Ken-ichi Kuroda

Pyrolysis-trimethylsilylation analysis of lignin: preferential formation of cinnamyl alcohol derivatives

Abstract This paper describes a pyrolysis-trimethylsilylation procedure that is a new pyrolysis-derivatization thermochemolysis procedure of lignin. N , O -Bis(trimethylsilyl)trifluoroacetamide (BSTFA) was used as a trimethylsilylating reagent. A bulk dehydrogenative polymer of coniferyl alcohol (G-DHP) and a Japanese cedar ( Cryptomeria japonica D. Don) wood were pyrolyzed in the presence of BSTFA at 500°C for 4 s. The resultant volatile products were analyzed by gas chromatography/mass spectrometry (GC/MS). The G-DHP and the wood produced large abundances of trimethylsilyl (TMS) derivatized coniferyl alcohol (CA-(TMS) 2 ), in which both the phenolic and alcoholic hydroxyl groups are derivatized with TMS. CA-(TMS) 2 accounted for about 68% of the TMS derivatized products in the G-DHP pyrolysis, and about 24% of those in the wood pyrolysis. The results indicated that pyrolysis in the presence of trimethylsilylating reagents such as BSTFA is a potentially useful technique for drawing information on the pyrolytic precursors of cinnamyl alcohols (such as cinnamyl alcohol-end groups) from lignin. Pyrolysis-trimethylsilylation occurs in a one-step process and provides the TMS derivatives that are immediately available for the subsequent GC(/MS) analysis. This method is applicable to all lignocellulosic materials.

Structural characterization of kenaf lignin: differences among kenaf varieties

Abstract The differences in lignin were studied among three kenaf varieties: Everglades ( Hibiscus cannabinus L.), Aokawa-3 ( H. cannabinus L.), and Mesta ( H. sabdariffa L.). The bast, inner bast, and core samples were each prepared from the four different positions, top, upper middle, lower middle and bottom, of the kenaf stems. With increasing height of the stems, the lignin content decreased. In all kenafs studied, the bast samples contained lignin in lower amounts than the core samples prepared from the same positions. The differences in lignin contents between the core and bast samples were larger in Everglades and Aokawa-3 than in Mesta. The inner bast samples showed similar results to those of the core samples prepared from the same positions. The bast samples produced nitrobenzene oxidation products with larger syringaldehyde/vanillin (S/V) ratios than the core samples prepared from the same positions. Most bast and core from Everglades and Aokawa-3 showed ratios of more than approximately 3.0 and 1.2 S/V, respectively. The average S/V ratios in Mesta were 2.1 for the bast samples and 1.9 for the core samples. These findings showed, the bast samples of the Everglades and Aokawa-3, syringyl lignin units were predominant. Thioacidolysis also provides similar results. These results show that (1) the core lignin is a mixed lignin with guaiacyl and syringyl type, and the bast lignin is syringyl type, from the viewpoint of the lignin composition; and (2) lignin in Everglades and Aokawa-3 is heterogeneous compared to that in Mesta.

Analysis of lignin by pyrolysis-gas chromatography. I. Effect of inorganic substances on guaiacol-derivative yield from softwoods and their lignins

To obtain lignin-derived pyrolysis products in larger yields. Curie-point pyrolysis was performed 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- and 4-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 made of 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.

Analytical pyrolysis products derived from cinnamyl alcohol-end groups in lignins

The contributions of cinnamyl alcohol-end groups to lignin-derived pyrolysis products were studied using coniferyl alcohol benzyl ether I, a model compound for cinnamyl alcohol-end groups. The profile of the pyrolysis product distribution of I demonstrated that cinnamyl alcohol-end groups are greatly responsible for the formation of propenylphenols, and cinnamyl compounds (dihydrocinnamyl alcohols, cinnamaldehydes, and cinnamyl alcohols), but play a small role in the formation of the products with a short side-chain (<C3). The contributions of coniferyl alcohol-end groups were examined in pyrolyses of reference lignins, a bulk dehydrogenative polymer of coniferyl alcohol (DHP), a Japanese cedar (Cryptomeria japonica D. Don) wood and its milled wood lignin. Large similarity of the distribution profile of the cinnamyl compounds in the DHP pyrolyzate to that in the I pyrolyzate showed that coniferyl alcohol-end groups play a large role in the DHP pyrolyzate. The distribution profiles of the cinnamyl compounds in the cedar wood and its lignin pyrolyzates were greatly differed from that of the I pyrolyzate.

