Method for recovering PGME and PGIE from HPPO process wastewater

Abstract

According to the method for recovering the PGME and the PGIE from the HPPO process wastewater, the HPPO process wastewater is concentrated through the membrane separation device, the content of the PGME and the PGIE in the wastewater is greatly increased, and compared with the prior art, the energy consumption can be greatly reduced, the recovery efficiency can be improved, and the recovery cost can be reduced; 2-pentanone or 3-pentanone and a mixture of 2-pentanone and 3-pentanone are used as an azeotropic solvent to replace benzene, and the solvent circulation amount in the dehydration process can be reduced by 50% under the same pressure, so that the dehydration energy consumption is remarkably reduced, and the green and environment-friendly process requirements are met; the water layer of the dehydrated fraction is recycled into the HPPO process wastewater and then is subjected to membrane separation, so that the loss of trace PGME entrained in the dehydrated fraction can be avoided, and the yield of the PGME is increased; according to the technical scheme, the recovery rates of the PGME and the PGIE can reach 99%.

Description

Technical Field

[0001] This invention belongs to the field of wastewater treatment, specifically relating to a method for recovering PGME and PGIE from HPPO process wastewater. Background Technology

[0002] Propylene oxide (PO), a significant derivative of propylene, accounts for 6% of total propylene consumption and is a crucial basic chemical raw material. With increasingly stringent national environmental protection requirements and restrictions imposed by industrial restructuring catalogs, the direct hydrogen peroxide oxidation process for propylene oxide (HPPO) has become the mainstream PO production technology due to its green, low-carbon, efficient, and economical characteristics. However, the HPPO process generates substantial amounts of byproducts such as propylene glycol monomethyl ether (PGME) and propylene glycol isomethyl ether (PGIE), with varying amounts produced at different reaction stages (approximately 1-5% of the main product, propylene oxide). These byproducts ultimately end up in wastewater, and direct treatment not only increases the difficulty of wastewater treatment but also significantly increases treatment costs. PGME, as a low-toxicity and excellent solvent, is widely used in industrial and consumer products and is also an important raw material for fuel antifreeze, detergents, and extractants. Recovering the byproducts PGME and PGIE can generate considerable economic benefits.

[0003] Because PGME, PGIE, and water form an azeotropic mixture with an azeotropic temperature close to that of water, existing methods involve introducing wastewater containing PGME and PGIE into a concentration tower for distillation, followed by benzene azeotropic distillation to remove water, and then further separation of PGME and PGIE products by distillation. However, due to the low water content in the benzene-water azeotrope, the distillation process involves a large benzene recycling volume and high energy consumption. Furthermore, the high toxicity of benzene poses a serious potential threat to the environment. Therefore, there is an urgent need to develop a more efficient, energy-saving, and environmentally friendly method for the separation and recovery of PGME to replace the existing process. Summary of the Invention

[0004] The purpose of this invention is to address the high energy consumption caused by the azeotropic reaction of PGME, PGIE, and water in HPPO process wastewater. This invention provides a method for recovering PGME and PGIE from HPPO process wastewater. Membrane separation is used instead of negative pressure distillation to concentrate the light wastewater from the HPPO process, reducing recovery energy consumption. 2-Pentanone and 3-Pentanone are used as azeotropic agents to replace benzene, significantly reducing solvent circulation and dehydration energy consumption, thus meeting the requirements of green and environmentally friendly processes.

[0005] To achieve the above objectives, the present invention provides the following technical solution: A method for recovering PGME and PGIE from HPPO process wastewater includes the following steps: (1) The HPPO process wastewater passes through a membrane separation device, and the by-products are concentrated before entering the dehydration tower; (2) The concentrate enters the dehydration tower, an azeotropic solvent is added, and the water in the organic matter is removed by azeotropic distillation. After the dehydrated fraction is separated into oil and water in the separator, the oil layer is returned to the dehydration tower for reuse, and the water layer is reused in the deionization of light wastewater. (3) The material in the bottom of the dehydration tower is separated by a monomethyl ether tower and an isomethyl ether tower to obtain PGME and PGIE products.

[0006] Furthermore, the HPPO process wastewater contains 0.1-5% PGME, 0.1-5% PGIE, and 0-3% other organic matter.

[0007] Furthermore, the pressure of the membrane separation device is 0.5~4 MPa, which is used for the preliminary concentration of PGME and PGIE in HPPO process wastewater. After membrane concentration, the content of PGME and PGIE can be increased by 10~50 times.

[0008] Furthermore, the azeotropic solvent is at least one of 2-pentanone and 3-pentanone, and the initial feed amount of the azeotropic solvent is approximately 3 to 10 times the mass ratio of the material after membrane concentration.

