Title of Invention	"A PROCESS FOR PREPARATION OF ALUMINA BASED ADSORBENT OF CHELATED ORGANOMETALLIC COMPOUNDS"
Abstract	Process for the adsorption of chelated organometallic compounds which comprises contacting said compounds with an alumina-based adsorbent, said adsorbent resulting from shaping by coagulation in droplets or by extrusion or being obtained by crushing, and said adsorbent having a volume of pores with a diameter greater than 80 A of at least 0.15 cm3/g and a particle size of less than 4 mm.

Full Text

The invention relates to a prpcess for the adsorption of chelated organometallic compounds on alumina-based adsorbents, in which the said compounds are brought into contact with an alumina-based adsorbent having suitable characteristics- It relates more particularly to a process for the purification of polyolefins obtained by polymerization of olefins in the presence of coordination catalysts. It also relates to alumina-based adsorbents comprising a chelated organometallic compound. Polyolefins are in general prepared by polymerization of monomers with the possible addition of comonomers such as 1-butene or 1-octene, in the presence of polymerization catalysts comprising elements from groups IVB, VB, VIB of the Periodic Table of the elements, more particularly vanadium, titanium and zirconium. These catalysts also comprise, as reducing agents, organometallic (e.g. metal alkyl) compounds, metal hydrides or metal hydroxides. These catalysts, which are generally called transition catalysts, have great catalytic activity for the polymerization of olefins. However, once polymerization is complete, the polyolefins obtained are polluted by the metallic residues from the catalysts, and it is therefore vital to purify them before their use, so as to avoid any toxicity, such as interfering colouration or degradation. In addition, olefin polymerization processes generally comprise a recovery stage of the monomers which have not reacted during the polymerization and of the solvents present in the polyolefins, these solvents and monomers being recycled into the polymerization unit. The presence of metals in these compounds gives rise to problems of corrosion of the installation. In order to eliminate the metallic residues obtained from the catalysts, one process consists in contacting the medium which results from the polymerization with organic compounds. This gives rise to a complexation reaction between the metallic residues and the organic compounds introduced, leading to chelated organometallic compounds. Subsequently, in order to separate these chelated organometallic compounds from the polyolefins, it is known to use various adsorbents, especially aluminas. Among the adsorbents used, it is known to use adsorbents in the form of beads. These beads are shaped by rotating technology of the film coater or rotating drum type. US 5288849 discloses alumina-based adsorbents containing at least one compound of an alkali or alkali earth metal. FR-E-73525 describes the use of an alumina-based adsorbent to eliminate metal compounds from a medium that contains polyolefins. This document gives no information on the characteristics of the alumina used, other than its grain size. US-A-306728 describes catalysts or catalyst carriers based on alumina gels. It does not teach the use of alumina as adsorbent for organometallic compounds, or the characteristics of the alumina needed for this use. EP-A-03 79394 describes the use of an alumina doped by alkaline earth metals for the adsorption of organometallic compounds in the presence of olefins, but does not disclose the specific characteristics of the alumina used in the process according to the present invention; this is also the case for DE-A-36029802. The present invention seeks to provide alumina-based adsorbents for the adsorption of chelated organometallic compounds, which adsorbents exhibit a degree of adsorption which is improved relative to those of the prior-art products, and especially relative to the alumina beads resulting from a shaping operation using rotating technology. Thus the present invention provides a process for the adsorption of chelated organometallic compounds which comprises contacting said compounds with an alumina-based adsorbent, said adsorbent resulting from shaping by coagulation in droplets or by extrusion or being obtained by crushing, and said adsorbent having a volume of pores with a diameter greater than 80 A of at least 0.15 cm3/g and a particle size of less than 4 mm. The invention additionally provides an alumina-based adsorbent comprising a chelated organometallic compound which has been obtained by the process defined above. The invention also provides the use of an alumina-based adsorbent as defined above as a catalyst. The adsorption process according to the invention can employ adsorbents which may be in various forms. First of all, these adsorbents may be alumina beads resulting from shaping by coagulation in droplets. This type of bead can be prepared, for example, by a process according to the teaching of EP-B-15,801 or EP-B-97,539. The porosity can be controlled, in particular, according to the process described in EP-B-97,539 by coagulation in droplets of an aqueous dispersion or suspension of alumina or of a solution of a basic aluminium salt which is in the form of an emulsion consisting of an organic phase, an aqueous phase and a surfactant