CA2298227A1

CA2298227A1 - Catalyst for the dehydrogenation of ethylbenzene to styrene

Info

Publication number: CA2298227A1
Application number: CA002298227A
Authority: CA
Inventors: Michael Baier; Hermann Petersen; Herbert Wanjek; Christian Walsdorff
Original assignee: BASF SE
Current assignee: BASF SE
Priority date: 1999-02-10
Filing date: 2000-02-09
Publication date: 2000-08-10
Also published as: DE50012271D1; TWI234487B; KR20010014480A; EP1027928A1; JP2000296335A; EP1027928B1; CN1270851A; CN1118324C

Abstract

A catalyst containing iron oxide, for the preparation of which an iron oxide is used which has been obtained by spray-roasting an iron salt solution, a process for the preparation of the catalyst and also a process for the dehydrogenation of ethylbenzene to styrene in the presence of the catalyst.

Description

Catalyst for the dehydrogenation of ethylbenzene to styrene Description The invention relates to a catalyst containing iron oxide, to a process for the preparation thereof and to a process for the de-hydrogenation of ethylbenzene to styrene in the presence of said catalyst.
Far the preparation of styrene catalysts based on Fe203 and K20 natural and synthetic iron oxides such as a-Fe00H, a-Fez03, y-Fe203 and Fe304 are usually employed. The synthetic iron oxides are usually prepared by precipitation of iron salt solutions and thermal decomposition.
Besides conventional iron oxides, specific iron oxides or modi-fied iron oxides have also been described as the iron component for use in the preparation of dehydrogenation catalysts.
The iron-containing compound used for the manufacture of the de-hydrogenation catalysts described in EP-A 0,532,078 contains from 10 to 100 wt~ of a micaceous iron oxide having a preferred maxi-mum lamella size of less than 100 Nm.
US 5,023,225 describes the use of chromium-modified iron oxide for the preparation of dehydrogenation catalysts. The red iron oxide is prepared by mixing yellow iron hydrate with chromium ox-ide or a chromium salt and heating the mixture.
WO 96/18593 describes an iron-containing dehydrogenation cata-lyst, whose iron component exhibits a bimodal pore-size distribu-tion in the catalyst. Preferably magnetic iron oxid compounds, such as magnetite, are used.
A pretreated (predoped) iron oxide is used in WO 96/18458. Pre-treatment is carried out using a predoping substance containing an element selected from the group comprising Be, Mg, Ca, Sr, Ba, Sc, Ti, Zr, Hf, V, Ta, Mo, W, Mn, Tc, Re, Ru, Os, Co, Rh, Ir, Ni, Pd, Pt, Cu, Ag, Au, Zn, Cd, Hg, Al, Ga, In, T1, Ge, Sn, Pb, Bi, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb and Lu, and heating the iron oxide mixture to at least 600°C. Forming of the catalyst is then carried out.
WO 96/18594 describes an iron oxide catalyst containing iron ox-ide particles having an average longest dimension in the range of from 2 to 10 ~.m. The mean pore diameters are between 0.22 and 0.30 N,m, the pore volume being between 0.16 and 0.22 cm3/g. Prepa-ration was carried out using an iron oxide a-Fe00H prepared from iron filings by dehydration of a yellow a-Fe(OOH) intermediate (Penniman iron oxide).
WO 96/18457 describes a process for the preparation of iron oxide catalysts, in which the iron oxide is restructured, prior to mix-ing with one or more promoters, to form iron oxide particles hav-ing a surface area (BET) of less than 1.9 m2/g, a particle length of from 0.3 to 3 ~m and a particle width of from 0.2 to 2 ~,m. The restructuring agents used are compounds of the elements Mo, Cu, Ca, Zn, Mn, Sn, Ti, Bi, Co, Ce, W, Cr, Mg and V.
The said catalysts require, as starting materials, iron oxides demanding elaborate preparation or modification.
It is thus an object of the present invention to overcome the said drawbacks and to find a catalyst for the dehydrogenation of ethylbenzene to styrene that is cheap and simple to synthesize.
In particular, the catalyst should exhibit a high pore volume whilst at the same time showing high activity, high selectivity and high mechanical stability.
Accordingly, we have found a catalyst containing iron oxide, for the preparation of which an iron oxide is used which has been ob-tained by spray-roasting an iron salt solution.
Preferably the iron oxide used is obtained by spray-roasting a hydrochloric solution containing iron chloride by the Ruthner process, as described, for example, in EP-A 0,850.881.
The iron oxides obtained by spray-roasting hydrochloric acid solutions containing iron chloride usually have a residual con-tent of chlorine. This should be below 3000 ppm, preferably below 2000 ppm and more preferably below 1500 ppm.
For the preparation of the catalysts of the invention an iron ox-ide prepared by spray-roasting is suitable which has a stamped density ranging from 0.6 to 1, preferably from 0.6 to 0.8 g/cm3 and a specific surface area in the range of from 1 to 10, prefer-ably from 2 to 7 and more preferably from 3 to 5 m2/g.
The pore volume of the catalysts of the invention is at least 0.2 cm3/g and is preferably in the range of from 0.25 to 0.5 cm3/g. The mean pore diameter (median value) is at least 0.3 N.m and is preferably in the range of from 0.4 to 0.8 dun.

