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Researchers Use Ultrasonic Processing for Fast Biodiesel Production

An example of inline ultrasonic processing for biodiesel production. Click to enlarge. Source: Hielscher.

Researchers at Mississippi State University report that 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. The work is described in the current issue of the journal Energy & Fuels.

Ultrasonication can also help to reduce the separation time from 5 to 10 hours required with conventional agitation, to less than 15 minutes, according to Hielscher, a small German company providing ultrasonic processing equipment for a variety of sonochemical applications, biodiesel production being one.

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.

Sonochemistry—the application of ultrasound to chemical reactions and processes—is based on the phenomenon of cavitation: the formation, growth and implosive collapse of bubbles in a liquid.

Cavitation can be produced through different means, including high pressure nozzles, high velocity rotation, or ultrasonic transducers. The input energy is transformed into friction, turbulences, waves and cavitation.

Cavitation bubbles are vacuum bubbles, created by a fast moving surface on one side and an inert liquid on the other. The resulting pressure differences serve to overcome the cohesion and adhesion forces within the liquid. Cavitational collapse produces intense local heating (~5,000 K), high pressures (~1,000 atm), and enormous heating and cooling rates (>109 K/sec and liquid jet streams (~400 km/h).

The fraction of the input energy that is transformed into cavitation depends on several factors describing the movement of the cavitation generating equipment in the liquid, according to Hielscher.

The intensity of acceleration is one of the most important factors influencing the efficient transformation of energy into cavitation. Higher acceleration creates higher pressure differences. This in turn increases the probability of the creation of vacuum bubbles instead of the creation of waves propagating through the liquid. Thus, the higher the acceleration the higher is the fraction of the energy that is transformed into cavitation.

In case of an ultrasonic transducer, the intensity of acceleration is described by the amplitude of oscillation. Higher amplitudes result in a more effective creation of cavitation. In addition to the intensity, the liquid should be accelerated in a way to create minimal losses in terms of turbulences, friction and wave generation. For this, the optimal way is a unilateral direction of movement.

—Hielscher backgrounder on Sonochemistry

Biodiesel conventionally is produced by the base-catalyzed transesterification of fatty acids from vegetable oils or animal fats with methanol in a batch reactor using heat and mechanical mixing energy as energy inputs. Glycerol is a byproduct of the reaction, and must be separated from the biodiesel product.

The use of ultrasonic processing not only can provide energy for the reaction, but can achieve better mixing and more rapid separation.

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.

Other researchers and companies are using ultrasonic processing for other bio- and alternative-fuel products:

  • Researchers at Iowa State University are exploring the use of ultrasonics to boost ethanol production from corn. (Earlier post.)

  • Advanced Plant Pharmaceuticals, through its merger with World Health Energy, is adopting ultrasonication as its biodiesel process to provide itself with production cost advantages. (Earlier post.)

  • GreenShift Corporation formed General Ultrasonics Corporation, a development stage company that owns patented technologies that use ultrasonic energies to enhance physical and chemical reactions including more efficient steam reformation to produce hydrogen. (Earlier post.)



Rafael Seidl

Of course, producing the ultrasound requires energy, probably electricity. It's probably still well worth it in terms of TCO for the transesterification plant.

The more serious problem, of course, is where you get the feedstock from. Growing it locally in temperate climes is expensive in terms of land use etc. Importing it from tropical countries puts rain forests there in jeopardy and can lead to methane outgassing of the soil. Both of these side effects overcompensate the global warming reductions of substituting biodiesel for petrodiesel. This would not apply if the feedstock were produced instead using open-ocean algaculture in tropical waters. Unfortunately, the requisite technology does not yet exist and, neither does an environmental impact assessment on the marine ecosystem.

Reality Czech

Please make some effort to render scientific notation correctly.  The note above reading "(>109 K/sec" is almost certainly ten-to-the-ninth-power, or 1,000,000,000.  Omitting superscripts is extremely misleading and a disservice to all readers.

Reality Czech

Please make some effort to render scientific notation correctly.  The note above reading "(>109 K/sec" is almost certainly ten-to-the-ninth-power, or 1,000,000,000.  Omitting superscripts is extremely misleading and a disservice to all readers.


Czech: My impression was that the ">109 K/sec" meant 'greater than 109 Kelvin per second', based on the context of talking about heating/cooling rates. Perhaps the article poster can clarify.

