(447q) Unconventional Strategies in Industrial Melt Crystallization

Unconventional
strategies in industrial melt crystallization

GUILLOU
L.

Fives
Proabd, 20C rue de Chemnitz – F-68100 Mulhouse

The
melt static crystallization (MSC) is usually described through an arrangement
of steps consisting in:

-         
Controlled
cooling and crystallization

-         
Draining
of mother liquor containing impurities

-         
Controlled
partial melting of the crystals to remove remaining wetting impurities a.k.a.
“sweating”

-         
Melting
of remaining purified crystals

This
arrangement of steps defines one purification stage which can be multiplied in
order to develop fractional crystallization processes that allow improvement of
recovery yield or purity.

It
is quite often considered that these features limit the scope of application of
the MSC to very specific cases such as the treatment of concentrated feedstock
and applicability to limited capacities only.

Through
this contribution different cases of unconventional strategies for
crystallization from the melt will be examined:

-         
Supercharging
and in situ recrystallization for lean concentrations

-         
Substitution
of the sweating step by a washing step

-         
Extractive
crystallization

We
will show how supercharging is used to treat feedstock containing less than 20%
of crystallizable compound and how it contributes to increase the recovery
yield per pass vs. suspension crystallization.

We
will present and discuss the advantages of washing vs. sweating in terms of
improvement of impurity removal for very high capacity plants (beyond 100 ktpy).

Finally
we will show how extractive crystallization can be advantageously used for
separating a three crystallizable compounds blend and allow achieving better
recovery than an alternate based distillation approach.

Through
selected industrial examples, the declination will be introduced. It will be
shown that they are not necessary meant to be considered as specific tools used
for solving specific issues. They can in fact be considered as generic
strategies For sure they are not as much widespread than the standard MSC step
arrangement which remains the most common. But they are neither to be
considered as being that rare: more than 20% of the industrial purification
plants using a Proabd® MSC process nowadays involve one or more of such strategies.

Keywords: Crystallization,
purification, energy optimization.