The catalysts of the invention usually contain, in addition to iron oxide, at least one potassium compound. The potassium com-pound used is preferably potassium carbonate, potassium hydroxide or potassium oxalate. Preferably, the catalyst contains from 5 to 40 wt~ of potassium, calculated as KZO.
Furthermore, the catalyst can contain, in conventional concentra-tions, one or more conventional promoters to increase selectiv-ity, activity or stability. Suitable promoters are compounds of elements selected from the group comprising Be, Mg, Ca, Sr, Ba, Sc, Ti, Zr, Hf, V, Ta, Mo, W, Mn, Tc, Re, Ru, Os, Co, Rh, Ir, Ni, Pd, Pt, Cu, Ag, Au, Zn, Cd, Hg, A1, Ga, In, T1, Na, Cs, La, Li, Ge, Sn, Pb, Bi, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb and Lu, which can be used singly or intermixed. Preferred pro-moters are compounds selected from the group comprising Mg, Ca, Ce, V, Cr, Mo, W, Ti, Mn, Co and Al. Particularly preferred pro-moters are Mg, Ca, Ce, V, Cr, Mo and W. The catalysts can contain one, preferably two and more preferably three or more promoters of the group Mg, Ca, Ce, V, Cr, Mo, W. The promoters are prefer-ably added in amounts of from 0 to 15 wt~, in particular from 1 to 10 wt~, calculated as the most stable oxides.
The iron oxides used in the present invention may, if desired, contain some or all of the potassium compound or said promoters.
To this end a portion of the potassium compound and/or a portion of the promoters can for example be added to the iron salt solu-tion used for spray-roasting:
The catalysts of the invention can be obtained by the known single-stage or multi-stage manufacturing processes, as de-scribed, for example, in EP-A 0,195,252 or EP-A 0,866,731. To this end the iron oxide produced by spray-roasting of an iron salt solution can be used alone or in addition to the convention-al natural or synthetic iron oxides, such as a-Fe00H, y-Fe00H, a-Fe203, y-Fe203 or Fe304. The content of iron oxide produced by spray-roasting an iron salt solution is from 10 to 100 mold, pre-ferably from 50 to 100 mold, based on all iron compounds used.
The finely powdered catalyst components can be mixed dry or sus-pended in water and spray-dried. The dry powders are then pel-leted to mechanically stable shaped articles or converted to a pasty composition by the addition of water and extruded, the ex-trudates then being chopped to specific lengths. For this purpose shaping aids, such as stearates, Walocel, graphite or starch, may be used. Preferably the catalyst composition is processed to form solid or hollow extrudates having a diameter of from 2.5 to 6 mm and a length of from 5 to 50 mm. Particular preference is given to extrudates having a star-shaped cross-section, as depicted in Figure l, and 3 mm solid extrudates.
The extrudates are then dried continuously or batchwise at tem-peratures usually in the range of from 80° to 140°C. The dried shaped articles can then be tempered and/or calcined in one or more stages at temperatures in the range of from 200° to 1000°C.
The catalysts of the invention are suitable for the non-oxidative dehydrogenation of hydrocarbons, in particular for the dehydro-genation of ethylbenzene to styrene. To this end, generally a mixture of steam and ethylbenzene in a molar ratio of from 2 to 20, preferably from 5 to 15, is passed over the catalyst at a temperature in the range of from 500° to 700°C. In the adiabatic process the temperature at the reactor inlet is usually from 600°
