A recovery system and method for by-products propylene glycol and propylene glycol ether in a process for producing propylene oxide by hydrogen peroxide method

Abstract

The application discloses a recovery system and method for by-products propylene glycol and propylene glycol ether in a hydrogen peroxide method for producing propylene oxide, characterized by comprising a demethanol column, an ether concentration column, a first ether dehydration column, a first phase separator, a second ether dehydration column and an ether refining column; a material inlet is arranged in the middle of the demethanol column, a bottom discharge port of the methanol column is connected with a middle inlet of the ether concentration column, a top gas outlet of the ether concentration column is connected with a top inlet of the ether concentration column and a middle inlet of the first ether dehydration column respectively, a top gas outlet of the first ether dehydration column is connected with the first phase separator through a first ether dehydration column top condenser, a heavy phase outlet of the first phase separator is connected with a top inlet of the first ether dehydration column, a bottom discharge port of the first ether dehydration column is connected with a middle inlet of the second ether dehydration column, and a bottom discharge port of the second ether dehydration column is connected with a middle inlet of the ether refining column, so that the system has the advantages of low energy consumption, high product purity and high recovery rate.

Description

Technical Field

[0001] This invention relates to an alcohol and ether recovery system, and more particularly to a system and method for recovering propylene glycol and propylene glycol ether, byproducts of the hydrogen peroxide process for producing propylene oxide. Background Technology

[0002] Currently, the industrialized PO production processes both domestically and internationally include: the chlorohydrin process, the co-oxidation process, and the direct hydrogen peroxide oxidation process. The chlorohydrin process suffers from high costs, severe equipment corrosion, and large volumes of wastewater and waste residue. The co-oxidation process has a long process flow, demanding operating conditions, and high investment costs. The direct hydrogen peroxide oxidation process offers advantages such as safety, environmental friendliness, cleanliness, high efficiency, and fewer byproducts, and is becoming increasingly mature, demonstrating promising industrial prospects.

[0003] In the process of producing propylene oxide by direct oxidation with hydrogen peroxide, byproducts such as propylene glycol and propylene glycol ether are generated.

[0004] Propylene glycol is a colorless and transparent liquid widely used in the manufacture of various chemicals, pharmaceuticals, food additives, lubricants, solvents, and other products. Propylene glycol ethers are multifunctional chemicals that can be used as solvents, dispersants, and diluents, as well as fuel antifreeze agents and extractants. The existing hydrogen peroxide process for producing propylene oxide, as shown in patent CN113135817, involves the separation of propylene glycol and propylene glycol ethers as byproducts. This process uses multi-effect evaporation, resulting in the evaporation of large amounts of wastewater followed by ether separation. This process is characterized by high impurity content in the wastewater and high energy consumption. Summary of the Invention

[0005] The technical problem to be solved by the present invention is to provide a system and method for recovering propylene glycol and propylene glycol ether, byproducts of the hydrogen peroxide process for producing propylene oxide, which has low energy consumption and high product purity and recovery rate.

[0006] The technical solution adopted by this invention to solve the above-mentioned technical problems is as follows: a recovery system for propylene glycol and propylene glycol ether, byproducts of the hydrogen peroxide process for producing propylene oxide, comprising a methanol removal tower, an ether concentration tower, a first ether dehydration tower, a first phase separator, a second ether dehydration tower, and an ether purification tower; the methanol removal tower has a material inlet in the middle, the bottom outlet of the methanol tower is connected to the middle inlet of the ether concentration tower, and the top outlet of the ether concentration tower is connected to both the top inlet of the ether concentration tower and the middle inlet of the first ether dehydration tower. The bottom outlet of the ether concentration tower is connected to the wastewater treatment unit. The top outlet of the first ether dehydration tower is connected to the first phase separator via the top condenser of the first ether dehydration tower. The organic phase outlet of the first phase separator is connected to the top inlet of the first ether dehydration tower. The aqueous phase outlet of the first phase separator is connected to the wastewater treatment unit. The bottom outlet of the first ether dehydration tower is connected to the middle inlet of the second ether dehydration tower. The bottom outlet of the second ether dehydration tower is connected to the middle inlet of the ether refining tower.

[0007] Furthermore, the methanol removal tower is equipped with a methanol removal tower top condenser at the top outlet and a methanol removal tower bottom reboiler at the bottom.

[0008] Furthermore, a gas compressor is installed at the top outlet of the ether concentration tower, and a bottom reboiler is installed at the bottom of the ether concentration tower. The gas compressor is connected to the top inlet of the ether concentration tower and the middle inlet of the first ether dehydration tower through the bottom reboiler.

[0009] Furthermore, the bottom of the first ether dehydration tower is equipped with a reboiler, and the top outlet of the second ether dehydration tower is connected to the second phase separator in sequence through the reboiler, the condenser, and the organic phase outlet of the second phase separator. The top feed inlet of the second ether dehydration tower is connected to the water phase outlet of the second phase separator. The bottom reboiler is also provided at the bottom of the second ether dehydration tower.

