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    • 专利摘要:
    Electrochemical process for bleaching fabrics containing natural cellulose fibers. The present invention relates to an electrochemical bleaching process of raw fabrics comprising natural cellulose fibers, comprising the steps of a) immersing the fabric in a tank containing a solution of an alkali metal chloride at an equal or higher ph to 7, wherein the solution is in contact with at least one anode and at least one cathode; and b) carrying out an electrolysis of the alkali salt of chloride in solution to obtain hypochlorite. (Machine-translation by Google Translate, not legally binding)
    公开号:ES2584436A1
    申请号:ES201630869
    申请日:2016-06-28
    公开日:2016-09-27
    发明作者:César QUIJADA TOMÁS；Felipe Nicolás VITERO PÉREZ；Pablo MONLLOR PÉREZ；María Angeles BONET ARACIL；Emilia MORALLÓN NÚÑEZ
    申请人:Universidad Politecnica de Valencia；Universidad de Alicante；
    IPC主号:
    专利说明:

    The present invention relates to a bleaching process of fabrics containing natural cellulosic fibers, specifically an electrochemical bleaching process in which hypochlorite / hypochlorous acid is generated as an active species. The present invention can be framed in the field of industry
    10 textile STATE OF THE TECHNIQUE
    Raw cellulosic fibers contain a significant amount of impurities not
    15 natural cellulosics. Among the natural non-cellulosic components are hemicelluloses, pectins, natural waxes, proteins and, except for cotton fibers, lignin. Furthermore, these components are found together with colored matter of complex chemical composition, which give a typical yellowish-brown color.
    On the other hand, raw cellulosic fabrics usually contain a coating of polymeric materials or glues, added to minimize thread breakage during the production process. The presence of all these non-cellulosic substances makes the textile substrate not very hydrophilic and very heterogeneous from the point of view of whiteness, absorbency and chemical composition, which prevents tinting or uniform finishes. In the textile production process, one of the primary stages is the preparation or pretreatment, which includes a set of operations dedicated to eliminating the maximum amount of non-cellulosic material. The bleaching is the central part of the operations of preparation of the textile material, and consists of the
    30 removal of colored matter to provide a pure white appearance to the fibers. At the same time it is able to remove part of other impurities.


    In almost all cases, the bleaching of cellulosic fibers is carried out by contacting the textile material with an aqueous solution of an oxidative bleaching agent, which is depleted during the process. Traditionally, sodium hypochlorite has been used as a low cost and fast method at room temperature. Its main disadvantages are: 1) it is a corrosive and harmful reagent for the environment and, therefore, its transport, storage and handling present risks whose prevention requires demanding industrial safety standards, 2) the stability of the stored reagent is not very high , which makes it necessary to frequently determine the exact content of active chlorine in order to avoid a lack of reproducibility in bleaching and 3) the effluents produced contain levels of absorbable organohalogenated compounds (AOX) and chloroform that are higher than allowed, Be treated before discharge. Additionally, chemical bleaching baths contain a series of auxiliaries such as detergents, surfactants or others, necessary to achieve optimal and uniform bleaching. This type of substances implies an increase in the pollutant load of bleaching effluents.
    The potential application of electrochemical techniques for tissue bleaching has been described in the literature. Kokot et al. (Textile Res. J., 63 (1993) 313) and Fukatsu et al. (Textile Res. J., 69 (1999) 769) examined the bleaching and structural damage produced in cotton fibers subjected to electrolysis with Pt electrodes in electrolytes containing Na2SO4 / NaOH. The effect was attributed to the formation of hydroxyl radicals in the anode during oxygen electrogeneration, as well as in the cathode. Fukatsu et al. (Textile Res. J., 70 (2000) 340), also studied electrochemical discoloration of cotton fabrics dyed with reactive dyes using a Pt anode. These authors observed a significant discoloration in the presence of potassium chloride, as a consequence of electro -generation of hypochlorite. Bechtold et al. (J. Appl. Electrochem., 36 (2006) 287) described a process for discoloration of indigo in cowboy tissues, by electrochemical generation of hypochlorite from sodium chloride solutions. As regards the bleaching of cotton and other textile materials, patent GB190104014A claims the design of a plant for the electrolytic production of a bleaching liquor from common salt. Said liquor is stored until later use. When this is required, the amount of liquor needed is extracted, which is transferred to


    a bleach tank or tub, where it is contacted with the textile material and recirculated by spraying until the end of the bleaching process. US579236A describes an electrolyser designed for the bleaching of fibrous materials, which generates bleaching agents by electrolytic decomposition of alkali metal salts and the means for introducing the material into the electrolyzer in contact with the electrodes. With regard to other raw lignocellulosic materials, the electrolytic generation of chlorinated oxidants (chlorine, hypochlorous acid and hypochlorite) has also been proposed as a viable technology for the delignification and bleaching of wood pulp in the paper industry. In US4617099 a process is described which comprises an electrochemical chlorination stage, a suspension pulp extraction stage and a final stage of bleaching with electrogenerated hypochlorite. In the first stage the electrolysis is carried out in an electrolyte containing 0.5-2.5% NaCl, pH 0-2 and a current density of 0.04 to 0.16 A / cm2. In the last stage the pH is set between 8 and 12, maintaining the rest of electrolysis conditions. A cylindrical electrochemical reactor with a disk-shaped anode at the bottom of the reactor and a parallel cathode in the form of a mesh is used.
    Electrochemical bleaching, defined as a process in which bleaching agents exert their action on textile materials at the time of being generated by electrolytic decomposition of a suitable precursor, has a number of important advantages over the conventional chemical process. The bleaching agent is produced on demand from a harmless and easily storable precursor. For example, in the case of electrochemical bleaching with hypochlorite, an alkali metal chloride, preferably NaCl, is used as it is the most abundant and cheap. This eliminates the costs and risks related to the transport, storage and handling of corrosive and dangerous products, such as hypochlorite. Electrolysis is a very versatile technology, since the electron can be dosed with an energy (voltage) and a quantity (electric current) adjusted very precisely, so that the control in the formation of oxidants is simple, precise and reproducible . During the bleaching process the precursor regenerates. For example, the oxidizing action of hypochlorite is due to the semi-reaction:
    ClO- + H2O + 2e- → Cl- + 2 OH-,


