RU2310602C1 - Method of production of the high-structured carbon-mineral composites produced out of the high-ash biomass - Google Patents

Abstract

FIELD: chemical industry; methods of production of the carbon-mineral absorbents.

SUBSTANCE: the invention is pertaining to production of the carbon-mineral absorbents - the high-carbonized amorphous silicon dioxide out of the high-ash lignocellulose raw. The lignocellulose raw is treated either in the solid state, or in suspension, or in the form of solution of the carbonates of the metals of the first (1а) Group of Periodic system, or their combinations in the ratio of 2-15 mole of the carbonate to 1 kg of the source biomass, the optimal version is 5 mole/kg. In case of the solution the produced mixture at first is evaporated at 110-120°C, then any mixture is subjected to the fusion at the temperature of 750-950°C, it is preferential - at 850-900°C or - in the inert medium, or in the reducing medium of the gases of the fusion phase. The produced solid residue at the temperature of 30-60°C solve in the minimum water volume (the mass ratio of the water/alloy = 3-4). The optimal ratio of the water/alloy = 3.3. Through the produced solution gate the gaseous carbon dioxide, or the gases containing the gaseous carbon dioxide, up to pH=8-9. The settled gel is aged within 10-100 hours, the preferable version is 20-30 hours. After washing of the gel SiO₂ with the carbonic particles contained in it is withdrawn, the produced material is dried at the temperature of up to 100°C and incinerated at the temperature of 130-200°C. The invention allows to produce the composite material with the specific surface of up to 700 m²/g using the simple and ecologically safe method.

EFFECT: the invention ensures production of the composite material with the specific surface of till 700 m²/g using the simple and ecologically safe method.

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Description

The invention relates to the production of carbon-mineral sorbents - carburized amorphous silicon dioxide, in particular to the production of biomass from high-ash lignin-cellulose raw materials, for example, crop wastes of highly structured carbon-mineral composites having a high ash content of up to 95%. The invention can find application as sorbents for the purification of liquid and gaseous media from organic substances, compounds of heavy metals, catalysts, reinforcing fillers in tires and rubber products, fillers for textiles, paper, plastic, paints, colored varnishes, in analytical chemistry, raw materials for chemical industry in the synthesis of all silicon compounds (for example, carbide, nitride, chloride, organosilicon), to obtain silicon, silicon ferroalloys, in the aluminum industry, material for growing quartz for radio electronics, in the production of phosphors, quartz glass, refractories, abrasives, foundry molds, sound and heat insulation materials, liquid glass and high-quality concrete for construction, as well as in other fields of science and technology.

Known methods for producing carbon-mineral materials by pyrolysis of hydrocarbons such as naphthalene, branched alkanes on the surface of silicon dioxide (R. Leboda, J. of Thermal Analysis, vol. 32 (1987) 1435-1448). In this case, a crusty coating of silica carbon is achieved.

However, a homogeneous distribution of the two phases and a high affinity of the carbon and silica phases are not ensured. The specific surface of such carbonized silica does not exceed 100 m ² / g.

Known methods for producing carbon-mineral materials, such as activated carbons, which are obtained by activating the action of mineral catalysts introduced into the starting material, for example, Friedel-Crafts catalysts — ZnCl ₂ , AlCl ₃ , H ₃ PO ₄ , or redox catalysts — salts or oxides alkali and alkaline earth metals. (Whitekurst D.D., Mitchell T.O., Farkashi K. Liquefaction of coal. - M .: Mir, 1986, p. 256. US patent 6537947, B01J 020/02, priority 11.04.1997, publ. 25.03.2003 , McKee DW Fuel. - 1983, v. 63, p. 170. US patent 6030922, B01J 020/02, priority 10.07.1998, publ. 02.29.2000). Using these methods, it is possible to obtain activated carbon with an ash content of not more than 10%.

The main disadvantage of the known methods is the inability to obtain carbon-mineral materials having an amorphous distribution of at least two phases and a high ash content of up to 95%. This is primarily due either to the use of low-ash raw materials, or to the features of the method for producing carbon-mineral materials and the use of high oxidation temperatures.

On the other hand, mineral forms are currently the main source of amorphous silicon dioxide. Technological schemes for the production of amorphous silicon dioxide are associated with high costs for the preparation of feedstock to obtain a silicate block. The technology includes the fusion of quartz sand with soda or sodium sulfate with coal at 1400-1500 ° C, grinding silicate blocks, washing with water, boiling in an autoclave with steam for 3-6 hours, clarification by settling a silicate solution to 4 days or by vacuum filtration, adjusting the density of the silicate solution, stabilizing the solution by settling for up to 3 days, as well as the complex procedure of reprecipitation of SiO ₂ , washing, aging and calcination (Enterprise Standard (Dalzavod) STP 23-261-85 "Sodium glass - to Alium liquid. Technological process of preparation and preparation for the batch "Vladivostok, 1985).

