MULTI-ZONED CATALYST SYSTEM FOR OXIDATION OF O-XYLENE AND/OR NAPHTHALENE TO PHTHALIC ANHYDRIDE

Abstract

The present invention relates to a catalyst system for oxidation of o-xylene and/or naphthalene to phthalic anhydride (PA) comprising at least four catalyst zones arranged in succession in the reaction tube and filled with catalysts of different chemical composition wherein the active material of the catalysts comprise vanadium and titanium dioxide and the active material of the catalyst in the last catalyst zone towards the reactor outlet has an antimony content (calculated as antimony trioxide) between 0.7 to 3.0 wt. %. The present invention further relates to a process for gas phase oxidation in which a gas stream comprising at least one hydrocarbon and molecular oxygen is passed through a catalyst system which comprises at least four catalyst zones arranged in succession in the reaction tube and filled with catalysts of different chemical composition wherein the active materials of the catalysts comprise vanadium and titanium dioxide and the active material of the catalyst in the last catalyst zone towards the reactor outlet has an antimony content (calculated as antimony trioxide) between 0.7 to 3.0 wt. %.

Claims

1.-14. (canceled)

15. A catalyst system for oxidation of o-xylene and/or naphthalene to phthalic anhydride comprising at least four catalyst zones arranged in succession in the reaction tube and filled with catalysts of different chemical composition wherein the catalytically active material of the catalyst is applied to an inert catalyst carrier and comprises vanadium and titanium dioxide and the active material of the catalyst in the last catalyst zone towards the reactor outlet has an antimony content (calculated as antimony trioxide) between 0.7 to 3.0 wt. %.

16. The catalyst system according to claim 15, wherein the active materials of the catalysts in the last two catalyst zones towards the reactor outlet have a lower average antimony content than the active materials of the catalysts in the remaining catalyst zones towards the reactor inlet.

17. The catalyst system according to claim 15, wherein the active material of the catalysts in the last two catalyst zones towards the reactor outlet have a higher vanadium content than in the other catalyst zones.

18. The catalyst system according to claim 15, wherein the last catalyst zone has a length of between 10 and 40% of the total length of the catalyst system.

19. The catalyst system according to claim 15, wherein the active material does not comprise silver and/or bismuth.

20. The catalyst system according to claim 15, wherein the active material comprises 1% to 40% by weight of vanadium (calculated as vanadium oxide V.sub.2O.sub.5) and 60% to 99% by weight of titanium dioxide TiO.sub.2.

21. The catalyst system according to claim 15, wherein the average active material content in the catalysts of the whole catalyst system is between 2% and 25% by weight based on the whole catalyst system.

22. A process for production of a catalyst system for oxidation of o-xylene and/or naphthalene to phthalic anhydride with at least four catalyst zones arranged in succession in the reaction tube and filled with catalysts of different chemical composition, comprising the step of applying a catalytically active material comprising antimony, vanadium and titanium dioxide to a catalyst carrier in one or more shells, wherein the active material of the catalyst in the last catalyst zone towards the reactor outlet has an antimony content (calculated as antimony trioxide) between 0.7 to 3.0 wt. %.

23. A process for gas phase oxidation in which a gas stream comprising at least one hydrocarbon and molecular oxygen is passed through a catalyst system according to claim 15.

24. The process according to claim 23, wherein o-xylene and/or naphthalene are oxidized to phthalic anhydride.

Description

EXAMPLES

Production of Five-Zone Catalyst System

Catalyst Zone CZ1:

Preparation of the Vanadium Antimonate:

[0046] A thermostated jacketed glass vessel was initially charged with 5 L of demineralized water and 1566.1 g of antimony trioxide, which consisted of 99% by weight of senarmontite and 1% by weight of valentinite, were suspended therein by stirring at 90° C. for 18 hours. Then 2446.9 g of vanadium pentoxide and a further liter of demineralized water were added and the mixture was stirred at 90° C. for 25 hours. Thereafter, the suspension was cooled to 80° C. and dried by spray drying. The inlet temperature was 340° C., the outlet temperature 120° C. The spray powder thus obtained had a vanadium content of 32% by weight and an antimony content of 30% by weight.

Preparation of the Suspension and Coating:

[0047] 3.87 g of cesium carbonate, 349.69 g of titanium dioxide (Fuji TA 100CT, anatase, BET surface area 28 m.sup.2/g), 188.29 g of titanium dioxide (Fuji TA 100, anatase, BET surface area 8 m.sup.2/g), and 75.43 g of vanadium antimonate (synthesized as described above) were suspended in 1583 g of demineralized water and stirred for 18 hours, in order to obtain a homogeneous distribution. To this suspension were added 85 g of organic binder, consisting of a copolymer of vinyl acetate and vinyl laurate in the form of a 50% by weight aqueous dispersion. In a fluidized bed apparatus, 750 g of this suspension were sprayed onto 2 kg of steatite (magnesium silicate) in the form of rings having dimensions of 7 mm×7 mm×4 mm and dried. After the catalyst had been calcined at 450° C. for one hour, the active material applied to the steatite rings was 8.3% by weight. The analyzed composition of the active material consisted of 7.1% by weight of V (calculated as V.sub.2O.sub.5), 4.5% by weight of Sb (calculated as Sb.sub.2O.sub.3), 0.50% by weight of Cs, remainder TiO.sub.2.