[0009] Furthermore, the dehydration tower is a packed tower or a plate tower with 20 to 60 plates, a bottom temperature of 105 to 125°C, and a top temperature of 80 to 95°C; the separator is used for oil-water separation, with the oil layer circulating into the dehydration tower and the water layer returning to the HPPO process wastewater for reuse.

[0010] Furthermore, the material from the bottom of the dehydration tower enters the monomethyl ether tower for distillation to recover PGME, and the PGME product is obtained at the top of the distillation tower; the monomethyl ether tower is a packed tower or a plate tower with 40 to 60 plates, atmospheric pressure, bottom temperature of 130 to 140°C, top temperature of 115 to 125°C, and reflux ratio of 10 to 15:1.

[0011] Furthermore, the bottom material of the monomethyl ether tower enters the isomethyl ether tower for PGIE recovery, the top of the isomethyl ether tower yields PGIE product, and the bottom material of the isomethyl ether tower is sent for incineration. The isomethyl ether tower is a packed tower or a plate tower with 30 to 60 plates, atmospheric pressure, bottom temperature of 140 to 145°C, top temperature of 130 to 135°C, and reflux ratio of 5 to 10:1.

[0012] The beneficial effects of this invention are: This invention concentrates HPPO process wastewater using a membrane separation device, significantly increasing the content of PGME and PGIE in the wastewater. Compared with existing technologies, it can significantly reduce energy consumption, improve recovery efficiency, and reduce recovery costs. By using 2-pentanone or 3-pentanone, or a mixture thereof, as an azeotropic solvent to replace benzene, the solvent circulation volume during dehydration can be reduced by 50% under the same pressure, significantly reducing dehydration energy consumption and meeting the requirements of green and environmentally friendly processes. The dehydrated distillate water layer is reused in the HPPO process wastewater for further membrane separation, which can avoid the loss of trace amounts of PGME entrained in the dehydrated distillate and improve the PGME yield. The recovery rates of PGME and PGIE in this invention can both reach 99%. Attached Figure Description

[0013] Figure 1 This is a material flow diagram of the technical solution of the present invention; The components are: 1. HPPO process wastewater; 2. Material after membrane concentration; 3. Membrane separation wastewater; 4. Dehydrated fraction; 5. Material in the bottom of the dehydration tower; 6. Oil layer; 7. Water layer; 8. PGME product; 9. Material in the bottom of the monomethyl ether tower; 10. PGIE product; 11. Material in the bottom of the isomethyl ether tower. Detailed Implementation

[0014] To make the technical means, features and effects of the present invention easier to understand, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments.

[0015] Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0016] Example 1 A method for recovering PGME and PGIE from HPPO process wastewater includes the following steps: (1) The PGME content in the HPPO process wastewater is 0.1%, and the PGIE content is 0.2%, such as Figure 1 As shown, the feed rate is 50 t / h into the membrane separation unit, the operating pressure is 0.5 MPa, the material after membrane concentration is 0.35 t / h, the PGME content in the material after membrane concentration is 14.7%, the PGIE content is 12.5%, and the water content is 72.5%; the membrane separation wastewater flow rate is 49.65 t / h, which is sent to wastewater treatment. (2) After membrane concentration, the material enters the dehydration tower. The azeotropic solvent is 2-pentanone. The dehydration tower is a packed tower with 20 theoretical plates. The bottom temperature is 105℃ and the top temperature is 80℃. The bottom flow rate of the dehydration tower is 0.1t / h, of which the PGME content is 53.4% ​​and the PGIE content is 45.5%. The dehydration fraction has a flow rate of 1.5t / h and enters the separator for oil-water separation. The water layer has a flow rate of 0.25t / h, with a PGME content of 0.05% and a PGIE content of 0.01%, which is recycled to the HPPO process wastewater. The oil layer has a flow rate of 1.25t / h and is recycled back to the dehydration tower for reuse. (3) The material from the bottom of the dehydration tower enters the monomethyl ether tower. The monomethyl ether tower is a packed tower with 40 theoretical plates. The tower pressure is atmospheric pressure, the bottom temperature is 130℃, the top temperature is 115℃, and the reflux ratio is 10:1. The PGME product obtained at the top of the tower has a flow rate of 53.3 kg / h and a purity of 99.95%. The material from the bottom of the tower enters the isomethyl ether tower. The isomethyl ether tower is a packed tower with 40 theoretical plates. The tower pressure is atmospheric pressure, the bottom temperature is 145℃, the top temperature is 130℃, and the reflux ratio is 5:1. The PGIE product obtained at the top of the tower has a flow rate of 45.4 kg / h and a purity of 99.90%. The flow rate of the isomethyl ether tower bottom is 1.2 kg / h, mainly for high-boiling impurities to be incinerated.

