Treatment process

A process for treatment of a liquid stream, optionally comprising solids such as minerals, comprises passing at least two different treating reagents through contactors each comprising a drum with a rotor having axially spaced discs compartmentalizing the drum interior and carrying receptacles which rotate with the rotor and cause transfer of portions of one phase in the contactor to the other phase as the rotor turns. The liquid stream being treated is caused to flow along a path including, in succession, parts of each contactor so that the liquid stream is brought into contact with the reagents successively and in rotation.

BACKGROUND OF THE INVENTION 
This invention relates to a process for the treatment of a liquid stream 
with two different reagents. The invention is particularly concerned with, 
but is not limited to, the deionisation of a stream of liquid employing 
deionising agents and particularly deionising resins. 
It is known to deionise liquid by passing the latter first through a bed of 
anionic deionising resin and subsequently through a bed of cationic 
deionising resin; in theory in that way salts can be removed from the 
liquid. In practice, it is found that the treatment of the liquid in two 
such beds is not wholly effective and that, instead, it is necessary to 
pass the liquid subsequently and alternately in contact with the two types 
of resin. Thus, it has been proposed to pass the liquid through a column 
containing alternate layers of anionic and cationic resins. While such a 
column may be effective in removing salts from the liquid, it has the 
attendant problem of subsequently separating the resins for regeneration. 
OBJECTS OF THE INVENTION 
It is an object of the present invention to provide a liquid treatment 
process using at least two reagents, in which the reagents are kept 
separate from one another. 
It is a further object of the invention to provide a process for the 
desalting of a liquid stream optionally containing solids with an anionic 
deionising agent and a cationic deionising agent in which the deionising 
agents are independently contacted with the liquid stream. 
These and other objects of the invention will appear from the following 
description and claims. 
SUMMARY OF THE INVENTION 
The invention makes use of a contactor which comprises a drum through which 
the phases pass, usually in countercurrent, a rotor within the drum 
including a plurality of axially spaced discs dividing the drum interior 
into a series of compartments, spaces being formed between the drum and 
the edges of the discs to allow passage of the phases from compartment to 
compartment, and, for each of at least some of the compartments, a 
plurality of receptacles arranged to rotate with the rotor and designed to 
receive material of one phase and to discharge it into the other phase as 
the rotor turns. The phases, which can be both liquid or which can 
comprise a liquid phase and a solids phase, pass through the drum and are 
brought into contact with one another in the compartments by virtue of the 
action of the rotating receptacles. Such a contactor is described in U.S. 
Pat. No. 3,649,209. A contactor as described above will be referred to in 
this specification as "a contactor of the type described". 
One aspect of the present invention resides in a process for the treatment 
of a liquid stream in which at least two different reagents are 
respectively continually passed through at least a first and second 
contactor of the type described and the liquid stream is caused to flow 
along a path which includes succession parts of one of the contators and 
parts of the other contactor or contactors, so that the liquid stream is 
brought into contact with the reagents successively and in rotation. The 
liquid stream may be caused to follow that path by providing connections 
between selected compartments of one contactor and selected compartments 
of the other contactor or contactors. It will be understood that the 
liquid stream may contain solids carried therein. 
Preferably the liquid stream is brought into contact successively and 
alternately with two reagents in respectively a first and second 
contactor. 
When the invention is applied to the deionisation of a liquid stream, 
streams of anionic and cationic deionising agents are passed respectively 
through the two contactors so that the liquid is brought into contact with 
each as it passes through the respective contactor. 
Preferably, the deionising reagents are in the form of particulate resins 
having a specific gravity less than that of the stream being treated. In 
that case, the liquid stream in each contactor flows in countercurrent to 
the resin streams, with the resin, preferably with the carrier liquid, 
occupying the upper part of each contactor and the liquid stream occupying 
the lower part. Alternatively, the deionising reagents may flow co-current 
with the liquid stream, in which case each resin may have a specific 
gravity greater than that of the liquid stream and occupy the lower part 
of each contactor.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
The apparatus for performing the process consists essentially of two 
contactors of the type described in U.S. Pat. No. 3,649,209, arranged with 
their axes parallel and at an inclination to the horizontal of the order 
of 7.degree.. The contators are shown schematically in the drawing at 12 
and 13, each being represented merely by its stationary drum 14 and the 
discs 15 which are mounted on the rotor 21 and which divide the respective 
contactor into a series of compartments 16. 
