Efficient extraction of lignin from walnut shell and peanut shell blend by using ionic liquid

Abstract

Lignin is a valuable product with numerous applications such as Nano-lignin and an important renewable energy source, however, isolation of lignin from biomass is a challenging prospect. The present study aims to extract lignin from Walnut Shell and Peanut Shell blend using three different solvents; Ionic Liquid (IL), Organic Liquid and Aqueous Alkali. IL (Pyridnium Formate) is used to extract lignin from 1:1 blend of Walnut Shell and Peanut Shell. The performance of IL is compared with Alkali (Sodium Hydroxide) and Organic Liquid (Ethanol) where IL proved to be the most effective in lignin extraction. Consequently, the preservation of lignin structure and presence of aromatic rings as well as Syringyl (S) ring and Guaicyl (G) rings was confirmed by FTIR. It showed the existence of conjugated and non-conjugated aromatic rings which are needed for further lignin application like epoxy resins. TGA of untreated biomass and treated biomass showed easier thermal decomposition at lower temperature proving that IL pre-treatment was effective in breaking down the biomass. SEM revealed the changes in surface morphology which occurred due to pre-treatment. The treated sample had a much more amorphous and porous structure. In conclusion, at operating conditions temperature 140ºC, retention time 120 min and IL to biomass ratio of 1:20 (wt/wt), maximum lignin yield is achieved by IL which is equal to 73.6%. The yield for Alkali, at temperature 120ºC and retention time 180 min along with addition of concentrated Sulfuric acid as catalyst, is 37.6%, whereas the yield for Organic Liquid, at temperature 210ºC and retention time 90 min, is the lowest 23.4%. Moreover, the IL is regenerated and recycled to make it cost effective for lignin extraction. Hence, the present study establishes that IL is most suitable in extracting lignin efficiently.