Patent Application
20210381166
The present disclosure relates to methods and systems for processing cellulose-containing materials such as textiles, including textile garments (used and un-used) and scraps, biomass, wood pulp, and the like and for isolating cellulose molecules for use in a variety of downstream applications. In particular applications, the present disclosure relates to methods and systems for treatment of cellulose-containing materials to isolate cellulose molecules and to produce regenerated polymers, fibers, fabrics, the like, or combinations or multiples thereof from the isolated cellulose molecules. Recycling and regeneration of textiles is described in detail and provides significant social, environmental and economic benefits.
Global sales of apparel are estimated to have exceeded $1 trillion in 2011, and some estimate that over 85% of the garments purchased are discarded in a landfill within one year. This cycle wastes valuable materials and the considerable resources required to produce them, and it exacerbates waste disposal issues.
Cotton clothing is estimated to represent about 35% of the total apparel market. Cotton fibers are composed of cellulose, a naturally occurring polymer found in all plants, wood, and natural fibers. Cotton fibers are harvested from cotton plants and consist of long, interwoven chains of cellulose polymers. These fibers are spun into thread or yarn, dyed, and ultimately woven, knit, and assembled into textiles. Natural fibers, including cotton, have a generally high and variable raw material cost due, in part, to natural disasters and climate unpredictability, regional socio-economic and political instability, human rights issues, and resource requirements.
Growing and harvesting cotton fibers is resource-intensive. It is estimated, for example, that over 700 gallons of water are required to grow enough cotton to produce one pound of fiber. Growing cotton frequently involves heavy pesticide use, significant land resources, and produces significant levels of heat-trapping gases. Considerably more land is required for growing organic cotton than for growing “conventional” cotton. With demand for agricultural land use increasing and fresh water supplies decreasing, the cost of producing natural cotton is increasing. At some point, the current scale of cotton production may become unprofitable and unsustainable.
Cotton has been recycled to provide raw material for paper pulping plants. Re-processing methods that convert used cotton into rags, mattress ticking, seat stuffing, insulating materials, and the like are also available, but these processing methods have been adopted in limited applications because the value of the converted material is relatively low.
In contrast to cotton, which is a natural fiber, rayon fibers are manufactured from wood pulp using the viscose process. In this process, purified cellulose is solubilized and then converted or regenerated into cellulose fiber. This process requires steeping, pressing, shredding, aging, xanthation, dissolving, ripening, filtering, degasing, spinning, drawing and washing. This process is time sensitive, requires multiple chemical treatments, produces lignin and other waste from unusable wood material and is, at best, a semi-continuous manufacturing process.
The present disclosure is directed to providing systems and methods for processing cellulose-containing feedstocks, such as recycled fabric, fabric scraps and other cellulose containing materials, many of which would otherwise be wasted or used to produce low value products, to isolate their constituent cellulosic polymeric structures. The polymeric cellulosic structures are then used in industrial processes such as fabric production. Implementation of the disclosed processing schemes with a variety of garment/fabric feedstock materials may produce regenerated fibers and textile products having improved, customizable, or both properties using processes having low environmental impacts.
Methods and systems of the present disclosure relate to processing of cellulose-containing materials including, for example, postconsumer cellulosic waste, cellulose-containing textiles and garments (e.g., recycled or used or waste textiles and garments), virgin cotton, wood pulp, biomass, and the like, to produce isolated cellulose polymers for use in downstream processing applications. In some embodiments, cellulose-containing materials used as raw feed material for processing comprise discarded garments, scrap fabric materials, or both, and processing produces isolated cellulose polymers that can be further processed and extruded to provide regenerated fibers having improved, customizable, or both properties for use in textile industries or for other purposes.
A multi-stage process is described, incorporating one or more pretreatment stages providing removal of contaminants and preparation of cellulosic materials, followed by pulping, molecular separation of cellulose polymers, or both. In some embodiments, the pretreatment and pulping processes may be carried out in a continuous, semi-continuous or batch system. In some embodiments, the pretreatment and pulping processes may be carried out in one or more closed reaction vessel(s), and processing reagents may be recovered and re-used or processed for other uses.
Numerous pretreatment processing stages are described and may be used alone or in combination to remove non-cellulosic constituents of the feed and prepare cellulosic components for pulping and dissolution. Pretreatment is followed by at least one cellulose pulping or dissolution stage that promotes the molecular separation and isolation of cellulose polymers, such as by disrupting intermolecular hydrogen bonds. In some embodiments, cellulosic polymers isolated during the pulping stage, the dissolution stage, or both, are substantially thermoplastic and are moldable when energy (e.g., heat below the char point) is introduced to the system.
Isolated cellulose polymers produced using the processes described herein may be used in a variety of downstream applications, as described in more detail below and, in some embodiments, may be extruded to form regenerated cellulosic fibers. In some aspects, isolated cellulose polymers may be re-generated to provide longer chain polymers and fibers (or polymers and fibers having other desirable characteristics different from the characteristics of the cellulose-containing feedstock) that are useful in various industrial processes, including textile production. In addition to employing a raw feedstock materials that are typically discarded (wasted, at a cost), processing steps having generally low environmental impacts are preferred.
In one aspect, methods and systems of the present disclosure provide a closed-loop garment recycling process that transforms reclaimed garments and textiles into high-quality, bio-based fiber for use in creating new textiles, apparel, and other fiber-based products. Used and waste garment collection, sorting, transport and processing may all be involved as part of a closed loop process. Retail enterprises (and others) may serve as collection stations and may offer incentives, rewards, or the like for donations. Further garment processing may take place at the donation site or at one or more remote sites. Cotton, cotton-like regenerated fabrics, rayon and other fibers may be produced using the reclaimed garments and textiles.
It will be understood that the appended drawings present many alternatives and various specific embodiments, and that there are many variations and combinations of processing steps, as well as additional aspects of systems and methods of the present invention. Specific process design features may be modified and used in different combinations, for example, for use in various intended applications and environments.
