Production of cellulose from cotton or cotton blends

Abstract

The invention relates to a method for producing a cellulose polymer with a cellulose content of at least 92 % from textile waste material, wherein an educt of a mixture of cotton and PET with a fibre length of at the most 1 mm is treated in a reactor with subcritical water at a temperature of between 130 °C - 200 °C, particularly preferably between 160 °C - 200 °C and in a pressure range of between 1 - 25 bar, preferably between 1 - 10 bar for about 1 - 120 mins and wherein a cellulose polymer with an average degree of polymerisation of between 450 - 650 is formed.

Description

[0001] 7

[0002] Title: Manufacture of pulp from cotton or cotton blends

[0003] Applicant: EEDEN GerMan UG

[0004] The present invention relates to the production of pulp from cotton and cotton blends.

[0005] The circular economy is one of the most current topics influencing joint efforts toward a sustainable and environmentally conscious use of raw materials and energy consumption. Ranging from the question of reuse (can I still wear this?) to orderly sorting and collection, to recycling and repurposing the resulting "raw materials," many problems must be considered and then resolved. Political efforts partially support these processes, for example, through a revised EU directive addressing used textiles and their collection. A hindrance to the reprocessing and reuse of used textiles is the fact that recycling the fibers is usually more expensive than producing new ones.This is due, among other things, to the complexity of the fiber material, which in many cases consists of more than one fiber, as well as the large fluctuations in the molecular properties of cellulose, as reflected, for example, in the DP. This naturally has advantages in terms of the functionality of the materials, but when returning them to the product cycle, fiber mixtures must now be processed, which necessitates complex separation processes.

[0006] The processing of pure starting materials such as cotton into cellulose is known in the art, but the products are not of the desired quality. This is due to the use of aggressive additives and the energy-consuming processing steps. These cause the quality of the end products to suffer. The addition of acids and / or bases as catalysts or other reactants leads to unstable polymer fibers and undesirable by-products such as terephthalic acid, which are difficult to remove from the reaction mixture. In addition to purity, the decisive quality parameters of cellulose include, above all, the average degree of polymerization. Therefore, the object of the present invention is to provide a process for obtaining high-quality polymer fibers with a cellulose content of at least 90%, wherein the DP value is additionally within a specific range.

[0007] This object is achieved by a process for producing a cellulose polymer with a cellulose content of at least 90%, preferably 92%, from textile waste material. A starting material, cotton or a mixture of cotton and PET with a fiber length of no more than 1 mm, is treated in a reactor with subcritical water at a temperature of 130-180 °C and a pressure in the range of 1-10 bar for approximately 1-120 minutes, resulting in a cellulose polymer with an average degree of polymerization (DP), which can be predetermined, of 300-1000 DP, preferably 450-650. The starting material can of course also consist of pure cotton. The predetermination of the DP value plays a crucial role here, since the quality of the end materials to be produced is designed for purity within a specific DP value range.For example, lyocell is obtained from pulp with a DP value of 550-600, while viscose is obtained from pulp with a DP value of 300-700. For both, the consistency of the DP in the pulp is a guarantee for the quality of the final product. This process thus allows the DP range of the pulp to be determined in advance.

[0008] A cellulose polymer with a purity of 90%-92% or more is a high-quality starting material that can be used to create a wide variety of other high-quality products. Viscose and lyocell, as mentioned above, are examples of these fibers. Viscose is typically made from chemical pulp, which is obtained from various types of wood or cotton. The quality of this pulp differs from that used for paper production, as the latter requires pulp with a specific chain length and purity. Lyocell fibers are known for their high dry and wet strength; they are soft and absorb moisture very well. The textiles made from them have a "smooth" and "cool" feel with a flowing drape. They are virtually wrinkle-free and can be washed and dry-cleaned.To ensure these characteristics, only extremely pure raw materials can be used in production. Furthermore, the DP values ​​must be adjusted to ensure seamless further processing by the fiber manufacturer. They should meet the fiber-specific requirements and be within a DP range predefined by the fiber manufacturer. Depending on the viscose fiber, this ranges between 300 and 700. Pulp for lyocell fibers has a DP of 500–700, or even better, 550–600.

