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Date palm residues are one of the most promising lignocellulosic biomass for bioethanol production in the Middle East. In this study, leaflets and rachis were subjected to hydrothermal pretreatment to overcome the recalcitrance of the biomass for enzymatic conversion. Evident morphological, structural, and chemical changes were observed by scanning electron microscopy, X-ray diffraction, and infrared spectroscopy after pretreatment. High glucan (>90% for both leaflets and rachis) and xylan (>75% for leaflets and >79% for rachis) recovery were achieved. Under the optimal condition of hydrothermal pretreatment (210°C/10 min) highly digestible (glucan convertibility, 100% to leaflets, 78% to rachis) and fermentable (ethanol yield, 96% to leaflets, 80% to rachis) solid fractions were obtained. Fermentability test of the liquid fractions proved that no considerable inhibitors to Saccharomyces cerevisiae were produced in hydrothermal pretreatment. Given the high sugar recovery, enzymatic digestibility, and ethanol yield, production of bioethanol by hydrothermal pretreatment could be a promising way of valorization of date palm residues in this region.

alm tree trimmings represent primary landscaping residue in the United Arab Emirates, making it an easily accessible feedstock for bio-based products generation. This study examines organosolv treatment of the palm fronds as a method of delignification and fractionation of this lignocellulosic biomass. The results revealed that treating palm fronds with ethanol-water mixture at elevated temperature (200oC) results in up to 43% lignin recovery with no catalyst added. This corresponds to production of 13 g lignin per 100 g raw dry biomass. Over 90% glucan was found to be retained in the solid fiber fraction after the treatment, producing cellulose-rich pulp. Previous article in issue

Seagrass (Halodule uninervis) native to Abu Dhabi was sampled in various locations thorough February to June 2013. Chemical composition was analyzed, which included ash, extractives, structural carbohydrates, acid insoluble residue and CHNSO content. The theoretical methane yield was calculated based on the CHN content using Buswell's formula. Anaerobic digestion was performed with the use of sewage sludge. Three concentrations of seagrass biomass were tested (1%, 3%, 5% of VS) to evaluate the practical methane yield. The highest specific methane yield was obtained for 1% loading rate and resulted in 122 ml/gVS, which corresponds to 30% of theoretical methane yield.

Salicornia bigelovii straw was characterized and evaluated as a potential lignocellulosic bioethanol feedstock. S. bigelovii used in the study was grown in the United Arab Emirates using saltwater (40 ppt) for irrigation. Salt removal was performed prior to pretreatment to protect the processing equipment and avoid inhibition of enzymes and yeast. Composition of the washed biomass was comparable to traditional lignocellulosic biomasses with relatively high glucan and xylan content (26 and 22 g/100 gDM, respectively) but with lower lignin content (7 g/100 gDM). The washed feedstock was subjected to hydrothermal pretreatment, producing highly digestible (up to 92% glucan-to-glucose conversion) and fermentable (up to 100% glucose-to-ethanol conversion) fiber fractions. Liquid fractions obtained in the pretreatment did not show inhibition towards Saccharomyces cerevisiae. No significant differences among the enzymatic convertibility and microbial fermentability of the fibers as well as low xylose recoveries suggest that lower severity pretreatment conditions could be exploited for S. bigelovii. Previous article in issue

Straw of the halophyte Salicornia bigelovii was chemically analyzed for lignocellulosic components, extractives, and ash in relation to varying cultivation conditions (namely, irrigating water salinity and fertilizer grade). Irrigation water contained 10–50 ppt salt, and fertilizer application varied between 1 and 2 gN/m2. Composition of the biomass was comparable to traditional lignocellulosic biomasses, containing glucan (up to 27 g/100 g total solids (TS)), xylan (up to 23 g/100 g TS), and lignin (24 g/100 g TS), but also high amounts of ash (up to 53 g/100 g TS) and water–ethanol soluble extractives (up to 25 g/100 g TS). As most of the ash is extractable (up to 90%), a simple water wash is sufficient to bring the ash content down to a typical value found in the lignocellulosic materials. It was found that increasing water salinity used for the plant irrigation decreases lignocellulosic components content, increases ash content, and does not affect extractives content. The fertilizer application rate was not found to influence any of the responses, except for ash composition (lowering mineral content) and its amount in the flowering spike fraction. Stem and spike fractions were found to be significantly different in composition, with stems being closer to a typical lignocellulosic material.

