GB2027607A

GB2027607A - Contacting immiscible liquids

Info

Publication number: GB2027607A
Application number: GB7803608A
Authority: GB
Original assignee: RTL Contactor Holding SA
Current assignee: RTL Contactor Holding SA
Priority date: 1978-08-16
Filing date: 1978-08-16
Publication date: 1980-02-27
Also published as: GB2027607B

Abstract

A liquid/liquid contacting process is described for use with a contactor as described in U.K. Specification 972,035, constituted by a vessel through which flow two substantially immiscible liquid phases of different specific gravities. Rotating conveying means within the vessel cause droplets of each phase to be conveyed into the other phase through the interface. A fine, inert granular material is included in the contactor and causes to continuously fall through the liquid phases.

Description

SPECIFICATION Contacting method This invention relates to a method of operating a continuous liquid/liquid contactor, and particularly a contactor (to be described hereinafter as a contactor of the type described) constituted by a vessel through which two substantially immiscible liquid phases of different specific gravities are caused to flow with an interface between the two phases and rotating conveying means within the vessel causing droplets of each phase to be conveyed into the other phase. Normally the vessel is stationary and the rotating means is a rotor rotating relative to the vessel; but, instead the vessel and rotating means may turn together.

British patent specification No. 972035 describes a contactor of the type described, in which the vessel contains a rotor comprising a series of partitions which are spaced apart along the vessel to divide the interior into a plurality of compartments, and buckets, which are normally carried between the partitions and which, in each compartment, carry liquid of each phase into the other. The passage of the phases along the vessel is made possible by spacing the edges of each partition from the wall of the vessel and/or by having openings through the partitions at selected points. It is preferred to have the two phases moving through the vessel in counter-current, although co-current flow is possible.

As each bucket passes from one phase tithe other, it carries with it a quantity of the first phase, which becomes progressively displaced by the second phase. The first phase is thus released as droplets enter the second phase and because of the difference in specific gravities, migrates back to the first phase in the form of droplets. In other words, as the buckets on one side of the rotor travel in an upward direction, they carry the heavier phase into the lighter one and discharge their contents in a shower of droplets which fall back into the heavier phase. Similarly as the buckets descend on the other side, they carry the lighter phase downwards into the heavier phase and the lighter phase discharged from the buckets floats upwards in a series of droplets, back into the lighter phase.It is by this action of contacting the two phases that mass transfer takes place.

Because of the large surface area to volume of the droplets during their passage from one phase to the other, high mass transfer efficiency is obtainable. That efficiency increases with the speed of rotation of the rotor for given throughput rates of the two phases, and decreases with increasing throughput rates for a given speed of rotation.

We have discovered that, if, in addition to the two liquid phases, the contactor contains a granular material such as silica sand, and this material is caused to shower downwardly through the liquid phases by the lifting and discharging action of the buckets, the efficiency of mass transfer increases. Consequently, for a given speed of rotation, and for a specific mass transfer efficiency, the flow rates of the liquid phases can be increased and greater output obtained from the contactor.

Thus, the present invention provides a liquid/liquid contacting process using a contactor of the type described, in which a fine inert granular material is caused by the conveying means continuously to fall through the liquid phases.

The granular material is showered through the two liquid phases and, in falling through those phases, it alters the size distribution of the droplets in both phases and increases the extent of interaction between them, whereby an improved mass transfer efficiency is obtained. In certain conditions, and again as a consequence of the interaction of the showering particles of sand on the liquid droplets which are moving through - the liquid phases, a further improvement in mass transfer efficiency may be obtained by increasing the speed of rotation of the buckets, which increases the rate at which showering particles pass through the liquid phases.

The granular material is preferably present in the contactor in a volume which is between two percent and ten percent of the volume of the contactor, and maintained at such a level in the bottom of the contactor that the rotating buckets pick up a mixture of sand along with the liquid in the lower part of the contactor. The particle size of the granular material is preferably between 75-and 750 microns.

For the effective operation of the system, it is important to maintain a substantially constant level of sand in the bottom of the contactor. In order to do this, the sand is caused to flow through the contactor by being carried by the lower and heavier phase liquid. The sand is then separated from the liquid externally of the contactor, and recycled to the contactor where it is reintroduced with the heavier liquid.

By virtue of the invention, i.e. by the addition of granular material to the system, it is possible to increase the throughput of the contactor by increasing the flow rates of the phases, and additionally, an improved mass transfer efficiency can be achieved by increasing the speed of rotation of the rotor, whereby particles of granular material are showered through the liquid phases at an increased rate.

1. A liquid/liquid contacting process comprising passing two substantially immiscible liquid phases of differing specific gravities through a contactor of the type described, while fine, inert granular material is caused by the conveying means to continuously fall through the liquid phases.

