Role Of Inherent Active Minerals And Neutral Extractives In Pyrolysis Of Agricultural Crop Residues

In this paper,the slow pyrolysis of five agricultural crop residues,peanut straw(PS),cotton straw(CTS),sorghum stalk(SS),corn stalk(CS)and reed(RD),was carried out at the final temperature of 700℃ using thermogravimetric analyzer and a fixed bed reactor.The aim of this study is to investigate the influences of AAEMs and NDS on product distribution,bio-oil composition and quality by comparing different varties of biomass,water washing and neutral detergent extraction of biomasses.The main contents are outlined as follows.The role of AAEMs and NDS in the pyrolysis of agricultural crop residues were investigated through an indirect comparative study.The concentrations of AAEMs in five crop residues were PS(4.43%)>CS(2.46%)>CTS(1.91%)>SS(1.66%)>RD(0.58%).PS had the highest concentration of NDS(47.4%)as compared with 14.9-17.4%for the other biomasses.RD showed the highest bio-oil yield of 31.5 wt%(dry basis),but with the lowest HHV of 25.9 MJ/kg due to its highest oxygen O/C atomic ratio.PS exhibited the lowest bio-oil yield of 24.3 wt%,but the bio-oil had a higher proportion of hydrocarbons of 27.2%and a higher proportion of nitrogenous compounds of 35.8%,with the lowest O/C atomic ratio and a high HHV of 36.0 MJ/kg.The bio-oils produced from CS and SS contained the most oxygenates,with the proportions of 87.8-88.5%,but the HHV was higher due to the abundant presence of long chain fatty acids.These differences in the pyrolysis results were closely related to the different concentrations of AEMMs and NDS in these biomasses.A water washing pretreatment method was adopted to remove a fraction of AAEMs and NDS from three selected agricultural crop residues(PS,SS and RD).The characteristics of pyrolysis were investigated by comparing the results obtained from the original biomasses and pretreated biomasses.The results showed that 73.4-92.6%of K and 47.0-56.1%of NDS were removed from three biomasses,and RD had the highest K removal and PS had the highest NDS removal.The onset release gases was shifted to a higher temperature for three washed crop biomasses,with a reduced gas yield by 3.1-5.8 wt%,while the bio-oil yield and the moisture yield increased by 1.3-2.3 wt%and 4.4-5.7 wt%,respectively.Among three biomasses,RD had the largest increase in the yields of bio-oil and moisture,and PS showed the most signifincant increase in the proportion of oxygenates,from 35.74%to 74.24%,with many longchain fatty acids appearing in the bio-oil.The results indicated that the pyrolysis behaviors were strongely affected by how much of AAEMs and NDS present in biomasses.The role of AAEMs and NDS in the pyrolysis was further investigated by deeply removing AAEMs and NDS from three biomasses(PS,SS and RD)via a neutral extraction approach.After the neutral extraction,the gas yield decreased for PS,opposite to the results of SS and RD.The bio-oil increased for all three biomases,but the extent of increase was lower compared to the results obtained after the water washing.The proportions of hydrocarbons and nitrogen compounds in the bio-oils substaintially decreased after the netural extraction;meanwhile,not only the varities but also the proportions of long-chain compounds decreased significantly,while the O/C ratio increased for all three bio-oils.The results further suggested that NDS had a tendancy of producing long chain compounds,hydrocarbons and nitrogenous compounds,while AAEMs could facilitate the decomposition and deoxgenation of bio-oil.