The application of highly integrated centrifugal contactor ... - Biocoup

The application of highly integrated centrifugal contactor-separator devices
for reactive extractions
Boelo Schuur 1 , Carolus B. Rasrendra 1 , Gerard N. Kraai 1 , Jos G. M. Winkelman 1 , Johannes. G.
de Vries 2 and Hero J. Heeres 1
1 Department of Chemical Engineering, University of Groningen, The Netherlands
2 Stratingh Institute for Chemistry, University of Groningen, The Netherlands
ABSTRACT
Process intensification (PI) is a powerful concept to reduce energy and material use in chemical
processes. We here report the application of highly intensified Centrifugal Contactor Separator (CCS)
equipment for reactive extractions and related biphasic reactive liquid-liquid systems. In these devices
reaction and separation are efficiently combined, making them good examples of process
intensification. Highlighted applications in this contribution are enantioselective chiral reactive
extractions and acetic acid recovery from an aqueous biomass stream derived from fast pyrolysis oil.
Extraction efficiencies for both systems were determined experimentally. The efficiencies were close to
the equilibrium values as determined in batch for the enantioselective liquid-liquid extraction (ELLE)
system though considerably lower for the acetic acid recovery case. Further yield improvements are
possible by using multistage processing using a cascade of CCS devices, as was successfully
demonstrated for the ELLE system. The use of the CCS devices for catalytic liquid-liquid reactions
was also explored and results for biodiesel synthesis will be provided.
INTRODUCTION
Process intensification (PI) is currently one of the most significant trends in process engineering and
aims at replacing large, energy consuming processes [1] by small, highly integrated processes to
reduce the size and energy consumption of process plants. Some well known examples of PI are
reactive distillation, reactive extraction and the application of micro reactors [1,2]. In the past years,
we have explored the use of highly intensified Centrifugal Contactor Separation (CCS) equipment [3]
for reactive extractions and other reactive biphasic liquid-liquid systems. The CCS devices (Erreur !
Source du renvoi introuvable.) basically consist of a rotating centrifuge in a static housing. The
immiscible liquids are fed to the CCS and dispersed in the annular zone between the static housing and
the rotating centrifuge. The dispersion is subsequently transferred to the hollow centrifuge through a
hole in the bottom. Inhere, the phases are separated by centrifugal forces of up to 900 g, making it
possible to separate fluids with densities differing only 10 kg·m -3 . The liquid phases are collected
individually by a sophisticated weir system.
Figure 1: Schematic cross-sectional view of a CCS device

The CCS was originally developed for waste water cleaning in the nuclear industry [4] and has been
used successfully for oil-water separation [5] (e.g. for cleaning oils spills), for extraction of
fermentation broths [6] and several other extraction processes [7, 8].
In this paper, we will provide two examples of the use of reactive extractions in the CCS devices. The
first involves ELLE of amino-acid derivatives with a chiral host in a single CCS device as well in a
cascade of a number of CCS devices is series. A second example deals with acetic acid recovery by
reactive extraction from an aqueous biomass feed obtained from a fast pyrolysis oil upgrading unit. In
addition, the application for catalytic liquid-liquid reactions was also explored and an example for
biodiesel synthesis will be provided.
METHODOLOGY
All continuous reactive extraction experiments were performed in a CCS from the CINC company
(model V02). A schematic cross section of the CSS is depicted in Erreur ! Source du renvoi
introuvable.. The CCS is equipped with a rotor (diameter of 5.04 cm) which has a maximum
rotational frequency of 100 Hz (6000 rpm). The maximum total liquid throughput of the CCS is 2
L/min. The CCS was operated in a once-through mode (without recycling of the liquid feeds) at
ambient pressure and temperature. Detailed process conditions (flow rates, feed concentrations and
rotational speeds) are given in the main text. A capillary electrophoresis (CE) system from Agilent
Technologies was used to determine the amount of acetic acid in the aqueous phase. A detailed
description of the CE method is described elsewhere [9]. Analytical details for the ELLE system are
given in reference 10.
RESULTS AND DISCUSSION
Enantioselective liquid-liquid extraction (ELLE) using CCS devices
ELLE is a promising and emerging technology to separate the two enantiomers of a racemate using a
chiral extractant [11]. Although the technique is already known since the late 1960’s, it has to the best
of our knowledge not yet been applied on larger, commercial scale. Possible reasons are the high
liquid hold-up in conventional continuous extraction equipment leading to large inventories of the
expensive chiral hosts and the relatively low extraction efficiencies requiring multi-stage processing.
In this respect, CCS devices may bridge the gap between typical ELLE on lab scale in batch and
conventional continuous processing. The devices are compact, flexible and combine a low liquid holdup
with high throughput rates. We have explored [12] the use of the CCS devices for ELLE using a
model system consisting of an amino-acid derivative, 3,5-dinitrobenzoyl-d,l-leucine (DNB-d,l-leu, see
Figure 2, left) and a chiral cinchona alkaloid host (O-(1-t-butylcarbamoyl)-11-octadecylsulfinyl-10,11-
dihydro-quinine (CA, see Figure 2 right) [13]. The DNB-d,l-leu is present in the aqueous phase and
extracted by the host dissolved in an organic solvent (typically 1,2-dichloroethane).
Figure 2: Chemical structures of DNB-d,l-leu (left) and extractant CA (right)
The proof of principle for the use of the CCS devices for ELLE was obtained by performing
experiments with equal flow rates of both phases (F aq = F org = 30 mL min -1 ) and a rotational frequency
of 50 Hz. Initially, the CINC was fed with pure 1,2-dichloroethane as organic solvent and a buffered
aqueous solution of racemic DNB-d,l-leu (1 mM). After several minutes steady-state was achieved
(Figure 3). Subsequently, the organic feed was switched from pure 1,2-dichloroethane to a CA
solution in 1,2-dichloroethane (0.5 mM).

