Patent Publication Number: US-2023150961-A1

Title: Method for synthesizing oxetane compound by microreactor

Description:
TECHNICAL FIELD 
     The invention relates to the field of organic synthesis, in particular to a method for synthesizing an oxetane compound by a microreactor. 
     BACKGROUND 
     3-Ethyl-3-hydroxymethyloxetane and bis[1-ethyl(3-oxetanyl)methyl]ether are the most widely used monomers in the photocurable cationic system and are extensively applied in the fields of photocurable coatings, inks, adhesives, and the like. Their structural formulas are as follows: 
     
       
         
         
             
             
         
       
     
     The cyclocarbonate cracking method is commonly used in industry to prepare oxetane products. For example, the reaction process for producing 3-ethyl-3-hydroxymethyloxetane by the cyclocarbonate cracking method is as follows: 
     
       
         
         
             
             
         
       
     
     In the formula, R is alkyl, generally methyl or ethyl. 
     The process is as follows: trimethylolpropane and carbonate ester are subjected to the transesterification reaction in a rectifying still at a temperature of 80° C. to 120° C., the alcohol as by-product is continuously fractionated out during the reaction, the excess carbonate ester is removed by distillation after the reaction has been completed, and the transesterification procedure takes 10 h to 12 h; then the cracking procedure is started, wherein the cracking is conducted at a temperature of 160° C. to 200° C. for 12 h to 15 h to remove carbon dioxide and the finished product is finally obtained by rectification under negative pressure. The whole process takes 30 h to 40 h to complete, and the production efficiency is relatively low. The cracking reaction is conducted at high temperature for a long time, which will lead to the production of high-boiling by-products, so the yield of the finished product is low (65% to 75%), and a large amount of distillation residues will be generated after the completion of rectification, which can only be disposed as solid wastes. 
     In view of the existence of the above problems, it is necessary to provide a method for synthesizing an oxetane compound with relatively high yield and short reaction time. 
     SUMMARY 
     A main object of the invention is to provide a method for synthesizing an oxetane compound by a microreactor, so as to solve the problems present in the existing synthesis methods for oxetane compounds such as low yield and long reaction time. In view of this, the invention further provides a method for adjusting the product distribution by controlling relevant parameters in the reaction process, to realize the co-production of three oxetane compounds. 
     In order to achieve the above object, the invention provides a method for synthesizing an oxetane compound by a microreactor, including feeding trimethylolpropane and a carbonate ester into a microreactor in the presence of a basic catalyst, and synthesizing the oxetane compound under solvent or solvent-free condition through a microreaction continuous flow process. 
     Further, the basic catalyst comprises a first basic catalyst and a second basic catalyst, and the method for synthesizing an oxetane compound by a microreactor includes: continuously feeding the first basic catalyst, trimethylolpropane, and carbonate ester into a first microreactor for transesterification reaction, to obtain a reaction product system containing an esterified intermediate; extracting the esterified intermediate from the reaction product system containing the esterified intermediate; feeding the esterified intermediate and the second basic catalyst into a second microreactor for cracking reaction, to obtain a cracked reaction product system; and subjecting the cracked reaction product system to gas-liquid separation treatment, to obtain the oxetane compound. 