In one aspect, systems and methods disclosed herein process cellulose-containing materials to produce isolated cellulosic polymers suitable for use in downstream processing and a variety of downstream applications and production pathways. Cellulose-containing materials that are useful as raw materials for this process include a wide range of materials, such as cellulose-containing postconsumer waste, biomass materials and pulp (e.g., wood pulp), cotton and cotton-containing materials, and the like, including unworn or worn and discarded cotton and cotton-containing apparel, as well as scrap cotton fiber and fabric. The cellulose-containing feedstock undergoes at least one pretreatment stage (and optionally multiple pretreatment stages) and at least one pulping or dissolution stage to produce isolated cellulose molecules suitable for use in various different application pathways.
The raw cellulose-containing feed material may be substantially homogeneous (e.g., pre- or post-consumer waste, scrap textile fiber and fabric, cotton-containing fabrics, biomass or pulped wood or biomass, etc.), or it may be at least somewhat heterogeneous (e.g., cellulose-containing materials from mixed sources and of mixed types). When post-consumer textile materials are used as feedstock, used clothing collection and sorting may be accomplished via clothing retailers, manufacturers, recyclers, and various other organizations, providing access to large volumes of used, cellulose-containing garments and scrap materials that would otherwise be discarded. Depending on the type and homogeneity of the cellulose-containing feedstock, optional sorting and removal of non-cellulosic components may be carried out prior to pretreatment of the cellulose-containing feedstock.
When reclaimed garments and textiles are used as cellulose-containing feed material, initial sorting of reclaimed garments and textiles according to fiber content may be advantageous prior to feedstock pretreatment and dissolving. In some embodiments, for example, reclaimed material (e.g., garments and textiles) may be sorted by cellulosic content—e.g., reclaimed materials may be separated into groups having different cellulosic contents, such as >90% or >80% or >70% or >50%, or other cellulosic contents, and less than 50% cellulosic content. Reclaimed fabric material having other fiber contents and compositions may also be sorted and separated, and reclaimed material may also be sorted by composition, such as separating cotton-wool blends, cotton-polyester blends, cotton-elastane blends, cotton-spandex blends, and the like. Separation of non-cellulosic-containing materials such as buttons, zippers, and the like may take place at the time of or following sorting and process pretreatment. Likewise, mechanical sizing or comminution, such as shredding, pulling, grinding, cutting, tearing, and the like may take place prior to or following sorting and process pretreatment.
Cellulosic feedstocks such as reclaimed garments and textiles typically incorporate a variety of dyes, chemical finishes, or both, and may be contaminated with other materials, such as dirt, grease, and the like. Other types of cellulosic feedstocks, such as biomass, postconsumer waste, and the like, also contain contaminants that are desirably removed prior to a pulping stage. Raw cellulose-containing feedstock (optionally treated to remove non-cellulose-containing materials, and optionally sized) is typically processed in one or more pre-treatment stage(s) to remove dyes, finishes, contaminants (oils, grease, etc.) and the like from the feedstock. Cellulosic feedstocks including textile materials may optionally be mechanically treated to provide smaller sized, or more uniformly sized, feedstock. The fabric feedstock may be sized if desired, such as by shredding, to provide a sized feedstock having a fragmented, high surface area for fiber pulping. Feedstock sizing is typically accomplished using mechanical cutting, shredding, or other mechanical size reduction techniques. Processing to remove non-cellulosic components, such as buttons, zippers, fasteners, and the like may take place, if desired, prior to pretreatment, following pretreatment, or both.
Several different pre-treatment stages are described below, and various combinations of pretreatment stages may provide benefit, depending on the nature of the cellulosic feedstock. Depending on the properties of the raw textile feedstock, one or more of the pretreatments may be used, alone or in combination with other pretreatments. Several (optional) pre-treatment stages are described below, and several advantageous pre-treatment combinations are also described. It will be appreciated that additional pre-treatments may be used in combination with the pre-treatments described, and that various specific combinations other than those specifically illustrated and described may be used.
In general, cellulose-containing feed materials may undergo optional feedstock preparation stages, such as feedstock sorting, removal of non-cellulosic components, or both. The cellulose-containing feedstock then undergoes at least one pretreatment stage, followed by pulping or, dissolution of, or both, the pretreated cellulose-containing feedstock and filtration to produce isolated cellulose polymers. Several pretreatment stages are described below and are illustrated in the accompanying diagrams. Depending on the composition of the cellulose-containing feedstock and the attributes of the cellulosic product desired, one or more than one of the pretreatment stages may be used alone or in combination with other pretreatment stages. Specific combinations of pretreatments that may be useful in particular applications are described in greater detail below with reference to
In one embodiment, methods disclosed herein provide pretreatment of cellulose-containing feed materials using a high temperature aqueous washing process. This pretreatment stage is particularly useful for pretreatment of cellulose-containing feed materials comprising recycled garments and may facilitate removal of contaminants such as soils, deodorants, lanolin, silicone and cationic softeners from the feedstock, as well as stripping various fabric treatments, such as optical brighteners, moisture wicking enhancers, and the like, from the feed material. Aqueous media maintained at a temperature above 100° C., optionally above the boiling point of the aqueous media, generally above 120° C., often between 120° C. and 170° C., sometimes between 130° C. and 150° C., and up to 200° C., may be used. In some embodiments, the high temperature aqueous washing pretreatment stage is conducted in a closed vessel batch system with circulation or agitation or mixing of the hot aqueous media. Pressure conditions in a closed vessel system, as described, may range from about 100 kPa to about 2000 kPa, depending on the temperature of the aqueous media, with higher pressure conditions accompanying higher temperature media.
