US 3652223 A
The concentration of a reactant in a liquid carrier is continuously determined by continuously mixing the carrier with another one containing a reactant capable to react with the tested reactant under gas generation, and by continuously measuring changes in either the overall specific gravity of the resulting gas/liquid mixture, or the overall electrical conductivity of the mixture. Suitable simple apparatus is shown.
Description (OCR text may contain errors)
United States Patent Ludvikt 51 Mar. 28, 1972  METHOD AND APPARATUS FOR 56] References Cited CONCENTRATION OF A REACTANT IN STATES PATENTS 3,018,654 1/1962 Gordon et al ..73/23 A LIQUID CARRIER Appl. No.: 847,546
[1.8. CI. ..23/230 R, 23/253 R, 73/401, 73/438, 324/30 Int. Cl. ..G0ll 7/18, G01n 9/26, G0ln 27/10 Field of Search ..23/230, 253; 324/30 B; 73/438, 73/401 3,468,764 9/ 1969 Cohen et a1 3,527,571 9/1970 Neubergeretah ..23/253 Primary Examiner-Morris O. Wolk Assistant Examiner-R. M. Reese AttorneyRichard Low  ABSTRACT tivity of the mixture. Suitable simple apparatus is shown.
12 Claims, 2 Drawing Figures PATENTEDMAR28 I972 @NVENTOR METHOD AND APPARATUS FOR CONTINUOUSLY MEASURING THE CONCENTRATION OF A REACTANT IN A LIQUID CARRIER BACKGROUND OF THE INVENTION This invention relates to continuous analysis of process streams, and more particularly to the determination of a constituent of such a stream which is capable of generating a gas in a stoichiometric ratio when interacting with a suitable reagent.
Hydrogen peroxide is a common constituent of textile bleaching liquors. It has been determined quantitatively in such liquors heretofore by titration in an acid medium with potassium permanganate solution. The titration is relatively time consuming, cannot be fully automated without the use of very complex equipment, and the results of the titration cannot readily be converted into signals suitable for controlling the peroxide concentration in the bleaching liquor. Moreover, relatively large amounts of the expensive permanganate standard solution are needed.
The primary object of this invention is the provision of an analytical method for determining the concentration of hydrogen peroxide in bleaching liquor which is simple and inexpensive, permits continuous sampling of the liquid in a bleaching tank, and may provide control signals for keeping the concentration of hydrogen peroxide in the tank practically uniform.
Another object is the provision of apparatus for performing the method.
With these and other objects in view, as will hereinafter become apparent, the method of the invention involves the continuous independent feeding of first and second liquid carriers at respective constant first and second rates to a reaction vessel having an overflow, first and second reactants, such as hydrogen peroxide and an oxidizing agent, being respectively dissolved or dispersed in the carriers. The reactants are selected for their ability of reacting with each other in the resulting mixture of the carriers and of forming reaction products including a gas which is formed by the reaction at a rate proportional to the concentration of the first reactant in the first carrier. The second rate must be high enough to maintain in the vessel an excess of the second reactant. The carriers should be miscible, and the gas formed at least partly insoluble in the mixture of the carriers. When the resulting gas/liquid reaction mixture is continuously permitted to be withdrawn by overflow from the reaction vessel at a third rate sufficient to keep the combined volume of the reactants, the carriers, and the reaction products in the vessel substantially constant, a physical property of the mixture in the vessel may be measured as an indication of the concentration of the gas present in the mixture as a dispersed separate phase. The measurement is thus uniquely related to the initial concentration of the first reactant in the first carrier.
Suitable apparatus for performing the method may include an upright reaction tube having an opening at the top, feeding means for separately feeding the carriers to the bottom portion of the reaction tube for flow of the resulting reaction mixture from the bottom portion to the top portion of the tube to be withdrawn outward of the tube through the opening. A manometer arrangement may then measure the hydrostatic pressure in the bottom portion of the tube as an indicator of the concentration of the first reactant in the first carrier.
Alternatively, the carriers may be fed to the bottom of the reaction tube through two conductivity cells, the cells and the tube being equipped each with a pair of spaced electrodes, and the electrodes connected in a bridge circuit for measuring the changes in electrical conductivity of the reaction mixture in the reaction tube' Other features, additional objects, and many of the attendant advantages of this invention will readily be appreciated as the same becomes better understood by reference to the following description of preferred embodiments when considered in connection with the appended drawing.
