(533f) Effect of Dielectric Oxides on Microwave Assisted Deconstruction of Lignin   | AIChE

(533f) Effect of Dielectric Oxides on Microwave Assisted Deconstruction of Lignin  

Authors 

Dhar, P. - Presenter, Indian Institute of Technology Madras
Vinu, R., Indian Institute of Technology Madras, Chennai, India

Lignin, a natural polymer is a potential source of fuels and platform chemicals due to its aromatic structure. The conventional industrial processes which utilize plant polysaccharides, burn lignin to generate process heat. With the depletion of fossil fuels, cellulosic biorefineries would generate surplus lignin than required to fuel the biomass conversion process [1]. Conventional lignin conversion methods require temperatures greater than 200°C and longer reaction time. A non-conventional source of energy such as microwave reduces the reaction time and gives higher heating rates. The heating of reaction medium by microwaves is through the mechanism of dipolar polarization and ionic conduction. In this study, alkali lignin was solubilized in 1:1 Dimethyl Sulfoxide (DMSO)/water mixture. The DMSO/water mixture has a high polarity (0.7) and solubilizes lignin completely. Metal oxides such as lanthanum ferrate (LaFeO3), iron oxide (Fe2O3) and zirconium oxide (ZrO2) were synthesized by the combustion method. Experiments were carried out in a microwave reactor at different temperatures (80-100°C) and samples were withdrawn at regular intervals between 0-120min. The catalysts were suspended in the reaction media and the solution vessel was continuously stirred for the entire reaction time. The microwave treated samples were analyzed using Gel Permeation Chromatography to study the effect of catalysts on reduction in the average molecular weight of lignin. Liquid chromatography Mass Spectrometry was used for the identification of phenolic monomers produced. The formation of products such as vanillin, acetoguaiacone, homovanillic acid and coniferaldehyde were observed at temperatures as low as 80°C while using LaFeO3 and Fe2O3 as catalysts. The effect of different catalyst properties such as structure, dielectric constant and surface area, on the yield of monomers was studied and possible reaction mechanisms were proposed.

References:

1. A.J. Ragauskas et.al., Lignin valorization:improving lignin processing in the biorefinery. Science, 344 (2014).

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