GB2108860A - Catalyst structure - Google Patents

Abstract

A catalyst structure comprises a shape-retaining metal core of a desired shape, a particle holding layer attached to the core and made of a glass fibre product and catalyst particles held in the layer. Preferably two layers of glass fibre product are provided comprising a particle holding layer made from a glass fibre product having a relatively large number of filament-to-filament interstices and a particle release-preventing layer attached to the particle holding layer and made of a glass fibre product having a relatively small number of filament-to-filament interstices.

Description

SPECIFICATION Catalyst structure The present invention relates to novel catalyst structures prepared with use of glass fiber products.

Granular catalysts 5 to 10 mm in size have been generally used for vapor-phase catalytic reaction systems. Such catalysts have been found empirically favourable in view of the pressure loss of the reactant gas involved in the catalyst layer and the possible clogging of the catalyst layer due to various causes and further from the viewpoint of economy. On the other hand, however, such granular catalysts do not permit gaseous reactants to diffuse into the catalyst effectively, that is, fail to permit a high rate of mass transfer. A great difference therefore occurs in the reactant concentrations within the grains or pellets, with the result that the-catalyst is low in the effectiveness factor defined by Thiele et al. Thus there is the likelihood that almost all the charge of catalyst is unable to function substantially effectively.

The low catalyst effectiveness factor poses a serious problem with expensive noble metal catalysts and is very unfavorable economically even in the case of relatively inexpensive catalysts of metallic oxides in respect of the pressure loss of reactant gases, the size of the reactor, the selectivity of reaction, etc.

Generally catalysts for use in industries must fulfill the following requirements: 1 ) High activity per unit weight of the catalyst.

2) High activity per unit volume of the reactor.

3) Small pressure loss of the reactant gases in the catalyst layer.

4) High overall strength enabling the catalyst to fully withstand the impact of charging.

5) High surface strength against the external forces to be exerted on the catalyst during use.

6) Reduced variations in activity despite the lapse of time.

7) Low cost.

The true activity of a catalyst, free from mass transfer resistance, per unit weight thereof is dependent on the composition of the catalyst, the structure of the crystals thereof, etc. and is inherent in the catalyst, but the actual activity varies with the grain size, the pore structure of the grain, the flow rate, i.e. linear velocity, of the reactant gas, etc. Generally the activity increases with decreasing grain size, increasing pore size, increasing pore volume and increasing flow rate of the reactant gas.

Nevertheless, these factors contributing to the increase in activity are entirely in conflict with the requirements in respect of the reactant gas pressure loss and catalyst strength. Accordingly it is extremely difficult to fulfill all the foregoing requirements 1) to 7).

In order to satisfy the above requirements 1) to 7), several catalysts of the honeycomb type have been developed in recent years. These catalysts include those prepared by forming a paste from a catalytic component and a binder, extruding the paste into a honeycomb body and baking the body under suitable conditions, and those prepared by making a honeycomb structure from ceramics having no catalytic activity and depositing a catalytic component on the surface of the structure with a binder.

With the former catalysts, there is the need to form a honeycomb body with a large wall thickness and to obtain a compacted baked body which is less amenable to the diffusion of reactant gases into the catalyst, in order to give the desired strength to the catalyst. It is therefore impossible to afford an improved catalyst effectiveness factor. Thus difficulties are encountered in improving both strength and activity at the same time. With the latter case, the tough ceramics honeycomb structure has ideal overall strength fulfilling the requirement 4), but the use of the binder reduces the inherent activity of the catalyst. Further the layer of deposited catalytic component, which is made very thin to assure high surface strength 5) and high activity per unit weight 1), reduces the activity per unit volume of the reactor 2) and impairs the stability of reaction.

SUMMARY OF THE INVENTION The main object of the present invention, which has been accomplished in view of the foregoing problems, is to provide novel catalyst structures which fulfill all the foregoing requirements 1) to 7) for industrial catalysts.

