A process for the continuous rectification of propylene glycol methyl ether and propylene glycol methyl ether acetate diluent

Abstract

The present application relates to organic solvent recycling technical field, provide a kind of continuous rectification separation propylene glycol methyl ether and propylene glycol methyl ether acetate diluent method, comprising the following steps: waste diluent is removed from slag rectification, obtain the slag raw material;Slag raw material is imported into crude dehydration tower and is subjected to negative pressure rectification, top is removed from water head oil, the bottom is obtained with PM, PMA mixed solvent;Mixed solvent is imported into PM separation tower, PMA separation tower in turn and is subjected to subsection rectification, respectively obtain PM semi-finished product and PMA semi-finished product with water content less than 1000ppm;The water head oil of crude dehydration tower top is mixed with azeotrope rectification tower after azeotrope rectification tower, while liquid phase feed azeotrope auxiliary agent;Top is separated and drains, organic solvent reflux, bottom product is imported into azeotrope recovery tower.The present application realizes the efficient separation and recovery of each component in waste diluent, especially solves the technical problem that organic solvent in ternary azeotrope is difficult to recover.

Description

Technical Field

[0001] This invention relates to the field of organic solvent recycling technology, and more specifically, to a method for continuous distillation to separate propylene glycol methyl ether and propylene glycol methyl ether acetate diluent. Background Technology

[0002] Propylene glycol methyl ether acetate (PMA) and propylene glycol methyl ether (PM) are mixed diluents widely used organic solvents in the electronics industry. Due to their excellent solubility and cleaning properties, they are widely used in the chip and other electronic industries, and these diluents have extremely high recycling value. Currently, the main method for recycling such waste diluents in the chemical industry is distillation separation. However, this method has significant technical drawbacks: Firstly, the difference in boiling points between PM and PMA at atmospheric pressure is less than 30°C, requiring a large number of distillation trays and a high reflux ratio for separation, leading to a significant increase in equipment procurement and installation costs as well as production energy consumption costs. Secondly, water is inevitably mixed into the waste diluent, and water forms a ternary azeotrope with PM and PMA. This ternary azeotrope cannot be effectively separated by separate distillation, resulting in a large loss of organic components and ultimately a significant reduction in the diluent's recycling rate.

[0003] Current technologies for the distillation recovery of such mixed solvents only employ a single distillation column for simple separation, failing to design targeted processes to address the issues of small boiling point differences and ternary azeotropes. This approach cannot solve the high cost problem, nor can it achieve the recovery of organic components from the ternary azeotrope, making it difficult to meet the demands of large-scale, high-recovery industrial-scale waste diluent recovery. Therefore, developing an efficient, continuous, and low-cost method for diluent separation and recovery, achieving high-purity separation of PMA and PM while simultaneously recovering organic components from the ternary azeotrope, is a pressing technical problem to be solved in this field. Summary of the Invention

[0004] To address the high cost and low recovery rate of PM-PMA mixed diluent distillation recovery in existing technologies, this invention provides a method for continuous distillation separation of propylene glycol methyl ether and propylene glycol methyl ether acetate diluents. Through a five-tower coupled, segmented continuous distillation process, coupled with a cyclohexane azeotropic distillation system, the method achieves efficient separation and recovery of various components in waste diluents, and in particular solves the technical problem of difficult recovery of organic solvents in ternary azeotropes.

[0005] The embodiments of the present invention are achieved through the following technical solutions:

[0006] A method for continuous distillation to separate propylene glycol methyl ether and propylene glycol methyl ether acetate diluent includes the following steps:

[0007] (1) The waste diluent containing propylene glycol methyl ether and propylene glycol methyl ether acetate was subjected to slag removal and distillation to obtain the slag-removed raw material;

[0008] (2) The slag-removed raw material is fed into the crude dehydration tower for negative pressure distillation. Water-containing head oil is collected from the top of the tower, and a mixed solvent containing PM and PMA is obtained from the bottom of the tower.

