ni 96.3 2.1 0.4 1.2 85.3 b) 301 99.7 - 1.4 - 100.0 - 0.0 - - 0.0 0.0 - 16 c) 349 - 95.3 56.0 - - 87.6 1.0 5.7 0.6 2.0 3.1 - 274 - 94.5 80.1 98.1 - - tr ni 96.1 2.1 0.4 1.4 83.8

[0294]

[0295] d)

[0296] ] tr = small amount formed, no quantitative analysis

[0297] comparative exampleAs can be seen from the results shown in Table 3 (entries 12 to 16), full conversion of 2-propanol was obtained for all dehydration temperatures (301 to 340 °C) in the inventive examples (entries 12 to 16) of Example 3a. Under the conditions of Example 3a, the (unwanted) oxidation side product acetone was not formed. Compared to direct propylene conversion of the comparative example, comparable to equal selectivities (96.x%) towards acrylic acid were obtained in all inventive examples.

[0298] Example 3b - Conversion of 2-propanol

[0299] In Example 3b, conversion of 2-propanol at different dehydration temperatures was investigated. For this purpose, a gaseous alcohol stream was obtained as follows: 16.8 mL / min of N2; 2.3 mL / min of O2; 3.5 mL / min of He; 1.2 mL / min of 2-propanol. The gaseous alcohol stream was subjected to the inventive process as described in General Procedure 1. As solid dehydration catalyst, 0.006 g (0.0086 mL) of Y-AI2O3 was used. As catalyst for oxidizing propylene to produce acrolein, 1 g (0.63 mL) of MoBiFeCoK-oxide was used. As catalyst for oxidizing acrolein to produce acrylic acid, 0.15 g of MoVWCuSb-oxide mixed with 5 g of SiC (total volume 3.6 mL) was used.able 4. Conversion and selectivity calculated based on respective reaction step.

[0300] Conversion [%] Selectivity [%] Yield [%] # Step T [°C] 2-PrOH C3= O2ACR C3= ACR AcAI AA AcOH CO CO2AA b) 327 99.8 - 0.8 - 100.0 - 0.0 - - 0.0 0.0 - 17 c) 351 - 93.7 57.1 - - 85.7 1.2 6.0 0.8 2.4 4.0 - d) 273 - 95.0 76.3 97.5 - - tr ni 95.9 2.4 0.4 1.3 80.4 b) 318 97.8 - 1.9 - 100.0 - 0.0 - - 0.0 0.0 - 18 c) 351 - 96.2 56.3 - - 85.7 1.2 5.9 0.8 2.5 4.0 - d) 273 - 95.0 82.0 96.4 - - tr ni 95.6 2.4 0.5 1.5 79.9 b) 306 97.4 - 0.5 - 100.0 - 0.0 - - 0.0 0.0 - 19 c) 351 - 94.0 58.6 - - 85.4 1.2 5.9 0.9 2.5 4.1 - d) 273 - 95.5 78.1 97.9 - - tr ni 95.9 2.3 0.4 1.3 78.8 b) 297 98.0 - 0.3 - 100.0 - 0.0 - - 0.0 0.0 - 20 c) 351 - 96.6 54.2 - - 85.5 1.1 5.9 0.8 2.5 4.2 - d) 273 - 94.9 81.3 97.0 - - tr ni 95.4 2.4 0.6 1.6 80.5 b) 288 92.8 - 1.9 - 100.0 - 0.0 - - 0.0 0.0 - 21 c) 351 - 95.2 56.1 - - 85.4 1.2 5.9 0.8 2.4 4.2 - d) 273 - 94.7 81.9 96.4 - - tr ni 95.4 2.5 0.6 1.5 74.7

[0301]

[0302] 1] tr = small amount formed, no quantitative analysisIn contrast to Example 3a, lower amounts of the solid dehydration catalyst were used in Example 3b (0.1 g vs.

