Method for recycling cellulosic fibres from waste materials for obtaining cellulose and product obtained thereof

Abstract

All the steps are performed within the same tank reactor that comprises a central tube, a tank, comprising first orifices in the tube allowing liquid to enter from inside the tube into the tank and second orifices in the tank allowing liquid to enter from a jacketed tank into the tank.

Description

[0001] METHOD FOR RECYCLING CELLULOSIC FIBRES FROM WASTE

[0002] MATERIALS FOR OBTAINING CELLULOSE AND PRODUCT OBTAINED

[0003] THEREOF

[0004] DESCRIPTION

[0005] Method for recycling cellulosic fibres from waste materials for obtaining cellulose characterized in that all steps are performed within the same tank reactor that comprises a central tube, a tank, comprising first orifices in the tube allowing liquid to enter from inside the tube into the tank and / or second orifices in the tank allowing liquid to enter from a jacketed tank into the tank, the method comprises at least the following steps: - a first step in which a fibre bed made of shredded material and / or unravelled material is formed into a homogeneous cake:- at a pressure of between 6-8 bar, - with a density above 200 g / l and - at room temperature; where NaOH with a concentration between 20-35% is added to the tank and mixed for one minute, with a final liquid-to-solid ratio between 1 :5 to 1 :10, - a second step in which NaOH with a concentration of 5-15% is added to the tank, with a temperature inside the tank between 120-140°C, and flowing and circulating for 45-100 minutes, while the hydroxyl anion OH- destroys the remaining polyethylene terephthalate and any other type of polyester, and also in which polyvinyl pyrrolidone from K10 to K120 is added removing the vat dyes from the homogeneous cake of the first step, - a third step in which a carboxylic acid, that is a complexing agent, is added to the second step mixture to neutralise it, resulting in a mixture with a pH <9,5, and - a fourth step in which the cake is extracted and dried, defining the cake as having a DP between 550-1100, <0.1% in weight of the cake, of non-cellulosic materials and an off-white to beige colour.

[0006] The present application generally relates to a method for recycling cellulosic fibres from waste materials, and more particularly to a process for efficiently extracting and reusing cellulosic fibres from various sources of waste. Associated I PC classes describe working-up, general processes of compounding, preparation or pretreatment of the material to be shaped, making granules or preforms, recovery of plastics or other constituents of waste material containing plastics and chemical or physical processes, e.g. catalysis or colloid chemistry, their relevant apparatus. BACKGROUNDS OF THE INVENTION

[0007] It belongs to the state of the art the EP3411415 “METHOD FOR PRODUCING REGENERATED CELLULOSE FIBERS FROM COTTON CONTAINING TEXTILE WASTE”, dated 2017, from the same applicant of the present application, that relates to a method for regenerating cellulose fibers from cotton-containing textile, wherein the degree of polymerization (DP) of cellulose in cotton is reduced by using a DP decreasing agent, which is an endo-cellulase of the type EC Number 3.2.1.4, together with mechanical energy. The DP of cellulose in cotton is reduced to under 1500, which makes it particularly suitable for the following steps, especially the spinning step. The cellulose is further dissolved using cellulose solvent comprising NMMO or an aqueous mixture of NMMO and the obtained cellulose-containing liquid is subjected to a spinning process to produce cellulose fibers.

[0008] Chinese Patent n° CN 106674588 “METHOD FOR SEPARATING AND RECOVERING WASTE COTTON-POLYESTER BLENDED FABRIC UNDER A SUBCRITICAL WATER CONDITION”, in the name of University Taiyuan Technology, dated 2017, that discloses a method for separating and recovering waste cotton-polyester blended fabric under a subcritical water condition, and belongs to the field of resource recycling and reuse of waste fabric. Under the conditions that the mass fraction of hydrochloric acid is 0.5-2% and reaction temperature is 130-160DEG C, reaction is carried out for 3-5h, cotton fibers in the waste cotton-polyester blended fabric are decomposed into microcrystalline celluloses, but polyester fibers are not changed, and therefore, the polyester fibers and the microcrystalline celluloses are separated and recovered. The method is suitable for the cotton-polyester blended fabric formed at any ratio and has the advantages of simpleness in operation, short technological process, low energy consumption, light environment pollution and the like. In addition, this patent creates microcrystalline cellulose, that is not suitable for the lyocell process, that requires certain DP values.

