Microchannel reactor and method for synthesizing oxamide by using microchannel reactor

Abstract

The invention relates to the technical field of oxamide synthesis, and provides a microchannel reactor and a method for synthesizing oxamide by using the microchannel reactor. The micro-channel reactor sequentially comprises a feeding area, a reaction area and a discharging area along the flowing direction of reaction materials; the feeding area comprises a main feeding hole; the reaction area comprises an 8-shaped reaction flow channel, and a plurality of segmented feeding holes are formed in the reaction flow channel; the discharging area comprises a discharging opening. According to the micro-channel reactor provided by the invention, full mixing of raw materials can be realized through segmented feeding, the reaction temperature is effectively controlled, and the local temperature is prevented from being too high; when the microchannel reactor provided by the invention is used for synthesizing oxamide, the process is simple, the reaction conditions are mild, efficient conversion of oxalate can be realized in a short time, continuous production of oxamide is realized, and the microchannel reactor is suitable for industrial production.

Description

Technical Field

[0001] The present invention relates to the technical field of oxamide synthesis, and more particularly, to a microchannel reactor and a method for synthesizing oxamide using the microchannel reactor. Background Art

[0002] Oxamide is a high-quality slow-release nitrogen fertilizer and can also be used as a stabilizer for nitrocellulose products, a gas generator in a gas generator, a refrigerant, etc. Currently, the main methods for synthesizing oxamide are: the oxidative hydrolysis method using hydrocyanic acid as a raw material, but hydrocyanic acid is highly toxic, flammable, explosive, volatile, and has a high production cost; the thermal decomposition method using ammonium oxalate or urea oxalate, but the raw material cost is high, the reaction yield is low, and the feasibility of industrial production is poor; the ester aminolysis method using urea and dimethyl oxalate as raw materials, which can co-produce dimethyl carbonate or carbamate, but this process involves multiple-stage reactions, and the temperature and pressure are relatively high, and the reaction time is too long; the aminolysis method of oxamide derivatives, which prepares an intermediate through the oxidative carbonylation of an amine compound and then generates oxamide under the action of a catalyst. The reaction process is complex, the production cost is high, and the oxamide yield is low.

[0003] With the popularization of the technology for synthesizing ethylene glycol from syngas, the technology for producing dimethyl oxalate is mature and the raw materials are abundant. Using dimethyl oxalate as a raw material for aminolysis to obtain oxamide not only expands the product chain of dimethyl oxalate, increases the flexibility of the ethylene glycol plant from syngas, but also reduces the production cost of oxamide, which is conducive to the further popularization and application of oxamide. However, due to the large heat release of the aminolysis reaction of oxalate ester, there is often a problem of high reaction temperature when using this reaction to prepare oxamide; moreover, the existing methods for preparing oxamide by aminolysis of dimethyl oxalate generally also have problems such as long reaction time and inability to carry out continuous reaction.

[0004] CN 110862331B discloses a method for continuously producing oxamide, which gasifies liquid ammonia and dimethyl oxalate and respectively introduces them into an oxamide synthesis reactor, and the reaction temperature reaches 130-160°C and the residence time is 5-180 min. Although this method can continuously obtain oxamide, the process conditions are harsh, high-temperature reaction is required, the energy consumption is high, and it is not conducive to temperature control.

[0005] CN 111153823B discloses a method for preparing oxamide from dimethyl oxalate. Using dimethyl oxalate, methanol and liquid ammonia as raw materials, the synthesis of oxamide is realized under relatively mild conditions, and both the conversion rate of dimethyl oxalate and the yield of oxamide are relatively high. However, this method cannot be continuously produced, and the reaction time is relatively long.

[0006] Therefore, it is very meaningful to develop a method for synthesizing oxamide with mild reaction conditions, high reaction efficiency and continuous production. Summary of the Invention

[0007] The object of the present invention is to provide a microchannel reactor and a method for synthesizing oxamide by using the microchannel reactor, so as to solve the technical problems of high reaction temperature, low reaction efficiency, long reaction time and non - continuous reaction in the prior art.

[0008] To achieve the above object, the technical solution adopted by the present invention is as follows:

[0009] In the first aspect, the present invention provides a microchannel reactor, which sequentially includes a feeding area, a reaction area and a discharging area along the flowing direction of reaction materials; the feeding area includes a main feeding port; the reaction area includes an "8 - shaped" reaction channel, and a plurality of segmented feeding ports are arranged on the reaction channel; the discharging area includes a discharging port.

