TECHNICAL FIELD

The present subject matter, in general, relates to dispersions and, in particular, relates to occurrence of phase inversion in a liquid-liquid dispersion.

BACKGROUND OF THE INVENTION

Usage of liquid-liquid dispersions, which include one liquid phase dispersed in another immiscible liquid phase, in chemical processing industries is well known. A dispersed phase in the dispersion is the liquid that is trapped in another liqi'id forming a continuous phase of the dispersion. Typically, the industries employ the dispersions in agitated form to provide a high contact area between two immiscible liquids. The high contact area between two phases is exploited to achieve a high rate of transport of mass and energy from one phase to other. In certain chemical industries, a turbulent flow field maintained with a continuous supply of mechanical energy is used to break one of the phases of the dispersion into drops to provide the high contact area. Since the drops move randomly and relative to each other in turbulent flow field, the drops collide and tend to coalesce with each other. Usually, under steady conditions, a dynamic equilibrium exists between the break up and coalescence of drops.

Further, it is often desirable to increase the volume fraction of the dispersed phase in the agitated dispersion to increase the processing capacity and efficiency of a processing machinery. However, an increase in the volume fraction of the dispersed phase beyond a critical value results in an instability that disrupts smooth and stable operation of the processing machinery. This instability named as 'inversion of phases' or 'phase inversion' inverts dispersion of phase one (e.g an oil/organic phase) in phase two (e.g. an aqueous solution) to dispersion of phase two in phase one. The phase inversion adversely affects various chemical processes as these processes are typically designed to handle only a single type of dispersion.

SUMMARY

The present subject matter describes a system and method for predicting phase inversion in a dispersion. The phase inversion prediction system includes a pair of electrodes inserted in the dispersion and connected to a conductivity meter. A data acquisition system monitors a voltage signal across a pair of nodes of the conductivity meter and then samples the voltage signal at a pre-determined sampling rate to produce a digital signal. A data logger is connected to the data acquisition system to ascertain presence of a plurality of voltage pulses within the digital signal for predicting the phase inversion.

These and other features, aspects, and advantages cf the present subject matter will be better understood with reference to the following description and appended claims. This summary is provided to introduce a selection of concepts in a simplified form. This summary is not intended to identify key features or essential features of the claimed subject matter, nor is it intended to be used to limit the scope of the claimed subject matter.

BRIEF DESCRIPTION OF DRAWINGS

The detailed description is described with reference to the accompanying figures. In the figures, the left-most digit(s) of a reference number identifies the figure in which the reference number first appears. The same numbers are used throughout the drawings to reference like features and components. For simplicity and clarity of the illustration, elements in the figures are not necessarily to scale.

Fig. 1 shows a block diagram of a phase inversion prediction system, according to an embodiment of the present subject matter.

Fig. 2 illustrates an exemplary method for predicting phase inversion within the phase inversion prediction system of Fig. 1, in accordance with an embodiment of the present subject matter.

Fig. 3 illustrates a voltage scan of a first dispersion with a dispersed phase volume fraction of0.33.

Fig. 4 illustrates a voltage scan of the dispersion of Fig. 3 with a dispersed phase volume fraction of 0.38.

Fig. 5 illustrates a voltage scan of the dispersion of Fig. 3 with a dispersed phase volume fraction of 0.48.

Fig. 6 illustrates a voltage scan of a second dispersion with a dispersed phase volume fraction of 0.40.

DETAILED DESCRIPTION

Phase inversion in an agitated dispersion occurs almost instantaneously, on timescales of seconds, and cannot be reversed during its occurrence. The restoration of the inverted dispersion to the original dispersion is complicated, time consuming, and may require shutdown of a processing machinery operating upon the dispersion. In certain circumstances, the phase inversion may cause serious safety implications.

