Abstract:
The invention relates to a material for treating gaseous media containing volatile organic components. According to the invention, the material is porous and exhibits an absorption capacity of approximately 20-30% in relation to the dry weight thereof, containing approximately 47-52% by weight of a composite carbon and silicon structure, approximately 12-20 wt. % carbon, approximately 5-7 wt % hydroxyl, and approximately 1-2 wt % oxygen. The invention can be used in atmospheric treatment for the preservation of living matter.

Description:
FIELD OF THE INVENTION 
     This invention pertains to a material for the treatment of gaseous media containing volatile organic compounds, such as ethylene, as well as a process for the treatment of gaseous media using this material. 
     The invention also concerns a process and a device for obtaining the material. 
     This material and the associated treatment process are used for the treatment of atmospheres in which living materials are stored, particularly in refrigerators or coolers. 
     BACKGROUND 
     Ripening of living materials generates volatile organic compounds, such as ethylene, some of which cause autocatalysis of the ripening process. These compounds are also responsible for unpleasant odors, and usually generate microorganisms and contaminants such as bacteria, molds, and yeasts. Therefore, they are harmful to the proper storage of living materials because they can cause biological degradation, which is detrimental to storage and to consumer health. 
     These compounds are very light, and therefore they can circulate readily through ventilation or air conditioning systems. 
     In known storage systems, the atmospheres receive no particular treatment, and this results in a number of sanitary risks. 
     SUMMARY OF THE INVENTION 
     The purpose of the invention is to remedy these disadvantages by offering a material for the treatment of gaseous media containing volatile organic compounds and a treatment process using this material which allows for chemical transformation of the volatile organic compounds into harmless gases; the structure of this material makes this treatment process particularly effective. 
     Thus, the invention concerns a material for the treatment of gaseous media comprising volatile organic compounds, this porous material presenting an adsorption capacity of about 20 to 30% of its dry weight and comprising about 47 to 52 wt % of a composite structure of silicon and carbon, about 12 to 20 wt % carbon, about 5 to 7 wt % hydroxyl, and about 1 to 2 wt % oxygen. 
     It is preferable for this material to comprise a peripheral volume corresponding to essentially one-third of the total volume of the material, of about 75 to 85% porosities, with pores having dimensions between 10 and 50 Å and, in the remaining central volume, about 80 to 90% cavities whose dimensions are between about 200 Å and 2 μm. 
     It is preferable for the specific surface of the material according to the invention to be between 1200 and 2200 m 2 /g. 
     The material may advantageously include about 20 wt % aluminum oxides and about 5 wt % iodides. 
     It is also advantageous for the relative humidity of this material to be less than 2 wt % with respect to the dry weight of the material. 
     The invention also concerns a process for the treatment of a gaseous medium containing volatile organic compounds, consisting of directing a flow of said gaseous medium over a porous material according to the invention, to bring about adsorption of this flow which penetrates the pores and the cavities of the material, in the process of which a chemical reaction occurs between the volatile organic compounds of the flow and the material itself, to transform the volatile organic compounds into nontoxic gases, particularly CO 2  and/or SO 2 . 
     The process according to the invention is more effective when the porous material according to the invention presents a very high number of pores and cavities which allow diffusion of the gaseous flow throughout the material with a large specific surface. The chemical transformation of the gas flow is favored by the relatively long contact time between the gas flow and the material when the latter is penetrated by the flow. 
     Thus, the treatment process according to the invention provides a contact time between the gas flow and the material which is between 0.08 and 0.12 sec. 
     The invention also pertains to a device and a process for obtaining the material for the treatment of gaseous media according to the invention. 
