Process and apparatus for the catalytic synthesis of trioxane

Abstract

The application belongs to the field of catalytic synthesis of trioxane, and particularly relates to a catalytic synthesis process and device of trioxane. The process comprises the following steps: step one, a mixture of methylal and methanol is mixed with oxygen-containing gas as raw material, and reacts to generate formaldehyde under the action of a first catalyst; step two, formaldehyde is dissolved and absorbed by water to obtain concentrated formaldehyde; step three, the concentrated formaldehyde is subjected to catalytic synthesis reaction under the action of a second catalyst to generate trioxane. The device comprises, in sequence in the feeding direction, an oxidation reactor, a heat exchanger, a formaldehyde absorption tower, a fixed bed reactor and a catalytic distillation tower; compared with pure methanol or pure methylal, the raw material of the application is easier to obtain and has lower production cost; the application obtains higher formaldehyde concentration through improved catalyst, and does not need to prepare high-concentration formaldehyde again by negative pressure concentration, so that the single-pass utilization rate of formaldehyde is improved, and various technical problems in the prior art are properly optimized.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of catalytic synthesis of trioxane, and particularly relates to a catalytic synthesis process and device of trioxane. BACKGROUND

[0002] Trioxane is a stable low degree of polymerization solid polymer of formaldehyde, which is relatively stable in nature, easy to store, and can depolymerize into formaldehyde monomer under certain conditions. Therefore, trioxane can replace formaldehyde to participate in almost all reactions using formaldehyde as raw material. At the same time, trioxane is also an important compound downstream of methanol, which can be used to synthesize clean fuel and high-performance materials.

[0003] At present, the commonly used trioxane synthesis process in industry is to synthesize trioxane from high-concentration formaldehyde aqueous solution as raw material and sulfuric acid as catalyst. However, this process has problems such as long process flow, low formaldehyde conversion rate, high energy consumption, many by-products, and serious equipment corrosion. Among them, reducing energy consumption and improving conversion rate are the more prominent problems in the existing process.

[0004] In order to solve this problem, workers in this field have made a lot of efforts. The Chinese patent application with publication number CN110256399A and the invention name of a device and method for preparing trioxane by oxidation of methylal, by adopting technical means such as "methylal oxidation, water absorption to prepare high-concentration formaldehyde, fixed bed plus catalytic rectification and extractive rectification", the formaldehyde single-pass conversion rate reaches 15%; the Chinese patent application with publication number CN112174931A and the invention name of a process and device for preparing trioxane from methanol, by adopting technical means such as "methanol oxidation, water absorption to prepare high-concentration formaldehyde, acid catalysis", the trioxane yield is 31.4%; the Chinese patent application with publication number CN111978288A and the invention name of a preparation process and device of trioxane, by adopting technical means such as "concentrated formaldehyde acid catalytic synthesis of trioxane, polyol hemiacetal de-methanol", the trioxane yield is 34.4%; the Chinese patent application with publication number CN111100109A and the invention name of a trioxane production process and device, by adopting technical means such as "concentrated formaldehyde aqueous solution, fixed bed reaction and vacuum flash separation", the trioxane yield is 50%~60%.

[0005] Although the existing technology has made many improvements on the synthesis process of trioxane, there are still the following problems to be solved:

[0006] 1. When preparing formaldehyde with methanol, high-concentration formaldehyde is often prepared by negative pressure concentration, which is not economical. When preparing formaldehyde with pure methylal, the explosion limit is wide, the safety and stability are low, and the probability of production accidents is increased. If a mixture of methanol and methylal is used to prepare formaldehyde, how to adapt the concentrations of the two to production needs to consider multiple factors (such as the mutual influence between raw materials, the redesign of the reaction process, the change of the system explosion limit, the selection of the catalyst, etc.), which is a technical problem that cannot be solved by limited experiments.

[0007] 2. When preparing methanol by oxidation, the catalytic efficiency of the traditional iron-molybdenum catalyst can be improved, resulting in low formaldehyde yield and low raw material utilization.

[0008] 3. When preparing trioxane by catalyzing concentrated formaldehyde, the catalytic efficiency of the traditional catalytic process (such as acid catalysis or common solid acid cation resin catalysis) is low, and the temperature resistance is poor.

[0009] Therefore, it is urgent to develop a new oxidation catalyst and trioxane catalyst and a new trioxane catalytic synthesis process to overcome the defects of the above-mentioned prior art. SUMMARY

[0010] In order to overcome the above-mentioned problems existing in the prior art, the purpose of the present application is to provide a catalytic synthesis process and device of trioxane to solve the above-mentioned technical problems.

[0011] In a first aspect, the present application provides a catalytic synthesis process of trioxane, comprising the following steps:

[0012] Step one, a mixture of methylal and methanol is used as raw material, and an oxygen-containing gas is introduced into the raw material, and formaldehyde is generated under the action of a first catalyst;

[0013] Step two, formaldehyde is dissolved and absorbed by water to obtain concentrated formaldehyde;

[0014] Step three, the concentrated formaldehyde is subjected to a catalytic synthesis reaction in a fixed bed reactor and a catalytic distillation column under the action of a second catalyst to generate trioxane;

[0015] The first catalyst is a modified iron-molybdenum catalyst, and the second catalyst is a halogen element or halide modified cation resin catalyst.

[0016] Preferably, the preparation method of the first catalyst is:

[0017] Step S1. Adjust the pH of the ammonium molybdate aqueous solution to 1.2-2.5 with concentrated nitric acid to obtain solution A;

[0018] Step S2. Iron salt solution is prepared according to Mo / Fe atomic ratio of 2.5:1~1.7:1, while adding one or any 2~4 kinds of Cr, Mn, Cu, Co and Ni ions, and then solution B is obtained;

[0019] Step S3. Solution B is added dropwise into solution A under sufficient stirring;

[0020] Step S4. After the dropwise addition is completed, the reaction is kept going under sufficient stirring, and the pH value of the system is adjusted to 1.5~3, and then a reaction product is obtained;

[0021] Step S5. The obtained reaction product is subjected to solid-liquid separation, washing and preliminary drying, then a silicon sol or aluminum sol binder is added, and a paste is obtained through binding, and then extrusion molding is performed;

[0022] Step S6. The molded product is dried and then dried and shaped, and then calcination is performed at 450℃~550℃ for 36~48h, and then a first catalyst is obtained.

