(311e) Influence of the Energy Criteria for the Development of Industrialization Strategies in Melt Crystallization | AIChE

(311e) Influence of the Energy Criteria for the Development of Industrialization Strategies in Melt Crystallization

Influence
of the energy criteria for the development of industrialization strategies in
melt crystallization

GUILLOU
L., DENAGNON Y., RIGAUT E.

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

The
main purpose of melt crystallization technologies is the purification of organic
chemicals. These technologies are in general regarded as being alternatives to
other unit operations. Crystallizations from the melt are therefore quite often
restricted to limited amount of situations:

-         
Separation
of compounds with close boiling points or forming azeotropic systems

-         
Purification
of heat sensitive or explosive compounds

-         
Ultrapurifications
for 99.95+ grades

-         

This
framework definition implies that crystallization from the melt is eventually
at best a complementary technique that is used to overcome issues that would
not have been successfully addressed by other approaches. That being said melt
crystallization is, within exception of a very limited number of widespread
applications, a kind of fifth wheel of the cart in the process designer
toolbox.

The
melt static crystallization (MSC) is one of the embodiments of the melt
technologies. Being by nature a batch process, the MSC is quite often regarded
as being, despite its efficiency, applicable only to limited capacities. Quite
often a limit set at 10 ktpy is considered. It is associated to applications
dealing with ultrapurifications. This combination narrows a little bit more the
potential scope of application as it is understood and expressed in most of the
reference literature.

As
a resulting feature the MSC is regarded as being irrelevant for purifications
implying a large composition difference between the feedstock to be treated and
the targeted final product. It is indeed considered that these cases will
require using fractional crystallization approaches thus multiplying the number
of crystallization stages. Such multiplication of recrystallizations would
imply additional energetic expenses, lowering of the recovery yield…

Nothing
could be anything but wrong. A majority of applications including the ones
dealing with ultrapurification requirements or significant concentration of the
compound to be purified (purity raised over 50 wt.% or more in concentration
difference) are achieved with one or two MSC stages (cf. Fig 1).

Though
selected examples, different purification processes organization taken from
industrial plants will be presented and rated. The underlying process design
strategies will be examined under the scope of energy consumption optimization
between processes i) without, ii) including or iii) fully based on MSC. This
comparative examination is based on the same performances in terms of
capacities achieved and qualities of the feedstock and main products.

We
will show how only by optimization of the energy consumption target function
the technical solutions built around a MSC core process can match or even
overtake the most direct and obvious approaches often favored by process
designers.

Figure 1: topology of industrial MSC plants
(based on Fives Proabd® reference portfolio)

Keywords: Crystallization,
purification, energy optimization.