Catalytic extraction process for preparing polyoxymethylene dimethyl ether

Abstract

The invention discloses a multistage catalytic extraction process for preparing polyoxymethylene dimethyl ether. The method comprises the following steps: introducing raw materials formaldehyde and methanol into a multi-stage catalytic extraction reaction system, carrying out countercurrent contact on reaction materials and an extraction agent, carrying out catalytic reaction and extraction repeatedly and alternately, and extracting an extraction phase mainly containing an OME product and the extraction agent and a raffinate phase containing unreacted formaldehyde and methanol, namely a water phase. And washing the extract phase with water to remove a small amount of formaldehyde and methanol, carrying out rectification separation, extracting a target product, and returning the rest of polyoxymethylene dimethyl ether to the multistage catalytic extraction reaction system for circular reaction. A water-phase material enters a catalytic rectifying tower, most of formaldehyde reacts with methanol to generate methylal, and the methylal, a small amount of unreacted methanol, formaldehyde, a small amount of water and the like are extracted from the tower top and enter a multi-stage catalytic extraction reaction system for continuous reaction or are washed and separated together with an extraction phase. The process disclosed by the invention has the advantages of low raw material cost, high reaction efficiency, easiness in product separation, flexible product scheme and the like.

Description

Technical Field

[0001] The present application relates to a catalytic extraction process for preparing polyoxymethylene dimethyl ethers from methanol and aqueous formaldehyde solution, belonging to the field of chemical engineering. Background Art

[0002] Polyoxymethylene dimethyl ethers, also known as polyoxymethylene methylal, polyformaldehyde dimethyl ether, abbreviated as OME, OMEn, DMMn or PODEn (polyoxymethylene dimethyl ethers).

[0003] OME 1 Namely, methylal, also known as dimethoxymethane, abbreviated as DMM, is a colorless, non-toxic and environmentally friendly chemical raw material, usually prepared by the aldol condensation reaction of methanol and aqueous formaldehyde solution. Due to the large amount of water in the reaction process, including the water brought in by the aqueous formaldehyde solution and the water generated by the reaction, the reaction is restricted by the chemical equilibrium. At present, catalytic distillation technology is generally used in industrial production to break the limitation of the chemical equilibrium.

[0004] OME 3-4 It has the characteristics of high cetane number and high oxygen content, can be miscible with diesel, and its various performance indicators are close to those of diesel, and is considered to be an ideal oxygen-containing additive component for diesel. Although OME with a higher degree of polymerization has a potential risk of low-temperature solidification, generally the content of OME in the product of polyoxymethylene dimethyl ethers synthesis 5-8 is very low and is not sufficient to cause fuel low-temperature solidification. Therefore, OME containing a small amount of high-polymerization components 3-5 and OME 3-8 are also suitable diesel additive components.

[0005] OMEn is generally synthesized from a compound providing a formaldehyde group (aqueous formaldehyde solution, trioxymethylene or paraformaldehyde, etc.) and a compound providing a capping methyl group (methanol, dimethyl ether or methylal, etc.) in the presence of an acidic catalyst. This reaction is restricted by the chemical equilibrium, and the larger the degree of polymerization n of the product, the lower the yield.

[0006] Asahi Kasei Corporation of Japan disclosed a catalytic distillation method for producing methylal from aqueous formaldehyde solution and methanol in Chinese Patent CN 1020450 C, adopting the form of a secondary reactor arranged outside the catalytic distillation column, with macroporous or gel-type cation exchange resin as the catalyst.

[0007] Chinese Patent CN 102351666 A disclosed a catalytic distillation method for continuously producing high-concentration methylal from formaldehyde solution and methanol, also adopting the form of a secondary reactor.

[0008] Chinese Patent CN 102070417 A discloses a catalytic distillation process and production equipment for producing methylal from formaldehyde solution and methanol. Using cation exchange resin as the catalyst, a catalytic distillation column filled with catalyst bale is adopted.

[0009] Chinese Patents CN 101182367 and 101665414 respectively disclose a method for preparing polyoxymethylene dimethyl ethers using methanol and trioxymethylene as reactants and ionic liquid or functionalized acidic ionic liquid as the catalyst, which has the characteristics of mild reaction conditions, high catalyst activity, high conversion rate, simple reaction process, easy operation, good reaction product distribution, etc.

[0010] Chinese Patent CN 101768057 discloses a method for preparing polyoxymethylene dimethyl ethers using methanol and trioxymethylene as reaction raw materials. Using solid superacid catalyst, the reaction temperature is 70 - 200 °C and the reaction pressure is 0.5 - 6 MPa.

[0011] Chinese Patent CN 102040488 discloses a method for preparing polyoxymethylene dimethyl ethers using methanol, methylal and trioxymethylene as reaction raw materials. Using molecular sieve catalyst, the reaction temperature is 50 - 200 °C and the reaction pressure is 0.1 - 10 MPa.

[0012] Chinese Patent CN 102040490 discloses a method for preparing polyoxymethylene dimethyl ethers using methanol, methylal and paraformaldehyde as reaction raw materials. Using solid superacid catalyst, the reaction temperature is 70 - 200 °C and the reaction pressure is 0.2 - 6 MPa.

[0013] Chinese Patents CN 102372611 and 102372612 respectively disclose a method for preparing polyoxymethylene dimethyl ethers by reacting methylal and trioxymethylene in a catalytic distillation column.

[0014] Most of the above patents for preparing polyoxymethylene dimethyl ethers use trioxymethylene or paraformaldehyde as the raw material providing formaldehyde groups, and the reaction system contains no water or very low water content. The yield of OME n is high, and the selectivity of OME 3-8 in the product is also relatively high. However, the price of trioxymethylene or paraformaldehyde is relatively high, so the production cost is relatively high.

[0015] One of the main problems faced in producing polyoxymethylene dimethyl ethers using cheap methanol and aqueous formaldehyde solution as raw materials is that the reaction system contains a large amount of water, including the water brought in by the aqueous formaldehyde solution and the water generated by the reaction. Affected by a large amount of water, the equilibrium conversion rate of methanol and formaldehyde to produce OME n is greatly reduced. At the same time, the generated OME n product is mainly OME1-2 , OME 3-8 has very low selectivity.

[0016] Another problem is that in the presence of liquid water and methanol, only a very small part of formaldehyde exists in the form of formaldehyde monomer molecules. Most of the formaldehyde reacts with water to form methylene glycol and its polymer polyoxymethylene glycol, or reacts with methanol to form hemiacetals with different degrees of polymerization. These reactions are all reversible reactions and can proceed without a catalyst. Monomeric formaldehyde, diols, and hemiacetals are easily converted into each other during the distillation separation process, making it difficult to completely separate the target product OME n from these substances by general distillation methods.

[0017] Chinese Patent CN 106542977 discloses a method for preparing polyoxymethylene dimethyl ethers. An extractant is introduced into the reaction system, and under the catalysis of an acidic catalyst, the reaction and extraction are integrated. After the reaction is completed, the organic phase and the aqueous phase are separated, and the organic phase is refined to obtain polyoxymethylene dimethyl ethers. By introducing the extractant, the reaction raw materials are extracted into the extractant phase for reaction, effectively avoiding side reactions between the reaction products and water, and can effectively improve the conversion rate of raw materials, the selectivity, and the yield of products. However, the conversion rate of formaldehyde is still not high, which still causes great difficulties in subsequent separation, including the separation of water in the reaction mixture and the recovery of formaldehyde, etc.

[0018] Chinese Patent CN 110372477 discloses a method for preparing polyoxymethylene dimethyl ethers. A multi-stage catalytic extraction process is adopted. An aqueous formaldehyde solution and methanol are introduced into the catalytic extraction reaction zone, and the reaction materials are in countercurrent contact with the extractant, and the catalytic reaction and extraction are carried out multiple times and alternately, having the advantages of low raw material cost, easy product separation, and flexible product scheme.

