HK1058188B - Process for the production of vinyl acetate - Google Patents

Description

Process for the production of vinyl acetate

The present invention relates generally to an integrated process for the production of vinyl acetate and more particularly to an integrated process for the production of vinyl acetate from a gaseous feedstock comprising primarily ethane.

Vinyl acetate is generally produced industrially by contacting acetic acid and ethylene with molecular oxygen in the presence of a catalyst active for the production of vinyl acetate. Suitably, the catalyst may comprise palladium, an alkali metal acetate promoter and optionally a co-promoter (e.g. gold or cadmium) on a catalyst support. Acetic acid produced by carbonylation generally requires extensive purification to remove, among other things, iodide formed from the commonly used catalyst systems, as iodide is considered a potential vinyl acetate catalyst poison.

Combinations of processes for producing vinyl acetate are known in the art. Thus, WO98/05620 discloses a process for the production of vinyl acetate and/or acetic acid which comprises first contacting ethylene and/or ethane with oxygen to produce a first product stream comprising acetic acid, water and ethylene, contacting the first product stream with oxygen in a second reaction zone in the presence or absence of additional ethylene and/or acetic acid to form a second product stream comprising vinyl acetate, water, acetic acid and optionally ethylene; separating the product stream of the second step by distillation into an overhead azeotrope fraction comprising vinyl acetate and water and a bottoms fraction comprising acetic acid; recovering acetic acid from the bottom fraction and optionally recycling the azeotrope fraction or recovering vinyl acetate from the azeotrope fraction. The catalysts proposed in WO98/05620 for the oxidation of ethylene to acetic acid or ethane to an acidic acid (acidic) are of the formula:

Pd_aM_bTiP_cO_x

wherein M is selected from Cd, Au, Zn, Tl, alkali metals and alkaline earth metals; other catalysts for the oxidation of ethane to acetic acid are catalysts of the formula:

VP_aM_bO_x

wherein M is selected from the group consisting of Co, Cu, Re, Fe, O, Nb, Cr, W, U, Ta, Ti, Zr, Zn, Hf, Mn, Pt, Pd, Sn, Sb, Bi, Ce, As, Ag and Au or

Catalyst for the oxidation of ethane and/or ethylene to form ethylene and/or acetic acid, comprising the elements A, X and Y, wherein a is Mo_dRe_eW_fX is Cr, Mn, Nb, Ta, V or W, Y is Bi, Ce, Co, Cu, Fe, K, Mg, Ni, P, Pb, Sb, Si, Sn, Tl or U.

Other catalysts proposed in WO98/05620 for the oxidation of ethane to acetic acid and ethylene are those of the formula:

Mo_xV_yZ_z

wherein Z is selected from Li, Na, Be, Mg, Ca, Sr, Ba, Zn, Cd, Hg, Sc, Y, La, Ce, Al, Tl, Ti, Zr, Hf, Pb, Nb, Ta, As, Sb, Bi, Cr, W, U, Te, Fe, Co, Ni.

An example in which A catalyst having A space-time yield of 555-993g of vinyl acetate/h.l was obtained is described in U.S. Pat. No. 3, 5,185,308 cited in WO 98/05620.

It is an object of the present invention to provide an integrated process for the production of vinyl acetate from a gaseous feed comprising essentially ethane as the sole external carbon source supplied, which process exhibits a time/space yield of 100-2000g vinyl acetate/hr-liter catalyst, preferably 500-1500g vinyl acetate/hr-liter catalyst.

Accordingly, the present invention provides an integrated process for the production of vinyl acetate comprising the steps of:

1) contacting in a first reaction zone a gaseous feedstock comprising primarily ethane with a molecular oxygen-containing gas in the presence of a catalyst to form a first product stream comprising acetic acid;

2) contacting in a second reaction zone a gaseous feed comprising primarily ethane with a molecular oxygen-containing gas in the presence of a catalyst to form a second product stream comprising ethylene;

3) contacting the first gaseous product stream and the second gaseous product stream with a molecular oxygen-containing gas in the presence or absence of additional ethylene or acetic acid in a third reaction zone in the presence of a catalyst to form a fourth product stream comprising vinyl acetate;

4) separating the product stream of step (3) and recovering vinyl acetate from said product stream of step (3).

