Industrial use of wood: new method of dissolution

New wood dissolution process for the paper industry, biofuels, textiles and clothing ...

An American-British collaboration between two scientists from the Department of Chemistry at Queen's University in Belfast and researchers from the University of Alabama (United States) has made it possible to develop a new ecological process for dissolving coniferous wood or hardwoods such as southern yellow pine and red oak to facilitate its transformation into biofuels, textiles, clothing and paper.

Today, most manufacturers use the Kraft process [1] to dissolve wood. In the paper industry, this process represents about 80% of the world production of pulp. Unlike the highly polluting Kraft process, the technique developed at Queen's University in Belfast is low in toxicity and biodegradable. This consists of completely dissolving wood chips in a liquid ionic solution, [C2mim] OAc (Ethyl-3-methylimidazolium acetate). The complete dissolution of the wood is completed by heating the product resulting from the dissolution in an oil bath. It is also possible to accelerate this dissolution by microwave pulsations or by ultrasonic irradiation. The team of researchers also demonstrated that [C2mim] OAc is a better solvent for wood than [C4mim] Cl (1-butyl-3-methylimidazolium chloride). In addition, three variables, namely the type of wood, the initial mass of the sample to be dissolved or the size of the wood particles; affect dissolution as well as dissolution rates. For example, red oak wood dissolves much better and faster than swamp pine.

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According to Dr. Héctor Rodriguez: “This discovery is an important step towards the development of the concept of biorefinery, where biomass is transformed to produce a wide variety of chemicals. This could give rise to a truly sustainable chemical industry based on renewable bio-resources ”.

In order to improve the technique, scientists are considering the addition of environmentally friendly additives to the ionic liquid or the use of catalysts. The researchers hope in the long term to achieve better dissolution, even under more flexible conditions of temperature and pressure, and also strive to achieve a complete separation of the different elements contained in the wood (cellulose, lignin) in a single step . The two teams also wish to extend the process to organic materials rich in essential oils which can then be used in processes such as the manufacture of perfumes.

[1] The Kraft Process

It is the most widely used production method among chemical pulp manufacturing processes. During this process, the wood, cut into pieces or shavings, is cooked in caustic soda in order to eliminate as much lignin as possible while retaining the cellulose. In this process, the active cooking chemicals (white liquor) are sodium hydroxide (NaOH) and sodium sulfide (Na2S).

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The paste obtained at the end of this process makes it possible to obtain dark-colored cardboard, due to the lignin residues which remain after cooking. To obtain a more or less white paper, several types of bleaching agents can be used: chlorine, chlorine dioxide (or chlorine dioxide), oxygen, ozone or hydrogen peroxide. However, the best results during the bleaching phases are obtained using chlorine which dissolves all the lignin still present without damaging the cellulose, which becomes completely white and remains white for several years.

Due to the chemical nature of this process, the pulp and paper industry releases a large quantity of polluting substances diluted in a large volume of effluent. These effluents may contain, for example, organochlorine compounds such as chlorinated dioxins and furans, traces of PCBs, phenolic compounds, etc.

Source: BE UK

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