RU2495177C2 - Peroxide-alkaline treatment of waste products on integrated neutral-alkaline pulp and paper plant - Google Patents

Abstract

FIELD: textiles, paper.

SUBSTANCE: production processes of mechanical wood pulp using refiners are disclosed, and more particularly, the wood-pulp plant is disclosed which is integrated with the neutral-alkaline processes of paper production, generating printing paper from mechanical wood pulp. The waste products are treated with hydrogen peroxide, alkali and an organic stabilising additive immediately before or during refining, that provides improved optical and physical properties of the refined waste products and uses electrical energy more efficiently to achieve the desired quality of the fiber after bleaching for cost-effective production of a wide variety of coated and uncoated printing paper from mechanical wood pulp.

EFFECT: improvement of quality of rejected material.

4 cl, 2 tbl, 12 dwg

Description

FIELD OF THE INVENTION

The present invention is directed to processes for the production of mechanical pulps using refiners to improve the quality of sorting waste, and more specifically, to a wood-mass mill integrated with a neutral-alkaline paper manufacturing process for the production of grades of printing paper from mechanical pulp. To provide improved optical and physical properties of refined waste, the waste is treated with hydrogen peroxide, alkali and an organically stabilizing agent.

BACKGROUND OF THE INVENTION

Obtaining wood pulp is a process of mechanical grinding of wood into its fibers in order to produce wood pulp. A key advantage of wood pulp production is its high yield compared to chemical wood pulp, which removes most or all of the lignin that binds cellulose fibers. Lignin is not removed from machined wood, and this implies that scarce resources are used more efficiently. Pulps made using traditional methods of producing mechanical pulps are mainly used for newsprint and other printing paper intended for direct mail advertising, catalogs and some magazines and books, and, as a rule, are unsuitable for better or more durable ready-made final paper products. This is partly due to the fact that mechanical wood pulps are generally more difficult to bleach, can return to their original state in terms of brightness under the influence of light and humidity, and, as a rule, have lower strength than chemical wood pulps.

There are many options for producing mechanical pulp, including producing defibre pulp (SGW), press defibre pulp (PGW), refined pulp (RMP), thermomechanical pulp (TMP), and thermo-mechanical pulp (CTMP). The last three types can be further grouped as a whole as processes for the production of refined wood pulps. In the process of obtaining refined wood pulps, the chips are crushed between rotating metal disks. Usually the process is carried out in two stages. The first stage is mainly used to separate the fibers, while the second stage is used to modify the surface of the fibers in order to improve the sizing of the fibers in the paper manufacturing process.

The preceding list is by no means exhaustive. There are countless combinations and variations of wood pulp processes. Among the processes of obtaining wood pulp, the TMP-process is considered by many experts in this field as the most preferable, taking into account market conditions and environmental standards.

The TMP process, as a rule, consists of two stages of refining. The first stage is carried out under pressure, which allows the capture of thermal energy released in the form of steam when mechanical energy is applied to the chips between two rotating refiner disks. Steam pressure control allows the primary refiner to operate at elevated temperatures and provides steam for heating and moisturizing the chips before refining. The second stage refiner can operate at atmospheric pressure, but it is more common to carry out this stage also under pressure in order to capture more energy and better control the process. Wood pulps made by TMP and STMP processes have higher strength, which makes these processes more preferred processes for producing mechanical wood pulps. However, there is additional potential for improvement. The TMP process consumes large amounts of electricity, and the wood pulp produced by the TMP process tends to be darker than most other pulps due to thermal darkening of the fiber during refining. In addition, the presence of large quantities of lignin in refined fiber makes it highly susceptible to alkaline darkening.

In all processes for the production of mechanical pulp, the sorting waste is further processed in order to improve their favorable properties (for example, gluing ability) and in order to make them more attractive as fiber for a paper machine. The treatment of mechanical pulp waste with sodium sulfite (sulfonation of the waste) before refining has shown that strength improvements can be achieved. However, loss of brightness during refining and an increase in BOD and COD of wastewater, as well as refining energy, make it unattractive for commercial practice.

