Method for recovering byproduct propylene glycol from HPPO process

Abstract

The invention relates to the technical field of energy conservation and consumption reduction in chemical production, in particular to an HPPO process byproduct propylene glycol recovery method which comprises a wastewater evaporator, a concentrated wastewater pump, a preheater, a propylene glycol flash tank, a waste liquid pump, a propylene glycol recovery tower, a recovery tower reflux tank, a recovery tower kettle pump, a propylene glycol reflux pump, a crude propylene glycol tank and a crude propylene glycol delivery pump. Compared with the prior art, the HPPO byproduct propylene glycol recovery method provided by the invention has the following beneficial effects: compared with the prior art, the process is optimized, alkali addition of a wastewater feeding pipeline is omitted, equipment materials are upgraded, the salt content in a propylene glycol recovery system is reduced, the concentration ratio of the system is reduced, and propylene glycol in the wastewater is recovered as much as possible; meanwhile, the propylene glycol process of the tower kettle of the propylene glycol recovery tower is optimized, crude propylene glycol recovery equipment is additionally arranged, crude propylene glycol in the tower kettle is recycled again, and the loss of propylene glycol is reduced.

Description

Technical Field

[0001] The invention relates to the technical field of energy saving and consumption reduction in chemical production, and in particular to a method for recovering propylene glycol as a by-product of a HPPO process. Background Art

[0002] Propylene oxide (PO) is an important basic organic chemical raw material and the third largest organic chemical product among propylene derivatives, second only to polypropylene and acrylonitrile. It is mainly used to produce polyether polyols, propylene glycol and polyurethane, and is also the main raw material for non-ionic surfactants for fourth-generation detergents, oilfield demulsifiers and pesticide emulsifiers, with broad development prospects. Propylene oxide derivatives are also widely used in food, tobacco, pesticides and cosmetics industries, with nearly 100 downstream products, and are important raw materials for fine chemical products.

[0003] The main industrial production processes for propylene oxide are the chlorohydrin process and the co-oxidation process, which account for about 90% of the global production of propylene oxide. This device adopts the hydrogen peroxide direct oxidation process (HPPO process), using propylene and hydrogen peroxide as raw materials and methanol as solvent to produce propylene oxide, and by-products include propylene glycol, monomethyl ether and isomethyl ether.

[0004] Propylene glycols (PGs), including monopropylene glycol (1,2-propylene glycol), dipropylene glycol and tripropylene glycol, are organic compounds with the chemical formula C3H8O2, which are miscible with water, ethanol and a variety of organic solvents. Propylene glycols are colorless, viscous, hygroscopic, low-toxic liquids. They are commercially produced from propylene oxide by hydration or by transesterification with propylene carbonate, and are also produced from renewable raw materials, such as bio-based propylene glycol from glycerol. Propylene glycol can be used as a raw material for unsaturated polyester resins and can be used as a wetting agent in cosmetics, toothpastes and soaps in combination with glycerol or sorbitol. It is widely used as a hygroscopic agent, antifreeze agent, lubricant and solvent in the food and pharmaceutical industries.

[0005] At present, in the propylene glycol recovery system of the existing HPPO process of this device, in order to avoid acid corrosion of the equipment, it is necessary to add alkali before feeding the evaporator, resulting in a high salt content in the propylene glycol recovery system, and the system concentration ratio is about 2.0wt% (ratio of waste liquid discharge to wastewater feed amount), resulting in that the propylene glycol cannot be fully concentrated and recovered; at the same time, when the propylene glycol recovery tower recovers propylene glycol, a high concentration of about 95wt% of propylene glycol is extracted through the side extraction and sent to the refining to obtain 99.8wt% of refined propylene glycol, and the bottom of the tower is a crude propylene glycol mixture of propylene glycol, dipropylene glycol, tripropylene glycol, etc. In order to stabilize the operation and ensure the quality of the refined propylene glycol product, the crude propylene glycol in the bottom of the tower needs to be extracted and sent to the waste liquid furnace for incineration treatment, resulting in the loss of propylene glycol. Summary of the invention