[0010] Furthermore, the wastewater treatment unit includes a first wastewater separation tower, a second wastewater separation tower, a third wastewater separation tower, a fourth wastewater separation tower, a propylene glycol dehydration tower, a propylene glycol refining tower, and a wastewater collection tank. The upper inlet of the first wastewater separation tower is connected to the ether concentration tower, the first phase separator, and the second phase separator, respectively. The bottom outlet of the first wastewater separation tower is connected to the upper inlet of the second wastewater separation tower. The bottom outlet of the second wastewater separation tower is connected to the upper inlet of the third wastewater separation tower. The bottom outlet of the third wastewater separation tower is connected to the upper inlet of the fourth wastewater separation tower. The bottom outlet of the fourth wastewater separation tower is connected to the upper inlet of the propylene glycol dehydration tower. The bottom outlet of the propylene glycol dehydration tower is connected to the propylene glycol refining tower.

[0011] Furthermore, the first wastewater separation tower is equipped with a first reboiler at its bottom; the second wastewater separation tower is equipped with a second reboiler at its bottom; the third wastewater separation tower is equipped with a third reboiler at its bottom; and the fourth wastewater separation tower is equipped with a fourth reboiler at its bottom. The gas outlet at the top of the first wastewater separation tower is connected to the wastewater collection tank via the second reboiler, the gas outlet at the top of the second wastewater separation tower is connected to the third reboiler, and the gas outlet at the top of the third wastewater separation tower is connected to the fourth reboiler, respectively.

[0012] Furthermore, the ether refining column is equipped with an ether refining column top condenser at the top and an ether refining column bottom reboiler at the bottom.

[0013] The present invention also provides a method for recovering propylene glycol and propylene glycol ether, byproducts of the hydrogen peroxide process for producing propylene oxide based on the above-mentioned recovery system, comprising the following steps:

[0014] (1) The ether- and alcohol-containing wastewater from the hydrogen peroxide process for producing propylene oxide is sent to the methanol removal tower to remove methanol. The top pressure of the methanol removal tower is controlled at -30 to 100 kPaG and the top temperature is controlled at 60 to 120°C. The water vapor with a small amount of methanol mixed in the top of the tower is condensed and removed by a condenser. The water with methanol removed from the bottom of the tower is sent to the ether concentration tower. (2) The top pressure of the ether concentration tower is controlled at 10 to 100 kPaG and the top temperature is controlled at 95 to 120°C. The steam composed of ether and water azeotropically obtained from the top of the tower is pressurized and heated by a gas compressor and then sent to the reboiler at the bottom of the ether concentration tower for heating. Then, it flows to the ether concentration tower and the first ether dehydration tower respectively at a reflux ratio of 0.05 to 2. The wastewater with ether removed from the bottom of the tower is sent to the wastewater treatment unit for separation.

[0015] (3) The pressure at the top of the first ether dehydration tower is controlled at 0.01-0.04 MPaG and the temperature at the top of the tower is controlled at 65-75℃. An azeotropic agent is added. The mixture of water and azeotropic agent obtained at the top of the tower is condensed and sent to the first phase separator for separation. The organic phase azeotropic agent obtained by separation is refluxed, and the aqueous phase is sent to the wastewater treatment unit for separation. The mixture of propylene glycol methyl ether and propylene glycol isomonomethyl ether obtained at the bottom of the tower after removing part of the water is sent to the second ether dehydration tower for azeotropic separation. The azeotropic agent is one of benzene, cyclohexane and methylcyclohexane.

[0016] (4) The pressure at the top of the second ether dehydration tower is controlled at 0.03-0.05 MPaG and the temperature at the top of the tower is controlled at 115-125℃. An azeotropic agent is added. The steam obtained at the top of the tower is sent to the reboiler at the bottom of the first ether dehydration tower for heating. After being condensed by the condenser, it is sent to the second phase separator for phase separation. The organic phase azeotropic agent is refluxed, and the aqueous phase is sent to the wastewater treatment unit for separation. The mixture of propylene glycol methyl ether and propylene glycol isomonomethyl ether that does not contain water obtained at the bottom of the tower is sent to the ether refining tower for refining.

[0017] (5) The pressure at the top of the ether refining column is controlled at 5-50 kPaA and the temperature at the top of the column is controlled at 55-100℃. A propylene glycol monomethyl ether product with a purity of 99.9 wt% is obtained at the top of the column, and a propylene glycol isomethyl ether product with a purity of 99.5 wt% is obtained at the bottom of the column.

[0018] Furthermore, the separation steps of the wastewater treatment unit are as follows:

[0019] (1) Wastewater from the ether concentration tower, the first phase separator and the second phase separator is sent to the first wastewater separation tower. The pressure at the top of the first wastewater separation tower is controlled at 0.7-1.0 MPaG and the temperature is controlled at 165-180℃. The steam obtained at the top of the tower is used to heat the second reboiler and then sent to the wastewater collection tank. The bottom material is sent to the second wastewater separation tower. (2) The pressure at the top of the second wastewater separation tower is controlled at 0.4-0.6 MPaG and the temperature is controlled at 150-170℃. The steam obtained at the top of the tower is used to heat the third reboiler and then sent to the wastewater collection tank. The bottom material is sent to the third wastewater separation tower.

