MXPA99001151A - Selective preparation process of acetic acid and catalysts therefor - Google Patents

Abstract

A process for selectively preparing acetic acid from a feed gas substance such as ethane, ethylene or mixtures thereof, as well as oxygen, at an increased temperature, is disclosed. The feed gas substance is brought together with a catalyst which contains the elements Mo, Pd, X and Y in the gram-atomic ratio a:b:c:d in combination with oxygen, according to formula (I) in which MoaPdbXcYd. The symbols X and Y have the following meanings:X stands for one or several elements selected from the group composed of Cr, Mn, Nb, Ta, Ti, V, Te and/or W, in particular Nb, V and W;Y stands for one or several elements selected from the group composed of B, Al, Ga, In, Pt, Zn, Cd, Bi, Ce, Co, Cu, Rh, Ir, Au, Ag, Fe, Ru, Os, K, Rb, Cs, Mg, Ca, Sr, Ba, Sr, Ba, Zr, Hf, Ni, P, Pb, Sb, Si, Sn, Tl and U, in particular Ca, Sb, Te and Li. Also disclosed is a catalyst for selectively preparing acetic acid which contains the elements Mo, Pd, X and Y in the gram-atomic ratio a:b:c:d in combination with oxygen. The indices a, b, c and x represent the gram-atomic ratio of the corresponding elements, and a=1;b>0, and d=0.05-2.

Description

PROCEDURE FOR THE SELECTIVE PREPARATION OF ACETIC ACID AND CATALYSTS ARE SUITABLE FOR THIS PURPOSE DESCRIPTIVE MEMORY The present invention relates to a process for the selective preparation of acetic acid by catalytic oxidation in the gas phase of ethane and / or ethylene in the presence of a palladium-containing catalyst. The oxidative dehydrogenation of ethane to ethylene in the gas phase at temperatures of greater than 500 ° C is known, for example from US-A-4 250 346, US-A-4 524 236 and US-A-4 568 790. For example, US-A-4 250 346 describes the use of a catalyst composition containing the molybdenum, X and Y elements in the ratio a.-b: c to convert ethane to ethylene, wherein X is Cr, Mn, Nb. , Ta, Ti, V and / oe Y is Bi, Ce, Co, Cu, Fe, K Mg, Ni, P, Pb, Sb, Si, Sn, Ti and / or U, since it is 1, b is 0.05 a 1 and c is from 0 to 2. The total value of c for Co, Ni and / or Fe must in this case be less than 0.5. The reaction is preferably carried out in the presence of added water. The exposed catalysts can also be used for the oxidation of ethane to acetic acid, the efficiency of the conversion to acetic acid being about 18%, in a conversion of ethane of 7.5%.