    with which most of the chloride consumed in the electro-generation is recovered. In this way the bleaching bath can be reused with a minimal addition of NaCl solution. Compared to chemical bleaching, where the bleaching agent must be replaced as it runs out, the regeneration of the precursor means significant savings in reagents and water, as well as a smaller volume of effluents. Thus, electrochemical bleaching is economically advantageous and more environmentally friendly. DESCRIPTION OF THE INVENTION
    The present invention relates to an electrochemical process of bleaching raw fabrics comprising cellulosic fibers. The bleaching agent is generated by electrolysis. This procedure can also be applied to the discoloration of dyed fabrics. The bleaching of the fabric can be carried out in a tank or tank attached to the electrochemical cell (or electrochemical tank) or inside it.
    The present invention has the following advantages:
    - the costs and risks of transport, storage and handling of large quantities of corrosive, toxic or unstable reagents are eliminated by generating the active chlorine necessary for bleaching in situ from solutions of an alkali metal chloride,
    - the precursor chloride is regenerated during the bleaching process, which considerably reduces the consumption of raw material and the volume of residual effluents,
    - The densities of necessary currents are very low and therefore their efficiency in chlorine generation current is high, which implies a lower electrical consumption.
    A first aspect of the present invention relates to a process of electrochemical bleaching of raw fabrics comprising natural cellulosic fibers, comprising the following steps:


    a) immersing the fabric in a tank containing a solution of an alkali metal chloride at a pH equal to or greater than 7, preferably greater than 7 where the solution is in contact with at least one anode and at least one cathode;
    b) carry out an electrolysis of the alkali metal chloride in solution to obtain hypochlorite.
    Preferably the electrolysis is galvanostatic.
    Natural cellulosic fibers are understood as fibers comprising cellulose, that is, fibers of plant origin.
    The alkali metal chloride comprises chlorides selected from lithium, sodium, potassium, rubidium, cesium chlorides and any of their mixtures, preferably the chloride comprises sodium chloride. Preferably it is sodium chloride.
    In the anode oxidation of the chloride to chlorine ion occurs, and in the cathode the reduction of water occurs to generate hydrogen and hydroxyl ions. During electrolysis the dissolved chlorine is rapidly hydrolyzed to hypochlorous acid or hypochlorite, or a mixture of both according to the pH of the electrolyte.
    In an embodiment of the first aspect of the present invention, the fabrics comprise fibers selected from cotton, coconut fiber, ceiba, flax, hemp, ramie, jute, esparto, abaca, formium, henequen, miraguan, oceanic posidonia and any of their mixtures, preferably the fabrics comprise fibers selected from cotton, linen, hemp and any of their mixtures, more preferably the fabric comprises cotton.
    Cotton is the vegetable fiber from the seeds of the cotton plant, a shrub of the genus Gossypium, mainly Gossypium arboreum L., Gossypium barbadense L., Gossypium herbaceum L., Gossypium hirsutum L. Coconut fiber is the fiber obtained from Cocos nucifera. Ceiba fiber is the fiber obtained from the ceiba tree, also called lupuna, bonga or bongo, pochote or kapok, named


    Ceiba pentandra scientist. Flax is a fiber that is obtained from flax or linseed, Linum usitatissimum. Hemp, also called industrial hemp, is the fiber that is obtained from Cannabis plant varieties. Ramie is a fiber that is obtained from the bark of ramie, Boehmeria nívea. Jute is a fiber obtained from the jute herbaceous plant Corchorus capsularis and also from Corchorus olitorius. Abaca, also called Manila hemp is a fiber obtained from abaca (Musa textileis). Forium, also known as harakeke or New Zealand flax, is the fiber that is extracted from the Phormium tenax plant. Henequen is the fiber that is obtained from the Agave fourcroydes. The miraguano is the fiber that is obtained from the miraguano or yuraguana, Coccothrinax miraguama. Oceanic Posidonia is the fiber that belongs to the Posidoniaceae family.
    In an embodiment of the first aspect of the present invention, the pH of the solution is between 8 and 12, preferably between 8.5 and 10.5. In this pH range the predominant active chlorine species are a mixture of hypochlorous acid and hypochlorite, or hypochlorite. In divided cells the optimum pH of the anodic compartment is adjusted with a buffer or by adding alkali. In undivided cells, the hydroxyl ions formed in the cathode react with hypochlorous acid, so that the pH is spontaneously in the preferred range between 8.5 and 10.5.
    In another embodiment of the first aspect of the present invention, the current density of the anode is between 4 A / m2 and 250 A / m2, preferably the current density of the anode is between 8 A / m2 and 100 A / m2. In a preferred embodiment, the current is applied in pulsed mode, with periodic decreases or interruptions of the current. This produces a decrease in the operational cost of the procedure. During the period of current flow hypochlorite / hypochlorous acid are generated, while in the period of interruption-decrease they are consumed as a result of their reaction with the fabric. Preferably the current is kept constant for 0.5 to 1 h and is subsequently interrupted for 5 to 15 min, then recover its initial value for another 5 to 15 min. When the cathode material is susceptible to degradation by corrosion in a medium with a high chloride content, the current is not interrupted but reduced to a suitable value to keep the electrode cathodically protected. This sequence is repeated until the desired target level is reached.


