Reverse Osmosis

Fauzi Ismail, Kailash Chandra Khulbe, Takeshi Matsuura

• Publisher: Elsevier
• Year: 2018
• Print ISBN: 9780128114681
• eBook ISBN: 9780128115398
• Topic: Physical Sciences
• Subtopic: Industrial & Technical Chemistry

Reverse Osmosis starts with an overview of the historic development of the RO membrane, the RO process, and its effect on other membrane separation processes. Other chapters cover the development of nanocomposites of TFC membranes and modern membrane characterization techniques, such as TEM, AFM and PALS, the RO membrane transport model, and RO membrane fouling. The book also describes, in detail, experimental methods for setting up RO experiments, RO membrane modules, RO membrane systems, and desalination and water treatment by RO. Applications in food, pharmaceutical, chemical, biochemical, petroleum and petrochemical industries are also summarized. Other sections cover the development of RO membranes with high thermal and chemical stability, attempts to develop polymeric or inorganic membranes, and hybrid processes where RO is combined with forward osmosis (FO) or membrane distillation (MD). - Written by renowned experts in the field who have complementary expertise - Provides an in-depth discussion of reverse osmosis transport based on nano-level membrane structure - Comprehensively reviews recent progresses in novel reverse osmosis membrane development

Chapter 1

Introduction—Do RO Membranes Have Pores?

Abstract

In this chapter an attempt is made to review the progress in membrane characterization and transport theory in historical perspective. Its central theme is the membrane “pore” around which all progress has been revolving, irrespective of whether the researcher is “for” or “against” the existence of pores at the top dense layer of the RO membrane.

Keywords

Reverse osmosis membrane; Membrane transport; Preferential sorption-capillary flow model; Solution-diffusion model; Membrane characterization; Molecular dynamic simulation; Bimodal pore size distribution

Acronym

AFM atomic force microscopy

CA cellulose acetate

DMSO dimethyl sulfoxide

FO forward osmosis

MD molecular dynamics

MF microfiltration

MPD metaphenylene diamine

NF nanofiltration

PA polyamide

PALS positron annihilation spectroscopy

PRO pressure retarded osmosis

PS-CF preferential sorption-capillary flow

RO reverse osmosis

SANS small-angle neutron scattering

S-D model: solution-diffusion model

SEM scanning electron microscope

SWCNTs single walled carbon nanotubes

TFC thin film composite

TMC trimesoyl chloride

UF ultrafiltration

When one of the coauthors (TM) arrived at Dr. Sourirajan's laboratory at the National Research Council of Canada in October 1968, Dr. Sourirajan gave him a manuscript of the book “Reverse Osmosis,” which was later published in 1970 [1]. He read the book eagerly and was especially fascinated by the chapter, where Sourirajan wrote how he had launched his reverse osmosis (RO) research. According to the book, the invention of the Loeb-Sourirajan RO membrane for seawater desalination was made on the basis of the Preferential Sorption-Capillary Flow (PS-CF) model. As the name of the model implies, pores are required for the transport of water through the RO membrane.

In the 1960s, the solution-diffusion model (S-D model) was presented by Lonsdale [2] and it soon became the mainstream of the RO transport model. Since Lonsdale regarded the pores as the defects of the nonporous semipermeable membrane, S-D model has been used for a long time to justify the nonexistence of pores in the perfect dense layer of the RO membrane. It should, however, be pointed out that the S-D model is neutral on this issue and does not say anything about the presence or the absence of pores. It might also be noteworthy to mention that many researchers seemed to believe the presence of pores in the RO membrane deep in their mind. One of the coauthors (TM) remembers the Gordon Conference held in the 1980s where many heated discussions were exchanged on the presence or the absence of pores in the RO membrane. In one of the conferences W. Pusch, Max Planck Institute, Germany, asked the conference participants if they were pore-philic or pore-phobic. To my surprise, more than half raised their hands to show that they were pore-philic.

In Sourirajan's laboratory, attempts were continued to interpret the experimental data based on the pore model, which eventually led to the concept of the bimodal pore size distribution comprising the “network pore” and “aggregate pore” [3, 4]. However, when the bimodal distribution was proposed in 1984, it was almost completely ignored by the membrane community, evidenced by very few citations the paper received. Computer did not count the number of citations those days but we could feel how unpopular the theory was.

In the meantime, the membrane characterization techniques were making remarkable progress. In the 1960s and 1970s, the only characterization tool was scanning electron microscope (SEM) that did not allow the resolution below 10 nm when the polymeric membrane surface was investigated. Needless to say that it was impossible to observe the sub-nanometer pores at the membrane surface and, therefore, the top skin layer was generally thought to be dense and homogeneous.

In 1994, a paper on the characterization of cellulose acetate (CA) RO membranes by small-angle neutron scattering (SANS) appeared all of a sudden. In the paper S. Krause, Rensselaer Polytechnic Institute, Troy, New York, concluded that SANS data could be explained by the bimodal distribution of pores in the dense skin layer of CA RO membrane.

As the industrial membrane fabrication method shifted from the phase inversion technique of CA membrane to thin-film composite (TFC) polyamide membrane, so did the membranes as the object of membrane characterization. Nowadays most of the characterization methods are applied to TFC polyamide membranes.

Particularly, positron annihilation spectroscopy (PALS) gained popularity in the beginning of the millennium to characterize the synthetic polymeric membranes for various applications. In the PALS papers the term “free volumes” ...

Table of contents

• Cover image
• Title page
• Table of Contents
• Copyright
• Preface
• Chapter 1: Introduction—Do RO Membranes Have Pores?
• Chapter 2: RO Membrane Preparation
• Chapter 3: RO Membrane Characterization
• Chapter 4: RO Membrane Transport
• Chapter 5: RO Membrane Module
• Chapter 6: Hybrid System
• Chapter 7: RO Economics
• Chapter 8: RO Membrane Fouling
• Chapter 9: RO Applications
• Chapter 10: Organic Solvent NF (OSN)
• Index