BR112017027022B1 - METHOD FOR FORMING A COMPOSITION FOR BLEACHING AQUEOUS CELLULOSIC MASS, COMPOSITION AND KIT OF INGREDIENTS - Google Patents

Abstract

METHODS FOR BLEACHING AQUEOUS CELLULOSIC MASS AND COMPOSITIONS FOR USE IN THESE METHODS. The present invention relates to compositions for use in an aqueous cellulose bleaching process, comprising one or more alkaline earth metal oxides and/or one or more alkaline earth metal hydroxides; one or more alkaline earth metal salts; and, optionally, one or more pitch control additives. Methods and kits for forming these compositions are also part of the invention, as are the use of these compositions, methods and kits.

Description

Field of Invention

[001] The present invention relates to compositions for use in bleaching cellulose masses. In particular, the compositions are suitable for use as additives for pH adjustment and/or control of unwanted substances in a cellulosic mass during a pulp bleaching step. Also part of the present invention is the use of the compositions, for example, the use of the compositions in a cellulose preparation or papermaking process, as well as methods of bleaching cellulosic stocks using these compositions. Finally, sets of ingredients for forming compositions according to the invention, or for use in a method according to the invention, are also part of the present invention.

Background of the Invention

[002] Traditional bleaching processes of cellulose masses generally employ alkaline hydrogen peroxide as a bleaching agent. For this purpose, hydrogen peroxide and a water-soluble alkaline compound, such as sodium hydroxide and/or water glass, are introduced into the cellulose in order to improve the whiteness and/or brightness of a wood cellulose, a recycled paper or any other chemical or mechanical pulp, such as a pulp for papermaking processes. Using chelating agents such as EDTA to remove some of the metal ions from the cellulose prior to the addition of peroxide allows the peroxide to be used more efficiently. Magnesium salts and sodium silicate can also be added to enhance alkaline peroxide bleaching. Magnesium salts are also typically used to protect cellulose fibers from too much degradation and therefore loss of strength during the delignification and bleaching process steps.

[003] More recently, alkaline earth metal hydroxides and/or alkaline earth metal oxides have been employed to replace sodium hydroxide and water glass and reduce the need for chelating agents and sodium silicate (see, for example, as described in Li and others, Pulp & Paper Canada, 106:6 (2005), pages T125 to T129, "Using magnesium hydroxide (Mg(OH)2) as the alkali source in peroxide bleaching at Irving paper"). WO 2014/195478 A1 describes the use of pitch control additives (deposits) in combination with Mg(OH)2 and/or MgO in cellulose pulps in paper bleaching, in order to avoid the formation of Magnesium-based fatty acid salts and resins in paper pulps.

[004] Alkaline earth metal hydroxides and alkaline earth metal oxides are only sparingly soluble in aqueous solutions, which can lead to reduced bleaching efficiency and reduced fiber protection efficiency. In addition, the use of MgSO4 in paper bleaching pulps as a radical scavenger and cellulosic mass stabilizing agent is known. MgSO4 is expensive and difficult to store due to its hygroscopic properties.

[005] Finally, maintaining high pulp viscosity is a consideration in pulp processing, including pulp bleaching. Cellulose viscosity is a measure of fiber strength. The installation of pulp processing plants, such as pulp bleaching plants, is specially designed to maintain the viscosity of the pulp while achieving the desired bleaching result. Variation of cellulose viscosity can therefore be problematic.

[006] The state of the art, therefore, presents several problems.

Concise Description of the Invention

[007] The present invention is defined in the appended claims.

[008] In particular, the present invention comprises a composition for use in an aqueous cellulose bleaching process, which composition comprises (i) one or more alkaline earth metal oxides and/or one or more alkaline earth metal hydroxides ; (ii) one or more alkaline earth metal salts; and (iii) optionally, one or more pitch control additives. It was found that in the presence of an alkaline earth metal salt, such as an alkaline earth metal sulfate, the alkalinity of the described chemical preparation was reduced, leading to better solubility of the alkaline earth metal oxide and/or the alkaline earth metal hydroxide. in that preparation which is then dosed into the cellulose, while obtaining the beneficial effects of the alkaline earth metal salt, such as an alkaline earth metal sulfate, in scavenging radicals and stabilizing the cellulosic mass. For example, the alkaline earth metal can be selected from magnesium, calcium or a mixture of magnesium and calcium.

[009] According to one embodiment, the alkaline earth metal salt is an alkaline earth metal sulfate, such as, for example, calcium sulfate or magnesium sulfate.

[0010] According to one embodiment, the pitch control additive is selected from talc, bentonite, zeolite, diatomaceous earth, cationic mica, hydrophobic carbonates, resin decomposition enzymes, cationic polymers designed to capture and immobilize resins or resinous components on fiber surfaces, aluminum sulphate, polyaluminum chloride and dispersing agents specially designed for dispersing resins and resinous components, and mixtures thereof. These pitch control agents have been found to lead to a reduction in fatty acid salts and resins in cellulose paper. According to one embodiment, the pitch reducing agent is talc, such as, for example, micronized talc, bimodal talc, cationic talc or mixtures thereof. According to one embodiment, the pitch control additive is bentonite, such as an activated bentonite. In certain embodiments, the bentonite is activated by the alkaline earth metal oxide and/or the alkaline earth metal hydroxide and/or the alkaline earth metal salt. Bentonite can bind heavy metals in the paper bleaching composition and reduce their interference in the bleaching process, for example by degrading the peroxide responsible for the bleaching process.