    In another embodiment of the first aspect of the present invention, the concentration of the alkali metal chloride is between 10 g / l and 80 g / l, preferably between 20 g / l and 30 g / l.
    The species of active chlorine are generated by oxidation in the anode of the chloride ions present in an aqueous chloride electrolyte of an alkali metal, according to the following reactions:
    2 Cl- → Cl2 + 2e-Cl2 + H2O → HClO + Cl- + H +HClO⇋ClO- + H +
    In another embodiment of the first aspect of the present invention, electrolysis is carried out for a time of 1 to 4 hours.
    In another embodiment of the first aspect of the present invention, the bath ratio (kilos of fabric per liter of solution) is between 1/100 Kg / l and 1/400 kg / l.
    In another embodiment of the first aspect of the present invention, the ratio between the area of the anode and the volume of the solution is between 0.1 cm-1 and 0.6
    - one
    cm.
    In another embodiment of the first aspect of the present invention, the process temperature is between 15 ° C and 65 ° C. As the temperature increases, the bleaching speed increases and the necessary electrolysis time decreases, although there is a greater degradation of the fabric manifested by a loss of tensile strength.
    In another embodiment of the first aspect of the present invention, the solution further comprises a humectant. Preferably the concentration of the humectant is 50 µg / l at 400 µg / l of solution, more preferably the concentration of the humectant is 100 µg / l at 300 µg / l.


    A humectant is a surfactant with a medium hydrophilic lipophilic balance (HLB). When dissolved in water, it decreases the contact angle, wetting or moisturizing a larger proportion of surface.
    In another embodiment of the first aspect of the present invention, the anode and / or cathode is in the form of a plate, grid, expanded mesh or foam electrode. Particularly useful are the electrodes in the form of expanded mesh, due to their greater flexibility, economy in the use of the base material, ease in the exchange of electrolyte and transverse flow, as well as the ease of gas evacuation.
    A plate electrode means a flat electrode, thin (thin) and rectangular, non-porous and formed by smooth or rough faces.
    By grid electrode is meant an electrode formed by a series of rigid plates or wires placed parallel, uniformly spaced and joined together by separating plates or wires uniformly welded perpendicularly and arranged in an equidistant manner, so that holes with a square contour are formed or rectangular
    An expanded mesh electrode means an electrode formed by a structure containing diamond-shaped holes of regular appearance and size, surrounded by metal bars of a certain thickness and width interconnected with each other without the need to be woven or welded.
    A foam electrode means an electrode with an isotropic structure of open pores of micrometric size interconnected and randomly distributed, to confer permeability, a high surface area ratio volume and low density.
    In another embodiment of the first aspect of the present invention, the anode comprises a conductive material comprising Ti, Ta, Nb, Zr or any of its mixtures with a coating selected from Pt, Pt oxides, mixed Ti-Ru oxides, oxides Ti-Ir mixed, Ti-Ru-Ir mixed oxides and any of their mixtures. The material


    Conductive comprises said metals, any of their mixtures, and also alloys comprising said metals or mixtures. Pt oxides are understood as PtO, PtO2, PtO3, Pt3O4 or any of their mixtures. Mixed oxides of Ti-Ru, mixed oxides of Ti-Ir and mixed oxides of Ti-Ru-Ir are understood as oxides comprising the mixtures of said metals, in any proportion and with any oxidation state. Preferably the anode comprises a conductive material comprising Ti with a coating of mixed Ti-Ru-Ir oxides. The mixed oxides of Ti-Ru-Ir are usually TiO2-RuO2-IrO2.
    In another embodiment of the first aspect of the present invention, the cathode comprises stainless steel, nickel or titanium with a coating of Pt or Pt oxides.
    When the cathode is nickel it can be made of nickel foam. Nickel foam means a foam electrode that is formed by metallic nickel.
    In another embodiment of the first aspect of the present invention, the cathode and / or anode comprise a conductive material comprising Ti, Ta, Nb, Zr, Si, SiC or any combination thereof with a diamond or diamond coating coated with an element selected from B, N, P and S preferably the coating is diamond doped with B.
    In another embodiment of the first aspect of the present invention, the electrolysis of the alkali metal chloride takes place in a second tank communicated with the tank containing the fabric (ex situ arrangement).
    This embodiment is illustrated in Figure 1. The fabric is immersed in a tank or tank (1) attached to the tank where the electrolysis is performed, the electrochemical cell (3). The tank (1) can be in continuous agitation by means of a mechanical agitator (2). The tank (1) and the electrolytic cell tank (3) are connected by a solution recirculation system comprising the alkali metal chloride (4). Preferably, the solution is pumped between the tanks. This solution is driven by a pumping system (5) from the electrolytic cell to the tank (1) and vice versa. Preferably the flow rate between tanks is


