Few studies have directly compared the efficiency of IL pretreatments to other pretreatments, such as the ammonia or organosolv pretreatment. Rice straw particles were pretreated with [EMIM][OAc] (1 g biomass in 20 ml of [EMI- M][OAc] at 130°C for 24 h) or ammonia (1 g biomass in 10 ml of 10 vol.% ammonia at 100°C for 6 h). In these conditions, the amount of cellulose regen­erated was comparable for the two pretreatments. However, the conversion rate of cellulose to glucose was significantly higher with the IL pretreatment and the improvement due to IL was most remarkable for larger particles (>10 mm) [46].

In another study, switchgrass was subjected to an acid pretreatment (3 wt% biomass in 1.2% sulfuric acid heated at 160°C for 20 min) or an IL pretreatment with [EMIM][OAc] (3 wt% biomass heated at 160°C for 3 h). Analysis of the recovered biomass after IL pretreatment showed lower lignin content and higher hemicellulose content, compared to the recovered biomass after acid pretreatment. X-ray diffraction measurement of the cellulose crystallinity showed a significant decrease in crystallinity after IL pretreatment, whereas the acid pretreatment caused an increase in crystallinity, which was attributed to the preferential breakdown of the amorphous cellulose during the acid pretreatment. Scanning electron microscopy showed that the cell wall structure was mostly preserved during the acid pretreatment, while the IL pretreatment left no fibrous structure. For the same enzyme loading, the enzymatic hydrolysis had faster kinetics and higher reducing sugar yields after the IL pretreatment. After a 24 h saccharifica­tion process, 96% of the cellulose was hydrolyzed for the IL-pretreated sample, while only 48% were hydrolyzed for the acid-pretreated sample [41].