     This process consists of: 
     preparing a clay base constituent comprising about 30 wt % clay with a particle size which is greater than 180 μm, and about 70 wt % clay with a particle size which is between 10 and 20 μm; 
     impregnating this base constituent with an aqueous solution containing about 10% by volume of acetic acid, between 5 and 10% by volume of citric acid, and between 15 and 20% by volume of hydrogen peroxide, the volume of the solution being essentially equal to the volume of the base constituent, 
     applying a pretreatment of the base constituent impregnated with the solution by mixing it at a first pre-determined speed to create a porous structure, 
     mixing, at a pressure between 2 and 10 bar, the constituent which has been pretreated with an acidified liquid having a strong oxidizing potential, at a second speed lower than the first, to cause the liquid to penetrate the pretreated constituent and to form a gel, the quantity of pretreated constituent being between 42 and 48% of the total volume mixed, while the quantity of liquid is between 58 and 52% of the total volume mixed, 
     mixing the gel with complementary products comprising a solution with a strong oxido-reductive potential representing about 10% of the total volume, a mixture of carbon and alumina representing about 12 to 15% of the total volume and calcium sulfate representing about 2% of the total volume 
     drying the resulting mixture by ultrasound treatment of the material which has been mixed and transferred linearly, and 
     pressing the dried material under a pressure of 8 to 10 bar. 
     It is preferable for the process according to the invention to be implemented continuously. 
     It is preferable if the process also consists of heating the base constituent impregnated with aqueous solution, at the time of pretreatment, to a temperature between 200 and 250° C. 
     The process of the invention also consists, advantageously, of emitting ultrasound waves at the time of this pretreatment, at a unit power of 2000 W and with an amplitude of 15 to 30 μm. 
     Heating and treatment by ultrasound waves contribute to the creation of a porous structure. 
     It is preferable, at the time of pretreatment, for the process to carry out another mixing operation at a third speed lower than the first and second speeds, to enlarge the cavities and porosities of the resulting structure. 
     The process according to the invention consists advantageously of filtering the liquid which results from the pretreatment of the preimpregnated base constituent. 
     The liquid associated with the pretreated constituent preferably comprises about 10% by volume of a solution with a strong oxidizing potential. 
     The pretreated constituent and the liquid are advantageously mixed by being heated to a temperature between 90 and 120° C. 
     The mixing of the gel and the complementary products is advantageously carried out at a temperature between 70° C. and 80° C. 
     The treatment with ultrasound to dry the mixture may advantageously be carried out over a length of 20 to 30 cm, under a specific output of 3 to 5000 W, an amplitude of 15 to 60 μm and a frequency of about 20 MHz. 
     The material is preferably dried under a partial vacuum of 120 to 150 mbar and at a temperature between 90 and 100° C. 
     Finally, the process according to the invention advantageously comprises a final stage of extrusion of the material. 
     The invention also pertains to a device for implementation of the production process according to the invention, which includes: 
     an impregnator comprising a first mixer turning at a speed between 1200 and 1400 rpm to form a first mixture, 
     a first reactor comprising a second mixer turning at a speed between 800 and 1000 rpm to accomplish mixing under a pressure between 2 and 10 bar, to obtain a second mixture of the gel type; 
     a second reactor comprising a mixer for a third mixture; 
     a device which accomplishes linear transfer of the third mixture and at least one ultrasound device delivering a power of 3 to 5000 W, on at least one part of the trajectory of the third mixture, and 
     a high-pressure extrusion device. 
     It is preferable for the impregnator of the device according to the invention to include a heating device which heats to a temperature between 200 and 250° C., as well as a device for the emission of ultrasound waves. 
     It is advantageous for the impregnator to be combined with a device for filtration of the liquid evacuated from the impregnator. 
     It is preferable for the impregnator to comprise another mixer turning at a speed between 500 and 800 rpm. 
     The first reactor advantageously includes a heating device for heating to a temperature between 90 and 120° C. 
     The second reactor advantageously includes a heating device for heating to a temperature between 70 and 80° C. 
     Finally, the device for linear transfer of the second reactor is advantageously made up of a double screw whose rotation speed is between 5 and 150 rpm. 
     Finally, the extrusion device preferable includes a variable screw which subjects the material from the first reactor to a pressure between 8 and 10 bar. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The invention is more completely understood and its other purposes, advantages, and characteristics more clear upon reading of the following description related to the attached drawings which represent nonlimiting examples of embodiments of the invention, and in which: 
     FIG. 1 is a cross section of the device for producing the material for the treatment of gaseous media according to the invention, 
     FIG. 2 is an enlarged cross section of the preimpregnator illustrated in FIG. 1, 
     FIG. 3 is an enlarged view of the first and second reactors illustrated in FIG. 1, 
     FIG. 4 is a diagram showing the evaluation of the pressure and the viscosity in the first reactor illustrated in FIG.  1  and FIG. 3, 
     FIG. 5 is a perspective view of a piece of material according to the invention for the treatment of gaseous media, and 
     FIG. 6 is a cross-sectional view along VI—VI of FIG.  5 . 
