Catalyst – solid sorbent – or support therefor: product or process – Catalyst or precursor therefor – Metal – metal oxide or metal hydroxide
Reexamination Certificate
2000-03-27
2004-01-27
Wood, Elizabeth D. (Department: 1755)
Catalyst, solid sorbent, or support therefor: product or process
Catalyst or precursor therefor
Metal, metal oxide or metal hydroxide
C502S308000, C502S309000, C502S319000, C502S320000, C502S237000, C502S240000, C502S254000, C502S256000
Reexamination Certificate
active
06683022
ABSTRACT:
The invention relates to a method for the discontinuous thermal treatment of catalyst material and the use of the resulting products in polyolefin production.
The activation of catalysts for olefin polymerization and the calcination of catalyst supports are carried out using reactors which are operated discontinuously. Both calcination and activation usually take place at temperatures above 100° C. The reactors concerned have to be heated from the initial temperature, generally ambient temperature, to the appropriate temperature at which activation or calcination is to take place. After the activation or calcination is complete, the reactor is cooled again and the catalyst is subsequently taken from the reactor. Both the reactor and catalyst or catalyst support are thus brought back to the initial temperature.
For the purposes of the present invention, the term reactor temperature refers to the spatial mean temperature measured on the surface of the inner wall of the reactor, not the temperature measured in the internal, frequently gas-filled volume of the reactor. This differentiation is important because the temperature measured in the interior space of the reactor is, owing to the low heat capacity of gases which are usually present in the interior space of the reactor, generally subject to greater fluctuations than is the temperature of the reactor material measured on the inner wall of the reactor. As a matter of definition, fluctuations of ±20° C. in the reactor temperature should not be counted as such. In such a case, the reactor temperature is classified as constant despite this fluctuation. This means that maintaining a constant reactor temperature can involve a maximum fluctuation of ±20° C.
For the purposes of the following, catalyst materials are initiators, catalysts, catalyst supports, supported catalysts and supported initiators. No differentiation between initiators and catalysts will be made at this point, since it is frequently difficult to determine whether a reaction is being initiated or catalyzed. Catalyst material is generally present in the form of particles, although catalyst material can in principle also be present in any other form, for example as powder, packing or mesh.
For the purposes of the present invention, thermal treatment refers to processes of all types which are associated in any way with heating and/or cooling events, for example calcination or activation of catalyst material.
Suitable reactors for the thermal treatment of catalyst material are, in particular, apparatuses which ensure intimate contact of the catalyst material with the surrounding gas and at the same time result in only brief contact with heated walls, for example the interior wall of such a reactor. This is the case, for example, in fluidized-bed reactors and discontinuous mixing reactors. In the case of discontinuous mixing reactors, which are configured as discontinuous rotary tube reactors, the catalyst material is located in a tube which rotates about its longitudinal axis so that the catalyst material present in loose form in the tube is kept in motion. During thermal treatment in a fluidized-bed reactor, the catalyst material is usually mostly present in the fluidized bed, although nonfluidized material may occur on horizontal surfaces in the lower region of the fluidized-bed reactor.
An essential aspect is that both the catalyst material and the material of the reactor are subjected to great stress during the thermal treatment. This stress is caused by the heating and cooling events which are associated with the thermal treatment. The material affected is continually under strong mechanical stress. This generally leads to material fatigue after a prolonged operating time: cracks form in the material and the material is damaged or even destroyed. In order to protect reactors which are subjected to wide temperature fluctuations from material fatigue or to limit this material fatigue, they have to be constructed of more resistant material. This is generally comparatively expensive so that it has an adverse effect on the costs of plant construction.
Particularly in the case of rapid heating and cooling events, cracks can also form in the catalyst material and the catalyst material can, at least partly, disintegrate to fine dust as a result. Fine dust formation means that material of differing quality is produced, since finer particles have different properties than do larger particles. Material of uniform quality is usually desired. For this reason, it is generally necessary to use separation devices, e.g. cyclones or filters, in the event of fine dust formation. This is generally quite costly. A further problem is caused by solvent (in particular organic solvent) frequently being still present in the particles of the catalyst material prior to the treatment of this material. The solvent vaporizes suddenly on rapid heating and the abrupt pressure shock resulting from the solvent vapors liberated in the particles can cause destruction of the particles. This in turn leads to undesirable dust formation.
The above-described problems caused by the thermal stress make it necessary for heating and cooling procedures to be carried out very slowly. However, long heating and cooling periods mean nonproductive times in which the desired thermal treatment does not take place, so that the process becomes less economical.
This can be described by way of example as follows:
A catalyst material is to be thermally treated for 10 hours at a constant temperature of 600°C. At the beginning of the procedure, the catalyst material and the reactor are at room temperature. In industrial practice it is necessary to heat for 10 hours and, after the subsequent 10 hour thermal treatment, to cool for another 10 hours. For a “reaction time” (thermal treatment) of 10 hours, a process residence time of three times that is therefore required. In the case of shorter heating and cooling periods, severe damage to the catalyst material and to the reactor material may be expected.
A further disadvantage resulting from the heating and cooling periods is that considerable amounts of energy are needed. Particularly for heating the reactors used industrially, a great deal of energy is required since the reactors have high masses.
It is an object of the invention to provide a method for thermally treating catalyst material without the material of the reactor used being subject to great material fatigue. It is important here that material which has a relatively low resistance to material fatigue can be used for the construction of an appropriate reactor. In addition, the amount of energy required for the thermal treatment of catalyst material should be reduced.
This object is achieved by a method for the discontinuous thermal treatment of catalyst material comprising the steps
(a) introducing the catalyst material into a reactor,
(b) heating the catalyst material,
(c) thermally treating the catalyst material in the reactor at the reactor temperature,
(d) discharging the catalyst material from the reactor and
(e) cooling the catalyst material,
wherein the reactor temperature is kept constant during the steps (a) to (e), step (b) is carried out during and/or after step (a), step (e) is carried out during and/or after step (d), and step (c) is carried out after step (b) and before step (e).
The introduction of the catalyst into the reactor can be carried out, for example, using a blower or a feed screw. Emptying of the reactor by discharge of the catalyst material can be carried out, for example, by simple “pouring out”. However, the introduction of the catalyst material and the discharge thereof can in principle be carried out using any method suitable for this purpose.
For the purposes of the present invention, thermally treating the catalyst material at the reactor temperature means that the catalyst material is at the reactor temperature; heating is continually applied to the reactor in order to keep the temperature constant.
In a preferred embodiment, the heating of the catalyst material occu
Brauch Thomas
De Lange Paulus
Evertz Kaspar
Feindt Hans-Jacob
Kämmerer Michael
Basell Polyolefine GmbH
Wood Elizabeth D.
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