Method for purifying crude polymer polyol

Abstract

The invention provides a method for purifying crude polymer polyol, which comprises the following steps: step 1, carrying out first purification operation on the crude polymer polyol by adopting one or more of the following operations: flash evaporation, nitrogen distillation and nitrogen steam stripping; step 2, carrying out second purification operation on the crude polymer polyol subjected to the first purification operation, wherein the second purification operation is carried out by adopting one or more of the following operations: steam distillation and steam stripping; thereby obtaining a purified polymer polyol; the method also optionally comprises a third step of condensing the gas phase generated in the step 1 and / or the step 2 twice or more times, and optionally conveying the liquid material of the condensing operation to the equipment for synthesizing the crude polymer polyol. According to the method disclosed by the invention, the organic volatile impurities can be effectively removed from the crude polymer polyol, and the aims of simplifying the process, saving materials and reducing the production cost are fulfilled.

Description

Technical Field

[0001] The present invention relates to the field of chemical industry, and more specifically to a method for removing organic volatile impurities from polymer polyols by a combined purification process. Background Art

[0002] Polymer polyols (POP), also known as vinyl polymer grafted polyether polyols, are prepared by grafting vinyl monomers onto polyether polyols (referred to as base polyethers) through free radical in-situ polymerization. POP has a wide range of applications. For example, industrial products (such as polyurethanes) synthesized using POP as a raw material have better properties (such as hardness, load bearing capacity, resilience, open porosity, etc.) than polyurethanes synthesized using ungrafted base polyethers as raw materials. Therefore, the chemical industry has a very high demand for high-purity POP.

[0003] Unfortunately, however, the synthesis of high-purity POP in the prior art still has great problems to be solved. Specifically, the grafting monomers commonly used to synthesize POP include various unsaturated nitriles containing carbon-carbon double bonds, (meth) alkyl acrylates and hydroxyalkyl esters, halogenated olefins, carboxylates of enols, etc. For example, the most commonly used examples of grafting monomers include acrylonitrile, styrene, methyl methacrylate, hydroxypropyl acrylate, vinyl chloride, etc., especially acrylonitrile and styrene. In addition, in the process of preparing polymer polyols, low molecular weight chain transfer agents are usually used to control the molecular weight of the polymer and achieve the effect of controlling the viscosity of POP. Commonly used chain transfer agents include various alkyl alcohols, alkyl mercaptans, halogenated hydrocarbons, etc., and specific examples are isopropanol, isobutyl alcohol, dodecyl mercaptan, etc. The POP product obtained by the above-mentioned grafting reaction will inevitably contain a large amount of residual small molecule grafting monomers and chain transfer agents, etc., and it is necessary to remove these residual impurities before using polymer polyols to prepare polyurethane products, otherwise these residual impurities will have a serious negative impact on the performance of polyurethane products. In addition, the above-mentioned grafting monomers and chain transfer agents after removal will cause harm to the environment and must not be discharged into the ambient atmosphere or water bodies. They need to be recycled and harmlessly treated. In order to solve the above problems, the existing technology has invested a lot of money and manpower for research, but all the developed technologies inevitably have the problems of too complicated processes (thereby resulting in reduced efficiency and significantly increased related operating costs), too high process costs (some are even so high that they cannot be commercialized), less than ideal purification efficiency of POPs, and difficult recycling and harmless treatment of separated small molecule impurities (prone to additional material costs and labor costs, and poor treatment of these impurities will also cause serious secondary environmental hazards). People are eager to develop a new technology to effectively remove organic impurities such as small molecule grafting monomers and chain transfer agents remaining in POPs in a simple and low-cost manner, and to achieve the recycling and recycling of separated organic impurities.

[0004] In view of the above problems existing in the prior art, the inventors of the present application have developed a new POP purification method through extensive and in-depth research, which unexpectedly solves the long-standing problem in the prior art that needs to be solved. Summary of the invention

[0005] The first aspect of the present application provides a method for purifying a crude polymer polyol, the method comprising the following steps:

[0006] Step 1: performing a first purification operation on the crude polymer polyol, wherein the first purification operation is performed by one or more selected from the following: flash evaporation, nitrogen distillation, and nitrogen stripping;

[0007] Step 2: performing a second purification operation on the crude polymer polyol after the first purification operation, wherein the second purification operation is performed by one or more selected from the following: steam distillation, steam stripping;

[0008] Thus, a purified polymer polyol is obtained.

