Use of formaldehyde for making wheat straw cellulose pulp

Abstract

A central composite design was used to investigate the influence of the cooking conditions (time, temperature and formaldehyde concentration) for wheat straw with formaldehyde–water mixtures on the properties of the pulp obtained (yield and holocellulose, α-cellulose, lignin and ethanol–benzene extractives contents) and the pH of the resulting wastewater. A second-order polynomial model consisting of three independent process variables was found to accurately describe the organosolv pulping of wheat straw. The equations derived predicted the yield, the holocellulose, α-cellulose, lignin and ethanol–benzene extractives contents of the pulp, and the pH of the wastewater with multiple- R, R 2, adjusted- R 2 and Snedecor F values of 0.99, 0.99, 0.99 and 321.33; 0.98, 0.95, 0.92 and 35.01; 0.92, 0.86, 0.78 and 10.68; 0.99, 0.97, 0.96 and 68.19; 0.91, 0.83, 0.80 and 29.68; and 0.97, 0.95, 0.93 and 46.10, respectively. While ensuring a high holocellulose content and low lignin and ethanol–benzene-extractive contents entails using high levels of the process variables involved, a compromise can be made in order to achieve both the previous objectives and a high α-cellulose content provided a long cooking time, a high temperature and a low formaldehyde concentration are used – alternatively, a long time, a high formaldehyde concentration and a low temperature can be equally effective and save energy. The yield, pH and holocellulose, α-cellulose, lignin and alcohol/benzene extractive contents are more sensitive to changes in the cooking time than they are to modifications of the formaldehyde concentration.