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Description  |
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The present invention relates to transferring heat between relatively cold
and hot locations.
In this specification, the relatively hot location will be termed the hot
heat sink or hot heat source, and the relatively cold location the cold
heat source.
The transfer of heat from a cold source to a hot source is well known in
the fields of refrigeration of the cold source and heating of the hot
source by so-called heat pumps. The commonest types of refrigeration and
heat pump equipment are of two well-known types, viz (i) the mechanical
compression type in which a working fluid in the vapour phase is
mechanically compressed and heat exchanged against the hot heat source to
discharge heat thereto with possible liquefaction of at least some working
fluid, and then expanded to a lower pressure and heat exchanged against
the cold heat source with vapourization of liquid working fluid to extract
heat therefrom, the vapour phase working fluid then being recovered and
mechanically compressed for further use, and (ii) an absorption type in
which a solution of a working fluid in an absorbent liquid is heated to
produce hot vapour phase working fluid at a pressure below its critical
pressure and hot absorbent liquid which is impoverished in working fluid,
the vapour phase working fluid being heat exchanged against the hot heat
source to discharge heat thereto so that the working fluid liquefies,
expanding the liquid working fluid to a lower pressure and heat exchanging
the expanded working fluid against the cold heat source to extract heat
therefrom, and contacting the expanded working fluid with cooled,
impoverished absorbent liquid to form a solution of working fluid in the
absorbent liquid, and re-using the solution.
The efficiency of equipment for transferring heat between a cold heat
source and a hot heat source is usually judged by its coefficient of
performance (C.P.) which is the ratio of the heating effect produced to
the energy supplied, both expressed in the same units. The C.P. must be
greater than unity if heat is transferred between the relatively hot and
cold locations. In the case where the working fluid is mechanically
compressed, a C.P. exceeding 1.5 may be obtained.
In the case where the working fluid is separated under pressure by heating
a solution of the working fluid in an absorbent liquid, C.P's have
heretofore been no higher than 1.5 or thereabouts because a significant
proportion of the heat supplied is used to ensure efficient separation of
the hot working fluid from the absorbent liquid by distillation
techniques.
It is an object of this invention to provide a method of, and equipment
for, transferring heat from a cold heat source to a hot heat source by
means of an improved heat pump or refrigerator of the absorption type.
According to one aspect of this invention, there is employed a combination
of a working fluid and an absorbent liquid which are so selected that in
the range of thermodynamic conditions encountered, the combination has a
lower critical solution temperature (t.sub.c) at, and below which, the
absorbent liquid is capable of forming a liquid solution of the working
fluid but above which the absorbent liquid and working fluid separate from
such a solution into absorbent liquid-rich and working fluid-rich phases,
and heat is transferred from a cold heat source at a temperature T.sub.c
to a hot heat source or heat sink at a temperature T.sub.s by passing
"rich" working fluid (i.e., working fluid mixed with no more than a minor
proportion of any other fluid) under a first pressure (p.sub.1) and at a
first temperature (t.sub.1) in a first heat exchange step in heat exchange
relationship with the cold source of heat at a second pressure (p.sub.2)
lower than the first pressure (p.sub.1) and at a second temperature
(t.sub.2) lower than the first temperature ( t.sub.1) and lower than the
temperature T.sub.c of the cold source of heat, thereby extracting heat
from the cold heat source, mixing the fluid in a mixing step, at a mixing
pressure (p.sub.m) and at a mixing temperature (t.sub.m) not exceeding the
lower critical solution temperature (t.sub.c), with absorbent-rich liquid,
rich in absorbent liquid, which at the mixing pressure (p.sub.m) forms a
liquid solution of the working fluid in the absorbent liquid substantially
at the mixing temperature (t.sub.m) and mixing pressure (p.sub.m), and
passing the liquid solution substantially at the mixing temperature
(t.sub.m), but substantially at the first pressure (p.sub.1) in a second
heat exchange step in heat exchange relationship with a source of heat to
heat the solution to a third temperature (t.sub.3) exceeding the
temperature T.sub.s and also exceeding the critical solution temperature
(t.sub.c) whereby the solution separates into a first phase which is rich
in working fluid and a second phase which is rich in absorbent liquid at a
temperature greater than T.sub.s, separately recovering rich working fluid
and absorbent-rich liquid from the two phases, passing recovered rich
working fluid in a third heat exchange step in heat exchange relationship
with the hot heat source or heat sink at the temperature T.sub.s thereby
transferring heat to the heat sink and reducing the temperature of the
rich working fluid substantially to the first temperature (t.sub.1), then
passing the rich working fluid substantially at the first temperature
(t.sub.1) and first pressure (p.sub.1) to the first heat exchange step,
and passing recovered absorbent-rich liquid to the mixing step.
