Enzymatic Transesterification of Non-Edible Oils for Biodiesel Production

Introduction to Biodiesel

Biodiesel is a renewable fuel made from vegetable oils or animal fats. It offers a clean-burning alternative to fossil diesel. Transesterification is the biodiesel production process that converts oils into biodiesel using alcohol and a catalyst.

In the U.S. and Europe, soybean and rapeseed oils are the main feedstocks. However, non-edible oils like jatropha, karanja, and putranjiva are gaining attention. These oils do not compete with food supplies, making them more sustainable.

Why Choose Enzymatic Transesterification?

Traditional biodiesel production uses acid or base catalysts. These methods involve high energy and produce soap as a byproduct. Enzymatic transesterification uses lipase enzymes. This method is eco-friendly and works at lower temperatures.

Lipase enzymes act at the oil-water interface, converting triglycerides to fatty acid esters and glycerol. The reaction reverses under low water conditions, favoring ester synthesis over hydrolysis.

Feedstock Selection and Source

Researchers used jatropha, karanja, and putranjiva seeds for oil extraction. These seeds were collected from the Arabari forest in Midnapur, India. Oils were extracted mechanically from the seed kernels.

Putranjiva and karanja seeds yield about 33% oil by dry mass. However, these oils are still underutilized for biodiesel production. Jatropha is more studied but still holds promise for further optimization.

Materials and Methods Used

The catalyst was Candida antarctica lipase, obtained from Sigma-Aldrich. Methanol and propan-2-ol served as acyl acceptors. Analytical-grade chemicals were used without further purification.

Transesterification took place in screw-capped flasks with shaking at 250 rpm. Hexane acted as a solvent. The reaction proceeded for 8 hours at 40°C. Product formation was monitored using thin-layer chromatography (TLC). Final ester content was analyzed using 400 MHz ^1H NMR.

Physical Properties of Non-Edible Oils

Table 1 summarizes the fuel properties of the three oils and compares them to diesel. All three oils showed higher viscosity than diesel. For instance, karanja oil has a viscosity of 43.67 cSt at 40°C, compared to diesel’s 2.6 cSt.

The flash point and fire point were also significantly higher for the oils. This makes them safer for storage but poses challenges for direct engine use. Degumming the oils helped reduce viscosity and improve transesterification yields.

Gas Chromatographic Analysis

Fatty acid profiles were studied using gas chromatography. Nitrogen served as the carrier gas at 1 ml/min. Common fatty acids in these oils include oleic acid (C18:1), stearic acid (C18:0), and linoleic acid (C18:2).

Methyl esters of these fatty acids form the biodiesel product. The composition affects fuel quality parameters such as cetane number and oxidative stability.

Importance of Degumming

Gums and phospholipids in vegetable oils hinder enzyme activity. The oils were degummed using sulfuric acid and purified with charred sawdust. Acid concentration varied from 0% to 5%.

Degumming significantly reduced the oils’ viscosity. For example, jatropha oil showed its lowest viscosity at 1% acid treatment. Karanja oil reached optimal viscosity reduction at 4% acid concentration.

Effect on Transesterification Efficiency

Table 3 shows the impact of degumming on conversion rates. Without degumming, jatropha gave a 52% yield. After degumming, the yield rose to 66.6%. Karanja and putranjiva showed similar improvements.

Degumming removes substances that bind to the enzyme’s active sites. This increases the efficiency of the lipase and boosts biodiesel yields.

Optimizing Reaction Conditions

Several variables affect the transesterification process. The molar ratio of alcohol to oil, reaction time, and temperature are key factors. A 3:1 molar ratio of methanol to oil gave the best results. The optimal temperature was 40°C, and the best reaction time was 8 hours.

Higher methanol levels can deactivate the enzyme. Methanol is polar and forms droplets in the oil. These droplets can adsorb onto the enzyme and block access to the oil substrate.

Using Propan-2-ol as an Alternative

Researchers tested propan-2-ol as a replacement for methanol. Propan-2-ol is less polar and more miscible with oils. It also has less deactivating effect on lipase enzymes.

With propan-2-ol, jatropha oil achieved a 72% conversion rate. Karanja oil reached 45%. These rates were higher than with methanol. The NMR spectra confirmed the formation of 2-propyl esters, indicating successful transesterification.

Challenges and Future Scope

One challenge is the deactivation of enzymes by methanol and glycerol. Methanol can inactivate lipase even at low concentrations. Glycerol, a byproduct, can also reduce enzyme activity.

Future research can focus on continuous processes with in situ glycerol removal. Enzyme immobilization techniques may enhance stability and allow enzyme reuse.

Conclusion

Enzymatic transesterification offers a promising route to biodiesel from non-edible oils. Jatropha, karanja, and putranjiva oils showed varying yields based on reaction conditions and oil pretreatment. Degumming and using propan-2-ol significantly improved conversion rates.

This process aligns with green chemistry principles. It provides an eco-friendly, sustainable solution to biodiesel production. With further research, enzyme-catalyzed methods can become industrially viable.

Also check out, “Biodiesel Industry“, “Enzymatic Process“