Process for limiting the emissions of gases from porous particles

Abstract

A process is disclosed for limiting the emissions of gases from a porous material in the form of particles comprising a porous inorganic support and at least 0.1% by weight of one or more compounds chosen from organic compounds, halogen compounds, boron compounds and phosphorus compounds. The particles are placed in motion within a hot gas stream traversing them, and a liquid composition containing one or more film-forming polymer(s) is sprayed over the moving particles by means of a twin-fluid atomization nozzle, in which the liquid composition is mixed with a pressurized gas, with a relative atomization pressure of greater than or equal to 0.7100.sup.5 Pa, until a protective layer containing the film-forming polymer(s) and exhibiting a mean thickness of less than or equal to 20 m is obtained on the surface of the said particles. A material resulting from this process is also disclosed.

Claims

1. A process for limiting the emissions of gases from a porous material in the form of particles comprising a porous inorganic support and at least 0.1% by weight of one or more compounds chosen from organic compounds, halogen compounds, boron compounds and phosphorus compounds, the process comprising: placing the particles in motion within a hot gas stream traversing the particles; spraying, while the particles are in motion, a liquid composition containing one or more film-forming polymer(s) over the moving particles by means of a twin-fluid atomization nozzle, in which the liquid composition is mixed with a pressurized gas, with a relative atomization pressure of greater than or equal to 0.710.sup.5 Pa to provide particles each having a protective layer containing the film-forming polymer(s), where the relative atomization pressure is the difference in pressure between the pressure of the gas inside the nozzle and atmospheric pressure; where the protective layer is characterized as having a mean thickness of less than or equal to 20 m on the surface of said particles, and where the particles having the protective layer containing the film-forming polymer(s) exhibit decreased emission of gas relative to identical particles without a protective layer containing the film-forming polymer.

2. The process according to claim 1, characterized in that the relative atomization pressure ranges from 0.710.sup.5 to 410.sup.5 Pa.

3. The process according to claim 1, characterized in that the liquid composition is a solution or a dispersion of the film-forming polymer(s) in a solvent.

4. The process according to claim 3, where the liquid composition contains from 0.1 to 50% by weight of film-forming polymer.

5. The process according to claim 1, characterized in that it is carried out in a perforated drum in which the particles are placed in motion, the said perforated drum being continuously traversed by a stream of hot gas.

6. The process according to claim 5, characterized in that it is carried out in a perforated drum operating in continuous mode.

7. The process according to claim 1, characterized in that it is carried out by placing the particles in fluidized bed using the stream of hot gas.

8. The process according to claim 1, characterized in that the stream of gas traversing the particles exhibits a temperature ranging from 30 to 150 C.

9. The process according to claim 1, characterized in that the flow rate of the stream of gas is from 5 to 100 m.sup.3 per hour and per kilogram of catalyst.

10. The process according to claim 1, characterized in that the protective layer comprises from 50 to 100% by weight of one or more film-forming polymer(s).

11. The process according to claim 1, characterized in that the film-forming polymer(s) are chosen from a group consisting of: vinyl alcohol homo- and copolymers; polyethylene glycols; collagen; polyethylene terephthalates (PET); polyethylene naphthalates (PEN); polyamides; polysaccharides; polyvinyl chlorides (PVCs); polyvinylidene chlorides (PVDCs); polyacrylonitriles (PANs); polyacrylate resins; copolymers, at least one of the monomers of which is of acrylate type; and their mixtures.

12. The process according to claim 1, characterized in that the mean thickness of the protective layer ranges from 0.1 to 10 m.

13. The process according to claim 1, characterized in that the total amount of film-forming polymer employed ranges from 0.1 to 4% by weight, with respect to the total weight of the initial particles.

14. The process according to claim 1, characterized in that the porous material in the form of particles is a catalyst comprising a refractory oxide support on which is deposited at least one metal or metal compound.

15. The process according to claim 14, characterized in that the at least one metal or metal compound is chosen from the metals of Group VIII and the metals of Group VIb of the Periodic Table of the Elements and/or at least one inorganic compound of such a metal.

16. The process according to claim 1, characterized in that the porous material in the form of particles is an adsorbent agent in the form of porous particles comprising one or more porous materials chosen from a group consisting of active charcoals, zeolites, aluminas, silica gels and activated clays.

17. The process according to claim 1, where for the porous material in the form of particles comprising at least 0.1% by weight of one or more compounds chosen from organic compounds, halogen compounds, boron compounds and phosphorus compounds, the particles contain one or more organic compounds which comprise from 1 to 15 carbon atoms.

