Method for catalyzing alcoholysis of waste polylactic acid by metal-free bicuculline acetate salt

Abstract

The application discloses a method for efficiently catalyzing alcoholysis of waste polylactic acid by using metal-free bicyclic guanidine acetate salt. The catalyst used in the application is metal-free bicyclic guanidine acetate salt, and the catalyst has high catalytic activity for alcoholysis of waste polylactic acid; under certain conditions, the waste polylactic acid can be 100% degraded, and lactic acid ester with a high yield (the yield ranges from 91.4% to 95.6%) can be obtained, so that the waste polylactic acid can be upgraded and reused. Meanwhile, the catalyst has strong thermal stability and is not easy to decompose at high temperature, and can be recycled. The method solves the problems of slow reaction rate, low yield and metal residues in products in the alcoholysis process of waste polylactic acid, and the catalyst has the advantages of green pollution-free and recyclable use.

Description

Technical Field

[0001] This invention belongs to the field of metal-free green catalysis and biodegradable plastic chemical recycling; in particular, it relates to a method for the catalytic alcoholysis of waste polylactic acid using bicyclic guanidine acetate salt. Background Technology

[0002] Polylactic acid (PLA) is widely used in disposable packaging materials, drug delivery systems, and vascular stents due to its excellent biodegradability, ease of processing, and biocompatibility. In recent years, the amount of waste PLA has increased dramatically, making the search for suitable methods to recycle waste PLA a current research hotspot. Chemically degrading waste PLA into high-value-added chemicals is currently an effective way to utilize waste PLA resources. Chemical recycling of PLA mainly includes hydrolysis, photolysis, pyrolysis, and alcoholysis. Among these, alcoholysis has advantages such as mild reaction conditions, suitability for industrial operation, and the ability to degrade waste PLA into corresponding lactic acid esters, thereby increasing the economic benefits of recycling waste PLA. Lactic acid esters are an important class of chemicals widely used in the production of coatings, fragrances, resins, adhesives, cleaning agents for precision electronic components, and fine chemical processing.

[0003] Currently, the commonly used catalysts in PLA alcoholysis processes are metal catalysts and their complexes, ionic liquids, and other metal-containing compounds. These catalysts leave metal residues during use, increasing the difficulty of purifying the resulting lactate esters and limiting their application in some fine chemical industries. Metal-free catalysts, with their advantages of being environmentally friendly and having low toxicity, have gained increasing attention in the catalytic application of PLA alcoholysis. However, they also suffer from problems such as low catalyst activity and poor stability. Summary of the Invention

[0004] Purpose of the invention: To address the problems of low reaction rate, low lactate yield, and metal residue in the product during the alcoholysis of waste polylactic acid in the existing technology, a method for catalytic alcoholysis of waste polylactic acid using bicyclic guanidine acetate salt was designed and developed to improve the reaction rate and reaction conditions.

[0005] To achieve the above objectives, the specific technical solution provided is as follows:

[0006] A method for catalyzing the alcoholysis of polylactic acid using bicyclic guanidine acetate salts is disclosed, relating to the application of bicyclic guanidine acetate salts in the alcoholysis waste polylactic acid.

[0007] Specifically, using alcohol as a solvent, the bicyclic guanidine acetate catalyst is reacted with waste polylactic acid to obtain the corresponding lactate ester.

[0008] The reaction equation is as follows:

[0009]

[0010] The alcohol is any one of methanol, ethanol, propanol, butanol, isoamyl alcohol, isooctanol, n-dodecyl alcohol, or benzyl alcohol.

[0011] The polylactic acid (PLA) mentioned herein includes, but is not limited to, waste PLA, wherein the waste PLA is any one or a combination of several of the following: waste PLA packaging bags, waste PLA straws, and waste PLA 3D printing materials.

[0012] The guanidine acetate salt is obtained by reacting 1,5,7-triazidobicyclo(4.4.0)dec-5-ene (organic base TBD) with acetic acid in a molar ratio of 1:1.

[0013] The mass ratio of the bis-guanidine acetate catalyst to PLA is 1:40 to 1:10, preferably 1:20 to 3:40.

[0014] The mass ratio of the alcohol to the waste polylactic acid is 5:1 to 12.5:1, preferably 7.5:1 to 10:1.

