Development of integrated bioprocess for ethanol production from sugar beet
Dr. sc. Božidar Šantek, Full Professor Department of Biochemical Engineering, Faculty of Food
Technology and Biotechnology, University of Zagreb,Pierotijeva 6/IV, HR-10000, Zagreb, Croatia
Introduction
- biofuels are viable and realistic alternative in the energy market due to rising environmental concerns and oil prices - biodiesel from plant oils and from animal waste fats - bioethanol from grains, sugar cane and sugar beet - bioethanol production from lignocellulose raw materials at the beginning of the large- scale commercial production (e.g. new plants in the USA)- the production costs of biofuels are higher than production costs of gasoline from fossil oil (e.g. gasoline is 2 times cheaper than bioethanol)
Figure 1. General unit operations in bioethanol production from sugar beet.
LCA -bioethanol prodution from sugar beet
Table 1. Unit operations incorporated in different ethanol production plants used for determination of total and specific area for embedding processes.
Unit operations Process assignation
1 1a 2 3 4 5 6 7 8
Washing /slicing + + + + + + + + +
Diffusion + + + + + - - A A
Evaporation + + + - - - - - -
Sterilization - - - + + - - - -
Juice fermentation + + + + + - - - -
Beet pulp fermentation - - - - - + + A A
Centrifugal separation + + + + + - - - -
Distillation + + + + + + + A A
Ethanol dehydration + + + + + + + + +
Stillage evaporation + + + + - + - - -
Pulp pressing - - - - - + - + -
Pellets forming/drying + + + + - - - + -
Biogas production - - - - + - + - +
Heat recuperation - +* + - - - - + -
(+) incorporated in the process; (-) not incorporated in the process; (*) the calculation with the 50 % of heat recuperation; (A) simultaneous sugar extraction, fermentation and product recovery.
Table 2. Total energy consumption for different processes of bioethanol production from sugar beet
Process No.
Specific energy consumption(kWh/kg)
1 14.875
1a 7.538
2 3.148
3 7.121
4 4.467 (1)
5 3.281
6 0.619 (1)
7 3.068
8 0.411 (1)
(1) Energy obtained from biogas counted in as goodness
0
300
600
900
1200
1500
1 1a 2 3 4 5 6 7 8
Process No.
ato
t (m
2 a/k
g)
Figure 2. The ecological footprint (specific area; atot)
of examined processes for ethanol production.
Experimental set-up of stirred tank bioreactorSugar beet juice- addition of NH4H2PO4 as N and P suorce (1 g/L) - medium sterilization at 121 oC for 20 min prior to inoculation with yeast Saccharomyces cerevisiae - ethanol production in STB (5 L) at 28 oC with 10 % v/v yeast suspension - batch and fed batch cultivation techniques were used - pH value was maintained in the range of 4.5 - 5.0 by the addition of 0.1 M NaOH and 0.1 M H2SO4 - feeding in the fed batch process started when carbon source was almost completely depleted by the addition of a few portions of concentrated sugar beet juice (200 mL; approx. 800 g/L of sugar)
Figure 3. Alteration of substrate (S,●), ethanol (P1,▲) and glycerol (P2,∆) concentration during batch fermentation of raw sugar beet juicein stirred tank bioreactor
0
20
40
60
80
100
120
140
160
0 10 20 30 40 50 60 70 80 90 100
t /h
S, P
1/(g/
L)
0
2
4
6
8
10
12
P2/(
g/L
)
Figure 4. Alteration of substrate (S,■), ethanol (P1,▲), glycerol (P2, □) and biomass (X, ●) concentration, pH (○) and broth absorbance (A600nm,∆) during fed batch fermentation of raw sugar beet juice in stirred tank bioreactor. Arrows represent the addition of concentrated fresh medium during the fed batch process.
