Experimental Researches on Milled Wood Lignin Pyrolysis Based on Analysis of Bio-oil

CHEM. RES. CHINESE UNIVERSITIES 2011, 27(3), 426- -430Experimental Researches on Milled Wood LigninPyrolysis Based on Analysis of Bio-oilGUO Xiu-juan, WANG Shu-rong', WANG Kai-ge and LUO Zhong-yangState Key Laboratory of Clean Energy Utilzation, Zhejiang Universiy Hangzhou 310027, P. R ChinaAbstract The structure of milled wood lignin(MWL), isolated via the Bjorkman procedure, was studied by meansof 'H NMR spectroscopy and Fourier transform infrared spectroscopy, and then its pyrolytic product distribution wasinvestigated on a pyrolysis device. MWL obtained from Manchurian Ash(MA) contained more methoxyl and freephenolic hydroxyI groups per C9 unit than MWL from Mongolian Pine(MP) duc to the existence of both guaiacyl andsyringyl units, which have a major inluence on the pyrolysis behavior of lignin. The results of pyrolysis show thatMWL from MA generated a higher yield of bio-oil, mainly composed of phenols, guaiacols, syringols and catechols,and a less yield of char, in addition to the gaseous products CO, CO2, methane and methanol, compared with MWLfrom MP. Guaiacol and syringol were the typical products from G-lignin and S-lignin, probably atributed to the easi-er cleavage of the ayl-alkyl linkage in the side chain compared with the C- -0CH bond in the benzene ring. The de-gradation of MWL from MP was dominated by the demethylation reaction and the cleavage of aliphatic - -CH2OH atthe y-position, followed by the cracking of the Ca- -Cp and Co- Co bonds.Keywords Pyrolysis; Milled wood lignin(MWL); Guaiacyl unit; Syringyl unitArticle ID 1005-9040(2011)-03- 426-051 Introductionof lignin, isolation is needed. This has been achieved via rea-gents such as hydrochloric acid, Klason and Organosolv (Orga)As an option for mitigating the threat of global warming,as well as enzymatic and steam explosion methods. The Orgathe utilization of biomass energy, regarded as carbon dioxidelignin shows obvious changes in content and quality due to theemission neutral fuel, is under consideration as a supply ofhigh temperature and pressure present in the solvent extractionenergy for today's society'". Thermochemical processes are theproess". The Van Soest method is often used to extract themost common route for convering the biomass to energy, andlignin indirectly from biomass to obtain strong acid detergentfast pyrolysis has the potential to produce subtituted fuels afterfiber(SADF), which mainly consists of lignin and insoluble ash.upgrading2). Fast pyrolysis is a thermochemical decompositionIn consideration of the efect of organic solvents on the ligninof organic material at clcvated temperatures in the absence ofstructure, the Bjorkman procedure has been widely used tooxygen with a good heat transfer rate and very short residenceisolate lignin from diferent kinds of biomassl2l. Milled woodtime to produce bio oil, gaseous products and char'). The py-lignin(MWL) obtained in this way has minimal structural mo-rolysis bchavior of biomass has been widely investigated,dification due to the absence of reactive chemicals and elevatedwhich depends on the three main components, i.e. cellulose,temperatures, so it is the most representative form of lignin,hemi-ellulose and lignin'4. Following cllulose, lignin is thecompared with other extracted lignins!'). The complexity ofmost abundant component in biomass that can readily be pro-the lignin structure and disadvantages of extracted lignin haveduced as a residue in pulp mils's. Lignin units are divided intocompelled researchers to adopt model compounds for the in-three types, guaiacyl(4-hydroxy-3-methoxyphenyI), syringyl(3,vestigation of their pyrolysis behavior. Most researches into5-dimethoxy-4-hydroxypheny) and p-hydroxyphenyl6.7I. Thelignin have been focused on mechanism studies, frequentlyspecific structure of lignin