Method for extracting and separating polyether polyol in waste salt slag by water-based method

Abstract

The invention relates to a method for extracting and separating polyether polyol in waste salt slag by a water-based method, and belongs to the technical field of separation and purification. The method comprises the following steps: (1) slurrying extraction: mixing polyether polyol salt slag with water according to a certain mass ratio, and carrying out slurrying extraction under a stirring condition to obtain oil-water-salt mixed slurry; (2) performing centrifugal separation to obtain an oil-water mixture rich in polyether polyol; (3) demulsifying and layering to obtain a polyether polyol phase; and (4) refining and purifying: dehydrating the polyether polyol phase to obtain a recycled polyether polyol product. According to the method, water is used as an extraction solvent, so that the use of toxic and flammable organic solvents is completely avoided, the safety and health hidden dangers are fundamentally eliminated, and secondary organic pollution is avoided. By optimizing parameters such as the temperature and the liquid-solid ratio of extraction water and combining centrifugal separation, the polyether polyol can be efficiently extracted and separated from the thick salt slag, and the recovery rate can reach 95% or above.

Description

Technical Field

[0001] This invention relates to the technical field of separation and purification, specifically to a water-based method for extracting and separating polyether polyols from waste salt residue. Background Technology

[0002] Polyether polyols, as key raw materials for the preparation of polyurethane foams, elastomers, adhesives, and other products, play an indispensable role in the chemical industry. In the polymerization process of polyether polyols, the catalyst is the core auxiliary agent ensuring the smooth progress of the reaction. The industry conventionally uses substances such as bimetallic cyanide or potassium hydroxide as catalysts for this polymerization reaction. To achieve catalyst removal and product purification, an acidic substance (such as phosphoric acid) is added to the system after the reaction for neutralization, causing the catalyst to be converted into an inorganic salt (such as potassium phosphate) and precipitate. During this process, a large amount of viscous waste salt residue is simultaneously generated. This waste salt residue is mainly composed of inorganic salts, and due to the viscosity of the reaction system and interfacial interactions, it encapsulates a large amount of incompletely separated polyether polyol.

[0003] Currently, the main methods for treating the aforementioned waste salt residue are landfilling or incineration of hazardous waste. This treatment model has significant technical bottlenecks and environmental risks: on the one hand, a large amount of polyether polyol encapsulated in the waste salt residue cannot be effectively recovered, resulting in a serious waste of valuable raw material resources. At the same time, the reduced utilization rate of raw materials indirectly increases the total production cost of polyether polyol. On the other hand, landfilling of hazardous waste can easily lead to soil and groundwater pollution, while incineration may produce harmful gases, putting multiple pressures on the ecological environment.

[0004] To address the problem of recovering polyether polyols from waste salt residue, existing technologies have attempted extraction and recovery using organic solvents (such as toluene, xylene, and alcohols). However, these methods have inherent drawbacks that are difficult to overcome: First, the organic solvents used are generally toxic, volatile, and flammable and explosive, which not only places extremely high demands on safety control in production workshops but also poses a direct threat to the health of operators. Second, the organic solvents need to be recovered through distillation after extraction, a process with high energy consumption, and solvent residues can easily lead to a decrease in the purity of the recovered polyether polyols, affecting their subsequent application performance. Third, secondary waste residue containing organic solvent residues is still generated after extraction. If the subsequent treatment of this waste residue is not properly controlled, it can easily cause secondary environmental pollution problems.

[0005] In summary, developing a green, environmentally friendly, safe, reliable, highly efficient, and low-cost method for treating and recycling waste salt residue from polyether polyol production is of vital practical significance and industrial value for improving the raw material utilization rate of the polyether polyol industry, reducing production costs, alleviating environmental pressure, and ultimately promoting cleaner production and sustainable development in the industry. Summary of the Invention

[0006] To address the technical problems of high pollution and easy solvent residue in polyether polyols when using organic solvents to recover polyether polyols, this invention provides a water-based method for extracting and separating polyether polyols from waste salt residue, thereby solving the above problems.