[0023] Preferably, the concentration of the ammonium molybdate aqueous solution is 0.05~0.2mol / L; the mass ratio of solution A and solution B is 96:4; and the temperature in steps S1, S2, S3 and S4 is controlled to be 30~60℃.

[0024] Preferably, the total amount of Cr, Mn, Cu, Co and Ni ions added is 3%~15% of the molar amount of iron ions.

[0025] Preferably, the molar ratio of Fe, Co, Mn, Cu and Cr is 100:3:1:2:4.

[0026] Preferably, in the mixture of dimethylformamide and methanol in step one, the mass concentration of dimethylformamide is 70%~95%; the concentration of oxygen in the oxygen-containing gas is 6~15vol%; the reaction temperature is 280~350℃, and the reaction pressure is 0.03~0.2MPa.

[0027] Preferably, in step two, the mass concentration of concentrated formaldehyde is 60%~70%.

[0028] Preferably, in step three, concentrated formaldehyde is reacted in a solid bed reactor, the reaction temperature is 90~115℃, and the reaction pressure is 0.03~0.2MPa.

[0029] Preferably, in step three, the reaction is performed in a catalytic distillation column, the reaction pressure is 0.01~0.5MPa, the reaction temperature in the catalytic section is 95~125℃, and the temperature at the top of the column is 93~110℃.

[0030] In a second aspect, the application provides a synthesis device for catalytic synthesis of trioxane, comprising, in sequence along the material feeding direction and the process flow direction, an oxidation reactor, a heat exchanger, a formaldehyde absorption tower, a fixed bed reactor and a catalytic distillation column;

[0031] The oxidation reactor is provided with a feeding port at the top and a discharging port at the bottom, and a first catalyst is loaded in the oxidation reactor, and the discharging port of the oxidation reactor is communicated with the formaldehyde absorption tower below;

[0032] The formaldehyde absorption tower is used for absorbing formaldehyde, and is provided with a discharging port at the top, which is divided into two pipelines by a switching valve, one of which enters the oxidation reactor through the heat exchanger to regulate the oxygen concentration in the oxygen-containing gas, and the other enters the tail gas treatment device; the middle part of the formaldehyde absorption tower is also provided with a water inlet for water feeding, and the bottom of the formaldehyde absorption tower is communicated with the fixed bed reactor;

[0033] The fixed bed reactor is used for catalytically generating trioxane from formaldehyde, and the top of the fixed bed reactor is used for feeding concentrated formaldehyde, and the bottom of the fixed bed reactor is communicated with the catalytic distillation column;

[0034] The catalytic distillation column is divided into a stripping section, a catalytic section and a rectification section from bottom to top; part of the wastewater at the bottom of the catalytic distillation column enters a sewage treatment unit, and part enters the formaldehyde absorption tower, and the trioxane generated at the top of the catalytic distillation column enters a subsequent refining process;

[0035] The fixed bed reactor and the catalytic distillation column are both loaded with a second catalyst.

[0036] The application has the following beneficial effects:

[0037] Firstly, the application realizes efficient generation of the reaction of simultaneously catalyzing the generation of formaldehyde from methylal and methanol by using the improved first catalyst; secondly, the raw material of the application is methylal containing methanol, which is easier to obtain and has lower production cost compared with pure methylal; finally, the application optimizes the mixing ratio of methylal and methanol, which has a narrower explosion limit range, higher safety, greater operational flexibility and stronger stability compared with using pure methylal as a reactant.

[0038] Secondly, the application proposes an improved iron-molybdenum catalyst in the process of synthesizing formaldehyde from methanol / methylal, and gives the specific preferred ratio of the catalyst, and the iron-molybdenum catalyst is improved to make the yield of formaldehyde higher.

[0039] Thirdly, the application divides the step of generating trioxane from formaldehyde into two steps. In the first step, formaldehyde generates trioxane reversibly in the presence of the second catalyst in the fixed bed reactor. In the second step, trioxane enters the catalytic distillation column, breaks the reaction equilibrium in the fixed bed reactor, and increases the conversion rate of formaldehyde to trioxane.

[0040] Fourthly, the application adopts the catalytic distillation process under pressure when synthesizing trioxane, which improves the single-pass conversion rate of formaldehyde and reduces the wastewater production of the device, further reducing the operation cost of the device.

[0041] Fifthly, the second catalyst in the application has higher catalytic efficiency and temperature resistance than ordinary cationic resin catalysts due to the addition of modified components. BRIEF DESCRIPTION OF DRAWINGS

[0042] Figure 1 The process flow chart of the application is shown in the figure;

[0043] Figure 2 The device schematic diagram of the application is shown in the figure.

[0044] BRIEF DESCRIPTION OF DRAWINGS DETAILED DESCRIPTION

[0045] In view of various technical problems in the prior art, the applicant has conducted long-term research based on actual production experience, and finally found a breakthrough: first, optimize the preparation principle and raw material ratio; second, improve the traditional iron-molybdenum catalyst; third, optimize the process of synthesizing trioxane from concentrated formaldehyde.