changes with the biomass speciescarried out on a TG-FTIR analysis14-I1]. Wang et al.1'] studiedand is sometimes influenced by the extraction methods'"!. Thethe pyrolysis behavior of MWL obtained by the Bjorkman pro-methoxyI groups commonly exist in lignin and are necessarycedure from Mongolian Scots pine(MP) and Manchurianfor char formation!9]. Lignin from hardwood has a higherash(MA). The result indicates that MWL from MA shows amethoxyl group content than that from sofwood, due to themuch higher thermal degradation rate than MP in the tempera-presence of both guaiacyl and syringyl unitslo.ture range of 290- 430 °C, and the final residue yields wereIn order to investigatc the property and thermal bchavior26% and 37%(mass fraction), respectively. The objective of*Corresponding author. E-mail: srwang@zju.cdu.cn中国煤化工Received June 7, 2010; acceptcd October 2, 2010.Supported by the National High Technology Research and DevelopJYHCN M H GAo5z407. the lternational Science and Technology Cooperation Program(No.2009DFA61050), the National Natural Science Foundation(No.90610035), the National Basic Research Program of China(No.2007CB210200) and the Doctoral Foundation of the Ministryof Education of China(No.20090101110034).No.3GUO Xiu-juan et al.427this study was to investigate the pyrolysis behavior of MWLThe radiation source temperature was measured by three ther-from different tree specics on a pyrolysis device, combinedmocouples inserted into the surface of the pipe. Nitrogen ofwith structural analysis via 'H NMR and FTIR.over 9% purity was used as the carrier gas in the experi-ments to ensure pyrolysis taken place in an inert atmosphere,2 Materials and Methodswhich was pre-heated to 200。C before entering the reactor.The sample weight was maintained at about 3g and the reac-2.1 Samplestion zone temperature was kept at 540 °C. Bio-oil was cllctedMongolian Pine(MP) and Manchurian Ash(MA) were se-in a multi condensation system, which consisted of four con-lected for the preparation of MWL via the Bjorkman mechodI2.densers and a cotton fiter. The first-stage condenser uilized aCellulose, purchased from the FMC Biopolymer Co, was alsomixture of ice and water as the condensation medium, whichselected to make a comparison. Before further experiment,reduced the temperature of the volatiles to below 100 °C. And athese samples were ground to powder with a size less than 0.3mixture of dry ice and acctone, which had a temperature ofmm and dried for use. The contents of carbon, hydrogen, and-45 °C, was utilized as the cooling medium in the other threenitrogen were measured on a CHNS-932 elemental analyz-condensers to ensure thorough condensation of the volatiles.er(LECO Co.. USA). The oxygen content was calculated bysubtracting the C, H and N contents from 100%. The procedurer -Gas bagincluded first taring a silver capsule and adding about I mg of13sample in it crimping and foling the capsulc, recording theweight, and analyzing. Table 1 summarizes the elemental anal-⑦ysis of samples, as required for following calculation.10 11 12|Table 1 Elemental analysis of samples on air-dry basisDCondensation sy stemElemental analysis(%)SamplecCellulose43.644.3352.030.00MWL from MP64.243.9630.950.09MWL from MA61.705.0533.140.11Fig.1 Schematic of the pyrolysis device1. Nitrogen; 2. Prcheater; 3. Silicon carbide pipe; 4. Quartube reactor, s.2.2FTIR and 'H NMRChar filter;6, 8. Valve; 7. Feeder;9, 10, 11. 