EA041989B1 - CONTINUOUS METHOD FOR THE PRODUCTION OF PULP MASS FROM GRASS MIXTURES - Google Patents

Description

Technical field

The invention relates to an improved method for the production of pulp for the production of paper from grassy raw materials, such as dried plant mass from the leaves and/or stems of sorghum (Sorghum varieties L.) or corn (Zea mays L.).

Technical problem

The technical problem solved by the present invention is the efficient production of high quality pulp for papermaking from herbal raw materials such as sorghum (Sorghum variety L.), which includes the efficient solution of the following technological details:

(i) preparing grass-like raw materials under mild reaction conditions to maximize the preservation of native cellulose fibers while removing lignin and other by-products by dissolving them in a solution of digestion chemicals;

(ii) bleaching brown pulp; with such a solution of bleaching chemicals that provides effective bleaching under as mild reaction conditions as possible to preserve the cellulose fibers; and, (iii) efficient removal of black liquor from the pulping stage and from wastewater from the bleaching stage, which ensures minimal chemical consumption and therefore minimal environmental impact.

The pulping phase is further improved by the use of freshly made or electrolytically regenerated white liquor, which contains minimal sodium hydroxide (NaOH; 0.5-2.0 wt.%) and sodium chloride (NaCl; 0.5-2.0 wt.%) .

The present invention is the first continuous method for the production of pulp, which includes:

(i) environmentally friendly bleaching - technology with electrochemical generation of oxygen (O ₂ ) and chlorine (Cl ₂ ) in the presence of sodium hydroxide (NaOH) and sodium chloride (NaCl);

(ii) nearly 100% recovery of all chemicals in the process;

(iii) efficient electrolytic removal of lignin and other non-cellulosic by-products from black liquor in the pulping stage and from wastewater in the bleaching stage; and, (iv) conditions that fully comply with the general criteria for environmentally friendly technologies.

State of the art

The production of paper pulp from a renewable, fast growing and economical raw material is of great importance for the modern paper industry. Classical methods based on wood as raw material are being replaced more and more by technologies that rely on herbaceous raw materials such as miscanthus (Miscanthus x giganteus, Andersson), sorghum (Sorghum, Linne species), straw of various cereals, etc. .; see for example link 1:

1) C. Cappelletto, F. Mongardini, B. Barberi, M. Sannibale, M. Brizzi, V. Pignatelli. Cellulose for making paper from the fiber fraction of Miscanthus x Giganteus, Ind. Crops Prod. 11 (2000) 205-210.

In pulp manufacturing processes, the cooking phase is the most important. It involves cooking pulverized lignocellulosic material in an aqueous solution of suitable chemicals. A greater number of different methods for pulping lignocellulosic materials are known, which are generally classified according to the types of chemicals used in the process. The most well-known technologies are based on the following solutions:

(i) based on sulfur: sodium carbonate (Na ₂ CO ₃ ) and sodium sulfite (Na ₂ SO ₃ ); magnesium hydroxide [Mg(OH) ₂ ] and magnesium sulfite (MgSO ₃ ); ammonium hydroxide (NH4OH) and ammonium sulfite [(NH ₄ ) ₂ SO ₃ ]; calcium hydrogensulfite [Ca(HSO ₃ ) ₂ ]; magnesium hydrosulfite [Mg (HSO ₃ ) ₂ ]; sodium hydroxide (NaOH), sodium sulfide (Na2S) and sodium sulfate (Na2SO4);

(ii) without sulfur: sodium carbonate (Na2CO3); sodium hydroxide (NaOH); and, (iii) based on acids such as nitric acid (HNO3).

A solution of cooking chemicals is commonly referred to as white liquor and is a freshly made or regenerated solution of chemicals for cooking lignocellulosic material. The white liquor helps to remove the non-cellulosic material, turning it into a solution, while the relatively pure cellulose fibers remain suspended in this liquid phase. Such a pulp suspension is known as pulp.

Thus referred to, the liquid phase (supernatant) in which the cellulose fibers are suspended after the cooking phase is called black liquor and contains dissolved non-cellulosic components of the lignocellulosic feedstock and excess cooking chemicals. Thus, the product of the pulping process is a suspension of brown cellulose fibers in black liquor.

With regard to the type of chemistry that is used in the pulping process, all technologies that do not use sulfur-based chemicals have significant advantages for both technological and environmental reasons. Technologies that do not contain sulfur-containing chemicals protect process equipment from corrosion and the environment from unnecessary pollution and, as such, do not have a significant negative impact on the environment.

- 1 041989

One of the most important processes, which is considered environmentally friendly, uses sodium hydroxide (NaOH) as the key chemical to make white liquor. The use of NaOH as the sole chemical for the digestion of lignocellulosic materials is known in the art. One typical method is based on the use of a 5% NaOH aqueous solution, which is used as white liquor to boil herbal raw materials at 90°C for several hours; see link 2:

2) GB 770687; Method for producing cellulose; applicant: Aschaffenburger Zellstoffwerke (Germany).

The cooking phase can be carried out using microwaves (MW) to heat a slurry of lignocellulosic material in white liquor. For example, Zhu and co-workers have described a method for pre-treatment of miscanthus (Miscanthus x giganteus, Andersson) with an aqueous solution of NaOH at very high temperatures (130-200°C), at elevated pressure, for 20 min, with heating by MB. Thus, pre-treated miscanthus gave a significantly higher yield in sulfuric acid (H ₂ SO ₄ ) catalyzed hydrolysis to glucose, which was subsequently used as a feedstock for the production of bioethanol by fermentation; see link 3:

3) Z. Zhu, DJ Macquarrie, R. Simister, LD Gomez, SJ McQueen-Mason: Microwave Chemical Pretreatment of Miscanthus at Various Temperatures, Sustain. Chem. Method 3 (2015) DOI: 10.1186/s40508-015-0041-6.

Although this method is focused on the production of glucose from miscanthus, the pre-treatment described suggests the potential use of MW for the preparation of miscanthus and other grassy raw materials in the production of pulp. Of course, the reaction conditions described in reference 3 are very harsh and clearly incompatible with the production of high quality cellulose fibers.

In addition to the pulping process, another important step in the production of high quality pulp is the bleaching process. The best known pulp bleaching systems are based on the use of chlorine-based chemicals such as sodium hypochlorite (NaOCl), chlorine (Cl2) in the presence of NaOH, chlorine dioxide (ClO2) or hydrogen peroxide (H2O2). The use of HO2 is preferred.

For example, US Pat. No. 2,903,326 describes a process for bleaching pulp with chlorine (Cl ₂ ), sodium hypochlorite (NaOCl) or calcium hypochlorite [Ca(OCl) ₂ ] and sodium hydroxide (NaOH) with the addition of sodium chlorate (NaClO ₃ ) at pH 2- 7, preferably at pH 5-7, at a temperature of 0-50°C; see link 4:

4) US 2,903,326; JB Heitman: Improved pulp bleaching process using chlorate; applicant: Pennsalt Chemicals Corporation (USA).

Although the use of H ₂ O ₂ is preferred for environmental reasons, some oxidizers that are formally based on chlorine are also acceptable. They do not lead to the formation of chlorinated organic compounds such as chloroform, which are undesirable environmental pollutants. An example is chlorine dioxide (ClO2), which has been successfully used as an oxidizing agent in pulp bleaching. Chlorine dioxide (ClO ₂ ) is usually produced separately by the reaction of sodium chlorite (NaClO2) and hydrogen peroxide (H2O2); then from sodium chlorite (NaClO2) and hydrogen peroxide (H2O2) in the presence of sulfuric acid (H2SO4); or in other ways; for example, see links 5 and 6:

5) GB 655056; Improvements in the method of suppressing the formation of chlorine dioxide; applicant: Tennants Consolidated Ltd (UK);

6) US 5,366,714; TD Bigauskas: Production of chlorine dioxide based on hydrogen peroxide; Applicant: Sterling Canada Inc. (CA).

