Abstract
Background: Utilization of crude glycerol obtained during the bio-diesel production for the synthesis of fine chemicals and fuel additives by catalytic routes is very important from cost-effective and environmental perspectives. Among all alkylpyrazines, the 2,6-DMP is one of the valuable compounds for the production of various agro-chemicals, food flavoring agent and as a ligand for catalyst synthesis. In this study, 2,6-dimethylpyrazine (2,6-DMP) has been synthesized by dehydrocyclization of crude glycerol and 1,2-propanediamine (1,2-PDA) over CuO-CuCr2O4 (Cu-Cr-O) catalyst and the surface active sites are analyzed by adsorption and spectroscopic techniques.
Methods: The Cu-Cr-O sample was prepared by simple co-precipitation method in order to obtain a Cu- Cr hydrotalcite precursor. The dried Cu-Cr sample was calcined at 400, 550, 650 and 750 °C for 5 h in a static air. The alkali metal (Na, K, Cs) modified Cu-Cr-O calcined at 550 °C samples were prepared by a simple wet impregnation method. Results: The Cu-Cr-O calcined at 550 °C demonstrated higher 2,6-DMP yield when compared to other samples. The rate of 2,6-DMP is in good correlation with the Cu metal surface area and the NH3 uptakes of the catalysts. The 2,6-DMP selectivity is improved over potassium modified CC550. A structure activity correlation is established based on the pyridine and formic acid adsorbed IR spectra. Conclusion: At a calcination temperature of 400 °C; the Cu-Cr-O demonstrated a lower dehydrocyclization activity due to a poor dispersion of Cu. The experimental results showed that the dehydrocyclization rate is higher in Cu-Cr-O calcined at 550 °C, and at high temperature, calcination leads to loss of Cu metal surface area occurred as a result decline in the overall activity.Keywords: Dehydrocyclization, crude glycerol, 2, 6-dimethylpyrazine, Cu-Cr-O, NH3-TPD, pyridine-formic acid-DRIFTS.
Graphical Abstract
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