Our current project to build a better bio-diesel processor was selected because of two technologies that will increase the productivity and accuracy of bio-diesel production. We decided to use ultrasonic wave's transducers to generate cavitations' for a clean and efficient chemical reaction. Also we decided to use a decanter centrifuge to create a systematic separation of post reaction chemicals.

Today, biodiesel is primarily produced in batch reactors. Ultrasound allows for inline commercial processing. Ultrasonication can achieve a biodiesel yield in excess of 99%. Ultrasound reduces the processing time from the conventional 1 to 5 hour batch processing to less than 5 minutes. Ultrasonication can also help to reduce the separation time from 5 to 10 hours (using conventional agitation) to less than 30min using ultrasound. The ultrasonication does also help to decrease the amount of catalyst required by 50 to 60% due to the increased chemical activity in the presence of cavitation. Another benefit is the increase in purity of the glycerol.

Most commonly, the sonication is performed at elevated pressure (1 to 3bar, gauge pressure) using a feed pump and an adjustable back-pressure valve. Industrial biodiesel processing does not need much ultrasonic energy. The table above shows typical power requirements for various flow rates. The actual energy requirement can be determined using a 1kW ultrasonic processor in bench-top scale. All results from such bench-top trials can be scaled up easily. With ultrasonic processors of up to 16kW power per single device, there is no limit in plant size or processing capacity.

Ultrasound waves have frequencies beyond the normal range of hearing, which consists of 20 kHz to 100 MHz and beyond. High power ultrasound waves can generate cavitation within a liquid. Cavitation provides a source of energy which can facilitate chemical processes. In this case, cavitation is an induced bubble activity. Cavitation can generate very high local pressure (up to 1000 atm) and very high local temperatures (up to 5000 K).

Ultrasound waves

The relevant effects of this are:

1. reduction in particle/molecule size
2. generation of free radicals facilitating mechanisms/pathways which involve free radicals
3. increasing the fluid velocity, which facilitates mass transfer during the reactions.

While ultrasonochemistry is now a well-established area, ultrasonoenzymology has been carried out less extensively. In view of harsh local environments during ultrasonication, it is expected that enzymes in nonaqueous media would be able to withstand ultrasonication better. Thus, it is not surprising that attempts have been made to use ultrasonicators in nonaqueous enzymology.

Two distinct types of approaches have been used. Either ultrasonication has been used as a pretreatment step (for the biocatalyst) or the reaction has been carried out in the presence of ultrasonic waves. Both ultrasonic probes and ultrasonic baths have been used in ultrasonoenzymology.

Unfortunately, in many cases, temperature has not been controlled. In such cases, one does not know whether the effects on reaction rates are due to ultrasonication alone or due to the rise in temperature as well. It is also difficult for others to reproduce results obtained with such ill-defined conditions. In other cases, temperature has been controlled either by use of a water-cooled reactor or interrupting ultrasonication so that the temperature does not rise. In the latter cases, cycles of ultrasonication and cooling have been used.