DE102008038273A1 - Producing acrylic acid, useful as superabsorbent, comprises dehydrating glycerol in presence of dehydration catalysts to obtain gaseous acrolein phase and oxidizing acrolein in presence of oxidation catalyst to gaseous acrylic acid phase - Google Patents

Abstract

Producing acrylic acid from glycerol comprises (a) dehydrating glycerol to acrolein in the gas phase in a dehydration unit in the presence of dehydration catalysts to obtain a gaseous acrolein phase and (b) oxidizing the acrolein in an oxidation unit (9) in the presence of oxidation catalysts to obtain a gaseous acrylic acid phase. The dehydration unit includes two catalyst portion separated from each other and having different catalyst activity. The first catalyst portion catalyzes the dehydration of glycerol to the formation of acrolein, while the second catalysis portion is regenerated. Independent claims are included for: (1) a device for producing acrylic acid from glycerol, comprising (A) an evaporation unit (1) including at least an evaporator, (B) a dehydration unit containing (B1) at least one dehydration reactor and (B2) at least one regenerator, where both the dehydration reactor and the regenerator include a dehydration catalyst, (C) an oxidation unit comprising at least an oxidation reactor that includes an oxidation catalyst, (D) optionally a condensing unit (15) containing at least a capacitor that is located between the dehydration unit (B) and the oxidation unit (C) and (E) optionally an analysis device (7) for the determination of glycerol-turnover in the dehydration unit (B); and (2) use of a Riser-Downer-reactor system in the conversion of glycerol to acrolein.

Description

The The present invention relates to a process for the preparation of Acrylic acid from glycerin, a device for the production of acrylic acid from glycerol, purified acrylic acid, an acrylic acid based polymer, acrylic ester and the use of a riser-downer reactor system.

The Preparation of acrolein, acrylic acid and the derivatives derived therefrom Compounds such as butyl acrylate or crosslinked acrylic acid polymers, which can be used as a superabsorbent takes place so far exclusively on an industrial scale based on propene as raw material. Recently Published various ways, these products of glycerin manufacture.

In DE-A-42 38 493 For example, routes for the production of acrolein from glycerin over acidic catalysts are shown via the gas phase and via the liquid phase, wherein the acid strength, expressed as Hammett's acid function, must be less than +2. However, the synthesis of acrylic acid or derivatives thereof is not described.

In WO-A-2006/087083 and in WO-A-2006/087084 discloses processes for producing acrolein from glycerol in the gas phase to acidic catalysts. WO 2006/114506 describes a process that depicts the possibility of producing acrylic acid from glycerine.

In the publication WO-A-2007/013296 Nippon Shokubai describes a gas-phase process in which crystalline metal silicates are used as a catalyst with a ratio of silicon to metal of less than or equal to 800 for the conversion of glycerol to acrolein. However, the synthesis of acrylic acid or derivatives thereof is not described.

The Chinese official journal CN-A-101070276 describes the use of zeolites with a silicon to aluminum ratio of 5: 1 to 500: 1 and a pore size greater than 3 angstroms. However, the synthesis of acrylic acid or derivatives thereof is not described.

One general problem in the synthesis of acrolein from aqueous Glycerol solutions through the gas phase is the applied Evaporation energy. At high glycerol concentrations could so far no sufficiently high yields of acrylic acid achieved so that in the conventional methods of production Glycerol solutions diluted in acrylic acid from glycerol were used. Especially with dilute glycerol solutions However, it is a comparatively high water evaporation capacity to provide. Another problem with the synthesis of acrolein from glycerol is that those catalysts which enable effective conversion of glycerine to acrolein, tend to deactivate quickly through the formation of coke, this deactivation being correlated with glycerol levels.

So will in WO-A-2006/087083 described that the coke formation and thus the formation of aromatic secondary components can be minimized by the supply of oxygen. A statement on the long-term stability of the catalyst is still not made and the maximum glycerol concentration in the in the WO-A-2006/087083 described method is given as 50 wt .-%.

Of the Present invention was based on the object resulting from the State of the art resulting disadvantages in connection with the production of acrylic acid from glycerin overcome.

moreover There was a task in it, even with the use of starting materials with high glycerol concentrations a industrially usable To create procedures.

Especially the present invention was based on the object, a method to provide for the production of acrylic acid from glycerol, which characterized by a very high acrylic acid yield is. In addition, the energy needs of this process should be be as low as possible.

• a) Dehydratisierung von Glycerin zu Acrolein in der Gasphase in einer Dehydratisierungseinheit in Gegenwart von Dehydratisierungskatalysatoren unter Erhalt einer vorzugsweise gasförmigen Acroleinphase;
• b) Oxidation des Acroleins in einer Oxidationseinheit in Gegenwart von Oxidationskatalysatoren unter Erhalt einer gasförmigen Acrylsäurephase;

wobei

• – die Dehydratisierungseinheit eine erste Katalysatorteilmenge KT₁ und mindestens eine weitere, von der ersten Katalysatorteilmenge KT₁ räumlich getrennt vorliegende Katalysatorteilmenge KT₂ aufweist, die sich hinsichtlich ihrer spezifischen Katalysatoraktivität unterscheiden,
• – wobei der Katalysator der ersten Katalysatorteilmenge KT₁ die Dehydratisierung von Glycerin unter Bildung von Acrolein katalysiert, während der Katalysator der mindestens einen weiteren Katalysatorteilmenge KT₂ regeneriert wird.

A contribution to the solution of the abovementioned objects is provided by a process for the production of acrylic acid from glycerol, comprising the process steps:

• a) dehydration of glycerol to acrolein in the gas phase in a dehydration unit in the presence of dehydration catalysts to obtain a preferably gaseous acrolein phase;
• b) oxidation of the acrolein in an oxidation unit in the presence of oxidation catalysts to obtain a gaseous acrylic acid phase;

in which

• The dehydration unit has a first partial catalyst fraction KT ₁ and at least one further partial catalytic converter KT ₂ present in a spatially separated form from the first partial catalytic converter KT ₁ , which differ with respect to their specific catalyst activity,
• Wherein the catalyst of the first catalyst portion KT ₁ catalyzes the dehydration of glycerol to form acrolein, while the catalyst of the at least one further catalyst portion KT _{2 is} regenerated.

Surprisingly, but not min advantageous, it has been found that the yield of acrylic acid in the production of acrylic acid from glycerol can be improved even when using highly concentrated, aqueous glycerol solutions vis-à-vis the processes known from the prior art, in which during the dehydration of a at least partially spent catalyst is changed to an at least partially unused catalyst. If the at least partially spent catalyst is regenerated during the time interval in which the at least partially unconsumed catalyst is used, the service lives of the catalysts used for the production of the catalyst can be used despite the use of highly concentrated glycerol solutions and the associated rapid deactivation of the dehydration catalyst Acrylic acid from glycerol used device are kept comparatively short.

in the Process step a) of the process according to the invention for the production of acrylic acid from glycerol is glycerol in the gas phase in a dehydration unit to obtain a preferably gaseous acrolein phase dehydrated to acrolein, this dehydration of the glycerol is preferably at least partially in the gas phase. In this context it is Particularly preferred that the gas phase by the evaporation of a obtained in aqueous form glycerol phase is obtained.

Preferably is therefore in process step a) one in aqueous form present glycerol used, which initially in a suitable evaporation unit is evaporated. The obtained, vaporous glycerol phase then becomes the dehydration unit fed. In this connection, it is particularly preferred that the glycerol concentration in the aqueous glycerol phase preferably more than 30% by weight, more preferably more than 40 Wt .-%, moreover more than 50 wt .-%, above even more preferably more than 60% by weight, and most preferably more than 70 wt .-%, each based on the total weight of the aqueous Glycerol phase, is.

When aqueous glycerol phase are preferably those aqueous glycerin compositions used in the production of liquid fuels from natural Incurred in raw materials, for example in the production of biodiesel.

