A dimethyl carbonate still residue resource recycling system and method

Abstract

The application discloses a dimethyl carbonate still residue resource recycling system and method, and belongs to the technical field of chemical by-product resource utilization. The system comprises a first-stage jet carbonization unit, a second-stage maturation carbonization unit and a precision separation unit. The application replaces the traditional thin film evaporation process with low-temperature pre-carbonization, and the ester exchange discharge can be directly introduced into the system without concentration after removing trace light components through vacuum flash evaporation; excess CO2 is used as a gas phase carrier gas to carry trace precise feed of atomized soft water, and under the condition of low temperature and low water, the excess CO2 does not have side reactions with sodium methoxide and 1,2-propanediol, the free water content of the system is low, and the carbonization reaction is strengthened through micro-interface; the precision separation unit has the dual functions of precise solid-liquid separation and solid compression drying. The application realizes the overall efficient resource recycling of the still residue under the condition of 65-85 DEG C, normal pressure-0.2 MPaG, with the conversion rate of sodium methoxide being greater than or equal to 98%, low foam in the whole process, no material overflow, effectively avoiding the problems of high-temperature side reactions and evaporator fouling, and realizing the overall efficient resource recycling of the still residue.

Description

Technical Field

[0001] This invention relates to the field of chemical by-product resource utilization technology, specifically to a system and method for the resource recovery of dimethyl carbonate reactor residue. Background Technology

[0002] Dimethyl carbonate (DMC) is an important green chemical intermediate. The mainstream industrial production method is the propylene oxide transesterification process. The transesterification process produces residues, which mainly contain 1,2-propanediol, sodium methoxide catalyst, and trace impurities. It is a strongly alkaline and viscous material with high resource utilization value.

[0003] Currently, the mainstream process for treating reactor residue in the industry is thin-film evaporation concentration followed by high-temperature post-carbonization, which has significant shortcomings: High-temperature concentration causes serious side reactions: In a high-temperature and strong alkaline environment of 100-120℃, 1,2-propanediol is prone to dehydration, polymerization, and discoloration, resulting in quality degradation and significant losses. Evaporators are prone to scaling and clogging: Sodium salts precipitate and adhere to the heating surface at high temperatures, resulting in short operating cycles, frequent cleaning, and high energy consumption. High free water content and high energy consumption: A large amount of water is added at once before carbonization, resulting in a high amount of free water in the system and a large subsequent evaporation load; Poor crystal quality and low separation efficiency: High temperature and high water ratio result in small crystals, high filtration resistance, high filter cake moisture content, and a large amount of propylene glycol entrainment.

[0004] Another niche methanol extraction route for recovering sodium methoxide has problems such as difficulty in separating methanol and propylene glycol, high solvent consumption, high safety risks, and lack of industrialization.

[0005] In summary, existing incineration routes suffer from severe resource waste and significant environmental pressure, while carbonization desalination routes suffer from poor reaction control, poor crystal performance, unreasonable process sequence, and low separation efficiency. Neither can simultaneously achieve efficient recovery, product quality, and long-term stable operation. Therefore, there is an urgent need to develop a system and method for the resource recovery of reactor residues that utilizes low-temperature pre-desalination, replaces thin-film evaporation, enhances reactions through micro-interfaces, provides precise micro-water replenishment, and achieves efficient solid-liquid separation. This system would mitigate the risks of high-temperature side reactions and equipment scaling at the source, enabling high-value recovery of 1,2-propanediol and efficient separation of sodium salts, while simultaneously reducing energy consumption and environmental pressure. Summary of the Invention

[0006] This invention provides a system and method for the resource recovery of dimethyl carbonate (DMC) reactor residue, aiming to overcome the shortcomings of existing technologies such as resource waste from incineration, crude reaction control in carbonization desalination processes, low gas-liquid mixing efficiency, poor crystal filtration performance, unreasonable process sequence, easy equipment scaling, numerous side reactions, and low solid-liquid separation efficiency. This invention replaces traditional thin-film evaporation with low-temperature pre-carbonization, directly treating reactor residue without concentration. It utilizes excess CO2 gas phase water carrying, micro-interface enhancement, precise micro-water replenishment, staged carbonization crystal growth, and precise metal membrane separation as its core technologies to achieve efficient resource recovery of reactor residue. This results in reduced side reactions, increased propylene glycol yield and quality, reduced propylene glycol consumption, unchanged solid content, stable process, no equipment scaling, and long-term operation.

