Study On Liquefaction Of Tannery Sludge In Supercritical Ethanol

Traditional sludge landfill can neither achieve sludge reduction,harmlessness,nor can it achieve resource utilization since it can waste abundant organic content in tannery sludge.Based on the direct thermochemical liquefaction that enables resource utilization without drying the sludge,this study innovatively proposed a liquefaction technology in supercritical ethanol,which was performed in a self-designed and constructed supercritical pyrolysis liquefaction experiment system.The ethanol solvent,instead of water,was used because ethanol solvent with strong surface tension and uniform dispersion can realize supercritical condition easier than water.The research work and achievements of this paper are as follows:(1)The physicochemical and pyrolysis kinetics of tannery sludge samples were studied through elemental analysis,industrial analysis and TG&DTG analysis.The results showed that the pyrolysis process of the sludge was divided into three stages,and the last two stages were the main pyrolysis stage,meanwwhile,the kinetic parameters and equations at different heating rates were obtained by Coats-Redfern integral method.(2)The key influencing factors of the direct supercritical liquefaction reaction,were discussed.The effects of temperature,residence time,sludge-to-methanol ratio(w/v),ethanol filling rate and catalyst on the oil production process were investigated to find the optimal reaction conditions.The results showed that the yield of oil obtained was the highest(up to 42.7%)at the temperature of 290? and the residence time of 60 min,when the solid-liquid ratio of sludge/ethanol was 1/20 and 200mL ethanol was added,and the catalyst could effectively promote the oil production.After that,through L9 orthogonal experiment,the effect order of the oil production rate was obtained:temperature>the amount of ethanol added>the residence time>the type of catalyst.(3)The composition and characteristics of the oil production and solid residue obtained by supercritical liquefaction were qualitatively and quantitatively analyzed by gas chromatography-mass spectrometer(GC-MS)and X ray fluorescence(XRF).The result showed that the oil produciton had a good oil performance since the pyrolysis oil calorific value reached 30.29MJ/kg,and most of the heavy metal ions in the tanning sludge were transferred to the solid residue.