     Further, the solvent is one or more of the group consisting of halogenated hydrocarbons, benzene, toluene, xylene, nitrobenzene, and acetonitrile. 
     Further, the temperature of the first microreactor is 50 to 300° C., the residence time of the first microreactor is 1 to 60 min; and the reaction temperature of the second microreactor is 150 to 400° C., and the residence time of the second microreactor is 1 to 8 min. 
     Further, the temperature of the first microreactor is 100 to 200° C.; and the reaction temperature of the second microreactor is 200 to 300° C. 
     Further, the molar ratio of trimethylolpropane to carbonate ester is 1:(1 to 5), and the content of the basic catalyst is 100 ppm to 50,000 ppm. 
     Further, the molar ratio of trimethylolpropane to carbonate ester is 1:(1.5 to 3), and the content of the basic catalyst is 100 ppm to 10,000 ppm. 
     Further, the carbonate ester is selected from one or more of the group consisting of dimethyl carbonate, diethyl carbonate, and dipropyl carbonate; and the basic catalyst is selected from one or more of alkali metal hydroxides, sodium alkoxides, potassium alkoxides, or alkali metal carbonates. 
     Further, the first basic catalyst and the second basic catalyst are independently selected from one or more of alkali metal hydroxides, sodium alkoxides, potassium alkoxides, or alkali metal carbonates, respectively; preferably, the first basic catalyst and the second basic catalyst are independently selected from one or more of the group consisting of sodium methoxide, sodium ethoxide, lithium hydroxide, sodium hydroxide, potassium hydroxide, lithium carbonate, sodium carbonate, and potassium carbonate, respectively; preferably, the amount of the first basic catalyst is 200 to 500 ppm, and the amount of the second basic catalyst is 300 to 3,000 ppm. 
     Further, in the process of the cracking reaction, the synthesis method further includes: adding water to the esterified intermediate, and the water content of the system in the process of the cracking reaction is 10 to 100,000 ppm. 
     Further, the first microreactor has a reaction channel having an inner diameter selected from 200 to 10,000 μm, and the second microreactor has a reaction channel having an inner diameter independently selected from 200 to 10,000 μm respectively; preferably, the first microreactor has a reaction channel having an inner diameter selected from 200 to 2,000 μm, and the second microreactor has a reaction channel having an inner diameter selected from 500 to 10,000 μm. 
     Further, the device used in the extraction process is selected from a thin-film evaporator or a rectification tower. 
     By applying the technical solution of the invention, the microreactor has the advantages such as high heat and mass transfer coefficient, good mixing performance, easy temperature control, and safe and controllable process as compared to conventional reactors. Making use of the advantages of the microreactor to produce the above three oxetane products can greatly improve the mass and heat transfer performances of the reaction system, reduce the reaction time, improve the production efficiency, especially avoid the long-term high temperature process in the cracking procedure and reduce the production of high-boiling by-products, improve the yield, realize the process continuity and automation, and improve the process safety. In addition, the above synthesis process requires small size for reaction device, small floor space for production site, and less human resources, and has high safety. 
    