Halophyte species of United Arab Emirates are a source of unique active phytochemicals, potentially due to the extreme environmental conditions under which the plants grow in the UAE. These phytochemicals make the native halophytes possibly interesting crops for biorefining, where biofuel production is combined with the production of value added chemicals, improving the economic feasibility of both process. Phytochemicals found in these species are widely recognized and researched as potential pharmaceutical and nutraceutical products. We reviewed the literature for secondary metabolites from species from the following halophyte families: Aizoaceae, Amaranthaceae (incl. Chenopodiaceae), Avicenniaceae, Zygophyllaceae. The review revealed that plant species belonging to these families contain valuable phytochemicals, such as fatty acids, terpenoids, flavonoids, alkaloids, steroids, tannins, saponins, quinones and coumarins, many of which have been reported to have therapeutic effects in humans.

The purpose of this study was to fractionate switchgrass (SG) to obtain hemicellulose-, lignin-rich fractions and highly digestible pulp, using a clean fractionation (CF) approach. The main objective was to produce highest glucose yield in the enzymatic hydrolysis of pulp. Effects of processing factors such as time (10–50 min), temperature (120–160 °C), catalyst concentration (0.21–0.93% w/w sulfuric acid) and organic solvent mixture composition (7–43% w/w methyl isobutyl ketone) were evaluated. Response surface methodology and central composite design were used for process optimization and statistical analyses. High lignin (75–93%) and xylan (83–100%) removal from biomass were obtained, leaving solid pulp rich in glucan (78–94%). High enzymatic hydrolysis glucose yields (more than 90%) were obtained for selected optimal conditions. Pulp can be used for ethanol production while separated xylan and lignin fractions can be used as a feedstock for value-added products which suggests the applicability of clean fractionation technology in a biorefinery concept.

Prairie cordgrass (PCG) was pretreated by sequential extrusion and clean fractionation (CF) processing. Following CF, PCG was fractionated into cellulose, hemicellulose and lignin-rich fractions. Cellulose pulp was then enzymatically hydrolyzed, producing glucose. The main purpose of this study was to produce the highest glucose yield as possible. The effects of time, temperature, catalyst concentration and solvent mixture composition on the fractionation were tested. Different proportions of methyl isobutyl ketone (MIBK), ethanol and water with sulfuric acid as a catalyst were evaluated. Optimal conditions for sequential extrusion and clean fractionation (39 min, 129 °C, 0.69% catalyst, and 28% MIBK) resulted in higher glucose yield (92%), and more lignin (87%) and xylan (95%) removal than for clean fractionation alone. Pairwise comparison of raw PCG with extruded PCG clean fractionation revealed no difference in glucose yields, but xylan and AIL removal were higher in the case of clean fractionation of the pre-extruded PCG.

Switchgrass was used as a lignocellulosic feedstock for second generation ethanol production, after pretreatment using sulfuric acid-catalyzed modified clean fractionation based on NREL’s (National Renewable Energy Laboratory) original procedure. Optimization of temperature, catalyst concentration and solvent composition was performed using Response Surface Methodology, and 59.03 ± 7.01% lignin recovery, 84.85 ± 1.34% glucose, and 44.11 ± 3.44% aqueous fraction xylose yields were obtained at 140.00 °C, 0.46% w/w catalyst concentration, 36.71% w/w ethyl acetate concentration, and 25.00% w/w ethanol concentration. The cellulose fraction did not inhibit the fermentation performance of Saccharomyces cerevisiae and resulted in an ethanol yield of 89.60 ± 2.1%.