Catalyst Zone CZ2:

[0048] 2.86 g of cesium carbonate, 427.54 g of titanium dioxide (Fuji TA 100C, anatase, BET surface area 20 m.sup.2/g), 127.71 g of titanium dioxide (Fuji TA 100, anatase, BET surface area 8 m.sup.2/g), 43.47 g of vanadium pentoxide and 11.13 g of antimony trioxide (77% by weight of senarmontite and 23% by weight of valentinite) were suspended in 1588 g of demineralized water and stirred for 18 hours, in order to obtain a homogeneous distribution. To this suspension were added 103 g of organic binder, consisting of a copolymer of vinyl acetate and vinyl laurate in the form of a 50% by weight aqueous dispersion. In a fluidized bed apparatus, 910 g of this suspension were sprayed onto 2 kg of steatite (magnesium silicate) in the form of rings having dimensions of 7 mm×7 mm×4 mm and dried. After the catalyst had been calcined at 450° C. for one hour, the active material applied to the steatite rings was 10% by weight. The analyzed composition of the active material consisted of 7.1% by weight of V (calculated as V.sub.2O.sub.5), 1.8% by weight of Sb (calculated as Sb.sub.2O.sub.3), 0.38% by weight of Cs, remainder TiO.sub.2.

Catalyst Zone CZ3:

[0049] 2.40 g of cesium carbonate, 468.67 g of titanium dioxide (Fuji TA 100C, anatase, BET surface area 20 m.sup.2/g), 76.29 g of titanium dioxide (Fuji TA 100, anatase, BET surface area 8 m.sup.2/g), 48.67 g of vanadium pentoxide and 16.69 g of antimony trioxide (77% by weight of senarmontite and 23% by weight of valentinite) were suspended in 1588 g of demineralized water and stirred for 18 hours, in order to obtain a homogeneous distribution. To this suspension were added 88 g of organic binder, consisting of a copolymer of vinyl acetate and vinyl laurate in the form of a 50% by weight aqueous dispersion. In a fluidized bed apparatus, 770 g of this suspension were sprayed onto 2 kg of steatite (magnesium silicate) in the form of rings having dimensions of 7 mm×7 mm×4 mm and dried. After the catalyst had been calcined at 450° C. for one hour, the active material applied to the steatite rings was 8.5% by weight. The analyzed composition of the active material consisted of 7.95% by weight of V (calculated as V.sub.2O.sub.5), 2.7% by weight of Sb (calculated as Sb.sub.2O.sub.3), 0.31% by weight of Cs, remainder TiO.sub.2.

Catalyst Zone CZ4:

[0050] 1.65 g of cesium carbonate, 370.08 g of titanium dioxide (Fuji TA 100CT, anatase, BET surface area 28 m.sup.2/g), 158.60 g of titanium dioxide (Fuji TA 100, anatase, BET surface area 8 m.sup.2/g), 67.34 g of vanadium pentoxide and 14.84 g of antimony trioxide (77% by weight of senarmontite and 23% by weight of valentinite) were suspended in 1588 g of demineralized water and stirred for 18 hours, in order to obtain a homogeneous distribution. To this suspension were added 88 g of organic binder, consisting of a copolymer of vinyl acetate and vinyl laurate in the form of a 50% by weight aqueous dispersion. In a fluidized bed apparatus, 775 g of this suspension were sprayed onto 2 kg of steatite (magnesium silicate) in the form of rings having dimensions of 7 mm×7 mm×4 mm and dried. After the catalyst had been calcined at 450° C. for one hour, the active material applied to the steatite rings was 8.5% by weight. The analyzed composition of the active material consisted of 11.0% by weight of V (calculated as V.sub.2O.sub.5), 2.4% by weight of Sb (calculated as Sb.sub.2O.sub.3), 0.2% by weight of Cs, remainder TiO.sub.2.

