:: Invited Lectures
Development of Crystallization Processes for Separating
Multicomponent Mixtures
Ka Ming Ng
Nano and Advanced Materials Institute Ltd., Department of Chemical Engineering, Hong Kong University
of Science and Technology, Hong Kong, China
In principle, crystallization, as distillation, is
capable of separating a multicomponent mixture. In practice,
while distillation is the workhorse for separating small
molecules, crystallization is often used only for purifying
high molecular weight compounds, leaving the burden of
separations to liquid-liquid extraction, chromatography and
other unit operations. There are a number of difficulties
for further development. Crystallization is perceived to be
a unit operation controlled by kinetics and, for a long
time, relatively little was done to elucidate the conditions
under which a pure product can be recovered from a
multicomponent mixture from a thermodynamics point of view.
Without such a foundation, rational process design is
difficult. This is complicated by the fact that solids might
exist in a variety of forms such as enantiomers, solvates,
compounds and polymorphs, the crystals can have different
habits and shapes, and the kinetic behaviors of electrolyte
system, reactive system, and biological system can be very
different in crystallization. Also, unlike distillation
where a product from a distillation column is a pure liquid,
the product from a crystallizer is actually a slurry
consisting of the pure crystals and a mother liquor
containing all the impurities in the original feed. There
is, however, renewed motivation to advance the fundamentals
of multicomponent crystallization in view of the shift of
emphasis in the chemical processing industry from commodity
chemicals to products such as pharmaceuticals, advanced
materials and natural compounds which are normally in solid
form.
This presentation describes efforts to address the
aforementioned challenges in the past decade.
High-dimensional phase diagrams provide a roadmap to recover
the desirable component(s). Since solid-liquid equilibrium
data are generally not available in thermodynamic databases,
high throughput experimental techniques along with software
tools have been developed for determining and representing
the phase behavior. Kinetic issues are considered alongside
process scaleup. Systematic methods and accompanying
experiments are used for designing a plant for impurity
management downstream of the crystallizer. Examples on
monomers, pharmaceuticals, electrolytes and natural products
will be discussed to illustrate this approach.
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 Prof Ka M. Ng is CEO of Nano and Advanced
Materials Institute Ltd, Chair Professor of Chemical
Engineering, and Director of the Consortium of Chemical
Products and Processes at the Hong Kong University of
Science and Technology. He obtained his B.S. degree from the
University of Minnesota in 1976 and his Ph.D. from the
University of Houston in 1980. From 1980-2000, he served as
Professor of Chemical Engineering at the University of
Massachusetts, Amherst. He joined the faculty in Hong Kong
in 2000 and served as Head of Department from 2002-2005. He
held visiting positions at DuPont, MIT, and the National
University of Singapore. His research interests center on
product conceptualization, process design and business
development involving water, biochemicals, natural herbs,
polymers, pharmaceuticals, nanomaterials and advanced
materials.
He serves as a consultant, technical advisor and independent
non-executive director for various companies and government
bodies around the world, and is at present the Corporate
Science and Technology Advisor of Mitsubishi Chemical Corp.
He was a team member in the development of a novel 50,000
tonne monomer plant that won the Japan Petroleum Institute
Award for Technological Progress in 2004. A computer program
on the design of crystallization processes has been
commercialized by his research collaborators in 2003. He is
a member of the editorial board of the Korean J. Chem. Eng.,
Chinese J. Chem. Eng., Comp. & Chem. Eng. and Chem. Eng.
Res. Des.
Professor Ng is the recipient of the General Electric
Outstanding Teaching Award in 1992. He is a fellow of the
American Institute of Chemical Engineers where he received
the Excellence in Process Development Research Award in
2002.
More:
http://www.ust.hk/ccpp/kmng.html |