18. The process according to claim 1, characterized in that the organic, halogen, boron and/or phosphorus compounds are present in a total content ranging from 0.1 to 20% by weight, with respect to the total weight of the said particles.

19. A porous material in the form of particles which are covered with a protective layer comprising one or more film-forming polymer(s), the film-forming polymer(s) representing from 0.1 to 4% by weight, with respect to the total weight of the particles, and being chosen from a group consisting of: vinyl alcohol homo- and copolymers; polyethylene glycols; collagen; polyethylene terephthalates; polyethylene naphthalates; polyamides; polysaccharides; polyvinyl chlorides; polyvinylidene chlorides; polyacrylonitriles; polyacrylate resins; copolymers, at least one of the monomers of which is of acrylate type; and their mixtures, where the protective layer is characterized as having a mean thickness of less than or equal to 20 m on the surface of said particles.

20. The porous material according to claim 19, characterized in that the particles exhibit a homogeneity in layer thickness of greater than or equal to 65%.

Description

EXAMPLES

(1) Preparation of the Adsorbent Material A:

(2) Examples 1 to 5 below were carried out starting from an adsorbent material of commercial -alumina type which has a specific surface of 200 m.sup.2/g and which is provided in the form of extrudates of trilobal shape having a number-average diameter of 1.2 mm and with a number-average length of 3.8 mm. In order to simulate the final state of this adsorbent after use in a hydrotreating process, 2 kg of adsorbent were solely impregnated with 160 g of crude gas oil and then treated at 70 C. under a nitrogen stream of 10 m.sup.3/h for 1 h, this second stage being used to mimic an in-situ stripping stage. The adsorbent A is thus obtained.

(3) The analysis of the adsorbent A shows that it contains 6.9% by weight of carbon. The analysis of the VOCs (measurement method described below) shows an emission of 215 ppm of hydrocarbons into the air.

Example 1: (In Accordance with the Invention)

(4) 2 kg of adsorbent A were placed in a completely perforated stainless steel drum having a volume of 18 liters (working volume of 5 l), at a rotational speed of 22 revolutions/minute, completely traversed by a stream of hot air of 150 m.sup.3/h at 90 C. A solution of film-forming polymer is sprayed over the particles using a twin-fluid atomization nozzle, in the way described below. The stream of hot air is produced parallel to the spray jet and in the same direction (downward stream).

(5) A solution of 250 g of polyethylene/polyvinyl alcohol copolymer (sold under the name Exceval by Kuraray) at 8% by weight in water was injected over the adsorbent particles using a twin-fluid atomization nozzle (970/0 S75 model of the Schlick brand, with liquid insert with an internal diameter of 1 mm), with a flow rate of solution of 10 g/min and a relative pressure of compressed air (relative atomization pressure) of 1.210.sup.5 Pa.

(6) The water is continuously evaporated, which results in the formation of a layer of polymer at the surface of the adsorbent particles.

(7) After complete injection of the liquid, the adsorbent is stirred for a further 5 minutes and then cooled to ambient temperature.

(8) The adsorbent B according to the invention, the particles of which are covered with a layer of polyethylene/polyvinyl alcohol copolymer, was thus obtained.

(9) The analysis of the adsorbent B shows that it contains 7.4% by weight of carbon. High definition observation in 200 zoom of 10 grains carried out by scanning electron microscopy has made it possible to measure a homogeneity in layer thickness of 68% (measurement method described below) and also a mean thickness of the layer of 2.5 m. The analysis of the VOCs (measurement method described below) shows an emission of 16 ppm of hydrocarbons into the air.

Example 2: (In Accordance with the Invention)

(10) 2 kg of adsorbent A were placed in a completely perforated stainless steel drum having a volume of 18 liters (working volume of 5 l), at a rotational speed of 22 revolutions/minute, completely traversed by a stream of hot air of 150 m.sup.3/h at 90 C. A solution of film-forming polymer is sprayed over the particles using a twin-fluid atomization nozzle, in the way described below. The stream of hot air is produced parallel to the spray jet and in the same direction (downward stream).

(11) A solution of 250 g of polyethylene/polyvinyl alcohol copolymer (sold under the name Exceval by Kuraray) at 8% by weight in water was injected over the adsorbent particles using a twin-fluid atomization nozzle (970/0 S75 model of the Schlick brand, with liquid insert with an internal diameter of 1 mm), with a flow rate of solution of 10 g/min and a relative pressure of compressed air (relative atomization pressure) of 1.610.sup.5 Pa.

