Process for preparing methylal

Abstract

The invention discloses a process for preparing methylal from methanol and a formaldehyde aqueous solution, the process combines a multi-stage catalytic extraction process and a catalytic rectification process, an extraction agent does not need to be completely separated from a product, and the process has the advantages that the raw material cost is low, the product separation is easy, the product scheme is flexible, the product methylal does not contain methanol, and the like. The method comprises the following steps: introducing raw materials formaldehyde and methanol into a multistage catalytic extraction reaction system (CE system), carrying out countercurrent contact with an extraction agent, and carrying out catalytic reaction and extraction alternately for multiple times to obtain an extraction phase material C and a raffinate phase material D; the material C is washed with water to remove formaldehyde and methanol, then rectification separation is carried out, methylal is separated out or part or all of OME2 is further separated out, and other components are returned to a CE system together with the extraction agent for recycling. The water washing liquid returns to the CE system for continuous reaction. The material D enters a catalytic rectifying tower, methylal, unreacted methanol, formaldehyde and a small amount of water are extracted from the tower top, and the methylal, the unreacted methanol, the formaldehyde and the material C are washed and separated together; wastewater is discharged from the tower bottom.

Description

Technical Field

[0001] The present application relates to a process for preparing dimethoxymethane from aqueous methanol and formaldehyde solutions, belonging to the field of chemical engineering and chemistry. Background Art

[0002] Dimethoxymethane, also known as methylal, abbreviated as DMM, has the molecular formula CH 3 OCH 2 OCH 3 , is a colorless, non-toxic and environmentally friendly chemical raw material, usually prepared by the aldol condensation reaction of methanol and aqueous formaldehyde solution. The reaction formula is as follows. 2 CH 3 OH + CH 2 O ⇋ CH 3 OCH 2 OCH 3 + H 2 O (1)

[0003] Meanwhile, a certain amount of by-product polyoxymethylene dimethyl ethers, abbreviated as OMEn (n≥2) or OME 2+ , is also generated, where OME 2 can be used as a new type of environmentally friendly solvent. Its molecular formula is CH 3 O(CH 2 O) n CH 3 , and when n = 1, it is dimethoxymethane.

[0004] Due to the presence of a 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, this reaction is greatly restricted by the chemical equilibrium. At present, catalytic distillation technology is generally used in industrial production to break the limitation of the chemical equilibrium, but generally only an azeotrope of dimethoxymethane and methanol can be obtained, and further separation is required to obtain high-purity dimethoxymethane. Catalytic extractive distillation technology is also used, which combines the catalytic reaction and the extractive distillation process (adding a high-boiling third component, called an extractant or solvent, to the feed liquid to change the relative volatility between the original components and enable their separation), breaking the azeotrope formed by dimethoxymethane and methanol and directly producing high-purity dimethoxymethane, but the added extractant needs to be recovered and the energy consumption is relatively high.

[0005] Asahi Kasei Corporation of Japan disclosed a catalytic distillation method for producing dimethoxymethane from aqueous formaldehyde solution and methanol in Chinese Patent CN 1020450 C, which adopts the form of a secondary reactor arranged outside the catalytic distillation column and uses macroporous or gel-type cation exchange resin as the catalyst.

[0006] Chinese Patent CN 102351666 A discloses a catalytic distillation method for continuously producing high-concentration methylal from formaldehyde solution and methanol, which also adopts the form of a secondary reactor.

[0007] Chinese Patent Authorization Publication No. CN 100344596 C discloses a method for preparing high-purity methylal by combining continuous reactive distillation and liquid-liquid extraction. The mixture of methylal, methanol, and water obtained after reactive distillation is extracted in a liquid-liquid extraction column to obtain high-purity methylal. The extractant is glycerol or dimethanolamine, but a large amount of extractant needs to be separated, resulting in high energy consumption.

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

[0009] Chinese Patent CN 102351665 A discloses a process for continuously catalytic extractive distillation to prepare high-purity methylal. Using modified resin as the catalyst, the two processes of extractive distillation and catalytic distillation are coupled into one distillation column. Using water or formaldehyde aqueous solution as the extractant, after the raw materials fully react in the column, the azeotrope formed by methanol, methylal, and a small amount of water undergoes extractive distillation in the rectifying section, and high-purity methylal is obtained at the top of the column, and wastewater is withdrawn from the bottom of the column.

[0010] 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 liquid-liquid 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 extractive phase for reaction, effectively avoiding side reactions between the reaction products and water, and can effectively improve the conversion rate of raw materials and the selectivity and yield of products. However, formaldehyde cannot react completely, which still causes great difficulties in subsequent separation, including the separation of water in the reaction mixture and the recovery of formaldehyde, etc.

[0011] Chinese Patent CN 110372477 discloses a method for preparing methylal and polyoxymethylene dimethyl ethers. Adopting a multi-stage catalytic extraction process, introducing the raw material formaldehyde aqueous solution and methanol 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.

[0012] Chinese Patent CN 110372478 discloses a method for preparing methylal, which adopts a multi-stage catalytic extraction process. The raw material formaldehyde and methanol aqueous solution first enter a pre-reactor for reaction, and then are introduced into a catalytic extraction column or a multi-stage catalytic extraction reactor to contact the extractant countercurrently, and the catalytic reaction and extraction are carried out multiple times and alternately.

[0013] In the technical solutions disclosed in Chinese Patents CN 110372477 and CN 110372478, by adopting a multi-stage catalytic extraction process, the formaldehyde in the raffinate phase can be completely converted. However, limited by the chemical equilibrium, a large amount of methanol needs to be added, resulting in a large amount of methanol recovery and high energy consumption. Moreover, the extractant needs to be separated by distillation from the light and heavy reaction products and by-products, which also significantly increases the energy consumption. Summary of the Invention

[0014] The present application provides a process for preparing methylal from methanol and formaldehyde aqueous solution. This process combines a multi-stage catalytic extraction process and a catalytic distillation process. The extractant does not need to be completely separated from the reaction products and by-products, and has the advantages of low raw material cost, easy product separation, flexible product scheme, and the product methylal basically containing no methanol.

[0015] As an embodiment of the present application, the process for preparing methylal from methanol and formaldehyde aqueous solution includes the following steps:

[0016] 1. Mix the material A containing formaldehyde and the material B containing methanol and introduce them into a multi-stage catalytic extraction reaction system (CE system). First, enter the reaction zone of the first stage of the CE system to contact the catalyst for reaction, and then contact the extractant countercurrently, and carry out the catalytic reaction and extraction process multiple times and alternately to obtain the extraction phase material C and the raffinate phase (i.e., aqueous phase) material D.

