CONTINUOUS PROCESS FOR PRODUCTION OF CELLULOSE PULP FROM GRASS-LIKE FEEDSTOCK

Abstract

An improved continuous process for production of cellulose from glass-like feedstock, which includes: (i) cooking of comminuted grass-like feedstock in white liquor which contains 0.5-2.0% w/w NaOH and 0.5-25.0% w/w NaCl at 95-100° C.; (ii) bleaching process of the brown cellulose in the white liquor of the same composition with oxygen (O.sub.2) and chlorine (Cl.sub.2) at 70-100° C., yielding bleached cellulose pulp; where, (iii) lignin and other side-products are separated by continuous electrolysis, where the white liquor is regenerated, together with O.sub.2 and Cl.sub.2 for the bleaching purpose, thereby closing the cycle of the process.

Claims

1. A continuous process for production of cellulose pulp from a grass-like feedstock by using electrolytic process for continuous electrolytic separation of lignin and other side-products, with simultaneous production of white liquor and oxygen <O.sub.2> and chlorine <Cl.sub.2>, which is carried out in an electrolytic cell which includes: one or more electrolytic pre-cells; made from material inert to chemistry of the process, in which cathode and anode electrodes are immersed, with no membrane between cathode and anode compartments; one or more electrolytic cells; made from material inert to chemistry of the process, in which cathode and anode electrodes are immersed, where cathode compartment is completely separated from anode compartment with a porous membrane, which enables electrical contact of anode and cathode via ion-exchange, but prevents passing of suspended organic molecules in electrolyte; where the electrolyte is, after processing in the pre-cells, transferred into anode compartment of electrolytic cells, and, optionally, composition of the electrolyte is modified during a course of the process by addition of a fresh sodium chloride (NaCl) solution into the pre-cells; the said process comprising the following steps: A) preparing a suspension of comminuted and dedusted grass-like feedstock by addition of a white liquor from the cathode compartment of the electrolytic cells into a preliminary digester where the grass-like feedstock is subjected to cooking at 80-100° C. in solution of the white liquor including the following composition: (ii) 0.50-2.00 w/w NaOH; (ii) NaCl; by keeping a concentration of grass-like feedstock at a level of 5-15% w/w; B) performing quasi-continuous cooking and separation through two or more parallel lines including primary digesters, cooking mills, cooking dewaterers, secondary digesters, during 3-6 hours, wherein the feedstock prepared in step A is sequentially pumped into the two or more parallel lines by a way that output from the secondary digesters produces continuous process; wherein: suspension of the grass-like feedstock in the white liquor during cooking in all the primary digesters and the secondary digesters is maintained at temperature from 95-100° C.; brown cellulose suspension at a level 8-12% w/w dry matter at an output from every primary digester is subjected to milling in the corresponding cooking mills and separation in the cooking dewaterers, from which a part of black liquor is transferred into the electrolytic pre-cells, while thus obtained concentrated suspension of brown cellulose with about 30% w/w dry matter enters into the secondary digesters, with introduction of white liquor solution from the cathode compartment of the electrolytic cells; C) transferring quasi-continuous combined output from all the secondary digesters with the cooked brown cellulose suspension into a first mixing vessel and a first mill, where separation of milled brown cellulose is performed in a first dewaterer which concentrates the brown cellulose suspension with 5-15% w/w dry matter up to the content of 27-33% dry matter, and accompanied with separation of black liquor which is transferred to the pre-cells of the electrolytic cells; D) preparing bleaching suspension in a bleaching reactor, in which, besides the suspension from the step C: regenerated fresh white liquor from the cathode compartment of the electrolytic cells; mixture of oxygen <O.sub.2> and chlorine <Cl.sub.2> enveloped in the anode compartment of the electrolytic cells; and optionally, hydrogen peroxide <H.sub.2O.sub.2> or sodium peroxide <Na.sub.2O.sub.2>, are introduced, yielding the bleaching suspension with a content of 5-15% w/w, E) performing quasi-continuous bleaching process through two or more parallel lines including primary reactors, bleaching mills, bleaching dewaterers, and secondary reactors during 3-6 hours, at temperature from 70-100° C., where the feedstock from the step D is prepared and sequentially pumped into said two or more parallel lines in a way that output from all the secondary reactors (makes a continuous process; where the primary bleaching process is performed in the primary reactors and where, at the output from the primary reactors (, a suspension of bleached cellulose with 8-12% w/w dry matter is obtained, which is subjected to milling in the corresponding bleaching mills and separation in the bleaching dewaterers from which, a part of waste-solution is transferred into the electrolytic pre-cells, while a concentrated bleached cellulose suspension with about 30% w/w dry matter is entering into the secondary reactors with introduction of: white liquor solution from the cathode compartment of the electrolytic cells, mixture of oxygen <O.sub.2> and chlorine <Cl.sub.2> evolved in the anode compartment of the electrolytic cells; and optionally, hydrogen peroxide <H.sub.2O.sub.2> or sodium peroxide <Na.sub.2O.sub.2>, yielding the cellulose suspension for bleaching with 8-12% w/w; and F) transferring quasi-continuous combined output from all the secondary bleaching reactors from the step E into a second mixing vessel and a second dewaterer, whose waste water is returned back to the pre-cells of the electrolytic cells, while a drained cellulose comes out from the process in a form of a pure white cellulose pulp, at a concentration from 48-55% w/w dry matter, with maximally 5% w/w lignin, calculated on the dry matter.

2. The continuous process according to claim 1, wherein the white cellulose pulp from the step F is further dried in a drier, yielding a dry cellulose powder.

