Patent Grant
11976416
The present disclosure relates to an improved process for production of cellulose pulp for paper manufacturing from grass-like feedstock such as dried plant mass of leaves and/or stems of sorghum (Sorghum species L.) or maize (Zea mays L.).
A technical problem to be solved by the present disclosure is effective production of high-quality cellulose for paper manufacturing from grass-like feedstock such as sorghum (Sorghum species L.), which includes efficient solving of the following technological details:
The cooking phase is additionally improved by the use of freshly prepared or electrolytically regenerated white liquor, which minimally contains sodium hydroxide (NaOH; 0.5-2.0% w/w) and sodium chloride (NaCl; 0.5-2.0% w/w).
According to our best knowledge, the present disclosure represents the first continuous process for cellulose production which includes:
Cellulose pulp production for paper manufacturing from renewable, fast-growing and economical feedstock is of a great importance for the modern paper industry. Classical processes which are based on wood as the starting feedstock are more and more substituted by technologies that rely on grass-like feedstock such as miscanthus (Miscanthus x giganteus, Andersson), sorghum (Sorghum species, Linne), straw from various cereals, etc.; see for instance literature reference 1:
In the cellulose pulp production processes, the most important is the cooking/digesting phase. It includes the cooking of comminuted lignocellulosic material with aqueous solution of suitable chemicals. A larger number of different processes for cooking lignocellulosic materials is known, which are usually divided by the sort of chemicals that are employed in the process. The most known technologies are based on the following digesting solutions:
The cooking chemicals solution is commonly called “white liquor” and represents a freshly prepared or regenerated solution of chemicals for digesting lignocellulosic material. The white liquor helps to remove non-cellulosic material by converting them into the solution, while relatively pure cellulose fibres remain suspended in this liquid phase. Such cellulose suspension is known as cellulose pulp.
The above-mentioned liquid phase (supernatant), in which cellulose fibres are suspended after the digesting phase, is called “black liquor”, and contains dissolved non-cellulosic components of the starting lignocellulose feedstock and excess of cooking chemicals. Therefore, the cooking process product is a suspension of brown cellulose fibres in the black liquor.
Regarding the type of chemistry that is employed in the cooking (digesting) process, all technologies that do not use sulphur-based chemicals have significant advantage from both process and ecological reasons. Technologies without sulphur chemicals preserve process equipment from corrosion, and environment from unnecessary pollution, and are essentially without significant negative environmental footprint.
One of the most important processes which is considered as environmentally-friendly is based on sodium hydroxide (NaOH) as a key chemical for preparation of the white liquor. The use of NaOH as the sole chemical for digesting lignocellulose materials is known in the art. One of typical processes is based on the use of 5% w/w aqueous NaOH solution, which is employed as the white liquor for cooking grass-like feedstock at 90° C. during several hours; see literature reference 2:
The cooking phase can be carried out by the use of microwave (MW) for heating of lignocellulose material suspension in the white liquor. For instance, Zhu and co-workers described a process for pre-treatment of miscanthus (Miscanthus x giganteus, Andersson) with aqueous NaOH solution at very high temperatures (130-200° C.), at elevated pressure, for 20 minutes, with heating by MW. Thus, pre-treated miscanthus gave significantly higher yield in the sulphuric acid (H2SO4)-catalysed hydrolysis to glucose, which was subsequently employed as a starting raw material for manufacturing of bioethanol by fermentation; see literature reference 3:
Although this process is focused on glucose production from miscanthus, described pre-treatment suggests potential possibility to use MW for cooking miscanthus and other grass-like feedstock in the cellulose pulp production. Of course, the reaction conditions described in the literature reference 3 are very harsh and clearly not compatible with manufacturing of high-quality cellulose fibres.
Beside the cooking process, another important phase in the production of high-quality cellulose pulp is the bleaching process. The most known systems for cellulose bleaching 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 H2O2 is being preferred.