Jeff R


I agree that biofuels are a waste of land, but in a sense we're already wasting that same land--raising corn to feed to cows to eat as meat, a very inefficient way to feed people. If the corn crop doesn't go to cows, it goes to corn syrup, which is just plain bad for you in the quantities we consume, anyway. Same thing in the tropics-- if sugarcane weren't used to make ethanol, it would be used for sugar, also bad for you. So it's kind a (delicious?) irony that the market may be forcing a choice--if you want to keep driving that gas/ethanol-guzzling SUV to the burger joint, you may have to forgo the increasingly expensive burger and coke for a veggie burger and a glass of water.

Okay, so that was my vegetarian daydream :-) (Instead, we'll probably just stop exporting so much grain, and further subsidize meat prices...)


"veggie burger and a glass of water"

lol ... that's a vegetarian nightmare!


Rafael, I share your concerns about large scale biodiesel production. The one technology that seems to hold promise is Greenfuels algal bioreactor that uses powerplant emissions to grow the algae. I haven't heard much about this for a while but I gather that it is quite expensive and maybe the technology still needs some development. If it fufills its promise, it could be a win-win solution, supplying feedstock for biodiesel and stopping CO2 from enetering the atmosphere. Not perfect because you'll still get emission from the biodiesel, but pretty good.


What about the great waste of land and resources used to produce the corn, rice, and barley etc., used for all our alcoholic beverages and candy?

This does sound like a good step forward in the creation of biofuels.



Last I read GreenFuel Tech is constructing their engineering scale unit at the test facility in Arizona. Their tests there were a resounding success and right now they're bumping up the production to a commercial pilot scale. The way things are going I'm hoping to see first production next year.

Rafael Seidl

aero engr -

czech's almost certainly right, the temperature dynamics in collapsing cavitation bubbles are stupendous but very short-lived. It would also be rather strange to see all th e other data being presented as rough numbers and this one as precisely 109 (not 108 nor 110).

critta -

Greenfuel's closed reactors are intended for super-intensive algaculture near a ready source of CO2, e.g. a gas-fired power generation plant.

What I had in mind was just the opposite, super-extensive algaculture in vast (10^3-10^5 sq. km) enclosed sections of the open ocean, which happens to contain dissolved CO2. The vast surface area (A) would compensate for the fact that marine algal blooms are very thin layers floating on the surface. The enclosure would be a suitable floating skirt of minimum length Lmin = 2*[pi()*A]^0.5 and held in position by a fleet of tug boats. The algae crop would be harvested using three ships on parallel headings, arranged in a triangle. The two in front would drag a contraption that acts as a funnel, concentrating the algae at the midpoint. The third ship, perhaps a catamaran, would scoop up the biomass and immediately process it. Keeping an algal bloom in check merely by continuous harvesting at its perimeter would be much cheaper but probably infeasible.


Rafael: I've heard you mention the ocean algae farm before. Have you ever written down all of the details? Anticipated costs/returns. Have you answers to all of the likely problems? Temperature, disease, storms, predators, nutrients? Sounds like it would be a Doctoral thesis. The details should be posted along with eng-poets charcoal concept.

Gerald K. Brells

Regardless of how clever we are in developing energy sources the main problem we have is too many people requiring more and more units of energy for the "good life".If we could control our reproductive activity and reduce our worldwide population we would not be so desperate for new energy production.We should reward one child families and not Oprahize(new word,)poor families who have an over abundance of children.


This Ultra sonic technology in making biodiesel is an excellent method.and it is so economicaland so modern in scientific method....
we wish to see many plants in future in India
with best regards



Birthrates in most industrialized countries are already well below replacement level without needing draconian one-child laws. And that's bringing with it a whole other set of problems. How long can an economy sustain itself with a shrinking population?

As the average age of the population increases, health care costs increase. And in nations with socialized health care and other government services, a much smaller tax base has to sustain a larger and larger portion of the population.


Cervus: Don't plan on retiring at 60 or 65. They're just going to move the bar and the rules to keep you working till you're 70. The good news is that you'll probably still get a 20 year retirement. People used to work till 65 and drop dead by 75. The only problem with a shrinking population is finding another way of keeping score (i.e. GDP). For example in an aging population what does it matter if housing starts are down if everyone already has a house. The GDP goes down but average wealth may even increase. (example Europe after the black death)

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