學(xué)版)Journal of Zhe jiang University(Science Edition)Vol 31 No,第31卷第6期http://www.journalszju.eduen/sci石油瀝青質(zhì)的熱解動力學(xué)研究董喜貴,雷群芳',俞慶森(1.浙江大學(xué)化學(xué)系,浙江杭州310027;2.大慶采油二廠,黑龍江大慶163414)摘要:從國內(nèi)外5種不同原油中分離提取正己炕瀝青質(zhì),分別進(jìn)行10,15,20,25C·min四↑加熱速率下的熱重分析(TGA),關(guān)聯(lián)系列不同揮發(fā)度下的瀝青質(zhì)裂解活化能和指前因子等動力學(xué)參數(shù),活化能和指前因子隨揮發(fā)度變化而變化,指前因子的對數(shù)與活化能之同有很好的直線關(guān)系,雖示出良好的補(bǔ)償效應(yīng),說明瀝青質(zhì)裂解反應(yīng)由許多具有不同動力掌參數(shù)的平行反應(yīng)組成,用活化能分布模型計(jì)算了活化能和指前因子的分布函數(shù),該模型能較好地表達(dá)瀝青質(zhì)的熱裂解特征關(guān)鍵詞:瀝青質(zhì);裂解;動力學(xué);熱重分析中圖分類號:O642.4;TE622.1文獻(xiàn)標(biāo)識碼:A文章編號:1008-9497(2004)06-652-05DONG Xi-gui, LEI Qun-fang, YU Qing-sen'(I. Department of Chemistry, Zhejiang University, Hangzhou310027, China; 2. No, 2 Oil Production Company, Daqing Oil Field Co. Ltd, Daqing 163414, China)Thermal pyrolysis kinetics of asphaltenes from several crude oils. Journal of Zhejiang University(Science Edition)Abstract: Five kinds of asphaltenes were extracted from different crude oils by n-hexane precipitation. Thermo-gravimetric analysis (TGA) was carried out for these asphaltenes with four different heating rate of 10, 15, 20 and25 C. min, respectively. The kinetic parameters, active energy(E)and preexponential factor (k.). of thermalpyrolysis for asphaltenes at different conversion levels were correlated from the experimental TG data. The con-version-dependent E and ko values were obtained. The compensation effect is clearly observed from a straight lineof the plot of In (ko)versus E. It follows that many parallel reactions with different rate parameters occur simultaneously during the thermal pyrolysis of asphaltenes. The distribution functions, f(E) and ko(E), were then estimated satisfactorily by the distributed activation energy model (DAEM).Key words: asphaltene; pyrolysis; kinetics; thermogravimetric analysis (TGA); distributed activation energymodel (DAEM)瀝青質(zhì)是石油中的重要化學(xué)組分,它是指不溶度的燃燒或注入水蒸氣,增加重油的流動性和溶解于低碳正構(gòu)烷烴(nC3~nC8)而溶于苯、甲苯等溶能力,以提高重質(zhì)油藏的采出效果,但存在熱損失劑的一類物質(zhì),是石油中分子量最大、極性最強(qiáng)的組大、瀝青質(zhì)等熱敏性物質(zhì)沉積等問題,甚至存在轉(zhuǎn)變分.