The disadvantages of this method are the high energy intensity, the complexity and duration of the process of obtaining precipitated silica, a significant number of the main stages of the main process, the inability to ensure the constancy of the properties of the liquid glass solution, since the silicate block usually has an unstable composition, which leads to incomplete passage of the dissolution process with the formation of a non-solvent residue, reaching 15% by weight of the silicate block. Due to the variability of the composition of liquid glass, it is necessary to adjust the characteristics of liquid glass obtained from a silicate block by mixing different solutions of the previously obtained solutions.

A known method of producing silica from plant materials using the example of rice husks, which is characterized by fine dispersion and an amorphous state, due to which the material is chemically more reactive than crystalline forms such as quartz or cristobalite (Waste Treat. Util. Proc. Int. Symp., 1978 (pub 1979), 363-368). The amorphous form of silicon dioxide easily dissolves when interacting with alkalis with the formation of silicates - "water glass". Under similar conditions, the mineral forms of silicon dioxide (quartz, cristobalite) practically do not dissolve with the formation of silicates, and preliminary intensive dispersion (grinding) is required, which is an undesirable stage due to the high abrasiveness of the starting material. A known method of obtaining silica from rice husk with low carbon content (US Patent No. 4049464, C04B 31/00, priority 02.09.1977, publ. 09.20.1977). The method consists in a two-stage annealing of crushed rice husk in air at temperatures first of 200-450 ° C, and then at 450-1000 ° C. A gray product is obtained with a carbon content of about 2% and an admixture of crystalline phase.

The disadvantage of this method is that the resulting silica has a specific surface area of not higher than 100 m ² / g, low microstructure of the silica phase and low carbon content.

There is a method of obtaining amorphous silicon dioxide and carbon from rice husks by acid etching, washing with a water, drying in a centrifuge, preliminary burning in a closed reactor with exhaust of smoke and trapping of amorphous carbon, grinding and oxidative combustion sequentially in a stream of air and oxygen. Acid etching is carried out with a 0.01-0.1 M solution of sulfuric or hydrochloric acid at 80-90 ° C for 3-4 hours with stirring, washing with hot water for 1-2 hours, followed by drying in a centrifuge at 105-120 ° FROM. Preliminary combustion is carried out simultaneously with grinding and stirring at 350-400 ° C with a suction of smoke through a cooled labyrinth filter, where amorphous carbon is precipitated. Oxidative combustion is carried out at 700-780 ° C, first in an air stream until the flame no longer disappears, and then in an oxygen stream for 20-60 minutes with constant stirring (RF Patent No. 2144498, C1 В 33/12, priority 01.02.1999, publ. . 01.20.2000).

As a result, finely divided silica with a purity of 99.979% is formed, and soot - 99.79%. The yield of amorphous carbon does not exceed 3.2% by weight of the original husk. The texture characteristics of the materials obtained are not given.

The disadvantages of this method are the complex technical design of the method, the formation of significant amounts of acidic effluents at the stage of acid leaching and washing, the presence of three stages of firing rice husk, one of which is using oxygen, a low yield of amorphous carbon product (up to 3.2% by weight), low microstructure of the silica phase and the inability to obtain a dual carbon-mineral composite.

A known method of producing silicic acid xerogel by fusion in air at 700-900 ° C of a natural flask with sodium carbonate to form sodium silicate and hydrolysis of the alloy in the presence of 6.0 M hydrochloric acid to obtain a gel, followed by the addition of complexon III solution (RF Patent No. 2230027 , СВВ 33/142, priority 13.03.2003, publ. 06/10/2004). In the absence of any data on the properties of the obtained xerogel and data on the yield of the final product, the proposed method has several disadvantages: the need for fine grinding of abrasive natural flask (up to 50 μm) to ensure a noticeable degree of interaction with sodium carbonate, the use of large excesses of Na ₂ CO ₃ , HCl and complexone III, which will not ultimately lead to a reduction in the cost of the technology as a whole, even taking into account cheap raw materials. In addition, in this way it is impossible to obtain carbon-mineral material.