Farther it is preferred that the dehydration in the gas phase according to process step a) preferably at a temperature in the range between 200 ° C and 400 ° C, more preferably between 240 and 360 ° C and most preferably between 270 and 320 ° C.

The Dehydration in process step a) takes place in the presence of Dehydration catalysts, which the dehydration of Glycerol catalyze to obtain acrolein.

Suitable dehydration catalysts are both acidic and alkaline catalysts. Acid catalysts are particularly preferred because of the low tendency to oligomer formation. The dehydration catalyst can be used both as a homogeneous and as a heterogeneous catalyst, wherein the use of heterogeneous catalysts is particularly preferred. When the dehydration catalyst is a heterogeneous catalyst, it is preferred that the dehydration catalyst be supported by a carrier x. in contact. As a carrier x. all suitable to the expert appear suitable solids into consideration. In this context, it is preferred that these solids have suitable pore volumes which are suitable for good binding and absorption of the dehydration catalyst. In addition, total pore volumes are after DIN 66133 in a range of 0.01 to 3 ml / g, and more preferably in a range of 0.1 to 1.5 ml / g. In addition, it is preferred that the carrier x. suitable solids have a surface area in a range of 0.001 to 1000 m ² / g, preferably in a range of 0.005 to 450 m ² / g and moreover preferably in a range of 0.01 to 300 m ² / g according to BET test according to DIN 66131 exhibit. The carrier for the dehydration catalyst may on the one hand be a bulk material comprising at least 50% by weight, more preferably at least 75% by weight and most preferably at least 90% by weight, of particles having an average particle diameter in the range of 0 1 to 60 mm, preferably in a range of 1 to 50 mm and moreover preferably in a range of 1.5 to 10 mm. Further, the wall of the dehydration reactor may serve as a carrier. Furthermore, the carrier per se may be acidic or basic, or an acidic or basic dehydration catalyst may be applied to an inert carrier. In particular, dipping or impregnating or incorporation into a carrier matrix may be mentioned as application techniques.

Suitable carriers x., Which may also have dehydration catalyst properties, are in particular natural or synthetic silicatic substances, in particular mordenite, montmorillonite, acidic zeolites; With mono-, di- or polybasic inorganic acids, in particular phosphoric acid, or acidic salts of inorganic acids occupied carriers, such as oxidic or silicate substances. Particular preference is given to catalysts which contain oxygen-containing Al, Zr, Ti, Si, S, P or W compounds, heteropolyacids of silicon, of molybdenum, of tungsten and of phosphorus or mixtures thereof. As concrete examples are, in particular Al ₂ O _3, TiO _2, ZrO _2, with Ca, Y or Yb-stabilized ZrO _2, H ₃ called PMO ₁₂ O ₄₀ or H ₄ SiW ₁₂ O _40th

It corresponds to an embodiment according to the invention, that the carrier x. at least partially made of an oxide Connection exists. Such oxidic compounds should be at least one of the elements of Si, Ti, Zr, Al, P or a combination of have at least two of them. Such carriers can also by their acidic or basic properties as dehydration catalyst Act. A preferred both as a carrier as x. as well as include a class of compounds acting as a dehydration catalyst Silicon, aluminum, phosphorus oxides. Preferred basic both as Dehydration catalyst as well as a carrier x. acting Substances include alkali, alkaline earth, lanthanum, lanthanides or a Combination of at least two of them in their oxidic form. such acidic or basic dehydration catalysts are both in Degussa AG as well as Südchemie AG commercial available. Another class is ion exchangers These can also be in both basic and in acidic form.

In addition, it is preferred that in process step a) of the process according to the invention a dehydration catalyst having an H ₀ value in a range from -3 to -8.2 is used. The H ₀ value corresponds to the acid function according to Hammett and can be determined by the so-called amine tritium and the use of indicators or by absorption of a gaseous base - see "Studies in Surface Science and Catalytic", Volume 51, 1989: "New Solid Acids and Gases, their Catalytic Properties", K Tannabe et al. Further details on the production of acrolein from glycerol are still available DE 42 38 493 C1 refer to.

Very particularly preferred catalysts according to the invention which catalyze the dehydration of glycerol to form acrolein include Al ₂ O ₃ , ZrO ₂ , TiO ₂ , SiO ₂ or mixtures thereof, these systems being able to be crystalline or amorphous. The crystalline systems also include natural and synthetic zeolites. These catalysts can also contain phosphorus, as is the case with zeolites of the APO or SAPO type. Furthermore, tungsten oxide and heteropolyacids, such as tungsten silicic acid, are very particularly preferred. The same applies to combinations thereof, such as WO ₃ with ZrO ₂ , WO ₃ with TiO ₂ or aluminum silicate with WO ₃ . These catalyst systems can be mixed with other metals that promote regeneration. For this precious metals such as Pt or Pd are suitable, but also Hopcalite systems containing, for example, Cu and Mn. Furthermore, the catalysts may contain promoters such as V, Cu, Zn, La, Mg, Ca, Sr, Ba, Ce or Y and their oxides.

in principle For example, dehydration can be carried out in all reactor types known to those skilled in the art with fixed-bed reactors, moving-bed reactors, fluidized bed reactors, transport reactors, such as riser-downer reactor systems or fluidized bed reactors are particularly preferred.

in the Process step b) of the process according to the invention is the acrolein in an oxidation unit to obtain a oxidized gaseous acrylic acid phase, wherein the gaseous acrolein phase immediately to the oxidation unit can be supplied.

According to one preferred embodiment of the invention Process is from the obtained in step a), gaseous Acroleinphase at least part of the glycerol separated, wherein This separation is preferably carried out by that in the process step a) obtained gaseous acrolein first at least partially condensed. At least partial condensation the gaseous acrolein phase is preferably an aqueous Glycerol phase and one enriched in acrolein, obtained gaseous acrolein phase, the latter then the process step b) is supplied.

The separated glycerol can be recycled to process step a) become. If the separation is carried out by the above-described partial condensation, Thus, the aqueous glycerol phase the process step a) are supplied. This can be done by that the aqueous glycerol phase obtained in the partial condensation immediately returned to the process step a) becomes. It is also conceivable, however, before the return this aqueous glycerol phase in the process step a) at least part of the in this aqueous glycerol phase possibly still contained acrolein by means of distillation Separation process to obtain a glycerol-enriched, separate aqueous glycerol phase and then enriched this, aqueous glycerol phase in the process step a).

For the condensation described above, a condensation device is preferably used, which at a pressure of 0.5 to 15 bar and a temperature in the range of 80 to 300 ° C., more preferably at a pressure of 1 to 5 bar and a temperature of 100 to 250 ° C is operated. The said pressures and temperatures are adjusted in a conventional manner, for example by pressure control valves, front or rear switched compressor, or by suitable heating or cooling devices, for example by heating or cooling jackets.

The oxidation of the acrolein in process step b) is preferably carried out in the form of a gas phase oxidation in the presence of one or more oxidation catalysts which have transition metals in elemental or in chemically bonded form or both. In the case of the oxidation catalysts, it is preferred that these include at least one of molybdenum, tungsten, vanadium, antimony, copper or a combination of at least two of them in at least partially oxidized form. Such oxidation catalysts are preferably used as heterogeneous catalysts with a carrier y. used in contact. It is preferred that the oxidation catalysts in this carrier y. are incorporated. As a suitable carrier y. basically come in connection with the carriers x. cited compounds, silicon oxide, alumina or aluminum-silicon oxide based supports being particularly preferred. Such oxidation catalysts are described in detail in the literature. This is exemplified DE-A-26 26 887 . EP-A-0 534 294 as well as on US-A-2002/0198406 directed. Such oxidation catalysts for the conversion of acrolein to acrylic acid are commercially available, for example, from Mitsubishi Corp., Japan.

