Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Polymers from only ethylenic monomers or processes of...
Reexamination Certificate
2000-03-10
2002-04-16
Wu, David W. (Department: 1713)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Polymers from only ethylenic monomers or processes of...
C526S105000, C526S130000, C526S901000
Reexamination Certificate
active
06372867
ABSTRACT:
The present invention relates to a process for gas phase polymerisation of olefins with the aid of a supported chromium oxide based catalyst.
It is known from GB 1,429,174 to prepare olefin polymerisation catalysts by impregnating a refractory oxide carrier with a titanium compound, subjecting the resulting product to a calcination step by heating at a temperature T1 of between 150 and 1200° C., adding a chromium compound and subjecting the resulting product to an activation step by heating at a temperature T2 of between 100 and 1200° C. Thus, according to GB 1,429,174, two separate thermal treatments (T1, T2), which will be hereinafter referred to as a calcination procedure and an activation procedure are necessary for obtaining the desired catalyst.
It is known from U.S. Pat. No. 3,622,521 to use titanium modified chromium oxide based catalysts for the polymersation of ethylene in slurry. This patent discloses a final activation step of the catalyst which can be carried out in dry air for from 1 to 50 hours using a temperature in the range from 350° to 2000° F. (176° to 1093° C.). All the catalysts of U.S. Pat. No. 3,622,521 are prepared using an activation procedure of 5 hours in dry air at 1300° F. (704° C.).
It is known from U.S. Pat. No. 4,011,382 to prepare ethylene polymers by a gas phase polymerisation process with the aid of a titanium modified chromium oxide based catalyst. This patent describes a final activation step of the catalyst which can e be performed by heating the catalyst in air or oxygen at a temperature of 300° to 900° C., and preferably at 700° to 850° C. All the catalysts of U.S. Pat. No. 4,011,382 are prepared using an activation procedure of 8 hours in dry air at either 750° C. or 825° C.
It is known from EP 0 055 863, to use a chromium supported catalyst for polymerising olefins. All the catalysts disclosed in said patent application are supported on an aluminium phosphate-containing base.
It is also common general knowledge that there is a quasi linear relationship between the temperature of activation and both the activity of the catalyst and the melt index of the ethylene polymer prepared from said chromium oxide catalyst. The higher the temperature of activation, the higher the activity and the melt index.
Therefore, the man in the art knows that in order to properly activate the chromium oxide based catalyst activation temperatures above at least about 500° C. should be used.
These calcination/activation procedures applied to the modified support are long and costly. However, as these procedures are necessary to obtain good activity of the final catalyst and a high melt index of the resulting ethylene polymer the man in the art continues to proceed in the same way.
It is therefore an objective of the present invention to provide a process for preparing ethylene (co-)polymers having a high melt index in the presence of a supported chromium oxide based catalyst having reasonably good activity and which does not require these lengthy and/or high temperature calcination/activation procedures.
It has now unexpectedly been found that while said aforementioned quasi linear relationship between the activation temperature and the catalyst activity and melt index of the resulting (co)polymer could systematically be verified in slurry polymerisation, this is not the case when using supported chromium oxide based catalyst in gas phase (co)polymerisation of ethylene.
The present invention makes it possible to avoid or at least mitigate the disadvantages referred to above. In particular, a gas phase polymerisation process has now been found which makes it possible to manufacture polymers having a high melt index with a supported chromium based catalyst showing good activity and which is prepared according to a simple and economical process. Furthermore, the polymers obtained according to the present invention have good stress cracking resistance and a high critical shear rate. As a result the polymers are easy to process. Furthermore, the polymers obtained can have a low volatile content i.e. they give rise to a very small quantity of volatile matter (fumes) during the manufacture of articles. They also can have a high impact strength and a low die swell.
The subject of the invention is therefore a process for the gas phase polymerisation of at least one alpha olefin containing from 2 to 12 carbon atoms, characterised in that the polymerisation is performed with the aid of a chromium oxide based catalyst supported on a granular or microspherical refractory oxide which has been subjected to a sole calcination/activation step consisting of a single thermal treatment performed at a temperature ranging from 200 to 450° C. under an oxygen-containing atmosphere.
According to the invention a polymerisation reaction of at least one alpha-olefin is carried out with the aid of such a supported chromium oxide based catalyst.
Another object of the present invention is a method for the preparation of a chromium oxide based catalyst supported on a granular or microspherical refractory oxide for the gas phase polymerisation of olefin(s) characterised in that the supported chromium oxide based catalyst is subjected to a sole calcination/activation step consisting of a single thermal treatment performed at a temperature ranging from 200 to 450° C. under an oxygen-containing atmosphere.
Still another object of the present invention is to provide an improved chromium oxide based catalyst supported on a granular or microspherical refractory oxide for the gas phase polymerisation of olefin(s), wherein the catalyst is obtainable by a preparation which is characterised in that the supported chromium oxide based catalyst is subjected to a sole calcination/activation step consisting of a single thermal treatment performed at a temperature ranging from 200 to 450° C. under an oxygen-containing atmosphere.
The supported chromium oxide based catalyst contains in most cases from 0.1 to 3% of chromium. According to a preferred embodiment of the present invention, the catalyst is advantageously a titanium or aluminium modified supported chromium oxide based catalyst, most preferably a titanium modified supported chromium oxide based catalyst. For example, the catalyst can be modified with from 0.1 to 8% by weight titanium or 0.1 to 6% by weight of aluminium.
The catalyst is supported on a granular or microspherical refractory oxide such as silica, alumina, zirconia oxide or a mixture or a coprecipitate of these oxides. The support can be obtained by various known processes, especially by precipitation of silicon compounds such as, for example, silica, from a solution of an alkali metal silicate, (or else by coprecipitation of a refractory oxide gel or hydrogel from solutions containing at least two compounds chosen from silicon, titanium, zirconium or aluminium compounds).
The granular support advantageously has a specific (BET) surface of between 200 and 1200 m
2
/g, a pore volume ranging from 1 to 3.5 ml/g, and can consist of particles which have a diameter of between 20 and 250 &mgr;m, preferably between 30 and 150 &mgr;m. It advantageously contains hydroxyl functional groups and is preferably free from water at the time of its use during the preparation of the catalyst. For this purpose it can be heated to a temperature ranging e.g. from 100 to 200° C.
The catalyst is preferably prepared by a process comprising a first stage during which the support is impregnated with a chromium compound, and a second optional stage during which the product originating from the first stage is impregnated with either a titanium or an aluminium compound. The chromium compound employed can be a chromium oxide, generally of formula CrO
3
, or a chromium compound which can be converted into chromium oxide by calcining, such as, for example, a chromium nitrate or sulfate, an ammonium chromate, a chromium carbonate, acetate or acetylacetonate or else a tertbutyl chromate.
Titanium compounds which can advantageously be employed are titanium alcoholate such as, for example, titanium tetraisopropylate or tit
BP Chemical Limited
Cheung William K
Finnegan Henderson Farabow Garrett & Dunner L.L.P.
Wu David W.
LandOfFree
Process for the gas phase polymerization of olefins does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Process for the gas phase polymerization of olefins, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Process for the gas phase polymerization of olefins will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2917640