Research On The Effect Of Low Molecular Compounds And Catalysts On The Coal Pyrolysis Products Distribution

Shenmu bituminous coal(SM),Daliuta bituminous coal(DLT),Xianfeng lignite(XF)and Xiaolongtan lignite(XLT)were used as raw coals.Solvents extraction was used to separate the low molecular compounds(LMC)in low rank coals to study the components and structures of LMC in different coals.The results show that the contents of low molecular compounds in lignites are higher than the contents of LMC in bituminous coals and LMC is mainly composed of aliphatics,aromatics and oxygen-contained compounds.The aliphatics are composed of C10-C31 alkanes.The contents of aromatics increase with the increase of coal rank.The aromatics in lignites are mainly monocyclic aromatics and bicyclic aromatics,aromatics in bituminous coal are mainly bicyclic aromatics and tricyclic aromatics.The oxygen-contained compounds contain phenols,ethers,ketones,acids and esters,its total content decreases with the increase of coal rank.The pyrolysis experiments of coals before and after extraction was carried out by the fixed bed reactor.The effect of LMC on the distributions of coal pyrolysis products and its transformation was researched.The results show that parts of pyrolysis water,tar and char generate by the pyrolysis of LMC.The oxygen-contained compounds decompose to form pyrolysis water.The oxygen containing functional groups in lignites was easily to break below 400 ? because of its weaker stability compared to that in bituminous coals which was broken under higher temperatures.The condensation degree of LMC in lignites is also lower so that the tar was formed in a lower temperature.The macromolecular structure of char was formed by the low temperature cross-linking reaction of hdrogen bond-linked LMC during pyrolysis process.The analysis of n-hexane soluble content in tars found that the contents of light component in tars from extracted coals were reduced corresponding with the LMC content.It indicates that parts of the light tar is contributed to the pyrolysis of LMC in coals.The GC/MS analysis showed that the tar derived from extracted SM coal had a lower content of polycyclic aromatics and a higher content of aliphatics.Otherwise,catalytic pyrolysis experiments were carried out to regulate the SM coal pyrolysis products.The pyrolysis of Shenmu coal with physically mixing three additives(USY zeolite,CaO,K2CO3)were studied in a quartz tube reactor at a heating rate of 5 ?/min from room temperature to 600 ? for a resident time of 15 min.The catalytic effect of three additives all made the lower total tar yield and the higher fraction of light components in the tar.And the biggest increase in light tar yield can be obtained by adding USY zeolite.The yield of light components in the tar increased from 9.5 wt.%to 11.1 wt.%on daf coal with adding 1 wt.%zeolite.The GC/MS analysis of the tar shows that the contents of both phenol and alkyl-phenols have the largest increase with the addition of USY zeolite.The content of phenol increased from 3.08%to 4.01%,increased by 30.19%.The content of C1-C3 alkyl-phenol increased from 6.84%,5.86%and 1.66%to 9.62%,8.25%and 2.59%,increased by 40.64%,40.78%and 56.02%,respectively.The GC analysis of gas component shows that CaO significantly inhibites the release of CO2,USY promotes the release of hydrocarbons gases and K2CO3 promotes the formation of hydrogen and gas yield.The addition of USY increases the high calorific value of pyrolysis.The 13C-NMR analysis of chars indicates that the increase of total phenols content in the tar was attributed to the catalytic cracking of aromatic oxygen carbon in coal structure.And the cracking effect of USY produced more CHx radicals that lead to the alkylation of phenols in tar to form more alkyl-phenols and the formation of C1-C4 hydrocarbons to release.And the effect on formation of phenols followed the order:USY>K2CO3>CaO.