From levulinic acid biorefineries to γ-valerolactone (GVL) using a bi-functional Zr-Al-Beta catalyst†
The integration of GVL production in a lignocellulosic biorefinery where furfural and levulinic acid are co-produced is investigated in a one-pot process over a Zr-Al-Beta bi-functional catalyst. Under the synthesis and reaction conditions previously optimized for the transformation of furfural, the yield of GVL for different mixtures of levulinic acid–furfural over this catalyst is very high (60–90%). Complete conversion of the reagents (both furfural and levulinic acid) is achieved after 2 hours of reaction. As the percentage of levulinic acid in the mixture increases, higher yields of GVL are obtained. The results indicate the presence of a synergistic effect due to an improvement of the catalyst stability against furfural-deactivation phenomena. In addition, the mass balances obtained are high, evidencing the efficient use of both platform molecules. An optimization of the transformation of levulinic acid into GVL has shown that it is possible to work with highly concentrated reaction media, allowing excellent productivities of GVL per gram of catalyst (levulinic acid concentration of 300 g L−1, catalyst loading = 12.5 g L−1) leading to a GVL productivity of up to 8 gGVL gCAT−1 after 6 h at 190 °C. Under these conditions, a pseudohomogeneous kinetic model has been fitted to the experimental data. Also remarkable is that the Zr-Al-Beta catalyst is stable and reusable in this transformation, since no activity loss was evidenced after repeated reaction cycles without any kind of regeneration treatment.