The method of the invention is based on the following findings: certain types of catalysts are capable of converting ethane to acetic acid or ethylene with very high selectivity and very high space time yields. This separate ethylene and acetic acid product streams are then mixed in the appropriate ratio and fed directly to the reactor to form vinyl acetate.

The advantage of using ethane as a feedstock instead of ethylene is that it can be obtained in natural gas. During natural gas processing, several ethane-containing mixtures are obtained, which can usually be simply ignited, but which all can be used as carbon feedstock for carrying out the process of the invention.

A particular advantage in the integrated process for the production of vinyl acetate according to the invention is that in principle it is possible to combine infrastructure, ancillary equipment and other features, for example only one feed gas compressor and off-gas scrubbing system is required, whereas separate acetic acid and vinyl acetate processes each require their own feed gas compressor and off-gas scrubbing system.

By combining steps 1, 2 and 3 of the present invention, the intermediate storage requirements are reduced compared to the two separate methods. All of these advantages result in reduced capital and operating costs.

According to the invention, a gaseous feedstock comprising primarily ethane is contacted in a first reaction zone with a molecular oxygen-containing gas in the presence of a catalyst active for the oxidation of ethane to acetic acid to produce a first product stream comprising acetic acid.

Catalysts active for the oxidation of ethane to acetic acid may include any suitable catalyst as described in DE-A19745902, which is incorporated herein by reference. These catalysts have the following structural formula:

Mo_aPd_bX_cY_d

wherein X and Y have the following meanings:

x is one or more elements selected from Cr, Mn, Nb, Ta, Ti, V, Te and W;

y is selected from one or more elements of B, Al, Ga, In, Pt, Zn, Cd, Bi, Ce, Co, Rh, Ir, Cu, Ag, Au, Fe, Ru, Os, K, Rb, Cs, Mg, Ca, Sr, Ba, Nb, Zr, Hf, Ni, P, Pb, Sb, Si, Sn, Tl and U,

and wherein a, b, c and d are gram atom ratios and represent

a＝1；

b is 0.0001-0.01; preferably 0.0001 to 0.005;

c is 0.4-1; preferably 0.5 to 0.8 and

d is 0.005-1; preferably 0.01-0.3.

Preferred catalysts are those wherein X is V and Y is Nb, Sb and Ca. A ratio of Pd above the gram atom limit favors the formation of carbon dioxide; the Pd ratio below the gram atom limit favors the formation of ethylene and thus acetic acid. A particularly preferred catalyst for use in the process of the present invention is Mo_1.00Pd_0.00075V_0.55Nb_0.09Sb_0.01Ca_0.01。

In a second reaction zone, which is spatially separated from the first reaction zone, a gaseous feed comprising primarily ethane is contacted with a molecular oxygen-containing gas in the presence of a catalyst active for the oxidation of ethane to ethylene, thereby producing a second product stream comprising ethylene.

The catalyst having activity for oxidizing ethane to ethylene may comprise the same catalyst as the catalyst disclosed above for oxidizing ethane to acetic acid. The two processes differ in their reaction conditions, in particular in total pressure, residence time and water content in the feed. The oxidation of ethane to acetic acid is more advantageous at higher total pressures than the oxidative dehydrogenation of ethane to ethylene. When steam is fed together with ethane and molecular oxygen-containing gas, acetic acid formation is the preferred reaction product, while steam can optionally be used for the oxidative dehydrogenation of ethane to ethylene, but it is not absolutely necessary.

