ES2347125B1 - ACTIVATED CARBONS AND THEIR OBTAINING PROCEDURE. - Google Patents

Abstract

Activated carbon and its procedure obtaining.

The present invention describes a process for obtaining an activated carbon comprising the steps of: (i) nut shell pyrolysis; (ii) activation; e (iii) impregnation with triethylene diamine. Activated carbon has some physicochemical, textural and surface chemistry, which make it suitable for effective use as filters in the retention of radioactive isotopes, with retention efficiencies of radioactive methyl iodide up to 98.1% The invention also describes its use for example in nuclear power plants

Description

Activated carbon and its procedure obtaining.

Field of the Invention

The present invention relates to carbons activated suitable for use as filters in the retention of radioactive materials for example in central units nuclear. The invention also relates to a method for their obtaining and their use.

Background of the invention

The use of activated carbons in plants nuclear for the retention of radioactive compounds is well known in the state of the art. Various are known procedures for obtaining them that vary in the starting materials, in the process steps and in the mode to impregnate them. One of the most starting products commonly used in obtaining active carbons is the coconut husk, scarce in countries like Spain, which well need import it or need to acquire activated carbon directly already prepared Activated carbons are products they find application among others in nuclear power plants as a filter for the retention of radioactive compounds in various units.

On the other hand, the nutshell constitutes a by-product of the food industry of countries like Spain, which It is generally a serious problem at the industrial level because of its huge volume In this sense the usual fate of the shells Nut has been its dumping as waste to the environment.

That is why there is a need in the state of technique of having a method of treating these wastes, that is able to eliminate them, while they are revalued, by recovery of value-added products and commercial interest.

It would also be interesting in the state of the technique of having an alternative procedure to obtain active carbons that overcome the disadvantage of activated carbons Current mentioned above.

In the present invention the inventors propose a new procedure to obtain activated carbons that Use nutshell as a starting product.

Brief description of the figures

Figure 1: shows the analysis by absorption of IR of the coals CN / C850 / 120 and CN / V850 / 30.

Description of the invention

Therefore in one aspect the invention relates to a procedure for obtaining activated carbons that Use nutshell as a starting product. This procedure hereinafter method of the invention comprises the following stages:

(i)

nut shell pyrolysis that understands its carbonization;

(ii)

activation of the resulting carbonized from the previous stage;

(iii)

impregnation of the resulting product from the previous stage with triethylenediamine.

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In the pyrolysis stage a amount of nutshell. This stage is carried out in a conventional reactor under an inert atmosphere, for example nitrogen, at temperature generally between 500 and 900ºC and during a time typically between 30 and 90 minutes. In a particular embodiment starts from 20 grams of nutshell and the Carbonization is carried out at 600 ° C for 60 minutes. One time after the carbonization, the inert atmosphere remains until the temperature is reduced to room temperature. The reactor is provided with a heating medium to achieve the temperature of carbonization.

The activation step can be carried out by any conventional method. In it, a quantity of carbonized material is generally placed in a conventional reactor and contacted with an activating agent under an inert atmosphere, for example nitrogen. In a particular embodiment said agent is selected from CO2 and water vapor. Activation is carried out at temperatures between 800-900 ° C, and the conditions depend on the activation agent used. In this sense, CO2 flows between 20 and 20 are used.
50 cm 3 min -1 and activation times between 30 and 240 min; The initial inert gas flow until the desired temperature is reached is stopped and replaced by the CO2 flow. In a particular embodiment, the initial flow is 120 cm 3 min -1. Water vapor can also be used, with flows between 0.11 and 0.25 g min -1 and activation times between 30 and 60 min; in this case the water vapor is added to the inert gas stream. In a particular embodiment CO2 is used, the activation temperature is 850 ° C and is carried out for 120 minutes. In another particular embodiment water vapor is used at 850 ° C for 30 minutes. After activation, the inert atmosphere is maintained while the temperature is reduced again to room temperature.

The impregnation stage of the resulting product of the previous stage is carried out by sublimation with triethylene diamine (TEDA) according to the procedure described in US 5,792,720. This procedure is carried out in an isolated system. from the outside and uses solid state triethylene diamine in a quantity by weight with respect to coal of 5-10%. He procedure comprises sublimating TEDA by direct heating and direct the resulting steam through a bed of coal to impregnate.

Activated carbons obtained through procedure of the invention constitute an additional aspect of the same. These coals have characteristics physicochemical, textural and chemical superficial, which make them suitable for effective use as filters in the retention of radioactive isotopes. In this sense it have determined retention efficiencies of methyl iodide radioactive up to 98.1%. Activated carbons have characterized physically and chemically by various techniques as set out below. It has been seen that its structure is essentially microporous, with a certain presence of macropores and low mesopores to facilitate the admission and transport of methyl iodide towards micropores; have a value of specific surface area (S BET) between 750 and 900 m 2 g -1; a high micropore volume value (V_ {mi}) between 0.40-0.50 cm 3 g -1; as well as a value of (V_ {maP}) moderate between 0.05-0.12 cm3 g <-1> to facilitate diffusion of the adsorbate.