or emulsifier. Said organic phase may in particular be a hydrocarbon, while the surfactant or emulsifier is, for example, Galoryl EM 10®. The adsorbents may also be crushed alumina. These crushed forms may be the result of the crushing of any type of alumina-based material such as, for example, beads obtained by any type of process (e.g. coagulation in droplets, film coater or rotating drum) or extrudates. The porosity of these crushed forms is controlled by the choice of the alumina-based material which is crushed in order to obtain them. Finally, the adsorbents may be alumina extrudates. These can be obtained by kneading and then extruding an alumina-based material, which may have resulted from, for example, the rapid dehydration of hydrargillite (flash alumina) or from the precipitation of an alumina gel. The porosity of the extrudates can be controlled by the choice of alumina employed and by the conditions for the preparation of this alumina, or by the operating conditions for the kneading of this alumina prior to extrusion. The alumina can accordingly be mixed with pore-forming agents in the course of kneading. By way of example, the extrudates can be prepared by the preparation process described in US-3,856,708. The process according to the invention employs adsorbents having a volume of pores with a diameter greater than 80 A of more than 0.15 cm3/g, preferably more than 0.3 cm3/g and, with even greater preference, of more than 0.4 cm3/g. The volume of pores with a diameter greater than 80 A represents the cumulative volume of all of the pores with a size greater than a diameter of 80 A. This volume is measured by the mercury penetration technique in which Kelvin's Law is applied. In the case of shaping by coagulation in droplets, the particle size corresponds to the diameter of the beads; in the case of extrudates, it corresponds to their cross-sectional diameter, and in the case of crushed forms, it corresponds to the length of their larger section. The adsorbents employed have a particle size of less than 4 mm. In the case of beads shaped by coagulation in droplets or of extrudates, it is possible advantageously to use adsorbents with a particle size of less than 3 mm, and still more advantageously less than 2.4 mm. Preferably, the process according to the invention employs adsorbents comprising at least one alkali metal or alkaline earth metal compound. This compound may, for example, be an oxide, a hydroxide or a salt of the element or a mixture of these. By way of example it is possible to mention, in addition to the hydroxides, the sulphates, nitrates, halides, acetates, formates and carbonates and, more generally, the carboxylic acid salts. Use is preferably made of elements chosen from sodium, potassium and calcium. The content of the alkali metal or alkaline earth metal compound may, for example, be from 15 mmol to 7 50 mmol per 100 g of alumina, preferably from 15 to 500 mmol per 100 g of alumina, and still more preferably from 15 to 150 mmol. These compounds can be incorporated according to the teaching of EP-A-379,394. According to a first, preferred embodiment of the process according to the invention, crushed forms are used which have a specific surface area of greater than 200 m2/g. This specific surface area is a BET surface area. The term BET surface area is understood to be the specific surface area determined by an adsorption of nitrogen in accordance with ASTM standard D 3663-78, established on the basis of the Brunauer - Emmett - Teller method described in "The Journal of the American Society", 6j0, 309 (1938). In the case where the process employs adsorbents obtained by crushing, those used preferably have a specific surface area of greater than 200 m2/g. When the process according to the invention employs beads or extrudates, it is advantageous for the specific surface area to be at least 20 m2/g. The process according to the invention makes it possible to obtain improved degrees of adsorption of the chelated organometallic compounds, which may reach more than 7 5%, this degree representing the proportion of metal adsorbed by the beads relative to the initial quantity of metal introduced into the reaction medium, under the conditions defined in the adsorption test below. The present invention relates more particularly to the process employing the adsorbents described above for the adsorption of any chelated organometallic compound, more particularly those based on metals chosen from groups IVB, VB, VIB, VIIB, VIII, IB and IIB of the Periodic Table, and still more particularly those based on vanadium, titanium, zirconium or copper. The process according to the invention is particularly suitable for the adsorption of any organometallic compound which has been chelated by organic compounds such as acetylacetone, 2-ethylhexane-l,3-diol or di-2-ethylhexyl phosphate. Consequently, the process according to the invention is suitable for the purification of polyolefins obtained by polymerization of olefins in the presence of a coordination catalyst system. The purification process can be of the type described above in the introduction to the present description, in which the adsorbents are contacted with the actual medium resulting from the polymerization, which has been brought together with organic compounds beforehand. In the process according to the invention, said alumina-based adsorbents are