[0009] According to one embodiment of the present application, the method further comprises step three: performing two or more condensation operations on the gas phase produced in step one and / or step two, and optionally conveying the liquid material obtained by the condensation operation to a device for synthesizing crude polymer polyols.

[0010] According to another embodiment of the present application, the flash evaporation in step 1 is carried out at a pressure of 3-70 kPa and a temperature of 80-200°C.

[0011] According to another embodiment of the present application, for the nitrogen distillation or nitrogen stripping in step one, the nitrogen mass flow rate is 1%-20% of the feed mass flow rate.

[0012] According to another embodiment of the present application, the nitrogen distillation or nitrogen stripping in step one is carried out at a pressure of 3-70 kPa and a temperature of 80-200°C.

[0013] According to another embodiment of the present application, the steam distillation or steam stripping in step 2 is carried out at a pressure of 3-70 kPa and a temperature of 80-200°C.

[0014] According to another embodiment of the present application, the gas phase produced in step one and / or step two is subjected to three condensation operations, wherein the first stage of condensation brings the high-temperature and high-pressure steam into contact with the first cooling medium to condense the steam into saturated steam; the second stage of condensation brings the saturated steam into contact with the second cooling medium to condense the saturated steam into a supercooled liquid; and the third stage of condensation brings the supercooled liquid into contact with the third cooling medium to cool it to the target temperature.

[0015] According to another embodiment of the present application, the crude polymer polyol is prepared by subjecting the grafting monomer to free radical in situ polymerization in the presence of a polyether polyol and an optional chain transfer agent to form a graft connected to the polyether polyol, thereby obtaining a crude polymer polyol comprising a polymer polyol, unreacted grafting monomer and unreacted chain transfer agent.

[0016] According to another embodiment of the present application, the grafting monomer is selected from one or more of the following: C1-C8 alkyl (meth)acrylates, C1-C8 hydroxyalkyl (meth)acrylates, C6-C16 aromatic olefins, C2-C12 halogenated olefins, C3-C12 ethylenically unsaturated nitriles, and C1-C6 carboxylic acid C2-C8 olefin esters.

[0017] According to another embodiment of the present application, the chain transfer agent is selected from one or more of the following: C1-C12 fatty alcohol, C2-C12 aliphatic thiol, C1-C8 halogenated alkane.

[0018] According to another embodiment of the present application, the grafting monomer is selected from one or more of the following: (meth)acrylonitrile, styrene, methyl (meth)acrylate, hydroxypropyl (meth)acrylate, and vinyl chloride.

[0019] According to another embodiment of the present application, the chain transfer agent is selected from one or more of the following: isopropanol, isobutanol, and C1-C4 halogenated alkane.

[0020] According to another embodiment of the present application, based on the total weight of the crude polymer polyol, the content of unreacted grafting monomer is 1-15% by weight, and the content of unreacted chain transfer agent is 1.5-16% by weight; the content of volatile organic impurities in the purified polymer polyol obtained after step 2 is less than 1 ppm. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 The schematic diagram of the process design used in Example 1 of the present application is shown;

[0022] Figure 2 The schematic diagram of the process design used in the second embodiment of the present application is shown;

[0023] Figure 3 The schematic diagram of the process design used in the third embodiment of the present application is shown;

[0024] Figure 4 A schematic diagram of the process design used in Example 4 of the present application is shown.

[0025] In the attached drawings, 1-H1 and 2-H1 are primary condensers, 1-H2 and 2-H2 are secondary condensers, and 1-H3 and 2-H3 are tertiary condensers. DETAILED DESCRIPTION

[0026] "Range" disclosed herein is in the form of lower limit and upper limit. It can be one or more lower limits, and one or more upper limits respectively. A given range is defined by selecting a lower limit and an upper limit. The selected lower limit and upper limit define the boundaries of a particular range. All ranges that can be defined in this way are inclusive and combinable, i.e. any lower limit can be combined with any upper limit to form a range. For example, a range of 60-120 and 80-110 is listed for a particular parameter, and it is understood that a range of 60-110 and 80-120 is also expected. In addition, if the minimum range values ​​1 and 2 are listed, and if the maximum range values ​​3, 4 and 5 are listed, the following ranges can all be expected: 1-3, 1-4, 1-5, 2-3, 2-4 and 2-5.

[0027] In this application, unless otherwise specified, the numerical range "ab" represents an abbreviation of any real number combination between a and b, where a and b are real numbers. For example, the numerical range "0-5" means that all real numbers between "0-5" are listed in this document, and "0-5" is just an abbreviation of these numerical combinations.

[0028] In this application, unless otherwise specified, all embodiments and preferred embodiments mentioned herein can be combined with each other to form a new technical solution.