[0007] To achieve the above objectives, the technical solution adopted by the present invention is as follows: A system for the resource recovery of dimethyl carbonate reactor residue is provided, comprising: The primary carbonization unit includes a jet reactor, a first carbonization vessel, a first circulating pump, a circulating heat exchanger, and an atomizing feeder. The discharge end of the jet reactor is connected to the top of the first carbonization vessel, and the bottom of the first carbonization vessel forms an external circulation loop with the feed end of the jet reactor via the first circulating pump and the circulating heat exchanger. The atomizing feeder is located at the top of the first carbonization vessel and is used to carry a small amount of atomized soft water for precise feeding using excess CO2 as a gaseous carrier gas. The strong hygroscopic property of sodium methoxide allows it to preferentially absorb water and generate sodium carbonate under the action of CO2. Under low temperature and low water conditions, excess CO2 does not undergo side reactions with sodium methoxide and 1,2-propanediol, and the system has no large amount of free water. The secondary carbonization unit includes a second carbonization vessel, a stirrer, and a micro-interface CO2 distributor. The discharge end of the primary carbonization unit is connected to the top of the second carbonization vessel. The second carbonization vessel is equipped with a stirrer and a micro-interface CO2 distributor, which is used to enhance gas-liquid contact through micro-interface dispersion, further deepen dealkalization, promote crystal growth, and consume trace amounts of free water. The precision separation unit includes a second feed pump and a filtration and drying device; the bottom of the second carbonization kettle is connected to the feed end of the filtration and drying device via the second feed pump. The filtration and drying device has both precision solid-liquid separation and solid drying functions, with a 1,2-propanediol outlet at the top and a sodium salt outlet at the bottom.

[0008] Furthermore, the atomizing feeder adopts a gas-liquid two-phase atomizing nozzle, using 0.15-0.25 MPaG of excess circulating CO2 in the reactor as the atomizing power, with a droplet size of 10-80 μm, to achieve low-temperature micro-uniform dispersion of soft water.

[0009] Furthermore, the jet reactor is a Venturi jet structure, in which a high-speed jet with negative pressure draws in excess CO2, generating 10-30 μm microbubbles, thereby achieving enhanced mixing at the gas-liquid micro-interface.

[0010] Furthermore, the filtration and desiccation device employs an asymmetric sintered metal membrane to achieve precise solid-liquid separation at the 0.5–2 μm level, with a filtration accuracy of 0.5–2 μm; it is equipped with a nitrogen purging and desiccation assembly to achieve deep solid desiccation; the material is selected from one or more combinations of SS316L, SS317LN, 904L, 321, Ni200, 316Ti, Monel400, Inconel600 / 625, HastalloyB / C22 / C276 / X.

[0011] This invention also provides a method for the resource recovery of dimethyl carbonate reactor residue, comprising the following steps: Direct feeding of transesterification product: After removing trace light components by vacuum flash evaporation, the DMC transesterification product is directly fed into the first carbonization reactor without the need for thin-film evaporation concentration or pretreatment. The reactor residue contains 1,2-propanediol, sodium methoxide and trace impurities. CO2-carrying atomized soft water micro-precision feeding: Excess CO2 is used as a gas phase carrier gas to carry atomized soft water micro-precision feeding. The molar ratio of soft water to sodium methoxide is 1.05 to 1.2. The strong water absorption property of sodium methoxide makes it preferentially absorb water and generate sodium carbonate under the action of CO2. Under low temperature and low water conditions, excess CO2 does not cause side reactions, and the system has no large amount of free water. First-stage injection carbonization: Start external circulation, the liquid at the bottom of the vessel is pulsed into the Venturi injection reactor to draw in excess CO2, and sodium carbonate crystal nuclei are gently generated at 65-75℃, with the foam height controlled within 20%; Secondary aging and carbonization: The primary carbonized material is fed into the second carbonization kettle and heated to 75-80°C. The gas-liquid contact is enhanced by micro-interface dispersion, which further dealkalizes the material and promotes crystal growth while consuming trace amounts of free water. Metal membrane filtration and pressing: The carbonized material is fed into the filtration and pressing device, where it undergoes 0.5-2μm precision solid-liquid separation, followed by deep pressing through nitrogen purging. The filtrate is a 1,2-propanediol mixture that is then processed in the next step, and the filter cake is a high-purity sodium salt.

