Mining carbon fiber from paper and biorefinery waste
Forget taxes on imports. If a new development from Texas A&M lives up to expectations, the real job creator for the US could lie in harnessing lignin waste. The team behind a new study has discovered a way to make high quality carbon fiber from the material, which could turn the paper and biofuel industries' discards into a major money spinner and lead to the creation of new manufacturing and jobs on US soil.
Present in all land-based vascular plants, lignin is a water-resistant polymer that gives them their sturdy structure and keeps them from collapsing, among other things. It is also responsible for a lot of waste – about 50 million tons of it ends up being discarded each year by the paper industry in the US, a figure that shoots up by another 100 to 200 million tons when you take into account biorefineries, which use plants to produce ethanol.
Currently, only about two percent is recycled into new products, such as the bioplastic Arboform. The rest is burned, which is akin to setting a goldmine on fire because there is a lot that could be done with the material if there was a cost-effective and efficient way of breaking it down into its individual components.
Apart from being the most abundant natural polymer in the world after cellulose, lignin is also unique in that it is made of aromatic polymers. Given that plastics, drugs and paints are made using aromatic compounds found in coal, tar and petroleum, this makes it a potential alternative source for such materials, as well as a valuable building block in the chemicals industry.
The problem is that breaking lignin down is not easy. The tightly cross-linked chain molecules that give trees and shrubs their rigid and woody characteristics are also the same ones that make it so resistant to degradation. Breaking it down typically requires temperatures as high as 500° C (932° F) and pressures of 200 bar – and even then, this poses another problem as the resulting by-product comprises a hodgepodge of compounds containing oxygen that are difficult to separate.
And then there is the matter of economics, especially where biofuels are concerned. In order for renewable energy or fuel to be competitive, it has to be product cost-effective, as biotechnologist and lead researcher Joshua Yuan pointed our back when his team was awarded a US$2.5 million grant to study ways to give biorefinery waste a second lease of life. "We cannot compete with $30-per-barrel petroleum – it has to be more like $80-per-barrel petroleum for a biorefinery to complete, unless we have another product for which we can use the waste to make something wonderful."
Thanks to a new approach for breaking lignin down into its individual components, that product could be carbon fiber. Though its price has dropped over the last decade, standard grades, such as those used in automotive applications, still cost around $10-$17 per pound. By fractionating lignin using an enzyme-mediator system, the researchers found that they were able to separate it into different molecular weights, functional groups, and chemical bonds. In particular, they found that the high-density, high molecular weight portion was particularly suitable for producing high-quality carbon fiber.
"We are still improving and fine-tuning the quality, but eventually this carbon fiber could be used for windmills, sport materials and even bicycles and cars," says Yuan. "Carbon fiber is much lighter but has the same mechanical strength as other materials used for those products now. This material can be used for a lot of different applications."
Another benefit this process brings is that it allows every single part of lignin to be used, thus eliminating waste altogether. In the long run, it could even make the prospect of a multi-stream integrated biorefinery, one where lignin is first broken down into its various components so that a broad range of materials can be made in one facility, a reality.
"The beauty of this technology is that it allows us to use lignin completely," he continues. "Basically what we do is fractionate lignin so that the high molecular weight fraction can be used for carbon fiber and the low molecular weight fraction can be used use for bioplastics and products like the asphalt binder modifier used on roads."
Apart from its environmental benefits, Yuen also sees this having a positive impact on the American economy and job market, especially in rural areas.
"The biomass is grown, harvested and transported [in the United States], which means the jobs would be here," he says. "It would be difficult to ever ship that much waste to another country for production. It all stays here. It would put agriculture production and industry together in a bioeconomy making renewable products."
The study was published in Green Chemistry.
Source: Texas A&M