CS239737B1 - A method for recovering mother liquors from polyphenylene oxide production - Google Patents

Abstract

The invention relates to the production of polyphenylene oxide by oxidative polycondensation of phenol with oxygen catalyzed by copper complexes with nitrogenous bases. In the regeneration of solvents on a rotary film evaporator, the condensate formed during the chemical purification of 2,6-xylenol by reaction with formaldehyde or paraformaldehyde is used as a liquefier of distillation residues.

Description

The invention relates to the production of polyphenylene oxide by oxidative condensation in the presence of a catalytic complex based on metal salts and nitrogen bases in an organic solvent environment.

For economic reasons, it is necessary to regenerate the nitrogen base and organic solvents after the isolation of high molecular weight polyphenylene oxide from the mother liquors. The recovery yield of solvents and especially of the nitrogen base significantly affects the economics of production, since the concentration ratios of these components during polymerization are very unfavorable. The volumes of the main reaction streams and auxiliary substances are in most cases approximately in the relationship:

nitrogenous base dissociator

- - — = 5 to 15 ' - - 0.1 to 0.3 polymer polymer solvent catalyst

- — = 0.01 to 0.1 · - = 0.01 to 0.05 nitrogen base polymer

However, mother liquors contain, in addition to organic components, dissolved oligomers of polyphenylene oxide with a high melting point, which cause difficulties when using a rotary film evaporator.

To ensure the fluidity of the evaporator, which forms a plastic film on the evaporation surface of the film rotary evaporator, organic solvents of polyphenylene oxide with a boiling point at least 10 °C higher than the boiling point of the highest boiling regenerated component of the reaction mixture are added according to CS 187008. Such substances are referred to as thickeners.

It has been shown that, in addition to the price and the ability to ensure the plasticity of the evaporator, the behavior of the plasticizer at high temperatures is a decisive factor. In particular, their transition to distillates is undesirable, as they complicate its further use in the production of polyphenylene oxide and can adversely affect the polymerization reaction or even the properties of the polymer.

Ideal liquefiers are substances with minimal vapor pressure. Therefore, the liquefiers used so far are mainly various high-boiling fractions obtained during the processing of diesel fuel. However, their use is not without problems. Some components of these liquefiers probably form azeotropes with the regenerated substrates.

The subject of the invention is a method for regenerating mother liquors from the production of polyphenylene oxide by oxidative polycondensation of phenol with oxygen catalyzed by copper complexes with nitrogenous bases in the presence of organic solvents of polyphenylene oxide as a fluidizer, in which the condensate formed during the chemical purification of 2,6-xylenol by reaction with formaldehyde or paraformaldehyde is used as a fluidizer.

The source of 2,6-xylenol for the production of polyphenylene oxide is the reaction mixture after the ethylation of phenol, which contains mainly methylphenol, o- _, m-, and p-cresols. To a lesser extent, and quantitatively insignificant, other products of the ethylation of phenol.

Depending on the reaction conditions of the phenol ethylation, the reaction mixture contains a different ratio of o-cresol and 2,6-xylenol. After distilling off a substantial part of the o-cresol, 2,6-xylenol remains in the remainder of the reaction mixture as the main and most important component. Of the other phenol ethyl derivatives, the individual o-, α-, and p-cresols constitute 90 to 95% of the weight of impurities.

Recently, very advantageous procedures for refining crude xylene by the chemical method described in the descriptions of inventions to Czechoslovak copyright certificates Nos. 231 085, 230 842 and 232 834 have been found.

The methods are based on the fact that the by-products accompanying 2,6-xylenol, phenol derivatives having at least one free o-position relative to the phenolic OH-group, can be practically eliminated by heating this mixture with paraformaldehyde, an aqueous solution of formaldehyde or formaldehyde-releasing substances in the presence of catalysts ensuring the condensation of phenol with formaldehyde predominantly in the o-position.

Linear condensates of such phenolic substances with a free o-position with formaldehyde form the main component of the residue after chemical refining of xylenol. In addition, depending on the distillation regime, xylenol is also present in the residue. The melting point of the waste condensate usually ranges from 60 to 90 °C and is essentially determined by the xylenol content.

The condensate is very remeltable and soluble in most organic solvents and their mixtures.

