PROCESS FOR PRODUCING AN SI-BONDED FLUIDIZED-BED CATALYST

Abstract

The invention relates to a process for producing a particulate, Si-bonded fluidized-bed catalyst having improved abrasion resistance, which comprises the steps I. provision of an aqueous suspension comprising zeolite particles, II. addition of a silicone resin mixture comprising one or more hydrolyzable silicone resin precondensates and mixing of the aqueous suspension and the silicone resin mixture, III. spray drying of the mixture obtained from step II, with the mixture being homogenized before spray drying, and IV. calcination of the spray-dried fluidized-bed catalyst obtained from step III,
and an Si-bonded fluidized-bed catalyst which can be produced by this process and also its use for the nonoxidative dehydroaromatization of C.sub.1-C.sub.4-aliphatics.

Claims

1. (canceled)

2. A particulate fluidized-bed catalyst, obtained by a process comprising: (I) forming an aqueous suspension comprising zeolite particles; (II) adding a silicone resin mixture comprising a hydrolyzable silicone resin precondensate to the aqueous suspension and mixing the aqueous suspension and the silicone resin mixture, to obtain an intermediate mixture; (III) homogenizing the intermediate mixture and then spray draying the intermediate mixture, to obtain a spray-dried fluidized-bed catalyst; and (IV) calcinating the spray-dried fluidized-bed catalyst, to obtain a calcinated fluidized-bed catalyst.

3. The particulate fluidized-bed catalyst according to claim 2, comprising, based on a total weight of the fluidized-bed catalyst: from 5 to 40% by weight of silicon dioxide; and from 60 to 95% by weight of zeolite.

4. The particulate fluidized-bed catalyst according to claim 2, comprising a zeolite having at least one structure selected from the group consisting of a pentasil structure and a MWW structure.

5. The particulate fluidized-bed catalyst according to claim 2, comprising: from 0.1 to 20% by weight of an active metal selected from the group consisting of Mo, W, Re, Ir, Ru, Rh, Pt, Pd and mixtures thereof, based on the total weight of the particulate fluidized-bed catalyst.

6. The particulate fluidized-bed catalyst according to claim 5, further comprising: at least one metal selected from the group consisting of W, Cu, Ni, Fe, Co, Mn, Cr, Nb, Ta, Zr, V, Zn and Ga.

7. A process for dehydroaromatizing a C.sub.1-C.sub.4-aliphatic, the process comprising: reacting a feedstream comprising a C.sub.1-C.sub.4-aliphatic and less than 5% by weight of oxidants, based on a total weight of the feedstream, in the presence of a fluidized-bed catalyst according to claim 5.

8. A process for dehydroaromatizing a C.sub.1-C.sub.4-alipahtic, the process comprising: reacting a feedstream E comprising a C.sub.1-C.sub.4-alipahtic in the presence of a fluidized-bed catalyst according to claim 6.

9. The particulate fluidized-bed catalyst according to claim 3, wherein the zeolite has at least one structure selected from the group consisting of a pentasil structure and a MWW structure.

10. The particulate fluidized-bed catalyst according to claim 2, wherein at least one further Si-comprising binder selected from the group consisting of silica, silica suspensions and silica sols is further added to the aqueous suspension during the adding (II).

11. The particulate fluidized-bed catalyst according to claim 10, wherein the zeolite particles are H-ZSM-5.

Description

EXAMPLES

[0112] A Production of the Particulate Fluidized-Bed Catalyst

[0113] A1. Ammonium Exchange

[0114] A commercially available H-ZSM-5 zeolite from Zeochem was used as zeolite. Since the zeolite was already present in the H form, only one ammonium exchange was carried out.

[0115] 19 kg of the H-ZSM-5 zeolite were added to a solution of 19 kg of ammonium nitrate in 170 l of water and stirred at 80 C. for 2 hours. After cooling, the suspension was filtered in a filter press and washed with water. The filtercake was subsequently dried overnight at 120 C.

[0116] A2. Milling of the Zeolite

[0117] The zeolite from A1 was milled by wet milling in a stirred mill (Bhler DCP SF 12) as 50% strength suspension of zeolite in water until the D.sub.90 was <3 m.

[0118] A3. Addition of the Binder and Mixing

[0119] One part of the aqueous zeolite suspension from A2 was in each case stirred and the appropriate amount of the respective binder was slowly added. The respective proportions by weight of zeolite and silica in the individual catalysts are shown in the tables, based on the total weight of zeolite and SiO.sub.2 after calcination of the spray-dried catalyst particles. The mixture was mixed for 1 hour.

[0120] A4. Spray Drying

[0121] Spray drying was carried out using the suspension from A3 in a commercial atomization dryer from Niro using nitrogen as atomizer gas. Two different nozzles, one a two-fluid nozzle and a pressure nozzle, were used. The temperature during drying was in the range from 100 to 280 C.