Methods for bleaching pulp with chlorine dioxide (ClO ₂ ), with or without additional oxidizing agents, are known in the art; for example, see links 7 and 8:

7) US 2006201642 A1; H.X. Shin, P.J. O'Leary, O. Pikka: Chemical Pulp Processing Methods; Applicant: Andritz Inc. (USA)

8) US 4421598; DW Reeve: A bleaching procedure using chlorine dioxide and chlorine solutions; Applicant: Ergo Industries Ltd (CA).

As an example of a bleaching method based on hydrogen peroxide (H2O2), document

9) GB 681661 which discloses the use of the following bleaching system:

(a) 0.30-1.75 wt% H ₂ O ₂ ;

(b) 0.75-3.25 wt% NaOH;

(c) 20-65 wt.% pulp (in terms of dry matter); and (d) up to 100% process water;

where the bleaching is carried out at a temperature below 54.4°C.

Optionally, a sodium silicate solution (xNa ₂ O-ySiO ₂ ) can be used as a hydrogen peroxide stabilizer; see reference 9: GB 681661 A; Processing of chemical pulp; Applicant: Buf

- 2 041989 fal Electro-Chemical Co., Inc. (USA).

This document proposes to use a combination of hydrogen peroxide (H2O2) and sodium hydroxide (NaOH) as a pulp bleaching system under relatively mild reaction conditions below 54.4°C.

In addition to conventional heating of the pulp bleaching reactor, it is known in the art to use microwaves (MW) in this pulp processing step; see link 10:

10) SA 2038651 A1; K.-H. Law: Method and apparatus for pulp bleaching; applicant: K.-N. Law, JL Valade (USA)

In addition, Lo and co-workers have disclosed a pulp bleaching process based on microwave heating using a combination of hydrogen peroxide (H ₂ O ₂ ) and sodium hydroxide (NaOH); see link 11:

11) KN Law, SG Luo, JL Valade: Peroxide bleaching characteristics of microwave-heated thermomechanical pulp, J. Pulp Paper Sci. 19 (1993) J181-J-186.

The removal of lignin and other by-products from black liquor using an electrolytic reactor (cell) is known in the art. A typical example is the technology disclosed by Edel et al., which is based on direct current (DC) black liquor electrolysis between suitable electrodes. Lignin is released in the anode compartment, and sodium hydroxide is regenerated in the cathode compartment as white liquor; see link 12:

12) US4584076A; E. Edel, J. Feckl, S. Grambow, A. Huber, D. Wabner: a method for obtaining lignin from its alkaline solutions; applicant: MD Organically Zellst Umwelt Tec (Germany).

Mikulic has described a continuous process for the production of pulp from various herbaceous materials, preferably miscanthus. (Miscanthus x giganteus, Andersson), where:

(i) a mixture of NaOH (0.5-2.0 wt.%) and NaCl (0.5-1.5 wt.%) was used as a cooking medium at a temperature of 70-120°C for 1.5- 3 h;

(ii) H ₂ O ₂ (0.5-2.0 wt.%) was used as a bleaching agent in the presence of sodium silicate (xNa ₂ O-ySiO ₂ ; 0.5-2.0 wt.%) at a temperature of 70 -100°C for 45 min - 1.5 h; where, (iii) black liquor is processed by electrolysis in a cell whose cathode and anode compartments are separated by a membrane; which is carried out under the conditions: i. voltage from 3-30 V, preferably 310 V; ii. current density from 1-10 A/dm ² , preferably 3-7 A/dm ² ; and iii. temperature 10-95°C;

at the same time, aqueous sodium hydroxide (NaOH) with a small amount of residual sodium chloride (NaCl) is regenerated at the cathode and hydrogen (H2) is released, while oxygen (O ₂ ) and lignin are released at the anode.

To the best of our knowledge, this document represents the closest prior art to the present invention, see reference 13:

13) WO 2017/178849 A1; M. Mikulitz: Continuous method for the production of pulp from grassy raw materials; applicant: M. Mikulits.

Compared to the method described in WO 2017/178849 A1, the present invention is based on:

(i) a special system of serially connected devices for the following processes:

(a) pulping: primary digester - mill (for defibration/defibration) - drier (separator) - secondary digester, and (b) bleaching: primary bleaching reactor - mill (for defibration/defibration) - desiccant (separator) - a secondary bleaching reactor that provides a quasi-continuous processing method and efficient separation of black liquor from the pulping phase and spent chemicals from the bleaching phase, as well as the addition of fresh pulping and bleaching chemicals, which significantly increases the efficiency of the process under relatively mild reaction conditions, which subsequently provides a high degree of preservation of cellulose fibers;

(ii) a method for bleaching brown pulp with a mixture of white liquor that contains NaOH (0.5-2.0 wt.%) and NaCl (0.5-25.0 wt.%) and a gas mixture of oxygen (O ₂ ) and chlorine (Cl ₂ ) at a temperature of 70 -100°C, which is created in the anode compartment of the cell; with the implementation, (iii) electrolytic removal of lignin from the black liquor of the cooking phase and the spent liquid from the bleaching phase, since the electrolytic cell contains an electrolytic preliminary cell that does not contain a membrane between the anode and cathode, which increases the efficiency of the electrolytic part of the process and minimizes the tendency to fouling of the membrane inside the electrolytic cell (7B) which is connected downstream in the process after said electrolytic preliminary cell (7B).

These key improvements provide higher process efficiency and higher pulp quality for the production of grass paper, as described in the detailed description of the invention.

Brief description of the essence of the invention

The present invention includes a continuous method for the production of pulp from grass raw materials using an electrolytic method for the continuous separation of lignin and other

- 3 041989 dry by-products with simultaneous regeneration of white liquor and oxygen (O2) and chlorine (Cl ₂ ), which is carried out in an electrolytic cell consisting of:

one or more electrolytic pre-cells, made of a material inert with respect to the chemical composition of the method, in which the cathode and anode electrodes are immersed, without a membrane between the cathode and anode compartments;

one or more electrolytic cells made from a material that is inert with respect to the chemical composition of the method, in which the cathode and anode electrodes are immersed, where the cathode compartment is completely separated from the anode compartment by a porous membrane that provides electrical contact between the anode and cathode through ion exchange, but prevents the passage of suspended organic molecules in the electrolyte; where the electrolyte after treatment in the preliminary cells is transferred to the anode compartment of the electrolytic cells and, if necessary, the composition of the electrolyte is modified during the process by adding fresh sodium chloride (NaCl) solution to the preliminary cells; and the production method consists of the following steps:

A) preparation of a suspension of crushed and dust-free herbal raw materials by adding white liquor from the cathode compartment of the electrolytic cell to a digester, where the herbal raw material is boiled at a temperature of 80-100 ° C in a white liquor solution of the following composition:

(i) 0.50-2.00 wt% NaOH;

(ii) NaCl;

maintaining the concentration of herbal raw materials at the level of 5-15, preferably 8-12 wt.% dry matter, to obtain stage B;

B) quasi-continuous digestion and separation, realized with two or more parallel lines [primary digester - mill - dewaterer - secondary digester] for 3-6 hours, where the raw material from stage A is prepared and sequentially pumped into two or more of the mentioned parallel lines in such a way that a continuous production process is formed at the outlet of all secondary digesters, with the addition of:

suspensions of grassy raw materials in white liquor during cooking in all primary and secondary digesters is maintained at a temperature of 95-100°C;

suspension of brown pulp at a level of 8-12 wt.% dry matter at the outlet of each steamer is subjected to grinding in appropriate mills and separation in dehydrators, from which part of the black liquor is transferred to the electrolytic pre-cell, while the thus obtained concentrated suspension of brown pulp with about 30 wt.% dry matter enters the secondary digesters with the introduction of a solution of white liquor from the cathode compartment of the cells, which forms a suspension of approximately the same composition as the suspension in the digester stage A;

