RU2566275C1 - Method of obtaining of cellulose from half-wit flax for paper industry - Google Patents

Abstract

FIELD: textile, paper.

SUBSTANCE: method of obtaining of cellulose from half-wit flax is offered which comprises the pre-treatment stage at the pre-set temperature, two-phase pulping in water solutions of acid and sodium hydroxide, the raw material is half-wit flax straw, the pre-treatment is performed by nitric acid solution, pulping is performed in sodium hydroxide solution, then in nitric acid water solution, then double washing with solution of sodium hydroxide of various concentration and final treatment with nitric acid solution are performed.

EFFECT: creation of efficient and cost-saving method using fast-renewable vegetable raw materials - straw of half-wit flax and allowing to exclude energy-intensive stages of machining.

4 tbl, 1 dwg

Description

The invention relates to the pulp industry, namely to the production of cellulose from plant cellulose-containing raw materials, and can be used for the production of pulp in the paper industry.

Cellulose is a multivariate raw material and can be used in various industries depending on its physical, mechanical and chemical properties, which are individual for each type of production. The mechanical properties differ from the standard ones, adopted, for example, for the textile industry, but make it possible to use noodle fillers for diapers as components for the production of different-grade paper, cardboard, packaging materials.

Mezeum flax (oil flax) is a crop grown to produce seeds from which oil is squeezed out for food and technical needs (technical flaxseed oil serves as the basis for varnishes), flax seed is used in the manufacture of pharmacy products - as a filler for pillows and mattresses for bedridden patients in hospices.

Flax can grow in various climatic zones of the country, including regions in which the cultivation of other crops is ineffective. Guaranteed yield of flax, the multivariance of its processing can significantly increase the profitability and employment of the population of agricultural regions of Russia. The yield of flax seeds reaches 14-16 kg / ha, while the mass of straw is 1.5 tons.

Currently, the demand for flaxseed seed forms the foreign pharmaceutical market.

The problem of deep processing of flax is primarily associated with the replacement of wood pulp with cellulose of annual plants (flax, kenaf, hemp, rice and wheat straw, etc.). The problem of deforestation in the world today is one of the main global environmental problems, therefore, there is currently a tendency to use non-wood pulp-containing raw materials, as evidenced by a significant number of publications on the development of methods for producing cellulose from non-traditional sources - rice and wheat straw, agricultural waste, stalks of cotton flax, hemp, miscanthus.

Currently, flax straw-mezhumka does not find any practical application, it is either burnt in the fields, or a field with the remnants of last year's straw is plowed immediately before sowing. Flax straw left in the fields increases the concentration of acetic acid in the soil, which is an inhibitor of plant growth, which leads to a decrease in crop yields.

As a cellulose-containing raw material, the Mezeum flax currently does not find worthy application due to the lack of technology for the separation of cellulose and its processing.

A widely known method of producing cellulose from any plant material by the sulfate method (sodium hydroxide + sodium sulfide). However, the use in production of sulfur-containing compounds and active chlorine is now recognized as environmentally unacceptable.

To obtain cellulose, it is advisable to use flax, unsuitable for processing in the textile industry. Such flaxseed wastes contain up to 80% cellulose. Unlike wood, the main domestic raw material for the production of cellulose, flax is an annually renewable raw material. In this area, technical and technological solutions are needed to create highly efficient flexible technologies for the deep processing of short flax fiber. To obtain linen yarn in accordance with the requirements of a very labor-intensive technology of wet spinning and fabric production, only a long fiber of 12-14% is used. The remaining short fiber (16-18%), as a rule, is used for rough technical materials, such as a basis for carpet weaving, packaging materials, tow.

The prior art method for the production of cellulose from plant materials, including pre-treatment in an alkaline solution, washing, bleaching (RF patent No. 2378432, publ. 02/10/2010), including pre-treatment, washing.

The disadvantages of the described method include the presence of a two-stage thermomechanical processing of the feedstock in a twin-screw apparatus, in addition to the fact that the proposed treatment involves additional energy costs, high rigidity of plant materials (flax-bag), leads to rapid wear of the equipment, the proposed method also requires additional mechanical equipment.

