review article recent development in chemical...

Hindawi Publishing CorporationJournal of Applied ChemistryVolume 2013 Article ID 838645 9 pageshttpdxdoiorg1011552013838645

Review ArticleRecent Development in Chemical Depolymerizationof Lignin A Review

Hai Wang1 Melvin Tucker2 and Yun Ji1

1 Department of Chemical Engineering University of North Dakota Grand Forks ND 58202 USA2National Renewable Energy Laboratory Golden CO 80401 USA

Correspondence should be addressed to Yun Ji yunjiengrundedu

Received 29 March 2013 Revised 21 June 2013 Accepted 24 June 2013

Academic Editor Lingjie Meng

Copyright copy 2013 Hai Wang et alThis is an open access article distributed under theCreativeCommonsAttribution License whichpermits unrestricted use distribution and reproduction in any medium provided the original work is properly cited

This article reviewed recent development of chemical depolymerization of lignins There were five types of treatmentdiscussed including base-catalyzed acid-catalyzed metallic catalyzed ionic liquids-assisted and supercritical fluids-assisted lignindepolymerizations The methods employed in this research were described and the important results were marked Generallybase-catalyzed and acid-catalyzed methods were straightforward but the selectivity was low The severe reaction conditions (highpressure high temperature and extreme pH) resulted in requirement of specially designed reactors which led to high costs offacility and handling Ionic liquids and supercritical fluids-assisted lignin depolymerizations had high selectivity but the high costsof ionic liquids recycling and supercritical fluid facility limited their applications on commercial scale biomass treatment Metalliccatalyzed depolymerization had great advantages because of its high selectivity to certainmonomeric compounds andmuchmilderreaction condition than base-catalyzed or acid-catalyzed depolymerizations It would be a great contribution to lignin conversionif appropriate catalysts were synthesized

1 Introduction

Lignin is a natural resource which exists in woody materialsagricultural residues and other plant materials (so-calledlignocellulosicmaterials) Lignocellulosicmaterials consist of10ndash30 lignin by weight and 40 by energy [1] Howeverit has mainly been used as an energy source in combustionprocesses and less than 5 lignin has been used for otherpurposes nowadays [2] Because of its high energy contentand polymer structure lignin is considered as a potentialrenewable resource of chemicals and fuels especially incondition of escalating petroleumprice and renewable energydemand Lignin depolymerization is very promising processwhich can generate value added products from lignin rawmaterials The primary purpose of lignin depolymerizationis to convert the complex lignin compound into smallmolecules for fuels and basic chemicals or oligomers forfurther application Considerable amount of research hasbeen done to convert lignin into renewable fuels and chemi-cals using pyrolysis and gasification methods [3ndash8] Pyrolysisrefers to the thermal treatment of the biomass or lignin in the

absence of oxygen with or without any catalyst usually at thetemperature between 300 and 600∘C [3] The cleavage of OHfunctional group linked to aliphatic side chain the breakingof alkyl side chain aryl ether and linkage between aromaticrings occur when temperature increases forming a mixtureof phenol guaiacol syringol and catechols Moreover thearomatic ring cracking occurs at the temperature above 500∘C[9] However the process is highly complex and is affectedby several factors including feedstock type heating rate andreaction temperature [10] Gasification represents a processthat converts lignocellulosic materials into CO

2 CO and H

2

at the temperature between 700 and 1000∘C The mixtures ofthe gases are referred to as ldquosyngasrdquo which is the only usefulproduct from the process [3] Biochemical method such asfungi depolymerization of lignin was also employed but ittook several weeks for fungi to grow which made the processhave very low efficiency [11 12] Compared to pyrolysis andbiochemical depolymerization chemical treatment of ligninhas its advantages on both reaction control and high selec-tivity which provides great potential in lignin conversion forrenewable fuels and chemicals production

2 Journal of Applied Chemistry

OH

OO

HO

O

HOHO

OH

OH

OHO

HO

OHO

O

OH

OHO

OHO

HO OH

HO

OHO

HO

O

HO

HO

OHO

HO O

HOOH

OH

HO

O

OO

HO

O

HOHO

OH

OHO

HO

OHO

OHO

OHHO

LIGNIN-O

OH

OHO

OO

OHLIGNIN

HOOH

O

OH

OH

HO

Aryl glycerol ether

DibenzodioxocinDiphenyl ether

H3CO

H3CO

H3CO

H3CO

H3CO

H3CO

H3CO

H3CO

OCH3OCH3

OCH3

OCH3

OCH3

OCH3

OCH3

OCH3

OCH3

OCH3

OCH3

OCH3OCH3

OCH3

120573-O-4

5-5998400-120572120573-O-49984005-O-4998400

Figure 1 Common chemical structure of lignin [15]

Lignin can be categorized to softwood and hardwoodlignins according to their raw biomass sources Dependingon the fractionation methods lignin can also be categorizedto steam explosion kraft organosolv alkaline oxidationpyrolysis lignins and so forth [13]The commonly recognizedchemical structure of lignin is exhibited in Figure 1 Etherbond was the target for chemical attacking during chemicalconversion processes Generally softwood has 45ndash48wtand hardwood has 60wt of 120573-O-4 aryl glycerol etherbonds Softwood has about 5wt and hardwood has 0ndash2wt of dibenzodioxocin 5-51015840-120572 120573-O-41015840 bonds In additionsoftwood has 35ndash8wt and hardwood has 6ndash9wt ofdiphenyl ether 5-O-41015840 linkages [13 14] The differences ofthese linkages have effects on the depolymerization productsfrom these biomass materials Moreover the amounts ofsome CndashC linkages are also varying such as 5-5 linkage(softwood 19ndash22wt hardwood 3ndash9wt) [14] All thechemical patterns of ether bonds were marked in circle inFigure 1 Therefore the reactions of ether cleavage including120572-aryl ether and 120573-aryl ether were mainly investigatedVarious chemicals were selected with the purpose of breakingthe mentioned chemical bonds by which lignin could bedepolymerized Generally there are five categories of thechemical depolymerization of lignin according to different

chemicals applied in the depolymerization process whichincludes (1) base-catalyzed (2) acid-catalyzed (3) metalliccatalyzed (4) ionic liquids-assisted and (5) supercriticalfluids-assisted lignin depolymerizations