12. Condenser; 13. Aerosolsfiter.Samples were prepared via the KBr pellet technique andThe yields of char and bio-oil produced during pyrolysisFTIR spectra were measured using a Nicolet Impact 830Dwere determined by weighing the amounts of them ollcted,spectrometer manufactured by Thermo Fisher Scientific Inc.while the gas production rate was calculated by subtraction.USA. Measurements were taken at wave numbers from 400The permanent gas was ollcted in a bag and analyzed bycm' to 4000 cm ' with a resolution of 4 cm ', and ceach spec-SP-3420A gas chromatography. The chemical components oftrum was based on the average of 36 scans.bio-oil were analyzed on a Voyager GC-MS system. The gasEach sample of 100 mg was acetylated for 72 h at roomchromatograph was equipped with a 30 m>0.25 mm*0.25 mmtemperature with 2 mL of the mixture of purified pyridine-Agilent DB-WAXctr capillary column. And the oven wasacetic anhydride(1:1, volume ratio). Ether was used to quenchmaintained at 60。C for 5 min, heated at 10 °C/min to 240 °C,the remained acetic anhydride and wash the deposition repeat-and then held at 240 °C for 40 min. In order to reduce the lossedly ill no smell of pyridinc remained. Then a flow of nitrogenof the oil components, 0.1山of aliquots of bio-oil were in-was applied to evaporating the solvent and the samples werejected directly into the GC-MS system without pre-treatment.dried to obtain completed acetylated ones. 'H NMR spectra ofthe actylated samplcs, dissolved in 0.6 mL of CDCI, were3 Results and Discussionrecorded on a DMX-500 apparatus with tetramethy lsilane(TMS)as an internal standard. Proton signals were integrated from the3.1 Structural Analysis of Samplesbascline and rferred to the integrated signal of the mcthoxy1The spectra of MWL from MP show the typical features ofprotons for proton quanification of aliphatic and phenolic hy-guaiacyl lignin, while those of MWL from MA clearly exhibitdroxyl.the features of guaiacyl and syringyl lignin"sl,, The visible dis-tinction was the presence of bands at 1125 and 1329 cm-'.3Fast Pyrolysis and Analysis Methodswhich can be used to discriminate between MWLs from soft-Pyrolysis experiments were conducted on an apparatuswood and hardwood"l. Fig.2 shows comparative FTIR spectrawhose main parts are a pre-heating section, a pyrolysis section_stic bands were ob-and a condensation scction, as shown in FigI. The main partserved中国煤化工ingtheO- H sret.was a quartz glass reactor and its dimensions were the extermalching achingat 2970- -2850CNMHGhingatdiameter(20 mm), wall thickness(2 mm) and lengh(1 m). Thecm^silicon carbide pipe supplied the heat required for biomassplane bending vibrations of HCH and OCH at 1429 cm', thepyrolysis by radiation at a maxima cectrical power of8 kW.C-H deformation vibration at 1375 cm 1 the superposition of428CHEM. RES. CHINESE UNIVERSITESVoL.27C- 0 stretching and deformations at 1247- -925 cm-1 and theC-OH out-of-plane bending mode at 668 cm~'. These weredifferent in band location or vibration intensity for differentMWLs. Bands at 4000- -2995, 2900, 1430, 1375 and 900 cm-lare epecially sensitive to the state of the crstalline anamorphous species respectivelyl19. In Fig.2(B), the spectrum ofMWL from MP shows the typical features of G-lignin: 1636cm~' <<1508 cm-1 >>1458 cmr'; 1269 cm-' >>1224 cm~'; amaximum at 1139 cm); 1031 cm-' >1224 cm*; two separate10bands at 864 and 818 cm^ ', according to the lignin clssifica-tion system(20). In the spectrum of MWL from MA, all theFig3 'H NMR spectra of acetylated MWLs frombands are well- defined, which is the characteristic of syringylMA(a), MP(b) and ellulose(c)units, while bands corresponding to guaiacyl units are alsointegrated intensity by the regional integrated intensity. Thepresent. Compared to the spectrum of MWL from MP, theproton assignments are summarized in Table 2, from which wespectrum of MWL from MA exhibits relatively lower intensityobserve that MWL from MP shows the typical features ofbands at 1508, 1269 and 1031 cm'; and the presence of aG-lignin with only the guaiacyl unit, while MWL from MAmaximum band at 1124 cm", because of the concurrence ofrepresents the characteristics of G-S-lignin, with both guaiacylguaiacyl and syingyl unis. The resuts are well agreed with theand syringyl units. The average formula Cg shown in Table 3previous studyI5), which shows that MWLS have a stablewas calculated from the elemental analysis and methoxyl con-structure with comparability.ent, which contained some information about the lignin struc-0.7(A)ture23. The formulae of the MWLs from MP and MA were。