    
     
       DESCRIPTION OF THE DRAWINGS 
       The accompanying drawing as a part of the subject application is used to provide further understandings on the invention. The exemplary embodiments and their descriptions in the invention are used to explain the invention and do not serve as improper limitations to the invention. In the accompanying drawing: 
         FIG.  1    shows a schematic diagram for the structure of a synthesis device for oxetane compound provided according to a typical embodiment of invention. 
     
    
    
     The above drawing includes the following reference signs: 
       10 . Raw material storage tank;  11 . First feeding pump;  20 . First microreactor;  30 . Thin-film evaporator;  40 . Esterified intermediate storage tank;  41 . Second feeding pump;  50 . Light end collection tank;  60 . Second microreactor;  70 . Micro heat exchanger;  80 . Gas-liquid separation tank;  90 . Rectification device. 
     DESCRIPTION OF EMBODIMENTS 
     It should be noted that, in the case of no conflict, the embodiments in the subject application as well as the features therein can be combined with each other. The invention will be described in detail below with reference to the embodiments. 
     As described in the background, the existing synthesis methods for oxetane compounds have problems such as low yield and long reaction time. In order to solve the above technical problems, the invention provides a method for synthesizing an oxetane compound by a microreactor, including: feeding trimethylolpropane and a carbonate ester into a microreactor in the presence of a basic catalyst, and synthesizing the oxetane compound under inert solvent or solvent-free condition through a microreaction continuous flow process. 
     The microreactor has the advantages such as high heat and mass transfer coefficient, good mixing performance, easy temperature control, and safe and controllable process as compared to conventional reactors. Making use of the advantages of the microreactor to produce the above three oxetane products can greatly improve the mass and heat transfer performances of the reaction system, reduce the reaction time, improve the production efficiency, especially avoid the long-term high temperature process in the cracking procedure and reduce the production of high-boiling by-products, improve the yield, realize the process continuity and automation, and improve the process safety. In addition, the above synthesis process requires small size for reaction device, small floor space for production site, and less human resources, and has high safety. 
     In a preferred embodiment, the basic catalyst comprises a first basic catalyst and a second basic catalyst, and the method for synthesizing an oxetane compound by a microreactor includes: continuously feeding the first basic catalyst, trimethylolpropane, and carbonate ester into a first microreactor for transesterification reaction, to obtain a reaction product system containing an esterified intermediate; extracting the esterified intermediate from the reaction product system containing the esterified intermediate; feeding the esterified intermediate and the second basic catalyst into a second microreactor for cracking reaction, to obtain a cracked reaction product system; and subjecting the cracked reaction product system to gas-liquid separation treatment, to obtain the oxetane compound. 
     After the above gas-liquid separation, the resulting product is a mixture, which can be further separated by those skilled in the art as required. The separation method includes but is not limited to distillation. 
     The solvent used in the above synthesis method can be selected from those commonly used in the art. In a preferred embodiment, the solvent includes but is not limited to one or more of the group consisting of halogenated hydrocarbons, benzene, toluene, xylene, nitrobenzene, and acetonitrile. Under comprehensive consideration of cost factors, the solvent-free condition is preferred. 
     In a preferred embodiment, the temperature of the first microreactor is 50 to 300° C., the residence time of the first microreactor is 1 to 60 min; and the reaction temperature of the second microreactor is 150 to 400° C., and the residence time of the second microreactor is 1 to 8 min. 
     Compared with the uncontrollability of the product composition in the conventional process, limiting the process conditions of the transesterification reaction and the cracking reaction to the above ranges in the subject application can improve the total yield of oxetane products. At the same time, the method of the subject application can also control the distribution of different products, realize the co-production of three oxetane compounds, and improve the economic values. For example, the temperature of the first microreactor can be 50° C., 80° C., 100° C., 160° C., 200° C., or 300° C.; and the reaction temperature of the second microreactor can be 150° C., 200° C., 260° C., 300° C., or 400° C. 
     In a preferred embodiment, the temperature of the first microreactor is 100 to 200° C.; and the reaction temperature of the second microreactor is 200 to 300° C. The temperature of the first microreactor and the temperature of the second microreactor include but are not limited to the above ranges, while limiting them to the above ranges is beneficial to further improving the yield of target product and shortening the reaction time. 
