Process for starting up a gas phase oxidation reactor

Abstract

A process for preparing carboxylic acids and/or carboxylic anhydrides by gas phase oxidation of aromatic hydrocarbons, in which a gas stream comprising at least one aromatic hydrocarbon and molecular oxygen is passed continuously over a catalyst thermostatted by a heat carrier medium, which comprises keeping the temperature of the heat carrier medium constant during the startup of the reactor for at least 24 hours, during which neither the loading of the gas stream with hydrocarbons nor the gas stream volume is increased by more than 3%.

Claims

1. A process for preparing carboxylic acids and/or carboxylic anhydrides by gas phase oxidation of aromatic hydrocarbons selected from the group consisting of benzene, xylenes, naphthalene, toluene, durene, and combinations thereof, the process comprising: passing a gas stream comprising at least one aromatic hydrocarbon selected from the group consisting of benzene, xylenes, naphthalene, toluene, and durene, and molecular oxygen continuously over a catalyst thermostatted by a heat carrier medium in a reactor, during startup of the reactor, lowering the temperature of the heat carrier medium from a temperature in the range from 380 to 410 C. to a temperature in the range of 340 to 365 C., maintaining the temperature of the heat carrier medium constant by pausing the lowering of the temperature for at least 24 hours during the startup of the reactor, during which neither the loading of the gas stream with hydrocarbons nor the gas stream volume is increased by more than 3%.

2. The process according to claim 1, wherein the temperature of the heat carrier medium is kept constant for at least 48 hours.

3. The process according to claim 1, wherein the loading of the gas stream with hydrocarbons in the period during which the temperature of the heat carrier medium is kept constant is increased by a maximum of 1.5%.

4. The process according to claim 1, wherein the gas stream volume in the period during which the temperature of the heat carrier medium is kept constant is increased by a maximum of 2.5%.

5. The process according to claim 1, wherein the loading of the gas stream with hydrocarbons is increased in the course of startup from 25 to 30 g/m.sup.3 (STP) to 70 to 120 g/m.sup.3 (STP).

6. The process according to claim 1, wherein phthalic anhydride is prepared from o-xylene and/or naphthalene.

7. The process according to claim 1, wherein the catalytically active material of the catalyst comprises vanadium pentoxide and titanium dioxide.

Description

Example A

Oxidation of o-xylene to Phthalic Anhydride

(1) Preparation of the Catalyst Zones

(2) Catalyst zone 1 (CZ1) (vanadium antimonate as V and Sb source):

(3) Preparation of Vanadium Antimonate:

(4) 2284.1 g of vanadium pentoxide and 1462 g of antimony trioxide (Antraco ACC-BS, approx. 4% valentinite and 96% senarmontite; Sb.sub.2O.sub.399.8% by weight; As800 ppm by weight, Pb800 ppm by weight, Fe30 ppm by weight, mean particle size =1.4 m) were suspended in 5.61 of demineralized water and the suspension was stirred under reflux for 15 hours. Thereafter, the suspension was cooled to 80 C. and dried by means of spray drying. The inlet temperature was 340 C., the exit temperature 110 C. The spray powder thus obtained had a BET surface area of 89 m.sup.2/g and had a vanadium content of 32% by weight and an antimony content of 30% by weight. The product had the following crystalline constituents: valentinite (ICPDS: 11-0689): approx. 3%; senarmontite (ICPDS: 43-1071): approx. 2%; vanadium antimonate (ICPDS: 81-1219): approx. 95%. The mean crystal size of the vanadium antimonate was approx. 9 nm.

(5) Suspension Mixing and Coating:

(6) 2 kg of steatite rings (magnesium silicate) having dimensions of 7 mm7 mm4 mm were coated in a fluidized bed apparatus with 752 g of a suspension of 4.4 g of cesium carbonate, 413.3 g of titanium dioxide (Fuji TA 100 CT; anatase, BET surface area 27 m.sup.2/g), 222.5 g of titanium dioxide (Fuji TA 100; anatase, BET surface area 7 m.sup.2/g), 86.9 g of vanadium antimonate (as prepared above), 1870.1 g of demineralized water and 76.7 g of organic binder (copolymer of vinyl acetate and vinyl laurate in the form of a 50% by weight aqueous dispersion).