[0029] In this application, unless otherwise specified, all technical features and preferred features mentioned herein can be combined with each other to form a new technical solution.

[0030] In this application, if there is no special explanation, the "including" mentioned herein means open or closed. For example, the "including" may mean that other components not listed may also be included, or only the listed components may be included.

[0031] The crude polymer polyol (crude POP) to be purified by the method of the present invention is prepared by using a polyether polyol (hereinafter referred to as a base polyol) as a raw material, and allowing a grafting monomer having a carbon-carbon double bond to undergo in-situ free radical polymerization to form a graft connected to the main chain of the base polyol. The grafting monomer also plays the role of a solvent during the synthesis of POP, and is therefore also referred to as a "solvent" or "solvent compound". The grafting monomer is selected from one or more of the following: C1-C8 alkyl (meth)acrylates, C1-C8 hydroxyalkyl (meth)acrylates, C6-C16 aromatic olefins, C2-C12 halogenated olefins, C3-C12 ethylenically unsaturated nitriles, and C1-C6 carboxylic acid C2-C8 olefin esters; preferably, the grafting monomer is selected from one or more of the following: C1-C6 alkyl (meth)acrylates, C1-C6 hydroxyalkyl (meth)acrylates, C6-C12 aromatic olefins, C2-C6 halogenated olefins, C3-C6 ethylenically unsaturated nitriles, and C1-C3 carboxylic acid C2-C4 olefin esters; more preferably, the grafting monomer is selected from one or more of the following: acrylonitrile, styrene, methyl methacrylate, vinyl acetate, and vinyl chloride; most preferably, the grafting monomer is styrene, acrylonitrile, or a combination thereof.

[0032] The grafting reaction temperature for synthesizing the crude POP is 80-140° C., preferably 100-120° C. The reaction is carried out under the protection of an inert atmosphere, preferably under a nitrogen atmosphere. In addition, components such as initiators, chain transfer agents, and dispersants are also required. Examples of the initiators include azobisisobutyronitrile (AIBN), benzoyl peroxide (BPO), and the like. The POP synthesis process described above and the various reagents used (such as chain transfer agents and dispersants, etc.) are known in the art.

[0033] According to one embodiment of the present application, the product directly obtained by the above reaction or the product after a simple purification step is used as the crude POP to be purified by the method of the present invention. Based on the total weight of the crude POP, the content of the residual initiator is 1-15% by weight, and the content of the chain transfer agent is 1.5-16% by weight. After the purification method of the present invention is used for purification, the above small molecule impurities are separated and removed, and a high-purity POP (also referred to as "purified POP" in the present invention) that meets large-scale commercial purposes can be obtained, and based on the total weight of the purified POP, the total content of small molecule organic compounds (also referred to as volatile organic compounds) is less than 1ppm.

[0034] The crude POP purification method of the present invention comprises the following steps:

[0035] Step 1: performing a first purification operation on the crude polymer polyol, wherein the first purification operation is performed by one or more selected from the following: flash evaporation, nitrogen distillation, and nitrogen stripping;

[0036] Step 2: performing a second purification operation on the crude polymer polyol after the first purification operation, wherein the second purification operation is performed by one or more selected from the following: steam distillation, steam stripping;

[0037] Thus, a purified polymer polyol is obtained.

[0038] According to a preferred embodiment of the present application, nitrogen stripping is used in step one, and water vapor stripping is used in step two.

[0039] According to another preferred embodiment of the present application, flash evaporation is used in step one, and steam stripping is used in step two.

[0040] According to another preferred embodiment of the present application, flash evaporation and nitrogen stripping are used in step one, and steam stripping is used in step two.

[0041] According to another preferred embodiment of the present application, flash evaporation and nitrogen distillation are used in step one, and two steam distillations are used in step two.

[0042] According to one embodiment of the present application, the gas phase material obtained by the purification operation of the above step 1 and / or step 2 is subjected to two or more condensation operations to recover small molecule volatile substances, such as the grafting monomer (or solvent) described above, from the gas phase material. According to another embodiment of the present application, the small molecule volatile substances recovered by one or more condensation operations described above are partially or completely recycled, for example, transported to a reactor for preparing POP for recycling.

[0043] According to another embodiment of the present application, a flash evaporator is arranged downstream of the one or more condensation operations described above to facilitate separation of gaseous and liquid components in the condensed material.