The condensate is non-toxic, does not form deposits, is not corrosive or aggressive and is hygienically harmless.

The main component of the mother liquor evaporation from the preparation of polyphenylene oxide consists of low molecular weight polyphenylene oxides with a melting point above 220 °C. The close chemical structure of these oligomers and residues after refining is probably the cause of their mutual solubility, enabling the described use.

The advantage of this application is the high fluidity of the residue even at relatively low dilution and a significant decrease in the melting point of the mixed evaporator.

A significant advantage of using the refining residue as a liquefier is that the refining residue contains only 2,6-xylenol as volatile components, so that no other undesirable substances enter the distillate from the film rotary evaporator, even at high operating temperatures of the evaporator. This circumstance is essential for achieving high yields.

The procedure is very simple. The hafnating residue dissolves well in mixtures of aromatics with alcohols or in alcohols alone, which are simultaneously used as a solvent for polymerization. This allows easy dosing and control of the feed of mother liquors from polymerization and refining residues through a film rotary evaporator. However, their low melting point allows for possible dosing in the form of a melt. Their use increases the yield of regenerated amides.

The invention will be illustrated by the following examples. X in the examples are by weight. Unless otherwise stated.

Example a/ From the residue after chemical refining of xylenol obtained during the reproduction of example 1 according to Czechoslovak copyright certificate No. 231 085, a 50X solution in alcohol I was prepared.

/ b/ According to example 1a, see Czechoslovak author's certificate No. 167 575, 270 kg of xylenol was polymerized into polyphenylene oxide. After isolation of the polymer and its washing, a mother liquor containing 3.05 g/l of non-volatile substances IX was obtained.

c/ A 50X solution in benzene III was prepared from petroleum fuel oil /UNSN 657 991/.

d/ The solutions were mixed in the volume ratios given in Table 1 and processed together on a film rotary evaporator with an evaporation area of 0.25 m. The main parameters of the experiment were the yield of volatile substances, the melting point of the evaporator and the qualitative composition of the distillate by gas chromatography depending on the evaporator temperature at the given volume ratios of the evaporated solutions (Table 1).

Table 1

Proportion of the fluidizer Temperature on Softening point Note Yield in a mixture with II evaporator evaporator volatile substances I III % by volume °C °C % 0 0 220(1) cannot be processed on an evaporator 0.5 - 130 117 in condensate >94.9 no foreign substances present 1.0 - 130 92 - - >93.3 10.0 - 130 77 - >92 0.5 150 121 traces of 2.6 xy- >96.9 lenol 1.0 - 170 112 0.06% xylene- >99.0 lu 5 120 83 difficult to process-

90.1 heavy contaminated condensate

Comment:

1/ determined after drying to constant weight in a vacuum oven at 60 °C,

Example 2 a/ The residue after chemical refining of xylenol obtained in the reproduction of Example 4 was melted and the melt was maintained at a temperature of t00 °C IV.

b/ According to AO 155 745, example 3, xylenol was polymerized to form polyphenylene oxide. After isolation of the polymer and its washing, the filtrates containing organic solvents were combined and neutralized with a solution of potassium hydroxide in methanol. The mother liquor contained 5.75 g/l of non-volatile substances V.

c/ Melt IV was dosed into mother liquor V. fed to the head of a rotary film evaporator heated to 140 °C by a dosing pump in the ratio given in Table 2. The softening temperature of the evaporator, the yield of volatile substances depending on the amount of dosed melt and the presence of foreign substances were monitored.

Table 2

Amount of melt Temperature Volatile yield Note Presence on V 1 regenerated- softening substances foreign substances of its solution g/1 /1/ /2/ °C /%/ 0 220 Cannot be re- to retreat piece 5 120 99.5 negative 10 108 97 15 79 95.2

Notes: 1/ determined after drying to constant weight in a vacuum oven at 60 °C. 2/ determined by gas chromatography

Claims (1)

SUBJECT OF THE INVENTION Process for the regeneration of mother liquors from the production of polyphenylene oxide by oxidative polycondensation of phenol with oxygen-catalyzed copper complexes of nitrogenous bases in the presence of organic polyphenylene oxide solvents as the liquefaction agent, characterized in