Review of biomass pyrolysis oil properties and upgrading research

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Abstract

Biomass fast pyrolysis liquefaction has aroused great attention and interests both at home and abroad extensively in recent years. This paper reviews the physicochemical properties and discusses the characteristics of the components and compositions of biomass pyrolysis oil. Furthermore, the problems and focuses were summarized with some suggestions presented on upgrading and applications of bio-oil in the decades.

Introduction

Considering the fact that energy consumption is increasing and limited fossil fuels are nearly exhausted, with increasing populations and economic developments, renewable energy should be widely explored in order to renovate the energy sources structure and keep sustainable development safe. Biomass is clean for it has negligible content of sulphur, nitrogen and ash, which give lower emissions of SO2, NOx and soot than conventional fossil fuels. Zero net emission of CO2 can be achieved because CO2 released from biomass will be recycled into the plants by photosynthesis quantitatively. The energy crisis and fuel tension made biomass fast pyrolysis liquefaction a more important area of research and development [1], [2], [3]. Pyrolysis has been supported with the highest amount of funds provided by the European Union for liquid bio-fuel technologies [4]. Bio-oil from biomass fast pyrolysis is mainly produced from biomass residues in the absence of air at atmospheric pressure, a low temperature (450–550 °C), high heating rate (103–104 K/s) and short gas residence time to crack into short chain molecules and be cooled to liquid rapidly. Fast pyrolysis, an effective biomass conversion with high liquid yield, as much as 70–80% and a high ratio of fuel to feed, is regarded as one of the reasonable and promising technologies to compete with and eventually replace non-renewable fossil fuel resources [5]. Recent research on the physicochemical properties of biomass pyrolysis oil was reviewed and some recommendations were put forward based on the upgrading status and application demands for future improvements.

Section snippets

Bio-oil

The liquid product from biomass pyrolysis is known as biomass pyrolysis oil, and bio-oil, pyrolysis oil, or bio-crude for short. Bio-oil is not a product of thermodynamic equilibrium during pyrolysis but is produced with short reactor times and rapid cooling or quenching from the pyrolysis temperatures. This produces a condensate that is also not at thermodynamic equilibrium at storage temperatures. The chemical composition of the bio-oil tends to change toward thermodynamic equilibrium during

Upgrading of bio-oil

The deleterious properties of high viscosity, thermal instability and corrosiveness present many obstacles to the substitution of fossil derived fuels by bio-oils. So, an upgrading process by reducing the oxygen content is required before its application. The recent upgrading techniques are described as follows.

Conclusions and recommendations for future work

Bio-oils have received extensive recognition from international energy organizations around the world for their characteristics as fuels used in combustors, engines or gas turbines and resources in chemical industries. Some problems blocking its industrialization processes and recommendations are described as follows:

  • Since bio-oils are complex and chemically unstable mixtures, biomass fast pyrolysis should corresponded with the characteristics of the biomass feedstocks, products uses, suitable

Acknowledgements

The supports from National natural science foundation of China (50476090) and Guangdong natural science foundation (04000378) are greatly appreciated.

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