Method for continuously removing light components from polyether polyol

Abstract

The present invention relates to the technical field of polyether polyol refining. Specifically disclosed is a method for continuously removing light components from polyether polyol. In the present invention, polyether polyol and deoxygenated water are mixed, and are then continuously added into a light component removal column and a dehydration column to remove light components and water from the polyether polyol by means of a process in which reduced-pressure flash evaporation, heating via bubbling, steam stripping and nitrogen stripping are combined, thereby obtaining purified polyether polyol. Compared with common stripping, the present invention has the advantages of an enhanced removal effect on light components, an effective reduction in the amount of steam and a lowered level of difficulty in controlling polyol quality control in a production stage; and the content of formaldehyde, acetaldehyde and propionaldehyde in the purified polyether polyol product obtained in the present invention can be as low as 10 ppm or less.

Description

A method for continuous removal of light components from polyether polyols

[0001] This invention is based on and claims priority to Chinese Patent Application No. 202411442750.4, filed on October 16, 2024, with the State Intellectual Property Office of China, the entire contents of which are incorporated herein by reference. Technical Field

[0002] This invention belongs to the field of polyether polyol refining technology, specifically, it relates to a method for continuously removing light components from polyether polyols. Background Technology

[0003] The existing production process of polyether polyols (using the KOH batch process for polyether production) mainly includes initiator preparation, prepolymer preparation, polyol polymerization, neutralization and dehydration, and polyol filtration. Through these processes, the polyether polyol product is temporarily stored in a polyol quality control tank, meeting the requirements of low-end products in the market. However, trace amounts of volatile monomers still exist in the finished polyol at this stage, which have an odor. Although the content is very small and the odor is very low, they can affect the sales and quality of the final product. Therefore, obtaining low-odor polyol products has become a crucial task for the industry.

[0004] Chinese patent application CN105440275A discloses a method for reducing residual ethylene oxide in polyether polyols. The method involves adding amines to a closed reactor and reacting them under specific pressure and temperature, followed by post-treatment to obtain high-quality polyols. However, this method is limited to reducing ethylene oxide and has no effect on other volatile components.

[0005] Chinese patent application CN110885439A discloses a method for reducing volatile components in polyether polyols. The method involves adding an aldehyde removal agent to a reaction vessel, reacting the mixture, then adding water and an adsorbent, followed by stirring, drying, and filtering to obtain a qualified product. The volatile components are effectively removed using chemical methods and nitrogen bubbling.

[0006] Chinese patent application CN105037703A discloses a method for extracting formaldehyde and acetaldehyde from polyether polyols. The method involves directly introducing steam and nitrogen into a reaction vessel, followed by long-term vacuum extraction to remove formaldehyde and acetaldehyde from the polyol. This method uses a reaction vessel directly and operates intermittently, with each batch requiring 4-10 hours to process.

[0007] Existing methods for preparing polyether polyols only remove ethylene oxide. The process is intermittent, complex, and may generate solid waste. Summary of the Invention

[0008] The present invention aims to provide a method for continuously removing light components from polyether polyols. This method is a continuous operation, which makes up for the shortcomings of product quality fluctuations caused by intermittent operation in traditional processes and reduces energy consumption.

[0009] The method for continuously removing light components from polyether polyols of the present invention further reduces the residual light components in polyether polyols, thereby improving the quality of polyether polyol products.

[0010] The present invention employs a method for continuously removing light components from polyether polyols, comprising: mixing polyether polyols and deoxygenated water to obtain a first mixture; continuously adding the first mixture to a light component removal tower, forming a countercurrent with the water vapor introduced into the light component removal tower to remove light components from the polyether polyol; and a second mixture discharged from the bottom of the light component removal tower entering a dehydration tower, where water is removed from the polyether polyol under the action of inert gas stripping.

[0011] Optionally, the second mixture discharged from the bottom of the light removal tower enters the dehydration tower, forming a countercurrent with the inert gas introduced into the dehydration tower to remove water from the polyether polyol.

[0012] Inert gases are gases that do not react chemically with the substances being treated, such as nitrogen.

[0013] Compared with conventional stripping, the method for continuous removal of light components from polyether polyols of the present invention adds a process of premixing polyether polyol and deoxygenated water and vacuum flash evaporation. Before entering the tower, the polyether polyol and deoxygenated water are mixed to add a small amount of water. Water acts as a volatile medium and makes full use of the pressure drop at the top of the tower to form flash evaporation, which promotes the volatilization of light components, mainly aldehydes such as formaldehyde, acetaldehyde, and acrolein.

[0014] In some technical solutions, the mass ratio of deoxygenated water to polyether polyol is 0.1%-0.5%, and the mixing temperature is 100℃-130℃.