[0006] The invention aims to provide a method for recovering propylene glycol as a by-product of a HPPO process. Aiming at the propylene glycol loss problem of a propylene glycol recovery system of a current HPPO process, the invention optimizes the process, cancels the addition of alkali in a wastewater feed pipeline, upgrades equipment materials, reduces the salt content in the propylene glycol recovery system, reduces the system concentration ratio, and recovers propylene glycol in wastewater as much as possible; at the same time, the propylene glycol process of a propylene glycol recovery tower and a bottom, and crude propylene glycol recovery equipment is added to recycle the crude propylene glycol in the bottom of the tower, thereby reducing the loss of propylene glycol.

[0007] The above technical objectives of the present invention are achieved through the following technical solutions: a method for recovering propylene glycol as a by-product of a HPPO process, comprising a wastewater evaporator, a concentrated wastewater pump, a preheater, a propylene glycol flash tank, a waste liquid pump, a propylene glycol recovery tower, a recovery tower reflux tank, a recovery tower kettle pump, a propylene glycol reflux pump, a crude propylene glycol tank, and a crude propylene glycol delivery pump. The ether-containing wastewater of the wastewater evaporator is transported to a downstream unit after heating and evaporation. The concentrated wastewater of the wastewater evaporator is transported to a preheater through a concentrated wastewater pump to preheat the material and then enter the propylene glycol flash tank; the propylene glycol-containing material evaporated from the top of the propylene glycol flash tank enters the propylene glycol recovery tower, and the concentrated waste liquid at the bottom of the propylene glycol flash tank is transported through a waste liquid pump. The outlet of the waste liquid pump is divided into two paths, one of which is used as a circulating material to be transported to the inlet of the preheater, and the other is connected to a waste liquid pipeline. The waste liquid is transported to a waste liquid furnace for treatment; after the materials in the propylene glycol recovery tower are heated and evaporated for separation, the light components at the top of the tower enter the reflux tank of the recovery tower, and the materials in the reflux tank of the recovery tower are transported by a propylene glycol reflux pump, a part of which is returned to the propylene glycol recovery tower as reflux, and a part of which is transported to a downstream unit; the propylene glycol recovered by evaporation in the propylene glycol recovery tower is collected in a liquid collection tray on the side of the propylene glycol recovery tower, and the propylene glycol with a higher purity of about 95wt% is transported to a downstream propylene glycol refining unit for distillation to produce more than 99.8wt% of refined propylene glycol; the crude propylene glycol in the tower kettle of the propylene glycol recovery tower is transported in three ways by a recovery tower kettle pump, one way is transported to a waste liquid pump for concentration recovery, one way is transported to a waste liquid furnace for incineration treatment, and another way is transported to a crude propylene glycol tank buffer and then transported to the downstream for recovery treatment by a crude propylene glycol transport pump.

[0008] Preferably, the wastewater evaporator, concentrated wastewater pump, preheater, propylene glycol flash tank, waste liquid pump, propylene glycol recovery tower, recovery tower reflux tank, recovery tower kettle pump, propylene glycol reflux pump, crude propylene glycol tank, crude propylene glycol delivery pump, and related pipelines are all made of acid-corrosion-resistant materials.

[0009] Preferably, the wastewater evaporator, propylene glycol flash tank and propylene glycol recovery tower are operated under vacuum conditions.

[0010] Preferably, the operating pressure of the propylene glycol recovery tower is controlled at -70 to -90 kPa.

[0011] Preferably, the waste liquid pipeline is provided with heating to prevent the pipeline from being blocked due to viscosity of the material.

[0012] Preferably, the propylene glycol content in the reflux tank of the recovery tower is controlled within 1.0 wt%.

[0013] Preferably, the waste liquid pipeline is provided with a hot water flushing facility, and when the waste liquid pipeline stops delivering waste liquid, hot water is used for flushing to avoid pipeline blockage.

