HK1159076B - Ethylene production from acetic acid utilizing dual reaction zone process - Google Patents

Description

Production of ethylene from acetic acid using a dual reaction zone process

Priority

This application is based on U.S. patent application serial No.12/221,138 filed on 31/7/2008, having the same title, and therefore claims priority thereto and the disclosure of which is incorporated herein by reference.

Technical Field

The present invention generally relates to a process for producing ethylene from acetic acid. More specifically, the invention relates to a method comprising: acetic acid is hydrogenated with a first catalyst composition in a first reaction zone, and the hydrogenated intermediate is dehydrated or cracked with a second catalyst in a second reaction zone to form ethylene with high selectivity.

Background

There is a long felt need for an economically viable process for converting acetic acid to ethylene. Ethylene is an important commercial feedstock for a variety of industrial products; for example, ethylene can then be converted into various polymers and other monomer products. Fluctuating natural gas and crude oil prices contribute to fluctuating costs of conventionally produced petroleum or natural gas derived ethylene, thereby creating a greater demand for alternative sources of ethylene than ever before as oil prices rise.

Ethylene from various ethyl esters was reported to be produced in the gas phase over a zeolite catalyst at temperatures in the range of 150-300 ℃. Types of ethyl esters that can be used include ethyl esters of formic acid, acetic acid, and propionic acid. See, for example, U.S. Pat. No.4,620,050 to Cognion et al, where selectivity is reported to be acceptable.

U.S. Pat. No.4,270,015 to Knifton describes a process involving a two-step process to obtain ethylene: wherein a mixture of carbon monoxide and hydrogen, commonly referred to as synthesis gas, is reacted with a carboxylic acid containing 2 to 4 carbon atoms to form the corresponding ethyl ester of said carboxylic acid, which is subsequently pyrolyzed in a quartz reactor at elevated temperatures of about 200 ℃ to 600 ℃ to obtain ethylene. The ethylene so produced contains other hydrocarbons, particularly ethane as an impurity. It has also been reported that pyrolysis of pure ethyl propionate at 460 ℃ can bring the concentration of ethane to high values, close to 5%. More importantly, very low ester conversion and ethylene yields are reported.

U.S. Pat. No.4,399,305 to Schreck describes the use of DuPont de Nemours&Co under the trade nameThe cracking catalyst, which is composed of a commercially available perfluorosulfonic acid resin, obtains high purity ethylene from ethyl acetate.

On the other hand, ball. Soc. Chim. Belg. by Malinowski et al (1985), 94(2), 93-5 disclose the use of a substrate, such as acetic acid, on a support material such as Silica (SiO) (SiO. RTM. I. B₂) Or titanium dioxide (TiO)₂) The reaction on the lower titanium, which is heterogenized above, produces a product mixture comprising diethyl ether, ethylene and methane, with poor selectivity.

WO 2003/040037 discloses the use of crystalline microporous metalloaluminophosphates (ELAPO), particularly SAPO-type zeolites such as SAPO-5, SAPO-11, SAPO-20, SAPO-18 and SAPO-34, having Si/Al ratios of 0.03 to 017, as adsorbents or catalysts for the production of olefins from oxygenated feedstocks containing methanol, ethanol, n-propanol, isopropanol, C4-C20 alcohols, methyl ethyl ether, dimethyl ether, diethyl ether, diisopropyl ether, formaldehyde, dimethyl carbonate, dimethyl ketone and/or acetic acid. Similar disclosures utilize silicoaluminophosphate molecular sieves comprising at least one intergrown phase of molecular sieve. It is reported that in this process an oxygenate-containing feedstock contacts a catalyst comprising a molecular sieve in a reaction zone of a reactor under conditions effective to produce light olefins, particularly ethylene and propylene. See U.S. patent No.6,812,372 to Janssen. Reference to such an oxygenate feedstock includes acetic acid, but the disclosure appears to be limited to methanol or dimethyl ether. See, also, U.S. Pat. No.6,509,290 to Vaughn, which also discloses converting an oxygenate feedstock to olefins.

