Sıvı sıvı ekstraksiyonu ile maya atıksuyu membran çıkışından uçucu yağ asidi geri kazanımı
Recovery of volatile fatty acids from anaerobic fermantation broth by liquid liquid extraction
Yazar: AYŞEGÜL NALAN ÖZTÜRK
Danışman: YRD. DOÇ. DR. MAHMUT ALTINBAŞ
İstanbul Teknik Üniversitesi / Fen Bilimleri Enstitüsü / Çevre Mühendisliği Ana Bilim Dalı / Çevre Bilimleri ve Mühendisliği Bilim Dalı
Derece: Yüksek Lisans, 2014
Konu: Çevre Mühendisliği = Environmental Engineering

Özet:
Uçucu yağ asitleri anaerobik arıtmanın fermantasyon aşamasında oluşan kısa zincirli yağ asitleridir. Değerli kimyasal ürünler olarak piyasada geniş bir kullanım alanları olmasına karşın, yüksek uçucu yağ asidi konsantrasyonuna sahip atıksuların alıcı ortamlara ulaşması ciddi çevresel sorunlara yol açmaktadır. Ticari olarak kullanılan birçok kimyasal gibi uçucu yağ asitleri de genellikle fosil kaynaklardan kimyasal işlemler sonucu üretilmektedir. Ancak; sürdürülebilir kalkınma ve insan sağlığı açısından bakıldığında uçucu yağ asitlerinin fermantasyon sularından ayrılıp saflaştırılması büyük önem taşımaktadır.
Bu deneysel çalışmanın amacı değerli fermantasyon ürünleri olan uçucu yağ asitlerinin maya atıksuyu hidroliz reaktörü membran çıkışından sıvı sıvı ekstraksiyonu yöntemi ile geri kazanımlarının sağlanmasıdır.
Bu amaç doğrultusunda yapılan çalışmanın birinci aşamasında organik solvent olarak dietil eter kullanılarak uygulanacak sıvı sıvı ekstraksiyonu deneylerinin optimizasyonu yapılmıştır. Çalkalama süresinin ve faz ayrımı için gerekli olan santrifüj süresinin belirlenmesi amacıyla çeşitli denemeler yapılmıştır. Bu çalışmalara göre su banyosunda 170 rpm çalkalama hızında 2 saat çalkalama süresi ile faz ayrımı için 15 dakika ve 9000 rpm'de santrifüj yapılmasına karar verilmiştir. Daha sonra organik solvent olarak dietil eter, trioktilamin (seyreltici: 2-etilhekzanol) ve toluen kullanılarak çeşitli pH'larda ekstraksiyon deneyleri yürütülerek kimyasalların ekstraksiyon verimleri hesaplanmıştır. Optimum ekstraksiyon veriminin elde edildiği pH 3'te kademeli ekstraksiyon deneyleri yürütülerek kademelerin ekstraksiyon verimi üzerindeki etkisi incelenmiş ve kimyasallar birbirleri ile kıyaslanmıştır.
Bu çalışmada elde edilen sonuçlar doğrultusunda maya atıksuyu hidroliz reaktörü membran çıkış suyunda en yüksek miktarda bulunan uçucu yağ asitleri olan asetik asit, propiyonik asit ve bütirik için pH 3'te ekstraksiyon verimleri sırasıyla dietil eter için %29, %64 ve %87; trioktilamin için %53, %80 ve %93; toluen için %4, %16 ve %45 olarak bulunmuştur. Toplam uçucu yağ asidi ekstraksiyon verimleri dietil eter, trioktilamin ve toluen için sırasıyla %51, %70 ve %32'dir. Üç kademeli ekstraksiyon denemelerinde ise asetik asit, propiyonik asit ve bütirik için pH 3'te ekstraksiyon verimleri sırasıyla dietil eter için %64, %95 ve %100; trioktilamin için %55, %85 ve %97; toluen için %7, %33 ve %75 olarak bulunmuştur. Üç kademeli ekstraksiyon denemelerinde elde edilen toplam uçucu yağ asidi ekstraksiyon verimleri dietil eter, trioktilamin ve toluen için sırasıyla %82, %76 ve %43'tür.
Elde edilen sonuçlara göre üç kimyasalla ayrı ayrı yürütülen sıvı sıvı ekstraksiyonu deneylerinde tek kademeli ekstraksiyon çalışmalarındaki en yüksek ekstraksiyon verimleri kıyaslandığında trioktilamin › dietil eter › toluen olduğu bulunmuştur. İkinci kademe için de bu sıralama değişmezken; üçüncü kademede ekstraksiyon verimleri kıyaslandığında dietil eter › trioktilamin › toluen sıralaması görülmektedir. Dietil eter ile 3 kademeli ekstraksiyon denemelerinde bütün deneysel çalışmada elde edilen en yüksek ekstraksiyon verimi olan %82 değerine ulaşılmıştır.
