Hydroconversion of Methyl Laurate as a Model Compound
to Hydrocarbons on Bifunctional Ni<sub>2</sub>P/SAPO-11: Simultaneous
Comparison with the Performance of Ni/SAPO-11
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Abstract
The
bifunctional Ni<sub>2</sub>P/SAPO-11 was tested for the hydroconversion
(involving deoxygenation and hydroisomerization) of methyl laurate
as a model compound to hydrocarbons. The influences of reaction conditions,
catalyst stability, and catalyst deactivation were investigated. For
comparison, the performance of Ni/SAPO-11 was also examined. The result
shows that the increase of temperature and the deceases of weight
hourly space velocity (WHSV) and H<sub>2</sub> pressure favored the
conversion of methyl laurate meanwhile promoted the decarbonylation
and hydroisomerization as well as cracking reactions. Apart from the
Ni sites that were dominating for deoxygenation, the acid sites also
affected the deoxygenation pathway. Due to more medium strength acid
sites, Ni/SAPO-11 gave higher selectivity to isoalkanes and more preferentially
catalyzed the hydrodeoxygenation pathway to produce the C12 hydrocarbons
than Ni<sub>2</sub>P/SAPO-11. During the test for 101 h, Ni<sub>2</sub>P/SAPO-11 exhibited greatly superior stability to Ni/SAPO-11 for
the deoxygenation of methyl laurate, while both Ni<sub>2</sub>P/SAPO-11
and Ni/SAPO-11 were deactivated for the hydroisomerization. Under
the condition of 360 °C, 3.0 MPa, WHSV of 2 h<sup>–1</sup>, and H<sub>2</sub>/methyl laurate molar ratio of 25, the conversion
of methyl laurate was close to 100% and the total selectivity to isoundecane
and isododecane decreased from 36.9% to 28.6% on Ni<sub>2</sub>P/SAPO-11.
To explore the catalyst deactivation, the fresh and the used catalysts
were characterized by X-ray diffraction, transmission electron microscopy,
scanning electron microscopy, thermogravimetric analysis, Raman spectroscopy,
and N<sub>2</sub> adsorption–desorption. The sintering of Ni
particles and carbonaceous deposit contribute to inferior stability
of Ni/SAPO-11 for both deoxygenation and hydroisomerization, while
no obvious sintering of Ni<sub>2</sub>P particles took place and the
carbonaceous deposit mainly led to the loss of the activity for hydroisomerization
on Ni<sub>2</sub>P/SAPO-11. We propose that carbonaceous deposit mostly
formed on the acid sites that are indispensible for hydroisomerization