Bimetallic ruthenium-tin/silica catalysts are prepared by reacting tetrabutyltin with ruthenium dioxide supported on silica. These catalysts are reported to be based on their tin/ruthenium ratio (Sn/Ru)The value (content) shows different selectivities. Specifically, the selectivity of the hydrogenolysis of ethyl acetate was reported to be very different depending on the Sn/Ru ratio in the catalyst. For example, for ruthenium alone in SiO₂The reaction is not selective: producing methane, ethane, carbon monoxide, carbon dioxide, and ethanol and acetic acid. However, for low tin contents, the catalyst is reported to have considerable selectivity for the formation of acetic acid, and at the same time at higher Sn/Ru ratios, ethanol is the only product detected. See students in surface science and Catalysis (1989), Volume Date 1988, 48(struct. React. surf.), 591-600, Loessard et al.

Catalytic reduction of acetic acid was also investigated. For example, j.chem.res, Synopses (1980), (11), 373, by Hindermann et al, discloses the catalytic reduction of acetic acid on iron and on base-promoted iron. In their studies they found that the reduction of acetic acid on base-promoted iron follows at least two different paths depending on the temperature. For example, they found that at 350 ℃, the pira (Piria) reaction predominates and produces acetone and carbon dioxide, and they also observed the decomposition products methane and carbon dioxide. However at lower temperatures these decomposition products are reduced. On the other hand, a conventional (normal) reduction reaction leading to the formation of acetaldehyde and ethanol was observed at 300 ℃.

From the foregoing it is evident that existing processes do not have the necessary selectivity to ethylene or that the prior art specifies expensive starting materials other than acetic acid and/or aims to produce products other than ethylene.

Disclosure of Invention

A process for selectively forming ethylene from acetic acid, the process comprising: contacting a feed stream containing acetic acid and hydrogen with a first catalytic composition comprising a suitable hydrogenation catalyst at an elevated temperature in a first reaction zone to form an intermediate mixture preferably comprising acetic acid, ethanol and ethyl acetate; and subsequently reacting the hydrogenated mixture in a second reaction zone over a suitable dehydration and/or cracking catalyst to form ethylene.

Drawings

The invention is described in more detail below with reference to the single figure, which is a schematic illustration of a layered fixed bed reactor.

Detailed Description

The invention is described in detail below with reference to a number of embodiments for illustrative purposes only. Various modifications to the specific embodiments within the spirit and scope of the invention as set forth in the appended claims will be readily apparent to those skilled in the art.

Unless more specifically limited as follows, the terms used herein take their ordinary meaning. Unless otherwise indicated,% and the like refer to mole%.

"conversion" is expressed as a mole percent based on acetic acid in the feed.

"selectivity" is expressed as mole% based on converted acetic acid. For example, if the conversion is 50 mole% and 50 mole% of the converted acetic acid is converted to ethylene, it means that the ethylene selectivity is 50%. Ethylene selectivity was calculated from Gas Chromatography (GC) data using the following equation:

without intending to be bound by theory, it is believed that the conversion of acetic acid to ethylene according to the present invention proceeds according to one or more of the following chemical equations:

step 1 a: the ethanol is obtained by hydrogenating acetic acid.

Step 1 b: the acetic acid is hydrogenated to obtain ethyl acetate.

Step 1 c: the ethyl acetate is cracked to obtain ethylene and acetic acid.

Step 2 a: dehydrating the ethanol to obtain the ethylene.

The process of the present invention may be practiced in various configurations (configurations) using fixed bed reactors or fluidized bed reactors as those skilled in the art can readily appreciate. Adiabatic reactors may be used, or shell and tube reactors provided with a heat transfer medium may be used. In any case, the two reaction zones may be housed in a single vessel having different layers within a fixed bed reactor or may be housed in a single vessel fluidized bed system having baffles and partitions to provide the two different zones. Alternatively, two vessels may be used to house different reaction zones. In any case, it is possible to operate a plurality of reactors having two zones in parallel, for example, if convenient, it is possible to use a plurality of tubular reactors having a layered fixed bed arranged in parallel.