[0009] (3) The mixed solvent obtained in step (2) is sequentially fed into the PM separation tower and the PMA separation tower for fractional distillation to obtain PM semi-finished product and PMA semi-finished product with a water content of less than 1000 ppm, respectively.

[0010] (4) The water-containing head oil at the top of the crude dehydration tower is mixed with the azeotropic agent and then fed into the azeotropic distillation tower for azeotropic distillation. At the same time, the azeotropic auxiliary agent is fed into the liquid phase. The top phase is drained and the organic solvent is refluxed. The bottom product is fed into the azeotropic agent recovery tower for distillation. The azeotropic agent recovered at the top of the tower is recycled and reused. The azeotropic auxiliary agent recovered in the tower is recycled and reused.

[0011] The technical solutions of the embodiments of the present invention have at least the following advantages and beneficial effects:

[0012] 1. This invention employs a segmented continuous distillation method using a PM separation tower and a PMA separation tower connected in series, replacing the single-tower distillation technology of the prior art. Simultaneously, it utilizes gradient negative pressure operation (coarse dehydration tower -0.05MPa, separation tower ≤ -0.09MPa), which reduces operating temperature while ensuring separation efficiency, minimizing the decomposition of heat-sensitive substances. This allows for the step-by-step separation of PM and PMA, which have a small boiling point difference, significantly reducing the theoretical plate number and reflux ratio requirements of a single distillation tower. This effectively reduces equipment procurement and installation costs, while also lowering energy consumption in the distillation process, resulting in a significant reduction in production costs.

[0013] 2. This invention addresses the ternary azeotrope formed by water, PM, and PMA. It employs a dual-tower azeotropic distillation system, consisting of an azeotropic distillation tower and an azeotropic agent recovery tower. Cyclohexane combined with isopropyl ether is used as the azeotropic agent, supplemented with 1-butyl-3-methylimidazolium tetrafluoroborate as an azeotropic aid. This achieves effective separation of water and organic components from the ternary azeotrope, while simultaneously enabling the recovery and recycling of cyclohexane. This reduces cyclohexane consumption, increases system safety and selectivity, and recovers all PM and PMA from the high-water-content head oil (15% of the feed weight). This solves the problem of organic component loss caused by the inability to separate ternary azeotropes in existing technologies, significantly improving the overall recovery rate of the diluent and resulting in significant economic benefits.

[0014] 3. This invention realizes continuous and automated production throughout the entire process from raw material pretreatment to product blending. At the same time, the unqualified reflux products from each tower are returned to the crude dehydration tower for rectification, which effectively ensures the purity of the finished product (water content less than 1000ppm) and realizes full utilization of raw materials. Compared with the intermittent rectification technology of the prior art, it greatly improves the recycling efficiency of waste diluent and is more suitable for large-scale industrial application. Attached Figure Description

[0015] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings used in the embodiments will be briefly introduced below. It should be understood that the following drawings only show some embodiments of the present invention and should not be regarded as a limitation on the scope. For those skilled in the art, other related drawings can be obtained based on these drawings without creative effort.

[0016] Figure 1 The flowchart for the continuous distillation separation of propylene glycol methyl ether and propylene glycol methyl ether acetate diluent provided in Example 1 of the present invention is shown. Detailed Implementation

[0017] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below. Where specific conditions are not specified in the embodiments, conventional conditions or conditions recommended by the manufacturer shall apply. Reagents or instruments whose manufacturers are not specified are all conventional products that can be purchased commercially.

[0018] The following is a detailed description of a method for continuous distillation to separate propylene glycol methyl ether and propylene glycol methyl ether acetate diluent provided by an embodiment of the present invention.

