JP3422647B2 - Method for obtaining dialkyl carbonate and bisphenol from polycarbonate - Google Patents

Description

Detailed Description of the Invention

[0001]

[Industrial application] Polycarbonate (hereinafter abbreviated as PC) has excellent mechanical properties, electrical properties, heat resistance, cold resistance, transparency, etc., and is widely used as engineering plastics. It is used for various purposes. The used PC waste material is chemically decomposed and the raw material monomer
If Bisphenol-A (hereinafter abbreviated as BPA) can be recovered, a useful raw material can be obtained and the amount of waste can be reduced.

[0002]

2. Description of the Related Art Generally, when a polymer material is recovered and reused, it has no choice but to be used for very low-valued applications because of deterioration of performance, dirt, etc. After all, they often end up relying on the treatment method of incineration.

PC has an ester bond in the main chain, and from the results of studies on its stability, it is generally found that the ester bond of PC is easily hydrolyzed or alcohol-decomposed in the presence of an acid or basic catalyst. Are known. However, since PC is insoluble in water and alcohol, a severe reaction condition such as a long reaction time or high temperature and high pressure is required to decompose it into a monomer. Therefore, a study has been reported that decomposes PC using a mixed solvent of an aqueous ammonia solution and methylene chloride instead of water [[Recovering bisphenols from scrap po
lyesters ”DWFox et al., US Pat. No. 4,885,407 (198
9)]. Also, a study has been reported in which PC is decomposed in a phenol solvent or a mixed solvent of chlorophenol and methylene chloride in the presence of an alkali catalyst to recover BPA and diaryl carbonate [[Method for recovering bishydroxy a
romatic monomers and bisarylcarbo-nates from scrap
`` aromatic crystals '' SJ Shafer, US Pat. No. 5,
336,814 (1994)], but the separation and recovery process is complicated,
There are also problems in terms of recovery rate and cost. Further, a method of depolymerizing PC into an oligomer in an aryl carbonate in the presence of an alkali or metal oxide catalyst and then synthesizing PC again has been reported [[Cyclic carbonates by the depropagati].
on of carbon '' Q, Li, MABuese, Polym. Mater.
Sci. Eng. 67, pp. 457, (1992)].

However, in any of the above-mentioned methods, as an industrial method for safely and inexpensively processing PC in plastics produced in large quantities and discharged, to obtain valuable dialkyl carbonate and bisphenol. It is clear that it is not satisfactory.

[0005]

SUMMARY OF THE INVENTION In order to solve the above problems, the present inventors have conducted a study on alkaliolysis in lower alcohols, and found an efficient method for transesterification of PC with alkali. As a result of repeated systematic studies and experiments, finally, by using benzene, toluene, xylenes or dioxane for the alcohol added to the system, PC can be used within a short time under relatively mild conditions. It can be decomposed to dialkyl carbonate, the separation operation of bisphenol and solvent is easy, and their recovery rate is also high.
Acquired new knowledge that it can be continuously decomposed and recovered,
The present invention has been completed.

That is, according to the present invention, a solvent such as lower alcohol and toluene is added to PC, a recovered product of PC, or the like, and 2 to 1 is added.
The present invention relates to a method in which bisphenol produced is agitated in the presence of 2 mol% alkali to separate the produced bisphenol as crystals (adding water if necessary), and one dialkyl carbonate produced is recovered by fractional distillation.

[0007]

The above technical problems can be achieved by the present invention as follows. That is,
As the PC, a small particle, a powder, a small piece, an aggregate of these, or a mixture of two or more thereof is used. Examples of the alcohol include methanol, ethanol, propanols, and butanols, and at least one of these alcohols can be used as a mixture of two or more.

Examples of the solvent used for the alcohol include benzene, toluene, xylene, dioxane and the like, and these solvents can be used as at least one or a mixture of two or more. To accelerate the reaction, a solvent of 0.25 is added to the alcohol.
˜0.4 volume ratio may be added. The volume ratio of addition is 0.
If it is less than 25, it takes a long time to disassemble, and if it is 0.4 or more, it takes time to separate and it is disadvantageous in terms of safety and economy. As the alkali used, NaOH, KO
H, Na ₂ CO ₃ , K ₂ CO ₃ , CaO, BaO, ZuO,
Examples thereof include SnO and PbO.