     In a preferred embodiment, in the process of transesterification reaction, the molar ratio of trimethylolpropane to carbonate ester is 1:(1 to 5), and the content of the basic catalyst is 100 ppm to 50,000 ppm. The amounts of trimethylolpropane, carbonate ester, and basic catalyst include but are not limited to the above ranges, while limiting them to the above ranges is beneficial to further improving the conversion rate of reaction raw materials. More preferably, the molar ratio of trimethylolpropane to carbonate ester is 1:(1.5 to 3), and the content of the basic catalyst is 100 ppm to 10,000 ppm. 
     In the above synthesis method, the carbonate ester and the basic catalyst can be selected from those commonly used in the art. In a preferred embodiment, the carbonate ester includes but is not limited to one or more of the group consisting of dimethyl carbonate, diethyl carbonate, and dipropyl carbonate. 
     In a preferred embodiment, the first basic catalyst and the second basic catalyst are independently selected from one or more of hydroxides formed by alkali metals, sodium alkoxides, potassium alkoxides, and carbonates formed by alkali metals, respectively. More preferably, the first basic catalyst and the second basic catalyst are independently selected from one or more of the group consisting of sodium methoxide, sodium ethoxide, lithium hydroxide, sodium hydroxide, potassium hydroxide, lithium carbonate, sodium carbonate, and potassium carbonate. 
     In order to further improve the catalytic effect and shorten the reaction time, further preferably, the first basic catalyst and the second basic catalyst are independently selected from one or more of sodium methoxide, sodium ethoxide, sodium hydroxide, or potassium hydroxide, respectively; and the amount of the first basic catalyst is 200 to 500 ppm, and the amount of the second basic catalyst is 300 to 3,000 ppm. 
     In a preferred embodiment, in the process of the cracking reaction, the above synthesis method further includes: adding water to the esterified intermediate, and the water content of the system in the process of the cracking reaction is 10 to 100,000 ppm. Compared with other ranges, limiting the water content of the system in the process of the cracking reaction to the above range is beneficial to improving the cracking rate of the esterified intermediate, thereby contributing to the yield of the oxetane compound. 
     In a preferred embodiment, the first microreactor has a reaction channel having an inner diameter selected from 200 to 10,000 μm, and the second microreactor has a reaction channel having an inner diameter selected from 200 to 10,000 μm. Compared with other ranges, limiting the reaction channel of the first microreactor and the reaction channel of the second microreactor to the above ranges is beneficial to improving the yield of the target product. For example, the first microreactor can have a reaction channel having an inner diameter selected from 200 μm, 500 μm, 1,000 μm, 5,000 μm, or 10,000 μm, and the second microreactor can have a reaction channel having an inner diameter selected from 200 μm, 500 μm, 1,000 μm, 8,000 μm, or 10,000 μm. More preferably, the first microreactor has a reaction channel having an inner diameter selected from 200 to 2,000 μm, and the second microreactor has a reaction channel having an inner diameter selected from 500 to 10,000 μm. 
     In order to further improve the purity of the target product and reduce the energy loss of the synthesis method, preferably, the above synthesis method further includes subjecting the cracked reaction product system to heat exchange in a micro heat exchanger, removing carbon dioxide through a gas-liquid separation device, and then rectificating it, to obtain the desired product. 
     The subject application is further described in detail below with reference to specific examples, which cannot be understood as limiting the claimed scope in the subject application. 
     The microchannel device system used in Examples 1 to 5 was provided by Shanghai Timo Fluid Technology Co., Ltd. (model: Shanghai Timo TMP/53047-32-3/A2000), wherein the first microreactor had a reaction channel having an inner diameter of 1,000 μm, and the second microreactor had a reaction channel having an inner diameter of 8,000 μm. 
     In the examples, the device shown in  FIG.  1    was used to prepare the oxetane compound, and the synthesis method included the following steps: 
     Transesterification section: trimethylolpropane (TMP) and dimethyl carbonate (DMC) were mixed at a certain molar ratio, and a stoichiometric amount of a basic catalyst was added based on the weight of TMP, mixed well, and placed in the raw material storage tank  10  to be preheated; the mixture was fed through the first feeding pump  11  into the first microreactor  20  for transesterification reaction, and remained for certain time, to obtain a reaction product system containing an esterified intermediate; methanol and remaining DMC were removed from the above reaction product system containing an esterified intermediate in the thin-film evaporator  30 , the recovered raw materials were placed in the light end collection tank  50 , and the esterified intermediate was stored in the esterified intermediate storage tank  40 . 
     Cracking section: a basic catalyst was added into the esterified intermediate, and an appropriate amount of water was selectively added and mixed well; then the mixture was fed through the second feeding pump  41  into the second microreactor  60  and remained for certain time to carry out the cracking reaction; after having been cooled through the micro heat exchanger  70 , it was fed into the gas-liquid separation tank  80  to remove carbon dioxide, to obtain a crude product; 
     Product separation: the crude product was fed to the rectification device  90  for rectification separation, to obtain the corresponding product. 
     The process parameters in Examples 1 to 5 were shown in Table 1. 
     