Aqueous media used in a high temperature pretreatment stage may comprise water alone, or it may comprise an aqueous solution having one or more additives. In some embodiments, the aqueous media may comprise water enriched with ozone. In some embodiments, the aqueous media may comprise water enriched with oxidative agents such as hydrogen peroxide or sodium perborate. In additional embodiments, surfactants (e.g., Sodium stearate, Fatty Alcohols, 4-(5-Dodecyl) benzenesulfonate, Alcohol ethoxylates and the like), various hydroxide compositions (e.g., Ca, Mg, Na, K, and Li hydroxides), the like, or combinations or multiples thereof, may be mixed and circulated with the aqueous media in a high temperature aqueous pretreatment stage and may act as wetting agents. In some embodiments, the high temperature aqueous washing stage incorporates an aqueous solution comprising NaOH at a concentration of from about 1% to about 15%, at a pHin excess of about 11, and in some embodiments in excess of about 12. Residence times are sufficient to substantially remove impurities from the cellulose-containing feedstock.
The aqueous wash solution may be evacuated following a suitable residence time. In some embodiments, multiple aqueous washing stages may be implemented, using the same or different aqueous solutions, all at high temperature and pressure conditions. Optional rinsing of the solids with an aqueous solution may be implemented following evacuation of the wash solution. Rinsing may take place at ambient temperatures and pressures, with optional agitation and mixing, and the rinse solution is removed following a suitable residence time. Cellulose-containing treated solids may undergo one or more additional pretreatment stage(s) or may be further processed in a pulping stage, a dissolution stage, or both.
In some embodiments, a water-less pretreatment, “non-toxic” pretreatment, or both, may be used to remove contaminants such as dyes, finishes, surface impurities and other contaminants from cellulose-containing feed materials, and particularly from feed materials comprising recycled garments or textiles. In this treatment stage, cellulose-containing feed material may be introduced to a closed and pressurized chamber, where the feed material contacts supercritical carbon dioxide, alone or in combination with additional reagent(s). In some embodiments, the supercritical CO2 may be enriched with ozone. In some embodiments, the supercritical CO2 may enriched with oxidative agents such as hydrogen peroxide or sodium perborate. In additional embodiments, surfactants (e.g., Sodium stearate, Fatty Alcohols 4-(5-Dodecyl) benzenesulfonate, Alcohol ethoxylates and the like) may be mixed and circulated with the supercritical CO2 in a pretreatment stage. Following a suitable residence time, supercritical carbon dioxide containing dissolved contaminants is withdrawn to a separator, where the carbon dioxide may be decompressed and returned to a gaseous state, while the contaminants may be collected and removed. The gaseous carbon dioxide may be recycled in a closed loop process and re-used for additional pretreatment cycles. Cellulose-containing treated solids may undergo one or more additional pretreatment stage(s) or may be further processed in a pulping stage, a dissolution stage, or both.
In some embodiments, cellulose-containing feedstock, cellulose-containing treated solids, or both, are treated, prior to pulping or dissolution, with a high temperature (>320° C.), high pressure (>2.5 Mps) aqueous treatment, in a closed and substantially rigid reaction vessel. This pretreatment stage promotes breakdown of the crystalline structure of cellulose and facilitates modification of cellulosic constituents to an amorphous, non- or less-crystalline structure that is more amenable to pulping, dissolution, or both.
In some embodiments, a pretreatment stage involves exposing the cellulose-containing feed material (or cellulose-containing treated solids, or both) to a “bleaching” agent, such as an oxidative or reducing agent, typically in an aqueous solution, at an oxidative/reducing agent concentration and for a residence time sufficient to remove materials such as dyes, finishes, and other contaminants from the cellulosic feedstock. Suitable oxidative agents, reducing agents, or both, include, for example, peroxide compositions (e.g., H202, Na2O2) and perborate (e.g., NaBO3) compositions. Additional oxidative agents, reducing agents, or both, that may be used in pretreatment stages as described herein include one or more of the following compositions: per carbonate compositions; sodium carbonate; per acetic acid compositions; potassium permanganate; persulfate compositions; ozone; sodium chloride; calcium oxychloride, sodium hypochlorite; calcium hypochlorite; lithium hypochlorite; cloramine; isocynual trichloride; Sulphur dioxide; sodium hydrosulfite; sulphoxylates; acidic sodium sulphite; sodium bosulphite; sodium meta bisulphite; TAED (tetra-acetyl-ethylene-diamine); and sodium hydrosulfite.
In some embodiments, bleaching agent treatment may involve treatment in an aqueous solution of calcium hypochloride (bleach powder) or sodium hypochlorite (NaOCl) in combination with sodium carbonate (soda ash) at a pH in excess of 8 and, in some embodiments, at a pH in excess of 9. Agitation or mixing of the materials in the bleaching agent pretreatment stage may be provided, and treatment with an oxidative, a reducing agent, or both, may take place in a closed reaction vessel.
The bleaching agent solution may be evacuated following a suitable residence time and optional rinsing of the solids with an aqueous solution may be implemented. Aqueous rinsing may take place at ambient temperatures, with the rinse solution removed following a suitable residence time. The bleaching agent may be neutralized, following this treatment, by introduction of a weak acid such as hydrogen peroxide. In some embodiments, multiple bleaching agent treatment cycles may be implemented using different oxidative or reducing reagents to treat the solids at different concentrations, pH conditions, temperature, residence times, the like, or combinations or multiples thereof, as appropriate. Recycling and regeneration of the oxidative or reducing agent(s) may be incorporated in the process, as is known in the art. Introduction of other weak acids may be effective to reduce the pH of the treated, cellulose-containing solids, if desired, following optional rinsing steps.
