Salt - Solvay Plastics

Focus on SolVin
Salt: SolVin’s
white gold
As a great lover of salt, the main raw material for PVC, SolVin consumes
over a million tonnes a year. It is not just any salt, however: this is highly
purified salt appropriate for use in electrolysis
Borth: one of the world’s largest salt mines.
Salt from the Borth mine (on
the banks of the Rhine, in
North Rhine-Westphalia)
dates back 200 million years! There
was then an arm of the sea at this
location and, little by little, it dried
up. Since 1926, Solvay has been
exploiting an area (quite a big one,
though, at 88 square kilometers) of
these enormous deposits, which are
200 meters thick 1 .
Some 700 meters underground, the
miners excavate galleries 20 meters
high, 20 meters wide and 600 meters
long in the purest seam of the
deposits. They are assisted by tunnelboring
machines guided by laser
beams, and by explosives to break up
the large salt blocks so that they can
be loaded into trucks for transport to
a grinding machine and then hauled Lillo
up to the surface. Of the 2 million At Lillo, a crane operator “digs up” an
tonnes mined each year, 300,000 to average of 1,000 tonnes a day of salt
400,000 tonnes are sent by barge to from the small mountain supplied by the
the SolVin plant at Lillo (Antwerp). Borth mine to feed the brine circuit.
The salt from the Borth mine supplies SolVin’s electrolysis unit at Lillo.
1
The Borth mine is now owned by Esco, a Solvay-K+S joint venture which is Europe’s largest salt producer.
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Exploiting the salt deposits by drilling
400
Height in meters
ground
old drilling
sites
injection of
fresh water
Direction in which the deposits are exploited
brine pumped out
300
200
salt
100
insoluble deposits
brine
On the way to undergo electrolysis! Tavaux, Solvay’s
largest site, alone consumes 600,000 tonnes of salt a
year.
“We add salt to the brine and send it to a saturator,
which it leaves containing 250 grams
of salt per kilo,” explains Peter Van
Laarhoven, who is in charge of the quality
of electrolysis end-products at Lillo.
“The brine is then refined by adding reagents
that trap the impurities (sulfates,calcium,iron,
etc.) as particles that fall to the bottom of the
tank, and we remove them. After that, the
brine goes through filters to remove the last
impurities; it is warmed by heat exchangers,
and finally reaches the electrolysis unit.”
Some of the salt contained in the brine
is consumed to produce chlorine and
caustic soda. The brine that leaves the
electrolysis unit, now with a salt content
of only 180 grams per kilo, is treated to
remove the surplus dissolved chlorine,
and then goes back to the beginning,
with salt being added for another round.
Ludwigshafen
Rock salt has been extracted by the
Südwestdeutsche Salzwerke company
from the mine at Heilbronn for over
180 years.The salt comes from a depth
of about 200 meters, in deposits over
200 millions years old. It is processed
similarly to what happens at Borth, and
has been used for over 130 years at the
Ludwigshafen site. The high-quality
rock salt is carried there in barges that
can hold 1,800 tonnes of blocks. After
a voyage of almost 10 hours along the
Neckar and the Rhine, the salt is
unloaded at an open-air storage area. It
is dissolved and purified, the brine then
being conveyed by pipeline to the
electrolysis unit.
Martorell
Salt can also come from potash mines.
This is the case with salt from Suria
(northern Spain), which supplies the
electrolysis unit at Martorell. “Once the
company Iberpotash, which operates the
mine, has extracted the salt from the potash,
it is purified on site by Solvay Química and
then sent by train to Martorell,” explains
Manuel Ampudia, who is in charge of
electrolysis at Martorell. “We recently
invested 6 million euros in modernizing the
installations at Suria, in order to obtain still
purer salt. This should mean that the
Martorell electrolysis unit produces less
residue, and that the plant’s environmental
performance is improved.”
When it leaves the Suria mine, the salt is separated from the potash and mixed with brine to obtain a slurry,
which is then washed.The salt crystals are subsequently ground up to facilitate removal of the impurities concealed
inside.After washing for a second time, the slurry undergoes a number of further cleaning operations and then
reaches a band filter, where it is finally separated from the brine, and the latter is recycled.
