BG60545B1 - Adsorbent for polyolefine purification and method for its preparation - Google Patents

Abstract

The absorbent is used for the purification of polyolefines produced by polymerization in the presence of coordination catalysts. It contains aluminium oxide and at least one element selected among the alkali and alkali-earth metals having concentrations between 15 and 100 mmols/100 g aluminium oxide and has exceptionally low isomerization capability towards olefines. The absorbent is produced when aluminium oxide is impregnated with a compound of the above-mentioned elements with subsequent drying and heat treatment for the stabilization of its surface.

Description

^{1 The} invention relates to an aluminum oxide adsorbent for the purification of polyolefins obtained by polymerization of olefins in the presence of a coordination catalyst system and a corresponding reaction medium in this polymerization method.

The polymerization of olefins is usually carried out in the presence of polymerization catalysts containing elements of the IVB, VB, VIB of the batch system and, above all, vanadium, titanium and zirconium. These catalysts also include, as reducing agents, organometallic compounds (alkylmetallic), metal hydrides or metal hydroxides. These catalysts are commonly referred to as transition metal catalysts and have high catalytic activity in the polymerization of olefins.

The resulting polyolefins are contaminated with metal residues derived from these catalysts and it is inconceivable to purify them before use to remove any discoloration, degradation and toxicity reduction.

In addition, methods for the polymerization of olefins typically involve the step of recovering the solvents or monomers contained in the polyolefins, with these solvents and monomers being recycled in the polymerization step. The presence of metals in these compounds causes corrosion of the installation.

It is known that adsorbents, and in particular aluminum oxide, are used to purify these olefins.

Among the adsorbents used are those which are spherical, which are easier to handle, as well as powders or pieces of different shapes. In fact, the product in the form of spherical can be a carrier, both for filling and for emptying purification columns through pneumatic systems.

Among the adsorbents, aluminum oxide can be easily converted to spherical, but aluminum oxide, which is interesting for its easy handling and because of its good properties for adsorbing metals, has one major disadvantage, namely that it favors the isomerization of solvents containing in polyolefins such as butene-1. Subsequently, recovered solvents cannot be completely recycled and often need to be further purified) to remove the isomerized products.

The invention aims to eliminate these disadvantages by offering an aluminum oxide-based adsorbent with low isomerisation capacity and which can be easily converted into spheres and, usually in shape, easily utilized.

To this end, the invention provides an aluminum oxide-based adsorbent for the purification of olefins, wherein the aluminum oxide contains at least one compound of an element of the alkali or alkaline earth group in an amount of 15 and 100 mmol of the element per 100 g of aluminum oxide.

Unless otherwise stated, concentrations are expressed in millimoles of the element per 100 g calcined at 300 ° C for 3 hours of alumina.

This adsorbent has poor isomerization capacity for olefins.

The isomerisation capacity of an adsorbent is determined

5 by the following test: . ·.-5 / The ability of these products to be isomerized is determined by determining the ability of butene-1 to isomerize to cis- and trans-butene-2. 1 For this purpose, 500 mg of ground adsorbent (particle size between 400 and 500 microns) is introduced into the reactor. The product was placed for 2 hours at 250 ° C under purge with helium at a flow rate of 2.5 l / h. The product was then placed at 400 ° C and inserted 1 ml of butene in helium stream. -.-4 The analysis by chromatography of the gas leaving the outlet allows you to determine the amount of butene-i as well

of cis- and trans-butene-2.

The theoretical equilibrium thermodynamic constant K _m (T) is calculated and the actual equilibrium constant K _m is determined by the results of the measurements.

[cis-butene-2] _is + [trans-butene-2] _is [butene-1] _is + [cis-butene-2] _is + [trans-butene-2] _is [cis-butene-2] + [ trans-butene-2]

K (T) [butene-1] + [cis-butene-2] + [trans-butene-2]

T is the temperature of the butene at the outlet of the reactor and the other quantities are the concentrations at the outlet of the reactor or at equilibrium [] θ at the temperature T.

The isomerization capacity or percentage isomerization A (T) is given by the following Formula:

K (T)

A (T) = ----------- X 100

K _t (T)

According to the invention, the compound of the element is its oxide, hydroxide or salt, or a mixture thereof.

As examples of compounds, they can also * 4

to cite hydroxides, sulfates, nitrates, halides, aietates, formates, carbonates and most commonly salts of carbolic acids.

Preferred compounds according to the invention are hydroxides and chlorides. The latter have an important economic advantage, leading to an adsorbent having

very low isomerization rate.

It is also possible to use a mixture of elements, the total content of the elements being between 15 and 100 mmol per 100 g of alumina.

Among the appropriate elements, preferred ones can be

cite sodium, potassium and calcium.

However, when potassium is selected, the content of this element is preferably between 15 and 80 mmol.

As suitable aluminum oxides according to the invention

Ϊ Aluminum oxides having a specific surface area can be cited to obtain an acceptable amount of metal adsorption. The specific surface area of aluminum oxide is greater than 50 m ^g / g.

These aluminum oxides are obtained by conventional methods, such as by the precipitation or gel method and the rapid dehydration method of aluminum hydroxide.

? The latter aluminum oxides are preferred according to the invention.

,. _Mr. | The incorporation of an element or elements into aluminum oxide may be accomplished by any method, such as co-precipitation, precipitation of the element with aluminum oxide, or impregnation with a solution of the compound or compounds of the element or elements,

'-.G r ··, * te.