[0015] Alternatively, the first mixture of deoxygenated water and polyether polyol is an emulsion.

[0016] Optionally, the mass ratio of deoxygenated water to polyether polyol is 0.4%.

[0017] This invention employs an oil-water mixer to mix deoxygenated water and polyether polyol. Various types of oil-water mixers can be used. While polyether polyol and water are immiscible, their densities are relatively close within the temperature range of 100℃ to 130℃. Therefore, this invention selects a temperature range of 100℃ to 130℃ for mixing deoxygenated water and polyether polyol, ideally forming an emulsion. The smaller the droplet diameter and the more uniform the distribution within the polyol in the emulsion, the more thoroughly the deoxygenated water and polyether polyol are mixed. The more thoroughly the polyether polyol and deoxygenated water are mixed, the easier it is for the light components in the polyether polyol to evaporate with the water during flash evaporation in the light component removal tower, resulting in better removal of light components. Simultaneously, the ratio of steam to deoxygenated water introduced in the subsequent bubbling heating section is generally greater than 1.15. To reduce steam consumption and ensure effective light component removal, the mass ratio of deoxygenated water to polyether polyol is maintained at 0.1%-0.5%.

[0018] In some technical solutions, the operating temperature of the light-removal tower for polyether polyols is 120-145℃, and the pressure at the top of the tower is controlled at 3-10 kPaG.

[0019] Optional operating temperature is 135℃ and tower top pressure is 5kPaG.

[0020] The first mixture is preheated to 120℃-145℃ and then flash-evaporated under reduced pressure in the light component removal tower to remove moisture and some light components from the polyether polyol. This is the first stage of light component removal. If the preheating temperature of the first mixture is too low, the light components will not be effectively removed; if it is too high, the polyether polyol will decompose. If the mass ratio of deoxygenated water to polyether polyol is too low, the flash-evaporation effect will be insignificant. Furthermore, the temperature of the polyether polyol will decrease when the first mixture enters the light component removal tower for flash-evaporation under reduced pressure. Therefore, it is necessary to control the feed mass ratio of deoxygenated water and the pressure at the top of the tower, and to control the temperature decrease within the light component removal tower within 5℃-10℃.

[0021] In some technical solutions, a bubbling heating section is set up inside the light-weight removal tower. A first packing section and a second packing section are placed in the areas above and below the bubbling heating section, respectively. Water vapor is introduced into the bubbling heating section. The mass of the water vapor introduced is 0.5%-0.75% of the mass of the polyether polyol, and the steam pressure is greater than 300 kPaG.

[0022] Optionally, the mass of steam introduced is 0.5% of the mass of the polyether polyol, and the steam pressure is 350 kPaG.

[0023] Optionally, a bubble distributor can be installed in the bubbling heating section.

[0024] Optionally, the bubble distributor can be in the form of a liquid collector.

[0025] This invention integrates steam bubbling inside the stripping tower and adds a packing section, thus solving the problem of the reduced temperature of polyether polyol after flash evaporation affecting the stripping effect. The bubbling heating section achieves two main objectives. First, it uses superheated steam bubbling to further increase gas-liquid contact, allowing for re-mixing and contact of the steam within the polyether polyol. The water-saturated polyether polyol can then serve as the liquid phase for the next stage of stripping, improving stripping efficiency. Second, the bubbled steam enters the first packing section. Here, through contact between the packing and the superheated steam, the temperature of the flash-evaporated polyether polyol is restored to its normal operating temperature, simultaneously improving the removal efficiency of light components – this is the second step in removing light components.

[0026] The steam introduced into the bubbling heating section should be greater than 300 kPaG to avoid excessively low temperatures that would affect the heating effect. The steam volume should be slightly higher than that of the deoxygenated water. The bubbling residence time should be controlled at 5-10 minutes. Prolonged high temperatures can cause the self-decomposition of polyether polyol, which will actually increase the amount of light components. The bubbling distributor in this section can evenly disperse the steam inside the polyether polyol to improve the removal efficiency of light components.

[0027] In some technical solutions, the specific surface area of ​​the packing in the first packing section is smaller than that of the packing in the second packing section; the height of the first packing section is smaller than that of the second packing section.

[0028] Optionally, the height of the second packing section can be 2 to 6 times the height of the first packing section.

[0029] Optionally, the height of the second packing section is four times the height of the first packing section.

[0030] The height of the first packing section above the bubbling heating section does not need to be too high. Mass transfer is not a concern; the focus is on the temperature recovery of the polyether polyol to enhance the bubbling removal effect and the efficiency of the subsequent stripping section. The height of the second packing section below the bubbling heating section is primarily determined by separation efficiency. Its height needs to be determined based on the content of light components in the polyether polyol and should not be too high to avoid increasing the pressure drop within the column, which would negatively impact the removal of light components.