A tubular reactor with a layered fixed bed 10 is schematically shown in fig. 1. The bed 10 is a fixed bed in a vessel 12, said vessel 12 including a mixing zone or layer 14 of inert particulate material layer, a first reaction zone or layer 16, an optional separation zone or layer 18, a second reaction zone or layer 20 and a spacer zone or layer 22. A reaction mixture comprising acetic acid, hydrogen and optionally an inert carrier gas is fed to bed 10 as stream 24 under pressure to mixing zone 14. This stream is then fed (by pressure drop) to the first reaction zone or layer 16. Reaction zone 16 contains a first catalytic composition comprising a suitable hydrogenation catalyst, where a hydrogenated acetic acid intermediate is produced. Suitably, the first catalytic composition is in particulate form.

After hydrogenation, the mixture is advanced through an optional separation zone 18 to a second reaction zone or layer 20 containing a second catalytic composition comprising a suitable dehydration and/or cracking catalyst.

In zone 20, the hydroacetic acid intermediates, such as ethyl acetate and ethanol, are dehydrated and/or cracked to produce ethylene, which product is forwarded to a spacer zone 22 at a pressure less than the inlet pressure of vessel 12, ultimately exiting bed 10 as product stream 26.

Layers 14, 18 and 22 are all optional in the configuration shown in fig. 1 and may be formed of an inert particulate material of suitable size. In other arrangements or configurations, equivalent devices may have any suitable design effective to facilitate mixing, separation, heat transfer, and the like, as will be appreciated by those skilled in the art.

Various hydrogenation catalysts known to those skilled in the art may be used in hydrogenating acetic acid to ethanol in the first step of the process of the present invention. Suitable hydrogenation catalysts are metal catalysts on a suitable support. As examples of such catalysts, the following catalysts may be mentioned without any limitation: copper, nickel, aluminum, chromium, zinc, and mixtures thereof. Typically, a single metal or bimetallic catalyst on a suitable support may be used as the hydrogenation catalyst. Copper alone or in combination with aluminum, chromium or zinc is therefore particularly preferred.

Various catalyst supports known in the art may be used to support the catalyst of the present invention. Examples of such supports include, without any limitation, iron oxide, silica, alumina, titania, zirconia, magnesia, calcium silicate, carbon, graphite, and mixtures thereof.

In embodiments of the present invention, specific examples of supported hydrogenation catalysts include iron oxide, silica, alumina, titania, zirconia, magnesia, calcium silicate, carbon, graphite, and mixtures thereof. In particular, as described above, copper and copper-aluminum catalysts supported on iron oxide are preferred.

Some commercially available catalysts include the following: copper-aluminum catalyst sold by Sud Chemie under the name T-4489; copper-zinc catalysts sold under the names T-2130, T-4427 and T-4492; copper-chromium catalysts sold under the names T-4419 and G-99B; and nickel catalysts sold under the names NiSAT 310, C47-7-04, G-49 and G-69; all sold by Sud Chemie. Particular preference is given to the copper-aluminum catalysts sold under the name T-4489.

The amount of metal supported on the support is not critical in the present invention and can range from about 3% to about 10% by weight. Metal loadings of about 4 wt% to about 6 wt% based on the weight of the support are particularly preferred. Thus, for example, 4 to 6 wt.% copper supported on iron oxide is a particularly preferred catalyst.

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

For supports with low surface area, such as alpha-alumina or iron oxide, an excess of metal solution is added until fully wet or excess liquid impregnation is achieved in order to obtain the desired metal loading.

As noted above, some hydrogenation catalysts are of the bimetallic type. Typically, in such cases, one metal acts as a promoter metal while the other metal is the primary metal. Such as copper, nickel, cobalt and iron, are considered the primary metals used in the preparation of the hydrogenation catalysts of the present invention. The primary metal may be combined with a promoter metal such as tungsten, vanadium, molybdenum, chromium or zinc. It should be noted, however, that sometimes the primary metal may also act as a promoter metal or vice versa. For example, nickel may be used as a promoter metal when iron is used as the primary metal. Similarly, chromium may be used as the primary metal in combination with copper (i.e., Cu — Cr as the primary bimetallic metal), which may be further combined with a promoter metal such as cerium, magnesium, or zinc.

