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Technical and Environmental Assessment of Chemical Pretreatment of Rice Straw

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Pretreatment process selection and optimization is one of the main challenges for obtaining the highest benefits from rice straw. This work aims at studying the effect of alkali type and loading on rice straw composition, delignification percentage and black liquor characteristics. The first group of experiments has been conducted using only alkaline pretreatment (NaOH, Ca(OH)2 ,and a mixture of them) with loadings (2-10 g/l) at 90 °C for 2 h. The second group of experiments, conducted at ambient temperature, has included alkaline, acidic, and acidic followed by alkaline pretreatment. Results have showed that at 90 °C both the type and the loading of alkali have a significant effect on rice straw delignification percentage, which has ranged from 59.3-87.17% at reduced reaction time. Furthermore, at ambient temperature conditions, the delignification percentage has ranged between (47.2-66.48%) with a significant decrease in ash content. Pre-treatment at ambient temperature could significantly decrease both lignin and ash in a longer period. Finally, environmental assessment related to chemical pretreatment showed that black liquor with high COD, BOD, ash contents, and low biodegradability represents a major constraint for environmentally accepted rice straw pretreatment. Endeavors to mitigate this effect are mandatory through the recovery of a great portion of the solid content of the black liquor.
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Alkaline; Acidic; Bioethanol; Rice Straw; Pretreatment

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