C) The quasi-continuous combined output from all secondary digesters with the prepared brown pulp slurry is transferred to the mixing vessel and mill, while the separation of the ground brown pulp is carried out in the dryer, which concentrates the brown pulp slurry from 5-15 wt.% dry matter to a content of 27-33 wt.% dry matter, which is accompanied by the separation of black liquor, which is transferred to the pre-cell of the electrolytic cell, while for stage D prepare a concentrated suspension of brown pulp;

D) preparation of the bleaching slurry is carried out in a bleaching reactor in which, with the exception of the slurry from step C, regenerated fresh white liquor from the cathode compartment of the electrolytic cell; a mixture of oxygen (O ₂ ) and chlorine (Cl ₂ ) in the anode compartment of the electrolytic cell; and, optionally, hydrogen peroxide (H ₂ O ₂ ) or sodium peroxide (Na ₂ O ₂ ) is introduced, to obtain a bleaching slurry with a content of 5-15, preferably 10 wt.% dry matter; and the preliminary method for bleaching brown pulp from step C is carried out at a temperature of 70-100°C for step E;

E) A quasi-continuous bleaching process is implemented through two or more parallel lines [primary reactor - mill - dryer - secondary reactor] for 3-6 hours at a temperature of 70 to 100 ° C, where the raw material from stage D is prepared and sequentially pumped into these two or more parallel lines so that at the outlet of all secondary reactors a continuous production process is obtained, wherein the primary bleaching process is carried out in the primary reactors and where at the outlet of the primary reactors a bleached pulp slurry with 8-12 wt.% dry matter is obtained, which is subjected to grinding in appropriate mills and separation in dryers, from which part of the spent solution is transferred to the preliminary electrolytic cell, and such a concentrated suspension of bleached pulp with a dry matter content of about 30 wt.% enters the secondary reactors, with the addition of a white liquor solution from the cathode compartment of the cells, mixtures of oxygen (O ₂ ) and chlorine (Cl ₂ ), which are released in the anode compartment of electrolytic cells; and optionally, hydrogen peroxide (H ₂ O ₂ ) or sodium peroxide (Na ₂ O ₂ ), to obtain a suspension of bleached pulp with 8-12, preferably 10 wt.% dry matter;

- 4 041989

F) The quasi-continuous combined output from all secondary bleaching reactors from stage E is transferred to the mixing vessel and dryer, the effluent from which is returned back to the electrolytic cell pre-cell while the dried pulp exits the process as pure white pulp at a concentration of 48- 55 wt.% dry matter, with a maximum lignin content of 5 wt.% dry matter.

The continuous process for producing grass pulp using the electrolytic process according to the present invention optionally includes further processing of the white pulp from step F, which includes further drying a viscous suspension of white pulp with 48-52 wt.% dry matter, which gives a dry pulp powder .

The key, electrolytic part of the continuous process for the production of pulp or dry cellulose powder from herbal raw materials is carried out under the following conditions:

the cathode is made of carbon or stainless steel, and graphite or magnetite is used for the anode;

between the electrodes in the electrolytic cell and the electrodes in the electrolytic cell, a direct current voltage of 1.5 to 20 V, preferably 3 to 6 V, is set at a current density of 1 to 10 A/dm ² , preferably 4 to 6 A/dm ² , at a cell temperature of 80-95°C;

electrolysis in the electrolytic preliminary cell is carried out by introducing black liquor from all lines of stage B, black liquor from stage C, part of the spent solution from stage E and waste water from stage F, while separating lignin and other by-products that are mechanically removed from the upper part of the electrolyte solution, while the electrolyte solution from the pre-cell is pumped to the anode compartment of the electrolytic cell for further processing, in which:

(i) white liquor of the following composition is regenerated at the cathode:

a) 0.50-2.00 wt% sodium hydroxide (NaOH);

b) sodium chloride (NaCl);

which is distributed to the digester in stage A; secondary digesters in stage B; to the bleaching reactor in step C; and to secondary bleaching reactors in stage D; and the produced hydrogen is transferred to an appropriate storage tank;

(ii) at the anode, oxygen gas (O ₂ ) and chlorine (Cl ₂ ) are formed and then introduced into the bleaching reactor at stage C and into the secondary bleaching reactors at stage E, and where the remaining lignin and other by-products are separated and mechanically separated from the solution electrolyte.

Of particular importance is the membrane that physically separates the cathode from the anode compartment inside the electrolytic cell. It consists of a material selected from the following group: asbestos, rock wool, hydrated portland cement, kaolin and sodium silicate product, aluminum oxide (Al ₂ O ₃ ), titanium oxide (TiO ₂ ), zirconia (ZrO ₂ ), polyethylene ( PE), polysulfone (PSU), polyvinylpyrrolidone (PVP), polyvinyl chloride (PVC), polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), sulphonated polytetrafluoroethylene (SPTFE) or composite materials obtained from combinations of these materials.

Preferably, the membrane of the electrolytic cell is made of a composite material consisting of:

(i) zirconia (ZrO ₂ ); 80 to 90, preferably 85% by weight; and (ii) polysulfone (PSU); from 10-20, preferably 15% by weight.

The working concentration of sodium chloride (NaCl) in white liquor is 0.50-25%, preferably 0.50-1.50% by weight.

Various grass-like feedstocks, preferably sorghum (Sorghum species, Linne) and corn (Zea mays, Linne), can be used as feedstock in the present process.

Description of drawings

Fig. 1 shows a block diagram of a continuous process for the production of pulp, which includes the following steps: A) preparing a slurry of herbaceous raw materials for cooking; C) quasi-continuous cooking of herbaceous raw materials; and also, C) post-treatment of brown pulp.

Fig. 2 shows a block diagram of a continuous pulp production process which includes the following steps: D) preparing a brown pulp slurry for bleaching; E) quasi-continuous bleaching of brown pulp; and F) white pulp finishing.

Fig. 3 shows a flowchart of a continuous pulp production process which relates to the black liquor electrolytic treatment phase.

Detailed Description of the Invention

The present invention relates to an improved method for the production of pulp for the production of paper from grassy raw materials such as dried leaves of plants or stalks of sorghum (L. sorghum species) or corn (Zea Mays L. species). Such raw materials typically contain 30-50 wt.% cellulose, 18-30 wt.% hemicellulose and 5-20 wt.% lignin; see references 14 and 15:

14) C. Ververis, K. Georghiou, N. Christodoulakis, P. Santas, R. Santas. Fiber sizes, lignin and cellulose content of various plant materials and their suitability for paper production,

- 5 041989

Industrial Crops Prod. 19 (2004) 245-254.

15) B. Gaudin, F. Gisel, R. Agnissens, T. Schmitt, S. Gofflot, S. Lamodiere, G. Sinnev, J.-P. Goffart, P.A. Guerin, D. Stillmant, J. Delcarte. Determination of cellulose, hemicellulose, lignin and other lignocellulosic cultures created in the production of bioethanol, biotechnology. Agron. soc. Environ. 14 (2010) 549-560.

The present invention includes a continuous method for the production of pulp from grass raw materials using an electrolytic method for the continuous electrolytic recovery of lignin and other by-products while producing white liquor and oxygen (O ₂ ) and chlorine (Cl ₂ )), where the method consists of the following steps:

A) preparing a suspension of herbaceous raw materials for cooking;

B) quasi-continuous cooking of herbaceous raw materials;

C) post-treatment of brown pulp;

D) preparing a brown pulp slurry for bleaching;

E) quasi-continuous bleaching of brown pulp;

F) white pulp finishing; and,

G) electrolytic treatment with black liquor.

