EP4303358A1

EP4303358A1 - The use of boron compounds in paper pulping, paper production and caustic recovery

Info

Publication number: EP4303358A1
Application number: EP23182956.5A
Authority: EP
Inventors: Ayhan Tozluoglu; Bilge Aslan Tanriverdi; Derya Maraslioglu; Ebru Karacay; Halil Ibrahim UGRAS; Zeki Candan
Original assignee: ETI MADEN ISLETMELERI GENEL MUDURLUGU
Current assignee: ETI MADEN ISLETMELERI GENEL MUDURLUGU
Priority date: 2022-07-04
Filing date: 2023-07-03
Publication date: 2024-01-10

Abstract

The invention relates to a method of using sodium borate compounds (borax pentahydrate and borax decahydrate) for pulp fiber, paper production and caustic recovery.

Description

Technical Field

The invention relates to a method of using sodium borate compounds (borax pentahydrate and borax decahydrate) for pulp fiber, paper and caustic recovery.

Prior Art

The demand for pulp and paper is growing rapidly every day. In order to meet the high volume of production, great difficulties arise in the supply of raw materials.
Chemical methods (soda, kraft, sulfite and organosolv methods), semi-chemical methods (NSSC, high efficiency sulfite and kraft methods) and mechanical methods (methods using stone groundwood pulpingand refining) can be used in pulp production from lignocellulosic raw materials (wood, annual plants, agricultural wastes, etc.).
In the first stage of paper production, pulp is produced. Pulp is the basic raw material used in the production of writing and printing papers, all kinds of paper, cardboard and cardboard used in packaging and tissue paper, napkins, toilet paper and paper towels called cleaning papers. In addition to these three main areas of use, pulp can also be used in the production of special papers for some industrial uses (e.g. insulator paper in electricity and electronics) and as the main raw material source for industries such as textiles, plastics, food, cosmetics and pharmaceuticals by enriching the cellulose content and chemically modifying it.
The aim of pulp production by chemical methods is to dissolve and remove the lignin, which is around 20-40% in the wood. The process of removing lignin is called delignification. With this process, both the fibers disperse without the need for any mechanical process and the cells soften and become suitable for paper making. However, it is not possible to produce pulp with kraft pulping solution without losing the carbohydrate part. Especially alkali intolerant hemicellulose fractions with low molecular weight pass into the pulping solution at the very beginning of pulping. The peeling, hydrolysis and oxidation reactions that occur during the kraft pulping process cause the degradation of carbohydrates, which both reduces the pulp yield and negatively affects the resistance properties of the papers obtained from the pulp.
The paper and pulp industry uses mechanical, chemical or a combination of these methods. Approximately 25% of pulp production is obtained by mechanical methods. Although pulp yields are high in mechanical pulp production, the disadvantage is the high consumption of electrical energy. Another disadvantage of the mechanical method is that mechanical doughs have lower resistance properties compared to chemical doughs. In chemical methods, the approach is to dissolve the lignin (delignification) under high temperature and pressure using appropriate chemicals and to separate the wood fibers from each other.
In the past, the paper industry has been able to obtain inputs such as wood, water, air and energy abundantly and cheaply. But in recent years the prices of these inputs have risen rapidly. Therefore, more efficient and economical use of resources has become a necessity. The main problems encountered in paper production are insufficient raw materials, low yield, more economical use of energy, reduction of environmental pollution, recovery and utilization of wastes. The most important of these problems are raw material shortage and low yield. Therefore, considering today's conditions, the continuous increase in the world population has pushed the industrial branches to search for different raw materials and to investigate the more efficient use of existing raw materials.
Although the kraft method is the most widely used pulp production method in the world, the yield loss due to polysaccharide degradation reactions (mainly peeling reaction) occurring under strong alkaline conditions is high. For this reason, kraft pulp produced with the same residual lignin content using the same raw material is always obtained at a lower yield than sulfite pulp. However, it is possible to increase the yield of kraft pulp within a certain success limit by modifying the original kraft pulping with the addition of some additives or some changes in the reinforcement where the pulping is carried out. The increase in kraft pulp yield can be realized in three ways. Reducing carbohydrate loss, reducing the amount of lignin removed or a combination of these two factors.