[0122] A5. Calcination

[0123] The spray-dried catalyst particles from A4 were subsequently after-dried overnight at 120 C. and subsequently calcined at 500 C., unless indicated otherwise, for 4 hours in an air atmosphere.

[0124] A6. Application of Mo

[0125] 1 kg of the particulate catalyst from AS was impregnated with an aqueous solution of ammonium heptamolybdate (>99%, Aldrich) so that the amount of molybdenum on the catalyst particles was 6% by weight, based on the total weight of the catalyst, with the amount of water necessary for pore impregnation of the catalyst particles being used. The catalyst was mixed for 1 hour.

[0126] A7. Drying and Calcination

[0127] The catalyst from A6 was subsequently dried overnight at 120 C. and calcined at 500 C. for 4 hours in an air atmosphere. In the case of the catalysts of examples 1 to 10, steps A1 to A5 were carried out, and in the case of the catalysts of examples 11 and 12, steps A1 to A7 were carried out.

Example 1

According to the Invention

[0128] A methylmethoxysiloxane marketed under the trade name Silres MSE 100 by Wacker Silikon was used as silicone resin precondensate for the binder. Silres MSE 100 comprises from 60 to 100% by weight of polymethoxymethylsiloxane/methylsilsesqisiloxane, from 1 to 5% by weight of toluene and varying amounts of methanol. Spray drying was carried out using a two-fluid nozzle.

Examples 2 and 3

Not According to the Invention

[0129] Colloidal silica I, a 40% strength suspension in water (Ludox AS 40, Aldrich), is used as binder. Spray drying was carried out using a two-fluid nozzle.

Example 4

Not According to the Invention

[0130] Colloidal silica II, a dispersion of amorphous, colloidal silica particles in water, is used as binder. The concentration of SiO.sub.2 is 30% by weight (Nalco DVSZN006, Nalco Company). Spray drying was carried out using a two-fluid nozzle.

Example 5

Not According to the Invention

[0131] The aqueous silica suspension I (AERODISP WS1836, Evonik) having an SiO.sub.2 content of 34% by weight and an average aggregate size of 0.3 m was used as binder. Spray drying was carried out using a two-fluid nozzle.

Example 6

Not According to the Invention

[0132] The silica suspension II, an aqueous suspension of pyrogenic silica marketed under the trade name AEROSIL 200 (Evonik), was used as binder. Spray drying was carried out using a two-fluid nozzle.

Example 7

According to the Invention

[0133] The silicone resin precondensate from example 1 was used as binder. Spray drying was carried out using a pressure nozzle.

Example 8

According to the Invention

[0134] The silicone resin precondensate from example 1 was used as binder. Spray drying was carried out using a pressure nozzle.

Example 9

Not According to the Invention

[0135] The silicone resin precondensate from example 1 was used as binder. A pressure nozzle was used for spray drying. In contrast to example 8, the mixture of aqueous zeolite suspension and silicone resin precondensate was allowed to stand after mixing and not homogenized before spray drying. The organic phase was separated off before spray drying.

Example 10

According to the Invention

[0136] The procedure of example 8 was used for producing the catalyst particles, but spray drying and after-drying were followed by calcination overnight at 800 C. instead of 500 C. as in example 8.

Example 11

Not According to the Invention

[0137] Mo was applied as per A6 and A7 to the catalyst particles from example 4.

Example 12

According to the Invention

[0138] Mo was applied as per A6 and A7 to the catalyst particles from example 1.

Example 13

According to the Invention

[0139] The procedure of example 1 was repeated with the amount of methylmethoxysiloxane being selected so that the amount of zeolite in the finished catalyst was 71% by weight.

Example 14

According to the Invention

[0140] A mixture of the silicone resin precondensate from example 1 (polymethoxysiloxane) and the colloidal silica II from example 4 was used as binder. The two components were mixed at 60 C. before addition to the zeolite. 1000 g of binder (amount of solids in the binder) having a weight ratio of polymethoxysiloxane:colloidal silica II of 0.25:1 (corresponds to 20% by weight of polymethoxysiloxane to 80% by weight of colloidal silica II) were used per 2500 g of zeolite. The temperature at the inlet of the spray dryer was 280 C.

Example 15

According to the Invention

[0141] The procedure of example 13 was repeated using a weight ratio of polymethoxysiloxane to colloidal silica II of 1:1 (corresponds to 50% by weight of polymethoxysiloxane to 50% by weight of colloidal silica II).

Example 16

According to the Invention

[0142] The procedure of example 14 was repeated with the calcination being carried out at 800 C.

