FR2825356A1 - ACTIVE CARBON-BASED AGGLOMERS THEIR PREPARATION PROCESS AND THEIR USES - Google Patents

Abstract

The invention concerns an active carbon agglomerate based on coal derived from vegetable matter and tar-based binder. The invention is characterised in that it has a sulphur content not more than 500 ppm, a packing density ranging between 0.3 and 0.6 g/cm<3>, a benzene index ranging between 25 and 30, a crush resistance >/= 2 kg, an ASTM D4058-96 standard attrition strength </= 10 %, and an average particle-size distribution ranging between 0.5 and 10 mm. The invention also concerns the method for preparing said agglomerate. The invention is for use in catalysis as catalyst or catalyst support and in liquid-phase or gas-phase adsorption processes.

Description

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ACTIVE CARBON-BASED AGGLOMERS THEIR PROCESS FOR
PREPARATION AND THEIR USES
The invention relates to the field of activated carbons and more particularly of activated carbons agglomerated with a binder.

Activated carbons are products resulting from the carbonization of various carbonaceous materials, such as plant materials (wood, fruit shells), mineral materials (coal), synthetic materials (polymers), which have undergone an activation treatment which gives them high porosity and high adsorbing power. These adsorbent properties have long been exploited for the treatment, separation and purification of gases as well as for the decolorization, purification and deodorization of liquids.

When the activated carbon is brought into contact with gases, for example in an adsorbent bed, too fine grain sizes are avoided, the pressure drop of which is too high and which increases the risk of the equipment becoming clogged.

One method of preparing agglomerated activated carbon consists of mixing a finely divided solid hydrocarbon material with a hydrocarbon binder, agglomerating the mixture by compaction or extrusion in the form of grains of the desired size. The agglomerated products are then carbonized at a temperature of 400 to 700 C and then activated by partial gasification in an oxidizing atmosphere (water vapor and / or C02) at a temperature of 700 to 1000 C.

The finely divided carbonaceous solid can be coal, peat, peat or lignite or coconut shell coke or charcoal.

In order to make it possible to obtain an agglomerate of useful activated carbon, the hydrocarbon-based binder preferably has the following characteristics: it is not very ashy; - it has agglomerating properties which allow a mechanical resistance to green yarns (resistance to transport, resistance to impact and abrasion) and - it has a good yield of coke in order to ensure a good overall yield of the final product and good mechanical strength, in particular in resistance to crushing.

From FR 2 228 031, parts molded from material containing carbon and a binder based on a phenol and an aldehyde are known.

FR 2 219 114 and FR 2 215 461 describe processes for preparing agglomerates of carbonaceous material using thermosets as binder.

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Although these resins may be suitable, their cost, however, is high.

Finally, application FR 2 780 052 discloses a process for preparing agglomerates of activated carbon using in particular thermosetting and hot-melt binders.

One of the binders meeting these criteria and economically more advantageous is coal tar. However, it is found that the use of these agglomerates of activated carbon in catalysis processes leads to rapid degradation of the catalyst.

The new problem therefore arises of providing agglomerates of activated carbon that are economical and compatible with use in catalysis processes.

3 préférence entre 0, 35 et 0, 45 g/cm3, un indice de benzène compris entre 25 et 50, de préférence compris entre 30 et 45, une résistance à l'écrasement 2 : 2 kg, de préférence 2 : 4 kg, une résistance à l'attrition selon ASTM D4058-96 ; : ; ; 10 %, de préférence 5% et une granulométrie moyenne comprise entre 0,5 à 10mm, de préférence entre 0,8 à 6 mm. The first object of the invention is then aimed at an agglomerate of activated carbon based on carbon of plant material (s) and on a binder based on tar (s), characterized in that it has a lower sulfur content. or equal to 500 ppm, preferably less than or equal to 300 ppm, a packed density of between 0.3 and 0.6 g / cm3, of

3 preferably between 0.35 and 0.45 g / cm3, a benzene number between 25 and 50, preferably between 30 and 45, a crushing strength 2: 2 kg, preferably 2: 4 kg, attrition resistance according to ASTM D4058-96; :; ; 10%, preferably 5% and an average particle size of between 0.5 to 10mm, preferably between 0.8 to 6mm.

