RU2621758C1 - Production process of composite fiber based on hydrolysis lignin with polyacrylonitril - Google Patents

Abstract

FIELD: technological processes.

SUBSTANCE: invention relates to the production of sorbents having a well-developed microporous structure, controlled pore size and strength characteristics sufficient for use as sorbents made from activated carbon fibers obtained from polyacrylonitrile with the highest content of hydrolytic lignin. A method for producing a composite fiber based on hydrolytic lignin with polyacrylonitrile obtained by wet spinning with forcing-through the spinneret holes of mixtures of hydrolytic lignin and polyacrylonitrile solutions in dimethylsulfoxide in which the amount of hydrolysing lignin is from 70 to 80 wt % is fed into a precipitation bath with distilled water for coagulation of a polymer composite solution in the form of a fiber in which subsequent carbonization is carried out under nitrogen and activation by chemical reaction, and the composite fiber is subjected to an additional orientation stretching by 5-10% during the coagulation step in the precipitation bath, with the formation of micropores after carbonization with a monodisperse distribution of 3-18 mcm with channels having a regular combination of outer and closed pores of an elongated shape with expansion from the center of the fiber to its outer surface and anisotropic orientation along the entire length of the composite fiber.

EFFECT: composite fiber with sorption properties is obtained.

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Description

The invention relates to the production of sorbents with a developed microporous structure, adjustable pore size and strength characteristics sufficient for use as sorbents made on the basis of activated carbon fibers obtained from polyacrylonitrile with the highest possible content of hydrolysis lignin. The invention can be used for sorption technologies.

Sorbents based on fibers are known, having a developed microporous structure, adjustable pore size and high strength characteristics obtained by changing the amount of lignin included in the polymer matrix. So, [Shen, Q. Lignin-Based Activated Carbo n Fiber sand Controllable Pore Sizeand Properties [Text] / Qing Shen, Tao Zhang, Wen-XinZhang, Shua iChen, Mebrahtu Mezgebe // Journal of Applied Polymer Science. - 2011. - T. 121. B. 2. - C. 989-994] carbon fibers obtained from a mixture of lignin with phenol-formaldehyde resin have high adsorption properties. However, the data of thermogravimetric analysis, electron microscopy and IR spectra showed that carbon fibers obtained from polymer solutions with a lignin content of not more than 14% have the best pore structure and adsorption properties.

Received [Kuznetsov, B.N. Heat treatment of hydrolysis lignin in a circulating bed reactor [Text] / B.N. Kuznetsov, Yu.G. Golovin, V.A. Vink, V.V. Golovin // Chemistry of plant materials. - 1999. No. 2 - P. 53-59] an experimental batch of activated carbons from hydrolytic lignin by steam-gas activation of carbonized products of lignin pyrolysis. However, samples of sorption materials mainly had a microporous structure with a specific surface area of 360 to 460 m ² / g.

The closest of the technical solutions is [Patent - No. 2526380 of the Russian Federation, IPC D01F 6/54, C08L 97/00, D01F 8/00. A method of producing a composite fiber based on hydrolytic lignin with polyacrylonitrile / Yu.N. Sazanov and others; patent holder FGBUN IVS RAS (RU). - No. 2012153414/05; declared 12.12.2012; publ. 08/20/2014] and can be used to form precursor composite fibers as a starting material for the formation of heat-resistant carbon fibers. The use of the invention provides an increase in the amount of utilized hydrolysis lignin, which improves the ecology of production, obtaining a precursor fiber with a strength of up to 50 MPa, with increased heat resistance up to 30-40% at 800 ° C compared to 20% for pure hydrolysis lignin. However, this prototype does not consider the possibility of creating sorbents based on carbon fibers obtained from developed composite fibers based on polyacrylonitrile with the highest lignin content, with a depth of microporous fiber layer that determines its sorption properties.

The technical result of the claimed solution is to impart sorption properties to the composite fiber due to the formation of longitudinal channels after orientational drawing and carbonization of the fiber, combining elongated external and closed micropores having an extension from the center to the outer surface in the structure and anisotropic orientation along the entire length of the composite fiber.

