DE4435534A1 - Safe continuous prodn. of homogeneous graft polyolefin without sticking - Google Patents

Abstract

In the prodn. of graft polyolefins (I) by contacting ethylenically unsatd. graft monomers (II) and opt. free radical initiator (III) with solid polyolefin particles (IV) in a fluidised bed, steam and opt. 1-8C alkanol vapour is used for fluidisation.

Description

The invention relates to a method for grafting polyolefins in one Fluid bed reactor. It is known to use polyolefins in the presence of free radicals itiators or by radical formation with high-energy rays with polymerized cash monomers, such as. B. ethylenically unsaturated compounds fen.

For example, EP-A-437 808 describes a grafting process in irradiated the polyolefin in solid form by means of electron beams and then be in a reactor with the liquid or dissolved graft monomers sprayed and grafted. According to JP-A-63/90523 or DD-PS-2 75 159 he follows the grafting reaction of polypropylene in aqueous dispersion, where as Ra dical former peroxides or azo compounds can be used. The disadvantage The known grafting process lies primarily in the fact that long reaction times are required, or that the yields of grafted polyolefins are very low are low.

It was therefore the task of an operationally reliable grafting process for Po to find lyolefins in which high-quality grafted polyolefins, ins produce special ones with good homogeneity and with high space / time yield are cash. The problem was solved by using a polyolefin Fluid bed found to carry out the grafting reaction using water steam is fluidized.

The invention accordingly relates to a method for producing ge grafted polyolefins in which ethylenically unsaturated graft monomers and optionally free radical generator with solid polyolefin particles that bil a fluidized bed which are brought into contact, characterized in that the polyolefin Fluid bed by blowing in steam and possibly from C₁ to C₈ Alkanol vapors is fluidized.

With the method according to the invention it is in particular possible to graft Olefin homo- or copolymers in a continuous high process  Space / time yield and with good homogeneity and a large variation range of process conditions while ensuring safe operation even with poorly flowing ones, for gluing to one another and to the walls tend to develop solids. Under process conditions are before especially the reaction temperature, the reaction pressure and the concentrations of the understand the components involved in the reaction.

In addition, the residence time distribution is essential for the Structure and properties of the polymers. For the production of homogeneous It is inevitable for products to have narrow residence time distributions, such as those with the The method according to the invention can be realized.

The polyolefins used for the grafting are by conventional methods such as e.g. B. prepared by solution, slurry or gas phase polymerization. As a polyo Examples of lefins are the homo- or copolymers of ethylene, propylene, 1-butene, 1-hexene, 4-methyl-1-pentene, 1-octene or cyclopentene possible. Be the homo- and copolymers of ethylene, propene and 1-butene are preferred. Be polypropylenes and propylene-ethylene copolymers are particularly preferred.

The grafting is particularly easy if it is immediately after the polymerization takes place. The gas becomes quasi-continuous phase reactor or Po discharged from the flash chamber of a slurry reactor lyolefin with superheated steam of a mixture of water and optionally an alkanol, such as. As methanol or ethanol, in a fluidized stir promoted bed reactor and heated to reaction temperature. The Reacti on is preferred at a pressure of 0.1 to 5 bar, particularly preferably at 0.5 to 3 bar and at a temperature of 60 to 150 ° C, particularly preferred carried out at 90 to 130 ° C.

In addition to methanol or ethanol vapor, this can be used to fluidize the fluidized bed tes water vapor also used vapors of C₃ to C₈ alkanols be set. The use of C₁ to C₄ alkanols is preferred, in particular methanol is preferably added. Water can be used as the fluidizing agent steam either alone or in a mixture with alkanols, where  in the steam mixture of 0.1 to 1.0, preferably 0.4 to 1.0 parts by weight Water and 0 to 0.9, preferably 0 to 0.5 parts by weight of alkanol.