[0015] The degradation reaction is carried out under normal pressure and at a reaction temperature of 140℃~200℃, preferably 160℃~200℃.

[0016] The degradation reaction time is 0.5h to 3h, preferably 2h to 3h.

[0017] After the degradation reaction is completed, the catalyst is recovered. The catalyst recovery process involves vacuum filtration and extraction of the degradation reaction solution. The filtrate is then extracted with water to obtain a solution containing bicyclic guanidine acetate. The water is evaporated to recover bicyclic guanidine acetate or an alcoholic solution of bicyclic guanidine acetate. The raffinate is an alcoholic solution containing lactate.

[0018] The recovered bicyclic guanidine acetate salt or the alcoholic solution of bicyclic guanidine acetate salt can be recycled as a catalyst, exhibiting excellent recycling performance. After being reused 5 times, the catalytic activity does not decrease significantly.

[0019] The conversion rate of PLA and the yield of lactate were calculated according to formulas (1) and (2), respectively.

[0020]

[0021]

[0022] Beneficial effects:

[0023] This invention utilizes bicyclic guanidine acetate as a catalyst to alcoholyze waste polylactic acid (PLA) to produce lactate esters. The catalyst exhibits high catalytic activity and thermal stability, yielding high yields of lactate esters under certain conditions. The bicyclic guanidine acetate is metal-free and highly stable, effectively addressing the issue of metal residues in the product. Furthermore, the catalyst is recyclable, providing a novel process for the alcoholysis and recycling of waste PLA, demonstrating excellent prospects for industrial application. Attached Figure Description

[0024] The present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments, and the advantages of the present invention in the above and / or other aspects will become clearer.

[0025] Figure 1 The image shows a comparison of the DSC heating curves (a) and TGA curves (b) of the catalyst bicyclic guanidine acetate salt (HTBD-OAc) and TBD in this invention.

[0026] Figure 2 The image shows the 1H NMR spectrum of benzyl lactate, the product generated using benzyl alcohol as a solvent.

[0027] Figure 3 Comparison of gas chromatography (a) and mass spectrometry (b) of benzyl lactate standard and the main product of polylactic acid catalyzed by bicyclic guanidine acetate in benzyl alcohol as solvent. Detailed Implementation

[0028] The present invention will now be described with reference to specific embodiments.

[0029] The gas chromatography analysis method described in the following examples is as follows:

[0030] The yield of PLA reaction products was determined using a Shimadzu (Shanghai) Trading Co., Ltd. GC 2010plus gas chromatograph. The column temperature was 100℃, increased to 280℃ at a rate of 10℃ / min, with N2 as the protective atmosphere, a carrier gas flow rate of 3 ml / min, and a split injection volume of 1 μL.

[0031] Example 1

[0032] 5 g of the organic base 1,5,7-triazidobicyclo(4.4.0)dec-5-ene (TBD) was dissolved in deionized water. Then, a 4% acetic acid aqueous solution was added dropwise to the TBD aqueous solution through a constant-pressure dropping funnel, maintaining a molar ratio of TBD to acetic acid of 1:1. The reaction was carried out at 30°C with stirring for 12 h to obtain the target product. After removing water from the solution by rotary evaporation, the solid product was dried in a vacuum drying oven for 48 h to obtain a white solid product, which was HTBD-OAc, weighing 6.8 g, with a yield of 95.1%. Differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA) were performed on HTBD-OAc and the organic base (TBD).

[0033] The DSC method described is as follows: using a DSC Q20 (TA Instruments, USA), two temperature increases are performed in a nitrogen atmosphere. The first temperature increase is performed by heating from 40°C to 220°C at a rate of 10°C / min, holding at the high temperature for 1 minute, and then cooling from 220°C to 40°C at a rate of 10°C / min, holding at the low temperature for 1 minute. The second temperature increase is performed by heating from 40°C to 220°C at a rate of 10°C / min, holding at the high temperature for 1 minute.

[0034] The TGA method described is as follows: thermogravimetric analysis is used to determine the thermal decomposition of the catalyst. The model used is TGAQ550. In a nitrogen atmosphere, the sample is heated from 25°C to 600°C at a rate of 10°C / min.

