Chemistry of inorganic compounds – Modifying or removing component of normally gaseous mixture – Halogenous component
Reexamination Certificate
2001-11-09
2004-02-03
Silverman, Stanley S. (Department: 1754)
Chemistry of inorganic compounds
Modifying or removing component of normally gaseous mixture
Halogenous component
Reexamination Certificate
active
06685901
ABSTRACT:
The present invention relates to a method for removing a halogen series gas comprising a halogen element or a halogen compound. It relates to a method for removing a halogen series gas from e.g. dry etching exhaust gas containing a halogen series gas for example.
Conventionally, as a method of treating e.g. dry etching exhaust gas or an exhaust gas from a CVD (chemical vapor deposition) chamber containing a halogen series gas comprising a halogen element or a halogen compound, a treatment method by dry process employing an adsorbent such as activated carbon has been employed in order to miniaturize equipments and to simplify operation. However, there are drawbacks such as firing due to heat of adsorption during gas adsorption, odor of a used adsorbent and making a solid waste residue.
In consideration of these circumstances, it is an object of the present invention to provide a method for removing a halogen series gas, which suppresses firing of an adsorbent, which has a high performance of treating a halogen series gas, and which reduces odor of a used adsorbent and making a solid waste residue.
The present invention provides a method for removing a halogen series gas, which comprises bringing a halogen series gas comprising a halogen element or a halogen compound into contact with a granulated product, wherein the granulated product is obtained by granulating a powder of a hydrogencarbonate having a mean particle diameter of primary particles of from 10 to 500 &mgr;m, and has a mean particle diameter of from 0.5 to 20 mm and an average hardness as defined below:
in a case where the granulated product has a mean particle diameter of at least 0.5 mm and less than 1.0 mm, the average hardness of granulated product particles having particle diameters of at least 0.5 mm and less than 1.0 mm is at least 1 N;
in a case where the granulated product has a mean particle diameter of at least 1.0 mm and less than 1.5 mm, the average hardness of granulated product particles having particle diameters of at least 1.0 mm and less than 1.5 mm is at least 4 N;
in a case where the granulated product has a mean particle diameter of at least 1.5 mm and less than 2.0 mm, the average hardness of granulated product particles having particle diameters of at least 1.5 mm and less than 2.0 mm is at least 10 N; and
in a case where the granulated product has a mean particle diameter of from 2.0 mm to 20 mm, the average hardness of granulated product particles having particle diameters of at least 2.0 mm is at least 30 N.
Now, the present invention will be described in detail with reference to the preferred embodiments.
In the present invention, as the hydrogencarbonate, sodium hydrogencarbonate or potassium hydrogencarbonate may, for example, be used. Particularly preferred is sodium hydrogencarbonate since it can be available in large quantities at a low cost and it is thereby suitable for industrial use, and it has no hygroscopicity, such being convenience for production and preservation of a granulated product. On the other hand, potassium hydrogencarbonate is preferred in a case where inclusion of sodium in e.g. an exhaust gas after the removal treatment has to be prevented.
In the present invention, a powder of the hydrogencarbonate is formed into a granulated product. The granulated product preferably contains the hydrogencarbonate in an amount of at least 70 mass %. If the hydrogencarbonate is less than 70 mass % in the granulated product, a gas removal capacity as a halogen series gas removing agent tends to decrease, whereby a removing agent packed bed has to be renewed frequently. The content of the hydrogencarbonate is particularly preferably at least 80 mass %. Here, as another material which may be contained in the granulated product, an adsorbent other than a hydrogencarbonate or a binder may, for example, be mentioned.
In the present invention, as the powder of a hydrogencarbonate, one having a mean particle diameter of primary particles of from 10 to 500 &mgr;m is used, in view of easiness in granulation and availability in an industrial scale. If the mean particle diameter of primary particles is less than 10 &mgr;m, flowability tends to be poor and operation such as particle handling tends to be difficult. If it exceeds 500 &mgr;m, production of such a granulated product tends to be technically difficult, thus causing increase in cost. Here, primary particles are single crystals of a hydrogencarbonate, and the mean particle diameter is a mean particle diameter on the basis of mass.
In the present invention, the mean particle diameter of the granulated product of the powder of a hydrogencarbonate is from 0.5 to 20 mm. When the mean particle diameter of the granulated product is from 0.5 to 20 mm, a conventionally used packed tower or the like can be used during treatment of a halogen series gas. If the mean particle diameter of the granulated product is less than 0.5 mm, pressure drop tends to be high when a halogen series gas or a gas to be treated containing it passes through e.g. a packed bed. If the mean particle diameter exceeds 20 mm, the contact area of the granulated product with the gas to be treated tends to decrease, thus decreasing an exhaust gas removal performance. The mean particle diameter of the granulated product is particularly preferably from 0.5 to 10 mm.
In the present invention, the mean particle diameter of the granulated product is measured as follows. Sieves having sieve openings within ranges fit for the particle diameters of the granulated product are overlaid on top of one another, a bottom tray is disposed at the basement, and the granulated product is sprinkled on the top sieve, followed by shaking by a Ro-Tap Sieve Shaker. Then, a mass of oversize particles remaining on each standard sieve is measured, a cumulative mass of the oversize particles on each of the sieves having the respective sieve opening values is shown by a line graph, and the particle diameter when the cumulative mass of the oversize particles is 50% is taken as the mean particle diameter. As the difference in the sieve opening between adjacent sieves, a pitch of 0.5 mm is preferably employed, although it depends on the particle diameters of the granulated product.
In the present invention, the granulated product can be obtained by various methods such as compression molding, extrusion molding, rotating granulation and agitation granulation. Here, compression molding is particularly preferred since steps are simple and can be carried out industrially easily, and the granulated product can be obtained without using a binder, and further, a granulated product having a high hardness and is less likely to break, which has a large gas treatment capacity, can be obtained.
As a method to obtain the granulated product, a method of carrying out molding by dry process by using a compression molding machine, followed by coarse crushing and sieving may, for example, be mentioned. Further, a method of carrying out molding by a wet type granulating machine by using a water-soluble binder, followed by drying, may also be mentioned.
In the present invention, in a case where the granulated product of the powder of a hydrogencarbonate is packed in a packed bed to treat a halogen series gas, if the strength is low, the granulated product tends to be powdered and the pressure drop tends to increase when the halogen series gas is passed through the packed bed in some cases. Accordingly, the strength of the granulated product is made high.
As a method of evaluating the strength of the granulated product in the present invention, hardness may be mentioned. Here, the hardness is a force which is required to break one particle of the granulated product by vertically applying a load from above for compression.
The method of evaluating hardness in the present invention is carried out with respect to a group of particles having uniform particle diameters, obtained by classifying particles of the granulated product depending upon the mean particle diameter. For example, with respect to the granulated product having
Hirano Hachiro
Kawabe Yoshikatsu
Mori Yoichi
Asahi Glass Company Limited
Johnson Edward M.
Oblon & Spivak, McClelland, Maier & Neustadt P.C.
Silverman Stanley S.
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