RU2732142C1 - Micro-disperser with periodic structure with variable pitch for generation of drops - Google Patents

Abstract

FIELD: micro dispersing agents.SUBSTANCE: invention relates to micro dispersers, in which micro droplets of mainly spherical shape of nanoliter and sub-nanoliter volume are generated, and further generated drops can be used in chemical, pharmaceutical and other technologies, including for mass exchange processes and chemical reactions between reagents dissolved in drops or dissolved in drops and in a solid medium, as well as for subsequent application of biologically active substances on the surface of formed drops. Micro disperser for generation of drops of one liquid in another with a narrow disperse composition includes a body in the form of a channel of extended shape, a nozzle for input of the disperse phase coaxially to it and one or more branch pipes for input of the continuous phase attached to the side surface of the body. Cross-section of the casing from the section of the branch pipe for disperse phase introduction is periodically varied. In the initial portion of the periodic structure of internal size narrowest part of channel his calculated according to the formula:, where d is average size of drops to be obtained in microdisperser, m; Qis disperse phase flow rate, m/s; Qis solid phase flow rate, m/s. Spatial period between adjacent waves in periodically varying structure of housing on initial section is made in accordance with design formula. On each subsequent i-th section of housing, where i is number of section (i=1, 2, … k), wavelength λand width hdecrease in 1.17–1.864 times relative to previous section of housing so that on last section of periodically changing structure of housing internal size of narrow part of housing his made in accordance with design formula. Spatial period between adjacent waves on last section of housing λis made in accordance with design formula. Inner size of the wide part on each i-th section of the housing is made in accordance with the design formula H=(1.5–3.0)h(5).EFFECT: possibility of formation in a liquid in micro channels of spherical drops (microspheres) with dimensions distributed in a sufficiently narrow range, with reduction of pressure and energy losses.1 cl, 3 dwg, 1 tbl

Description

The invention relates to microdispersers, in which microdroplets of a predominantly spherical shape of nanoliter and subnanoliter volume are generated, and then the generated drops can be used in chemical, pharmaceutical and other technologies, including for carrying out mass transfer processes and chemical reactions between reagents dissolved in drops, or dissolved in drops and in a continuous medium, as well as for the subsequent application of biologically active substances on the surface of the formed drops.

A device is known for dispersing drops or bubbles in microchannels and carrying out mass transfer and reaction processes in liquid-liquid and liquid-gas systems (IPC ⁷ С01В 3/26, С07С 5/03, С07С 5/00, С07С 5/10, US Pat. No. 6632414, 2003). The apparatus comprises an elongated body with a monolithic catalyst installed in it, consisting of a large number of microchannels located parallel to each other, nozzles for introducing the initial components into the body, and a gas dispersion device. Gas and liquid (or two immiscible liquids) are fed into the microchannels. In an apparatus with a monolithic catalyst, depending on the ratio of gas and liquid flow rates, one of the following main flow regimes can be implemented: bubble, slug, emulsion and film (annular).

In the known invention, no measures are provided for the formation of droplets or bubbles of the dispersed phase with predetermined sizes. This leads to the formation of bubbles with a large scatter of sizes in each of the channels. As a result, a significant part of the microchannels operates with indicators (heat and mass transfer coefficients) that are significantly lower than the calculated values obtained on the assumption of the ideal pattern of the formation of a two-phase flow in microchannels.

Known device - an analogue of the proposed invention - T-mixer (T-mixer) (Rebrov E.V. Modes of two-phase flow in microchannels // Theoretical foundations of chemical technology, 2010, vol. 44, No. 4, pp. 371-383 ), which is characterized by the formation of bubbles (or drops) by squeezing a bubble (drop) formed in the mixer. In this case, a bubble (drop) is formed in a narrow microchannel, flowing around with a flow of liquid - a continuous phase moving in the form of a thin film. The process of bubble (drop) formation is influenced by a large number of factors: shear stresses on its surface, pressure drop between the frontal and rear parts of the bubble (drop), surface tension forces at the boundary of the hole from which the bubble (drop) emanates, as well as interfacial tension on surface of the microchannel, which can be asymmetric due to the difference in the angles of inflow and outflow in the frontal and rear parts of the bubble (droplet). The complex hydrodynamic situation around the forming bubble (droplet), as well as the effect of the proximity of the microchannel walls and their roughness on it, predetermines significant instability of the conditions of the resulting bubbles (drops) and their sizes, as well as the sizes of liquid projectiles between them. All of this, as mentioned above, causes a deterioration in the stability of the sizes of the generated drops.