[0031] In some technical solutions, the mass ratio of stripping steam to polyether polyol is 1%-4%, and the steam pressure is greater than 300 kPaG.

[0032] Optional, steam pressure greater than 350 kPaG.

[0033] After the stripping steam enters the tower, it undergoes initial distribution to improve the uniformity of the gas phase load within the tower. The tower utilizes a steam and vacuum system to create a high-temperature / high-vacuum environment conducive to volatility. The steam and polyether polyol form a large-area gas-liquid contact on the packing surface, achieving complete removal of light components. This is the third and final stage of light component removal.

[0034] The tail gas at the top of the light component removal tower mainly consists of water vapor, with the remainder being the volatilized light components. No demister or similar device is needed inside the tower to prevent dissolved light components from being carried into the polyether polyol by falling droplets. Instead, all gas phases enter the condenser for condensation. Most of the water is condensed and discharged as wastewater, while a small amount of gas containing water and light components enters the vacuum system. This operation significantly reduces the load on the subsequent vacuum system. Considering the vacuum level at the top of the tower, the temperature of the condensed gas phase should be controlled at around 15°C, at which point most of the water in the tail gas condenses into wastewater.

[0035] In some technical solutions, the operating temperature of the dehydration tower polyether polyol is 120℃-145℃, and the pressure at the top of the tower is controlled at 1-5KPaG.

[0036] Optional operating temperature is 135℃ and tower top pressure is 1 kPaG.

[0037] In some technical solutions, the dehydration tower uses nitrogen as the stripping medium, the nitrogen temperature does not exceed 145℃, and the mass ratio of nitrogen to polyol is 0.1%-0.5%.

[0038] The nitrogen temperature is optional, ranging from 85℃ to 120℃.

[0039] Optionally, the mass ratio of nitrogen to polyol is 0.2%.

[0040] When using steam to strip polyether polyols in a light component removal tower, the material contains a small amount of moisture, which needs to be further removed. The material after the light component removal is removed flows out from the bottom of the light component removal tower. The polyether polyol is preheated to a temperature of 120℃ before entering the dehydration tower.

[0041] -145℃; The dehydration tower uses hot nitrogen as the stripping medium, which flows counter-currently with the polyether polyol inside the tower to remove moisture. The tail gas at the top of the dehydration tower contains nitrogen and water vapor, which is condensed by a condenser and extracted by a vacuum pump. The nitrogen can be heated using the tail gas discharged from the top of the light ether removal tower. The temperature of the heated nitrogen does not exceed the temperature at the top of the dehydration tower, thus not increasing energy consumption.

[0042] In some technical solutions, the internal temperature of the light-weight removal tower and the dehydration tower is between 120℃ and 145℃.

[0043] Optionally, the light-weight removal tower and the dehydration tower can be equipped with external jacketed heat tracing.

[0044] Optionally, the heating temperature of the light-removal tower and the dehydration tower can be within ±5°C of the operating temperature of the polyether polyol.

[0045] The temperature changes at the top and bottom of the light-weight removal tower and the dehydration tower are small and negligible. Using external jacket heating in the light-weight removal and dehydration towers can prevent poor tower wall insulation from causing the wall temperature to be significantly lower than the internal temperature, thus improving the flowability of polyether polyols near the tower wall.

[0046] This invention provides an apparatus for stripping light components from polyether polyols, comprising: an oil-water mixer connected to a light component removal tower preheater and a light component removal tower via pipelines; a nitrogen preheater and a light component removal tower condenser connected to the top of the light component removal tower via pipelines; a water removal tower preheater and a water removal tower top connected to the bottom of the light component removal tower via pipelines; and a water removal tower top connected to a water removal tower condenser via pipelines.

[0047] By adopting the above technical solution, the present invention has the following beneficial effects compared with the prior art.

[0048] Compared with conventional stripping, this invention adds a process of premixing polyether polyol and deoxygenated water and vacuum flash evaporation, which increases the contact between water and polyether polyol, enhances the removal effect of light components, and effectively reduces the amount of steam used.

[0049] This invention integrates a steam bubble distributor inside the stripping tower and increases the packing section, thus solving the problem of the impact of the decrease in temperature of polyether polyol after flash evaporation on the stripping effect.

[0050] This invention allows for continuous operation and does not have high requirements for the content of light components in the raw materials (tens to 1000 ppm can be removed), thus overcoming the shortcomings of product quality fluctuations caused by intermittent operation in traditional processes. At the same time, it reduces the difficulty of quality control of polyether polyols during the production stage. The steam consumption of this invention can be reduced to 2.5%-6% of the mass flow rate of polyether polyols, which is significantly lower than the steam consumption during intermittent processing.

