NANOPARTICULATE-AEROSOL GENERATOR AND METHOD FOR CONTINUOUSLY GENERATING AEROSOLS, ASSOCIATED WITH SAID GENERATOR

Abstract

The object of the present invention relates to a nanoparticulate aerosol generator comprising a compressed gas reservoir (1) connected to a nanoparticulate material receptacle (2) through an operational valve (8), wherein said receptacle (2) comprises an outlet hole (3) for the aerosol. Advantageously, the outlet of said nanoparticulate material receptacle (2) is connected to or inserted into a pressurized aerosol distribution chamber (4) equipped with a hole (9) for the exit of said aerosol out of the chamber (4). The invention provides the possibility of using different types of nanoparticles with sizes less than 100 nanometers continuously over time during long production periods of more than three hours. The invention also relates to a method for continuously generating nanoparticulate aerosols associated with the mentioned generator.

Claims

1. A nanoparticulate aerosol generator comprising a compressed gas reservoir (1) connected to a nanoparticulate material receptacle (2) through an operational valve (8), wherein said receptacle (2) comprises an outlet hole (3) for the aerosol; characterized in that the outlet of said nanoparticulate material receptacle (2) is connected to or inserted into a pressurized aerosol distribution chamber (4) equipped with a hole (9) for the exit of said aerosol out of the chamber (4).

2. The nanoparticulate aerosol generator according to the preceding claim, wherein the compressed gas reservoir (1) is connected to a first source (5) of gas flow subjected to controlled pressure.

3. The nanoparticulate aerosol generator according to the preceding claim, wherein the connection between the first source (5) of gas flow and the reservoir (1) is made through a dryer (6) and/or a filter (7).

4. The nanoparticulate aerosol generator according to any of the preceding claims, wherein the compressed gas reservoir (1) comprises a receptacle having a volume comprised between 30 and 50 cm.sup.3, with gas stored at a pressure of 7-10 barg.

5. The nanoparticulate aerosol generator according to any of the preceding claims, wherein the distribution chamber (4) comprises a controlled atmosphere chamber or a dispersion tube.

6. The nanoparticulate aerosol generator according to the preceding claim, wherein the distribution chamber (4) comprises a dispersion tube and is formed by a plurality of sections (4), wherein each section (4) contains one or more holes (9, 9) for accessing the inside of the chamber (4) once it is assembled and the generator is in operation.

7. The nanoparticulate aerosol generator according to any of the preceding claims, wherein the ends of the distribution chamber (4) consist of terminal closure sections (4), wherein the nanoparticulate material receptacle (2) is inserted or connected through one of said terminal sections (4) and a second source (5) of gas flow at controlled pressure is connected through the other one of the terminal sections (4).

8. The nanoparticulate aerosol generator according to the preceding claim, wherein the connection of the second source (5) of gas flow to the distribution chamber (4) is made by means of a valve (8), a dryer (6), and/or a filter (7).

9. The nanoparticulate aerosol generator according to any of the preceding claims, wherein the pressurized distribution chamber (4) and/or the compressed gas reservoir (1) comprises one or more working pressure control points (10, 10).

10. The nanoparticulate aerosol generator according to any of the preceding claims, wherein the pressurized distribution chamber (4) comprises one or more moisture sensors (11) for monitoring the generated aerosol.

11. The nanoparticulate aerosol generator according to any of the preceding claims, comprising a third source (5) of diluting gas flow at the outlet of the pressurized distribution chamber (4), optionally connected to a mass flow controller (12) and/or a filter (7).

12. The nanoparticulate aerosol generator according to any of the preceding claims, comprising a measuring point (14) for measuring the flow rate of the aerosol (13) released at the outlet of the pressurized distribution chamber (5), said measuring point (14) comprising a rotameter optionally connected to a filter (7).

13. A method for continuously generating nanoparticulate aerosols by means of using a generator according to any of the preceding claims, wherein said method is characterized in that it comprises performing the following steps: a) introducing a gas flow in the generator, compressing it in the compressed gas reservoir (1) where it is stored at controlled pressure; b) instantaneously releasing the compressed gas from the reservoir (1) causing it to go through the nanoparticulate material receptacle (2), generating an aerosol of said material and causing it to reach the pressurized distribution chamber (4) through an outlet hole (3) of said receptacle (2), said aerosol being stored in said chamber (4) at controlled pressure; c) continuously releasing the aerosol stored in the pressurized distribution chamber (4) through an outlet hole (9) out of said chamber.