[0035] The DSC heating curves (a) and TGA curves (b) of bicyclic guanidine acetate salt (HTBD-OAc) and organic base (TBD) are shown below. Figure 1 As shown in the figure. DSC results indicate that the melting point of HTBD-OAc is increased to 155℃ compared to TBD. TGA curves show that HTBD-OAc has better thermal stability than TBD, with significant weight loss only beginning at approximately 200℃, indicating that HTBD-OAc can stably exist in the alcoholysis reaction.

[0036] Example 2

[0037] 1 g PLA, 7.5 g methanol, and 50 mg bicyclic guanidine acetate (prepared in Example 1) were added to a 50 mL magnetically stirred high-pressure reactor. The reaction was carried out at 160 °C for 2 h. After the reaction, the reaction solution was cooled to room temperature and filtered under reduced pressure to separate the unreacted PLA residue, which was then dried to constant weight in a vacuum drying oven. Under these conditions, the conversion rate of PLA was 100%. The reaction product, methyl lactate, was quantitatively analyzed by gas chromatography using the external standard method, and the yield of methyl lactate was found to be 95.6%.

[0038] Example 3

[0039] 1 g PLA, 7.5 g ethanol, and 50 mg bicyclic guanidine acetate (prepared in Example 1) were added to a 50 mL magnetically stirred high-pressure reactor. The reaction was carried out at 160 °C for 2 h. After the reaction, the reaction solution was cooled to room temperature and filtered under reduced pressure to separate the unreacted PLA residue, which was then dried to constant weight in a vacuum drying oven. Under these conditions, the conversion rate of PLA was 100%. The reaction product, ethyl lactate, was quantitatively analyzed by gas chromatography using the external standard method, and the yield of ethyl lactate was found to be 94.4%.

[0040] Example 4

[0041] 1 g PLA, 7.5 g propanol, and 50 mg bicyclic guanidine acetate (prepared in Example 1) were added to a 50 mL magnetically stirred high-pressure reactor. The reaction was carried out at 160 °C for 2 h. After the reaction, the reaction solution was cooled to room temperature and filtered under reduced pressure to separate the unreacted PLA residue, which was then dried to constant weight in a vacuum drying oven. Under these conditions, the conversion rate of PLA was 100%. The reaction product, propyl lactate, was quantitatively analyzed by gas chromatography using the external standard method, and the yield of propyl lactate was found to be 93.1%.

[0042] Example 5

[0043] 1 g PLA, 7.5 g butanol, and 50 mg bicyclic guanidine acetate (prepared in Example 1) were added to a 50 mL magnetically stirred high-pressure reactor. The reaction was carried out at 160 °C for 2 h. After the reaction, the reaction solution was cooled to room temperature and filtered under reduced pressure to separate the unreacted PLA residue, which was then dried to constant weight in a vacuum drying oven. Under these conditions, the conversion rate of PLA was 100%. The reaction product, butyl lactate, was quantitatively analyzed by gas chromatography using the external standard method, and the yield of butyl lactate was found to be 92.9%.

[0044] Example 6

[0045] 1 g PLA, 7.5 g isoamyl alcohol, and 50 mg bicyclic guanidine acetate (prepared in Example 1) were added to a 50 mL magnetically stirred high-pressure reactor. The reaction was carried out at 160 °C for 3 h. After the reaction, the reaction solution was cooled to room temperature and filtered under reduced pressure to separate the unreacted PLA residue, which was then dried to constant weight in a vacuum drying oven. Under these conditions, the conversion rate of PLA was 100%. The reaction product, isoamyl lactate, was quantitatively analyzed by gas chromatography using the external standard method, and the yield of isoamyl lactate was found to be 92.3%.

[0046] Example 7

[0047] 1 g PLA, 7.5 g isooctyl alcohol, and 50 mg bicyclic guanidine acetate (prepared in Example 1) were added to a 50 mL single-necked flask and stirred continuously in an oil bath at 160 °C for 3 h. After the reaction was complete, the reaction solution was cooled to room temperature and filtered under reduced pressure to separate the unreacted PLA residue, which was then dried to constant weight in a vacuum drying oven. Under these conditions, the conversion rate of PLA was 100%. The reaction product, isooctyl lactate, was quantitatively analyzed by gas chromatography using the external standard method, and the yield of isooctyl lactate was found to be 91.8%.