The bimetallic catalyst is typically impregnated in two steps. First, the "promoter" metal is added, followed by the "primary" metal. Each impregnation step is followed by drying and calcination. Bimetallic catalysts may also be prepared by co-impregnation. In the case of trimetallic Cu/Cr containing catalysts as described above, sequential impregnation may be used with initial addition of the "promoter" metal. The second impregnation step may comprise co-impregnation of the two main metals, i.e. Cu and Cr. For example, it can be prepared on SiO by first impregnating cerium nitrate, followed by co-impregnation of copper nitrate and chromium nitrate₂Cu-Cr-Ce. Again, each impregnation is followed by drying and calcination. 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 may also be used. Examples of other suitable metal salts for impregnation include metal hydroxides, metal oxides, metal acetates, ammonium metal oxides such as ammonium heptamolybdate hexahydrate, metal acids such as perrhenic acid solution, metal oxalates, and the like.

In another aspect of the process of the present invention, any known dehydration catalyst may be used in the second step of the process of the present invention. Typically, a zeolite catalyst is used as the dehydration catalyst. While any zeolite having a pore size of at least about 0.6nm may be used, preferably used in such zeolites are dehydration catalysts 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 in mol.sieves pap.conf., 1967, 78, soc.chem.ind.london, to d.domine and j.quabex.

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 catalysis of chemical reactions. For example, U.S. Pat. No.3,702,886 to Argauer discloses a class of synthetic zeolites referred to as "ZSM-5 zeolites" which are effective for the catalysis of various hydrocarbon conversion processes.

Zeolites suitable for the process of the invention may be in the basic form, partially or fully acidified form, or partially dealuminated form.

The active catalyst, referred to as an "H-ZSM-5" or "H-mordenite" zeolite in the process of the present invention, is prepared from the corresponding "ZSM-5" or "mordenite" zeolite by replacing a substantial portion, usually at least about 80% of the cations of the latter zeolite 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 neutral form, i.e. in a well-defined crystalline structure. Among the zeolite catalysts of the particularly preferred class for the purposes of the present invention are those in which SiO is present₂With Al₂O₃Is about 10 to 60.

As previously described, ethylene is produced by dehydration and decomposition or "cracking" of ethyl acetate to ethylene and acetic acid. This may be a catalytic reaction using a cracking catalyst if desired. Suitable cracking catalysts include sulfonic acid resins such as the perfluorosulfonic acid resins disclosed in the above-mentioned U.S. patent No.4,399,305 (the disclosure of which is incorporated herein by reference). Zeolites are also suitable as cracking catalysts, as described in U.S. Pat. No.4,620,050, the disclosure of which is also incorporated herein by reference. Thus, in the highly efficient process of the present invention, a zeolite catalyst can be used to simultaneously dehydrate ethanol to ethylene and decompose ethyl acetate to ethylene.

The selectivity of acetic acid to ethylene is suitably greater than 10%, for example at least 20%, at least 40%, at least 60% or at least 80%. Depending on the mixture of by-products, if for undesired products such as CO₂The selectivity of (a) is kept low, operation at moderate selectivities may be desirable.

Preferably, for the purposes of the process of the present invention, a suitable hydrogenation catalyst is copper on iron oxide or a copper-aluminum catalyst sold by Sud Chemie under the trade name T-4489, and the dehydration catalyst is H-mordenite. In this embodiment of the process of the present invention, the copper loading on the iron oxide support or in the bimetallic copper-aluminum catalyst is typically from about 3 wt.% to about 10 wt.%, preferably it is from about 4 wt.% to about 6 wt.%.

In one embodiment of the present invention, layered hydrogenation and dehydration catalysts are preferred. Preferably, the top layer of the catalyst bed is a hydrogenation catalyst and the bottom layer is a dehydration catalyst.

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

The reaction can be carried out under a wide variety of conditions, in either the gaseous or liquid state. Preferably, the reaction is carried out in the gas phase. Reaction temperatures of, for example, from about 200 ℃ to about 375 ℃, preferably from about 250 ℃ to about 350 ℃, may be used. The pressure is generally not critical to the reaction and subatmospheric, atmospheric or superatmospheric pressures may be used. However, in most cases, the reaction pressure may be about 1 to 30 atmospheres absolute.

