CZ30614U1 - A membrane module containing membranes in the form of hollow fibres of polyethersulfone surface-enriched with silver nanoparticles - Google Patents

Description

Technical field

The invention relates to the field of membrane modules suitable for use in the filtration of water containing microorganisms, e.g. in the filtration of surface water or waste water, in particular membrane modules containing membranes in the form of hollow fibers of polyethersulfone surface enriched with silver nanoparticles.

BACKGROUND OF THE INVENTION

Membranes are currently used in a wide range of industries, for example in the processing of process fluids, drinking, sea, service and waste water.

One of the major problems associated with the use of membranes is clogging of the membrane surface, which represents the greatest limitation of membrane technology. This is a negative phenomenon not only in the filtration of biologically contaminated water (surface or waste water), but across all application directions of membrane technologies. The fouling of the membrane surface is caused by the interaction between the membrane surface and the components of biological, organic and inorganic origin present in the filtered suspension. Clogging of the membrane surface results in a decrease in permeability (flow rate per unit area of the membrane relative to the pressure gradient required for filtration). This in turn leads to a decrease in the economic efficiency of the membrane processes, both due to increased operating costs (pressure increase, less filtered water - the need for larger membrane areas, larger tanks, etc.) and the need for more frequent chemical cleaning of membranes to remove fixed contamination.

The two most commonly used polymers currently used to produce membranes suitable for microorganism filtration applications are polyethersulfone (PES) and polyvinyldifluoride (PVDF). For these applications, the membranes are manufactured in two basic spatial configurations. These are hollow fibers and plate (flat) membranes, and PES is currently used exclusively for the production of plate membranes and PVDF for the production of hollow fiber membranes (Dvořák et al., 2015; Judd, 2011). Each configuration has its advantages and disadvantages and its choice depends on the specific conditions of the application. The main advantage of membranes in the form of hollow fibers compared to the plate configuration is mainly a high specific surface, ie the surface of the membrane in relation to its volume (or volume of the whole membrane module) and further the possibility of more intensive cleaning by so called backwashing. In this type of membrane, it is regularly applied in order to remove some of the components adhering to the surface and responsible for decreasing the hydraulic performance of the membrane.

The advantage of PES is its high thermal and dimensional stability and chemical resistance, in particular to the action of hydroxide solutions, which is a significant advantage in some cases (Peters et al., 2000). Moreover, it is a polar material (Branco et al., 2002) and can thus be easily modified by a variety of methods (Pearce et al., 2007). In contrast, PVDF exhibits higher resistance to many acids and oxidants, including high concentrations of chlorine compounds, compared to PES (Wu et al., 2010). Although hollow fiber membranes made of PES offer indisputable advantages, manufacturers supplying these commercial microfiltration / ultrafiltration membranes are minimal on the market.

Many methods of surface modification of PES membranes have been developed and tested. Since PES is a material: hydrophobic in nature with relatively low surface energy and a high contact angle (all these factors increase the tendency to clog the membrane surface and reduce the hydraulic performance of the membrane), the modification methods aim to create a more polar, less hydrophobic surface thereby minimizing clogging membrane surface. The methods of surface modification of PES membranes tested so far can be divided into 6 main groups: the method of coating, blending method, composite method, chemical method, grafting method and combined methods.

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In the application method, thin layers are formed from a suitable material, which are then non-covalently bound to the surface of the original membrane. For this purpose, various approaches and conditions are used which can be further subdivided (usually into several subgroups) (Nady et al., 2011). As an example of a suitable material used for modification by the " deposition " method, a variety of organic substances can be mentioned, such as polyethylene glycol diacrylate or sulfonated poly (2,6-dimethyl-1,4-phenylene oxide) (Hamza et al., 1997; Mu and Zhao) (2009).

In the blending method, two or more polymers are physically blended to obtain the desired properties. Organic substances such as polyethylene glycol, polyvinylpyrrolidone, cellulose acetate, cellulose acetate phthalate are added to the PES base polymer (Idrisa et al., 2007; Marchese et al., 2003; Lu et al., 2007; Rahimpour and Madaeni, 2007) and other complex organic compounds (eg n-butyl methyl acrylate (Su et al., 2008)).