2 Lignin Depolymerization by UsingDifferent Chemicals

21 Base-Catalyzed Lignin Depolymerization The treatmentof lignin using sodium hydroxide aqueous solution athigh temperature was straightforward process from whichphenols and phenol derivatives were obtained Lavoie etal used softwood and hemp lignin pretreated by steamexplosion with 5wt of NaOH aq at the temperaturebetween 300 and 330∘C under the pressure ranging from9 to 13MPa [16] There were 26 compounds identified byGC-MS after the reaction in which guaiacol catechol andvanillin were more abundant Different contents of guaiacolcatechol and vanillin were obtained mainly because of thedifferent ether linkages proportions in the softwood andhemp lignin Similar base-catalyzed treatment was carriedout for commercial organosolv lignin at 300∘C and 25MPaby Roberts et al [17] Syringol hydroxyacetophenone and

Journal of Applied Chemistry 3

Table 1 Base-calalyzed lignin depolymerization

Lignin Base catalyst aqueoussolution

Reaction conditions Major products Yield Reference119879 (∘C) 119875 (MPa) wt

Steam explosionhemp lignin 5wt NaOH 300ndash330 35

Guaiacol 09ndash28[16]Catechol 08ndash30

Vanillin 05ndash08

Steam explosionsoftwood lignin 5wt NaOH 300ndash330 35


Vanillin 03ndash05

Organosolv lignin 2wt NaOH 300 25Syringol 41

[17]Hydroxyacetophenone 16Guaiacol 11

Kraft lignin 5wt NaOH 270ndash315 13 Pyrocatechol 05ndash49 [18]

Organosolv olivetree pruning lignin

4wt NaOH KOHCa(OH)2 LiOH orK2CO3

300 90 Catechol 01ndash24 [19]

catechol were the major products but this research foundthe yield of phenols was increased by adding boric acid inthe following treatment of base-catalyzed products Similartreatment was carried out by Beauchet for treatment of kraftlignin [18] By optimizing the reaction temperature andtime it was found that pyrocatechol was the most abundantproduct at 315∘C with selectivity up to 258 Toledano etal provided a different way of base-catalyzed organosolv-processed olive tree pruning lignin depolymerization byusing various bases including KOH NaOH Ca(OH)

2

LiOH and K2CO3 in aqueous solution instead of alcohols

[19] Catechol was the most abundant components identifiedafter the lignin was treated by different bases

In general base-catalyzed lignin depolymerizations werecarried out at temperature above 300∘C and a high pressurefromwhich catechol syringol and derivatives were identifiedto be the most abundant components The mechanism wasthe cleavage of the aryl-alkyl bond which occurred above270∘C The most abundant aryl-alkyl bond was 120573-O-4 bondespecially in lignin Sodium cation helped to form the cationadducts which catalyzed the formation of six-memberedtransition on 120573-O-4 bond during the reaction [17]Thereforethe concentration of base or the concentration ratio of ligninto base played a very important role in the process Althoughbase-catalyzed process was simple it needed to be carriedout at high temperature and the selectivity was still difficultto control The experiment details of cited literatures aresummarized in Table 1

22 Acid-Catalyzed Lignin Depolymerization The applica-tion of acid treatment of lignin could be traced back to1940s Hewson and Hibbert did a series treatment of maplewoodmeal using different combination of acids and alcoholsincluding HClethanol and formic acidethylene glycol withthe purpose of separating the lignin into water-soluble andwater-insoluble components [40] A relatively low temper-ature range of 78 to 200∘C used in this research was not

high enough to break the complex lignin structure intomonomeric compounds for further usage

Recently acid-catalyzed method was investigated at ahigher temperature range in order to depolymerize lignin [2021] 10 wt of formic acid associated with 77wt of ethanolwas employed in the reaction with wheat straw lignin byGasson et al [20] A different proportion of formic acid andethanol solution which contained 10wt of formic acid and81 wt of ethanol was used in the reaction with wheat strawlignin but in aCSTRbyForchheim et al [21]Methoxyphenolcatechol and phenol were the major components when thereaction temperature was raised from 360 to 400∘CThemax-imum yields occurred at reaction time below 200 minutesOther attempts were carried out using acidethanol solutionsystem but associated with metallic catalyst enhancers [2324] These researches were summarized in the section ofmetallic catalyzed lignin depolymerization

The acid-catalyzed depolymerization also focused on thecleavage of 120573-O-4 bond of the lignin and the reaction wascompleted in the first 2 to 4 hours of the reaction Formic acidor other acids provided hydrogen sources in the hydrolysiswith the purpose of forming H

3O+ on the 120573-O-4 bond or

the cationic aromatic rings The function of co-catalysts wasusually to increase the selectivity According to the experi-ments carried out palladium or platinum did not decreasethe activation energy of the depolymerization In generalacid-catalyzed depolymerization required a harsh reactioncondition which could increase the cost of reaction facilityand posthandling The experiment details of acid-catalyzedlignin depolymerization are summarized in Table 2

23 Metallic Catalyzed Lignin Depolymerization Metalliccatalysts were studied to increase the selectivity of lignindepolymerization It was reported that the treatment of alcell-derived lignin was carried out in presence of NiCl

2or FeCl

3

by Hepditch and Thring [41] But only 25 wt yield ofcatechol was obtained at 305∘C More recently several other