These technological steps of the continuous process of the present invention include the following important steps:

A) Preparation of a suspension of herbaceous raw materials for cooking.

The preparation of herbal raw materials includes: (i) supplying herbal raw materials in the form of bales, which are conveyed by a conveyor (1) to the plant, (ii) while said bales enter the bale cutter (2), where the bales are cut into plant material of an approximate size, which subsequently sent for (iii) grinding in a mill (3), which serves to grind herbaceous raw materials to the level of fine particles, which, (iv) remove impurities such as dust, soil, natural silicates, etc. in a dust collector (4).

The method uses dried leaves and/or stems of herbaceous plants in the form of longitudinal pieces, the length of which is at least 90% from 0.2 to 2 cm. The moisture content of the grass feedstock is usually less than 10, preferably less than 5 weight.%.

The raw material for grass prepared in this way enters the digester (5), where a suspension is prepared for the cooking stage.

In the digester (5), the herbal raw material slurry is formed from white liquor, which is fed through the pipeline (6) from the cathode compartment of the electrolytic cell (7B), and herbal raw material. The resulting suspension of herbal raw materials has the following composition: a) 0.50-2.00 wt.; sodium hydroxide (NaOH); and also, (b) sodium chloride (NaCl);

with a concentration of grassy raw materials at the level of 5-15, preferably 8-12 wt.% of dry matter, which is subjected to heat treatment to a temperature of 80-100 ° C, and then ready for stage B.

The working concentration of sodium chloride (NaCl) in white liquor is 0.50-25.0, preferably 0.50-1.50% by weight.

A schematic diagram of the preparation of a suspension of herbal raw materials for the brewing method is shown in Fig. 1.

C) Quasi-continuous cooking of herbaceous raw materials.

Quasi-continuous pulping of herbaceous raw materials and separation of spent black liquor is carried out using two or more parallel lines, for example N lines, [primary digester (8, 8', ...) - mill (9, 9', ...) - dryer /separator (10, 10',...) - secondary digester (12, 12',...)] for 3-6 hours, where the raw material from stage A is prepared and sequentially pumped into these two or more parallel lines by means of a method in which the production of all secondary digesters (12, 12',...) provides a continuous production method in which the suspension of grassy raw materials in white liquor during the digestion in all primary digesters (8, 8',...) and secondary digesters (12, 12'...) maintained at a temperature of 95-100°C;

suspension of brown pulp at a level of 8-12 wt.% dry matter at the outlet of each primary digester (8, 8',...) is subjected to grinding in the respective mills (9, 9',...) and separation in dryers ( 10, 10',...), from which part of the black liquor is transferred through the collector (11, 11',...) into the electrolytic pre-cell (7A), whereby a concentrated suspension of brown pulp is obtained, containing about 30 wt.% dry matter, enters the secondary digesters (12, 12',...) with the introduction of a solution of white liquor from the cathode compartment of the cells (7B) through the collector (13, 13',...), which forms a suspension of approximately the same composition as the slurry in the digester (5) stage A; where the suspension of brown pulp in fresh white liquor is additionally subjected to cooking in all secondary digesters (12, 12',...) at a temperature of 95-100°C; whereas after completion of the cooking process in each line of devices [primary digester (8, 8',...)

- 6 041989 mill (9, 9',...) - dryer (10, 10',...) - secondary digester (12, 12',...)], the cooked suspension of brown pulp is alternately transferred to the mixing container (14).

In other words, the cooking phase of the herbaceous raw material is carried out by the fact that the suspension prepared in the digester (5) is first pumped and processed in one of the lines of devices [primary digester (8) - mill (9) - dryer (10) - secondary digester boiler (12)], and then in the next line of alternative devices [primary digester (8') - mill (9') - dryer (10') - secondary digester (12')]. Suspension of raw materials in the form of grass in white liquor during cooking in digesters (8) and (12) or (8') and (12') is maintained at a temperature of 95-100°C. The number of parallel lines [primary digester - mill - dewaterer - secondary digester] can be arbitrary and adjusted to achieve a quasi-continuous process.

Suspension of brown pulp with a dry matter content of about 10 wt.% at the outlet of the primary digesters (8, 8',...) is crushed / crushed in mills (9, 9',...) and further processed in drying plants . (10, 10',...), which are equipped with sieves with a pore size of 0.5-1.2 mm, in which a certain part of the black liquor is separated by pressing. It contains lignin and other by-products and is transferred through the collector (11, 11') to the pre-cell (7A) of the electrolytic cell (7). A concentrated suspension of brown pulp with a concentration of about 30 wt.% dry matter is sent to the secondary digesters (12, 12',...), in which fresh white liquor solution is added through a collector (13, 13',...).

From the line of devices [primary digester (8, 8',...) - mill (9, 9',...) - dryer (10, 10',...) - secondary digester (12, 12' ,...)] the prepared suspension of brown pulp exits into the mixing vessel (14). When the mixing vessel (14) is filled with the cooked pulp slurry from the line of devices [primary digester (8) - mill (9) - dewaterer (10) - secondary digester (12)], the contents are immediately pumped to the mill. (15). After emptying all contents, the cooked pulp slurry from the accessory line [primary digester (8') - mill (9') - dryer (10') - secondary digester (12')] is pumped into the mixing vessel (14), etc. d. - all in order to get a continuous way. During the time of pumping the brown pulp slurry from one line of devices [primary digester (8 inches) - mill (9 inches) - dryer (10 inches) - secondary digester (12 inches)], the preparation of the initial mixture of grassy raw materials occurs in the digester (5) for another line of devices [primary digester (8) - mill (9) - dryer (10) - secondary digester (12)]. Thus, the method is performed alternately between 1...N lines of devices, as explained here in this short example, from 1...3 parallel examples, and a quasi-continuous effect is achieved. As mentioned earlier, the minimum number of cooking lines is two. The preparation of the initial suspension of herbal raw materials takes place in the digester (5) for another line of devices [primary digester (8) - mill (9) - dryer (10) - secondary digester (12)]. Thus, the method is performed alternately between 1...N device lines, as explained here in this short example, from 1...3 parallel examples, and achieves a quasi-continuous effect. As mentioned earlier, the minimum number of cooking lines is two. The preparation of the initial suspension of herbal raw materials takes place in the digester (5) for another line of devices [primary digester (8) - mill (9) - dryer (10) - secondary digester (12)]. Thus, the method is performed alternately between 1...N lines of devices, as explained here in this short example, from 1...3 parallel examples, and achieves a quasi-continuous effect. As mentioned earlier, the minimum number of cooking lines is two.

The total cooking time of herbaceous raw materials in white liquor, which is the retention time of one batch of material in each of the lines of devices [primary digester (8, 8', ...) mill (9, 9', ...) - dryer ( 10, 10',...) - secondary digester (12, 12',...)] - 3-6 h. (9, 9',...)-drier (10, 10',...) - secondary digester (12, 12',...)] allows to achieve an effect in which herbaceous raw materials cannot enter a mixing vessel (14) from which the cooked (cooked) suspension of brown pulp is pumped further into the mill (15).

A schematic diagram of the quasi-continuous cooking of a herbaceous raw material slurry during the entire process is shown in FIG. 1, where the number of parallel lines is limited to at least two.

C) Additional processing of brown pulp.

The additional treatment of the brown pulp slurry after digestion is carried out in such a way that the quasi-continuous combined output from all secondary digesters (12, 12',...) with the prepared brown pulp slurry is transferred to the mixing vessel (14) and the mill (15), where grinding of brown pulp and separation in a dryer (16) where a suspension of brown pulp with 5-15 wt.% dry matter is concentrated to a content of 27-33 wt.% dry matter, and this method is followed by separation of black liquor (17), which is transferred to pre-cell (7A) of the electrolytic cell (7), while a concentrated suspension of brown cellulose is prepared for stage D.

