Study On Thermochemical Characteristics Of Cassava Dregs And Preparation Of Hydrogen-rich Pyrolysis Gas

With the rising of petroleum price, production of fuel ethanol with non-grain cropssuch as cassavas, has drawn much attention and cassavas has been listed as thesignificant energy crop for the development of our country. Cassavas dregs, the solidwaste of the fuel ethanol production, can be used to high productivity and easydegradation. Therefore it is of great importance to make rational use of the cassavasdregs to create considerable economic benefits in the development of cassavasindustry. However, only a few researchs were focused on the solid waste of the fuelethanol production and on the thermal chemistry characteristics analysis of thecassavas dregs with or without anaerobic treatment. In this study, we determined thechemical composition of the cassavas dregs and analyzed the thermal chemistrycharacteristics of the cassavas dregs. We also used a self-built tube furnace reactor tostudy the parameters of the pyrolysis process of the cassavas dregs.The results illustrated that the air-dried cassavas dregs were solid waste which havehigh organic contents. For the cassavas dregs without pyrolysis, the organic contentwas61.45%: the C content was38.42%and the H content was5.32%, while thecellulose content was25.45%and hemicellulose content was17.34%. The higherorganic content than that of anaerobic treated cassavas dregs demonstrated that theair-dried cassavas dregs were pyrolytic raw materials with high quality and highcarbohydrate content.The results of the thermal chemistry characteristics analysis showed that thepyrolysis of cassava dregs processes could be divided into three stages: volatilizationof water(25-200°C)、decomposition of organic substances(200-600°C)、decompositionof inorganic substances(600-1000°C). The amount of the organic substances releasedfrom the anaerobic digested cassava dregs was smaller than that from undigestedcassava dregs. The content of the pyrolysis residue was decreased with the increase ofthe pyrolysis temperature. The main resultant gases were H2，H2O，CO，CH4，CO2etc., with the similar tendency of the gas production curves. It could also be revealedthat with the increase of the heating rate, the productivity of H2was enhanced. Thecassavas dregs with larger size showed more H2yield and the optimal moisturecontent was43%.The pyrolysis experiments of two different kinds of cassavas dregs were carried oututilizing the self-built tube furnace reactor under the atmosphere of N2+H2O and temperature ranged from600to900°C. The results demonstrated that the increase ofthe pyrolysis temperature, the heating rate and the particle size could have certaineffects on the states of the products, such as the increase of the gas yield, especiallythe yields of H2and CO. At900°C, the H2content of the gas products could reachabout35%for the cassavas dregs without anaerobic treatment and24%for theanaerobic treated ones. The component analysis of the tar revealed that thewater-soluble tar contained50%of acetic acid while the water-insoluble tar containedmostly oxy-organics, aliphatic hydrocarbons, aromatic hydrocarbons andnitrogen-containing heterocyclic compounds.The FTIR spectra showed the changes of the chemical groups of the cassavas dregswith the proceeding of the pyrolysis process. The XRD analysis showed that thecarbonization degree was enhanced with the proceeding of the pyrolysis process. TheSEM photographs illustrated that the cassavas dreg surface was damaged moreseriously with more defects and higher roughness as the pyrolysis temperature wasincreased.