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Topics in Catalysis

, Volume 55, Issue 3–4, pp 129–139 | Cite as

Catalytic Hydroprocessing of p-Cresol: Metal, Solvent and Mass-Transfer Effects

  • Haijun Wan
  • Raghunath V. Chaudhari
  • Bala Subramaniam
Original Paper

Abstract

A systematic study of the comparative performances of supported Pt, Pd, Ru and conventional CoMo/Al2O3, NiMo/Al2O3, NiW/Al2O3 catalysts as well as the effects of solvent, H2 pressure and temperature on the hydroprocessing activity of a representative model bio-oil compound (e.g., p-cresol) is presented. With water as solvent, Pt/C catalyst shows the highest activity and selectivity towards hydrocarbons (toluene and methylcyclohexane), followed by Pt/Al2O3, Pd and Ru catalysts. Calculations indicate that the reactions in aqueous phase are hindered by mass-transfer limitations at the investigated conditions. In contrast, with supercritical n-heptane as solvent at identical pressure and temperature, the reactant and H2 are completely miscible and calculations indicate that mass-transfer limitations are eliminated. All the noble metal catalysts (Pt, Pd and Ru) show nearly total conversion but low selectivity to toluene in supercritical n-heptane. Further, conventional CoMo/Al2O3, NiMo/Al2O3 and NiW/Al2O3 catalysts do not show any hydrodeoxygenation activity in water, but in supercritical n-heptane, CoMo/Al2O3 shows the highest activity among the tested conventional catalysts with 97 % selectivity to toluene. Systematic parametric investigations with Pt/C and Pt/Al2O3 catalysts indicate that with water as the solvent, the reaction occurs in a liquid phase with low H2 availability (i.e., low H2 surface coverage) and toluene formation is favored. In supercritical n-heptane with high H2 availability (i.e., high H2 surface coverage), the ring hydrogenation pathway is favored leading to the high selectivity to 4-methylcyclohexanol. In addition to differences in H2 surface coverage, the starkly different selectivities between the two solvents may also be due to the influence of solvent polarity on p-cresol adsorption characteristics.

Keywords

Hydroprocessing p-cresol Noble metal catalysts Conventional hydrotreating catalysts Water n-Heptane 

List of Symbols

\( a_{\text{b}} \)

Gas–liquid interfacial area per unit volume of reactor, m2/m3

\( a_{\text{p}} \)

Liquid–solid interfacial area, m−1

\( C_{\text{A}}^{ *} \)

Saturation solubility of H2 in liquid phase, kmol/m3

\( C_{\text{AS}} \)

H2 concentration on the catalyst surface, kmol/m3

\( D_{\text{e}} \)

Effective diffusivity, m2/s

\( d_{\text{i}} \)

Impeller diameter, m

\( D_{\text{M}} \)

Molecular diffusivity, m2/s

\( d_{\text{p}} \)

Particle diameter, m

\( d_{\text{t}} \)

Reactor diameter, m

\( H_{\text{e}} \)

Henry’s law constant, kmol/m3/atm

\( h_{\text{l}} \)

Height of the first impeller from the bottom, m

\( h_{2} \)

Height of the liquid, m

\( K_{\text{l}} \)

Liquid film mass-transfer coefficient, m/s

\( K_{\text{l}} a_{\text{b}} \)

Overall gas–liquid mass-transfer coefficient, s−1

\( K_{\text{s}} \)

Liquid–solid mass-transfer coefficient, m/s

\( m \)

Order of reaction with respect to hydrogen

\( M_{\text{w}} \)

Molecular weight of solvent, g/mol

\( n \)

Moles of gas at constant pressure, kmol

\( N \)

Agitation speed, Hz

\( N_{\text{p}} \)

Power number

\( P_{\text{H2}} \)

Partial pressure of hydrogen, MPa

\( R \)

Universal gas constant, kJ/kmol/K

\( R_{\text{H2}} \)

Overall rate of hydrogenation, (kmol/m3) s−1

\( r_{ \max }^{{}} \)

Maximum rate of hydrogenation, (kmol/m3) s−1

\( T \)

Temperature, K

\( V_{\text{g}} \)

Volume of the gas in the reactor, m3

\( V_{\text{l}} \)

Volume of the liquid in the reactor, m3

\( w \)

Catalyst loading, kg/m3

Greek Letters

\( {{\upalpha}}_{ 1} \)

Parameter defined by Eq. 1

\( {{\upalpha}}_{ 2} \)

Parameter defined by Eq. 3

\( \phi_{ \exp } \)

Parameter defined by Eq. 12

\( \rho_{\text{l}} \)

Density of liquid, kg/m3

\( \mu_{\text{l}} \)

Viscosity of liquid, centipoise

\( \chi \)

Association factor

\( {{\upupsilon}}_{\text{M}} \)

Molar volume of the solute, cm3/mol

\( \rho_{\text{p}} \)

Density of particle, kg/m3

\( \in \)

Porosity of the catalyst particle

τ

Tortuosity

Notes

Acknowledgments

Funding for this work was provided by US Department of Agriculture (Grant 2011-10006-30362) and core funds from the Center for Environmentally Beneficial Catalysis (CEBC) at the University of Kansas. Helpful discussions with Drs Juan J. Bravo Suarez and Debdut Roy are gratefully acknowledged.

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Copyright information

© Springer Science+Business Media, LLC 2012

Authors and Affiliations

  • Haijun Wan
    • 1
  • Raghunath V. Chaudhari
    • 1
    • 2
  • Bala Subramaniam
    • 1
    • 2
  1. 1.Center for Environmentally Beneficial CatalysisUniversity of KansasLawrenceUSA
  2. 2.Department of Chemical and Petroleum EngineeringUniversity of KansasLawrenceUSA

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