Y l , Y d (-)
0.8
0.7
0.6
0.5
0.4
0.3
chemically aided
extraction
physical
extraction
0.2
-10 -5 0 5 10 15 20 25 30
t (min)
Figure 3: Extraction profiles. Faq = Forg = 30 mL min -1 , N = 50 Hz, pH = 5.12, c DNB-d,l-leu,aq,0 = 1 mM, C A,org,0 = 0.5 mM. □:
Y l , ○: Y d
As expected, the enantiomeric excess (ee) is negligible when applying 1,2-dichloroethane without host
(t < 0). At t > 0, the extraction yields of both enantiomers increase dramatically due to complexation
with CA in the organic phase. Steady-state operation is achieved in less than 10 minutes. The steadystate
yield of the l-enantiomer, DNB-l-leu is 0.78 and 0.53 for the d-enantiomer. Here, the yields are
defined as:
Y
i
Forg
ci,
org,
tot
[ i l,
d]
(eq 1)
F c
aq
i,
aq,
in
Furthermore, it is clear that the host has a preference for the l-enantiomer, leading to an organic phase
ee of 19%. The ee in the aqueous phase is 37%. This experiment clearly illustrates the suitability of the
CCS device for enantioselective liquid-liquid extraction. Further optimization studies were performed
by varying relevant process conditions like input concentrations, aqueous pH, flow rates and rotational
frequency of the rotor. The yield was shown to be essentially independent of the flow rates (up to 500
ml/min for both F aq and F org ), indicating that the chemical compositions in the outlet, even at these
high flow rates, are at equilibrium. At optimised conditions, the ee org was 34% and the l-enantiomer
yield, Y l was 0.61, leading to a performance factor (PF) of 0.21. Recycle of the expensive chiral host
by a backextraction step, of paramount importance for the process economy, was investigated in a
single CCS device and was shown to be sufficient for efficient host recovery.
To increase the extraction yields and performance factors, the chiral extraction was carried out in a
countercurrently operated cascade of CCS devices including a back extraction step (Figure 4) [14].
DNB-l-leu
99 + % ee
Single stage
back-extraction
BE
Strip water
full organic extract recycle
Wash water
1
2 F-1 F
F+1
N-1
Cascade with N stages for extraction
N
DNB-d-leu
99 + % ee
Racemic
aqueous feed
Figure 4: Schematic representation of a countercurrent setup of N CCS devices for separation of a racemate into its
enantiomers with full recycle of the extract stream