2. A liquld/liquid contacting process according to claim 1, wherein the fine, inert granular material is sand.

3. A iiquid/liquid contacting process according to claim 1 or 2 wherein the granular material is present in the contactor in a volume of from 2 to 10 percent of the volume of the contactor.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. SPECIFICATION Contacting method This invention relates to a method of operating a continuous liquid/liquid contactor, and particularly a contactor (to be described hereinafter as a contactor of the type described) constituted by a vessel through which two substantially immiscible liquid phases of different specific gravities are caused to flow with an interface between the two phases and rotating conveying means within the vessel causing droplets of each phase to be conveyed into the other phase. Normally the vessel is stationary and the rotating means is a rotor rotating relative to the vessel; but, instead the vessel and rotating means may turn together. British patent specification No. 972035 describes a contactor of the type described, in which the vessel contains a rotor comprising a series of partitions which are spaced apart along the vessel to divide the interior into a plurality of compartments, and buckets, which are normally carried between the partitions and which, in each compartment, carry liquid of each phase into the other. The passage of the phases along the vessel is made possible by spacing the edges of each partition from the wall of the vessel and/or by having openings through the partitions at selected points. It is preferred to have the two phases moving through the vessel in counter-current, although co-current flow is possible. As each bucket passes from one phase tithe other, it carries with it a quantity of the first phase, which becomes progressively displaced by the second phase. The first phase is thus released as droplets enter the second phase and because of the difference in specific gravities, migrates back to the first phase in the form of droplets. In other words, as the buckets on one side of the rotor travel in an upward direction, they carry the heavier phase into the lighter one and discharge their contents in a shower of droplets which fall back into the heavier phase. Similarly as the buckets descend on the other side, they carry the lighter phase downwards into the heavier phase and the lighter phase discharged from the buckets floats upwards in a series of droplets, back into the lighter phase.It is by this action of contacting the two phases that mass transfer takes place. Because of the large surface area to volume of the droplets during their passage from one phase to the other, high mass transfer efficiency is obtainable. That efficiency increases with the speed of rotation of the rotor for given throughput rates of the two phases, and decreases with increasing throughput rates for a given speed of rotation. We have discovered that, if, in addition to the two liquid phases, the contactor contains a granular material such as silica sand, and this material is caused to shower downwardly through the liquid phases by the lifting and discharging action of the buckets, the efficiency of mass transfer increases. Consequently, for a given speed of rotation, and for a specific mass transfer efficiency, the flow rates of the liquid phases can be increased and greater output obtained from the contactor. Thus, the present invention provides a liquid/liquid contacting process using a contactor of the type described, in which a fine inert granular material is caused by the conveying means continuously to fall through the liquid phases. The granular material is showered through the two liquid phases and, in falling through those phases, it alters the size distribution of the droplets in both phases and increases the extent of interaction between them, whereby an improved mass transfer efficiency is obtained. In certain conditions, and again as a consequence of the interaction of the showering particles of sand on the liquid droplets which are moving through - the liquid phases, a further improvement in mass transfer efficiency may be obtained by increasing the speed of rotation of the buckets, which increases the rate at which showering particles pass through the liquid phases. The granular material is preferably present in the contactor in a volume which is between two percent and ten percent of the volume of the contactor, and maintained at such a level in the bottom of the contactor that the rotating buckets pick up a mixture of sand along with the liquid in the lower part of the contactor. The particle size of the granular material is preferably between 75-and 750 microns. For the effective operation of the system, it is important to maintain a substantially constant level of sand in the bottom of the contactor. In order to do this, the sand is caused to flow through the contactor by being carried by the lower and heavier phase liquid. The sand is then separated from the liquid externally of the contactor, and recycled to the contactor where it is reintroduced with the heavier liquid. By virtue of the invention, i.e. by the addition of granular material to the system, it is possible to increase the throughput of the contactor by increasing the flow rates of the phases, and additionally, an improved mass transfer efficiency can be achieved by increasing the speed of rotation of the rotor, whereby particles of granular material are showered through the liquid phases at an increased rate. CLAIMS

4. A liquid/ liquid contacting process according to claim 1, 2 or 3, wherein rotating conveying means of the contactor comprise rotating buckets.

5. A liquid/liquid contacting process according to claim 4, wherein the granular material is maintained at such a level in the bottom of the contacor that the rotating buckets pick up a mixture of granular material along with the liquid in the lower part of the contactor.

6. A liquid/liquid contacting process according to any one of the preceding claims, wherein the granular material is of particle size 75 to 750 microns.

7. A liquid/liquid contacting process according to any one of the preceding claims, wherein the granular material is carried through the contactor by the lower heavier phase, separated externally of the contactor and recycled.

8. A liquid/liquid contacting process according to claim 1, substantially as described herein.