WO2006077055A1 - Procede pour supprimer des monomeres residuels qui sont contenus dans du polyoxymethylene, par application d'une surpression - Google Patents

Procede pour supprimer des monomeres residuels qui sont contenus dans du polyoxymethylene, par application d'une surpression Download PDF

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Publication number
WO2006077055A1
WO2006077055A1 PCT/EP2006/000290 EP2006000290W WO2006077055A1 WO 2006077055 A1 WO2006077055 A1 WO 2006077055A1 EP 2006000290 W EP2006000290 W EP 2006000290W WO 2006077055 A1 WO2006077055 A1 WO 2006077055A1
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degassing
pressure
temperature
pom
bar
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PCT/EP2006/000290
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German (de)
English (en)
Inventor
Knut ZÖLLNER
Jessica Rylander
Jens Assmann
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Basf Aktiengesellschaft
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Publication of WO2006077055A1 publication Critical patent/WO2006077055A1/fr

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    • C—CHEMISTRY; METALLURGY
    • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
    • C08G—MACROMOLECULAR COMPOUNDS OBTAINED OTHERWISE THAN BY REACTIONS ONLY INVOLVING UNSATURATED CARBON-TO-CARBON BONDS
    • C08G2/00—Addition polymers of aldehydes or cyclic oligomers thereof or of ketones; Addition copolymers thereof with less than 50 molar percent of other substances
    • C08G2/12—Polymerisation of acetaldehyde or cyclic oligomers thereof
    • C—CHEMISTRY; METALLURGY
    • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
    • C08G—MACROMOLECULAR COMPOUNDS OBTAINED OTHERWISE THAN BY REACTIONS ONLY INVOLVING UNSATURATED CARBON-TO-CARBON BONDS
    • C08G2/00—Addition polymers of aldehydes or cyclic oligomers thereof or of ketones; Addition copolymers thereof with less than 50 molar percent of other substances
    • C08G2/08—Polymerisation of formaldehyde
    • C—CHEMISTRY; METALLURGY
    • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
    • C08G—MACROMOLECULAR COMPOUNDS OBTAINED OTHERWISE THAN BY REACTIONS ONLY INVOLVING UNSATURATED CARBON-TO-CARBON BONDS
    • C08G2/00—Addition polymers of aldehydes or cyclic oligomers thereof or of ketones; Addition copolymers thereof with less than 50 molar percent of other substances
    • C08G2/10—Polymerisation of cyclic oligomers of formaldehyde

Definitions

  • the invention relates to a process for removing unreacted residual monomers from polyoxymethylene homopolymers or copolymers by the following process steps:
  • the polymer is at a pressure of 10 to 100 bar to a temperature of
  • the melt is degassed at a pressure of 1, 05 to 9 bar and a temperature of 160 to 240 0 C in at least one degassing.
  • the invention relates to the use of this method during or after the preparation of Polyoxymethylenhomo- or copolymers.
  • the invention further relates to a process for the preparation of polyoxymethylene homopolymers or copolymers, which comprises first preparing or storing monomers suitable for use in a monomer system, then polymerizing the monomers in a polymerization reactor to give said polymers, and during or after this polymerization the residual monomers contained in the polymers removed by the above method.
  • the invention relates to the polyoxymethylene homopolymers or copolymers obtainable by the latter method.
  • Polyoxymethylene polymers are obtained by homo- or copolymerization of 1, 3,5-trioxane (trioxane in short), formaldehyde or other formaldehyde source. The conversion is usually not complete, but the POM crude polymer still contains up to 40% unreacted monomers. Such residual monomers are, for example, trioxane and formaldehyde, and optionally comonomers used, such as 1,3-dioxolane, 1, 3-Bjtandiolformal or ethylene oxide. In summary, POM stands for homo- and copolymers.
  • POM is degassed at atmospheric or subatmospheric pressure:
  • EP-A 638 599 describes a process for the preparation of polyacetals in which the residual monomers in a degassing part are vaporized by lowering the pressure: in the examples, vaporization takes place via a throttle valve to atmospheric pressure (page 4, lines 22 and 43).
