華南理工大學(xué)學(xué)報(bào)(自然科學(xué)版)第42卷第10期Jourmal of South China University of TechnologyVol.42 No. 102014年10月( Natural Science Edition)October 2014文章編號(hào): 100-5658<(2014) 10-0070-05木質(zhì)素單體?；餆峤膺^程的理論分析武書彬鄧裕斌劉超(華南理工大學(xué)制漿造紙工程國(guó)家重點(diǎn)實(shí)驗(yàn)室,廣東廣州510640)摘要: 為了深入研究木質(zhì)素的熱解機(jī)理,選用香草醛、香草醇和香草酸作為木質(zhì)素單體模化物模擬熱解過程.運(yùn)用密度泛函理論探討不同化學(xué)連接鍵的解離順序,并設(shè)計(jì)了4條反應(yīng)路徑(Path 1-Path 4):Path 1和Path2都生成愈創(chuàng)木酚,但中間過程不同,Path 3和Path4則分別以優(yōu)先過程生成鄰苯二酚和苯酚.結(jié)果表明:?；锏膫?cè)鏈甲基會(huì)優(yōu)先解離生成CH,C,取代基的解離順序取決于其吸電子能力;在熱解過程中,C,取代基不易直接解離,而是會(huì)優(yōu)先發(fā)生外界參與下的解離;3種目標(biāo)產(chǎn)物(愈創(chuàng)木酚、鄰苯二酚和苯酚)都是可能的,且會(huì)優(yōu)先生成鄰苯二酚,其次是苯酚,較難生成愈創(chuàng)木酚;從動(dòng)力學(xué)角度分析,Path2和Path4要優(yōu)于Path 1和Path3進(jìn)行;生成同種目標(biāo)產(chǎn)物時(shí)總是香草醇最易進(jìn)行,香草醛次之，,最難進(jìn)行的是香草酸.關(guān)鍵詞:木質(zhì)素;單體?；?熱解;密度泛函理論中圖分類號(hào): TK6; 0641.12doi: 10.3969/j. issn. 1000-565X. 2014. 10. 012近年來,世界各國(guó)都在研究生物質(zhì)能的開發(fā)和理 ;Liu等[8]以木質(zhì)素β-0_4高聚?；餅樵线M(jìn)行利用,生物質(zhì)熱化學(xué)轉(zhuǎn)化是生物質(zhì)轉(zhuǎn)化利用中的一了熱解實(shí)驗(yàn).但這些都是從原料到產(chǎn)物的宏觀變化個(gè)重點(diǎn)，而熱解在其中發(fā)揮著重要的作用21.由于推測(cè),并未真正解釋清楚木質(zhì)素的熱解過程.黃曉生物質(zhì)原料組成的復(fù)雜性,在熱解過程中可能發(fā)生露[9]和王華靜等(10]則結(jié)合量化計(jì)算的方法,從理論的化學(xué)反應(yīng)也非常復(fù)雜.鑒于這種復(fù)雜性,對(duì)組成生上解釋了木質(zhì)素?；锏牧呀鈾C(jī)理,但他們的研究物質(zhì)各組分的熱解過程進(jìn)行單獨(dú)研究,把握生物質(zhì)多偏重?zé)峤獾臒崃W(xué)過程,而忽略了熱解的動(dòng)力學(xué)的總體熱解過程是非常必要的31.植物生物質(zhì)主要過程.由纖維素、半纖維素和木質(zhì)素組成,其中,木質(zhì)素由文中選取香草醛、香草醇和香草酸為木質(zhì)素單于結(jié)構(gòu)復(fù)雜、化學(xué)鏈接形式多樣,相比于纖維索和半體模化物,采用量化計(jì)算的方法給出了各取代基的纖維素的熱解機(jī)理更為復(fù)雜.因此,了解木質(zhì)素的熱解離順序,探討了生成目標(biāo)產(chǎn)物的可能路徑.解機(jī)理對(duì)探索生物質(zhì)熱解機(jī)理具有重要的意義.國(guó)內(nèi)外對(duì)木質(zhì)素?zé)峤獾奈墨I(xiàn)報(bào)道很多[45],筆1實(shí)驗(yàn)部分者曾對(duì)木質(zhì)纖維生物質(zhì)的理化特性和熱解規(guī)律進(jìn)行了全面的研究[°6];婁瑞(7]則以不同種類非木材1.1 計(jì)算模型原料的EMAL(酶解/溫和酸解木質(zhì)素)為原料,系選取香草醛、香草醇、香草酸為木質(zhì)素單體?；y(tǒng)地研究了不同條件下的熱解特性及其產(chǎn)物分布，物,并參考文獻(xiàn)[ 11-13]給出的實(shí)驗(yàn)構(gòu)象,以此為基并嘗試推斷了木質(zhì)素中部分化學(xué)連接鍵的斷裂機(jī)礎(chǔ) 進(jìn)行后續(xù)的理論計(jì)算.收稿日期: 2013-12-16*基金項(xiàng)目:國(guó)家“973"計(jì)劃項(xiàng)目(2013CB228101);國(guó)家自然科學(xué)基金資助項(xiàng)目(31270635 ,21176095 )作者簡(jiǎn)介:武書彬(1965-),男,教授,博士生導(dǎo)師，主要從事植物纖維類生物質(zhì)化學(xué)結(jié)構(gòu)、植物纖維類生物質(zhì)轉(zhuǎn)化為清潔能源和化工原料等的研究E-mail: shubinwu@ seut. edu. cn第10期武書彬等:木質(zhì)素單體?