The activated carbons of the present invention find application in several Central filtration systems Nuclear Specifically, these adsorbents are used in the fuel building, hydrogen purge, safeguards building, auxiliary building, purge building, pre-access enclosure and purge of enclosure, requiring all these applications efficiencies of retention less than 97.5%. Therefore, in an additional aspect the The present invention relates to the use of activated carbon obtained according to the method of the invention as a filter to retain a radioactive compound In a particular embodiment said compound It is methyl iodide.

By way of illustration, the following Table shows retention efficiencies required for activated carbons used in different systems of the Nuclear Power Plant of Almaraz

one

Below are examples illustrative of the invention set forth for a better understanding of the invention and in no case should be considered a Limitation of its scope.

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Examples Example 1 Activated carbon preparation procedure 1. Pyrolysis

The basket was introduced, with an initial mass of 20 g walnut shell, in a reactor positioning it in the part top of it. Then the system was turned on heating (20 ° C min -1), and the N2 feed was opened (120 cm 3 min -1). Once the temperature of 600 ° C, the basket was lowered through the reactor until it was made reach the oven and kept 60 minutes at that temperature to carry out the carbonization of the sample. Finished this period of time, the heating system was disconnected and raised the basket to the top of the reactor, keeping the inert atmosphere until room temperature was reached, proceeding to determine the yield of carbonized (24.0%).

2. Activation

A mass of 5 g was introduced into the basket of activation and was deposited at the bottom of the reactor. During the process of heating, N 2 (120 cm 3 min -1) was supplied with in order to maintain an inert atmosphere in the system. One time reached the temperature of 850 ° C, the inert agent stream is replaced by the one of CO2 as activating agent. The conditions employed were: 40 cm 3 min -1 of CO 2, with a time 120 min activation

The activation time is over the system heating was switched off and the activating agent was replaced by N2, which was maintained until the reactor was found at room temperature.

3. Impregnation

Then the impregnation of the solid state triethylenediamine carbon (5-10% in weight with respect to coal) by sublimation. In a particular case from an impregnation at 10% by weight, the starting point was 3.15 g of coal activated was placed on the mesh support mentioned above. In the ceramic crucible was placed 0.35 g of triethylene diamine and proceeded to assemble the aforementioned installation. Then you He connected the heating system. At about 75-100ºC the sublimation of the TEDA began and was maintained for 3 hours approximately until disappearance of TEDA in the crucible. Subsequently the heating system and coal were disconnected impregnated was stored in a dry glass container.

An activated carbon named CN / C850 / 120 (10% TEDA).

Example 2 Activated carbon preparation procedure

The same procedure described in the Example 1 except the activation stage that was performed with steam Water. At this stage once the desired temperature has been reached (850 ° C), the agent was added to the N2 stream. The conditions were: 0.19 g min -1 water vapor, with a activation time of 30 min.

An activated carbon named CN / V850 / 30.

Example 3

The coals obtained in Examples 1 and 2 They were characterized as follows:

Burn-off or conversion of Coal

The degree of burn-off or Carbon conversion was determined from the initial mass of carbonized (m 0 = 5 g) and the mass of activated carbon obtained in The activation process according to:

Burn-off (%) = (m_ {0} - m_ {f}) / m_ {0}

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Physical characterization

3.1. The adsorption of N2 at 77 K, was performed in a semi-automatic AUTOSORB-1 device (Quantachrome) equipped with two stations for degassing at 300ºC for 12 hours and sample analysis. From the data of adsorption of N 2, the model of Brunauer, Emmett and Teller (BET) for the calculation of the specific BET surface (S BET, m 2 g -1); the method of Dubinin-Radushkevich (DR) for the calculation of micropore volume (V mi, cm 3 g -1); he Gregg and Sing procedure for estimating the volume of mesopores (V me, cm 3 g -1); and the method \ bullet_ {s} Sing, for the calculation of the external surface (S_ {EXT}, m 2 g -1). From the values of S_ {BET} and S_ {EXT}, % S_ {INT} value was calculated by approximation (% S_ {INT} = 100 \ cdot (S_ {BET} -S_ {EXT}) / S_ {BET}).

3.2. The adsorption of CO2 at 273 K, was carried carried out in a volumetric adsorption equipment, manual, prior degassing of the sample at 300 ° C for 12 hours. From the experimental data of adsorption of CO2, the micropore volume (W 0, cm 3 g -1) by applying the Dubinin-Radushkevich model. Radio value equivalent pore mean (r e, nm) and characteristic energy (E 0, kJ mol -1) were determined according to the model of Medek.

