A carbonation crystallization system and method for sodium methoxide

Abstract

The application discloses a carbonization crystallization system and method of sodium methoxide. The application realizes accurate control of the carbon dioxide gas addition amount in the carbonization process through a tubular crystallizer with a ring plate, so as to control the supersaturation of the carbonization process, obtain uniformly distributed sodium carbonate crystals, avoid fouling caused by fine crystal coalescence, and reduce the equipment footprint. Meanwhile, a thermal decomposition zone is designed to reduce the content of sodium bicarbonate dissolved in propylene glycol, and avoid the blockage caused by the precipitation of sodium bicarbonate in the subsequent rectification process.

Description

Technical Field

[0001] This invention relates to a carbonization crystallization system, and more particularly to a carbonization crystallization system and method for sodium methoxide. Background Technology

[0002] In the transesterification process for producing dimethyl carbonate, sodium methoxide is commonly used as a catalyst. Dimethyl carbonate is synthesized through reactive distillation, with the bottom of the distillation column containing a crude propylene glycol solution containing sodium methoxide. The sodium methoxide needs to be removed to recover the propylene glycol. In industrial-scale plants, the method involves introducing carbon dioxide and water into the crude propylene glycol solution to initiate a carbonation reaction, causing the sodium methoxide to react and produce sodium carbonate and methanol. Sodium carbonate has very low solubility in propylene glycol and precipitates as crystals; this solid is removed by filtration.

[0003] In current practical applications, the carbonization equipment is a batch reactor, in which carbon dioxide is introduced from below the liquid surface. The uniform distribution of gas and the suspension of solids are achieved by stirring. In order to enhance the carbonization effect, two-stage carbonization batch reactors are often connected in series to ensure the complete reaction of sodium methoxide, such as the device provided by patent CN201848238U. However, actual operation revealed many problems with this carbonization system, severely hindering long-term stable production: 1. The carbonization reaction is essentially a crystallization reaction with very high supersaturation. If the stirring effect of the vessel is poor, fine crystals are easily precipitated. These fine crystals easily aggregate and adhere to the stirring paddle and wall surface, forming a scale layer. This requires periodic shutdowns for cleaning. The byproduct allyl alcohol contained in the crude propylene glycol solution is a highly toxic substance, making cleaning extremely difficult. 2. The two-stage carbonization process makes it difficult to accurately add carbon dioxide. The carbonization vessel is large, and it is also difficult to achieve a uniform concentration distribution within the vessel. The precipitated sodium carbonate easily reacts with carbon dioxide and water to form sodium bicarbonate. Sodium bicarbonate has a much higher solubility in propylene glycol, causing a decrease in the efficiency of the subsequent filtration system. When propylene glycol containing sodium bicarbonate enters the distillation column, sodium bicarbonate is extremely unstable when heated, causing sodium carbonate to precipitate, resulting in blockage of the distillation column and production interruption.

[0004] Therefore, designing a carbonization crystallization system and method for sodium methoxide is an urgent problem to be solved in the industry. Summary of the Invention

[0005] To address the aforementioned technical problems, this invention proposes a carbonization crystallization system and method for sodium methoxide. This invention utilizes a tubular crystallizer with an annular plate to precisely control the amount of carbon dioxide gas added during the carbonization process, thereby regulating the supersaturation and obtaining uniformly distributed sodium carbonate crystals. This avoids scaling caused by fine crystal aggregation and reduces equipment footprint. Simultaneously, a thermal decomposition zone is designed to reduce the amount of sodium bicarbonate dissolved in propylene glycol, preventing blockage caused by sodium bicarbonate precipitation in subsequent distillation processes.

[0006] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0007] A carbonization crystallization system for sodium methoxide, the system comprising a tubular crystallizer; the interior of the tubular crystallizer is provided with annular plates 1, 2, 3, 4, and 5 arranged sequentially from front to back, the surface of each annular plate being perpendicular to the axial direction of the tubular crystallizer, each annular plate dividing the inner cavity of the tubular crystallizer into a feeding mixing zone, a nucleation zone 1, a nucleation zone 2, a growth zone 1, a growth zone 2, and a thermal decomposition zone from front to back, wherein the feeding mixing zone is located between the front sealing plate and the annular plate 1 of the tubular crystallizer, and the thermal decomposition zone is located between the annular plate 5 and the rear sealing plate of the tubular crystallizer;

[0008] The upper opening of each annular plate is connected to the air inlet pipe on the tubular crystallizer, and each air inlet pipe is equipped with a flow control valve; online particle size monitoring devices AT1, AT2, AT3, and AT4 are respectively installed on the nucleation zone 1, nucleation zone 2, growth zone 1, and growth zone 2; gas distribution holes are opened on each annular plate.