    between 25 l / h and 100 l / h, more preferably the flow rate between 30 l / h and 60 l / h. The temperature is maintained by a heat exchanger (6). The electric current is applied by a DC power supply. In a particular embodiment, prior to step (a), a partial electrolysis of the alkali metal chloride in solution is performed. That is, a pre-electrolysis is performed to achieve an adequate concentration of active chlorine, before introducing the raw cloth into the auxiliary tank. Preferably, an anodic current density of 250 A / m2 is used for a period of one hour.
    In a preferred embodiment of the first aspect of the present invention a conventional filter-press electrochemical cell is used, placing the fabric to be treated in an attached reservoir or reservoir in which the electrolyte received from the electrochemical cell is continuously agitated and recirculated again. to the electrochemical cell or tank. The filter-press reactor has been described by Molina et al. (Design and Development of Filter-Press Type Electrochemical Reactors for their Application in the Resolution of Environmental Problems, Chapter IV, p 383, in "Trends in Electrochemistry and Corrosion at the Beginning of the 21st Century", Ed. PL Cabot and E Brillas, 2004). This reactor can be configured in an undivided arrangement, with a common compartment for anode and cathode, or in a divided arrangement comprising an anodic compartment and a cathodic compartment separated for example by a porous separator, preferably by an ion exchange membrane. This type of reactor can be formed by parallel electrodes in the form of a plate or mesh, a set of joints and spacers, one or more flow distributors with inlet and outlet holes for pumping the solution comprising the alkali metal chloride from an auxiliary tank or tank, and can have separators with porous ceramic diaphragms or ion exchange membranes. The flow distributors would be integrated in the electrode chambers or compartments. The set can be compressed with the help of tightening plates. The electrode area can be easily increased by stacking various cells or pairs of anode and cathode. The reactor preferably consists of a single cell and has rectangular flow compartments and a turbulence promoter system to facilitate the transport of matter and the evacuation of bubbles.


    In another embodiment of the first aspect of the present invention, the anode and cathode are not separated by an ion exchange membrane. Preferably, the interelectrode distance is 0.8 to 1.5 cm, more preferably 1.2 cm.
    In another embodiment of the first aspect of the present invention, the anode and cathode are in compartments separated by an ion exchange membrane. A volume similar or smaller than that of the anodic compartment is preferably used in the cathodic compartment. Preferably both electrodes are immersed in solutions of the same alkali metal chloride. Preferably, the distance between electrodes and membrane is 0.8 to 1.5 cm, more preferably 1.2 cm. To obtain the preferred pH range using the divided arrangement, periodic addition of suitable amounts of alkali, such as NaOH or Na2CO3, or a buffer may be necessary.
    The regeneration of the chloride in the bleaching process allows the reuse of the bath for the bleaching of successive batches of fabric, with a minimal addition of NaCl solution according to the needs.
    In another embodiment of the first aspect of the present invention, the electrolysis of the alkali metal chloride takes place in the same tank in which the fabric is submerged (in situ arrangement).
    In another embodiment of the first aspect of the present invention, the tank comprises a rectangular flow compartment with an electrolyte inlet port (7) and a rectangular flow compartment with an electrolyte outlet port (8).
    Figure 2 illustrates an electrochemical cell or modified split press filter tank to insert the fabric to be bleached inside. The cell consists of flow compartments: one with an inlet port (7) and the other with an electrolyte outlet port (8).
    In another embodiment of the first aspect of the present invention, at the inlet of the tank there is a set of meshes of a chemically inert material (9), which act


    as promoters of turbulence. The meshes can be shapedpreferably by materials chosen from fiberglass, teflon or mixtures thereof.
    In another embodiment of the first aspect of the present invention the fabric (10) is incontact with at least one face of the anode, preferably the fabric (10) is arranged incontact with both faces of the anode (11).
    In another embodiment of the first aspect of the present invention, the fabric (10) iscompressed between at least two anodes (14) connected monopolarly. TheFigure 3 shows a detail of another preferred embodiment in which the fabric (10) isIt is compressed between three anodes (14) connected in monopolar form. Henumber of pieces of cloth inside the cell can be easily increasedstacking successive fabric-anode sets.
    The electrolyte enters the cell or tank through the lower flow chamber, passes through the fabric(10), the anode (11) and the cathode (12) until finally reaching the exit compartmenthigher. Among all these elements a series of joints or spacers is inserted(13). Both the anode (11) and the cathode (12) are porous or shaped electrodes.mesh or grid, electrolyte permeable. The inter-electrode distance ispreferably 0.3 cm to 0.8 cm, more preferably 0.5 cm.
    In another embodiment of the first aspect of the present invention, the tank comprisesa selective ion membrane (16).
    In another embodiment of the first aspect of the present invention, the electrolysis of thealkali metal chloride takes place in the same tank in which the fabric issubmerged and the tank (17) comprises driving means (18, 21) for drivingthe fabric (20), where the conduction means comprise:- at least two rotating drive rollers (21); where at least one of the rollersDrag swivels drives the fabric into the tank (17) and at least one ofthe rotating drag rollers drives the fabric out of the tank;-a central rotating roller (18), to rotate the fabric inside the tank;where the anode (19) is arranged around the central rotating roller (18).Preferably the anode is surrounded by a flexible and chemically inert mesh.