[0019] Chinese Patent CN 110372478 discloses a method for preparing methylal. A multi-stage catalytic extraction process is adopted. Raw materials formaldehyde and aqueous methanol solution first enter the pre-reactor for reaction, and then are introduced into the catalytic extraction tower or multi-stage catalytic extraction reactor, and are in countercurrent contact with the extractant, and the catalytic reaction and extraction are carried out multiple times and alternately.

[0020] Chinese Patent CN 110372479 discloses a method for preparing polyoxymethylene dimethyl ethers. Similarly, a multi-stage catalytic extraction process is adopted. An aqueous formaldehyde solution and the recycled polyoxymethylene dimethyl ethers are introduced into the pre-reactor for reaction, and then are respectively introduced into the catalytic extraction tower or multi-stage catalytic extraction reactor together with methanol, and are in countercurrent contact with the extractant, and the catalytic reaction and extraction are carried out multiple times and alternately.

[0021] In the technical solutions disclosed in Chinese patents CN 110372477, CN 110372478, and CN 110372479, a multi-stage catalytic extraction process is adopted, which can completely convert formaldehyde in the raffinate phase. However, limited by chemical equilibrium, a large amount of methanol needs to be added, resulting in a large amount of methanol recovery and high energy consumption. Summary of the Invention

[0022] The present application provides a multi-stage catalytic extraction process for preparing polyoxymethylene dimethyl ethers (including methylal) from methanol and aqueous formaldehyde solution. This method has the advantages of low raw material cost, easy product separation, and flexible product scheme. It can produce high-purity methylal, OME 2 、OME 3-4 、OME 3-5 or OME 3-8 any one of several products alone, or these products can be produced simultaneously in any proportion.

[0023] As an embodiment of the present application, the catalytic extraction process for preparing polyoxymethylene dimethyl ethers includes the following steps: 1. Introduce material A containing formaldehyde and material B containing methanol into a multi-stage catalytic extraction reaction system. First, enter the reaction zone of the multi-stage catalytic extraction reaction system to contact the catalyst for reaction, and then contact countercurrently with the extractant, and perform catalytic reaction and extraction processes multiple times and alternately to obtain extract phase material C and raffinate phase (i.e., aqueous phase) material D; 2. The aqueous phase material D mainly contains water, unreacted formaldehyde, and methanol, and is introduced into a catalytic distillation column. Most of the formaldehyde reacts with methanol in the catalytic distillation column to form methylal, and is taken out from the top of the column together with a small amount of unreacted methanol, formaldehyde, and a small amount of water to obtain material E, and wastewater is discharged from the bottom of the column.

[0024] Among them, the reaction zone of the multi-stage catalytic extraction reaction system is equipped with a solid acid catalyst. The catalyst only contacts the aqueous phase and causes it to undergo a catalytic reaction, and does not directly contact the extract phase; the catalytic distillation column is also equipped with a solid acid catalyst.

[0025] The above-mentioned extract phase material C mainly consists of OME products and extractant, and the contents of formaldehyde, methanol, and water are very low. Among them, formaldehyde mainly exists in the forms of methylene glycol, polyoxymethylene glycol, and hemiacetal, and can be decomposed into monomer formaldehyde, water, and methanol without a catalyst, and it is difficult to effectively remove it by using common distillation methods. It can enter a water washing device for reverse extraction with water. After washing and removing formaldehyde and methanol therein, it enters a distillation separation system to separate the required products and extractant. The extractant returns to the multi-stage catalytic extraction reaction system for recycling, and the polyoxymethylene dimethyl ethers can be divided into methylal, OME 2 、diesel additive component (OME 3-4 ,OME 3-5or OME 3-8 ), heavy components (OME with a polymerization degree higher than that of the diesel additive component), and other components.

[0026] The washing liquid obtained by washing mainly contains water, formaldehyde, methanol, and a small amount of OME, and can enter the multi-stage catalytic extraction reaction system from the feed inlet of the reaction zone at a certain intermediate stage or the raffinate phase (aqueous phase) feed inlet of the extraction column; preferably, the formaldehyde concentration in the washing liquid is similar to the formaldehyde concentration in the aqueous phase material originally entering this stage.

[0027] DMM, OME 2 , components such as diesel additive components can all be used as final products. Any one of these products can be produced alone, or these several products can be produced simultaneously in any proportion. The excess OME, including heavy components, is returned to the multi-stage catalytic extraction reaction system for cyclic reaction and converted into the required final products.

[0028] Since the methanol in the extraction phase can be completely removed by washing, the methylal obtained by the technical solution of this application is basically free of methanol, avoiding the disadvantage that the general catalytic distillation process can only obtain an azeotrope of methylal and methanol.

[0029] The multi-stage catalytic extraction reaction system described above can be divided into two forms.

[0030] One form is a plurality of serially connected extraction devices, and a solid acid catalyst is filled in the aqueous phase feed channels of each or part of the extraction devices. The aqueous phase reaction material first flows through the solid acid catalyst filled in the first extraction device and then enters the extraction member to contact the extraction phase, while the extraction phase does not contact the catalyst; after discharging from this extraction device, it enters the next extraction device filled with a solid acid catalyst, or flows through one or more extraction devices without a catalyst to achieve the required extraction effect and then enters the next extraction device filled with a solid acid catalyst; in this way, the reaction and extraction are carried out alternately multiple times until the raffinate phase of the last extraction device in the last stage flows out of the multi-stage catalytic extraction reaction system. Each extraction device filled with a solid acid catalyst and the extraction device without a catalyst downstream of it form a primary catalytic extraction unit of the multi-stage catalytic extraction system. The extractant enters from the last stage of the multi-stage catalytic extraction reaction system, flows countercurrently to the aqueous phase, and finally exits as the extraction phase from the first stage without contacting the catalyst.

[0031] Alternatively, multiple catalyst beds and multiple sets of extraction components are alternately arranged in an extraction device. In this case, one extraction device contains multiple stages of catalytic extraction units, and one or more such extraction devices constitute a multi-stage catalytic extraction reaction system. For example, the extraction device uses a sieve-plate extraction column, in which catalyst beds and extraction trays are alternately arranged. The catalyst beds are arranged in the aqueous-phase channels of the catalytic extraction column, and the aqueous-phase reaction materials are first introduced into the first catalyst bed. Among them, the first catalyst bed can be arranged in a reactor outside the catalytic extraction column, and the aqueous-phase reaction materials first flow through the reactor and then enter the catalytic extraction column.

[0032] Another form is that multiple independent reactors and extraction devices are connected in series. Among them, solid acid catalysts are loaded in the reactors, and the reactors can be in the form of fixed-bed reactors or fluidized-bed reactors, etc. The aqueous-phase materials first enter the first reactor and then enter one or more series-connected extraction devices. This is the first stage of the multi-stage catalytic extraction reaction system. Multiple stages in series constitute the multi-stage catalytic extraction reaction system. The aqueous phase flows out as the raffinate phase from the last extraction device of the last stage, while the extractant enters from this extraction device, flows countercurrently to the aqueous phase, and finally exits as the extract phase from the first extraction device of the first stage without contacting the catalyst. Thus, the reaction and extraction processes are carried out multiple times and alternately.

[0033] In this application, the sequence and upstream-downstream relationship of each stage of the multi-stage catalytic extraction reaction system are defined according to the flow direction of the aqueous-phase materials. The reaction zone of the multi-stage catalytic extraction reaction system refers to the aqueous-phase feed channel of the extraction device filled with solid acid catalysts or an independent reactor filled with solid acid catalysts.

[0034] The above-mentioned extraction device refers to various conventional devices used in the extraction process, including various mixer-settlers, centrifugal extractors, and extraction columns with various different structural forms.