It is a known fact that under alkaline conditions and at relatively low temperatures of 100-120°C, polysulfide (PS) compounds oxidize the reducing end groups in the polysaccharide chain to aldonic acids. However, this technique requires the use of sulfur to obtain sufficient polysulfide concentration and losses during the recovery process are quite high.
It is known that a more selective delignification can be achieved if kraft pulping is carried out using a pulping liquor containing high sulfidity. However, with high sulfidity pulping, a higher viscosity dough can be obtained with a limited increase in yield.
By oxygen delignification of the kraft pulp obtained at high yields, a bleachable pulp can be obtained at higher yields. Although this practice has been introduced in some mills in Norway and the USA, it is reported to provide only a limited yield increase of 1-1.5%.
The fact that anthraquinone (AQ) increases yield by stabilizing carbohydrates in the pulping medium and accelerates delignification reactions was first discovered by Holton. However, there is no significant change in the quality of the pulps obtained by kraft-AQ pulping. Although the use of additives such as polysulfide (PS) and anthraquinone (AQ) has been among the opportunities developed for improvements in basic kraft technology, neither additive has attracted significant commercial interest.
In recent years, it has been reported in the literature that the yield increase in kraft pulping trials using various boron-containing compounds has increased at rates ranging from 1-4%. However, this production increase should not negatively affect the existing advantages of the kraft method. At this point, sodium borohydride (NaBH₄) based reduction reactions have been extensively studied. In this process, sodium borohydride is added directly to the pulping liquor and the initiation of reduction in this way generates the heat required for the reaction. The yield increase depends on the increase of hemicellulose in the pulp content. However, the papers produced by this method show lower quality characteristics due to more hemicellulose in the structure.
Another disadvantage of all the modification chemicals mentioned above and already studied in the literature is their high cost.
On the other hand, one of the main research topics in the process of obtaining pulp by kraft method is the environmental impacts of the method. One of the most important problems of kraft pulp mills is the problem of bad odor. Although this problem has been solved to some extent with the studies, air emissions such as sulfur compounds and waste sludge residues continue to be a problem. Considering that chlorine-based bleaching chemicals are used in the production of kraft pulp and that one of the most important causes of environmental pollution is the chemicals from bleaching, the importance of the issue once again emerges.
Pulp producers want the highest possible yield and fiber quality using the least amount of energy and chemicals. Lower energy and chemical use in production is desired. This minimizes the environmental impact of the chemicals used. Due to the fact that higher profitability can be achieved if the pulp yield is increased by only 1%, pulp producers are constantly searching for alternative pulp production. In this direction, many pulping methods and modifications to these methods have been developed until today and these studies continue today.
In the kraft method, there is a connection between the change in dough yield during pulping and the mechanism of loss and degradation of wood polysaccharides caused by alkaline solution. The degree of polymerization of polysaccharides exposed to alkali during pulping decreases through peeling reaction and alkaline hydrolysis. This decrease in the degree of polymerization of polysaccharides is directly proportional to the decrease in dough yield. These reactions that cause yield loss can be prevented by reducing the carbonyl group in the end group of the polysaccharide to hydroxyl group with a reductant such as sodium borohydride (NaBH₄) or by oxidizing it to carboxyl group with an oxidant such as polysulfide (PS) and anthraquinone (AQ). NaBH₄ has been used in the majority of studies on the effects of boron compounds on pulp and paper properties. NaBH₄ stops the possible peeling reaction by reducing the carbonyl group at the reducing end of the cellulose chain to hydroxyl group during pulping. Thus, the decrease in yield during pulping is prevented.
Another important stage for producers in pulp and paper production by chemical methods is the causticization stage, which refers to the recovery of the chemicals used. The main objectives of the recovery systems in the kraft process are the recovery of the inorganic pulping chemicals used, obtaining electricity and heat energy by burning the dissolved organic substances in the black liquor, recovery of valuable by-products such as tall oil and pollution prevention.
With this process, on the one hand, hazardous chemicals are recovered and on the other hand, the heat energy generated during the process is utilized within the factory.
In facilities producing pulp by kraft method, the recovery unit is installed to realize four main obj ectives:

Preparation of white solution used in pulping from kraft black liquor,
Production of water steam and hot water for plant use from the energy generated during the combustion of the concentrated black liquor,
Minimizing the water pollution impact of the plant, as the recovery process means recovering the inorganic substances in the black liquor and disposing of the organic substances by incineration,
Obtaining valuable by-products such as alkaline lignin from resin (tall-oil) and, if desired, by precipitation.

In a conventional causticization plant, lime (CaO) is reacted with an aqueous solution of sodium carbonate (Na₂CO₃) (green liquor) to recover sodium hydroxide (white liquor). The lime causticization process is carried out in three main steps:

Dissolving the melt from a back-feed boiler with water in a melt tank to produce green liquor, usually composed of sodium carbonate (Na₂CO₃) and sodium sulfide (Na₂S).
To convert green liquor into white liquor by causticizing it with lime in a lime extinguisher, clarifiers and a series of causticizers (this reaction is known as the causticization process. In particular, it is the step where the white solution is prepared. The reaction is based on the ion exchange of Na₂CO₃ and milk of lime (Ca(OH)₂). The milk of lime required for this process is obtained by quenching quicklime in water.
Drying and roasting of the precipitated lime sludge (CaCO₃) in a lime kiln to produce lime that is then reused (the CaCO₃ produced by the causticization reaction is insoluble in water. It is removed from the solution by precipitation, filtration or centrifugation).

The reactions are as follows:

Lime Quenching: CaO _(k) + H2O _(s) → Ca(OH)_{2 (k)}

Caustication Na₂CO_{3 (aq)} + Ca(OH)_{2 (k)} ↔ 2NaOH _(aq) + CaCO_{3 (k)}

Lime Incineration CaCO_{3 (k)} → CaO _(k) + CO2 _(g)
The resulting lime is used for causticization, completing the calcium cycle.
In the European patent document numbered EP1388522A2 , which is in the known state of the art, a study is mentioned for improving the properties of paper produced by adding the borosilicate composition to the mixture of waste paper or primary pulp fibers or applying it to the surface of paper produced from these fibers. The borosilicate materials used are preferably an aqueous solution. The document mentions a methodological study to improve the properties of paper produced by adding borosilicate compounds obtained using sodium tetraborate decahydrate or sodium tetraborate pentahydrate to a mixture of waste paper or origin (primary) pulp fibers or applying them to the surface of paper produced from these fibers.
In the Canadian patent document numbered CA2513488C , which is in the known state of the art, it is mentioned that the method of making paper uses a boron-containing compound believed to interact with cellulose to provide improved physical and mechanical properties in paper. In the relevant document, a methodological study was mentioned to improve the properties of paper produced by adding boron-containing compounds (such as sodium borate pentahydrate) to the original (primary) pulp fibers obtained from soft or hard woods together with starch in the fiber suspension before paper production or by applying it to the surface of the produced papers (size press).
In the United States Patent document numbered US7608166B2 , which is in the known state of the art, paper substrates and production methods containing starch or sizing pressed starch and boron-added compounds with improved physical and mechanical properties are mentioned. In the relevant document, a methodological study is mentioned to improve the properties of paper produced by adding boron-containing compounds (such as sodium borate pentahydrate) to the original (primary) pulp fibers obtained from soft or hard woods together with starch to the fiber suspension before paper production or by applying it to the surface of the produced papers (size press).
When the existing studies in the art were examined, there was a need to realize a method in which sodium borate compounds were used in pulp production (paper fiber production) and causticization.

Objectives of the Invention

The object of the present invention is to provide a method wherein sodium pentahydrate and borax decahydrate compounds are used to increase the efficiency of pulp (fiber), paper production and subsequent causticizing process.
Another object of the invention is to provide a method for improving the quality of paper by means of borax pentahydrate and borax decahydrate compounds.