Example 17

According to the Invention

[0143] The procedure of example 13 was repeated using a weight ratio of polymethoxysiloxane to colloidal silica II of 2.3:1 (corresponds to 70% by weight of polymethoxysiloxane to 30% by weight of colloidal silica II).

Example 18

According to the Invention

[0144] The procedure of example 13 was repeated using a weight ratio of polymethoxysiloxane to colloidal silica II of 4:1 (corresponds to 80% by weight of polymethoxysiloxane to 20% by weight of colloidal silica II).

Example 19

According to the Invention

[0145] The procedure of example 17 was repeated with the calcination being carried out at 800 C.

Example 20

According to the Invention

[0146] The procedure of example 17 was repeated with the temperature at the inlet of the spray dryer being 155 C.

Example 21

According to the Invention

[0147] The procedure of example 13 was repeated using a weight ratio of polymethoxysiloxane to colloidal silica II of 9:1 (corresponds to 90% by weight of polymethoxysiloxane to 10% by weight of colloidal silica II).

Example 22

According to the Invention)

[0148] 6% by weight of Mo was applied to the catalyst from example 18 in accordance with procedures A6 and A7, with the impregnation with the ammonium heptamolybdate and drying at 120 C. being followed by a second impregnation with nickel nitrate (<99%, Aldrich) so that the amount of Ni on the catalyst particles was 0.5% by weight, based on the total weight of the catalyst. The catalyst was then again dried at 120 C. and subsequently calcined at 500 C. for 5 hours.

[0149] B Determination of the Degrees of Abrasion

[0150] The measurement of the degrees of abrasion was carried out in a jet abrasion apparatus using a method analogous to ASTM D5757.

[0151] The abrasion test simulates the mechanical stresses to which fluidized material (e.g. a catalyst) is subjected in a gas/solid fluidized bed and gives a degree of abrasion and a proportion of fines which describe the strength behavior. The abrasion apparatus comprises a nozzle plate (holes diameter=0.5 mm) which is connected in a gastight and solids-tight manner to a glass tube. Above the glass tube, a steel tube having a conical widening is attached, likewise in a gastight and solids-tight manner. The apparatus is connected to the 4 bar compressed air network. A reducing valve decreases the pressure to 2 bar absolute upstream of the apparatus. 60.0 g of catalyst are introduced into the apparatus. The flow rate of compressed air for carrying out the experiment is 350 l/h. The apparatus itself is operated under atmospheric conditions (1 bar, 20 C.). The particles are abraded or broken up by particle/particle and particle/wall impacts as a result of the high gas velocity at the nozzle. The discharged solid goes via a pipe dent into a filter paper thimble (pore opening 10-15 m). The collected solid (particles<20 m) is weighed after one hour (defined as proportion of fines) and after 5 hours (defined as abrasion). The degree of abrasion is defined as the solid discharged per hour between the first and sixth hours, based on the mass of solid weighed in. [Degree of abrasion [g/kg h]=discharge in 5 h after 1 h prestressing/(5*mass weighed in)].

[0152] The degrees of abrasion shown below were determined before application of the Mo.

[0153] The results of the measurement of the degrees of abrasion for the catalysts from examples 1 to 6 are summarized in table 1. It can clearly be seen that the catalyst particles of example 1 produced according to the invention using the silicone resin precondensate as binder display the best abrasion resistance.

TABLE-US-00001 TABLE 1 Zeolite Degree of (% by abrasion Example Binder weight) (g/kgh) 1 Polymethoxysiloxane 78 13 (according to the invention) 2 Colloidal silica I 71 68 (not according to the invention) 3 Colloidal silica I 62 42 (not according to the invention) 4 Colloidal silica II 71 29 (not according to the invention) 5 Silica suspension I 71 too high, (not according to the invention) outside the measurement range 6 Silica suspension II 71 31 (not according to the invention)

[0154] The influence of the binder concentration is shown by examples 7 and 8 in table 2: a smaller amount of binder gives a better degree of abrasion. Furthermore, table 2 gives the results of the abrasion test for example 9 in which only the aqueous phase was fed to spray drying after the organic phase had been separated off. This example shows that omission of the homogenization of the mixture obtained in step III before spray drying leads to catalyst particles having significantly poorer degrees of abrasion.

TABLE-US-00002 TABLE 2 Zeolite Degree of (% by abrasion Example Binder weight) (g/kgn) 7 Polymethoxysiloxane 83 10 (according to the invention) 8 Polymethoxysiloxane 78 21 (according to the invention) 9 Polymethoxysiloxane, with 78 56 removal of the organic phase (not according to the invention)

[0155] Table 3 reports the results of the measurement of the degrees of abrasion for the catalysts from examples 8 and 10 and also for the catalysts from examples 13 to 20. A higher calcination temperature leads to catalysts having improved degrees of abrasion.