[0017] 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 a catalytic reaction to occur, and does not directly contact the extraction phase.

[0018] 2. The main components of the extraction phase material C are the product methylal and the by-product OME 2+ and the 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. Introduce it into a water washing device for back-extraction with water to remove the formaldehyde and methanol therein.

[0019] The main components of the water washing liquid obtained by water washing are water, formaldehyde, methanol, and a small amount of methylal and OME 2+and the extractant are returned to the CE 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 for continuous reaction; preferably, the formaldehyde concentration in the washing liquid is close to the formaldehyde concentration of the aqueous phase material originally entering this stage.

[0020] 3. The extracted phase material C after washing enters the rectification separation system to separate out methylal, and other components are returned to the CE system for recycling with the extractant. Optionally, part or all of OME is further separated out 2 As a product, other components are returned to the CE system for recycling with the extractant. Compared with separating out high-purity extractant for recycling, a large amount of energy consumption can be saved.

[0021] 4. The aqueous phase material D mainly contains water, unreacted formaldehyde, methanol, and a small amount of OME and extractant, and is introduced into the catalytic distillation column. Most of the formaldehyde reacts with methanol in the catalytic distillation column to form methylal. Methylal, a small amount of unreacted methanol, formaldehyde, a small amount of water, extractant, etc. are taken out from the top of the column to obtain material E, and wastewater is discharged from the bottom of the column.

[0022] A solid acid catalyst is also installed in the catalytic distillation column.

[0023] The main components of material E are the product methylal and a small amount of formaldehyde, methanol, water, and extractant, and are introduced into the washing device together with material C.

[0024] Recover a small amount of OME carried by the extractant 2+ or OME 3+ A part of it will enter material D, react with methanol in the catalytic distillation column and be converted into methylal and taken out from the top of the catalytic distillation column; the rest enters the reaction zone of the CE system for reaction and is finally converted into methylal.

[0025] Since the methanol in the extracted phase can be completely removed by washing, the methylal obtained by the technical solution of this application is basically methanol-free, avoiding the disadvantage that the general catalytic distillation process can only obtain an azeotrope of methylal and methanol.

[0026] The extracted phase material C after washing contains a small amount of water, which is taken out in the form of an azeotrope with methylal during rectification separation, that is, the methylal obtained by the technical solution of this application contains a certain amount of water, and the water content does not exceed the azeotropic composition of methylal and water (methylal 98.6 wt%, water 1.4 wt%); when there is more water, the excess water is taken out with OME 2 or the extractant.

[0027] The multi-stage catalytic extraction reaction system described above can be divided into two forms.

[0028] A form of multiple series-connected extraction devices, where a solid acid catalyst is loaded in the aqueous phase feed channels of each or some of the extraction devices. The aqueous phase reaction material first flows through the solid acid catalyst loaded in the first extraction device and then enters the extraction component 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 equipped with a solid acid catalyst, or flows through one or more extraction devices without a loaded catalyst to achieve the required extraction effect and then enters the next extraction device equipped with a solid acid catalyst; in this way, the reaction and extraction are carried out multiple times and alternately until the raffinate phase flowing out of the last extraction device of the last stage flows out of the CE system. Each extraction device equipped with a solid acid catalyst and the extraction device without a loaded catalyst downstream of it form a stage of catalytic extraction unit of the multi-stage catalytic extraction system. The extractant enters from the last stage of the CE system and flows countercurrently to the aqueous phase, and finally discharges as the extraction phase from the first-stage unit without contacting the catalyst.

[0029] Or multiple catalyst beds and multiple groups of extraction components are alternately arranged in one extraction device. In this case, one extraction device contains a multi-stage catalytic extraction unit, and one or more such extraction devices form a multi-stage catalytic extraction reaction system. For example, a sieve plate extraction tower is used as the extraction device, and catalyst beds and extraction trays are alternately arranged in the tower. The catalyst beds are arranged in the aqueous phase channels of the catalytic extraction tower, and the aqueous phase reaction material is first introduced into the first catalyst bed. Among them, the first catalyst bed can be arranged in a reactor outside the catalytic extraction tower, and the aqueous phase reaction material first flows through this reactor and then enters the catalytic extraction tower.

[0030] Another form is that multiple independent reactors and extraction devices are connected in series, where a solid acid catalyst is loaded in the reactor. The reactor can be in the form of a fixed bed reactor or a fluidized bed reactor, etc. The aqueous phase material first enters the first reactor and then enters one or more series-connected extraction devices, which is the first-stage catalytic extraction unit of the CE system. The multi-stage catalytic extraction units are connected in series to form the CE system. The aqueous phase flows out as the raffinate phase from the last extraction device of the last stage, and the extractant enters from this extraction device and flows countercurrently to the aqueous phase, and finally discharges as the extraction 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.

[0031] In this application, the order 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 material. The reaction zone of the multi-stage catalytic extraction reaction system refers to the aqueous phase feed channel of the extraction device loaded with a solid acid catalyst or an independent reactor loaded with a solid acid catalyst.

[0032] The extraction devices mentioned above refer to various conventional devices used in the extraction process, including various mixer-settlers, centrifugal extractors, and extraction towers of various structural forms.

[0033] In an aqueous solution, methanol and formaldehyde can undergo a condensation reaction under the action of an acid catalyst to produce methylal and polyoxymethylene dimethyl ethers with different degrees of polymerization. This reaction is a reversible reaction, and the conversion rate is greatly restricted by 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 rates 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 smaller the molar ratio of formaldehyde group to methyl group (FA / Me), the lower the average degree of polymerization n of the produced OMEn product, and the higher the proportion of methylal in the reaction products.

[0034] 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 reaction products such as methylal are enriched in the extract phase. Only the aqueous-phase materials can come into contact with the catalyst to carry out the catalytic reaction; while the extract phase does not come into contact with the catalyst, and methylal and the like therein will not undergo reverse reactions such as hydrolysis. In this way, although the reaction in the aqueous phase is still restricted by chemical equilibrium, no catalytic reaction occurs in the extract phase, and the content of products such as methylal is not restricted by chemical equilibrium. Therefore, the conversion rates of methanol and formaldehyde can greatly exceed the equilibrium conversion rate.

