RU2776518C2 - Methods for production of kraft cellulose with high yield - Google Patents

Abstract

FIELD: woodworking industry.

SUBSTANCE: claimed group of inventions relates to methods for the production of kraft cellulose with high yield. Methods include: the production of kraft cellulose with a permanganate number of at least 20; the processing of kraft cellulose with a composition including: a) organic aminophosphonate, b) magnesium salt, and c) one or more anionic linear alcohols and ethoxylates or anionic polyacrylate, while organic aminophosphanate is selected from diethylenetriaminepentamethylenephosphonic acid (DTMP), aminotrismethylenephosphonate (ATMP), (bis)hexamethylenetriaminepentamethylenephosphonic acid (BHMTPMP), polyaminopolyestermethylenephosphonate (PAPEMP) and combinations thereof, while anionic linear alcohols and ethoxylates are selected from sodium laurylestersulfate (SLES), sodium laurylesterphosphate (SLEP), sodium laurylsulfate (SLS) and combinations thereof; and the decrease in the initial permanganate number of kraft cellulose to a given final permanganate number, while kraft cellulose is processed with the composition before a two-stage process of oxygen delignification, while final viscosity of cellulose remains high compared to kraft cellulose unprocessed with oxygen delignification.

EFFECT: methods improve a process of cellulose fiber delignification in the chemical production of wood pulp.

5 cl, 8 dwg, 38 tbl, 12 ex

Description

Cross-reference to related application

This application claims priority over U.S. Provisional Application No. 62/556,706, filed September 11, 2017, the entire contents of which are hereby incorporated by reference in their entirety.

BACKGROUND OF THE INVENTION The present invention relates to a composition for improving the delignification of cellulose fiber in wood pulps. First of all, the composition can be added after chemical pulping and washing of wood pulps.

Wood pulp can be obtained from any wood, hardwood or softwood, as well as agricultural biomass, including, but not limited to, bamboo, cane-sugar bagasse, cereal straw and annual grasses. The pulping process for converting wood particles into pulp includes the kraft process, the neutral and acid sulfite processes, the soda process (with or without the addition of additional catalysts such as anthraquinone), and the solvent process.

Wood pulp is mainly delignified using compressed oxygen (oxygen delignification) to reduce the level of lignin by up to 40-70%. Delignification is usually carried out before a multi-stage bleaching procedure. The wood pulp commonly used in this process is obtained from softwood with a lignin content of 3-7%, and from hardwood containing 2-4% lignin. Such pulp is usually produced by the kraft method according to standard techniques, whereby if the kraft pulp is stopped earlier (or after pulping under milder conditions), the result is a large amount of wood pulp (higher yield) with a high content of lignin.

The currently used method for improving pulp delignification refers to pulp that is treated with the composition in a two-stage oxygen delignification process. To delignify a pulp with a high kappa number, it is usually necessary to use more aggressive or harsh conditions to obtain a pulp with the required lower kappa number. The term "aggressive conditions" means that the reduction in permanganate number must be carried out at a higher temperature, more alkaline pH, for a longer time, or using various combinations of these factors in order to reduce the level of lignin by 40-70%. As a result of processing under such severe or aggressive conditions, the loss of cellulose can be increased compared to the loss under less severe conditions. However, such conditions can also lead to lower pulp quality as measured by the solution viscosity (TAPPI T230 om-13). During the stages of oxygen delignification during the processing of wood pulp, the residual lignin in it decreases to the limiting level, but at the same time, the oxidative splitting of cellulose chains (depolymerization) and the deterioration of the physical properties of the pulp occur. These disadvantages limit the more efficient use of this method. By improving or increasing the efficiency of the oxygen delignification process, even more lignin can be removed, but this currently results in unacceptable degradation of the fibrous product as measured by pulp viscosity and fiber tensile strength (TAPPI T231 cm-07).

The main chemical reactions, the industrial application of the method and the limitations mentioned above are described in the review article by McDonough, Thomas J., Oxygen Delignification, ch. IV-1, Pulp Bleach. Principles and Practices, ed. Dence & Reeve Eds. (1996). Pulp quality control has historically been about optimizing reaction parameters to minimize cellulose depolymerization. Useful chemical additives, other than the original discovery of magnesium salts as cellulose stabilizers, are described very briefly. A recent paper by Widiatmoko "Oxygen Delignification Process Chemistry for ACACIA" Georgia Institute of Technology (December 2006) describes in detail the process of delignification in the production of kraft pulp. However, magnesium additives are only mentioned to describe one of the most important factors in improving oxygen delignification, which is the effective mixing of chemical agents with the appropriate wood pulp. There is no indication that the chemical additives described above have any effect on reducing the kappa number of kraft pulp.

US Pat. No. 6,454,900 B2 describes a two-stage oxygen delignification process for reducing the permanganate number of medium viscosity cellulose, the process optimizing the temperature, pressure and pH of the system. However, there is no mention of specific chemical additives that improve the process of oxygen delignification.

Currently, chemical additives are used in practice in the process of oxygen delignification to inhibit the depolymerization of cellulose and stabilize its mechanical properties. Magnesium salts are most commonly used (Epsom's salt, MgSO ₄ .7H ₂ O is often used), but it has also been found that additional organic complexing or chelating agents can be used to stabilize the cellulose.