Next, the PC decomposition mechanism functioning in the chemical decomposition reaction of the present invention is extremely specific and characterizes the present invention. The mechanism will be described.

First, even in the same transesterification reaction, if the reaction is carried out using only the methanol solvent, Na
Whereas precipitation of ₂ CO ₃ is produced, in a mixed solvent we have observed that we do not generate this Na ₂ CO _3. The reason can be explained as follows.

The main reason is carbonic acid (pK _a1 = 6, pK _a2 =
10.2), phenol (pK _a = 10), and the difference in acidity of the reaction intermediates. First, PC reacts with an alkali to be converted into an intermediate having carbonic acid monosalt 1 ester and phenolic hydroxyl group (hereinafter referred to as (1)). (1) is further carbonated with NaOH (hereinafter (2)
) And BPA1 salt (hereinafter, (3) referred to hereinafter) to is cleaved, pK _a is (Na ₂ CO ₃ becomes the low since the acid-base balance than that of 3), for this to precipitation of (2) The equilibrium shifts further, producing free BPA. NaO
The amount of H used is a catalytic amount, and when all of this is converted to Na ₂ CO ₃ , BPA is not converted into a phenoxide group.

On the other hand, in the mixed solvent containing toluene or dioxane, the surface of the pellet swells or is partially dissolved. Therefore, since the number of ester bonds involved in the initial alkaline reaction is relatively increased with respect to the amount of the alkali catalyst, many alkaline molecules are consumed by reacting with the ester bonds of PC in the initial stage of the reaction. (1) is generated. However, since there is no excess alkali, (1) reacts with methano-and the N of monomethyl carbonate is reacted.
The a salt and BPA are produced, and the former further reacts with MeOH to produce dimethyl carbonate (hereinafter abbreviated as DMC), and at the same time, alkali is regenerated. Since the alkali regenerated here reacts with PC existing in the system faster than it reacts with DMC in an equilibrium reaction, it is considered that a catalytic reaction cycle is established.

[0013]

EXAMPLES Next, the embodiments of the present invention will be described to further clarify the effectiveness of the present invention. However, the scope of the present invention is not limited only to this description without departing from the gist of the present invention.

[Experimental method] PC has a molecular weight Mw =
2.2 × 10 ⁴ pellet sample [2.2 mm × 3 mm
(Diameter x length)] was used. A mixed solvent of methanol and toluene, or methanol and dioxane (0.6 to 2)
(mL / 0.5-2 mL) into a test tube, and 0.01-
0.063 g (2.4 × 10 ^{−4 to} 1.5 × 10 ⁻³ mo)
1) NaOH was added and dissolved, and then 1.27 g (5 × 10 ⁻³ mol) of PC pellet was added, and 40 to 60
After the PC was completely decomposed by stirring at ℃, the decomposed product in the test tube was put into 40 mL of distilled water (or 5 to 10 mL of toluene) and left at room temperature for about 1 hour to completely crystallize BPA. (In the case of complete decomposition, the crystallization rate of BPA is high especially in the presence of toluene, and complete crystallization takes place within a few minutes). The crystals were not fine and could easily be filtered. After filtration, the product was thoroughly dried at room temperature, and the yield was calculated from its weight. Further, the obtained BPA was FT-
It was analyzed by IR, ¹ H NMR and fluorescent X-ray.

On the other hand, DMC produced by decomposition of PC
Was analyzed by gas chromatography (hereinafter abbreviated as GC). After reacting for a certain period of time, 50 μL of the decomposition solution was sampled, 10 mL of n-pentane was added thereto, and B in the decomposition solution was added.
After precipitating PA (in the case where decomposition has not progressed completely, PC oligomers are included), 1 μL of the supernatant liquid
Was injected into the GC with a microsyringe. The amount of DMC produced was determined by a calibration curve prepared using a DMC standard solution.

