Reverse osmosis membranes oxidation by hypochlorite and chlorine dioxide: spectroscopic techniques vs. Fujiwara test (original) (raw)
Related papers
Journal of Membrane Science, 2010
The present work addresses the mechanistic aspect of hypochlorite attack on a commercial polyamide membrane and the oxidative degradation taking place under active (applied pressure with constant stirring) and passive (unpressurised and unstirred) conditions. The degree of membrane degradation was enumerated in terms of the decline in membrane performance, calculated from permeability and salt rejection for reverse osmosis (RO) feed water. For active exposures both permeability and salt rejection changed significantly whilst only permeability varied for passive exposure. The structural changes in the polymeric backbone of the active surface layer were studied with attenuated total reflectance–Fourier transform infrared spectroscopy (ATR–FTIR). For the chlorine damaged membranes, distinct peak suppression has been observed around 3330 cm−1. Minor but significant shift in amide I and II bands and peak suppression in the ring stretching vibration at 1609 cm−1 was also noticed. The suppression or shift in the characteristic peaks was observed for both active and passive contact, however the extent differed. The progress of membrane damage has been confirmed to advance up to ring chlorination, however the N-chlorinated substituent may not be considered as a short-lived intermediate in view of the fact that the chlorine substitution on nitrogen has been indicated through a change in the amide II band in the final product. Perhaps the reaction products are both N-chlorinated products and ring chlorinated compounds, most likely their existence being influenced by operating parameters. Especially pressure seems to have effect on the chlorine attack of polyamide surface, seeing that the rearrangement of N-chlorinated substituent to ring chlorination is favored by pressurized environment. Formation of ring chlorinated products appears to be the destroying phenomenon for the polyamide surface resulting in salt passage. Chlorine damaged membranes were tested for Fujiwara test, which is an indicative test generally performed in membrane autopsies to check the degradation of polyamide membranes with halogens. Whilst the membrane degradation was evident from the salt rejection values and the FT-IR patterns, Fujiwara analysis failed to diagnose the chlorine exposure at low concentrations, especially under passive conditions.
Degradation of Polyamide Nanofiltration and Reverse Osmosis Membranes by Hypochlorite
Environmental Science & Technology, 2012
The degradation of polyamide (PA) nanofiltration and reverse osmosis membranes by chlorine needs to be understood in order to develop chlorine-resistant membranes. Coated and uncoated fully aromatic (FA) and piperazine (PIP) semi-aromatic PA membranes were treated with hypochlorite solution and analyzed by X-ray photoelectron spectroscopy (XPS) and Fourier transform infrared (FTIR). XPS results showed that in chlorine treated FA PA membranes the ratio of bound chlorine to surface nitrogen was 1:1 whereas it was only 1:6 in the case of PIP PA membranes. Surface oxygen of uncoated FA and PIP membranes increased with increasing hypochlorite concentration whereas it decreased for coated FA membranes. High resolution XPS data support that chlorination increased the number of carboxylic groups on the PA surface, which appear to form by hydrolysis of the amide bonds (C(O)−N). FTIR data indicated the disappearance of the amide II band (1541 cm −1 ) and aromatic amide peak (1609 cm −1 ) in both coated and uncoated chlorinated FA membranes, consistent with the N-chlorination suggested by the XPS results. Furthermore, the surface charge of chlorinated membranes at low pH (<6) became negative, consistent with amide-nitrogen chlorination. Chlorination appeared to both increase and decrease membrane hydrophobicity depending on chlorination exposure conditions, which implied that Nchlorination and hydrolysis may be competing processes. The effects of property changes on the membrane performance were also observed for NF90, BW30, and NF270 membranes.
