RU2393990C1 - Method of making activated charcoal - Google Patents

Abstract

FIELD: chemistry. ^ SUBSTANCE: invention relates to production of activated charcoal meant for cleaning gaseous and liquid media. The method involves combined grinding of thermally treated pieces of fruit trees or coconut shells and hard pitch to micropore volume of 0.3-0.5 cm3/g, addition of aqueous potassium hydroxide solution to the ground mixture, moulding granules or tablets from the obtained paste, drying, carbonisation while raising temperature to 500C, activation at 850-900C to total pore volume of 1.3-1.7 cm3/g and washing. ^ EFFECT: invention enables to obtain activated charcoal with high dimethylformamide adsorption capacity and mechanical strength. ^ 2 cl, 3 ex, 2 tbl

Description

The invention relates to the field of production of activated carbon and can be used to clean gas and liquid media from toxic substances.

A known method of producing activated carbon, including co-grinding a mixture of coal and solid pitch, forming a crushed mixture, carbonization in the temperature range from room temperature to 550-650 ° C with a rate of rise of 20-25 ° C / min and activation of water vapor in the medium at 870-900 ° C (see RF patent No. 2184080 of 05/21/2001, application No. 20011113848, CL. C01B, 31/08).

The disadvantage of this method is the low micropore volume of the obtained coal and, as a consequence, the low adsorption activity of dimethylformamide (DMF) in the purification of industrial exhaust gases and vapors.

The closest to the proposed technical essence and the achieved result is a method for producing activated carbon, including co-grinding a composition of carbon-containing (coal grade "CC") raw materials and solid pitch, introducing an aqueous solution of potassium hydroxide (KOH) into the crushed composition, molding the resulting paste into granules, tablets, balls, etc., carbonization in the temperature range from room temperature to 450-500 ° C with a rate of temperature rise of 10-15 ° C / min, carbonization activation at a temperature of 850-900 ° C (see RF patent No. 2344075 dated November 9, 2007, Cl. C01B, 31/08, application No. 2007141272/15).

The disadvantage of this method is the low adsorption activity on dimethylformamide (DMF), as well as the low mechanical strength of the obtained coal.

The task of the invention is to increase the adsorption activity of coal on DMF by increasing the volume of micropores, as well as increasing their mechanical strength.

The problem is solved by the proposed method, including co-grinding thermally processed to a micropore volume of 0.3 to 0.5 cm ³ / g of fruit tree seeds or coconut shells and solid pitch, introducing an aqueous solution of potassium hydroxide into the crushed mixture, molding granules from the resulting paste or tablets, their drying, carbonization in the temperature range from room temperature to 500 ° C with a heating rate of 1-6 ° C / min, activation at a temperature of 850-900 ° C to a total pore volume of 1.3-1.7 cm ³ / g, and after activation, coal is washed up to a pH of 6.5-7.0.

The difference of the proposed method from the known one is that carbon-containing raw materials are used that are thermally processed to a micropore volume of 0.3-0.5 cm ³ / g of fruit tree bones or coconut shells, carbonization is carried out at a heating rate of 1-6 ° C / min, and after activation to a total pore volume of 1.3-1.7 cm ³ / g, coal is washed to a pH of 6.5-7.0.

An analysis of patent and scientific literature shows that the proposed method for producing active carbons is new.

Activated carbon obtained by the proposed method allows you to remove dimethylformamide - a highly toxic solvent that poses a great danger to the respiratory system, which has rather large molecules (CH ₃ ) ₂ NCHO and is the most difficult component to remove toxic emissions from chemical industries.

The resulting activated carbon is characterized by a developed volume of micropores with a size of 1.0-1.6 nm, which, according to the classification of ac. M.M.Dubinina are supermicropores.

Our further experiments found that it is possible to improve the porous structure in the direction of development of larger pores, and therefore to increase the adsorption activity by DMF, using heat-treated products of stone raw materials with a developed micropore volume of 0.3 to 0.5 cm ³ / g, which makes it possible, upon further activation, not only to increase the micropore volume, but also their size.