BRIEF DESCRIPTION OF THE DRAWINGS In the drawings:
FIG. 1 shows apparatus for analyzing a bleaching liquor containing hydrogen peroxide by measuring the hydrostatic pressure of a reaction mixture of the liquor with a sodium hypochlorite solution, the apparatus being shown in side elevation; and
FIG. 2 illustrates apparatus for analyzing the aforementioned liquor by measuring the overall electrical conductivity of the aforementioned reaction mixture, the view being as in FIG. 1.
DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring initially to FIG. 1, there are shown the two supply conduits 1, 2 of two commonly driven positive displacement pumps, not otherwise shown, such as two peristaltic pumps whose rotors are mounted on a common drive shaft. The conduits 1,2 are joined to an inlet tubulure of an upright, cylindrical reaction tube 3. A flexible hose 4 connects the lower end of the tube 3 to one end of a measuring tube 5 of uniform bore. A scale 6 attached to the tube 5 is calibrated in units of length along the axis of the tube 5, as will presently be described in more detail.
The end of the tube 5 remote from the hose 4 communicating with ambient atmosphere is attached to an upright supporting plate 24 by a pivot pin 7 having a horizontal axis on the same level as the upper end of the reaction tube 3 which is surrounded by an overflow vessel 8 equipped with a drain 9 for withdrawal of fluid. The friction in the pivot is sufficient to hold the tube 5 in the angular position in which it is set by hand. The zero point of the scale 6 coincides with the pivot axis and is not affected by angular movement of the tube 5.
A fixed electrode 11 in the metering tube 5 adjacent the hose 4 and an electrode 10 axially entering the tube 5 through a loosely fitting plug 25 near the pivot pin 7 are connected to respective terminals 26 and 27 on the plate 24. The upper end of the metering tube 5 is then open to atmosphere due to loosely fitting plug 25.
The apparatus shown in FIG. 1 is operated as follows:
The nonillustrated; ganged,. positive displacement pumps are respectively connected to a bleaching tank and to a reagent supply vessel for pumping bleaching liquor containing hydrogen peroxide and a large excess of sodium hypochlorite solution at respective constant rates into the reaction tube 3 where the hydrogen peroxide is decomposed almost instantaneously to water and oxygen gas. The reaction mixture rises in the tube 3 and overflows from the open top of the tube into the vessel 8 and flows into waste through the drain 9, to maintain the combined volume of the reactants, the carriers and reaction products in the vessel substantially constant.
At a constant pumping rate and otherwise reasonably uniform conditions, the amount of oxygen dispersed in bubbles in the liquid flowing through the reaction tube 3 is a unique function of the hydrogen peroxide content of the bleaching liquor. When the liquor or sodium hypochlorite solution contains a small amount of surfactant or wetting agent, the oxygen bubbles in the flowing liquid are too small to travel upwardly at a significantly higher rate than the enveloping liquid, and they do not adhere to the walls of the tube.
The reaction tube 3 and the measuring tube 5 communicate through the hose 4. In pumping the sodium hypochlorite solution and, into the reaction tube initially, the level thereof in the measuring tube remains aligned with the overflow edge of the reaction tube. The difference in specific gravity between bleaching liquor and the sodium hypochlorite reagent solution isinsignificant, so that when afterwards the bleaching liquor is pumped into the reaction tube simultaneously, as described, changes in the liquid level in the wetting tube correspond to the changes of the hydrostatic pressure in the bottom portion of the tube 3 or of the specific gravity of the reaction mixture in the reaction tube 3, depending on the amount of oxygen dispersed in the tube 3. The scale 6 may be calibrated directly in grams of active oxygen per liter of bleaching liquor or in similar units.
If the characteristics of the system are changed, for example, after replacement of a resilient tube in the peristaltic pump supplying the bleaching liquor or the reagent solution or by major changes in ambient temperature of pressure, the
measuring tube 5 is reset angularly on the pivot pin 7 to restore proper calibration.
