Ethanol–acetone pulping of wheat straw. Influence of the cooking and the beating of the pulps on the properties of the resulting paper sheets

Abstract

The influence of independent variables in the pulping of wheat straw by use of an ethanol–acetone–water mixture [processing temperature and time, ethanol/(ethanol + acetone) value and (ethanol + acetone)/(ethanol + acetone + water) value] and of the number of PFI beating revolutions to which the pulp was subjected, on the properties of the resulting pulp (yield and Shopper–Riegler index) and of the paper sheets obtained from it (breaking length, stretch, burst index and tear index) was examined. By using a central composite factor design and the BMDP software suite, equations that relate each dependent variable to the different independent variables were obtained that reproduced the experimental results for the dependent variables with errors less than 30% at temperatures, times, ethanol/(ethanol + acetone) value, (ethanol + acetone)/(ethanol + acetone + water) value and numbers of PFI beating revolutions in the ranges 140–180 °C, 60–120 min, 25–75%, 35–75% and 0–1750, respectively. Using values of the independent variables over the variation ranges considered provided the following optimum values of the dependent variables: 78.17% (yield), 15.21 °SR (Shopper–Riegler index), 5265 m (breaking length), 1.94% (stretch), 2.53 kN/g (burst index) and 4.26 mN m 2 /g (tear index). Obtaining reasonably good paper sheets (with properties that differed by less than 15% from their optimum values except for the burst index, which was 28% lower) entailed using a temperature of 180 °C, an ethanol/(ethanol + acetone) value of 50%, an (ethanol + acetone)/(ethanol + acetone + water) value of 75%, a processing time of 60 min and a number of PFI beating revolutions of 1750. The yield was 32% lower under these conditions, however. A comparison of the results provided by ethanol, acetone and ethanol–acetone pulping revealed that the second and third process-which provided an increased yield were the best choices. On the other hand, if the pulp is to be refined, ethanol pulping is the process of choice.