Pyrolysis-mass spectrometry analysis of dehydrogenation lignin polymers with various syringyl/guaiacyl ratios

The present paper describes the application of pyrolysis-mass spectrometry (PYMS) to the analyses of lignocellulosic materials. Dehydrogenation lignin polymers (DHPs) with various syringyl/guaiacyl (S/G) ratios, and a standard, milled wood lignin from Aesculus turbinata Blume, were pyrolyzed at 500 °C for 4 s and the volatile products were ionized by low-voltage (20 eV) electron impact. The PYMS spectra of the lignins are shown with identification of most mass peaks. Of the observed mass peaks, the intensitities of the monomeric peaks corresponding to monomethoxyphenols (m/z 124, 137, 138 and 180) and dimethoxyphenols (m/z 154, 167, 182 and 210) were sensitive to the S/G ratio shifts of the DHPs. Changes in the monomeric mass peak intensities reflected those in the yields of the corresponding products determined by pyrolysis-gas chromatography (PYGC). The S/G pryolytic ratios, calculated from the summed mass peak intensities of syringyl and guaiacyl monomeric products, showed a linear correlation with syringaldehyde/vanillin (S/V) ratios determined by nitrobenzene oxidation. This finding suggested that the S/V ratios of lignocellulosic materials are predicted from the S/G pyrolytic ratios obtained by PYMS. Similar linear correlations were observed also between the S/G pyrolytic ratios determined by PYGC and the S/V ratios, for the DHPs and for Japanese hardwoods. Unlike the PYGC method, however, the PYMS method does not need time-consuming determinations of the response factor of each product to a flame ionization detector. This advantage may outweigh the inherent problems of PYMS, such as the ambiguous structural assignment of the mass peaks in the quantitative PYMS analyses of lignocellulosic materials. The dimeric mass peaks, which were hardly detected in an analytical system with a gas chromatograph, also contributed to the mass spectra.

Electron-impact (EI) mass spectra of 1,2-dimethoxybenzenes related to the pyrolysis products of guaiacyl lignin in the presence of tetramethylammonium hydroxide (TMAH)

Abstract This paper collects the mass spectra of 1,2-dimethoxybenzenes related to the pyrolysis products of guaiacyl lignin in the presence of tetramethylammonium hydroxide (TMAH), most of which were non-commercial products or not easily derived from commercial products. The syntheses employed enol etherification of the corresponding dimethyl acetals and on-line methylation of the corresponding acetates with TMAH.

Analysis of rice (Oryza sativa L.) lignin by pyrolysis-gas chromatography

Abstract Curie-point pyrolyses of four paddy rice ( Oryza sativa L.) cultivars were carried out at 500 °C for 4 s. The products were analyzed by gas chromatography (GC) and/or GC/mass spectrometry. Analytical pyrolysis showed that rice lignin is a mixed p -hydroxyphenyl-guaiacyl-syringyl lignin, as did the results of alkaline nitrobenzene oxidation. The main pyrolysis products were 4-vinylphenol (VP) and 4-vinylguaiacol (VG). The determination of the vinyl compounds showed that the yield of VP had good correlation with the cultivars and the maturity of rice. p -Coumaric and ferulic acids in rice were determined on the basis of the yields of VP and VG produced on pyrolysis. The results were in good agreement with the amount of the acids determined by hot alkaline hydrolysis.

Anatomy and Properties of Japanese Hardwoods I. Variation of Fibre Dimensions and Tissue Proportions and their Relation to Basic Density

Variations of tissue proportions and fibre dimensions (fibre length, fibre cross sectional area, fibre wall thickness, fibre wall area, percentage of fibre wall area) of 50 Japanese hardwoods are compared. The fibre cross sectional area showed large variations as compared to fibre length. There is no significant correlation between fibre cross sectional area and fibre wall thickness.The multiple regression analysis showed that fibre wall thickness, percentage of fibre wall material and ray volume are the parameters most closely correlated with basic density.

Pyrolysis of arylglycol-β-propylphenyl ether lignin model in the presence of borosilicate glass fibers.: I. Pyrolysis reactions of β-ether compounds

Abstract Two β-aryl ether type model compounds, guaiacylglycol- and veratrylglycol-β-propylphenyl ethers, were copyrolyzed with borosilicate glass fibers. The results provided a better understanding of the effect of copyrolysis with the fibers on the yields of lignin-derived products from lignocellulosics. The observed products indicated the following reactions occurring in the models; (1) cleavage of the Cα-aromatic ring bond, (2) cleavage of the β-ether bond, (3) cleavage of the Cα-Cβ bond, (4) α,β-dehydration, and (5) demethylation, and others. Of these reactions, reactions (1), (2) and (4) were the main pyrolysis reactions and fully explained the increase in the total yield of lignin-derived pyrolysis products from Japanese red pine ( Pinus densiflora Sieb. et Zucc.) in the presence of borosilicate glass fibers. Reaction (1) was a particularly characteristic reaction in copyrolysis with the fibers. Important reactions relating to the increase in the total yield of lignin-derived pyrolysis products were reproduced on the models used.

Classification of Japanese softwood species by pyrolysis-gas chromatography

Abstract Japanese softwoods were pyrolyzed at 500 °C for 4 s. The resultant pyrolysates were analyzed by gas chromatography. All the softwoods yielded the same lignin-derived monomer pyrolysis products, 21 guaiacyl and four p -hydroxyphenyl type products. The profiles of lignin fragmentation patterns and the levels of the main lignin-derived products in the pyrolysates allowed the classification of the Japanese softwood pyrograms into three types.