A method and system for pre-separation of dimethyl oxalate

Abstract

The application provides a pre-separation method and system of dimethyl oxalate, which realizes pre-separation of DMO in a CO ester synthesis reaction product by multiple cooling, step-by-step liquid separation of the reaction product and fractional distillation of the DMO solution. Pre-separation of DMO from the synthesis reaction product can greatly reduce the DMO concentration in the reaction product in subsequent separation processes, reduce the energy consumption of subsequent units, and avoid crystallization and plugging of equipment or pipelines when the DMO is cooled to a lower temperature in subsequent separation processes.

Description

Technical Field

[0001] This invention relates to the field of separation technology of reaction products in chemical processes, and specifically to a pre-separation method and system for dimethyl oxalate. Background Technology

[0002] The outlet of a CO esterification synthesis reactor is a complex mixture, which typically requires a series of steps, including absorption, desorption, and distillation, to separate and purify the main product and by-products. Dimethyl oxalate (DMO) is widely present in the CO esterification synthesis reaction products. DMO has a high boiling point (163.5℃ at 760mmHg) and is prone to crystallization (melting point 51-55℃), causing equipment or pipeline blockage. Furthermore, the removal process of DMO from the reaction products significantly impacts the energy consumption and reliable operation of the product separation and purification system.

[0003] Chinese Patent 201310339767.2 discloses a method and apparatus for separating products from syngas-to-ethylene glycol, comprising: 1) the syngas-to-ethylene glycol product enters a fractionation column to obtain a light component, a mixture of methyl glycolate and dimethyl oxalate, and a heavy component; 2) the light component enters a partitioned wall distillation column, with methanol collected at the top and an ethanol solution containing a small amount of water collected from the side stream; 3) the mixture containing methyl glycolate and dimethyl oxalate enters a conventional distillation column, with methyl glycolate collected at the top and dimethyl oxalate collected at the bottom; 4) the heavy component enters a scraped-plate molecular evaporator, with ethylene glycol collected from the inner wall and a mixture of 1,2-propanediol and 1,2-butanediol collected from the outer wall, part of which is returned to the scraped-plate molecular evaporator and part of the mixture enters a scraped-plate molecular evaporator; 5) 1,2-propanediol is collected from the inner wall and 1,2-butanediol from the outer wall of the scraped-plate molecular evaporator. Although the invention effectively separates each product, it does not effectively pre-separate dimethyl oxalate, which is prone to crystallization and clogging of equipment and pipelines, or hydrogenation dimethyl oxalate required for the production of ethylene glycol. As a result, a large amount of dimethyl oxalate is carried into the ordinary distillation column, resulting in low purity of dimethyl oxalate and high separation energy consumption.

[0004] Chinese Patent 201910990978.X discloses a method and system for purifying a mixture stream containing dimethyl oxalate (DMO). The method involves introducing the mixture stream into a distillation column, obtaining a circulating stream at the top, a stream containing heavy components at the bottom, and collecting the purified DMO product as a side stream liquid phase. Preferably, the mixture stream is the DMO-containing stream separated from the coupling unit of the syngas-to-ethylene glycol process. This invention describes the possibility of side-stream DMO collection. However, if the side-stream DMO reaches a certain purity, it would result in an excessive number of theoretical plates in the distillation column, making the column too tall and difficult to implement. Furthermore, without a side-stream stripping column, the purity of the DMO product would also be affected. Summary of the Invention

[0005] To address the technical problems existing in the prior art, the present invention provides a pre-separation method and system for dimethyl oxalate, which achieves pre-separation of DMO from the CO esterification synthesis reaction products by repeatedly cooling and separating the product stepwise, and by fractionally distilling the DMO solution.

[0006] This invention discloses a method for the pre-separation of dimethyl oxalate, characterized by comprising the following steps:

[0007] 1) The DMO-containing mixture is fed into a separatory tank after cooling, and the liquid phase product in the separatory tank is pressurized and sent to the DMO stripping tower.

[0008] 2) The gaseous product from the separator in step 1) enters the next stage of cooling, and step 1) is repeated;

[0009] 3) The gas from the top of the last stage separator is combined with the gas from the top of the DMO stripping tower and then sent to the downstream processing unit;

[0010] 4) Part of the DMO stripping column bottom liquid is heated and returned to the bottom of the column, while the other part is sent to the downstream unit.