[0012] Furthermore, the molar ratio of soft water to sodium methoxide is 1.05 to 1.2.

[0013] Furthermore, the total conversion rate of sodium methoxide is ≥98%, and the sodium content of the mother liquor is ≤100ppm and the water content is ≤300ppm.

[0014] Compared with the prior art, the present invention has the following advantages: This invention replaces traditional thin-film evaporation with low-temperature pre-carbonization. The ester exchange product can be directly fed after vacuum flash evaporation, resulting in a short process flow, low equipment investment and energy consumption, and avoiding premature hydrolysis of sodium methoxide and quality degradation of propylene glycol. It uses excess CO2 gas phase to carry water for precise atomization and water replenishment, ensuring a single reaction path and no side reactions under low temperature and low water conditions, resulting in high carbonization efficiency. High-quality crystals are obtained through micro-interface graded carbonization, combined with a precision solid-liquid separation and deep pressing unit, resulting in high product purity and good separation effect. The low-temperature operation throughout the process effectively avoids side reactions and equipment scaling, achieving efficient, stable, and low-cost resource recovery of reactor residues.

[0015] In summary, this invention employs an integrated process of low-temperature pre-carbonization, excess CO2 gas phase carrying water, and precision separation, which solves the pain points of existing technologies such as resource waste, numerous side reactions, easy scaling of equipment, low separation efficiency, and unstable operation. It achieves efficient, stable, and low-cost resource recovery of dimethyl carbonate reactor residue, and has significant economic and environmental value. Attached Figure Description

[0016] Figure 1 This is a schematic diagram of a dimethyl carbonate reactor residue resource recovery system provided in an embodiment of the present invention.

[0017] Explanation of reference numerals in the attached drawings: 11. Jet reactor; 12. First carbonization vessel; 13. First circulating pump; 14. Circulating heat exchanger; 15. Atomizing feeder; 21. Second carbonization vessel; 22. Stirring; 23. Micro-interface CO2 distributor; 31. Second feed pump; 32. Filtering and drying device.

[0018] A. Reactor residue; B. Carbon dioxide; C. Deionized water; D. Gas mist mixed feed; E. First carbonized material; F. Light phase discharge; G. Sodium salt; H. Circulating water inlet; I. Circulating water outlet. Detailed Implementation

[0019] To make the technical problems to be solved, the technical solutions, and the beneficial effects of the present invention clearer, the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the present invention and are not intended to limit the present invention.

[0020] System composition and equipment connection A dimethyl carbonate reactor residue resource recovery system includes a primary carbonization unit, a secondary carbonization unit, and a precision separation unit.

[0021] The primary carbonization unit includes a jet reactor, a first carbonization vessel, a first circulating pump, a circulating heat exchanger, and an atomizing feeder. The discharge end of the jet reactor is connected to the top of the first carbonization vessel, and the bottom of the first carbonization vessel is connected to the feed end of the jet reactor via the first circulating pump and the circulating heat exchanger, forming an external circulation loop. The atomizing feeder is located at the top of the first carbonization vessel and is used to carry atomized soft water in a precise manner by using excess CO2 as a gas phase carrier gas.

[0022] The secondary carbonization unit includes a second carbonization vessel, a stirring device, and a micro-interface CO2 distributor; the discharge end of the first carbonization vessel is connected to the upper part of the second carbonization vessel, and the stirring device and the micro-interface CO2 distributor are installed inside the second carbonization vessel.

[0023] The precision separation unit includes a second feed pump and a filtration and drying device; the bottom of the second carbonization kettle is connected to the feed port of the filtration and drying device via the second feed pump. The filtration and drying device has both precision solid-liquid separation and solid drying functions, with a 1,2-propanediol outlet at the top and a sodium salt outlet at the bottom.

[0024] Key equipment characteristics Atomizing feeder: It adopts a gas-liquid two-phase atomizing nozzle, with 0.15-0.25MPaG excess circulating CO2 in the reactor as the atomizing power, and the droplet size is 10-80μm, so as to realize the low-temperature micro-uniform dispersion feeding of soft water.