For example, U.S. Pat. No. 2,903,326 describes the process for bleaching cellulose pulp with chlorine (Cl2), sodium hypochlorite (NaOCl) or calcium hypochlorite [Ca(OCl)2] and sodium hydroxide (NaOH) with addition of sodium chlorate (NaClO3) at pH 2-7, preferably at pH 5-7, at temperature from 0-50° C.; see literature reference 4:
Although from the ecological reasons the H2O2 application is preferred, some oxidants that are formally chlorine-based, are also acceptable. These do not lead to the formation of chlorinated organic compounds such as chloroform, which are unwanted environmental pollutants. The example is chlorine dioxide (ClO2) which is successfully used as an oxidant for cellulose pulp bleaching. ClO2 is usually separately prepared by the reaction of: sodium chlorite (NaClO2) and hydrogen peroxide (H2O2); then from sodium chlorate (NaClO3) and hydrogen peroxide (H2O2) in the presence of sulphuric acid (H2SO4); or by other methods; for instance, see literature references 5 and 6:
The cellulose pulp bleaching processes with chlorine dioxide (ClO2), with or without additional oxidants, are known in the art; for example, see literature references 7 and 8:
As an example of hydrogen peroxide (H2O2)-based bleaching process, herein is outlined the document no. 9)—GB 681661, which discloses the use of the following bleaching system:
(a) 0.30-1.75% w/w H2O2;
(b) 0.75-3.25% w/w NaOH;
(c) 20-65% w/w cellulose pulp (calculated on dry matter); and
(d) up to 100% w/w process water;
where the bleaching is performed at temperature below 54.4° C. Optionally, the solution of sodium silicate (xNa2O•ySiO2) can be employed as a stabilizer for hydrogen peroxide; see literature reference 9:
This document suggests the use of a combination of hydrogen peroxide (H2O2) and sodium hydroxide (NaOH) as cellulose pulp bleaching system under relatively mild reaction conditions, below 54.4° C.
Apart from conventional heating of the bleaching reactor for cellulose pulp, the use of microwave (MW) in this phase of cellulose processing is known in the art; see literature reference 10:
Moreover, Law and co-workers disclosed the method for bleaching cellulose pulp which is based on MW heating by the use of hydrogen peroxide (H2O2) and sodium hydroxide (NaOH) combination; see literature reference 11:
The removal of lignin and other side-products from the black liquor with the use of electrolytic reactor (cell) is known in the prior art. Typical example is technology disclosed by Edel and co-workers that is based on electrolysis of the black liquor with direct current (DC) between suitable electrodes. Lignin is released at the anode compartment, while at the cathode compartment sodium hydroxide is regenerated as the white liquor; see literature reference 12:
Mikulic described a continuous process for cellulose pulp production from various grass-like feedstock, preferably miscanthus (Miscanthus x giganteus, Andersson), where:
According to our best knowledge, this document represents the closest prior art to the present disclosure; see literature reference 13:
In comparison to the process described in WO 2017/178849 A1, one embodiment of the present disclosure is based on:
Said key improvements provide higher efficiency of the process and higher quality of the cellulose pulp for paper manufacturing from grass-like feedstock, as is described in the detailed description of the disclosure.
The present disclosure includes a continuous process for production of cellulose pulp from grass-like feedstock by the use of electrolytic process for continuous isolation of lignin and other side-products, with simultaneous regeneration of the white liquor and oxygen (O2) and chlorine (Cl2), which is performed in an electrolytic cell which may include:
A continuous process for cellulose pulp production from grass-like feedstock by the use of electrolytic process according to the present disclosure optionally includes further work-up of white cellulose from the step F, which involves further drying of viscous white cellulose suspension with 48-52% w/w dry matter, yielding dry cellulose powder.
Optionally, a key, electrolytic part of the continuous process for cellulose pulp production or dry cellulose powder from grass-like feedstock is performed under the following conditions:
A membrane that physically separates cathode from anode compartment within the electrolytic cell 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 (Al2O3), titanium dioxide (TiO2), zirconium dioxide (ZrO2), 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.
Preferably, the membrane in the electrolytic cell is made of composite material including:
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. As the starting raw material in the present process, various grass-like feedstock can be employed, preferably sorghum (Sorghum species, Linne) and maize (Zea mays, Linne).
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:
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 (O2) and chlorine (Cl2), where the process may include the following steps:
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
The preparation of the grass-like feedstock involves:
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.
The prepared grass feedstock enters into the preliminary digester or digester (5), where the suspension for the cooking process is prepared.
