Preparation Of Industrial Alkali Lignin-based Slow Release Nitrogen Fertilizer And Its Slow Release Behavior

As the crucial procreative material in agriculture,nitrogen fertilizer has made significant contribution to increase food production.With the exponential growth of global population and the increase of per capital food requirement,the agricultural sector is bound to employ enormous quantities of fertilizers to meet the increasing food demands.Unfortunately,the excessive use of conventional urea would result in not only low fertilizer use efficiency and high agricultural cost,but also adverse environmental impact,such as the emission of greenhouse gases,the eutrophication of river,soil acidification and so on,which has caused the high attention of researchers.Owing to the slow nutrient release behavior and high nitrogen use efficiency,slow release nitrogen fertilizer is considered as one promising solution to solve these issues caused by the excessive use of urea.Therefore,two novel lignin-based slow release nitrogen fertilizers were prepared in this study by chemosynthesis and physical loading using industrial alkali lignin as the raw material.The main contents of this research were shown as follows.The chemical modification of industrial alkali lignin was conducted by phenolation reaction under acidic condition.Subsequently,the reaction mechanism and the optimal reaction condition were investigated in detail by the optimizing of reaction condition and various characterization methods.These results showed that the attachment of phenol occurred in side chain region of lignin and both the para-substitution and ortho-substitution of phenolic hydroxyl group existed in the reaction,while the para-substitution was predominant.In addition,the amounts of active sites in lignin were significantly increased to 8.26 mmol/g from the original 2.91 mmol/g by phenolation.Furthermore,an optimal reaction condition was obtained,namely a phenol/lignin(g/g)ratio of 2 at 110?for 20min.A novel lignin-based slow release nitrogen fertilizer was synthesized by Mannich reaction using the phenolated lignin as raw material.Subsequently,the reaction mechanism and the optimal reaction condition were investigated in detail by the optimizing of reaction condition and various characterization methods.These results showed that the Mannich reaction mainly occurred at the ortho-and para-positions of the phenolic hydroxyl groups in lignin and the para-substitution was favored.In addition,as compared with the proportion of reactants,reaction temperature and reaction time,the type of amination reagent was the main factor for influencing the nitrogen content of product.Moreover,an optimal product with high nitrogen content(10.13%)could be obtained under a feed ratio of1:3:4(lignin/ethanediamine/formaldehyde;g/g/g)at 70?for 3 h during Mannich reaction.Besides,results of the soil column leaching experiment suggested that when employed as nitrogen fertilizer with urea,the lignin-based slow release nitrogen fertilizer could not only delay the decomposition and release of urea,but also slowly release nitrogen into soil by soil microorganism degradation,which enable it to be a favourable slow release fertilizer.The biochar-based slow release nitrogen fertilizer was prepared by an extrusion process using urea-embedded porous carbon material prepared by hydrothermal carbonization of industrial alkali lignin and chemical activation.Subsequently,the optimal preparation condition was investigated in detail by the optimizing of parameters governing hydrothermal carbonization and feed ratio(lignin/porous carbon material/urea)in the extrusion process.These results showed that the parameters of hydrothermal carbonization of lignin have a significant influence on the specific area,pore volume and yield of porous carbon material.In addition,a porous carbon material with high specific area(1923.51m~2/g),pore volume(0.82 cm~3/g)and yield(37.59%)could be obtained under an optimal condition.Besides,results of the soil column leaching experiment indicated that as compared with urea,the prepared biochar-based fertilizer has an excellent slow release behavior.And the increasing use of porous carbon material during the preparation of fertilizer could further improve the slow-release effect.