    Preferably the flexible mesh is made of a material selected from fiberglass, Teflon and any of its mixtures. Particularly appropriate is a Teflon coated fiberglass mesh. In a particular embodiment, prior to step (a), a partial electrolysis of the alkali metal chloride in solution is performed. That is, a pre-electrolysis is performed to achieve an adequate concentration of active chlorine, before introducing the raw cloth into the auxiliary tank. Preferably, an anodic current density of 250 A / m2 is used for a period of one hour.
    Preferably, the cathode (23) is separated from the anode (19) and the fabric (20) by a separator (24), more preferably the separator (24) is an ion selective membrane. Preferably, the cathode (23) is in the form of a mesh. Preferably, the rotational speed of the rotating rollers (18, 21) is between 10 m / min and 150 m / min.
    Figure 4 shows another preferred embodiment in which a modified divided filtroprense type cell is used to house fabric inside. In addition to the elements described in Figure 2, this cell consists of an outflow chamber for the anolyte (15) and an ion selective membrane (16). The upper flow compartment has an inlet and outlet hole for recollection of catholyte. A volume similar or smaller than that of the anodic compartment is preferably used in the cathodic compartment. The electrolyte used as a catholyte is preferably sodium chloride. The distance between electrodes and membrane is preferably 0.8 to 1.5 cm, more preferably 1.2 cm. To obtain the preferred pH range using the divided arrangement, periodic addition of suitable amounts of alkali, such as sodium hydroxide or sodium carbonate, or the addition of a buffer may be necessary.
    Surprisingly, using lower currents the contact between the fabric and the anode provides degrees of white similar to those obtained in the ex situ embodiment, described in Figure 1, with the consequent saving in electricity consumption.
    In another embodiment of the first aspect of the present invention, electrochemical bleaching is done by inserting the fabric into the electrochemical cell (in situ arrangement) by drag rollers. The fabric to be bleached moves towards


    The inside of the electrochemical cell with the help of drag rollers, finallybe removed again from the cell and reintroduced in successive cycles. Figure 5shows a diagram of the electrochemical cell, which comprises a tank (17) and acentral rotating roller (18), around which a flexible cylindrical anode orin the form of mesh or grid (19). The fabric (20) crosses the cell in contact with theSwivel anode thanks to drive rollers (21) arranged outside the tank.Optionally, the anode can be surrounded with a mesh or cylindrical porous fabricflexible (22), so that it is part of the rotating assembly. The purpose of thiselement is to be sandwiched between the anode and the raw cloth. This mesh or clothIt consists of a chemically inert material, chosen from among fiberglass,Teflon or its mixtures. Particularly appropriate is a fiberglass meshTeflon coated The cathode is a hemicylindrical electrode (23), preferably inMesh shape to facilitate gas evacuation. In another preferred embodiment theTank itself (17) can function as a cathode if it is formed by a materialChemically stable conductor, typically stainless steel. The fabric iscontinuously recirculated through the electrochemical reactor until thedesired target index.
    In an undivided configuration, the speed of matter transport is increasedthanks to the hydrodynamic effect of the rotating anode and the agitation produced by thegas bubbles formed in the electrodes. Typically interelectronic distanceIt is 1 to 10 cm. Optionally, a separator (24) can be inserted,preferably an ion selective membrane, between the electrodes. TypicallyThe distance between electrode and separator is 1 to 5 cm.
    A second aspect of the present invention relates to an electrochemical cell.for electrochemical bleaching of fabrics (20) comprising:- a tank (17) intended to contain a chloride solution of an alkali metal;-electrodes (19, 23) to carry out electrolysis;- conduction means (18, 21) to drive the fabric (20);where the driving means include:- at least two rotating drive rollers (21); where at least one of the rollersDrag swivels drives the fabric into the tank (17) and at least one ofthe rotating drag rollers drives the fabric out of the tank;


    -a central rotating roller (18), to rotate the fabric inside the tank;where the anode (19) is arranged around the central rotating roller (18). Thisconfiguration allows the fabric to be in contact with the anode so that thehypochlorite diffuses locally.
    Preferably, the cathode (23) is separated from the anode (19) and the fabric (20) by aseparator (24), more preferably the separator (24) is a selective membrane ofions Preferably, the cathode (23) is in the form of a mesh.
    In another embodiment of the second aspect of the present invention, the anode issurrounded by a flexible and chemically inert mesh. Preferably the flexible meshIt is a material selected from fiberglass, Teflon and any of itsmixtures Particularly appropriate is a fiberglass mesh covered withTeflon
    A third aspect of the present invention relates to the use of the electrochemical cell.as described above for the bleaching of fabrics comprisingnatural cellulosic fibers.
    Throughout the description and claims the word "comprises" and itsvariants are not intended to exclude other technical characteristics, additives, components orSteps. For experts in the field, other objects, advantages and characteristics of theinvention will come off in part from the description and in part from the practice ofinvention. The following examples and figures are provided by way of illustration, andThey are not intended to be limiting of the present invention. BRIEF DESCRIPTION OF THE FIGURES
    FIG. 1. Scheme of the electrochemical process of bleaching of ex situ fabrics.FIG. 2. Expanded scheme of the cross section of a non-electrochemical celldivided modified to place the fabric in contact with the anode.FIG. 3. Multi-anode arrangement with monopolar connection.