Catalyst Zone CZ5:

[0051] 8.63 g of ammonium hydrogenphosphate, 435.8 g of titanium dioxide (Fuji TA 100CT, anatase, BET surface area 28 m.sup.2/g), 48.42 g of titanium dioxide (Fuji TA 100, anatase, BET surface area 8 m.sup.2/g), 122.44 g of vanadium pentoxide and 3.09 g of antimony trioxide (66% by weight of senarmontite and 34% by weight of valentinite) were suspended in 1582 g of demineralized water and stirred for 18 hours, in order to obtain a homogeneous distribution. To this suspension were added 93 g of organic binder, consisting of a copolymer of vinyl acetate and vinyl laurate in the form of a 50% by weight aqueous dispersion. In a fluidized bed apparatus, 820 g of this suspension were sprayed onto 2 kg of steatite (magnesium silicate) in the form of rings having dimensions of 7 mm×7 mm×4 mm and dried. After the catalyst had been calcined at 450° C. for one hour, the active material applied to the steatite rings was 9.1% by weight. The analyzed composition of the active material consisted of 20% by weight of V (calculated as V.sub.2O.sub.5), 0.38% by weight of P, 0.5% by weight of Sb (calculated as Sb.sub.2O.sub.3), remainder TiO.sub.2.

Catalyst Zone CZ6:

[0052] 8.63 g of ammonium hydrogenphosphate, 434.71 g of titanium dioxide (Fuji TA 100CT, anatase, BET surface area 28 m.sup.2/g), 48.24 g of titanium dioxide (Fuji TA 100, anatase, BET surface area 8 m.sup.2/g), 122.44 g of vanadium pentoxide and 4.95 g of antimony trioxide (66% by weight of senarmontite and 34% by weight of valentinite) were suspended in 1582 g of demineralized water and stirred for 18 hours, in order to obtain a homogeneous distribution. To this suspension were added 93 g of organic binder, consisting of a copolymer of vinyl acetate and vinyl laurate in the form of a 50% by weight aqueous dispersion. In a fluidized bed apparatus, 820 g of this suspension were sprayed onto 2 kg of steatite (magnesium silicate) in the form of rings having dimensions of 7 mm×7 mm×4 mm and dried. After the catalyst had been calcined at 450° C. for one hour, the active material applied to the steatite rings was 9.1% by weight. The analyzed composition of the active material consisted of 20% by weight of V (calculated as V.sub.2O.sub.5), 0.38% by weight of P, 0.8% by weight of Sb (calculated as Sb.sub.2O.sub.3), remainder TiO.sub.2.

Catalyst Zone CZ7:

[0053] 8.63 g of ammonium hydrogenphosphate, 431.97 g of titanium dioxide (Fuji TA 100CT, anatase, BET surface area 28 m.sup.2/g), 48.00 g of titanium dioxide (Fuji TA 100, anatase, BET surface area 8 m.sup.2/g), 122.44 g of vanadium pentoxide and 8.04 g of antimony trioxide (66% by weight of senarmontite and 34% by weight of valentinite) were suspended in 1582 g of demineralized water and stirred for 18 hours, in order to obtain a homogeneous distribution. To this suspension were added 93 g of organic binder, consisting of a copolymer of vinyl acetate and vinyl laurate in the form of a 50% by weight aqueous dispersion. In a fluidized bed apparatus, 820 g of this suspension were sprayed onto 2 kg of steatite (magnesium silicate) in the form of rings having dimensions of 7 mm×7 mm×4 mm and dried. After the catalyst had been calcined at 450° C. for one hour, the active material applied to the steatite rings was 9.1% by weight. The analyzed composition of the active material consisted of 20% by weight of V (calculated as V.sub.2O.sub.5), 0.38% by weight of P, 1.3% by weight of Sb (calculated as Sb.sub.2O.sub.3), remainder TiO.sub.2.

Catalyst Zone CZ8:

[0054] 8.63 g of ammonium hydrogenphosphate, 427.56 g of titanium dioxide (Fuji TA 100CT, anatase, BET surface area 28 m.sup.2/g), 47.51 g of titanium dioxide (Fuji TA 100, anatase, BET surface area 8 m.sup.2/g), 122.44 g of vanadium pentoxide and 12.24 g of antimony trioxide (66% by weight of senarmontite and 34% by weight of valentinite) were suspended in 1582 g of demineralized water and stirred for 18 hours, in order to obtain a homogeneous distribution. To this suspension were added 93 g of organic binder, consisting of a copolymer of vinyl acetate and vinyl laurate in the form of a 50% by weight aqueous dispersion. In a fluidized bed apparatus, 820 g of this suspension were sprayed onto 2 kg of steatite (magnesium silicate) in the form of rings having dimensions of 7 mm×7 mm×4 mm and dried. After the catalyst had been calcined at 450° C. for one hour, the active material applied to the steatite rings was 9.1% by weight. The analyzed composition of the active material consisted of 20% by weight of V (calculated as V.sub.2O.sub.5), 0.38% by weight of P, 2.0% by weight of Sb (calculated as Sb.sub.2O.sub.3), remainder TiO.sub.2.