[0046] Specifically, the improvement of the catalyst includes the following aspects:

[0047] ①The first catalyst is proposed to optimize the process path of catalytic conversion of methylal and formaldehyde to formaldehyde; the first catalyst is an improved iron-molybdenum catalyst, and its preparation method is as follows:

[0048] Step S1: prepare 0.05-0.2 mol / L ammonium molybdate aqueous solution, adjust pH to 1.2-2.5 with concentrated nitric acid under sufficient stirring, keep the system temperature at 30-60℃, and obtain solution A;

[0049] Step S2: Iron salt solution is prepared according to Mo / Fe atomic ratio of 2.5:1~1.7:1, while adding one or any 2~4 kinds of ions of Cr, Mn, Cu, Co and Ni, thereby obtaining solution B, wherein the total amount of Co, Mn, Cu, Cr and Ni ions added is 3%~15% of the iron ions. The addition of these ions can improve the affinity of the formaldehyde and methanol molecules to the active sites on the surface of the catalyst, thereby improving the oxidation capacity of the catalyst for the formaldehyde and methanol molecules. The improvement of the catalytic effect is achieved by simultaneously improving the decomposition capacity of the formaldehyde and the oxidation capacity of the formaldehyde. Ni, Mn and Cu can help to improve the formaldehyde decomposition capacity of the catalyst, so as to avoid the entrainment of formaldehyde in the product and tail gas. Cr and Co can help to improve the oxidation capacity of the catalyst, so as to reduce the methanol content in the product and tail gas. It should be noted that the mechanism of the present application is explained in combination with the final experimental results, and therefore the present application claims protection for the synergistic modification of each doped metal, rather than the superposition of the contribution of each metal to the existing iron-molybdenum catalyst.

[0050] Step S3: B is slowly added to A under sufficient stirring (the temperature of the system is maintained at 30~60℃);

[0051] Step S4: After the addition is completed, the system is maintained under sufficient stirring for continuous reaction, and the pH of the system is adjusted to 1.5-3 by using a base (ammonia water);

[0052] Step S5: After the obtained reaction product is subjected to solid-liquid separation, washing and preliminary drying, silica sol or aluminum sol binder is added, and a paste is obtained through binding, and then extrusion molding is performed;

[0053] Step S6: After the molded product is dried, it is dried and shaped, and then heated in a muffle furnace, and finally stabilized at 480℃~550℃ for 36~48h, thereby obtaining the final product catalyst.

[0054] ②The second catalyst is proposed, and the process path for preparing formaldehyde from methylene is optimized; the second catalyst is a halogen-modified cation resin catalyst, and its preparation method can be (taking AlCl3 as an example):

[0055] 100 parts by weight of H-type KC113 type strong acid cation resin (water content <1%) is loaded in a glass column, the temperature of the glass column is increased to 120℃, hot N2 (115-120℃) carrying aluminum chloride vapor is introduced, the N2 flow is controlled at 1L / min, the reaction is performed for 20h, the N2 introduction is stopped, and the temperature is lowered, thereby obtaining the final product.

[0056] The exchange capacity of the resin catalyst can reach 3.5~4.5, the water content is about 55%, and the maximum temperature resistance is about 150℃.

[0057] The application will be further described in detail below with reference to specific embodiments, preparation examples and drawings.

[0058] Preparation Example 1: Preparation of improved iron-molybdenum catalyst (Co, Mn, Cu, Cr co-doped)

[0059] Step S1: An aqueous solution of 0.12 mol / L ammonium molybdate was prepared, and the pH was adjusted to 2.0 with concentrated nitric acid under sufficient stirring, and the system temperature was maintained at 30-60°C to obtain solution A;

[0060] Step S2: An iron salt solution was prepared according to an atomic ratio of Mo / Fe of 2:1, and Co, Mn, Cu and Cr ions were added to obtain solution B; the total amount of Co, Mn, Cu and Cr ions added was 10% of the amount of iron ions; specifically, Co, Mn, Cu and Cr were added in the form of their respective nitrate salts in a ratio of n(Fe):n(Co):n(Mn):n(Cu):n(Cr)=100:3:1:2:4;

[0061] Step S3: B was slowly added to A under sufficient stirring (the system temperature was maintained at 30-60°C);

[0062] Step S4: After the addition was completed, the system was kept under sufficient stirring for continuous reaction, and the pH of the system was adjusted to 2 with ammonia water;

[0063] Step S5: After the reaction product obtained was subjected to solid-liquid separation, washing and preliminary drying, a silica sol binder was added, and the mixture was thoroughly mixed to obtain a paste, which was then extruded into a shape;

[0064] Step S6: The shaped product was dried and then dried and shaped in a muffle furnace, and finally stabilized at 500°C for 36 h to obtain the final product catalyst.

[0065] Preparation Example 2: Preparation of improved iron-molybdenum catalyst (Co, Ni co-doped)

[0066] Step S1: An aqueous solution of 0.2 mol / L ammonium molybdate was prepared, and the pH was adjusted to 1.2 with concentrated nitric acid under sufficient stirring, and the system temperature was maintained at 30-60°C to obtain solution A;

[0067] Step S2: An iron salt solution was prepared according to an atomic ratio of Mo / Fe of 2.2:1, and Co and Ni ions were added to obtain solution B, wherein the amount of Co ions added was 5% of the amount of iron ions, and the amount of Ni ions added was 10% of the amount of iron ions;

[0068] Step S3: B was slowly added to A under sufficient stirring (the system temperature was maintained at 30-60°C);

[0069] Step S4: After the dropwise addition is completed, the system is kept under full stirring for continuous reaction, and ammonia water is used to adjust the pH of the system to 3;

[0070] Step S5: After the obtained reaction product is subjected to solid-liquid separation, washing and preliminary drying, an aluminum sol binder is added, and a paste is obtained after full mixing, and then extrusion molding is performed;

[0071] Step S6: After the molded product is dried and shaped, it is heated and calcined in a muffle furnace, and finally, the final product catalyst is obtained after being stabilized at 550 DEG C for 48 h.

