Preparation method of fatty acid methyl ester ethoxylate

Abstract

The invention discloses a method for preparing high-purity fatty acid methyl ester ethoxylate (FMEE) through catalytic ester exchange by taking methoxy polyethylene glycol (mPEG) and fatty acid methyl ester (FAME) as raw materials. According to the method, a reaction is carried out at 120-150 DEG C in an inert atmosphere under the action of a basic catalyst. According to the method, mPEG only containing one active hydroxyl is selected as a raw material, the generation path of diester byproducts is fundamentally eradicated from the molecular structure, and the problems that a traditional direct ethoxylation method is high in process risk and many in byproducts and a traditional ester exchange method is low in product purity are solved. The method has the advantages of safe and mild process, simplicity and convenience in operation, high product purity and the like, the purity of the obtained FMEE product can reach 95% or above, and the method is suitable for multiple fields such as spinning, printing and dyeing, cleaning and the like.

Description

Technical Field

[0001] This invention relates to the field of chemical technology, specifically to a process for synthesizing nonionic surfactants, and particularly to a method for synthesizing high-purity fatty acid methyl ester ethoxylates (FMEE) in high yield based on methoxy polyethylene glycol and fatty acid methyl esters via catalytic transesterification. Background Technology

[0002] Fatty acid methyl ester ethoxylates are double-terminated ester-ether type nonionic surfactants, belonging to the low-tension surfactant class, and possess strong emulsifying ability. As an environmentally friendly surfactant, compared with traditional products (such as fatty alcohol ethoxylates AEO and alkylphenol polyoxyethylene ethers TX / NP / OP series), they exhibit superior performance in many aspects: rapid defoaming, easy rinsing, excellent dispersing properties, and effective prevention of back-fogging by oils, waxes, etc. during the washing process. Due to these superior properties, they are used in various fields such as textile printing and dyeing industries and industrial hard surface cleaning.

[0003] Currently, there are two main industrial synthesis routes for fatty acid methyl ester ethoxylates: direct ethoxylation and transesterification. The biggest challenge in producing ethoxylated fatty acid methyl esters via direct ethoxylation is that the fatty acid methyl ester molecule lacks active hydrogen, making addition reactions difficult. Traditional alkaline catalysts such as sodium hydroxide and sodium methoxide are also insufficient for ethoxylation, and problems arise such as a wide molecular weight distribution, dark color, and difficulties in subsequent purification. Ethylene oxide is a flammable, explosive, and highly hazardous chemical, requiring harsh reaction conditions (high temperature and high pressure), placing extremely high demands on equipment and safety.

[0004] Another route is transesterification, which involves the transesterification of polyethylene glycol (PEG) with fatty acid methyl esters under the action of a conventional alkaline catalyst. While this method avoids the use of ethylene oxide, it still has inherent drawbacks: because conventional PEG molecules have active hydroxyl groups at both ends, when reacting with FAME, not only is the target product monoester (FMEE) generated, but it also further reacts to generate the undesirable diester (FMEEE) byproduct. This leads to a complex product composition, reduced purity, and affects its application performance.

[0005] Therefore, there is an urgent need in this field to develop a new high-purity FMEE synthesis process with mild reaction conditions, high safety, and the ability to suppress diester formation at the source. Summary of the Invention

[0006] To overcome the shortcomings of existing technologies, this invention provides a safe, simple, and high-purity FMEE preparation method. The method uses mPEG containing only one active hydroxyl group as a raw material, fundamentally eliminating the formation pathway of diester byproducts from a molecular structure perspective. This solves the problems of high risk, numerous byproducts, and low purity of products obtained through traditional direct ethoxylation methods and transesterification methods.

[0007] To achieve the above objectives, the present invention provides a method for preparing fatty acid methyl ester ethoxylates, the method comprising the following steps: [The method is described in the original text, but the provided text is incomplete and requires further context to translate accurately.] 1 -(CH2CH2O) n -H alkoxy polyethylene glycol and general formula R 2 The fatty acid methyl ester of -COOCH3 undergoes transesterification under negative pressure in the presence of an alkaline catalyst, and is then neutralized to obtain the fatty acid methyl ester ethoxylate. Among them, R 1 Selected from C 1-6 Alkoxy, preferably C 1-3 Alkyl groups, such as methoxy, ethoxy, and isopropoxy; R 2 Selected from C 11 -C 20 alkyl or alkenyl groups, where n is 5 to 20; preferably, R 2 Selected from C 12 -C 18 Alkyl or alkenyl groups.

