A Barley Straw based Bio-refinery

The individual components of a biorefinery concept based on a ligno-cellulose biomass such as straw have been studied but a complete technical, economic and environmental analysis of such an integrated process is lacking. A detailed analysis on barley wax was performed as a part of the experiment. In addition to further research in wax, the aim of this project is to study the difference, also improvement made, when utilising wax extracted and un-extracted straw on thermal pyrolysis products. The composition of bio-oil char and biogas as pyrolysis products were also studied and the reproducibility of bio-oil using different microwave machines were investigated. The effect on product yield and composition when changing pyrolysis reaction temperature was also tested. The green chemistry metrics was applied to the whole process to measure the environmental impact of the experiment.

Wax was extracted from various kinds of barley straws by different methods and its chemical compositions were analysed using GC-MS and GC. The result indicated that components in the extracted wax can be grouped into several categories: fatty acids was the most dominating group in wax (32.5%), followed by fatty alcohols (14.6%), 14,16-hentriacontanedione (11.3%) and β-diketones (8.6%). When comparing to previous supercritical carbon dioxide (SC-CO2) extraction results of other straws, barley wax has the highest yield. The yield from different variety barley straw also varies; Carat barley has a slightly higher yield than Saffron barley.

Previous studies show that wheat straw wax comprises a similar blend of compounds found in ladybird footprints (trace of material found on the path of the insect), which is the aphid’s natural enemy and could cause the aphid avoidance.1 In order to test whether other straw wax contains the similar semiochemicals and causes the same effect, previous column chromatography extracted wheat straw, barley straw, and apple peel wax was characterised by GC-MS and GC; and the research was particularly focused in branched and long chain alkane regions. The analysis showed wax extracts all contain similar long-chain and branched-chain components, which may also induce aphid avoidance.

Pyrolysis was applied on both raw and de-waxed straw to produce bio-oil, char and bio-gas. The difference in bio-oil produced using raw and de-waxed straw was mainly caused by wax. Through analysis, bio-oil was identified mainly containing aromatic compounds, where the high content compound in it was (acetyloxy)-acetic acid (7.0%), 3-methyl-1,2-cyclopentanedione(5.2%) and 2,6-dimethoxyphenol(4.6%). Bio-oil’s reproducibility was tested on an additional CEM microwave machine. When increasing the pyrolysis temperature, bio-oil yield was slightly increased while char yield was dramatically decreased. However the temperature impact on char was disappeared when reaction reached to 140°C and above.

Char and bio-gas were analysed by FTIR. From the spectra, the decrease intensity of char compared to straw was obvious and caused by decomposing of the chemical groups (e.g. phenolic groups, C-O group) during pyrolysis. The high concentrated peak in bio-gas spectrum was caused by the CO2; other peaks were due to the exultance of CO, CO2, CH4, C2H4 and C2H6.

The environmental impact of both wax extraction and pyrolysis were investigated by performing calculation of their E-factors. The results showed that although the processes were generally environmental benign, there were great potential for improvements, such as employ solvent recycling and broaden products applications.