[0035] In the CE system, the aqueous-phase materials and the extract-phase materials 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 materials, the water concentration is low, while the concentrations of the reactants formaldehyde and methanol are high, and the restriction of chemical equilibrium is small. Therefore, under the action of the catalyst, the concentration of products such as methylal in the aqueous phase is high; while the extract phase carrying methylal and other products (with a lower concentration) extracted from the downstream aqueous phase comes into contact with it for further extraction, and methylal and the like will reach a higher concentration. Near the outlet of the aqueous-phase materials, the water concentration in the aqueous phase is high, while the concentrations of formaldehyde and methanol are low, and the restriction of chemical equilibrium is large. After the reaction under the action of the catalyst, the concentration of products such as methylal in the aqueous phase is low. It comes into contact with fresh extractant to extract most of the reaction products such as methylal therein, and the remaining small amounts of unreacted formaldehyde, methanol, water, etc. are discharged from the CE system together; the extract phase flows in the opposite direction to the aqueous phase, and the concentration of reaction products such as methylal therein gradually increases and is finally discharged from the CE system.

[0036] The material A containing formaldehyde can use commercially available industrial formaldehyde with a concentration of 37, 44, 50 wt% levels, or a dilute formaldehyde solution with a lower concentration. The material B containing methanol can use commercially available industrial methanol.

[0037] After the material A and the material B are mixed, they enter the multi-stage catalytic extraction reaction system from the reaction zone of the first stage, and their FA / Me ratio (molar ratio of formaldehyde to methanol) is 0.3 – 0.8.

[0038] The basic requirement for selecting the extractant is that the distribution ratio of methylal (the ratio of the weight percentage concentration of methylal in the extract phase to the weight percentage concentration of methylal in the aqueous phase) is greater than the distribution ratios of methanol and formaldehyde (the ratios of the weight percentage concentrations of methanol and formaldehyde in the extract phase to the weight percentage concentrations of methanol and formaldehyde 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 methylal, the better its enrichment effect in the extract phase, the less the amount of extractant used, the lower the energy consumption required for distillation separation, and the lower the production cost. The smaller the distribution ratios of methanol and formaldehyde, the lower the concentrations of methanol and formaldehyde in the extract phase, and the easier the water washing and recovery.

[0039] The extractant described in this application is at least one of halogenated hydrocarbons, aromatic hydrocarbons, alkanes, and cycloalkanes. Preferably, the halogenated hydrocarbon is selected from at least one of 1,2-dichloroethane, 1,2-dichloropropane, chlorobenzene, and bromobenzene; the aromatic hydrocarbon is selected from at least one of benzene, toluene, ethylbenzene, xylene, ethylbenzene, n-propylbenzene, isopropylbenzene, methyl ethylbenzene, and butylbenzene; the alkane is selected from at least one of normal or isomeric alkanes with 6 to 10 carbon atoms; the cycloalkane is selected from at least one of cyclohexane, methylcyclopentane, methylcyclohexane, and ethylcyclohexane.

[0040] In this application, the weight ratio of the feed amount of the extractant entering the CE system to the total feed amount of the methanol and formaldehyde aqueous solution and the water washing solution (Material A + Material B + water washing solution) is 0.1 - 2:1. The larger the feed amount of the extractant, the higher the conversion rate of raw material formaldehyde and methanol in the CE system, and the fewer the number of stages required for the CE system, but the energy consumption for recovering the extractant increases.

[0041] Since the condensation reaction of methanol and formaldehyde in the aqueous solution to generate OME and water under the action of an acid catalyst is restricted by the chemical equilibrium, and the higher the water content in the reaction system, the greater the restriction of the chemical equilibrium. Downstream of the CE system, as the reaction proceeds, the water content in the aqueous phase becomes larger and larger. To make formaldehyde react completely, a large amount and an excessive amount of methanol need to be added to promote the forward movement of the reaction equilibrium and promote the conversion of formaldehyde. Not only are too many stages of the CE system required, but also a relatively high energy consumption is needed for the distillation recovery of a large amount of unreacted methanol.

[0042] 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 CE system into the catalytic distillation column.

[0043] The catalytic distillation column body is divided into a rectifying section, a reaction section, and a stripping section from top to bottom. A condenser is provided at the top of the column, and a reboiler is provided at the bottom of the column. The reaction section can alternately be provided with catalyst beds and distillation trays or packings, or a wire mesh packing filled with a catalyst can be used, or multiple reactors can be provided outside the column, and the liquid phase materials are respectively led out from different positions in the reaction section of the column, fully reacted through the reactors, and then returned to the column. Other catalyst loading structures can also be used.

[0044] The aqueous-phase material D is fed above 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. Methylal, together with a small amount of unreacted methanol, formaldehyde, 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 in material D 2+ reacts with methanol in the reaction section to be converted into methylal. The extractant forms a low-boiling azeotrope with methanol or water and is also taken out from the top of the tower with material E.

[0045] At normal pressure, the boiling point of methylal is 42.3 °C, and its azeotropic boiling point with methanol and water is 41.8 °C. The azeotropic composition is 92% methylal, 7.5% methanol, and 0.5% water. Its boiling point or azeotropic boiling 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 smaller 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 the energy consumption of recovering the same amount of methanol, and is also lower than the energy consumption of the catalytic distillation column for producing 86-92% methylal (treating the same amount of formaldehyde and methanol).

[0046] In the reaction section, the condensation reaction of formaldehyde and methanol will generate a small amount of OME with a higher boiling point 2 、OME 3 , and they all form low-boiling azeotropes with water. The azeotropic boiling points are between those of methanol and water. Under the rectification action of the catalytic distillation column, OME 2 、OME 3 is enriched in the reaction section in the middle of the tower and reacts with methanol to be converted into methylal, and will not be taken out from the bottom of the tower. A very small amount may be taken out from the top of the tower with methylal and will eventually be taken out as products, by-products or enter the CE system to participate in the reaction.

[0047] Optionally, a certain amount of methanol can be fed between the reaction section and the stripping section of the catalytic distillation column to promote the conversion of formaldehyde, reduce the formaldehyde content in the wastewater at the bottom of the tower, reduce the reflux ratio, further reduce the energy consumption, and at the same time promote the reaction of OME 2 、OME 3 to be converted into methylal.

[0048] The reaction zones of the aforementioned multi-stage catalytic extraction reaction system and the reaction sections of the catalytic distillation column are both filled with solid acid catalysts, and they can be the same or different. Optionally, the solid acid catalyst is selected from strongly acidic cation exchange resins.

[0049] 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).