• – der im Verfahrensschritt a) erhaltenen, gasförmigen Acroleinphase bzw. der angereicherten, gasförmigen Acroleinphase vor ihrem Eintritt in die Oxidationseinheit, oder
• – unmittelbar der Oxidationseinheit, oder
• – der im Verfahrensschritt a) erhaltenen, gasförmigen Acroleinphase bzw. der angereicherten, gasförmigen Acroleinphase vor ihrem Eintritt in die Oxidationseinheit und unmittelbar der Oxidationseinheit

Furthermore, the oxidation of the acrolein in process step b) takes place in the presence of oxygen, so that

• The gaseous acrolein phase obtained in process step a) or the enriched gaseous acrolein phase before it enters the oxidation unit, or
• - directly to the oxidation unit, or
• - The gaseous acrolein phase or the enriched, gaseous acrolein phase obtained in process step a) before it enters the oxidation unit and immediately the oxidation unit

oxygen or an oxygen-containing gas mixture, for example air, is supplied.

The Gas phase oxidation is preferred in a temperature range of 200 to 400 ° C, preferably in a range of 250 to 350 ° C and more preferably in one range from 280 to 340 ° C performed.

• – weist die Dehydratisierungseinheit eine erste Katalysatorteilmenge KT₁ und mindestens eine weitere, von der ersten Katalysatorteilmenge KT₁ räumlich getrennt vorliegende Katalysatorteilmenge KT₂ auf, die sich hinsichtlich ihrer spezifischen Katalysatoraktivität unterscheiden,
• – wobei der Katalysator der ersten Katalysatorteilmenge KT₁ die Dehydratisierung von Glycerin unter Bildung von Acrolein katalysiert, während der Katalysator der mindestens einen weiteren Katalysatorteilmenge KT₂ regeneriert wird.

According to the method of the invention

• The dehydration unit has a first catalyst subset KT ₁ and at least one further partial catalyst fraction KT ₂ which is spatially separated from the first catalyst subset KT ₁ and which differ with regard to their specific catalyst activity,
• Wherein the catalyst of the first catalyst portion KT ₁ catalyzes the dehydration of glycerol to form acrolein, while the catalyst of the at least one further catalyst portion KT _{2 is} regenerated.

Under the "specific activity" of a catalyst is preferably the catalyst activity according to the invention in grams of product (acrolein) per hour and gram of catalyst (without substrate content in non-catalytically active substrate) understood.

The Regeneration of the catalyst can take place under oxidative conditions, for example, by introducing oxygen-containing gas such as air, or under reductive conditions, for example by the Incorporation of hydrogen-containing gas, take place. In both cases can regeneration in a water vapor-containing atmosphere respectively. Also, it can be beneficial in both cases to dilute the reductively or oxidatively acting gas by nitrogen, which is particularly favorable at the beginning of a regeneration, to minimize the onset of exothermic regeneration. It is in the case of oxidative regeneration with oxygen in particular preferred if at the beginning of the regeneration less than 10% by volume Oxygen, balance nitrogen, more preferably less than 5 vol% oxygen, balance nitrogen and most preferably less be used as 2% by volume of oxygen, balance nitrogen. In the event of a reductive regeneration with hydrogen, it is preferable if at the beginning of regeneration less than 10% by volume of hydrogen, Balance nitrogen, more preferably less than 5% hydrogen by volume, Nitrogen and most preferably less than 2% hydrogen by volume, Rest of nitrogen can be used. The temperature should be during the regeneration preferably at least 300 ° C, even more preferably at least 350 ° C, wherein a temperature of 600 ° C, more preferably not exceeded by 550 ° C. should be. Basically, the regeneration in Normal pressure to be carried out.

The fact that the catalyst of the first partial catalyst amount KT ₁ catalyzes the dehydration of glycerol to form acrolein while the catalyst is regenerated of the at least one further partial catalyst amount KT ₂ can be realized in different ways.

According to a first particular embodiment of the method according to the invention, the dehydration unit comprises a first dehydration reactor and at least one further dehydration reactor, wherein the first catalyst portion KT ₁ in the first dehydration reactor and the at least one further Ka Kys ₂ KT ₂ in the at least one further dehydration reactor is located. First, the dehydration takes place in the first dehydration reactor, wherein the specific activity of the catalyst of the first partial catalyst amount KT ₁ decreases steadily. As soon as the value of the specific catalyst activity of the catalyst of the first catalyst subset KT ₁ has fallen below a certain value, the system switches over to the at least one further dehydration reactor. The term "is switched to the at least one further dehydration reactor" means that now the glycerol is at least partially, preferably completely, introduced into the at least one further dehydration reactor, so that now the catalyst of the partial catalyst KT ₂ the dehydration of glycerol to form Acrolein catalyzes. Preferably, at the same time now the catalyst of the first partial catalyst amount KT _{1 is} regenerated. If the value of the specific catalyst activity of the catalyst of the at least one further catalyst partial amount KT ₂ has fallen below a certain value, from the at least one further dehydration reactor to the first dehydration reactor (or, if more than two dehydration reactors are used, of the at least one further dehydration reactor switched to another, further dehydration reactor), wherein now the catalyst of the first dehydration reactor or the other, further dehydration reactor catalyses the reaction of glycerol to acrolein, while the catalyst of the further dehydration reactor is regenerated. In principle, it should be noted at this point that the regeneration of the catalyst of the first partial catalyst amount KT ₁ or of the second partial catalytic converter amount KT _{2 can} also take place outside the dehydration unit.

at according to this first particular embodiment used the method according to the invention Dehydration reactors may be at least in particular two fluidized bed reactors or at least two fixed bed reactors act. It is also conceivable that the first dehydration reactor a fluidized bed reactor and the at least one further dehydration reactor is a fixed bed reactor.

According to a second particular embodiment of the method according to the invention, the dehydration unit comprises a so-called "riser-downer reactor system". This reactor system is distinguished from conventional circulating fluidized beds by an increased solids concentration in the reaction space and by a high circulation rate of the solid. The reactor system consists of two separate reaction spaces (the reactor and the regenerator) through which the catalyst solid circulates in a cycle. At the bottom of the upflow, the reactant phase is fed to the reactor, which vaporizes on contact with the hot catalyst and, together with the catalyst solid, flows vertically upwards through an inert gas stream and reacts at the catalyst surface. Here, the catalyst (corresponding to the catalyst of the first partial catalyst amount KT ₁ ) is deactivated so that it loses activity. Via a stripper at the top of the plant, the deactivated catalyst passes into the regenerator, which is usually carried out as a bubbling fluidized bed. There are deposits (coke) burned on the catalyst (which now corresponds to the catalyst of the catalyst portion KT ₂ ). The regenerated catalyst is then transported back into the riser. Since the desired conversion of glycerol to acrolein takes place in the riser, it is referred to as a reactor. In the regenerator, as the name expresses, the deactivated catalyst is regenerated. In contrast to the first particular embodiment, therefore, takes place in the second particular embodiment, a continuous transport of the catalyst, which is associated with its regeneration or its inactivation.

If the dehydration in fluidized bed reactors or in riser-downer reactor systems, it is particularly preferred that in process step a) powdered catalysts or powdery, catalyst-coated support materials for the catalysts of the catalyst portion KT ₁ and the catalyst portion KT ₂ are used, wherein the Particle size of these powdered catalysts or these powdery, catalyst-coated support materials in the case of the use of fluidized bed reactors or riser-downer reactor systems preferably between 5 and 500 .mu.m, more preferably between 50 and 300 microns.

If, on the other hand, the dehydration is carried out in fixed bed reactors, for example in tube bundle reactors, it is particularly preferred that in process step a) shaped catalysts be used as catalysts of catalyst partial amount KT ₁ and catalyst partial amount KT ₂ , these shaped catalysts preferably being at least 50% by weight. , even more preferably at least 75% by weight and most preferably at least 90% by weight of particles having a particle size in a range of 0.5 and 60 mm, more preferably between 1 and 50 mm. The catalysts may be in the form of spheres, tablets, extrudates, ring extrudates, granules or other shaped catalyst bodies known to the person skilled in the art.

