WO2004022838A1

WO2004022838A1 - Method of the electric pulse treatment of fibrous materials

Info

Publication number: WO2004022838A1
Application number: PCT/UA2003/000025
Authority: WO
Inventors: Nikolai Aleksandrovich Platonov
Original assignee: Simonov, Sergii Vadimovich; Kraynov, Viktor Gennadiyevich
Priority date: 2002-09-06
Filing date: 2003-07-11
Publication date: 2004-03-18
Also published as: AU2003245236A1; AU2003245236A8; UA72027C2

Abstract

A method of the electric pulse treatment of fibrous materials includes preparing a suspension of a selected fibrous material in a liquid medium of suitable chemical composition, treating the suspension with at least one electric pulsed discharge between at least two electrodes immersed in the liquid medium, and separating the treated fibers from the liquid medium and side products. To increase the efficiency of scouring of arbitrary fibers from impurities, prior to the treatment a specific electrical resistance of the liquid medium not higher than 2•1011 Ω/m and a volume density of the pulse energy during the treatment below 50 kJ/I are set.

Description

METHOD OF THE ELECTRIC PULSE TREATMENT OF FIBROUS MATERIALS

Technical field

This invention relates to methods of treating fibrous materials containing natural fibers and rayon in a liquid medium by means of electrical pulses. Such methods can be used for the economic and essentially environmentally friendly removal of cellulose associates of arbitrary chemical composition mainly from cellulose fibers, for finishing viscose or cuprammonium fibers and, as desired, for the initial treatment of wool.

For the purpose of this description, the following terms as employed herein and in the appended claims refer to the following concepts: "Fibrous materials" are: cotton ginned from mechanical impurities such as remainders of pods and soil clots; short and long fibers of flax and hemp, other fibrous materials; viscose and cuprammonium cellulose fibers and wool of animals (sheep mainly);

"Cellulose associates" are: lignin, pectin, nitrous substances, pentosans, hemicelluloses and other vegetable polymeric and ^■ oligomeric materials having admixtures of low-molecular substances containing cellulose fibers that can be ginned and scoured as a final product;

"Liquid medium" is preferably water, ethanol and aqueous or alcoholic solutions of bleaches, saponifiers and other agents that can be chosen by those skilled in the art from the commercially available reagents taking into consideration the chemical composition and physical-and-chemical properties of the fibers to be produced and/or fiber impurities; "Electric pulse treatment" is generation of high-power mechanical pulses and cavitation by electric discharges in a suspension of a fibrous material in a liquid medium confined in a closed vessel (not obligatorily hermetically sealed) with the aim of: mechanical-and-chemical destruction and fine dispersion of cellulose associates or other impurities (e.g. fat and other wool staining substances), which can be accompanied by chemical modification of products of dispersion under the effect of suitable agents, and/or intensification of chemical treatment, e.g. bleaching or degreasing of respective cellulose or wool fibers;

"Modulus of treatment" is a ratio of the mass of the liquid, wherein the reagents are dispersed, to the mass of the dry fibrous material.

Background Art Separation of cellulose fibers from cellulose associates and scouring the animals' wool from stains of grease and mechanical impurities for the following processing of the fibrous raw materials into products such as cotton wool, yarn, threads, fabric and knit cloth of arbitrary types are the purpose of many heavy-duty processes.

Naturally, such processes must be as economic as possible considering the consumption of time, energy and reagents and must create as little danger to the environment as possible.

Nowadays, the traditional methods of cellulose separation from wood by way of sulfite or alkaline (sulfate) cooking of wood chips, mainly of valuable coniferous woods, obviously do not comply with the above requirements (see monograph by Nikitin N.I. Wood and Cellulose Chemistry. Moscow-Leningrad, USSR Science Academy Publishing House, 1962, chapters XXVII and XXVIII - HMKMTMH H.M. XiiMiifl flpeβecuHbi I I i βnπιonθ3bi. - M.-Jl.: l bfl-BO AH CCCP, 1962, maβbi XXVII n XXVIII).