3. The continuous process according to claim 1, wherein: the cathode is made of carbon steel or rust-free steel, and the anode is made of graphite or magnetite; between the electrodes in the electrolytic pre-cell and electrodes in the electrolytic cell, a voltage of direct current from 1.5-20 V is established, at a current density from 1-10 A/dm.sup.2, at a temperature of the cell from 80-95° C.; the electrolysis in electrolytic pre-cell is carried out by introducing the black liquor from the step B, the black liquor from the step C, a part of waste solution from the step E, and wastewater from the step F, wherein evolution of lignin and other side-products takes place, which are mechanically removed from a top of the electrolyte solution; the electrolyte solution from the pre-cell is pumped into the anode compartment of the electrolytic cell for further processing wherein: (i) at the cathode, the white liquor of the following composition is regenerated: (a) 0.50-2.00% w/w NaOH; (b) NaCl; which is distributed into: the preliminary digester in the step A; the secondary digesters in the step B; the bleaching reactor in the step D; and the secondary bleaching reactors in the step E; and generated hydrogen is transferred into a storage tank for hydrogen; (ii) at the anode, gaseous oxygen <O.sub.2> and chlorine <Cl.sub.2> are generated and subsequently introduced into the bleaching reactor in the step D, and into the secondary reactors in the step E; and wherein the rest of lignin and other side-products are isolated and mechanically separated from the top of the electrolyte solution.

4. The continuous process according to claim 1, wherein a concentration of sodium chloride <NaCl> in the white liquor is 0.50-25.0% w/w.

5. The continuous process according to claim 4, wherein the concentration of sodium chloride <NaCl> in the white liquor is 0.50-1.5% w/w.

6. The continuous process according to claim 1, where the starting grass-like feedstock is in the form of longitudinal pieces, whose fraction by length is minimally 90% between 0.2-2.0 cm, and comprises dried leaves and stems of plant species selected from the group consisting of: sorghum/Sorghum species, Linne/; maize/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/; oat/Avena sativa, Linne/; common flax/Linum usitatissimum, Linne/; proso millet/Panicum miliaceum, Linne/and other species from the genus Panicum; triticale/x Triticosecale, Wittm. ex 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 from the genus Phragmites; bagasse from sugarcane processing; jute/Corchorus olitorius, Linne/; bamboo/Bambusoideae spp., Linne/; and their mixtures.

7. The continuous process according to claim 6, wherein the starting grass-like feedstock comprises sorghum/Sorghum species, Linne/and maize/Zea mays, Linne/.

8. The continuous process according to claim 1, wherein: (i) the preliminary digester, the primary digesters, the secondary digesters, the bleaching reactor, the primary reactors, the secondary reactors and the first and second mixing vessels are equipped with mixing elements which enable intensive stirring of suspended material at more than 900 revolutions per minute; and (ii) the preliminary digester, the secondary digesters, the bleaching reactor, and the secondary reactors are equipped with heating jackets which provide their heating to the working temperature.

9. The continuous process according to claim 6, wherein the preliminary digester, the secondary digesters, the bleaching reactor, and the secondary reactors are equipped with magnetrons for alternative heating via microwaves.

10. The continuous process s according to claim 8, wherein: (i) the preliminary digester, the primary digesters the secondary digesters, (ii) the bleaching reactor, the primary reactors, the secondary reactors, and, (iii) the first and second mixing vessels, are additionally equipped with vibrator to facilitate the mixing, which generates 10,000-14,000 oscillations per minute.

11. The continuous process according to claim 1, wherein the bleaching process is performed at temperature from 70-80° C.

12. The continuous process according to claim 3, wherein the process of electrolytic separation of lignin and other side-products and simultaneous regeneration of the white liquor is carried out at the voltage from 3-6 V and current density from 4-6 A/dm.sup.2.

13. A continuous process according to claim 1, wherein the membrane in the electrolytic cell comprises at least a material selected from the group consisting of: asbestos, mineral wool, hydrated Portland cement, product of kaolin and sodium silicate, aluminium oxide <Al.sub.2O.sub.3>, titanium dioxide <TiO.sub.2>, zirconium dioxide <ZrO.sub.2>, polyethylene <PE>, polysulfone <PSU>, polyvinyl pyrrolidone <PVP>, polyvinyl chloride <PVC>, polytetrafluoroethylene <PTFE>, polyvinylidene fluoride <PVDF>, sulfonated polytetrafluoroethylene <SPTFE>, and composite materials obtained from the combinations of these materials.

14. The continuous process according to claim 13, wherein the membrane in the electrolytic cell comprises the material selected from: (i) zirconium dioxide <ZrO.sub.2>; from 80-90% w/w, preferably 85% w/w; and, (ii) polysulfone <PSU>; from 10-20% w/w, preferably 15% w/w.

15. A process for production of cellulose pulp from a grass-like feedstock using electrolytic process which is carried out in an electrolytic cell which includes: one or more electrolytic pre-cells; made from material inert to the chemistry of the process, in which cathode and anode electrodes are immersed, with no membrane between cathode and anode compartments; one or more electrolytic cells; made from material inert to the chemistry of the process, in which cathode and anode electrodes are immersed, where cathode compartment is completely separated from anode compartment with a porous membrane, which enables electrical contact of anode and cathode via ion-exchange, but prevents passing of suspended organic molecules in electrolyte; where the electrolyte is, after processing in the pre-cells, transferred into anode compartment of the electrolytic cells, and, optionally, a composition of the electrolyte is modified during a course of the process by addition of a fresh sodium chloride (NaCl) solution into the pre-cells; the said process comprising: performing quasi-continuous cooking and separation through two or more parallel lines including primary digesters, cooking mills, cooking dewaterers, secondary digesters during 3-6 hours, wherein: suspension of the grass-like feedstock in the white liquor during cooking in all the primary digesters and the secondary digesters is maintained at temperature from 95-100° C.; brown cellulose suspension at a level 8-12% w/w dry matter at output from every primary digester is subjected to milling in the corresponding cooking mills and separation in the cooking dewaterers, from which a part of black liquor is transferred into the electrolytic pre-cells, while thus obtained concentrated suspension of brown cellulose with about 30% w/w dry matter enters into the secondary digesters, with introduction of white liquor solution from the cathode compartment of the electrolytic cells; performing quasi-continuous bleaching process through two or more parallel lines including primary reactors, bleaching mills, bleaching dewaterers, and secondary reactors during 3-6 h, at temperature from 70-100° C., wherein at output from the primary reactors, a suspension of bleached cellulose with 8-12% w/w dry matter is obtained, which is subjected to milling in the corresponding bleaching mills and separation in the bleaching dewaterers from which, a part of waste-solution is transferred into the electrolytic pre-cells, while a concentrated bleached cellulose suspension with about 30% w/w dry matter enters the secondary reactors with introduction of: white liquor solution from the cathode compartment of the electrolytic cells, mixture of oxygen <O.sub.2> and chlorine <Cl.sub.2> evolved in the anode compartment of the electrolytic cells; and optionally, hydrogen peroxide <H.sub.2O.sub.2> or sodium peroxide <Na.sub.2O.sub.2>, yielding the cellulose suspension for bleaching with 8-12% w/w; and transferring quasi-continuous combined output from all the secondary bleaching reactors into a second mixing vessel and a second dewaterer, whose waste water is returned back to the pre-cell of the electrolytic cells, while a drained cellulose comes out from the process in a form of a pure white cellulose pulp, at a concentration from 48-55% w/w dry matter, with maximally 5% w/w lignin, calculated on the dry matter.