[0051] The purified polyether polyol product obtained by this invention can have formaldehyde, acetaldehyde, and propionaldehyde contents as low as 10 ppm, which is at a relatively advanced level in the industry.

[0052] Generally speaking, deoxygenated water refers to water with an oxygen content of less than 0.015 mg / L.

[0053] The method of this invention can purify various types of polyether polyols, such as polypropylene glycol (PPG). Polyether polyols that are liquid at room temperature can be purified using this method to remove byproducts.

[0054] The specific embodiments of the present invention will now be described in further detail with reference to the accompanying drawings. Attached Figure Description

[0055] The accompanying drawings, as part of this invention, are used to provide a further understanding of the invention. The illustrative embodiments and descriptions of the invention are used to explain the invention, but do not constitute an undue limitation of the invention. Obviously, the drawings described below are merely some embodiments, and those skilled in the art can obtain other drawings based on these drawings without creative effort. In the drawings:

[0056] Figure 1 is a schematic diagram of a process for continuous removal of light components from polyether polyols according to the present invention.

[0057] Figure 2 is a schematic diagram of the structure of the light-weight removal tower of the present invention.

[0058] Figure reference numerals: 1-Light precipitator removal tower; 2-Dehydration tower; 3-Light precipitator removal tower preheater; 4-Dehydration tower preheater; 5-Light precipitator removal tower condenser; 6-Dehydration tower condenser; 7-Oil-water mixer; 8-Nitrogen preheater; 9-Deoxygenated water; 10-Polyether polyol; 11-Flash section; 12-First packed section; 13-Bubble heating section; 14-Second packed section; 15-Stripping section; 16-Steam; 17-Condensate; 18-Nitrogen; 19-Condensate wastewater; 20-Tail gas; 21-Purified polyether polyol product.

[0059] It should be noted that these accompanying drawings and textual descriptions are not intended to limit the scope of the invention in any way, but rather to illustrate the concept of the invention to those skilled in the art by referring to specific embodiments. Detailed Implementation

[0060] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments will be clearly and completely described below with reference to the accompanying drawings. In this application, the molecular weight of polyether polyol is the weight-average molecular weight. The following embodiments are used to illustrate the present invention, but are not intended to limit the scope of the present invention.

[0061] Referring to Figure 1, a schematic diagram of the process flow for continuous removal of light components from polyether polyols according to the present invention is shown. The oil-water mixer 7, the light component removal tower preheater 3, and the light component removal tower 1 are connected sequentially via pipelines. The top of the light component removal tower 1 is connected sequentially to a nitrogen preheater 8 and a light component removal tower condenser 5. The bottom of the light component removal tower 1 is connected sequentially to the top of the dehydration tower preheater 4 and the dehydration tower 2 via pipelines. The top of the dehydration tower 2 is connected to the dehydration tower condenser 6. Condensed wastewater 19 and tail gas 20 are discharged from the lower ends of the light component removal tower condenser 5 and the dehydration tower condenser 6.

[0062] As shown in Figure 2, the interior of the light-weight material removal tower 1, from top to bottom, consists of a flash section 11, a first packing section 12, a bubbling heating section 13, a second packing section 14, and a stripping section 15. The height of the second packing section is 2-6 times that of the first packing section, more preferably, the height of the second packing section is 4 times that of the first packing section. Water vapor 16 for heating is introduced from the bottom of the bubbling heating section, which is located in the middle of the light-weight material removal tower 1. Water vapor 16 for stripping is introduced from the bottom of the light-weight material removal tower 1, with the steam flow direction counter-current to the material flow. The light-weight material removal tower 1 is equipped with an outer jacket. Water vapor 16 for heating enters from the top of the outer jacket from top to bottom, and condensate 17 is discharged from the bottom.

[0063] The flash section is a specific region or stage where rapid vaporization and separation occur when a high-pressure saturated liquid enters a low-pressure environment.

[0064] Dehydration tower 2 uses hot nitrogen as the stripping medium. Nitrogen gas 18 is heated by heat exchange with the tail gas from the top of the light-weight gas removal tower through nitrogen preheater 8. The heated nitrogen gas enters from the bottom of dehydration tower 2, and the nitrogen flow direction is countercurrent with the material flow. Dehydration tower 2 is equipped with an outer jacket. Water vapor 16 for heating enters from the top of the outer jacket from top to bottom, and condensate 17 is discharged from the bottom.