[0011] According to the present invention, the composition may be a dry particulate composition, or the composition may be an aqueous cellulosic mass, or the composition may be present as a constituent of an aqueous cellulosic mass comprising other components, such as, for example, the composition may be present as a constituent of an aqueous cellulose paper bleaching system. According to the present invention, a particulate composition according to the present invention can be mixed with water in order to prepare an aqueous cellulosic mass, which is also a part of the present invention.

[0012] According to the present invention, the composition may be an aqueous cellulosic mass with a solids content of up to 75% by weight, such as, for example, from 10 to 75% by weight, based on the total weight of the cellulosic mass.

[0013] According to the present invention, the proportion by weight of (i) alkaline earth metal oxide and/or alkaline earth metal hydroxide, on the one hand, and of (ii) alkaline earth metal salt, on the other hand, is from 1:10 to 100:1. It has been found that the advantageous effects according to the present invention are best obtained if the components are present in such proportions. For example, the weight ratio can be in the range 1:5 to 50:1, such as, for example, in the range 1:2 to 25:1, or 1:1 to 10:1, such as, for example about 2:1, or about 70:30, or about 80:20, or about 90:10.

[0014] According to one embodiment, the composition may further comprise one or more of the following additives: dispersing agents; loads; surfactants; bleaching agents; chelating agents; and pH buffering agents.

[0015] According to another aspect of the present invention, there is provided a kit of components comprising a first container including an alkaline earth metal oxide and/or an alkaline earth metal hydroxide, and one or both a second and a third containers, the second container comprising an aqueous mineral acid solution and the third container comprising sulfur dioxide or carbon dioxide. It has been found that compositions according to the present invention can be easily obtained using said kit. In one embodiment, the aqueous mineral acid is aqueous sulfuric acid.

[0016] Also part of the present invention are methods for producing the compositions of the present invention, including a step of mixing an alkaline earth metal oxide and/or an alkaline earth metal hydroxide with an acid such as a mineral acid, such as acid sulfuric acid or sulfur dioxide, or carbon dioxide, or an alkaline earth metal salt, such as, for example, an alkaline earth metal sulfate or an alkaline earth metal carbonate, optionally in the presence of one or more pitch control agents (pitch ). The alkaline earth metal can be selected, for example, from magnesium, calcium and mixtures thereof.

[0017] According to one aspect of the present invention, the method can be carried out in situ on an aqueous cellulose bleaching composition. It was found that the alkaline earth metal oxide and/or the alkaline earth metal hydroxide reacted efficiently in situ with an acid such as a mineral acid, such as sulfuric acid, and/or sulfur dioxide or carbon dioxide to form a mixing alkaline earth metal oxide and/or alkaline earth metal hydroxide with an alkaline earth metal salt, such as an alkaline earth metal sulfate, in situ. For example, the method according to the present invention can be carried out by adding a mineral acid, such as, for example, sulfuric acid, or carbon dioxide, or sulfur dioxide, to a cellulose paper bleach comprising the oxide of alkaline earth metal and/or alkaline earth metal hydroxide. For example, the method according to the present invention can be carried out by adding the alkaline earth metal oxide and/or alkaline earth metal hydroxide to an acidic cellulose composition (e.g., where the only acid present in the acidic cellulose composition is acid that is naturally present in the cellulose composition (i.e. derived from wood) or with no acid added).

[0018] According to one aspect of the present invention, the method may include a step of mixing an alkaline earth metal hydroxide with a mineral acid, in which the base-acid normality, that is, the molar ratio of hydroxide ions in the alkaline earth metal hydroxide and the hydrogen cations in the mineral acid is between 10:1 and 1:5, such as, for example, about 10:1, or about 5:1, or about 4:1, or about 3:1, or about 2:1, or about 1.5:1, or about 1:1, or about 1:1.5, or about 1:2, or about 1: 5. Corresponding acid/base ratios should be employed in the case of alkaline earth metal oxide and carbon dioxide or sulfur dioxide, for example.

[0019] According to an aspect of the present invention, the method can be carried out by mixing the kit ingredients according to an aspect of the present invention into a cellulose paper bleach. It was found that the kit was easily transported, stored and applied for use in the method of the invention.

[0020] Also part of the present invention is the use of the composition, method or kit, as described according to the present invention, in a pulp bleaching process. It has been found that the pulp pulp bleaching process can be made simpler, more efficient and less expensive by using the present invention, while at the same time reducing the need for expensive raw materials or complex procedures.

[0021] According to some embodiments, the composition, method or kit according to the present invention can be used in a process to reduce the pitch of a cellulose and/or in a process to protect the cellulose from depolymerization and/or degradation (eg resulting in the formation of sticky impurities). In that context, methods for reducing depolymerization and/or degradation of a cellulose and/or for protecting cellulose from the formation of degradation products (eg sticky impurities) are also part of the present invention. Depolymerization or degradation occurs due to the attack of the bleaching chemicals on the cellulose molecules, leading to a reduction in the length of the polymeric chain and, consequently, to lower strength properties of the cellulose. Very often this degradation is measured as fiber viscosity. Less chain length through depolymerization or degradation leads to lower viscosity values and therefore lower strength properties which reduce the value of the pulp produced.