In some embodiments, methods disclosed herein provide pretreatment of cellulose-containing feed materials (or cellulose-containing treated solids, or both) by exposure to aqueous media containing one or more organic solvents. Suitable organic solvents may be selected from the group consisting of: acetic acid; acetone; acetonitrile; benzene; 1-butanol; 2-butanol; 2-butanone; t-butyl alcohol; carbon tetrachloride; chlorobenzene; chloroform; cyclohexane, 1,2-di chloroethane; diethylene glycol; di ethyl ether; diglyme (diethylene glycol dimethyl ether); 1,2-dimethoxy-ethane (glyme, DME); dimethyl formamide (DMF); dimethyl sulfoxide (DMSO); 1,4-dioxane; ethanol, ethyl acetate; ethylene glycol; glycerin; heptane; hexamethylphosphoramide (HMPA); hexamethylphosphorous tramide (HMPT); hexane; methanol; methyl t-butyl ether (MTBE); methylene chloride; nitromethane; pentane; 1-propanol; 2-propanol; pyridine; tetrahydrofuran (THF); toluene; triethyl amine; a-xylene; and m-xylene. The aqueous media containing organic solvent(s) is generally maintained at a basic pH, generally at a pH in excess of 9, and often at a pH of 10 or above. Treatment with organic solvents may be achieved using high temperature or cooler aqueous media.
In some embodiments, methods disclosed herein may optionally employ enzymatic treatment to shorten cellulose molecules, increase cellulose solubility, reduce reaction times, or both, in subsequent treatment stages. Suitable enzymes may include endogluconases (e.g., Cel 5A, Cel 7B, Cel 12A, Cel 45, Cel 61A); Cellobiohydrolases (e.g., Cel 6A, Cel 7A); LPMO/GH6 l; cellulases; and the like. In general, temperatures of from about 30° to 90° C., pH between about 4 to about 9 and dwell times of from about 20 min to 48 hours may be suitable for enzymatic treatment.
Enzymatic treatment(s) involving xylanases, alkaline pectinases, lipases, esterases, the like, or combinations or multiples thereof may also be used for feedstock pretreatment prior to pulping. In yet additional embodiments, feedstock may be treated using enzymatic cultures containing biological organisms (fungi, bacteria, etc.) that secrete cellulolytic enzymes (e.g., cellulases). Enzyme cultures such as Trichoderma Reesei, Trichoderma viride, Penicillium janthinellum, Halorhabdusutahensis, A Niger, Humicola, and mixtures of such enzyme-producing cultures, are suitable. Mechanical treatments such as pulverization, emulsification treatment(s), or both, may be implemented following enzymatic treatment.
For some applications (for example, those in which natural or light-colored or undyed regenerated fiber is desired as an end-product), optional treatment using a swelling agent, such as an ionic liquid, is employed prior to pulping to enhance the absorption of and penetration of the pulping agent. Treatment with a swelling agent (e.g. an ionic liquid) may be preceded by or implemented in combination with one or more other pretreatment stage(s). Ionic liquids may comprise hydroxides, such as Ca, Mg, Na, K, Li hydroxides, the like, or combinations or multiples thereof. Swelling agents suitable for use as reagents in a pretreatment stage may alternatively or additionally comprise one or more of the following reagents: [AMIM]Cl 1-Allyl-3-methylimidazolium chloride; [BzPy]Cl Benzylpyridinium chloride; [BMIM]Ace 1-Butyl-3-methylimidazolium acesulphamate; [BMIM]DBP 1-Butyl-3-methylimidazolium dibutylphosphate; [BMIM]Cl 1-Butyl-3-methylimidazolium chloride; [BMIM]PF6 1-Butyl-3-methylimidazolium hexafluorophosphate; [BMIM]BF4 1-Butyl-3-methylimidazolium tetrafluoroborate; [BMPy]Cl 1-Butyl-3-methylpyridinium chloride; [DBNH]AcO 1,8-Diazabicyclo[5.4.0]undec-7-enium acetate; [DBNH]EtCOO 1,8-Diazabicyclo[5.4.0]undec-7-enium propionate; [DMIM]DEP 1,3-Dimethylimidazolium diethylphosphate; [DMIM]DMP 1,3-Dimethylimidazolium dimethylphosphate; [EMBy]DEP 1-Ethyl-3-methylbutylpyridinium diethylphosphate; [EMIM]AcO 1-Ethyl-3-methylimidazolium acetate; [EMIM]Br 1-Ethyl-3-methylimidazolium bromide; [EMIM]DBP 1-Ethyl-3-methylimidazolium dibutylphosphate; [EMIM]DEP 1-Ethyl-3-methylimidazolium diethylphosphate; [EMIM]DMP 1-Ethyl-3-methylimidazolium dimethylphosphate; [EMIM]MeS04 1-Ethyl-3-methylimidazolium methanesulphonate; [HPy]Cl 1-Hexylpyridinium chloride; [E(OH)MIM]AcO 1-Hydroxyethyl-3-methylimidazolium acetate; [DBNMe]DMP 1-Methyl-1, 8-diazabicyclo[5.4.0]undec-7-enium dimethylphosphate; [P4444]0H Tetrabutylphosphonium hydroxide; [TMGH]AcO 1,1,3,3-Tetramethylguanidinium acetate; [TMGH]n-PrCOO 1,1,3,3-Tetramethylguanidinium butyrate; [TMGH]COO 1,1,3,3-Tetramethylguanidinium formiate; [TMGH]EtCOO 1,1,3,3-Tetramethylguanidinium propionate; [P8881]Ac0 Trioctylmethylphosphonium acetate; and HEMA Tris-(2-hydroxyethyl)methylammonium methyl sulphate.