Although the reaction consumes 2 moles of hydrogen per mole of acetic acid to produce 1 mole of ethanol, the actual molar ratio of acetic acid to hydrogen in the feed stream may vary over a wide range, e.g., from about 100:1 to 1: 100. However, it is preferred that such a ratio is from about 1:20 to 1: 2.

The feed used in connection with the process of the present invention may be obtained from any suitable source, including natural gas, petroleum, coal, biomass, and the like. It is well known to produce acetic acid by methanol carbonylation, acetaldehyde oxidation, ethylene oxidation, oxidative fermentation, anaerobic fermentation, and the like. As petroleum and natural gas become more expensive, processes for producing acetic acid and intermediates such as methanol and carbon monoxide from alternative carbon sources have attracted greater attention. Of particular interest is the production of acetic acid from synthesis gas (syngas) which may be obtained from any suitable carbon source. U.S. patent No.6,232,352 to Vidalin, the disclosure of which is incorporated herein by reference, for example, teaches a method of retrofitting a methanol plant for the manufacture of acetic acid. By retrofitting a methanol plant, the substantial capital costs associated with CO production for a new acetic acid plant are significantly reduced or largely eliminated. All or a portion of the syngas is split from the methanol synthesis loop (loop) and fed to a separation unit to recover CO and hydrogen, which are then used to produce acetic acid. In addition to acetic acid, the process may also be used to produce hydrogen for use in connection with the present invention.

U.S. patent No. re 35,377 to Steinberg et al, also incorporated herein by reference, provides a process for the production of methanol by the conversion of carbonaceous materials such as oil, coal, natural gas and biomass materials. The method comprises hydro-gasification of solid and/or liquid carbonaceous material to obtain a process gas, which is steam pyrolyzed together with additional natural gas to form synthesis gas. The synthesis gas is converted to methanol which can be carbonylated to acetic acid. This process also produces hydrogen for use in connection 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 may be fed with hydrogen either undiluted or diluted with a relatively inert carrier gas such as nitrogen, argon, helium, carbon dioxide, and the like.

Alternatively, acetic acid in vapor form may be withdrawn directly as a crude product from 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 acetic acid and light ends or remove water, thereby saving overall processing costs.

The contact or residence time may also vary widely depending on such variables as the amount of acetic acid, catalyst, reactor, temperature and pressure. Typical contact times range from fractions of a second to more than several hours when using catalyst systems other than fixed beds, with contact times of about 0.5 to 100 seconds being preferred, at least for 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 hydrogenation and zeolite catalysts in combination with inert materials such as glass wool to adjust the pressure drop of the reactant stream across the catalyst bed and the contact time of the reactant compounds with the catalyst particles.

Also provided in a preferred embodiment is a process for selectively forming ethylene from acetic acid, the process comprising: contacting a feed stream of acetic acid and hydrogen with a hydrogenation catalyst selected from copper or copper-aluminum catalysts supported on iron oxide at a temperature of about 250 ℃ to 350 ℃ to form an intermediate mixture comprising acetic acid, ethanol, and ethyl acetate; and simultaneously reacting the mixture over a dehydration catalyst selected from H-mordenite or sodium Y zeolite to form ethylene.

In this embodiment of the process of the invention, the preferred hydrogenation catalyst is 5 wt% copper on iron oxide or 5 wt% copper in a copper-aluminum catalyst and the dehydration catalyst is H-mordenite. In this embodiment of the process of the present invention, the hydrogenation and dehydration catalyst is preferably layered in a fixed bed and reacted in the vapor phase at a temperature of from about 300 ℃ to 350 ℃ and at a pressure of from about 1 to 30 atmospheres absolute with a contact time of the reactants of from about 0.5 to 100 seconds.

The following examples describe the procedures used to prepare the various catalysts used in the process of the present invention.

