The Relationship between Structural Features of Lignocellulosic Materials and Ethanol Production Yield

Abstract

Lignocellulosic materials are a mixture of natural polymers which can be considered a great alternative source of chemical products and energy. Hence, pinewood, poplar wood, and rice straw, as representatives of different types of lignocelluloses, were subjected to several pretreatment types in order to increase ethanol production yield. All pretreatments increased enzymatic hydrolysis and ethanol yield, specifically pretreatment with phosphoric acid. This pretreatment increased ethanol yields by 304.6% and 273.61% for poplar wood and pinewood, respectively, compared to untreated substrates. In addition, a number of analyses, including a BET test, buffering capacity, crystallinity, accessible surface area, and composition measurement, were conducted on the pretreated substrates to investigate their structural modifications in detail. Accessible surface area, as one of the most important parameters for performance of enzymes and microorganisms in the fermentation process, was examined by the water retention value test. The results of this method (using centrifuge) showed that the maximum accessible surface area was related to the pretreated samples with phosphoric acid so that it increased WRV to 132.19%, 149.41%, and 68.44% for poplar wood, pinewood, and rice straw, respectively, as compared to untreated substrates. On the whole, pretreatments restructured and opened up the tangled structure of lignocelluloses, resulting in a considerable increase in ethanol yields. Moreover, in this study, for the first time, a new correlation was presented for each substrate which indicates the relationship between ethanol yield and structural features of the lignocellulosic substrate.

Municipal green waste as substrate for the microbial production of platform chemicals

“…In the literature, the composition of the resulting hydrolysate used for cultivations is rarely given; mostly cellulose conversion rates are indicated. Bay et al obtained glucose yields between 44.6 and 49.3% from poplar and pine wood as well as rice straw after phosphoric acid treatment and enzymatic hydrolysis (Bay et al 2022 ). Cui et al report glucose yields of up to 46.3% from paper mulberry ( Broussonetia papyrifera ) after pretreatment with deep eutectic solvents at elevated temperatures followed by saccharification (Cui et al 2022 ).…”

Bioethanol Production from Woody Biomass: Recent Advances on the Effect of Pretreatments on the Bioconversion Process and Energy Yield Aspects

“…All of this indicates that deacetylated biomass positively influences the overall process. However, Bay et al [53] reported that the removal of those acetyl groups with an alkaline PT will limit enzyme accessibility and partially depolymerize glucose, which then highlights the importance of further understanding the influence of xylose acetylation on the efficiency of the bioconversion process. Finally, when it comes to the PT's duration, coupling either high temperature and short treatment time (e.g., 270 • C, 1 min) or low temperature and long duration time (e.g., 190 • C-10 min) has been highlighted as a way to effectively solubilize hemicelluloses [26,107].…”

“…Over the years, various chemical PTs have been tested on woody lignocellulosic biomasses. For instance, five different chemical solvents were used for the PT of poplar wood (hardwood), pine wood (softwood), and rice straw (herbaceous) [53]. In this study, the samples were subjected to distilled water (180 • C, 30 min), dilute sulfuric acid (H 2 SO 4 , 0.5% w/w H 2 SO 4 /H 2 O), concentrated phosphoric acid (H 3 PO 4 , 85% w/w H 3 PO 4 /H 2 O), sodium hydroxide (NaOH, 2 M), and sodium carbonate (Na 2 CO 3 , 0.5 M).…”

“…Thermal and thermochemical PTs have been used for the production of bioethanol from hemp hurds [145], aspen wood [67], pine wood [67,146,147], beech chips [146], teak wood residues [148], sal sawdust [149], and acacia wood [150,151]. The work of Dessie et al [53] described three PTs: autohydrolysis, thermal hydrolysis (121 • C), and a thermochemical PT that consisted of an oxalic acid-assisted thermal hydrolysis at 121 • C. Thermochemical PTs of pine and aspen wood [67] have further confirmed pine's resistance to PT [117] due to its high lignin content, just as these studies have determined that temperatures above 200 • C are essential for the efficient PT of aspen wood. In addition, Wang et al [64] reported that untreated aspen wood had an S/G ratio of 1.68, as opposed to untreated birch wood, in which the S/G ratio was about 3.25, which could indicate why aspen wood requires a more severe PT.…”

“…Chemically pretreated pine and poplar wood [53], sawdust mixture [126], hemp [126], spruce [133], olive wastes [131], and paper mulberry wood [115] were subjected to an enzymatic hydrolysis step separate from the fermentation phase, while chemically pretreated poplar wood, pine wood [50,68], and furniture boards [114] were subjected to SSF. In the study led by Bay et al [53], the structural analyses confirmed that amorphous parts are broken down by enzymes before the crystalline parts [180][181][182]. This is due to the fact that glycosidic bonds exist within the crystalline fraction and are less reactive to hydrolysis [183].…”