JP3367234B2 - Streaming potential measurement method - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a streaming potential method which is one of methods for obtaining a zeta potential indicating a charged state at an interface. [0002] The streaming potential method is generated between a pair of streaming potential measuring electrodes when a solid sample such as powder or fiber is filled and a flowing liquid is allowed to permeate the packed layer. This is a method of obtaining a zeta potential by measuring a potential difference, that is, a streaming potential, which is based on the following principle. Now, consider a case in which a liquid is pushed into a single capillary tube. The radius of the capillary at this time is r, and the length is l.
And Further, if there is an electric double layer on the wall of the tube, which is considered to be the molecular weight, the thickness is δ, and the potential difference is ζ, the charge q per unit area is given by the following equation (1). Q = εζ / 4πδ (1) where ε: A pressure difference P is applied to both ends of the liquid dielectric tube, and the moving speed of the liquid at that time is u (moving speed at the tube wall) Is u, at a distance of 0, δ. At this time, the frictional force F on the inner surface per unit axial length is given by equation (2). F = 2πrηu / δ (2) where η: In the steady state of the viscosity coefficient of the liquid, F is in balance with the applied pressure, so 2πrηu / δ = Pπr ² / l (3) If δ is eliminated from equations (1) and (3) and deformed, 2πruq = Pεr ² ζ / 4ηl (4) The left side of equation (4) is a current accompanying the movement of the liquid. Therefore,
Assuming that the induced voltage is E, the current i in the capillary is given by equation (5). I = (πr ² λ / l) E (5) where λ: specific conductivity of the liquid. Therefore, from equations (4) and (5), ζ = 4πηλE / εP (6) The equation (6) is called the Helmholz-Smoluchowski equation, and is used when calculating the zeta potential from the streaming potential. In equation (6), since 4πηλ / ε is constant with respect to the measurement sample, the zeta potential (ζ) is related to the ratio of the streaming potential (E) to the pressure (P), and E and P are linear. It turns out that it becomes a relationship. By the way, in order to obtain the zeta potential based on the above principle, the conventional streaming potential method measures, for example, as follows. That is, as shown in FIG. 4, a streaming potential measurement cell 53 is provided on a passage 52 that connects the flowing liquid container 50 and the drainage container 51, and a solid is placed between a pair of electrodes 54 provided in the cell 53. With the sample 55 filled, the liquid 56 in the fluid container 50 is
A constant pressure (P ₂ ) higher than the pressure on one side (in the illustrated example, the atmospheric pressure P ₁ ) is applied, and a pressure difference (ΔP = P ₂ −P ₁ ) between the _two.
The liquid 56 flows from the fluid container 50 side to the drain container 51 side through the packed layer of the sample 55 in the cell 53 by the pressure difference. At this time, a potential difference (flow potential) generated between the electrodes 54 of the cell 53 is measured,
The zeta potential was determined using the measured streaming potential E and the flowing pressure (ΔP). In the streaming potential method described above, the sample 55 is generally filtered with a filter 57 as shown in FIG. 4 in order to prevent the sample from flowing out together with the flowing liquid. , 57. In this case, even if the measurement is performed using the same kind of sample, if the type of the filter 57 is different, the value of the streaming potential generated between the electrodes 54 is different, and therefore, the value of the zeta potential obtained is different. Had occurred. The present invention has been made to solve such a problem, and an object of the present invention is to provide a streaming potential measurement method capable of removing the influence of the zeta potential of a filter and obtaining an original correct zeta potential of only a sample. Aim. In order to achieve the above-mentioned object, the present invention fills and holds a solid sample through a filter between a pair of electrodes and, when a liquid flows through the packed layer, fills and holds the solid sample. A streaming potential measurement method for determining the zeta potential of the same sample by measuring the streaming potential generated between a pair of electrodes and the flowing pressure of the liquid, is characterized in that it is configured as follows. That is, while the zeta potential is measured with the solid sample held between the electrodes via a filter,
Before or after the measurement, measure the zeta potential with only the filter set between the electrodes, and subtract the data or zeta potential obtained by the latter measurement from the data or zeta potential obtained by the former measurement. Is used to determine the zeta potential of only the sample. The relationship between the streaming potential generated between the electrodes when the liquid flows and the flow velocity (or pressure) of the liquid at that time is as follows:
For example, it is as shown in FIG. The absolute value of the streaming potential increases as the flow rate of the flowing liquid increases.