[0044] According to one embodiment of the present application, the flash evaporation operation used is carried out in a flash evaporator (e.g., a flash tank), and the flash evaporator has a relatively low pressure, so that at least a portion of the components of the material input into the flash evaporator (e.g., a crude POP material or a liquid stream obtained by gas phase condensation, etc.) boils and rapidly vaporizes under the suddenly reduced pressure, thereby phase separation occurs. According to one embodiment of the present application, each flash evaporation operation in step one and step two is carried out at a pressure of 3kPa-70kPa, preferably at a pressure of 10kPa-50kPa. According to one embodiment of the present application, the flash evaporation in step one is carried out at a temperature of 80-200°C, preferably at a temperature of 100-150°C.

[0045] The working principle of the nitrogen stripping used in step one of the present invention is to use nitrogen as a stripping agent, and the nitrogen is countercurrently contacted with the liquid raw material (crude POP) in the tower, and the nitrogen carries the volatile small molecular substances to rise and is discharged at the top of the tower. During the stripping process, the equilibrium partial pressure of the small molecular volatile substances in the liquid phase (crude POP) is greater than the partial pressure of the solute in the gas phase. According to one embodiment of the present application, the nitrogen stripping operation in step one is carried out at a pressure of 3kPa-70kPa, preferably at a pressure of 10kPa-50kPa. According to one embodiment of the present application, the nitrogen stripping operation in step one is carried out at a temperature of 80-200°C, preferably at a temperature of 100-150°C. According to another embodiment of the present application, in the nitrogen stripping operation, the mass flow rate of the input nitrogen is 1-20% of the mass flow rate of the feed (crude POP), preferably 3-15%.

[0046] The principle of the steam distillation or steam stripping adopted in step 2 of the present invention is to use steam as a stripping agent, and the water vapor is countercurrently contacted with the liquid raw material (crude POP) in the stripping tower, and the water vapor carries the volatile small molecular substances to rise and is discharged at the top of the tower. During the stripping process, the equilibrium partial pressure of the small molecular volatile substances in the liquid phase (crude POP) is greater than the partial pressure of the solute in the gas phase. According to one embodiment of the present application, the steam stripping operation in step 2 is carried out at a pressure of 3kPa-70kPa, preferably at a pressure of 10kPa-50kPa. According to one embodiment of the present application, the steam stripping operation in step 2 is carried out at a temperature of 80-200°C, preferably at a temperature of 100-150°C. According to another embodiment of the present application, in the nitrogen stripping operation, the mass flow rate of the input water vapor is 1-30% of the mass flow rate of the feed (crude POP), preferably 5-20%.

[0047] The advantages of the present invention are:

[0048] 1. The purification method of the present invention efficiently purifies crude POP in a simple and low-cost manner to obtain high-purity POP that is urgently needed in the commercial field;

[0049] 2. The purification method of the present invention can effectively recover and reuse the organic volatile components separated from the crude POP, thereby further saving costs and avoiding environmental pollution;

[0050] 3. The various equipment and processes used in the purification method of the present invention do not have particularly complex designs and can be easily operated using existing equipment (stripping tower, condenser, distillation tower, flash evaporator, etc.), and have wide adaptability.

[0051] The method of the present application is specifically described in the following examples, the purpose of which is to provide a better understanding of the content of the present application. It should be understood that these examples are merely illustrative and not restrictive.

[0052] Example

[0053] In the following examples, the crude POP used was produced by in-situ graft polymerization reaction on the POP production line of Shanghai Chlor-Alkali Chemical Co., Ltd. The composition of the crude POP measured by gas chromatography was as follows: POP 84% by mass, styrene 3% by mass, acrylonitrile 2% by mass, and isopropanol 11% by mass.

[0054] Other reagents used in the examples were of analytical grade and used directly without further treatment.

[0055] Example 1

[0056] In this embodiment, according to Figure 1 The purification system is constructed as shown. First, the crude POP is fed into the stripping tower 1 at a mass flow rate of 210 kg / h, the size of the stripping tower 1 is 65 cm×500 cm, the tower section temperature is about 130° C., the stripping tower pressure is 27 kPa, and nitrogen is fed into the stripping tower at a mass flow rate of 5.5 kg / h.

[0057] The liquid stream POP-1 output from the bottom of the stripping tower 1 contains 99.50 mass% of POP, 0.25 mass% of styrene, 0.12 mass% of acrylonitrile, and 0.13 mass% of isopropanol; the gas stream N2-1 output from the top of the stripping tower 1 contains 6 mass% of nitrogen, 12 mass% of styrene, 10 mass% of acrylonitrile, and 72 mass% of isopropanol.