[0017] Example 2 A method for recovering PGME and PGIE from HPPO process wastewater includes the following steps: (1) The PGME content in the alcohol ether wastewater of the HPPO process is 0.5% and the PGIE content is 0.4%. It is fed into the membrane separation unit at a feed rate of 50t / h and an operating pressure of 1MPa. The material after membrane concentration is 1.6t / h. The PGME content in the material after membrane concentration is 15.5%, the PGIE content is 11.5%, and the water content is 72.2%. The flow rate of membrane separation wastewater is 48.4t / h, which is then sent to wastewater treatment. (2) After membrane concentration, the material enters the dehydration tower. The azeotropic solvent is a mixture of 3-pentanone and 2-pentanone. The dehydration tower is a plate tower with 30 plates. The bottom temperature is 110℃ and the top temperature is 85℃. The bottom flow rate of the dehydration tower is 0.45t / h, of which the PGME content is 55.5% and the PGIE content is 41.3%. The dehydration fraction flow rate is 6.90t / h, which enters the separator for oil-water separation. The water layer flow rate is 1.15t / h, and the PGME content in the water layer is 0.03% and the PGIE content is 0.01%. It is recycled to the HPPO process wastewater. The oil layer flow rate is 5.75t / h, and the oil layer is recycled back to the dehydration tower for reuse. (3) The material from the bottom of the dehydration tower enters the monomethyl ether tower. The monomethyl ether tower is a packed tower with 40 theoretical plates. The tower pressure is atmospheric pressure, the bottom temperature is 135℃, the top temperature is 120℃, and the reflux ratio is 10:1. The PGME product obtained at the top of the tower has a flow rate of 249 kg / h and a purity of 99.95%. The material from the bottom of the tower enters the isomethyl ether tower. The isomethyl ether tower is a packed tower with 30 theoretical plates. The tower pressure is atmospheric pressure, the bottom temperature is 140℃, the top temperature is 130℃, and the reflux ratio is 10:1. The PGIE product obtained at the top of the tower has a flow rate of 185 kg / h and a purity of 99.90%. The flow rate of the isomethyl ether tower bottom is 16 kg / h, mainly for high-boiling impurities to be incinerated.

[0018] Example 3 A method for recovering PGME and PGIE from HPPO process wastewater includes the following steps: (1) The PGME content in the alcohol ether wastewater of the HPPO process is 1.0% and the PGIE content is 0.8%. It is fed into the membrane separation unit at a feed rate of 50t / h and an operating pressure of 2MPa. The material after membrane concentration is 2.5t / h. The PGME content in the material after membrane concentration is 19.5%, the PGIE content is 15.8%, and the water content is 63.5%. The flow rate of membrane separation wastewater is 47.5t / h, which is then sent to wastewater treatment. (2) After membrane concentration, the material enters the dehydration tower. The azeotropic solvent is 3-pentanone. The dehydration tower is a plate tower with 40 plates. The bottom temperature is 110℃ and the top temperature is 95℃. The bottom flow rate of the dehydration tower is 0.92t / h, of which the PGME content is 53.4% ​​and the PGIE content is 43.1%. The dehydration fraction flow rate is 9.50t / h, which enters the separator for oil-water separation. The water layer flow rate is 1.58t / h, and the PGME content in the water layer is 0.02% and the PGIE content is 0.01%. It is recycled to the HPPO process wastewater. The oil layer flow rate is 7.92t / h, and the oil layer is recycled back to the dehydration tower for reuse. (3) The material from the bottom of the dehydration tower enters the monomethyl ether tower. The monomethyl ether tower is a packed tower with 50 theoretical plates. The tower pressure is atmospheric pressure, the bottom temperature is 140℃, the top temperature is 125℃, and the reflux ratio is 15:1. The PGME product obtained at the top of the tower has a flow rate of 491 kg / h and a purity of 99.95%. The material from the bottom of the tower enters the isomethyl ether tower. The isomethyl ether tower is a packed tower with 40 theoretical plates. The tower pressure is atmospheric pressure, the bottom temperature is 145℃, the top temperature is 135℃, and the reflux ratio is 10:1. The PGIE product obtained at the top of the tower has a flow rate of 396 kg / h and a purity of 99.90%. The flow rate of the isomethyl ether tower bottom is 63 kg / h, mainly for high-boiling impurities to be incinerated.

