Process Biochemistry 35 (1999) 143 – 148 Influence of process variables on the properties of pulp obtained by ethanol pulping of wheat straw L. Jime ´nez *, M.J. de la Torre, J.L. Ferrer, J.C. Garcı ´a Departamento de Ingenierı ´a Quı ´mica, Facultad de Ciencias, Uniersidad de Co ´rdoba, 14004 Cordoba, Spain Received 8 December 1998; received in revised form 10 March 1999; accepted 20 March 1999 Abstract The influence of independent variables in the cooking of wheat straw with ethanol-water mixtures (ethanol concentration, cooking time and temperature) on various properties of the pulp (yield and holocellulose,  -cellulose and lignin contents) was studied with a view to determining the best operating conditions to obtain quality pulp (pulp with high holocellulose and  -cellulose contents and a low lignin content). The results were fitted to a second-order polynomial function using a BMDP system package and a 2 m central composite design. In this way, equations that reproduce yield and the holocellulose and  -cellulose contents with errors less than 3.5% and lignin content with errors less than 15% were derived. Additional equations were obtained that relate dependent variables to the treatment severity parameter, R o and reproduce the experimental yields and holocellulose,  -cellulose and lignin contents with errors less than 10, 4, 4 and 15%, respectively. Obtaining pulp with high holocellulose and  -cellulose contents and a low lignin content, entails using a high temperature (190°C) and ethanol concentration (80%) for a long time period (2 h). © 1999 Elsevier Science Ltd. All rights reserved. Keywords: Wheat straw; Organosolv; Ethanol; Pulp; Treatment severity www.elsevier.com/locate/procbio 1. Introduction The primary current goals of the pulp and paper industry are the production of economical pulp of good quality while preserving the environment by minimizing the polluting effects of waste effluents from cooking and bleaching processes and using alternative material sources in order to relieve the shortage of wood raw materials. The cooking process generates large amounts of con- centrated waste water especially that from sulphite and sulphate processes. One solution to this problem is the use of organic solvents. Although their favourable ef- fects on the pulping process are established, the use of this type of solvent for this purpose dates from recent times and only on the pilot or small industrial scale [1]. Prominent among the pulping processes that use organic solvents are those based on alcohols, particu- larly the Alcell (ethanol – water), MD Organocell (ethanol – soda), Organocell (methanol – soda – anthra- quinone), ASAM (alkali – sulphite – anthraquinone – methanol) and ASAE (alkali – sulphite – anthraquin- one – ethanol) processes [1–7]. These processes have been applied with varying success to different types of hardwood and softwood and also, anecdotally, to non- wood plants. The annual production of pulp can hardly meet current demand, which is growing dramatically in de- veloping countries and, to a lesser extent, in developed countries (e.g. by 2–3% in the USA). This is leading to an increasing shortage of wood raw materials and the gradual deforestation of some areas on the planet. For this reason, the use of alternative, non-wood materials such as wheat Straw and other agricultural cropping residues, which are especially abundant in Spain [8], is of particular interest. Pulp production processes have been analysed in the light of a variety of models intended to provide equa- * Corresponding author. Tel.: +34-957-218624; fax: +34-957- 218606. 0032-9592/99/$ - see front matter © 1999 Elsevier Science Ltd. All rights reserved. PII:S0032-9592(99)00045-X