• i) dass die spezifische katalytische Aktivität des Katalysators der ersten Katalysatorteilmenge KT₁ bei seinem erstmaligen Kontakt mit dem Glycerin den Wert AKT₁₍₀₎ und die spezifische katalytische Aktivität des Katalysators der mindestens einen weiteren Katalysatorteilmenge KT₂ bei seinem erstmaligen Kontakt mit dem Glycerin den Wert AKT₂₍₀₎ aufweist; und
• ii) dass zunächst der Katalysator der ersten Katalysatorteilmenge KT₁ die Dehydratisierung von Glycerin unter Bildung von Acrolein solange katalysiert, bis die spezifische Aktivität des Katalysators der ersten Katalysatorteilmenge KT₁ auf 90% oder weniger des Wertes AKT₁₍₀₎ abgefallen ist; und
• iii) dass sodann der Katalysator der mindestens einen weiteren Katalysatorteilmenge KT₂ die Dehydratisierung von Glycerin unter Bildung von Acrolein katalysiert, während der Katalysator der ersten Katalysatorteilmenge KT₁ regeneriert wird; und
• iv) dass der Katalysator der mindestens einen weiteren Katalysatorteilmenge KT₂ solange regeneriert wird, bis spezifische Aktivität des Katalysators der mindestens einen weiteren Katalysatorteilmenge KT₂ auf mindestens 90%, vorzugsweise auf mindestens 95%, noch mehr bevorzugt auf mindestens 97%, noch mehr bevorzugt auf mindestens 99% und am meisten bevorzugt auf 100% des Wertes AKT₂₍₀₎ angestiegen ist.

Furthermore, it is preferred according to the invention

• i) that the specific catalytic activity of the Catalyst of the first partial catalyst amount KT ₁ at its first contact with the glycerol the value AKT _{1 (0)} and the specific catalytic activity of the catalyst of the at least one further catalyst portion KT ₂ at its first contact with the glycerol value AKT _{2 (0)} ; and
• ii) firstly the catalyst of the first partial catalyst fraction KT ₁ catalyzes the dehydration of glycerol to form acrolein until the specific activity of the catalyst of the first partial catalyst fraction KT _{1 has} fallen to 90% or less of the value of AKT _{1 (0)} ; and
• iii) that then the catalyst of the at least one further catalyst portion KT ₂ catalyzes the dehydration of glycerol to form acrolein, while the catalyst of the first partial catalyst amount KT _{1 is} regenerated; and
• iv) that the catalyst of the at least one further catalyst portion KT _{2 is} regenerated until specific activity of the catalyst of the at least one further catalyst portion KT ₂ to at least 90%, preferably at least 95%, more preferably at least 97%, even more preferably has risen to at least 99% and most preferably to 100% of the AKT _{2 (0)} value.

In one embodiment of the present invention, the catalysts of the partial catalyst amount KT ₁ and the catalyst partial amount KT _{2 have} a specific catalyst activity AKT _{1 (0)} or AKT _{2 (0)} of at least 30 g of acrolein per hour and gram of catalyst, more preferably of at least 80 g Acrolein per hour and gram of catalyst, and most preferably at least 250 grams of acrolein per hour and gram of catalyst. Depending on the catalyst, a maximum, specific catalyst activity of up to 400 g of acrolein per hour per gram of catalyst may possibly be achieved.

It is further preferred in this context, that the time interval At = t ₂ - t ₁ between the time t _2, at which the change of the catalyst subsets according to iii), and the time t _1, at the specific activity of the catalyst of the first catalyst subset KT _{1 has} fallen to the limits given under ii), preferably less than 60 minutes, more preferably less than 30 minutes, more preferably less than 15 minutes, and most preferably less than 1 minute. Preferably, Δt approaches zero in order to achieve continuous operation.

• c) Aufreinigung der Acrylsäure aus der gasförmigen Acrylsäurephase.

According to a particular embodiment of the method according to the invention, this further comprises the method step

• c) purification of the acrylic acid from the gaseous acrylic acid phase.

• c1) in Kontakt bringen der gasförmigen Acrylsäurephase mit einem Quenchmittel unter Erhalt einer Acrylsäure aufweisenden Quenchphase;
• c2) Aufarbeiten der Quenchphase unter Erhalt einer Acrylsäure beinhaltenden Monomerphase.

Preferably, this purification of the gaseous acrylic acid phase comprises the process steps

• c1) contacting the gaseous acrylic acid phase with a quenching agent to obtain an acrylic acid-containing quenching phase;
• c2) working up the quench phase to obtain a monomer phase containing acrylic acid.

there it is particularly preferred that as a quenching agent in the process step c1) water or an organic compound with a boiling point in a range of 50 to 250 ° C, preferably in one Range of 70 to 180 ° C and beyond preferred in a range of 105 to 150 ° C or water and these be used organic compound. As such organic In particular aromatics and beyond come in connection preferably alkylated aromatics into consideration. Usually is the quench with the monomer gas in a suitable column, preferably in countercurrent, brought into contact.

It is particularly preferred in this context that the quenching phase the acrylic acid in an amount in a range of 30 to 90 wt .-%, preferably in a range of 35 to 85 wt .-%, and moreover, preferably in a range of 45 to 75 % By weight, based in each case on the quench phase. Farther it is preferred that the working up of the quenching phase at temperatures below the boiling point of acrylic acid. A appropriate measure is that the quenching phase by using a correspondingly cold quenching agent already has a temperature of less than 40 ° C. The tempered quench phase can then be an extraction or crystallization or both Workup according to process step c2) supplied with temperatures preferably in the range of -40 to + 40 ° C, preferably in a range of -20 to + 39 ° C, and more preferably within a range of -10 to + 35 ° C.

In process step c2), the quench phase is then worked up. In the event that the quenching agent to at least 50 wt .-%, preferably at least 70 wt .-%, consists of water, it is preferred that the charged with acrylic acid aqueous quenching agent in a further step with a release agent, preferably not with Water is well soluble, is worked up. The acrylic acid-rich phase is subjected to either a distillation or a crystallization or both, preferably first a crystallization. The crystallization can be used both as a layer and as a suspension sion crystallization can be carried out. Suitable layer crystallization devices are commercially available from Sulzer AG. Suitable suspension crystallization processes usually make use of a crystal generator followed by a wash column. Such devices and methods are commercially available from Niro Prozesstechnologie BV. As extraction / release agent is in particular an aromatic compound, moreover preferably an alkylaromatic and further preferably toluene into consideration. Should an organic compound be used as a release agent, this acrylic acid-loaded organic compound may also be subjected to both distillation and crystallization or a combination of both. A suitable crystallization is in EP-A-1 015 410 disclosed.

• d) Veresterung der aufgereinigten Acrylsäure unter Erhalt eines Acrylsäureesters

umfassen, wobei diese Veresterung vorzugsweise durch Umsetzung der Acrylsäure mit geeigneten Alkoholen, beispielsweise mit Methanol oder Ethanol, in Gegenwart geeigneter Veresterungskatalysatoren erfolgt.Also, in connection with the particular embodiment of the process according to the invention described above, in which the acrylic acid is purified from the gaseous acrylic acid phase, it may also be preferred that the process according to the invention also comprises the process step

• d) esterification of the purified acrylic acid to obtain an acrylic ester

This esterification is preferably carried out by reacting the acrylic acid with suitable alcohols, for example with methanol or ethanol, in the presence of suitable esterification catalysts.

• e) Polymerisation der aufgereinigten Acrylsäure unter Erhalt eines auf Acrylsäure basierenden Polymers oder des Acrylsäureesters unter Erhalt eines auf Acrylsäureestern basierenden Polymers

umfasst.Furthermore, in connection with the particular embodiment of the process according to the invention described above, in which the acrylic acid is purified from the gaseous acrylic acid phase, it may also be preferred that the process according to the invention further comprises the process step of

• e) Polymerization of the purified acrylic acid to obtain an acrylic acid-based polymer or the acrylic ester to give an acrylic acid ester-based polymer

includes.