[0009] The polymer fiber produced in this process according to the invention is therefore an "upcycling" product. The fiber length of the starting material, which is no more than one millimeter, simply means that the starting material has been previously comminutioned. This facilitates the subsequent reaction. The fiber length also serves to standardize the process parameters, which must be selected differently for different fiber lengths. We will discuss this again later. It has been shown that the process according to the invention is particularly advantageous for the production of high-purity pulp with a predefined DP in the range of 300-1000 from textile waste. In a very special embodiment, fiber lengths of the starting material in the range of 0.2 mm to 8 mm are used. The shorter fibers mix better in the water.

[0010] The process relies on the use of a reactor with subcritical water. Subcritical water refers to liquid water at temperatures between the atmospheric boiling point, i.e., 100 °C, and the critical temperature, i.e., 374 °C. Under these conditions, water exhibits special, otherwise unusual properties. Its density, dielectric constant, ion concentration, diffusivity, and solubility are affected in the subcritical state. The ionization constant increases with temperature in this state and is approximately three orders of magnitude higher than that of water in its normal state. The dielectric constant drops from 80 to 20. Such a drastic change in physical properties ensures rapid dissolution of the cross-linking in the textile waste material, which consists of cotton and PET.

[0011] This is partly due to the fact that the water assumes a different pH value due to the increase in the ionization constant. This is sufficient to break down the cellulose chains of the cotton fibers and thus achieve a targeted DP adjustment to a target DP range. This shows that the resulting pulp, in addition to the DP, also exhibits good dissolving properties and high purity.

[0012] The treatment of materials in an aqueous system at high temperature and pressure is called a hydrothermal process. The reactor is therefore a hydrothermal reactor. The temperature used in the reactor is in the range between 130°C and 200°C, or more preferably, 160°C and 200°C. The pressure is regulated between 1 and 25 bar. The reaction time is between 1 and 120 minutes. With the set parameters, the reactor can attack the starting material, i.e., the textile waste, at the fiber level and weaken the bond strength between the fibers or even separate the adjacent and interwoven fiber strands. Any polyester residues that may be present are also decomposed at the same time. The degree of polymerization of the products can also be influenced by the operating parameters that determine the operation of the reactor.It should be noted that subcritical water is a non-toxic, environmentally friendly, and cost-effective solvent. It is naturally pH-neutral and therefore non-aggressive.

[0013] The product, the cellulose polymer, not only exhibits a purity of at least 90%-92%, but also has an average degree of polymerization (DP) of 300-1000 or even 450-650. If the reaction is very well controlled, the product even has an average degree of polymerization (DP) of 550-600. This degree of polymerization indicates a homogeneous reaction, with the reactant being degraded to such an extent that it can be optimally processed further into lyocell. The degree of polymerization indicates the number of basic building blocks per polymer molecule. It is identical to the quotient of the average molar mass of the polymer and the molar mass of its repeating unit (the monomer unit). The exact number can usually only be an average value for the sample under consideration. This average value is referred to as the average degree of polymerization (DP).For fiber-forming polymers, it is an important parameter for processing and usage properties.