Canadian Patent 1120210 (Monsanto) describes the addition of a chelating aminomethylene phosphonate in combination with a magnesium salt, which has been shown to be effective when the phosphonate is added in amounts greater than 0.01% based on dry weight of wood pulp (in this context referred to as dried weight). in wood pulp kiln, OD). The patent describes the addition of diethylenetriaminepentamethylenephosphonic acid (DTPMP) to a neutral pH solution in which DTPMP is typically replaced by about 7 sodium cations (DTPMP⋅7Na). However, there is no description of additional materials such as surfactants or polymers that can improve the efficiency of delignification and cellulose stabilization.

US Pat. No. 2007/0272378 A1 describes a method for reducing extractables in peroxide bleaching of wood pulp by adding an anionic surfactant and polymeric peroxide stabilizers that inhibit the deposition of extractables on cellulose fibers, leaving the extractables in the aqueous phase. However, there is no description or discussion of the use of wood pulp or the oxygen delignification process used for wood pulp to stabilize pulp or improve delignification that is not part of the peroxide bleaching process.

Japanese Patent JP2000/080582 (Mitsubishi) discloses that the permanganate number of medium density wood pulp can be reduced in an oxygen bleaching process by adding a chelating phosphonate alone or in combination with a surfactant to the pulp. An alternative two-stage method is described, in which one stage is carried out under acidic conditions and the other under alkaline conditions, there is no description of the addition of magnesium sulfate to stabilize the viscosity of the cellulose.

According to other oxygen bleaching processes, as described in US Pat. US Pat. No. 4,372,811 describes alkaline oxygen delignification and bleaching of pulp with inhibition of hydrocarbon degradation in the pulp by adding one or more aromatic diamines in addition to magnesium and a chelating agent that includes aminomethylphosphonic acids such as diethylenetriaminepentamethylenephosphonic acid (DTPMP). The addition of materials such as surfactants or polymers to improve delignification and stabilize pulp viscosity is not described.

A published study indicates that the use of surfactants in soda-boiled bagasse reduces the permanganate number and improves the yield and whiteness of the resulting wood pulp. However, this study is limited to bleaching experiments and bleaching method (Hamzeh et al. BioResources, 4(4): 1267-1275, "Soda Pulping with Surfactants" (2009). US Patent Application No. 2005/0217813 A1 describes, that diethylenetriaminepentamethylenephosphonic acid (DTPMP) can maintain or increase the brightness of the pulp and at the same time reduce the level of bleaching chemicals, however, oxygen delignification is not described.

A disadvantage of wood pulp that has been delignified with oxygen is degradation, which is higher when the pulp is treated in a one-step process compared to when treated in a two-step process when delignified to the same final kappa number (as defined in TAPPI T 236 om-13 ), which is an indication of the residual lignin content or degree of bleaching. In a two-stage process, the pulp is first treated at a higher pH, higher oxygen pressure, and at a lower temperature for a shorter period of time compared to a one-stage process, after which the pulp can be treated in a second stage at a lower pressure, lower pH and higher temperature for a longer period of time. The method of two-stage oxygen delignification is described in US patent No. 6454900 (Sunds 2002). The method refers to two separate oxygen treatment processes under two different conditions.

The present methods provide an improvement in the oxygen delignification process, whereby lower levels of phosphonates are realized and in some embodiments complete removal of magnesium salts is observed. There is also a need for improved environmental performance of pulp and paper mills while reducing the amounts of phosphorus and nitrogen containing compounds used in the processing and bleaching of wood pulp. In addition, there is a clear need to improve the oxygen delignification process, which will result in reduced levels of lignin, increased strength of the resulting fibers, and increased fiber yield. It has been found that the present compositions are characterized by all the advantages listed above.

Brief description of the present invention

The present method relates to the production of high yield kraft pulp. First of all, the method includes the addition of a composition comprising an aminophosphonate and a linear sulfonated alcohol ethoxylated surfactant, primarily sodium lauryl ether sulfate (SLES). The composition may optionally contain a source of magnesium in the form of a divalent cation (Mg ²⁺ ) in the form of a magnesium salt such as magnesium sulfate (MgSO ₄ ), magnesium sulfate heptahydrate (MgSO ₄ ⋅7H ₂ O), magnesium oxide (MgO), magnesium hydroxide ( Mg(OH) ₂ ), magnesium acetate (Mg(CH ₃ COO) ₂ ), magnesium acetate tetrahydrate (Mg(CH ₃ COO) ₂ ⋅4H ₂ O), and magnesium carbonate (MgCO ₃ ).

In another aspect, a process is provided for making high yield oxygen delignified kraft pulp wherein the kappa number of kraft pulp is at least about 30 and may be at least about 23 and may be at least about 20 for hardwood species. , or the kappa number of kraft pulp is at least about 40, and may be at least about 33, and may be at least about 30 for softwood pulp. Kraft pulp is treated with a composition comprising: a) an organic aminophosphonate in an amount of from about 0.6 kg/t by weight of dry pulp to about 1.2 kg/t, based on the weight of active acid, b) a magnesium salt in an amount of from about 0, 1 kg/t to about 3.2 kg/t, based on the weight of the anhydrous substance; and c) from about 0.08 kg/t to about 0.16 kg/t of active surfactant base, which is selected from the group consisting of linear sulfonated alcohol ethoxylates. Prior to the oxygen delignification process, kraft pulp is treated with the composition. The terms "active acid" or "active solids" or "active substances", used in the context of the present invention, means the weight of each chemical in the composition, which is treated wood pulp.

