Acid Hydrolysis of Lignocellulosic Biomass: Sugars and Furfurals Formation

Abstract

Hydrolysis of lignocellulosic biomass is a crucial step for the production of sugars and biobased platform chemicals. Pretreatment experiments in a semi-continuous plant with diluted sulphuric acid as catalyst were carried out to measure the time-dependent formation of sugars (glucose, xylose, mannose), furfurals, and organic acids (acetic, formic, and levulinic acid) at different hydrolysis temperatures (180, 200, 220 °C) of one representative of each basic type of lignocellulose: hardwood, softwood, and grass. The addition of the acid catalyst is followed by a sharp increase in the sugar concentration. Xylose and mannose were mainly formed in the initial stages of the process, while glucose was released slowly. Increasing the reaction temperature had a positive effect on the formation of furfurals and organic acids, especially on hydroxymehtylfurfural (HMF) and levulinic acid, regardless of biomass type. In addition, large amounts of formic acid were released during the hydrolysis of miscanthus grass. Structural changes in the solid residue show a complete hydrolysis of hemicellulose at 180 °C and of cellulose at 200 °C after around 120 min reaction time. The results obtained in this study can be used for the optimisation of the hydrolysis conditions and reactor design to maximise the yields of desired products, which might be sugars or furfurals.

Hydrothermal Conversion of Spent Sugar Beets into High-Value Platform Molecules

“…At 200 °C, the trend was opposite for conversion products like acids and HMF, whose yield decreased with longer reaction times. The highest concentration of HMF was obtained at 200 °C and 0 h with 3.4 g/L, which was comparable to the yield of the semi-batch process with a catalyst of lignocellulosic biomasses at the same temperature [ 75 ]. Compared with the theoretically possible concentrations using a model compound like fructose, the concentration in the present study did not reach the maximum yet [ 6 ].…”

“…At 160 °C and 0 h, the hydrolysis of biopolymers like cellulose had already started, expressed by the highest sugar contents in the liquid with 25 g/L of glucose and 22 g/L of fructose, while the conversion to degradation products of the sugars was comparatively low. This revealed a higher yield of sugars compared with other biomasses like miscanthus or other lignocellulosic biomass at any time at 160 °C in a batch or at 180 °C in a semi-batch process, each with a catalyst [ 75 , 76 ]. With longer reaction times, the concentration of the sugars decreased until 15 g/L of glucose and 13 g/L of fructose were found.…”

Synthesis of poly-3-hydroxybutyrate (PHB) by Bacillus cereus using grape residues as sole carbon source

“…A decrease of sugars such as glucose, galactose, arabinose, xylose and mannose during acid hydrolysis at high temperatures and high acid concentrations has been reported in previous studies [48][49][50][51][52]. At these conditions, sugar derivative products such as organic acids increase, which causes lower sugar yields [53]. From these results, we can conclude that grape peels already contain high amounts of simple sugars prior to the acid hydrolysis step.…”

Isomerization of Glucose to Fructose in Hydrolysates from Lignocellulosic Biomass Using Hydrotalcite

“…A semi-continuous test rig was used for pretreatment, where the liquid phase was continuously exchanged [30]. This has the advantage that liberated water-soluble molecules like sugar monomers are removed from the hot reactor and thus largely protected from secondary reactions.…”