Optimization of biodiesel production from non-edible oils using heterogeneous catalysts in supercritical CO2 medium

Project Abstract

Optimizing biodiesel production from non-edible oils via heterogeneous catalysts in a supercritical CO2 (SC-CO2) medium presents a scalable, sustainable route to renewable liquid fuels while addressing feedstock competition with food crops. This study investigates the transesterification of non-edible oil feedstocks, such as jatropha, pongamia, and karanja, under SC-CO2 conditions to enhance reaction kinetics, selectivity, and catalyst longevity. A range of solid acid and base catalysts (e.g., CaO, MgO, zeolites, mesoporous aluminosilicates, and sulfonic-functionalized polymers) were screened for activity, stability, and ease of separation. Process variables including temperature (320–420 K), pressure (8–25 MPa), CO2 density, methanol-to-oil molar ratio, catalyst loading, and reaction time were systematically optimized using response surface methodology to maximize fatty acid methyl ester (FAME) yield while minimizing glycerol by-product formation and catalyst leaching. The SC-CO2 medium serves dual roles acting as a non-polar solvent that improves mass transfer and co-solvent effects that modulate reactant solubility and phase behavior, and enabling easy product separation via depressurization, reducing downstream energy demand and effluent complexity. Kinetics were modeled to differentiate homogeneous and heterogeneous contributions, with attention to catalyst surface reconstruction, methanol diffusion under high CO2 density, and potential saponification in base-catalyzed systems. The study also evaluates catalyst reusability over multiple cycles, identifying fouling mechanisms and regeneration strategies to extend catalyst life. A techno-economic assessment integrates capital and operating costs, including SC-CO2 equipment, catalyst preparation, and plant-scale methanol management, with a life-cycle assessment to quantify greenhouse gas reductions, energy payback period, and feedstock land-use implications. Product quality was verified by standard GC-FID and GC-MS analysis to ensure compliance with regional biodiesel standards, focusing on cetane number, kinematic viscosity, flash point, acidity, iodine value, cloud point, and sulfur content. Additionally, the research explores the environmental footprint of non-edible feedstocks under SC-CO2 conditions, comparing emissions, toxicity, and waste streams with conventional base-catalyzed transesterification in supercritical methanol or conventional reactors. Results indicate that certain mesoporous solids exhibit high base strength and stability under SC-CO2, achieving FAME yields above 98% within feasible residence times, with negligible catalyst leaching and robust recyclability. Optimal conditions reveal a synergistic effect of SC-CO2 density and methanol co-solvent, enabling lower methanol usage and reduced energy input for phase separation. The findings demonstrate the viability of a continuous-flow SC-CO2 transesterification process with solid heterogeneous catalysts as a green, scalable alternative for biofuel production from non-edible oils, offering improved process efficiency, reduced environmental impact, and compatibility with existing refinery infrastructure. The study provides a roadmap for industrial adoption, highlighting critical parameters for scale-up, catalyst design criteria, and integrated process control strategies to maintain product quality and economic competitiveness.

Project Overview

What This Project Is About

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This project looks at making biodiesel from oils that are not used for food, using a special solid catalyst and a solvent system called supercritical CO2. The goal is to find a cleaner, safer, and potentially cheaper way to turn waste or non-edible oils into useful fuel, while reducing processing steps and unwanted byproducts.

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The Problem It Addresses

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Many biodiesel processes use liquid acids or bases and can produce soaps or require expensive setups. Non-edible oils often contain impurities that complicate processing. There is a need for a greener, catalyst-based method that works well with challenging oils and minimizes waste and energy use.

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Objectives of the Project

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1. Identify a suitable solid catalyst that works well with non-edible oils in supercritical CO2.
2. Optimize reaction conditions (temperature, pressure, catalyst amount) for high biodiesel yield.
3. Evaluate the quality of produced biodiesel against standard fuel specs.
4. Assess the process in terms of energy use and environmental impact.

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What You Will Do Step by Step

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1. Review background literature on biodiesel production and supercritical CO2 methods.
2. Prepare non-edible oil samples and select a heterogeneous catalyst.
3. Set up experiments varying key parameters and collect yield data.
4. Analyze fuel properties of the biodiesel (e.g., viscosity, flash point).
5. Use simple statistical methods to find optimal conditions.
6. Discuss practicality, safety considerations, and scalability.

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Expected Outcome

Expected to identify a practical, greener route to biodiesel from non-edible oils with solid catalysts in supercritical CO2, achieving higher yields and cleaner product with better process safety and lower waste.