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Increase of the product recovery of Clostridium acetobutylicum
fermentation product by pervaporation
P. Izák1, V. Jarmarová1, K. Schwarz2, W. Ruth2,H. Bahl2, U. Kragl2
1Institute of Chemical Process Fundamentals, Rozvojová 135, 165 02 Prague 6, Czech Republic2Institute of Chemistry, University of Rostock, Albert Einstein Str.3a, 18059 Rostock, Germany
Supported ionic liquid membranes offer a range of possible advantages:
Molecular diffusion - higher in liquids than in solids, allowing high fluxes;
The selectivity of the separation can be influenced by variation of the liquid - especially ionic liquids offer the advantage of a wide variety of properties;
Ionic liquids as liquid membranes - allow three-phase systems due to their special mixing behavior;
Due to their good thermal stability, reactive processes - at high temperatures (up to around 250 ºC), which leads to faster kinetics in the case of endothermic reactions;
The use of nano-, ultra- and micro-filtration ceramic modules - diminish concentration polarization due to rough liquid-membrane surface;
Contrary to the extraction, only small amounts of liquids are necessary to form the liquidmembrane, thus allowing the use of more expensive materials.
The “only” problem is long time stability of the liquid in the pores.
ceramic module IL
pore size (nm) C14H24N+BF4
- C4mim+PF6- C8H26N2
+B(CN)4- C27H54F6N2O4S2
200 0.1 - - -
60 0.5 - - -
5 - 1.3 1.9 -0.9 1.2 2.4 3.5 0.15
Stability of the hydrophobic ILs inside the pores (in hours)
Experimental
• As a support matrix for the polymer-IL membrane the ceramic ultrafiltration module made from TiO2 with pore size 60 nm was used.
• The PDMS was prepared by mixing a solution of RTV 615A and RTV 615B (General Electric) in 10:1 ratio at 60°C for 0.5 hour.
• 15 wt% of tetrapropylammonium tetracyano-borate ionic liquid and 85 wt% polydimethylsiloxane (IL1).
• 50 wt% of 1-ethenyl-3-ethyl-imidazolium hexafluorophosphate ionic liquid was mixed with 50 wt% polydimethylsiloxane - (IL2).
• The ternary system - practical application in biotransformation processes, where the fermentation broth from Clostridium acetobutylicum is normally used
• The compound of interest is biofuel, namely BIObutanol
• It is the main product of butan-1-ol fermentation and it is also the primary inhibitory product affecting the bioconversion
Sorption apparatus for determination of sorption and diffusion coefficients
Dependence of butan-1-ol sorption
isotherm on relative pressure at 37°C
0
200
400
600
800
0 0.2 0.4 0.6 0.8 1
prel
So
rbe
d a
mo
un
t o
f b
uta
n-1
-ol
[mg
/g]
PDMS
PDMS+IL1
PDMS+IL2
Dependence of butan-1-ol diffusion
coefficient on relative pressure
1,E-11
1,E-10
2,E-10
3,E-10
4,E-10
5,E-10
0 0,2 0,4 0,6 0,8 1
prel
Db
uta
n-1
-ol [
m2s-1
]
PDMSPDMS+IL1PDMS+IL2
Pervaporation set-up
Pervaporation experiment – standard laboratory pervaporation set-up with effective membrane area of 5 cm2 ; downstream pressure p = 60 Pa
Reaction vessel
Cold trap
Retentate
Permeate
Permeate
Vacuumpump
Feed
Thermostat
Dependence of permeate permeation flux
on feed concentration at 37°C
0
5
10
15
20
0 0.5 1 1.5 2
Feed concentration of butan-1-ol [(%w/w)]
Per
mea
tio
n f
lux
of
bu
tan
-1-o
l.
[g
m-2
h-1
]
PDMSPDMS-IL1PDMS-IL2
Dependence of enrichment factor of
permeate on feed concentration at 37°C
0
4
8
12
0 0.5 1 1.5 2
Feed concentration of butan-1-ol [(%w/w)]
En
rich
men
t fa
cto
r o
f b
uta
n-1
-ol
PDMS
PDMS-IL1
PDMS-IL2
• The enrichment factor of butan-1-ol increased from 2.2 (PDMS) up to 10.9 (IL2-PDMS) (Izák P, Ruth W, Dyson P, Kragl U (2007) Selective Removal
of Acetone and Butan-1-ol from Water with Supported Ionic Liquid - Polydimethylsiloxane Membrane by Pervaporation, Chem. Eng. J., 139/2 (2008) 318-321)
• Fermentation was carried out at 37°C and pH 4.5.