The documents mentioned above are mainly related to the preparation of ethylene, less in degree with the final preparation of acetic acid. In contrast, EP-BO 294 845 discloses a process for the selective preparation of acetic acid from ethane, ethylene or mixtures thereof, using oxygen in the presence of a catalyst mixture containing at least A calcined catalyst of the formula MoxVy or MoxVyZy, where Z is one or more of the metals Li, Na, Be, Mg, Ca, Sr, Ba, Zn, Cd, Hg, Se, Y, La, Ce, Al, Ti, Ti, Zr, Hf, Pb, Nb, Ta, As, Sb, Bi, Cr,, U, Te, Fe, Co, and Ni, and x is 0.5 to 0.9, and is 0.1 to 0.4 and z is 0.001 al, and B) a catalyst for the hydration of ethylene and / or a catalyst for the oxidation of ethylene. The second catalyst component B is, in particular, a molecular sieve catalyst or an oxidation catalyst containing palladium. When the described catalyst mixture is used and a gas mixture consisting of ethane, oxygen, nitrogen and steam is passed through the catalyst-containing reactor, the maximum selectivity is 27% at a conversion of 7% ethane . The high conversion rates of ethane are achieved, according to EP 0 294 845, using only the catalyst mixture described, but not using a single catalyst containing components A and B. EP-B-0 407 091 describes a further process for preparing a product consisting of ethylene and / or acid acetic. In this case, ethane and / or ethylene and a gas consisting of molecular oxygen are brought into contact at an elevated temperature with a catalyst composition containing the elements A, X and Y. In this case, Mo¿ReeWf X is Cr, MN, Nb, Ta, Ti, V and / oe and is Bi, Ce, Co, Cu, Fe, K, Mg, Ni, P, Pb, Sb, Si, Sn, Ti and / or U. The selectivities maximums that could be achieved when using the catalyst described in the oxidation of ethane to acetic acid are 78%. Other secondary products that are formed are carbon dioxide, carbon monoxide and ethylene. However, none of the publications listed above disclose the use of a catalyst containing the palladium and molybdenum elements for the selective oxidation of ethane and / or ethylene to acetic acid. In addition, the selectivities achieved hitherto in the prior art for oxidation to acetic acid are still not satisfactory. It is therefore an object of the invention to provide a process that allows ethane and / or ethylene to be oxidized in a simple and oriented manner, and with high selectivity under very mild reaction conditions to give acetic acid. It has now surprisingly been found that the use of a catalyst containing the molybdenum and palladium elements and one or more elements selected from the group consisting of chromium, manganese, niobium, tantalum, titanium, vanadium, tellurium and / or tungsten, makes it possible to oxidize ethane and / or ethylene under relatively mild conditions, in a simple manner with high selectivity to give acetic acid. The present invention therefore provides a process for the selective preparation of acetic acid from a gaseous supply consisting of ethane, ethylene and mixtures thereof, plus oxygen at elevated temperature, which consists in placing the gaseous supply in contact with a catalyst that contains the elements Mo, Pd, X and X in gram-atom ratios of a: b: c: d in combination with oxygen MoaPdbXcYd wherein the symbols X and Y have the following meanings: X is one or more elements selected from the group consisting of: Cr, Mn, Nb, Ta, Ti, V, Te and / or W, in particular Nb, V and W; And it is one or more elements selected from the group consisting of B, Al, Ga, In, Pt, Zn, Cd, Bi, Ce, Co, Cu, Rh, Ir, Au, Ag, Fe, Ru, Os, K, Rb, Cs, Mg, Ca, Sr, Ba, Zr, Hf, Ni, P, Pb, Sb, Si, Sn, Ti and U, in particular Ca, Sb and Li. The indices a, b, c and d are the atom-gram relations of the corresponding elements, where a = 1, b > 0, c > 0, and d = 0-2. If X and Y are a plurality of different elements, the indices c and d can also adopt a plurality of different values. The present invention also provides a catalyst for the selective preparation of acetic acid containing the elements Mo, Pd, X and Y in the gram-atom ratios of a: b: c: d in combination with oxygen. The gram-atom ratios of a: b: c: de are preferably within the following ranges: a = 1; b = 0.0001 to 0.5; c = 0.1-1.0 and d = 0-1.0.

The content of palladium in the catalyst that is greater than the specified upper limit promotes the formation of carbon dioxide in the process of the invention. In addition, the high palladium content is also generally avoided because it makes the catalyst unnecessarily expensive. On the other hand, the palladium content less than the specified limiting value favors the formation of ethylene. The catalyst used according to the invention preferably contains not only the molybdenum and palladium elements, but also vanadium, nibium, antimony and calcium in combination with oxygen. The gram-atom ratios of a: b: c1: c2 id1: d2: of the elements Mo: PD: V: Nb: Sb: Ca are preferably as follows: a (Mo) = 1; M b (Pd) = 0.0001-0.5, in particular 0.0001-0.05; c1 (V) = 0.1-1.0; c2 (Nb) = 0.1-0.5; (Sb) = 0-0.5; (Ca) = 0-0.2.