[0303] 0.006 g of Y-AI2O3). As can be seen from the results shown in Table 4 (entries 17 to 21), under the conditions of Example 3b, partial conversion of 2-propanol was obtained for all dehydration temperatures (288 to 327 °C). In other words, higher amounts of unconverted 2-propanol were obtained at lower amounts of the solid dehydration catalyst.

[0304] List of reference signs

[0305] I Reservoir

[0306] 2 Dehydration reactor

[0307] 3 First shell-and-tube reactor

[0308] 4 Second shell-and-tube reactor

[0309] 10 Ca-alcohol

[0310] I I Gaseous stream comprising diluent gas

[0311] 12 Oxygen or oxygen-containing gaseous mixture

[0312] 13 Gaseous alcohol stream

[0313] 14 Olefin-containing stream

[0314] 15 Acrolein-containing stream

[0315] 16 Acrylic acid-containing stream

Claims

Claims1. A process for producing acrolein or products derived therefrom, the process comprising the steps of:a) evaporating a Ca-alcohol selected from 1 -propanol, 2-propanol and mixtures thereof, to obtain a gaseous alcohol stream,b) subjecting the gaseous alcohol stream to dehydration in the presence of a solid dehydration catalyst, to obtain an olefin-containing stream comprising at least propylene and water, and c) subjecting the olefin-containing stream to oxidation with molecular oxygen in the presence of a catalyst for oxidizing propylene to produce acrolein, to obtain an acrolein-containing stream.

2. The process of claim 1 , further comprising:d) subjecting the acrolein-containing stream to oxidation with molecular oxygen in the presence of a catalyst for oxidizing acrolein to produce acrylic acid, to obtain an acrylic acid-containing stream.

3. The process of claim 1 or 2, wherein the gaseous alcohol stream comprises a diluent gas.

4. The process of claim 3, wherein the diluent gas comprises nitrogen.

5. The process of claim 3 or 4, wherein step a) comprises sparging a gaseous stream comprising diluent gas through liquid Cs-alcohol, or injecting liquid Ca-alcohol into a gaseous stream comprising diluent gas, or a combination thereof, to obtain the gaseous alcohol stream.

6. The process of claim 5, additionally comprising- cooling the acrylic acid-containing stream, to condense condensable constituents out of the acrylic acid-containing stream, and- separating the condensed constituents from gaseous uncondensable constituents.

7. The process of claim 6, additionally comprising returning a part of the gaseous uncondensable constituents as the diluent gas to step a).

8. The process of claim 6 or 7, comprising- introducing the acrylic acid-containing stream into a column having a plurality of separatory trays, - withdrawing crude acrylic acid from the column via a sidedraw,- withdrawing water from the column via a sidedraw, and- withdrawing gaseous uncondensable constituents from the top of the column.

9. The process of claim 8, additionally comprising purifying the crude acrylic acid by absorption, crystallization, distillation, or a combination thereof.

10. The process of any one of the preceding claims, comprising feeding molecular oxygen to the diluent gas prior to step a), to the gaseous alcohol stream prior to step b) and / or to the olefin-containing stream prior to step c).

11. The process of any one of the preceding claims, wherein the solid dehydration catalyst comprises an acidic solid catalyst, preferably selected from alumina, aluminosilicates, aluminophosphate, silica aluminophosphate, zeolite, solid phosphoric acid, zirconia, and mixtures thereof.

12. The process of any one of the preceding claims, wherein the catalyst for oxidizing propylene to produce acrolein and / or the catalyst for oxidizing acrolein to produce acrylic acid comprises a molybdenum-containing catalyst.

13. The process of any one of the preceding claims, comprising carrying out step b) at a temperature in the range of 280 to 400 °C.

14. The process of any one of the preceding claims, comprising carrying out step c) at a temperature in the range of 300 to 450 °C.

15. The process of any one of claims 2 to 14, comprising carrying out step d) at a temperature in the range of 240 to 360 °C.

Images