Because the separation of the solution of the working fluid in absorbent
liquid into the first working fluid-rich phase and second absorbent-rich
phase may take place merely by heating the solution, the heat input to
effect this separation will be relatively small as compared to that
required in prior systems using conventional distillation, and
accordingly, the coefficient of performance of systems embodying the
invention will be relatively high.
In another aspect, the present invention comprises apparatus for
transferring heat from a relatively cold heat source at a temperature
T.sub.c to a relatively hot heat sink at a temperature T.sub.s wherein
T.sub.s exceeds T.sub.c, and adapted for employing a combination of a
working fluid and an absorbent liquid which are so selected that within
the range of thermodynamic conditions encountered in the apparatus, the
said combination is capable of forming a solution having a lower critical
solution temperature t.sub.c, the apparatus comprising a conduit for
conducting rich working fluid under a first pressure p.sub.1 and at a
first pressure t.sub.1 to a first heat exchange means adapted for being in
heat exchange relationship with the cold heat source via expansion means
permitting expansion of the working fluid to a second pressure p.sub.2
lower than p.sub.1 and a second temperature t.sub.2 lower than t.sub.1 and
lower than T.sub.c for extracting heat from the cold heat source, a
conduit for the passage of working fluid from the first heat exchange
means to mixing means operative for mixing the working fluid at a mixing
pressure p.sub.m and mixing temperature t.sub.m not exceeding t.sub.c with
a liquid rich in absorbent liquid whereby to form a solution of working
fluid in absorbent liquid, means for recovering said solution, means for
causing the solution to pass at substantially the pressure p.sub.1
exceeding p.sub.m and substantially at the mixing temperature t.sub.m to a
second heat exchange means adapted for being in heat exchange relationship
with a source of heat operative to raise the temperature of the solution
to a temperature t.sub.3 which is greater than T.sub.s and greater than
t.sub.c, separating means connected for receiving the solution from the
second heat exchange means for permitting and/or facilitating the
separation of rich working fluid from the solution, means for recovering
absorbent liquid, depleted in working fluid, and for circulating said
liquid to said mixing means for forming a further quantity of a solution
of working fluid in absorbent liquid, means for conducting separated
working fluid to pass to third heat exchange means adapted for being in
heat exchange relationship with the hot heat sink whereby to furnish heat
thereto, and means for conducting working fluid from said third heat
exchange means substantially at said pressure p.sub.1 and temperature
t.sub.1 for re-use in transferring further quantities of heat.
The lower critical solution temperature t.sub.c will depend on the nature
of the working fluid and absorbent liquid, the relative concentrations of
the working fluid and absorbent liquid, and on the pressure.
Preferably, the relative concentrations of working fluid and absorbent
liquid at the mixing step are so chosen that the best separation of
working fluid is obtained when the resulting solution is subsequently
heated to the temperature t.sub.3.
