Experimental and modelling study of nanofiltration focused on seawater desalination
- Autores: Laia Llenas Argelaguet
- Directores de la Tesis: Miquel Rovira Boixaderas (dir. tes.), Xavier Martínez-Lladó (codir. tes.)
- Lectura: En la Universitat Politècnica de Catalunya (UPC) ( España ) en 2011
- Idioma: español
- Tribunal Calificador de la Tesis: José Luis Cortina Pallás (presid.), Andriy Yaroshchuk (secret.), Verónica García Molina (voc.), Joan Llorens Llacuna (voc.), Darren L. Oatley (voc.)
- Materias:
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- Resumen
The hydrosphere covers more than the 70% of the Earth¿s surface, which represents 1.38 billion Km3 of water. However, only the 3% of this water corresponds to freshwater, and saline sources represent the 97% of the total water on the Earth.
Consequently, to capture even just a tiny fraction of these salty sources to obtain freshwater could have a huge positive impact on water scarcity.
The main problem of seawater desalination as a freshwater source is the high cost of obtaining desalted water, so there is a need to improve desalination technologies with the final aim of supplying low-cost freshwater. In seawater reverse osmosis desalination, one of the options to reach this goal is to add a good pretreatment in order to avoid membrane fouling, and for the specific case of scaling, nanofiltration is one of the most suitable solutions.
Nowadays it has been demonstrated that the use of nanofiltration membranes for seawater desalination pretreatment is a very good option for scale prevention. However, the most suitable NF membranes for this purpose are still to be determined.
Currently, there are many different types of NF membranes, and one of the objectives of this thesis is to research, at laboratory scale, the productivity and the selectivity of various NF membranes in order to resolve which of these are more suitable for scale prevention in seawater reverse osmosis desalination.
To select the most suitable nanofiltration membrane, as well as to design and optimise a process, an indispensable tool is to have a good model to describe the membrane rejection mechanisms. Nanofiltration is an extremely difficult process to describe theoretically as several complex physic-chemical phenomenons are occurring simultaneously. The events leading to rejection at nanofiltration membranes are taking place on a length scale of the order of 1 nm, a scale not much greater than atomic dimensions. At present, there are so many models to describe the behaviour of nanofiltration membranes and to predict their rejection. A good predictive model allows us ers to obtain membrane¿s characteristics, to predict a process performance and to optimise it. In this thesis, different descriptions of the nanofiltration process are studied and improved in order to contribute to the development of models for nanofiltration behaviour prediction.
One of the simplest models for describing the rejection of nanofiltration membranes is the so called Spiegler Kedem model. This model has been applied to different one single salt rejection data, and the variations of the model parameters have been studied.
Another option to describe nanofiltration is using the Solution Diffusion Model. This model has been applied to different single salt rejection experiments taking into account the concentration polarisation. But the most innovative thing is that an extended version of Solution Diffusion Film Model has been developed to predict the performance of NF membranes in case of having a solution with a dominant salt and trace ions. Different permeability values have been obtained in order to know which is the membrane¿s behaviour in different case studies.
One of the most used models in the literature, the Donnan Steric Partitioning Model, has also been studied. Previous to the model application, a characteris ation of the nanofiltration membranes has been carried out by determining the membrane's pore size, roughness and isoelectric point. As an innovative as pect, the dielectric constant inside the membrane¿s pores has been determined for three NF membranes: firstly, the only data of this parameter available in the literature has been verified, and it was for the Desal-5-DK membrane; then the dielectric constant inside the pores has also been determined for two other membranes, NF270 and NF99HF. Finally, also as an innovative thing, the dependence of the dielectric constant inside the pore with the salt present in the feed solution has also been studied.