To fulfill this object, the present invention provides a catalyst structure comprising a shape retaining metal core of the desired shape, a particle holding layer attached to the core and made of a glass fiber product, and catalyst particles held in the layer. The glass fiber product forming the particle holding layer has a relatively large number of filament-to-filament interstices. The particle holding layer is externally covered with a layer for preventing release of the catalyst particles which is made of a glass fiber product having a relatively small number of filament-to-filament interstices.

Embodiments of the invention will now be described by way of example only and with reference to the accompanying drawings in which:~ Figs. 1 and 2 are sectional views showing sandwich-type catalyst structures; Figs. 3 and 4 are front views partly in section and showing columnar catalyst structures; Fig. 5 is a graph showing the relation between the concentration of slurry and the amount ot particles held by glass cloth; Fig. 6 is a view in vertical section showing a reactor; Fig. 7 is a graph showing reactivities and selectivities at varying reaction temperatures; and Fig. 8 is a perspective view showing a reactor.

The shape retaining core gives the desired overall strength to the catalyst structure. The core is in the shape of a flat plate or cylinder or is otherwise shaped suitably in accordance with the shape of the reactor. The core is made generally of steel.

Useful glass fiber products include nonwoven fabric, paper, mat, cloth and roving cloth of glass fibers. Throughout the specification and the appended claims, these terms mean the following.

The glass nonwoven fabric or glass paper is a planar web of glass filaments which are bonded to one another with an adhesive. The web is nonwoven fabric when long fibers are used, or is paper when short fibers are used.

The glass mat is prepared for forming a wad of specified thickness from rovings of glass filaments and making the wad into a mat.

The glass cloth is woven of yarns made by twisting from a multiplicity of glass filaments about 5 to 1 5 ju in diameter. The weaving method is plain weave, twill weave, satin weave or the like.

The glass roving cloth is prepared by forming rovings from long glass fibers and weaving the rovings into a cloth without twisting.

All of these glass fiber products have filament-to-filament interstices which hold particles therein and permit diffusion of gaseous reactants therethrough. Thus these glass fiber products are useful as a component of the catalyst structure of the invention.

Since the glass nonwoven fabric, paper and mat each have a large number of filament-to-filament interstices, and further because component filaments thereof are easily shiftable relative to one another when subjected to an external force, they hold a large amount of catalyst particles therein. Accordingly these nonwoven fabric, paper and mat are well suited as glass fiber products for forming particle holding layers.

Fibers are incorporated into the glass cloth with increased tension and with a reduced number of filament-to-filament interstices, while the component filaments thereof are less shiftable relative to one another, therefore hold a smaller amount of catalyst particles therebetween, but will not permit the release of such particles therefrom when subjected, for example, to vibration. Accordingly the glass cloth is well suited as a glass fiber product for forming the layer for preventing release of particles.

The glass roving cloth as it is is similar to usual cloth, but when the roving cloth is subjected to a needling, brushing or like process to nap one side thereof, the napped surface is given suitable properties to hold particles. Accordingly when glass roving cloth having a napped surface is fitted to the core with the napped surface inside, the roving cloth serves as a glass fiber product having the functions of both the particle holding layer and the release preventing layer.

Useful catalyst particles are those not larger than 100 mesh. Especially particles in the range of 1 to 20 y are most preferable since they are easy to hold but difficult to release. Particles smaller than 1 y in size are somewhat easily releasable but are still satisfactorily usable under conditions free of strong mechanical vibration. Although particles exceeding 20 ym in size have difficulty in entering filament-tofilament interstices of the layer, a sufficient amount of such particles can be held in the layer if the layer is pressed with rubber rollers an increased number of times as will be described later.

To cause a glass fiber product to hold catalyst particles, the product is immersed in a slurry comprising water or a suitable dispersing medium and catalyst particles and having a viscosity of 100 to 1000 cps. It is desirable to press the glass fiber product with rubber rollers in the slurry to force the slurry into the filament-to-filament interstices and thereby cause the product to hold the particles effectively. To squeeze an excess of the slurry from the glass fiber product, the product is then passed between rubber rollers under a pressure of 5 to 30 kg per unit length (m) of the rollers. The wet product is thereafter fitted to a shape retaining core and fixed thereto with fasteners. The glass fiber product thus fitted to the core is dried and, when desired, baked. The fiber product may be dried first and then attached to the core.In this case the product will release some amount of dust during handling, so that -care should be taken to assure a good work environment.