；餆峤膺^程的理論分析711.2 路徑設(shè)計(jì)量極小值的穩(wěn)定結(jié)構(gòu);過渡態(tài)經(jīng)過頻率驗(yàn)證均有唯一大量的實(shí)驗(yàn)結(jié)果表明,木質(zhì)素及其?；镌跓崽擃l,且通過了內(nèi)稟反應(yīng)坐標(biāo)( IRC)方法的驗(yàn)證.解過程中會(huì)產(chǎn)生較高含量的愈創(chuàng)木酚、鄰苯二酚和鍵解離能( BDE)利用以下公式['5]進(jìn)行計(jì)算:苯酚{6-7].為解釋這-過程,以木質(zhì)素單體?；餅锽DE =ArH°=H(A.) +H(B.) -H(A-B).起始物設(shè)計(jì)了以下4條反應(yīng)路徑:Path 1,C,取代基式中,A- -B代表反應(yīng)物,A.和B.代表均裂A-B鍵在熱解過程中均裂離去,生成愈創(chuàng)木酚;Path2,C所得的自由基產(chǎn)物,ArH%是物質(zhì)的標(biāo)準(zhǔn)摩爾反應(yīng)取代基在.H的協(xié)助下離去,生成愈創(chuàng)木酚;Path3.焓變.和Path4則是以優(yōu)先過程分別生成鄰苯二酚和苯反應(yīng)能壘(E.)為過渡態(tài)能量E(TS)與反應(yīng)物酚.其中, R-=-CH0/-CH20H/- -COOH, R.=能量E(R)之差,即CH0/ CH2OH/ .COOH.E.=E(TS) - E(R).式中,TS為過渡態(tài)對(duì)于沒有過渡態(tài)的均裂反應(yīng),這里用鍵解離能- +H.>Path 1:BDE來作為反應(yīng)能壘E.OCH,HOH2結(jié)果與討論RIM1PI2.1不同基團(tuán)解離能力 的比較.Path 2:熱解時(shí),木質(zhì)素主要發(fā)生結(jié)構(gòu)單元中C取代基的裂解和苯環(huán)上取代基的脫落,為探討不同取代基IMP的解離能力,文中計(jì)算了3種木質(zhì)素單體模化物中的主要連接鍵C。- C，、C3-0、0- -CH3、C.-0和_-CH,,+H,0-H的鍵解離能,并將數(shù)據(jù)列于表1中.Path 3:表1木質(zhì)素單體?；镏?主要連接鍵的鍵解離能0HTable 1 Bond dissociation energy of main connections in mono-IM3-1meric model compounds of ligninkJ/molRH連接鍵 _香草醛香草醇香草酸TS3-2'C。-C414. 690395.345443.865)H~0C,-0405. 149401. 263403.0170-CH224. 173208. 126216.278P3C.-0470. 480462. 929468.7650一H331. 806 .321. 049330. 756-OCH;Path 4:TS4-1,H TS4-2從表1中可以看出,模化物中不同連接鍵鍵解離能的相對(duì)大小具有一致的規(guī)律,總是0- -CH3的.R4IM4-1鍵解離能最低,其次是0-H,最高的是C.-0,這表明在熱解過程中側(cè)鏈甲基會(huì)優(yōu)先斷裂,生成.CH，和C3位上的酚氧自由基,而后分別被H.中和.+H。TS4-3TS4-4?；镏蠧。--C連接鍵鍵解離能的排序?yàn)橄悴菟?香草醛>香草醇,這取決于C.取代基的吸電IM4-2IM4-3?4子能力.其他各連接鍵的鍵解離能雖然差別不大,但1.3 計(jì)算方法在C,取代基的影響下表現(xiàn)出了一定的規(guī)律性,總是文中所有的計(jì)算均在Gaussian 034]中進(jìn)行,方香草醛>香草酸>香草醇.這說明不同C,取代基對(duì)法與基組均選用B3LYP/6-31G(d).首先對(duì)文獻(xiàn)給模化物的熱解行為有一-定程度的影響.出的實(shí)驗(yàn)構(gòu)象進(jìn)行優(yōu)化，然后計(jì)算其單點(diǎn)能與頻率，2.2 熱解路徑分析得到經(jīng)振動(dòng)零點(diǎn)能(ZPE)校正的單點(diǎn)能.文中出現(xiàn)的表2列出了B3LYP/6-31G(d)方法計(jì)算所得的反應(yīng)物、中間體和產(chǎn)物經(jīng)過頻率驗(yàn)證均無虛頻,為能反應(yīng)各駐點(diǎn)(反應(yīng)物R、中間體IM、過渡態(tài)TS和產(chǎn)72華南理工大學(xué)學(xué)報(bào)(自然科學(xué)版)第42卷.物P)經(jīng)過零點(diǎn)能校正的總能量.其中,過渡態(tài)能量+香草醛值都是基于過渡態(tài)理論按照前述方法計(jì)算得到的.一香草醇一香草酸表2反應(yīng)物.中間體、過渡態(tài)及產(chǎn)物在B3LYP/6-31C(d)水6443.865平下的總能量之|414.690Table 2 The energy of the recant ,nenedias,transitiono states| 395.345and products at B3LYP/6-31C(d) levelHartreeRI路徑駐點(diǎn)香草醛香草酸R-535. 