[0009] A static mixer is provided in the feeding and mixing zone; a hot water jacket is provided on the outside of the pyrolysis zone; a feed inlet is provided on the front sealing plate of the tubular crystallizer and a discharge outlet is provided on the rear sealing plate.

[0010] In a preferred embodiment of the present invention, the length of the tubular crystallizer is 10-30m, wherein the length of the feeding and mixing zone is 0.5-3m, the length of nucleation zone 1 is 1-5m, the length of nucleation zone 2 is 1-3m, the length of growth zone 1 is 2-6m, the length of growth zone 2 is 1-5m, and the length of the thermal decomposition zone is 4.5-8m.

[0011] In a preferred embodiment of the present invention, the inner diameter D1 of the tubular crystallizer is the same as the outer diameter of each annular plate, which is 0.025-0.15m; the inner diameter D2 of each annular plate is 0.01-0.02m.

[0012] In a preferred embodiment of the present invention, the thickness H1 of each annular plate is 0.01-0.015m, and the diameter H2 of the air inlet pipe on the tubular crystallizer is 0.002-0.01m.

[0013] In a preferred embodiment of the present invention, the gas distribution holes on each annular plate are all disposed on the front side plate surface of the annular plate, the opening area is 5-15% of the total area of ​​the front side plate surface, and the diameter of the gas distribution holes is 0.1-1mm.

[0014] In this invention, the static mixer can be any known SV type, SK type, SX type, SH type, or SL type static mixer, and its plate form can be any one or more of corrugated plate, inclined plate, and filter element.

[0015] In a preferred embodiment of the present invention, the sleeve diameter D3 of the hot water jacket is 0.04-0.2m.

[0016] As a preferred embodiment of the present invention, the online particle size monitoring device is selected from a PCM crystallization monitoring system, a real-time online particle analyzer, and an online particle imaging analyzer;

[0017] Preferably, the online particle size monitoring device is positioned from the middle to the rear of each zone to monitor the crystal growth in each zone in real time.

[0018] The present invention also provides a method for sodium methoxide carbonization crystallization using the sodium methoxide carbonization crystallization system described above. Specifically, crude propylene glycol solution and water are introduced into a tubular crystallizer and mixed uniformly in the feed mixing zone. Then, they are introduced into nucleation zone 1, nucleation zone 2, growth zone 1, growth zone 2, and thermal decomposition zone in sequence. At the same time, carbon dioxide is introduced from each gas inlet pipe on the tubular crystallizer and enters the tubular crystallizer through the gas distribution holes on each annular plate. It then contacts and reacts with the mixed solution in a counter-current manner to generate sodium carbonate crystals.

[0019] During the reaction, by adjusting the flow rates of carbon dioxide entering from nucleation zone 1, nucleation zone 2, growth zone 1, growth zone 2, and thermal decomposition zone, the number of sodium carbonate crystals in nucleation zone 1 was made to reach 0.05 × 10⁻⁶. 9 -5×10 9 pcs / m 3 The particle size is 10-30 μm, and the number of sodium carbonate crystals in nucleation region 2 reaches 0.1 × 10⁻⁶. 9 -5×10 9 pcs / m 3 The particle size is 20-50 μm, and the number of sodium carbonate crystals in growth zone 1 reaches 0.1 × 10⁻⁶. 9 -5×10 9 pcs / m 3 The particle size is 80-120 μm, and the number of sodium carbonate crystals in growth zone 2 reaches 0.1 × 10⁻⁶. 9 -5×10 9 pcs / m 3 The particle size is 100-150 μm, and the number of sodium carbonate crystals in the thermal decomposition zone reaches 0.1 × 10⁻⁶. 9 -5×10 9 pcs / m 3The particle size is 120-200μm, and the total carbon dioxide flow rate is (1-1.1):1, which is calculated as the molar ratio of carbon dioxide to sodium methoxide in crude propylene glycol solution. This allows for precise control of the amount of carbon dioxide added and reduces the generation of sodium bicarbonate as a reaction byproduct.

[0020] During the reaction, the temperature in the thermal decomposition zone is controlled at 100-150℃ to allow the sodium bicarbonate generated in the reaction to re-decompose into sodium carbonate, thereby improving the crystallization efficiency. The method of controlling the temperature in the thermal decomposition zone can be jacket heating, and the heating medium can be high-temperature water, hot oil, or steam, etc.

[0021] After the reaction is complete, the mixed slurry is processed from the tubular crystallizer and enters the filtration equipment to remove the sodium carbonate generated by carbonation and obtain a propylene glycol solution; preferably, the filtration equipment is selected from centrifuges, plate and frame filters, and leaf filters.

[0022] In a preferred embodiment of the present invention, the flow rate of the crude propylene glycol solution is 3-45 t / h, the flow rate of water is 1-250 kg / h, and the feed pressure is 1-5 barG.