[0019] Example 4 A method for recovering PGME and PGIE from HPPO process wastewater includes the following steps: (1) The PGME content in the alcohol ether wastewater of the HPPO process is 2.5% and the PGIE content is 2.0%. It is fed into the membrane separation unit at a feed rate of 30t / h and an operating pressure of 3MPa. The material after membrane concentration is 4.0t / h. The PGME content in the material after membrane concentration is 18.5%, the PGIE content is 14.8%, and the water content is 66.2%. The flow rate of membrane separation wastewater is 26.0t / h, which is then sent to wastewater treatment. (2) After membrane concentration, the material enters the dehydration tower. The azeotropic solvent is 3-pentanone. The dehydration tower is a plate tower with 50 plates. The bottom temperature is 120℃ and the top temperature is 95℃. The bottom flow rate of the dehydration tower is 1.35t / h, of which the PGME content is 54.6% and the PGIE content is 43.5%. The dehydration fraction flow rate is 15.9t / h, which enters the separator for oil-water separation. The water layer flow rate is 2.65t / h, and the PGME content in the water layer is 0.02% and the PGIE content is 0.01%. It is recycled to the HPPO process wastewater. The oil layer flow rate is 13.25t / h, and the oil layer is recycled back to the dehydration tower for reuse. (3) The material from the bottom of the dehydration tower enters the monomethyl ether tower. The monomethyl ether tower is a packed tower with 50 theoretical plates. The tower pressure is atmospheric pressure, the bottom temperature is 140℃, the top temperature is 125℃, and the reflux ratio is 15:1. The PGME product obtained at the top of the tower has a flow rate of 735 kg / h and a purity of 99.95%. The material from the bottom of the tower enters the isomethyl ether tower. The isomethyl ether tower is a packed tower with 40 theoretical plates. The tower pressure is atmospheric pressure, the bottom temperature is 145℃, the top temperature is 135℃, and the reflux ratio is 10:1. The PGIE product obtained at the top of the tower has a flow rate of 587 kg / h and a purity of 99.90%. The flow rate of the isomethyl ether tower bottom is 28 kg / h, mainly for high-boiling impurities to be incinerated.

[0020] Example 5 A method for recovering PGME and PGIE from HPPO process wastewater includes the following steps: (1) The PGME content in the alcohol ether wastewater of the HPPO process is 5.0% and the PGIE content is 4.5%. It is fed into the membrane separation unit at a feed rate of 20t / h and an operating pressure of 4MPa. The material after membrane concentration is 6.5t / h. The PGME content in the material after membrane concentration is 45.5%, the PGIE content is 13.8%, and the water content is 70.2%. The flow rate of membrane separation wastewater is 13.5t / h, which is then sent to wastewater treatment. (2) After membrane concentration, the material enters the dehydration tower. The azeotropic solvent is 3-pentanone. The dehydration tower is a plate tower with 60 plates. The bottom temperature is 125℃ and the top temperature is 95℃. The bottom flow rate of the dehydration tower is 1.94t / h, of which the PGME content is 51.5% and the PGIE content is 46.3%. The dehydration fraction flow rate is 27.4t / h, which enters the separator for oil-water separation. The water layer flow rate is 4.56t / h, and the PGME content in the water layer is 0.05% and the PGIE content is 0.02%. It is recycled to the HPPO process wastewater. The oil layer flow rate is 22.84t / h, and the oil layer is recycled to the dehydration tower for reuse. (3) The material from the bottom of the dehydration tower enters the monomethyl ether tower. The monomethyl ether tower is a packed tower with 60 theoretical plates. The tower pressure is atmospheric pressure, the bottom temperature is 140℃, the top temperature is 125℃, and the reflux ratio is 15:1. The PGME product obtained at the top of the tower has a flow rate of 990 kg / h and a purity of 99.95%. The material from the bottom of the tower enters the isomethyl ether tower. The isomethyl ether tower is a packed tower with 60 theoretical plates. The tower pressure is atmospheric pressure, the bottom temperature is 145℃, the top temperature is 135℃, and the reflux ratio is 10:1. The PGIE product obtained at the top of the tower has a flow rate of 895 kg / h and a purity of 99.90%. The flow rate of the isomethyl ether tower bottom is 55 kg / h, mainly for high-boiling impurities to be incinerated.