[0022] According to some other embodiments of the present invention, the composition or product of the method or one or more of the kit components according to embodiments of the present invention are added to the pulp to be bleached, before the addition of any other alkaline bleaching agents such as water glass, NaOH, sodium silicate and/or hydrogen peroxide.

[0023] It is understood that the following detailed description and references to the Figures relate to exemplary embodiments of the present invention and should not be limiting the scope of the claims.

Detailed Description of the Invention

[0024] The present invention according to the appended claims provides improvements to pulp production processes, including bleaching, such as oxygen bleaching, peroxide-oxygen bleaching, oxygen-peroxide bleaching or oxygen delignification, for example. The improvements can be obtained by the products and kits as defined in the appended claims, as well as by their application in accordance with the methods and uses as defined in the appended claims.

[0025] It was found that the combination of alkaline earth metal hydroxides and/or alkaline earth metal oxides, together with certain alkaline earth metal salts and optionally pitch control agents, provides a number of advantages over the state of the technique.

[0026] One advantage is the reduction in the formation of harmful deposits in the cellulose. This is accomplished by using, on the one hand, the combination of alkaline earth metal oxide and/or alkaline earth metal hydroxide with the alkaline earth metal salt, and, on the other hand, by the presence of certain pitch control agents (pitch ).

[0027] Furthermore, it was also found that the presence of certain salts of alkaline earth metals leads to a reduction of the radicals formed in the bleaching process. The presence of radicals, although on the one hand desirable for bleaching, can lead to the formation of unwanted secondary products, for example, of depolymerization and/or degradation of cellulose, such as pitch (pitch), or "sticky residues", which can lead to coagulation of cellulosic mass and damage to downstream paper handling facilities.

[0028] Furthermore, the presence of certain alkaline earth metal salts, such as alkaline earth metal sulfate, leads to a stabilization of the viscosity of the cellulose and improvement of the strength properties of the cellulose. This is important for the usability of pulp in the production of paper and board and other end uses of pulp. In accordance with some aspects of the present invention, viscosity stability is achieved by using the compositions or kit of the invention, and leads to a maintenance of viscosity or a reduction in the drop in viscosity. For example, according to the present invention, the use of the compositions or kit components leads to a change in viscosity that is not more than 10%, such as, for example, not more than 5%, or not more than 4%, or not more than 3%, or not more than 2%, or not more than 1%, or not more than 0.5%, or which essentially leads to an unmeasurable change in viscosity.

[0029] This viscosity "protection" is thought to be caused by the presence of free alkaline earth metal ions, such as magnesium ions, in a cellulosic mass. The formation of alkaline earth metal salts from the alkaline earth metal hydroxide or alkaline earth metal oxide and a cellulose papermaking acid leads to the formation of free alkaline earth metal ions, such as magnesium ions, and viscosity stabilization of cellulose paper.

[0030] Furthermore, the use of alkaline earth metal salts in the present invention makes it possible to adapt the pH value of the cellulose bleaching preparation. Due to the presence of alkaline earth metal oxide and/or alkaline earth metal hydroxide, an alkaline cellulosic mass is normally obtained, with a high pH of 10 or more, or 11 or more. According to the present invention, the use of alkaline earth metal salt leads to a control of the alkalinity in the pulp bleaching preparation, and it is possible to reduce the pH to a value between 7 and 10.5, such as, for example, about of 8.5. It is advantageous to work in the pH region below 10 or close to the neutral pH value region, in order to protect the equipment from alkaline degeneration and, of course, for safety reasons. Furthermore, the lower pH leads to better bleaching performance and/or reduction in depolymerization and/or cellulose degradation. Therefore, the charge of alkaline earth metal hydroxide and/or alkaline earth metal oxide in cellulose papermaking can be reduced according to the present invention.

[0031] Finally, according to some embodiments of the present invention, such as the kit or the method according to the present invention, said alkaline earth metal salt is obtained by combining an alkaline earth metal oxide and/or a alkaline earth metal hydroxide with a mineral acid or with sulfur dioxide or carbon dioxide, in situ before or during a bleaching process. Consequently, for example, a composition comprising magnesium hydroxide and magnesium sulfate can be obtained in a cellulose bleaching preparation by introducing magnesium hydroxide and an acid such as sulfuric acid, according to the following reaction: Mg(OH )2 + H2SO4 (aq) ^ MgSO4 + 2H2O

[0032] Acids such as aqueous sulfuric acid are readily available and easy to store in large quantities for an extended period of time at the papermaking site. On the other hand, salts of alkaline earth metals, such as, for example, magnesium sulfate, are often expensive in terms of acquisition and storage and difficult to handle, due to their low durability or hygroscopic behavior. The methods and kits according to the present invention, therefore, lead to the formation of the composition according to the present invention, and they also form part of the present invention and present additional advantages over the state of the art.

[0033] The alkaline earth metal hydroxide or alkaline earth metal oxide may be selected from magnesium hydroxide, calcium hydroxide, magnesium oxide and calcium oxide, or mixtures thereof. If an alkaline earth metal oxide is employed, it functions in the same way as an alkalinity agent by forming the corresponding alkaline earth metal hydroxide in an aqueous medium. These compounds have a low solubility in water and therefore are released into pulp only at the rate they are being consumed during the bleaching process. According to the present invention, the pH control is improved, since it can be regulated by the addition of alkaline earth metal salt, or acid, in accordance with the embodiments of the invention.