The closest in technical essence (prototype) is a method for producing cellulose from flax-bag with a pre-treatment at a given temperature, two-stage cooking in aqueous solutions of acid and sodium hydroxide (Izgorodin A.K. Research on the possibility of using flax-bag as a raw material for production of cellulose // Chemical fibers. - 2004. - No. 5. - P. 30-33; Konoplev Yu.V., Izgorodin AK, Voronov MI, Prusov AN Study of structural changes in flax pulp after exposure to alkaline and acidic creates / Materials Smartex VII International Seminar - Ivanovo. ISTA, 2004. - P. 109-114).

However, the described method relates to the processing of flax-mezumum fibers, cleaned of fires. An attempt to isolate flax fiber is extremely unproductive - 3%, i.e. from a ton of straw flax-mezumum get only 3 kilograms of fiber. Thus, the described technical solution cannot be used for industrial production.

The objective of the proposed technical solution is to create an effective and economical method using straw flax as a raw material and eliminates the energy-consuming stage of mechanical processing.

The problem is solved by the proposed method for producing cellulose from flax-bag, including a pretreatment stage at a given temperature, two-stage cooking in aqueous solutions of sodium hydroxide and acid, while the flax-bag is used as raw material, pre-treatment is carried out with a solution of nitric acid, cooking is carried out in an aqueous solution of sodium hydroxide, then in an aqueous solution of nitric acid, followed by a double wash with an aqueous solution of sodium hydroxide of various concentrations In the final stage, the product is processed with an aqueous solution of nitric acid.

The proposed technical solution differs from the prototype in that the raw material used is flax straw, pre-treatment is carried out with a solution of nitric acid, cooking is carried out in an aqueous solution of sodium hydroxide, then in an aqueous solution of nitric acid, followed by a double wash with an aqueous solution of sodium hydroxide of various concentrations , at the final stage, the product is treated with an aqueous solution of nitric acid.

In addition, the proposed technical solution differs from the prototype in a different sequence of operations during two-stage cooking, in the prototype - first in an aqueous solution of acid, then in an aqueous solution of sodium hydroxide, in our case, vice versa.

An aqueous solution of nitric acid was selected for pretreatment of flax-straw bag (prehydrolysis). Nitric acid has an oxidizing effect on aromatic compounds of raw materials (lignin) and easily hydrolyzable polysaccharides (hemicelluloses) and has a fiber splitting effect.

The choice of an aqueous solution of sodium hydroxide as a cooking solution is due to the high solubility with respect to lignin, as well as the low degree of destruction of cellulose fibers.

Cooking in an aqueous solution of nitric acid allows you to remove residual lignin from cellulose and provides the final longitudinal razvolenie pulp.

In connection with the deposition of lignin on cellulose fibers, the product is then washed twice with an aqueous solution of sodium hydroxide of various concentrations.

The final stage - acidification (decationization), which consists in treating the product with nitric acid, is necessary to reduce the ash content and remove sodium ions.

Table 1 shows the chemical compositions of samples of flax straw-mezumum of crops in 2011, 2012 and 2013.

The yield of cellulose obtained by the proposed method directly from straw flax-border: 2011 - 37.80%; 2012 - 39.00%; 2013 - 39.00%.

The average yield of cellulose from the flax-straw bag was 38.6% in terms of raw materials or 76.3% in terms of native cellulose.

Table 2 shows the physico-chemical characteristics of cellulose samples obtained from flax-mezumum straw in a combined (claimed) way.

It should be noted that the sum of the mass fractions of α-cellulose, ash, lignin and pentosans is less than 100%, which is explained by the presence of low molecular weight cellulose that is not included in α-cellulose.

