Physicochemical properties and pyrolysis characteristics of mild liquefaction solid product of Hami coal
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摘要: 为了合理利用哈密煤温和液化固体产物(MLS),对MLS的理化性质进行了考察,并利用热重分析技术研究了MLS及其萃取组分的热解特性和各萃取组分在热解过程中的相互作用。结果表明,相比于神华煤直接液化残渣,MLS中重质油含量较高(HS,36%),沥青烯(A,13%)、前沥青烯(PA,9%)含量较低。GC-MS结果表明,HS中烷烃含量较高(41.8%)。红外结果表明,HS中含较多烷烃侧链和取代官能团,A、PA次之,而四氢呋喃不溶物(THFIS)中基本不存在,表明其芳香性较高。MLS中的矿物质主要有液化过程生成的CaCO3、原煤中的惰性组分SiO2、NaCl、Al2O3·2SiO2·2H2O和残留的催化剂转化产物Fe1-xS。热重结果表明,MLS起始热解温度和最大失重峰温均偏低,950 ℃失重率较高(54%),说明其热解活性较高。MLS各萃取组分在热解过程中存在正负两种相互作用,且与MLS中HS含量有关:当HS含量较高时,HS为MLS热解过程提供小分子自由基以促进挥发分逸出;当脱除部分HS或将HS全部脱除后,MLS各萃取组分中大分子自由基之间相互结合而抑制挥发分逸出。Abstract: In order to make rational use of mild liquefaction solid product of Hami coal (MLS), the physicochemical properties of MLS were investigated, and the characteristics and interactive effects of MLS and its extraction fractions during pyrolysis were studied by thermogravimetric analyzer (TGA) in this work. The results show that MLS contains higher content of hexane soluble fraction (HS, 36%) than Shenhua direct liquefaction residue, but has the lower asphaltene (A, 13%) and preasphaltene (PA, 9%). The results of GC-MS show that HS consists of higher content of alkane (41.8%) and the results of infrared spectra indicate that the contents of alkane side chains and substituted functional groups decrease in the order of HS, A, and PA. Whereas, alkane side chains and substituted functional groups do not exist in THFIS, indicating its high aromaticity. The minerals in MLS are mainly CaCO3 produced by liquefaction process, and inert components of SiO2, NaCl, Al2O3·2SiO2·2H2O in raw coal and Fe1-xS, which is the product of catalyst. The results of TGA show that, compared with Shenhua direct liquefaction residue, the temperatures of initial decomposition and the maximum rate of mass loss of MLS are lower, however, the final mass loss (54%) up to 950 ℃ is higher, which suggest that the pyrolysis activity of MLS is higher. In addition, there are two kinds of interactive effects among the extraction fractions of MLS during pyrolysis, which are related to the amount of HS. When the content of HS is high, it can supply small free radicals and play a driving role for the evolution of volatile during the pyrolysis process. However, when the content of HS is low, large free radicals in MLS extraction fractions will combine with each other, which inhibits the release of volatile.
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表 1 MLS的灰成分分析
Table 1 Ash compositions of MLS
Content w/% SiO2 Al2O3 Fe2O3 CaO MgO SO3 TiO2 K2O Na2O P2O5 12.18 8.89 27.69 25.18 1.3 18.73 0.22 0.22 2.61 0.21 表 2 MLS及其萃取组分的工业分析和元素分析
Table 2 Proximate and ultimate analyses of MLS and its extraction fractions
Sample Proximate analysis w/% Ultimate analysis wdaf/% H/C (atomic ratio) Ad Vdaf C H O* N S MLS 15.39 59.40 88.13 6.49 2.14 1.09 2.15 0.88 HS - - 89.16 7.97 2.01 0.79 0.07 1.07 A - - 86.75 5.85 5.59 1.69 0.12 0.81 PA - - 81.31 5.61 11.26 1.69 0.13 0.83 THFIS 35.80 44.31 86.81 4.85 0.58 1.40 6.36 0.67 T-MLS 19.86 47.46 88.68 5.61 1.46 1.40 2.85 0.76 HIS 21.94 37.38 88.56 5.32 1.33 1.43 3.28 0.72 *: by difference -
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