Preferred catalysts are those wherein X is V and Y is Nb, Sb and Ca. A ratio of Pd above the gram atom limit favors the formation of carbon dioxide; the ratio of Pd below the gram atom limit favors the formation of ethylene. A particularly preferred catalyst for use in the process of the present invention is Mo_1.00Pd_0.00075V_0.55Nb_0.09Sb_0.01Ca_0.01。

Useful catalysts for the oxidative dehydrogenation of ethane to ethylene can also be the oxide based oxides briefly described as V-Al, V-Nb-Al, Cr-Nb-Al and Cr-Ta-Al (Liu, Y.; Cong, P.; Doolen, R.D.; Turner, H.W.; Weinberg, H.; Second int. symposiumon Deactivation and Testing of Catalysts Presented Before theDivision of Petroleum Chemistry，Inc.；219^th National Meeting，ACS，San Francisco，CA，March 26-31，2000；298-302)。

Moreover, several other patents more generally describe the oxidative dehydrogenation of paraffins. Three patents are cited here as examples describing the oxidative dehydrogenation of alkanes over Ni oxide based catalysts, for example, US 4,751,342 describes the use of base doped Ni-P-Sn oxide catalysts, GB 2050188 describes Ni-Pb catalysts, and US 3,886,090 describes Ni-Mg oxide catalysts modified with several other elements.

It is an advantage of the present invention that the ratio of selectivity for acetic acid to selectivity for ethylene formed in the first reaction zone can be varied over a wide range, i.e. from 0 to 95%, each by varying reaction parameters such as reaction temperature, total pressure, partial pressure of reactants, residence time, etc.

The reactions in the first and second reaction zones are preferably carried out in such a way that the amounts of acetic acid and ethylene formed in these reactions are in a suitable ratio so that the combined first and second product streams can be fed directly to the third reaction zone to form vinyl acetate without the need to feed additional acetic acid or ethylene.

Supported or unsupported catalysts active for the oxidation of ethane may be used. Examples of suitable supports include silica, diatomaceous earth, montmorillonite, alumina, silica-alumina, zirconia, titania, silicon carbide, activated carbon, and mixtures thereof. The catalyst having activity for oxidizing ethane may be used in the form of a fixed bed or a fluidized bed.

The molecular oxygen-containing gas used in all the reaction zones may be air or a gas rich or lean in molecular oxygen than air. A suitable gas may for example be oxygen diluted with a suitable diluent, such as nitrogen or carbon dioxide. Preferably, the molecular oxygen-containing gas and the ethane feedstock are each independently fed to the first and second reaction zones.

The ethane feedstock for the process of the present invention may be substantially pure or lightly diluted with other gases such as that produced by natural gas separation, i.e. for example 90 wt% (PERP-report "natural gases Extraction 94/95S 4, page 60") or may be a mixture mixed with one or more of nitrogen, carbon dioxide, hydrogen and low levels of C3/C4 alkenes/alkanes. Catalyst poisons such as sulfur should be excluded. Likewise, it is advantageous to minimize the amount of acetylene. The amount of inert components is limited only by economic considerations.

Step (1) of the process of the present invention is suitably carried out by passing ethane, molecular oxygen-containing gas, steam and, if necessary, additional inert materials over the catalyst. The amount of steam may suitably be in the range of 0-50 Vol%. The molar ratio of ethane to oxygen may suitably be in the range 1: 1 to 10: 1, preferably 2: 1 to 8: 1.

Step (1) of the process of the present invention may suitably be carried out at a temperature of 200 ℃ and 500 ℃, preferably 200 ℃ and 400 ℃.

Step (1) of the process of the present invention may suitably be carried out at atmospheric or superatmospheric pressure, for example at from 1 to 100 bar, preferably from 1 to 50 bar.

Generally, in step (1) of the process of the present invention, ethane conversions of 10 to 100%, in particular 10 to 40%, can be obtained, which reactors may also be reactor cascades with an interstitial oxygen feed, depending on the reactor design of step (1).

Generally, in step (1) of the process of the present invention, oxygen conversions of 90 to 100% can be obtained.

In step (1) of the process of the present invention, the catalyst suitably has a productivity ("space time yield" ═ STY ") of 100-.

Step (1) of the present invention may be carried out in a fixed bed as well as a fluidized bed reactor.