[0050] The present application also provides another embodiment, which is different from the first embodiment described above in that: The extractant not only feeds from the last stage of the CE system, but also part of the extractant can be fed from one or several intermediate stages. The extraction phase materials originally entering this stage or these stages are then withdrawn from the CE system.

[0051] This embodiment can improve the extraction and reaction efficiency, but the amount of extractant used is relatively large.

[0052] The following is a specific implementation of the technical solution of the present invention.

[0053] The process for producing DMM using 37 wt% aqueous formaldehyde solution and methanol as reaction raw materials and toluene as the extractant is as shown in the appendix Figure 1 as follows.

[0054] The raw material methanol (MEOH) and 37% aqueous formaldehyde solution (37FA) are mixed, and the fresh extractant toluene (TO) is mixed with the recycled toluene (TO + OME2+). The two respectively enter the multi-stage catalytic extraction reaction system (CE) and flow countercurrently.

[0055] The raffinate phase (H2O + MEOH + FA) withdrawn from the multi-stage catalytic extraction reaction system enters the catalytic distillation column (CD column). The extraction phase is 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 toluene), and then fed into the bottom of the water scrubber (SCRUBBER column). After being back-extracted with water (H2O) fed from the top of the column to remove formaldehyde and methanol, it is withdrawn from the top of the column and enters the DMM distillation column (DMM column). The water scrubbing liquid mainly containing formaldehyde and methanol withdrawn from the bottom of the back-extraction column is returned to the multi-stage catalytic extraction reaction system for continuous reaction. Waste water (W - H2O) is discharged from the bottom of the catalytic distillation column.

[0056] The product DMM is obtained at the top of the DMM distillation column, and the toluene (TO + OME2+) recycled from the bottom of the column is recycled for use, which contains a certain amount of OME 2+ .

[0057] The beneficial effects that can be produced by the technical solution of the present application include: Using low-cost methanol and aqueous formaldehyde solution as raw materials, producing methylal substantially free of methanol at a low cost, and OME can also be produced simultaneously 2 . Description of the Drawings

[0058] Appendix Figure 1 It is a simplified process flow diagram for producing DMM using toluene as an extractant. Specific embodiments

[0059] The present application will be described in detail below in conjunction with embodiments, but the present application is not limited to these embodiments.

[0060] The methanol and aqueous formaldehyde solution used in the examples and comparative examples of the present application are all commercially available industrial products, and various extractants are all analytical pure reagents.

[0061] The strongly acidic cation resin catalysts used in the examples and comparative examples of the present application include DMM and DMMn resin catalysts, which are all provided by Kerry Environmental Protection Technology Co., Ltd.

[0062] Example 1 A 5-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 mesh rings; 5 stages are connected in series to form a catalytic extraction reaction system.

[0063] 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 50 °C, the operating temperature of the extraction column is room temperature (25 - 27 °C), and the system operating pressure is 0.25 MPa.

[0064] An industrial formaldehyde aqueous solution with a formaldehyde content of 50 wt% is mixed with methanol and then enters the reactor of the first stage. The feed rates are 2.0 ml / min and 1.9 ml / min respectively, and then enters the extraction column of the first stage, and then sequentially enters the reactors and extraction columns of the subsequent stages, and is taken out as the raffinate phase from the extraction column of the last stage. Mixed xylene is used as the extractant, which contains 2.6 wt% OME 3+ 3+ , with a feed rate of 5.9 ml / min, enters from the extraction column of the last stage, and then sequentially enters the extraction columns of the previous stages, and finally is taken out as the extraction phase from the extraction column of the first stage.

[0065] The extraction phase discharge rate is 7.2 g / min, including 1.8 wt% formaldehyde, 0.5 wt% methanol, 1 wt% water, 15.8 wt% DMM, OME 2 2 3.2 wt%, OME 3+ 3+ 2 wt%, and the rest is mixed xylene.

[0066] The raffinate phase discharge rate is 1.6 g / min, including 3.9 wt% methanol, 1.9 wt% formaldehyde, 0.16 wt% mixed xylene, 0.6 wt% DMM, OME 2 20.06 wt%, OME 3+ 1.2 wt%, with the balance being water.

[0067] Example 2 The same catalytic extraction reaction system and operation mode as in Example 1 were adopted, except that the catalytic extraction reaction system was 3-stage, each extraction column used the raffinate phase (aqueous phase) as the continuous phase and the extract phase as the dispersed phase. Each reactor was filled with 18 ml of DMM resin catalyst, the reaction temperature was 120 °C, and the system operating pressure was 0.6 MPa.

[0068] A 10 wt% aqueous formaldehyde solution (diluted from a 37 wt% industrial formaldehyde aqueous solution) was mixed with methanol and then entered the reactor of the first stage, with the feed rates being 6.0 ml / min and 1.7 ml / min respectively. Toluene was used as the extractant, which contained 6 wt% OME 2+ , and the feed rate was 1.65 ml / min.

[0069] The extract phase discharge rate was 2.8 g / min, in which formaldehyde was 0.6 wt%, methanol was 2 wt%, water was 1 wt%, DMM was 45.5 wt%, OME 2+ 3 wt%, and the rest was toluene.

[0070] The raffinate phase discharge rate was 6 g / min, in which methanol was 1.8 wt%, formaldehyde was 1.1 wt%, toluene was 0.19 wt%, DMM was 0.46 wt%, OME 2+ 1.2 wt%, and the rest was water.

[0071] Example 3 The same catalytic extraction reaction system and operation mode as in Example 1 were adopted, except that the catalytic extraction reaction system was 4-stage, the reactor height was 40 cm and it was filled with 60 ml of DMMn resin catalyst. Each extraction column used the raffinate phase (aqueous phase) as the continuous phase and the extract phase as the dispersed phase. The reaction temperature of each reactor was 45 °C, the operation temperature of each extraction column was room temperature (26 - 29 °C), and the system operating pressure was 0.2 MPa.

[0072] A 37 wt% aqueous formaldehyde solution was mixed with methanol and then entered the reactor of the first stage, with the feed rates being 2.4 ml / min and 2.7 ml / min respectively; benzene was used as the extractant, which contained 10.1 wt% OME 2+ , and the feed rate was 2.2 ml / min.

[0073] The extract phase discharge rate was 4.2 g / min, in which formaldehyde was 0.15 wt%, methanol was 1 wt%, water was 0.6 wt%, DMM was 53.2 wt%, OME 2+ 4.6 wt%, and the rest was benzene.