[0072] Preparation Example 3: Preparation of an improved iron-molybdenum catalyst (Cu and Co co-doped)

[0073] Step S1: An ammonium molybdate aqueous solution with a concentration of 0.1 mol / L is prepared, and concentrated nitric acid is used to adjust the pH to 2.5 under full stirring, and the system temperature is kept between 30 DEG C and 60 DEG C to obtain solution A;

[0074] Step S2: An iron salt solution is prepared according to an atomic ratio of Mo / Fe of 2.5:1, and Cu and Co ions are added to obtain solution B, wherein the addition amount of Co ions is 7% of the iron ions, and the addition amount of Cu ions is 7% of the iron ions;

[0075] Step S3: Solution B is slowly added to solution A under full stirring (the system temperature is kept between 30 DEG C and 60 DEG C);

[0076] Step S4: After the dropwise addition is completed, the system is kept under full stirring for continuous reaction, and ammonia water is used to adjust the pH of the system to 2.5;

[0077] Step S5: After the obtained reaction product is subjected to solid-liquid separation, washing and preliminary drying, an aluminum sol binder is added, and a paste is obtained after full mixing, and then extrusion molding is performed;

[0078] Step S6: After the molded product is dried and shaped, it is heated and calcined in a muffle furnace, and finally, the final product catalyst is obtained after being stabilized at 550 DEG C for 48 h.

[0079] Preparation Example 4: Preparation of an improved iron-molybdenum catalyst (only doped with Mn)

[0080] Step S1: An ammonium molybdate aqueous solution with a concentration of 0.1 mol / L is prepared, and concentrated nitric acid is used to adjust the pH to 2.5 under full stirring, and the system temperature is kept between 30 DEG C and 60 DEG C to obtain solution A;

[0081] Step S2: An iron salt solution is prepared according to an atomic ratio of Mo / Fe of 2.5:1, and Cu and Co ions are added to obtain solution B, wherein the addition amount of Co ions is 7% of the iron ions, and the addition amount of Cu ions is 7% of the iron ions;

[0082] Step S3: Solution B is slowly added to solution A under stirring (keeping the system temperature between 30-60°C);

[0083] Step S4: After the addition is completed, the system is kept under stirring and the pH is adjusted to 2.5 with ammonia;

[0084] Step S5: The obtained reaction product is separated, washed and dried, then a silica sol binder is added, and the mixture is extruded into a paste;

[0085] Step S6: The extruded product is dried and then calcined in a muffle furnace, and finally stabilized at 550°C for 36h to obtain the final product.

[0086] Preparation Example 5: Preparation of modified iron-molybdenum catalyst (only doped with Cu)

[0087] Step S1: An aqueous solution of 0.15 mol / L ammonium molybdate is prepared, and the pH is adjusted to 2.5 with concentrated nitric acid under stirring (keeping the system temperature between 30-60°C) to obtain solution A;

[0088] Step S2: An iron salt solution is prepared according to the atomic ratio of Mo / Fe of 2.2:1, and Cu ions are added to obtain solution B, wherein the amount of Cu ions added is 3% of the iron ions;

[0089] Step S3: Solution B is slowly added to solution A under stirring (keeping the system temperature between 30-60°C);

[0090] Step S4: After the addition is completed, the system is kept under stirring and the pH is adjusted to 2.5 with ammonia;

[0091] Step S5: The obtained reaction product is separated, washed and dried, then a silica sol binder is added, and the mixture is extruded into a paste;

[0092] Step S6: The extruded product is dried and then calcined in a muffle furnace, and finally stabilized at 550°C for 36h to obtain the final product.

[0093] Preparation Example 6: Preparation of modified iron-molybdenum catalyst (only doped with Co)

[0094] Step S1: An aqueous solution of 0.1 mol / L ammonium molybdate is prepared, and the pH is adjusted to 2.5 with concentrated nitric acid under stirring (keeping the system temperature between 30-60°C) to obtain solution A;

[0095] Step S2: An iron salt solution is prepared according to the atomic ratio of Mo / Fe of 2.2:1, and Co ions are added to obtain solution B, wherein the amount of Co ions added is 10% of the iron ions;

[0096] Step S3: slowly add B to A under sufficient stirring (maintain the system temperature between 30-60°C);

[0097] Step S4: after the addition is completed, maintain the system under sufficient stirring and continue the reaction, and adjust the system pH to 2.5 with ammonia water;

[0098] Step S5: after the obtained reaction product is subjected to solid-liquid separation, washing and preliminary drying, add silica sol binder, mix thoroughly to obtain a paste, and then extrude into a shape;

[0099] Step S6: after the shaped product is dried, dry and shape, then heat and calcine in a muffle furnace, and finally stabilize at 550°C for 36h to obtain the final product catalyst.

[0100] Preparation Example 7: preparation of modified iron-molybdenum catalyst (doped with Mn, Cr)

[0101] Step S1: prepare a 0.16 mol / L ammonium molybdate aqueous solution, adjust the pH to 1.5 with concentrated nitric acid under sufficient stirring, and maintain the system temperature between 30-60°C to obtain solution A;

[0102] Step S2: prepare an iron salt solution according to the atomic ratio of Mo / Fe of 1.7:1; at the same time, add Mn and Cr ions to obtain solution B, wherein the addition amount of Mn ions is 5% of the iron ions, and the addition amount of Cr ions is 6% of the iron ions;

[0103] Step S3: slowly add B to A under sufficient stirring (maintain the system temperature between 30-60°C);

[0104] Step S4: after the addition is completed, maintain the system under sufficient stirring and continue the reaction, and adjust the system pH to 2.5 with ammonia water;

[0105] Step S5: after the obtained reaction product is subjected to solid-liquid separation, washing and preliminary drying, add silica sol binder, mix thoroughly to obtain a paste, and then extrude into a shape;

[0106] Step S6: after the shaped product is dried, dry and shape, then heat and calcine in a muffle furnace, and finally stabilize at 550°C for 36h to obtain the final product catalyst.

