Catalyst – solid sorbent – or support therefor: product or process – Regenerating or rehabilitating catalyst or sorbent – Gas or vapor treating
Reexamination Certificate
2001-07-17
2004-03-30
Silverman, Stanley S. (Department: 1754)
Catalyst, solid sorbent, or support therefor: product or process
Regenerating or rehabilitating catalyst or sorbent
Gas or vapor treating
Reexamination Certificate
active
06713422
ABSTRACT:
The present invention relates to a process for working up at least partially deactivated polymerization catalysts and to the use of the worked-up polymerization catalysts.
It is known that sheet silicates such as smectites, kaolin and attapulgite can be used as polymerization catalysts for the polymerization of tetrahydrofuran (THF) to polytetrahydrofuran (pTHF). This polymerization can be carried out in the presence of telogens. For example, montmorillonite, which belongs to the smectite class, is used for the polymerization of THF in the presence of acetic anhydride as telogen to form pTHF diacetate. Copolymerization of THF with ethylene oxide or propylene oxide, for example using kaolin or attapulgite as catalysts, gives polybutylene-alkylene glycol ethers.
As the time for which they have been used as polymerization catalysts increases, the sheet silicates lose catalytic activity and finally have to be replaced. However, the replacement of exhausted, deactivated catalysts is associated with a complicated cleaning procedure in which the exhausted catalyst is freed of adhering products of the polymerization reaction. The cleaning process is necessary, inter alia, to restore the flow properties of the catalyst bed so that the catalyst can be removed from the polymerization reactor without problems by suction. The customary procedure is to wash the exhausted catalyst contaminated by highly viscous pTHF diacetate with water and methanol, for example as described in U.S. Pat. No. 5,268,345. To free the catalyst of adhering extractant, the catalyst bed has to be rinsed a number of times with water before it is removed by suction. This results in large amounts of washing water which are contaminated by the extractant. The cleaning procedure described is time-consuming and costly. The large amounts of solvent-containing washing water have to be treated. The catalyst removed from the reactor is, even after this cleaning procedure, generally still so contaminated with solvent that it does not meet the pollutant thresholds prescribed in Germany for disposal of the catalyst in a landfill and therefore has to be incinerated.
It is an object of the present invention to provide a process for working up exhausted polymerization catalysts for the polymerization of THF which allows quick and inexpensive replacement of catalyst and which gives a worked up catalyst which is largely free of pollutants and can be disposed of in a landfill.
We have found that this object is achieved by a process for working up at least partially deactivated polymerization catalysts for the polymerization or copolymerization of THF which are contaminated with the products of the polymerization or copolymerization of THF, which process comprises cleaning the polymerization catalyst by treatment with steam at generally from 80 to 250° C., preferably from 100 to 200° C., and an absolute pressure of generally from 0.5 to 40 bar, preferably from 1 to 16 bar. The clean polymerization catalyst can, in a second step, be disposed of in a landfill, regenerated, used in another way or incinerated. The clean polymerization catalyst can also be used, for example, for the depolymerization of pTHF which is not within specification.
The clean polymerization catalyst is preferably regenerated. Preference is therefore given to a process for working up polymerization catalysts in at least two steps, which comprises
(a) in a first step, cleaning the polymerization catalyst in the manner described above, and
(b) regenerating the clean polymerization catalyst.
The process of the present invention is used for working up at least partially deactivated polymerization catalysts for the polymerization or copolymerization of THF. The polymerization catalyst is partially deactivated when it has lost its original catalytic activity or when the color number of the polymer exceeds the specification limit. A partially deactivated polymerization catalyst can, for example, still have a residual activity of 80% of the original activity. It is possible to work up polymerization catalysts which have been used for the polymerization of THF to pTHF or for the copolymerization of THF with alkylene oxides, for example ethylene oxide or propylene oxide, to give the corresponding polybutylene-alkylene glycol ethers, where both the polymerization and the copolymerization may have been carried out in the presence of telogens. Telogens are, for example, water, monohydric and polyhydric alcohols such as methanol, ethanol, propanol, ethylene glycol, butylene glycol, glycerol, neopentyl glycol, 1,4-butanediol, also aliphatic carboxylic acids having from 1 to 8 carbon atoms, e.g. formic acid, acetic acid, propionic acid, butyric acid, and aromatic carboxylic acids such as benzoic acid, and also their anhydrides.
The at least partially deactivated polymerization catalysts are contaminated with the products of the polymerization or copolymerization. Products of the polymerization or copolymerization are pTHF, polybutylene-alkylene glycol ethers or their reaction products with the abovementioned telogens.
The process of the present invention is preferably used for working up polymerization catalysts based on silicates. Polymerization catalysts based on silicates are naturally occurring or synthetic sheet silicates, for example naturally occurring smectites, in particular sodium montmorillonite or calcium montmorillonite, also kaolin, attapulgite and sepiolite. Other polymerization catalysts based on silicates are zeolites. The silicates or sheet silicates mentioned are usually activated by treatment with acids and are subsequently calcined. The acid treatment generates acid centers in the clay minerals by ion exchange and/or increases the surface area of the catalyst. Some minerals such as attapulgite and sepiolite have sufficient acid centers even without acid treatment. Acid centers can also be obtained by calcining ammonium compounds of the minerals concerned.
In a preferred embodiment of the process of the present invention, polymerization catalysts based on sheet silicates, in particular acid-activated montmorillonite, which are used for the polymerization or copolymerization of THF are worked up. In particular, polymerization catalysts of this type for the polymerization of THF in the presence of acetic anhydride as telogen to give pTHF diacetate are worked up. The latter are mainly contaminated with pTHF diacetate.
In a first step of the process of the present invention, the polymerization catalyst is treated with steam at from 80 to 250° C., preferably from 100 to 200° C., and an absolute pressure of from 0.5 to 40 bar, preferably from 1 to 16 bar. For this purpose, the exhausted polymerization catalyst can be left in the polymerization reactor and, if appropriate after blowing-off the reaction mixture, steam is introduced into the polymerization reactor. At the specified temperature and the specified pressure, hydrolytic cleavage of the polymer molecules into low molecular weight units occurs and these can readily be leached from the polymerization catalyst and transported away by means of the steam. In the case of polymerization catalysts contaminated with pTHF diacetate, for example, hydrolysis with elimination of acetic acid and subsequent depolymerization of pTHF into THF and THF oligomers occur. The hydrolytic cleavage and depolymerization of the highly. viscous pTHF restores the flow properties of the polymerization catalyst, so that this can be removed from the polymerization reactor without problems. Any catalyst beds in any reaction apparatuses can be worked up in this way. For example, the catalyst can be in the form of granules, extrudates, spheres or other shaped bodies. The clean catalyst can, for example, be removed by sucking it from the polymerization reactor or by blowing it out downward.
The steam treatment cleans the polymerization catalysts to the extent where the organic constituents, measured as loss on ignition of the dry residue, are less than 10% by weight and the TOC content (total organic carbon) in the eluate of the steam-treated
Eller Karsten
Hesse Michael
Meier Anton
Menger Volkmar
BASF - Aktiengesellschaft
Keil & Weinkauf
Silverman Stanley S.
Strickland Jonas N.
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