[0009] PCT Application WO2024038227 “SYSTEM FOR DECOLORIZATION OF MATERIAL COMPRISING CELLULOSE”, in the name of ANDRITZ OY, dated 2023, refers to a system for decolorization of material comprising cellulose, the system comprising: a purification stage for removing non-cellulosic components from the material comprising cellulose in alkaline process conditions; followed by a first decolorization stage for decolorizing the material comprising cellulose in alkaline process conditions; and a second decolorization stage for decolorizing the material comprising cellulose in alkaline process conditions; wherein the first and second decolorization stage comprise a decolorization stage using ozone and a decolorization stage using hydrogen peroxide; at least the purification stage and the second decolorization stage comprise a washing arrangement comprising at least one washer for washing the material treated in said stage; each of the purification stage, the first decolorization stage and the second decolorization stage are connected to the subsequent stage by a process line for feeding the material treated and washed in said stage to the subsequent stage; and wherein each washing arrangement is connected to the washing arrangement of a preceding stage by a filtrate line for feeding at least a part of the wash filtrate of the at least one washer of said washing arrangement to a preceding stage for use as wash water.

[0010] It is also known the EP3737783 “METHODS FOR RECYCLING COTTON AND POLYESTER FIBERS FROM WASTE TEXTILES”, in the name of TYTON BIOSCIENCES LLC, dated 2019, that refers to systems and methods are provided that involve a subcritical water reaction to recycle the cellulose and polyester components of waste cotton and cotton / polyester blend textiles that would otherwise be discarded or disposed of. Specifically, the disclosed methods provide for treatment of the waste textiles to produce advanced materials including cellulose and terephthalic acid (TPA) with a low environmental impact. The cellulose and TPA that are produced are of a high quality allowing for production of regenerated cellulose and regenerated polyethylene terephthalate (PET) suitable for fiber spinning and textile applications.

[0011] BRIEF DESCRIPTION OF THE INVENTION

[0012] This application addresses the problem of efficiently recycling cellulosic fibres from waste materials to obtain cellulose. It can also be suitable for a textile application and would also be for the new lyocell process. The application provides solutions for forming a homogeneous cake of shredded and unravelled material, effectively removing polyethylene terephthalate and any other type of polyester through the use of NaOH, neutralizing the mixture, and extracting and drying the resulting cake.

[0013] The closest prior art is the EP3737783.

[0014] This patent solves the problem of recycling cellulose and TPA. This patent uses hypochlorites to remove the colour. The problem comes because both hypochlorites and other harsh chemicals used are highly polluting. In addition, large quantities of water are used and have to be treated, which entails considerable economic costs because neutralisation and cleaning are costly.

[0015] The present application employs a combination of agents such as NaOH, which helps to neutralise the metals, plays with lowering the pH at the end compared to the nearest document, and finally due to the combinations of density, DP and pressure, manages to keep energy and water consumption low, giving a final product with less than 0.1 % of non-cellulosic material and no need to remove the colour, because the final product is already white to off-white to (slightly) beige, which means that the final product is ready. This final product is also ready for lyocell application.

[0016] It also solves the problem about the insolubility in water of the vat dyes. Adding polyvinyl pyrrolidone to the tank causes that vat dyes become water soluble and can be removed from the homogeneous cake.

[0017] It is an object of the present invention a method for recycling cellulosic fibres from waste materials for obtaining cellulose characterized in that all steps are performed within the same tank reactor that comprises a central tube, a tank, comprising first orifices in the tube allowing liquid to enter from inside the tube into the tank and / or second orifices in the tank allowing liquid to enter from a jacketed tank into the tank, the method comprises at least the following steps: - a first step in which a fibre bed made of shredded material and / or unravelled material is formed into a homogeneous cake:- at a pressure of between 6-8 bar, - with a density above 200 g / l and - at room temperature; where NaOH with a concentration between 20-35% is added to the tank and mixed for one minute, with a final liquid-to-solid ratio between 1 :5 to 1 :10, - a second step in which NaOH with a concentration of 5-15% is added to the tank, with a temperature inside the tank between 120-140°C, and flowing and circulating for 45-100 minutes, while the hydroxyl anion OH- destroys the remaining polyethylene terephthalate and any other type of polyester, and also in which polyvinyl pyrrolidone from K10 to K120 is added removing the vat dyes from the homogeneous cake of the first step, - a third step in which a carboxylic acid, that is a complexing agent, is added to the second step mixture to neutralise it, resulting in a mixture with a pH <9,5, and - a fourth step in which the cake is extracted and dried, defining the cake as having a DP between 550-1100, <0.1% in weight of the cake, of non-cellulosic materials and an off-white to beige colour.

