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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.