14. The method for continuously generating nanoparticulate aerosols according to the preceding claim, which comprises repeating step a) as many times as desired throughout said method to maintain aerosol supply to the distribution chamber (4).

15. The method for continuously generating nanoparticulate aerosols according to any of claims 13 to 14, which comprises filtering or drying the gas entering and/or exiting the compressed air reservoir (1) and/or the distribution chamber (4), and/or monitoring the properties of the gas entering the compressed air reservoir (1) and/or the distribution chamber (4), and/or monitoring the properties of the aerosol exiting the generator.

16. Use of a generator according to any of claims 1 to 12 or of a method according to any of claims 13 to 15 for breaking up aerosols by means of a plurality of successive expansions of the gas in the compressed air reservoir (1).

Description

DESCRIPTION OF THE DRAWINGS

[0029] To complete the description of the invention and for the purpose of helping to better understand the technical features thereof, a set of drawings is appended herein in which the following is depicted in an illustrative and non-limiting manner:

[0030] FIGS. 1a-1b show respective illustrative diagrams of the main elements of the generator of the invention according to a preferred embodiment thereof. FIG. 1a shows the general design of the generator, whereas FIG. 1b shows an inner detail of said generator in which the nanoparticulate material receptacle is depicted inserted into the pressurized aerosol distribution chamber.

[0031] FIG. 2a shows a graph with the results of the total concentration of particles generated by the invention according to the preferred embodiment of FIGS. 1a-1b as a function of time and for nanoparticle size distributions taken after 10 and 140 min, after opening the outlet valve of the distribution chamber, using 25 mg of TiO.sub.2 nanoparticles having a nominal diameter of 25 nm (Aeroxide P25, Evonik, Germany).

[0032] FIG. 2b shows a graph with the results of the concentration of particles (per cm.sup.3) generated by the invention according to the preferred embodiment of FIGS. 1a-1b as a function of the size of said particles.

[0033] FIG. 2c shows nanoparticle size distributions in aerosol phase after one expansion and after two expansions through selected holes for different TiO.sub.2 P25 and ZnO nanomaterials, performed by means of the generator of the invention.

REFERENCE NUMBERS USED IN THE DRAWINGS

[0034] For the purpose of helping to better understand the technical features of the invention, the mentioned drawings are accompanied by a series of reference numbers where the following is depicted in an illustrative and non-limiting manner:

TABLE-US-00001 (1) Compressed gas reservoir (2) Nanoparticulate material receptacle (3) Outlet hole of the nanoparticulate material receptacle (4) Pressurized aerosol distribution chamber (4) Intermediate sections of the aerosol distribution chamber (4) Terminal sections of the aerosol distribution chamber (5, 5, 5) Gas flow inlets (6, 6) Incoming gas dryers (7, 7, 7) Incoming gas filter (8, 8, 8, 8) Gas regulating/shut-off control valves (9, 9) Holes for accessing the pressurized distribution chamber (10, 10) Incoming gas pressure control points (11) Moisture sensors of the pressurized distribution chamber (12) Mass flow controller (13) Generated aerosol (14) Generated aerosol flow rate control point

DETAILED DESCRIPTION OF THE INVENTION

[0035] A detailed description of the invention in reference to a preferred embodiment thereof is set forth below based on FIGS. 1-2 of the present document.

[0036] As shown in FIGS. 1a-1b, the present invention relates to a nanoparticulate aerosol generator essentially comprising a compressed gas reservoir (1) connected to a nanoparticulate material receptacle (2) (see detail in FIG. 1b), wherein said receptacle (2) comprises an outlet hole (3) connected to a pressurized aerosol distribution chamber (4). According to this configuration, the compressed gas reservoir (1) is a receptacle, for example a stainless steel receptacle, which can have a variable volume depending on the chosen application and receives a first source (5) of gas flow (said gas being, for example, air) subjected to controlled pressure. In an example of use for laboratory applications, said volume can be comprised between 30 and 50 cm.sup.3, with air stored at a pressure of 7-10 barg. Preferably, the connection between the first source (5) of gas flow and the reservoir (1) is made through a dryer (6) and/or a filter (7) (for example, a HEPA or High Efficiency Particle Arresting filter), for the purpose of eliminating moisture from the air generator of the aerosol, as well as the impurities present therein. In other embodiments of the generator, it is also possible to provide a shut-off valve (8) between the first source (5) of gas flow and the reservoir (1), as means for regulating said flow.