In this way, a catalyst structure of this invention is obtained.

The catalyst structures of this invention can be in various forms. Figs. 1 to 4 show typical examples. The catalyst structure shown in Fig. 1 is of the sandwich type. This drawing shows a metal core 1 in the form of a flat plate, a pair of planar particle holding layers 2 fitted to the opposite sides of the core 1, and fasteners 3 for fixing the layers 2 to the core 1. The catalyst structure shown in Fig. 2 further includes planar layers 4 for preventing release of catalyst particles which layers are fitted to the outer sides of the pair of particle holding layers. Fig. 3 shows a columnar catalyst structure comprising a cylindrical metal core 1 1, a particle holding layer 12 fitted around the core, and fasteners 13 for fixing the layer 12 to the core 1 1. Fig. 4 shows a catalyst structure further comprising a release preventing layer 14 covering the particle holding layer 12.

The catalyst structures thus constructed according to the invention have the following advantages.

The core, which is made of metal, gives high mechanical strength to the structure.

The particle holding layer, which is a glass fiber product, effectively holds a large amount of catalyst particles therein without using any binder, permits efficient diffusion of reactant gases through the interior of the structure with a reduced pressure loss and assures effective contact between the gases and the catalyst, enabling the catalyst to exhibit exceedingly high activity.

The materials of the structure are all inexpensive and easily available.

Accordingly the catalyst structures of the invention are ideal and fulfill all the foregoing requirements 1) to 7).

REFERENCE EXAMPLE 1 Different kinds of particulate materials were checked for differences in the amount of particles held by glass cloth.

A glass cloth was prepared which was 0.2 mm in thickness, 200 g/m2 in weight and 19 yarns/25 mm in yarn density and which was woven of yarns each having one twist/25 mm and composed of 800 glass filaments 14 4m in diameter. Surries of varying concentrations were prepared by adding water to 200- to 500-mesh particles of y-alumina. A piece of the glass cloth was immersed in each of the slurries and pressed with rollers twice in the slurry. The piece of glass cloth thus impregnated with the slurry was dried at 1 000C for 1 hour and then baked or fired at 4000C for 3 hours. The amount of particles held in each of the cloth pieces thus treated was measured.

The same procedure as above was repeated except that in place of the y-alumina particles, silicaalumina particles or magnesia particles, the same as the y-alumina particles in size, were used. The amount of particles held in each of the resulting cloth pieces was measured.

The relation between the concentration of slurry and the amount of particles held in the glass cloth was determined for each kind of the particles. Fig. 5 is a graph showing the results. The graph reveals that the amount of each kind of particles increases with the increase of the slurry concentration.

REFERENCE EXAMPLE 2 Different kinds of glass fiber products were caused to hold particles therein and checked for differences in the amount of the particles.

The same glass cloth as used in Reference Example 1 was used as a glass fiber product. Water was added to 200- to 500-mesh magnesia particles to prepare a slurry having a concentration of 25% by weight. In the same manner as in Reference Example 1, the glass cloth was caused to hold magnesia particles, and the amount of particles held therein was measured.

The same procedure as above was repeated with the exception of using glass nonwoven fabric, mat or roving cloth napped on one side (by needling with 108 needles/cm2) instead of the glass cloth.

The amount of magnesia particles held in each of the resulting glass fiber products was measured.

Table 1 shows the results.

TABLE 1 Particles Glass fiber product Amount Weight* held** Amount held/weight Kind (kg/m3) (kg/m3) of fiber product Cloth 1000 550 0.55 Nonwoven fabric 600 520 0.87 Mat 80 650 8.1 Napped roving cloth 470 620 1.32 * Weight of product per apparent unit volume of the product.

