Investigation into the physical–chemical properties of chemically pretreated sugarcane bagasse (original) (raw)
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Thermal and Morphological Evaluation of Chemically Pretreated Sugarcane Bagasse
—Enzymatic hydrolysis is one of the major steps involved in the conversion from sugarcane bagasse to yield ethanol. This process offers potential for yields and selectivity higher, lower energy costs and milder operating conditions than chemical processes. However, the presence of some factors such as lignin content, crystallinity degree of the cellulose, and particle sizes, limits the digestibility of the cellulose present in the lignocellulosic biomasses. Pretreatment aims to improve the access of the enzyme to the substrate. In this study sugarcane bagasse was submitted chemical pretreatment that consisted of two consecutive steps, the first with dilute sulfuric acid (1 % (v/v) H 2 SO 4), and the second with alkaline solutions with different concentrations of NaOH (1, 2, 3 and 4 % (w/v)). Thermal Analysis (TG/ DTG and DTA) was used to evaluate hemicellulose, cellulose and lignin contents in the samples. Scanning Electron Microscopy (SEM) was used to evaluate the morphological structures of the in natura and chemically treated samples. Results showed that pretreatments were effective in chemical degradation of lignocellulosic materials of the samples, and also was possible to observe the morphological changes occurring in the biomasses after pretreatments.
Investigation of Porosity, Wettability and Morphology of the Chemically Pretreated Sugarcane Bagasse
Enzymatic hydrolysis is one of the major steps involved in the conversion from sugarcane bagasse to ethanol production. This process shows a higher potential on yields and selectivity, a lower energy costs and a milder operating conditions in comparison to conventional chemical processes. However, the presence of some factors limit the digestibility of the cellulose present in the lignocellulosic biomasses, such as lignin content, degree of crystallinity of cellulose and particle sizes. Pretreatment aims to improve the enzyme access to the substrate. Differences in BET and BJH surface area, pores diameter and volume, structural and morphological changes were investigated by SEM images, X-Ray, FTIR and Wettability for sugarcane bagasse in natura and submitted to two pretreatments: diluted sulfuric acid (1% H 2 SO 4) and alkaline-solution concentrations (1, 2, 3 and 4% NaOH). Results showed that it was possible to observe morphological changes occurred after pretreatments. Acid and alkaline treatments had an increase for both BET and BJH surface areas about 9.2%, diameter and volume of pores also increased. Crystallinity index also increased about 3.6% in the amorphous cellulose and lignin regions degradation. Other experimental techniques, such as FTIR (functional groups, bands and vibrations) and wettability (hydrophobicity and hydrophilicity), were also confirmed the increase in these structural changes. In summary, the pretreatments employed were effective in chemical degradation of lignocellulosic materials for the bioenergy generation.
The structural changes, lignin content and enzymatic hydrolysis of dilute acid pretreated bagasse from 19 varieties of sugarcane were investigated. Chemical compositions varied significantly between the materials. Glucose yield after enzymatic hydrolysis also differed significantly among the samples. The differences in glucose yields were not eliminated by increasing the pretreatment severity. Glucose yield showed a positive correlation with total dye and orange dye adsorption, whereas with blue dye adsorption it showed a weak correlation. The crystallinity index increased with the increasing pretreatment severity as a result of the removal of the amorphous components of the biomass. The degree of polymerization decreased with the increase in pretreatment severity. However, the change in either crystallinity index or degree of polymerization did not correlate with glucose yield. The results suggest that the lignin modification/real-location is a key factor for improving cellulose accessibility of sugarcane bagasse.
Industrial Crops and Products, 2018
Economical sustainability of cellulosic ethanol technology still requires considerable improvements in efficacies of both pretreatment and enzymatic hydrolysis steps. In this work a number of physical techniques were applied to characterize sugarcane bagasse samples that underwent hydrothermal and/or organosolv pretreatments under variable conditions and to correlated the observed changes with the efficiency of enzymatic hydrolysis. Confocal and field emission scanning electron microscopy studies revealed morphological changes in lignin distribution in the plant cell wall. The hydrothermal pretreatment caused a disorder in the arrangement of the lignin, whereas organosolv pretreatment partially removed lignin from bagasse and fraction of it redeposited at the surfaces of cellulose fibers. The delignification process was also analyzed by both chemical composition analysis and nuclear magnetic resonance. Pretreatment conditions leading to a significant increase of the efficiency of enzymatic hydrolysis were identified. Our studies open avenues for further biophysical investigations of pretreated lignocellulosic biomass, which could lead to its improved enzymatic hydrolysis.
The structural and physicochemical characteristics are associated with resistance of plant cell walls to saccharification by enzymes. The effect of physicochemical properties on glucose yield of bagasse from different varieties of sugarcane at low and high enzyme dosages was investigated. The result showed that glucose yield at low enzyme dosage was positively linear correlated with the yield at high enzyme dosage, for both the untreated and pretreated materials. The pretreatment significantly increased the accessibility of substrates by enzyme due to the increase of internal and external surface area. Glucose yield also showed a linear correlation with dye adsorption. However, the increase in glucose yield as a result of pretreatment did not correlate with the increases in crystallinity index and decreases in degree of polymerization. The Principal Component Analysis of infrared data indicated that lignin was the main component that differentiated the varieties before and after pretreatment. These results suggested that the key differences in pretreatment responses among varieties could be mainly attributed to their differences in the internal and external surface area after pretreatment.
