Hydrogenation of fats

Wilhelm Norman patented the first liquid phase hydrogenation of fatty acids in 1902, and this led to the first production plants (England 1906, Procter Gamble in the USA a few years later). The hydrogenation of fats is thus one of the earliest commercial organic processes using heterogeneous catalysis, and it now represents a 15 Mt/a business. 

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SOURCE From Patterson, Hydrogenation of Fats and Oils, Applied Science Pubbsbers, 1983. 

Toxicity, chemicals and, 25-26 Trans fatty acid, from hydrogenation of fats, 232-233 from vegetable oils, 1063 Transamination, 1165-1168 mechanism of, 1167... 

In stirred-slurry reactors, momentum is transferred to the liquid phase by mechanical stirring as well as by the movement of gas bubbles. Small particles are used in most cases, and the operation is usually carried out in tank reactors with low height-to-diameter ratios. The operation is in widespread use for processes involving liquid reactants, either batchwise or continuous— for example, for the batchwise hydrogenation of fats as referred to in Section II. 

Stirred-slurry reactors are of considerable industrial importance in batch-wise processing. The catalytic hydrogenation of fats and fatty acids is an example of a process that is carried out almost exclusively in mechanically stirred slurry reactors. The operation is of less significance with respect to continuous processing. 

Hydrogenations involving consecutive reactions are common in the organic process industry and even in the hydrogenation of fats. In the fine chemicals industry we have examples of acetylenic (triple) bonds to be selectively converted to olefinic (double) bonds. Lange et al. (1998) have shown, for the comversion of the model substance 2-hexyne into cis-2-hexene, how catalytically active microporous thin-film membranes can accomplish 100% selectivity. This unusual selectivity is attributed to avoidance of backmixing. 

Hydrogenation of fats and edible oils H2 + unsaturated oil Ni Saturated oil... 

In the industrial scale of hydrogenation of fats and oils, the most frequently used catalysts are Ni based. The 20-30% Ni is supported on silica. When partial hydrogenation is needed, the temperature applied is between 140 and 200 °C and the pressure between 4 and 10 bar. The total hydrogenation requires higher temperature and pressure (200 °C, 20 bar). Nickel is not a perfect catalyst due to its relative low activity and also due to the formation of Ni-soaps. Recently, a colloidal Pd catalyst was applied successfully in a two-phase system for this type of hydrogenation, at room temperature and atmospheric pressure. The complete conversion of multiunsaturated compounds could be achieved during 15-45 minutes. In dimethylformamide as the second phase solvent, 92% monoene yield with a 70/30 cis/trans ratio could be produced48. 

Table 3.3 gives the total uses of hydrogen. Ammonia production is by far the most important application, followed by methanol manufacture. Hydrogenations in petroleum refineries are an important use. Many other industries utilize hydrogen. Miscellaneous uses include hydrogenation of fats and oils in the food industry, reduction of the oxides of metals to the free metals, pure hydrogen chloride manufacture, and liquid hydrogen as rocket fuel. 

Figure 17.17. Examples of reactors for specific liquid-gas processes, (a) Trickle reactor for synthesis of butinediol 1.5 m dia by 18 m high, (b) Nitrogen oxide absorption in packed columns, (c) Continuous hydrogenation of fats, (d) Stirred tank reactor for batch hydrogenation of fats, (e) Nitrogen oxide absorption in a plate column, (f) A thin film reactor for making dodecylbenzene sulfonate with S03. (g) Stirred tank reactor for the hydrogenation of caprolactam, (h) Tubular reactor for making adiponitrile from adipic acid in the presence of phosphoric acid.

Supported copper catalysts are widely used in industrial chemical processes far the hydrogenation of different compounds. Of great importance are the synthesis of methanol in the presence of CuO/ZnO/Al203 catalyst and hydrogenation of fat oxo-aldehydes to alcohols with mixed copper-chromium oxides. 

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]. 

Pure fatty acids can be further treated (e.g. by hydrogenation, isomerization, and dimerization). The hydrogenation of fats and fatty acids leads to partially or fully unsaturated molecules under retention of the carboxylic group. This is known as hardening because the melting point is increased. Hardened products exhibit a higher stability to air and thermal treatment. Hydrogenation is mostly catalyzed by nickel catalysts and carried out under increased temperature and pressure [23],... 

Poisoning is not always bad. There are situations where a catalyst is intentionally poisoned to decrease activity towards an undesirable reaction. In the hydro-desulfurization and -demetallization of a petroleum feedstock the catalyst is presulfided prior to introducing the feed to decrease its activity and minimize cracking reactions that will produce unwanted gases. Another is the use of ammonia to slightly poison a Pt catalyst used in the hydrogenation of fats and oils to decrease undesirable oversaturation. 

The hydrogenation of fats and oils is a very old technology. It was invented in... 

Hydrogenation of Fats and Oils at Supercritical Conditions Magnus Harroda and PoulMellerb... 

Ever since W. Normann in the beginning of the century invented his process for hydrogenation of fats and oils, it has mainly been performed in the original way, i.e. in a batch reactor where the oil, hydrogen and the catalyst as a slurry are mixed intensively. Alternatively, the loop reactor by Buss AG and some continuous systems have been in operation. 

With this type of catalyst, the hydrogenation is usually carried out in the ranges 110-190°C, under 1-5 bar H2 with 0.01-0.15% Ni catalyst (w/w). The hydrogenation of fats is somewhat special due to the need to work in all three phases (gas, liquid, and solid, with corresponding mass and heat transfer problems), and since the natural feedstocks used show significant variations in composition. For these reasons batch reactors are still preferred because of their simplicity, lower cost, and since they have the flexibility to be adapted to different feedstocks or different end products. 

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