GB2302291A

GB2302291A - Ammoxidation of propane

Info

Publication number: GB2302291A
Application number: GB9512124A
Authority: GB
Inventors: Michael Bowker; Paul Kerwin; Hans-Dieter Eichhorn
Original assignee: BASF PLC
Current assignee: BASF PLC
Priority date: 1995-06-15
Filing date: 1995-06-15
Publication date: 1997-01-15
Anticipated expiration: 2015-06-15
Also published as: GB9512124D0; GB2302291B

Abstract

Propane is ammoxidised in the gas phase by contacting with oxygen, ammonia and, if desired, water, in the presence of a catalyst based on iron, antimony and oxygen under elevated temperature and pressure, using a catalyst represented by the formula E d Fe a Sb b O c I where E is vanadium, chromium and/or niobium, a is 1, b is a real number from 1 to 8, c is a real number from 2.5 to 18, and d/c is in the range from 0.01:1 to 1:1.

Description

Ammoxidation of propane Description The present invention relates to a process for the ammoxidation of propane in the gas phase by contacting propane with oxygen, ammonia, and, if desired, water in the presence of a catalyst based on iron, antimony and oxygen under elevated temperature and pressure.

The present invention also relates to catalysts based on vanadium, iron, and antimony, their preparation and use.

Centi et al. (Appl. Catal. 33 (1987) 343 - 359) describes a process for the ammoxidation of propane with a Fe/Sb/04-catalyst, wherein the Sb/Fe-ratio is 2:1. The used catalyst has the disadvantage, that the reported activity is low: at 5020C, the conversion of propane is 18%, giving a selectivity to acrylonitrile of 10% and hence a yield of only 1.8%.

It is an object of the present invention to provide a process for the ammoxidation of propane using a metal oxide catalyst essentially based on iron, antimony, vanadium, chromium and/or niobium which does show a higher yield compared with the yield obtained with the process of Centi et al.

It is a further object of the present invention to provide new catalysts for the ammoxidation of propane with a higher activity compared with Centi et al's catalyst.

We have found that this object is achieved by the process for the ammoxidation of propane in the gas phase by contacting propane with oxygen, ammonia, and, if desired, water in the presence of a catalyst based on iron, antimony and oxygen under elevated temperature and pressure comprising a catalyst represented by the formula EdFeasbboc where E is vanadium, chromium and/or niobium, preferably vanadium and/or chromium, particularly preferred vanadium, a is 1, b is a real number from 1 to 8, preferably from 2 to 5, c is a real number from 2.5 to 18, preferably from 4 to 12, and d/c is in the range from 0.01:1 to 1:1, particularly preferred from 0.05:1 to 0.8:1.

The catalysts I of the present invention are usually prepared by preparing first or using an already prepared catalyst II, then (a) adding the desired Lewis base, containing E (vanadium, chromium or niobium) preferably in the form of an oxidic salt or oxide, such as NH4V03 or Cr03, in the desired amount. Usually a wet paste is obtained thereby, which (b) can be dried and then (c) calcined in air, oxygen or nitrogen, preferably air. The process of adding Lewis base, drying and calcining can be repeated as often as desired in order to be sure the desired amount of Lewis base had been incorporated into the pores of the catalyst II. In general, the catalysts I have a coarse particle diameter in the range of from 600 to 1000 Fm.

The catalysts II Feasbboc II where a is 1, b is a real number from 1 to 8, preferably from 2 to 5, and c is a real number from 2.5 to 18, preferably from 4 to 12, usually are obtainable according to the method of Keulks et al. (J.Phys.Chem., 90 (1986) 4768) and Fattore et al. (J.Catal., 37 (1975) 223), in heating a desired amount of ferric nitrate, Fe(NO3)3-9H2O, with antimony (III) oxide, Sb203, then neutralizing the obtained mixture, drying and calcinating it in air, whereby oxygen or nitrogen can also be used instead of air.

In general, the catalysts II have a particle diameter in the range of from 600 to 1000 pxn.

If it is desired to have the catalyst supported on a support material, the catalysts are usually prepared in the same manner, but adding the support to the slurry obtained after the first heating and before neutralization.

In general inorganic support materials are selected from silica, alumina, titania, zirconia, silica-zirconia, silica-titania, silica-alumina and magnesia, preferably alumina, silica-alumina, and silica.