The cold source may be any convenient extensive body, such as the
atmosphere or, more preferably, a body of water such as a river, sea or
lake, to reduce the amount of heat exchange surface necessary to provide
the required heat input at the cold source. In the temperate zones of
northern Europe, the temperature of such cold sources will be generally in
the range 8.degree. to 15.degree. C., with possible seasonal variations
outside this range, and depending on the cold source, the working fluid
and absorbent liquid, their relative concentrations in the second heat
exchange step are preferably so selected that the temperature of the hot
source need be only relatively slightly higher (e.g. 10.degree. to
15.degree. C.) than t.sub.c for domestic heating uses.
Preferably, there is employed a combination of a working fluid and an
absorbent liquid which form a solution at the LCST and below, for at least
some relative amounts of the working fluid and absorbent liquid, and which
separate into a substantially pure working fluid phase when the
temperature of the solution is raised above the LCST.
The working fluid may have a relatively high specific heat and/or latent
heat of vapourization. For many uses, water may be employed as the working
fluid as it has both a high specific heat and a high latent heat of
vapourization, and is cheap and readily available.
The absorbent liquid may be any which is chemically stable over the
operating temperature range to which it is subjected during the heat
transfer operation. Specific types are glycol ethers and liquid
condensation products of alkylene oxides with glycols.
The absorbent liquid may comprise one or more absorbent liquid components
such that the LCST is higher than the temperature of the cold source.
In order to reduce the power for circulating absorbent liquid between the
stage in which it absorbs working fluid and the stage in which it
separates from working fluid, it is preferred that the viscosity of the
absorbent fluid be relatively low. In many instances, a low molecular
weight absorbent liquid will give a low viscosity.
The combination of working fluid and absorbent liquid is preferably so
selected that at temperatures exceeding the LCST, separation of working
fluid from solutions of working fluid and absorbent liquid take place
relatively rapidly.
Similarly, it is preferred that the absorption of the working fluid in the
absorbent liquid should take place relatively rapidly at the absorption
temperatures; a suitable choice of component(s) of the absorbent liquid
and of the working fluid will ensure this.
The solution of working fluid and absorbent liquid should be such that
substantially no foaming occurs, particularly during the separation of
working fluid from the absorbent liquid.
After the separation of working fluid from the absorbent liquid, e.g., by
decantation or passage over a weir, the absorbent liquid should preferably
contain no more than a minor proportion of the working fluid and the
working fluid should preferably contain substantially no absorbent liquid,
or only a very minor proportion thereof.
The range of relative concentrations of working fluid and absorbent liquid
giving LCST properties with a desired operating temperature range may be
extended by providing in the solution of working fluid and absorbent
liquid, or in the latter, an additive which is soluble or partly soluble
in both the working fluid and the absorbent liquid. When such an additive
is so provided, the amount of absorbent liquid may be reduced since it is
then possible to form a solution of the working fluid at a higher
concentration of the latter relative to the absorbent liquid. In
embodiments wherein the working fluid is water and the absorbent liquid is
a glycol ether or polyoxyalkyleneglycol or polyoxyalkylenepolyglycol
ether, suitable non-limitative examples of additives are sodium alkyl
sulphates, where the alkyl group is butyl, octyl or dodecyl, for example,
and para-chlorobenzene sodium sulphonate. Such additives are preferably
provided in relatively low concentrations (e.g., 0.1 to 1.0 wt.%, based on
the absorbent liquid).
Examples of other suitable combinations or working fluids, W, absorbent
liquids A and their minimum lower critical solution temperatures, t.sub.c,
are given in the following table:
__________________________________________________________________________
Combination No.
Absorbent Liquid (A)
Molecular Weight
Working Fluid (W)
Minimum t.sub.c (.degree.
__________________________________________________________________________
C.)
