Hot Water Extraction: Short Rotation Willow, Mixed Hardwoods, and Process Considerations

Christopher D Wood,Rachel M Emerson,Timothy A Volk,Thomas E Amidon

doi:10.3390/en13082071

Abstract

Short rotation woody crops (SRWC) like shrub willow are highly productive biomass resources of interest for energy and fuel applications. Hot water extraction (HWE) as an upgrading tool to enable the use of willow biomass in pellet applications has been proposed, and is of increasing interest. This study treats willow and mixes of willow and conventional mixed hardwood feedstock with HWE in a tumbling laboratory reactor to elucidate the effects of time, temperature, feedstock mixes, and other process considerations (water:biomass ratio, presteaming, counter-current processing) on mass removals and other extraction outcomes (e.g., sugar, acetate, and furan yields). Results demonstrated alignment of extraction outcomes with P-factor from 155 °C to 175 °C, with a good compromise of removed mass and co-product potential in the range from 575–800 P-factor. The preferred condition was chosen as 575 P-factor. HWE of mixes of willow and hardwood feedstocks showed a linear response of extraction outcomes to willow:hardwood ratios. Testing of water:biomass ratios demonstrated that this is a significant consideration, with each outcome being affected somewhat differently, and indicating that HWE is more diffusion dependent than expected. Presteaming shows little to no effect on extraction outcomes, while multi-stage cooks simulating counter-current operation indicate a significant potential value in counter-current extraction.

Highlights

The interest in replacing non-renewable chemicals and fuels with renewably sourced products has continued to grow over the past decade
1.2–1.5 billion tons of biomass could be available in the United States by 2040 to support the production of fuels, chemicals, and other products [1]
Willow biomass crop (WBC) feedstock was harvested and chipped as a whole-stem, bark-on material sourced from willow biomass crops at the State University of New York College of Environmental Science and Forestry (SUNY ESF) research station in Tully, New York State (NY), which included a mixture of cultivars

Summary

Introduction

The interest in replacing non-renewable chemicals and fuels with renewably sourced products has continued to grow over the past decade. Mg of this is expected to come from energy crops such as switchgrass, miscanthus, southern pine, hybrid poplar, and willow. Willow biomass crops (WBC), is of particular interest to the northeastern United States, being well adapted to the climate and soils, and managed using coppicing with short rotation times of 2–4 years. These biomass crops are highly productive, generating 4–16 Mg/ha/year of dry biomass [2]. This high productivity led the New York State Energy

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