Recovery of Dialcohol Cellulose using Micro- and Ultrafiltration Processes

Abstract: The waste management and production of plastic play a concerning part in global warming and continues to have a negative effect on the environment. A promising strategy to address this challenge is to develop new sustainable materials, to replace current fossil-based plastics. Cellulose is of interest to be used for bio-based materials since it has many desired properties. However, it lacks the formability that petroleum-based materials provide. Converting cellulose into dialcohol cellulose (DAC) is a way to increase the flexibility. DAC is achieved by an oxidation followed by a reduction of cellulose, resulting in an open-ring structure. When producing DAC, it is of interest to increase the yield in the production by implementing a membrane filtration step to concentrate and separate the otherwise lost DAC in the process water. As separation processes commonly account for a major part of the energy and capital cost of a plant, it is of interest to optimise this process to keep costs low whilst still achieving a sufficient separation. The aim of this thesis was to optimise a membrane filtration process for separating reactants, products, and by-products in process water from the production of DAC. This was done by screening six different membranes, three microfiltration (MF) and three ultrafiltration (UF) membranes, to find the best membrane and optimal operating conditions, based on flux, retention of solutes and fouling. When the optimal conditions and most suitable membrane was chosen, it was examined to what degree it was possible to concentrate the solutes and if the membrane filtration process was affected by using process water provided by Tetra Pak compared to process water produced for this thesis. DAC with different degree of oxidation (DO) was successfully produced for this thesis. The produced DAC used for the concentration had a DO of 58% and a yield of 45%. If using the process water from different reaction steps in the production of DAC affected the concentration was also examined. The results from the screening showed that an ultrafiltration membrane, ETNA10PP, was the most suitable to concentrate the solutes. The optimal operating conditions were concluded to a cross flow velocity of approximately 0.3 m/s with a transmembrane pressure of 8 bar. These parameters gave a retention of 0.943 when using the reduction step process water from Tetra Pak and a retention of 0.980 when using the reduction step process water produced for this thesis. Further, it was seen that the retention for the process water from the oxidation step was significantly lower than that from the reduction step.