JPH0441465A - Recovery of phenols - Google Patents

Abstract

PURPOSE:To extract and recover residual phanols by reacting phenols with phosgene in an alkaline aqueous phase, separating generated diphenyl carbonates (DPC) and adding DPC to residual aqueous phase. CONSTITUTION:Phenols are reacted with phosgene in an alkaline aqueous phase at 5-110 deg.C, preferably 20-100 deg.C and reacted solution is subjected to phase separation to separate to an oil phase containing DPC and phenols and to a water phase containing inorganic salts and phenols. The oil phase is washed with water and subjected to a purification process to separate purified DPC and phenol, then the recovered phenol is reused as a reacting raw material. The water phase separated by phase separation and washed water washed said oil phase are sent to a phenol-exetracting process and unreacted phenol contained in the water phase is extracted using purified DPC as an extracting solvent, then the DPC in which phenol migrated is sent to a purification process, thus phenol is recovered and reused as a reacting raw material.

Description

DETAILED DESCRIPTION OF THE INVENTION Technical Field of the Invention The present invention relates to a novel method for recovering unreacted phenols during the production of diphenyl carbonates from phenols and phosgene.

Polycarbonate resins are used as engineering plastics, laminating resins, coating resins, photographic films and sheets, etc. This polycarbonate resin is manufactured by a method such as a transesterification method using diphenyl carbonates. These diphenyl carbonates have conventionally been produced, for example, by the method described below.

First, phenols are dissolved in an aqueous sodium hydroxide solution. Phosgene is blown into this alkaline aqueous solution to cause the phenols and phosgene to react to produce diphenyl carbonates. Since this diphenyl carbonate is insoluble in water, crude diphenyl carbonate can be obtained by separating the produced diphenyl carbonate from oil and water. High purity diphenyl carbonates can be obtained by washing the crude diphenyl carbonates thus obtained.

In the process of preparing the diphenyl carbonates exemplified above, not all of the phenols used as raw materials react, but they are contained in the alkaline aqueous phase after separating the crude diphenyl carbonates or in the water washing solution of the crude diphenyl carbonates. Approximately a few percent remains in these areas.

Since an aqueous solution containing phenols cannot be released as is, the phenols are recovered.

The method for recovering phenols is to adjust the pH value of the aqueous solution as described above, and then bring the aqueous solution into contact with an organic solvent such as methyl isobutyl ketone, toluene, or cumene to recover the phenol remaining in the aqueous solution. A method has been adopted in which the organic solvent is transferred to an organic solvent phase, the organic solvent phase is separated, and then the organic solvent is removed. By adopting this method, phenols can be effectively recovered, but as part of the organic solvent is transferred to the aqueous phase during this recovery operation, this transferred organic solvent must be further recovered. Must be. In order to recover this organic solvent, a heating evaporation method is adopted, which has the problem of requiring a large amount of energy and being very complicated.

OBJECTS OF THE INVENTION An object of the present invention is to provide a method for efficiently recovering phenols remaining in alkaline water when diphenyl carbonates are produced by contacting phenols with phosgene in water.

Summary of the Invention The method for recovering phenols according to the present invention is a process for producing diphenyl carbonates by contacting phenols with phosgene in an alkaline aqueous phase, and after the produced diphenyl carbonates have been separated, the aqueous phase is recovered. It is characterized by extracting the phenols remaining in the liquid using diphenyl carbonates.

The method of the present invention does not use organic solvents unlike conventional methods for recovering phenols.

That is, in the method of the present invention, since diphenyl carbonates are used as the extraction solvent for phenols,
Separation of the extracted phenols and diphenyl carbonates, which are extraction solvents, can be performed in the step of purifying diphenyl carbonates. Moreover, since diphenyl carbonates are insoluble in water, diphenyl carbonates do not migrate into the aqueous phase during the extraction operation of phenols, which is an essential step in conventional methods. There is no need to perform a step to remove the extraction solvent from post-extraction hydration.

Detailed Description Next, the method for recovering phenols of the present invention will be described in detail with reference to the drawings.