[0023] Preferably, the carbon dioxide flow rates entering the tubular crystallizer from nucleation zone 1, nucleation zone 2, growth zone 1, growth zone 2, and thermal decomposition zone are 0.01-2 kg / h, 0.1-5 kg / h, 5-160 kg / h, 10-350 kg / h, and 0.3-4.5 kg / h, respectively, and the carbon dioxide feed pressure is 3-10 barG.

[0024] In a preferred embodiment of the present invention, the crude propylene glycol solution contains 90-98 wt% propylene glycol, 0.5-3 wt% sodium methoxide, and the balance being light component impurities, such as one or more of allyl alcohol, dipropylene glycol condensate, propylene glycol methyl ether, and methanol. This crude propylene glycol solution originates from the bottom liquid of the transesterification process for producing dimethyl carbonate.

[0025] By using the system and method provided by this invention to perform carbonization crystallization of sodium methoxide, sodium carbonate crystals with an average crystal size of 120-200 μm can be obtained, and the content of sodium bicarbonate dissolved in the propylene glycol solution is less than 10 ppm.

[0026] The beneficial effects of this invention are as follows:

[0027] (1) The present invention eliminates moving equipment such as stirring and pump, avoiding the uneven distribution of crystal particle size caused by them, simplifying the equipment structure, reducing the risk of scaling, and the resulting sodium carbonate crystals have a uniform particle size distribution and larger size, which is beneficial for filtration.

[0028] (2) The present invention can achieve precise control of the amount of carbon dioxide added, avoid the generation of more sodium bicarbonate due to excessive carbon dioxide addition, and reduce the risk of blockage of the distillation column; at the same time, by designing a thermal decomposition zone, the amount of sodium bicarbonate dissolved in propylene glycol is further reduced, thus avoiding blockage of the subsequent distillation column. Attached Figure Description

[0029] Figure 1 This is a schematic diagram of the overall structure of the carbonization crystallization system provided by the present invention.

[0030] Figure 2 This is a schematic diagram of the longitudinal section structure of the annular plate in the thermal decomposition zone of the carbonization crystallization system.

[0031] Figure 3 This is a schematic diagram of the longitudinal section structure of the annular plate in the thermal decomposition zone of the carbonization crystallization system. Detailed Implementation

[0032] The present invention will be further illustrated below with specific embodiments. These embodiments are merely illustrative and do not limit the scope of the invention.

[0033] Main raw material sources:

[0034] Crude propylene glycol solution 1: Composition: 90 wt% propylene glycol, 2 wt% sodium methoxide, 2 wt% allyl alcohol, and 6 wt% methanol.

[0035] Crude propylene glycol solution 2: Composition: 90 wt% propylene glycol, 1.5 wt% sodium methoxide, 3 wt% allyl alcohol, and 5.5 wt% methanol.

[0036] Crude propylene glycol solution 3: Composition: 95 wt% propylene glycol, 1 wt% sodium methoxide, 1 wt% allyl alcohol, and 3 wt% methanol.

[0037] Crude propylene glycol solution 4: Composition: 92 wt% propylene glycol, 3 wt% sodium methoxide, 0.5 wt% allyl alcohol, and 4.5 wt% methanol.

[0038]

Example 1

[0039] A carbonization crystallization system A for sodium methoxide, the system comprising a tubular crystallizer; the interior of the tubular crystallizer is provided with annular plates 1, 2, 3, 4, and 5 arranged sequentially from front to back, the surface of each annular plate being perpendicular to the axial direction of the tubular crystallizer, each annular plate dividing the inner cavity of the tubular crystallizer into a feeding mixing zone, a nucleation zone 1, a nucleation zone 2, a growth zone 1, a growth zone 2, and a thermal decomposition zone from front to back, wherein the feeding mixing zone is located between the front sealing plate and the annular plate 1 of the tubular crystallizer, and the thermal decomposition zone is located between the annular plate 5 and the rear sealing plate of the tubular crystallizer;

[0040] The upper opening of each annular plate is connected to the air inlet pipe on the tubular crystallizer, and each air inlet pipe is equipped with a flow control valve; online particle size monitoring devices AT1, AT2, AT3, and AT4 are respectively installed on the nucleation zone 1, nucleation zone 2, growth zone 1, and growth zone 2; gas distribution holes are opened on each annular plate.

[0041] A static mixer is provided in the feeding and mixing zone; a hot water jacket is provided on the outside of the pyrolysis zone; a feed inlet is provided on the front sealing plate of the tubular crystallizer and a discharge outlet is provided on the rear sealing plate.

[0042] The tubular crystallizer is 10.5m long, with the feeding and mixing zone being 0.5m long, nucleation zone 1 being 1.2m long, nucleation zone 2 being 1.1m long, growth zone 1 being 2.1m long, growth zone 2 being 1m long, and thermal decomposition zone being 4.6m long.