Since this PC decomposition method is a transesterification reaction with methanol, in order to completely decompose it into a monomer, an equimolar amount of methanol or more relative to the ester bond of PC is required. Therefore, the relationship with the decomposition efficiency of PC was examined by changing the amount of methanol added in a mixed solvent with toluene.

When the molar amount of methanol added to the ester bond of PC (1.27 g) is 1.0 (1.0
Upon reaction with MeOH (0.4 mL in mL mL) at 60 ° C. for 330 minutes, the PC pellets dissolved and disappeared. However, when analyzed by GC, the amount of DMC produced was only 80% of the theoretical value, and even if the reaction solution was put into water, clean crystals did not crystallize, and a viscous solid substance was obtained. It was shown that PC could not be completely decomposed into monomers. When the molar amount is 1.5 (0.6 mL of MeOH), the PC pellets are almost dissolved in the reaction for 60 minutes.
5% DMC was produced. After reacting for another 60 minutes, D
The amount of MC produced reached 100% and was completely decomposed. When this reaction solution was poured into water and crystallized, 96% of BPA was obtained.

From these results, the PC is completely monomeric.
It was shown that 1.5 mol or more of methanol was required for 1 mol unit of the ester bond of PC in order to decompose up to. However, since BPA dissolves well in alcohol, if the amount of methanol is too large, the crystallization rate when crystallized in water after decomposition is lowered and a large amount of water is required. For example, add MeOH from 0.6mL to 2.5mL
When it was increased to (6.3 mols per 1 mol of ester bond of PC), the crystallization yield of BPA decreased to 91%.
From the results of these experiments, 1.5 to 2.5 mol of methanol was used per 1 mol of ester bond of carbonic acid of PC.
It is believed that the addition of a ruthenium is appropriate. After decomposition, instead of throwing into water to crystallize BPA, 5-10 mL after decomposition
BPA can be rapidly crystallized and separated by adding toluene. Since NaOH solids are mixed in the BPA separated by filtration by this operation, it is washed with water.

[Effect of NaOH Addition] The effect of catalyst concentration on the decomposition of PC was examined by changing the addition amount of NaOH catalyst. Various concentrations of NaOH and 1.27 g of PC were put into 1 mL / 1 mL mixed solvent of methanol and toluene and reacted at 60 ° C., and after 30 minutes, the amount of DMC produced and the amount of PC pellet required for complete decomposition. I asked for the time. The results are shown in FIG. The amount of NaOH is 2.5 to 10 mo for 1 mol unit of ester bond of PC.
It was found that the DMC increased linearly with the increase of the addition amount when it was changed within the range of 1%. Also, N
Addition of aOH is 2.5, 5.0, 7.5, 8.2 and 1
When it was increased to 0 mol%, the time required for complete decomposition of PC pellets was 250, 180, 140, 70 and 30 minutes, respectively. That is, the time required for the complete disassembly of PC also decreased linearly. If the amount of added NaOH increases, P
Although the decomposition rate of C increases, if the addition amount is too large,
As shown in, the crystallization yield decreases. Therefore, the optimum ratio is 5 to 1 unit of —O—CO— bond mole of PC.
It is 10%.

[0020]

[Table 1]

[Additional effect of toluene or dioxane]
First, the decomposition of PC was examined in a solvent containing only methanol. After taking 2 mL of methanol into a test tube and dissolving 0.034 g of NaOH, 1.27 g of PC pellet was added and reacted at 60 ° C. while stirring. As the reaction proceeded, the weight of the PC pellet was slightly reduced, and a white precipitate was formed. However, the weight of the PC pellets hardly decreases from the middle. When a small amount of an acid solution is added to this decomposed solution, the precipitate is dissolved and bubbles are generated, so it can be seen that the precipitate is Na ₂ CO ₃ . However, when PC was decomposed under the same conditions as described above in a mixed solvent system in which 0.5 mL of toluene or 1,4-dioxane was added to methanol, the weight of PC pellets was rapidly reduced with the reaction, It completely dissolved in the solvent after 240 minutes. Moreover, when the amount of toluene added was increased, the decomposition rate of PC also increased, and the time until pellets disappeared was shortened. 0.5 mL for 1 mL of methanol, 1 mL,
If 1.5 mL and 2 mL of toluene were added,
The PC pellets were completely dissolved in the solvent at 230 minutes, 70 minutes, 40 minutes and 15 minutes, respectively.