The gaseous product stream from step (1) comprises acetic acid and water and may also contain ethane, ethylene, oxygen, nitrogen and by-products carbon monoxide and carbon dioxide. Usually, no or very small amounts (< 100ppm) of carbon monoxide are produced in step (1). In the case of carbon monoxide produced in relatively high amounts of up to 5%, it can, if necessary, be removed after step (1), for example by adsorption or by combustion with a molecular oxygen-containing gas to carbon dioxide. Acetic acid is preferably present in the gaseous product stream of step (1) in an amount required to convert ethylene contained in the second product stream, which will be combined with the first product stream, directly to vinyl acetate.

Step (2) of the process of the present invention may suitably be carried out by passing ethane, molecular oxygen-containing gas, steam and, if necessary, additional inert materials over the catalyst. The amount of steam may suitably be in the range of 0-50 Vol%. The molar ratio of ethane to oxygen may suitably be in the range 1: 1 to 10: 1, preferably 2: 1 to 8: 1.

Step (2) of the process of the present invention may suitably be carried out at a temperature of 200 ℃ and 500 ℃, preferably 200 ℃ and 400 ℃.

Step (2) of the process of the present invention may suitably be carried out at atmospheric or superatmospheric pressure, for example at a pressure of from 1 to 50 bar, preferably from 1 to 30 bar.

Generally, in step (2) of the process of the invention, ethane conversions of 10 to 100%, in particular 10 to 40%, can be achieved, depending on the reactor design of step (2), which can also be a reactor cascade with an interstitial oxygen feed.

Generally, an oxygen conversion of 90 to 100% can be obtained in step (2) of the process of the present invention.

In step (2) of the process of the invention, the catalyst suitably has a productivity (STY) of 100-.

Step (2) of the present invention may be carried out in a fixed bed as well as a fluidized bed reactor.

The gaseous product stream from step (2) comprises ethylene and water and may also contain ethane, acid acids, oxygen, nitrogen and by-products carbon monoxide and carbon dioxide. Usually, no or very small amounts (< 100ppm) of carbon monoxide are produced in step (2). In the case of carbon monoxide produced in relatively high amounts of up to 5%, it can, if necessary, be removed after step (2), for example by adsorption or by combustion with a molecular oxygen-containing gas to carbon dioxide. Ethylene is preferably present in the gaseous product stream of step (2) in an amount required for direct conversion to vinyl acetate of the acid acids contained in the first product stream which will be combined with the second product stream.

The ethylene/acid ratio necessary to supply the vinyl acetate reactor of the present invention (step (3)) can be suitably adjusted by varying the reaction parameters of step (1) and/or step (2), such as the reaction temperature, total pressure, gas hourly space velocity, partial pressures of the reactants, and in particular by varying the partial pressure of steam in the feed to step (1).

The gaseous product from step (1) and the gaseous product from step (2) may be fed directly to the third reaction zone of step (3) together with optionally other molecular oxygen-containing gas, optionally additional ethylene and optionally additional acetic acid, which may preferably be taken from step (4) -vinyl acetate separation step.

The catalyst having activity for the production of vinyl acetate used in step (3) of the process of the present invention may comprise any suitable catalyst known in the art, for example those described in GB 1559540, US5,185,308 and WO 99/08791.

EP-A0330853 describes a fully impregnated catalyst for the production of vinyl acetate which contains Pd, K, Mn and Cd as additional promoters instead of Au.

GB 1559540 describes a catalyst active in the reaction of ethylene, acetic acid and oxygen to produce vinyl acetate, the catalyst consisting essentially of:

(1) a catalyst support having a particle diameter of from 3 to 7mm and a pore volume of from 0.2 to 1.5ml/g, a 10% by weight aqueous suspension of the catalyst support having a pH of from 3.0 to 9.0,

(2) a palladium-gold alloy distributed over a surface layer of the catalyst support, the surface layer protruding less than 0.5mm from the surface of the support, the palladium in the alloy being present in an amount of 1.5 to 5.0g/L of catalyst and the gold being present in an amount of 0.5 to 2.25g/L of catalyst, and

(3)5-60g/L of alkali metal acetate.

