When biofuels are made, tough plant material is left over as waste. The material is lignin, which is a main component of plant cell walls that gives plants their structural integrity. Lignin is made up of many valuable compounds, but taking it apart to extract them is very difficult.
There have basically been two ways to deconstruct lignin: with chemicals or with microorganisms. Chemicals can do the job quickly – in hours or even minutes – but requires expensive catalysts, often uses toxic materials, and produces too many different compounds that must be isolated. Biological methods are gentler and more selective, but are extremely slow, taking weeks or even months.
A research team at Sandia National Laboratory has come up with two new techniques that combine the speed of chemical methods and the precision and sustainability of biological methods.
The first technique pretreats the lignin with a weak peroxide solution to produce intermediary molecules. Then a specially-modified strain of E. coli bacteria consumes those molecules, ultimately producing the chemicals muconic acid and pyrogallol. Muconic acid is what is known as a platform chemical and can easily be turned into nylon, plastics, resins or lubricants. Pyrogallol has anti-cancer applications.
The second technique skips the pretreatment stage entirely. Instead, a genetically-engineered tobacco plant that the team has developed can produce large amounts of a chemical called PCA which then can be broken down by the modified E. coli to produce muconic acid.
If successfully scaled up, these efficient methods for producing muconic acid and pyrogallol from lignin could be a huge boost for the economics of biofuel production. What is now a waste product of producing fuel could become feedstock for two chemicals with a combined market value of over $250 billion dollars.
Photo, posted July 4, 2017, courtesy of Johan Neven via Flickr.