Examples of such catalyst compositions that are preferably used in the process of the invention are: Mol .00v0.2512pd0.0005 Mo1.00v0.25Nb0.12pd0.0004 Mo1.00v0.25Nb0.12pd0.0003 Mol .00v0.36Nb0.03sb0.01Ca0.01pd0.0005 Mol .00v0.50Nb0.15Te0.2PD0.0002 Mol .00v0.25Nb0.3W0.2PD0.0003 Mol .00v0.25Nb0.3sb0. lPd0.0004 Catalysts which are used according to the invention can be prepared by conventional methods. These start from a diluted mixture, in particular an aqueous solution, which contain the individual starting components of the elements according to their proportions. The starting materials for the individual components in the preparation of the catalyst of the invention are, apart from the oxides, preferably water-soluble substances such as ammonium salts, nitrates, sulfates, halides, hydroxides and salts of organic acids which can be converted to the corresponding oxides by heating. To mix the components, aqueous solutions or suspensions of the metal salts are prepared and mixed. In the case of molybdenum, it is advisable to use the corresponding molybdates, for example ammonium molybdate, as starting compounds due to their commercial availability. Suitable palladium compounds are, for example, palladium (II) chloride, palladium (II) sulfate, tetraminpalladium (II) nitrate, palladium (II) nitrate and also palladium (II) acetylacetonate. The reaction mixture obtained is then stirred at 50 and up to 100 ° C for 5 minutes and up to 5 hours. The water is subsequently removed and the remaining catalyst is dried at a temperature of 50 to 150 ° C., in particular from 80 to 120 ° C. If the catalyst obtained is subsequently subjected to a calcination process, it is advisable to calcine the dried and pulverized catalyst at a temperature in the range of 100 ° C to 800 ° C, in particular from 200 to 500 ° C, in the presence of nitrogen , oxygen or a gas that contains oxygen. The duration is from 2 to 24 hours. The catalyst can be used without support material or mixed with or applied to an appropriate support material. Suitable support materials are the usual materials such as porous silicon dioxide, activated silicon dioxide, diatomaceous earth, silica gel, porous or non-porous aluminum oxide, titanium dioxide, zirconium dioxide, thorium dioxide, lanthanum oxide, manganese oxide, calcium oxide, barium oxide, oxide tin, cerium dioxide, zinc oxide, boron oxide, boron nitride, boron carbide, boron phosphate, zirconium phosphate, aluminum silicate, silicon nitride or silicon carbide, but also meshes made of glass, carbon fibers, metal or metal oxides or corresponding monoliths. Preferred support materials have a surface area of less than 100m / g. Preferred support materials are silicon dioxide and aluminum oxide having a low specific surface area. Catalyst can be used, after being configured, as a regular or irregularly shaped support mass or in the form of a powder as a heterogeneous oxidation catalyst. The reaction can be carried out in a fluidized bed or in a fixed bed reactor. For use in a fluidized bed, the catalyst is crushed to a particle size in the range of 10 to 220 μm. The gaseous supply contains ethane and / or ethylene which are supplied to the reactor as pure gases or mixed with one or more other gases. Suitable additional supporting gases of this type are, for example, nitrogen, methane, carbon monoxide, carbon dioxide, air and / or water vapor. The gas containing molecular oxygen can be air or gas containing more or less molecular oxygen than air, for example oxygen. The water vapor ratio can be in the range of 0 to 50% by volume. Higher concentrations of water vapor would make the aqueous acetic acid resulting unnecessarily more expensive for reasons of technical procedures. The ratio of ethane / ethylene to oxygen is advantageously in the range between 1: 1 and 10: 1, preferably between 2: 1 and 8: 1. The relatively high oxygen content is preferred, since the conversion of ethane achievable and hence the yield of acetic acid are higher. Preference is given to adding oxygen or the molecular oxygen-containing gas in a concentration range outside the explosive limits under reaction conditions, since this means the ratio of the process. However, it is also possible to set the ratio of ethane / ethylene to oxygen within the explosive limits. The reaction is carried out at temperatures between 200 and 500 ° C, preferably 200 to 400 ° C. The pressure can be atmospheric or super-atmospheric, for example in the range from 1 to 50 bar, preferably from 1 to 30 bar. The reaction can be carried out in a fixed bed or fluidized bed reactor. Advantageously, ethane is first mixed with inert gases such as nitrogen or water vapor, before it enters the oxygen or gas that It contains molecular oxygen. The mixed gases are preferably heated prior to the reaction temperature in a preheating zone, before the gas mixture is brought into contact with the catalyst. The acetic acid is separated from the gas leaving the reactor by condensation. The remaining gases are recirculated at the reactor inlet, where oxygen or gas containing molecular oxygen plus ethane and / or ethylene are dosed. Comparison of the catalysts of the invention with those known from the prior art show that, under identical reaction conditions (reaction inlet gas, pressure, residence time in the reactor) but at significantly lower temperatures, the present catalysts achieve even higher selectivities of acetic acid (Table 1, Example 3 (according to the invention): acetic acid selectivity = 77%, Example 13 (EP-0 407 091): acetic acid selectivity = 60%). In comparison with the catalyst composition described in US-A-4 250 346, the selectivity of the reaction to acetic acid can be markedly increased, by means of the catalysts of the invention even at pressures, temperatures and residence times of reaction more reduced (refer to example 1 (according to the invention): T = 250 ° C, p = 7 bar, residence time = 14 s, acetic acid selectivity = 84%, example 12 (US-A-4 250 346 ), T = 280 ° C, p = 15 bar, residence time = 30 s, acetic acid selectivity = 32%).