Closest to the proposed technical solution, which was taken as a prototype, is a method for producing precipitated silica gels containing carbon by leaching alkaline (NaOH) silica phase from the product of thermal pyrolysis of rice husk with the formation of an aqueous solution of alkali metal silicate containing carbon particles. Next, the silicate solution was heated to 50-55 ° C and acidified with a solution of either sulfuric or hydrochloric acid, first, until gel formation at pH = 8-9. After this, acidification was stopped, and the reaction mass aged for half an hour with stirring and 50 ° C. Next, the mixture continued to acidify to pH = 3.4-4.2. The resulting precipitate was separated from the liquid, washed and dried in any way possible. The result is reprecipitated silica containing inclusions of carbon particles with a SiO ₂ / C ratio of 1.2 to 14.7 (by weight). The BET specific surface area of the obtained composites varies from 155 to 267 m ² / g, and the sorption capacity for dibutyl phthalate is from 129 to 223 ml / 100 g (US 6375735, 2002).

The disadvantage of this method is the complex technical design of the method, the use of relatively expensive and dangerous reagents (NaOH, mineral acids), the formation of significant amounts of liquid waste, such as solutions of Na ₂ SO ₄ , NaCl, Na ₂ PO ₄ , and the failure to achieve high texture characteristics of the materials obtained .

The authors were tasked with developing a simpler, cheaper, and environmentally friendly method for producing a highly structured twin carbon-mineral material with a highly structured silicon dioxide phase (the size of primary SiO ₂ globules is less than 20 nm), high coalescence of the carbon and silica phases, and a wide ash range (from 35 to 95%), with a specific surface area of up to 700 m ² / g from high-ash lignocellulosic biomass waste, including crop waste (husk of rice, oats, wheat straw and other zl ak).

The problem is solved in that in a method for producing highly structured carbon-mineral composites from high-ash biomass, including the use of lignocellulosic material selected from the group of rice husks or oats, or wheat straw, obtaining a mixture of carbon and alkali metal silicate, reprecipitation with an acidifying agent, xerogel aging, filtering, washing and drying, obtaining a mixture of carbon and alkali metal silicate is carried out by treating the biomass with alkali metal carbonates followed by alloying leniem at 750-950 ° C in an inert or reducing atmosphere and further dissolving the solid residue, is carried out either reprecipitation with carbon dioxide or a gas containing carbon dioxide. In this case, the processing of lignocellulosic material with alkali metal carbonates is carried out either by impregnating the lignocellulosic material with carbonate solutions, followed by drying, or by mechanical mixing, or by spraying a solution, or a suspension of carbonate with simultaneous or subsequent drying. Heat treatment with alkali metal carbonates is performed at a ratio of 2-15 mol of carbonate per 1 kg of high-ash biomass in an oxygen-free atmosphere for 0.5-5 hours.

The use of carbon dioxide or gases containing carbon dioxide as an acidifying agent makes it possible to simplify and reduce the cost of the procedure for producing carbon-mineral materials by implementing the recycling of alkali metal carbonates and, in part, carbon dioxide. The proposed method for producing carbon-mineral composites corresponds not only to a resource-saving, but also an energy-saving principle due to the possibility of using the heat of combustion of gases generated during heat treatment of a mixture of the original lignocellulosic material and alkali metal carbonate in a non-oxidizing atmosphere.

Figure 1 presents a block diagram of a process for producing a highly structured carbon-mineral material.

Figure 2 presents a snapshot of high resolution electron microscopy (TEM) of the obtained carbon-mineral material, explaining the structure of the obtained carbon materials. It can be seen from the TEM image that the carbon and mineral (silicon dioxide) phases are in a dispersed amorphous state, which in turn ensures their high degree of interaction. In addition, fragments of the direct interaction of the carbon and silica phases are present in the carbon-mineral material.

The inventive method is carried out by two-stage processing of lignocellulosic raw materials (Fig. 1), including treatment with metal compounds of either the first (Ia) or second (IIa) groups of the Periodic system, or a combination thereof, heat treatment in an oxygen-free atmosphere and reprecipitation of the silicon dioxide phase through acidification of the solution or carbon dioxide, or gases containing carbon dioxide, followed by drying and calcination.

The initial biomass, if necessary, is ground to a size of 0.5-2 mm

Lignocellulosic raw materials are processed either in the solid state, or in suspension, or in the form of a solution of carbonates of metals of the first (Ia) group of the Periodic System, or by their combination in the ratio of 2-15 mol of carbonate to 1 kg of the initial biomass, optimally 5 mol / kg. In the case of a solution, the resulting mixture is first evaporated at 110-120 ° C, then any mixture is subjected to fusion at a temperature of 750-950 ° C, preferably at 850-900 ° C, either in an inert atmosphere or in the atmosphere of gases formed during the heat treatment of lignocellulosic raw materials with metal carbonates of the first (Ia) group.