[0018] It is an additional object of the present invention a product obtained in accordance with the method of claim 1 characterized in that is a recycled cellulosic cake that comprises: - a DP between 550-1100, - <0.1 % in weight of the cake, of non- cellulosic materials, and - an off-white to beige colour.

[0019] CONCRETE EMBODIMENT OF THE INVENTION

[0020] Thus, the method for recycling cellulosic fibres from waste materials for obtaining cellulose is characterized in that all steps are performed within the same tank reactor. This has the advantage that all reactions can be controlled within the same device, and all parameters can also be controlled more easily.

[0021] The tank reactor comprises a central tube and a tank. The central tube is located inside the tank, as an axis of the tank.

[0022] The tube comprises first orifices in the tube allowing liquid or fluid to enter from inside the tube into the tank, in other words, the orifices are non-return.

[0023] There are also a second group of orifices in the tank 3 allowing liquid to enter from a storage tank outside the reactor via a pump into the tank with the same effects of the first orifices, non-return. It could be possible to work only with a configuration with only the tube and the first orifices, with only the second group of orifices, or a combination of both.

[0024] The method comprises at least the following steps:

[0025] A first step in which a fibre bed, that is made of shredded material and / or unravelled material is formed into a homogeneous cake.

[0026] This cake is under a pressure of between 6-8 bar. Below 6 bar it can generate channelling that will produce preferential pathways and therefore only partial reaction where the liquid is contact with.

[0027] If pressure is higher than 8 bar, the cake will be too compressed that the liquid may not go through.

[0028] The density of the cake is above 200 g / l. Actually, the inventors are working between 200-300 g / l. If it is lower than 200 g / l there can be difficulties with the fluid when passes through the first and / or second orifices. Over 300 g / l, nowadays is technologically very complicated. This means that if it is technologically feasible in the future, over 300 g / l would be a possible option.

[0029] Also, the system is at room temperature.

[0030] The NaOH, with a concentration between 20-35%, is added to the tank and mixed for one minute, with a final liquid-to-solid ratio between 1 :5 to 1 :10. The cake is wet because otherwise is difficult to make it homogenous when cake formation. Cake is also wet by water and an agent that reduce the density of the liquid, e.g. surfactant, that helps cake formation.

[0031] A NaOH concentration from 30% or above is considered high concentration.

[0032] In the second step NaOH with a concentration of 5-15% is added to the tank, with a temperature inside the tank 3 between 120-140°C, and flowing and circulating for 45-100 minutes (the liquid flows through the cake), while the hydroxyl anion OH- destroys the remaining polyethylene terephthalate. Flowing occurs because that liquid is pumped through the cake and circulates via a storage tank. In total from 2500-5000 litres of NaOH in water are used for 500 kg of cake.

[0033] NaOH has even more affinity to cellulose than only water, so when NaOH is added in the first step, and the reactor is flushed, the cake remains wet with also some NaOH. That liquid, in the first step, that wets the cake does not have the same NaOH concentration than the liquid that just left the reactor, as one can assume, but higher concentration. In the second step, that also contains NaOH but less concentrated, it requires less NaOH that originally planned. The resultant concentration is between 5 - 15% of NaOH

[0034] As it can be seen there is no use of a metal catalyst, which means that there is a better control over the cellulose and less contamination. Also, metal free processes are more environmentally friendly and avoids metal ions present during wet spinning.

[0035] Metal catalyst often needs harsh conditions, high pressures, high temperatures that leads to reactor corrosion, for example. A metal free process means that conditions are mild, and the reactor can last longer in principle and are less contaminant.

