DMMn production process

Abstract

The invention relates to the technical field of chemical production, and discloses a DMMn production process. The DMMn production process comprises: concentrating a formaldehyde aqueous solution with a concentration of 50-55wt% to obtain a formaldehyde solution with a higher concentration and a formaldehyde solution with a lower concentration, wherein the two formaldehyde solutions react in different areas of a reaction distillation tower, and excess water is extracted during the reaction, which is beneficial to reducing the influence of water on the entire reaction system, improving the conversion rate of formaldehyde, avoiding self-polymerization of formaldehyde, and improving the purity of the obtained DMM3-DMM6 products.

Description

Technical Field

[0001] The invention relates to the technical field of chemical production, and in particular to a DMMn production process. Background Art

[0002] Polyoxymethylene dimethyl ether, referred to as DMMn, is a new type of clean fuel additive that has the advantages of reducing combustion smoke generation, improving combustion performance, and reducing tail gas emissions. It has broad application prospects in the fields of energy and environmental protection.

[0003] Among them, the physical properties of polyoxymethylene dimethyl ether (DMM3-DMM6) with a degree of polymerization of 3-6 are similar to those of diesel, and have a higher oxygen content (mass fraction of 47%-50%) and a high cetane number (greater than 78). It can improve the combustion state of diesel in the engine and effectively reduce the emission of particulate matter in the exhaust gas without making any changes to the diesel engine. It is recognized as a more ideal diesel additive.

[0004] Formaldehyde is the main raw material for synthesizing DMMn. The reaction of synthesizing DMMn is greatly affected by water in the system. Increasing the formaldehyde concentration is beneficial to reducing the influence of water on the reaction system and obtaining DMM3-DMM6 products with higher purity. However, high concentration of formaldehyde is easy to self-polymerize, and the generated polyformaldehyde adheres to the reactor and is difficult to remove, which can easily cause serious blockage of the reactor. Summary of the invention

[0005] The main purpose of the present invention is to provide a DMMn production process, aiming to solve the problem that formaldehyde self-polymerization is easily caused in the production of polyoxymethylene dimethyl ether in the prior art.

[0006] To achieve the above object, the present invention proposes a DMMn production process, comprising the following steps:

[0007] S10, providing a formaldehyde aqueous solution with a concentration of 50-55wt% and a methanol with a concentration of more than 95wt%;

[0008] S20, concentrating the 50-55 wt % formaldehyde aqueous solution in step S10 to obtain a 70-80 wt % concentrated formaldehyde solution and a 15-25 wt % dilute formaldehyde solution;

[0009] S30, mixing the 15-25wt% dilute formaldehyde solution in step S20 with more than 95wt% methanol in step S10 and passing the mixture into the upper reaction section of a reaction distillation tower, passing the 70-80wt% concentrated formaldehyde solution in step S20 into the lower reaction section of the reaction distillation tower, under the action of catalytic distillation, the materials in the upper reaction section react to generate methylal, DMM2 and DMM3, the materials in the lower reaction section react to generate DMM2-DMM6, the water between the upper reaction section and the lower reaction section is extracted, and the bottom material of the reaction distillation tower is the crude product DMM2-DMM6;

[0010] S40, extracting the crude products DMM2 to DMM6 in step S30 and subjecting them to reactive distillation to obtain products DMM3 to DMM6.

[0011] Optionally, in step S30, the operating pressure of the reaction distillation tower is 0-1.0 MPa, the tower top temperature is 43-120° C., and the tower bottom temperature is 80-150° C.; and / or,

[0012] In step S30, the reflux ratio of the reaction distillation tower is 2 to 10, and both the upper reaction section and the lower reaction section are filled with a solid acid catalyst; and / or,

[0013] In the step S30, the azeotrope of methylal and methanol is extracted from the top of the reactive distillation tower.

[0014] Optionally, in the step S40, in the extracted crude products of DMM2 to DMM6, the concentration of formaldehyde is less than 1wt%, and the remainder is methylal and DMM2 to DMM6.

