煤提取物的特征和碳化行为 外文翻译.doc

内蒙古科技大学本科生毕业设计英文翻译 题 目：煤提取物的特征和碳化行为 学生姓名：xxx学 号：xxx专 业：过程装备与控制工程班 级：装备xxxx班指导教师：xxx内蒙古科技大学本科生毕业设计英文翻译characteristics and carbonization behaviorsof coal extractsjianli yang a,*, peter g. stansberry b,john w. zondlo b, alfred h. stiller bastate key laboratory of coal conversion, institute of coal chemistry, chinese academy of sciences,27 taoyuan nan road, taiyuan 030001, pr chinabdepartment of chemical engineering, west virginia university, morgantown, wv 26506, usareceived 1 february 2002; received in revised form 8 april 2002; accepted 15 april 2002abstractn-methyl pyrrolidone (nmp) raw coal extract (ext), hydrogenated coal extract (hext) and theblend of ext and hext in nmp (bld), from two bituminous coals, were studied. the extractswere carbonized in both tube-bomb and a temperature programmable furnace. elemental analysis,ftir spectroscopy and optical microscopy techniques were employed to characterize the extractsand the carbonization residues. it was found that the extracts resembled petroleum-derived pitches inthe hydrogen content and (c/h)atomic ratio. higher oxygen and nitrogen contents differentiated thecoal extracts from commercial petroleum pitch. more carbon and hydrogen, and lesser oxygen andsulfur differentiated hext from ext. the ratios of integrated ir band intensity for aromatic andaliphatic ch stretching indicate that the relative content of aliphatic hydrogen in ext is higher thanin hext. hext contains comparatively more aromatic hydrogen, a feature necessary for thermalstability and fluidity during carbonization. bld materials are at a place somewhere in between.kinetic modeling of the aliphatic hydrogen change during carbonization reveals that ext has highcarbonization rate and low apparent activation energy. this can be related to the optical texture sizeof carbonization residues. the residues made from exts exhibited fine mosaic optical texture andlimited mesophase development. hexts were readily converted into highly anisotropic coke. bldsproduced carbonization residues with intermediate properties. extracts with similar activationenergies produced similar residues in the same coal series. the degree or extent of anisotropydisplayed by the carbonization residues was found to be dependent on the relative distribution ofaromatic and aliphatic hydrogen.d 2002 published by elsevier science b.v.keywords: coal extract; carbonization residue; carbonization behavior0378-3820/02/$ - see front matter d 2002 published by elsevier science b.v.pii: s0378-3820(02)00177-7* corresponding author. tel./fax: +86-351-4048571.e-mail address: (j. yang)./locate/fuprocfuel processing technology 79 (2002) 207 2151. introductioncoal tar and petroleum pitches, by-products of other industrial activities, are usefuland valuable materials in the fabrication of carbon artifacts and artificial graphite 1,2.there are advantages in terms of availability, quality and consistency to seek alternativepitches which in themselves are primary products. the key feature that makescommercial pitch attractive and practical to carbon industry is its polyaromatic nature3. in this regard, pitches derived from coal by solvent extraction are promisingalternatives.to assess the suitability of coal extracts for pitch involves obtaining information onchemical composition and the reactivity of carbonization. it has been recognized that theultimate structure and properties of carbon are determined at the early stages of carbonizationbefore the infusible, solid carbon stage 4. the structure and reactivity of theprecursor materials and reactive intermediates are important not only in charting the courseof thermal polymerization reactions but also in controlling the crystalline development thatoccurs at the mesophase stage.chemically, coal tar and petroleum pitches as well as synthetic mesophase pitches frompure aromatic hydrocarbons are a complex mixture of polyaromatic hydrocarbons (pah).these are necessary and required starting materials in the formation of nearly allpolycrystalline, coke-based articles 5,6. the chemical characteristics of pitches such asaromaticity, aliphaticity, heteroatom content and hydrogen distribution determine themechanisms of carbonization 7,8.the purpose of this work is to examine the nature and the carbonization behaviors ofsix coal