Analysis of Lignin by Pyrolysis-gas Chromatography

8/4/2019 Analysis of Lignin by Pyrolysis-gas Chromatography

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Journal of Analytical an d Applied Pyr olysis, 18 (1990) 59-69Elsevier Science Pu blishers B.V., Amster da m

A N A LY S I S O F L I G N I N B Y P Y R O L YS I S - G A S C H R O M AT O G R A P H YI E F F E C T O F I N O R G A N I C S U B S TA N C E S O N G U A I AC O L -D E WAT I V E YI E L D F R O M S O F T W O O D S A N D T W I R L I G N I N S

KEN-ICHl KURODA * and YOSHIYUKI INOUE

Wood Chem istr y, Inst itut e of Agricult ur al a nd F orest A En gineering, University of Tku ku ba,

Tsuku ba,Ibara ki 305 (J apan )

KOKKI SAKAI

Wood Chem istr y ,Depar tm ent of Forest Pr oducts,Fa cult y of Agricultur e,

Kyushu University 46-08, Fukuoka 812 (Ja pan)

(Received J an ua ry 4, 1990; accepted March 22. 1990)

ABSTRACT

To obta in lignin-derived pyrolysis pr oducts in larger yields. Cur ie-point pyrolysis was

perform ed on th e softwood species Ja pan ese red pine (Pinu s densiflora Sieb. et Zucc.),J apa nese cedar (cryptomeria japonica D. DON) and J apa nese cypress ( Cha ma ecypar is obtu sa

Endl.), and their dioxane lignins treat ed with various inorganic substan ces, over th e tempera -

tur e ra nge 358-764 . The resu lting gua iacol derivat ives (guaia col, 4-met hyl-, 4-eth yl- an d

4-vinylguaiacols, eugenol, vanillin, cis- and trans-isoeugenol, and acetovanillone) were de-

termined by gas chromatography.

The softwood samp les sandwiched between t wo sheets of heat -resistan t filter pa per ma de

of borosilicate glass fibers yielded from 1.56 to 1.64 tim es more guaia col derivat ives tha n

unsa ndwiched sam ples. Sandwiching th e dioxane lignins between heat-resistant papers a lso

increased the guaiacol-derivative yield. by 13 to 27%.

The san dwich-2 meth od developed in th is study is widely applicable as a sa mple prepa ra -

tion m eth od for increasin g th e yield of lignin-derived products on Cur ie-point pyrolysis.

Gas chr omalo8rqh y; glass fiber. borosilicat e; gua iacol der ivat ives; lignin; pyrolysis, Cur ie-

point., softwoods.

INTRODUCTION

Pyrolysis combined with gas chromatography (Py-GC) is a powerful tool

for synth etic and n at ur al polymer an alysis. Early applications of Py-GC in

lignin a na lysis can be foun d in th e reports of Kra tzl et al. [1] an d Kitao and

Wat an abe [2], who suggested th at th is meth od offered a convenient an alyti-

cal t echn ique for t he r apid char acterizat ion of a very sma ll amount of lignin.


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Despite obvious a dvant ages, th e Py-GC meth od has been la rgely neglected

compared with other lignin degra dat ion t echn iques such as a cidolysis, al-

kaline nitr obenzene oxidation an d perma ngana te oxidation, which are time-

consum ing and deman d large sample amoun t.

The development of modern ana lytical inst rum ents has recently resultedin th e publicat ion of a n um ber of reports describing th e possibility an d th e

usefulness of the P y-GC meth od for lignin chara cterization [3-8]. In t hese

report s, investigators separa ted a nd identified many guaiacyl an d syringyl

derivatives, and pr edicted t ha t t he Py-GC meth od would be extensively

used in various ar eas of lignin chemist ry in t he fut ur e. Boon et al. [6l point ed

out th at combined Cur ie-point pyrolysis-GC/ MS (mass spectr ometly) is an

interesting m icroanalytical chara cterization meth od for plant mat erial an d

its d erived fra ctions. However, few reports [7,8] ar e available oft: th e qua nt i-

ta tive determ inat ion of th e result ing volatile phenols. In pa rt icular, we ha ve

found n o report ed at temp ts t o increase t he yield of lignin-derived phen ols.

The object of th e present stu dy was t o increase t he gua iacol-derivat ive

yield by pyrolyzing softwoods a lignins in the presence of inorganic

subst an ces. To our knowledge, ther e ar e few reports [9] dealing with th e

exact r elationship bet ween inorganic subst an ces an d th e yield of lignin-de-

rived pyrolysis phenols, whereas consider able docum ent at ion exists on t he

effects of inorganic salts on cellulose from the viewpoint of the development

of fire-retardant chemicals [10-16].