In another aspect of the present method, the composition that is added to wood kraft pulp comprises an organic aminophosphonate and an anionic polyacrylate, especially a salt of poly-α-hydroxyacrylate (PHAS).

In another aspect of the present method, the organic aminophosphonate may be diethylenetriaminepentamethylenephosphonic acid (DTPMP), aminotrismethylenephosphonate (ATMP), (bis)hexamethylenetriaminepentamethylenephosphonic acid (BHMTMP) and polyaminopolyethermethylenephosphonate (PAREMP) and the anionic polyacrylate is a salt of poly-α-hydroxyacrylate (PHAS).

In other aspects of the method, the temperature in the first stage of the two-stage oxygen delignification process is from about 80° C. to about 100° C. and the temperature in the second stage is from about 90° C. to about 120° C. and the pressure in the first stage is from about 80 lbs. /square inch to about 120 psi O ₂ may be from 90 psi to 110 psi O ₂ and the pressure in the second stage is from about 25 psi to about 90 psi O ₂ , may be 50 psi to 90 psi O ₂ , may be 60 psi to 90 psi O ₂ .

In still other aspects of the method, kraft pulp has an kappa number of at least about 30, at least about 23, and at least about 20 for hardwood pulp, or an kappa number of at least about 40, at least about 33 and at least about 30 for softwood pulp, and treating kraft pulp with a composition comprising: acid, b) a magnesium salt in an amount of from about 0 kg/t to about 3.2 kg/t, based on the weight of the anhydrous substance, and c) from about 0.43 kg/t to about 1.43 kg/t, based on an anionic polyacrylate active base such as a poly-α-hydroxyacrylate (PHAS) salt, and wherein the kraft pulp is treated with the composition prior to the oxygen delignification process.

According to the present method, kraft pulp is treated with the composition prior to the oxygen delignification process.

Brief description of the drawings

In FIG. 1 shows the preferred lignin removal/KAP reduction in the right-to-left direction and the preferred higher viscosity stabilization in the upward direction.

In FIG. 2 shows permanganate numbers under poor mixing conditions of various surfactants and in the absence of surfactants.

In FIG. 3 shows the viscosities of treated and untreated wood pulp at different permanganate numbers.

In FIG. 4 shows the viscosities of treated and untreated wood pulp at different permanganate numbers.

In FIG. 5 shows the final permanganate numbers of treated and untreated pulps.

In FIG. 6 shows the final values of the viscosity of the treated and untreated wood pulp.

In FIG. 7 shows the final permanganate numbers of wood pulp treated under various reaction conditions.

In FIG. 8 shows the final viscosities of wood pulp treated under various reaction conditions.

Detailed description of embodiments of the present invention

The following detailed description is illustrative in nature and is not intended to limit the invention or the application and use of the invention. Moreover, there is no intention of linking with any theory given in the prior art or in the following detailed description.

In one aspect, the present method relates to the production of high yield kraft pulp comprising

obtaining kraft pulp with a high kappa number of at least about 30, at least about 23, and at least about 20 for hardwood pulp or an kappa number of at least about 40, at least about 33, and at least about 30 for softwood pulp,

treating the kraft pulp with a composition comprising a) an organic aminophosphonate, b) a magnesium salt, and c) one or more sulfonated ethoxylates, wherein the kraft pulp is treated with the composition prior to the oxygen delignification process. First of all, one or more sulfated ethoxylates are sodium lauryl ethersulfonate (SLES), sodium lauryl ether phosphate (SLEP), or sodium lauryl sulfate (SLS). See formulas I-III below.

In another aspect, the organic aminophosphonate in the composition is selected from diethylenetriaminepentamethylenephosphonic acid (DTPMP), aminotrismethylenephosphonate (ATMP), (bis)hexamethylenetriaminepentamethylenephosphonic acid (BHMTMP), and polyaminopolyethermethylenephosphonate (PAREMP), and the divalent magnesium cation Mg ²⁺ is selected from a magnesium salt such as magnesium sulfate or magnesium sulfate heptahydrate. See formulas IV-VII below.

Formula VI:

(bis)hexamethylenetriaminepentamethylenephosphonic acid (BHMTMP)

Formula VII: polyaminopolyethermethylenephosphonate (PAREMP)

In yet another aspect, the oxygen delignification process is a one- or two-stage oxygen delignification process, wherein the process for producing high yield oxygen delignified kraft pulp includes: producing kraft pulp with a kappa number of at least about 30, at least about 23, and at least about 20 for hardwood pulp, or with a kappa number of at least about 40, at least about 33, and at least about 30 for softwood pulp, treating kraft pulp with a composition comprising: a) organic aminophosphonate in an amount of from about 0.6 kg/t to about 1.2 kg/t, based on the weight of active acid, b) a magnesium salt in an amount of from about 0.1 kg/t to about 3.2 kg/t, calculated by weight of the anhydrous base; and c) a surfactant in an amount of from about 0.08 kg/t to about 0.16 kg/t, based on a an active base that is selected from the group consisting of linear sulfonated alcohol ethoxylates, and where the kraft pulp is treated with the composition prior to the oxygen delignification process.