In one exemplary embodiment, cellulose-containing feed materials (or cellulose-containing treated solids, or both) may be treated with an ionic solution such as an aqueous solution comprising Ca, Mg, Na, K, Li hydroxides, the like, or combinations or multiples thereof, followed by exposure to a sodium hydrosulfite (Na2S204) reducing agent, a bleaching agent such as peroxide, perborate, persulfate, and sodium or calcium hypochlorite, or both. Small amounts of Bromium (Br) may be used as a catalyst during this treatment. This treatment is generally carried out at a pH in excess of 9, and often at a pH of 10 or 10.5 or above. Treatment with swelling agents such as ionic liquids may be achieved using high temperature or cooler aqueous wash media. In some embodiments, treatment with a swelling agent (e.g., an ionic liquid) is conducted at temperatures of 0° C. or lower, provided the aqueous solution or slurry is prevented from freezing, and provided the viscosity of the solution is maintained at an acceptable level. In some embodiments, and particularly when ionic liquids having an acetate group are used, the treatment may be carried out at an acidic pH, typically at a pH less than 6, and in some embodiments at a pH less than 5. In some embodiments, the proportion of cellulose-containing feed materials (or cellulose-containing treated solids, or both) in the ionic solution is from about 2% to about 40%; in some embodiments, the proportion of cellulose-containing feed materials (or cellulose-containing treated solids, or both) in the ionic solution is from about 5% to about 25%.
It will be appreciated that numerous (optional) pretreatment processes are described herein and are illustrated in
Pretreatment preferably takes place in a closed vessel and, in batch treatment schemes, one or more pretreatment reagents may be introduced to and withdrawn from a closed vessel during various pretreatment stages, with or without intermediate rinsing or washing stages. In some embodiments, the vessel may be provided in the form of a rotating cylinder with a pressurized hull (housing) capable of withstanding pressures in the range of from 1000-5000 kPa, having inlet and outlet ports, pH and rpm control features, and having liquid agitation or circulation features. The inner reaction vessel surfaces may comprise anticorrosive metal(s) capable of withstanding concentrated acidic and alkali solutions. In some processes, both pretreatment and pulping may take place in the same vessel.
Specific pretreatment combinations are described below with reference to the schematic flow diagrams shown in
Treated cellulose-containing solids are subjected to a pulping or dissolving stage, in which the cellulose-containing solids are treated in a pulping reagent to promote molecular separation of cellulose polymers and destruction of intermolecular hydrogen bonds and other non-covalent bonds, converting cellulose-containing solids to their constituent cellulose polymers. In some embodiments, the number of intermolecular hydrogen bonds present in the cellulose polymers is reduced by at least 20% in the fiber pulping stage; in some embodiments the number of intermolecular hydrogen bonds present in the cellulose polymers is reduced by at least 50% in the fiber pulping stage; in yet other embodiments, the number of intermolecular hydrogen bonds present in the cellulose polymers is reduced by at least 70% in the fiber pulping stage. The viscosity of pulped cellulose, following the pulping treatment, is generally from about from 0.2 to as high as 900 cP, often from about 0.5 to about 50 cP.
A variety of pulping techniques and pulping chemistries are available, and one or more of the pretreatment stages described above may be used with a variety of known pulping reagents, including those described in PCT Int'l Patent Publication WO 2013/124265 A1, the disclosure of which is incorporated herein by reference in its entirety.
In some embodiments, copper-containing reagents are preferred for use as pulping reagents. In one embodiment, for example, Schwiezer's Reagent (the chemical complex tetraaminecopper (II) hydroxide —[Cu(NH3) 4(H20)2]) or tetraamminediaquacopper dihydroxide, [Cu(NH3) 4(H20) 2](0 H)2 is a preferred pulping agent to isolate and promote molecular separation of cellulose polymers. Schweizer's reagent may be prepared by precipitating copper(II) hydroxide from an aqueous solution of copper sulfate using sodium hydroxide or ammonia, then dissolving the precipitate in a solution of ammonia. In some embodiments, a combination of caustic soda, ammonium and cupramonium sulfate may be formulated to provide Schwiezer's Reagent.
Solutions comprising copper(II) hydroxide and ammonia may be introduced and used in the pulping stage to form Schweizer's Reagent according to the following reaction: Cu(OH)2+4NH3+2H2O→[Cu(NH3)4(H2O)2]2++20H. In this scheme, the copper hydroxide reagent may be manufactured from recycled copper recovered, for example, from electronics and computer component waste materials. Copper hydroxide is readily made from metallic copper by the electrolysis of water using copper anodes. Ammonia may be manufactured by an innovative use of the Haber-Bosch process (3H2+N2→2NH3) capturing hydrogen from organic wastes and combining it with atmospheric nitrogen. This method may produce ammonia at low cost and eliminate greenhouse gas emissions from organic waste feedstock. Using these reagent resources and methods for generating Schweizer's Reagent, all or substantially all of the materials used in the fiber pulping process described herein (including the cellulose-containing feedstock) may be sourced as waste products, resulting in minimal or no use of nonrenewable resources.
Other cellulose-dissolving agents may also be used in the pulping stage, such as iron-containing and zinc-containing reagents. In one embodiment, iron tartrate complex solvents (e.g., FeTNa) may be used as pulping reagents. FeTNa solutions may be prepared according to the procedure published by Seger et al. (B. Seger, et al., Carbohydrate Polymers 31 (1996) 105.) FeTNa solutions are prepared and stored while protecting them from light. The FeTNa complex may be prepared, for example, by dissolving sodium tartrate dehydrate (Alfa Assar, Cat. #16187) in deionized water, stirring and optionally heating. When the sodium tartrate dissolved, iron nitrate nonahydrate (Alfa Aesar, Cat. #12226) is added to the solution with continuous stirring. The solution is then cooled to 10-15° C. to prevent precipitation of the iron complex. 12 M sodium hydroxide solution is slowly added to the tartrate-ferric acid under controlled conditions to prevent the temperature from rising over 20° C. The solution color shifts from reddish-brown to yellowish-green, signifying the formation of the FeTNa complex. After this transition, the remaining sodium hydroxide may be added without regard to temperature. Sodium tartrate is added at the end to ensure long-term stability of the solution.