A sam ple. prepar at ion met hod for increasing t he yield of lignin-derived

pyrolysis phen ols was also developed. This m eth od is applicable t o the

Curie-point pyrolysis of all lignocllulosic materials.

. EXPERIMENTAL

Materials

The extra ctive-free softwoods used in t his st udy were J apa nese red pine

( Pinu s den siflora Sieb: et Zhcc.), J apa nese cedar (Crypyomeria japonica D.

Don) and J apa nese cypress (Cham aecypar is obtu sa E ndl.). Dioxan e lignins

(DLs) from t hese softwoods were prepa red by t he m eth od of Pepper et al.

[17].

The commercial inorgan ic salt s used were potassiu m carb6ha te, sodium

tet ra bora te, sodium carbona te, boron t rioxide, sodium chloride, nickel,

alum inium oxide, silicic anh ydride an d calcium oxide.

Thr ee types of hea t-resista nt filter pa per m ade of glass fibers (GB100R)/

an d silica fibers (QR100 an d 80) were supp lied by the Advan tecTOYO Co.


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Pyrolysis

Pyrolysis un it an d gas chromatograph y

A Curie-point pyrolyzer (JH P-2 model, J apa n Analytical In dust ry Co.)

was coupled directly with a gas chr oma tograph (GC) (Shima dzu GC-14A).

Ea ch sample, prepar ed as described below, was wrapp ed with a ferroma g-net ic pyrofoil and kept in t he pyrolyzer a t 140 for 5 m in (wood) or 1 m in

(DL samples), after t he un it ha d been flush ed with h elium for 15 s. The

sam ples were th en pyrolyzed by indu ction h eat for 4 s, and th e result ing

volat ile compoun ds were tr an sferr ed to the GC. The GC an alysis was ru n on

a 25 m Th ikote fused-silica capillary column (0.53 mm I .D.) with a chem-

ically bonded m eth yl silicone coat ing 5.0 m t hick (Qua drex Corp.). Helium

was used as carrier gas. The temperatu re program used was 1 min at 70,

and 4/min from 70 to 250, after which isotherm al condit ions wer e

ma int ained. The injection port a nd t he flame ionizat ion det ector (FID) were

kept at 260. The peak areas were measured by an integrator (Shimadzu

Chroma topac C-R6A). Identificat ion of peaks was carried out by compa ri-

son with r etent ion t imes of known su bsta nces and/or using a P y-GC/MS

system (Finn igan MAT ITD-800) fitt ed with a 30 m fused-silica capillary

colum n (0.25 mm I .D.) with a 0.25 m film chemically bonded Dur abond

DB-5 coating (J. & W. Scientific Inc.). Known amounts of authentic

guaia col-derivat ive solut ions wer e injected int o the pyrolyzer a nd t ra nsferred

into GC with out pyrolysis to obta in exact r etent ion t imes an d calibrat ion

cur ves for the qua nt itat ive deter mina tion of guaia col derivat ives.

Sam ple prepar at ion for pyr olysis

(a) Stan dar d meth od. About 0.5 mg of th e star tin g mat erial was weighed

precisely, wrapped with a pyrofoil, and subjected to Py-GC.

(b) Addition met hod. The salt or t he glass fiber pa per powder (about 50 m g)

was ad ded to the st ar tin g mat erial (0.5 mg) on a pyrofoil. The pr epar ed

sam ple was su bjected t o Py-GC.

(c) Mixing met hod. The salt or t he glass fiber paper powder wa s mixed with

th e star tin g mat erial by grind ing in a vibra tory samp le mill (Model TI-1,

Hira ko Seisak usyo) for 5 min. The mixtur e, conta ining 0.5 mg of th e sta rt ing

ma ter ial, was wrap ped with a pyrofoil, an d th en pyrolyzed. .

(d) Sandwich-1 met hod. The sta rt ing ma ter ial (0.5 mg) on a glass fiber

paper was wra pped with a pyrofoil, an d th en pyrolyzed.

(e) San dwich-2 meth od. The st ar tin g mat erial (0.5 mg) was sa ndwichedbetween t wo Pieces of glass fiber p aper, wrap ped with a pyrofoil, and th en pyr olyzed.


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RESULTS AND DISCUSSION

A typical pyrogram of the volatile compounds from pine wood at 500

is shown in Fig. 1. The pyrograms of pine wood treat ed with a nd with out

inorganic substa nces were qualita tively identical. The main pyrolysis prod-

ucts wer e th e nin e gua iacol derivat ives gua iacol, 4-met hy1-, 4-eth yl- an d

4-vinylguaiacol, eugenol, vanillin, cis-and trams-isoeugenol, and acetovanil-

lone, which confirms p revious work as r eport ed by Kitao an d Wat an abe [2],

who pyrolyzed pine milled wood lignin u nder similar condit ions. In addit ion

to t hese gu aiacol derivat ives, small am ount s of 4-propylgua iacol, vanillic

acid and propiovanillone were a lso ident ified. Cont ra ry , to th e report s of

Obst [5], Boon et al. [6] an d F aix et al. [7,8], coniferaldeh yde an d coniferyl

alcohol were ra rely detected u nder t he condit ions u sed in th e present work.