[0048] Example 8

[0049] 1 g PLA, 7.5 g n-dodecyl alcohol, and 50 mg bicyclic guanidine acetate (prepared in Example 1) were added to a 50 mL single-necked flask and stirred continuously in an oil bath at 180 °C for 2 h. After the reaction was complete, the reaction solution was cooled to room temperature and filtered under reduced pressure to separate the unreacted PLA residue, which was then dried to constant weight in a vacuum drying oven. Under these conditions, the conversion rate of PLA was 100%. The reaction product, lauryl lactate, was quantitatively analyzed by gas chromatography using the external standard method, and the yield of lauryl lactate was found to be 93.2%.

[0050] Example 9

[0051] 1 g PLA, 7.5 g benzyl alcohol, and 50 mg bicyclic guanidine acetate (prepared in Example 1) were added to a 50 mL single-necked flask and stirred continuously in an oil bath at 180 °C for 2 h. After the reaction was complete, the reaction solution was cooled to room temperature and filtered under reduced pressure to separate the unreacted PLA residue, which was then dried to constant weight in a vacuum drying oven. Under these conditions, the conversion rate of PLA was 100%. The reaction product, benzyl lactate, was quantitatively analyzed by gas chromatography using the external standard method, and the yield of benzyl lactate was found to be 94.4%. The 1H NMR spectrum of benzyl lactate is shown below. Figure 2 As shown, the gas chromatogram is as follows: Figure 3 As shown in (a), the mass spectrum is as follows: Figure 3 As shown in (b).

[0052] Example 10

[0053] 1 g PLA, 7.5 g benzyl alcohol, and 50 mg bicyclic guanidine acetate (prepared in Example 1) were added to a 50 mL single-necked flask and stirred continuously in an oil bath at 140 °C for 2 h. After the reaction was complete, the reaction solution was cooled to room temperature and filtered under reduced pressure to separate the unreacted PLA residue, which was then dried to constant weight in a vacuum drying oven. Under these conditions, the conversion rate of PLA was 71.2%. The reaction product, benzyl lactate, was quantitatively analyzed by gas chromatography using the external standard method, and the yield of benzyl lactate was found to be 57.8%.

[0054] Example 11

[0055] 1 g PLA, 7.5 g benzyl alcohol, and 50 mg bicyclic guanidine acetate (prepared in Example 1) were added to a 50 mL single-necked flask and stirred continuously in an oil bath at 160 °C for 2 h. After the reaction was complete, the reaction solution was cooled to room temperature and filtered under reduced pressure to separate the unreacted PLA residue, which was then dried to constant weight in a vacuum drying oven. Under these conditions, the conversion rate of PLA was 93.4%. The reaction product, benzyl lactate, was quantitatively analyzed by gas chromatography using the external standard method, and the yield of benzyl lactate was found to be 90.6%.

[0056] Example 12

[0057] 1 g PLA, 7.5 g benzyl alcohol, and 50 mg bicyclic guanidine acetate (prepared in Example 1) were added to a 50 mL single-necked flask and stirred continuously in an oil bath at 200 °C for 2 h. After the reaction was complete, the reaction solution was cooled to room temperature and filtered under reduced pressure to separate the unreacted PLA residue, which was then dried to constant weight in a vacuum drying oven. Under these conditions, the conversion rate of PLA was 100%. The reaction product, benzyl lactate, was quantitatively analyzed by gas chromatography using the external standard method, and the yield of benzyl lactate was found to be 91.4%.

[0058] Example 13

[0059] 1 g PLA, 7.5 g benzyl alcohol, and 50 mg bicyclic guanidine acetate (prepared in Example 1) were added to a 50 mL single-necked flask and stirred continuously in an oil bath at 180 °C for 0.5 h. After the reaction was complete, the reaction solution was cooled to room temperature and filtered under reduced pressure to separate the unreacted PLA residue, which was then dried to constant weight in a vacuum drying oven. Under these conditions, the conversion rate of PLA was 68.7%. The reaction product, benzyl lactate, was quantitatively analyzed by gas chromatography using the external standard method, and the yield of benzyl lactate was found to be 62.5%.