Detailed Description of the Invention

The invention relates to pulp fiber, paper production and causticization method and includes the steps of:

obtaining paper pulp by applying kraft pulping method containing borax pentahydrate and borax decahydrate to chips prepared from lignocellulosic biomass,
pretreatment of the black liquor after pulping by first drying and then ashing and converting the solution into a green liquor,
causticization of the green liquor with borax pentahydrate and borax decahydrate compounds.

In the inventive method, wood was preferred as lignocellulosic biomass. Within the scope of the study, optimum cellulose production was achieved by using sodium borate compounds (borax penrahydrate and borax decahydrate).
Half-meter logs obtained from felled trees were separated into 3 cm thick discs and the bark was peeled off. The knots on the disks were removed from the disks in order not to affect the results obtained in the method due to the difference in their chemical structure. From these discs, 3 discs were taken from each half-meter sample and chipped by hand in 0.3×1.5×3 cm dimensions. From the samples whose moisture content was determined, 400 g (oven dry) samples for each pulping were taken into polyethylene bags and stored until the pulping was carried out.
In sodium borate modified kraft pulping processes, active alkali ratio was 10-20%, sulfidity was 20-30%, sodium borate compounds were taken at 0.25-15% ratios and the pulping time to maximum temperature was 45-90 minutes, pulping time at maximum temperature was 60-120 minutes, max. temperature was 160-180 °C, and liquor/chip ratio was 4/1-5/1.
The pulpings were carried out in a 15 lt capacity, electrically heated, 25 kg/cm² pressure resistant, laboratory type rotary pulping vessel which can make 2 cycles per minute and whose temperature can be controlled thermostatically with an automatic control table. The H factor value, which gives the relationship between pulping time and temperature, was also calculated to control the homogeneity between the pulpings.
At the end of the pulping time, the fibers were taken in a 150 mesh sieve and washed until the washing water became clear and each fibers was opened in a fiber opener for 5 minutes each. The opened fibers were screened on a Somerville type shaking vacuum sieve according to TAPPI T 275 sp-02 standard and the screened yield and residue ratios were determined as % by gravimetric measurements in the laboratory environment according to TAPPI T 210 cm-03 standard. In addition, kappa numbers of the pulps were determined according to TAPPI T 236om-99 and viscosities were determined according to SCAN-CM 15-62 standard. As a result of the yield, kappa and viscosity determinations, some of the black solution from the firings determined as optimum for both boron compounds was taken and tested in causticization studies.
In the selection of the optimum sodium borate modified kraft pulping processes, the concentration of the chemical used and the related cost of production as well as the kappa, viscosity and yield of the pulps were taken into consideration, and paper production was carried out from the pulps determined as optimum and compared with the control pulp. In this context, the screened fibers were beaten up to 50 °SR in Hollander according to TAPPI T 200 sp-01 standard. The degree of freeness of the fibers was determined by Schopper Riegler device according to ISO 5267-1 standard. 5 pieces of test papers with a weight of 90±2 g/m² were made from the pulps beaten up to 50 °SR and from the unbeaten pulps according to ISO 5269-2 standard.
On the other hand, mechanical (tensile index-TAPPI T494, bursting index-TAPPI T403 and tearing test-TAPPI T414), drainage (ISO Standard method 5267-1) and physical (thickness-ISO 534/1998, density- TAPPI T220, bulk-TAPPI T220, air permeability-ISO 5636/3, surface smoothness test-ISO 8791/2 and Cobb value- TAPPI T432) properties were determined according to the relevant standards. In addition, optical properties (brightness-TAPPI T525 and opacity-TAPPI T519) were also tested.

Causticization phase;

In order to examine the effect of sodium borate compounds on the efficiency of causticization process in kraft pulp production, firstly, the effect of sodium borate addition in an aqueous Na₂CO₃ solution on causticization efficiency was examined as a blind experiment. Then, the effect of sodium borate addition on the causticization efficiency of green liquor obtained from a paper mill was studied in order to evaluate the results obtained on a commercial scale. Finally, the effect of sodium borate modification on causticization efficiency was evaluated by studying the causticization efficiency without sodium borate addition in the solution obtained from sodium borate doped cellulose production.

