WO2008110468A1

WO2008110468A1 - Method for producing acetic and formic acid by the gas phase oxidation of ethanol

Info

Publication number: WO2008110468A1
Application number: PCT/EP2008/052499
Authority: WO
Inventors: Christoph RÜDINGER; Hans-Jürgen EBERLE; Harald Voit
Original assignee: Wacker Chemie Ag
Priority date: 2007-03-12
Filing date: 2008-02-29
Publication date: 2008-09-18
Also published as: DE102007011847A1

Abstract

The invention relates to a method for producing acetic and formic acid by the gas phase oxidation of ethanol or mixtures containing ethanol in the presence of oxygen on a catalyst containing a.) a component I consisting of one or more oxides from the group comprising titanium dioxide, zirconium dioxide, tin dioxide, aluminium oxide and b.) a component II containing between 0.1 and 1.5 % by weight, in relation to the weight of component I and per m2/g specific surface of component I, of vanadium pentoxide. According to the invention, said method is carried out in a recycling procedure and the resultant crude acid is separated from the cycle by water absorption. This aqueous phase is subsequently separated into pure acetic and formic acid by means of one extraction step and several distillation steps.

Description

Process for the preparation of acetic and formic acids by gas phase oxidation of ethanol

The invention relates to a process for the preparation of acetic and formic acid by gas phase oxidation of ethanol with oxygen using a catalyst in a cyclic process.

It is known that acetic acid can be prepared by gas phase oxidation of ethanol by means of catalysts.

Particularly suitable catalysts for this application included

Vanadium and / or molybdenum and titanium oxides. So far, however, no economically and operationally fully satisfactory method could be found.

DE 1642938 describes a process for the preparation of a

Vanadium pentoxide and titanium dioxide containing

Supported catalyst and its use for the oxidation of o-xylene to phthalic anhydride.

US 1,636,952 describes a process for the preparation of

Acetaldehyde from ethanol by gas phase oxidation with oxygen on a vanadium oxide catalyst.

US 5,840,971 describes a process for the production of acetic acid by oxidation of ethanol with oxygen using VTi _y O _x catalysts. In the oxidation of ethanol, a yield of 84% and a maximum acetic acid production of 356 g per liter of catalyst and hour is achieved. The crude acid is obtained as an aqueous solution. The concentration and purification of the thus obtained crude acid, the removal of acetaldehyde and especially the economic separation of formic acid is not described. A disadvantage of the process is the high pressure drop in the reactor and the low acetic acid concentration in the reaction gas, which requires expensive apparatus for operation and product isolation. BR 19960315 and BR 9601959 similarly describe US 5,840,971 processes for the production of acetic acid by oxidation of ethanol with oxygen using VTi _y O _x catalysts inter alia on a silicon carbide support. In this case, especially the

Recovery of acetaldehyde mentioned, but special devices or procedures for economic product isolation and product separation are not described.

EP 0294846 describes a process for the catalytic

Oxidation of an alcohol by means of a Mo _x V _y Z _z catalyst. The process gives as by-products ethylene and ethane and only a low acetic acid yield. There is no information about an economical processing of the products.

A disadvantage of all these processes and catalysts is poor controllability of the oxidation reaction and the low cost of acetic acid production or acetic acid workup at high space-time performance.

It was therefore an object to provide a process for the economical production of acetic and formic acid by gas phase oxidation, which avoids the disadvantages of the prior art.

It has surprisingly been found that the production of acetic and formic acid by gas phase oxidation is particularly economical when catalysts and in particular shell catalysts are used, in which the active composition is applied as a thin layer on a nonporous carrier body, and ethanol-containing starting material and pure oxygen are used in a circulation process and the separated from this cycle via water absorption raw or dilute acid prepared by a special integrated process and separated into the two pure target products acetic and formic acid. The invention relates to a process for the preparation of acetic acid and formic acid by gas phase oxidation of mixtures containing ethanol or ethanol in the presence of oxygen over a catalyst comprising a) a component I of one or more oxides of the

Group titanium dioxide, zirconium dioxide, tin dioxide,

Alumina and b.) A component II containing 0.1 to 1.5% by weight, based on the weight of component I and per m ² / g specific surface area of component I,

Vanadium pentoxide, wherein the process is carried out in a circulatory system, and the resulting crude acid is separated by water absorption from the circulation and this aqueous phase is then separated by an extraction and several distillation steps in pure acetic and formic acid.