[0020] (3) Control the pressure at the top of the third wastewater separation tower to 0.1-0.3 MPaG and the temperature to 120-140℃. Use the steam obtained at the top of the tower to heat the fourth reboiler and then send it to the wastewater collection tank. Send the material at the bottom of the tower to the fourth wastewater separation tower.

[0021] (4) Control the pressure at the top of the fourth wastewater separation tower to 0.01-0.05 MPaG and the temperature to 100-110℃. Send the concentrated propylene glycol and water mixture obtained at the bottom of the tower to the propylene glycol dehydration tower for dehydration.

[0022] (5) Control the pressure at the top of the propylene glycol dehydration tower to 5-20 kPa and the temperature at the top of the tower to 60-70°C. Send the material obtained at the bottom of the tower into the propylene glycol refining tower for refining.

[0023] (6) The pressure at the top of the propylene glycol refining column is controlled at 5-20 kPa and the temperature at the top of the column is controlled at 100-135℃. Propylene glycol product with a purity of 99.9 wt% is obtained at the top of the column.

[0024] Furthermore, the first, second, third, and fourth wastewater separation towers are all packed towers, filled with bulk packing material, specifically rectangular saddle rings, Raschig rings, and Pall rings. The reflux ratio of each of the four wastewater separation towers is 0.05–0.5. This saves energy and ensures a high PG recovery rate.

[0025] Compared with the prior art, the advantages of the present invention are as follows:

[0026] 1. In the hydrogen peroxide process for producing propylene oxide, the wastewater first enters the deetherification unit to remove ethers from the water. This results in less impurities in the wastewater, higher product yield, better quality, and lower energy consumption. The ether yield is 99%, the purity of propylene glycol monomethyl ether is 99.9%, and the purity of propylene glycol isomonomethyl ether is 99.5%.

[0027] 2. The steam at the top of the ether concentration tower is first pressurized and heated by a compressor, then used to heat the reboiler at the bottom of the ether concentration tower. Utilizing the principle of a heat pump, the reboiler at the bottom of the ether concentration tower no longer uses steam, thus saving energy.

[0028] 3. The top pressure of the first ether dehydration tower is 0.01-0.05 MPaG, and the top temperature is 65-75℃. The top pressure of the second ether dehydration tower is 0.3-0.5 MPaG, and the top temperature is 115-125℃. The heat source for the reboiler at the bottom of the first ether dehydration tower is the heat from the top gas of the second ether dehydration tower. By reasonably adjusting the pressure of the two towers, double-effect distillation can be achieved. The use of double-effect distillation in both towers saves 40% of steam consumption.

[0029] 4. The steam from the top of the first wastewater separation tower provides heat to the reboiler at the bottom of the second wastewater separation tower; the steam from the top of the second wastewater separation tower provides heat to the reboiler at the bottom of the third wastewater separation tower; and the steam from the top of the fourth wastewater separation tower provides heat to the reboiler at the bottom of the fourth wastewater separation tower. This scheme saves approximately 40% of steam consumption compared to using two wastewater separation towers. Although the equipment cost increases with the use of four-tower distillation, the amount of steam used is significantly reduced. Considering both equipment and energy costs, the four-tower wastewater separation method offers better economic benefits. Attached Figure Description

[0030] Figure 1 This is a schematic diagram of the structure of the recovery system for propylene glycol and propylene glycol ether, byproducts of the hydrogen peroxide process for producing propylene oxide in this invention. The components are labeled as follows: 1-Methanol removal tower, 2-Methanol removal tower top condenser, 3-Methanol removal tower bottom reboiler, 4-Ether concentration tower, 5-Gas compressor, 6-Ether concentration tower bottom reboiler, 7-First ether dehydration tower, 8-First ether dehydration tower top condenser, 9-First phase separator, 10-First ether dehydration tower bottom reboiler, 11-Second ether dehydration tower, 12-Second ether dehydration tower top condenser, 13-Second phase separator, 14-Second ether dehydration tower bottom reboiler, 15-Ether purification tower, 16-Ether purification tower top condenser, 17-Ether purification tower bottom reboiler;

[0031] Figure 2 The diagram shows the structure of the wastewater treatment unit of the present invention, with the following labels: 18-first wastewater separation tower, 19-first reboiler, 20-second wastewater separation tower, 21-second reboiler, 22-third wastewater separation tower, 23-third reboiler, 24-fourth wastewater separation tower, 25-fourth reboiler, 26-propylene glycol dehydration tower, 27-propylene glycol refining tower, 28-wastewater collection tank. Detailed Implementation

[0032] The present invention will be further described in detail below with reference to the accompanying drawings and embodiments. Specific Implementation Example 1