[0010] By setting the reaction area as an "8 - shaped" reaction channel, the microchannel reactor provided by the present invention can change the flow curve of the reaction materials. The reaction materials are first divided into two streams in the "8 - shaped" reaction channel and then converge in the middle of the "8 - shaped" reaction channel. Through the impact of the two fluids, the sufficient contact reaction of the reaction materials is realized.

[0011] In the present invention, the axial length of the "8 - shaped" reaction channel from the entrance of the reaction area to the middle convergence point and the axial length from the middle convergence point to the outlet of the reaction area may be equal or unequal. Preferably, the lengths of the two are equal or the length of the latter is greater than the length of the former.

[0012] By arranging a plurality of segmented feeding ports on the reaction channel, the microchannel reactor provided by the present invention can, on the one hand, control the distribution of the reaction temperature and avoid too high local temperature, and on the other hand, avoid the concentrated generation of solid products and block the pipeline.

[0013] According to some embodiments of the present invention, at least 3 segmented feeding ports are arranged on the "8 - shaped" reaction channel, and 2 of the segmented feeding ports are respectively arranged on two channels at the positions of 1 / 20 - 1 / 10 of the axial length of the "8 - shaped" reaction channel.

[0014] It should be noted that the axial length of the "8 - shaped" reaction channel refers to the length in the vertical direction from the top to the bottom of the "8 - shaped" reaction channel.

[0015] In the microchannel reactor provided by the present invention, first, 2 segmented feed ports are symmetrically arranged in the first half of the "8-shaped" reaction channel. In addition, at least one segmented feed port is arranged at the channel intersection in the middle of the "8-shaped" reaction channel and / or 2 segmented feed ports are symmetrically arranged in the second half of the "8-shaped" reaction channel. According to actual application needs, one or more groups of 2 symmetrically arranged segmented feed ports can be further added in the first half and / or the second half of the "8-shaped" reaction channel. Therefore, the number of segmented feed ports in the microchannel reactor provided by the present invention can be set to 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, etc. according to the usage requirements.

[0016] The microchannel reactor provided by the present invention has at least 3 segmented feed ports arranged on the "8-shaped" reaction channel, and 2 of the segmented feed ports are respectively arranged on two channels at the 1 / 20 - 1 / 10 of the axial length of the "8-shaped" reaction channel, and 1 segmented feed port is arranged at the intersection of the "8-shaped" reaction channel or at least 2 segmented feed ports are symmetrically arranged in the second half of the "8-shaped" reaction channel. This can give the reactants sufficient contact time and ensure the full progress of the reaction.

[0017] According to some embodiments of the present invention, the reaction zone includes at least one "8-shaped" reaction channel. The reaction zone may include multiple "8-shaped" reaction channels, and the multiple "8-shaped" reaction channels are connected in series or in parallel.

[0018] According to some embodiments of the present invention, the cross-section of the reaction channel is quasi-circular, preferably circular or elliptical.

[0019] According to some embodiments of the present invention, the axial angle between the segmented feed port and the reaction channel along the flow direction of the reaction material is 45 - 90°, preferably 90°. By defining the direction of the segmented feed port, the two streams can collide and contact fully, which is beneficial to the mixing of the materials and thus promotes the progress of the reaction.

[0020] According to some embodiments of the present invention, the inner diameter of the channel in the feed zone is 2 - 10 mm, the inner diameter of the reaction channel is 1 - 6 mm, the inner diameter of the channel in the discharge zone is 3 - 10 mm, and the inner diameter of the segmented feed port is 0.2 - 4 mm.

[0021] According to some embodiments of the present invention, the inner diameter of the channel in the feed zone is larger than the inner diameter of the reaction channel.

[0022] According to some embodiments of the present invention, the inner diameter of the segmented feed port arranged at the channel intersection in the middle of the "8-shaped" reaction channel is 0.1 - 1 mm larger than the inner diameter of other segmented feed ports.

[0023] According to some embodiments of the present invention, a temperature control jacket is provided outside the microchannel reactor. A heating medium or a cooling medium can be introduced into the temperature control jacket for controlling the reaction temperature.

[0024] According to some embodiments of the present invention, the material of the microchannel reactor can be selected from heat-resistant glass, stainless steel, alkali-resistant polymer materials, etc.