The inventive method provides in contrast to the methods known from the prior art equally high acid yields and thus good raw material utilization, high crude acid concentrations, which are reflected in low processing costs and at the same time an increased volume-related acid productivity (high space / time performance), which in turn reflected in lower equipment costs.

The process according to the invention is preferably suitable for the preparation of acetic acid and formic acid. A significant advantage of the procedure according to the invention is that, in the production of acetic acid, the by-products formed thereby in small amounts are obtained as valuable substances, especially in the form of formic acid. In contrast, especially in the known from the prior art, the intermediate formic acid portion is largely decomposed and there are CO and CO2, which must be disposed of. Ethanol is a readily available, industrially produced chemical. Usually, ethanol is produced by fermentation of biological sugars and / or starch and / or cellulose-containing, generally carbohydrate-containing vegetable raw materials.

The inventive method is equally suitable for the use of pure ethanol, ethanol-containing mixtures and / or ethanol-containing crude products as Eduktstrom and thus ethanol as a partial or sole

Carbon source for the gas phase oxidation. Preference is given to using particularly inexpensive water-containing ethanol mixtures which can be produced with less energy expenditure and have a water content of between 4 and 96% by weight of water, preferably between 10 and 90% by weight, more preferably with a water content of between 20 and 80% by weight. , Due to the particular insensitivity of the process to impurities in the feed, it is also possible to use undistilled, only mechanically clarified, ethanol-containing aqueous solutions or fermentation broths as raw material for the process.

By this possible due to the special process design low requirement for the feed quality can be saved in contrast to the known methods practically all the workup, dewatering and Absolutierungskosten the ethanol production and thus make the method over the prior art particularly economical.

The reaction temperature of the gas-phase oxidation is generally from 100 ⁰ C to 400 ⁰ C, preferably 150 ° C to 300 ⁰ C, particularly preferably 180 ° C to 250 ° C.

The reaction is generally carried out at pressures between 1.2 * 10 ⁵ and 51 * 10 ⁵ Pa, preferably between 3 * 10 ⁵ and 21 * 10 ⁵ Pa, more preferably between 4 * 10 ⁵ and 12 * 10 ⁵ Pa. Suitable catalysts for the process according to the invention are all catalysts which are generally described for the partial oxidation of alcohols. Preferably, mixed oxide catalysts containing vanadium oxides are used. Particularly preferred are mixed oxide materials which

a) one or more oxides from the group titania, zirconia, tin dioxide, alumina and

b) 0.1 to 1.5% by weight, based on the weight of the component

a) and per m ² / g specific surface of component a), vanadium pentoxide.

In addition, component a) may also contain one or more oxides of the metals from the group boron, silicon, hafnium, niobium, tungsten, lanthanum and cerium. In the doping of component a) with the oxides mentioned, these are generally present in an amount of from 1 to 30% by weight, based on the total weight of component a).

In component b), a part of the vanadium pentoxide, preferably 10 to 90 wt .-%, be replaced by one or more oxides of molybdenum, chromium and antimony, and / or as additional component b) one or more oxides of alkali metals, Alkaline earth metals, elements of the 5th and 6th main group of the Periodic Table of the Elements (PSE) and the transition metals to be included. In general, the amount of these dopants 0.005 to 15 wt .-%, calculated as oxides and based on the total weight of component b).

Preference is given to compositions having a high surface area of component a) of from 40 to 300 m ² / g, it being possible where appropriate for tin, niobium or tungsten oxide to be present, and to a component b) which reacts with Mo, and / or Cr, and / or Sb and / or Au is doped. The catalytically active mixed oxide composition may optionally contain from 10 to 50% by weight, based on the total weight of the catalytically active mixed oxide composition, of inert diluents from the group comprising silicon dioxide, silicon carbide and graphite.

The catalytically active composition is preferably applied as a supported shell catalyst on an unsporous support. The catalytically active mixed oxide composition is preferably applied in a proportion of 1 to 40 wt .-%, preferably 5 to 25 wt .-%, each based on the total weight of carrier body and active mass, as a shell on the outer surface of the carrier body.

