Textile fiber

Abstract

The present invention relates to textile fibers, in particular, but not limited to, textile microfibers and / or textile nanofibers, and their conversion to carbon nanomaterials. The present invention extends to methods for converting non-biodegradable textile microfibers and nanofibers, as well as microplastics and nanoplastics, into harmless non-toxic and / or biodegradable / bio-compatible end products, and includes the apparatus and / or reactors used to implement these methods.

Description

Technical Field

[0001] The present invention relates to textile fibers, in particular, but not limited to, textile microfibers and / or textile nanofibers, and their conversion to carbon nanomaterials. The present invention extends to methods for converting non-biodegradable textile microfibers and nanofibers, as well as microplastics and nanoplastics, into harmless, non-toxic and / or biodegradable / bio-compatible end products, and includes the apparatus and / or reactors used to carry out these methods.

Background Art

[0002] Textiles are materials made by weaving, knitting, felting, or bonding together (by mechanical, thermal, or chemical processes) thread-like fibers and are generally used for clothing. The properties of textiles depend on the type of fibers used and the treatments applied to them. There are three main types of textiles: (i) natural textiles obtained from renewable resources such as cotton fibers (cellulose) and wool (protein-based); (ii) synthetic textiles mostly derived from non-renewable petrochemical resources such as polyester and nylon, which are a major cause of microplastic / nanoplastic pollution; and (iii) semi-synthetic or regenerated textiles manufactured from cellulose derived from wood and other resources dissolved into spin filament cellulose fibers. These latter textiles have different names depending on the process and solvent used to manufacture them, for example, rayon, lyocell, tencel, etc.).

[0003] Plastics are increasingly present in our daily lives and activities due to their delicacy, diversity, light weight, and relatively low manufacturing cost. In addition to the production of daily necessities such as clothing and cosmetics, plastics play an important role in the construction of transportation vehicles such as automobiles and aircraft. In pharmaceuticals, plastic products are important as disposable containers and equipment with anti-corrosive properties that provide the highest level of hygiene. However, despite the value of plastics for today's consumers, the environmental impact associated with post-use plastics is troubling human society and beginning to disrupt the balance of ecosystems.

[0004] The environmental and health consequences of plastics are not currently fully understood. Environmental problems include the capture and destruction of wildlife habitats, the risk of ingestion, and the plastic-facilitated movement of organisms to new ecosystems. Human exposure to plastic pollution can affect the respiratory, circulatory, and lymphatic systems and may accumulate in the liver, kidneys, and gastrointestinal tract. The transport and deposition of plastic particles in the human body have an adverse effect on the endocrine system, most notably causing endocrine disruption. Carcinogenicity and endocrine disruption can occur when certain polymers and their associated additives are inhaled or ingested over a long period of time. Plastics have been shown to have reproductive effects, including breast cancer, prostate cancer, decreased sperm count, ovarian cancer, and overall impairment of fetal development. Furthermore, as a result of consumption, it can lead to metabolic diseases, bladder cancer, colorectal cancer, diabetes, liver diseases, etc.

[0005] Furthermore, most waste plastics ultimately break down into microplastics and nanoplastics under weathering and aging conditions. Microplastics and nanoplastics have increasingly attracted attention in recent years due to their widespread presence in large quantities and the potential for negative impacts on animals, humans, and ecosystems. Currently, microplastics and nanoplastics are classified into primary and secondary microplastics and nanoplastics according to their origin. Due to their small size and large surface-to-volume ratio, microplastics and nanoplastics are prone to absorbing and accumulating contaminants and are accumulated by the digestive or respiratory systems in all types of organisms, causing toxicity through the food chain.

[0006] Inhalation, ingestion, and dermal absorption of microplastics and nanoplastics have been identified as three basic exposure modes. Respiratory-related disorders, including nasal cancer, airway obstruction, respiratory diseases, lung cancer, and lung deposition, are epidemiologically associated with inhaled polymer particles. Microplastics and nanoplastics ingested through food products may have neurological and psychological consequences. Macroplastics, microplastics, and nanoplastics used on the skin are mainly associated with irritation. The consequences for these systems can be exacerbated by chronic exposure; nevertheless, much remains unknown regarding their relevance to the human population.

[0007] Microplastic and nanoplastic contaminants in the environment are classified as primary and secondary depending on their source. Primary microplastics / nanoplastics are manufactured as microparticles and directly released into the environment through sewage effluents or domestic and industrial wastewaters. Primary microplastics and nanoplastics can consist of plastic pellets, nurdles, powders, and fibers used as additives in personal care and cleaning products or as industrial materials. These particles can have a spherical shape or be amorphous. For example, microbeads are derived from scrubbing facial cleansers; artificial microspheres are used in cosmetics and detergents; and artificial resin pellets are used as raw materials for industrial purposes. Secondary microplastics and nanoplastics result from the breakdown of larger plastic pieces. The disintegration of these polymers is driven by UV irradiation, thermal aging, biofilm growth, and oxidation. Degradation is classified as photodegradation, thermal degradation, biodegradation, and thermo-oxidative degradation. These microplastics and nanoplastics are mainly generated by the breakdown of plastic products widely used in packaging, construction, agriculture, transportation, textiles, and household goods.

[0008] Careful consideration should be given to one of the main sources of microplastic and nanoplastic generation, namely textile fibers, also known as microfibers or nanofibers, which are schematically shown in Figure 1. Microplastics and nanoplastics derived from laundry account for 35% of all microplastics / nanoplastics discharged from primary sources into the sea. However, there are other textile microplastic and nanoplastic emissions to air and soil that indirectly reach the sea and need to be considered (see Figure 1). In addition, microfibers and nanofibers emitted into the air in the form of dust from clothing use, as well as particle emissions from clothes dryers, need to be considered. These microfibers and nanofibers move through the air and reach the sea and the human respiratory system.

[0009] Plastic items entering the environment from secondary sources that are larger than 5 millimeters in size are known to be even more harmful and have the potential to generate microplastics and nanoplastics. This is true for fishing and aquaculture facilities, as well as for sanitary products and geotextiles. Additionally, the landfilling of synthetic clothing is another major source of micro- and fibers. The nature of fast fashion disposal and the throwaway culture are creating a profound environmental, social, and economic crisis. According to the American Apparel and Footwear Association (AAFA), in 2015, more than 16 million tons of textile waste were generated in the United States, only 15% of which was recycled, 19% was burned for energy recovery, and the remainder (66%) was discarded in landfills. Synthetic polymer-based clothing is estimated to take 200 years to decompose in landfills, and they first fragment into microfibers and nanofibers.

[0010] Currently, some approaches for valorizing plastic waste use liquefaction, gasification, and / or pyrolysis. Several new technologies for the upcycling of plastics, such as hydrothermal carbonisation, microwave-assisted conversion, plasma-assisted conversion, and photoreforming, are also being explored. SUMMARY OF THE INVENTION

[0011] However, there are no conversion technologies available in the market that are specifically designed for textile microfibers and nanofibers. The main routes being investigated for the valorization of bulk plastic waste are the biochemical decomposition and thermochemical treatment of plastics. The biochemical approach decomposes polymers into monomers and oligomers by enzymes, but is typically effective only for cellulose and other natural polymer products. The thermochemical approach is based on converting polymers into a mixture of products consisting of gas, oil, and carbon / tar. Nevertheless, none of these approaches have led to high-value, biodegradable, environmentally friendly, and safe products.

[0012] Therefore, there is an urgent need to provide a new and effective method for converting textile microfibers and nanofibers into high-value, biodegradable and / or amorphous / bio-compatible and / or useful end products.

[0013] Accordingly, in a first aspect of the present invention, there is provided a method for converting textile microfibers and / or textile nanofibers into carbon nanomaterials, the method comprising thermally cracking the textile microfibers and / or textile nanofibers under conditions suitable for converting the textile microfibers and / or textile nanofibers into carbon nanomaterials.

[0014] Advantageously, the method of the present invention effectively converts textile microfibers and nanofibers into high-value carbon products (i.e., carbon nanomaterials), and in some embodiments, one or more gases mainly containing hydrogen, which, when used as an energy source, show minimal environmental impact and no carbon emissions. Surprisingly, the method of the present invention can achieve both the solid-to-solid conversion of fiber waste and the selective production of high-value products from gas-phase or liquid-phase intermediate species. The inventors believe that this may be energy-saving due to the microstructured / nanostructured nature of the starting materials. Also surprisingly, since synthetic fibers behave very differently compared to natural fibers, it is possible to process mixed fiber feedstocks in reaction separation methods and control access to catalytic sites by different reactors in mixed fiber waste feedstocks.

[0015] Preferably, the method of the present invention comprises thermally cracking textile microfibers and / or textile nanofibers that are of natural, synthetic or semi-synthetic origin. Textile or garment finishing and treatment procedures (e.g., dyeing) can negatively affect the biodegradation of natural fibers. Furthermore, since natural fibers are often mixed with synthetic or semi-synthetic textile fabrics or are mixed during washing, the method of the present invention can be effectively applied to the thermal cracking of natural textile microfibers and / or textile nanofibers. However, more preferably, the method comprises thermally cracking synthetic or semi-synthetic textile microfibers and / or textile nanofibers. Advantageously, the method enables the use of microfiber / nanofiber feedstocks to control product formation, taking advantage of improved conversion efficiency due to existing micro-nano structures and well-defined properties of synthetic versus natural fibers.

[0016] The textile microfibers and / or textile nanofibers can be obtained from any of the textiles in Table 1 below.

[0017]

Table 1

[0018] In a preferred embodiment, the textile microfiber and / or textile nanofiber may be cotton or polyethylene terephthalate (PET).

