Isobutanol
derived from biomass can serve as a potential renewable
candidate for the production of light olefins and aromatics, which
are the building blocks to manufacture fuels and chemicals in the
petrochemical industry. Dependent upon the product requirements, the
product selectivity toward olefins or aromatics can be tuned by adjusting
the reaction conditions and the properties of HZSM-5 catalysts. On
bare HZSM-5, mild conditions (low temperature, low space time, and
low acidity) favored the production of olefins and harsh conditions
(high temperature, high space time, and high acidity) were more likely
to produce aromatics. Ga was impregnated onto HZSM-5 to enhance the
production of aromatics. Unexpectedly, Ga introduction only induced
the intertransformation between olefins and aromatics without significantly
impacting the selectivity of low-value paraffins. The exchanged Ga
sites functioning together with Brønsted acid were identified
as active Ga species and strengthened the direct dehydrogenation of
C6–C8 olefins. The in situ-generated water from isobutanol dehydration affected the formation
of Ga species. This resulted in different promotional effects of Ga
on the transformation of isobutanol and isobutene. The reaction pathways
were developed on the basis of the catalyst evaluation results, in
tandem with an in situ diffuse reflectance infrared
Fourier transform spectroscopy study on the intermediates formed during
isobutanol transformation. Selectivity of olefins and aromatics from
isobutanol transformation can be tuned by adjusting reaction conditions
and properties of HZSM-5 catalysts.
In
the present study, wood biomass from Acacia mangium and its main components (hemicellulose (xylan), cellulose, and lignin)
were blended with a sub-bituminous coal in 20:80 wt % ratio and subsequently
were heat-treated at 900 °C using CO2 or N2 atmospheres. The reactivity (ignition temperature and activation
energy) under oxy-fuel conditions (21% O2–79% CO2) was studied by thermogravimetry (TGA). It has been observed
that adding biomass or its main components to coal improved the combustion
efficiency. Coal/biomass and coal/xylan/cellulose/lignin char blends
showed lower ignition temperatures when they were devolatilized using
CO2 instead of N2. In addition, the activation
energies were lower for blends thermally treated with CO2. Differences in reactivity are discussed considering changes in
physical-chemical properties characterized by SEM, N2 adsorption
at −196 °C, Raman spectroscopy, and XPS.
In the present study, 20 wt % K 2 CO 3 was added to coal and coal/biomass blends in 20:80 wt % ratio and subsequently were heating-treated at 600 °C using CO 2 or N 2 atmospheres.The reactivity under oxy-combustion conditions (21 % O 2 + 79 % CO 2 ) was studied by thermogravimetry, and characterization of chars was carried out by N 2 adsorption, scanning electron microscopy, Raman and X-ray photoelectron spectroscopy. It was observed higher activation energy for impregnated coal/biomass blends compared to impregnated coal, likewise, for materials thermally treated with CO 2 . It is demonstrated that CO 2 gasification takes place together with O 2 combustion under oxy-combustion conditions. Isotopic labelled 13 C 18 O 2 was used to confirm the participation of CO 2 gasification reactions at 450, 500, 550 and 600 ᵒ C in both catalyzed and uncatalyzed systems under O 2 + CO 2 . The catalytic effect of potassium promotes CO 2 gasification, and highest CO ( 12 C 18 O) desorption was obtained with impregnated samples. It is possible to suggest that CO 2 gasification reactions follow different reaction pathways in presence or absence of potassium. The catalytic gasification reaction proceeded preferentially through a molecular CO 2 ( 13 C 18 O 2 ) adsorption route while the non-catalyzed systems advanced using a dissociative adsorption pathway.
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