ABSTRACT
The application of potassium hydroxide (KOH) extracts from four different biomass materials: Water hyacinth, Coconut husk, ripe plantain peels and palm frond in the trans-esterification of two vegetable oils; refined rapeseed and crude jatropha oils has been carried out. Potassium hydroxide
obtained from the ash of ripe plantain peels recorded the highest
biodiesel conversion with both vegetable oils. The highest percentage
conversion obtained with rapeseed oil was 71.01% using 1g of KOH
extract from ripe plantain ash at reaction temperature and time of 75oC
and 4 hours respectively. Under the same reaction conditions, 1g of
commercial caustic potash recorded 70.06% conversion of the rapeseed
oil at the same reaction conditions. From the optimized batch process,
97.15% conversion was achieved with crude jatropha oil using 1g caustic
potash extract from ripe plantain peels ash; at reaction temperature
and time of 83oC and 4 hours respectively. Under the same condition,
the conversions of the oils to biodiesel using KOH from coconut husk,
palm fronds and water hyacinth recorded low values of; 53.11%,
46.88% and 33.31% respectively. Generally, the percentage conversion
increased with both time and temperature of trans-esterification of the
vegetable oils using potassium hydroxide extracted from the ash of the
agricultural waste materials. Using KOH from ripe plantain peels, the
conversion increased from 75.20% at 83oC and 1 hour to 97.15% at 83oC
and 4 hours while the conversion increased from 35.18% at 75oC and 1
hour to 95.73% at 75oC and 4 hours. The Potash content recorded per g
of the biomass materials investigated was: palm fronds (13.9%),
coconut
husk (17.5%) water hyacinth (18.9%), and ripe plantain peels (40.1%).
These respective amounts represent the total recoverable KOH from the
optimized extraction process of the ashes of the four biomass materials,
at well defined extraction temperatures of 30 - 50oC and varied
times of 1-6 hours as against 100oC
(boiling water) and 24 hours employed in the traditional
extraction method. The cumulative weights of KOH obtained per g of
ash at the different temperatures and times, increased progressively
with water volume for the 1st and 2nd stages of extraction (100ml/200ml,
150ml/300ml and 200ml/400ml). The effectiveness in using 400ml water in
two equal portions in the two stages of KOH extraction was about 9.3%
better on the average than using the least volume of 200ml under the
same conditions. To attain optimized extraction; 5-10 times the weight
of ash is required in water for a given biomass ash extraction on a two-
stage basis.
