A method for recycling heavy components in a TDI production process

Abstract

The application discloses a new method for recycling heavy component resources in a TDI production process, and comprises the following steps: step 1, injecting an extractant into a reactor, and controlling the temperature of the extractant to be in the range of-10 to 25 DEG C, preferably-10 to-5 DEG C; step 2, mixing TDI production tailings and an extraction solvent according to a proportion, uniformly mixing the liquid, and stably keeping the temperature of the liquid in the range of-10 to 25 DEG C, and then standing and separating upper clear liquid; and step 3, obtaining TDI through rectification separation of the upper clear liquid extracted in the step 2. The method provided by the application can effectively recover TDI in tailings treated by incineration, and can prepare high-rebound soft foam from the recovered TDI, thereby reducing TDI production cost and alleviating environmental pollution caused by incineration; the industrial production process is simple, and energy consumption is low.

Description

Technical Field

[0001] This invention relates to the field of liquid waste treatment technology, specifically to a method for the resource utilization of heavy components in the TDI production process. Background Technology

[0002] TDI is short for toluene diisocyanate. The typical 2,4-yl / 2,6-yl ratios of TDI are 100 / 0, 80 / 20, and 65 / 35, respectively, and are referred to as T-100, T-80, and T-65. As one of the most important raw materials in the polyurethane industry, TDI is mainly used in the production of flexible polyurethane foams, polyurethane coatings, elastomers, adhesives, sealants, and other products. Currently, the mainstream process for producing TDI is the phosgene process, which involves a photochemical reaction between toluene diamine and phosgene to generate TDI. The photochemical side reaction produces a large amount of tar-like heavy components, which mix with TDI. After multi-stage distillation purification, the final product is TDI, solid tar, liquid tar, a large TDI component containing a small amount of liquid tar, and a light TDI component containing a small amount of solvent.

[0003] Chinese patent CN106753180 A provides a method for treating crude TDI containing a large amount of tar. This invention mixes crude TDI in a molten state with polymeric MDI (PAPM) to generate a modified isocyanate mixture, which can be used as a raw material for single-component polyurethane adhesives. The single-component polyurethane adhesives produced have excellent performance, effectively reduce the generation of tar solid waste, reduce environmental pollution, and have good economic benefits.

[0004] Chinese patent CN109913255A discloses a method for preparing liquid fuel using TDI tar residue. The method involves grinding, digesting, and filtering the tar residue particles generated during TDI production. The digestion filtrate is then mixed with a fuel accelerator in a certain proportion to obtain the liquid fuel. The prepared liquid fuel has advantages such as high calorific value and low risk of secondary pollution from combustion emissions.

[0005] The heavy TDI fraction contains chlorine-containing substances produced during distillation, polycyclic aromatic hydrocarbons generated from TDI self-polymerization, and a small amount of tar. The conventional treatment approach is incineration, which produces low-pressure steam as a byproduct. Incineration also generates NO... X CO X The waste gas from substances such as nitrogen oxides needs to be treated by denitrification and other processes. Conventional treatment methods result in a large waste of TDI and high treatment costs, leading to serious environmental pollution.

[0006] Compared to crude TDI, the heavier components of TDI have poorer thermal stability. Direct purification via distillation can lead to the decomposition of impurities and the generation of HCl at high temperatures, placing higher demands on the materials used in the distillation column and packing, resulting in higher equipment investment costs. Therefore, to address the current problems and development trends in the TDI industry, it is necessary to develop simple and effective methods for handling production waste. Summary of the Invention

[0007] This invention provides a novel method for the resource utilization of TDI production waste. By using a low-boiling-point solvent, tar, polycyclic aromatic hydrocarbons, and TDI monomers in TDI production waste can be separated. The low-boiling-point solvent can be recycled, and the recovered TDI monomers can be reacted with polyols to prepare high-resilience soft foam, thus achieving low-cost and low-energy recovery and utilization of production waste.

[0008] The inventors discovered through experiments that when using solvent extraction to separate TDI from various impurities in production tailings, the separation effect can be enhanced by lowering the extraction temperature, and the color of the purified TDI changes from dark brown to slightly yellow.

[0009] This invention's experiments revealed that purified TDI, when applied to high-resilience foam, exhibits significantly higher mechanical strength and resilience than normal TDI products. Research indicates this is due to the role of toluene triisocyanate (TDI) in the production waste. TDI effectively enhances the foam's resilience without affecting the foam's aeration and gelation processes. However, existing TDI production processes involve multi-stage distillation to reduce impurities, resulting in TDI that does not contain TDI. The method provided in this invention allows for the purification of TDI containing a certain amount of TDI from production waste.

