HK1159069A - Direct and selective production of acetaldehyde from acetic acid utilizing a supported metal catalyst - Google Patents

Description

Direct selective production of acetaldehyde from acetic acid using supported metal catalysts

Priority

This application is based on U.S. patent application serial No. 12/221,135, filed on 31/7/2008, under the same name, from which priority is claimed, and the contents of which are incorporated herein by reference.

Technical Field

The present invention relates generally to a process for the production of acetaldehyde from acetic acid. More particularly, the invention relates to a process comprising hydrogenating acetic acid using a supported metal catalyst (e.g., iron, platinum or ruthenium on a suitable catalyst support, optionally containing one or more other hydrogenation metals) to form acetaldehyde with high selectivity.

Background

There is a long felt need for an economically viable process for converting acetic acid to acetaldehyde. Acetaldehyde is an important commodity feedstock for a variety of industrial products. For example, ethanol can be readily hydrogenated to ethanol, which itself has a wide variety of industrial applications, including its widespread use as a gasoline additive. Acetaldehyde can also be converted to ethyl acetate by a quaternionic (Tischenko) reaction, or reacted with other compounds to form other products. Acetaldehyde is currently produced by the oxidation of ethylene, the Wacker oxidation of ethylene. Fluctuations in the prices of natural gas and crude oil contribute to the cost fluctuations of traditionally produced oil or natural gas derived acetaldehyde, so that an all-around (all the grease) alternative source of acetaldehyde is required as the oil prices rise. Therefore, it is of interest to develop a commercially viable route for the selective hydrogenation of acetic acid to acetaldehyde.

The catalytic hydrogenation of aromatic carboxylic acids to aromatic aldehydes has been reported in the literature. For example, U.S. patent No. 4,613,700 to Maki et al discloses that aromatic aldehydes can be prepared from aromatic carboxylic acids using a catalyst comprising zirconium oxide and comprising as an essential component at least one element selected from the group consisting of chromium, manganese, iron, cobalt, zinc, bismuth, lead, rhenium and group III elements in periods 3-6 of the periodic table. However, no examples of catalytic hydrogenation of aliphatic carboxylic acids (e.g. acetic acid) are provided in this publication.

U.S. Pat. No. 5,306,845 to Yokohama et al discloses a process for the preparation of acetaldehyde comprising adding a high purity chromium oxide having a particle size of at least 10m²Hydrogenating a carboxylic acid or an alkyl ester thereof with molecular hydrogen in the presence of a catalyst having a total sodium, potassium, magnesium and calcium content of not more than 0.4 wt% per g of specific surface area. It is further reported herein that the hydrogenation reaction is carried out while maintaining the concentration of the carboxylic acid or alkyl ester thereof at no more than 10 vol%. Furthermore, the only example reported here is the hydrogenation of stearic acid to stearyl aldehyde. Most importantly, even if the total sodium, potassium, magnesium and calcium content is increased from about 0.3 wt% to about 0.46 wt%, the selectivity to aldehyde is significantly reduced, thus making the process unsuitable for commercial operation.

U.S. patent No. 5,476,827 to Ferrero et al describes a process for the preparation of aldehydes by the catalytic hydrogenation of carboxylic acids, esters or anhydrides using a bimetallic ruthenium/tin catalyst. Preferred carboxylic acids are alpha, beta-unsaturated or aromatic carboxylic acids having an aromatic backbone. No examples of aliphatic carboxylic acids including acetic acid are provided.

U.S. patent No. 6,121,498 to Tustin et al discloses a process for producing acetaldehyde from acetic acid. In the process, acetic acid is hydrogenated with hydrogen at elevated temperature in the presence of an iron oxide catalyst comprising 2.5 to 90 wt% palladium. However, the optimum reported here consists of an iron oxide catalyst comprising at least about 20 wt% palladium, which provides an acetaldehyde selectivity of about 80% for about 50% acetic acid conversion. In addition, significant amounts of by-products are generated, including methane, ethane, ethylene, ethanol, and acetone.

In view of the foregoing, it is apparent that none of the prior art processes have the catalysts required for the selective conversion of acetic acid to acetaldehyde or that the prior art processes use catalysts that are expensive and/or are not selective for the formation of acetaldehyde and produce undesirable by-products.

Summary of The Invention

Surprisingly, it has now been unexpectedly found that acetaldehyde can be directly prepared from acetic acid on an industrial scale with very high selectivity and yield. More particularly, the present invention provides a process for the selective production of acetaldehyde from acetic acid comprising: acetic acid is hydrogenated in the presence of hydrogen over a hydrogenation catalyst comprising at least one metal selected from the group consisting of iron, copper, gold, platinum, palladium and ruthenium supported on a suitable catalyst support. Optionally, the catalyst further comprises one or more metal catalysts selected from the group consisting of tin, aluminum, potassium, cobalt, molybdenum, tungsten, and vanadium. More particularly, the catalyst suitable for use in the process of the present invention is typically composed of ruthenium supported alone or in combination with tin or iron, iron supported alone or in combination with platinum or cobalt, or palladium/gold (Pd/Au) or palladium/copper (Pd/Cu), which can further include potassium acetate. Also suitable are palladium/iron (Pd/Fe), iron/cobalt (Fe/Co), copper/molybdenum (Cu/Mo) or copper/aluminum combinations. Suitable catalyst supports include, but are not limited to: silica, alumina, calcium silicate, carbon, zirconia-silica, titania-silica, iron oxide and zeolite catalysts, such as H-ZSM-5. Silica and iron oxide are particularly preferred catalyst supports in the process of the present invention.

Detailed Description

The invention is described in detail below with reference to a number of embodiments for purposes of illustration and explanation only. Modifications to particular embodiments within the spirit and scope of the invention set forth in the appended claims will be readily apparent to those of skill in the art.

Unless more specifically defined below, the terms used herein are given their ordinary meaning.

Typically, the catalyst metal loading is expressed as a weight percentage of the catalyst metal based on the total dry weight of the metal and the catalyst support. Thus, for example, 1 wt% metal on the support means that 1 gram of pure metal is present in 100 grams of supported metal catalyst (i.e., the total weight of support (99 grams) and metal (1 gram)).

"conversion" is expressed as a mole percent based on acetic acid in the feed. The conversion of acetic acid (AcOH) was calculated from Gas Chromatography (GC) data using the following equation:

"selectivity" is expressed as a mole percentage based on converted acetic acid. For example, if the conversion is 50 mole% and 50 mole% of the converted acetic acid is converted to acetaldehyde (AcH), we call the selectivity to acetaldehyde 50%. Selectivity was calculated from Gas Chromatography (GC) data using the following equation:

wherein "total mmol of C eluted (GC)" represents the total mmol of carbon in the whole product analyzed by gas chromatography.