  • EP-A 999 224 describes the preparation of polyacetal copolymers in which the unreacted monomers are removed by "reduced pressure" and absorbed in a water cycle (page 3, lines 8 and 49 and page 4, line 23) Information on pressure and temperature of the residual monomer separation is not provided.
  • DE-A 31 47 309 discloses the preparation of oxymethylene polymers in which the unreacted monomers are removed by venting to normal pressure or by applying a vacuum - in the example 0.01 bar - in a degassing and confectioning reactor (page 6, line 21) and page 7, line 23).
  • the polymer undesirably foams, which further effects its handling e.g. in the case of additization or preparation, it is more difficult to recycle the separated residual monomers into the POM preparation, but they must be compacted in an intermediate compressor or worked up with the aid of solvents, for example water, and the separated residual monomers must be recycled before reuse
  • the residence time of the POM in the degassing device usually a degassing pot is used - is quite time-consuming liberated from the deactivator used (stopping agent). As a result, the polymer is thermally stressed, which favors unwanted degradation reactions and can lead to adverse discoloration of the material.
  • the polyoxymethylene homopolymers or copolymers (POM) from which the unreacted residual monomers are removed by the process according to the invention are known as such and are commercially available.
  • the homopolymers are prepared by polymerization of formaldehyde or, preferably, trioxane; Comonomers are also used in the preparation of the copolymers.
  • POM polymers have at least 50 mole percent of repeating units - CH 2 O - in the polymer backbone.
  • Polyoxymethylene copolymers are preferred, especially those in addition to the repeating units
  • -CH 2 O- even up to 50, preferably 0.01 to 20, in particular 0.1 to 10 mol% and very particularly preferably 0.5 to 6 mol% of recurring units.
  • R 1 to R 4 independently of one another are a hydrogen atom, a C 1 - to C 4 -alkyl group or a halogen-substituted alkyl group having 1 to 4 C atoms and R 5 is a - CH 2 -, -CH 2 O-, a C 1 - represent C 4 alkyl or C 1 - to C 4 haloalkyl-substituted methylene group or a corresponding oxymethylene group and n has a value in the range of 0 to 3.
  • these groups can be introduced into the copolymers by ring opening of cyclopic ethers.
  • Preferred cyclic ethers are those of the formula
  • R 1 to R 5 and n have the abovementioned meaning.
  • Oxymethylenterpolymerisate for example, by reacting trioxane, one of the cyclic ethers described above with a third monomer, preferably bifunctional compounds of the formula
  • CH 2 -CH - CH 2 - Z is -CH 2 -CH-CH 3
  • Preferred monomers of this type are ethylene diglycide, diglycidyl ether and diether from glycidylene and formaldehyde, dioxane or trioxane in the molar ratio 2: 1 and diether from 2 mol glycidyl compound and 1 mol of an aliphatic diol having 2 to 8 carbon atoms such as the diglycidyl ethers of ethylene glycol, 1 , 4-butanediol, 1, 3-butanediol, cyclobutane-1, 3-diol, 1, 2-propanediol and cyclohexane-1, 4-diol, to name just a few examples.
  • End-group-stabilized polyoxymethylene polymers which have predominantly C-C or -O-CH 3 bonds at the chain ends are particularly preferred.
  • the preferred polyoxymethylene copolymers have melting points of at least 150 ° C. and weight average molecular weights M.sub.w in the range from 5,000 to 300,000, preferably from 7,000 to 250,000, g / mol. Particular preference is given to POM copolymers having a nonuniformity (M w / M n ) of from 2 to 15, preferably from 2.5 to 12, particularly preferably 3 to 9.
  • the measurements are generally carried out by gel permeation chromatography (GPC) -SEC (size exclusion chromatography), the Mn (number average molecular weight) is generally determined by GPC-SEC.
  • the molecular weights of the polymer can be adjusted to the desired values by means of the regulators which are customary in the case of Tn oxanpolymerisation and by the reaction temperature and residence time.