Catalyst Zone CZ9:

[0055] 7.96 g of ammonium hydrogenphosphate, 387.05 g of titanium dioxide (Fuji TA 100CT, anatase, BET surface area 28 m.sup.2/g), 96.76 g of titanium dioxide (Fuji TA 100, anatase, BET surface area 8 m.sup.2/g) and 126.12 g of vanadium pentoxide were suspended in 1582 g of demineralized water and stirred for 18 hours, in order to obtain a homogeneous distribution. To this suspension were added 93 g of organic binder, consisting of a copolymer of vinyl acetate and vinyl laurate in the form of a 50% by weight aqueous dispersion. In a fluidized bed apparatus, 820 g of this suspension were sprayed onto 2 kg of steatite (magnesium silicate) in the form of rings having dimensions of 7 mm×7 mm×4 mm and dried. After the catalyst had been calcined at 450° C. for one hour, the active material applied to the steatite rings was 9.1% by weight. The analyzed composition of the active material consisted of 20% by weight of V (calculated as V.sub.2O.sub.5), 0.38% by weight of P, remainder TiO.sub.2.

Catalyst Zone CZ10:

[0056] 8.63 g of ammonium hydrogenphosphate, 430.31 g of titanium dioxide (Fuji TA 100CT, anatase, BET surface area 28 m.sup.2/g), 47.81 g of titanium dioxide (Fuji TA 100, anatase, BET surface area 8 m.sup.2/g), 122.44 g of vanadium pentoxide and 9.27 g of antimony trioxide (100% by weight of senarmontite) were suspended in 1582 g of demineralized water and stirred for 18 hours, in order to obtain a homogeneous distribution. To this suspension were added 93 g of organic binder, consisting of a copolymer of vinyl acetate and vinyl laurate in the form of a 50% by weight aqueous dispersion. In a fluidized bed apparatus, 820 g of this suspension were sprayed onto 2 kg of steatite (magnesium silicate) in the form of rings having dimensions of 7 mm×7 mm×4 mm and dried. After the catalyst had been calcined at 450° C. for one hour, the active material applied to the steatite rings was 10.0% by weight. The analyzed composition of the active material consisted of 20% by weight of V (calculated as V.sub.2O.sub.5), 0.38% by weight of P, 1.5% by weight of Sb (calculated as Sb.sub.2O.sub.3), remainder TiO.sub.2.

Catalyst Zone CZ11:

[0057] 8.63 g of ammonium hydrogenphosphate, 430.37 g of titanium dioxide (Fuji TA 100CT, anatase, BET surface area 28 m.sup.2/g), 53.37 g of titanium dioxide (Fuji TA 100, anatase, BET surface area 8 m.sup.2/g), 67.34 g of vanadium pentoxide and 9.27 g of antimony trioxide (100% by weight of senarmontite) were suspended in 1582 g of demineralized water and stirred for 18 hours, in order to obtain a homogeneous distribution. To this suspension were added 93 g of organic binder, consisting of a copolymer of vinyl acetate and vinyl laurate in the form of a 50% by weight aqueous dispersion. In a fluidized bed apparatus, 820 g of this suspension were sprayed onto 2 kg of steatite (magnesium silicate) in the form of rings having dimensions of 7 mm×7 mm×4 mm and dried. After the catalyst had been calcined at 450° C. for one hour, the active material applied to the steatite rings was 12.0% by weight. The analyzed composition of the active material consisted of 11% by weight of V (calculated as V.sub.2O.sub.5), 0.38% by weight of P, 1.5% by weight of Sb (calculated as Sb.sub.2O.sub.3), remainder TiO.sub.2.

Examples with a Five-Zone Catalyst System

Example 1a to 1e

[0058] The catalytic oxidation of o-xylene to phthalic anhydride was conducted in a salt bath-cooled tubular reactor having an internal tube diameter of 25 mm and a length of 350 cm. From reactor inlet to reactor outlet, 80 cm of CZ1, 60 cm of CZ2, 70 cm of CZ3, 50 cm of CZ4 and 60 cm of CZ5 (Example 1a, comparative) or CZ6 (Example 1 b) or CZ7 (Example 1c) or CZ8 (Example 1d) or CZ9 (Example 1e, comparative) were introduced. For temperature regulation, the tubular reactor was surrounded by a salt melt; a thermowell of external diameter 4 mm with an installed thermocouple served for catalyst temperature measurement. An air flow of 4.0 Nm.sup.3(STP)/h with loadings of 99 to 99.4% by weight o-xylene of 30 to 100 g.sub.o-xylene/Nm.sup.3(STP).sub.air was passed through the tubular reactor.

[0059] FIG. 1 shows the concentration of CO.sub.x (CO+CO.sub.2) as a function of the Sb content (calculated as Sb.sub.2O.sub.3) in the last catalyst zone. Apparently there is an optimum Sb content at which total oxidation processes are kept to a minimum.