Pulping conditions using an FeTNa pulping reagent are generally basic and may be carried out at pH above 12, or above 13, or at a pH of about 14 in a closed reaction vessel. Reactions carried out using FeTNa pulping reagent at a pH of 14 in a closed reaction vessel kept at 4° C. successfully dissolved cotton feedstock. Carrying out the pulping reaction in an inert atmosphere is generally preferred, and circulating an inert gas such as argon through the pulping solution prior to and during addition of pretreated feedstock may improve dissolution rates, yields, or both.
In another embodiment, zinc-containing reagents such as Zincoxen solutions may be used as pulping reagents. The active ingredients of the zincoxen solution are zinc oxide (ZnO) and EDA. Zincoxen solutions may be prepared according to the procedures published by Shenouda and Happey (S. G. Shenouda and F. Happey, European Polymer Journal 12 (1975) 289) or Saxena, et al. (V. P Saxena, et al., Journal of Applied Polymer Science 7 (1963) 181). Ethylenediamene-water solutions are chilled to 0° C. followed by stirring in zinc oxide powder. Continuous stirring for 72 hours while maintaining the temperature at 0° C. produces a suitable Zincoxen solution. Pulping conditions using a Zincoxen pulping reagent are generally basic and may be carried out at pH above 12, or above 13, or at a pH of about 14 in a closed reaction vessel.
In general, residence times of up to 4-48 hours in the pulping stage are suitable to dissolve and promote molecular separation of cellulose molecules present in the treated cellulose-containing feedstock. In some embodiments, the pulping stage takes place in a closed chamber and an inert gas, such as nitrogen or argon, is introduced in the airspace to inhibit or prevent oxidation of pulping solution constituents. Oxygen-containing gases may be substantially evacuated from the pulping stage. In some embodiments, agitation of the pulping mixture, mixing of the pulping mixture, or both, may be provided; in some embodiments, an inert gas, such as nitrogen or argon, may be bubbled through the pulping mixture prior to pulping, during pulping, or both.
The cellulose molecules are substantially isolated and may be fully or partially dissolved to form substantially linear cellulose chains in the pulping stage, depending on the reagent used and the residence time. The pulping solution is filtered, following a suitable residence time, to remove non-cellulosic constituents with the solution and isolate substantially purified cellulose polymers, which are typically suspended in a viscous media. Filtration may involve multiple stages, including an optional centrifugation stage and one or more size exclusion filtration stages. A final filtration stage using pore sizes of 1 micron or less may be employed. The isolated, substantially purified cellulose polymers may be used in a wide range of downstream applications (See, e.g.,
The conditions of the pulping stage and the composition of the fabric feedstock are important factors in determining whether a cotton-like fiber or rayon is produced form the pulped cellulosic materials in subsequent processing. Full dissolution of the cellulosic fibers is generally desirable for the production of rayon-like fibers, cotton-like fibers and other regenerated cellulosic fibers. Suitable solvent concentrations, reagent to feedstock ratios, residence times, and the like, may be determined using routine experimentation. While Schwiezer's Reagent and the other iron- and zinc-containing pulping reagents described above are suitable pulping solvents for many applications, it will be appreciated that other pulping reagents may be available, or may be developed, and would be suitable for use in the processes described herein.
In some embodiments, energy is introduced to the pulped solution during a desired degree of pulping, following a desired degree of pulping, or both. When the pulping stage is carried out in a closed reaction chamber, mechanical energy, electrical energy, such as radio frequency energy, or both, may be introduced during or following pulping to enhance separation of different components and promote sedimentation of heavier components. If the cellulose-containing feedstock was not pretreated to remove non-cellulosic components, suitable filtration, screening exclusion treatment, size exclusion treatment, the like, or combinations or multiples thereof, may be performed, during or following pulping, to remove non-organic materials (e.g., buttons, fasteners, zippers, etc.), as well as impurities and non-cellulosic materials from the fiber pulp solution. Suitable f filtration, screening exclusion treatment, size exclusion treatment, the like, or combinations or multiples thereof, will depend on the types and level of contaminants remaining in the fiber pulp solution. Filtration may involve scraping the top of the reaction vessel, the bottom of the reaction vessel, or both, to remove floating or sinking debris; simple size exclusion filtration; gravitation separation or centrifugation to separate solids from the dissolved cellulosic materials; the like, or combinations or multiples thereof. In some embodiments, a cascade of progressively smaller pore size filtration stages may follow preliminary separation by gravitation or centrifugation.
Separated by-products may be isolated and purified (if appropriate) for re-sale or distribution to secondary markets.
In some embodiments, the pulping solution may be optionally treated with glycerin or glycerol or another agent to impart softness to the texture of the fiber.
After pulping, isolated cellulose molecules may be extruded to form regenerated fibers and textile materials. The isolated cellulose molecules are generally filtered or otherwise separated, and may be acidified and processed in a wet extrusion stage to precipitate cellulose fibers and produce cotton fibers, rayon fibers, or a mixture of cotton and rayon fibers. Various acids may be used in this precipitation stage, such as sulfuric, citric or lactic acids. In one embodiment, a sulfuric acid bath is used in combination with a wet extrusion process, wherein the viscous cellulose polymer solution is pumped through a spinneret, and the cellulose is precipitated to form fibers as it contacts the acid bath. The extrusion process, system, or both, may be modified and adjusted to produce fibers having different lengths, diameters, cross-sectional configurations, durability, softness, moisture wicking properties, and the like. In this process, the newly formed fibers are stretched, blown, or both, to produce desired configurations, washed, dried, and cut to the desired length.
Closed vat, continuous fiber extrusion techniques may be used. Closed vat systems allow recovery, recycling, or both, of any produced gases and by-products. Using fiber extrusion techniques is highly advantageous when applied to the regeneration of cellulosic materials to produce cotton fibers, rayon fibers, or both, since it allows a high degree of custom design and engineering of cellulosic fibers to achieve targeted comfort and performance characteristics (e.g., fiber length, diameter, cross-sectional shape, durability, softness, moisture wicking, etc.). Naturally grown fibers cannot be produced in desired or specified fiber lengths, diameters, cross-sectional profiles, or the like and cellulosic fibers regenerated using this process may therefore have different, and superior, properties compared to the natural fibers present in the initial recycled fabric feedstock.