The layer thickness is preferably 10 to 2000 .mu.m, in particular 100 to 1000 microns. The shell catalyst may also contain multiple layers differing in composition. It is also possible for one or more components of the active components a) and b) to be present in different concentrations in the individual layers. In a further embodiment, the inner layer contains only component a) and the outer layer contains components a) and b). A conceivable embodiment is a multilayer coated catalyst, wherein the inner and the outer layer each contain the components a) and b) and for the inner layer, a higher specific surface area is selected for the component a) than for the outer layer.

Suitable materials for the inert, non-porous carrier body are generally all inert under the operating conditions of the gas phase oxidation and on the

Operating period of stable non-porous materials. Examples include steatite, Duranit, silicon carbide, magnesium oxide, silica, silicates, aluminates, metals such as stainless steel, and optionally mixtures of these substances. Preferred are ceramic materials, such as steatite.

The shape of the inert, non-porous carrier body of the shell catalyst is arbitrary. Examples of suitable Shapes are spheres, cylinders, hollow cylinders, cuboids, tori, saddles, spindles, helices. The basic body can also have one or more recesses, such as depressions, grooves, holes, or protruding parts, such as pins, tips, webs. Other examples are rings, ring segments, bar rings, pierced balls, spherical segments. Also suitable as carriers are ordered packings, such as monoliths or cross-channel structures. Carrier shapes with the highest possible geometric surface area per volume, for example rings or hollow cylinders, are preferred. In a particularly preferred

Embodiment, the inert support body have the form of hollow cylinders, which have one or more notches on the upper and / or lower flat side of the hollow cylinder walls, so that the interior of the hollow cylinder is connected to the cavities surrounding the hollow spaces via openings.

The dimensions of the carrier bodies are generally predetermined by the reactors for gas phase oxidation. Preferably, the shaped bodies have a length or a diameter of 2 to 20 mm. The wall thickness, for example in the case of rings or hollow cylinders, is advantageously 0.1 to 4 mm.

Further details on preferred embodiments of the catalysts are described in EP 095135, EP 0960874 and EP 1108470, the disclosures of which are intended to be part of this application and are hereby incorporated by reference.

As reactors for carrying out the process according to the invention, it is generally possible to use embodiments which are suitable for carrying out oxidation reactions in the gas phase and are capable of removing the high heat of reaction without excessively heating the reaction mixture. The process according to the invention can be carried out continuously or intermittently, that is to say the feed of the reactor input mixture can be carried out with a constant feed or with a cyclically varying feed composition. The gas mixture may preferably be attached to the catalyst in a Fixed bed, for example, react in a tube-bundle reactor or tray reactor, or in a fluidized bed or fluidized bed.

Especially preferred are cooled tube bundle reactors with a fixed catalyst bed. Particular preference is given to designs with tube bundles arranged individual tubes with an inner tube diameter of 10 mm to 50 mm and a tube length of 1 m to 6 m.

The flow rate in the reaction tubes, based on the unfilled tube, is generally between 0.1 m / s and 10 m / s, preferably between 0.3 m / s and 5 m / s, more preferably 0.5 to 3 m / s.

The reaction tubes can be filled with catalyst of different composition, shape and dimension. The filling may preferably be introduced into the reaction tubes in a homogeneous or zone-wise manner in the axial direction. Each zone may preferably contain a randomly diluted or mixed catalyst.

The source of oxygen necessary for gas phase oxidation is generally an oxygen-containing gas. As the oxygen-containing gas, e.g. Air, optionally after mechanical purification, preferably oxygen-enriched air, and more preferably pure oxygen can be used. In the method according to the invention, however, an inert gas, preferably nitrogen and / or argon, may additionally be present.

The oxygen content of the gas stream fed to the reactor is preferably from 1 to 35% by volume, more preferably from 3 to 20% by volume, in particular from 4 to 12% by volume.

Optionally, an inert gas of 0 to 25 vol .-% can be supplied. The volume fraction of water vapor of the reactor input gas fed to the reactor is generally from 0 to 80% by volume, preferably from 1 to 40% by volume, particularly preferably from 3 to 30% by volume, of water vapor.

The proportion of ethanol in the reaction gas, measured at the reactor inlet, is generally 0.1 to 20% by volume, preferably 0.3 to 10% by volume, particularly preferably 0.5 to 3.0% by volume.

