Researchers at the Leibniz Institute of Plasma Science and Technology are testing plasma formation in biomass and finding a promising method for the pretreatment of biomass.

Producing biogas from the bacterial breakdown of biomass presents options for a greener energy future, but the complex composition of biomass comes with challenges. Cellulose and woody lignocellulose are especially hard for bacteria to digest but pretreatment can make it easier. The researchers are testing plasma formation in biomass and finding a promising method: A plasma-liquid interaction forms reactive species that help break down the biomass and decrease the viscosity of the biomass material.

Schematic of the experimental setup. The plasma was formed from the gas given by the vaporization of the liquid contained in plasma cavity. (a) Components of the microwave circuit. (b) Dimensions and relative positions of ceramic, tungsten, and brass in WR340 waveguide. Image Credit: Leibniz Institute of Plasma Science and Technology. Click image for the largest view.

Cellulose and woody lignocellulose in biomass are especially hard for bacteria to digest, making the process inefficient. Chemical, physical, or mechanical processes, or several of them combined, can be used for pretreatment to make biomass easier to digest, but many of the current solutions are expensive or inefficient or rely on corrosive chemicals.

The research is supported by the European Regional Development Fund, and the study paper has been published in AIP Advances, by AIP Publishing.

Study paper author Bruno Honnorat said, “The plasma can be seen as a reactive gas, which contains populations of particles that contain several electron volts of kinetic energy. This energy can be used to break the bond of the chemicals and break the bonds of molecules with which they interact. The most surprising thing was to be able to obtain plasma discharge conditions in a moving liquid. The presence of a flow considerably complicates the situation compared to all the other experimental setups studied in the literature.”

The work involves creation of a reactor in which 2-kilowatt microwave pulses injected into a moving liquid model induce plasma formation within one millisecond. The totality of the microwave power is concentrated to a small cavity, containing less than 1 milliliter of liquid, which is heated, vaporized, and finally ignited, forming an expanding plasma bubble.

The plasma-liquid interaction forms reactive species, including oxidizing agents, such as hydroxyl radicals and hydrogen peroxides, that help break down the biomass and decrease the viscosity, or resistance to flow, of the biomass material.

In partnership with an industrial agriculture partner, the process will be further tested at full scale in a biogas plant.

The research group plans to continue their work by more closely examining whether the plasma breaks the polymer chain and investigating plasma-bubble dynamics to evaluate the size and shape evolution, lifetime, and pressure of bubbles in the plasma to better understand the reactive species created in the plasma.

Their work could be used for increasing biogas production, improving the efficiency of microwave-plasma-liquid interactions, and functionalizing and modifying polymer length in polymer science.

This is one of those results that seems to come from some braistorming session. One does wonder where the original idea to flood a biomass with plasma came from. Its quite an interesting concept that seems to work.

Now lets hope the group’s plan include some metrics. Right off, 2 thousand watts is a pretty good shot of energy so one has to wonder what the payback might be. Your humble writer wishes this group some good luck, we’re all looking for their next research paper.


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