Combined hydrothermal carbon-based and lewis acid catalysts for conversion of cellulose

Abstract

The production of 5-hydroxymethylfurfural (HMF) and levulinic acid (LA) from cellulose is gaining considerable interests as these compounds are suitable starting materials for the preparation for valuable compounds. This study proposes a novel catalysis system, the combination of hydrothermal carbon based acid catalyst (HTCG-Sul) and Lewis acid, for the synergistic one-pot conversion of cellulose to HMF and LA. The CrCl3 (Chromium chloride) Lewis acid, when used alone was a suitable catalyst for cellulose conversion, giving highest HMF and LA yields compared with other metal chloride catalysts. When CrCl3 was combined with HTCG-Sul, the results showed that approximately 2 times higher of HMF (6.8 wt. % vs. 3.9 wt. %) and LA (22.9 wt. % vs. 11.2 wt. %), yields were obtained. Using combination of HTCG-Sul and CrCl3 as catalyst, the effect of operating conditions: including reaction temperature (160oC - 220oC), reaction time (0 - 60 min), CrCl3 concentration (0 - 0.02 molar) and HTCG-Sul dosage (0 – 40 wt. %) on cellulose conversion was studied first in a single phase reaction system. At the condition HTCG-Sul dosage of 5 wt. %, temperature of 200oC, reaction time of 5 min and CrCl3 concentration of 0.005 molar), the highest HMF yield of 6.8 wt. % operating conditions of the highest LA yield was found however at a different condition: HTCG-Sul dosage 5 wt. %, 200oC for 5 min and 0.015 molar CrCl3 concentration, which gave 40 wt. % LA yield. Furthermore, a biphasic system using methyl isobutyl ketone (MIBK)/2-butanol (7:3) as an extractive phase, water as a reactive phase, and acetone as a co-solvent and the combination of HTCG-Sul and CrCl3 as catalyst was employed to improve the stability and the yield of HMF (17.7 wt. %).