0.CHs23O28u(OCH3).63 and CHs650:.0o(OCH3).as. respec-tively, both of them are similar to CgHs soO2.79(OCH;)0.86 for thei0MWL from spruce23). MWL from MA contained more me-0.thoxyl groups, namely 1.035 compared with 0.63 for MWL曼0.from MP, per Cq unit. The lower methoxyl group content indi-cates that lignin has more ortho-positions in its phenyl ringsunblocked by methoxyl groups and is suitable for producinglignin phenol-formaldehyde resins.40003500 300025002000D/cm~'Table2 Assignments of proton in the 'H NMR spectra07 (B)8Main assignmentProton per 100 g MWLfrom MP from MA; 0.7.25- -6.8 Aromatic proton in guaiacyl units0.580.296.80- -6.25 Aromatic proton in syringyl units0.416.25- -5.75 Ha of B-0-4 and B-1 structures0.130.195.75- -5.24 Ha of B-5 structures0.150.175.24- 4.90 H of xylan residue0.070.094.90- 4.30 Ha and H in B-0-4 structures0.20.35 .4.30- -4.00 Ha of B-β structures and H ofxylan 0.170.2715001000504.00- -3.48 H of methoxyl groups1.051.59p/cm'2.50- -2.20 H of aromatic acetates0.570.78Fig.2 FTIR spectra of MWLs and cellulose at2.20-1.60 H of aliphatic acctatcs0.900.89high (A) and low wavenumber(B)<1.60H of carbohyrats0.08a. Cllulose; b. MWL from MP;cTotal protons per 100 g samples3.965.0'H NMR spectra of the acetylated samples are shown inTable3 Calculation of C, formuls and contentFig.3. These spectra could be used to investigate the methoxylof hydroxyI groupand hydroxyl groups prior to the analysis of the pyrolysis beha-SampleAliphatic PhenolicFormulavior. MWL from MP has the same peaks but different vibra-MWL from MP 1.6201.026 CsHs 2mnO2 s(OCH)o63tions compared with MWL from MA. The obvious diferenceMWL from MA 1.7381.523CcH6 ss0 orMOCHhObetween cellulose and MWLs was observed due to the distinctThe content of aliphatic and phenolic hydroxyl groupsstructural units. On the basis of numerous reports, it has beenper Cq unit is determined by the corresponding acetate signals.fimly established that only the most stable conformation ofThe中国煤化工-oup were 1.62 andglucopyranose cycles(C1) is present in cellulose and conside-1.738nd the numbers ofrable distortions of C1 take place only on the introduction of phenoCN M H G 1.523, rspetivly.additional closed bonds(like compounds with a-oxide cycles,Lignin reactivity is essentially affected by the content of2,3- and 3,6 anhydride dervaives of clsel)1,2I.,phenolic hydroxyI group due to the activation of aromaticThe specifec proton ratio is obtained by dividing the totalring at the ortho-position and the possibility of fomming someNo.3GUO Xiu-juan et al.429intermediates, which are susceptible to nucleophilic reaction at600 °C in a quartz tubel27. Major components are also identi-the benzylic carbon atom/24. Therefore, MWL from MA has afied from the Py-GC/MS lest of MWL from Paulownia fortuneihigher pssibilily to produce formaldehyde during the forma-wood operated at 500 oCl121. The significant difference is thetion process of phenolie resin.absence of catcchols in the referred data, which exist in the tarfraction obtained by the pyrolysis of MWL from Japanese ce-3.2 Product Distributiondar at 600 °C21.Table 4 Main components of bio-oil fromThe product distribution is shown in Fig.4. MWLs had asample pyrolysishigher char yicld and a lower bio-oil yield than ellulose. MWLContent(%)from MP produced more char and less bio-oil compared withCompoundMWL MWLMWL from MA, duc to the promotion of char formation causedCellulose fromMp FromMA MWL'HIby the cross-interactions among guaiacyl units.Acetic aeid0.420.91 0.72The yields of CO(about 60%- -70%) and CO2(aboutFurfural0.580.28 5.2420%- -30%) generated from cllulose and MWLs were similar,2,5-Dicthoxy-(4/)furan9.74but the