       
         
           
               
               
               
               
               
               
               
             
               
                 TABLE 1 
               
               
                   
               
               
                 Section 
                 Parameter 
                 Example 1 
                 Example 2 
                 Example 3 
                 Example 4 
                 Example 5 
               
               
                   
               
             
            
               
                 Transesteri- 
                 Weight of 
                   402.0 
                   402.0 
                   402.0 
                   402.0 
                   402.0 
               
               
                 fication 
                 TMP, g 
               
               
                   
                 n (TMP):n 
                 1:1.5 
                 1:3 
                 1:3 
                 1:2.25 
                 1:2.25 
               
               
                   
                 (DMC) 
               
               
                   
                 Content of 
                 300 
                 300 
                 300 
                 300 
                 300 
               
               
                   
                 catalyst (NaOH), 
               
               
                   
                 ppm 
               
               
                   
                 Flow rate for the 
                   10.3 
                   15.5 
                   15.5 
                   12.4 
                   12.4 
               
               
                   
                 first feeding pump, 
               
               
                   
                 mL/min 
               
               
                   
                 Reaction 
                 100 
                 120 
                 120 
                 120 
                 120 
               
               
                   
                 temperature, ° C. 
               
               
                   
                 Residence time, 
                  12 
                  15 
                  15 
                  13 
                  13 
               
               
                   
                 min 
               
               
                 Cracking 
                 Water content, 
                 30,000   
                  80 
                  80 
                  80 
                  80 
               
               
                 Reaction 
                 ppm 
               
               
                   
                 Content of 
                 300 
                 3,000   
                 300 
                 300 
                 3,000   
               
               
                   
                 catalyst (KOH), 
               
               
                   
                 ppm 
               
               
                   
                 Flow rate for the 
                    8.2 
                    8.6 
                    8.6 
                    8.3 
                    8.3 
               
               
                   
                 second feeding 
               
               
                   
                 pump, mL/min 
               
               
                   
                 Cracking 
                 300 
                 300 
                 260 
                 260 
                 300 
               
               
                   
                 temperature, ° C. 
               
               
                   
                 Pressure, MPa 
                 3.0 to 3.5 
                 3.0 to 3.5 
                 3.0 to 3.5 
                 3.0 to 3.5 
                 3.0 to 3.5 
               
               
                   
                 Residence time, 
                  6 
                   8 
                   1 
                   1 
                   6 
               
               
                   
                 min 
               
               
                 Product 
                 Total yield, % 
                   92.3 
                   93.4 
                   96.1 
                   95.7 
                   94.0 
               
               
                 Separation 
                 Product 
                 96.4:0.8:2.8 
                 6.1:92.8:1.1 
                 2.5:5.6:91.9 
                 56.3:1.4:42.3 
                 58.4:40.9:0.7 
               
               
                   
                 proportion (%) 
               
               
                   
                 A:B:C 
               
               
                   
               
            
           
         
       
     
     The products in Table 1 have the following structures: 
     Product A: 3-ethyl-3-hydroxymethyloxetane 
     
       
         
         
             
             
         
       
     
     Product B: bis[1-ethyl(3-oxetanyl)methyl]ether 
     
       
         
         
             
             
         
       
     
     Product C: bis[1-ethyl(3-oxetanyl)methyl]carbonate 
     
       
         
         
             
             
         
       
     