(7) After calcination of the catalyst at 450 C. for one hour, the active material applied to the steatite rings was 8.3%. The analyzed composition of the active material consisted of 7.1% V205, 4.5% Sb203, 0.50% Cs, remainder TiO.sub.2.

(8) Catalyst zone 2 (CZ2) (vanadium pentoxide and antimony trioxide, respectively, as V and Sb sources):

(9) 2 kg of steatite rings (magnesium silicate) having dimensions of 7 mm7 mm4 mm were coated in a fluidized bed apparatus with 920 g of a suspension of 3.0 g of cesium carbonate, 446.9 g of titanium dioxide (Fuji TA 100 C; anatase, BET surface area 20 m.sup.2/g), 133.5 g of titanium dioxide (Fuji TA 100; anatase, BET surface area 7 m.sup.2/g), 45.4 g of vanadium pentoxide, 11.6 g of antimony trioxide, 1660.1 g of demineralized water and 104.5 g of organic binder (copolymer of vinyl acetate and vinyl laurate in the form of a 50% by weight aqueous dispersion).

(10) After calcination of the catalyst at 450 C. for one hour, the active material applied to the steatite rings was 10.0%. The analyzed composition of the active material consisted of 7.1% V.sub.2O.sub.5, 1.8% Sb.sub.2O.sub.30.38% Cs, remainder TiO.sub.2.

(11) Catalyst zone 3 (CZ3) (vanadium pentoxide and antimony trioxide, respectively, as V and Sb sources):

(12) 2 kg of steatite rings (magnesium silicate) having dimensions of 7 mm7 mm4 mm were coated in a fluidized bed apparatus with 750 g of a suspension of 2.33 g of cesium carbonate, 468.7 g of titanium dioxide (Fuji TA 100 C; anatase, BET surface area 20 m.sup.2/g), 76.3 g of titanium dioxide (Fuji TA 100; anatase, BET surface area 7 m.sup.2/g), 48.7 g of vanadium pentoxide, 16.7 g of antimony trioxide, 1588.0 g of demineralized water and 85.2 g of organic binder (copolymer of vinyl acetate and vinyl laurate in the form of a 50% by weight aqueous dispersion).

(13) After calcination of the catalyst at 450 C. for one hour, the active material applied to the steatite rings was 8.5%. The analyzed composition of the active material consisted of 7.95% V.sub.2O.sub.5, 2.7% Sb.sub.2O.sub.3, 0.31% Cs, remainder TiO.sub.2.

(14) Catalyst Zone 4 (CZ4) (Vanadium Pentoxide and Antimony Trioxide, Respectively, as V and Sb Sources):

(15) 2 kg of steatite rings (magnesium silicate) having dimensions of 7 mm7 mm4 mm were coated in a fluidized bed apparatus with 760 g of a suspension of 1.7 g of cesium carbonate, 370.1 g of titanium dioxide (Fuji TA 100 CT; anatase, BET surface area 27 m.sup.2/g), 158.6 g of titanium dioxide (Fuji TA 100; anatase, BET surface area 7 m.sup.2/g), 67.3 g of vanadium pentoxide, 14.8 g of antimony trioxide, 1587.9 g of demineralized water and 86.3 g of organic binder (copolymer of vinyl acetate and vinyl laurate in the form of a 50% by weight aqueous dispersion).

(16) After calcination of the catalyst at 450 C. for one hour, the active material applied to the steatite rings was 8.5%. The analyzed composition of the active material consisted of 11% V.sub.2O.sub.5, 2.4% Sb203, 0.22% Cs, remainder Ti02.