The use of peroxide-alkaline treatment of waste mechanical pulp, as has been shown, leads to improved physical properties and a higher degree of whiteness equal to or superior to that of sulfonation. However, effective peroxide-alkaline treatments to maximize improvements have been described to require treatment times of five to forty minutes or more. See, for example, "HIGH ALKALINE PEROXIDE TREATMENT OF WHITE SPRUCE / LODGEPOLE PINE RMP REJECTS ', SGBook, pp1-17, CPPA Pacific Coast Brach Mini-Conference April 1990 and" ALKALINE PEROXIDE TREATMENT OF SOUTHERN PINE TMP REJECTS ", MJfer et al., pp 617-629, 1988 Pulping Conference. In the processes described, 4.4-8.9 wt.% NaOH based on fiber was used for waste treatment to achieve significant improvements in physical strength and caustic / peroxide ratio (C / P ) 2-3: 1.

In "OPTIMIZATION OF IN-REFINER BRIGHTENING WITH H ₂ O ₂ FOR PRODUCTION OF HI-BRITE MECHANICAL PRINTING PAPER", V. Simard et al., Pp 1-10, 1995 CPPA Spring Conference of Pacific Coast and Western Branches, disclosed use of peroxide alkaline waste treatment without cooking time or retention time in the RMP process, and it was found that this requires the addition of 3.0 wt.% caustic or more. The system described in Simard et al. Used a recirculated wastewater stream to a TMP mill with a pH of 5.0-5.5, since the paper machine integrated with it worked within this range.

The later improvement of TMP wastes and the reduction of specific energy of refining by adding a perxino-alkaline solution before refining of waste was discussed in conjunction with the production of value-added printing paper grades of mechanical pulp in IMPROVING TMP REJECTS REFINING THROUGH ALKALINE PEROXIDE PRETREATMENT; AN OPPORTUNERITY FOR SCA ", Y.Bian et al, 2006 PAPTAC Pacific Coast Branch Spring Mini-Conference. However, as in previously published studies, including processing softwood fibers, it was found that in order to achieve the required fiber quality (for example, tensile strength, reduce coarse grain of coniferous fibers) and save operating costs (for example, reduce specific refining energy , reducing the need for chemical fiber during papermaking) before refining, the combined use of alkali is more than 5.2 wt.% and the reaction time is 30 minutes at a highly concentrated fiber at elevated temperature.

US Patent Publication No. 2009/0032207 discloses a mechanical or chemomechanical process for the manufacture of wood pulp in which, after fibrillation, the pulp is bleached under alkaline conditions. After that, the waste is sorted and bleached separately from the conditioned mass, and the bleached waste is mixed with the conditioned mass.

US Patent Publication No. 2008/0035286 discloses a peroxide-alkaline process for producing mechanical wood pulp, which includes the step of treating the dissolved wood-cellulosic material with a peroxide-alkaline chemical product for some time and under conditions sufficient to produce a pulp of the desired concentration.

"Bleaching" is a term associated with the process of obtaining wood pulp, where certain chemical products are thoroughly mixed with the fiber and then held on the fiber for a predetermined amount of time in order to increase the brightness of the wood pulp. Bleaching is practiced on chemical and mechanical pulp. Upon receipt of mechanical wood pulp, an increase in the degree of whiteness is achieved by changing the chemical structure of the conjugated double bonds in lignin. Compounds with conjugated double bonds are called chromophores. “Lightening” is a term that is often used to refer to the bleaching of mechanical pulps in order to indicate its difference from the bleaching process of chemical pulps, which is characterized by the removal of all lignin. Hereinafter, the term "whitening" will be understood as covering also the process of "lightening".

In mechanical pulps, clarification is often carried out at a single stage in the process of obtaining wood pulp. The bleaching process is traditionally carried out at a bleaching station in one or more tanks (bleaching towers or stages) in a separate section of the plant, in contrast to the section for producing wood pulp from the plant. Clarification may be carried out using oxidizing agents such as hydrogen peroxide and / or reducing agents such as sodium dithionite or sodium hydrosulfite.

Typically, hydrogen peroxide, an oxidizing agent, is used with sodium hydroxide. Sodium hydroxide is a strong alkali and provides the required high pH value, which is necessary to obtain an active perhydroxyl-ion, HOO ^- in order to obtain a whitening effect in wood pulps. The cost of sodium hydroxide increases due to changes in its availability and cost of energy. Concern for environmental issues also means reducing the sources of available sodium hydroxide. Therefore, other alkali sources and other methods have been tested with limited commercial success to find a suitable alternative to bleaching solutions and bleaching processes.