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:
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.
Schematic diagram of the grass-like feedstock suspension preparation for the cooking process is shown in
B. Quasi-Continuous Cooking of Grass-Like Feedstock
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:
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.
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).
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.
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).
Schematic diagram of quasi-continuous cooking of the grass-like feedstock suspension within the whole process is shown in
C. Additional Processing of Brown Cellulose
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.
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”.
Schematic diagram of the additional processing of brown cellulose is shown in
D. Preparation of Brown Cellulose Suspension for Bleaching
The preparation of the bleaching suspension is performed in bleaching reactor (19) in which, beside the suspension from the step C via pipeline (18):
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.
Preferably, the bleaching process is performed at temperature from 70-80° C.
As optional additional oxidants in the phase of brown cellulose bleaching, hydrogen peroxide (H2O2) or sodium peroxide (Na2O2) can be employed. As hydrogen peroxide source, typically commercially available H2O2 solution at about 30% w/w is used. In the case of Na2O2, it is clear that it yields an equimolar mixture of NaOH and H2O2, which is further used in the same manner as an additional oxidant in the bleaching process according to the present disclosure.
Schematic diagram of the phase of the preparation of brown cellulose suspension for bleaching process is shown in
E. Quasi-Continuous Bleaching of Brown Cellulose
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:
yielding the bleached cellulose suspension with 8-12% w/w, preferably 10% w/w dry matter.
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 (O2) and chlorine (Cl2) 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).
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.
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”.
As an oxidant for bleaching in the present disclosure, gaseous mixture of oxygen (O2) and chlorine (Cl2) 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 O2 and Cl2 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.
Schematic diagram of the phase of quasi-continuous bleaching of brown cellulose suspension is shown in
F. Final Processing of White Cellulose
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.
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.
The combined outputs of:
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.
Schematic diagram of final processing of white cellulose is shown in
G. Electrolytic Processing of Black Liquor
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:
Preferably, the working voltage in the electrolytic cell is 3-6 V, while the current density is kept between 4-6 A/dm2.
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 (Al2O3), titanium dioxide (TiO2), zirconium dioxide (ZrO2), 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.
Preferably, the membrane (M) in the electrolytic cell (7B) is made of composite material including:
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.
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.
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).
Schematic diagram of electrolytic part of the whole process is shown in
Equipment of Key Digesters and Bleaching Reactors
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.).
The digesters (5, 12, 12′, . . . ) and bleaching reactors (19, 27, 27′, . . . ) are equipped with heating jackets which provide their heating to the working temperature.
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.
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
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.
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.
Preferably, as the starting raw material in the present process, sorghum (Sorghum species, Linne) and maize (Zea mays, Linne) are used.
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:
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.
| Number | Date | Country | Kind |
|---|---|---|---|
| P20190259A | Feb 2019 | HR | national |
This application is a continuation of International App. No. PCT/EP2020/051957 filed Jan. 27, 2020, which claims the benefit of priority to Croatian (HR) Patent App. No. P20190259A filed Feb. 7, 2019, wherein the entire contents and disclosure of each of the foregoing applications is incorporated by reference herein in its entirety.
| Number | Name | Date | Kind |
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| 4421598 | Reeve | Dec 1983 | A |
| 4584076 | Edel et al. | Apr 1986 | A |
| 5061343 | Azarniouch et al. | Oct 1991 | A |
| 5366714 | Bigauskas | Nov 1994 | A |
| 20060201642 | Shin et al. | Sep 2006 | A1 |
| Number | Date | Country |
|---|---|---|
| 2038651 | Dec 1995 | CA |
| 655056 | Jul 1951 | GB |
| 681661 | Oct 1952 | GB |
| 770687 | Mar 1957 | GB |
| 9412720 | Jun 1994 | WO |
| 0138607 | May 2001 | WO |
| 2017178849 | Oct 2017 | WO |
| WO-2017178849 | Oct 2017 | WO |
| Entry |
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| Number | Date | Country | |
|---|---|---|---|
| 20210355636 A1 | Nov 2021 | US |
| Number | Date | Country | |
|---|---|---|---|
| Parent | PCT/EP2020/051957 | Jan 2020 | US |
| Child | 17386557 | US |