In another aspect, the present method relates to the production of high yield kraft pulp, producing kraft pulp with a kappa number of at least about 30, at least about 23, and at least about 20 for hardwood pulp, or kappa a number of at least about 40, at least about 33, and at least about 30 for softwood pulp. The resulting pulp is treated with a composition comprising a) an organic aminophosphonate (DTMP) and b) a polyacrylate polymer such as poly-α-hydroxyacrylate (PHAS, see below) and wherein the kraft pulp is treated with the composition prior to the oxygen delignification process.

In yet another aspect, a process for producing high yield oxygen delignified kraft pulp refers to producing kraft pulp with a kappa number of at least about 30, at least about 23, and at least about 20 for hardwood pulp, or kappa a number of at least about 40, at least about 33, and at least about 30 for softwood pulp, and treating kraft pulp with a composition comprising: a) an organic aminophosphonate in an amount of from about 0.17 kg/ton to about 0.57 kg/t based on the weight of the active acid, b) from about 0.43 kg/t to about 1.43 kg/t based on the weight of the active basis of the poly-α-hydroxyacrylate (PHAS), and where kraft- the pulp is treated with the composition prior to the oxygen delignification process.

In another aspect, the method may include optionally adding magnesium to the kraft pulp before, simultaneously with or after the addition of the organic aminophosphonate/polyacrylate composition.

Examples

Example 1

Treatment of unbleached wood pulp (Brownstock) with magnesium sulfate (MgSO ₄ ) in an oxygen delignification step resulted in a final wood pulp with a higher lignin content (as measured by permanganate number, which is determined according to TAPPI T236 om-13) compared to untreated wood pulp . This treatment resulted in lower levels of the diethylenetriaminepentamethylenephosphonate (DTPMP) salt in the reaction mixture, and intermediate levels when both compounds were used in the mixture at different ratios. Surprisingly, the addition of a specific type of surfactant to the combined chelating agents in the resulting product resulted in low permanganate numbers. Of particular importance were anionic linear alcohols and ethoxylates in the form of sodium lauryl ether sulfate (SLES) and sodium lauryl ether phosphate (SLEP).

Eucalyptus kraft pulp with a high lignin content (in this context, indicating its permanganate number, i.e., a permanganate number of 23) was subjected to delignification in a two-stage method under "aggressive" conditions, as shown in table. 1. The product was obtained using other surfactants that were used in the delignification reaction at the same dosage in relation to the wood mass.

An oxygen delignification improvement product was obtained in the absence of a surfactant (B), in the absence of a phosphorylated chelating agent (C), and in the absence of both compounds (A). Other products were obtained (table. 3) using surfactants of various types (D-J), as described in table. 2 below.

The compositions of the products, the permanganate number of the obtained wood pulp and the measurement of viscosity after the reaction of oxygen delignification are given in table. 3.

The results obtained indicated that the addition of a surfactant based on SLES to the composition provided a decrease in the permanganate number while maintaining a high viscosity. In FIG. 1 shows the preferred lignin removal/KAP reduction in the right-to-left direction and the preferred high viscosity stabilization in the upward direction. As seen in FIG. 1, "composition D", containing the surfactant sodium lauryl ether sulfate, was characterized by the highest viscosity and the lowest kappa number. Other ethoxylated anionic surfactant sodium lauryl ether phosphate (E) and non-ethoxylated anionic surfactant sodium lauryl sulfate (F) provided less improvement. Other surfactants did not provide such an unexpected improvement.

Example 2

The final permanganate value of the resulting pulp after the oxygen delignification step is of paramount importance to pulp producers. The cost of bleaching wood pulp to the final desired whiteness depends on this permanganate number of the pulp entering the bleaching plant. The introduction of surfactants improves the efficiency of the stage of oxygen delignification and reduces the cost of processing throughout the bleaching plant while reducing the permanganate number. The amount of surfactant of a particular preferred type (anionic linear ethoxylated alcohol) can be adjusted to influence delignification while stabilizing pulp viscosity.

High lignin kraft pulp (KM 23) from eucalyptus was delignified by 52% under "aggressive" conditions in a single stage oxygen treatment at 103° C., 4% caustic, 90 psi O ₂ pressure for 60 min. The delignification enhancement product was obtained with similar levels of MgSO ₄ and DTPMP but contained different levels of sodium lauryl ether sulfate surfactant (SLES) as shown in Table 1. 4 and was added at the same level as in all experiments.

The results presented in the last two columns of the table indicate that increasing the dose of surfactant reduced the permanganate number. The pulp viscosity (given in centipoise (cP) in this context) remained relatively unchanged at lower doses (<0.03% for cellulose OD) of the surfactant.

Example 3

The efficiency of oxygen delignification depends on the ability of O ₂ to interact with the fiber. This requires diffusion of O ₂ from the gaseous phase into the water surrounding the fibers in the emulsion, then from the aqueous phase into the fiber to interact with lignin. Only a small fraction of the oxygen at any given time is dissolved in solution. The bulk of the oxygen is in the gaseous phase in the form of small bubbles mixed into the emulsion with very vigorous agitation with O ₂ in a medium consistency pump before entering the reactor. Insufficient mixing of oxygen with the wood pulp slurry results in the removal of oxygen from the mixture, and insufficient oxygen to diffuse into the delignification solution.