In a preferred embodiment of the invention, the process according to the invention is operated with gas recirculation as circulation process. In the case of processes with gas recirculation, the proportion of carbon oxides and further reaction by-products in the reactor input gas depends on the reaction regime and acid separation and is generally from 0 to 95% by volume, preferably 10 to 95% by volume, particularly preferably 55 to 85% by volume. ,

The proportions in Vol .-% of the individual components of the

Reactor input gases add up to 100% by volume in each case.

As apparatus for carrying out the reaction according to the invention can in general devices with simple

Gas passage through the reactor and circulation process can be used. In the circulation process, preference is given to devices in which high boilers, such as the carboxylic acids acetic and formic acid, are deposited from the recirculated gas stream, preferably over the low-boiling educts and by-products and by-products. The crude acid from the reaction starting gas is preferably separated off with a countercurrent wash, direct current wash, crossflow wash, quench cooling, partial condensation or a combination of these processes. Further details on preferred embodiments are described in EP 0960875 and EP 1035101, the disclosures of which are intended to be part of this application and hereby incorporated by reference.

In a particularly advantageous embodiment of the invention, the reaction gas cycle is carried out so that the reaction starting gas, either the reactor leaving or the recirculated gas mixture, a portion of the resulting in the gas phase oxidation acetic acid and formic acid, via a partial condenser or a countercurrent wash with a suitable solvent, preferably water, a portion of acids and other compounds is withdrawn. The separation is carried out so that the partial pressure of these acids at the reactor inlet remains low, unreacted ethanol and further convertible intermediates such as acetaldehyde, ethyl acetate, methyl acetate, ethyl formate, methyl formate, etc. but mostly remain in the recycle gas and are returned to the reactor inlet.

It is possible in this case for one part of the reactor outlet gas, generally from 60 to 99.8% by weight, preferably from 90 to 99.5% by weight, to remove the acid fraction up to the abovementioned residual acid content, and then this part the reactor outlet gas is returned to the reactor. The untreated portion of the reactor exit gas is discarded and may be flared, for example. The proportion of untreated reactor starting gas depends on how much carbon oxides CO _{x have been} formed because they have to be removed via this branch stream. They can then be disposed of by incineration.

It is also possible to proceed by separating the acid fraction up to the abovementioned residual fraction from the reactor outlet gas immediately after it has left the reactor, and treating the reactor starting gas thus treated in whole or in part, preferably in an amount of from 60 to 99.8% by weight. %, particularly preferably from 90 to 99.5 wt .-% is recycled to the reactor. This embodiment is particularly preferred because it the target products, the carboxylic acids, previously largely separated and do not go into the combustion.

The recirculated gas mass flow is generally between 1 and 100 times the freshly fed Eduktmassenstroms, preferably between 10 times and 80 times, more preferably between 30 to 60 times.

The water vapor content of the gas stream exiting the absorber is generally determined by the temperature prevailing at the absorber outlet and the operating pressure. The temperature is usually determined by the amount of heat removed from the absorber and the amount and temperature of the washing water stream and is generally from 50 ⁰ C to 200 ⁰ C. The remaining acid content in the gas stream leaving the absorber is generally about pressure and temperature , the number of separation stages of the absorber and the amount of absorbent supplied (water supply). In general, the process is carried out so that the residual acid concentration of the recycled back into the reactor gas stream is reduced to 0.01 to 12 vol .-%, preferably 0.1 to 8 vol .-% by countercurrent washing.

The separated crude acid is generally removed by suitable conventional methods alone or in combination, such as

Liquid extraction, extractive rectification, rectification,

Azeotropic rectification, crystallization and

Membrane separation process drained and cleaned. The low boilers separated off before further fractionation of the crude acid into its pure substances can likewise be recycled, in whole or in part, into the gas phase reactor, either alone or together with low boilers from the purification and concentration.

Cost-optimized processes, such as those described in DE 19934411, DE 19934410 and German patent application DE 10065466, are particularly suitable for working up the diluted crude acid Revelations should be part of this application. These are hereby incorporated by reference.

