PRODUCING BIODIESEL FROM WASTE-COOKING OIL
This project investigates a low-cost method for converting waste cooking oil into biodiesel using small-scale chemical processing. The work focuses on developing a simple, reproducible system that can be built and operated with minimal infrastructure. The goal is to create an accessible energy solution that supports local fuel production, reduces waste, and can be realistically implemented in resource-limited environments.
Biodiesel Production
The Problem
Many South African households and small food businesses generate large volumes of waste cooking oil (WCO), which is often discarded down drains or into soil. This leads to blocked sewage lines, environmental contamination, and unnecessary waste of a potentially valuable resource. Access to clean, affordable energy also remains a challenge in rural and peri-urban communities, where paraffin lamps and unreliable grid electricity are still common. I wanted to explore whether WCO could be transformed into a usable fuel through a controlled, small-scale biodiesel process.
My Approach
Multiple biodiesel batches were produced from waste cooking oil while varying NaOH concentration to study its effect on soap formation and phase separation. Mixing intensity was adjusted incrementally, starting gentle and increasing until just before bubble formation, to achieve effective agitation without excessive emulsification.
Each batch was heated to approximately 70 °C to remove excess methanol and improve clarity. After settling, separation quality was evaluated and combustion behaviour compared across formulations. The focus was on building a practical understanding of how catalyst loading, mixing design, and thermal control influence biodiesel quality.
Key Objectives
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Convert WCO into biodiesel through base-catalyzed transesterification
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Minimize soap formation by optimising NaOH concentration and mixing intensity
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Achieve a clear biodiesel layer with low cloudiness
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Evaluate burn quality and fuel characteristics in simple tests
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Explore potential real-world applications in low-cost energy systems
Key Challenges & Solutions
Soap Formation (Saponification)
Soap formation occurred during transesterification, producing a thick, whitish layer that interfered with clean phase separation between biodiesel and glycerol.
Higher catalyst concentrations combined with overly aggressive agitation increased saponification, resulting in persistent cloudiness and emulsion-like layers. Reducing the NaOH concentration and lowering agitation to just below bubble formation allowed effective mixing without excessive shear. Phase separation improved significantly, producing a clearer biodiesel layer with minimal soap residue and sharply defined glycerol boundaries.
Soap Yield and Quantification
Early batches showed inconsistent soap levels, making it difficult to determine which processing variables were improving fuel quality.
Soap content was visible but not measured in a structured way, which made comparisons between runs subjective and unreliable. Batch size, catalyst mass, and agitation time were standardised, and soap layers were compared visually after identical settling periods. This made soap formation easier to evaluate across test conditions, helped identify the most stable operating window, and produced more repeatable, predictable results.
Residual Methanol Causing Cloudiness
Even when soap levels were controlled, some biodiesel samples remained cloudy after separation due to entrapped or unreacted methanol.
Cloudiness persisted after overnight settling, and burn tests showed unstable flames in batches with higher methanol carryover. Gently heating the biodiesel to approximately 70 °C drove off excess methanol without degrading the fuel or inducing further saponification. Clarity improved significantly, and combustion tests became more consistent, producing a cleaner burn that matched expected biodiesel behaviour.
Real World Applications
The final biodiesel samples formed a clean, golden fuel layer with minimal soap content and stable separation from the glycerol phase. Combustion tests showed a stronger, cleaner flame with reduced visible residue compared to earlier batches, confirming improved fuel quality through controlled catalyst loading, mixing, and thermal treatment.This laboratory project demonstrates a practical pathway for communities that rely on expensive or unreliable energy sources. Biodiesel produced from waste cooking oil can replace paraffin in household lamps, providing a cleaner-burning and potentially safer alternative. At larger scales, locally produced biodiesel can power small generators for clinics, farms, informal traders, and low-income households during outages. Converting waste cooking oil into usable fuel represents a community-level energy solution that reduces pollution, supports circular resource use, and improves access to affordable energy.
What Was Learned
Small changes in how the process is run have a strong impact on final fuel quality and yield. Along with mixing, temperature control, and catalyst balancing all play a critical role, and even minor inconsistencies can lead to poor separation or unwanted by-products. The work reinforces how important process control and repeatability are, not just the chemistry itself.
Next steps focus on improving measurement accuracy, increasing process reliability, and testing the fuel in simple, real-world systems such as household lamps and small generators. This will help link laboratory performance to practical energy output and real operating conditions.