An oxygen delignification improvement product was prepared using a delignification enhancing surfactant as shown in Examples 1 and 2. This surfactant also improved the delignification of undermixed systems.

Kraft pulp (KM 20) from eucalyptus was delignified under "aggressive" conditions in a single step oxygen treatment at 90° C., 4% NaOH in wood pulp, for 60 minutes at 90 psi. Surfactants were dosed at the level of 0.5 kg/t based on the mass of active substances. An insufficiently mixed system was simulated by turning off the mixer at a fixed time interval in all experiments. The final permanganate number of the "well mixed" reaction mixture was 10 (50% delignification), as shown in the right column of Table. 5. The effect of the "not mixed enough" system was to increase the permanganate number to 15.1. The addition of various surfactants to the wood pulp slurry in the case of an "under-mixed" system is also shown in Table 1. 5.

The addition of SLES (see Sample C) to the slurry resulted in improved delignification of the slurry as evidenced by a significant reduction in permanganate number under under-mixing conditions compared to other surfactants and in the absence of surfactants (see FIG. 2).

Example 4

An important advantage of the oxygen delignification improvement product is that a higher kappa number pulp can be used and that this pulp can be produced in a higher yield than standard pulp with a lower kappa number. Pulp with a higher kappa number should be delignified under more aggressive conditions to achieve the same desired kappa number as standard wood pulp entering the bleaching plant. For more "aggressive" oxygen delignification it is necessary to use higher alkali concentrations, higher temperatures, longer time intervals, or combinations thereof.

Higher lignin (KP 23) kraft pulp from eucalyptus was delignified to a final KP of 10 in one-step oxygen delignification reactions under two different aggressive conditions (alkali and temperature). These conditions and the conditions of the "standard" reaction are given in table. 6.

The oxygen delignification improvement product consisted of components in amounts as shown in Table 1. 7.

The product of improved delignification due to viscosity stabilization was compared in all cases with no treatment or treatment with magnesium sulfate. In table. Figure 8 summarizes the effect on woodpulp with a high kappa number of 23 and compared with the effect of a standard oxygen delignification step on woodpulp with a low kappa number of 16.

Oxygen delignification is used almost exclusively for wood pulps, which are then bleached to a high degree of whiteness. The use of additional bleaching steps provides additional opportunities to reduce the viscosity of the wood pulp, whereby the increase in viscosity with the use of the delignification improvement product should not be lost during bleaching. This was demonstrated using the same pulps from Example 4 treated with the bleaching sequence D _HT E _P D ₁ giving the pulp a whiteness of 85 TAPPI where D _HT is the delignification step when heated at 90° C. with chlorine dioxide, Ep means a peroxide-enhanced extraction step; and D ₁ means a chlorine dioxide brightening step.

The results presented in table. 9 indicate that the use of a delignification-enhancing composition in the pre-oxygen delignification step results in stronger fibers as measured by elongation at break (as determined using TAPPI T 231 cm-07 at zero clamp spacing for breaking elongation of wood pulp) , which was carried out in all experiments of the described bleaching sequence.

Example 5

The oxygen delignification reaction can be carried out under more selective conditions in two steps, and many pulp and paper mills use such systems to their advantage. In general, the viscosity of wood pulp is reduced to a greater extent when it is processed in one stage compared to two stages in delignification to ensure the same final kappa number. In a two-stage process, the wood pulp is first treated at higher pH, high oxygen pressure, and lower temperature for a shorter period of time, after which it is treated in a second stage at lower pressure, lower pH, and higher temperature for a longer time. . Such conditions improve the kinetics of lignin removal compared to the rate of reduction in pulp viscosity.

The higher lignin (KM 23) kraft pulp from eucalyptus was delignified to 10 KP in one- and two-stage oxygen delignification processes under aggressive conditions. This process was compared with one-step oxygen delignification of standard eucalyptus kraft pulp with a lower starting kappa number of 16 under mild conditions. The conditions are presented in table. ten.

The oxygen delignification improvement product as shown in Example 4 was used at the same dosage of 5.5 kg/t in all treatment experiments. Experimental data presented in table. 11 indicate that the product stabilizes pulp viscosity during delignification using a higher alkaline pH in two stages more effectively than stabilization provided in one stage. Changes in the process from one to two stages do not reduce the benefits provided by the oxygen delignification improvement product, but result in a synergistic effect in which both delignification and viscosity are increased.

Example 6

Several aminophosphonate chelating agents can be used in formulating to provide benefits that improve the oxygen delignification reaction by stabilizing the viscosity of the wood pulp. Chelating agents described in table. 12 was prepared and used in a neutral pH solution in which the phosphonate groups are usually replaced by sodium cations. They were characterized and added to the composition in an amount equivalent to the mass of the active acid (see Table 12).

A high lignin kraft pulp from eucalyptus (KAM 21) was delignified to a KP of 9 in a single step oxygen delignification under aggressive alkaline conditions. This process was used for comparison with one-stage oxygen delignification under mild alkaline conditions of standard eucalyptus kraft pulp with an initial lower KM value (K16) to a final KM value of 10. Conditions are presented in Table 1. 13.

The product of improved oxygen delignification was obtained and used for experiments with wood pulp according to table. fourteen.

