Sulu çözeltilerden alkoletoksilatların kimyasal yöntemler ile arıtımı
Treatment of aqueous alcohol ethoxylates solution by chemical treatment processes
Yazar: ÇİSEM ECER
Danışman: PROF. DR. IŞIK KABDAŞLI
İstanbul Teknik Üniversitesi / Fen Bilimleri Enstitüsü / Çevre Mühendisliği Ana Bilim Dalı / Çevre Bilimleri ve Mühendisliği Bilim Dalı
Derece: Yüksek Lisans, 2012
Konu: Çevre Mühendisliği = Environmental Engineering
Dizin: Kimyasal arıtma = Chemical treatment ; Kimyasal çözeltiler = Chemical solution

Özet:
Düşük köpürme özelliğine sahip, soğuk suda iyi çözünebilen ve bu özellikleri nedeniyle düşük konsantrasyonlarda bile etkili olan noniyonik yüzey aktif maddeler çok geniş bir kullanım alanına sahiptirler. Noniyonik yüzey aktif maddelerden nonil fenol etoksilatlar kısa süre öncesine kadar yüzey aktif madde pazarının % 80'ini oluşturan türler olarak bu pazarda ciddi bir paya sahiptiler. Sucul ortamda yarattıkları olumsuz etkiler anlaşılana kadar nonil fenol etoksilatlar kağıt, tekstil, deri, gıda, boya gibi bir çok endüstriyi kapsayan geniş bir yelpazede yaygın olarak kullanılmaktaydılar. Ancak 1990'lı yılların başlarında endokrin bozucu ve toksik etkilerinin fark edilmesinin ardından nonil fenol etoksilatların yerine kullanılabilecek başka bir noniyonik yüzey aktif madde arayışına girilmiştir. Gelinen bu aşamada birinci alternatif olarak toksik etkileri bilinmeyen, yüksek biyolojik bozunurluğa sahip ve yüzey aktif madde olarak uygulamada nonil fenol etoksilatları ikame edebilecek nonil alkol etoksilatlar görülmektedir. Bahsedilen özellikleri nedeniyle nonil alkol etoksilatların üretimleri ve kullanımları gün geçtikçe artmakta ve yaygınlaşmaktadır.Her ne kadar bilinen herhangi toksik, kanserojenik veya mutajenik etkiye sahip olmasalar da, giderek artan miktarda üretilen ve kullanılan alkol etoksilatların arıtılabilirliklerinin araştırılması ihtiyacı doğmuştur. Literatürde alkol etoksilatların biyolojik olarak arıtılabilirlikleri ile ilgili gün geçtikçe artan sayıda araştırma yer almasına karşın söz konusu yüzey aktif maddelerin fiziko-kimyasal, elektrokimyasal ve fotokimyasal arıtılabilirlikleri ile ilgili sınırlı ve yetersiz sayıda araştırma mevcuttur.Bu çalışmanın amacı alkol etoksilatlara örnek teşkil etmek üzere seçilen polioksietilen (4) loril eter (Brij 30)'in 20 mg/L konsantrasyonundaki sulu çözeltilerinin koagülasyon, elektrokoagülsyon ve TiO2/UV-A fotokatalitik oksidasyon prosesleri esas alınarak fizikokimyasal ve kimyasal yöntemler ile arıtılabilirliğinin incelenmesi ve maksimum Brij 30 ve organik madde (TOK) giderimini sağlayacak en uygun proses reaksiyon koşullarının belirlenmesidir.Yukarıda belirtilen amaç doğrultusunda yürütülen deneysel çalışmadan elde edilen sonuçlar koagülasyon-flokülasyon ve çelik elektrotların kullanıldığı elektrokoagülasyon proseslerinin gerek Brij 30 gerekse organik madde gideriminde istenilen verimi sağlamadığını göstermiştir. İki farklı TiO2 katalizörü kullanılarak yürütülen fotokatalitik oksidasyon deneylerinde Aeroxide PF2 heterojen katalizörü ile yine istenilen düzeyde giderme verimleri elde edilememiştir. Buna karşılık Degussa P25 TiO2 heterojen katalizörü kullanılarak yürütülen fotokatalitik oksidasyon denemelerinde uygun reaksiyon koşulları seçildiğinde gerek Brij 30'un tamamı giderilmiş, gerekse %90 civarında organik madde minerilizasyonu gerçekleştirilmiştir. Elde edilen bu sonuçlardan hareketle Degussa P25 TiO2 heterojen katalizörü kullanılarak UV-A ışınımı altında alkol etoksilatları temsil etmek üzere seçilen polioksietilen (4) loril eterin sulu çözeltilerden uygun reaksiyon koşulları seçildiğinde etkin şekilde arıtılabildiği sonucuna varılmıştır.