Example A

Preparation of 5 wt.% copper on iron oxide

Powdered and sieved iron oxide (100g) with a uniform particle size distribution of about 0.2mm was dried overnight at 120 ℃ in an oven under nitrogen atmosphere and then cooled to room temperature. A solution (100ml) of copper nitrate (17g) in distilled water 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 B

Preparation of H-mordenite

The H-mordenite was prepared by calcining the ammonium form of mordenite at 500-550 deg.C for 4-8 hours. If the sodium form of mordenite is used as a precursor, the sodium mordenite is ion-exchanged to the ammonium form prior to calcination.

Gas Chromatography (GC) analysis of the product

Product analysis was performed by online GC. The reactants and products were analyzed using a three-channel integrated GC equipped with 1 Flame Ionization 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 quantitation:

acetaldehyde

Ethanol

Acetone (II)

Acetic acid methyl ester

Vinyl acetate (VAA)

Ethyl acetate

Acetic acid

Ethylene diacetate

Ethylene glycol

Ethylidene diacetate

Paraldehyde

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

CO₂

ethylene

Ethane (III)

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

helium gas

Hydrogen gas

Nitrogen gas

Methane

Carbon monoxide

Prior to the reaction, the retention times of the different components were determined by spiking with individual compounds and the GC was calibrated with a calibration gas of known composition or with a liquid solution of known composition. This allows the response factors of the individual components to be determined.

Example 1

The catalysts used are copper on iron oxide catalyst, T-4489 available from Sud Chemie, and H-mordenite prepared by replacing sodium ions with approximately 500ppm of hydrogen ions based on the weight of the zeolite in a sodium aluminosilicate mordenite catalyst prepared according to U.S. Pat. No.4,018,514 or an equivalent in which the silica to alumina ratio is preferably in the range of from about 15: 1 to about 100: 1. A suitable catalyst is CBV21A from Zeolyst International having a silica to alumina ratio of about 20: 1.

In a tubular reactor made of stainless steel with an internal diameter of 30mm and capable of being brought to a controlled temperature, 30ml of catalyst of 5% by weight of copper on iron oxide as top layer and 20ml of H-mordenite as bottom layer were placed. The length of the combined catalyst bed after loading was approximately about 70 mm.

The feed liquid consists essentially of acetic acid. The reaction feed liquid was vaporized and charged to the reactor at an average total Gas Hourly Space Velocity (GHSV) of 2500h "1 along with hydrogen and helium as carrier gas at a temperature of about 300 ℃ and a pressure of 100 psig. The feed stream contains a mole percent of acetic acid of from about 6.1% to about 7.3% and a mole percent of hydrogen of from about 54.3% to about 61.5%. The feed stream is first fed to the (top) layer of hydrogenation catalyst and then the stream with the hydrogenated acetic acid intermediate is contacted with the dehydration catalyst layer. A portion of the vapor effluent from the reactor was passed through a gas chromatograph for analysis of the effluent contents. The acetic acid conversion was 65% and the ethylene selectivity was 85%. The selectivity to acetone was 3%, the selectivity to ethyl acetate was 2%, and the selectivity to ethanol was 0.6%. Carbon dioxide is relatively low; measured acetic acid converted vs CO₂The selectivity of (3) was 4%.

Example 2

The catalyst used was 5 wt% copper on iron oxide prepared according to the procedure of example a and H-mordenite prepared as described in example 1 above by replacing the sodium ions with approximately 500ppm of hydrogen ions based on the weight of the zeolite in a sodium aluminosilicate mordenite catalyst.

The procedure given in example 1 was substantially repeated with an average total Gas Hourly Space Velocity (GHSV) of the vaporized feed stream of acetic acid, hydrogen and helium at a temperature of about 350 ℃ and a pressure of 100psig of 2500h "1. The resulting feed stream contained about 7.3 mole percent acetic acid and about 54.3 mole percent hydrogen. A portion of the vapor effluent was passed through a gas chromatograph for analysis of the effluent contents. The acetic acid conversion was 8% and the ethylene selectivity was 18%.