[0015] Optionally, the step S40 includes the following steps:

[0016] S41, mixing the extracted DMM2-DMM6 crude products with hydrogen, so that the formaldehyde in the DMM2-DMM6 crude products undergoes a hydrogenation reaction to generate methanol;

[0017] S42, subjecting the material after the hydrogenation reaction in step S41 to atmospheric distillation to separate the light components containing methylal and methanol, the DMM2 solution containing DMM2, and the heavy components containing DMM3 to DMM6, and sending the light components containing methylal and methanol to the lower reaction section of the reaction distillation tower in step S30, and the heavy components of DMM3 to DMM6 are the DMM3 to DMM6 products.

[0018] Optionally, in step S41, the hydrogenation reaction is carried out under the condition of a copper-based catalyst, the pressure of the hydrogenation reaction is 1.0-2.0 MPa, and the temperature is 100-150°C.

[0019] Optionally, the DMM2 solution in step S42 is side-lined and DMM2 is reformed to generate DMM3 to DMM6 with a higher degree of polymerization, and methylal, methanol and formaldehyde are also generated;

[0020] The material after the reforming reaction is taken out and mixed with hydrogen, so that the formaldehyde in the material undergoes a hydrogenation reaction to generate methanol. The material after the hydrogenation reaction is mixed with the material after the hydrogenation reaction in step S41 and separated by atmospheric distillation.

[0021] Optionally, in step S42, the reforming reaction is carried out under the condition of an acidic resin catalyst, and the pressure during the reforming reaction is 0.6-1.0 MPa and the temperature is 60-100°C.

[0022] Optionally, in step S42, the hydrogenation reaction is carried out under the condition of a copper-based catalyst, the pressure of the hydrogenation reaction is 1.0-2.0 MPa, and the temperature is 100-150°C.

[0023] Optionally, in step S10, in the 50-55wt% formaldehyde aqueous solution and more than 95wt% methanol raw material, the feed molar ratio of methanol to formaldehyde is 1:(1.5-2.0).

[0024] Optionally, in step S20, a 50-55 wt% formaldehyde aqueous solution is pressurized and gasified and then subjected to vacuum flash evaporation, and the concentrated solution is a 70-80 wt% concentrated formaldehyde solution, and the formed flash steam is cooled to form a 15-25 wt% dilute formaldehyde solution.

[0025] The technical solution of the present invention concentrates a 50-55wt% formaldehyde aqueous solution to obtain a formaldehyde solution with a higher concentration and a formaldehyde solution with a lower concentration. The two formaldehyde solutions react in different areas, and excess water is extracted during the reaction, which is beneficial to reducing the impact of water on the entire reaction system, improving the conversion rate of formaldehyde, avoiding self-polymerization of formaldehyde, and improving the purity of the obtained DMM3-DMM6 products. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on the structures shown in these drawings without paying creative work.

[0027] Figure 1 This is a schematic structural diagram of an embodiment of the DMMn production equipment provided by the present invention.

[0028] Description of Figure Numbers:

[0029] 1. Formaldehyde concentration separator; 2. Formaldehyde absorption tower; 3. Pre-reactor; 4. Reaction distillation tower; 49. Upper reaction section; 410. Lower reaction section; 5. Light removal distillation tower; 6. First hydrogenation reactor; 63. First cooler; 64. First gas-liquid separator; 7. Separation distillation tower; 8. Converter; 9. Second hydrogenation reactor; 93. Second cooler; 94. Second gas-liquid separator.

[0030] The realization of the purpose, functional features and advantages of the present invention will be further explained in conjunction with embodiments and with reference to the accompanying drawings. DETAILED DESCRIPTION

[0031] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0032] It should be noted that if the embodiments of the present invention involve directional indications (such as up, down, left, right, front, back, etc.), the directional indications are only used to explain the relative position relationship, movement status, etc. between the components under a certain specific posture (as shown in the accompanying drawings). If the specific posture changes, the directional indication will also change accordingly.

[0033] In addition, if there are descriptions involving "first", "second", etc. in the embodiments of the present invention, the descriptions of "first", "second", etc. are only used for descriptive purposes and cannot be understood as indicating or implying their relative importance or implicitly indicating the number of technical features indicated. Therefore, the features defined as "first" and "second" may explicitly or implicitly include at least one of the features. In addition, the meaning of "and / or" appearing in the full text includes three parallel schemes. Taking "A and / or B" as an example, it includes scheme A, or scheme B, or a scheme that satisfies both A and B. In addition, the technical solutions between the various embodiments can be combined with each other, but it must be based on the ability of ordinary technicians in the field to implement. When the combination of technical solutions is contradictory or cannot be implemented, it should be deemed that such a combination of technical solutions does not exist and is not within the scope of protection required by the present invention.

