DE1493845A1 - Process for the separation of volatile accompanying substances from epoxy resins - Google Patents

Description

Dipl.-Ing. H.Weickmann, Dipl.-Phys. Dr. K. Fincke Dipl.-Ing. F. A. Weickmann, Dipl.-Chem. B. Huber

8 MUNICH 27, THE ^

HGS MÖHLSTRASSE 22, CALL NUMBER 48 3921/22

P U.95.845.5

INVENTA AG for research and patent exploitation, Zurich / SWITZERLAND

Process for the separation of volatile accompanying substances

Epoxy resins

The present invention relates to a method for separating volatile accompanying substances from curable epoxy resins or I Epoxy resin solutions, d. H. for dehydration, to drive off solvents or unreacted, volatile starting materials.

It is known that epoxy resins can be hardened by reacting polyphenols with epihalohydrins in the presence of alkali hydroxide. Alkali salts are formed as a by-product, which

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must be separated. The alkali salts can be separated off using various known methods. Since that Reaction product in most cases has a relatively high viscosity, "prepares the complete separation of the salts mostly difficulties. You can either wash the reaction mixture repeatedly with water at elevated temperatures or take up the reaction mixture in an organic solvent and wash the organic layer with water until it is free of salts, or else wash the reaction mixture completely dehydrate the anhydrous resin / salt mixture in an organic Pick up solvent, which only dissolves the resin and not the salt, and then the salt by centrifugation or Remove filtration (see S.P. application no. 77 631). This latter method has been used for the technical execution of the Method proved to be the most economical and cheapest. Difficulties only caused the dehydration of the reaction mixture, as it should be carried out completely and in a relatively short time.

The cause of this difficulty in the technical implementation of the salt separation is in particular that the actual condensation carried out in a heated stirred vessel must be, but this is due to the unfavorable ratio of heating surface to content and the poor heat transfer coefficient of the resin is not suitable for complete drainage, as this would take a very long time. One such long period of dehydration of the crude reaction mixture at higher temperatures, however, side reactions can occur

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lead that affect the quality of the finished epoxy resin, such. B. duroh discoloration, change in the degree of condensation and irreversible crosslinking of the resin molecules, which is undesirable before the resin hardens. The same difficulties are caused by evaporation of any superfluous epihalohydrin from the reaction mixture and the driving off of the solvent when the resin is taken up in organic solvents, for example triohloroethylene, to remove the alkali salt obtained during the condensation of the starting materials.

It has now been found that, contrary to expectations, falling film evaporators can be used for the above-mentioned purpose if a special operating mode is adhered to. The method according to the invention for separating volatile accompanying substances from curable epoxy resins or epoxy resin solutions is characterized in that the aqueous resins or resin solutions are heated in a pressure vessel to a temperature which is at least the boiling point of the highest boiling accompanying substance or the highest boiling azeotropic mixture of accompanying substances and then relieved via a pressure control valve in the head of a falling film evaporator ^{, which is heated to 20 - 200 0} C above the boiling point of the highest boiling accompanying substance or azeotropic mixture of accompanying substances, after which the molten aqueous resins or the resin solutions to the Evaporator surfaces flow downwards and are drawn off at the bottom of the evaporator, while the evaporated volatile accompanying substances flow through a pipeline

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discharged and condensed in a condenser «

Not only can crude epoxy resins, i.e. those that contain the alkali salts formed during the condensation of epihalohydrins and polyphenols in the presence of alkali hydroxide, be practically completely dehydrated on the dredged catfish, but other volatile accompanying substances, e.g. not converted during the condensation, can also be practically completely dehydrated Halohydrins or solvents are completely separated from resin solutions. Falling film evaporators are generally only used for the concentration of solutions, but complete dehydration of the relatively high viscosity condensation product can be achieved by changing the usual operating conditions as described above. This fact is all the more surprising as a sohmelzflttseigee resin containing ζ.Β? ^ 5θ wt .- # water at the top of the falling-film evaporator has a viscosity of about 9000 oP and despite the relatively thick film after leaving the falling-film evaporator, only a water content of about 0.19 wt .- ^. In addition, the raw resin has an extremely unfavorable heat transfer coefficient of 125 koal / hour. χ ⁰ O χ m ² .

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example 1

31 »6 1 of a crude epoxy resin, ie a condensation product containing sodium chloride, which was prepared by reacting 1 mol of ρ, ρ'-dihydroxydiphenyldimethylmethane with 1.4 mol of epichlorohydrin and 1.4 mol of NaOH and approx. 30 wt. # Contains water, passed through a pressure vessel in which the resin was heated ^{to 115 ° C.} The molten, aqueous resin heated in this way, which has a viscosity of 9000 cP (absolute), is then released into the head of a full-film evaporator via a pressure-maintaining valve. The evaporator was heated from the outside with heating steam at 208 ^{° C.} The residence time of the resin on the 0.262 m heating surface of the evaporator was less than one minute. The temperature of the resin emerging at the bottom of the evaporator was 152 ^° C. It still had a water content of 0.19% by weight.

Example 2

To separate the sodium chloride from the crude resin dehydrated according to Example 1, the same amount by weight of triohloroethylene was dissolved and the solution was freed from undissolved salt by filtration. The clear solution was let down in a pressure maintaining valve in a falling film evaporator with 0.262 m ² heating surface, which was kept under a pressure of 100 I Dorr. The temperature of the steam used for heating the Pallfilmverdampfers was 218 ⁰ C, and the temperature of the

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drawn by the swamp of the evaporator virtually solventless resin 150 ⁰ O. The thus freed of solvents resin was virtually colorless and had a residual content of Trichlorethylene 0.16

Example 3

Per hour, 19.8 1 of a liquid Reaktionsgemische8 by condensation of 1 Mpl p ^ '- dihydroxydiphenyldimethylmethane with 10 moles of epichlorohydrin (8 mol excess) and 2 moles of alkali was obtained after passage through a Vorwärmgefäss in which it at 95 ⁰ O was heated, expanded via a pressure control valve in the head of a fall-film evaporator with 0.262 m2 heating surface. The pressure in the evaporator was 100 torr. The evaporator-heating steam had a temperature of 200 ⁰ C and taken off at the evaporator sump resin such of 158 ⁰ C, the reaction mixture initially the entire Epichlorhydrinüberschuss containing or resin had after passage duroa ^ the evaporator still a Epiohlorhydringehalt 0.23 Gew .- # and naturally still contained the sodium chloride originally formed during the condensation.

This salt was separated off analogously to the method described in Example 2.

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Claims (1)

Claim Procedures similar to at least the boiling point of the boiling highest accompanying substance or boiling at höohsten azeotropic mixture of accompanying substances corresponds to the separation of volatile accompanying substances from curable epoxy resins or Epoxydharzlösungen, characterized in that the aqueous resins or resin solutions are heated in a pressure vessel to a temperature and then relieved of pressure via a pressure holding valve in the head of a falling film evaporator, which is heated 20 to 20O ⁰ O above the boiling point of the highest boiling accompanying substance or azeotropic Gtemisohes of accompanying substances, after which the sohmelzflüseigen aqueous resins or resin solutions flow on the evaporator surface near the bottom and on The bottom of the evaporator can be drawn off, during which the evaporated volatile accompanying substances are removed through a pipe and condensed in a condenser. 909821/1094 _J η «-.»