Basic Study On The Synthesis Of Carbon Microspheres From Corn Cob

Since fullerenes and carbon nanotubes were found, carbon materials is becomingan attractive research field due to its unique applications, such as good electrical andthermal properties, can be used in lithium batteriers, as catalyst supports and otherfields. In particular, the spherically shaped carbon materials stand out for its excellentproperties. But carbon source used in the synthesis of carbon microspheres are mostlypure carbohydrate, which is an industrial product, it will create some issues such ashigh production costs, the complex production of raw materials, economic efficiencyis not significantly, environmental pollution, and so on. Therefore the challenge onlooking for an alternative and low cost carbon source is tremendous for researchers.The corn cob is a kind of lignocellulosic agricultural by–products, which is richin Carbon, and the content of hemicellulose and cellulose is high. The hemicellulosesand cellulose could be converted into pentose and hexose by acid hydrolysis method,and this can be used as the carbon source to prepare carbon materials instead of fossilresources. This route can make full use of renewable biomass resources, and reducethe production cost of carbon materials, so as to achieve the gold of sustainabledevelopment. Therefore, efficient use of corn cob and improved the hydrolysis rateand the rate of carbon spheres have important research value.In this paper, hemicelluloses and cellulose could be converted into pentose andhexose by acid hydrolysis method, which could be used as a carbon source tosynthesis carbon microspheres. A study on the experimental conditions of corn cobwas carried out in detail. This method could be obtained sugar solution from corn cob,and the solution could be used to prepare carbon microspheres. The nature of the particle size, morphology and surface functional groups on carbon microspheres werestudied. Our main research was as follows:1. Preparation and properties of pentose based carbon microspheresHemicellulose was converted into pentose solution which included xylose mainlyby sulfuric acid hydrolysis, the hydrolysis rate is42%，the concentration of solution is21.57g/L, and then pentose based carbon microspheres was synthesized by situpolymerization reaction, the yield of the product is81.64%. The texture of theobtained pentose based carbon microspheres is black. The sample surface is very richin hydroxyl, carboxyl and other functional groups. The carbon microspheresmanifested localized graphitization in the (100) plane.2. Preparation and properties of hexose based carbon microspheresFirstly, corn cob residue which was removed hemicellulose was used to separatelignin using a traditional alkali extraction of lignin method, and then concentratedsulfuric acid was used to hydrolysis cellulose in corn cob, obtained hexose solutionincluded glucose mainly, the concentration of glucose was40.24g/L. The diameter ofthe prepared hexose based carbon microspheres is about1-5μm, the yield of theproduct is about38%. With the extension of the temperature and reaction time, thesample began to agglomerate. This may be related to the formation process of hexosein preparation of carbon microspheres. Therefore, the diameter of carbonmicrospheres could be controlled by the reaction temperature and reaction time.3. The study on hydrolysis of hemicellulose and cellulose in Corn cob(1) Factors of concentrated acid hydrolysis of corn cob were hydrolysistemperature, sulfuric acid concentration, hydrolysis time and ratio of corn cob tosulfuric acid. Within the experimental range, investigated by single factors, the mainfactors affecting the hydrolysis of corn cob was temperature and acid concentration,the hydrolysis ratio of corn cob increased with acid concentration increases, but whenthe acid concentration is too high, the obtained solution with serious carbonization, which was not conducive to the subsequent preparation of carbon microspheres.When the acid concentration was72%and temperature was55oC, the hydrolysis ratioachieved a satisfactory result, and sugar content in the solution was relatively high.(2) An orthogonal experimental design was needed to solve the concentrated acidhydrolysis of corn cob. According to range analysis, the hydrolysis time andtemperature were found to be the most important determinant of hydrolysis ratio andthe parameters influencing hydrolysis ratio were listed in a decreasing order asfollows: hydrolysis time> sulfuric acid concentration> hydrolysis temperature> ratioof corn cob to sulfuric acid.(3) The orthogonal experiment results showed that hemicellulose and cellulose inthe corn cob optimal hydrolysis conditions were as follows: hydrolysis time20min,acid concentration72%, hydrolysis temperature55oC, ratio of corn cob to sulfuricacid1:8, hydrolysis ratio was77.31%under the optimal hydrolysis conditions, thesugar content in the hydrolysis solution was43.22g/L.4. Preparation and Properties of the mixed sugar-based carbon microspheresUnder the optimal hydrolysis conditions hydrolysis corn cob, obtained mixedsugar solution was used to prepare carbon microspheres under different conditions.With temperature rising carbon microspheres began to agglomerate in the inner wallof the reactor. For describing the influence of acid concentration on the morphologyof the carbon microspheres, only low temperature160oC and the hydrothermaltreatment6h, the samples were compared under the acid concentrations29%,37%,40%,47%. The diameter of mixed sugar-based carbon microspheres is small, between0.5μm and1μm. When the acid concentration was40%, the agglomeration betweencarbon microspheres was lower and spherical-like more regular, diameter distributionis more uniform, easy to be dispersed, the yield of the product is about40%.Corncob which is rich of carbon element, can be used as raw materials to producehigh value-added carbon microspheres, this can solve the problems in the process of production of carbon microspheres and industrial use of corn cob, while can solvecorncob waste and environment pollution, thereby creating a higher economic valueand social value.