Study On Auto-catalyzed Ethanol Pulping Of Aspen

Poplar resource distributes widely in China. The mills usually use traditional sulfite orsoda pulping on poplar in pulp and paper making industry of China. The waste liquor of thesemethods is disposed with difficulty and causes certain pollution to the environment. Theauto-catalyzed ethanol pulping is characterized with that having no chemical reagent andrelying on acidity offered by acid from pulping. Furthermore, ethanol can be recovered easilyand can be used circularly. So the problem of traditional pulping on pollution is solved well.Besides, the advantages of auto-catalyzed ethanol pulping are saving total investment,high-yield of pulping, effective utility of byproduct etc.Nowadays, many researchers studied auto-catalyzed ethanol pulping of nonwoodsystematically （such as reed, tobacco haulm, wheat and straw）, while poplar hasn’t beenresearched more. This paper used poplar as raw material and studied auto-catalyzed ethanolpulping. The purpose was to discuss the optimal parameters of pulping, reaction course ofdelignification, kinetics and lignin structural changes during delignification.The optimal parameters were temperature of205℃, liquid ratio of1:10, heat reservationtime150min and ethanol consistency60%. A pulp with yield56.65%, kappa number45.93and the residual lignin content4.62%was produced.The results showed that delignification reaction of auto-catalyzed ethanol-water pulpingof poplar followed first order reaction. Delignification reaction occured during two phases,principal delignification phase （from beginning of heat reservation to90min） and residualdelignification phase（from90min to the end of heat reservation）. Under the optimal cookingconditions, to principal delignification phase, reaction velosity constant is0.0132min^-1,activation energy is47.9980KJ/mol; To residual delignification phase, reaction velosityconstant is0.0038min^-1, activation energy is78.7751KJ/mol. This activation energy is lowerthan KP of poplar, which shows that delignification during auto-catalyzed ethanol-waterpulping is easier than KP method. So poplar is adaptive to auto-catalyzed ethanol-waterpulping.The structural changes of aspen lignin of auto-catalyzed ethanol-water pulping were also studied by IR and1H-NMR. It can be speculated that lignin molecule changed as followed:First, plentiful cleavage of α-ether linkages （α-O-4） and β-ether linkages （β-O-4） occured, α-Cand β-C created C+. Meanwhile phenol part of α-ether and β-ether was electronegative, so itwould change into phenol when getting H+. Second, α-C+occured structural recompositionbecause of benzene electron cloud having electronegative gravitation. So α-ether andα-hydroxyl recomposited to β-C, then α-C change into C+, β-C created β-ether and β-hydroxyl.Then cleavage of new β-ether linkages reoccured, more lignin of small molecular weight wasdissolve by ethanol. Finally, α-C+recreated α-O-4linkages with other electronegativephenolic hydroxyl.Lignin molecule of material is comprised of plentiful guaiacyl and syringyl units. Theratio of guaiacyl to syringyl is6:5and the ratio of alkyl hydroxyl to phenolic hydroxyl is2:1.Lignin molecule includes α-O-4and β-O-4alkylphenol aether structure, β-5phenyl cumarinstructure, β-β pine oleoresin hydroxybenzene structure, β-1guaiacyl hydroxybenzenestructure.Because theory of ethanol-pulping needs to be investigated clearly, machines andequipments need to be exploited, so in the future, when going on studying its theory, weshould emphasize on realization of industrialization.