A method for preparing regenerated polyether polyol by degrading polyurethane semi-rigid foam waste foam by acidolysis

Abstract

The application discloses a method for preparing regenerated polyether polyol from polyurethane semi-rigid foam waste foam by acidolysis, and comprises the following steps: (1) cleaning and drying the polyurethane semi-rigid foam waste foam, crushing, removing impurities, and obtaining foam particles; (2) dehydrating the foam particles; (3) putting the foam particles, an acidolysis agent and a catalyst into a reaction kettle; (4) three-stage heating of the material, the first stage being 140-160 DEG C for 2-3 hours, the second stage being 180-200 DEG C for 1-2 hours, and the third stage being 200-210 DEG C for 0.5-1 hour, and inert gas protection; (5) separating solid residues from the reacted mixture to obtain liquid product, regenerated polyether polyol; wherein the acidolysis agent is a mixture of maleic acid and succinic anhydride. The acidolysis method recycles regenerated polyether polyol from the polyurethane semi-rigid foam waste foam, the degradation rate is greater than or equal to 98%, and the content of aromatic amine in the regenerated polyether polyol is reduced, which is beneficial to the later application.

Description

Technical Field

[0001] This invention relates to the field of polyurethane waste foam degradation, recycling and reuse, and particularly to a method for preparing recycled polyether polyols by acid hydrolysis of polyurethane semi-rigid foam waste. Background Technology

[0002] Polyurethane is one of the polymer materials closely related to people's lives. Its enormous consumption not only requires the use of large amounts of fossil fuels but also leads to a significant amount of waste, which is difficult to degrade in the natural environment. Therefore, recycling and utilizing polyurethane waste is beneficial for reducing the consumption of fossil resources at the source, thereby achieving carbon emission reduction.

[0003] For decades, landfill disposal has been a common method for treating polyurethane waste. Landfilled waste gradually decomposes into smaller molecules, severely polluting the environment and wasting significant resources. Researchers have dedicated themselves to finding efficient technologies for polyurethane recycling, encompassing both physical and chemical methods. Chemical recycling methods have received increasing attention in recent years. Acid hydrolysis is one of the promising chemical recycling methods for PU. Washed and pulverized PU waste can be acid-hydrolyzed under relatively mild conditions; for example, hydrochloric acid hydrolysis can be carried out at 60°C and normal pressure. The recovered products do not contain aromatic amines; for example, using dicarboxylic acids will not lead to the formation of aromatic primary amines in the products, which is beneficial for the application of recycled polyether polyols.

[0004] Semi-rigid polyurethane foam is a type of foam material that falls between flexible and rigid polyurethane foam. It combines certain rigidity, elasticity, and support properties, with a moderate degree of crosslinking (crosslinking density higher than flexible foam but lower than rigid foam), and a density typically ranging from 30 to 100 kg / m³. 3 Rigid polyurethane foam (PU) is a key functional material in the automotive, home appliance, and building materials industries. Because PU is a cross-linked polymer composed of soft segments (polyether polyols) and hard segments (isocyanate-derived segments), it possesses a unique microphase separation structure and a moderate degree of cross-linking. Existing acid hydrolysis processes, which involve reacting at a fixed temperature, are unsuitable for the chemical recycling of PU. This is because existing acid hydrolysis processes react rapidly and simultaneously with the soft segments at a fixed temperature, leading to a loss of selectivity. Furthermore, the high temperature causes the urethane bonds to react too quickly, inhibiting the complete breaking of urea bonds and resulting in incomplete depolymerization of the hard segments. Additionally, the large number of small molecules generated in the initial stage of the reaction at high temperatures hinders mass transfer, thus reducing overall efficiency.

[0005] The alcoholysis process inevitably produces free aromatic amines (1-3%) because the alcoholysis agent induces the breaking of CN bonds. Aromatic amines are a class of compounds with strong toxicity, carcinogenicity, and sensitization. Their hazards extend to three dimensions: human health, ecological environment, and industrial production. They are also key pollutants to be controlled in polyurethane chemical recycling processes.

[0006] Therefore, in the chemical recycling process of waste polyurethane semi-rigid foam, it is desirable to improve the degradation efficiency while reducing the content of aromatic amines in the recycled polyol, or to avoid the generation of aromatic amines. Summary of the Invention

[0007] Purpose of the invention: The purpose of this invention is to provide a method for preparing recycled polyether polyols by acid hydrolysis of waste polyurethane semi-rigid foam, thereby improving the degradation rate and reducing the aromatic amine content in the recycled polyether polyols.