[0019] In the most preferred embodiment, the textile microfiber and / or textile nanofiber is textile waste, which may be collected from the filter of a washing machine (referred to herein as "hard textile waste") and / or may be collected from the filter of a dryer (referred to herein as "linty textile waste").

[0020] The textile microfiber and / or textile nanofiber may be naturally formed, knitted, woven, non-woven, felted, or preferably bonded together by mechanical, thermal, or chemical treatment. The textile microfiber and / or textile nanofiber may contain a plastic material.

[0021] "Microfiber" (or "microfibre") and / or "nanofiber" (or "nanofibre") are used interchangeably with "microplastic" and / or "nanoplastic" and have the same meaning in the context of the present invention.

[0022] The diameter may be measured by sieving, and the diameter or length can be measured optically, for example, by a fiber quality analyzer that optically analyzes the dimensions of the fiber (e.g., diameter and / or length). The textile microfiber and / or textile nanofiber may have an average diameter or length between 0.1 μm and 5 mm, between 0.1 μm and 4 mm, between 0.1 μm and 3 mm, or between 0.1 μm and 2 mm.

[0023] The textile microfiber and / or textile nanofiber may have an average diameter or length less than 5 mm, 4 mm, or 3 mm. Preferably, the textile microfiber and / or textile nanofiber have an average diameter or length less than 2 mm or 1 mm. Preferably, the textile microfiber and / or textile nanofiber have an average diameter or length less than 750 μm, 500 μm, 250 μm, or 150 μm. Preferably, the textile microfiber and / or textile nanofiber have an average diameter less than 100 μm, 75 μm, 50 μm, or 35 μm.

[0024] The textile microfiber and / or textile nanofiber may have an average diameter or length between about 0.01 and 1 mm, between about 0.01 and 0.9 mm, between about 0.01 and 0.8 mm, between about 0.01 and 0.7 mm, between about 0.01 and 0.6 mm, or between about 0.01 and 0.5 mm. The textile microfiber and / or textile nanofiber may have an average diameter or length between about 0.02 and 1 mm, between about 0.02 and 0.75 mm, or between about 0.02 and 0.5 mm. The textile microfiber and / or textile nanofiber may have an average diameter or length between about 0.02 and 0.9 mm, between about 0.02 and 0.8 mm, between about 0.03 and 0.7 mm, between about 0.03 and 0.6 mm, or between about 0.04 and 0.5 mm.

[0025] Textile microfibers preferably have an average diameter or length of less than 10 μm, 9 μm, 8 μm, 7 μm, 6 μm, or 5 μm. Textile microfibers preferably have an average diameter or length of less than 4 μm, 3 μm, 2 μm, or 1 μm.

[0026] Textile nanofibers preferably have an average diameter or length between 1 nm and 1000 nm, or between 5 nm and 900 nm, or between 10 nm and 800 nm. Textile nanofibers preferably have an average diameter or length between 20 nm and 700 nm, or between 30 nm and 600 nm, or between 50 nm and 500 nm.

[0027] Textile microfibers and / or textile nanofibers can have an average length between 0.01 mm and 0.5 mm, or between 0.02 mm and 0.3 mm, or between 0.05 mm and 0.15 mm.

[0028] Textile microfibers and / or textile nanofibers can have an average diameter between 1 and 100 μm, or between 1 and 75 μm, or between 1 and 50 μm, or between 1 and 40 μm, or between 6 and 36 μm.

[0029] Surprisingly, the inventors have demonstrated that by using thermal degradation, particularly thermal decomposition and superheated steam carbonization, to upcycle textile microfibers and / or nanofibers of different origins, large amounts of hydrogen (H2) and high-value nanostructured carbon are produced. Previous attempts to upcycle bulk textiles have been limited to the thermochemical conversion of natural polymers and aimed at producing gases, oils, and carbon / tar. The upcycling of microfibers and / or nanofibers obtained from washing has not been studied. However, carbon / tar generally contains carcinogenic polycyclic aromatic hydrocarbons (PAHs) and thus poses a significant health threat.

[0030] Decomposition refers to a series of chemical events that result in the breakdown of the structure of plastic polymers and may involve the conversion from solid to solid and the subsequent formation of intermediate liquid or gas-phase species that react to form products. "Thermal cracking" or "cracking" can refer to a process that uses heat and pressure to break large hydrocarbon molecules into smaller, lighter molecules. "Thermal cracking" or "cracking" can also refer to a process that thermally reacts large, inert hydrocarbon molecules with water under specific temperature and pressure conditions to form smaller, lighter molecules.

[0031] In one embodiment, the thermal cracking of textile microfibers and / or textile nanofibers includes pyrolysis to effect the thermal cracking.

[0032] Pyrolysis is a thermochemical conversion process commonly used to produce liquid hydrocarbon oils, char, and gas due to the thermal alteration of organic reactants under an inert atmosphere. The distribution of products highly depends on the reaction temperature, heating rate, residence time, and type of reactor. Pyrolysis fluidized bed reactors are often used because they can be heated better and transported in large quantities, resulting in increased thermal cracking and high oil yields.

[0033] Typically, pyrolysis produces oils that can be upgraded for use as fuels in automotive engines and power plants or as feedstocks for producing valuable chemicals. Pyrolysis further produces char as a solid product. As a result of the dehydration, deamination, decarboxylation, and dehydrogenation of organic materials during pyrolysis and gasification, aromatic carbon is created.

[0034] Examples of industrial efforts aimed at converting plastic into carbon black are being developed by Makeen energy. A schematic process for converting plastic waste through pyrolysis is shown in Figure 2. The process, named "Plastcon", uses chemical conversion via pyrolysis following the physical and chemical separation of plastics. Plastcon processes bulk plastic waste from both households and industries. The resulting carbon black is useful in the manufacture of other plastic materials. It is important to consider the entire life cycle of the final product before converting plastic waste into a product that may be more harmful to the environment.

[0035] However, to date, there have been no successful reports regarding the use of pyrolysis to convert textile microfibers and / or nanofibers into carbon nanomaterials as described in the methods herein. The inventors have surprisingly observed evidence of the nanostructuring of the original microfibers and nanofibers, thereby demonstrating a direct solid-to-solid conversion to a potentially useful final product. They have, therefore, successfully optimized a pyrolysis process that specifically targets textile microfibers and / or nanofibers, resulting in surprisingly higher quality and large quantities of carbon nanomaterials.

[0036] The pyrolysis reaction may be batch, fed-batch, or continuous. The pyrolysis reaction may be carried out in a single-stage or multi-stage reactor, which may be a fixed-bed or fluidized reactor. However, preferably, the reaction is carried out in a single-stage fixed-bed reactor for a dry feed or a batch superheated steam reactor for a wet feedstock. Advantages of having a fixed-bed reactor include lower energy requirements compared to a fluidized bed, as well as ease of construction and operation.

[0037] The pyrolysis reaction can be carried out in a temperature range between 100°C and 1000°C. Preferably, the pyrolysis reaction is carried out in a temperature range between 200 and 900°C, between 300 and 800°C, between 400 and 700°C, or between 450 and 600°C. Preferably, the pyrolysis reaction is carried out in a temperature range between 460 and 550°C, between 470 and 540°C, between 480 and 530°C, or between 490 and 520°C. Preferably, the pyrolysis reaction is carried out in a temperature range between 491 and 510°C, between 492 and 509°C, between 493 and 508°C, or between 493 and 507°C. Preferably, the pyrolysis reaction is carried out in a temperature range between 494 and 506°C, between 495 and 505°C, between 496 and 504°C, or between 497 and 504°C. Preferably, the pyrolysis reaction is carried out in a temperature range between 498 and 503°C, between 499 and 502°C, or between 499 and 501°C, or at about 500°C.

[0038] Preferably, the pyrolysis reaction is carried out at a temperature of less than 1000°C, 900°C, 800°C, 700°C, 600°C, or 550°C. Preferably, the pyrolysis reaction is carried out at a temperature of more than 100°C, 200°C, 300°C, 400°C, or 450°C.

[0039] Preferably, the pyrolysis reaction is carried out at a temperature of less than 525°C, 500°C, 475°C, 450°C, 425°C, or 400°C. Preferably, the pyrolysis reaction is carried out at a temperature of more than 250°C, 275°C, 300°C, 325°C, or 350°C.

[0040] The pyrolysis reaction can be carried out with a residence time of 1 to 200 minutes. Preferably, the pyrolysis reaction has a residence time between 1 and 175 minutes, between 1 and 150 minutes, between 1 and 125 minutes, between 1 and 100 minutes, between 1 and 75 minutes, between 1 and 50 minutes, or between 1 and 25 minutes. Preferably, the pyrolysis reaction has a residence time between 25 and 200 minutes, between 25 and 175 minutes, between 25 and 150 minutes, between 25 and 125 minutes, between 25 and 100 minutes, between 25 and 75 minutes, or between 25 and 50 minutes.

[0041] The pyrolysis reaction can be carried out in a closed environment, in a vacuum environment, or at atmospheric pressure in an inert gas (e.g., nitrogen) or carbonizing (e.g., carbon dioxide) environment. Preferably, the pyrolysis reaction is carried out at atmospheric pressure because it is more efficient in terms of energy consumption.

[0042] The pyrolysis reaction may be carried out using a carrier gas, which is used to maintain an inert or carbonizing atmosphere inside the reaction and thus prevent the combustion of the feed. The carrier gas may be an inert / rare gas or carbon dioxide, or a mixture thereof. The inert / rare gas can be selected from the group consisting of helium, neon, and argon, or a combination thereof. Other gases that are not rare gases but are inert or carbonizing can also be used. Preferably, the carrier gas is argon or nitrogen.