As a solution, the phase inversion can be avoided by operating the processing machinery away from an unstable mode of operation. This may be done by using the dispersion having a particular range of volume fraction of the dispersed phase. Such range of volume fraction lies away from a particular value of the volume fraction at which the phase inversion is generally observed. However, the range of volume fraction corresponding to a stable mode of operation varies substantially with the variation in physical properties of the two phases of the dispersion, intensity of agitation, and fluctuations in concentrations of impurities within the two phases. Accordingly, the prediction of the range of volume fraction of the dispersed phase corresponding to safe mode of operation is prone to suffer from errors.

Conventionally, various phase inversion detection systems have been employed to detect the occurrence of phase inversion within the dispersion. One such detection system is a conductivity meter. As an example, in case of water in oil dispersion, measurements of electrical conductivity of the dispersion by the conductivity meter show a high resistance. Once the instability sets in due to the phase inversion, the conductivity of the dispersion increases by several orders of magnitude. The increased value corresponds to the conductivity of water phase, which forms the continuous phase. Accordingly, the conductivity meter shows steady values of resistance before and after phase inversion, and fluctuating values during the phase inversion.

The present subject matter describes a method and system for predicting phase inversion in a liquid-liquid dispersion. The phase inversion prediction system determines proximity of operating conditions of an agitated dispersion to the phase inversion. Due to prediction, an ample time for preventive measures or corrective actions to avoid the phase inversion is obtained. Accordingly, the present subject matter describes sensing of the precursor to phase inversion and accordingly provides an indication of the precursor.

Further, the below-mentioned explanation of figures illustrates the phase inversion prediction in terms of a two phase liquid-liquid dispersion, which is a water phase dispersed in an oil phase. However, the phase inversion prediction system shall not be construed as being limited towards two phase dispersions and can be extended to cover dispersions with more than two phase as well as other types of two phase dispersions such as oil phase dispersed in water phase.

Fig. 1 shows a block diagram of a phase inversion prediction system 100, according to an embodiment of the present subject matter.

As depicted in Fig. 1, the phase inversion prediction system 100 includes a container 105 in which a two phase liquid-liquid dispersion 110 is kept. In an implementation, the two phase liquid-liquid dispersion 110 is composed of a water phase dispersed in an oil phase and is agitated to facilitate the occurrence of the phase inversion therein. A pair of electrodes 107a & 107b is immersed in the dispersion and connected to a Wheatstone bridge 115. The electrodes 107a & 107b are spaced apart from each other by a pre-determined distance, which in an embodiment may be 7 centimeters. The Wheatstone bridge 115 measures electrical resistance between the electrodes 107a & 107b to derive electrical conductivity exhibited by the dispersion 110. Accordingly, the Wheatstone bridge 115 acts as a conductivity meter 115 for the dispersion 110.

Further, a data acquisition system 120 is connected to the Wheatstone bridge 115 to monitor a voltage signal across a pair of opposite nodes of the Wheatstone bridge 115. On monitoring the voltage signal, the data acquisition system 120 quantifies the voltage signal by sampling the voltage signal at a high sampling rate to convert the analog form of signal into a digital signal. In an implementation, the sampling is performed at a sampling rate or a sampling frequency of 1000 samples per second to 50,000 samples per second.

A data logger 125 is connected to the data acquisition system 120 to record the voltage signal in the digital format and predict the phase inversion. In an implementation, the data logger 125 may be a computing system comprising a memory, at least one processor and a display in order to output results in a user-friendly way. Accordingly, the data logger 125 records the digital signal and ascertains presence of voltage pulses in the digital signal for predicting the phase inversion.

Thereafter, the data logger 125 displays the digital signal. The display of the digital signal may be referred to as a voltage scan, as elaborated in the description to Fig. 2 to Fig. 5.

In operation, the volume fraction of the dispersed phase within the agitated dispersion is increased by a processing machinery (not shown in the figure) operating upon the dispersion. Corresponding to a particular volume fraction of the dispersed phase, the water phase acting as the dispersed phase begins to form long transiently connected domains of water. The data acquisition system 120 monitors a voltage signal across the nodes of the Wheatstone bridge 115 and samples the monitored voltage signal to produce a digital signal corresponding to the voltage signal. Due to formation of the transiently connected water domains, a number of voltage pulses occur in the digital signal. As an inversion point of the dispersion is approached, the average size of the connected water domains increases.