[0034] In certain embodiments, the alkaline earth metal hydroxide can be magnesium hydroxide. In some embodiments, the magnesium hydroxide can be crystalline (e.g., brucite). In other embodiments, the magnesium hydroxide can be an amorphous form.

[0035] In certain embodiments, magnesium hydroxide, calcium hydroxide and mixtures thereof may be provided by dolomitic limestone being converted to dolomitic lime, which is then converted to magnesium hydroxide, calcium hydroxide and mixtures thereof. Such modalities that include magnesium hydroxide and calcium hydroxide can provide the cellulose bleaching benefits described herein, as well as a reduction in deposits (e.g., calcium oxalate deposits) and/or an increased availability of soluble hydroxide ions. The ratio of magnesium hydroxide to calcium hydroxide in these embodiments can vary from 10:1 to 1:10, such as, for example, from 5:1 to 1:5, such as, for example, in the range of 1:2 to 2:1.

[0036] The alkaline earth metal salt for use in the present invention may be, for example, an alkaline earth metal sulfate, such as, for example, magnesium sulfate. Magnesium sulfate is a hygroscopic particulate salt. The use of the alkaline earth metal salt helps to adjust the pH of the cellulosic mass and can also stabilize the cellulosic mass. Alternatively, magnesium chloride or magnesium nitrate can be used.

[0037] The pitch control agent for use in the composition according to certain embodiments of the present invention may be talc, a natural magnesium silicate with a lamellar structure. Alternatively, the pitch control agent for use in the composition in accordance with certain embodiments of the present invention can be bentonite, an absorbent aluminum phyllosilicate, including montmorillonite. In particular embodiments, the bentonite can be activated by alkaline earth metal hydroxide or alkaline earth metal oxide (eg, Mg(OH) 2 or Mg(OH)). In certain embodiments, bentonite can act as an ion exchanger for heavy metals such as Mn, Cr, Fe and/or Ni, which provides the advantage of making these ions less available to disturb the bleaching process. In other embodiments, the bentonite can stabilize the peroxide used in bleaching and/or reducing the silicate content.

[0038] In certain embodiments, the pitch control agent may be a mixture of talc and bentonite. For example, the ratio of talc to bentonite in such embodiments can vary from 10:1 to 1:10, such as, for example, from 5:1 to 1:5, such as, for example, in the range of 2:1 to 1:2. This mixture of two different pitch control agents shows the benefit of treating a wide variety of harmful substances in the process, as both substances have different adsorption properties. Talc's hydrophobic surface preferentially adsorbs hydrophobic materials, while bentonite is more attracted to hydrophilic substances.

[0039] According to certain embodiments of the present invention, the compositions for use in bleaching cellulose masses may be present as an aqueous cellulosic mass. Aqueous cellulosic stocks are generally used, for example in papermaking, for introducing solids into cellulosic cellulose. As such, a composition in accordance with certain embodiments of the present invention in the form of an aqueous cellulosic mass can be introduced into cellulose in order to withstand bleaching with hydrogen peroxide. By placing certain embodiments of the composition of the present invention in the form of a cellulosic mass, the overall weight of the composition is increased. In order to limit weight gain, for example to maintain the efficiency of transporting the compositions, it is preferred that the aqueous cellulosic masses comprising the composition according to certain embodiments of the present invention have a solids content of 10% by weight or more, based on the total weight of the cellulosic mass, such as 30% by weight or more, or 30% by weight or more, or 40% by weight or more, or 45% by weight or more, or 50% by weight or more, or even 60% by weight or more, such as up to 70% by weight, or 72% by weight, or 75% by weight. In order to obtain cellulosic masses with high solids contents, it may be necessary to include dispersing agents in the cellulosic mass. Cellulosic pulps can also comprise additional components such as fillers, surfactants, bleaching agents, pH buffering agents or other additives.

[0040] In certain embodiments, the compositions are in the form of dry particulate powders. In order to reduce the weight of the composition and improve transportability, the compositions can be transported as dry powders and cellulosic masses will be formed only at the location of use of the compositions in a bleaching process. Said dry particulate powders can be obtained, for example, using a spray drying process. Spray-dried particulate compositions in accordance with certain aspects of the present invention may have a low or very low moisture content, such as, for example, 5% by weight moisture or less, based on the total amount of solids in the powder. spray-dried particulate, or 4% by weight moisture or less, or 3% by weight moisture or less, or even 2% by weight moisture or less, such as, for example, about 1% by weight of moisture or 0.5% by weight of moisture. Dry compositions can also comprise additional components such as dispersing agents, fillers, surfactants, bleaching agents, chelating agents, pH buffering agents or other additives.

[0041] In certain embodiments, the compositions are in the form of pellets. According to one aspect, the pellets can have a moisture content of from 0.1% by weight to 25% by weight, based on the total weight of the composition, such as, for example, from 2% by weight to 20% by weight. weight, or from 5% by weight to 15% by weight, such as, for example, from about 15% by weight. According to a further aspect, the pellets may comprise from 2% by weight to 50% by weight of pitch control additive and from 98% by weight to 50% by weight of particulate alkaline earth metal oxide or hydroxide. of particulate alkaline earth metal or mixtures thereof, based on the total solids content of the pellets.

[0042] According to certain embodiments of the present invention, the compositions for use in bleaching cellulose masses may have a proportion by weight of alkaline earth metal oxides and/or alkaline earth metal hydroxides, on the one hand, and the metal salt alkaline earth, on the other hand, in the range from 1:1 to 100:1, such as, for example, from 2:1 to 50:1, such as, for example, in the range from 3:1 to 25:1, or from 5:1 to 10:1, such as, for example, from about 70:30, or from about 80:20, or from about 90:10.