The illustrated apparatus may also control the supply of hydrogen peroxide to the bleaching tank in order to make up for consumption of the oxidizing agent and for drag-out losses. The terminals 26, 27 are arranged in a nonillustrated; and entirely conventional circuit with a relay, a current source and a normally closed solenoid valve in a supply line connecting a storage vessel for hydrogen peroxide with the bleaching tank.
When the peroxide content in the liquor pumped to the reaction tube 3 decreases, the specific gravity of the liquid in the reaction tube increases and the level of the gas-free liquid in the measuring tube 5 rises. The liquid in the tube 5 is sufficiently conductive to energize the relay when the liquid connects the electrodes 10,11, and the relay closes the energizing circuit of the solenoid valve to supply fresh hydrogen peroxide to the bleaching tank. The resulting gradual increase in the gas content and decrease in the specific gravity of the liquid in the reaction tube 3 causes the liquid level to fall in the measuring tube 5 until the circuit between the electrodes 10,11 is broken,.and the non-illustrated solenoid valve interrupts the flow of oxidant to the bleaching tank. The hydrogen peroxide concentration in the bleaching liquor may be changed by shifting the electrode 10.
The illustrated apparatus may be used without change for measuring hypochlorite concentration in an alkaline chlorine bleaching liquor when hydrogen peroxide in excess is used as the reagent. The scale 6 may be calibrated in grams of available chlorine per liter of bleaching liquid or similar units.
The apparatus shown in FIG. 1 combines simplicity with good sensitivity, and has been operated successfully over extended periods. It needs to be cleaned periodically from gross contaminants carried over from the bleaching tank, but does not require any other maintenance work. It may be modified, if so desired, by substituting any other type of indicating and controlling manometer for the tube 5 and its electrodes 10,11.
The analyzer shown in FIG. 2 has an upright reaction tube 3 whose open top is received in an overflow vessel 8 equipped with a drain 9, as described above. The lower end of the reaction tube 3 is connected by a Y-fitting with two conductivity cells 12,13 which are open-ended tubes equipped with respective pairs of axially spaced electrodes 14,15 and 16,17. Two electrodes 18,19 are similarly spaced axially in the reaction tube 3.
A proportionating pump 21, which may consist of two ganged peristaltic pumps as described above, is arranged to pump bleaching liquor containing hydrogen peroxide from a non-illustrated bleaching tank through one of the cells 12,13 into the reaction tube 3, and sodium hypochlorite reagent solution from a non-illustrated storage vessel through the other cell into the reaction tube 3' where the two liquids are mixed at fixed rates and oxygen bubbles are formed by the reaction of hydrogen peroxide and sodium hypochlorite.
The electrodes 14 19 are connected with each other, with a potentiometer 20, a galvanometer 23, and an alternating current source in a resistance or conductivity bridge circuit. The electrodes of the two cells 12,13 are arranged in parallel circuit in one arm of the bridge circuit, and the electrodes 18,19 in the reaction tube 3 provide the second arm. The portions of the potentiometer 20 between the two fixed terminals respectively and the movable terminal provide the third and fourth arms of the bridge. The current source 28 is connected across one diagonal of the bridge, and the galvanometer 23 equipped with a rectifier 22 is connected across the other diagonal, as is conventional.
Conductivity changes in the two pumped liquids do not affect the readings of the device illustrated in FIG. 2 which indicate the distribution of liquid and gas in the fluid flowing through the reaction tube 3'. At a constant pumping rate, and in the presence of a large excess of the reagent over the analyzed compound, the readings of the bridge circuit are uniquely related to the variable concentration of the analyzed compound which may be read from a nonillustrated; experimentally calibrated scale cooperating with the movable potentiometer contact when the galvanometer 23 reads zero. The apparatus shown in FIG. 2 may be modified in an obvious and well-known manner to control the flow of hydrogen peroxide or of sodium hypochlorite solution to a bleaching tank in the manner of the device illustrated in FIG. 1.
The apparatus illustrated in FIGS. 1 and 2 may be employed to measure the quantitative relationship of a known liquid and a gas dispersed in the liquid as a separate phase regardless of the reaction which produces the mixture of gas and liquid, and may thus be employed for measuring the concentration of reagents other than those specifically described with reference to the drawing. Potassium permanganate and other soluble salts of hypochlorous acid such as the calcium salt may be substituted for the sodium hypochlorite in a known manner for determining the concentration of hydrogen peroxide or of the permanganate or calcium hypochlorite, and other reactants will readily suggest themselves to those skilled in the art.
