Method for measuring solubility and diffusion coefficient of partially mutually soluble liquid system

Abstract

The invention relates to a method for measuring the solubility and the diffusion coefficient of a partially intersoluble liquid system, and belongs to the technical field of solubility and diffusion coefficient measurement. The width of the widest part of a diffusion image of partially intersoluble liquid is consistent with the width of a saturated solution image for the first time; collecting width images of different solutions with known mass fractions, obtaining a relation omega-W between the mass fractions of the solutions and the image widths, substituting the saturated solution layer width of the diffusion image into the relation omega-W to obtain the mass fraction of the saturated solution, and obtaining the solubility of the solutions through a solubility calculation formula; when the diffusion coefficient is measured, the diffusion coefficient is obtained based on a one-dimensional semi-infinite long diffusion model by adopting an equal refractive index thin layer method. According to the invention, the solubility and diffusion coefficient parameters can be obtained at the same time, the experiment efficiency is improved, and the device can be suitable for measuring the solubility and diffusion coefficient of different parts of mutually soluble system liquid.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of solubility and diffusion coefficient measurement, in particular, relates to a method for measuring solubility and diffusion coefficient of partially miscible liquid system. BACKGROUND

[0002] Dissolution refers to the process of one or more substances (solute) dispersing into another substance (solvent) to form a uniform and stable mixture. This process relies on the diffusion of particles (such as molecules, atoms or ions) along the concentration gradient. Partially miscible liquid systems are very common in the fields of chemistry, biology and industry, and their dissolution behavior is particularly relevant to the fields of separation and purification, material synthesis and environmental remediation. Solubility (S) and diffusion coefficient (D) are basic parameters that describe the mass transfer mechanism of partially miscible liquid systems, and their accurate measurement is of great significance. Accurate measurement of S and D values in partially miscible systems is crucial for optimizing reaction conditions, improving reaction efficiency and product purity, and thus improving the overall performance of the product.

[0003] Common methods for measuring S values include cloud point method, shake flask method, etc. In the cloud point method, the solute is slowly added to the transparent solvent, and the transition from transparent to turbid is monitored in real time, and the inflection point corresponds to the saturated solution. Although this method is simple and clear, it is difficult to detect the critical point, which limits its measurement accuracy. In the shake flask method, excess solute is mixed with the solvent, then thoroughly shaken and left to separate the phases. Then the S value is determined by analyzing the concentration of one of the phases, which eliminates the concern about the amount of solute used, but requires the use of other techniques such as chromatography or spectroscopy to measure the saturation concentration, which is a tedious and equipment-intensive process. Common methods for measuring D values include membrane cell method, optical interferometry and Taylor dispersion method, etc. The membrane cell method requires measuring the concentration of the solution in the upper and lower cell regions in the initial state and the steady state, and since it takes a long time for the diffusion system to reach a steady state, this process is very time-consuming. The optical interferometry method analyzes D by measuring the spatial and temporal distribution of concentration in the diffusion solution reflected by the interference fringes, which has the outstanding advantage of high measurement accuracy of solution refractive index and concentration, but its susceptibility to environmental interference is still a limitation. The Taylor dispersion method is to inject a small amount of solute into the solvent flowing through the capillary, and calculate D by measuring the concentration distribution of the solution along the capillary axis at different times. However, the uneven flow rate of the flowing phase and the inaccuracy of the concentration distribution detection reduce the measurement accuracy of this method. Moreover, the above methods can only measure D values or S values, and when both S and D values of miscible liquids are needed, different methods are required to measure S and D values respectively, which is inefficient and complex. SUMMARY

[0004] In order to overcome the problems in the prior art, the present application provides a method for measuring the solubility and diffusion coefficient of a partially miscible liquid system, which can measure the solubility and diffusion coefficient of a partially miscible liquid, and has the characteristics of simple operation, fast and accurate measurement.

