Waste paper valorization for bioethanol production: Pretreatment and acid hydrolysis optimization

Abstract

ABSTRACT The dramatic fluctuations of oil cost and climate change have together concentrated political and scientific attention on the search of alternative fuels. The aim of this work is to recycle waste paper for producing bioethanol. The production process includes two main stages: the conversion of polysaccharides into simple sugars and the fermentation of these sugars into ethanol. In order to maximize the total sugars content, the parameters of both thermal pretreatment and acid hydrolysis steps are optimized by using the response surface methodology combined with Box–Behnken design. In the thermal pretreatment stage, temperature (100–140°C), residence time (20–60 min), and paper–water ratio (0.5–1.5% w/v) are adjusted. For acid hydrolysis step, temperature (60–100°C), reaction time (20–60 min), and amount of sulfuric acid (1–3% v/v) are the investigated parameters. Total sugars evolution is monitored during fermentation reaction using the yeast Saccharomyces cerevisiae under the optimal parameters of both pretreatment and acid hydrolysis steps. The optimum of thermal pretreatment step was found for the following operation conditions: Temperature = 100.46°C, time = 20.11 min, and paper–water ratio = 1.45% (w/v) with a yield of 48.69% (w/v) of total sugars while the best conditions for the acid hydrolysis step: Temperature = 96.31°C, time = 20.64 min, and amount of sulfuric acid = 1% (v/v), which led to a yield of 79.65% (w/v) of total sugars. Moreover, physicochemical and thermodynamic characteristics of the produced bioethanol (purity degree of 90% v/v) have shown a good agreement with the standards.