Aaems Migration And Effects On Peanut Shell Pyrolysis Process

In order to solve the problems such as instability of equipment operation and low product quality caused by AAEMs element in biomass structure,peanut shell was selected as the research object in this paper.The migration and precipitation of alkali and alkaline earth metals and its influence on products were investigated during the pyrolysis process.Firstly,the peanut shell sample is subjected to the leaching treatment using de-ion water,NH₄Ac solution and HCl solution to determine contents and patterns of alkali and alkaline earth metals（AAEMs）,and the micro-structure and functional group are checked to analyze the effect of leaching treatments.As a result,potassium mainly exists as water-soluble components.Calcium and magnesium exist bonded with organo-functional groups,while sodium exists as water-soluble and indissoluble salts.De-ion water leaching treatment affects the structure slightly and NH₄Ac solution and HCl solution obviously changed the surface structure and portion of functional groups.Chemical fractionation pretreatment decreased ash content and increased calorific value and volatile content of peanut shell samples.Secondly,the pyrolysis experiments of peanut shells which are before and after de-ion water leaching were carried out in a fixed bed reactor to explore the migratory behavior of AAEMs and its effect on pyrolysis products.It was found that during pyrolysis process of unwashed peanut shell,contents of AAEMs in char increased with the increase of pyrolysis temperature,while contents of AAEMs in volatile decreased.The water-soluble AAEMs in peanut shell were removed by water leaching treatment,which play a dominant role in tiny releasing contents of AAEMs.Then,compared the change of pyrolysis yield and the bio-oil components of peanut shell before and after removal of water-soluble alkali metal（AAEMs）in pyrolysis condition at 350℃,450℃,550℃and 650℃.It was shown that the occurrence of water-soluble AAEMs promoted the secondary decomposition of pyrolysis products into small molecules and reduced the yield of bio-oil.Simultaneously,with the increase of reaction temperature,the exist of AAEMs had a little effect on acids and alkenes,but promoted the formation of ketones and inhibited the formation of alcohols,esters,aldehydes,sugars,etc.Although AAEMs have no obvious inhibitory effect on phenolic substances,they promote the thermal decomposition of cellulose and hemicellulose,and indirectly reduce the relative content of phenols.Finally,the kinetic study on the effects of different forms of AAEMs,water-soluble alkali metal and heating rates for peanut shell pyrolysis were investigated by TGA.The activation energy of the sample increased by 11.75k J/mol when it was treatmented by de-ion water leaching treatment,and pyrolysis process was facilitated.The removal of AAEMs bond with functional groups decreased the activation energy of peanut shell by9.42k J/mol,which could inhibit the pyrolysis process.The removal of acid-soluble AAEMs promotes the activation energy,up to 1.56k J/mol.