In order to maximize the stability of hydrogen peroxide and perhydroxyl ion ions during the bleaching of mechanical pulp, sodium silicate and one of many organic and inorganic stabilizing agents are usually used on the fiber before and during the addition of hydrogen peroxide to the fiber. These materials are most beneficial due to their ability to control metal ions, such as manganese, iron and copper, which are contained in the wood chips entering the pulp production process. In the absence of treatment, the ions of these metals destroy hydrogen peroxide and perhydroxyl ion before they acquire the ability to clarify chromophores, which makes the process much less cost-effective and reduces the efficiency of clarification.

Although most of the previously published works related to the addition of alkaline peroxide to sorting waste in a refiner discussed the addition of sodium silicate, the present invention specifically excludes the use of sodium silicate to stabilize peroxide and perhydroxyl ion. The presence of silicates can lead to the formation of deposits (for example, calcium silicate, sodium carbonate), for example, on the refiner grinding disks, which may limit the refiner's ability to refine waste. The exclusion of sodium silicate from use in the present invention avoids this potential difficulty.

BRIEF DESCRIPTION OF GRAPHIC MATERIALS

figure 1 is a histogram of the degree of whiteness of refined waste sorting according to the ISO standard based on Example 1.

Figure 2 is a graph of the degree of whiteness of refined waste sorting according to the ISO standard on the percentage of peroxide based on Example 1.

Figure 3 is a graph of the thickness of paper from refined sorting waste from caustic based on Example 1.

Figure 4 is a graph of the degree of whiteness according to the ISO standard on the peroxide used when bleaching the sorted TMP mass based on Example 1.

Figure 5 is a graph of the percentage reduction in paper thickness and the percentage increase in tensile strength compared to the baseline of APTR with an increase in C / P of the conditioned mass from the sorting waste based on Example 2.

6 is a graph of the percentage of coniferous fiber due to APTR with increasing C / P of the conditioned mass from the sorted waste and the sorted TMP mass based on Example 2.

7 is a graph of a percentage reduction in paper thickness and a percentage increase in strength compared to the baseline with increasing C / P of the sorted TMP mass based on Example 2.

Fig. 8 is a graph of the degree of whiteness measured at various points of the mass passing through the TMP plant before, during and after the 7-day APTR test at C / P 1.0 based on Example 2.

Fig.9 is a graph of the total specific energy of waste refinement from the dryness of the final waste in comparison with the absence of APTR after a 7-day APTR test at C / P 1.0 based on Example 2.

Figure 10 is a graph of interruptions on wet parts depending on the day for all paper machines in the downstream direction before, during and after a 7-day APTR test at C / P 1.0 based on Example 2.

11 is a graph of key wood pulp properties for wood pulp samples taken at a waste refiner outlet after applying an average dosage of hydrogen peroxide based on Example 3.

12 is a graph of key wood pulp properties for wood pulp samples taken at a waste refiner outlet after applying a higher dosage of hydrogen peroxide based on Example 3.

DETAILED DESCRIPTION OF THE PROCESS

The present invention is aimed at improving the processing of fiber from waste wood pulp using alkaline hydrogen peroxide treatment, which does not require retention time on the fiber before highly concentrated refining and which is effective at low levels of chemical treatment. The use of zero retention time when adding alkaline treatment products to thickened waste prior to refining has been found to be effective when caustic addition ratio of less than or equal to 3.5% by weight in pulp and paper mills that use at least one integrated neutral-alkaline paper machine and recycle the water from it back to the wood-based mill. In this description, percentages are given in weight percent, unless specifically indicated otherwise. Eliminating the requirement to retain alkaline peroxide on the fiber from the waste prior to refining allows the present invention to be implemented with minimal capital outlay. Waste water recycling of a neutral-alkaline paper machine to a wood-processing mill and the related appearance of buffering properties due to filling pigment, precipitated calcium carbonate (PCC) or finely divided calcium carbonate (GCC) minimizes the operating costs of chemical products by reducing the alkali mechanical fiber requirement . This results in less total alkali added to the waste. The amount of hydrogen peroxide added to the alkali-treated waste is correlated with the addition of caustic; therefore, a decrease in the requirements for the amount of caustic leads to a decrease in the requirements for the amount of hydrogen peroxide and makes the process more cost-effective.

