Research on lignin and biorefineries on the cover of "ChemSusChem"
Today's major biorefineries operate on a "sugar basis." No matter whether it is the production of pulp (for paper, fibers, cellulose derivatives), biofuels or other fermentation products - biorefineries are optimized to use carbohydrates (cellulose, starch, hemicelluloses). The corresponding technologies and chemical processes have been known and thoroughly optimized for decades. By contrast, lignin that also results from the utilization of wood and other agricultural products in biorefineries cannot yet be used nearly as well as cellulose in terms of materials and chemicals. Today it is still mainly burned. According to a rule of thumb, as much lignin is produced as cellulose in a first approximation – millions of tons annually. Nevertheless, lignin represents one of the most important carbon sources for future chemistry based on renewable raw materials. Biorefinery lignins are usually still classified as low-value products (fuel or low-cost chemical feedstock), mainly due to low lignin purities in the feedstock.
However, recent research has shown that "cellulose residues" previously considered as "impurities" in lignin can provide a decisive quality boost in many important applications, so that biorefinery lignins have a great chance to be successfully used as high-value products in wood adhesives, carbon fibers and nanofibers or thermoplastics. Raw biorefinery lignins, which contain a significant amount of residual crystalline cellulose, perform significantly better in these applications than high-purity lignins (which additionally also require expensive and complex purification steps). Where previously high-purity and/or functionalized lignins with narrow molecular weight distributions were required for certain applications, simple green processes for upgrading biorefinery crude lignin are now increasingly emerging as an alternative. This is currently leading to a rethinking and economic renaissance of the whole biorefinery idea.
The review article on technical lignins in biorefinery concepts summarizes recent developments from the involved research groups at BOKU, in Finland and in Canada, and discusses the state of the art and future trends in the utilization of technical lignins.
More information can be found at:
https://chemistry-europe.onlinelibrary.wiley.com/doi/10.1002/cssc.202002553