[0014] Preferably, the kettle of the propylene glycol recovery tower is provided with sampling and analysis facilities, and the main analysis indicators are: water, propylene glycol, dipropylene glycol and tripropylene glycol.

[0015] Preferably, when the water content in the bottom of the propylene glycol recovery tower is greater than 20 wt%, the bottom material is returned to the inlet of the waste liquid pump for concentrated recovery.

[0016] Preferably, when the propylene glycol content in the bottom of the propylene glycol recovery tower is greater than 80 wt%, the bottom material is sent to a crude propylene glycol tank for buffering.

[0017] In summary, the present invention has the following beneficial effects: compared with the existing process, the method for recovering HPPO by-product propylene glycol provided by the present invention optimizes the process, cancels the addition of alkali in the wastewater feed pipeline, upgrades the equipment material, reduces the salt content in the propylene glycol recovery system, reduces the system concentration ratio, and recovers propylene glycol in the wastewater as much as possible; at the same time, the propylene glycol process of the propylene glycol recovery tower bottom is optimized, crude propylene glycol recovery equipment is added, the crude propylene glycol in the tower bottom is recycled again, and the loss of propylene glycol is reduced. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 It is a process flow chart of an embodiment.

[0019] In the figure, 1. wastewater pipeline; 2. wastewater evaporator; 3. ether-containing wastewater pipeline a; 4. concentrated wastewater pump; 5. concentrated wastewater pipeline; 6. preheater; 7. propylene glycol flash tank; 8. propylene glycol feed pipeline; 9. waste liquid circulation pipeline; 10. waste liquid pump; 11. waste liquid pipeline; 12. propylene glycol recovery tower; 13. recovery tower top pipeline; 14. recovery tower reflux tank; 15. recovery tower reflux pipeline; 16. propylene glycol side sampling pipeline; 17. recovery tower bottom pump; 18. crude propylene glycol pipeline; 19. propylene glycol reflux pump; 20. ether-containing wastewater pipeline b; 21. propylene glycol recovery pipeline; 22. crude propylene glycol tank; 23. crude propylene glycol delivery pump; 24. tower bottom crude methanol pipeline. DETAILED DESCRIPTION

[0020] The present invention is further described in detail below in conjunction with the accompanying drawings.

[0021] This specific embodiment is merely an explanation of the present invention and is not a limitation of the present invention. After reading this specification, those skilled in the art may make non-creative modifications to the present embodiment as needed. However, as long as they are within the scope of the claims of the present invention, they are protected by the patent law.

[0022] Example:

[0023] like Figure 1 As shown, the wastewater from the wastewater pipeline 1 enters the wastewater evaporator 2. The wastewater containing ether is evaporated by steam heating in the wastewater evaporator 2 and transported to the downstream unit through the top ether-containing wastewater pipeline a3. The concentrated wastewater in the wastewater evaporator 2 is transported to the preheater 6 through the concentrated wastewater pump 4 and the concentrated wastewater pipeline 5. The material is preheated and then enters the propylene glycol flash tank 7. The propylene glycol flash tank 7 is operated under vacuum conditions with an operating pressure of -70 to -90 kPa and a temperature of 120 to 130 ° C.

[0024] The propylene glycol-containing material evaporated from the top of the propylene glycol flash tank 7 enters the propylene glycol recovery tower 12 through the propylene glycol feed pipeline 8, and the concentrated waste liquid at the bottom of the propylene glycol flash tank 7 is transported through the waste liquid pump 10. The outlet of the waste liquid pump 10 is divided into two paths, one of which is transported as a circulating material through the waste liquid circulation pipeline 9 to the inlet of the preheater 6 and merged with the concentrated waste water pipeline 5 to maintain the waste liquid circulation and avoid pipeline blockage caused by material viscosity; the other path transports the waste liquid to the waste liquid furnace for treatment through the waste liquid pipeline 11.