    
    
     DETAILED DESCRIPTION 
     With reference to FIG. 1, the device according to the invention for producing material intended for the treatment of gaseous media generally includes an impregnator  1  which makes it possible to impregnate the base constituent of this material with an aqueous solution and to accomplish pretreatment to obtain a porous structure, a first reactor  2  to form a gel from the pretreated base constituent, and in which physicochemical reactions occur, and finally a second reactor  3  for drying the mixture obtained from the first reactor, and which ends with a device  4  for extrusion and shaping of the mixture from the second reactor. 
     FIG. 2 illustrates the impregnator  1 , which is made up of a jacket  101 , preferably heated to a temperature between 200 and 250° C., in which the base constituent  10  of the material to be obtained can be introduced through conduit  102 . 
     In this jacket  101 , a liquid  19  can also be introduced, for example, by means of injection nozzles  103 . 
     This base constituent is clay and comprises about 30 wt % of clay having a particle size greater than 180 μm and about 70 wt % of clay having a particle size between 10 and 20 μm. 
     The liquid  19  is an aqueous solution comprising, by volume, 10% acetic acid, 5 to 10% citric acid, and 15 to 20% hydrogen peroxide. 
     The introduction of the material  10  and the liquid  19  is regulated so that the volume of aqueous solution and the volume of base constituent introduced into the jacket  101  are essentially equal. 
     The device  1  comprises, in the jacket  101 , a first mixer  110  comprising a blade  111  and a blade  112 , driven by a geared motor  113 . It is preferable for the rotation speed of the blades  111  and  112  to be between 1200 and 1400 rpm. 
     This mixer  110  mixes the base constituent  10  and the aqueous solution  19 , and the bell shape of the blade  111  transmits a high peripheral speed to the mixer  11 . 
     Thus, in the enclosure  101 , the base constituents, from which the metal atoms have been reduced, is restructured into light assemblies with high porosity with a large number of cavities and pores, favored by the ultrasound treatment. The blade  112  finalizes the molecular reorganization of the cavities and pores formed in this first mixture and makes them larger. 
     This loss of cohesion is favored by heating of the enclosure  101  and by the additional mechanical action of the ultrasound waves emitted by the means  104 . 
     Preferably, this means  104  for emission of sound waves has a unit capacity of 2000 W and an amplitude of 15 to 30 μm, and these emissions are centered on the median part of the blade  111 . 
     Thus, in the enclosure  101 , the base constituents, from which the metal atoms have been reduced, is restructured into light assemblies with high porosity with a large number of cavities and pores, favored by the ultrasound treatment. The blade  112  finalizes the molecular reorganization of the cavities and porosities formed in this first mixture and makes them larger. 
     The impregnator  1  comprises another jacket  120  in which there is provided a blade  121  rotated by a geared motor  122 , particularly at a speed between 500 and 800 rpm. 
     This blade  121  causes the mixture  11  to exit peripherally through the conduit  123 . 
     The blade  121  allows a certain dispersion of the mixture, but in particular it transmits weaker binding forces to the molecular assemblies. This structural relaxation increases the sizes of the pores and cavities, and favors their impregnation by a diffusion of the preimpregnated material to the core. 
     The liquid, which is lighter than the mixture, is recovered in the conduits  124 ,  125 ,  126 , and  127 . These conduits all end at the removal loop  128 . 
     On the removal loop  128 , there is provided a filtration device  129  which filters out the recovered metal atoms by isotopic separation. 
     In fact, the clay base constituent contains metal ions in its atomic make-up, essentially iron, aluminum, chromium, manganese, and nickel, which are desirable to separate from the molecular assemblies, which should have as much capacity as possible to open into pores and cavities. 
     Returning to FIG. 1, the mixture  11  from the preimpregnator  1  is introduced into the first reactor  2  through the conduit  123 . 
     The liquid  12  from the removal loop  128  of the impregnator  1  is also introduced into the first reactor  2 , with a solution  13  having a strong oxidizing capacity brought by conduit  220 . The liquid  14  which results from this mixture is introduced into the first reactor  2  through the conduit  221 . 
