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The valorization of industrial by-products has garnered significant attention in recent years due to its potential to enhance sustainability and economic efficiency within various sectors. Basic Oxygen Furnace slag (BOF-S), a by-product generated in the steelmaking process characterized by its complex composition, presents an opportunity for waste management and resource recovery. This study investigates the potential of BOF-S as a catalyst in converting waste cooking oil to biodiesel via the transesterification reaction. To improve its efficiency, BOF-S was calcined at 850 °C (BOF-S 850), and 1000 °C (BOF-S 1000), for 5 h. The BOF-S was characterized using XRF, N2 sorption, XRD, TGA-DSC, SEM-EDS and FTIR. The characterization techniques showed that the BOF-S 850 had superior characteristics as a catalyst: rough surface, increased pore size and more active basic sites compared to the BOF-S and the BOF-S 1000 slag samples. The transesterification reaction was conducted at a methanol: oil ratio of 20:1, a catalyst loading of 20 wt %, a reaction time of 12 h, a reaction temperature of 60 °C, and a stirring speed of 750 rpm. The findings established that the BOF-S 850 was the best catalyst, with a 90.77 % biodiesel yield and was able to sustain a maximum of two transesterification cycle runs.

Blast furnace slag (BFS), a waste product from the blast furnace during iron extraction, has severe environmental impacts but is also rich in compounds that, if adequately extracted or recycled, could contribute to economic growth and reduce the demand for virgin raw materials. This research, therefore, seeks to investigate the effectiveness of the BFS composition before and after impregnation with potassium hydroxide (KOH) at different concentrations (10, 30, 60, and 90 %) in catalyzing the transesterification of waste cooking oil (WCO) to biodiesel. The transesterification process was optimized using a central composite design (CCD) for response surface modeling (RSM). The catalyst amount (3–11 wt%), reaction time (2–6 h), and methanol: oil ratio (10–30:1 mol/mol) were varied while keeping the reaction temperature (60 °C) and stirring speed (750 rpm) constant. The CCD generated a quadratic model that correlated with the experimental data with an R2 of 0.9545. The maximum yield obtained after model validation was 93.15 % at a methanol: oil ratio of 15:1, a reaction time of 3 h, and a catalyst amount of 5 wt% using the 30 % KOH/BFS catalyst. The biodiesel produced met the ASTM D6751 standards for fatty acid content, kinematic viscosity, density, and cloud point. The catalyst was able to sustain activity for a maximum of three cycles.

Chlor-alkali process industries produce a million tonnes of brine sludge which are dumped in landfills. Brine sludge waste can be thermally modified and applied as a heterogeneous basic catalyst to synthesise biodiesel from waste cooking oil (WCO). In this work, an experimental design obtained by response surface methodology was used to study the effects of process parameters and hence, optimise the transesterification process. A quadratic model was generated to estimate the yield of biodiesel to its process variables. A biodiesel yield of value 97.8 wt % was optimally achieved using numerical optimisation method at a reaction period; methanol to oil weight ratio, a catalyst to oil weight ratio, and temperature of 1.53 hr, 29.8 wt %, 2.47 wt %, and 60.31°C, respectively. The brine sludge waste catalyst was reutilised up to four times without being deactivated. Morphological modifications of the brine sludge after calcination and transesterification were characterised using a scanning electron microscope (SEM) and X-ray diffraction (XRD). From the basic fuel properties specifications stipulated in the ASTM standard, it was found WCO biodiesel properties were within the acceptable range.

In the present study, calcined phosphate rock was used as a heterogeneous catalyst for biodiesel production from waste cooking oil (WCO). Response surface methodology was used to optimize and determine the significant process variables that affected the experiment. A 5-level-4 factor Central composite design consisting of 30 experiments was used to develop a quadratic polynomial model. The following parameters were optimized, namely, reaction temperature (40–90 °C), catalyst to oil weight ratio (1–5 %), reaction time (40–120 min), and methanol to oil ratio (10:1–18:1). Maximum biodiesel yield of 96.07 % was obtained through numerical optimization at reaction temperature 62.63 °C, catalyst to oil weight ratio of 3.32 %, reaction time 79.07 min, and alcohol to oil ratio 14.79:1. Fourier transform Infrared Spectra (FTIR) analysis was used to characterize the phosphate rock in its raw form, after calcination at 1000 °C and after the first and the fourth reuse cycle. According to the American society for testing and material (ASTM D6751), the fuel properties such as kinematic viscosity, pour point, cloud point, and density were measured and were found to be within the stipulated range.

Biodiesel is an environmentally friendly fuel, produced by a transesterification process using homogeneous catalyst which causes water pollution and cannot be recycled. The present study utilizes industrial brine sludge waste (IBSW) as a heterogeneous catalyst in the transesterification of waste cooking oil (WCO) into biodiesel. One variable at a time design was applied to optimize the transesterification process. The process variables were varied as follows: methanol to oil weight ratio (10–50 %), reaction time (0.5–2.5 h), reaction temperature (30–90 °C) and catalyst to oil weight ratio (0.84–4.2 %). The IBSW before and after calcination and the transesterification process was characterized using X-ray fluorescence (XRF), Fourier-transform infrared spectroscopy and scanning electron microscope (SEM). Biodiesel was produced at maximum yield of 95.51 wt% at reaction time, temperature methanol to oil weight ratio, and catalyst to oil weight ratio of 1 hour, 60 °C, 30 wt%, and 2.52 wt% respectively. The FTIR and SEM results confirms that before and after the transesterification process the modification of IBSW took place. Using the ideal process conditions, biodiesel was produced and vital fuel properties such as viscosity, density, pour point and flash point were measured and were found to be within the specification as per American Society for Testing and Material (ASTM) standards for biodiesel. The reusability of the IBSW catalyst was tested by recycling and it can be established that the catalyst can be utilized up to four times without affecting its catalytic activity.