[0034] Formaldehyde is the main raw material for synthesizing DMMn. The reaction of synthesizing DMMn is greatly affected by water in the system. Increasing the formaldehyde concentration is beneficial to reducing the influence of water on the reaction system and obtaining DMM3-DMM6 products with higher yields. However, high-concentration formaldehyde is easy to self-polymerize, and the generated polyformaldehyde adheres to the reactor and is difficult to remove, which easily causes serious blockage of the reactor. In view of this, the present invention proposes a DMMn production process to solve the problem that formaldehyde self-polymerization is easy to cause in the production of polyoxymethylene dimethyl ether in the prior art.

[0035] See also Figure 1 In the present invention, the DMMn production process comprises the following steps:

[0036] S10, providing a formaldehyde aqueous solution with a concentration of 50-55wt% and a methanol with a concentration of more than 95wt%;

[0037] S20, concentrating the 50-55 wt % formaldehyde aqueous solution in step S10 to obtain a 70-80 wt % concentrated formaldehyde solution and a 15-25 wt % dilute formaldehyde solution;

[0038] S30, mixing the 15-25wt% dilute formaldehyde solution in step S20 with more than 95wt% methanol in step S10 and passing the mixture into the upper reaction section 49 of the reaction distillation tower 4, passing the 70-80wt% concentrated formaldehyde solution in step S20 into the lower reaction section 410 of the reaction distillation tower 4, under the action of catalytic distillation, the materials in the upper reaction section 49 react to generate methylal, DMM2 and DMM3, the materials in the lower reaction section 410 react to generate DMM2-DMM6, the water between the upper reaction section 49 and the lower reaction section 410 is extracted, and the bottom material of the reaction distillation tower 4 is the crude product DMM2-DMM6;

[0039] S40, extracting the crude products DMM2 to DMM6 in step S30 and subjecting them to reactive distillation to obtain products DMM3 to DMM6.

[0040] In the technical solution of the present invention, a formaldehyde aqueous solution with a concentration of 50-55wt% is sent to a formaldehyde concentration separator 1, pressurized (0.3MPa) and gasified, and then vacuum (vacuum degree -90kPa) flash evaporated, and the concentrated liquid is a 70-80wt% concentrated formaldehyde solution, and the formed flash steam is sent to a formaldehyde absorption tower 2.

[0041] Flash steam and water (temperature may be 25° C.) are fed into the formaldehyde absorption tower 2 , and the flash steam and water are mixed to form a 15-25 wt % dilute formaldehyde solution, and the 15-25 wt % dilute formaldehyde solution is fed into the pre-reactor 3 .

[0042] A dilute formaldehyde solution with a concentration of 15-25wt% and a methanol with a concentration of more than 95wt% are fed into the pre-reactor 3, and the temperature is controlled at 50-80°C. Part of the methanol and formaldehyde react to form methylal. The pre-reacted materials (formaldehyde 8-10wt%, water 40-50wt%, methanol 25-30wt%, methylal 5-10wt%) are fed to the upper reaction section 49 of the reaction distillation tower 4; and a 70-80wt% concentrated formaldehyde solution is fed into the lower reaction section 410 of the reaction distillation tower 4.

[0043] The upper reaction section 49 and the lower reaction section 410 of the reaction distillation tower 4 are both filled with a solid acid catalyst. Under the action of catalytic distillation, the material in the upper reaction section 49 reacts to generate methylal, DMM2 and DMM3. The reactions that occur are as follows:

[0044]

[0045] Since the boiling point of water is lower than DMM2~DMM6, but higher than methanol, formaldehyde and methylal, most of the water is accumulated between the upper reaction section 49 and the lower reaction section 410. During the reaction distillation, the water between the upper reaction section 49 and the lower reaction section 410 is extracted, which is beneficial to the reaction equilibrium moving toward the direction of consuming water, and is also beneficial to reducing the water content in the material entering the lower reaction section 410 from the upper reaction section 49.