[0107] Preparation Example 8: preparation of modified iron-molybdenum catalyst (doped with Ni, Cu, Mn)

[0108] Step S1: prepare a 0.12 mol / L ammonium molybdate aqueous solution, adjust the pH to 2.0 with concentrated nitric acid under sufficient stirring, and maintain the system temperature between 30-60°C to obtain solution A;

[0109] Step S2: Iron salt solution is prepared according to Mo / Fe atomic ratio of 2:1, and Ni, Cu, Mn ions are added, thereby obtaining solution B; the addition amount of Ni ion is 3% of iron ion, the addition amount of Cu ion is 6% of iron ion, and the addition amount of Mn ion is 3% of iron ion;

[0110] Step S3: B is slowly added to A under sufficient stirring (the system temperature is maintained between 30-60°C);

[0111] Step S4: After the addition is completed, the system is maintained under sufficient stirring for reaction to continue, and ammonia water is used to adjust the pH of the system to 2.5;

[0112] Step S5: After the obtained reaction product is subjected to solid-liquid separation, washing and preliminary drying, silica sol binder is added, and the mixture is sufficiently mixed to obtain a paste, which is then extruded into a shape;

[0113] Step S6: The shaped product is dried and then baked in a muffle furnace, and finally, the product is stabilized at 550°C for 36h to obtain a final product catalyst.

[0114] The results of running the iron-molybdenum catalysts obtained in Preparation Examples 1-8 under actual working conditions for 72h are shown in Table 1:

[0115] Table 1

[0116] Sample Methanol content in product formaldehyde Methylal content in product formaldehyde Methanol content in tail gas absorption liquid Methylal content in tail gas absorption liquid Traditional iron-molybdenum catalyst 0.73 0.12 2.13 1.24 Preparation Example 1 0.34 0 1.32 0.57 Preparation Example 2 0.37 0 1.76 0.61 Preparation Example 3 0.52 0 1.54 0.78 Preparation Example 4 0.58 0 1.96 0.81 Preparation Example 5 0.71 0 1.95 0.75 Preparation Example 6 0.59 0 1.87 0.92 Preparation Example 7 0.53 0 1.41 0.62 Preparation Example 8 0.45 0 1.51 0.67

[0117] Through the preliminary performance test of the first catalyst, it can be seen that the catalytic effect of the catalyst prepared by doping with multiple metal ions is better than that of the traditional iron-molybdenum catalyst, and it can also be seen that the effect of metal ion synergistic doping is significantly better than that of single metal ion doping. In each preparation example, the iron-molybdenum catalyst co-doped with Co, Mn, Cu and Cr is the best, and the impurities in the product are the least, which is helpful for the subsequent synthesis of trioxane.

[0118] Preparation Example 9: Preparation of aluminum chloride modified cation resin catalyst

[0119] 100 parts of H-type KC113 type strong acid cation resin (water content <1%) by weight are loaded in a glass column, the temperature of the glass column is increased to 120°C, hot N2 (120°C) carrying aluminum chloride vapor is introduced, the N2 flow is controlled at 1L / min, and the reaction is carried out for 20h. Stop the N2 flow, and cool down to obtain the finished product.

[0120] Through detection, the exchange capacity of the resin catalyst is 4, the water content is 55%, and the maximum temperature resistance is 150°C.

[0121] The catalysts prepared in Preparation Examples 1-9 are used to complete the experiments of the following examples.

[0122] Example 1

[0123] The present embodiment provides a device for catalytic synthesis of trioxane. The device comprises an oxidation reactor 1, a heat exchanger 5, a formaldehyde absorption tower 2, a fixed bed reactor 3 and a catalytic distillation column 4, which are sequentially connected along the material feeding direction and the process flow direction.

[0124] The oxidation reactor 1 is provided with a feeding port at the top for feeding of the raw materials of methanol and methylal and oxygen-containing gas; the oxygen-containing gas and the raw materials are first heated in the heat exchanger 5 and then enter the oxidation reactor 1; the oxidation reactor 1 is provided with a discharging port at the bottom, and the discharge is fed into the formaldehyde absorption tower 2 through the heat exchanger 5. The oxidation reactor 1 can be filled with the modified iron-molybdenum catalyst prepared according to any one of Preparation Examples 1-8.

[0125] The formaldehyde absorption tower 2 is used for absorbing formaldehyde, and the top thereof is provided with a discharging port, which is divided into two pipelines by a switching valve, one of which enters the oxidation reactor 1 through the heat exchanger 5 for regulating the oxygen concentration in the oxygen-containing gas, and the other enters the tail gas treatment device; the middle part of the formaldehyde absorption tower 2 is also provided with a water inlet for water feeding; the bottom of the formaldehyde absorption tower 2 is connected with the fixed bed reactor 3.

[0126] The fixed bed reactor 3 is used for providing a reaction site for catalytic generation of trioxane from formaldehyde. Concentrated formaldehyde undergoes a reversible reaction in the fixed bed reactor 3 to generate trioxane; the top of the fixed bed reactor 3 is used for feeding of concentrated formaldehyde, and the bottom thereof is connected with the catalytic distillation column 4.

[0127] The trioxane generated in the fixed bed reactor 3 enters the catalytic distillation column 4, which is divided into a stripping section, a catalytic section and a rectification section from bottom to top; part of the waste water at the bottom of the catalytic distillation column 4 enters a sewage treatment unit, and part thereof enters the formaldehyde absorption tower 2 for absorption of formaldehyde gas, thereby reducing the consumption of pure water; the trioxane generated at the top of the catalytic distillation column 4 enters a subsequent refining process. The fixed bed reactor 3 and the catalytic distillation column 4 are both filled with the aluminum trichloride modified cation resin catalyst prepared according to Preparation Example 9, and the catalyst filled in the catalytic distillation column 4 is in the form of a module catalyst integrated with the structured packing.