[0074] The raffinate phase discharge rate is 2.7 g / min, containing 4.5 wt% methanol, 2.1 wt% formaldehyde, 0.14 wt% benzene, 0.62 wt% DMM, 2+ 2.2 wt% OME, and the rest is water.

[0075] 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 4 stages, the height of each extraction column is 70 cm, filled with 42 cm high Φ2.5×2.5 mm stainless steel θ wire rings. 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 90 °C, and the system operating pressure is 0.6 MPa.

[0076] The 20 wt% formaldehyde aqueous solution (diluted from 37% industrial formaldehyde aqueous solution) is mixed with methanol and then enters the reactor of the first stage. The feed rates are 4.3 ml / min and 2.2 ml / min respectively. Isopropylbenzene is used as the extractant, containing 17.8 wt% OME 2+ , and the feed rate is 0.75 ml / min.

[0077] The extraction phase discharge rate is 2.6 g / min, containing 0.32 wt% formaldehyde, 1 wt% methanol, 0.45 wt% water, 66.8 wt% DMM, 2+ 5.6 wt% OME, and the rest is isopropylbenzene.

[0078] The raffinate phase discharge rate is 4.2 g / min, containing 3.2 wt% methanol, 1.3 wt% formaldehyde, 0.2 wt% isopropylbenzene, 0.36 wt% DMM, 2+ 2 wt% OME, and the rest is water.

[0079] 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, filled with 60 ml of DMMn resin catalyst, the height of each extraction column is 70 cm, filled with 42 cm high Φ2.5×2.5 mm stainless steel θ wire rings. The reaction temperature of each reactor is 40 °C, and the system operating pressure is 0.05 MPa.

[0080] The feed rate of 37 wt% formaldehyde aqueous solution is 2.6 ml / min, and the feed rate of methanol is 2.3 ml / min. After mixing, they enter the reactor of the first stage; an aromatic hydrocarbon mixture (n-propylbenzene, ethylmethylbenzene, butylbenzene account for 40 wt%, 30 wt%, 30 wt% respectively) is used as the extractant, containing 2 wt% OME 3+ , and the feed rate is 5.2 ml / min.

[0081] The extraction phase discharge rate is 8.1 g / min, containing 1 wt% formaldehyde, 2.2 wt% methanol, 0.5 wt% water, 18.2 wt% DMM, 3.9 wt% OME, 1.5 wt% OME, and the rest is an aromatic hydrocarbon mixture. 2 3.9 wt%, OME 3+ 1.5 wt%, and the rest is an aromatic hydrocarbon mixture.

[0082] The raffinate phase discharge rate is 2.3 g / min, containing 4.1 wt% methanol, 1.5 wt% formaldehyde, 0.8 wt% aromatic hydrocarbon mixture, 0.32 wt% DMM, 0.05 wt% OME, 1.2 wt% OME, and the rest is water. 2 0.05 wt%, OME 3+ 1.2 wt%, and the rest is water.

[0083] 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 6 stages, each extraction column is 130 cm high and filled with Φ2.5×2.5 mm stainless steel θ wire rings with a height of 104 cm. Each extraction column uses the raffinate phase (aqueous phase) as the continuous phase and the extraction phase as the dispersed phase. The reaction temperature is 60 °C, and the system operating pressure is 0.3 MPa.

[0084] A 10 wt% aqueous formaldehyde solution and methanol are mixed and fed, with feed rates of 3.5 ml / min and 1.0 ml / min respectively; 1,2-dichloroethane is used as the extractant, containing 6.9 wt% OME 2+ , and the feed rate is 0.78 ml / min.

[0085] The extraction phase discharge rate is 1.64 g / min, containing 0.4 wt% formaldehyde, 2.2 wt% methanol, 1.0 wt% water, 44.6 wt% DMM, 3.7 wt% OME, and the rest is 1,2-dichloroethane. 2+ 3.7 wt%, and the rest is 1,2-dichloroethane.

[0086] The raffinate phase discharge rate is 3.8 g / min, containing 3.2 wt% methanol, 1.3 wt% formaldehyde, 2.1 wt% 1,2-dichloroethane, 0.26 wt% DMM, 1.0 wt% OME, and the rest is water. 2+ 1.0 wt%, and the rest is water.

[0087] 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 4 stages, each extraction column is 130 cm high and filled with Φ2.5×2.5 mm stainless steel θ wire rings with a height of 104 cm. Each extraction column uses the raffinate phase (aqueous phase) as the continuous phase and the extraction phase as the dispersed phase. The operating temperature of the extraction column is room temperature (28 - 30 °C), and the system operating pressure is 0.2 MPa.

[0088] A 37 wt% aqueous formaldehyde solution is mixed with methanol and then fed into the reactor of the first stage, with the feed rates being 2.1 ml / min and 2.3 ml / min respectively; 1,2-dichloropropane is used as the extractant, which contains 16.5 wt% OME 2+ , and the feed rate is 1.1 ml / min.

[0089] The extraction phase discharge rate is 3.3 g / min, in which formaldehyde is 1.8 wt%, methanol is 3 wt%, water is 1 wt%, DMM is 57.8 wt%, OME 2+ is 6 wt%, and the rest is 1,2-dichloropropane.

[0090] The raffinate phase discharge rate is 2.3 g / min, in which methanol is 3.7 wt%, formaldehyde is 1.5 wt%, 1,2-dichloropropane is 0.57 wt%, DMM is 0.32 wt%, OME 2+ is 3.7 wt%, and the rest is water.

[0091] Example 8 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 4 stages, the height of each extraction column is 130 cm, and it is filled with Φ2.5×2.5 mm stainless steel θ mesh rings with a height of 104 cm. Each extraction column uses the raffinate phase (aqueous phase) as the continuous phase and the extraction phase as the dispersed phase. The operating temperature of each extraction column is room temperature (28 - 30 °C), and the system operating pressure is 0.2 MPa.

[0092] A 37 wt% aqueous formaldehyde solution is mixed with methanol and then fed into the reactor of the first stage, with the feed rates being 2.2 ml / min and 2.4 ml / min respectively; a mixture of chlorobenzene and bromobenzene (weight ratio 2:1) is used as the extractant, which contains 18 wt% OME 2+ , and the feed rate is 1.2 ml / min.

[0093] The extraction phase discharge rate is 3.5 g / min, in which formaldehyde is 1.6 wt%, methanol is 3.2 wt%, water is 1.2 wt%, DMM is 59.2 wt%, OME 2+ is 6.2 wt%, and the rest is chlorobenzene and bromobenzene.