[0011] The present invention provides a pre-separation method for dimethyl oxalate, which is further characterized in that the cooling temperature of each stage is decreased sequentially.

[0012] The present invention discloses a pre-separation method for dimethyl oxalate, which is further characterized in that: the liquid phase products of the separator in step 1) are pressurized by their respective bottom pumps and sent to different feed positions of the DMO stripping tower.

[0013] The present invention provides a pre-separation method for dimethyl oxalate, which is further characterized in that: the bottom liquid in step 4) is partially heated by a bottom reboiler and then returned to the bottom of the column.

[0014] This invention discloses a pre-separation system for dimethyl oxalate, characterized in that it comprises a cooler, a separator, a bottom pump, a DMO stripping column, a bottom reboiler, and a bottom pump; each stage cooler is connected to the corresponding separator; the liquid phase outlet of each separator is connected to the corresponding bottom pump, and the outlet of each bottom pump is connected to the DMO stripping column; the vapor phase outlet of each separator is connected to the next stage cooler, and the vapor phase outlet of the last separator is connected to the top outlet of the DMO stripping column; the DMO stripping column is equipped with a bottom reboiler, and the bottom liquid phase outlet of the DMO stripping column is connected to the bottom pump.

[0015] The present invention discloses a pre-separation system for dimethyl oxalate, which is further characterized in that: the separation tanks of each stage are stacked and arranged, sharing a common equipment base.

[0016] The present invention discloses a pre-separation system for dimethyl oxalate, which is further characterized in that: the DMO stripping column adopts a packing arrangement, and a feed distributor is provided above each section of packing.

[0017] The present invention provides a pre-separation system for dimethyl oxalate, further characterized in that: the outlets of the bottom pumps at each stage are respectively connected to the corresponding feed distributors.

[0018] The beneficial effects of this invention are as follows:

[0019] 1. The synthesis reaction products undergo multiple stages of cooling and distillation separation to separate heavy components such as DMO. The lighter components are then returned to the recycle gas system after distillation. Compared to directly feeding the synthesis reaction products into subsequent units without cooling, this process not only allows for the pre-enrichment of DMO and its discharge as a product or feedstock, but also saves energy in subsequent units. Pre-separating DMO from the synthesis reaction products significantly reduces the DMO concentration in subsequent separation processes and prevents crystallization and blockage of equipment or pipelines when DMO is cooled to lower temperatures in later separation steps.

[0020] 2. The concentration of DMO in the condensate at the bottom of each separatory tank varies. DMO of different concentrations at the bottom of each separatory tank enters different feed points in the DMO stripping tower for stripping. Compared with conventional stripping methods, this process allows for the separation of materials with different volatility at different locations within the stripping tower, resulting in energy savings in the stripping operation.

[0021] 3. The multi-stage liquid separators are stacked, which can not only allow the gas phase at the top of the first-stage liquid separator to rise smoothly to the second-stage liquid separator, simplifying the pipeline design process and saving pipeline design materials; it can also achieve integrated equipment layout, saving space.

[0022] 4. The internal components of the DMO stripping column adopt multi-stage packing or trays. The DMO stripping column has a low vapor load and large vapor load variation. Therefore, the preferred packing material can improve the stripping effect.

[0023] 5. The temperature of multi-stage cooling can be flexibly adjusted for different CO esterification synthesis reaction products and systems, and the flow rate and concentration of DMO pre-separation can be flexibly adjusted within a wide range. Attached Figure Description

[0024] Figure 1 This is a flowchart illustrating Embodiment 1 of the present invention.

[0025] Figure 2 This is a flowchart illustrating Embodiment 2 of the present invention.

[0026] In the diagram: 1. Primary cooler; 2. Primary separator; 3. Secondary cooler; 4. Secondary separator; 5. Primary tank bottom pump; 6. Secondary tank bottom pump; 7. DMO stripping column; 8. Column bottom reboiler; 9. Column bottom pump; 10. Tertiary cooler; 11. Tertiary separator; 12. Tertiary tank bottom pump. Detailed Implementation

[0027] The present invention will now be described in detail with reference to the accompanying drawings:

[0028] Example 1

[0029] CO esterification to methyl formate (MF) is a process technology that uses CO and H2 obtained from coal-based syngas separation, O2 and N2 obtained from air separation, and industrial methanol as raw materials. These materials undergo esterification and synthesis reactions to produce methyl formate. This technology is a widely recognized new coal chemical technology worldwide. In this example, the feedstock comes from the reaction products of the CO esterification to methyl formate synthesizer.