Table 2 Acid-catalyzed lignin depolymerization

Lignin Acid catalystalcoholaqueous solution


Wheat straw lignin10wt formic acid Methoxyphenols 13

[20]77wt ethanol 360 25 Catechols 05

Phenols 03



Phenols 15


[21]81 wt ethanol 380 25 Catechols 15Phenols 20

attempts showed higher efficiency and selectivity [22ndash29]A two-step treatment process was carried out by Yoshikawaet al in the treatment of kraft lignin [22] Kraft lignin wastreated by Si-Al catalyst in H

2Obutanol medium first fol-

lowed by reaction on ZrO2-Al2O3-FeO119909catalyst to increase

the total recovery of phenols The phenols yield was 65 to86 and the conversion of lignin to methoxyphenols was92ndash94 In order to increase the yield of low-molecularweight fraction 20wt of PtC catalyst was usedwith formicacid and ethanol by Xu et al in the treatment of organosolvswitchgrass lignin [23] An obvious increase of the guaia-col derivatives yield was observed in presence of metallicenhancer Another attempt of optimizing the formic acid-catalyzed system was carried out by Liguori and Barth [24]Pd catalyst andNafion SAC-13 were used in treatment of bothlignin mode compounds and spruce dry lignin pretreatedby different methods in water medium at 300∘C Guaiacolpyrocatechol and resorcinol were isolated but the yieldswereall lower than 5wtThe slight difference of the yield of gua-iacol pyrocatechol and resorcinol is probably because of thedifferent lignin pretreatment methods Although depolymer-ization at lower temperature was carried out in presence of Ptand Pdmetallic enhancers compared to simple acid-catalyzeddepolymerization mentioned in Section 22 no activationenergy decrease has been reported Future research needsto be conducted to clarify the mechanism and function ofmetallic enhancer in acid-catalyzed lignin depolymerization

Base- or acid-catalyzed cracking was usually performedat very high temperature (above 300∘C) [16ndash21 23 24] How-ever efforts were made to decrease the reaction activationenergy in order to carry out the lignin depolymerizationunder mild condition (below 250∘C) Research from Songet al exhibited a method of nickel compound catalyzeddepolymerization of lignosulfonate into guaiacols [25] Thenickel catalyst provided a high conversion of above 60 and ahigh selectivity of 75 to 95 to guaiacols More importantlythe reaction temperature was decreased to 200∘C fromaround 380∘C compared with the pyrolysis process onlyin presence of acid or base as mentioned in Section 22Another attempt from Song et al on the treatment ofbirch wood lignin by nickel catalyst showed a selectivity ofabove 90 to propanyguaicol and propenylsyringol and a

conversion of more than 50 [26] Ye et al reported theirwork on mild hydrolysis of enzymatic hydrolysis corn stalklignin between 200 and 250∘C [27] In the presence of RuCPtC or PdC catalysts the maximum yields are 31 of4-ethylphenol and 14 of 4-ethylguaiacol Toledano etal used metal nanoparticles including nickel palladiumplatinum and ruthenium supported by mesoporous Al-SBA-15 with the assistance of microwave in the treatment oflignin separated from organosolv olive tree pruning lignin[28] The results showed that the most abundant productwas diethyl phthalate in presence of Ni or Pd catalyst andtetralin solvent Although the yield was 11 wt the reactiontemperature was only 140∘C which was lower than 200 to300∘C in other published research K10 montmorilloniteclay (Al

2O3-4SiO

2-xH2O) was applied in the treatment of

guaiacyl dehydrogenation oligomers at only 100∘C which ledto a degradation of 35wt of the model compounds [29]

By introducingmetallic catalysts the activation energy ofthe depolymerization was decreased to great extent whichresulted in mild reaction condition Metallic catalyzing stilltargeted the CndashO and CndashC cleavages of the lignin in presenceof hydrogen sources like ethanol or water Nickel or othersolid catalysts provided accessible metal sites in the externalsurface where the chemical reaction took place in thedepolymerization process This kind of method not onlyincreased the selectivity but decreased the required reactiontemperature which showed great potential The experimentdetails of metallic catalyzed lignin depolymerization aresummarized in Table 3

The deactivation issue in metallic catalysts is well knownin the biomass pyrolysis Some of the research to which thisarticle referred mentioned their concern on this point [25ndash27] For example the work done by Song et al on ligno-sulfonate depolymerization by using nickel heterogeneouscatalyst mentioned that the nickel catalysts helped generateactive H species These active H species combined withnickel sulfides to form H

2S and regenerated Ni(0) site for

next catalyzing cycle This mechanism made the nickelheterogeneous catalysts recyclable [25] Another researchfrom Song et al also mentioned that the NiC catalysts wererecycled 4 times without showing obvious deactivation inbirch wood lignin depolymerization [26] In the work of


Table 3 Metallic catalyzed lignin depolymerization

Lignin Catalyst Reaction conditions Major products Yield Reference119879 (∘C) 119875 (MPa)

Kraft lignin(1) Si-AlcatalystH2Obutanol

200ndash350 11ndash23 Phenols 65 [22](2) ZrO2-Al2O3-FeO119909 300

Organosolv switchgrasslignin

16wt formic acid350

4-Propylguaiacol 78[23]4wt PtC 4-Methylguaiacol 50

80wt ethanol

Acidic hydrolysis sprucelignin

44 wt formic acid300 96

Guaiacol 20[24]015 wt Pd catalyst Pyrocatechol 18

094wt NafionSAC-13 Resorcinol 05

Enzymatic hydrolysis sprucelignin


Guaiacol 17

[24]015 Pd catalyst Pyrocatechol 13094wt NafionSAC-13 Resorcinol 10

Kraft spruce lignin44 wt formic acid

300 96Guaiacol 47

[24]015 wt Pd catalyst Pyrocatechol 49094wt NafionSAC-13 Resorcinol 12

LignosulfonateNiC NiLaCNiPtC NiCuCNiPdC and NiCeC

200 5 Guaiacol 10 [25]

Birch sawdust lignin NiC 200 Propenylguaiacol 12[26]Propenylsyringol 36

Enzymatic hydrolysis cornstalk lignin PtC PdC RuC 200ndash250 1ndash6 4-Ethylphenol 013ndash31

