RU2578147C1 - Method of producing carbon molecular sieve - Google Patents

Abstract

FIELD: chemistry.

SUBSTANCE: invention relates to production of carbon sorbents with molecular sieve properties. Method involves fine grinding of hard coal of grade SSOM or SSPK. Obtained dust is mixed with coal-tar resin, containing coke in amount of not less than 15 %, and potash. Composition is moulded, followed by drying, carbonisation, devolatilisation and activation. Carbonisation is conducted at a temperature of 450-500 °C with heating rate of not more than 5 °C per minute. Activation is carried out at 900 °C to ablation in range of 5-10 %.

EFFECT: invention provides a sorbent suitable for separation of molecules in gaseous media.

1 cl, 3 tbl

Description

The invention relates to the field of production of carbon sorbents with molecular sieve properties, which can be used for fine separation of vapor-air mixtures.

The term "molecular sieve" implies the presence of very narrow pores in it. Based on molecular sieves, processes of separation of molecules by critical sizes, purification and drying of gaseous media, obtaining substances of high purity, short-cycle, non-heating adsorption are realized. Synthetic zeolites are widely used as molecular sieves, but they have a number of serious drawbacks:

- poisoning by H ₂ O vapors, practically excluding their use in wet conditions;

- high catalytic activity in relation to organic compounds.

To eliminate these disadvantages allow carbon molecular sieves.

There are three main methods for processing carbon raw materials into carbon molecular sieves (UMS).

The first one uses industrial activated carbons as raw materials, which are subjected to mechanical grinding to suppress transport porosity (macroporosity), followed by secondary molding and heat treatment to create a polymer shell granule with a given permeability on the outer surface.

The second one uses raw materials of uniform composition, molecular and spatial structure - synthetic polymers, heat treatment and further activation of soft oxidizing agents which ensures the formation of a developed homogeneous microporous structure with fixed availability for molecules with different critical sizes.

The third - uses charcoal or fossil fuels, which are crushed, mixed with a binder, molded, and then subjected to carbonization or de-volatilization.

A known method of producing a carbon molecular sieve according to the patent of the Russian Federation No. 2467793 (publ. 11/27/2012), in which the crushed source of charcoal is mixed with medium-temperature coal tar pitch. The cooled mixture is further crushed. The lignosulfonate solution and oleic acid are successively added to the resulting mixture. Mixed. The resulting mass is forced through dies. The granules are dried and then carbonized.

The disadvantage of this invention is that the use of highly porous charcoal as a starting material (base) does not allow ultrathin pores to be obtained during carbonization, on the sorption processes of which the molecular sieve effect is based. In addition, the use of charcoal as a basis does not provide sufficient strength UMS.

Fossil fossil fuels are known to have significantly lower initial porosity and pore size compared to charcoal. The initial size of the inner pores of coal is so small that their inner surface is practically inaccessible to adsorbed molecules.

A known method of producing activated carbon with molecular sieve properties according to the United States patent No. 3955944 (publ. 08/08/1974).

The method according to patent No. 3955944 includes grinding the carbon material to obtain a particle size passing through a 325 mesh sieve in an amount of at least 65%, mixing the resulting dust with 5-15% by weight of the ground binder, agglomeration or pressing into molds, which, in turn, crush, and the resulting product is sifted. This pre-treatment provides a more rational basis for comparison with non-agglomerated coal.

Then the molded product is treated with air (flow rate 5-8 l / g) at t = 300-400 ° C for 120-130 minutes. Further, the oxidized product is maintained at t = 850-960 ° C for 5-20 minutes to completely remove volatiles.

Active carbon should have an iodine number (characterizes the specific surface area) of at least 450 and carbon tetrachloride (characterizes the pore size) of not more than 2.

The disadvantage of this method is the relatively low molecular sieve properties due to the irrational ratio of the iodine number to the adsorption rate of CCl ₄ .

The closest in technical essence and the achieved result is a method for producing activated carbon "Method for the production of molded activated carbon" (according to the application US 20010829917 from 2001.04.11, patent holder Westvaco Corporation [US]), comprising the steps of: mixing and mixing in a mixing device of powdered activated carbon (coal), a polymeric binder (polystyrene resin), a solvent, a modifier substance and a cross-linking material to form a mixed material, mixed material Al includes 2-30% of a polymeric binder, up to 5% of a cross-linking substance for the manufacture of mixed material, potassium carbonate (potash) is used as a catalyst. The method includes mixing the material and drying the molded mixed material at temperatures up to 270 ° C.