The composite method is based on the principle of preparing a material that is composed of two or more materials with different physical and / or chemical properties. The materials remain separated, even at the macroscopic level, clearly visible in the final structure of the modified membrane. As an example, a solution of Ν, Ο-carboxymethyl chitosan in which the PES membrane has been immersed and sewn together with glutaraldehyde (Zhao et al., 2003).

The chemical method is based on the principle of modification of the original material by various chemical agents and reactions, which lead to the formation of new functional groups generated directly on the surface of the original membrane. However, the main disadvantage of chemical modification methods is that chemical agents lead to partial blockage of membrane pores and thus to lower hydraulic performance of modified membranes (Nady et al., 2011). Also, the possibility to control the course of the reaction itself is often very complicated. Therefore, in some cases, modifications through chemical reagents and reactions are already utilized during membrane preparation. However, this can have a negative effect on the membrane preparation process itself, especially the hollow fiber membrane.

The grafting method results in covalent attachment of suitable monomers to the original membrane surface. In order to bind the monomers, the reaction must first be initiated, again using several methods: chemical, photochemical and / or utilizing high energy radiation, plasma or enzymes. The choice of a particular monomer and initiation method is dependent upon the chemical structure of the membrane and the desired characteristics of the membrane surface after modification. Again, however, these are complex reactions, the course of which must be controlled accurately and complicatedly.

The last option is a combination of the above techniques, eg mixing a suitable solution and then "grafting" specific components onto the membrane surface. E.g. Bae et al. (2006) exposed the commercial PES membrane to a sulfonation reaction and then immersed it in a titanium dioxide solution. This created new functional groups on the surface of the original membrane. The membrane thus modified showed a lower tendency to fouling than the unmodified membrane. Another example of a combined method is the use of graphene oxide. First, allylamines were grafted onto the PES membranes by UV initiation and subsequently grafted onto graphene oxide (Igbinigun et al., 2016).

Thus, in most cases organic compounds and the most diverse process conditions, often with the necessary energy-intensive initiation, are used for surface modification of PES ultrafiltration or micro filtration membranes. If inorganic substances are used for modification of PES membranes, these are for example titanium dioxide, silicon particles, aluminum oxides or silver. However, these compounds / particles are incorporated into the base polymer (or blend) prior to membrane preparation. Thus, it is not a surface modification or an additional modification of an already manufactured membrane. Although the addition of the above components may lead to the desired properties of the final membrane surface, modification of the base polymer matrix may negatively affect the preparation of the PES membrane as a hollow fiber. For this reason, most studies have been devoted to the preparation of membranes from such modified matrices in a plate (flat) configuration.

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Thus, there is a clear demand in the art for other solutions which both meet the condition of significantly improved surface properties of the membranes and their permeability and which are relatively easy to implement, under favorable economic conditions.

The essence of the technical solution

The present inventors have now unexpectedly found that a membrane module comprising one or more membranes in the form of hollow fibers of polyethersulfone surface-enriched with silver nanoparticles results in a significant elimination of the above problems.

The membrane module comprises one or more membranes in the form of hollow fibers made of polyethersulfone (PES). The outer diameter of the fibers is typically about 1 to 2 mm and the linear fibers are linearly arranged in a module having a diameter of several cm. However, other dimensions are possible depending on the intended application.

The hollow fiber membrane made of polyethersulfone (PES) is then enriched with silver nanoparticles that are generated in situ on its surface by treating the membrane with a silver compound solution and reducing agent under suitable process conditions. This effect results in surface enrichment of the membrane with silver nanoparticles, i.e. the presence of nanoparticles fixed on the membrane surface, but also in the presence of silver nanoparticles inside the top layer of the polymer matrix of the membrane. Silver nanoparticles are homogeneously distributed over the entire membrane surface and do not form agglomerates.

No toxic or otherwise hazardous reagents or high initiation energies are required for the described membrane surface modification, as with some of the surface modification methods mentioned in the Prior Art chapter.

The presence of silver nanoparticles on the surface of the modified membrane can be demonstrated by advanced microscopic techniques as well as by EDS analysis, which can also determine the content of silver nanoparticles on the membrane surface.

Preferably, the membrane surface comprises 1 to 5 wt. of nanoparticles of silver, based on the total weight of all elements present on the surface.