The reaction proceeds according to the following chemical equation:

in accordance with the present invention, the conversion of acetic acid to acetaldehyde can be carried out in a variety of configurations, for example, in a single reaction zone, which can be a layered fixed bed, if desired. An adiabatic reactor can be used, or a shell-and-tube reactor with a heat transfer medium can be used. The fixed bed can comprise a mixture of different catalyst particles or catalyst particles comprising multiple catalysts as further described herein. The fixed bed may also include a layer of particulate material that constitutes a mixing zone for the reactants. A reaction mixture comprising acetic acid, hydrogen and optionally an inert carrier gas is supplied to the bed as a stream under pressure to a mixing zone. This stream is then fed to the reaction zone or layer (by pressure reduction). The reaction zone includes a catalytic composition comprising a suitable hydrogenation catalyst wherein acetic acid is hydrogenated to produce acetaldehyde. Any suitable particle size may be used depending on the type of reactor, throughput requirements, and the like.

Although various metal-supported hydrogenation catalysts known to those skilled in the art can be used in hydrogenating acetic acid to acetaldehyde in the process of the present invention, it is preferred that the hydrogenation catalyst used comprises at least one or more metals selected from the group consisting of iron, copper, gold, platinum, palladium and ruthenium supported on a suitable catalyst support. Optionally, the second or third metal can be selected from the group consisting of tin, aluminum, potassium, cobalt, molybdenum, tungsten, and vanadium. Preferably, the catalyst suitable for use in the process of the invention consists of ruthenium alone or a combination of ruthenium and tin or ruthenium and iron on a suitable support, for example iron oxide or silica. Similarly, preferred hydrogenation catalysts are iron alone supported on a suitable support (e.g., silica) or a combination of iron and platinum or a combination of iron and cobalt supported on a suitable catalyst support (e.g., silica). Similarly, other catalysts suitable for use in the process of the invention include supported palladium alone or a combination of palladium/gold (Pd/Au) or palladium/copper (Pd/Cu), which can further include potassium acetate. Also suitable are palladium/iron (Pd/Fe), iron/cobalt (Fe/Co), copper/molybdenum (Cu/Mo) or copper/aluminum combinations.

Typically, when a bimetallic catalyst is used, it is preferred to be able to use a suitable weight ratio of the combination of metals on a suitable support as the hydrogenation catalyst. Thus, for example, combinations of ruthenium and iron (Ru/Fe), ruthenium and tin (Ru/Sn), palladium/copper (Pd/Cu), palladium/iron (Pd/Fe) in a weight ratio of about 0.1 to 1 are particularly preferred. More preferably, the weight ratio of Ru/Fe or Ru/Sn or Pd/Cu or Pd/Fe is about 0.2-0.5, and most preferably the weight ratio of Ru/Fe or Ru/Sn or Pd/Cu or Pd/Fe is about 0.2. Similar weight ratios can be used for platinum and iron Pt/Fe catalyst combinations, i.e., weight ratios of 0.1 to 1, preferably 0.2 to 0.5, and most preferably 0.2. When a combination of cobalt and iron (Co/Fe) or copper/molybdenum (Cu/Mo) or copper/aluminum (Cu/Al) supported on a suitable catalyst support is used, the preferred weight ratio of Co/Fe or Cu/Mo or Cu/Al is in the range of 1 to 5. For example, a combination of 17.4 wt% cobalt and 4.8 wt% iron supported on silica is commercially available. Similarly, a copper-aluminum catalyst is sold by Sud Chemie under the name T-4489.

Where ruthenium alone or palladium alone or iron alone is used as the metal catalyst on a suitable support, any loading level of ruthenium, palladium or iron can be used to achieve selective hydrogenation of acetic acid to acetaldehyde. Typically, however, the ruthenium or palladium loading level can range from 0.5 wt% to about 20 wt%, preferably from 1 wt% to about 10 wt%, and most preferably from 1 wt% to about 5 wt%. Generally, when only noble metals (e.g., ruthenium or palladium) are used in the process of the present invention, 0.5 to 1 wt% of the catalyst metal may be sufficient to obtain the optimum catalytic benefit. Preferred catalyst supports for ruthenium or palladium are iron oxide or silica. Similarly, when iron is used solely as the metal catalyst, the loading level of iron can range from 1 wt% to about 20 wt%, preferably from 2 wt% to about 10 wt%, and most preferably from 3 wt% to about 8 wt%. A preferred catalyst support for iron is silica.

When the bimetallic catalyst employed is two noble metals, such as palladium and gold, then the metal loading of each noble metal loading is in the range of about 0.5 wt.% to about 20 wt.%, preferably 1 wt.% to about 10 wt.%, and most preferably 1 wt.% to about 5 wt.%. However, as is known above, loadings of about 0.5 wt% or 1 wt% of each noble metal (e.g., palladium or gold) produce the most suitable catalytic effect in the process of the present invention.

Various catalyst supports known in the art can be used to support the catalyst of the present invention. Examples of such carriers include, but are not limited to: zeolites (e.g., H-ZSM-5), iron oxide, silica, alumina, titania, zirconia, magnesia, calcium silicate, carbon, graphite, and mixtures thereof. Preferred supports are silica and iron oxide. Most preferably, silica is used as the catalyst support in the process of the invention. It is also important to note that the higher the purity of the silica, the better it acts as a support. Various forms of commercially available silica supports can be used in the present invention, including high surface area silica (HSA silica) and low surface area silica (LSA silica).

In another aspect of the process of the present invention, any known zeolite catalyst can also be used as a catalyst support. Although any zeolite having a pore size of at least about 0.6nm can be used, among these zeolites, preferably used are catalyst supports selected from the group consisting of mordenite, ZSM-5, zeolite X and zeolite Y.

The preparation of large pore mordenite is described, for example, in U.S. patent No. 4,018,514 and mol.sieves pap.conf., 1967, 78, soc.chem.ind.london, d.domine and j.qualobex.

Zeolite X is described, for example, in U.S. patent No. 2,882,244 and zeolite Y is described in U.S. patent No. 3,130,007.

Various zeolites and zeolite-type materials are known in the art for catalyzing chemical reactions. For example, U.S. Pat. No. 3,702,886 to Argauer discloses a group of synthetic zeolites, characterized as "Zeolite ZSM-5", which are useful in catalyzing various hydrocarbon conversion processes.

Zeolites suitable for use in the procedure of the present invention can be in basic form, partially or fully acidic form, or partially dealuminated form.

