Volume 9 Issue 2

A process for the production of biogas through the anaerobic digestion (AD) of date palm tree waste (DPTW) was developed. The effects of different substrate pretreatments and operating conditions on the yield of biogas and on the chemical composition of DPTW before and after AD were studied. The best results were obtained using alkali pretreatment, with a particle size of 2 to 5 mm, a C:N ratio of 30:1, a digestion temperature of 40 °C, an initial pH of 7.0, and a volatile solids concentration of approximately 10%. The production of flammable biogas containing up to 50% methane started after about one week of operation and continued for approximately 11 weeks. The highest average biogas yield obtained was 342.2 L gas/kg of volatile solids fed to the digester. The highest maximum and average volumetric biogas production rates obtained were 674.5 and 404.4 L/m3 of digester volume per day, respectively. After digestion, there was up to a 58% reduction in the organic matter content of the substrate. Reductions in the contents of cellulose, hemicellulose, and soluble organic compounds were 68.7, 73.4, and 71.9%, respectively, while the ash and lignin contents remained mostly constant. The remaining sludge contained nutrient minerals and some organic matter which qualifies it as a potential soil fertilizer for crop production.

The Miscanthus sacchariflorusstrain Goedae-Uksae 1 has recently been developed as an energy crop, because of its rapid growth, ease of culture, and large size. In this study, Miscanthus pellets were investigated for further practical use of renewable resources. The pellets were produced on a pilot scale and their characteristics and quality were investigated. Moisture content, density of raw materials, and die ratio (L/D) were determined to be the main factors affecting Miscanthus pelletizing. Thus, a central composite design using response surface methodology (RSM) was applied to optimize conditions for standard grade Miscanthus pellet production. The optimal values predicted by the model equation were confirmed by the experimental data. The optimum ranges of parameters for pellet production were identified as moisture content, 20 to 25%; density of raw materials, 240 to 300 kg/m3; and die ratio, 4.5:1 to 5.0:1. Under these conditions, Miscanthus pellets were produced meeting the standards of qualities, such as size, bulk density, durability, moisture content.

Lignin is an important renewable source of phenolic products. In this study, alkali lignin was depolymerized to produce phenolic compounds. The effects of catalyst, solvent, reaction time, and reaction temperature on the yields of liquid products and volatile fractions were investigated in detail. Compared with the solvents water and octane, alcohols can significantly promote depolymerization of lignin due to the excellent solubility of the degradation products and intermediates. Under the conditions of 300 °C for 2 h in the solvent ethanol, the highest yields of liquid products (75.8 wt%) and volatile fraction (38.1 wt%) were obtained over a ZnCl2 catalyst. Gas chromatograph-mass spectroscopy analysis demonstrated that the volatile fraction was composed of guaiacols (15.09 wt%), phenols (15.79 wt%), and syringols (2.28 wt%). Furthermore, the mechanism for lignin depolymerization is discussed.

A three-factor two-level (23) full factorial design analysis was conducted to identify the significant factors that influence glucose production from tapioca slurry with an encapsulated enzymatic saccharification process using a stirred bioreactor. The factors investigated were pH (5 to 7), temperature (40 to 60 °C), and agitation speed (80 to 160 rpm). From the statistical analysis, a mathematical model for tapioca slurry saccharification was derived, and the variance analysis resulted in a high determination coefficient (R2=0.9993). The main effects and their interactions were also investigated. The results showed that all the main factors and the two-way interaction factors were statistically significant. The most significant factor in the tapioca slurry saccharification was found to be pH, while the interaction between pH and agitation speed was the most influential two-way interaction.

Shape-controlled bio-chars were synthesized in two steps: (i) ionothermal carbonization of biomass (e.g., glucose, cellulose, lignin, and bamboo) at low temperatures (150 to 180 °C) in an acidic ionic liquid (IL), and (ii) subsequent activation with carbon dioxide at higher temperature (500 °C).Acidic IL was used as both the medium and catalyst for advanced carbon materials production. During the first step the primary structurs of spherical particles were obtained. The surfactants sodium dodecyl sulfonate (SDS), ethylene glycol (EG), and sodium oleate (SO) were also used to modify the surface morphology of bio-chars and activated bio-chars. After the second step, the primary structures of bio-chars were still preserved or improved. The Brunauer-Emmett-Teller surface area and the pore diameter of activated bio-chars were 289 to 469 m2/g and 3.5 to 3.6 nm, respectively. Scanning electron microscope and transmission electron microscope images show that after modification of bio-chars with SDS, EG, and SO, activated bio-char particles agglomerated into rod-like (~200 nm diameter),nano-membrane (~70 nm thickness), and spherical (~200 nm) morphologies, respectively. The morphology of activated bio-chars was easily controlled during the synthesis, which is important for the exploitation of their peculiar properties and unique applications.