Similarly, the space-time yields can be greatly increased by means of the present catalysts (Table 1). The space yields of one time represent the amount of acetic acid known per unit time and per unit volume of the catalyst. Higher space-time yields are desirable, as this allows the size of the reactors and also the amount of circulated gas to be reduced. When the catalyst of the invention is used, the selectivity in the oxidation of ethane and / or ethylene to acetic acid is -60 mol%, preferably -75 mol%, in particular -80 mol%, in a conversion of ethane > 4%, preferably > 5%, in particular > 6%, so that, compared to the prior art, the process in the invention makes it possible to achieve an increase in the yields of acetic acid in a simple manner, while simultaneously reducing the formation of unwanted by-products.

EXAMPLES The catalyst composition specified in the examples is given in atom-gram ratios.

PREPARATION OF CATALYSTS Catalyst (I) A catalyst having the following composition was prepared: Mol .00V0.25Nb0.12pd0.0005 Solution 1: 10.22 g of ammonium metavanadate in 250 ml of water. Solution 2: 61.75 g of ammonium molybdate and 0.039 g of palladium acetate in 200 ml of water. Solution 3: 27.51 g of niobium oxalate in 25 ml of water.

The solutions were stirred separately at 90 ° C for 15 minutes. The third solution was then added to the first. The combined mixtures are stirred at 90 ° C for 15 minutes before the second is added. The resulting mixture is stirred at 90 ° C for 15 minutes. The water is subsequently extracted on a stove until a thick paste forms. This is dried at 120 ° C overnight. The solid is crushed (size fraction: 0.35-2 mm) and subsequently calcined in static air at 400 ° C for 4 hours. It is atomized after the catalyst in order to obtain a fraction of tamis of between 0.35 and 1 mm.

Catalyst (II) A catalyst having the following composition is prepared: Mol .00v0.25Nb0.12P 0.0004 The preparation was carried out as described in example I of catalysts except that 0.031 g was used instead of 0.039 g of palladium acetate.

Catalyst (III) A catalyst having a following composition was prepared: Mol .00v0.36Nb0.03sb0.01Ca0.01pd0.0005 Solution 1: 20.0 g of ammonium ammonium hydroxide in 100 mm of water. Solution 2: 4.8 g of ammonium metavanate in 100 ml of water. Solution 3: 2.6 g of niobium oxalate, 0.48 g of antimony oxalate, 0.34 g of calcium nitrate in 50 ml of water. Solution: 0.013 g of palladium acetate in 50 ml of acetone.

Solutions 1 to 3 were stirred separately at 70 ° C for 15 minutes. The third solution was then added to the second. The combined mixtures are stirred at 70 ° C for 15 minutes, before the first one is added. Solution 4 is subsequently added thereto. The resulting mixture is stirred at 70 ° C for 15 minutes. The water / acetone mixture is subsequently evaporated rapidly until a thick paste forms. This is dried at 120 ° C overnight. The solid is ground (fraction of tamis: 0.35-2 mm) and subsequently calcined in static air at 300 ° C for 5 hours. It is atomized after the catalyst in order to obtain a fraction of tamis between 0.35 and 0.7 mm.