extracts obtained by n-methyl pyrrolidone (nmp) extraction of two bituminousraw/hydrogenated coals. an attempt was made to relate the properties of the extracts to theoptical textures of the carbonization residues. the carbonization kinetics of the extracts atthe initial stage was studied by means of fourier-transformed infrared spectroscopy(ftir).2. experimentalthe six nmp-soluble extracts used were derived from two coals, wvgs 13421 andwvgs 13423 coal. the properties of the coals are shown in table 1. the extracts alongwith their parent coals and their designated identification are summarized in table 2. extdenotes nmp-soluble extract from raw coal. hext denotes nmp-soluble extracts fromhydrogenated (in tetralin) coal. blds were obtained by blending ext and hext with aratio of 75:25 in nmp.nmp was removed by rotary evaporation. the extracts were dried in a vacuum ovenat 150 jc overnight with a nitrogen purge and pulverized to pass through a 60 tylermesh screen. details on the preparation of the coal extracts are reported elsewhere9.the carbonization residues for optical texture analysis were made in a temperatureprogrammable furnace. typically, 200500 g of the extract were sealed under nitrogen.the temperature was programmed as the following: 5 jc/min to 350 jc; then 1 jc/min to208 j. yang et al. / fuel processing technology 79 (2002) 207215420 jc with soak time at 420 jc of 90 min; and then 3 jc/min to 600 jc with soak timeat 600 jc of 3 h.the carbonization residues for kinetic study were made in tube-bomb reactors with anominal volume of 25 ml. typically, 3 g of the sample were charged into a reactor. thereactor was purged with nitrogen gas, sealed and immersed into a preheated fluidized sandbath. at the end of the desired time, the reactor was quenched to room temperature in awater bath. the kinetic study was carried out at three temperatures, 400, 410 and 420 jc.the residence time of 4, 6, 10, 15, 20 and 30 min were used for the determination of therate constants.all the carbonization residues were subjected to drying in a vacuum oven undernitrogen at 110 jc to remove water and light distillation products before furtheranalysis.a nicolet 510-p fourier-transform infrared spectrometer was used to determine therelative distribution of aromatic and aliphatic hydrogen of the extracts and carbonizationresidues. all spectra were obtained by co-adding 514 interferograms at a resolution of 2cm _ 1. the potassium bromide (kbr) pellet method was used. plots of integrated bandintensities versus weight of the sample were made to obtain normalized values. at leastthree pellets of different concentrations (0.10.6 wt.%) were prepared for eachmeasurement and three duplicate measurements were made for each sample. allregression coefficients of the plots are greater than 0.99. standard deviations of sixmeasurements for one typical sample are 0.0508 (for the normalized integrated aromaticch stretching band, iar), 0.4289 (for the normalized integrated aliphatic ch stretchingband, ial) and 0.0014 (for iar/ial), respectively. special attention was made in pelletpreparation for quantitative analysis and detailed descriptions were reported elsewhere9.table 1astm rank and proximate analysis of coalscoal astm rank proximate analysis (wt.%, as received)moisture fixed carbon volatile matter ashwvgs 13421 mvb 0.98 67.87 27.96 3.19wvgs 13423 hvab 0.82 60.49 34.41 4.27table 2coal extracts and their designated identificationparent coal coal extracts idwvgs 13421 raw coal nmp-soluble ext21wvgs 13421 450 jc hydrogenated coal nmp-soluble hext21wvgs 13421 blend of ext21 and hext21 (75/25 wt.%) bld21wvgs 13423 raw coal nmp-soluble ext23wvgs 13423 450 jc hydrogenated coal nmp-soluble hext23wvgs 13423 blend of ext23 and hext23 (75/25 wt.