A preferred method for the separation and purification of the dilute crude acid, an aqueous mixture of the main components low boilers, acetic acid, formic acid and high boilers, is the extraction, by means of a solvent, preferably one or more compounds from the group consisting of ethers, esters, ketones and alcohols, especially preferably one or more compounds selected from the group comprising methyl tertiary butyl ether, diisopropyl ether, methyl secondary butyl ether, methylcyclopentyl ether, ethyl butyl ether, ethyl acetate and isopropyl acetate in a circular process, characterized in that the raffinate stream with a large part of the water

Solvent stripper is fed to the elimination of the water and the extract stream is passed into a solvent distillation column, from the top in a first step, a mixture (A) consisting of water and solvent, over the bottom of a mixture (B) consisting of acetic acid, formic acid and High boilers is separated, the mixture (B) after removal of the formic acid in a optionally equipped with side draw column then in a

Acetic acid distillation column is separated into pure acetic acid and high boilers, and the mixture (A) is fed to a phase separator, wherein the aqueous phase is recycled with residual amounts of solvent to the solvent stripping column, and the organic phase to the extractor.

Another preferred process is the extraction, by means of a solvent, preferably one or more compounds from the group consisting of ethers, esters, ketones and alcohols, more preferably one or more compounds from the group comprising methyl tertiary butyl ether, diisopropyl ether, ethyl butyl ether, cyclopentyl methyl ether, methyl 2- butyl ether, ethyl acetate and isopropyl acetate in a circular process, characterized in that the raffinate stream is supplied with a large part of the water to a solvent stripper column for the elimination of the water and the extract stream is passed into a solvent distillation column, from which in a first step overhead a mixture (A) with a large part of the solvent, from a side draw a mixture (B) consisting of formic acid, water and solvent and on the bottom a mixture (C) consisting of acetic acid and high boilers are separated, and for further processing, the mixture (B) in a

Formic acid distillation column is transferred, and the mixture (C) is transferred to an acetic acid distillation column, then in the Essigsäuredestillationskolonne overhead the pure acetic acid is isolated, in the formic acid distillation column at the bottom of the pure

Formic acid is isolated and removed overhead a mixture of solvent and water, which is recycled together with the mixture (A) after separation of the water content, in the extractor.

Another preferred method is the extraction, by means of a solvent, preferably one or more compounds from the group consisting of ethers, esters, ketones, hydrocarbons and alcohols, particularly preferably one or more compounds from the group comprising methyl tertiary butyl ether,

Diisopropyl ether, di-n-propyl ether, ethyl butyl ether, cyclopentyl methyl ether, methyl 2-butyl ether, ethyl acetate and isopropyl acetate in a cyclic process wherein the raffinate stream is fed with a major portion of the water to a solvent stripper column for water scavenging and the extract stream is passed to a

Solvent distillation column is passed from the first step in a mixture (A) consisting of water and solvent, over the bottom of a mixture (B) consisting of acetic acid, formic acid and high boilers is separated, the mixture (B) after separation of the Formic acid in a column using an adjuvant in the manner of azeotropic distillation then in a Acetic acid distillation column is separated into pure acetic acid and high boilers, and the mixture (A) is fed to a phase separator, wherein the resulting aqueous phase with residual amounts of solvent of the solvent stripper column and the organic phase is returned to the extractor.

At very high concentrations of acetic acid in the crude acid less complex procedures for the drainage, such as azeotropic rectification, cheaper.

The resulting in the concentration and purification of the crude acid water is partially, optionally after a chemical and / or physical treatment, fed back into the countercurrent absorption. The excess water from the feed and the small amount of total oxidation, which still contains very small amounts of acetic and formic acid, can be disposed of easily via a biological treatment plant.

Figures 1 and 2 describe in a schematic representation apparatus for the production of acetic and formic acid by gas phase oxidation of ethanol by the novel process with complete or partial recycling of the reaction starting gas. The crude acid is separated off, preferably by a countercurrent absorption by means of a solvent. The preferred solvent is water. In this case, oxygen and ethanol-containing feed stream is mixed with the recirculated gas stream via a mixing zone (1) and together with this fed to the tube bundle reactor (2), which is cooled by means of circulation cooling (3). The gas mixture leaving the reactor is passed in the main stream through a gas cooler (4) which is cooled by a circulation cooler (5). Following this, the reaction gas is passed into an absorption column (6) which is filled with one or more