The weight ratio of the catalyst having the formula I or II to the support material can vary from 10:1 to 0.1:1.

Furthermore, the calcined catalyst can be comminuted and shaped in a known matter per se, for example by pressing hollow cyclinders or extrudates by methods known per se. It is of course also possible to employ the catalysts in powder form.

In the ammoxidation of the present invention, the reaction is carried out in the gas phase by contacting a mixture of propane, ammonia, water and a molecular oxygen containing gas, such as air or oxygen, with one of the above mentioned catalysts contained in usually a fixed bed, a gravity flowing bed, a fluidized bed or a fast transport reactor mode.

The mole ratio of oxygen to propane can vary from 0.1:1 to 10:1, preferably from 1:1 to 5:1, particularly preferably from 1:1 to 3:1.

The ammonia to propane ratio can vary from 0.1:1 to 10:1, preferably from 1:1 to 5:1, particularly preferably from 1:1 to 3:1.

It is possible to carry out the ammoxidation in the presence or in the absence of water. If water is used, the water to propane ratio can vary from 0.1:1 to 10:1, preferably from 0.3:1 to 4:1, particularly preferably from 0.5:1 to 2:1.

The catalyst to propane ratio, based on antimony, can vary from 0.1:1 to 100:1, preferably from 0.1:1 to 50:1, particularly preferably from 1:1 to 20:1.

The reaction temperature can vary from 300 to 650, preferably from 400 to 550, particularly preferably from 420 to 5300C.

The reaction pressure usually varies from 50 to 1000, preferably from 100 to 500, particularly preferably from 100 to 300 kPa.

The total flow of gas, i.e. the flow rate of all gases added together, usually is in the range of from 1 to 100, preferably from 5 to 20 ml per minute, which corresponds to a space velocity usually in the range of from 100 to 10,000, preferably from 500 to 2,000 h-1.

The contact time (volume (catalyst)/volume (gas) * flow rate), in general, varies from 0,3 to 30, preferably from 1 to 6 seconds.

However, higher or lower contact times are within the scope of the process of the invention.

Acrylonitrile is used as solvent and as an important intermediate for the manufacture of hexamethylene diamine and nylon 6,6.

The advantage of the present invention is a process for the ammoxidation of propane showing a higher yield in acrylonitrile compared with the yield obtained with the process of Centi et al.

In addition, better catalysts for the ammoxidation of propane with a higher activity compared with Centi et al's catalyst have been found.

Examples Example 1 - preparation of iron antimonate catalyst II (Sb:Fe = 1:1) 20 g of Fe(NO3)3-9H2O was heated to 600C until all the ferric nitrate dissolved in its own water of crystallization. 1.23 g of antimony (III) oxide, Sub203, was then added to the ferric nitrate solution and stirred. The mixture was then heated to 800C until no further brown fumes were evolved, the resulting solution was then neutralized to pH 7 using an aqueous NH40H solution (33% by weight ammonia), suction filtered and dried at 1100C for 24 h. The brown solid was then calcined in air for 20 h at 5000C and then for 2 hours at 9000C in air. After cooling the catalyst was screened to a particle diameter between 600 and 1000 Sm using a 600 to 1000 pzn mesh sieve.

Example 2 - preparation of iron antimonate catalyst (Sb:Fe = 2:1) Example 1 was repeated, but 20 g of Fe(NO3)3-9H2O and 14.5 g of antimony (III) oxide, Sb203, was used.

Example 3 - preparation of iron antimonate catalyst (Sb:Fe = 5:1) Example 1 was repeated, but 20 g of Fe(NO3)3-9H2O and 36.1 g of antimony (III) oxide, Sb2O3, was used.

Example 4 - preparation of iron antimonate catalyst modified with vanadium (3% by weight V), catalyst I To 48.5 g of the iron antimonate catalyst of example 2 and 20 ml of an aqueous solution of NH4VO3 (prepared by mixing 3.2 g of NH4V03 and 20 ml of water) was added dropwise with mixing, until a wet paste was obtained. The paste was dried at 1200C overnight and then calcined at 5800C for 6 hours. Thereafter, the obtained sample was rehydrated with 20 ml of the above used aqueous solution of NH4VO3, dried (at 1200C overnight) and recalcined at 5800C for 6 hours. After cooling, the obtained catalyst was screened to a particle diameter between 600 and 1000 Sm.