16. The process according to claim 15, further comprising, before performing the quasi-continuous cooking and separation, preparing a suspension of comminuted and dedusted grass-like feedstock by addition of a white liquor from the cathode compartment of the electrolytic cell into a preliminary digester where the grass feedstock is subjected to cooking at 80-100° C. in solution of the white liquor including the following composition: (i) 0.50-2.00 w/w NaOH; (ii) NaCl; by keeping the concentration of grass feedstock at the level of 5-15% w/w.

17. The process according to claim 16, further comprising, before performing the quasi-continuous bleaching process, transferring quasi-continuous combined output from all the secondary digesters with the cooked brown cellulose suspension into a first mixing vessel and a first mill, wherein separation of milled brown cellulose is performed in a first dewaterer which concentrates the brown cellulose suspension with 5-15% w/w dry matter up to a content of 27-33% dry matter, and accompanied with separation of black liquor which is transferred to the pre-cell of the electrolytic cells; and preparing bleaching suspension in a bleaching reactor, in which, besides the suspension: regenerated fresh white liquor from the cathode compartment of the electrolytic cells; mixture of oxygen <O.sub.2> and chlorine <Cl.sub.2> enveloped in the anode compartment of the electrolytic cells; and optionally, hydrogen peroxide <H.sub.2O.sub.2> or sodium peroxide <Na.sub.2O.sub.2>, are introduced, yielding the bleaching suspension with a content of 5-15% w/w.

18. The process according to claim 15, wherein: the cathode is made of carbon steel or rust-free steel, and the anode is made of graphite or magnetite; between the electrodes in the electrolytic pre-cell and electrodes in the electrolytic cell, a voltage of direct current from 1.5-20 V is established, at a current density from 1-10 A/dm.sup.2, at a temperature of the cell from 80-95° C.; the electrolysis in electrolytic pre-cell is carried out by introducing the black liquor and the wastewater into the electrolytic pre-cells where evolution of lignin and other side-products takes place, which are mechanically removed from a top of the electrolyte solution; the electrolyte solution from the pre-cells is pumped into the anode compartment of the electrolytic cell for further processing wherein: (i) at the cathode, a white liquor of the following composition is regenerated: (a) 0.50-2.00% w/w NaOH; (b) NaCl; which is distributed into: the preliminary digester; the secondary digesters; the bleaching reactor; and the secondary bleaching reactors; and generated hydrogen is transferred into a storage tank for hydrogen; (ii) at the anode, gaseous oxygen <O.sub.2> and chlorine <Cl.sub.2> are generated and subsequently introduced into the bleaching reactor and the secondary reactors; wherein the rest of lignin and other side-products are isolated and mechanically separated from the top of the electrolyte solution.

19. The process according to claim 15, wherein a concentration of sodium chloride <NaCl> in the white liquor is 0.50-25.0% w/w.

20. The process according to claim 15, where the starting grass-like feedstock is in a form of longitudinal pieces, whose fraction by length is minimally 90% between 0.2-2.0 cm, and comprises dried leaves and stems of plant species selected from the group consisting of: sorghum/Sorghum species, Linne/; maize/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/; oat/Avena sativa, Linne/; common flax/Linum usitatissimum, Linne/; proso millet/Panicum miliaceum, Linne/and other species from the genus Panicum; triticale/x Triticosecale, Wittm. ex 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 from the genus Phragmites; bagasse from sugarcane processing; jute/Corchorus olitorius, Linne/; bamboo/Bambusoideae spp., Linne/; and their mixtures.

Description

DESCRIPTION OF FIGURES

[0107] FIG. 1—shows a block diagram of continuous process for cellulose production which includes the following phases according to one embodiment of the present disclosure: [0108] A. preparation of grass-like feedstock suspension for cooking; [0109] B. quasi-continuous cooking of grass-like feedstock; and, [0110] C. additional processing of brown cellulose.

[0111] FIG. 2—shows a block diagram of continuous process for cellulose production which refers the following phases according to one embodiment of the present disclosure: [0112] D. preparation of brown cellulose suspension for bleaching; [0113] E. quasi-continuous bleaching of brown cellulose; and, [0114] F. final processing of white cellulose.

[0115] FIG. 3—shows a block diagram of continuous process for cellulose production which refers to the phase of electrolytic processing of the black liquor according to one embodiment of the present disclosure.

DETAILED DESCRIPTION OF THE DISCLOSURE

[0116] The present disclosure relates to the improved process for cellulose pulp production intended for paper manufacturing, from grass-like feedstock such as dried plant leaves or stems of sorghum (Sorghum species L.) or maize (Zea mays L.). Such feedstock typically contains 30-50% w/w cellulose, 18-30% w/w hemicellulose, and 5-20% w/w lignin; see literature references 14 and 15: [0117] 14) C. Ververis, K. Georghiou, N. Christodoulakis, P. Santas, R. Santas: Fiber dimensions, lignin and cellulose content of various plant materials and their suitability for paper production, Industrial Crops Prod. 19 (2004) 245-254. [0118] 15) B. Godin, F. Ghysel, R. Agneessens, T. Schmit, S. Gofflot, S. Lamaudière, G. Sinnaeve, J.-P. Goffart, P. A. Gerin, D. Stilmant, J. Delcarte: Détermination de la cellulose, des hémicelluloses, de la lignine et des cendres dans diverses cultures lignocellulosiques dédiées à la production de bioéthanol de deuxième génération, Biotechnol. Agron. Soc. Environ. 14 (2010) 549-560.