(12) The water is continuously evaporated, which results in the formation of a layer of polymer at the surface of the adsorbent particles.

(13) After complete injection of the liquid, the adsorbent is stirred for a further 5 minutes and then cooled to ambient temperature.

(14) The adsorbent C according to the invention, the particles of which are covered with a layer of polyethylene/polyvinyl alcohol copolymer, was thus obtained.

(15) The analysis of the adsorbent C shows that it contains 7.3% by weight of carbon. High definition observation in 200 zoom of 10 grains carried out by scanning electron microscopy has made it possible to measure a homogeneity in layer thickness of 73% (measurement method described below) and also a mean thickness of the layer of 2.5 m. The analysis of the VOCs (measurement method described below) shows an emission of 10 ppm of hydrocarbons into the air.

Example 3: (Comparative)

(16) 2 kg of adsorbent A were placed in a non-perforated stainless steel drum having a volume of 18 liters (working volume of 5 l), at a rotational speed of 22 revolutions/minute, and a stream of hot air of 150 m.sup.3/h at 90 C. is directed onto the surface of the adsorbent bed. The hot air enters via an inlet located within the drum and exits via the opening located in the front of the drum, without traversing the adsorbent bed (seep-flow bed).

(17) A solution of 250 g of polyethylene/polyvinyl alcohol copolymer (sold under the name Exceval by Kuraray) at 8% by weight in water was injected over the adsorbent particles using a twin-fluid atomization nozzle (970/0 S75 model of the Schlick brand, with liquid insert with an internal diameter of 1 mm), with a flow rate of solution of 10 g/min and a relative pressure of compressed air (relative atomization pressure) of 1.210.sup.5 Pa.

(18) The water is continuously evaporated, which results in the formation of a layer of polymer at the surface of the adsorbent particles.

(19) After complete injection of the liquid, the adsorbent is stirred for a further 5 minutes and then cooled to ambient temperature.

(20) The adsorbent D not in accordance with the invention, the particles of which are covered with a layer of polyethylene/polyvinyl alcohol copolymer, was thus obtained.

(21) The analysis of the adsorbent D shows that it contains 7.5% by weight of carbon. High definition observation in 200 zoom of 10 grains carried out by scanning electron microscopy has made it possible to measure a homogeneity in layer thickness of 51% (measurement method described below) and also a mean thickness of the layer of 2.8 m. The analysis of the VOCs (measurement method described below) shows an emission of 42 ppm of hydrocarbons into the air.

Example 4: (Comparative)

(22) 2 kg of adsorbent A were placed in a completely perforated stainless steel drum having a volume of 18 liters (working volume of 5 l), at a rotational speed of 22 revolutions/minute, completely traversed by a stream of hot air of 150 m.sup.3/h at 90 C. A solution of film-forming polymer is sprayed over the particles using a twin-fluid atomization nozzle, in the way described below. The stream of hot air is produced parallel to the spray jet and in the same direction (downward stream).

(23) A solution of 250 g of polyethylene/polyvinyl alcohol copolymer (sold under the name Exceval by Kuraray) at 8% by weight in water was injected over the adsorbent particles using a twin-fluid atomization nozzle (970/0 S75 model of the Schlick brand, with liquid insert with an internal diameter of 1 mm), with a flow rate of solution of 10 g/min and a relative pressure of compressed air (relative atomization pressure) of 0.610.sup.5 Pa.

(24) The water is continuously evaporated, which results in the formation of a layer of polymer at the surface of the adsorbent particles.

(25) After complete injection of the liquid, the adsorbent is stirred for a further 5 minutes and then cooled to ambient temperature.

(26) The adsorbent E not in accordance with the invention, the particles of which are covered with a layer of polyethylene/polyvinyl alcohol copolymer, was thus obtained.

(27) The analysis of the adsorbent E shows that it contains 7.4% by weight of carbon. High definition observation in 200 zoom of 10 grains carried out by scanning electron microscopy has made it possible to measure a homogeneity in layer thickness of 60% (measurement method described below) and also a mean thickness of the layer of 2.6 m. The analysis of the VOCs (measurement method described below) shows an emission of 28 ppm of hydrocarbons into the air.