TABLE-US-00003 TABLE 3 % by Calci- Degree of weight of nation abrasion Example Binder zeolite ( C.) (g/kgh) 8 Polymethoxysiloxane 78 500 21 (according to the invention) 10 Polymethoxysiloxane 78 800 6 (according to the invention) 13 Polymethoxysiloxane 71 500 27 (according to the invention) 14 Polymethoxysiloxane: 500 12 colloidal silica II (according to the invention) 0.25:1 15 Polymethoxysiloxane: 500 19 colloidal silica II (according to the invention) 1:1 16 Polymethoxysiloxane: 800 18 colloidal silica II (according to the invention) 1:1 17 Polymethoxysiloxane: 500 15 colloidal silica II (according to the invention) 2.3:1 18 Polymethoxysiloxane: 71 500 7 colloidal silica II (according to the invention) 4:1 19 Polymethoxysiloxane: 71 800 5 colloidal silica II (according to the invention) 4:1 20 Polymethoxysiloxane: 71 500 6 colloidal silica II (according to the invention) 4:1 21 Polymethoxysiloxane: 500 23 colloidal silica II (according to the invention) 9:1

[0156] The use according to the invention of a silicone resin precondensate leads, particularly when colloidal silica conventionally known as binder is simultaneously used, to significantly improved degrees of abrasion of the finished shaped catalyst body. This can be seen, in particular, when examples 13 to 20 are compared with example 4. Particularly good results are obtained using a mixture of silicone resin precondensate and colloidal silica in a weight ratio of 4:1.

[0157] C N.sub.2 Absorption Measurement

[0158] The nitrogen absorption isotherms were determined for the catalysts from examples 1 (according to the invention) and 4 (not according to the invention). The measurements were carried out using the Quantachrom Autosorb 6b: nitrogen sorption at 196 C., outgassing temp.=200 C., outgassing time=14 h, determination of the micropore volume by the DR method.

[0159] The measured values are shown in table 4. The catalyst from example 1 shows a nitrogen absorption isotherm corresponding to class I (classification in accordance with IUPAC), while the catalyst from example 4 shows a nitrogen absorption isotherm corresponding to class IV. This indicates that the catalyst from example 4 has more micropores having a pore size in the nanometer range (pore diameter<2 nm) than the catalyst according to the invention from example 1 which has more pores in the mesopore and macropore range (pore diameter>2 nm).

TABLE-US-00004 TABLE 4 Mesopore and Total pore Micropore macropore BET volume volume volume (m.sup.2/g) (cm.sup.3/g) (cm.sup.3/g) (cm.sup.3/g) Example 1 285 0.29 0.12 0.17 Example 4 324 0.28 0.15 0.13

[0160] D Nonoxidative Dehydroaromatization of Methane

[0161] The experiments were carried out using 100 g of the respective catalyst in a fluidized-bed reactor. Before the reaction, the catalysts were carburized by passing a stream of methane through the reactor at a flow rate of 100 standard l/h until the reaction temperature had been reached. The flow rate was calculated for STP. The reaction began immediately thereafter at 700 C. and 2.5 bar and was carried out using a mixture of CH.sub.4/He (90:10) at a flow of 20 standard l/h. The catalysts were regenerated at regular intervals by passing hydrogen through the reactor at 4 bar and 750 C. for 5 hours. A reaction cycle took 10 hours.

[0162] The results for the catalyst according to the invention from example 1 and the noninventive catalyst from example 4 are summarized in table 5. X.sub.CH4 is the proportion of methane reacted based on the total amount of methane used in %; S.sub.C6H6 is the proportion of benzene based on the amount of methane reacted, in %. The reported Mo concentration is based on the total weight of the catalyst including Mo.

TABLE-US-00005 TABLE 5 8th and 10th % by 3rd reaction cycle, 6th reaction cycle, reaction cycle, Catalyst from weight measured at 6 h measured at 6 h measured at 6 h Example example of Mo X.sub.CH4 (%) S.sub.C6H6 (%) X.sub.CH4 (%) S.sub.C6H6 (%) X.sub.CH4 (%) S.sub.C6H6 (%) 11 4 (not 5.9 8.9 59 8.6 52 according to the invention) 12 1 (according to 6.0 8.4 65 8.4 70 7.9 69 the invention) (10th) (10th) 21 21 (according to 6.0 + 10.8 67 9.0 75 8.9 75 the invention) 0.5 (8th) (8th) % by weight of Ni

[0163] The measurement for the noninventive catalyst (example 11) was stopped after the 6th cycle since selectivities of only 50% are not of interest for industrial use. It can clearly be seen that the catalysts comprising, according to the invention, silicone resin precondensates as binder display a better selectivity to benzene at comparable methane conversions.