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The judicious choice of the binder and of the tar makes it possible to obtain such an agglomerate of activated carbon meeting the severe criteria applied to the activated carbon used in catalysis.

The quality of the tar is indeed an important element. The tar used advantageously has a Dean Stark extract of less than 15%. The Dean Stark extract indicates the water-soluble content by azeotropic entrainment with toluene. Preferably, it has a Dean Stark extract of less than 10% and in particular of less than 5%. The sulfur content of the tar used alone or as a mixture is less than 500 ppm, advantageously less than 300 ppm and in particular less than 100 ppm.

The charcoal of vegetable material (s) is charcoal obtained from vegetable material, such as, for example, wood or fruit shells such as coconut shells.

faible teneur en soufre. On choisira de préférence le charbon de bois. Celui-ci peut être obtenu par exemple par carbonisation de bois à une température de 600 à 700 C The charcoal of plant material (s) preferably also has a

low sulfur content. We will preferably choose charcoal. This can be obtained for example by carbonization of wood at a temperature of 600 to 700 C

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under conventional conditions. Then the charcoal is ground, preferably to a diameter d50 of about 20 µ. mr.

The agglomerate can also include a curing and / or activating additive. Such curing and activating additives are, for example, K2CO3 or phosphoric acid. These additives make it possible to obtain a hardening of the agglomerates on leaving the press or the extruder and thus make them easier to handle. Furthermore, they have an activating effect insofar as they accelerate the kinetics of gasification. Finally, they make it possible to orient the spectrum of the sizes of the pores towards a microporosity, namely a pore diameter of less than 2 nm. Depending on the application, one or the other of the two additives will be chosen, in particular according to the undesirable impurities (potassium or phosphorus).

The agglomerate is in particular in the form of a yarn.

The preparation process
The second object of the invention is a process for preparing such an agglomerate. It comprises the steps of: (a) mixing of charcoal of plant material (s) with tar or a mixture of tars having a Dean Stark extract of less than 15% and a sulfur content of less than or equal to 500 ppm and where appropriate with the curing and / or activating additives; (b) shaping the mixture resulting from (a); (c) carbonization of the agglomerate resulting from (b); and (d) activating the carbonized agglomerate from (c).

According to one embodiment, the charcoal of plant material (s) has a diameter dso of between 15 and 30 µ. mr.

Advantageously, the charcoal of vegetable material (s) is charcoal.

The tar or mixture of tars advantageously has a Dean Stark extract of less than 10%. Preferably, the tar or the mixture of tars has a sulfur content of less than or equal to 300 ppm, preferably less than or equal to 100 ppm.

Preferably, the kneaded mixture comprises 100 parts by weight of charcoal of plant material (s) and 50 to 70 parts by weight of tar. The mixture to be kneaded may further comprise up to 6 parts by weight of hardening and / or activating additive (s) per 100 parts of carbon of plant material (s). A mixing of one hour will generally be sufficient.

The operation of shaping the mixture of charcoal and kneaded wood tar is also called spinning. It can be produced by extrusion, molding or compacting, for example by means of devices such as a

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roller press, screw extruder, piston press, press mold or any other device allowing such shaping. The average diameter of the agglomerates is typically between 0.5 and 10 mm. The agglomerates are preferably in the form of yarns with a diameter generally between 0.8 and 6 mm and preferably between 1 and 5 mm.

The step of carbonization of the agglomerates is preferably carried out at approximately 700 ° C., for example by combustion fumes. This step eliminates the volatiles contained in the tar and condenses the residue. It also has the advantage of hardening agglomerates.

Finally, the carbonized agglomerates are activated, preferably by heat treatment at 900 to 1000 C in the presence of water vapor and / or carbon dioxide.

Uses
Owing to their particular properties, these agglomerates can be used with advantage in catalytic processes, for example as a catalyst or as a catalyst support.

The agglomerates according to the invention can also serve as adsorbents to separate the components of a mixture comprising at least two different compounds in an adsorption process comprising the following steps: - bringing the mixture into contact with the agglomerate under conditions allowing preferential adsorption of certain compounds of the mixture; - Separation of the agglomerate and of the compounds adsorbed by the latter from the mixture thus depleted in preferentially adsorbed compounds; and - regeneration of the agglomerate by desorption of the adsorbed compounds.