[0008] The method for preparing recycled polyether polyols by acid hydrolysis of waste polyurethane semi-rigid foam according to the present invention includes the following steps:

[0009] (1) Clean and dry the waste polyurethane semi-rigid foam, crush it, remove impurities, and obtain foam particles;

[0010] (2) Dehydrate the foam particles to remove residual moisture;

[0011] (3) Add foam particles, acid hydrolysate and catalyst into the reactor and enhance mass transfer by stirring and shearing inside the reactor;

[0012] (4) The material undergoes a three-stage acid hydrolysis reaction. The first stage is maintained at 140~160℃ for 2~3 h, the second stage is maintained at 180~200℃ for 1~2 h, and the third stage is maintained at 200~210℃ for 0.5~1 h, under inert gas protection.

[0013] (5) Separate the solid residue from the mixture after acid hydrolysis in step (4) to obtain the liquid product, recycled polyether polyol;

[0014] The acid hydrolysate is a mixture of maleic acid and succinic anhydride.

[0015] In this invention, experiments revealed that, under the action of a catalyst, the activation energy for the cleavage of urethane bonds is 40–80 kJ / mol, and significant cleavage can occur at 140–160 °C; the activation energy for the cleavage of urea bonds is 62–83 kJ / mol, requiring 180–200 °C for substantial cleavage; while more stable chemical bonds such as crosslinking bonds require 200–210 °C for complete cleavage. Therefore, by sequentially passing through three temperature zones, the material achieves stepwise cleavage of soft and hard segments through gradient heating, improving bond-breaking efficiency and achieving a depolymerization rate ≥98%. Furthermore, the acid hydrolysis method, due to the selective bond-breaking mechanism of acid catalysis (preferential cleavage of CO bonds) and the amidation and sealing effect of organic acids (acylation reaction), blocks the formation of aromatic amines from the reaction pathway, thereby effectively reducing the content of aromatic amines in the product, which is beneficial for subsequent applications.

[0016] Preferably, in step (1), the diameter of the foam particles is less than 10 mm.

[0017] Preferably, in step (1), the removal of impurities includes removing large particulate impurities and foreign matter other than foam particles. Preferably, the large particulate impurities are removed by screening with a vibrating screen. Preferably, the foreign matter other than foam particles is separated by a near-infrared separator.

[0018] Preferably, in step (2), the dehydration is vacuum dehydration, the temperature is 80~100℃, and the vacuum degree is -0.09 MPa to -0.095 MPa.

[0019] Preferably, in step (3), the mass ratio of maleic acid to succinic anhydride is 1:1.3~1.6. By using anhydride and organic acid in combination, the anhydride preferentially opens the ring and breaks the bond, the organic acid is deeply degraded, the amount of acid used is reduced and the aromatic amine by-product is reduced, and the purity of the product is improved.

[0020] Preferably, in step (3), the catalyst is zinc acetate or sodium propionate.

[0021] Preferably, in step (3), the mass ratio of foam particles: acid hydrolysate: catalyst is 100: 30~40: 1~2.

[0022] Preferably, in step (4), the pressure of the inert gas protection is 0.1~0.2 MPa.

[0023] Preferably, in step (5), the solid residue is separated using a plate and frame filter press with a filtration temperature of 160~180℃ and a filtration pressure of 0.2~0.4 MPa.

[0024] Beneficial effects: Compared with the prior art, the present invention has the following advantages: (1) The acid hydrolysis method of the present invention recovers and regenerates polyether polyol from polyurethane semi-rigid foam waste, which improves the degradation rate and reduces the content of aromatic amines in the regenerated polyether polyol, which is beneficial to the later application; (2) The degradation rate of polyurethane semi-rigid foam waste by the acid hydrolysis method of the present invention is ≥98%; (3) No additional alcohol solvent is needed in the acid hydrolysis method of the present invention, which saves raw material costs. Detailed Implementation

[0025] The present invention will be further described below with reference to specific embodiments.