• Firstly, a continuous fermentation with removal of ABE by pervaporation was measured without any butan-1-ol addition to test, if the SILM was selective and stable.
Experiment• C. Acetobutylicum ATCC 824 was grown under
anaerobic phosphate-limited conditions.
• In the chosen fermentation system, especially the phosphate concentrations as well as the dilution rates were responsible for the amount of produced solvents.
dilution rate (h-1)
phosphate (mM)
OD600
acetone
(g l-1) butan-1-ol
(g l-1) acetate (g l -1)
butyrate (g l -1)
ethanol (g l -1)
solvent productivity
(g l -1h-1) 0.05 0.75 7.12 3.82 7.12 0.97 0.64 0.67 0.66
0.075 0.75 7.1 2.82 5.44 0.98 0.65 0.50 0.78 0.075 0.5 8.52 5.00 10.38 1.62 0.44 0.94 1.38 0.09 0.75 6.25 3.18 7.07 0.93 0.69 0.77 1.14
Schema of continuous culture fermentation connected with pervaporation
1.Waste tank; 2. Tank with substrate; 3. Culture vessel; 4. Pervaporation cell; 5. Cold trap; 6. Vacuum pump
1 2
65
3
4
Permeate
Retentate
Feed
Vac
Dependence of permeate concentration on fermentation time at 37°C, at dilution rate 0.075 h-1, 0.5 mM phosphate concentration in supplying vessel and pH 4.5.
● Butan-1-ol (summary of the produced and added butan-1-ol); ∆ Acetone; □ Ethanol; Acetate; x Butyrate
0
4
8
12
16
20
0 100 200 300 400 500
Time of fermentation (hours)
Con
cent
ratio
n of
but
an-1
-ol
in c
ultu
re v
esse
l [g/
L]
0
1
2
3
4
5
6
Con
cent
ratio
n of
ace
tone
, et
hano
l, ac
etat
e, b
utyr
ate
in c
ultu
re v
esse
l [g/
L]
Butan-1-ol addition Pervaporation off
Dependence of optical density and butan-1-ol concentration on time of fermentation
─ Butan-1-ol concentration; Optical density
0
5
10
15
20
0 100 200 300 400 500
Time (hours)
OD
600
0
5
10
15
20
bu
tan
-1-o
l co
nce
ntr
atio
n [g
/L]
Butan-1-ol
OD600
Butan-1-ol addition Pervaporation off
• After successful tests, the concentration of butan-1-ol was several times increased to test the SILM under more stringent conditions and to study the effect of pervaporation on the cells.
• After 3 months of the experiment we did not observe any change of mass or selectivity of IL in the pores of the ultrafiltration membrane.
Dependence of butan-1-ol and acetone permeation flux on its culture vessel concentration.
0
5
10
15
20
0 3 6 9 12 15 18
Permeate concentration in the feed [g/L]
Per
mea
tio
n f
lux
of
per
mea
te
[g m
-2h
-1]
Acetone - PDMS+ILButanol - PDMS+IL
● Butan-1-ol; ∆ Acetone
Dependence of butan-1-ol and acetone enrichment factor on its culture vessel concentration.
0
4
8
12
16
20
0 3 6 9 12 15 18
Permeate concentration in the feed [g/L]
En
ric
hm
en
t fa
cto
r o
f p
erm
ea
te
Acetone - PDMS+ILButanol - PDMS+IL
● Butan-1-ol; ∆ Acetone
Conclusions
• To get more effective ABE removal from fermentor we used pervaporation with IL-PDMS nonporous membrane.
• Using this membrane we were able to remove ABE from the culture supernatant more effectively than it was described by others (Qureshi et al. (1992), Soni et al. (1987), Liu et al. (2004)).
Conclusions
• The supported ionic liquid membranes were weighted after all experiments and no weight changes were observed – stable SILM.
• Higher diffusion coefficient is most probably responsible for higher permeation flux and enrichment factors of butan-1-ol in IL-PDMS membrane.
• If we would run pervaporation with continuous and complete removal of butan-1-ol from the culture supernatant, it would lead to more stable fermentation process with higher production of BIObutanol.
Acknowledgement
This research was supported partially by grant No. 104/08/0600 from Czech Science Foundation and Marie Curie Reintegration Fellowships within the 6th European Community Framework Programme.