Study On Catalytic Cracking Reaction Of Fatty Acid Methyl Esters And Deoxygenation Mechanism

Producing biofuels by catalytic cracking of waste oil is an effective way to relieve the energy crisis of petroleum.However,oxygen-containing compounds in the liquid product makes the inferior stability of the biofuel and reduces the calorific value.Thus,effectively controlling the generation of oxygen-containing compounds is the key to improving the catalytic cracking technology of fatty acid ester.In this paper,influences of carbon chain length of fatty acid methyl ester?FAME?and reaction conditions on product distribution in the catalytic cracking process were investigated in a fixed-bed microreactor.Different carbon chain length of FAMEs were used as feeds.Catalytic cracking reaction path of FAME was revealed according to the analyzed results by gas chromatography,gas chromatography-mass spectrometry and Fourier transform infrared spectrometer.Effect of carbon chain length on catalytic cracking of FAME was studied firstly.With the increase of carbon number of FAME,the conversion of FAME increases.The yields of dry gas,liquefied petroleum gas?LPG?,propylene,CO and CO₂ increase gradually.The yields of alkanes,alkenes,aromatic in liquid products also increase,while the content of oxygen containing compounds in organic liquid product decrease.The longer the length of carbon chain of FAME is,the easier it is to crack.With the increase of temperature,the conversion rate of FAME increases gradually,and the conversion rate could reach 100%at 500?.The gas product yields of dry gas,LPG,propylene increase gradually,and the molar yield of CO and CO₂ also increase with the increase of reaction temperature.At lower temperature,CO₂ is the main product of deoxygenation,and aldehydes,esters,carboxylic acids and ketones are the main organic oxygenated compounds generated from catalytic cracking of FAME.However,at higher temperature,liquid products contain almost no organic oxygenated compound,and CO is the main product of deoxygenation.Catalyst-to-oil ratio and weight hourly space velocity?WHSV?have less effect on the catalytic cracking process.The conversion rate of FAME increases with the increase of the catalyst-to-oil ratio and the decrease of WHSV.Catalytic cracking of fatty acid methyl ester has four possible paths.One of the four paths is the dominate path.The cleavage of C-O bond take place readily before C-C bond cleavage,which results macromolecular oxygen-containing compounds?carboxylic acids,aldehydes,ketones?,and then the macromolecular oxygen-containing compounds take the secondary reaction to generate alkanes,alkenes,aromatic,CO,CO₂ and H₂O.Aromatic hydrocarbons generate coke through condensation.The composition of coke mainly includes soft coke I,soft coke ? and hard coke.Soft coke I and soft coke ? mainly contains some alkanes,aromatics and oxygen compounds.Soft coke I coming from catalytic cracking of octanoic acid methyl ester?OAME?contains polycyclic aromatics and the highest aromatic ring number is 3.However,the highest aromatic ring number of polycyclic aromatics in soft coke ? is 6.The condensation degree of aromatic in catalyst pore is higher than that of aromatic on catalyst surface.