Even more preferably, the membrane surface comprises 2 to 4 wt. of nanoparticles of silver, based on the total weight of all elements present on the surface.

Most preferably, the membrane surface comprises 3 to 4 wt. of nanoparticles of silver, based on the total weight of all elements present on the surface.

In one preferred embodiment, the membrane module is a tubular module formed of hollow fiber membranes.

Clarification of drawings

Figure 1 represents a comparison of spectra (EDS surface analysis) demonstrating the presence of silver on the surface of the modified membrane.

Figure 2 shows the hydraulic power (flux) of a hollow fiber membrane enriched with silver nanoparticles and an identical membrane prior to modification as a function of the applied transmembrane pressure (TMP) during distilled water filtration.

Figure 3 shows the time evolution of permeability (K) values relative to the initial permeability value of a given membrane (K _o ) during filtration of biologically contaminated water.

Figure 4 represents the percentage difference of modified membrane permeability (dK) versus reference membrane (KREF) values during filtration of biologically contaminated water.

Examples of technical solutions

It is to be understood that the examples described below are for illustrative purposes only and are not intended to limit the invention to these examples. Of course, one of ordinary skill in the art will be able to prepare equivalents to the specific embodiments described herein by routine experimentation. These equivalents are also included in the scope of protection defined by the following protection claims.

Example 1

A modified membrane in the form of hollow fibers made of polyethersulfone (PES) was prepared as follows.

The PES hollow fiber membrane was immersed in 3.5 wt. solution of silver nitrate (AgNO ₃ ) and leached in this solution for 4 hours at room temperature and under continuous slow (0.2 l.min ^-1 ) flow of the solution directly in the membrane module. Subsequently, the membrane was rinsed intensively with distilled water three times. Silver reduction (in-situ genesis of silver nanoparticles) was achieved by subsequent embedding of the membrane with 2 wt. solution of ascorbic acid (C ₆ H ₈ O ₆ ). The silver reduction was carried out for 2 hours. Then the membrane was again rinsed intensively with distilled water three times. This was followed by embedding the membrane with pure distilled water, heating to 60 ° C for 2 hours, and continuously recirculating the hot water in the membrane module. The membranes were then rinsed with distilled water at room temperature.

Example 2

A spectra comparison (EDS analysis) was performed to demonstrate the presence of silver on the surface of the modified membrane, with the corresponding graph being shown in Figure 1.

The representation of the individual elements on the surface of the reference membrane is shown in Table 1.

The representation of the individual elements on the surface of the modified membrane prepared according to Example 1 is shown in Table 2.

Table 1: Representation of individual elements on the surface of the reference membrane.

Element Weight Í% 1 ^ratio Molar ratio [%] Carbon 69.74 77.57 Oxygen 23.48 19.61 Sulfur 6.78 2.82 Total 100.0 100.0

Table 2: Representation of individual elements on the surface of modified membrane.

Element Weight ratio [%] Molar ratio [%] Carbon 67.77 77.84 Oxygen 21.73 18.74 Sulfur 6.87 2.95 Silver 3.63 0.46 Total 100.0 100.0

Example 3

The average contact angles (6 measurements per value) of the modified membrane prepared according to Example 1 and the reference membrane were measured. The measurement results are shown in Table 3.

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Table 3. Mean values of contact angles of modified and reference membranes.

Membrane Average contact angle [°] Authoritative deviation Modified 86.1 ± 1,6 Reference 91.6 + 3,3

The modified membrane showed slightly higher surface hydrophilicity compared to the reference membrane, due to the presence of silver nanoparticles on the surface of the membrane.

Example 4

Filtration tests were performed with distilled water at various transmembrane pressures (TMP) and steady-state operating conditions, ie constant TMP and constant cross-flow rate. The aim was to determine the stability of permeability values (normalized hydraulic power) under different TMP, ie the effect of modification on the membrane hydraulic characteristics. It can be seen from Figure 2 that the modification did not lead to a deterioration in the permeability values of the membrane prepared according to Example 1. The average flux values at different TMPs found for the modified hollow fiber membrane enriched with silver nanoparticles and for the non-enriched membrane were almost identical.