The term quasi-continuous combined output refers to the combined amount of all

- 7 041989 brown pulp slurry outlets from each line of slurry preparation devices [primary digester (8, 8',...) - mill (9, 9',...) - dryer (10, 10',.. .) - secondary digester (12, 12',...)], where by alternating the outlets of the cooked suspension of brown pulp from each of the lines of the device, the effect of the continuity of the method is achieved. However, since this method is not really continuous, the term quasi-continuous method is quite correct. Combined output from all parallel device lines [primary digester (8, 8',...) - mill (9, 9',...) - dryer (10, 10',...) - secondary digester ( 12, 12',...)] is most accurately defined as a quasi-continuous combined output.

A schematic diagram of the post-treatment of brown pulp is shown in FIG. 1.

D) Preparation of brown pulp bleaching slurry.

The preparation of the bleaching suspension is carried out in the bleaching reactor (19), in which, in addition to the suspension from stage C through the pipeline (18):

regenerated fresh white liquor from the cathode compartment of the electrolytic cell (7B) via pipeline (20);

a mixture of oxygen (O ₂ ) and chlorine (Cl ₂ ) covered by the anode compartment of the electrolytic cell (7B) through the pipeline (21); and also optionally hydrogen peroxide (H ₂ O ₂ ) or sodium peroxide (Na ₂ O ₂ ) is introduced through line (22), to obtain a bleaching slurry with 5-15 wt.% dry matter, preferably 10 wt.%, and the preliminary method bleaching of brown pulp from stage C is carried out at a temperature of 70-100°C for stage E.

Preferably, the bleaching process is carried out at a temperature of 70-80°C. Hydrogen peroxide (H ₂ O ₂ ) or sodium peroxide (Na ₂ O ₂ ) can be used as optional additional oxidizing agents in the brown pulp bleaching step. As a source of hydrogen peroxide, a commercially available solution of H ₂ O ₂ with a concentration of about 3 wt.% is usually used. In the case of Na ₂ O ₂ , it is clear that it gives an equimolar mixture of NaOH and H ₂ O ₂ , which is further used in the same way as an additional oxidizing agent in the bleaching process according to the present invention.

The schematic diagram of the brown pulp bleaching slurry preparation phase is shown in FIG. 2.

E) Quasi-continuous bleaching of brown pulp.

The quasi-continuous bleaching process is carried out using two or more parallel lines [primary reactor (23, 23',...) - mill (24, 24',...) - dryer (25, 25',...) - secondary reactor (27, 27',...)] for 3-6 hours at a temperature of from 70 to 100°C, preferably from 70-80°C, where the feed from stage D is prepared and sequentially pumped into these two or more parallel lines in a way that the output from all secondary reactors (27, 27',...) provides a continuous process, where the further bleaching process is carried out in the primary reactors (23, 23',...) and where at the outlet of the primary reactors (23, 23',...) a suspension of bleached pulp with a content of 8-12 wt.% a substance is obtained, which is subjected to grinding in appropriate mills (24, 24',...) and separation in dryers (25, 25',... ), of which part of the spent solution (26, 26',...) is transferred to the electrolytic pre-cell (7A), while the concentrated suspension of bleached cellulite vines with about 30 wt.% dry matter enters the secondary reactors (27, 27',...) with the addition of white liquor solution (28) from the cathode compartment of the cells (7B) through the collector (28, 28 of the oxygen mixture (O ₂ ) and chlorine (Cl ₂ ) are released in the anode compartment of the electrolytic cells (7B) through the collector (29, 29',...); and, optionally, hydrogen peroxide (H ₂ O ₂ ) or sodium peroxide (Na ₂ O ₂ ) through line (30, 30',...), to obtain a suspension of bleached pulp with 8-12, preferably 10 wt.% dry substances.

In other words, the phase of quasi-continuous bleaching of brown pulp in a solution of bleach chemicals is carried out by preparing a suspension of brown pulp in a bleach reactor (19). It is then transferred to a line of devices [primary bleaching reactor (23, 23',...) - mill (24, 24',...) - dryer (25, 25',...) - secondary bleaching reactor (27 , 27',...)], in which the bleaching process is carried out at a temperature of 70-100°C, preferably at a temperature of 7080°C. During this process, brown pulp is bleached with oxygen (O ₂ ) and chlorine (Cl ₂ ) in the presence of sodium hydroxide (NaOH; 0.5-2.0 wt.%) and sodium chloride (NaCl; 0.5-25.0 wt. .%), forming a suspension of bleached pulp, which is then continuously transferred to the mixing vessel (31).

After the entire amount of the original suspension of brown pulp, which enters the bleaching process, is fed into the line of devices [primary bleaching reactor (23) - mill (24) - dryer (25) - secondary bleaching reactor (27)], and in the reactor (19) a new batch of brown pulp slurry is prepared, which is then pumped into a parallel line of devices [primary bleaching reactor (23') - mill (24') - dryer (25') - secondary bleaching reactor (27')]. After the bleaching of a batch in the line of devices [primary bleaching reactor (23) - mill (24) - dryer (25) - secondary bleaching reactor (27)] is completed, all the contents of them are transferred through the mixing tank (31) for further processing in the dryer (32). In the mixing tank (31), then bleaching pulp slurry from a parallel line of devices [reactor per

- 8 041989 secondary bleaching (23') - mill (24') - dryer (25') - secondary bleaching reactor (27')]. The number of such parallel lines should be optimal to achieve a quasi-continuous production process.

The term quasi-continuous bleaching is used because it describes this bleaching method most accurately. Bleaching in the indicated parallel lines of devices [primary bleaching reactor (23, 23',...) - mill (24, 24',...) - dryer (25, 25',...) - secondary bleaching reactor (27 , 27',...)] due to the periodic output of bleached pulp from each of these lines of devices, gives the effect of a continuous process. Because it is not actually a continuous bleaching process, it is most accurately referred to as quasi-continuous bleaching.

The present invention uses a gas mixture of oxygen (O ₂ ) and chlorine (Cl ₂ ) as the oxidizing agent for bleaching. The latter is produced electrolytically in the anode compartment of an electrolytic cell (7B) which bleaches brown pulp under basic conditions (0.5-2.0 wt% NaOH) and under relatively mild reaction conditions. The relative weight ratio of O ₂ and Cl ₂ in this mixture depends on the weight percentage of sodium chloride (NaCl) in the white liquor, which can be 0.5-25.0 wt%.

The schematic diagram of the quasi-continuous bleaching phase of the brown pulp slurry is shown in FIG. 2.

F) White Pulp Finishing.

The final treatment of the white pulp is carried out in such a way that the quasi-continuous combined output from all secondary bleaching reactors (27, 27',...) from stage E is transferred to the mixing vessel (31) and dryer (32), where the waste solution containing the chemicals, from the bleach, and said waste water are returned back to the pre-cell (7A) of the electrolytic cell (7) via conduit (33), while the drained pulp exits as pure white pulp, at a concentration of 48-55 wt.% dry matter, with a maximum lignin content of 5 wt.% dry matter.

The continuous process for producing grass pulp using the electrolytic process according to the present invention optionally includes further processing the white pulp from step F so that the viscous white pulp slurry is at 48-52 wt.% dry matter, then it is dried in a dryer (34) to obtain dried cellulose powder.