[0043] According to certain embodiments of the present invention, the component kit may include amounts of ingredients such that a weight ratio as described above can be obtained. It is understood by one skilled in the art that such a weight ratio as a result of the reaction of, for example, magnesium hydroxide with sulfuric acid to obtain magnesium sulfate, as described above, may depend on many factors, such as concentration, temperature, relative amounts of ingredients, acidity/alkalinity before reaction, etc. According to certain embodiments of the present invention, the method for obtaining a composition according to the invention can be carried out in such a way that a weight ratio as described above can be obtained.

[0044] If a pitch control agent is employed in the present invention, the proportion by weight of the alkaline earth metal oxides, alkaline earth metal hydroxides and alkaline earth metal salt, on the one hand, and the agent pitch control, on the other hand, can be variable from 1:9 to 9:1, such as, for example, between 3:7 and 7:3, such as, for example, variable from 2:3 to 3:2, for example in a weight ratio of 1:2 or 1:1 or 2:1.

[0045] According to certain embodiments of the present invention, compositions for use in bleaching cellulose pulps may comprise one or more alkaline earth metal oxides or alkaline earth metal hydroxides in an amount of from 10% by weight to 90% by weight of the total solids content of the composition, such as, for example, in an amount of 30% by weight to 70% by weight of the total solids content of the composition, such as, for example, in an amount of 40% by weight to 60 % by weight of the total solids content of the composition, such as, for example, in an amount of 50% by weight of the total solids content of the composition.

[0046] According to certain embodiments of the present invention, compositions for use in bleaching cellulose pulps may comprise the alkali metal salt in an amount of 0.1% by weight to 50% by weight of the total solids content of the composition, such as, for example, in an amount of 1% by weight to 30% by weight of the total solids content of the composition, such as, for example, in an amount of 5% by weight to 15% by weight of the content of total solids of the composition, such as, for example, in an amount of 10% by weight of the total solids content of the composition.

[0047] According to certain embodiments of the present invention, the compositions for use in bleaching cellulose masses may comprise one or more pitch control additives (pitch) in an amount of 1% by weight to 90% by weight of the content of total solids of the composition, such as, for example, in an amount of 10% by weight to 70% by weight of the total solids content of the composition, such as, for example, in an amount of 20% by weight to 60% by weight of the total solids content of the composition, such as, for example, in an amount of 50% by weight of the total solids content of the composition.

[0048] Another aspect of the present invention is the use of the compositions or kits of ingredients according to certain embodiments of the present invention in the process of bleaching cellulosic pulps, such as in the process of bleaching cellulose for papermaking. For example, compositions according to certain embodiments of the present invention can be used in combination with other additives, such as hydrogen peroxide, complexing agents, water glass or others, in a pulp bleaching process in a papermaking process. .

[0049] The compositions according to the present invention can totally or partially replace known alkaline compositions, such as NaOH. For example, NaOH can be completely omitted as an alkaline agent in an H2O2 bleaching process, or the amount of NaOH can be reduced by simultaneous addition of a composition according to the present invention.

[0050] According to certain embodiments of the present invention, it is not necessary that said one or more alkaline earth metal oxides or alkaline earth metal hydroxides, or mixtures thereof, on the one hand, and said one or more salts of alkaline earth metals, on the other hand, are mixed together before being introduced into a pulp to be bleached. A further aspect of the present invention is the use of a composition obtained by separately introducing one or more (e.g. all) of the components of a composition into a cellulose paper manufacture, or by separately introducing one or more components (e.g. all) from an ingredient kit in a pulp paper mill, thereby forming the composition into a pulp during the bleaching of that pulp.

[0051] In the bleaching process, the composition or kit of components according to certain embodiments of the present invention can be introduced into the cellulose in an amount such that the amount of one or more particulate alkaline earth metal oxides or alkaline earth metal hydroxides or mixtures thereof in the cellulose is from 0.1% by weight to 8% by weight of the total solids content of the cellulose during bleaching, such as from 0.2% by weight to 4% by weight of the total solids content in the cellulose during bleaching, such as from 0.5% by weight to 2.5% by weight of the total solids content of the cellulose pulp, such as, for example, from 1% by weight or 2% by weight of the solids content of the cellulose, and that the amount of one or more alkaline earth metal salts in the cellulose is from 0.01% by weight to 5% by weight of the total solids content of the cellulose during bleaching, such as from 0.02% by from 0.05% by weight to 1% by weight of the total solids content of the pulp pulp during bleaching, such as from 0.05% by weight to 0.5% by weight of the total solids content of the pulp pulp, such as, for example , about 0.1% by weight or about 0.25% by weight of the total solids content of the cellulose.

[0052] According to certain embodiments of the present invention, the composition or ingredients of a kit of components for use in bleaching a cellulose paper manufacture can be included in said cellulose, for example, during the bleaching phase, or at the beginning of the bleaching phase, or before the bleaching phase. They can also be included during or before the delignification phase. For example, the composition for use in bleaching a cellulose paper making can be included in said cellulose as early as the milling phase, during which the cellulose components are milled, or at any time between the milling phase and the bleaching stage. The various components of the composition according to certain embodiments of the present invention may also be added to the papermaking pulp at separate stages, such as, for example, during the milling stage and/or immediately before the start of the bleaching or delignification stage.

