(507c) Theoretical Investigation of a Semicontinuous Distillation Process for the Separation of Bio-Based Impurities

The transition from fossil-based raw materials to bio-based raw
materials is necessary in order to produce chemical products in a sustainable
way. For example, n-butyl acrylate is currently produced through a
synthetic route using chemicals derived from petroleum, but new research into
its production from biological sources (such as wood) is showing promise as a
more sustainable alternative.  However, the composition of the impurities
contained in bio-derived n-butyl-acrylate (and its precursors)
significantly differs from traditional, fossil-derived n-butyl
acrylate. Furthermore both the composition and the amount of impurities in
bio-derived n-butyl acrylate change depending on the biomass feedstock
used and even from natural batch-to-batch variations in the biosynthetic
reactions. Therefore highly flexible processes which can achieve the required
final product purity even with varying initial impurity concentrations need to
be developed.

In a previous study, a reactive distillation column for the
esterification reaction of bio-n-butanol and
bio-acrylic acid to produce n-butyl acrylate was investigated, which is
a promising candidate to replace the conventional process, reducing the
production costs for n-butyl acrylate. Besides the development of the
reactive distillation process, the potential impurities resulting from the
biosynthetic production of the reactants were identified. However, the use of
bio-based raw materials resulted in insufficient final product purities.
Therefore, new and flexible downstream process concepts are investigated in this
work in order to remove the impurities.

A promising process concept for the purification of bio-based chemicals
is semicontinuous distillation. Semicontinuous distillation processes allow for
the separation of three or more streams simultaneously by tightly integrating
one or more middle vessels to a distillation column. In this study, the
application of a ternary semicontinuous distillation process for the removal of
bio-based impurities is studied for the purification of three different
material streams: the purification of high-purity bio-based n-butyl
acrylate (see Fig. 1) as well as for the purification of bio-n-butanol and bio-acrylic acid which are the reactants fed to
the reactive distillation column which produces n-butyl acrylate. The
simulation studies are performed using Aspen Dynamics? V7.3. Three performance
criteria which are the specific heat study, the specific product loss and the
cycle time of the semicontinuous process are used to characterize and compare
the feasibility of the different case-studies. Simulations with varying initial
and final impurity concentrations are performed to demonstrate a high
flexibility. It is shown that the semicontinuous technology is feasible for two
of the investigated case-studies, the purification of bio-n-butanol and the purification of the final product n-butyl
acrylate. Purities of up to 99.95 wt.-% are achieved
with varying initial purities of 99.00 wt.-% or higher. Different impurity
compositions can be handled by this technology and varying final purities are
achieved by only changing the cycle time of the process.

Hence, this
technology shows a high potential for the purification of bio-based chemicals,
offering a high flexibility in respect to initial and final impurity
concentrations. Furthermore, it should be noted that the same semicontinuous
set-up (meaning the same column height and diameter) used to remove bio-based
impurities from the final product n-butyl acrylate can also be used to
remove impurities from the reactants bio-n-butanol
and bio-acrylic acid.  This demonstrates the potential of semicontinuous
systems to be used as a multipurpose column which may reduce capital costs.

Acknowledgement: The
research leading to these results has received funding from the European Union
Seventh Framework Programme (FP7/2007-2013) under
grant agreement n° 241718, EuroBioRef. Financial
support of the Martin-Schmeißer-Stiftung
is gratefully acknowledged.