When implementing a “zero retention time” scenario involving peroxide-alkaline waste treatment (APTR), caustic and hydrogen peroxide can be added directly to the waste refiner or to the wood pulp waste stream exiting the waste thickener, or at any available addition point between the two provisions. To maximize brightness, the ratio of caustic to peroxide (C / P), as a rule, is about 0.35-0.75. To maximize the strength, C / P, as a rule, is about 1.25-1.5. The combination of a simultaneous increase in brightness and strength can be achieved with intermediate C / P ratios based on the particular requirements of a particular installation.

As used herein, “alkali” is intended to include any source of alkaline properties, such as, for example, sodium hydroxide or caustic soda (NaOH), sodium carbonate (Na ₂ CO ₃ ) and sodium bicarbonate (NaHCO ₃ ). Na ₂ CO ₃ and NaHCO ₃ also provide buffering that prevents wide variations in pH. When peroxide-alkaline bleaching is carried out at high temperatures, an improved degree of whiteness is obtained with buffer systems. Giving the system buffering properties at lower pH values (preferably from about 9 to about 10.5) prevents peroxide decomposition and browning, but still provides adequate alkaline properties to produce the desired compounds. If necessary, the buffer releases alkaline properties and provides sufficient alkaline properties for the slow and uniform production of perhydroxyl ions. In wastewater from a neutral-alkaline paper machine that uses PCC or GCC pigment-filling agents, calcium carbonate acts as a buffer, which is expected to improve clarification during APTR in a high-temperature refiner. When added to the fiber in front of the waste refiner or in the waste refiner, the components of the APTR solution can be added separately or simultaneously, where “simultaneously” means that two or more components are added together as a premixed stream, and “separately” means that one after times as separate threads.

When a pre-mixed solution for APTR treatment is used, a Vordorod peroxide stabilizer, such as, for example, a suitable chelating agent, may be included. Chelating agents may include, but are not limited to, aminopolycarboxylic acids, (for example) ethylenediaminetetraacetic acid (EDTA), diethylene triamine pentaacetic acid (DTPA), nitrilotriacetic acid (NTA); phosphonic acids, (for example) ethylene diamine tetramethylene phosphonic acid (EDTMP), diethylene triamine pentamethylene phosphonic acid (DTPMP), nitrilotrimethylene phosphonic acid (NTMP); polycarboxylic acids, gluconates, citrates, polyacrylates and polyaspartates, or any combination thereof. The chelating agent can be added to the bleaching solution in an amount of up to 0.5 wt.% Based on fiber, but is preferably added with degrees of addition from about 0.1-0.25% based on fiber. Like all other components of the bleaching solution, chelating agents can be added separately or simultaneously with one or more components of the bleaching solution at one or more points of addition of chemical products in the refining system. It is believed that chelating agents bind metals, preventing the decomposition of hydrogen peroxide, which can lead to darkening of the manufactured paper.

An alkaline peroxide refiner waste stream treatment without holding time has been found to provide increased strength and brightness with economically significantly lower levels of caustic and hydrogen peroxide treatment for systems that use a recycled waste water stream from a neutral alkaline paper machine as a diluent water at a two-mass plant. By “neutral alkaline” is meant a pH of from about 7.0 to 7.5. In addition, it was found that neutral alkaline wastewater containing significant amounts of unoxidized sulfur compounds leads to an increase in brightness during APTR, which is lower than when neutral alkaline wastewater does not contain these impurities.