     Example 6 
     It differed from Example 1 in that: the reaction temperature of the transesterification reaction was 80° C., and the temperature of the cracking reaction was 300° C. 
     The total yield of products was 83.4%, wherein the proportions (%) of products A, B, and C were 95.7%, 1.2%, and 3.1%, respectively. 
     Example 7 
     It differed from Example 1 in that: the reaction temperature of the transesterification reaction was 160° C., and the temperature of the cracking reaction was 260° C. 
     The total yield of products was 90.8%, wherein the proportions (%) of products A, B, and C were 92.0%, 4.6%, and 3.4%, respectively. 
     Example 8 
     It differed from Example 1 in that: the molar ratio of trimethylolpropane to carbonate ester was 1:1, and the content of the basic catalyst in the transesterification reaction was 800 ppm. 
     The total yield of products was 80.7%, wherein the proportions (%) of products A, B, and C were 94.5%, 3.3%, and 2.2%, respectively. 
     Example 9 
     It differed from Example 1 in that: the molar ratio of trimethylolpropane to carbonate ester was 5:1, and the content of the basic catalyst in the transesterification reaction was 100 ppm. 
     The total yield of products was 84.7%, wherein the proportions (%) of products A, B, and C were 95.1%, 2.9%, and 2.0%, respectively. 
     Example 10 
     It differed from Example 1 in that: the reaction temperature of the transesterification reaction was 50° C., the residence time of the transesterification reaction was 60 min, and the temperature of the cracking reaction was 400° C. 
     The total yield of products was 85.7%, wherein the proportions (%) of products A, B, and C were 98.3%, 1.3%, and 0.4%, respectively. 
     Example 11 
     It differed from Example 1 in that: the reaction temperature of the transesterification reaction was 300° C., the residence time of the transesterification reaction was 1 min, and the temperature of the cracking reaction was 200° C. 
     The total yield of products was 86.2%, wherein the proportions (%) of products A, B, and C were 39.5%, 46.9%, and 13.6%, respectively. 
     Example 12 
     It differed from Example 1 in that: the reaction temperature of the transesterification reaction was 200° C., the residence time of the transesterification reaction was 30 min, and the temperature of the cracking reaction was 150° C. 
     The total yield of products was 96.8%, wherein the proportions (%) of products A, B, and C were 29.3%, 50.1%, and 20.6%, respectively. 
     Example 13 
     It differed from Example 1 in that: the content of the basic catalyst in the transesterification reaction was 50,000 ppm. 
     The total yield of products was 91.3%, wherein the proportions (%) of products A, B, and C were 95.2%, 2.0%, and 2.8%, respectively. 
     Example 14 
     It differed from Example 1 in that: the content of the basic catalyst in the transesterification reaction was 10,000 ppm. 
     The total yield of products was 93.4%, wherein the proportions (%) of products A, B, and C were 96.8%, 1.2%, and 2.0%, respectively. 
     Example 15 
     It differed from Example 1 in that: the content of the basic catalyst in the transesterification reaction was 30,000 ppm. 
     The total yield of products was 91.8%, wherein the proportions (%) of products A, B, and C were 95.3%, 1.6%, and 3.1%, respectively. 
     Example 16 
     It differed from Example 1 in that: the content of the basic catalyst in the transesterification reaction was 8,000 ppm. 
     The total yield of products was 93.1%, wherein the proportions (%) of products A, B, and C were 96.0%, 1.8%, and 2.2%, respectively. 
     Example 17 
     It differed from Example 1 in that: the content of the basic catalyst in the transesterification reaction was 5,000 ppm. 
     The total yield of products was 92.8%, wherein the proportions (%) of products A, B, and C were 96.2%, 1.9%, and 2.3%, respectively. 
     Example 18 
     It differed from Example 1 in that: the first microreactor had a reaction channel having an inner diameter of 100 μm, and the second microreactor had a reaction channel having an inner diameter of 100 μm. 
