Publication: Synthesis and characterization of heteropoly acid-based catalysts supported on sba-15 for single step glycerol oxydehydration to acrylic acid
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Date
2024-01-01
Authors
Muhammad Yusri, Ahmad
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Abstract
Glycerol is a sustainable platform molecule, which has attracted significant attention in downstream industries due to its potential for producing a diverse array of value-added products. Among them, acrylic acid has received a lot of attention due to its numerous applications in the production of superabsorbents, synthetic rubbers, plastics and polymers. However, the process is usually limited to the gaseous phase which requires relatively high temperatures, longer reaction time, and complex reaction setup. Although there are few studies on liquid phase glycerol oxydehydration, the available information is still limited and needs further exploration. Hence, a suitable bi-functional catalyst to catalyze one-pot oxydehydration of glycerol in the liquid phase is needed. In this study, heteropoly acids (phosphomolybdic acid (HPMo), phosphotungstic acid (HPW), and silicotungstic acid (HSiW)) were supported on mesoporous SBA-15 and employed in the reaction. The reaction was conducted for 5 h at 230 °C with 10 wt. % of catalyst loading. Among these catalysts, PW/SBA-15 showed high activity and was selected for the following study. PW/SBA-15 catalysts have been synthesized at different acid loadings (10 – 40 wt. %) and calcination temperatures (400 – 700 °C). Different analyses were utilized to characterize the synthesized catalysts. On the basis of glycerol conversion and acrylic acid yields, the catalyst’s characteristics were correlated with its catalytic activity in single-step glycerol oxydehydration to acrylic acid. The effect of reaction parameters including reaction time (1 – 7 h), reaction temperature (210 – 240 °C) and catalyst loading (6 – 12 wt. %) was also investigated to identify the best reaction conditions. The catalyst 30PW/SBA-15(500), prepared with 30 wt. % of HPW loading and calcined at 500 °C showed remarkable activity in acrylic acid production. The optimal reaction conditions were determined to be at 3 h reaction time, 240 °C reaction temperature, and 10 wt. % catalyst loading. When using this catalyst under these conditions, the glycerol conversion rate was 98.7 %, and the yield of acrylic acid was 22.5 %. Regarding reusability, the 30PW/SBA-15(500) catalyst showed potential for two cycles of reuse with some decrease in catalytic activity. This decline was caused by the loss of active material through leaching and the collapse of the catalyst’s pores structure. Glycerol oxydehydration obeyed a pseudo second-order kinetic model with an activation energy of 134.4 kJ/mol. In conclusion, the 30PW/SBA-15(500) catalyst demonstrated a well-defined structure, and could effectively catalyze glycerol oxydehydration to acrylic acid, owing to the presence of strong acid sites and the appropriate amount of redox sites. This catalyst is recommended as a viable alternative bi-functional catalyst for the glycerol-to-acrylic acid synthesis.