extraction efficiency, E (%)
Experiments in a cascade of six CCS devices for the extraction steps and one for the back extraction
were performed successfully. For a 6 h run, the average ee of the l-enantiomer was 98% [15].
Recovery of organic acids from aqueous pyrolysis oil streams
A very promising and versatile technology for lignocellulosic biomass valorization to biofuels and
biobased chemicals is fast pyrolysis. The process yields a liquid product, known as fast pyrolysis oil or
bio-oil, in high yields [16]. Pyrolysis oil is a complex mixture comprising of oxygenated organic
compounds belonging to various organic groups (carboxylic acids, alcohols, ketones, aldehydes and
sugars) and water [17]. Our interest concerns the recovery of high valued added value chemicals from
fast pyrolysis oil. This study reports our activities aimed to isolate organic acids from fast pyrolysis oil
with an emphasis on acetic acid. Acetic acid is the major organic acid in pyrolysis oil with
concentrations up to 10 wt%, depending on the feedstock and process conditions applied in the
pyrolysis process [18]. Acetic acid is an important industrial commodity chemical with a total
production of 6.94 million tons in 2009. One of the possible isolation routes for acetic acid involves
separation of the oil in an organic and a water fraction. This is possible by the addition of water to the
pyrolysis oil, leading to phase separation and the formation of an oil and aqueous phase. The oil phase
may be upgraded and used as a co-feedstock in a standard refinery [19] or as a liquid transportation
fuel [16]. The water phase is enriched in acetic acid and is a very suitable feed for a reactive liquidliquid
extraction process using a long chain aliphatic tertiary amine in a suitable diluent.
Exploratory batch experiments with a typical waterphase (3.3 wt% of acetic acid) showed highest
equilibrium extraction efficiencies (86%) for acetic acid when using a reactive extraction system
consisting of tri-n-octylamine (TOA) in 2-ethyl-hexanol (40 wt%) at room temperature.
The continuous reactive extraction of the aqueous phase in the CCS device was also investigated. The
aqueous and organic flow rates (TOA dissolved in 2-ethyl-hexanol, 40 wt%) were both set at 30
ml/min. Experiments were carried out at room temperature with a rotor frequency of 50 Hz. To avoid
emulsion formation in the CCS device [20], the low shear option was investigated. This involves the
use of an insert in the annular zone which prevents direct contact between the liquids in the annular
zone and the rotor. The experiment was run for 1.25 h in a once through mode and a total of 2.25 L of
organic phase was collected. The results are depicted in
Figure 5. The extraction efficiency, η E (eq 2), increased between 0-15 minutes and was about constant
throughout the remaining run time. This implies that steady state operation in the CCS device was
achieved after about 15 minutes.
100
90
80
70
0 15 30 45 60 75
100
90
80
70
60
50
40
30
20
10
60
50
40
30
20
10
0
0
0 15 30 45 60 75
t (min)

Figure 5: Extraction efficiencies for acetic acid as a function of time in the continuous CCS device (low shear option, line for
illustrative purposes only).
mass
aqueous outlet
acetic acid
1
100%
(eq 2)
E
aqueous inlet
mass
of acetic acid
The average extraction efficiency at steady state was 48%. This value is considerably lower than the
equilibrium value obtained in the batch setup under similar conditions. Thus, equilibrium is not
achieved in the CCS device at the operating conditions of these experiments. Apparently, the overall
kinetics of the process are much slower than that for ELLE with the DNB-d,l-leu and CA system,
where liquid throughputs up to 500 ml for each phase were possible without significant changes in the
composition of the output streams. Higher reactive extraction efficiencies for the acetic acid case are
likely possible by reduction of the flow rates (higher residence times) or preferably by performing the
experiments in a cascade of CCS devices operated in a countercurrent mode like for the ELLE
example and these are in progress.
Biodiesel synthesis in CCS devices
The CCS devices are also suitable for catalytic chemical reactions in liquid-liquid systems. As an
example, we here provide the results of our study on the base catalysed production of biodiesel
(FAME) from sunflower oil and methanol in a CCS device [21, 22]. Process parameters like catalyst
loading (sodium methoxide), temperature, rotational frequency and flow rates of the feed streams were
investigated and at optimized conditions, a reproducible FAME yield of 96% was achieved (feed rate
of 12.6 mL. min -1 sunflower oil and a six-fold molar excess of MeOH (3.15 mL.min -1 )). The CCS
device was equipped with a jacket to allow for reactions at elevated temperature (75 o C jacket
temperature). The productivity under those conditions (61 kg FAME.m -3 liquid.min -1 ) was slightly
higher than for a conventional batch process. The main advantage is the combined reaction-separation
in the CCS, eliminating the necessity of a subsequent liquid-liquid separation step. Recent
investigations have shown that further purification of the crude biodiesel with a methanol wash is also
possible in a CCS, allowing the synthesis of purified biodiesel from a plantoil and methanol in two
CCS devices in series, one for reaction/separation and one for biodiesel purification [23].
CONCLUSIONS
CCS devices are very suitable to intensify liquid-liquid reaction like reactive extractions as well as
catalytic liquid-liquid reactions. This was illustrated with three examples, two on reactive extractions
(ELLE to separate enantiomers and acetic acid recovery) and one for a catalytic liquid-liquid system
(biodiesel synthesis). The devices allow for continuous processing, are compact, flexible and combine
a low liquid hold-up with high throughput rates. Multistage extractions are possible by applying a
series arrangement of CCS devices, as was experimentally demonstrated for ELLE. The devices are
commercially available in a wide range of throughputs, which will facilitate further scale up and
ultimate commercialisation of the processes.
ACKNOWLEDGEMENTS
The research on ELLE was financially supported by the Dutch Foundation for Scientific Research
(NWO) through the Separation Technology program in cooperation with DSM and Organon. The
BIOCOUP project (EU 6th framework, contract number 518312) is acknowledged for financial
support for the research activities concerning the reactive extraction of acetic acid.
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