CHEMICAL RECOVERY IN NONWOOD PULPING BASED ON FORMIC ACID

摘要

Because the supply of wood cannot meet the growing demand for paper, utilization of nonwood materials is becoming increasingly important. One of the main drawbacks in nonwood papermaking to date has been an incomplete chemical recovery in conventional alkaline pulping technology, which has led to poorly profitable and polluting production. The present paper describes the principles of chemical recovery in a novel nonwood pulping process based on formic acid. The main parts of the chemical recovery are evaporation of spent cooking liquor and distillation of washing filtrates. Based on experimental and computational results, the present paper illustrates the favourable features of evaporation and principles of distillation in such a process. According to results, spent cooking liquor can be evaporated to over 90% dry solids and formic acid can be recovered practically completely. Evaporation consumes minor quantities of energy and favourable features of chemical recovery enable self-sufficiency of the pulping process in terms of energy. The load and cost of distillation depend on the selected cooking conditions and applied quantity of water in washing.