[0014] The degree of polymerization of a sample is usually determined via its molar mass. There are a number of methods for this, e.g. GPC, some procedures for determining colligative properties (such as cryoscopy, vapor pressure osmosis, etc.), as well as viscometry, light scattering, etc. Other methods are also technically important, but they require precise calibration of the sample system. The melt flow index method is worth mentioning here. For example, the viscosity of a plastic melt increases with increasing degree of polymerization; the average value can be determined indirectly (i.e., relative to a chemically comparable standard) using the MFL method. The degree of polymerization and the spatial geometric distribution of the monomers in the molecule (i.e., the stereochemical arrangement of the molecular branches) have a significant influence on the physical and, in particular, the mechanical properties of a polymer.However, according to Staudinger, fiber strength does not change proportionally with the degree of polymerization. For example, the DP for cotton is 3000, for viscose fibers 250-700, for polyamides 100-180, and for polyester 130-220. Determining the average degree of polymerization is particularly important for cellulose fibers because it allows chemical damage to these fibers to be numerically characterized. In a favorable case, the cotton / PET blend consists of a composition with a PET content of up to 5%. However, it does not pose a problem for the present inventive process if the foreign fiber content consists of another fiber rather than PET. These foreign fibers are also processed without affecting the final product. Tests with a foreign fiber content of up to 5% show no impairment of the process or the final product at all.If the foreign fibers are made of elastane or PES / PET, they will be lost in the final product. It is also irrelevant whether the fiber blend contains dyed components. Azo dyes, sulfur dyes, diphenylmethane dyes, thiazole dyes, triphenylmethane dyes, nitro dyes, anthraquinone dyes, nitroso dyes, indigoid dyes, quinoline dyes, indigosols, acridine dyes, quinoneimine dyes, cyanine dyes (azines, oxazines, thiazines), and phthalocyanine dyes are completely unproblematic. These are the most commonly used textile dyes currently. In some processes, the dyes are removed from the reactant in an upstream step. However, this is not the case in the present process. Furthermore, the reactant can have a metal content of > 10 ppm. Both small metal residues and large metal contents are reliably removed from the reactant.However, alkaline earth and alkali metals, as well as many heavy metals, are responsible for clumping in the reaction mixture. This clumping can clog the filter and thus impair the reaction. It has also been observed that heavy metals have a catalytic effect and thus cause undesirable side reactions. However, if the heavy metals are present in concentrations below 10 ppm, the reaction is not impaired. The addition of antioxidants can be used to support the reaction at high heavy metal levels. Likewise, the process according to the invention is not impaired by the presence of the reactant in suspension form. If the reactant has a degree of polymerization of more than 700, the product has the stated DP of 450-650. The process thus enables the reduction of the cellulose fibers in the textile waste material, the dissolution of the cellulose fibers from the textile waste material, or both.

[0015] The catalyst-free reaction process is important. In known processes, the existing fibers are usually broken down using acids or bases, the DP is adjusted, and then further processed. The disadvantage of this pH-adjusting substance addition is the adverse effect on the final product caused by the aggressive chemicals. These are then removed from the reaction mixture in an additional step, but the damage has already occurred. The additional cleaning step, of course, also causes effort, expense, and is very time-consuming. Contamination also complicates solvent disposal. Therefore, the catalyst-free reaction in the inventive process represents a significant step toward a sustainable, environmentally friendly, and, at the existing reaction temperatures, energy-saving process for textile recycling. pH neutralization of the pulp is no longer necessary.The pH value throughout the process is approximately 5.0 to 9.0. The reaction takes place in subcritical water at temperatures between 130 and 180°C. The reaction time is between 1 and 120 minutes, and a pressure of 1 to 25 bar is applied. The pH-neutral reaction medium (values ​​of 5 to 7 have been measured here) has a solid / liquid ratio of 1:10 to 1:20. No acids, bases, or other catalysts are added. The process takes place in the absence of oxygen. However, controlled addition or admission of oxygen can cause oxidative changes, particularly in the DP value. Furthermore, it has been shown that even lower applied pressures of up to 1 or 10 bar are sufficient to allow the process to proceed effectively.

[0016] Therefore, only filtering, washing, pressing, and drying by evaporation (to a dry matter content of approximately 90%) are necessary to obtain the product. No pH neutralization step is performed on the pulp; this is unnecessary. The product is then simply prepared for further use.

