Biodiesel is biodegradable, non-toxic, renewable, and has reduced emissions of CO, SO2, particulates, and hydrocarbons as compared to conventional diesel. Furthermore its properties are very close to petroleum-based diesel making it a possible substitute of conventional diesel in diesel engines. The most common method for producing biodiesel is transesterification of triglycerides or fatty acids with an alcohol in the presence of a strong catalyst (acid, base, or enzymatic), producing a mixture of fatty acid alkyl esters and glycerol (=glycerine). Glycerine (the heavier phase) will sink to the bottom, while biodiesel (the lighter phase) floats on top and can be separated.
At present, biodiesel is primarily produced in batch reactors in which the required energy is provided by heating accompanied by mechanical mixing. Since fats and alcohols are not totally miscible, the conventional transesterification reaction in batch processing is relatively slow, and phase separation of the glycerin is time-consuming. Whereas, ultrasonic processing used in biodiesel production delivers a biodiesel yield in excess of 99% in five minutes or less, compared to one hour or more using conventional batch reactor systems. This is what the Hielscher Ultrasound Technology offers. Hielscher is a small German company providing ultrasonic processing equipment for a variety of sonochemical applications, biodiesel production being one.
Ultrasonic Processing
Ultrasound is cyclic sound pressure with a frequency greater than the upper limit of human hearing. Ultrasound frequencies range from ~20 kHz to l0 MHz, with associated acoustic wavelengths in liquids of roughly 100-0.15 mm. The application of ultrasound to chemical reactions and processes is called sonochemistry. The chemical effects of ultrasound (sonochemical) in liquids derive from several nonlinear acoustic phenomena, of which cavitation is the most important. Acoustic cavitation is the formation, growth, and implosive collapse of bubbles in a liquid irradiated with sound or ultrasound. Acoustic cavitation can lead to implosive compression if treated under proper conditions which will produce inetense local heating, high pressures, enormous heating and cooling rates, and liquid jet streams. Ultrasonication provides the mechanical energy for mixing and the required activation energy for initiating the transesterification reaction. Ultrasonication can help to reduce the separation time from 5 to 10 hours required with conventional agitation, to less than 15 minutes, according to Hielscher. The ultrasonication also helps to decrease to 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.
Continuous Processing and Separation
A flow-chart showing a typical setup for the in-line sonication of oil for the conversion into biodiesel
A flow-chart showing a typical setup for the in-line sonication of oil for the conversion into biodiesel
Since ultrasonication could reduce the transesterification retention times to 5 min compared to over 1 hour or more necessary for conventional batch processing, this method could be effectively used for continuous production of biodiesel using plug-flow or continuous stirred tank reactor systems. In a setup for the continuous processing and continuous separation, the oil is circulated through a heater before it is mixed with the catalyst continuously using adjustable pumps.
In a setup for the continuous processing and continuous separation, the heated oil and the catalyst premix are mixed together continuously using adjustable pumps. The oil/catalyst heated mixture passes the flow cell, where it is being sonicated inline for approximately 5 to 30 seconds. The sonicated mix enters the reactor column with specific volume to give approximately 1 hour retention time in the column, just enough for the transesterification reaction to be completed. The reacted biodiesel/glycerin mix is pumped to the centriguge where it is separated into the biodiesel and glycerin fractions. Post-processing can be done continuously, too.
Cost Effective
The overall energy efficiency of the industrial ultrasonic devices is approx. 80-90% from the power plug into the liquid
The overall energy efficiency of the industrial ultrasonic devices is approx. 80-90% from the power plug into the liquid
The installation of Hielscher ultrasonic reactors into your biodiesel process line reduces your operational for the following reasons:
* Less excess methanol
The reduced methanol levels were able to be achieved due to enhanced reaction kinetics afforded by the Hielscher reactors
* Raw material savings
It is possible to switch to cheaper raw materials with poorer quality such as animal fats, recycled restaurant oils or waste oils, because the ultrasonic process intensification improves the conversion results for any feedstock.
* Less catalyst
Ultrasonic mixing improves the methanol-in-oil emulsification and generates more and smaller droplets.
This leads to a better distribution and increased catalyst efficiency. As a consequence, you can save up to 50% catalyst when compared with shear mixers or stirrers.
* Higher glycerine quality
A higher conversion rate and lower excess methanol lead to a much faster chemical conversion and to a sharper separation of the glycerin.
* Electric energy and heating
A comparisonin energy consumption between ultrasonic cavitation, high-shear mixing and hydrodynamic cavitation.
A comparison in energy consumption between ultrasonic cavitation, high-shear mixing and hydrodynamic cavitation.
Hielscher ultrasonic devices require s about 1.4kWh/m³. To achieve a similar result using hydrodynamic magnetic impulse cavitation, requires about 32.0kWh/m³. High-Shear mixing requires about 4.4kWh/m³. This means, that hydrodynamic impulse cavitation requires approx. 23 times more energy and high shear mixing approx. 3 times more energy than Hielscher ultrasonic devices to provide the same throughput.
Hielscher estimates that costs for ultrasonication in biodiesel processing will vary between €0.002 and €0.015 per liter (€0.008 to €0.06/gallon) when used in commercial scale, depending on the flow rate.
Reference: http://www.hielscher.com/ultrasonics/
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