     The solution  13  with a strong oxidizing capacity represents about 10% of the total volume of the liquid  14  introduced into the first reactor  2 . The liquid  12  from the impregnator  1  is an acidified liquid. 
     In addition, among the materials introduced into the first reactor  2 , the mixture  11  represents 42 to 48% of the total volume, while the liquid  14  represents between 58 and 52% of the total volume. 
     Reference in now made to FIG. 3, which illustrates the first and second reactors,  2  and  3 . 
     The first reactor  2  comprises an envelope  201 , essentially cylindrical, which is closed on its upper part by a cover  202 . 
     The cover  202  supports a geared motor  203 , which drives mixer  210  by rotation. 
     The jacket  201  preferably comprises the means for heating to a temperature between 90 and 120° C. 
     The cover  202  is under pressure, because of an intake of gas under pressure through the conduit  222 , and because of the sealing mechanism  204  between the motor  203  and the cover  202 . The pressure in the enclosure  201  is preferably between 2 and 10 bar. 
     The mixer  210  comprises a barrel-shaped rotor  211  to which there is attached, on top, mixing blades  212  with a scissor effect and, on the bottom, streamlined blades  213 . 
     Within the rotor  211 , there are an external chamber  230  and an internal chamber  231 , separated by a barrel-shaped element  232 . 
     An evacuation tube  233  is provided within the internal chamber  231 . The tube  233 , the bell-shaped element  232 , and the internal and external chambers are all concentric. 
     The mixture  11  and the liquid  14  introduced into the enclosure  201  are mixed vigorously by the blades  212  and  213  driven by the motor  203 . The resulting mixture  15  progressively causes the formation of a gel, whose viscosity increases in the internal chamber  231 . 
     The speed of the mixer  210  is between 800 and 1000 rpm. 
     The mixture  15  present in the internal chamber  231  then pours into the removal tube  233  through the overflow ports  234  presented by the tube on its upper part. 
     The resulting gel  15  is then transferred by gravity to the second reactor  3 . 
     The first reactor  2  also comprises a drainage device  234  on its lower part. 
     Pressurization of the external chamber  230  is regulated by a level of deposit resulting from the distance between the level of the material between the external chamber  230  and the internal chamber  231 , delimited by E. 
     The pressure regulates the time of the chemical reaction; the viscosity characterizes the transfer of the material in transit from the external chamber to the internal chamber. 
     Reference is now made to FIG. 4, which is a diagram showing, in schematic form, with the curve  5 , the evolution of pressure inside the first reactor  1  and, with curve  6 , the evolution of viscosity in the same reactor. 
     The transit time from the external chamber  230  to the exit of the internal chamber  231  is defined by the time interval (t 1 , t 3 ), while the transit time in the internal chamber  231  is defined by the time interval (t 2 , t 3 ). 
     The integral of the distance between the curves  5  and  6  for the transit time in the internal chamber is represented by the shaded surface  7 . This integral defines the essential indicator for setting the parameters of the control system associated with the first reactor  2  which regulates pressurization, speed of the mixer  210 , the transit times (t 1 , t 3 ) and (t 2 , t 3 ), as well as the viscosity v s  at the exit of the lower chamber  231  prior to overflow into the tube  233 . 
     This type of control characterizes the continuous operation of the first reactor  1 , to assure the quality of the material produced. 
     Reference is made again to FIG. 3 to describe the second reactor  3 . 
     This reactor includes a tank  301  into which the removal tube  233  for the gel  15  formed in the first reactor  2  empties. 
     At the upper part of the tank  301 , additional products  16  are introduced, preferably by means of an introduction ring  302 . 
     These additional products  16  include a solution with a strong oxido-reductive potential representing about 10% of the total volume introduced into the second reactor  3 , a mixture of carbon and alumina representing about 12 to 15% of the total volume introduced, and calcium sulfate representing about 2% of the total volume introduced into the second reactor  3 . 
     Inside the tank  301 , the second reactor includes a mixer  310 . 
     The tank  301  is preferably a heating tank, with its heating temperature being between 70 and 80° C. 