[0094] The raffinate phase discharge rate is 2.4 g / min, in which methanol is 3.5 wt%, formaldehyde is 1.4 wt%, chlorobenzene and bromobenzene is 0.62 wt%, DMM is 0.5 wt%, OME 2+ is 3.5 wt%, and the rest is water.

[0095] Example 9 The same catalytic extraction reaction system and operation mode as in Example 1 are adopted, except that the catalytic extraction reaction system has 4 stages. In each extraction column, the raffinate phase (aqueous phase) is the continuous phase and the extract phase is the dispersed phase. Each reactor is filled with DMM resin catalyst, the reaction temperature is 80 °C, the operation temperature of each extraction column is room temperature (28 - 30 °C), and the system operation pressure is 0.2 MPa.

[0096] A 37 wt% aqueous formaldehyde solution is mixed with methanol and then enters the reactor of the first stage, with the feed rates being 3.3 ml / min and 3.6 ml / min respectively. The extractant is a mixture containing 25 wt% each of cyclohexane, methylcyclopentane, methylcyclohexane, and ethylcyclohexane, and it contains 10.1 wt% OME 2+ , with a feed rate of 3.7 ml / min.

[0097] The extract phase discharge rate is 6.4 g / min, among which formaldehyde is 0.6 wt%, methanol is 1.3 wt%, water is 0.8 wt%, DMM is 48.8 wt%, OME 2+ is 4.9 wt%, and the rest is a mixture of naphthenes.

[0098] The raffinate phase discharge rate is 3.5 g / min, among which methanol is 3.7 wt%, formaldehyde is 1.7 wt%, the mixture of naphthenes is 0.14 wt%, DMM is 0.28 wt%, OME 2+ is 3.1 wt%, and the rest is water.

[0099] Example 10 The same catalytic extraction reaction system and operation mode as in Example 1 are adopted, except that the operation temperature of each extraction column is room temperature (32 - 35 °C), and the system operation pressure is 0.2 MPa.

[0100] A 37 wt% aqueous formaldehyde solution is mixed with methanol and then enters the reactor of the first stage, with the feed rates being 1.0 ml / min and 1.1 ml / min respectively. The extractant is n - heptane, which contains 2 wt% OME 2+ , with a feed rate of 4.6 ml / min.

[0101] The extract phase discharge rate is 5 g / min, among which formaldehyde is 0.36 wt%, methanol is 0.8 wt%, water is 0.1 wt%, DMM is 19.6 wt%, OME 2+ is 1.6 wt%, and the rest is n - heptane.

[0102] The raffinate phase discharge rate is 1.1 g / min, among which methanol is 3.9 wt%, formaldehyde is 1.8 wt%, n - heptane is 0.12 wt%, DMM is 0.37 wt%, OME 2+ is 0.88 wt%, and the rest is water.

[0103] Example 11 The same catalytic extraction reaction system and operation mode as in Example 1 are adopted, except that the catalytic extraction reaction system has 6 stages, the operation temperature of the extraction column is room temperature (32 - 35°C), and the system operation pressure is 0.2 MPa.

[0104] The aqueous formaldehyde solution with a concentration of 37 wt% is mixed with methanol and then enters the reactor of the first stage, and the feed rates are 1.9 ml / min and 2.1 ml / min respectively; the washing liquid of the extraction phase (the composition is 6.6 wt% methanol, 3 wt% formaldehyde, 0.27 wt% alkane mixture, 10.2 wt% DMM, 2+ 0.42 wt% OME, 79.6 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 0.55 ml / min; the extractant is an alkane mixture (20 wt% each of n - hexane, n - heptane, iso - heptane, n - octane and iso - octane), which contains 4.7 wt% OME 2+ , and the feed rate is 3.8 ml / min.

[0105] The discharge rate of the extraction phase is 4.6 g / min, in which formaldehyde is 0.36 wt%, methanol is 0.8 wt%, water is 0.2 wt%, DMM is 41.6 wt%, OME 2+ is 2.7 wt%, and the rest is alkane mixture.

[0106] The discharge rate of the raffinate phase is 2.6 g / min, in which methanol is 2.3 wt%, formaldehyde is 1 wt%, alkane mixture is 0.1 wt%, DMM is 0.27 wt%, OME 2+ is 1.2 wt%, and the rest is water.

[0107] Example 12 The stripping column uses a glass tube with an inner diameter of 14 mm and a height of 100 cm, which is filled with Φ2.5×2.5 mm stainless steel θ - shaped wire rings with a height of 73 cm.

[0108] The extraction phase material (the composition is 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) is fed from the bottom of the stripping column, and the feed rate is 5 ml / min; water is used as the stripping agent and is fed from the top of the stripping column, and the feed rate is 0.44 ml / min. The extraction phase material is the continuous phase, and the aqueous phase is the dispersed phase. The stripping temperature is room temperature 30 - 32°C, and the operation pressure is 0.1 MPa.

[0109] The extraction phase discharge amount after water washing at the top of the stripping column is 4.2 g / min, including 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% OME, and 25.2 wt% toluene.

[0110] The aqueous phase discharge amount at the bottom of the stripping column is 0.66 g / min, including 1.9 wt% formaldehyde, 7.4 wt% methanol, 22.4 wt% DMM, 2 1.8 wt% OME, 3+ 0.21 wt% OME, 0.1 wt% toluene, and 66.2 wt% water.

[0111] Example 13 The same stripping experiment device as in Example 12 is used. The difference is that the height of the glass tube of the stripping column is 150 cm, and the packing height of the θ wire rings is 122 cm.

[0112] The extraction phase material (composed of 2 wt% formaldehyde, 2.8 wt% methanol, 1 wt% water, 57.2 wt% DMM, 2+ 5.6 wt%, and the rest is ethylbenzene) is fed from the bottom of the stripping column at a feed rate of 4.2 ml / min; water is used as the stripping agent and fed from the top of the stripping column at a feed rate of 1.1 ml / min; the stripping temperature is 28 °C, and the operating pressure is atmospheric pressure.

[0113] The extraction phase discharge amount after water washing at the top of the stripping column is 3.4 g / min, including 0.005 wt% formaldehyde, 0.004 wt% methanol, 0.21 wt% water, 59.3 wt% DMM, 2+ 5.9 wt% OME, and 34.6 wt% ethylbenzene.

[0114] The aqueous phase discharge amount at the bottom of the stripping column is 1.5 g / min, including 7.1 wt% methanol, 5.1 wt% formaldehyde, 8.7 wt% DMM, 2+ 0.71 wt% OME, 0.12 wt% ethylbenzene, and 78.3 wt% water.