[0008] In this invention, as one embodiment, the above preparation method includes the following steps: Make the general formula CH3O-(CH2CH2O) n -H methoxy polyethylene glycol and general formula R 2 The fatty acid methyl ester of -COOCH3 undergoes transesterification under negative pressure in the presence of an alkaline catalyst, and is then neutralized to obtain the fatty acid methyl ester ethoxylate. Where n is 5-20, R 2 C 11 -C 20 Alkyl or alkenyl groups.

[0009] The methoxy polyethylene glycol (mPEG) has the general formula CH3O-(CH2CH2O). n -H, its molecule has an inert methoxy group (-OCH3) at one end and an active hydroxyl group (-OH) at the other end, where n is the number of additions to ethylene oxide, preferably n is 7 to 15, more preferably n is 9 to 12.

[0010] It should be further noted that methoxy-terminated PEG (mPEG), due to its relatively high reactivity and smaller steric hindrance, is more likely to achieve better reaction results, and its product structure is closer to that of conventional FMEE. As the terminal alkyl chain grows and branches (such as ethoxy or isopropoxy), the steric hindrance effect becomes more significant, which may adversely affect the efficiency and final conversion rate of the transesterification reaction.

[0011] In this invention, as one embodiment, the molecular weight of the methoxy polyethylene glycol ranges from 252 to 912 g / mol, preferably from 340 to 692 g / mol, and more preferably from 428 to 560 g / mol.

[0012] In this invention, as one embodiment, the fatty acid methyl ester (FAME) is selected from methyl laurate (C... 12 ), methyl palmitate (C 16 ), methyl stearate (C 18 ), methyl cocoate (C 12 ~C 18 It may be one or more of the following: methyl oleate or methyl oleate, wherein the plurality includes two, three or more, or mixtures formed from the various fatty acid methyl esters mentioned above.

[0013] In this invention, as one embodiment, the amount of fatty acid methyl ester fed is in excess relative to methoxy polyethylene glycol. Preferably, the molar ratio of methoxy polyethylene glycol to fatty acid methyl ester is 1:1 to 1.2. For example, it can be 1:1.02, 1:1.05, 1:1.08, 1:1, 1:1.15, or 1:1.2; preferably 1:1.08 to 1.15. An appropriate excess of FAME can ensure sufficient conversion of mPEG.

[0014] In this invention, as one embodiment, the alkaline catalyst is selected from one or more of sodium methoxide, sodium ethoxide, potassium hydroxide, and potassium carbonate, and the plurality of catalysts includes two, three, or more.

[0015] In this invention, as one embodiment, the amount of the alkaline catalyst is 0.05% to 0.25% of the total mass of the methoxy polyethylene glycol and fatty acid methyl ester, preferably 0.09% to 0.15%.

[0016] In this invention, as one embodiment, the temperature of the transesterification reaction is 120-150°C, preferably 130-140°C. The reaction environment is under an inert gas atmosphere such as nitrogen or argon, and the reaction time is 2-6 hours.

[0017] In this invention, as one of the embodiments, the reaction is carried out under a slight negative pressure condition, with a pressure range of -0.098 to -0.07 MPa. The slight negative pressure condition is conducive to the distillation of the byproduct methanol and pushes the reaction equilibrium to the right.

[0018] In this invention, the post-treatment process of the transesterification reaction includes: after the reaction is completed, cooling the system to 70-85°C, adding an appropriate amount of acid to neutralize the system to a pH of 6-7, in order to destroy and neutralize the catalyst, and obtaining a light yellow to colorless transparent liquid, which is the FMEE product. Further dehydration or decolorization treatment can be performed as needed.