1 Polyisobutylene 4.7 .times. 10.sup.2
propane 85
2 " 4.7 .times. 10.sup.2
isobutane 114
3 " 1.6 .times. 10.sup.6
n-pentane 75
4 "
5 " .infin.
n-pentane 71
6 " 1.6 .times. 10.sup.6
isopentane 54
7 " 6.2 .times. 10.sup.4
isopentane 71
--Mw
8 " 2.3 .times. 10.sup.6
isopentane 52
9 " .infin.
isopentane 45
10 " 1.6 .times. 10.sup.6
cyclopentane
71
11 " .infin.
cyclopentane
188
12 " 1.6 .times. 10.sup.6
n-hexane 128
" .infin.
n-hexane 129
13 " 1.6 .times. 10.sup.6
2,2-dimethyl-
103
butane
14 " 1.6 .times. 10.sup.6
2,3-dimethyl-
131
butane
15 " .infin.
2-methylpentane
103
16 " .infin.
3-methylpentane
132
17 " .infin.
methylcyclopentane
205
18 " .infin.
cyclohexane
243
19 " 1.6 .times. 10.sup.6
cyclohexane
139
20 " 1.6 .times. 10.sup.6
n-heptane 168
21 " .infin.
n-heptane 169
22 " .infin.
2-methylhexane
153
23 " .infin.
3-methylhexane
173
24 " .infin.
3-ethylpentane
185
25 " .infin.
2,2-dimethylpentane
131
26 " .infin.
2,3-dimethylpentane
178
27 " .infin.
2,4-dimethylpentane
130
28 " .infin.
3,3-dimethylpentane
176
29 " .infin.
2,2,3-trimethylbutane
172
30 " .infin.
ethylcyclopentane
251
31 " .infin.
methylcyclohexane
253
32 " .infin.
cycloheptane
299
33 " .infin.
n-octane 204
34 " 1.6 .times. 10.sup.6
n-octane 180
35 " .infin.
2-methylheptane
193
36 " .infin.
3-methylheptane
205
37 " .infin.
2,2-dimethylhexane
181
38 " .infin.
2,4-dimethylhexane
185
39 " .infin.
2,5-dimethylhexane
173
40 " .infin.
3,4-dimethylhexane
224
41 " .infin.
2,2,4-trimethylpentane
162
42 " .infin.
n-propylcyclopentane
274
43 " .infin.
cyclooctane
364
44 " .infin.
n-decane 262
45 " .infin.
n-dodecane 309
46 Polystyrene 1.3 .times. 10.sup.6
cyclopentane
150
47 " 2.5 .times. 10.sup.5
cyclopentane
164
48 " 8.9 .times. 10.sup.4
cyclopentane
172
49 " 4.3 .times. 10.sup.4
cyclopentane
178
50 " 9.5 .times. 10.sup.4
methyl acetate
132
51 5.5 .times. 10.sup.4
methyl acetate
150
52 " --Mn 5.9 .times. 10.sup.4
methyl acetate
154
53 " 4.8 .times. 10.sup.4
methyl acetate
155
54 Polybutadiene 1.5-3.0 .times. 10.sup.5
n-hexane 145
55 " 1.5- 3.0 .times. 10.sup.5
toluene 300
56 " 1.5-3.0 .times. 10.sup.5
benzene 270
57 Polyethylene 10.sup.6 ?
n-hexane 127
58 " 10.sup.6 ?
