| China is a big country for livestock raising.The amount of dairy cattle has always been at the forefront in the world and there is a large amount of cow dung produced each year.If it is handled improperly,the environment will be greatly threatened,but handling properly will not only to reduce the harm to the environment,but also can produce a lot of products and get benefits for human beings.Hence,how to treat cow dung as a resource and make it harmless has become a key issue.The main components of dried cow dung are the same as plant biomass,including cellulose,hemicellulose,and lignin.Therefore,it can be defined as a kind of lignocellulose.At present,the utilization of cow dung is mainly concentrated on traditional methods,such as composting,pyrolysis and anaerobic fermentation.This article focus on the new utilization of cow dung and use cow dung for the preparation of high value-added chemicals and carbonaceous solid acid catalyst.Agricultural waste cow dung was used as feedstock for the production of levulinic acid in dilute acid aqueous solutions.We explored the effect of factors on product yield,such as KOH pretreatment,the types of acid,reaction time,reaction temperature,amount of substrate and acid concentration.We optimized the maximum yield of levulinic acid.The yield of levulinic acid was only 135 g/kg when the cow dung had not been pretreatment.The highest levulinic acid yield of 338.9 g/kg was obtained from the pretreated cow dung.Meanwhile,another value-added chemical formic acid could be obtained with a yield of ca.160 g/kg in the process,implying a total production of ca.500 g/kg yield for levulinic and formic acid from the pretreated cow dung with the proposed process.This is mainly because KOH pretreatment removed a large amount of lignin hemicellulose form cow dung and destroyed the ligocellulose structure.The increase of the contact of cellulose in the cow dung with acid sites promoted the conversion of cow dung into levulinic acid.In the next experiment,the cow dung was still used as the substrate,the NaOH alkali treatment was used to pretreat the cow dung to destroy the lignocellulose structure.Then,the low-cocentration sulfuric acid was used a catalyst in the alcoholysis of cellulose into ethyl levulinate.The reaction solvent is ethanol.During the alcoholysis reaction,the effects of reaction time,reaction temperature,substrate amount and acid concentration were investigated.The optimal conditions for the production of ethyl levulinate were optimized.The results showed that when the substrate was untreated cow manure,the highest yield of ethyl levulinate was 120 g/kg;when the substrate was pretreated cow dung,the yield of levulinic acid could reach 293.8 g/kg.At the end of this article,a carbonaceous solid acid catalyst bearing weakly acidic carboxylic and phenolic functional groups was facilely prepared by KOH activation.When the activation temperature was 600 ? the catalytic activity of the solid acid catalyst was proved to be the best by characterizations and cellulose hydrolysis experiment.The prepared solid acid catalyst showed low activity for the catalytic hydrolysis of raw cellulose in water.However,after the cellulose was pretreated by mixing with the solid catalyst in a ball mill,cellulose hydrolysis afforded a high glucose yield of 59.3% in water,and the glucose yield increased to 74% under the same reaction condition in 0.015 wt% HCl aqueous solution.The increases proved the dual promoting effect of the mixed ball milling on cellulose hydrolysis.Finally,we applied the carbonaceous solid acid catalyst preparation method to other agricultural residues.The results showed that the cellulose hydrolysis can also achieve a high glucose yield catalyzed by the prepared solid acid.This article proposed a new approach for the utilization of cow dung,which can not only avoid the enviromental pollution caused by cow dung,but also bring economic benefits.When the test conditions are futher improved and applied to large-scale production,it will have a rosy prospects. |
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