When toluene or 1,4-dioxane is added, the produced BPA is oxidized under basic conditions and the reaction solution is easily colored, but 0.2 to 1 wt% of PC is used as an antioxidant. This coloring can be sufficiently prevented by adding NaHSO ₃ .

After the PC pellet was completely dissolved, another 3
The reaction was allowed to proceed for 0 minutes or longer, and the decomposed solution was put into about 40 mL of water, whereupon white crystals of BPA were crystallized rapidly. If the reaction was carried out for 330 minutes only in methanol (2 mL), P
The reduction amount of C pellets was only 9%, and only 7% BPA crystals were obtained from the acidic aqueous solution of the decomposition solution. However, in the decomposition in which 0.5 mL of toluene or dioxane was added, about 195% of BPA was obtained by reacting for 270 minutes and then crystallizing in distilled water. Also, 0.5 mL, 1 mL, for 1 mL of methanol,
260 minutes after adding 1.5 mL and 2 mL of toluene
When reacted for 100 minutes, 70 minutes and 45 minutes, 94-
96% BPA was obtained. Further, since the BPA yield did not change even if the reaction was continued for a longer time, it is presumed that the crystallized product contained almost no low-molecular weight oligomer of PC.

[Production of Dimethyl Carbonate] In this PC decomposition method, an alkali addition amount does not require an equimolar amount to the ester bond of PC, and NaOH / PC =
The decomposition proceeds sufficiently with 0.034 g / 1.27 g (1 mol unit of ester bond of carbonate to 8 mol% of NaOH). The decomposition reaction is an ester exchange reaction with alcohol, and when PC is decomposed, DMC is also formed along with the formation of BPA. Therefore, the generated DMC was analyzed by GC.

0.034 g of N in various mixing ratios of solvent
Fig. 2 shows the relationship between the amount of DMC produced and the decomposition time when 1.27 g of PC was added after decomposition of aOH and decomposition was carried out at 60 ° C.
Shown in. When the reaction was carried out in 2 mL of methanol alone for 5 minutes, about 4% of DMC was produced, but thereafter it hardly increased, and even after reacting for 300 minutes, the production amount of DMC was only 6%. However, if 0.5 mL of toluene or 1,4-dioxane was added under similar conditions,
PC pellet completely dissolved in the solvent in 100 minutes, 100% DM
C generated. Further, it is 0.
When 5 mL, 1 mL, 1.5 mL, and 2 mL of toluene were added, the PC pellet was completely dissolved in the solvent in 230 minutes, 70 minutes, 40 minutes, and 15 minutes, respectively, and was 100%.
Of DMC was produced.

[Effect of decomposition temperature] The effect of the reaction temperature on the decomposition of PC is 0.034 g of NaOH in a mixed solvent of toluene and methanol (1.5 mL / 1 mL).
Was dissolved, and then 1.27 g of PC was added and reacted at 40 to 60 ° C. to examine the effect of the reaction temperature on the decomposition of PC. Changes in the amount of DMC produced when decomposed at each reaction temperature are shown in FIG. Corresponding to the increase of decomposition temperature, the decomposition rate rapidly increases, PC is completely decomposed and DMC100
% To produce 40%, 50 ° C and 6%
It was about 350 minutes, about 140 minutes and about 40 minutes at 0 ° C., respectively. After complete decomposition, the yields of BPA obtained by crystallization in water were 96%, 95% and 96%, respectively.