The data logger records the digital signal and ascertains the presence of pulses within the digital signal. Accordingly, the data logger predicts the phase inversion based on presence of voltage pulses within the digital signal. In an example, the data logger may be connected to an alarming gadget like a siren or a hooter to provide an alert. Accordingly, the formed water domains that give rise to voltage pulses are picked up by the combination of the data acquisition system 120 and the data logger 125. In other words, the voltage pulses acts as an indication of precursor to the inversion point of the dispersion.

In order to substantiate the phase inversion prediction as performed by the phase inversion prediction system of the present subject matter, a number of experiments as illustrated by the forthcoming description of Fig. 2 to Fig. 5 have been conducted. However, such experiments does not limit the scope of the present subject matter and can be increased or decreased in number to cover various implementations of the phase inversion prediction system 100.

Fig. 2 illustrates an exemplary method 200 for predicting phase inversion in accordance with the present subject matter. The order in which the method 200 is described is not intended to be construed as a limitation, and any number of the described method blocks can be combined in any order to implement the method, or an alternate method. Additionally, individual blocks may be deleted from the method without departing from the spirit and scope of the subject matter described herein. Furthermore, the method can be implemented in any suitable hardware, software, firmware, or a combination thereof.

In accordance with one embodiment of the present subject matter, the method 200 may be implemented in the previously described prediction system 100. However, it will be appreciated by one skilled in the art that such an embodiment is not limiting. The method 200 may be implemented in a variety of other identical prediction systems.

The method 200 is initiated at block 202 upon insertion of a pair of electrodes within the dispersion, such that the electrodes are connected to a conductivity meter. The conductivity meter measures the electrical conductivity of the dispersion.

At block 204, a voltage signal is monitored across a pair of nodes of the conductivity meter.

Further at block 206, the monitored voltage signal is sampled at a pre-determined sampling rate to generate a digital signal.

Finally at block 208, presence of a number of voltage pulses is ascertained within the digital signal. The presence of the voltage pulses in the digital signal predicts the occurrence of the phase inversion within the dispersion.

Fig. 3 illustrates a voltage scan 300 of a dispersion corresponding to a phase volume fraction of 0.33.

The voltage scan refers to the digital voltage signal or digital representation of the voltage signal across the opposite nodes of the Wheatstone bridge 115. As mentioned before, the digital voltage signal is produced by the data acquisition system 120 after sampling the analog voltage signal across the Wheatstone bridge 115 at a sampling rate of 10,000 samples per second.

In the present experiment, the dispersion includes a water phase dispersed in a toluene phase '""N and the electrodes are immersed in the dispersion at a distance of 2 cm. This dispersion is expected to phase invert at the water phase volume fraction of 0.49. As depicted in the figure, no voltage pulse is observed in the voltage scan, as there is no conduction within the dispersion. Accordingly, the continuous phase is retained by toluene as the dispersion is yet to undergo phase inversion.

Fig. 4 illustrates a voltage scan 400 of the dispersion of Fig. 3 with a dispersed phase volume fraction of 0.38.

As shown in the voltage scan 400 of Fig. 4, the data acquisition system 120 starts detecting voltage pulses, which correspond to, formation of large connected water domains between the electrodes 107a & 107b placed 2 centimeters apart in an aspect of the preset subject matter. Such phenomenon is observed despite a substantially lesser value (0.38) of water phase volume fraction as compared to the value at an inversion point i.e. (0.49). Duration and frequency of voltage pulses show that that the connected water domains though transient are formed frequently.

Further, if the electrodes 107a & 107b are spaced 7 cm instead of 2 cm, the voltage scan 400 changes to the scan 300 as depicted in Fig. 3. Accordingly, it may be inferred that although precursor to the phase inversion point has been detected, increment in the distance between electrodes 107 is essential to determine accuracy.

Fig. 5 illustrates a voltage scan 500 of the dispersion of Fig. 1 with a dispersed phase volume fraction of 0.48. The electrodes 107a & 107b are kept 7 centimeters apart.