石油中,瀝青質(zhì)膠質(zhì)烴構(gòu)成一個(gè)連續(xù)的動態(tài)穩(wěn)成無用的焦炭的現(xiàn)象.考慮到瀝青質(zhì)在原油開采與定系統(tǒng)2),類似于膠體系統(tǒng)瀝青質(zhì)是該系統(tǒng)的核加工中的作用和影響探討瀝青質(zhì)的物理化學(xué)性質(zhì)心,石油烴為分散介質(zhì),膠質(zhì)是穩(wěn)定化劑.當(dāng)該系統(tǒng)和熱解動力學(xué)具有實(shí)際意義.因?yàn)r青質(zhì)組成和結(jié)構(gòu)受到破壞,瀝青質(zhì)發(fā)生聚集、沉淀,給油藏開發(fā)、原油十分復(fù)雜,雖然已經(jīng)開展了許多研究工作,但是仍存運(yùn)輸和后處理帶來困難;瀝青質(zhì)也是原油加工中主在不少問題和爭議.目前,關(guān)于瀝青質(zhì)的化學(xué)組成、要的生焦母體,其熱穩(wěn)定性與結(jié)焦、管線堵塞等有害結(jié)構(gòu)和性質(zhì)研究是油田化學(xué)和石油化工領(lǐng)域的熱點(diǎn)現(xiàn)象密切相關(guān).油田開采和原油加工的許多新技課題之一,本文在提取幾種原油瀝青質(zhì)后,通過術(shù)都需要加強(qiáng)對瀝青質(zhì)的認(rèn)識,比如:重油和油頁巖熱重分析手段研究其熱穩(wěn)定性,獲得活化能、指前因開采中的熱力開采工藝,通過在油層內(nèi)進(jìn)行一定程子以及它們的分布函數(shù)等重要?jiǎng)恿W(xué)參數(shù)收稿日期:20040422基金項(xiàng)目:浙江省分析測試基金資助項(xiàng)目(03101)作者簡介:董喜貴(1964),男,博土生,主要從事石油化學(xué)和物理化學(xué)研究第6期董喜貴,等:石油瀝青質(zhì)的熱解動力學(xué)研究6531實(shí)驗(yàn)部分1.3熱重分析采用德國產(chǎn) NETZSCH STA409PG/PC型熱重1.1瀝青質(zhì)的提取分析系統(tǒng)程序升溫速率為10、15、20、25C·min-,選擇伊朗(YL)、俄羅斯(RU)和我國遼河最終實(shí)驗(yàn)溫度為800℃.熱裂解在高純氮?dú)猸h(huán)境中進(jìn)(LH)、新疆(XJ)、華北(HB)等5種原油,原料油取行,氮?dú)饬髁靠刂圃?0mL·min-2,試樣用量6~8自國內(nèi)有關(guān)煉油廠.以正己烷為溶劑提取瀝青質(zhì)提mg.熱重(TG)及微分熱重(DTG)數(shù)據(jù)由軟件自動取步驟:準(zhǔn)確稱取一定原料油,放于磨口錐形瓶中,采集按每克試樣加約20mL正已烷,在加熱板上回流1h左右,冷卻后放置暗處約8h左右,用定量濾紙過結(jié)果與討論濾出沉淀物,用兩層濾紙包好,放于索氏提取器中進(jìn)2.1基本性質(zhì)行抽提,至抽提液無色為止.取出濾紙,刮下沉淀物,瀝青質(zhì)的元素組成等基本性質(zhì)列于表1.瀝青在蒸空烘箱中除去溶劑,得到有金屬光澤的瀝青質(zhì).質(zhì)主要有碳、氫兩種元素組成,質(zhì)量分?jǐn)?shù)達(dá)到90%1.2瀝青質(zhì)的基本性質(zhì)測定~93%左右;HC原子比在1~1.3左右;SN、O等采用 Carlo erba ea1110型元素分析儀測定瀝雜原子的質(zhì)量分?jǐn)?shù)可達(dá)6.4%~9.6%.用蒸氣壓滲青質(zhì)的碳(C)氫(H)氮(N)元素的質(zhì)量分?jǐn)?shù)采用透(VPO)法測定的瀝青質(zhì)相對分子質(zhì)量為3300氧彈法測定硫(S),差減得到氧(O).采用蒸氣壓滲透5600,不同瀝青質(zhì)的相對分子質(zhì)量之間差別較大(VPO)法測定相對分子質(zhì)量,苯作溶劑,實(shí)驗(yàn)溫度45NMR測得不同種類H和C的質(zhì)量分?jǐn)?shù),其中HC,用光譜純聯(lián)苯甲酰和菲進(jìn)行標(biāo)定采用 Bruker為與芳香環(huán)上碳原子相連接的氫原子,H為與烷碳Avance dmX500型超導(dǎo)核磁共振波譜儀測定H原子相連接的氫原子,C為芳碳原子,C為烷碳NMR和CNMR譜,CDCl3為溶劑,TMS為內(nèi)標(biāo)原子表1瀝青質(zhì)的基本性質(zhì)Table 1 Fundamental properties of asphaltenesYL82.78一H8N% S%0%M640.877.3255000.11860.88140.42410.5759RU85.597.5210.12890.87110.44830.5517LH 