In the case of the polymerization of the purified acrylic acid, it is preferably carried out in the form of an aqueous solution polymerization or an emulsion or suspension polymerization, in which the acrylic acid is preferably polymerized in free-radically preferably neutralized form in the presence of crosslinked to give a polymer gel. The polymer gel thus obtained is then, if it has been obtained by solution polymerization, comminuted and then dried. In this way, water-absorbing polymer structures are obtained, which are particularly suitable as superabsorbent for use in hygiene articles, such as diapers. Further details for the preparation of such water-absorbing polymer structures by free-radical polymerization of acrylic acid may include the 3rd chapter in "Modern Superabsorbent Polymer Technology", FL Buchholz and AT Graham (Editor), Wiley-VCH, New York, 1998 , are taken.

• (β1) eine Verdampfungseinheit umfassend mindestens einen Verdampfer;
• (β2) eine Dehydratisierungseinheit, beinhaltend
• (β2a) mindestens einen Dehydratisierungsreaktor und
• (β2b) mindestens einen Regenerator, wobei der mindestens eine Dehydratisierungsreaktor (β2a) und der mindestens eine Regenerator (β2b) jeweils einen Dehydratisierungskatalysa tor beinhalten, welcher die Dehydratisierung von Glycerin unter Erhalt von Acrolein katalysiert,
• (β3) eine Oxidationseinheit umfassend mindestens einen Oxidationsreaktor beinhaltend einen Oxidationskatalysator, welcher die Oxidation von Acrolein unter Erhalt von Acrylsäure katalysiert;
• (β4) gegebenenfalls eine zwischen der Dehydratisierungseinheit (β2) und der Oxidationseinheit (β3) angebrachte Kondensationseinheit, beinhaltend mindestens einen Kondensator;
• (β5) gegebenenfalls eine Analysevorrichtung zur Ermittlung des Glycerin-Umsatzes in der Dehydratisierungseinheit (β2).

A contribution to the solution of the abovementioned objects is also provided by a device for the production of acrylic acid from glycerol, comprising as device components

• (β1) an evaporation unit comprising at least one evaporator;
• (β2) a dehydration unit containing
• (β2a) at least one dehydration reactor and
• (β2b) at least one regenerator, wherein the at least one dehydration reactor (β2a) and the at least one regenerator (β2b) each contain a dehydration catalyst which catalyzes the dehydration of glycerol to give acrolein,
• (β3) an oxidation unit comprising at least one oxidation reactor including an oxidation catalyst which catalyzes the oxidation of acrolein to obtain acrylic acid;
• (β4) optionally, a condensation unit disposed between the dehydration unit (β2) and the oxidation unit (β3), including at least one condenser;
• (β5) optionally an analysis device for determining the glycerol conversion in the dehydration unit (β2).

As vaporization unit (β1), it is possible to use all vaporization devices known to those skilled in the art, which are suitable for converting a preferably aqueous glycerol phase at least partially into a vaporous glycerol phase, examples of a suitable vaporization apparatus being a falling film or short path evaporator. This evaporation unit (β1) preferably comprises at least one feed line for an aqueous glycerol phase and at least one discharge for a gaseous glycerol phase. If appropriate, the feed line for an aqueous glycerol phase can be connected to a fat splitting unit which is still upstream of the evaporation unit. In such a splitting unit animal fats, which are obtained for example in the carcass utilization, or vegetable fats, which are obtained in large quantities in oil extraction from oil crops such as rapeseed, soy, sesame, olives and sunflower seeds, cleaved to form glycerol, said glycerol in Form of aqueous glycerol solutions is retained. Large amounts of glycerol are particularly in the production of so-called "Bio diesel "from rapeseed oil, such as the WO-A-2004/029016 can be seen.

The dehydration unit (β2) according to a first particular embodiment of the device according to the invention comprises a first dehydration reactor (β2a) and at least one further dehydration reactor (β2b), each containing a catalyst which inhibits the dehydration of glycerol to give. Acrolein catalyzes. In this case, both the first dehydration reactor (β2a) and the at least one further dehydration reactor (β2b) each comprise a feed line for the gaseous glycerol phase and a discharge for a gaseous acrolein phase. The catalyst present in the first dehydration reactor (β2a) corresponds to the catalyst of the partial catalyst amount KT ₁ and the catalyst present in the at least one further dehydration reactor (β2b) corresponds to the catalyst of the partial catalyst amount KT ₂ in the sense of the process according to the invention described above. The dehydration reactors belonging to this first particular embodiment of the dehydration unit (β2) thus function as a reactor (β2a) as well as a regenerator (β2b), depending on the time. In this first particular embodiment of the device according to the invention, the dehydration reactors (β2a) and (β2b) are preferably reactors selected from the group consisting of fixed bed reactors, such as tube bundle reactors, moving bed reactors, fluidized bed reactors and fluidized bed reactors.

falls the specific activity of the catalyst in the one Dehydration reactor in which just the dehydration reaction takes place at a certain value (as determined by, for example the determination of the glycerol concentration in the gaseous Acroleinphase by means of the analyzer (β5), so is in this first particular embodiment of the device according to the invention changed to the other dehydration reactor. Includes the device advantageously comprises control units (β6a and β6b), by means of the control unit (β6a) the glycerol feed to the dehydration reactor from the first the at least one further dehydration reactor and by means the control unit (β6b) the supply of gaseous Acrolein phase in the oxidation unit from the first to the at least another dehydration reactor can be switched.

According to a second particular embodiment of the device according to the invention, the dehydration unit (β2) comprises a riser-downer reactor system which consists of two separate reaction spaces (the reactor (β2a) and the regenerator (β2a)), through which the catalyst solid in one Circulation circulates. The dehydration catalyst present in the reactor at any time t _x corresponds to the catalyst of the partial catalyst amount KT ₁ and the catalyst present in the regenerator at the same time corresponds to the catalyst of the partial catalyst fraction KT ₂ in the sense of the process according to the invention described above. In contrast to the first particular embodiment of the process according to the invention, the reactor of the riser-downer reactor system functions exclusively as a reactor (β2a) and the regenerator of the riser-downer reactor system exclusively as a regenerator (β2b).

Farther it is in connection with the invention Preferred device that the dehydration unit (β2) a feed line for the gaseous glycerol phase and a derivative for a gaseous acrolein phase includes, wherein the supply line for the gaseous Glycerinphase preferably fluid-conducting with the derivative for a gaseous glycerol phase of the evaporation unit (β1) and the derivative for a gaseous acrolein phase preferably fluid-conductively connected to the oxidation unit (β3) is.

When Oxidation Reactors in the oxidation unit (β3) come all reactors, which for the gas phase oxidation of acrolein can be used to form acrylic acid. In this context, preference is given to tube bundle reactors or plate reactors containing a coolant, preferably a molten salt, to be cooled. These tube bundles or plate reactors take on the side facing away from the coolant Page on a suitable catalyst. This can for one as Powder fill are present and the other can the surfaces of the tubes or plates with the catalyst be coated. Preferably, the oxidation reactor respectively a feed line for a gaseous acrolein phase or an enriched gaseous acrolein phase, which fluid conducting with the discharge for a gaseous Acrolein phase of the dehydration unit (β2) or fluid-conducting with the derivative for an enriched, gaseous Glycerin phase of the evaporation unit (β1) is connected.

When Dehydration catalyst in the dehydration unit (β2) and as an oxidation catalyst in the oxidation unit (β3) Preferably, those catalysts are used, which already initially in connection with the invention Process for the preparation of acrylic acid from glycerol as preferred catalysts have been mentioned.