Elde edilen bu sonuçlardan hareketle maya atıksuyu hidroliz reaktörü membran çıkış suyundan sıvı sıvı ekstraksiyonu yöntemi ile uçucu yağ asitleri geri kazanımının uygulanabilir bir çalışma olduğu sonucuna varılmıştır.

Abstract:
Volatile fatty acids are short-chain fatty acids which are produced either synthetically from fossil resources or as metabolic intermediates in acidification (fermentation) step of anaerobic digestion process. As it is the case for most of other commodity chemicals, they are usually derived form fossil fuels through chemical synthesis. However fermentation, using renewable resources, is more preferable from the viewpoint of sustainable development and human health. 
Being valuable chemical products, volatile fatty acids have diverse uses in the market. They are utilized for the manufacture of various organic compounds including alcohols, aldehydes, ketones, esters and olefins. They are used for bioplastic production. 
The major barrier in the use of fermentation process for volatile fatty acid production is the technical difficulty associated with their recovery from the fermentation broths. In addition, separation and purification of the organic acids from bulk liquids represent the majority of the production cost. Therefore topics about the effective recovery of these fermentation products have received considerable attention.
There are various techniques, applied for the recovery of organic acids from fermentation broths, including; electrodialysis, ion-exchange, adsorption and liquid liquid extraction. Among these methods, liquid liquid extraction is accepted as an efficient, economical and environmentally friendly method for separation of carboxylic acids. 
Liquid liquid extraction is one of the oldest and well-established chemical operations. Efficiency of organic acid extraction depends highly on the nature of the acid extracted, the concentration of the extractant, the type of diluent and pH. Alcohols, ketones, ethers and aliphatic hydrocarbons can be used as solvents for the extraction of organic acids from fermentation broths. 
Many separation processes in chemical industries utilize a reactive extraction system. A reactive liquid liquid extraction process, which exploits reversible chemical complexation in the extractant phase, provides an effective separation, especially for relatively dilute solutions, such as the aqueous solution of carboxylic acids in a fermentation broth. The solutions of long-chain tertiary amines in diluents such as ketones, alcohols, chloroform, and so forth are very effective extractants for carboxylic acids. The specific chemical interactions among the amines and the acid molecules to form acid-amine complexes in the extractant phase allow more acid to be extracted from the aqueous phase.
In recent years, solvent extraction have received attention for the recovery of carboxylic acids from dilute aqueous solutions, notably with hydrophobic tertiary amines dissolved in various organic diluents. The specific affinity of long-chain tertiary amines for carboxylic acids gives high selectivity for this type of solute with respect to water and eventually nonacidic species in the mixture. The formation of acid-amine complexes depends on the nature of diluents, which affect the basicity of the amine and the stability of the ion-pair association in the extractant phase, and these diluents may hydrogen bond with the oxygen accessible on the carboxylic acid. Since the presence of the hydroxyl and carboxylic groups increases the solubility of acids in the water phase, the strong interactions of solvent with solutes are necessary to extract carboxylic acids from dilute aqueous solutions. Polar diluents that enhance the extraction power of amines are more favorable than nonpolar diluents.
The aim of this experimental study is the recovery of volatile fatty acids, valuable fermentation products, from anaerobic fermentation broth by liquid liquid extraction.
In this study; diethyl ether, trioctylamine and toluene are used for the recovery of volatile fatty acids from the anaerobic membrane bioreactor filtrate by liquid liquid extraction. 
First of all, for the optimization of the method which will be used in this study, diethyl ether has been chosen as organic solvent. Different shaking times for maximum contact of acids and organic solvent, and santrifuge times for phase seperation has been tried and optimum times has been chosen for the experimental study. 2 hours shaking at 170 rpm in water bath and 15 minutes santrifuge at 9000 rpm has been chosen for this study, and all experiments were done with this method. 
Diethyl ether, trioctylamine (diluent: 2-ethyl hexanol) and toluene experiments were carried out 2 hours shaking at 170 rpm in water bath and 15 minutes santrifuge at 9000 rpm for different pH values and extraction yields has been calculated for each experiment. Gas choromatography is used for the determination of volatile fatty acids in aqueous and organic phases. Internal and external standards has been used for the calculation of the amounts of volatile fatty acids and extraction yields. Maximum extraction yields has been reached after pH has dropped below pH 3, so pH 3 has been chosen as optimum pH. 