** Weight of particles per apparent unit volume of the fiber product.

EXAMPLE 1 The same glass cloth as used in Reference Example 1 was caused to hold magnesia particles in the same manner as in Reference Example 2, and was then attached to the opposite sides of a core of stainless steel plate, 35 mm x 50 mm x 1.5 mm, whereby a catalyst structure A of the sandwich type shown in Fig. 1 was prepared. Catalyst structures B, C and D were prepared in the same manner as above except that glass nonwoven fabric, glass mat or glass roving cloth napped on one side was used for the particle holding layers in place of the glass cloth. The roving cloth, the same as the one used in Reference Example 2, was attached to the steel plate with the napped surface inside.

EXAMPLE 2 Glass nonwoven fabric, mat and cloth were caused to hold magnesia particles therein in the same manner as in Reference Example 2. In the same manner as in Example 1, the glass nonwoven fabric was attached to a steel panel serving as the core to provide particle holding layers thereon. The glass cloth having magnesia particles held therein as above was placed over the holding layers to provide particle release preventing layers thereon, whereby a catalyst structure E of the same construction as shown in Fig. 2 was prepared. Further a catalyst structure F was prepared in the same manner as above except that the above glass mat having magnesia particles held therein was used in place of the glass nonwoven fabric to provide particle holding layers.

Table 2 shows the thicknesses and weight of the layers included in the catalyst structures prepared in the foregoing examples, and also the amounts of magnesia held in the layers.

TABLE 2 Holding layer Preventing layer Catalyst Fiber Weight Fiber Weight Thickness of Amount of magnesia structure product (g/m2) product (g/m2) layer (mm) (9/m2) A Cloth 200 - - 0.2 110 B Non-woven fabric 300 - - 0.5 260 C Mat 400 - - 3.0 1900 D Napped roving -570 - - 1.2 260 cloth E Non-woven fabric 300 Cloth 200 0.8 380 F Mat 400 Cloth 200 3.1 1900 * The thickness of the particle holding layer or the combined thickness of the holding layer and the particle release preventing layer.

REFERENCE EXAMPLE 3 The catalyst structures A to F were tested for abrasion resistance.

The catalyst structure A was fixed to the center of a 30-mesh metal screen having a diameter of 300 mm, 200 g of alumina balls with a diameter of 5 mm were placed into the screen, and the screen was vibrated on an automatic screening device (290 vibrations/min with an amplitude of 30 mm) for 4 hours. The amount of catalyst released was measured 1 hour, 2 hours and 4 hours after the start of the vibration to determine the amount of particles held in the structure. The same procedure as above was repeated for the catalyst structures B to F. Table 3 shows the results.

TABLE 3 Amount of magnesia held (g/m2) Catalyst structure Initial In 1 hour In 2 hours In 4 hours A 110 90 86 84 B 260 180 110 40 C 1900 1100 620 120 D 260 235 228 225 E 380 345 330 321 F 1900 1550 1420 1400 Table 3 reveals that all the structures have great ability to hold particles.

REFERENCE EXAMPLE 4 The catalyst structures A to F were tested for resistance to vibrations.

The catalyst structure A was fixed to a 6-mesh metal screen and subjected to vibrations for 2 hours by a 50-Hz vibrator mounted on the structure A. The amount of particles released was measured 0.5 hour, 1 hour and 2 hours after the start of the vibration to determine the amount of particles held in the structure. The same procedure as above was repeated for the catalyst structures B to F. Table 4 shows the results.

TABLE 4 Amount of magnesia held (g/m2) Catalyst structure Initial In 0.5 hour In 1 hour In 2 hours A 115 108 105 100 B 260 202 145 83 C 1830 1620 1400 1250 D 255 250 248 245 E 390 350 325 318 F 1900 1750 1720 1700 Table 4 reveals that all the catalyst structures have high resistance to vibrations.