Example 5

Filter tests were performed with broad-spectrum consortia of microorganisms. The outflow from the municipal sewage treatment plant was used as an inlet to the membranes. The filtration test was performed at a constant TMP (0.15 bar) and a cross-flow rate maintained between 0.9 and 1.1 l.min ¹ . The test was performed under identical conditions with both the modified and reference membranes under the following process protocol: 24 h filtration (TMP = 0.15 bar), 10 min reverse flow through the membrane module (ie opposite direction of inflow to membrane module) through the filtrate at a constant filtrate flow of 2 Emin ' ¹ .

The results are shown in Figure 3. In the case of a modified hollow fiber membrane surface enriched with silver nanoparticles prepared according to Example 1, a rapid increase in permeability values during filtration is seen. This indicates that the fouling components were not firmly fixed on the surface of the modified membrane and were released and eluted from the module, unlike the reference membrane.

In addition, the modified membrane rapidly reached higher permeability values than the reference membrane. Also after reversed flux (after 24 h test) a clearly higher recovery of permeability values was observed, which in case of modified membrane was higher than original values. In the further course of the test, the permeability values of the modified membrane were already about 10% higher than in the case of the reference membrane.

Figure 4 shows the percentage difference (increase) of modified membrane permeability values relative to reference membrane permeability values.

Example 6

Permeability tests with distilled water were performed before and after the test with a wastewater treatment effluent. The decrease in permeability expresses the extent to which the components involved in the fouling process are trapped on the membrane surface. The results of these tests are shown in Table 4.

Table 4. Modified membrane permeability (K) values (according to Example 1) and reference membranes measured during distilled water filtration before and after the end of the wastewater treatment effluent filtration test, including percent decrease.

Membrane

K before test K after test Drop [1m ^ -M-bar ¹ ] [1m ^ -h ^ -bar ⁴ ] [%]

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Modified (according to example 1) 242 206 14.9 Reference 262 185 29.4

Separation ability of membranes, resp. retention of organic compounds (expressed as chemical oxygen consumption parameter - COD _Cr ) were not negatively affected by the modification. Organic retention (CODc _r ) was 31% for the modified membrane and 28% for the reference membrane.

Industrial applicability

Membrane modules containing one or more hollow fiber membranes made of polyethersulfone (PES) surface enriched with silver nanoparticles showed improved flow properties and a lower tendency to clog the filter surface than the reference membrane, ie the membrane not enriched on the surface in the bio-contaminated water test. silver nanoparticles. Moreover, the deposition of silver nanoparticles in addition to the positive effect on the surface properties of the membranes did not affect any other properties of the membrane, i.e. it did not reduce its selectivity (separation ability), did not affect the internal structure or mechanical properties.

Thus, membrane modules containing one or more hollow fiber membranes made of polyethersulfone (PES) surface enriched with silver nanoparticles will find particular application in the filtration of water, including water containing microorganisms, e.g. in the filtration of surface or waste water.

List of literature

Bae TH, Kim IC, TakTM (2006). Preparation and characterization of TiO ₂ self-assembled nanocomposite membranes. Journal of Membrann Science, 275, 1-5.

Basri H., Ismail A.F., Aziz M. (2011). Polyethersulfone (PES) -silver composite UF membrane: effect of silver loading and PVP molecular weight on membrane morphology and antibacterial activity. Desalination, 273, 72-80.

Basri H., Ismail A.F., Aziz M., Nagai K., Matsuura T., Abdullah M. S., Ng B. C. (2010). Silverfilled polyethersulfone membranes for antibacterial applications-effect of PVP and TAP addition on silver dispersion. Desalination, 261,264-271.

Branco. L. C., Crespo. J.G., and Afonso. C.A. (2002). Studies on the selective transport of organic compounds by using ionic liquids as novel supported liquid membranes. Chemistry-A European Journal, 8, 3865-3871.

Cao X., Tang M., Liu F., No Y., Zhao C. (2010). Immobilization of silver nanoparticles onto sulfonated polyethersulfone membranes and as antibacterial materials. Colloids Surface B, 81,555562.

Dvořák. L., Gómez. M. Dolina. J., Cemin. A. (2015). Anaerobic membrane bioreactors - a mini review with emphasis on industrial wastewater treatment: applications, limitations and perspectives. Desalination Water Treatment, 1-15.