In addition, it has been shown by IR spectroscopy that, according to the main characteristic frequencies, cellulose samples obtained from flax-mezumum straw are precisely cellulose. A comparison of the IR spectra of the experimental celluloses from flax straw with the reference cotton cellulose showed the presence of all peaks characteristic of cellulose in the reference [New reference chemist and technologist. Raw materials and products of the industry of organic and inorganic substances. Part II. - St. Petersburg: ANO NPO Professional, 2005, 2007. - P. 455]. The spectra are characterized by the following frequencies: 3470-3125 cm ^-1 - stretching vibrations (VK) of the BUT groups participating in the intermolecular and intramolecular H bonds; 2940-2860 cm ^-1 - VK bonds in the groups CH and CH ₂ ; 1630 cm ^-1 - deformation vibrations (DC) of HOH bonds due to the presence of bound water; 1433 cm ^-1 , 1374 cm ^-1 - DC of CH ₂ groups; 1339 cm ^-1 - DC OH in CH ₂ OH; 1164, 1114, 1059, 1031 cm ^-1 - VK bonds CO. The intense blurred band of 3200–3600 cm ^–1 and less intense in the region of 2800–3000 cm ^–1 is caused by stretching vibrations of the hydroxyl groups included in the hydrogen bond and the CH, CH ₂ groups, respectively. In the spectra of all experimental celluloses, there are no vibrations in the region of 1600 cm ^-1 characteristic of aromatic compounds — residual lignin.

For comparison, they were determined in the bioconversion laboratory of IPKhET SB RAS according to generally accepted methods of cellulose analysis [Obolenskaya A.V., Elnitskaya Z.P., Leonovich A.A. Laboratory work on the chemistry of wood and cellulose. - M .: Ecology, 1991. - S. 73-75, 79-80, 106-107, 119-120, 161-164, 200-203, 229, 250-254; GOST 25438-82 Cellulose for chemical processing. Methods for determining the intrinsic viscosity. The publication is official. - M .: Publishing house of standards, 1982. - 20 p .; GOST 10820-75 Cellulose. Method for determining the mass fraction of pentosans. The publication is official. M .: Publishing house of standards, 1991. - 8 pp.] Physico-chemical parameters of samples of bleached pulp from softwood and sulfate bleached pulp from a mixture of hardwood, the results are shown in the table.

Table 3 shows the physicochemical parameters of samples of sulphate bleached pulp from softwood and sulphate bleached pulp from a mixture of hardwood.

As follows from the presented results, the physicochemical parameters of the flax-mezeum straw cellulose are close to the bleached sulphate pulps shown in Table 3: the content of α-cellulose in the range of 77.5-85.7% overlaps with the range for Gostov sulphate pulp 81 , 6-88.4%, non-cellulosic components, in particular ash and lignin, slightly exceed wood pulp, which is explained by the nature of the raw materials: it is known that the ash content of wood is much less than non-wood types of raw materials. The content of pentosans of 2.6-3.9% is much lower than the indicator of sulphate pulp 6.0-16.8%, which indicates the possibility of increasing the yield of cellulose from flax-bag without reducing the quality of the product. The degree of polymerization of cellulose from flax-bag 430-530 is less than that of wood 1040-1270, due to the nature of the raw material.

Such high quality and high yield of cellulose from flax-bag is ensured by the sequence of processing of raw materials with dilute solutions of sodium hydroxide and nitric acid. When alkali interacts with raw materials at a temperature of 98 ° C, a sequential alkaline hydrolysis of chemical bonds between cellulose, hemicelluloses and lignin occurs with the dissolution of part of the hemicelluloses and lignin in the cooking solution and the release of holocellulose. At this stage, part of the active alkali is not spent on delignification, but on the dissolution of hemicelluloses and their secondary reactions.

At the next stage, during the interaction of nitric acid with residual lignin, holocellulose, electrophilic substitution takes place in the aromatic nucleus (nitrosation, nitration), electrophilic displacement, aliphatic substitution, addition, oxidation [V. Nikitin Theoretical foundations of delignification / V.M. Nikitin. - M .: Forest. industry, 1981. - 295 p.]. In the next step of the treatment with a sodium hydroxide solution, the lignin so modified is extracted with the release of cellulose. To reduce the ash content, a stage of processing the obtained cellulose with an acid solution is carried out. It should be emphasized that in this process only two chemical reagents are used: sodium hydroxide and nitric acid, which are publicly available, cheap and whose regeneration issues in the country have been resolved on an industrial scale.