[0019] A method for continuous distillation to separate propylene glycol methyl ether and propylene glycol methyl ether acetate diluent includes the following steps:

[0020] (1) Deslag removal pretreatment: Waste diluent containing propylene glycol methyl ether acetate (PMA), propylene glycol methyl ether (PM) and water is introduced into the deslag removal distillation kettle for stirring and distillation; the deslag removal raw material is collected from the top of the distillation column and enters the subsequent organic solvent component separation process; the colloidal residue is removed from the bottom of the distillation column.

[0021] (2) Crude dehydration: The deslag-removed raw material is fed into the crude dehydration tower (C2101) for negative pressure distillation. The ternary azeotrope formed by water, PM and PMA is distilled and discharged from the top of the crude dehydration tower (C2101) to obtain a high water content head oil with a water content of about 40%. This water content head oil accounts for about 15% of the total raw material. The bottom of the crude dehydration tower (C2101) yields a PM-PMA mixed solvent with a water content of less than 1000ppm. The mixed solvent is then sent to the subsequent organic component fractional distillation process.

[0022] (3) Fractional distillation of organic components

[0023] Fractional distillation of organic components is achieved through a PM separation column (C2201) and a PMA separation column (C2301) connected in series. The PM separation column (C2201) and the PMA separation column (C2301) have 26 and 24 trays respectively, and their heights are approximately 29m and 24m respectively. Due to the reduction in the overall column height, there is no need for a more stable equipment foundation, high-rise cranes, or manual high-altitude installation, thus reducing overall installation costs by 10% to 20%.

[0024] Specifically:

[0025] (3.1) The bottom product mixed solvent of the crude dehydration tower (C2101) is sent to the PM separation tower (C2201) for negative pressure distillation; PM semi-finished product with water content of less than 1000 ppm and purity ≥ 99.0% is distilled from the top of the tower; PM-PMA mixed solvent with water content of less than 1000 ppm is collected from the bottom of the tower; wherein, the main component of the mixed solvent is propylene glycol methyl ether acetate, and it also contains a small amount of propylene glycol methyl ether;

[0026] (3.2) The mixed solvent of the bottom product of the PM separation tower (C2201) is fed into the PMA separation tower (C2301) for negative pressure distillation; a PM-PMA mixed solvent with a water content of less than 1000 ppm is obtained from the top of the tower. The top product is refluxed to the crude dehydration tower (C2101) for redistillation as a slag removal feed; high-boiling-point heavy components generated by long-term heating remain at the bottom of the tower; PMA semi-finished product with a water content of less than 1000 ppm is distilled out from the bottom of the tower.

[0027] It should be noted that during the distillation process, the crude dehydration tower C2101, PM separation tower C2201, and PMA separation tower C2301 continuously remove heavy components from the system at a rate of 200 kg / d to 300 kg / d.

[0028] (4) Azeotropic distillation of ternary azeotropes:

[0029] The ternary azeotropic compound is recovered through azeotropic distillation using an azeotropic distillation column (C2401) and an azeotropic agent recovery column (C2501), with cyclohexane as the azeotropic agent. Specifically:

[0030] 4.1 The water-containing head oil collected from the top of the crude dehydration tower (C2101) is mixed with an azeotropic agent and then fed into an azeotropic distillation tower (C2401) for azeotropic distillation. Simultaneously, the liquid phase is fed with the azeotropic auxiliary agent. After condensation and phase separation, the aqueous phase is discharged as wastewater, and the organic phase is refluxed back to the azeotropic distillation tower (C2401). The bottom of the azeotropic distillation tower (C2401) yields a mixed solvent containing PM and PMA. The azeotropic agent comprises, by mass percentage: 50-60% cyclohexane and 40-50% isopropyl ether, and the azeotropic auxiliary agent is 0.1-0.5% of the total mass of the azeotropic agent, 1-butyl-3-methylimidazolium tetrafluoroborate.

