Study On Production Of Bio-oil By Sub-supercritical Hydrothermal Liquefaction Of Municipal Wet Sewage Sludge

Direct liquefaction of municipal sewage sludge(MSS)to product bio-oil could not only achieve reduction and harmless disposal of MSS,but also solve the current energy crisis.This work based on sub-supercritical hydrothermal liquefaction technology(HTL)combined with using organic–water mixed solvents as liquefied solvent to improve the yield and quality of bio-oil.The modern analytical instruments such as proximate analyzer,elemental analyzer,oxygen bomb calorimeter,Fourier transform infrared spectrometry(FT-IR),chromatography and mass spectrometry(GC-MS),thermo gravimetric analyzer were used for the comparative analysis of MSS,bio-oil and solid residue.Firstly,the orthogonal numerical analysis method was used to research the major effect factors during HTL of dried sewage sludge.The results showed that the most notable factor was temperature,followed by residence time and catalyst.At the same time,the yields of product obtained by HTL of dried and wet sewage sludge were compared,and the characteristics of bio-oils were also analyzed.The results indicated that a higher yield of biooil could be obtained under the conditions of lower temperature and shorter residence time when wet sewage sludge was used as a raw material for hydrothermal liquefaction,which solid residue yield was also declined.Besides,the composition of bio-oil obtained from HTL of wet sewage sludge was relatively simple.The effect of different organic–water mixed solvents on liquefaction of wet sewage sludge was investigated.The highest bio-oil yield of 46.51 wt% was achieved in methanol–water mixed solvent,of which ester content was increased to 38.11%.The lowest oxygen content was 7.65% of bio-oil achieved in n-hexane–water mixed solvent,of which the highest fatty acid compounds content was 54.86% and were in saturated state.The thermal stability of solid residue was enhanced in n-hexane–water mixed solvent.