[0025] In a second aspect, the present invention provides an application of the microchannel reactor described in the first aspect in the synthesis of oxamide.

[0026] In a third aspect, the present invention provides a method for synthesizing oxamide by using the microchannel reactor described in the first aspect, comprising: introducing an alcohol solution of oxalate into the microchannel reactor through a main feed port, and introducing an alcohol solution of ammonia into the microchannel reactor through a plurality of segmented feed ports respectively; reacting oxalate and ammonia in the microchannel reactor; and discharging the reaction product from a discharge port.

[0027] Since the microchannel reactor uses a microchannel tube as a reaction vessel, it has a very large specific surface area, which can reach several hundred times or even thousands of times that of a stirred tank, so it has excellent heat transfer and mass transfer capabilities, can achieve instantaneous uniform mixing of materials and efficient heat transfer, and is more suitable for application in strongly exothermic reactions. However, the biggest drawback of the microchannel reactor is that the passage of solid materials through the microchannels is restricted. If a large amount of solids are generated during the reaction, the microchannels are extremely prone to blockage, resulting in the inability to continuously carry out production.

[0028] Although the microchannel reactor has certain advantages in strongly exothermic reactions, due to the strong heat release of the ammonolysis reaction of oxalate, it is difficult for existing ordinary microreactors to well solve the problem of high reaction temperature. Moreover, since the reaction product oxamide is a poorly soluble solid, a large amount of solids will be rapidly generated during the ammonolysis reaction of oxalate, which is extremely prone to block the microchannels. Therefore, it is difficult for existing ordinary microchannel reactors to be applied to the ammonolysis of oxalate to produce oxamide.

[0029] In the present invention, the oxalate is prepared as a solution with an alcohol solvent and introduced into the microchannel reactor for reaction. On the one hand, part of the reaction heat can be carried away by the alcohol solvent, which is convenient for temperature control; on the other hand, since the generated oxamide is a poorly soluble solid, the flow of the alcohol solvent is convenient for carrying it out of the reactor. In addition, by means of segmented feeding, it is possible to avoid the local short-time large-scale generation of solid product precipitation in the reaction flow channels of the microchannel reactor, which is convenient for the flow scouring of the alcohol solvent.

[0030] The method for synthesizing oxamide provided by the present invention uses a reaction channel configured in an "8" shape and a microchannel reactor with segmented feed ports arranged on the "8"-shaped reaction channel, enabling the alcohol solution of oxalate to be fed through the main feed port and the alcohol solution of ammonia to be fed in segments through the segmented feed ports on the "8"-shaped reaction channel, effectively solving the problems of locally excessive reaction temperature caused by strong exotherm during the ammonolysis of oxalate to oxamide and blockage of the reaction channel of the microchannel reactor due to the generation of a large amount of solid products in a short time.

[0031] Since the oxamide formed by the ammonolysis of oxalate is insoluble in the alcohol solution, the reaction product is a solid-liquid mixture. To avoid the accumulation of solids, the microchannel reactor is preferably placed vertically, that is, the reaction materials are fed from top to bottom, and by the action of gravity, it is convenient for the oxamide solid to be washed out by the reaction liquid. After using the microchannel reactor for a period of time, an alcohol solvent can be used to flush the reaction channel of the microchannel reactor at a high speed to avoid the deposition of solids.

[0032] The reaction product of the method for synthesizing oxamide provided by the present invention is a solid-liquid mixture, mainly containing oxamide, solvent and ammonia. Under insufficient reaction conditions, it may also contain a small amount of oxalate and / or ammonium oxalate monoester. The reaction product can be filtered, centrifuged and other treatments through separation methods well-known in the art to obtain the crude oxamide, and then refined by washing with methanol or ethanol and dried to obtain the final oxamide product. The filtrate and washing liquid can be recycled and used as the reaction solvent again.

[0033] According to some embodiments of the present invention, the oxalate includes any one of dimethyl oxalate, diethyl oxalate, and methyl ethyl oxalate.

[0034] According to some embodiments of the present invention, the alcohol includes methanol and / or ethanol.

