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Update: July 20, 2011

	Scientific report of the LGP2 (2006-2009)
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Researchers of the LGP2 (May 2011)

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II - Chemical Processes

II - 1 - Introduction

The manufacture of cellulosic fibres from lignocellulosics material is a complex and sophisticated chemical process. The objective is to remove lignin with chemicals which do not affect cellulose severely. The fact that these two components are intimately mixed inside the fibre walls makes this operation particularly difficult. A mixture of sodium hydroxide and sodium sulphide is generally, applied under drastic conditions (160 – 170° C). Lignin is then depolymerised by cleavage of interunit alkyl–aryl ether bonds. However, the carbohydrate fraction (hemicelluloses, cellulose) is also partly hydrolysed by the alkaline medium. About 80 % of the hemicelluloses are lost. Cellulose depolymerisation occurs too, but can be limited at a level which does not impair the fibre properties.

The problems on which most of the research effort of the Chemical Processes department is focused are:

• The low yield of fibre production. More than 50 % of the wood components are dissolved during this operation. As said before, this reflects the loss of most of the hemicelluloses. Increasing the pulp yield would save the raw materials.
• Hemicelluloses valorisation by pre-extraction prior to cooking. Hexoses (glucoses, mannose, galactose) can be fermented into biofuel whereas pentoses (xylose, arabinose) can serve as base molecules for the chemical industry.
•  After alkaline cooking, the fibres are brown because of the presence of coloured residual lignin fragments. Performing bleaching stages is necessary at least for the production of white papers. Nowadays, oxidising chlorinated agents based on chlorine dioxide and its derivatives are mainly used and processes necessitate high temperatures. For the future, replacing all the chlorinated reagents by cleaner oxidising chemicals such as oxygen, hydrogen peroxide and ozone, and if possible, working at lower temperature (< 50°C) would be expected.

The more relevant topics under investigation in our team are the following:

• Macromolecular structure of lignin in lignocellulosic substrates. ¹³C NMR, ¹⁹F NMR, FTIR, GC–MS spectroscopies are used in combination with isolation or controlled degradation techniques (enzymatic extraction, acidolysis, pyrolysis …).
• Effect of lignin structure on delignification and bleaching.
• Modelling of delignification and bleaching processes from mechanistic and kinetic data.
• Development of clean cooking and bleaching processes (catalysis oxygenated bleaching reactants).
• Behaviour of fibre components during ageing and recycling.
•  Development of hemicelluloses extraction by prehydrolysis and fermentation processes integrated in the fiberline operations of a conventional pulp mill.

The main partners in these studies are the French Environment and Energy Management Agency (ADEME), The French National Research Agency (ANR), le Centre Technique du Papier (CTP), the Institut Technologique Forêt Cellulose Bois-construction Ameublement (FCBA), Arkema, Air Liquide, EDF, Tembec, Degrémont, Wedeco. Cooperation with foreign companies and institutes is also very active in the frame work of European Projects.

The main areas of research investigated these last four years are shortly presented below.

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