Furfural and hydroxymethylfurfural as by-products of FORMACELL pulping

The formation and stability of furans formed from pentoses and hexoses were studied in acetic acid / formic acid mixtures which are applied in the FORMACELL pulping process. For comparison, acetic acid / water mixtures with and without addition of HCl were included in the study. The investigations demonstrated that furfural can be obtained in high yields from xylose and xylan. Hexoses are converted to hydroxymethylfurfural (HMF), acetoxymethylfurfural (AMF) and furfural. Here, the water content of the reaction mixture influences the ratio of HMF and AMF in the solution. Stability studies revealed that furfural and HMF exhibit a high stability in acetic acid / formic acid mixtures. This explained the high furfural yields previously published for acetic acid pulping. The long-time stability of furans was investigated for 275 days at room temperature. No significant losses occurred suggesting that organic acids act as radical scavengers inhibiting oxidative degradation.