Process for treating textile waste
The present disclosure relates to a process for treating mixed textile waste comprising cotton, polyester, nylon, and spandex. The process is based on selective solubilization of different component polymers followed by controlled depolymerization, enabling efficient recovery. The process of the present disclosure is simple, cost-effective, and environmentally sustainable, providing a practical solution to the growing problem of mixed textile waste pollution.
1 . A process for treating a textile waste, said process comprising the following steps:
a) mixing a textile waste in a first fluid medium under stirring at a temperature in the range of 40° C. to 120° C. for a time period in the range of 30 minutes to 240 minutes to obtain a first mixture comprising a first filtrate and first solids containing undissolved textile waste followed by separating to obtain a separated first filtrate and a separated first solids; and subjecting said separated first filtrate to a predetermined method to obtain nylon;
b) optionally mixing said separated first solids in a second fluid medium under stirring at a temperature in the range of 40° C. to 120° C. for a time period in the range of 30 minutes to 240 minutes to obtain a second mixture comprising a second filtrate and second solids containing undissolved textile waste followed by separating to obtain a separated second filtrate and a separated second solids; and subjecting said separated second filtrate to a predetermined method to obtain spandex;
c) depolymerizing said separated first solids or said separated second solids in a third fluid medium by using a nucleophilic agent at a temperature in the range of 170° C. to 200° C. for a time period in the range of 20 minutes to 150 minutes to obtain third mixture comprising a third filtrate and third solids containing undissolved textile waste followed by separating to obtain a separated third filtrate and a separated third solids; and subjecting said separated third filtrate to a predetermined method to obtain Bis(2-hydroxyethyl) terephthalate; and
d) optionally treating said separated third solids in an aqueous acid solution at a temperature in the range of 30° C. to 80° C. for a time period in the range of 15 minutes to 240 minutes to obtain microcrystalline cellulose,
wherein said first solids and said second solids are independently decolorized prior to or after depolymerization.
2 . The process as claimed in claim 1 , wherein said first solids, said second solids and said third solids are independently dried before subjecting to next step.
3 . The process as claimed in claim 1 , wherein
a. said decolorization of said first solids prior to depolymerization is carried out by immersing said first solids in a decolorizing agent at a temperature in the range of 100° C. to 160° C. for a time period in the range of 1 hour to 6 hours followed by separating to obtain a decolorized product; and
b. said decolorization of said second solids after depolymerization is carried out by immersing said second solids in a decolorizing agent at a temperature in the range of 100° C. to 160° C. for a time period in the range of 1 hour to 6 hours followed by separating to obtain a decolorized product.
4 . The process as claimed in claim 1 , wherein said predetermined method is at least one selected from the group consisting of cooling, filtration, rotary evaporation, drying, distillation, centrifugation, skimming, settling, by using agitated thin film dryer (ATFD), by using short path distillation unit (SPDU), and by adding an anti-solvent to obtain solids.
5 . The process as claimed in claim 1 , wherein said first fluid medium, said second fluid medium, said third fluid medium and said nucleophilic agent is recovered in each respective step.
6 . The process as claimed in claim 1 , wherein
said first fluid medium is at least one selected from the group consisting of formic acid (FA), propanediol (PDO), dimethyl sulfoxide (DMSO), hydrogen peroxide, acetic acid, formic acid, chloro acetic acid, acrylic acid, benzoic acid, propionic acid, butyric acid, methacrylic acid, and isobutyric acid;
said second fluid medium is at least one selected from the group consisting of tetrahydrofuran (THF), N,N-dimethylformamide (DMF), N,N-dimethylacetamide (DMAc), dimethyl sulfoxide (DMSO) and N-methylpyrrolidone (NMP);
said third fluid medium is at least one selected from the group consisting of dimethylformamide, ethylamine, dimethylamine, aniline, pyridine and imidazole-based solvents; and
said nucleophilic agent is at least one selected from ethylene glycol and water.
7 . The process as claimed in claim 1 , wherein said aqueous acid solution is at least one selected from the group consisting of aqueous acetic acid, aqueous citric acid, aqueous lactic acid, aqueous formic acid, aqueous oxalic acid, aqueous tartaric acid, aqueous sulphuric acid, and aqueous hydrochloric acid.
8 . The process as claimed in claim 7 , wherein the concentration of said aqueous acid solution is in the range of 5 mass % to 70 mass %.
9 . The process as claimed in claim 3 , wherein said decolorizing agent is at least one selected form the group consisting of aqueous sodium hydroxide, aqueous sodium dithionite, aqueous sodium hydrosulfide, aqueous sodium hydrogen sulphate, aqueous potassium hydroxide, aqueous calcium hydroxide, aqueous ammonia, aqueous sodium sulfite, aqueous sodium carbonate, 1-methylimidazole, aqueous potassium hydrogen phthalate, aqueous calcium hypochlorite, aqueous sodium dihydrogen phosphate, aqueous potassium persulphate, aqueous ammonium sulphate, aqueous sodium thiosulphate, and aqueous sodium lauryl sulphate.
10 . The process as claimed in claim 1 , wherein said depolymerization is done prior to the recovery of nylon, spandex and microcrystalline cellulose.
11 . The process as claimed in claim 3 , wherein said decolorization after depolymerization results in a slightly colored BHET which is further decolorized by dissolving said slightly colored BHET in water and heating to a temperature in the range of 60° C. to 80° C. followed by passing through an activated charcoal bed and subjecting to recrystallization to obtain white BHET crystals.