[0043] In one embodiment, the pyrolysis reaction can be carried out in the absence of a catalyst, i.e., it can be non-catalytic pyrolysis. Alternatively, in another embodiment, the pyrolysis reaction can be carried out in the presence of a catalyst, i.e., it can be catalytic pyrolysis. The use of a catalyst increases the energy efficiency of the thermochemical conversion, the stimulation of the desired reaction, and the product selectivity. In addition, the inventors have shown that the use of non-catalytic pyrolysis can convert non-biodegradable textile microfibers and / or textile nanofibers into potentially biologically harmless amorphous carbon products. Therefore, in embodiments where the thermal cracking of textile microfibers and / or textile nanofibers into carbon nanomaterials is carried out without using a catalyst, more energy and a longer residence time are required, but this is preferred when the method is used to convert harmful microfiber and nanofiber waste materials into harmless carbon waste.

[0044] Therefore, in one embodiment, the pyrolysis reaction is non-catalytic pyrolysis.

[0045] In another embodiment, the pyrolysis reaction is catalytic pyrolysis.

[0046] In embodiments where the pyrolysis is a catalytic pyrolysis reaction, the catalyst may be added to the reaction before, simultaneously (i.e., mixed with them), or after the textile microfibers and / or textile nanofibers, and the pyrolysis is initiated. Preferably, the catalyst contacts (preferably, is mixed with) the textile microfibers and / or textile nanofibers.

[0047] The selection of a suitable catalyst can contribute to influencing the final structure of the carbon nanomaterial end product, the carbonization temperature, and the selectivity for the desired gas-phase or liquid-phase products in the method of the present invention. Due to its high catalytic activity and low cost, a heterogeneous nickel (Ni)-based catalyst is preferred.

[0048] In one embodiment, the catalyst may be a single or multi-metal catalyst. Preferably, the catalyst is a multi-metal catalyst. The multi-metal catalyst can be selected from the group consisting of Ni-Mg, Ni-Fe, Ni-Mg-Al, Ni / γ-Al2O3, Ni / α-Al2O3, Fe / γ-Al2O3, Fe / α-Al2O3, and Ni-Fe / γ-Al2O3.

[0049] In a preferred embodiment, however, the catalyst is Ni-Fe, a bimetallic catalyst.

[0050] The catalyst may or may not be supported by a support composition. However, preferably, in some embodiments, the catalyst is supported by a support composition.

[0051] The support composition can have a great influence on the activity and stability of the catalyst. A good support composition should have a large surface area, and an appropriate pore size or distribution, and strong metal-support interaction, mechanical strength, and thermal stability. The most commonly used supports are metal oxides, zeolites, and activated carbon (AC). Furthermore, alumina is an excellent support material due to its strong chemical and mechanical resistance, large surface area, and specific acidic properties

[0153] .

[0052] The support composition can be selected from the group consisting of metal oxides, zeolites, carbon, and alumina. The support has a high surface area, which enables the formation of polymetallic nanoparticles distributed in its pore structure. In some examples, the nanoparticle size plays a role in influencing the final dimensions of carbon nanomaterials formed from textile microfibers and nanofibers.

[0053] The catalyst system may also need to be changed for certain polymers. Certain compounds contained in plastic waste may interfere with the catalytic thermochemical conversion process. The catalyst for the thermochemical conversion of plastic waste should be resistant to air, moisture, and organic contaminants and be effective in a heterogeneous combination.

[0054] For supported metal catalysts, metal sintering is a major issue under high-temperature and / or superheated steam operating conditions, leading to a significant loss of active sites / surface. This is mainly caused by Ostwald ripening, metal migration, and coalescence. Therefore, preferably, the supported metal catalyst has a high metal dispersion, homogeneous metal clusters / particle sizes, and / or strong metal-support contact that minimize metal mobility and sintering. A further difficulty in catalyst design is to minimize coke formation on the active sites and instead target the formation of structured carbon nanomaterials.

[0055] The catalyst composition determines the relative rates of cracking of the initial polymer and graphitization of the deposited carbon. The catalyst composition is also important for promoting hydrogen formation with respect to other gas-phase hydrocarbon products. As discussed in the examples, the inventors have also studied the use of superheated steam carbonization (HTC), another thermal cracking method for upcycling textile microfibers and nanofibers into high-value nanocarbon products and hydrogen.

[0056] Thus, in another embodiment, the thermal cracking of textile microfibers and / or textile nanofibers involves hydrothermal carbonization (HTC) to effectuate thermal cracking.

[0057] Advantageously, the inventors have observed evidence of direct nanostructuring of solid fibers showing that, surprisingly, HTC is a promising low-energy input process for making nanomaterials from already nanostructured waste.

[0058] Hydrothermal carbonization (HTC) is a relatively recent approach for treating wet organic waste. HTC (also called "hydrothermal decomposition") has also been considered for the valorization of polymeric waste such as biomass. The technique itself is a way to mimic the natural phenomenon of mineralization in an aqueous medium as found in natural biomass.

[0059] The use of HTC in the valorization of polymeric waste is becoming common. Modern HTC applications use various waste forms of biomass, municipal waste, plastics, and bulk textiles as reactants to produce solid carbon, various gases (e.g., CO2, CO, CH4, and C2H4), and oil products.

[0060] Conventionally, the products resulting from the HTC process typically include a gas (or non-condensable vapor), a liquid rich in unreacted components derived from absorbed inorganic substances and reactants, and a solid rich in carbon similar to coal. Modern HTC applications use various waste forms of biomass, municipal waste, plastics, and bulk textiles as reactants, aiming for solid carbon, various gases (e.g., CO2, CO, CH4, and C2H4), and oil products. In the simulation of the process, successful production of solids rich in microporous structure carbon and in the form of nanomaterials has been achieved. Further research on the solid integrated structure indicates the presence of functional groups of oxides, sulfides, and halides based on the selection of feedstock used. Nevertheless, to date, the use of HTC to convert textile microfibers and / or nanofibers into high-quality carbon nanomaterials and hydrogen has not been successful.

[0061] The HTC process can use a solvent to adjust the pressure to the desired reaction conditions inside the reactor. In the case of water or other organic solvents, these can be reactants at the same time and have a dual function. Furthermore, when water is utilized, water has an autocatalytic effect on carbonization.

[0062] Water is an excellent solvent for the superheated steam conversion process due to its low cost, non-toxicity, and abundance. Organic materials are hydrolyzed into low molecular weight molecules during HTC. Due to the instability and reactivity of intermediate molecules, they recombine into high molecular weight compounds.

[0063] Therefore, in a preferred embodiment, the HTC process uses water as a solvent.

[0064] The HTC process may be batch, fed-batch, or continuous. In the case of a batch superheated steam reactor, the advantages of this reactor design are the exothermicity of the reaction that allows for lower temperature operation and the ability to easily process wet feedstocks, such as fibers collected from laundry.

[0065] HTC demonstrates a highly practical and sustainable method as it requires low temperatures, produces versatile products, and is suitable for treating wet feedstock, which is essential for microfiber / nanofiber waste recovered from an aqueous environment. HTC can operate at a lower reaction temperature than combustion, pyrolysis, and gasification. While this requires highly pressurized water to enable hydrolysis, aromatization, dehydration, recondensation, and decarboxylation processes, high-value products are generated. Compared to traditional liquefaction, this method does not require high-pressure H2 and uses water as a hydrogen donor for the reaction. The inventors have shown that by using textile microfibers / nanofibers as feedstock, the surface area increases, thus improving the efficiency of the HTC reaction. The inventors have observed the nanofabrication of fibers (i.e., the conversion from solid to solid), which means that they can achieve a more energy-efficient conversion by using microfiber / nanofiber waste.

[0066] The inventors conducted a temperature screening analysis of superheated steam carbonization on actual textile microplastic / nanoplastic waste. Surprisingly, this study revealed that HTC performed on actual textile microplastic / nanoplastic waste under certain conditions produces not only carbon materials such as carbon nanotubes but also other types of carbon materials such as graphite, graphene, carbon fiber, and amorphous carbon. This new application of HTC advantageously converts hazardous waste into useful products while retaining carbon in the solid phase, thus avoiding greenhouse gas emissions.

[0067] Furthermore, the inventors optimized the process (i.e., determined the optimal temperature and residence time experimentally) to target specific products according to the desired results. For example, at a temperature of approximately 250 °C, potentially biocompatible and harmless amorphous carbon is formed. However, when the temperature rises to approximately 300 °C, carbon fibers composed of graphite are produced.

[0068] These experiments were conducted in the absence of a synthetic catalyst. However, the presence of iron and silica impurities from the actual washing machine on the collected microfibers suggests the occurrence of an autocatalytic reaction. This then indicates that a catalyst may not be a prerequisite, but its presence can promote and accelerate the reaction.

[0069] The inventors have successfully demonstrated that it is possible to manipulate the outcome of the process solely by adjusting the temperature and pressure. This ability to control the reaction enables the production of either harmless carbon for disposal or valuable nanomaterials with benefits. Furthermore, the incorporation of a solid catalyst can further improve the selective production of specific carbon nanomaterials such as nanotubes.

[0070] Preferably, the HTC reaction can be carried out in a temperature range between 50 °C and 650 °C. Preferably, the HTC reaction is carried out in a temperature range between 100 and 600 °C, between 150 and 550 °C, between 200 and 500 °C, or between 250 and 450 °C. Preferably, the HTC reaction is carried out in a temperature range between 300 and 440 °C, between 320 and 430 °C, between 330 and 420 °C, or between 340 and 410 °C, or between 350 and 400 °C.