  • Suitable regulators are acetals or formals of monohydric alcohols, the alcohols themselves and the small amounts of water which act as chain transfer agents and whose presence can generally never be completely avoided.
  • the regulators are used in amounts of from 10 to 10,000 ppm, preferably from 20 to 5,000 ppm.
  • Initiators also referred to as catalysts
  • catalysts are the cationic initiators customary in the trioxane polymerization.
  • Proton acids are suitable, such as fluorinated or chlorinated alkyl- and arylsulfonic acids, for example perchloric acid, trifluoromethanesulfonic acid or Lewis acids, for example tin tetrachloride, arsenic pentafluoride, phosphoric pentafluoride and boron trifluoride, and their complex compounds and salt-like compounds, for example boron trifluoride etherates and triphenylmethylene hexafluorophosphate.
  • the initiators (catalysts) are used in amounts of about 0.01 to 1000 ppnri, preferably 0.01 to 500 ppm and in particular from 0.01 to 200 ppm.
  • Suitable solvents for this purpose are inert compounds such as aliphatic, cycloaliphatic hydrocarbons such as cyclohexane, halogenated aliphatic hydrocarbons, glycol ethers, etc. can be used. Particular preference is given to triglyme (triethylene glycol dimethyl ether) as solvent and 1,4-dioxane.
  • cocatalysts can be included.
  • alcohols of any kind e.g. aliphatic alcohols having 2 to 20 C atoms, such as t-amyl alcohol, methanol, ethanol, propanol, butanol, pentanol, hexanol; aromatic alcohols having 2 to 30 C atoms, such as hydroquinone; halogenated alcohols having 2 to 20 C atoms, such as hexafluoroisopropanol;
  • glycols of any type in particular diethylene glycol and triethylene glycol
  • aliphatic dihydroxy compounds, in particular diols having 2 to 6 carbon atoms such as 1, 2-ethanediol, 1, 3-propanediol, 1, 4-butanediol, 1, 6-hexanediol, 1, 4-hexanediol, 1,4-cyclohexanediol, 1, 4-cyclo
  • Monomers, initiators, cocatalyst and, if appropriate, regulators may be premixed in any way or may also be added to the polymerization reactor separately from one another.
  • the stabilizing components may contain sterically hindered phenols as described in EP-A 129369 or EP-A 128739.
  • the polymerization mixture is preferably deactivated directly after the polymerization, preferably without a phase change taking place.
  • the deactivation of the Initiatprreste (catalyst residues) is usually carried out by adding deactivators (terminators) to the polymerization melt.
  • deactivators are, for example, ammonia and primary, secondary or tertiary, aliphatic and aromatic amines, for example trialkylamines such as triethylamine, or triacetonediamine.
  • basic-reacting salts such as soda and borax, furthermore the carbonates and hydroxides of the alkali metals and alkaline earth metals, and also alkoxides, such as sodium ethanolate.
  • the deactivators are usually added to the polymers in amounts of preferably 0.01 ppmw (parts per million by weight) up to 2 wt .-%.
  • alkali metal or alkaline earth metal alkyls are preferred as deactivators which have 2 to 30 C atoms in the alkyl radical.
  • Particularly preferred metals are Li, Mg and Na, with n-butyllithium being particularly preferred.
  • Formaldehyde POM can be prepared in a customary manner by polymerization in the gas phase, in solution, by precipitation polymerization or in bulk (substance).
  • Trioxane POMs are typically obtained by bulk polymerization using any reactors with high mixing efficiency.
  • the reaction can be carried out homogeneously, e.g. in a melt, or heterogeneous, e.g. as polymerisation to a solid or solid granules.
  • Suitable examples are tray reactors, plowshare mixers, tubular reactors, list reactors, kneaders (e.g., Buss kneaders), extruders with, for example, one or two screws, and stirred reactors, which reactors may comprise static or dynamic mixers.
  • kneaders e.g., Buss kneaders
  • extruders with, for example, one or two screws
  • stirred reactors which reactors may comprise static or dynamic mixers.
  • the melted polymer produces a so-called melt seal, whereby volatile constituents remain in the extruder.