The resulting solid residue at a temperature of 30-60 ° C is dissolved in a minimum volume of water (weight ratio water / spav = 3-4). The optimum ratio of water / alloy = 3.3. Carbon dioxide is either passed through the resulting solution, or gases containing carbon dioxide, to pH = 8-9. The precipitated gel is aged within 10-100 hours, preferably 20-30 hours. After washing the SiO ₂ gel with the carbon particles contained in it, the resulting material is dried at a temperature of up to 100 ° C and calcined at 130-200 ° C.

The resulting product is a carbon-mineral composite with an ash content in a wide range from 35% to 95%, specific surface area up to 750 m ² / g, size of primary SiO ₂ globules _of 5-15 nm and high coalescence of the carbon and silica phases. The degree of leaching of the mineral part from the carbon matrix at the fusion stage is 95-99%. The SiO ₂ content in the samples is characterized by ash values, the carbon content is defined as 100% -% ash content. The total content of other elements does not exceed 0.5% weight.

The inventive method is characterized by a simpler and faster way to obtain a carbon-mineral composite through fusion in an inert or reducing atmosphere of the original high-ash lignocellulosic raw materials with alkali metal carbonates and reprecipitation of the silica phase using carbon dioxide without the use of separate pyrolysis stages, mineral acids and without the formation of significant quantities of liquid waste. Unlike the prototype, the proposed method allows to implement the process as a whole without the formation of liquid waste and in non-volatile and resource-saving mode. The stage of fusion with alkali metal carbonates in an atmosphere of gases - gasification products of the lignocellulosic component of high-ash biomass - allows you to further develop the texture of the carbon phase due to the interaction of carbon with water vapor and carbon dioxide. In this case, alkali metal carbonates also act as catalysts for gasification. Obtained by the proposed method, carbon-mineral composites have a more structured morphology, high values of specific surface area, ash content in a wider range and a homogeneous phase distribution.

Specific surface measurements were performed on an ASAP-2400 (Micrometrics) setup for nitrogen adsorption at 77 K after preliminary training of the samples at 300 ° C and a residual pressure of less than 0.001 mm Hg. until gas evolution ceases without contact with the atmosphere after training. Nitrogen adsorption isotherms were measured in the range of relative pressures from 0.005 to 0.995 atm and their standard processing with calculation of the total surface by the BET method, micropore volume (with a size of less than 2 nm) and the surface of the mesopores remaining after micropore filling (see Gregg S., Sign K ..S.V. Adsorption, specific surface area, porosity (Moscow: Mir, 1984).

Electron microscopic studies of the samples were carried out using a transmission electron microscope JEM-2010 (resolution 0.14 nm).

The invention is illustrated by the following examples.

Example 1

37 g of rice husk (lignin content - 15 wt.%, Cellulose - 31%, ash - 19%) was treated with a solution of Na ₂ CO ₃ with a content of 19 g of Na ₂ CO _{3 in it} . The solution was dried and the resulting residue was heated and alloyed at 900 ° C for 2 hours under a nitrogen atmosphere. The alloy is dissolved in 100 g of H ₂ O at a temperature of 50 ° C. The solution is neutralized with a 2 M hydrochloric acid solution to pH = 7. The resulting gel is aged within 24 hours. The gel is washed with water, dried at 90 ° C and calcined at 150 ° C for 2 hours. The degree of leaching of the mineral part from the carbon matrix at the fusion stage is 98%. The specific surface (S _beats ), pore volume is estimated by nitrogen adsorption by the BET method, and it is 528 m ² / g, total pore volume (V _Σ ) is 0.74 cm ³ / g. The content of SiO ₂ - 67.5%, carbon - 32%, impurities - 0.5%. The average size of the primary globules of SiO ₂ is 8 nm. The yield of the final product for rice husk is - 28%.

Example 2

It differs from Example 1 in that wheat straw is used as the initial lignocellulosic raw material (lignin content - 10 wt.%, Cellulose - 40%, ash - 8%). 35 g of straw are mechanically mixed with 20 g of K ₂ CO ₃ and fusion is carried out at 850 ° C for 1.5 hours. The solution is neutralized with a 3 M sulfuric acid solution to pH = 7. The resulting gel is aged for 30 hours. The degree of leaching of the mineral part from the carbon matrix at the fusion stage is 97%. The specific surface (S _beats ) is 479 m ² / g, the total pore volume (V _Σ ) is 0.98 cm ³ / g. The content of SiO ₂ - 64.7%, carbon - 35%, impurities - 0.3%. The average size of the primary SiO ₂ globules is 5 nm. The yield of the final product is 14%.