[27]4-Ethylguaicol 006ndash14

Organosolv olive treepruning lignin

Ni Pd Pt or Rusupported bymesoporousAl-SBA-15

140 Diethyl phthalate 11 [28]

Guaiacyl dehydrogenationoligomers

K10 montmorilloniteclay (Al2O3-4SiO2-119909H2O)HCl

100 Low-molecular weight products mdash [29]

Ye et al the RuC catalyst was also recycled and showed verygood activity [27]The other research cited in this section didnot mention the recycle of catalysts which made it necessaryto study the deactivation of metallic catalysts in the future

24 Ionic Liquids-Assisted Lignin Depolymerization Ionicliquid was found to be used in separation of lignin andcellulose from raw lignocellulosic materials Ionic liq-uids includzing 1-butyl-3-methylimidazolium acesulfamate([BMIM][Ace]) and 1-ethyl-3-methylimidazolium acesulfa-mate ([EMIM][Ace]) were applied in the treatment of woodpowder of Pinus radiata lignin by Pinkert et al [42] To breakthe 120573-O-4 bond under the mild conditions (below 250∘C)ionic liquid was also employed in the depolymerization oflignin The depolymerization of organosolv beech lignin inpresence of 1-ethyl-3-methylimidazolium-trifluoromethans-ulfonate ([EMIM][CF

3SO3]) associated with Mn(NO

3)2was

carried out at 100∘C and 84MPa by Stark et al [30] Themost important point drawn from their research was that

26-dimethoxy-14-benzoquinone (DMBQ) was separated asa pure substance in 115 overall yield as the final prod-uct Another attempt of [EMIM][CF

3SO3] associated with

Broslashnsted acid was carried out by Binder et al in depoly-merization of lignin model compound [31] The reaction wascarried out at 200∘C and 116mol or 79 wt of guaiacolwas obtained from 2-methoxy-4-(2-propenyl)phenol andcleaved 2-phenylethyl phenyl ether a model for lignin ethersFor both the lignin and the model compounds ionic liquidassociated with ionic salt exhibited high selectivity Acidicionic liquid 1-H-3-methylimidazolium chloride [HMIM][Cl]was used in the depolymerization of oak wood lignin at 110to 150∘C by Cox and Ekerdt [32] The alkyl-aryl ether linkagecleavages were observed in the research A series of workweredone by Jia et al with the purpose of degrading lignin in vari-ous ionic liquids [33ndash35] 1-H-3-methylimidazolium chloridewas used in depolymerization of both guaiacylglycerol-120573-guaiacyl ether and veratrylglycerol-120573-guaiacyl ether modelcompounds to produce guaiacol with the yield of 70 at


Table 4 Ionic liquids-assisted lignin depolymerization

Lignin Ionic liquidReaction conditions

Major products Yield Reference119879 (∘C) 119875 (MPa) wt

Organosolv beechlignin

N S

O

O

CH3

CH3

N+∙

F3C Ominus

+Mn(NO3)2

100 84 26-Dimethoxy-14-benzoquinone 115 [30]

Eugenol N S

O

O

CH3N+∙

CH3

F3C Ominus

+Broslashnsted acid

200 Guaiacol 79 [31]

Oak wood lignin N

CH3N+∙

CH3

minusCl 110ndash150 Alkyl-aryl etherlinkages cleavage mdash [32]

Guaiacylglycerol-120573-guaiacylether

N

CH3N+∙

CH3

minusCl150 Guaiacol 715 [33]

Veratrylglycerol-120573-guaiacylether

N

CH3N+∙

CH3

minusCl 150 Guaiacol 70 [33]


N

N

NHN

CH3N+∙

∙

CH3

minusCl

+

150 120573-O-4 Ether bondcleavage mdash [34]


Table 4 Continued

Lignin Ionic liquid Reaction conditions Major products Yield Reference119879 (∘C) 119875 (MPa) wt


N S

O

O

O

CH3N+∙

CH3

Ominus

H3C150 Guaiacol 75 [35]

Table 5 Supercritical fluids-assisted lignin depolymerization

Lignin Supercritical fluid Reaction condition Major products Yield Reference119879 (∘C) 119875 (MPa) wt

Kraft lignins MethanolKOH 290 Catecholmdash [36]EthanolKOH Phenol

Organosolv lignin MethanolKOH 290 Catecholmdash [36]EthanolKOH Phenol

Alkaline lignin Water 300 25Catechol 2837

[37]Phenol 753Cresol 1167

Organosolv lignin Water + p-cresol 350ndash420 2-(Hydroxy-benzyl)-4-methyl-phenol lt75 [38]

Organosolvhardwood lignin CO2acetonewater 300ndash370 10

Syringol 36[39]Guaiacol 16

2-Methyoxy-4-methyl-phenol 16

Organosolv wheatstraw lignin CO2acetonewater 300ndash370 10 Syringic acid 22

[39]Guaiacol 16

150∘C [33] 1-H-3-methylimidazolium chloride with 157-triazabicyclo[440]dec-5-ene was used in depolymeriza-tion of guaiacylglycerol-120573-guaiacyl ether model compoundsfrom which 40 cleavage of 120573-O-4 bond was found [34]The 75 yield of guaiacol was observed in depolymerizationof guaiacylglycerol-120573-guaiacyl ether model compounds inpresence of 1-H-3-methylimidazolium chloridemethylsulfate[35]

Currently it has been proofed that some ionic liquidsare appropriate solvents for lignin dissolution [43] Acidassociated with ionic liquid such as Broslashnsted acid wasbelieved to be the catalyst which provided the hydrogensources However the high cost of the ionic liquids limitedtheir application on large quantity of lignin depolymeriza-tion The recycle of ionic liquid is very necessary due to itshigh cost [44] However there is difficulty in separation ofionic liquid with lignin-derived molecules because of the 120587-120587 interaction between ionic liquid and aromaticmoieties [13]Therefore the use of ionic liquid in lignin depolymerizationmay be limited A summary of ionic liquid-assisted lignindepolymerization is shown in Table 4

