As described in part 1 of this series, sonochemistry is the study of the effect of acoustic waves on chemical, biological, and physical systems. The sonochemistry effects are based on a physical process known as acoustic cavitation, that is the formation, growth, and the implosion of bubbles in a liquid.
The use of acoustic waves is very useful in chemical reactions at an industrial level. The chemical reaction speed and yield can be increased significantly by using acoustic waves. Biodiesel production, that is the transesterification of vegetable oils and animal fats into what is commonly known as biodiesel, can benefit significantly from sonochemistry. In fact, traditional batch biodiesel production methods can be transformed into a continuous flow processing with sonochemistry, reducing, thus, investment and operational costs.
Production of biodiesel from vegetable oils (e.g. soy oil, algae oil, canola, or jatropha oil) or from animal fats, involves a chemical reaction known as transesterification of fatty acids. Fats and oils are made of triglycerides (fatty acids bound by a glycerin molecule). During biodiesel production triglycerides are broken down from the TG molecule freeing the glycerin (glycerol) molecule. Free fatty acids are converted to alkyl esters (biodiesel). The net result is a mix of biodiesel and glycerol, which later is separated into two fractions: the biodiesel and the by-product glycerol.
Today, the conventional method to manufacture biodiesel is batch processing. In a chemical reaction reactants (oils and methanol) are mixed mechanically and heated. After a period of time the mix is allowed to partition into biodiesel (top phase) and glycerol (bottom phase). This separation process may take between 5 to 10 hours.
What is gained from using sonochemistry in biodiesel production?
The use of acoustic waves has many advantages when compared with the traditional biodiesel manufacturing process. First, it reduces significantly processing time. Conventional batch transesterification of oils and fats may take 1 to 4 hours while using sonication batch processing is reduced to less than 1 minute. Second, The use of ultrasound decreases the separation time from 5 -10 hours to less than 1 hour. Third, sonochemistry helps reduce the amount of catalyst needed (lye) by up to 45%. Also, less reactants are needed and glycerin purity (a by-product of biodiesel production) is increased.
All these benefits, and many others, can be realized by using sonochemistry. In the end a better processing and product cost is achieved making the manufacturing operation a more profitable endeavor.