Estudo do pré-tratamento hidrotérmico e hidrólise enzimática da palha de cana-de-açúcar
Abstract
The complex cell wall structure of lignocellulosic biomass makes pretreatment one of the most
relevant 2G ethanol production process steps due to the difficulty of hydrolyzing lignocellulose
to fermentable sugars and the cost of the process as a whole. The optimization of enzymatic
hydrolysis conditions is crucial for reaching high yields that make the process feasible. In this
way, the aim of this work is to assess the stages of pretreatment and enzymatic hydrolysis of
the cellulosic fraction of straw sugarcane. All samples were chemically characterized before
and after the pretreatment step. Hydrothermally pretreatment was evaluated in four conditions:
170ºC / 5 min, 170ºC / 15 min, 220°C / 5 min, 220°C / 5 min, and 195ºC / 10 min. Higher
hemicellulose removal (85.58%) was found at 195ºC / 10 min. This operational condition was
set as a reference. Hydrolysis experiments were carried out in Erlenmeyer flasks at 50ºC, 250
rpm and pH 4.8, with a reaction volume of 50 mL. Two sets of experiments were performed.
In the first, the effect of substrate concentration was evaluated varying solid load (5; 10; 15;
20% msolid/vsolution) with enzyme load constant in 13 FPU.gbiomass. At 72h of enzymatic reaction,
cellulose conversions were: 72% (5% of solids), 84% (10% of solids), 72% (15% of solids),
and 59% (20% solids). In the second set, the enzyme (Cellic®CTec2) load effect (3; 7; 10; 13;
16; 40 FPU/gbiomass) with solid load settled at 15% (msolid/vsolution), was assessed. For assays with
15% of solid load, cellulose conversions were: 48% (3 FPU/gbiomass), 58% (7 FPU/gbiomass), 66%
(10 FPU/gbiomass), 72% (13 FPU/gbiomass), 71% (16 FPU/gbiomass), and 74% (40 FPU/gbiomass). A
trade-off between solid load and enzyme dosage was found (15% m/v and 13 FPU/gbiomass)
which results in 72,4% of cellulose to glucose conversion. After that it was studied the products
inhibition effect on hydrolysis was assessed. glucose and cellobiose (10 and 30g.L-1) caused a
higher inhibitory effect. Xylose did not show the significant inhibitory effect on β-glucosidase.
However, glucose and cellobiose had significant inhibitory effects on endoglucanase and
exoglucanase as well as on β-glucosidase. Hydrolysis experiments were conducted in the batch
reactor (3 L) with 10% solids to compare the performance with the hydrolysis conducted in
Erlenmeyer flasks. At 72h hydrolysis cellulose to glucose, conversion was obtained in 84.8%
(Erlenmeyer flask) and 80.2% (in the reactor); hydrolysis profiles obtained were similar in both
conditions evaluated. In face of this, it was opted by conduct experiments in bioreactor (50 mL)
using solid loads of 15 and 20% showed the best cellulose to glucose conversions when
compared to those carried out in shake flasks in the same conditions.