The final permanganate number of standard wood pulp reaches 10 while maintaining a viscosity of 27.5 cps. The final kappa number of wood pulp with an kappa number of 21, delignified under aggressive conditions, is reduced to 8.6-9.4 (average 9.0) depending on the type of phosphonate, as shown in table. 14. The highest selectivity of delignification is achieved with formulations containing DTPMP "compositions A-D", while the use of "composition B" results in a 35% increase in equivalent permanganate number compared to the control. The graphic in Fig. 3 indicates improved viscosity (up on the y-axis) for a lower permanganate number required (left on the x-axis). The use of the phosphonate chelating agents PIPPA (Formulation E), PAREMP (Formulation F), BHMPTMP (Formulation G), HEDP (Formulation H), and ATMP (Formulation I) also results in varying degrees of viscosity increase compared to formulation without phosphonate (see Fig. 3).

Example 7

There is a need to develop an oxygen delignification improvement product that reduces lignin content (permanganate number) while maintaining pulp strength (viscosity). Formulations containing phosphonate chelating agents and magnesium salts can be improved in both respects. To increase the effectiveness of chelating agents, polymeric compounds can be added to the composition. Examples of typical polymers used in this way may include polyacrylates and copolymers of acrylic and maleic acids, such as the product Solenis LLC, Infinity® ^SL4393 / ^Polystabil® 922, ^Infmity® SL4335 and Infinity® ^SL4342 / ^Aquatreat® AR410.

Stabilization of woody viscosity using a phosphonate chelating agent such as diethylenetriaminepentamethylenephosphonate (DTPMP) can be enhanced by the addition of such polymers. Negatively charged groups can also directly interact (bond) to some extent with transition metal ions. This interaction can be enhanced by including various functional groups in the polymer chain, primarily hydroxyl groups attached to the α-carbon atom of polyhydroxyacrylic acid (PHAS), shown below. An unexpected synergistic increase in pulp viscosity stabilization with formulations containing DTPMP was observed with formulations containing PHAS, and this effect was greater than with other acrylate polymers.

In view of the problems of pulp processing, there is a need for oxygen delignification improving compositions that can reduce or remove non-recycled elements (NPIs) such as inorganic mineral salts such as magnesium salts. Such salts are recycled in the regeneration cycle due to the fact that they are not removed by incineration and their concentration increases over time.

Increasing the NPI content can reduce pulp processing efficiency, interact with some chemicals, complicate regeneration cycles in pulp processing, and create problems when scaling up the process. To be effective, formulations containing magnesium sulfate also need to be used in large quantities, typically 5-10 kg Epsom salt/ton wood pulp. This presents a logistical challenge as modern mega mills can produce over 5,000 tons of pulp per day using 50 tons of Epsom salt per day. As a result of extensive research, it was found that the composition containing organic aminophosphonate and polymeric PHAS provides complete removal of magnesium salts. The polymer composition also allows the delignification reaction to be improved to obtain a lower permanganate number compared to compositions containing MgSO ₄ under similar conditions.

Eucalyptus kraft pulp with high permanganate number (K20) was delignified by more than 50% under the aggressive conditions of a one-stage oxygen delignification process, as indicated in table. fifteen.

The amount of phosphonate was 2.5 kg/t based on the weight of wood pulp and the amount of polymer was 2.5 kg/t, as shown in table. 16. Polymer was used in place of any MgSO ₄ . These formulations were compared with a formulation containing a standard factory amount of magnesium sulfate, as well as a formulation containing no processing aid, as shown in Table 1. 16.

Permanganate number and viscosity of the resulting wood pulp are shown in table. 17.

Treatment with DTPMP alone results in some stabilization of the wood pulp, but does not achieve a lower kappa number, while the addition of polymers results in a decrease in kappa number (lignin content) while stabilizing the pulp to varying degrees, as shown in FIG. 4. The use of Formulation D and Formulation C resulted in a reduced permanant number compared to using DTPMP alone (Formulation A), but the most improved efficacy was observed with poly-α-hydroxyacrylate (PHAS) (Formulation B), resulting in a favorable higher viscosity (up on the y-axis) with decreasing permanganate number (to the left on the x-axis, see Fig. 4).

Example 8

There is a need to improve the environmental performance of pulp and paper mills while reducing the content of phosphorus- and nitrogen-containing compounds used in the processes of obtaining and bleaching wood pulp.

The eucalyptus wood pulp from Example 7 (20 KM) was subjected to oxygen delignification under slightly milder conditions, as shown in Table 1. 18, while achieving a delignification of approximately 50%.

The amount of phosphonate was reduced to 1.5 kg/t compared to the previous 2.5 kg/t (example 7), while providing a 40% reduction. The amount of polymer was maintained at 2.5 kg/t. Treatment with a combination of DTPMP and polymers was compared with treatment with DTPMP alone (A), and with treatment with DTPMP in combination with magnesium sulfate (E), as shown in Table 1. 19.

At lower levels of phosphonate, the polymers provide synergistic stabilization of the wood pulp while obtaining a similar permanganate number. The PHAS polymer (composition B) provides the maximum improvement in delignification, as indicated in table. twenty.

Example 9

The previous example demonstrated the unexpected benefit of the combination of a phosphonate chelating agent and acrylate polymers in improving oxygen delignification and stabilizing pulp viscosity. The results obtained in the previous example were further investigated using the PHAS (poly-α-hydroxyacrylate) polymer in a milder delignification mode. Eucalyptus wood pulp with K20 permanganate number was delignified in one stage using oxygen under the following conditions:

The viscosity of the wood pulp was measured as a function of the reduction in the amount of DTPMP, while the content of the PHAS component in the composition was not changed. The results obtained were compared with treatment with DTPMP alone, PHAS alone, magnesium sulfate alone, and with the untreated sample. The compositions of these experiments are presented in table. 22.

