Method for preparing polyoxymethylene dimethyl ether by using ethylene glycol and glycerol extraction technology

Abstract

The invention discloses a method for preparing polyoxymethylene dimethyl ether by using an ethylene glycol and glycerol extraction technology, and belongs to the technical field of preparation of new energy synthetic fuels and environment-friendly solvents. Aiming at the problems of rectification tower blockage, low product yield and environmental pollution caused by an impurity removal process due to the fact that a synthetic product contains impurities such as formaldehyde, water and formic acid in an existing process, the invention adopts the following technical scheme: formaldehyde and methylal are used as raw materials, and a DMM2-5 product mixture is synthesized under the catalysis of a solid acid catalyst; ethylene glycol or glycerol is adopted as a single extraction agent, strong polar impurities are removed through 5-10 stages of extraction, and a target product and methylal are enriched in a light phase; and carrying out multi-tower continuous rectification and purification to obtain high-purity DMM2 and DMM3-5 products. The extraction agent and unreacted raw materials can be recycled and reused, so that closed-loop production is realized. The process is green and waste-free, impurities are thoroughly removed (formaldehyde is less than 0.5%, and water is less than 0.1%), the product purity is more than or equal to 99.1%, the yield is 85-95%, the operation is mild and safe, the adaptability is high, and the process conforms to the coal clean and efficient utilization policy and is suitable for production of environment-friendly solvents and national VI standard clean diesel components.

Description

Technical Field

[0001] This invention relates to the field of new energy synthetic fuel and environmentally friendly solvent preparation technology, specifically to a method for preparing polyoxymethylene dimethyl ether using ethylene glycol and glycerol extraction technology. Background Technology

[0002] Polyoxymethylene dimethyl ether (DMM) n Its chemical formula is CH3O(CH2O). n CH3 is an internationally recognized environmentally friendly solvent and clean fuel component. Due to its excellent properties such as high oxygen content (42-53%), high cetane number (CN>70), and good compatibility with diesel, it can significantly reduce the emission of black smoke and PM2.5 particles in diesel vehicle exhaust.

[0003] Currently, formaldehyde and methyl acetal are commonly used in industry to synthesize polyoxymethylene dimethyl ether under the action of an acidic catalyst. However, this synthesis reaction is a reversible chemical equilibrium reaction, and the product mixture inevitably contains 5-11% unreacted formaldehyde, 1-3% water, and formic acid produced by the disproportionation reaction of formaldehyde. These impurities have a serious negative impact on the subsequent separation and purification process: First, residual formaldehyde is prone to condensation at the top of the distillation column, causing column blockage and directly affecting product purity and continuous distillation operation; Second, in the high acidity environment of formic acid, water and methyl acetal are prone to hydrolysis. Further generation of formaldehyde and methanol worsens the separation effect; thirdly, formic acid, as an acidic catalyst, will promote the reverse decomposition of polyoxymethylene dimethyl ether. It significantly reduces product yield and purity, and may even make continuous distillation impossible.

[0004] To address the aforementioned issues, existing technologies attempt to remove impurities using methods such as alkaline washing and adsorption. However, alkaline washing processes generate large amounts of waste alkaline solution, causing environmental pollution and increasing treatment costs. Adsorption methods suffer from drawbacks such as limited adsorption capacity, frequent regeneration, and unstable removal efficiency, making it difficult to meet the demands of continuous industrial production. Therefore, developing a green, environmentally friendly, highly efficient, and low-consumption method for preparing polyoxymethylene dimethyl ether that can deeply remove impurities such as formaldehyde, water, and formic acid has become a pressing technical challenge in this field. Summary of the Invention

[0005] To address the shortcomings of existing technologies where impurities such as formaldehyde, water, and formic acid in the synthesis products of polyoxymethylene dimethyl ether (POMED) affect subsequent distillation and purification, resulting in low product yield and insufficient purity, and where existing impurity removal processes are environmentally polluting and energy-intensive, this invention provides a method for preparing POMED using ethylene glycol and glycerol extraction technology. This method achieves deep removal of impurities, efficient product purification, and resource recycling, combining environmental friendliness and economic efficiency.