[0005] In order to achieve the above-mentioned purpose, the present application is realized by the following technical solutions:

[0006] The method for measuring the solubility of a partially miscible liquid system is carried out using a measuring device comprising a laser, an attenuating sheet, a beam expander, a slit, a composite liquid core column lens, and a CCD, and comprises the following steps:

[0007] (1) using the measuring device to image at least 8 groups of different known mass fraction solutions respectively;

[0008] (2) processing the width images of different mass fraction solutions received by the CCD, measuring the width of each image, and obtaining the corresponding image width of different known mass fraction solutions;

[0009] (3) using the least squares method to fit the mass fraction and the corresponding image width data to obtain the relationship ω-W between the mass fraction of the solution and the image width;

[0010] (4) sequentially injecting the solute and the upper liquid into the composite liquid core column lens, injecting the solute into the bottom of the liquid core of the composite liquid core column lens, and after the solute is stable, injecting the upper liquid into the upper part of the solute along the inner wall of the liquid core of the composite liquid core column lens, without obvious convection between the solute and the upper liquid during the injection process;

[0011] (5) as the solute and the upper liquid diffuse with each other, a diffusion solution is formed, and after the diffusion solution tends to be stable in the composite liquid core column lens, the diffusion image of the partially miscible liquid is collected by the CCD, and the width of the widest part of the diffusion image is taken as the width of the saturated solution;

[0012] (6) the width of the saturated solution in step (5) is brought into the relationship ω-W between the mass fraction of the solution and the image width in step (3) to obtain the mass fraction of the saturated solution;

[0013] (7) the mass fraction of the saturated solution is brought into the solubility calculation formula to obtain the solubility S of the partially miscible liquid.

[0014] Further, the upper liquid is a low concentration solution or a solvent of the solute.

[0015] Further, before step (1), a target observation thin layer solution is configured, the target observation thin layer solution is injected into the composite liquid core column lens, and the images of steps (1) and (5) fix the CCD at the focal plane position of the imaging of the target observation thin layer solution.

[0016] Further, the target observation thin layer solution concentration is greater than the concentration of the upper liquid.

[0017] Further, the solubility calculation formula of step (7) is,

[0018]

[0019] Wherein, s is the solubility, ω s is the mass fraction of saturated solution.

[0020] Further, the diffusion coefficient measurement is carried out at the same time of measuring the solubility, the diffusion coefficient measurement method is, based on one-dimensional semi-infinite diffusion model and using equal refractive index thin layer method, according to the diffusion image data collected by CCD collection device at different times, the diffusion coefficient of part of mutually soluble liquid system is calculated by using Fick's second law combined with boundary conditions; Specifically, the beam waist position at different times is recorded, and the diffusion coefficient is obtained by least square fitting.

[0021] Further, the expression of the diffusion coefficient is:

[0022]

[0023] Linear fitting Z and And the slope is set as k, then the diffusion coefficient,

[0024]

[0025] Wherein, Z is the position of the target observation thin layer solution, ω(Z, t) is the mass fraction of the liquid at position Z and time t, erfinv is the inverse error function, ω s is the mass fraction of saturated solution, ω1 is the mass fraction of the upper liquid, D is the diffusion coefficient, ω c is the mass fraction of the target observation thin layer solution.

[0026] Further, the measurement step of the measuring device is,

[0027] (1) The laser, attenuator, beam expander, slit, composite liquid core column lens and CCD collection device are placed in order from left to right;

[0028] (2) The target observation thin layer solution is injected into the composite liquid core column lens, and the CCD collection device is moved to the focal plane position of the target observation thin layer solution imaging, at this time the CCD can collect a thin sharp bright line;

[0029] (3) after the composite liquid core column lens is thoroughly cleaned, a solute is first added to the composite liquid core column lens, and after the solute is stable, an upper liquid is injected into the composite liquid core column lens, and a diffusion solution is formed between the solute and the upper liquid;

[0030] (4) after the diffusion solution tends to be stable in the composite liquid core column lens, a laser is started to emit monochromatic laser to the attenuating sheet, the monochromatic laser is reduced in light intensity by the attenuating sheet, and the monochromatic laser with reduced light intensity is expanded into a wide light beam by the beam expander, and the wide light beam is filtered and adjusted in width by the slit, and then is incident into the composite liquid core column lens to form an optical path;

[0031] After a predetermined time interval, an image in the composite liquid core column lens is collected by a CCD to obtain a diffusion image of the diffusion solution.

[0032] Further, the predetermined time interval is greater than 20 min; and in step (4), the image in the composite liquid core column lens is collected at a fixed time interval.

