Elephant grass leaves have lower recalcitrance to acid pretreatment than stems, with higher potential for ethanol production

Abstract

Elephant grass is gaining attention among lignocellulosic materials due to its high growth potential, biomass yield, limited requirement for cultivation land and high rates of carbon dioxide absorption. Here was investigate the effect of pretreatment with different concentrations (5, 10 and 20%, mass acid/mass material) of diluted sulfuric acid on the whole elephant grass plant compared with its leaf and stem fractions. The stem was the most recalcitrant fraction, judging from the high recovery of water insoluble solids (WIS) and lower enzymatic hydrolysis yield, upon acid pretreatment. In enzymatic hydrolysis assays, the glucose yield increased with increasing concentrations of acid, reaching maximum values of 89.20 (leaf), 43.54 (stem) and 76.01% (whole plant). The crystallinity index (CrI) increased in both elephant grass fractions, which correlated with the solubilization of amorphous materials such as hemicellulose. Also, the stem fraction had a slightly higher heating value than the leaf fraction (3958.45 and 3939.49 cal/g, respectively). Scanning electron microscopy (SEM) analysis showed drastic morphological changes in the samples with increasing pretreatment severity, although the stem fraction suffered less structural damage than other materials. Taken together, the results suggest that the separation of elephant grass in different fractions decreases biomass heterogeneity and generates a fraction (leaf) with lower inherent recalcitrance and, thus, higher susceptibility to pretreatment and enzymatic hydrolysis, increasing the efficiency of fermentable sugar release. The results indicate that the leaf fraction of elephant grass has higher potential for use in second-generation ethanol production, while the stem fraction may be more useful for energy co-generation by combustion.

Sieving process selects sugarcane bagasse with lower recalcitrance to xylan solubilization

“…The diluted acid pretreated material was characterized in order to determine its chemical composition in terms of cellulose/glucan, xylan, arabinan and acetyl groups (Table 3). The mass recovery after the pretreatment may be indicative of the material recalcitrance since the lowest mass loss can be associated with the most resistant material 27,29 . The pretreated material solid recovery decreased along with the particle size.…”

“…A lower mass recovery was observed with the material retained in the base, reaching 49.33%. The solubilized components could be part of the xylan, cellulose and extractives 29 …”

“…Lignin, on the other hand, was not significantly removed. As a characteristic of the diluted acid pretreatment conditions used, hemicellulose was removed, 2,11,29 up to 28.01%.…”

Effect of Elephant Grass Genotypes to Bioenergy Production

“…), one of the most widespread tropical forage species in the world, used on livestock properties as a roughage [4]. Included among energy crops, it can be the most important renewable source for future energy production [5], due to its versatility such as fiber for paper industry [6]; biomass for the production of bioethanol [7]; direct combustion of biomass as a substitute for charcoal [8,9]; co-products generated in biorefineries [10,2]. In addition, it presents excellent energy balance elucidated by [11] in the use of in-kind burning of elephant grass, obtaining 21.3 units of renewable energy for each unit of fossil energy used in the production process.…”

Potential of a new seed propagated elephant grass cultivar for lignocellulosic bioethanol production via alkaline pretreatment

“…More recently,Santos et al (2018) studied elephant grass cultivated in the Experimental Station at Embrapa Agrobiology (Centro Nacional de Pesquisa em Agrobiologia -CNPAB, Embrapa Agrobiologia) and reported, not surprisingly, that leaves had lower recalcitrance than stems under pretreatment with sulfuric acid (5, 10 and 20% mass acid/biomass). Although the biomass was locally cultivated, it was probably propagated by stalks with no further information regarding genotype.5.6.3.2 Alkaline pretreatmentAlkaline pretreatment for lignocellulosic biomass feedstocks involves saponification of intermolecular bonds of esters of uronic acid associated with xylan chains.…”