US5,185,308 describes a shell impregnated catalyst active for the production of vinyl acetate from ethylene, acetic acid and an oxygen-containing gas, the catalyst consisting essentially of:

(1) a catalyst support having a particle diameter of from about 3 to about 7mm and a pore volume of from 0.2 to 1.5ml/g,

(2) palladium and gold distributed in the outermost 1.0mm thick layer of the catalyst support particles, and

(3) about 3.5 to about 9.5 weight percent potassium acetate, wherein the weight ratio of gold to palladium in the catalyst is in the range of 0.6 to 1.25.

WO 99/08791 describes a process for the production of a catalyst comprising metal nanoparticles on a porous support, which catalyst is particularly useful for the gas phase oxidation of ethylene and acetic acid to form vinyl acetate. The invention relates to a method for producing a catalyst comprising one or several metals selected from the group of metals comprising subgroups Ib and VIIIb of the periodic table on porous support particles, characterized in that in a first step one or several precursors selected from the group of compounds of the metals of subgroups Ib and VIIIb of the periodic table are applied to a porous support, and in a second step the porous, preferably nanoporous support, to which at least one precursor has been applied, is treated with at least one reducing agent in order to obtain metal nanoparticles produced in situ in the pores of the support.

In general, step (3) of the process of the invention is carried out heterogeneously, with the reactants being present in the gas phase.

The molecular oxygen-containing gas used in step (3) of the process of the present invention may comprise unreacted molecular oxygen-containing gas from step (1) or (2) and/or other molecular oxygen-containing gas. Preferably, at least some molecular oxygen-containing gas is fed to the third reaction zone independently of the acetic acid and ethylene reactants.

Step (3) of the process of the present invention may suitably be carried out at a temperature of 140 ℃ and 220 ℃.

Step (3) of the process of the present invention may suitably be carried out at a pressure of from 1 to 100 bar.

Step (3) may be carried out in any suitable reactor design that is capable of removing the heat of reaction in a suitable manner; the preferred solution is a fixed or fluidized bed reactor.

In step (3) of the process of the present invention, acetic acid conversions of 5 to 50% can be obtained.

An oxygen conversion of 20 to 100% can be obtained in step (3) of the process of the present invention.

In step (3) of the process of the invention, the catalyst suitably has a productivity (STY) of 100-2000g of vinyl acetate per hour per liter of catalyst, but > 10000g of vinyl acetate per hour per liter of catalyst are also suitable.

The third product stream from step (3) of the process comprises vinyl acetate and water, optionally together with unreacted acetic acid, ethylene, ethane, nitrogen, carbon monoxide, carbon dioxide and other by-products which may be present in trace amounts. In the middle between step (3) and step (4) of the process of the present invention, ethylene, and if any ethane, carbon monoxide and carbon dioxide, suitable as the top gas fraction of the wash column, are preferably removed from the third product stream, with a liquid fraction comprising vinyl acetate, water and acetic acid being removed from the bottom.

The third product stream of step (3) comprising vinyl acetate, water and acetic acid (with or without an intermediate washing step) is separated by distillation in step (4) into an overhead azeotrope fraction comprising vinyl acetate and water and a bottoms fraction comprising acetic acid.

Vinyl acetate is recovered from the azeotrope fraction separated in step (4), suitably by decantation, for example. The recovered vinyl acetate may be further purified in a known manner, if desired. The bottom fraction comprising acetic acid separated in step (4) (with or preferably without further purification) is preferably recycled to step (3) of the process.

The total Space Time Yield (STY) of vinyl acetate (reference ethane) produced in the process is in the range of 100-.

The overall yield can be adjusted in a number of ways, including independently adjusting the reactant ratios and/or reaction conditions of step (1) and/or step (2) and/or step (3) of the process, for example by independently adjusting the oxygen concentration and/or reaction temperature and pressure.

The process of the invention will now be described by way of example with reference to figure 1, which represents in diagrammatic form the apparatus used in the process of the invention.

The apparatus comprises a first reaction zone (1), a second reaction zone (2), a third reaction zone (3) and a scrubber (4).