The graft monomers used according to the invention are Vinyl monomers such as those found in EP-A-437 808 or in DE-OS 43 30 356 are described. Typical examples of this are ethylenically unsaturated Tigt carboxylic acids or their derivatives, such as. B. anhydrides, esters, amides, nitri le or halides, vinyl-substituted aromatic or heteroaromatic Compounds or aliphatic vinyl compounds or mixtures thereof. Be preferred graft monomers are compounds from the group of unsaturated Carboxylic acids or their derivatives, the vinyl or divinyl aromatics and aliphatic dienes. Maleic anhydride, styrene, Acrylonitrile, methacrylonitrile, acrylic acid ester and methacrylic acid ester.

If radical formers are used, in particular peroxidic ones Initiators, such as B. perester, diacyl peroxides, for example dilauroyl and di benzoyl peroxide, dialkyl peroxide carbonates, for example diisopropyl and di (2- ethylhexyl) peroxydicarbonate, peroxyketals, alkyl peroxides or diazo compounds conditions such. B. 2,2'-azo-bis (isobutyronitrile). Another possible radical Formers are described for example in EP-A-461 881. Preferred as Radi Calcium formers are organic peroxides with half-lives of 4 to 40 minutes 100 ° C, such as B. t-butyl peroxypivalate, t-butyl peroxy-2-ethylhexanoate and di benzoyl peroxide.

Grafting monomers and radical formers can either directly be the ones to be grafted Polyolefins are added, in a preferred process the Graft monomers and, if appropriate, the radical formers together with the Steam is injected to fluidize the fluidized bed.

The steam mixture blown into the lower part of the fluidized bed exists preferably from 0.1 to 1.0 parts of water, 0 to 0.9 parts of methanol, 0.1 up to 0.9 parts of graft monomers and 0 to 0.03 parts of the radical generator.  

The fluidized fluidized bed preferably consists of polypropylene powder or -Granules. In addition, by blades that are mounted on a shaft, moved and thus prevented from coagulating particularly effectively. By any other suitable internals will be a back mixing of the granules largely prevented.

By usual procedures, such as. B. Lowering Pressure and Increasing temperature, much of the mono dissolved in the grafted polyolefin meren removed. The extracted monomer vapors are compressed, ge cools and fed back to the steam circuit of the reactor.

In a further preferred process, the grafted polyolefins are Following the graft reaction melted and with maleic anhydride (MSA) brought into contact, with a large part possibly not yet implemented Residual monomer is removed. The reaction proceeds particularly in the case of remaining styrene is particularly good. The melting preferably takes place in an extruder, preferably in a twin-screw extruder, the MSA preferably as a solution in a volatile solvent, such as. B. acetone, is added.

The fluid bed can be maintained in either a standing or lying reactor. In Fig. 1, a particularly preferred United process variant with a horizontal reactor ( 1 ) is shown as an example. ( 2 ) denotes the feed of the polyolefin, ( 3 ) a powder separator. The polyolefin powder is fluidized by a circulating gas mixture ( 4 ) which contains water vapor ( 6 ), optionally alkanol vapors, graft monomers ( 7 ) and radical formers ( 8 ). The radical formers and graft monomers are optionally added via suitable evaporators. The ( 5 ) emerging from the reactor ( 1 ) circulating gas, which contains in particular non-absorbed graft monomers, water vapor and possibly alkanol vapors, is compressed with a gas compressor and again promoted ge in the lower part of the reactor ( 1 ). After a residence time of approx. 30 to 150 min, the modified polyolefin, which may contain unreacted graft monomers and free radical formers, passes through a lock ( 9 ) into the after-reactor ( 10 ), through the water vapor ( 6 ), which may contain small amounts contains volatile stabilizers, is promoted in countercurrent. The polyolefin is then continuously conveyed from the after-reactor ( 10 ) into an extruder ( 12 ), where it is melted in the entry zone. At ( 13 ) volatile solvents such. B. acetone or water, the optionally reactive compo nents, such as. B. maleic anhydride, contain ( 14 ) polymer auxiliaries such. B. stabilizers, lubricants, antiblocking agents, fillers, etc. who added.