[0026] Example 1

[0027] The method for preparing recycled polyether polyols by acid hydrolysis of waste polyurethane semi-rigid foam of the present invention includes the following steps:

[0028] (1) Collect polyurethane semi-rigid foam waste (waste foam comes from Jiangsu Saisheng New Material Technology Co., Ltd.), clean and dry it, put the polyurethane semi-rigid foam waste into a twin-shaft shredder for crushing, remove large particle impurities by vibrating screen, and then separate the foam from foreign objects such as fabric and metal by near-infrared separator to obtain high-purity foam particles with a diameter of less than 10 mm.

[0029] (2) The sorted foam particles are put into a vacuum oven and dehydrated under vacuum at 80°C with a vacuum degree of -0.095MPa to remove residual moisture from the foam.

[0030] (3) Add foam particles, acid hydrolysate (mass ratio of maleic acid to succinic anhydride 1:1.3) and catalyst (zinc acetate) into the reactor. Stir and shear in the reactor to enhance mass transfer. The material ratio is foam particles: acid hydrolysate: catalyst = 100:30:1 by mass.

[0031] (4) The material undergoes a three-stage acid hydrolysis reaction with a temperature of 140℃ for 3 hours in the first stage, 180℃ for 2 hours in the second stage, and 200℃ for 1 hour in the third stage, with nitrogen gas under slight positive pressure protection (0.1 MPa).

[0032] (5) The mixture after acid hydrolysis (containing liquid product and a small amount of incompletely depolymerized solid residue) is fed into a plate and frame filter press while hot to separate the solid residue and obtain the liquid product, regenerated polyether polyol. The filtration temperature is 160℃ and the filtration pressure is 0.2 MPa.

[0033] Example 2

[0034] The method for preparing recycled polyether polyols by acid hydrolysis of waste polyurethane semi-rigid foam of the present invention includes the following steps:

[0035] (1) Collect polyurethane semi-rigid foam waste, clean and dry it, then put the polyurethane semi-rigid foam waste into a twin-shaft shredder for crushing, remove large particle impurities by screening with a vibrating screen, and then separate the foam from foreign objects such as fabric and metal by a near-infrared separator to obtain high-purity foam particles with a diameter of less than 10 mm.

[0036] (2) The sorted foam particles are put into a vacuum oven and dehydrated under vacuum at 85°C with a vacuum degree of -0.095MPa to remove residual moisture from the foam.

[0037] (3) Add foam particles, acid hydrolysate (mass ratio of maleic acid to succinic anhydride 1:1.4) and catalyst (sodium propionate) into the reactor. Stir and shear in the reactor to enhance mass transfer. The material ratio is foam particles: acid hydrolysate: catalyst = 100:35:1.5 by mass.

[0038] (4) The material undergoes a three-stage acid hydrolysis reaction with a temperature of 145℃ for 2.5 h in the first stage, 185℃ for 2 h in the second stage, and 205℃ for 1 h in the third stage, with nitrogen gas under slight positive pressure protection (0.15 MPa).

[0039] (5) The mixture after acid hydrolysis (containing liquid product and a small amount of incompletely depolymerized solid residue) is fed into a plate and frame filter press while hot to separate the solid residue and obtain the liquid product, regenerated polyether polyol. The filtration temperature is 165℃ and the filtration pressure is 0.3 MPa.

[0040] Example 3

[0041] The method for preparing recycled polyether polyols by acid hydrolysis of waste polyurethane semi-rigid foam of the present invention includes the following steps:

[0042] (1) Collect polyurethane semi-rigid foam waste, clean and dry it, then put the polyurethane semi-rigid foam waste into a twin-shaft shredder for crushing, remove large particle impurities by screening with a vibrating screen, and then separate the foam from foreign objects such as fabric and metal by a near-infrared separator to obtain high-purity foam particles with a diameter of less than 10 mm.

[0043] (2) The sorted foam particles are put into a vacuum oven and dehydrated under vacuum at 90°C with a vacuum degree of -0.09 MPa to remove residual moisture from the foam.

[0044] (3) Add foam particles, acid hydrolysate (mass ratio of maleic acid and succinic anhydride 1:1.5) and catalyst (zinc acetate) into the reactor. Stir and shear in the reactor to enhance mass transfer. The material ratio is foam particles: acid hydrolysate: catalyst = 100:35:2 by mass.

