Ağır metallere karşı seçici olan selüloz matris yapılı iyon değiştirici üretimi

Abstract

Bu tez çalışması selüloz bazlı bir iyon değiştirici eldesine yöneliktir. Elde edilen sclülozik iyon değiştirici, ticari iyon değiştirici reçinelerle ve selülozik diğer iyon değiştiricilerle kıyaslandığında iyon değiştirme kapasitesinin yüksek olması, kolayca rejenere edilebilmesi, su dahil bilinen tüm solventlerde çözünmemesi ve matris yapısının petrol kökenli maddelerden oluşmaması, buna karşılık selüloza bağlı obuası nedenleri ile önemli bir avantaja sahiptir. Bu iyon değiştiricinin matris yapısını lüdroksietil selüloz ve fonksiyonel grubunu da titalil klorür oluşturmuştur. Bu özel iyon değiştirici ile uygun deneysel şartlar altında demir(II), çinko, kobalt, bakır ve krom(III) gibi ağır metaller üzerinde çalışılmıştır. Hazırlanan iyon değiştiricinin nemli toplam iyon değiştirme kapasitesi 2.28 meq /g ve kuru toplam iyon değiştirme kapasitesi 9.66 meq/g'dır.

In this study, an ion exchange resin based on the semi-ester of cellulose was prepared and used to remove the heavy metals such as iron, chromium, cobalt, cupper, and zinc in aqueous solutions. Hydroxyethyl cellulose was chosen as a cellulose derivative and esterified with phthalyl chloride to obtain semi-ester which would be used as an ion exchanger. It is obvious that earboxyl groups were inserted to the matrix, structure by esterification reaction. hi general, ion exchange resins separate ionic constituent by means of several medianisms or bases of selectivity. First, they absorb ionic constituents in the presence of norûüiıic substances. Second, cationic substances are taken up by cation excliange resins and anionic ones by anionic resins. Third, ions of higher valences are preferentially absorbed in dilute solutions. Fourth, with resins of high degrees of cross-linking, an ion having a smaller ionic volume is captured. Filth, organic ions may be adsorbed by the hydrocarbon matrix of resin. Sixth, an ion may interact with a fixed excliange group and in that mariner be taken up preferentially. While a resin may thus take up one ion species over another, this selectivity usually occurs to but a limited extend and ion seperations can be affected only by careful elution procedures in a column, where many hundreds of fractionations can occur. The conventional ion exchange resins should than be classified as selective in that they are characteristic for a comparatively small number of ions. Cellulose as isolated from its natural sources (e.g., from wood or cotton) lias fibrous macrostructure. Aggregates of glucosidic chains in various states of order and disorder are randomly oriented along the fiber axes. The liigher cl tains are described as fibrillar ix "crystalline" areas or bridges and these dense centers are interconnected by longer axial fiber composed of low-ordered amorphous chains. Hydrogen bonding between the neighboring cellulose chains, and especially in the fibril centers, provides dimensional stability for the cellulose matrix, and it is these forces that restrict the matrix to only moderate swelling and make cellulose insoluble in water. Within and in between the cellulose cliains are locaied "holes" or pores with a wide range as to size. When ionizable groups are introduced into such a matrix, the natural polymer cellulose becomes an ion exchange material. Chemical reaction to attach ionized groups to the cellulose matrix proceeds with difficulty in die crystalline regions, but takes place more readily in the amorphous areas. Tlie substitution of functional groups into cellulose has a disruptive effect on its structure. If carried out to completion, the cellulose matrix would be destroyed and ultimately water soluble polymers would be formed. Even at lıiglı levels of substitution, much before solubility occurs, cellulose derivatives lose their attractiveness as a cfuromatograpldc material for the fractionation of large solutes. A high density of uniform eliarges makes difiucult the elution of large polyelectrolytes, or even may prevent the removal of macromolecules from highly substituted exchangers. Therefore chemical reactions to introduce functional groups are not carried to completion. Substitution is restricted to the more reactive centers (e.g., the most accessible regions) in the amorphous regioius and is seldom carried out beyond the level of 1 meq per g of dry exchanger. At this level of substitution, the native configuration of the cellulose structure is Oiîly sligthly modified and the low density nonuniform exchange sites are readily accessible to large polyelectrolytes. Ion exchange celluloses have been used extensively in the purification and fractionation of proteins, including enzymes, hemoglobins, hormones, serum proteins, viruses, and seed proteins. They have also been used in the chromatography of peptides, nucleic acids, nucleotites, amino acids, alkaloids, and metallic ions. Ion exeliange celluloses are made by attaching substituent groups with basic or acidic properties to tlie cellulose molecule, usually by etherification or esterifieation reactions. The degree of substitution (DS) is low, since the various uses of ion exchange celluloses require tîıat they do not dissolve or swell