[0006] To solve the above-mentioned technical problems, the present invention adopts the following technical solution:

[0007] A method for preparing polyoxymethylene dimethyl ether using ethylene glycol and glycerol extraction technology includes the following steps:

[0008] S1. Synthesis Reaction: Using formaldehyde and dimethyl acetal (DMM) as raw materials, the mixture is introduced into a fixed-bed reactor and reacted under the catalysis of a solid acid catalyst to synthesize polyoxymethylene dimethyl ether (DMM) containing formaldehyde, water, formic acid, methanol, dimethyl ether, and methyl formate. 2-5 Product mixture;

[0009] S2. Extraction Process: Environmentally friendly ethylene glycol or glycerol is used as the single extractant to process the polyoxymethylene dimethyl ether (DMM) in an extraction apparatus. 2-5 The product mixture undergoes multi-stage extraction, separating the heavy and light phases based on density difference, partition coefficient, and the principle of like compatibility. Formaldehyde, formic acid, water, and methanol are extracted into the heavy phase, while the raffinate (light phase) is enriched with methyl acetal and polyoxymethylene dimethyl ether (DMM). 2-5 ;

[0010] S3. Distillation and purification: The light phase is directly subjected to multi-tower continuous distillation, sequentially passing through a light phase removal distillation tower, a dehydration distillation tower, and a vacuum distillation tower to separate high-purity DMM2 product and high-purity DMM. 3-5 product.

[0011] Furthermore, the method further includes the following steps:

[0012] S4. Recycling: The heavy phase obtained from the extraction in step S2 is passed into a distillation recovery column to treat the heavy phase. Formaldehyde, methanol, water, and formic acid are recovered from the top of the column and returned to the methyl acetal preparation unit. Ethylene glycol or glycerol is recovered from the bottom of the column and recycled as an extractant for the extraction treatment in step S2. At the same time, the top of the distillation column for removing light phases is returned to the polyoxymethylene dimethyl ether synthesis unit in step S1 for recycling.

[0013] Preferably, in step S1, 50%–95% by volume of formaldehyde and 92%–99% by volume of methylal are added, wherein the molar ratio of formaldehyde to methylal is 1:(2–5); to synthesize polyoxymethylene dimethyl ether (DMM). 2-5 The reaction temperature is 80–100℃, the reaction pressure is 0.4–0.6 MPa, and the mass hourly space velocity is 0.1–0.5 h⁻¹. -1 The synthesized product contains 3-7% unreacted formaldehyde, 1-3.5% water, and formic acid, measured by acidity, not exceeding 40 mg KOH / 100 ml.

[0014] Preferably, the solid acid catalyst added in step S1 is a sulfonic acid-type macroporous cation exchange resin catalyst with an exchange capacity of 4.5–5.5 mmol / g and a specific surface area of ​​30–50 m². 2 / g.

[0015] Preferably, in step S2, the extraction device is one of a multi-stage rotating disc tower, a centrifugal extractor, or a packed extraction tower, and the number of extraction stages is 5 to 10.

[0016] More preferably, the multi-stage rotary disc tower has 20 to 30 trays and a rotary disc speed of 150 to 300 r / min; the centrifugal extractor has a speed of 3000 to 5000 r / min; and the packed extraction tower uses θ-ring packing with a packing layer height of 1.5 to 3 m.

[0017] Preferably, in step S2, the added extractant and polyoxymethylene dimethyl ether (DMM) 2-5 The volume ratio of the products was (20-40):(60-80), and the extraction temperature was 20-40℃.

[0018] More preferably, the extraction temperature is 25-35℃, the yield of the light phase rich in polyoxymethylene dimethyl ether is 85-95%, and the formaldehyde content, water content and acidity of the extracted polyoxymethylene dimethyl ether product are less than 0.5%, less than 0.1% and less than 7 mg KOH / 100 ml.

[0019] Furthermore, the multi-tower continuous distillation in step S3 includes:

[0020] The distillation column for removing light pollutants has a top temperature of 41–43°C and a bottom temperature of 89–95°C. The methyl acetal collected at the top is recycled, while the material at the bottom enters the distillation dehydration column.

[0021] The distillation dehydration column has a top temperature of 85-90℃ and a bottom temperature of 115-126℃. Water, formaldehyde, formic acid, and a small amount of DMM2 are collected from the top of the column and returned to step S2. The bottom material enters the vacuum distillation column.

[0022] The vacuum distillation column has a top temperature of 48–51°C, a bottom temperature of 97–118°C, and an operating pressure of 14.4–14.6 kPa. DMM2 is collected from the top of the column, and DMM is collected via a side stream. 3-5 The extractant collected from the bottom of the tower is recycled.

[0023] Preferably, in step S4, the distillation recovery column is an atmospheric distillation column with 5 to 10 trays, a bottom temperature of 112 to 129°C, and a top temperature of 45 to 100°C. The formaldehyde, methanol, formic acid, and water collected from the top are returned to the methanol and formaldehyde catalytic distillation unit to produce methyl acetal, so as to fully utilize methanol and formaldehyde to produce methyl acetal. The ethylene glycol or glycerol collected from the bottom is recycled as an extractant.