    FIG. 4. Expanded scheme of the cross section of an electrochemical celldivided modified to locate fabric in contact with the anode.FIG. 5. Scheme of an electrochemical cell with fabric drag by systemrollers and contact with rotary anode. EXAMPLES
    The invention will now be illustrated by tests carried out by the inventors, which demonstrates the effectiveness of the product of the invention. Example 1. Variation of the target index of a raw cotton fabric during electrochemical bleaching "ex situ" in conventional undivided filter-press reactor
    In an auxiliary tank or tank, 1 l of aqueous NaCl solution of 20 g / l concentration is poured. The inlet and outlet of the tank are connected to the outlet and inlet of a conventional filter-press reactor comprising an expanded titanium anode coated with a mixture of Ti, Ru and Ir dioxides and a cathode formed by an AISI stainless steel mesh 304, both rectangular and 100 cm2 of projected area, and without any separation. The electrolyte is recirculated by the system with the help of a centrifugal pump with a flow rate of 50 l / h.
    The raw cotton fabric is an openwork fabric with a weight of approximately 210 g / m2 and a CIE white index (WCIE) of approximately 16. An amount of fabric suitable for maintaining a 1/100 bath ratio is introduced into the tank, where it remains submerged for 30 min before starting electrolysis, in order to allow wetting of the fabric and faster penetration of the active chlorine produced.
    Electrolysis is carried out by passing a constant direct current between the electrodes through a DC power supply. The anodic current density applied is 100 A / m2. During the process the temperature is kept constant at 25 ° C. The pH of the electrolyte increases rapidly in the initial instants and it


    stabilizes in a range of approximately 8.5 and 10.5, in which the predominant free chlorine species is the hypochlorite ion. This pH value is achieved due to the mixing and neutralization of the weak HClO acid, pKa (25 ° C) = 7.5, formed by hydrolysis of the chlorine generated at the anode with the hydroxyl ions formed at the cathode in the
    5 hydrogen gas formation:
    HClO + OH- → ClO- + H2O
    The experiment is repeated with identical samples of cloth during different time of
    10 electrolysis, after which the tissue is removed from the tank, washed with water, neutralized by the addition of HCl and subjected to an anti-chlorine treatment consisting of a washing solution of 2 g / l sodium bisulfite. Finally, it is washed with water and dried at 60 ° C for 120 minutes before measuring the target indica. In another set of experiments the electrolyte contains 200 µg of Leophen humectant
    15 RA (BASF), which is a non-hydrolysable sodium salt of an ester of sulfosuccinic acid, and the waiting time prior to electrolysis is omitted.
    The results are summarized in table 1.
    Time (min) WCIE
    Without moisturizer With moisturizer
    0 16.416.4
    30 29.452.7
    60 40.065.2
    120 55.870.7
    240 69.974.3
    20 Table 1. Variation of the white index (WCIE) of a raw cotton fabric during electrochemical bleaching "ex situ" in conventional undivided filter-press reactor.
    For comparative purposes, the white tissue index subjected to an industrial oxidative chemical bleaching process is 69.7.


    The electrochemical bleaching process preserves the mechanical properties of the tissue, which suffers losses of tensile strength of less than 10%.
    Example 2. Effect of the temperature in the electrochemical bleaching “ex situ” of a raw cotton fabric in conventional undivided filter-press reactor
    In the present example the tissue and electrodes are the same as those used in example 1.
    In an auxiliary tank or tank, 1 l of aqueous NaCl solution of 20 g / l concentration is poured and without the addition of any type of humectant. The inlet and outlet of the tank are connected to the outlet and inlet of a conventional filtroprensa reactor of the same characteristics as in the previous example. The electrolyte is recirculated by the system with the help of a centrifugal pump with a flow rate of 50 l / h.
    An adequate amount of tissue to maintain a 1/100 bath ratio is introduced into the tank, where it remains submerged for 30 min before starting electrolysis, in order to allow wetting of the fabric and faster penetration of active chlorine. produced.
    Electrolysis is carried out by passing a constant direct current between the electrodes through a DC power supply. In a series of experiments the applied anodic current density is 50 A / m2 and in another 100 A / m2. During the process the temperature is kept constant at 25ºC, 45ºC or 65ºC. The experiments are repeated with identical samples of cloth during different electrolysis times, after which the tissue is removed from the tank and subjected to the treatment described in the previous example.
    The white index results obtained are summarized in table 2.
    Time (min) WCIE
    50 A / m2 100 A / m2


    25ºC 45 ° C65 ° C 25ºC45 ° C65 ° C
    30 31.835.2-29.440.9-
    60 35.548.953.240.056.175.6
    120 47.355.977.355.869.280.9
    240 67.468.379.269.977.978.4
    Table 2. Effect of the temperature in the electrochemical bleaching “ex situ” of a raw cotton fabric in conventional undivided filter-press reactor.
    At 25 ° C, the electrochemical bleaching process preserves the properties
    5 mechanical tissue, which suffers losses of tensile strength less than 10%. At 45 ° C, the tensile strength losses remain below 10% in the whole set of conditions except for electrolysis at 100 A / m2 for 240 min. Finally, at the highest temperature the tensile strength retains acceptable values only after treatment at 50 A / m2 and lasting no longer than 120 min.
    10 Example 3. Reuse of electrolyte during “ex situ” electrochemical bleaching of successive batches of cotton fabrics in conventional undivided filter-press reactor
    In the present example the tissue and electrodes are the same as those used in example 1.
    In an auxiliary tank or tank, 1 l of aqueous NaCl solution of 20 g / l concentration is poured together with 200 µg of Leophen RA (BASF) humectant. The entrance
    20 and outlet of the tank are connected to the outlet and inlet of a conventional filter-press reactor of the same characteristics as in the previous example. The electrolyte is recirculated by the system with the help of a centrifugal pump with a flow rate of 50 l / h.
    25 An adequate amount of tissue to maintain a 1/400 bath ratio is introduced into the tank. The presence of humectant makes the previous period of wetting of the tissue unnecessary.


