| Summary: | 博士 === 國立中央大學 === 化學工程學系 === 86 === A highly pure mixture of carbon and silica was obtained on
pyrolysis rice husk leached with acid at high temperature in a
nonoxidizing atmosphere. The product was suitable for use as a
stsrting material in the manufacture of ceramic material.The
effect of acid sources, acid concentration and leaching time on
the impurities contents in rice husk were studied in acid
leaching operation. In the rice husk pyrolysis part,there were
performed the effect of pyrolysis time, pyrolysis temperatureand
gas flow rate on the weight remaining of rice husk. Kinetic
tests on pyrolysis of rice husk in a nitrogen atmosphere were
carried out with athermal gravimetric analysis(TGA) techingue at
every kind of heatingrates. The results show that hydrochloric
acid is superior to other acid for acid leaching. The higher
concentration of acid is used, theimpurities is decreased, but,
when the concentration is above 3N thes effect is less marked.
When the concentration of acid is 3N, the effectiveness of acid
leaching is not affected with time.In the range of 573K to 873K,
there is amarked change for the weight remaining after
pyrolysis. It is sure in thisstudy that rice husk reached a
essentially constant weight after two hoursof pyrolysis at 77K.
Variation of the pyrolysis temperature between 873Kand 1173K has
no effect on the weight remaining. At lower temperature(573~873
K), there is more solid residue remaining with nitrogen
flowingthan without nitrogen during the pyrolysis processes,
however, the effect is not appreciable when the pyrolysis
temperature is higier than 873K. Thermogravimetric analysis was
used to measure the rate of pyrolysisof rice husk in nitrogen at
various heating rates. A two stahe pyrolysismechanism is
proposed to account for possible thermal decomposition.
Themechanism comprises depolymerization of orhanic materials
(cellulosesand lignin) to yield gaseous volatiles and
intermediates ; then theseintermediates further decompose to
yield other volatiles and char. Theaverage activation energise
and order of reaction in the first stahe are 143,205kJ/mol and
1,1 respectively; The average activation energies and order of
reaction in the second clear proof that the pyrolyzed husk is
suitableto produce highly pure the benefit not only to pyoduce
valuable materials,such as Si3N4,SiCl4,SiC, and Si,but also to
solve problems of disposaland pollution created during burning
of rcie husk.
|
|---|