Combined outputs:

black liquor from the pulping phase, which is fed into the electrolyser (7) from the dryer (10, 10',...) through the manifold (11, 11',...);

residual black liquor that separates from the brown pulp slurry after being drained to the dryer (16) via conduit (17);

wastewater from the bleaching process, which is separated in the dryer (25, 25',...) through the collector (26, 26',...); and also, the waste water from the final treatment of white pulp from the dryer (32) through the pipeline (33), is mixed together and transferred to the pre-cell (7A) of the electrolytic cell (7), where the black liquor is electrolytically processed, phase G.

A schematic diagram of the final processing of white pulp is shown in Fig. 2.

G) Electrolytic processing of black liquor.

The key part of the continuous process for the production of pulp or dry cellulose powder from grassy raw materials according to the present invention is precisely the mentioned continuous electrolytic treatment of black liquor, which is carried out in an electrolytic cell (7) consisting of one or more electrolytic pre-cells (7A) made of inert material in which the cathode and anode electrodes are immersed, without a membrane between the cathode and anode compartments; one or more electrolytic cells (7B) made of an inert material in which the cathode and anode electrodes are immersed, where the cathode compartment is completely separated from the anode compartment by a porous membrane that provides electrical contact between the anode and cathode through ion exchange, but prevents the passage of contained suspended organic molecules in the electrolyte;

where is the electrolyte, after treatment in the pre-cells (7A), transferred to the anode compartment of the electrolytic cells (7B), and, if necessary, the composition of the electrolyte is changed during the process by adding a fresh solution of sodium chloride (NaCl) in the pre-cells (7A); the cathode is made of carbon steel or stainless steel (AISI 304, 316, 321, etc.), and graphite or magnetite is used for the anode; where, between the electrodes in the electrolytic cell (7A) and the electrodes in the electrolytic cell (7B), a DC voltage is set from 1.5 to 20 V, at a current density of 1 to 10 A / dm ² , at a cell temperature of 80-95 ° C ; and also, electrolysis in the electrolytic cell (7A) is carried out by introducing black liquor (11, 11',...) from stage B, black liquor (17) from stage C, part of the spent solution (26, 26',... ) from stage E and waste water (33) from stage F, in which the separation of lignin and other by-products occurs, which are mechanically removed from the top of the electrolyte solution; where, the electrolyte solution from the pre-cell

- 9 041989 (7A) is pumped into the anode compartment of the electrolytic cell (7B) for further processing, while:

(i) white liquor of the following composition is regenerated at the cathode:

a) 0.50-2.00 wt% NaOH;

b) NaCl; which extends to the digester (5) through the pipeline (6) at stage A; digesters (12, 12',...) through manifold (13, 13',...) in step B; bleach reactor (19) through conduit (20) at stage C; and also, the bleaching reactors (27, 27',...) through the header (28, 28',...) in step D; and the resulting hydrogen is transferred to a hydrogen storage tank (39);

(ii) gaseous oxygen (O ₂ ) and chlorine (Cl ₂ ) are formed at the anode, which are subsequently introduced into the bleach reactor (19) through conduit (21) in step C; and also, the bleaching reactors (27, 27',...) through the manifold (29, 29',...) in step E; and also, while the rest of the lignin and other by-products are isolated and mechanically separated from the top of the electrolyte solution.

Preferably, the operating voltage in the electrolytic cell is 3-6 V, and the current density is maintained within 4-6 A/dm ² .

The membrane (M) that physically separates the cathode from the anode compartment inside the electrolytic cell (7B) is of particular importance. It consists of a material selected from the following group: asbestos, rock wool, hydrated portland cement, kaolin and sodium silicate product, aluminum oxide (Al ₂ O ₃ ), titanium oxide (TiO ₂ ), zirconia (ZrO ₂ ), polyethylene ( PE), polysulfone (PSU), polyvinylpyrrolidone (PVP), polyvinyl chloride (PVC), polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), sulphonated polytetrafluoroethylene (SPTFE) or composite materials obtained from combinations of these materials.

Preferably, the membrane (M) in the electrolytic cell (7B) is made of a composite material consisting of:

(i) zirconia (ZrO ₂ ); 80 to 90, preferably 85% by weight; and also, (ii) polysulfone (PSU); from 10-20, preferably 15% by weight.

The material inert to the chemical composition of the process from which the electrolytic pre-cell (7A) and the electrolytic cell (7B) are made is selected from the group consisting of plastics such as polyvinyl chloride (PVC), polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF) , polysulfone (PSU); or metals such as mild steel, stainless steel (AISI 304, 316, 321 and others) or aluminum which are coated or lined with resistance to process chemicals: polysulfone (PSU), polyvinylpyrrolidone (PVP), polyvinyl chloride ( PVC), polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), sulfonated polytetrafluoroethylene (SPTFE), polychloroprene, mixtures thereof and other polymers.

The working concentration of sodium chloride (NaCl) in white liquor is 0.50-25.0, preferably 0.50-1.50% by weight.

For the necessary adjustment of the content (weight percent) of sodium chloride (NaCl) in the white liquor for the pulping and bleaching processes, a fresh solution of sodium chloride (NaCl) is introduced via conduit (38) into the anode compartment of the electrolytic pre-cell (7A) inside the electrolytic cell (7). This solution is prepared in the mixing vessel (35) by adding the NaCl stored in the storage vessel (36) and purified water from the storage vessel (37).

A schematic diagram of the electrolytic part of the entire process is shown in Fig. 3.

Equipment for main digesters and bleaching reactors.

Digesters (5, 8, 8',...; 12, 12',...), bleaching reactors (19, 23, 23',..., 27, 27',...) and mixing tanks (14, 31) are equipped with mixing elements that provide intensive mixing of the suspended material at a speed of > 900 revolutions per minute (rpm).

The digesters (5, 12, 12',...) and the bleaching reactors (19, 27, 27',...) are equipped with heating jackets that bring them up to operating temperature.

Optionally, the digesters (5, 12, 12',...) and the bleaching reactors (19, 27, 27',...) are equipped with magnetrons for alternative microwave heating (MW) instead of heating jackets. Microwave heating is well known in the art (see, for example, reference 13 cited earlier).

In addition, digesters (5, 8, 8',...; 12, 12',...), bleaching reactors (19, 23, 23',...; 27, 27',...) and mixing tanks (14, 31) can optionally be equipped with a vibrator that generates 10000-14000 vibrations per minute to facilitate mixing; this method is well known in the art.

Initial herbaceous raw material.

Dried leaves and/or stems of herbaceous plant species in the form of longitudinal pieces, the proportion of which in length is at least 90% from 0.2 to 2.0 cm, can be used as initial herbaceous raw materials in the present method.

Herbaceous plant species are selected from the group consisting of the following: sorghum (Sorghum views, Linne); corn (Zea mays, Linne); miscanthus (Miscanthus x giganteus, Andersson; sugar beet (Saccharum officinarum, Linne); wheat (Triticum vulgare, Linne); hemp (Cannabis sativa, Linne); barley

- 10 041989 (Horedum vulgare, Linne); oats (Avena sativa, Linne); common flax (Linum usitatissimum, Linne); millet (Panicum miliaceum, Linne) and other species of the genus Panicum; triticale (x Triticosecale, Wittm. ex A. Camus); buckwheat (Fagopyrum esculentum, Moench); rice (Oryza sativa, Linne); alpha grass (Stipa tenacissima, Linne and Lygeum spartum, Linne); reed (Phragmites australis, Adanson) and other species of the genus Phragmites; cake from sugar cane processing; jute (Corchorus olitorius, Linne); bamboo (Bambusoideae spp., Linne) and mixtures thereof.

Preferably, sorghum (Sorghum species, Linne) and corn (Zea mays, Linne) are used as feedstock in the present process.