    Electrolysis is carried out by passing a constant direct current between the electrodes through a DC power supply. The anodic current density applied is 100 A / m2. The temperature is kept constant at 25 ° C. The electrolysis time is set at 120 min. After this period the electrolysis is interrupted, the tissue
    5 is removed from the tank and subjected to the treatment described in the previous example. A new batch of tissue is then introduced into the tank and a new electrolysis stage is started under the same conditions as the first. This operation is repeated until the bleaching of 6 lots in total is completed. The results are summarized in table 3.
    Lot WCIE% Tensile strength loss
    one 72.314.2
    2 73.411.6
    3 73.314.9
    4 73.53.4
    5 73.45.7
    6 73.18.6
    Table 3. White index of successive batches of cotton fabrics treated "ex situ" in conventional undivided filter-press reactor.
    The different batches of bleached fabric suffer from tensile strength losses of less than 15%.
    Example 4. Variation of the white index of a raw cotton fabric during electrochemical bleaching "in situ" in modified undivided filter-press reactor
    In the present example the tissue and electrodes are the same as those used in example 1.
    The electrolyser is a modified filter-press reactor as described in Figure 2, which comprises an expanded titanium anode coated with a mixture of


    Ti, Ru and Ir dioxides and a cathode formed by an AISI 304 stainless steel mesh, both rectangular and 200 cm2 of projected area, and without any separation. A tissue sample is arranged in intimate contact with one of the anode faces. The reactor elements with the tissue inside are assembled and
    5 compress by tightening plates.
    The inlet and outlet of the reactor are connected to the outlet and inlet of an auxiliary tank in which 1 l of aqueous NaCl solution of 20 g / l concentration is poured. The electrolyte is recirculated by the system with the help of a centrifugal pump with a
    10 flow of 50 l / h. The bathroom ratio used is 1/400. The tissue remains in contact with the electrolyte for 30 min before starting electrolysis.
    Electrolysis is carried out by passing a constant direct current between the electrodes through a DC power supply. Anode current density
    15 applied is 50 A / m2. The temperature is kept constant at 25 ° C. The experiments are repeated with identical samples of cloth during different electrolysis times, after which the tissue is removed from the tank and subjected to the treatment described in example 1.
    20 The white index results are summarized in table 4.
    Time (min) WCIE
    30 36.8
    60 48.4
    120 67.9
    240 70.3
    Table 4. Variation of the white index of a raw cotton fabric during electrochemical bleaching "in situ" in a modified undivided filter-press reactor.
    25 In this example bleached fabrics experience tensile strength losses of less than 5%.

    权利要求:
    Claims (39)
    [1]
    1. Electrochemical bleaching process of raw fabrics comprising natural cellulosic fibers, comprising the following steps:
    a) immersing the fabric in a tank containing an electrolyte that is a solution of an alkali metal chloride at a pH equal to or greater than 7, where the solution is in contact with at least one anode and at least one cathode;
    10 b) carry out an electrolysis of the alkali metal chloride in solution to obtain hypochlorite.
    [2]
    2. Method according to the preceding claim, wherein the fabrics comprise fibers selected from cotton, coconut fiber, ceiba, flax, hemp, ramie, jute,
    15 esparto, abaca, formium, henequen, miraguano, oceanic posidonia and any of their mixtures.
    [3]
    3. Method according to the preceding claim, wherein the fabrics comprise fibers selected from cotton, linen, hemp and any of their mixtures.
    [4]
    4. Method according to any of the preceding claims, wherein the pH of the solution is between 8 and 12.
    [5]
    5. Method according to any of the preceding claims, wherein the current density of the anode is between 4 A / m2 and 250 A / m2.
    [6]
    6. Method according to the preceding claim, wherein the current density of the anode is between 8 A / m2 and 100 A / m2.
    Method according to any of the preceding claims, wherein the concentration of the alkali metal chloride is between 10 g / l and 80 g / l.

    [8]
    8. Method according to any of the preceding claims, wherein the electrolysis is carried out for a time of 1 to 4 hours.
    [9]
    9. Method according to any of the preceding claims, wherein the ratio of bath in kilos of fabric per liter of solution is between 1/100 Kg / l and 1/400 kg / l.
    [10]
    10. Method according to any of the preceding claims, wherein the ratio between the area of the anode and the volume of the solution is comprised between 0.1 cm-1 and 0.6 cm-1.
    [11]
    eleven. The process according to any of the preceding claims, wherein the process temperature is between 15 ° C and 65 ° C.
    [12]
    12.  The method according to any of the preceding claims, the solution further comprises a humectant.
    [13]
    13. Process according to the preceding claim, wherein the concentration of the humectant is 50 µg / l to 400 µg / l of solution.
    [14]
    14.  Method according to any one of the preceding claims, wherein the anode and / or the cathode is in the form of a plate, grid, expanded mesh or foam electrode.
    [15]
    fifteen.  Process according to any of the preceding claims, wherein the anode comprises a conductive material comprising Ti, Ta, Nb, Zr or any of its mixtures with a coating selected from Pt, Pt oxides, mixed Ti-Ru oxides, mixed oxides of Ti-Ir, mixed oxides of Ti-Ru-Ir and any of their mixtures.
    [16]
    16. Process according to the preceding claim, wherein the anode comprises a conductive material comprising Ti with a coating of mixed Ti-Ru-Ir oxides.

