Method for recycling PC

Abstract

The invention discloses a method for recovering BPA and DMC from waste PC, and the method comprises the following steps: a, crushing PC, pre-dissolving the crushed PC in a solvent, adding a solid catalyst and an alcoholysis agent to carry out an alcoholysis reaction on PC to generate a reaction liquid containing BPA and DMC, the solid catalyst being metal Mo and Li modified hydrometallurgy iron-aluminum slag; b, filtering the reaction liquid; c, extracting the filtrate by using alkali liquor to enrich the BPA in the water phase and enrich the DMC in the oil phase; d, recovering part of the solvent and the alcoholysis agent after the water phase is rectified, and carrying out acidification-phenol crystallization refining on a tower bottom solution to obtain polycarbonate-grade BPA; and e, carrying out two-stage rectification on the oil phase to obtain the electronic-grade DMC. The method has the advantages of mild reaction conditions, high catalyst utilization efficiency, easiness in separation and reutilization, and can realize efficient conversion from solid waste PC to resource products BPA and DMC.

Description

Technical Field

[0001] The present invention relates to a method for recovering BPA and DMC, and in particular to a method for recovering BPA and DMC from waste PC. Background Art

[0002] Polycarbonate (PC) is widely used in the production of optical discs, beverage bottles, computers and automotive parts. With the increasing production and demand of PC, the amount of waste PC materials generated is increasing. Since it is difficult to degrade under natural conditions, it will not only have a great impact on the environment, but also a huge waste of resources. Therefore, it must be recycled.

[0003] There are two main methods for recycling polycarbonate: physical method and chemical method. The former is to prepare other low value-added products through melt remolding, which significantly reduces its utilization value. The latter is to chemically depolymerize PC materials to generate corresponding monomers, which can be used as raw materials for producing PC or synthesizing other products after separation and purification, thus realizing the recycling of resources.

[0004] Currently, waste polycarbonate is mainly recycled through point-to-point physical recycling. Due to the inconsistency of the sources of waste plastic collection, the performance of the final recycled product is highly dependent on the quality of the recycling source. Simple mechanical crushing and blending modification cannot fundamentally solve this inconsistency problem. Therefore, chemical recycling has also become a hot topic in industry research.

[0005] Chinese patent CN106748665B uses CaO-SBA-15 as a catalyst and performs alcoholysis at 130° C. The catalyst preparation of this process is relatively difficult and costly, and the yield of the product BPA is only 93%.

[0006] Chinese patent CN101407450A uses alkali metal as alcoholysis catalyst, but the reaction efficiency is low and the alkali metal catalyst cannot be recovered after the reaction.

[0007] Therefore, seeking an efficient and easily separable catalyst and a mild process for alcoholysis and refining of waste PC is one of the keys to improving the recovery of waste PC. Summary of the invention

[0008] In order to solve the above technical problems, the present invention proposes a method for recovering BPA and DMC (dimethyl carbonate) from waste PC. The method has the advantages of mild reaction conditions, high catalyst utilization efficiency, easy separation and reusability, and can achieve efficient conversion from waste PC to resource products BPA and DMC.

[0009] To achieve the above purpose, the technical solution adopted by the present invention is as follows:

[0010] A method for recovering BPA and DMC from waste PC comprises the following steps:

[0011] a. After PC is crushed and pre-dissolved in a solvent, a solid catalyst and an alcoholysis agent are added, and under an inert atmosphere, at 40-50°C and normal pressure, an alcoholysis reaction of PC is performed to generate a reaction solution containing BPA and DMC;

[0012] b. filtering the reaction solution and recovering the solid catalyst from the filter residue;

[0013] c. Extract the filtrate with alkaline solution to enrich BPA in the water phase and DMC in the oil phase;

[0014] d. After distillation of the aqueous phase, part of the solvent and alcoholysis agent are recovered, and the bottom liquid of the tower is subjected to acid precipitation-phenol crystallization for purification to obtain polycarbonate grade BPA;

[0015] e. The oil phase is distilled in two stages to obtain electronic grade DMC.