1.1 - Boron Effect on Na₂CO₃ Solution Causticization

This method involves reacting an aqueous Na₂CO₃ solution with lime to obtain NaOH in the presence of borate to improve the causticization reaction efficiency. It is believed that this increase in efficiency is due to the buffering effect of sodium metaborate (NaBO₂) in alkaline solution and that sodium metaborate suppresses the concentration of hydroxyl ions on or near the surface of Ca(OH)₂ particles, allowing the equilibrium of the causticization reaction to shift to the right, thereby increasing process efficiency.

1.1.1 - Preparation of initial solutions;

Na₂CO₃ solution: 300 g Na₂CO₃ per liter
Na₂B₄O₇.10H₂O solution: 137 g Na₂B₄O₇.10H₂O per liter

The solution is prepared at 80°C. The solubility of borax decahydrate, one of the sodium borate compounds, at 80°C is approximately 40 g/100 g water. The solution is not saturated; it is calculated and determined according to the required B/Na ratio. For the most effective efficiency, experiments are calculated and performed according to the B/Na ratio.
Na₂B₄O₇.5H₂O solution: 137 g Na₂B₄O₇.5H₂O per liter
The solution is prepared at 80°C. The solubility of borax pentahydrate, one of the sodium borate compounds, at 80°C is 33.84 g/100 g water. The solution is not saturated; it is calculated and determined according to the required B/Na ratio. For the most effective efficiency, experiments are calculated and performed according to the B/Na ratio.

BaCl₂ solution: 160 grams BaCl₂.2H₂O per liter
Lime: Directly supplied CaO.

1.1.2 - Process steps

1. The following solutions were prepared.
- For B/Na = 0.0045; 100 ml Na₂CO₃ solution and 1.75 ml Na₂B₄O₇.10H₂O solution were mixed in a beaker at 80°C. (Solution A1)
- For B/Na = 0.0045; 100 ml Na₂CO₃ solution and 1.33 ml Na₂B₄O₇.5H₂O solution were mixed in a beaker at 80°C. (Solution A2)
- For B/Na = 0.33; 100 ml of Na₂CO₃ solution and 156 ml of Na₂B₄O₇.10H₂O solution were mixed in a beaker at 80°C. (Solution A3)
- For B/Na = 0.33, 100 ml of Na₂CO₃ solution and 120 ml of Na₂B₄O₇.5H₂O solution were mixed in a beaker at 80°C. (Solution A4)
- For B/Na = 0.50, 100 ml Na₂CO₃ solution and 265 ml Na₂B₄O₇.10H₂O solution were mixed in a beaker at 80°C. (Solution A5)
- For B/Na = 0.50, 100 ml of Na₂CO₃ solution and 202 ml of Na₂B₄O₇.5H₂O solution were mixed in a beaker at 80°C. (Solution A6)
- For B/Na = 1.00, 100 ml of Na₂CO₃ solution and 790 ml of Na₂B₄O₇.10H₂O solution were mixed in a beaker at 80°C. (Solution A7)
- For B/Na = 1.00, 100 ml of Na₂CO₃ solution and 606 ml of Na₂B₄O₇.5H₂O solution were mixed in a beaker at 80°C. (Solution A8)
- For B/Na = 0.70, 100 ml of Na₂CO₃ solution and 430 ml of Na₂B₄O₇.10H₂O solution were mixed in a beaker at 80°C. (Solution A9)
- For B/Na = 0.40, 100 ml of Na₂CO₃ solution and 150 ml of Na₂B₄O₇.5H₂O solution were mixed in a beaker at 80°C. (Solution A10)
2. Each solution (A1-A10) was stirred and heated on a hot plate and the solution temperatures were maintained at about 80 °C.
3. 15.70 g of lime was added to each solution (A1-A10) to make the CaO:Na₂CO₃ mole ratio equal to 1:1.
4. The mixtures were stirred continuously and the temperatures were maintained in the range of 80-90 °C for 60 min.
5. The resulting sludge (CaCO₃ precipitate) was filtered, washed with 100 ml of hot water and the clean sludge was dried in an oven at 150 °C for 24 hours.
6. The solutions obtained from step 5 were Solution B 1, Solution B2, Solution B3, Solution B4, Solution B5, Solution B6, Solution B7 and Solution B8. Solution Bs were analyzed for unreacted Na₂CO₃ and the causticization efficiency (CE) was determined according to the following procedures.