[0043] The inner diameter D1 of the tubular crystallizer is the same as the outer diameter of each annular plate, which is 0.025m; the inner diameter D2 of each annular plate is 0.01m.

[0044] The thickness H1 of each annular plate is 0.01m, and the diameter H2 of the air inlet pipe on the tubular crystallizer is 0.002m.

[0045] The gas distribution holes on each annular plate are all located on the front side of the annular plate, with an opening area of ​​5% of the total area of ​​the front side plate and a hole diameter of 0.2 mm.

[0046] The static mixer is an SV-type static mixer.

[0047] The diameter D3 of the hot water jacket is 0.04m.

[0048] The online particle size monitoring device is a PCM crystallization monitoring system; the monitoring position of the online particle size monitoring device is the middle and rear part of each corresponding zone, so as to monitor the crystal growth in each zone in real time.

[0049]

Example 2

[0050] A sodium methoxide carbonization crystallization system B has a basic system structure as in Example 1, except that the tubular crystallizer is 14.9m long, with the feed mixing zone being 1m long, nucleation zone 1 being 1.8m long, nucleation zone 2 being 1.5m long, growth zone 1 being 2.8m long, growth zone 2 being 2m long, and thermal decomposition zone being 5.8m long.

[0051] The inner diameter D1 of the tubular crystallizer is the same as the outer diameter of each annular plate, which is 0.04m; the inner diameter D2 of each annular plate is 0.012m.

[0052] The thickness H1 of each annular plate is 0.012m, and the diameter H2 of the air inlet pipe on the tubular crystallizer is 0.003m.

[0053] The gas distribution holes on each annular plate are all located on the front side of the annular plate, with an opening area of ​​8% of the total area of ​​the front side plate and a hole diameter of 0.25 mm.

[0054] The static mixer is an SV-type static mixer.

[0055] The diameter D3 of the hot water jacket is 0.05m.

[0056] The online particle size monitoring device is a real-time online particle analyzer; the monitoring position of the online particle size monitoring device is the middle and rear part of each corresponding zone, so as to monitor the crystal growth in each zone in real time.

[0057]

Example 3

[0058] A sodium methoxide carbonization crystallization system C has a basic system structure as in Example 1, except that the tubular crystallizer is 21.3m long, with the feed mixing zone being 1.5m long, nucleation zone 1 being 2.5m long, nucleation zone 2 being 2.8m long, growth zone 1 being 3.8m long, growth zone 2 being 3.5m long, and thermal decomposition zone being 7.2m long.

[0059] The inner diameter D1 of the tubular crystallizer is the same as the outer diameter of each annular plate, which is 0.05m; the inner diameter D2 of each annular plate is 0.018m.

[0060] The thickness H1 of each annular plate is 0.012m, and the diameter H2 of the air inlet pipe on the tubular crystallizer is 0.004m.

[0061] The gas distribution holes on each annular plate are all located on the front side of the annular plate, with an opening area of ​​12% of the total area of ​​the front side plate and a hole diameter of 0.25 mm.

[0062] The static mixer is an SV-type static mixer.

[0063] The diameter D3 of the hot water jacket is 0.08m.

[0064] The online particle size monitoring device is a real-time online particle analyzer; the monitoring position of the online particle size monitoring device is the middle and rear part of each corresponding zone, so as to monitor the crystal growth in each zone in real time.

[0065]

Example 4

[0066] A sodium methoxide carbonization crystallization system D has a basic system structure as in Example 1, except that the tubular crystallizer is 29.2m long, with the feed mixing zone being 2.8m long, nucleation zone 1 being 4.9m long, nucleation zone 2 being 3m long, growth zone 1 being 5.8m long, growth zone 2 being 4.7m long, and thermal decomposition zone being 8m long.

[0067] The inner diameter D1 of the tubular crystallizer is the same as the outer diameter of each annular plate, which is 0.15m; the inner diameter D2 of each annular plate is 0.02m.

[0068] The thickness H1 of each annular plate is 0.015m, and the diameter H2 of the gas inlet pipe on the tubular crystallizer is 0.005m. The gas distribution holes on each annular plate are all located on the front side of the annular plate, with an opening area of ​​15% of the total area of ​​the front side plate, and the diameter of the gas distribution holes is 0.28mm.

[0069] The static mixer is an SV-type static mixer.

[0070] The diameter D3 of the hot water jacket is 0.2m.

[0071] The online particle size monitoring device is a real-time online particle analyzer; the monitoring position of the online particle size monitoring device is the middle and rear part of each corresponding zone, so as to monitor the crystal growth in each zone in real time.