formation mechanisms were diferent. For ellulosc, CO-Hydroxy-2-propanone6.27formation was strongly afected by the secondary cracking of2-Cyclopenten- 1-one3.153-Sugar alcohol11.30intermediates with low molecular weight, and CO2 was pro-Cedrol11.2duced by primary reactions or at an early stage2.26. For MWL,3,4-Altrose5.78CO formation was caused by degradation or reforming reac-Levoglucosan6.25tions of unstable functional groups in the side chain of phenyI4-Hydroxybenzenaldehyde0.400.propyl units and secondary decomposition of volatiles with aryl6.15 0.239cther functional groups. The yield of methane from the pyroly-4-Methyl guaiacol17.29 6.936.sis of MWL from MA was 11%, which was slightly higher than4-Ethyl guaiacol0.59 0.221.that from MP(9%) due to its higher content of methoxyI group.Phenols.90 7.27As methane formation was attributed to the decomposition of2-Methylphenol8.4711.98methoxyl group9, yiclds of other gas products, such as H2 and2.4-Dimethylphenol4.52 7.29hydrocarbons, were extremely low(less than 59%).Eugenol0.415.14Syringol4.047.)0「o CelluloseVanillin1.134.2 MWL from MP70 -2 MWL drom MA2.,4-Dimethoxyphenol60 -Catechol20.45 18.294-Mecthylcatcchol20.05 1344-Ehylcalcchol3.19 1.81Polymers with benzy| propyl units in lignin to decom-20 tposed into monolignol monomers through fragmentation, fol-lowed by rearrangement, H-transfer, fragmentation andH-abstraction reactions to form guaiacols, catechols, phenolsCharBio-oilGasand so on. Small molecular compounds, such as co, CO2 andFig.4 Product distribution of pyrolysis of samplesmethane, are formed from further cleavage of the intermc-3.3 Bio-oil Compositiondiates.Table 4 summarizes the main components of bio-oil ob-3.4 Discussion of Lignin Pyrolysis Mechanismtained by the pyrolysis of MWLs from MA and MP. CelluloseChemical pathways for lignin pyrolysis, especially for thegencrated more acids, aldehydes, alcohols, ketones and saccha-formation of phenols( shown in Scheme 1), were proposed. Therides during pyrolysis, while MWL produced more guaiacols,syringols, catechols and phenols. The major difference betweendegradation of G-lignin takes place via two reaction pathways:MWLs from MP and MA was in regard to the formation of(1) the first is related to the demethylation reaction and thecleavage of aliphatic - -CH2OH at the y-position, ollowed byguaiacol and syringol, corresponding to the guaiacyl and sy-ringyl units, respectively. It was also observed that MWL fomcrackingofC.- -C%, C4- -Ca bonds to generate large amounts ofMA produced more vaillin, with aldchyde functional group,catechol and its alkyl substitutes, with some relcase of smallthan MWL from MP. It is mainly formed through the decompo-molecular compounds such as co, methane and methanol; inpathway (2), the cleavage of Ca- -Cpoccurs firs, followed bysition of high molecular weight polymers at low temperatures.In other words, the thermal stability determines the formationthe cracking of the C2- -O bonds to form the final productof aldehydes. The guaiacyl unit has a better thermal stabilityphenol中国煤化工be akylated by ole.fin conacid catalysts to in-than the syringyl unit, which is the probable explanation of thiscreaseYHC N M H Gpared with he pyro.experimental result. These kinds of compound groups agreelysis pathway of MWL from MP, the pathway of MWL fromwith the results obtained by the pyrolysis of MWL isolatedMA is more complex in view of the combination of coniferyIfrom milled Scots pine by means of the Bjorkman method atalcohol and sinapyl alcohol by means of A(side chain-side430CHEM. RES. CHINESE UNIVERSTIESVol.27chain), B(ring-ring) and C(ring side chain) shown in Scheme 1,Chinese Univrites, 2006, 2(4), 524which has been ientified by Deacon!o0. More groups and rad-[2] Xiong W. M, Fu Y, Lai D. M, Guo Q. X, Chem. J. Chineseicals are obtained, giving the unpredictable cracking of chemi-Unersite, 2009, 309), 1754cal bonds. The formation of guaiacol and syringol is typical of[3] Onay o, Fuel Process Technol. 