Ethyl laurate is an organic ester with tuberose essence and fruity odor, slightly sweet, fruity and soft, with a light coconut or floral scent. Therefore, it is widely used in flavoring, food and cosmetic industries. It is non-toxic and suitable for most skin types, including sensitive skin.

Synthesis

Ethyl laurate can be transesterified with ethanol by using layered zinc laurate as a catalyst. At 180°C and a molar ratio of ethanol to lauric acid of 8:1, its conversion rate is 92%. However, this method is costly and environmentally unfriendly, so researchers have developed a solvent-free enzymatic method to prepare ethyl laurate. This method has the characteristics of low cost, short reaction time and high yield.

Experimental method: The experimental apparatus includes a mechanically stirred reactor with an inner diameter of 4.5 cm and a capacity of 50 ml, equipped with 4 baffles and a 3-blade turbine impeller. The entire reactor is immersed in a constant temperature water bath. The desired temperature was maintained at ±1 °C. A typical reaction mixture included ethanol (50 mmol) and lauric acid (50 mmol) stirred at 200 rpm for 10 min at 60 °C. To start the reaction, the immobilized enzyme Fermase CALB?10000 (2% w/w substrate) and molecular sieves (12% w/w substrate) were added to the reactor. Liquid samples were taken regularly and analyzed by titration. The product was confirmed by gas chromatography. To investigate reusability, after each reaction cycle, the fermented enzyme was filtered and washed three times with acetone to remove any substrate or product. The enzyme was then dried at 40 °C and continuously reused in the next batch of reactions.

The immobilized lipase Fermase CALB?10000 was shown to be an ideal catalyst for the solvent-free esterification of ethyl laurate. Under the conditions of ethanol to lauric acid molar ratio of 2:1, catalyst content of 2.5% (by weight), molecular sieve content of 12% (by weight), and temperature of 60°C, the total conversion rate reached 92.46% within 4 hours. The calculated activation energy was 28.49 kJ/mol, which is within the range of typical enzymatic reactions. The calculated external mass transfer coefficient (KSL) was 3.58 × 10-5 m/s. The immobilized lipase could be reused for 5 cycles with a final conversion rate of 71%. However, the highest conversion rate and the lowest loss of enzyme activity were obtained after 3 cycles of reuse. Therefore, the solvent-free enzymatic synthesis of fatty acid ethyl esters is more efficient, time-saving, and environmentally friendly than solvent synthesis.