Experimental Evaluation and RSM Optimization of Bio-Grease from Cottonseed Oil Using Sodium Hydroxide and Bio-Based Additives

Abstract

This study focuses on the optimization of biogrease through glycerin extraction of cottonseed oil glycerin, using lye sourced from empty palm fruit bunches as an alkali and Moringa oleifera as a natural antioxidant. Moringa oleifera leaf extract was used as a corrosion-inhibiting agent and was characterized using Fourier Transformed Infrared Mass Spectrometry (FT-IR). The glycerin was obtained through a transesterification process. Response Surface Methodology was used to predict the glycerin yield. FT-IR and RSM was used to characterize and optimize the bio-grease’s dropping point, and biochemical oxygen demand (BOD). The optimum glycerin yield of 48.51% was attained under the following parameters: a 3:1 methanol-to-oil ratio, a catalyst concentration of 1.5 wt.%, a reaction temperature of 55°C, and a duration of 60 minutes. The optimum dropping point for the grease samples from palm bunch lye and sodium hydroxide was achieved at 167.77°C and 166.32°C respectively, with corresponding BOD values of 14.94 and 17.67 ppm at lye dosages of 7.71 and 9.00 wt.%, temperatures of 152.87°C and 160.00°C, and durations of 4.35 and 3.00 hours. The model-predicted values revealed an error margin of 1.48% and 2.98%, which is less than the 5.00% acceptable margin, showing that the developed quadratic models accurately captured the relationships between the dropping point, BOD, and considered parameters, including lye concentration, temperature, and reaction time. The FTIR analysis of the grease samples shows double-bond structures and heteroatoms making it suitable for lubrication functions. The grease produced using palm bunch lye performed better than grease from sodium hydroxide, showing superior biodegradability and model consistency.