(17) Catalyst zone 5 (CZ5) (vanadium pentoxide and antimony trioxide, respectively, as V and Sb sources):

(18) 2 kg of steatite rings (magnesium silicate) having dimensions of 7 mm7 mm4 mm were coated in a fluidized bed apparatus with 850 g of a suspension of 389.8 g of titanium dioxide (Fuji TA 100 CT; anatase, BET surface area 27 m.sup.2/g), 97.5 g of titanium dioxide (Fuji TA 100; anatase, BET surface area 7 m.sup.2/g), 122.4 g of vanadium pentoxide, 1587.9 g of demineralized water and 96.5 g of organic binder (copolymer of vinyl acetate and vinyl laurate in the form of a 50% by weight aqueous dispersion).

(19) After calcination of the catalyst at 450 C. for one hour, the active material applied to the steatite rings was 9.1%. The analyzed composition of the active material consisted of 20% V.sub.2O.sub.5, 0.38% P, remainder TiO.sub.2.

Example 1 (INVENTIVE)

Catalytic Oxidation of o-xylene to Phthalic Anhydride on the Industrial Scale

(20) The catalytic oxidation of o-xylene to phthalic anhydride was performed on the industrial scale in a salt bath-cooled shell-and-tube reactor having a total of 18 900 tubes. From the reactor inlet to the reactor outlet, in each case 80 cm of CZ1, 60 cm of CZ2, 70 cm of CZ3, 50 cm of CZ4 and 60 cm of CZ5 were introduced into the individual tubes having an internal width of 25 mm. The catalyst layers, based on the above-described preparation of CZ1 to CZ5, were prepared in batches of in each case 150 kg of steatite rings. The iron tubes were surrounded by a salt melt for temperature regulation.

(21) Preforming of the catalyst was effected under air at 400 C.

(22) The catalyst was started up at 386 C. and the following gas streams were passed through the tubes from the top downward (calculated as flow rate per individual tube): air 3.0 to 4.0 M.sup.3 (STP)/h of air with loadings of 98.8 to 99.4% by weight o-xylene of 30 to 100 g/m.sup.3 (STP). The thermal bed temperature (salt bath temperature) was lowered proceeding from 386 C. and, at the same time, the loading of o-xylene was varied according to the table which follows. The PA yields were measured in the reactor outlet gas and are reported in % by mass (kg of PA per kg of o-xylene converted), based on 100% o-xylene.

(23) TABLE-US-00001 o-Xylene Phthalide Salt bath Gas Loading in the in the Run temper- stream [g of o- reactor reactor time ature volume xylene/ outlet gas outlet gas [hours] [ C.] [m.sup.3 (STP)/h] m.sup.3 (STP)] [% by wt.] [% by wt.] 24 386 3.0 35.0 0.002 0.009 48 382 3.25 37.0 0.002 0.008 72 380.1 3.5 38.5 0.003 0.009 96 378 3.75 40.0 0.004 0.021 120 376 3.8 40.5 0.003 0.009 144 374 3.8 43.5 0.004 0.014 168 373 3.8 45.0 0.004 0.014 192 372 3.85 46.0 0.014 0.031 216 371 3.88 47.0 0.004 0.019 240 370 3.83 48.0 0.005 0.022 264 369 3.83 49.0 0.007 0.022 288 368 3.83 50.0 0.007 0.025 312 367 3.83 51.0 0.007 0.026 336 366 3.83 53.6 0.008 0.028 360 365 3.83 54.8 0.007 0.031 384 363 3.83 56.6 0.009 0.035 408 361 3.83 57.4 0.010 0.041 432 359 3.83 59.2 0.014 0.062 456 358.5 3.83 60.9 0.026 0.059 480 357.5 3.83 62.7 0.030 0.064 504 356.6 3.85 63.7 0.031 0.066 528 355.5 3.85 65.0 0.043 0.083 552 354.5 3.85 66.0 0.068 0.102 576 354.4 3.85 67.0 0.088 0.123 600 354.4 3.85 67.1 0.079 0.100 624 354.4 3.85 68.0 0.060 0.092 648 353.9 3.85 69.3 0.067 0.100 672 353.9 3.85 70.0 0.060 0.090 696 353.4 3.88 71 0.069 0.098

(24) It is apparent that the contents of o-xylene and phthalide, an underoxidation product, in the reactor outlet gas are reduced by pausing the lowering of the temperature (after 576 to 624 h or after 648 to 672 h), with a simultaneous slight increase in the loading of o-xylene in this case.