3.3. Mercury porosimetry was obtained with an AUTOPORE IV 4900 porosimeter (Micromeritics), whose limit of detection is 3 nm. This technique allows volume determination of macropores, V_ {maP}, (as the intrusion volume of corresponding to the pore diameter of 50 nm) and mesopores, V_ {meP}, (as the difference between the intrusion volume at diameter of 3 nm and the previous one).

3.4. Density measurement by displacement of helium was obtained by means of a helium stereopicnometer of Quantachrome The total pore volume (V_ {t}) can be determined by determining the densities of helium (\ rho_ {He}) and mercury (\ rho_ {Hg}). The determination of the density of Hg is performed using the Hg porosimeter mentioned above. The V_ {t} It is determined by the expression:

2

3.5. The study of the characteristics Morphological carbon was performed by microscopy scanning electronics (SEM-EDX), in a microscope variable pressure (Hitachi, model S-3600N). This technique indicates that prepared coals have pores cylindrical

Table 1 shows the properties textures determined from the adsorption data of N 2 at 77 K and CO 2 at 273 K of the coals. In line the properties of the CN / C850 / 120 coal are collected and in the lower than carbon CN / V850 / 30.

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TABLE 1

3

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The following Table 2 shows the Textural properties determined from the analysis of Hg porosimetry and He stereopicnometry.

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TABLE 2

4

Chemical characterization

Infrared spectroscopy was performed by Fourier transform (FT-IR), using a Perkin-Elmer 1720 spectrometer operating in the wave number range between 450 and 4000 cm -1.

Prior to the analysis, pills were prepared using KBr as dispersing agent and binder. To do this mixed the sample to be analyzed (after drying at 110 ° C for 12 h) with KBr, and a mixture with a total mass of 250 mg was obtained, and a Sample ratio: KBr of 1: 450. The mixture was taken to a press Hydraulics (Perkin-Elmer), where a load was applied of 10 t cm -2 for 10 min.

IR absorption analysis (figure 1) shows that the two coals have a similar surface chemistry; with links (O-H) and links carbon-oxygen, mainly, as well as the possible existence of groups of ketones, phenolic or aromatic.

Example 4 Iodine retention efficiency of activated carbons

The activated carbons of Example 3 were previously impregnated. They were then analyzed with regarding the determination of its iodine retention efficiency, which was performed in accordance with ASTM D3803 / 198993.

The conditions used to perform the retention test were those required according to the applications of the coals currently used in the Central Nuclear of Almaraz, these conditions oscillate between temperatures of 30-70ºC and relative humidity of 70-95%

Table 3 shows the efficiency results of retention (%) obtained with the two proposed carbons, and with different amounts of impregnating agent used.

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TABLE 3 Retention efficiencies of 131 ICH 3 of the impregnated coals

5

Impregnation significantly increases the retention efficiency of CH 3 I by promoting adsorption chemistry of this, through alkylation reactions, to give stable quaternary salts. The two proposed coals reach high retention efficiencies, although its behavior suggests a change in the adsorption mechanism of CH 3 I when they are impregnated

Claims (12)

1. Procedure for obtaining a coal activated comprises the following stages:

(i)

nut shell pyrolysis that understands its carbonization;

(ii)

activation of the resulting carbonized from the previous stage;

(iii)

impregnation of the resulting product from the previous stage with triethylenediamine.

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2. Procedure for obtaining a coal activated according to claim 1, wherein the pyrolysis of Nutshell is performed in an inert atmosphere at a temperature between 500-900 ° C for a while between 30-90 min to obtain a carbonized 3. Procedure for obtaining a coal activated according to claim 1 or 2, wherein the activation is starts in an inert atmosphere and the activating agent is selected from CO2 and water vapor. 4. Procedure for obtaining a coal activated according to any one of the claims 1-3, in which the impregnation is carried out by sublimation with an amount of triethylenediamine between 5-10% by weight with respect to coal. 5. Procedure for obtaining a coal activated according to any one of the claims 1-4, in which the activation is carried out with CO2 at 850 ° C for 120 minutes. 6. Procedure for obtaining a coal activated according to any one of the claims 1-4, in which the activation is carried out with steam of water at 850 ° C for 30 minutes. 7. Activated carbon obtainable through method according to any one of the claims previous. 8. Activated carbon according to claim 7, which has a specific surface value, SBET, included between 750 and 900 m 2 g -1; a micropore volume value, V mi, between 0.40 and 0.50 cm 3 g -1; and a macropore volume value, V_ {maP}, between 0.05 and 0.12 cm 3 g -1. 9. Activated carbon according to claim 7 8, which has a retention efficiency of methyl iodide radioactive up to 98.1%. 10. Use of activated carbon according to one of the claims 8-9, as a retention filter of a radioactive compound. 11. Use according to claim 10, wherein The radioactive compound is methyl iodide. 12. Use according to claim 10-11 in a dependency of a nuclear power plant.