1705 - 536.3406 - 610.4119Path IIM-421.1755 -421.1755 - 421.17550反應(yīng)進(jìn)程_P. -421.8510 -421.8510 -421.8510(向)Path I-535. 1705 -536. 3406 -610.4119-香草醛TS2-1- 535.6620 - 536.8333 - 610.9024Path2 .IM2-535.6946 -536.8756 - 610.9379香草酸.TS2-2-535.6729 -536.8477 - 610.9086P:-421.8510 -421.8510 - 421.8510--16.042219.985R3-535. 1705 -536. 3406 - 610.4119IM3-1-495.2767 - 496.4529 - 570.521021--45.216IM3-2 .-495.8918-497.0624 - 571.1334623691731626- ◆- -64.561Path3TS3-1-496.3831 -497.5548 -571.6238IM3-3-496.4159 -497.5970 - 571.6593TS3-2-496.3943 -497. 5694 -571.6302(b) Pabh2P3-382.5728 - 382.5728 - 382.5728R4-535.1705 -536. 3406 - 610.4119圖1Path1和Path2的勢(shì)能剖面圖TS4-1 -535.6611 -536.8327 - 610.9032Fig.1 Potential energy profiles along reaction Path 1 and Path2IM4-1-535.6989 -536.8728 -610. 9417-535.6815 -536.8552 - 610.9246Path2是在.H存在下，協(xié)助C取代基解離生Path4 .IM4-2-420.6778 -421.8490 - 495.9204成愈創(chuàng)木酚.首先,.H進(jìn)攻C。,經(jīng)過渡態(tài)TS2-1生TS4-3-421.1685 -422.3418 - 496.4103成中間產(chǎn)物IM2 ,這一-步 所需的活化能較低,分別為IM4-3-421.2007 -422. 3824 - 496. 448TS4-4-421.1800 -422.3566 - 496.416423. 262、19.985和25. 578 kJ/mol.接著中間體IM2P4-307.3601 -307.3601 二 307.3601經(jīng)過渡態(tài)TS2-2生成愈創(chuàng)木酚P2,這一步所需的活反應(yīng)路徑中,除了存在表2中列出的各物質(zhì)及其化能分別為56. 942 .73.162和76.793 kJ/mol. 整個(gè)能量外,還有H、.CH3、.CHO、.CH2OH和.COOH這過程的能量變化同樣為-45. 216、-64.561和5種自由基參與,其能量分別為-0. 5003、-39. 8085、- 16. 042 kJ/mol,這說明只要目標(biāo)產(chǎn)物相同,無論-113. 8371、-115.0145和- 189. 0673 Hartree利經(jīng)過怎樣的路徑,能量變化都是相同的. Path 2需要用表2中各駐點(diǎn)和上述5種自由基的能量,計(jì)算出克服兩個(gè)能壘,第一個(gè)能壘較低,決定著反應(yīng)能否開各步反應(yīng)的活化能,并繪制反應(yīng)路徑的勢(shì)能剖面圖.始,比較3種?；锇l(fā)現(xiàn)香草醇最易進(jìn)行,其次是Path 1和Path 2的目標(biāo)產(chǎn)物同為愈創(chuàng)木酚,圖1香草醛,最難的是香草酸;第二個(gè)能壘相對(duì)較高,決是兩條路徑的勢(shì)能剖面圖. Path 1中,C。一C,連接定著反應(yīng)能否繼續(xù)進(jìn)行,是反應(yīng)的決速步驟,此步的鍵在熱化學(xué)作用下均裂成愈創(chuàng)木酚自由基IM1和能壘為香草醇>香草酸>香草醛,出現(xiàn)了反差,這是3種側(cè)鏈自由基,這一步所需的活化能分別為414. 690、由TS2-1、TS2-2和IM2的性質(zhì)和能量造成的.395. 345和443.865 kJ/mol ,接著愈創(chuàng)木酚自由基與Path1和Path 2有著相同的反應(yīng)物和產(chǎn)物,不.H結(jié)合,生成愈創(chuàng)木酚P1.整個(gè)過程的能量變化分同的是中間過程,由此可以看出不同路徑對(duì)同--產(chǎn)別為-45.216. -64. 561和- 16.042kJ/mol,其值均物生成的影響.