[0019] In this invention, as one embodiment, the acid used in the neutralization reaction during the above-mentioned post-treatment process is glacial acetic acid, phosphoric acid, or citric acid.

[0020] Compared with the prior art, the beneficial effects of the present invention are as follows: High safety: The reaction is carried out under normal or negative pressure, eliminating the need for highly hazardous ethylene oxide, reducing equipment requirements, and significantly lowering operational safety risks.

[0021] High product purity: Since the raw material mPEG has an inert methoxy group at one end and an active hydroxyl group at the other end, the possibility of generating diester byproducts (FMEEE) is completely eliminated from the molecular structure. The main reaction has extremely high selectivity, and the purity of the obtained FMEE product can reach more than 95%.

[0022] The process is simple and easy to control: the reaction is a simple transesterification process that does not require high-pressure and complex equipment. The process flow is short, the parameters are easy to control, and the product quality is stable.

[0023] It is environmentally friendly: the main byproduct of the reaction is methanol, which is easy to recycle and reuse, and generates little waste, which meets the requirements of green chemistry.

[0024] The method of this invention has a wide range of applications. It can control the production of differentiated fatty acid ester ethoxylate products according to different molecular weights of mPEG and the number of carbon atoms of aliphatic methyl esters, and has broad application value. Detailed Implementation

[0025] The present application will be further described in detail below through embodiments. Through these descriptions, the features and advantages of the present application will become clearer and more apparent.

[0026] The term “exemplary” as used herein means “serving as an example, embodiment, or illustration.” Any embodiment illustrated herein as “exemplary” is not necessarily to be construed as superior to or better than other embodiments. Although various aspects of the embodiments are shown, they are not necessarily drawn to scale unless specifically indicated.

[0027] Furthermore, the technical features involved in the different embodiments of this application described below can be combined with each other as long as they do not conflict with each other.

[0028] The R described in this invention 2 C 11 -C 20 Alkyl or alkenyl means an alkyl or alkenyl group containing 11 to 20 carbon atoms. The numerical ranges used herein are for illustrative purposes only. For example, “11-20” refers to each integer within a given range. For example, “11-20 carbon atoms” means that the group may have 11, 12, 13, 14, 15, 16, 17, 18, 19, or 20 carbon atoms.

[0029] The term "alkyl" refers to an optionally substituted straight-chain or optionally substituted branched saturated aliphatic hydrocarbon group, which is connected to the rest of the molecule by a single bond. The term "alkenyl" refers to an optionally substituted straight-chain or optionally substituted branched monovalent hydrocarbon group, which has at least one C=C double bond.

[0030] The methoxy polyethylene glycol (mPEG) described in this invention is a mixture of homologues with different degrees of polymerization, with the general formula CH3O-(CH2CH2O)nH, where n represents the average number of ethylene oxide additions. In this invention, the value of n ranges from 5 to 20, preferably from 7 to 15, and more preferably from 9 to 12. Those skilled in the art will understand that the range of n corresponds to the range of its number-average molecular weight. For example, when n is 5 to 20, its number-average molecular weight range is approximately 252 to 912 g / mol; when n is 7 to 15, its number-average molecular weight range is approximately 339 to 691 g / mol; and when n is 9 to 12, its number-average molecular weight range is approximately 428 to 560 g / mol. This invention does not impose any particular limitation on the molecular weight distribution of the polymer, and various commercially available mPEG products in the art can be used.

[0031] Example 1 To a 1000 mL four-necked flask equipped with a stirrer, thermometer, distillation column, condenser, and nitrogen inlet, add 214.0 g (0.50 mol) of methoxy polyethylene glycol mPEG-9 (n≈9, M≈428 g / mol) and 115 g (0.54 mol, molar ratio 1:1.08) of methyl laurate. Start stirring and purge the air three times with nitrogen. Then, establish a vacuum system, maintaining a system pressure of -0.085 MPa, and heat to 110°C for dehydration for 30 minutes. Remove the vacuum, maintain a nitrogen atmosphere, and add 0.34 g (0.1% of the total feed mass) of potassium hydroxide catalyst. Slowly heat to 135°C to initiate the reaction. Methanol generated during the reaction is distilled off through the distillation column and collected. Maintain this temperature for 2 hours. After the reaction, cool the system to 75°C and add 1.0 g of glacial acetic acid to neutralize to pH≈6.5. Approximately 310 g of a light yellow, transparent, flowing liquid product was obtained. High-performance liquid chromatography (HPLC) analysis showed that the FMEE content was 97.2%, no diester components were detected, the conversion rate (calculated based on mPEG) reached 97.6% using HPLC area normalization, and the color was ≤80.