  • the above monomers are metered into the polymer melt present in the extruder, taken together or separately from the initiators (catalysts), at a preferred temperature of the reaction mixture of 62 to 114 ° C. Loading vorzugt the monomers (trioxane) are metered into a molten state, for example at 60 to 12O 0 C. Due to the exothermic nature of the process must typically only the polymer are melted in the extruder at the start of the process; Subsequently, the amount of heat released is sufficient to melt the molten POM polymer or to keep it molten.
  • the melt polymerization is generally carried out at 1, 5 to 500 bar and 130 to 300 0 C, and the residence time of the polymerization mixture in the reactor is usually 0.1 to 20, preferably 0.4 to 5 min.
  • the polymerization is preferably carried out to a conversion of more than 30%, for example 60 to 90%.
  • a crude POM which, as mentioned, contains considerable proportions, for example up to 40%, of unconverted residual monomers, in particular trioxane and formaldeyde.
  • Formaldehyde can also be present in the crude POM if only trioxane was used as the monomer since it can be formed as a degradation product of the trioxane.
  • other oligomers of formaldehyde may also be present, e.g. the tetrameric tetroxane.
  • Trioxane is preferably used as the monomer for the preparation of the POM, which is why the withdrawn residual monomers also contain trioxane, moreover usually 0.5 to 10% by weight of tetroxane and 0.1 to 75% by weight of formaldehyde.
  • the process according to the invention can be operated batchwise or, preferably, continuously.
  • step a) of the process according to the invention the polymer (POM) is brought at a pressure of 10 to 100 bar to a temperature of 165 to 27O 0 C, wherein a melt is formed.
  • step a) If the POM is present at the end of the polymerization reactor or the deactivation under these pressure and temperature conditions, the features of step a) are already satisfied. Otherwise, the POM is brought by conventional measures for pressure and temperature adjustment to a pressure of 10 to 100 bar and to a temperature of 165 to 270 0 C. Usually, the temperature of the POM before step a) is below the temperature to be set in step a), ie the polymer is heated in step a). This heating is also called overheating.
  • the POM temperature - in particular in the POM production by melt polymerization - prior to step a) can also be above the temperature to be set in step a); In this case, the polymer is cooled in step a).
  • the pressure is preferably from 15 to 60 bar, more preferably from 17 to 50 bar.
  • the temperature is 170 to 24O 0 C, more preferably 180 to 220 ° C.
  • the pressure is 15 to 60 bar and the temperature is 170 to 24O 0 C; and more preferably, the pressure is 17 to 50 bar and the temperature is 180 to 22O 0 C.
  • the residence time of the polymer in step a) is generally 10 seconds to 30 minutes, preferably 20 seconds to 15 minutes.
  • the temperature control of the polymer in step a) is carried out in the usual way by heat exchangers, double jacket heating (or cooling), tempered static mixers, internal heat exchangers or other suitable devices.
  • the adjustment of the pressure is also carried out in a manner known per se, e.g. by means of pressure control valves or pumps.
  • step a) follows immediately after the polymerization or deactivation. In terms of apparatus, this can be accomplished in a simple manner by directly following the polymerization zone or deactivation zone of the reactor with a tempering zone (eg overheating zone) which adjusts the temperature of step a). This tempering zone can be configured, for example, as a heat exchanger.
  • the pressure of step a) is preferably adjusted by the reactor geometry and the reaction conditions of the POM preparation.
  • the pressure and the temperature of step a) are to be adjusted such that the polymer is in the form of a melt.
  • melt should not exclude that the polymer contains small amounts of solids, for example at most 5% by weight.
  • step b) of the process according to the invention the melt obtained in step a) is degassed at a pressure of 1.05 to 9 bar and a temperature of 160 to 240 0 C in at least one degassing device.
  • the degassing is therefore - in contrast to the methods of the prior art - not in vacuum or at atmospheric pressure, but under pressure instead, namely at least 1, 05 bar (absolute).
  • step b) pressure and temperature are lower than in step a); this is also referred to below as a pressure jump or a temperature jump.