1.1.3 - Unreacted Na₂CO₃ Analysis and CE Calculation

BaCl₂ Precipitation Method

1. To precipitate unreacted CO₃ ^-2 ions as BaCO₃, 50 ml of BaCl₂ solution was added to the B solutions (B1-B8) obtained by the above procedures.
2. An extra 10 ml of BaCl₂ was added to the filtrates to ensure that all CO₃ ions were removed.
3. The BaCO₃ precipitates were filtered, dried in an oven and the dried mass weighed.
4. The amount of mass weighed will have given the amount of unreacted Na₂CO₃ in the B solutions (B1-B10).
5. CE was calculated using Equation I $CE = \frac{[{Na}_{2} {CO}_{3}] SolutionA - [{Na}_{2} {CO}_{3}] SolutionB}{[{Na}_{2} {CO}_{3}] SolutionA} \times 100 (%)$

1.2 - Boron Effect on Green Liquor Causticization

For this method, green liquor was obtained from any pulp mill.

Na₂CO₃ determination

For this experiment, a sample of green liquor was taken from a pulp factory; the liquor container was filled with nitrogen and kept below 4°C to keep the chemical composition unchanged. The amount of Na₂CO₃ in the solution was compared by the ABC titration method described below:

1. Excess barium chloride was added to precipitate sodium sulfate and the liquor was titrated with 0.5 N HCl to a phenol phthalate endpoint. (Part A)
2. Then 5 mL of a 37% formaldehyde solution was added and the pink color was redetermined. Titrated with HCl solution until the pink color disappeared again (Part B).
3. Methyl orangine was titrated to the endpoint (Part C).
4. The concentrations of sodium hydroxide, sodium sulfide and sodium carbonate were determined from compartment A, compartment B and compartment C and the total alkali and active alkali values were determined according to the following relationships:
- A is equivalent to NaOH + 1/2 Na₂S charge;
- B is equivalent to NaOH + Na₂S charge;
- 2 (B - A) is equivalent to Na₂S charge and
- C is equivalent to the total charge of alkali or NaOH + Na₂S + Na₂CO₃.

Effect of Borax Addition

According to the amount of Na₂CO₃ calculated in the previous step, the starting chemicals in step 1.1.1 were calculated and the procedure in step 1.1.2 was repeated. According to the result of the procedure, unreacted Na₂CO₃ and causticization yield were calculated using step 1.1.3.

1.3. Boron Effect in the Solution Obtained from Boron Additive Cellulose Production

For this method, the black liquor obtained from the optimum cellulose production using sodium borate in this project was used. The black liquor is not suitable for titration and causticization due to its viscous opaque nature and organic waste content. Therefore, it was pretreated before starting the experiment. To characterize the salt content, it was first dried and then ashed to remove all organic matter, leaving only the salts. The salts were then dissolved in deionized water and 20 ml of water was added for every 50 ml of solution. In this way the black liquor was converted into a green solution.

Na₂CO₃ determination

The ABC titration method described below was used to determine the amount of Na₂CO₃ in the solution.

