Fabrication of thin film nanocomposite pressure retarded osmosis (PRO) membranes using cellulose nanocrystal (CNC) and evaluation of performances in the processes

Abstract

Nowadays, owing to quick world population growth and abrupt economy, high water demands desire innovative technologies in order to ensure clean and safe water with lower energy use. Severe environmental emissions arising by the consumption of fossil fuels often needs us to build energy harvesting technology which are environmentally sustainable. As an advanced technology, osmotic membrane processes consisting of forward and pressure-retarded osmosis, are conceived to be conspicuous technologies for the treatment, recycling and reuse of wastewaters and the harvesting of salinity gradient energy which is called "Blue Energy". Nevertheless, forward osmosis (FO) and pressure retarded osmosis (PRO) are at the level of growth yet. It is difficult piece of work to fabricate osmotic membranes obtaine high water permeability and perfect ion retention. The ideal osmotic membrane candidate can be a thin film composite membrane satisfy the conditions which has high water permeation and as soon as low reverse salt flux ratio. Furthermore, for the membrane to endure relatively high hydraulic pressures in PRO systems, certain mechanical properties are vital. Thankfully, membranes that are fabricated with electrospinning method have an excellent capability to overcome all specifications of the perfect support layer in consequence of porous structure characteristics and simplicity with that nanomaterials may be integrated to enhance the nanofibers mechanical strength. Apart from this, interfacial polymerization (IP) may be accomplished to electrospun nanofiber membrane to achieve a very thin selective polyamide coating. TFN membranes may show tremendous potential in osmotically driven membrane processes after integrating nano additives into their support layer. The aim of this thesis to carry out and design a comprehensive study on the development of reinforced pressure retarded osmosis membranes. Specifically, this thesis presents the development of novel nanofiber supported thin film composite membranes with high water permeability and excellent selectivity for solvents, while showing an excellent mechanical strength for PRO processes. Interfacial polymerization reactions were used to construct very thin polyamide selective layer on the support, and electrospinning process was used to fabricate a number of support layers. Initially, we investigated the potential to use flat sheet electrospun polyacrylonitrile nanofibers as support support layer to fabricate PRO membranes. Polyamide TFCs were successfully applied on five different substrate containing 0,1,2,5,10% crystal nanocellulose (CNC) in 16% PAN polymer solution. PRO membranes successfully fabricated via tailor-made flat sheet fabrication unit. It is concluded that PAN and CNC generated a complete mixture according to SEM, FTIR, DMA & contact angle analysis findings.The addition of CNC improved the mechanical strength of PAN support layers which is the main phenomenon in PRO applications. The newly developed membrane can achieve a higher PRO water flux of 300 LMH, using a 1 M NaCl draw solution and deionized water feed solution. The corresponding salt flux is only 1.5 gMH. The reverse flux selectivity represented by the ratio of water flux to reverse salt flux (Jw/Js) was able to be kept as high as 200 L/g for PRO operation. Following the success of flat-sheet TFN PRO membrane fabrication, improvements need to be done to increase packing density of fabricated final membrane modules. In this point, we used a novel technique to fabricate tubular membranes for PRO applications. The newly fabricated membrane achieves a higher PRO water flux of 405.38 LMH with using a 1 M NaCl and a DI as feed water. The corresponding salt flux is found as 2.10 gMH which is higher than flat sheet membranes. The selectivity of the reversed flux represented by the ratio of the water flow to the reversed salt flux (Jw/ Js) was able to be kept as high as 193.03 L/g for PRO operation.As far as we know, the performance of the work developed membrane in this study has shown better performance than all PRO membranes reported in the literature previously.