[0035] In the present invention, methanol and ethanol are used as solvents to prepare the solution of oxalate because alcohol solvents have good solubility for oxalate, and the specific alcohol solvent can be selected according to the alkyl type in the structure of the raw material oxalate, which can simplify the subsequent rectification separation process. For example, if the raw material is dimethyl oxalate, methanol can be selected as the solvent; if the raw material is diethyl oxalate, ethanol can be selected as the solvent; if the raw material is methyl ethyl oxalate, methanol and / or ethanol can be selected as the solvent. In addition, methanol and ethanol also have good solubility for ammonia.

[0036] According to some embodiments of the present invention, the concentration of the oxalate in the alcohol solution is 0.08 - 0.63 g / mL, and for example, it can be 0.08 g / mL, 0.10 g / mL, 0.12 g / mL, 0.16 g / mL, 0.24 g / mL, 0.30 g / mL, 0.35 g / mL, 0.40 g / mL, 0.45 g / mL, 0.50 g / mL, 0.56 g / mL, 0.60 g / mL, 0.63 g / mL, etc.

[0037] According to some embodiments of the present invention, the concentration of the ammonia in the alcohol solution is 0.07 - 0.2 g / mL, and for example, it can be 0.07 g / mL, 0.10 g / mL, 0.13 g / mL, 0.15 g / mL, 0.20 g / mL, etc.

[0038] According to some embodiments of the present invention, the residence time of the reaction materials in the "8-shaped" reaction channel is 25 s - 5 min.

[0039] According to some embodiments of the present invention, the feeding flow rate of the alcohol solution of the oxalate is 2 - 15 mL / min, preferably 5 - 10 mL / min. Keeping a relatively high feeding flow rate of the alcohol solution of the oxalate is beneficial for the oxamide to rush out with the alcohol solution and avoid blocking the reaction channel.

[0040] According to some embodiments of the present invention, the reaction temperature is 20 - 60 °C. Increasing the reaction temperature is beneficial for increasing the initial reaction rate. However, since the ammonolysis reaction of the oxalate is a strong exothermic reaction, the reaction temperature should not be too high. As the reaction progresses, it is also necessary to reasonably control the reaction temperature to prevent runaway temperature.

[0041] In the present invention, the influence of the reaction pressure on the reaction is relatively small.

[0042] According to some embodiments of the present invention, the reaction pressure is 0.1 - 1 MPa.

[0043] In the present invention, the theoretical molar ratio of ammonia to oxalate is 2:1, and since the ammonolysis reaction rate of the oxalate is relatively fast, it is sufficient to use ammonia slightly higher than the theoretical molar ratio.

[0044] According to some embodiments of the present invention, the molar ratio of ammonia to oxalate is (2.1 - 4):1.

[0045] The beneficial effects of the present invention are at least as follows:

[0046] The microchannel reactor provided by the present invention can achieve sufficient mixing of raw materials through segmented feeding, effectively control the reaction temperature, and avoid excessive local temperature. When using the microchannel reactor provided by the present invention to synthesize oxamide, the process is simple, the reaction conditions are mild, and high-efficiency conversion of oxalate can be achieved in a relatively short time, realizing continuous production of oxamide, which is suitable for industrial production. Brief Description of the Drawings

[0047] Figure 1 It is a schematic structural diagram of an exemplary microchannel reactor provided by the present invention.

[0048] Among them, 1 - main feed inlet, 2 - first segmented feed inlet, 3 - second segmented feed inlet, 4 - third segmented feed inlet, 5 - fourth segmented feed inlet, 6 - fifth segmented feed inlet, 7 - discharge outlet, 8 - reaction channel, 9 - heat transfer medium, S1 - alcohol solution logistics of oxalate, S2 - alcohol solution logistics of first ammonia, S3 - alcohol solution logistics of second ammonia, S4 - alcohol solution logistics of third ammonia, S5 - alcohol solution logistics of fourth ammonia, S6 - alcohol solution of fifth ammonia, S7 - reaction product logistics, S8 - heat transfer medium inlet logistics, S9 - heat transfer medium outlet logistics. Detailed Embodiments

[0049] In order to make the technical problems to be solved, technical solutions and beneficial effects of the present invention clearer, the following further details the present invention in combination with specific embodiments. It should be understood that the specific embodiments described here are only used to detail the patent and do not limit the protection scope of the present invention in any way.