[0034] A system for recovering propylene glycol and propylene glycol ether, byproducts of the hydrogen peroxide-based propylene oxide production process, such as... Figure 1 As shown, the system includes a methanol removal tower 1, an ether concentration tower 4, a first ether dehydration tower 7, a first phase separator 9, a second ether dehydration tower 11, and an ether refining tower 15. The methanol removal tower 1 has a material inlet in its middle section. The bottom outlet of the methanol tower is connected to the middle inlet of the ether concentration tower 4. The top outlet of the ether concentration tower 4 is connected to both the top inlet of the ether concentration tower 4 and the middle inlet of the first ether dehydration tower 7. The bottom outlet of the ether concentration tower 4 is connected to a wastewater treatment unit. The top outlet of the first ether dehydration tower 7 is connected to the first phase separator 9 via the top condenser 8 of the first ether dehydration tower. The heavy phase outlet of the first phase separator 9 is connected to the top feed inlet of the first ether dehydration tower 7. The light phase outlet of the first phase separator 9 is connected to the wastewater treatment unit. The bottom outlet of the first ether dehydration tower 7 is connected to the middle feed inlet of the second ether dehydration tower 11. The bottom outlet of the second ether dehydration tower 11 is connected to the middle feed inlet of the ether refining tower 15.

[0035] In this specific embodiment, a methanol stripping tower 1 is equipped with a methanol stripping tower top condenser 2 at its top outlet and a methanol stripping tower bottom reboiler 3 at its bottom. An ether concentration tower 4 is equipped with a gas compressor 5 at its top outlet and an ether concentration tower 4 bottom reboiler 6 at its bottom. The gas compressor 5 is connected to the top inlet of the ether concentration tower 4 and the middle inlet of the first ether dehydration tower 7 via the ether concentration tower bottom reboiler 6. The first ether dehydration tower 7 is equipped with a reboiler 10 at its bottom. The gas outlet at the top of the second ether dehydration tower 11 is connected to the first ether dehydration tower reboiler 10, the second ether dehydration tower top condenser 12, and the second phase separator 13 in sequence. The organic phase outlet of the second phase separator 13 is connected to the feed inlet at the top of the second ether dehydration tower 11, and the aqueous phase outlet of the second phase separator 13 is connected to the wastewater treatment unit. The second ether dehydration tower 11 is equipped with a reboiler 14 at its bottom. The ether purification tower 15 is equipped with an ether purification tower top condenser 16 at its top and an ether purification tower bottom reboiler 17 at its bottom.

[0036] In this specific embodiment, such as Figure 2 As shown, the wastewater treatment unit includes a first wastewater separation tower 18, a second wastewater separation tower 20, a third wastewater separation tower 22, a fourth wastewater separation tower 24, a propylene glycol dehydration tower 26, a propylene glycol refining tower 27, and a wastewater collection tank 28. The upper inlet of the first wastewater separation tower 18 is connected to the ether concentration tower 4, the first phase separator 9, and the second phase separator 13, respectively. The bottom outlet of the first wastewater separation tower 18 is connected to the upper inlet of the second wastewater separation tower 20. The bottom outlet of the second wastewater separation tower 20 is connected to the upper inlet of the third wastewater separation tower 22. The bottom outlet of the third wastewater separation tower 22 is connected to the upper inlet of the fourth wastewater separation tower 24. The bottom outlet of the fourth wastewater separation tower 24 is connected to the upper inlet of the propylene glycol dehydration tower 26. The bottom outlet of the propylene glycol dehydration tower 26 is connected to the middle inlet of the propylene glycol refining tower 27.

[0037] In this specific embodiment, a first reboiler 19 is provided at the bottom of the first wastewater separation tower 18; a second reboiler 21 is provided at the bottom of the second wastewater separation tower 20; a third reboiler 23 is provided at the bottom of the third wastewater separation tower 22; and a fourth reboiler 25 is provided at the bottom of the fourth wastewater separation tower 24. The gas outlet at the top of the first wastewater separation tower 18 is connected to the wastewater collection tank 28 through the second reboiler 21, the gas outlet at the top of the second wastewater separation tower 20 is connected to the third reboiler 23, and the gas outlet at the top of the third wastewater separation tower 22 is connected to the fourth reboiler 25. Specific Implementation Example 2

[0039] The method for recovering propylene glycol and propylene glycol ether, byproducts of the hydrogen peroxide process for producing propylene oxide, based on the above-mentioned recovery system, includes the following steps:

[0040] 1. The ether-containing alcohol wastewater from the hydrogen peroxide process for producing propylene oxide is fed into methanol removal tower 1 to remove methanol. The top pressure of methanol removal tower 1 is controlled at -30 to 100 kPaG, and the top temperature is controlled at 60 to 120°C. The water vapor with a small amount of methanol mixed in the top of the tower is condensed and removed by a condenser. The water with removed methanol obtained from the bottom of the tower is sent to ether concentration tower 4. 2. The top pressure of ether concentration tower 4 is controlled at 10 to 100 kPaG, and the top temperature is controlled at 95 to 120°C. The steam composed of ether and water azeotropically obtained from the top of the tower is pressurized and heated by gas compressor 5, and then sent to the reboiler 6 at the bottom of the ether concentration tower for heating. Then, it flows to ether concentration tower 4 and the first ether dehydration tower 7 respectively at a reflux ratio of 0.05 to 2. The wastewater with removed ether obtained from the bottom of the tower is sent to the wastewater treatment unit for separation.

