Chemical Engineering November 2017 - 37

away from a solid product. Other
times, this can be accomplished by
changing the solid-liquid separation
technique. A new type of centrifuge
or filter may be beneficial. Adjusting
the washing procedure might give
rise to incremental improvements as
well. In still other cases, the crystals
are small, and growing larger crystals
can help improve solid-liquid
separation. Yet another factor influencing
purity is the rate of crystallization.
In general, slower crystallization
yields a better quality product. When
all else fails to produce the target
purity, recrystallization of a first stage
product could be a solution.
When a higher yield is needed, the
approach might also include growing
larger crystals or selecting another
solid-liquid separation device
to decrease the loss of solids. Incorporating
recycle streams might also
be a way to increase overall yields,
since the product contained in the
saturated mother liquor has another
opportunity to undergo crystallization.
For certain systems, concentrating
the crystallizer feed or cooling
to a lower temperature might be an
option to improve yields, but when
slurry density (solids in suspension)
becomes too high, solids handling
issues can be a challenge. It may be
necessary to add an additional crystallizer
stage to manage the higher
mass of solids.
For boosting production capacity,
more effective heat transfer is usually
the answer. This allows the crystallizer
to accommodate a higher
feedrate, which in turn, decreases
the residence time. As a result, particle
size may decrease, and purity
follows suit. Thus, increasing capacity
must be approached with regard
to the proper balance of capacity
versus yield and purity. However,
engineers can attempt to compensate
by improving washing or solidliquid
separation, or both.
Closing thoughts
It is more efficient to make the effort
to understand an issue and solve
problems early in process development
than after a poor design is in
place. Nonetheless, in many situations,
issues must be solved at a
later stage. In either case, following
the work process outlined in this article
is an effective way to approach
the matter.
When presented with any crystallization
problem, it is important to
begin with a strong understanding of
the system's solubility data. Careful
assessment of solubility curves and
yield charts, as covered in this article,
can provide valuable insight into the
root cause of an issue as well as potential
solutions before proceeding
to experimental testing. Laboratory
tests provide the basis to work out
the fundamental design and operating
conditions of the system. There
is no substitute for gaining hands-on
experience in working with a specific
material and directly observing the
crystallization process. This often reveals
characteristics that can impact
processing, but are subtle and might
not be appreciated otherwise.
Once the basic process design
has been established and operation
is reasonably well-understood,
a pilot plant is recommended to define
recycle schemes and to gather
scaleup data before finally implementing
at commercial scale. n
Edited by Scott Jenkins
Authors
Brooke Albin is a project manager
at MATRIC (Mid-Atlantic
Technology, Research and Innovative
Center; 1740 Union Carbide
Drive, South Charleston, WV
25303; Email:
matricinnovates.com;
www.matricinnovates.com).
this role, she is responsible for
the coordination and execution of
research and development (R&D) activities for numerous
clients. She has 10 years of experience in development
of new processes to produce chemicals from
biofeedstocks, and has specialized skills in the area of
solids handling and crystallization. She received her
B.A. in chemistry and B.S. in biology from AldersonBroaddus
College, and earned her M.S. in chemical
engineering at West Virginia University.
Charles Moyers is a senior engineering
scientist at MATRIC (MidAtlantic
Technology, Research
and Innovative Center; same addresss
as above; Email: charles.
moyers@matricinnovates.com;
Website:
www.matricinnovates.
com). He is a fellow of AIChE and
has co-taught several AIChE education
courses, including Industrial
Crystallization, Liquid-Solid Separation, and Drying.
He holds a B.S. from Virginia Tech, an M.S. from
West Virginia University and a Ph.D. from the University
of Delaware, all in chemical engineering.
For details visit adlinks.chemengonline.com/66434-12
CHEMICAL ENGINEERING WWW.CHEMENGONLINE.COM
NOVEMBER 2017
37
brooke.albin@
Website:
In
http://www.matricinnovates.com http://www.matricinnovates.com http://www.matricinnovates http://adlinks.chemengonline.com/66434-12 http://WWW.CHEMENGONLINE.COM
Chemical Engineering November 2017

Table of Contents for the Digital Edition of Chemical Engineering November 2017