[0024] The technical solution of this invention has the following advantages:

[0025] A. Excellent environmental performance, product suitable for high-end needs: This invention uses sulfur-free, nitrogen-free, and aromatic-free ethylene glycol or glycerol as a single extractant, generating no waste alkali liquid or solid waste residue throughout the entire process, making the process green and environmentally friendly; the prepared polyoxymethylene dimethyl ether (DMM) n The product is also free of harmful impurities such as sulfur, nitrogen, and aromatics. It can be used as an environmentally friendly solvent and as a component of high cetane-number clean diesel fuel that meets the China VI standard. It effectively reduces black smoke and PM2.5 particulate matter emissions from diesel vehicle exhaust, which is in line with the industrial policy of clean and efficient utilization of coal.

[0026] B. Overcoming existing technological pain points, achieving efficient and stable distillation purification: This invention precisely removes highly polar impurities such as formaldehyde, water, and formic acid from the synthesized products through multi-stage extraction, resulting in formaldehyde content below 0.5%, water content below 0.1%, and acidity below 7 in the light phase. This completely solves the problems of formaldehyde blockage in the distillation tower, hydrolysis reaction of water and methyl acetal, and formic acid catalysis of DMM in traditional processes. n Problems such as reverse decomposition are eliminated; the light phase can be directly fed into multi-tower continuous distillation without additional pretreatment steps, which greatly shortens the process flow. Moreover, atmospheric and vacuum distillation technologies are mature and easy to implement, significantly improving production continuity and stability.

[0027] C. High resource recycling rate and reduced production costs: In this invention, the extractant (ethylene glycol / glycerol) can be recycled after being processed by the distillation recovery tower, with high recovery rate and stable performance; the formaldehyde and methanol separated by extraction, as well as the 96-99% high-purity methyl acetal recovered by the distillation light removal tower, can all be returned to the methyl acetal preparation unit or the polyoxymethylene dimethyl ether synthesis unit for reuse, realizing a closed-loop recycling of raw materials, greatly reducing resource waste, and lowering the cost of raw material procurement and waste disposal.

[0028] D. High product yield and purity, with outstanding application value: After multi-stage extraction, the light phase rich in the target product of this invention achieves a yield of 85-95%, and subsequent distillation purification can yield DMM2 and DMM with a purity of not less than 99.1%. 3-5 Products, including DMM 3-5 It retains the advantages of a high cetane number of 78-100 and a high oxygen content of 47-48.9%, which not only result in high combustion efficiency and good combustion-supporting effect, but also excellent compatibility with diesel fuel. It can significantly improve the combustion performance of diesel engines and has a strong market competitiveness in the field of clean fuels.

[0029] E. The process is safe and reliable, and the operating conditions are mild: The extraction process of this invention is a physical separation process, which does not require high temperature and high pressure reaction conditions. The operating temperature is controlled at 20-40℃, the process is safe and controllable, and the risks of equipment corrosion and production safety are reduced. At the same time, there is no need to use strong acids, alkalis and other hazardous chemicals, the operating environment is more friendly, the material requirements of the production equipment are lower, and the equipment investment and operation and maintenance costs are further reduced.

[0030] F. Strong process adaptability and flexible adaptation to different production needs: The extraction device of this invention can flexibly select multi-stage rotating disc tower, centrifugal extractor or packed extraction tower (preferably 5-10 stage high-efficiency mass transfer equipment) according to the production scale. The volume ratio of extractant to synthesis product can be adjusted in the range of 20-40:60-80. It can also adapt to different raw material ratios with formaldehyde content of 50-95% and methylal content of 92-99%, meet the production needs under different production capacity and raw material supply conditions, and has a wide range of applications. Attached Figure Description

[0031] To more clearly illustrate the specific embodiments of the present invention, the accompanying drawings used in the specific embodiments will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0032] Figure 1 This is a schematic diagram of the process flow for preparing polyoxymethylene dimethyl ether using ethylene glycol multi-stage extraction in this invention;

[0033] Figure 2 This is a schematic diagram of the process flow for preparing polyoxymethylene dimethyl ether using glycerol multi-stage extraction in this invention.

[0034] Figure 3 Schematic diagram of a multi-stage extraction device for a rotating disc tower or sieve plate tower;

[0035] Figure 4 A schematic diagram of the recovery and recycling process of ethylene glycol / glycerol extractant;

[0036] Figure 5 This is a schematic diagram of the process for recovering ethylene glycol / glycerol extractant and recycling methanol and methylal.

[0037] The diagram is labeled as follows:

[0038] 1-Fixed bed reactor; 2-Extraction device; 3-Distillation column for removing light pollutants; 4-Distillation column for dehydration; 5-Vacuum distillation column; 6-Distillation recovery column. Detailed Implementation

[0039] This invention can be embodied in many different forms and should not be construed as limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the inventive concept to those skilled in the art. All other embodiments derived by those skilled in the art based on the embodiments of this invention without inventive effort are within the scope of protection of this invention.

