This work provides an assessment on the fractionation of Eucalyptus globulus wood by sequential stages of autohydrolysis (to cause the solubilization of hemicelluloses) and organosolv pulping (to dissolve lignin, leaving solids enriched in cellulose). With this approach, valuable products (hemicellulose-derived saccharides, sulphur-free lignin fragments and cellulosic substrates with low contents of residual hemicelluloses) are obtained in separate streams, according to the biomass refinery approach. Autohydrolysis was carried out under optimized operational conditions, and organosolv pulping was performed using uncatalyzed ethanol-water solutions. The effects of the most influential operational variables (autohydrolysis severity, delignification temperature and ethanol concentration in the organosolv stage) on solid yield, solid composition, cellulose susceptibility and recovery of the various fractions was assessed using statistical methods, which enabled the identification of the most favourable operational conditions.

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)

A method for the selective extraction of hemicellulose from wheat straw involving cold alkaline extraction and subsequent separation by precipitation with ethanol is proposed. Wheat straw affords selective separation of the hemicellulose fraction from the cellulose and lignin fractions with the proposed method. The hemicellulose yield was optimized by using a 2n factor design to examine the influence of temperatures (temperature was designed between 20 and 40 ◦C), operation times (operation time was designed between 30 and 60 min) and alkali concentrations (alkali concentration was designed between 80 and 120 g L−1). These conditions allowed 56.1% of all hemicellulose initially present in the raw material, and 59.1% of the lignin, to be extracted. Subsequent separation of hemicellulose in the liquid phase from the cold alkaline extraction by precipitation with ethanol provided a fraction containing 39.4% of all hemicellulose (45.2% hemicellulose in extract/total extract) and only 12% of all lignin in the raw material.The authors are grateful for the FPU grant from the Spanish Ministry of Education. Also they thank to Spanish Ministry of Economy and Competitiveness (former Ministry of Science and Innovation) contracts. The authors acknowledge financial support for this investigation has been provided by CDTI (CENIT-E-CDTI-BioSos-CEN-2009-1040) and supported by Ministry of Economy and Competitiveness, "Local Investment fund for employment". Government of Spain, Junta de Andalucia, CICYT-FEDER (Science and Technology Inter Ministerial Commission, Spanish Government - European Regional Development Fund), project number AGL2009-13113 and the business group ACCIONA INFRAESTRUCTURAS, S.A