Ultrasonic Processors for Biodiesel Production

When you make biodiesel, slow reaction kinetics and poor mass transfer are lowering your biodiesel plant capacity and your biodiesel yield and quality. Global NRG ultrasonic reactors improve the transesterification kinetics significantly. Therefore lower excess methanol and less catalyst are required for biodiesel processing.

Biodiesel is commonly produced in batch reactors using heat and mechanical mixing as energy input. Ultrasonic cavitational mixing is an effective alternative means to achieve a better mixing in commercial biodiesel processing. Ultrasonic cavitation provides the necessary activation energy for the industrial biodiesel transesterification.

Transesterification (Chemical Conversion to Biodiesel)

Manufacturing biodiesel from vegetable oils (e.g. soy, canola, jatropha, sunflower seed or algae) or animal fats, involves the base-catalyzed transesterification of fatty acids with methanol or ethanol to give the corresponding methyl esters or ethyl esters. Glycerin is an inevitable byproduct of this reaction.

Vegetable oils as animal fats are triglycerides composed of three chains of fatty acids bound by a glycerin molecule. Triglycerides are esters. Esters are acids, like fatty acids, combined with an alcohol. Glycerine (= glycerol) is a heavy alcohol. In the conversion process triglyceride esters are turned into alkyl esters (= biodiesel) using a catalyst (lye) and an alcohol reagent, e.g. methanol, which yields methyl esters biodiesel. The methanol replaces the glycerin.

The glycerine - the heavier phase - will sink to the bottom. Biodiesel - the lighter phase - floats on top and can be separated, e.g. by decanters or centrifuges. This conversion process is called transesterification.

The conventional esterification reaction in batch processing tends to be slow, and phase separation of the glycerin is time-consuming, often taking 5 hours or more.

Ultrasonics for Biodiesel Processing

Today, biodiesel is primarily produced in batch reactors. Ultrasonic biodiesel processing allows for the continuous inline processing. Ultrasonication can achieve a biodiesel yield in excess of 99%. Ultrasonic reactors reduce the processing time from the conventional 1 to 4 hour batch processing to less than 30 seconds. More important, ultrasonication reduces the separation time from 5 to 10 hours (using conventional agitation) to less than 60 minutes. The ultrasonication does also help to decrease to amount of catalyst required by up to 50% due to the increased chemical activity in the presence of cavitation (see also sonochemistry). When using ultrasonication the amount of excess methanol required is reduced, too. Another benefit is the resulting increase in the purity of the glycerin.

Ultrasonic processing of biodiesel involves the following steps:

1. the vegetable oil or animal fat is being mixed with the methanol (which makes methyl esters) or ethanol (for ethyl esters) and sodium or potassium methoxide or hydroxide
2. the mix is heated, e.g. to temperatures between 45 and 65degC
3. the heated mix is being sonicated inline for 5 to 15 seconds
4. glycerin drops out or is separated using centrifuges
5. the converted biodiesel is washed with water

Most comonly, the sonication is performed at an elevated pressure (1 to 3bar, gauge pressure) using a feed pump and an adjustable back-pressure valve next to the flow cell.

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. If required, FM and ATEX-certified ultrasonic devices are available, such as the GIP1000-Exd.

Hielscher supplies industrial ultrasonic biodiesel processing equipment, worldwide. With ultrasonic processors of up to 16kW power per single device, there is no limit in biodiesel plant size or processing capacity.

Costs of Ultrasonic Biodiesel Manufacturing

Ultrasonication is an effective means to increase the reaction speed and conversion rate in the commercial biodiesel processing. Ultrasonic processing costs result mainly from the investment for ultrasonic equipment, utility costs and maintenance. The outstanding energy efficiency  of Global NRG ultrasonic devices helps to reduce the utility costs and by this to make this process even greener. The resulting costs for the ultrasonication vary between 0.1ct and 1.0ct per liter (0.4ct to 1.9ct/gallon) when used in commercial scale.