(122d) Effective Gasoline Production Strategies for the Catalytic Cracking of a Rapeseed Vegetable Oil Under Realistic FCC Conditions

Our heavily dependence on the finite fossil fuel resources forced
many counties to look at the possibilities for other alternatives, especially
renewable energy sources, to meet the sustainable future energy and
transportation fuel supply and demand. Of the many available sources,
converting the raw materials from the biomass (e.g., vegetable oils) in the
existing equipments (e.g., fluid catalytic cracking (FCC) process) into valuable
transportation fuels and light olefins would be a very attractive option.

            Most of the studies available on the catalytic cracking
of vegetable oils have been carried out in a fixed bed micro-activity (MAT)
reactor, which does not have the hydrodynamics of a commercial unit. Dupain et
al. [1] have, however, studied the thermal and catalytic cracking of a rapeseed
oil in an isothermal plug flow microriser reactor, which mimics the actual
riser unit very well and in addition to that it has the ability to operate at
various contact times and catalyst-to-oil (CTO) ratios. Despite the differences
in the reactors, the catalytic cracking of vegetable oils resulted in very large
amounts of aromatics in the liquid fuel product in both the gasoline and diesel
product slate. The aromatic formation depends, however, on the degree of
unsaturation (presence of double bonds) of vegetable oils; the higher the
unsaturation, the higher the aromatic content in the fuel. Furthermore, the LCO
(diesel blending component) and gasoline yields were also found to depend on
the degree of unsaturation: saturated vegetable oils result in more gasoline
selectivity and yield, while unsaturated ones give more LCO selectivity and
yield [1]. The thermodynamic is favorable for aromatization under the FCC
operation conditions (high temperature and low pressures). Additionally, the
oxygen of the triglycerides is removed mainly in the form of water [1], though
carbon oxides (CO_x) formation is also possible, but is observed to
minor extent [1]. The above observations clearly emphasize that there is a need
to improve the process in terms of reducing the aromatic content of the liquid
fuel product to the gasoline product distribution and also removing the oxygen
at the same time. Thus, the present study aims to design a process that can
overcome the above problems associated with vegetable oils, especially,
unsaturated oils.

            The main strategy to address the above issue is
considering an option of co-processing H₂ into the system that may
help removing water and/or saturating the double bonds present in the system.
However, H₂ alone is not expected to serve the purpose under
realistic FCC conditions (near atmospheric pressure). This means we need to
have a catalyst that can make H₂ to function in an efficient way
under such conditions. To achieve this, the catalysts that can have a control
over the rate of dehydrogenation activity, would be ideal because this would consequently
reduce the aromatic formation as well. Thus, in this study, we have chosen some
metals such as nickel (Ni) and platinum (Pt) along with H₂
co-feeding into the system to understand the their presence on the aromatic formation
and also on the liquid product yields.

            For this study, both the same commercial equilibrium
catalyst (Ecat) and vegetable oil were used [1]. Initially, the incorporation
of Ni and Pt onto the commercial equilibrium catalyst (Ecat) is achieved by the
incipient wetness impregnation method and calcined at 600 °C. The catalysts are
not reduced in H₂ atmosphere before testing. Therefore, the Ni and
Pt are essentially in their oxide form since this same oxidation state as the
FCC catalyst enters the riser reactor from the regenerator. The Ni and Pt
loadings used are 1 and 0.25 wt%, respectively. The reactions are performed in
the microriser reactor at a temperature of 525 °C and CTO ratio of ~5. The
details of the microriser are given elsewhere [1]. The base Ecat and other
metal-containing Ecats are tested for the cracking of a rapeseed oil with and
without co-feeding H₂ into the system. The liquids products are
analyzed by SIMDIS gas chromatograph (GC), while the gas by the standard GC.
The coke on the spent catalysts is measured by LECO analyzer. The aromatic
content was determined by standard HPLC analysis.

             The results clearly demonstrated that the H₂
presence indeed helps in improving the gasoline yield on both the E-cat and
Ni-Ecat systems. This means H₂ alone (no metal on Ecat) some
beneficial effects on the product yields. Similarly, Ni alone (no H₂
co-feeding) also resulted in improved gasoline yields. On the other hand, the
Ni-Ecat system in the presence of H₂ showed a remarkable activity
for improving both the gasoline yield (by 10 wt%) and reducing the aromatic
content of the gasoline fraction by 15 % and in fact the total aromatics by 17
%. On the other hand, Pt has not improved the process, and rather reduced the
liquid product yield compared to that of the base Ecat. The coke yield for the
Pt-Ecat is much higher than that for the Ecat and Ni-Ecat.

            In summary, the enhancement of gasoline yield and the
reduction of aromatic content of the liquid fuel products by the cracking of (unsaturated)
vegetable oils, a renewable feedstock can be improved substantially by
co-feeding H₂ along with the incorporation of metal functionality.
These results certainly would  trigger many people interests in the refining
catalysis field to focus more on the rational catalyst design to improve the
catalytic cracking performance of vegetable oils.

Reference:  

1. X. Dupain,
D.J. Costa, C.J. Schaverein, M. Makkee, J.A. Moulijn, Appl. Catal. B: Env. 72
(2007) 44.