Yağ+ yağ asidi+ çözücü sisteminin sıvı-sıvı faz dengelerinde kısmi gliseridlerin etkisi
Effect of partial glycerides on equilibrium data for the system of vegetable oil+ fatty acids+ solvent
Yazar: BURCU SÖZER
Danışman: PROF. DR. HALE GÜRBÜZ
İstanbul Teknik Üniversitesi / Fen Bilimleri Enstitüsü / Kimya Mühendisliği Ana Bilim Dalı
Derece: Yüksek Lisans, 2013
Konu: Kimya Mühendisliği = Chemical Engineering
Dizin: Sıvı-sıvı dengesi = Liquid-liquid equilibrium ; Yağ asitleri = Fatty acids

Özet:
Ham bitkisel yağlardan, gıda veya endüstriyel amaçlı kullanıma uygun yağ elde etmek üzere yağın oksidasyon direncini, tadını ve kokusunu bozarak tüketiminde sorun yaratan serbest yağ asitlerinin (SYA) giderilmesi, rafine yağ kalitesi ve fiyatına en fazla etkiyi yapan adım olarak büyük önem taşır. Asit giderme işlemi için sıvı-sıvı ekstraksiyonuna dayanan prosesler, endüstride uygulanmakta olan geleneksel (alkali nötralizasyonu ve distilasyon) yöntemlere alternatif olarak geliştirilen diğer yöntemlere göre öne çıkmaktadır. Ortam sıcaklığında ve atmosfer basıncında uygulanması nedeniyle daha az enerji tüketen ılımlı bir ayırma yöntemi olması ve atık probleminin olmaması, sıvı-sıvı ekstraksiyonunun en önemli avantajlarını oluşturmaktadır.Sıvı-sıvı ekstraksiyonuna dayanan alternatif proseslerin endüstriyel ölçekte geliştirilmesi için bitkisel yağ+yağ asidi+çözücü sistemlerine ilişkin sıvı-sıvı faz denge verileri temel oluşturmaktadır. Ancak, bu konuda literatürde yer alan veriler son yıllarda gerçekleştirilen sınırlı sayıdaki çalışmalara dayanmaktadır. Konuyla ilgili verilerin azlığı; ayrıca, bu verilerin genellikle rafine yağ+saf yağ asidi+çözücüden oluşan model karışımlarla elde edilmiş olması nedeniyle konu hala araştırmaya açık bir alan olarak önem taşımaktadır.Rafine yağ+saf yağ asidi+çözücüden oluşan model sistemler, yağların doğal hidrolizi sonucunda SYA ile birlikte oluşan kısmi gliseridleri içermezler. Hidrolizlenmiş yağlarda doğal olarak bulunan kısmi gliseridlerin, sıvı-sıvı ekstraksiyon için önemli olan faz dengeleri üzerine etkisi olabileceği öngörüldüğünden, bu çalışmada bu etkinin incelenmesi amaçlanmıştır. Bu amaçla gerçekleştirilen deneysel çalışmada, sıvı-sıvı faz dengelerinin belirlenmesi için kullanılan yağ-yağ asidi-çözücü sistemleri, asit değeri doğal olarak hidrolizle değişen, dolayısıyla içerdiği SYA yanında hidroliz reaksiyonu ile oluşan farklı miktarlarda kısmi gliseridleri de içeren bir yağ kullanılarak hazırlanmıştır. % 82 etanol içeren sulu etanol veya mutlak saflıkta metanol olmak üzere iki farklı çözücü için farklı sürelerde hidroliz sonucunda SYA ve kısmi gliserid içeriği değiştirilen çörek otundan elde edilen yağ (çözücü/yağ oranı 2:1) kullanılarak hazırlanan ÇOY+SYA+%82EtOH ve ÇOY+SYA+MeOH karışımları, 25ºC veya 30ºC'de çalkalamalı bir su banyosunda 24 saat bekletilmesi ile dengeye ulaşması sağlanmış; karışımın santrifüjlenmesi ile ayrılan rafinat ve ekstrakt fazlarının SYA, çözücü ve nötr yağ içerikleri ile bu çalışmada etkisi incelenen kısmi gliseridlerin ham yağ, rafinat ve ekstrakt fazlardaki içerikleri belirlenmiştir. Elde edilen iki sıvı-sıvı faz diyagramının benzer koşullarda (sıcaklık, çözücü cinsi) saf sistemler için elde edilmiş literatür verileriyle kıyaslanmıştır. Ayrıca, kısmen asitliği giderilmiş ve doğal olarak kısmi gliserid içeriği düşürülmüş çörek otu yağı kullanılarak yağ+saf yağ asidi+çözücü sistemi hazırlanarak kısmi gliserid etkisinin sıvı-sıvı faz dengelerinde belirgin olarak görüldüğü yüksek asitlik bölgesi için kıyaslama yapılmıştır. Bu kıyaslamalar sonucunda elde edilen bulgulara göre: KG'lerin ÇOY+SYA+çözücü sistemi sıvı-sıvı faz dengeleri üzerinde dikkate değer bir etkisi bulunmaktadır. Yağda SYA oluşumunun sonucunda doğal olarak meydana gelen polar yapılı KG'lerin ikili heterojen faz bölgesini biraz daralttığı belirlenmiştir. Bu etki özellikle KG derişiminin de yüksek olduğu yüksek SYA içerikli bileşimlerde (faz diyagramı üst bölgesi) belirginleşmektedir. KG'lerin varlığı, her iki çözücü sisteminde de bağlantı doğrularının eğimini rafine yağ + saf yağ asidi + çözücüden oluşan model karışımlarda elde edilen bağlantı doğrularına kıyasla belirgin şekilde değiştirmektedir. Bu değişimin sonucu olarak SYA'lerinin dağılım katsayısı KG'lerin varlığında düşmektedir. Bu durum çözücülerin SYA ekstraksiyon kapasitesini düşürmektedir ve özellikle yüksek asitli yağlardan sıvı-sıvı ekstraksiyonuna dayanan asit giderme proseslerinin tasarımında dikkate alınması gereklidir.? Kullanılan çözücülerin polaritelerinin hemen hemen aynı olması nedeniyle, hem ÇOY+SYA+%82EtOH hem de ÇOY+SYA+MeOH sistemlerinde çözücülerin SYA seçicilikleri hemen hemen aynı olup, başlangıç yağındaki SYA derişiminin ve buna paralel olarak KG derişiminin artmasıyla azalmaktadır. Çözücü ekstraksiyonu ile asit giderme yönteminin endüstriyel uygulamalarda kullanımı için sıvı-sıvı faz denge verileri üzerine daha çok çalışma yapılmasına ihtiyaç vardır. Bu çalışmalarda, ham yağdan kaynaklanan bütün önemli bileşenlerin etkisi göz önünde bulundurulmalıdır.