Abstract:
Nonionic surfactants have low foaming properties, are highly soluble in cold water and are effective even in very low concentrations in water. Because of these advanteges, nonionic surfactants are widely used surface active substances especially in the industries such as leather, food, pulp and paper, cosmetics etc.Nonylphenol ethoxylates which used to dominate the surfactant market with a consumption rate of 80 %, have been the most preferred nonionic surface active compound. Nonylphenol ethoxylates are functionally used as cleaning and washing agents, surface active agents and foaming agents. The industrial activities use nonylphenol ethoxylates for industrial and institutional cleaning, textile auxiliaries, leather auxiliaries, emulsion polymerization, agricultural pesticides, cosmetics, cleaning products and office products such as correction fluids and ink.In early 90?s the toxic and endocrine distrupting effects of nonylphenol ethoxylates in the aquatic environment have been revealed. Nonylphenol, a breakdown product of nonylphenol ethoxylates, has been shown to mimic the action of the female hormone oestrogen. Concerns have focused on the potential for nonylphenol and nonylphenol ethoxylates to cause feminisation in wildlife, such as fish exposed to nonylphenol and nonylphenol ethoxylates contaminated effluents, as well as being a potential factor in the increasing incidence of reproductive organ disorders and decreasing sperm counts in men. Whereas nonylphenol ethoxylates is reasonably readily degradable, its breakdown product nonylphenol is more persistent. It has been determined that these compouns exhibit the estrogenetic activity by mimicing the hormones mentioned. Especially in the aquatic environment, fishes are the most affected organisms. It is known that nonylphenol ethoxylates are also very slowly biodegredable and have bioaccumulating property. After realizing the adverse effects of nonylphenol ethoxylates in the environment, espacially in aquatic environment, several countries have been taken act by regulations restricting production and consumption of nonylphenol ethoxylates.It was necessary to replace nonylphenol ethoxylates with another nonionic surface active agent. At this point alcohol ethoxylates seem to be the most appropriate alternative due to it?s high biodegredability, low toxicity, high water solubility and surface active effectiveness. Alcohol ethoxylates are the second largest group of surfactants in terms of manufacture (after linear alkylbenzenesulphonates) and the main group of non-ionic surfactants.The main area of alcohol ethoxylate application is in the manufacture of washing powders, liquids etc. Alchol ethoxylates are classifed as easily biodegradable surfactants, in contrast to previously used oxyethylated alkylphenols or oxyethylene-oxypropylene block copolymers.However, the massive stream of alcohol ethoxylates directed into sewage systems and then to sewage treatment, is required strict control in order to prevent pollution of the aquatic environment. A very important chain in this control is the examination of the biodegradability of surfactants prior to their uses in washing powder formulations. After replacing nonylphenol ethoxylates, production and consumption of alcohol ethoxylates have rapidly increased. This progression brought on the requirement of knowlege on the treatability, biodegradability and toxicity properties of alcohol ethoxylates. There are several research on the biodegradability of nonyl alcohol ethoxylates, however there are very little information about the chemical treatablity of these compounds.The purpose of this study is to investigate the treatability of alcohol ethoxylates in aqueous solutions by coagulation, electrocoagulation and TiO2/UV-A photocatalitic oxidation processes and to determine the optimum process conditions for the most effective treatment process. As a model nonyl alcohol ethoxylate compound poly(oxyethylene) (4) loryl ether, Brij30 was selected to be used in the experiments. This study consists of seven chapters.In the first chapter, the purpose and scope of the study was described briefly.In the second chapter, classification of surfactants, properties of surfactants, a brief explanation about toxicity of nonylphenol ethoxyltes, properties of alcohol ethoxylates and treatability of alcohol ethoxylates were defined.In the third chapter, fundamentals