[0040] like Figures 1-5 As shown, the overall process flow of this invention is as follows:

[0041] (1) Formaldehyde with a content of 50-95% and methyl acetal with a content of 92-99% are synthesized into a mixture of polyoxymethylene dimethyl ether products by solid acid catalysis in a fixed-bed reactor 1. The reactor outlet stream is fed from the middle and lower part of the multi-stage extraction tower 2, and ethylene glycol or glycerol extractant is fed from the middle and upper part of the multi-stage extraction tower 2. The volume ratio of extractant to polyoxymethylene dimethyl ether synthesis product is controlled at 20-40:60-80. The heavy phase is collected from the bottom of the multi-stage extraction tower 2 and is rich in polyoxymethylene dimethyl ether (DMM). n The light phase of the product is collected from the top of the multistage extraction column 2;

[0042] (2) Rich in polyoxymethylene dimethyl ether (DMM) n The light phase of the product, after heat exchange, enters the atmospheric distillation column 3 for light phase removal. The top of the column yields 96-99% high-purity methyl acetal, which is used as a raw material for synthesis. The bottom product enters the distillation dehydration column 4. The top of the distillation dehydration column 4 yields water, formaldehyde, and formic acid, which are returned to the methyl acetal production unit. The bottom product is high-purity DMM, free of water, formaldehyde, and formic acid. 2-5 The product enters vacuum distillation column 5; high-purity product DMM2 is collected from the top of the vacuum distillation column, and high-purity product DMM is collected from the measuring line. 3-5 (DMM3 and DMM can be flexibly sampled as needed) 3-4 (Flexible product solutions) The ethylene glycol or glycerol extractant collected from the bottom of the tower can be recycled;

[0043] (3) The methanol, formaldehyde, formic acid and water in the heavy phase (extracting phase) are separated from the top of the column by the atmospheric distillation recovery column 6 and returned to the methyl acetal preparation unit to make full use of methanol and formaldehyde, while ethylene glycol or glycerol is collected from the bottom of the column and used as an extractant.

[0044] Example 1

[0045] like Figure 2 As shown, this embodiment provides a method for preparing polyoxymethylene dimethyl ether using glycerol extraction technology, including the following steps:

[0046] S1. Using 50% formaldehyde solution and 99% methyl acetal as raw materials, with a formaldehyde:methyl acetal molar ratio of 1:5, the mixture is introduced into fixed-bed reactor 1. The synthesis reaction is carried out under the action of a sulfonic acid-type macroporous cation exchange resin catalyst at a reaction temperature of 100℃, a reaction pressure of 0.6MPa, and a reaction space velocity of 0.5h⁻¹. -1 DMM in polyoxymethylene dimethyl ether synthesis materials 2-5 Content 9.7%, formaldehyde content 2.64%, water content 3.26%, methanol content 6.8%, methyl acetal 77.3%, acidity 22;

[0047] S2. At 35°C, the synthesized material and the extractant glycerol were fed into the upper and lower sections of a rotating disc column at a volume ratio of 80:20 for multi-stage extraction to obtain light and heavy phases. The light phase, rich in polyoxymethylene dimethyl ether, had a yield of 91%. The light phase contained DMM... 2-5 Content 17.3%, methanol content 2.94%, methyl acetal 79.6%, residual formaldehyde content 0.06%, water content 0.1%, acidity 6.5;

[0048] S3. The light phase is fed from the column into the atmospheric distillation delight removal column 3 for continuous distillation. The bottom temperature of the column is 89-95℃ and the top temperature is 41-43℃. 97% pure methyl acetal is collected from the top (to be returned to the synthesis unit as a raw material for the synthesis of polyoxymethylene dimethyl ether). The bottom material enters the atmospheric distillation dehydration column 4. The bottom temperature of the distillation dehydration column 4 is 115-126℃ and the top temperature is 85-90℃. Water, formaldehyde, formic acid, and a small amount of DMM2 are collected from the top (returned to step S2). DMM2 is collected from the bottom. 2-5 The purity is 92.3%, and the glycerol content is 7.7%. The bottom material enters vacuum distillation column 5, with a bottom temperature of 97–118℃, a top temperature of 48–51℃, and an operating pressure of 14.4–14.6 kPa. The top product is DMM2 with a purity of 99.53%, and the test line is DMM with a purity of 99.4%. 3-5 The product, glycerol extracted from the bottom of the tower, is recycled.

