Classifications

• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08F—MACROMOLECULAR COMPOUNDS OBTAINED BY REACTIONS ONLY INVOLVING CARBON-TO-CARBON UNSATURATED BONDS
  • C08F6/00—Post-polymerisation treatments
  • C08F6/001—Removal of residual monomers by physical means
  • C08F6/003—Removal of residual monomers by physical means from polymer solutions, suspensions, dispersions or emulsions without recovery of the polymer therefrom
• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08F—MACROMOLECULAR COMPOUNDS OBTAINED BY REACTIONS ONLY INVOLVING CARBON-TO-CARBON UNSATURATED BONDS
  • C08F20/00—Homopolymers and copolymers of compounds having one or more unsaturated aliphatic radicals, each having only one carbon-to-carbon double bond, and only one being terminated by only one carboxyl radical or a salt, anhydride, ester, amide, imide or nitrile thereof
  • C08F20/02—Monocarboxylic acids having less than ten carbon atoms, Derivatives thereof
  • C08F20/04—Acids, Metal salts or ammonium salts thereof
  • C08F20/06—Acrylic acid; Methacrylic acid; Metal salts or ammonium salts thereof
• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08F—MACROMOLECULAR COMPOUNDS OBTAINED BY REACTIONS ONLY INVOLVING CARBON-TO-CARBON UNSATURATED BONDS
  • C08F20/00—Homopolymers and copolymers of compounds having one or more unsaturated aliphatic radicals, each having only one carbon-to-carbon double bond, and only one being terminated by only one carboxyl radical or a salt, anhydride, ester, amide, imide or nitrile thereof
  • C08F20/02—Monocarboxylic acids having less than ten carbon atoms, Derivatives thereof
  • C08F20/42—Nitriles
  • C08F20/44—Acrylonitrile
• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08F—MACROMOLECULAR COMPOUNDS OBTAINED BY REACTIONS ONLY INVOLVING CARBON-TO-CARBON UNSATURATED BONDS
  • C08F6/00—Post-polymerisation treatments
  • C08F6/006—Removal of residual monomers by chemical reaction, e.g. scavenging
• • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
  • Y10S—TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y10S526/00—Synthetic resins or natural rubbers -- part of the class 520 series
  • Y10S526/919—Catalyst injection technique in addition polymerization processes

