Paulownia as raw material for solid biofuel and cellulose pulp

The influence of the process conditions of pulping of a trihybrid clone Paulownia on pulp properties in the soda-anthraquinone process has been investigated. A composite central experimental design and a multiple regression were used to find the relationship between independent process variables and pulp properties. The ash content (8.9 g kg−1) is lower and cellulose content (440 g kg−1) is higher than those found for other species of Pauwlonia and other energetic crops. The elemental composition has a low content in S and N (2.1 g kg−1) in comparation with poplar or willow. With a gross heating value of 20.3 MJ kg−1. This is somewhat higher than those for hardwood, slightly higher than those for Pinus pinaster and softwood, and much higher than those for residues of food plants and agricultural crops. This supports the use of the genus Paulownia as an energy crop. Fiber length (0.97 mm) is similar to hardwoods and suitable physical characteristics of paper sheets (tensile index) and acceptable chemical characteristics and yield pulping could be obtained by operating at low-intermediate temperature (163–171 °C) and alkali concentration (200 g kg−1) and high or medium values for operation time (120–150 min). The pulp obtained at these conditions has suitable chemical (pulp) and physical (paper sheets) characteristics: yield (470 g kg−1), ethanol-benzene extractives (22.2 g kg−1), holocellulose contents (960 g kg−1), α-cellulose contents (758 g kg−1), lignin contents (82.8 g kg−1), Shopper–Riegler degree (23.2 °SR), and tensile index (36.0 kN m kg−1). ► Soda-anthraquinone pulping of a trihybrid clone Paulownia have been investigated. ► The soda-anthraquinone pulping could be an adequate process for clone Paulownia. ► The results are similar to hardwoods and physical characteristics of paper sheets. ► Trihybrid clone Paulownia is a suitable feedstock for use as solid biofuel.