[0033] The present application has the following beneficial effects:

[0034] The measuring device of the present application comprises a laser, an attenuating sheet, a beam expander, a slit, a composite liquid core column lens and a CCD, and first images of different known mass fraction solutions are obtained, the width images of the different mass fraction solutions received by the CCD are processed, the width of each image is measured, the least square method is used to fit the mass fraction and the corresponding image width data, and the relationship ω-W between the mass fraction and the image width is established.

[0035] The present application first finds that the image width of a saturated solution is the same as the width of the widest part in a diffusion image, the width of the saturated solution is directly obtained from the width of the widest part in the diffusion image, the mass fraction of the saturated solution is obtained according to the relationship ω-W between the mass fraction and the image width, and the solubility of the partially miscible liquid is obtained from the solubility calculation formula, thereby providing a new method for measuring the solubility of the partially miscible liquid.

[0036] The measuring method of the present application compares the width of the widest part in the diffusion image with the width of the saturated solution image, the width of the widest part in the diffusion image remains unchanged and is consistent with the width of the saturated solution image, which can indicate that the diffusion model of the partially miscible liquid system is a one-dimensional semi-infinite diffusion model, and the solution thin layer corresponding to the widest part in the diffusion image is a saturated solution thin layer. On this basis, the diffusion image data at different times collected by the CCD collection device are used to solve the problem by using the second Fick's law combined with the boundary conditions, and the diffusion coefficient of the partially miscible liquid system is calculated.

[0037] The measuring device of the present application can simultaneously measure the solubility and the diffusion coefficient of the partially miscible liquid, thereby simplifying the measurement steps of the solubility and the diffusion coefficient of the partially miscible liquid. Attached Figure Description

[0038] Figure 1 This is a schematic diagram of the measurement method of the present invention;

[0039] Figure 2 This is a schematic diagram of the measuring device architecture of the present invention;

[0040] Figure 3 This is an example diagram of a composite liquid-core column lens that can be used in this invention;

[0041] Figure 4 This is a width image of triacetylglycerol solutions with different mass fractions entering the composite liquid core lens in Example 2 of the present invention;

[0042] Figure 5 This is a schematic diagram of the diffusion image and the width of the saturated solution acquired in Embodiment 2 of the present invention;

[0043] Figure 6 This is a graph showing the change of the waist position of the triacetin solution at five temperatures (288K, 293K, 298K, 303K, 308K) over time in Example 2 of the present invention. Detailed Implementation

[0044] To make the objectives, technical solutions, and beneficial effects of this invention clearer, the technical solutions of this invention will be described in detail below. Obviously, the described embodiments are only a part of the embodiments of this invention, and not all of them. Other embodiments obtained by those skilled in the art based on the embodiments of this invention without creative effort are all within the scope of protection of this invention.

[0045] To illustrate the present invention more clearly, the following embodiments will be described in detail.

[0046] Example 1

[0047] The measurement method of the present invention uses a measuring device including a liquid core lens (hereinafter referred to as the measuring device). The measuring device includes, from left to right, a laser, an attenuator, a beam expander, a slit, a compound liquid core lens, and a CCD acquisition device. The arrangement of the measuring devices is shown in the attached figure. Figure 2 . Figure 3 This is an example diagram of a composite liquid-core column lens.

[0048] The method for simultaneously measuring the solubility and diffusion coefficient of a partially miscible liquid system using this measuring device includes the following steps:

[0049] Step S10: Acquire width images of solutions with different known mass fractions and establish the relationship ω-W between mass fraction and corresponding image width.

[0050] The steps to obtain the image width are as follows: a low-concentration solution with a concentration slightly greater than that of the upper liquid is injected into the composite liquid core column lens as the target observation thin layer solution, and a solution with a mass concentration of 2%-10% is usually selected as the target observation thin layer solution. Adjust the position of the CCD to be at the focal plane position of the composite liquid core column lens, at which time a thin and sharp bright line appears on the CCD. Fix the position of the CCD, pour out the target observation thin layer solution, and thoroughly clean the composite liquid core column lens.

[0051] Different known mass fractions of the to-be-measured solution are injected respectively; the image width data corresponding to different mass fractions of the to-be-measured solution are recorded, and during the imaging process, the CCD is fixed at the focal plane position of the image formed by the target observation thin layer solution (hereinafter the imaging process will be described with the CCD fixed at the focal plane position of the image formed by the target observation thin layer solution).