[0007] The technical solution of this invention is as follows: A water-based extraction and separation method for polyether polyols from waste salt residue includes the following steps: (1) Slurry extraction: Polyether polyol salt residue and water are mixed in a certain mass ratio and slurry extraction is carried out under stirring conditions to obtain an oil-water-salt mixed slurry; the temperature of the water is 50℃~60℃ and the amount of water used is 1~5mL / g based on the mass of polyether polyol salt residue. (2) Centrifugal separation: The oil-water-salt mixture obtained in step (1) is centrifuged to separate the oil-water phase from the solid salt residue, and to obtain an oil-water mixture rich in polyether polyol and wet solid salt residue. (3) Demulsification and stratification: The oil-water mixture obtained in step (2) is allowed to stand or centrifuged to demulsify it, so that it is separated into the upper polyether polyol phase and the lower wastewater phase; (4) Refining and purification: Collect the upper polyether polyol phase, dehydrate it, and obtain the recovered polyether polyol product.

[0008] Furthermore, the wastewater phase from step (3) is cooled and then filtered, and the filtrate is heated and used as the extraction water for the next batch.

[0009] Furthermore, in step (1), the amount of water used is 1.5~3 mL / g based on the mass of polyether polyol salt residue.

[0010] Furthermore, in step (1), the pulping extraction time is 30~120 minutes and the stirring speed is 100~400 rpm.

[0011] Furthermore, in step (2), the centrifugal force for centrifugal separation is 1000~4000G, and the separation time is 5~20 minutes.

[0012] Furthermore, in step (3), a demulsifier can be added during centrifugal demulsification. The demulsifier is an inorganic salt demulsifier; the amount added is 0.1% to 5% of the total mass of the oil-water mixture.

[0013] Furthermore, the inorganic salt demulsifier is one or more of sodium chloride, sodium sulfate, or ammonium sulfate.

[0014] Furthermore, in step (4), the dehydration process is carried out by vacuum distillation; the vacuum degree is -0.095 to -0.098 MPa and the temperature is 80℃ to 110℃; until the moisture content is less than 0.1 wt%.

[0015] The beneficial effects of this invention are as follows: The water-based extraction and separation method for polyether polyols from waste salt residue provided by this invention uses water as the extraction solvent, completely avoiding the use of toxic and flammable organic solvents, fundamentally eliminating safety and health hazards, and producing no secondary organic pollution. By optimizing parameters such as the temperature and liquid-to-solid ratio of the extraction water, and combining this with centrifugal separation, polyether polyols can be efficiently extracted and separated from viscous salt residue, with a recovery rate of over 95%. Simultaneously, the recovered polyether polyols have a light color, and key indicators such as hydroxyl value and viscosity are similar to the raw material, exhibiting stable quality and can be directly reused in polyurethane production, achieving a closed-loop cycle.

[0016] The water-based extraction and separation method for polyether polyols from waste salt residue provided by this invention has a simple process flow and is easy to operate. Water and some wastewater can be recycled, greatly reducing treatment and raw material costs and resulting in significant economic benefits. Furthermore, it achieves high-value-added recovery of polyether polyols from salt residue, while simultaneously improving the purity of the separated inorganic salt residue, facilitating subsequent disposal or utilization as a by-product, truly realizing the "reduction, resource recovery, and harmlessness" of waste. Detailed Implementation

[0017] To enable those skilled in the art to better understand the technical solutions of this invention, the technical solutions in the embodiments of this invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of this invention, and not all embodiments. Based on the embodiments of this invention, all other embodiments obtained by those skilled in the art without creative effort should fall within the scope of protection of this invention.

[0018] Example 1 A water-based extraction and separation method for polyether polyols from waste salt residue includes the following steps: (1) Slurry extraction: Take 500g of potassium salt residue of polyether polyol (PPG-3000) (the content of polyether polyol was found to be about 60wt%) and place it in a 2L reaction flask equipped with stirring and heating. Add 1000mL of water at 50℃ and keep stirring at 200rpm for 60min to obtain a milky white slurry.

[0019] (2) Centrifugal separation: The milky white slurry obtained in step (1) is transferred to a centrifuge and centrifuged for 10 minutes under a centrifugal force of 2500G to separate the upper oil-water mixture and the bottom wet salt residue.

[0020] (3) Demulsification and stratification: Add 1% of sodium chloride by mass to the upper oil-water mixture obtained in step (2), stir slightly and let stand for 30 minutes. The mixture quickly separates into a clear upper oil phase (recovered polyether) and a lower water phase.

