Etil alkol su karışımlarında ekstraktif distilasyonun tuz etkisi

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Tarih
1998
Yazarlar
Mertoğlu Elmas, Gülnur
Süreli Yayın başlığı
Süreli Yayın ISSN
Cilt Başlığı
Yayınevi
Fen Bilimleri Enstitüsü
Institute of Science and Technology
Özet
Bu çalışmada etil alkol çözeltilerinin saflaştırılması ve azeotrop bileşiminin değiştirilmesi için bilinen distilasyon yöntemine alternatif bir yöntem olarak önerilen tuz katkılı ekstraktif distilasyonda tuzun etkisi incelenmiştir. Etil alkolün su ile seyreltilmiş çözeltileri, değişik inorganik tuzlar kullanılarak belirli koşullarda tuz katkılı distilasyon işlemi ile, saflaştırmaktadır. Bunun için su ile seyreltilmiş etil alkol ve mayşe olarak isimlendirilen ham alkol çözeltileri ve inorganik tuzlar olarak CaCI2 CH3COOK, CH3COONa, CaO, NaCI ve KBr kullanılmıştır. Deneysel çalışmalar laboratuvar ölçekteki bir deney düzeneği kullanılarak yürütülmüştür. Bir cam bölmeden ibaret olan 28 cm yüksekliğinde ve 6 cm çapında olan bir dolgulu kolonda denemelere başlanmış, bunun yetersizliği görülerek iki (aynı çapta, 56 cm yüksekliğinde) ve üç (aynı çapta, 84 cm yüksekliğinde) cam bölmeden oluşan dolgulu kolonda esas çalışmalar gerçekleştirilmiştir. Baş ürünün bir kısmı, tuz katılıp riflaks olarak kolona geri beslenmektedir. Baş ürünün etil alkol içeriği gaz kromotografi yöntemi kullanılarak tespit edilmiştir. Tuz ayırmaya olan etkisini saptamak için tuz kullanılmadan gerçekleştirilen deneylerde referans ayırma verimi, inorganik tuzlar kullanılarak gerçekleştirilen deneylerde tuz katkılı distilasyon verimi elde edilmiştir. Distilasyonda tuz etkinliğini ise tuz katkılı ekstraktif distilasyon veriminin, referans ayırma verimine oranı olarak tanımlanmıştır. Deneylerde üç temel değişkenle distilasyon etkinliği arasındaki değişim incelenmiştir. Bu değişkenler besleme akımı derişimi, riflaksdaki tuz derişimi ve riflaks oranıdır. Her bir değişkenin etkisi diğer iki değişken sabit tutularak gözlenmiştir. Balona başlangıçta alınan çözeltinin tuz derişimi sabit tutularak gerçekleştirilen distilasyon işlemlerinde distilasyon etkinliğini etkileyen değişkenler besleme akımı derişimi, riflakstaki tuz derişimi ve riflaks oranı olduğu saptanmıştır. Çalışmalar yaklaşık 5 denge kademesine denk gelen üst üste yerleştirilmiş 3 dolgulu kolon kullanılarak gerçekleştirilmiştir. Distilasyonda tuz etkinliğini etkileyen değişkenler arasında en uygun model denklemin 2. derece eğrisel denklem olduğu tesbit edilmiştir. Su ile azeotrop oluşturan etil alkol çözeltisinin azeotrop bileşimini değiştirmesi ve yüksek bir verimle saflaştırmasında en etkili tuz CaCI2'dür. Bunu CH3COOK tuzu izlemektedir. Besleme akımı çözeltisinin % 50 Mol'den daha seyrettik olması durumunda ise CH3COONa ve CaO tuzlan kullanılması önerilmektedir.