to 650°C and then drops to from 530° to 570°C on account of the endothermy of the reaction. The reaction is preferably carried out at atmospheric pressure or below.
The catalysts of the invention exhibit a large pore volume. As a result, the weight per liter of the catalyst is reduced to less than 1.3 kg/L, as measured on 3 mm solid catalyst extrudates, without there being any reduction in the activity or selectivity.
At the same time the knife-edge hardness of more than 20 N suf-fices for industrial applications.
Examples Example 1 900 g of iron oxide Hoogovens RIO-200 (sold by Hoogovens Staal BV) were added to a suspension of 168 g of K2C03, 200 g of Ce2(C03)3, 46 g of CaC03, 29 g Mo03 and 61 g of alkaline magnesium carbonate (4-MgC03xMg(OH)3~4H20) in 4.3 L of water with stirring.
The spray mash was then spray-dried at a solids content of 25 wt~. The spray powder obtained containing ca 340 mL of water was processed over a period of 30 minutes so as to form a pasty composition and was then shaped in an extruder to cylindrical solid extrudates having a diameter of 3 mm, which were chopped into lengths of ca 10 mm. The catalyst extrudates were then dried in a forced air oven over a period of 1 hour at 120°C and calcined in a calcinating furnace first of all over a period of 2 hours at 300°C and then over a period of 1 hour at 875°C.
Comparative Examples C1 to C3 Example 1 was repeated except that the iron oxide was replaced by the following synthetic iron oxides used in the same quantities:
CI: precipitated a-Fe203: Bayferrox 1360 C2: synthetic y-Fez03: Bayferrox E AB 21 and C3: precipitated a-Fe203: Bayferrox 720 N respectively.
The readings taken on the catalyst extrudates are listed in Table 1.
Example 2 900 g of iron oxide Hoogovens Rio-250 (sold by Hoogovens Staal BV) were added, with stirring, to a suspension of 168 g of pot-ash, 249 g of Ce(C03)3, 34 g of hydrated white lime, 35 g of ammo-nium heptamolybdate and 26 g of magnesite in 4.3 L of water. The resulting spray powder was worked over a period of approximately 30 min with ca. 500 mL of water to form a pasty composition, which was then extruded to produce solid cylinders having a di-mater of 3 mm, these being cut up into lengths of ca. 1 mm. These catalyst extrudates were then dried for 1 h at a temperature of 120~C and calcined in a calcining furnace at 300~C for 2 hours and then at 875~C for one hour.
Comparative Example C4 Example 2 was repeated except that iron oxide Bayferrox 1360 was used instead of Rio-250.
The catalysts E1 and Cl to C3 were tested using catalyst grit. To this end grit fractions having particle diameters of from 0.5 to 0.7 mm were installed in tubular reactors heated isothermally by fused salt and were tested under standard pressure operating with an LHSV of 1.46/h and a D/EB of 1.25 kg/kg. The relevant perfor-mance data are listed in Table 2.
The catalysts E2 and C4 were also tested using solid extrudates.
In such solid-cyclinder tests, 250 mL of the respective catalyst were placed in an isothermal tubular reactor having an internal diameter of 30 mm. The catalysts were tested under a pressure of 0.4 bar operating with an LHSV of 0.45/h and a D/EB of 1.25 kg/kg and also a D/EB of 1.45 kg/kg. Following a period of 10 days, the catalysts had reached a steady state as regards conversion rate and selectivity, and the composition of the liquid and gaseous effluent was balanced.