[0035] Methanol and formaldehyde can undergo a condensation reaction in an aqueous solution under the action of an acid catalyst to form polyoxymethylene dimethyl ethers with different degrees of polymerization. This reaction is a reversible reaction, and the conversion rate is greatly limited by the chemical equilibrium. Moreover, the higher the degree of polymerization of the product, the lower the selectivity. This reaction is greatly affected by water. The higher the water content in the reaction system, the lower the equilibrium conversion rate of formaldehyde and methanol, and the average degree of polymerization of the OMEn product also decreases to a certain extent. The distribution of the reaction products is more concentrated in low-degree-of-polymerization products such as methylal. And the larger the molar ratio of formaldehyde group to methyl group (FA / Me), the higher the average degree of polymerization n of the generated OMEn product, and the distribution of the reaction products is more concentrated in high-degree-of-polymerization products.

[0036] In the technical solution of the present invention, in the presence of an extractant immiscible with water, methanol and formaldehyde mainly exist in the aqueous phase, while the reaction product polyoxymethylene dimethyl ethers are enriched in the extract phase. Only the aqueous phase material can contact the catalyst, diffuse into the interior of its particles and react; at the same time, the extract phase does not contact the catalyst, so the polyoxymethylene dimethyl ethers in the extract phase will not be hydrolyzed under the action of the catalyst. In this way, although the reaction in the aqueous phase is still restricted by the chemical equilibrium, no catalytic reaction occurs in the extract phase, and the content of polyoxymethylene dimethyl ethers is not restricted by the chemical equilibrium. Therefore, the conversion rates of methanol and formaldehyde can greatly exceed the equilibrium conversion rate.

[0037] In a multi-stage catalytic extraction reaction system, the aqueous phase material and the extract phase material are in countercurrent contact, and the catalytic reaction process and the extraction process are carried out multiple times and alternately. In the aqueous phase near the inlet of the aqueous phase material, the water concentration is low, while the concentrations of the reactants formaldehyde and methanol are high, and the limitation of the chemical equilibrium is small. Therefore, under the action of the catalyst, the OME concentration in the aqueous phase is high; while the extract phase carries OME (with a lower concentration) extracted from the downstream aqueous phase and contacts it for further extraction, and the OME in it will reach a higher concentration. Near the outlet of the aqueous phase material, the water concentration in the aqueous phase is high, while the concentrations of formaldehyde and methanol are low, and the limitation of the chemical equilibrium is large. After the reaction under the action of the catalyst, the OME concentration in the aqueous phase is low. It contacts with fresh extractant and extracts the OME in it, and the remaining small amounts of unreacted formaldehyde, methanol and water are discharged from the multi-stage catalytic extraction reaction system together.

[0038] According to the reaction characteristics of methanol and formaldehyde in aqueous solution, when methylal is the main target product, a smaller FA / Me ratio should be adopted; when polyoxymethylene dimethyl ethers (OME 2+ ) are the main target products, a larger FA / Me ratio should be adopted and the water content should be reduced as much as possible. Therefore, when reaction raw materials such as formaldehyde, methanol and recycled reaction OME enter the multi-stage catalytic extraction reaction system, different feeding methods can be adopted accordingly.

[0039] The material A containing formaldehyde can adopt an aqueous solution with a formaldehyde concentration of 10 - 55 wt%, which may contain a small amount of methanol. The material B containing methanol can adopt commercially available industrial methanol.

[0040] When methylal is the main target product, the material A can directly adopt commercially available industrial formaldehyde with a concentration of 37, 44, 50 wt% or a dilute formaldehyde solution with a lower concentration. After the material A and the material B are fully mixed, they enter the multi-stage catalytic extraction reaction system from the reaction zone of the first stage, and the FA / Me ratio is 0.3 - 0.8. The small amount of OME 2+ generated can be separated by rectification as a by-product, or can be returned in whole or in part and enter the multi-stage catalytic extraction reaction system for cyclic reaction together with formaldehyde and methanol.

[0041] When OME 2+ , especially OME used as a diesel fuel additive component 3-8 is the main target product, material A can be concentrated to 55 - 80% by vacuum evaporation and enter a multi-stage catalytic extraction reaction system from the reaction zone of the first stage to reduce the water content in the aqueous phases of the first few stages, improve the product yield and the selectivity of the target product; meanwhile, the dilute formaldehyde generated during concentration enters the multi-stage catalytic extraction reaction system from the reaction zone of a certain intermediate stage. Preferably, the concentration of dilute formaldehyde is similar to the formaldehyde concentration of the aqueous phase material originally entering this stage. A part of material B is fed from the reaction zone of the first stage together with the concentrated formaldehyde, and the FA / Me ratio is 0.8 - 2.5; another part is fed from the reaction zone of a certain intermediate stage, and the feeding position can be the same as or different from that of the dilute formaldehyde to increase the FA / Me ratio in the aqueous phases of the first few stages and improve the selectivity of the target product. In this feeding mode, downstream of the multi-stage catalytic extraction reaction system (below the feeding position of the dilute formaldehyde), an excess of methanol can ensure that most of the formaldehyde reacts, and the main reaction product is methylal; upstream, a relatively high FA / Me ratio is maintained, which is beneficial to improving the selectivity of the target product OME 2+ . After the extraction phase is washed with water and separated by distillation, the methylal and OME 2 (when OME 3-8 is the main target product) in it can be used as by-products in whole or in part, or can be returned to the multi-stage catalytic extraction reaction system for cyclic reaction together with the heavy components in whole or in part from the reaction zone of the first stage. When the feeding amount of OME in the cyclic reaction is relatively large, all of material B can be fed from the reaction zone of a certain intermediate stage.

[0042] The basic requirement for selecting an extractant is that the distribution ratio of OME (the ratio of the OME concentration in the extraction phase to the OME concentration in the aqueous phase) is greater than the distribution ratios of methanol and formaldehyde (the ratios of the methanol and formaldehyde concentrations in the extraction phase to the methanol and formaldehyde concentrations in the aqueous phase). Meeting this requirement can achieve the effect of breaking the chemical equilibrium limitation, and the greater the difference between the two, the more obvious the effect. The larger the distribution ratio of OME, the better the enrichment effect of the reaction product polyoxymethylene dimethyl ethers in the extraction phase, the less the amount of extractant used, and the lower the energy consumption required for recovering the extractant and the lower the production cost. The smaller the distribution ratios of methanol and formaldehyde, the lower the methanol and formaldehyde concentrations in the extraction phase, and the easier the water washing and recovery.

[0043] The OME n distribution ratio of most extractants increases with the increase of n, which is beneficial to increasing the proportion of OME 3-8 in the product and is more suitable for producing OME 3-8 ; the OME n distribution ratio of some extractants decreases with the increase of n, which is beneficial to increasing the proportion of DMM in the product and is more suitable for producing DMM.

[0044] The extractant described in this application is at least one of halogenated hydrocarbons, aromatic hydrocarbons, and naphthenic hydrocarbons. The halogenated hydrocarbons are selected from at least one of 1,2-dichloroethane, 1,2-dichloropropane, chlorobenzene, and bromobenzene; the aromatic hydrocarbons are selected from at least one of benzene, toluene, ethylbenzene, xylene, ethylbenzene, n-propylbenzene, isopropylbenzene, methyl ethylbenzene, and butylbenzene; the naphthenic hydrocarbons are selected from at least one of cyclohexane, methylcyclopentane, methylcyclohexane, and ethylcyclohexane.

[0045] In this application, the weight ratio of the feed amount of the extractant entering the multi-stage catalytic extraction reaction system to the total feed amount of methanol, aqueous formaldehyde solution, and washing liquid (Material A + Material B + washing liquid) is 0.1 - 2.8:1. The larger the feed amount of the extractant, the higher the conversion rate of raw formaldehyde and methanol in the multi-stage catalytic extraction reaction system, and the fewer the number of stages required for the multi-stage catalytic extraction reaction system. However, the energy consumption for recovering the extractant increases.