[0010] To achieve the above-mentioned objectives, the present invention provides the following technical solution:

[0011] This invention provides a method for recovering TDI from TDI production tailings, comprising the following steps:

[0012] Step 1: Inject the extractant into the reactor and control the extractant temperature between -10 and 25°C, preferably between -10 and -5°C;

[0013] Step 2: Mix the TDI production tailings and extraction solvent in a certain proportion. Stable the temperature of the uniformly mixed liquid to -10 to 25°C, let it stand, separate the upper clear liquid, and incinerate the lower viscous liquid containing a small amount of solvent.

[0014] Step 3: The supernatant extracted in step 2 is separated by distillation to obtain TDI.

[0015] In a preferred embodiment, the extractant in step 1 is selected from one or more of C2-C8 alkanes, ethers, ketones, and aromatics. Further, the alkanes are selected from one or more of cyclohexane, n-hexane, isooctane, and n-heptane; the ethers are selected from one or more of diethyl ether, acetone, propylene oxide, and methyl ethyl ketone; and the aromatics are selected from one or two of toluene and xylene.

[0016] The production tailings mentioned in this invention refer to the photochemical liquid produced by the photochemical reaction of toluene diamine, which, after dephosgene and desolventization to produce crude TDI, and then undergoes two-stage distillation to produce the bottom liquid, mainly containing 75-85% TDI, 8-12% toluene triisocyanate, 5-10% chloromethylphenyl isocyanate, 0.5-1% tar, and 5-10% TDI polycyclic substances, such as TDI biuret, TDI dimer, trimer, pentamer, etc. (self-polymers of TDI at high temperatures).

[0017] The chloromethylphenyl isocyanate in this invention includes chlorotoluene diisocyanate, benzyl chlorophenyl diisocyanate, dichlorotoluene diisocyanate, etc.

[0018] In a preferred embodiment, the mass ratio of production tailings to extraction solvent in step 2 is controlled at 10:1-1:10, and the mixing is carried out under stirring conditions. The mixing speed is controlled at 300-600 rpm, and the stirring time is 5-10 min to ensure that the extraction solvent and production tailings are mixed evenly.

[0019] In a preferred embodiment, the settling time in step 2 is 1-120 minutes, preferably 1-10 minutes.

[0020] In a further preferred embodiment, in step 2, after extraction, the supernatant is extracted by a peristaltic pump. To avoid the impact of extracting the raffinate on the extraction efficiency, a small amount of supernatant is retained.

[0021] Further optimization involves cooling the extractant before mixing it with the production waste for extraction. This is to enhance the efficiency of extraction and separation. Furthermore, to improve production efficiency, the extraction solvent can be directly mixed with the production waste for cooling, reducing the time required for pre-cooling.

[0022] Further preferably, the distillation separation conditions in step 3 are: pressure 50-100 kPaA, preferably 60-70 kPaA, temperature 80-120°C, preferably 100-110°C; preferably, the solvent separated by distillation is returned to step 1 for recycling.

[0023] Preferably, the distillation separation is carried out in a plate column or a structured packed column.

[0024] On the other hand, the present invention provides a high-resilience foam, which is prepared from the following raw materials:

[0025] raw material Dosage / wt% polyols 68.96-70.39 water 1.75-1.91 silicone oil 1.26-1.45 Amine catalysts 0.10-0.30 Organometallic catalysts 0.07-0.14 TDI 26.39-27.26

[0026] In this invention, the polyol is selected from polymer polyols or polyether polyols, one or more of POP2045, F3156D, F3135, and F3156.

[0027] In this invention, the silicone oil is selected from one or more of L570, L580, and L8002;

[0028] In this invention, the amine catalyst is selected from one or more of triethylenediamine, bis(dimethylaminoethyl) ether, triethylamine, and tetramethylhexanediamine;

[0029] In this invention, the organometallic catalyst is selected from one or more of stannous isooctanoate (T9), dibutyltin dilaurate (T12), tetraisobutyl titanate, ferric octanoate, and lead octanoate.

[0030] Finally, the present invention also provides a method for preparing high-resilience foam, the method comprising the following steps:

[0031] 1) Premix preparation: Polyol, water, and amine catalyst are stirred and mixed evenly to obtain premix 1;

[0032] 2) Accurately weigh premix 1 and tin-based catalyst, and mix them evenly;

[0033] 3) Add the measured amount of TDI to the mixture in step 2, stir and foam. When the foam height no longer changes, let it mature.