[0031] The inventors, recognizing the unique characteristics of PM, PMA, and water ternary azeotropes, selectively recovered PM and PMA. By using cyclohexane and isopropyl ether to adjust the azeotropic point of the system to 65-75℃, a balance between safety and energy efficiency was achieved. Among commonly used azeotropic agents, cyclohexane has relatively low toxicity, lower than that of traditional benzene or toluene. Moreover, its azeotropic temperature with water is 69℃, which is significantly lower than the azeotropic temperature of 100℃ for ternary azeotropes (water, propylene glycol methyl ether, and propylene glycol methyl ether acetate). This difference is even greater than the azeotropic temperature of toluene with water (84℃). Furthermore, cyclohexane in azeotropes can more easily separate into layers with water, making phase separation of the azeotropic agent easier and facilitating reflux of the separated azeotropic agent.

[0032] Most importantly, although 1-butyl-3-methylimidazolium tetrafluoroborate cannot function as an azeotropic agent, the inventors discovered that if a large amount of cyclohexane is used in the azeotropic recovery process, the total hydrocarbon vapor concentration in the system inside the column becomes too high, even approaching the explosion limit. This is especially true in the gas phase spaces such as the top condensation and reflux, which increases the liquid phase load inside the column, leading to flooding and a decrease in separation efficiency. Furthermore, excessive cyclohexane may increase the dissolution loss of PM / PMA in the organic phase. Therefore, the inventors added a small amount of 1-butyl-3-methylimidazolium tetrafluoroborate to the liquid phase. It forms strong hydrogen bonds with water, increasing the relative volatility of water / organic phase, while changing the polarity of the liquid phase, reducing the dissolution of organic phase in the aqueous phase, and reducing the loss of PM / PMA with water, thereby reducing the total amount of azeotropic agent used. Experiments have shown that it can reduce cyclohexane consumption by 40-60%, increase the safety and high selectivity of the system, and improve the overall recovery rate of the diluent.

[0033] 4.2 The mixed solvent of the bottom product of the azeotropic distillation column (C2401) is fed into the azeotropic agent recovery column (C2501) for negative pressure distillation; cyclohexane is returned to the azeotropic distillation column (C2401) to be recycled as an azeotropic agent; the PM-PMA mixed solvent obtained at the bottom of the column is recycled as a raw material to the crude dehydration column (C2101) for recycling.

[0034] The overall material recovery rate of this invention is ≥95%, including ≥70% propylene glycol methyl ether and ≥25% propylene glycol methyl ether acetate. Currently, the overall organic solvent recovery rate of existing single-tower distillation methods is approximately 80%, demonstrating that this invention achieves a significantly higher overall recovery rate.

[0035] Compared with existing distillation recovery technologies, this invention firstly recovers approximately 10% of the organic solvent, and the actual production control parameters are not significantly different. Therefore, the production cost per ton of raw material is reduced by about 10%, from approximately 700 yuan / ton to approximately 600 yuan / ton.

[0036] Meanwhile, since current batch distillation production requires periodic removal of distillation residue and refeeding, it is impossible to carry out distillation simultaneously during this period. However, the continuous distillation production of this invention does not have the above-mentioned concerns. Therefore, the daily material processing capacity of this invention is approximately 30 tons / day, which is about 17% higher than the daily material processing capacity of approximately 25 tons / day of the original batch distillation production.

[0037] Regarding product purity, the material purity of this invention achieves the following results: ①PMA: propylene glycol methyl ether acetate content greater than 99.9%, water content less than 250 ppm; ②PM: propylene glycol methyl ether content greater than 99.9%, water content less than 250 ppm. Existing material specifications are: ①PMA: propylene glycol methyl ether acetate content greater than 99.5%, water content less than 500 ppm; ②PM: propylene glycol methyl ether content greater than 99.5%, water content less than 500 ppm. It is evident that the product separation effect of this invention is higher than that of the original batch distillation production.