Such a method can operate, for example, cyclically.

Another object of the invention relates to uses of the agglomerates described in the adsorption processes. The agglomerates described can in particular be used in liquid phase adsorption processes, in particular water, such as the purification of chemical compounds resulting from synthesis reactions and polluted by by-products or else purification and / or water pollution control. The agglomerates described can also be used in gas phase adsorption processes, such as the depollution of air containing gaseous organic compounds.

However, these agglomerates are also useful for conventional activated carbon applications.

The invention is described in more detail in the examples which follow.

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EXAMPLES
Example 1
60 kg of pulverized charcoal (dso approximately 20 dm) are mixed with 37 kg of wood tar and then 2.5 kg of a 75% H3PO4 solution are added. After one hour of mixing, the mixture is extruded into agglomerates with a diameter of 3mm with a roller press. The agglomerates obtained are then carbonized at 650 ° C. and finally activated in the presence of water vapor and CO2 at 900 to 1000 ° C.

Example 2
60 kg of pulverized charcoal (about 20 film) is mixed with 37 kg of wood tar and then 4 kg of a solution of K2CO3 at 45% by weight is added.

After one hour of mixing, the mixture is extruded into agglomerates with a diameter of 3mm with a roller press. The agglomerates obtained are then carbonized at 650 C and finally activated in the presence of water vapor and CO2 at 900 to 1000 C.

Example 3 (comparison example)
60 kg of pulverized charcoal (around 20 μm) are mixed with 9.5 kg of wood tar and 28 kg of coal tar and then 2.5 kg of a 75% H3PO4 solution are added. After one hour of mixing, the mixture is extruded into agglomerates with a diameter of 3mm with a roller press. The agglomerates obtained are then carbonized at 650 ° C. and finally activated in the presence of water vapor and CO2 at 900 to 1000 ° C.

The activated carbons obtained are characterized by their packed density according to the following procedure. A 250ml graduated cylinder is installed on a tamping device comprising a fixed base which carries 6 rollers. The product is then poured slowly into the test tube, so that the product reaches approximately the 200 ml graduation. On this base rests a movable steel plate with 6 saw teeth horizontally. This plate, while being able to move vertically by sliding on an axis, receives a rotational movement of a worm, coupled to an electric motor at a rate of 30 rpm. By turning on itself, the movable plate (by means of the ramps of its saw teeth raised by the rollers) is subjected to a series of climbs, followed by sudden drops from 4 1 mm in height. These drops cause a series of vertical shocks which are transmitted to the graduated cylinder. After 10 minutes of operation of the machine, the mass of packed product is weighed and the density is calculated.

The benzene number is determined by measuring the weight of benzene adsorbed to saturation at 20 ° C. per 100 g of dry activated carbon crossed by a stream of dry air containing benzene vapors at a partial pressure of 0.1.

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Attrition is used to determine the propensity of agglomerated products to produce fines during transportation, handling and use. It is measured according to the ASTM D4058-96 standard.

The crushing resistance is measured using an IndelcoChatillon type device (ADS / 801) fitted with a TCM 200 support and a DFGS 50 dynamometer, the descent speed of which is set at 23 mm / min. . The breaking load (expressed in kg) of an agglomerated product subjected to increasing pressure is measured. The mechanical resistance to crushing R is defined by the arithmetic mean of 25 measurements.

The sulfur content of the samples is determined from the analysis of S02 (by UV fluorescence) emitted by combustion / oxidation of the sample at 1000 C., The phosphorus and potassium contents of the samples are determined after complete mineralization and ICP analysis.

The results are collated in Table 1.

It is noted that the agglomerates of activated carbon according to the invention have, for equal or even higher quality, a considerably reduced sulfur content which allows their use in applications sensitive to the presence of sulfur such as catalysis.