[0046] Under the action of catalytic distillation, the material of the lower reaction section 410 includes the material leaving the upper reaction section 49 and entering the lower reaction section 410, and also includes the input concentrated formaldehyde solution with a concentration of 70-80wt%. Since the water content in the material leaving the upper reaction section 49 and entering the lower reaction section 410 is relatively low, and the water content in the input 70-80wt% concentrated formaldehyde solution is also relatively low, and the boiling point of water is less than DMM2-DMM6, water is basically gathered between the upper reaction section 49 and the lower reaction section 410. The water between the upper reaction section 49 and the lower reaction section 410 is extracted, so that the reaction in the lower reaction section 410 is almost not affected by water, and formaldehyde has a higher conversion rate. At the same time, DMM3-DMM6 with a higher degree of polymerization can be further generated. The reaction occurring in the lower reaction section 410 is as follows:

[0047]

[0048] In the lower reaction section 410, the conversion rate of formaldehyde is high, and crude products DMM2 to DMM6 (formaldehyde concentration <1wt%, the remainder is methylal and DMM2 to DMM6) are extracted from the bottom of the reaction distillation tower 4, and the extracted crude products DMM2 to DMM6 are further subjected to reaction distillation to obtain high-purity products DMM3 to DMM6. A azeotrope of methylal and methanol (methylal 92 to 93wt%, methanol 7 to 8wt%, water <0.5wt%) is extracted from the top of the reaction distillation tower 4.

[0049] The technical solution of the present application is to concentrate a 50-55wt% formaldehyde aqueous solution to obtain a formaldehyde solution with a higher concentration and a formaldehyde solution with a lower concentration. The two formaldehyde solutions react in different areas, and excess water is extracted during the reaction, which is beneficial to reduce the impact of water on the entire reaction system, improve the conversion rate of formaldehyde, avoid self-polymerization of formaldehyde, and improve the purity of the obtained DMM3-DMM6 products.

[0050] It should be noted that DMM2 to DMM6 include DMM2, DMM3, DMM4, DMM5 and DMM6. In step S10, the molar ratio of methanol to formaldehyde in the 50-55 wt% formaldehyde aqueous solution and more than 95 wt% methanol raw material is 1: (1.5-2.0).

[0051] Specifically, the reaction distillation tower 4 is a plate tower or a packed tower, the reflux ratio of the reaction distillation tower 4 is 2-10, the operating pressure of the reaction distillation tower 4 is 0-1.0 MPa, the tower top temperature is 43-120°C, the tower bottom temperature is 80-150°C, and the azeotropic product extracted from the tower top of the reaction distillation tower 4 is condensed, and part of the condensate is refluxed to the reaction distillation tower 4, and the remaining part of the condensate is sent to the light removal distillation tower 5. The light removal distillation tower 5 is a plate tower or a packed tower, the reflux ratio of the light removal distillation tower 5 is 1-5, the operating pressure of the light removal distillation tower 5 is 0.4-0.6 MPa, the tower bottom temperature is 95-100°C, and the tower top temperature is 65-70°C. After distillation treatment, methyl formate is extracted from the tower top of the light removal distillation tower 5 to remove light components such as by-product methyl formate, and the tower bottom material is refluxed to the reaction distillation tower 4 to improve the utilization rate of methylal.

[0052] Furthermore, the step S40 includes the following steps:

[0053] S41, mixing the extracted DMM2-DMM6 crude products with hydrogen, so that the formaldehyde in the DMM2-DMM6 crude products undergoes a hydrogenation reaction to generate methanol;

[0054] S42, subjecting the material after the hydrogenation reaction in step S41 to atmospheric distillation to separate the light components containing methylal and methanol, the DMM2 solution containing DMM2, and the heavy components containing DMM3 to DMM6, and sending the light components containing methylal and methanol to the lower reaction section 410 of the reaction distillation tower 4 in the step S30, and the heavy components of DMM3 to DMM6 are the DMM3 to DMM6 products.

