ABSTRACT

Hydrothermal liquefaction (HTL) is an important thermochemical technology which uses hot pressurized water to convert wet biomass or biowaste feedstocks into biocrude oils and other marketable bio-chemicals. The presence of hot pressurized water, aggressive catalyst, and organic products can lead to serious corrosion damage and even stress corrosion cracking risk on the HTL reactors. Up to now, very limited information is available about the corrosion of HTL reactor alloys under HTL processes. In this study, the corrosion of a candidate constructional steel (UNS S31000) was investigated under the batch-mode HTL conversion of different biomass feedstocks, including bamboo (a typical lignocellulosic biomass) and black liquor (a common industrial biowaste). The bio-oil produced from black liquor had higher contents of organic acids and phenols compared to that converted from bamboo. The corrosion rate of the steel in the HTL of black liquor was about twenty-five times higher than that in the HTL of bamboo. The corrosion layer formed in the HTL of black liquor is spalling.

INTRODUCTION

Over the past decade, serious environmental concerns induced by fossil fuel production/combustion and increasing daily demand on energy supply have stimulated intensive research to develop reliable and sustainable energy supply and production technologies. Among the identified alternatives, raw biomass materials, such as food residues, energy crops, agricultural residues, and waste from industry, farms and households, have been widely recognized as one of the most promising resources due to their environmental-friendly and renewable nature. It is estimated that the annual global primary production of biomass can be equivalent to the 4,500 EJ of solar energy captured per year.1 More attractively, abundant industrial and municipal biowastes can also be directly and quickly transformed into green bioenergy products via biochemical and thermochemical processes. Compared with the biochemical method, the thermochemical pathways are more efficient than biochemical processes in terms of process retention time and the ability to decompose the biomass fractions.2

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