Tavaux
It is not always possible – or may not
be cost-effective – to excavate mines.
When this is the case, salt can still be
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Focus on SolVin
extracted by drilling. The salt at
Poligny (Franche-Comté, France) is,
like the Borth deposits, 200 millions
years old, and is at a depth of 150-200
meters, accessible by drilling. Fresh
water is injected to dissolve the salt,
and also to separate it from the clays
with which it is mixed. The saturated
brine is then pumped up and sent by
pipeline to the Tavaux site.
Once the impurities have been
removed, the brine can be crystallized
(salt crystals being precipitated). An
This pipeline carries brine from Poligny almost
40 km to Tavaux, simply by gravity.
aerial conveyor transports the salt produced
to the electrolysis unit, where it
is redissolved, in demineralized water.
Jemeppe-sur-Sambre and
Zandvliet
The drilling site at Epe (west Rhine-
Westphalia, Germany) supplies both
the Zandvliet and Jemeppe-sur-
Sambre sites 2 , the latter involving a
brine pipeline of no less than 240 km!
As at Tavaux, the brine is finally purified
in a “saltworks”. “It is heated by
means of steam in heat exchangers, and
brought to boiling point in a first evaporator,”
explains Philippe Migeot, who is
in charge of electrolysis at Jemeppe.
“As it passes through a number of evaporators,
the brine becomes a thick ‘soup’, which
is allowed to settle and then dried.The ‘wet
salt’ that leaves contains no more than 3%
of water, and is 99.9 % pure.” The
Jemeppe saltworks has sufficient capacity
to meet not only the site’s own
needs but also those of the Zandvliet
electrolysis unit (to which the salt is
dispatched by barge, via the port of
Antwerp).
❑
Grains of salt
Brine from drilled salt
• Salt – or sodium chloride (NaCl) –
is not used just to season food! It
is used to produce numerous
chemicals, for de-icing of roads,
and for water softening, etc.
• PVC is made up from 57% salt
and 43% oil.To make 1 tonne of
chlorine (itself used to produce
VCM, and then PVC), you need
1.7 tonnes of salt.
• Salt reserves are tremendous.The
substance is found in abundant
quantities in seawater (about 30
grams per liter), and underground
in crystalline form, when it is
known as “rock salt”.
• Worldwide, we consume 26
million tonnes of salt a year:
6 million in Europe.
Settling tank at the Tavaux saltworks.
2 Solvay’s Rheinberg plant also receives salt from this drilling site, but its electrolysis unit does not supply chlorine to SolVin.
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Focus on SolVin
Fundamental
research:
SolVin’s contribution
PVC molecular chain.
It is not easy to improve a material’s intrinsic qualities, and yet this is
just what some players in the PVC industry, by far not all, are trying to
do, convinced that investment in fundamental research is needed to
ensure the future for PVC
Contrary to certain received
ideas, fundamental research
into PVC is alive and well.
“In the first decades of the PVC production,
it was sufficient to exploit the original
strengths of PVC. A variety of applications
were developed and ensured a
growing market,” acknowledged
Vincent Bodart, an expert in radical
polymerization at Solvay’s Nederover-Heembeek
(NOH, Brussels)
research center. “While research into
PVC throughout an interim period was
essentially geared to perfecting industrial
processes, the other plastic materials moved
on. In particular, new catalysts (chemicals
that stimulate the reaction by which a
plastic is manufactured) were developed
that improved the properties of polyolefins.
Today we need to assure the further development
of PVC by a far greater effort”.
Faced with competition from other
materials, and with criticisms relating
to certain PVC additives, the industry
reacted by launching new programs
of fundamental research. The aim, of
course, was to enhance the qualities of
PVC, so as to retain the material’s
existing markets and develop some
new ones.
Unity is strength!
