Effect Of Cellulose Supramolecular Structure On The Conversion Of Waste Paper Fiber To 5-Hydroxymethyl Furfural In Hot Compressed Water

Waste paper fiber which contains abundant cellulose can be converted into 5-HMF(5-hydroxymethyl furfural) and other high value-added biopolymers in HCW(hot compressed water), and it not only reduce the environment pollution but also ensure the efficient resource utilization of waste paper fiber. This is significant to change the energy structure, improve ecological environment, and promote the sustainable development of society. However, the order degree of cellulose molecule chains is increased and the rearrangement is took place between different hydrogen bonds after the treatment of the physical and chemical process of the papermaking. It makes a contribution to the more complex supramolecular structure of cellulose in waste paper fiber. All these can influence the rate of decrystallization and depolymerization of cellulose and the subsequent reactions. Therefore, study on the relationship between cellulose supramolecular structure and the conversion property of waste paper fiber in HCW is essential.Waste paper fiber was treated in HCW to study the conversion property and the changes of cellulose supramolecular structure. This paper also analyzed quantificationally the influence of supramolecular structure changes on yield of 5-HMF. Finally, the different kinetics characteristics between cellulose de-crystallization and depolymerization in HCW was investigated. This study aimed to preliminarily clarify the conversion mechanism of waste paper fiber in HCW, and lay a theoretical foundation for waste paper fiber to reusable resource, especially value-added products. It was found that:It’s benefit for the accumulation of hexoses at higher concentration of waste paper fiber in HCW, but it helped produce more LA at lower concentration of waste paper fiber in HCW. Pressure had great influence on 5-HMF yield. The maximum yield of 5-HMF can be obtained with 10.92%±0.51% under the optimal conditions as follows: the raw material concentration 2.4%, pressure 19.2MPa, temperature 375°C, reaction time 200 s.Reciprocal transformation occurred between intermolecular and intramolecular hydrogen bonds during cellulose hydrolysis process. Crystallinity and microcrystalline parameters of cellulose increased first and then decreased while the increasing of reaction time. The 5-HMF yield was increased with the increase of intermolecular hydrogen bonds content in cellulose residual and was increased first and then decreased with the increase of crystallinity of cellulose residue. Reaction time as a macro method for adjusting and controlling supramolecular structure of cellulose during conversion of waste paper in HCW was feasible.Cellulose Iβ converted to cellulose Iα in HCW under the combined action of hydrogen bonds rearrangement and the generation of unusual conformations of the glycosidic linkage. Waste paper with lower crystallinity can produce more oligosaccharides in HCW. And the yield of oligosaccharides with low degree of polymerization(DP) was influenced by the molecule structure of waste paper fiber more obviously.The rate of cellulose dissolution was increased with temperature. Arrhenius of de-crystallization was 140.7 k J/mol which was higher than that of depolymerization(EH = 84.5 k J/mol). The rate of cellulose de-crystallization was always slower than that of depolymerization in HCW. Cellobiose decomposition was faster than their formation in supercritical water but was slower than their formation in subcritical water. Based on the differences between cellulose de-crystallization and depolymerization, we can choose the suitable reaction conditions(eg. temperature, time and so on) to obtain different target products. This is instrumental in the conversion of waste paper fiber in HCW.