Example 5: (Comparative)

(28) 2 kg of adsorbent A were placed in a completely perforated stainless steel drum having a volume of 18 liters (working volume of 5 l), at a rotational speed of 22 revolutions/minute, completely traversed by a stream of hot air of 150 m.sup.3/h at 90 C. By way of comparison, water not containing polymer is sprayed over the particles using a twin-fluid atomization nozzle, in the way described below. The stream of hot air is produced parallel to the spray jet and in the same direction (downward stream).

(29) 250 g of water were injected over the adsorbent particles using a twin-fluid atomization nozzle (970/0 S75 model of the Schlick brand, with a liquid insert with an internal diameter of 1 mm), with a flow rate of 10 g/min and a relative pressure of compressed air (relative atomization pressure) of 1.210.sup.5 Pa.

(30) After complete injection of the liquid, the adsorbent is stirred for a further 5 minutes and then cooled to ambient temperature.

(31) The adsorbent F not in accordance with the invention was thus obtained.

(32) The analysis of the adsorbent F shows that it contains 6.7% by weight of carbon. The analysis of the VOCs (measurement method described below) shows an emission of 110 ppm of hydrocarbons into the air.

(33) Examples 6 to 10 below were carried out starting from a commercial regenerated hydrotreating catalyst which contains 20% by weight of MoO.sub.3 and 5% by weight of CoO on an alumina support and which is provided in the form of extrudates of cylindrical shape having a number-average diameter of 1.3 mm and with a number-average length of 3.2 mm.

(34) Preparation of Catalyst G:

(35) 2 kg of regenerated catalyst are placed in a mixing pan and then impregnated to saturation of the pore volume with a solution consisting of 200 g of polyethylene glycol 200 (PEG-200) and 660 g of demineralized water.

(36) After impregnation, the catalyst was subjected to a maturing stage for 17 hours at a temperature of 70 C., and then dried under nitrogen in an oven heated to 200 C., in order to obtain catalyst G.

(37) The CO analysis (measurement method described below) shows an emission of 144 ppm of CO into the air.

Example 6 (In Accordance with the Invention)

(38) 2 kg of catalyst G were placed in a completely perforated stainless steel drum having a volume of 18 liters (working volume of 5 l), at a rotational speed of 22 revolutions/minute, completely traversed by a stream of hot air of 160 m.sup.3/h at 90 C. A solution of film-forming polymer is sprayed over the particles using a twin-fluid atomization nozzle, in the way described below. The stream of hot air is produced parallel to the spray jet and in the same direction (downward stream).

(39) A solution of 800 g of polyethylene/polyvinyl alcohol copolymer (sold under the name Exceval by Kuraray) at 5% by weight in water was injected over the catalyst particles using a twin-fluid atomization nozzle (970/0 S75 model of the Schlick brand, with liquid insert with an internal diameter of 1 mm), with a flow rate of solution of 7 g/min and a relative pressure of compressed air (relative atomization pressure) of 1.210.sup.5 Pa.

(40) The water is continuously evaporated, which results in the formation of a layer of polymer at the surface of the catalyst particles.

(41) After complete injection of the liquid, the catalyst is stirred for a further 5 minutes and then cooled to ambient temperature.

(42) The catalyst H according to the invention, the particles of which are covered with a layer of polyethylene/polyvinyl alcohol copolymer, was thus obtained.

(43) High definition observation in 200 zoom of 10 grains carried out by scanning electron microscopy has made it possible to measure a homogeneity in layer thickness of 76% (measurement method described below) and also a mean thickness of the layer of 5.8 tam. The CO analysis (measurement method described below) shows an emission of 6 ppm of CO into the air.

Example 7 (Comparative)

(44) 2 kg of catalyst G were placed in a non-perforated stainless steel drum having a volume of 18 liters (working volume of 5 l), at a rotational speed of 22 revolutions/minute, and a stream of hot air of 160 m.sup.3/h at 90 C. is directed onto the surface of the adsorbent bed. The hot air enters via an inlet located within the drum and exits via the opening located in the front of the drum, without traversing the adsorbent bed (seep-flow bed).

(45) A solution of 800 g of polyethylene/polyvinyl alcohol copolymer (sold under the name Exceval by Kuraray) at 5% by weight in water was injected over the catalyst particles using a twin-fluid atomization nozzle (970/0 S75 model of the Schlick brand, with liquid insert with an internal diameter of 1 mm), with a flow rate of solution of 7 g/min and a relative pressure of compressed air (relative atomization pressure) of 1.210.sup.5 Pa.

(46) The water is continuously evaporated, which results in the formation of a layer of polymer at the surface of the catalyst particles.