[0021] (4) Refining and purification: The upper oil phase was collected and vacuum dehydrated for 2 hours at a vacuum degree of -0.098 MPa and a temperature of 120℃ to obtain 295 g of light yellow, transparent recovered polyether polyol. Testing showed that its moisture content was 0.08% and its hydroxyl value was 56.1 mgKOH / g, comparable to that of freshly prepared PPG-3000 (hydroxyl value 56.5 mgKOH / g). The calculated recovery rate of the polyether polyol was 98.3%.

[0022] (5) Cool the lower aqueous phase obtained in step (3) to 10℃~20℃, stir for 60 min and then filter. The filtrate is used for subsequent extraction of waste salt residue.

[0023] Example 2 A water-based extraction and separation method for polyether polyols from waste salt residue includes the following steps: (1) Slurry extraction: Take 500g of the same batch of potassium salt residue of polyether polyol (PPG-3000) as in Example 1 and place it in a 2L reaction flask equipped with stirring and heating. Take the filtrate recovered in step (5) of Example 1, add pure water to make up to 1000mL, heat to 50℃ and add to the reaction flask. At a stirring speed of 250rpm, keep warm and stir for 90min to obtain a milky white slurry.

[0024] (2) Centrifugal separation: The milky white slurry obtained in step (1) is transferred to a centrifuge and centrifuged for 15 minutes under a centrifugal force of 3000G to separate the upper oil-water mixture and the bottom wet salt residue.

[0025] (3) Demulsification and stratification: The oil-water mixture obtained in step (2) was centrifuged at 500G for 5 minutes to achieve demulsification and stratification. After standing for 30 minutes, the mixture quickly separated into a clear upper oil phase (recovered polyether) and a lower water phase.

[0026] (4) Refining and purification: The upper oil phase was collected and vacuum dehydrated for 2 hours at a vacuum degree of -0.098 MPa and a temperature of 120℃ to obtain 290 g of light yellow, transparent recovered polyether polyol. Testing showed that its moisture content was 0.08% and its hydroxyl value was 55.8 mgKOH / g, comparable to that of freshly prepared PPG-3000 (hydroxyl value 56.5 mgKOH / g). The calculated recovery rate of the polyether polyol was 96.7%.

[0027] Example 3 A water-based extraction and separation method for polyether polyols from waste salt residue includes the following steps: (1) Slurry extraction: Take 500g of potassium salt residue of polyether polyol (PPG-3000) (the content of polyether polyol was found to be about 75wt%) and place it in a 2L reaction flask. Add 800mL of water at 60℃ and keep stirring at 300rpm for 45min to obtain a very viscous milky white slurry.

[0028] (2) Centrifugal separation: The slurry is transferred to a centrifuge and centrifuged for 15 minutes under a centrifugal force of 3500G to separate the upper oil-water mixture and the bottom wet salt residue.

[0029] (3) Demulsification and stratification: Due to the high oil content and severe emulsification of the extract, a heating demulsification method is adopted. The oil-water mixture is heated to 80°C and kept at that temperature for 20 minutes, and then naturally cooled to room temperature. The mixture separates into a clear upper oil phase and a lower water phase.

[0030] (4) Refining and purification: The upper oil phase was collected and dehydrated under vacuum at -0.098 MPa and 120°C for 2 hours to obtain 368 g of light yellow transparent recovered polyether polyol. The hydroxyl value was measured to be 56.0 mg KOH / g. The recovery rate of the polyether polyol was calculated to be 98.1%.

[0031] (5) After the aqueous phase is cooled to 10°C, it is filtered and the filtrate is reused.

[0032] Example 4 A water-based extraction and separation method for polyether polyols from waste salt residue includes the following steps: (1) Slurry extraction: Take 500g of potassium salt residue of polyether polyol (PPG-3000) (polyether content about 60wt%) and place it in a 2L reaction flask. Add 1200mL of water at 55℃ and add 0.5% of demulsifier SP-169. At a stirring speed of 150rpm, keep warm and stir for 120min to obtain slurry.

[0033] (2) Centrifugal separation: The slurry is centrifuged at 2000G for 10 minutes to separate the upper oil-water mixture and wet salt residue.

[0034] (3) Demulsification and stratification: Thanks to the demulsifier added during extraction, the oil-water mixture quickly separates into two clear phases after standing for 15 minutes.