[0053] For example, according to one embodiment of the present invention, the composition or ingredients of a component kit for use in bleaching a papermaking pulp according to some embodiments of the present invention can be introduced into a pulp to be bleached prior to the introduction of any alkaline bleaching agents such as NaOH, water glass, sodium silicate and/or hydrogen peroxide. In this case, the alkaline earth metal oxide or alkaline earth metal hydroxide has been activated by the presence of alkaline earth metal salt (such as alkaline earth metal sulfate), and/or wood-derived organic acids present in the cellulose mixture, and/or the mineral acid before starting the bleaching process. For example, according to one embodiment of the invention, the alkaline earth metal hydroxide and/or the alkaline earth metal oxide is added to an acidic cellulose mixture (e.g., in which the only acids present are those found naturally in cellulose and/or or without any external acid added) before starting the bleaching process and/or before adding any alkaline bleaching agents.

[0054] As discussed above, this "protection" of viscosity is believed to be caused by the presence of free alkaline earth metal ions, such as magnesium ions, in the mixture or cellulosic mass. This effect is accentuated when alkaline earth metal ions form before the start of bleaching by introducing any alkaline bleaching agents.

[0055] According to a further embodiment of the present invention, the ingredient composition or the ingredients of an ingredient kit can be added in a previous step, such as during an acid bleaching phase, during the addition of agents chelating agents such as EDTA or chlorine dioxide. This embodiment includes all uses of the ingredient composition or the ingredients from an ingredient kit in a bleaching step that takes place at a pH of 7 or less.

[0056] In order to avoid confusion, embodiments according to the following numbered periods all form part of the present invention:

[0057] 1. Composition for use in a pulp bleaching process, the composition comprising one or more alkaline earth metal oxides and/or one or more alkaline earth metal hydroxides; one or more alkaline earth metal salts; and, optionally, one or more pitch control additives.

[0058] 2. Composition, in accordance with sentence numbered 1, in which said pitch control additive (pitch) is selected from talc, bentonite, zeolite, diatomaceous earth, cationic mica, hydrophobic carbonates, decomposition enzymes resins, cationic polymers designed to capture and immobilize resins or resin components on the fiber surface, aluminum sulfate, polyaluminum chloride and dispersing agents specifically designed for dispersing resins and resin components, and mixtures thereof.

[0059] 3. Composition, according to any one of the preceding numbered sentences, in which the alkaline earth metal is selected from magnesium, calcium and mixtures thereof.

[0060] 4. Composition, according to any of the preceding numbered sentences, in which said pitch control additive (pitch) is selected from micronized talc, bimodal talc and cationic talc.

[0061] 5. Composition according to any one of sentences numbered 1 to 3, wherein said pitch control additive is a bentonite, such as, for example, activated bentonite.

[0062] 6. Composition, according to any one of the preceding numbered sentences, which is a cellulosic mass.

[0063] 7. Composition, according to sentence numbered 6, wherein said aqueous cellulosic mass has a total solids content of 10 to 75% by weight, based on the total weight of the cellulosic mass.

[0064] 8. Composition according to any one of the preceding numbered sentences, in which the proportion by weight of (i) an alkaline earth metal oxide and/or an alkaline earth metal hydroxide and (ii) an alkaline earth metal salt is from 1:2 to 100:1.

[0065] 9. Composition according to any of the preceding numbered sentences, further comprising at least one of the following additives: (a) dispersing agents; (b) loads; (c) surfactants; (d) bleaching agents; (e) chelating agents; and (f) pH buffering agents.

[0066] 10. Kit of components comprising an alkaline earth metal oxide and/or an alkaline earth metal hydroxide stored in a first container, and one or both of a second and third containers with an aqueous mineral acid solution stored in the second container, and sulfur dioxide and/or carbon dioxide stored in the third container.

[0067] 11. Method for forming a composition, according to any one of the sentences numbered 1 to 9, comprising a step of mixing an alkaline earth metal oxide and/or an alkaline earth metal hydroxide with a mineral acid, or sulfur dioxide, or carbon dioxide, optionally in the presence of one or more pitch control agents.

[0068] 12. Method according to sentence numbered 11, when carried out on an aqueous cellulose bleaching composition.

[0069] 13. Method according to sentence numbered 12, in which the mixing step is carried out by adding sulfuric acid or sulfur dioxide or carbon dioxide to a paper bleaching mass comprising the alkaline earth metal oxide and /or alkaline earth metal hydroxide.

[0070] 14. Method according to any one of sentences numbered 11 to 13, comprising the step of mixing the kit ingredients of sentence numbered 10 in a paper bleaching mass or a delignification pulp.

[0071] 15. Use of a composition or a method or a kit, according to any of the preceding numbered sentences, in a pulp bleaching process or a pulp delignification process.

[0072] 16. Use, in accordance with sentence numbered 15, in a process to reduce the pitch of cellulosic mass.

[0073] 17. Use, in accordance with sentence numbered 15, in a process to protect cellulose from depolymerization and/or degradation.

[0074] 18. Use, in accordance with sentence numbered 15, in or after an acid bleaching step.

[0075] 19. Use, in accordance with any of the sentences numbered 15 to 18, in which said composition or the product of the method or the components of the kit are added to the pulp to be bleached, before the addition of any other agents alkaline bleaches such as water glass, sodium silicate, NaOH and/or hydrogen peroxide.