[0041] 3. The pressure at the top of the first ether dehydration tower 7 is controlled at 0.01-0.04 MPaG, and the temperature at the top of the tower is controlled at 65-75℃. An azeotropic agent is added. The mixture of water and azeotropic agent obtained at the top of the tower is condensed and sent to the first phase separator 9 for separation. The heavy phase azeotropic agent obtained by separation is refluxed, and the light phase water phase is sent to the wastewater treatment unit for separation. The mixture of propylene glycol methyl ether and propylene glycol isomonomethyl ether obtained at the bottom of the tower after removing part of the water is sent to the second ether dehydration tower 11 for azeotropic separation. The azeotropic agent is one of benzene, cyclohexane and methylcyclohexane.

[0042] 4. Control the top pressure of the second ether dehydration tower 11 to 0.03-0.05 MPaG and the top temperature to 115-125℃. Add an azeotropic agent. The steam obtained from the top of the tower is sent to the reboiler 10 at the bottom of the first ether dehydration tower for heating. After being condensed by the condenser, it is sent to the second phase separator 13 for phase separation. The obtained organic phase azeotropic agent is refluxed, and the aqueous phase is sent to the wastewater treatment unit for separation. The mixture of anhydrous propylene glycol methyl ether and propylene glycol isomonomethyl ether obtained from the bottom of the tower is sent to the ether purification tower 15 for purification.

[0043] 5. Control the pressure at the top of the ether refining column 15 to 5-50 kPaA and the temperature at the top of the column to 55-100℃. A propylene glycol monomethyl ether product with a purity of 99.9 wt% is obtained at the top of the column, and a propylene glycol isomethyl ether product with a purity of 99.5 wt% is obtained at the bottom of the column.

[0044] The separation process in the wastewater treatment unit is as follows:

[0045] (1) Wastewater from ether concentration tower 4, first phase separator 9 and second phase separator 13 is sent to first wastewater separation tower 18. The pressure at the top of the first wastewater separation tower 18 is controlled at 0.7-1.0 MPaG and the temperature is controlled at 165-180℃. The steam obtained at the top of the tower is used to heat the second reboiler 21 and then sent to the wastewater collection tank 28. The material at the bottom of the tower is sent to the second wastewater separation tower 20.

[0046] (2) The pressure at the top of the second wastewater separation tower 20 is controlled at 0.4-0.6 MPaG and the temperature is controlled at 150-170℃. The steam obtained at the top of the tower is used to heat the third reboiler 23 and then sent to the wastewater collection tank 28. The material at the bottom of the tower is sent to the third wastewater separation tower 22.

[0047] (3) The pressure at the top of the third wastewater separation tower 22 is controlled at 0.1-0.3 MPaG and the temperature is controlled at 120-140℃. The steam obtained at the top of the tower is used to heat the fourth reboiler 25 and then sent to the wastewater collection tank 28. The material at the bottom of the tower is sent to the fourth wastewater separation tower 24.

[0048] (4) The pressure at the top of the fourth wastewater separation tower 24 is controlled at 0.01-0.05 MPaG and the temperature is controlled at 100-110℃. The concentrated mixture of propylene glycol and water obtained at the bottom of the tower is sent to the propylene glycol dehydration tower 26 for dehydration.

[0049] (5) Control the pressure at the top of the propylene glycol dehydration tower 26 to 5-20 kPa and the temperature to 60-70°C, and send the material obtained at the bottom of the tower to the propylene glycol refining tower 27 for refining.

[0050] (6) The pressure at the top of the propylene glycol refining tower 27 is controlled at 5-20 kPa and the temperature is controlled at 100-135℃. Propylene glycol product with a purity of 99.9 wt% is obtained at the top of the tower.

[0051] The first wastewater separation tower 18, the second wastewater separation tower 20, the third wastewater separation tower 22, and the fourth wastewater separation tower 24 mentioned above are all packed towers, filled with bulk packing material, specifically one of rectangular saddle rings, Raschig rings, and Pall rings. The reflux ratio of the wastewater collection tank 28 is 0.05-0.2. This saves energy and ensures the recovery rate of PG.

[0052] Example 1

[0053] This example illustrates a production of 3800 tons of ether and 2900 tons of propylene glycol per year as byproducts. The wastewater containing ether and alcohol is 16.5 t / h, with the following content by mass: methanol 0.9%, water 93%, ether 2.9%, and propylene glycol (PG) 3.1%.