In some embodiments, fiber extrusion may produce fibers having a denier of from about 0.1 to 70 or more denier. In some embodiments, fiber extrusion may involve extruding multifilaments having from about 20 to 300 single monofilaments, each having a denier of from about 0.1 to about 2. Extruding fine denier filaments produces woven fabric that feels softer to the touch and is desired in many embodiments. In some embodiments, fiber extrusion may additionally involve adding a false twist to the extruded filaments and texturizing them to resemble spun yarn. These treatments may obviate the necessity of using opening and spinning processes to produce yarn from the extruded fibers. Further handling of the fibers may involve cutting the continuous fiber to specific uniform lengths (stapling), missing, opening, carding, drawing, rowing, spinning, etc.
Following fiber extrusion and spinning to form yarns, fabrics, textiles and the like, waterless dyeing techniques may be used to further reduce the environmental impact of the overall process. Waterless dyeing technologies are available and typically use supercritical carbon dioxide as a solvent and carrier for dyestuff. In some embodiments, color treatment of regenerated fibers may involve determining the absorbency of the regenerated fiber and determining the color properties of fibers using spectrophotometric techniques. Color signatures and dye formulations may then be customized according to the specific properties of regenerated fibers to eliminate differences in coloration that may result from different batch qualities. In some embodiments, regenerated fibers or yarns may be surface treated (e.g., using a bleaching composition) and then dyed or overprinted using, for example, reactive, direct, pigment, sulfur, vat dye types and prints, the like, or combinations or multiples thereof. In some applications, all fiber regeneration process steps, from garment reclamation to fiber extrusion, may be located at a common geographic site (or at nearby sites). For some purposes, it may be desirable to locate different stages of the process at different physical locations. It may be desirable, in some applications, for example, to locate garment reclamation sites in populous areas, while locating other processing facilities and, in particular, the wet extrusion facility, in locations proximate textile processing facilities—e.g. near textile mills, garment manufacturing facilities, the like, or combinations or multiples thereof. In some applications, garment reclamation and initial processing may take place at one location and cellulosic pulp may then be shipped or transported to a different location for wet extrusion and other downstream processing (e.g., dying, garment manufacturing, etc.).
Regenerated cellulosic fibers (e.g., cotton, rayon, or both) produced as described above may be twisted into thread, dyed, bleached, woven into textiles and, ultimately, cut and sewn into garments.
In another aspect, fiber pulping of low grade cotton fibers, harvested naturally or produced from a raw material fabric feedstock as described above, is provided. In this process, low grade natural cotton fibers (e.g., low staple length cotton fibers) may be pulped as described herein, and then acidified and subjected to a wet extrusion process to produce newly formed fibers which may be stretched, blown, or both, to a desired diameter, cross-sectional profile or the like, washed, dried, and cut to a desired length. In this fashion, low grade (natural, recycled, or both) cotton fibers may be regenerated and converted to newly formed, higher value fibers having more desirable properties than those of the original natural cotton fibers, recycled cotton fibers, or both.
Although the process has been described primarily with reference to using cotton garments and feedstock containing cotton materials, it will be appreciated that other types of fabrics may be pulped and regenerated using the same or similar processes to produce regenerated fibers. It will also be appreciated that additional process steps may be employed, as is known in the art, and that equivalent treatment steps may be substituted for those described above.
Wood pulp includes three components: cellulose, hemicellulose, and lignin. The percentage of the components can be affected by type of wood (e.g., hard vs. soft), climate (e.g., temperate), the like, or combinations thereof. Cellulose maintains the strength in wood fiber due, at least in part, to the high degree of polymerization and linear orientation of the cellulose. Hemicellulose acts as the matrix. Lignin acts as the glue, thereby holding the fibers together and the cellulose together within the fiber cell wall. The wood can be processed to obtain pulp having a cellulose content based on the subsequent use. Wood pulp can be formed by any appropriate process or system, including, for example, mechanically, chemically, thermochemically, chemi-thermochemically, the like, or combinations or multiples thereof.
For example, a first wood pulp having the highest cellulose content (e.g, >90%) can be used to form textile fibers, derivatized celluloses, cellulose ethers, or the like. As another example, a second wood pulp having an intermediate cellulose content (e.g., 20-45%) can be used to form paper products. As yet another example, a third wood pulp having the lowest cellulose content (e.g, <10%) can be used to form cardboard.
Before textile pulping, during textile pulping, or after textile pulping, the textiles can undergo additional processing to change a size characteristic or parameter of a textile fiber or cellulose fiber derived from processing the textile. The textiles, whether as a pulp or otherwise, can be processed with a Tornado pulper, a refiner, a valley beater, the like, or combinations or multiples thereof. The size characteristic or parameter of the textile fiber or cellulose fiber derived from processing the textile can be the same as or substantially the same as (i.e., ±20%) as a size characteristic or parameter of the wood pulp fibers (e.g., average size of textile fiber or cellulose fiber is within a 20% difference of an average size of fibers of the wood pulp). The size characteristic or parameter of the textile fiber or cellulose fiber derived from processing the textile can be reduced to prevent a paper or cardboard production machine from jamming, malfunctioning, or the like due to the excessive size of the textile fiber or cellulose fiber derived from processing. For example, a textile fiber or cellulose fiber derived from processing the textile can have a length of 4-8 millimeters (mm). The length of the textile fiber or cellulose fiber can be reduced to, for example, 0.5 to 4 mm by undergoing the additional processing. As another example, a textile fiber or cellulose fiber derived from processing the textile can have a weight of 2.2-2.5 Deniers per filament (Dpf). The weight of the textile fiber or cellulose fiber can be reduced to, for example, 0.5 to 1 Dpf by undergoing the additional processing.