%) bld23j. yang et al. / fuel processing technology 79 (2002) 207215 209samples of the carbonization residues were prepared for optical microscopy study usingconventional techniques. the specimens were embedded in epoxy and then polished to asmooth surface. observation was made with a zeiss axioskop reflected light microscopeusing cross-polarizers.3. results and discussion3.1. characteristics of the extractsall six extracts used in this work are free of quinoline-insoluble (qi) materials. thedata from elemental analysis are given in table 3 along with the results for a typical coaltarpitch (ctp) and a petroleum pitch (a-240). it is clear that the elemental composition ofthe coal extracts differs from that of a typical coal-tar pitch that contains less hydrogen andmore qis. the extracts resembled petroleum-derived pitches in the hydrogen content and(c/h)atomic ratio. higher oxygen and nitrogen contents differentiated the coal extracts fromcommercial petroleum pitch. comparing the elemental composition of ext21 withhext21 and ext23 with hext23, it can be found that an increase in carbon andhydrogen associated with the decrease in oxygen and sulfur are the most pronouncedchange induced by hydrogenation.the coal extracts were also characterized by ftir. the normalized integrated bandintensities of aromatic (iar, near 3050 cm _ 1) and aliphatic (ial, between 2990 and 2800cm _ 1) ch stretching bands were obtained. the ratios of (iar/ial)ch are listed in table 3and used to measure the relative distribution of the aromatic and aliphatic hydrogen ofthe extracts. it can be seen that the value of (iar/ial)ch increases in the order of ext,bld to hext. the extracts derived from the higher rank coal (wvgs 13421) havehigher (iar/ial)ch values than the corresponding extracts derived from the lower rank coal(wvgs 13423).table 3properties of coal extracts and typical coal-tar and petroleum pitchessample composition (wt.%) (c/h)atomic qia iar/ialbc h n s ocext21 85.0 5.3 2.1 0.8 6.9 1.36 0 0.081bld21 86.8 5.4 2.2 0.5 5.2 1.34 0 0.108hext21 88.1 5.8 2.2 0.5 3.4 1.27 0 0.152ext23 84.9 5.3 2.0 0.7 7.0 1.34 0 0.068bld23 87.2 5.8 2.2 0.6 4.2 1.27 0 0.084hext23 88.5 5.9 1.9 0.4 3.4 1.27 0 0.126ctp 93.8 3.7 0.9 0.6 1.0 2.11 13.6 ndda-240 91.2 5.1 0.5 2.5 0.7 1.49 0.6 ndda qi denotes quinoline insolubles.b iar and ial denote normalized integrated ir band intensity of aromatic and aliphatic ch stretching.c by difference.d nd denotes not determined.210 j. yang et al. / fuel processing technology 79 (2002) 207215it should be noted that in the same coal group, the value of (c/h)atomic for ext ishigher than that for hext, while the value of (iar/ial)ch for ext is lower than that forhext. this fact indicates that ext possess more condensed and/or conjugated ringsystems than hext.3.2. optical texture of the carbonization residuesthe carbonization residues from the coal extracts differ in their optical texture as shownin fig. 1. the optical textures of residues, a3 and b3, from hext21 and hext23 containextensive flow patterns while the residues, a1 and b1, from ext21 and ext23 consist offine mosaic textures. the low oxygen contents in hexts are favorable to the developmentof mesophase.generally, the optical texture size of the carbonization residues increases with theparent extracts in the order of ext23, ext21cbld23, bld21, hext23 and hext21.it is important to recall that the (iar/ial)ch values of the extracts also increased in the sameorder. these suggest that the optical texture size of the carbonization residues increaseswith an increase in relative content of the aromatic to aliphatic hydrogen of the extracts. asimilar phenomenon was observed by eser and jenkins 10 for a series of asphaltenes.moreover, the residues, a2 and b2, from blds exhibit an intermediate optical texturebetween the residues obtained from ext and hext. it suggests that the optical textures ofresidues could be modified by the co-carbonization of the two extracts. this can be explainedbecausehextacts as a hydrogen donor agent in the co-carbonization system. as the mixturebegins to carbonize, the more reactive ext (see next section) abstracts hydrogen fromhext, stabilizing the free radicals and promoting the development of mesophase 11.it should be noted that the residues (a2 and b2) derived from two blds have differentoptical textures. bld21 forms a residue containing flow-pattern texture while bld23fig. 1. the optical micrographs of carbonized residues from ext21 (a1); bld21 (a2); hext21 (a3); ext23(b1); bld23 (b2) and hext23 (b3).j. yang et al. / fuel processing technology 79 (2002) 207215 211produces fine mosaic texture residue. it is agreed with the fact that the (iar/ial)ch ratio ofbld23 is lower than that of bld21 and similar to that of ext21. the extract bld21from a higher rank coal contains more aromatic hydrogen. it was reported that a higherrank coal is