Preferably, the zeolite catalyst support in the process of the present invention is in the proton form, characterized as an "H-ZSM-5" zeolite or "H-mordenite", which is prepared from the corresponding "ZSM-5" zeolite or "mordenite" by replacing most (typically at least about 80% of the latter zeolite) of the cations with hydrogen ions using techniques well known in the art. These zeolite catalysts are essentially crystalline aluminosilicates or a combination of silica and alumina in a well-defined crystal structure in neutral form. In a particularly preferred group of zeolite catalysts for use in the present invention, the SiO in these zeolites₂∶Al₂O₃The molar ratio is in the range of about 10 to 60.

In another aspect of the invention, the ruthenium is supported on silica or iron oxide. The combination of ruthenium and tin, iron only or platinum and iron, iron and cobalt, iron and ruthenium, and platinum and tin are supported on high purity low surface area silica or high purity high surface area silica using procedures well known in the art or further described herein. Other preferred catalyst supports for platinum or ruthenium based metal catalysts are titania and zirconia.

As noted above, the loading level of a combination of two metals is generally referenced to the content of the procatalyst metal and the weight ratio of the combination. For example, the weight ratio of Ru/Sn, Ru/Fe, Pt/Sn, or Pt/Fe is in the range of about 0.1-2. Thus, when the weight ratio of Ru/Sn, Ru/Fe or Pt/Fe is 0.1, the ruthenium or platinum content can be 0.1 or 1 wt% and thus 1 or 10 wt% of tin or iron is present on the catalyst support. Preferably, the weight ratio of Ru/Sn, Ru/Fe, Pt/Sn or Pt/Fe is about 0.5, so that the content of ruthenium or platinum on the catalyst support can be 0.5 or 1 wt% and the content of tin or iron 1 or 2 wt%. More preferably, the weight ratio of Ru/Sn, Ru/Fe, Pt/Sn or Pt/Fe is 1 or 0.2. Thus, when the weight ratio is 1, the content of ruthenium or platinum on the support is 0.5, 1 or 2 wt%, and the content of tin or iron is also 0.5, 1 or 2 wt%. Similarly, when the weight ratio of Ru/Sn, Ru/Fe or Pt/Fe is 0.2, the content of ruthenium or platinum on the support can be 0.5 or 1 wt% and the content of tin or iron 2.5 or 5 wt%.

The loading of the third metal on the support, if present, is not very critical in the present invention and can vary from about 0.1 wt.% to about 10 wt.%. Particular preference is given to metal loadings of from about 1 wt% to about 6 wt%, based on the weight of the support.

The metal impregnation can be carried out using any method known in the art. Typically, the support is dried at 120 ℃ and shaped into particles having a particle size distribution in the range of about 0.2-0.4mm prior to impregnation. Optionally, the carrier may be extruded, crushed and sieved to the desired particle size distribution. Any known method for shaping the support material to the desired particle size distribution can be used.

For supports with low surface area, such as alpha-alumina, the metal solution is added in excess until fully wetted or excess liquid impregnation to obtain the desired metal loading.

As mentioned above, the hydrogenation catalyst used in the process of the present invention is typically a bimetallic hydrogenation catalyst comprising platinum/iron, ruthenium/tin, ruthenium/iron, iron/cobalt, and the like. Generally, although not intending to be bound by any theory, it is believed that one metal acts as a promoter metal while the other metal is the primary metal. For example, in the process of the present invention, platinum, ruthenium and iron are considered as the main metals for preparing the hydrogenation catalyst of the present invention, respectively in the above combinations. Other metals, tin along with ruthenium and iron along with cobalt, platinum or ruthenium, are considered promoter metals depending on various reaction parameters (including but not limited to the catalyst support used, reaction temperature and pressure, etc.). The catalyst may include other promoter metals such as tungsten, vanadium, molybdenum, chromium or zinc.

The bimetallic catalyst is typically impregnated in two steps. Each impregnation step is followed by drying and calcination. The bimetallic catalyst may also be prepared by co-impregnation. In most cases, the impregnation can be carried out using a metal nitrate solution. However, various other soluble salts that release metal ions upon calcination can also be used. Examples of other metal salts suitable for impregnation include metal oxalates, metal hydroxides, metal oxides, metal acetates, ammonium-based metal oxides (e.g., ammonium heptamolybdate hexahydrate), metal acids (e.g., perrhenic acid solution), and the like.

Thus in one embodiment of the invention there is provided a hydrogenation catalyst wherein the catalyst support is silica or iron oxide, having only ruthenium as the hydrogenation catalyst. In this aspect of the invention, the metal loading of ruthenium can range from 1 wt% to about 20 wt%, preferably 1 to 10 wt%, most preferably 1 to 5 wt%.

In another embodiment of the present invention, a hydrogenation catalyst is provided wherein the catalyst support is silica with only iron as the hydrogenation catalyst. In this aspect of the invention, the metal loading of iron can range from 1 wt% to about 20 wt%, preferably from 2 to 10 wt%, most preferably from 3 to 8 wt% iron.

In another embodiment of the present invention, bimetallic loading of ruthenium and tin or platinum and tin is provided. In this aspect of the invention, the loading of ruthenium or platinum is from about 0.5 wt% to about 2 wt% and the loading of tin is from about 2.5 wt% to about 10 wt%. In particular, 1/1, 1/5, 0.5/5, and 0.5/2.5 wt% ruthenium/tin or platinum/tin can be used on the silica.

In another embodiment of the invention, there is also provided a hydrogenation catalyst wherein the catalyst support is a high purity, low surface area silica having a bimetallic loading of platinum and iron or ruthenium and iron. In this aspect of the invention, the loading of platinum or ruthenium is from about 0.5 wt% to about 2 wt% and the loading of iron is from about 4 wt% to about 10 wt%. In particular, platinum/iron or ruthenium/iron loading levels of 1/1, 1/5, 0.5/5, and 0.5/2.5 wt.% can be used on high purity low surface area silica. Other preferred supports in this aspect of the invention include H-ZSM-5, graphitized carbon, zirconia, titania, iron oxide, silica-alumina and calcium silicate.

In another embodiment of the present invention, there is also provided a hydrogenation catalyst, wherein the bimetallic catalyst is cobalt and iron supported on silica. In this aspect of the invention, the loading level of cobalt is from about 12 wt% to about 22 wt% and the loading level of iron is from about 3 to 8 wt%. In particular, a cobalt loading level of 17.4 wt% and an iron loading level of 4.8 wt% on silica are commercially available.

Generally, acetic acid can be selectively converted to acetaldehyde at a very high rate by practicing the present invention. The selectivity to acetaldehyde is generally very high and may be at least 60%. Under preferred reaction conditions, acetic acid is converted to acetaldehyde with a selectivity of at least 70% or more preferably in excess of 80% (e.g., at least 90%).

With the catalyst of the invention, the conversion of acetic acid is at least 10% and can be as high as 40%, and the selectivity to acetaldehyde is at least 60%, preferably 70%, most preferably 80%.