Industrial Applicability

As shown in the detailed description, the present invention includes a continuous process for the production of pulp from grass-like raw materials, which is based on (i) a special system of serially connected devices for the following steps:

a) cooking: [primary digester (8, 8',...) - mill 9, 9',...) - dryer (10, 10',...) - secondary digester (12, 12' ,...)]; and,

b) bleaching: [primary bleaching reactor (19, 19', ...) - mill (24, 24', ...) - dryer (25, 25', ...) - secondary bleaching reactor (27, 27 , 27,...)];

which provides a quasi-continuous processing method and efficient separation of black liquor from the pulping phase and spent chemicals from the bleaching phase, as well as the addition of fresh pulping and bleaching chemicals, which greatly increases the efficiency of the process under relatively mild reaction conditions, which subsequently ensures a high degree of preservation of cellulose fibers;

(ii) a method for bleaching brown pulp using electrolytically generated oxygen (O ₂ ) in the presence of sodium hydroxide (NaOH; 0.5-2.0 wt.%) and sodium chloride (NaCl; 0.5-25.0 wt.% ), which are formed in the electrolytic cell (7); and, (iii) electrolytic removal of lignin;

a) from the black liquor of the cooking phase; and

b) waste liquid from the bleaching phase;

so that the electrolytic cell contains an electrolytic pre-cell (7A) that does not contain a membrane between the anode and cathode, which increases the efficiency of the electrolytic part of the process and minimizes the tendency for membrane fouling inside the electrolytic cell (7B), which is connected downstream of said preliminary electrolytic cell (7A).

These key improvements result in higher process efficiency and higher pulp quality for grass-based papermaking. This invention effectively solves all of these three key problems identified in the technical problem. Therefore, the industrial applicability of the invention is not in doubt.

Positions on the drawings:

- a conveyor for feeding herbal raw materials in the form of bales;

- cutter for bales;

- a mill for mowing grassy raw materials to finely chopped parts;

- dust collector;

- a digester for preparing a suspension of crushed grassy raw materials in white liquor;

- a pipeline for introducing white liquor from the cathode compartment of the electrolyzer (7B) into the digester (5);

- electrolytic cell, a system of two or more electrolytic cells connected in series.

A - a block of electrolytic preliminary cells, one or more series-connected electrolytic cells without a membrane (M);

7B - electrolytic cell, one or more series-connected electrolytic cells with a membrane (M);

, 8' - primary digester;

, 9' - mill for milling/grinding cellulose fibers;

, 10' - dryer/separator to remove most of the black liquor from the brown pulp slurry, increases the solids concentration in the slurry from 8-12 to 27-33 wt.%.

, 11' - collector, drains part of the black liquor from the dryer (10) and (10') into the electrolytic preliminary cell (7A);

, 12' - secondary digester;

, 13' - collector; for supplying white liquor from the cathode compartment of the cell (7B) to the digester (12) and (12').

- mixing tank;

- a mill for milling/grinding cellulose fibers;

-

Claims (12)