[0065] Polyether polyol 10 and deoxygenated water 9 are thoroughly mixed in oil-water mixer 7. The mixture is preheated in light component removal tower preheater 3 and then enters from the top of light component removal tower 1. After undergoing vacuum flash evaporation, bubbling heating, and steam stripping, it flows out from the bottom of the light component removal tower 1, yielding the light component removed polyether polyol. The removed light components are discharged from the top of light component removal tower 1 with steam and discharged as condensate wastewater through light component removal tower condenser 5.

[0066] The polyether polyol after light removal is heated by the preheater 4 of the dehydration tower, enters from the top of the dehydration tower 2, is stripped by nitrogen, and flows out from the bottom of the dehydration tower 2 to obtain purified polyether polyol product 21; the removed water is discharged from the top of the dehydration tower 2 with nitrogen and discharged as condensed wastewater through the dehydration tower condenser 6.

[0067] Example 1

[0068] Referring to the process flow for continuous removal of light components from polyether polyols shown in Figure 1, the polyether polyols produced by the PPG unit are post-processed to obtain purified polyether polyol products. In the examples, the pressure unit "KPaA" represents absolute pressure, and "KPaG" represents gauge pressure. The polyether polyol is polypropylene glycol.

[0069] 1) Raw material situation:

[0070] The polyether polyol to be purified has a number-average molecular weight of approximately 4800, is heated to 50°C, and contains 0.11 wt% of light components (mainly aldehydes such as formaldehyde and acetaldehyde).

[0071] 2) Main equipment and specifications:

[0072] Lightweight material removal tower: 1000mm in diameter, 15000mm in height, with external jacket heat tracing.

[0073] The packing material for the heating section is 1 meter high and has a specific surface area of ​​250 m². 2 / m 3

[0074] Stripping section packing: 4 meters high, 250 m² specific surface area 2 / m 3

[0075] Dehydration tower: 800mm in diameter, 13000mm in height, with external jacket heat tracing.

[0076] Stripping section packing: 4 meters high, 250 m² specific surface area 2 / m 3

[0077] Lightweight tower preheater: heat exchange area 114m² 2 Dehydration tower preheater: heat exchange area 76m² 2

[0078] Lightweight tower condenser: heat exchange area 120m² 2 Dehydration tower condenser: heat exchange area 70m² 2

[0079] Oil-water mixer: 200mm in diameter, 500mm in height

[0080] Nitrogen preheater: internal coil heat exchanger.

[0081] 3) Main operating steps:

[0082] S1: Deoxygenated water and polyether polyol are introduced into an oil-water mixer at flow rates of 10 kg / h and 10 t / h, respectively, and are thoroughly mixed at 50°C to obtain the first mixture;

[0083] S2: The first mixture is preheated by the light-duty tower preheater;

[0084] S3: The first mixture after preheating enters the light-light stripping tower from the top of the tower at a flow rate of 10t / h and a temperature of 121℃. Bubbling heating steam is introduced into the light-light stripping tower at a flow rate of 15kg / h, and stripping steam is introduced into the light-light stripping tower from the bottom of the tower at a flow rate of 235kg / h for mixing and stripping.

[0085] The top temperature of the light component removal tower is 119℃, and the top pressure is 3-5.4 kPaA; the pressure of the bubbling heating steam is 300 kPaG, and the pressure of the stripping steam is 250 kPaG.

[0086] S4: The light components (mainly aldehydes such as formaldehyde and acetaldehyde) removed in the light component removal tower are discharged from the top of the tower with steam at a flow rate of 271 kg / h and a temperature of 121℃; the second mixture after light component removal is discharged from the bottom of the tower.

[0087] S5: The second mixture is preheated by the dehydration tower preheater;

[0088] S6: The preheated second mixture enters from the top of the dehydration tower at a flow rate of 10t / h and a temperature of 122℃. Nitrogen gas, after being heated, enters from the bottom of the dehydration tower at a flow rate of 15kg / h and a temperature of 90℃. The second mixture comes into contact with the nitrogen gas and undergoes stripping.

[0089] The temperature at the top of the dehydration tower is 120℃, and the pressure is 1.5 kPaA.

[0090] S7: The removed moisture is discharged from the top of the dehydration tower along with nitrogen gas as tail gas, with a tail gas temperature of 20℃; the purified polyether polyol product obtained after stripping flows out from the bottom of the dehydration tower.

[0091] 4) Removal effect:

[0092] The light components were not detected in the purified polyether polyol, and it had a slight odor or was basically odorless.

[0093] 5) Stripping medium usage:

[0094] Total steam consumption: 250 kg / h; nitrogen consumption: 15 kg / h

[0095] Example 2

[0096] Based on the process flow for continuous removal of light components from polyether polyols shown in Figure 1, the polyether polyols produced by the PPG unit are post-processed to obtain purified polyether polyol products.