Table 1

<tb>
<tb> Example <SEP> 1 <SEP> Example <SEP> 2 <SEP> Example <SEP> 3
<tb> Adsorption <SEP> of <SEP> benzene <SEP> [%] <SEP> 37 <SEP> 33 <SEP> 35
<tb> Density <SEP> packed <SEP> [g / cm] <SEP> 0.43 <SEP> 0.45 <SEP> 0.45
<tb> Attrition <SEP> ASTM <SEP> D4058-96 <SEP> [%] <SEP> 1.5 <SEP> 1 <SEP> 2
<tb> Resistance <SEP> to <SEP> crushing <SEP> [kg] <SEP> 6 <SEP> 7 <SEP> 7
<tb> S <SEP> [ppm] <SEP> 250 <SEP> 100 <SEP> 1500
<tb> P <SEP> [ppm] <SEP> 15000 <SEP> 400 <SEP> 15000
<tb> K <SEP> [ppm] <SEP> 4700 <SEP> 25000 <SEP> 4000
<tb>

Claims (4)

CLAIMS 1. Agglomerate of activated carbon based on carbon of plant material (s) and tar-based binder (s), characterized in that it has a sulfur content of less than or equal to 500 ppm, a packed density between 0.3 3 and 0.6 g / cm3, a benzene number between 25 and 50, a crush resistance 2 kg, an attrition resistance according to ASTM D4058-96 10% and an average particle size between 0.5 to 10 mm. 2. Agglomerate according to claim 1 having a sulfur content of less than or equal to 300 ppm. 3. Agglomerate according to claim 1 or 2 having a packed density

3 between 0.35 and 0.45 g / cm3. 4. Agglomerate according to one of claims 1 to 3 having a benzene number of between 30 and 45. 5. Agglomerate according to one of claims 1 to 4 having a crushing strength greater than or equal to 4 kg. 6. Agglomerate according to one of claims 1 to 5 having an attrition resistance according to ASTM D4058-96 less than or equal to 5%. 7. Agglomerate according to one of claims 1 to 6 having an average particle size between 0.8 to 6 mm. 8. Agglomerate according to one of claims 1 to 7 further comprising at least one curing and / or activating additive. 9. Agglomerate according to one of claims 1 to 8, wherein at least one of the curing and / or activating additives is K2CO3 or phosphoric acid. 10. Agglomerate according to one of claims 1 to 9, wherein the charcoal of vegetable material is charcoal. 11. Agglomerate according to one of claims 1 to 10 in the form of a yarn. <Desc / Clms Page number 8> 12. A process for preparing an agglomerate according to one of the preceding claims, comprising the steps of: (a) mixing the charcoal of plant material (s) with tar or a mixture of tars having a Dean extract. Stark less than 15% and a sulfur content less than or equal to 500 ppm and where appropriate with curing and / or activating additives; (b) shaping the mixture resulting from step (a); (c) carbonization of the agglomerate resulting from step (b); and (d) activating the carbonized agglomerate resulting from step (c). 13. The method of claim 12, wherein the charcoal of plant material (s) has a diameter d 50 of between 15 and 30 film. 14. The method of claim 12 or 13, wherein the charcoal of plant material (s) is charcoal. 15. Method according to one of claims 12 to 14, wherein the tar or the mixture of tars has a Dean Stark extract of less than 10%. 16. Method according to one of claims 12 to 15, wherein the tar or the mixture of tars has a sulfur content of less than or equal to 300 ppm and preferably less than or equal to 100 ppm. 17. Method according to one of claims 12 to 16, wherein 100 parts by weight of charcoal of plant material (s) are mixed with 50 to 70 parts by weight of tar. 18. Method according to one of claims 12 to 17, wherein the mixture to be kneaded comprises up to 6 parts by weight of additive (s) for hardening and / or activation per 100 parts of carbon material (s). ) vegetable (s) 19. Method according to one of claims 12 to 18 wherein the shaping is carried out by extrusion, molding or compacting. 20. Use of the agglomerate according to claims 1 to 11 in catalysis as a catalyst. <Desc / Clms Page number 9> 21. Use of the agglomerate according to claims 1 to 11 in catalysis as a catalyst support. 22. Use of the agglomerate according to claims 1 to 11 in liquid phase adsorption processes. 23. Use of the agglomerate according to claims 1 to 11 in gas phase adsorption processes.