[0119] The present disclosure includes a continuous process for cellulose pulp production from grass-like feedstock by the use of electrolytic process for continuous electrolytic isolation of lignin and other side-products, with simultaneous production of the white liquor and oxygen (O.sub.2) and chlorine (Cl.sub.2), where the process may include the following steps:

[0120] A. preparation of grass-like feedstock suspension for cooking;

[0121] B. quasi-continuous cooking of grass-like feedstock;

[0122] C. additional processing of brown cellulose;

[0123] D. preparation of brown cellulose suspension for bleaching;

[0124] E. quasi-continuous bleaching of brown cellulose;

[0125] F. final processing of white cellulose; and,

[0126] G. electrolytic processing of black liquor.

[0127] These technological phases of the continuous process from the present disclosure include the following key details:

A. Preparation of Grass-Like Feedstock Suspension for Cooking

[0128] The preparation of the grass-like feedstock involves: [0129] (i) an input of grass-like feedstock in the form of bales, which are introduced into the plant via conveyor (1), [0130] (ii) wherein said bales enter the bale cutter (2) where the bales are cut to roughly sized plant material, which subsequently goes to, [0131] (iii) the milling into the mill (3), which serves for cutting the grass-like feedstock up to the level of small particles, which are, [0132] (iv) dedusted in deduster (4) from impurities like dust, soil, natural silicates and so on.

[0133] As the starting grass-like feedstock in the process, dried leaves and/or stems of grass plant species are used, in the form of longitudinal pieces, whose length in minimally 90% fraction is from 0.2-2 cm. The moisture content in the starting grass feedstock is typically below 10% w/w, preferably below 5% w/w.

[0134] The prepared grass feedstock enters into the preliminary digester or digester (5), where the suspension for the cooking process is prepared.

[0135] In digester (5), the suspension of the grass-like feedstock is being formed from the white liquor, which is supplied by the pipeline (6) from the cathode compartment of the electrolytic cell (7B), and grass-like feedstock. The obtained suspension of grass-like feedstock may be of the following composition:

[0136] (a) 0.50-2.00% w/w sodium hydroxide (NaOH); and,

[0137] (b) sodium chloride (NaCl);

[0138] with the concentration of grass-like feedstock at the level from 5-15% w/w, preferably 8-12% w/w dry matter, which is being cooked to 80-100° C. and then is ready for the step B.

[0139] The working concentration of sodium chloride (NaCl) in the white liquor is from 0.50-25.0% w/w, preferably from 0.50-1.50% w/w.

[0140] Schematic diagram of the grass-like feedstock suspension preparation for the cooking process is shown in FIG. 1.

B. Quasi-Continuous Cooking of Grass-Like Feedstock

[0141] Quasi-continuous cooking of grass-like feedstock and separation of waste black liquor is realized through two or more parallel lines, for example N lines, [primary digester (8, 8′, . . . )-cooking mill (9, 9′, . . . )-cooking dewaterer/separator (10, 10′, . . . )-secondary digester (12, 12′, . . . )] during 3-6 h, where the feedstock from the step A is prepared and sequentially pumped into said two or more parallel lines by the way that the output from all secondary digesters (12, 12′, . . . ) produces a continuous process; where: [0142] the suspension of grass-like feedstock in the white liquor during cooking in all primary digesters (8, 8′, . . . ) and secondary digesters (12, 12′ . . . ) is maintained at temperature from 95-100° C.; [0143] the brown cellulose suspension, at the level from 8-12% w/w of dry matter, at the output from every primary digester (8, 8′, . . . ) is subjected to milling/grinding in corresponding mills (9, 9′, . . . ) and separation in dewaterers (10, 10′, . . . ), from which a part of black liquor through manifold (11, 11′, . . . ) is transferred into the electrolytic pre-cell (7A), while thus obtained concentrated suspension of brown cellulose containing about 30% w/w dry matter enters into secondary digesters (12, 12′, . . . ), with introduction of the white liquor solution from the cathode compartment of the cells (7B) via manifold (13, 13′, . . . ), what forms the suspension of approximately the same composition as is the suspension in digester (5) of the step A; where, [0144] the brown cellulose suspension in the fresh white liquor is additionally subjected to the cooking process in all secondary digesters (12, 12′, . . . ) at temperature from 95-100° C.; while, [0145] after finishing the digesting process in every line of devices [primary digester (8, 8′, . . . )-mill (9, 9′, . . . )-dewaterer (10, 10′, . . . )-secondary digester (12, 12′, . . . )], the cooked brown cellulose suspension is alternately transferred into the mixing vessel (14).

[0146] In other words, the digesting phase of grass-like feedstock is performed by the way that the suspension prepared in the digester (5) is pumped and processed first in one of devices line [primary digester (8)-mill (9)-dewaterer (10)-secondary digester (12)], and then in the following alternative devices line [primary digester (8′)-mill (9′)-dewaterer (10′)-secondary digester (12′)]. The grass-like feedstock suspension in the white liquor during the digesting in digesters (8) and (12), or (8′) and (12′), is maintained at temperature from 95-100° C. The number of parallel lines [primary digester-mill-dewaterer-secondary digester] can be arbitrary and is adjusted to achieve quasi-continuous process.

[0147] The brown cellulose suspension with about 10% w/w dry matter at the exit from the primary digesters (8, 8′, . . . ) is subjected to milling/grinding in mills (9, 9′, . . . ), and further processed in dewaterers (10, 10′, . . . ) which are equipped with sieves of pores size 0.5-1.2 mm, in which certain part of the black liquor is separated by pressing. It contains lignin and other side-products, and is transferred through manifold (11, 11′) into the pre-cell (7A) of the electrolytic cell (7). The concentrated brown cellulose suspension, with concentration at about 30% dry matter, is forwarded into the secondary digesters (12, 12′, . . . ) in which the fresh solution of the white liquor is added via manifold (13, 13′, . . . ) from the cathode compartment of the electrolytic cell (7B) forming the suspension of approximately the same composition as is the suspension in digester (5).

