Abstract

Biomass derived pyrolysis oil is a promising renewable energy source. Due to the variety of biomass feedstocks, the bio-oils could contain a wide range of organic constituents which would provide unique corrosive environments for structural materials. A preliminary work exposed different classes of steels and stainless steels to selected organic constituents of biomass pyrolysis oils and found that corrosion susceptibility, assessed using electrochemical impedance spectroscopy (EIS), was prominent in the steels with Cr lower than 11 wt.%. Although this result suggests stainless steels will resist corrosion by certain organic constituents, it may not be sufficient to predict the corrosion performance in real bio-oils. Therefore, this study attempted electrochemical measurements on Cr-alloyed steels and stainless steels directly exposed to a biomass derived pyrolysis oil. To overcome the low conductivity of bio-oils, a customized Luggin capillary was designed to minimize the ohmic path in bio-oils. The results of this work will be reported.

Introduction

Biomass-derived pyrolysis oil, or simply bio-oil, is a renewable energy source that could substitute for fossil derived fuel. One concern for bio-oils is their potential corrosivity attributed to the water and organic acid contents.1-5 Therefore, the corrosion compatibility of structural steels used to transport, and store bio-oils should be investigated to avoid any maintenance issue or failure caused by corrosion. Previous studies reported that raw bio-oil exposure tests caused significant mass loss of plain steels but minimal or no loss in different grades of stainless steels.6,7

While the mass loss measurement allows direct and quantitative comparison of alloy corrosion resistance, it usually involves long exposure times. To determine the corrosion resistance for various ferrous alloys in shorter time, electrochemical impedance spectroscopy (EIS) was attempted using selected constituents of bio-oils.8-10 These works clearly distinguished corrosion susceptibility of low Cr steel from high corrosion resistance of stainless steels in three aggressive bio-oil constituents by comparing the resistance elements determined from the impedance spectra. However, the results obtained from the previous work are not sufficient to assess the corrosivity of bio-oils that have more complex compositions. In present work, EIS measurements were conducted on the alloys immersed in a bio-oil with a customized electrochemical cell to minimize the ohmic drop due to the low conductivity of the bio-oil. Per author’s best knowledge, this is the first reported attempt to electrochemically assess the corrosion behavior of structural steels in a real bio-oil. Similarly, another work presented by the authors for this conference also assessed corrosion behavior of Cr-Mo alloyed steels in real bio-oils.11

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