tion acceptable for practical pretreatment operation in a FT mode. Since the skeletal density of bagasse is about 1500 kg/m3 (Rasul et al., 1999), this corresponds to a low bound of 6:1 on the allow- able mass ratio of liquid to solids for FT operation. The sharp rise in pressure seen at pretreatment conditions is a consequence of the non-ideality of the reaction fluid mechanics and indicates that the pressure drop at reaction conditions cannot be predicted from the reactor behavior at room temperature.
4. Conclusions
Bagasse and switchgrass require more water than poplar to pro- cess in a flow-through mode. Higher pressure drop was associated with greater biomass compaction, greater water absorption, more fine particles and smaller average particle size. The instability of the bagasse bed during pretreatment above 140 kg/m3 sets an upper bound on the allowable concentration for continuous stable flow. The data provided in this study provide useful information to identify conditions for which FT pretreatment can be implemented in a practical context. Further work on thermodynamic and eco- nomic considerations is required to define the feasible operating region for FT pretreatment.
Acknowledgements
The authors are grateful for the support provided by funding Grants from the Link Energy Foundation, the BioEnergy Science
V. Archambault-Léger, L.R. Lynd / Bioresource Technology 157 (2014) 278–283 283
on the bagasse concentra-