Study On Catalytic Pyrolysis Of Biomass By Potassium And Catalytic Cracking Of Tar Over Char From Biomass Pyrolysis

Even if biomass resources in China is abundant and have a large reserves,its utilization rate as a resource is relatively low.In this work,some typical agricultural and forestry biomass resources including rice husk,corncob and pine wood were converted into clean syngas by high-temperature pyrolysis,which can not only realize efficient conversion of biomass but also have great significance for reducing greenhouse gas emissions.Potassium enriched in biomass matrix was chosen as catalyst for conversion of tar from biomass pyrolysis.On one hand,tar yield in gas product can be reduced.On the other hand,tar can be converted into small molecules gases,such as H₂ and CO,thereby recovering the energy in tar.The specific research work is as follows:?1?Potassium ion impregnated pine wood was obtained by impregnation.The effects of a heating rate and potassium ion concentration on the biomass pyrolysis process were studied under non-isothermal condition by TGA.Meanwhile,the denpendence of the apparent activation energy on the conversion degree?x?was calculated based on iso-conversional method?Flynn-Wall-Ozawa,FWO?.The results showed that the addition of potassium reduced initial and peak temperature in TGA curves,promoting the decomposition process of biomass.The values of apparent activation energy decreased with the increase in potassium concentration at the initial stage of biomass pyrolysis?x?0.3?,indicating that potassium has catalytic effect on biomass pyrolysis.?2?Potassium ion impregnated rice husk was obtained by impregnation and then the effect of potassium ion concentration on releasing of the main gas components?H₂,CO,CH₄ and CO₂?was inverstigated using micro-fluidized bed reactor analyzer?MFBRA?.In addition,the corresponding kinetic parameters for these four gas components were calculated by the Friedman and model-fitting methods to clarify the effect of potassium ion on the pyrolysis characteristics of biomass from the perspective of the product.The results indicated that the evolution profiles of the gaseous components were significantly influenced by temperature and potassium concentration.The reaction rate of H₂,CO and CO₂ increased with the increasing of the potassium impregnation amount,while CH₄ showed a reverse trend.The equal apparent activation energies for H₂,CO,and CO₂ obtained by the Friedman method decreased from 23.10 to 12.00kJ/mol,15.48 to 14.03kJ/mol and 10.14 to 7.61kJ/mol respectively with an increase in potassium concentration from 0 to 0.5mol/kg,while that for CH₄ increased from 16.85 to 19.40kJ/mol.The results indicated that the catalytic effect potassium could promote the releasing of H₂,CO and CO₂ in rice husk and inhibit the generation of CH₄ during the biomass pyrolysis process.?3?The effects of pyrolysis temperature and potassium ion concentration on in-situ catalytic conversion of tar from biomass pyrolysis tar were investigated by a fixed bed reactor.The results showed that when the pyrolysis temperature increased from 500?to 800?,the char and tar yields exhibited a downward trend,while the syngas yield showed an upward trend.In addition,the addition of potassium caused lower tar yield and higher gas yield in a certain concentration range.The production of H₂ and CO₂ was enhanced by the presence of potassium.However,excessive concentration of potassium led to agglomeration problem at higher temperature,resulting in higher tar yield and lower gas yield.Consequentially,adding of appropriate potassium had significant promoting effects on biomass pyrolysis and the agglomeration problem can be avoided.?4?Char-supported potassium catalysts were prepared by impregnation method.The effects of reforming temperature and potassium ion concentration on ex-situ catalytic conversion of tar from biomass pyrolysis were investigated by a two-stage fixed bed.The results indicated that the synthesized K-char catalysts exhibited high activity on the tar reforming.Heavy tar conversion efficiency increased with the increase of concentration of potassium ions in catalysts and reforming temperature in a certain extent.The highest catalyst activity was obtained at potassium ion impregnating concentration of 1.5mol/kg and 700?,with tar conversion efficiency of95.8%.Additionally,the carbon content decreased from 89.10 to 88.40%by using fresh and used 1.5K-char catalyst,and the potassium content was almost unchanged,contributing to prolong its service life.All these results indicated that the K-char catalysts have a potential to be used for tar elimination during biomass pyrolysis or gasification.