[0016] In the present invention, the solid catalyst is a hydrometallurgical iron-aluminum slag modified with metal Mo and Li. In the solid catalyst, the content of metal Mo is 1.5-2.5% of the mass of the hydrometallurgical iron-aluminum slag, preferably 1.5-2%; the content of metal Li is 2-3.5% of the mass of the hydrometallurgical iron-aluminum slag, preferably 2-2.5%;

[0017] Furthermore, the preparation method of the solid catalyst is:

[0018] 1) crushing the hydrometallurgical iron-aluminum slag, first placing it in an oxidant solution for pretreatment to remove a small amount of organic matter in the hydrometallurgical iron-aluminum slag, then filtering and drying; the crushed particle size is preferably 0.1-0.2 mm;

[0019] 2) immersing the pretreated hydrometallurgical iron-aluminum slag in a mixed solution of Mo salt and Li salt for metal loading;

[0020] 3) After the metal loading is completed, the solid is filtered out and calcined at 500-700° C. for 3-6 hours to obtain the solid catalyst.

[0021] Furthermore, in step 1), the oxidant solution is an aqueous solution of hydrogen peroxide, preferably with a mass concentration of 1-3%;

[0022] Furthermore, in step 1), the mass ratio of the hydrometallurgical iron-aluminum slag to the oxidant solution is (1-3):1, preferably (1-2):1;

[0023] The pretreatment conditions in step 1) are: reaction at 20-80°C for 0.5-8h;

[0024] Furthermore, the Mo salt is a molybdate, preferably ammonium molybdate; the Li salt is an organic lithium salt, preferably lithium formate or lithium acetate. The organic metal salt is preferably used to avoid the introduction of other non-metallic anions.

[0025] Furthermore, in step 2), the immersion conditions are: immersion at 20-80° C. for 0.5-1.5 h.

[0026] The catalyst of the invention can efficiently alcoholyze waste PC into BPA and DMC, the reaction conditions are mild, the product recovery rate is high, and the main component of the carrier hydrometallurgical iron-aluminum slag is yellow sodium iron vanadium generated by trivalent iron ions under the action of sodium carbonate, which can be recovered by filtration, the separation procedure is simple, the process cost is low, and it has potential economic benefits.

[0027] In the present invention, the alcoholysis agent is methanol, ethanol and ethylene glycol, etc., preferably methanol; the solvent is dichloromethane, tetrahydrofuran and dioxane, etc., preferably dichloromethane.

[0028] Furthermore, in step a, based on the total mass of the reaction liquid as 100%, the contents of the various components are controlled to be: 10-20% of waste PC, 1-3% of solid catalyst, 48-60% of solvent, and 20-40% of alcoholysis agent.

[0029] Furthermore, in step a, the alcoholysis reaction time is 1-3h.

[0030] Furthermore, in step a, the inert atmosphere is one or more of nitrogen, argon, and helium.

[0031] Furthermore, in step c, the base is NaOH, KOH, etc., preferably NaOH.

[0032] The extraction conditions are: the concentration of the alkali is 5-6wt%, and the molar ratio of the alkali to BPA is 1:1-1:3.

[0033] Furthermore, in step d, the distillation conditions are as follows: the extraction ratio is 0.2-0.3, the reflux ratio is 2-4, the tower bottom temperature is 99-102°C, and the tower top temperature is 63-65°C.

[0034] Furthermore, in step d, the acid precipitation conditions are: acid precipitation uses an acid of a certain concentration (such as 32% hydrochloric acid, sulfuric acid), and the acid precipitation pH is 4-7; the phenol crystallization conditions are: the mass ratio of phenol to crude BPA is 3:1-4:1, and the crystallization temperature is 49-53°C.

[0035] Compared with the prior art, the present invention has the following beneficial effects:

[0036] (1) The hydrometallurgical iron-aluminum slag carrier used in the catalyst of the present invention is a by-product of the hydrometallurgical process, which is simple, easy to obtain, and low in cost, thus achieving the recycling of waste.

[0037] (2) The active metals Mo and Li were loaded on the iron-aluminum slag carrier. It was unexpectedly found that it could catalyze the alcoholysis of waste PC to produce BPA and DMC, with high catalytic efficiency and mild reaction conditions.

[0038] (3) The present invention can efficiently recover BPA and DMC, with a high product recovery rate, and by recycling the co-catalyst and the solid catalyst, the present invention has significant economic benefits and environmental friendliness. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] Figure 1 This is the mass spectrum of BPA (bisphenol A)

[0040] Figure 2 It is the mass spectrum of DMC (dimethyl carbonate). DETAILED DESCRIPTION

[0041] The present invention is further described below by means of specific examples. The examples described in the present invention are only used to illustrate the present invention and do not limit the scope of the present invention.

