Introduction and Review of literature
Importance of bioethanol in the transportation sector
In addition, the transport sector (such as aviation, shipping, roads and railways) is one of the largest contributors to greenhouse gas (GHG) emissions. In addition, the European Union has set a specific target to reduce greenhouse gas emissions by up to 6% by using 10% renewable energy in the transport sector by 2020 [9].
Ethanol
- Ethanol production processes
- Material source for bioethanol production
- Process for bioethanol production
- Factors affecting the lignocellulosic biomass conversion into bioethanol . 19
Acetic acids are also found to be present in the prehydrolysates, which are generally formed due to the hydrolysis of acetylated hemicellulose [71]. Furthermore, by-products in the form of metal ions can also be seen during dilute acid pretreatment of lignocellulosic biomass.
Introduction
Hemicellulose is the second most abundant polymeric carbohydrate in nature and an important component of lignocellulosic biomass. It is also known to inhibit the hydrolysis of polymeric carbohydrate components of lignocellulosic biomass.
Materials and Methods
- Chemicals
- Source of lignocellulosic biomass
- Sugars recovery standard (SRS)
- High performance liquid chromatography
Liquid fraction containing monomeric sugars (derived from cellulose and hemicellulose) was analyzed by high performance liquid chromatography (Eq. 2.3), while acid-soluble lignin (AIL) was determined by UV-Vis spectrometer (Eq. 2.4). According to the following equations (Eq. 2.7 and Eq. 2.8) percentage sugar loss during the hydrolysis can be calculated which is further substituted for the correction of corresponding sugar concentration values (loss of sugars) during the hydrolysis of biomass sample (Eq. 2.9). Therefore, according to the following equations (Eq. 2.10 and Eq. 2.11), sugar and lignin content of raw biomass can be calculated.
Results and discussion
- Compositional analysis of different sorghum biomass varieties
- Theoretical bioethanol potential of various genetically modified sorghum
- Factors affecting the bioethanol production
Apart from holocellulose, lignin was found in the smallest amount in the genetically modified sorghum biomass varieties, at 14.3–18.3%. Therefore, in the present study, holocellulose content of approximately 52.7% to 64.7% was observed in the genetically modified sorghum biomass varieties. Therefore, the theoretical bioethanol potential of different genetically modified sorghum biomass varieties is calculated using the following equations (Equation 2.14 and Equation 2.15) and listed in Table 2.2.
Summary
The results of the study revealed that due to the presence of furans in the pre-hydrolyzate, the estimation of reducing sugars was found to be 68%. During the pretreatment of sorghum biomass, xylose (an important hemicellulose component) was found to be the predominant sugar present in the prehydrolyzate liquid. This may be due to an increase in the concentration of fermentative inhibitors in the medium.
Optimization of pretreatment process for the production fermentable
Materials and methods
- Chemicals
- Compositional analysis of sorghum (bmr IS 11861) biomass
- Dilute acid pretreatment of biomass
- DNS assay
At the optimal condition for the release of reducing sugars, the solid and liquid fractions were separated through a 0.2 μm nylon membrane filter. Additionally, synthetic hydrolyzing medium containing a mixture of reducing sugars and furans (furfural and 5-HMF) was prepared and listed in Table 3.3. MRS, Mixture of reducing sugars; SH, Synthetic hydrolyzate; Xyl, Xylose; Glucose, Glucose; Arab, Arabinose; HMF, Hydroxymethyl furfural.
Results and Discussion
- Effect of pretreatment parameters on reducing sugars yield
- Mass Balance analysis
Furthermore, the decomposition of reducing sugars was also increased with an increase in treatment reaction time. As such, an absorption enhancement of almost 68% was observed during the quantification of reducing sugars in the presence of furans. Henceforth, it is suggested that the use of the DNS method results in an inaccurate estimation of the reducing sugars present in the prehydrolysates of lignocellulosic biomass.
Summary
This may be due to the presence of a low concentration of fermentative inhibitors in the pre-hydrolyzate which does not deter the microbial growth during the fermentation of conditioned hydrolyzate. Therefore, in this study, xylose is found to be a predominant sugar present in the pre-hydrolyzate. As shown in the Table 7.4, during the fermentation of pre-treatment derived hydrolyzate, approximately and the found to be 0.45 gp/gs ethanol yield was observed.