[0038] Finally, the obtained products can be blended. For example, the PM semi-finished product and PMA semi-finished product obtained in step (3) can be fed into a mixing tank for blending. The mixing ratio of PM and PMA semi-finished products can be adjusted to obtain high-purity PM or PMA finished products. For example, the diluent finished product can be obtained by mixing 30% PMA semi-finished product and 70% PM semi-finished product evenly.

[0039] More specifically, the control parameters for the five towers are shown in Table 1.

[0040] Table 1 - Control parameter data for the five towers

[0041] Tower name parameters Crude dehydration tower C2101 PM Separator Tower C2201 PMA Separation Tower C2301 Azeotropic distillation column C2401 Azeotropic agent recovery tower C2501 Feed rate (kg / h) 1300~1500 1200~1300 400~500 300~400 200~400 Recirculation flow rate (kg / h) 900~1100 2000~2100 500~600 0 500~700 Tower pressure (MPa) -0.02~-0.08 ≤-0.09 ≤-0.09 Atmospheric pressure -0.02～-0.08 Tower top temperature (°C) 70～90 60～80 80～100 40～60 50～70 Temperature at the bottom of the tower (°C) 90～110 80～100 80～100 80～100 90～110 Top of the tower content (%) H2O≈40%; PM≈20%; PMA≈40% PM≥99.0% Mixed solvents (circulation) H2O≥99% Cyclohexane ≥99% Content at the bottom of the tower (%) H2O≤0.1% PMA-containing mixture PMA ≥ 99.0% Cyclohexane-containing mixed solvents PM+PMA (cycle)

[0042] Example 1

[0043] A method for continuous distillation to separate propylene glycol methyl ether and propylene glycol methyl ether acetate diluent includes the following steps:

[0044] (1) Deslag removal pretreatment: Waste diluent containing propylene glycol methyl ether acetate (PMA), propylene glycol methyl ether (PM) and water is introduced into the deslag removal distillation kettle for stirring and distillation; the deslag removal raw material is collected from the top of the distillation column and enters the subsequent organic solvent component separation process; the colloidal residue is removed from the bottom of the distillation column.

[0045] (2) Crude dehydration: The deslag-removed raw material is fed into the crude dehydration tower (C2101) for negative pressure distillation. The feed rate is controlled at 1400 kg / h, the reflux rate is 1000 kg / h, the tower pressure is -0.05 MPa, the top temperature is 80℃, and the bottom temperature is 100℃. The ternary azeotrope formed by water, PM and PMA is distilled and discharged from the top of the crude dehydration tower (C2101) to obtain a high water content head oil with a water content of about 40%, which accounts for 15% of the total raw material. The bottom of the crude dehydration tower (C2101) yields a PM-PMA mixed solvent with a water content of less than 1000 ppm. The mixed solvent is sent to the subsequent organic component fractional distillation process.

[0046] (3) Fractional distillation of organic components

[0047] (3.1) The bottom product mixed solvent of the crude dehydration tower (C2101) is fed into the PM separation tower (C2201) for negative pressure distillation. The feed rate is controlled at 1250 kg / h, the reflux rate is 2050 kg / h, the tower pressure is -0.05 MPa, the top temperature is 70℃, and the bottom temperature is 90℃. The PM semi-finished product with a water content of less than 1000 ppm and a purity of 99.8% is distilled from the top of the tower. The PM-PMA mixed solvent with a water content of less than 1000 ppm is collected from the bottom of the tower. The main component of the mixed solvent is propylene glycol methyl ether acetate, and it also contains a small amount of propylene glycol methyl ether.

[0048] (3.2) The mixed solvent of the bottom product of the PM separation tower (C2201) is fed into the PMA separation tower (C2301) for negative pressure distillation. The feed rate is controlled at 450 kg / h, the reflux rate at 550 kg / h, the tower pressure at -0.05 MPa, the top temperature at 90°C, and the bottom temperature at 90°C. A PM-PMA mixed solvent with a water content of less than 1000 ppm is obtained from the top of the tower. This top product is refluxed to the crude dehydration tower (C2101) for redistillation as a slag removal feed. High-boiling-point heavy components generated by long-term heating remain at the bottom of the tower. A PMA semi-finished product with a water content of less than 1000 ppm is distilled from the bottom of the tower.