[0071] In a preferred embodiment, the HTC reaction is carried out in a temperature range between 150 °C and 350 °C, more preferably between 175 °C and 325 °C, and most preferably between 195 °C and 305 °C.

[0072] Preferably, the HTC reaction is carried out in a temperature range between 150 °C and 250 °C, more preferably between 175 °C and 225 °C, and most preferably between 190 °C and 210 °C. Preferably, the HTC reaction is carried out at a temperature of about 200 °C.

[0073] Preferably, the HTC reaction is carried out in a temperature range between 200 °C and 300 °C, more preferably between 225 °C and 275 °C, and most preferably between 240 °C and 260 °C. Preferably, the HTC reaction is carried out at a temperature of about 250 °C.

[0074] Preferably, the HTC reaction is carried out in a temperature range between 250 °C and 350 °C, more preferably between 275 °C and 325 °C, and most preferably between 290 °C and 310 °C. Preferably, the HTC reaction is carried out at a temperature of about 300 °C.

[0075] The HTC reaction can be carried out with a residence time between 15 minutes and 24 hours. Preferably, the HTC reaction has a residence time between 30 minutes and 23 hours, 1 to 22 hours, 2 to 21 hours, 3 to 20 hours, 4 to 19 hours, 5 to 18 hours, or 6 to 17 hours. Preferably, the HTC reaction has a residence time between 7 and 16 hours, 8 to 16 hours, 9 to 15 hours, 10 to 14 hours, 11 to 13 hours, or about 12 hours.

[0076] In a preferred embodiment, the HTC reaction is carried out with a residence time between 1 and 8 hours. More preferably, the HTC reaction is carried out with a residence time of 1 hour, 4 hours, and / or 8 hours.

[0077] The HTC reaction can be carried out at a pressure that varies depending on the temperature. For example, a pressure of 22 bar can be used at 200 °C, while a pressure of over 99 bar can be used at 350 °C. Thus, in one embodiment of the present invention, the HTC reaction can be carried out at a pressure between atmospheric pressure and 200 bar, or between 5 bar and 200 bar. Preferably, the HTC pressure is carried out at a pressure between 15 and 150 bar, 20 to 150 bar, 30 to 150 bar, or 40 to 150 bar.

[0078] The HTC pressure is carried out at a pressure between 20 and 100 bar. Most preferably, the HTC pressure is carried out at a pressure of 20, 40 and / or 99 bar.

[0079] In a preferred embodiment, the HTC reaction is carried out at a temperature between about 150 °C and 250 °C (preferably 200 °C), a pressure between about 5 and 30 bar (preferably 20 bar), and a residence time of at least 1 hour.

[0080] In a preferred embodiment, the HTC reaction is carried out at a temperature of about 200 °C and 300 °C (preferably 250 °C), a pressure between about 30 and 50 bar (preferably 40 bar), and a residence time of at least 1 hour.

[0081] In a preferred embodiment, the HTC reaction is carried out at a temperature of about 250 °C and 350 °C (preferably 300 °C), a pressure between about 90 and 110 bar (preferably 99 bar), and a residence time of at least 1 hour.

[0082] The method may include the use of a purging gas during the HTC process to purge any air that may be present from the reactor. The purging gas may be an inert gas, such as nitrogen or argon.

[0083] In a preferred embodiment, however, the purging gas is nitrogen.

[0084] The HTC reaction can be carried out with or without a catalyst, i.e., catalytic HTC or non-catalytic HTC, respectively.

[0085] Thus, in one embodiment, the HTC reaction may include a non-catalytic HTC reaction. The inventors have shown that as a result of the use of a non-catalytic HTC reaction, non-biodegradable textile microfibers and / or textile nanofibers are converted into amorphous / bio-compatible carbon nanomaterial products.

[0086] Preferably, when actual textile waste is used as the starting material, the HTC reaction is a non-catalytic HTC reaction.

[0087] In another embodiment, the HTC reaction may be a catalytic HTC reaction.

[0088] In embodiments where HTC is a catalytic HTC reaction, the catalyst may be introduced into the reactor before, simultaneously (i.e., mixed with them), or after the textile microfibers / nanofibers. Preferably, the catalyst is introduced simultaneously with the textile microfibers / nanofibers.

[0089] The catalyst used in the catalytic HTC reaction can be as described herein with respect to the pyrolysis reaction. Thus, in one embodiment, the catalyst may be a single or multi-metal catalyst. Preferably, the catalyst is a multi-metal catalyst. The multi-metal catalyst can be selected from the group consisting of Ni-Mg, Ni-Fe, Ni-Mg-Al, Ni / γ-Al2O3, Ni / α-Al2O3, Fe / γ-Al2O3, Fe / α-Al2O3, and Ni-Fe / γ-Al2O3.

[0090] In a preferred embodiment, however, the catalyst is Ni-Fe, a bimetallic catalyst. The catalyst may be supported on a support composition.

[0091] As shown in Figure 3, several different products can be produced by the methods of the present invention, e.g., by pyrolysis or superheated steam carbonization. In particular, and more importantly, two important products, namely high-value carbon and hydrogen, are produced using the two methods described herein, and the methods enable higher yields and higher quality of these final products.

[0092] Carbon nanomaterials such as CNT, carbon nanofiber (CNF), carbon nanosheet (CNS), cup-stacked carbon nanotube (CS-CNT), and hollow carbon sphere (HCS) have been produced from plastic waste. However, until now, it has been impossible to produce carbon nanomaterials from textile microfibers and nanofibers.

[0093] Thus, in a preferred embodiment, the carbon nanomaterial produced by the method of the present invention can be selected from the group consisting of carbon nanofiber (CNF), carbon nanosheet (CNS), carbon nanotube (CNT), cup-stacked carbon nanotube (CS-CNT), hollow carbon sphere (HCS), quasi-crystalline carbon nanoparticles, graphite, or graphene.

[0094] These carbon nanomaterials have a wide range of utilities including in batteries, solar cells, and medical devices, and they can also be isolated for subsequent use. Carbon nanotubes (CNT) have attracted great interest due to their thermal stability, excellent thermal and electrical conductivity, high mechanical strength, high elasticity, excellent tensile strength, flexibility, and semi-conductive properties. CNTs have found use in the automotive field where they are used as conductive polymers, for plastic reinforcement, as catalyst materials, etc. Further, CNTs are used as catalysts or catalyst supports in various essential scientific fields such as energy production and storage, electronics, and pharmaceuticals. Chemical vapor deposition of synthetic hydrocarbons is the most common technique for producing CNTs.

[0095] Carbon nanotubes are made of a carbon-bonded material, namely graphene, in which carbon atoms are tightly organized in an atomic-scale honeycomb (hexagonal) pattern. CNTs are cylinders made of rolled-up graphene sheets and offer potentially substantial revenues for upscaling the scheme. Various types of single-walled (SWCNT), double-walled (DWCNT), and multi-walled carbon nanotubes (MWCNT) are envisioned to be produced by the carbon nanomaterial products resulting from the methods described herein.

[0096] The most established methods for synthesizing CNTs use hydrocarbon process gases at vacuum or atmospheric pressure. However, these methods currently used to produce CNTs are energy-intensive, not environmentally friendly due to gas emissions, and costly. Thus, the price of the material is very high. Therefore, more sustainable and cost-effective methods for manufacturing carbon nanomaterials (CNM) are of great business interest. Advantageously, the methods described herein address these issues.

[0097] In one embodiment, the method produces hydrogen in addition to carbon nanomaterials.

[0098] Advantageously, hydrogen gas (H2) plays an important role in our current energy landscape and its use will become increasingly widespread as an energy carrier in the future. Its applications as a coolant, energy carrier, and rocket propellant are found in the petrochemical and semiconductor industries. All of the thermal conversion technologies for textile microfiber and nanofiber upcycling described herein enable the production of H2, while polymer chemical upcycling focuses only on producing hydrocarbon products. Processes devised for selective hydrogen production require the development of robust catalysts with stable activity and mechanical integrity at various potential operating conditions and reactor geometries as described above.

[0099] Currently, due to the rising greenhouse gas emissions and the rapid increase in the use of renewable energy sources for power generation in recent years, the production of green hydrogen is expected to increase significantly over the next few decades. Hydrogen can be used as a storage medium for renewable energy, in which case hydrogen is considered "green hydrogen" that helps balance energy production and demand while assisting in decarbonizing energy systems, especially in transportation and industrial heating applications.

[0100] The environmental benefits of hydrogen utilization depend significantly on the technology and primary sources used to produce hydrogen. Therefore, it is important to establish scalable low-emission hydrogen production technologies that reduce costs and produce hydrogen on a global scale. Most hydrogen is produced using the steam reforming of methane (SRM) route, which is low in cost and high in environmental impact. Since steam reforming of methane is the most established and cheapest industrial technology for hydrogen production, most hydrogen is produced by steam reforming of methane. As a result, 900 Mt of CO2 is emitted annually due to global hydrogen production.

[0101] Therefore, the methods disclosed therein further provide means for producing hydrogen without negatively impacting the environment. Furthermore, these methods simultaneously remove harmful nanoplastic waste from the environment.