25 Supercritical Fluids-Assisted Lignin DepolymerizationSupercritical fluid was selected to be the medium for lignin

depolymerization The treatment of kraft- and organosolv-derived lignins using KOH or other bases in supercriticalmethanol or ethanol was reported in 1990s indicating thatthe supercritical liquid had effects on lignin depolymer-ization [36 45] Recently the use of supercritical fluid onthe treatment of lignin attracted researchersrsquo interest againSupercritical water treatment of alkaline lignin was carriedout by Wahyudiono et al [37] Under the condition of 300∘Cand 25ndash40MPa identified products included mainly cate-chol (2837wt) phenol (753 wt) and cresol (1167 wt)Supercritical water associatedwith119901-cresolwas applied as themedium in treatment of organosolv lignin at the temperaturebetween 350 and 420∘C by Takami et al [38] 2-(Hydroxy-benzyl)-4-methyl-phenol (BMP) with a 75wt yield wasrecovered from the reaction mixtures Another attempt byGosselink et al was using CO

2acetonewater supercritical

fluid to treat organosolv hardwood and wheat straw ligninsat the temperature between 300 and 370∘C under 10MPafrom which syringol and guaiacol were obtained [39] Thedifference of the yield of some depolymerization productsis mainly because of the different linkage contents betweenhardwood and wheat straw lignin

Similar to ionic liquid supercritical fluid was employedas the solvent in the depolymerization system due to its


good solubility Hydrogen sources for the hydrolysis wereprovided from acid and alcohol Even though supercriticalliquid exhibited high selectivity and convenience on prod-ucts and solvent separation the high cost still restrictedits development to be a widely used method for ligninconversion A summary of supercritical fluids-assisted lignindepolymerization is made in Table 5

3 Summary

Base-catalyzed acid-catalyzed metallic catalyzed ionicliquids-assisted and supercritical fluids assisted lignindepolymerizations were summarized and compared inthis article In general base-catalyzed and acid-catalyzedmethods required high reaction temperature (above 300∘C)and high pressure (10MPa) which resulted in high costsof facility and handling High selectivity and conversionare great advantages of ionic liquids- and supercriticalfluids-assisted lignin depolymerizations However the highcost is the major obstacle to their wide applications Metalliccatalyzed depolymerization had great potential because ofits high selectivity to some target products and less severereaction conditions Current research on metallic catalyzeddepolymerization showed that Ni- and Pt-based catalystshave relatively high conversion of lignin model compoundsand high selectivity to certain monomeric products Thedevelopment of new transition metal-based catalysts forlignin depolymerization will be the trend in the future as wellas the performance of these catalysts on lignin rather thanmodel compounds

Acknowledgments

The authors acknowledge the funding from the NationalRenewable Energy Laboratory (NREL) in Golden CO (Con-tract no AEV-0-40634-01) North Dakota EPSCoR and theUniversity of North Dakota Faculty Seed Grant

References

[1] R D Perlack L L Wright A F Turhollow R L Graham B JStokes and D C Erbach ldquoU S Department of Energy Biomassas feedstock for a bioenergy and bioproducts industry thetechnical feasibility of a billion-ton annual supplyrdquo 2005

[2] M Kleinert and T Barth ldquoPhenols from ligninrdquo Chemical Engi-neering and Technology vol 31 no 5 pp 736ndash745 2008

[3] GW Huber S Iborra and A Corma ldquoSynthesis of transporta-tion fuels from biomass chemistry catalysts and engineeringrdquoChemical Reviews vol 106 no 9 pp 4044ndash4098 2006

[4] R Zanzi K Sjostrom and E Bjornbom ldquoRapid pyrolysis ofagricultural residues at high temperaturerdquo Biomass and Bioen-ergy vol 23 no 5 pp 357ndash366 2002

[5] A Demirbas ldquoEffects of temperature and particle size onbio-char yield from pyrolysis of agricultural residuesrdquo Journalof Analytical and Applied Pyrolysis vol 72 no 2 pp 243ndash2482004

[6] L Wei S Xu L Zhang et al ldquoCharacteristics of fast pyrolysisof biomass in a free fall reactorrdquo Fuel Processing Technology vol87 no 10 pp 863ndash871 2006

[7] T Hosoya H Kawamoto and S Saka ldquoPyrolysis behaviors ofwood and its constituent polymers at gasification temperaturerdquoJournal of Analytical and Applied Pyrolysis vol 78 no 2 pp328ndash336 2007

[8] C Gustafsson and T Richards ldquoPyrolysis kinetics of washedprecipitated ligninrdquo BioResources vol 4 no 1 pp 26ndash37 2009

[9] M P Pandey and C S Kim ldquoLignin depolymerization and con-version a review of thermochemical methodsrdquo Chemical Engi-neering and Technology vol 34 no 1 pp 29ndash41 2011

[10] D Ferdous A K Dalai S K Bej and R W Thring ldquoPyrolysisof lignins experimental and kinetics studiesrdquo Energy and Fuelsvol 16 no 6 pp 1405ndash1412 2002

[11] S M Geib T R Filley P G Hatcher et al ldquoLignin degradationin wood-feeding insectsrdquo Proceedings of the National Academyof Sciences of the United States of America vol 105 no 35 pp12932ndash12937 2008

[12] N S Reading K D Welch and S D Aust ldquoFree radicalreactions of wood-degrading fungirdquoACS Symposium Series vol845 pp 16ndash31 2003

[13] J Zakzeski P C A Bruijnincx A L Jongerius and BMWeck-huysen ldquoThe catalytic valorization of lignin for the productionof renewable chemicalsrdquo Chemical Reviews vol 110 no 6 pp3552ndash3599 2010