比較兩條路徑可以發(fā)現(xiàn),無論是啟動(dòng)小于零,勢(shì)能降低,說明Path 1是可能的，且香草醇反應(yīng)的能壘,還是決速步驟的能壘, Path 1都要遠(yuǎn)遠(yuǎn)最有可能進(jìn)行,香草醛次之，最難進(jìn)行的是香草酸.高于Path 2.從動(dòng)力學(xué)角度判斷, Path 2在很大程度從動(dòng)力學(xué)角度來看, Path 1只需要克服- -次反應(yīng)的上優(yōu)先于Path1發(fā)生,這表現(xiàn)在生成愈創(chuàng)木酚的過能壘,即Ca -C,連接鍵均裂所需的活化能,這決定程中.H參與誘導(dǎo)C取代基解離在很大程度上降著Path 1的動(dòng)力學(xué)可能性.低了反應(yīng)的活化能，說明3種?；镌跓峤鈺r(shí)側(cè)鏈第10期武書彬等:木質(zhì)素單體模化物熱解過程的理論分析7:不會(huì)直接解離,而是會(huì)優(yōu)先發(fā)生外界參與下的解離.Path 4是生成苯酚的過程.首先,反應(yīng)物在.H的Path 3和Path 4的設(shè)計(jì)考慮到了基團(tuán)解離方式參與下,經(jīng)過渡態(tài)TS4-1生成中間體IM4-1 ,此步過程的優(yōu)先性,圖2是其勢(shì)能剖面圖.Path3是生成鄰苯的活化能分別為25. 543、21. 351和23.582kJ/mol.接二酚的過程.首先,0- CH, 連接鍵在熱化學(xué)作用下著,中間產(chǎn)物IM4-1經(jīng)過渡態(tài)TS4-2生成中間產(chǎn)物均裂成中間產(chǎn)物IM3-1和.CH3,這步過程的活化能IM4-2,這步的活化能分別為45. 626、46. 041和分別為224. 173、208.126和216.278 kJ/mol.接著中44. 844kJ/mol. H再次進(jìn)攻中間產(chǎn)物IM4-2,經(jīng)過渡態(tài)間產(chǎn)物IM3-1與.H結(jié)合生成中間產(chǎn)物IM3-2, 放出TS4-3生成中間產(chǎn)物IM4-3,此步過程所需的活化能分能量.在.H存在下，中間產(chǎn)物IM3-2經(jīng)過渡態(tài)TS3-1別為24. 919、19.520和27.148 kJ/mol.中間產(chǎn)物IM4-3生成中間產(chǎn)物IM3-3,此步反應(yīng)的活化能較低，分別再經(jīng)過渡態(tài)TS4-4轉(zhuǎn)變生成苯酚P4 ,這步過程所需的為23. 527、20. 484和25. 990 kJ/ mol.隨后中間產(chǎn)物活化能分別為54. 259.67. 706和74. 798 kJ/mol.整個(gè)IM3-3經(jīng)過渡態(tài)TS3-2生成鄰苯二酚P3 ,此步過程的過程的能量變化分別為- 104. 254、- 123. 598和活化能分別為56. 763、72. 411和76. 407 kJ/mol.整個(gè)-75. 079kJ/mol,均小于零,勢(shì)能降低,且3種反應(yīng)物反應(yīng)過程的能量變化分別為- 124.018、- 143. 363和生成苯酚的可能性與生成愈創(chuàng)木酚和鄰苯二酚是一-94.844kJ/mol,勢(shì)能降低,說明這是可能的過程.從致的.從動(dòng)力學(xué)角度分析,雖然Path 4需要克服4次勢(shì)能角度分析,3種反應(yīng)物生成鄰苯二酚的難易程度能壘才能生成苯酚,但每次需提供的能量都較低,這與愈創(chuàng)木酚是一致的. 從動(dòng)力學(xué)角度分析, Path 3需表明有.H存在時(shí), Path 4基本就能進(jìn)行到底.要克服3段能壘，第一段能壘最高,是反應(yīng)的決速3種反應(yīng)物在相同條件下生成愈創(chuàng)木酚分別放出了45.216.64. 561和16.042kJ/mol的能量,生成鄰苯二過程.酚放出了124. 018、143.363和94. 844 kJ/mol的能量，生成苯酚放出了104. 254、123. 598和75. 079 kJ/mol士香草醛的能量,單從勢(shì)能角度可以看出相同反應(yīng)物在同一條←香草醇一香草酸件下會(huì)優(yōu)先生成鄰苯二酚,其次是苯酚,最后才是愈創(chuàng)木酚.從動(dòng)力學(xué)角度來看, Path 2和Path4啟動(dòng)反應(yīng)所需的能量和決速步驟的能壘都比較低,是動(dòng)力之蘭。B3學(xué)優(yōu)先的過程.Path1和Path3反應(yīng)的啟動(dòng)需要克24.17208.126服化學(xué)連接鍵解離所需的能量,這個(gè)能量較大,也使216.278M32:聲三P324.844得反應(yīng)的第- -步成為決速步驟,相比于Path 2和87332/// 3M3-3 ，124.01820.484/ 25.990095萬Path 4不是動(dòng)力學(xué)優(yōu)先的反應(yīng).-68.88........