Hydrogenation 34 iodine value

Mild hydrogenation iodine value 90 to 100 about 14% trans. 

Extensive hydrogenation iodine value 70-80 about 30-50% trans. 

Infrared spectra of fats and oils are similar regardless of their composition. The principal absorption seen is the carbonyl stretching peak which is virtually identical for all triglyceride oils. The most common appHcation of infrared spectroscopy is the determination of trans fatty acids occurring in a partially hydrogenated fat (58,59). Absorption at 965 - 975 cm is unique to the trans functionaHty. Near infrared spectroscopy has been utilized for simultaneous quantitation of fat, protein, and moisture in grain samples (60). The technique has also been reported to be useful for instmmental determination of iodine value (61). 

The determination of iodine value (IV), AOCS Tg 1-64, is sometimes used to determine the extent of unsaturation. Because the tertiary aUyflc hydrogen ia the compounds is capable of substitution by halogen atoms, this only approximates a value for the degree of unsaturation. 

The composition of an oil and the progress of its hydrogenation is expressed in terms of its iodine value (IV). Edible oils are mixtures of unsaturated compounds with molecular weights in the vicinity of 300. The IV is a measure of this unsaturation. It is found by a standardized procedure. A solution of ICl in a mixture of acetic acid and carbon tetrachloride is mixed in with the oil and allowed to reac t to completion, usually for less than I h. Halogen addition takes place at the double bond, after which the amount of unreacted iodine is determined by analysis. The reaction is... 

TABLE 23-13 Time/ Temperature/ and Iodine Value of Tallow Hydrogenation ... 

The catalyst system of TOP18 and TOT is remarkably stable and long-lived if the reaction system is kept free of water and air. Contamination of the reaction mixture with water will lead to TOT decomposition (17). This reaction produces hydrogen iodide which reacts with epoxide 1. Air is deleterious to both catalyst components. Introduction of air into the process can cause oxidation of iodide anion to iodine which will dealkylate TOT. These reactions lead to loss of iodine value from the catalyst system which is monitored by XRF during production. 

The iodine value is reported as the number of grams of iodine that bind to 100 g of sample. As such, the IV can only be used as an index of unsaturation, especially in a mixed triacyl-glyceride system. This means that it can be compared to the same data from other mixed triacylglyceride systems, i.e., comparing to a competitor oil/fat. The other possible use is to reflect changes in the value based on treatment effects occurring in the system in question, e.g., to monitor hydrogenation. 

Fig. 82. Melting points and iodine values of cottonseed oil, hydrogenated at different temperatures, according to Williams. ...

Fig. 83. Iodine value vs. refractive index for various hydrogenated oils, according to Bailey71.

The final element of the hydrophobe which can be manipulated is the cis/trans ratio of the unsaturated hydrocarbon fragments. Natural tallow has a cis/trans ratio of about 8-20 [39]. Metal catalyzed hydrogenation of fats and oils results in the reduction of the cis/trans ratio and an increase in the melting point of the oil when compared to a material of similar iodine value and a higher cis/trans ratio [40]. For concentrated fabric softeners, high cis/trans ratios are preferred to reduce the likelihood of gel formation in the final product or during processing [24, 40-42]. 

Iodine Value of Fats and Oils—Cyclohexane Method (IV) (Cd lb-87) measures the unsaturation of fats and oils in terms of centigrams of iodine absorbed per gram of sample. The method is applicable to all normal fats that do not contain conjugated double bonds. It often is used to estimate the degree of hydrogenation of oils. 

In the hardening of free tallow fatty acids in sc CO2 we measured iodine values (IV) below 1 g I2/IOO g product at a space velocity of 15 h1. In comparison to trickle bed hardening reactions with activated carbon and titania supported 2 wt. % palladium fixed bed catalysts, between 6 to 15 times higher space time yields were determined when the hardening was carried out in sc CO2. The hydrogen partial pressures in both processes were comparable (2.0 MPa H2). 

When the hydrogenation function is embedded in the crystal voids of an MFI topology, the formation of trans-isomers is strongly reduced. After partial reduction of soy bean oil with such catalyst from an iodine value of 140 to 80, virtually no trans-isomers are obtained (56). This is the result of pore mouth catalysis combined with zeolite shape selectivity. Due to the bent character of the cts-isomer chains in triglycerides, trans-configured chains preferentially enter the pore mouths for hydrogenation. In this environment, metal-catalyzed cis-trans isomerization is restricted for steric reasons as multiple readsorption is minimal. 

Halphen Reaction. The halphen test is a very sensitive and reliable method for detecting the presence of cottonseed oil in another oil. A reaction with sulfur in carbon disulfide mixed with equal amounts of amyl alcohol gives a cherry red color when cyclopropenoid fatty acids unique to the Malvacae family, which includes cottonseed and okra, are present. This test is capable of detecting 0.25% or less cottonseed oil in an oil blend. The oil is no longer responsive to the halphen test after hydrogenation, which decreases the iodine value 2-5 units. 

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