Distillation: processes – separatory – With measuring – testing or inspecting
Reexamination Certificate
1997-12-17
2003-01-21
Manoharan, Virginia (Department: 1764)
Distillation: processes, separatory
With measuring, testing or inspecting
C159S044000, C159S047300, C159SDIG001, C203S001000, C203S002000, C203S003000, C203S041000, C423S390100, C423S394200
Reexamination Certificate
active
06508915
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a distilling apparatus for distilling and purifying waste liquids such as sulfuric acid employed for chemical treatment in processes for producing semiconductors, etc.
As semiconductor devices such as LCD (Liquid Crystal Display) are produced in increasing numbers, huge amounts of solutions, such as of sulfuric acid, are employed. To achieve distillatory purification of waste liquids employed in production processes efficiently and accurately reduces production costs and contributes to environmental conservation.
In a process of producing semiconductor devices, for example, in a step of cleaning wafers, a solution prepared by adding about 2% by weight (wt %) of hydrogen peroxide to about 97 wt % of a commercially available sulfuric acid and heated to 80 to 120° C. is employed. When the waste liquid left after use of the solution is to be recovered, the added hydrogen peroxide is partly converted into water, and also, water migrates into the solution. Accordingly, the concentration of the sulfuric acid in the waste liquid drops to 80 to 90 wt %. Further, impurities such as silicon, iron, sodium and organic materials are contained in the waste liquid. The recovered waste liquid is sold or recycled by subjecting it to distillatory purification under atmospheric pressure.
FIG. 1
shows an example of a prior art sulfuric acid distilling apparatus for distilling and purifying a sulfuric acid waste liquid.
As shown in
FIG. 1
, the sulfuric acid distilling apparatus is equipped with a concentrating column
101
and a purifying column
102
. A contact type liquid level sensor
103
is disposed in the concentrating column
101
. A valve
104
is opened and closed based on detection results of the liquid level sensor
103
such that a fixed amount of sulfuric acid waste liquid may be in the concentrating column
101
. The waste liquid supplied to the concentrating column
101
is heated by a heater
105
to a predetermined temperature required to achieve distillation (e.g., 300° C. under the atmospheric pressure). The water content formed by distillation is condensed by a condenser
106
, stored in a tank
107
, and discharged by opening a valve
108
. Water is supplied as a cooling medium to the condenser
106
. The sulfuric acid thus concentrated is supplied to the purifying column
102
.
The concentrated sulfuric acid is heated to a predetermined temperature (about 300° C. under atmospheric pressure) by a second heater
109
provided in the purifying column
102
, and thus a purified sulfuric acid solution is formed. The purified sulfuric acid solution is passed through a condenser
110
, stored in a tank
111
and can be discharged by opening a valve
112
. Water is supplied as a cooling medium to the condenser
110
. The residue in the purifying column
102
left, after purification, is condensed by a condenser
113
and stored in a tank
114
. The residue in the tank
114
is discharged by opening a valve
115
.
It is important to control the liquid level such that the amount of sulfuric acid waste liquid in the concentrating column
101
is constant in order to carry out correct control of distillation in the concentrating column
101
. However, in the concentrating column
101
, when the solution is heated, the hydrogen peroxide contained in the solution is vaporized to form foams, and also a large amount of hydrogen peroxide is decomposed to form oxygen foams. Such foaming greatly changes the level of the sulfuric acid waste liquid. Accordingly, the liquid level sensor
103
may erroneously detect the liquid level, making it is very difficult to control the amount of solution in the concentrating column
101
.
Further, since the sulfuric acid in the concentrating column
101
is heated to about 300° C. or higher, related parts in the concentrating column
101
should have sufficient resistance to high temperatures of 300° C. or higher. Further, when the concentrating column
101
is heated to a high temperature, leakage at junctions and damage of the junctions can be induced by heat shock.
Japanese Unexamined Patent Publication No. 61-291407 discloses a process in which hydrogen peroxide contained in a sulfuric acid waste liquid is removed before the waste liquid is treated. According to this process, hydrogen peroxide is preliminarily removed from the sulfuric acid waste liquid by adding a sulfurous acid gas in an amount equal to or more than the equivalent amount of hydrogen peroxide to effect a chemical reaction. This process can prevent oxidation of a membrane for filtering the sulfuric acid waste liquid by hydrogen peroxide. However, the sulfurous acid does not entirely react with the hydrogen peroxide, and can form a reaction product of sulfuric acid and sulfurous acid. The reaction product is present in the sulfuric acid waste liquid as an impurity. As a result, the state of the sulfuric acid waste liquid is changed to lower the sulfuric acid purification accuracy.
The present invention provides a distilling apparatus which facilitates control of the amount of waste liquid.
SUMMARY OF THE INVENTION
Briefly stated, the present invention provides a distilling apparatus including: a distiller which stores therein a solution to be treated and distills the solution to form a distillate; a liquid level detector disposed in the distiller which detects the liquid level of the to be treated solution; a state detector for detecting a physical state of the to be treated solution contained in the distiller; and a control unit for controlling the amount of to be treated solution stored in the distiller based on detection results of the liquid level detector and the state detector.
The present invention further provides a distilling apparatus for distilling a hydrogen peroxide-containing solution to be treated. The apparatus includes: a remover for removing a substantial part of the hydrogen peroxide from the to be treated solution; a distiller, connected to the remover, for storing therein the to be treated solution from which the hydrogen peroxide has been removed and distilling the solution to form a distillate; and a control unit for controlling the amount of to be treated solution stored in the distiller based on a liquid level of the to be treated solution in the distiller.
The present invention provides a method for distilling a solution to be treated. The method includes the steps of: storing the to be treated solution in a distiller; detecting a liquid level of the to be treated solution stored in the distiller with a liquid level detector disposed in the distiller; detecting a physical state of the to be treated solution in the distiller with a state detector; controlling the amount of to be treated solution to be supplied to the distiller based on the liquid level and physical state detection results; and heating the to be treated solution stored in the distiller to form a distillate.
The present invention further provides a method for distilling a hydrogen peroxide-containing solution to be treated. The method includes the steps of: removing a substantial part of the hydrogen peroxide from the to be treated solution; storing the to be treated solution from which hydrogen peroxide has been removed in a distiller; controlling the amount of to be treated solution supplied to the distiller based on a liquid level of the to be treated solution in the distiller; and heating the to be treated solution stored in the distiller to form a distillate.
Other aspects and advantages of the invention will become apparent from the following description, taken in conjunction with the accompanying drawings, illustrating by way of example the principles of the invention.
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patent: 4342625 (1982-08-01), Dennison
patent: 4344826 (1982-08-01), Smith
patent: 4364797 (1982-12-01), Beck et al.
patent: 4963231 (1990-10-01), Ryham
patent: 4985118 (1991-01-01), Kurematsu et al.
patent: 5032218 (1991-07-01), Dobson
patent: 5061348 (1991-10-01), McCormick e
Adachi Daisuke
Fukuizumi Masataka
Matoba Toru
Osuda Hiroshi
Armstrong Westerman & Hattori, LLP
Fujitsu Limited
Manoharan Virginia
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