[14] W Boerjan J Ralph and M Baucher ldquoLignin BiosynthesisrdquoAnnual Review of Plant Biology vol 54 pp 519ndash546 2003

[15] C Crestini M Crucianelli M Orlandi and R Saladino ldquoOxi-dative strategies in lignin chemistry a new environmentalfriendly approach for the functionalisation of lignin and ligno-cellulosic fibersrdquoCatalysis Today vol 156 no 1-2 pp 8ndash22 2010

[16] J-M Lavoie W Bare and M Bilodeau ldquoDepolymerization ofsteam-treated lignin for the production of green chemicalsrdquoBioresource Technology vol 102 no 7 pp 4917ndash4920 2011

[17] V M Roberts V Stein T Reiner A Lemonidou X Li and JA Lercher ldquoTowards quantitative catalytic lignin depolymer-izationrdquo Chemistry vol 17 no 21 pp 5939ndash5948 2011

[18] R Beauchet F Monteil-Rivera and J M Lavoie ldquoConversionof lignin to aromatic-based chemicals (L-chems) and biofuels(L-fuels)rdquo Bioresource Technology vol 121 pp 328ndash334 2012

[19] A Toledano L Serrano and J Labidi ldquoOrganosolv lignin dep-olymerization with different base catalystsrdquo Journal of ChemicalTechnology andBiotechnology vol 87 no 11 pp 1593ndash1599 2012

[20] J R Gasson D Forchheim T Sutter U Hornung A Kruseand T Barth ldquoModeling the lignin degradation kinetics in anethanolformic acid solvolysis approach Part 1 Kinetic modeldevelopmentrdquo Industrial and Engineering Chemistry Researchvol 51 no 32 pp 10595ndash10606 2012

[21] D Forchheim J R Gasson UHornung A Kruse and T BarthldquoModeling the lignin degradation kinetics in an ethanolformicacid solvolysis approach Part 2 Validation and transfer to vari-able conditionsrdquo Industrial and Engineering Chemistry Research vol 51 no 32 pp 15053ndash1 15063 2012

[22] T Yoshikawa T Yagi S Shinohara et al ldquoProduction of phenolsfrom lignin via depolymerization and catalytic crackingrdquo FuelProcessing Technology vol 108 pp 69ndash75 2012

[23] W Xu S J Miller P K Agrawal and C W Jones ldquoDepoly-merization and hydrodeoxygenation of switchgrass lignin withformic acidrdquo ChemSusChem vol 5 no 4 pp 667ndash675 2012

[24] L Liguori and T Barth ldquoPalladium-Nafion SAC-13 catalyseddepolymerisation of lignin to phenols in formic acid and waterrdquoJournal of Analytical and Applied Pyrolysis vol 92 no 2 pp477ndash484 2011


[25] Q Song F Wang and J Xu ldquoHydrogenolysis of lignosulfonateinto phenols over heterogeneous nickel catalystsrdquo ChemicalCommunications vol 48 no 56 pp 7019ndash77021 2012

[26] Q Song F Wang J Cai et al ldquoLignin depolymerization (LDP)in alcohol over nickel-based catalysts via a fragmentation-hydrogenolysis processrdquo Energy and Environmental Science vol6 no 3 pp 994ndash1007 2013

[27] Y Ye Y Zhang J Fan and J Chang ldquoSelective production of4-ethylphenolics from lignin via mild hydrolysisrdquo BioresourceTechnology vol 118 pp 648ndash651 2012

[28] A Toledano L Serrano A Pineda A A Romero R Luque andJ Labidi ldquoMicrowave-assisted depolymerisation of organosolvlignin via mild hydrogen-free hydrogenolysis catalyst screen-ingrdquo Applied Catalysis B 2012

[29] F Bouxin S Baumberger B Pollet AHaudrechy J-H Renaultand P Dole ldquoAcidolysis of a lignin model investigation of het-erogeneous catalysis using Montmorillonite clayrdquo BioresourceTechnology vol 101 no 2 pp 736ndash744 2010

[30] K Stark N Taccardi A Bosmann and P Wasserscheid ldquoOxi-dative depolymerization of lignin in ionic liquidsrdquo Chem-SusChem vol 3 no 6 pp 719ndash723 2010

[31] J B Binder M J Gray J F White Z C Zhang and J EHolladay ldquoReactions of lignin model compounds in ionicliquidsrdquo Biomass and Bioenergy vol 33 no 9 pp 1122ndash11302009

[32] B J Cox and J G Ekerdt ldquoDepolymerization of oak woodlignin under mild conditions using the acidic ionic liquid 1-H-3-methylimidazolium chloride as both solvent and catalystrdquoBioresource Technology vol 118 pp 584ndash588 2012

[33] S Jia B J Cox X Guo Z C Zhang and J G Ekerdt ldquoDecom-position of a phenolic lignin model compound over organic N-bases in an ionic liquidrdquo Holzforschung vol 64 no 5 pp 577ndash580 2010

[34] S Jia B J Cox X Guo Z C Zhang and J G Ekerdt ldquoCleavingthe 120573-O-4 bonds of lignin model compounds in an acidic ionicliquid 1-H-3-methylimidazolium chloride an optional strategyfor the degradation of ligninrdquo ChemSusChem vol 3 no 9 pp1078ndash1084 2010

[35] S Jia B J Cox X Guo Z C Zhang and J G Ekerdt ldquoCatalysisof lignin depolymerization in ionic liquidsrdquo in Proceedings ofthe 240th ACS National Meeting and Exposition Boston MassUSA August 2010

[36] J E Miller L Evans A Littlewolf and D E Trudell ldquoBatchmicroreactor studies of lignin and lignin model compounddepolymerization by bases in alcohol solventsrdquo Fuel vol 78 no11 pp 1363ndash1366 1999

[37] WWahyudionoM Sasaki andMGoto ldquoRecovery of phenoliccompounds through the decomposition of lignin in near andsupercritical waterrdquo Chemical Engineering and Processing vol47 no 9-10 pp 1609ndash1619 2008

