Process and plant for removing dyes from waste textiles

Abstract

In a process for removing dyes from a textile material, comprising or consisting of polyester fibers, or comprising or consisting of cotton fibers, a batch of said textile material is reduced to clippings having small size, treated with a solvent under stirring in an extraction chamber and centrifugated to remove the solvent, the solution comprising solvent and extracted material is used as a solvent to extract dye from another batch of textile material.

1 . A process for removing dyes from a textile material, said textile material including a dye and at least 50% by weight of polyester fibers, or said textile material comprising a dye and including at least 80% by weight of cellulosic fibers, said process comprising the following steps:
 a) providing said textile material and a solvent suitable to remove said dye from said textile in an extraction chamber to provide a mixture of textile and solvent;   b) extracting said textile material with said solvent to provide a solution comprising said solvent and extracted material, said extracted material including at least said dye, wherein said extracting includes stirring said textile material and said solvent within said extraction chamber during at least part of said extraction step;   c) removing said solution of said solvent and extracted material from said textile material,   said process further comprising the steps of   a1) reducing said textile material into pieces having maximum dimension of 5 cm prior to said step a) of providing;   b1) after said step b), feeding said solution and said pieces of textile material to a centrifuge to perform said step c); and   c1) feeding said solvent or a further solvent to said textile pieces after step c) to wash said textile and remove dye from said textile;   wherein a bath ratio of textile (kg) to solvent (liters) is within the range of 1:3 (kg/l) to 1:20 (kg/l) and wherein at least in said steps a), b) and c1) the temperature of said solvent is in the range of 80° C. to 140° C.   
     
     
         2 . A process for removing dyes from a textile material, wherein said textile material includes at least 50% by weight of polyester, or wherein said textile material includes at least 80% by weight of cellulosic fibers, said process comprising the steps of:
 a) providing a batch of said textile material in an extraction chamber;   b) extracting said batch of said textile material with a solvent to provide a solution comprising said solvent and extracted material, said extracted material including at least a dye, wherein said extracting includes stirring said textile material and said solvent within said extraction chamber during at least part of said extracting step; and   c) removing said solution of solvent and extracted material from said textile material;   
       wherein said solution comprising solvent and extracted material of said step b) and/or said step c) is used as a solvent to extract dye from another batch of textile material, and 
       wherein said steps b) and c) are repeated for a preset number of cycles or until an amount of extracted material in said solution comprising solvent and extracted material reaches a concentration whereby further dye extraction is impaired. 
     
     
         3 . The process according to  claim 1 , wherein said extracting includes rotating said extraction chamber containing said solvent and textile material around its horizontal axis, or wherein said stirring includes rotating stirring means within said extraction chamber containing said solvent and textile material, whereby said textile material is stirred within said extraction chamber during the entire extracting step. 
     
     
         4 . The process according to  claim 1 , wherein said step c) includes separating said solution comprising said solvent and said extracted material from said textile by centrifuging and is carried out in said centrifuge said centrifuge selected from the group consisting of a vertical peeler type bottom discharge centrifuge, a horizontal peeler type centrifuge, a horizontal pusher type centrifuge, and a decanter type centrifuge. 
     
     
         5 . The process according to  claim 4 , wherein, after said step c) clean solvent is fed to the textile material present in said centrifuge and a hot solvent washing step of said textile material is carried out in said centrifuge, wherein said centrifuge is rotated at a speed lower than a centrifugation speed. 
     
     
         6 . The process according to  claim 5 , wherein after said hot solvent washing step said textile material is washed with water to remove solvent before a drying step. 
     
     
         7 . The process according to  claim 1 , wherein said textile material is reduced by mechanical treatment into pieces, at least 90% of said pieces having size in a range of 1 mm to 50 mm before said step a) of providing. 
     
     
         8 . A process according to  claim 1 , wherein said textile material, after said extraction step b), is fed from said extraction chamber to a first centrifuge for said removal step c), and further comprising feeding said textile material from said first centrifuge to a further extraction chamber for a further extraction step b′) and from said further extraction chamber to a second centrifuge for a further removal step c′), whereby 
       said extraction step b) and said further extraction step b′) and said removal step c) and said further removal step c′) are carried out in two different extraction chambers and two different centrifuges, respectively, wherein solvent removed from the further extraction chamber and/or said second centrifuge is fed to said extraction chamber. 
     