[0102] Various colors are used to distinguish various methods of hydrogen production based on the main energy sources and the levels of greenhouse gas (GHG) emissions [

[0158] ]. Currently, most of the hydrogen is gray hydrogen. Gray hydrogen represents hydrogen produced without carbon capture, utilization, or storage (CCUS) by steam reforming of natural gas or coal. The main drawback of gray hydrogen is that a large amount of CO2 is emitted during hydrogen production, which is predicted to be approximately 830 Mt of CO2 per year. Blue hydrogen is hydrogen produced from fossil fuels with carbon capture and storage. Hydrogen production plants currently only need to install CCUS devices to be eligible as blue hydrogen. The exact amount that must be captured has not been specified. When applied to SRM, recovery rates of up to 90% including post-combustion CO2 capture have been recorded. Blue hydrogen is currently regarded as a technology that serves as a bridge between green hydrogen and a complete transition to green hydrogen.

[0103] Green hydrogen is hydrogen produced electrochemically from water using renewable energy sources. This type of hydrogen is particularly valuable as we move towards a more sustainable energy and transportation system. Although hydrogen production from nuclear energy is not strongly advocated in the European hydrogen program, it could be a viable option in other parts of the world such as China and Russia. This is sometimes called "purple hydrogen" and is produced electrochemically using electricity generated from nuclear power plants.

[0104] In contrast to the conventional methods mentioned hitherto, the by-product of turquoise hydrogen via methane pyrolysis is solid carbon. The by-product can be used in subsequent manufacturing processes, or can be more easily stored, resulting in a lower carbon footprint. Nevertheless, it has only recently attracted attention to produce hydrogen mainly by thermal conversion. Pyrolysis is not yet commercially competitive with steam reforming of methane (SRM) in terms of hydrogen production, but there are also examples of large-scale commercial applications where the carbon product is solid. The hydrogen produced by the technology considered in this disclosure can be classified as turquoise hydrogen, which is produced by thermal conversion of plastics and simultaneously produces low emissions. This is a way to recycle or upcycle residues that currently damage the environment and take decades to decompose naturally. If the process can be powered by a low-emission energy source, the carbon emissions associated with hydrogen production can be further reduced.

[0105] Accordingly, in one embodiment, the hydrogen obtained is turquoise hydrogen (when synthetic microfibers and / or nanofibers are used as feedstock) or green hydrogen (when natural microfibers and / or nanofibers are used as feedstock), or a combination thereof.

[0106] Low-carbon hydrogen production technologies are essential for a decarbonized economy. Waste valorization technologies should be developed in line with the hydrogen economy vision, and the present invention meets these goals.

[0107] As described herein, various embodiments of the method of the first aspect convert non-biodegradable textile microfibers and / or textile nanofibers into biodegradable and / or amorphous / bio-compatible carbon nanomaterial products. This applies to both pyrolysis and thermal decarbonization when used in the absence of a catalyst. Accordingly, the inventors believe that they are the first to devise a method for converting non-biodegradable textiles into biodegradable and / or bio-compatible waste.

[0108] Accordingly, in a second aspect of the present invention, there is provided a method for converting non-biodegradable textile microfibers and / or textile nanofibers into biodegradable and / or biocompatible waste, the method comprising thermally cracking the textile microfibers and / or textile nanofibers under conditions suitable for converting the textile microfibers and / or textile nanofibers into biodegradable and / or biocompatible waste.

[0109] Advantageously, the inventors have demonstrated that the methods disclosed herein can be used, without a catalyst, to convert textile microfibers and nanofibers into solid carbon masses that are readily biodegradable and / or biocompatible.

[0110] Thus, in one embodiment of the method, the thermal cracking of the textile microfibers and / or textile nanofibers comprises pyrolysis to effect the thermal cracking. Preferably, the pyrolysis is carried out in the absence of a catalyst.

[0111] In another embodiment of the method, the thermal cracking of the textile microfibers and / or textile nanofibers comprises hydrothermal carbonization (HTC) to effect the thermal cracking. Preferably, the hydrothermal carbonization is carried out in the absence of a catalyst.

[0112] Preferably, the biodegradable and / or biocompatible waste is a carbon by-product. The carbon by-product can be solid.

[0113] When the carbon by-product is a solid carbon compound, the solid carbon by-product can be amorphous or crystalline low surface area carbon.

[0114] The non-catalytic pyrolysis and non-catalytic hydrothermal carbonization can be carried out as described herein with respect to the methods of the first aspect.

[0115] In a third aspect of the present invention, an apparatus for implementing the method according to any of the first or second aspects is provided.

[0116] The apparatus is preferably configured to thermally crack textile microfibers and / or textile nanofibers under conditions suitable for converting them into carbon nanomaterials.

[0117] The apparatus may comprise a furnace or a heat exchanger. The apparatus may comprise a reaction vessel in which the thermal cracking reaction takes place.

[0118] The thermal cracking of textile microfibers and / or textile nanofibers can be carried out by pyrolysis. In this embodiment, the apparatus preferably comprises a fixed bed continuous flow reactor and optionally a condenser.

[0119] The thermal cracking of textile microfibers and / or textile nanofibers can be carried out by hydrothermal carbonization (HTC). In this embodiment, the apparatus preferably comprises a batch reactor equipped with temperature and pressure controllers.

[0120] All of the features described in this specification (including any of the accompanying patent claims, abstract and drawings), and / or all of the steps of any method or process so disclosed, may be combined in any combination, except combinations in which at least some of such features and / or steps are mutually exclusive, with any of the above aspects.

[0121] For a better understanding of the present invention and to show how its embodiments can be carried out and take effect, reference is made hereinafter, by way of example, to the accompanying drawings.

Brief Description of the Drawings

[0122]

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Mode for Carrying Out the Invention

[0123] [Examples] The present invention relates to the direct conversion of microstructured and / or nanostructured waste fibers into microstructured and / or nanostructured carbon (possibly including solid-to-solid conversion), and the conversion of microfiber and / or nanofiber waste into harmless (biocompatible or biodegradable) carbon. Thus, the present inventors have developed and optimized a thermal conversion method (i.e., thermal cracking) that enables the conversion of non-biodegradable textile microfibers and nanofibers into high-value and high-quality carbon nanomaterial products and hydrogen. In a first embodiment of the method, the present inventors optimized catalytic and non-catalytic pyrolysis processes using microfibers and nanofibers of cotton and PET. In a second embodiment of the method, the same starting materials were then subjected to a superheated steam carbonization process. Each step of these two methods was optimized to achieve a higher yield of the resulting product. After testing various catalyst combinations, the present inventors carefully selected the optimal catalyst and / or catalyst combination for use in the various processes discussed below.

[0124] Starting materials (textile microfibers and / or nanofibers) As a proof of concept, heat conversion experiments were conducted using natural fiber cotton and synthetic fiber polyester as starting materials. These materials are commonly used in the textile industry. Plain interlock fabrics without finishing were prepared by incorporating cotton. The spun yarns contained 100% cotton and 100% polyester. The horizontally knitted interlock structure was produced on a 24 cut circular knitting machine (24 needles / inch). The fabric was knitted using staple fiber-derived spun yarns with a size of 40 / 1 Ne (English cotton count, a single yarn of 40×840 yards, weighing 1 pound).

[0125] Alternatively, actual textile microfiber / nanofiber waste was used. These highly heterogeneous samples were provided by the Xeros company. As seen in Figure 18, two different textures called "hard" and "woolly" were identified. The "hard" samples contained aggregated textile microfibers collected from the washing machine filter and showed a homogeneous color and texture. The "woolly" samples consisted of soft textile microfibers collected from the dryer filter and had different colors due to textile dyeing.

[0126] [Example 1] Pretreatment of the starting textile materials As a pretreatment, the fabrics were washed with sodium hydroxide to remove impurities such as wax, fat, pectin, protein, and organic acids from the fibers and improve the wettability of the fabrics. Furthermore, the cotton fabrics were also bleached. These fabrics were dyed in different colors (cotton was purple and polyester was pink) (Figure 5)

[97] . Tables 2, 3, and 4 summarize the chemical element compositions and morphological characteristics of the microfibers and nanofibers obtained from the pretreatment of the textiles. Subsequently, the microfibers and nanofibers were used in the heat conversion experiments discussed below.

[0127] For the actual waste samples, the experiment was standardized by identifying seven different regions in the "fluffy" samples, using homogeneous samples, selecting equal amounts of each of the seven regions, and then grinding and mixing them using a endless screw. In contrast, since the hard samples were considered to be homogeneous, an endless screw was used to break up the aggregates.

[0128] The reaction was carried out using a mixture containing equal amounts of each of the "hard" and "fluffy" samples.

[0129] [Table 2]

[0130] [Table 3]

[0131] [Table 4]

[0132] [Example 2] Catalyst Preparation The bimetallic catalyst Ni-Fe was prepared in a molar ratio of 1:3 and used in subsequent thermal conversion experiments. The wet impregnation synthesis method was selected for consideration below over other approaches not only because it requires fewer preparatory steps but also because it is commonly utilized for supported catalysts and typically results in the active material. The metal loading was 10 wt% and the support loading was 90%. Together, these form a heterogeneous catalyst.

[0133] First, the required amounts of metal precursors, (Ni(NO3)2·6H2O) and Fe(NO3)3·9H2O, were dissolved in ethanol and added to gamma Al2O3, the support. Subsequently, the mixture was stirred for 4 hours at room temperature using a magnetic stirrer to homogenize the suspension. Second, the excess ethanol was removed in a rotary evaporator under reduced pressure (50 °C and 150 mbar), and the material was dried in an oven at 80 °C for 12 hours. The final step of the method was calcination at 800 °C (10 °C / min ramp) for 3 hours.

[0134] [Example 3] Pyrolysis - Catalytic Method The catalytic pyrolysis process of textile microplastics and nanoplastics was carried out in a one - stage fixed - bed reactor. The reaction system essentially consisted of a quartz tube reactor with one temperature zone (catalytic / non - catalytic pyrolysis zone), a gas supply system, a gas product condensation system, a gas cleaning system, followed by an on - line and off - line gas measurement system.

