TG-MS与Py-GC相结合法研究惰性气氛下含硫模型化合物热解过程中硫的脱除及释放行为研究

采用热重-质谱法(TG-MS)和热解-气相色谱法(Py-MS)相结合的方法对模型化合物(十四硫醇、二丁基硫醚、苯硫醚、二甲基噻吩、苯并噻吩和二苯并噻吩等)在惰性气氛下硫的脱除及释放行为进行研究。惰性气氛下硫的脱除顺序为:十四硫醇>二丁基硫醚>二甲基噻吩>苯并噻吩>苯硫醚>二苯并噻吩,苯硫醚除外,该顺序与含硫官能团的热分解顺序一致。在热解过程中,所有模型化合物在质谱和气相色谱仪上均被检测到SO₂;除苯硫醚和二苯并噻吩外,其他模型化合物中均检测到了COS;而只在十四硫醇、二丁基硫醚和二甲基噻吩中检测到了H₂S。且热解气中SO₂含量要显著高于H₂S和COS。这是由于活性炭作载体时,惰性气氛下内部氢的含量显著小于内部氧的含量,所以大多数的含硫自由基易与内部氧结合以SO₂的形式逸出。对于苯硫醚、苯并噻吩和二苯并噻吩中没有检测到H₂S,是由于内部氢的不足,使得含硫自由基不能与内部氢结合,所以没有检测到H₂S逸出。

Sulfur removal and release behaviors of sulfur-containing model compounds during pyrolysis under inert atmosphere by TG-MS connected with Py-GC

Sulfur containing model compounds, tetradecyl mercaptan, dibutyl sulfide, phenyl sulfide, 2-methyl thiophene, benzothiophene and dibenzothiophene, were selected to investigate their sulfur removal and release behaviors during pyrolysis under inert atmosphere by thermo-gravimetric analyzer with mass spectrometer (TG-MS) and pyrolysis connected with gas chromatogram (Py-GC). It was found that the order of sulfur removal was tetradecyl mercaptan > dibutyl sulfide > 2-methyl thiophene > benzo thiophene > phenyl sulfide > dibenzothiophene. Except for phenylsulfide, this rule is contrary to the decomposition temperature order of the sulfur functional groups. SO₂ evolution was detected by MS and GC for all those model compounds and COS evolution was also found except for phenylsulfide and dibenzothiophene; while H₂S evolution was measured only for tetradecyl mercaptan, dibutyl sulfide and 2-methyl thiophene. However, SO₂ content was much higher than H₂S and COS in pyrolysis gas for each model compound, which may be caused by that indigenous hydrogen was much less than indigenous oxygen under inert atmosphere, when actived carbon was used as carrier. Thus, most of sulfur radicals can connect with indigenous oxygen and release in the form of SO₂. For phenyl sulfide, benzothiophene and dibenzothiophene, as their indigenous hydrogen was not enough to react with sulfur radicals, no H₂S was detected during pyrolysis under inert atmosphere, while SO₂ was found and its content was very high in pyrolysis gas.