[0055] By adopting the above technical scheme, the extracted DMM2-DMM6 crude products contain a small amount of formaldehyde (formaldehyde < 1wt%), and the DMM2-DMM6 crude products and hydrogen are sent to the first hydrogenation reactor 6. Under the condition of a copper catalyst, the pressure is controlled to be 1.0-2.0MPa and the temperature is 100-150°C, so that the formaldehyde in the DMM2-DMM6 crude products and the hydrogen undergo a hydrogenation reaction to generate methanol. The material after the hydrogenation reaction is cooled by the first cooler 63 and enters the first gas-liquid separator 64. The separated hydrogen is pressurized by the compressor and returned to the first hydrogenation reactor 6 for recycling. The separated hydrogenation reaction liquid (0.5-2wt% methanol, 30-50wt% methylal, and 48-69wt% DMM2-DMM6) is sent to the separation distillation tower 7.

[0056] The separation distillation tower 7 is a plate tower or a packed tower, and the reflux ratio of the separation distillation tower 7 is 1 to 3. The operating pressure of the separation distillation tower 7 is normal pressure, the tower bottom temperature is 160-180°C, and the tower top temperature is 42-43°C. The light components containing methylal and methanol are extracted from the top of the separation distillation tower 7, the lower material of the separation distillation tower 7 is the DMM2 solution, and the tower bottom material of the separation distillation tower 7 is the DMM3 to DMM6 products. The light components containing methylal and methanol are sent to the lower reaction section 410 of the reaction distillation tower 4. The DMM2 solution is extracted from the side line.

[0057] The DMM2 solution produced from the side line is sent to the converter 8, which is filled with an acidic resin catalyst. The pressure is controlled at 0.6-1.0 MPa and the temperature is 60-100°C, so that DMM2 undergoes a reforming reaction to generate DMM3-DMM6 with a higher degree of polymerization. At the same time, methylal, methanol and formaldehyde are produced. The material composition after the reforming reaction is: methylal 40-55wt%, DMM2 20-30wt%, DMM3-5 20-25wt%, and a small amount of methanol and formaldehyde.

[0058] The material after the reforming reaction and hydrogen are sent to the second hydrogenation reactor 9. Under the condition of a copper-based catalyst, the pressure is controlled to be 1.0-2.0 MPa and the temperature is 100-150°C, so that the formaldehyde in the material undergoes a hydrogenation reaction to generate methanol. The material after the hydrogenation reaction is cooled by the second cooler 93 and then enters the second gas-liquid separator 94. The separated hydrogen is pressurized by the compressor and returned to the second hydrogenation reactor 9 for recycling. The separated hydrogenation reaction liquid is sent to the separation distillation tower 7.

[0059] The technical solution of the present invention is further described in detail below in conjunction with specific embodiments and drawings. It should be understood that the following embodiments are only used to explain the present invention and are not used to limit the present invention.

[0060] Example 1

[0061] Combination Figure 1 , a DMMn production process, comprising the following steps:

[0062] S10, providing a 50 wt % formaldehyde aqueous solution and a 99.5 wt % methanol, wherein the feed molar ratio of methanol to formaldehyde in the 50 wt % formaldehyde aqueous solution and the 99.5 wt % methanol raw materials is 1:1.7.

[0063] S20, concentrating the 50 wt % formaldehyde aqueous solution in step S10 to obtain a 75 wt % concentrated formaldehyde aqueous solution, and mixing the resulting flash steam with water at room temperature (25° C.) to obtain a 20 wt % dilute formaldehyde aqueous solution.

[0064] S30, mixing the 20wt% dilute formaldehyde aqueous solution in step S20 with the 99.5wt% methanol in step S10 and heating them to 60°C, pre-reacting part of the methanol with formaldehyde to generate methylal (the material after the pre-reaction includes 10wt% formaldehyde, 50wt% water, 30wt% methanol and 10wt% methylal), and passing the pre-reacted material into the upper reaction section of a reaction distillation tower; and passing the 75wt% concentrated formaldehyde aqueous solution in step S20 into the lower reaction section of the reaction distillation tower, under the action of catalytic distillation, the material in the upper reaction section reacts to generate methylal, DMM2 and DMM3, and the material in the lower reaction section reacts to generate DMM2~DMM6, and the water between the upper reaction section and the lower reaction section is extracted, and the bottom material of the reaction distillation tower is the crude product DMM2~DMM6, and the bottom material is extracted. The azeotropic product (methylal 92.5wt%, methanol 7wt%, water <0.5wt%) taken out from the top of the reaction distillation tower is partially refluxed after condensation, and the rest is sent to the light component removal distillation tower, and then refluxed to the reaction distillation tower after the light components are removed.

