溴改性低温煤沥青制备高软化点沥青及其中间相转化行为
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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。
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 1 H NMR, LDI-TOF/MS and FT-IR. The introduction of bromine significantly facilitated polycondensation of the component molecules and Br_2 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(L_c = 117 Å) of all samples examined.
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 1 H NMR, LDI-TOF/MS and FT-IR. The introduction of bromine significantly facilitated polycondensation of the component molecules and Br_2 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(L_c = 117 Å) of all samples examined.
引文
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[19] 葛传长.高品质合成沥青的制备,结构和性能研究[D].华东理工大学,2016.(GE Chuan-chang.Synthesis,structure and properties of high performance synthetic pitch and mesophase pitch[D].East China University of Science and Technology,2016.)
[20] Diaz C,Blanco C G.NMR:A powerful tool in the characterization of coal tar pitch[J].Energy & fuels,2003,17(4):907-913.
[21] Blanksby S J,Ellison G B.Bond dissociation energies of organic molecules[J].Accounts of Chemical Research,2003,36(4):255-263.
[22] Kim B J,Eom Y,Kato O,et al.Preparation of carbon fibers with excellent mechanical properties from isotropic pitches[J].Carbon,2014,77:747-755.
[2] Mochida I,Korai Y,Ku C H,et al.Chemistry of synthesis,structure,preparation and application of aromatic-derived mesophase pitch[J].Carbon,2000,38(2):305-328.
[3] Mochida I,Yoon S H,Korai Y.Mesoscopic structure and properties of liquid crystalline mesophase pitch and its transformation into carbon fiber[J].The Chemical Record,2002,2(2):81-101.
[4] Burgess W A,Pittman J J,Marcus R K,et al.Structural identification of the monomeric constituents of petroleum pitch[J].Energy & Fuels,2010,24(8):4301-4311.
[5] Klett J,Hardy R,Romine E,et al.High-thermal-conductivity,mesophase-pitch-derived carbon foams:Effect of precursor on structure and properties[J].Carbon,2000,38(7):953-973.
[6] Mochida I,Fujiura R,Kojima T,et al.Carbon disc of high density and strength prepared from heat-treated mesophase pitch grains[J].Carbon,1995,33(3):265-274.
[7] Mochida I,Ku C H,Yoon S H,et al.Anodic performance and mechanism of mesophase-pitch-derived carbons in lithium ion batteries[J].Journal of Power Sources,1998,75(2):214-222.
[8] Yu B,Wang C,Chen M,et al.Two-step chemical conversion of coal tar pitch to isotropic spinnable pitch[J].Fuel Processing Technology,2012,104:155-159.
[9] Li M,Liu D,Lv R,et al.Preparation of the mesophase pitch by hydrocracking tail oil from a naphthenic vacuum residue[J].Energy & Fuels,2015,29(7):4193-4200.
[10] 花双平,张博,宋怀河,等.煤沥青基中间相沥青的制备研究[J].炭素技术,2009,28(6):6-10.(Hua Shuang-ping,Zhang Bo,Song Huai-he,et al.Preparation of msophase pitch from purified coal tar pitch[J].Carbon Techniques,2009,28(6):6-10.)
[11] Obara T,Yokono T,Miyazawa K,et al.Carbonization behavior of hydrogenated ethylene tar pitch[J].Carbon,1981,19(4):263-267.
[12] Mochida I,Kudo K,Fukuda N,et al.Carbonization of pitches-IV:Carbonization of polycyclic aromatic hydrocarbons under the presence of aluminum chloride catalyst[J].Carbon,1975,13(2):135-139.
[13] Mochida I,Shimizu K,Korai Y,et al.Preparation of mesophase pitch from aromatic hydrocarbons by the aid of HFBF3[J].Carbon,1990,28(2-3):311-319.
[14] Korai Y,Nakamura M,Mochida I,et al.Mesophase pitches prepared from methylnaphthalene by the aid of HFBF3[J].Carbon,1991,29(4-5):561-567.
[15] Mochida I,Shimizu K,Korai Y,et al.Mesophase pitch catalytically prepared from anthracene with HF/BF3[J].Carbon,1992,30(1):55-61.
[16] Ge C,Yang H,Miyawaki J,et al.Synthesis and characterization of high-softening-point methylene-bridged pitches by visible light irradiation assisted free-radical bromination[J].Carbon,2015,95:780-788.
[17] 葛传长,孙振龙,杨海潇,等.溴诱导法乙烯渣油基高软化点各向同性沥青的制备及表征[J].新型炭材料,2018,33(1):71-81.(GE Chuan-chang,SUN Zhen-long,YANG Hai-xiao,et al.Preparation and characterization of high softening point and homogeneous isotropic pitches from distillated ethylene tar via a novel bromination method[J].New Carbon Materials,2018,33(1):71-81.)
[18] AlHumaidan F S,Hauser A,Rana M S,et al.Changes in asphaltene structure during thermal cracking of residual oils:XRD study[J].Fuel,2015,150:558-564.
[19] 葛传长.高品质合成沥青的制备,结构和性能研究[D].华东理工大学,2016.(GE Chuan-chang.Synthesis,structure and properties of high performance synthetic pitch and mesophase pitch[D].East China University of Science and Technology,2016.)
[20] Diaz C,Blanco C G.NMR:A powerful tool in the characterization of coal tar pitch[J].Energy & fuels,2003,17(4):907-913.
[21] Blanksby S J,Ellison G B.Bond dissociation energies of organic molecules[J].Accounts of Chemical Research,2003,36(4):255-263.
[22] Kim B J,Eom Y,Kato O,et al.Preparation of carbon fibers with excellent mechanical properties from isotropic pitches[J].Carbon,2014,77:747-755.
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