CHEMICAL ENGINEERING TRANSACTIONS VOL. 63, 2018 A publication of The Italian Association of Chemical Engineering Online at www.aidic.it/cet Guest Editors: Jeng Shiun Lim, Wai Shin Ho, Jiří J. Klemeš Copyright © 2018, AIDIC Servizi S.r.l. I SBN 978-88-95608-61-7; I SSN 2283-9216 A Technique to Smartly Re-Use Alkaline Solution in Lignocellulose Pre-treatment Quan Dinh Nguyen*, Thi Kim Phung Le, Tuong An Thi Tran Laboratory of Biofuel and Biomass Research, VNU – Ho Chi Minh City University of Technology (HCMUT), Ho Chi Minh City, Vietnam ndquan@hcmut.edu.vn Alkaline solution was collected from alkali-treatment of steam-exploded rice straw and then reused as is or with addition of NaOH for the next pre-treatment batch. The as-is-reused solution (without addition of NaOH) showed a significant decrease of alkali-treatment efficiency because NaOH has already reacted with substrates from rice straw in the previous batch. Based on the comparison of alkali-treatment efficiencies between the first-used and as-is-reused alkaline solutions, corresponding reasonable amounts of supplementary NaOH were calculated. The results showed that reused alkaline solutions, with the addition of calculated amounts of NaOH, produce an alkali-treatment efficiency as that of the first-use, while the total amount of NaOH for both batches reduced to around 70 %, implying an impressive saving of chemicals, fresh water, and reduction of volume of waste water. 1. Introduction For the last twenty years, bioethanol has been receiving an intensive and widespread interest all over the world. Differing from fossil fuels, bioethanol is regarded as a promising renewable fuel, or called as neutral- carbon energy source (Sheehan, 1994). The security of sustainable feedstock is one of the vital trends for bioethanol production. While sugar-based or starch-based bioethanol production disagrees with food security, lignocellulose-based bioethanol can be produced from any kind of popular botanic feedstock, especially agricultural residues (Azuma et al., 1985), which mainly comprise of cellulose, hemicellulose, and lignin (Souza et al., 2014) In general, cellulose is similar to starch as polymers of glucose, but due to its structural complexity, along with the existence of lignin, lignocellulose has a very strong resistance to enzymatic hydrolysis and inhibit yeast growth. Lignocellulose conversion to bioethanol requires three major processes: physical and chemical pre- treatment to liberate cellulose and hemicellulose; enzymatic hydrolysis of cellulose and hemicellulose to produce fermentable sugars (Bes et al., 1989); and fermentation of sugars to bioethanol by microorganisms (Talebnia and Taherzadeh, 2006). The high costs of chemicals, enzymes (Koullas et al., 1992), and energy consumed (Ramos et al., 1993;) make commercialisation of lignocellulose-based bioethanol face many obstacles (Sarkar et al., 2012). Among the chemical pre-treatment techniques, alkali-treatment of steam-exploded biomass is applied in pilot scales (Sluiter et al., 2008). The use of an alkali cracks ester and glycosidic side chains, leading to structural alteration of lignin, cellulose swelling, partial decrystallisation of cellulose, and partial solvation of hemicellulose (Cheng et al., 2010). In our study employing NaOH as the agent of alkali-treatment, the waste solution after treatment still has a strong basicity, which implies some degree of delignification ability. In this context, the reusability of this solution is investigated based on the following concept. Consider C1 the initial concentration of an alkaline solution, ATE1 and ATE2 the alkali-treatment efficiencies at the first use and as-is-reuse of solution C1. Consider C2 the concentration of another solution, which has its first-use alkali-treatment efficiency equal to ATE2 as illustrated in Figure1. It is expected that if an amount of NaOH and water added to solution C2 can make up solution C1, the same amount of NaOH and water added to the as-is-reuse solution C1 can restore its treatment efficiency of ATE1. DOI: 10.3303/CET1863027 Please cite this article as: Quan Dinh Nguyen, Thi Kim Phung Le, Tuong An Thi Tran, 2018, A technique to smartly re-use alkaline solution in lignocellulose pre-treatment, Chemical Engineering Transactions, 63, 157-162 DOI:10.3303/CET1863027 157