FIG. 1 is a process diagram schematically showing the steps of the phenol recovery method of the present invention. Here, an example is shown in which diphenyl carbonate is produced using phenol as the phenol.

As shown in FIG. 1, in the method of the present invention, phenols and phosgene are reacted as raw materials in an alkaline aqueous phase.

Here, as the phenol, a compound represented by the following formula [r] can be used.

...[I] However, in the above formula [r], R1 each independently represents an atom or group selected from the group consisting of an alkyl group having 1 to 40 carbon atoms, a phenyl group, and an alkylphenyl group. Moreover, m is an integer of 0 to 2, preferably O. Furthermore, n represents O (when n is O, it represents a hydrogen atom) or the number of groups that can be substituted for the phenol represented by this formula [r], and when m is 0, n is , preferably 0 to 5, particularly preferably 0.

Specific examples of such phenols include phenols in which n and m are both O and have no substituents; n is 1. 0 where m is 0 and the substituent is a methyl group
-cresol, m-cresol, p-cresol, o, m, where n is 2, m is 0, and the substituent is a methyl group,
Examples include p-xylenol, naphthol where n is 0 and m is 1, and the like.

In the present invention, the phenols include phenol,
It is preferable to use cresol, naphthol, etc., and phenol is particularly preferable.

In the present invention, phenols and phosgene are contacted in an alkaline aqueous phase.

Here, the aqueous alkaline phase is prepared by adding hydroxides of alkali metals and alkaline earth metals to water. Specifically, lithium hydroxide, potassium hydroxide, sodium hydroxide, calcium hydroxide, tributylamine, triphenylamine, etc. can be used, and sodium hydroxide is particularly preferably used.

This reaction between phenols and phosgene in the alkaline aqueous phase is shown as the "DPC reaction step" in FIG.

The chemical formula for the reaction in the DPC reaction step with , for example, is as shown in the following formula.

2 @OH+COC1゜+2NaOHIn this DPC reaction, phosgene is theoretically used at a ratio of 0.5 mole per mole of phenols, but if this amount is
．． 35-0.70 mol, preferably 0.40-0.60
It can be set within a molar range. In addition, the alkali metal hydroxide is theoretically used at a ratio of 1 mole to 1 mole of phenols, but this amount is 0.9 to 1 mole.
．． It can be set within the range of 2 mol, preferably 1.0 to 1.1 mol.

The reaction temperature of this DPC reaction is not particularly restricted, but is usually 5 to 110°C, preferably 20 to 100°C.
Set within the range. Under such reaction conditions, the reaction time is typically 0.1 seconds to 5 hours.

By using 2 moles of phenols in the PC reaction as described above, theoretically, 1 mole of diphenyl carbonates, 2 moles of sodium chloride, and 2 moles of water are produced.

Furthermore, in addition to the above-mentioned compounds, trace amounts of sodium carbonate, sodium hydrogen carbonate, etc. are produced as by-products.

Since the diphenyl carbonates produced by this DPC reaction are insoluble in water, the produced diphenyl carbonates form an oil phase as the reaction progresses.

However, in the above DPC reaction, the reaction rate of phenols is not 100%, so the oil phase contains unreacted phenols in addition to the generated diphenyl carbonates.

On the other hand, in the aqueous phase, inorganic salts such as sodium chloride, sodium bicarbonate, and sodium carbonate produced or by-produced by the above DPC reaction are dissolved, and a portion of unreacted phenols is present in a few percent (by weight). ) is dissolved at a concentration of about

The reaction liquid obtained by the DPC reaction is then separated into an oil phase and an aqueous phase in a phase separation step. In this phase separation step,
Conventional oil/water separation operations can be utilized.

The separated oil phase is washed with water and then sent to a DPC refining process. In this DPC purification step, the oil phase forming components are separated into diphenyl carbonates (purified diphenyl carbonates) and phenols (recovered phenol) by, for example, distillation. The recovered phenol is recycled to the DPC reaction process and used again as a raw material.