[0128] The implementation principle of the present embodiment can be summarized as follows:

[0129] First, methylal containing methanol is used as a raw material, which is then fed into the oxidation reactor 1 together with oxygen-poor air through the heat exchanger 5; the methanol and methylal are catalytically converted into formaldehyde in the oxidation reactor 1 under the catalytic action of the catalyst; and the formaldehyde is fed into the formaldehyde absorption tower 2 through the heat exchanger 5.

[0130] The formaldehyde absorption tower 2 produces concentrated formaldehyde by water absorption, and the concentrated formaldehyde is introduced into the fixed bed reactor 3, and under the catalysis of the aluminum chloride modified cation resin catalyst, part of the formaldehyde undergoes a reversible equilibrium reaction to generate trioxane.

[0131] The material at the outlet of the fixed bed is introduced into the catalytic distillation tower 4, and after catalytic distillation, the single-pass conversion rate of formaldehyde is improved, and the finally generated trioxane enters the subsequent refining step.

[0132] Example 2

[0133] According to the device of Example 1, this embodiment provides a catalytic synthesis process of trioxane, which comprises the following steps:

[0134] The formaldehyde absorption tower 2 produces concentrated formaldehyde by water absorption, and the concentrated formaldehyde is introduced into the fixed bed reactor 3, and under the catalysis of the aluminum chloride modified cation resin catalyst, part of the formaldehyde undergoes a reversible equilibrium reaction to generate trioxane.

[0135] The oxidation reactor used in this embodiment is provided with the catalyst prepared in Preparation Example 1; the fixed bed reactor and the catalytic distillation tower are both provided with the second catalyst, the aluminum chloride modified cation resin catalyst prepared in Preparation Example 9.

[0136] Example 3

[0137] According to the device of Example 1, this embodiment provides a catalytic synthesis process of trioxane, which comprises the following steps:

[0138] The methyoxymethyl ether containing methanol as raw material (mass concentration of methyoxymethyl ether is 90%, concentration of methanol is 10%), mass flow is 1050 kg / h, mass of oxygen-poor air is 8917 kg / h, oxygen concentration is 10%, after mixing, the mixture is heated to 180℃ by a preheater, and then is introduced into an oxidation reactor. The reaction temperature is controlled at 300℃, the reaction pressure is 0.1 MPa, and the oxidation reaction occurs under the action of the first catalyst. After the reaction, the material in the gas phase is cooled in a heat exchanger, and the temperature of the cooled material is 110℃. Then the material is introduced into a methyoxymethyl ether absorption tower, 220 kg / h of pure water is added from the top of the tower, and the circulating liquid of the tower is used to absorb the gaseous methyoxymethyl ether. The concentrated methyoxymethyl ether with a concentration of 69% is obtained from the tower bottom. Then the concentrated methyoxymethyl ether is introduced into a fixed bed reactor, and the reaction temperature is controlled at 100℃ and the reaction pressure is 0.1 MPa. Then the pre-reacted material is further reacted and distilled in a catalytic distillation column, and the reaction pressure is 0.01 MPa, the temperature of the catalytic section is 95-100℃, and the temperature of the tower top is 93℃. Under the action of the resin catalyst, the reaction generates trioxymethylene. The waste water with a mass flow of 390 kg / h is obtained from the tower bottom through the liquid phase outlet. The mixture containing 710 kg / h of trioxymethylene, 381 kg / h of methyoxymethyl ether and 113 kg / h of water is obtained from the tower top, and is introduced into a subsequent refining unit after condensation.

[0139] In the oxidation reactor used in the example, the catalyst prepared in Preparation Example 2 is loaded; the second catalyst, aluminum chloride modified cation resin catalyst prepared in Preparation Example 9, is loaded in the fixed bed reactor and the catalytic distillation column.

[0140] Example 4

[0141] According to the device of Example 1, the example provides a catalytic synthesis process of trioxymethylene, which comprises the following steps:

[0142] The methyloxymethyl ether containing methanol is used as raw material (the mass concentration of methyloxymethyl ether is 70% and the mass concentration of methanol is 30%), the mass flow is 1100 kg / h, the mass of the oxygen-poor air is 9200 kg / h, the oxygen concentration is 6%, and after mixing, the mixture is heated to 180°C by a preheater and then is introduced into an oxidation reactor. The reaction temperature is controlled to be 350°C and the reaction pressure is controlled to be 0.2 MPa, and the oxidation reaction is carried out under the action of the first catalyst. After the reaction, the material is in a gaseous phase and is cooled in a heat exchanger, and the temperature of the cooled material is 110°C. Then, the material is introduced into a methyloxymethyl ether absorption tower, and 160 kg / h of pure water and the circulating liquid of the tower itself are added from the top of the tower to absorb the gaseous methyloxymethyl ether. The concentrated methyloxymethyl ether with a concentration of about 67% is obtained from the tower bottom. Then, the concentrated methyloxymethyl ether is introduced into a fixed bed reactor, and the reaction temperature is controlled to be 115°C and the reaction pressure is controlled to be 0.2 MPa. Then, the pre-reacted material is further reacted and is distilled in a catalytic distillation tower, and the reaction pressure is 0.5 MPa, the temperature of the catalytic layer is 115-125°C, the temperature of the tower top is 110°C, and the reaction is carried out under the action of the resin catalyst. The waste water with a mass of 380 kg / h is obtained from the tower bottom through a liquid phase outlet, and the mixture containing 800 kg / h of trioxymethylene, 293 kg / h of methyloxymethyl ether and 148 kg / h of water is obtained from the tower top. After condensation, the mixture is introduced into a subsequent refining unit.

