Journal of Analytical and Applied Pyrolysis, 18 (1990) 59-69
Elsevier Science Publishers B.V., Amsterdam

ANALYSIS OF LIGNIN BY PYROLYSIS-GAS CHROMATOGRAPHYI EFFECT OF INORGANIC SUBSTANCES ON GUAIACOLDEWATIVE YIELD FROM SOFTWOODS AND TWIR LIGNINSKEN-ICHl KURODA * and YOSHIYUKI INOUE

Wood Chemistry, Institute of Agricultural and Forest A Engineering, University of Tkukuba,Tsukuba,Ibaraki 305 (Japan)
KOKKI SAKAI

Wood Chemistry ,Department of Forest Products,Faculty of Agriculture,Kyushu University 46-08, Fukuoka 812 (Japan)(Received January 4, 1990; accepted March 22. 1990)
ABSTRACT
To obtain lignin-derived pyrolysis products in larger yields. Curie-point pyrolysis wasperformed on the softwood species Japanese red pine (Pinus densiflora Sieb. et Zucc.),
Japanese cedar (cryptomeria japonica D. DON) and Japanese cypress ( Chamaecyparis obtusa
Endl.), and their dioxane lignins treated with various inorganic substances, over the temperature range 358-764℃. The resulting guaiacol derivatives (guaiacol, 4-methyl-, 4-ethyl- and4-vinylguaiacols, eugenol, vanillin, cis- and trans-isoeugenol, and acetovanillone) were determined by gas chromatography.
The softwood samples sandwiched between two sheets of heat-resistant filter paper madeof borosilicate glass fibers yielded from 1.56 to 1.64 times more guaiacol derivatives than
unsandwiched samples. Sandwiching the dioxane lignins between heat-resistant papers also
increased the guaiacol-derivative yield. by 13 to 27%.
The sandwich-2 method developed in this study is widely applicable as a sample preparation method for increasing the yield of lignin-derived products on Curie-point pyrolysis.
Gas chromalo8rqhy; glass fiber. borosilicate; guaiacol derivatives; lignin; pyrolysis, Curiepoint., softwoods.
INTRODUCTION
Pyrolysis combined with gas chromatography (Py-GC) is a powerful toolfor synthetic and natural polymer analysis. Early applications of Py-GC in
lignin analysis can be found in the reports of Kratzl et al. [1] and Kitao andWatanabe [2], who suggested that this method offered a convenient analytical technique for the rapid characterization of a very small amount of lignin.

Despite obvious advantages, the Py-GC method has been largely neglectedcompared with other lignin degradation techniques such as acidolysis, alkaline nitrobenzene oxidation and permanganate oxidation, which are timeconsuming and demand large sample amount.
The development of modern analytical instruments has recently resulted
in the publication of a number of reports describing the possibility and theusefulness of the Py-GC method for lignin characterization [3-8]. In thesereports, investigators separated and identified many guaiacyl and syringyl
derivatives, and predicted that the Py-GC method would be extensivelyused in various areas of lignin chemistry in the future. Boon et al. [6l pointed
out that combined Curie-point pyrolysis-GC/ MS (mass spectrometly) is aninteresting microanalytical characterization method for plant material andits derived fractions. However, few reports [7,8] are available oft: the quantitative determination of the resulting volatile phenols. In particular, we havefound no reported attempts to increase the yield of lignin-derived phenols.
The object of the present study was to increase the guaiacol-derivative
yield by pyrolyzing softwoods a lignins in the presence of inorganicsubstances. To our knowledge, there are few reports [9] dealing with theexact relationship between inorganic substances and the yield of lignin-derived pyrolysis phenols, whereas considerable documentation exists on theeffects of inorganic salts on cellulose from the viewpoint of the developmentof fire-retardant chemicals [10-16].
A sample. preparation method for increasing the yield of lignin-derived
pyrolysis phenols was also developed. This method is applicable to theCurie-point pyrolysis of all lignocllulosic materials.
. EXPERIMENTAL
Materials
The extractive-free softwoods used in this study were Japanese red pine
( Pinus densiflora Sieb: et Zhcc.), Japanese cedar (Crypyomeria japonica D.
Don) and Japanese cypress (Chamaecyparis obtusa Endl.). Dioxane lignins(DLs) from these softwoods were prepared by the method of Pepper et al.
[17].
The commercial inorganic salts used were potassium carb6hate, sodium
tetraborate, sodium carbonate, boron trioxide, sodium chloride, nickel,
aluminium oxide, silicic anhydride and calcium oxide.
Three types of heat-resistant filter paper made of glass fibers (GB100R)/and silica fibers (QR100 and 80) were supplied by the Advantec
TOYO Co.