In use, a molecular oxygen-containing gas, optionally steam and a gaseous feed (5) comprising predominantly ethane, are fed to a first reaction zone (1) containing a catalyst active in the oxidation of ethane to form acetic acid. Depending on the scale of the process, the first reaction zone (1) may comprise a single reactor or several reactors connected in parallel or in series. The first reaction zone may also comprise a reactor cascade, wherein further molecular oxygen-containing gases can be fed in between the individual reactors. A first gaseous product stream comprising acetic acid, unreacted starting material, optionally unconsumed molecular oxygen-containing gas and water is withdrawn from the first reaction zone (1) together with carbon monoxide, carbon dioxide and inerts.

A molecular oxygen-containing gas, optionally steam and a gaseous feed (6) comprising predominantly ethane, are supplied to the second reaction zone. The reaction zone (2) contains a catalyst active for the oxidation of ethane to ethylene. Depending on the scale of the process, the second reaction zone (2) may comprise a single reactor or several reactors in parallel or in series. The second reaction zone may also comprise a reactor cascade, wherein between the individual reactors, further molecular oxygen-containing gases can be fed. A second gaseous product stream comprising ethylene, unreacted starting material, optionally unconsumed molecular oxygen-containing gas and water is withdrawn from the second reaction zone (2) together with carbon monoxide, carbon dioxide and inerts.

The first and second product streams are fed to a third reaction zone (3). The other molecular oxygen-containing gas (7) may be mixed together with the product streams withdrawn from the first and second reaction zones (1) and (2). In the third reaction zone (3), acetic acid and ethylene are contacted with a molecular oxygen-containing gas in the presence of a catalyst active for the production of vinyl acetate. Depending on the scale of the process, the third reaction zone (3) may comprise a single reactor or several reactors in parallel or in series. A product stream comprising vinyl acetate, water, optionally ethane, gaseous by-products and unreacted acetic acid and ethylene is withdrawn from the third reaction zone (3) and sent to a scrubber (4) where a gaseous stream comprising ethylene and optionally ethane is withdrawn overhead together with inerts, carbon monoxide and carbon dioxide by-products and recycled to the first or second reaction zone (1)/(2). The liquid stream of the process comprising vinyl acetate, water, unreacted acetic acid and possibly other high-boiling products is discharged from the bottom of the washing column (4) and the vinyl acetate is separated in a prior art apparatus which is not shown. For example, it is passed to a distillation column where vinyl acetate and water are removed as an azeotrope and acetic acid and other high boilers that may be present are withdrawn from the bottom of the distillation column as an effluent. The water in the overhead stream from the distillation column can be separated from the vinyl acetate in a decanter from which the vinyl acetate product stream removed can be purified by conventional means known in the art.

The carbon dioxide by-product may be produced by any of the available techniques known in the art, for example by reaction at K₂CO₃Reversible absorption in aqueous solution is removed and regenerated in a desorption column (not shown)。

The invention is illustrated by the following examples.

Examples

Preparation of the catalyst

Example (1)

Preparation of catalyst I: mo_1.00Pd_0.00075V_0.55Nb_0.09Sb_0.01Ca_0.01O_x

Solution 180 g ammonium molybdate (Riedel-de Haen) in 400ml water.

Solution 229.4 g of ammonium metavanadate (Riedel-de Haen) are dissolved in 400ml of water.

319.01 g of ammonium niobium oxalate (H.C. Starck),

1.92g of antimony oxalate (Pfaltz & Bauer), and

1.34g of calcium nitrate (Riedel-de Haen) in 200ml of water.

Solution 40.078 g Palladium (II) acetate (Aldrich) in 200ml ethanol.

Solutions 1, 2 and 3 were separately stirred at 70 ℃ for 15 minutes. Then, solution 3 was poured into solution 2, and stirred together at 70 ℃ for another 15 minutes before being added to solution 1. Thereafter, solution 4 was added.

The resulting mixture was evaporated to obtain a remaining total volume of 800 ml. The mixture was spray dried at 180 ℃ and the powder was subsequently dried in still air at 120 ℃ for 2 hours and calcined at 300 ℃ for 5 hours.