[0143] In the oxidation reactor used in the example, the catalyst prepared in Preparation Example 7 is loaded; the second catalyst, the aluminum chloride modified cation resin catalyst prepared in Preparation Example 9, is loaded in the fixed bed reactor and the catalytic distillation tower.

[0144] Example 5

[0145] The difference between the example and Example 2 is that the first catalyst used in the example is the catalyst prepared in Preparation Example 3.

[0146] Example 6

[0147] The difference between the example and Example 2 is that the first catalyst used in the example is the catalyst prepared in Preparation Example 4.

[0148] Example 7

[0149] The difference between the example and Example 2 is that the first catalyst used in the example is the catalyst prepared in Preparation Example 5.

[0150] Example 8

[0151] The difference between the example and Example 2 is that the first catalyst used in the example is the catalyst prepared in Preparation Example 6.

[0152] Example 9

[0153] The difference between the example and Example 2 is that the first catalyst used in the example is the catalyst prepared in Preparation Example 8.

[0154] Comparative Example 1

[0155] The difference between the present comparative example and Example 2 is that the first catalyst selected in the present comparative example is a traditional iron-molybdenum catalyst.

[0156] Comparative Example 2

[0157] The difference between the present comparative example and Example 2 is that the second catalyst selected in the present comparative example is a strong acid cation resin of KC113 type in H form, which is not modified by AlCl3.

[0158] Comparative Example 3

[0159] The difference between the present comparative example and Example 2 is that the synthesis step of concentrated formaldehyde is omitted in the present comparative example, and the concentrated formaldehyde (mass concentration of formaldehyde is 37%) is directly purchased, and the purchased concentrated formaldehyde is passed through a fixed bed reactor.

[0160] Comparative Example 4

[0161] The difference between the present comparative example and Example 2 is that the device of the present application is modified in the present comparative example, and the trioxane prepared by fixed bed catalytic reaction is directly discharged without further catalytic distillation.

[0162] Comparative Example 5

[0163] The difference between the present comparative example and Example 2 is that the mass concentration of the raw material dimethyl ether is 98% and the concentration of methanol is 2% in the present comparative example.

[0164] Result detection

[0165] Under the same process conditions, the products were collected, and the single-pass conversion rates of formaldehyde in Examples 2-9 and Comparative Examples 1-5 were calculated, and the results are shown in Table 2.

[0166] Table 2

[0167] Sample Formaldehyde conversion per pass Yield of trimeric formaldehyde Example 2 68% 67% Example 3 65% 64% Example 4 73% 72% Example 5 66% 64% Example 6 65% 63% Example 7 67% 66% Example 8 70% 68% Example 9 65% 64% Comparative Example 1 60% 58% Comparative Example 2 65% 60% Comparative Example 3 40% 39% Comparative Example 4 8% 7% Comparative Example 5 65% 64%

[0168] Through analysis, it can be seen that the trioxane yield is all above 63% and the highest can reach 72% by using the prepared first catalyst and second catalyst of the application and using the raw material ratio optimized by the application, compared with the trioxane yield of 50%-60% disclosed in the Chinese patent application CN111100109A with the invention name of a trioxane production process and device. This is because the catalytic activity and trioxane yield are significantly improved by the synergistic effect of the multiple metal co-doping in the application, especially in Example 4, the metal co-doping has the optimal catalytic activity. First, the synergistic effect of different transition metals optimizes the electronic structure of the active site and the surface properties, Co promotes electron transfer, Mn enhances oxidation capacity, Cu adjusts the acid sites to inhibit side reactions, Cr improves thermal stability, and together forms a composite active center, realizing efficient regulation of the trioxane ring-opening and polymerization reaction path; second, multiple metal doping significantly improves the structural stability and anti-sintering ability of the catalyst by forming a stable composite oxide, while the traditional iron-molybdenum catalyst is prone to sintering of the active phase at high temperature, leading to performance degradation; third, the precise balance of the distribution of acid sites and redox sites by multiple components not only promotes the formation of monomers by Lewis acid through trioxane ring-opening, but also accelerates the coupling of formaldehyde into polyformaldehyde chains through oxidation sites, while inhibiting the formation of deep oxidation byproducts. Compared with the traditional catalyst selected for the first catalyst in the comparative example, the catalyst of the application has obvious advantages in metal doping.

[0169] The second catalyst in Comparative Example 2 is not modified, and the effect is worse than that of the application, because the unmodified H-type resin only contains Bronsted acid sites, while the modified one introduces AlCl3 Lewis acid sites. Lewis acid can polarize the formaldehyde carbonyl oxygen and enhance its electrophilicity; Bronsted acid provides protons to activate formaldehyde, and the two work together to promote aldol condensation and cyclization. The strong Lewis acidity of AlCl3 increases the overall acid strength of the catalyst, which further leads to the protonation of formaldehyde and the formation of carbocation intermediates, accelerating the trioxane cyclization kinetics. The 55% water content after modification may adjust the swelling degree of the resin, expand the pore structure, benefit the diffusion of reactants and the desorption of trioxane product, and reduce side reactions. The modified resin can withstand temperatures up to 150°C, and the acid site stability at high temperatures is better than that of the original resin, avoiding the loss of active components and maintaining long-term catalytic performance. Therefore, the modified second catalyst improves the selectivity and yield of trioxane.

[0170] Comparative Examples 3-5 have higher activity of the first catalyst and the second catalyst due to the improvement of the raw material ratio and the device, but the reaction process may not promote the forward reaction, resulting in a yield lower than the yield achieved by the protection scheme defined in the application.

[0171] The above merely describes the preferred embodiments of the present application, and is not intended to limit the present application in any form. Although the present application has been disclosed with the preferred embodiments as above, it is not intended to limit the present application. Any person skilled in the art, without departing from the technical solution range of the present application, can make some more changes or modifications to the equivalent embodiments of the equivalent changes, as long as it does not deviate from the technical solution content of the present application. Any concise modification, equivalent change and modification made to the above embodiments according to the technical essence of the present application are still within the scope of the technical solution of the present application.