[0034] In this invention, the mixing temperature in step 1) is 20-30℃, and the mixing speed is 500-1500 rpm.

[0035] In this invention, the mixing speed in step 2) is 200-1000 rpm.

[0036] In this invention, the stirring speed in step 3) is 2000-4000 rpm, the stirring time is 5-10 s, the maturation temperature is 20-25℃, and the maturation time is 24-48 h.

[0037] The beneficial effects of this invention are as follows: using a low-boiling-point solvent at a lower temperature can separate tar, polycyclic aromatic hydrocarbons, and TDI monomers from TDI production waste. Low-temperature conditions can improve the extraction and separation effect and avoid the problem of low-boiling-point solvent volatilization. The solvent used can be recycled, which can effectively recover TDI components from the waste compared to the current incineration treatment method, reducing the production cost of TDI. In addition, the recovered TDI monomers contain components that improve the performance of sponges and can react with polyols to prepare high-resilience soft foam, realizing low-cost and low-energy recovery and utilization of production tailings. Detailed Implementation

[0038] The present invention will be further illustrated below with specific embodiments. These embodiments are merely illustrative and do not limit the scope of the invention.

[0039] The main raw material sources involved in the various embodiments and comparative examples of this invention are as follows. Unless otherwise specified, all other raw materials are obtained from ordinary commercial channels: TDI-80, purity ≥99.9%, Wanhua Chemical Group Co., Ltd.

[0040] The TDI heavy component production waste used was generated during the normal operation of the TDI unit of Wanhua Chemical Fujian Co., Ltd.

[0041] Toluene, xylene, acetone, isooctane, n-hexane, cyclohexane, analytical grade, Inokai Chemical Reagent Co., Ltd.

[0042] Stannous isooctanoate, 33% triethylenediamine octane solution (A33 catalyst), 70% dipropylene glycol solution of bis(dimethylaminoethyl) ether (A1 catalyst), analytical grade, Evonik Specialty Chemicals (Shanghai) Co., Ltd.

[0043] POP2045 and F3156D, industrial grade, Wanhua Chemical Group Co., Ltd.

[0044] Silicone oil L580, industrial grade, Momentive Advanced Materials Group.

[0045] The main analytical methods used in the embodiments and comparative examples of this invention are as follows:

[0046] Composition of TDI heavy component waste: analyzed by Agilent 7890B gas chromatograph;

[0047] Polycyclic aromatic hydrocarbons and tar-like substances within the TDI recombinant fraction were determined using gel permeation chromatography (GPC).

[0048] Detector: FID 300℃; H2: 30mL / min; Air: 300mL / min; Make-up gas: 25mL / min;

[0049] Chromatographic column: Agilent 19091J-413HP-5 30m×320μm×0.25μm.

[0050] Test methods for the physical properties of high resilience sponge:

[0051] 1) Use a cutting machine to cut the slow-rebound sponge into standard strips.

[0052] 2) Tensile strength and elongation at break shall be tested according to GB / T 6344—2008; tear strength shall be tested according to GB / T 10808—2006; indentation hardness shall be tested according to GB / T 10807—2006; oxygen index shall be tested according to GB / T2406.2—2009; and drop ball rebound shall be tested according to GB / T 6670—2008.

[0053] In the embodiments of this invention, the quality evaluation data of TDI production waste is as follows:

[0054] Analysis Project Analysis results Appearance Dark brown, with a small amount of mechanical impurities. TDI content / % 75.98 Toluene triisocyanate / % 8.70 Chloromethylphenyl isocyanate / % 8.70 Polycyclic substances / % 5.82 tar / % 0.80

[0055] Implementation Case 1

[0056] 1) The extraction solvent is injected into the reaction vessel, and the reaction vessel is rapidly cooled using a mixture of ethylene glycol and water, with the temperature controlled at 10°C. The extraction solvent includes xylene, isooctane, n-hexane, cyclohexane, and acetone.

[0057] 2) After the mechanical impurities are removed by filtration, the production waste is added to the extraction solvent at a ratio of 10:1.

[0058] 3) After mixing thoroughly at 400 rpm, let the mixture stand for 10 minutes and then separate the supernatant.

[0059] 4) The supernatant was subjected to extraction solvent removal at 100℃ and 50kPa to obtain TDI. The relevant indicators of the TDI after the above treatment were analyzed, and the results are as follows:

[0060]

[0061] By comparing the TDI data with that before treatment, it can be seen that after treatment by the method of the present invention, when isooctane is used as the extraction solvent, the TDI recovery in the TDI heavy component waste is the highest, the tar and polycyclic substances are basically removed, and the chlorinated substances are removed to the maximum extent while retaining a large amount of methyl phenyl triisocyanate.