COMPARATIVE EXAMPLES Catalyst (IV): By comparison, A catalyst corresponding to US 4,250,346 having the following composition was prepared: Mo1.00v0.25Nb0.12 The preparation was carried out as described in Example I of catalysts, except that palladium acetate was not used.

Catalyst (V) For comparison, a catalyst corresponding to EP 0 407 091 having the following composition was prepared: Mo0.370Re0.248v0.259NB0.070sb0.030Ca0.019 Solution 1: 10.0 g of ammonium perrenate and 9.7 g of ammonium bleach in 50 ml of water. Solution 2: 4.5 g of ammonium metavanadate in 50 ml of water. Solution 3: 6.5 g of niobium oxalate, 1.34 of antiminium oxalate, 0.58 g of calcium nitrate in 180 ml of water.

These solutions are stirred separately at 70 ° C for 15 minutes. The third solution is then added to the second. The combined ones are stirred at 70 ° C for 15 minutes before they are added to the first one. The resulting mixture is stirred at 70 ° C for 15 minutes. The water is subsequently removed over a burner until a thick paste is formed. This is dried at 120 ° C overnight. The solid is ground (fraction of tamis: 0.35-2 mm) and subsequently calcined in static air at 300 ° C for 5 hours. The catalyst is atomized afterwards in order to obtain a fraction of tamis between 0.35 and 1 mm.

METHODS TO TEST THE CATALYST A steel reactor having an internal diameter of 10 mm was charged with 10 ml of catalyst. The catalyst was heated at 250 ° C in a stream of air. The pressure was subsequently set by means of an admission pressure regulator. The desired mixture of ethane: oxygen: nitrogen was dosed together with water to a vaporizing zone where water was vaporized and mixed with the gases. The reaction temperature was measured using a thermocouple in the catalyst bed. The reaction line on the line was smoothed by a gas chromatography. In the examples, the following terms are defined as: Conversion of ethane (%) = 100x ([CO] / 2 + [C02] / 2 + [C2H4] + [CH3COOH]) / ([CO] / 2 + [C02 ] / 2 + [C2H4] + [C2H6] + [CH3COOH]) Ethylene selectivity (%) = 100x ([C2H4]) / ([CO]) / 2 + [C02]) / 2 + [C2H4] + [CH3COOH]) Acetic acid selectivity (%) = 100x ([CH3COOH]) / ([CO] / 2 + [C02] / 2 + [C2H4] + [CH3COOH]) where [] = concentrations in% mol and [C Hg] = ethane etching without reacting The residence time is defined as: T_ (s) = catalyst bed volume (ml) / volume flow of the gas through the reactor based on the reaction conditions (ml / s).

Process for the reaction The reactor gas supply consisted of 40% by volume of ethane, 8% by volume of oxygen, 32% by volume of nitrogen and 20% by volume of water vapor. The conditions of the results of the reaction are summarized in the following table.

TABLE 1 Compared to the comparative catalysts (IV) and (V), the catalysts (I), (II) and (III) achieve significantly higher selectivities to acetic acid at lower reaction temperatures and pressures. The catalysts I ((? T_ 0V0.25Nb0.12pd0.0005) 'IT- (Mo1.0V0.25Nbo.? Pdo.o? 04) and HI (M? 1.0V0.36Nb0.03sb0.01Ca0.01P 0.0005) give higher space-time yields compared to the IV catalysts (M? 1-0v0.25Nb0.12 = US-A-4 250 346) and V (M? 1.0Reo.ß7V? .7? Nbo.i9Sb0.? 8 a0.05 = EP "° 407 091).

COMPARATIVE EXPERIMENTS ON THE THERMAL STABILITY OF THE CATALYSTS In order to test the thermal stability of the catalysts, the catalysts (I) and (V) were installed in the reactor and treated for 100 hours (reaction conditions: 280 ° C, 15 bar, 30 seconds time). permanence, composition of the reaction gas: see above). After the treatment time, a sample was taken in each case from the beginning of the catalyst bed and the composition was analyzed quantitatively. The compositions of the catalysts that were used and those that were not used are compared in the following table.