richer in planar aromatic molecule 12. planar aromatic hydrocarbonspromote mesophase formation.3.3. carbonization kinetics of the extractsby comparison of the ftir spectra for the coal extracts and their carbonization residues(see fig. 2), it was found that the most significant changes induced by the carbonizationprocess are associated with the aliphatic hydrogen which is evidenced by reductions of thealiphatic ch stretching (between 2990 and 2800 cm _ 1) and bending (between 1460 and1370 cm _ 1) bands. the aromatic ch stretching (near 3050 cm _ 1), out-of-plane bending(between 900 and 700 cm _ 1) and the ring-stretching (near 1600 cm _ 1) bands in thecarbonization residues appeared to be relatively unchanged or slightly increased. in thisregard, the following assumptions are made:1. the rate of carbonization can be described by the change in aliphatic hydrogen content;2. the overall process of carbonization at the early stage follows first-order kinetics.the rate equation can be defined asdhal=dt ? _khal e1tfig. 2. ftir spectra of ext21 (a); and its carbonization residues made at 300 jc (b); 375 jc (c); and 420 jc(d) for 60 min soak time.212 j. yang et al. / fuel processing technology 79 (2002) 207215where k is the first-order rate constant and hal is the aliphatic hydrogen content incarbonization residue.since the aliphatic hydrogen content, hal, can be expressed as the product of ir bandintensity, ial, and the corresponding ir extinction coefficient, eal. eq. (1) can be rewrittenasdeealialt=dt ? _keealialt e2tassuming eal is independent of the heat treatment time under the conditions used in thisstudy, eq. (2) may be simplified asdial=dt ? _kial e3twith the boundary condition of ial=(ial)0 at t = 0, eq. (3) can be integrated intolneialt ? _kt t lneialt0 e4tby plotting of ln(ial) against residence time, the first-order rate constants for three specifiedtemperatures were obtained and listed in table 4. correlation coefficients, associated withthe regressions are also given in table 4. the reasonably high values of the correlationcoefficients for most of the cases indicate good fitting of the data to the first-order kinetics.apparent arrhenius activation energies were also obtained and listed in table 4 along withcorrelation coefficients for regressions.coal extracts bld21 and hext21 appear to have similar reaction rates and apparentactivation energies, as do the coal extracts ext23 and bld23 at the three temperaturestested (except bld21 at 410 jc). these observations can be related to the optical textureof the carbonization residues shown in the previous section. the optical texture pattern ofthe carbonization residues from extracts bld21 and hext21 are similar, so are thosefrom the extracts ext23 and bld23. furthermore, the reaction rate of bld21 is less thanthat of bld23. this is in agreement with the fact that the optical texture of carbonizationresidue produced from bld21 exhibits flow-type pattern while bld23 gives fine mosaiccarbonization residue.in general, the carbonization rate in the temperature range studied decreased in theorder of ext, bld and hext for both coals. correspondingly, the order of the opticaltexture size of the resultant residues increased from ext, bld to hext. it is consistenttable 4rate constant, k, and apparent activation energies, easample k (_103 min _ 1) ea (kcal/mol)400 jc 410 jc 420 jcext21 7.5 (0.96) 8.2 (0.98) 10.7 (1.00) 17 (0.96)bld21 2.8 (0.93) 7.3 (0.99) 7.9 (0.96) 48 (0.90)hext21 2.8 (0.92) 4.3 (0.87) 7.7 (0.97) 47 (0.99)ext23 5.2 (0.90) 8.2 (0.98) 10.9 (0.95) 34 (0.99)bld23 4.6 (0.90) 8.2 (0.97) 11.3 (0.94) 41 (0.99)hext23 1.3 (0.82) 5.8 (0.93) 6.1 (0.95) 71 (0.89)values in parentheses denote the correlation coefficients of the regressions.j. yang et al. / fuel processing technology 79 (2002) 207215 213with that the exts contain more aliphatic structure that lead to generation of more freeradicals during cracking. in the absence of adequate radical acceptors, the free radicalscombine and polymerize to form a fine mosaic residue.table 5 assembled some of the experimentally determined apparent activation energiesfor the carbonization of a range of pitches and organic feedstock reported in the literature.the values obtained in this study are within the range.4. conclusionsin general, the coal extracts studied rese