Now it’s obvious that in a wood-mass mill with water-diluting water from a paper machine or paper machines that operate at neutral-alkaline pHs rather than acidic pH, there is a need for caustic soda (and thus hydrogen peroxide) for achieving the desired improvement in fiber quality can be reduced up to 20%. This is due to the fact that wood resin acids, which are released from high yield wood pulp during the primary and secondary refining steps, are partially neutralized by subsequent dilution with wastewater replenished from wastewater from a neutral-alkaline paper machine. Together, these disclosures constitute a process that enables neutral-alkaline pulp and paper mills for the production of printing paper from mechanical pulp to adapt APTR to their process of producing mechanical pulp with minimal appropriate capital costs. In addition, it is now known that the APTR process when operating in this way is able to eliminate the need for restorative clarification during the subsequent process. This will result in wood pulp with equivalent or superior optical properties and superior physical properties in a paper machine with a neutral or positive effect on supply costs. In addition, if the wood pulp is processed in the APTR process described herein, it can also be clarified in a traditional hydrogen peroxide bleaching plant, producing wood pulp that has: a) superior optical and physical properties for an already achievable whiteness range at a lower cost, or b) equivalent optical and physical properties at an equivalent cost for a higher interval of whiteness than the interval currently achievable. Also, by means of an APTR operating as described herein, adverse effects on fiber properties, such as, for example, loss of yield and degree of whiteness, are minimized between the pulp mill and the paper machine while minimizing the loading of anionic charges in the paper machines and the loads of BOD and COD of wastewater . In addition, there is evidence that, through APTR, the specific energy of the waste refiner, depending on the freeness, can be controlled more precisely, realizing savings on operating costs.

Examples

Example 1

Production tests were carried out at the integrated neutral-alkaline pulp and paper mill for the production of printing paper from mechanical pulp, producing a number of grades of paper having a degree of whiteness of 57.5-80% according to ISO standard according to technical conditions and an opacity of printing of 91.5-96% according to specifications. Fourteen tests were carried out, which included the simultaneous mixing of concentrated DTPA, NaOH and H ₂ O ₂ in dilution water and the rapid addition of this solution through the dilution water nozzle to the TMP waste refiner hole. A chelating agent (DTPA) was additionally added before thickening and sorting waste with a constant degree of addition of 1.5 kilograms per absolutely dry ton (kg / AST).

The addition of 10, 20, 30, or 40 kg / AST of peroxide per 100% was studied to determine the effect on the optical and physical properties of the fiber, since the C / P ratio varied for each added percentage of peroxide. The proportion of DTPA added per fiber was kept constant. Table 1 summarizes the various combinations of DTPA, NaOH and H ₂ O ₂ used in the refiner.

Table 1 Test No. NaOH (C) / H ₂ O ₂ (P) NaOH, kg / AST H ₂ O ₂ , kg / AST DTPA, kg / AST one 0 0 1,0 2 0.5 5,0 10.0 1,0 3 0.75 7.5 10.0 1,0 four 0.5 10.0 20,0 1,0 5 1,0 10.0 10.0 1,0 6 0.5 15.0 30,0 1,0 7 0.75 15.0 20,0 1,0 8 1,5 15.0 10.0 1,0 9 1,0 20,0 20,0 1,0 10 0.75 22.5 30,0 1,0 eleven 1,0 30,0 30,0 1,0 12 1,5 30,0 20,0 1,0 13 0.5 20,0 40,0 1,0 fourteen 0 0 1,0 fifteen 0 0 0

Samples of refined waste (including basic samples that did not receive the addition of chemical products) were mixed with the conditioned mass from the line, and the properties of the mixture were determined. Some mixtures of refined waste and conditioned mass were clarified with sodium hydrosulfite or hydrogen peroxide to determine the savings of bleaching chemicals. When applied to waste, 22.5 kg / AST of NaOH and 30 kg / AST of H ₂ O _{2 the} tensile strength of the conditioned mass / waste is increased by 5 -10%, the thickness of the paper from the conditioned pulp / waste is reduced by 5-10%, the whiteness of the conditioned pulp / waste is increased by 4-6% according to the ISO standard, while the use of hydrosulfite for clarification is reduced by 100%, the use of kau stick and peroxide during peroxide clarification decreases by 10-15%, and the bound SO ₂ for acidification also decreases, since alkaline and peroxide residues after clarification decrease.

In Figures 1-4 summarized the relationship observed after APTR on the fiber from laboratory sheets of manual cast paper made from refined sorting waste and clarified samples of the purified TMP mass.

Example 2

The tests were carried out at the integrated neutral-alkaline pulp and paper mill for the production of printing paper from mechanical wood pulp, producing a number of grades of paper having a degree of whiteness of 58-84% according to ISO standard according to specifications and printing opacity 85-97% according to technical conditions. During long periods of work of 12 hours and, separately, 7 days, APTR was estimated using a solution containing diluting water, DTPA, caustic soda and hydrogen peroxide on the feedstock for two waste refiners working in parallel.