The stamped density (weight per liter) was measured with a stamp-ing volumeter JEL sold by Engelsmann (Ludwigshafen). The stamped density was measured after the extrudates had been stamped 750 times. The bulk density is the density of the extrudates be-fore stamping. The pore volumes were determined as described in DIN Standard 66133.
The contact angle of the mercury used for determination of the average pore diameter was 140° (DIN 66133).

Determination of the knife-edge hardness was carried out using a knife edge of 0.3 mm applied to the extrudate under increasing load until scission occurred (instrument sold by Zwick, Ulm). The mean of 25 readings was taken.
Table 1: Properties of the catalysts Catalyst E1 C1 C2 C3 bulk density kg/L 0.870 1.126 0.994 0.900 compacted density kg/L 0.978 1.26 1.107 1.008 surface area (BET) m2/g 3.4 2.6 6.8 6.9 pore volume g/cm3 0.38 0.23 0.30 0.35 average pore diame- ~.un 0.65 0.38 0.20 0.30 25ter (median value) Ce02 crystallite sizenm 24 24 23 25 knife-edge hardness N 27 75 30 34 Table 2:
Temp. E1 Cl C2 C3 Catalyst 27.9 29.1 25.3 24.7 conversion [$]

selectivity (~] 97.7 97.7 97.4 97.7 styrene content 26.9 28.1 24.3 23.8 [wt~]

580C conversion [~] 40.7 40.1 37.2 35.6 selectivity [~] 97.1 97.3 97.0 97.3 styrene content 39.1 38.7 35.7 34.3 [mold]

600C conversion [~] 54.5 50.8 48.1 50.3 selectivity [~] 96.2 96.4 96.5 96.4 styrene content 52.1 49 46.0 48.1 [molg]

630C conversion [~] 71.5 68.7 66.7 67.5 selectivity [~] 94.0 95.4 94.8 94.6 styrene content 67.4 65.6 63.3 63.8 [molg]

The properties and performance data of catalysts E2 and C4 are listed in Table 3.

Table 3: Properties and performance of catalysts E2 and C4 Knife-edge hardness 44N 57N

stamped 1.142 kg/L 1.304 kg/L
density Surface (BET) 2.9 m2/g 2.5 m2g area Pore volume 0.28 mL/g 0.22mL/g Mean poredia meter 0 . 4 8 E,im 0 Nm .

Performance extrudates on solid H20/EB=1.45 0.4 kg/kg; bar:

C (600C) /S (600C) 80.4 ~ / 94.8 ~ 79.7 ~ / 94.7 C (575C) /S (575C) 69.8 ~ / 96.4 ~ 65.8 ~ / 96.8 C (550C) /S (550C) 50.8 $ / 97.7 ~ 44.5 ~ / 97.9 HZO/EB=1.45 0.4 kg/kg; bar:

C (575C) /S (575C) 80.4 ~ / 94.8 $ 65.1 ~ / 96.6 C (590C) /S (590C) 75.5 ~ / 95.2 ~ 73.3 0 / 95.7 C (600C) /S (600C) 79.4 $ / 94.6 ~ 78.6 ~ / 95.0 Performance grit on H20 /EB=1.25 kg/kg; 1 bar:

C (560C) /S (560C) 31.2 $ / 97.4 ~ 26.6 ~ / 97.7 C (580C) /S (580C) 44.6 ~ / 96.7 ~ 38.0 ~ / 97.3 C (600C) /S (600C) 57.9 ~ / 95.9 ~ 50.1 ~ / 96.7 C (610C) /S (610C) 65.2 ~ / 95.5 ~ 54.2 $ / 96.4 C (630C) /S (630C) 74.3 ~ / 93.5 $ 65.9 $ / 95.3 C = conversion rate S = selectivity

Claims

1. A catalyst containing iron oxide, wherein an iron oxide which has been obtained by spray-roasting an iron salt solution is used for the preparation of the catalyst.

2. A catalyst as defined in claim 1, wherein the iron oxide used has been produced by spray-roasting a hydrochloric solution containing iron chloride by the Ruthner process.

3. A catalyst as defined in claim 1 or claim 2, wherein the iron oxide used has a stamped density in the range of from 0.6 to 1 g/cm3 and a specific surface area in the range of from 1 to m2/g.

4. A catalyst as defined in any of claims 1 to 3, wherein the pore volume of the catalyst is at least 0.2 cm3/g.

5. A catalyst as defined in any of claims 1 to 4, wherein the mean pore diameter (median value) of the catalyst is at least 0.3 µm.

6. A catalyst as defined in any of claims 1 to 5, additionally containing at least one potassium compound.

7. A catalyst as defined in any of claims 1 to 6, additionally containing at least one promoter selected from compounds of the group Mg, Ca, Ce, V, Cr, Mo, W.

8. A catalyst as defined in claim 6 or claim 7, wherein at least a portion of the potassium compound or a portion of the promoters has been added to the iron salt solution prior to spray-roasting.

9. A process for the preparation of a catalyst as defined in any of claims 1 to 8, wherein use is made of an iron oxide produced by spray-roasting an aqueous iron solution.

10. A process for the dehydrogenation of ethylbenzene to styrene, wherein dehydrogenation is carried out in the presence of a catalyst as defined in any of claims 1 to 8.