Process for producing spherical catalyst particles, catalyst...

Details Process for producing spherical catalyst particles, catalyst... Process for producing spherical catalyst particles, catalyst...

2000-07-12

2002-10-15

Hendrickson, Stuart L. (Department: 1754)

Catalyst, solid sorbent, or support therefor: product or process

Forming or treating a sphere, process only

Forming other than by liquid immersion

C502S064000, C502S071000, C502S077000, C502S242000, C502S070000

Reexamination Certificate

active

06465382

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates to a method for producing spherical catalyst particles containing a zeolite as active element, to catalyst particles containing a zeolite as active element and to the use of these particles in epoxidation reactions.
BACKGROUND OF THE INVENTION
It is known, for instance from the European patent application EP-A2-0 200 260, to use microspheres having an average diameter close to 20 &mgr;m and constituted by oligomeric silica and by titanium-silicalite crystals as catalyst particles for the epoxidation of olefins. It is further known that such catalysts tend to desactivate and that they consequently need to be regenerated regularly. When these catalyst particles of relative small average diameter are used as such in epoxidation reactors, they are difficult to isolate from the reaction medium in order to be transferred to the regeneration treatment. In order to avoid this problem, larger catalyst particles can be used. However, these particles present a lower activity and inferior mechanical properties. Moreover, the known relatively small particles are not suitable for use in a fluid bed reactor because at a normal velocity of the fluid, they tend to be carried over.
SUMMARY OF THE INVENTION
It is an object of the invention to provide a method for the production of spherical catalyst particles which permits the shaping of particles which are suitable to be isolated easily from the reaction medium and which present a high catalytic activity and good mechanical properties.
Consequently, the invention concerns a process for producing spherical catalyst particles containing a zeolite as active element, according to which a sol containing zeolite crystals and at least one gel-forming compound is sprayed from below directly into a reaction zone containing a reaction gas such that the sol breaks up into individual sol beads immediately before or upon entry into the reaction zone, the sol beads flow through the reaction zone on a curved trajectory, in so doing are pre-consolidated and the sol beads are collected on a collecting means.
One of the essential characteristics of the invention is that the particle size range of the sol beads can be modulated and controlled by the kind of spraying device used and this particle size range can be maintained without deformation during the process due to the special process conditions. Consequently, the size range of the catalyst particles can easily be controlled. This allows the production of catalyst particles of the desired granulometry, which makes it possible to easily isolate them from the (epoxidation) reaction medium, to have a high catalytic activity and good mechanical properties.
Another advantage of the invention is that the place and time of the formation of the sol beads is advantageously matched to the beginning of gelling (pre-consolidation) of the sol beads. This means that at the time at which the sol beads are produced, they are still liquid sol drops having a virtually ideal spherical shape and largely identical sphere diameters. The sol beads are then fixed, i.e. pre-consolidated, in their virtually ideal uniform spherical shape as they pass through the reaction zone, so that they are largely protected from deformative effects. Finally the sol beads pre-consolidated in their spherical shape are stably fixed by additional known measures of the generally known sol-gel process. To this end, the spraying-in device is arranged at a certain distance (as described below) below the entry opening into the reaction zone. This distance corresponds approximately to the distance, starting from the spraying device, in which the sol breaks up into sol beads. In addition, the sol is sprayed out of the spraying device from below, i.e. counter to the force of gravity. This means that the sol is sprayed at a given angle &agr; which is formed by a horizontal axis at right-angles to the force of gravity and the tangent of the sprayed sol at the exit point from the spraying system.
DETAILED DESCRIPTION OF THE INVENTION
The process according to the invention is suitable for the production of catalyst particles containing zeolite as active element by gelling gellable sols containing zeolite crystals and one or more gel-forming compounds.
“Zeolite” is to be understood to mean synthetic crystalline materials presenting a zeolite crystalline structure. The zeolite crystals can have a crystalline structure of the ZSM-5 type. The zeolite crystals can also have a structure of the ZSM-11 or MCM-41 type. They advantageously contain oxides of silicon and titanium. Usually the zeolite crystals contain at most 2% by weight of titanium. Zeolite crystals of the titanium silicalite type are preferably used. They are in particular represented by the formula xTiO
2
(1−x)SiO
2
in which x is from 0.0001 to 0.5 and preferably from 0.001 to 0.05. The zeolite crystals present advantageously an infrared absorption band at approximately 950-960 cm
1
. The best results are obtained with zeolite crystals of the TS-1 type which presents a microporous crystalline zeolite structure of the ZSM-5 type wherein several silicon atoms are replaced by titanium atoms. The properties of these TS-1 crystals are known (B. Notari; Structure-Activity and Selectivity Relationship in Heterogeneous Catalysis; R. K. Grasselli and A. W. Sleight Editors; Elsevier; 1991; p. 243-256). Their synthesis is also known (A. Van der Poel and J. Van Hooff, Applied Catalysis A, 1992, volume 92, pages 93-111). The zeolite crystals used generally present an average diameter of at most 10 &mgr;m. The average diameter is generally of at least 0.1 &mgr;m but can even be smaller. Average diameters ranging from 1 to 5 &mgr;m are preferred. Such crystals present the advantage that the mechanical strength of the catalyst particles is improved.
The zeolite crystals and the gel-forming compound are generally used in a quantity such that the catalyst particles contain from 5 to 95 wt % of zeolite preferably from 20 to 50 wt %.
The gel-forming compounds can be based on inorganic oxides such as magnesium oxide, aluminium oxide, silicon dioxide, alumosilicate, zinc oxide, titanium dioxide, chromium oxide, manganese oxide, cerium oxide, tin oxide, iron oxide, nickel oxide, lead oxide, molybdenum oxide, vanadium oxide, thorium oxide, zirconium oxide and/or hafnium oxide. Preferred gel-forming compounds are based on silicon dioxide. The sols can in addition to the gel-forming compounds contain additional additives which can improve the use-related and/or catalytic properties of the catalyst particles.
According to the process of the invention a gellable sol containing zeolite crystals and at least one gel-forming compound is sprayed from bottom to top into the reaction zone at an angle which depends on the dimensions of the equipment used. The angle is preferably such that the flow of sol beads does not touch the walls of the equipment. In practice the angle is often chosen from 80 to 88°. Depending on the particle size range, syringes with cannulae of different diameters or known spray nozzles, centrifugal discs, spray wheels, ultrasonic nozzles or bells, spray guns, turbo bells, magnetic valves, mechanically operated nozzles or spraying systems, such as are used in electrostatic spraying or in jet printers (e.g. piezo-excited nozzles), may be used as spraying devices. The particle size range in this case is varied by means of the spraying device used. For a desired particle size in the range from 0.01 mm to 0.3 mm, therefore, expediently turbo bells, micromagnetic valves or spray nozzles, e.g. known spiral nozzles (e.g. spiral nozzles manufactured by SPRAYBEST) or preferably ultrasonic nozzles are used. For a desired particle size in the range from 0.3 to 5 mm, in particular 0.3 mm to 3.5 mm, expediently spray wheels or preferably cannulae of corresponding diameter are used. If there is a very short distance from the spraying device to the entry opening of the reaction zone containing the reaction gas, it may be expedient, e.g. when using spray nozzles or cannula

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