[0115] Example 14 The distillation column for separating DMM 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 packed with Φ2.5×2.5 mm stainless steel θ wire rings with heights of 100 cm and 60 cm. The top of the column is cooled with circulating water at 20 °C.

[0116] The extraction phase after water washing in Example 13 (with a composition of 0.005 wt% formaldehyde, 0.004 wt% methanol, 0.21 wt% water, 59.3 wt% DMM, 2+ 5.9 wt% OME, and 34.6 wt% ethylbenzene) 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, an operating pressure of the rectifying column being atmospheric pressure (top pressure), and a reflux ratio of 2.

[0117] The overhead product flow rate is 1.93 g / min, which contains 0.008 wt% formaldehyde, 0.007 wt% methanol, 0.35 wt% water, 99.5 wt% DMM, 2+ 0.08 wt% OME, and 0.06 wt% ethylbenzene; the bottom product flow rate is 1.31 g / min, which contains 0.06 wt% DMM, 2+ 14.5 wt% OME, and 85.4 wt% ethylbenzene.

[0118] Example 15 The same rectifying column as in Example 14 is used to separate OME 2 .

[0119] The bottom product from Example 14 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, an operating pressure of the rectifying column being atmospheric pressure (top pressure), a reflux ratio of 3.5, and an effective heating power of the reboiler being 24 W.

[0120] The overhead product flow rate is 0.38 g / min, which contains 0.16 wt% DMM, 2 99.7 wt% OME, and 0.1 wt% ethylbenzene; the bottom product flow rate is 2.86 g / min, which contains 2 0.35 wt% OME, 3+ 2.7 wt% OME, and 96.9 wt% ethylbenzene.

[0121] Example 16 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, which is filled with catalyst packages and Φ2.5×2.5 mm stainless steel θ-rings in a mixed manner; the catalyst package has a diameter of ~20 mm and a height of 40 mm, is 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.

[0122] The raffinate phase (aqueous phase) material (with a composition of 2 wt% methanol, 1 wt% formaldehyde, 0.1 wt% toluene, 0.8 wt% DMM, OME2+ 1.2 wt%, with the rest being water) is fed from the top of the reaction section at a feed rate of 3.6 ml / min and a feed temperature of 40°C. Methanol is fed between the reaction section and the stripping section at a feed rate of 0.025 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 3.5.

[0123] The overhead product flow rate is 0.2 g / min, containing 82.7 wt% DMM, 11.4 wt% methanol, 3.5 wt% formaldehyde, 1.8 wt% toluene, and 0.7 wt% water. The bottom product flow rate is 3.44 g / min, containing 0.005 wt% methanol, 0.004 wt% formaldehyde, and 99.99 wt% water.

[0124] Example 17 The same catalytic distillation column as in Example 16 is used.

[0125] The raffinate phase (aqueous phase) material (composed of 4.5 wt% methanol, 1.5 wt% formaldehyde, 0.5 wt% benzene, 0.6 wt% DMM, OME 2+ 1 wt%, with the rest being water) is fed from the top of the reaction section at a feed rate of 3.6 ml / min and a feed temperature of 40°C. The operating pressure of the catalytic distillation column is atmospheric pressure (top pressure), the reflux ratio is 3, and the effective heating power at the bottom of the column is 26 W.

[0126] The overhead product flow rate is 0.26 g / min, containing 78 wt% DMM, 12.6 wt% methanol, 1.6 wt% formaldehyde, 7 wt% benzene, and 0.8 wt% water. The bottom product flow rate is 3.34 g / min, containing 0.008 wt% methanol, 0.004 wt% formaldehyde, and 99.99 wt% water.

[0127] Example 18 The same catalytic distillation column as in Example 16 is used.

[0128] The raffinate phase (aqueous phase) material (composed of 4.2 wt% methanol, 1.8 wt% formaldehyde, 0.12 wt% mixed xylene, 0.6 wt% DMM, OME 2 0.1 wt%, OME 3+ 1.2 wt%, with the rest being 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. Methanol is fed between the reaction section and the stripping section at a feed rate of 0.08 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 3.5.

[0129] The overhead product flow rate is 0.32 g / min, among which DMM is 73.5 wt%, methanol is 20.4 wt%, formaldehyde is 4.3 wt%, mixed xylene is 1.2 wt%, and water is 0.6 wt%. The bottom product flow rate is 2.95 g / min, among which methanol is 0.008 wt%, formaldehyde is 0.003 wt%, and water is 99.99 wt%.

[0130] Comparative Example 1 The same catalytic extraction reaction system and operation mode as in Example 1 are adopted, except that the catalytic extraction reaction system has 10 stages.

[0131] An industrial formaldehyde aqueous solution with a formaldehyde content of 50 wt% is mixed with methanol and then enters the reactor of the first stage, and the feed rates are 2.0 ml / min and 2.2 ml / min respectively. Mixed xylene is used as the extractant, which contains 2.6 wt% of OME 3+ , and the feed rate is 5.9 ml / min.

[0132] The extract phase discharge rate is 7.3 g / min, among which formaldehyde is 1.6 wt%, methanol is 0.5 wt%, water is 0.9 wt%, DMM is 16 wt%, OME 2 3.3 wt%, OME 3+ 2 wt%, and the rest is mixed xylene.

[0133] The raffinate phase discharge rate is 1.8 g / min, among which methanol is 13.2 wt%, formaldehyde is 0.008 wt%, mixed xylene is 0.18 wt%, OME 3+ 1.3 wt%, and the rest is water.

[0134] Comparing Comparative Example 1 with Example 1 shows that under the same other conditions, it is necessary to increase the number of stages of the catalytic extraction reaction system and the methanol feed rate to basically completely convert the formaldehyde in the raffinate phase, but the amount of methanol to be recovered in the raffinate phase increases.

[0135] Comparative Example 2 The same catalytic distillation column and operation conditions as in Example 17 are adopted, including the feed raffinate phase (aqueous phase) material composition, feed temperature, feed position, etc. The difference is that the feed rate of the raffinate phase (aqueous phase) is 1.2, the reflux ratio is 20, and the effective heating power of the bottom of the column is 48 w.

[0136] The overhead product flow rate is 0.09 g / min, among which DMM is 82.9 wt%, methanol is 9.3 wt%, formaldehyde is 0.004 wt%, benzene is 7.1 wt%, and water is 0.7 wt%. The bottom product flow rate is 1.12 g / min, among which methanol is 0.008 wt%, formaldehyde is 0.004 wt%, and water is 99.99 wt%.