[0135] Before each reaction, 30 mg of textile microfibers and / or nanofibers, which had been previously mixed together, and 15 mg of catalyst were loaded into the quartz reactor. High - purity argon (99.99%) was supplied as the inert gas (110 ml / min). The pyrolysis temperature was heated from ambient temperature to 500 °C in 10 °C increments. Once the temperature of 500 °C was reached, the reaction was maintained at 500 °C for 30 minutes. After pyrolysis, the condensable vapors were collected by a condenser. The small - branched non - condensable gases were introduced into a mass spectrometer (MS) to monitor the gas generation on - line. The signals were recorded and identified based on the atomic mass units of 2, 16, 26, 28, 30, 44 corresponding to the mainly produced gases H2, CH4, C2H2, CO + C2H4, C2H6, and CO2, respectively.

[0136] [Example 3] Pyrolysis - Non - catalytic Method The non-catalytic pyrolysis process of textile microplastics and nanoplastics was carried out as described in Example 2, except that this time it was carried out without a catalyst.

[0137] [Example 4] Hydrothermal carbonization (HTC) - Catalytic method The HTC reaction was carried out in a batch reactor (Parr series 5500 HPCL reactor equipped with a 4848 reactor controller) using a 300 mL PTFE gasket. An amount of 0.30 g of textile fibers, 50 g of water, and 0.15 g of catalyst were charged into a glass-lined steel vessel. To avoid any air entrainment, N2 was bubbled through the solution for 5 minutes at a stirring speed of 100 rpm before closing the reaction vessel. The reactor was then heated to the desired temperature (200 °C) and maintained at this temperature for 12 hours under a stirring speed of 300 rpm. The pressure of the vessel was fixed at 22 bar during each reaction according to the natural pressure generated by the solvent (water). After the reaction, the used catalyst was recovered from the liquid by filtration and subsequently dried.

[0138] [Example 5] HTC - Non-catalytic method The non-catalytic HTC process of textile microplastics and nanoplastics was carried out as described in Example 4, except that it was carried out without a catalyst.

[0139] Alternatively, the HTC - non-catalytic method was carried out as follows.

[0140] Non-catalytic HTC reaction The HTC reaction was carried out in a batch reactor (Parr series 5500 HPCL reactor equipped with a 4848 reactor controller) using a 300 mL PTFE gasket. An amount of 0.30 g of textile fiber and 50 g of water were charged into a glass-lined steel vessel. To avoid any air entrainment, N2 was bubbled through the solution for 5 minutes at a stirring speed of 100 rpm before closing the reaction vessel. The reactor was then heated to the desired temperature (200 °C, 250 °C, or 300 °C) and maintained at this temperature for the set residence time (1 hour, 4 hours, or 8 hours) under a stirring speed of 300 rpm. The pressure of the vessel was fixed during each reaction according to the natural pressure generated by the solvent (water). After the reaction, the post-reaction samples were recovered from the liquid by centrifugation and subsequently dried.

[0141] After completion of the HTC reaction, the post-reaction samples were collected and then subjected to the characterization experiments described below.

[0142] Elemental analysis Elemental analysis measurements were performed using a LECO TruSpec CHNS microanalyzer (TruSpec Micro Elemental Series). TruSpec Micro utilizes a through-flow carrier gas and a combination of individual highly selective infrared (IR) and thermal conductivity detectors to simultaneously determine CHNS. Samples of 1 - 2 mg were loaded into the sample holder. Several measurements were taken to calculate the error due to sample inhomogeneity.

[0143] Scanning electron microscope (SEM) SEM was performed on the pre- and post-reaction samples by using a JEOL JSM-7100F instrument which also has an energy-dispersive X-ray spectroscopy (EDS) analyzer. The samples were fixed to the holder using carbon paint and gold-coated to eliminate charging effects.

[0144] Transmission electron microscope (TEM) Information on the supported metal particles was obtained by operating at 200 kV with a JEOL 2100 F field emission gun microscope equipped with an energy dispersive X-ray detector, EDX. The sample was milled to powder and a small amount was suspended in an acetone solution using an ultrasonic bath. A few drops were added to a copper grid (Aname, lacey carbon 200 mesh), the solvent was evaporated at room temperature, and then introduced into the microscope. EDX mapping analysis was performed in STEM mode with a probe size of 1 nm using an INCA x-sight (Oxford Instruments) detector.

[0145] Results and discussion Thermal conversion using thermal decomposition Mass spectrometry was used to obtain data on the generation and distribution of the final products. The ion current changes over time during the thermal decomposition catalytic process of textile microfibers and nanofibers with NiFe catalyst are shown in Figs. 6A and 6B), and the real-time temperature for each test was also plotted. The oxygen contents of the cotton and PET samples are very limited, 38.2% and 29.4% respectively, and it is suggested that oxygen-containing compounds such as CO and CO2 are easily released at the start of the reaction because the oxygen groups are present inside the polymer chains. In that sense, for the signal of 28 a.u which is the superposition of C2H4 and CO, the first peak was due to the generation of CO and the second peak was due to the generation of C2H4. It has been demonstrated that the gas derived only from the thermal cracking of bulk plastic waste consists mainly of CH4 and C2H4. Although fossil-derived CH4 and C2H4 have been reported to be good carbon sources for catalytic reactions for the production of CNTs, this experiment demonstrates that it is surprisingly effective to use Ni-Fe catalyst for these carbon formation reactions when starting from microfiber and / or nanofiber textile waste. When the Ni-Fe catalyst was applied to PET and cotton textile microfibers and nanofibers, H2 was produced and the maximum value was achieved at 500 °C for both samples (see Figs. 6C and 6D). The production of H2 is delayed compared to the other gas streams produced, and it should be recognized that this may be due to the fact that complex reactions such as catalytic redox and carbon deposition occur.

[0146] Figure 7 shows the FT-IR patterns of the samples compared to the unused / used samples. The patterns indicate that the heat treatment caused a clear change in the chemical functionality, and thus the chemical composition, of both samples, providing information on the functional groups formed on the material surface, which is very important for evaluating the degree of carbonization.

[0147] 3670~2979cm -1The broad spectral bands between can indicate the presence of surface groups such as phenols, carboxylic acids, and carboxylic acid derivatives, as well as water physically adsorbed on the surface of the material. These bands are generated by O-H stretching, but usually, the signal of the O-H stretching band of carboxylic acids is strong in a wide range of spectra. The coupling bands (C=O and C-O-C) between 1800 and 1900 cm-1 are assigned to the symmetric and antisymmetric stretching of carboxylic acids derived from anhydrides, which usually appear with a 60 cm-1 shift. Furthermore, the broad band around 1000 to 1300 cm-1 may be related to the C-O stretching of ethers, lactones, and phenols.

[0148] As confirmed by TGA measurements, the plot in Figure 7 shows a clear decrease in C-O-R chemical functionality, which may be due to the decomposition of ethers, lactones, phenols, etc. The decrease or disappearance of these chemical functionalities can be seen in Figure 3. Compared with the unused sample, the destruction of the C-O-R bond is detected as indicating the carbonization process occurring during the reaction.

[0149] Figure 8 shows the TGA and DSC (thermogravimetric analysis and differential scanning calorimetry) curves of the combustion (air atmosphere) of used samples of PET (plot A) and cotton (plot B). The curves show a clear separation mark between two types of carbon species and moisture for both the cotton and PET feedstocks, that is, 1) Below 100 °C, there is moisture in the sample; 2) Between 100 and 400 °C, there is low-quality / amorphous carbon; 3) From 400 °C to 600 °C, there is high-quality / nanostructured carbon.

[0150] From the TGA-DSC plot, the various percentages present in the sample can be calculated by combining information related to weight loss and heat flow. Each positive peak in the heat flow corresponds to an exothermic reaction; due to the oxidative atmosphere, this reaction is the combustion of the different carbonaceous materials present. As can be recognized in Figure 8A, the TGA curve shows two different combustion peaks, the one at 398 °C is thought to be low-quality or more amorphous carbon, and the second peak at 451 °C is thought to be high-quality carbon nanomaterials or more crystalline carbon. Furthermore, when extracting the various weight percentages of the total sample, it is determined that approximately 70 wt% produced in the pyrolysis process carried out on the polyester textile nanofibers / microfibers used as feedstock act as a catalyst, 9 wt% is thought to be high-quality carbon, and 17 wt% is thought to be low-quality carbon. The remaining percentage up to 100% is thought to be weight loss due to moisture present in the sample. In summary, from all the carbon materials produced after the catalytic pyrolysis process, from PET as the feedstock, it can be determined that approximately 35% is converted to high-quality carbon that can contain CNTs, and 65% is converted to low-quality carbon that has a low economic value but is not environmentally harmful and can be used in other applications.

[0151] Furthermore, as can be recognized in Figure 8B, the TGA curve shows two different combustion peaks. The one at 381 °C is thought to be low-quality or more amorphous carbon, and the second peak at 471 °C is thought to be high-quality carbon nanomaterials or more crystalline carbon. Furthermore, when extracting the various weight percentages of all samples, it is found that approximately 69 wt% produced in the pyrolysis process carried out on cotton textile nanofibers and microfibers as feedstock is catalyst, 16 wt% is considered high-quality carbon, and 11 wt% is considered low-quality carbon. The remaining percentage up to 100% is considered to be the weight loss due to the moisture present in the sample. In summary, it can be determined that approximately 59 percent of all carbon materials produced after the catalytic pyrolysis process, from cotton as the feedstock, was converted to high-quality carbon that could contain CNTs, and 41 percent was converted to low-quality carbon.