[0148] From the devices line [primary digester (8, 8′, . . . )-mill (9, 9′, . . . )-dewaterer (10, 10′, . . . )-secondary digester (12, 12′, . . . )] the cooked suspension of brown cellulose exits out into the mixing vessel (14). When the mixing vessel (14) is filled with the cooked cellulose suspension from the devices line [primary digester (8)-mill (9)-dewaterer (10)-secondary digester (12)], the content is immediately pumped into the mill (15). Once all content is emptied, then the cooked cellulose suspension from further devices line [primary digester (8′)-mill (9′)-dewaterer (10′)-secondary digester (12′)] is pumped into the mixing vessel (14), etc.—all in order to obtain apparently continuous process. During the course of the time of pumping the brown cellulose suspension from one devices line [primary digester (8″)-mill (9″)-dewaterer (10″)-secondary digester (12″)], the preparation of the starting suspension of grass-like feedstock is taking place in the digester (5) for another devices line [primary digester (8)-mill (9)-dewaterer (10)-secondary digester (12)]. By this way the process is carried out alternately between 1 . . . N devices lines, as explained herein in this short example of 1 . . . 3 parallel examples, and achieves quasi-continuous effect. As mentioned earlier, the minimal number of the devices lines for cooking is two.

[0149] Overall time for digesting the grass-like feedstock in the white liquor, which represents a retention time of one batch of the material in every of the devices line [primary digester (8, 8′, . . . )-mill (9, 9′, . . . )-dewaterer (10, 10′, . . . )-secondary digester (12, 12′, . . . )] is 3-6 h. The use of said devices line [primary digester (8, 8′, . . . )-mill (9, 9′, . . . )-dewaterer (10, 10′, . . . )-secondary digester (12, 12′, . . . )] enables the effect in which the raw uncooked grass-like feedstock cannot get into the mixing vessel (14), from which, the digested (cooked) brown cellulose suspension is pumped further into the mill (15).

[0150] Schematic diagram of quasi-continuous cooking of the grass-like feedstock suspension within the whole process is shown in FIG. 1, where the number of parallel lines is limited to minimally two.

C. Additional Processing of Brown Cellulose

[0151] Additional processing of the brown cellulose suspension after the digesting is carried out in a manner that quasi-continuous combined output from all secondary digesters (12, 12′, . . . ) with cooked brown cellulose suspension is transferred into a first mixing vessel (14) and a first mill (15), where the milling of brown cellulose is performed and separation in a first dewaterer (16) takes place, where the brown cellulose suspension with 5-15% w/w dry matter concentrates up to the content of 27-33% dry matter, this process is accompanied with separation of the black liquor (17), which is transferred to the pre-cell (7A) of the electrolytic cell (7), whilst the concentrated brown cellulose suspension is prepared for the step D.

[0152] The term “quasi-continuous combined output” refers to the combined amount of all outputs of the brown cellulose suspension from every devices line for cooking [primary digester (8, 8′, . . . )-mill (9, 9′, . . . )-dewaterer (10, 10′, . . . )-secondary digester (12, 12′, . . . )], where, due to the alternating outputs of cooked brown cellulose suspension from each of devices line, the effect of continuous process is achieved. However, since this process is actually not really continuous, the fully correct term is “quasi”-continuous process. The combined output from all parallel devices lines [primary digester (8, 8′, . . . )-mill (9, 9′, . . . )-dewaterer (10, 10′, . . . )-secondary digester (12, 12′, . . . )] is the most precisely termed as “quasi-continuous combined output”.

[0153] Schematic diagram of the additional processing of brown cellulose is shown in FIG. 1.

D. Preparation of Brown Cellulose Suspension for Bleaching

[0154] The preparation of the bleaching suspension is performed in bleaching reactor (19) in which, beside the suspension from the step C via pipeline (18): [0155] regenerated fresh white liquor from the cathode compartment of the electrolytic cell (7B) through pipeline (20); [0156] mixture of oxygen (O.sub.2) and chlorine (Cl.sub.2) enveloped in the anode compartment of the electrolytic cell (7B) through pipeline (21); and [0157] optionally, hydrogen peroxide (H.sub.2O.sub.2) or sodium peroxide (Na.sub.2O.sub.2) via pipeline (22),

[0158] are introduced, giving the bleaching suspension with 5-15% w/w dry matter, preferably 10% w/w; and the preparatory bleaching process of brown cellulose from the step C is performed at 70-100° C. for the step E.

[0159] Preferably, the bleaching process is performed at temperature from 70-80° C.

[0160] As optional additional oxidants in the phase of brown cellulose bleaching, hydrogen peroxide (H.sub.2O.sub.2) or sodium peroxide (Na.sub.2O.sub.2) can be employed. As hydrogen peroxide source, typically commercially available H.sub.2O.sub.2 solution at about 30% w/w is used. In the case of Na.sub.2O.sub.2, it is clear that it yields an equimolar mixture of NaOH and H.sub.2O.sub.2, which is further used in the same manner as an additional oxidant in the bleaching process according to the present disclosure.

[0161] Schematic diagram of the phase of the preparation of brown cellulose suspension for bleaching process is shown in FIG. 2.

E. Quasi-Continuous Bleaching of Brown Cellulose

[0162] Quasi-continuous bleaching process is realized through two or more parallel lines [primary reactor (23, 23′, . . . )-bleaching mill (24, 24′, . . . )-bleaching dewaterer (25, 25′, . . . )-secondary reactor (27, 27′, . . . )] during 3-6 h, at temperature from 70-100 CC, preferably from 70-80° C., where the feedstock from the step D is prepared and sequentially pumped into said two or more parallel lines by the way that the output from all secondary reactors (27, 27′, . . . ) produces a continuous process; where further bleaching process is performed in primary reactors (23, 23′, . . . ) and where, at the output from the primary reactors (23, 23′, . . . ), the suspension of bleached cellulose with 8-12% w/w dry matter is obtained, which is subjected to milling/grinding in corresponding mills (24, 24′, . . . ) and separation in dewaterers (25, 25′, . . . ) from which, a part of waste solution (26, 26′, . . . ) is transferred through manifold (26, 26′, . . . ) into the electrolytic pre-cell (7A), while the concentrated bleached cellulose suspension with about 30% w/w dry matter is entered into secondary reactors (27, 27′, . . . ) with introduction of: [0163] white liquor solution (28) from the cathode compartment of the cells (7B) through manifold (28, 28′, . . . ), [0164] mixture of oxygen (O.sub.2) and chlorine (Cl.sub.2) evolved in the anode compartment of the electrolytic cells (7B) via manifold (29, 29′, . . . ); and, [0165] optionally, hydrogen peroxide (H.sub.2O.sub.2) or sodium peroxide (Na.sub.2O.sub.2) through pipeline (30, 30′, . . . ),

[0166] yielding the bleached cellulose suspension with 8-12% w/w, preferably 10% w/w dry matter.