Known device - an analogue of the proposed invention - Y-shaped mixer (Y-mixer) (Rebrov E.V. Modes of two-phase flow in microchannels // Theoretical foundations of chemical technology, 2010, vol. 44, No. 4, pp. 371-383 ), which is characterized by the formation of bubbles (or drops) by stretching and tearing off a bubble (drop). A large number of influencing conditions and the proximity of the walls of the microchannels, in this case, also cause the instability of the sizes of the resulting bubbles (drops). Thus, in the Y-shaped mixer, unfavorable conditions are formed for controlling the dimensions of the elements of the dispersed and continuous phases, and hence the performance indicators of the equipment.

The closest in technical essence to the device we propose is a microdisperser integrated with a microreactor (Ueno M., Hisamoto N., Kitamori T., Kobayashi S. Phase-transfer alkylation reactions using microreactors // Chem. Commun., 2003, pp. 936 -937; Wegmann A., von Rohr PR Two phase liquid-liquid flows in pipes of small diameters // International Journal of Multiphase Flow, V. 32, 2006, pp. 1017-1028) which is a tube with a transverse diameter of 100- 200 μm to 7 mm, into which the phases are introduced either at a right angle (T-shaped mixer) or at an acute angle of about 30 ° (Y-shaped mixer).

The disadvantages of the known device include the inability to regulate the dispersion conditions. As in analogous devices, in this device (in the T-shaped and in the Y-shaped mixers) unfavorable conditions are formed for the formation of the sizes of the elements of the dispersed and continuous phases (drops and bubbles) and their control. This leads to the limitation of the field of application of the device to narrow ranges of the flow rates of the continuous and dispersed phases, since when the flow rates change, the hydrodynamic situation in the apparatus changes significantly and the flow regime of the two-phase mixture is disturbed.

In addition, studies have shown (RK Shah, H.S. Shum, A.C. Rowata, D. Lee, JJ Agresti, AS Utada, L.-Y. Chu, J.-W. Kim, A. Fernandez-Nieves , CJ Martinez, DA Weitz, Designer emulsions using microfluidics, Materials today, 2008, V. 11, N. 4, pp. 18-27; SK Luther, A. Braeuer, High-pressure microfluidics for the investigation into multi-phase systems using the supercritical fluid extraction of emulsions (SFEE), The Journal of Supercritical Fluids, 2012, V. 65, pp. 78-86; W. Wang, M.-J. Zhang, L.-Y. Chu, Functional Polymeric Microparticles Engineered from Controllable Microfluidic Emulsions. Accounts of chemical research, 2014, Vol. 47, No. 2, 373-384) that when using a Y-shaped mixer (and its three-dimensional analogs), small droplets (microspheres are formed as a result of drawing out a rather long stream with the formation of a thickening at its end, the subsequent growth and separation of this thickening in the form of a drop.The length of the jet before its separation depends on the ratio of the viscosities of the media and at high viscosity of the dispersed phase, it can reach 30-60 calibers of the microchannel before the start of separation.

In (T. Cubaud, TG Mason Capillary threads and viscous droplets in square microchannels. Physics of Fluids 20, 053302 (2008); https://doi.org/10.1063/1.2911716) it is shown that the jet length L ₀ (m) up to onset of disintegration into droplets can be calculated by the formula

where C is a dimensionless coefficient of the order of unity;

μ ₁ - coefficient of dynamic viscosity of the dispersed phase, Pa s;

h — internal channel size, m;

σ - coefficient of interfacial tension at the interface, N / m;

Q ₁ - flow rate of the dispersed phase, m ³ / s;

Q ₂ - continuous phase flow rate, m ³ / s;

It was found experimentally that the length of the jet L ₀ before its disintegration into droplets is 30-60 times greater than its diameter. As a result, it is necessary to unnecessarily increase the length of the microdisperser. Against the background of the desire to reduce the overall dimensions of the device as a whole, when carrying out a chemical reaction including, in addition to the dispersant, the microreactor and separation parts, an exorbitant increase in the length of the microdisperser leads to a deterioration in its compactness characteristics as a microscale device. Moreover, with some deviation from the marginal flow rates that ensure the dispersion of drops, the jet may not break up at all into drops over an observable length, leading to a violation of the operating mode of the entire device.

