Iodine value selected oils

Selective hydrogerration over low-loading, supported Cu catalysts has shown to be a valuable tool for the production of high quality biodiesel from Tall Oil, a byproduct of the Pulp Paper indrrstry. These resrrlts allow planning the use of a great variety of non-conventiorral oils with high iodine value for the production of biodiesel. 

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. 

TABLE 3. Melting Point, Titer, and Iodine Value of Selected Oils (10). 

Some new rare-earth based oxide catalysts are used to partially hydrogenated the rapeseed oil. The binary oxide Ce-Ni-O presents a good selectivity in the partial hydrogenation but a large extent of Z/E isomerization. The ratio of the iodine value (IV) variation over the pourpoint (PP) variation is lower than one. The introduction of aluminium in the catalyst formulae leads to a signiHcant decrease in the pourpoint variation due to the quasi-elimination of the Z/E isomerization. The oils obtained are more resistant to oxidation. 

Because of the presence of highly unsaturated fatty acids (as indicated by a high iodine value IV = 117) the rapeseed oil shows poor stability. It must be partially hydrogenated to increase this stability. The rapeseed oil conversion and the product distribution both depend on the Ni/Ce ratio of the mixed Ni-Ce-oxides and on the temperature. These catalwts appear more selective than Ni alone but lead to an important Z/E isomerization which gives rise to a drastic increase in the pourpoint value, llie use of a temaiy oxide (Ce-Ni-Al) allows a decrease in the extent of the Z/E isomerization. The results depend on the relative amount of each metal and the isomerization can be almost totally eliminated. Moreover, from some DSC experiments under an oxidative atmosphere, it appears that the resistance to oxidation can be improved, even at relatively high temperatures. 

The development of low-erucic acid rapeseed edible oil cultivars began after the identification of the discussed genetic sources of low erucic acid in both rapeseed species. Generic breeding objectives were still to develop locally adapted rapeseed cultivars with improved productivity and seed quality. Selection in both species was for maturity, seed yield, uniformity, lodging resistance, oil content, and iodine value in the oil. Seed quality improvement now included seed oil containing less than 5% erucic acid. 

The usual practice for the process operator is to determine the refractive index of a sample of the oil during hydrogenation, since this can be done in a few minutes, on site. It correlates well with the iodine value of the oil and also the solid fat index. If a hydrogen gas meter is available, this will have been set at a precalculated amount of gas at which to stop the reaction for determination of the refractive index. Calculation of the amount of gas required is based on the stoichiometry of hydrogenation (Mattil 1964). When the desired refractive index is reached, the batch is cooled for filtration and the solid fat index is determined in the laboratory. This is by far the most important analysis method in hydrogenation control. Typical solid fat indices for selectively and nonselectively hydrogenated canola oil are given in Table IV (Teasdale, 1975). 

Because linolenic acid (a minor but significant component of soybean oil) with its n—3 (A 15) double bond furnishes undesirable flavours after oxidation and also because linoleic acid has a desirable dietary value considerable effort has gone into making catalysts with high linolenic/linoleic selectivity. For nickel catalyst this is only 2-3 but with copper catalysts it may be 15-20. Thus soybean oil, reduced to an iodine value of 110 for use as a salad oil, would contain <1% or 4-5% linolenate with copper or nickel catalysts respectively. 

Thiocyanogen value Vsl- a-no-jon val-(i)yii. Measure of the number of single double bonds in a substance, for example, an oil. Whereas thiocyanogen is selective in its action, adding on to isolated double bonds only, iodine is not selective and thus a combination of both thiocyanogen and iodine values provides a means of assessing quantitatively the different types of unsaturated components in a material. 

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