Characterization of biochar derived from tapioca wastes
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Date
2014-08
Authors
Mohamed Noor, Nurhidayah
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Abstract
The main objective of this study is to investigate the impacts of various pyrolysis parameters
such as terminal temperature, heating rate, holding time and ash content of feedstock on the
biochar yield and its characteristics. The biochars were produced using tapioca stem and
tapioca rhizome feedstocks via laboratory scale slow pyrolysis process. The biochars were
characterized using the proximate analysis, ultimate analysis, Scanning Electron Microscope
(SEM) analysis and Brunauer, Emmett and Teller (BET) surface area analysis. Prior to the
experiment, the feedstocks have been characterized and it was found that both tapioca stem
and tapioca rhizome contained fairly high percentage of volatile matter and calorific values.
This indicated that both feedstocks are suitable to undergo the thermochemical process such
as slow pyrolysis. Both feedstocks were also found to be the environmental friendly
feedstocks as it contains low nitrogen and sulphur content. High lignin and cellulose contents
in both tapioca stem and tapioca rhizome indicated that the feedstocks were suitable for the
biochar production. The increment of pyrolysis terminal temperature had significantly
reduced the yield of tapioca stem biochar (TSB) and tapioca rhizome biochar (TRB). As the
terminal temperature increased from 400 °C to 650 °C, the yield of TSB had decrease from
35.86 mf wt. % to 25.79 mf wt. % while the yield of TRB decreased from 36.98 mf wt. % to
28.82 mf wt. % respectively. Biochar produced at higher terminal temperature had higher
fixed carbon content. As the pyrolysis terminal temperature rose from 400 °C to 650 °C, the
TSB produced increased in fixed carbon content from 78.39 mf wt. % to 87.88 mf wt. %
while the fixed carbon content of TRB increased from 79.20 mf wt. % to 84.46 mf wt. %.
The increment of terminal temperature from 400 °C to 600 °C had increase the surface area
of TSB from 0.83 m2/g to 36.12 m2/g and the surface area of TRB also increased from
0.24 m2/g to 12.29 m2/g. The heating rate parameter did not give pronounced effect on the
biochar yield and its composition. However, higher heating rate developed more pores on the
surface of TSB and TRB thus increased its surface areas. The TSB produced at a heating rate
of 25 °C/min had the surface area of 10.58 m2/g, which is 12 times larger than the
surface area of the TSB produced at a heating rate of 5 °C/min. The surface area of TRB
produced at a heating rate of 25 °C/min was found to be 10.98 m2/g, which is 45 times larger
than the surface area of TRB produced at a heating rate of 5 °C/min. The yield of TSB and
TRB decreased as the holding time of pyrolysis was increased. As the holding time was
prolonged from 1.0 hours to 3.5 hours, the yield of TSB reduced from 35.86 mf wt. % to
33.27 mf wt. % while the yield of TRB also reduced from 36.98 mf wt. % to 32.23 mf wt. %.
The increment of holding time from 1.0 hours to 3.5 hours had increase the fixed carbon
content of TSB from 78.39 mf wt. % to 81.88 mf wt. % and increased the fixed carbon
content of TRB from 79.20 mf wt. % to 83.29 mf wt. %. The effect of holding time on the
surface morphology of biochar was more apparent on the TRB compared to the TSB. The
increment of holding time from 1.0 hours to 3.0 hours increased the surface area of TSB and
TRB by 5 times and 29 times respectively. The water washing pre-treatments reduced the
ash content of the tapioca rhizome feedstock from 7.28 mf wt. % to 2.24 mf wt. %. The
effect of ash content of the tapioca rhizome feedstock was not apparent on the characteristics
of the biochar produced, but feedstock with lower ash content was found to decrease the
biochar yield. The reduction of ash content of the tapioca rhizome feedstock from 7.28 mf wt. % to 2.24 mf wt. % decreased the biochar yield from 36.98 mf wt. % to 31.83 mf wt. %.
Description
Keywords
Tapioca Wastes