[0032] Example 2 The procedure was the same as in Example 1, except that the raw materials were changed to: 280.0 g (0.50 mol) of mPEG-12 (n≈12, M≈560 g / mol) and 161.2 g (0.54 mol, molar ratio 1:1.08) of methyl stearate. The catalyst was 0.43 g (0.1%) of potassium hydroxide, the reaction temperature was 135°C, and the reaction time was 2 hours. Approximately 413.3 g of a light yellow, transparent, viscous liquid product was obtained. HPLC analysis showed that the FMEE content was 96.8%, the conversion rate was 96.9%, there was no diester, and the color was ≤80.

[0033] Example 3 The procedure was the same as in Example 1, except that the raw materials were changed to: 126 g (0.50 mol) of mPEG-5 (n≈5, M≈252 g / mol) and 115.4 g (0.54 mol, molar ratio 1:1.08) of methyl lauryl acetate. The catalyst was 0.24 g (0.1%) of potassium hydroxide, the reaction temperature was 135°C, and the reaction time was 2 hours. Approximately 225.6 g of a light yellow, transparent, flowing liquid product was obtained. HPLC analysis showed that the FMEE content was 95.4%, the conversion rate was 99.2%, there was no diester, and the color was ≤80.

[0034] Example 4 The procedure was the same as in Example 1, except that the raw materials were changed to: 300 g (0.33 mol) of mPEG-20 (n≈20, M≈912 g / mol) and 75.93 g (0.36 mol, molar ratio 1:1.08) of methyl lauryl acetate. The catalyst was 0.38 g (0.1%) of potassium hydroxide, the reaction temperature was 135°C, and the reaction time was 2 hours. Approximately 360.2 g of a yellow, transparent, viscous liquid product was obtained. HPLC analysis showed that the FMEE content was 94.7%, the conversion rate was 94.5%, there was no diester, and the color was ≤100.

[0035] Example 5 The procedure was the same as in Example 1, except that the FAME feedstock was changed to 160.11 g (0.54 mol, molar ratio 1:1.08) of methyl oleate with an olefinic structure. The catalyst was 0.37 g (0.1%) of potassium hydroxide, the reaction temperature was 135°C, and the reaction time was 2 hours. Approximately 345.5 g of a brownish-yellow flowing liquid product was obtained. HPLC analysis showed that the FMEE content was 97%, the conversion rate was 96.9%, there was no diester, and the color was ≥250.

[0036] Example 6 The procedure was the same as in Example 1, with the catalyst changed as follows: 0.2 g sodium methoxide + 0.29 g potassium hydroxide, the total amount of the composite catalyst was 0.15% of the total feed amount, the system pressure was controlled at -0.085 MPa, the reaction temperature was 125°C, and the reaction time was 2 hours. HPLC analysis showed that the FMEE content was 97.5%, the conversion rate reached 98.1%, there was no diester, and the color was ≤60.

[0037] Example 7 The procedure was the same as in Example 1, except that PEG was terminally capped with isopropoxy groups, with the EO addition number being the same as mPEG at 9, i.e., 227 g (0.50 mol) of iPrO-PEG-OH (M≈456 g / mol) and 115 g (0.54 mol, molar ratio 1:1.08) of methyl lauryl ester. The catalyst was 0.34 g (0.1%) of potassium hydroxide, the reaction temperature was 135°C, and the reaction time was 2 hours. Approximately 326 g of a brownish-yellow, transparent, viscous liquid product was obtained. HPLC analysis showed that the FMEE content was 89.6%, the conversion rate reached 98.2%, there was no diester, and the color was ≥200.