[38] S Takami K Okuda X Man M Umetsu S Ohara and TAdschiri ldquoKinetic study on the selective production of 2-(Hydroxybenzyl)-4-methylphenol from organosolv lignin ina mixture of supercritical water and p-cresolrdquo Industrial andEngineering Chemistry Research vol 51 no 13 pp 4804ndash48082012

[39] R J A Gosselink W Teunissen J E G van Dam et alldquoLignin depolymerisation in supercritical carbon dioxideace-tonewater fluid for the production of aromatic chemicalsrdquoBioresource Technology vol 106 pp 173ndash177 2012

[40] W B Hewson and H Hibbert ldquoStudies on lignin and relatedcompounds LXV Re-ethanolysis of isolated ligninsrdquo Journal ofthe AmericanChemical Society vol 65 no 6 pp 1173ndash1176 1943

[41] M M Hepditch and R W Thring ldquoDegradation of solvolysislignin using Lewis acid catalystsrdquoCanadian Journal of ChemicalEngineering vol 78 no 1 pp 226ndash231 2000

[42] A Pinkert D F Goeke K N Marsh and S Pang ldquoExtractingwood lignin without dissolving or degrading cellulose investi-gations on the use of food additive-derived ionic liquidsrdquoGreenChemistry vol 13 no 11 pp 3124ndash3136 2011

[43] I Kilpelainen H Xie A King M Granstrom S Heikkinenand D S Argyropoulos ldquoDissolution of wood in ionic liquidsrdquoJournal of Agricultural and Food Chemistry vol 55 no 22 pp9142ndash9148 2007

[44] S Zhu ldquoUse of ionic liquids for the efficient utilization oflignocellulosic materialsrdquo Journal of Chemical Technology andBiotechnology vol 83 no 6 pp 777ndash779 2008

[45] E Dorrestijn M Kranenburg D Poinsot and P MulderldquoLignin depolymerization in hydrogen-donor solventsrdquo Holz-forschung vol 53 no 6 pp 611ndash616 1999

Submit your manuscripts athttpwwwhindawicom

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Inorganic ChemistryInternational Journal of

Hindawi Publishing Corporation httpwwwhindawicom Volume 2014

International Journal ofPhotoenergy


Carbohydrate Chemistry

International Journal of


Journal of

Chemistry


Advances in

Physical Chemistry

Hindawi Publishing Corporationhttpwwwhindawicom

Analytical Methods in Chemistry

Journal of

Volume 2014

Bioinorganic Chemistry and ApplicationsHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

SpectroscopyInternational Journal of


The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014

Medicinal ChemistryInternational Journal of


Chromatography Research International


Applied ChemistryJournal of



Theoretical ChemistryJournal of


Journal of

Spectroscopy

Analytical ChemistryInternational Journal of


Journal of


Quantum Chemistry


Organic Chemistry International

ElectrochemistryInternational Journal of



CatalystsJournal of


OH

OO

HO

O

HOHO

OH

OH

OHO

HO

OHO

O

OH

OHO

OHO

HO OH

HO

OHO

HO

O

HO

HO

OHO

HO O

HOOH

OH

HO

O

OO

HO

O

HOHO

OH

OHO

HO

OHO

OHO

OHHO

LIGNIN-O

OH

OHO

OO

OHLIGNIN

HOOH

O

OH

OH

HO

Aryl glycerol ether

DibenzodioxocinDiphenyl ether

H3CO

H3CO

H3CO

H3CO

H3CO

H3CO

H3CO

H3CO

OCH3OCH3

OCH3

OCH3

OCH3

OCH3

OCH3

OCH3

OCH3

OCH3

OCH3

OCH3OCH3

OCH3

120573-O-4

5-5998400-120572120573-O-49984005-O-4998400

Figure 1 Common chemical structure of lignin [15]

Lignin can be categorized to softwood and hardwoodlignins according to their raw biomass sources Dependingon the fractionation methods lignin can also be categorizedto steam explosion kraft organosolv alkaline oxidationpyrolysis lignins and so forth [13]The commonly recognizedchemical structure of lignin is exhibited in Figure 1 Etherbond was the target for chemical attacking during chemicalconversion processes Generally softwood has 45ndash48wtand hardwood has 60wt of 120573-O-4 aryl glycerol etherbonds Softwood has about 5wt and hardwood has 0ndash2wt of dibenzodioxocin 5-51015840-120572 120573-O-41015840 bonds In additionsoftwood has 35ndash8wt and hardwood has 6ndash9wt ofdiphenyl ether 5-O-41015840 linkages [13 14] The differences ofthese linkages have effects on the depolymerization productsfrom these biomass materials Moreover the amounts ofsome CndashC linkages are also varying such as 5-5 linkage(softwood 19ndash22wt hardwood 3ndash9wt) [14] All thechemical patterns of ether bonds were marked in circle inFigure 1 Therefore the reactions of ether cleavage including120572-aryl ether and 120573-aryl ether were mainly investigatedVarious chemicals were selected with the purpose of breakingthe mentioned chemical bonds by which lignin could bedepolymerized Generally there are five categories of thechemical depolymerization of lignin according to different

chemicals applied in the depolymerization process whichincludes (1) base-catalyzed (2) acid-catalyzed (3) metalliccatalyzed (4) ionic liquids-assisted and (5) supercriticalfluids-assisted lignin depolymerizations

2 Lignin Depolymerization by UsingDifferent Chemicals

21 Base-Catalyzed Lignin Depolymerization The treatmentof lignin using sodium hydroxide aqueous solution athigh temperature was straightforward process from whichphenols and phenol derivatives were obtained Lavoie etal used softwood and hemp lignin pretreated by steamexplosion with 5wt of NaOH aq at the temperaturebetween 300 and 330∘C under the pressure ranging from9 to 13MPa [16] There were 26 compounds identified byGC-MS after the reaction in which guaiacol catechol andvanillin were more abundant Different contents of guaiacolcatechol and vanillin were obtained mainly because of thedifferent ether linkages proportions in the softwood andhemp lignin Similar base-catalyzed treatment was carriedout for commercial organosolv lignin at 300∘C and 25MPaby Roberts et al [17] Syringol hydroxyacetophenone and