1. Excess barium chloride was added to precipitate sodium sulfate and the liquor was titrated with 0.5 N HCl to a phenol phthalate endpoint (Part A).
2. Then 5 mL of a 37% formaldehyde solution was added and the pink color was redetermined. Titrated with HCl solution until the pink color disappeared again (Part B).
3. Methyl orangine was titrated to the endpoint (Part C).
4. Sodium hydroxide, sodium sulfide and sodium carbonate concentrations were estimated from 3 titers and total alkali and active alkali values were determined according to the following relationships:
- A is equivalent to NaOH + 1/2 Na₂S charge;
- B is equivalent to NaOH + Na₂S charge;
- 2 (B - A) is equivalent to Na₂S charge and C is equivalent to total alkali or NaOH + Na₂S + Na₂CO₃ charge.

1.3.1. Causticization Process without Borax Addition

1. According to the amount of Na₂CO₃3 calculated from the previous step, the calculated amount of CaO was added to the solution so that the CaO:Na₂CO₃ mole ratio was 1:1.
2. The mixture was stirred at 80-90°C for 60 minutes.
3. The resulting sludge (CaCOs precipitate) was filtered, washed with 100 ml of hot water and the clean sludge was dried in an oven at 150°C for 24 hours.
2. 50 ml of BaCl₂ solution was added to the filtrate obtained from step 3 to precipitate unreacted CO3-2 ions as BaCO₃
3. The BaCO₃ precipitates were filtered, dried in an oven and the dried mass weighed.
4. An extra 10 ml of BaCl₂ was added to the filtrates to ensure that all CO3 ions were removed.
5. The amount of unreacted Na₂CO₃ in the filtrate was calculated based on the amount of BaCO₃ precipitate.
6. CE was calculated using the following equation: $CE = \frac{[Na 2 CO 3] Solution - [Na 2 CO 3] Filtrate}{[Na 2 CO 3] Solution} \times 100 (%)$