contacted with the organometallic compounds and adsorb them. At the end of the process of adsorption of the organometallic compounds, the adsorbents are withdrawn from the reactor to give alumina-based adsorbents on which the organometallic compounds are adsorbed. These adsorbents can be employed directly as supported metal catalysts in any type of precious-metal catalysis which is suited to the nature of the adsorbed metal. Accordingly, the present invention relates to a process for preparation of alumina-based adsorbent for adsorbing chelated organometallic compounds wherein metals chosen from vanadium, titanium, zirconium and copper and chelating agents chosen from acetylacetone, 2-ethylhexane-l,3-diol and di-2-ethylhexyl phosphate which comprises the following steps: (i) preparing an alumina-based adsorbent by shaping by coagulation in droplets, by extrusion or by crushing; and (ii) contacting the chelated organometallic compounds with the alumina-based prepared in (i) above, characterized in that the adsorbent has a volume of pores having a diameter greater than 80 A of at least 0.15 cm3/g and a particle size of less than 4 mm. The examples which follow further illustrate the invention. EXAMPLES Adsorption test The adsorption tests were conducted on adsorbents which had been activated beforehand at 300°C for 2 h in order to remove any trace of humidity following their storage and in order to enable a comparison to be made of their-efficiency under identical conditions. The adsorbents were introduced into a beaker which contained vanadium chelated with acetylacetonate (VO(acac)2), which was present in 2 00 ml of toluene at a concentration of 0.1% (by weight relative to the volume of toluene). They were left with stirring and in contact with the compound for 48 h at 25°C in the absence of air. The degree of adsorption of the vanadium chelated with acetylacetonate by the alumina was measured by the change in the concentration of the solution, as measured by UV-visible spectroscopy. EXAMPLE 1 - Crushed alumina. Adsorbents 1 to 5 were obtained by crushing alumina beads obtained by shaping alumina resulting from the rapid dehydration of hydrargillite by rotating technology. (Table Removed) It was noted that the crushed forms of alumina having a volume of pores with a diameter greater than 80 A of more than 0.2 cm3/g and a particle size of less than 4 mm, have a high degree of adsorption. EXAMPLE 2 - Beads of alumina shaped by coagulation in droplets, and extruded alumina beads. The adsorbents tested were shaped either by coagulation in droplets from an alumina resulting from the precipitation of an alumina gel (adsorbent 8) or by extrusion of this alumina gel (adsorbents 6 and 7). (Table Removed) It was noted that these adsorbents, which have a volume of pores with a diameter greater than 80 A of more than 0.2 cm3/g and a particle size of less than 4 mm, have a high degree of adsorption. COMPARATIVE EXAMPLE 3 – Alumina beads resulting from shaping in a rotary film coater. (Table Removed) It was observed that alumina beads obtained by shaping of alumina resulting from the rapid dehydration of hydrargillite in a rotary film coater have a degree of adsorption which is less than that of the adsorbents according to the invention. CLAIM: 1. A process for preparation of alumina-based adsorbent for adsorbing chelated organometallic compounds wherein metals chosen from vanadium, titanium, zirconium and copper and chelating agents chosen from acetylacetone, 2-ethylhexane-l,3-diol and di-2-ethylhexyl phosphate which comprises the following steps: (i) preparing an alumina-based adsorbent by shaping by coagulation in droplets, by extrusion or by crushing; and (ii) contacting the chelated organometallic compounds with the alumina-based prepared in (i) above, characterized in that the adsorbent has a volume of pores having a diameter greater than 80 A of at least 0.15 cm3/g and a particle size of less than 4 mm. 2. A process as claimed in claim 1, wherein the said aluminium-based adsorbent comprises at least one alkali metal or alkaline earth metal compound. 3. A process as claimed in claim 2, wherein the alkali metal or alkaline earth metal compound is present in an amount of from 15 mmol to 750 mmol per lOOg of alumina. 4. A process as claimed in any of claims 1 to 3, wherein the said alumina-based adsorbent comprises coagulated droplets or extrudates and has a specific surface area of at least 20 m2/g. 5. A process as claimed in any of claims 1 to 3, wherein the said alumina-based adsorbent comprises crushed forms and has a specific surface area of greater than 200 m2/g. 6. A process as claimed in any of claims 1 to 3 and 5, wherein the said alumina-based adsorbent comprises crushed alumina beads. 7. A process for adsorbing chelated organometallic compounds substantially herein before described with reference to the foregoing Example 1 or 2.

Documents:

1485-del-1996-abstract.pdf

1485-del-1996-assignment.pdf

1485-del-1996-claims.pdf

1485-del-1996-complete specification (granted).pdf

1485-del-1996-correspondence-others.pdf

1485-del-1996-correspondence-po.pdf

1485-del-1996-description (complete).pdf

1485-del-1996-form-1.pdf

1485-del-1996-form-13.pdf

1485-del-1996-form-2.pdf

1485-del-1996-form-3.pdf

1485-del-1996-form-4.pdf

1485-del-1996-form-6.pdf

1485-del-1996-gpa.pdf

1485-del-1996-petition-137.pdf

1485-del-1996-petition-138.pdf