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Improvement of the enzymatic hydrolysis of paperboard fines by ionic liquids based on choline
Lignocellulosic material classified as ‘’paper mill mud’’, received a pretreatment with choline - ionic liquids which extract lignin selectively. The purpose of this pretreatment is to facilitate the later enzymatic hydrolysis of the residual solid, and thus increase the carbohydrates yield. The effects of anion in the ionic liquid (lysine or acetic acid), temperature (0 or 90 °C) and concentration of water (0 or 50 %) on the extraction of lignin are studied. The liquids’ synthesis was carried out by potentiometric technique; their correct formation was checked by FT-IR and RMN 1H of liquids. The lignin extraction was evaluated by UV spectroscopy at a wave length of 280 nm, using the pure liquid as a blank and the used liquid as the problem sample, with an extinction coefficient of 2.19 L g-1 cm-1 for the concentration calculation. After the pretreatment the remnant solid was submitted to enzymatic hydrolysis with a cocktail of commercial cellulases during 24 hours, the carbohydrates content of the hydrolysis was determined by the DNS technique. The results clearly show that the enzymatic yield is improved with a choline ionic liquid pretreatment, achieving a 100 % increment in the carbohydrate concentration respect to the untreated sample. Additionally, an analysis of crystallinity of cellulose by XRD was carried out after the pretreatment to the remnant solid; the results of this analysis show a reduction in the crystallinity due to the pretreatment. This reduction in crystallinity indicates that the ionic liquid also acts breaking the crystalline zones of cellulose allowing a better access to the enzymes. Finally, reuse tests were carried out in the conditions that proved being the best; the effect of this factor on the concentration of the enzymatic hydrolysis was evaluated.