[0062] Implementation Case 2

[0063] 1) Inject isooctane solvent into the reactor and use a mixture of ethanol and water to rapidly cool the reactor, controlling the temperature at -15, -10, -5, 0, 10, 25, and 30℃ respectively.

[0064] 2) After the mechanical impurities are removed by filtration, the production waste is added to the production waste at a ratio of 5:1 to the extraction solvent.

[0065] 3) After mixing thoroughly at 600 rpm, let the mixture stand for 5 minutes and then separate the supernatant.

[0066] 4) The supernatant was subjected to vacuum distillation at 80℃ and 100kPa to remove the extraction solvent, yielding TDI. The relevant parameters of the TDI after the above treatment were analyzed, and the results are as follows:

[0067]

[0068] This case study revealed that when the extraction temperature is above 25℃, the separated TDI contains a large amount of chloromethylphenyl isocyanate, resulting in a lower TDI content, a darker color, and poorer separation. Lowering the temperature can reduce the solubility of polycyclic and chlorinated substances in nonpolar solvents, thereby improving extraction efficiency. -5℃ and -10℃ show excellent extraction and separation effects.

[0069] When the temperature is below -10℃, the stratification effect is poor within the same static time. The separated supernatant has a low TDI content and a high content of polycyclic aromatic hydrocarbons and chloromethyl phenyl isocyanate.

[0070] Implementation Case 3

[0071] 1) Hexane solvent is injected into the reactor, and a mixture of ethylene glycol and water is used to rapidly cool the reactor, with the temperature controlled at -5℃.

[0072] 2) After the mechanical impurities are removed by filtration, the production waste is added to the extraction solvent in a ratio of 10:1, 5:1, 1:1, 1:5, or 1:10.

[0073] 3) After mixing thoroughly at 300 rpm, let the mixture stand for 1 minute and then separate the supernatant.

[0074] 4) The supernatant was subjected to vacuum distillation at 80℃ and 100kPa to remove the extraction solvent, yielding TDI. The relevant parameters of the TDI after the above treatment were analyzed, and the results are as follows:

[0075]

[0076]

[0077] By comparing this implementation case with previous data, the optimal separation efficiency is achieved when the extractant and TDI heavy component waste are in a 1:1 weight ratio.

[0078] Application Example 1

[0079] In this embodiment of the invention, the processed TDI and normal quality assessment data are used as follows:

[0080] Analysis Project TDI after treatment Normal TDI-80 Appearance Slightly yellow Colorless and transparent TDI content / % 96.36 99.97 Toluene triisocyanate / % 3.02 Not detected Chloromethylphenyl isocyanate / % 0.56 Not detected Polycyclic substances / % 0.05 Not detected tar / % 0.01 Not detected

[0081] 1) Premix preparation: 820g of polyether polyol F3156D, 180g of polymer polyol POP20245, 4.45g of water, 12g of silicone oil L580, 0.3g of A1 catalyst and 1.5g of A33 catalyst are stirred and mixed evenly at 25℃ and 1000rpm to obtain the premix.

[0082] 2) Accurately weigh 80g of polyether premix and 0.19g of T9 catalyst, and mix them evenly at 500rpm using a turbine agitator;

[0083] 3) Add 35.9g TDI to the mixture in step 2, stir rapidly at 3000rpm for 10s, transfer to a FOEMATE foam riser to monitor the foaming process, and perform mechanical property testing after the foam has fully matured. The specific results are as follows:

[0084]

[0085]

[0086] The performance test results in this embodiment show that using the purification method of this invention to purify the TDI in the heavy components and mixing it with TDI-80 in a certain proportion for high-resilience foaming, high-resilience foam with a foam density in the range of 8.0-8.6 kg·m⁻³ can be obtained by adjusting the content of the purified heavy components. Increasing the amount of TDI recovered from the heavy components within a certain range increases the content of methyl phenyl triisocyanate in the system, which can improve the mechanical properties of the high-resilience foam and enhance its flame retardant properties.

[0087] Application Example 2

[0088] In this embodiment of the invention, experiments were conducted using TDI recovered at different temperatures as described in Example 2:

[0089] 1) Premix preparation: 820g of polyether polyol F3156D, 180g of polymer polyol POP20245, 4.45g of water, 12g of silicone oil L580, 0.3g of A1 catalyst and 1.5g of A33 catalyst are stirred and mixed evenly at 25℃ and 1000rpm to obtain the premix.