Within the scope of the inventive method; studies have been carried out on how industrial sodium borate compounds (borax decahydrate and borax pentahydrate) affect the causticization process in the related paper production sector both in cellulose production and in the recovery process in the presence of boron compounds compared to traditionally used methods, and the results obtained reveal that sodium borate compounds can be used as an alternative raw material to modified pulping chemicals traditionally used in paper production.
The most important parameters for paper manufacturers in pulp production are the yield, kappa number and viscosity of the pulp. In the inventive method, it was determined that the addition of sodium borate compounds caused a general decrease in the kappa number of the pulps and an overall increase in their viscosity. In addition, it was determined in the study that the addition of sodium borate compounds caused an increase in the screened yields of the pulps and a decrease in the screen residue ratio depending on the optimal use. From this point of view, it is thought that the use of sodium borate compounds in pulp production will be an advantage for pulp producers in terms of increased pulp yield as well as reduced energy consumption as a result of reaching the desired kappa number in a shorter pulping time.
Thanks to the inventive method, it was observed that the quality of the papers produced was positively affected as well as the pulp yield, viscosity and kappa. In the method, the addition of sodium borate compounds increased the tensile index values of the papers and the highest tensile index increase (18.2%) was obtained with borax pentahydrate modification compared to the papers obtained from the control pulp. Tear index values were also positively affected by sodium borate modification and the highest tear index increase (45.5%) was obtained with borax decahydrate modification after the beating process. On the other hand, in this study, it was determined that the addition of sodium borate compounds also increased the burst index values of the papers. The highest burst index (37.5%) was obtained with borax pentahydrate modification in the papers obtained after the beating process.
During both production and printing, there are some physical properties that paper manufacturers and paper users should know and pay attention to. Physical parameters such as paper weight, thickness, moisture, Cobb value, surface smoothness and porosity values are extremely important for paper - ink - printing machine compatibility during the printing phase. It was determined that the addition of sodium borate compounds used in the inventive method caused a significant decrease in the air permeability values of the papers. In the papers obtained after the beating process, the air permeability values decreased by 93.5% and 93.7% after borax pentahydrate and borax decahydrate modifications, respectively. On the other hand, it was determined that the addition of sodium borate compounds provided a significant decrease in the surface roughness values of the papers, and a decrease of 7.41% and 12.7% was realized after borax pentahydrate and borax decahydrate modifications, respectively, in the papers obtained after the forging process. After the modifications of sodium borate compounds, the papers obtained from these pulps were lower porosity, thinner, more compact, denser and less bulky than the control kraft papers. As a result of these results obtained on the basis of physical properties, it is thought that sodium borate modified papers will positively affect the printing properties of the papers to be produced due to their increased surface properties and can be successfully used in the production of papers with improved barrier-protective properties such as packaging papers.
Opacity, one of the most important optical properties of paper, is an important feature for printing papers and envelope papers. It is more prominent especially in low weight papers. Since the thinness of the paper increases the risk of the print appearing on the back side, the opacity should be high. It was determined that the addition of sodium borate compounds used in the inventive method did not significantly change the opacity values of the papers. On the other hand, it was determined in the study that the addition of sodium borate compounds increased the brightness values of the papers. In the papers obtained after the beating process, increases of 26.2% and 26.4% were obtained for borax pentahydrate and borax decahydrate modification, respectively, compared to the control papers. As a result, it was observed that sodium borate compounds gave better results in terms of pulp and paper properties compared to control kraft pulps.
In the inventive method, the effect of the addition of sodium borate compounds on the causticization of sodium carbonate in the green liquor content in kraft pulp mills was also investigated. Firstly, the effect on the aqueous solution of sodium carbonate in the laboratory environment was examined and it was determined that the addition of borax decahydrate at a molar ratio of 0.50 B/Na and borax pentahydrate at a molar ratio of 0.40 B/Na provided optimum causticization efficiency. In line with the data obtained from this study, borax decahydrate was added to the green liquor obtained from the paper mill at a molar ratio of 0.50 B/Na and borax pentahydrate was added at a molar ratio of 0.40 B / Na. It was determined that the addition of borax decahydrate improved the causticization efficiency of green liquor by 9%, while the addition of borax pentahydrate improved the efficiency by about 8%.
In addition, the causticization process was also performed on the solution obtained by adding borax pentahydrate and borax decahydrate during cellulose production and it was found that the addition of borax decahydrate improved the causticization efficiency by about 7% and the addition of borax pentahydrate by 3.5% compared to the green liquor taken from the paper mill.
Considering that the price of sodium borate compounds is 1 in 3000 of NaBH₄ and KBH₄, which are currently used for modification purposes in the kraft method, and 1 in 300 of AQ, it is seen that domestic boron compounds are considerably cheaper than their counterparts. Although the production cost of domestic boron compounds increases as a result of their use in pulp production, this cost increase is negligible compared to other compounds that provide yield increase due to the fact that these compounds increase pulp yield (3-4 points) and enable the production of paper with higher strength (10-20%).
The results of the study show that sodium borate compounds, which are not currently used in the literature and commercially, can be used as an alternative to their existing counterparts in pulp and paper production as well as in causticization studies.

Claims

The invention relates to pulp fiber, paper production and causticization method and characterized in that the method comprising;
- obtaining paper pulp by applying kraft pulping method containing borax pentahydrate and borax decahydrate to chips prepared from lignocellulosic biomass,

- pretreatment of the black liquor after pulping by first drying and then ashing and converting the liquor into a green liquor,

- causticization of the green liquor with borax pentahydrate and borax decahydrate compounds.
The method according to the claim 1, characterized in that the sodium borate-modified kraft pulping processes are characterized in that the active alkali ratio is 10-20%, the sulfidity is 20-30%, the borax pentahydrate and borax decahydrate compounds are taken in the ratios of 0.25-15%, and the pulping time to maximum temperature is 45-90 minutes, the pulping time at maximum temperature is 60-120 minutes, the temperature is 160-180 °C, and the liquor/chip ratio is 4/1-5/1.
The method according to the claim 1, characterized in that, after the pretreatment step, the salts are dissolved in deionized water and 20 ml of water is added to the solution for every 50 ml of solution.
The method according to the claim 1, characterized in that in the causticization step borax decahydrate is added in a molar ratio of 0.0045 - 0.50 Boron/Sodium (B/Na) and borax pentahydrate is added in a molar ratio of 0.0045 - 0.40 Boron/Sodium (B/Na).