of coagulation and electrocoagulation were defined. Basic chemicals? reactions which occur during these processes were explained.In the fourth chapter, photochemical oxidation process was described, the fundamentals and basic reactions were explained. The factors which effecting photocatalitic activity were also explained in the end of the chapter.In the fifth chapter, the materials and methods were introduced which were used during the experimental part of the thesis. Since three different processed were used, three different treatment methods were explained. These processes were: classical coagulation-floculation process, electrocoagulation process and TiO2 catalized photocatalitic oxidation process. For every process the same analytical analysis were applied to the sampes in order to follow the treatment efficiency such as colourimetric surfactant determination and TOC analysis.In the sixth chapter all of the experimental results were evaluated and discussed.In the last chapter of the study the results were briefly evaluated and the most important results were stressed by the explanation of importance.In this experimental study, three different chemical treatment alternatives were evaluated and it was determined that only one of them was suitable to treat model pollutant, Brij 30 compound from its aqueos solution.The first alternative was classical coagulation-flocculation process derived in different coagulant (FeCl3) concentrations varing between 100 and 1000 mg/L, in pH 6.5 and 20 mg/L Brij 30 concentration. In this process the least Brij 30 removal was observed with 25% Brij 30 removal in 100 mg/L FeCl3 dosage and the highest Brij 30 removal efficiency was achieved with 39% in 750 mg/L FeCl3 dosage. These results showed that coagulation-floculation process was not practical for removing Brij 30 from its aqueous solution.The second process was electrocoagulation process using stainless steel electrodes and NaCl as electrolyte. Electrocoagulation experiments were conducted at original pH of 20 mg/L Brij 30 solution (~ 6), various NaCl concentrations (500, 1000, 1500, 2000 mg NaCl/L) and two different current densities (9,3 and 18,6 mA/cm2). When experimental results were evaluated; in 500 mg/L NaCl concentration, current density of 18,6 mA/cm2 after 180 minutes 70 % of Brij 30 removal was achieved. In the coagulation-flocultion experiments there was no significant removal result neighter in Brij 30 nor in TOC.The last but the most effective process was photocalalytic oxidation using TiO2 as catalyst under UV-A radiation. In this experiments firstly two different TiO2 types (Degussa P25 and Aeroxide P2) were compared and it was proved that Degussa P25 was significantly more effective than Aeroxide P2 in removing Brij 30 and TOC. The experiments were conducted in 20 mg/L Brij 30 concentrations, in two different pH (original pH ~ 6 and pH= 3) to determine the effect of initial pH, in two different TiO2 concentrations (1 and 1.5 g/L) to determine the effect of TiO2 dosages and for the selected test periods (5, 10, 15, 60, 240, 480 minutes). The aim of experiments were to determine the optimum process terms. In these experiments that in the original pH of 20 mg/L Brij 30 solution (~6) and 1 g/L Degussa P25 TiO2 dosage after 15 minutes more than 96% Brij 30 removal was obtained. Under these experimental conditions only after 240 minutes 64% TOC removal was achieved. After increasing the Degussa P25 TiO2 dosage to 1.5 g/L, after 480 minutes of photocatalitic oxidation TOC removal increased to 86 %. In general after decreasing the pH to 3 resulted in decreases the Brij 30 removal efficiencies.The experimental results showed that coagulation-floculation and electrocoagulation processes were not suitable effective treatment methods in removing Brij 30 from aqueous solutions. Additionally very limited organic matter removal efficiencies in terms of TOC could be obtained by appliying these processes. The most effective process was photocatalitic oxidation under UV-A radiation from the three different processes. By using photocatalitic oxidation it is possible to remove practically all of the model pollutant and most of the TOC from the water under mentioned conditions. Even in short reaction periods (15 minutes) high rates of Brij 30 removals are achieved but longer experiment periods (240-480 minutes) are needed in order to reach significant TOC removals.