After virtually all the unreacted graft monomers have been removed by vacuum degassing ( 16 ), the polyolefin melt is granulated with an underwater pelletizer ( 15 ).

example 1

In a stirred with blades fluidized bed reactor (1) m³ having a capacity of 0.4, as it is schematically shown in Fig. 1, were added at (2) 200 kg / h of polypropylene powder (PP homopolymer MFI 3 dg / min, Fa FCD polymers) pneumatically fed. The fluidized bed was maintained with 950 Nm³ / h of a recycle gas ( 4 ) consisting of 40 mol% water, 58 mol% styrene and 2 mol% t-butylperoxy-2-ethylhexanoate (Akzo). The temperature in the reactor was 110 ° C., the pressure was 0.19 bar and the average residence time of the polypropylene was 60 min. The grafted polypropylene was then fed continuously into the after-reactor ( 10 ) (103 ° C., 0.09 bar), in a twin-screw extruder with an L / D ratio of 30 at 250 ° C. with the addition of 0.25 kg / h of a 1: 1 stabilizer mixture of Irgaphos 168 and Irganox 1010 (Ciba) melted and granulated.

No caking was observed in the reactor during the grafting reaction, a homogeneous product with an output of 250 kg / h was obtained.

The styrene-grafted polypropylene had the following characteristics:

MFI (melt flow index at 230 ° C / 2.16 kg): 2 dg / min
E-module (DIN 53452/57): 2100 MPa
Polystyrene content: grafted 10% by mass
8% by weight homopolymer

The polystyrene content was measured by extraction with dichloroethane over 24 h at boiling point in a Soxhlet apparatus. After completing the Extrak tion, the samples were dried under vacuum to constant weight.

Examples 2 and 3

Analogously to Example 1, a polypropylene grafted with styrene was produced, however, the process parameters listed in Table 1 are used were. In Example 3, t-butyl peroxybenzoate was used as the radical generator.  

No caking was found in the reactor. The products received were homogeneous and had the property values listed in Table 2.

Comparative Example V1

Analogously to Example 1, a polypropylene grafted with styrene was produced, however, nitrogen is used instead of water vapor in the cycle gas and the process parameters listed in Table 1 were applied. As Free radical generator was used t-butyl peroxybenzoate.

The product obtained was very inhomogeneous. Due to caking on The reactor had to be taken out of operation after 6 hours.  

Table 1

Grafting conditions

Table 2

Product characteristics

Claims (6)

1. A process for the preparation of grafted polyolefins, in which ethylenically unsaturated graft monomers and optionally free radical formers are brought into contact with solid polyolefin particles which form a fluidized bed, characterized in that the polyolefin fluidized bed by blowing in steam and, if appropriate, from C 1 to C₈ alkanol vapors is fluidized. 2. The method according to claim 1, characterized in that the steam from a mixture of 0.1 to 1.0, preferably 0.4 to 1.0 parts by weight of what water and 0 to 0.9, preferably 0 to 0.5 parts by weight of alkanol. 3. The method according to claim 1 or 2, characterized in that the Graft monomers and, if appropriate, free radical generator together with the Steam is blown into the fluid bed. 4. The method according to any one of claims 1 to 3, characterized in that as polyolefins polypropylenes or propylene-ethylene copolymers be set. 5. The method according to any one of claims 1 to 4, characterized in that as grafting compounds from the group of unsaturated Carboxylic acids or their derivatives, the vinyl or divinyl aromatics and aliphatic dienes can be used. 6. The method according to any one of claims 1 to 5, characterized in that the grafted polyolefins melted and mixed with maleic acid drid, preferably as a solution in a volatile solvent, in con be brought to the beat.