[0046] Since the condensation reaction of methanol and formaldehyde in aqueous solution to form OME and water under the action of an acid catalyst is restricted by chemical equilibrium, and the higher the water content in the reaction system, the greater the restriction of chemical equilibrium. In the downstream of the multi-stage catalytic extraction reaction system, the water content in the aqueous phase becomes larger and larger. To completely react formaldehyde, a large amount of methanol needs to be added to shift the reaction equilibrium to the positive direction and promote the conversion of formaldehyde. Not only does the number of stages required for the multi-stage catalytic extraction reaction system become too many, but the rectification and recovery of a large amount of unreacted methanol also require high energy consumption.

[0047] To solve the above problems, as described above, the technical solution of the present invention proposes to introduce the aqueous phase material D discharged from the multi-stage catalytic extraction reaction system into the catalytic distillation column.

[0048] The catalytic distillation column tower body is divided into a rectification section, a reaction section, and a stripping section from top to bottom. A condenser is provided at the top of the tower, and a reboiler is provided at the bottom of the tower. The reaction section can alternately be provided with catalyst beds and distillation trays or packing, or a wire mesh packing filled with a catalyst can be used, or multiple reactors can be provided outside the tower, and the liquid phase material is respectively led out from different positions in the reaction section of the tower, fully reacted through the reactor, and then returned to the reaction section. Other catalyst loading structures can also be used.

[0049] The aqueous phase material D is fed from the top of the reaction section. This material mainly contains water, unreacted formaldehyde, methanol, and a small amount of OME and extractant. Most of the formaldehyde reacts with methanol under the action of the catalyst in the reaction section to form methylal, and together with a small amount of unreacted methanol, formaldehyde, and a small amount of water, extractant, etc., is taken out from the top of the tower (Material E), and wastewater is discharged from the bottom of the tower. The small amount of OME contained therein 2+ Reacts to convert methanol to methylal in the reaction section, and the extractant forms a low-boiling azeotrope with water and is also taken out from the top of the tower with Material E.

[0050] At normal pressure, the boiling point of methylal is 42.3 °C. Its azeotropic point with methanol and water is 41.8 °C, and the azeotropic composition is 92% methylal, 7.5% methanol, and 0.5% water. Its boiling point or azeotropic point is significantly lower than that of methanol (64.7 °C), and the heat of vaporization of methylal (392 kJ / kg, 20 °C) is much lower than that of methanol (1185 kJ / kg, 20 °C). Especially, the technical solution of this application allows a certain amount of formaldehyde to be contained at the top of the tower. Therefore, the energy consumption of the catalytic distillation column in the technical solution of this application is significantly lower than that of recovering the same amount of methanol, and also lower than that of the catalytic distillation column for producing 86 - 92% methylal (processing the same amount of formaldehyde and methanol).

[0051] In the reaction section, the condensation reaction of formaldehyde and methanol will generate a small amount of OME with a relatively high boiling point 2 、OME 3 , both of which form low-boiling azeotropes with water, and the azeotropic points are between methanol and water. Under the rectification effect of the catalytic distillation column, OME 2 、OME 3 are enriched in the reaction section in the middle of the tower and react with methanol to be converted into methylal, and will not be withdrawn from the bottom of the tower. A very small amount may be withdrawn from the top of the tower along with methylal and will ultimately be withdrawn as products, by-products or enter the multi-stage catalytic extraction reaction system to participate in the reaction.

[0052] Optionally, a certain amount of methanol can be fed into the bottom of the reaction section of the catalytic distillation column to promote the conversion of formaldehyde, reduce the formaldehyde content in the bottom wastewater, reduce the reflux ratio, further reduce the energy consumption, and at the same time promote the reaction of OME 2 、OME 3 being converted into methylal.

[0053] The material E withdrawn from the top of the catalytic distillation column can enter the multi-stage catalytic extraction reaction system to continue the reaction from the reaction zone of the first stage or a certain intermediate stage, or enter the water washing tower together with the extraction phase for water washing separation, which is applicable to the cases where polyoxymethylene dimethyl ethers (OME 2+ ) or methylal are the main target products respectively.

[0054] The reaction zones of the aforementioned multi-stage catalytic extraction reaction system and the reaction section of the catalytic distillation column are both filled with solid acid catalysts, which can be the same or different. Optionally, the solid acid catalyst is selected from strongly acidic cation exchange resins.

[0055] The reaction temperature in the reaction zone of the aforementioned multi-stage catalytic extraction reaction system is 40 - 120 °C, and the operating pressure is 0.05 - 0.6 MPa (gauge pressure). The operating pressure (top pressure) of the catalytic distillation column is 0 - 0.5 MPa (gauge pressure).

[0056] The present application also provides another implementation manner, which is different from the first implementation manner described above in that: The extractant not only feeds from the last stage of the multi-stage catalytic extraction reaction system, but also part of the extractant can be fed from one or several intermediate stages. The extract phase materials originally entering this stage or these stages are withdrawn from the multi-stage catalytic extraction reaction system.

[0057] This implementation manner can improve the extraction and reaction efficiency, but the amount of extractant used is relatively large.

[0058] The following are two specific implementation schemes of different final products of the technical solution of the present invention.

[0059] 1 DMM and OME 2 As the final product As shown in the appendix Figure 1 When producing DMM and OME using toluene (TO) as the extractant, raw material methanol (MEOH) and 37% aqueous formaldehyde solution (37FA) are fed from the top of the catalytic extraction tower (CE) filled with a strongly acidic cation exchange resin catalyst, and the fresh extractant toluene is mixed with the recycled toluene (TO-RECYCLE) and fed from the bottom. 2 The raffinate phase (H2O + MEOH + FA) is withdrawn from the bottom of the catalytic extraction tower and enters the catalytic distillation tower (CD). The extract phase is withdrawn from the top of the catalytic extraction tower, mixed with the material withdrawn from the top of the catalytic distillation tower (DMM + MEOH, containing DMM, methanol, formaldehyde, a small amount of water and toluene), and fed from the bottom of the scrubber tower. After being back-extracted for formaldehyde and methanol by water (H2O) fed from the top of this tower, it is withdrawn from the top and enters the DMM tower. The aqueous solution of formaldehyde and methanol withdrawn from the bottom of the scrubber tower returns to the middle of the catalytic extraction tower for continued reaction. Waste water (W-H2O) is discharged from the bottom of the catalytic distillation tower.

[0060] The product DMM is obtained at the top of the DMM tower, and the bottom liquid enters the OME

[0061] tower. The product OME is obtained at the top of the tower 2 and the toluene is recycled from the bottom of the tower for use. 2

[0062] 2 Simultaneously producing DMM, OME 2 , OME 3-5 As shown in the appendix Figure 2 When using mixed xylene as the extractant and methanol and 37% aqueous formaldehyde solution as raw materials to simultaneously produce DMM, OME 2 , OME 3-5When, the 37% aqueous formaldehyde solution (37FA) is divided into two feed streams, namely, a 65 - 75% concentrated solution (65 - 75FA) and a 15% dilute solution (15FA) (by vacuum evaporation). The concentrated formaldehyde solution is mixed with methanol (MEOH) and the recycled heavy components from the reaction (OME6+) and then fed into the top of the catalytic extraction column (CE) filled with a strongly acidic cation exchange resin catalyst. The fresh extraction agent, mixed xylene (DMB), and the recycled xylene (DMB - RECYCLE) are mixed and fed into the bottom of the column.

