Bioethanol is by far the most widely used biofuel for transportation worldwide. Production of bioethanol from biomass is one way to reduce both consumption of c.
Cell- wall structural changes in wheat straw pretreated for bioethanol production | Biotechnology for Biofuels. Straw composition. As seen in Table 1, the main effect of the hydrothermal pretreatment on the composition of the biomass is the partial but substantial removal of hemicelluloses. All measurable arabinan is removed and the xylan content is reduced from 2. Consequently, the overall cellulose content increases. After delignification of the pretreated material, no Klason lignin can be detected. The composition of the straw that has undergone SO2- impregnated steam explosion is similar to that of the hydrothermally pretreated straw except for a slightly higher xylan content at 7.
A biofuel is a fuel that is produced through contemporary biological processes, such as agriculture and anaerobic digestion, rather than a fuel produced by geological processes such as those involved in the formation of fossil. ENERGY BALANCE OF 2nd GENERATION BIOETHANOL PRODUCTION IN DENMARK Niclas Scott Bentsen1 Claus Felby1 Karen Hvid Ipsen2 1 Royal Veterinary and Agricultural University Danish Centre for Forest, Landscape and Planning 2 Elsam.
Straw, untreated. Pretreated straw. Delignified, pretreated straw. Steam- exploded straw.
Founded in Mannheim in 2006, CropEnergies is one of the leading European manufacturers of sustainably produced bioethanol for the fuel sector today. In our modern production facilities in Germany, Belgium, the UK and France. “Second generation” bioethanol, with lignocellulose material as feedstock, is a promising alternative for first generation bioethanol. This paper provides an overview of the current status and reveals the bottlenecks.
Bioethanol Fact Sheet What is bioethanol? Bioethanol (also known as ethyl or grain alcohol) is a clear, colourless liquid that can be produced by the fermentation of virtually any source of sugar or starch, the most common.
ATR- FTIR spectroscopic analysis. ATR- FTIR spectroscopy was used as an analytical tool to qualitatively determine the chemical changes in the surface of pretreated straw to complement and understand the microscopic investigations. The FTIR spectra of untreated, hydrothermally pretreated, delignified hydrothermally pretreated and steam- exploded straw samples are shown in Fig. A. Excerpts of the four spectra are presented in Fig. B. Figure 1. Spectroscopy.
ATR- FTIR spectra of untreated, hydrothermally pretreated, delignified hydrothermally pretreated and steam- exploded wheat straw. A) Complete spectra of all treatments.
B) Excerpt of spectra. All spectra are separated to ease comparison. The arrow in A points to the bands at 2.
CH2- stretching bands ascribed to wax). The vertical lines in B mark the positions of the bands at 1.
One of the effects of the pretreatment is the removal of wax from the straw: Fig. A shows that the CH2- stretching bands at approximately 2. Two interesting features are shown in Fig.
B. First, it can be seen that the carbonyl band at 1. This is expected as the pretreatment is known to remove a large portion of the hemicelluloses as shown in Table 1 and in Thomsen et al. Second, lignin bands at approximately 1. Fig. 1. B). One explanation for this could be a relative increase in the amount of lignin due to the removal of hemicelluloses. Another reason could be that lignin is released and re- deposited on the surface (ATR- FTIR spectroscopy is a surface technique; according to [2.
Ојm with the signal intensity exponentially decreasing with penetration depth). The increase in lignin is believed to be too significant to be only due to the hemicellulose removal. One of the strategies employed in increasing enzymatic convertibility is to decrease cellulose crystallinity [1. Differences between samples with regard to the relative amounts of amorphous and crystalline cellulose have earlier been described through infrared peak ratios.
At least four different peak pairs have been proposed [3. Of these, only the peak pair 1. The peak ratio for the untreated straw was 0. In the study by Wistara et al. When comparing their results with ours, it appears that the pretreatment does not adversely affect the degree of cellulose crystallinity. More precise measurements of cellulose crystallinity are needed to confirm this result. SEM and AFM images.
Based on the results from ATR- FTIR spectroscopy, SEM and AFM were used to gather information on the effect of the hydrothermal pretreatment on the ultrastructure and possible disruption of the cell wall. When untreated, the anatomy of the harvested, chopped wheat straw is easily recognisable, with sheath leaves surrounding the straw itself (Fig. A). The various cell types of the straw wall can be seen, including epidermis cells, parenchyma cells, vascular bundles (phloem and xylem) as well as thick- walled fibre cells, as seen in the SEM micrograph presented in Fig. B. Imaging by AFM of parenchyma cells lining the straw cavity reveals the appearance of interwoven cellulose microfibrils of the primary wall (Fig. C). These particular cells are largely unlignified [3.
Fig. 2. C). Figure 2. Microscopy images.