[0152] By comparing both total carbon conversions, it can be determined that using cotton as the feedstock produced carbon of better quality (59% vs. 35%) than PET. This could be due to the differences in the chemical structures of both feedstocks. Cotton is a natural textile microfiber and nanofiber. This indicates that the quality of the existing carbon materials was improved by the pyrolysis process, which is supported by the previous FT-IR analysis.

[0153] The TGA measurements are in accordance with the obtained Raman measurement data. Raman spectroscopy provides insights into the properties of the carbon produced by the catalytic pyrolysis process (see Figure 9). For all of the used samples, the primary Raman spectra of cotton and PET are significantly different from the Raman spectra of the unused samples, and the appearance of two characteristic peaks can be seen at approximately 1350 and 1580. These peaks are sp 2It is typical of the combined carbon. The Raman spectrum of disordered graphite shows two modes, the G peak at 1580 - 1600 1 / cm and the D peak at 1350 1 / cm, which are often attributed to phonons with E 2g and A 1g symmetry respectively.

[0154] The presence of the D peak band indicates the presence of aromatic compounds with ring sizes larger than 6 - condensed rings. The G band involves in - plane bond stretching motion of C sp 2 atom pairs (E 2g ), and is generally called the "graphite band", while the D band provides information about morphological irregularities and defects characteristic of disordered graphite (A 1g ), and is generally called the "defect band".

[0155] As can be seen in Figure 9, the shape and position of these bands vary slightly across different used samples of cotton and PET, indicating structural differences between the carbonaceous structures produced by catalytic pyrolysis of unused samples. In particular, the D band shifts towards higher Raman shift values in the used samples of cotton, while the G band is quite stable at the same value for both used samples (cotton and PET). This phenomenon indicates the nature of both carbons produced from different samples. However, the D band, which is a double - resonance process in Raman, is closely linked to the band structure and its position provides some information about the diameter of the carbonaceous species. Due to low temperature and short pyrolysis periods, as seen in SEM micrographs, there is negligible graphitization in these samples (see Figures 10 and 11). When the number of defects increases, the D band usually moves to higher frequencies.

[0156] Raman spectra provide valuable qualitative information, while preliminary quantitative analysis yields insights into the structural development of the manufactured carbonaceous materials. In this context, the D / G ratio is semi - quantitative data derived from the Raman experiments of interest. Generally, the ratio of the intensities of these bands (D / G) is an important parameter for identifying the types of carbon generated during the thermal alteration caused by the catalytic pyrolysis process. The conversion of nanocrystalline graphite to amorphous carbon increases the D / G ratio. The D / G ratio values obtained for the used cotton and PET samples were 0.65 and 0.75, respectively. Therefore, it could be determined that the carbon produced by using cotton as the feedstock is a more crystalline and better - quality type of carbon.

[0157] To examine the morphological characteristics and structural changes of the manufactured carbonaceous materials, SEM images were generated. Figure 10A shows the SEM image obtained for the unused cotton sample, and Figure 10B shows the SEM image obtained for the used cotton sample after the catalytic pyrolysis process. By comparison, morphological changes of the sample from fiber shape to round carbonaceous materials can be observed. Similarly, Figure 11A shows the SEM image obtained for the unused PET sample, and Figure 11B shows the SEM image obtained for the used PET sample after being subjected to the catalytic pyrolysis process. The same structural changes from fibrous materials to round carbonaceous particles can be observed.

[0158] The distribution of the active metal phase of the heterogeneous catalyst and the possible juxtaposition of carbon growth during the catalytic pyrolysis process were studied using energy - dispersive X - ray spectroscopy (EDS) mapping analysis. Figure 12 shows nickel, iron, and carbon marked in blue, pink, and red, respectively, and in addition to the prominent distribution of carbon particles juxtaposed on the surface of the catalyst, it shows a homogeneous distribution of the active phases of both catalysts when cotton is used as the feedstock. Similarly, it can be observed in Figure 13, where nickel, iron, and carbon are marked in blue, yellow, and red, respectively.

[0159] Conclusions on the Pyrolysis Method After undergoing the catalytic pyrolysis process, H2 gas and two different types of carbonaceous materials were produced from textile microfibers and nanofibers using a bimetallic Ni-Fe catalyst. For comparison purposes, textile microfibers and nanofibers of two different types: cotton, a natural fiber, and PET, a synthetic fiber, were tested. At an ideal pyrolysis temperature of 500 °C, maximum H2 production was achieved. TGA, SEM, and Raman analysis confirmed that high-quality carbon was obtained from both materials (cotton and PET) used as feedstocks. In addition, it was demonstrated that more crystalline carbonaceous materials were produced from cotton microfibers and nanofibers.

[0160] Thermal conversion using hydrothermal carbonization (HTC) Figure 14 illustrates the FT-IR patterns of samples subjected to hydrothermal carbonization compared to those taken from unused / used samples. The patterns show that as a result of the heat treatment, there were distinct changes in the chemical functionality and, consequently, the chemical composition of both samples, providing information on the functional groups formed on the surface of the material, which is important for determining the degree of carbonization.

[0161] The plot reveals a significant decrease in the C-O-R chemical functionality. Thus, Figure 14 shows a decrease or disappearance of some chemical functionalities. The presence of broken C-O-R bonds when compared to the unused sample indicates that the carbonization process occurred during the hydrothermal carbonization reaction.

[0162] Raman spectroscopy provides insights into the properties of the carbon produced by the catalytic HTC process (see Figure 15). For all of the used samples, the primary Raman spectra of cotton and PET are significantly different from the Raman spectra of the unused samples. In the case of cotton, the appearance of two characteristic peaks can be observed at approximately 1350 and 1580. These peaks are sp 2Typical of combined carbon [

[0102] ]. The Raman spectrum of irregular graphite shows two modes, the G peak at 1580 - 1600 1 / cm and the D peak at 1350 1 / cm, which are often attributed to phonons with E 2g and A 1g symmetry respectively.

[0163] As shown in Fig. 15, the shape and position of these bands vary slightly across different used samples of cotton and PET, indicating the structural differences between the carbonaceous structures produced by HTC of the unused samples.

[0164] The characteristic D and G bands do not appear for the used PET samples, clearly indicating that a reaction has occurred. However, as the TGA data shows, there is some material that can be burned, although this material is not a pure carbonaceous material. It can be assumed that the material produced from HTC using PET as the feedstock is an intermediate between the unused samples and the carbonaceous material. Due to the low temperature and low pressure during the HTC process, as seen in the SEM micrographs, there is negligible graphitization in these samples (see Figs. 16 and 17).

[0165] In addition, experiments conducted on actual waste samples were analyzed. To detect the conversion in solid materials caused by variations in the temperature / pressure and residence time of the process, the properties of the carbonaceous products formed by HTC of actual textile microfibers / nanofibers were thoroughly investigated. The test temperatures were 200 °C, 250 °C, and 300 °C. When the pressure was automatically generated in a batch reactor and 50 g of water was constantly added as the reaction medium, the resulting pressures were approximately 20, 40, and 99 bar, respectively. The selected residence times were 1 hour, 4 hours, and 8 hours. Therefore, for the sake of the continuity of this study, the samples were labeled according to the temperature and residence time. For example, the carbonaceous product obtained from the reaction at 200 °C (20 bar) and a residence time of 1 hour was labeled 200-1.

[0166] In this study, the inventors performed elemental analysis to study the elemental composition and distribution in the samples. The samples were subjected to strict preparation techniques including drying, grinding, and homogenization to ensure reliable typical analysis. Elemental analysis was carried out using X-ray fluorescence spectroscopy (XRF), a non-destructive analytical technique capable of determining the elemental composition of solid, powder, and liquid samples. The elemental concentrations of important elements such as carbon, nitrogen, hydrogen, and sulfur were determined and expressed as weight percentages. The different values are summarized in Table 4. Table 4 shows the weight percentages of carbon (C), hydrogen (H), nitrogen (N), and sulfur (S) in the pre-reaction samples (fluffy and hard), as well as in the post-reaction microfibers obtained by HTC reaction at various temperatures and residence times.

[0167]

Table 5

[0168] This elemental analysis study provides valuable insights into the elemental composition of the samples. In particular, trace amounts of sulfur or nitrogen were not detected in any of the samples. To account for the high heterogeneity of the pre-reaction samples, the percentage error was calculated based on six measurements. When focusing on the carbon percentage, it was observed that it ranged from approximately 43% in the pre-reaction microfibers to approximately 70% in the post-reaction samples obtained at 300 °C with a residence time of 4 hours. Similarly, as the temperature increases, the hydrogen percentage decreases. These findings indicate that increased carbonization and dehydrogenation are promoted at higher temperatures. Furthermore, it can be concluded that the effect of residence time on the degree of carbonization is minimal.

[0169] SEM images were acquired to examine the surface morphology and microstructure of the microfibers. The SEM images provide high-resolution visualization and enable detailed analysis of the topography, particle size, shape, and surface features of the samples. The samples were carefully prepared by attaching them to conductive stubs and subsequently sputter-coating them with a thin layer of a conductive material such as gold. This coating helps to reduce the charging effect and provides enhanced conductivity during imaging. The SEM images were analyzed to extract information regarding the surface morphology of the carbonaceous products obtained under various reaction temperatures and residence times. This is shown in Figure 19.

[0170] At 200 °C, minimal changes in the morphology of the samples were observed, which can be seen to be consistent with the elemental analysis data presented in Table 4. At 250 °C, the fibers began to disappear, and amorphous carbonaceous fragments were formed. However, at 300 °C, some fibers were again observed, suggesting the production of filamentous carbon at this temperature. Therefore, it is clear that there is a "sweet spot" in the reaction temperature between 200 °C and 300 °C.

