Holzforschung, Vol. 58, pp. 122–128, 2004 • Copyright  by Walter de Gruyter • Berlin • New York Organosolv pulping of olive tree trimmings by use of ethylene glycol/soda/water mixtures Luis Jimenez 1, *, Alejandro Rodrıguez 2 , Manuel ´ ´ Jasus Dıaz 3 , Francisco Lopez 3 and Jose Ariza 3 ´ ´ ´ ´ 1 Department of Chemical Engineering, University of Cordoba, Spain ´ 2 Department of Environmental Science, University Pablo de Olavide, Seville, Spain 3 Department of Chemical Engineering, University of Huelva, Spain *Corresponding author. Departamento de Ingenierıa Quımica, Campus de Rabanales. ´ ´ Edificio C-3, Universidad de Cordoba, Cordoba, Spain. ´ ´ Tel: q34 957 218658 Fax: q34 957 218625 E-mail: iq1jiall@uco.es Abstract This paper reports on the influence of independent vari- ables in the ethylene glycol/soda pulping of olive wood trimmings (165–1958C, 30–90 min, ethylene glycol con- centration 5–15%, soda concentration 2.5–7.5% and liq- uid/solid ratio 4–6), on the yield and Kappa index of the pulps and the strength properties (breaking length, burst index and tear index) of paper sheets. By using a central composite factorial design, equations that relate each dependent variable to the different independent variables were obtained which reproduced the experimental results for the dependent variables with errors less than 12%. Using a temperature of 1848C, ethylene glycol and soda concentrations of 15% and 7%, respectively, a liquid/sol- id ratio of 5:1 and a cooking time of 30 min results in yield, Kappa index, breaking length, burst index and tear index values that depart by 14.3%, 8.2%, 17.1%, 17.0% and 2.3%, respectively, from their optimum levels. These conditions result in substantial savings in power con- sumption and immobilised capital investments as they involve a lower temperature, a lower liquid/solid ratio, and a shorter time than the maximum values tested. Keywords: organosolv; ethylene glycol; soda pulping; pulp; paper; strength properties; agricultural residues; olive tree. Introduction The current annual production of pulp falls short of the demand, which is growing very rapidly especially in developing countries, and even in some developed ones; with antecedent gradual shortage of wood raw materials and the consequent deforestation of some areas of the planet. This has aroused interest in the use of wood and non-wood agricultural residues as pulp raw materials. In Spain, olive tree trimmings are very abundant and a promising source of pulp. Spain produces a vast amount of trimming residues from olive trees (over 2 million tons each year, of which more than 60% is generated in Anda- lusia) (Jimenez et al. 1997a). Such residues lack specific ´ uses, so they are generally burned on site, which increas- es air pollution and the risk of fire. The pulping of raw materials to obtain cellulose pulp produces large amounts of highly polluting waste water (particularly if it contains sulphur compounds, as in the sulphite and kraft pulping processes). Although the pos- sibility of obtaining cellulose pulp, using sulphur-free methods, has been known for some time, few such methods have been used on an industrial scale; also, many of them (particularly those based on organic sol- vents) have only recently started to be tested on a pilot plant scale (Jimenez et al. 1997b; Hergert 1998; Gilarranz ´ et al. 1998). Scarcity of effective alternatives to conventional pulp- ing has generated substantial interest in new procedures, and even some processes that were discarded on vari- ous grounds long ago are being revisited in the light of the new economic and environmental demands. As not- ed earlier, the annual production of pulp falls short of the demand; this has fostered the establishment of new industrial plants requiring modest investment, lower pro- duction costs and lower environmental impact, as well as efficient use of the raw materials (by maximising yields); all this can be achieved by using sulphur-free, solvent-based pulping processes. According to Aziz and Sarkanen (1989) and Dahlmann and Schroeter (1990), the earliest references to deligni- fication with organic solvents date from 1983, when Kla- son used ethanol and hydrochloric acid to obtain pulp. In the 1930s, Aronovsky and Gortner, and Kleinert and Tayenthal conducted interesting research on this topic that was followed by the work of Brounstein in the 1950s and that of Kleinert in the 1970s (cited in Aziz and Sar- kanen 1989; Dahlmann and Schroeter 1990; Jimenez et ´ al. 1997b; Gilarranz et al. 1999); until then the prevalence of traditional chemical pulping processes had never been challenged. Since the 1970s, however, attempts at circumventing the typical shortcomings of the traditional processes (viz., unpleasant odours, poor yields, heavy pollution, dif- ficulties in bleaching pulp, large investments and high water, power, reagent and raw material consumption, among others) were made by modifying the existing pro- cesses first and then developing new, sulphur-free ones; the new processes, however, were also confronted with other problems such as the difficulty of recovering the reagents and their polluting nature (Cox and Worster 1971). Since the 1980s, organic solvent-based pulping pro- cesses have been revisited as alternatives to the tradi- tional processes. The principal advantage of processes using organic solvents was that they extracted the full