[0037] As mentioned, the compressed gas reservoir (1) is connected to a nanoparticulate material receptacle (2). Said receptacle (2) comprises a container (FIG. 1b shows a cylindrical container, for example) equipped with an outlet hole (3) for releasing the nanoparticulate aerosol. Typically, for a cylindrical laboratory generator, said receptacle (2) has a length of between 80 and 120 mm, an inner diameter of between 5 and 20 mm, and an outlet hole (3) with an inner diameter between 1.0-1.4 mm. Preferably, the receptacle (2) is manufactured with stainless steel.

[0038] By means of the opening of another shut-off valve (8) arranged between the compressed gas reservoir (1) and the nanoparticulate material receptacle (2), the compressed gas is released instantaneously, driving said solid material through the outlet hole (3). The increased speed the gas experiences as it goes through the hole (3) gives rise to significant shearing forces which break up the agglomerates formed in the powder nanoparticulate material, releasing a cloud of nanoparticles of the desired scale.

[0039] For the purpose of providing the generator of the invention with the capacity to continuously supply the aerosol, the nanoparticulate material receptacle (2) is connected to or inserted into the pressurized distribution chamber (4), which allows keeping the aerosol, once generated, in the state of dispersion as a result of the inner pressure at which said chamber (4) is maintained. In different embodiments of the invention, the distribution chamber (4) can be, for example, a controlled atmosphere chamber or a dispersion tube. This second case is shown in the depiction illustrated by FIGS. 1a-1b, in which said dispersion tube consists of a chamber (4) formed by several (preferably stainless steel) sections (4), for example, cylindrical sections, each of them with an inner diameter comprised between 8 and 12 cm and a height of 15-25 cm. Each section preferably contains one or more holes (9, 9) for accessing the inside of the chamber (4) once it is assembled and the generator is in operation. Likewise, the ends of the chamber (4) consist of corresponding terminal closure sections (4). The nanoparticulate material receptacle (2) which will be used for generating the aerosols is inserted or connected through one of said terminal sections (4) (see FIG. 1b), whereas a second source (5) of gas flow which serves to maintain the inner pressure at different values, depending on the specific generation needs, is connected through the other one of the terminal sections (4). The connection of said source (5) to the distribution chamber (4) is made, for example, by means of a valve (8), optionally including the presence of a dryer (6) and/or a filter (7) (for example, a HEPA filter). It is possible to include one or more working pressure control points (10, 10) both in the pressurized distribution chamber (4) and in the compressed gas reservoir (1).

[0040] In the preferred embodiment illustrated in FIGS. 1a-1b, the total volume of the distribution chamber (4) is 8-10 liters once arranged with the nanoparticulate material receptacle (2) therein. Under normal working conditions, the chamber (4) can be kept at pressures comprised between 1 and 50 barg at the moment of ejecting the nanoparticulate aerosol therein. Once the aerosol has been generated and subjected to pressure, the opening of a valve (8) connected to one of the holes (9) causes the exit thereof at the desired output concentration and flow rate in a continuous manner while said valve (8) remains open.

[0041] In an optional embodiment of the pressurized distribution chamber (4), it can additionally include one or more moisture sensors (11) for monitoring the generated aerosols, thereby allowing precise control of the dry generation properties thereof.

[0042] In other additional embodiments of the invention, it is also possible to couple a third source (5) of gas flow to the outlet of the valve (8) (optionally connected to a mass flow controller (12) and/or a filter (7)), which releases the aerosol out of the pressurized distribution chamber (4), using said third source (5) as means for diluting the final aerosol (13) released at the outlet of the pressurized chamber (5). Likewise, in other embodiments of the invention it is also possible to couple a measuring point (14) for measuring the flow rate of the final aerosol (13) released at the outlet of the pressurized chamber (5), said measuring point (14) comprising, for example, a rotameter optionally connected to a filter (7). This provides different additional control systems for the properties of the aerosols generated with the invention, contributing to increased precision.