     
         9 . A process according to  claim 1 , wherein steps b) and c) are repeated more than twice in more than two said extraction chambers and centrifuges, and wherein the solvent removed from any said extraction chamber except a first extraction chamber of said more than two said extraction chambers, is fed to the previous extraction chamber. 
     
     
         10 . The process according to  claim 1 , wherein said solvent used in said step b) is in the form of solution comprising said solvent and extracted material including at least a dye. 
     
     
         11 . The process according to  claim 1 , wherein said solvent comprises Dimethylformamide (DMF) or Dimethylacetamide (DMAC), or a mixture of DMF or DMAC with alkali water, or mixtures thereof and the temperature of said solution comprising solvent and extracted material in said extraction chamber is in a range of 80° C. to 140° C. 
     
     
         12 . The process according to  claim 1 , wherein a bath ratio of said textile material/solvent is in a range from ⅓ to 1/20 kg/liter. 
     
     
         13 . The process according to  claim 1 , wherein said step c) is carried out in said centrifuge at a g-force in a range of from 250 to 5000 for a time in a range of 1 to 5 minutes. 
     
     
         14 . The process according to  claim 1 , wherein said textile material comprises polyester fibers and further comprises at least a polyurethane material; said textile material comprises at least 90% by weight of said polyester fibers and at most 10% by weight of elastane fibers, wherein at least part of said polyester fibers is dyed with at least one disperse dye, wherein said solvent is DMF, wherein the temperature of said solvent or said solution comprising solvent and extracted material in said extraction chamber is in a range of from 85° C. to 105° C., wherein prior to said step a) of providing said textile material is reduced by mechanical treatment into pieces, at least 90% of said pieces having size from 2.0 mm to 2.5 mm; 
       or 
       wherein said textile comprises polyester fibers and further comprises at least a cellulosic material, said textile material comprises at least 50%, by weight of polyester fibers and at most 50% by weight of cotton fibers, wherein at least part of said polyester fibers is dyed with at least one disperse dye and wherein at least part of said cotton fibers is dyed with at least a dye selected from vat dyes, reactive dyes, pigments, direct dyes and sulfur dyes, wherein said solvent is a mixture of DMF and water comprising at least one base or a mixture of DMF and water comprising at least one base and at least one reducing agent, wherein the temperature of said solvent or said solution comprising solvent and extracted material in said extraction chamber is in the range of from 85° C. to 110° C., wherein prior to said step a) of providing said textile material said textile material is reduced by mechanical treatment into pieces, at least 90% of said pieces having size from 2.0 mm to 50 mm. 
     
     
         15 . The process according to  claim 1 , wherein said textile material comprises polyester fibers and further comprises elastane and at least a cellulosic material comprising cotton-fibers, wherein said textile material comprises at least 50% by weight of said polyester fibers and at most 50% by weight of said cotton fibers and said elastane fibers, 
       wherein at least part of said polyester fibers is dyed with at least one disperse dye and wherein at least part of said cotton fibers is dyed with at least a dye selected from vat dyes, reactive dyes, pigments, direct dyes and sulfur dyes, 
       wherein said solvent is a mixture of DMF and water comprising a base or a mixture of DMF and water comprising a base and at least one reducing agent, 
       wherein the temperature of said solvent or said solution comprising solvent and extracted material in said extraction chamber and optionally in said step c1) is in a range of 95° C. to 105° C., 
       wherein prior to said step of providing said textile material, said textile material is reduced by mechanical treatment into pieces, at least 90% of said pieces having size from 2.0 mm to 50 mm; 
       or 
       wherein said textile material comprises at least 90% by weight of cotton fibers and at most 10% of elastane fibers, 
       wherein at least part of said cotton fibers is dyed with at least a dye selected from vat dyes, reactive dyes, pigments, direct dyes and sulfur dyes, 
       wherein said solvent is a mixture of DMF and water comprising a base or a mixture of DMF and water comprising a base and at least one reducing agent, 
       wherein the temperature of said solvent or said solution comprising solvent and extracted material in said extraction chamber is in the range of from 95° C. to 105° C., 
       wherein prior to said step of providing said textile material to said extraction chamber, said textile material is reduced by mechanical treatment into pieces, at least 90% of said pieces having size above 20 mm. 
     