[0049] S4, the heavy phase is the glycerol extraction phase. The feed enters atmospheric distillation recovery column 6, with 10 trays, a bottom temperature of 112–129°C, and a top temperature of 45–100°C. The top product contains methylal, methanol, formaldehyde, water, and a small amount of DMM2 (DMM2 and water azeotropic temperature 87°C). The top product is returned to the methanol and formaldehyde catalytic distillation unit to produce methylal, fully utilizing methanol, formaldehyde, and DMM2 to produce high-purity methylal. The glycerol collected from the bottom is recycled as an extractant (e.g.,...). Figure 5 (As shown).

[0050] Example 2

[0051] like Figure 2As shown, this embodiment provides a method for preparing polyoxymethylene dimethyl ether using glycerol extraction technology, including the following steps:

[0052] S1. Using 85% formaldehyde solution and 92% methyl acetal as raw materials, with a formaldehyde:methyl acetal molar ratio of 1:3, the mixture is introduced into fixed-bed reactor 1. The synthesis reaction is carried out under the action of a sulfonic acid-type macroporous cation exchange resin catalyst at a reaction temperature of 90℃, a reaction pressure of 0.4MPa, and a reaction space velocity of 0.4h. -1 DMM in polyoxymethylene dimethyl ether synthesis materials 2-5 Content, formaldehyde content, water content, methanol content, methyl acetal content, and acidity are shown in Table 1;

[0053] Table 1. Compositional distribution of polyoxymethylene dimethyl ether synthesis products

[0054] Dimethyl ether (%) 0.03％ Methanol (%) 7.68％ Methyl formate (%) 0.23％ Methylal (%) 71.46％ DMM2 (%) 16.59％ DMM3 (%) 3.32％ DMM4 (%) 0.61％ DMM5 (%) 0.09％ DMM6 (%) 0.00％ formaldehyde(%) 6.86％ Acid value (mgKOH / 100mL) 10.5 Moisture (%) 1.39％ DMMn% 20.61％

[0055] S2. At 25°C, the synthetic material and extractant glycerol were fed into the upper and lower sections of a rotating disc column at a volume ratio of 75:25 for multi-stage extraction to obtain light and heavy phases. The light phase, rich in polyoxymethylene dimethyl ether, had a yield of 95%. The light phase contained DMM... 2-5 Content 31.7%, methanol content 1.98%, methyl acetal content 65.7%, residual formaldehyde content 0.42%, water content 0.13%, acidity 3;

[0056] S3. The light phase is fed from the column into the atmospheric distillation delight removal column 3 for continuous distillation. The bottom temperature of the column is 89-95℃ and the top temperature is 41-43℃. 97% pure methyl acetal is collected from the top (to be returned to the synthesis unit as a raw material for the synthesis of polyoxymethylene dimethyl ether). The bottom material enters the atmospheric distillation dehydration column 4. The bottom temperature of the distillation dehydration column 4 is 115-126℃ and the top temperature is 85-90℃. Water, formaldehyde, formic acid, and a small amount of DMM2 are collected from the top (returned to step S2). DMM2 is collected from the bottom. 2-5 The purity is 93.1%, and the glycerol content is 6.9%. The bottom material enters vacuum distillation column 5, with a bottom temperature of 97–118℃, a top temperature of 48–51℃, and an operating pressure of 14.4–14.6 kPa. The top product is DMM2 with a purity of 99.5%, and the test line yields DMM with a purity of 99.2%. 3-5 The product, glycerol extracted from the bottom of the tower, is recycled.

[0057] S4, the heavy phase is the glycerol extraction phase. The feed enters atmospheric distillation recovery column 6, with 10 trays, a bottom temperature of 112–129°C, and a top temperature of 45–100°C. The top product contains methylal, methanol, formaldehyde, water, and a small amount of DMM2 (DMM2 and water azeotropic temperature 87°C). The top product is returned to the methanol and formaldehyde catalytic distillation unit to produce methylal, fully utilizing methanol, formaldehyde, and DMM2 to produce high-purity methylal. The glycerol collected from the bottom is recycled as an extractant (e.g.,...). Figure 5 (As shown).

[0058] Example 3

[0059] like Figure 2 As shown, this embodiment provides a method for preparing polyoxymethylene dimethyl ether using glycerol extraction technology, including the following steps:

[0060] S1. Using 75% formaldehyde solution and 99% methyl acetal as raw materials, with a formaldehyde:methyl acetal molar ratio of 1:2, the mixture is introduced into fixed-bed reactor 1. The synthesis reaction is carried out under the action of a sulfonic acid-type macroporous cation exchange resin catalyst at a reaction temperature of 80℃, a reaction pressure of 0.6MPa, and a reaction space velocity of 0.2h. -1 DMM in polyoxymethylene dimethyl ether synthesis materials 2-5 The content of formaldehyde, water, methanol, methyl acetal, and acidity are shown in Table 2.