     The total yield of products was 81.3%, wherein the proportions (%) of products A, B, and C were 95.6%, 1.0%, and 3.4%, respectively. 
     Example 19 
     It differed from Example 1 in that: the first microreactor had a reaction channel having an inner diameter of 10,000 μm, and the second microreactor had a reaction channel having an inner diameter of 10,000 μm. 
     The total yield of products was 91.8%, wherein the proportions (%) of products A, B, and C were 95.5%, 2.0%, and 2.5%, respectively. 
     Example 20 
     It differed from Example 1 in that: the first microreactor had a reaction channel having an inner diameter of 200 μm, and the second microreactor had a reaction channel having an inner diameter of 200 μm. 
     The total yield of products was 90.7%, wherein the proportions (%) of products A, B, and C were 94.9%, 2.1%, and 3.0%, respectively. 
     Example 21 
     It differed from Example 1 in that: the catalyst in the cracking reaction was sodium methoxide and the content thereof was 1,000 ppm, and the water content of the cracking reaction was 100,000 ppm. 
     The total yield of products was 93.5%, wherein the proportions (%) of products A, B, and C were 97.2%, 2.0%, and 0.8%, respectively. 
     Example 22 
     It differed from Example 1 in that: the catalyst in the transesterification reaction was sodium methoxide and the content thereof was 10,000 ppm, the catalyst in the cracking reaction was sodium methoxide and the content thereof was 1,000 ppm, and the water content of the cracking reaction was 100,000 ppm. 
     The total yield of products was 95.8%, wherein the proportions (%) of products A, B, and C were 97.5%, 1.9%, and 0.6%, respectively. 
     Example 23 
     It differed from Example 1 in that: the catalyst in the transesterification reaction was sodium methoxide and the content thereof was 10,000 ppm, the catalyst in the cracking reaction was sodium methoxide and the content thereof was 300 ppm, and the water content of the cracking reaction was 10 ppm. 
     The total yield of products was 96.5%, wherein the proportions (%) of products A, B, and C were 3.5%, 94.6%, and 1.9%, respectively. 
     Example 24 
     It differed from Example 1 in that: the temperature of the cracking reaction was 100° C. 
     The total yield of products was 66.8%, wherein the proportions (%) of products A, B, and C were 3.9%, 1.7%, and 94.4%, respectively. 
     Example 25 
     It differed from Example 1 in that: the temperature of the cracking reaction was 450° C. 
     The total yield of products was 82.9%, wherein the proportions (%) of products A, B, and C were 43.4%, 56.5%, and 0.1%, respectively. 
     Example 26 
     It differed from Example 1 in that: the temperature for transesterification was 30° C. 
     The total yield of products was 78.6%, wherein the proportions (%) of products A, B, and C were 94.1%, 2.4%, and 3.5%, respectively. 
     Example 27 
     It differed from Example 1 in that: the temperature for transesterification was 350° C. 
     The total yield of products was 79.0%, wherein the proportions (%) of products A, B, and C were 94.5%, 2.6%, and 2.9%, respectively. 
     In the Comparative Examples, a conventional reaction device was used to prepare the oxetane compound, and the synthesis method included the following steps: 
     (1) Transesterification section: TMP, DMC, and toluene were charged into a stainless steel stirred tank with rectification tower and condenser, stirred and mixed well, then a catalyst was added; the mixture was heated for reaction; the generated methanol was collected at the top of the tower, until there was no methanol distilled out from the top of the tower; it was continued to be distilled by heating to remove the solvent toluene and remaining DMC, to obtain an esterified intermediate; 
     (2) Cracking section: a basic catalyst was added and an appropriate amount of water was selectively added for cracking at a certain temperature and under negative pressure while distilling, to obtain a product. 
     The process parameters in Comparative Examples 1 to 5 were shown in Table 2. 
     