[0052] The least square method is used to fit the solution mass fraction and the corresponding image width data to obtain the functional relationship ω-W between the solution mass fraction and the image width.

[0053] In step S20, the solute and the upper liquid are sequentially injected into the composite liquid core column lens. The solute is injected into the bottom of the liquid core of the composite liquid core column lens; after the solute is stable, a certain time length is waited, and the same volume of the upper liquid is injected along the inner wall of the liquid core of the composite liquid core column lens to the upper part of the composite liquid core column lens, wherein it is ensured that there is no obvious convection between the two liquids during the injection process. Optionally, the reference injection speed of the digital injection pump is 0.25 mL / min.

[0054] It should be noted that the upper liquid can be a pure solvent for dissolving the solute, or a low-concentration solution formed by dissolving the solute with a solvent. When the upper liquid is a low-concentration solution, the concentration of the upper liquid is not specifically required, and only a sufficient concentration difference between the solute and the upper liquid is required to generate diffusion.

[0055] After the diffusion solution tends to be stable in the composite liquid core column lens, the laser is started to emit monochromatic light to the attenuating sheet, the light intensity of the monochromatic light is reduced through the attenuating sheet, the monochromatic light with reduced light intensity is expanded into a wide light beam through the beam expander, and the wide light beam is filtered and width-adjusted through the slit and then enters the composite liquid core column lens to form an optical path; after 60 min, the diffusion image is collected by the CCD collection device every 5 min.

[0056] The diffusion image is widest at the interface between the two liquids and remains unchanged during the diffusion process, and the width of the diffusion image is consistent with that of the saturated solution, so it can be concluded that the diffusion model of the partially miscible liquid system is a one-dimensional semi-infinite diffusion model. The liquid thin layer corresponding to the widest part of the diffusion image is the saturated liquid thin layer, and the width of the widest part of the diffusion image is equal to the image width of the saturated solution.

[0057] Step S30, the saturated liquid thin layer width of the diffusion image is substituted into the ω-W relationship to obtain the mass fraction of the saturated solution, and the solubility S is obtained by using the solubility calculation formula.

[0058] The solubility calculation formula is:

[0059]

[0060] In the formula, s is the solubility, ω s is the mass fraction of the saturated solution.

[0061] Step S40,

[0062] The moment when the solute is in contact with the solvent is recorded as t=0, and after waiting for 60 minutes, the CCD acquisition device acquires images in the composite liquid core lens every 5 minutes, and diffusion images at different times are obtained.

[0063] It should be noted that since the composite liquid core lens deflects only in one direction, the focal length of each position of the column lens is different after the diffusion starts. Therefore, the CCD only needs to be placed at the focal plane of the target observation thin layer solution (the mass fraction is ω c ), and the image of different widths at each position will appear on the light screen. Only the change of the "beam waist" position with time needs to be read.

[0064] As the diffusion proceeds, the solution at the interface (Z=0) between the solute and the diffusion solution is saturated, and the mass fraction is constant ω s (obtained by the ω-W relationship in step S20); the mass fraction of the upper liquid upper boundary (Z=+∞) is constant ω1, and the boundary condition is:

[0065]

[0066] Substitute the boundary condition into the second law of Fick:

[0067]

[0068] Then the following can be obtained:

[0069]

[0070] Finally, the diffusion coefficient of the partially miscible liquid can be obtained:

[0071]

[0072] In the formula, Z is the position of the observation target thin layer solution, erfinv is the inverse error function, ω s is the mass fraction of the saturated solution layer, ω1 is the mass fraction of the injected upper liquid, D is the diffusion coefficient, and ω cTo observe the thin layer solution mass fraction.

[0073] Example 2

[0074] This example is an application example, the solubility and diffusion coefficient of triacetin solution are measured by the method and measuring device of example 1, as follows:

[0075] First, inject 2% triacetin aqueous solution into the composite liquid core column lens, adjust the position of the CCD acquisition device to be at the focal plane position of the composite liquid core column lens, at this time a thin sharp bright line appears on the CCD. Pour away the 2% triacetin solution and thoroughly clean the composite liquid core column lens.