Typically, the active catalyst of the present invention is a single metal or bimetallic catalyst as described herein. More particularly, bimetallic catalysts comprising ruthenium and tin, ruthenium and iron, platinum and tin, platinum and iron, and cobalt and iron supported on silica having a ruthenium or platinum loading of 0.5 to 1 wt% and a tin and iron loading of 5 wt% and a cobalt loading of about 18 wt% are preferred. Using the catalyst, acetic acid can be converted with a conversion of about 40% and an acetaldehyde selectivity of at least 60%, more preferably at least 80% acetaldehyde selectivity can be achieved in accordance with the practice of the present invention.

Similar conversions and selectivities were achieved using zirconia, graphite or titania as the support and similar loadings of ruthenium, platinum, tin, iron and cobalt as described above. Other promoter metals can also be used in combination with the ruthenium or platinum described above.

In another aspect of the invention, high conversion levels of about at least 25% and high acetaldehyde selectivity of at least about 80% can also be obtained using ruthenium or iron loadings of 1 wt% to about 5 wt% on silica or iron oxide as the catalyst support. Other preferred catalyst supports in this aspect of the invention include graphitized carbon, titania, zirconia, silica-alumina, and calcium silicate.

In another aspect of the process of the invention, the hydrogenation is carried out at a pressure just sufficient to overcome the pressure drop across the catalytic bed.

The reaction can be carried out in the gaseous or liquid state under a variety of conditions. Preferably, the reaction is carried out in the gas phase. Reaction temperatures that may be used are, for example, in the range of from about 250 ℃ to about 350 ℃, preferably from about 290 ℃ to about 310 ℃. The pressure is generally not critical to the reaction and subatmospheric, atmospheric or superatmospheric pressures may be employed. However, in most cases, the pressure of the reaction will be in the range of about 5 to 30 atmospheres absolute, most preferably the pressure of the reaction zone is in the range of about 8 to 20 atmospheres absolute.

Although the reaction consumes 1 mole of hydrogen per mole of acetic acid to produce 1 mole of acetaldehyde, the actual molar ratio of acetic acid to hydrogen in the feed stream may vary over a wide range, for example from about 100: 1 to 1: 100. However, it is preferred that the ratio be in the range of about 1: 20 to 1: 2. More preferably, the molar ratio of acetic acid to hydrogen is about 1: 5.

The feedstock used in connection with the process of the present invention may be from any suitable source, including natural gas, petroleum, coal, biomass, and the like. The production of acetic acid by methanol carbonylation, acetaldehyde oxidation, ethylene oxidation, oxidative fermentation, anaerobic fermentation, and the like is well known. As petroleum and natural gas become more expensive, processes for producing acetic acid and intermediates (e.g., methanol and carbon monoxide) from alternative carbon sources have gained increased attention. Of particular interest is the production of acetic acid from synthesis gas which may be derived from any suitable carbon source. For example, U.S. patent No. 6,232,352 to Vidalin, the disclosure of which is incorporated herein by reference, teaches a method of retrofitting a methanol plant for the production of acetic acid. By retrofitting a methanol plant, the large capital costs associated with CO production for a new acetic acid plant are significantly reduced or greatly eliminated. All or a portion of the synthesis gas is diverted from the methanol synthesis loop and sent to a separator unit to recover CO and hydrogen, which is then used to produce acetic acid. In addition to acetic acid, the process can also be used to produce hydrogen for use in connection with the present invention.

U.S. patent No. RE35,377 to Steinberg et al, also incorporated herein by reference, provides a process for the production of methanol by conversion of carbonaceous materials such as oil, coal, natural gas and biomass materials. The process comprises hydrogenating solid and/or liquid carbonaceous material to obtain a process gas, which is steam pyrolyzed with additional natural gas to generate synthesis gas. The synthesis gas is converted to methanol, which may be carbonylated to acetic acid. This process also produces hydrogen which can be used in conjunction with the present invention as described above. See also U.S. Pat. No. 5,821,111 to Grady et al, which discloses a process for converting waste biomass to syngas by gasification, and U.S. Pat. No. 6,685,754 to Kindig et al, the disclosures of which are incorporated herein by reference.

The acetic acid may be vaporized at the reaction temperature and then supplied undiluted with hydrogen or diluted with a relatively inert carrier gas (e.g., nitrogen, argon, helium, carbon dioxide, etc.).

Alternatively, acetic acid in vapor form may be taken directly from the crude product of the flash vessel of a methanol carbonylation unit of the type described in U.S. Pat. No. 6,657,078 to Scates et al, the disclosure of which is incorporated herein by reference. The crude vapor product can be fed directly to the reaction zone of the present invention without the need to condense the acetic acid and light ends or remove water, saving overall process costs.

Contact or residence time can also vary widely depending on a number of variables (e.g., amount of acetic acid, catalyst, reactor, temperature, and pressure). Typical contact times range from fractions of a second to over several hours when using a catalyst system other than a fixed bed, with preferred contact times being in the range of about 0.5 to 100 seconds for at least gas phase reactions.

Typically, the catalyst is used in a fixed bed reactor, for example in the shape of an elongated tube or pipe, in which reactants, typically in vapor form, pass over or through the catalyst. Other reactors, such as fluidized bed or ebullated bed reactors, can also be used if desired. In some cases, it is advantageous to use the hydrogenation catalyst in combination with an inert material to adjust the pressure drop, flow rate, heat balance, or other process parameters in the catalyst bed, including the contact time of the reactant compounds with the catalyst particles.

In a preferred embodiment, there is also provided a process for the selective direct formation of acetaldehyde from acetic acid comprising: a feed stream comprising acetic acid and hydrogen is contacted at an elevated temperature with a suitable hydrogenation catalyst comprising from about 0.5 wt.% to about 1 wt.% platinum or ruthenium and from about 2.5 wt.% to about 5 wt.% tin or iron on a suitable catalyst support. The preferred catalyst support in this embodiment of the invention is silica.

In this embodiment of the process of the present invention, the preferred hydrogenation catalyst comprises about 0.5 wt% or about 1 wt% platinum and about 5 wt% iron or tin; or about 0.5 wt% or about 1 wt% ruthenium and about 5 wt% tin or iron. In this embodiment of the process of the present invention, it is preferred that the hydrogenation catalyst is layered in a fixed bed and that the reaction is carried out in the vapor phase using a feed stream of acetic acid and hydrogen in a molar ratio of from about 1: 20 to about 1: 5 at a temperature in the range of from about 290 ℃ to 310 ℃ and a reaction zone pressure in the range of from about 8 to about 20 atmospheres absolute, with a contact time for the reactants in the range of from about 0.5 to about 100 seconds.