According to a preferred feature of the invention, the method for producing the adsorbents consists in impregnating the aluminum oxide, preferably in the form of spheres with an aqueous solution of the salt or hydroxide of the inclusion element, then washing the aluminum oxide and optionally subjecting it to heat treatment. stabilization of the specific surface

aluminum oxide.

This heat treatment is carried out at a temperature determined as a function of either the temperature of use of the adsorbent or the desired specific surface.

It is also possible to carry out heat treatment at a higher temperature to achieve at least partial thermal decomposition of the compound, for example in the form of oxide.

However, this decomposition is optional and no

example, especially when compounds such as chlorides, nitrates and hydroxides are used.

The adsorbent according to the invention is particularly useful for the purification of polyolefins obtained by polymerization-

tion of olefins in the presence of coordination catalysts by adsorption of metals derived from these catalysts.

In addition, the olefins contained in the reaction mixture are purified without isomerization and can be completely recycled.

The invention is illustrated by the examples given below.

t

The adsorbents described below are obtained by treating agglomerated in beads 1.5 to 2.5 mm in diameter with aluminum oxide having a specific surface area of 295 square meters, m / g, measured by BET, full free pore volume 0, 5 cubic centimeters / g and whose residual sodium content is between 0, 2 and 0, 4 wt. / ..

These aluminum oxide beads are manufactured by

Societe Rhone-Poulenc under the trade name ”A 1.5-2.5,

These beads of aluminum oxide are then reactivated in air for 3 hours at 300 ° C, then ^g impregnated with a solution of a salt of the element or elements or saedizShtyZ pertain to requirements such as a hydroxide of the element. The volume and concentration of this solution were determined to give

the desired concentration of the element in alumina.

The impregnated products were then air-dried at 110 ° C for 12 hours.

Their isomerization capacity is determined using the test described above.

The individual results and characteristics of the adsorbents are presented in the table below.

Uh:

I

'Uh' • ua.G, · X diss i Bone on X in adsorbent 1 evil / 1SSrA ^ O- Ъ V V- Crisis ability A £ 1 (2) - - 0 63 % 2 On NaOH 25 14 % 3 On NaOH 62 5 % 4 (1) On NaOH 250 54 % 5 to KOH ²⁶ 8 % 6 X KOH 68 14 % 7 X KOH 15 16 % 8 (2) A Ca. Ca (COOCH3) 2 44 13 % 9 (2) </ Ca. Ca (OOCCH ₃ ) 2 18 21 % 10 (2) On NaOOCCH3 36 9 % 11 (2) On CH3COONA 90 9 % 12 On NaCl UJ 1 % 13 (1) On NaOH 12 42 % 1 * 4 (15 X KOH 130 77 % 15 (2) Li CH3COOLi 45 14 % 16 (2) Sr Sr (OOCCH ₃ ) 2 65 36 % 17 (2) Mg Mg (00CH _{3) 2} 65 36 % 18 Ca CaC12 45 11 %

/ 1 / comparative experience / 2 / yo! : ρ: OSO ^, * '? ; sa ssd spr stopped t

The results clearly show that aluminum oxide, including an element such as sodium, potassium or calcium, has a distinct lower isomerisation capacity than unprocessed aluminum oxide (Example 1). In addition, these examples also say that a decrease in the isomerization capacity of alumina is achieved in a particular concentration range.

Thus, untreated aluminum oxides containing sodium as impurity are inappropriate since the sodium concentration is very low.

I i

The same applies to aluminum oxides with a high sodium content (5% or more), used mainly for the adsorption of acidic impurities.

Aluminum oxides containing elements such as lithium, strontium and magnesium also have a pronounced reduced isomerisation capacity than that of untreated aluminum oxide.

Claims (10)

An aluminum oxide-based adsorbent for olefin purification, characterized in that it contains at least one compound of an element of the group of alkali or alkaline earth metals, said element being contained in a concentration between 15 and 100 mmol per 100 g of aluminum oxide. An adsorbent according to claim 1, characterized in that the compound of this element is its oxide, hydroxide or salt. An adsorbent according to claim 1 or 2, characterized in that the compound of this element is its sulphate, nitrate, halide, acetate, formate, carbonate or carboxylic acid salt. An adsorbent according to any one of claims 1 to 3, characterized in that the compound of this element is its chloride or hydroxide. An adsorbent according to any one of claims 1 to 4, characterized in that the element is selected from the group consisting of sodium, potassium and calcium. An adsorbent according to claim 5, characterized in that the sodium is present at a concentration of between 15 and SO mmol per 100 g of alumina. An adsorbent according to one of the preceding claims, characterized in that the alumina has a specific surface area greater than 50 square meters / year. An adsorbent according to one of the preceding claims, characterized in that it is in the form of spherical. .Jr. one of the preceding claims, characterized in that aluminum oxide is obtained by rapid dehydration of aluminum hydroxide. 10. An adsorbent according to one of the preceding claims, characterized in that it is used for the purification of polyolefins obtained by the polymerization of olefins in the presence of a coordination catalyst system. Process for the preparation of an adsorbent according to claim 1, characterized in that the aluminum oxide is impregnated with a solution of the compound of element A with subsequent drying of the impregnated aluminum oxide and subjected to thermal treatment to stabilize its surface. 12. The method of claim 11, wherein the impregnation is carried out prior to the formation of the alumina. A method according to claim 11, characterized in that the impregnation is carried out after the formation of alumina.