0
10
20
30
40
50
60
70
80
90
100
0 25 50 75 100 125 150 175 200 225 250
t /h
S, X
, P
1/(g/
L)
0
1
2
3
4
5
6
7
8
9
10
11
12
A60
0nm
, pH
, P2/(
g/L
)
Experimental set-up of HRTB
Sugar beet cossettes- ethanol production at room temperature after bioreactor sterilization at 121 oC for 30 min. - 5 kg of non-sterile raw sugar beet cassettes (23 % dry matter) - addition of NH4H2PO4 (1 g/kg raw sugar beet cossettes) - inoculum Saccharomyces cerevisiae - different quantities of inoculum (9.1-23.7 % V/m of raw sugar beet cossettes) in order to define the broth minimal liquid content - different operational conditions of HRTB [rotation, the working volume of bioreactor (range 20 – 70 %)]
0
20
40
60
80
100
120
140
0 10 20 30 40 50 60 70 80 90 100 110
t /h
P2,P
3/(g/
L);
DM
/%
0
5
10
15
20
25S
, P1/(
g/L
)
Figure 6. Alteration of substrate (S,●), ethanol (P1,▲), glycerol (P2,∆), acetate (P3,□) concentration and dry mass of sugar beet cossettes (DM,○) inside raw sugar beet cossettes during fermentation in HRTB with the inoculum of 16.7 % V/m by periodical rotation
Figure 7. Alteration of substrate (S,●), ethanol (P1,▲), glycerol (P2,∆), acetate (P3,□) concentration in the liquid part of the fermentation broth in the HRTB with inoculum of 16.7 % V/m by periodical rotation
0
20
40
60
80
100
120
0 10 20 30 40 50 60 70 80 90 100 110
t /h
S, P
1/(g/
L)
0
2
4
6
8
10
12
14
P2,P
3/(g/
L)
Table 3. Comparison among different systems for ethanol production from intermediates of sugar beet processing
Production system t / h Y P/S / g/g E /% Pr / g/(L·h)
RSBJ+STB+BP 98.5 0.424 78.8 0.608
RSBJ+STB+FBP 234 0.502 93.4 0.503
RSBC+HRTB (9.1 % V/m of INM) 93 0.386 71.7 0.497
RSBC+HRTB(13 % V/m of INM) 99 0.369 68.6 0.464
RSBC+HRTB(16.7 % V/m of INM) 102 0.428 79.5 0.476
RSBC+HRTB (20 % v/m of INM) 90 0.281 52.3 0.357
RSBC+HRTB (23.1 % V/m of INM) 68 0.308 57.3 0.467
RSBJ - raw sugar beet juice, RSBC - raw sugar beet cossettes, STB - stirred tank bioreactor, BP - batch process, FBP - fed batch process, INM - inoculum
Rotational set-up of HRTB during ethanol production from raw sugar beet cossettes
Table 4. Investigation of the manner of HRTB rotation
Table 5. Investigation of optimal rotation interval and speed of HRTB
Interval of HRTB rotation (min/h)
3 6 9 12 15
HRTB rotation speed (min-1)
5 + + + + +
10 + + + + +
15 + + + + +
Manner of HRTB rotation Periodical(3-4 rotation/ day)
Constant rotation
HRTB rotation speed (min-1)
5 + +
10 + +
15 + +
Figure 8. Alteration of substrate (S,●), ethanol (P1,▲), glycerol (P2,∆), acetate (P3,□) concentration and dry mass of sugar beet cossettes (DM,○) inside raw sugar
beet cossettes the fermentation broth in HRTB with the inoculum of 16.7 % V/mby 3 min/h rotation and the rotation speed of 15 min-1
020406080
100120140160180200
0 20 40 60
t(h)
S(gL
-1),
P1 (g
L-1)
0
5
10
15
20
25
P2 (g
L-1),
P3 (g
L-1),
DW
(%)
Figure 9. Alteration of substrate (S,●), ethanol (P1,▲), glycerol (P2,∆), acetate (P3,□) concentration in the liquid part of the fermentation broth in HRTB with the inoculum of 16.7 % V/m by 3 min/h rotation and the rotation speed of 15 min-1
020406080
100120140160180200
0 20 40 60
t(h)
S(gL
-1),
P1 (g
L-1)
0
5
10
15
20
25
P2 (g
L-1),
P3 (g
L-1),
DW
(%)
Conclusions
- sugar beet juice and cossettes can be successfully used for ethanol production. - the use of raw sugar beet cossettes in ethanol production eliminates extraction process of sugar beet cossettes by hot water, which considerably reduces energy demand for bioethanol production and final ethanol price. - further research of ethanol production from the raw sugar beet cossettes is required combined with improvement of sampling techniques due to the system heterogeneity
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