[0050] Figure 1Exemplarily, a specific structure of the microchannel reactor provided by the present invention is given. Specifically, the microchannel reactor sequentially includes a feeding zone, a reaction zone, and a discharging zone along the flowing direction of the reaction materials; the microchannel reactor has a total of six feeding ports, including the main feeding port 1 in the feeding zone and five segmented feeding ports on the "8-shaped" reaction channel 8 in the reaction zone. Among them, the first segmented feeding port 2 and the second segmented feeding port 3 are arranged at the 1 / 20 of the axial length of the reaction zone, the third segmented feeding port 4 is arranged at the intersection of the "8-shaped" reaction channel at the 1 / 2 of the axial length of the reaction zone, and the fourth segmented feeding port 5 and the fifth segmented feeding port 6 are arranged at the 3 / 4 of the axial length of the reaction zone. The cross-section of the reaction channel is circular. The axial included angle between the 5 feeding ports in the reaction zone and the reaction channel is 90°. The inner diameter of the channel in the feeding zone is 5 mm, the inner diameters of the first segmented feeding port 2 and the second segmented feeding port 3 are 1.2 mm, the inner diameter of the third segmented feeding port 4 is 1.8 mm, the inner diameters of the fourth segmented feeding port 5 and the fifth segmented feeding port 6 are 1 mm, the inner diameter of the "8-shaped" reaction channel 8 is 3 mm, the length of any one of the channels of the "8-shaped" reaction channel (i.e., the length of the channel that the reaction materials pass through from entering the reaction zone to flowing out of the reaction zone) is 45 cm, and the inner diameter of the channel in the discharging zone is 5 mm. An external temperature control jacket is arranged on the microchannel reactor, and water is used as the heat transfer medium in the temperature control jacket.

[0051] When synthesizing oxamide using the above microchannel reactor, the segmented feeding ports generally use methanol solutions of ammonia with the same concentration for feeding. The proportions of the feeding amounts of the methanol solutions of ammonia at the first to fifth segmented feeding ports in the total feeding amount of the methanol solutions of ammonia are 20 - 30%, 20 - 30%, 25 - 50%, 5 - 15%, and 5 - 15% respectively. The feeding proportions at the first and second segmented feeding ports generally remain the same, and the feeding proportions at the fourth and fifth segmented feeding ports generally remain the same.

[0052] The method for synthesizing oxamide by applying the microchannel reactor provided by the present invention will be described in detail below with reference to specific embodiments.

[0053] Unless otherwise defined, the technical terms used in the following embodiments have the same meanings as commonly understood by those skilled in the art to which the present invention belongs. The reagents used in the following embodiments are all conventional biochemical reagents unless otherwise specified; the raw materials, instruments, and equipment used in the following embodiments can all be obtained through market purchase or can be obtained by existing methods; the reagent dosages are all the dosages of reagents in conventional experimental operations unless otherwise specified; the experimental methods are all conventional methods unless otherwise specified.

[0054] Example 1

[0055] Adopt Figure 1 the shown microchannel reactor to synthesize oxamide.

[0056] A 0.16 g / mL dimethyl oxalate methanol solution enters from the main feed inlet 1 at a flow rate of 10 mL / min. A 0.13 g / mL ammonia methanol solution enters from five segmented feed inlets respectively. The flow rates of the first segmented feed inlet 2 and the second segmented feed inlet 3 are 0.90 mL / min respectively. The flow rate of the third segmented feed inlet 4 is 1.80 mL / min. The flow rates of the fourth segmented feed inlet 5 and the fifth segmented feed inlet 6 are 0.45 mL / min respectively. After passing through the microchannel reaction zone, it flows out from the outlet 7. The residence time of the material in the reaction zone is about 30 s. The reaction temperature is 30 °C and the reaction pressure is 0.3 MPa. The obtained paste is separated by centrifugation and washed with methanol to obtain oxamide. The conversion rate of dimethyl oxalate and the yield of oxamide are shown in Table 1.

[0057] Example 2

[0058] Use Figure 1 the shown microchannel reactor to synthesize oxamide.

[0059] A 0.40 g / mL dimethyl oxalate methanol solution enters from the main feed inlet 1 at a flow rate of 8 mL / min. A 0.13 g / mL ammonia methanol solution enters from five segmented feed inlets respectively. The flow rates of the first segmented feed inlet 2 and the second segmented feed inlet 3 are 2.16 mL / min respectively. The flow rate of the third segmented feed inlet 4 is 4.32 mL / min. The flow rates of the fourth segmented feed inlet 5 and the fifth segmented feed inlet 6 are 1.08 mL / min respectively. After passing through the microchannel reaction zone, it flows out from the outlet 7. The residence time of the material in the reaction zone is about 27 s. The reaction temperature is 50 °C and the reaction pressure is 0.5 MPa. The obtained paste is separated by centrifugation and washed with methanol to obtain oxamide. The conversion rate of dimethyl oxalate and the yield of oxamide are shown in Table 1.

