Soya yağının yerinde alkolizi

Abstract

Bitkisel ve hayvansal yağların alifatik monohidroksi alkollerle alkoliz reaksiyonu sonucu üretilen yağ asidi mono esterleri, kullanı rın ve önemi giderek artan yağ kimyasal larındandır. 1980 'li yıllarda bu maddelerin yenilenebil en enerji kaynağı olarak No. 2 dizel yakıtı yerine kullanılabileceğinin saptanması, bunların üretim ve özellikle rinin çok daha yoğun bir şekilde incelenmesine neden olmuştur. Bu çalışmada soya yağından yağ asidi mono esterlerinin üretimi, halen endüstriyel olarak uygulanmakta olan alkoliz yönteminden farklı olarak "yerinde (in-situ) alkoliz" yöntemi ile incelenmiştir. Yerin de alkoliz yönteminde yağ tohumdan ekstrakte edilmeden, doğrudan al kol ile reaksiyona sokulmaktadır. Bu durumda alkol hem yağ çözücüsü hem de esterleştirme reaktifi olarak görev yapmakta ve ekstraksiyon ve rafinasyon işlemleri uygulanmadan yağ asidi esterleri elde edile bilmektedir. Çalışmada hammadde olarak soya fasulyesinin seçilme sindeki en önemli nedenlerden biri Çukurova Bölgesindeki buğday eki lebilen alanlara ikinci ürün olarak soya fasulyesi ekiminin olumlu sonuçlar vermesi ve buna bağlı olarak Türkiye'de soya fasulyesi e- kiminin giderek artmasıdır. îkincı bir neden olarak da, yağı alın mış soya küspesinin %50 civarındaki protein içeriği ile insan ve hayvan beslenmesi için önemli bir hammadde olmasıdır. Deneysel çal ışırıacta öğütülmüş soya, fasulyeleri, aynı koşullarda ve katalizör olarak derişik sülfürik asit kul! cintl arak, metanol, %96 lık etanol, %98.75'lik etanol, n-propano1!.v^ n-butanol ile reaksiyona sokulmuş ve partikül büyüklüğü, reaksiyon süresi, alkol cinsi gibi de ğişkenlerin yerinde alkoliz reaksiyonuna etkisi incelenmiştir. Reak siyon ürünlerinin verim ve safiyet yönünden karşı laştınlması ile ye rinde alkoliz reaksiyonlarına etki eden en önemli faktörün yağın al- kollerdeki çözünürlüğü olduğu anlaşılmıştır.