[0038] Comparative Example 1 In the same apparatus as in Example 1, the following were added: 200.0 g (0.50 mol) of polyethylene glycol (PEG-400, M≈400 g / mol, hydroxyl groups at both ends) and 108.17 g (0.54 mol, molar ratio 1:1.08) of methyl lauryl acetate. The operating procedures, catalyst, and other conditions were exactly the same as in Example 1. After the reaction was complete, neutralization was performed using the same procedure to obtain the product.

[0039] High performance liquid chromatography (HPLC) analysis showed that the FMEE content was 84.5%, the conversion rate was 93.4%, the diester component (FMEEE) content was 8.9%, the unreacted PEG content was 6.6%, and the color was ≤150.

[0040] Comparative Example 2 FMEE was prepared by ethoxylation. 100 g of methyl laurate was used as an initiator and mixed with 0.57 g of MgO / Al₂O₃ binuclear metal oxide (0.2%). The mixture was heated to 100°C and stirred until uniformly dispersed. The temperature was maintained at 100°C, and the mixture was stirred and dehydrated under vacuum for 2 hours. The temperature was then raised to 170°C, and 10 g of ethylene oxide was added to the reaction vessel. The pressure change was observed. When the pressure dropped to half of the initial pressure, 174.75 g of ethylene oxide was continuously added to the reaction vessel. The reaction temperature was controlled at 170 ± 5°C, and the pressure at 0.3–0.6 MPa (gauge pressure). The reaction was allowed to proceed for 3–6 hours, and after the material flow was completed, the mixture was kept at this temperature for 1 hour until the pressure no longer decreased. After the reaction was completed, the reactor was cooled to 60–70°C. After releasing the residual pressure in the reactor, the material was discharged. A yellow, slightly turbid crude product of methyl laurate ethoxylate was obtained. After separation by centrifugation at 3000 rpm / 10 min, the supernatant was neutralized with glacial acetic acid to pH 6.5 to obtain the product FMEE.

[0041] High performance liquid chromatography (HPLC) analysis showed that the FMEE content was 92%, the unreacted methyl laurate content was 1.5%, the content of the byproduct PEG was 5.6%, and the color was ≥200.

[0042] Comparative Example 3 The procedure was the same as in Example 1, maintaining the system pressure at -0.05 MPa throughout the reaction, with a reaction time of 4 hours. Methanol distilled off during the reaction and was collected. After the reaction was complete, the system was cooled to 75°C, and 1.0 g of glacial acetic acid was added to neutralize to pH ≈ 6.5. Approximately 360 g of a light yellow, transparent, flowing liquid product was obtained.

[0043] High-performance liquid chromatography (HPLC) analysis showed that the FMEE content was 90.8%, significantly lower than 97.2% in Example 1, with a conversion rate of 91.5%. Unreacted mPEG residue was 7.2%, and no diester content was detected. The color was ≥100, slightly darker than in Example 1 due to the longer reaction time and incomplete conversion. The amount of methanol collected was approximately 14.8 g, significantly lower than the theoretical amount (17.6 g), confirming that the methanol was not effectively removed.

[0044] Table 1. Analysis results of the products obtained from each embodiment and comparative example.

[0045] The product obtained in Example 1 of this invention and the product obtained in Comparative Example 1 were prepared into a 1% aqueous solution and subjected to key application performance tests.

[0046] Table 2 shows the application performance test results obtained from Example 1 and Comparative Example 1.

[0047] The above examples and comparative examples fully demonstrate that the transesterification method using methoxylated polyethylene glycol (mPEG) as a raw material, compared with the traditional transesterification method using polyethylene glycol (PEG) as a raw material, fundamentally avoids the formation of diester byproducts, thus obtaining FMEE products with significantly higher purity. Simultaneously, the method of this invention avoids the inherent technical defects of the direct ethoxylation method for synthesizing FMEE: harsh reaction conditions (high temperature and high pressure), use of high-risk raw materials (ethylene oxide), low product purity (containing byproducts such as PEG), and safety hazards related to dark color. These problems limit its production safety and product quality. The higher purity product obtained through the method of this invention also brings superior and more stable application performance (such as emulsification, dispersion, and low foaming properties).

