Caracterização de ligninas de Eucalyptus spp. pela técnica de pirólise associada à cromatografia gasosa e à espectrometria de massas / Characterizing the lignins of Eucalyptus spp. by the pyrolysis technique associated to both gas chromatography and mass spectrometry

AUTOR(ES)
DATA DE PUBLICAÇÃO

2006

RESUMO

Lignin is one of the main wood components as well as the cellulose and hemicellulose. It is known that the composition of lignin relative to the amounts of unit syringyl (S) and guaiacyl (G) can affect the efficiency of the kraft pulping. Thus, this work was carried out to develop a methodology for the determination of the S/G relationship in the Eucalyptus spp. wood, by using the pyrolysis coupled to the gas chromatography and mass spectrometry (Pi-CG/EM), in order to selecting eucalyptus clones for kraft pulping. Some analyses were accomplished for Pi-CG/EM of the wood, extractive-free wood, acetone extractive and lignin (MWL) of the Eucalyptus grandis and Eucalyptus urograndis species at the temperatures of 300, 350, 400, 450, 500, 550 and 600 C. When analyzing the pyrograms of the wood under several temperatures, The presence of many phenolic monomers from the lignin and several furanic and pyranic compounds originating from either dehydration and the carbohydrate rearrangements were observed, when analyzing the wood pyrograms. At 600 oC temperature, the relative abundance of the compounds from the carbohydrates overcame that of the compounds originating from lignin. The S/G relationship largely varied as a function of the temperature, and the maximum S/G relationship in both species of Eucalyptus were obtained at 300 C. Besides the temperature, the amount of the sample to be pyrolised was observed to interfere into S/G relationship. The analyzed pyrograms of the extractive-free woods showed a similar behavior to that of the wood with extractive. When analyzing the pyrograms of the acetone extractives, the following presence were observed: several fatty acids, hydrocarbons, alcohols, aromatic compounds and fatty ester. In the analyses of the lignin pyrograms (MWL), however, the S/G relationship was very similar to that of the wood with extractive at 550 C temperature. At the lowest temperatures, only few compounds were volatilized, whereas at 600 C many compounds were degraded, therefore composing lignin-modified derivatives, such as 3-methoxycatechol. The accomplished studies showed the uses of the Pi-CG/EM to be a powerful tool for the characterization of the S/G relationship because its high sensibility. The temperature at 550 C showed to be most appropriate for the pyrolysis of the wood. In the pyrolysis of the extractiveless wood, acetone extractives and lignin (MWL), it was noticed that the extractives have just few influence on the determination of the S/G relationship, and the carbohydrates more than the extractives. The methodology developed in this work showed to be effective for determination of the S/G relationship in both wood with and without extractives, since the use of those eight marker compounds for lignin derivatives (guaiacol, 4-methylguaiacol, 4-vinylguaiacol and trans-isoeugenol, syringol, 4-methylsyringol, 4-vinylsyringol and trans-propenylsyringol) at 550 C temperature were satisfactory in determining the S/G relationship. This result will be useful to the industries, as making possible the determination of the S/G relationship in Eucalyptus species on a faster way than by the nitrobenzene oxidation.

ASSUNTO(S)

pirólise pyrolysis lignin quimica organica gas chromatography espectrometria de massas mass spectrometry lignina cromatografia gasosa

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