Example 5 - preparation of iron antimonate catalyst modified with vanadium (5% by weight V), catalyst I To 47.5 g of the iron antimonate catalyst of example 2 and 20 ml of an aqueous solution of NH4V03 (prepared by mixing 5.82 g NH4VO3 and 20 ml of water) was added dropwise with mixing, until a wet paste was obtained. The paste was dried at 1200C overnight and then calcined at 5800C for 6 hours. Thereafter, the obtained sample was rehydrated with 20 ml of the above used aqueous solution of NH4VO3, dried (at 1200C overnight) and recalcined at 5800C for 6 hours. After cooling, the obtained catalyst was screened to a particle diameter between 600 and 1000 Fm.

Example 6 - preparation of iron antimonate catalyst modified with vanadium (5% by weight V incorporated into the bulk of the cata lust) , catalyst I 20 g of Fe(N03)3.9H20 was heated to 600C until all the ferric nitrate dissolved in its own water of crystallization. 14.5 g of antimony (III) oxide, Sb203, was then added to the ferric nitrate solution and stirred. The mixture was then heated to 800C until no further brown fumes were evolved, then 20 ml of an aqueous solution of NH4VO3 (5.82 g in 20 ml solution) was added to the slurry, thereafter the resulting solution was neutralized to pH 7 using an aqueous NH40H solution (33% by weight ammonia), suction filtered and dried at 1100C for 24 h. The brown solid was then calcined in air for 20 h at 5000C and then for 2 hours at 9000C in air.After cooling the catalyst was screened to a particle diameter between 600 and 1000 pzn.

Example 7 - preparation of iron antimonate catalyst modified with chromium (5% by weight Cr),catalyst I To 47.5 g of the iron antimonate catalyst of example 2 and 20 ml of an aqueous solution of Cr03 (prepared by mixing 4.81 g CrO3 and 20 ml water) was added dropwise with mixing, until a wet paste was obtained. The paste was dried at 1200C overnight and then calcined at 580at for 6 hours. Thereafter, the obtained sample was rehydrated with 20 ml of the above used aqueous solution of Cr03, dried (at 1200C overnight) and recalcined at 5800C for 6 hours.

After cooling, the obtained catalyst was screened to a particle diameter between 600 and 1000 pm.

The catalysts were tested for propane ammoxidation using an online plug flow microreactor. The system consisted of four gases (02,N2,C3H8 and NH3) and each passed through 1/8' (0,32 cm) o.d.

stainless steel tubing to a one way valve and seven micron filter. The pressure was held constant using a pressure regulator and the gases then passed through a two-way tap to thermal mass flow controllers. After mixing, the gases travelled into a 'U"-shaped bed (15 cm long, stainless steel with o.25#(0,64 cm) o.d. and 0.173 (0,44 cm) i.d.) in which one gram of catalyst (1000-600 microns particle size) was held between quartz wool plugs and a Chromel-Alumel thermocouple was inserted into the bed. A Pye 104 Unicam oven maintained an isothermal temperature for the catalyst bed and the resulting products were passed along a heated tube for online analysis using a Varian 3400 series gas chromatograph, fitted with a T.C. detector.The hydrocarbon 'heavies' were separated using a Hayesep 'B' column (2m long) and the lighter N2, 2 and CO were separated on a MS13X column (lOA and 2m in length). The separation process began with a column temperature of 700C for 9 minutes. In this time an air actuated Valco six-port sampling valve was used to inject the contents of the loop on to the columns. The lighter gases, 02, N2 and CO passed through the Hayesep 'B' column quickly and after 0.4 minutes were isolated on the MS13X column using a second six-port valve. CO2, N20, NH3 and H20 then elute from Hayesep 'B'. After three minutes the MS13X was switched back in and 2, N2 and CO elute. The column was closed after 5 minutes and then HCN, propene and propane elute.The column temperature was then raised at a rate of 300C min-1 for 3.3 minutes until it reached 1700C, where it remained constant for 4.7 minutes. After this, acrolein acetonitrile and acrylonitrile elute, giving a fifteen minute chromatogram.

