(445f) Process Intensification in Millistructured Extraction Columns

Process
intensification in millistructured extraction columns

The downstream process of biochemical and pharmaceutical products can
account up to 80% of the cost of production. [1,2] To reduce the cost it is necessary
to develop new process intensified equipment with higher time-volume-yield. Process
intensification is one important part to make the industry more economical and
ecological. Some mass or heat transport limited chemical reactions are only
technical possible or cost-efficient with process intensified equipment. The
small channels and structures in this equipment gives
the potential to control the fluids on the sub-millimeter scale. The known
characteristics of transport phenomena enable an easy and fast scale up for
bulk chemicals from lab to industrial scale.

We
investigated the process intensification in millistructured
extraction columns with an inner diameter of 15 mm, see figure 1. The column has 20 stirred cells and an active
extraction high of 440 mm. The total internal volume with head and bottom is
220 ml with total height of 760 mm. With stirred cells we achieved high energy
input, high specific surface between the two phases and thus good mass
transfer.  The backflow was decreased
with narrow plates between the plates. Thus, the dispersed phase coalesces at
the plates and plugs the stirred cells. With axial pulsation of the fluid the
coalescence area is destroyed and the dispersed phase is transported into the
next cell. This new technique allows for controlled flow of the
dispersed phase into the next stage. The retention times for counter current
processes can be adjusted for transport limited processes or reactive
extraction systems.

The hydrodynamics and mass transfer inside the column was characterized
with the European Federated Chemical Engineering (EFCE) testsystem
n-butylacetate(d)/acetone/water(c). The mass transfer from
continuous-to-disperse (c-d) and from dispers-to-continuous (d-c) and the
droplet size distribution with extraction efficiency was investigated.
Different to conventional columns, the energy input inside the stirred cells
are higher and the influence on the coalescenc and mass transport direction is
not so large. We achieved specific surfaces between the two fluids up to 3200
m^2/m^3 and measured the mass transfer up to 7 theoretical extraction stages
per active high (H = 440 mm). This correspondsto 16 theoretical stages per
meter, see figure 1. The experiments show that higher total throughput yields
higher extraction efficiencies, hence, high mass flow rates are preferred.

The enantioselective extraction of (R/S)-α-cyclohexyl-mandelic
acid will be investigated as an example; see the molecules in figure 2. The enantioselective
extraction is an organic/aqueous reactive extraction. The enantiomers create in
the aqueous phase a complex with hydroxy-propyl-ß-cyclodextrin. The (S)-complex is preferred to the
(R)-complex, so that the extraction is selective. The whole process is mass
transport limited and has a low selectivity. In conventional columns the
extraction is impossible, because the retention time of the dispersed phase and
the specific surface between the two fluids are too small. In process
intensified extraction columns with high specific surfaces and many extraction
stages the counter current extraction is possible. First results show a
considerable separation of the two enantiomers.

[1] Lowe C. R., Lowe
A. R., Gupta G., New developments in affinity chromatography with potential
application in the production of biopharmaceuticals, J. Biochem. Biophys.
Methods 49, 2001, 561?574

[2]
Strube J., Sommerfeld S., Challenges in
biotechnology production?generic processes and process optimization for
monoclonal antibodies, Chemical Engineering and Processing,
44, (10), 2005, 1123-1137

Figure 1: Millistructured extraction column; left side: sketch and
picture of the column with two sections; right side: experimental extraction
efficiency with different mass flow rates

Figure 2:
Molecular structure of (S) and (R)- α-cyclohexyl-madelic
acid