Multistage extraction experiments were carried out up to three stages at optimum pH. After first liquid liquid extraction process with 2 hours shaking at water bath and phase seperation with 15 minutes santrifuge, rafinate phase (water phase) has been taken. Rafinate phase of first extraction step is extracted with fresh solvent using the same procedure. At third extraction stage, rafinate phase of second extraction step has been extracted with fresh solvent using the same procedure again. Samples has been taken at every stage and extraction yields has been calculated as total extraction yield after every stage. 
The wastewater used in this study is gathered from the concentrated flow of Izmit Pakmaya Yeast Factory's production process. Yeast wastewater, which has very high COD content, has been used to produce volatile fatty acids in anaerobic membrane bioreactor with 10 days hydrolic retention time under thermophillic temperature (55 oC). Effluent of anaerobic membrane bioreactor has been collected for two months and composite sample kept at 4 oC. This effluent has been used for liquid liquid extraction experiments in this study.
Effluent of the acidification reactor contains 40.4 gCOD/L of total COD and 30.2 gCOD/L of total volatile fatty acids. Acetic acid is the dominant volatile fatty acid in the effluent being the 58% of total volatile fatty acids. Propionic acid is 16% and butyric acid is 17% of the total volatile fatty acids. Three dominant acids acetic acid, propionic acid and butyric acid are 90% of total volatile fatty acids in the anaerobic broth used in this experimental study.
The results of single stage liquid liquid extraction study for diethyl ether, trioctylamine and toluene are 51%, 70% and 32%, respectively for total volatile fatty acids extraction yield. The most common acids of anaerobic broth: acetic acid, propionic acid and butyric acid extraction yields are calculated as 29%, 64%, 87% for diethyl ether; 53%, 80%, 93% for trioctylamine and 4%, 16%, 45% for toluene, respectively. 
The results of two stage liquid liquid extraction experiments gave the extraction yields for total volatile fatty acids 73% for diethyl ether, 76% for trioctylamine and 40% for toluen. Acetic acid, propionic acid and butyric acid extraction yields are calculated as 47%, 87%, 98% for diethyl ether; 54%, 85%, 97% for trioctylamine and 7%, 25%, 65% for toluene, respectively after the second stage of liquid liquid extraction experiments.
The results of multistage liquid liquid extraction gave total volatile fatty acids extraction yields 82% for diethyl ether, 76% for trioctylamine and 43% for toluene after third stage. Acetic acid, propionic acid and butyric acid extraction yields are calculated as 64%, 95%, 100% for diethyl ether; 55%, 85%, 97% for trioctylamine and 7%, 33%, 75% for toluene, respectively. 
The extraction yields of three different organic solvents used in this study are compared with each other and for single stage extraction trioctylamine diluted with 2-ethyl hexanol gave the best extraction results as 70% volatile fatty acids extraction yield. For single stage liquid liquid extraction, extraction yields of three different chemicals used in this study are: trioctylamine › diethyl ether › toluene. For two stage liquid liquid extration this order doesn't change. For three stage liquid liquid extraction experiments, diethyl ether gave the best results of all the study as 82% total volatile fatty acids extraction yield. For three stage liquid liquid extraction, extraction yields of three different chemicals used in this study are in the order of diethyl ether › trioctylamine › toluene.
COD removal rates of three organic solvents used in this study are calculated 35% for diethyl ether, 46% for trioctylamine and 15% for toluene. Before extraction total volatile fatty acids/COD rate is 72% for anaerobic fermantation broth, which means 72% of the total COD is volatile fatty acids in the fermantation broth. This amount drops 54% for diethyl ether, 41% for trioctylamine and 58% for toluene after liquid liquid extracton experiments, which can be interpreted as these three organic solvents have more affinity for volatile fatty acids than other carbon containing materials so the rate of total volatile fatty acids/COD has dropped.
Diethyl ether, having the best extraction yield with multistage extraction and having a very low boiling point (34.6°C), has been choosen for further purification trials. After phase seperation organic phases has been taken. Using a distillation set, diethyl ether has been distilled and collected to reuse. Below 1% of total volatile fatty acids has been vapourized and collected with diethyl ether. Volatile fatty acid rich phase also contains some diethyl ether after distillation process, though it could be possible to purify them with higher technology.
Having the best extraction results with multistage liquid liquid extraction and low boiling point, which makes the further purification experiments much easier, diethyl ether is a very promising organic solvent for the recovery of volatile fatty acids from anaerobic fermentation broth. Trioctylamine (diluent: 2-ethylhexanol) also has good extraction yields even at a single stage liquid liquid extraction process, but being a very expensive chemical and having harder purification processes it doesn't seem like the best alternative.