[0171] To complete the characterization study, TEM (transmission electron microscope) images and EDX (energy-dispersive X-ray) scans were used to obtain insights into the microstructure and composition of the microfibers. As shown in Figure 20, the production of valuable carbonaceous products was observed in the post-reaction textile microfiber waste after a reaction at 300 °C for 4 hours, i.e., some layers of graphite / graphene were found.

[0172] Conclusion of the superheated steam carbonization method After the superheated steam carbonization procedure, three different types of materials were produced from textile microfibers / nanofibers using a bimetallic Ni-Fe catalyst. Two types: textile microfibers and nanofibers of cotton, a natural fiber, and PET, a synthetic fiber, were studied for comparison. TGA, SEM, and Raman examinations showed that several types of amorphous carbon compounds were produced by utilizing cotton as the feedstock. When PET was used as the feedstock, the resulting material was considered to be an intermediate between the unused fiber and the carbonaceous material.

[0173] Furthermore, in the absence of a catalyst, when actual textile waste is used as the feedstock or starting material, different carbonaceous products can be targeted by adjusting the temperature during the reaction process.

Claims

1. A method for converting textile microfibers and / or textile nanofibers into carbon nanomaterials, comprising thermal cracking the textile microfibers and / or textile nanofibers under conditions suitable for converting the textile microfibers and / or textile nanofibers into carbon nanomaterials.

2. A method for converting non-biodegradable textile microfibers and / or textile nanofibers into biodegradable and / or biocompatible waste, comprising thermal cracking the textile microfibers and / or textile nanofibers under conditions suitable for converting the textile microfibers and / or textile nanofibers into biodegradable and / or biocompatible waste.

3. The method according to claim 1 or 2, comprising thermal cracking natural textile microfibers and / or nanofibers.

4. The method according to claim 1 or 2, comprising thermal cracking synthetic or semi-synthetic textile microfibers and / or textile nanofibers.

5. The method according to claim 1 or 2, wherein the textile microfibers and / or textile nanofibers are obtained from any of the textiles in Table 1, and optionally the textile microfibers and / or textile nanofibers are textile waste collected from a washing machine filter as hard textile waste and / or from a dryer filter as fuzzy textile waste.

6. The method according to claim 1 or 2, wherein the textile microfiber and / or textile nanofiber is cotton or polyethylene terephthalate (PET).

7. The method according to claim 1 or 2, wherein the textile microfibers and / or textile nanofibers are naturally formed, knitted, woven, felted, nonwoven, or optionally bonded together by mechanical, thermal or chemical treatment, and optionally the textile microfibers and / or textile nanofibers include a plastic material.

8. The method according to claim 1 or 2, wherein the textile microfiber and / or textile nanofiber has an average diameter or length between 0.1 μm and 5 mm, between 0.1 μm and 4 mm, between 0.1 μm and 3 mm, and between 0.1 μm and 2 mm.

9. The textile microfibers and / or textile nanofibers are (i) less than 750 μm, 500 μm, 250 μm, or 150 μm; and / or (ii) Less than 100 μm, 75 μm, 50 μm, or less than 35 μm The method according to claim 1 or 2, having an average diameter or length.

10. The method according to claim 1 or 2, wherein the textile microfiber and / or textile nanofiber has an average length between 0.01 mm and 0.5 mm, or between 0.02 mm and 0.3 mm, or between 0.05 mm and 0.15 mm.

11. The method according to claim 1 or 2, wherein the textile microfiber and / or textile nanofiber has an average diameter between 1 and 100 μm, or between 1 and 75 μm, or between 1 and 50 μm, or between 1 and 40 μm, or between 6 and 36 μm.

12. The method according to claim 1 or 2, wherein the thermal cracking of the textile microfibers and / or textile nanofibers includes thermal decomposition.

13. The method according to claim 12, wherein the thermal decomposition reaction is in a batch, fed-batch, or continuous manner.

14. The method according to claim 12, wherein the pyrolysis reaction is carried out in a one-stage or multi-stage reactor, which is a fixed-bed or fluidized-bed reactor.

15. The method according to claim 12, wherein the reaction is carried out in a one-stage fixed-bed reactor in the case of a dry feed, or in a batch-type superheated steam reactor in the case of a wet feed.

16. The aforementioned thermal decomposition reaction, (i) Between 100°C and 1000°C, between 200°C and 900°C, between 300°C and 800°C, between 400°C and 700°C, or between 450°C and 600°C; (ii) Between 460 and 550°C, between 470 and 540°C, between 480 and 530°C, or between 490 and 520°C; (iii) 1000°C, 900°C, 800°C, 700°C, less than 600°C, or less than 550°C; and / or (iv) 100°C, 200°C, 300°C, above 400°C, or above 450°C The method according to claim 12, which is carried out within a temperature range.

17. The aforementioned thermal decomposition reaction, (i) between 1 and 200 minutes, 1 and 175 minutes, 1 and 150 minutes, 1 and 125 minutes, 1 and 100 minutes, 1 and 75 minutes, 1 and 50 minutes, or between 1 and 25 minutes; and / or (ii) Between 25 and 200 minutes, 25 and 175 minutes, 25 and 150 minutes, 25 and 125 minutes, 25 and 100 minutes, 25 and 75 minutes, or between 25 and 50 minutes. The method according to claim 12, which is carried out to have a residence time.

18. The method according to claim 12, wherein the thermal decomposition reaction is carried out at atmospheric pressure.

19. The method according to claim 12, wherein the thermal decomposition reaction is carried out using a carrier gas that maintains an inert or carbonized atmosphere inside the reaction to prevent combustion of the feed, and preferably the carrier gas is argon or nitrogen.

20. The method according to claim 12, wherein the thermal decomposition reaction is carried out in the absence of a catalyst.

21. The method according to claim 12, wherein the thermal decomposition reaction is carried out in the presence of a catalyst.

22. The method according to claim 21, wherein the catalyst is a single-metal catalyst or a multi-metal catalyst.

23. wherein the multi-metal catalyst is Ni-Mg, Ni-Fe, Ni-Mg-Al, Ni / γ-Al ２ O ３ , Ni / α-Al ２ O ３ , Fe / γ-Al ２ O ３ , Fe / α-Al ２ O ３ , and Ni-Fe / γ-Al ２ O ３ The method according to claim 22, selected from the group consisting of

24. The method according to claim 21, wherein the catalyst is a dimetallic catalyst Ni-Fe.

25. The method according to claim 21, wherein the catalyst is supported by a support composition, and optionally the support composition is selected from the group consisting of metal oxides, zeolites, activated carbon, and alumina.

26. The method according to claim 1 or 2, wherein the thermal cracking of the textile microfibers and / or textile nanofibers comprises superheated steam carbonization (HTC).

27. The method according to claim 26, wherein the HTC process uses a solvent to adjust the pressure to desired reaction conditions, and preferably the solvent for the HTC is an organic compound or water.

28. The HTC reaction described above (i) Between 50°C and 650°C, between 100°C and 600°C, between 150°C and 550°C, between 200°C and 500°C, or between 250°C and 450°C; (ii) Between 300 and 440°C, between 320 and 430°C, between 330 and 420°C, or between 340 and 410°C, or between 350 and 400°C; (iii) 525°C, 500°C, 475°C, 450°C, below 425°C, or below 400°C; (iv) 250°C, 275°C, 300°C, above 325°C, or above 350°C; and / or (v) Between 150 and 350°C The method according to claim 26, wherein the HTC reaction is carried out in the temperature range, and optionally, the HTC reaction is carried out at a temperature of about 200°C, 250°C, or 300°C.

29. The HTC reaction described above (i) Between 15 minutes and 24 hours, 30 minutes and 23 hours, 1 to 22 hours, 2 to 21 hours, 3 to 20 hours, 4 to 19 hours, 5 to 18 hours, or 6 to 17 hours; (ii) Between 7 and 16 hours, 8 and 16 hours, 9 and 15 hours, 10 and 14 hours, 11 and 13 hours, or about 12 hours; and / or (iii) Between 1 and 8 hours The method according to claim 26, wherein the reaction of the HTC is carried out to have a residence time, and optionally the reaction of the HTC is carried out to have a residence time of 1 hour, 4 hours, or 8 hours.

30. The method according to claim 26, wherein the HTC reaction is carried out at a pressure between atmospheric pressure and 200 bar, between 5 bar and 200 bar, between 15 and 150 bar, between 20 and 150 bar, between 30 and 150 bar, between 40 and 150 bar, or between 20 and 100 bar, and optionally, the HTC reaction is carried out at a pressure of 20, 40, or 99 bar.

31. The method according to claim 26, wherein the HTC reaction includes a non-catalytic HTC reaction or a catalytic HTC reaction.

32. The method according to claim 31, wherein the catalyst is as defined in claim 22.

33. The method according to claim 1 or 2, wherein the carbon nanomaterial produced by the method is selected from the group consisting of carbon nanofibers (CNF), carbon nanosheets (CNS), carbon nanotubes (CNT), cup-stacked carbon nanotubes (CS-CNT), hollow carbon spheres (HCS), quasicrystalline carbon nanoparticles, graphite, or graphene.

34. The method according to claim 1 or 2, wherein hydrogen is produced in addition to the carbon nanomaterial.

35. An apparatus for carrying out the method according to claim 1 or 2.

36. The apparatus according to claim 35, configured to thermal crack textile microfibers and / or textile nanofibers under conditions suitable for converting the textile microfibers and / or textile nanofibers into carbon nanomaterials.

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