     
         16 . The process according to  claim 1 , wherein said textile material comprises cotton fibers, 
       wherein at least part of said cotton fibers is dyed with at least a dye selected from vat dyes, reactive dyes, pigments, direct dyes and sulfur dyes, 
       wherein said solvent is a mixture of DMF and water comprising at least a base or a mixture of DMF and water comprising a base and at least one reducing agent, 
       wherein the temperature of said solvent or said solution comprising solvent and extracted material in said extraction chamber is in a range of from 85° C. to 110° C. 
     
     
         17 . The process according to  claim 1 , wherein said solution obtained in step b) and/or c) is used as the solvent to extract dye from another batch of textile material, and wherein said steps b) and c) are repeated using said solution as said solvent up to 20 times. 
     
     
         18 . An apparatus for removing dyes from a textile comprising 
       at least one extraction chamber configured to treat a textile material with a solvent, at least one centrifuge for separating a solution comprising said solvent and extracted material from said textile material, 
       at least one fresh solvent storage tank and at least one distillation device, 
       means to reduce the size of said textile material by mechanical treatment into textile pieces, 
       means to feed said textile pieces and said solvent to said at least one extraction chamber, duct means for feeding a mixture of solvent and textile pieces from said at least one extraction chamber to said at least one centrifuge and 
       means to feed said solvent to said at least one centrifuge to carry out a washing step, wherein 
       said at least one extraction chamber and said duct means for feeding said mixture to said at least one centrifuge are provided with insulation that thermally insulates them. 
     
     
         19 . The apparatus according to  claim 18 , wherein said at least one fresh solvent storage tank is configured to feed said fresh solvent to said at least one extraction chamber, and configured to receive said solvent from said distillation device, and wherein said distillation device is configured to receive said solution comprising said solvent and extracted material from said at least one extraction chamber and/or from said at least one centrifuge, to separate said extracted material from said solvent; said apparatus comprising at least one storage tank, configured to receive said textile material from said at least one extraction chamber and to feed said textile material to said at least one centrifuge. 
     
     
         20 . The apparatus according to  claim 18 , wherein said at least one centrifuge has a lateral wall to which said textile pieces adhere after solvent removal by centrifugation, and further includes a scraper to remove the textile pieces from said lateral wall of the centrifuge after centrifugation. 
     
     
         21 . The apparatus according to  claim 18 , wherein said apparatus comprises a plurality of extraction chambers and a plurality of centrifuges, wherein said extraction chambers and said centrifuges are arranged in a series, and means for feeding said textile material along said series of extraction chambers and centrifuges to provide a flow of textiles, 
       wherein at least one said centrifuge is connected, directly or indirectly, with an extraction chamber of said plurality of extraction chambers upstream with respect to the flow of textiles and is connected to another extraction chamber of said plurality of extraction chambers downstream with respect to said flow of textiles, each said extraction chamber being connected to a previous extraction chamber of said plurality of extraction chambers with solvent feeding means, 
       said solvent feeding means being configured to feed said solution comprising said solvent and extracted material exiting from each said extraction chamber to said previous extraction chamber and 
       wherein only the last extraction chamber of said series is connected to a first fresh solvent storage tank of said at least one fresh solvent storage tank, said fresh solvent storage tank being configured to feed said solvent to said last extraction chamber only. 
     
     
         22 . The process according to  claim 2 , wherein said extracting includes rotating said extraction chamber containing said solvent and textile material around its horizontal axis, or wherein said stirring includes rotating stirring means within said extraction chamber containing said solvent and textile material, whereby said textile material is stirred within said extraction chamber during the entire extracting step. 
     
     
         23 . The process according to  claim 2 , wherein said step c) includes separating said solution of said solvent and said extracted material from said textile by centrifuging and is carried out in a centrifuge selected from the group consisting of a vertical peeler type bottom discharge centrifuge, a horizontal peeler type centrifuge, a horizontal pusher type centrifuge, and a decanter type centrifuge. 
     
     
         24 . The process according to  claim 23 , wherein, after said step c) clean solvent is fed to the textile material present in said centrifuge and a hot solvent washing step of said textile material is carried out in said centrifuge, wherein said centrifuge is rotated at a speed lower than a centrifugation speed.