Parametric and Statistical Optimization of Key Operating Conditions for Efficient Single-Step Hydrodeoxygenation of Bioglycerol to Propylene over the MoO_<i>x</i>-Based Catalyst

Abstract

Significant progress has been made in catalyst design and reaction steps’ fine-tuning and promotion in the bioglycerol-to-propylene (GTP) reaction; however, suboptimal conditions often result in incomplete glycerol hydrodeoxygenation or excessive propylene hydrogenation, hence limiting the process efficiency. In this study, high-throughput testing was combined with response surface methodology (RSM) and AspenPlus process modeling (APM) to optimize key GTP parameters─temperature, pressure, H2/glycerol molar ratio, and space velocity─using a highly active MoOx-based catalyst, with the goals of maximizing propylene yield, minimizing byproducts, and preliminary assessing GTP process cost. The GTP route is mostly governed by temperature and H2 availability, which drive two major pathways: (i) at low temperatures and high H2 pressure, allyl alcohol undergoes direct hydrogenolysis to propylene, whereas in low-H2 environments, it isomerizes to propionaldehyde; and (ii) higher temperatures promote both the hydrogenation of allyl alcohol and propionaldehyde, followed by thermodynamically driven dehydration of 1-propanol to propylene. Balanced mixing between glycerol, H2, and the catalyst’s active sites is crucial for enhancing propylene formation. Face-centered central composite design within RSM predicted a maximum propylene yield of 71.83% under optimal GTP conditions: T ∼ 358.5 °C, H2/glycerol (mol.) ∼ 80.45, WHSV ∼ 9.5 h–1, and P ∼ 50 bar. The predictive models showed strong agreement with experimental data (R2 = 91.29%, and R2adj = 83.44%). Experimental validation tests repeated three times under these optimized conditions yielded 70.77–72.49% biopropylene, with relative errors below 1.47%, confirming the model’s accuracy and reliability. The preliminary APM-based assessment confirms the technical feasibility of producing chemical-grade biopropylene (95 mol %) from bioglycerol/water mixtures (10–30 wt %), while also highlighting current economic challenges. It identifies new avenues for process optimization and underscores the environmental benefits of the single-step GTP route, in line with zero-carbon and circular economy objectives.