Effects of iron catalyst and atmosphere on sulfur transformation during pressurized low-temperature pyrolysis of Baishihu coal
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摘要: 选取镜质组含量高的白石湖煤为研究对象，考察了高分散铁催化剂及热解气氛对煤加压低温热解过程中硫元素迁移影响。采用GC-SCD和FT-ICR MS研究了热解焦油中含硫化合物分子组成，采用XANES研究了热解半焦中硫分子结构。结果表明，白石湖煤中的硫化物主要是煤主体结构中侧链的S1类。催化剂中的单质硫助剂在热解过程中部分会进入焦油中形成硫醇或硫醚化合物。高分散铁系催化剂能活化煤中的氢原子，促进焦油中芳香硫化物的氢化饱和及裂解。该催化剂优先捕获硫化氢，增加了焦炭中黄铁矿的含量，抑制了半焦中硫酸盐的生成。在H2气氛和高分散铁系催化剂的作用下，噻吩类化合物明显减少，亚砜类化合物减少。Abstract: A vitrinite-rich low rank coal, Baishihu (BSH) coal with moderate sulfur content was treated by dehydration and crushing. The treated samples were pyrolyzed in an alloy tubular reactor under 2 MPa. Influence of iron catalyst and atmosphere on sulfur transformation during pressurized low-temperature coal pyrolysis was investigated. Molecular composition of sulfur compounds in tar was characterized by gas chromatography with sulfur chemiluminescence detector (GC-SCD) combined with Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS). Sulfur K-edge XANES was used to study sulfur molecular structure after pyrolysis. Sulfur compounds in BSH coal are predominantly S1 class species in branch chain of the coal. Elemental sulfur in catalyst enters the tar and forms mercaptan or thioether compounds during pyrolysis. Iron catalyst promotes activation of hydrogen atoms in coal and contributes to hydrogenation saturation and cracking of aromatic sulfide in tar. The catalyst preferentially captures H2S to increase content of pyrite in char and inhibits formation of sulfate. Under H2 atmosphere, significant decrease of thiophene compounds is observed with catalyst coupled with decrease of sulfoxide compounds.
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Key words:
- sulfur transformation /
- FT-ICR MS /
- XANES /
- coal pyrolysis /
- iron catalyst
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Figure 2 GC-SCD analysis of tar by pyrolysis of (a)BSH-R-A, (b)BSH-C-A, (c)BSH-R-H, (d)BSH-C-H
sulfur-containing compounds are denoted by the following letters: mercaptan (MN), sulfoether (SF), thiophene (T), thiophene derived compounds (Ts), benzothiophene (BT), benzothiophene derived compounds (BTs), dibenzothiophene (DBT), dibenzothiophene derived compounds (DBTs)
Figure 3 Relative abundance of heteroatom classes for the methylated tar by pyrolysis of (a) BSH-R-A, (b) BSH-C-A, (c) BSH-R-H, (d) BSH-C-H ESI FT-ICR mass spectrum
Figure 4 Plots of DBE versus the carbon number for S1 class species in methylated tar by pyrolysis of (a) BSH-R-A, (b) BSH-C-A, (c) BSH-R-H, (d) BSH-C-H ESI FT-ICR mass spectrum
the largest dot corresponds to the most abundant monosulfur species in the sample
Figure 6 Sulfur K-edge XANES spectra of BSH coal and its chars under different atmospheres
Table 1 Proximate and ultimate analyses of coal samples
Ultimate analyses wdaf/% Proximate analyses w/% C H N S O Mad Ad Vdaf FCdaf 75.01 4.82 0.96 1.16 18.05 16.67 6.37 50.60 49.4 note: ad is air-dried basis; daf is dried and ash-free basis 
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Table 2 Sulfur forms analysis of coal samples
Sulfur forms in coal w/% Sulfur form ratio in total S w/% St Ss Sp So Ss Sp So 1.16 0.07 0.04 1.05 6.17 3.17 90.66 note: St is total sulfur; Ss is sulfate sulfur; Sp is pyrite; So is organic sulfur
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Table 3 Effect of iron catalysts and atmosphere on pyrolysis
Sample# Tar yield w/% Char yield w/% BSH-R-A 8.21 63.57 BSH-C-A 8.37 63.50 BSH-R-H 8.24 63.47 BSH-C-H 8.54 63.11 #: sample code A-B-C means that the sample was obtained by pyrolysis of coal A (BSH = Baishihu coal) with the addition of B (R = raw coal, C = iron catalyst) in atmosphere C (H = H2, A = Ar)
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Table 4 Sulfur distribution in different phases
BSH-R-A w/% BSH-C-A w/% BSH-R-H w/% BSH-C-H w/% gas tar char gas tar char gas tar char gas tar char 5.22 57.97 36.81 9.28 43.46 47.26 5.51 63.85 30.64 10.26 40.76 48.98
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Table 5 GC-SCD analysis result of tar by pyrolysis of (a)BSH-R-A, (b)BSH-C-A, (c)BSH-R-H, (d)BSH-C-H
Sample MN&SF/% T&Ts/% BT&BTs/% DBT&DBTs/% BSH-R-A 45.66 19.28 32.41 2.65 BSH-C-A 49.43 16.37 31.75 2.45 BSH-R-H 41.39 31.81 24.35 2.45 BSH-C-H 42.16 30.73 25.02 2.09
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