[0025] The material from the propylene glycol flash tank 7 enters the propylene glycol recovery tower 12, which is also operated under vacuum conditions at a pressure of -70 to -90 kPa. After the material in the tower is heated and evaporated by steam, the light component (mainly ether, water, and a small amount of propylene glycol) is at the top of the tower, and enters the recovery tower reflux tank 14 through the recovery tower top pipeline 13. The material in the recovery tower reflux tank 14 is transported by a propylene glycol reflux pump 19, a part of which is returned to the propylene glycol recovery tower 12 as reflux through the recovery tower reflux pipeline 15, and a part of which is sent to the downstream unit after merging with the ether-containing wastewater pipeline a3 through the ether-containing wastewater pipeline b20; most of the propylene glycol recovered by evaporation in the propylene glycol recovery tower 12 is collected in the side liquid collection tray of the propylene glycol recovery tower 12, and the propylene glycol with a higher purity of about 95wt% is sent to the downstream propylene glycol refining unit through the propylene glycol side collection pipeline 16 for distillation to produce more than 99.8wt% of refined propylene glycol.

[0026] The crude propylene glycol in the bottom of the propylene glycol recovery tower 12 is transported in three ways through the recovery tower bottom pump 17 and the bottom crude methanol pipeline 24. By sampling and analyzing the bottom, when the water content of the bottom material is greater than 20wt%, it is transported to the inlet of the waste liquid pump 10 through the propylene glycol recovery pipeline 21 and then returned to the propylene glycol flash tank 7 for re-concentration and recovery; when the propylene glycol content of the bottom material is greater than 80wt%, it is transported to the crude propylene glycol tank 22 for buffering through the crude propylene glycol pipeline 18 and then sent to the downstream for recovery through the crude propylene glycol delivery pump 23; when there are more impurities (such as salt) in the propylene glycol recovery tower 12 or the propylene glycol recovery system needs to be emptied, the process is switched to the waste liquid pipeline 11 and sent to the waste liquid furnace for incineration.

[0027] The material flow rate of the wastewater pipeline 1 is 50 t / h, and the propylene glycol content is 1.0 wt%.

[0028] The material flow rate at the bottom of the wastewater evaporator 2 is 2.0 t / h, and the propylene glycol content is 24 wt%.

[0029] The material flow rate of the waste liquid pipeline 11 is 350 kg / h, and the propylene glycol content is 18 wt%.

[0030] The material flow rate of the crude methanol pipeline 24 at the bottom of the propylene glycol recovery tower 12 is 150 kg / h, and the propylene glycol content is 85 wt%.

[0031] The material flow rate in the ether-containing wastewater pipeline b is 1460 kg / h, and the propylene glycol content is 0.12 wt%.

[0032] The material flow rate in the propylene glycol side sampling pipeline 16 is 300 kg / h, and the propylene glycol content is 95.8 wt%.

[0033] The recovery rate of propylene glycol is as follows:

[0034]

[0035] By optimizing the propylene glycol process of the bottom of the propylene glycol recovery tower 12 and adding crude propylene glycol recovery equipment, the crude propylene glycol in the bottom of the tower is recycled again to reduce the loss of propylene glycol; the propylene glycol recovered in the bottom of the propylene glycol recovery tower 12 is about 127.5 kg / h, and the total propylene glycol recovery rate is about 83%.