[0167] In other words, the phase of quasi-continuous bleaching of the brown cellulose in the bleaching chemicals solution is performed by the way that the brown cellulose suspension is prepared in the bleaching reactor (19). It is then transferred into the devices line [primary bleaching reactor (23, 23′, . . . )-mill (24, 24′, . . . )-dewaterer (25, 25′, . . . )-secondary bleaching reactor (27, 27′, . . . )], in which the bleaching process in carried out at 70-100° C., preferably at 70-80° C. During the course of this process, brown cellulose is bleached with oxygen (O.sub.2) and chlorine (Cl.sub.2) in the presence of sodium hydroxide (NaOH; 0.5-2.0% w/w) and sodium chloride (NaCl; 0.5-25.0% w/w), furnishing the bleached cellulose suspension, which is subsequently continuously transferred into the mixing vessel (31).

[0168] After all amount of the starting brown cellulose suspension, that enters into the bleaching process, is transferred into the devices line [primary bleaching reactor (23)-mill (24)-dewaterer (25)-secondary bleaching reactor (27)], a new batch of brown cellulose suspension is preparing in the reactor (19), which is subsequently pumped into parallel devices line [primary bleaching reactor (23′)-mill (24′)-dewaterer (25′)-secondary bleaching reactor (27′)]. Once the bleaching of the batch in the devices line [primary bleaching reactor (23)-mill (24)-dewaterer (25)-secondary bleaching reactor (27)] is finished, then all the content from them is transferred through the mixing vessel (31) for further processing, in dewaterer (32). To the mixing vessel (31), further bleaching cellulose suspension from parallel devices line [primary bleaching reactor (23′)-mill (24′)-dewaterer (25′)-secondary bleaching reactor (27′)] is transferred. The number of such parallel lines should be optimal to achieve quasi-continuous manufacturing process.

[0169] The term “quasi-continuous bleaching” is used because it describes this bleaching process in the most precise manner. The bleaching in said parallel devices lines [primary bleaching reactor (23, 23′, . . . )-mill (24, 24′, . . . )-dewaterer (25, 25′, . . . )-secondary bleaching reactor (27, 27′, . . . )] by intermittent output of bleached cellulose from each of said devices line, gives the effect of continuous process. Due to the fact that it is not really a continuous bleaching process, it is the most precisely termed as “quasi-continuous bleaching”.

[0170] As an oxidant for bleaching in the present disclosure, gaseous mixture of oxygen (O.sub.2) and chlorine (Cl.sub.2) is employed. The latter is generated electrolytically in anode compartment of the electrolytic cell (7B), which, in basic conditions (0.5-2.0% w/w NaOH) and under relatively mild reaction conditions, bleaches brown cellulose. Relative weight ratio of O.sub.2 and Cl.sub.2 in this mixture depends on weight percentage of sodium chloride (NaCl) in the white liquor, which can be from 0.5-25.0% w/w.

[0171] Schematic diagram of the phase of quasi-continuous bleaching of brown cellulose suspension is shown in FIG. 2.

F. Final Processing of White Cellulose

[0172] The final processing of the white cellulose is carried out in such a way that quasi-continuous combined output from all secondary bleaching reactors (27, 27′, . . . ) from the step E is transferred into the second mixing vessel (31) and second dewaterer (32), where the draining of the waste chemicals-containing solution from the bleaching process is taking place, and said waste water is returned back to the pre-cell (7A) of the electrolytic cell (7) through pipeline (33), while the drained cellulose comes out from the process in the form of pure white cellulose pulp, at the concentration from 48-55% w/w dry matter, with maximally 5% w/w lignin, calculated on the dry matter.

[0173] Continuous process for cellulose pulp production from grass-like feedstock by the use of electrolytic process according to the present disclosure optionally includes further processing of the white cellulose from the step F., in a way that the viscous white cellulose suspension, at the level of 48-52% w/w dry matter, is further dried in drier (34), yielding dried cellulose powder.

[0174] The combined outputs of: [0175] the black liquor from the digesting phase, which is brought into the electrolytic cell (7) from dewaterer (10, 10′, . . . ) through manifold (11, 11′, . . . ); [0176] residual black liquor which is separated from brown cellulose suspension after draining in dewaterer (16) via pipeline (17); [0177] waste water from the bleaching process which is separated in dewaterer (25, 25′, . . . ) through manifold (26, 26′, . . . ); and, [0178] waste water from the final processing of white cellulose from dewaterer (32) via pipeline (33);

[0179] are mixed together and transferred into the pre-cell (7A) of the electrolytic cell (7), where the electrolytic work-up of the black liquor is performed, phase G.

[0180] Schematic diagram of final processing of white cellulose is shown in FIG. 2.