[0048] Maintaining a sufficiently high vacuum (such as -0.085 MPa in Example 1) is crucial for efficient methanol removal, shifting the reaction equilibrium to the right, and thus achieving high conversion and high product purity. It is not an obvious parameter, but rather a key point that requires careful control and optimization in the process of this invention, providing strong data support for the preferred process conditions of this invention.

[0049] Furthermore, Example 7 used isopropoxy-terminated PEG as a raw material. Compared with Examples 1-6, which used methoxy groups as the terminating group, the FMEE content (%) of Example 7 was slightly lower, and the conversion rate was also relatively lower. In comparison, it can be seen that the best implementation method of this invention is to use methoxy polyethylene glycol (mPEG) as the terminating group to prepare the fatty acid methyl ester ethoxylate, and the product content and conversion rate are both at a better level.

[0050] Therefore, this invention provides a new process for synthesizing FMEE that is efficient, safe, green, and produces products with excellent quality.

[0051] The present application has been described above with reference to preferred embodiments; however, these embodiments are merely exemplary and illustrative. Various substitutions and modifications can be made to the present application based on these embodiments, all of which fall within the protection scope of the present application.

Claims

1. A method for preparing fatty acid methyl ester ethoxylates, characterized in that, Includes the following steps: Make the general formula R 1 -(CH2CH2O) n -H alkoxy polyethylene glycol and general formula R 2 The fatty acid methyl ester of -COOCH3 undergoes transesterification under negative pressure in the presence of an alkaline catalyst, and is then neutralized to obtain the fatty acid methyl ester ethoxylate. Among them, R 1 Selected from C 1-6 Alkoxy, preferably C 1-3 Alkoxy; R 2 Selected from C 11 -C 20 Alkyl or alkenyl groups, where n is 5 to 20.

2. The preparation method according to claim 1, characterized in that, Includes the following steps: Make the general formula CH3O-(CH2CH2O) n -H methoxy polyethylene glycol and general formula R 2 The fatty acid methyl ester of -COOCH3 undergoes transesterification under negative pressure in the presence of an alkaline catalyst, and is then neutralized to obtain the fatty acid methyl ester ethoxylate. Where n is 5~20, R 2 Selected from C 11 -C 20 Alkyl or alkenyl groups.

3. The preparation method according to claim 2, characterized in that, The methoxy polyethylene glycol has a molecular weight range of 252~912 g / mol, preferably 340~692 g / mol, and more preferably 428~560 g / mol.

4. The preparation method according to claim 2, characterized in that, The amount of fatty acid methyl ester fed is in excess relative to methoxy polyethylene glycol. Preferably, the molar ratio of methoxy polyethylene glycol to fatty acid methyl ester is 1:1 to 1.

2.

5. The preparation method according to claim 2 or 4, characterized in that, The alkaline catalyst is selected from one or more of sodium methoxide, sodium ethoxide, potassium hydroxide, and potassium carbonate.

6. The preparation method according to claim 2, characterized in that, The amount of alkaline catalyst used is 0.05% to 0.25% of the total mass of the methoxy polyethylene glycol and fatty acid methyl ester, preferably 0.09% to 0.15%.

7. The preparation method according to claim 1 or 2, characterized in that, The temperature of the transesterification reaction is 120-150°C, preferably 130-140°C.

8. The preparation method according to claim 1 or 2, characterized in that, The reaction is carried out under negative pressure conditions, with a pressure range of -0.098 to -0.07 MPa.

9. The preparation method according to claim 1 or 2, characterized in that, The fatty acid methyl ester is selected from one or more of methyl laurate, methyl palmitate, methyl stearate, methyl cocoate, or methyl oleate.

10. The preparation method according to claim 1 or 2, characterized in that, The post-reaction processing is as follows: cool the reaction system to 70-85°C, neutralize with acid to pH 6-7, and obtain a transparent fatty acid methyl ester ethoxylate product.

11. The preparation method according to claim 10, characterized in that, The acid used in the neutralization reaction is glacial acetic acid, phosphoric acid, or citric acid.

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