[0060] FIG. 1: Comparison of CO.sub.x concentration in the reactor out gas as function of the Sb content in the last catalyst zone at a salt bath temperature of 364° C., o-xylene loading of 69 g.sub.o-x/Nm.sup.3, and a total air flow rate of 4 Nm.sup.3(STP)/h.

Example 2

[0061] The catalytic oxidation of o-xylene to phthalic anhydride was conducted in a salt bath-cooled tubular reactor having an internal tube diameter of 25 mm and a length of 350 cm. From reactor inlet to reactor outlet, 70 cm of CZ1, 50 cm of CZ2, 60 cm of CZ3, 50 cm of CZ4 and 90 cm of CZ10 were introduced. For temperature regulation, the tubular reactor was surrounded by a salt melt; a thermowell of external diameter 4 mm with an installed thermocouple served for catalyst temperature measurement. An air flow of 4.0 Nm.sup.3(STP)/h with loadings of 99 to 99.4% by weight o-xylene of 30 to 100 g.sub.o-xylene/Nm.sup.3(STP).sub.air was passed through the tubular reactor.

TABLE-US-00001 TABLE 1 Catalyst composition of five-layer catalyst system of example 2. Catalyst zone CZ1 CZ2 CZ3 CZ4 CZ10 Active material % 8.30 10.0 8.50 8.50 10.00 V.sub.2O.sub.5 % 7.10 7.10 7.95 11.00 20.00 Sb.sub.2O.sub.3 % 4.50 1.80 2.70 2.40 1.50 Cs % 0.50 0.38 0.31 0.22 0 P % 0 0 0 0 0.38 TiO.sub.2 % 87.90 90.72 89.04 86.38 78.12 BET-Surface area m.sup.2/g 20 17 18 21 26 Zone length cm 70 50 60 50 90

TABLE-US-00002 TABLE 2 Catalytic performance of the example 2 catalyst system at a total air flow rate of 4 Nm.sup.3(STP)/h. Salt bath Loading temperature Y.sub.PA .sup.a Y.sub.o-X .sup.b Y.sub.PHD .sup.c [g.sub.o-X/m.sup.3 (STP).sub.air] [° C.] [% by wt.] [% by wt.] [% by wt.] 61.0 370.0 113.8 0.00 0.07 79.0 362.0 115.1 0.00 0.07 90.0 356.0 115.0 0.01 0.06 100.0 353.5 115.0 0.02 0.07 .sup.a PA yield .sup.b o-xylene yield .sup.c phthalide yield

Example 3

[0062] The catalytic oxidation of o-xylene to phthalic anhydride was conducted in a salt bath-cooled tubular reactor having an internal tube diameter of 25 mm and a length of 350 cm. From reactor inlet to reactor outlet, 70 cm of CZ1, 50 cm of CZ2, 60 cm of CZ3, 50 cm of CZ4 and 90 cm of CZ7 were introduced. For temperature regulation, the tubular reactor was surrounded by a salt melt; a thermowell of external diameter 4 mm with an installed thermocouple served for catalyst temperature measurement. An air flow of 4.0 Nm.sup.3(STP)/h with loadings of 99 to 99.4% by weight o-xylene of 30 to 100 g.sub.o-xylene/Nm.sup.3(STP).sub.air was passed through the tubular reactor.

TABLE-US-00003 TABLE 3 Catalyst composition of five-layer catalyst system of example 3. Catalyst zone CZ1 CZ2 CZ3 CZ4 CZ7 Active material % 8.30 10.0 8.50 8.50 9.10 V.sub.2O.sub.5 % 7.10 7.10 7.95 11.00 20.00 Sb.sub.2O.sub.3 % 4.50 1.80 2.70 2.40 1.30 Cs % 0.50 0.38 0.31 0.22 0 P % 0 0 0 0 0.38 TiO.sub.2 % 87.90 90.72 89.04 86.38 78.12 BET-Surface m.sup.2/g 20 17 18 21 26 area Zone length cm 70 50 60 50 90

TABLE-US-00004 TABLE 4 Catalytic performance of the example 3 catalyst system at a total air flow rate of 4 Nm.sup.3(STP)/h. Salt bath Loading temperature Y.sub.PA .sup.a Y.sub.o-X .sup.b Y.sub.PHD .sup.c [g.sub.o-X/m.sup.3 (STP).sub.air] [° C.] [% by wt.] [% by wt.] [% by wt.] 66.0 366.0 113.1 0.03 0.15 85.0 360.6 114.0 0.04 0.12 90.0 348.5 115.3 0.06 0.08 .sup.a PA yield .sup.b o-xylene yield .sup.c phthalide yield

Example 4

[0063] The catalytic oxidation of o-xylene to phthalic anhydride was conducted in a salt bath-cooled tubular reactor having an internal tube diameter of 25 mm and a length of 350 cm. From reactor inlet to reactor outlet, 70 cm of CZ1, 50 cm of CZ2, 60 cm of CZ3, 50 cm of CZ4 and 90 cm of CZ11 were introduced. For temperature regulation, the tubular reactor was surrounded by a salt melt; a thermowell of external diameter 4 mm with an installed thermocouple served for catalyst temperature measurement. An air flow of 4.0 Nm.sup.3(STP)/h with loadings of 99 to 99.4% by weight o-xylene of 30 to 100 g.sub.o-xylene/Nm.sup.3(STP).sub.air was passed through the tubular reactor.