Column coolers (7) is equipped. In the uppermost column bottom, a solvent, preferably water, is fed through a pipeline (8). In this absorption column is the crude acid separated by countercurrent washing and fed through a pipe (9) for further processing. The remaining reaction gas is returned via a pipe (10) by means of a cycle gas compressor (11) to the mixing zone. The apparatus and the method can also be carried out so that the ethanol-containing educt via line (16) is not fed to the mixing nozzle, but in front of the cooling device (7). Via line (12) a small stream of exhaust gas is removed to maintain stationary conditions in the reaction cycle and cooled in the exhaust gas cooler (13), wherein the resulting condensate via line (15) is returned to the reactor inlet. The exhaust gas stream taken off via line (14) predominantly contains carbon oxides and residues of combustible hydrocarbons and may be subject to thermal utilization, for example to exhaust gas combustion, of a material

Use or other exhaust treatment, fed.

The following example serves to further explain the invention.

The selectivity [in mol%] was calculated as follows:

Acetic acid selectivity with respect to ethanol conversion (mol%) => ((mol / h acetic acid in the crude acid)) / (mol / h ethanol reacted) * 100

Formic acid selectivity with respect to ethanol conversion (mol%) => ((mol / h formic acid in the crude acid) / 2) / (mol / h of reacted ethanol) * 100

Catalyst used in the example:

Catalyst: The preparation of the catalyst used was carried out analogously to DE-19649426, characterized in that the active composition consists of oxides of titanium, vanadium, molybdenum and antimony of the empirical formula Ti _a V _b Mo _c Sb _d O _e (a: 256; b: 27, c: 4, d: 20, e: 611) and in a proportion of 20% by weight, based on the weight of the carrier, of steatite rings of Dimension 3.8mm outside diameter * 2mm inside diameter * 2.7mm height is applied.

The experiments were carried out in an apparatus according to FIG. 2 with a single-tube reactor with 15 mm internal diameter of

Reaction tube and an absorption column with structured packing, an inner diameter of 43 mm and a packing height of 3240 mm with thermostatically controlled head part condenser as a column cooler performed.

Example:

In a reactor with a reaction tube inside diameter of 15 mm, the catalyst was introduced with a filling height of 3000 mm. The oxygen content at the reactor inlet was automatically controlled by the addition of pure oxygen at the reactor inlet to 8 vol .-%. The reaction feed was 95.6 g of ethanol in the recycle gas flow direction directly after the column overhead condenser of the absorption column and 502 g / h of water in the recycle gas flow direction directly in front of the column overhead condenser of the absorption column, corresponding to a water / ethanol reaction.

Mixture with 16 wt .-% ethanol, fed. The cycle gas flow was adjusted so that the reactor reached a cycle gas flow of 3500 g / h in the steady state. The reactor was operated at 6, 1 x 10 ⁵ Pa pressure and 181.5 ° C coolant temperature.

The acid separation from the reaction gas was carried out by absorption in a countercurrent absorber with structured packing, an inner diameter of 43 mm and a packing height of 3240 mm at a head temperature of the absorber of 130 ° C.

Under these conditions, an ethanol conversion of 99.9% was achieved. The acetic acid selectivity with respect to the conversion was 86 mol%, the formic acid selectivity with respect to the conversion was 9 mol%. The volume specific acetic acid productivity was 200 g / lh. The crude acid contained 80 wt .-% water. The low boiler content (boiling point lower than water) in the crude acid was below 0.3 wt .-%. The high boiler fraction (boiling point higher than acetic acid) in the Crude acid was below 0.01 wt .-%.

Claims

Claims:

A process for the preparation of acetic acid and formic acid by gas phase oxidation of mixtures containing ethanol or ethanol in the presence of oxygen over a catalyst comprising a) a component I of one or more oxides from the

Group titanium dioxide, zirconium dioxide, tin dioxide,

Vanadium pentoxide, wherein the process is carried out in a circulatory system, and the resulting crude acid is separated by water absorption from the circulation and this aqueous phase then via an extraction and several

Distillation is separated into pure acetic and formic acid.