  • the conditions are to be selected in step b) such that the POM is degassed as a melt.
  • the pressure is preferably 1.05 to 8 bar, more preferably 1.05 to 7 bar.
  • the temperature is 170 to 22O 0 C, more preferably 175 to 210 0 C.
  • the pressure is preferably 1.05 to 8 bar and the temperature 170 to 220 ° C.; and more preferably the pressure is 1.05 to 7 bar and the temperature is 175 to 21O 0 C.
  • the pressure in step b) is 5 to 50, in particular 10 to 25, bar under the pressure in step a).
  • the temperature in step b) is from 5 to 50, in particular 10 to 40 0 C below the temperature of step a).
  • the residence time of the polymer in step b) is generally 1 second to 15 minutes, preferably 5 seconds to 3 minutes. In a multi-stage degassing (see below), these times refer to one single stage at a time. Additional residence time can be introduced by connecting pipes. In order to minimize damage to the polymer as a result of thermal stresses, this additional residence time through connecting pipes is preferably a maximum of 30 minutes.
  • the temperature control of the polymer in step b) is usually carried out by means of heat exchangers, double jacket, tempered static mixers, internal heat exchangers or other suitable devices.
  • the adjustment of the pressure is also carried out in a manner known per se, e.g. by means of pressure control valves.
  • the pressure jump can also be achieved by stuffing or pinch tubes or cross-sectional constriction with subsequent re-expansion.
  • degassing suitable degassing flash pots
  • degassing extruder with one or more screws Filmtruder, thin film evaporator, spray dryer and other conventional degassing.
  • Degassing extruders or degassing pots are preferably used. The latter are particularly preferred.
  • the degassing in step b) can be carried out in one stage (in a single degassing device). Likewise, it can be multi-stage - for example, two stages - done in several degassing devices, which are arranged one behind the other and / or in parallel. Preferably, the series-connected arrangement.
  • the degassing devices can be the same or different in type and size.
  • the variant with two (identical or different) Entgasungstöpfen is preferred. Particularly preferred to use two different Entgasungstöpfe one behind the other, wherein the second pot has a smaller volume.
  • the pressure in the first stage is preferably 2 to 18, in particular 3 to 15 and particularly preferably 4 to 10 bar, and in the second stage preferably 1.05 to 4, in particular 1.05 to 3.5 and especially preferably 1, 05 to 3 bar.
  • the pressure range of step b), 1, 05 to 9 bar mentioned in claim 1 is thus achieved only in the second - or in a degassing with more than two stages, in the last - degassing.
  • the temperature generally does not differ significantly from the temperatures already mentioned above for step b).
  • the inventive method is characterized in that in the two-stage degassing b) in the first stage, the pressure 2 to 18 bar and the temperature 160 to 240 0 C, and in the second stage, the pressure 1, 05 to 4 bar and the temperature is 160 to 240 0 C.
  • the residual monomers liberated during degassing are separated off as vapor stream. Regardless of the design of the degassing (single or multi-stage, degassing or extruder, etc.), the residual monomers are usually selected from trioxane, formaldehyde, tetroxane, 1, 3-dioxolane, 1,3-dioxepane, ethylene oxide and oligomers of formaldehyde.
  • the residual monomers separated off by the process according to the invention are drawn off in the customary manner. They can be condensed and recycled to the polymerization.
  • the quantitative ratio of trioxane and formaldehyde in the vapor stream can be varied by adjusting the corresponding pressures and temperatures. The higher the pressure, the greater the proportion of formaldehyde in the vapor stream
  • the degassing according to the invention regardless of whether one or more stages - takes place under overpressure, operating conditions (inter alia, pressure and temperature) can be adjusted, in which the vapor stream can be condensed without expensive prior intermediate compression. However, it is understood that the vapor stream may also be subjected to an additional densification step.
  • step b Due to the high pressure in step b), the temperature can be kept lower there, which advantageously reduces the thermal load on the POM.
  • the degassed POM is usually removed with conventional conveyors from the degassing.
  • Such devices are for example melt pumps, in particular gear pumps.