[0063] The raffinate phase (H2O + MEOH + FA) is withdrawn from the bottom of the catalytic extraction column and enters the catalytic distillation column (CD). The extract phase is withdrawn from the top of the catalytic extraction column, mixed with the material withdrawn from the top of the catalytic distillation column (DMM + MEOH, containing DMM, methanol, formaldehyde, a small amount of water, and mixed xylene), and then fed into the bottom of the scrubber. After being scrubbed with water (H2O) fed into the top of this column to extract formaldehyde and methanol, the mixture is withdrawn from the top and enters the DMM column. The aqueous solution of formaldehyde and methanol withdrawn from the bottom of the scrubber is returned to the middle of the catalytic extraction column for continuous reaction. Waste water (W - H2O) is discharged from the bottom of the catalytic distillation column.

[0064] The product DMM is obtained at the top of the DMM column, and the bottom liquid sequentially enters the OME2 column, DMB column, and OME column to obtain OME 2 products, recycled DMB, OME 3-5 products and the recycled heavy components OME from the reaction 6+ 。

[0065] The beneficial effects that can be produced by this application include: Inexpensive aqueous formaldehyde solution can be used as the raw material to produce polyoxymethylene dimethyl ethers, including DMM (basically methanol - free), OME 2 、OME 3-4 、OME 3-5 or OME 3-8 one or several of them. BRIEF DESCRIPTION OF THE DRAWINGS

[0066] Figure 1 is a simplified process flow diagram for producing DMM and OME using toluene as the extraction agent. 2

[0067] Figure 2 is a simplified process flow diagram for simultaneously producing DMM, OME 2 、OME 3-5 using mixed xylene as the extraction agent. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0068] The following describes this application in detail with reference to the embodiments, but this application is not limited to these embodiments.

[0069] The methanol, aqueous formaldehyde solution, paraformaldehyde, and OME used in the examples and comparative examples of this application 2 , OME 3-4 are all commercially available industrial products. Methylal, benzene, toluene, mixed xylene, ethylbenzene, n-propylbenzene, isopropylbenzene, methylethylbenzene, butylbenzene, 1,2-dichloroethane, 1,2-dichloropropane, chlorobenzene, bromobenzene, cyclohexane, methylcyclopentane, methylcyclohexane, ethylcyclohexane, etc. are analytical pure reagents. OME 5+ is provided by the manufacturer.

[0070] The strongly acidic cation resin catalysts used in the examples and comparative examples of this application include DMM and DMMn resin catalysts, both of which are provided by Kerry Environmental Protection Technology Co., Ltd.

[0071] Example 1 A 4-stage catalytic extraction reaction system is adopted. Each stage is composed of a glass tube reactor with an inner diameter of 14 mm, a height of 20 cm, and filled with 30 ml of DMMn resin catalyst in series with a glass tube extraction column with an inner diameter of 14 mm, a height of 100 cm, and filled with 73 cm high Φ2.5×2.5 mm stainless steel θ wire rings; 4 stages are connected in series to form a catalytic extraction reaction system.

[0072] Each extraction column uses the raffinate phase (aqueous phase) as the continuous phase and the extraction phase as the dispersed phase. The reaction temperature of each reactor is 60 °C, the operating temperature of the extraction column is room temperature (28 - 30 °C), and the system operating pressure is 0.3 MPa.

[0073] The feed rate of 20 wt% aqueous formaldehyde solution (diluted from 37% industrial formaldehyde aqueous solution) is 4.8 ml / min, and the feed rate of methanol is 2.6 ml / min. After mixing, it first enters the reactor of the first stage, then enters the extraction column of the first stage, and then enters the reactors and extraction columns of the subsequent stages in turn, and is taken out as the raffinate phase from the extraction column of the last stage. Toluene is used as the extraction agent, which is fed into the extraction column of the last stage with a feed rate of 0.7 ml / min, and then enters the extraction columns of the previous stages in turn, and is finally taken out as the extraction phase from the extraction column of the first stage.

[0074] The extraction phase discharge rate is 2.8 g / min, including 0.28 wt% formaldehyde, 1.1 wt% methanol, 0.22 wt% water, 66.8 wt% DMM, OME 2 6.8 wt%, OME 3+ 0.8 wt%, and the rest is toluene.

[0075] The raffinate phase discharge rate is 4.5 g / min, including 2 wt% methanol, 1 wt% formaldehyde, 0.24 wt% DMM, 0.1 wt% toluene, and the rest is water.

[0076] Example 2 The same catalytic extraction reaction system and operation mode as in Example 1 are adopted. The difference is that in each extraction column, the raffinate phase (aqueous phase) is the dispersed phase and the extraction phase is the continuous phase. The reaction temperature of each reactor is 70°C, and the system operating pressure is 0.5 MPa.

[0077] The feed rate of 37 wt% formaldehyde aqueous solution is 2.8 ml / min, and the feed rate of methanol is 2.4 ml / min. After mixing, they are fed. Benzene is used as the extractant, and the feed rate is 6.4 ml / min.

[0078] The extraction phase discharge rate is 8.4 g / min, among which formaldehyde is 2.4 wt%, methanol is 0.8 wt%, water is 0.5 wt%, DMM is 13.8 wt%, OME 2 is 6.4 wt%, OME 3+ is 3.6 wt%, and the rest is benzene.

[0079] The raffinate phase discharge rate is 2.4 g / min, among which methanol is 4.2 wt%, formaldehyde is 1.5 wt%, DMM is 0.36 wt%, benzene is 0.8 wt%, and the rest is water.

[0080] Example 3 The same catalytic extraction reaction system and operation mode as in Example 1 are adopted. The difference is that the catalytic extraction reaction system has 6 stages, the reactor height is 40 cm, and 60 ml of DMMn resin catalyst is filled. In each extraction column, the raffinate phase (aqueous phase) is the dispersed phase and the extraction phase is the continuous phase. The reaction temperature of each reactor is 45°C, the operation temperature of each extraction column is room temperature (26 - 29°C), and the system operating pressure is 0.2 MPa.

[0081] Paraformaldehyde is mixed with an appropriate amount of water and heated to dissolve to make a 50 wt% formaldehyde aqueous solution, which is mixed with OME 1-2 (DMM accounts for 60 wt%) and then enters the reactor of the first stage. The feed rates are 1.5 ml / min and 1.6 ml / min respectively. Methanol is fed into the reactor of the fourth stage, and the feed rate is 0.65 ml / min. Mixed xylene is used as the extractant, and the feed rate is 11.5 ml / min.

[0082] The extraction phase discharge rate is 11.8 g / min, among which formaldehyde is 2.1 wt%, methanol is 1 wt%, water is 0.2 wt%, DMM is 6.8 wt%, OME 2 is 4.5 wt%, OME 3+ is 6.6 wt%, and the rest is mixed xylene.

[0083] The raffinate phase discharge rate is 1.1 g / min, among which methanol is 6 wt%, formaldehyde is 4 wt%, DMM is 0.8 wt%, mixed xylene is 0.4 wt%, and the rest is water.

[0084] Example 4 The same catalytic extraction reaction system and operation mode as in Example 1 are adopted. The difference is that the catalytic extraction reaction system has 5 stages, each extraction column is filled with stainless steel θ wire rings with a height of 42 cm and a diameter of Φ2.5×2.5 mm. In each extraction column, the raffinate phase (aqueous phase) is the dispersed phase and the extraction phase is the continuous phase. The reaction temperature of each reactor is 90 °C, and the system operating pressure is 0.6 MPa.

[0085] Paraformaldehyde is mixed with an appropriate amount of water, heated and dissolved to prepare an aqueous formaldehyde solution with a formaldehyde content of 55 wt%. After mixing with methanol, it enters the reactor of the first stage, and the feed rates are 2.1 ml / min and 2.0 ml / min respectively. Ethylbenzene is used as the extractant, and the feed rate is 6.6 ml / min.

[0086] The extraction phase discharge rate is 8.13 g / min, including 1.8 wt% formaldehyde, 0.5 wt% methanol, 1 wt% water, 10.2 wt% DMM, 2 7.2 wt% OME 3+ 9.7 wt%, and the rest is ethylbenzene.