847.971.783.56400.10780.8922XJ85,307.65233800.12850.87150.47750.5225HB85.168.461.622.172.644500.08010.919900.60302.2熱解動力學(xué)由實(shí)驗(yàn)結(jié)果可知,瀝青質(zhì)在惰性氣氛下加熱,發(fā)2.2.1熱裂解過程分析生明顯的物理和化學(xué)變化,熱解過程主要發(fā)生在以俄羅斯原油瀝青質(zhì)的熱裂解為例,TG和400~520C范圍內(nèi),約占整個(gè)失重質(zhì)量分?jǐn)?shù)的DTG曲線如圖1所示,裂解轉(zhuǎn)化率(V/v)與溫度80%,小于400C,失重質(zhì)量分?jǐn)?shù)大約為10%,大于的關(guān)系如圖2所示,其中V為某時(shí)刻的揮發(fā)率,V520C,失重質(zhì)量分?jǐn)?shù)大約為20%為時(shí)間趨于無窮時(shí)的最終揮發(fā)率.特定轉(zhuǎn)化率所對應(yīng)的轉(zhuǎn)化溫度列于表2,其它瀝青質(zhì)類似△10℃minEDTG00。=350400450505060LLL01020304050607080圖2俄羅斯原油瀝青質(zhì)熱解轉(zhuǎn)化率與溫度的關(guān)系圖1俄羅斯原油瀝青質(zhì)熱解的TG-DTG曲線Fig. 2 Conversion ratio against temperature of pyrolyFig 1 TG-DTG curve of pyrolysis of asphaltenes fromsis of asphaltenes from Russia crude oil漸江大學(xué)學(xué)報(bào)(理學(xué)版)第31卷表2俄羅斯原油瀝青質(zhì)熱解過程特定轉(zhuǎn)化率者用活化能分布模型來處理瀝青質(zhì)的熱裂解動力對應(yīng)的溫度學(xué).主要包括以下幾個(gè)步驟:(a)由熱重實(shí)驗(yàn)獲得至Table 2 Temperatures at selected conversion levels of少三個(gè)加熱速率B下的V/V‘~T關(guān)系;(b)選擇pyrolysis of asphaltenes from Russia crude oil系列固定的v/V·值,分別計(jì)算不同B下的對應(yīng)溫v/Vt/c度T和/T2的值;(c)給定v/V·值時(shí),以ln(B/T2)10C·min-l15C·min-120c·min-125c·min對1/T作圖,由式(2)的直線斜率和截距計(jì)算活化0.1392.6396.1399.5403.8能E和指前因子k;(d)以V/V‘對E作圖,根據(jù)0.2429.3432.7436.441.2448.9456.9V/v·~E函數(shù)關(guān)系求得分布函數(shù)f(E);(e)關(guān)聯(lián)460.4468.2k。和E的關(guān)系,求得k(E)470.3474.2478.2圖3給出俄羅斯原油瀝青質(zhì)熱裂解過程的476.4480.5484.4488.3n(B/72)對1/T關(guān)系,由這些直線的斜率和截距計(jì)算相應(yīng)活化能E和指前因子k.V/與E的關(guān)系0.8513.1516.8519.3521.7示于圖4,由圖4中曲線求得的活化能分布函數(shù)2.2.2動力學(xué)計(jì)算f(E),見圖5對于熱重動力學(xué)處理已經(jīng)有不少報(bào)道,主要有Friedman法等微分模型和 Coats- Redfern法、Chen-13.880.78Nutt祛法等積分模型1,還有根據(jù)DTG峰溫計(jì)算-140的 Ozawa法 Kissinger法等),以及多升溫速率等溫法2等.對于純物質(zhì),可以假設(shè)全濃度范圍內(nèi)滿-144足相同反應(yīng)機(jī)理函數(shù)1來關(guān)聯(lián)動力學(xué)參數(shù),但有時(shí)會得出模棱兩可的結(jié)論.特別是對于組成非常復(fù)雜的煤、干酩根、瀝青、生物質(zhì)等系統(tǒng),與純物質(zhì)一樣用單一反應(yīng)模型來描述存在嚴(yán)重缺陷19,一般難以-152L1070030s0.r00gg0.06達(dá)到滿意的關(guān)聯(lián)效果,必須建立新的處理方法.