-143.36362.3 熱解路徑的競(jìng)爭(zhēng)反應(yīng)進(jìn)程(a)Path 3上述分析表明，愈創(chuàng)木酚、鄰苯二酚和苯酚都是可能的目標(biāo)產(chǎn)物, Path 2和Path4會(huì)優(yōu)先于Path 1-+香草醛和Path3進(jìn)行,這是因?yàn)?H的參與很大程度地降低+香草醇了反應(yīng)所需的活化能,但問題在于.H從何而來.熱解過程一般是在N2或Ar等惰性氣體保護(hù)下進(jìn)行，? 25.343/TS4-2是絕對(duì)無水無氧的熱化學(xué)過程, H的提供只能依靠言23.582三21.351/熱解過程中的解離.表3列出了3種模化物結(jié)構(gòu)中起|-28110、P所有不同化學(xué)環(huán)境H的鍵解離能.從表3中可以看-37.692出,苯環(huán)酚羥基H最容易解離,其解離分別需要-11852716706-104.254331. 806、321. 049和330.756kJ/mol的能量,而Path 3-120922/ 7.798*+123.598-144.027.↓中0- -CH, 連接鍵斷裂分別只需要224. 173、208. 1260和216.278kJ/mol的能量,對(duì)比兩組數(shù)據(jù)可以發(fā)現(xiàn)，(b)Path4在熱解過程中,當(dāng)體系中未有.H產(chǎn)生之前，側(cè)鏈甲圖2Path3和Path4的勢(shì)能剖面圖基已經(jīng)解離,即Path 3已經(jīng)啟動(dòng),隨后.H產(chǎn)生,當(dāng)其Fig.2 Potential energy profiles along reaction Path 3 and Path 4參與Path2和Path4反應(yīng)時(shí),Path3或已進(jìn)行完畢.第10期.袁騰等:毛細(xì)力學(xué)在超親水膜分離過程中的應(yīng)用及力學(xué)模型89Application of Capillary Mechanics to Separation Process ofSuperhydrophilic Membrane and Its Mechanical ModelYuan Teng' Chen Zhuo' Liu Wenjt' Zhou Xian-hong'’Tu Wei-ping' Wang Feng'(1. School of Chemistry and Chemical Engineeing, South China Universty of Technology, Guangzhou 510640 , Guangdong,China; 2. School of Light Industry and Food Sciences, South China University of Technology , Guangzhou 510640, Guangdong,China; 3. School of Chemistry and Environmental Engineering, Dongguan University of Technology , Dongguan 523808,Guangdong, China)Abstract: The current oil/ water separation membrane researches based on special wettability are seldom involved inthe dynamic process of the membrane separation and the relevant quantitative calculations. In this paper, by analy-zing the physical quantties of the superhydrophilic membrane separation process based on the capillary mechanicsand by classifying the membrane pores of membrane materials based on special wettability as capillary pores, amathematical model is constructed, and it is used to analyze the force distibution condition in the separationprocess of oil-water mixture by using the superoleophilic membrane. Then, the principle of the superhydrophilicand superoleophilic membrane in the air transforming to be superoleophobic underwater is analyzed from the per-spective of surface tension, and the capillary flow rate ，the capillary permeation rate, the