SORPTION ENHANCED CATALYTIC PYROLYSIS OF RICE HUSK USING HIERARCHICAL ZSM-5 CATALYST
SORPTION ENHANCED CATALYTIC PYROLYSIS OF RICE HUSK USING HIERARCHICAL ZSM-5 CATALYST
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Date
2021-04
Authors
ADAMU, Sulaiman Yahaha
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Abstract
The necessity to source clean energy and contain CO2 emissions has brought about a global interest in
the use of biomass as an environmental friendly renewable energy route. One of the drawbacks in the
conversion of biomass to energy via pyrolysis/gasification is the liberation of CO2 from the syngas.This
study was carried out in a two- stage catalytic process using rice husk as feed, ZSM-5 catalysts for
cracking and reforming of the pyrolysis volatiles and calcineddolomite as CO2 capture material
(sorbent).The catalyst include commercial ZSM-5, hierarchical ZSM-5 which was prepared by
desilication method using 0.2 mol/dm3 NaOH, and 2 wt.% Zn-wt.%and hierarchical ZSM-5 which was
prepared by doping metal on the hierarchical ZSM-5 through wetness impregnation.Calcineddolomite
was prepared by size reduction and calcination of the dolomite precursor.Sorbent and catalysts were
characterized using XRD, FTIR, BET and TGA techniques. The XRD results of the catalysts
indicatedthat the crystalline zeolite structure of HZSM-5 was maintained after alkali treatment and
metal modification with slight reduction in intensities of some noticeable peaks as a result of
desilication. The structure stability confirmed with XRD was supported with the FTIR resultswhich
showed no loss in major functional groups of the HZSM-5 such as the Bands observed at 450 cm-1
represents the T-O-T bending vibration (T=Si or Al) and 550 cm-1 which represents the five membered
ring pentasil unit of ZSM-5. At 790 and 1225 cm-1 which represents the external symmetric and
asymmetric stretching of the Si-O-Si bond Although on critical examination of the band at 1100 cm-1
which signifies internal tetrahedral bridged Si-OH-Al vibrations in the asymmetric regionit appears that
the peak has broadened on alkaline treatment of the catalyst, as compared to the shaper peak of the
parent HZSM-5, while the band at 1100 cm-1 signifies internal tetrahedral bridged Si-OH-Al vibrations
in the asymmetric region.TGA affirmed the thermal stability of the catalyst with a total percentage
weight loss of less than 6% and a notable thermal change at 4000C for parent, hierarchical and Zn-Ni/
hierarchical catalyst. The BETresults showed an increase in surface mesopores from 111 m2 /g in the
parent ZSM-5 catalyst to
141 m2 /g and 136 m2 /g in the hierarchical and metal treated hierarchal catalyst respectively.There was
also an increase in the volume mesopores and average pore width. These increase was observed after
desilication, this is to say there was successful introduction of mesopores into the system hence
converting the catalyst to a hierarchical catalyst.Introduction of calcineddolomite into the reformer
displayed a reduction of CO2 andCO with a surge in H2 liberated. Upon loading of fractions of
hierarchical catalyst to calcineddolomite, it was observed that there was an increase in the generation of
non-condensable volatiles with the highest amount of gases produced at 3.0 g hierarchical ZSM-5
catalyst in ratio to 7.0 g calcineddolomite. However, the best in terms of CO2 capture and H2 was noted
at 1.5g hierarchical ZSM-5 catalyst in ratio to 8.5g calcineddolomite which gave a high amount of H2
and traces of CO2 with an average of 72 wt. % (vol) and 4wt. %(vol) respectively. Hierarchical catalyst
incorporated with metal promoter (2 wt. %Zn- 2 wt. %Ni hierarchical ZSM-5) displayed improved
H2yields at the expense of other syngas produced as compared to the hierarchical ZSM-5 and
commercial ZSM-5 at similar catalyst to calcineddolomite ratios (1.5g: 8.5g).Increase in loading of
hierarchical ZSM5 also led to changes in the composition of the condensates. The FTIR as well as the
GC-MS results showed an increase in the aromatic compounds and a decrease in the aliphatic and
oxygenated compounds for the catalytic pyrolysis. The GC-MS results confirmed that, hierarchical
catalyst showed selectivity towards aconversion of condensates to mostly BTX compounds. Aromatic
hydrocarbons composition increased to about 71% of the reformed condensates when Zn/Ni -
hierarchical ZSM-5 was used as compared to 61% for hierarchical ZSM-5 and 58% for the parent ZSM-5.
Description
A DISSERTATION SUBMITTED TO THE SCHOOL OF POSTGRADUATE STUDIES
AHMADU BELLO UNIVERSITY IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR
THE AWARD OF MASTER OF SCIENCE DEGREE IN CHEMICAL ENGINEERING
DEPARTMENT OF CHEMICAL ENGINEERING,
FACULTY OF ENGINEERING,
AHMADU BELLO UNIVERSITY,
ZARIA, NIGERIA
Keywords
SORPTION ENHANCED CATALYTIC PYROLYSIS,, RICE HUSK,, HIERARCHICAL ZSM-5 CATALYST.