The objective of the present invention is to form spherical droplets (microspheres) in a liquid in microchannels with sizes distributed in a fairly narrow range, while reducing pressure and energy losses in comparison with existing analogues.

The task is achieved by the fact that in a microdisperser for generating drops of one liquid in another with a narrow dispersed composition, which includes a body in the form of an extended channel, a branch pipe connected to the body coaxially to it for introducing a dispersed phase, and one or more branch pipes connected to the side surface of the body for input of a continuous phase, according to the invention, the cross-section of the body from the cut of the branch pipe for the input of the dispersed phase is made periodically changing, while in the initial section of the periodic structure, the inner size of the narrow part of the channel h _{0 is} made in accordance with the calculation formula:

where d is the average droplet size to be obtained in the microdisperser, m;

Q ₁ - flow rate of the dispersed phase, m ³ / s;

Q ₂ - continuous phase flow rate, m ³ / s,

in this case, the spatial period between adjacent waves in the periodically changing structure of the body in the initial section is made in accordance with the calculation formula:

and on each subsequent i-th section of the hull, where i is the number of the section (i = 1, 2, ... k), the wavelength λ _i and width h _i decrease by 1.17-1.864 times with respect to the previous section of the hull, thus that in the last section of the periodically changing structure of the body, the inner size of the narrow part of the body h _{k is} made in accordance with the calculation formula:

and the spatial period between adjacent waves in the last section of the hull λ _{k is} made in accordance with the calculation formula:

moreover, the internal size of the wide part at each i-th section of the channel is made in accordance with the calculation formula:

The task is also achieved by the fact that in the microdisperser the initial section of the body includes from 3 to 6 waves, and each subsequent section - from 2 to 4 waves in a periodically changing structure of the body, the total number of sections with a periodically changing structure is from 2 to 5.

The proposed device can be made in both planar (2D) and three-dimensional (3D) geometry.

The claimed technical solution is new, has an inventive step and is industrially applicable.

FIG. 1 and 2 show a diagram of the proposed microdisperser in an inoperative state (before feeding it with liquids): FIG. 1 - with a single decrease in wavelength λ _i and width h _i (i = 1, 2) in Fig. 2 - with a twofold decrease in the wavelength λ _i and the width h _i (i = 1, 2, 3). FIG. 3 shows a picture of a two-phase displacement flow in a microdisperser with a single decrease in wavelength and width (Fig. 1) when continuous and dispersed phases are fed into it: a - the beginning of the growth of the dispersed phase jet, its passage through the first section (time t ₁ ); b - stabilized state - the jet begins to disintegrate into drops closer to the end of the second section (time t ₂ > t ₁ ).

FIG. 1 and 2 depict the proposed microdisperser for generating droplets of one liquid in another with a narrow dispersed composition, including a housing 1 in the form of an extended channel, connected to the housing 1 coaxially with a branch pipe 2 for introducing a dispersed phase and one or more branch pipes attached to the side surface of the housing 1 3 to enter a continuous phase. In this case, the cross-section of the housing 1 from the cut 4 of the branch pipe 2 for introducing the dispersed phase is made periodically changing, i.e. is a periodic structure in the form of waves 5-7 having a shape close to sinusoidal.

The section of the channel with periodically changing geometry is followed by section 8 with a constant cross-section, in which the final formation of spherical drops and their movement with the flow of the continuous phase towards the collection container (not shown in Figs. 1-3) occurs. The cross-sectional shape of the branch pipe 2 is preferably round.

The cross-sectional shape of channel 1 can be elliptical (predominantly round) or rectangular (in the latter case, predominantly square).