  • a degassed, low-residue POM is obtained.
  • the residual monomer content of the POM is 0.1 to 10, preferably 0.5 to 7 and particularly preferably 1 to 5 wt .-%.
  • the method according to the invention has, inter alia, the following advantages: Due to the overpressure, the flow behavior of the polymer in the degassing device improves. In particular, it does not foam up, as a result of which the further handling, for example when adding additives or the packaging, is significantly facilitated.
  • a certain minimum filling level is required in the degassing device.
  • the level creates pressure on the gear wheels of the melt pump, which grip and promote the polymer melt.
  • a high level means a long average residence time of the polymer.
  • degassing according to the invention does not require a minimum fill level in the degassing device under overpressure. Rather, it can also be operated without level. This shortens the average residence time of the polymer and narrows the residence time distribution of the polymer in the degassing considerably; the thermal load of the POM is much lower. Unwanted discoloration is minimized in this way. Accordingly, a further advantage of the method according to the invention is the product protection.
  • the deactivator added during the deactivation does not boil and therefore does not or only to a very small extent pass into the residual monomers (vapor stream). Rather, the excess, not chemically bonded deactivator remains predominantly in the degassed POM melt. This eliminates the costly removal of the deactivator from the vapor stream, which would otherwise be required if the vapor stream to be reused in the polymerization. This saved separation of the deactivator from the residual monomers improves the economy of the method according to the invention.
  • the inventive degassing under pressure has the further advantage that the penetration of ambient air or oxygen is avoided in the degassing.
  • POM decomposes in an inert atmosphere at from about 260 0 C, in an oxygen-containing atmosphere, however, already from 160 ° C, which is why in the vacuum degassing according to the prior art even the smallest leaks of the degassing must be avoided.
  • the over-pressure degassing found here is leak-tolerant.
  • the residual monomers can be freed of other impurities.
  • This can be carried out in known purification or separation operations, for example by distillation, rectification, pervaporation, sublimation, crystallization, thermal diffusion, thickening, concentration, evaporation, drying, freeze-drying, freezing, condensation, melting, electrophoresis, etc.
  • Another object of the invention is the use of the above-described method for residual monomer removal (hereinafter "degassing") during or after the preparation of Polyoxymethylenhomo- or co-polymers (in short: POM).
  • suitable monomers are usually first prepared in a so-called monomer plant, e.g. Trioxane from aqueous formaldehyde solution, and / or suitable monomers stored. Thereafter, the monomers are transferred from the monomer plant in a polymerization reactor and polymerized there to POM, as already described above.
  • the crude POM described is obtained, from which the unreacted residual monomers are removed by the degassing process according to the invention.
  • POM method for the preparation of Polyoxymethylenhomo- or copolymers, characterized in that first prepared or stored in a monomer monomer suitable monomers, then polymerizing the monomers in a polymerization reactor to said polymers , and during or after this polymerization, the residual monomers contained in the polymers are removed by the above degassing process.
  • the residual monomers can also be removed during and after the polymerization.
  • the POM process according to the invention accordingly comprises the degasification process according to the invention as a process step.
  • the crude POM obtained is in an extruder or other suitable mixing device with conventional additives and processing aids
  • additives provided in the usual amounts for these substances.
  • additives are e.g. Lubricants or mold release agents, colorants, e.g. Pigments or dyes, flame retardants, antioxidants, light stabilizers, formaldehyde scavengers, polyamides, nucleating agents, fibrous and powdery fillers or reinforcing agents or antistatic agents, as well as other additives, or mixtures thereof.
  • the POM products are already freed from the residual monomers after the preparation of the crude POM, that is to say before the addition of the additives on the extruder, using the degassing method according to the invention, for example by leaving the crude POM leaving the polymerization reactor promotes in a degassing pot (flash pot) or degassing extruder and there separates the residual monomers according to the invention.
  • the POM products are freed from the residual monomers only with the addition of the additives on the extruder or the other mixing device with the degassing process according to the invention.
  • the mixing device for adding the additives may be identical to the degassing device which is used in the degassing process. For example, you can mix in the same extruder, both the additives as well as perform the degassing, so remove the residual monomers.