The results are presented in table. 23.

The results indicate that the amount of phosphonate can be reduced by a further 150% when using 0.5 kg/t mixed with 2.5 kg/t PHAS (composition C) while maintaining sufficient pulp stabilization. The use of PHAS also ensures complete removal of magnesium sulfate from formulations.

The lower amount of phosphonate provided by the synergistic effect of the PHAS polymer was also tested under more aggressive conditions, as shown in Table 1. 24. Kraft pulp with higher K23 permanganate number was delignified by 57% in one-step oxygen delignification under the following conditions.

The data given in table. 25 indicate the synergistic effect that is observed when PHAS is mixed with the chelating agent DTPMP, which is expressed in an increase in delignification under aggressive alkaline and temperature conditions.

Example 10

The previous example demonstrated that the combination of a phosphonate chelating agent and acrylate polymers, including poly-α-hydroxyacrylate (PHAS), is sufficiently functional to provide stabilization of cellulose during oxygen delignification reactions under aggressive conditions at low levels of phosphonate, even in the absence of magnesium sulfate MgSO ₄ . This improvement was investigated further during two-stage oxygen delignification under aggressive conditions.

Eucalyptus kraft pulp with a high K23 permanganate number was delignified in a two-stage oxygen delignification under the following aggressive conditions.

Additional components were mixed using a combination of chelating agent DTPMP and polymer PHAS (ratio 3:5), as shown in table. 28.

When using the mixed product, the same synergistic stabilization of pulp viscosity was observed in the two-stage reaction as in the one-stage reaction, and no reduction in viscosity was observed. Also demonstrated a distinct dose-dependent response, as shown in table. 29. The lowest blended product (composition C) was 1.33 kg/ton wood pulp and produced a 48% higher viscosity of 21.3 cps compared to an untreated viscosity of 14.4 cps.

A similar improvement in delignification was observed when processing wood pulp even with a high permanganate number (K25) under slightly more aggressive or harsh conditions during a two-stage oxygen delignification process, as shown in table. thirty.

Additional components were mixed using a combination of chelating agent DTPMP and polymer PHAS (ratio 3:5) in the same way as described in the previous example and as indicated in table. 31.

The results indicate that there is a similar dose-dependent response (Table 32) for the combination of components to the increase in viscosity for wood pulp with an initial permanganate number of 25 (K25) compared to wood pulp with an initial lower permanganate number (K23).

Example 11

The combination of a phosphonate chelating agent and acrylate polymers, including polyhydroxyacrylate (PHAS), is also favorable for two-stage oxygen delignification under aggressive conditions, carried out at higher temperatures and shorter reaction times. The higher permanganate number (K23) eucalyptus wood pulp was treated in an abbreviated two-stage oxygen delignification at higher temperatures as described in Table 1. 33. The first stage was reduced to only 5 minutes, while the final stage lasted 60 minutes, 50 minutes or 40 minutes.

A 3:5 combination of DTPMP and PHAS was added in varying amounts (Formulations B and C) and compared with untreated samples, samples treated with magnesium sulfate (Formulation A), and samples containing magnesium sulfate and DTPMP (Formulation D) as shown in tab. 34.

The results of all experiments are shown in table. 35. The values in the second row of the table "5+60", "5+50" and "5+40" indicate a reaction time of 5 minutes in the first stage and 60, 50 or 40 minutes in the second stage.

The permaganate numbers obtained after processing under such aggressive conditions are graphically represented in FIG. 5, where a clear trend can be observed for shorter reaction times to hinder delignification to some extent (higher permanganate numbers), but not equally for all treatment conditions. The results indicate that when the present compositions are used under appropriate industrial conditions, the reaction time required to reduce the permanganate number of wood pulp can be significantly reduced.

The results shown in FIG. 5 indicate that with a significant reduction in delignification reaction time, the final kappa number is higher for wood pulp treated with magnesium sulfate compared to untreated pulp. However, when processed with a two-component composition, i.e. DTPMP and PHAS, wood pulp is produced with the same final kappa number as raw pulp, but with higher viscosity, as shown in FIG. 6. These results indicate that efficient delignification with good viscosity stabilization can be achieved even with reduced reaction times.

DTPMP and PHAS based formulations also result in the benefits of a significant reduction in the amount of product required to stabilize the pulp viscosity (about 4 times lower) compared to formulations containing magnesium sulfate. Two-component formulations stabilize the pulp viscosity to a greater extent (up to 27% higher) than untreated pulp.

Example 12

There are many combinations of temperatures and reaction times in two-stage oxygen delignification that may be suitable for pulp and paper mills. High temperatures and short reaction times are commonly used to increase productivity, but the combination can reduce both delignification efficiency and pulp viscosity. The addition of a phosphonate chelating agent in combination with acrylic polymers, including poly-a-hydroxyacrylate (PHAS), is suitable for two-stage oxygen delignification under aggressive conditions, carried out at high temperatures and short reaction times, as shown in example 11. To achieve the lowest permanganate number while minimizing viscosity loss, there are a number of combinations of temperatures and reaction times during the two-stage delignification process, as well as the levels of alkali used. Some of these combinations were used in the experiments, as indicated in table. 36.