SEM and AFM images of untreated (A)- (C), hydrothermally pretreated (D)- (F), delignified hydrothermally pretreated (G)- (I) and steam- exploded wheat straw (J)- (L). In untreated wheat straw, the straw itself is surrounded by a sheath leaf (A, SEM image) and at slightly higher magnification the individual cells of the straw wall can be identified (B, SEM image).
A high- resolution AFM scan (amplitude image) of a primary cell wall lining the straw cavity shows interwoven cellulose microfibrils, partially imbedded in non- cellulosic polymers (left- hand side of C). In hydrothermally pretreated wheat straw, the defibrating effect of the pretreatment causes the individual fibres to partially separate, as can be seen in D (SEM image). The pretreatment leaves a surface layer of debris and re- deposited cell- wall polymers on the individual fibres (E, SEM image). An AFM scan (amplitude image) of fibre surface shows the 'globular' deposits characteristic of lignin (F). No microfibrils are visible. Delignification of pretreated fibres causes no further separation of fibres (G and H, SEM images) but removes most of the surface layer/deposits seen in (E).
Cellulose lamellae/agglomerates are now visible (H). An AFM scan (amplitude image) shows that delignification exposes intact, interwoven cellulose microfibrils (I). Steam explosion causes partially separated fibres with 9.
В° compression bends (J, SEM image) and a surface layer with debris and droplets (K, SEM image). Droplets are indicated with arrows.
High- resolution imaging of AFM shows globular surface deposits (L, amplitude image), similar to those seen on hydrothermally pretreated straw (F). Initially, the most apparent effect of the hydrothermal pretreatment apart from a colour change from yellow into dark brown is the partial defibration, or separation of individual fibres and cell types of the wheat straw.
Although the pretreated material is quite heterogeneous and contains larger pieces (up to about 1 cm) that are easily recognised as straw, a significant fraction consists of cells that are either completely or partially separated from each other (Fig. D). All individual fibres (and most other cell types) seem to be intact despite the hydrothermal treatment, rather than being broken or otherwise disrupted (Fig. D and 2. E). When looking more closely at the pretreated fibres it becomes apparent that the surface is covered with 'debris' and a thin layer of deposits that seems to be covering the whole surface (Fig. E). This debris could be fractions of middle lamellae.
When further investigating the pretreated fibre surfaces through AFM, it was not possible to identify any primary or secondary wall cellulose microfibrils (such as seen in untreated fibre cell walls; Fig. C). Instead, an uneven surface of spherical and globular shapes was seen (Fig. F). These globular shapes (diameter approximately 2. Initially, delignification did not have a great effect on the overall structure of the pretreated material apart from a change in colour; the straw was still only partially defibrated (Fig. G), presumably due to the hemicellulose content of the middle lamella [3. However, upon closer observation, the surface of the individual fibres had changed drastically. The uneven surface now appeared smooth and cellulose aggregates (macrofibrils) running in the direction of the fibre could be seen, as in the SEM image in Fig.
H. When investigating the delignified fibre surfaces with AFM, the globular shapes of deposited lignin were not seen. Instead, intact surfaces believed to be primary and secondary wall lamellae were observed. Due to the mixing of fibres and other cell types during the pretreatment it was not possible to investigate the same straw cavity parenchyma cells as with the untreated straw. However, numerous scans of different cells revealed several surfaces with similar primary walls to the parenchyma cells.
The microfibrils of these primary walls displayed the same interwoven structure as previously seen and were partially embedded in non- cellulosic polymers (Fig. I). It should be added, that with AFM only relatively smooth surfaces are successfully imaged. Surprisingly, neither the overall or fibrillar structure of the individual fibres seems to show large structural changes such as the rupture of fibres or a visible increase of porosity, which are believed to be associated with thermal pretreatments. No holes or cracks were seen in the fibres and AFM did not indicate that the accessibility of the internal parts of the cell wall matrix had been improved due to structural dislocations. Rather, the primary and secondary cell walls appeared to be fully intact, except for the pits and simple perforations that already exist in certain cell types [3.
Despite these observations of a substrate where the skeletal structure is intact and the crystallinity of the cellulose does not appear to have been lowered, the hydrothermally pretreated straw has been shown to be easily digestible by enzymes [1. Consequently, the effectiveness of the pretreatment must be related to hemicellulose removal and lignin re- localisation. This is in spite of the fact that lignin is not removed by the pretreatment and that lignin is known to be responsible for unproductive adsorption of cellulases [3. It is well known that lignin encases the cellulose in the cell- wall matrix, hindering cellulases from reaching cellulose fibrils. We hypothesise that the migration of lignin to the outer surface exposes internal cellulose surfaces. More investigations are needed in order to confirm this.
Selig et al. [3. 9] have also observed the formation and migration of spherical lignin deposits onto the surface of fibres as a result of pretreatment. They also suggest that the deposited lignin can have a negative impact on the enzymatic cellulose hydrolysis. It is possible, however, that the surface lignin layer is easily removed by simple mechanical forces through mixing, due to lignin being less strongly bound to carbohydrate polymers compared with its native linkages.