Example (2)

Preparation of catalyst II: k, Pd, Au/TiO₂

2.11g of palladium acetate (Aldrich) and 1.32g of gold acetate were dissolved in 30ml of acetic acid. Preparation of the gold acetate used, for example, inAs described in US-A-4,933,204. 100ml of TiO₂The support (P25 pellets, Degussa, Hanau) was added to a solution of palladium acetate and gold acetate. Then, most of the acetic acid was evaporated at 70 ℃ using a rotary evaporator, followed by evaporating the residue at 60 ℃ using an oil pump, and finally placed in a vacuum drying oven at 60 ℃ for 14 hours.

The resulting pellets were reduced with a gas mixture of 10 Vol% hydrogen in nitrogen, while the gas (40l/h) was passed directly into the pellets for 1 hour at 500 ℃ and 1 bar pressure. To load the potassium ions, the reduced pellets were added to a solution containing 4g of potassium acetate in 30ml of water and mixed in a mixing device for 15 minutes.

The solvent was then evaporated using a rotary evaporator. The pellets were dried at 100 ℃ for 14 hours.

Three batches of catalyst II were prepared using the same method; they are referred to as IIa, IIb and IIc, respectively.

All catalysts were then compressed, crushed and sieved to a particle fraction between 0.35 and 0.70mm for catalytic testing.

Catalytic test

In order to carry out the catalytic reaction described in steps (1), (2) and (3) of the present invention, a double-walled fixed-bed reactor having inner diameters of 14mm and 20mm, respectively, and a length of 350mm was used. The reactor was heated with an oil bath through the external tube. Typically, 5ml and 15ml of catalyst are mixed with some inert substance, e.g. typically glass, quartz or alumina particles or bead fractions, respectively, in a catalyst to inert substance volume ratio of, e.g., 2: 1, 1: 2, 1: 5. To reduce the dead volume of the reactor, inert material (as described above) is packed before and after the catalyst bed. The volumetric flow rates are typically regulated by mass and liquid flow controllers, respectively.

The analysis of the reaction product was performed by on-line gas chromatography.

The results of the catalytic measurements of catalysts I to XIII (examples (1 to 13)) using a single reactor for steps (1) and (2) according to the invention are given in tables 1 and 2. The determination of step (1) was carried out at a pressure of 15 bar (results are given in table 1).

The data in tables 1 and 2 are defined as follows:

conversion of ethane [% ] ═

(0.5*[CO]+0.5*[CO₂]+[C₂H₄]+[CH₃COOH])/(0.5*[CO]+0.5*[CO₂]+[C₂H₄]+[C₂H₆]+[CH₃COOH]*100

Selectivity of ethylene [% ] ═

([C₂H₄])/(0.5*[CO]+0.5[CO₂]+[C₂H₄]+[CH₃COOH])*100

Selectivity of acetic acid [% ] ═

([CH₃COOH])/(0.5*[CO]+0.5*[CO₂]+[C₂H₄]+[CH₃COOH])*100

Wherein

[] Concentration (mol%)

[C₂H₆]Concentration of unconverted ethane

τ [ s ] ═ volume of catalyst (ml) under the reaction conditions/volume flow of gas (ml/s)

STY ═ g product/(I catalyst ═ h)

TABLE 1

Catalytic results of the Oxidation of ethane to acetic acid by catalyst I

	Reaction conditions						Results
															Composition of raw materials				Conversion rate	Selectivity is			Space time yield
Numbering	T[℃]	τ[s]	V(C2H6)[ml/s]	V(O2)[ml/s]	V(N2)[ml/s]	V(H2O)[ml/h]	X(C2H6)[％]	S(HOAc)[％]	S(C2H4)[％]	S(CO+CO2)[％]	STY(HOAc)[g/(hl)]
												1	280	14.8	1.0	0.2	0.8	1.4	13.3	91.5	0.7	7.8	235
2	280	7.4	2.0	0.4	1.6	2.9	10.5	90.4	3.5	6.0	362
												3	300	7.1	2.0	0.4	1.6	2.9	13.2	89.0	2.0	9.0	447
4	300	4.8	3.0	0.6	2.4	4.3	11.3	87.2	5.5	7.3	564
												5	300	4.1	3.5	0.7	2.8	5.0	10.2	86.2	7.4	6.4	584
6	300	3.7	4.0	0.8	3.2	5.0	9.9	84.1	9.2	6.6	630

Catalyst II (example (2)) was used in step (b) of the present invention for the production of vinyl acetate. The catalytic tests were carried out at reaction temperatures in the range of 150 ℃ and 170 ℃ and at reaction pressures of 8 to 9 bar.

