Optimization by Box–Behnken experimental design for synthesis of n-hexyl levulinate biolubricant over hierarchical H-ZSM-5: An effort towards agricultural waste minimization

• Waste minimization by levulinic acid (LA) esterification over Herarchical-HZ-5.
• RSM optimization study on esterification of LA to n-hexyl levulinate biolubricant.
• Catalyst to LA ratio gave most significant effect on esterification reaction.
• Herarchical-HZ-5 found to promising catalyst with 97% yield of n-hexyl levulinate.
• Herarchical-HZ-5 was active and stable for six catalytic cycles.

The present study is devoted to develop efficient catalytic process for conversion of agricultural waste feedstock to value added chemicals. In this context, the n-hexyl levulinate, a renewable biolubricant was synthesized by esterification of biomass derived levulinic acid (LA) with n-hexanol in a closed batch system. Hierarchical-HZ-5 (modified H-ZSM-5) was used as a heterogeneous acid catalyst. There are no reports available on the synthesis of n-hexyl levulinate biolubricant using renewable levulinic acid.The process variables such as catalyst to LA ratio (X1), n-hexanol to LA molar ratio (X2), reaction time (X3) and reaction temperature (X4) were optimized by response surface methodology (RSM), using the Box–Behnken model. Analysis of variance was done to check the suitability and significance of the quadratic model. The yield of n-hexyl levulinate obtained was 97% with 100% selectivity at optimum process parameters.The RSM analysis predicted that catalyst to LA ratio is most significant (value of p < 0.0001) and n-hexanol to LA molar ratio is least significant (value of p = 0.0064) process parameter in esterification. The quadratic model established was revealed to be suitable and statistically precise with correlation value (R2) of 0.9837 to predict the yield of n-hexyl levulinate.