In our conceptual design shown in Figure , the first 10 UF stages are employed to purify CNC by adding fresh water to the feed stream for each UF stage. The UF stages will be constrained by the post-treatment: a low CNC concentration means a high energy consumption for water evaporation, while a CNC concentration higher than 2 wt.% can cause clogging issues for the spray-drying nozzle . As such, the 11 th stage stops the addition of water and is desired to concentrates the CNC suspension from 1 to 2 wt.%. Purity of the final CNC product is determined by the amount of water used in the UF cascades and the total membrane surface area. Details of the UF models are given in SI Eqs. 13-20. In the current design, each UF stage can roughly reduce 50% of the impurities (sugars or acid), so the 10 th UF can achieve a negligible impurity concentration at 0.01 wt.% while maintaining CNC concentration at 1 wt.% on the retentate side (SI Figure ). The energy consumption for UF is mainly due to the pumps for increasing feed pressure and for water. More details for the design and calculations of the UF sub-systems can be found in SI S1.3.