Optionally, in the device according to the invention a condensation unit (β4), be containing at least one condenser, between the dehydration unit (β2) and the oxidation unit (β3). In this condensation unit (β4), the gaseous acrolein phase obtained in the dehydration unit (β2) may be at least partially condensed before it enters the oxidation unit (β3) to form an aqueous glycerol phase and an enriched gaseous acrolein phase. All capacitors which are known to those skilled in the art can be used as capacitors which are suitable for separating off at least part of the glycerol from the gaseous acrolein phase obtained in the dehydration unit (β2) by condensation. Preferably, such a condenser has a cooling device, for example in the form of a cooling jacket, with the aid of which the gaseous acrolein phase can be at least partially cooled and thus condensed. Furthermore, the condensation unit (β4) preferably also has a feed line for a gaseous acrolein phase which is fluidically connected to the outlet for a gaseous acrolein phase of the dehydration unit (β2), a first discharge for a liquid glycerol phase and a second discharge for an enriched, gaseous acrolein phase , which is fluid-conductively connected to the supply line for a gaseous acrolein phase of the oxidation unit (β3). The derivative for a liquid glycerol phase, in turn, may advantageously be fluidly connected to the vaporization unit (β1) or directly to the dehydration unit (β2) to recycle the unreacted glycerol into the process. It is also conceivable to connect the discharge for a liquid glycerol phase with a further purification unit (β7), which is, for example, a distillation apparatus, so that this liquid glycerol phase can be fed to such a distillation apparatus. The distillation device (β7) preferably has at least one aqueous glycerin phase lead, acrolein-depleted aqueous glycerol phase lead, and a vapor phase acrolein derivative lead, the acrolein-depleted aqueous glycerin phase lead advantageously comprising the vaporization unit (β1) or is directly connected to the dehydration unit (β2). Furthermore, the device according to the invention optionally has an analysis device (β4) for determining the glycerol conversion in the dehydration unit (β2). This is particularly the case when, according to the first particular embodiment of the device according to the invention, the dehydration unit (β2) comprises a first dehydration reactor (β2a) and at least one further dehydration reactor (β2b) each containing a catalyst which inhibits the dehydration of glycerol Obtained acrolein catalysis

• A) innerhalb des Reaktors (β2a) der Dehydratisierungseinheit (β2);
• B) am Auslass für eine gasförmige Acroleinphase der Dehydratisierungseinheit (β2);
• C) am Einlass für eine gasförmige Acroleinphase der gegebenenfalls vorhandenen Kondensationseinheit (β4);
• D) innerhalb der Kondensationseinheit (β4);
• E) am Auslass für eine angereicherte, gasförmige Acroleinphase der Kondensationseinheit (β4);
• F) am Auslass für eine wässrige Glycerinphase der Kondensationseinheit (β4);
• G) am Einlass für eine gasförmige Acroleinphase der Oxidationseinheit (β3).

In this case, the analysis device is preferably arranged so that it allows the determination of the glycerol concentration at at least one of the following points of the device according to the invention:

• A) within the reactor (β2a) of the dehydration unit (β2);
• B) at the outlet for a gaseous acrolein phase of the dehydration unit (β2);
• C) at the inlet for a gaseous acrolein phase of the optional condensation unit (β4);
• D) within the condensation unit (β4);
• E) at the outlet for an enriched gaseous acrolein phase of the condensation unit (β4);
• F) at the outlet for an aqueous glycerol phase of the condensation unit (β4);
• G) at the inlet for a gaseous acrolein phase of the oxidation unit (β3).

From Alternative B) is particularly preferred for these alternatives.

at the analyzer (β4) may be any analyzer which is suitable, directly or indirectly, the concentration to glycerol in the streams, which in the above Points A) to G) incurred to determine. In this case, the analysis device directly suitable for determining the concentration of glycerol. However, it is also conceivable, for example, an analysis device which, for example, the determination of the acrolein concentration allows. From the glycerol concentration or the acrolein concentration In turn, conclusions about the specific activity of the dehydration catalysts to be pulled. If this decreases, the concentration of glycerol decreases in the streams, which at the above points A) to G) accumulate, while the concentration of acrolein decreases accordingly.

at the analyzer (β4) is preferably a separating device for separating the components, which in the at the points A) to G) arising streams are included, followed by a detection device for identification the separated components. As a separation device, for example a mass spectrometer, a gas chromatograph or a HPLC system be used while as a detection device, for example IR spectrometer or UV spectrometer can be used.

• (β8) eine Aufreinigungseinheit zur Aufreinigung der Acrylsäure aus der gasförmigen Acrylsäurephase

auf, wobei diese Aufreinigungseinheit vorzugsweise eine Quenchvorrichtung, eine Destillationsvorrichtung, eine Extraktionsvorrichtung, eine Kristallisationsvorrichtung oder eine Kombination aus mindestens zwei dieser Vorrichtungen umfasst. Als Quenchvorrichtung werden vorzugsweise die bei der bisherigen großtechnischen Gasphasenoxidation von Acrolein zu Acrylsäure gängigen Typen bevorzugt eingesetzt. Derartige Quenchvorrichtungen sind als Kolonnen oder Türme ausgebildet und können genauso wie die Reaktoren beispielsweise von der Deggendorfer Werft GmbH kommerziell erworben werden. Auch als Destillations-, Extraktions- und Kristallisationsvorrichtungen kommen vorzugsweise eben falls diejenigen Vorrichtungen in Betracht, die dem Fachmann aus der großtechnischen, über die Gasphasenoxidation von Acrolein laufenden Acrylsäuresynthese bekannten sind.According to a particular embodiment of the device according to the invention, this has as a further device component

• (β8) a purification unit for purifying the acrylic acid from the gaseous acrylic acid phase

This purification unit preferably comprises a quenching device, a distillation device, an extraction device, a crystallization device or a combination of at least two of these devices. As quenching apparatus, the types commonly used in the previous large-scale gas-phase oxidation of acrolein to acrylic acid are preferably used. Such quenching devices are designed as columns or towers and, like the reactors, can be purchased commercially, for example, from Deggendorfer Werft GmbH. Also as distillation, extraction and crystallization devices are preferably just if those devices into consideration, which are known to those skilled in the large-scale, on the gas phase oxidation of acrolein ongoing acrylic acid synthesis.

• (β9) eine Polymerisationseinheit zur Polymerisation der aufgereinigten Acrylsäure

auf, welche im Falle der Herstellung von wasserabsorbierenden Polymergebilden (Superabsorbern) vorzugsweise Polymerisationsreaktoren, Zerkleinerungsvorrichtungen, Trocknungsvorrichtungen, Mischvorrichtungen oder Kombinationen aus mindestens zwei davon umfasst. Als Polymerisationsreaktoren sind zum einen diskontinuierlich arbeitende Rührkessel und zum anderen kontinuierlich arbeitende Systeme, wie Bandpolymerisationsvorrichtungen, Extruder und dergleichen geeignet. Auf diese Polymerisationsreaktoren folgt eine Zerkleinerung und Trocknung. Der so erhaltene Superabsorberprecursor kann weiterhin einer Oberflächen- oder Nachvernetzung unterzogen werden. Hierzu finden sich nähere Angaben in dem eingangs erwähnten Werk von Graham & Buchholz. Wenn es sich bei den Polymeren um vernetzte, teilneutralisierte Polyacrylate handelt, so wird hinsichtlich der genauen Vorgehensweise wiederum auf das 3. Kapitel (Seite 69 ff) in „Modern Superabsorben Polymer Technology”, F. L. Buchholz und A. T. Graham (Herausgeber) in, Wiley-VCH, New York, 1998 verwiesen, das einen Teil dieser Offenbarung bildet.According to another, special embodiment of the device according to the invention, this has, in addition to the purification unit (β8), as a further device component

• (β9) a polymerization unit for polymerization of the purified acrylic acid

which, in the case of the production of water-absorbing polymer structures (superabsorbers), preferably comprises polymerization reactors, comminution devices, drying devices, mixing devices or combinations of at least two thereof. Suitable polymerization reactors are, on the one hand, discontinuously operating stirred tanks and, on the other hand, continuously operating systems, such as belt polymerization devices, extruders and the like. These polymerization reactors are followed by comminution and drying. The superabsorbent precursor thus obtained can be further subjected to surface or postcrosslinking. For details please refer to the aforementioned work by Graham & Buchholz. When the polymers are cross-linked, partially neutralized polyacrylates, the exact procedure is again referred to 3rd chapter (page 69 ff) in "Modern Superabsorbent Polymer Technology", FL Buchholz and AT Graham (editors) in, Wiley-VCH, New York, 1998 which forms part of this disclosure.