EXAMPLE 3 A 300 g quantity of a-alumina particles not larger than 200 mesh in size were placed into a solution of 11.8 g of ammonium metavanadate, 3.8 g of ammonium molybdate tetrahydrate and 8 g of oxalic acid in 130 g of water. The mixture was evaporated to dryness with stirring in a vacuum at a temperature of up to 600C and was further fired at 4000C for 3 hours. The fired product was pulverized to obtain 200- to 500-mesh catalyst particles, to which water was added to prepare a slurry having a concentration of 25% by weight.

A strip of glass roving cloth napped on one side and having a thickness of 1.2 mm, width of 20 mm and weight of 570 g/m2 was immersed in the slurry and pressed with rollers twice in the slurry.

The strip thus impregnated with the slurry was fitted, with the nap inside, around a mild steel cylinder 18 mm in diameter and 80 mm in length and fastened thereto at its upper and lower portions. The strip was then dried at 1000C for 1 hour and thereafter fired at 4000C for 1 hour, whereby a columnar catalyst structure was prepared which had the construction shown in Fig. 3, with the roving cloth covering measuring 60 mm in length. The amount of particles held in the cloth layer was 240 g/m2.

Activity Test The columnar catalyst structure (having about 0.9 g of catalyst particles held therein) indicated at 22 and prepared in Example 3 was placed into a large-diameter portion 21,23 mm in inside diameter, of a reactor of quartz as seen in Fig. 6. The reactor was controlled to a predetermined reaction temperature. A benzene-air gaseous mixture (with a benzene concentration of 0.8 to 0.9%) was led into the reactor through a small-diameter portion 23 at a flow rate of 60 Nl/h, and the resulting outflow was collected from the upper end of the large-diameter portion 21 to measure the amount of maleic anhydride formed by the oxidation of benzene. The same procedure as above was repeated at varying reaction temperatures.The same procedure as above was further repeated at varying reaction temperatures with the exception of using a benzene-air mixture having an increased benzene concentration of 1.2 to 1.3%.

For comparison, 0.9 g of 6- to 8-mesh alumina 300 grains were admixed with 9 g of 6- to 8mesh silica glass grains to obtain a catalyst in the form of small pellets, which was tested for activity under the same conditions as above. Fig. 6 further shows a heater 24, a molten salt bath 25 and a thermocouple 26.

Reactivities and selectivities were calculated from the above measurements at each of the rection temperatures according to the following equations.

Benzene concn. of outflow Reactivity = (1~ ) x 100 Benzene concn. of charge Amount of maleic anhydride formed (mol/h) Selectivity= x 100 Amount of benzene reacted (mol/h) The results are shown in Fig. 7, which reveals that the columnar catalyst structure of Example 3 is much more excellent than the pellet catalyst in both reactivity and selectivity.

EXAMPLE 4 To a slurry composed of 30 parts by weight of anatase-type TiO2 particles not larger than 200 mesh and 70 parts by weight of water made acidic with sulfuric acid and having a pH of 2 to 3 was added ammonium metavanadate in an amount corresponding to 0.05 in atomic ratio relative to the TiO2. The mixture was stirred at room temperature for 5 hours to dissolve the ammonium metavanadate in the slurry and cause the TiO2 to adsorb the vanadate radical, affording a slurry of TiO2 retaining vanadium therein. Glass roving cloth weighing 300 g/m2 was immersed in the slurry and pressed with rollers twice in the slurry.The cloth thus impregnated with the slurry was attached to the opposite sides of a stainless steel plate. 50 mm x 29 mm x 0.3 mm, then dried at 1500C for 1 hour and therafterfired at 4000C for 3 hours, whereby a catalyst structure G of the sandwich type shown in Fig. 1 was prepared.

Catalyst structures H to N were prepared in the same manner as above with the exception of using the glass fiber products shown in Table 5 in place of the glass roving cloth. The napped roving cloth was used with the nap inside.