[0043] As described in the preceding paragraphs, the presence of the pressurized distribution chamber (5) provides the aerosol generator of the invention with two advantages. On one hand, it allows continuous supplying nanoparticulate aerosol having a stable concentration by means of actuating the valve (8) for time periods of several hours, depending on the inner pressure values and the amount of material placed in the receptacle of the inner generator. On the other hand, nanoparticulate aerosols with a stable particle size distribution throughout the entire generation period, even after long periods of time, can be generated. This is due to the fact that the inner pressure of the tube and the disaggregation effect of the outlet valve (8) prevents the aggregation of the nanoparticles contained inside the chamber (5), so a constant stream of small sized nanoparticles over time is achieved. The size of the nanoparticles generated in the aerosol exiting the complete system ultimately depends on the grain size of the starting material and its chemical nature, the system being highly versatile as regards these two parameters.

[0044] In short, the pressurized distribution chamber (5) allows controlling the concentration and particle size distribution in the aerosol stream. These two parameters are of great interest in all applications which entail the use of nanoparticulate aerosols in different technological fields, from the synthesis of gas phase materials to the validation of personal protection equipment in industrial hygiene, as well as in eco-toxicity studies, toxicological research of nanomaterials by inhalation, quality controls, dispersion studies, personal protection equipment and filter testing, calibration of nanoparticle measuring equipment, simulation of accidents involving nanomaterials, or medical applications.

[0045] FIGS. 2a and 2b show the results of generating aerosols using 25 mg of TiO.sub.2 nanoparticles having a nominal diameter of 25 nm (Aeroxide P25, Evonik, Germany) for a period of about 150 min, by means of using a generator according to the embodiment illustrated in FIGS. 1a-1b. It can be observed therein that the concentration of the particles in the aerosol stream (FIG. 2a) remains stable at about of 5.10.sup.5 #/cm.sup.3 throughout the entire generation time, without any drop in this value being observed for more than two hours. The blank spaces in the concentration curve are due to the equipment for measuring the amount of material in the aerosol being used for determining the measurement of particle size distribution. These distributions, as can be observed in FIG. 2b, give similar average size and amplitude values, both at the beginning and end of the test. It must also be highlighted that the average size of the generated particles is about 50 nm, corresponding to small aggregates of 25 nm primary particles. These results therefore confirm that the aerosols generated with this system have a constant size and concentration for long periods of time.

[0046] Another aspect of the invention relates to a method for continuously generating nanoparticulate aerosols by means of using a generator according to any of the embodiments herein described. Said method preferably comprises the following steps:

[0047] a) introducing a gas flow in the generator, compressing it in the compressed gas reservoir (1) where it is stored at controlled pressure;

[0048] b) instantaneously releasing the compressed gas from the reservoir (1) causing it to go through the nanoparticulate material receptacle (2), generating an aerosol of said material and causing it to reach the pressurized distribution chamber (4) through an outlet hole (3) of said receptacle (2), said aerosol being stored in said chamber (4) at controlled pressure;

[0049] c) continuously releasing the aerosol stored in the pressurized distribution chamber (4) through a hole (9) for the exit out of said chamber.

[0050] The described method preferably comprises repeating step a) as many times as desired throughout said method to maintain aerosol supply to the distribution chamber (4).

[0051] Likewise, the method of the invention preferably comprises filtering or drying the gas entering and/or exiting the compressed air reservoir (1) and/or the distribution chamber (4).

[0052] Optionally, the properties of the gas entering the compressed air reservoir (1) and/or the distribution chamber (4) are monitored, and/or the properties of the aerosol exiting the generator are monitored.

[0053] As described above, the generation of the aerosol produced by means of the method of the invention can be kept continuous for times of more than 3 hours, with concentrations of particles in the nanometric scale or greater.

[0054] FIG. 2c compares nanoparticle size distributions in the aerosol phase after one expansion and after two expansions through selected holes for different TiO.sub.2 P25 and ZnO nanomaterials. These results confirm the effectiveness of the shearing force generated by the expansion for reducing the size of the nanoparticle aggregates in the aerosol. In this sense, an additional object of the present invention relates to the use of a generator or of a method for generating aerosols according to any of the embodiments herein described by means of a plurality of successive expansions of the gas in the compressed air reservoir (1).