Pyrolysis
Pyrolysis unit and gas chromatography
A Curie-point pyrolyzer (JHP-2 model, Japan Analytical Industry Co.)was coupled directly with a gas chromatograph (GC) (Shimadzu GC-14A).
Each sample, prepared as described below, was wrapped with a ferromagnetic pyrofoil and kept in the pyrolyzer at 140℃ for 5 min (wood) or 1 min(DL samples), after the unit had been flushed with helium for 15 s. The
samples were then pyrolyzed by induction heat for 4 s, and the resulting
volatile compounds were transferred to the GC. The GC analysis was run on
a 25 m Thikote fused-silica capillary column (0.53 mm I.D.) with a chemically bonded methyl silicone coating 5.0 μm thick (Quadrex Corp.). Helium
was used as carrier gas. The temperature program used was 1 min at 70℃,
and 4℃/min from 70 to 250℃, after which isothermal conditions weremaintained. The injection port and the flame ionization detector (FID) werekept at 260℃. The peak areas were measured by an integrator (Shimadzu
Chromatopac C-R6A). Identification of peaks was carried out by comparison with retention times of known substances and/or using a Py-GC/MS
system (Finnigan MAT ITD-800) fitted with a 30 m fused-silica capillarycolumn (0.25 mm I.D.) with a 0.25 μm film chemically bonded Durabond
DB-5 coating (J. & W. Scientific Inc.). Known amounts of authentic
guaiacol-derivative solutions were injected into the pyrolyzer and transferred
into GC without pyrolysis to obtain exact retention times and calibration
curves for the quantitative determination of guaiacol derivatives.
Sample preparation for pyrolysis(a) Standard method. About 0.5 mg of the starting material was weighed
precisely, wrapped with a pyrofoil, and subjected to Py-GC.
(b) Addition method. The salt or the glass fiber paper powder (about 50 mg)
was added to the starting material (0.5 mg) on a pyrofoil. The preparedsample was subjected to Py-GC.
(c) Mixing method. The salt or the glass fiber paper powder was mixed withthe starting material by grinding in a vibratory sample mill (Model TI-1,Hirako Seisakusyo) for 5 min. The mixture, containing 0.5 mg of the starting
material, was wrapped with a pyrofoil, and then pyrolyzed.

.

(d) Sandwich-1 method. The starting material (0.5 mg) on a glass fiber
paper was wrapped with a pyrofoil, and then pyrolyzed.
(e) Sandwich-2 method. The starting material (0.5 mg) was sandwiched
between two Pieces of glass fiber paper, wrapped with a pyrofoil, and then pyrolyzed.

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 treated with and without
inorganic substances were qualitatively identical. The main pyrolysis products were the nine guaiacol derivatives guaiacol, 4-methy1-, 4-ethyl- and4-vinylguaiacol, eugenol, vanillin, cis-and trams-isoeugenol, and acetovanillone, which confirms previous work as reported by Kitao and Watanabe [2],who pyrolyzed pine milled wood lignin under similar conditions. In addition
to these guaiacol derivatives, small amounts of 4-propylguaiacol, vanillicacid and propiovanillone were also identified. Contrary , to the reports ofObst [5], Boon et al. [6] and Faix et al. [7,8], coniferaldehyde and coniferyl
alcohol were rarely detected under the conditions used in the present work.
Peaks of phenols, xylenols and cresols

