Gas separation: apparatus – Solid sorbent apparatus – Plural diverse separating means
Reexamination Certificate
2000-03-31
2002-03-05
Spitzer, Robert H. (Department: 1724)
Gas separation: apparatus
Solid sorbent apparatus
Plural diverse separating means
C096S142000, C096S147000, C055S385200, C055S521000, C055S528000
Reexamination Certificate
active
06352579
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a chemical filter unit and a gas cleaning system.
The present invention relates to a chemical filter unit and a gas cleaning system which can decrease the chemical pollutants in a gas, particularly in the air supplied to a clean room, clean booth or clean bench, etc. (hereinafter called a closed clean space) to very low levels by using ion exchange or electric charge adsorbing action, are low in the pressure loss of the gas to be treated and can be used for a long period.
BACKGROUND ARTS
In recent years, in the electric and electronic industry, biochemical industry, etc., the demand for closed clean spaces has been sharply increasing. With the improvement of production techniques in the respective industries, the demand for cleanness becomes very severe. In this connection, techniques for analyzing pollutants are also improving dramatically in these years. As a result, the necessity of removing conventionally overlooked substances has been noticed.
The conventional cleaning of air in closed clean spaces is to mainly remove solid particulates by using particulate removing filters such as HEPA filters, and the removal of solid particulates is now controlled to the greatest possible extent.
However, it has been found that when the air in a closed clean space is used cyclically through filters, some of the misty or gaseous chemical substances contained in the air are rather concentrated to levels higher than those in open air. The reason is that in the conventional cleaning of air, the necessity of removing misty or gaseous chemical substances contained in the air has not been noticed, and therefore that the conventional air cleaners did not have such a function.
In the electronic industry where products like very large scale integrated circuits are produced, the necessity of removing the chemical substances began to be noticed. Especially in the photolitho process, the phenomena that the yields of products are lowered by the presence of these chemical substances have been found, and the necessity of developing chemical substance removing techniques of a concept quite different from that adopted in the conventionally used HEPA filters has been noticed.
Especially it is demanded to develop techniques for removing ammonia and amines such as organic amines. Ammonia causes haze and dielectric breakdown in the product, and its presence greatly lowers the yield of the product.
In the chemically amplified resist production process of the photolitho process, protons are generated in the regions irradiated with light as a chemical amplifying agent, to promote the dissolution into the developer. According to this mechanism, the device is formed. If ammonia exists in the atmosphere, protons are neutralized, and dissolution into the developer in this portion is inhibited. This causes a very serious problem called T-TOP failure.
This phenomenon occurs when the ammonia concentration in the air is as small as several parts per billion. The ammonia concentration of the air to be treated is usually tens to hundreds of parts per billion, though different from place to place. To solve the problem, it is necessary that the ammonia concentration in the cleaned air is 5 ppb or less.
LSI manufacturers are required to solve this problem, and desire the development of any filter unit which can keep the ammonia concentration in the air of a closed clean production space as very low as possible.
Japanese Patent Laid-Open No. 1-317512 discloses a method for removing sea salts (including ammonia) in air by letting the air pass through a filter medium containing ion exchange fibers. However, this technique does not state any possibility of removing ammonia by adsorption down to a very low concentration (order of ppb), or any method for lessening the pressure loss of the filter using the filter medium, or any method for increasing the substance adsorption capacity per unit volume of the filter medium which indicates the filter service life.
Japanese Patent Laid-Open No. 61-138543 discloses a filter medium obtained by corrugating a laminate formed by overlaying pulp sheets on both sides of an ion exchange fiber-containing sheet. However, the filter medium is used in the crossflow method in which a gas is fed from the front sheet face of the filter medium to the back sheet face. The technique does not state any method for lessening the pressure loss of the filter using the filter medium or any method for increasing the substance adsorption capacity per unit volume of the filter medium which indicates the filter service life.
Japanese Patent Laid-Open No. 60-183022 discloses a filter composed of cation exchange fibers for arresting mutagenic substances in air. However, the filter medium is used in the crossflow method. The technique does not state any method for lessening the pressure loss of the filter using the filter medium or any method for increasing the substance adsorption capacity per unit volume of the filter medium which indicates the filter service life.
Japanese Laid-Open No. 8-24564 discloses a filter unit containing ion exchange fiber sheets. However, the technique does not state any method for lessening the pressure loss of the filter in the filter unit or any method for increasing the substance adsorption capacity per unit volume of the filter medium which indicates the filter service life.
Therefore, the above prior art cannot meet the demand in the above technique field.
The object of the present invention is to provide a filter unit and a gas cleaning system capable of responding to the above demand.
The present invention provides a filter unit with a very large adsorption capacity of the filter medium compared to the conventional filter media and small in the pressure loss of the filter medium compared to the conventional filter media.
To solve the above problems, it has been considered to increase the quantity of the filter medium per volume, but this method does not solve the latter problem. To solve the latter problem, it has been considered to decrease the quantity of the filter medium per volume, but this method does not solve the former problem. The present invention solve these contradictory problems all at once.
DISCLOSURE OF THE INVENTION
First Version of the Invention
A chemical filter unit, which comprises a filter medium formed by laminating a plurality of fiber sheets and a housing for containing the filter medium, and has a gas inlet open on one face of the housing and a gas outlet open on the other face substantially opposite to the gas inlet, characterized in that gas passages to allow the flow of the gas along the surfaces of the fiber sheets are formed between the respectively adjacent fiber sheets of the filter medium from the gas inlet to the gas outlet, and that the adsorption capacity of the filter medium is 300 eq/m
3
or more.
The gas passages allow the raw gas to flow mainly along the surfaces of the fiber sheets constituting the filter medium. This means that the flow of the raw gas through the filter medium is parallel flow. Since this structure is formed substantially by fiber sheets only, the adsorption capacity of the filter medium can be kept at 300 eq/m
3
or more and the pressure loss of the filter medium can be kept small.
The adsorption capacity refers to the amount of plus charged particulates, mist and gas adsorbed per unit volume (1 m
3
) of the is filter medium under chemical balance. For example in the case of active carbon fibers carrying phosphoric acid, the adsorption capacity is calculated from the total weight of the carried phosphoric acid, based on the maximum balancing capacity achieved when all the reactive groups have reacted to form salts.
In the case of ion exchange fibers, the ion exchange capacity is the adsorption capacity. The method for measuring the ion exchange capacity is not specified. In general, a filter medium with a certain capacity is cut off and caused to react in an acid or alkali with a known normality, and the residue is neutralized for titration.
Second Version of the Inventi
Amano Masaki
Fujumura Yoichi
Hirata Nami
Saruyama Hideo
Schnader Harrison Segal & Lewis LLP
Spitzer Robert H.
Toray Industries Inc.
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