When the streaming potential (and thus the zeta potential) is measured with a filter interposed between the electrode and the sample (for example, powder), the potential of the algebraic sum of the potential generated by the filter and the potential generated by the sample is measured. It is thought that. In this case, it is conceivable that a third potential may be generated due to the interaction between the filter and the sample. Usually, however, the purpose of the measurement is to perform such an interaction (for example, to remove the powder which is the filter and the sample). Since the analysis is not in the case of performing a chemical reaction, a filter that is chemically inert to the sample is used. Therefore, since it is not necessary to consider the potential due to the interaction between the filter and the sample, the streaming potential generated when the liquid flows with the filter interposed between the electrode and the sample is as described above. It is considered that the potential generated from the sample and the potential generated from the filter were combined. Therefore, while the zeta potential is measured with the sample held between the electrodes via a filter, the zeta potential is measured before or after the measurement with only the filter set between the electrodes, and the zeta potential is measured. The data obtained by the latter measurement is subtracted from the data obtained by the measurement (the streaming potential in the example of FIG. 1), or the zeta potential obtained by the latter measurement is subtracted from the zeta potential obtained by the former measurement. . In this way, the zeta potential of the filter can be removed from the zeta potential measured while holding the sample via the filter between the electrodes, so that the zeta potential of only the original sample can be obtained. . The method of the present invention is also useful as an analysis means when there is an interaction between the filter and the sample. Specifically, for example, from the measurement data of the sample measured using an inert filter to the sample and the measurement data of only the filter, while determining data such as zeta potential or streaming potential of only the sample at that time, From the measurement data of the sample measured using the filter whose interaction is to be observed and the measurement data of only the filter, data such as zeta potential or streaming potential of only the sample at that time is obtained, and both zeta potentials or streaming potentials are obtained. By comparing such data, the interaction between the latter filter and the sample can be examined. Embodiments of the present invention will be described below. The method of the present invention can be carried out using, for example, a streaming potential measuring device as shown in FIG. First, the streaming potential measuring device will be described. As shown in FIG.
Is a streaming potential measurement cell (hereinafter, referred to as a cell) 4 in which a packed layer 2 of a solid sample (powder in this embodiment) is sandwiched between a pair of electrodes 3 and 3 via filters f and f; Fluid liquid container 7 containing fluid 6 to be supplied via supply passage 5
And a drainage container 9 that collects the fluid 6 having passed through the cell 4 through a drainage passage 8. Here, the drainage passage 8
Is provided with a flow valve 10 for opening and closing the passage. The cell 4 also applies a flowing potential generated between the electrodes 3 and 3 when the flowing liquid 6 passes through the packed bed 2 to the electrodes 3 and 3.
CPU built into the device via an amplifier 11 connected to
(Not shown). The fluid container 7 is constituted by a container having a pressure-resistant airtight structure. The container 7 has a gas introduction passage 12 for introducing a liquid flow gas (for example, N ₂ gas) supplied from a pressure source (not shown) into the container 7.
A leak passage 14 whose one end is open to the atmosphere and is opened and closed by a leak valve 13 is connected to a pressure gauge 16 which measures the pressure of gas introduced into the container 7 and outputs the measured pressure to the CPU via an amplifier 15. ing. Among them, the gas introduction passage 12 is provided with a pressure regulator 17 for adjusting the pressure of the gas supplied from the pressure source to a predetermined pressure, and a gas introduction valve 18 for opening and closing the passage 12. Then, by opening the gas introduction valve 18 with the leak valve 13 closed, a gas at a constant pressure is introduced into the container 7, and conversely, by closing the gas introduction valve 18 and opening the leak valve 13, the inside of the container 7 is opened. Can be made equal to the atmospheric pressure. On the other hand, in this embodiment, the drainage container 9 is constituted by a sealed container having a pressure-resistant airtight structure. On the upper side of the drainage container 9, a pressure gauge 20 that measures the pressure of the space in the container and outputs the measured pressure to the CPU via the amplifier 19.
A thermometer (not shown) that measures the temperature of the space and a leak passage 22 that is open at one end to the atmosphere and that is opened and closed by a leak valve 21 are connected. Then, when measuring the streaming potential, the flow valve 1
0 and with the drain container side leak valve 21 closed,
The valve 21 is opened once, the inside of the drainage container 9 is opened to the atmosphere, and then closed again to keep the container 9 side airtight. When the measurement is completed, the leak valve 21 is opened to open the inside of the container 9. Can be opened to the atmosphere via the leak passage 22. Next, a description will be given of a method of the present embodiment when the streaming potential is measured using such a streaming potential measuring apparatus 1. In this embodiment, while the packed layer 2 of the solid sample is held between the pair of electrodes 3 and 3 of the cell 4 via the filters f and f, the streaming potential and the like are measured to obtain the zeta potential. Alternatively, a zeta potential is obtained by measuring a streaming potential or the like in a state where only the filters f and f are set between the electrodes 3 and 3 after the measurement (a state where the solid sample is not filled). The flow potential is measured by introducing a gas at a constant pressure into the fluid container 7 and applying the gas pressure to the fluid container 7.