[0072]

Example 5

[0073] Sodium methoxide was carbonized using the carbonization crystallization system A provided in Example 1, specifically as follows:

[0074] Crude propylene glycol solution 1 and water were introduced into a tubular crystallizer at flow rates of 3 t / h and 10 kg / h, respectively, with the two streams having the same feed pressure of 3 barG. The carbon dioxide inlet pressure was 5 barG. The carbon dioxide flow rate in nucleation zone 1 was 0.05 kg / h. The average particle size of sodium carbonate crystals in nucleation zone 1 was found to be 20 micrometers, and the number of crystals reached 0.55 × 10⁻⁶. 9 pcs / m 3 The carbon dioxide flow rate in nucleation zone 2 was 0.15 kg / h. The average particle size of sodium carbonate crystals in nucleation zone 2 was 30 micrometers, and the number of crystals reached 0.69 × 10⁻⁶. 9 pcs / m 3 The carbon dioxide flow rate in growth zone 1 was 7.05 kg / h. The average particle size of sodium carbonate crystals in growth zone 1 was 100 micrometers, and the number of crystals reached 0.69 × 10⁻⁶. 9 pcs / m 3 The carbon dioxide flow rate in growth zone 2 was 12.63 kg / h. The average particle size of sodium carbonate crystals in growth zone 2 was 140 μm, and the number of crystals reached 0.69 × 10⁻⁶.9 pcs / m 3 The slurry. The carbon dioxide flow rate in the thermal decomposition zone was 4.57 kg / h. The average particle size of sodium carbonate crystals in the thermal decomposition zone was 150 micrometers, and the number of crystals reached 0.69 × 10⁻⁶. 9 pcs / m 3 The temperature in the thermal decomposition zone of the slurry is controlled at 120℃.

[0075] The slurry from the tubular crystallizer was fed into a centrifuge, yielding a filtrate with a flow rate of 2975.6 kg / h and sodium carbonate crystals (particle size 150 μm) with a flow rate of 58.86 kg / h. The composition of the filtrate was analyzed as follows: propylene glycol 90.74 wt%, methanol 7.25 wt%, allyl alcohol 2.01 wt%, and sodium bicarbonate 100 ppm.

[0076]

Example 6

[0077] The carbonization of sodium methoxide was carried out using the carbonization crystallization system B provided in Example 2, specifically as follows:

[0078] Crude propylene glycol solution 1 and water were introduced into the tubular crystallizer at flow rates of 7.7 t / h and 19.3 kg / h, respectively, with the same feed pressure of 3.5 barG for both streams. The carbon dioxide inlet pressure was 6 barG. The carbon dioxide flow rate in nucleation zone 1 was 0.16 kg / h. The average particle size of sodium carbonate crystals in nucleation zone 1 was found to be 25 micrometers, and the number of crystals reached 1.25 × 10⁻⁶. 9 pcs / m 3 The carbon dioxide flow rate in nucleation zone 2 was 0.26 kg / h. The average particle size of sodium carbonate crystals in nucleation zone 2 was 32 micrometers, and the number of crystals reached 1.56 × 10⁻⁶. 9 pcs / m 3 The carbon dioxide flow rate in growth zone 1 was 14.21 kg / h. The average particle size of sodium carbonate crystals in growth zone 1 was 105 μm, and the number of crystals reached 1.56 × 10⁻⁶. 9 pcs / m 3 The carbon dioxide flow rate in growth zone 2 was 18.58 kg / h. The average particle size of sodium carbonate crystals in growth zone 2 was 138 μm, and the number of crystals reached 1.56 × 10⁻⁶. 9 pcs / m 3 The slurry. The carbon dioxide flow rate in the thermal decomposition zone was 13.84 kg / h. The average particle size of sodium carbonate crystals in the thermal decomposition zone was 155 micrometers, and the number of crystals reached 1.56 × 10⁻⁶. 9 pcs / m 3 The temperature in the thermal decomposition zone of the slurry is controlled at 125℃.

[0079] The slurry from the tubular crystallizer was fed into a centrifuge, yielding filtrate with a flow rate of 7653 kg / h and sodium carbonate crystals (particle size 155 μm) with a flow rate of 113.3 kg / h. The composition of the filtrate was analyzed as follows: propylene glycol 90.55 wt%, methanol 6.43 wt%, allyl alcohol 3 wt%, and sodium bicarbonate 120 ppm.

