Air Pre-oxidation Assisted Humic Acid Preparation From Lignite And Pyrolysis Characteristics Of Its Residue

In this paper,the pre-oxidation of lignite was studied by the fixed bed and the process conditions of the fixed bed pre-oxidation experiment were optimized in order to increase the yield of humic acid in lignite and improve the deflocculation ability of humic acid.The study found that there were still more organic matters in the residual coal after extracting humic acid from lignite.Therefore,fixed bed pyrolysis experiments of lignite and residue were studied to explore the effects of different temperature on yields of pyrolytic products of lignite and residue.The humic acid is extracted from lignite firstly,then the residue is pyrolyzed for utilization.It is an effective way for the clean and efficient utilization of lignite resource.The effects of oxidation temperature and oxidation time on the yield of humic acid and flocculation characteristics of humic acid were studied by air pre-oxidation experiment.The optimum parameters of air pre-oxidation experimentwere obtained.The results show that the optimum process conditions are as follows: oxidation temperature is 150℃,oxidation time is 2 h.Under such conditions,the yield of total humic acid and free humic acid reaches the maximum.After air pre-oxidation of lignite,the total yield of humic acid increased from 48.30% to 56.30%,the yield of total humic acid increased by 16.56%;the yield of free humic acid increased from 46.00% to 51.90%,the yield of free humic acid increased by 12.83%.Moreover,the flocculation limit of lignite humic acid increased from 8.4 mmol/L to 8.8 mmol/L after preoxidation.The analysis indicates that oxygen yield in lignite increases significantly after preoxidation,oxygen-containing functional groups increase and carbon yield reduces.Humic acid and fulvic acid have high oxygen yield.Compared with humic acid,fulvic acid has higher oxygen yield and lower molecular weight.The flocculation limit of humic acid extracted from pre-oxidized lignite is higher than that of raw coal.The oxygen-containing functional groups are simultaneously extracted when the humic acid is extracted from lignite.Therefore,the yield of minerals in the residue is relatively high and the yield of organic matter in the residue reduces.The oxygen-containing functional groups mainly that phenol hydroxyl,carboxyl and carbonyl functional groups in humic acid are higher than the raw coal and residue.The fixed bed pyrolysis experiment of lignite and residue was adopted under the conditions of nitrogen flow rate of 50 mL/min,holding time 20 min and pressure 0.1 Mpa.The effect of oxidation temperature(400~600°C)on the yield and property of pyrolysis products of lignite and residue was investigated.The proper pyrolysis temperature for lignite and residue was 500°C.Under this condition,the yield of coal tar was 8.35% and the residue tar was 5.88%.In order to explore the influence of pyrolysis temperature,industrial analysis for char and GC analysis for gas at different temperature were studied.Then,we got the change of the properties of char and the distribution of gas.With the increasing pyrolysis temperature,the degree of pyrolysis of lignite and residue increases,the yield of char decreases and the yield of gas inceases.Tar of pyrolysis lignite and pyrolysis residue at 500°C was treated with picking,alkaline cleaning and column chromatography for separating into five fractions.Then we got the distribution information of each component by GC/MS analysis.