Example 2 (INVENTIVE)

Catalytic Oxidation of o-xylene to Phthalic Anhydride on the Pilot Tube Scale

(25) The catalytic oxidation of o-xylene to phthalic anhydride was conducted in a salt bath-cooled tubular reactor having an internal diameter of the tubes of 25 mm. From the reactor inlet to the reactor outlet, in each case 80 cm of CZ1, 60 cm of CZ2, 70 cm of CZ3, 50 cm of CZ4 and 60 cm of CZ5 were introduced into an iron tube of length 3.5 m with an internal width of 25 mm, The iron tube was surrounded by a salt melt for temperature regulation; a 4 mm external diameter thermowell with installed tensile element served for catalyst temperature measurement.

(26) Preforming of the catalysts was effected under 0.1 M.sup.3 (STP)/h of air at 400 C. for about 38 hours.

(27) After starting up the catalyst at 386 C., 3.0 to 4.0 m.sup.3 (STP) of air per hour flowed through the tube from the top downward with loadings of 99-99.4% by weight o-xylene of 30 to 100 g/m.sup.3 (STP). The thermal bed temperature (salt bath temperature) was lowered proceeding from 386 C. The PA yields were measured in the reaction outlet gas and are reported in % by mass (kg of PA per kg of o-xylene converted) based on 100% o-xylene.

(28) The different operating parameters are summarized in the following table:

(29) TABLE-US-00002 o-Xylene Phthalide Salt bath Gas Loading in the in the Run temper- stream [g of o- reactor reactor time ature volume xylene/ outlet gas outlet gas [hours] [ C.] [m.sup.3 (STP)/h] m.sup.3 (STP)] [% by wt.] [% by wt.] 24 386 3.3 33 n.d. n.d. 48 382 3.3 33 n.d. n.d. 72 380 3.3 33 0.00 0.05 96 378 3.5 43 0.01 0.06 120 376 3.7 45 0.02 0.09 144 374 4.0 46 0.04 0.14 168 372 4.0 48 0.05 0.16 192 370 4.0 51 n.d. n.d. 216 368 4.0 51 n.d. n.d. 240 366 4.0 51 n.d. n.d. 264 365 4.0 51 0.12 0.23 288 365 4.1 51 0.11 0.23 312 365 4.0 51 0.08 0.19 336 367 4.0 51 0.06 0.10 n.d.: not determined

(30) It is apparent that the contents of o-xylene and of phthalide, an underoxidation product, in the reactor outlet gas are reduced by pausing the lowering of the temperature (after 288 to 312 h), with a simultaneous slight increase in the volume flow rate in this case.

(31) Examples 3 to 8 which follow were started up analogously to examples 1 and 2 at 386 C., and the salt bath temperature was lowered continuously until the operating points described had been attained.

Example 3 (INVENTIVE)

(32) The different operating parameters are summarized in the following table:

(33) TABLE-US-00003 Phthalide o-Xylene in in the Salt bath Gas stream Loading [g of the reactor reactor Run time temperature volume o-xylene/m.sup.3 outlet gas outlet gas PA yield [hours] [ C.] [m.sup.3 (STP)/h] (STP)] [% by wt.] [% by wt.] [% by wt.] 192 368 4 63 0.07 0.19 112.3 216 366 4 66 0.11 0.23 112.0 240 365 4 68 0.12 0.24 112.2 264 365 4 68 0.10 0.22 112.4 288 365 4 68 0.09 0.19 112.3

Example 4 (INVENTIVE)

(34) The different operating parameters are summarized in the following table:

(35) TABLE-US-00004 Phthalide o-Xylene in in the Salt bath Gas stream Loading [g of the reactor reactor Run time temperature volume o-xylene/m.sup.3 outlet gas outlet gas PA yield [days] [ C.] [m.sup.3 (STP)/h] (STP)] [% by wt.] [% by wt.] [% by wt.] 192 370 4.0 67 0.09 0.22 111.7 216 368 4.0 71 0.11 0.24 111.8 240 368 4.0 71 0.08 0.21 111.9

(36) Pausing the lowering of the salt bath temperature in examples 3 and 4 led to an improvement in the product gas composition, while the other reaction parameters remained unchanged.