On the other hand, the aqueous phase separated in the phase separation step is sent to the phenol extraction step. Further, the washing water used to wash the oil phase is also sent to this phenol extraction step.

Diphenyl carbonates are then introduced into this phenol extraction step. As the diphenyl carbonates, separately prepared diphenyl carbonates can be used, but usually at least a part of the diphenyl carbonates purified through the above-mentioned DPC purification step is used.

Since this diphenyl carbonate acts as an extraction solvent to extract phenols in the phenol extraction process, it is preferable to use one with a low phenol content. Carbonates are preferably used.

The amount of diphenyl carbonates introduced into this phenol extraction step is usually 0.1 to 10Q1, preferably 0.2 to 10Q1, relative to the IQ of the aqueous solution containing phenols.
It is set within the range of 311.

In this phenol extraction step, an aqueous solution containing phenols and diphenyl carbonates as an extraction solvent are brought into contact to transfer the phenols contained in the aqueous solution into the diphenyl carbonates, and then the diphenyl carbonates are separated. to recover phenols.

In this phenol extraction step, contact between the aqueous solution containing phenols and the extraction solvent diphenyl carbonate is sufficient for a relatively short time, usually 1 second to 1 second.
The time is 20 minutes, preferably 10 seconds to 10 minutes. That is, diphenyl carbonates generally decompose into carbon dioxide and phenols when they are in contact with water for a long time, but diphenyl carbonates hardly decompose when they are brought into contact for a short time as described above. Furthermore, phenols can be effectively extracted even with a short contact period as described above. Note that in order to prevent the decomposition of diphenyl carbonates and to increase the extraction efficiency of phenols, the pH value of the aqueous phase is not particularly regulated, but is usually 3 to 3.
10. In particular, it is preferably in the range of 5 to 9.

In addition, in this phenol extraction step, it is preferable to repeat the extraction operation two or more times.

The oil phase consisting of diphenyl carbonates to which the phenols in the aqueous phase have been transferred is separated from the aqueous phase, and then fed to the DPC purification step to separate the diphenyl carbonates and phenols.

The extraction operation can be carried out either batchwise or continuously. As the extractor, mixer-settler type, countercurrent differential type extractor, stirred type and non-stirred stage type extractor can also be used.

The aqueous phase from which the oil phase consisting of diphenyl carbonates has been separated is sent as is to the final treatment step.

That is, since diphenyl carbonates are not dissolved in water, the diphenyl carbonates used as extraction solvents in the above extraction step do not migrate to the aqueous phase. Therefore, by using diphenyl carbonate as an extraction solvent, it is possible to eliminate the extraction solvent dissolved in water, which is an essential step when using conventionally used organic solvents such as methyl isobutyl ketone, toluene, or cumene. The removal process becomes unnecessary. Therefore, in the method of the present invention, the aqueous solution from which phenols have been extracted and separated in the phenol extraction step can be sent to the final treatment step without passing through the extraction solvent removal step.

In this final treatment step, organic substances that may be contained in trace amounts in the aqueous solution are removed. That is, for example,
The aqueous solution discharged from the phenol extraction step is treated using an adsorbent such as activated carbon or activated sludge. By this treatment, organic substances are removed from the aqueous phase, and the aqueous phase is discharged as an aqueous solution of inorganic substances containing sodium chloride as the main dissolved component.

On the other hand, purified diphenyl carbonates from which phenols have been removed in the DPC purification process can be used, for example, as raw materials for producing polycarbonate and the like.

Effects of the Invention In the method for recovering phenols of the present invention, diphenyl carbonates are used as an extraction solvent for phenols from an aqueous phase. The main process, DPC, is used to separate diphenyl carbonates and phenols after extraction.
Purification steps can be used.

Furthermore, since diphenyl carbonates are substantially insoluble in water, there is no need to perform an operation to remove diphenyl carbonates as an extraction solvent from the aqueous phase after the extraction operation.

Therefore, according to the present invention, the process for producing diphenyl carbonates itself is significantly streamlined.