TABLE 5 Catalyst Number of structure Glass fiber product needles/cm2* G Roving cloth (300 g/m2) 0 H Napped roving cloth (300 g/m2) 162 Napped roving cloth (300 g/m2) 216 J Roving cloth (570g/m2) 0 K Napped roving cloth (570 g/m2) 108 L Napped roving cloth (570 g/m2) 216 M Nonwoven fabric, 0.8 mm in thickness (300 g/m2) N Cloth, 0.2-mm-thick (200 g/m2) * The number of needles used for napping.

COMPARISON EXAMPLE One hundred parts by weight of TiO2 powder (not larger than 44 # in particle size, and 1 50 n Vg in surface area) and 100 parts by weight of colloidal silica (containing about 20% by weight of SiO2) serving as a binder were thoroughly mixed together to obtain a slurry. The slurry was applied to the opposite sides of 18-mesh metal netting (30 mm x 50 mm in size and made of wires, 0.5 mm in diameter, of SUS 304 steel), then dried at 1 000C for 1 hour and thereafter fired at 4000C for 3 hours.

whereby a TiO2 carrier was formed on the netting in the form of a plate about 0.8 mm in thickness. The netting was immersed in a 2N oxalic acid solution of ammonium metavanadate (1.0 mole/liter) at room temperature for 30 minutes, then withdrawn from the solution, thereafter dried at 1 000C for 1 hour and further fired at about 4000C for 3 hours, affording a catalyst 0 having the catalytic component supported on the metal netting.

Activity Test Into a tubular stainless steel reactor 32 having a reactant gas flow channel 31,6 mm x 30 mm, were placed three catalyst structures 33 as arranged in a row longitudinally of the channel and supported by metal nets 34 as shown in Fig. 7. A test reaction gas having the composition shown in Table 6 was passed through the reactor 32 at a flow rate of 13 Nl/min to test the catalyst for activity to reduce NO with NH3.

TABLE 6 Component Proportion (by volume) NO About 150 ppm NH3 About 1 50 ppm H20 10% CO, 10% O2 5% N2 Balance In this way, the catalyst structures G to N and catalyst 0 were tested for activity at varying reaction temperatures to calculate values K defined by: K=-(AV)xln(1 -x) where: Flow rate of reaction gas (Nm3/h) AV= Geometric surface area of catalyst (m2) x = NO reactivity The relation between K and the amount of TiO2 supported was established. Table 7 shows the results.

TABLE 7 K Catalyst Amount of structure TiO2(g/m2) 2000C 2500C 3000C 3500C G 62 10.3 29.8 47.8 69.0 H 265 30.7 66.4 98.9 132 1 305 32.1 67.9 100 137 J 70 10.9 28.2 41.4 54.1 K 362 35.1 67.0 103 141 L 361 36.7 73.4 122 172 M 120 17.5 42.2 70.0 99.5 N 65 9.8 24.9 36.2 47.3 0 400 12.3 26.3 40.9 49.4 Table 7 reveals that the catalyst structures G to N of Example 4 have higher K values per unit amount of TiO2 and higher activity than the catalyst 0 of Comparison Example.

Claims (5)

1. A catalyst structure comprising a shape retaining metal core of the desired shape, a particle holding layer attached to the core and made of a glass fiber product, and catalyst particles held in the layer.

2. A catalyst structure as defined in claim 1 wherein the particle holding layer comprises a product selected from the group consisting of glass fiber nonwoven fabric, paper, mat, cloth and roving cloth.

3. A catalyst structure as defined in claim 1 wherein the particle holding layer comprises glass fiber roving cloth napped on its inner side.

4. A catalyst structure comprising a shape retaining metal core of the desired shape, a particle holding layer attached to the core and made of a glass fiber product having a relatively large number of filament-to-filament interstices, a particle release preventing layer attached to the outer side of the holding layer and made of a glass fiber product having a relatively small number of filament-to-filament interstices, and catalyst particles held in the holding layer.

5. A catalyst structure as defined in claim 4 wherein the holding layer comprises a glass fiber product selected from the group consisting of glass nonwoven fabric, glass paper and glass mat, and the preventing layer comprises glass cloth.