12-hour evaluations made it possible: a) to compare the results from two different points of addition near the refiners, b) to evaluate the low and (0.6) and average (1.0) C / P ratios with the constant addition of hydrogen peroxide of 30 kg / AST to determine the effects on the fiber of the quality of the various provisions at the TMP plant where these waste refiners operate, and c) determining what the effect of APTR on the specific energy of waste refining is.

At C / P 1.0 with the addition of 30 kg / AST of peroxide, a 7-day and 24-hour daily assessment was carried out, which a) allowed the wastewater of the paper machine to return to the TMP mill, making a full turn, b) assessed the impact of APTR when bleaching TMP on paper machines in a downward direction for various grades of paper, and c) provided data showing a decrease in specific energy during waste refining.

Table 2 summarizes the laboratory data for samples of conditioned mass taken for one week of primary, secondary sorting and sorting of waste, when two periods of operation of APTR with a duration of 12 hours each can be compared with three surrounding periods of operation where APTR is not functioning.

Figures 5-7 illustrate the key benefits of APTR at a TMP mill during a 12-hour test, while Figures 8-10 summarize the key results of continuous automated testing at a TMP mill and three downstream paper machines over a long 7- daily test.

During the 12-hour and 7-day tests, hydrosulfite designed to whiten TMP to a low degree of brightness after the APTR was functioning for 4 hours was no longer used in the downstream direction (when the effect of APTR on the brightness and pH stabilized relative to the baseline). Then, after APTR was running for 4 hours, the degree of addition of peroxide and caustic to the working bleaching plants was reduced by 50% equivalent to those used in the sorted TMP mass, and further optimization to achieve a 100% reduction and equivalent chemical costs was shown by subsequent laboratory studies.

After 36 hours of APTR operation, the whiteness at the TMP mill starts to drop, and the pH starts to rise, indicating that the wastewater of the paper machine has made a full turn, and thus there is no longer any need for alkali to neutralize the acid properties of the TMP wastewater. At this point, C / P decreased from 1.0 to 0.9 and remained unchanged for the remaining 48 hours of testing.

Example 3

The tests were carried out at the integrated neutral-alkaline pulp and paper mill for the production of printing paper from mechanical wood pulp, producing a number of grades of paper having a degree of whiteness of 58-60% according to ISO standard according to technical conditions and an opacity of 85-95% according to technical conditions. During long working periods of 12-36 hours, APTR was evaluated by using a solution containing diluting water, DTPA, caustic soda and hydrogen peroxide in diluting high pressure feed water added to the refining zone of one or two refiners under atmospheric pressure, operating in series. These refiners process the sorted, treated TMP waste, which is then bleached separately from the additional TMP conditioner / waste by sodium hydrosulfite and used as reinforcing fiber on two downstream paper machines.

Figures 11 and 12 illustrate the beneficial effects of APTR on brightness, elasticity and other key properties using C / P ratios in the range of 0.35-0.40 in the treatment solution and DTPA used in unrefined waste prior to refining.

Claims (4)

1. A method of processing mechanical pulp, which includes the following steps:
a) providing cellulosic material derived from softwood or hardwood;
b) introducing cellulosic material into the main line of the refining system for conversion to main wood pulp;
c) separation of waste from the main wood pulp by sorting or fractionation;
d) mixing (i) a stream of neutral-alkaline wastewater recycled from the papermaking process, substantially free of oxidizable sulfur compounds and containing a buffering agent, (ii) a treatment solution containing hydrogen peroxide and alkali, with said fibers from waste, where the amount of alkali does not exceed 3.5 wt.% (calculated on 100%) per fiber, and the ratio of alkali to hydrogen peroxide is from about 0.35 / 1.0 to about 1.5 / 1.0 ; and (iii) a chelating agent for controlling metal ions that adversely affect the stability of hydrogen peroxide, with the specified waste during refining. 2. The method according to claim 1, where the specified alkali is selected from the group consisting of sodium hydroxide, sodium carbonate or sodium bicarbonate. 3. The method according to claim 1, where the specified chelating agent is selected from the group consisting of aminopolycarboxylic acids, phosphonic acids, polycarboxylic acids, polyacrylates, polyaspartates, gluconates and citrates. 4. The method according to claim 1, where the specified buffering agent is selected from the group consisting of precipitated calcium carbonate (RCC) and finely divided calcium carbonate.

Images