[0036] The control of the reaction comes from controlling temperature, the pressure of the cake / concentration of fibres and the concentration of NaOH.

[0037] The time is from 45-100 minutes because it depends on the concentration of the cake, if there is a low concentration it could go in the range of 45 minutes to 60 minutes, while higher concentrations would be from 90-100 minutes.

[0038] Also, under the temperatures between 120-140°C the conditions of the polyethylene terephthalate (PET) change, in other words, under these temperatures the hydroxyl anion OH- destroys the remaining PET, helping to eliminate all the elements that are not cellulose. It takes benefit that the polyester polymer is in a glass transition temperature which means the polymer is soft and pliable, making the polymer hydrophilic instead of hydrophobic, making the depolymerisation of PET reaction faster.

[0039] It is over its glass transition temperature, making polyester more hydrophilic, that is the media where OH' is present. This natural hydrophobic barrier is often overcome with the use of BTBAC (Benzyltributylammonium chloride) or similar, a phase- transfer catalyst that helps aqueous OH' reach hydrophobic polyester below its transition glass temp interact. The problem is that this type of catalyst is not environmentally friendly, its considered hazardous.

[0040] The inventors overcome this problem by increasing temperature that changes the polyester behaviour.

[0041] In this second step is also added polyvinyl pyrrolidone from K10 to K120. This is done in order to remove the vat dyes from the homogeneous cake of the first step.

[0042] Vat dyes are very common in textiles, for example the blue indigo colour. Vat dyes are insoluble in water. It is after a reduction in an alkaline solution that it becomes soluble, but after being exposed to the air, it recuperates the original insoluble property versus the water. This means that when the textile was worn the vat dyes are insoluble due to the contact with the air. Then the vat dyes are an issue if those textiles want to be recycled and those vat dyes separated from the cellulose in order to remove the blue indigo colour.

[0043] This is a serious problem when recycling textile materials, because plenty of them (for example the jeans) use the indigo blue colour.

[0044] The inventors, after several studies, solve the problem adding polyvinyl pyrrolidone (hereinafter PVP) to the tank, which causes that blue indigo becomes again water- soluble and can be removed, then.

[0045] PVP converts the vat dyes in a water-soluble dye. PVP forms bonding like h- bridges or Van de Waals and even ionic bonds with the ionised vat dye and so to say “drags” the vat dye molecule into the water. PVP is water soluble. When it is referred as PVP, it does not comprise those modifications of the PVP, as Polyvinylpolypyrrolidone (PVPP), that can be water insoluble.

[0046] The inventors propose to use a PVP with a K from K10 to K120, because it will depend on the concentration of the vat dyes in the textile. For example, a blue indigo light will allow a K from the low part K10-K30, an intense blue indigo will need a K from K90-K120.

[0047] Lower values of K are more water-soluble than higher values, due to the fact that PVP has higher viscosity, higher molecular weight, in higher values.

[0048] When dissolving higher values, as for example K90, in water, it could be done previously it in warm water depending on the water temperature in the tank. Water should be higher than 40°C, before adding the PVP to the tank, in order that it can more easily disperse and the dissolution does not form dumps.

[0049] In a third step, a carboxylic acid is added to the second step mixture to neutralise it, resulting in a mixture with a pH <9,5. The acid has an impact on the neutralisation, as it captures some cations from the following elements: iron, copper, manganese, silicon, calcium and chrome, among others. These cations are very dangerous and catalyse the decomposition of the solvent N- Methylmorpholine N-oxide, also known as NMMO, that is used in lyocell process. For this reason, their capture provides an almost metal-free final product.

[0050] It would be recommendable that the carboxylic acid is in an acidic buffer in order to stabilize the mixture. Chelators are active at basic pH, when are deprotonated. When in contact to reaction media, the resultant pH of the reaction media is lowered with the buffer acid to more acidic values, pH below 10, so that the chelator will bind cations, as well as help to neutralization.