Each catalyst was held for several hours under reaction conditions before testing. The initial bed temperature was 1500C, at this temperature no alkane, oxygen or ammonia feed was converted.

At each temperature, three product injections were made over the column after a 20 minute thermal stabilization period.

Selectives to products were calculated as follows: Total number moles* of X in product stream % Selectivity to X= x 100% Total number of moles* of products in eluent Conversion of hydrocarbon feed was defined as follows: Total number moles of hydrocarbon reacted e Conversion = x 100% Total number of moles of hydrocarbon in feed Yields of various products were calculated as follows: % Yield of X= Total number moles* of X in product stream x 100% Total number of moles of hydrocarbon in feed * The number of moles used for the calculation was subject to correction as follows: exam. 2 C3H8 + 502 # 3CO2 + 4H2O (% vol. CO2 in eluent was divided by 3 before calculation).

C3HS + 7/202 # 3CO + 4H2O (% vol. CO in eluent was divided by 3 before calculation).

C3H8 + 3NH3 + 7/202 b 3HCN + 7H20 (% vol. HCN in eluent was divided by 3 before calculation).

C3H8 + 3/2NH3 + 202 > 3/2CH3CN + 4H20 (% vol. CH3CN in eluent was divided by 3/2 before calculation).

Example 8 - ammoxidation of propane (comparative) A propane/oxygen/ammonia/nitrogen gas mixture in the volume ratio 1/2/2/7 with a flow of 10 ml per minute was reacted in the above described reactor. The temperature in the reaction zone was 5000C.

The contact time (measured on a soap bubble meter, whereby contact time was calculated from volume (catalyst)/ volume (gas) * flow time]) was 3 seconds. The catalyst employed was the catalyst from example 1. The results of the ammoxidation are shown in Table 1 below.

Example 9 - ammoxidation of propane (comparative) Example 8 was repeated using the catalyst from example 2. The results of the ammoxidation are shown in Table 1 below.

Example 10 - ammoxidation of propane (comparative) Example 8 was repeated using the catalyst from example 3. The results of the ammoxidation are shown in Table 1 below.

Table 1 - Summary of activity of iron antimonate catalysts

ex. catalyst from yield of ACN selectivity of - conversion of ACN propane 8 ex. 1 1.6% 4.5% 36% 9 ex. 2 4.8% 22.5% 21.4% 10 ex. 3 2.0% 17.3% 11.7% Example 11 - ammoxidation of propane (comparative) Example 8 was repeated using the catalyst from example 2. The results of the ammoxidation are shown in Table 2 below.

Example 12 - ammoxidation of propane Example 8 was repeated using the catalyst from example 4. The results of the ammoxidation are shown in Table 2 below.

Example 13 - ammoxidation of propane Example 8 was repeated using the catalyst from example 5. The results of the ammoxidation are shown in Table 2 below.

Example 14 - ammoxidation of propane Example 8 was repeated using the catalyst from example 6. The results of the ammoxidation are shown in Table 2 below.

Example 15 - ammoxidation of propane Example 8 was repeated using the catalyst from example 7. The results of the ammoxidation are shown in Table 2 below. Table 2 - Yield of acrylonitrile from various catalytic systems

temperature [0] ex. catalyst from 420 T450 485 500 11 ex. 2 (comp.) 1.2 2.6 4.4 4.8 12 ex. 4 (V, 3%) 5.4 1 8.6 11.9 11.4 13 ex. 5 (V, 5%) 2.5 10.3 15.4 15.3 14 ex. 6 (V, 5%) 1.1 2.6 11.7 12.1 15 ex. 7 (Cr,5%) 0 0 0.64 0.64 (yield defined as vol-* of original hydrocarbon feed) Comparative examples with vanadium antimonates Comparative example 1 (V:Sb = 1:1) A mixture 24.9 g of Sb203 and 150 ml of water was heated to 600C with stirring. A solution of 20 g of NH4VO3 in 200 ml water was added to the above and the mixture was left under reflux with stirring for 14 h. The resultant black solid was moved to a large beaker and heated with stirring until a paste remained. The solid was then dried overnight at 1200C and calcined in air at 3500C for 5 h and 5300C for 3 h, yielding a black solid. The catalyst was then screened to a particle diameter between 600 and 1000 pm.