TABLE-US-00005 TABLE 5 Catalyst composition of five-layer catalyst system of example 4. Catalyst zone CZ1 CZ2 CZ3 CZ4 CZ11 Active material % 8.30 10.0 8.50 8.50 12.00 V.sub.2O.sub.5 % 7.10 7.10 7.95 11.00 11.00 Sb.sub.2O.sub.3 % 4.50 1.80 2.70 2.40 1.50 Cs % 0.50 0.38 0.31 0.22 0 P % 0 0 0 0 0.38 TiO.sub.2 % 87.90 90.72 89.04 86.38 87.12 BET-Surface area m.sup.2/g 20 17 18 21 26 Zone length cm 70 50 60 50 90

TABLE-US-00006 TABLE 6 Catalytic performance of the example 4 catalyst system at a total air flow rate of 4 Nm.sup.3(STP)/h. Salt bath Loading temperature Y.sub.PA .sup.a Y.sub.o-X .sup.b Y.sub.PHD .sup.c [g.sub.o-X/m.sup.3 (STP).sub.air] [° C.] [% by wt.] [% by wt.] [% by wt.] 65.0 370.0 112.5 0.01 0.08 79.0 360.0 113.9 0.01 0.09 88.0 357.0 114.7 0.02 0.08 98.0 352.0 114.2 0.02 0.06 .sup.a PA yield .sup.b o-xylene yield .sup.c phthalide yield

Example 5 (Comparative)

[0064] The catalytic oxidation of o-xylene to phthalic anhydride was conducted in a salt bath-cooled tubular reactor having an internal tube diameter of 25 mm and a length of 350 cm. From reactor inlet to reactor outlet, 80 cm of CZ1, 60 cm of CZ2, 70 cm of CZ3, 50 cm of CZ4 and 60 cm of CZ9 were introduced. For temperature regulation, the tubular reactor was surrounded by a salt melt; a thermowell of external diameter 4 mm with an installed thermocouple served for catalyst temperature measurement. An air flow of 4.0 Nm.sup.3(STP)/h with loadings of 99 to 99.4% by weight o-xylene of 30 to 100 g.sub.o-xylene/Nm.sup.3(STP).sub.air was passed through the tubular reactor.

TABLE-US-00007 TABLE 7 Catalyst composition of five-layer catalyst system of example 5. Catalyst zone CZ1 CZ2 CZ3 CZ4 CZ9 Active material % 8.30 10.0 8.50 8.50 9.10 V.sub.2O.sub.5 % 7.10 7.10 7.95 11.00 20.00 Sb.sub.2O.sub.3 % 4.50 1.80 2.70 2.40 0 Cs % 0.50 0.38 0.31 0.22 0 P % 0 0 0 0 0.38 TiO.sub.2 % 87.90 90.72 89.04 86.38 79.62 BET-Surface area m.sup.2/g 20 17 18 21 23 Zone length cm 80 60 70 50 60

TABLE-US-00008 TABLE 8 Catalytic performance of the example 5 catalyst system (comparative) at a total air flow rate of 4 Nm.sup.3(STP)/h. Salt bath Loading temperature Y.sub.PA .sup.a Y.sub.o-X .sup.b Y.sub.PHD .sup.c [g.sub.o-X/m.sup.3 (STP).sub.air] [° C.] [% by wt,] [% by wt,] [% by wt,] 66.0 364.0 111.5 0.02 0.05 78.0 359.5 112.3 0.02 0.06 95.0 354.5 112.1 0.04 0.08 100.0 350.5 113.5 0.09 0.12 .sup.a PA yield .sup.b o-xylene yield .sup.c phthalide yield

Production of a Four-Zone Catalyst System

Catalyst Zone CZ12;

[0065] 2.86 g of cesium carbonate, 427.54 g of titanium dioxide (Fuji TA 100C, anatase, BET surface area 20 m.sup.2/g), 127.71 g of titanium dioxide (Fuji TA 100, anatase, BET surface area 8 m.sup.2/g), 43.47 g of vanadium pentoxide and 11.13 g of antimony trioxide (77% by weight of senarmontite and 23% by weight of valentinite) were suspended in 1588 g of demineralized water and stirred for 18 hours, in order to obtain a homogeneous distribution. To this suspension were added 103 g of organic binder, consisting of a copolymer of vinyl acetate and vinyl laurate in the form of a 50% by weight aqueous dispersion. In a fluidized bed apparatus, 910 g of this suspension were sprayed onto 2 kg of steatite (magnesium silicate) in the form of rings having dimensions of 7 mm×7 mm×4 mm and dried. After the catalyst had been calcined at 450° C. for one hour, the active material applied to the steatite rings was 10% by weight. The analyzed composition of the active material consisted of 7.1% by weight of V (calculated as V.sub.2O.sub.5), 1.8% by weight of Sb (calculated as Sb.sub.2O.sub.3), 0.38% by weight of Cs, remainder TiO.sub.2.