cyclohexane
163
59 Polypropylene 1.7 .times. 10.sup.4
n-pentane 152
60 " 1.8 .times. 10.sup.6
n-pentane 105
61 " .gtoreq.2 .times. 10.sup.6
n-pentane 136
62 " --(Mn)
1.1 .times. 10.sup.4
n-pentane 172
63 " 3.7 .times. 10.sup.4
n-pentane 157
64 " 9.7 .times. 10.sup.4
n-pentane 153
65 " 1.2 .times. 10.sup.5
n-pentane 152
66 " 4.9 .times. 10.sup.3
n-pentane 149
67 " 3.1 .times. 10.sup.3
n-pentane 177
68 " 4.5 .times. 10.sup.3
n-pentane 175
69 " 1.2 .times. 10.sup.4
n-pentane 163
70 " 5.2 .times. 10.sup.4
n-pentane 154
71 Polybutene-1 1.8 .times. 10.sup.5
n-pentane 153
72 " 5.0 .times. 10.sup.5
n-pentane 151
73 " --(Mw)
1.2 .times. 10.sup.5
n-pentane 153
74 " 2.3 .times. 10.sup.6
n-pentane 148
75 Polyoctene-1 2.5 .times. 10.sup.6
propane 36
76 " 2.5 .times. 10.sup.6
isobutane 84
77 " --(Mw)
2.5 .times. 10.sup.6
n-butane 114
78 " 2.5 .times. 10.sup.6
neopentane 111
79 " 2.5 .times. 10.sup.6
n-pentane 166
80 2,3 dimethylpyridine
-- water 16.5
81 2,4 dimethylpyridine
-- water 23.4
82 2,5 dimethylpyridine
-- water 13.1
83 2,6 dimethylpyridine
-- water 34.0
84 Ethyl-2 pyridine
-- water -2.0
85 Ethylene glycol-n-
-- water 49.1
butyl ether
86 Ethylene glycol-
-- water 24.5
isobutyl ether
87 1,2 propylene glycol-
propyl ether -- water 34.5
88 1,2 propylene
glycol 2-
propyl ether -- water 42.6
89 polycondensation water 25 to 100
product of ethylene
oxide and poly-
propyleneglycols*
__________________________________________________________________________
*of the types of various molecular weight available under the trade name
"EmKalyx - Pluronics".
Combinations 85 to 89 have the merit of being readily available at
comparatively low cost. Of course, the list of combinations given above is
by no means exhaustive.
The separation and recovety of the absorbent liquid and working fluid may
be simply by overflow over a weir or by a decantation technique.
In some operations of the system of the invention, the heat content of one
or both of the working fluid and of the absorbent liquid at the mixing
step may be excessively high for the formation of a solution of working
fluid in absorbent liquid, and it may then be necessary to reject heat
from one or both of the working fluid and absorbent liquid so that a
solution may be formed. Generally speaking, it will usually be more
convenient to reject heat from the absorbent liquid than the working
fluid. The heat rejection may be performed in a fourth heat exchange step
wherein the absorbent liquid and/or the working fluid are passed in heat
exchange relationship with a suitable heat sink which is at a temperature
(t.sub.4) lower than the temperature of the said recovered first and/or
second phase. A suitable heat sink may comprise, at least in part, the
solution of working fluid in absorbent liquid recovered from the mixing
step. The heat sink may additionally or alternatively comprise the cold
heat source at the temperature T.sub.c and/or the hot heat sink at the
temperature T.sub.s. Thus, for example, a heat exchange fluid may be
passed in heat exchange with the absorbent liquid passing to the mixing
step and/or with working fluid, the heat exchange fluid being circulated
to the heat sink where heat is discarded or rejected. In one embodiment,
heat exchange fluid may be passed in heat exchange relationship with the
absorbent liquid passing to the mixing step, and the heat exchange fluid
or a stream in parallel therewith passed in heat exchange relationship
with the working fluid passing from the separation step, the heat exchange
fluid stream(s) then being circulated for heat exchange with the heat sink
at temperature T.sub.s.
The circulation of the absorbent liquid may be by a pump or by thermosiphon
or other convenient means or expedients. The working fluid may circulate
under the influence of pressure differences between the pressure
(c.p.sub.1) at the first phase-recovery step and pressure (p.sub.m) at the
mixing step. The circulation of the absorbent liquid and working fluid may
further be assisted by providing a "permanent" or non-condensible gas such
as hydrogen in the circulation route of the working fluid.