有1.251.301.351.401.451.501.551.60l000/T的分若干個(gè)溫度段,再分別加以關(guān)聯(lián)求出各段的動力學(xué)參數(shù),但很難得到準(zhǔn)確結(jié)果4;有的41假圖3俄羅斯原油瀝青質(zhì)熱裂解過程的ln(Bm2)~1/T關(guān)系設(shè)裂解反應(yīng)由無限多平行反應(yīng)組成,且它們的指前Fig 3 Polts of In(B/T2)versus 1/T at selected V/V因子相同,活化能可以用 Gaussian分布函數(shù)描述values pyrolysis of asphaltenes from RussiaMiura等7-10通過仔細(xì)對比和研究,認(rèn)為對于燃料rude oil等復(fù)雜組分物質(zhì)的熱裂解,應(yīng)當(dāng)采用更一般的活化能分布模型( Distributed Activation Energy Model,DAEM).它假設(shè)復(fù)雜組分系統(tǒng)的熱裂解由許多具有不同動力學(xué)參數(shù)的不可逆一級平行反應(yīng)組成,且有關(guān)系:expe-E/kdr f(e)dE(1)其中,r為反應(yīng)時(shí)間,k為指前因子,R為氣體常數(shù)E為活化能,(E)為歸一化的活化能分布函數(shù).經(jīng)0100200300400500600700過適當(dāng)近似和數(shù)學(xué)推導(dǎo),還得到In(s=In/, RE/+0.6075-E圖4瀝青質(zhì)熱裂解過程的v/V‘~E關(guān)系(2)Fig. 4 Plots of V/V. versus E for pyrolysis of as-其中,β為加熱速率.該模型用于煤的熱裂解計(jì)算取hastens得良好效果,但尚未見用于瀝青質(zhì)的報(bào)道.瀝青質(zhì)的由圖5可見,不同來源原油瀝青質(zhì)的熱裂解活匕能及其分布差別較大,YL和HB的活化能分布第6期董喜貴,等:石油瀝青質(zhì)的熱解動力學(xué)研究655較寬,而LH和XJ的活化能分布在很窄的范圍內(nèi);根據(jù) Arrhenius方程和過渡狀態(tài)理論,有YL、RU、LH、XJ和HB的活化能峰值Emx分別為k= koexpRr).(3)500、345、270、350、220kJ·mol-,它們大體可以代表瀝青質(zhì)熱裂解的平均活化能.可以注意到,Emx與cx(2)x(-瀝青質(zhì)中雜原子(特別是硫元素)質(zhì)量分?jǐn)?shù)有相似的△S遞變趨勢,說明雜原子對瀝青質(zhì)結(jié)構(gòu)的穩(wěn)定性可能-exp起到重要的作用其中,kB為 Boltzmann常數(shù),h為 Planck常數(shù),△S為活化熵變.瀝青質(zhì)在熱裂解初期,首先以低活化能LH0.06的反應(yīng)途徑進(jìn)行降解,主要是雜原子化學(xué)鍵和一些活性基團(tuán)的優(yōu)先斷裂,此時(shí)瀝青質(zhì)分子之間活性基0.05團(tuán)的相互作用使得△S·為較大的負(fù)值,表現(xiàn)為活化能E較低時(shí)指前因子k也較小.隨著分子中弱化學(xué)0.03鍵不斷破壞,活性基團(tuán)不斷減少,瀝青質(zhì)分子從較為松弛的結(jié)構(gòu)轉(zhuǎn)變?yōu)檩^緊密堆積的結(jié)構(gòu),分子之間的HB相互作用減弱,降解反應(yīng)的活化能增大,瀝青質(zhì)降解反應(yīng)可能過渡到以單分子反應(yīng)或準(zhǔn)單分子反應(yīng)占優(yōu)100150200250300350400450500550600E/(kJ.mol-I)勢,此時(shí)ΔS‘為較小的負(fù)值甚至可能轉(zhuǎn)變?yōu)檎祱D5活化能分布函數(shù)f(E)表現(xiàn)在活化能較高時(shí)k也較大.指前因子k呈指數(shù)Fig.5 The distribution function f(E)of activation增大對反應(yīng)速度常數(shù)有較大的貢獻(xiàn),這在一定程度energy上可以補(bǔ)償由于活化能增大而造成的速度常數(shù)減k。