In this study, in situ alcoholysis of soybean oil with mono- hydroxy, aliphatic alcohol, such as methanol, ethanol, n-propanol and n-butanol were investigated. Soybean is now easily the World's largest oilseed crop. In the 1990 s, production of beans exceeded 100 million tons providing over 16.9 million tons of oil. Soybeans account in cash terms for over 70% of world oilseed trade, whilst groundnut, rape and sunflo wer together barely account for a quarter; in value of crude vege table oil trades, soybean and palm each comprise almost a quarter. In Turkey, the production of soybeans in 1980-81 was nearly 2300 tons. In this year, the Turkish government has initiated and encouraged soybean plantation in Southern Anatolia as the second crop, and it was officially planned that maximum benefit be attained by its proper utilization. In 1986-87, the production of soybean reached to 90.000 tons. The soybean is a short day plant, i.e. it begins to flower when the days begin to shorten and is harvested in October and November. It is grown primarily in the temperate zones. The soybean is different from other oilseeds is that the oil content is ca. 35-40% of the value and the remaining value is in the high protein meal. The approximate composition of the soybean is 40% protein, 20% lipid, 17% cellulose and hemicellulose, 7% sugar, 5% crude fiber and 6% ash. Probably the single most important factor in the soybean success story is the amount of high-quality protein meal produced, are when soybeans are crushed and extracted to remove the oil, the residual meal is a valuable feed with enhanced protein content (relative to the whole bean) for poultry, hog, and some beef production. The use of soybean meal in feeds has grown from 5,7 million tons in 1950 to 14.1 million tons in 1976-a growth of 145%, while total commercial feeds have growth about 30% in the U.S.A. yet only about 2% of soy protein produced goes into edible protein products, but this amount can be expected to increase in future years along with denvand for protein. Soybean oil has shown growth similar to that of the meal. The increase in domestic soybean oil disappearance was 470% in the 1950- 1977 period, while total food fats and oils disappearence increased only 79% over the same period in the United States. Soybean oil is less expensive that corn, safflower and sunflo wer oils, yet it has many of the desirable characteristics of these so-called premium vegetable oils. It has a high linoleic acid con tent and a low saturated fatty acid content, and thus it is more desirable nutritionally than the more saturated oils. Typical com positions of crude and refined soybean oils are given in Table.1. Table 1. Average Compositions for Crude and Refined Soybean Oil Soybean oil triglycerides contain both saturated and unsatura ted fatty acids. The composition of crude soybean oil varies over a rather wide range, particularly for the type of unsaturated fatty acids, depending upon variety and climatic conditions. The fatty acid average composition and range of composition are given in Table 2. Most soybean oil is produced by solvent extraction. A schematic diagram of the unit processes used in modern solvent extraction plants is shown in Figure 1. Alcoholysis of vegetable oils and animal fats is an important reaction that produces fatty acid alkyl esters that are valuable in termediates in oleochemistry, and methyl and ethyl esters, which are excellent substitutes for Diesel fuel. Because vegetable oils have much greater viscosities and much less volatile than No. 2 diesel oil, problems have arisen when vegetable oils have been used as a substitute for diesel fuel. One promising solution to this problem is to use fatty esters that can be obtained from the vegetable oils by alcoholysis. VI Table 2. Fatty Acid Composition of Soybean Oil WHOLE SOYBEANS i r 1 ! H DRYING H L _J I. PREPARATION STORAGE CLEANING WEIGHING CRACKING i r, I *j OEHULLING f-j I J CONDITIONS II. SOLVENT EXTRACTION. 0|L m OIL t SOLVENT RECOVERY FLAKING - \ MEAL IV MEAL DESOLVENTglNG: FINISHING Figure 1. Typical Soybean Solvent Extraction Process. Vll The alcoholysis of soybean and sunflowers oils, because of their relatively high yield per hectare and widespread production, are being studied by many researchers. The reaction of triglyceri des with alcohols, in the presence of a catalyst, yields fatty es ters and glycerol. Pi- and monoglycerides are intermediates. The reactions variables that affect yield and purity of the product es ters include molar ratio of alcohol to vegetable oil, type of ca talyst (alkaline vs acidic), temperature and degree of refinement of the vegetable oil. To obtain maximum ester formation by alco holysis of vegetable oils, refined oils, substantially anhydrous with a free fatty acid content of less than 0.5 % should be used. The alcohol should also be moisture free. A molar ratio of alcohol to oil of 6:1 gives optimum conversion to the ester. Alkali cataly sis is considerably faster than acid catalysis. Even at ambient temperature, the alkali -catalyzed reaction proceeds rapidly, where as acid-catalyzed reactions commonly require temperatures above 100°C. With acid-catalysis, reaction times of 3-48 hr have been reported, except when reactions were conducted. under high tempera ture and pressure. Acid catalyzed alcoholysis can be used when the starting materials are lov; -grade fats or have a high free fatty content; the fatty acids would deactivate an alkaline catalyst. The concept of alcoholysis of sunflower seed oil in situ was described by Harrington and D'Arcy-Evans, and it was demonstrated that significant increases in ester yields could be achieved by such a method. The technique of alcoholysis in situ of sunflower seed oil provided an yield of fatty acid methyl and ethyl esters qualitatively similar to, but quantitatively greater than, the yield obtained from treatment of the preextracted oil. In this study, in situ alcoholysis of soybean oil with methanol, ethanol, n-propanol and n-butanol were investigated, because this method offers the advantage that it eliminates the extraction step and, thus, it could be possible to recover the oil directly as a valuable product. The soybeans used in this study was obtained from a soybean extraction plant in Adana. The oil contents of soybeans ground completely to *1 mm and <0.5 mm were 20.9% and 23.1%"- respectively. For in situ alcoholysis reaction, ground soybeans £50 g) were trans ferred to a flask, and 150 ml alcohol and 6 ml concentrated sulfuric acid were added. The mixture was refluxed in a water both while stirring with a magnetic stirrer for 1 to 5 h. At the end of the reaction, the mixture was filtered and the meal was washed with 200 ml of alcohol. After drying at room temperature, the meal was reextracted in a Soxhlet apparatus with hexane to obtains the oil fraction left in the meal. The filtrate was transferred to a se- paratory funnel and was extracted with hexane to remove the esteri- fied product. The oil left in the bran and the estefified product obtained in each reaction were investigated by TLC V1XX TLC was performed on glass plates coated with Silica Gel G and developed in a solvent system of riexane: diethyl etherracetic acid (90:10:1). Spots were detected by iodine vapor staining. The ester content of the esterified products was determined by column chromatography. Table 3 shows the results obtained from in situ alcoholysis of soybean oil with various alcohols for 3 h. Tablo 3. In Situ Alcoholysis of Soybean Oil, A typical chromatogram of ester fractions obtained from in situ alcoholysis of soybean oil is shown in Figure 2. As can be seen in Tablo 3, the yield and purity of the ester fractions were dependent to the alcohol used in the reaction. When the molecular weight of alcohol increased, yield and purity of ester fractions also increased. It was not possible to obtain a high yield and purity of ester fractions with methanol and ethanol (96%) alcoholysis j because these alcohols are not good solvents for soy bean oil. In alcoholysis with ethanol (98.75%), n-propanol and n-butanol it was possible to extract '.practically all the oil in soy beans and to convert them to esters. Based on these experiments, it was concluded that the main parametre that affected in situ alooholysis reaction was the solu bilities of oil in alcohol used in the reaction. IX D C B A II- III IV V VI VII Figure 2. Typical chromatogram of ester fractions obtained from in situ alcoholysis of soybean oil. I: standart mixture, II: soybean oil, III: fraction obtained with n-propanol, IV: fraction obtained with n-butanol, V: fraction obtai ned with ethanol (96%), VI and VII: fractions obtained with ethanol (98.75%).