However, positive results were achieved only if slow carbonization was carried out with a temperature rise rate of 1-6 ° C / min.

Another important factor in solving the problem of the invention is, firstly, carrying out deep activation to a total pore volume of 1.3-1.7 cm ³ / g, which, as it turned out, made it possible to obtain a volume ratio of micropores and supermicropores of 1: 3 ± 0 , 1, and secondly, the implementation of an additional operation - washing the finished coal from potassium ions. Washes, mainly from potassium ions, lead to a pH of 6.5-7.0, which corresponds to a degree of washing of 95-98%.

The method is as follows.

Carbonized (i.e. heat-treated, carbonized) fruit tree bones are taken, having a developed micropore volume of 0.3 to 0.5 cm ³ / g with an ash content of 2-4%, mixed with solid pitch in a ratio of 3 ± 0.5 :one. The resulting mixture is ground in a ball, disk or vibratory mill to a grinding fineness of less than 90 microns. Then, a solution of potassium hydroxide (40-50% wt.) Is added to the coal-pitch composition. The paste is mixed for 20-25 minutes and then molded on screw granulators or other types of presses into granules, balls, tablets, etc. at a specific pressure of 100-130 kg / cm ² . The resulting product is dried to a residual moisture content of 1-5%. The dried product is placed in an oven and heated from room temperature (25 ° C) to 500 ° C at a heating rate of 1-6 ° C / min. The discharged carbonizate is placed in a rotary kiln and activated at 850-900 ° C to a total pore volume of 1.3-1.7 cm ³ / g. In this case, the burning is from 60 to 70%, which makes it possible to achieve a ratio of the volume of micropores proper to supermicropores 1: 3 ± 0.1. Then the product is washed with distilled water to a pH of 6.5-7.0, which corresponds to a degree of washing of 95-98%. The following examples illustrate the invention.

Example 1. Take 3.0 kg of heat-treated peach seeds with a micropore volume of 0.3 cm ³ / g and an ash content of 2% and mix them with solid pitch - 1.0 kg. The resulting mixture is ground in a vibratory mill to dispersion - the residue on the grid of 90 microns is not more than 1%. Then, potassium hydroxide solution is added to the resulting mixture. The resulting paste is mixed for 20 minutes, then molded into granules on a screw press at a specific pressure of 100-130 kg / cm ² , after which the obtained granules are dried to a residual moisture content of 1%, then placed in an oven and subjected to heating at a rate of temperature rise of 1 ° C / min 25 to 500 ° C. The carbonizate discharged after 500 ° C is placed in a furnace and activated at 900 ° C to a total pore volume of 1.3 cm ³ / g; water vapor is used as an activator.

The volume of supermicropores is 0.70 cm ³ / g. Then the coal is unloaded and washed with water (preferably distilled) to a residual content of potassium ions of 0.1-0.2%. The degree of washing is equal to 95%, which is controlled by the determination of the PH, which in this case is 6.5-7.0.

Coal is unloaded and analyzed.

The DMF adsorption capacity of coal is 190 mg / g, and the mechanical strength is 92.5%.

Example 2. Analogously to example 1, except that the heat-treated bone or shell (carbonizate) is taken with a micropore volume of 0.4 cm ³ / g, carbonization is carried out with a temperature rise rate of 3.5 ° C per minute, and activation is carried out up to a total pore volume of 1.5 cm ³ / g. The obtained coal is washed to PH = 6.9, which corresponds to a degree of washing of 96%.

The adsorption activity on dimethylformamide in this case is 210 mg / g, and the mechanical strength is 87.0%.

Example 3. Analogously to example 1 except that they take a carbonizate with a micropore volume of 0.5 cm ³ / g, and subsequent carbonization is carried out at a rate of temperature rise of 6 ° C / min. The product is activated to a total pore volume of 1.7 cm ³ / g. Coal is washed to a pH of 7.0, which corresponds to a degree of washing of 98%.