[0049] (4) Azeotropic distillation of ternary azeotropes:

[0050] 4.1 The water-containing head oil collected from the top of the crude dehydration tower (C2101) is mixed with an azeotropic agent and then fed into an azeotropic distillation tower (C2401) for azeotropic distillation. The feed rate is controlled at 350 kg / h, the tower pressure is atmospheric pressure, the top temperature is 50℃, and the bottom temperature is 90℃. Simultaneously, the azeotropic auxiliary agent is fed as a liquid phase. After the top vapor is condensed and separated, the aqueous phase is discharged as wastewater, and the organic phase is refluxed to the azeotropic distillation tower (C2401). The bottom of the azeotropic distillation tower (C2401) yields a mixed solvent containing PM and PMA. The azeotropic agent comprises, by mass percentage, 60% cyclohexane and 40% isopropyl ether, and the azeotropic auxiliary agent is 0.3% by mass of 1-butyl-3-methylimidazolium tetrafluoroborate.

[0051] 4.2 The mixed solvent from the bottom product of the azeotropic distillation column (C2401) is fed into the azeotropic agent recovery column (C2501) for negative pressure distillation. The feed rate is controlled at 300 kg / h, the reflux rate at 600 kg / h, the column pressure at -0.05 MPa, the top temperature at 60℃, and the bottom temperature at 100℃. Cyclohexane is returned to the azeotropic distillation column (C2401) and reused as an azeotropic agent. The PM-PMA mixed solvent obtained at the bottom of the column is refluxed as feed to the crude dehydration column (C2101) for recycling.

[0052] In this embodiment, the daily processing capacity is 32 tons / day, the recovery rate of propylene glycol methyl ether is 73%, the recovery rate of propylene glycol methyl ether acetate is 26%, and the content of propylene glycol methyl ether acetate is greater than 99.9% and the water content is less than 250 ppm; the content of propylene glycol methyl ether is greater than 99.9% and the water content is less than 250 ppm.

[0053] Example 2

[0054] The difference between this embodiment and Embodiment 1 is that the control parameters for the five towers are different, as detailed in Table 2.

[0055] Table 2 - Control parameter data for the five towers in Example 2

[0056] Tower name parameters Crude dehydration tower C2101 PM Separator Tower C2201 PMA Separation Tower C2301 Azeotropic distillation column C2401 Azeotropic agent recovery tower C2501 Feed rate (kg / h) 1300 1200 400 300 200 Recirculation flow rate (kg / h) 900 2000 500 0 500 Tower pressure (MPa) -0.02 -0.05 -0.05 Atmospheric pressure -0.02 Tower top temperature (°C) 70 60 80 40 50 Temperature at the bottom of the tower (°C) 90 80 80 80 90

[0057] In this embodiment, the daily processing capacity is 33 tons / day, the recovery rate of propylene glycol methyl ether is 74%, the recovery rate of propylene glycol methyl ether acetate is 25%, and the content of propylene glycol methyl ether acetate is greater than 99.9% and the water content is less than 250 ppm; the content of propylene glycol methyl ether is greater than 99.9% and the water content is less than 250 ppm.

[0058] Example 3

[0059] The difference between this embodiment and Embodiment 1 is that the control parameters for the five towers are different, as detailed in Table 3.