The invention is now described in a non-limitative way with reference to
the accompanying drawings, wherein the working fluid is designated A and
the absorbent liquid is designated B, and in which:
FIG. 1 shows an examplary graph of the variation of LCST with varying
concentrations of A and B;
FIG. 2 is a diagrammatic flow sheet of a heat pump or refrigerator using
the principle of the invention;
FIGS. 3 and 4 are graphs of the type shown in FIG. 1 but wherein A is
water, and B is diethylene glycol monoethylether in FIG. 3, and the
polycondensation product of ethylene oxide and propylene glycol available
under the trade name "Pluronic 31" and having a molecular weight of about
1100 in FIG. 4.
FIG. 5 shows graphically the variation of coefficient of performance
("C.P.") versus weight ratios of Pluronic 31: water for different
temperatures of B on entering an absorber for absorbing A, as obtained by
calculation.
FIG. 6 depicts graphically calculated ranges of C.P. for a range of weight
ratios of Pluronic 31:water assuming different heats of solution of water
in Pluronic 31 in the absorber;
FIG. 7 is a graph of C.P. versus weight ratio of Pluronic 31 to water
showing the effect of operating an evaporater at different temperatures;
FIG. 8 shows calculated values of the C.P. for systems using A = water, B =
either n-butyl-Cellosolve (commercial name for diethylene glycol
monobutylether) or Pluronic 31; and
FIG. 9 shows graphically the variation of C.P. with different ratios of A
to B in the absorber.
Reference is first made to FIG. 1.
FIG. 1 is a typical graph of lower critical solution temperatures t.sub.c
at and below which the working fluid W and absorbent liquid A form a
solution, the percentage concentrations of absorbent liquid A and working
fluid W being depicted along the abscissa. The graph shows that for the
selected combination of working fluid W and absorbent liquid A, t.sub.c
has a minimum value for reasonable concentrations of working fluid. It
will be appreciated that if the value of t.sub.c corresponding to a
selected solution of W in A is slightly above the mixing temperature
t.sub.m, the amount of heat required to separate the solution into its two
phases may be relatively low, so that the coefficient of performance of
the system is relatively high. It is not necessary to operate at the
minimum t.sub.c for the combinations exhibiting a minimum t.sub.c such as
that depicted in FIG. 1. For example, it might be convenient to operate
along the vertical line B--B over the temperature range C--C, in FIG. 1.
Reference is now made to FIG. 2.
A solution of the working fluid A in absorbent liquid B at a temperature
slightly below the lower critical solution temperature t.sub.c is passed
via line 11 to heat exchanger 12 wherein the solution is heated to a
temperature at or above its lower critical solution temperature. The
components of the solution pass to a separating or decantation vessel 13
wherein they form two phases. As depicted, the lower phase in vessel 3 is
a liquid which is rich in B and the upper phase is rich in A. The A-rich
phase circulates via line 14 to a heat exchanger 15 wherein it surrenders
heat to a hot source or heat sink which is at a lower temperature than the
A-rich phase, thereby providing heat at the hot heat source or sink and
cooling the A-rich phase. The cooled A-rich phase passes via line 16 and a
heat exchanger 17 and an expansion device 17a (e.g., an expansion valve
and/or engine) wherein it expands to a lower pressure and its temperature
falls considerably. The thus expanded A-rich phase is passed into a flash
chamber 18 which is in heat exchange relationship with a cold heat source
(e.g. river or sea-water) and heat is transferred from the cold heat
source to the cold, expanded A. Any heavy contaminant (e.g. a contaminant
comprising vapourized or entrained B) separates at the bottom of flash
chamber 18. The expanded A is passed from chamber 18 via line 20 to the
heat exchanger 17 wherein it is in heat transfer relationship with the A
passing to the flash chamber 18, thereby reducing the temperature of the
latter (and increasing its heat extraction from the cold heat source) and
increasing the temperature of the expanded A leaving the heat exchanger
17. The thus warmed, expanded A circulates to the top region of an
absorption tower 21 wherein it is contacted by a downward flow of B from
line 22. Further down the tower 21, heavy contaminants which may have
separated at the bottom of chamber 18 are introduced via line 23
substantially at their flash chamber temperature. The relative
concentrations of A and B and their temperatures during contact in the
tower 21 are so arranged that component A will form a solution in
component B. Thus, the B stream may be passed in heat exchange
relationship with a cooling fluid in a heat exchanger (not shown)
immediately before it is passed into the tower 21. The cooling fluid may
be employed to supply heat to the heat sink and may be combined in series
or parallel with a cooling fluid stream in heat exchanger 15, the cooling
fluid supplying heat to the heat sink. If the dissolution of A in B
evolves heat which may inhibit the absorption of substantially all of A in
B, tower 21 may be provided with any known suitable means (not shown) for
removing heat from the interior thereof.
