Biobased products: Selective hydrogenation of levulinic acid and
γ-valerolactone on copper supported zirconia catalysts to
1,4-pentanediol and 2-methyltetrahydrofuran
Saurabh. C Patankar1, Ganapati. D Yadav1*, Flora. T T Ng2
1
Department of Chemical Engineering, Institute of Chemical Technology, Matunga, Mumbai
400019, India
2
Department of Chemical Engineering, University of Waterloo, 200 University Avenue West,
Waterloo, ON N2L3G1, Canada
Email: scpatankar@gmail.com, gd.yadav@ictmumbai.edu.in, gdyadav@yahoo.com, fttng@uwaterloo.ca
Phone: 022-3361-1001
Fax: 022-3362-1002
Introduction
One of the aspects in the current strategy to utilize bio based energy is to synthesize platform chemicals
from biological source which can then be valorized to compounds used as liquid fuels and intermediate
chemicals. Levulinic acid (LA) and γ-valerolactone (GVL) have been developed as platform chemicals
[1]. GVL and the derived compounds have properties which are suitable for handling and usage with
the existing liquid fuel infrastructure [2]. The synthesis of GVL from LA involves hydrogenation of LA
to form hydroxypentanoic acid and dehydration of the acid to form GVL. 1,4-pentanediol (PDO) and 2methyl tetrahydrofuran (MTHF) can be obtained by additional cycles of hydrogenation and dehydration
of GVL. Direct vapour phase hydrocyclization of LA to MTHF was reported in which 1,4-dioxane was
used as a solvent with nanocomposite copper/silica catalyst [3]. The objective of the current work was
to study liquid phase synthesis of PDO and MTHF from LA in a single pot using eco-friendly solvents
and Cu/zirconia catalyst. Hence LA hydrogenation and GVL hydrogenation using ethanol as a solvent
were studied separately to understand mechanism and kinetics. The results of this study were then used
to design a robust catalyst for the single pot synthesis of PDO and MTHF from LA.
Materials and Methods
Chemicals. Copper (II) nitrate hemipentahydrate [Cu(NO3)2.2.5 H2O], zirconium(IV)oxynitratehydrate
[Zr(NO3)2. x H2O], Oxalic acid [C2H2O4], LA [C5H8O3], GVL [C5H8O2], ethanol [C2H6O] were
procured from Sigma Aldrich Chemical Co. Canada. All the chemicals were of AR grade and used as
received.
Catalyst Synthesis. Required amount of copper (II) nitrate hemipentahydrate and zirconium(IV)
oxynitrate hydrate were mixed in ethanol such that the concentration of the nitrate solution was 0.1M.
20% Molar excess of oxalic acid ethanolic solution was added rapidly to the nitrate solution. This
resulted in the precipitation of copper oxalate and zirconyl oxalate. The slurry was stirred for 30 min
1
and the precipitate was separated by centrifugation. The precipitate was then calcined at 673 K for 3 h
in air. The material obtained was used as the catalyst.
Reaction setup and analysis. All experiments for hydrogenation of LA and hydrogenation of GVL
were carried out in a 300 cm3 Parr autoclave provided with 45° pitched bladed turbine impeller ,and
temperature and pressure controllers. The reaction mixture consisted of known quantities of LA or
GVL dissolved in ethanol; the catalyst and n-decane as internal standard. The reactor was purged with
nitrogen to remove traces of air and pressurized with hydrogen. The reactor was then heated to desired
temperature. During the reaction, periodic samples were withdrawn and analyzed on GC (Agilent
7980A). A HP-INNOwax column and flame ionization detector were used. The formation of products
was confirmed by matching the residence time of pure samples.
Results and Discussion
The synthesized catalyst was thoroughly characterized using TPD-NH3, TPD-CO2, TPR, XRD, and
BET analysis (Table 2); per se and after reuse to understand the nature of active sites and their role in
catalyzing the reaction. It was ensured that the reactions of LA hydrogenation and GVL hydrogenation
were intrinsically kinetically controlled. Mathematical models were developed and validated to predict
the rate of LA hydrogenation and GVL hydrogenation.
Table 1: Surface area and pore size of fresh and used copper supported on zirconia catalyst
Catalyst: Cu/ZrO2
Surface area (m2/g)
Pore size (nm)
Pore volume (cm3/g)
Fresh
74
12.2
0.25
Reuse 1
69
12.6
0.24
Reuse 2
64
13.4
0.19
The activation energies were calculated from the reaction rate constant values at different temperatures
for both LA and GVL hydrogenation reactions. The activation energy for LA hydrogenation was found
to be 18.0 kcal/mol and 25.8 kcal/mol for GVL hydrogenation (Fig. 1 and Fig. 2). The reactions give
100% conversion after 6 h for reactions done at 473K. In case of levulinic acid hydrogenation, γvalerolactone was formed with 70% selectivity and ethyl levulinate was 30%. In the case of γvalerolactone
hydrogenation,
1,4-pentanediol
was
formed
with
ln k4
methyltetrahydrofuran was 50%.
0
y = -13008x + 23.778
-2
R² = 0.9911
-4
-6
-8
0.0021
0.0022
0.0023
-1
1/T (K )
2
0.0024
50%
selectivity
and
2-
Figure 1: Arrhenius plot for LA hydrogenation reaction
0
ln k1
-2
-4
y = -9059.6x + 15.146
R² = 0.9866
-6
-8
0.0021
0.0022
0.0023
1/T (K-1)
0.0024
Figure 2: Arrhenius plot for GVL hydrogenation reaction
Conclusion
The GVL hydrogenation involves the breaking of the C-O bond in the furan ring and hence has higher
activation energy than LA hydrogenation. It was observed that the values of adsorption constants of
hydrogen on metal sites in LA hydrogenation and of GVL and hydrogen on metal sites in GVL
hydrogenation were high. Thus the temperature is the critical aspect for the efficacy of the catalyst. As
the temperature increases, the value of adsorption constant decreases and rate of reaction increases. In
order to develop a cascade engineered process for synthesis of PDO and MTHF directly from LA, the
process must operate at a high temperature ~473 K and at a higher pressure ~ 60 atm so that the
reactants and products are in liquid phase. The catalyst for the cascade engineered synthesis must have
metal and acid sites with higher pore size ~ 12nm or greater to eliminate the diffusion resistance. The
catalyst also needs to be robust so that it doesn’t get deactivated due to multiple sequential steps.
References
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[10] P. Upare, J. M. Lee, Y. Hwang, D. Hwang, J. H. Lee, S. Halligudi, J. S. Hwang, J. S. Chang, ChemSusChem. 2011, 4,
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