[0137] Comparing Comparative Example 2 with Example 17 shows that when recovering high-value components from the same raffinate phase material and discharging wastewater, with the same throughput and basically the same other conditions, when the overhead product in Example 17 contains a certain amount of formaldehyde, the required reflux ratio is greatly reduced and the energy consumption is greatly reduced.

[0138] Comparative Example 3 The same catalytic distillation column and operating conditions as in Example 17 are adopted, including the feed rate, feed temperature and feed location of the raffinate phase (aqueous phase), etc. The difference is that the composition of the raffinate phase (aqueous phase) material is 4.5 wt% methanol, 1.5 wt% formaldehyde, 0.5 wt% benzene, 0.6 wt% DMM, and the rest is water, and basically no OME is contained. 2+ 。

[0139] Under the conditions of a reflux ratio of 3 and an effective heating power at the bottom of the column of 24 w, the overhead product flow rate is 0.23 g / min, among which DMM is 67.3 wt%, methanol is 22.3 wt%, formaldehyde is 1 wt%, benzene is 8 wt%, and water is 0.7 wt%. The bottom product flow rate is 3.4 g / min, among which methanol is 0.008 wt%, formaldehyde is 0.004 wt%, and water is 99.99 wt%.

[0140] Comparing Comparative Example 3 with Example 17 shows that when the extractant in the extract phase is separated by distillation from OME 2 、OME 3+ and recycled, the obtained raffinate phase material basically does not contain OME 2+ (Comparative Example 3). When recovering high-value components and discharging wastewater in the catalytic distillation column, with the same throughput and basically the same other conditions, the required energy consumption is slightly lower than that of the raffinate phase material containing OME 2+ (Example 17), but the saved energy consumption is far lower than the energy consumption required for separating the extractant from OME 2 、OME 3+ by distillation (Reference Example 15).

[0141] Comparative Example 4 The distillation column is made of glass and includes a top condenser refluxer, a rectifying section, a stripping section and a bottom of the column. The inner diameters of the rectifying section and the stripping section are 25 mm, and they are respectively filled with Φ2.5×2.5 mm stainless steel θ wire rings with a height of 100 cm and 60 cm.

[0142] A 4.5% methanol aqueous solution is fed between the rectifying section and the stripping section, with a feed rate of 3.6 ml / min and a feed temperature of 40 °C. The operating pressure of the distillation column is atmospheric pressure (top pressure).

[0143] When the reflux ratio is 3.5 and the effective heating power of the reboiler is 35 w, the overhead product flow rate is 0.164 g / min, which contains 99 wt% methanol and 1 wt% water; the bottom product flow rate is 3.44 g / min, which contains 0.008 wt% methanol and 99.99 wt% water.

[0144] When the reflux ratio is 4.5 and the effective heating power of the reboiler is 39 w, the overhead product flow rate is 0.16 g / min, which contains 99.5 wt% methanol and 0.5 wt% water; the bottom product flow rate is 3.45 g / min, which contains 0.008 wt% methanol and 99.99 wt% water.

[0145] Comparing Comparative Example 4 with Example 17 shows that under the conditions of equivalent theoretical plates in the distillation column and the same feed flow rate, the energy consumption for recovering methanol from a 4.5 wt% methanol aqueous solution by distillation is higher than that for recovering high-value components such as DMM and methanol from an aqueous solution containing 4.5 wt% methanol, 1.5 wt% formaldehyde, and 0.5 wt% benzene using catalytic distillation technology.

[0146] 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 technical solutions of the present application, can make some changes or modifications using the disclosed technical content, which are equivalent to the embodiments and all fall within the scope of the technical solutions of the present application.

Claims

1. A catalytic extraction process for preparing methylal, characterized in that: The following steps are involved: 1) Material A containing formaldehyde and material B containing methanol are mixed and introduced into a multi-stage catalytic extraction reaction system, first entering the reaction zone of the first stage of the multi-stage catalytic extraction reaction system to contact the catalyst for reaction, and then countercurrently contacting with the extractant, and performing catalytic reaction and extraction processes multiple times and alternately to obtain an extract phase material C and a raffinate phase, i.e., an aqueous phase material D; 2) Material C is introduced into the water washing device for water stripping to remove formaldehyde and methanol; 3) After washing, the material C enters the distillation separation system to separate the methylal, and the other components are returned to the multi-stage catalytic extraction reaction system together with the extractant for cyclic reaction; Wherein, the reaction zone of the multi-stage catalytic extraction reaction system is equipped with a solid acid catalyst.

2. The method according to claim 1, characterized in that After the methylal is separated from the washed material C, part or all of OME2 is further separated, and the other components are returned to the multi-stage catalytic extraction reaction system together with the extractant for cyclic reaction.

3. The method according to claim 1 or 2, characterized in that: The raffinate phase material D is introduced into a catalytic distillation tower, and methylal, methanol, etc. are extracted from the top of the tower; wherein the catalytic distillation tower is equipped with a solid acid catalyst.

4. The method according to claim 1 or 2, characterized in that: The washing liquid obtained by washing material C enters the multi-stage catalytic extraction reaction system from a certain intermediate stage.

5. The method according to claim 1 or 2, 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.

6. The method according to claim 1 or 2, characterized in that: The multi-stage catalytic extraction reaction system is composed of a plurality of independent reactors and extraction equipment connected in series, wherein the reactor is filled with a solid acid catalyst and only water phase material flows through the reactor.

7. The method according to claim 1, 2 or 4, 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:

1.

8. The method according to claim 1 or 2, characterized in that: The extractant is at least one of halogenated hydrocarbons, aromatic hydrocarbons, alkanes and cycloalkanes.

9. The method according to claim 3, characterized in that: The material D is introduced into the catalytic distillation tower from above the reaction section.

10. The method according to claim 3, characterized in that: A certain amount of methanol is fed between the reaction section and the stripping section of the catalytic distillation tower.

11. The method according to claim 3, characterized in that A certain amount of methanol is fed between the reaction section and the stripping section of the catalytic distillation tower.

12. The method according to claim 1, 2 or 3, characterized in that: The solid acid catalyst is a strongly acidic cation exchange resin.

13. The method according to claim 1 or 2, characterized in that: Part of the extractant is fed simultaneously from one or several middle stages of the multi-stage catalytic extraction reaction system, and the extraction phase material originally entering the middle stage or these stages is extracted from the multi-stage catalytic extraction reaction system.

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