Example 5 (NONINVENTIVE)

(37) The different operating parameters are summarized in the following table:

(38) TABLE-US-00005 o-Xylene Phthalide Gas stream in the in the Salt bath volume Loading [g of reactor reactor Run time temperature [m.sup.3 o-xylene/m.sup.3 outlet gas outlet gas PA yield [days] [ C.] (STP)/h] (STP)] [% by wt.] [% by wt.] [% by wt.] 240 368 4.0 54 0.05 0.14 109.7 264 366 4.0 57 0.08 0.16 111.2 288 365 4.0 60 0.12 0.18 110.8 312 364 4.0 60 n.d. n.d. n.d. 336 363 4.0 62 0.13 0.19 110.5 360 362 4.0 64 n.d. n.d. n.d. 384 361.3 4.0 64 n.d. n.d. n.d. 408 360.6 4.0 64 0.14 0.21 112.0 n.d.: not determined

(39) Constantly lowering the salt bath temperature leads to a deterioration in the product gas composition.

Example 6 (NONINVENTIVE)

(40) The different operating parameters are summarized in the following table:

(41) TABLE-US-00006 Phthalide o-Xylene in in the Salt bath Gas stream Loading [g of the reactor reactor Run time temperature volume o-xylene/m.sup.3 outlet gas outlet gas PA yield [days] [ C.] [m.sup.3 (STP)/h] (STP)] [% by wt.] [% by wt.] [% by wt.] 192 370 4.0 64 0.08 0.25 111.5 216 368 4.0 67 0.11 0.26 112.2 240 366 4.0 70 0.12 0.28 112.1

(42) Constantly lowering the salt bath temperature (combined with an increase in the loading of o-xylene) in examples 5 and 6 led to a deterioration in the product gas composition.

Example 7 (NONINVENTIVE)

(43) The different operating parameters are summarized in the following table:

(44) TABLE-US-00007 Phthalide o-Xylene in in the Salt bath Gas stream Loading [g of the reactor reactor PA yield Run time temperature volume o-xylene/m.sup.3 outlet gas outlet gas [% by [days] [ C.] [m.sup.3 (STP)/h] (STP)] [% by wt.] [% by wt.] wt.] 168 368 4 58.5 0.08 0.21 113.0 192 366 4 60.5 0.11 0.23 113.0 216 364 4 60.5 0.15 0.28 113.8 240 364 4 55.5 0.12 0.24 114.0 264 364 3.5 60.5 0.04 0.11 112.5

(45) Continuous lowering even in the case of identical loading and gas stream volume (analyses after 192 and 216 h) leads to a deterioration in the product gas composition. By reducing the loading or the residence time, the product quality can be improved at the cost of productivity (analyses after 240 h and after 264 h).

Example B

Oxidation of Naphthalene or Mixtures of Naphthalene and o-xylene to Phthalic Anhydride

(46) Preparation of the Catalyst Zones

(47) Catalyst Zone 1 (CZ1)

(48) 2 kg of steatite rings (magnesium silicate) in the form of rings having dimensions of 8 mm6 mm5 mm were coated in a fluidized bed apparatus with 860 g of a suspension of 6.92 g of cesium carbonate, 562.34 g of titanium dioxide (Fuji TA 100 C; anatase, BET surface area 20 m.sup.2/g), 4.,86 g of vanadium pentoxide, 1.75 g of niobium pentoxide, 1587.96 g of demineralized water and 97.7 g of organic binder (copolymer of vinyl acetate and vinyl laurate in the form of a 50% by weight aqueous dispersion).

(49) After calcination of the catalyst at 450 C. for one hour, the active composition applied to the steatite rings was 9.0%. The analyzed composition of the active material consisted of 7% V.sub.2O.sub.5, 0.2% Nb.sub.2O.sub.5, 0.92% Cs, remainder TiO.sub.2.