To increase the chances of achieving
success from their research, 20 or so of
the world’s producers of PVC (including
Solvay) or of additives decided late
in 1998 to form a consortium for the
joint financing of 12 programs. These
were to be managed by the Edison
Polymer Innovation Corporation
(EPIC), an association encouraging
contacts between universities and industrial
firms active in the polymer field,
with American research laboratories
carrying out the programs.
The action being taken is intended to
deal with structural weakness in the
PVC.The fact is that PVC suffers from
thermal instability because of small
defects in the molecular structure,
which is why stabilizers are needed. If
we were able to prevent these imperfec-
About 20 producers of PVC or of additives are jointly financing 12 research programs.The consortium has a budget of several millions dollars per year.
Here we see two scientists from the Neder-over-Heembeek research center.
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Focus on SolVin
tions in the structure, PVC could be
used at higher temperatures and would
thus be able to enter new markets. It
could, for example, be used for injection
molding of large components. Another
area where there is scope for improvement
is that the temperatures at which
rigid PVC can be used are limited.This
precludes certain applications such as
pipes for hot water supply. Also, the
volatile nature of the plasticisers in flexible
PVC tends to result in the objects
losing flexibility as they age. One solution
could be the development of new
copolymer resins (incorporating other
materials into the PVC).
There are currently two approaches that
particularly interest the researchers, and
some patent applications have already
been made:
- modifying the radical mechanism: in
other words acting on the molecular
structure of PVC to reduce its imperfections;
- changing the polymerization mechanism
by discovering new catalysts.
Once the basic research is finished, the
consortium members are responsible for
validating the laboratory results and seeing
whether it is possible to convert
them into industrial processes. That is
what the scientists at Solvay’s NOH
research center have been doing since
December 2001. They are working on
controlled radical polymerization 1 and,
Mr Bodart says, “within two to three years
we will know whether it was worthwhile
going down that road.There are a lot of hazards,
but I think that today’s fundamental
research will bear fruit within 10 years.”
❑
Organization of research at SolVin
Some of SolVin’s researchers.The separation between development and basic research demonstrates SolVin’s desire
to give emphasis to the long term.When the two are dealt with together, the short-term issues tend to get more
attention, because its concerns are often perceived more urgent.
construction materials. The department
is also working to improve the mechanical
properties of PVC. “By mixing PVC
with ultrafine inorganic fillers (to obtain
“nanocomposites”), we would be able to get
a material that is more rigid while retaining
great shock-resistance,” explained Jean-
Marc Coisne, the department’s head.
“We have the first interesting results, but
developing them to the stage where they can
be applied industrially is still likely to take
many years.”
❑
SolVin together with Solvay is concerned
to carry out development as well
as basic research programs. The SolVin
scientists are collaborating closely with
Solvay’s, and are split into three departments
based at the Brussels research
center:
- Research & Development
- Research & Technology – suspension
PVC
- Research & Technology – emulsion
PVC.
In addition, pilot plants at the Jemeppesur-Sambre
and Ludwigshafen sites are
carrying out tests on a semi-industrial
scale.
“In our department, we are further improving
the existing applications, and trying to develop
new ones. For example,‘decking’ (boards
for the garden or for port jetties, etc.) and pallets
made of PVC profiles are being developed
in collaboration with the converters,”
says Joël Fumire, head of R&T
Suspension PVC. “They could be on the
market within three years.” Their advantages
compared to the timber generally
used in Europe are that they are waterproof
(not absorbing water, unlike
wood) and can be disinfected.
The R&D department is working on
improving the fire resistance of PVC,
with a view to responding to a probable
tightening up of the regulations on
Seekers able
to find
In Wave No. 2 (January 2001), we
told you about the new seeded
microsuspension process. SolVin
now makes considerable use of this
technology to produce emulsion
PVC.The new resins allow:
- either a lesser use of plasticiser, to
produce a plastisol (“paste”) with
the usual amount of flexibility,
- or the usual admixture of
plasticiser, to produce plastisols
that are more flexible, and thus
easier to handle.
1 This research corresponds to some of the projects promoted by Solvay’s Corporate New Business Development department.
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