Delignification of wood with p-toluenesulfonic acid as a recyclable water soluble additive

Lignin is an important component of plant cell wall, which can make bark and other parts of plant have rigid structure It is a kind of water-insoluble organic polymer, by attaching to hemicellulose, a polysaccharide, to wrap cellulose fiber Lignin needs to be removed in papermaking Therefore, researchers are keen to find a simple and environmentally friendly way to remove lignin to obtain biofuel cellulose and other biological products However, delignification often requires severe reaction conditions, such as high temperature and pressure, and caustic reagents A team of researchers from China, Finland and the United States, led by Professor Zhu Junyong of the forest products Research Institute of the Forest Products Bureau of the U.S Department of agriculture, has proved that p-toluenesulfonic acid (p-TsOH) can be used as a good water-soluble additive, almost completely dissolving the lignin of wood at a temperature not higher than 80 ℃ In addition, the new method takes less than half of the traditional delignification time The water soluble additive can separate the sugars in the wood structure, and retain the complete lignin structure, and can be reused Relevant research was recently published on science advanced Figure 1 Experimental process source of p-toluenesulfonic acid dissolving wood: one of the methods for science advanced to recover polysaccharide from cellulose biomass is to separate lignin Considering the cost of solvent recovery and environmental problems, the separation process is the best in the water system Water soluble additives can dissolve the lignin components which are usually insoluble in water, and leave the sugar which is insoluble in water at the same time P-TsOH has hydrophilic sulfonic acid and hydrophobic toluene, which is a good choice of water-soluble additives The results showed that when the concentration of p-TsOH was high enough, it would form aggregates 90% of the lignin in the wood samples could be dissolved at the temperature of no higher than 80 ℃, and then it was divided into two parts The solid part mainly contains water-insoluble cellulose, which can be converted into cellulose nanomaterials, fibers or monosaccharides as biofuels or biochemical products through the action of enzymes The liquid part contains dissolved lignin and some hemicellulose, which can be further converted into furfural under the action of p-TsOH Figure 2 Schematic diagram of lignin dissolution and precipitation source: science advanced can obtain solid lignin of dissolved part through dilution and precipitation P-TsOH is a water-soluble additive, which must form aggregates to dissolve lignin This means that there is a minimum concentration of p-TsOH aggregate, i.e minimum additive concentration (MHC) It is found that the MHC of p-TsOH is about 11.5 wt% After the separation of wood samples, the liquid containing lignin will be diluted under MHC, and the lignin will precipitate Then, the precipitation of lignin was observed by atomic force microscopy (AFM) They found that this milder lignin dissolution process resulted in lignin aggregates ranging in size from 100 nm to 1.5 μ M It has application value in the field of biodegradable materials Figure 3 Sources of microscopic properties of dissolved lignin: after science advanced understood the effect of concentration and temperature on the dissolution of p-TsOH, the author analyzed the solid part of Poplar with two-dimensional NMR, and compared this part with the complete cell wall of poplar They then used these results to optimize concentration and temperature conditions to achieve the separation of Polysaccharides from the cell wall NMR results showed that the optimal concentration of p-TsOH was 70 wt% When the temperature decreased from 80 ℃ to 60 ℃, lignin could still be separated from polysaccharides in cell wall Finally, the author carried out a preliminary experiment to prove that p-TsOH can be separated from the waste liquid by recrystallization and reused The results show that the amount of lignin dissolved in the second use of p-TsOH is almost the same as that in the first use, which proves that p-TsOH has good recycling In general, the new research of Professor Zhu Junyong's team shows that p-toluenesulfonic acid is a feasible candidate for large-scale delignification process, because it can be reused, applied in relatively mild conditions, and can dissolve almost all the lignin in wood samples Paper link: http://advances.sciencemag.org/content/3/9/e1701735