Chemical production processes often require a lot of energy and involve the use of environmentally harmful substances. A team at TU Hamburg is working on an alternative that essentially gets by with water, electricity and enzymes.
The thing is reminiscent of a takeaway coffee mug. However, the lid does not have a simple drinking opening, but is studded with screws and tubes. And metal tubes protrude into the glass cup, vaguely reminiscent of straws."This is our 200-milliliter reactor," explains Victoria Bueschler, a doctoral student at the TU Institute of Technical Biocatalysis. "It can produce hydrogen peroxide and then react with other substances using enzymes." The idea: the new process should one day replace toxic and expensive chemicals in industry and also save energy.
Hydrogen peroxide (H2O2) is an important basic material for chemistry. Like water, it consists of hydrogen and oxygen - except that it has two oxygen atoms instead of one. This makes the molecule extremely reactive and an effective oxidizing agent, for example to bleach hair or convert hydrocarbons. "One example is the production of phenol from benzene," explains Bueschler. "Today, this requires high temperatures, toxic chemicals and expensive precious metal catalysts." If these catalysts could be replaced by enzymes, the reaction could take place under milder conditions - in other words, in a more environmentally friendly and energy-saving way. Bioelectrochemistry is the name of this still young, promising approach.
An electrode made of carbon
There are already enzymes that convert hydrogen peroxide into other substances as a reaction accelerator. However, if too much H2O2 is involved, it attacks the enzymes and checkmates them. It would be better if only as much hydrogen peroxide was present in the reaction as was needed at any given time.This is exactly what the TU team is aiming for in its "AIO-eChemBIO" project: The coffee cup reactor produces H2O2, which is immediately converted on the spot - a combination apparatus for production and synthesis. Hydrogen production takes place in a finger-thick rod that protrudes into the cup. "This is an electrode, it is essentially made of a special form of carbon," explains Bueschler's colleague Giovanni Sayoga, pointing to a deep black, ultra-light material. "This carbon has pores like a sponge. It consists of 90 percent air and is produced here at the TU." If this carbon sponge is placed in water and exposed to electricity, water molecules are split. This produces oxygen and hydrogen, which combine under suitable conditions to form hydrogen peroxide.
"All you really need is electricity and water and no additional chemicals," says Sayoga. The amount of hydrogen peroxide to be produced can be precisely adjusted via the applied current. And if the electricity comes from wind turbines and solar cells, production can be climate-neutral.
Follow-up project is already planned
The working group has already been able to show that the drinking cup reactor works in principle. However, there is still a lot of research work to be done before the process can be put into practice. For example: "Up to now, we have always had to refill the reactor after the reactions have run their course," explains Institute Director Prof. Andreas Liese. "In a follow-up project, we now want to try to make the process continuous." The bioelectrochemical reactor could then run day and night - an important prerequisite for use in industry. One day, such permanent reactors could then be modularly combined into larger units.
Victoria Bueschler and Giovanni Sayoga will soon have their doctoral theses in the bag. While Bueschler will remain at the institute as a group leader, Sayoga is toying with the idea of founding a start-up. "We have already sat down with a company that finds our project very interesting," he says. "Using our new process as a start-up for such a company would be an appealing idea."
More information
The activities in the "AIO-eChemBIO" technical biocatalysis project are embedded in the DFG priority program 2240 "eBiotech", in which research groups from all over Germany are working on the fundamentals of bioelectrochemistry.
More information: www.e-biotech.de/de/projekte.html