Vanillin 05ndash08



Vanillin 03ndash05








2











2or FeCl

3








Phenols 03



Phenols 15









2O3-4SiO













16wt formic acid350


80wt ethanol







Guaiacol 17



300 96Guaiacol 47



200 5 Guaiacol 10 [25]













3)2was










N S

O

O

CH3

CH3

N+∙

F3C Ominus

+Mn(NO3)2


Eugenol N S

O

O

CH3N+∙

CH3

F3C Ominus

+Broslashnsted acid


Oak wood lignin N

CH3N+∙

CH3



N

CH3N+∙

CH3



N

CH3N+∙

CH3



N

N

NHN

CH3N+∙

∙

CH3

minusCl

+



Table 4 Continued



N S

O

O

O

CH3N+∙

CH3

Ominus













[39]Guaiacol 16










3 Summary


Acknowledgments


References
























































Journal of

Chemistry


Advances in

Physical Chemistry



Journal of

Volume 2014














Journal of

Spectroscopy



Journal of


Quantum Chemistry






CatalystsJournal of







Vanillin 05ndash08



Vanillin 03ndash05








2











2or FeCl

3








Phenols 03



Phenols 15









2O3-4SiO













16wt formic acid350


80wt ethanol







Guaiacol 17



300 96Guaiacol 47



200 5 Guaiacol 10 [25]













3)2was










N S

O

O

CH3

CH3

N+∙

F3C Ominus

+Mn(NO3)2


Eugenol N S

O

O

CH3N+∙

CH3

F3C Ominus

+Broslashnsted acid


Oak wood lignin N

CH3N+∙

CH3



N

CH3N+∙

CH3



N

CH3N+∙

CH3



N

N

NHN

CH3N+∙

∙

CH3

minusCl

+



Table 4 Continued



N S

O

O

O

CH3N+∙

CH3

Ominus













[39]Guaiacol 16










3 Summary


Acknowledgments


References
























































Journal of

Chemistry


Advances in

Physical Chemistry



Journal of

Volume 2014














Journal of

Spectroscopy



Journal of


Quantum Chemistry






CatalystsJournal of







Phenols 03



Phenols 15









2O3-4SiO













16wt formic acid350


80wt ethanol







Guaiacol 17



300 96Guaiacol 47



200 5 Guaiacol 10 [25]













3)2was










N S

O

O

CH3

CH3

N+∙

F3C Ominus

+Mn(NO3)2


Eugenol N S

O

O

CH3N+∙

CH3

F3C Ominus

+Broslashnsted acid


Oak wood lignin N

CH3N+∙

CH3



N

CH3N+∙

CH3



N

CH3N+∙

CH3



N

N

NHN

CH3N+∙

∙

CH3

minusCl

+



Table 4 Continued



N S

O

O

O

CH3N+∙

CH3

Ominus













[39]Guaiacol 16










3 Summary


Acknowledgments


References
























































Journal of

Chemistry


Advances in

Physical Chemistry



Journal of

Volume 2014














Journal of

Spectroscopy



Journal of


Quantum Chemistry






CatalystsJournal of







16wt formic acid350


80wt ethanol







Guaiacol 17



300 96Guaiacol 47



200 5 Guaiacol 10 [25]













3)2was










N S

O

O

CH3

CH3

N+∙

F3C Ominus

+Mn(NO3)2


Eugenol N S

O

O

CH3N+∙

CH3

F3C Ominus

+Broslashnsted acid


Oak wood lignin N

CH3N+∙

CH3



N

CH3N+∙

CH3



N

CH3N+∙

CH3



N

N

NHN

CH3N+∙

∙

CH3

minusCl

+



Table 4 Continued



N S

O

O

O

CH3N+∙

CH3

Ominus













[39]Guaiacol 16










3 Summary


Acknowledgments


References
























































Journal of

Chemistry


Advances in

Physical Chemistry



Journal of

Volume 2014














Journal of

Spectroscopy



Journal of


Quantum Chemistry






CatalystsJournal of






N S

O

O

CH3

CH3

N+∙

F3C Ominus

+Mn(NO3)2


Eugenol N S

O

O

CH3N+∙

CH3

F3C Ominus

+Broslashnsted acid


Oak wood lignin N

CH3N+∙

CH3



N

CH3N+∙

CH3



N

CH3N+∙

CH3



N

N

NHN

CH3N+∙

∙

CH3

minusCl

+



Table 4 Continued



N S

O

O

O

CH3N+∙

CH3

Ominus













[39]Guaiacol 16










3 Summary


Acknowledgments


References
























































Journal of

Chemistry


Advances in

Physical Chemistry



Journal of

Volume 2014














Journal of

Spectroscopy



Journal of


Quantum Chemistry






CatalystsJournal of


Table 4 Continued



N S

O

O

O

CH3N+∙

CH3

Ominus













[39]Guaiacol 16










3 Summary


Acknowledgments


References
























































Journal of

Chemistry


Advances in

Physical Chemistry



Journal of

Volume 2014














Journal of

Spectroscopy



Journal of


Quantum Chemistry






CatalystsJournal of



3 Summary


Acknowledgments


References
























































Journal of

Chemistry


Advances in

Physical Chemistry



Journal of

Volume 2014














Journal of

Spectroscopy



Journal of


Quantum Chemistry






CatalystsJournal of
































Journal of

Chemistry


Advances in

Physical Chemistry



Journal of

Volume 2014














Journal of

Spectroscopy



Journal of


Quantum Chemistry






CatalystsJournal of

review article recent development in chemical...

Documents