16 - dryer for removing part of the black liquor from the suspension of brown pulp, increases the concentration of dry matter in the suspension from 8-12 to 27-33 wt.%. 17 - pipeline for separating part of the black liquor from the dryer (16) into the electrolytic cell (7A); 18 - pipeline for transferring a concentrated suspension of brown pulp with about 30 wt.% dry matter from the dryer (16) to the bleaching reactor (19); 19 - bleaching reactor; 20 - pipeline for supplying white liquor from the cathode compartment of the electrolytic cell (7B) to the bleaching reactor (19); 21 - pipeline for supplying gaseous oxygen (O ₂ ) and chlorine (Cl ₂ ) from the anode compartment of the electrolytic cell (7B) to the bleaching reactor (19); 22 - pipeline for supplying a solution of hydrogen peroxide (H ₂ O ₂ ) or sodium peroxide (Na ₂ O ₂ ) to the bleaching reactor (19); 23, 23' - primary bleaching reactor; 24, 24' - mill; 25, 25' - desiccant; 26', 26' - manifold for removing wastewater from the bleaching process from the dryer (25) and (25') to the electrolytic pre-cell (7A); 27, 27' - secondary bleaching reactor; 28, 28' - manifold for adding white liquor from the cathode compartment of the electrolytic cell (7B) to the bleach reactor (27) or (27'); 29 , 29' - collector for transporting gaseous oxygen (O2) and chlorine (Cl2) from the anode compartment of the electrolytic cell (7B) to the bleaching reactors (27) and (27'); 30, 30' - manifold for supplying a solution of hydrogen peroxide (H ₂ O ₂ ) or sodium peroxide (Na ₂ O ₂ ) to the bleaching reactors (27) and (27'); 31 - mixing tank; 32 - dryer; 33 - pipeline for removing the spent solution in the bleaching process from the dryer (32) to the electrolytic preliminary cell (7A); 34 - dryer; 35 - mixing tank; 36 - capacity for storage of sodium chloride (NaCl); 37 - water tank; 38 - pipeline for the optional addition of fresh aqueous sodium chloride (NaCl) solution to the electrolytic pre-cell (7A); 39 - hydrogen storage tank (H ₂ ); M is the membrane inside the electrolytic cell (7B) which physically separates the cathode and anode chambers. CLAIM 1. A continuous method for the production of pulp from grassy raw materials, such as dried vegetable pulp from leaves and/or stems, using an electrolytic method for the continuous electrolytic separation of lignin and other by-products while producing white liquor and oxygen (O2) and chlorine (Cl2 ), which is carried out in an electrolytic cell (7), consisting of one or more electrolytic preliminary cells (7A), made of an inert material, in which the cathode and anode electrodes are immersed, without a membrane between the cathode and anode compartments; one or more electrolytic cells (7B) made of an inert material in which the cathode and anode electrodes are immersed, where the cathode compartment is completely separated from the anode compartment by a porous membrane that provides electrical contact between the anode and cathode through ion exchange, but prevents the passage of suspended organic molecules in the electrolyte; where the electrolyte after treatment in the preliminary cells (7A) is transferred to the anode compartment of the electrolytic cells (7B), and if necessary, the composition of the electrolyte is changed during the process by adding fresh chloride solution (NaCl) to the preliminary cells (7A); characterized in that it consists of the following steps: A) preparing a suspension of crushed and dust-free herbaceous raw materials by adding white liquor from the cathode compartment of the electrolytic cell (7B) to the digester (5), where the herbaceous raw material is cooked at a temperature of 80-100 ° C in a white liquor solution of the following composition: (i) 0.50-2.00 wt% NaOH; (ii) NaCl; maintaining the concentration of herbal raw materials at the level of 5-15, preferably 8-12 wt.% dry - 12 041989 substances to obtain stage B; B) quasi-continuous cooking and separation, realized with two or more parallel lines, consisting of the following devices: primary digester (8, 8'), mill (9, 9'), dryer (10, 10'), secondary digester (12, 12') for 3-6 hours, where the raw material from stage A is prepared and subsequently pumped into two or more of the parallel lines mentioned, so that the output from the digesters (12, 12') is a continuous production method, in in which the suspension of grassy raw materials in white liquor during cooking in all primary digesters (8, 8') and secondary digesters (12, 12') is maintained at a temperature of 95-100°C; suspension of brown pulp with a content of 8-12 wt.% dry matter at the outlet of each primary digester (8, 8') is subjected to grinding in the respective mills (9, 9') and separation in dryers (10, 10'), of which part of the black liquor (11) is transferred to the electrolytic treatment of the pre-cell (7A), while the thus obtained concentrated suspension of brown pulp with about 30 wt.% dry matter enters the secondary digesters (12, 12') with the introduction of a solution of white liquor from the cathode compartment of the cells (7B), which forms a slurry of approximately the same composition as the slurry in the digester (5) of stage A; C) The quasi-continuous combined output from all secondary digesters (12, 12') with the prepared brown pulp slurry is transferred to the mixing vessel (14) and mill (15) where the separation of the ground brown pulp is carried out in a dryer (16) which concentrates the brown pulp slurry from 5-15 wt.% dry matter to a content of 27-33 wt.% dry matter, which is accompanied by the separation of black liquor (17), which is transferred to the preliminary cell (7A) of the electrolytic cell (7), while the concentrated brown suspension pulps are prepared for stage D; D) preparation of the bleaching slurry is carried out in the reactor (19), in which, in addition to the slurry from step C), regenerated fresh white liquor from the cathode compartment of the electrolytic cell (7B) is used; a mixture of oxygen (O ₂ ) and chlorine (Cl ₂ ) in the anode compartment of the electrolytic cell (7B); enter to obtain a bleaching suspension with a content of 5-15, preferably 10 wt.% dry matter; and the preliminary method for bleaching brown pulp from step C is carried out at a temperature of 70-100°C for step E; E) a quasi-continuous bleaching process is implemented using two or more parallel lines, consisting of the following devices: primary reactor (23, 23'), mill (24, 24'), dryer (25, 25'), secondary reactor (27, 27 '), for 3-6 hours at a temperature of 70-100°C, where the raw material from stage D is prepared and sequentially pumped into these two or more parallel lines so that the product output from all secondary reactors (27, 27') is continuous production method; where the primary bleaching process is carried out in the primary reactors (23, 23') and where at the outlet of the primary reactors (23, 23') a suspension of bleached pulp is obtained with a content of 8-12 wt.% dry matter, which is subjected to grinding in the respective mills (24 , 24') and separation in dryers (25, 25'), from which part of the waste solution (26, 26') is transferred to the electrolytic pre-cell (7A), while the concentrated pulp bleaching slurry with about 30 wt.% dry the substance enters the secondary reactors (27, 27') with the addition of white liquor solution (28) from the cathode compartment of the cells (7B); mixtures of oxygen (O ₂ ) and chlorine (Cl ₂ ) released in the anode compartment of the electrolytic cells (7B); to obtain a bleaching slurry of cellulose with 8-12, preferably 10 wt.% dry matter; F) The quasi-continuous combined output from all secondary bleaching reactors (27, 27') from stage E is transferred to the mixing vessel (31) and dryer (32), whose waste water (33) is returned back to the pre-chamber (7A) of the electrolytic cell (7 ), and the dried pulp leaves the process as a pure white pulp with a concentration of 48-55 wt.% dry matter with a maximum lignin content of 5 wt.% dry matter. 2. A continuous method for producing grass pulp using the electrolytic method according to claim 1, wherein hydrogen peroxide (H ₂ O ₂ ) or sodium peroxide (Na ₂ O ₂ ) is added in step D) when preparing the bleach slurry. 3. A continuous method for producing grass pulp using the electrolytic method according to claim 1, wherein hydrogen peroxide (H ₂ O ₂ ) or sodium peroxide (Na ₂ O ₂ ) is added in step E) when preparing the bleaching slurry. 4. A continuous method for producing grass pulp using the electrolytic method according to claim 1, wherein the white pulp from step F is further dried in a dryer (34) to obtain a dry pulp powder. 5. A continuous method for the production of pulp or dry powder of cellulose from grassy raw materials using the electrolytic method according to any one of the preceding paragraphs, in - 13 041989 in which the cathode is made of carbon or stainless steel, and graphite or magnetite is used for the anode; between the electrodes in the electrolytic cell (7A) and the electrodes in the electrolytic cell (7V), a DC voltage is set from 1.5 to 20 V, at a current density of 1 to 10 A/dm ² , at a cell temperature of 80 to 95°C; electrolysis in the electrolytic cell (7A) is carried out by introducing black liquor (11, 11') from stage B, black liquor (17) from stage C, part of the spent solution (26, 26') from stage E and wastewater (33) from stage F, in which the separation of lignin and other by-products occurs, which are mechanically removed from the top of the electrolyte solution; the electrolyte solution from the pre-cell (7A) is pumped into the anode compartment of the electrolytic cell (7B) for further processing, in which: (i) white liquor of the following composition is regenerated at the cathode: (a) 0.50-2.00 wt% NaOH; (b) NaCl; which is distributed to the digester (5) in stage A, to the digesters (12, 12') in stage B, to the bleaching reactor (19) in stage C; and into the bleaching reactors (27, 27') in step D according to claim 1; and the resulting hydrogen is transferred to a hydrogen storage tank (39); (ii) at the anode, oxygen gas (O ₂ ) and chlorine (Cl ₂ ) are formed and then introduced into the bleach reactor (19) in step C and the bleach reactors (27, 27') in step E according to claim 1, and at In this the rest of the lignin and other by-products are isolated and mechanically separated from the top of the electrolyte solution. 6. A continuous method for the production of pulp or dry powder of cellulose from grassy raw materials using the electrolytic method according to any one of the previous paragraphs, in which the concentration of sodium chloride (NaCl) in white liquor is 0.50-25.0 wt.%. 7. A continuous method for the production of pulp or dry powder of cellulose from grassy raw materials using the electrolytic method according to claim 4, in which the concentration of sodium chloride (NaCl) in white liquor is 0.50-1.5 wt.%. 8. Continuous method for the production of pulp or dry powder of cellulose from grassy raw materials using the electrolytic method according to any one of the previous paragraphs, where the original grassy raw material is in the form of longitudinal pieces, the proportion of which in length is at least 90% from 0.2 to 2.0 cm and consists of dried leaves and stems of plants selected from the group consisting of the following species: sorghum (sorghum species, Linne); corn (Zea mays, Linne); miscanthus (Miscanthus x giganteus, Andersson); sugar beet (Saccharum officinarum, Linne); wheat (Triticum vulgare, Linne); hemp (Cannabis sativa, Linne); barley (Horedum vulgare, Linne); oats (Avena sativa, Linne); common flax (Linum usitatissimum, Linne); millet (Panicum miliaceum, Linne) and other species of the genus Panicum; triticale (x Triticosecale, Wittm. former A. Camus); buckwheat (Fagopyrum esculentum, Moench); rice (Oryza sativa, Linne); esparto grass (Stipa tenacissima, Linne and Lygeum spartum, Linne); reed (Phragmites australis, Adanson) and other species of the genus Phragmites; pulp from sugar cane processing; jute (Corchorus olitorius, Linne); bamboo (Bambusoideae spp., Linne); and their mixtures. 9. A continuous process for producing grass pulp or dry pulp powder using an electrolytic method according to any one of the preceding claims, wherein sorghum (sorghum species, Linne) and corn (Zea mays, Linne) are used as the grass feedstock. 10. A continuous process for the production of pulp or dry powder of cellulose from herbal raw materials using the electrolytic method according to any one of the preceding claims, in which: (i) digesters (5, 8, 8'; 12, 12'), bleaching reactors (19, 23, 23', 27, 27') and mixing tanks (14, 31) are equipped with mixing elements that allow intensive mixing weighed material at a speed of more than 900 rpm, as well as (ii) digesters (5, 12, 12') and bleaching reactors (19, 27, 27') are equipped with heating jackets that allow them to be heated to operating temperature. 11. A continuous method for the production of pulp or dry powder of cellulose from grassy raw materials using the electrolytic method according to claim 10, characterized in that the digesters (5, 12, 12') and bleaching reactors (19, 27, 27') instead of heating shirts are equipped with magnetrons for alternative heating with microwaves. 12. A continuous process for the production of pulp or dry powder of cellulose from grass raw materials using the electrolytic method according to any one of the preceding claims, in which (i) digesters (5, 8, 8', 12, 12'), (ii) reactors bleaching (19, 23, 23', 27, 27') and (iii) mixing tanks (14, 31) -