[0021] Comparative Example 1 The HPPO process wastewater contains 1.0% PGME and 0.8% PGIE. It is fed into a distillation column at a rate of 50 t / h for concentration, consuming 20 t / h of medium-pressure steam. The top material of the distillation column, i.e., the concentrated material, has a flow rate of 3.5 t / h, containing 13.8% PGME, 10.8% PGIE, and 74.4% water. The concentrated wastewater flow rate is 46.5 t / h, which is then sent to wastewater treatment. Compared to using membrane separation for concentration, this method results in an additional 20 t / h of medium-pressure steam loss. After concentration, the material enters a dehydration tower with benzene as the azeotropic solvent. The dehydration tower is a packed tower with 40 theoretical plates, a bottom temperature of 115℃, a top temperature of 80℃, and a bottom flow rate of 0.90 t / h. The PGME content is 54.5%, and the PGIE content is 42.9%. The top flow rate is 26.0 t / h, and the material enters a separatory tank for oil-water separation. The water layer has a flow rate of 2.60 t / h, with a PGME content of 0.10% and a PGIE content of 0.05%, and is then treated as wastewater. The oil layer has a flow rate of 23.4 t / h and is recycled back to the dehydration tower. Compared to using 3-pentanone as the azeotropic dehydration solvent, the circulation rate increases by 16.5 t / h, and the steam volume increases by 50%. The dehydrated material enters the monomethyl ether (GME) tower, a packed tower with 50 theoretical plates, atmospheric pressure, a bottom temperature of 140°C, a top temperature of 125°C, and a reflux ratio of 15:1. The top product yields PGME with a flow rate of 490 kg / h and a purity of 99.90%. The bottom material enters the isomethyl ether (IME) tower, a packed tower with 40 theoretical plates, atmospheric pressure, a bottom temperature of 145°C, a top temperature of 135°C, and a reflux ratio of 10:1. The top product yields PGIE with a flow rate of 376 kg / h and a purity of 98.50%. The bottom flow rate of the IME tower is 34 kg / h, primarily for high-boiling-point impurities to be incinerated.

[0022] Finally, it should be noted that the above content is only used to illustrate the technical solution of the present invention, and is not intended to limit the scope of protection of the present invention. Simple modifications or equivalent substitutions made by those skilled in the art to the technical solution of the present invention do not depart from the substantive protection scope of the technical solution of the present invention.

Claims

1. A method for recovering PGME and PGIE from HPPO process wastewater, characterized in that, Includes the following steps: (1) The HPPO process wastewater passes through a membrane separation device, and the by-products are concentrated before entering the dehydration tower; (2) The concentrate enters the dehydration tower, an azeotropic solvent is added, and the water in the organic matter is removed by azeotropic distillation. After the dehydrated fraction is separated into oil and water in the separator, the oil layer is returned to the dehydration tower for reuse, and the water layer is reused in the deionization of light wastewater. (3) The material in the bottom of the dehydration tower is separated by a monomethyl ether tower and an isomethyl ether tower to obtain PGME and PGIE products.

2. The method for recovering PGME and PGIE from HPPO process wastewater according to claim 1, characterized in that, The HPPO process wastewater contains 0.1-5% PGME and 0.2-4.5% PGIE.

3. The method for recovering PGME and PGIE from HPPO process wastewater according to claim 1, characterized in that, The pressure of the membrane separation device is 0.5~4 MPa.

4. The method for recovering PGME and PGIE from HPPO process wastewater according to claim 1, characterized in that, The azeotropic solvent is at least one of 2-pentanone and 3-pentanone.

5. The method for recovering PGME and PGIE from HPPO process wastewater according to claim 1, characterized in that, The dehydration tower is a packed tower or a plate tower with 20 to 60 plates, a bottom temperature of 105 to 125°C, and a top temperature of 80 to 95°C. The separator is used for oil-water separation, with the oil layer circulating into the dehydration tower and the water layer returning to the HPPO process wastewater for reuse.

6. The method for recovering PGME and PGIE from HPPO process wastewater according to claim 1, characterized in that, The material from the bottom of the dehydration tower enters the monomethyl ether tower for distillation to recover PGME, and the PGME product is obtained at the top of the distillation tower. The monomethyl ether tower is a packed tower or a plate tower with 40 to 60 plates, atmospheric pressure, bottom temperature of 130 to 140°C, top temperature of 115 to 125°C, and reflux ratio of 10 to 15:

1.

7. The method for recovering PGME and PGIE from HPPO process wastewater according to claim 1, characterized in that, The bottom material of the monomethyl ether tower enters the isomethyl ether tower for PGIE recovery. PGIE product is obtained at the top of the isomethyl ether tower. The bottom material of the isomethyl ether tower is sent for incineration. The isomethyl ether tower is a packed tower or a plate tower with 30 to 60 plates, atmospheric pressure, bottom temperature of 140 to 145°C, top temperature of 130 to 135°C, and reflux ratio of 5 to 10:1.

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