A bottle of yellow liquid boiling on a lab bench could contain some surprising revelations. In a broth of water, sugar, and bacteria, chemical engineer Adriano Mariano, of the State University of Campinas (Unicamp), managed to extract butanol, a potential fuel, using a method declared as inappropriate in past decades: the vacuum. “We broke a paradigm,” says Rubens Maciel Filho, also of Unicamp, who is a chemical engineer and the project supervisor of Bioen, a part of the FAPESP Research Program in Bioenergy.
“The use of a vacuum is nothing new, what is new is using it to extract butenol,” reinforces Mariano. Based on his own calculations, Mariano challenged the established wisdom that vacuum extraction only works for substances that are more volatile than water, such as ethanol, which boils at 78 degrees Celsius (° C), while water boils at 100° C. The dogma was that the technique would not be worth trying for butanol extraction because it has a much higher boiling point than water, 117° C.
In his postdoctoral work, the Brazilian researcher transformed this former certainty to doubt, but it was not only in theory. “Nobody would believe me unless I could show that it works in practice, so I went to the United States, where there were resources to conduct the necessary experiments,” he says. This happened in the laboratory of Nigerian microbiologist Thaddeus Ezeji, at Ohio State University, in collaboration with the Indian chemical engineer Nasib Qureshi, of the Department of Agriculture (USDA). In the experiment, Mariano assembled a vacuum apparatus in which he could heat a solution of sugar mixed with the bacterium Clostridium beijerinckii, a micro-organism used for fermentation in situations where there is no air available. Because of the vacuum, the solution boils at only 37 ° C, a comfortable temperature for the bacteria. “We showed that, when the concentration of butanol is not very high, a vacuum is sufficient to extract it from the solution,” he explains. The results yielded an article in the August issue of Biotechnology and Bioengineering, one of the leading journals in the field, and was noted as the highlight of that issue.
An important aspect of the technique is that it allows the butanol to be removed as it is being produced. As it is being constantly withdrawn, the concentration of butenol in the solution is never high, which would be toxic to the bacteria, so it can continue to convert all of the sugar in the solution into butanol, ethanol and acetone.
Also in collaboration with Ezeji and Maciel Filho, Mariano aims to optimize the process and perhaps make it practical at a scale of industrial production. There is already a plant in Brazil producing butanol using traditional methodology, that has a low degree of productivity because of the toxicity of the substance itself to the microorganisms. Butanol has an energy content that is 30% higher than ethanol, which makes it a good option for blending with fuels that drive Brazilian transport. “Butanol will not compete with the productivity of ethanol, but it can be used to increase fuel efficiency,” explains the researcher.
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