[0060] Table 3 - Control parameter data for the five towers in Example 3

[0061] Tower name parameters Crude dehydration tower C2101 PM Separator Tower C2201 PMA Separation Tower C2301 Azeotropic distillation column C2401 Azeotropic agent recovery tower C2501 Feed rate (kg / h) 1500 1300 500 400 400 Recirculation flow rate (kg / h) 1100 2100 600 0 700 Tower pressure (MPa) -0.08 -0.07 -0.07 Atmospheric pressure -0.08 Tower top temperature (°C) 90 80 100 60 70 Temperature at the bottom of the tower (°C) 110 100 100 100 110

[0062] In this embodiment, the daily processing capacity is 31 tons / day, the recovery rate of propylene glycol methyl ether is 72%, the recovery rate of propylene glycol methyl ether acetate is 25%, and the content of propylene glycol methyl ether acetate is greater than 99.9% and the water content is less than 250 ppm; the content of propylene glycol methyl ether is greater than 99.9% and the water content is less than 250 ppm.

[0063] Example 4

[0064] The difference between this embodiment and Embodiment 1 is that the control parameters for the five towers are different, as detailed in Table 4.

[0065] Table 4 - Control parameter data for the five towers in Example 4

[0066] Tower name parameters Crude dehydration tower C2101 PM Separator Tower C2201 PMA Separation Tower C2301 Azeotropic distillation column C2401 Azeotropic agent recovery tower C2501 Feed rate (kg / h) 1350 1250 450 380 350 Recirculation flow rate (kg / h) 1050 2050 550 0 650 Tower pressure (MPa) -0.06 -0.08 -0.07 Atmospheric pressure -0.08 Tower top temperature (°C) 75 75 85 55 65 Temperature at the bottom of the tower (°C) 105 90 95 95 95

[0067] In this embodiment, the daily processing capacity is 30 tons / day, the recovery rate of propylene glycol methyl ether is 72%, the recovery rate of propylene glycol methyl ether acetate is 27%, and the content of propylene glycol methyl ether acetate is greater than 99.9% and the water content is less than 250 ppm; the content of propylene glycol methyl ether is greater than 99.9% and the water content is less than 250 ppm.

[0068] Example 5

[0069] The difference between this embodiment and embodiment 1 is that in step (4), the azeotropic agent includes 50% cyclohexane and 50% isopropyl ether by mass percentage, and the azeotropic aid is 0.5% of the total mass of the azeotropic agent, which is 1-butyl-3-methylimidazolium tetrafluoroborate.

[0070] In this embodiment, the daily processing capacity is 30 tons / day, the recovery rate of propylene glycol methyl ether is 74%, the recovery rate of propylene glycol methyl ether acetate is 25%, and the content of propylene glycol methyl ether acetate is greater than 99.9% and the water content is less than 250 ppm; the content of propylene glycol methyl ether is greater than 99.9% and the water content is less than 250 ppm.

[0071] Example 6

[0072] The difference between this embodiment and embodiment 1 is that in step (4), the azeotropic agent includes 55% cyclohexane and 45% isopropyl ether by mass percentage, and the azeotropic auxiliary agent is 0.4% of the total mass of the azeotropic agent, which is 1-butyl-3-methylimidazolium tetrafluoroborate.

[0073] In this embodiment, the daily processing capacity is 32 tons / day, the recovery rate of propylene glycol methyl ether is 74%, the recovery rate of propylene glycol methyl ether acetate is 25%, and the content of propylene glycol methyl ether acetate is greater than 99.9% and the water content is less than 250 ppm; the content of propylene glycol methyl ether is greater than 99.9% and the water content is less than 250 ppm.

[0074] Comparative Example 1

[0075] The difference between this comparative example and Example 1 is that step (4) is not included.

[0076] In this embodiment, the recovery rate of propylene glycol methyl ether was 63%, and the recovery rate of propylene glycol methyl ether acetate was 12%.

[0077] Comparative Example 2

[0078] The difference between this comparative example and Example 1 is that it does not contain an azeotropic additive.

[0079] In this embodiment, the recovery rate of propylene glycol methyl ether was 66%, and the recovery rate of propylene glycol methyl ether acetate was 13%.