Definitions

• the invention relates to a method for reducing the residual monomer content in a liquid polymer system by postpolymerization with the addition of a redox initiator system.
• the polymerization reaction usually only goes up to a monomer conversion of 90 to 99% by weight, regardless of whether the polymerization is carried out in solution, in bulk, in suspension or in dispersion.
• the reasons for the incomplete reaction of the monomers are known to the person skilled in the art (Trommsdorf-Norrish effect, reduction in the rate of diffusion, transfer and branching reactions, etc.).
• the unreacted monomers (“residual monomers”) remaining in the system as a result are undesirable for various reasons (reduction in conversion, polymer contamination, odor, toxicity and / or flammability of the monomers etc.).
• This process step is to be understood below as post-polymerization.
• EP-A 92508 EP-A 241127, EP-A 357287, EP-A 417 960, EP-A 455 379, EP-A 474415 , EP-A 492847, EP-A 522791, EP-A 623659).
• a double aftertreatment is often recommended, in EP-A 9258 even a three times aftertreatment in order to polymerize residual monomers.
• repeated aftertreatment is undesirable in order to be able to use the polymerization reactor again as quickly as possible for its main task.
• the large number of approaches recommended in the prior art also shows that there is no satisfactory solution.
• the success of the corresponding aftertreatment also depends on the size of the reactor used. For example the temperature control and the homogenization behavior of large production reactors are significantly different from that of laboratory reactors, and it is generally not possible to simply transfer the experience described for reducing residual monomers to large production reactors.
• the present invention is based on the object of providing a process which can be carried out on a large scale for successful residual monomer reduction by postpolymerization in a liquid system in a production reactor, which is to be understood as a reactor with more than 20 and preferably more than 100 liters .
• the mixing time ⁇ of the liquid system in the production reactor used is understood to mean the time required to achieve a certain degree of homogenization by mixing and in particular stirring.
• the Schlieren method and the chemical decolorization method are usually used to determine the mixing time.
• the liquid is mixed with a reaction partner and stained with an indicator.
• the second reaction partner is then added and the time at which the color disappears is measured.
• the degree of homogenization present in the color change depends on the excess of the added reaction component.
• the mixing time depends, among other things, on the Reynolds number, which in turn depends on the shape of the reactor, the speed and the type of stirrer, but also on the density and viscosity of the liquid system.
• a scale transfer of the mixing time is difficult and always with errors, since there is no reliable literature data for the calculation of non-Newtonian liquids, such as dispersions.
• the literature see, for example, Ullmanns Encyklopadie der techn. Chemie, 4th edition, volume 2, pages 259 ff, in particular pages 263-264 and Fig. 9) provides idealized relationships for liquids without differences in density or viscosity, one allow rough calculation of a minimum mixing time.
• the Reynolds number of the system can be calculated taking into account the boundary conditions and the mixing time ⁇ can be determined from this:
• the liquid system in the production reactor should have the shortest possible mixing time.
• the added substances must be stirred in effectively. This can be done by a suitable choice of the geometric parameters of the production reactor, the choice of a very effective stirrer with suitable speeds or a combination thereof.
• the mixing time can be reduced by using a wall-mounted spiral stirrer or coaxial stirrer. The use of a multi-stage stirrer with a strong axial mixing effect is also suitable for this.
• a wall-mounted stirrer is understood to mean one in which the ratio of stirrer diameter to reactor diameter, reduced by twice the width of a flow breaker which may be present, reaches at least the value 0.9.
• Each stirrer has a radial, i.e. a direction of flow directed against the reactor wall, the axial direction of flow, on the other hand, is little pronounced in many stirrers.
• the use of a multi-stage stirrer in which a plurality of stirrers are attached along the axial, vertical stirrer axis, increases the axial mixing.
• the highest possible degree of axial mixing is required in order to achieve rapid stirring and to reduce reaction of the reaction component during the mixing time.
• the mixing time can also be reduced by using a wall-mounted MIG or INTERMIG stirrer, an impeller, propeller or disc stirrer or a wall-mounted anchor stirrer or wall-mounted grid stirrer. It is often advantageous to increase the action of the stirrer by baffles, baffles or other flow deflections built into the production reactor.
• stirrer and other reactor internals provide stirrer speed, viscosity, density, reagent species and governance regimes concentration and 'the metering significant mixing time influencing optimizable factors.
• the viscosity of the fluid medium takes exceptionally high influence on the Mischzeitver- keep the reactor. For this reason, in the case of heterophasic polymers, ie polymer dispersions and polymer suspensions, »Rf * Ul u ⁇ to t F"
• Suitable reducing agents are ascorbic acid, iso-ascorbic acid, organic compounds with thiol or disulfide groups, reducing inorganic alkali and ammonium salts of sulfur-containing acids, such as sodium sulfite, disulfite, thiosulfate, hydrosulfite, sulfide, or hydrosulfide -dithionite, form amidinsulfinic acid, hydroxymethanesulfinic acid, acetone bisulfite, amines such as ethanolamine or endiols.
• Gaseous oxidizing agents such as oxygen, ozone or air or gaseous reducing agents such as sulfur dioxide can also be used as reaction components of the redox system even under normal conditions.
• the components of the redox system can be metered into the reaction mixture at the same time or in succession (e.g. both from above, one from above, one from below), a spatially separate addition (reactor cover, reactor bottom, reactor side wall) being very advantageous. It is also possible that the reaction mixture already contains sufficient oxidizing agent, reducing agent or metal catalyst from the main polymerization phase, which is generally carried out up to a monomer conversion of 90, in particular 95 and preferably 99,% by weight that in the aftertreatment only the missing component has to be metered in in sufficient quantity.