[0058] Next, the liquid stream POP-1 is transported to the stripping tower 2, where water vapor stripping is performed. The stripping tower 2 has a size of 55 cm×475 cm, a tower section temperature of about 130° C., a pressure of 28 kPa, and water vapor is input into the stripping tower 2 at a mass flow rate of 5.5 kg / h.

[0059] The liquid stream output from the bottom of stripping tower 2 is high-purity POP, in which the total content of styrene, acrylonitrile and isopropanol is less than 0.001 mass%. The stream (aqueous phase 1) output from the top of stripping tower 2 contains 94 mass% of water vapor, 5 mass% of styrene, about 0.5 mass% of acrylonitrile, and 0.5 mass% of isopropanol. The stream is then condensed in condensers 2-H1 and 2-H2, and then separated by flash evaporator 3, condenser 2H3 and flash evaporator 4. The temperature of condenser 2-H1 is 50°C and the pressure is 27kPa; the temperature of condenser 2-H2 is 20°C and the pressure is 27kPa; the temperature of condenser 2-H3 is 3°C and the pressure is 27kPa; the temperature of flash evaporator 3 is -15°C and the pressure is 27kPa; the temperature of flash evaporator 4 is 35°C and the pressure is 27kPa. The organic flows L2-1 and L2-2 flowing out from the bottom of the flasher 3 and the flasher 4 are combined into the mixed material 2 and transported back to the POP synthesis process for recycling.

[0060] At the same time, the gas stream N2-1 flowing out from the top of the stripping tower 1 is condensed in condensers 1-H1 and 1-H2, and then separated through flash evaporator 1, condenser 1-H3 and flash evaporator 2. The temperature of condenser 1-H1 is 35°C and the pressure is 27kPa; the temperature of condenser 1-H2 is 22°C and the pressure is 27kPa; the temperature of condenser 1-H3 is -17°C and the pressure is 27kPa; the temperature of flash evaporator 1 is 25°C and the pressure is 27kPa; the temperature of flash evaporator 2 is 5°C and the pressure is 27kPa. The organic streams L1-1 and L1-2 flowing out from the bottom of flash evaporator 1 and flash evaporator 2 are combined into mixed material 1 and transported back to the POP synthesis process for recycling.

[0061] Through the process of Example 1, a high-purity POP product with extremely low volatile organic impurity content is obtained simply and efficiently, and the separated organic impurity components (acrylonitrile, isopropanol and styrene) are fully and effectively recycled.

[0062] Example 2

[0063] In this embodiment, according to Figure 2 The purification system is constructed as shown. First, the crude POP is fed into a flash evaporator at a mass flow rate of 210 kg / h, the temperature of the flash evaporator is 130°C, and the pressure is 27 kPa. The liquid stream POP-1 output from the bottom of the flash evaporator contains 96.1% by mass of POP, 3.5% by mass of styrene, 0.2% by mass of acrylonitrile, and 0.2% by mass of isopropanol; the stream F-1 output from the top of the flash evaporator contains 14% by mass of styrene, 12% by mass of acrylonitrile, and 74% by mass of isopropanol.

[0064] Next, the liquid stream POP-1 is transported to a stripping tower, where water vapor stripping is performed. The stripping tower has a size of 55 cm x 475 cm, a tower section temperature of about 130°C, a pressure of 28 kPa, and water vapor is fed into the stripping tower at a mass flow rate of 5.5 kg / h.

[0065] The liquid stream output from the bottom of the stripping tower is a high-purity POP, in which the total content of styrene, acrylonitrile and isopropanol is less than 0.001% by mass. The stream (aqueous phase 1) output from the top of the stripping tower contains 58.0% by mass of water vapor, 20.5% by mass of styrene, about 5.5% by mass of acrylonitrile, and 16.0% by mass of isopropanol. The stream is then condensed in condensers 2-H1 and 2-H2, and then separated by flash evaporator 3, condenser 2-H3 and flash evaporator 4. The temperature of condenser 2-H1 is 45°C and the pressure is 27kPa; the temperature of condenser 2-H2 is 20°C and the pressure is 27kPa; the temperature of condenser 2-H3 is -3°C and the pressure is 27kPa; the temperature of flash evaporator 3 is 35°C and the pressure is 27kPa; the temperature of flash evaporator 4 is 20°C and the pressure is 27kPa. The organic flows L2-1 and L2-2 flowing out from the bottom of the flasher 3 and the flasher 4 are combined into the mixed material 2 and transported back to the POP synthesis process for recycling.

