Abstract
This study evaluates the pre-treatment of cellulose from kenaf plant to yield sugar precursors for the production of ethanol or butanol for use as biofuel additives. In order to convert the crystalline cellulosic form to the amorphous form that can undergo enzymatic hydrolysis of the glycosidic bond to yield sugars, kenaf pulp samples were subjected to two different pre-treatment processes. In the acid pre-treatment, the pulp samples were treated with 37.5% hydrochloric acid in the presence of FeCl3 at 50 °C or 90 °C whereas in the alkaline method, the pulp samples were treated with 25% sodium hydroxide at room temperature and with 2% or 5% sodium hydroxide at 50 °C. Microwave-assisted NaOH-treatment of the cellulose was also investigated and demonstrated to be capable of producing high glucose yield without adverse environmental impact by circumventing the use of large amounts of concentrated acids i.e., 83–85% phosphoric acid employed in most digestion processes. The treated samples were digested with the cellulase enzyme from Trichoderma reesei. The amount of glucose produced was quantified using the Quantichrom™ glucose bioassay for assessing the efficiency of glucose production for each of the treatment processes. The microwave-assisted alkaline pre-treatment processes conducted at 50 °C were found to be the most effective in the conversion of the crystalline cellulose to the amorphous form based on the significantly higher yields of sugar produced by enzymatic hydrolysis compared to the untreated sample.
Highlights
Kenaf (Hibiscus cannabinus) is a woody plant cited by the researchers at the United StatesDepartment of Agriculture (USDA) as one of the most promising crops for industrial development [1].The crop is an excellent choice for soil and water remediation as well as a top producer of bioenergy feedstock
The present study investigates the effectiveness of cellulose decrystallization in kenaf pulp using NaOH and ethanol pre-treatment with a microwave reactor versus an acidcatalyzed method
The kenaf pulp treated with 25% NaOH at room temperature without the use of microwave energy resulted in about 2.6 times the relative glucose yield of the untreated pulp after 24 hours of cellulase digestion (Table 3b) suggesting that the pre-treatment improved the accessibility of the pulp to the cellulase enzyme
Summary
Kenaf (Hibiscus cannabinus) is a woody plant cited by the researchers at the United States. Techniques including mercerization [8,9] and dissolution [10,11] procedures have been used to transform the natural cellulose (CI) structure of wood, cotton linter, and sugar cane bagasse to the cellulose II (CII) and amorphous form In these studies, the degrees of transformation were evaluated using the wide-angle X-ray scattering (WAXS) technique [12,13], the 13C NMR spectroscopy [14,15], or the 13C-CP/MAS NMR spectroscopy techniques [16], all of which are effective for monitoring changes in cellulose crystals. The procedure requires two stages including initial enzyme hydrolysis, which result in about 40% conversion followed by the decrystallization process for the residual cellulose that is recalcitrant toward the initial hydrolysis. The outcome was evaluated by the amount of glucose produced after enzymatic hydrolysis by the cellulase enzyme from Trichoderma reesei
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