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Communication Dans Un Congrès Année : 2015

The Potential of a Continuous Process for the Valorization of Lignin in Aqueous Media Assisted By Heterogeneous Catalysts

W. Sebhat
  • Fonction : Orateur
L. Djakovitch
P. Fongarland

Résumé

Introduction The emerging bio-based economy presents a huge potential to ease our dependence on fossil carbon, this paradigm shift from a petroleum based economy to a lignocellulose based one is still at its infancy stage. Aside from modern bioreffinerie concept, the paper and pulp industry developed knowledge on this feedstock for over two century. Lignocellulose is fractioned into cellulose, hemicelluloses and lignin with good yield and a relatively high purity [1]. Even though the use of cellulose in the paper industry is well established, the upgrading of lignin and hemicelluloses will be an interesting route to improve the profitability of modern day bioreffineries. In the present work the catalytic valorization of lignin in aqueous media with heterogeneous catalysts was investigated. The ultimate goal of our approach is to i) depolymerize lignin in small units that can be used directly after purification, ii) cleave the lignin matrix into smaller fractions easily convertible afterwards, iii) maintain a low level of char formation. Materials and Methods The experiments were carried out in either in a batch or in a micro pilot trickle-bed reactor (d=1.5 cm, L= 33 cm). The operating conditions are: a pressure of 40-80 bar of N2 or H2 and temperatures ranging from 150-275°C. A commercial Kraft lignin was used, it contained 4 wt% of sulfur and atomic ratios O/C, H/C were respectively 0.7 and 0.1. The ash content is 20 wt%, this lignin is used without any purification to represent real feedstock from pulp mills. A multistep protocol was developed to quantify lignin loss and yield of the different oligomeric and monomeric fractions (Fig.1). Gas and liquid chromatography coupled with a mass spectrometer was used for the analysis of the oil fraction (light weight molecules), the residual lignin is analyzed with size-exclusion chromatography, IR and NMR (1H, 13C and 31P). Results and Discussion We first studied the depolymerisation of lignin without any catalyst under hydrothermal conditions between 150°C and 275°C. An important amount of char was formed for 275°C clogging the fixed bed reactor. The significant salts content seems to promote the char formation at higher temperature [2]. Elemental analysis showed no change of O/C and H/C ratios, the sulfur content however was reduced to 2%. Under these conditions we were able to isolate monomeric aromatics with up 11% in yield. The use of Pt/Al2O3 helped increase the monomeric when contact time was increased, but the 40% barrier for the precipitable lignin was not affected (Fig. 2a). This suggests oligomers to monomers mechanism rather than lignin to monomers directly. We observed that the use of ethanol as a co-solvent can increase the aromatic yield (Fig. 2b) but also reduce the amount of the precipitable lignin, consistent to previous reports [3]. Nevertheless the components formed remain unstable and tend to repolymerise when in contact with air. Working under hydrogen atmosphere can help produce stable end-products which are less prone to recondensation. Over-hydrogenation can occur, leading to highly reduced products (cyclohexanes) and consuming much hydrogen.
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hal-01165558 , version 1 (19-06-2015)

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  • HAL Id : hal-01165558 , version 1

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W. Sebhat, L. Djakovitch, P. Fongarland. The Potential of a Continuous Process for the Valorization of Lignin in Aqueous Media Assisted By Heterogeneous Catalysts. 24th North American Catalysis Society Meeting, Jun 2015, Pittsburgh, United States. ⟨hal-01165558⟩
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