[0054] Methanol removal tower 1: Top pressure: 0.03 MPaG, top temperature: 90℃, theoretical plate number: 15-25;

[0055] Ether Concentration Tower 4: Top pressure: 20 MPaG, Top temperature: 104℃, Theoretical plate number: 10;

[0056] First ether dehydration tower 7: Top pressure: 0.03 MPaG, top temperature: 70℃, theoretical plate number: 50, using benzene as an azeotropic agent to extract water;

[0057] Second ether dehydration tower 11: Top pressure: 0.04 MPaG, top temperature: 120℃, theoretical plate number: 50, using benzene as an azeotropic agent to extract water;

[0058] Ether refining column 15: Top pressure: 20 kPaA, top temperature: 70℃, theoretical plate number: 52;

[0059] First wastewater separation tower 18: Tower top pressure: 0.85 MPaG, tower top temperature: 170℃, theoretical plate number: 5;

[0060] Second wastewater separation tower 20: Tower top pressure: 0.5MPaG, tower top temperature: 160℃, theoretical plate number: 5;

[0061] Third wastewater separation tower 22: Tower top pressure: 0.2 MPaG, tower top temperature: 135℃, theoretical plate number: 5;

[0062] Fourth wastewater separation tower 24: Tower top pressure: 0.03 MPaG, tower top temperature: 105℃, theoretical plate number: 5;

[0063] Propylene glycol dehydration tower 26: Top pressure: 10 kPaG, top temperature: 65℃, theoretical plate number: 25;

[0064] Propylene glycol refining column 27: Top pressure: 10 kPaA, top temperature: 120℃, theoretical plate number: 22.

[0065] After passing through the ether separation unit (ether purification tower 15), 1820 t / a of propylene glycol monomethyl ether with a purity of 99.9% and 2000 t / a of propylene glycol isomethyl ether with a purity of 99.5% can be obtained. The recovery rate is 99%.

[0066] The wastewater separation unit yielded a concentrated PG aqueous solution of 950 kg / h (approximately 50% of which was PG), demonstrating excellent wastewater separation efficiency. The PG refining unit produced 2900 t / a of PG product with a purity of 99.5% and a PG product recovery rate of 99%.

[0067] Example 2

[0068] This example illustrates a production of 3800 tons of ether and 2900 tons of propylene glycol per year as byproducts. The wastewater containing ether and alcohol is 16.5 t / h, with the following content by mass: methanol 0.9%, water 93%, ether 2.9%, and propylene glycol (PG) 3.1%.

[0069] Methanol Removal Column 1: Top pressure: -30 kPaG, Top temperature: 60℃, Theoretical plate number: 15-25.

[0070] Ether Concentration Tower 4: Top pressure: 10 kPaG, Top temperature: 95℃, Theoretical plate number: 10;

[0071] First ether dehydration tower 7: Top pressure: 0.01 MPaG, Top temperature: 65℃, Azeotropic agent is cyclohexane;

[0072] Second ether dehydration tower 11: Tower top pressure: 0.03 MPaG, tower top temperature: 115℃, azeotropic agent is cyclohexane;

[0073] Ether refining column 15: Top pressure: 5 kPaA, Top temperature: 55℃;

[0074] First wastewater separation tower 18: Tower top pressure: 0.7 MPaG, tower top temperature: 165℃;

[0075] Second wastewater separation tower 20: Tower top pressure: 0.4 MPaG, tower top temperature: 150℃;

[0076] Third wastewater separation tower 22: Tower top pressure: 0.1 MPaG, tower top temperature: 120℃;

[0077] Fourth wastewater separation tower 24: Tower top pressure: 0.01 MPaG, tower top temperature: 100℃;

[0078] Propylene glycol dehydration tower 26: Top pressure: 5 kPa, Top temperature: 60℃;

[0079] Propylene glycol refining column 27: Top pressure: 5 kPa, Top temperature: 100℃.

[0080] After passing through the ether separation unit (ether purification tower 15), 1820 t / a of propylene glycol monomethyl ether with a purity of 99.9% and 2000 t / a of propylene glycol isomethyl ether with a purity of 99.5% can be obtained. The recovery rate is 99%.

[0081] The wastewater separation unit yielded a concentrated PG aqueous solution of 950 kg / h (approximately 50% of which was PG), demonstrating excellent wastewater separation efficiency. The PG refining unit produced 2900 t / a of PG product with a purity of 99.5% and a PG product recovery rate of 99%.

[0082] Example 3

[0083] This example illustrates a production of 3800 tons of ether and 2900 tons of propylene glycol per year as byproducts. The wastewater containing ether and alcohol is 16.5 t / h, containing, by mass: 0.9% methanol, 93% water, 3.8% ether, and 2.9% propylene glycol (PG).

[0084] Methanol removal tower 1: Top pressure: 100 kPaG, Top temperature: 120℃, Theoretical plate number: 15-25;

[0085] Ether Concentration Tower 4: Top pressure: 100 kPaG, Top temperature: 120℃, Theoretical plate number: 10;

[0086] First ether dehydration tower 7: Top pressure: 0.04 MPaG, Top temperature: 75℃, Azeotropic agent is one of benzene, cyclohexane and methylcyclohexane;

[0087] Second ether dehydration tower 11: Tower top pressure: 0.05 MPaG, tower top temperature: 125℃, azeotropic agent is one of benzene, cyclohexane and methylcyclohexane;

[0088] Ether refining column 15: Top pressure: 50 kPaA, Top temperature: 100℃;

[0089] First wastewater separation tower 18: Tower top pressure: 1.0 MPaG, tower top temperature: 180℃;

[0090] Second wastewater separation tower 20: Tower top pressure: 0.6 MPaG, tower top temperature: 170℃;

[0091] Third wastewater separation tower 22: Tower top pressure: 0.3 MPaG, tower top temperature: 140℃;

[0092] Fourth wastewater separation tower 24: Tower top pressure: 0.05 MPaG, tower top temperature: 110℃;

[0093] Propylene glycol dehydration tower 26: Top pressure: 20 kPaA, Top temperature: 70℃;

[0094] Propylene glycol refining column 27: Top pressure: 20 kPaA, Top temperature: 135℃.