Degradation of polyamide reverse osmosis membranes in the presence of chloramine
Desalination, 2011
Exposure to relatively low concentrations of chlorinated chemicals such as hypochlorite can reduce the performance and ultimately result in the failure of polyamide (PA) reverse osmosis membranes. Whereas the tolerance of PA membranes to chloramine solutions is considerably higher than that of hypochlorite, the presence of some metal ions can potentially catalyze and accelerate degradation reactions. Spectroscopic techniques are commonly used to qualitatively assess the chemical degradation of membranes by observing changes in structural peaks. This paper presents a technique to quantitatively evaluate changes in PA membranes exposed to chloramine by means of a peak ratio derived from a typical amide peak and an invariant peak in the same spectrum. The effect of some common metal ions and combinations of these on the peak ratio parameter derived from a typical amide peak is also reported.
Journal of Applied Polymer Science, 2003
Selected aromatic amides were used to model the chemical reactivity of aromatic polyamides found in thin-film composite reverse osmosis (RO) membranes. Chlorination and possible amide bond cleavage of aromatic amides upon exposure to aqueous chlorine, which can lead to membrane failure, were investigated. Correlations are made of the available chlorine concentration, pH, and exposure time with chemical changes in the model compounds. From the observed reactivity trends, insights are obtained into the mechanism of RO membrane performance loss upon chlorine exposure. Two chemical pathways for degradation are shown, one at constant pH and another that is pH-history dependent. An alternative strategy is presented for the design of chlorine-resistant RO membranes, and an initial performance study of RO membranes incorporating this strategy is reported. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 90: 1173–1184, 2003
Degradation by Free Chlorine of Aromatic Polyamide Active Layers of Thin-Film Composite Membranes
Polyamide-based thin-film composite membranes are the current technology of choice to meet the growing demand for drinking water desalination applications. One significant drawback to the use of this class of membranes is the high sensitivity of their polyamide active layer to oxidation by free chlorine. The current understanding of the mechanisms of chlorine uptake and eventual polymer degradation that lead to membrane failure has been gained mostly through the quantitative study of the effects of chlorination on molecular model polyamide compounds and membrane surfaces (top~5nm) with X-ray photoelectron spectroscopy (XPS), as well as through qualitative analyses of chlorinated membrane samples with attenuated total reflectance-Fourier transformed infrared (ATR-FTIR)spectroscopy. The physico-chemical changes induced by chlorination within the bulk of the active layer, however, have not been characterized by means other than ATR-FTIR, and therefore it has not been confirmed in the l...
Environmental Science & Technology, 2012
The degradation of polyamide (PA) nanofiltration and reverse osmosis membranes by chlorine needs to be understood in order to develop chlorine-resistant membranes. Coated and uncoated fully aromatic (FA) and piperazine (PIP) semi-aromatic PA membranes were treated with hypochlorite solution and analyzed by X-ray photoelectron spectroscopy (XPS) and Fourier transform infrared (FTIR). XPS results showed that in chlorine treated FA PA membranes the ratio of bound chlorine to surface nitrogen was 1:1 whereas it was only 1:6 in the case of PIP PA membranes. Surface oxygen of uncoated FA and PIP membranes increased with increasing hypochlorite concentration whereas it decreased for coated FA membranes. High resolution XPS data support that chlorination increased the number of carboxylic groups on the PA surface, which appear to form by hydrolysis of the amide bonds (C(O)−N). FTIR data indicated the disappearance of the amide II band (1541 cm −1 ) and aromatic amide peak (1609 cm −1 ) in both coated and uncoated chlorinated FA membranes, consistent with the N-chlorination suggested by the XPS results. Furthermore, the surface charge of chlorinated membranes at low pH (<6) became negative, consistent with amide-nitrogen chlorination. Chlorination appeared to both increase and decrease membrane hydrophobicity depending on chlorination exposure conditions, which implied that Nchlorination and hydrolysis may be competing processes. The effects of property changes on the membrane performance were also observed for NF90, BW30, and NF270 membranes.