The wavelength λ ₁ for the initial section of the periodic structure of the housing 1 is determined by the formula (2), and at each subsequent i-th section of the housing, the wavelength λ _i decreases C times with respect to the wavelength λ _{i-1 of the} previous section of the housing, i.e. e.

where C is the reduction factor taken in the range 1.17-1.864 (in accordance with equation (8));

i - section number; i = 1, 2, ... k;

k - the number of the last section (coincides with the total number of sections of the hull with a periodically changing structure).

The waveform in the general case may be different (for example, in the form of conical confusers and diffusers connected in series, or cylindrical sections with stepped transitions), but studies have shown that a shape close to sinusoidal has optimal characteristics: the fastest separation of drops from liquid jets with a minimum hydraulic resistance of the microdisperser.

At the initial section of the periodic structure, the internal size (width) of the narrow part of the channel h _{1 is} made in accordance with the calculated formula (1), and at each subsequent i-th section of the body, the width h _i decreases C times in relation to the width h _{i-1 of the} previous section of the body, i.e.

The specific value of the coefficient C in formulas (6) and (7) is determined by the total number of k sections with a periodically changing structure in accordance with the calculation formula

where N is the ratio of the sizes of the initial and final sections with a periodically changing structure, determined by the formula:

Taking into account the coefficients included in pairs in formulas (1) and (3), (2) and (4), the value of the parameter N is on average N = 1.864. The values of the coefficient C, calculated by the formula (8), depending on the total number k of sections of the body with a periodically changing structure, are presented in Table 1.

The system of equations (6) - (9) has such a structure that in the last section of the periodically changing structure of the body, the value of the inner size of the narrow part of the body h _k , found by formula (7), coincides with that calculated by formula (3), and the spatial period between by adjacent waves in the last section of the body λ _k , found by formula (6), coincides with that calculated by formula (4).

The inner dimension H _{i of the} wide part on each i-th section of the housing 1 is made in accordance with the calculation formula (2). The coefficient in formula (2) in the range of 1.5-3.0 determines the optimal efficiency of the proposed device: At lower values (H _i <1.5 h _i ), the waves do not have a strong enough effect on the jet of the dispersed phase. At large values (H _i > 3.0 h _i ), stagnant zones with secondary currents appear in the wide parts (recesses) of channel 1, which leads to a decrease in the efficiency of the device.

Studies have shown that for the initial section of body 1, from 3 to 6 waves are sufficient, since when the number of waves exceeds 6, pressure losses increase, and when the number of waves is less than 3, a significant effect of the primary deformation of the jet is not achieved. For subsequent sections, according to the results of experiments, the optimal number of waves was from 2 to 4. The total number of sections with a periodically changing structure, according to the studies, is from 2 to 5 (the number depends on the properties of the media - viscosity, density and interfacial tension). When the number of sections is less than 2, the effect of the repetitive impulse action on the jet of the dispersed phase is significantly reduced, with their number exceeding 5, the energy consumption for the supply of media increases significantly.

FIG. 3 shows a diagram of a microdisperser in working condition and a picture of a two-phase displacement flow when continuous (with a flow rate Q ₂ ) and dispersed (with a flow rate Q ₁ ) phases are fed into it.

EXAMPLE 1. Generation of microspheres in the proposed device with two sections with a periodically changing structure with optimal parameters.

The microdisperser body is made of brass, with a mineral glass lid according to the diagram shown in FIG. 1, i.e. has two sections with a periodically changing structure - 5 and 6. To stabilize the generated drops in the continuous phase, the required amount of surfactant - sodium dodecyl sulfate was previously dissolved.

When the continuous phase (water) and dispersed phases (cyclohexane) are fed into the nozzles 3 and 2 of the microdisperser, respectively, with flow rates Q ₂ = 16 ml / min and Q ₁ = 2 ml / min, the dispersed phase flows out of the nozzle 2 into the channel of body 1 in the form of a jet 9. Body 1 is made with dimensions in accordance with formulas (1) - (5):

- the inner dimension h _{1 of the} narrow part of the housing 1 in the initial section 5 is made equal to 0.119 mm (in the range from 0.112 to 0.127 mm, according to formula (1));

- the inner size h _{k of the} narrow part of the housing 1 in the last section 6 is made equal to 0.064 mm (in the range from 0.060 to 0.068 mm, according to formula (3));