The following examples describe the procedures used to prepare the various catalysts used in the subsequent examples.

Example A

Preparation of 1 wt% ruthenium on iron oxide

The milled and sieved iron oxide (99g) with a uniform particle size distribution of about 0.2mm was dried overnight in an oven at 120 ℃ under a nitrogen atmosphere and then cooled to room temperature. To this was added a solution of ruthenium nitrosylnitrate (Heraeus) (3.14g) in distilled water (32 ml). The resulting slurry was dried in an oven with gradual heating to 110 ℃ (> 2 hours, 10 ℃/min). The impregnated catalyst mixture was then calcined at 500 deg.C (6 hours, 1 deg.C/min).

Example B

Preparation of 3 wt% ruthenium on iron oxide

The procedure of example A was substantially repeated, except that a solution of ruthenium nitrosyl nitrate (Heraeus) (9.42g) in distilled water (96ml) and 97 g of iron oxide were used.

Example C

Preparation of 5 wt% iron on high purity low surface area silica

Milled and sieved high purity low surface area silica (95g) having a uniform particle size distribution of about 0.2mm was dried overnight in an oven at 120 ℃ under a nitrogen atmosphere and then cooled to room temperature. A solution of iron nitrate nonahydrate (Alfa Aesar) (36.2g) in distilled water (36ml) was added thereto. The resulting slurry was dried in an oven with gradual heating to 110 ℃ (> 2 hours, 10 ℃/min). The impregnated catalyst mixture was then calcined at 500 deg.C (6 hours, 1 deg.C/min).

Example D

Preparation of 5 wt% tin and 0.5 wt% ruthenium on high purity low surface area silica

Milled and sieved high purity low surface area silica (94g) having a uniform particle size distribution of about 0.2mm was dried overnight in an oven at 120 ℃ under a nitrogen atmosphere and then cooled to room temperature. To this was added a solution of tin oxalate (Alfa Aesar) (8.7g) in dilute nitric acid (1N, 45 ml). The resulting slurry was dried in an oven with gradual heating to 110 ℃ (> 2 hours, 10 ℃/min). The impregnated catalyst mixture was then calcined at 500 deg.C (6 hours, 1 deg.C/min). To the calcined and cooled material was added a solution of ruthenium nitrosyl nitrate (Heraeus) (1.57g) in distilled water (16 ml). The resulting slurry was dried in an oven with gradual heating to 110 ℃ (> 2 hours, 10 ℃/min). The impregnated catalyst mixture was then calcined at 500 deg.C (6 hours, 1 deg.C/min).

Example E

Preparation of 1 wt% ruthenium and 5 wt% iron on high purity low surface area silica

Milled and sieved high purity low surface area silica (94g) having a uniform particle size distribution of about 0.2mm was dried overnight in an oven at 120 ℃ under a nitrogen atmosphere and then cooled to room temperature. To this was added a solution of ruthenium nitrosylnitrate (Heraeus) (3.14g) in distilled water (32 ml). The resulting slurry was dried in an oven with gradual heating to 110 ℃ (> 2 hours, 10 ℃/min). The impregnated catalyst mixture was then calcined at 500 deg.C (6 hours, 1 deg.C/min). To the calcined and cooled material was added a solution of iron nitrate nonahydrate (Alfa Aesar) (36.2g) in distilled water (36 ml). The resulting slurry was dried in an oven with gradual heating to 110 ℃ (> 2 hours, 10 ℃/min). The impregnated catalyst mixture was then calcined at 500 deg.C (6 hours, 1 deg.C/min).

Example F

Preparation of 5 wt% iron and 1 wt% platinum on high purity low surface area silica

Milled and sieved high purity low surface area silica (94g) having a uniform particle size distribution of about 0.2mm was dried overnight in an oven at 120 ℃ under a nitrogen atmosphere and then cooled to room temperature. A solution of iron nitrate nonahydrate (Alfa Aesar) (36.2g) in distilled water (36ml) was added thereto. The resulting slurry was dried in an oven with gradual heating to 110 ℃ (> 2 hours, 10 ℃/min). The impregnated catalyst mixture was then calcined at 500 deg.C (6 hours, 1 deg.C/min). To the calcined and cooled material was added a solution of platinum nitrate (Chempur) (1.64g) in distilled water (16 ml). The resulting slurry was dried in an oven with gradual heating to 110 ℃ (> 2 hours, 10 ℃/min). The impregnated catalyst mixture was then calcined at 500 deg.C (6 hours, 1 deg.C/min).

Example G

Preparation of 1 wt% platinum and 5 wt% tin on high purity low surface area silica

Milled and sieved high purity low surface area silica (94g) having a uniform particle size distribution of about 0.2mm was dried overnight in an oven at 120 ℃ under a nitrogen atmosphere and then cooled to room temperature. To this were added a solution of platinum nitrate (Chempur) (1.64g) in distilled water (16ml) and a solution of tin oxalate (Alfa Aesar) (8.7g) in dilute nitric acid (1N, 43.5 ml). The resulting slurry was dried in an oven with gradual heating to 110 ℃ (> 2 hours, 10 ℃/min). The impregnated catalyst mixture was then calcined at 500 deg.C (6 hours, 1 deg.C/min).

Example H

Preparation of 1 wt% Palladium, 1 wt% gold and 5 wt% Potassium acetate on high purity, Low surface area silica

The procedure of example D was substantially repeated, except that a solution of palladium nitrate (Heraeus) (2.17g) in distilled water (22ml), a solution of gold (III) hydroxide (Alfa Aesar) (1.26g) and potassium hydroxide (0.28g) in distilled water (10ml), a solution of potassium acetate (Sigma) (5g) in distilled water (10ml) and 93 g of silica were used. The catalyst was impregnated sequentially, first with palladium, then with gold and finally with potassium acetate.

Example I

Preparation of 1 wt% Palladium, 5 wt% copper and 5 wt% Potassium acetate on high purity, Low surface area silica

The procedure of example D was substantially repeated except that a solution of palladium nitrate (Heraeus) (2.17g) in distilled water (22ml), a solution of copper nitrate trihydrate (Alfa Aesar) (19g) in distilled water (20ml), a solution of potassium acetate (Sigma) (5g) in distilled water (10ml) and 89 g of silica were used. The catalyst was impregnated sequentially, first with copper, then with palladium, and finally with potassium acetate.

Example J

Preparation of 1 wt% Palladium and 5 wt% copper on carbon

The procedure of example D was substantially repeated except that a solution of palladium nitrate (Heraeus) (2.17g) in distilled water (22ml), a solution of copper nitrate trihydrate (Alfa Aesar) (19g) in distilled water (20ml) and 94g of carbon were used. The catalyst was impregnated sequentially, first with copper and then with palladium.