Dilute acid pretreatment of sorghum biomass to maximize the
Introduction
From the above literature, the development of pretreatment conditions for maximization of pentose sugar yield along with minimized level of fermentative inhibitors from sorghum biomass would be a challenging task. Therefore, the current chapter mainly focused on the development of an effective dilute acid pretreatment process that maximizes hemicellulose hydrolysis to achieve a high yield of pentose sugars with a minimal concentration of fermentative inhibitors. In addition, response surface methodology (RSM) was used to determine the effects of different pretreatment parameters on pentose sugar yield and furfural formation.
Materials and methods
- Biomass source
The equation was used to evaluate the effect of independent variables on the response, which was further analyzed to obtain the optimal pretreatment conditions [157]. Where Y is the response (pentose sugar and furfural yield), β0 is the constant coefficient βi is the ith linear coefficient, βii is the quadratic coefficient, and βij is the ijth interaction coefficient. The CCD consists of 2k factorial points, 2k axial points (± α) and six central points, where k is the number of independent variables.
Results and discussion
- Effect of pretreatment parameters on the reducing sugars yield
- Statistical impact of pretreatment parameters on pentose sugars release and
From Figure 4.1, it can be observed that hemicellulose hydrolysis increases with increasing reaction temperature (80 °C to 121 °C). Similar trend of increasing furfural concentration with increasing sulfuric acid concentration and reaction time at 121 °C was seen in the present study (Figure 4.2c). Further, furfural decomposes to form formic acid with an increase in the severity of the pretreatment [33] as shown in Figure 4.2d.
Summary
Sorghum biomass (IS 21549/bmr 6 A) is used in this study and its chemical composition is shown in Table 5.1. This may be because about 8.6% lignin was still present in the 1% NaOH-treated substrate (Table 7.2). However, the increase in cellulose hydrolysis between 3-5% NaOH treated sample was found to be less than 5% (Figure 7.2a).
Development of dilute sulfuric acid pretreatment method for the
Introduction
The main disadvantage of the pretreatment with dilute acid was the degradation of sugar, leading to the formation of fermentative inhibitors such as furans (Furfural, 5-hydroxymethylfurfural), which are further converted into organic acids (formic acid and levulinic acid). Therefore, conditioning of pre-hydrolysates (hydrolysates derived from the pre-treatment) is an essential step applied prior to the successful fermentation of pre-hydrolyzate [101]. Among them, overliming with calcium hydroxide is the most economical and widely used method for detoxification, which helps in the removal of furrans such as furfural and 5-hydroxymethylfurfural (HMF) from the pre-hydrolysates [83,162].
Materials and methods
- Dilute sulfuric acid pretreatment
- Detoxification of prehydrolysates
- Microorganism
- Analytical methods
The inlet port was connected to the 0.2 µm solvent filter (Chrome Tech, A-242, USA) and immersed in the reaction mixture. According to the following equation (Equ. 5.1), the concentration of sugars and fermentation inhibitors was calculated. The residual carbohydrates and lignin content present in the pretreated solid residue are analyzed according to the NREL procedure [31].
Results and discussion
- Monomeric sugars yield during the pretreatment of biomass
- Conditioning of pre-hydrolysates
- Fermentation
The comparative analysis of the results obtained in the present study with the literature is shown in Table 5.3. Apart from the sugar loss, a decrease in furan concentrations was observed by increasing the pH values of overliming. Interestingly, in this study, dynamic cell growth was observed until the maximum ethanol production, after which cell growth was found.
Summary
The obtained results are found to be promising for the future trend of the enzymatic hydrolysis process. During the enzymatic hydrolysis of biomass pretreated at 50 mM, 5 mM and 0.5 mM citrate buffer strengths, about 54.3% cellulose conversion was achieved at 2% (w/v) solid loading using 60 mg cellulase protein/ g cellulose. The importance of the delinification process can be affirmed by the efficiency of cellulose conversion during enzymatic hydrolysis.
A sustainable process development towards the industrial titer of
Introduction
Subsequent enzymatic hydrolysis must be performed to convert cellulose to glucose for the production of cellulosic ethanol. Although high solids loading increases glucose concentration, it inhibits the efficiency of enzymatic hydrolysis, ultimately reducing cellulose conversion [152]. In addition, citrate buffer strengths of 50 mM, 5 mM, and 0.5 mM were used for enzymatic hydrolysis at different substrate loadings to investigate the effect of citrate buffer strength on sugar release.