[0087] The raffinate phase discharge rate is 1.63 g / min, including 4.5 wt% methanol, 2.2 wt% formaldehyde, 0.51 wt% DMM, 0.18 wt% ethylbenzene, and the rest is water.

[0088] Example 5 The same catalytic extraction reaction system and operation mode as in Example 1 are adopted. The difference is that the catalytic extraction reaction system has 6 stages, the reactor height is 40 cm, and it is filled with 60 ml of DMMn resin catalyst. In each extraction column, the raffinate phase (aqueous phase) is the dispersed phase and the extraction phase is the continuous phase. The reaction temperature of each reactor is 40 °C, and the system operating pressure is 0.05 MPa.

[0089] Paraformaldehyde is mixed with an appropriate amount of water, heated and dissolved to prepare an aqueous formaldehyde solution with a formaldehyde content of 50 wt%. After mixing with OME 1-2 (DMM accounts for 60 wt%), it enters the reactor of the first stage, and the feed rates are 1.3 ml / min and 1.5 ml / min respectively. Methanol is fed into the reactor of the fourth stage, and the feed rate is 0.62 ml / min. The washing liquid of the extraction phase (with a composition of 3.9 wt% methanol, 7.5 wt% formaldehyde, 0.42 wt% isopropylbenzene, 1.9 wt% DMM, OME 2 1 wt%, OME 3+ 1.5 wt%, 83.8 wt% water) is mixed with the discharge of the reactor of the fifth stage and then enters the extraction column of the fifth stage, and the feed rate is 1.1 ml / min. Isopropylbenzene is used as the extractant, and the feed rate is 9.8 ml / min.

[0090] The extraction phase discharge rate is 10.9 g / min, including 0.82 wt% formaldehyde, 0.42 wt% methanol, 0.1 wt% water, 7.1 wt% DMM, 2 5.4 wt% OME, 3+ 8.0 wt% OME, and the rest is cumene.

[0091] The raffinate phase discharge rate is 1.8 g / min, including 4.7 wt% methanol, 2.4 wt% formaldehyde, 0.42 wt% DMM, 0.1 wt% cumene, and the rest is water.

[0092] Example 6 The same catalytic extraction reaction system and operation method as in Example 1 are adopted. The difference is that the catalytic extraction reaction system has 3 stages, each reactor is filled with 20 ml of DMM resin catalyst, the reaction temperature is 120 °C, and the system operation pressure is 0.6 MPa.

[0093] A 10 wt% aqueous formaldehyde solution (diluted from a 37 wt% industrial formaldehyde aqueous solution), methanol, and OME 2+ (OME 2 accounting for 90 wt%, OME 3-4 accounting for 10 wt%) are mixed and then enter the reactor of the first stage, and the feed rates are 6.8 ml / min, 1.87 ml / min, and 0.13 ml / min respectively. An aromatic hydrocarbon mixture (n-propylbenzene, methyl ethylbenzene, and butylbenzene account for 40 wt%, 30 wt%, and 30 wt% respectively) is used as the extractant, and the feed rate is 1.7 ml / min.

[0094] The extraction phase discharge rate is 3.2 g / min, including 0.4 wt% formaldehyde, 2.2 wt% methanol, 1.2 wt% water, 45.2 wt% DMM, PODE 2+ 3.2 wt%, and the rest is the aromatic hydrocarbon mixture.

[0095] The raffinate phase discharge rate is 7.08 g / min, including 1.8 wt% methanol, 1.1 wt% formaldehyde, 0.22 wt% DMM, 0.2 wt% aromatic hydrocarbon mixture, and the rest is water.

[0096] Example 7 The same catalytic extraction reaction system and operation method as in Example 1 are adopted. The difference is that the catalytic extraction reaction system has 5 stages, each extraction column uses the raffinate phase (aqueous phase) as the dispersed phase and the extraction phase as the continuous phase, the reaction temperature of each reactor is 70 °C, and the system operation pressure is 0.4 MPa.

[0097] A 37 wt% aqueous formaldehyde solution and OME 1-2After mixing (DMM accounts for 60 wt%), it enters the reactor of the first stage, and the feeding rates are 2.7 ml / min and 1.8 ml / min respectively. Methanol is fed into the reactor of the fourth stage, and the feeding rate is 0.98 ml / min. 1,2-dichloropropane is used as the extractant, and the feeding rate is 9 ml / min.

[0098] The discharge rate of the extract phase is 13.1 g / min, including 1.8 wt% formaldehyde, 0.6 wt% methanol, 0.2 wt% water, 6.8 wt% DMM, 2 5.2 wt% PODE 3+ 8.2 wt%, and the rest is 1,2-dichloropropane.

[0099] The discharge rate of the raffinate phase is 2.02 g / min, including 5.9 wt% methanol, 2.7 wt% formaldehyde, 0.6 wt% DMM, 1.5 wt% 1,2-dichloropropane, and the rest is water.

[0100] Example 8 The same catalytic extraction reaction system and operation mode as in Example 1 are adopted. The difference is that the reaction temperature of each reactor is 50 °C, and the system operation pressure is 0.2 MPa.

[0101] After mixing 37 wt% aqueous formaldehyde solution with methanol, it enters the reactor of the first stage, and the feeding rates are 3.8 ml / min and 2.8 ml / min respectively. 1,2-dichloroethane is used as the extractant, and the feeding rate is 5 ml / min.

[0102] The discharge rate of the extract phase is 8.9 g / min, including 2.6 wt% formaldehyde, 1.8 wt% methanol, 1.2 wt% water, 17.2 wt% DMM, 2 7.6 wt% OME 3+ 4.2 wt%, and the rest is 1,2-dichloroethane.

[0103] The discharge rate of the raffinate phase is 3.3 g / min, including 3.2 wt% methanol, 1.6 wt% formaldehyde, 0.35 wt% DMM, 1.8 wt% 1,2-dichloroethane, and the rest is water.

[0104] Example 9 The same catalytic extraction reaction system and operation mode as in Example 1 are adopted. The difference is that the catalytic extraction reaction system has 5 stages, the height of each extraction column is 130 cm, filled with Φ2.5×2.5 mm stainless steel θ mesh rings with a height of 104 cm, the reaction temperature of each reactor is 50 °C, the operation temperature of the extraction column is room temperature (32 - 35 °C), and the system operation pressure is 0.2 MPa.

[0105] Mix paraformaldehyde reagent with an appropriate amount of water, heat and dissolve it to prepare a formaldehyde aqueous solution with a formaldehyde content of 50 wt%, and mix it with OME n (DMM accounts for 55 wt%, OME 2 accounts for 35 wt%, OME 5+ accounts for 10 wt%) and then enter the reactor of the first stage. The feeding rates are 4.2 ml / min and 5.5 ml / min respectively. Methanol is fed into the reactor of the third stage with a feeding rate of 2 ml / min. A mixture of chlorobenzene and bromobenzene (weight ratio 3:1) is used as the extractant with a feeding rate of 6 ml / min.

[0106] The discharge rate of the extract phase is 15.4 g / min, in which formaldehyde is 5.6 wt%, methanol is 2.6 wt%, water is 0.8 wt%, DMM is 14.2 wt%, PODE 2 is 11.5 wt%, PODE 3+ is 16.2 wt%, and the rest is a mixture of chlorobenzene and bromobenzene.

[0107] The discharge rate of the raffinate phase is 2.8 g / min, in which methanol is 5.1 wt%, formaldehyde is 2.4 wt%, DMM is 0.52 wt%, and the total of chlorobenzene and bromobenzene is 2.9 wt%, and the rest is water.

[0108] Example 10 Use the same catalytic extraction reaction system and operation mode as in Example 1. The difference is that the catalytic extraction reaction system has 3 stages. The height of each extraction column is 130 cm and it is filled with Φ2.5×2.5 mm stainless steel θ wire rings with a height of 104 cm. Each reactor is filled with 30 ml of DMM resin catalyst, the reaction temperature is 60 °C, the operation temperature of the extraction column is room temperature (33 - 37 °C), and the system operation pressure is 0.36 MPa.