It is known that the suitability of pulp for areas of the paper industry is assessed by indicators of paper strength: sheet density, breaking length, bursting, tensile stiffness, work failure, breaking stress and breaking deformation. Silent production, which does not require high paper strength, is based on the use of both primary (bleached softwood and hardwood pulp) and secondary fiber (waste paper). The main indicators of the strength of paper samples made from experimental cellulose from flax-straw bag and mechanical pulp in the production of sulfate pulp are shown in table 4. The drawing shows a photograph of a laboratory sample of paper from flax-straw bagel.

As follows from the table, the main strength indicators of paper samples from flax-mezeum cellulose are comparable to samples of mechanical masses that are used as components in compositions of sanitary-hygienic grades of paper and newsprint. There are paper grades that use cellulose with strength indices similar to those shown in the table, in particular paper for sanitary purposes intended for processing into toilet paper, paper towels, napkins, disposable medical paper products, etc.

Case Studies

Example 1

Flax straw of the 2011 harvest was used as an experimental raw material. Humidity 7%. Loading of raw materials amounted to 130 g. Cooking is carried out in a 4-l round bottom flask. Cooking straw flax-baggage (prehydrolysis) is carried out in an aqueous solution of 0.6% nitric acid with module 20 at a temperature of 95 ° C for 3 hours. After that, the product is washed to a neutral wash water reaction. The next step is cooking in a 4% solution of sodium hydroxide with module 20 at a temperature of 98 ° C for 16 hours. Next, the product is washed to a neutral wash water reaction, then the resulting product is cooked in a 3% solution of nitric acid with module 17 at a temperature of 98 ° C for 10 hours, after filtration on a funnel to remove lignin, washing is carried out twice, first 2.5 % sodium hydroxide solution, then 0.3% sodium hydroxide solution, then water. To remove sodium, the product is washed with a 1.5% solution of nitric acid, then with water until neutral.

The yield is 37.8%.

Example 2

As an experimental raw material, flax straw of the 2012 harvest was used. Humidity 7.5%. Loading of raw materials amounted to 130 g. Cooking is carried out in a 4-l round bottom flask. Cooking flax-mezumum straw (prehydrolysis) is carried out in a solution of 1.5% nitric acid with module 20 at a temperature of 98 ° C for 2.5 hours. This is followed by washing the product to a neutral wash water reaction. The next step is cooking in a 5% solution of sodium hydroxide with module 20 at a temperature of 98 ° C for 15 hours. Next, rinse the product until neutral wash water. Then cooking is carried out in a 4% solution of nitric acid for 8 hours. After filtering on a funnel to remove lignin, washing is carried out twice, first with a 2.5% sodium hydroxide solution, then with a 0.3% sodium hydroxide solution, then with water. To remove sodium, the product is washed with 1% nitric acid solution, then with water until neutral.

The product yield is 38.9%.

Example 3

As an experimental raw material, flax straw of the 2012 harvest was used. Humidity 7.8%. Loading of raw materials amounted to 130 g. Cooking is carried out in a 4-l round bottom flask. Cooking flax-mezumum straw (prehydrolysis) is carried out in a solution of 0.5% nitric acid with module 15 at a temperature of 92 ° C for 6 hours. Then the product is washed until the washings are neutral. Then carry out cooking in 1.5% sodium hydroxide with module 20 at a temperature of 95 ° C for 26 hours. Then rinse the product until the washings are neutral. The next step is the treatment with 4% nitric acid for 14 hours with module 15 at a temperature of 95 ° C. After filtration on a funnel to remove lignin, the product is washed twice with 2.5% sodium hydroxide solution for 2 hours with stirring, then with water. To remove sodium, the product is washed with a 1.2% solution of nitric acid for 1 hour with stirring, then with water until neutral.

The yield is 39.1%.