[0076] Inject different known mass fractions of triacetin aqueous solution into the composite liquid core column lens, respectively, collect the width images of different mass fractions of triacetin aqueous solution (as shown in Figure 4 (a)-(h)), measure the image width, and obtain the mass fraction and image width as shown in table 1.

[0077] Table 1 Relationship between mass fraction and image width of triacetin aqueous solution at 298K

[0078]

[0079]

[0080] The mass fraction and corresponding image width data are fitted by the least squares method to obtain the relationship between the mass fraction and image width of triacetin aqueous solution at 298K ω-W,

[0081] ω = 0.0086W + 1.9721

[0082] Where ω is the mass fraction and W is the image width.

[0083] Similarly, the mass fraction and width relationship ω-W at five temperatures (T) are as follows:

[0084]

[0085] Fix the CCD at the position where the 2% triacetin solution can be clearly imaged in the composite liquid core column lens, that is, the thin layer solution corresponding to the "waist" of the diffusion image. That is, during the diffusion process, we will focus on observing the 2% triacetin thin layer solution (ω c = 2%).

[0086] After thoroughly cleaning the composite liquid core lens, pure triacetyl ester (solute) was first injected into it. The triacetyl ester was allowed to stand for 10 minutes to eliminate turbulence. Then, an equal volume of pure water (solvent, ω1 = 0%) was slowly injected into the composite liquid core lens at a rate of 0.25 mL / min. To avoid interference from turbulence during liquid injection, diffusion images were recorded every 5 minutes after 60 minutes of injection. The diffusion images are shown below. Figure 5 As shown in (a)-(k).

[0087] Analysis of the diffusion image indicates that in the region immediately adjacent to the solute and solvent (upper liquid), due to the partial miscibility of the solute and solvent, diffusion occurs in the upper layer of the liquid. Figure 5 The interface between the miscible region and the solute can be clearly seen in (a)-(k). Figure 5 The obtained image is a diffusion image of the miscible region. Analysis of the diffusion image shows that a constant width W1 (e.g., ...) is maintained above the interface between the miscible region and the solute. Figure 5 (as shown by the short red line in (a)-(k)), and Figure 5 (l) The image width W2 (corresponding to) when the composite liquid-core lens is injected with a homogeneous saturated triacetyl ester solution. Figure 4 (i) The width above the interface is consistent. Therefore, the model of the partially miscible liquid system is a one-dimensional semi-infinite diffusion model. This also indicates that the thin layer of solution above the interface between the miscible region and the solute is a saturated triacetylglycerol aqueous solution. Therefore, the width at the widest point of the diffusion image can be taken as the width of the saturated solution.

[0088] Measurement Figure 5 The width of the miscible region above the solute interface in the image is used as the basis for calculating the mass fraction ω of the saturated solution by substituting it into the ω-W relationship. s The mass fraction of the saturated solution was converted to its corresponding solubility S using the solubility calculation formula. Table 2 lists the ω of triacetylglycerol at different temperatures. s and S value.

[0089] Table 2. ω of triacetylglycerol in water at different temperatures s and S value

[0090]

[0091]

[0092] Figure 6 Z was displayed i (The distance between the liquid interface and the "waist" is equivalent to) Figure 5 The variation of the 2% solution layer (indicated by arrows in (a)-(k)) with diffusion time at five different temperatures. Linear fitting Z and and the slope is set as k, based on one-dimensional semi-infinite diffusion model, according to the ω s value in Table 2 into the formula:

[0093]

[0094] The D value of triacetin diffusing in water at 288K-308K temperature can be determined, as shown in Table 3.

[0095] Table 3 D value of triacetin at different temperatures

[0096]

[0097] Finally, it should be pointed out that the above preferred embodiments are only used to illustrate the technical solutions of the present application and are not limiting. Although the present application has been described in detail through the above preferred embodiments, those skilled in the art should understand that various changes can be made in form and details without departing from the scope defined by the claims of the present application.