[0065] Wherein, in step S30, the reaction distillation tower is a plate tower with 80 effective plates, 22 plates in the distillation section, 18 plates in the upper reaction section, 18 plates in the lower reaction section, and 22 plates in the stripping section; both the upper reaction section and the lower reaction section are filled with Amberlyst-70 sulfonic acid resin solid acid catalyst. The reflux ratio of the reaction distillation tower is 2, the operating pressure is 0.8MPa, the reactor temperature is 120°C, and the tower top temperature is 110°C; among the crude products of DMM2-DMM6, formaldehyde is less than 1wt%, and the rest are methylal and DMM2-DMM6. The light removal distillation tower is a plate tower with 40 effective plates, of which the distillation section has 13 plates, the middle section has 14 plates, and the stripping section has 13 plates; the reflux ratio of the light removal distillation tower is 2, the operating pressure is 0.5 MPa, the bottom temperature is 99°C, and the top temperature is 68°C. Methyl formate is produced from the top of the light removal distillation tower, and the bottom material is methylal solution, which is refluxed to the reactive distillation tower.

[0066] S41, mixing the crude DMM2-DMM6 products extracted in step S30 with hydrogen, so that the formaldehyde in the crude DMM2-DMM6 products undergoes a hydrogenation reaction to generate methanol, and extracting the material after the hydrogenation reaction. The hydrogenation reaction is carried out under the conditions of Mn-CZ / SBA-15 catalyst, the pressure of the hydrogenation reaction is 1.5MPa, the temperature is 135°C, and the material composition after the hydrogenation reaction is: 1wt% methanol, 40wt% methylal, and 59wt% DMM2-DMM6.

[0067] S42, transport the material after the hydrogenation reaction in step S41 to a separation distillation tower, perform atmospheric distillation operation, extract methylal and methanol from the top of the separation distillation tower, and reflux the extracted methylal and methanol to the lower reaction section of the reaction distillation tower, extract DMM2 solution from the lower side line of the separation distillation tower, the bottom material of the separation distillation tower is DMM3~DMM6 products, extract the bottom material, and obtain DMM3~DMM6 products. Wherein, the separation distillation tower is a plate tower with 60 effective plates, 22 plates in the distillation section, 14 plates in the middle section, 24 plates in the stripping section, the reflux ratio of the separation distillation tower is 2, the bottom temperature is 170℃, and the top temperature is 42.5℃.

[0068] It was measured that in the step S42, among the DMM3-DMM6 products collected, the mass fraction of DMM3-DMM6 was ≥99%, and contained a trace amount of water.

[0069] Example 2

[0070] This embodiment is based on the embodiment 1, and the difference is that after step S42, the following steps are further included:

[0071] S43, the DMM2 solution side line of the lower part of the distillation tower is taken out, so that DMM2 undergoes a reforming reaction to generate DMM3-DMM6 with a higher degree of polymerization, and methylal, methanol and formaldehyde are produced at the same time, and the material after the reforming reaction (methylal 50wt%, DMM2 25wt%, DMM3-DMM5 23.5wt%, and the rest are methanol and formaldehyde) is taken out and mixed with hydrogen, so that formaldehyde undergoes a hydrogenation reaction to generate methanol, and the material after the hydrogenation reaction (without formaldehyde) is transported to the separation distillation tower. Wherein, the reforming reaction is carried out under the condition of Amberlyst-70 sulfonic acid resin solid acid catalyst, the pressure during the reforming reaction is 0.8MPa, and the temperature is 90°C; the hydrogenation reaction is carried out under the condition of Mn-CZ / SBA-15 catalyst, and the pressure during the hydrogenation reaction is 1.5MPa and the temperature is 135°C.

[0072] It was measured that in the step S42, among the DMM3-DMM6 products collected, the mass fraction of DMM3-DMM6 was ≥99%, and contained a trace amount of water.

[0073] The above are only preferred embodiments of the present invention, and do not limit the patent scope of the present invention. For those skilled in the art, the present invention may have various changes and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the patent protection scope of the present invention.

