Mechanism of xanthation reaction in viscose process

Xanthation reaction in viscose process is heterogeneous reaction (gaseous CS 2 -wet alkaline cellulose) complicated with side reactions. Commercial requirement of CS 2 in viscose process is 32–34%, which is significantly higher than the stoichiometric requirement (23.5% w/w of the cellulose) due to formation of byproducts. Detailed xanthation reaction kinetics study was performed to understand the xanthate and by-products formation mechanism along with effect of mass transfer and its possible impact on CS 2 consumption. Heterogeneous nature of the xanthation reaction offers significant mass transfer resistance and was hypothesized to be driven by CS 2 partitioning into wet alkali cellulose and its unstable complex (DTC—dithiocarbonate) formation with alkali. Xanthation reaction mechanism in the form of physico-chemical process steps has been proposed with experimental justification. Graphical abstract