Peak s of phen ols, xylenols and cresols often overlapped those of

car bohydra te-derived compoun ds.

Effects of inorganic substances on pyrolysis

Table 1 shows the effects on t he pyr olysis of pine woods at 500 of

various in organ ic substa nces, selected according t o th e classificat ion of Tan g


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[11]. The yield from pine wood in the absence of inorganic substances

(sta nda rd m eth od) is also shown, as a contr ol. The gua iacol-derivat ive yield

is expressed as a sum of th e yields of guaia col, 4-met hylguaia co1, 4-eth yl-

plus 4-vinylguaiaco1, eugenols (eugenol and cis- and t r ans -isoeugenol) an d

car bonyl compoun ds (van i1lin, an d acetovan illone).

Fr om th e dat a in Table 1, th e borosilicate glass fiber paper (GB100R),

sodium an d potassiu m carbonat es were effective in increasing th e total yield

of gua iacol derivatives. Mixing with t he glass fiber paper increased t he

guaiacol-derivat ive yield by about 1.9% compared with th at of pine wood

alone (stan dard meth od). Sodium a nd potassium carbonates also increased

th e gua iacol-derivat ive yield by about 1.0%, despite t he finding of Gar dner

et a l. [9] tha t s odium carbonat e did not in crea se th e yield of pyrolysis

products. This discrepa ncy is probably due to their h aving deter mined only

four p yrolysis products, a nd also to t he differen t pyrolysis condit ions

employed. The addit ion of pulverized GB100R and s odium car bona te t o

pine wood pr oduced no ser ious increase in th e 8ua iacol-derivat ive yield

compar ed with th at from the st anda rd meth od, but th e addition of potas-

sium carbonat e great ly decreas ed t he gu aiacol-derivative yield (4.73%).

Upon m ixing with the carbonates in th e sample rh il1. the sa mples took on

a st rong yellowish colour. This suggests t ha t t he pine wood rea cted with th e

carbonates during grinding, an d t he r esulting sample pa rt ly decomposed

before pyrolysis. Sodium chloride slightly decreased the guaiacol-derivative

yield. In th is conn ection, Richa rds et al. [16] detected polyhydroxybenzenes


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from the pyrolysis of cellulose in the presence of sodium chloride, probably

because th ey pyrolyzed at lower tempera tu re for a longer time add tr imeth-

ylsilylat ed pyrolysis pr oducts prior t o GC ana lysis.

Therefore, we concluded th at of th e procedur es test ed in th e present

stu dy, th e glass fiber pa per (GB100R) meth od was th e most effective for

catalyzing pyrolysis.

Figur e 2 shows th e cha nge in t he gua iacol-derivative yield on pyrolysis (at

500) of pine wood m ixed with pu lverized GB100R. The yield clearly

increased on mixing with sm all am oun ts of GB100R powder, and gra dua lly

increased furt her with in creas ing am ount s of GB100R. However, the yield

appea red t o level off after r eaching about 15.20% at ra tio of GB100R to pine

wood 2.0. Consequently, the largest yield of guaiacol derivatives obtained by

th e mixing method was 15.76% at th e rat io of 10.0. Thus, Fig. 2 shows th at it

is technically difficult to obtain th e guaia col derivat ives with a yield lar ger

th an 16.0% from pin e wood by the m ixing met hod.

Effects of sam ple prepar at ion m eth od on pyr olysis

Figur e 3 shows guaiacol-derivat ive yields from pine sa mples pr epar ed by

various methods. Pine wood sandwiched between two pieces of GB100R (i.e.

th e san dwich-2 meth od) gave th e largest yield (18.86%), wherea s th e san d-

wich-1 meth od gave 15.32%, a value similar to th at obta ined by th e mixing

method.

Fr om these findin gs, th e effects of th e sample prepa ra tion meth ods on t he

guaia co1-derivat ive yield a re ordered a s follows: san dwich-2 met hod > m ixing

method = sandwich-1 method > addition m ethod = stan dard meth od. The

largest yield of guaia col derivatives obtained by t he sa ndwich-2 met hod was

due t o the increase of gua iaco1, 4-vinylgua iacol an d eugen ols, alth ough wecan not explain th e mecha nism of th is effect at t his st age.


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Effects of heat -resistan t filter pa per on pyrolysis

The effects of types of heat -resist an t filter pa per on pyrolysis (at 500)

of pine woods pr epar ed by the sa ndwich-2 met hod ar e shown in F ig. 4.