often overlapped those ofcarbohydrate-derived compounds.
Effects of inorganic substances on pyrolysis
Table 1 shows the effects on the pyrolysis of pine woods at 500℃ ofvarious inorganic substances, selected according to the classification of Tang[11]. The yield from pine wood in the absence of inorganic substances(standard method) is also shown, as a control. The guaiacol-derivative yield
is expressed as a sum of the yields of guaiacol, 4-methylguaiaco1, 4-ethylplus 4-vinylguaiaco1, eugenols (eugenol and cis- and trans-isoeugenol) andcarbonyl compounds (vani1lin, and acetovanillone).
From the data in Table 1, the borosilicate glass fiber paper (GB100R),
sodium and potassium carbonates were effective in increasing the total yieldof guaiacol derivatives. Mixing with the glass fiber paper increased theguaiacol-derivative yield by about 1.9% compared with that of pine woodalone (standard method). Sodium and potassium carbonates also increased
the guaiacol-derivative yield by about 1.0%, despite the finding of Gardneret al. [9] that sodium carbonate did not increase the yield of pyrolysis
products. This discrepancy is probably due to their having determined only
four pyrolysis products, and also to the different pyrolysis conditions
employed. The addition of pulverized GB100R and sodium carbonate topine wood produced no serious increase in the 8uaiacol-derivative yieldcompared with that from the standard method, but the addition of potassium carbonate greatly decreased the guaiacol-derivative yield (4.73%).
Upon mixing with the carbonates in the sample rhil1. the samples took on
a strong yellowish colour. This suggests that the pine wood reacted with thecarbonates during grinding, and the resulting sample partly decomposed
before pyrolysis. Sodium chloride slightly decreased the guaiacol-derivative
yield. In this connection, Richards et al. [16] detected polyhydroxybenzenes

from the pyrolysis of cellulose in the presence of sodium chloride, probably
because they pyrolyzed at lower temperature for a longer time add trimethylsilylated pyrolysis products prior to GC analysis.
Therefore, we concluded that of the procedures tested in the present
study, the glass fiber paper (GB100R) method was the most effective forcatalyzing pyrolysis.
Figure 2 shows the change in the guaiacol-derivative yield on pyrolysis (at500℃) of pine wood mixed with pulverized GB100R. The yield clearly
increased on mixing with small amounts of GB100R powder, and gradually
increased further with increasing amounts of GB100R. However, the yieldappeared to level off after reaching about 15.20% at ratio of GB100R to pine
wood 2.0. Consequently, the largest yield of guaiacol derivatives obtained by
the mixing method was 15.76% at the ratio of 10.0. Thus, Fig. 2 shows that it
is technically difficult to obtain the guaiacol derivatives with a yield larger
than 16.0% from pine wood by the mixing method.

Effects of sample preparation method on pyrolysis
Figure 3 shows guaiacol-derivative yields from pine samples prepared byvarious methods. Pine wood sandwiched between two pieces of GB100R (i.e.
the sandwich-2 method) gave the largest yield (18.86%), whereas the sandwich-1 method gave 15.32%, a value similar to that obtained by the mixing
method.
From these findings, the effects of the sample preparation methods on theguaiaco1-derivative yield are ordered as follows: sandwich-2 method > mixing
method = sandwich-1 method > addition method = standard method. The
largest yield of guaiacol derivatives obtained by the sandwich-2 method wasdue to the increase of guaiaco1, 4-vinylguaiacol and eugenols, although wecannot explain the mechanism of this effect at this stage.

