Cross-polymerisation between the model furans and carbohydrates in bio-oil with acid or alkaline catalysts

Understanding the potential cross-polymerisation between the main components in bio-oil is essential to develop the method to minimize the coking in hydrotreatment of bio-oil or to maximize the production of carbon material from bio-oil. In this study, the potential cross-polymerisation between furfural and the sugars (xylose and glucose) and the impacts of acid/base catalysts on the polymerisation reactions were investigated. The results indicated that the cross-polymerisation of furfural/xylose and furfural/glucose existed in absence of catalyst, and the extent was more significant for that between furfural and glucose. The strong acid promoted the cross-polymerisation while the weak organic acid like acetic acid and the strong base like NaOH did not. The cross-polymerisation of furfural/sugars produced the more hydrophilic carbonaceous spheres that tended to merge to form bigger particles. The polymerisation of furfural involved opening of the furan ring via hydrolysis, forming oxygen-containing intermediates, while glucose/xylose were more reactive towards polymerisation reaction via dehydration route. The polymers from the sugars were more aliphatic than that from furfural, especially for that from glucose, leading to their lower thermal stabilities. The cross-polymerisation also affected the size/ abundance of the pi-conjugated structures in the soluble polymers and the relative ratio of the C=O/C=C in the resulting insoluble polymer. (C) 2020 Energy Institute. Published by Elsevier Ltd. All rights reserved.