Low-pressure steam explosion (LPSE) combined with alkaline peroxide (AP) pretreatment was first employed to separate hemicellulose from Lespedeza stalks. The monosaccharide composition and molecular weight distribution of the obtained hemicellulose fractions were characterized in this study. The results show that the hemicellulose extracted from Lespedeza stalks consisted of xylose, glucose, galactose, and mannose, which was a mixture of arabinoxylans and xyloglucans or β-glucans. The yield of hemicellulose fractions after AP pretreatment ranged from 11.2% (2.5% hydrogen peroxide (H2O2), w/v for 12 h) to 12.2% (3.3% H2O2, w/v for 72 h). The molecular weight of hemicellulose decreased from 2,458 g/mol to 1,984 g/mol after AP pretreatment, indicating its degradation reaction. The structure of hemicellulose was analyzed by Fourier transform infrared spectroscopy, proton nuclear magnetic resonance, and heteronuclear single quantum coherence. The AP pretreatment partially cleaved the backbone and the ether linkage between lignin and hemicelluloses. Also, branched-chain α-D-arabinofuranosyl in which β-D-xylose substituted at the C-3 position (monosubstituted) was removed, illustrating a partial debranching reaction. Therefore, the combination of low-pressure steam explosion and alkaline peroxide pretreatment (LPSE-AP) is an effective pretreatment method to separate hemicellulose from Lespedeza stalk.

Matrix-assisted laser desorption/ionisation time of flight (MALDI-TOF) mass spectrometry is a suitable method for examining polyflavonoid tannin oligomers because it has the capability to determine aspects of their oligomeric structure and characteristics that are too difficult to determine by other techniques. For non-purified industrially extracted Aleppo pine polyflavonoid tannin, it was possible to determine by MALDI-TOF that: (i) oligomers formed by catechin/epicatechin are present in tannin, as are mixed oligomer units with fisetinidin and robinetinidin units; the presence of flavonoid gallate and other structures was confirmed; (ii) oligomers up to 12 to 13 repeating monoflavonoid units, in which the repeating unit is at 264 Da, have been confirmed; and (iii) oligomers of the two types covalently linked to each other also occur. The presence of a small proportion of hydrolysable tannins by chemical analysis can also be explained by gallate residues attached to some of the flavonoid oligomers.

Freshly harvested alfalfa was fractionated using centrifugation and filtration, whereby alfalfa was separated into a fiber-rich cake and a nutrient-rich juice. The solid cakes from the above separation processes were used as the feedstock for ethanol production using separate hydrolysis and fermentation. The filtration process proved to be more efficient at reducing the solids mass transfer to the juice than the centrifuge process. Glucose from filtered alfalfa solid cake can be efficiently fermented to ethanol with 75% of the theoretical yield. In conclusion, centrifugation was not as effective as filtration in removing particulates and colloidal matter from alfalfa. The filtration process resulted in a solid cake with a higher cellulose digestibility, which leads to a higher ethanol production.

The Hildebrand solubility parameter (d-value) was applied to explain the effect of organic solvent concentration on lignin removal during organosolv extraction of lignin from enzymatically hydrolyzed cornstalks under atmospheric pressure and low temperature (≤ 75 °C) without additional catalyst. The d-value of lignin, calculated using the group-contribution method, was 13.70 (cal/cm3)1/2. The proximity of the d-value between organic solvent-water and lignin explained the delignification capacity of the organic solvent-water. The concentration of organic solvent in the aqueous mixture that led to the highest delignification (i.e., 34.5%, 41.8%, and 53.7% delignification for ethanol-water, 1,4-dioxane-water, and tetrahydrofuran-water, respectively) was around 65 to 75% vol., which was in keeping with the prediction by the solubility parameter theory.

In the present paper changes of validity in Euler-Bernoulli’s elementary theory of flexural vibration for homogeneous materials were tested with respect to changing severity and position of a single defect in wood. As an orthotropic material, wood has different material properties or strengths in different orthogonal directions. A set of absolutely clear specimens of oriental beech was chosen and hand drilled in different diameters (severities) at different relative distances from an end oriented in the R direction. A clear specimen showed a steady decrease in evaluated moduli of elasticity related to increasing mode numbers. After creating the defects, this steady decrease line showed some breakages. The slope breakages of modally evaluated elastic moduli in LT and LR vibrations are suggested as potential finger-prints of single hole defects in the specimen by considering the shape and rate of breakages in the decreasing lines. The recognition scenarios of slope breakages for defect severity and position are summarized.