[0045] (4) The material undergoes a three-stage acid hydrolysis reaction with a temperature of 150℃ for 2.5 h in the first stage, 190℃ for 1.5 h in the second stage, and 210℃ for 0.5 h in the third stage, with nitrogen gas under slight positive pressure protection (0.2 MPa).

[0046] (5) The mixture after acid hydrolysis (containing liquid product and a small amount of incompletely depolymerized solid residue) is fed into a plate and frame filter press while hot to separate the solid residue and obtain the liquid product, regenerated polyether polyol. The filtration temperature is 170℃ and the filtration pressure is 0.3 MPa.

[0047] Example 4

[0048] The method for preparing recycled polyether polyols by acid hydrolysis of waste polyurethane semi-rigid foam of the present invention includes the following steps:

[0049] (1) Collect polyurethane semi-rigid foam waste, clean and dry it, then put the polyurethane semi-rigid foam waste into a twin-shaft shredder for crushing, remove large particle impurities by screening with a vibrating screen, and then separate the foam from foreign objects such as fabric and metal by a near-infrared separator to obtain high-purity foam particles with a diameter of less than 10 mm.

[0050] (2) The sorted foam particles are put into a vacuum oven and dehydrated under vacuum at 100°C with a vacuum degree of -0.09MPa to remove residual moisture from the foam.

[0051] (3) Add foam particles, acid hydrolysate (mass ratio of maleic acid and succinic anhydride 1:1.6) and catalyst (sodium propionate) into the reactor. Stir and shear in the reactor to enhance mass transfer. The material ratio is foam particles: acid hydrolysate: catalyst = 100:40:2 by mass.

[0052] (4) The material undergoes a three-stage acid hydrolysis reaction with a temperature of 160℃ for 2 hours in the first stage, 200℃ for 1 hour in the second stage, and 210℃ for 0.5 hours in the third stage, with nitrogen gas under slight positive pressure protection (0.2 MPa).

[0053] (5) The mixture after acid hydrolysis (containing liquid product and a small amount of incompletely depolymerized solid residue) is fed into a plate and frame filter press while hot to separate the solid residue and obtain the liquid product, regenerated polyether polyol. The filtration temperature is 180℃ and the filtration pressure is 0.2MPa.

[0054] Example 5

[0055] The method for preparing recycled polyether polyols by acid hydrolysis of waste polyurethane semi-rigid foam of the present invention includes the following steps:

[0056] (1) Collect polyurethane semi-rigid foam waste, clean and dry it, then put the polyurethane semi-rigid foam waste into a twin-shaft shredder for crushing, remove large particle impurities by screening with a vibrating screen, and then separate the foam from foreign objects such as fabric and metal by a near-infrared separator to obtain high-purity foam particles with a diameter of less than 10 mm.

[0057] (2) The sorted foam particles are put into a vacuum oven and dehydrated under vacuum at 100°C with a vacuum degree of -0.09MPa to remove residual moisture from the foam.

[0058] (3) Add foam particles, acid hydrolysate (mass ratio of maleic acid and succinic anhydride 1:1.5) and catalyst (zinc acetate) into the reactor. Stir and shear in the reactor to enhance mass transfer. The material ratio is foam particles: acid hydrolysate: catalyst = 100:40:2 by mass.

[0059] (4) The material undergoes a three-stage acid hydrolysis reaction with a temperature of 160℃ for 2 hours in the first stage, 195℃ for 1.5 hours in the second stage, and 205℃ for 1 hour in the third stage, with nitrogen gas under slight positive pressure protection (0.1 MPa).

[0060] (5) The mixture after acid hydrolysis (containing liquid product and a small amount of incompletely depolymerized solid residue) is fed into a plate and frame filter press while hot to separate the solid residue and obtain the liquid product, regenerated polyether polyol. The filtration temperature is 180℃ and the filtration pressure is 0.2 MPa.

[0061] Comparative Example 1

[0062] Based on Example 1, in step (4), the three-stage heating is changed to 140℃ and maintained for 6 hours, while the other conditions remain unchanged.

[0063] Comparative Example 2

[0064] Based on Example 2, in step (4), the three-stage heating is changed to 185℃ and maintained for 5.5 h, while the other conditions remain unchanged.

[0065] Comparative Example 3

[0066] Based on Example 3, in step (4), the three-stage heating is changed to 210℃ and maintained for 4.5 h, while the other conditions remain unchanged.