[0090] 2) Accurately weigh 80g of polyether premix and 0.19g of T9 catalyst, and mix them evenly at 500rpm using a turbine agitator;

[0091] 3) Add 35.9g of recycled TDI to the mixture in step 2, stir rapidly at 3000rpm for 10s, transfer to a FOEMATE foam riser to monitor the foaming process, and perform mechanical property testing after the foam has fully matured. The specific results are as follows:

[0092]

[0093] The performance test results in this implementation case show that when the extraction temperature is selected as -10 to -5℃, the produced high-resilience foam has better mechanical properties.

Claims

1. A method for recycling TDI from TDI production tailings, comprising the following steps: Step 1: Inject the extractant into the reactor and control the extractant temperature between -10 and 25°C, preferably between -10 and -5°C; Step 2: Mix the TDI production tailings and extraction solvent in a certain proportion. Stable the temperature of the well-mixed liquid to -10 to 25°C, let it stand, and separate the supernatant. Step 3: The supernatant extracted in Step 2 is separated by distillation to obtain TDI.

2. The method as described in claim 1, characterized in that, The extractant in step 1 is selected from one or more of C2-C8 alkanes, ethers, ketones, and aromatics. Preferably, the alkanes are selected from one or more of cyclohexane, n-hexane, isooctane, and n-heptane; the ethers are selected from one or more of diethyl ether, acetone, propylene oxide, and methyl butyl ketone; and the aromatics are selected from one or two of toluene and xylene.

3. The method as described in claim 1 or 2, characterized in that, The production tailings refer to the photochemical liquid produced by the photochemical reaction of toluene diamine, which, after dephosgene and desolventization to produce crude TDI, and then undergoes two-stage distillation to produce the bottom liquid, mainly containing 75-85% TDI, 8-12% toluene triisocyanate, 5-10% chloromethylphenyl isocyanate, 0.5-1% tar, and 5-10% TDI polycyclic compounds; preferably, the chloromethylphenyl isocyanate includes chlorotoluene diisocyanate, benzyl chlorophenyl diisocyanate, and dichlorotoluene diisocyanate.

4. The method according to any one of claims 1-3, characterized in that, In step 2, the mass ratio of production tailings to extraction solvent is controlled at 10:1-1:10, and the mixing is carried out under stirring conditions. The mixing speed is controlled at 300-600 rpm, and the stirring time is 5-10 min; and / or, the standing time in step 2 is 1-120 min, preferably 1-10 min.

5. The method according to any one of claims 1-4, characterized in that, The distillation separation conditions described in step 3 are: pressure 50-100 kPaA, preferably 60-70 kPaA, and temperature 80-120°C, preferably 100-110°C.

6. A high-resilience foam, prepared from the following raw materials: Polyols 68.96-70.39 Water 1.75-1.91 Silicone oil 1.26-1.45 Amine catalysts: 0.10-0.30 Organometallic catalysts 0.07-0.14 TDI 26.39-27.26; The TDI includes TDI recovered from TDI production tailings as described in any one of claims 1-5.

7. The high-resilience foam as described in claim 6, characterized in that, The polyol is selected from polymeric polyols or polyether polyols, one or more of POP2045, F3156D, F3135, and F3156; and / or, the silicone oil is selected from one or more of L570, L580, and L8002; and / or, the amine catalyst is selected from one or more of triethylenediamine, bis(dimethylaminoethyl) ether, triethylamine, and tetramethylhexanediamine; and / or, the organometallic catalyst is selected from one or more of stannous isooctanoate (T9), dibutyltin dilaurate (T12), tetraisobutyl titanate, ferric octanoate, and lead octanoate.

8. The method for preparing high-resilience foam as described in claim 6 or 7, wherein the method comprises the following steps: 1) Premix preparation: Polyol, water, and amine catalyst are stirred and mixed evenly to obtain premix 1; 2) Accurately weigh premix 1 and tin-based catalyst, and mix them evenly; 3) Add the measured amount of TDI to the mixture in step 2, stir and foam. When the foam height no longer changes, let it mature.

9. The preparation method according to claim 8, characterized in that, The mixing temperature in step 1) is 20-30℃, and the mixing speed is 500-1500 rpm; and / or, the mixing speed in step 2) is 200-1000 rpm; and / or, the mixing speed in step 3) is 2000-4000 rpm, and the mixing time is 5-10 seconds; the maturation temperature is 20-25℃, and the maturation time is 24-48 hours.

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