Catalyst Zone CZ13:

[0066] 2.40 g of cesium carbonate, 468.67 g of titanium dioxide (Fuji TA 100C, anatase, BET surface area 20 m.sup.2/g), 76.29 g of titanium dioxide (Fuji TA 100, anatase, BET surface area 8 m.sup.2/g), 48.67 g of vanadium pentoxide and 16.69 g of antimony trioxide (77% by weight of senarmontite and 23% by weight of valentinite) were suspended in 1588 g of demineralized water and stirred for 18 hours, in order to obtain a homogeneous distribution. To this suspension were added 88 g of organic binder, consisting of a copolymer of vinyl acetate and vinyl laurate in the form of a 50% by weight aqueous dispersion. In a fluidized bed apparatus, 770 g of this suspension were sprayed onto 2 kg of steatite (magnesium silicate) in the form of rings having dimensions of 7 mm×7 mm×4 mm and dried. After the catalyst had been calcined at 450° C. for one hour, the active material applied to the steatite rings was 8.5% by weight. The analyzed composition of the active material consisted of 7.95% by weight of V (calculated as V.sub.2O.sub.5), 2.7% by weight of Sb (calculated as Sb.sub.2O.sub.3), 0.31% by weight of Cs, remainder TiO.sub.2.

Catalyst Zone CZ14:

[0067] 1.65 g of cesium carbonate, 370.08 g of titanium dioxide (Fuji TA 100CT, anatase, BET surface area 28 m.sup.2/g), 158.60 g of titanium dioxide (Fuji TA 100, anatase, BET surface area 8 m.sup.2/g), 67.34 g of vanadium pentoxide and 14.84 g of antimony trioxide (77% by weight of senarmontite and 23% by weight of valentinite) were suspended in 1588 g of demineralized water and stirred for 18 hours, in order to obtain a homogeneous distribution. To this suspension were added 88 g of organic binder, consisting of a copolymer of vinyl acetate and vinyl laurate in the form of a 50% by weight aqueous dispersion. In a fluidized bed apparatus, 775 g of this suspension were sprayed onto 2 kg of steatite (magnesium silicate) in the form of rings having dimensions of 7 mm×7 mm×4 mm and dried. After the catalyst had been calcined at 450° C. for one hour, the active material applied to the steatite rings was 8.5% by weight. The analyzed composition of the active material consisted of 11.0% by weight of V (calculated as V.sub.2O.sub.5), 2.4% by weight of Sb (calculated as Sb.sub.2O.sub.3), 0.2% by weight of Cs, remainder TiO.sub.2.

Catalyst Zone CZ15:

[0068] 8.63 g of ammonium hydrogenphosphate, 430.31 g of titanium dioxide (Fuji TA 100CT, anatase, BET surface area 28 m.sup.2/g), 47.81 g of titanium dioxide (Fuji TA 100, anatase, BET surface area 8 m.sup.2/g), 122.44 g of vanadium pentoxide and 9.27 g of antimony trioxide (100% by weight of senarmontite) were suspended in 1582 g of demineralized water and stirred for 18 hours, in order to obtain a homogeneous distribution. To this suspension were added 93 g of organic binder, consisting of a copolymer of vinyl acetate and vinyl laurate in the form of a 50% by weight aqueous dispersion. In a fluidized bed apparatus, 820 g of this suspension were sprayed onto 2 kg of steatite (magnesium silicate) in the form of rings having dimensions of 7 mm×7 mm×4 mm and dried. After the catalyst had been calcined at 450° C. for one hour, the active material applied to the steatite rings was 10.0% by weight. The analyzed composition of the active material consisted of 20% by weight of V (calculated as V.sub.2O.sub.5), 0.38% by weight of P, 1.5% by weight of Sb (calculated as Sb.sub.2O.sub.3), remainder TiO.sub.2.