[0030] The synthesis reaction yielded approximately 38.6 t / h of product at a temperature of 135℃ and a pressure of 0.28 MPa(G). The mass composition was as follows: N2 29.63%, NO 25.62%, MF 22.82%, DMO 10.8%, CO 7.9%, MN 2.06%, CH3OH 0.5%, DMC 0.25%, CH4 0.21%, DMM 0.13%, CH2O 0.05%, H2O 0.03%, and CO2 0.01%.

[0031] like Figure 1 As shown, the primary separator 2 and the secondary separator 4 are stacked together, with the secondary separator 4 located above the primary separator 2. The two separators are integrated into a single cylindrical body and share a single equipment foundation.

[0032] The synthesis reaction product is cooled to 90°C by heat exchange with the reaction feed in the primary cooler 1 and then enters the primary separator 2 for separation. The bottom of the primary separator can discharge about 2.0 t / h of a solution with a DMO concentration of 94.34%. The top gas flow rate of the primary separator is 36.6 t / h, and the DMO concentration is about 6.14%.

[0033] The vapor phase at the top of the primary separator is cooled to 65°C by the secondary cooler 3 and then enters the secondary separator 4 for separation. Approximately 1.8 t / h of a DMO solution with a concentration of 89.25% can be discharged from the bottom of the secondary separator. The gas flow rate at the top of the secondary separator is 34.8 t / h, and the DMO concentration is approximately 6.14%.

[0034] The DMO stripping column 7 employs a two-stage packing arrangement, with feed distributors installed above both the upper and lower packing sections. The discharge from the primary separator is pressurized by the primary tank bottom pump 5 and then fed into the lower feed distributor of the DMO stripping column 7. The discharge from the secondary separator is pressurized by the secondary tank bottom pump 6 and then enters the upper feed distributor of the DMO stripping column 7. With a heat load of 264kW in the reboiler 8 at the bottom of the column, the DMO stripping effect meets the process requirements. The top temperature of the DMO stripping column is 125℃, the top gas flow rate is approximately 0.3t / h, and the DMO content is approximately 11.31%. The bottom temperature of the DMO stripping column is 204℃, the bottom liquid flow rate is approximately 3.5t / h, and the DMO content is 98.36%, which can be used as DMO product and sent to downstream units via the bottom pump 9.

[0035] The combined flow rate of the top gas from the secondary separator and the top gas from the DMO stripping tower is approximately 35.1 t / h, with a DMO concentration of 18.9%. After merging, the gas is sent to the downstream unit.

[0036] Example 2

[0037] Coal-to-ethylene glycol (CTO) is a process technology that uses coal to produce syngas, and then uses the CO and H2 in the syngas as raw materials to produce ethylene glycol. The most mature and industrially promising technology is the two-step CTO process, which first uses CO and alcohols through oxidative coupling to produce dimethyl oxalate, and then hydrogenates the dimethyl oxalate to produce ethylene glycol. In this example, the feedstock comes from the effluent of the CO and alcohol oxidative coupling esterification reactor.

[0038] The synthesis reactor produced approximately 455.56 t / h of product at a temperature of 125℃ and a pressure of 0.27 MPa(G). The mass composition was: CO2 0.58%, NO 19.67%, N2 18.52%, DMO 17.21%, MN 12.64%, CO2 9.36%, CH3OH 1.12%, MF 0.48%, DMC 0.28%, and CH4 0.14%.

[0039] like Figure 2 As shown, the primary separator 2, secondary separator 4, and tertiary separator 11 are stacked and arranged, from top to bottom as tertiary separator 11, secondary separator 4, and primary separator 2. The three tanks are integrated into a single cylindrical body and share a single equipment foundation.

[0040] The synthesis reaction product is cooled to 100°C by heat exchange with the reaction feed in the primary cooler 1 and then enters the primary separator 2 for separation. The bottom of the primary separator can discharge about 34.25 t / h of a solution with a DMO concentration of 97.03% (wt%). The top gas flow rate of the primary separator is 421.31 t / h, and the DMO concentration is about 10.58%.

[0041] The vapor phase at the top of the primary separator is cooled to 80°C by the secondary cooler 3 and then enters the secondary separator 4 for separation. The bottom of the secondary separator can discharge approximately 27.27 t / h of a DMO solution with a concentration of 98.03%. The gas flow rate at the top of the secondary separator is 394.05 t / h, and the DMO concentration is approximately 4.53%.