Claims

1. A process for the catalytic synthesis of parformaldehyde, characterized in that, It comprises the following steps: Step one, a mixture of methylal and methanol as raw material, and into the raw material into the oxygen-containing gas, under the action of the first catalyst, reaction to generate formaldehyde; Step two, formaldehyde is dissolved and absorbed by water to obtain concentrated formaldehyde; Step three, concentrated formaldehyde is subjected to catalytic synthesis reaction in a fixed bed reactor and a catalytic distillation column under the action of the second catalyst to generate trioxane; The second catalyst is an aluminum chloride modified cation resin catalyst, and the preparation method is as follows: 100 parts of H type KC113 type strong acid cation resin, wherein the water content of the strong acid cation resin is less than 1%, is loaded into a glass column, the temperature of the glass column is increased to 120 DEG C, hot N2 loaded with aluminum chloride vapor is introduced, wherein the temperature of N2 is 120 DEG C, the flow rate of N2 is controlled to be 1 L / min, the reaction is carried out for 20 h, the introduction of N2 is stopped, and the temperature is lowered to obtain the finished product; The first catalyst is a modified iron-molybdenum catalyst, The preparation method of the first catalyst is as follows: Step S1. Adjust the pH of the ammonium molybdate aqueous solution to 1.2-2.5 with concentrated nitric acid to obtain solution A; Step S2. Prepare an iron salt solution according to the atomic ratio of Mo / Fe of 2.5:1-1.7:1, and simultaneously add one or any 2-4 kinds of Cr, Mn, Cu, Co and Ni ions to obtain solution B; Step S3. Drop solution B into solution A under sufficient stirring; Step S4. After the drop is completed, the reaction is continuously carried out under sufficient stirring, and the pH value of the system is adjusted to 1.5-3 to obtain a reaction product; Step S5. After the obtained reaction product is subjected to solid-liquid separation, washing and preliminary drying, a silica sol or alumina sol binder is added, and a paste is obtained through adhesion, and then extrusion molding is carried out; Step S6. The molded product is dried and then dried and shaped at 450 DEG C-550 DEG C for 36-48 h to obtain the first catalyst; In the mixture of methylal and methanol in step one, the mass concentration of methylal is 70%-95%.

2. A process for the catalytic synthesis of parformaldehyde according to claim 1, characterized in that, The concentration of the ammonium molybdate aqueous solution is 0.05-0.2 mol / L; the mass ratio of solution A to solution B is 96:4; and the temperature is controlled to be 30-60 DEG C in steps S1, S2, S3 and S4.

3. A process for the catalytic synthesis of parformaldehyde as claimed in claim 1, wherein, The total amount of the added Cr, Mn, Cu, Co and Ni ions is 3%-15% of the molar amount of iron ions.

4. A process for the catalytic synthesis of parformaldehyde as claimed in claim 1, wherein, The molar ratio of Fe, Co, Mn, Cu and Cr is 100:3:1:2:

4.

5. A process for the catalytic synthesis of parformaldehyde as claimed in claim 1, wherein, The concentration of oxygen in the oxygen-containing gas is 6-15 vol%; the reaction temperature is 280-350 DEG C, and the reaction pressure is 0.03-0.2 MPa.

6. A process for the catalytic synthesis of parformaldehyde according to claim 1, characterized by, In step two, the mass concentration of concentrated formaldehyde is 60%-70%.

7. A process for the catalytic synthesis of parformaldehyde as claimed in claim 1, wherein In step three, the concentrated formaldehyde is reacted in a solid bed reactor, the reaction temperature is 90-115 DEG C, and the reaction pressure is 0.03-0.2 MPa.

8. A process for the catalytic synthesis of parformaldehyde as claimed in claim 1, wherein, In step three, the reaction is carried out in a catalytic distillation column, the reaction pressure is 0.01-0.5 MPa, the reaction temperature of the catalytic section is 95-125 DEG C, and the temperature at the top of the column is 93-110 DEG C.

9. A synthesis apparatus for the catalytic synthesis of parformaldehyde according to any one of claims 1 to 8, characterized in that The oxidation reactor (1), the heat exchanger (5), the formaldehyde absorption tower (2), the fixed bed reactor (3) and the catalytic distillation tower (4) are sequentially connected along the material feeding direction and the process flow direction; The oxidation reactor (1) is provided with a feeding port at the top and a discharging port at the bottom, and is internally provided with a first catalyst; the discharging port of the oxidation reactor (1) is communicated with the formaldehyde absorption tower (2) below; The formaldehyde absorption tower (2) is used for absorbing formaldehyde, and is provided with a discharging port at the top; the discharging port is divided into two pipelines through a conversion valve, one pipeline enters the oxidation reactor (1) through the heat exchanger (5) and is used for regulating the oxygen concentration in the oxygen-containing gas, and the other pipeline enters the tail gas treatment device; the formaldehyde absorption tower (2) is further provided with a water inlet for water feeding at the middle part; the bottom of the formaldehyde absorption tower (2) is communicated with the fixed bed reactor (3); The fixed bed reactor (3) is used for catalytically generating trioxane from formaldehyde, and the top of the fixed bed reactor (3) is used for feeding concentrated formaldehyde; the bottom of the fixed bed reactor (3) is communicated with the catalytic distillation tower (4); The catalytic distillation tower (4) is divided into a stripping section, a catalytic section and a rectifying section from bottom to top; the waste water at the bottom of the catalytic distillation tower (4) is partially introduced into a sewage treatment unit and partially introduced into the formaldehyde absorption tower (2); the trioxane generated at the top of the catalytic distillation tower (4) is introduced into a subsequent refining unit; The fixed bed reactor (3) and the catalytic distillation tower (4) are both internally provided with a second catalyst.

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