The adsorption activity of dimethylformamide is 240 mg / g, and the mechanical strength is 87%.

Note

Adsorption capacity was determined by the weight gain of coal:

- the concentration of the gas stream was 0.5 mg / g;

- gas flow rate - 0.2 l / min × cm ² ;

- layer temperature - 25 ± 1 ° C;

- layer height - 3.5 cm.

The tables show examples 4-15, obtained analogously to example 1.

Table 1 The influence of the initial volume of micropores of stone raw materials on the adsorption activity according to DMF and the strength of activated carbons The volume of micropores of the feedstock, cm ³ / g Adsorption activity for DMF, mg / g Mechanical strength of activated carbons,% 0.2 142 80.1 0.3 190 92.5 0.4 210 87.1 0.5 240 87.5 0.6 150 82.5 0.7 140 80.0 Prototype 140 80.0

As follows from the data of table 1, the maximum activity indicators for dimethylformamide, as well as mechanical strength are achieved in the case of using raw materials with a micropore volume of 0.3-0.5 ³ / g With a decrease in micropore volume in the initial product, the adsorption activity for DMF significantly decreases due to insufficient development of the volumes of supermicropores. A decrease in adsorption activity with an increase in the initial micropore volume is associated with the predominance of small micropore volumes.

In the change in strength, the same patterns are observed. The effect of the rate of temperature rise during carbonization on the quality of the obtained coal-pitch sorbents is presented in table 2.

table 2 The influence of the rate of temperature rise during carbonization on the adsorption activity according to DMF and the strength of activated carbons The rate of temperature rise, ° C / min Adsorption activity for DMF, mg / g Mechanical strength of activated carbons,% 0.5 148 80.1 1,0 200 87.3 3.0 220 87.4 5,0 240 87.5 6.0 240 87.0 7.0 148 80.0

The experiments showed that an increase in the rate of temperature rise during carbonization above 6 ° C / min leads to a deterioration in adsorption activity due to, obviously, the intensive development of ballast transport porosity, and a heating rate of less than 1 ° C / min leads to the predominant development of small micropores, as a result of which for larger molecules decreases (“collapse effect”).

The best adsorption capacity for DMF and the mechanical strength of the obtained coal were achieved by washing to PH = 6.5-7.0. A decrease in the degree of washing to PH = 7.2-7.5 leads to a deterioration of these indicators, probably due to the blocking of micropore particles with tiny particles of potassium. Increasing the degree of washing to PH = 6.3-6.5 does not lead to an improvement in quality indicators, but is technically difficult to implement, which seems to us inappropriate.

In addition, it was experimentally proved that a change in the total pore volume upon activation significantly affects the adsorption and mechanical properties of the resulting activated carbons. The best results are observed in the range of the total pore volume of 1.3-1.7 cm ³ / g. When the total pore volume leaves this range, the adsorption capacity of activated carbon for DMF drops sharply.

Thus, the proposed method allows to obtain activated carbon with high adsorption capacity for DMF and mechanical strength.

From the foregoing, it follows that each of the signs of the claimed combination to a greater or lesser extent affects the solution of the problem, and the entire population is sufficient to characterize the claimed technical solution.

Claims (2)

1. A method of producing activated carbon, including grinding a mixture of carbon-containing raw materials with solid pitch, introducing an aqueous solution of potassium hydroxide into it, molding granules or tablets from the resulting paste, drying, carbonizing in the temperature range from room temperature to 500 ° C and subsequent activation at a temperature of 850 -900 ° C, characterized in that as the carbonaceous raw material is heat-treated to micropore volume of 0.3-0.5 cm ³ / g bone fruit trees or coconut husks, milled mixture was subjected to mass the ratio of said carbonaceous feedstock to a pitch equal to (2.5-3.5): 1, the carbonization is carried out at a heating rate of 1-6 ° C / min and the charcoal is washed after activation to pH 6.5-7.0. 2. The method according to claim 1, characterized in that the activation is carried out to a total pore volume of 1.3-1.7 cm ³ / g.