[0066] At the same time, the above-mentioned logistics F-1 flowing out from the top of the stripping tower 1 is condensed in condensers 1-H1 and 1-H2, and then separated through flash evaporator 1, condenser 1-H3 and flash evaporator 2. The temperature of condenser 1-H1 is 33°C and the pressure is 27kPa; the temperature of condenser 1-H2 is 26°C and the pressure is 27kPa; the temperature of condenser 1-H3 is 10°C and the pressure is 27kPa; the temperature of flash evaporator 1 is 25°C and the pressure is 27kPa; the temperature of flash evaporator 2 is 5°C and the pressure is 27kPa. The organic flows L1-1 and L1-2 flowing out from the bottom of flash evaporator 1 and flash evaporator 2 are combined into mixed material 1 and transported back to the POP synthesis process for recycling.

[0067] Through the process of Example 2, a high-purity POP product with a very low content of volatile organic impurities is obtained simply and efficiently, and the separated organic impurity components (acrylonitrile, isopropanol and styrene) are fully and effectively recycled.

[0068] Example 3

[0069] In this embodiment, according to Figure 3The purification system is constructed as shown. First, the crude POP is fed into the flash evaporator 1 at a mass flow rate of 210 kg / h. The temperature of the flash evaporator 1 is about 130°C and the pressure of the stripping tower is 27 kPa. The liquid stream L output from the bottom of the flash evaporator contains 96.0% by mass of POP, 3.5% by mass of styrene, 0.2% by mass of acrylonitrile, and 0.3% by mass of isopropanol; the stream V output from the top of the flash evaporator 1 contains 14% by mass of styrene, 11% by mass of acrylonitrile, and 75% by mass of isopropanol.

[0070] Then the stream L is transported to the stripping tower 1 for treatment. The size of the stripping tower 1 is 65 cm×500 cm, the tower section temperature is about 130° C., the pressure is 27 kPa, and nitrogen is input into the stripping tower at a mass flow rate of 5.5 kg / h.

[0071] The liquid stream POP-1 output from the bottom of the stripping tower 1 contains 99.85 mass% of POP, 0.06 mass% of styrene, 0.04 mass% of acrylonitrile, and 0.05 mass% of isopropanol; the gas stream N2-1 output from the top of the stripping tower 1 contains 6 mass% of nitrogen, 14 mass% of styrene, 12 mass% of acrylonitrile, and 68 mass% of isopropanol.

[0072] Next, the liquid stream POP-1 is transported to the stripping tower 2, where water vapor stripping is performed. The stripping tower 2 has a size of 55 cm×475 cm, a tower section temperature of about 130° C., a pressure of 28 kPa, and water vapor is input into the stripping tower 2 at a mass flow rate of 5.5 kg / h.

[0073] The liquid stream output from the bottom of the stripping tower 2 is a high-purity POP, in which the total content of styrene, acrylonitrile and isopropanol is less than 1ppm. The stream (aqueous phase 2) output from the top of the stripping tower 2 contains 78% by mass of water vapor, 11% by mass of styrene, about 5% by mass of acrylonitrile, and 6% by mass of isopropanol. The stream is then condensed in condensers 2-H1 and 2-H2, and then separated by a flash evaporator (2-VL-1), a condenser 2H3 and a flash evaporator (2-VL-2). The temperature of condenser 2-H1 is 45°C and the pressure is 27kPa; the temperature of condenser 2-H2 is 20°C and the pressure is 27kPa; the temperature of condenser 2-H3 is 0°C and the pressure is 27kPa; the temperature of flash evaporator (2-VL-1) is 25°C and the pressure is 27kPa; the temperature of flash evaporator (2-VL-2) is 20°C and the pressure is 27kPa. The organic flows L-4 and L-5 flowing out from the bottom of the flash evaporator (2-VL-1) and the flash evaporator (2-VL-2) are combined into a mixed material 3 and transported back to the POP synthesis process for recycling.

[0074] At the same time, the flow V flowing out from the top of the flash tower 1 and the flow N2-1 flowing out from the top of the stripping tower 1 are combined to form a mixed material 1, which is condensed in the condensers 1-H1 and 1-H2, and then separated by the flash evaporator (1-VL-1), condenser 1-H3 and flash evaporator (1-VL-2). The temperature of condenser 1-H1 is 40°C and the pressure is 27kPa; the temperature of condenser 1-H2 is 15°C and the pressure is 27kPa; the temperature of condenser 1-H3 is -18°C and the pressure is 27kPa; the temperature of flash evaporator (1-VL-1) is 20°C and the pressure is 27kPa; the temperature of flash evaporator (1-VL-2) is 5°C and the pressure is 27kPa. The organic flows L1-1 and L1-2 flowing out from the bottom of the flash evaporator (1-VL-1) and the flash evaporator (1-VL-2) are combined into a mixed material 2 (L3) and transported back to the POP synthesis process for recycling.