[0095] After passing through the ether separation unit (ether purification tower 15), 1810 t / a of propylene glycol monomethyl ether with a purity of 99.9% and 1990 t / a of propylene glycol isomonomethyl ether with a purity of 99.5% can be obtained. The recovery rate is 98.5%.

[0096] The wastewater separation unit yielded a concentrated PG aqueous solution of 950 kg / h (approximately 50% of which was PG), demonstrating excellent wastewater separation efficiency. The PG refining unit produced 2900 t / a of PG product with a purity of 99.5% and a PG product recovery rate of 99%.

[0097] The foregoing description is not intended to limit the invention, nor is the invention limited to the examples given. Any changes, modifications, additions, or substitutions made by those skilled in the art within the scope of the invention should also be considered within the protection scope of the invention.

Claims

1. A recovery system of by-products propylene glycol, propylene glycol ethers in a process for the production of propylene oxide by hydrogen peroxide, characterized in that: The application relates to a methanol removal tower, an ether concentration tower, a first ether dehydration tower, a first phase separator, a second ether dehydration tower and an ether refining tower; a material inlet is arranged in the middle of the methanol removal tower; a bottom discharge port of the methanol removal tower is connected with a middle feeding port of the ether concentration tower; a top gas outlet of the ether concentration tower is connected with a top feeding port of the ether concentration tower and a middle feeding port of the first ether dehydration tower; a bottom discharge port of the ether concentration tower is connected with a wastewater treatment unit; a top gas outlet of the first ether dehydration tower is connected with the first phase separator through a first ether dehydration tower top condenser; a heavy phase outlet of the first phase separator is connected with a top feeding port of the first ether dehydration tower; a light phase outlet of the first phase separator is connected with the wastewater treatment unit; a bottom discharge port of the first ether dehydration tower is connected with a middle feeding port of the second ether dehydration tower; a bottom discharge port of the second ether dehydration tower is connected with a middle feeding port of the ether refining tower; a bottom of the first ether dehydration tower is provided with a first ether dehydration tower bottom reboiler; a top gas outlet of the second ether dehydration tower is connected with a second phase separator in sequence through the first ether dehydration tower bottom reboiler and a second ether dehydration tower top condenser; a heavy phase outlet of the second phase separator is connected with a top feeding port of the second ether dehydration tower; a light phase outlet of the second phase separator is connected with the wastewater treatment unit; a bottom of the second ether dehydration tower is provided with a second ether dehydration tower bottom reboiler; the wastewater treatment unit comprises a first wastewater separation tower, a second wastewater separation tower, a third wastewater separation tower, a fourth wastewater separation tower, a propylene glycol dehydration tower, a propylene glycol refining tower and a wastewater collecting tank; upper feeding ports of the first wastewater separation tower are connected with the ether concentration tower, the first phase separator and the second phase separator; a bottom discharge port of the first wastewater separation tower is connected with an upper feeding port of the second wastewater separation tower; a bottom discharge port of the second wastewater separation tower is connected with an upper feeding port of the third wastewater separation tower; a bottom discharge port of the third wastewater separation tower is connected with an upper feeding port of the fourth wastewater separation tower; a bottom discharge port of the fourth wastewater separation tower is connected with an upper feeding port of the propylene glycol dehydration tower; a bottom discharge port of the propylene glycol dehydration tower is connected with a middle feeding port of the propylene glycol refining tower; a bottom of the first wastewater separation tower is provided with a first reboiler; a bottom of the second wastewater separation tower is provided with a second reboiler; a bottom of the third wastewater separation tower is provided with a third reboiler; a bottom of the fourth wastewater separation tower is provided with a fourth reboiler; a top gas outlet of the first wastewater separation tower is connected with the wastewater collecting tank through the second reboiler; a top gas outlet of the second wastewater separation tower is connected with the wastewater collecting tank through the third reboiler; a top gas outlet of the third wastewater separation tower is connected with the wastewater collecting tank through the fourth reboiler.

2. The recovery system of by-products propylene glycol and propylene glycol ethers in the process of producing propylene oxide by hydrogen peroxide method according to claim 1, characterized in that: The top outlet of the demethanol column is provided with a demethanol column top condenser, and the bottom of the demethanol column is provided with a demethanol column bottom reboiler.

3. The recovery system of by-products propylene glycol and propylene glycol ethers in the process for producing propylene oxide by hydrogen peroxide method according to claim 2, characterized in that: The top outlet of the ether concentration column is provided with a gas compressor, the bottom of the ether concentration column is provided with an ether concentration column bottom reboiler, and the gas compressor is connected with the top inlet of the ether concentration column and the middle inlet of the first ether dehydration column through the ether concentration column bottom reboiler respectively.