     The mixer  310  mixes the gel  15  and the additional products  16 , the mixture  17  obtained being entrained by a double screw  320  which is provided on the upper part of the tank  301  of the second reactor  3 . 
     This double screw, which rotates in opposite directions, is driven by a geared motor  321  fed by a speed variator (not shown) which drives the double screw  320  at a speed between 5 and 150 rpm, depending on the high and low levels,  303  and  304 , of the mixture  17  in the reactor  3 . 
     The double screw  320  transfers the mixture  17  along a linear trajectory from left to right on FIG.  3 . 
     The second reactor  2  also includes the means  305  for emission of ultrasound waves, of the sonotrode type. 
     It is preferable for this means  305  to deliver a specific output of 3 to 5000 W, over a length of 20 to 30 cm, under an amplitude of 15 to 60 μm and with a frequency of approximately 20 MHz. 
     The temperature of the mixture  17  is then between 90 and 100° C. 
     At the time of this ultrasound treatment, the cavities and pores present in the mixture  17  are emptied and dried by diffusion in the microporous structure, which causes reimpregnation of the material  18  obtained by microscopic diffusion of the impregnation liquid progressively constituted from the preimpregnator  1  to the means of ultrasound emission  305 . 
     This drying is favored by the application of a partial vacuum within the enclosure  301 , this partial vacuum being between 120 and 150 mbar. 
     In particular, this partial vacuum can be obtained by an exhaust fan  306  which aspirates the gases inside the enclosure  301  through the nozzles  307 ,  308  to accelerate the circulation rates of the extracted gases. 
     Finally, the device according to the invention comprises an extruding device  4 . 
     This device  4  comprises an enclosure  401  in which there is a screw  410  which is rotated by a geared motor  411 . 
     Thus, the material  18  from the second reactor  3  is pressed onto the variable screw  410  up to a pressure between 8 and 10 bar. The flow rate of the material  20  coming from the extruding device  4  is between 14 and 20 kg/min. 
     The device  4  preferably includes a molding plate  412  so that the material  20  will be obtained in the form of granules or sheets, depending on the type of molding plate used. 
     The material obtained at the exit of the extrusion device  4  is shown schematically in FIGS. 5 and 6. 
     The material  20  illustrated in FIGS. 5 and 6 is a porous material which includes about 47 to 52 wt % of a composite structure of silicon and carbon, about 12 to 20 wt % carbon, about 5 to 7 wt % hydroxyl, and about 1 to 2 wt % oxygen. 
     This material may also include about 20 wt % aluminum oxides and about 5 wt % iodides. 
     As shown in FIG. 6, this material comprises, in a peripheral volume 21 corresponding essentially to one-third the total volume of material, about 75 to 85% porosity including pores  22  having dimensions between 10 and 20 Å and, in the remaining central volume 23, about 80 to 90% cavities  24  whose dimensions are between about 200 Å and 2 μm. 
     Thus, since the pores  22  empty into the cavities  24  of the central volume, a gaseous flow can penetrate into the material through the pores  22  which constitute circulation routes, as far as cavities  24 , in which the gaseous flow can swirl. 
     Therefore, the material  20  adsorbs a significant flow of gas circulating in the pores  22  and the cavities  24 , then absorbs these gases by chemically transforming the volatile organic compounds present in this gas flow. 
     In general, these volatile organic compounds are transformed into nontoxic gases such as SO 2  and/or CO 2 . 
     In particular, this material makes it possible to convert the ethylene present in a flow of carbon dioxide gas. Tests already conducted have demonstrated the efficacy of the porous material according to the invention. 
     The efficacy of treatment of the volatile organic compounds is greater when the porous material of the invention has an equally large specific surface, specifically between 1200 and 2200 m 2 /g. 
     In addition, the large number of pores and cavities inside the porous material results in a relatively long contact time between the gas flow and the porous material when this flow penetrates it. In particular, this contact time can be between 0.08 and 0.12 sec. 
     Finally, the relative humidity of the porous material is advantageously less than 2% of the dry weight of the material. 
     This material has an absorption capacity on the order of 20 to 30% with respect to its dry weight, and it is particularly suitable for treatment of ethylene, ethylene dichlorides, ethylene oxides, aldehydes, and amines. It also neutralizes odors, particularly those resulting from hydrogen sulfide and other organic sulfides.