Water, Water Everywhere . . .
87
,
Stage. Evidence suggests that the osmotic powers
cellulose
acetate membranes gradually tailo” when sea—water‘iS treated, and
that under the high pressurès needed to
reasonable eputity
physical changes occur whichlead to a further=deteriorationof their
property. Numerous groups, particularly in the USA andBritain,
are 'engaged in the searchfor new materials which will yièldmem—
branes Superior to the cellulose acetate ones—but so far with very
little success. In the August 1966 issue. of Science ÿoumal Dr Alan
Sharples of Arthur D. Little Ltd. described‘four basic require—,
ments: ‘The rst is a material which can dissolve water toa limited
extent (and hence transmit it by» di"usion) but which has a reduced
_
afnity for sodium and chloride ions;
.
.
The second is a process
for casting the material in the form of a suitably exible lm, with
the special structure characteristic of the high throughput mem—
branes developed by Loeb
'S’ourirajan. '. . . The third is ability
of the structure to Withstand high pressùres . . . and nally, it must
be free=from defect pores… . .’
.
<
'
;
H
.
One promisihg approach being pioneered by Du Pont replacés
theàtmembrane by a maSs of ne hollow plastic bres; T heipùt
water, under high pressure, ows over the outside surface ofithe
bres and a portion of the water passes through intothe inside.
This product water, containing very
salt,isthenrun o“ from
the bres at the same time as the saltywater surrounding the bres.
Known as “‘Permasep’ perméators, units builton"these lines Jean
demineralize brackishwater when operated at a pressure0f“ 600,
‘
pounds per square inch. '
.
‘
*
»
:
—
”::‘
for reverse osmosis‘lies in the growing understanding-of,
‘
howthe‘ membranes work and in exp‘loring …thediversity o'materials
available. 'Unfortunately;understanding is
enough—:_ scientists know how brine»becomes tfapped
spaces
between ice crystals
Closely‘packed'Ztogethe‘rgïthey know“.
how to Vary the rate of formation of iceand the size Ofïthe crystals,
but ï‘for many years—problems met
preitented :
the fre€zing’ “processes from
theoretical—… advantagesover
example the low “ theoretical requirement
of '
reduction ofcc)rrosion. 0ne AmeriCan pilot .» plant—
haS'
and
plant yat—Eilat
slow to
coh1e‘“into‘full operation,
now
: at :m0re than
the
‘
:“»Ë< =:
;
«’
»
lnthe early.ôos, frœz”ing
enthusiastic folleing.
87
,
Stage. Evidence suggests that the osmotic powers
cellulose
acetate membranes gradually tailo” when sea—water‘iS treated, and
that under the high pressurès needed to
reasonable eputity
physical changes occur whichlead to a further=deteriorationof their
property. Numerous groups, particularly in the USA andBritain,
are 'engaged in the searchfor new materials which will yièldmem—
branes Superior to the cellulose acetate ones—but so far with very
little success. In the August 1966 issue. of Science ÿoumal Dr Alan
Sharples of Arthur D. Little Ltd. described‘four basic require—,
ments: ‘The rst is a material which can dissolve water toa limited
extent (and hence transmit it by» di"usion) but which has a reduced
_
afnity for sodium and chloride ions;
.
.
The second is a process
for casting the material in the form of a suitably exible lm, with
the special structure characteristic of the high throughput mem—
branes developed by Loeb
'S’ourirajan. '. . . The third is ability
of the structure to Withstand high pressùres . . . and nally, it must
be free=from defect pores… . .’
.
<
'
;
H
.
One promisihg approach being pioneered by Du Pont replacés
theàtmembrane by a maSs of ne hollow plastic bres; T heipùt
water, under high pressure, ows over the outside surface ofithe
bres and a portion of the water passes through intothe inside.
This product water, containing very
salt,isthenrun o“ from
the bres at the same time as the saltywater surrounding the bres.
Known as “‘Permasep’ perméators, units builton"these lines Jean
demineralize brackishwater when operated at a pressure0f“ 600,
‘
pounds per square inch. '
.
‘
*
»
:
—
”::‘
for reverse osmosis‘lies in the growing understanding-of,
‘
howthe‘ membranes work and in exp‘loring …thediversity o'materials
available. 'Unfortunately;understanding is
enough—:_ scientists know how brine»becomes tfapped
spaces
between ice crystals
Closely‘packed'Ztogethe‘rgïthey know“.
how to Vary the rate of formation of iceand the size Ofïthe crystals,
but ï‘for many years—problems met
preitented :
the fre€zing’ “processes from
theoretical—… advantagesover
example the low “ theoretical requirement
of '
reduction ofcc)rrosion. 0ne AmeriCan pilot .» plant—
haS'
and
plant yat—Eilat
slow to
coh1e‘“into‘full operation,
now
: at :m0re than
the
‘
:“»Ë< =:
;
«’
»
lnthe early.ôos, frœz”ing
enthusiastic folleing.