[0060] Example 14

[0061] 1 g PLA, 7.5 g benzyl alcohol, and 50 mg bicyclic guanidine acetate (prepared in Example 1) were added to a 50 mL single-necked flask and stirred continuously in an oil bath at 180 °C for 1 h. After the reaction was complete, the reaction solution was cooled to room temperature and filtered under reduced pressure to separate the unreacted PLA residue, which was then dried to constant weight in a vacuum drying oven. Under these conditions, the conversion rate of PLA was 88.4%. The reaction product, benzyl lactate, was quantitatively analyzed by gas chromatography using the external standard method, and the yield of benzyl lactate was found to be 85.2%.

[0062] Example 15

[0063] 1 g PLA, 7.5 g benzyl alcohol, and 50 mg bicyclic guanidine acetate (prepared in Example 1) were added to a 50 mL single-necked flask and stirred continuously in an oil bath at 180 °C for 3 h. After the reaction was complete, the reaction solution was cooled to room temperature and filtered under reduced pressure to separate the unreacted PLA residue, which was then dried to constant weight in a vacuum drying oven. Under these conditions, the conversion rate of PLA was 100%. The reaction product, benzyl lactate, was quantitatively analyzed by gas chromatography using the external standard method, and the yield of benzyl lactate was found to be 92.8%.

[0064] Example 16

[0065] 1 g PLA, 7.5 g benzyl alcohol, and 25 mg bicyclic guanidine acetate (prepared in Example 1) were added to a 50 mL single-necked flask and stirred continuously in an oil bath at 180 °C for 2 h. After the reaction was complete, the reaction solution was cooled to room temperature and filtered under reduced pressure to separate the unreacted PLA residue, which was then dried to constant weight in a vacuum drying oven. Under these conditions, the conversion rate of PLA was 85.5%. The reaction product, benzyl lactate, was quantitatively analyzed by gas chromatography using the external standard method, and the yield of benzyl lactate was found to be 79.1%.

[0066] Example 17

[0067] 1 g PLA, 7.5 g benzyl alcohol, and 75 mg bicyclic guanidine acetate (prepared in Example 1) were added to a 50 mL single-necked flask and stirred continuously in an oil bath at 180 °C for 2 h. After the reaction was complete, the reaction solution was cooled to room temperature and filtered under reduced pressure to separate the unreacted PLA residue, which was then dried to constant weight in a vacuum drying oven. Under these conditions, the conversion rate of PLA was 100%. The reaction product, benzyl lactate, was quantitatively analyzed by gas chromatography using the external standard method, and the yield of benzyl lactate was found to be 92.9%.

[0068] Example 18

[0069] 1 g PLA, 7.5 g benzyl alcohol, and 100 mg bicyclic guanidine acetate (prepared in Example 1) were added to a 50 mL single-necked flask and stirred continuously in an oil bath at 180 °C for 2 h. After the reaction was complete, the reaction solution was cooled to room temperature and filtered under reduced pressure to separate the unreacted PLA residue, which was then dried to constant weight in a vacuum drying oven. Under these conditions, the conversion rate of PLA was 100%. The reaction product, benzyl lactate, was quantitatively analyzed by gas chromatography using the external standard method, and the yield of benzyl lactate was found to be 92.6%.

[0070] Example 19

[0071] 1 g PLA, 5 g benzyl alcohol, and 50 mg bicyclic guanidine acetate (prepared in Example 1) were added to a 50 mL single-necked flask and stirred continuously in an oil bath at 180 °C for 2 h. After the reaction was complete, the reaction solution was cooled to room temperature and filtered under reduced pressure to separate the unreacted PLA residue, which was then dried to constant weight in a vacuum drying oven. Under these conditions, the conversion rate of PLA was 93.6%. The reaction product, benzyl lactate, was quantitatively analyzed by gas chromatography using the external standard method, and the yield of benzyl lactate was found to be 89.4%.

[0072] Example 20

[0073] 1 g PLA, 10 g benzyl alcohol, and 50 mg bicyclic guanidine acetate (prepared in Example 1) were added to a 50 mL single-necked flask and stirred continuously in an oil bath at 180 °C for 2 h. After the reaction was complete, the reaction solution was cooled to room temperature and filtered under reduced pressure to separate the unreacted PLA residue, which was then dried to constant weight in a vacuum drying oven. Under these conditions, the conversion rate of PLA was 100%. The reaction product, benzyl lactate, was quantitatively analyzed by gas chromatography using the external standard method, and the yield of benzyl lactate was found to be 93.1%.

