Study On H₃PO₄ Activation Process Of Lignin-based Activated Carbon

As an important part of plants,lignin has the advantages of large output,low price,and extensive source supply.However,its complicated structure and diverse types make it difficult to be effectively used.Focusing on the difficulty in the utilization of corncob enzymatic hydrolysis lignin,which is a by-product of enterprise production,it is of great significance to study the feasibility and activation process of preparing activated carbon from lignin as raw material,thus to realize the high-value utilization of lignin.Corncob enzymatic hydrolysis lignin has been used as raw material in this study.First,the pore structure and yield difference of ACs?activated carbons?obtained by different activators were compared,and the suitable activation reagent was determined.Orthogonal experiment method was used to determine the optimized process parameters for H₃PO₄activation of both lignin and white pine saw dust,which was widely used as raw material in activated carbons'commercialized production process.Compared the pore structure and yield difference under the optimized conditions,thus determined the rationality and feasibility of using lignin as feedstock to prepare ACs.Collected the information of gas product changes during the process of lignin's carbonization and H₃PO₄ activation The effect of activation temperature and mass ratio on the pore structure of ACs was systematically studied.The mechanism of H₃PO₄ activation on lignin was investigated.Finally,in view of the problems of expansion and wall-sticking phenomenon and incomplete product collection when the fixed bed reactor is used for H₃PO₄ activation,an externally-heated stirred reactor was designed and built,and carried out the thermal state and material balance experiments.The specific conclusions are as follows:?1?From the perspective of activated carbons'pores structure and yield,the pore structure of ACs obtained by H₃PO₄ activation is not as rich as KOH activation and slightly lower than K₂CO₃ activation,but it has the advantages of higher yield and lower reaction temperature.Thus H₃PO₄ is most suitable as activator to prepare lignin-based ACs.Under the optimized process conditions,the ACs obtained from the white pine saw dust and lignin by H3PO4 activation is similar in pore structure,but lignin-based ACs has a higher yield,which was suitable and reasonable for preparing ACs.?2?H3PO4 and its derivatives reduce the generation temperature of CO,CO₂,and CH₄by lowering the cleavage temperature of the side chain functional groups and monomers of lignin,promote the polycondensation reaction of aromatic ring compounds and the generation of H₂ at meantime.When the activation temperature is above 250°C,lignin first forms mesopores by the cross-linking effect of H₃PO₄,then the micropores formed by the heat shrinkage as the activation temperature increases.When the activation temperature is further increased,the excessive heat shrinkage reduced the mesopores and micropores,and the activation effect decreased.Through the dose variation of activator,the H₃PO₄/lignin mass ratio affects the cross-linking degree,which in turn affects the volume of mesopores and micropores.ACs with a specific surface area of 1050m²/g,yield of 55%and mesoporosity of60%can be prepared when the activation temperature is 500?and the mass ratio is greater than 2.?3?Hot state experiments were carried out of the preparation of ACs by H₃PO₄ activation under the optimized process conditions obtained in the previous investigation.The new device can solve the expansion problem with the aid of agitating paddles,but the material will agglomerate and the activation effect will be slightly reduced.The new device can effectively collect solid,liquid and gas phase products and perform material balance experiments,thus meet the design requirements.Subsequent methods such as changing the form of agitating paddles can provide powerful help for the subject's future development...