Into contactor 12 is introduced a stream 17 of anionic deionising resin 
particles in a non-polar carrier liquid, e.g. kerosene. The stream leaves 
the contactor on line 22. Similarly, a stream 18 of cationic deionising 
resin particles in a similar carrier liquid is caused to pass through the 
contactor 13 in the same direction. The stream leaves the contactor on 
line 23. A stream 20 of liquid to be treated, containing a salt or salts 
to be removed is introduced into contactor 13 in countercurrent to the 
resin stream 18 and passes through a number of the compartments 16, being 
there contacted by the cationic resin; the resin and its carrier liquid 
being lighter occupies the upper half of the contactor, while the 
treatment liquid 20 occupies the lower half. 
After the treatment liquid 20 has traversed a selected number of 
compartments 16 in the contactor 13, it is caused to leave the contactor 
and enter the other contactor 12. This is done by having an opening in the 
wall of the drum 14 below the centre line of the drum and connecting by 
piping 24 to a similar opening in the drum of the other contactor 12. The 
stream 20 next passes through a section consisting of a number of 
compartments of contactor 12 before returning to contactor 13 by a second 
pipe 25 connecting the two drums. The stream then passes in a similar 
manner repeatedly between the two contactors as indicated in the drawing 
so that it is contacted alternately by the two resin streams 17 and 18. 
Finally the stream exits from contactor 12 on line 26 at the end at which 
the anionic resin stream 17 enters. 
It is important that the resin of one contactor should not be transferred 
to the other contactor and intermingle with the resin of that other 
contactor. Locating the openings in the drum walls at levels below the 
interfaces between the resin streams 17, 18 and the treatment stream 20 
results in there being little possibility of resin being carried out of 
the respective contactor with the stream 20, but in addition each opening 
in the drum wall is provided with a mesh with a fineness preventing 
passage of the resin particles. 
The contactor drums are interconnected by the piping in such manner that, 
bearing in mind the inclination of the drum axes, the level at which the 
liquid leaves one contactor is above the level at which it enters the 
other contactor; that arrangement increases the proper flow of the liquid 
from one contactor into the other. It will be appreciated that only a part 
of the stream 20 will flow through the piping interconnecting the 
contactors, the remainder continuing through the contactor in contact with 
the resin. If desired, each contactor can be formed into separate sections 
by means of rotary seals surrounding the lower parts of selected discs 15, 
in order to ensure that the entire flow is transferred from one contactor 
to the other. 
Because the two streams 17 and 18 of the resins are kept entirely separate 
in the respective contactors 12 and 13, the need to separate the resins 
does not arise and each stream on leaving the respective contactor is 
immediately treated in a regeneration unit 27 to regenerate the resin and 
to return it to the entry of the contactor. This means that resins of 
identical physical specifications can be used in the two contactors with 
no separation problems. 
The resins can be used in the invention in a non-aqueous phase lighter than 
the liquid stream being treated. Thus solid material, such as minerals in 
the liquid stream will not interfere with the resin as is the case in a 
conventional resin bed where minerals may cause blocking. Alternatively 
the resin may be carried in an aqueous medium underlying an organic phase. 
The invention is applicable to two-phase treatment processes, where an 
entirely liquid stream is treated, for example in the desalting of salt 
water, beverages (such as freeze-concentrated alcohol) and monomer 
solutions of comparatively high density prior to polymerisation. 
The invention is also applicable to three-phase processes where the liquid 
stream contains a solid. Thus, for example, the invention can be used in 
the desalting of minerals such as kaolin (where the salt content has a 
substantial effect on the properties of the product). The invention may 
also be used for desalting solid suspensions obtained in chemical process, 
such as titania in sulphite liquor and alumina in caustic liquor as an 
alternative to filtration and countercurrent washing procedures. A further 
application is in the desalting of pH sensitive materials, such as 
antibiotics obtained by fermentation, in solid suspensions which are 
difficult to filter. 
Selective ion exchange resins may also be used in two or more contactors to 
selectively remove two or more species of ion from a solution or 
suspension.