[0017] Regarding the fiber length of the reactant, it should be noted that the length understandably influences the stirrability of the mixture. This also affects the reaction. Thus, with a reactant fiber length of 1 mm and a weight fraction of 2.5 wt.%, the mixture is stirrable; with a weight fraction of 5 wt.%, it is difficult to stir; and with a weight fraction of 7.5 wt.%, it is no longer stirrable.

[0018] However, for a reactant fiber length of 0.2 mm, the mixture is easily stirrable at a weight fraction of 2.5 wt.%, easily stirrable at a weight fraction of 5 wt.%, and still stirrable at a weight fraction of 7.5 wt.%.

[0019] The cutting mill used, namely the Fritsch PULVERISETTE 19 Universal Cutting Mill (5000 watts, 400V, 3~ 50 / 60Hz, 13Nm, speed: 300-3000rpm, sieve insert size: 0.24mm), has proven particularly suitable. However, the use of other cutting mills is also possible.

[0020] In the following, non-limiting embodiments of the present invention are discussed.

[0021] Old textiles consisting of cotton with a PE content of 5% are sorted and cut to a fiber length of 1 mm. This relatively short starting material length was initially only used to compare the many experiments and test series with one another. Naturally, the length of the starting materials plays a role in the reaction behavior during the ongoing process, simply due to the different surface areas. The shredding device can be a completely standard textile shredder. However, the lengths of the torn and reduced-size textile waste should be as uniform as possible. As already mentioned, the degree of dyeing of the waste is irrelevant. Almost all textile dyes are dissolved out during the ongoing process. Even the presence of the starting materials as a suspension, i.e., finely distributed in a liquid, is not detrimental to the process according to the invention.

[0022] The starting material can have an average degree of polymerization of more than 700 and still be easily processed. The higher the degree of polymerization of the starting product, the more complex the depolymerization process takes place. Average degrees of polymerization of 300–1000, usually 450–650, or even 550–600, are ultimately achieved. The more homogeneous and precise the DP of the final product is, the better it can be further processed. Therefore, no preparatory reaction step is necessary in this process according to the invention.

[0023] The starting materials were then filled into the high-pressure laboratory reactor type BR-300, known as the Berghof highpreactor. With a maximum achievable temperature of 300°C and a maximum pressure build-up of 200 bar, this reactor is perfectly adequate for the present inventive process. Among other things, the following six experiments were conducted in the reactor.

[0024] The average degrees of polymerization shown in the table below were measured at a solid-liquid ratio of 1:20 and temperatures ranging from 160°C to 200°C, reaction times from 60 minutes to 180 minutes, and a severity factor ranging from 3.54 to 5.20. The severity factor is a coefficient of severity for the subcritical liquid-hot water pretreatment of products, in this case used textiles. Mathematically speaking, the severity factor is the integral of the steam temperature and the exposure time. It is therefore a measure of the severity or intensity of the overall reaction conditions in a chemical reaction; in our case, the temperature and pressure. The time and temperature can be seen in the table. The reaction pressure is between 1 and 10 bar. The solid-liquid ratio in the tests ranged from 1:10 to 1:20.

[0025] No catalyst was added. This is a catalyst-free reaction process. The final mass is filtered, washed, pressed, and residual liquid is evaporated to a dry matter content of approximately 90%. It should be noted again that any additional steps, including pulp neutralization, are unnecessary. The product was then cut to size. The product now exhibited the following properties:

[0026] • Cellulose content >90% - 92%

[0027] • Average degree of polymerization 300 — 1000, better still 450-650, in the optimal case: 550 — 600. It should be noted that the different end products require different DP values.

[0028] • Uncolored / whiteness of >80 (according to ISO)

[0029] • Metal content: <10-20 ppm

[0030] Due to the small number of reactants, the byproducts that would otherwise be produced are also found only in small numbers and low concentrations. These include a few oligomers, glucose, fructose, and xylose. The concentrations of these substances are negligible, approaching 0 g / L.