       
         
           
               
               
               
               
               
               
               
             
               
                 TABLE 2 
               
               
                   
               
               
                   
                   
                 Comparative 
                 Comparative 
                 Comparative 
                 Comparative 
                 Comparative 
               
               
                 Section 
                 Parameter 
                 Example 1 
                 Example 2 
                 Example 3 
                 Example 4 
                 Example 5 
               
               
                   
               
             
            
               
                 Transesteri- 
                 TMP, g 
                 402.0 
                 402.0 
                 402.0 
                 402.0 
                 402.0 
               
               
                 fication 
                 Toluene, g 
                 300.0 
                 300.0 
                 300.0 
                 300.0 
                 300.0 
               
               
                   
                 n (TMP):n 
                 1:1.5 
                 1:3 
                 1:3 
                 1:2.25 
                 1:2.25 
               
               
                   
                 (DMC) 
               
               
                   
                 Content of 
                 300   
                 300   
                 300   
                 300   
                 300   
               
               
                   
                 catalyst (NaOH), 
               
               
                   
                 ppm 
               
               
                   
                 Reaction 
                  80 to 120 
                  80 to 120 
                  80 to 120 
                  80 to 120 
                  80 to 120 
               
               
                   
                 temperature, ° C. 
               
               
                   
                 Reaction time, h 
                 6     
                     8 
                     8 
                     8 
                     8 
               
               
                 Cracking 
                 Water content, 
                 30,000 
                 80  
                 80  
                 80  
                 80  
               
               
                   
                 ppm 
               
               
                   
                 Content of 
                 300   
                 3,000    
                 300   
                 300   
                 3,000    
               
               
                   
                 catalyst (KOH), 
               
               
                   
                 ppm 
               
               
                   
                 Cracking 
                 160 to 200 
                 160 to 260 
                 160 to 190 
                 160 to 200 
                 160 to 260 
               
               
                   
                 temperature, ° C. 
               
               
                   
                 Pressure, MPa 
                 −0.1 
                 −0.1 
                 −0.1 
                 −0.1 
                 −0.1 
               
               
                   
                 Cracking time, h 
                 10  
                 12  
                     8 
                     8 
                 12  
               
               
                 Product 
                 Total yield, % 
                 72.3 
                  67.5 
                  77.4 
                  71.8 
                  66.0 
               
               
                 Separation 
                 Product 
                 89.9:0.7:9.7 
                 4.1:21.7:74.2 
                 5.3:0.2:94.5 
                 52.7:0.3:47.0 
                 52.0:10.6:37.4 
               
               
                   
                 proportion, % 
               
               
                   
                 A:B:C 
               
               
                   
               
            
           
         
       
     
     From the results in the Comparative Examples, it can be seen that the production yield by the conventional tank reactor is lower than that of the microchannel device system, and the selectivity of bis[1-ethyl(3-oxetanyl)methyl]ether is significantly lower than expectation and cannot meet the design requirements for product distribution. 
     Based on the above descriptions, by comparing Examples 1 to 27 and Comparative Examples 1 to 5, it can be seen that the above embodiments of the invention achieve the following technical effects: the synthesis method provided by the subject application can greatly improve the yield of three oxetane compounds, shorten the reaction time, while realizing the co-production of three oxetane compounds. 
     By comparing Examples 1, 6, 7, 10 to 12, and 24 to 27, it can be seen that limiting the temperatures of the transesterification reaction and the cracking reaction to the preferred ranges of the subject application is beneficial to improving the total yield of three oxetane compounds, and can control the proportions of three products by controlling the cracking temperature. 
     By comparing Examples 1, 8, 9, 13 to 17, 21, and 23, it can be seen that limiting the molar ratio of trimethylolpropane to carbonate ester, the content of the basic catalyst used in the transesterification reaction, and the content of the basic catalyst used in the cracking reaction to the preferred ranges of the subject application is beneficial to improving the total yield of three oxetane compounds. 
     By comparing Examples 1, 18, 19, and 20, it can be seen that limiting the inner diameters of the channels of the first and second microreactors to the preferred ranges of the subject application is beneficial to improving the total yield of three oxetane compounds. 
     The above descriptions are merely preferred embodiments of the invention and are not intended to limit the invention. For those skilled in the art, the invention may have various modifications and changes. Any modification, equivalent replacement, and improvement made within the spirit and principle of the invention shall be included within the scope of the invention.