Slow pyrolysis of prot, alkali and dealkaline lignins for production of chemicals

•Optimisation of slow pyrolysis parameters for alkali, prot and dealkaline lignin.•Maximum biooil yield (34.1wt.%) obtained alkali lignin at 450°C.•Ca. 35wt.% of guaiacols obtained form prot lignin at 300°C.•Maximum yield (92%) of phenolic compounds from dealkaline lignin at 350°C.•Relative contents of each phenolic compound changes significantly with pyrolysis temperature. Effect of different lignins were studied during slow pyrolysis. Maximum bio-oil yield of 31.2, 34.1, and 29.5wt.% was obtained at 350, 450 and 350°C for prot lignin, alkali lignin and dealkaline lignin respectively. Maximum yield of phenolic compounds 78%, 80% and 92% from prot lignin, alkali and dealkaline lignin at 350, 450 and 350°C. The differences in the pyrolysis products indicated the source of lignins such as soft and hard wood lignins. The biochar characterisation revealed that the various ether linkages were broken during pyrolysis and lignin was converted into monomeric substituted phenols. Bio-oil showed that the relative contents of each phenolic compound changes significantly with pyrolysis temperature and also the relative contents of each compound changes with different samples.