2007, 88, 523C-lignin and S-lignin, which is probably atributable to the[4] Ranzi E.. Cuoci A. Farvelli T. Fassoldati A, MiglivaccaGo, Pieeasier cleavage of the aryl-alkyl linkage in the side chain com-rucci s., Sommariva s. Enengy Fuels, 2008. 22. 4292pared with the C- -OCH3 bond in the benzene ring, in agree-[5] Kreetachat T, Damrongsni M. Punsuwon V.。 Vaithanomst P,ment with the published researches!".Chiemnchaisi C, Chomsurin C, J. Hazard. Mater, 2007.142. 250[6] Caballero J. A, Font R, Mrila A, J. Anal.4ppl. Probsis, 1996,cHi; CHOHHCHHoOH38, 131'H0pOH yoH7] LiJ, Li B. Zhang x. Poym. Degrad. Slab.. 2002, 78,279HO'8] Brit P. F, Buchanan A C., Thomas K. B., Lee s. K, J Anal. ApplL4-Ethylcatechol 4-Mchylcatcchol CatechePyrolysis, 1995, 33, 1G-ligninQHj0ConiferylPhenol，[9] Hosoya T, Kawamo H, Saka S,1. Anal Appl. Proysis, 2009,84.alcoholOH旦CoGugiacol. goH10] Jakab E. Faix 0. T1I F.,J. Anal. App!. Probyris, 1997, 40141, 171792,4-Dimcthyl. 2-Methyl1] Willauer H. D, Huddeston J. G, Li M, Rogers R D, J. Chromalog:EthanolphenolCHE phenolCH;B-Biomed. Appl, 2000.0 743.127(B)12] Rencoret J, Marques G., Cutierrez A. Nieto L, Jimenez-Barbero J,Martinez T, del Rio 1. Ind Crops Protucts.2009, 30, 137Syringol[13] Guera A. Fipponen L, Lucia L. A, Saquing C, Baumberger s,G-ligning ， S-lignin(2)R、re AoArgyropoulos D. S,J Agric. Food Chem. 2006, 54, 5939HOJ[14] Bssilakis R, Carangelo R M, Wjiowicz M. A, Fuel, 2001, 80,acoboroH alcoho oHRHOH,COHHQ[15] Wangs. R, Wang K. G, LiuQ. Gu Y.L, LuoZ Y, CemK F.sicoFansson T., Bioechnol. Adv, 2009. 27, 562Furfural Eugenolv anilin 6-Mcthyl-2[16]Femandes D. M. Winkler Hecheneiner A. A.. Job A. E,benzenaldehydeRadovanocic E, Gomez Pineda E. A, Polym Degrad Siab, 2006,91, 92Scheme 1 Proposed pyrolysis pathways for MWLfrom[17] LiuQ, Wang s. R.. Zheng Y, LuoZ Y. Cem K. F,J. Anal. Appl.MP(A) and MA(B)Prolysis, 2008, 82, 170[18] Marques A. V, Perira H, Rodrigues J, Meier D, Faix O, J. Anal.4 ConclusionsAppL Prolysis, 2006.6 77. 169MWL from MA contains more methoxyl and free phenolic[19] OhS. Y, Yoo D. I, Shin Y. s, Seo o, Carbohyd. Res, 2005, 340,hydroxy1 groups than MWL from MP per Cg unit, due to the417existence of both guaiacyl and syringy| units. The products of20] Faix 0, Jakab E. TIl F, Sazckely T, FWood Sei Tehnol, 1988, 22.MWL pyrolysis are mainly phenols, guaiacols, syringols, cate-131chols and vanllin, as well as some small molecular compounds[21] Zhbankov R G, Firsov S. P. Buslov D. K. Nikonenko N. A,including CO, CO2. methane and methanol. Guaiacol and Sy-Marchewka M. K., Ratajczak H,J. Mol. Sruct. 2002, 614, 117ringol are the typical products from CG-lignin and S-lignin,2] Zugenmaier P, Prog. Polym. Sci, 200 26, 1341probably due to the easier cleavage of the aryl-alkyl linkage inthe side chain rather than the C-0CH3 bond in the benzene[24] Mansourn N.E E, Salvado J, Ind Crops Products, 2006, 24,8ring. The degradaion of MWL from MP is dominated by the[25) Shen D. K, Gu s, Bioresour. Technol. 2009. 100 64%626] Li s.. Lyons-HatJ. BanyaszJ, Shafer K. Fuel, 2001, 80, 1809demethylation reaction and the cleavage of aliphatic - -CH2OH[27] Alen R. Kuoppala E, Oesch P, J. Anal. Appl. Prolyris, 1996, 36,at the y-position, fllowed by the cracking of C&- Cp and137Ca- Ca bonds. Compared with the proposed pyrolysis pathway28] Hosoya T. Kawamoo H. Saka s.1 Anal. sppl. Probyie, 209.85,55of MWL from MP, that of MWL from MA is more complexdue to the combination of coniferyl alcohol and sinapyl alcohol[29] Yang x. L, Charles U. P. Zhu x F. Chem J. Chinese Univerilies,by cyclization to form new kinds of groups and radicals.2010, 317), 1754[30] Deacon1. W. Moderm Mhcology. Blackwell Scientifi Oxford, 1997References[31] Masuku C P, J. Anal. AppL Pralysis, 1992, 23, 195(1] YangC. Y, luX s, Lin W.G. Yang X. M, YaoJ. Z. Chem Res.中国煤化工YHCNMHG