[0097] 1) Raw material situation:

[0098] The polyether polyol to be purified has a number-average molecular weight of approximately 6000, is heated to 70℃, and contains light components (mainly aldehydes such as formaldehyde and acetaldehyde).

[0099] 2) Main equipment and specifications:

[0100] Light weight removal tower: flash head diameter 700mm, flash head height 1500mm, lower tower body diameter 600mm, total height of light weight removal tower 15000mm, external jacketed heating.

[0101] Heating section packing: 1 meter high, 100 m² specific surface area 2 / m 3

[0102] Stripping section packing: 4 meters high, 250 m² specific surface area2 / m 3

[0103] Dehydration tower: 600mm in diameter, 13000mm in height, with external jacket heat tracing.

[0104] Stripping section packing: 3 meters high, 350 m² specific surface area 2 / m 3

[0105] Lightweight tower preheater: heat exchange area 50m² 2 Dehydration tower preheater: heat exchange area 20m² 2

[0106] Lightweight tower condenser: heat exchange area 50m² 2 Dehydration tower condenser: heat exchange area 20m² 2

[0107] Oil-water mixer: 200mm in diameter, 500mm in height

[0108] Nitrogen preheater: internal coil heat exchanger.

[0109] 3) Main operating parameters:

[0110] S1: Deoxygenated water and polyether polyol are introduced into the oil-water mixer at flow rates of 12.5 kg / h and 5 t / h respectively, and are thoroughly mixed at 70°C to obtain the first mixture;

[0111] S2: The first mixture is preheated by the light-duty tower preheater;

[0112] S3: The first mixture after preheating enters the light component removal tower from the top of the tower at a flow rate of 5t / h and a temperature of 130℃. Bubbling heating steam is introduced into the light component removal tower at a flow rate of 10kg / h, and stripping steam is introduced into the light component removal tower from the bottom of the tower at a flow rate of 190kg / h for mixing and stripping.

[0113] The top temperature of the light component removal tower is 125℃ and the top pressure is 4-5 kPaA; the pressure of the bubbling heating steam is 300 kPaG and the pressure of the stripping steam is 250 kPaG.

[0114] S4: The light components (mainly aldehydes such as formaldehyde and acetaldehyde) removed in the light component removal tower are discharged from the top of the tower with steam at a flow rate of 217 kg / h and a temperature of 125℃; the second mixture after light component removal is discharged from the bottom of the tower.

[0115] S5: The second mixture is preheated by the dehydration tower preheater;

[0116] S6: The preheated second mixture enters from the top of the dehydration tower at a flow rate of 5t / h and a temperature of 130℃. Nitrogen gas, after being heated, enters from the bottom of the dehydration tower at a flow rate of 10kg / h and a temperature of 85℃. The second mixture comes into contact with the nitrogen gas and undergoes stripping.

[0117] The temperature at the top of the dehydration tower is 130℃, and the pressure is 1 kPaA.

[0118] S7: The removed moisture is discharged from the top of the dehydration tower along with nitrogen gas as tail gas, with a tail gas temperature of 20℃; the purified polyether polyol product obtained after stripping flows out from the bottom of the dehydration tower.

[0119] 4) Removal effect:

[0120] Purified polyether polyols are odorless. The content of light components in the products is compared in Table 1 below.

[0121] Table 1:

[0122] As shown in Table 1, the content of light components in the purified polyether polyol product obtained after post-treatment in Example 2 meets the requirements. The content of light components in the polyether polyol was determined by gas chromatography.

[0123] 5) Stripping medium usage:

[0124] Total steam consumption: 200 kg / h; nitrogen consumption: 10 kg / h

[0125] Comparative Example 1

[0126] A batch operation device was used to process polyether polyol. One ton of polyether polyol raw material, identical to that in Example 1, was prepared and placed in a reactor. Steam at 180°C was introduced into the reactor for light component removal treatment. The steam flow rate was 1 m³ / s. 3 The process involves applying nitrogen gas at a rate of 1000 μL / min for 2 hours. After removing light components, the material is dehydrated using nitrogen as the medium to obtain purified polyether polyol products.

[0127] According to the water vapor density table, the steam density is 0.8036 kg / m³. 3 The total steam consumption for batch processing of 1 ton of polyether polyol is 120 m³. 3 The calculated steam consumption was 96.4 kg. When processing 10 t of the same polyether polyol as in Example 1, the steam consumption was 964 kg, which is much higher than the 250 kg of steam used in Example 1.

[0128] Comparative Example 2

[0129] Based on the process flow for continuous removal of light components from polyether polyols shown in Figure 1, the polyether polyols produced by the PPG unit are post-processed to obtain purified polyether polyol products.