While aqueous carriers for the reactants have been described specifically, at least the apparatus of FIG. 1 may be employed without change for measuring concentration of the gas-generating reactant in a non-aqueous liquid carrier. The gas produced must be at least partly insoluble in the reaction mixture, but the carriers should be miscible with each other, and the physical property that is measured is a function of the amount of gas dispersed as a separate phase in the reaction mixture.
1. A method of continuously measuring the concentration of a first reactant in a first liquid carrier which comprises:
a. continuously feeding said first liquid carrier containing said first reactant to a reaction vessel at a constant first rate;
b. continuously feeding separately a second liquid carrier having a second reactant dispersed therein to said reaction vessel at a constant second rate, whereby a mixture of said carriers and said reactants is formed in said vessel,
1. said reactants being capable of reacting with each other in said mixture and of forming reaction products including a gas formed by the reaction at a rate proportional to the concentration of said first reactant in said mixture,
2. said second rate for feeding said second liquid carrier being sufficient to maintain in said vessel an excess of said second reactant,
3. said carriers being miscible, and said gas being at least partly insoluble in the mixture of said carriers,
continuously permitting the flow of reaction mixture from said reaction vessel at a third rate sufficient to keep the combined volume of said reactants, of said carriers, and of said reaction products in said vessel substantially constant; and
. continuously measuring a physical property of the reaction mixture in said vessel as an indication of the concentration of said gas present in said mixture as a dispersed separate phase. v
2. A method as set forth in claim 1, wherein said physical property is the overall specific gravity of said reaction mixture.
3. A method as set forth in claim 1, wherein said physical property is the overall electrical conductivity of said reaction mixture.
4. A method as defined in claim 1, wherein at least one of said liquid carriers contains a wetting agent.
5. A method as set forth in claim 1, wherein one of said reactants is hydrogen' peroxide, said gas is oxygen, and said carriers are aqueous liquids.
6. A method as set forth in claim 5, wherein the other reactant is a soluble salt of hypochlorous acid.
7. An apparatus suitable for measuring hydrogen peroxide concentration in an aqueous bleaching bath comprising, in combination:
a. an upright reaction tube having a top portion and a bottom portion, said top portion having an opening;
b. feeding means for separately feeding said bath and a reagent solution to said bottom portion for flow of the resulting mixture from said bottom portion to said top portion and outward of said tube through said opening; and
c. manometer means for measuring the hydrostatic pressure in said bottom portion.
8. An apparatus as defined in claim 7, wherein said manometer means includes a pressure measuring tube communicating by one of its ends with the ambient atmosphere and by the other end with the bottom portion of said reaction tube, said reaction tube and said pressure measuring tube forming communicating vessels; and comprising index means for indicating changes in liquid level in said pressure measuring tube.
9. An apparatus as defined in claim 8, wherein the liquid in said pressure measuring means is electrically conductive, and wherein a stationary electrode is mounted in said pressure measuring tube at its end adjacent the bottom of said reaction tube, and an adjustable electrode is arranged in said pressure measuring tube at its other end.
10. An apparatus as defined in claim 8, wherein said pressure measuring tube communicates with the bottom portion of said reaction tube via a flexible hose and is pivotally mounted at its upper part for changing the slant and thus the response thereof.
11. An apparatus suitable for measuring hydrogen peroxide concentration in an aqueous bleaching bath comprising, in combination:
a. an upright reaction tube having a top portion and a bottom portion, said top portion having an opening;
b. two tubular cells having each a first and a second end portion, said first end portions communicating with said bottom portion;
c. means for feeding said bath and a reagent solution to said second end portions respectively for flow through said cells into said reaction tube, and for discharge of the resulting mixture from said tube through said opening;
d. a pair of spaced electrodes in said reaction tube and in each of said cells; and
e. bridge circuit means conductively connecting said elec trodes for measuring the difference between the conductivity of the mixture in said tube and the combined conductivity of said bath and of said reagent solution in said cells.
12. An apparatus as defined in claim 1 1, wherein said bridge circuit means is a Wheatstone bridge circuit.