Materials and methods
- Dilute sulfuric acid pretreatment
- Enzymatic hydrolysis
- Preparation of pretreatment and enzymatically derived hydrolysates for the
- Microorganisms
- Analytical methods
An aliquot of 0.1 ml of sample was withdrawn from the reaction mixture every 24 hours and boiled for 10 minutes for enzyme inactivation and then analyzed by HPLC. The fermentation experiments were carried out in sterile 250 ml Erlenmeyer flasks containing 100 ml of fermentation medium, including several. Fermentation experiments were carried out in 250 ml Erlenmeyer flasks containing 100 ml of fermentation medium comprising various concentrations of cellulose hydrolysates, 4 ml of 25X YP (10 g yeast extract and 20 g peptone in 40 ml of distilled water) nutrient solution, and 6 ml of seed culture (which is an initial concentration yields 1.6 g/l based on the dry weight of the cells).
Results and discussion
- Optimization of enzyme loading for maximum cellulose hydrolysis
- Conditioning of pre-hydrolysate
- Fermentation
- Mass Balance Analysis
As shown in Table 6.7, citric acid concentration was increased with an increase in the CH load in the fermentation medium, thus, due to the inhibition effect of citric acid, reduction of sugar consumption rate and ethanol productivity trend in the first 6 hours of fermentation time. In the present study, the concentration of citric acid in CH-C (90 mM) was higher than that of CH-A (60 mM) which ultimately decreases the ethanol yield (0.30 gp/gs). Citric acid concentration present in the fermentation medium of CH-D and CH-E was found to be 8 mM and 9 mM (Table 6.8), therefore citric acid inhibition effect would be at negligible level.
Summary
Where Icc is the amount of cellulose before the enzymatic hydrolysis process, Ycb+glu represents the yield of cellobiose and glucose during the enzymatic hydrolysis. The optimal state of delignification (NaOH concentration) has been characterized based on the cellulose loss during the delignification process and the amount of cellulose hydrolyzed during the enzymatic hydrolysis process. Although lower cellulose loss was found at 1% NaOH concentration, the amount of unconverted cellulose present after the enzymatic hydrolysis was found to be 35% (Figure 7.1b).
Liquefaction of lignocellulosic biomass for the production of
Introduction
Dilute sulfuric acid pretreatment is the most used method, which can hydrolyze most of the hemicellulosic fraction of lignocellulosic biomass and it makes remaining biomass susceptible to the enzymatic hydrolysis [184]. Furthermore, in order to obtain high ethanol titer, high substrate loading (15-30% w/v) is generally used during enzymatic hydrolysis which reduces the rate of cellulose hydrolysis and deters the conversion efficiency. Therefore, in the present study, optimization of lignocellulosic biomass liquefaction was carried out to obtain maximum sugar content using the sequential steps including pretreatment, delignification and enzymatic hydrolysis for the characteristic bioethanol production.
Materials and methods
- Feed stock preparation
- Pretreatment
- De-lignification of pre-treated biomass
- Enzymatic hydrolysis
- Conditioning of pre-hydrolysates
- Fermentation
- X-ray Diffractometer analysis
Chemical composition analysis of pretreated biomass was performed according to the NREL procedure [31] and listed in Table 7.1. Based on the above results, another set of delignification process was carried out under similar conditions (such as temperature, time, and NaOH strength and solid-to-liquid ratio), and the biomass was washed with distilled water and then directly subjected to enzymatic hydrolysis without drying. To evaluate the ethanol conversion efficiency from the filter-sterilized hydrolysates of PHF-1 and PHF-2, fermentation experiments were conducted in batch mode to produce xylulose ethanol.
Results and Discussion
- Pretreatment
- De-lignification
- Enzymatic hydrolysis
- Fermentation
- Determination of optimum liquefaction process for sorghum biomass
- Cost analysis of developed process
During enzymatic hydrolysis of 1% NaOH treated substrate, about 55.2% and only increase) of cellulose hydrolysis was achieved in 72 hours of reaction time applying enzyme loading of 20 and 40 mg/g, respectively (Figure 7.1a and 7.1b). The optimal enzymatic hydrolysis condition for all delignified biomass at 72 h of reaction time was found to be 40 mg/g cellulase loading. In addition, the amount of lignin, cellulose and xylan remaining after enzymatic hydrolysis is shown in Figure 7.7.
Summary
Conclusions and future scope of the work
Conclusions
Future scope of the work