[0027]

INDUSTRIAL APPLICABILITY According to the present invention, PC can be rapidly decomposed into a monomer in a mixed solvent of alcohol and toluene or alcohol and dioxane using a small amount of an alkaline catalyst under mild conditions. After decomposition, BPA crystallized by throwing in water can be easily separated and recovered in high yield. When a water-insoluble co-solvent such as toluene is used, the solvent can be easily separated and recovered, and there is an advantage that it can be reused for the decomposition of PC. Also, BPA can be separated by crystallization in toluene. In this latter method, alcohol, toluene, and dimethyl carbonate can be separated and recovered by distilling the filtrate after BPA separation, so that they can all be reused. In other words, the feature of the present invention is that, under mild conditions, the BPA and DM of the constituent monomers can be easily and efficiently obtained from a PC.
The point is that C can be collected. Further, since both BPA and DMC are not only used as PC monomers but also as chemical raw materials with wide industrial applications, the present invention can be effectively utilized as an industrial recycling method of used PCs, and is industrially useful. It can be said that the availability is very high.

[0028]

[Brief description of drawings]

FIG. 1 A mixed solvent of methanol and toluene (1 mL /
It is a figure which shows the effect (decomposition temperature 60 degreeC) of NaOH concentration on the decomposition rate of PC (1.27g) in 1 mL).

FIG. 2 Effect of adding toluene or dioxane to methanol on the formation rate of DMC in the decomposition of PC (1.27 g) (decomposition temperature 60 ° C., NaOH 0.034
It is a figure which shows g).

FIG. 3 In a mixed solvent of methanol and toluene (1 mL /
D in the decomposition of PC (1.27 g) in 1.5 mL)
Effect of decomposition temperature on the formation rate of MC (NaOH0.
It is a figure which shows 034g).

[Explanation of symbols]

[Symbol in FIG. 1] Amount of DMC produced when decomposed for 30 minutes ● Time for complete decomposition of PC [Symbol in FIG. 2] ○ When only 2 mL of methanol was used × Toluene / methanol mixed solvent (0.5mL / 2m
L) Toluene / Methanol mixed solvent (0.5 mL / 1 m
L) □ Toluene / methanol mixed solvent (1 mL / 1 mL)
● Toluene / methanol mixed solvent (1.5 mL / 1 m
When L) is used: ΔMethanol / dioxane mixed solvent (2 mL / 0.5
mL) [reference numeral in FIG. 3] ○ 40 ° C △ 50 ° C ● 60 ° C

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁷ identification code FI // C07B 61/00 300 C07B 61/00 300 (58) Fields investigated (Int.Cl. ⁷ , DB name) C07C 27/02 C07C 37/01 C07C 39/16 C07C 68/06 C07C 69/96 C07B 61/00 300

Claims (3)

(57) [Claims] 1. A transesterification reaction of polycarbonate and lower alcohol with a small amount of alkali as a catalyst,
In the method for obtaining bisphenol and dialkyl carbonate, which are starting materials for polycarbonate, (1). At least one solvent selected from the group consisting of benzene, toluene, xylene and dioxane is mixed in the reaction system, and the mixture is heated at a temperature not higher than the boiling point of the mixture. After stirring, after the reaction is complete, the mixture is poured into water to precipitate bisphenol as a reaction product for recovery, or (2). Toluene is mixed in the reaction system as a solvent and stirred at a temperature not higher than the boiling point of the reaction to react. After completion, an additional amount of toluene was added, and the mixture was cooled to precipitate bisphenol as a reaction product for recovery, while (3). Dialkyl carbonate as a reaction product was recovered by fractional distillation. A method for obtaining bisphenol and dialkyl carbonate as starting materials from a characteristic polycarbonate. 2. The bisphenol starting material from the polycarbonate according to claim 1, wherein the lower alcohol is at least one selected from the group consisting of methanol, ethanol and propanol butanol, or a mixture of two or more thereof. Method for obtaining dialkyl carbonate. 3. A small amount of alkali, sodium hydroxide, potassium hydroxide, calcium oxide, barium oxide, zinc oxide, tin oxide, at least one or a mixture of two or more selected from the group consisting of lead oxide, polycarbonate ester bond 1
The method for obtaining bisphenol and dialkyl carbonate as starting materials from the polycarbonate according to claim 1, characterized in that the amount is in the range of 2 to 12 mol% with respect to the molar unit.