[0080]

Example 7

[0081] Sodium methoxide was carbonized using the carbonization crystallization system C provided in Example 3, specifically as follows:

[0082] Crude propylene glycol solution 1 and water were introduced into the tubular crystallizer at flow rates of 11.3 t / h and 19.3 kg / h, respectively, with the same feed pressure of 3.5 barG for both streams. The carbon dioxide inlet pressure was 5.5 barG. The carbon dioxide flow rate in nucleation zone 1 was 0.11 kg / h. The average particle size of sodium carbonate crystals in nucleation zone 1 was measured to be 22 micrometers, and the number of crystals reached 8.32 × 10⁻⁶. 8 pcs / m 3 The carbon dioxide flow rate in nucleation zone 2 was 0.38 kg / h. The average particle size of sodium carbonate crystals in nucleation zone 2 was 34 micrometers, and the number of crystals reached 1.04 × 10⁻⁶. 9 pcs / m 3 The carbon dioxide flow rate in growth zone 1 was 11.15 kg / h. The average particle size of sodium carbonate crystals in growth zone 1 was 98 micrometers, and the number of crystals reached 1.04 × 10⁻⁶. 9 pcs / m 3 The carbon dioxide flow rate in growth zone 2 was 23.76 kg / h. The average particle size of sodium carbonate crystals in growth zone 2 was 142 μm, and the number of crystals reached 1.04 × 10⁻⁶. 9 pcs / m 3 The slurry. The carbon dioxide flow rate in the thermal decomposition zone was 8.88 kg / h. The average particle size of sodium carbonate crystals in the thermal decomposition zone was 153 micrometers, and the number of crystals reached 1.04 × 10⁻⁶. 9 pcs / m 3 The temperature in the thermal decomposition zone of the slurry is controlled at 130℃.

[0083] The slurry from the tubular crystallizer was fed into a centrifuge, yielding filtrate with a flow rate of 11254 kg / h and sodium carbonate crystals (particle size 153 μm) with a flow rate of 110.85 kg / h. The composition of the filtrate was analyzed as follows: propylene glycol 95.39 wt%, methanol 3.61 wt%, allyl alcohol 1 wt%, and sodium bicarbonate 90 ppm.

[0084]

Example 8

[0085] Sodium methoxide was carbonized using the carbonization crystallization system D provided in Example 4, specifically as follows:

[0086] Crude propylene glycol solution 1 and water were introduced into the tubular crystallizer at flow rates of 45 t / h and 225.09 kg / h, respectively, with the two streams having the same feed pressure of 3 barG. The carbon dioxide inlet pressure was 6 barG. The carbon dioxide flow rate in nucleation zone 1 was 1.21 kg / h. The average particle size of sodium carbonate crystals in nucleation zone 1 was measured to be 21 micrometers, and the number of crystals reached 2.75 × 10⁻⁶. 9 pcs / m 3 The carbon dioxide flow rate in nucleation zone 2 was 4.65 kg / h. The average particle size of sodium carbonate crystals in nucleation zone 2 was 33 micrometers, and the number of crystals reached 3.44 × 10⁻⁶. 9 pcs / m 3 The carbon dioxide flow rate in growth zone 1 was 157.07 kg / h. The average particle size of sodium carbonate crystals in growth zone 1 was 100 micrometers, and the number of crystals reached 3.44 × 10⁻⁶. 9 pcs / m 3 The carbon dioxide flow rate in growth zone 2 was 303.58 kg / h. The average particle size of sodium carbonate crystals in growth zone 2 was 142 micrometers, and the number of crystals reached 3.44 × 10⁻⁶. 9 pcs / m 3 The slurry. The carbon dioxide flow rate in the thermal decomposition zone was 83.37 kg / h. The average particle size of sodium carbonate crystals in the thermal decomposition zone was 150 micrometers, and the number of crystals reached 3.44 × 10⁻⁶. 9 pcs / m 3 The temperature in the thermal decomposition zone of the slurry is controlled at 128℃.

[0087] The slurry from the tubular crystallizer was fed into a centrifuge, yielding a filtrate with a flow rate of 44450.7 kg / h and sodium carbonate crystals (particle size 150 μm) with a flow rate of 1324.27 kg / h. The composition of the filtrate was analyzed as follows: propylene glycol 93.14 wt%, methanol 6.36 wt%, allyl alcohol 0.5 wt%, and sodium bicarbonate 80 ppm.

[0088] Comparative Example 1

[0089] Sodium methoxide was carbonized and crystallized using essentially the same method as in Example 5, except that the temperature in the thermal decomposition zone was not adjusted. The slurry from the tubular crystallizer was centrifuged to obtain filtrate with a flow rate of 2985 kg / h and sodium carbonate crystals (particle size 150 μm) with a flow rate of 52.97 kg / h. The composition of the filtrate was analyzed as follows: propylene glycol 90.45 wt%, methanol 7.22 wt%, allyl alcohol 2 wt%, and sodium bicarbonate 0.3 wt%.

[0090] Comparative Example 2

[0091] Sodium methoxide was carbonized and crystallized using a method essentially the same as in Example 5, except that the temperature in the thermal decomposition zone was not adjusted, and carbon dioxide was introduced into the tubular crystallizer at the same flow rate (4.89 kg / h) through the inlet pipes corresponding to the annular plates 1-5. The particle size of sodium carbonate crystals generated in each zone was no longer controlled.