[0130] When the temperature of the first mixture entering the light-removal tower is changed to 115°C, the other raw materials, main equipment and specifications, and main operating steps are the same as in Example 1. The purified polyether polyol product obtained has formaldehyde and acetaldehyde content of less than 10 ppm, which meets the process requirements, and propionaldehyde content of 156 ppm, which is significantly higher than the technical requirements (generally, the technical requirements are propionaldehyde content of less than 20 ppm, preferably less than 10 ppm).

[0131] Comparative Example 3

[0132] Referring to the process flow for continuous removal of light components from polyether polyols shown in Figure 1, the polyether polyols produced by the PPG unit are post-processed to obtain purified polyether polyol products.

[0133] When the temperature of the first mixture entering the light component removal tower was changed to 150°C, the other raw materials, main equipment and specifications, and main operating procedures were the same as in Example 1. The formaldehyde and acetaldehyde contents in the purified polyether polyol product were 15 ppm and 23 ppm, respectively. Therefore, the excessively high temperature of the first mixture entering the light component removal tower increased the self-decomposition of the polyol and reduced the removal efficiency of the light components.

[0134] Comparative Example 4

[0135] Based on the process flow for continuous removal of light components from polyether polyols shown in Figure 1, the polyether polyols produced by the PPG unit are post-processed to obtain purified polyether polyol products.

[0136] In step S1, deoxygenated water and polyether polyol are introduced into an oil-water mixer at flow rates of 0 kg / h and 10 t / h, respectively, and are thoroughly mixed at 50°C to obtain the first mixture. At this point, the mass ratio of deoxygenated water to polyether polyol is <0.1%.

[0137] The other raw materials, main equipment and specifications, and main operating steps are the same as in Example 1. The polyol product of the same specifications requires as much as 450 kg / h of stripping steam, which significantly increases the amount of stripping steam used. However, the consumption of heating steam is reduced by only 15 kg / h. The total amount of steam used is significantly increased compared to Example 1. Therefore, the amount of deoxygenated water used should not be too low.

[0138] Comparative Example 5

[0139] Based on the process flow for continuous removal of light components from polyether polyols shown in Figure 1, the polyether polyols produced by the PPG unit are post-processed to obtain purified polyether polyol products.

[0140] In step S1, deoxygenated water and polyether polyol are introduced into the oil-water mixer at flow rates of 100 kg / h and 10 t / h respectively, and are fully mixed at 50°C to obtain the first mixture. At this time, the mass ratio of deoxygenated water to polyether polyol is 1%.

[0141] The other raw materials, main equipment and specifications, and main operating steps are the same as in Example 1, and the purified polyether polyol product of the same specifications is obtained. The required amount of bubbling heating steam is increased to 120 kg / h, and the amount of stripping steam is the same as in Example 1. The total amount of steam is significantly increased. Therefore, in order to reduce steam consumption and ensure the removal of light pollutants, the amount of deoxygenated water should not be too high.

[0142] The steam consumption in the indirect operation of Comparative Example 1 for treating polyether polyol was significantly greater than that in Example 1. The purified polyether polyol products obtained in Comparative Examples 2-3 showed lower light component removal efficiency than those in Example 1, indicating that excessively low or high temperatures after preheating the first mixture would reduce the removal efficiency of light components. Compared with Example 1, Comparative Examples 4-5 yielded purified polyether polyol products of the same specifications, but the steam consumption was significantly increased, indicating that to reduce steam consumption while ensuring the removal efficiency, the mass ratio of deoxygenated water to polyether polyol needs to be controlled at 0.1%-0.5%. Through the above examples and comparative examples, it can be demonstrated that the method for continuously removing light components from polyether polyol provided by the present invention reduces energy consumption compared to the intermittent operation of the traditional process, further reduces the residual light components in polyether polyol, and improves the quality of polyether polyol products.

[0143] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any way. Although the present invention has been disclosed above with reference to preferred embodiments, it is not intended to limit the present invention. Any person skilled in the art can make some modifications or alterations to the above-described technical content to create equivalent embodiments without departing from the scope of the present invention. Any simple modifications, equivalent changes, and alterations made to the above embodiments based on the technical essence of the present invention without departing from the scope of the present invention shall still fall within the scope of the present invention.

Claims

1. A method for continuously removing light components from a polyether polyol comprising: The polyether polyol and deoxygenated water are mixed to obtain a first mixture; the first mixture is continuously added to the light component removal tower, forming a countercurrent with the water vapor introduced into the light component removal tower to remove the light components from the polyether polyol; the second mixture discharged from the bottom of the light component removal tower enters the dehydration tower, where water is removed from the polyether polyol by stripping with inert gas.

