Study On The Catalytic Degradation Of Alkaline Lignin By Graphene/hemin And The Properties Of The Products

Lignin is the second largest natural aromatic polymer only inferior to cellulose in amount on earth.It is estimated that global annual discharge of industrial alkaline lignin,a waste polymer by-product from kraft-pulping process in the pulp and paper industry,has been more than 1.5 hundred million tons,and many paper industries usually have simply processing before direct emissions,causing serious resources waste and environment pollution.Effective catalytic degradation and conversion of alkaline lignin is the hot point in the research and industry.Metalloporphyrin is important for lignin degradation research.Hemin,a natural metalloporphyrin with simple structure,exhibits good catalysis based on the reversible redox of Fe(III)/Fe(II).However,it is unstable and liable to self-oxidise.To solve this problem,we promote the adhesion of hemin to the surface of graphene by ?-? bonds via "wet chemical method".Choosing alkaline lignin as raw material,we study on the degradation effect by graphene/hemin(H-GN)material to support the research on production of aromatic compound in industry.The results showed that while the mass ration of H2O2 to lignin,time,T(?)and pH were 10:1,5h,100?,and 13.2,the degradation rate could be high up to 92.89 wt.% with H-GN,which was higher than 34.92 wt.% for non-catalyst degradation.FT-IR,UV/Vis,EA,TGA and SEM were used to characterize the structure of raw lignin and lignin residue.It showed that most coloured group has been degraded and the thermostability was obviously lower.With porous structure occurred,the specific surface area and hydrophily of lignin increase,and it shows the possibility for lignin to use as surfactant or dye dispersant and so on.For the liquid products,styrene and bis(2-ethylhexyl)phthalate were identified as the main aromatic monomers via GC-MS,HR-MS and FT-IR.It showed that while the mass ration of H2O2 to lignin,time,T(?)and pH were 10:1,5h,60?,and 13,it was the most appropriate reaction condition to obtain styrene.And the conversion rate was 47.99 wt.% with the selectivity of styrene 82.61%.While the pH value increased to 13.2,the main product was bis(2-ethylhexyl)phthalate with the conversion rate 73.55 wt.% and the selectivity 34.95%.