The disadvantage of this method is the relatively low molecular sieve properties due to the irrational ratio of the iodine number to the adsorption rate of CCl ₄ .

The proposed method allows to eliminate these disadvantages by processing in rotary kilns non-sintering coal of a high degree of metamorphism, coal tar with a coke content of at least 15% with the addition of potash (K ₂ CO ₃ ). In the present invention, fossilized coal of a high degree of metamorphism is used as the basis of UMC, which is finely ground (to increase the availability of the common surface), mixed with coal tar and K ₂ CO ₃ potash to form a coal tar composition. The latter is forced through dies on an extrusion press. The granules obtained are dried, then carbonized, de-volatilized and activated with a slight excess of superheated steam to small burns.

As fossilized coal of a high degree of metamorphism, non-sintering coal of the SSOM, SSPK brands is taken, which is finely ground to a particle size of less than 0.1 mm, mixed with 29-33% of the mass. coal tar, add potash (K ₂ CO ₃ ) in an amount of 1.5-2% to the original batch, push through dies on an extrusion press. The granules obtained are dried at a temperature of 150-180 ° C, then carbonized at a temperature of 450-500 ° C with a heating rate of not more than 5 ° C per minute, volatilized at 800 ° C and activated in a small excess of steam relative to the activated product, equal to 1 , 1: 1, at 900 ° C until a burn in the range of 5-10% of the mass.

The use of a coal tar with a high coke residue as a binder makes it possible to obtain a homogeneous phase during the preparation of the coal tar composition and molding. A homogenized mixture - coal dust and coal tar, in addition, during the molding process develops significant mechanical strength.

The selected coal tar composition allows one to obtain a homogeneous solid phase with ultrafine pores with a sufficiently high iodine index at relatively low values of the adsorption index CCl ₄ due to the fact that during the heat treatment, coal tar, being a product of coal processing, is able to form a porous structure with pore sizes commensurate with the pores of coal. Carrying out carbonization at a slow heating rate does not allow the formation of undesirable ballast porosity.

During activation, with a small excess of steam until a burn is reached within 5-10%, the accessibility of the inner surface of the pores of pre-treated granules without increasing their size is ensured by the activating agent. Activated carbon is formed with molecular sieve properties for the fine separation of gas mixtures, which include compounds with a relatively close molecular size.

Carrying out gas-vapor activation under the indicated conditions makes it possible to directionally control the development of the specific surface (S _beats ) by increasing the volume of thin pores, while the pore size estimated by CCl ₄ adsorption practically does not change.

Examples of the invention

Non-sintering SSOM or SSPK coal is finely ground to a particle size of less than 0.1 mm, mixed with 29-33% of the mass. heated to a temperature of 40-50 ° C with coal tar with a coke content of at least 15%, it is pressed through dies with a diameter of 2-4 mm on an extrusion press. The obtained granules are dried at a temperature of 150-180 ° C, then they are carbonized at a temperature of 450-500 ° C with a heating rate of not more than 5 ° C per minute, volatilized at 800 ° C and activated with a slight excess of steam at 900 ° C until burning in the range 5-10% of the mass.

The drying, carbonization, de-volatilization and activation processes are carried out in rotary kilns with an average processing time of 40-120 minutes.

Characteristics of intermediates and products at various stages of heat treatment are presented in table 1.

The influence of the heating rate during carbonization on the molecular sieve properties of AC is presented in table 2.

The effect of the ratio “steam: activated product” on the quality of the UMC is presented in table 3.

As can be seen from tables 1-3, the selected method allows to obtain activated carbons with molecular sieve properties - UMS, estimated by the difference in the iodine number (indirect indicator S _beats ) and adsorption by CCl ₄ (indirect indicator of pore size). That is, this method provides the development of the specific surface area of very thin pores for the separation of the constituent molecules of gaseous media according to their critical sizes.

Claims (1)

A method of producing a carbon molecular sieve, including fine grinding of coal, mixing the dust with coal tar with potash to obtain a homogeneous composition, molding the composition by extrusion through dies, drying, carbonization, de-volatilization and activation, characterized in that the fossil coal of the brand is subjected to grinding SSOM or SSPK, mixing is carried out with coal tar with a coke content of at least 15%, 1.5-2% of the mass is added to the coal tar composition. potash, carbonization is carried out at a temperature of 450-500 ° C with a heating rate of not more than 5 ° C per minute, and activation is carried out at 900 ° C with an excess of steam relative to the processed granules, equal to 1.1: 1, to burn within 5 -10% of the mass.