(47) After complete injection of the liquid, the catalyst is stirred for a further 5 minutes and then cooled to ambient temperature.

(48) The catalyst I not in accordance with the invention, the particles of which are covered with a layer of polyethylene/polyvinyl alcohol copolymer, was thus obtained.

(49) High definition observation in 200 zoom of 10 grains carried out by scanning electron microscopy has made it possible to measure a homogeneity in layer thickness of 53% (measurement method described below) and also a mean thickness of the layer of 6.1 m. The CO analysis (measurement method described below) shows an emission of 26 ppm of CO into the air.

Example 8 (Comparative)

(50) 2 kg of catalyst G were placed in a completely perforated stainless steel drum having a volume of 18 liters (working volume of 5 l), at a rotational speed of 22 revolutions/minute, completely traversed by a stream of hot air of 160 m.sup.3/h at 90 C. A solution of film-forming polymer is sprayed over the particles using a twin-fluid atomization nozzle, in the way described below. The stream of hot air is produced parallel to the spray jet and in the same direction (downward stream).

(51) A solution of 800 g of polyethylene/polyvinyl alcohol copolymer (sold under the name Exceval by Kuraray) at 5% by weight in water was injected over the catalyst particles using a twin-fluid atomization nozzle (970/0 S75 model of the Schlick brand, with liquid insert with an internal diameter of 1 mm), with a flow rate of solution of 7 g/min and a relative pressure of compressed air (relative atomization pressure) of 0.610.sup.5 Pa.

(52) The water is continuously evaporated, which results in the formation of a layer of polymer at the surface of the catalyst particles.

(53) After complete injection of the liquid, the catalyst is stirred for a further 5 minutes and then cooled to ambient temperature.

(54) The catalyst J not in accordance with the invention, the particles of which are covered with a layer of polyethylene/polyvinyl alcohol copolymer, was thus obtained.

(55) High definition observation in 200 zoom of 10 grains carried out by scanning electron microscopy has made it possible to measure a homogeneity in layer thickness of 61% (measurement method described below) and also a mean thickness of the layer of 6.0 m. The CO analysis (measurement method described below) shows an emission of 18 ppm of CO into the air.

Example 9 (Comparative)

(56) 2 kg of catalyst G were placed in a completely perforated stainless steel drum having a volume of 18 liters (working volume of 5 l), at a rotational speed of 22 revolutions/minute, completely traversed by a stream of hot air of 160 m.sup.3/h at 90 C. By way of comparison, water not containing polymer is sprayed over the particles using a twin-fluid atomization nozzle, in the way described below. The stream of hot air is produced parallel to the spray jet and in the same direction (downward stream).

(57) 800 g of water were injected over the catalyst particles using a twin-fluid atomization nozzle (970/0 S75 model of the Schlick brand, with liquid insert with an internal diameter of 1 mm), with a flow rate of 10 g/min and a relative pressure of compressed air (relative atomization pressure) of 1.210.sup.5 Pa.

(58) After complete injection of the liquid, the catalyst is stirred for a further 5 minutes and then cooled to ambient temperature.

(59) The catalyst K not in accordance with the invention was thus obtained.

(60) The CO analysis (measurement method described below) shows an emission of 128 ppm of CO into the air.

(61) The properties of adsorbents and catalysts A to K described in the examples above were evaluated by determining the homogeneity in the layer thickness. For adsorbents A to F alone, the VOC measurement was additionally carried out. Likewise, the CO analysis was carried out for catalysts G to K alone. The measurement methods are described below:

(62) The Homogeneity in the Thickness of the Coating Layer and the Mean Thickness of the Layer:

(63) This parameter characterizes the homogeneity and thus the quality of the polymer layer deposited at the surface of the adsorbent grain.

(64) In order to obtain a representative sample, the product to be analyzed is randomly divided several times in succession by using, for example, a riffle splitter until approximately 20 grains to be analyzed are obtained. The first preparation consists of a clean cutting or splitting of each grain, which will make possible observation of the grain in section by microscopy. For the grains of extruded type, cooling with liquid nitrogen followed by manual splitting of the grain is generally sufficient to obtain a clean cut. For grains of different shapes, it is possible, for example, to use cutting tools customary in microscopy, such as a microtome. Among the split grains, ten are randomly chosen, care being taken to exclude the grains which have not been very cleanly cut/split. It is also important to note that, in the case where some grains were agglomerated with one another, these are not selected for the measurement.