• (β10) eine Veresterungseinheit zur Veresterung der aufgereinigten Acrylsäure

auf.According to yet another, special embodiment of the device according to the invention, this, in addition to the purification unit (β8), as a further device component

• (β10) an esterification unit for esterifying the purified acrylic acid

on.

a Contribute to the solution of the above-mentioned tasks also a process for the production of acrylic acid from glycerol, in which the device described above is used. Another contribution to the solution of the aforementioned A purified acrylic acid, available by the above-described processes for the preparation of Acrylic acid from glycerol, which preferably additionally comprise process step c), an acrylic acid or Acrylic acid ester based polymer, available by the above-described processes for the preparation of Acrylic acid from glycerol, which preferably additionally the method steps c) and e) or c), d) and e) include and Acrylic esters obtainable by the above described method for the production of acrylic acid from glycerol, which preferably additionally the process steps c) and d).

a Contribute to the solution of the above-mentioned tasks also the use of a riser-downer reactor system in the implementation of Glycerol to acrolein. Preferably, in this reaction of Glycerol to acrolein one in aqueous form Glycerol phase used, which is preferably more than 30 wt .-%, still more preferably more than 40% by weight, moreover preferred more than 50% by weight, moreover more preferable more than 60% by weight, and most preferably more than 70% by weight, in each case based on the total weight of the aqueous glycerol phase, Contains glycerol. This aqueous glycerin phase is either in the riser-downer reactor system or before entry at least partially evaporated in the riser-downer reactor system. The acrolein formed in the riser-downer reactor system may be mentioned below reacted in a suitable oxidation unit to acrylic acid be, as in the context of the invention Process for the preparation of acrylic acid from glycerol described.

a Contribute to the solution of the above-mentioned tasks also a process for the production of acrylic acid from glycerin by dehydration of the glycerol to form acrolein and subsequent oxidation of the acrolein to form Acrylic acid, wherein the dehydration of glycerol at least partially in a riser-downer reactor system.

The The invention will now be described by way of non-limiting drawings and examples explained in more detail.

1 1 schematically shows a sequence of a preferred embodiment of the method according to the invention, in which the dehydration unit comprises a first dehydration reactor and at least one further dehydration reactor, each containing a catalyst, which catalyzes the dehydration of glycerol to give acrolein.

2 schematically shows a sequence of a particular embodiment of in 1 shown, preferred embodiment of the method according to the invention, in which the gaseous acrolein phase, which is obtained in the dehydration unit, is first partially condensed before it is fed to the oxidation unit.

3 Figure 3 shows schematically a flow of another preferred embodiment of the process of the invention wherein the dehydration unit comprises a riser-downer reactor system.

In 1 is a glycerol-containing educt phase, which may be, for example, an aqueous glycerol solution (glycerol / water), via a feed line 2 in an evaporator 1 brought in. If this glycerol solution additionally has to be diluted with water in order to have an optimum glycerol content, the evaporator can also have a further supply line for water (not shown). This applies in particular when glycerol according to the 3 is returned to the evaporator. About a derivation 3 a gaseous glycerol phase first enters the dehydration reactor 5a in which there is a dehydration catalyst. In the dehydration reactor 5a the glycerol is dehydrated in the gaseous phase to form acrolein, via the derivative 6 a gaseous acrolein phase exits, which then the oxidation unit 9 is supplied. In the oxidation unit 9 the acrolein is oxidized in the presence of oxygen to acrylic acid, wherein the oxygen, for example in the form of air, via the supply line 10 into the oxidation unit 9 can be introduced.

By means of the analysis device 7 is, for example, via the determination of the glycerol concentration in the gaseous acrolein phase, which from the dehydration reactor 5a the drop in the specific activity of the catalyst in the dehydration reactor 5a tracked. When the specific activity has dropped to a certain value, so are the control units 8a and 8b the material flows changed so that now in the evaporation unit 1 gaseous glycerol phase obtained in the second dehydration reactor 5b is introduced and in the second dehydration reactor 5b gaseous acrolein phase of the oxidation unit obtained 9 is supplied.

Now catalyzes in the second dehydration reactor 5b Dehydration catalyst, the reaction of glycerol to acrolein.

While in the dehydration reactor 5b dehydration catalyst catalyzes the conversion of glycerol to acrolein, which is in the dehydration reactor 5a Regenerated present dehydration catalyst, this regeneration is carried out by the fact that via the supply line 4 Oxygen (in the case of an oxidative regeneration) or hydrogen (in the case of a reductive regeneration) contained gas through the dehydration reactor 5a is directed. Is the specific activity of the second dehydration reactor 5b located catalyst to a certain value and the catalyst in the first dehydration reactor 5a sufficiently regenerated, so are the control units 8a and 8b the material flows are rearranged, leaving mm on the catalyst in the first dehydration reactor 5a again catalyzes the dehydration of glycerol to acrolein, while the catalyst of the second dehydration reactor 5b is regenerated.

Of course Instead of two, you can also use three or even more dehydration reactors can be used, which are successively set for dehydration become. Also, for each dehydration reactor own evaporation device can be used (not shown).

The in the oxidation unit 9 about the derivative 11 discharged gaseous acrylic acid phase can a purification unit 12 be supplied. Out of this is about the derivative 13 a purified acrylic acid phase, which is then a polymerization unit 14 can be supplied.

2 schematically shows a sequence of a particular embodiment of the above-described embodiment of the method according to the invention. In this particular embodiment, the in the dehydration reactor 5a respectively. 5b gaseous acrolein phase obtained in a condensation unit 15 at least partially condensed to give an aqueous glycerol phase and an enriched gaseous acrolein phase. The aqueous glycerol phase can via the derivative 16 after evaporation in the evaporation unit 1 again the dehydration reactor 5a or 5b be supplied. The enriched gaseous acrolein phase becomes the oxidation unit 9 fed.

3 schematically shows a schematic sequence of another preferred embodiment of the method according to the invention, in which the dehydration unit comprises a riser-downer reactor system. This is the in the evaporation unit 1 obtained gaseous glycerol phase the reactor 5a fed to the riser-downer reactor system. There flows the gaseous Glycerol phase together with the in the reactor 5a driven dehydration catalyst, driven by an inert gas stream, vertically upward, wherein the glycerol is converted under the action of the catalyst to acrolein. The resulting gaseous acrolein phase passes over the outlet 6 into the oxidation unit 9 ,

In the reaction of glycerol in the reactor 5a the dehydration catalyst is deactivated or loses specific activity. About a Partialabscheider at the top of the system, the deactivated catalyst enters the regenerator 5b , which is usually carried out as a bubbling fluidized bed. There deposits (coke) are burned on the catalyst. The regenerated catalyst is then placed in the riser 5a transported back.

EXAMPLES

through an HPLC pump became an aqueous glycerine solution passed into an evaporator. The evaporated glycerol solution was then in a first Re action stage on a reactor passed with a reaction volume of 19 ml, the reactor with a catalyst for converting the glycerol into acrolein filled was. The product mixture of the first reaction stage was subsequently passed in the gaseous state into a second reaction stage, in the addition of oxygen or air, the selective oxidation of acrolein was carried out to acrylic acid. The reaction volume of the second reaction stage was also 19 ml, the reactor filled with a catalyst which was suitable for this selective oxidation. Both Reaction stages could each optionally with oxygen, nitrogen or air are applied. Each reaction step was independent temperature-controlled. After each reaction step, a sample could be taken which was analyzed by gas chromatography.

