Deep eutectic solvents and ionic liquids in enzymatic lignocellulose hydrolysis

Deep eutectic solvents (DESs) and ionic liquids (ILs) have been shown to be effective chemicals for lignocellulose pretreatment in sugar platform biorefineries. ILs are, however, known to significantly inactivate hydrolytic enzymes. In this paper, we compare the stability of hydrolytic enzymes in a set of different DESs and [EMIM]AcO, a cellulose-dissolving IL. The efficiency of these solvents in lignocellulose pretreatment is assessed in different process pathways, by carrying out enzymatic total hydrolysis on a) untreated substrates, b) pretreated and washed substrates, c) pretreated substrates in 30 % of DES/[EMIM]AcO and on d) pretreated substrates in 80 % of DES/IL. Microcrystalline cellulose, dissolving pulp, shredded barley straw and spruce saw dust were used as substrates. The results show that some of the DESs were stabilizing for the enzymes, whereas [EMIM]AcO was the most efficient pretreatment chemical under the used mild conditions. However, in the combined hydrolysis with DES/IL present, [EMIM]AcO inhibited enzymatic hydrolysis to a significantly higher degree than the DESs. The enzymatic hydrolysis yields were generally lower in DESs than in buffer, even if the enzymes showed significant stability in the DESs.