Example K

Preparation of 1 wt% Palladium and 5 wt% iron on high purity Low surface silica

The procedure of example D was substantially repeated except that a solution of palladium nitrate (Heraeus) (2.17g) in distilled water (22ml), a solution of iron nitrate nonahydrate (Alfa Aesar) (36.2g) in distilled water (30ml) and 94g of silica were used. The catalyst was impregnated sequentially, first with iron and then with palladium.

Example L

Preparation of 5 wt% iron and 5 wt% cobalt on high purity low surface silica

The procedure of example D was substantially repeated except that a solution of iron nitrate nonahydrate (Alfa Aesar) (36.2g) in distilled water (30ml), a solution of cobalt nitrate hexahydrate (24.7g) in distilled water (25ml) and 90 grams of silica were used. The catalyst was impregnated sequentially, first with iron and then with cobalt.

Example M

Preparation of 5 wt% copper and 5 wt% molybdenum on high purity low surface silica

The procedure of example D was substantially repeated, except that a solution of copper nitrate trihydrate (Alfa Aesar) (19g) in distilled water (20ml), a solution of ammonium heptamolybdate hexahydrate (Sigma) (9.5g) in distilled water (65ml) and 90 grams of silica were used. The catalyst was impregnated sequentially, first with copper and then with molybdenum.

Example N

Preparation of 5 wt% tin and 1 wt% ruthenium on high purity low surface silica

The procedure of example D was substantially repeated except that a solution of tin oxalate (Alfa Aesar) (8.7g) in dilute nitric acid (1N, 43.5ml), a solution of ruthenium nitrosyl nitrate (Heraeus) (3.14g) in distilled water (32ml) and 94 grams of silica were used. The catalyst was co-impregnated with tin and ruthenium.

Example O

Preparation of 1 wt% Palladium on iron oxide

The procedure of example D was substantially repeated except that a solution of palladium nitrate (Heraeus) (2.17g) in distilled water (22ml) and 99g of iron oxide were used.

Gas Chromatography (GC) analysis of the product

Analysis of the product was performed by online GC. The reactants and products were analyzed using a three-channel compact GC equipped with 1 Flame Ion Detector (FID) and 2 Thermal Conductivity Detectors (TCD). The front channel was equipped with FID and CP-Sil 5(20m) + WaxFFap (5m) columns and used for quantification of the following:

acetaldehyde

Ethanol

Acetone (II)

Acetic acid methyl ester

Vinyl acetate (VAA)

Ethyl acetate

Acetic acid

Ethylene glycol diacetate

Ethylene glycol

Ethylidene diacetate

Paraldehyde

The mesochannel was equipped with TCD and Porabond Q columns and used for quantitation:

CO₂

ethylene

Ethane (III)

The back channel was equipped with a TCD and Molsieve 5A column and used for quantitation:

helium gas

Hydrogen

Nitrogen gas

Methane

Carbon monoxide

The retention times of the different components were determined by spiking with a single compound, and the GC was calibrated with a calibration gas of known composition or with a liquid solution of known composition prior to the reaction. This allows the determination of response factors for various components.

Example 1

The catalyst used was 1 wt% ruthenium on iron oxide prepared according to the procedure of example a.

In a tubular reactor made of stainless steel having an internal diameter of 30mm and capable of being raised to a controlled temperature, 50ml of 1 wt% ruthenium supported on iron oxide were set. The length of the catalyst bed after loading was about 70 mm. The catalyst was reduced in situ by heating to a final temperature of 400 ℃ at a rate of 2 ℃/min prior to reaction. Then, 5 mol% hydrogen in nitrogen was used for 7500h^-1Is introduced into the catalyst chamber. After reduction, the catalyst was cooled to a reaction temperature of 350 ℃ by a continued flow of 5 mol% hydrogen in nitrogen. Once the reaction temperature has stabilized at 350 deg.C, e.g.Acetic acid hydrogenation was started.

The feed liquid consists essentially of acetic acid. The reaction feed liquid was evaporated and taken up with hydrogen and helium as carrier gas for about 2500hr^-1Is fed to the reactor at a temperature of about 350 c. The resulting feed stream comprises a molar percentage of acetic acid of from about 4.4% to about 13.8% and a molar percentage of hydrogen of from about 14% to about 77%. A portion of the vapor effluent was passed through a gas chromatograph for analysis of the effluent content. The acetaldehyde selectivity was 60% and the acetic acid conversion was 50%.

Example 2

The catalyst used was 5 wt% iron on silica prepared according to the procedure of example C.

With vaporized feed stream (H) of acetic acid and hydrogen₂The molar ratio of acetic acid to acetic acid is 5) of 2500hr^-1At a temperature of 350 ℃, the procedure set forth in example 1 was substantially repeated. A portion of the vapor effluent was passed through a gas chromatograph for analysis of the effluent content. Acetic acid conversion was 75% and acetaldehyde selectivity was 70%.

Example 3

The catalyst used was 0.5 wt% ruthenium and 5 wt% tin on silica prepared according to the procedure of example D.

With vaporized feed stream (H) of acetic acid and hydrogen₂Acetic acid molar ratio of 5) in 10000hr^-1At a temperature of 250 ℃ and a pressure of 1 bar the procedure set forth in example 1 was substantially repeated. A portion of the vapor effluent was passed through a gas chromatograph for analysis of the effluent content. Acetic acid conversion was 4% and acetaldehyde selectivity was 91%. Other products formed were ethane (1%) and ethanol (8%).

Example 4

The catalyst used was 1 wt% ruthenium and 5 wt% iron on silica prepared according to the procedure of example E.

With vaporized feed stream (H) of acetic acid and hydrogen₂The molar ratio of acetic acid to acetic acid is 5) of 2500hr^-1At a temperature of 300 ℃ the procedure set forth in example 1 was substantially repeated. A portion of the vapor effluent was passed through a gas chromatograph for analysis of the effluent content. Acetic acid conversion was 35% and acetaldehyde selectivity was about 70%.

Example 5

The catalyst used was 1 wt% platinum and 5 wt% iron prepared according to the procedure of example F on high purity low surface area silica.

With vaporized feed stream (H) of acetic acid and hydrogen₂The molar ratio of acetic acid to acetic acid is 5) of 2500hr^-1At a temperature of 350 ℃ and a pressure of 1 bar the procedure set forth in example 1 was substantially repeated. A portion of the vapor effluent was passed through a gas chromatograph for analysis of the effluent content. Acetic acid conversion was 65% and acetaldehyde selectivity was 60%. Other products formed were carbon dioxide (6%) and ethyl acetate (9%).

Example 6

The catalyst used was 0.5 wt% platinum and 5 wt% tin on silica prepared according to the procedure of example G.