[0042] The vapor phase at the top of the secondary separator is cooled to 65°C by the tertiary cooler 10 and then enters the tertiary separator 11 for separation. The bottom of the tertiary separator can discharge approximately 9.88 t / h of a DMO solution with a concentration of 97.03%. The vapor flow rate at the top of the secondary separator is 384.17 t / h, and the DMO concentration is approximately 2.15%.

[0043] The DMO stripping column 7 employs a three-stage packing arrangement, with feed distributors installed above each stage. The discharge from the first-stage separator is pressurized by the first-stage bottom pump 5 and fed into the lower feed distributor of the DMO stripping column 7. The discharge from the second-stage separator is pressurized by the second-stage bottom pump 6 and enters the intermediate feed distributor of the DMO stripping column 7. The discharge from the tertiary separator is pressurized by the tertiary bottom pump 12 and enters the upper feed distributor of the DMO stripping column 7. With a reboiler heat load of 5.0 MW at the bottom of the column, the DMO stripping effect meets process requirements. The top temperature of the DMO stripping column is 132℃, the top gas flow rate is approximately 1.46 t / h, and the DMO content is approximately 18.88%. The bottom temperature of the DMO stripping column is 213℃, the bottom liquid flow rate is approximately 69.93 t / h, and the DMO content is 99.9%, which can be used as intermediate DMO feedstock and sent to downstream units via the bottom pump 9.

[0044] The combined flow rate of the top gas from the three-stage separator and the top gas from the DMO stripping tower is approximately 385.63 t / h, with a DMO concentration of 2.22%. After merging, the gas is sent to the downstream unit.

[0045] The above are merely typical embodiments of the present invention. Those skilled in the art can make appropriate modifications and improvements based on them, but they are substantially the same as the present invention and also fall within the protection scope of the present invention.

Claims

1. A method for the pre-separation of dimethyl oxalate, characterized in that... Includes the following steps: 1) The DMO-containing mixture is fed into a separatory tank after cooling, and the liquid phase product in the separatory tank is pressurized and sent to the DMO stripping tower. 2) The gaseous product from the separator in step 1) enters the next stage of cooling, and step 1) is repeated; 3) The gas from the top of the last stage separator is combined with the gas from the top of the DMO stripping tower and then sent to the downstream processing unit; 4) Part of the DMO stripping column bottom liquid is heated and returned to the bottom of the column, while the other part is sent to downstream units; Step 1) The liquid phase products from the separatory tank are liquid phase products of different temperatures and different DMO concentrations after multiple stages of cooling and separation. After being pressurized by the corresponding tank bottom pump, they are sent to different feed positions of the DMO stripping tower. The liquid phase products from the separatory tank with higher temperature and higher DMO concentration are sent to the feed position at the lower part of the DMO stripping tower, while the liquid phase products from the separatory tank with lower temperature and lower DMO concentration are sent to the feed position at the upper part of the DMO stripping tower.

2. The pre-separation method for dimethyl oxalate according to claim 1, characterized in that: The cooling temperature decreases progressively with each stage.

3. The pre-separation method for dimethyl oxalate according to claim 1, characterized in that: The bottom liquid described in step 4) is partially returned to the bottom of the column after being heated by the bottom reboiler.

4. A pre-separation system for dimethyl oxalate, characterized in that: It includes a cooler, a separator, a bottom pump, a DMO stripping column, a bottom reboiler, and a bottom pump; each cooler is connected to the corresponding separator; the liquid phase outlet of each separator is connected to the corresponding bottom pump, and the outlet of each bottom pump is connected to the DMO stripping column; the vapor phase outlet of each separator is connected to the next cooler, and the vapor phase outlet of the last separator is connected to the top outlet of the DMO stripping column; the DMO stripping column is equipped with a bottom reboiler, and the liquid phase outlet of the DMO stripping column is connected to the bottom pump.

5. The pre-separation system for dimethyl oxalate according to claim 4, characterized in that: The various liquid separators are stacked together and share a single equipment foundation.

6. The pre-separation system for dimethyl oxalate according to claim 4, characterized in that: The DMO stripping column is packed with feed, and a feed distributor is installed above each section of the packing.

7. The pre-separation system for dimethyl oxalate according to claim 4, characterized in that: The outlets of each tank bottom pump are connected to the corresponding feed distributors.

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