The problem is achieved in that in the method for producing a composite fiber based on hydrolytic lignin and polyacrylonitrile, the fiber is formed by wet method by forcing through the holes of the spinneret mixture compositions from solutions of hydrolysis lignin (GL) and polyacrylonitrile (PAN) in dimethyl sulfoxide, in which the amount of hydrolysis lignin from 70 to 80% (mass), in a precipitation bath with distilled water for coagulation of a polymer composite solution in the form of a fiber followed by carbon by exposure to a stream of nitrogen for 2 h at a temperature of 800 ° С and activation by a chemical method, moreover, the composite fiber is subjected to additional orientational stretching by 5 to 10% at the coagulation stage in a precipitation bath, with the formation of micropores after carbonization with a monodisperse distribution of 3-18 microns with channels having a regular combination of external and closed pores of an elongated shape with expansion from the center of the fiber to its outer surface and anisotropic orientation along the entire length of the composite fiber.

A significant difference of the claimed method is an additional orientational stretching of the composite fiber by 5 to 10% when coagulating mixed compositions from solutions of GL and PAN in dimethyl sulfoxide in a precipitation bath with distilled water at the molding stage with the formation of micropores in the fiber structure after carbonization due to gradual purposeful destruction less heat-resistant than polyacrylonitrile, hydrolysis lignin, with the release of gaseous products of thermal decomposition, which lead to azovaniyu polyacrylonitrile micropores in combining exterior and closed pores elongated, extended from the fiber center to its outer surface, with monodisperse distribution of pores of 3 to 18 microns and anisotropic orientation along the entire length of the composite fiber. The microstructure of the carbonized fiber was confirmed by scanning electron microscopy, which was carried out on a SUPRA 55 VP electron microscope, which made it possible to study the surface with high resolution (from 200 μm to 10 nm).

Microphotographs of the surface image and the cross-sectional microstructure of the composite fiber with a GL: PAN ratio of 80:20, which is subjected to 10% orientational stretching during coagulation in a precipitation bath with distilled water at the stage of molding, subsequent carbonization and chemical activation, are shown in FIG. 1 (a, b)

The morphological features of the surface image and the transverse section made it possible to compose a structural model of a longitudinal section of a composite fiber with a GL: PAN ratio of 80:20, which is subjected to 10% orientational stretching during coagulation in a precipitation bath with distilled water at the stage of molding, subsequent carbonization and chemical activation, shown in FIG. 1 (c):

a) cross section of a composite fiber with an extract of 10%;

b) the surface of the composite fiber with an extract of 10% ;;

c) structural model of a composite fiber with a drawing of 10%;

The microstructure of the composite fiber with a GL: PAN ratio of 80:20, which is subjected to 10% orientational stretching during coagulation in a precipitation bath with distilled water at the stage of formation, subsequent carbonization and chemical activation, is characterized by the following indicators of the structural characteristics of the fibers:

- inclusion in the membrane of expressed fibrillar formations - 1 (a, b);

- the absence of transverse cracks on the surface of the fiber (b);

- the anisotropic nature of the arrangement of micropores along the axis of the fiber - 2 (c);

- uniform formation of holes on the surface of the fiber - 3 (b, c);

- clearly defined contours of the diameter of the fiber core - 4 (a, b);

- the presence of a layer with a radial orientation of micropores - 5 (a, b).

Modification of the surface of a composite fiber with a 10% orientation drawing after carbonization is a low-defect structure with regularly distributed pores. This effect is associated with the effect of polyacrylonitrile, whose linear macromolecules diffuse from the center to the fiber surface at high temperatures and, under the stresses created by orientational stretching, form a surface layer that includes fibrillar formations on the surface of the carbonized composite fiber.

Only the claimed combination of features, including the choice of the ratio of the components of the mixed composition of solutions of hydrolytic lignin from 70 to 80% (mass) and polyacrylonitrile from 30 to 20% in dimethyl sulfoxide, the conditions for forming the composite fiber by forcing through a die hole in a precipitation bath with distilled water during orientational drawing from 5 to 10%, followed by carbonization and chemical activation, leads to the formation of a microstructure in the form of elongated cavities located from the center of the fiber to its surface, their anisotropic orientation along the entire length of the fibrous sorbent, having a polydispersity range from 3 to 18 microns, provides the sorption properties of the composite fiber.

A method of producing composite fibers is implemented on a laboratory bench having a polyacrylonitrile and hydrolysis lignin polymer dissolution unit, a volume for mixing the obtained solutions, a device for controlling the feed rate of an airless molding solution to a spinneret kit with a diameter of holes for molding d = 1 mm, a precipitation bath and a receiving device provided by a fiber reception speed controller.

The following are specific examples of sorbent production.