G. Electrolytic Processing of Black Liquor

[0181] A key part of the continuous process for the production of the cellulose pulp or dry cellulose powder from grass-like feedstock according to one embodiment of the present disclosure is just said continuous electrolytic work-up of black liquor, which is carried out in electrolytic cell (7) including: [0182] one or more electrolytic pre-cell (7A); made from an inert material for the chemistry of the process, in which cathode and anode electrodes are immersed, with no membrane between cathode and anode compartments; [0183] one or more electrolytic cells (7B); made from an inert material for the chemistry of the process, in which cathode and anode electrodes are immersed, where cathode compartment is completely separated from anode compartment with porous membrane, which enables electrical contact of anode and cathode via ion-exchange, but prevents passing of suspended organic molecules in electrolyte; [0184] where the electrolyte is, after processing in the pre-cells (7A), transferred into anode compartment of electrolytic cells (7B), and, if necessary, the composition of the electrolyte is modified during the course of the process by addition of fresh sodium chloride (NaCl) solution into pre-cells (7A); [0185] cathode is made of carbon steel or rust-free steel (AISI 304, 316, 321 and others), while for anode, graphite or magnetite is employed; where, [0186] between the electrodes in the electrolytic pre-cell (7A) and electrodes in electrolytic cell (7B) the voltage of direct current from 1.5-20 V is established, at the current density from 1-10 A/dm.sup.2, at the temperature of the cell from 80-95° C.; and, [0187] the electrolysis in the electrolytic pre-cell (7A) is carried out by introducing the black liquor (11, 11′, . . . ) from the step B, the black liquor (17) from the step C, a part of waste solution (26, 26′, . . . ) from the step E, and waste water (33) from the step F, wherein the evolution of lignin and other side-products takes place, which are mechanically removed from the top of the electrolyte solution; where, [0188] the electrolyte solution from the pre-cell (7A) is pumped into the anode compartment of the electrolytic cell (7B) for further processing wherein: [0189] (i) at the cathode, the white liquor of the following composition is regenerated: [0190] (a) 0.50-2.00% w/w NaOH; [0191] (b) NaCl; [0192] which is distributed into: [0193] digester (5) through pipeline (6) in the step A; [0194] digesters (12, 12′, . . . ) via manifold (13, 13′, . . . ) in the step B; [0195] bleaching reactor (19) through pipeline (20) in the step C; and, [0196] bleaching reactors (27, 27′, . . . ) via manifold (28, 28′, . . . ) in the step D; [0197] and generated hydrogen is transferred into the storage tank for hydrogen (39); [0198] (ii) at the anode, gaseous oxygen (O.sub.2) and chlorine (Cl.sub.2) are generated and subsequently introduced into: [0199] bleaching reactor (19) through pipeline (21) in the step C; and, [0200] bleaching reactors (27, 27′, . . . ) via manifold (29, 29′, . . . ) in the step E; and, [0201] wherein the rest of lignin and other side-products are isolated and mechanically separated from the top of the electrolyte solution.

[0202] Preferably, the working voltage in the electrolytic cell is 3-6 V, while the current density is kept between 4-6 A/dm.sup.2.

[0203] The membrane (M) that physically separates cathode from anode compartment within the electrolytic cell (7B) is of a special importance. It may include material selected from the following group: asbestos, mineral wool, hydrated Portland cement, product of kaolin and sodium silicate, aluminium oxide (Al.sub.2O.sub.3), titanium dioxide (TiO.sub.2), zirconium dioxide (ZrO.sub.2), polyethylene (PE), polysulfone (PSU), polyvinyl pyrrolidone (PVP), polyvinyl chloride (PVC), polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), sulfonated polytetrafluoroethylene (SPTFE), or composite materials obtained from the combinations of these materials.

[0204] Preferably, the membrane (M) in the electrolytic cell (7B) is made of composite material including: [0205] (i) zirconium dioxide (ZrO.sub.2); from 80-90% w/w, preferably 85% w/w; and, [0206] (ii) polysulfone (PSU); from 10-20% w/w, preferably 15% w/w.

[0207] Material inert to the chemistry of the process from which is made electrolytic pre-cell (7A) and electrolytic cell (7B) is selected from the group consisting of: plastics such as polyvinyl chloride (PVC), polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), polysulfone (PSU); or metals such as common steel, rust-free steels (AISI 304, 316, 321 and others) or aluminium, which are coated with coatings or linings resistant to chemicals involved in the process: polysulfone (PSU), polyvinyl pyrrolidone (PVP), polyvinyl chloride (PVC), polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), sulfonated polytetrafluoroethylene (SPTFE), polychloroprene, their mixtures and other polymers.

[0208] The working concentration of sodium chloride (NaCl) in the white liquor is from 0.50-25.0% w/w, preferably from 0.50-1.50% w/w.

[0209] For necessary adjusting the content (weight percentage; % w/w) of sodium chloride (NaCl) in the white liquor for the cooking and bleaching processes, a fresh solution of sodium chloride (NaCl) is introduced through pipeline (38) into the anode compartment of electrolytic pre-cell (7A) within the electrolytic cell (7). This solution is prepared in mixing vessel (35) by addition of NaCl, which is stored in storage vessel (36), and purified water from storage tank (37).

[0210] Schematic diagram of electrolytic part of the whole process is shown in FIG. 3.

Equipment of Key Digesters and Bleaching Reactors

[0211] The digesters (5, 8, 8′, . . . ; 12, 12′, . . . ), bleaching reactors (19, 23, 23′, . . . , 27, 27′, . . . ) and mixing vessels (14, 31) are equipped with mixing elements which enable intensive stirring of suspended material at >900 revolutions per minute (r.p.m.).

[0212] The digesters (5, 12, 12′, . . . ) and bleaching reactors (19, 27, 27′, . . . ) are equipped with heating jackets which provide their heating to the working temperature.

[0213] Optionally, the digesters (5, 12, 12′, . . . ) and bleaching reactors (19, 27, 27′, . . . ) are, instead heating jackets, equipped with magnetrons for alternative heating via microwaves (MW). The microwave heating is a well-known in the prior art, see for instance literature reference 13), cited earlier.

[0214] Additionally, the digesters (5, 8, 8′, . . . ; 12, 12′, . . . ), bleaching reactors (19, 23, 23′, . . . ; 27, 27′, . . . ), and mixing vessels (14, 31) can be optionally equipped with vibrator, which generates 10,000-14,000 oscillations per minute, to facilitate the mixing; this manner is well-known in the prior art.

Starting Grass-Like Feedstock

[0215] As starting grass-like feedstock in the present process, dried leaves and/or stems of grass plant species in the form of longitudinal pieces can be used, whose fraction by length is minimally 90% between 0.2-2.0 cm.

[0216] The grass plant species are selected from the group consisting of: sorghum (Sorghum species, Linne); maize (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); oat (Avena sativa, Linne); common flax (Linum usitatissimum, Linne); proso millet (Panicum miliaceum, Linne) and other species from the genus Panicum; triticale (x Triticosecale, Wittm. ex 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 from the genus Phragmites; bagasse from sugarcane processing; jute (Corchorus olitorius, Linne); bamboo (Bambusoideae spp., Linne); and their mixtures.

