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Lignin from Eucalyptus spp. Kraft Black Liquor as Biofuel

Dieste, Andrés, Clavijo, Leonardo, Torres, Ana I., Barbe, Stéphan, Oyarbide, Ignacio, Bruno, Leonardo, Cassella, Francisco
Energy & Fuels 2016 v.30 no.12 pp. 10494-10498
Eucalyptus, acid deposition, biofuels, carbohydrate content, electricity, energy, filtration, fossil fuels, lignin, plantations, potassium, production costs, pulp, slurries, sodium, sulfuric acid, washing, waste liquors, wood, Uruguay
Pulp mills located in Uruguay process Eucalyptus spp. wood from plantations. Black liquor is burnt in the recovery boiler, generating an excess of energy that is converted to electricity and sold to the grid. Lignin, the main component of black liquor, is a natural polymer, abundant, and readily obtained by acid precipitation. A recovery process of lignin from black liquor in a pulp mill produces a biofuel to be used within at the plant or to be marketed locally, diversifying the energy offer of Uruguay, a country with no fossil fuels. In the present contribution, technical-grade lignin (average of 94% total lignin) was obtained experimentally in a pilot plant by acid precipitation (H₂SO₄), sedimentation, filtration, and washing of the slurry and assessed as fuel: it presented a high caloric value (26 MJ/kg), low carbohydrate content, and low K and Na contents. The results of the economic analysis showed that a production of 3400 tons of lignin per year could be produced at a cost of 692 US$/ton. At a small production scale, the production costs of the operation discourage the use of kraft lignin as biofuel and clearly direct the possible application of this polymer to the production of a technical chemical.