1

Evaporation unit

2

supply for an aqueous glycerol phase

3

derivation for a gaseous glycerol phase

4

supply for oxygen or hydrogen-containing gas mixture

5a, b

Dehydration reactor / regenerator

6

derivation for a gaseous acrolein phase

7

analyzer

8a, b

control units

9

oxidation unit

10

supply for oxygen / air

11

derivation for a gaseous acrylic acid phase

12

purification unit

13

derivation for purified acrylic acid

14

polymerization unit

15

condensation unit

16

derivation for an aqueous glycerol phase

QUOTES INCLUDE IN THE DESCRIPTION

This list The documents listed by the applicant have been automated generated and is solely for better information recorded by the reader. The list is not part of the German Patent or utility model application. The DPMA takes over no liability for any errors or omissions.

Cited patent literature

• - DE 4238493 A [0003]
• - WO 2006/087083 A [0004, 0008, 0008]
• - WO 2006/087084 A [0004]
• WO 2006/114506 A [0004]
• - WO 2007/013296 A [0005]
• - CN 101070276 A [0006]
• - DE 4238493 C1 [0022]
• DE 2626887A [0029]
• - EP 0534294A [0029]
• US 2002/0198406 A [0029]
• EP 1015410A [0049]
• WO 2004/029016 A [0054]

Cited non-patent literature

• - DIN 66133 [0019]
• - DIN 66131 [0019]
• "Studies in Surface Science and Catalytic", Volume 51, 1989: "New Solid Acids and Gases, their Catalytic Properties", K Tannabe et al. [0022]
• - 3rd chapter in "Modern Superabsorbent Polymer Technology", FL Buchholz and AT Graham (Editor), Wiley-VCH, New York, 1998 [0052]
• - 3rd chapter (page 69 ff) in "Modern Superabsorbent Polymer Technology", FL Buchholz and AT Graham (editors) in, Wiley-VCH, New York, 1998 [0067]

Claims (26)

A process for the production of acrylic acid from glycerol, comprising the process steps of: a) dehydration of glycerol to acrolein in the gas phase in a dehydration unit in the presence of dehydration catalysts to obtain a gaseous acrolein phase; b) oxidation of the acrolein in an oxidation unit in the presence of oxidation catalysts to give a preferably gaseous acrylic acid phase; wherein - the dehydration unit has a first portion of catalyst KT ₁ and at least one of the first portion of catalyst KT ₁ spatially separated catalyst portion KT ₂ , which differ in their specific catalyst activity, - wherein the catalyst of the first catalyst portion KT _1, the dehydration of glycerol Formation of acrolein catalyzes while the catalyst of the at least one further catalyst portion KT _{2 is} regenerated. The method of claim 1, wherein in the step a) the dehydration of glycerol at least partially in the Gas phase takes place. The method of claim 2, wherein the gas phase by the evaporation of an aqueous form Glycerol phase is obtained. The method of claim 2 or 3, wherein the glycerin concentration in the aqueous glycerol phase more than 30 wt .-%, based on the total weight of the aqueous glycerol phase. The method according to one of the preceding claims, wherein the dehydration catalysts are oxygen-containing Al, Zr, Ti, Si, S, P or W compounds, heteropolyacids of silicon, molybdenum, tungsten and phosphorus or Mixtures of these include. The method according to one of the preceding claims, wherein the dehydration in the gas phase according to process step a) at a temperature in the temperature range between 200 ° C and 400 ° C takes place. The method according to one of the preceding claims, wherein from the acrolein phase obtained in process step a) at least a part of the glycerol is separated. The method of claim 7, wherein the separated Glycerol the process step a) is supplied. The method according to one of the preceding claims, wherein the used in step b) oxidation catalyst at least one of the elements molybdenum, tungsten, vanadium, Antimony, copper or a combination of at least two of them in at least partially oxidized form. The method according to one of the preceding claims, wherein the gas phase oxidation in process step b) at a temperature in the range of 200 to 400 ° C is performed. The method according to one of the preceding claims, wherein the dehydration unit comprises a first dehydration reactor and at least one further dehydration reactor, wherein the first partial catalyst amount KT in the first dehydration reactor and the at least one further catalyst subset KT2 in the at least one further dehydration reactor is located and wherein the at least one further dehydration reactor is switched as soon as the value of the specific catalyst activity the catalyst of the first partial catalyst amount KT a certain Has fallen below value, so now the glycerin at least partly in the at least one further dehydration reactor is initiated. The method of claim 11, wherein the at least two dehydration reactors by at least two Fluidized bed reactors or at least two fixed bed reactors is. The method according to one of the claims 1 to 10, wherein the dehydration unit is a riser-downer reactor system includes. The method according to one of the preceding claims, furthermore including the process step c) purification the acrylic acid from the gaseous acrylic acid phase. The method of claim 14, further including the process step d) esterification of the purified acrylic acid to obtain an acrylic ester. The method of claim 14 or 15, further including the process step d) polymerization of the purified Acrylic acid to obtain an acrylic acid based Polymer or of the acrylic acid ester to obtain an acrylic acid esters based polymer. A device for producing acrylic acid from glycerol, comprising as device components (β1) an evaporation unit comprising at least at least one evaporator; (β2) a dehydration unit comprising (β2a) at least one dehydration reactor and (β2b) at least one regenerator, said at least one dehydration reactor (β2a) and said at least one regenerator (β2b) each containing a dehydration catalyst which inhibits the dehydration of glycerol to give Acrolein catalyzes (β3) an oxidation unit comprising at least one oxidation reactor including an oxidation catalyst which catalyzes the oxidation of acrolein to obtain acrylic acid; (β4) optionally, a condensation unit disposed between the dehydration unit (β2) and the oxidation unit (β3), including at least one condenser; (β5) optionally an analysis device for determining the glycerol conversion in the dehydration unit (β2). The apparatus of claim 17, wherein the evaporation unit (β1) a feed line for an aqueous Glycerol phase and at least one derivative for a gaseous Having glycerol phase. The device of claim 17, wherein the dehydration unit (β2) a supply line for the gaseous Glycerol phase and a derivative for a gaseous Acrolein phase includes, wherein the supply line for the gaseous Glycerol phase fluid conducting with the discharge for a gaseous Glycerol phase of the evaporation unit (β1) and the derivative for a gaseous acrolein phase fluidly conductive the oxidation unit (β3) is connected. The apparatus of claim 19, wherein the oxidation unit (β3) a supply line for a gaseous Acrolein phase or an enriched gaseous acrolein phase, which fluid conducting with the discharge for a gaseous Acrolein phase of the dehydration unit (β2) or fluid-conducting with the derivative for an enriched, gaseous Glycerol phase of the evaporation unit (β1) is included. The apparatus of claim 20, wherein the analyzer (β4) is arranged so that it determines the glycerol concentration allows at least one of the following locations of the device: A) within the reactor (β2a) of the dehydration unit (Β2); B) at the outlet for a gaseous Acrolein phase of the dehydration unit (β2); C) at the inlet for a gaseous acrolein phase of optionally existing condensation unit (β4); D) within the condensation unit (β4); E) at the outlet for an enriched gaseous acrolein phase of the condensation unit (Β4); F) at the outlet for an aqueous Glycerol phase of the condensation unit (β4); G) on Inlet for a gaseous acrolein phase of the oxidation unit (Β3). A process for the production of acrylic acid Glycerol in which a device according to any one of claims 17 to 21 is used. Purified acrylic acid, available by a method according to claim 14. On acrylic acid or on acrylic esters based polymer obtainable by a process according to Claim 16. Acrylic acid ester, available from a method according to claim 15. Use of a riser-downer reactor system the conversion of glycerol to acrolein.