[0092] The slurry from the tubular crystallizer was fed into a centrifuge, yielding a filtrate with a flow rate of 3022.2 kg / h and sodium carbonate crystals (80 μm in diameter) with a flow rate of 29.43 kg / h. The composition of the filtrate was analyzed as follows: propylene glycol 89.3 wt%, methanol 7.13 wt%, allyl alcohol 2 wt%, and sodium bicarbonate 1.5 wt%.

[0093] Comparative Example 3

[0094] Sodium methoxide was carbonized and crystallized using the same total feed rates of crude propylene glycol solution 1, water, and carbon dioxide as in Example 5, the only difference being that the crystallizer was a traditional two-stage, series-connected crystallizer with stirring. Each stage of the crystallizer was 5m in size. 3 The reactor is 1.4m in diameter and 2.8m in height, and is equipped with an agitator and a gas distribution device. The agitator consists of three layers of impellers, each spaced 900mm apart. The impellers are three-bladed, with a blade diameter of 700mm, and the agitation speed is 120rpm. The gas distribution device is a venting ring, located 300mm below the bottom of the lowest impeller. The venting ring has an outer diameter of 900mm, a ring tube diameter of 15mm, and 10 orifices with an 8mm diameter, all facing downwards. Crude propylene glycol solution 1 (flow rate 3t / h) and water (flow rate 10kg / h) are fed into the first-stage crystallizer and mixed with carbon dioxide before being pumped to the second-stage crystallizer for further reaction. The carbon dioxide flow rate in each crystallizer is 12kg / h.

[0095] The slurry from the second-stage crystallizer was fed into a centrifuge, yielding a filtrate with a flow rate of 2982.91 kg / h and sodium carbonate crystals (particle size 75 μm) with a flow rate of 41.2 kg / h. The composition of the filtrate was analyzed as follows: propylene glycol 90.5 wt%, methanol 6.87 wt%, allyl alcohol 2 wt%, and sodium methoxide 0.6%.

[0096] Comparative Example 4

[0097] Sodium methoxide was carbonized and crystallized using a crystallizer and method basically the same as in Comparative Example 3. The only difference was that the carbon dioxide gas flow rate of each crystallizer was changed to 50 kg / h, and the number of openings on the gas distribution device was adjusted to 30.

[0098] The slurry from the second-stage crystallizer was fed into a centrifuge, yielding a filtrate with a flow rate of 3012.9 kg / h and sodium carbonate crystals (60 μm in diameter) with a flow rate of 35.3 kg / h. The composition of the filtrate was analyzed as follows: propylene glycol 89.6 wt%, methanol 7.16 wt%, allyl alcohol 2 wt%, and sodium bicarbonate 1.24%.

[0099] The above description is only a preferred embodiment of the present invention. It should be noted that those skilled in the art can make several improvements and additions without departing from the method of the present invention, and these improvements and additions should also be considered within the scope of protection of the present invention.

Claims

1. A carbonization crystallization system for sodium methoxide, characterized in that, The system includes a tubular crystallizer; inside the tubular crystallizer, annular plates 1, 2, 3, 4, and 5 are arranged sequentially from front to back. The surface of each annular plate is perpendicular to the axis of the tubular crystallizer. Each annular plate divides the inner cavity of the tubular crystallizer into a feeding mixing zone, a nucleation zone 1, a nucleation zone 2, a growth zone 1, a growth zone 2, and a thermal decomposition zone from front to back. The feeding mixing zone is located between the front sealing plate and the annular plate 1 of the tubular crystallizer, and the thermal decomposition zone is located between the annular plate 5 and the rear sealing plate of the tubular crystallizer. The upper opening of each annular plate is connected to the air inlet pipe on the tubular crystallizer, and each air inlet pipe is equipped with a flow control valve; online particle size monitoring devices AT1, AT2, AT3, and AT4 are respectively installed on the nucleation zone 1, nucleation zone 2, growth zone 1, and growth zone 2; gas distribution holes are opened on each annular plate. A static mixer is provided in the feeding and mixing zone; a hot water jacket is provided on the outside of the pyrolysis zone; a feed inlet is provided on the front sealing plate of the tubular crystallizer and a discharge outlet is provided on the rear sealing plate.

2. The sodium methoxide carbonization crystallization system according to claim 1, characterized in that, The tubular crystallizer has a length of 10-30m, wherein the feeding and mixing zone is 0.5-3m long, nucleation zone 1 is 1-5m long, nucleation zone 2 is 1-3m long, growth zone 1 is 2-6m long, growth zone 2 is 1-5m long, and thermal decomposition zone is 4.5-8m long.

