**4. Conclusions**

This study utilized well defined wood particle samples to obtain torrefaction and low temperature pyrolysis data to more thoroughly understand the processes and aid future modeling studies. Treatment temperature has a grea<sup>t</sup> impact on biochemical composition, physical and chemical properties and microstructure of wood during torrefaction (220–300 ◦C) and low temperature pyrolysis (300–550 ◦C). The hemicellulose in the wood treated at 260 and 300 ◦C was mostly decomposed and resulted in the cell walls weakening and subsequent improvement in grindability as shown by the increase in the percentage of small particles as compared to the untreated wood. Treatment at higher temperatures (>300 ◦C) did not result in a significant increased improvement of grindability. The morphologies of the wood samples remained essentially intact over the treatment temperature range but the cell walls were observed to be thinner. Shrinkages of the treated woods in the three reference directions increased with increased treatment temperature and correlated well with each other. Losses of weight and volume of the pyrolyzed wood samples were much higher than those of the torrefied samples. The bulk densities of the treated wood samples decreased with increasing temperature over the temperature range of 220 to 350 ◦C but changed little over the range of 350 to 550 ◦C. The HHVs of the treated woods by weight increased with increased treatment temperature but the HHVs of the treated woods in a volumetric basis decreased. The low temperature pyrolyzed wood

samples resulted in an improved solid fuel high fuel ratio, which was close to that of lignite/bituminous coal. The selection of a biomass thermal pretreatment process should take into consideration the application because torrefaction and low temperature pyrolysis result in different product properties. These results improve the understanding of the property changes of the biomass during thermal pretreatment and will help in the development of models for process simulation and potential application of the treated biomass.

**Acknowledgments:** This report was prepared as an account of work sponsored by the Department of Energy, National Energy Technology Laboratory, an agency of the United States Government. Neither the United States Government nor any agency thereof, nor any of their employees, makes any warranty, express or implied, or assumes any legal liability or responsibility for the accuracy, completeness, or usefulness of any information, apparatus, product, or process disclosed, or represents that its use would not infringe privately owned rights. Reference herein to any specific commercial product, process, or service by trade name, trademark, manufacturer, or otherwise does not necessarily constitute or imply its endorsement, recommendation, or favoring by the United States Government or any agency thereof. The views and opinions of authors expressed herein do not necessarily state or reflect those of the United States Government or any agency thereof.

**Author Contributions:** The authors equally contributed to the work reported.

**Conflicts of Interest:** The authors declare no conflict of interest.