[0051] Finally, in a fourth step the cake is extracted from the tank 3 and dried, defining the cake as having a DP between 550-1100, <0.1 % in weight of the cake, of non- cellulosic materials and an off-white to beige colour. A <0,1 % in weight of the cake, of non-cellulosic material causes that the recycled material obtained is like an original cellulose in macroscopic scale. In addition, <0.1 % in weight of the cake, of non cellulosic material causes that the resultant cellulose pulp will be processable for lyocell process, facilitating its processing also in other chemical recycling processes, or anywhere where high cellulose purity is needed.

[0052] The cake could be dried for at least one of these three additional steps, that can also be combined:

[0053] - A fifth step is by air pressure while in the reactor.

[0054] - A sixth step would be extraction of the liquid by centrifuge and finally.

[0055] - A seventh step on a steam heated bed dryer or any other suitable fibre drying machine.

[0056] In the fifth step the reactor is fitted with a circulation pump, a heat exchanger and a buffer vessel.

[0057] In the sixth step the water is driven out till a moist content of 70-80%.

[0058] The cake is dried till a moist content up to a 15%.

[0059] An optional acid as complexing agent is the Ethylenediaminetetraacetic acid (EDTA). EDTA acts as a neutraliser of metal ions in aqueous solutions.

[0060] Another optional acid as complexing agent is the acetic acid. It is used as a solubilising agent and also for reducing the pH.

[0061] Optionally the cake has a DP between 650-900.

[0062] The pH of step 4 could be <7, even better 6.

[0063] The product obtained in accordance with the previous method is a recycled cellulosic cake that comprises:

[0064] - a DP between 550-1100,

[0065] - <0.1% in weight of the cake, of non-cellulosic materials, and

[0066] - an off-white to beige colour.

[0067] Optionally the cake has a DP between 650-900. The present invention describes a new method for recycling cellulosic fibres from waste materials for obtaining cellulose and product obtained thereof. The examples mentioned herein are not limiting of the present invention, therefore it may have different applications and / or adaptations, all of them within the scope of the following claims.

Claims

CLAIMS1.- Method for recycling cellulosic fibres from waste materials for obtaining cellulose characterized in that all steps are performed within the same tank reactor that comprises a central tube, a tank, comprising first orifices in the tube allowing liquid to enter from inside the tube into the tank and / or second orifices in the tank allowing liquid to enter from a jacketed tank into the tank, the method comprises at least the following steps:- a first step in which a fibre bed made of shredded material and / or unravelled material is formed into a homogeneous cake:- at a pressure of between 6-8 bar,- with a density above 200 g / l and- at room temperature where NaOH with a concentration between 20-35% is added to the tank and mixed for one minute, with a final liquid-to-solid ratio between 1 :5 to 1 :10,- a second step in which NaOH with a concentration of 5-15% is added to the tank, with a temperature inside the tank between 120-140°C, and flowing and circulating for 45-100 minutes, while the hydroxyl anion OH- destroys the remaining polyethylene terephthalate and any other type of polyester, and also in which polyvinyl pyrrolidone from K10 to K120 is added removing the vat dyes from the homogeneous cake of the first step,- a third step in which a carboxylic acid, that is a complexing agent, is added to the second step mixture to neutralise it, resulting in a mixture with a pH <9,5, and- a fourth step in which the cake is extracted and dried, defining the cake as having a DP between 550-1100, <0.1 % in weight of the cake, of non-cellulosic materials and an off-white to beige colour.2.- Method, in accordance to claim 1 , characterized in that the carboxylic acid of the third step is in the presence an acid buffer.3.- Method, in accordance to the claim 2, characterized in that the acid of the third step is the Ethylenediaminetetraacetic acid (EDTA).4.- Method, in accordance to Claim 2, characterized in that the acid of the third step is an acetic acid.5.- Method, in accordance to Claim 1 , characterized in that the pH is <7.6.- Method, in accordance to Claim 1 , characterized in that the DP is between 650- 900.7.- Method, in accordance to claim 1 , characterized in that the homogeneous cake of the first step has a density between 200-300 g / l.8.- Product obtained in accordance with the method of claim 1 characterized in that is a recycled cellulosic cake that comprises:- a DP between 550-1100, - <0.1 % in weight of the cake, of non-cellulosic materials, and- an off-white to beige colour.9.- Product, in accordance to Claim 8, characterized in that the DP is between 650- 900.