Catalyst – solid sorbent – or support therefor: product or process – Zeolite or clay – including gallium analogs – Support per se
Reexamination Certificate
2002-02-28
2003-11-11
Choi, Ling-Siu (Department: 1713)
Catalyst, solid sorbent, or support therefor: product or process
Zeolite or clay, including gallium analogs
Support per se
C502S257000, C502S256000, C502S228000, C526S106000, C526S130000, C526S348000
Reexamination Certificate
active
06645900
ABSTRACT:
The invention relates to a method for the production of silica gel catalyst supports and chromium oxide catalysts supported on silica gel, and to the corresponding catalyst supports and catalysts for the polymerization of olefin monomers.
Polymerization catalysts which comprise silica gel or modified silica gel as support material and chromium as active component play an essential role in the production of high density polyethylene (HDPE). The conditions during production of the supports and the catalysts determine the chemical composition, pore structure, particle size and shape of the catalysts. Before the polymerization, the catalysts are activated at high temperatures in order to stabilize chromium on the catalyst surface as Cr(VI) species. This species is reduced by addition of ethene or additional reducing agents in order to form the catalytically active species which catalyses the polymerization. The composition of the catalyst support and of the catalyst, its structure and the activation conditions have a crucial influence on the performance of the catalyst in the polymerization method, the activity of the catalyst, the structure and the properties of the resultant polymer.
DE-A 25 40 279 relates to a method for the production of a catalyst for the polymerization of unsaturated compounds which is suitable for the production of readily processable olefin polymers of low melt viscosity without the use of large amounts of hydrogen as molecular weight regulator. In this method, firstly a fine particle silicic acid xerogel is prepared starting from a silicic acid hydrogel having a solids content of from 10 to 25% by weight (calculated as SiO
2
), extraction of the water from the hydrogel, drying (xerogel formation), grinding and sieving of the xerogel. The xerogel is subsequently loaded with chromium oxide or a chromium compound which converts into chromium oxide, and activated. The starting material here is a spherical silicic acid hydrogel which has a particle diameter of from 1 to 8 mm.
EP-A 0 263 525, DE-A 36 40 802 and DE-A 36 40 803 relate to refinements of the method disclosed in DE-A 25 40 279 for the production of a catalyst for the polymerization of unsaturated compounds.
Thus, EP-A 0 263 525 describes a method for the production of polyethylene and copolymers of ethene using the catalyst prepared in accordance with DE-A 25 40 279 and an alkyllithium as cocatalyst. The alkyllithium here serves to increase the productivity of the catalyst, to reduce the induction time of the polymerization and the sensitivity of the catalyst to impurities, and to provide polymers having favourable morphological properties.
DE-A 36 40 802 relates to a method for the production of grit-form ethene homo-polymers and ethene copolymers in which a catalyst which has a narrow particle size distribution, enabling the production of polymers having a controllable, optimum particle morphology, is prepared on the basis of the method of DE-A 25 40 279. In accordance with DE-A 36 40 803, this catalyst is employed together with an alkyllithium as cocatalyst.
Of crucial importance for the pore volume of the catalyst support prepared by the method disclosed in DE-A 25 40 279 is the extraction of the water from the hydrogel employed. This is carried out using an organic solvent and generally takes about 12 hours. The extraction is thus the capacity-determining step in the method according to DE-A 25 40 279.
The object of the present invention is a refinement of the method according to DE-A 25 40 279 for the production of a catalyst support based on silica gel and of a chromium oxide catalyst supported on silica gel. The aim here is, in particular, for the method to be carried out more efficiently in terms of time than the known methods through a shortening of the extraction time, with the catalyst retaining its excellent properties.
This object is achieved by a method for the production of a catalyst support comprising the following steps:
a) production of a silicic acid hydrogel having a solids content of from 10 to 25% by weight (calculated as SiO
2
) whose particles are substantially spherical, by
a1) introduction of a sodium water-glass or potassium water-glass solution into a swirling stream of a mineral acid, both longitudinally and tangentially to the stream,
a2) spraying of the resultant silicic acid hydrosol in drop form into a gaseous medium,
a3) allowing the hydrosol to solidify in the gaseous medium to give hydrogel particles,
a4) washing of the resultant substantially spherical hydrogel particles in order to free the hydrogel from salts,
b) extraction of the hydrogel particles with an alcohol until at least 60% of the water present in the hydrogel has been removed,
c) drying of the resultant hydrogel until the residual alcohol content is less than 10% by weight (xerogel formation) at temperatures of ≧160° C. at atmospheric pressure using an inert entraining gas,
d) setting of the desired particle size of the resultant xerogel.
The method according to the invention is characterized in that the hydrogel particles have a particle size of ≧8 mm before the extraction.
The extraction of the water with an alcohol takes place significantly more quickly if the hydrogel particles have a diameter of ≧8 mm, preferably in the range from 10 to 15 mm, particularly preferably from 10 to 12 mm. At the same time, an alcohol consumption which is reduced by about 20% compared with known methods is observed as a secondary effect. The economic efficiency of the method is thus increased.
The extraction is generally carried out in a period of from 1 to 10 hours, preferably from 4 to 8 hours, particularly preferably from 2 to 6 hours. The total duration of the production method can thus be considerably shortened compared with known methods.
Step a)
The characteristic feature of step a) of the method according to the invention is the use of a substantially spherical silicic acid hydrogel having a relatively high solids content in the range from 10 to 25% by weight, preferably from 12 to 20% by weight, particularly preferably from 14 to 20% by weight (calculated as SiO
2
). The production method for this silicic acid hydrogel is carried out by steps a1) to a4), which are described in detail in DE-A 25 40 279 and the literature cited therein.
After introduction of a sodium water-glass or potassium water-glass solution into a swirling stream of a mineral acid, for example sulphuric acid, step a1), the resultant silicic acid hydrosol is sprayed into a gaseous medium by means of a nozzle, step a2). The nozzle orifice employed here results, after the hydrosol has been allowed to solidify in the gaseous medium, step a3), in hydrogel particles having a particle size distribution in which in general from 90 to 99% by weight, preferably from 95 to 98% by weight, of the particles have a particle diameter in the range from 8 to 15 mm. After the hydrogel particles have been washed, step a4), preferably with warm, weakly ammoniacal water at about 50° C., in a continuous countercurrent method, the spherical particles are sieved. Hydrogel particles having a diameter of ≧8 mm, preferably in the range from 10 to 15 mm, particularly preferably from 10 to 12 mm, are isolated and transferred into an extraction vessel.
Step b)
The extraction of the water from the silicic acid hydrogel by means of an alcohol can be carried out in conventional extraction apparatuses, for example a column extractor in co- or countercurrent.
Suitable alcohols are preferably C
1
- to C
4
-alcohols, such as tert-butanol, i-propanol, ethanol and methanol. Use can also be made here of a mixture of different alcohols. Methanol is very particularly preferably employed. The alcohol employed should comprise less than 5% by weight, preferably less than 3% by weight, of water before the extraction.
In a preferred embodiment, the silicic acid hydrogel particles are transferred into an extraction vessel for extraction of the water, and sufficient alcohol is added until the hydrogel particles are covered with the alcohol. The alcohol is subsequently allo
de Lange Paulus
Deckers Andreas
Funk Guido
Kölle Peter
Basell Polyolefine GmbH
Choi Ling-Siu
Connolly Bove & Lodge & Hutz LLP
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