first, and the remaining sugar was mainly sucrose (average of 82.16 g/L). Even though ... fermentation processes were treated with sulfuric acid. The final pH of ...
Lactic acid purification process using molecular distillation on a fermented molasses broth. R.A. OLIVEIRA; A. KOMESU; C.E. VAZ ROSSELL; M.R. WOLF MACIEL; R. MACIEL FILHO. L A B O R ATO R Y O F O P T I M I Z AT I O N , D E S I G N A N D A D VA N C E D P R O C E S S C O N T R O L , S C H O O L O F C H E M I C A L E N G I N E E R I N G , U N I V E R S I T Y O F CAMPINAS - UNICAMP O L I V E I R A A LV E S . R E @ G M A I L . C O M
Overview An increasing interest for discovery new environment-friendly sources of chemicals have been observed due to the current concerns related to the cost and environmental impact of using traditional petrochemical processes. One important technological biomass-based platform is the biotechnological process for lactic acid (LA) production by fermentation. A wide variety of applications and the development of new uses and products, such as, biodegradable polymers, green solvents and the use as building block molecule, has increased the LA production as well as has stimulated the research for economically viable technologies. The development of an efficient method of separation and purification of the LA from fermentation broth is necessary once the separation and purification process may reach 50% of the production costs. Molecular distillation (MD) is an alternative process of separation with potentiality for recovery and concentration of thermally unstable molecules as LA. Bearing this in mind, in this work, fermentation process for LA production was carried out using sugarcane molasses and Lactobacillus plantarum. The purification of the fermentation product, a mixture of LA, hexose and water was conducted by using MD.
Methodology Fermentations were carried out in a bioreactor of 1,5 L. The bioreactor equipped with probes of pH and temperature. The fermentation broth was prepared with 200 g/L of TRS from molasses; 20 g/L of yeast
Table 1: Fermented broth composition after the treatment with H2SO4 Sucrose Treated broth
Glucose
(g/L)
76.01
(g/L)
Fructose
6.46
(g/L)
Lactic acid
3.90
(g/L)
96.70
extract; and 5 g/L of sodium acetate. The bioreactor was adjusted at 37 °C and agitation speed of 200 rpm. Table 2: Central composite experimental design matrix with experimental ranges
The pH was maintained at 6.0 ± 0.1 by automatic dosing of a sterile 4 mol/L Ca(OH)2 solution. The total
Runs X1
time of fermentation process was 48 h in batch mode. A central composite experimental design with three
Y= β0 + β1X1 + β1X12 + β2X2 + β2X22 + β3X3 + β3X32 + β12X1X2 +β13X1X3 + β23X2X3
Tevap (°C)
Tcond (°C)
FFR (RPM)
-1.00
-1.00
100.00
10.00
11.00
2
-1.00
-1.00
1.00
100.00
10.00
19.00
3
-1.00
1.00
-1.00
100.00
16.00
11.00
4
-1.00
1.00
1.00
100.00
16.00
19.00
5
1.00
-1.00
-1.00
140.00
10.00
11.00
6
1.00
-1.00
1.00
140.00
10.00
19.00
7
1.00
1.00
-1.00
140.00
16.00
11.00
8
1.00
1.00
1.00
140.00
16.00
19.00
9
-1.68
0.00
0.00
86.40
13.00
15.00
10
1.68
0.00
0.00
153.60
13.00
15.00
11
0.00
-1.68
0.00
120.00
7.95
15.00
12
0.00
1.68
0.00
120.00
18.00
15.00
13
0.00
0.00
-1.68
120.00
13.00
8.27
14
0.00
0.00
1.68
120.00
13.00
21.70
15
0.00
0.00
0.00
120.00
13.00
15.00
16
0.00
0.00
0.00
120.00
13.00
15.00
17
0.00
0.00
0.00
120.00
13.00
15.00
this analysis were on lactic acid concentration. Real variables values were described in coded form and
was modeled using polynomial equation given by Equation 1
X3
-1.00
temperature (Tevap), internal condenser temperature (Tcond), and feed flow rate (FFR). The results used in
and their interactions was Statistica 7.0 from Statsoft Inc. The relationship between factors and response
X2
Real variables
1
replicates in central point was used to study the influence of three factors in MD process: evaporator
their experimental ranges were shown in Table 2. The software used to calculate the effect of each variable
Coded variables
(1)
Results The microorganism presented a homofermentative process with high lactic acid yield (Y = 0.98 g/g) and productivity (P = 2.84 ± 0.46 g
L-1
h-1).
Monosaccharides had been consumed
Table 3: Lactic acid concentrations from distilled and residue streams from molecular distillation.
first, and the remaining sugar was mainly sucrose (average of 82.16 g/L). Even though the final concentration of lactic acid was high (average of 100.13 g/L). The broth from the
LA Residue (g/L) Distilled LA (g/L)
LA Distilled (g/L) Residue LA (g/L)
fermentation processes were treated with sulfuric acid. The final pH of the treated broth was 3.85, and the composition is shown on the Table 1. This material was used to proceed the
1
59.43
247.69
2
47.74
139.71
experimental design (Table 2) and evaluate the HSPE process. The results of the experimental design for the distillate and residue streams are presented in Table 3. The light stream was
3
0.00
154.25
4
87.72
143.06
5
103.66
175.40
6
85.91
180.26
7
109.13
166.93
8
108.33
148.28
9
32.97
148.25
10
111.44
164.36
11
64.14
156.03
to a ANOVA analysis, and the predictivity of each model was evaluated using the F-test. Unfortunately, the model constructed for lactic acid concentration it was not predictive. Even so,
12
0.00
242.41
13
56.15
164.83
in the residue stream it was possible to concentrate the lactic acid in 2.5x in experiment 12, in which the lowest mass percentage was also obtained.
14
92.89
145.80
15
91.36
166.87
16
89.38
143.33
17
93.69
172.28
not submitted to statistical analysis, since it did not present lactic acid. For the residue stream analysis, the effects of the three studied variables were also estimated with a confidence level of 95 %. In this case, lactic acid concentration is not affected by any of the studied variables. For the distilled stream, it was developed a statistical analysis for lactic acid concentration (LA), with a confidence level of 95 %. After, it was generated a mathematical model considering only the statically significant variables. The models were latter submitted
Conclusions • The chosen microorganism and substrate were effective in produce a high concentration of lactic acid with a high conversion rate. Also, the productivity was satisfactory.
• Even it was not possible to obtain a model for lactic concentration, it is clear that this response is influenced by internal condenser temperature, evaporator temperature, and feed flow rate in the distilled stream. • The methodology used is appropriate for this study case, allowing the analyses of factors that could improve the process of lactic acid concentration. • The comparison of the results obtained with that described in the literature shows that molecular distillation parameters of operation should change for each different composition of the inlet stream. • The process of molecular distillation should be suitable and present advantages for lactic acid separation and purification, but the hole process has to be first completely understood.