[0075] Through the process of Example 3, a high-purity POP product with a volatile organic impurity content of less than 10 ppm is obtained simply and efficiently, and the separated organic impurity components (acrylonitrile, isopropanol and styrene) are fully and effectively recycled.

[0076] Example 4

[0077] In this embodiment, according to Figure 4 The purification system is constructed as shown. First, the crude POP is fed into the flash evaporator 1 at a mass flow rate of 210 kg / h. The temperature of the flash evaporator 1 is about 140°C and the pressure of the stripping tower is 27 kPa. The liquid stream L1 output from the bottom of the flash evaporator contains 96.7% by mass of POP, 1.4% by mass of styrene, 0.6% by mass of acrylonitrile, and 1.3% by mass of isopropanol; the stream V1 output from the top of the flash evaporator 1 contains 13% by mass of styrene, 10% by mass of acrylonitrile, and 77% by mass of isopropanol.

[0078] Then the stream L1 is conveyed to the flash evaporator 2 for treatment. The temperature of the flash evaporator 2 is 140° C. and the pressure is 27 kPa. Nitrogen is introduced into the flash evaporator 2 at a mass flow rate of 5.5 kg / h.

[0079] The liquid flow N2-L output from the bottom of the flasher 2 contains 99.2 mass% of POP, 0.4 mass% of styrene, 0.2 mass% of acrylonitrile, and 0.2 mass% of isopropanol; the gas flow N2-V output from the top of the flasher 2 contains 70 mass% of nitrogen, 13 mass% of styrene, 5 mass% of acrylonitrile, and 12 mass% of isopropanol.

[0080] Next, the liquid stream N2-L is transported to the flash evaporator 3 for treatment. The temperature of the flash evaporator 3 is about 140°C and the pressure is 26kPa. At the same time, water vapor is input into the flash evaporator 3 at a mass flow rate of 5.5kg / h. The liquid stream H2O-1-L output from the bottom of the flash evaporator 3 contains 99.97% by mass of POP, 0.01% by mass of styrene, 0.01% by mass of acrylonitrile, and 0.01% by mass of isopropanol; the gas stream H2O-1-V output from the top of the flash evaporator 3 contains 97.7% by mass of water vapor, 1.5% by mass of styrene, 0.3% by mass of acrylonitrile, and 0.5% by mass of isopropanol.

[0081] Next, the liquid stream H2O-1-L is transported to the flash evaporator 4 for treatment. The temperature of the flash evaporator 4 is about 140°C, the pressure is 26 kPa, and water vapor is input into the flash evaporator 4 at a mass flow rate of 5.5 kg / h. The liquid stream output from the bottom of the flash evaporator 4 is high-purity POP, in which the total amount of volatile organic impurities is less than 0.1 ppm; the gas stream H2O-2-V output from the top of the flash evaporator 4 contains 99.0% by mass of water vapor, 0.3% by mass of styrene, 0.4% by mass of acrylonitrile, and 0.2% by mass of isopropanol.

[0082] The streams output from the top of flash evaporator 3 and flash evaporator 4 are combined to form mixed material 3, which is then processed by condenser 2-H1, flash evaporator 2-1, condenser 2-H2, flash evaporator 2-2, condenser 2-H3 and flash evaporator 2-3. The temperature of condenser 2-H1 is 40°C and the pressure is 27kPa; the temperature of condenser 2-H2 is 5°C and the pressure is 27kPa; the temperature of condenser 2-H3 is -17°C and the pressure is 27kPa; the temperature of flash evaporator (2-1) is 40°C and the pressure is 27kPa; the temperature of flash evaporator (2-2) is 15°C and the pressure is 27kPa; the temperature of flash evaporator (2-3) is -17°C and the pressure is 27kPa. The organic flows M2-L1, M2-L3 and M2-L5 flowing out from the bottom of the flash evaporator (2-1), the flash evaporator (2-2) and the flash evaporator (2-3) are combined into a mixed material 4 and transported back to the POP synthesis process for recycling.