[0031] In the course of individual experiments and consultations with the various processing companies, it has become clear that the following requirements are also met by the raw materials, namely:

[0032] 1. A cellulose content >92%,

[0033] 2. a silicate content <80ppm

[0034] 3. a calcium content <80ppm,

[0035] 4. an iron content < lOppm and

[0036] 5. the moisture content 10%

[0037] The values ​​apply to viscose and even to lyocell as the final product.

[0038] Another processing plant stated the following:

[0039] - high purity = cellulose content (alpha cellulose / long-chain cellulose) >90%

[0040] - small amounts of hemicellulose: <5%

[0041] - small amounts of lignin: <0.1%

[0042] - small amounts of heavy metals: < lOppm

[0043] The x-axis shows the temperature / time reaction pair, while the y-axis shows the degree of polymerization (DP). It shows exactly which parameters can be used to adjust the DP values.

[0044] The average degree of polymerization was determined according to the corresponding DIN standard.

[0045] Here,

[0046] • the cellulose is dried overnight in an oven at 60°C,

[0047] • then 50mg of cellulose is transferred into a 50ml rotary-closing container (c=lg / L)

[0048] • Next, 2-4 copper coils and approximately 20 small ceramic balls are added. The copper coils serve as antioxidants, and the ceramic balls displace dead volume in the container.

[0049] • 50ml of Cuoxam solution is added to the container.

[0050] • The container is closed and shaken.

[0051] • The container is placed on a vibrating plate overnight so that the cellulose dissolves completely.

[0052] • For the DP measurement, the viscometer (e.g. Ubbelohde) is placed at 25°C (+ / - 0.1°C) using a water bath thermostat and

[0053] • The cellulose solution is filtered through a glass filter (glass frit por. 1) before measurement.

[0054] • Then 20ml of the filtrate is filled into the viscometer.

[0055] • The solution now rests in the viscometer to allow temperature adjustment.

[0056] • The solution is then pulled up (e.g. with a Peleus ball) and the flow time is stopped.

[0057] • The flow velocity is measured 4 times per sample and the average value is calculated.

[0058] • The specific viscosity is calculated from this.

[0059] • The DP is calculated using the specific viscosity. 77

[0060] Further experiments were conducted in which a pre- and / or post-vapor pressure explosion was used to increase the surface area of ​​the reactant and also reduce the degree of polymerization. Furthermore, the reactivity of the cellulose is subsequently also increased. These vapor pressure explosions impressively supported the process.

Claims

Title: Production of pulp from cotton or cotton blends Applicant: EEDEN GerMan UG Patent claims 1. A process for producing a cellulose polymer with a cellulose content of at least 90%, preferably 92%, from textile waste material, wherein • a starting material made from a mixture of cotton and PET with a fiber length of no more than 60 mm - 1 mm • is treated in a reactor with subcritical water at a temperature of 130–200 °C, particularly preferably 160–200 °C and a pressure in the range of 1–25 bar, preferably 1–10 bar, for about 1–120 min and wherein • a cellulose polymer with an average degree of polymerization, which can be predetermined, of 300 — 1000 DP, preferably 450-650, is formed.

2. A process for producing a cellulose polymer according to claim 1, characterized in that the starting material may additionally contain up to 5% foreign fiber and / or PET.

3. A process for producing a cellulose polymer according to one of the preceding claims, characterized in that the starting material may additionally have a metal content of up to 35 ppm.

4. Process for the production of a cellulose polymer according to one of the preceding Claims, characterized in that the process is catalyst-free.

5. Process for the production of a cellulose polymer according to one of the preceding Claims characterized in that a vapor pressure explosion is carried out upstream and / or downstream.

6. Pulp produced according to a process of claims 1 to 5.

7. Cellulose fiber, in particular viscose or lyocell, produced from the material according to claim 6.

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