Therefore, attempts have been made for a long time to create such methods and means for processing fiber-containing materials that would allow the separation of the fiber from associated substances to be essentially simplified and made cheaper.

Known in the art is a number of inventions of the sort (UA Patents 17136 A, 17179 A, 17283 A and 17284 A) that contemplate methods of the electric pulse treatment of fiber-containing materials and a utility model (UA Patent 1096 and RU Certificate 19841) that contemplates a production line for cellulose wool. All these documents describe processing a fiber-containing material in a liquid (preferably aqueous) medium, wherein high-power impact pulses are generated by means of electrical discharges.

The experiments preceding the filing of applications for the mentioned patents showed that a mechanical-and-chemical action on the cellulose associates reduces specific consumption of time, energy and reagents and the danger of the environmental pollution. However, the recent experiments helped to establish that the problem of effectively controlling the electric pulse treatment had not been feasibly solved.

Actually, the most alike, as for the technological essence, with the method of the invention method of treating fibrous materials by means of electrical pulses in a liquid medium (see UA Patent 17179) includes only preparing a suspension of fiber containing raw material in a liquid medium of suitable chemical composition; treating the obtained suspension by at least one pulsed discharge passed between at least two electrodes immersed in the liquid medium; and separating the treated fibers from the liquid medium and side products of said treatment. The only regulated (just if desired) parameters in said method are the temperature and pressure inside the apparatus and degree of contamination of the liquid medium by side products of electric pulse treatment, which is evidently not enough for effective mechanical-and-chemical separation of arbitrary fibrous materials from substances that are cellulose associates and/or other impurities of cellulose and protein fibers. Disclosure of the Invention

The invention is based on the problem of creation, by changing the parameters, of such method of electric pulse treatment of fibrous materials in a liquid medium, which allow obtaining highly purified cellulose and protein fibers for technical and other applications, especially for medical application, from various raw materials.

Said problem is solved in that in a method of the electric pulse treatment of fibrous materials, including preparing a suspension of a selected fibrous material in a liquid medium of suitable chemical composition, treating the obtained suspension by at least one electric pulsed discharge passed between at least two electrodes immersed in the liquid medium, and separating the treated fibers from the liquid medium and side products of the treatment, according to the invention, prior to the treatment a specific electrical resistance of the liquid medium not higher than 2*10¹¹ Ω/m and a volume density of the energy in the pulse during the treatment up to 50 kJ/I are set. Said limitation in the specific electrical resistance of the liquid medium prior to the treatment and the range of allowable values of the volume density of the energy in the pulse make it possible to select such optimal values of the set parameters that provide for essentially effective and environmentally friendly scouring of the vegetable fibers from cellulose associates or animals' wool from greasy contaminants (irrespective of the degree of their contamination). Actually, with the specific electrical resistance about 2*10¹¹ Ω/m and the volume density of the pulse energy greater than 10-15 kJ/I, the electric pulse treatment of a suspension of a fiber material in a liquid medium proceeds predominantly under the action of the impact waves and cavitation, which allows effective separation of cellulose fibers from the incrusting substances of wood and flax; and as the specific electrical resistance and the volume density of the pulse energy are reduced, the main effect occurs due to the regulated cavitation in the suspension, which allows intensifying the chemical treatment, e.g. for bleaching flax or degreasing wool. The following embodiments of the invention show by way of examples the possibilities of such optimization of the treatment taking into consideration the composition of raw materials. The first additional characteristic feature consists in that the pH of the liquid medium is set within the range of 1.0 to 13.5, which permits the conditions of the mechanical-and- chemical treatment to be adjusted to the peculiarities of the starting chemical composition of the fibrous materials.