[0109] Mix 37 wt% formaldehyde aqueous solution with methanol and OME 2+ (OME 2 accounts for 90 wt%, OME 3-4 accounts for 10 wt%) and then enter the reactor of the first stage. The feeding rates are 4.6 ml / min, 5.1 ml / min, and 0.56 ml / min respectively. The extractant is a mixture of cyclohexane, methylcyclopentane, methylcyclohexane, and ethylcyclohexane each accounting for 25 wt% with a feeding rate of 4.55 ml / min.

[0110] The discharge rate of the extract phase is 9 g / min, in which formaldehyde is 0.32 wt%, methanol is 1.4 wt%, water is 0.2 wt%, DMM is 49.6 wt%, PODE 2+ is 5.3 wt%, and the rest is a mixture of naphthenes.

[0111] The raffinate phase discharge rate is 4.7 g / min, containing 3.9 wt% methanol, 1.8 wt% formaldehyde, 0.18 wt% DMM, 0.15 wt% naphthene mixture, and the rest is water.

[0112] Example 11 The catalytic distillation column is made of glass and includes a top condenser refluxer, a rectifying section, a reaction section, a stripping section, and a reboiler. The inner diameters of the rectifying section and the stripping section are 25 mm, and each is filled with 60 cm high Φ2.5×2.5 mm stainless steel θ-rings. The inner diameter of the reaction section is 50 mm, and the effective height is 100 cm, filled with catalyst packages and Φ2.5×2.5 mm stainless steel θ-rings; the catalyst package has a diameter of ~20 mm and a height of 40 mm, made of 80-mesh stainless steel mesh, and each contains ~10 ml of DMM resin catalyst. A total of 100 ml of catalyst is filled in the reaction section.

[0113] The raffinate phase (aqueous phase) material obtained in Example 1 (with a composition of 2 wt% methanol, 1 wt% formaldehyde, 0.24 wt% DMM, 0.1 wt% toluene, and the rest is water) is fed from the top of the reaction section at a feed rate of 3.8 ml / min and a feed temperature of 40°C. Methanol is fed from the bottom of the reaction section at a feed rate of 0.015 ml / min and a feed temperature of 40°C. The operating pressure of the catalytic distillation column is atmospheric pressure (top pressure), and the reflux ratio is 5.

[0114] The top product discharge flow rate is 0.13 g / min, containing 72.4 wt% methylal, 21 wt% methanol, 3 wt% formaldehyde, 2.9 wt% toluene, and 0.8 wt% water. The bottom product discharge rate is 3.7 g / min, containing 0.008 wt% methanol, 0.005 wt% formaldehyde, and 99.99 wt% water.

[0115] Example 12 The same catalytic distillation column as in Example 11 is used.

[0116] The raffinate phase (aqueous phase) material obtained in Example 2 (with a composition of 4.2 wt% methanol, 1.5 wt% formaldehyde, 0.36 wt% DMM, 0.8 wt% benzene, and the rest is water) is fed from the top of the reaction section at a feed rate of 3.2 ml / min and a feed temperature of 40°C. The operating pressure of the catalytic distillation column is atmospheric pressure (top pressure), and the reflux ratio is 3.

[0117] The top product discharge flow rate is 0.19 g / min, containing 65.5 wt% methylal, 19.3 wt% methanol, 1.3 wt% formaldehyde, 13.3 wt% benzene, and 0.6 wt% water. The bottom product discharge rate is 3 g / min, containing 0.008 wt% methanol, 0.004 wt% formaldehyde, and 99.99 wt% water.

[0118] Example 13 The same catalytic distillation column as in Example 11 was used.

[0119] The raffinate phase (aqueous phase) material obtained in Example 3 (with a composition of 6 wt% methanol, 4 wt% formaldehyde, 0.8 wt% DMM, 0.4 wt% mixed xylene, and the rest being water) was fed into the top of the reaction section at a feed rate of 3.6 ml / min and a feed temperature of 40°C. Methanol was fed into the bottom of the reaction section at a feed rate of 0.16 ml / min and a feed temperature of 40°C. The operating pressure of the catalytic distillation column was atmospheric pressure (top pressure), the reflux ratio was 3.5, and the effective heating power of the reboiler was 35 w.

[0120] The overhead product flow rate was 0.45 g / min, containing 78 wt% methylal, 14.9 wt% methanol, 3.4 wt% formaldehyde, 3.2 wt% mixed xylene, and 0.5 wt% water. The bottom product flow rate was 3.3 g / min, containing 0.012 wt% methanol, 0.005 wt% formaldehyde, and 99.98 wt% water.

[0121] Example 14 The stripping column used was a glass tube with an inner diameter of 14 mm and a height of 100 cm, filled with 73 cm high Φ2.5×2.5 mm stainless steel θ-rings.

[0122] The extract phase material obtained in Example 1 (with a composition of 0.28 wt% formaldehyde, 1.1 wt% methanol, 0.22 wt% water, 66.8 wt% DMM, 2 6.8 wt% OME 3+ 0.8 wt%, and the rest being toluene) was fed into the bottom of the stripping column at a feed rate of 5 ml / min; water was used as the stripping agent and fed into the top of the stripping column at a feed rate of 0.44 ml / min. The extract phase material was the continuous phase and the aqueous phase was the dispersed phase. The stripping temperature was room temperature, 30 - 32°C, and the operating pressure was 0.1 MPa.

[0123] The flow rate of the washed extract phase discharged from the top of the stripping column was 4.2 g / min, containing 0.005 wt% formaldehyde, 0.01 wt% methanol, 0.36 wt% water, 66.7 wt% DMM, 2 6.87 wt% OME 3+ 0.81 wt%, and 25.2 wt% toluene.

[0124] The flow rate of the aqueous phase discharged from the bottom of the stripping column was 0.66 g / min, containing 1.9 wt% formaldehyde, 7.4 wt% methanol, 22.4 wt% DMM, 2 1.8 wt% OME 3+ 0.21 wt%, 0.1 wt% toluene, and 66.2 wt% water.

[0125] Example 15 The same counter-extraction experimental device as that in Example 14 was used, except that the height of the glass tube of the counter-extraction tower was 150 cm and the packing height of the θ wire ring was 122 cm.

[0126] The extraction phase material obtained in Example 3 (with a composition of 2.1 wt% formaldehyde, 1 wt% methanol, 0.2 wt% water, 6.8 wt% DMM, OME 2 4.5 wt%, OME 3+ 6.6 wt%, and the rest being mixed xylene) was fed from the bottom of the counter-extraction tower at a feed rate of 4.8 ml / min; water was used as the counter-extraction agent and fed from the top of the counter-extraction tower at a feed rate of 0.42 ml / min; the extraction phase material was the continuous phase and the aqueous phase was the dispersed phase. The counter-extraction temperature was room temperature of 32 - 34 °C, and the operating pressure was 0.2 MPa.

[0127] The extraction phase discharge amount after washing with water at the top of the counter-extraction tower was 4 g / min, among which formaldehyde was 0.006 wt%, methanol was 0.02 wt%, water was 0.5 wt%, DMM was 6.4 wt%, OME 2 4.3 wt%, OME 3+ 6.4 wt%, and mixed xylene was 82.4 wt%.

[0128] The aqueous phase discharge amount at the bottom of the counter-extraction tower was 0.61 g / min, among which formaldehyde was 14.5 wt%, methanol was 6.9 wt%, DMM was 4.7 wt%, OME 2 2.8 wt%, OME 3+ 3.6 wt%, mixed xylene was 0.27 wt%, and water was 67.2 wt%.

[0129] Comparative Example 1 The same catalytic extraction reaction system and operation mode as those in Example 4 were used, except that the catalytic extraction reaction system was 10-stage.

