From lignocellulosic biomass to levulinic acid: A review on acid-catalyzed hydrolysis

Catalytic conversion of renewable biomass to "green" chemicals and fuel additives has been extensively investigated in the past few decades. Interests on two top platform intermediates for biofuel production, i.e. levulinic acid (LA) and 5-hydroxymethylfurfural (HMF), have increased significantly. These two chemicals are generally produced from biomass through acid hydrolysis. This review summarizes the discoveries of the most recent studies on acid-catalyzed hydrolysis, including (i) biomass pretreatment, (ii) glucose production from cellulose hydrolysis, (iii) fructose formation from glucose isomerization, (iv) HMF formation from glucose/fructose dehydration and (v) LA production from HMF rehydration. Humins, the main byproducts, are also discussed in the aspect of their influence on the hydrolysis process, structure, formation mechanism, and applications.