Hamza A., Chowdhury G., Matsuura T., Sourirajan S. (1997). Sulfonated poles (2,6-dimethylphenylene oxide) -polyethersulphone composite membranes: effects of solvent system composition, prepared for casting solution, membrane-surface structure and reverse osmosis performance. Journal of Membrane Science, 129: 55-64.

Idrisa A., Zaina N. M., Noordin Μ. Y. (2007). Synthesis, characterization and performance of asymmetric polyethersulfone (PES) ultrafiltration membranes with polyethylene glycol of different molecular weights as additives. Desalination, 207: 324-339.

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Igbinigun E., Fennell Y., Malaisamy R., Jones K. L., Morris V. (2016). Graphene oxide functionalized polyethersulfone membrane to reduce organic fouling. Journal of Membrane Science, 514.518526.

Judd. S. (2011). The MBR book: principles and applications of membrane bioreactors for water and wastewater treatment. Elsevier.

Lu S., Zhuang L., Lu J. (2007). Homogeneous blend membrane made of poly (etherolphone) and poly (vinylpyrrolidone) and its application to water electrolysis. Journal of Membrane Science, 300, 205-210.

Marchese J., Ponce M., Ochoa N. A., Prádanos P., Palacio L., Hemández A. (2013). Fouling behavior of polyethersulfone UF membranes made with different PVP. Journal of Membrane Science, 211: 1-11.

Maximous N., Nakhla G., Wong K., Wan W. (2010). optimization of A12o3 / PES membranes for wastewater filtration. Separation and Purification Technology, 73,294-301.

Mu L. J., Zhao W. Z. (2009). Hydrophilic modification of polyethersulfone porous membranes via thermal-induced surface crosslinking approach. Applied Surface Science, 255: 7273-7278.

Nady N., Franssen M. C. R., Zuilhof H., Eldin M. S., Boom R., Schroen K. (2011). Modification methods for poly (arylsulfone) membranes: A mini-review focusing on surface modification. Desalination, 275, 1-9.

Pearce. G. (2007). Introduction to membranes: Membrane selection. Filtration & Separation, 44, 35-37.

Peters. E. N., Arisman. R.K. (2000). Engineering Thermoplastics. Elsevier. New York.

Rahimpour A., Madaeni S. S. (2007). Polyethersulfone (PES) / cellulose acetate phthalate (CAP) blend ultrafiltration membranes: preparation, morphology, performance and antifouling properties. Journal of Membrane Science, 305, 299-312.

Shen J., Ruan H., Wu L., Gao C. (2001). Preparation and characterization of PES-SiO ₂ organic inorganic composite ultrafiltration membrane for raw water pretreatment. Chemical Engineering Journal, 168, 1272-1278.

Su Y., Li C., Zhao W., Shi Q., Wang H., Jiang Z., Zhu S. (2008). Modification of polyethersulfone ultrafiltration membranes with phosphorylcholine copolymer can remarkably improve the antifouling and permeation properties. Journal of Membrane Science, 322: 171-177.

Wu. L., Sun. J., & He, C. (2010). Effects of solvent sort. PES and PVP concentration on properties and morphology of PVDF / PES blend hollow fiber membranes. Journal of Applied Polymer Science, 116, 1566-1573.

Zhao Z. P., Wang W., Wang S. C. (2003). Formation, charged characteristic and BSA adsorption behavior of carboxymethyl chitosan / PES composite MF membrane. Journal of Membrane Science, 217: 151-158.

Claims (5)

PROTECTION REQUIREMENTS A membrane module comprising one or more hollow fiber membranes made of polyethersulfone PES surface enriched with silver nanoparticles. Membrane module according to claim 1, characterized in that the membrane surface contains 1 to 5 wt. of nanoparticles of silver, based on the total weight of all elements present on the surface. -7GB 30614 Ul Membrane module according to claim 1, characterized in that the membrane surface contains 2 to 4 wt. of nanoparticles of silver, based on the total weight of all elements present on the surface. Membrane module according to claim 1, characterized in that the surface of the membrane 5 comprises 3 to 4 wt. of nanoparticles of silver based on the total weight of all elements present on the surface. Membrane module, characterized in that the hollow fibers according to claims 1 to 4 are arranged in a tubular shape module.