(65) These ten grains are introduced for observation into a scanning electron microscope, so as to be able to observe the cutting plane. For each grain, a portion of the external perimeter of the cutting/splitting plane of the grain, with a total length of at least 900 m, is randomly selected. The magnification and the definition of the image have to be sufficient to be able to measure the thickness of the polymer layer with a margin of error of less than 5%. The first measurement point is chosen at one end of the observation region. The thickness T1 of the coating is accurately measured at this point. A length of 60 m along the perimeter of the grain is then measured and a further measurement of thickness T2 is taken at this spot. This stage is repeated until between 15 and 20 measurements of thicknesses for this same grain have been carried out. From this list of measurements of thicknesses, the homogeneity of the thickness of the coating layer of the grain is calculated in the following way:

(66) Standardized Homogeneity with Regard to the Grain j (in %):

(67) $H_j=\left(1-\frac{\frac{1}{n}{.Math.}_1^n.Math.E_i-{\stackrel{\_}{E}}_j.Math.}{{\stackrel{\_}{E}}_j}\right)100$
where E.sub.J is the mean thickness of the layer on the grain j and n is the number of measurements carried out.

(68) The homogeneity in the layer thickness H.sub.T of the sample is defined as being the mean of the homogeneities H.sub.j measured on each of the ten grains.

(69) The mean thickness of the layer on the sample is defined as being the mean of the thicknesses E.sub.J measured on each of the ten grains.

(70) The VOCs (Volatile Organic Compounds) Emission at Low Temperature:

(71) A sample of 25 g of catalyst or adsorbent is weighed out and then placed in a 1 l leaktight container equipped with a septum. The container is subsequently placed for 24 h in an oven thermostatically controlled at 120 C. After 24 h, the container is taken out and allowed to cool to ambient temperature. An analysis of the volatile organic compounds (or VOCs) is then carried out on the gas present in the container, by withdrawing a sample through the septum. The analysis of the gas can, for example, be carried out with an analyzer using a photoionization detector (PID), such as the MiniRAE Lite sold by RAE Systems, which directly gives the result in ppm of total VOCs.

(72) The CO (Carbon Monoxide) Emissions at Low Temperature:

(73) A sample of 90 g of catalyst is weighed out and then placed in a 200 mL container under air which is subsequently rendered leaktight using a stopper equipped with a septum. The container is subsequently placed for two days (48 h) in an oven thermostatically controlled at 45 C. After 48 h, an analysis of carbon monoxide (CO) is then carried out on the gas present in the container, by withdrawing a sample through the septum. The carbon monoxide content is typically measured by a gas analyzer with a selective CO sensor, such as, for example, the 317-3 model of the Testo brand, which directly gives the result in ppm of CO.

(74) For each adsorbent A to F, a determination was carried out of the homogeneity in the thickness of the coating layer and of the emissions of VOCs immediately after their preparation.

(75) For each catalyst G to K, a determination was carried out of the homogeneity in the thickness of the coating layer and of the CO emissions immediately after their preparation.

(76) The results obtained are collated in Tables 1 and 2 below:

(77) TABLE-US-00001 TABLE 1 Relative atomization Emission of Homogeneity pressure VOCs layer thickness Equipment (10.sup.5 Pa) (ppm) (%) Adsorbent A 215 / (untreated) Adsorbent B Perforated 1.2 16 68 (invention) drum Adsorbent C Perforated 1.6 10 73 (invention) drum Adsorbent D Non- 1.2 42 51 (comparative) perforated drum Adsorbent E Perforated 0.6 28 60 (comparative) drum Adsorbent F Perforated 1.2 110 / (comparative) drum

(78) TABLE-US-00002 TABLE 2 Relative Homogeneity atomization CO layer pressure emission thickness Equipment (10.sup.5 Pa) (ppm) (%) Catalyst G 144 / (untreated) Catalyst H Perforated 1.2 6 76 (invention) drum Catalyst I Non- 1.2 26 53 (comparative) perforated drum Catalyst J Perforated 0.6 18 61 (comparative) drum Catalyst K Perforated 1.2 128 / (comparative) drum

(79) The above results demonstrate that the process according to the invention, combining the use of a technology in which the particles are traversed by a stream of gas and the spraying of film-forming polymer and carried out with an atomization pressure as claimed, makes it possible to obtain better results in terms of limitation of emissions of undesirable gases.

(80) Furthermore, this process makes it possible to obtain a thin coating layer at the surface of the particles which is more homogeneous.