Biochar, a carbon-rich and a potential solid biofuel, is produced during the liquefaction of
biomass. Biochar can be combusted for heat and power, gasified, activated for adsorption
applications, or applied to soils as a soil amendment and carbon sequestration agent. It is very
important and advantageous to produce biochar under controlled conditions so that most of the
carbon is converted. The main objective of the study was to investigate the effect of solvents,
reaction temperature and reaction atmosphere on biochar production during the liquefaction of
sunflower husks.
The liquefaction of sunflower husks was initially investigated in the presence of different
solvents (water, methanol, ethanol, iso-propanol and n-butanol) to study the effect of solvents on
biochar yields. The experiments were carried out in an SS316 stainless steel high pressure
autoclave at 280°C, 30 wt.% biomass loading in a solvent and starting pressure of 10 bar.
Secondly, sunflower husks were liquefied at various temperatures (240-320°C) to assess the
influence of reaction temperature on the biochar yield. Experiments were carried out under either
a carbon dioxide or nitrogen atmosphere with a residence time of 30 minutes.
Biochar samples obtained from sunflower husk liquefaction were structurally characterised by
scanning electron microscopy (SEM) and Brunauer-Emmet-Teller (BET) analysis to compare
surface morphological changes and pore structural changes at different reaction temperatures.
Compositional analysis was done on sunflower husk biochar samples by proximate analysis,
Fourier-transform infrared (FT-IR) spectroscopy, X-ray diffraction (XRD) and Elemental
analysis.
The results showed that biochar produced through the liquefaction of sunflower husks was
significantly affected by the type of solvent used. The highest biochar yields were obtained when
ethanol was used (57.35 wt. %) and the lowest yields were obtained when n-butanol was used as
a solvent (41.5 wt. %). A temperature of 240°C was found to produce the highest biochar yield
(64 wt. %). However, biochar yields decreased with increasing liquefaction temperature and the
lowest yield was 41wt. % at 320°C. Temperature had the most significant influence on biochar yield in an N₂ atmosphere, while solvent choice had the most significant influence on biochar yield in a CO₂ atmosphere. Temperature also had an effect on the structure of biomass, as the SEM analysis shows the biochar became more porous with increasing temperature. Generally, results from the CO₂ adsorption analysis, suggested that CO₂ develops microporosity to a greater extent than N₂ reaction.
The results of sunflower husk compositional analysis show that sunflower husks contain a high lignin content (34.17 wt. %), of which the high lignin content in biomass is associated with high heating value and high solid yield product. Sunflower husks as waste product can be used to produce useful products such as biochar through liquefaction, and biochar can be used to generate heat and as a soil amendment due to its high heating value and high porosity. While these preliminary studies appear promising for the conversion of sunflower husks to biochar, further studies are needed. / MSc (Engineering Sciences in Chemical Engineering), North-West University, Potchefstroom Campus, 2014
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:nwu/oai:dspace.nwu.ac.za:10394/11942 |
| Date | January 2014 |
| Creators | Piyo, Nontembiso |
| Source Sets | South African National ETD Portal |
| Language | English |
| Detected Language | English |
| Type | Thesis |
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