Liquid hot water pretreatment is considered to be a promising method for increaing biomass digestibility due to the moderate operational conditions without chemical additionA necessary step towards the scalability of this pretreatment process is performing pilot plant triaUpscaling was evaluated with a scaling factor of 500, by using 50 mL in the laboratory and 25 L in pilot plant batch reactor. Pretreatment times were varied from 30 to 240 min, and temperatures usewere 180–188^◦ C, while applying similar heating profiles at both scales. The initial mass fraction poplar wood chips ranged from 10% to 16%. Liquid hot water pretreatment at laboratory and pilscale led to analogous results. The acetic acid analysis of the liquid and solid fractions obtained aftpretreatment indicated that complete deacetylation of poplar biomass can be achieved.

Pretreatment of lignocellulosic biomass is required for many biorefinery processes. Previous studies have described hydrolysis of hemicelluloses by using liquid hot water (LHW) pretreatment. We evaluated the effect of carbonic acid originating from pressurized carbon dioxide during LHW pretreatment of poplar. The conditions applied covered temperatures from 120 to 200 °C, pretreatment times from 5 to 240 min and pressures from 1.0 to 2.2 MPa CO₂ or N₂. The pressure and the type of gas (CO₂ or N₂) did not have an effect on production of acetic acid, which functioned as a marker of progress of biomass hydrolysis. Results suggested that the presence of carbonic acid in the process does not significantly contribute to acidification. Deacetylation of lignocellulosic biomass can be achieved by LHW pretreatment irrespective of pressure and of gas type used, at the conditions tested.