High-softening-point pitches prepared by the Br2 modification of low-temperature coal tar pitch and their mesophase transformation behavior
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摘要: 以精制的低温煤焦油沥青（R-CTP）为原料，采用热溴化/脱溴聚合法制备了高软化点沥青，研究了溴添加量、脱溴温度和恒温时间对所得产物的结构和性质的影响。R-CTP与5 wt.%~20 wt.%的液溴反应后，经250~350℃下热处理发生脱溴聚合反应。偏光显微结构和XRD分析结果表明，当溴引入量为15 wt.%时，溴化沥青（BRC-15%）经410℃炭化形成100%光学各向异性的广域型中间相，且炭化产物具有最大的微晶堆积高度。BRC-15%经350℃热处理6 h得到软化点为232℃、残炭率为55.2 wt.%的脱溴沥青。通过1H NMR、LDI-TOF/MS和FT-IR等表征脱溴沥青的结构，结果表明溴的引入显著促进了沥青组分分子的聚合，与直接热缩聚法相比，溴改性法明显提高了沥青的软化点、残炭率和分子量。此外，脱溴沥青还具有较低的熔融黏度，其黏度随剪切速率的增大表现为剪切变稀且有明显的剪切平台。脱溴沥青经410℃炭化能够形成95%光学各向异性的广域中间相。Abstract: High-softening-point pitches were prepared from refined low-temperature coal tar pitch (R-CTP) by thermal bromination, followed by dehydrobromination/polymerization. R-CTP was first brominated in the presence of 5-20 wt.% bromine, and then heat-treated at 250-350℃ for dehydrobromination/polymerization. The structures of the dehydrobrominated pitches were characterized by 1H NMR, LDI-TOF/MS and FT-IR. The introduction of bromine significantly facilitated polycondensation of the component molecules and Br2 modification apparently increased the softening point, coking values and molecular weight of the obtained pitches compared with that formed by direct thermal condensation. The dehydrobrominated pitches showed relatively low melt viscosities and shearing-thinning rheological behavior with obvious plateau regions. An optimized dehydrobrominated pitch produced from R-CTP modified with 15 wt.% bromine (BRC-15%) by heat-treatment at 350℃ for 6 h had a softening point of 232℃ and a carbon yield of 55.2 wt.%. Polarized optical microscopy showed that the semicoke produced by the carbonization of BRC-15% at 410℃ appeared to be the most anisotropic with a large domain texture, and XRD patterns indicated that this sample also had the largest crystallite size (Lc=117 Å) of all samples examined.
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Key words:
- Coal tar pitch /
- Thermal bromination /
- Dehydrobromination /
- High-softening-point pitch /
- Mesophase
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