[0067] Comparative Example 4

[0068] Based on Example 4, in step (3), maleic acid and succinic anhydride are replaced with the same mass of maleic acid, while the other conditions remain unchanged.

[0069] Comparative Example 5

[0070] Based on Example 4, in step (3), maleic acid and succinic anhydride of the same mass are replaced with succinic anhydride, while the other conditions remain unchanged.

[0071] Comparative Example 6

[0072] According to patent 202411218325.7, a method for recovering low-odor recycled polyether polyols from polyurethane automotive headliner semi-rigid foam is disclosed. The recycled polyether polyols are prepared by alcoholysis, and the steps are as follows:

[0073] (1) Collect and dispose of waste polyurethane automotive roof semi-rigid foam plastic;

[0074] (2) The polyurethane automotive roof semi-rigid foam is crushed into particles with a diameter of less than 10 mm by a pulverizer and impurities are screened out.

[0075] (3) Add 400 g of diethylene glycol and 4 g of triethylenediamine to a 1000 ml reaction flask, and place it under nitrogen three times;

[0076] (4) Heat to 170°C and add 400 g of polyurethane semi-rigid foam particles in batches, with the alcoholysis agent and semi-rigid foam particles in a mass ratio of 1:1.

[0077] (5) After all the polyurethane semi-rigid foam particles are dissolved, the reaction is carried out at a constant temperature for 4 hours. Small molecules are removed by vacuum distillation, and the product is cooled and filtered to obtain recycled polyether polyol.

[0078] Performance testing

[0079] 1. The properties of the recycled polyether polyols prepared in Examples 1-5 and Comparative Examples 1-6 were tested using the following methods:

[0080] The acid value was determined using the industry standard method for determining the acid value of polyether polyols, as detailed below:

[0081] (1) Weigh a certain amount of sample (0.1~1 g, accurate to 0.0001 g) into a 150 mL conical flask;

[0082] (2) Add 25 mL of anhydrous ethanol solution, shake well, and dissolve the sample completely;

[0083] (3) Add 10 drops of phenolphthalein indicator;

[0084] (4) Titrate with 0.01 mol / L sodium hydroxide standard titration solution until the pink color remains unchanged for 30 seconds as the endpoint, and record the volume V1 (mL) of sodium hydroxide standard titration solution consumed.

[0085] (5) Perform a blank test under the same conditions and record the volume V0 (mL) of sodium hydroxide standard titration solution consumed; the acid value X of the sample is calculated according to the following formula:

[0086] ;

[0087] In the formula:

[0088] V1—The volume of sodium hydroxide standard titration solution consumed during the titration of the sample, in milliliters (mL).

[0089] V0—The volume of sodium hydroxide standard titration solution consumed during blank titration, in milliliters (mL);

[0090] C – Concentration of the sodium hydroxide standard titration solution, in moles per liter (mol / L).

[0091] m — Sample mass, in grams (g).

[0092] The test results show that the acid value is the average of two parallel samples, accurate to 0.001 mg / g. The allowable error is 0.05 mg / g for acid values ​​≤1 and 0.1 mg / g for acid values ​​>1.

[0093] Hydroxyl value: GB / T 12008.3-2009.

[0094] Viscosity: GB / T 12008.7-2010.

[0095] Aromatic amines: GB / T17592-2011.

[0096] Foam depolymerization rate: Depolymerization rate (%) = (1 - residual amount of undepolymerized material / initial effective amount of polyurethane waste foam) × 100%.

[0097] Note: "Undepolymerized material" refers to polyurethane solids that retain their original cross-linked structure after the depolymerization reaction; "Initial effective amount" should deduct the mass of impurities (such as fillers and metal fragments) in the waste foam.

[0098] The results are shown in Table 1.

[0099] Table 1. Performance indicators of the recycled polyether polyols prepared in Examples 1-5 and Comparative Examples 1-6

[0100]

[0101] As can be seen from the data in Table 1, the content of aromatic amines in the recycled polyether polyols prepared by acid hydrolysis of semi-rigid foam in Examples 1-5 was reduced by more than 98%. The acid hydrolysis method can significantly reduce the content of aromatic amines in the product through selective catalysis and amidation reaction of organic acids. The yield is more than 7% higher than that of the alcohol hydrolysis method. This shows that the depolymerization rate can be improved by acid hydrolysis and three-stage heating process, and good technical results have been achieved.