    [17]
    17. Process according to any of the preceding claims, wherein the cathode comprises stainless steel, nickel or titanium with a coating of Pt or Pt oxides.
    [18]
    18. Process according to any one of claims 1 to 14, wherein the cathode and / or anode comprise a conductive material comprising Ti, Ta, Nb, Zr, Si, SiC or any combination thereof with a diamond or diamond coating coated with an element selected from B, N, P and S.
    [19]
    19. Method according to any of the preceding claims, wherein the electrolysis of the alkali metal chloride takes place in a second tank communicated with the tank containing the fabric.
    [20]
    twenty. Process according to the preceding claim, wherein the solution of the alkali metal chloride is pumped between the tanks.
    [21]
    twenty-one. Method according to the preceding claim, wherein the flow rate between tanks is between 25 l / h and 100 l / h.
    [22]
    22 Process according to any one of claims 1 to 18, wherein the electrolysis of the alkali metal chloride takes place in the same tank in which the fabric is submerged.
    [23]
    2. 3. Method according to the preceding claim, wherein the tank comprises a rectangular flow compartment with an electrolyte inlet port (7) and a rectangular flow compartment with an electrolyte outlet port (8).
    [24]
    24. Method according to the preceding claim, where at the entrance of the tank there is a set of meshes of a chemically inert material (9).
    [25]
    25.  Method according to any of claims 22 to 24, wherein the fabric (10) is in contact with at least one face of the anode.

    [26]
    26.  Method according to the preceding claim, wherein the fabric (10) is compressed between at least two anodes (14) connected in a monopolar manner.
    [27]
    27.  Method according to any of claims 22 to 26, wherein the tank comprises an ion selective membrane (16).
    [28]
    28.  Method according to claim 22, wherein the tank (17) comprises driving means (18, 21) for driving the fabric (20), wherein the driving means comprise: - at least two rotating drive rollers (21); where at least one of the rotating drag rollers drives the fabric into the tank (17) and at least one of the rotating drag rollers drives the fabric out of the tank; -a central rotating roller (18), to rotate the fabric inside the tank; where the anode (19) is arranged around the central rotating roller (18).
    [29]
    29.  Method according to claim 28, wherein the cathode (23) is separated from the anode (19) and the fabric (20) by a separator (24).
    [30]
    30 Method according to the preceding claim, wherein the separator (24) is an ion selective membrane.
    [31]
    31. Method according to any of claims 28 to 30, wherein the cathode
    (23) has a mesh shape.
    [32]
    32 Method according to any of claims 28 to 31, wherein the anode is surrounded by a flexible and chemically inert mesh.
    [33]
    33. Method according to the preceding claim, wherein the flexible mesh is of a material selected from fiberglass, Teflon and any of its mixtures.
    [34]
    3. 4. Method according to any of claims 28 to 33, wherein the rotation speed of the rotating rollers (18, 21) is between 10 m / min and 150 m / min.

    [35]
    35. Electrochemical cell for electrochemical bleaching of fabrics (20) thatunderstands:- a tank (17) intended to contain a chloride solution of an alkali metal;-electrodes (19, 23) to carry out electrolysis;
    5-conduction means (18, 21) to drive the fabric (20); where the driving means comprise: - at least two rotating drive rollers (21); where at least one of the rotating drag rollers drives the tissue into the tank (17) and at least one of the rotating drag rollers drives the tissue out of the tank;
    10 -a central rotating roller (18), to rotate the tissue inside the tank; where the anode (19) is arranged around the central rotating roller (18).
    [36]
    36. Cell according to any one of claim 35, wherein the cathode (23) is separated from the anode (19) and the fabric (20) by a separator (24).
    [37]
    37.  Cell according to the preceding claim, wherein the separator (24) is an ion selective membrane.
    [38]
    38. A cell according to any one of claims 35 to 37, wherein the cathode (23) has a mesh shape.
    [39]
    39. A cell according to any one of claims 35 to 38, wherein the anode is surrounded by a flexible and chemically inert mesh.
    40. A cell according to the preceding claim, wherein the flexible mesh is of a material selected from fiberglass, Teflon and any of its mixtures.
    [41]
    41. Use of the electrochemical cell according to any of claims 35 to 40 for bleaching fabrics comprising natural cellulosic fibers.

    DRAWINGS
    FIG. one

    FIG. 2
    FIG. 3

    FIG. 4

    FIG. 5
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    同族专利:
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    引用文献:
    公开号 | 申请日 | 公开日 | 申请人 | 专利标题
    US4319973A|1977-12-06|1982-03-16|Battelle Memorial Institute|Method and machine for washing and bleaching textiles|
    US5456809A|1995-02-06|1995-10-10|The Regents Of The University Of California|Electrochemical mercerization, souring, and bleaching of textiles|
    JPH1136173A|1997-07-15|1999-02-09|Nishie Denimu:Kk|Decoloration of colored clothes|
    US20020129450A1|2001-03-15|2002-09-19|Kim Myung Han|Method of decolorizing blue jeans based on client-desired design|
    US20050028291A1|2001-12-13|2005-02-10|Thomas Bechtold|Changing the color or dyed textile substrates|
    法律状态:
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    申请号 | 申请日 | 专利标题
    ES201630869A|ES2584436B2|2016-06-28|2016-06-28|ELECTROCHEMICAL PROCEDURE FOR THE WHITENING OF FABRICS CONTAINING NATURAL CELL FIBERS|ES201630869A| ES2584436B2|2016-06-28|2016-06-28|ELECTROCHEMICAL PROCEDURE FOR THE WHITENING OF FABRICS CONTAINING NATURAL CELL FIBERS|
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