[0074] Example 21

[0075] 1 g PLA, 12.5 g benzyl alcohol, and 50 mg bicyclic guanidine acetate (prepared in Example 1) were added to a 50 mL single-necked flask and stirred continuously in an oil bath at 180 °C for 2 h. After the reaction was complete, the reaction solution was cooled to room temperature and filtered under reduced pressure to separate the unreacted PLA residue, which was then dried to constant weight in a vacuum drying oven. Under these conditions, the conversion rate of PLA was 100%. The reaction product, benzyl lactate, was quantitatively analyzed by gas chromatography using the external standard method, and the yield of benzyl lactate was found to be 92.4%.

[0076] Example 22

[0077] The regeneration performance of the catalyst was evaluated through a catalyst cycling experiment. Specifically, the PLA residue was separated by vacuum filtration of the degradation reaction solution, extracted with deionized water, and the supernatant was evaporated to dryness. The supernatant was then dried in a vacuum oven at 60°C for 12 hours to obtain a benzyl alcohol solution of bicyclic guanidine acetate. Fresh benzyl alcohol solution was added to bring the total mass of benzyl alcohol and bicyclic guanidine acetate required in Example 9, and then 1 g of PLA particles were added for the experiment. After repeating this process five times, the bicyclic guanidine acetate maintained high activity, with a benzyl lactate yield of 92%.

[0078] Comparative Example 1

[0079] Equal molar amounts of bicyclic guanidine acetate and the organic base TBD were added to two 50 mL single-necked flasks, respectively, and the reactions were carried out for 2 h under the conditions of Example 9. After the reaction, the reaction solution was cooled to room temperature and filtered under reduced pressure to separate unreacted PLA residue, which was then dried to constant weight in a vacuum drying oven. Under these conditions, the conversion rates of PLA benzyl alcoholysis catalyzed by both bicyclic guanidine acetate and the organic base TBD were 100%. The reaction product, benzyl lactate, was quantitatively analyzed by gas chromatography using the external standard method. The analysis showed that the yield of benzyl lactate catalyzed by bicyclic guanidine acetate in PLA alcoholysis was 94.1%, while the yield catalyzed by the organic base TBD was 86.2%. This indicates that bicyclic guanidine acetate has higher catalytic activity.

[0080] This invention provides a method for the catalytic alcoholysis of waste polylactic acid using a bicyclic guanidine acetate salt. There are many ways to implement this technical solution; the above description is merely a preferred embodiment of the invention. It should be noted that those skilled in the art can make various improvements and modifications without departing from the principle of the invention, and these improvements and modifications should also be considered within the scope of protection of this invention. All components not explicitly stated in this embodiment can be implemented using existing technologies.

Claims

1. A method for catalyzing alcoholysis of waste polylactic acid by bicine salt, characterized in that, The product lactic acid ester is obtained by mixing the catalyst bicine salt acetate with polylactic acid in alcohol as solvent and then performing degradation reaction; The mass ratio of the alcohol to the waste polylactic acid is 7.5:1-10:1; The mass ratio of the bicine salt acetate catalyst to the waste polylactic acid is 1:20-3:40; The reaction temperature of the degradation reaction is 160-200°C, and the reaction time is 2-3 hours; The alcohol is any one of methanol, ethanol, propanol, butanol, isoamyl alcohol, isooctanol, n-dodecanol or benzyl alcohol; The bicine salt acetate is obtained by reacting 1,5,7-triazidebicyclo(4.4.0)dec-5-ene with acetic acid at a molar ratio of 1:

1.

2. The method of claim 1, wherein, The waste polylactic acid is any one or combination of waste polylactic acid packaging bag, waste polylactic acid straw and waste polylactic acid 3D printing material.

3. The method of claim 1, wherein, The degradation reaction is performed under normal pressure.

4. The method of claim 1, wherein, After the degradation reaction, the catalyst is recovered.

5. The method of claim 4, wherein, The degradation reaction liquid is reduced and filtered to obtain a filtrate, the filtrate is extracted with water, the extraction liquid is a solution containing bicine salt acetate, water is removed by evaporation, and bicine salt acetate or an alcohol solution of bicine salt acetate is recovered.

6. The method of claim 5, wherein, The recovered bicine salt acetate or alcohol solution of bicine salt acetate is recycled as a catalyst.

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