Separation of Sulphuric Acid from an Acid Suspension of Cellulose Nanocrystals by Manual Shaking

In this paper, the separation of sulphuric acid from a suspension of cellulose nanocrystal by manual shaking is described. Cellulose nanocrystals are prepared from acid hydrolysis of cotton using 64 wt% sulphuric acid at ca. 45 degrees C for 45 minutes. After the hydrolysis was complete, water was added to dilute the mixture to a resulting concentration of 30 wt% of the acid. This mixture was shaken rigorously in a closed container and after 48 hours, separation occurs such that cellulose nanocrystals float, with the bubbles introduced by the shaking, to give clear acid solution at the bottom. This shaking-floating process is repeatable for several cycles after the acid was removed from the bottom and more water was added. Using this simple process, the total acid recovery of > 90% has been achieved, and the concentration of all the acid recovered combined was 17.5 wt%. This work demonstrates a method that allows energy efficient and up-scalable separation of cellulose nanocrystals from the acidic suspension from which it was extracted.