與E的關(guān)系示于圖6,顯然ln(k)與E呈直少所以,n(kn)與E的正相關(guān)性也可稱為補(bǔ)償效應(yīng)線關(guān)系,且具有較好的正相關(guān)性,k0(E)的關(guān)聯(lián)結(jié)果( Compensation effect9:1)見表3,其中R2為復(fù)相關(guān)系數(shù),SD為標(biāo)準(zhǔn)偏差由活化能和指前因子分布函數(shù)f(E)和k(E)代入式(1),進(jìn)行數(shù)值積分可以求得揮發(fā)度V/V日y計(jì)算結(jié)果與實(shí)驗(yàn)值對比于圖2中,兩者吻合較好,說80明活化能分布模型能較好地用于瀝青質(zhì)的熱解動力◆HB學(xué)描述3結(jié)論從國內(nèi)外5種不同原油中分離提取得到正己烷瀝青質(zhì),分別進(jìn)行了4個(gè)不同加熱速率下的TG0100200300400500600700DTG分析.不能簡單地用單個(gè)反應(yīng)來描述組成復(fù)雜圖6In(ka)與E的關(guān)系的瀝青質(zhì)的熱裂解動力學(xué).用活化能分布模型計(jì)算Fig6 Plots of In(ko) versus E了活化能和指前因子的分布函數(shù),效果良好.不同來表3ln(k。)與E的關(guān)聯(lián)結(jié)果:源的原油瀝青質(zhì)的熱裂解活化能及其分布有較大差I(lǐng)n(ko)=A+B(E-Em)別,指前因子與活化能之間存在明顯的補(bǔ)償效應(yīng)Table 3 Correlation results of in(ko) against E with theform of In(ko)=A+B(E-Emx)參考文獻(xiàn)( References):YL72.510.15255001.0002.06[1] PARK S J, MANSOORI G A. Aggregation and deposiRU50.330.14133450.9982.25LH38.190.15422700.9961.17tion of heavy organics in petroleum crudes[J]. EnergyXJ52.480.13433500.9932.39Sources,1988,10:109-12HB29.910.140720[2] STORM D A SHEU E Y. Characterization of col-656浙江大學(xué)學(xué)報(bào)(理學(xué)版)第31卷74(8):1140-1145HU Rong-zu, SHI Qi-zhen. Kinetics for Thermal[3]孫海云,郭永勝,方文軍,等.吸熱型碳?xì)淙剂蠠岚捕ㄐ訟nalysis[M]. Beijing: Science Press, 2001. 108.研究[J.浙江大學(xué)學(xué)報(bào)(理學(xué)版),2004,31(2):167[12]張偉南,袁譽(yù)洪,李麗清,等.二水草酸鋅脫水的熱分解動力學(xué)研究[].物理化學(xué)學(xué)報(bào),2004,20(1):33SUN Hai-yun, GUO Yong-sheng, FANG Wen-junet al. Study on thermal stability of endothermic hyZHANG Wei-nan, YUAN Yu-hong, LI L. i-ging, etdrocarbon fuels [J]. J of Zhejiang University(Scienceal. a description of thermal decomposition kinetics ofEdition),2004,31(2):167-170.dehydration of zinc oxalate dihydrate [J]. Acta Phys[4]王宗賢,張宏玉,郭愛軍,等渣油中瀝青質(zhì)的締合狀況Chim Sin,2004,20(1):33-37與熱生焦趨勢研究[J]石油學(xué)報(bào)(石油加工),2000,[13]GAOX, POLLIMORE D. a kinetic study of the16(4):60-64thermal decomposition of magnes(I1) oxalate dihy-WANG Zong-xian, ZHANG Hong-yu, GUO Ai-jundonate[J]. Thermochimica Acta, 1993. 215:47et al. A study of association of asphaltene moleculesin vacuum residues[J]. Acta Petrolei Sinica([14]朱學(xué)棟,朱子彬,張成芳,煤熱失重動力學(xué)的研究Petroleum Processing Section), 2000. 16(4): 60-64.[J].高校化學(xué)工程學(xué)報(bào),1999,13(3):223-228.