Abstract:
The crude oil, extracted from oilseeds is a mixture of triglycerides, partial glycerids (mono- and diglycerides), free fatty acids (FFA), phosphatides, pigments, sterols and tocopherols. The complete steps of treatment to make the oil suitable for edible use is called refining and usually refers to the operations of pretreatment, deacidification, bleaching and deodorization.Crude oils consist of varying quantity of FFA along with triglycerides and increase of that has negative effects on the oxidation rancidity, flavor and odor of edible oil. FFA can be formed, however, by enzyme (lipase) action, after the oilseeds harvested. Hydrolysis of ester bonds in oils resulting in the liberation of FFA, may be caused by enzym action or by heat and moisture.In oils industry, the removal of free fatty acids (deacidification) of oils is important not only for the consumer acceptance but also because it has the maximum economic impact on production.Industrially the two most commonly used methods for refining are chemical (alkali neutralization) and physical (distillation) deacidification. However, for oils with high acidity, chemical refining causes high loses of neutral oil due to saponification and emulsification. The physical method is also a feasible process for deacidification of high acid oils. For deacidification of high acid oils this method has several advantages over traditional alkali deacidification such as reduced oil losses, simplified operation, less steam, water and power consumption, and reduced generation of environmental pollutants. However, it has also some inconveniences such as very stringent pretreatment requirements and unsuitable for heat sensitive oils.The basic unit operations in vegetable oil processing have remained relatively unchanged for 6-7 decades. Because of the several drawbacks to today?s technology, alternative approaches are needed to overcome these drawbacks.New approaches for deacidification of vegetable oils have been proposed in literature, such as biological deacidification, chemical reesterification, supercritical fluid extraction, membrane processing and solvent (liquid-liquid) extraction.Liquid-liquid extraction, which is based on the differences in the solubility of FFA and triglycerides in a organic solvent, has been receiving attention due to its advantages in comparison to conventional and the other alternative processes. It can be carried out under mild conditions (at room temperature and atmospheric pressure), thereby reducing the energy consumption. Besides, liquid-liquid extraction has the advantages of avoiding the formation of waste products and reducing the loss of neutral oil. Furthermore, solvent stripping from deacidified oil and solvent recovery from extract stream can be easily performed by evaporation at relatively low temperatures.For industrial adoption of liquid-liquid extraction as a deacidification method, it is necessary to generate liquid-liquid equilibrium data of the vegetable oil + free fatty acid + solvent systems. However, the data existing in the related literature is limited to just a few studies conducted only in the recent years. Furthermore, most of these data has been obtained by using model systems, which consist of "refined oil + fatty acid + solvent".The model systems consisting of refined oil + pure fatty acid + solvent exclude partial glycerides as a result of hydrolyze reaction of neutral oils with the product of FFA. Because of the prediction of the partial glycerides in the hydrolised crude oil could affect the phase equilibrium important for the liquid-liquid extraction; the purpose of the present study is the investigation of this effect.As a result of hydrolyze reaction, raw vegetable oils contains partial glycerides in addition to FFAs. On the other hand, these compounds are not exist in the model systems prepared by using the refined vegatable oils. These compounds may have an important effect on the liquid-liquid phase diagram. The presence of partial glycerides may change the distribution of FFAs between the phases. Therefore, the aim of the present study is to investigate the effect of partial glycerides on the liquid-liquid equilibrium data of the vegetable oil + free fatty acid + solvent systems. For this aim, black cumin (Nigella Sativa L.) seed oil (BCS oil) was selected for preparing the vegetable oil + free fatty acid + solvent system. The reason for this choice is the increase in FFA and partial glyceride content of the oil in ground black cumin (Nigella Sativa L.) seeds by rapid hydrolysis reaction as a result of high lipase activity. In the dormant seeds lipase enzymes are generally inactive, but when the seeds are ground to obtain the oil, the lipase and oil come into direct contact and enzymatic hydrolysis reactions commence immediately. Since the black cumin (Nigella Sativa L.) seed oil contains both FFAs and partial glycerides, unlike the model systems, vegetable oil + free fatty acid + solvent systems were prepared by mixing the oil with the selected solvents without extra addition of FFAs.Aqueous ethanol (82% EtOH) and anhydrous methanol (MeOH) were selected as solvents.In the edible oil processing ethanol is considered as an appropriate solvent because it has low toxicity, easy recovery in the process, good values of selectivity and distribution for FFAs. Moreover, with EtOH, the loss of neutracetical compounds during liquid-liquid extraction is relatively low. Although FFA distribution coefficient decreases slightly by adding water to the ethanol, because of large increase in the heterogeneous region and in the selectivity in the presence of water, aqueous ethanol (82% EtOH) was preferred.MeOH is already used as reactant in the production of biodiesel. Therefore, it is appropriate for deacidification of high acidity vegetable oils by liquid-liquid extraction for using as raw material in biodiesel production.Based on the rapid hydrolysis of oil in the ground black cumin (Nigella Sativa L.) seed, in order obtain oils with varying FFAs and partial glyceride contents ground seeds were hold at ambient conditions for varying periods of time. The oil was obtained either by solvent extraction or by cold pressing of the seeds. For the determination of liquid-liquid equilibrium data, BCS oil were mixed with the selected solvents in the volume ratio solvent/oil 2:1. Then, the mixtures were hold in a thermostatic shaker (Julabo SW23) at a selected temperature for 24 hours. The shaking frequency was adjusted to 150 rpm in all experiments. After this treatment, the mixtures were centrifuged for 1 h at 3500 rpm and the clear phases were separated. For determining the composition of both phases the concentration of FFAs was determined by titration with an automatic buret. The total solvent concentration was determined by evaporation in a rotary evaporator. Having determined the concentration of FFAs and the solvent, the concentration of triglycerides was obtained by difference. The content of partial glycerides in the BCS oils and in the raffinate phases was determined by classical column chromatography. As stationary phase silica gel was used.The predicted effects of partial glycerides on the liquid-liquid equilibrium data were examined by comparing the experimental data obtained in this study with the data taken from the literature. For this comparison the data taken from the literature was selected among the data obtained under the same equilibrium conditions (temperature, type of solvent) but by using model systems, namely refined oil+FFA+solvent. The liquid-liquid equilibrium data of BCS oil +FFAs+82% EtOH? system was compared with the data of ?Refined Grapeseed Oil+Linoleic Acid+82% EtOH. The liquid-liquid equilibrium data of BCS oil +FFAs+ MeOH? system was compared with the data of Corn Oil+Oleic Acid+MeOH.In order to verify the conclussions obtained from the comparisons, additional equilibrium experiments with one selected initial acidity of BCS oil were performed for each system (?BCS oil +FFAs+82% EtOH? and BCS oil +FFAs+ MeOH). For these experiments the BCS oil was partially deacidified by ethanol extraction.After this treatment the acidity of the partially deacidified BCS oil was readjusted to a selected value. Because the differences between the equilibrium data of model systems and the systems investigated in this study are more pronounced on the high acidty region of the phase diagrams, these reference experiments were performed with BCS oil containing FFAs of about 31%.As a result of this study, it was concluded that: the partial glycerides have considerable impact on the liquid-liquid equilibrium data of BCS oil +FFAs+Solvent system. the presence of partial glycerides in raw vegetable oils slightly increases binary heterogeneous phase region. This effect is more noticable on the high acidity region of the phase diagrams. both in BCS oil +FFAs+82% EtOH? system and ?BCS oil +FFAs+ MeOH? system the more remarkable effect of partial glycerides on the liquid-liquid equlibrium is the change of the slopes of tie lines. This change is also more noticable on the high acidity region of the phase diagrams. This effect is to decrease the distribution coefficient of FFAs. Therefore, decreasing capacity of solvent for extracting FFAs should be considered in the design of liquid-liquid extraction processes for deacidification of high acidity vegetable oils.? the selectivity of 82% EtOH and anhydrous MeOH for FFAs is almost same because of their similar polarities. The selectivity of both solvents decreases with increasing partial glyceride content of the oil. industrial scale applications of solvent extraction as deacidification process require further investigations on the related liquid-liquid equilibrium data and models.