The results of the catalytic measurements of catalyst II (example (2)) used to carry out step (3) of the present invention are given in table 2.

The data in table 2 are defined as follows:

selectivity [% ] of Vinyl Acetate (VAM)

([VAM])/([VAM])+0.5*[CO]+0.5*[CO₂])*100

Wherein

[] Concentration (mol%)

STY ═ g product/(I catalyst ═ h)

TABLE 2

Catalytic results of catalyst II for vinyl acetate Synthesis

	Reaction conditions		Results
								Selectivity is	Space time yield
Numbering	T[℃]	P[bar]	S(VAM)[％]	STY[g/(hl)]
					a	155	9	98	1000
a	160	9	98	1050
					a	170	9	96	1000
b	160	9	98	1150
					b	170	9	97	700
c	170	9	98	1300

Claims (7)

1. An integrated process for the production of vinyl acetate comprising the steps of:

(1) contacting a gaseous feedstock comprising primarily ethane with a molecular oxygen-containing gas in the presence of a catalyst in a first reaction zone to produce a first product stream comprising acetic acid;

(2) contacting a gaseous feed comprising primarily ethane with a molecular oxygen-containing gas in the presence of a catalyst in a second reaction zone to produce a second product stream comprising ethylene;

(3) contacting the first gaseous product stream and the second gaseous product stream with a molecular oxygen-containing gas in a third reaction zone in the presence of a catalyst to produce a third product stream comprising vinyl acetate;

(4) separating the product stream of step (3) and recovering vinyl acetate from said product stream of step (3);

wherein the catalyst in the first and second reaction zones has the following structural formula:

Mo_aPd_bX_cY_d

wherein X and Y have the following meanings:

x is one or more elements selected from Cr, Mn, Nb, Ta, Ti, V, Te and W;

y is selected from one or more elements of B, Al, Ga, In, Pt, Zn, Cd, Bi, Ce, Co, Rh, Ir, Cu, Ag, Au, Fe, Ru, Os, K, Rb, Cs, Mg, Ca, Sr, Ba, Nb, Zr, Hf, Ni, P, Pb, Sb, Si, Sn, Tl and U,

and wherein a, b, c and d are gram atom ratios and represent

a＝1；

b＝0.0001-0.01；

c is 0.4-1; and

d＝0.005-1；

and wherein the partial pressure of steam in the feed to step (1) is varied to adjust the ethylene/acetic acid ratio.

2. The process according to claim 1, wherein the gaseous feed of step (1) comprises ethane, a molecular oxygen-containing gas, and from 0 to 50 Vol% steam, based on the total volume of the gaseous feed, wherein the ethane to oxygen ratio is from 1: 1 to 10: 1.

3. A process according to claim 1 or claim 2 wherein the gaseous feed to step (2) comprises ethane, a molecular oxygen-containing gas, wherein the ratio of ethane to oxygen is in the range 1: 1 to 10: 1.

4. The process according to claim 1 or 2, wherein additional ethylene and/or acetic acid from the recycle gas is fed to the third reaction zone.

5. A process according to claim 1 or 2, wherein a molecular oxygen-containing gas separate from the ethane feedstock is fed to the first and/or second reaction zone.

6. A process according to claim 1 or claim 2 wherein a molecular oxygen-containing gas is fed to the third reaction zone independently of the acetic acid and ethylene reactants.

7. The method of claim 1, wherein b-0.0001-0.005, c-0.5-0.8, and d-0.01-0.3.