(50) Catalyst zone 2 (CZ2): Preparation analogous to CZ1, variation of the composition of the suspension. After calcination of the catalyst at 450 C. for one hour, the active material applied to the steatite rings was 9.1%. The analyzed composition of the active material consisted of 7% V.sub.2O.sub.5, 0.2% Nb.sub.2O.sub.5, 0.67% Cs, remainder TiO.sub.2 with a mean BET surface area of 20 m.sup.2/g (Fuji TA 100 C anatase).

(51) Catalyst zone 3 (CZ3): Preparation analogous to CZ1, variation of the composition of the suspension. After calcination of the catalyst at 450 C. for one hour, the active material applied to the steatite rings was 9.0%. The analyzed composition of the active material consisted of 7% V.sub.2O5, 0.2% Nb205, 0.35% Cs, 0.04% K (introduced into the suspension as sulfate), 0.03% P (introduced into the suspension as dihydrogenphosphate), remainder TiO2 having a mean BET surface area of 22.1 m.sup.2/g (mixture of Fuji TA 100 C anatase, BET surface area of 20 m.sup.2/g, and Fuji TA 100 CT anatase, BET surface area of 27 m.sup.2/g).

(52) Catalyst zone 4 (CZ4): Preparation analogous to CZ1, variation of the composition of the suspension. After calcination of the catalyst at 450 C. for one hour, the active material applied to the steatite rings was 8.0%. The analyzed composition of the active material consisted of 20% V205, 0.18% P (introduced into the suspension as dihydrogenphosphate), 0.24% W (introduced into the suspension as W03), remainder TiO2 having a mean BET surface area of 20 m.sup.2/g (Fuji TA 100 C anatase).

(53) Catalytic Oxidation of Naphthalene or of a Mixture of Naphthalene and o-xylene to Phthalic Anhydride on the Model Tube Scale

(54) The catalytic oxidation of o-xylene to phthalic anhydride was performed in a salt bath-cooled tubular reactor having an internal diameter of the tubes of 25 mm. From the reactor inlet to the reactor outlet, in each case 80 cm of CZ1, 80 cm of CZ2, 90 cm of CZ3 and 90 cm of CZ4 were introduced into an iron tube of length 3.5 m with an internal width of 25 mm. The iron tube was surrounded by a salt melt for temperature regulation; a 4 mm external diameter thermowell with installed tensile element served for catalyst temperature measurement.

(55) Preforming of the catalysts was effected under 0.1 M.sup.3 (STP)/h of air at 400 C. for about 24 hours.

(56) After starting up the catalyst at 380 C., 3.0 to 4.0 M.sup.3 (STP) of air per hour flowed through the tube from the top downward with loadings of 97.5% by weight naphthalene or mixtures of 97.5% by weight naphthalene and 99-99.4% by weight o-xylene totaling 30 to 80 g/m.sup.3 (STP). The thermal bed temperature (salt bath temperature) was lowered proceeding from 386 C. The PA yields were measured in the reaction outlet gas and are reported in % by mass (kg of PA per kg of naphthalene or naphthalene and o-xylene converted), based on 100% reactant.

Example 8 (INVENTIVE)

(57) The different operating parameters are summarized in the following table:

(58) TABLE-US-00008 Naphthoquinone Gas Loading [g/m.sup.3 (STP)] in the Phthalide stream of reactor in reactor PA Run Salt bath volume which outlet outlet yield time temperature [m.sup.3 of which o- gas [% gas [% [% by [days] [ C.] (STP)/h] Sum naphthalene xylene by wt.] by wt.] wt.] 96 380 4 40.1 40.1 0 1.86 0.00 105.6 120 377 4 40.3 40.3 0 1.95 0.00 105.8 192 377 4 45.4 40.4 5 1.58 0.01 107.5 240 376 4 45.4 40.4 5 1.71 0.01 105.7 264 376 4 45.4 40.4 5 1.61 0.01 106.0

(59) Pausing the lowering of the salt bath temperature leads to a reduction in the level of naphthoquinone, an underoxidation product, and hence to an improved product gas composition.