[0035] (4) Refining and purification: The upper oil phase was collected and dehydrated under vacuum at -0.098 MPa and 120°C for 2.5 hours to obtain 292 g of recovered polyether polyol. The hydroxyl value was measured to be 55.9 mg KOH / g. The recovery rate was calculated to be 97.3%.

[0036] (5) After the lower water phase is adsorbed and filtered by activated carbon, most of it is recycled for step (1).

[0037] Example 5 A water-based extraction and separation method for polyether polyols from waste salt residue includes the following steps: (1) Multistage countercurrent slurry extraction: This was carried out in a two-stage stirred tank. First stage: 500 g of waste salt residue (60 wt% polyether content) was mixed with the secondary extract (approximately 800 mL, 50 °C) from the second stage extraction, and extracted for 40 min at 50 °C and 250 rpm. Second stage: The slurry residue obtained from the first stage was mixed with 500 mL of fresh hot water (50 °C), and extracted again for 30 min under the same conditions. Finally, the oil-rich extracts obtained from the first stage were combined.

[0038] (2) Centrifugal separation: The combined oil-rich extract was continuously centrifuged at 5000G using a tubular centrifuge to obtain an oil-water mixture.

[0039] (3) Demulsification and stratification: After the oil-water mixture passes through a static demulsifier, it flows into a gravity settling tank and remains for 1 hour to completely separate into layers.

[0040] (4) Refining and purification: The upper oil phase enters a thin-film evaporator and is dehydrated at -0.098 MPa and 120 °C to obtain 296 g of recovered polyether polyol. The hydroxyl value was measured to be 56.2 mg KOH / g. The recovery rate was calculated to be 98.7%.

[0041] (5) The lower aqueous phase is circulated to the second-stage extraction vessel as makeup water.

[0042] Comparative Example 1 The traditional organic solvent method is used, as follows: Take 500g of the same batch of salt residue as in Example 1, add 500mL of toluene, stir and extract at 70℃ for 60 minutes, filter, and distill the filtrate to recover toluene, obtaining 285g of recovered polyether polyol, with a recovery rate of 95.0%. However, the product has a slight toluene odor, and the process poses safety risks and environmental volatile organic compound emissions.

[0043] Comparative Example 2 The traditional organic solvent method is used, as follows: Take 500g of the same batch of salt residue as in Example 1, add 600mL of dichloromethane, and extract by stirring at 40°C for 40 minutes. After filtration, recover the dichloromethane from the filtrate by atmospheric distillation to obtain 288g of recovered polyether polyol, with a recovery rate of 96.0%. The recovery rate of this method is comparable to that of the water-based method. However, dichloromethane is far more toxic than toluene, posing a significant health hazard to operators; its boiling point is low (39.8°C), resulting in substantial volatilization losses and significant safety risks and fugitive VOC emissions; furthermore, solvent recovery consumes a high amount of energy.

[0044] Comparative Example 3 The organic solvent method is used to treat high-content waste residue, as detailed below: 500 g of salt residue with a high polyether content (approximately 75 wt%), similar to that in Example 3, was added to 400 mL of toluene and extracted with stirring at 70 °C. Due to the high polyether content and extremely high viscosity of the waste residue, solid-liquid mixing and mass transfer efficiency were extremely poor, making stirring difficult. The extraction time was extended to 90 minutes and the residue was filtered, but a large amount of polyether was still entrained in the filter residue. After distillation of the filtrate, only 355 g of recovered polyether polyol was obtained, with a recovery rate of 94.7%, significantly lower than the 98.1% in Example 3. In addition, the product also had a residual solvent odor, and the high viscosity of the material led to a complex solvent recovery process and increased energy consumption.

[0045] As can be seen from the comparison between Examples 1-5 and Comparative Examples 1-3, the method of the present invention is superior to or equivalent to the traditional organic solvent method in terms of recovery rate, and has significant advantages in terms of safety, environmental protection and product odor.

[0046] Comparative Example 4 The waste residue is treated using high-temperature solvents, as detailed below: (1) Slurry extraction: Take 500g of potassium salt residue of polyether polyol (PPG-3000) (the content of polyether polyol was found to be about 60wt%) and place it in a 2L reaction flask equipped with stirring and heating. Add 1000mL of water at 90℃ and keep stirring at 200rpm for 60min to obtain a milky white slurry.