TABLE 2 After only 100 hours of treatment, the catalyst (V) had lost 44.4% of the original rhenium. In contrast, the new and used catalyst (I) has the same composition.

Claims (11)

NOVELTY OF THE INVENTION CLAIMS

1. - A process for the selective preparation of acetic acid from a gaseous supply consisting of ethane, ethylene and mixtures thereof, plus oxygen at elevated temperature, which consists in placing the gaseous supply in contact with a catalyst containing the Mo, Pd, X and Y elements in gram-atom ratios of a: b: c: d in combination with oxygen MoaPdbXcYd (I) wherein the symbols X and Y have the following meanings: X is one or more elements selected from the group consisting of Cr, Mn, Nb, Ta, Ti, V, Te y; And it is one or more elements selected from the group consisting of B, Al, Ga, ln, Pt, Zn, Cd, Bi, Ce, Co, Rh, Ir, Cu, Ag, Au, Fe, Ru, Os, K, Rb, Cs, Mg, Ca, Sr, Ba, Zr, Hf, Ni, P, Pb, Sb, Si, Sn, Ti and U; the indices a, b, c, d and x are the gram-atom ratios of the corresponding elements, where a = 1; b > 0; c > 0; and d = 0.05-

2. 2. - The method according to claim 1, further characterized in that X and / or Y are a plurality of elements, in which, if desired, the indexes c and d adopt different values of different elements.

3. The method according to at least one of claims 1 and 2, further characterized in that the temperature is in the range of 200 to 500 ° C.

4. - The method according to at least one of claims 1 to 3, further characterized in that the pressure in the reactor is in the range of 1 to 50 bar.

5. The method according to at least one of claims 1 to 4, further characterized in that b is in the range of 0.0001 to 0.5.

6. The method according to at least one of claims 1 to 5, further characterized in that the gas mixed with at least one additional gas is supplied to the reactor.

7. - The method according to claim 6, further characterized in that the additional gas that is introduced is nitrogen, oxygen, methane, carbon monoxide, carbon dioxide, ethylene and / or water vapor.

8. The method according to at least one of claims 1 to 7, further characterized in that the catalyst contains at least one of the following compositions in combination with oxygen: Mol .00v0.25Nb0.12Pd0.0005 'Mol .00v0.25Nb0.12Pd0.0004 • Mo1.00v0.25Nb0.12pd0.0003 'M ?? _. Q0V0.36Nb0.03sb0.01Ca0.01pd0.0005 'Mol .00v0.50Nb0.15Te0.2pd0.0002 Mol .00v0.25Nb0.3W0.2pd0.0003 • Mol .00V0.25Nb0.3Sb0. l 0.0004 •

9. - The method according to at least one of claims 1 to 8, further characterized in that the catalyst is mixed with a support material or fixed on the support material.

10. The process according to at least one of claims 1 to 9, further characterized in that the selectivity of the oxidation reaction to acetic acid is • 60%, at a conversion of ethane of -4%.

11. A catalyst for the selective oxidation of ethane, ethylene or mixtures thereof, plus oxygen, comprising the elements Mo, Pd, X and Y in gram-atom ratios of a: b: c: d in combination with oxygen MoaPdbXcYd (I) wherein the symbols X and Y have the following meanings: X is one or more elements selected from the group consisting of Cr, Mn, Nb, Ta, Ti, V, Te y; And it is one or more elements selected from the group consisting of B, Al, Ga, ln, Pt, Zn, Cd, Bi, Ce, Co, Rh, Ir, Cu, Ag, Au, Fe, Ru, Os, K, Rb, Cs, Mg, Ca, Sr, Ba, Zr, Hf, Ni, P, Pb, Sb, Si, Sn, TI and U; the indices a, b, c, d and x are the gram-atom ratios of the corresponding elements, where a = 1; b > 0; c > 0; and d = 0.05-2.