[0060] Example 3

[0061] Use Figure 1 the shown microchannel reactor to synthesize oxamide.

[0062] A 0.40 g / mL dimethyl oxalate methanol solution enters from the main feed inlet 1 at a flow rate of 8 mL / min. A 0.13 g / mL ammonia methanol solution enters from five segmented feed inlets respectively. The flow rates of the first segmented feed inlet 2 and the second segmented feed inlet 3 are 2.70 mL / min respectively. The flow rate of the third segmented feed inlet 4 is 4.32 mL / min. The flow rates of the fourth segmented feed inlet 5 and the fifth segmented feed inlet 6 are 0.54 mL / min respectively. After passing through the microchannel reaction zone, it flows out from the outlet 7. The residence time of the material in the reaction zone is about 26 s. The reaction temperature is 50 °C and the reaction pressure is 0.5 MPa. The obtained paste is separated by centrifugation and washed with methanol to obtain oxamide. The conversion rate of dimethyl oxalate and the yield of oxamide are shown in Table 1.

[0063] Example 4

[0064] Use Figure 1 the microchannel reactor shown for the synthesis of oxamide.

[0065] A 0.56 g / mL dimethyl oxalate methanol solution enters from the main feed port 1 at a flow rate of 6 mL / min. A 0.13 g / mL ammonia methanol solution enters from five segmented feed ports respectively. The flow rates of the first segmented feed port 2 and the second segmented feed port 3 are 2.27 mL / min respectively, the flow rate of the third segmented feed port 4 is 4.53 mL / min, and the flow rates of the fourth segmented feed port 5 and the fifth segmented feed port 6 are 1.13 mL / min respectively. After passing through the microchannel reaction zone, it flows out from the discharge port 7. The residence time of the material in the reaction zone is about 32 s, the reaction temperature is 60 °C, and the reaction pressure is 0.5 MPa. The obtained slurry is separated by centrifugation and washed with methanol to obtain oxamide. The conversion rate of dimethyl oxalate and the yield of oxamide are shown in Table 1.

[0066] Example 5

[0067] Use Figure 1 the microchannel reactor shown for the synthesis of oxamide.

[0068] A 0.40 g / mL diethyl oxalate ethanol solution enters from the main feed port 1 at a flow rate of 8 mL / min. A 0.13 g / mL ammonia methanol solution enters from five segmented feed ports respectively. The flow rates of the first segmented feed port 2 and the second segmented feed port 3 are 2.18 mL / min respectively, the flow rate of the third segmented feed port 4 is 3.49 mL / min, and the flow rates of the fourth segmented feed port 5 and the fifth segmented feed port 6 are 0.44 mL / min respectively. After passing through the microchannel reaction zone, it flows out from the discharge port 7. The residence time of the material in the reaction zone is about 28 s, the reaction temperature is 50 °C, and the reaction pressure is 0.5 MPa. The obtained slurry is separated by centrifugation and washed with methanol to obtain oxamide. The conversion rate of dimethyl oxalate and the yield of oxamide are shown in Table 1.

[0069] Example 6

[0070] The microchannel reactor used in this example is Figure 1 basically the same, except that: the "8-shaped" reaction channel 8 in the reaction zone only includes three segmented feed ports, namely the first segmented feed port 2, the second segmented feed port 3 and the third segmented feed port 4. The synthesis of oxamide is carried out in this microchannel reactor.

[0071] A 0.40 g / mL dimethyl oxalate methanol solution enters from the main feed inlet 1 at a flow rate of 8 mL / min. A 0.13 g / mL ammonia methanol solution enters from three segmented feed inlets respectively. The flow rates of the first segmented feed inlet 2 and the second segmented feed inlet 3 are 2.70 mL / min respectively, and the flow rate of the third segmented feed inlet 4 is 5.40 mL / min. After passing through the microchannel reaction zone, it flows out from the outlet 7. The residence time of the material in the reaction zone is about 26 s, the reaction temperature is 50 °C, the reaction pressure is 0.5 MPa. The obtained slurry is separated by centrifugation and washed with methanol to obtain oxamide. The conversion rate of dimethyl oxalate and the yield of oxamide are shown in Table 1.