Lignin extracted from prairie cordgrass, switchgrass, and corn stover (using ethyl acetate–ethanol–water organosolv pretreatment) was analyzed and characterized using several methods. These methods included analysis of purity (by determination of Klason lignin, carbohydrate, and ash contents), solubility (with several organic solvents), phenolic group analysis (ultraviolet ionization difference spectra, and nitrobenzene oxidation), and general functional group analysis (by 1H NMR). Results showed that all the examined lignin samples were relatively pure (contained over 50% Klason lignin, less than 5% carbohydrate contamination, and less than 3% ash), but switchgrass-derived lignin was observed to be the purest. All the lignins were found to contain high amounts of phenolic groups, while switchgrass-derived lignin was the most phenolic, according to the ionization difference spectra. Nitrobenzene oxidation revealed that all the lignin samples contained available guaiacyl units in high amounts.

The main objective of this study was to fractionate prairie cordgrass (PCG) obtaining the highest cellulose digestibility. Following clean fractionation (CF) processing, the PCG lignocellulosic biomass was fractionated into three main building blocks: cellulose, hemicellulose and lignin. Effects of processing factors such as time, temperature, catalyst concentration and organic solvent mixture composition were evaluated. Organic solvent–aqueous mixture contained methyl isobutyl ketone (MIBK), ethanol and water in different proportions. Sulfuric acid was used as a catalyst. In order to evaluate the degree of pre-treatment, enzymatic saccharification was employed on the cellulose fraction obtained from the CF process. Response surface methodology was used for process optimization and statistical analysis. Optimal conditions (39 min, 154 °C, 0.69% catalyst and 9% MIBK) resulted in 84% glucose yield and 87% acid insoluble lignin (AIL).

The main purpose of this study was pretreatment of prairie cordgrass obtaining three fractions: lignin, hemicellulose and fermentable cellulose. Modified clean fractionation process (using ethyl acetate–ethanol–water mixture) was employed to extract lignin and hemicellulose fractions. Different proportions of constituents in the solvent mixture were tested. In order to improve lignin recovery, the process was catalyzed with sulfuric acid. Optimization was performed for fractionation processing conditions using lignin recovery and glucose yields as primary response variables. Optimal conditions resulted in a 51.33% lignin recovery, 53.82% hydrolysis glucose yield and 33.73% xylose yield in the aqueous fraction. To improve cellulose digestibility, solid fraction was subjected to hydrothermal post-treatment, for which optimal processing conditions were found, resulting in 78.93% hydrolysis glucose yield. This research represents a step forward for biomass pretreatment, and may open up new possibilities for utilization of prairie cordgrass.

A clean sequential process including clean fractionation and hydrothermal post-treatment was developed to fractionate and pretreat prairie cord grass (PCG) prior to ethanol fermentation. An optimized clean fractionation was applied to extract lignin; then, the remaining material was subjected to a hydrothermal treatment process to enhance cellulose digestibility. The main purpose of the hydrothermal post-treatment was to improve digestibility of delignified cellulose and reduce harshness of the clean fractionation process. Optimization was performed for solvent compositions as well as time and temperatures applied to each sequential process. The glucose yield was 89% from enzymatic hydrolysis and 92% from combined fractionation and hydrothermal treatments of PCG.

In this study, modified clean fractionation process was optimized for prairie cordgrass, with usage of alternative organic constituent –ethyl acetate. Other constituents of the solvent mixture included ethanol and water. Clean fractionation solvent was used in different proportions of the constituents. Process efficiency was determined by lignin recovery, solvent composition, as well as time and temperature applied to each sequential process. and overall pretreatment were calculated. Glucose yield during enzymatic hydrolysis Optimal conditions (125°C, 37 min, with the solvent composition of ester:ethanol:water = 32.5:22.5:45) yielded a 20% lignin recovery, 38% glucose yield during enzymatic hydrolysis and 26% xylose recovery in aqueous fraction.