The second additional feature consists in that the time of each electric discharge is not longer than 0.1 s. Under the multiple electric pulse impact on fibrous materials, this allows the reduction of the electrolysis of water in a water based liquid medium to such degree that the release of free hydrogen and oxygen would be substantially suppressed, and the occurrence of sodium hypochlorite would become substantially avoided in liquid media containing sodium chloride as a reagent. The third additional feature consists in that the liquid medium is pretreated with at least one electric discharge prior to impression of fibrous materials therein. This catalyzes molecules of a solvent (water as a rule) and dispersed reagents thus promoting intensification of chemical processes. The occurrence of atoms of induced oxygen (singlet oxygen) in the liquid medium should be particularly noted. They occur either from oxygen, which is usually present in an aqueous medium or intentionally introduced in it (including the oxygen introduction in the form of ozone), or from the molecules of water as a result of its partial electrolysis under the electric discharges and accompanying cavitation. High oxidizing potential of the singlet oxygen allows a sharp activation of oxidizing destruction of cellulose associates and bleaching the separated cellulose fibers. The fourth additional feature consists in that the fiber containing material is treated in a hermetically sealed reactor. This allows intensification of the separation of mainly cellulose containing fiber materials from strong cellulose associates such as lignin and reduction in specific consumption of energy.

The fifth additional feature consists in that the fibrous material is treated at a pressure of more than 0.1 MPa. This facilitates the plasticization of cellulose associates (especially lignin) and correspondingly improves the ginning of the fibrous material therefrom, which is very important when obtaining wood cellulose. The sixth additional feature consists in that the fiber containing material is treated at a temperature higher than the surrounding temperature, which provides for intensification of the mechanical-and-chemical destruction of impurities in fibrous materials.

The seventh additional feature consists in that fibrous materials are treated at a residual pressure of less than 0.1 MPa. This is expedient in the sparing mechanical-and- chemical treatment of rayon fibers with high content of hemicelluloses and in selective removal of only some fractions of cellulose associates from the starting fibers.

The eighth additional feature consists in that the reagents are introduced in a reactor filled with a liquid together with the fibrous material to be treated and dispersed simultaneously with the treatment of the suspension of this material by electrical discharges. This allows gradual dispersion of the reagents to be combined with separation of the fibrous materials from the impurities.

The ninth additional feature consists in that the ratio of the mass of the liquid in which the reagents are dispersed to the mass of the dry fibrous material makes up not less than three, because with a smaller modulus of treatment, oscillation damping in the suspension substantially increases and, correspondingly, efficiency and quality of the electric pulse treatment of fibrous materials reduce.

Brief Description of Drawing The invention will now be explained with reference to embodiments thereof represented in the accompanying drawing, wherein an experimental batch-operated reactor is schematically shown in longitudinal section.

Best Mode for Carrying out the Invention Referring to the drawing, a reactor having the working capacity of 10 I comprises: A body 1 made of 12X18H10T grade stainless steel in the shape of a cylindrical shell with a conical top part and a conical bottom part, said body serving as one of electrodes;

A cap 2 of the same material attached to a flange of the body 1 ; A central electrode 3 insulated along the perimeter and having a conductive protrusion facing the bottom part of the body 1 , said central electrode 3 being tightly mounted in the cap 2 for adjustable reciprocation;

A nipple 4 fixed in the cap 2 and intended for letting the gases, that release in the process of electric pulse treatment, out to the surroundings or for vacuuming the interior of the body 1 ; A stop-and-control element 5 mounted on the nipple 4; and

A hydraulic lock 6 mounted on the nipple 4 protrusion downstream of the stop-and- control element 5, said hydraulic lock being open to the surroundings.

In experiments, the reactor was connected to a pulse gap (not shown in the drawing) based on a bank of capacitors having a controlled capacity in the range between 2 μF and 100 μF with usual means for controlling frequency and power of the pulse well known to those skilled in the art.

The method of the invention was tested in the treatment of various fibrous materials. Thus, the examples are classified into six groups, namely (1) Production of cellulose medical absorbent cotton; (2) Production of cellulose from wood;

(3) Production of cellulose from cotton linters, flax and hemp;

(4) Production of cottonizing products, i. e. products of bast fiber materials possessing the properties intrinsic to the cotton staple;

(5) Initial treatment of wool; (6) Scouring of fibrous materials.