Desalination, 2009
The physiochemical properties of reserve osmosis (RO) and nanofiltration (NF) polyamide (PA) membranes are largely determined by their PA chemistry and coatings, if any. Knowledge on such inherent relationship is critically needed in advancing membrane technology. This paper presents a consistent and in-depth characterization on diagnosing the chemistry of polyamide and the presence of any coating or modifying agent. Fourier-transform infrared (FTIR) and x-ray photoelectron spectra (XPS) of 17 commonly used commercial thin film composite polyamide RO and NF membranes are presented. The FTIR spectra for fully aromatic trimesoyl chloride and 1,3benzenediamine based membranes had an amide II band (1541 cm-1) and an aromatic amide band (1609 cm-1) that were absent for the semi-aromatic membranes. Consistent with that, the XPS binding energy shift for carbon atoms in fully aromatic amide groups was higher than that for semi-aromatic ones likely due to the more electron withdrawing environment. An additional intermediate peak with a binding energy shift of 1.1-1.6 eV was present in the XPS spectra of C(1s) for some commercial RO and NF membranes. The additional peak, coupled with FITR analysis over the high wave number region and XPS elemental analysis, provided consistent evidence that these membranes were either coated with an additional coating layer or had a modified PA chemistry.
Journal of Membrane Science, 2004
A major concern with the use of polyamide thin film composite (TFC) membranes is their loss of performance when exposed to oxidizing agents such as aqueous chlorine that is used in membrane cleaning and water disinfection. A better understanding of this oxidative degradation process would facilitate the development of improved TFC membranes. This study utilizes pendant drop mechanical analysis (PDMA) to measure chlorine-exposure-induced changes in the behavior of polyamide barrier-layers formed by the interfacial polymerization (IP) of m-phenylenediamine (MPD) and trimesoyl chloride (TMC). PDMA enables the measurement of mechanical and transport properties of unsupported MPD-TMC thin films. Based upon the PDMA results as well as those obtained from experiments conducted on commercial TFC RO membranes, a hypothesis is presented describing a two-pathway mechanism for the chlorine degradation of polyamide TFC membranes. At a constant pH, a morphology change, not polymer chain scission, occurs leading to separation of the barrier layer from the support. A second degradation pathway is observed when chlorine exposure under acidic conditions is followed by exposure of the polyamide thin-film to caustic (pH >11) conditions. The results of this investigation provide a strong rationale for further refinement of the PDMA methodology for use in basic studies as well as for screening applications that could aid in the development of chlorine-resistant IP thin films.
Chlorine-resistance of reverse osmosis (RO) polyamide membranes
Polyamide (PA) reverse osmosis (RO) membranes suffer performance decay when exposed to oxidizing species, limiting their lifetime and increasing operation costs. This article aims at reviewing the effect of chlorine species on the performance and characteristics of PA-membranes. Experimental evidence supporting different competing mechanisms for chlorine-polymer interaction will be presented, together with the influence of operational parameters. Additionally, an overview of different modification methods that exist to render PA-membranes more chlorine-resistant is given.
Desalination, 2009
The physiochemical properties of reserve osmosis (RO) and nanofiltration (NF) polyamide (PA) membranes are largely determined by their PA chemistry and coatings, if any. Knowledge on such inherent relationship is critically needed in advancing membrane technology. This paper presents a consistent and in-depth characterization on diagnosing the chemistry of polyamide and the presence of any coating or modifying agent. Fourier-transform infrared (FTIR) and x-ray photoelectron spectra (XPS) of 17 commonly used commercial thin film composite polyamide RO and NF membranes are presented. The FTIR spectra for fully aromatic trimesoyl chloride and 1,3benzenediamine based membranes had an amide II band (1541 cm -1 ) and an aromatic amide band (1609 cm -1 ) that were absent for the semi-aromatic membranes. Consistent with that, the XPS binding energy shift for carbon atoms in fully aromatic amide groups was higher than that for semi-aromatic ones likely due to the more electron withdrawing environment. An additional intermediate peak with a binding energy shift of 1.1-1.6 eV was present in the XPS spectra of C(1s) for some commercial RO and NF membranes. The additional peak, coupled with FITR analysis over the high wave number region and XPS elemental analysis, provided consistent evidence that these membranes were either coated with an additional coating layer or had a modified PA chemistry.