Catalyst Zone CZ16:

[0069] 7.96 g of ammonium hydrogenphosphate, 387.05 g of titanium dioxide (Fuji TA 100CT, anatase, BET surface area 28 m.sup.2/g), 96.76 g of titanium dioxide (Fuji TA 100, anatase, BET surface area 8 m.sup.2/g) and 126.12 g of vanadium pentoxide were suspended in 1582 g of demineralized water and stirred for 18 hours, in order to obtain a homogeneous distribution. To this suspension were added 93 g of organic binder, consisting of a copolymer of vinyl acetate and vinyl laurate in the form of a 50% by weight aqueous dispersion. In a fluidized bed apparatus, 820 g of this suspension were sprayed onto 2 kg of steatite (magnesium silicate) in the form of rings having dimensions of 7 mm×7 mm×4 mm and dried. After the catalyst had been calcined at 450° C. for one hour, the active material applied to the steatite rings was 9.1% by weight. The analyzed composition of the active material consisted of 20% by weight of V (calculated as V.sub.2O.sub.5), 0.38% by weight of P, remainder TiO.sub.2.

Examples with a Four-Zone Catalyst System

Example 6

[0070] The catalytic oxidation of o-xylene to phthalic anhydride was conducted in a salt bath-cooled tubular reactor having an internal tube diameter of 25 mm and a length of 350 cm. From reactor inlet to reactor outlet, 90 cm of CZ12, 70 cm of CZ13, 70 cm of CZ14 and 90 cm of CZ15 were introduced. For temperature regulation, the tubular reactor was surrounded by a salt melt; a thermowell of external diameter 4 mm with an installed thermocouple served for catalyst temperature measurement. An air flow of 4.0 Nm.sup.3(STP)/h with loadings of 99 to 99.4% by weight o-xylene of 30 to 100 g.sub.o-xylene/Nm.sup.3(STP).sub.air was passed through the tubular reactor.

TABLE-US-00009 TABLE 9 Catalyst composition of four-layer catalyst system of example 6. Catalyst zone CZ12 CZ13 CZ14 CZ15 Active material % 9.10 8.50 8.50 10.00 V.sub.2O.sub.5 % 7.10 7.95 11.00 20.00 Sb.sub.2O.sub.3 % 1.80 2.70 2.40 1.50 Cs % 0.38 0.31 0.22 0 P % 0 0 0 0.38 TiO.sub.2 % 90.72 89.04 86.38 78.12 BET-Surface area m.sup.2/g 16 18 21 26 Zone lenght cm 90 70 70 90

TABLE-US-00010 TABLE 10 Catalytic performance of the example 6 catalyst system at a total air flow rate of 4 Nm.sup.3(STP)/h. Salt bath Loading temperature Y.sub.PA .sup.a Y.sub.o-X .sup.b Y.sub.PHD .sup.c [g.sub.o-X/m.sup.3 (STP).sub.air] [° C.] [% by wt,] [% by wt,] [% by wt,] 68.0 363.0 113.4 0.00 0.06 77.0 358.0 114.0 0.01 0.06 80.0 355.0 114.7 0.01 0.05 .sup.a PA yield .sup.b o-xylene yield .sup.c phthalide yield

Example 7 (Comparative)

[0071] The catalytic oxidation of o-xylene to phthalic anhydride was conducted in a salt bath-cooled tubular reactor having an internal tube diameter of 25 mm and a length of 350 cm. From reactor inlet to reactor outlet, 130 cm of CZ12, 70 cm of CZ13, 50 cm of CZ14 and 60 cm of CZ16 were introduced. For temperature regulation, the tubular reactor was surrounded by a salt melt; a thermowell of external diameter 4 mm with an installed thermocouple served for catalyst temperature measurement. An air flow of 4.0 Nm.sup.3(STP)/h with loadings of 99 to 99.4% by weight o-xylene of 30 to 100 g.sub.o-xylene/Nm.sup.3(STP).sub.air was passed through the tubular reactor.

TABLE-US-00011 TABLE 11 Catalyst composition of four-layer catalyst system of example 7. Catalyst zone CZ12 CZ13 CZ14 CZ16 Active material % 9.10 8.50 8.50 9.10 V.sub.2O.sub.5 % 7.10 7.95 11.00 20.00 Sb.sub.2O.sub.3 % 1.80 2.70 2.40 0 Cs % 0.38 0.31 0.22 0 P % 0 0 0 0.38 TiO.sub.2 % 90.72 89.04 86.38 79.62 BET-Surface area m.sup.2/g 16 18 21 23 Zone lenght cm 130 70 50 60

TABLE-US-00012 TABLE 12 Catalytic performance of the example 7 catalyst system (comparative) at a total air flow rate of 4 Nm.sup.3(STP)/h. Salt bath Loading temperature Y.sub.PA .sup.a Y.sub.o-X .sup.b Y.sub.PHD .sup.C [g.sub.o-X/m.sup.3 (STP).sub.air] [° C.] [% by wt,] [% by wt,] [% by wt,] 60.0 363.0 110.9 0.02 0.06 74.0 358.0 112.3 0.04 0.08 80.0 354.0 113.0 0.07 0.12 .sup.a PA yield .sup.b o-xylene yield .sup.c phthalide yield