Electric pulse treatment in all the examples included the following steps: a) preparing a selected fibrous material for the electric pulse treatment in accordance with standard methods, for example: ginning the cotton from remainders of pods and soil clots, hackling the flax or hemp with removal of shive etc.; b) preparing a suspension of a selected fibrous material in a solution (usually aqueous) of reagents, the applications, compositions and concentrations of which being specified in examples; c) setting a specific electrical resistance of the liquid medium at a level not higher than 2*10¹¹ Ω/m usually combined with operation (a); d) treating the obtained suspension by at least one electric pulsed discharge passing between the central electrode 3 and the body 1 of the reactor with a volume density of the energy in the pulse not greater than 50 kJ/I (and usually in the range of 0.1 to 50 kJ/I); e) scouring the fibers from the remainders of reagents and side products of the electric pulse treatment, drying the scoured fibers to the allowable remaining humidity, and, if needed, combing the dried fibers; f) analyzing the obtained products in conformity with the standard requirements applied to the quality of products with similar application. The specific conditions of carrying out this method with regard to the type of a fibrous raw material and composition of impurities are listed in the following tables. 1. Examples of production of cellulose medical absorbent cotton To test the efficiency of the method of the invention, experimental batches of medical absorbent cotton were produced from the traditional cotton raw material and non- traditional flax and hemp materials (see Table T1.1).

Electric pulse treatment was carried out in two stages, both in hermetically sealed and non-sealed reactors. The initial temperature of the suspension in all the cases was about 20°C. The variations of the temperature in the non-sealed reactor were not controlled, and it was not higher than 130°C in the sealed reactor at the end of the treatment. The pressure in the non-sealed reactor was similar to the atmospheric one, and in the sealed reactor, the pressure did not exceed 0.3 MPa at the end of the treatment. The compositions and concentrations of the reagents are listed in Table T1.2, and the conditions of treatment are given in Table T1.3.

In a number of examples, ozone was used as a bleach, the concentration of which in the air after leaving the ozonizer was about 24 g/tn³. The flow rate of 100% ozone during the treatment was 5 l/min. After the ozonizer, the air-ozone mixture was dispersed in the suspension inside the reactor in the form of tiny bulbs. The results of quality analysis of the obtained cellulose medical absorbent cotton in accordance with the generally accepted indices are given in Table T1.4

Table T1.1 Types and kinds of fibrous materials in the examples of the first group

Table Tϊ .2

Reagents used in the examples of the first group

Table Tϊ .3

Table T1.3 (completed)

Notes: ⁽¹⁾ - Treatment in a hermetically sealed reactor. ⁽²⁾ - Treatment in a non-sealed reactor.

(3) . Additional treatment with ozone.

(4) . Treatment in a pure water.

Table T1.4

The Table T1.4 clearly shows that medical absorbent cotton produced by the method of the invention from non-traditional flax and hemp raw materials is not inferior to cotton wool made of the traditional cotton raw material in quality and in some indices (ash content, content of greasy and waxy substances, whiteness) out-performs it. 2. Examples of production of cellulose from wood

To test the efficiency of the method of the invention experimental batches of cellulose from standard chips of aspen wood were produced.

The electric pulse treatment of the chips was carried out both in hermetically sealed and non-sealed reactors three times with rinsing the fibrous pulp after the first and second stages and introducing fresh reagents compositions and concentrations of which were usually modified for each next stage. The initial temperature of the suspension was always about 20°C. The variations in the temperature in the non-sealed reactor were not controlled, and it was not higher than 150°C in the sealed reactor at the end of the treatment. The pressure in the non-sealed reactor was similar to the atmospheric one, and in the sealed reactor, the pressure did not exceed 0.5 MPa at the end of the treatment.