Alth ough pine wood san dwiched wit h QR100 also gave gua iacol derivat ives

in modera tely good yield (15.44%), th is was s ma ller th an th e yield obtained

with GB100R. The yield with QR80, which cont ains a lumin a a s binders, was

only 3.40%. Therefore, th e effects of th e hea t-resista nt filter paper s on t he

guaia col-derivat ive yield when pyrolysis was perform ed by t he san dwich-2


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method are ordered as follows: GB100R > QR100 > untreated (11.79%) >

QR80. One rea son for th is great difference in th e yield lies in t he pr incipal

constit uen ts of th e various pa pers. GB100R is ma de of borosilicat e glass,

wherea s QR100 and 80 a re ma inly made of silic acid. Thu s, th e above resu lt

agrees well with t he dat a in Table 1.

Effect of temp erat ur e on pyrolysis

The effects of temp erat ur es in th e ran g 358-764 on th e pyrolysis of

pine wood, alone an d sa ndwiched with GB100R, were also investigated (Fig.

5).

The most u seful findin g was th at th e guaiacol-derivat ive yield was largest

at 500, regardless of whet her or not t he pine sam ples were san dwiched

with GB100R. Thus, 500 is the optimum pyrolysis temperature. Below

590 th e gua iacol-derivat ive yields obtained from pine woods sa ndwiched

with GB100R were much lar ger th an th ose from the un treat ed woods. At

670 and 764,I adverse results were obtained. Particularly at 764oC, the

san dwiched sa mple gave a mu ch sm aller yield of th e guaiacol derivat ives,

and a more complicat ed pyrogram, with ma ny peaks, tha n t hat obtained by

th e stan dar d meth od. This indicates th at GB100R may cat alyze pyrolysis of

guaiacol derivatives into smaller fragments at th is temperat ure.

Extensive degradation at a higher temperat ure h as been reported by

Nozawa an d Sat onak a [18]. These aut hors pyrolyz8d Ja panese oak (Quercus

mongolica var. grosseserra ta) at 400 and 800 and observed large mount s

of phenol an d cresol, while guaia col derivat ives were not a mong th e pyroly-

sis products obta ined at 800. Therefore, the small yield of guaiacol

derivat ives from our pyrolysis at 764 is probably due t o exten sive

conversion of the init ially produced guaia col derivat ives into oth er degra da-


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tion products su ch a s catechol an d cresol. Influen ce of pyrolysis temper at ur e

on t he composition of the pr oduct m ixtur e will be discussed elsewhere.

Fr om the above resu lts, th e most suita ble condit ions for our pu rpose were

(a) to san dwich t he sa mple with GB100R, an d (b) to pyrolyze the s an dwich

at 500.

Applicat ion of sand wich-2 meth od to oth er s am ples

The sa ndwich-2 met hod usin g GB100R was ,applied t o the pyrolysis of

oth er softwoods an d th eir DLs at 500.

The t otal yield of gua iacol der ivat ives increa sed from 13.97 to 22.85% for

J apa nese cedar, and from 13.50 to 21.03% for J apa nese cypress, a s compa red

with t he st an dar d met hod (Fig. 6). Thus, t he gua iacol-derivat ive yields from

J apa nese cedar a nd cypress san dwiched with GB100R were increased by

1.64 and 1.56 tim es, respectively, over th ose from t he u nt rea ted woods.

These values agree very closely with th ose (1.60 times) obta ined for t he

pyrolysis of J apa nese red pin e.

A similar ten dency was observed for th e pyrolysis of DL sam ples san d-

wiched wit h GB100R (Fig. 7). The gua iacol-derivat ive yields from DLs

san dwiched with GB100R were 5.53% for p ine, 7.68% for J apa nese cedar

and 7.01% for J apan ese cypress, whereas th ose from un tr eated DLs were

4.37, 6.55 and 6.17%, respectively. Thu s, th e san dwich-2 met hod us ing

GB100R increased the guaiacol-derivative yields from DLs 1.27 times for

pine, 1.17 times for J apa nese cedar an d 1.13 times for J apa nese cypress, over

th ose from th e unt reat ed DL sam ples. However, th e amount s oft gua iacol

derivat ives obta ined from th e DLs were redu ced t o one-thir d of th ose from


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the corresponding softwoods, probably as a result of modification of the

chemical str uctu re of lignin du ring t he isolat i6n process.

The above results suggest tha t th e sandwich-2 method using GB100R

could be widely a pplied t o the Cu rie-point pyrolysis of ma ny softwood

species and th eir lignin prepara tions.

AC K N O W L E D G E M E N T S

We wish to tha nk the st aff of Japa n Analytical Indust ry an d Finn igan

MAT Inst ru ment s, Inc., for perform ing th e Py-GC/MS ru ns.


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Documents

Analysis of Lignin by Pyrolysis-gas Chromatography