[0130] Paraformaldehyde was mixed with an appropriate amount of water, heated and dissolved to prepare an aqueous formaldehyde solution with a formaldehyde content of 55 wt%, and then mixed with methanol and fed into the reactor of the first stage, with feed rates of 2.1 ml / min and 2.4 ml / min respectively. Ethylbenzene was used as the extraction agent with a feed rate of 6.6 ml / min.

[0131] The extraction phase discharge amount was 8.4 g / min, among which formaldehyde was 1.9 wt%, methanol was 0.5 wt%, water was 1.1 wt%, DMM was 11 wt%, OME 2 7.7 wt%, OME 3+ 10.4 wt%, and the rest was ethylbenzene.

[0132] The raffinate phase discharge rate is 1.68 g / min, containing 8.3 wt% methanol, 0.01 wt% formaldehyde, 0.18 wt% ethylbenzene, and the rest is water.

[0133] Comparing Comparative Example 1 with Example 4 shows that when other conditions are the same, it is necessary to increase the number of stages of the catalytic extraction reaction system and the methanol feed rate to achieve almost complete conversion of formaldehyde, but the amount of methanol to be recovered in the raffinate phase increases.

[0134] Comparative Example 2 The same catalytic distillation column and operating conditions as in Example 13 are used, including the composition of the raffinate phase (aqueous phase) material and the feed location, etc. The difference is that the feed rates are different, the feed rate of the raffinate phase (aqueous phase) is 1.2, and the methanol feed rate is 0.053; the reflux ratio is 20, and the effective heating power of the reboiler is 34 w.

[0135] The overhead product flow rate is 0.15 g / min, containing 88.3 wt% methylal, 7.8 wt% methanol, 0.004 wt% formaldehyde, 3.2 wt% mixed xylene, and 0.6 wt% water. The bottom product discharge rate is 1.1 g / min, containing 0.009 wt% methanol, 0.004 wt% formaldehyde, and 99.99 wt% water.

[0136] Comparing Comparative Example 2 with Example 13 shows that when recovering high-value components from the same raffinate phase material and discharging wastewater, with the same treatment capacity and basically the same other conditions, the overhead product in Example 13 can contain a small amount of formaldehyde, and the required reflux ratio is greatly reduced and the energy consumption is greatly lowered.

[0137] Comparative Example 3 The distillation column is made of glass and includes a top condenser refluxer, a rectifying section, a stripping section, and a reboiler. The inner diameters of the rectifying section and the stripping section are 25 mm, and they are respectively filled with stainless steel θ wire rings with a height of 100 cm and 60 cm and a diameter of Φ2.5×2.5 mm.

[0138] A 6% methanol aqueous solution is fed between the rectifying section and the stripping section, with a feed rate of 3.6 ml / min, a feed temperature of 40 °C, and the operating pressure of the distillation column is atmospheric pressure (top pressure).

[0139] When the reflux ratio is 3 and the effective heating power of the reboiler is 37 w, the overhead product flow rate is 0.22 g / min, containing 99 wt% methanol and 1 wt% water; the bottom product discharge rate is 3.38 g / min, containing 0.008 wt% methanol and 99.99 wt% water.

[0140] When the reflux ratio is 3.5 and the effective heating power of the reboiler is 40 w, the overhead product flow rate is 0.218 g / min, which contains 99.6 wt% methanol and 0.4 wt% water; the bottom product flow rate is 3.38 g / min, which contains 0.008 wt% methanol and 99.99 wt% water.

[0141] Comparing Comparative Example 3 with Example 13 shows that under the conditions of equivalent number of theoretical plates in the distillation column and the same feed flow rate, the energy consumption for recovering methanol from a 6 wt% methanol aqueous solution by distillation is higher than that for recovering high-value components such as methylal and methanol from an aqueous solution containing 6 wt% methanol, 4 wt% formaldehyde, and 0.4 wt% mixed xylene using catalytic distillation technology, even if a certain amount of methanol is additionally added to the latter.

[0142] As described above, only some embodiments of the present application are provided. Although the present application is disclosed with preferred embodiments, it is not intended to limit the present application. Any person skilled in the art, without departing from the scope of the technical solution of the present application, making some changes or modifications using the disclosed technical content is equivalent to the implementation cases and falls within the scope of the technical solution of the present application.

Claims

1. A catalytic extraction process for preparing polyoxymethylene dimethyl ether, characterized in that: The following steps are involved: 1) Introducing material A containing formaldehyde and material B containing methanol into a multi-stage catalytic extraction reaction system, first entering the reaction zone of the multi-stage catalytic extraction reaction system to contact the catalyst for reaction, and then countercurrently contacting with the extractant, repeatedly and alternately performing the catalytic reaction and extraction process to obtain an extract phase material and a raffinate phase, i.e., an aqueous phase material; 2) The raffinate phase enters the catalytic distillation tower, and methylal, methanol, etc. are taken out from the top of the tower; Wherein, the reaction zone and the catalytic distillation tower of the multi-stage catalytic extraction reaction system are both equipped with solid acid catalysts.

2. The method according to claim 1, characterized in that The multi-stage catalytic extraction reaction system consists of one or more extraction devices connected in series, wherein the water phase feed channel of each or part of the extraction devices is filled with a solid acid catalyst.

3. The method according to claim 1, characterized in that The multi-stage catalytic extraction reaction system is composed of a plurality of independent fixed bed reactors and extraction equipment connected in series, wherein the fixed bed reactor is filled with a solid acid catalyst and only water phase material flows through the fixed bed reactor.

4. The method according to claim 1, characterized in that All of the material A and the material B are fed together, and the feeding position is the reaction zone of the first stage of the multi-stage catalytic extraction reaction system.

5. The method according to claim 1, characterized in that Material A is concentrated into concentrated formaldehyde solution and dilute formaldehyde solution. The concentrated formaldehyde solution is fed into the reaction zone of the first stage of the multi-stage catalytic extraction reaction system, and the dilute formaldehyde solution is fed into the reaction zone of a middle stage of the multi-stage catalytic extraction reaction system.

6. The method according to claim 5, characterized in that A portion of material B is fed together with the concentrated formaldehyde solution, and the rest is fed from the reaction zone of a middle stage of the multi-stage catalytic extraction reaction system.

7. The method according to claim 1, characterized in that The OME of the circulation reaction is returned from the reaction zone of the first stage to the multi-stage catalytic extraction reaction system for circulation reaction.

8. The method according to claim 7, characterized in that All the material B is fed from the reaction zone of a certain stage in the middle of the multi-stage catalytic extraction reaction system.

9. The method according to claim 1, characterized in that: The extract phase material is back-extracted with water to remove formaldehyde and methanol therein, and the obtained water washing liquid is returned to the multi-stage catalytic extraction reaction system from a certain intermediate stage.

10. The method according to claim 1 or 9, characterized in that: The weight ratio of the feed amount of the extractant entering the multi-stage catalytic extraction reaction system to the sum of the feed amounts of material A, material B and water washing liquid is 0.1-2.8:

1.

11. The method according to claim 1, characterized in that: The extractant is at least one of halogenated hydrocarbons, aromatic hydrocarbons and cycloalkanes.

12. The method according to claim 1, characterized in that The raffinate phase material is fed from the top of the reaction section of the catalytic distillation tower.

13. The method according to claim 12, characterized in that A certain amount of methanol is fed from the bottom of the reaction section of the catalytic distillation tower.

14. The method according to claim 1, characterized in that The material taken out from the top of the catalytic distillation tower enters the multi-stage catalytic extraction reaction system from the reaction zone of the first stage or a certain middle stage.

15. The method according to claim 1, characterized in that The material taken out from the top of the catalytic distillation tower is washed and stripped together with the extraction phase.

16. The method according to claim 1, characterized in that The solid acid catalyst is a strongly acidic cation exchange resin.

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