Pyrolysis Behaviors Of Sheng Li Lignite And Lignin Pretreated By Acidic Ionic Liquids

In view of the problems such as low tar yield and high content of heavy components that exist in the traditional process of lignite pyrolysis, the influence of acid ionic liquids pretreatment on the pyrolysis behavior of Shengli lignite is mainly studied in this paper.Also in order to regulate the composition of lignite pyrolysis tar through changing the weak bonding structure in lignite, new ideas for the lignite directionally transformed into high value-added products is provided. Based on that ionic liquids have shown good performance on the dissociating coal structure, the pyrolysis behaviors of SL were investigated by changing conditions of pretreatment, including 1-ethyl-3-methylimidazolium acetate?[Emim]Ac?, different acidic ionic liquids, pretreatment conditions?temperature, the ratio of ionic liquids to lignite?, pretreatment metheds?the order of different ionic liquids used? and the heating rate. Also the effect of 1-?4-sulfonic acid?-butyl-3-methylimidazolium trifluoromethanesulfonate?[B?SO₃H?mim]OTf?pretreatment on the change of structure of lignin and its pyrolysis behavior was studied.The results show that [Emim]Ac, acidic ionic liquids used in this paper,sequential pretreatment with 1-ethyl-3-methyl-imidazolium chloride?[Bmim]Cl? and[B?SO₃H?mim]OTf can improve the tar yield of SL lignite pyrolysis. Compared with that of raw coal, tar yield obtained from pretreated is increased by 1.91 times at most.At a heating rate of 10oC/mim, ionic liquid pretreatment can reduce the content of heavy components in SL lignite pyrolysis tar and its average molecular weight. The ionic liquids with neutral X- shows a better peformance on improving the tar yield than that with acidic X- in the case of pretreatment of SL with acidic ionic liquid[B?SO₃H?mim]X. Compared with that of raw coal, in the case of pretreatment with[Emim]Ac, [Bmim]Cl, 1-?4-sulfonic acid?-butyl-3-methylimidazolium benzene sulfonate?[B?SO₃H?mim]MBS?, the tar yields of aliphatic compounds, aromatic compounds, phenol compounds in light tar of SL lignite pyrolysis are increased by4.25 times, 14.25 times and 3.62 times respectively.FI-RT, TG/DTG and swelling analysis show that ionic liquid pretreatment results in the increase of the contents of aromatic ether and phenol/aliphatic ether; the damage of aromatic ring side chains and the release of short-chain structures of small molecules in SLlignite. [Emim]Ac pretreatment of SL can disrupt the methylene structure in SL lignite.Ionic liquid pretreatment improve volatile content in SL lignite. The polycondensation in SL lignite pyrolysis pretreated by [Emim]Ac is weakened, oppositely, which is strenghtened by sequentially pretreatment with [Bmim]Cl and [B?SO₃H?mim]OTf. Some minerals in SL lignite are removed by [E?CO2H?mim]Cl effectively.[B?SO₃H?mim]OTf pretreatment under mild conditions?such as 50oC? can improve the pyrolysis tar yield of lignin, with 11.8% increase than that of raw lignin. The heavy tar content obtained from pretreated lignin pyrolysis is decreased. The light tar obtained from lignin pyrolysis mainly contains oxygen containing compounds, the yield of oxygen containing compounds obtained from [B?SO₃H?mim]OTf pretreated lignin increased by1.51 times compared with that of raw lignin. FI-RT and TG/DTG analyses show that carbonyl and ether bond in lignin are increased after pretreatment. The volatile content of[B?SO₃H?mim]OTf pretreated lignin at higher temperature?such as 200oC? is decreased,and the polycondensation in lignin pyrolysis is weakened.