Study On Process Optimization And Structural Properties Of Lignite For Preparing Humic Acid

Coal,one of the important energy sources in the world,is an important raw materials of modern metallurgy and chemical industry.Lignites play a significant role in field of coal chemical industry.Humic acid(HA) is an important part of lignites with high application value.In this paper,Baoqing and Eshan lignites belong to high contain HA lignites.Basis on the efficient utilization,Response Surface Methodology(RSM) was investigated on optimal conditions for HA production under diverse solvents f or increasing the extraction ratio of HA,which can pave an academic way for the process of lignites to HA in industrial applications.Lignite and HA both are macromolecular organic compounds,and their structural features are hot issues and difficulties all the time.This paper was studied on the relationship between lignites and HAs followed by feedstocks.Differences and similarities of HAs prepared from diverse solvents were compared,and structural features were investigated.In conclusion,the results supported the further studies.The main contents of this paper are as follows:(1)Baoqing lignite(BQ) and Eshan lignite(ES) were selected as the main research objects.The oxygen-containing functional groups,rate of aromatic carbon,microcrystalline structures,surface elements,carbon chain structure and thermal stability of lignite were analyzed.Its research results are:BQ belongs to high ash coal,extra high volatile coal,and low sulfur coal,and ES belongs to low ash coal,extra high volatile coal,and extra low sulfur coal,and they contain many oxygen-containing functional groups.The microcrystalline structures of BQ and ES are similar;For the BQ,the ratios of aromatic carbon and aliphatic carbon are 29.20% and 67.09% respectively,while the ES are 42.73% and 51.75%respectively;These two lignites have great thermal stability;The contents of carbonate in BQ are more than that of ES,and ES contains more aromatic structures.(2)Three solvents including KOH,NaOH and Na ₄P₂O₇ were used as extractant to extract HA from BQ.Selecting extraction yield of HA as the response value,RSM was used to study the effects of reaction time,reaction temperature,extractant concentration and interactions on the response value.The results show that the effect of reaction temperature on response value is greatest,and the interactions also have effects on the response value.The optimization processes of extracting HA from BQ using KOH solution are:temperature is 86?,concentration of KOH solution is 0.04 mol/L,reaction time is 2.0 h,and the yield of HA is 82.99%;The optimization processes of extracting HA from BQ using NaOH solution are:temperature is 94?,concentration of NaOH solution is 0.047 mol/L,reaction time is 1.7 h,and the yield of HA is 87.96%;The optimization processes of extracting HA from BQ using Na₄P₂O₇ solution are:temperature is 72?,concentration of Na₄P₂O₇ solution is 0.027 mol/L,reaction time is 2.0 h,and the yield of HA is 86.13%.(3)KOH,NaOH and Na₄P₂O₇ solvents were used as extractant to extract HA from ES.Selecting extraction yield of HA as the response value,RSM was used to study the effects of reaction time,reaction temperature,extractant concentration and interactions on the response value.The results show that the effect of reaction temperature on response value is greatest,and the interactions also have effects on the response value.The optimization processes of extracting HA from ES using KOH solution are:temperature is 75?,concentration of KOH solution is 0.043 mol/L,reaction time is 2.0 h,and the yield of HA is 91.20%;The optimization processes of extracting HA from ES using NaOH solution are:temperature is 86?,concentration of NaOH solution is 0.039 mol/L,r eaction time is 2.4 h,and the yield of HA is 87.96%;The optimization processes of extracting HA from ES using Na₄P₂O₇solution are:temperature is 90?,concentration of Na₄P₂O₇ solution is 0.033 mol/L,reaction time is 1.6 h,and the yield of HA is 86.1 3%.(4)Differences in structural performance of HA extracted from lignites using different extractant.The element content,oxygen-containing functional groups,rate of aromatic carbon,microcrystalline structures,surface elements,carbon chain structure and thermal stability of lignite were analyzed.And the structural characteristics of lignites and HA were compared.The results show that the differences in structure characteristics of HA,extracted from lignites using three solvents,are minor.HA extr acted from lignite using NaOH and Na ₄P₂O₇ solution may contain more oxygen-containing functional groups.Generally,structural characteristics of them are minor.(5)Comparison of structural characteristics between HA and lignites.The results show that:The structural characteristics of HA are similar to lignites.However,HA contains more oxygen-containing functional groups,lower ash content;The comparison of the two microcrystalline parameters shows that the lamellar size(L_a) of HA is lower;The conte nts of polysaccharides structure in HA is lower.In HA,the ratio of aliphatic carbon is lower,while the ratio of aromatic carbon is higher;By comparing thermal analyses of HA and lignites,the results indicate that the thermal stability of HA is also very good,the structure is more stable,the cyclic organic matter is more,and there is no carbonate.