[5] XU Ying-nian, YOSHIKATA K, STRAUSZ O P.ZHU Xue-dong, ZHU Zi-bin, ZHANG Cheng-fang.Characterization of Athabasca asphaltenes by small-Study of the coal pyrolytic kinetics by thermogram-angle X-ray scattering [J].Fuel, 1995.74(7):960try[J]. J of Chemical Engineering of Chinese Universities,1999,13(3):223-228.[6] VICTOROV A 1. FIROOZABADI A Thermodynamic [15] BRAUN R L, BURNHAM A K, REYNOLDS Gmicellization model of asphaltene precipitation fromet al. Pyrolysis kinetics for Lacustrine and Marinepetroleum fluids [J]. AIChE J, 1996.42(6):1753-source rocks by programmed micropyrolysis [J]. En-1764rgy& Fuels,1991,5:192-204[7] TAYLOR S E. The electrodeposition of asphaltenes [16] LAKSHMANAN CC, BENNETT M L, WHITEand implications for asphaltene structure and stabilityN. Implications of multiplicity in kinetic parametersin crude and residual oils[J]. Fuel,1998,77(8):821to petroleum exploration distributed activation energy models[]. Energy &Fuels, 1991, 5:110-117[8]廖澤文耿安松油藏開發(fā)中瀝青質(zhì)的研究進(jìn)展[]科17] MIURA K. A new and simple method to estimate學(xué)通報(bào),199944(19):2018-2024f(E) and k(E) in the distributed activation energyLIAO Ze-wen, GENG An-song. Development of themodel from three sets of experimental data[J].Enerstudy on asphaltene in the oil reservoir exploitationgy& Fuels,1995,9:302-307[]. Science Bulletin,1999,44(19):2018-2024[18] MAKI T, TAKATSUNO A. MIURA K. Analysis[9]廖澤文,耿安松.瀝青質(zhì)熱解動力學(xué)研究及其應(yīng)用初探of pyrolysis reactions of various coals including ar-[].自然科學(xué)進(jìn)展,2000,10(2):183-189gonne premium coals using a new distributed activa-LIAO Ze-wen, GENG An-song, Study on the thermaltion energy model [J]. Energy &Fuels,1997,11pyrolysis kinetics of asphaltene and its application[J].Progress of Natural Science, 2000, 10(2): 183-189.[19] MIURA K, MAKI T A simple method for estimat[10] YUE C, WATKINSON A P. Pyrolysis of pitch[J].ing f(E) and ko(E) in the distributed activation en-Fuel,1998,77:695-71ergy model [J]. Energy Fuels, 1998, 12:864[11]胡榮祖,史啟楨.熱分析動力學(xué)[M]北京:科學(xué)出版社,2001.108(責(zé)任編輯涂紅)