- the inner dimension H _{1 of the} wide part of the body 1 at the initial section 5 is made equal to 0.268 mm (in the range from 0.179 to 0.358 mm, according to formula (5));

- the inner dimension H _{k of the} wide part of the body 1 in the last section 6 is made equal to 0.144 mm (in the range from 0.096 to 0.192 mm, according to formula (5));

- the spatial period between λ ₁ adjacent waves in the periodically changing structure of the body 1 in the initial section 5 is made equal to 0.550 mm (in the range from 0.500 to 0.600 mm, according to formula (2));

- the spatial period between λ _k adjacent waves in the periodically changing structure of the body 1 in the last section 6 is made equal to 0.280 mm (in the range from 0.270 to 0.290 mm, according to formula (4)).

On the surface of the jet 9, capillary waves with zones of expansion 10 and contraction 11 are formed; in the final section, drops 12 with the required size d detach from the jet 9.

Similar experiments were carried out on the lower and upper limits of the intervals of the coefficients indicated in formulas (1) - (5).

Measurements performed using micrographs of the device with a flow showed that the length of the jet before the moment of disintegration into droplets was on average L ₁ = 2.49 mm, and the diameter of the jet was d _c1 = 0.017 mm.

At the same time, the pressure loss in the proposed device turned out to be 3.24 times lower than in the microdisperser, which had constant characteristics of the periodically changing structure h, H and λ along the entire length, corresponding to the values in the last section 6 of the housing 1 of the proposed device (h _k , H _k , λ _k ).

The pressure loss in the proposed device turned out to be 6.4 times lower than in the microdisperser, which had a constant cross-section equal to h _k .

Analysis of micrographs of drops (the sample size in each experiment was 600-800 drops) was in the range from 47.1 to 53.1 µm, with an average value of the diameter of microspheres d = 50.1 µm and a standard deviation S = 1.0 µm; the coefficient of variation of the droplet (microsphere) size was V = S / d = 0.02. An equal distance is created between the generated adjacent droplets, approximately equal to their diameter, and they move in the flow of a continuous medium without collision and subsequent coalescence.

Thus, the proposed device allows the formation of spherical droplets (microspheres) with sizes distributed in a rather narrow range, with significantly lower pressure losses and energy costs compared to similar devices with a constant cross section, or variable cross section, but with constant characteristics periodically changing structure of h, H and λ.

Similar results were obtained by dispersing styrene droplets into an aqueous solution of NaCl in the proposed device shown in FIG. 2.

EXAMPLE 2. Generation of microspheres in the proposed device with three regions with a periodically changing structure with optimal parameters.

In the proposed device with three sections of the periodic structure of the housing 1 shown in FIG. 2, similar results were obtained.

In this case, the proposed device had the following dimensions, determined by formulas (1) - (5):

h ₁ = 0.119 mm; h ₂ = 0.087 mm; h _k = 0.064 mm;

H ₁ = 0.268 mm; H ₂ = 0.197 mm; H _k = 0.144 mm;

λ ₁ = 0.550 mm; λ ₂ = 0.403 mm; λ _k = 0.280 mm.

At the same time, the pressure loss in the proposed device turned out to be 4.53 times lower than in the microdisperser, which had constant characteristics of the periodically changing structure h, H and λ along the entire length, corresponding to the values in the last section 6 of the housing 1 of the proposed device (h _k , H _k , λ _k ), and 8.6 times lower than in a microdisperser with a constant cross section equal to h _k .

The average diameter of the microspheres was d = 48.2 μm and the standard deviation S = 1.0 μm; the coefficient of variation of the droplet (microsphere) size is equal to V = S / d = 0.02.

EXAMPLE 3. Generation of microspheres in the proposed device with non-optimal parameters.

Investigations into the microsphere generation process were carried out in the apparatus described in Examples 1 and 2 using the same procedure. The difference was that the internal dimensions h of the narrow part, the internal dimensions H of the wide part of the channel, and the spatial periods λ between adjacent waves were performed outside the intervals indicated in the calculation formulas (1) - (5).

