Recycling of isopropanol for cost-effective, environmentally friendly production of carboxymethylated cellulose nanofibrils

•Presence of water in the reaction medium derived from wet pulp decreases the carboxymethylation reaction of pulp.•Dehydration of reaction medium was achieved by molecular sieve treatment.•This dehydration treatment gave the same level of carboxylation irrespective of the recycling of reaction medium.•The characteristics of carboxymethylated pulp and CNF produced using dehydrated reaction medium remained the same.•This will provide the cost-saving and environmental protection opportunity in CNF production. An approach to recycling isopropanol used in the carboxymethylation of pulp fiber was investigated as a cost-effective and environmentally friendly method of producing cellulose nanofibrils (CNF). Carboxymethylation of pulp fiber was carried out using isopropanol (IPA) as the sole solvent. IPA was recovered after carboxymethylation reaction and recycled in the next carboxymethylation reaction. Simple recycling of IPA decreased the reaction efficiency of carboxymethylation due to the increase of water content in the IPA. To dehydrate the recovered IPA, a 4 Å molecular sieve was used as a drying material. It was shown that dehydration restored carboxymethylation efficiency to the same level as when fresh IPA was used. The characteristics of the carboxymethylated CNFs produced using the recycled IPA were evaluated, including fibrillation tendency, average width, and width distribution, and it was shown that the use of recycled IPA after dehydration treatment did not cause any changes in carboxymethylated CNF properties. Recycling IPA after simple dehydration using a molecular sieve is thus a cost-effective and environmentally friendly method of producing carboxymethylated CNF.