Example 3

It differs from example 1 in that oat husk is used as the initial lignocellulosic raw material (lignin content - 12 wt.%, Cellulose - 35%, ash content - 10%). 36 g of oat husk is treated with a suspension of a mixture of 10 g of Na ₂ CO ₃ and 13 g of K ₂ CO ₃ and heated and alloyed at 950 ° C for 1 hour in an argon atmosphere. The degree of leaching of the mineral part from the carbon matrix at the fusion stage is 99.5%. The specific surface area (S _beats ) is 522 m ² / g, the total pore volume (V _Σ ) is 0.74 cm ³ / g. The content of SiO ₂ - 59.6%, carbon - 40%, impurities - 0.4%. The average size of the primary SiO ₂ globules is 9 nm. The yield of the final product is 17%.

Example 4

It differs from example 1 in that the rice husk is heated and fused with 19 g of K ₂ CO ₃ and 6 g of NaOH at 750 ° C for 1.5 hours in an atmosphere of gases - gasification products of the lignocellulosic component of the rice husk. The solution is neutralized by barbation through the solution with carbon dioxide. The resulting gel is aged for 35 hours. The degree of leaching of the mineral part from the carbon matrix at the fusion stage is 99%. The specific surface (S _beats ) is 551 m ² / g, the total pore volume (V _Σ ) is 0.65 cm ³ / g. The content of SiO ₂ - 70.5%, carbon - 29%, impurities - 0.5%. The average size of the primary SiO ₂ globules is 10 nm. The yield of the final product is 26%.

Example 5

Differs from example 4 in that the rice husk is heated and fused with 20 g of Na ₂ CO ₃ for 2 hours in a nitrogen atmosphere. The acidification of the dissolved alloy is carried out by gases formed at the stage of carbonization of lignocellulosic raw materials and oxidized by atmospheric oxygen. The resulting gel is aged for 20 hours. The product is dried at 100 ° C and calcined at 200 ° C for 1.5 hours. The degree of leaching of the mineral part from the carbon matrix at the fusion stage is 98%. The specific surface (S _beats ) is 520 m ² / g, the total pore volume (V _Σ ) is 0.52 cm ³ / g. The content of SiO ₂ - 68.8%, carbon - 31%, impurities - 0.2%. The average size of the primary SiO ₂ globules is 11 nm. The yield of the final product is 29%.

Example 6

It differs from example 5 in that the fusion is carried out at 900 ° C in an atmosphere of gases formed at the stage of heat treatment of lignocellulosic raw materials and partially oxidized by atmospheric oxygen in the recirculation mode. The acidification of the dissolved alloy is carried out with the same gases. The resulting gel is aged for 20 hours. The product is dried at 80 ° C and calcined at 130 ° C for 5 hours. The degree of leaching of the mineral part from the carbon matrix at the fusion stage is 93%. The specific surface (S _beats ) is 650 m ² / g, the total pore volume (V _Σ ) is 0.70 cm ³ / g. The content of SiO ₂ - 81.7%, carbon - 18%, impurities - 0.3%. The average size of the primary SiO ₂ globules is 81 nm. The yield of the final product is 22%.

As can be seen from the above examples, the proposed method allows to obtain from high-ash lignocellulosic material by direct fusion in an inert or reducing atmosphere with carbonates of the first (Ia) group of the Periodic system and reprecipitation of the silica phase of carbon-mineral composites with a high specific surface, ash content in a wide range ( 55-96%), coalescence of the carbon and silica phases and high ordering of the microstructure (primary globule size 5-15 nm). The composite obtained by the proposed method can be widely used as a bifunctional sorbent, a carrier for various types of catalysts, and also as a reinforcing filler for the tire and rubber industry and in other fields.

Claims (4)

1. A method of obtaining a highly structured carbon-mineral composite by processing lignocellulosic raw materials selected from the group of husks of rice or oats, or wheat straw, comprising introducing an alkali metal compound, dissolving, neutralizing the solution to obtain a gel, aging, filtering, washing and drying, characterized in that an alkali metal carbonate is used as the alkali metal compound, which is introduced into the raw material and fused at 750-950 ° C in an inert or reducing atmosphere, while neutralization of the solution to obtain a gel is carried out with carbon dioxide. 2. The method according to claim 1, characterized in that the alkali metal carbonate is introduced into the raw material in the solid state, or in the form of a solution or suspension with drying of the mixture. 3. The method according to claim 1, characterized in that the drying is carried out at a temperature of up to 100 ° C. 4. The method according to claim 1, characterized in that after drying the product is calcined at 130-200 ° C.

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