The aim of this study is to investigate the effect of salt as an additive in the distillation. Inorganic salts are added to the solutions of aqueous ethyl alcohol which is to be separated. Therefore the solutions of aqueous diluted ethyl alcohol and the crude alcohol which are used in the alcoholic beverage industry, are distilled by using various inorganic salts operations and the effectiveness of inorganic salts used in the purification of ethyl alcohol are examined. An extraneous liquid can often be found that, when it is present in the column, it changes the relative volatilities of the original components and thus facilitates their separation. When extraneous liquid is employed, the operation is classified either as extractive or azeotropic distillation. If extraneous material is less volatile than the feed, it is called extractive distillation. A solvent charged to the top of the extractive distillation column, the bulk of it passing down and being withdrawn from bottom together with components whose volatilities are least affected by the solvent. The volatilities of some components are enhanced considerably, and they pass to the overhead product. When extraneous material is more volatile than the feed, it may be charged either from the top of the column or with the feed. In both cases, extraneous material is withdrawn by the overhead product. A more volatile extraneous liquid is usually called entrainer. It has volatile characteristics forming an azeotrope with one or more of the overhead products. Hence, this method is called azeotropic distillation. Both types of modified distillation require expensive auxiliary operations to separate the products from the solvent or the entrainer. Prefractionation of the feed stream may also be an expensive operation. Extractive distillation employing a dissolved salt instead of a liquid as a third component or an extraneous liquid separation agent is promising but it is a relatively neglected technique for achieving azeotropic and other difficult separations. Salt effect in distillation was studied under two general topics:. Salt effect in vapor-liquid equilibrium. Salt effect in extractive distillation. Salt Effect In Vapor - Liquid Equilibrium. In certain systems where solubility permits, to use a salt dissolved into the liquid phase, as the separating agent for extractive distillation is feasible, It refers to the ability of a salt which has been dissolved into XX the liquid phase consisting of two (or more) volatile components to alter the composition of the equilibrium vapor phase without itself being present in the vapor phase. The feed component in which the equilibrium vapor is enhanced is said to have been "salted ouf by the salt, while the other component is "salted in". Salt effect in extractive distillation: The use of dissolved salt rather than a liquid additive as the separating agent in extractive distillation is attracting interest, particularly among alcohol the producers and the alcohol plant manufacturers involved in the American gasohol program. The attractiveness of the salt- effect distillation technique lies in its greatly reduced energy requirements compared with the conventional extractive and azeotropic distillation procedures. Yet industrial applications based on this effect, such as extractive distillation employing a salt dissolved in the liquid phase as the separating agent, have been relatively neglected. In the United States for instance, a large scale application has been in the concentration of the nitric acid from its aqueous azeotrope by extractive distillation using magnesium nitrate in place of sulfuric acid as the separating agent. There are several advantages of using a completely nonvolatile agent, such as dissolved salt, as the separating agent in the extractive distillation for separating an azeotrope-containing system such as ethanol-water, nitric acid-water or isopropanol-water. Since none of these separating agents will appear in the vapor phase, there is no need to feed a "solvent knockback" section about the separating agent feedpoint strip agent from overhead vapor, as there is with a liquid. As a result, much less separating agent is normally required, with resulting economies in the separating agent inventory, in the agent recovery and recycle capacity required, and particularly in the overall energy requirements for the process. As the salt separating agents salt mixtures consisting of calcium chloride, potassium acetate, sodium acetate, calcium oxide, potassium bromide and sodium chloride are used for the ethanol-water system. When a salt is used in place of a liquid separating agent, it is normally fed to the column by dissolution into the reflux stream immediately prior to entry of the reflux at the top of the column. Because the salt is nonvolatile, it will reside entirely within the liquid phase and hence flow only downwards. It is recovered from the bottom product stream for cycle by evaporation or drying, rather than by distillation as is the normal procedure for liquid agents. In this thesis, extractive distillation studies are carried out in the laboratory scale. The primary object of this study is to concentrate ethyl alcohol and if possible, to prevent forming azeotropic composition, (making the alcohol extremely non aqueous). A further aim is to make the crude aqueous-diluted ethyl alcohol provided by the Tekirdağ Wine Factory, a subsidiary of Tekel Genel Müdürlüğü, concentrated and also to make it completely non-aqueous. For this purpose, studies are carried out both with crude alcohol (mayşe), aqueous alcohol solutions of various concentrations, and such inorganic salts as CaCI2, CH3COOK, CH3COONa, CaO, NaCI and KBr. The salt which is dissolved most in the aqueous ethyl alcohol is CaCb. Therefore, CaCb is used more frequently in our study. The azeotrope of ethyl alcohol has been broken down by using CaCI2 This study is carried out by using a packed column of 28 cm. in length and 6 cm. in XXI diameter, placed on a flask of 1 liter of volume. At first, the study is initiated by a column with only one glass division, and then by realizing it is not sufficient enough further, studies are performed with a column of 56 cm height with the same diameter. Extractive distillation started up by a certain weight of appropriate salt and aqueous-diluted ethyl alcohol solutions of 400 ml. in the flask. After the main product is obtained, continuing by dissolving the separating salt in a certain amount of main product and returning it from the top part of the column by reflux stream. The ethyl alcohol contents of main products obtained are determined by using gas chromatography. The experimental arrangement of this study is illustrated in Figure 1. The studies carried out with a distillation system of 28 cm height column are considered as preliminary studies. It is observed that mentioned system above causes some problems during the experiments as the number of equilibrium stages are determined between 2 and 4 is insufficient. The problem encountered in the 28 cm height distillation column is the increasing system pressure. Therefore few experiments are performed using this distillation column. Main experiments are carried out by using a column 3 times higher than the first one which corresponds to the number of equilibrium steps around 5.
Açıklama
Tez (Doktora)-- İTÜ Fen Bil. Enst., 1998.
Anahtar kelimeler
Damıtma, Etanol, Tuz, Distillation, Ethanol, Salt
Alıntı