Upgrading of Biomass Pyrolysis Oil by Low Temperature Plasma (LTP) Processing

An output from Dr Yang’s (Aston University) mobility award.

Dr Yang Yang

European Bioenergy Research Institute, Aston University


1. Introduction

Biomass pyrolysis oil is a promising renewable liquid that has a strong potential to substitute fossil fuels. However, some of its characteristics do not satisfy the engine fuel requirement, such as high contents of oxygen element and heavy organic fractions. Hydrodeoxygenation (HDO) has been a useful upgrading method, but conventional HDO process is exorbitant due to the use of hydrogen gas and catalysts under high pressure. Using LTP for upgrading pyrolysis liquid is an exciting new concept. LTP can be operated under ambient temperature and pressure and it can create a HDO environment for pyrolysis oil with a high energy efficiency. Moreover, no hydrogen gas is needed in plasma promoted HDO upgrading; as hydrogen can be simultaneously produced from the methoxyl and methyl radicals (existing in the chemical structure of the pyrolysis oil components) in the LTP environment.

This Researcher Mobility Award enabled researchers of two important Hub partner institutions- Aston University (Dr Yang Yang) and University of Liverpool (Dr Xin Tu) – to establish a new collaboration on the upgrading of biomass pyrolysis liquids by using advanced low temperature plasma (LTP) technology at ambient conditions.


2. Research and Achievement

Under this project, two PhD students (Mr Yichen Ma and Mr. Yaolin Wang) from Dr Xin Tu’s group at University of Liverpool spent a whole day at Aston University’s European Bioenergy Research Institute (EBRI) to undertake training on the thermal conversion of biomass (Figure 1). Dr Scott Banks and Dr Yang Yang of Aston explained the fundamentals about the thermal conversion technologies and characteristics of feedstock and products to the visitors, and they also demonstrated an experiment on slow pyrolysis of straw residue in an auger screw reactor for the production of pyrolysis oil, gas and char. The visitors were also shown around EBRI’s analytical and catalysis laboratories to see the comprehensive biofuels analysis and characterisation equipment.

Following the visit from Liverpool, Dr Yang Yang and Dr Jiawei Wang also visited Dr Xin Tu’s laboratory at University of Liverpool and carried out a set of experiments on LTP upgrading of straw residue derived pyrolysis oils. To study the effect of different processing conditions on the oil upgrading, the experiments were conducted under a range of different LTP processing power rates and times. All the liquid samples were examined by using a GC-MS for compositional analysis. The preliminary results showed that treating oils at 30 watt for a short period (3 minutes) can effectively convert the heavy organic compounds into smaller molecules, such as Anisole (see the gas chromatograms in Figure 2). The preliminary results were highly promising towards upgrading the pyrolysis oil by LTP processing, although further systematic research needs to be conducted. In the next step, the pyrolysis oil will be blended with organic solvents, such as methanol and acetone, which can provide enhanced hydrogen source for HDO upgrading. Heterogeneous metal based catalysts, such as MoO and NiO, will be also incorporated in the upgrading to promote the chemical conversion. The option for the direct integration of the pyrolysis reactor and LTP reactor for hot vapour cracking was also discussed by the project partners. Dr Yang has been working on the design of the joint and heating means for coupling.


3. Conclusions

This project enabled the bioenergy researchers from both institutes to develop their research capabilities by learning new knowledge and gaining experience in working on different thermal processing and product upgrading technologies. In addition, the preliminary results have shown a great opportunity in developing this cost-effective means for upgrading the liquid product from biomass pyrolysis. Upon completion of this project, the project partners will seek internal funding to maintain the collaboration and continue this research towards a publishable work. The partners will also prepare a more in-depth and comprehensive programme and big for a larger research grant from ESPRC or European Commission in early next year (subject to the status of the follow on research and calls for resaerch funding opportunity).


Figure 1. Visits and research carried out under the Researcher Mobility Award

(1) PhD students from Dr Xin Tu’s group (Mr Yichen Ma and Mr. Yaolin Wang) visited Aston University to carry out biomass slow pyrolysis experiment. (2) Pyrolysis bio-oil sample collected in the experiment. (3) Plasma upgrading of pyrolysis bio-oil. (4) Dr Yang Yang and visited Dr Xin Tu in Liverpool to carry out plasma upgrading experiment


Figure 2. Gas chromatograms of the original and LTP treated pyrolysis oil samples. (1) LTP treated oil 30 watt for 20 minutes. (2) LTP treated oil 30 watt for 3 minutes. (3) Original oil. (The chromatogram peaks 1, 2, 3 and 5 represent large organic molecule C19H28, C18H24O, C18H22O, and C20H28O; 6 represents Anisole C7H8O. It can be clearly seen that the heavy organics peaks 1-5 disappeared in (1) and (2) and there is an increase of peak 6).

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