[0061] Table 2 Compositional Distribution of Polyoxymethylene Dimethyl Ether Synthesis Products

[0062]

[0063]

[0064] S2. At 20°C, the synthesized material and the extractant glycerol were fed into the upper and lower sections of a rotating disc column at a volume ratio of 70:30 for multi-stage extraction to obtain light and heavy phases. The light phase, rich in polyoxymethylene dimethyl ether, had a yield of 92%. The light phase contained DMM... 2-5 Content 27.7%, methanol content 2.1%, methyl acetal 69.79%, residual formaldehyde content 0.35%, water content 0.11%, acidity 6.

[0065] S3. The light phase is fed from the column into the atmospheric distillation delight removal column 3 for continuous distillation. The bottom temperature of the column is 89-95℃ and the top temperature is 41-43℃. 97% pure methyl acetal is collected from the top (to be returned to the synthesis unit as a raw material for the synthesis of polyoxymethylene dimethyl ether). The bottom material enters the atmospheric distillation dehydration column 4. The bottom temperature of the distillation dehydration column 4 is 115-126℃ and the top temperature is 85-90℃. Water, formaldehyde, formic acid, and a small amount of DMM2 are collected from the top (returned to step S2). DMM2 is collected from the bottom. 2-5The purity is 94.2%, and the glycerol content is 5.8%. The bottom material enters vacuum distillation column 5, with a bottom temperature of 97–118℃, a top temperature of 48–51℃, and an operating pressure of 14.4–14.6 kPa. The top product is DMM2 with a purity of 99.46%, and the test line is DMM with a purity of 99.24%. 3-5 The product, glycerol extracted from the bottom of the tower, is recycled.

[0066] S4, the heavy phase is the glycerol extraction phase. The feed enters atmospheric distillation recovery column 6 with 5 trays. The bottom temperature is 112–129℃, and the top temperature is 45–100℃. The top product from distillation column IV contains methylal, methanol, formaldehyde, water, and a small amount of DMM2 (DMM2 and water azeotropic temperature 87℃). The top product is returned to the methanol and formaldehyde catalytic distillation unit to produce methylal, fully utilizing methanol, formaldehyde, and DMM2 to produce high-purity methylal. The glycerol from the bottom is recycled as an extractant (e.g.,...). Figure 5 (As shown).

[0067] Example 4

[0068] like Figure 1 As shown, this embodiment provides a method for preparing polyoxymethylene dimethyl ether using ethylene glycol extraction technology, including the following steps:

[0069] S1. Using 95% formaldehyde solution and 92% methyl acetal as raw materials, with a formaldehyde:methyl acetal molar ratio of 1:2, the mixture is introduced into fixed-bed reactor 1. The synthesis reaction is carried out under the action of a sulfonic acid-type macroporous cation exchange resin catalyst at a reaction temperature of 100℃, a reaction pressure of 0.6MPa, and a reaction space velocity of 0.1h. -1 DMM in polyoxymethylene dimethyl ether synthesis materials 2-5 The content of formaldehyde, water, methanol, methyl acetal, and acidity are shown in Table 3.

[0070] Table 3 Compositional distribution of polyoxymethylene dimethyl ether synthesis products

[0071] Dimethyl ether (%) 0.13％ Methanol (%) 8.78％ Methyl formate (%) 0.00％ Methylal (%) 65.54％ DMM2 (%) 20.27％ DMM3 (%) 5.55％ DMM4 (%) 1.42％ <![CDATA[DMM5(%)]]> 0.34％ <![CDATA[DMM6(%)]]> 0.08％ <![CDATA[DMM 2-6 ]]> 27.66％ formaldehyde(%) 6.94％ Acid value (mgKOH / 100mL) 10.5 Moisture (%) 1.90％

[0072] S2. At 40°C, the synthetic material and extractant ethylene glycol were fed into the upper and lower sections of a rotating disc column at a volume ratio of 60:40 for multi-stage extraction to obtain light and heavy phases. The light phase, rich in polyoxymethylene dimethyl ether, had a yield of 85%. The light phase contained DMM... 2-5 Content 35.9%, methanol content 1.28%, methyl acetal 79.6%, residual formaldehyde content 0.39%, water content 0.15%, acidity 4.5.

[0073] S3. The light phase is fed from the column into the atmospheric distillation delight removal column 3 for continuous distillation. The bottom temperature of the column is 89-95℃ and the top temperature is 41-43℃. 97% pure methyl acetal is collected from the top (to be returned to the synthesis unit as a raw material for the synthesis of polyoxymethylene dimethyl ether). The bottom material enters the atmospheric distillation dehydration column 4. The bottom temperature of the distillation dehydration column 4 is 115-126℃ and the top temperature is 85-90℃. Water, formaldehyde, formic acid, and a small amount of DMM2 are collected from the top (returned to step S2). DMM2 is collected from the bottom. 2-5 The purity is 93.3%, and the ethylene glycol content is 6.7%. The bottom material enters vacuum distillation column 5, with a bottom temperature of 97–118℃, a top temperature of 48–51℃, and an operating pressure of 14.4–14.6 kPa. The top product is DMM2 with a purity of 99.53%, and the test line is DMM with a purity of 99.4%. 3-4 The product, ethylene glycol and DMM5, are collected from the bottom of the tower and recycled.