Claims

1. A method for recovering propylene glycol as a by-product of a HPPO process, characterized in that: The invention comprises a wastewater evaporator (2), a concentrated wastewater pump (4), a preheater (6), a propylene glycol flash tank (7), a waste liquid pump (10), a propylene glycol recovery tower (12), a recovery tower reflux tank (14), a recovery tower kettle pump (17), a propylene glycol reflux pump (19), a crude propylene glycol tank (22), and a crude propylene glycol delivery pump (23). The wastewater evaporator (2) delivers the ether-containing wastewater to a downstream unit after heating and evaporation. The wastewater concentrated by the wastewater evaporator (2) is concentrated by a concentrated The condensed wastewater is pumped to a preheater (6) for preheating and then entering a propylene glycol flash tank (7); the propylene glycol-containing material evaporated from the top of the propylene glycol flash tank (7) enters a propylene glycol recovery tower (12), and the concentrated waste liquid at the bottom of the propylene glycol flash tank (7) is transported by a waste liquid pump (10). The outlet of the waste liquid pump (10) is divided into two paths, one of which is used as a circulating material channel to be transported to the inlet of the preheater (6), and the other is connected to a waste liquid pipeline (11) to transport the waste liquid. The propylene glycol recovery tower (12) is heated and evaporated to separate the materials, and the light components at the top of the tower enter the recovery tower reflux tank (14). The materials in the recovery tower reflux tank (14) are transported by a propylene glycol reflux pump (19), part of which is returned to the propylene glycol recovery tower (12) as reflux, and part of which is sent to the downstream unit; the propylene glycol recovered by evaporation in the propylene glycol recovery tower (12) is collected in the side collection liquid tray of the propylene glycol recovery tower (12), and the materials with relatively high purity are collected in the propylene glycol recovery tower (12). The high propylene glycol of about 95wt% is sent to the downstream propylene glycol refining unit for distillation to produce more than 99.8wt% refined propylene glycol; the crude propylene glycol in the bottom of the propylene glycol recovery tower (12) is divided into three routes for transportation through the recovery tower bottom pump (17), one route is transported to the waste liquid pump (10) for concentration recovery, one route is transported to the waste liquid furnace for incineration treatment, and the other route is transported to the crude propylene glycol tank (22) for buffering and then transported to the downstream for recovery treatment through the crude propylene glycol delivery pump (23).

2. The method for recovering by-product propylene glycol from a HPPO process according to claim 1, characterized in that: The wastewater evaporator (2), concentrated wastewater pump (4), preheater (6), propylene glycol flash tank (7), waste liquid pump (10), propylene glycol recovery tower (12), recovery tower reflux tank (14), recovery tower kettle pump (17), propylene glycol reflux pump (19), crude propylene glycol tank (22), crude propylene glycol delivery pump (23), and related pipelines are all made of acid corrosion resistant materials.

3. The method for recovering by-product propylene glycol from a HPPO process according to claim 1, characterized in that: The wastewater evaporator (2), the propylene glycol flash tank (7) and the propylene glycol recovery tower (12) are operated under vacuum conditions.

4. The method for recovering by-product propylene glycol from a HPPO process according to claim 1, characterized in that: The operating pressure of the propylene glycol recovery tower (12) is controlled at -70 to -90 kPa.

5. The method for recovering by-product propylene glycol from a HPPO process according to claim 1, characterized in that: The waste liquid pipeline (11) is provided with heating to prevent the pipeline from being blocked due to stickiness of the material.

6. The method for recovering by-product propylene glycol from a HPPO process according to claim 1, characterized in that: The propylene glycol content in the recovery tower reflux tank (14) is controlled within 1.0 wt%.

7. The method for recovering by-product propylene glycol from a HPPO process according to claim 1, characterized in that: The waste liquid pipeline (11) is provided with a hot water flushing facility. When the waste liquid pipeline (11) stops sending waste liquid out, hot water is used for flushing to avoid pipeline blockage.

8. The method for recovering by-product propylene glycol from a HPPO process according to claim 1, characterized in that: The propylene glycol recovery tower (12) is provided with a sampling and analysis facility in the bottom of the tower, and the main analysis indicators are: water, propylene glycol, dipropylene glycol, and tripropylene glycol.

9. The method for recovering by-product propylene glycol from a HPPO process according to claim 1, characterized in that: When the water content in the bottom of the propylene glycol recovery tower (12) is greater than 20 wt%, the bottom material is returned to the inlet of the waste liquid pump (10) for concentration and recovery.

10. The method for recovering by-product propylene glycol from a HPPO process according to claim 1, characterized in that: When the propylene glycol content in the bottom of the propylene glycol recovery tower (12) is greater than 80 wt%, the bottom material is sent to a crude propylene glycol tank (22) for buffering.

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