Obtaining a composite solution of GL and PAN in a ratio of 80:20 in DMSO is as follows:

on 20 ml of DMSO with a density ρ = 1,1004 g / ml, the amount of PAN is calculated to obtain a 20% (mass) solution. A portion of GL was 3.52 g, and PAN - 0.88 g (based on the ratio of 80:20 wt.%);

in a round-bottomed two-necked flask place a portion of PAN (0.88 g) and fill it with 20 ml of DMSO, mix and leave to swell for a day;

after the PAN is completely dissolved, the flask is connected to the mixer through a water trap and, with constant stirring, the calculated amount of GL (3.52 g) is added. Mixing of the composite solution is continued for 48 hours until a homogeneous composite molding solution is formed;

before molding, the homogeneous molding solution is filtered, degassed, fed through a filter to a die, immersed in a precipitation bath filled with water;

fiber is formed at room temperature using a single syringe pump SV-1000 at a speed of 150 ml / h

Example 1

A homogeneous composite molding solution, which is fed through the hole of the die into water at room temperature, coagulates and, in the form of a composite fiber, remains for 20 minutes in a precipitation bath with a tension that ensures its elongation by 5%. After drying at room temperature, the composite fiber has a diameter of 0.73 mm and a strength of 61 MP.

The heat treatment of the composite fiber is carried out in three modes:

heating at a rate of 15 ° C to 800 ° C in a stream of nitrogen;

heating in nitrogen;

steam activation.

A fibrous carbon sorbent is obtained having polydisperse pores ranging in size from 3 to 18 μm, the specific surface area is 470 mg ² / g (by BET (Bruner-Emmet-Teller), the adsorption activity by methylene blue is 153 mg / g.

Example 2. A homogeneous composite molding solution, which is fed through a hole in a die into water at room temperature, coagulates and in the form of a composite fiber is in a precipitation bath for 20 minutes with a tension that ensures its elongation by 7%. After drying at room temperature, the composite fiber has a diameter of 0.67 mm and a strength of 65.5 MP.

The heat treatment of the composite fiber is carried out in three modes:

heating at a rate of 15 ° C to 800 ° C in a stream of nitrogen;

heating in nitrogen;

steam activation.

A fibrous carbon sorbent is obtained having polydispersed pores ranging in size from 4 to 16 μm, a specific surface area of 500 mg ² / g (according to BET), and sorption activity according to methylene blue is 165 mg / g.

Example 3. A homogeneous composite molding solution, which is fed through a hole in a die into water at room temperature, coagulates and in the form of a composite fiber is in a precipitation bath for 20 minutes with a tension that ensures its elongation by 10%. After drying at room temperature, the composite fiber has a diameter of 0.60 mm and a strength of 60.0 MP.

The heat treatment of the fibers is carried out in three modes:

heating at a rate of 15 ° C to 800 ° C in a stream of nitrogen;

heating in nitrogen;

steam activation.

A fibrous carbon sorbent was obtained having polydispersed pores ranging in size from 5 to 12 μm, the specific surface area was 570 mg ² / g (by BET), and the sorption activity according to methylene blue was 173 mg / g.

Other examples (No. 4, 5) of obtaining a fibrous carbon sorbent are shown in table 1.

Thus, composite fibers based on hydrolysis lignin and polyacrylonitrile obtained by wet forming by pressing through apertures of a spinneret of mixed compositions from solutions of hydrolysis lignin and polyacrylonitrile in dimethyl sulfoxide, in which the amount of hydrolysis lignin varies from 70 to 80% (mass), into a precipitation bath distilled water for coagulation of a polymer composite solution in the form of a fiber after additional orientational stretching by 5-10% at the stage of coagulation in precipitation bath provides giving composite fibers of sorption activity, which is optimal ratio GL: PAN 80:20 (Example 3). Sorption characteristics and strength provide composite fibers with a set of properties that enable them to be processed into products capable of retaining the desired structure of the filter surface of the desired shape in the manufacture of filtration units designed to process the sorption of finely dispersed components from various media of natural and technological origin.

Claims (1)

A method of producing a composite fiber based on hydrolytic lignin with polyacrylonitrile obtained by wet molding by pressing through apertures of a spinneret of mixed compositions from solutions of hydrolytic lignin and polyacrylonitrile in dimethyl sulfoxide, in which the amount of hydrolysis lignin is from 70 to 80 wt.%, Into a precipitation bath with distillation water for coagulation of a polymer composite solution in the form of a fiber, followed by carbonization in a stream of nitrogen and chemically activated, different t we note that the composite fiber is subjected to additional orientational stretching by 5-10% at the coagulation stage in a precipitation bath, with the formation of micropores after carbonization with a monodisperse distribution of 3-18 microns with channels having a regular combination of external and closed pores of an elongated shape with expansion from the center fiber to its outer surface and anisotropic orientation along the entire length of the composite fiber.

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