excessively in dilute aqueous acids or bases. Crosslinking of the cellulose prior to chemical modification may be used to control swelling and permit a liigher DS. Although similiar to ion exeliange resins in ion exchange properties, they are much finer and present a larger surface; their porous structure permits the rapid entrance or attachment of huge molecules that are not readily adsorbed by the resins. This makes ion exchange celluloses particularly useful in the elıromatograpîuc separation of polielectrolytes, especially in biochemical research, where they are used in preference to the resins. They can be miide in the form of fabric, yanı, fiber, pulp or paper. The last three forms are made commercially by several companies' and are used routinely in biochemical research. Several chemically modified cellulose have been prepared wlueh exhibit ion-excliange properties similar to those of the well-known commercial ion exchangers. By introducing a substituent group with acidic properties into the cellulose molecule a cation exchanger is obtained. One limitation of most ion exchange celluloses is their low capacity in comparison with the ion exeliange resins. Low capacity appears to be no disadvantages in chromatographic work with proteins and other high molecular weight materials, but it is a disadvantage for some other possible uses. When, sets out to increase the ion exchange capacity by means of more effective or repeated chemical treatments, the physical properties of the cellulosic exchangers begin to suffer; excess swelling occurs which interferes with column operations or causes fiber structure to be lost so that the product becomes a soluble polyelectrolyte without value as an ion exchange material. Such material can be converted to insoluble, granular ion exchangers of lügh capacity by subsequent cross linking, but with loss of liter structure. However, if the celulose is cross-linked by a difunctional reagent before introduction of the ioıüc groups, fiber structure is retained and a much higher exeliange capacity may be reached, while maintaining properties suitable for cl ircmatography. XI The esleriiieaüon of the cellulose with diearboxy acids is not new. In early all previous reports celluloses were almost completely esterified and products were soluble in organic solvents as the free acids or in water as tlie sodium salts. There has been a few previous reports of the partial esteritication of celluloses with diearboxy acids for the preparation of cation exeliauge media. By effecting only partial esterification of the celluloses under conditions which, minimize clianges in meclianical structure, one can obtain products with physical properties which are desirable lor many cation exeliange procedures. These partially esterified products do not jel in organic solvents as the free acids or in water tiA the sodium salts, hi appeareance they resemble the original cellulose very closely. The cellulose acid esters participate rapidly in cation exchange reactions. Cations can be removed from them completely by regenerating with an equivalent (or slightly more) of dilute HC1. Some representative values for the degree of esterification and the sodium ion binding capacity of the cellulose acid esters are given in the following Table 1. Table 1. Sodium ion binding capacity and degree of esterification of typical cellulose-acid ester preparations. In the present study, resin preparation was performed through the esterification reaction between hydroxyethyl cellulose and phtlialyl chloride. This reaction can be represented as follows. xii Oil CH2CH2Ö- + HC1 The total ion excliange capacity of resin produced in this study was 2.28 meq /g as wet and 9.66 rneq/g as dry. It was seen that tliis capacity was larger than the capacity of the cationic ion exchange celluloses and that of the commercial carboxylic ion exchangers. It Wit* also seen tliat the resin produced by this study liad similar capacity compared with the strongly cation exchange resins. The resin prepared in this study was also tested with the aqueous solution of iron(II), zinc, cobalt, cupper and cluromiurn(III) in order to understand whether it is capable of dropping the metal concentration to the corresponding permitted concentrations in the waste water. At the end of the tests, it was understood that the resin can be used successfully to remove the above mentioned metals in their aqueous solutions to the permitted concentrations in waste water. The permitted concentrations for Fe(H), Zn, Co, Cu, Cr(III) are reported as 5, 2, 0.05, 0.2 and S^respectively. Up to this concentration, 1 gram resin captured 10.14 mg Fe, 5.07 mg Zn, 2.18 mg Co, 1.67 mg Cu resin and 3.493 mg Cr. The results showed that this resin removed the metals up to permitted concentrations. xm In the application of resin produced, the principle of reaction occurs between ion exchanger and heavy metals. O OH CHaCHaO-t- u ivf" o -fc-OH + II A- OH CH2CH2O-1 OM In tables shown below, chemical and physical properties, and operating conditions of the produced ion exchanger arc given. Table 2. Chemical and physical characteristics of the produced resin. XIV Table 3. Operating conditions of the produced resin. (Minimum bed deptli = 1000 mm)