[0047] (2) Centrifugal separation: The milky white slurry obtained in step (1) is transferred to a centrifuge and centrifuged for 10 minutes under a centrifugal force of 2500G to separate the upper oil-water mixture and the bottom wet salt residue.

[0048] (3) Demulsification and stratification: Add 1% of sodium chloride by mass to the upper oil-water mixture obtained in step (2), stir slightly and let stand for 30 minutes. The mixture quickly separates into a clear upper oil phase (recovered polyether) and a lower water phase.

[0049] (4) Refining and purification: The upper oil phase was collected and vacuum dehydrated for 2 hours at a vacuum degree of -0.098 MPa and a temperature of 120℃ to obtain 295 g of light yellow, transparent recovered polyether polyol. Testing showed that its moisture content was 0.09% and its hydroxyl value was 55.4 mgKOH / g, comparable to that of freshly prepared PPG-3000 (hydroxyl value 56.5 mgKOH / g). The calculated recovery rate of the polyether polyol was 97.6%.

[0050] As can be seen from the comparison between Example 1 and Comparative Example 4, the recovery rate did not decrease after the water extraction temperature was lowered, but the production energy consumption decreased significantly, and the requirements for equipment also decreased, which is conducive to the expansion of production scale.

[0051] Although the present invention has been described in detail by way of preferred embodiments, the present invention is not limited thereto. Various equivalent modifications or substitutions can be made to the embodiments of the present invention by those skilled in the art without departing from the spirit and essence of the invention, and such modifications or substitutions should all be within the scope of the present invention. Any variations or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention should also be covered within the protection scope of the present invention.

Claims

1. A water-based extraction and separation method for polyether polyols from waste salt residue, characterized in that, Includes the following steps: (1) Slurry extraction: Polyether polyol salt residue and water are mixed in a certain mass ratio and slurry extraction is carried out under stirring conditions to obtain an oil-water-salt mixed slurry; the temperature of the water is 50℃~60℃ and the amount of water used is 1~5mL / g based on the mass of polyether polyol salt residue. (2) Centrifugal separation: The oil-water-salt mixture obtained in step (1) is centrifuged to separate the oil-water phase from the solid salt residue, and to obtain an oil-water mixture rich in polyether polyol and wet solid salt residue. (3) Demulsification and stratification: The oil-water mixture obtained in step (2) is allowed to stand or centrifuged to demulsify it, so that it is separated into the upper polyether polyol phase and the lower wastewater phase; (4) Refining and purification: Collect the upper polyether polyol phase, dehydrate it, and obtain the recovered polyether polyol product.

2. The method for water-based extraction and separation of polyether polyols from waste salt residue as described in claim 1, characterized in that, The wastewater phase from step (3) is cooled and filtered, and the filtrate is heated and used as the extraction water for the next batch.

3. The method for water-based extraction and separation of polyether polyols from waste salt residue as described in claim 1, characterized in that, In step (1), the amount of water used is 1.5~3 mL / g based on the mass of polyether polyol salt residue.

4. The method for water-based extraction and separation of polyether polyols from waste salt residue as described in claim 1, characterized in that, In step (1), the pulping extraction time is 30~120 minutes and the stirring speed is 100~400 rpm.

5. The method for water-based extraction and separation of polyether polyols from waste salt residue as described in claim 1, characterized in that, In step (2), the centrifugal force for centrifugation is 1000~4000G, and the separation time is 5~20 minutes.

6. The method for water-based extraction and separation of polyether polyols from waste salt residue as described in claim 1, characterized in that, In step (3), a demulsifier can be added during centrifugal demulsification. The demulsifier is an inorganic salt demulsifier. The amount added is 0.1% to 5% of the total mass of the oil-water mixture.

7. The method for water-based extraction and separation of polyether polyols from waste salt residue as described in claim 6, characterized in that, The inorganic salt demulsifier is one or more of sodium chloride, sodium sulfate, or ammonium sulfate.

8. The method for water-based extraction and separation of polyether polyols from waste salt residue as described in claim 1, characterized in that, In step (4), the dehydration process is carried out by vacuum distillation; the vacuum degree is -0.095 to -0.098 MPa and the temperature is 80℃ to 110℃; until the moisture content is less than 0.1 wt%.