(640a) Effects of Warm Water Washing on the Fast Pyrolysis of Arundo Donax

D.S. Chandler, F.L.P. Resende

Arundo donax, also known as Giant Reed, is a fast growing herbaceous reed native to India, but pervasive throughout the tropics and subtropics. It grows faster than bamboo, miscanthus and switchgrass at a rate of 30 dry tons/acre/year [1]. The fresh water requirements of A. donax are much lower than those of many other potential bio-energy crops. Moreover, fast pyrolysis of an herbaceous weed such as A. donax can mitigate problems such as agricultural displacement associated with the use of other forms of biomass [2].

A major hurdle in fast pyrolysis of herbaceous biomass is its high inorganic content, specifically the very high content of alkali salts. The problems associated with pyrolysis of materials that contain inorganics are cracking of volatiles, char formation, and catalyst poisoning [3–7]. Many of these inorganic compounds act as unintended catalysts that crack the volatile pyrolysis products into smaller compounds, mainly permanent gases like CO₂, CO, and CH₄. They also promote the formation of char, though it is unclear if this takes place by increasing the rates of condensation reactions or by reducing the heat transfer rate to the particles [4,5,8].

In this talk, we will report how warm water washing of biomass affects fast pyrolysis. Specifically, we applied this concept to Arundo donax, a common herbaceous biomass, and studied the washing effects on fast pyrolysis yields in a Py-GC/MS and a fluidized bed reactor. We stir-washed samples in water at 20°C, 40°C and 60°C, and found that water at 60°C led to an 18% increase in the removal of ash and an 11% increase in the removal of potassium compared to a room temperature wash. We pyrolyzed these samples via Py-GC/MS-FID and found that the reduction in ash increased the pyrolysis yields of acetol, furanone and levoglucosan relative to the unwashed samples. Additionally, we pyrolyzed washed A. donax in a fluidized bed reactor and compared the results to those of unwashed A. donax. We found that A. donax washed at 60°C produced 9.7 wt% more bio-oil than unwashed, with increases in glycolaldehyde and levoglucosan yields of 0.78 wt% and 1.24 wt%, respectively. The yield of olefinic gases increased by 0.22 wt% and yields of carbon dioxide and alkane gases decreased 2.40 wt% and 0.11 wt% respectively. Char and water yields decreased 4.32 wt% and 10.08 wt% respectively. The gas produced from pyrolysis of washed A. donax has a greater HHV than that from unwashed A. donax (7.77 MJ/kg vs. 6.81 MJ/kg). We believe these results are a consequence of differences in the extent of secondary reactions catalyzed by the inorganic species present in herbaceous biomass.

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