[0080] The above are merely preferred embodiments of the present invention and are not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for continuous distillation to separate propylene glycol methyl ether and propylene glycol methyl ether acetate diluent, characterized in that: Includes the following steps: (1) The waste diluent containing propylene glycol methyl ether and propylene glycol methyl ether acetate was subjected to slag removal and distillation to obtain the slag-removed raw material; (2) The slag-removed raw material is fed into the crude dehydration tower for negative pressure distillation. Water-containing head oil is collected from the top of the tower, and a mixed solvent containing PM and PMA is obtained from the bottom of the tower. (3) The mixed solvent obtained in step (2) is sequentially fed into the PM separation tower and the PMA separation tower for fractional distillation to obtain PM semi-finished product and PMA semi-finished product with a water content of less than 1000 ppm, respectively. (4) The water-containing head oil at the top of the crude dehydration tower is mixed with the azeotropic agent and then fed into the azeotropic distillation tower for azeotropic distillation. At the same time, the azeotropic auxiliary agent is fed into the liquid phase. The top phase is drained and the organic solvent is refluxed. The bottom product is fed into the azeotropic agent recovery tower for distillation. The azeotropic agent recovered at the top of the tower is recycled and reused. The azeotropic auxiliary agent recovered in the tower is recycled and reused.

2. The method for continuous distillation separation of propylene glycol methyl ether and propylene glycol methyl ether acetate diluent according to claim 1, characterized in that, The azeotropic agent comprises, by mass percentage: 50-60% cyclohexane and 40-50% isopropyl ether; the azeotropic aid is 0.1-0.5% of 1-butyl-3-methylimidazolium tetrafluoroborate by mass of the total azeotropic agent.

3. The method for continuous distillation separation of propylene glycol methyl ether and propylene glycol methyl ether acetate diluent according to claim 1, characterized in that, The feed rate of the coarse dehydration tower is 1300~1500 kg / h, the reflux rate is 900~1100 kg / h, the tower pressure is -0.02~-0.08MPa, the tower top temperature is 70~90℃, and the tower bottom temperature is 90~110℃.

4. The method according to claim 1, characterized in that, In step (3), the feed rate of the PM separator is 1200~1300 kg / h, the reflux rate is 2000~2100 kg / h, the pressure is ≤-0.09MPa, the top temperature is 60~80℃, and the bottom temperature is 80~100℃.

5. The method according to claim 1, characterized in that, In step (4), the feed rate of the PMA separation tower is 400~500 kg / h, the reflux rate is 500~600 kg / h, the tower pressure is ≤-0.09MPa, the tower top temperature is 80~100℃, and the tower bottom temperature is 80~100℃.

6. The method according to claim 1, characterized in that, In step (5), the feed rate of the azeotropic distillation column is 300~400 kg / h, the column pressure is atmospheric pressure, the top temperature is 40~60℃, and the bottom temperature is 80~100℃.

7. The method according to claim 1, characterized in that, In step (6), the feed rate of the azeotropic agent recovery tower is 200~400 kg / h, the reflux rate is 500~700 kg / h, the tower pressure is -0.02~-0.08MPa, the tower top temperature is 50~70℃, and the tower bottom temperature is 90~110℃.

8. The method for continuous distillation separation of propylene glycol methyl ether and propylene glycol methyl ether acetate diluent according to claim 1, characterized in that, The top product of the PMA separation tower and the bottom product of the azeotropic agent recovery tower are refluxed to the crude dehydration tower.

9. The method for continuous distillation separation of propylene glycol methyl ether and propylene glycol methyl ether acetate diluent according to claim 1, characterized in that, The water-containing head oil accounts for 10-20% of the total raw material.

10. The method for continuous distillation separation of propylene glycol methyl ether and propylene glycol methyl ether acetate diluent according to claim 1, characterized in that, Heavy components are periodically discharged from the bottom of the coarse dehydration tower, PM separation tower and PMA separation tower, with an emission rate of 200-300 kg per tower per day.

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