• the amounts of the redox initiator components used it should be noted that usually amounts of 0.01 to 0.5, in particular 0.05 to 0.4 and preferably 0.2 to 0.3% by weight, based on the Total mass of the monomers used for the main polymerization can be used.
• initiators such as dialkyl or diacyl peroxides, azo compounds, percals or peracetals can also be used as radical sources, or by high-energy radiation or radicals generated by ultrasound.
• the process according to the invention is particularly suitable for reducing the residual monomers in liquid systems of acrylate, methacrylate (esters of acrylic acid or methacrylic acid with C 1 -C 1 -alkanols, in particular C ⁇ -Cs-alkanols, where methyl, ethyl, n- Butyl and 2-ethylhexyl acrylate and methacrylate are particularly preferred), styrene, vinyl chloride or vinyl acetate copolymers, such as styrene-butadiene copolymers or ethylene-vinyl acetate copolymers.
• the monomer mixtures used for the polymerization can also be used in smaller amounts, in particular 0.01 to 10% by weight of the total amount of monomers, polar monomers such as, for example, acrylic acid, methacrylic acid, methacrylamide, acrylamide and / or their N- Methyl derivatives, maleic acid or its anhydride or hydroxy contain alkyl (meth) acrylates.
• polar monomers such as, for example, acrylic acid, methacrylic acid, methacrylamide, acrylamide and / or their N- Methyl derivatives, maleic acid or its anhydride or hydroxy contain alkyl (meth) acrylates.
• the process is particularly suitable for reducing residual monomers in aqueous dispersions.
• the following examples are intended to illustrate but not limit the invention. Unless otherwise stated, parts and percentages are by weight.
• the residual monomer amounts given in the examples were determined by gas chromatography (GC).
• the solids contents (FG) were determined gravimetrically after drying.
• the LD value is the light transmission, a 0.01% by weight sample of the corresponding polymer dispersion with a layer thickness of 25 mm compared to pure water.
• the particle weight distribution (TGV) was determined by capillary hydrodynamic fractionation or using an ultracentrifuge.
• the viscosity of the dispersions was determined using a commercially available rotary viscometer (Rheomat) at a shear rate of 500 / second.
• the mixture was then heated to 80 ° C. and 10% of an initiator solution consisting of 1.23 kg sodium persulfate in 48 kg water was added. After 5 minutes the rest of the monomer emulsion was added over 2 hours, the rest of the initiator solution over 2.5 hours.
• an initiator solution consisting of 1.23 kg sodium persulfate in 48 kg water was added. After 5 minutes the rest of the monomer emulsion was added over 2 hours, the rest of the initiator solution over 2.5 hours.
• Example 3a The procedure is as given in Example la and a sample is taken for residual monomer determination (sample 3A).
• Example 1b The procedure is as given in Example 1b, but an inlet IIIA, which corresponded to inlet IA, is metered in through the reactor lid of the reaction mixture over 5 minutes, and then stirred into the latter for 5 minutes.
• Inlet IIIB which corresponded to inlet IB, was metered in through the reactor base during the 1.5 hour cooling from 80 ° C. to 30 ° C. (metering time 90 minutes).
• samples were taken to determine the residual monomer content (samples 3B, 3C, 3D, 3E, 3F). The results are shown in Table 1.
• Example 4a The procedure was as given in Example 1a and a sample was taken to determine the amount of residual monomers (sample 4A).
• Example 1b The procedure was as described in Example 1b, but an oxidant feed IVA, the composition of which corresponded to the feed IA, and a reducing agent feed IVB, the composition of which corresponded to the additive IB, simultaneously increased continuously during the 1.5 hour cooling time opposite sides through the reactor lid from above the reaction mixture (dosing time of both feeds 90 minutes each). As indicated in Example 1b, samples were taken to determine the amount of residual monomer (samples 4B, 4C, 4D, 4E, 4E). The results are shown in Table 1.
• Example 5a The procedure was as in Example 1a, but the monomer emulsion ME was metered in over 4 hours and the initiator solution over 4.5 hours, and the batch was then kept at the polymerization temperature for 30 minutes.
• Example 5A a sample was used for the determination of the residual monomer content after the main polymerization.
• Example 1b The procedure was as in Example 1b, but the inlets of the redox initiator components VA and VB, which correspond to the inlets IA and IB, were at the same time but spatially separated on opposite sides from above through the reactor lid during a metering time of 60 minutes metered the reaction mixture heated to 80 ° C. After 20, 40 and 60 minutes of dosing, samples were taken from the reaction mixture to determine the residual monomer content (samples 5B, 5C, 5D). The results are shown in Table 1.
• Example 6a The procedure was as given in Example la, and a sample (sample 6A) was taken to determine the residual monomers.
• feed VIA which corresponds to feed IA
• feed VIB which corresponds in its composition to the reducing agent from feed IB
• dosing time 120 minutes. After 20, 40, 60, 90 and 120 minutes, samples were taken to determine the residual monomer content (samples 6B, 6C, 6D, 6E, 6F). The results are shown in Table 1.
• Table 1 Type and time of addition of tert. -Butyl hydroperoxide solution (Ox) and acetone bisulfite solution as reducing agent (Red) in the aftertreatment as well as residual monomer contents of n-butyl acrylate (BA) and methyl methacrylate (MMA) from the product samples taken before and after the aftertreatment
• Example 1 Example 2 Example 3 Example 4 Example 5 Example 6
• a 7-12V monomer emulsion of the following composition was prepared:
• the polymer dispersions prepared were each mixed with 11.5 kg of a 10% strength solution of tert-butyl hydroperoxide. Then a solution of the following reducing agents was metered in over 2 hours: Comparative experiment W: water without reducing agent
• Example 7 18% aqueous solution of ascorbic acid
• Example 8 18% aqueous solution of ascorbic acid
• Example 9 18% aqueous solution of Rongalit® C.
• Example 10 Mix 10% sodium disulfite solution with

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• Chemical & Material Sciences (AREA)
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• Polymers & Plastics (AREA)
• Organic Chemistry (AREA)
• Dispersion Chemistry (AREA)
• General Chemical & Material Sciences (AREA)
• Addition Polymer Or Copolymer, Post-Treatments, Or Chemical Modifications (AREA)
• Polymerisation Methods In General (AREA)

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• 1997
  • 1997-09-18 DE DE19741184A patent/DE19741184A1/de not_active Withdrawn
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