Furfural (FF) is a typical pyrolytic product formed from both of cellulose and hemi — cellulose. It is widely used as an organic solvent or an organic reagent for the produc­tion of medicines, resins, food additives, fuel additives, and other special chemicals. Currently, FF is industrially produced from agricultural raw materials rich in pentosan. By aqueous acid catalysis (e. g., sulfuric acid or phosphoric acid), the pentosan is firstly hydrolyzed to pentose which is then dehydrated to form FF [96].

Similar as the LGO and LAC, the formation of FF can be promoted in the acid — catalyzed pyrolysis of biomass [2, 29, 30, 50, 85, 89]. Zinc chloride (ZnCl2) is one of the promising catalysts to produce FF. It was found that fast pyrolysis of cellulose impregnated with small amounts of ZnCl2 (below 10 wt%) would generate several dehydrated products as the primary pyrolytic products, mainly the FF, LGO, LAC, and 1,4:3,6-dianhydro-a-D-glucopyranose (DGP). With the increasing of ZnCl2 impregnation (at least 15 wt% or more), the ZnCl2 catalysis would increase the FF formation, while decrease the anhydrosugars. Moreover, the secondary catalytic cracking of the primary pyrolysis vapors by ZnCl2 could promote the conversion of LGO and other anhydrosugars to FF, leaving the FF as the only predominant product (Fig. 7). Compared with the cellulose, the ZnCl2-catalzyed fast pyrolysis of xylan would obtain the FF as the only predominant product, and the FF yield would be higher than that from cellulose, indicating that biomass rich xylan would be suitable for the FF production.

In another study, microwave-assisted fast pyrolysis was applied to treat biomass mixed with various catalysts, and the results revealed that the MgCl2 exhibited high selectivity on the FF production [93]. The highest FF content was more than 80% (peak area% on the GC/MS ion chromatograms) at the 8 g MgCl2 mixed with 100 g biomass.

In addition, ZnCl2 (or sometimes MgCl2 ) is an effective chemical activation agent for the production of activated carbons from biomass. Hence, for the biomass pretreated by ZnCl2 (or MgCl2) impregnation, they can be firstly subjected to fast pyrolysis to produce FF. The solid residues which contained char and ZnCl) (or MgCl2) could be further activated to produce activated carbons, so as to achieve the coproduction of FF and activated carbons.