Next, the present invention will be explained in more detail by showing examples of the present invention, but the present invention should not be construed as limited by these examples.

Example 1 Diphenyl carbonate was produced according to the process shown in FIG.

That is, 540 g (13.5 moles) of sodium hydroxide was added and dissolved in 2.2 g of water.

1200 g of phenol was added to this sodium hydroxide solution, and then, while maintaining the temperature of this solution at 85°C,
While stirring, 6.27 moles of 620Q phosgene were bubbled in over 1.5 hours.

An oily product formed as the phosgene was bubbled.

After completing the blowing of phosgene, the reaction solution was allowed to stand, and then an oil phase and an aqueous phase were separated. The pH value of the aqueous phase was 8.4.

Table 1 shows the compositions of the oil phase and water phase.

Measurement method (quantification of phenol) Liquid chromatography (-Takasu Seisakusho, LC-6A)
The amount of phenol in the oil phase and water phase was determined by the following method.

Table 1 Oil phase composition Diphenyl carbonate 91% by weight Phenol 9% by weight Aqueous phase dissolved component composition and pH value Sodium chloride Sodium bicarbonate Sodium carbonate Phenol pH value 23% by weight 065% by weight 1.2% by weight 1% by weight 8.4 The oil phase separated as described above was washed with water, transferred to a DPC purification step, and phenol and diphenyl carbonate were separated by distillation to obtain purified diphenyl carbonate.

Note that the separated phenol was used again as a raw material.

Purified diphenyl carbonate 2.29 obtained in the above DPC purification process was added to the aqueous phase 2.2Q shown in Table 1, stirred at 85°C for 1 minute, and then left to stand for 15 minutes to form the diphenyl carbonate phase. was separated (first extraction operation).

The above extraction operation was performed once again at 85°C (second extraction operation).

Table 2 shows the amount of phenol contained in the separated diphenyl carbonate phase (DPC phase) and the amount of phenol contained in the aqueous phase.

Table 2 First phenol content DPC phase aqueous phase 9900 ppm 10 ppm Second phenol content DPC phase aqueous phase 620 ppm 60 ppm The aqueous solution treated in the phenol extraction step as described above is transferred to the final treatment step and treated with activated carbon. After that, it was discharged.

This discharged water contained substantially no organic substances.

In Example 1, sulfuric acid was gradually added to the aqueous phase after the reaction was completed, and the pH value was adjusted to 6.4 (30'C).
Table 3 shows the results of two phenol extractions using the method described in Example 1.

An experiment was conducted in the same manner as in Example 1.

The results are shown in Table 4.

Table 3 Table 4 1st time phenol content 1st time phenol content DPC phase aqueous phase 9670 ppm 340 ppm DPC phase aqueous phase 17970 ppm 1030 ppm 2nd time phenol content 2nd time phenol content DPC phase aqueous phase 335 ppm 0 ppm DPC phase aqueous phase 1770 ppm 170 ppm Example 3 In Example 1, the amount of purified diphenyl carbonate supplied from the DPC purification step was varied from 2.2Q to 1.2Q. IQ
Example 4 In Example 3, sulfuric acid was added to the aqueous phase after the reaction was completed, except that the extraction operation was performed three times instead of
After adjusting the pH value to 5.3 (30° C.), phenol extraction was carried out twice in the manner described in Example 3.

The results are shown in Table 5.

[Brief explanation of drawings]

FIG. 1 is a process diagram schematically showing an example of the steps of the phenol recovery method of the present invention. Table 5 First phenol content DPC phase aqueous phase 18760 ppm 640 ppm Second phenol content DPC phase aqueous phase 1250 ppm 20 ppm Patent applicant Japan GE Plastics Co., Ltd. Patent attorney Shunichi Suzuki

Claims (1)

[Claims] (1) When producing diphenyl carbonates by contacting phenols with phosgene in an alkaline aqueous phase, the phenols remaining in the aqueous phase after the produced diphenyl carbonates are separated are converted into diphenyl carbonates. A method for recovering phenols, characterized by extraction using.