Claims

1. A DMMn production process, characterized in that: The following steps are involved: S10, providing a formaldehyde aqueous solution with a concentration of 50-55wt% and a methanol with a concentration of more than 95wt%; S20, concentrating the 50-55 wt % formaldehyde aqueous solution in step S10 to obtain a 70-80 wt % concentrated formaldehyde solution and a 15-25 wt % dilute formaldehyde solution; S30, mixing the 15-25wt% dilute formaldehyde solution in step S20 with more than 95wt% methanol in step S10 and passing the mixture into the upper reaction section of a reaction distillation tower, passing the 70-80wt% concentrated formaldehyde solution in step S20 into the lower reaction section of the reaction distillation tower, under the action of catalytic distillation, the materials in the upper reaction section react to generate methylal, DMM2 and DMM3, the materials in the lower reaction section react to generate DMM2-DMM6, the water between the upper reaction section and the lower reaction section is extracted, and the bottom material of the reaction distillation tower is the crude product DMM2-DMM6; S40, extracting the crude products DMM2 to DMM6 in step S30 and subjecting them to reactive distillation to obtain products DMM3 to DMM6.

2. The DMMn production process according to claim 1, characterized in that: In step S30, the operating pressure of the reaction distillation tower is 0-1.0 MPa, the tower top temperature is 43-120° C., and the tower bottom temperature is 80-150° C.; and / or, In step S30, the reflux ratio of the reaction distillation tower is 2 to 10, and both the upper reaction section and the lower reaction section are filled with a solid acid catalyst; and / or, In the step S30, the azeotrope of methylal and methanol is extracted from the top of the reactive distillation tower.

3. The DMMn production process according to claim 1, characterized in that: In the step S40, in the extracted crude products of DMM2 to DMM6, the concentration of formaldehyde is less than 1 wt %, and the remainder is methylal and DMM2 to DMM6.

4. The DMMn production process according to claim 1, characterized in that: The step S40 comprises the following steps: S41, mixing the extracted DMM2-DMM6 crude products with hydrogen, so that the formaldehyde in the DMM2-DMM6 crude products undergoes a hydrogenation reaction to generate methanol; S42, subjecting the material after the hydrogenation reaction in step S41 to atmospheric distillation to separate the light components containing methylal and methanol, the DMM2 solution containing DMM2, and the heavy components containing DMM3 to DMM6, and sending the light components containing methylal and methanol to the lower reaction section of the reaction distillation tower in step S30, and the heavy components of DMM3 to DMM6 are the DMM3 to DMM6 products.

5. The DMMn production process according to claim 4, characterized in that: In the step S41, the hydrogenation reaction is carried out under the condition of a copper-based catalyst, the pressure of the hydrogenation reaction is 1.0-2.0 MPa, and the temperature is 100-150°C.

6. The DMMn production process according to claim 4, characterized in that: The DMM2 solution in step S42 is side-lined and DMM2 is reformed to generate DMM3 to DMM6 with higher polymerization degree, and methylal, methanol and formaldehyde are also generated; The material after the reforming reaction is taken out and mixed with hydrogen, so that the formaldehyde in the material undergoes a hydrogenation reaction to generate methanol. The material after the hydrogenation reaction is mixed with the material after the hydrogenation reaction in step S41 and separated by atmospheric distillation.

7. The DMMn production process according to claim 6, characterized in that: In the step S42, the reforming reaction is carried out under the condition of an acidic resin catalyst, the pressure during the reforming reaction is 0.6-1.0 MPa, and the temperature is 60-100°C.

8. The DMMn production process according to claim 6, characterized in that: In the step S42, the hydrogenation reaction is carried out under the condition of a copper-based catalyst, the pressure of the hydrogenation reaction is 1.0-2.0 MPa, and the temperature is 100-150°C.

9. The DMMn production process according to claim 1, characterized in that: In the step S10, the molar ratio of methanol to formaldehyde in the 50-55 wt % formaldehyde aqueous solution and more than 95 wt % methanol raw material is 1:(1.5-2.0).

10. The DMMn production process according to claim 1, characterized in that: In step S20, the 50-55 wt% formaldehyde aqueous solution is pressurized and gasified and then vacuum flash evaporated to obtain a concentrated solution of 70-80 wt% concentrated formaldehyde solution. The flash steam is cooled to form a 15-25 wt% dilute formaldehyde solution.

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