Mechanism of purification of cellulose in acidified aqueous acetone

• Main Author: Awad El-Karim, Salah El-Din El-Siddique
• Language: English
• Published: 2009
• Online Access: http://hdl.handle.net/2429/7183

This project deals with solvent purification, a new approach for the preparation of high-yield dissolving pulp with characteristics similar to those recommended by the standards. At the same time, the solvent purification technique aims at removing and recovering chemically unmodified, low molecular weight sugars that could further be processed as by-products. In addition, the process offers a reduction in waste water amounts associated with dissolving pulp purification and economical reuse of the solvent. Thus, environmental abatement is also taken into account. The current technology is unable to achieve these goals. The major objective of this work is the elucidation and characterization of the mechanism of the solvent purification process, i.e., the acetonation mechanism. In this thesis a detailed study on the mechanism of purification of cellulose in acidified aqueous aceton has been carried out. The mechanism has been proved to be of a physico-chemical character. The physical phenomenon has been found to be based on the H-bond disruption/destruction in crystalline cellulose by acetone as a solvent. On the other hand, the chemical hypothesis of the mechanism is verified to be the formation of isopropylidene groups on carbohydrate chains that leads to disproportionation of the polymer and protection of the sugar ring. The validity of these hypotheses has been investigated as follows; cotton has been used throughout this study as a model compound and different techniques such as DRIFT, Ge, HPLC, C-13 CP/MAS solid state NMR, X-ray diffraction, GPC, and viscosity measurements have been employed. Factors affecting solvent purification treatment such as acidity, residence time, temperature, type of acid, and acetone concentration have also been investigated. The investigation of those factors was conducted in a manner that has helped elucidation of the acetonation mechanism rather than optimization of the solvent purification technique. Their impact on hydrogen bonding (1st hypothesis) and isopropylidenation (2nd hypothesis) has been observed to vary considerably. Results obtained on hydrogen bonding, sugar derivatives, crystallinity, molecular weight distribution, and viscosity of cotton residues are in accord with the above assumptions. Based on the experimental findings of this work, a mechanism of purification of cellulose in acidified aqueous acetone is described.