Example 4

As an experimental raw material, flax straw of the 2013 harvest was used. Humidity 8.1%. Loading of raw materials amounted to 130 g. Cooking is carried out in a 4-l round bottom flask. Cooking straw flax-baggage (prehydrolysis) is carried out with a solution of 1% nitric acid with module 15 at a temperature of 96 ° C for 8 hours. Next, rinse the product until neutral wash water. Then they cook in 3.5% sodium hydroxide with module 15 at a temperature of 99 ° C for 14 hours. Then rinse the product until the washings are neutral. After the treatment is carried out with 4% nitric acid for 15 hours with module 15 at a temperature of 96 ° C. After filtration on a funnel to remove lignin, washing is carried out twice with a 2% sodium hydroxide solution for 2 hours with stirring, then with water. To remove sodium, the product is washed with a 0.4% solution of nitric acid for 1 hour with stirring, then with water until neutral. The yield is 38.8%.

Example 5

As an experimental raw material, flax straw of the 2013 harvest was used. Humidity 8.6%. Loading of raw materials amounted to 130 g. Cooking is carried out in a 4-l round bottom flask. Cooking flax-mezumum straw (prehydrolysis) is carried out with a solution of 1.0% nitric acid with module 15 at a temperature of 98 ° C for 7 hours. This is followed by washing the product to a neutral wash water reaction. Then boil in 3.3% sodium hydroxide with module 15 at a temperature of 97 ° C for 15 hours. Then rinse the product until the washings are neutral. Then, treatment with 4% nitric acid with module 15 is carried out for 15 hours at a temperature of 96 ° C. After filtration on a funnel to remove lignin, the product was washed twice with a 2% sodium hydroxide solution for 2 hours with stirring, then with water. To remove sodium, the product was washed with a 1.0% nitric acid solution for 1 hour with stirring, then with water until neutral.

The yield is 38.9%.

Example 6

As an experimental raw material, flax straw of the 2013 harvest was used. Humidity 9%. Loading of raw materials amounted to 130 g. Cooking is carried out in a 4-l round bottom flask. Cooking straw flax-baggage (prehydrolysis) is carried out with a solution of 1.5% nitric acid with module 15 at a temperature of 99 ° C for 7 hours. This is followed by washing the product to a neutral wash water reaction. Then cook in 3.0% sodium hydroxide with module 15 at a temperature of 96 ° C for 13 hours. Then rinse the product until the washings are neutral. Then carry out the treatment with 3.5% nitric acid for 10 hours with module 15 at a temperature of 96 ° C. After filtration on a funnel to remove lignin, the product was washed twice with a 1.5% sodium hydroxide solution for 2 hours with stirring, then with water. To remove sodium, the product was washed with a 1.0% nitric acid solution for 1 hour with stirring, then with water until neutral.

The yield is 39.1%.

Example 7

As an experimental raw material, flax straw of the 2013 harvest was used. Humidity 8.8%. Loading of raw materials amounted to 130 g. Cooking is carried out in a 4-l round bottom flask. Cooking straw flax-bag (prehydrolysis) is carried out with a solution of 1.5% nitric acid with module 15 at a temperature of 98 ° C for 5 hours. This is followed by washing the product to a neutral wash water reaction. Then cook in 3.0% sodium hydroxide with module 15 at a temperature of 96 ° C for 13 hours. Then rinse the product until the washings are neutral. Then, treatment with 4.0% nitric acid is carried out for 15 hours with module 15 at a temperature of 96 ° C. After filtering on a funnel to remove lignin, it is washed twice with a 2.0% sodium hydroxide solution for 2 hours with stirring, then with water. To remove sodium, the product is washed in a funnel with a 1.0% solution of nitric acid for 1 hour with stirring, then with water until neutral. The yield is 39.2%.

Further development of work in the above areas and their introduction into production will make it possible in the near future to significantly increase the provision of the paper industry with pulp and energy-saving technologies. Implementation of the proposed method can be carried out with a slight modernization of existing equipment and will not require large investments.

Claims (1)

A method of producing cellulose from a flax-bag, comprising a pre-treatment step at a given temperature, two-stage cooking in aqueous solutions of acid and sodium hydroxide, characterized in that the flax-bag is used as raw material, the pre-treatment is carried out with a solution of nitric acid, cooking is carried out in water a solution of sodium hydroxide, then in an aqueous solution of nitric acid, followed by a double washing of the obtained product with an aqueous solution of sodium hydroxide of various concentrations and windows thorough treatment with an aqueous solution of nitric acid.

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