A solution of A in B is recovered via line 24 from the base of the tower
21, and circulated by a pump 25 back to line 11 for further use. As is
shown, the solution is passed to line 11 via a heat exchanger 26 wherein
it is in heat transfer relationship with B which is recovered from the
base of separating vessel 13 via line 27. By this expedient, the
temperature of B passing to the top of the absorption tower 21 via line 22
is reduced to a level at which the solution of A in B may be more readily
formed in the tower 21, while the temperature of the solution of A in B
passing to line 11 is raised to a temperature below the critical solution
temperature.
The apparatus of FIG. 2 functions to transfer heat from the cold heat
source in heat transfer relationship with the flash chamber 18 to the hot
heat source in heat exchange relationship with heat exchanger 15.
Accordingly, the apparatus may be employed as a refrigerator for the cold
heat source or as a heat pump for heating the hot heat source, or for both
functions. The "payload" of heat is the relatively small amount of heat
input at heat exchanger 12 and since this, together with the energy input
from the pump 25, represents a relatively small proportion of the heat
transferred to the hot heat source or heat sink at heat exchanger 15, the
coefficient of performance is relatively high.
The apparatus of FIG. 2 is, of course, not limitative as to the type of
equipment by which the LCST phenomenon can be exploited for use in heat
pumps or refrigeration equipment.
Reference is now made to FIGS. 3 and 4 from which will be seen the
different LCST curves of the systems water/diethyethylene monobutylether
(FIG. 3) and water/Pluronic 31 (FIG. 4). The latter system gives phase
separation at lower temperatures and higher water concentrations than the
former, which may be advantageous, other factors being equal, in that a
small proportion of absorbent liquid is required with Pluronic 31 than
with diethyleneglycol monobutylether. The "parabolic" curves of FIGS. 3
and 4 can be widened, and flattened at their minima so as to have a higher
LCST, by the addition of a compound which is dissolved in both components
of the system. Suitable compounds are butyl, octyl or dodecyl sodium
sulphate and p-chlorobenzene sodium sulphonate. These and other suitable
compounds can be employed to adjust or modify the LCST curves of other
systems. Examples of absorbent liquids which can be used when water is the
working fluid, together with their LCST with water are now given:
______________________________________
1. Diethyleneglycol monoamylether
LCST = 36.degree. C
2. Diethyleneglycol monohexylethylether
" 3.degree. C
3. Propyleneglycol monopropylether
" 32.degree. C
4. Triethyleneglycol monohexylether
" 37.degree. C
5. Triethyleneglycol monooctylether
" 10.degree. C
6. Ethylbenzeglycol mono-n-butylether
" 57.degree. C
7. Tetraethyleneglycol monohexylether
" 60.degree. C
8. Tetraethyleneglycol monooctylether
" 35.degree. C
9. Pentaethylene monooctylether
" 60.degree. C
10. Pluronic L31 " 37.degree. C
11. Pluronic L35 " 77.degree. C
12. Pluronic L42 " 37.degree. C
13. Pluronic P69 " 82.degree. C
______________________________________
Combinations of absorbent liquids, such as those given above, may be
employed, to furnish systems having an LCST appropriate for the duties
envisaged, and, if necessary, additives may be included in the absorbent
liquid(s) to modify or adjust the LCST curves, | | |