2. The method for continuously removing light components from polyether polyol according to claim 1, characterized in that, The second mixture discharged from the bottom of the light-weight removal tower enters the dehydration tower, where it forms a countercurrent with the inert gas introduced into the dehydration tower to remove water from the polyether polyol.

3. The method for continuously removing light components from polyether polyol according to claim 1, characterized in that, The mass ratio of deoxygenated water to polyether polyol is 0.1%-0.5%, and the mixing temperature is 100℃-130℃.

4. The method for continuously removing light components from polyether polyol according to claim 3, characterized in that, The first mixture of deoxygenated water and polyether polyol is an emulsion; Preferably, the mass ratio of deoxygenated water to polyether polyol is 0.4%.

5. A process for continuous removal of light components from polyether polyols according to any one of claims 1 to 4, characterized in that, The operating temperature of the light-weight removal tower for polyether polyols is 120-145℃, and the pressure at the top of the tower is controlled at 3-10 kPaG. Preferably, the operating temperature is 135℃ and the pressure at the top of the tower is 5 kPaG.

6. A process for continuous removal of light components from polyether polyols according to any one of claims 1 to 4, characterized in that, A bubbling heating section is set up inside the light-weight removal tower. The first packing section and the second packing section are placed in the areas above and below the bubbling heating section, respectively. Water vapor is introduced into the bubbling heating section. The mass of the water vapor introduced is 0.5%-0.75% of the mass of the polyether polyol, and the steam pressure is greater than 300 kPaG. Preferably, the mass of the steam introduced is 0.5% of the mass of the polyether polyol, and the steam pressure is 350 kPaG; Preferably, a bubble distributor is installed in the bubbling heating section.

7. The method for continuously removing light components from polyether polyol according to claim 6, characterized in that, The specific surface area of ​​the packing in the first packing section is smaller than that of the packing in the second packing section; the height of the first packing section is smaller than that of the second packing section. Preferably, the height of the second packing section is 2-6 times the height of the first packing section; More preferably, the height of the second packing section is four times the height of the first packing section.

8. A process for stripping light components from polyether polyols according to any one of claims 1 to 7, characterized in that, The interior of the light-weight removal tower is divided into the following sections from top to bottom: flash section, first packing section, bubbling heating section, second packing section, and stripping section. In the stripping section, the mass ratio of stripping steam to polyether polyol is 1%-4%, and the steam pressure is greater than 300 kPaG. Preferably, the steam pressure is greater than 350 kPaG.

9. A process for stripping light components from polyether polyols according to any one of claims 1 to 8, characterized in that, The operating temperature of the dehydration tower for polyether polyol is 120℃-145℃, and the pressure at the top of the tower is controlled at 1-5 kPaG. Preferably, the operating temperature is 135℃ and the pressure at the top of the tower is 1 kPaG.

10. A process for stripping light components from polyether polyols according to claim 9, characterized in that, The dehydration tower uses nitrogen as the stripping medium, with the nitrogen temperature not exceeding 145℃ and the mass ratio of nitrogen to polyol being 0.1%-0.5%. Preferably, the nitrogen temperature is 85℃-120℃; More preferably, the mass ratio of nitrogen to polyol is 0.2%.

11. A process for stripping light components from polyether polyols according to any one of claims 1 to 10, characterized in that The internal temperature of the light-weight removal tower and the dehydration tower is between 120℃ and 145℃.

12. A process for stripping light components from a polyether polyol according to claim 11, characterized in that The light-weight removal tower and the dehydration tower are equipped with external jacketed heat tracing. Preferably, the heating temperature of the light-removal tower and the dehydration tower is within ±5°C of the operating temperature of the polyether polyol.

13. An apparatus for use in a process for stripping light components from a polyether polyol as claimed in any one of claims 1 to 12, comprising: The oil-water mixer (7) is connected to the light-light tower preheater (3) and the light-light tower (1) through pipelines. The top of the light-light tower (1) is connected to the nitrogen preheater (8) and the light-light tower condenser (5) through pipelines. The bottom of the light-light tower (1) is connected to the dehydration tower preheater (4) and the top of the dehydration tower (2) through pipelines. The top of the dehydration tower (2) is connected to the dehydration tower condenser (6) through pipelines.

14. The apparatus of claim 13, wherein, The inside of the light-removing tower is divided into a flash evaporation section, a first packing section, a bubbling temperature-increasing section, a second packing section and a stripping section from top to bottom. Preferably, the height of the second packing section is 2-6 times the height of the first packing section. More preferably, the height of the second packing section is 4 times the height of the first packing section.

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