Generally, selectivities to ethylene of greater than about 10% are highly desirable; it is appreciated that other by-products such as ethanol or ethyl acetate may be reacted with unreactedIs recycled to the reactor, although other by-products may also be reprocessed or used for fuel value. Expected to be on CO₂Less than 10%, preferably less than 5%.

Comparative examples 1 to 5

These examples illustrate the reaction of acetic acid and hydrogen over various catalysts, wherein no ethylene is formed and/or very low ethylene levels are detected.

In all of these examples, the procedure given in example 1 was followed essentially except that the different catalysts listed in Table 1 were used. As summarized in table 1, only one single catalyst layer was used in all of these comparative examples. The reaction temperature and selectivity to ethylene are also listed in table 1.

TABLE 1

Various other products including acetaldehyde, ethanol, ethyl acetate, ethane, carbon monoxide, carbon dioxide, methane, isopropanol, acetone, and water were observed in these examples.

While the invention has been described by certain of the foregoing embodiments, it is not to be construed as being limited thereby; but that the invention include the general scope disclosed above. Various modifications and implementations can be made without departing from the spirit and scope thereof.

Claims (16)

1. A process for selectively forming ethylene from acetic acid, the process comprising:

contacting in a first reaction zone, in the vapor phase and at a temperature of from 200 ℃ to 375 ℃, a feed stream comprising acetic acid and hydrogen with a first catalytic composition comprising a supported hydrogenation catalyst selected from the group consisting of copper, nickel, aluminum, chromium, zinc, palladium, or mixtures thereof, to form a hydrogenated intermediate mixture; and

reacting the hydrogenated intermediate mixture in a second reaction zone over a second catalytic composition comprising a dehydration catalyst selected from the group consisting of H-mordenite, ZSM-5, zeolite X and zeolite Y to form ethylene.

2. The process according to claim 1, wherein the first and second reaction zones comprise a first layer of a first catalytic composition and a second layer of a second catalytic composition, respectively, in a fixed bed.

3. The process according to claim 1, wherein the first and second reaction zones are in separate vessels.

4. The process according to claim 1, wherein the selectivity to ethylene based on acetic acid consumed is at least 20%.

5. The process according to claim 1, wherein the selectivity to ethylene based on acetic acid consumed is at least 40%.

6. The process according to claim 1, wherein the selectivity to ethylene based on acetic acid consumed is at least 60%.

7. The process according to claim 1, wherein the support is selected from the group consisting of iron oxide, silica, alumina, titania, zirconia, magnesia, calcium silicate, carbon and mixtures thereof.

8. The method of claim 7, wherein the carbon is graphite.

9. The process according to claim 1, wherein the zeolite has a silica to alumina molar ratio of from 10 to 60.

10. The process according to claim 1, wherein the hydrogenated intermediate mixture comprises ethanol and ethyl acetate.

11. The process according to claim 1 wherein the hydrogenation catalyst is copper on iron oxide and the dehydration catalyst is H-mordenite.

12. The process according to claim 1 wherein the hydrogenation catalyst is a copper-aluminum catalyst and the dehydration catalyst is H-mordenite.

13. The process according to claim 1, wherein the hydrogenation and conversion to ethylene is carried out at a temperature of from 250 ℃ to 350 ℃.

14. The process of claim 1 wherein the reactants are comprised of acetic acid and hydrogen in a molar ratio of from 100:1 to 1:100 and the pressure in the reaction zone is from 1 to 30 atmospheres absolute.

15. The process of claim 1 wherein the reactants are comprised of acetic acid and hydrogen in a molar ratio of from 1:20 to 1:2, the temperature in the reaction zone is from 300 ℃ to 350 ℃, and the pressure in the reaction zone is from 1 to 30 atmospheres absolute.

16. A process for selectively forming ethylene from acetic acid, the process comprising:

contacting a feed stream of acetic acid and hydrogen with a hydrogenation catalyst selected from copper or copper-aluminum catalysts supported on iron oxide at a temperature of 250 ℃ to 350 ℃ to form an intermediate mixture comprising acetic acid, ethanol, and ethyl acetate; and simultaneously reacting the mixture over a dehydration catalyst selected from H-mordenite or sodium Y zeolite to form ethylene.