Utilization of Doum Shell Catalyst in Biodiesel Production from Palmitic Acid: Development of Statistical Optimization Approach

One specific advantage of using palmitic acid (PA) in biodiesel (Fatty Acid Methyl Esther, FAME) production is its availability and high cetane number. To produce FAME, the methodological steps followed in this study involved the sourcing and preparation of doum palm shell (DPS), carbonization and sulfonation of the biochar, and subsequent esterification of PA while DPS serves as catalyst. The objectives are to systematically explore the catalytic potential of DPS to optimize the biodiesel conversion by varying some process parameters, including methanol/oil ratio (8:1 to 12:1), reaction time (60-180 min) and catalyst load (1-5 wt.%). Ab initio, a Fourier Transform Infrared (FTIR) spectroscopy of the prepared DPS catalyst and char revealed the presence of sulfonic acid groups crucial for enhancing the acidic nature and catalytic activity of the catalyst, as well as the carbonyl groups which facilitates the esterification reaction. A sister characterization method known as the Atomic Force Microscopy (AFM) suggest that the biomass catalyst has a moderately rough surface with substantial peaks and valleys, that enhance FAME conversion. Later on, several statistical metrics, 3D surface plot, contour lines, fitted plot and a quadratic model relating the 3 factors and the response, helped in the selection of optimal combination. Under 100% desirability corresponding to 97.83% biodiesel conversion, Design Expert 7.0.0 points to 4.24 wt.%, 10.57:1 and 126.67 min as optimal combinations of catalyst load, methanol-oil ratio and reaction time, respectively, also in line with a validated experimental efficiency of 98.01%. Based on the aforementioned meritorious properties of the PA and DPS used, a biodiesel with better oxidative stability, lower levels of polyunsaturated fatty acids, longer shelf life and improved performance in diesel engines, is expected.