Experiments have shown that in all cases there is a deterioration in the stability of the droplet (microsphere) size, the coefficient of variation increases significantly and reaches values V = 0.06-0.08, and the pressure loss increases 1.3-2.1 times compared with the optimal conditions specified in examples 1 and 2.

Thus, the coefficients indicated in the calculation formulas (1) - (5) are based on the results of experimental studies, and characterize the optimal values of the dimensions of the body 1.

With an increase in the number of waves in the periodically changing structure of the body more than 6, an excessive increase in the hydraulic resistance of the device occurred, without an improvement in the effect.

With a decrease in the number of waves in the periodically changing structure of the body less than 3, the dispersion effect was not high enough, there was an increased scatter of droplet sizes compared to the number of waves from 3 to 6. With an increase in the number of sections with a periodically changing structure more than 5, the hydraulic resistance also significantly increased without improving the quality microspheres.

The basic version is illustrated by the following example

EXAMPLE 4. Generation of microspheres in a prototype device.

Generation of microspheres was carried out (T. Cubaud, TG Mason Capillary threads and viscous droplets in square microchannels. Physics of Fluids 20, 053302 (2008)) under the same conditions as in Examples 1 and 2, but in a microdisperser having a constant cross-section equal to h _k = 0.064 mm. The analysis of the two-phase flow and the obtained microspheres was carried out by the same methods.

The measurements showed that the length of the jet before the moment of disintegration into droplets was L ₀ = 17.7 mm with the jet diameter d _c0 = 0.017 mm. In this case, the hydraulic resistance of the known device turned out to be 6.4 and 8.6 times higher than for the proposed device described in examples 1 and 2, respectively.

Analysis of micrographs of drops (the sample size in each experiment was 600-800 drops) was in the range from 32.2 to 69.5 microns, with the average value of the diameter of the microspheres d = 50.9 microns and the standard deviation S = 6.2 microns; the coefficient of variation of the droplet (microsphere) sizes was V = S / d = 0.122, which is significantly higher than in the proposed device, even when it is operating in non-optimal modes.

The distance between the generated adjacent droplets is created equal, varies from 0.2 d to 1.3 d, they often collide, which leads to their subsequent coalescence.

Thus, the proposed device makes it possible to generate spherical drops (microspheres) in microchannels with sizes distributed in a rather narrow range, as well as to provide an equal distance between adjacent drops, which will prevent their collision and subsequent coalescence. When the channel dimensions vary within the limits indicated in the calculation formulas (1) - (5), a stably narrow distribution of the droplet size and distance between them remains, with a decrease in pressure and energy losses in comparison with the available analogs.

Claims (14)

1. Microdisperser for generating droplets of one liquid in another with a narrow dispersed composition, comprising a body in the form of an extended channel, a branch pipe connected to the body coaxially to it for introducing a dispersed phase and one or more branch pipes attached to the side surface of the body for introducing a continuous phase, characterized in that that the cross-section of the body from the cut of the branch pipe for introducing the dispersed phase is made periodically changing, while at the initial section of the periodic structure, the inner size of the narrow part of the channel h _{1 is} made in accordance with the calculation formula:

where d is the average droplet size to be obtained in the microdisperser, m; Q ₁ - flow rate of the dispersed phase, m ³ / s; Q ₂ - continuous phase flow rate, m ³ / s, in this case, the spatial period between adjacent waves in the periodically changing structure of the body in the initial section is made in accordance with the calculation formula:

and on each subsequent i-th section of the hull, where i is the number of the section (i = 1, 2, ... k), the wavelength λ _i and the width h _i decrease by 1.17-1.864 times in relation to the previous section of the hull in this way , that in the last section of the periodically changing structure of the body, the inner size of the narrow part of the body h _{k is} made in accordance with the calculation formula:

and the spatial period between adjacent waves in the last section of the hull λ _{k is} made in accordance with the calculation formula:

moreover, the inner size of the wide part on each i-th section of the body is made in accordance with the calculation formula:

2. Microdisperser according to claim 1, characterized in that the initial section of the body includes from 3 to 6 waves, and each subsequent one - from 2 to 4 waves in a periodically changing structure of the body, the total number of sections with a periodically changing structure is from 2 to 5.

Images