3. The sodium methoxide carbonization crystallization system according to claim 2, characterized in that, The inner diameter D1 of the tubular crystallizer is the same as the outer diameter of each annular plate, which is 0.025-0.15m; the inner diameter D2 of each annular plate is 0.01-0.02m.

4. The carbonization crystallization system for sodium methoxide according to any one of claims 1-3, characterized in that, The thickness H1 of each annular plate is 0.01-0.015m, and the diameter H2 of the air inlet pipe on the tubular crystallizer is 0.002-0.01m.

5. The sodium methoxide carbonization crystallization system according to any one of claims 1-3, characterized in that, The gas distribution holes on each annular plate are all located on the front side of the annular plate, with an opening area of ​​5-15% of the total area of ​​the front side plate and a hole diameter of 0.1-1mm.

6. The carbonization crystallization system for sodium methoxide according to any one of claims 1-3, characterized in that, The diameter D3 of the hot water jacket is 0.04-0.2m.

7. The sodium methoxide carbonization crystallization system according to any one of claims 1-3, characterized in that, The online particle size monitoring equipment is selected from PCM crystallization monitoring system, real-time online particle analyzer, and online particle imaging analyzer.

8. The sodium methoxide carbonization crystallization system according to claim 7, characterized in that, The online particle size monitoring device is positioned from the middle to the rear of each zone to monitor the crystal growth in each zone in real time.

9. A method for performing sodium methoxide carbonization crystallization using the sodium methoxide carbonization crystallization system according to any one of claims 1-8, characterized in that, The crude propylene glycol solution and water are fed into the tubular crystallizer and mixed uniformly in the feed mixing zone. Then, they are fed into the nucleation zone 1, nucleation zone 2, growth zone 1, growth zone 2, and thermal decomposition zone in sequence. At the same time, carbon dioxide is introduced from each gas inlet pipe on the tubular crystallizer and enters the tubular crystallizer through the gas distribution holes on each annular plate. It then contacts and reacts with the mixed solution in the opposite direction to generate sodium carbonate crystals. During the reaction, by adjusting the flow rates of carbon dioxide entering from nucleation zone 1, nucleation zone 2, growth zone 1, growth zone 2, and thermal decomposition zone, the number of sodium carbonate crystals in nucleation zone 1 was made to reach 0.05 × 10⁻⁶. 9 -5×10 9 pcs / m 3 The particle size is 10-30 μm, and the number of sodium carbonate crystals in nucleation region 2 reaches 0.1 × 10⁻⁶. 9 -5×10 9 pcs / m 3 The particle size is 20-50 μm, and the number of sodium carbonate crystals in growth zone 1 reaches 0.1 × 10⁻⁶. 9 -5×10 9 pcs / m 3 The particle size is 80-120 μm, and the number of sodium carbonate crystals in growth zone 2 reaches 0.1 × 10⁻⁶. 9 -5×10 9 pcs / m 3 The particle size is 100-150 μm, and the number of sodium carbonate crystals in the thermal decomposition zone reaches 0.1 × 10⁻⁶. 9 -5×10 9 pcs / m 3 The particle size is 120-200μm, and the total carbon dioxide flow rate is (1-1.1):1, which is calculated as the molar ratio of carbon dioxide to sodium methoxide in crude propylene glycol solution. This allows for precise control of the amount of carbon dioxide added and reduces the generation of sodium bicarbonate as a reaction byproduct. During the reaction, the temperature in the thermal decomposition zone is controlled at 100-150℃ to allow the sodium bicarbonate generated in the reaction to re-decompose into sodium carbonate, thereby improving the crystallization efficiency. After the reaction is complete, the mixed slurry is processed from the tubular crystallizer and enters the filtration equipment to remove the sodium carbonate generated by carbonation, and a propylene glycol solution is obtained.

10. The method for sodium methoxide carbonization crystallization according to claim 9, characterized in that, The filtration equipment is selected from centrifuges, plate and frame filters, and leaf filters.

11. The method for sodium methoxide carbonization crystallization according to claim 9, characterized in that, The flow rate of the crude propylene glycol solution is 3-45 t / h, the flow rate of water is 1-250 kg / h, and the feed pressure is 1-5 barG.

12. The method for sodium methoxide carbonization crystallization according to claim 11, characterized in that, The carbon dioxide flow rates entering the tubular crystallizer from nucleation zone 1, nucleation zone 2, growth zone 1, growth zone 2, and thermal decomposition zone are 0.01-2 kg / h, 0.1-5 kg / h, 5-160 kg / h, 10-350 kg / h, and 0.3-4.5 kg / h, respectively, and the carbon dioxide feed pressure is 3-10 barG for all zones.

13. The method for sodium methoxide carbonization crystallization according to any one of claims 9-12, characterized in that, The crude propylene glycol solution contains 90-98 wt% propylene glycol, 0.5-3 wt% sodium methoxide, and the balance being light component impurities.

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