The textile pulp and the wood pulp can be mixed by any appropriate process or system, including, for example, two pipes flowing into a single pipe, adding the different pulps to a single vessel for blending, the like, or combinations or multiples thereof. Mixing the textile pulp with the wood pulp can increase yield by combining a lower cellulose content pulp (i.e., wood pulp) with a higher cellulose content pulp (i.e., textile pulp). Additionally, typically discarded wood pulp components, such as lignin, can be retained in wood pulp, thereby reducing cost, increasing yield, or the like. For example, during the wood pulping process, lignin can be burned off with the resulting steam used to generate energy. In doing so, the volume of the pulp is reduced and an additional step is required. However, retaining the lignin increases the mechanical stress (e.g., compression, tension, shear, bending, torsion, fatigue, the like, or combinations of multiples thereof) capability of the resulting product, whether paper, cardboard, or the like.
Based on the respective cellulose content of the textile pulp and the wood pulp, the amount of textile pulp and the amount of wood pulp can be adjusted to form a combination pulp having the desired cellulose content. The ratio, as a percentage, of textile pulp and wood pulp in the combination pulp can range from 0.1:99.9 up to at least 55:45, including, for example 5:95, 10:90, 20:80, 30:70, 40:60, 50:50, and the like. For example, 150 kg of a wood pulp having 4% cellulose can be combined with 8 kg of a textile pulp having 90% cellulose to form a combination pulp having a cellulose content of 8.35%, such as for developing cardboard. As another example, 150 kg of a wood pulp having 15% cellulose can be combined with 120 kg of a textile pulp having 75% cellulose to form a combination pulp having a cellulose content of 41.67%, such as for forming paper products.
The textile pulp can also include non-cellulose material, such as a polyester, nylon, rayon (or Lyocell), acrylic, the like or combinations or multiples thereof. The non-cellulose material can increase the mechanical stress (e.g., compression, tension, shear, bending, torsion, fatigue, the like, or combinations of multiples thereof) of the resulting product, e.g., paper product or cardboard. Additionally, or alternatively, non-cellulose material can be added to the textile pulp, the wood pulp, the combination pulp, or combinations thereof to increase the mechanical stress of the resulting product.
The processing steps used to form the textile pulp, the textiles, fibers, or derivatives thereof can be adjusted based on the resulting product to be developed. For example, when the textile pulp is used to develop paper products, a bleaching step (e.g., bleach intensity, number of bleaching steps or sub-steps, or the like) can adjust the color of the fibers. As another example, when the textile pulp is used to develop cardboard, a sorting step can be less thorough (e.g., instead of separating recycled textiles in bins based on increments of 2-3% cellulose content, the recycled textiles can be separated into bins based on increments of 10-15% cellulose content).
Though textile pulp is discussed in reference to the combination pulp, the textile pulp can be further processed by one or more dissolving steps, as discussed above, before forming the combination pulp, when it is necessary or desirous to do so.
A small scale experiment was conducted to establish feasibility of cellulose pulping and fiber regeneration using shredded cotton garment material as a feedstock. The shredded feedstock material was treated with Schweizer's Reagent to form a dissolved pulping solution, and the pulp solution was acidified by treatment with sulfuric acid. Fibers were regenerated as a result of the acidification.
2 NaOH(aq)+CuSO4(aq)→Cu(OH)2(s)+Na2SO4(aq) 1.
Cu(OH)2(aq)→Cu2(aq)+2OH−(aq) 2.
n Cu2+(aq)+(cellulose)n+2n OH−→(CuC6H8O5)n+2n H2O 3.
In alternative schemes, chemical reaction (1), noted above, may be omitted when using copper hydroxide and ammonia reactants to form Schweitzer's reagent as follows: Cu(OH)2+4NH3+2H2O→[Cu(NH3)4(H2O)2]2++2OH This alternative chemistry does not require filtration (setp 5, above) and produces no by-products that require disposal or removal.
Analyses were conducted to compare regenerated cellulosic fibers, processed as described herein, with virgin cotton fibers. Regenerated cellulosic fiber produced as described above was tested using the ASTM D 2256-02 test method for tensile properties of yams by single-strand method. The regenerated cellulosic fibers exhibited uniform-diameter fiber properties, with the tenacity of cotton and the fineness of silk. Tenacity is a measure of the breaking strength of a fiber divided by the denier.
The tenacity tests indicate that regenerated cellulosic fiber produced as described above has similar strength to the tested cotton, for its diameter. Extrusion allows the diameter (and hence absolute strength of individual fibers) to be tightly controlled.
Though certain elements, aspects, components or the like are described in relation to one embodiment or example of a system or method for producing a paper or packaging material, those elements, aspects, components or the like can be including with any system or method for producing a paper or packaging material, such as when it desirous or advantageous to do so.
The foregoing description, for purposes of explanation, used specific nomenclature to provide a thorough understanding of the disclosure. However, it will be apparent to one skilled in the art that the specific details are not required in order to practice the systems and methods described herein. The foregoing descriptions of specific embodiments or examples are presented by way of examples for purposes of illustration and description. They are not intended to be exhaustive of or to limit this disclosure to the precise forms described. Many modifications and variations are possible in view of the above teachings. The embodiments or examples are shown and described in order to best explain the principles of this disclosure and practical applications, to thereby enable others skilled in the art to best utilize this disclosure and various embodiments or examples with various modifications as are suited to the particular use contemplated. It is intended that the scope of this disclosure be defined by the following claims and their equivalents.
This application claims the benefit of pending U.S. Provisional Patent Application No. 63/036,856, filed Jun. 9, 2020. The contents of which are herein incorporated by reference in their entirety.
| Number | Date | Country | |
|---|---|---|---|
| 63036856 | Jun 2020 | US |