[0072] Example 7

[0073] The microchannel reactor used in this example is basically the same as Figure 1 but the difference is only that: the "8-shaped" reaction flow channel 8 in the reaction zone only includes two segmented feed inlets, namely the first segmented feed inlet 2 and the second segmented feed inlet 3. The synthesis of oxamide is carried out in this microchannel reactor.

[0074] A 0.40 g / mL dimethyl oxalate methanol solution enters from the main feed inlet 1 at a flow rate of 8 mL / min. A 0.13 g / mL ammonia methanol solution enters from two segmented feed inlets respectively. The flow rates of the first segmented feed inlet 2 and the second segmented feed inlet 3 are both 5.40 mL / min. After passing through the microchannel reaction zone, it flows out from the outlet 7. The residence time of the material in the reaction zone is about 22 s, the reaction temperature is 50 °C, the reaction pressure is 0.5 MPa. The obtained slurry is separated by centrifugation and washed with methanol to obtain oxamide. The conversion rate of dimethyl oxalate and the yield of oxamide are shown in Table 1.

[0075] After reacting for a period of time, the reaction flow channel in the reaction zone becomes blocked, and the local temperature near the first segmented feed inlet 2 and the second segmented feed inlet 3 is too high.

[0076] Comparative Example 1

[0077] 100 mL of a 0.40 g / mL dimethyl oxalate methanol solution reacts with 135 mL of a 0.13 g / mL ammonia methanol solution in a reaction kettle. The reaction temperature is 50 °C, the reaction pressure is atmospheric pressure, and the two are mixed and stirred at high speed for 5 min to obtain oxamide. The conversion rate of dimethyl oxalate and the yield of oxamide are shown in Table 1.

[0078] Comparative Example 2

[0079] The microchannel reactor used in this comparative example has a linear single-channel flow path. There are a total of two feed ports, and the axial angle between the two feed ports is 90°. The inner diameters of the flow paths in the feed zone, reaction zone, and discharge zone are all 5 mm, and the length of the flow path in the reaction zone is 45 cm. A temperature control jacket is provided outside the microchannel reactor, and water is used as the heat transfer medium in the temperature control jacket. The synthesis of oxamide is carried out in this microchannel reactor.

[0080] The 0.40 g / mL dimethyl oxalate methanol solution enters from one of the feed ports at a flow rate of 8 mL / min; the 0.13 g / mL ammonia methanol solution enters from the other feed port at a flow rate of 10.80 mL / min. The residence time of the material in the reaction zone is about 28 s, the reaction temperature is 50 °C, and the reaction pressure is 0.5 MPa. The obtained slurry is separated by centrifugation and washed with methanol to obtain oxamide. The conversion rate of dimethyl oxalate and the yield of oxamide are shown in Table 1.

[0081] After reacting for a period of time, the flow path in the reaction zone of the microchannel reactor becomes blocked, and the local temperature near the inlet is too high.

[0082] Comparative Example 3

[0083] The microchannel reactor used in this comparative example has a linear single-channel flow path. It is provided with one main feed port and three segmented feed ports. The main feed port is set in the feed zone, and the three segmented feed ports are respectively distributed at 1 / 20, 1 / 2, and 3 / 4 of the flow path in the reaction zone. The axial angle between the segmented feed ports and the flow path in the reaction zone is 90°. The inner diameters of the flow paths in the feed zone, reaction zone, and discharge zone are all 5 mm, the inner diameters of the segmented feed ports are all 2 mm, and the length of the flow path in the reaction zone is 45 cm. A temperature control jacket is provided outside the microchannel reactor, and water is used as the heat transfer medium in the temperature control jacket. The synthesis of oxamide is carried out in this microchannel reactor.

[0084] The 0.40 g / mL dimethyl oxalate methanol solution enters from the main feed port at a flow rate of 8 mL / min; the 0.13 g / mL ammonia methanol solution enters from the three segmented feed ports. The flow rate of the first segmented feed port is 5.40 mL / min, the flow rate of the second segmented feed port is 4.32 mL / min, and the flow rate of the third segmented feed port is 1.08 mL / min. The residence time of the material in the reaction zone is about 36 s, the reaction temperature is 50 °C, and the reaction pressure is 0.5 MPa. The obtained slurry is separated by centrifugation and washed with methanol to obtain oxamide. The conversion rate of dimethyl oxalate and the yield of oxamide are shown in Table 1.