Ozone was used for bleaching in some examples, same as described above. In certain examples, the base for the liquid medium was 96% ethyl alcohol having a specific electrical resistance of 1.5-10¹¹ Ω/m.

The compositions and concentrations of the reagents are listed in Table T2.1 , and the conditions of treatment are given in Table T2.2. The results of quality analysis of the obtained wood cellulose in accordance with the generally accepted indices are given in Table T2.3

Table T2.1

Reagents used in the examples of the second group

Table T2.2 Conditions of treating raw materials in the examples of the second group

Table T2.2 (continued)

Table T2.2 (completed)

Notes: ⁽¹⁾ - Treatment in a hermetically sealed reactor.

⁽²⁾ - Treatment in a non-sealed reactor.

⁽³⁾ - Additional treatment with ozone.

⁽⁴⁾ - Cooking liquor based on 96% ethanol.

Table T2.3

Results of analysis of wood cellulose

It is clearly seen from the tables that the method of the invention in any of the given examples allows obtaining wood cellulose with a degree of purification not less than 97% in a processing period of 45 min. If, as in example 2.6, the electric pulse treatment of chips and fibrous pulp is carried out only in the sealed reactor using ethyl alcohol as the basis for the working suspension at the first stage, it is enough to use ozone and a trifle quantity of sulfuric acid and sodium hydroxide at the second and third stages to obtain highly purified cellulose. Naturally, such version of the process is the most environmentally friendly.

3. Examples of production of cellulose from cotton linter, flax and hemp To test the efficiency of the method of the invention experimental batches of cellulose from cotton linter and bast fiber materials such as flax and hemp were produced (see Table 3.1). Electric pulse treatment of said raw materials was carried out twice with rinsing and substitution of reagents after the first stage. All the rest was the same as in the process described above on the examples of the second group. In a number of examples, ozone was used for bleaching same as described above.

The compositions and concentrations of the reagents are listed in Table T3.2, and the conditions of treatment are given in Table T3.3. The results of quality analysis of the obtained cellulose in accordance with the generally accepted indices are given in Table T3.4. Table T3.1 Types and kinds of fibrous materials in the examples of the third group

Table T3.2

Table T3.3

Notes: ^(1>- Treatment in a hermetically sealed reactor. ^<2) - Treatment in a non-sealed reactor. ⁽³⁾ - Additional treatment with ozone. Table T3.4

It is seen from the tables that the method of the invention including double electric pulse treatment with total discharge time of not greater than 30 min allows obtaining high- purity end product containing about 97% of Alpha-cellulose and not more than 0.17% of impurities not soluble in concentrated sulfuric acid even from hemp. It is important to note that the values of dynamic viscosity, determined in standard cuprammonium solutions of all air-dry end products, indicate the possibility of their processing into rayon. Thus, the supplies of row materials for relevant enterprises can be substantially increased. 4. Examples of production of cottonizing products

To test the efficiency of the method of the invention samples of products of cottonizing bast fiber materials of the flax and hemp type were produced (see Table 4.1).

Electric pulse treatment of flax and hemp was carried out in a single stage because chemical purity of the textile raw materials intended to be produced of them is of no great importance (unlike the raw material for cuprammonium process in rayon production). In all other details, the process proceeded in the same way as described above on the examples of the first group. In a number of examples, ozone was used for bleaching same as described above.

The compositions and concentrations of the reagents are listed in Table T4.2, and the conditions of treatment are given in Table T4.3. The results of quality analysis of the products of cottonizing are given in Table T4.4

Table T4.1 Types and kinds of fibrous materials in the examples of the fourth group

Table T4.2

Table T4.3

Table T4.3 (completed)

Notes: ⁽¹⁾ - Treatment in a hermetically sealed reactor.

⁽²⁾ - Treatment in a non-sealed reactor.

⁽³⁾ - Additional treatment with ozone.

