Understanding the effect of severity factor of prehydrolysis on dissolving pulp production using prehydrolysis kraft pulping and elemental chlorine-free bleaching sequence

Abstract

Prehydrolysis kraft pulping is an effective approach to produce dissolving pulp, which can be used for viscose application. The prehydrolysis process using hot liquid water could remove hemicellulose and loosen the compact cell wall, thus facilitating subsequent pulping and bleaching processes. In this study, the composite severity factor (CSF) was used to reveal the intensity of prehydrolysis treatment and its effect on the pulping and bleaching process by combining the temperature, time, and pH variables. Results showed that the optimum CSF was 6.61, which produced a pulp with α-cellulose of 92.3%, degree of polymerization (DP) of 1081, brightness of 85.1% ISO, and Kappa number of 0.61. In addition, the fiber quality, crystalline structure, and microstructure of pulps were characterized by FQA (fiber quality analysis), XRD (X-ray diffraction), and SEM (scanning electron microscopy).

Processes and Challenges for the Manufacturing of Lyocell Fibres with Alternative Agricultural Feedstocks

“…The feedstock for L-MMCF is any lignocellulosic material (i.e., comprised of holocellulose (cellulose and hemicellulose), lignin, extractives, and ash), with the relative proportion of lignocellulosic content dictating the chemistry and conditions required for conversion to high alpha-cellulose suitable for L-MMCF production [71]. Regardless of the source, the fibres first need to be chipped or cut into consistently sized pieces to ensure evenness during the pulping process.…”

“…Additionally, PHK pulps typically have a higher alpha cellulose content when compared to AS pulps [62]. The prehydrolysis stage in PHK pulps is imperative for the removal of hemicellulose and partial removal of lignin prior to the pulping process [18,62,71]. This section and the rest of the paper focuses on PHK pulp preparation since it is readily available, utilises chemical recovery, has a higher fibre strength lending towards a higher DP, and has a higher alpha cellulose content when compared to AS pulp.…”

“…Feedstocks for PHK undergo prehydrolysis in a hot, weak acid solution (e.g., deionised water at 150-180 • C for 60 min; 0.5% H 2 SO 4 at 150 • C for 90 min) prior to the Kraft pulping process to remove the hemicellulose content [62,71,82,89]. During prehydrolysis, acetyl groups are liberated via auto-hydrolysis, creating an acidic solution, which is opposite of the highly alkaline Kraft pulping process [18,82].…”

“…During prehydrolysis, acetyl groups are liberated via auto-hydrolysis, creating an acidic solution, which is opposite of the highly alkaline Kraft pulping process [18,82]. The acid condition reduces the molecular size of hemicellulose, allowing it to be easily removed from the pulp [71]. Prehydrolysis results in a higher alpha-cellulose pulp than just Kraft pulping alone, which is ideal for the dissolving pulp stage.…”

“…Prehydrolysis results in a higher alpha-cellulose pulp than just Kraft pulping alone, which is ideal for the dissolving pulp stage. However, acid prehydrolysis can result in the hydrolysis of the alphacellulose, causing a decrease in DP, so careful monitoring is required to ensure higher yield pulps [71,90,91]. Additionally, under acidic conditions, lignin can self-condense or react with phenol, making it more difficult to remove lignin content (i.e., delignification) during the pulping process (i.e., cooking) [82].…”