As shown in the voltage scan 500, the voltage pulses are more frequently present as /*"^ compared to the scan 400 of Fig. 4, thereby indicating an increased conductivity and an accurate precursor to the phase inversion. This is because the value of water phase volume fraction is slightly lesser than a critical value of 0.49, which corresponds to the inversion point.

Fig. 6 illustrates a voltage scan 600 of a second dispersion with a dispersed phase volume fraction of 0.38.

The second dispersion refers to another type of dispersion of water in toluene, such that the second dispersion is configured to undergo phase inversion at the volume fraction of 0.40 instead of 0.48. As shown in Fig. 6, the voltage scan 600 is obtained for the second dispersion at the water phase volume fraction of 0.38 and the electrodes 107a & 107b are spaced 7 centimeters apart.

On observing the voltage scans of Fig. 4 to 6, it may be inferred that voltage scans corresponding to any value of volume fraction that is near the phase inversion point are identical. In other words, the behavior of the voltage scan in these figures is independent of the value of the volume fraction of the dispersed phase.

The phase inversion prediction system 100 described by the present subject matter adopts a technique that is independent of the physical or chemical composition of the liquid-liquid dispersion. Specifically, the prediction system 100 determines proximity of the operating conditions of a processing machinery operating upon the dispersion to a phase inversion point. In other words, the prediction system 100 provides an indication of the precursor to the phase inversion. Such provision allows timely corrective action to prevent the phase inversion, and stabilization of operation of the processing machinery.

Although the subject matter has been described with reference to specific embodiments, this description is not meant to be construed in a limiting sense. Various modifications of the disclosed embodiments, as well as alternate embodiments of the subject matter, will become apparent to persons skilled in the art upon reference to the description of the subject matter. It is therefore contemplated that such modifications can be made without departing from the spirit or scope of the present subject matter as defined.

I/We claim:

1. A method of predicting phase inversion in a dispersion comprising:

inserting at least two electrodes connected to a conductivity meter within the dispersion;

monitoring a voltage signal across a pair of nodes of the conductivity meter;

sampling the voltage signal at a pre-determined sampling rate to generate a digital signal; and

ascertaining presence of a plurality cf voltage pulses within the digital signal to predict the phase inversion.

2. The method as claimed in claim 1, wherein inserting comprises applying the electrodes in a liquid-liquid dispersion comprising a dispersed phase volume fraction in a range of about 0.25 to 0.80.

3. The method as claimed in claim 1, wherein monitoring comprises monitoring the voltage signal across the nodes of a Wheatstone bridge acting as the conductivity meter.

4. The method as claimed in claim 1, wherein the sampling comprises sampling the voltage signal at a sampling rate of about 1000 samples per second to 50,000 samples per second.

5. A system (100) for predicting phase inversion in a dispersion (110) comprising:

at least two electrodes (107a & 107b) inserted in the dispersion (110);

a conductivity meter (115) connected to the electrodes;

a data acquisition system (120) to monitor a voltage signal across a pair of nodes of the conductivity meter (115), wherein the data acquisition system (120) samples the voltage signal at a pre-determined sampling rate to produce a digital signal; and

a data logger (125) to ascertain presence of a plurality of voltage pulses within the digital signal to predict the phase inversion.

6. The system (100) as claimed in claim 5, wherein the electrodes (107a & 107b) are separated by a distance of about 2 to 7 centimeters within the dispersion (110).

7. The system (100) as claimed in claim 5, wherein the dispersion (110) is a liquid-liquid dispersion (110).

8. The system (100) as claimed in claim 5, wherein the conductivity meter (115) is a Wheatstone bridge (115).

9. The system (100) as claimed in claim 5, wherein the data acquisition system (120) samples the voltage signal at a sampling rate of about 1000 samples per second to 50,000 samples per second.

10. The system (100) as claimed in claim 5, wherein the dispersion (110) comprises a dispersed phase volume fraction in a range of about 0.25 to 0.80.