Study On Direct Liquefaction Properties Of Shengli Lignite And Co-liquefaction Properties Of It And Other Materials

China has abundant ligniteresources,and needs to be urgently exploited and utilized.Direct coal liquefaction to obtain fuels and chemicals is one of the most significant ways to high efficient and clean utilization of coal resource and is practical significance for national economy.Main research work and results in this paper are as follows:In this paper,direct liquefaction properties of Shengli lignite(SL)were studied firstlyunder four liquefaction systems which are hydrogen/tetralinsystem(H2/THN),hydrogen/n-hexanesystem(H2/HEX),carbon monoxide/water system(CO/H2O)and(hydrogen+carbon monoxide)/(tetralin+water)system((H2+CO)/(THN+H2O))).Meanwhile,kinetic models for heating-up and isothermal stages were developed under H2/THN system,respectively.The results show that the highest conversion and oil yield are obtained under(H2+CO)/(THN+H2O)system among four systems.Their values are 88.79%and 55.47%,respectively,at the liquefaction conditions(H2:CO=1:1(V/V),THN:H2O 1:1(V/V),400??initial pressure 4 MPa,30 min,the addition of catalyst 3%(Fe mass calculated),and S/Fe atom ratio 1.2).It indicates that the utilization of synthesis gas(H2+CO)is more feasible than pure hydrogen.In kinetic models,it is appropriate to divide SL into fast reactive part,slow reactive part and unreactive part.The main reaction approach is the quickly pyrolysis hydrogenation of fast reactive part in heating-up stage which converts to oil,gas,asphaltene and preasphaltene.The main reaction approach is the remaining fast reactive part reacted completely,slow reactive part converted into asphaltene and preasphaltene,meanwhile asphaltene and preasphaltene converted into oil and gas in isothermal stage.Results calculated from kinetic models show that the maximal conversion of SL is 97.02%,which is similar to the experimental result 97.19%(425?,180 min).Kinetic model reflects the process of SL liquefaction accurately.In H2/THN system,the active phases of iron-based catalyst(FC)were investigated with SL liquefaction in different conditions.The effect of Na2CO3(NC)on the activity of FC was also investigated in SL liquefaction.The results show that FC converts into the pyrrhotite(Fe1-xS)in H2/THN system and the corrosive reaction between Fe1-xS and H2 exists under liquefaction condition.The higher temperature reaction causes the faster rate of corrosive reaction,which results that converting Fe1-xS of a relatively sulfur-rich structure at low temperature into that of a relatively iron-rich structure at high temperature.Meanwhile,the crystallite size of Fej_xS increases as the temperature rises.Moreover,addition of NC obviously increases the conversion and oil yield of SL,and decreases the yields of asphaltene and water.With addition of NC from 0 to 5%,the conversion and oil yield increased from 74.95%to 86.34%,and 32.81%to 51.33%,respectively.The addition of NC is obviously beneficial for the asphaltene conversion into oil.The effect of NC on activity of FC in SL liquefaction is ascribed to two aspects.One is the promotion of hydrolyzation of ether and carbonyl group in SL.The other is the improvement of surface area of FC.The co-pyrolysis behavior of SL and CS was studied in thermogravimetric analyzer and the kinetic parameters were calculated.Further,the co-liquefaction behavior of SL and CS was also investigated,and FT-IR characterizations of asphaltene and preasphaltene from were obtained during individual liquefaction and co-liquefaction.The results show that there exists an synergistic effect during co-pyrolysis process,which results the increasing of volatile matter and decrease of char.Kinetic parameters indicate that addition of CS causes lower activation energy of SL pyrolysis between 350 ? to 500 ?.During the co-liquefaction of CS and SL,there also exists an obviously synergistic effect,which results in remarkable increase of conversion and oil yield.Compared FT-IR spectra of asphaltene and preasphaltene from individual liquefaction with that from co-liquefaction,it indicates that free radicals or intermediates produced by thermal degradation of CS promote the depolymerization of SL at low temperature.The new-formed free radicals or intermediates from co-liquefaction have higher activity of hydrogenated.The mass transfer and hydrogenation of SL and CS,and hydrogenation of product from liquefaction are enhanced in liquefaction system,resulting in strengthening the synergistic effect.The basic properties of biomass gasification tar were analyzed,while group composition was obtained by using column chromatography method.The separated fractions were characterized to obtain the relatively complete data.Further,hydro-thermal treatment of tar and co-process of SL and tar were investigated.The results show that the biomass gasification tar has some special properties(high water content,high viscosity,high heteroatom content,and high acid value)and has complex chemical composition of valuable compounds.Hydro-thermal treatment of tar can improve the content of oil,H/C atom ratio of oil,and the high heat value of oil.The content of oil increases 24.26%,the content of asphaltene and preasphaltene decrease 20.93%,and the content of residue decreases 5.81%with the optimum conditions(CO atmosphere,375 ?,addition of NC).During co-process of SL and tar,the conversion and oil yield are low,due to insufficiently activated hydrogen and insufficiently solubility of tar,resulting in that pyrolysis reaction of SL mainly occurred.