⁽⁴⁾ - Treatment in pure water. Table T4.4 Contents of certain chemical substances (%) in the air-dry pulp

As seen in Table 4.4, even a single treatment of flax and hemp by the method of the invention allows a notable reduction in contents of such cellulose associates in bast materials as pectins (in 3 to 4 times) and lignin (more than twice) in the end product. Moreover, the lignin remainder is present in the end products in essentially degraded form as for degree of polymerization. It is proved by the appearance of the bleached product of cottonizing, which the spinners accept as one similar to the appearance of the long-staple cotton.

5. Examples of initial treatment (scouring) of wool

Experiments in the triple electric pulse scouring of semi-fine sheep's wool in a non- sealed reactor were carried out with the modulus of treatment 20, initial temperature of the suspension about 20°C and the final temperature about 30°C the same for all the cases.

The compositions and concentrations of the reagents for each stage of treatment are listed in Table T5.1 , and the conditions of treatment are given in Table T5.2. The results of quality analysis of the scoured wool in terms of the residual content of grease are given in Table T5.3

Table T5.1 Rea ents used in the exam les of the fifth rou

Table T5.2

Table T5.3

Quality indices of the scoured wool

It is seen from the tables that the method of the invention provides highly effective scouring of wool to the residual grease content of less than 1% by mass.

6. Examples of scouring fibrous products Three samples of bleached flax with impurities of sodium chloride and rigidity salts sorbed on the fibers, which remained after the previous bleaching with the use of tap water, were taken for experiments in the electric pulse activation of scouring in a non- sealed reactor. The compositions and initial concentrations of salts are listed in Table T6.1 , and the conditions of treatment are given in Table T6.2. The suspension temperature was about 20°C, and the treatment modulus was 20 in all cases. The results of analysis of the scoured products are given in Table T6.3.

Table T6.1 Concentration of impurities in the bleached flax fibers prior to scouring

Table T6.2

Table T6.3 Concentration of impurities in the scoured bleached flax fibers

It is seen from the tables that the electric pulse activation of scouring allows reduction of concentration of impurities in the bleached flax fibers at least by one order

Industrial Applicability

The method of the invention ensures, as compared to traditional processes, obtaining highly purified cellulose fibers from arbitrary vegetable raw materials with significant reduction in specific consumption of time, reagents and energy and also decrease of danger for the environment.

To carry out the method, commercially available spacious chemical apparatuses equipped with pulse gaps and corresponding power sources based on available banks of capacitors can be utilized.

Claims

C L A I M S 1. A method of the electric pulse treatment of fibrous materials, including preparing a suspension of a selected fibrous material in a liquid medium of suitable chemical composition, treating the obtained suspension with at least one electric pulsed discharge passed between at least two electrodes immersed in the liquid medium, and separating the treated fibers from the liquid medium and side products of the treatment, characterized in that prior to the treatment a specific electrical resistance of the liquid medium not higher than 2-10¹¹ Ω/m and a volume density of the pulse energy during the treatment below 50 kJ/I are set.

2. The method of claim 1 characterized in that the pH of the liquid medium is set within the range of 1.0 to 13.5.

3. The method of claim 1 characterized in that the time of each electric discharge is not greater than 0.1 s.

4. The method of claim 1 characterized in that the liquid medium is pretreated with at least one electric discharge prior to impression of fibrous materials therein.

5. The method of claim 1 characterized in that the fibrous material is treated in a hermetically sealed reactor.

6. The method of claim 5 characterized in that the fibrous material is treated at a pressure of more than 0.1 MPa.

7. The method of claim 1 characterized in that the fibrous material is treated at a temperature higher than the surrounding temperature.

8. The method of claim 1 characterized in that the fibrous material is treated at a residual pressure of below 0.1 MPa.

9. The method of claim 1 characterized in that the reagents are introduced in a reactor filled with a liquid together with the fibrous material to be treated and dispersed simultaneously with the treatment of the suspension of this material by electrical discharges.

10. The method of claim 1 characterized in that the ratio of the mass of the liquid, in which the reagents are dispersed, to the mass of the dry fibrous material is not less than three.