[0042] (1) Main equipment models and raw material sources of the embodiments of the present invention

[0043] The reflux reactor was purchased from Yantai Keli Chemical Equipment Co., Ltd.;

[0044] Muffle furnace, model VULLIN 3-1750, purchased from Neytech, USA;

[0045] Hydrometallurgical iron and aluminum slag: by-product of Wanhua Chemical's hydrometallurgical equipment;

[0046] The waste PC comes from Wanhua Chemical’s PC unit;

[0047] (NH4)2MoO4, LiAc, methanol, and dichloromethane were purchased from Sinopharm Chemical Reagent Co., Ltd.

[0048] (2) Main analysis and testing methods

[0049] BPA was qualitatively analyzed by gas chromatography-mass spectrometry (GC-MS) and quantitatively analyzed by liquid chromatography (LC).

[0050] [Preparation Example 1]

[0051] 100 g of hydrometallurgical iron-aluminum slag was ground (average particle size 0.1 mm) and added to a flask, and 50 g of a 2% hydrogen peroxide aqueous solution was added to the flask; the flask was placed in a 70° C. water bath and stirred for 4 h; filtered, and dried at 150° C. for 8 h to obtain a catalyst carrier.

[0052] Take 50g of catalyst carrier, 1.53g of (NH4)2MoO4, 10g of LiAc and 20g of water, mix them evenly and immerse them in a 50℃ water bath for 1h; after taking them out, calcine them at 600℃ for 4h to obtain solid catalyst 1#.

[0053] [Preparation of Examples 2-5 and Preparation of Comparative Examples 1-3]

[0054] Solid catalysts 2# to 5# and 1'# to 3'# were prepared respectively in a manner substantially similar to that of Example 1, with the only difference being the amounts of raw materials and the processing conditions shown in Table 1.

[0055] Table 1. Different raw material amounts and processing conditions in various preparation examples

[0056]

[0057] [Example 1]

[0058] The granular PC was crushed to less than 200 mesh, pre-dissolved in dichloromethane, and solid catalyst 1# and alcoholysis agent methanol were added and mixed, wherein the weight ratio of PC, dichloromethane, solid catalyst 1# and alcoholysis agent (referred to as "raw material weight ratio" in Table 2) was 10:60:3:27. Under stirring, nitrogen was introduced to replace the air in the reflux reactor, and reflux reaction was carried out at 40°C and normal pressure for 2 hours.

[0059] The reaction solution was filtered, and the filtered clear liquid was sent to an extraction tower for countercurrent extraction with a 5.85% NaOH solution at a molar ratio of 1:1. An oil phase enriched in DMC was obtained at the bottom of the tower, and an aqueous phase enriched in BPA was obtained at the top of the tower.

[0060] The BPA-enriched aqueous phase was distilled under the following conditions: extraction ratio of 0.2, reflux ratio of 2, bottom temperature of 100°C, and top temperature of 63°C; methanol, an alcoholysis agent, and dichloromethane, a solvent, were recovered at the top of the tower, and an aqueous phase enriched in BPA was obtained at the bottom of the tower; the BPA-enriched aqueous phase at the bottom of the tower was acidified using 32% hydrochloric acid at a pH of 4, filtered and dried, and dissolved with phenol at a mass ratio of 1:3, and crystallized at 49-53°C to obtain a phenol-BPA crystalline adduct, which was vacuum desorbed at 220°C to obtain polycarbonate-grade BPA. The gas quality analysis results of the product were as follows after GC-MS analysis: Figure 1 As shown, it is proved that the structure of the obtained product is consistent with BPA; after liquid chromatography analysis, the yield of the product BPA is 99%.

[0061] The oil phase enriched with DMC is subjected to two-stage distillation to recover alcoholysis agent methanol and solvent dichloromethane, and electronic grade DMC is obtained at the top of the secondary distillation tower. The conditions of the first-stage distillation tower are: extraction ratio of 0.5, reflux ratio of 2, bottom temperature of 90°C, and top temperature of 40°C; the conditions of the second-stage distillation tower are: pressure of 30Kpa, extraction ratio of 0.7, reflux ratio of 3, bottom temperature of 60°C, and top temperature of 20°C; after GC-MS analysis, the gas quality analysis results of the product are as follows Figure 2 As shown, it is proved that the structure of the obtained product is consistent with DMC; after liquid chromatography analysis, the yield of the product DMC is 90%.