2. The method according to claim 1, characterized in that a coated catalyst is used as the catalyst.

3. The method according to claim 1 to 2, characterized in that the catalytically active mixed oxide of the

Shell catalyst as component I additionally contains one or more oxides of the metals from the group boron, silicon, hafnium, niobium, tungsten, lanthanum and cerium, in an amount of 1 to 15% by weight, based on the total weight of component I and in the catalytically active mixed oxide composition of the coated catalyst as component II, part of the vanadium pentoxide is replaced by one or more oxides of molybdenum, chromium and antimony, and / or as additional component II or one or more oxides of alkali metals, alkaline earth metals,

Elements of the 5th and 6th main group of the Periodic Table of the Elements (PSE) and the transition metals are included.

4. The method according to claim 1 to 3, characterized in that the coated catalyst contains a plurality of layers, wherein the inner layer contains only component I and the outer layer comprises the components I and II.

5. The method of claim 1 to 4, characterized in that the coated catalyst contains a plurality of layers, wherein the inner and outer layers each contain the components I and II, and for the inner layer, a higher specific surface area for the component I is selected for the outer layer.

6. The method according to claim 1 to 5, characterized in that the inert carrier body of the shell catalyst having the form of hollow cylinders having one or more notches on the upper and / or lower flat side of the hollow cylinder walls, so that the interior of the hollow cylinder with the Hollow cylinder surrounding space is additionally connected in the transverse direction to the hollow cylinder channels.

7. The method according to claim 1 to 6, characterized in that the reaction starting gas is partially recycled in a reaction gas circuit wherein the reaction gas cycle is carried out so that the reaction gas a part of the resulting during the gas phase oxidation organic acids are withdrawn, so that the acid content in the recirculated Proportion of the starting reaction gas is reduced to 0.01 to 6 vol .-%.

8. The method according to claim 7, characterized in that the crude acid is separated from the reaction starting gas by a countercurrent washing.

9. The method according to claim 1 to 8, characterized in that the separation and purification of the obtained aqueous A mixture of the main components acetic acid, formic acid and high boilers by extraction in an extractor, by means of a solvent in a cyclic process, wherein the raffinate from the extractor with a large part of the water of a

Solvent stripper column is fed to the elimination of the water and the extract stream is passed into a solvent distillation column, from the top in a first step a mixture (A) with a large part of the solvent from a side draw a mixture (B) consisting of formic acid, water and solvent and via the bottom a mixture (C) consisting of acetic acid and high boilers are separated, and for further processing, the mixture (B) is transferred to a formic acid distillation column, and the mixture (C) in a

Essigsäureäuredestillationskolonne is then isolated in the Essigsäuredestillationskolonne pure acetic acid is isolated in the formic acid distillation column, the pure formic acid is isolated and a mixture of solvent and water is removed, which is recycled together with the mixture (A) after removal of the water content in the extractor ,

10. The method according to claim 1 to 9, characterized in that the separation and purification of the resulting aqueous mixture of the main components of acetic acid, formic acid and high boilers by extraction in an extractor, by means of a solvent or a

A solvent mixture is carried out in a circular process, wherein the raffinate from the extractor with a major part of the water of a solvent stripper column for the circulation of the water is fed and the extract stream is passed into a solvent distillation column, from the top in a first step, a mixture (A) consisting of Water and solvent, over the sump a mixture (B) consisting of acetic acid, Formic acid and high boilers is separated, the mixture (B) after separating the formic acid in column then separated in an acetic acid distillation column in pure acetic acid and high boilers, and the mixture (A) is fed to a phase separator, wherein the aqueous phase with residual amounts of solvent to the solvent stripper column , And the organic phase is returned to the extractor.

11. The method according to claim 1 to 12, characterized in that the separation and purification of the resulting aqueous mixture of the main components of acetic acid, formic acid and high boilers by extraction in an extractor, by means of a solvent in a circular process, wherein the raffinate from the extractor with a Most of the water is supplied to a solvent stripper column for the elimination of the water and the extract stream is passed into a solvent distillation column, from the top in a first step a mixture (A) consisting of water and solvent, over the bottom of a mixture (B) consisting of Acetic acid, formic acid and high boilers is separated, the mixture (B) after separation of the formic acid in column using an adjuvant in the manner of azeotropic distillation is then separated in an acetic acid distillation column in pure acetic acid and high boilers, and the Mischu ng (A) is fed to a phase separator, wherein the resulting aqueous phase with residual amounts of solvent of the solvent stripper column, and the organic phase is recycled to the extractor.