Evaluating the composition and processing potential of novel sources of Brazilian biomass for sustainable biorenewables production

Abstract

Background: The search for promising and renewable sources of carbohydrates for the production of biofuels and other biorenewables has been stimulated by an increase in global energy demand in the face of growing concern over greenhouse gas emissions and fuel security. In particular, interest has focused on non-food lignocellulosic biomass as a potential source of abundant and sustainable feedstock for biorefineries. Here we investigate the potential of three Brazilian grasses (Panicum maximum, Pennisetum purpureum and Brachiaria brizantha), as well as bark residues from the harvesting of two commercial Eucalyptus clones (E. grandis and E. grandis x urophylla) for biofuel production, and compare these to sugarcane bagasse. The effects of hot water, acid, alkaline and sulfite pretreatments (at increasing temperatures) on the chemical composition, morphology and saccharification yields of these different biomass types were evaluated.

Results: The average yield (per hectare), availability and general composition of all five biomasses were compared. Compositional analyses indicate a high level of hemicellulose and lignin removal in all grass varieties (including sugarcane bagasse) after acid and alkaline pretreatment with increasing temperatures, whilst the biomasses pretreated with hot water or sulfite showed little variation from the control. For all biomasses, higher cellulose enrichment resulted from treatment with sodium hydroxide at 130°C. At 180°C, a decrease in cellulose content was observed, which is associated with high amorphous cellulose removal and 5-hydroxymethyl-furaldehyde production. Morphological analysis showed the effects of different pretreatments on the biomass surface, revealing a high production of microfibrillated cellulose on grass surfaces, after treatment with 1% sodium hydroxide at 130°C for 30 minutes. This may explain the higher hydrolysis yields resulting from these pretreatments, since these cellulosic nanoparticles can be easily accessed and cleaved by cellulases.

Conclusion: Our results show the potential of three Brazilian grasses with high productivity yields as valuable sources of carbohydrates for ethanol production and other biomaterials. Sodium hydroxide at 130°C was found to be the most effective pretreatment for enhanced saccharification yields. It was also efficient in the production of microfibrillated cellulose on grass surfaces, thereby revealing their potential as a source of natural fillers used for bionanocomposites production.

Figure 1

ELISA of xylans (LM10 and LM11) and mannan (LM21) polysaccharides on hemicellulose fraction from Brazilian grasses and Eucalyptus barks. SC, sugarcane bagasse; BB, Brachiaria brizantha; EG, Eucalyptus grandis bark; HGU, bark of hybrid between Eucalyptus grandis x urophylla; PM, Panicum maximum; PP, Pennisetum purpureum. Values expressed as relative absorbance to the positive control (xylan - μg/mL).

Figure 2

Chemical composition of non-pretreated and pretreated biomasses. (a) Sugarcane bagasse; (b)Panicum maximum; (c)Pennisetum purpureum; (d)Brachiaria brizantha; (e)Eucalyptus grandis bark; (f) bark of E. grandis x urophylla. Pretreatment types and temperatures are indicated.

Figure 3

Crystalline and amorphous cellulose content of pretreated samples and biomasses without soluble (control). (a) Sugarcane bagasse; (b)Panicum maximum; (c)Pennisetum purpureum; (d)Brachiaria brizantha; (e)Eucalyptus grandis bark; (f) bark of E. grandis x urophylla. Pretreatment types and temperatures are indicated.

Figure 4

Monosaccharide composition on the hemicellulose fraction of pretreated samples and biomasses without soluble (control). (a) Sugarcane bagasse; (b)Panicum maximum; (c)Pennisetum purpureum; (d)Brachiaria brizantha; (e)Eucalyptus grandis bark; (f)E. grandis x urophylla bark. Pretreatment types and temperatures are indicated.

Figure 5

CPMASTOSS spectra of the solid fractions of sugarcane bagasse sample submitted to the different pretreatments.(a) hot water; (b) sodium bisulfite; (c) sulfuric acid and (d) sodium hydroxide pretreatments, respectively. Lines 3 and 7: C6 and C4 carbons from amorphous cellulose [38-42]; lines 4 and 8: C6 and C4 carbons [35-37]; lines 2, 11, 12, 13, 14: and 15: lignin carbons [37,43]; lines, 1, 3, 6, 7, 9 and 17: hemicelluloses carbons [36,44]; the unmarked line at 39 ppm is due to ash from biomass burned.

Figure 6

CPMASTOSS spectra of the solid fractions of E.grandis x urophylla barks samples submitted to the different pretreatments.(a) hot water; (b) sodium bisulfite; (c) sulfuric acid and (d) sodium hydroxide pretreatments, respectively.

Figure 7

Monosaccharide composition in the liquor fraction from different pretreatments. (a) Sugarcane bagasse; (b)Panicum maximum; (c)Pennisetum purpureum; (d)Brachiaria brizantha; (e)Eucalyptus grandis bark; (f)E. grandis x urophylla bark. Pretreatment types and temperatures are indicated.

Figure 8

2-furaldehyde and 5-hydroxymethyl-furfural content in the liquor fraction from acid pretreatment at increasing temperatures, ranging from 50°C to 180°C.

Figure 9

Scanning electron microscopy images of sugarcane bagasse before and after different pretreatments at 130°C. (a) Raw sugarcane bagasse (no pretreatment); (b) sugarcane bagasse pretreated with hot water; (c) sugarcane bagasse after sulfuric acid pretreatment and (d) sugarcane bagasse obtained after sodium bisulfite pretreatment.

Figure 10

Scanning electron microscopy images of sugarcane bagasse submitted to sodium hydroxide pretreatment. (a) General view of sugarcane surface after alkali pretreatment and (b) higher magnification of cellulose whiskers on biomass surface.

Figure 11

Scanning electron microscopy images of different biomasses pretreated with sodium hydroxide at 130°C, revealing the production on cellulose whiskers. (a) sugarcane bagasse; (b)Panicum maximum; (c)Pennisetum purpureum; (d)Brachiaria brizantha; (e)Eucalyptus grandis bark; and (f)E. grandis x urophylla bark.

Figure 12

Automated enzymatic saccharification of raw biomasses and pretreated samples. (a) Sugarcane bagasse; (b)Panicum maximum; (c)Pennisetum purpureum; (d)Brachiaria brizantha; (e)Eucalyptus grandis bark; (f)E. grandis x urophylla bark. Pretreatment types and temperatures are shown.