  • the crude POM from the polymerization reactor can first be conveyed to a degassing apparatus where the residual monomers are separated off according to the invention, and / or thereafter the POM is provided with the additives on an extruder and at the same time the residual monomers are separated off according to the invention.
  • a degassing apparatus where the residual monomers are separated off according to the invention, and / or thereafter the POM is provided with the additives on an extruder and at the same time the residual monomers are separated off according to the invention.
  • the residual monomers removed by the degassing process can be used again as starting materials in the POM preparation, ie recycled (recycled) in the POM process according to the invention. You can adjust the destination of this return of the production plant. For example, one can return the residual monomers directly into the polymerization reactor or in its feed, or return them to the monomer plant.
  • the POM process is preferably characterized in that the removed residual monomers are recycled to the polymerization reactor or to the monomer plant. Of course you can also combine these two variants.
  • the subject of the invention is also the polyoxymethylene homo- or copolymers obtainable by the described POM process.
  • the degassing process according to the invention allows degassing without disturbing foaming of the polymer.
  • the vapor stream does not have to be compressed between re-use nor released from the deactivator. Due to the low residence time in the degassing, the polymer is protected and degradation reactions are reduced. Particularly in the case of two-stage degassing, formaldehyde and trioxane can be withdrawn separately from one another. Leaks in the degasser are far less problematic than in the prior art methods. Examples:
  • the reactor was a 0.255 L volume tubular reactor equipped with static mixers; the reactor temperature (T R ) is given in the table.
  • the amount of perchloric acid shown in the table was mixed in the monomer stream using a 1% by weight solution of 70% by weight aqueous perchloric acid in 1,4-dioxane.
  • a polymerization time (residence time) of 2 min triacetonediamine (as a 0.1% strength by weight solution in 1,3-dioxolane) was metered into the polymer melt as an inactivator with an HPLC pump and mixed in such a way that the deactivator was in 9-fold molar Excess to the initiator was present. After a further residence time of 7 minutes, the polymer melt was released into a degassing pot.
  • step a) of the process according to the invention corresponds to step a) of the process according to the invention - the pressure in the polymer melt (p s ) and the temperature of the polymer melt (Ts) were, see table.
  • the residence time of the melt in the degassing pot was determined. It was also assessed whether foam formed in the degassing pot.

Abstract

L'invention concerne un procédé pour supprimer les monomères résiduels n'ayant pas réagi qui sont contenus dans des homopolymères ou copolymères de polyoxyméthylène. Ce procédé comprend les étapes qui consistent : a) à porter le polymère à une température comprise entre 165 et 270 °C, à une pression comprise entre 10 et 100 bars, ce qui forme une masse fondue ; b) à dégazer cette masse fondue à une pression comprise entre 1,05 et 9 bars, et à une température comprise entre 160 et 240 °C, dans au moins un dispositif de dégazage.
PCT/EP2006/000290 2005-01-18 2006-01-14 Procede pour supprimer des monomeres residuels qui sont contenus dans du polyoxymethylene, par application d'une surpression WO2006077055A1 (fr)

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DE200510002413 DE102005002413A1 (de) 2005-01-18 2005-01-18 Verfahren zur Entfernung von Restmonomeren aus Polyoxymethylenen unter Überdruck
DE102005002413.0 2005-01-18

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Cited By (4)

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Publication number Priority date Publication date Assignee Title
WO2007023187A1 (fr) * 2005-08-26 2007-03-01 Basf Aktiengesellschaft Procede pour produire des homopolymeres ou des copolymeres de polyoxymethylene
US8354495B2 (en) 2008-04-16 2013-01-15 Ticona Gmbh Process for the preparation of oxymethylene polymers and apparatus suitable for this purpose
US8993709B2 (en) 2011-07-15 2015-03-31 Ticona Gmbh Process for producing oxymethylene polymers
CN109906239A (zh) * 2016-11-07 2019-06-18 三菱瓦斯化学株式会社 氧亚甲基共聚物的制造方法

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