membrane flux and thecritical penetration pressure in the membrane separation process are calculated based on capillary mechanics andare validated by experiments. On this basis , the separation mechanism of superhydrophilic and underwater supero-leophobic oil/ water separation membrane is preliminarily discussed based on capillary mechanics.Key words: capillary mechanics ; superhydrophilic membrane; capillary flow ; membrane separation; mechanicalmodel; quantitative calculation ; separation mechanism責(zé)任編輯:張娜娜(上接第74頁)Theoretical Analysis on Pyrolysis Processes ofMonomeric Model Compounds of LigninWu Shu-bin Deng Yu-bin Liu Chao(State Key Laboratory of Pulp and Paper Enginerig, South China University of Technology, Guanghou 510640, Guangdong, China)Abstract: In order to deeply investigate the pyrolysis mechanism of lignin, its pyrolysis process is simulated withvailin, vanillic alcohol and vanillic acid being selected as monomeric model compounds of lignin. In the investi-gation, the density functional theory is employed to analyze the dissociation sequences of chemical connectionbonds, and four reaction paths, namely, Path 1 - Path 4, are designed. Both Path 1 and Path 2 generate guaiacolbut their intermediate processes are not the same , while Path 3 and Path 4 generate catechol and phenol with priorityprocesses respectively. The results show that (1) the methyl in the side chains of the model compounds first disso-ciates with CH4 being released，and the dissociation sequences of the substituents on C1 depend on their ability towithdraw electrons; (2) in the pyrolysis process, it is difcult for the substituents on C1 to dissociate directly, butprior dissociation occurs instead with the help of outside factors; (3) it is possible for the target products of threekinds to be obtained in the priority sequence of catechol, phenol and guaiacol; (4) from the view of dynamics,Path2 and Path 4 are superior to Path 1 and Path 3; and (5) whenever the target products of the same kind aremade, it is always the easiest job for vanillic alcohol, and then vanillin, whereas vanillic acid is always the mostdifficult matter to be dealt with.Key words: lignin; monomeric model compound; pyrolysis ; density functional theory