[0074] S4, the heavy phase is the ethylene glycol extraction phase. The feed enters atmospheric distillation recovery column 6, with 10 trays, a bottom temperature of 112–129°C, and a top temperature of 45–100°C. The top product contains methylal, methanol, formaldehyde, water, and a small amount of DMM2 (DMM2 and water azeotropic temperature 87°C). The top product is returned to the methanol and formaldehyde catalytic distillation unit to produce methylal, fully utilizing methanol, formaldehyde, and DMM2 to produce high-purity methylal. The ethylene glycol collected from the bottom is recycled as an extractant (e.g.,...). Figure 5 (As shown).

[0075] This invention uses sulfur-free, nitrogen-free, and aromatic-free ethylene glycol or glycerol as a single extractant, producing no waste alkali liquid or solid waste residue throughout the entire process, making the process green and environmentally friendly; the prepared polyoxymethylene dimethyl ether (DMM) n The product is also free of harmful impurities such as sulfur, nitrogen, and aromatics. It can be used as an environmentally friendly solvent and as a component of high cetane-number clean diesel fuel that meets the China VI standard. It effectively reduces black smoke and PM2.5 particulate matter emissions from diesel vehicle exhaust, which is in line with the industrial policy of clean and efficient utilization of coal.

[0076] This invention precisely removes highly polar impurities such as formaldehyde, water, and formic acid from the synthesized product through multi-stage extraction, resulting in a formaldehyde content of less than 0.5%, a water content of less than 0.1%, and an acidity of less than 7 in the light phase. This completely solves the problems of formaldehyde blockage in the tower, hydrolysis of water and methyl acetal, and formic acid-catalyzed DMM in traditional processes. n Problems such as reverse decomposition are eliminated; the light phase can be directly fed into multi-tower continuous distillation without additional pretreatment steps, which greatly shortens the process flow. Moreover, atmospheric and vacuum distillation technologies are mature and easy to implement, significantly improving production continuity and stability.

[0077] In this invention, the extractant (ethylene glycol / glycerol) can be recycled after treatment in a distillation recovery tower, achieving high recovery rate and stable performance. The formaldehyde and methanol separated by extraction, as well as the 96-99% high-purity methylal recovered in the distillation light phase removal tower, can all be returned to the methylal preparation unit or the polyoxymethylene dimethyl ether synthesis unit for reuse, achieving a closed-loop raw material cycle, significantly reducing resource waste, and lowering raw material procurement and waste disposal costs. After multi-stage extraction, the light phase yield rich in the target product reaches 85-95%, and subsequent distillation purification can obtain DMM2 and DMM with a purity of not less than 99.1%. 3-5 Products, including DMM 3-5 It retains the advantages of a high cetane number of 78-100 and a high oxygen content of 47-48.9%, which not only result in high combustion efficiency and good combustion-supporting effect, but also excellent compatibility with diesel fuel. It can significantly improve the combustion performance of diesel engines and has a strong market competitiveness in the field of clean fuels.

[0078] The extraction process of this invention is a physical separation process, which does not require high temperature and high pressure reaction conditions. The operating temperature is controlled at 20-40℃, making the process safe and controllable, reducing equipment corrosion and production safety risks. At the same time, it does not require the use of strong acids, alkalis or other hazardous chemicals, making the operating environment more friendly and reducing the material requirements of the production equipment, further reducing equipment investment and operation and maintenance costs.

[0079] Any aspects not described in this invention are applicable to existing technologies.

[0080] Obviously, the above embodiments are merely illustrative examples for clear explanation and are not intended to limit the implementation. Those skilled in the art will recognize that other variations or modifications can be made based on the above description. It is neither necessary nor possible to exhaustively list all possible implementations here. However, obvious variations or modifications derived therefrom are still within the scope of protection of this invention.