[0217] Preferably, as the starting raw material in the present process, sorghum (Sorghum species, Linne) and maize (Zea mays, Linne) are used.

INDUSTRIAL APPLICABILITY

[0218] As is demonstrated in the detailed description, some embodiments of the present disclosure involve the continuous process for production of cellulose from grass-like feedstock, which is based on: [0219] (i) a special system of serially-connected devices for: [0220] (a) cooking: [primary digester (8, 8′, . . . )-mill 9, 9′, . . . )-dewaterer (10, 10′, . . . )-secondary digester (12, 12′, . . . )]; and, [0221] (b) bleaching: [primary bleaching reactor (19, 19′, . . . )-mill (24, 24′, . . . )-dewaterer (25, 25′, . . . )-secondary bleaching reactor (27, 27′, 27″, . . . )]; [0222] which enables quasi-continuous way of processing, and effective separation of the black liquor from the cooking phase and waste chemicals from the bleaching phase, as well as the addition of fresh chemicals for cooking and bleaching; this significantly enhances efficiency of the process under relatively mild reaction conditions, which subsequently provide high degree of cellulose fibres preservation; [0223] (ii) bleaching process of brown cellulose with electrolytically generated oxygen (O.sub.2) in the presence of sodium hydroxide (NaOH; 0.5-2.0% w/w) and sodium chloride (NaCl; 0.5-25.0% w/w), which are generated in the electrolytic cell (7); and, [0224] (iii) electrolytic removal of lignin; [0225] (a) from the black liquor of the cooking phase; and [0226] (b) waste liquid from bleaching phase; [0227] in a way that electrolytic cell contains electrolytic pre-cell (7A), which does not contain the membrane between anode and cathode, what enhances efficacy of the electrolytic part of the process and minimizes tendency of clogging the membrane within the electrolytic cell (7B) which is connected downstream in the process from said electrolytic pre-cell (7A).

[0228] Said key improvements provide higher efficiency of the process and higher quality of the cellulose pulp for manufacturing of paper from the grass-like feedstock. This disclosure effectively solves all these three key issues identified in the technical problem. Therefore, the industrial applicability is unquestionable.

REFERENCES

[0229] 1—conveyor for input of grass-like feedstock in the bales form [0230] 2—bales cutter [0231] 3—mill; for cutting the grass-like feedstock up to the level of fine comminuted parts [0232] 4—deduster [0233] 5—digester; for preparation of the suspension of comminuted grass feedstock in white liquor [0234] 6—pipeline; for entering white liquor from cathode compartment of the electrolytic cell (7B) into the digester (5) [0235] 7—electrolytic cell; a system of two or more serially-connected electrolytic cells [0236] 7A—electrolytic pre-cell unit; one or more serially-connected electrolytic cells without membrane (M) [0237] 7B—electrolytic cell: one or more serially-connected electrolytic cells with membrane (M) [0238] 8, 8′—primary digester [0239] 9,9′—mill; for milling/grinding of cellulose fibers [0240] 10,10′—dewaterer/separator; for removing of major part of black liquor from brown cellulose pulp suspension; elevates concentration of the dry matter in the suspension from 8-12% w/w to 27-33% w/w [0241] 11,11′—manifold; drains away part of black liquor from dewaterer (10) and (10′) into electrolytic pre-cell (7A) [0242] 12,12′—secondary digester [0243] 13,13′—manifold; for delivery of white liquor from cathode compartment of electrolytic cell (7B) into digester (12) and (12′) [0244] 14—mixing vessel [0245] 15—mill; for milling/grinding of cellulose fibres [0246] 16—dewaterer; for removing a part of black liquor from brown cellulose pulp suspension; elevates concentration of the dry matter in the suspension from 8-12% w/w to 27-33% w/w [0247] 17—pipeline; for separation of part of black liquor from dewaterer (16) into electrolytic pre-cell (7A) [0248] 18—pipeline; for transferring of concentrated brown cellulose suspension with about 30% w/w dry matter from dewaterer (16) into the bleaching reactor (19) [0249] 19—bleaching reactor [0250] 20—pipeline; for the white liquor supplying from cathode compartment of the electrolytic cell (7B) to the bleaching reactor (19) [0251] 21—pipeline; for delivery of gaseous oxygen (O.sub.2) and chlorine (Cl.sub.2) from anode compartment of the electrolytic cell (7B) to the bleaching reactor (19) [0252] 22—pipeline; for hydrogen peroxide (H.sub.2O.sub.2) solution or sodium peroxide (Na.sub.2O.sub.2) supply into the bleaching reactor (19) [0253] 23, 23′—primary bleaching reactor [0254] 24, 24′—mill [0255] 25, 25′—dewaterer [0256] 26, 26′—manifold; for removing waste water from bleaching process, from dewaterer (25) and (25′) into electrolytic pre-cell (7A) [0257] 27, 27′—secondary bleaching reactor [0258] 28, 28′—manifold; for addition of the white liquor from cathode compartment of electrolytic cell (7B) to the bleaching reactor (27) or (27′) [0259] 29, 29′—manifold; for transport of gaseous oxygen (O.sub.2) and chlorine (Cl.sub.2) from anode compartment of electrolytic cell (7B) into the bleaching reactor (27) and (27′) [0260] 30, 30′—manifold; for hydrogen peroxide (H.sub.2O.sub.2) solution or sodium peroxide (Na.sub.2O.sub.2) supply into the bleaching reactor (27) and (27′) [0261] 31—mixing vessel [0262] 32—dewaterer [0263] 33—pipeline; for removing waste solution from the bleaching process, from dewaterer (32) into the electrolytic pre-cell (7A) [0264] 34—drier [0265] 35—mixing vessel [0266] 36—storage vessel for sodium chloride (NaCl) [0267] 37—storage tank for water [0268] 38—pipeline; for optional addition of fresh aqueous sodium chloride (NaCl) solution into the electrolytic pre-cell (7A) [0269] 39—storage tank for hydrogen (H.sub.2) [0270] M—membrane; within electrolytic cell (7B), which physically separates cathode and anode compartment