Comparative example 2 (V:Sb = 1:2) Comparative example 1 was repeated with 50 g of Sb203 and 20 ml of the aqueous solution of NH4VO3. The catalyst was then screened to a particle diameter between 600 and 1000 Fm.

Comparative example 3 (V:Sb = 1:5) Comparative example 1 was repeated with 124.8 g of Sb2O3 and 20 ml of the aqueous solution of NH4VO3. The catalyst was then screened to a particle diameter between 600 and 1000 pm.

Comparative example 4 - ammoxidation of propane Example 8 was repeated using the catalyst from comparative example 1. The results of the ammoxidation are shown in Table 3 below.

Comparative example 5 - artimoxidation of propane Example 8 was repeated using the catalyst from comparative example 2. The results of the ammoxidation are shown in Table 3 below.

Comparative example 6 - ammoxidation of propane Example 8 was repeated using the catalyst from comparative example 3. The results of the ammoxidation are shown in Table 3 below.

Table 3 - Comparison of vanadium antimonate and iron antimonate catalysts on the basis of yield of ACN

catalyst from example Tem. comp. comp. comp. (comp.) exam. 3 exam. 4 ex. 1 ex. 2 ex. 3 ex. 2 [0] I VSbO VSbO VSbO FeSbO VFeSbO VFeSbO (1:1) (1:2) (1:5) (1:2) (3%V) (5%V) 450 8.8% 8.7% 6.5% 2.6% 8.6% 10.2% 485 5.9% 7.9% 106% 4.4% 11.9% 15.4% 500 5.1% 6.5% 128% 4.8% 11.4% 15.3% (yield defined as vol-% of original hydrocarbon feed)

Claims

1. A process for the ammoxidation of propane in the gas phase by contacting propane with oxygen, ammonia and, if desired, water under elevated temperature and pressure in the presence of a catalyst based on iron, antimony and oxygen, wherein the catalyst is represented by the formula EdFe.SbbOc where E is vanadium, chromium and/or niobium, a is 1, b is a real number from 1 to 8, c is a real number from 2.5 to 18, and dic is in the range from 0.01:1 to 1:1.

2. A process as claimed in claim 1, wherein E is vanadium.

3. A process as claimed in claim 2, wherein the molar ratio of vanadium to antimony is in the range of from 0.01:1 to 1:1.

4. A process as claimed in any of claims 1 to 3, wherein the catalyst is supported on an inorganic support material selected from silica, alumina, titania, zirconia, silica-zirconia, silica-titania, silica-alumina and magnesia.

5. A catalyst of the formula EdFe,sbbOc where E is vanadium, chromium and/or niobium, a is 1, b is a real number from 1 to 8, c is a real number from 2.5 to 18, and d/c is in the range from 0.01:1 to 1:1.

6. A catalyst as claimed in claim 5, obtainable by the following steps: (a) adding a Lewis base, containing E in the form of an oxidic salt or oxide, in the desired amount to a catalyst represented by the formula Fe,Sb,O, II where a is 1, b is a real number from 1 to 8, and c is a real number from 2.5 to 18, thereby obtaining a wet paste, (b) drying the wet paste and (c) calcining the dried wet paste.

7. A process for the preparation of a catalyst as claimed in claim 5 comprising (a) adding a Lewis base, containing E in the form of an oxidic salt or oxide, in the desired amount to a catalyst represented by the formula Fe,Sb,O, II where a is 1, b is a real number from 1 to 8, and c is a real number from 2.5 to 18, thereby obtaining a wet paste, (b) drying the wet paste and (c) calcining the dried wet paste.

8. The use of a catalyst I as claimed in claim 5 for the ammoxidation of propane.

9. A catalyst as claimed in claim 5 or 6 wherein b is a number from 2 to 5, c is a number from 4 to 12 and d/c is in the range from 0.05:1 to 0.8:1.

10. A catalyst for the ammoxidation of propane substantially as described in any of Examples 4 to 7.

11. A process for the ammoxidation of propane using a catalyst as claimed in claim 5, 6, 8 or 9 carried out substantially as hereinbefore described or illustrated in any of the foregoing Examples 12 to 15.

12. Acrylonitrile when obtained by a process as claimed in any of claims 1 to 4 or 11.

13. Hexamethylene diamine and nylon 6,6 when obtained from acrylonitrile claimed in claim 12.