[0062] In addition, the filter residue obtained by filtration was dried to obtain a catalyst, which was recycled. After 10 cycles, the yield of the product BPA was 95%, and the yield of DMC was 85%.

[0063] [Examples 2-9 and Comparative Examples 1-4]

[0064] Examples 2-9 and Comparative Examples 1-4 were carried out in substantially the same manner as Example 1, except that the reaction conditions shown in Table 2 were different:

[0065] Table 2. Different reaction conditions in various embodiments and comparative examples

[0066]

[0067] The yields of BPA prepared in some embodiments and comparative examples were analyzed by liquid chromatography, including the initial yield and the yield after the catalyst was recycled 10 times, which are summarized in Table 3:

[0068] Table 3, BPA / DMC yield

[0069]

[0070] The above is only a preferred embodiment of the present invention. It should be pointed out that ordinary technicians in this field can make several improvements and supplements without departing from the method of the present invention. These improvements and supplements should also be regarded as the scope of protection of the present invention.

Claims

1. A solid catalyst, which is a hydrometallurgical ferroaluminum slag modified with metal Mo and Li, wherein the content of metal Mo is 1.5-2.5% of the mass of the hydrometallurgical ferroaluminum slag, preferably 1.5-2%; the content of metal Li is 2-3.5% of the mass of the hydrometallurgical ferroaluminum slag, preferably 2-2.5%.

2. A method for preparing the solid catalyst according to claim 1, comprising: 1) crushing the hydrometallurgical iron and aluminum slag, first placing it in an oxidant solution for pretreatment, then filtering and drying; The crushed particle size is preferably 0.1-0.2 mm; preferably, the pretreatment conditions are: reacting at 20-80° C. for 0.5-8 h; 2) Immersing the pretreated hydrometallurgical iron-aluminum slag in a mixed solution of Mo salt and Li salt for metal loading; preferably, the Mo salt is a molybdate, preferably ammonium molybdate; the Li salt is an organic lithium salt, preferably lithium formate or lithium acetate; 3) After the metal loading is completed, the solid is filtered out and calcined to obtain the solid catalyst; preferably, the calcination condition is calcination at 500-700° C. for 3-6 hours.

3. The method according to claim 2, wherein: The oxidant solution in step 1) is an aqueous solution of hydrogen peroxide, preferably with a mass concentration of 1-3%; preferably, the mass ratio of the hydrometallurgical iron-aluminum slag to the oxidant solution in step 1) is (1-3):

1.

4. A method for recovering BPA and DMC from waste PC, characterized in that: The following steps are involved: a. After PC is crushed and pre-dissolved in a solvent, a solid catalyst and an alcoholysis agent are added to cause an alcoholysis reaction of PC to generate a reaction solution containing BPA and DMC; the solid catalyst is a hydrometallurgical iron-aluminum slag modified by metal Mo and Li; b. Filtering the reaction solution; c. Extract the filtrate with alkaline solution to enrich BPA in the water phase and DMC in the oil phase; d. The aqueous phase is distilled, and the bottom liquid of the tower is subjected to acid precipitation-phenol crystallization to obtain BPA; e. The oil phase is distilled to obtain DMC.

5. The method according to claim 4, wherein: In step a, based on the total mass of the reaction liquid as 100%, the contents of the various components are: 10-20% of waste PC, 1-3% of solid catalyst, 48-60% of solvent, and 20-40% of alcoholysis agent.

6. The method according to claim 4 or 5, wherein: The alcoholysis agent is selected from at least one of methanol, ethanol and ethylene glycol; and / or: The solvent is selected from at least one of dichloromethane, tetrahydrofuran and dioxane.

7. The method according to any one of claims 4 to 6, wherein: The alcoholysis reaction conditions are: in an inert atmosphere, at 40-50° C. and normal pressure for 1-3 hours.

8. The method according to any one of claims 4 to 7, wherein: In step c, the base is selected from NaOH and KOH.

9. The method according to any one of claims 4 to 8, wherein: In step c, the concentration of the alkali solution is 5-6wt%, and the molar ratio of the alkali to BPA is 1:1-1:

3.

10. The method according to any one of claims 4 to 9, wherein: In step d, the acid precipitation conditions are: using hydrochloric acid and / or sulfuric acid, the acid precipitation pH is 4-7; the phenol crystallization conditions are: the mass ratio of phenol to crude BPA is 3:1-4:1, and the crystallization temperature is 49-53°C.

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