Valorization of Bark from Short Rotation Trees by Temperature-Programmed Slow Pyrolysis.

Qing Zhao,Antti Haapala,Janne Jänis,Marko Mäkinen

doi:10.1021/acsomega.1c00434

Abstract

The tree bark represents an abundant but currently underutilized forest biomass side stream. In this work, temperature-programmed slow pyrolysis with fractional condensation was used for thermochemical conversion of the bark obtained from three short rotation tree species, aspen, goat willow, and rowan. Heating was performed in three stages, drying (135 °C), torrefaction (275 °C), and pyrolysis (350 °C), and the resulting vapors were condensed at 120, 70, and 5 °C, producing nine liquid fractions. An additional fraction was collected in the pyrolysis stage at 0 °C. The obtained liquid fractions were characterized in terms of their yields and bulk chemistry (i.e., CHNOS content, water content, pH, and total acid number) as well as their molecular level chemistry by high-resolution mass spectrometry. The highest liquid yields were obtained for the fractions condensed at 70 °C. The water content varied considerably, being the highest for the drying fractions (>96%) and the lowest for the pyrolysis fractions obtained at 120 °C (0.1–2%). Considerable compositional differences were observed between the liquid fractions. While the drying fractions contained mostly some dissolved phenolics, the torrefaction fractions contained more sugaric compounds. In contrast, the pyrolysis fractions were enriched lipids (e.g., suberinic fatty acids and their derivatives) and alicyclic/aromatic hydrocarbons. These fractions could be further refined into different platforms and/or specialty chemicals. Thus, slow pyrolysis with fractional condensation offers a potential route for the valorization of tree bark residues from forest industry.

Highlights

Bark accounts typically for 9−15% of the dry weight of a tree log[1,2] and is removed from the logs when the trees are processed in the saw or pulp mills
In comparison, is a cost-effective thermochemical method that possesses a great potential for large-scale conversion of tree bark residues[40] but requires feedstock drying and yields a complex mixture of chemical degradation products
The temperature-programmed slow pyrolysis was used for thermochemical conversion of bark obtained from three short rotation tree species, namely, aspen, goat willow, and rowan

Summary

■ INTRODUCTION

Bark accounts typically for 9−15% of the dry weight of a tree log[1,2] and is removed from the logs when the trees are processed in the saw or pulp mills. Cork from the cork oak (Quercus suber) has been applied in construction, cosmetics, and pharmaceutical applications.[16] Refined pine bark has been shown to function in bioherbicides and insecticides[17] and in the recovery of metals from wastewater.[18] Magnolia tree bark has shown anti-cancer, anti-inflammatory, anti-oxidant, and anti-depression activities,[19] while valorization of different triterpenoids (e.g., betulin) and suberin from birch bark has been extensively studied.[10,20−22] These assessments have focused largely on the tree species of large-scale industrial uses in mechanical or chemical wood refining from which significant volumes of bark are generated as side streams. ACS Omega http://pubs.acs.org/journal/acsodf pathways are still required to find their potential valorization

■ RESULTS AND DISCUSSION

■ CONCLUSIONS

■ ACKNOWLEDGMENTS

■ REFERENCES