Each of the conditions of delignification 1-4 described above in table. 36 was used when adding various chemical compositions, designated as compositions A-D, as indicated in table. 37.

Achievable final permanganate numbers are presented in table. 38.

Different delignification conditions had different effects on reaction efficiency, as indicated in FIG. 7. The permanganate number increases by limiting the reaction time (condition 1) or alkali level (condition 4). The combination of higher temperatures with lower alkali levels results in more intense delignification (condition 3 versus condition 2). In FIG. 7 indicates that treatment with different chemical agents affects delignification differently in any particular set of reaction conditions. For example, "composition B" and "composition C" proved to be the most effective in improving delignification under conditions of higher temperatures in the reaction steps, longer reaction times, and lower levels of added alkali.

The final viscosity of the wood pulp is shown in Table 39.

The viscosity of the wood pulp improved with the use of various additives, as shown graphically in FIG. 8. Different processing methods produced similar results under different conditions, and the improved viscosity level compared to the control may be due to both chemical additives and the level of reagents added. Depending on the conditions of delignification, a particular processing method may provide a significant advantage over other methods. For example, the "formulation B" treatment method is sufficient to stabilize the viscosity by an average of 22% compared to the control already at the addition of the composition in an amount of 1 kg/t and does not contain magnesium sulfate (0%, see Fig. 8). In addition, the "composition B" and "composition C" processing methods result in the best delignification and viscosity stabilization under conditions of higher reaction stage temperatures, longer reaction times, and lower levels of added alkali.

While the above detailed description has provided at least one exemplary embodiment of the present invention, it should be understood that many variations exist. It should also be understood that the exemplary embodiment or exemplary embodiments of the present invention are merely exemplary and are not intended to limit the scope, spirit or applicability of the present invention in any way. Rather, the foregoing detailed description will provide those skilled in the art with a schematic diagram of an embodiment of the present invention, and it should be understood that many changes can be made to the execution and arrangement of elements described in an exemplary embodiment of the invention without departing from the scope of the invention as defined. in the appended claims and their legal equivalents.

Claims (12)

1. A process for producing high yield kraft pulp, comprising: obtaining kraft pulp with an initial kappa number of at least 20 for hardwood pulp or a kappa number of at least 30 for softwood pulp; treating kraft pulp with a composition comprising: a) an organic aminophosphonate, b) a magnesium salt, and c) one or more anionic linear alcohols and ethoxylates; and wherein the organic aminophosphonate is selected from diethylenetriaminepentamethylenephosphonic acid (DTMP), aminotrismethylenephosphonate (ATMP), (bis)hexamethylenetriaminepentamethylenephosphonic acid (BHMTMP), polyaminopolyethermethylenephosphonate (PAREMP) and combinations thereof; wherein the anionic linear alcohols and ethoxylates are selected from sodium lauryl ether sulfate (SLES), sodium lauryl ether phosphate (SLEP), sodium lauryl sulfate (SLS), and combinations thereof; and reducing the initial kappa number of kraft pulp to a predetermined final kappa number; wherein the kraft pulp is treated with the composition prior to a two-stage oxygen delignification process; and yet the final viscosity of the pulp remains high compared to untreated oxygen delignified kraft pulp. 2. The method of claim 1 wherein the magnesium salt is selected from the group consisting of divalent magnesium cation Mg ²⁺ , magnesium sulfate and magnesium sulfate heptahydrate. 3. The method according to claim 1, where the temperature in the first stage of the two-stage oxygen delignification process is from 80°C to 100°C and the temperature in the second stage is from 90°C to 120°C, and where the O ₂ pressure in the first stage is from 80 psi to 120 psi, and the pressure of O ₂ in the second stage is from 25 psi to 90 psi. 4. The method according to any one of paragraphs. 1-3, including the treatment of kraft pulp with a composition containing: a) organic aminophosphonate in an amount of 0.6 kg/t to 1.2 kg/t based on the mass of active acid, b) a magnesium salt in an amount of 0.1 kg/t up to 3.2 kg/t based on the mass of anhydrous substance and c) from 0.08 kg/t to 0.16 kg/t of the active base of one or more anionic linear alcohols and ethoxylates, with one or more anionic linear alcohols and ethoxylates are selected from the group consisting of linear sulfonated alcohol ethoxylates. 5. A method for producing high yield oxygen delignified kraft pulp in a two-stage delignification process, comprising: obtaining kraft pulp with a permanganate number of at least 20; and treating kraft pulp with a composition comprising: a) an organic aminophosphonate, and b) a magnesium salt, and c) an anionic polyacrylate; wherein the organic aminophosphonate is selected from diethylenetriaminepentamethylenephosphonic acid (DTMP), aminotrismethylenephosphonate (ATMP), (bis)hexamethylenetriaminepentamethylenephosphonic acid (BHMTMP), polyaminopolyethermethylenephosphonate (PAREMP), and combinations thereof; and reducing the initial kappa number of kraft pulp to a predetermined final kappa number; wherein the kraft pulp is treated with the composition prior to a two-stage oxygen delignification process; and yet the final viscosity of the pulp remains high compared to untreated oxygen delignified kraft pulp.

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