Effects of heat-resistant filter paper on pyrolysis
The effects of types of heat-resistant filter paper on pyrolysis (at 500℃)
of pine woods prepared by the sandwich-2 method are shown in Fig. 4.
Although pine wood sandwiched with QR100 also gave guaiacol derivatives
in moderately good yield (15.44%), this was smaller than the yield obtainedwith GB100R. The yield with QR80, which contains alumina as binders, wasonly 3.40%. Therefore, the effects of the heat-resistant filter papers on theguaiacol-derivative yield when pyrolysis was performed by the sandwich-2

method are ordered as follows: GB100R > QR100 > untreated (11.79%) >QR80. One reason for this great difference in the yield lies in the principal
constituents of the various papers. GB100R is made of borosilicate glass,whereas QR100 and 80 are mainly made of silic acid. Thus, the above result
agrees well with the data in Table 1.

Effect of temperature on pyrolysis
The effects of temperatures in the rang 358-764℃ on the pyrolysis ofpine wood, alone and sandwiched with GB100R, were also investigated (Fig.
5).
The most useful finding was that the guaiacol-derivative yield was largest
at 500℃, regardless of whether or not the pine samples were sandwichedwith GB100R. Thus, 500℃ is the optimum pyrolysis temperature. Below
590 ℃ the guaiacol-derivative yields obtained from pine woods sandwichedwith GB100R were much larger than those from the untreated woods. At
670 and 764℃,I adverse results were obtained. Particularly at 764oC, thesandwiched sample gave a much smaller yield of the guaiacol derivatives,and a more complicated pyrogram, with many peaks, than that obtained by
the standard method. This indicates that GB100R may catalyze pyrolysis ofguaiacol derivatives into smaller fragments at this temperature.
Extensive degradation at a higher temperature has been reported by
Nozawa and Satonaka [18]. These authors pyrolyz8d Japanese oak (Quercus

mongolica var. grosseserrata) at 400 and 800 ℃ and observed large mountsof phenol and cresol, while guaiacol derivatives were not among the pyrolysis products obtained at 800℃. Therefore, the small yield of guaiacol
derivatives from our pyrolysis at 764℃ is probably due to extensive
conversion of the initially produced guaiacol derivatives into other degrada-tion products such as catechol and cresol. Influence of pyrolysis temperatureon the composition of the product mixture will be discussed elsewhere.
From the above results, the most suitable conditions for our purpose were(a) to sandwich the sample with GB100R, and (b) to pyrolyze the sandwich
at 500℃.

Application of sandwich-2 method to other samples
The sandwich-2 method using GB100R was ,applied to the pyrolysis ofother softwoods and their DLs at 500℃.
The total yield of guaiacol derivatives increased from 13.97 to 22.85% forJapanese cedar, and from 13.50 to 21.03% for Japanese cypress, as comparedwith the standard method (Fig. 6). Thus, the guaiacol-derivative yields fromJapanese cedar and cypress sandwiched with GB100R were increased by
1.64 and 1.56 times, respectively, over those from the untreated woods.
These values agree very closely with those (1.60 times) obtained for thepyrolysis of Japanese red pine.
A similar tendency was observed for the pyrolysis of DL samples sandwiched with GB100R (Fig. 7). The guaiacol-derivative yields from DLs
sandwiched with GB100R were 5.53% for pine, 7.68% for Japanese cedar
and 7.01% for Japanese cypress, whereas those from untreated DLs were4.37, 6.55 and 6.17%, respectively. Thus, the sandwich-2 method using
GB100R increased the guaiacol-derivative yields from DLs 1.27 times forpine, 1.17 times for Japanese cedar and 1.13 times for Japanese cypress, overthose from the untreated DL samples. However, the amounts oft guaiacol
derivatives obtained from the DLs were reduced to one-third of those fromthe corresponding softwoods, probably as a result of modification of thechemical structure of lignin during the isolati6n process.
The above results suggest that the sandwich-2 method using GB100R
could be widely applied to the Curie-point pyrolysis of many softwood
species and their lignin preparations.
ACKNOW LEDGEMENTS
We wish to thank the staff of Japan Analytical Industry and Finnigan
MAT Instruments, Inc., for performing the Py-GC/MS runs.