[0076] 20. Method of reducing pitch (pitch) in cellulose, including use according to any of the sentences numbered 15 to 19.

EXAMPLES

[0077] As used herein, the viscosity of the cellulose was measured in accordance with TAPPI T 230 om-08. Furthermore, as used herein, the kappa value which indicates the residual amount of lignin in cellulose was measured in accordance with ISO-302:2012.

[0078] In a process of bleaching a paper pulp using sodium hydroxide as the bleaching agent, the use of magnesium hydroxide as an additive was compared to the use of magnesium hydroxide in combination with mineral acid, as well as in combination with mineral acid and EDTA as a chelating agent.

[0079] An unbleached softwood kraft pulp was used as the starting material. The pulp was taken from industrial production at a softwood kraft pulp mill. The paper pulp was washed at the factory and then subjected to a bleaching process without further washing in the laboratory. Commercially available magnesium hydroxide, diluted before use to a concentration of 1 mol/L, was used in these tests.

[0080] In Comparative Examples 1 and 2, magnesium sulfate and a magnesium hydroxide solution, respectively, were added to papermaking pulp. In Examples 1 and 2, magnesium hydroxide solution and laboratory grade sulfuric acid were added. In Example 3, laboratory grade EDTA (10 g/L) was additionally charged. Sulfuric acid and EDTA were first mixed with commercial magnesium hydroxide. The additive mixtures are shown in Table I. This mixture was then blended with the cellulose. In all Examples, the cellulose charge was 120 g (oven dried). Bleaching was performed in a 2 L Teflon-lined autoclave placed in a preheated silicone oil bath. The total reaction time was about two and a half hours in each case. Table I

[0081] The % by weight indications are relative to the total dry weight of the cellulose.

[0082] The pulp test was carried out according to the usual standards according to the German institute Thünen Institute (Hamburg, Germany). Viscosity was determined according to ISO 5351 using copper ethylenediamine (cuen) solution. The results are shown in Table II. Table II

[0083] It is evident from the data obtained that (i) the viscosity values for the Examples of the invention are equivalent to those of Comparative Example 1, while the use of magnesium sulfate was avoided. At the same time, the viscosity values and coating value are improved over Comparative Example 2. Finally, the gloss values, coating value and overall yield were not adversely affected compared to Comparative Example 1.

[0084] Example 3, making use of EDTA in addition to the combination of Mg(OH)2/H2SO4, does not substantially modify the expected technical properties of the cellulose masses.

[0085] In a separate bleaching process of paper cellulose using sodium hydroxide and hydrogen peroxide as bleaching agents, the effect of using increasing amounts of magnesium hydroxide to replace sodium hydroxide on peroxide was determined. residual and shine.

[0086] An unbleached softwood kraft pulp was used as the starting material. The pulp was taken from industrial production at a softwood kraft pulp mill. The pulp was washed at the factory and then subjected to a bleaching process without further washing in the laboratory. The pressed water of the cellulose sample used in the laboratory bleaching tests had a pH value of 2.8, so the cellulose was clearly acidic. Commercially available magnesium hydroxide, diluted before use to a concentration of 1 mol/L, was used in these tests.

[0087] The cellulose mixtures shown in Table III were prepared by first mixing the additive components together and then adding this mixture to an aqueous cellulose. Bleaching was carried out in plastic bags, placed in a preheated 70°C water bath, with the opening of the bags out of the water to prevent additional water from remaining in the bags during bleaching. The total reaction time was about two hours in each case. Table III

[0088] After bleaching for about 2 hours, the residual peroxide was determined by pressing 1 ml of water from the cellulose and using iodometric titration well known to those skilled in this technique and described in the literature. ISO brightness of the pulp blend was also determined from a dried filter cake of bleached pulp using a Konica Minolta CM3700d spectrocolorimeter to ISO 2469 (R457). The results are shown in Table IV. The chemical oxygen demand (COD) was determined from the pulp water pressed after bleaching using the LCK614 Hach Lange cuvette test. Table IV

[0089] It has been found that magnesium hydroxide can be used to replace sodium hydroxide in the bleaching process when using an acidic cellulose mixture. Even at relatively low replacement rates of NaOH by Mg(OH)2, a significant drop in COD values can be observed. This is advantageous for pulp yield, as each kg of COD produced represents a loss in pulp yield. It also has a positive effect on the DOC in wastewater, thus providing an improved environmental impact.

[0090] In another bleaching process of paper cellulose, using sodium hydroxide and hydrogen peroxide as bleaching agents, the effect of adding magnesium hydroxide to cellulose before sodium hydroxide and any other alkaline additives was determined.

[0091] An unbleached softwood kraft pulp was used as the starting material. The pulp was taken from industrial production at a softwood kraft pulp mill. The pulp was washed at the factory and then subjected to a bleaching process without further washing in the laboratory. The pressed water of the cellulose sample used in the laboratory bleaching tests had a pH value of 2.8, so the cellulose was clearly acidic. Commercially available magnesium hydroxide, diluted before use to a concentration of 1 mol/L, was used in these tests.