Biotechnology for Biofuels, 2011
Background: In recent years, biorefining of lignocellulosic biomass to produce multi-products such as ethanol and other biomaterials has become a dynamic research area. Pretreatment technologies that fractionate sugarcane bagasse are essential for the successful use of this feedstock in ethanol production. In this paper, we investigate modifications in the morphology and chemical composition of sugarcane bagasse submitted to a two-step treatment, using diluted acid followed by a delignification process with increasing sodium hydroxide concentrations. Detailed chemical and morphological characterization of the samples after each pretreatment condition, studied by high performance liquid chromatography, solid-state nuclear magnetic resonance, diffuse reflectance Fourier transformed infrared spectroscopy and scanning electron microscopy, is reported, together with sample crystallinity and enzymatic digestibility.
Waste and Biomass Valorization, 2019
The aim of this study was to clarify the role of the relative amounts of hemicelluloses and lignin on the enzymatic hydrolysis of pretreated sugarcane bagasse, by using the glucans/lignin ratio and the glucans/xylans ratio as a quick estimation of the enzymes accessibility to cellulose. The samples were selected to contain about 3-20% lignin, 52-90% glucans, and 6-26% xylans (by extraction of hemicelluloses and delignification). The enzyme loads used for saccharification were 10 FPU of cellulases and 20 IU of β-glucosidases per gram of samples. Conversions of glucans to glucose were highly influenced by the chemical composition, varying between 18.1% and 83.4%. The concentration of lignin and xylans in the pretreated bagasse affects the conversion to glucose. High conversions are achieved when the substrates are highly delignified. Less delignified samples can also lead to high conversion when the percentage of xylans are also decreased. Thus, the removal of both lignin and xylans contributes to an increase in the accessibility of cellulases to cellulose.
Glucose production from sugarcane bagasse was investigated. Sugarcane bagasse was pretreated by four different methods: combined acid and alkaline, combined hydrothermal and alkaline, alkaline, and peroxide pretreatment. The raw material and the solid fraction of the pretreated bagasse were characterized according to the composition, SEM, X-ray and FTIR analysis. Glucose production after enzymatic hydrolysis of the pretreated bagasse was also evaluated. All these results were used to develop relationships between these parameters to understand better and improve this process. The results showed that the alkaline pretreatment, using sodium hydroxide, was able to reduce the amount of lignin in the sugarcane bagasse, leading to a better performance in glucose production after the pretreatment process and enzymatic hydrolysis. A good xylose production was also observed.
Biomass Conversion and Biorefinery, 2016
In lignocellulosic (LC) ethanol processes, to facilitate enzymatic hydrolysis of cellulose, a physical chemical pretreatment is vital. In this study, we explored a single as well as a two-step physical-chemical pretreatment involving steam and mixed acid on unwashed sugarcane bagasse at pilot-scale level in a continuous horizontal reactor. To serve as a largescale model, pretreatments were carried out at high solid levels of 18-20 % w/w. For the pretreatment, partial replacement of corrosive sulfuric acid with a milder acid-like oxalic acid was explored to derive possible advantages and synergies accruing by using a mixture of mineral acid and organic acid. The results of this work showed that first-step pretreatment carried out by the mixing of sulfuric acid (1.5 % w/w) and oxalic acid (1.5 % w/w) at 150°C followed by a second-step steam explosion pretreatment at 180°C gave significant synergies and advantages over other variants of pretreatments investigated, such as lower inhibitor levels and lower reaction severity. On post-pretreated bagasse, this study conducted comparative enzymatic hydrolysis study using a simple lab enzyme and a robust commercial enzyme. It was found that the addition of Tween 80 to the lab enzyme improved its performance to match the performance of the commercial enzyme. Scanning electron microscopy (SEM) studies were further carried out to correlate the morphology of pretreated samples with efficiency of enzyme hydrolysis. Besides morphological study, Fourier transform infrared (FTIR) studies of pretreated samples showed higher syringyl/guaiacyl ratio for all pretreatments, indicating lower levels of pseudo-lignins, which is beneficial for improved enzyme hydrolysis.
Physical and Chemical Pretreatment of Sugarcane Bagasse for Enhanced Acid Hydrolysis
Cellulose Chemistry and Technology, 2020
The second-generation ethanol production process proceeds in several stages. One of them is the pretreatment of lignocellulosic materials, which consists in the disruption of vegetal fibers, promoting partial removal of lignin and hemicelluloses. Pretreatment methods are of great importance to the effectiveness of the hydrolysis stage due to the increase in accessibility of hydrolysis reagents to the interior of the fibers, improving the conversion of lignocellulosic materials. In this study, a pretreatment of sugarcane bagasse was performed, involving milling and ultrasound treatment in alkaline or acidic medium. After the pretreatments, the materials were submitted to acid hydrolysis reactions. To evaluate the efficiency of the pretreatments, the amount of total reducing sugars (% TRS) of the hydrolysis products were assessed. The best results were obtained for the alkaline pretreatment of sugarcane bagasse, with almost 20% of TRS.