[0102] The recycled polyether polyol in Comparative Example 1 had higher viscosity and acid value, and significantly lower hydroxyl value and yield. This was because the polyurethane semi-rigid foam did not completely depolymerize when a single fixed temperature of 140°C was used.

[0103] The recycled polyether polyol in Comparative Example 2 had higher viscosity and acid value, and significantly lower hydroxyl value and yield. This is because the polyurethane semi-rigid foam was not completely depolymerized when a single fixed temperature of 185℃ was used.

[0104] The viscosity and acid value of the recycled polyether polyol in Comparative Example 3 were relatively high, while the hydroxyl value and yield were still lower than those in Examples 1-5. This is because the polyurethane semi-rigid foam was not completely depolymerized when a single fixed temperature of 210°C was used.

[0105] The viscosity and acid value of the recycled polyether polyols in Comparative Examples 4 and 5 were still relatively high because the polyurethane semi-rigid foam was not completely depolymerized when a single acid hydrolysate was used.

[0106] The aromatic amine content of the recycled polyether polyol in Comparative Example 6 was 15,100 ppm. This is because the preparation of recycled polyether polyol by alcoholysis will produce a large amount of aromatic amines, which is not conducive to the application and promotion of recycled polyether polyol. In addition, the yield was significantly lower than that of Examples 1-5, indicating that the depolymerization of polyurethane semi-rigid foam waste was incomplete.

Claims

1. A method for preparing a regenerated polyether polyol from polyurethane semi-rigid foam waste foam by acidolysis degradation, characterized in that, The method comprises the following steps: (1) cleaning and drying the polyurethane semi-rigid foam waste, crushing, removing impurities, and obtaining foam particles; (2) dehydrating the foam particles to remove residual moisture; (3) putting the foam particles, acidolysis agent, and catalyst into a reaction kettle, and strengthening mass transfer through in-kettle stirring and shearing; (4) subjecting the material to three-stage temperature-raising acidolysis reaction, keeping the first stage at 140-160 DEG C for 2-3 h, the second stage at 180-200 DEG C for 1-2 h, and the third stage at 200-210 DEG C for 0.5-1 h, and protecting with inert gas; (5) separating the solid residue from the mixture after the acidolysis reaction in step (4) to obtain liquid product, regenerated polyether polyol; wherein the acidolysis agent is a mixture of maleic acid and succinic anhydride; the mass ratio of maleic acid to succinic anhydride is 1:1.3-1.6; in step (3), the catalyst is zinc acetate or sodium propionate; the mass ratio of the foam particles: acidolysis agent: catalyst is 100:30-40:1-2.

2. The method for preparing a regenerated polyether polyol by degrading a semi-rigid polyurethane foam waste foam by acidolysis according to claim 1, characterized by, in step (2), the dehydration is vacuum dehydration, the temperature is 80-100 DEG C, and the vacuum degree is -0.09 MPa to -0.095 MPa.

3. The method of claim 1, wherein the acid hydrolysis method of degrading polyurethane semi-rigid foam waste foam to prepare a regenerated polyether polyol is characterized by, in step (5), the separation of the solid residue uses a plate-and-frame filter press, the filtration temperature is 160-180 DEG C, and the filtration pressure is 0.2-0.4 MPa.

4. The method of claim 1, wherein the acid hydrolysis method of degrading polyurethane semi-rigid foam waste foam to prepare a regenerated polyether polyol is characterized by, in step (1), the diameter of the foam particles is less than 10 mm.

5. The method of claim 1, wherein the acid hydrolysis method of degrading polyurethane semi-rigid foam waste foam to prepare a regenerated polyether polyol is characterized by, in step (1), the removal of impurities includes removing large-particle impurities and foreign matters other than the foam particles.

6. The method of claim 5, wherein the acid hydrolysis method of degrading polyurethane semi-rigid foam waste foam to prepare a regenerated polyether polyol is characterized by, the large-particle impurities are removed by a vibrating screen.

7. The method of claim 5, wherein the acid hydrolysis method of degrading polyurethane semi-rigid foam waste foam to prepare a regenerated polyether polyol is characterized by, the foreign matters other than the foam particles are separated by a near-infrared sorting machine.

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