[0092] The cellulose mixtures shown in Table V were prepared by mixing the additive components and then adding this mixture to aqueous cellulose, or, where magnesium hydroxide was added to the cellulose first, adding magnesium hydroxide to the aqueous cellulose and mixing the cellulose mixture by hand for about one minute, then mixing in the remaining additive components and adding this mixture to the magnesium hydroxide and cellulose mixture. Bleaching was carried out in plastic bags, placed in a preheated 70°C water bath, with the opening of the bags out of the water to prevent additional water from remaining in the bags during bleaching. The total reaction time was about 80 minutes in each case. Table V

[0093] After bleaching for about 80 minutes, the residual peroxide and ISO brightness of the cellulose blends were measured as described above. The results are shown in Table VI below. Table VI

[0094] It was found that the residual peroxide and ISO brightness of the cellulose mixtures to which magnesium hydroxide was first added are better than those of the cellulose mixture to which magnesium hydroxide was added at the same time as the other additive components .

[0095] In another bleaching process of paper pulp using sodium hydroxide and hydrogen peroxide as bleaching agents, the effect of using a reduced amount of hydrogen peroxide together with magnesium hydroxide was determined.

[0096] An unbleached softwood kraft pulp was used as the starting material. The pulp was taken from industrial production at a softwood kraft pulp mill. The pulp was washed at the factory and then subjected to a bleaching process without further washing in the laboratory. The pressed water of the cellulose sample used in the laboratory bleaching tests had a pH value of 2.8, so the cellulose was clearly acidic. Commercially available magnesium hydroxide, diluted before use to a concentration of 1 mol/L, was used in these tests.

[0097] The cellulose mixtures shown in Table VII were prepared by mixing the additive components and then adding this mixture to aqueous cellulose, or, where magnesium hydroxide was added to the cellulose first, adding magnesium hydroxide to the aqueous cellulose and mixing the cellulose mixture by hand for about 1 minute, then mixing the remaining additive components and adding this mixture to the magnesium hydroxide and cellulose mixture. Bleaching was carried out in plastic bags, placed in a water bath preheated to 70°C, with the opening of the bags out of the water to prevent additional water from remaining in the bags during bleaching. The total reaction time was about 80 minutes in each case. Table VII

[0098] After bleaching for about 80 minutes, the residual peroxide and ISO brightness of the cellulose blends were measured as described above. The results are shown in Table VIII below. Table VIII

[0099] It was found that similar results of residual peroxide and ISO brightness were obtained even when using reduced amounts of hydrogen peroxide when magnesium hydroxide was added first.

[00100] It should be noted that the present invention may comprise any combination of the features and/or limitations referred to herein, except combinations of these features that are mutually exclusive. The foregoing description refers to particular embodiments of the present invention for the purpose of illustrating it. It will be apparent, however, to one skilled in the art that many modifications and variations of the embodiments described herein are possible. All such modifications and variations are intended to be within the scope of the present invention as defined in the appended claims.

Claims (9)

1. Method for forming a composition for use in a pulp bleaching process, characterized in that it comprises: a step of mixing magnesium oxide and/or a magnesium hydroxide with a mineral acid, or sulfur dioxide , or carbon dioxide or magnesium salt, such as magnesium sulfate or a magnesium carbonate, optionally in the presence of one or more pitch control agents, wherein the pH of the resulting composition is between 7 and 10, 5. 2. Method according to claim 1, characterized in that the pitch control additive (pitch) is selected from talc, bentonite, zeolite, diatomaceous earth, cationic mica, hydrophobic carbonates, resin decomposition enzymes, cationic polymers designed to capture and immobilize resins or resinous components on the fiber surface, aluminum sulphate, polyaluminum chloride and dispersing agents specially designed for dispersing resins and resinous components, and mixtures thereof, for example, in which the pitch is selected from micronized talc, bimodal talc and cationic talc, or wherein the pitch control additive is a bentonite, such as, for example, activated bentonite. 3. Composition obtainable from the method as defined in claim 1 or 2, for use in a pulp bleaching process, characterized in that it comprises: (i) magnesium oxide and/or magnesium hydroxide; (ii) one or more magnesium salts; and (iii) optionally, one or more pitch control additives, wherein the pH of the resulting composition is between 7 and 10.5. 4. Composition according to claim 3, characterized in that the pitch control additive (pitch) is selected from talc, bentonite, zeolite, diatomaceous earth, cationic mica, hydrophobic carbonates, resin decomposition enzymes, sulphate aluminum, polyaluminum chloride and dispersing agents and mixtures thereof, for example, wherein the pitch control additive is selected from micronized talc, bimodal talc and cationic talc, or wherein the pitch control additive ) is a bentonite, such as activated bentonite. 5. Composition according to claim 3 or 4, characterized in that it is an aqueous cellulosic mass. 6. Composition according to claim 5, characterized in that the aqueous cellulosic mass has a total solids content of 10 to 75% by weight, based on the total weight of the cellulosic mass. 7. Composition according to any one of claims 3 to 6, characterized in that the proportion by weight of: (i) magnesium oxide and/or magnesium hydroxide, and (ii) a magnesium salt is 1: 10 to 100:1. 8. Composition according to any one of claims 3 to 7, characterized in that it further comprises at least one of the following additives: (a) dispersing agents; (b) loads; (c) surfactants; (d) bleaching agents; (e) chelating agents; and (f) pH buffering agents. 9. Kit of ingredients, characterized in that it comprises: (i) a composition as defined in claim 3, stored in a first container, and (ii) one or both of a second and third containers with an aqueous mineral acid solution stored in the second container and sulfur dioxide and/or carbon dioxide stored in the third container.