[0085] Evaluation of the conversion rate of dimethyl oxalate and the yield of oxamide

[0086] Conversion rate of dimethyl oxalate = (1 - m 1 / m 0 ) × 100%

[0087] Oxamide yield = m 3 / m 4 × 100%

[0088] Wherein,

[0089] m 0 is the feeding mass of dimethyl oxalate per unit time;

[0090] m 1 is the remaining mass of dimethyl oxalate at the reactor outlet per unit time;

[0091] m 3 is the mass of oxamide collected per unit time;

[0092] m 4 is the mass of oxamide that should be collected theoretically per unit time.

[0093] Wherein, the content of dimethyl oxalate is obtained by gas chromatography analysis.

[0094] Table 1 Dimethyl oxalate conversion rate and oxamide yield of each example and comparative example

[0095]

[0096] It should be noted that the above-described embodiments are only used to explain the present invention and do not constitute any limitation to the present invention. The present invention has been described by referring to typical embodiments, but it should be understood that the words used therein are descriptive and explanatory words rather than limiting words. Modifications can be made to the present invention within the scope of the claims of the present invention as stipulated, and the present invention can be revised without departing from the scope and spirit of the present invention. Although the present invention described therein relates to specific methods, materials and embodiments, it does not mean that the present invention is limited to the specific examples disclosed therein. On the contrary, the present invention can be extended to all other methods and applications with the same function.

Claims

1. A microchannel reactor, characterized in that, the microchannel reactor sequentially includes a feeding area, a reaction area and a discharging area along the flowing direction of the reaction materials; the feeding area includes a main feeding port; the reaction area includes an "8-shaped" reaction channel, and a plurality of segmented feeding ports are arranged on the reaction channel; the discharging area includes a discharging port.

2. The microchannel reactor according to claim 1, characterized in that, at least 3 segmented feeding ports are arranged on the "8-shaped" reaction channel, and 2 of the segmented feeding ports are respectively arranged on two channels at 1 / 20 to 1 / 10 of the axial length of the "8-shaped" reaction channel.

3. The microchannel reactor according to claim 1 or 2, characterized in that, the cross-section of the reaction channel is quasi-circular; and / or, the axial angle between the segmented feeding port and the reaction channel along the flowing direction of the reaction materials is 45 to 90°, preferably 90°.

4. The microchannel reactor according to any one of claims 1-3, characterized in that, the inner diameter of the channel in the feeding area is 2 to 10 mm, the inner diameter of the reaction channel is 1 to 6 mm, the inner diameter of the channel in the discharging area is 3 to 10 mm, and the inner diameter of the segmented feeding port is 0.2 to 4 mm.

5. The microchannel reactor according to any one of claims 1-4, characterized in that, a temperature control jacket is arranged outside the microchannel reactor.

6. Application of the microchannel reactor according to any one of claims 1-5 in synthesizing oxamide.

7. A method for synthesizing oxamide by using the microchannel reactor according to any one of claims 1-5, characterized in that, it includes: feeding an alcohol solution of oxalate into the microchannel reactor through the main feeding port, and feeding an alcohol solution of ammonia into the microchannel reactor through a plurality of segmented feeding ports respectively; oxalate and ammonia react in the microchannel reactor; the reaction product is discharged from the discharging port.

8. The method according to claim 7, characterized in that, the oxalate includes any one of dimethyl oxalate, diethyl oxalate, and methyl ethyl oxalate; and / or, the alcohol includes methanol and / or ethanol; and / or, the concentration of the oxalate in the alcohol solution is 0.08 to 0.63 g / mL; and / or, the concentration of the ammonia in the alcohol solution is 0.07 to 0.2 g / mL.

9. The method according to claim 7 or 8, characterized in that, the residence time of the reaction materials in the "8-shaped" reaction channel is 25 s to 5 min; and / or, the feeding flow rate of the alcohol solution of oxalate is 2 to 15 mL / min, preferably 5 to 10 mL / min.

10. The method according to any one of claims 7-9, characterized in that, the reaction temperature is 20 to 60 °C; and / or, the molar ratio of ammonia to oxalate is (2.1 to 4):1.

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