Claims

1. A method of measuring the solubility of a partially miscible liquid system, characterized by, The measuring device comprises a laser, an attenuator, a beam expander, a slit, a composite liquid core column lens and a CCD; the solubility measuring method comprises the following steps: (1) using the measuring device to image at least 8 groups of different known mass fraction solutions respectively; (2) processing the width images of different mass fraction solutions received by the CCD, measuring the width of each image, and obtaining the corresponding image width of different known mass fraction solutions; (3) using the least square method to fit the mass fraction and the corresponding image width data, and obtaining the relationship ω-W between the mass fraction of the solution and the image width; (4) sequentially injecting the solute and the upper liquid into the composite liquid core column lens, injecting the solute into the bottom of the liquid core of the composite liquid core column lens, and after the solute is stable, injecting the upper liquid into the upper part of the solute along the inner wall of the liquid core of the composite liquid core column lens, and there is no obvious convection between the solute and the upper liquid during the injection process; (5) as the solute and the upper liquid diffuse with each other, a diffusion solution is formed, and after the diffusion solution tends to be stable in the composite liquid core column lens, the diffusion image of part of the mutual solution is collected by the CCD, and the width of the widest part of the diffusion image is taken as the width of the saturated solution; (6) the width of the saturated solution in step (5) is brought into the relationship ω-W between the mass fraction of the solution and the image width in step (3), and the mass fraction of the saturated solution is obtained; (7) the mass fraction of the saturated solution is brought into the solubility calculation formula, and the solubility S of part of the mutual solution is obtained.

2. The method of claim 1, wherein, The upper liquid is a low-concentration solution or a solvent of the solute.

3. The method of claim 1, wherein, Before step (1), a target observation thin layer solution is configured, the target observation thin layer solution is injected into the composite liquid core column lens, and the images of steps (1) and (5) are fixed on the focal plane position of the image of the target observation thin layer solution.

4. The method of claim 3, wherein, The concentration of the target observation thin layer solution is greater than that of the upper liquid.

5. The method of claim 1, wherein, The solubility calculation formula in step (7) is where s is solubility, ω s is the mass fraction of the saturated solution.

6. The method according to any one of claims 1 to 5, characterized in that, The diffusion coefficient is measured at the same time as the solubility is measured, and the diffusion coefficient measuring method is Based on a one-dimensional semi-infinite diffusion model and an equal refractive index thin layer method, the diffusion coefficient of the mutual solution system is calculated according to the diffusion image data collected by the CCD collecting device at different times by using Fick's second law combined with boundary conditions; specifically, the positions of the beam waists at different times are recorded, and the diffusion coefficient is obtained by least square fitting.

7. The method of claim 6, wherein, The expression of the diffusion coefficient is Linear fit Z and and setting the slope to k, the diffusion coefficient is obtained, where Z is the location of the target observed thin layer solution, ω(Z, t) is the mass fraction of the liquid at location Z and time t, erfinv is the inverse error function, ω s is the saturated solution mass fraction, ω1 is the upper liquid mass fraction, D is the diffusion coefficient, ω c is the target observed thin layer solution mass fraction.

8. The method of claim 6, wherein, The measurement steps of the measuring device are (1) placing the laser, the attenuator, the beam expander, the slit, the composite liquid core column lens and the CCD collecting device in order from left to right; (2) injecting a target observation thin layer solution into the composite liquid core column lens, and moving the CCD collecting device to the focal plane position of the image of the target observation thin layer solution, so that the CCD can collect a thin and sharp bright line; (3) after thoroughly cleaning the composite liquid core column lens, the solute is first injected into the composite liquid core column lens, and after the solute is stable, the upper liquid is injected into the composite liquid core column lens, and the diffusion solution is formed between the solute and the upper liquid; (4) after the diffusion solution tends to be stable in the composite liquid-core column lens, starting the laser to emit monochromatic laser to the attenuator, reducing the light intensity of the monochromatic laser through the attenuator, expanding the monochromatic laser with reduced light intensity into a wide light beam through the beam expander, and then the wide light beam is filtered through the slit and adjusted in width, and then the wide light beam is injected into the composite liquid-core column lens to form an optical path; After the interval of the predetermined time length, the image in the composite liquid-core column lens is collected through the CCD collection device to obtain the diffusion image of the diffusion solution.

9. The method of claim 8, wherein, The predetermined time length is greater than 20 min, and in the step (4), the image in the composite liquid-core column lens is collected at intervals of the fixed time length.

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