The liquid 6 flows from the side to the drain container 9 side via the cell 4,
The measurement is performed by measuring a potential generated between the electrodes 3 at that time. Now, as shown in FIG. 3, the ordinate represents the streaming potential,
On the graph in which the pressure or flow velocity of the fluid 6 is plotted on the horizontal axis, a sample having the characteristic of a + (plus) gradient, that is, the characteristic that the potential increases as the flow velocity or pressure of the fluid 6 increases ((A It is assumed that the above measurement has been performed using In this case, if the filter f has a negative (-) gradient larger than the sample gradient, the streaming potential is measured with only the filter f set between the electrodes 3 and 3 as a result. (B) is obtained, and as a result of the measurement of the streaming potential and the like of the sample performed using the filter f, a graph as shown in (C) of FIG. The zeta potential of the graph and thus of-is obtained. On the other hand, +
When another filter f ′ having a gradient characteristic is used,
As a result of measuring the streaming potential in a state where only the filter f 'is set between the electrodes 3 and 3, a graph as shown in (D) of the figure is obtained, and the streaming potential of the sample performed using this filter f' As a result of the measurement, a graph as shown in FIG. As described above, even in the case of the same sample, a difference between + and-occurs in the measurement result due to the filter set between the electrode 3 and the sample (filled layer 2). There has been no sufficient study of such a point in the related art, and the problem has been treated as a problem of surface conduction or pressure loss or a problem of interaction between a sample and a filter. However, when the theory of the streaming potential method and the experimental results based thereon are analyzed in detail, it is thought that this is a problem caused by ignoring the potential component caused by the filter, which is rarely due to surface conduction or the like. Therefore, in the present embodiment, the potential component caused by the filter is removed from the result of measuring the streaming potential of the sample using the filter in consideration of the influence of the potential caused by the filter. Calculate the correct zeta potential of only the sample. Specifically, two types of zeta potentials obtained from the above-described two measurement results, that is, a state where the packed layer 2 of the solid sample is held between the pair of electrodes 3 and 3 of the cell 4 via the filters f and f The zeta potential ζ _m obtained as a result of measuring the streaming potential at
When only f is set (solid sample is not filled)
In using the zeta obtained results of the measurement of the streaming potential potential zeta _f, the latter of the zeta potential zeta _f from the former zeta potential zeta _m
By subtracting to determine the zeta potential zeta _s samples only. It is possible to find the original correct zeta potential zeta _s only sample has thus the ζ _s = ζ _m -ζ _f. Here, an experiment performed to confirm the effect of the method of this embodiment will be described. In the following experiment, a sample formed by combining the following solid (sample) and liquid was used. Solid: a glass ball obtained by repeating washing and decanting three to four times with an ion exchange resin. Liquid: After diluting a buffer solution 1 of PH9 with ion-exchanged water 4 and adding KCl to make it 0.001N, finally a pH of 9.1 and a conductivity of 6.84 × 10 ^-4 S / cm. Adjusted to become. Using such a sample, the following 2
For each type of filter (both are installed only on the liquid discharge side)
Was measured for zeta potential. At this time, a 2 mm cell was used to reduce the influence of the pressure loss of the packed bed of the sample. Experiment: A sample was measured using a glass fiber filter. Experiment: The sample was measured using a filter made of cellulose. Experiment: Measured only for the filter used in the measurement. Experiment: Measured only for the filter used in the measurement. Table 1 below shows the results of the measurements in the above experiments. [Table 1] From the results of the experiment and the experiment shown in this table, it can be seen that the zeta potential of the obtained sample varies depending on the filter used. Further, from the results of the experiment, it is understood that the filter itself also has a zeta potential. The method of the present invention is applied to the above measurement results. That is, when the measurement result of the experiment is subtracted from the measurement result of the experiment, the zeta potential value of only the sample is −10.
A value of 48 (mV, the same applies hereinafter) is obtained, and a value of −10.68 is obtained as the zeta potential value of only the sample by subtracting the experimental measurement result from the experimental measurement result. Although the two are slightly different, it can be said that such a difference is within an error range and almost coincides. Thus, according to the method of the present invention, it was confirmed that the influence of the zeta potential of the filter can be removed, and the original zeta potential value of only the sample can be obtained. As described above, according to the streaming potential measurement method of the present invention, the influence of the zeta potential of the filter can be removed from the measurement result of the sample measured using the filter. A correct zeta potential of only the original sample can be obtained. When there is an interaction between the filter and the sample, the method of the present invention can be used as a means for analyzing such an interaction.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is used to explain the operation of the method of the present invention, in which the flow potential of a sample is measured using a filter and the flow potential of only a filter is measured. FIG. 2 is a graph showing the relationship between the streaming potential and the flow velocity or pressure of the liquid at that time. FIG. 2 is a configuration diagram showing an example of a streaming potential measuring device used in the method of the embodiment of the present invention. FIG. 4 is a graph used to show that streaming potential measurement results differ depending on the type of filter. FIG. 4 is a configuration diagram schematically showing a configuration of a streaming potential measurement apparatus used to explain a conventional streaming potential method. DESCRIPTION OF SYMBOLS 2 ... Filled layer (sample) 3 ... Electrode 6 ... Liquid f ... Filter

Claims (1)

(57) [Claims 1] A solid sample is filled and held between a pair of electrodes via a filter, and a flow generated between the pair of electrodes when a liquid flows through the packed layer. In determining the zeta potential of the same sample by measuring the potential and the flowing pressure of the liquid, the zeta potential is measured while holding the solid sample via a filter between the electrodes, while before or after the measurement. The zeta potential is measured with only the filter set between the electrodes, and the data or zeta potential obtained by the latter measurement is subtracted from the data or zeta potential obtained by the former measurement, whereby only the solid sample is measured. A streaming potential measurement method comprising determining a zeta potential.