[0083] At the same time, the flow V1 flowing out from the top of the flash tower 1 and the flow N2-V flowing out from the top of the flash evaporator 2 are combined to form a mixed material 1, which is then processed by condenser 1-H1, flash evaporator 1-1, condenser 1-H2, flash evaporator 1-2, condenser 1-H3 and flash evaporator 1-3. The temperature of the condenser 1-H1 is 40°C and the pressure is 27kPa; the temperature of the condenser 1-H2 is 5°C and the pressure is 27kPa; the temperature of the condenser 1-H3 is -17°C and the pressure is 27kPa; the temperature of the flash evaporator (1-1) is 40°C and the pressure is 27kPa; the temperature of the flash evaporator (1-2) is 15°C and the pressure is 27kPa; the temperature of the flash evaporator (1-3) is -17°C and the pressure is 27kPa. The organic flows M1-L1, M1-L3 and M1-L5 flowing out from the bottom of the flash evaporator (1-1), the flash evaporator (1-2) and the flash evaporator (1-3) are combined into a mixed material 2 and transported back to the POP synthesis process for recycling.

[0084] Through the process of Example 4, a high-purity POP product with a volatile organic impurity content of less than 1 ppm is obtained simply and efficiently, and the separated organic impurity components (acrylonitrile, isopropanol and styrene) are fully and effectively recycled.

Claims

1. A method for purifying a crude polymer polyol, the method comprising the following steps: Step 1: performing a first purification operation on the crude polymer polyol, wherein the first purification operation is performed by one or more selected from the following: flash evaporation, nitrogen distillation, and nitrogen stripping; Step 2: performing a second purification operation on the crude polymer polyol after the first purification operation, wherein the second purification operation is performed by one or more selected from the following: steam distillation, steam stripping; Thus, a purified polymer polyol is obtained.

2. The method according to claim 1, characterized in that The method further comprises step three: performing two or more condensation operations on the gas phase produced in step one and / or step two, and optionally conveying the liquid material obtained by the condensation operation to a device for synthesizing a crude polymer polyol.

3. The method according to claim 1 or 2, characterized in that The flash evaporation in step 1 is carried out at a pressure of 3-70 kPa and a temperature of 80-200°C.

4. The method according to claim 1 or 2, characterized in that: For the nitrogen distillation or nitrogen stripping in step 1, the nitrogen mass flow rate is 1%-20% of the feed mass flow rate.

5. The method according to claim 1 or 2, characterized in that: The nitrogen distillation or nitrogen stripping in step 1 is carried out at a pressure of 3-70 kPa and a temperature of 80-200°C.

6. The method according to claim 1 or 2, characterized in that: The steam distillation or steam stripping in step 2 is carried out at a pressure of 3-70 kPa and a temperature of 80-200°C.

7. The method according to claim 2, characterized in that The gas phase produced in step one and / or step two is subjected to three condensation operations. In the first stage of condensation, the high-temperature and high-pressure steam is brought into contact with the first cooling medium to condense the steam into saturated steam. In the second stage of condensation, the saturated steam is brought into contact with the second cooling medium to condense the saturated steam into a supercooled liquid. In the third stage of condensation, the supercooled liquid is brought into contact with the third cooling medium to cool the supercooled liquid to the target temperature.

8. The method according to claim 1 or 2, characterized in that: The crude polymer polyol is prepared by free radically polymerizing a grafting monomer in situ in the presence of a polyether polyol and an optional chain transfer agent to form a graft attached to the polyether polyol, thereby obtaining a crude polymer polyol comprising a polymer polyol, unreacted grafting monomer and unreacted chain transfer agent; The grafting monomer is selected from one or more of the following: C1-C8 alkyl (meth)acrylates, C1-C8 hydroxyalkyl (meth)acrylates, C6-C16 aromatic olefins, C2-C12 halogenated olefins, C3-C12 ethylenically unsaturated nitriles, C1-C6 carboxylic acid C2-C8 olefin esters; The chain transfer agent is selected from one or more of the following: C1-C12 fatty alcohol, C2-C12 aliphatic thiol, C1-C8 halogenated alkane.

9. The method according to claim 8, characterized in that The grafting monomer is selected from one or more of the following: (meth)acrylonitrile, styrene, methyl (meth)acrylate, hydroxypropyl (meth)acrylate, vinyl chloride; The chain transfer agent is selected from one or more of the following: isopropanol, isobutanol, and C1-C4 halogenated alkane.

10. The method according to claim 8, characterized in that Based on the total weight of the crude polymer polyol, the content of unreacted grafting monomer is 1-15% by weight, and the content of unreacted chain transfer agent is 1.5-16% by weight; The content of volatile organic impurities in the purified polymer polyol obtained after step 2 is less than 1 ppm.

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