With vaporized feed stream (H) of acetic acid and hydrogen₂The molar ratio of acetic acid to acetic acid is 5) of 2500hr^-1At a temperature of 350 ℃ and a pressure of 1 bar the procedure set forth in example 1 was substantially repeated. A portion of the vapor effluent was passed through a gas chromatograph for analysis of the effluent content. Acetic acid conversion was 85% and acetaldehyde selectivity was 65%. Other products formed were methane (4%) and ethyl acetate (9%).

Example 7

The catalyst used was a commercially available Co/Fe catalyst containing 17.4 wt% cobalt and 4.8 wt% iron on silica.

With 2500hr of vaporized acetic acid and hydrogen feed stream^-1At a temperature of 350 ℃, the procedure set forth in example 1 was substantially repeated. A portion of the vapor effluent was passed through a gas chromatograph for analysis of the effluent content. Acetic acid conversion was about 65% and acetaldehyde selectivity was 75%.

Example 8

The catalyst used was 1 wt% palladium, 1 wt% gold and 5 wt% potassium acetate on silica prepared according to the procedure of example H.

With vaporized feed stream (H) of acetic acid and hydrogen₂Acetic acid molar ratio of 5) in 10000hr^-1At a temperature of 250 ℃ and a pressure of 1 bar the procedure set forth in example 1 was substantially repeated. A portion of the vapor effluent was passed through a gas chromatograph for analysis of the effluent content. The acetic acid conversion was 5% and the acetaldehyde selectivity was 98.5%. Other products formed were ethane (1%) and ethanol (0.5%).

Example 9

The catalyst used was 1 wt% palladium, 5 wt% copper and 5 wt% potassium acetate on silica prepared according to the procedure of example I.

With vaporized feed stream (H) of acetic acid and hydrogen₂Acetic acid molar ratio of 5) in 10000hr^-1At a temperature of 250 ℃ and a pressure of 1 bar the procedure set forth in example 1 was substantially repeated. A portion of the vapor effluent was passed through a gas chromatograph for analysis of the effluent content. The acetic acid conversion was 2% and the acetaldehyde selectivity was 97.5%. The other product formed was ethane (2.5%).

Example 10

The catalyst used was 1 wt% palladium and 5 wt% copper on carbon prepared according to the procedure of example J.

With vaporized feed stream (H) of acetic acid and hydrogen₂Acetic acid mol10000hr of ratio 5)^-1At a temperature of 250 ℃ and a pressure of 1 bar the procedure set forth in example 1 was substantially repeated. A portion of the vapor effluent was passed through a gas chromatograph for analysis of the effluent content. Acetic acid conversion was 1% and acetaldehyde selectivity was 97%. The other product formed was ethane (3%).

Example 11

The catalyst used was 1 wt% palladium and 5 wt% iron on silica prepared according to the procedure of example K.

With vaporized feed stream (H) of acetic acid and hydrogen₂Acetic acid molar ratio of 5) in 10000hr^-1At a temperature of 250 ℃ and a pressure of 1 bar the procedure set forth in example 1 was substantially repeated. A portion of the vapor effluent was passed through a gas chromatograph for analysis of the effluent content. Acetic acid conversion was 9% and acetaldehyde selectivity was 96%. Other products produced were ethane (0.6%) and ethanol (3.6%).

Example 12

The catalyst used was 5 wt% iron and 5 wt% cobalt on silica prepared according to the procedure of example L.

With vaporized feed stream (H) of acetic acid and hydrogen₂Acetic acid molar ratio of 5) in 10000hr^-1At a temperature of 250 ℃ and a pressure of 1 bar the procedure set forth in example 1 was substantially repeated. A portion of the vapor effluent was passed through a gas chromatograph for analysis of the effluent content. Acetic acid conversion was 11% and acetaldehyde selectivity was 95%. Other products formed were ethane (1%) and ethanol (4%).

Example 13

The catalyst used was 5 wt% iron and 5 wt% cobalt on silica prepared according to the procedure of example L.

With vaporized feed stream (H) of acetic acid and hydrogen₂The molar ratio of acetic acid to acetic acid is 5) of 2500hr^-1At a temperature of 350 ℃ and a pressure of 1 bar the procedure set forth in example 1 was substantially repeated. A portion of the vapor effluent was passed through a gas chromatograph for analysis of the effluent content. Acetic acid conversion was 75% and acetaldehyde selectivity was 70%. Other products formed were methane (4%) and carbon dioxide (3%).

Example 14

The catalyst used was 5 wt% copper and 5 wt% molybdenum on silica prepared according to the procedure of example M.

With vaporized feed stream (H) of acetic acid and hydrogen₂The molar ratio of acetic acid to acetic acid is 5) of 2500hr^-1At a temperature of 350 ℃ and a pressure of 1 bar the procedure set forth in example 1 was substantially repeated. A portion of the vapor effluent was passed through a gas chromatograph for analysis of the effluent content. Acetic acid conversion was 10% and acetaldehyde selectivity was 90%. Other products formed were ethane (1.5%) and acetone (6.6%).

Example 15

The catalyst used was 1 wt% ruthenium and 5 wt% tin on silica prepared according to the procedure of example N.

With vaporized feed stream (H) of acetic acid and hydrogen₂The molar ratio of acetic acid to acetic acid is 5) of 2500hr^-1At a temperature of 350 ℃ and a pressure of 1 bar the procedure set forth in example 1 was substantially repeated. A portion of the vapor effluent was passed through a gas chromatograph for analysis of the effluent content. Acetic acid conversion was 60% and acetaldehyde selectivity was 78%. Other products formed were methane (6%) and ethanol (12%).

Example 16

The catalyst used was 1 wt% palladium on iron oxide prepared according to the procedure of example O.

With vaporized feed stream (H) of acetic acid and hydrogen₂Acetic acid molar ratio of 5) in 10000hr^-1Average combined gas ofThe procedure set forth in example 1 was essentially repeated at a temperature of 350 ℃ and a pressure of 15 bar at hourly space velocity (GHSV). A portion of the vapor effluent was passed through a gas chromatograph for analysis of the effluent content. Acetic acid conversion was 66% and acetaldehyde selectivity was 59%. Other products formed were carbon dioxide (4%) and ethanol (18%).

Example 17

The catalyst used is a copper-aluminum catalyst available on the market under the name T-4489 by Sud Chemie.

With vaporized feed stream (H) of acetic acid and hydrogen₂The molar ratio of acetic acid to acetic acid is 5) of 2500hr^-1At a temperature of 350 ℃ and a pressure of 1 bar the procedure set forth in example 1 was substantially repeated. A portion of the vapor effluent was passed through a gas chromatograph for analysis of the effluent content. Acetic acid conversion was 88% and acetaldehyde selectivity was 51%. Other products formed were carbon dioxide (5%) and ethanol (16%).