[0025] Jet reactor: It has a Venturi jet structure, which uses a high-speed jet with negative pressure to draw in excess CO2 and generate microbubbles of 10-30μm, thereby enhancing the mixing of gas and liquid micro-interface.

[0026] Micro-interface CO2 distributor: enables the uniform dispersion of excess CO2, enhances gas-liquid contact, and promotes uniform crystal growth.

[0027] Filtration and drying device: Employs an asymmetric sintered metal membrane to achieve precise solid-liquid separation at the 0.5–2 μm level, with a filtration accuracy of 0.5–2 μm; equipped with a nitrogen-purged drying assembly to achieve deep solid drying; the material is selected from one or more combinations of SS316L, SS317LN, 904L, 321, Ni200, 316Ti, Monel400, Inconel600 / 625, HastalloyB / C22 / C276 / X to achieve precise solid-liquid separation and filter cake drying, with a filter cake moisture content ≤5%.

[0028] Running method Direct feeding of transesterification product: After removing trace amounts of methanol and low-boiling impurities by vacuum flash evaporation, the DMC transesterification product is directly fed into the first carbonization reactor without the need for thin-film evaporation concentration or pretreatment. The reactor residue contains 1,2-propanediol, sodium methoxide and trace impurities.

[0029] First-stage injection carbonization: Start external circulation and feed soft water with excess CO2 through the atomizing feeder. The molar ratio of soft water to sodium methoxide is 1.05 to 1.2. Control the temperature at 65 to 75°C and the pressure at atmospheric pressure to 0.2 MPaG to gently generate sodium carbonate crystal nuclei. The foam height is controlled within 20%.

[0030] Secondary aging and carbonization: The primary carbonized material enters the second carbonization kettle and is heated to 75-80℃; the stirring and micro-interface CO2 distributor are turned on to deeply dealkalize, promote crystal growth, consume trace amounts of free water, and fully convert sodium methoxide into sodium carbonate.

[0031] Metal membrane filtration and pressing: The carbonized material is fed into the filtration and pressing device, where it undergoes 0.5-2μm precision solid-liquid separation, followed by deep pressing with nitrogen purging. The filtrate is a mixture of 1,2-propanediol, which is discharged from the top and enters the next refining process. After the filter cake is purged and pressed with nitrogen, it is discharged from the bottom sodium salt outlet to obtain high-purity sodium salt. Example

[0032] The material being processed is DMC transesterification reactor residue, containing 72 wt% 1,2-propanediol, 16 wt% sodium methoxide, and other trace impurities, with a processing capacity of 2.5 t / h.

[0033] Operating parameters: Primary carbonization: temperature 70℃, pressure 0.1MPaG, soft water to sodium methoxide molar ratio 1.1, external circulation flow rate 15m³ / h, foam height 15%; Secondary carbonization: temperature 78℃, pressure 0.1MPaG, residence time 2h; Filtration and pressing: Metal membrane material SS316L, filtration accuracy 0.5μm, nitrogen pressure 0.3MPaG purging and pressing.

[0034] Execution result: The total conversion rate of sodium methoxide was 99.2%. 1,2-Propanediol recovery rate: 98.5%; The mother liquor contained 62 ppm sodium and 210 ppm water. The sodium carbonate filter cake had a moisture content of 4.2% and a purity of 98.8%. The evaporator is free of scale and can operate continuously for ≥90 days. Example

[0035] The material being processed is DMC transesterification reactor residue, containing 68 wt% 1,2-propanediol, 18 wt% sodium methoxide, and other trace impurities, with a processing capacity of 3.0 t / h.

[0036] Operating parameters: Primary carbonization: temperature 72℃, pressure 0.12MPaG, soft water to sodium methoxide molar ratio 1.15; Secondary carbonization: temperature 79℃, pressure 0.12MPaG, residence time 2.5h; Filtration and pressing: Metal membrane material SS316L, filtration accuracy 1μm, nitrogen pressure 0.3MPaG purging and pressing.

[0037] Execution result: The total conversion rate of sodium methoxide was 98.8%. 1,2-Propanediol recovery rate: 98.2%; Propylene glycol loss is reduced by 40% compared to traditional post-desalination processes; The evaporator cleaning cycle is extended by 5 times, and energy consumption is reduced by 18%.