4. The recovery system of by-products propylene glycol and propylene glycol ethers in the process for producing propylene oxide by hydrogen peroxide process according to claim 1, characterized in that: The top of the ether refining column is provided with an ether refining column top condenser, and the bottom of the ether refining column is provided with an ether refining column bottom reboiler.

5. A process for recovering propylene glycol, propylene glycol ethers, as by-products in a process for producing propylene oxide by the hydrogen peroxide method based on the recovery system according to any one of claims 1 to 4, characterized by The method comprises the following steps: (1) the ether and alcohol containing wastewater in the hydrogen peroxide method for producing propylene oxide process is sent to the demethanol column to remove methanol, the top pressure of the demethanol column is controlled to be-30-100 kPaG, the top temperature is controlled to be 60-120℃, the water vapor with a small amount of methanol obtained from the top is removed after being condensed by a condenser, and the water obtained from the bottom without methanol is sent to the ether concentration column; (2) the top pressure of the ether concentration column is controlled to be 10-100 kPaG, the top temperature is controlled to be 95-120℃, the vapor composed of ether and water obtained from the top is sent to the ether concentration column bottom reboiler for heating after being pressurized and heated by a gas compressor, and then flows to the ether concentration column and the first ether dehydration column at a reflux ratio of 0.05-2 respectively, the wastewater obtained from the bottom without ether is sent to a wastewater treatment unit for separation; (3) the top pressure of the first ether dehydration column is controlled to be 0.01-0.04 MPaG, the top temperature is controlled to be 65-75℃, azeotrope is added, the mixture of water and azeotrope obtained from the top is sent to a first phase separator for separation after being condensed, the organic phase azeotrope obtained by separation is refluxed, the water phase is sent to the wastewater treatment unit for separation, the mixture of propylene glycol methyl ether and propylene glycol isomonomethyl ether obtained from the bottom without part of water is sent to the second ether dehydration column for azeotropic separation, and the azeotrope is one of benzene, cyclohexane and methylcyclohexane; (4) the top pressure of the second ether dehydration column is controlled to be 0.03-0.05 MPaG, the top temperature is controlled to be 115-125℃, azeotrope is added, the vapor obtained from the top is heated by the first ether dehydration column bottom reboiler, condensed by a condenser and then sent to a second phase separator for phase separation, the organic phase azeotrope obtained is refluxed, the water phase is sent to the wastewater treatment unit for separation, and the mixture of propylene glycol methyl ether and propylene glycol isomonomethyl ether obtained from the bottom without water is sent to the ether refining column for refining; (5) the top pressure of the ether refining column is controlled to be 5-50 kPaA, the top temperature is controlled to be 55-100℃, the propylene glycol monomethyl ether product with a purity of 99.9wt% is obtained from the top, and the propylene glycol isomonomethyl ether product with a purity of 99.5wt% is obtained from the bottom.

6. The method according to claim 5, wherein the method is characterized in that The separation steps of the wastewater treatment unit are as follows: (1) the waste water from the ether condensing tower, the first phase separator and the second phase separator is sent into the first waste water separation tower, the tower top pressure of the first waste water separation tower is controlled to be 0.7-1.0 MpaG, the temperature is controlled to be 165-180℃, the steam obtained from the tower top is sent into the waste water collecting tank after heating by the second reboiler, and the tower bottom material is sent into the second waste water separation tower; (2) the tower top pressure of the second waste water separation tower is controlled to be 0.4-0.6 MpaG, the temperature is controlled to be 150-170℃, the steam obtained from the tower top is sent into the waste water collecting tank after heating by the third reboiler, and the tower bottom material is sent into the third waste water separation tower; (3) the tower top pressure of the third waste water separation tower is controlled to be 0.1-0.3 MpaG, the temperature is controlled to be 120-140℃, the steam obtained from the tower top is sent into the waste water collecting tank after heating by the fourth reboiler, and the tower bottom material is sent into the fourth waste water separation tower; (4) the tower top pressure of the fourth waste water separation tower is controlled to be 0.01-0.05 MpaG, the temperature is controlled to be 100-110℃, the mixture of propylene glycol and water obtained from the tower bottom is sent into the propylene glycol dehydration tower for dehydration; (5) the tower top pressure of the propylene glycol dehydration tower is controlled to be 5-20 kPa, the tower top temperature is controlled to be 60-70℃, and the material obtained from the tower bottom is sent into the propylene glycol refining tower for refining; (6) the tower top pressure of the propylene glycol refining tower is controlled to be 5-20 kPa, the tower top temperature is controlled to be 100-135℃, and the propylene glycol product with a purity of 99.9wt% is obtained from the tower top.

7. The method according to claim 5, wherein the method is characterized in that: The first waste water separation tower, the second waste water separation tower, the third waste water separation tower and the fourth waste water separation tower are all packed towers, which are filled with bulk packing, the packing is one of the matrix saddle ring, Rasching ring and Paul ring, and the reflux ratio of the waste water collecting tank is 0.05-0.2.

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