Comparative examples 1A to 4A

These examples describe the reaction of acetic acid and hydrogen over a variety of catalysts, wherein no formation of acetaldehyde and/or very low selectivity to acetaldehyde is observed at low acetic acid conversions.

In all of these examples, the procedure set forth in example 1 was substantially repeated, except that the different catalysts listed in Table 1 were used. The reaction temperature and selectivity to acetaldehyde and other products are also listed in table 1.

TABLE 1 acetic acid conversion and selectivity of the comparative examples

While the invention has been described in conjunction with specific embodiments, variations to these embodiments that are within the spirit and scope of the invention will be readily apparent to those of ordinary skill in the art. In view of the above discussion, the disclosures of which are discussed above in connection with the background and detailed description of the invention are incorporated herein by reference in their entirety for all relevant knowledge, and further description is not believed necessary.

Claims (31)

1. A process for selective direct formation of acetaldehyde from acetic acid comprising: a feed stream comprising acetic acid and hydrogen is contacted at elevated temperature with a suitable hydrogenation catalyst comprising at least one metal selected from the group consisting of iron, copper, gold, platinum, palladium and ruthenium, supported on a suitable catalyst support, and optionally in combination with one or more metal catalysts selected from the group consisting of tin, aluminum, potassium, cobalt, molybdenum, tungsten and vanadium.

2. The process of claim 1, wherein the catalyst support is selected from the group consisting of iron oxide, silica, alumina, silica-alumina, calcium silicate, carbon, zirconia, titania, and mixtures thereof.

3. The process of claim 2 wherein the catalyst support is silica.

4. The process of claim 3 wherein the catalyst support is high purity silica.

5. The process of claim 2 wherein the catalyst support is iron oxide.

6. The process of claim 1 wherein the hydrogenation catalyst comprises ruthenium on a suitable support.

7. The process of claim 6 wherein the catalyst support is silica or iron oxide.

8. The process of claim 1, wherein the hydrogenation catalyst comprises iron supported on silica.

9. The process of claim 1, wherein the hydrogenation catalyst comprises ruthenium and tin or a combination of ruthenium and iron in a Ru/Sn or Ru/Fe weight ratio in the range of about 0.1 to 1.

10. The process according to claim 9 wherein the loading of ruthenium is from about 0.5 wt.% to about 1 wt.% and the loading of tin or iron is from about 2.5 wt.% to about 10 wt.%, and the catalyst support is silica.

11. The process according to claim 9, wherein the loading of ruthenium is about 0.5 wt% and the loading of tin is about 5 wt%, the catalyst support is silica; or ruthenium loading was about 1 wt% and iron loading was about 5 wt%, the catalyst support was silica.

12. The process of claim 1, wherein the hydrogenation catalyst comprises a combination of platinum and iron or platinum and tin in a Pt/Sn or Pt/Fe weight ratio in the range of about 0.1 to 1.

13. The process according to claim 12, wherein the loading of platinum is from about 0.5 wt.% to about 1 wt.%, the loading of tin or iron is from about 2.5 wt.% to about 10 wt.%, and the catalyst support is silica.

14. The process of claim 1, wherein the hydrogenation catalyst comprises a combination of iron and cobalt, and wherein the loading level of iron is from about 3 wt% to 10 wt%, the loading level of cobalt is from about 8 wt% to about 20 wt%, and the catalyst support is silica.

15. The process of claim 1, wherein the selectivity to acetaldehyde based on acetic acid consumed is at least 60%.

16. The process of claim 1, wherein the selectivity to acetaldehyde based on acetic acid consumed is at least 70%.

17. The process of claim 1, wherein the selectivity to acetaldehyde based on acetic acid consumed is at least 80%.

18. The process of claim 1, wherein the hydrogenation to acetaldehyde is carried out in the vapor phase and at a temperature in the range of about 250 ℃ to 350 ℃.

19. The process of claim 18, wherein the hydrogenation to acetaldehyde is carried out in the vapor phase and at a temperature in the range of about 270 ℃ to 310 ℃.

20. The process of claim 18, wherein the feed stream comprises an inert carrier gas.

21. The process of claim 18 wherein the reactants are comprised of acetic acid and hydrogen in a molar ratio in the range of from about 100: 1 to 1: 100, the temperature of the reaction zone is in the range of from about 250 ℃ to 350 ℃, and the pressure of the reaction zone is in the range of from about 5 to 25 atmospheres absolute pressure.

22. The process of claim 18 wherein the reactants are comprised of acetic acid and hydrogen in a molar ratio in the range of from about 1: 20 to about 1: 2, the temperature of the reaction zone is in the range of from about 270 ℃ to about 310 ℃, and the pressure of the reaction zone is in the range of from about 8 to about 20 atmospheres absolute.

23. A process for selective direct formation of acetaldehyde from acetic acid comprising: a feed stream comprising acetic acid and hydrogen is contacted at an elevated temperature with a suitable hydrogenation catalyst comprising from about 0.5 wt.% to about 1 wt.% platinum or ruthenium and from 2.5 wt.% to about 5 wt.% tin or iron on a suitable catalyst support.

24. The process according to claim 23, wherein the catalyst support comprises platinum at a loading level of about 0.5 wt.% or about 1 wt.% and tin or iron at a loading level of about 5 wt.%, and the catalyst support is silica.

25. The process according to claim 23, wherein the catalyst support comprises ruthenium at a loading level of about 0.5 wt% or about 1 wt% and tin or iron at a loading level of about 5 wt% and the catalyst support is silica.

26. The process of claim 23 wherein the reactants are comprised of acetic acid and hydrogen in a molar ratio in the range of from about 1: 20 to about 1: 5, and the temperature in the reaction zone is in the range of from about 270 ℃ to about 310 ℃.

27. The process of claim 1 wherein the catalyst is selected from bimetallic combinations of palladium/gold (Pd/Au) or palladium/copper (Pd/Cu) supported on silica or carbon.

28. The process of claim 27 wherein the catalyst further comprises potassium acetate and the catalyst support is silica.

29. The process of claim 1, wherein the catalyst is selected from the bimetallic combination of palladium/iron (Pd/Fe), iron/cobalt (Fe/Co), copper/molybdenum (Cu/Mo), or copper/aluminum (Cu/Al) supported on silica.

30. The process of claim 29, wherein the catalyst is palladium/iron (Pd/Fe), iron/cobalt (Fe/Co), or copper/molybdenum (Cu/Mo) supported on silica.

31. The process of claim 1, wherein the catalyst is copper/aluminum (Cu/Al) supported on silica.