[0038] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A dimethyl carbonate reactor residue resource recovery system, characterized in that, include: The primary carbonization unit includes a jet reactor, a first carbonization vessel, a first circulating pump, a circulating heat exchanger, and an atomizing feeder. The discharge end of the jet reactor is connected to the top of the first carbonization vessel, and the bottom of the first carbonization vessel forms an external circulation loop with the feed end of the jet reactor via the first circulating pump and the circulating heat exchanger. The atomizing feeder is located at the top of the first carbonization vessel and is used to carry a small amount of atomized soft water for precise feeding using excess CO2 as a gaseous carrier gas. The strong hygroscopic property of sodium methoxide allows it to preferentially absorb water and generate sodium carbonate under the action of CO2. Under low temperature and low water conditions, excess CO2 does not undergo side reactions with sodium methoxide and 1,2-propanediol, and the system has no large amount of free water. The secondary carbonization unit includes a second carbonization vessel, a stirrer, and a micro-interface CO2 distributor. The discharge end of the primary carbonization unit is connected to the top of the second carbonization vessel. The second carbonization vessel is equipped with a stirrer and a micro-interface CO2 distributor, which is used to enhance gas-liquid contact through micro-interface dispersion, further deepen dealkalization, promote crystal growth, and consume trace amounts of free water. The precision separation unit includes a second feed pump and a filtration and drying device; the bottom of the second carbonization kettle is connected to the feed end of the filtration and drying device via the second feed pump. The filtration and drying device has both precision solid-liquid separation and solid drying functions, with a 1,2-propanediol outlet at the top and a sodium salt outlet at the bottom.

2. The dimethyl carbonate reactor residue resource recovery system as described in claim 1, characterized in that, The atomizing feeder uses a gas-liquid two-phase atomizing nozzle, with an excess circulation of 0.15–0.25 MPaG within the reactor. CO2 is used as the atomization power source, with droplet sizes of 10–80 μm, achieving low-temperature, micro-uniform dispersion of soft water.

3. The dimethyl carbonate reactor residue resource recovery system as described in claim 1, characterized in that, The jet reactor is a Venturi jet structure. A high-speed jet with negative pressure draws in excess CO2, generating 10-30 μm microbubbles, thereby achieving enhanced mixing at the gas-liquid micro-interface.

4. The dimethyl carbonate reactor residue resource recovery system as described in claim 1, characterized in that, The filtration and desiccant device uses an asymmetric sintered metal membrane with a filtration accuracy of 0.5–2 μm to achieve precise solid-liquid separation; it is equipped with a nitrogen purging and desiccant assembly to achieve deep solid desiccant drying; the material is one or more combinations of SS316L, SS317LN, 904L, 321, Ni 200, 316Ti, Monel 400, Inconel 600 / 625, Hastalloy B / C22 / C276 / X.

5. A method for recycling dimethyl carbonate reactor residues according to any one of claims 1 to 4, characterized in that, Includes the following steps: Direct feeding of transesterification discharge: After removing trace light components by vacuum flash evaporation, the DMC transesterification discharge is directly fed into the primary carbonization unit without the need for thin-film evaporation concentration or pretreatment. CO2 vapor-phase water-carrying precision feeding: Excess CO2 is used as a vapor-phase carrier gas to carry a small amount of atomized soft water for precise feeding. The molar ratio of soft water to sodium methoxide is... 1.05~1.2, under low temperature and low water conditions, excess CO2 does not cause side reactions, and the system has a low free water content; First-stage spray carbonization: At 65-75℃, the mixture is enhanced by Venturi spraying to gently generate sodium carbonate crystal nuclei, with the foam height controlled within 20%. Secondary aging and carbonization: At 75-80℃, micro-interface dispersion-enhanced carbonization is carried out to deeply remove alkali and promote crystal growth; Precision separation and pressing: Carbonized materials undergo precision solid-liquid separation + deep solid pressing, with the filtrate being... The feed solution was 1,2-propanediol, and the filter cake was a high-purity sodium salt.

6. The method for resource recovery of dimethyl carbonate reactor residue as described in claim 5, characterized in that, The molar ratio of soft water to sodium methoxide is 1.05 to 1.

2.

7. The method for resource recovery of dimethyl carbonate reactor residue as described in claim 5, characterized in that, The total conversion rate of sodium methoxide is ≥98%, and the sodium content of the mother liquor is ≤100ppm and the water content is ≤300ppm.

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