Efficiency And Mechanism Of Sludge Catalytic Pyrolysis Process

Sludge pyrolysis realize the conversion and utilization of bioenergy in sludge,and at the same time,high value-added materials such as sludge-based adsorbent,sludge-based biochar and sludge-based catalyst can be prepared.Scholars at home and abroad have carried out extensive research on sludge pyrolysis in recent years.In this thesis,sludge pyrolysis kinetics,gaseous products,transformation of nitrogen and sulfur were investigated;the efficiency and mechanism of in-situ catalytic pyrolysis with sintering and Bayer red muds,and the mechanism of preparation of magnetic sludge base adsorbents were investigated;the efficiency and mechanism of ex-situ catalytic pyrolysis with HZSM-5?H??HY?Mesoporous HY?LaY?Ce-LaY zeolites and Bayer red mud,rice husk ash and Mo C.Sludge pyrolysis can be divided into three weightlessness stages of 50-200°C,200-550°C,550°C and above;the average values of apparent activation energy calculated by Friedman,FWO and KAS methods are 255.09 k J/mol,224.11 k J/mol and 225.59 k J/mol,respectively;the pyrolysis of sludge is most in line with the secondary reaction mechanism.When the pyrolysis temperature increased,the content of acid organics in the pyrolysis gas products of sludge gradually decreased,the content of hydrocarbons generally showed an upward trend,and the percentage of nitrogenous organics and phenolic products gradually increased.As the pyrolysis temperature increased,the proportion of C16 and C18 organics gradually decreased,and the proportion of low-carbon organics gradually increased,with the smaller the average H/C and O/C of the pyrolyzed gaseous products,and the higher the high calorific value and effective calorific value of the gaseous products.The characteristic sulfur-containing compounds in the pyrolysis gaseous products of methionine in sludge are CH₄S and C₂H₆S₂;the characteristic sulfur-containing compounds in the gaseous pyrolysis products of cysteine are H₂S,thiophenes and ethylene sulfide;the characteristic sulfur compounds of cystine pyrolysis gaseous products are H₂S,CS₂and ethylene sulfide.Adding Bayer red mud as an in-situ catalyst can effectively reduce the proportion of C16 and C18 products in pyrolysis gaseous products.The proportion of red mud added by Bayer process increased,and the relative percentage content of gasoline-range organics in the gaseous products of sludge pyrolysis gradually increased;the acids in pyrolysis gaseous products showed a significant downward trend.When the goal is to obtain hydrocarbon products,Bayer red sludge/sludge=0.1 was the optimal addition ratio of sludge pyrolysis in-situ catalyst.The in-situ catalysis of red mud by sintering method and Bayer method can change the composition of gaseous products of sludge pyrolysis,mainly by changing its pyrolysis reaction path.The basic active center O^2-in Ca O,Fe₂O₃ and Al₂O₃ in red mud can capture protons in the carboxyl hydroxyl groups of fatty acids such as hexadecanoic acid and octadecanoic acid to form unstable intermediates such as carbanions and accelerate crack of long-chain fatty acids and make the acid products and long chain organics decrease overall.Adding 10%,20%and 30%Bayer red mud,the specific surface area of the sludge-based adsorbent is 2.97,5.09 and 6.44 times the specific surface area of the adsorbent prepared by pyrolysis of the original sludge;the magnetic particles in the sludge-based adsorbent percentages were all over 98%;the saturation magnetic induction strength of the prepared sludge-based adsorbents were 13.63,20.63 and26.83 times of the saturation magnetic induction strength of the adsorbent prepared by original sludge pyrolysis,respectively.The sludge pyrolysis process produced reductive H₂,C_xH_y,CO and amorphous carbon,which could undergo redox reaction with Fe₂O₃ in sludge and red mud under high temperature conditions and produce Fe₃O₄.Magnetic particles containing Fe₃O₄ and sludge pyrolytic particles were bound together to form a sludge-based adsorbent material which was magnetic overall.When the catalyst section was not filled with catalyst,the relative content of organic matter with higher carbon number decreased,as the relative increase in pyrolysis time,the pyrolysis gaseous products of sludge undergo further cracking in the catalyst section.When the HZSM-5 catalyst,HY catalyst and H?catalyst were loaded in the ex-situ catalytic section,the percentage of organic matter in the final gaseous product above C15 was reduced to below 1%.The three microporous zeolites HZSM-5,HY and H?can significantly increase the content of gasoline range organics in the final gaseous product.The hydrocarbons in the gaseous product increase significantly,reduce the content of diesel range organics and upgrade the quality of gaseous product.The mechanism of HZSM-5 catalytic pyrolysis was studied using molecular dynamics method based on reaction forcefield(Reax FF MD).The results showed that HZSM-5 catalyzed stearic acid pyrolysis mainly consisted of adsorption,carbon cation generation,carbon cation cracking and organic matter adsorption on zeolite with the main reaction process such as deoxygenation or carbon chain breaking reaction.When the mesoporous HY catalyst,La-loaded HY catalyst and Ce-La bimetal-supported HY catalyst were loaded in the ex-situ catalytic section,the organic content of the final gaseous product above C11 was less than 1%,and the three zeolite catalysts can significantly upgrade the final gaseous products.Comparing 9 kinds of ex-situ catalytic materials,LaY has the best ex-situ catalytic pyrolysis efficiency,the final gaseous products have higher organics in the gasoline range,lower organics in the diesel range,and higher hydrocarbon organics content.Among the non-zeolite catalysts,rice husk ash has the highest catalytic efficiency,and the content of gasoline range organic matter in the final pyrolysis product reaches 73%.Although other catalytic performance indicators are poor,considering its cost is much lower than that of zeolite catalysts,there are still certain applications value.