Claims

1. A method for preparing polyoxymethylene dimethyl ether using ethylene glycol and glycerol extraction technology, characterized in that, Includes the following steps: S1. Synthesis reaction: Formaldehyde and dimethyl acetal (DMM) are used as raw materials and introduced into a fixed-bed reactor (1). Under the catalysis of a solid acid catalyst, polyoxymethylene dimethyl ether (DMM) containing formaldehyde, water, formic acid, methanol, dimethyl ether, and methyl formate is synthesized. 2-5 Product mixture; S2. Extraction treatment: Using environmentally friendly ethylene glycol or glycerol as a single extractant, the polyoxymethylene dimethyl ether (DMM) is extracted in the extraction device (2). 2-5 The product mixture undergoes multi-stage extraction, separating the heavy and light phases based on density difference, partition coefficient, and the principle of like compatibility. Formaldehyde, formic acid, water, and methanol are extracted into the heavy phase, while the raffinate (light phase) is enriched with methyl acetal and polyoxymethylene dimethyl ether (DMM). 2-5 ; S3. Distillation purification: The light phase is directly subjected to multi-tower continuous distillation, passing sequentially through a light phase removal distillation tower (3), a dehydration distillation tower (4), and a vacuum distillation tower (5) to separate high-purity DMM2 product and high-purity DMM. 3-5 product.

2. The method for preparing polyoxymethylene dimethyl ether using ethylene glycol and glycerol extraction technology according to claim 1, characterized in that, It also includes the following steps: S4. Recycling: The heavy phase obtained from the extraction in step S2 is passed into the distillation recovery tower (6) to process the heavy phase. Formaldehyde, methanol, water, and formic acid are recovered from the top of the tower and returned to the methyl acetal preparation unit. Ethylene glycol or glycerol is recovered from the bottom of the tower and recycled as an extractant for the extraction process in step S2. At the same time, the distillation light phase removal tower (3) is returned to the polyoxymethylene dimethyl ether synthesis unit in step S1 for recycling.

3. The method for preparing polyoxymethylene dimethyl ether using ethylene glycol and glycerol extraction technology according to claim 1, characterized in that, In step S1, 50%–95% by volume of formaldehyde and 92%–99% by volume of methyl acetal are added, wherein the molar ratio of formaldehyde to methyl acetal is 1:(2–5); to synthesize polyoxymethylene dimethyl ether (DMM). 2-5 The reaction temperature is 80–100℃, the reaction pressure is 0.4–0.6 MPa, and the mass hourly space velocity is 0.1–0.5 h⁻¹. -1 .

4. The method for preparing polyoxymethylene dimethyl ether using ethylene glycol and glycerol extraction technology according to claim 1, characterized in that, The solid acid catalyst added in step S1 is a sulfonic acid type macroporous cation exchange resin catalyst.

5. The method for preparing polyoxymethylene dimethyl ether using ethylene glycol and glycerol extraction technology according to claim 1, characterized in that, In step S2, the extraction device (2) is one of a multi-stage rotating disc tower, a centrifugal extractor, or a packed extraction tower, and the number of extraction stages is 5 to 10.

6. The method for preparing polyoxymethylene dimethyl ether using ethylene glycol and glycerol extraction technology according to claim 1, characterized in that, In step S2, the added extractant and polyoxymethylene dimethyl ether (DMM) 2-5 The volume ratio of the products was (20-40):(60-80), and the extraction temperature was 20-40℃.

7. The method for preparing polyoxymethylene dimethyl ether using ethylene glycol and glycerol extraction technology according to claim 1, characterized in that, The multi-tower continuous distillation in step S3 includes: The distillation column for removing light pollutants (3) has a top temperature of 41-43℃ and a bottom temperature of 89-95℃. The methyl acetal collected at the top of the column is recycled, and the material at the bottom of the column enters the distillation dehydration column (4). The distillation dehydration column (4) has a top temperature of 85-90℃ and a bottom temperature of 115-126℃. Water, formaldehyde, formic acid and a small amount of DMM2 are collected from the top of the column and returned to step S2. The bottom material enters the vacuum distillation column (5). A vacuum distillation column (5) with a top temperature of 48–51°C, a bottom temperature of 97–118°C, and an operating pressure of 14.4–14.6 kPa, using glycerol as the extractant, produces DMM2 at the top and DMM2 by side stream. 3-5 The extractant is recycled from the bottom of the column; when ethylene glycol is used as the extractant, DMM2 is collected from the top of the column, and DMM is collected from the side stream. 3-4 DMM5 and extractant were collected from the bottom of the tower.

8. The method for preparing polyoxymethylene dimethyl ether using ethylene glycol and glycerol extraction technology according to claim 2, characterized in that, In step S4, the distillation recovery tower (6) is an atmospheric distillation tower with 5 to 10 trays, a bottom temperature of 112 to 129°C, and a top temperature of 45 to 100°C. Formaldehyde, methanol, formic acid, and water collected from the top of the tower are returned to the methanol and formaldehyde catalytic distillation unit to produce methyl acetal, so as to make full use of methanol and formaldehyde to produce methyl acetal. Ethylene glycol or glycerol collected from the bottom of the tower is recycled as an extractant.

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