Nanofiltration membranes review: Recent advances and future prospects

Advances in seawater desalination technologies

Desalination technologies improve water quality, greatly reduce water shortage problems, and improve quality of life and economic status. Two main technologies are currently used in water desalination: thermal (phase-change) processes and membrane processes. The primary thermal distillation processes include multistage flash distillation (MSF), multi-effect distillation (MED), and vapor compression (VC). The VC process encompasses two types: mechanical (MVC) and thermal (TVC). The common membrane desalination processes include reverse osmosis (RO) and electrodialysis (ED and EDR). Energy cost, operational and maintenance cost, and capital investment are the main contributors to the water production cost of any of these processes. The energy cost is responsible for about 50% of the produced water cost. For thermal distillation processes (MSF, MED, and TVC), two energy forms are required for the operation: (1) low-temperature heat, which represents the main portion of the energy input and is usually supplied to the system by a number of external sources (e.g., fossil fuel, waste energy, nuclear, solar) and (2) electricity, which is used to drive the system's pumps and other electrical components. For the MVC thermal distillation process, only electricity is needed. For membrane processes (RO and ED), only electricity is required as an energy input. Renewable energy systems such as solar thermal, solar photovoltaic, wind, and geothermal technologies are currently used as energy suppliers for desalination systems. These renewable resources are now a proven technology and remain economically promising for remote regions, where connection to the public electric grid is either not cost effective or feasible, and where water scarcity is severe. As the technologies continue to improve, and as fresh water becomes scarce and fossil fuel energy prices rise, renewable energy desalination becomes more viable economically. The technical features, energy consumption, environmental considerations, and potential of renewable energy use in driving the main desalination processes are reviewed and analyzed in this paper. The current and projected costs of water produced from conventional and renewable-energy-driven processes are discussed and compared.

Energy Consumption and Water Production Cost of Conventional and Renewable-Energy-Powered Desalination Processes

Desalination of seawater and brackish water is becoming an increasingly important means to address the scarcity of fresh water resources in the world. Decreasing the energy requirements and infrastructure costs of existing desalination technologies remains a challenge. By enabling the manipulation of matter and control of transport at nanometer length scales, the emergence of nanotechnology offers new opportunities to advance water desalination technologies. This review focuses on nanostructured materials that are directly involved in the separation of water from salt as opposed to mitigating issues such as fouling. We discuss separation mechanisms and novel transport phenomena in materials including zeolites, carbon nanotubes, and graphene with potential applications to reverse osmosis, capacitive deionization, and multi-stage flash, among others. Such nanostructured materials can potentially enable the development of next-generation desalination systems with increased efficiency and capacity.

https://iopscience.iop.org/article/10.1088/0957-4484/22/29/292001/pdf

Nanostructured materials for water desalination.

Due to the drive for better environmental protection and energy conversion efficiency, on-site generation of CO x -free hydrogen from ammonia decomposition for fuel cell applications has attracted much attention. The development of high performance solid catalysts is essential for the supply of such hydrogen from ammonia. In this mini-review, we provide a summary of the reaction kinetics of catalytic ammonia decomposition. Comparisons are then made among the catalysts that have different active components, supports, and promoters. According to the works reported in the literature and our recent research results, Ru is the most active catalyst, carbon nanotubes (CNTs) are the most effective support, and KOH is the best promoter. An increase in Ru dispersion results in better catalytic performance. Both support basicity and conductivity are important criteria for a NH 3 decomposition catalyst of high efficiency; and it seems possible to generate novel advanced support, such as oxide-CNTs nanocomposite materials, that bears such characteristics. Also, proper removal of the electron-withdrawing entities that originate from the precursors of active component, support or promoter can be effective in enhancing the catalytic activity of a Ru catalyst.

Ibrahim S. Al-Mutaz

Papers

Pretreatment and the effect of cations and anions on prevention of silica fouling

Comparative performance evaluation of conventional multi-effect evaporation desalination processes

Development of a steady-state mathematical model for MEE-TVC desalination plants

Adsorption-membrane filtration (AMF) hybrid process for boron removal from seawater : an overview

Prediction of physical properties of nanofiltration membranes using experiment and theoretical models