Application Hydrogenation of Oils

Peanut butter is a common consumer product that contains partially hydrogenated vegetable oil. 

Several ingredients are added to make margarine more closely resemble butter orange p-carotene (Section 10.5) is often added for color, salt for flavor, and 3-hydroxy-2-butanone [CHgCOCHTOHjCHa] or 2,3-butanedione (CH3COCOCH3) to mimic the flavor of butter. 

Many processed foods, such as peanut butter, margarine, and some brands of crackers, contain partially hydrogenated vegetable oils. These oils are produced by hydrogenating the long hydrocarbon chains of triacylglycerols. 

In Section 10.6 we learned that fats and oils are triacylglycerols that differ in the number of degrees of unsaturation in their long alkyl side chains. 

The number of double bonds in the R groups makes a triacylglycerol either a fat or an oil, j 

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The effect of physical processes on reactor performance is more complex than for two-phase systems because both gas-liquid and liquid-solid interphase transport effects may be coupled with the intrinsic rate. The most common types of three-phase reactors are the slurry and trickle-bed reactors. These have found wide applications in the petroleum industry. A slurry reactor is a multi-phase flow reactor in which the reactant gas is bubbled through a solution containing solid catalyst particles. The reactor may operate continuously as a steady flow system with respect to both gas and liquid phases. Alternatively, a fixed charge of liquid is initially added to the stirred vessel, and the gas is continuously added such that the reactor is batch with respect to the liquid phase. This method is used in some hydrogenation reactions such as hydrogenation of oils in a slurry of nickel catalyst particles. Figure 4-15 shows a slurry-type reactor used for polymerization of ethylene in a sluiTy of solid catalyst particles in a solvent of cyclohexane. 

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 some applications such as catalytic hydrogenation of vegetable oils, slurry reactors, froth flotation, evaporative crystallisation, and so on, the success and efficiency of the process is directly influenced by the extent of mixing between the three phases. Despite its great industrial importance, this topic has received only limited attention. 

The reactor system works nicely and two model systems were studied in detail catalytic hydrogenation of citral to citronellal and citronellol on Ni (application in perfumery industty) and ring opening of decalin on supported Ir and Pt catalysts (application in oil refining to get better diesel oil). Both systems represent very complex parallel-consecutive reaction schemes. Various temperatures, catalyst particle sizes and flow rates were thoroughly screened. 

One of the most important, and perhaps the best studied, applications of three-phase fluidization is for the hydrogenation of carbon monoxide by the Fischer-Tropsch (F-T) process in the liquid phase. In this process, synthesis gas of relatively low hydrogen to carbon monoxide ratio (0.6 0.7) is bubbled through a slurry of precipitated catalyst suspended in a heavy oil medium. The F-T synthesis forms saturated and unsaturated hydrocarbon compounds ranging from methane to high-melting paraffin waxes (MW > 20,000) via the following two-step reaction ... 

Skeletal catalysts are primarily used for hydrogenation and dehydrogenation reactions. The first application of skeletal nickel was hydrogenation of cottonseed oil [1], Skeletal catalysts have since... 

Meanwhile attempts to find an air oxidation route directly from p-xylene to terephthalic acid (TA) continued to founder on the relatively high resistance to oxidation of the /Moluic acid which was first formed. This hurdle was overcome by the discovery of bromide-controlled air oxidation in 1955 by the Mid-Century Corporation [42, 43] and ICI, with the same patent application date. The Mid-Century process was bought and developed by Standard Oil of Indiana (Amoco), with some input from ICI. The process adopted used acetic acid as solvent, oxygen as oxidant, a temperature of about 200 °C, and a combination of cobalt, manganese and bromide ions as catalyst. Amoco also incorporated a purification of the TA by recrystallisation, with simultaneous catalytic hydrogenation of impurities, from water at about 250 °C [44], This process allowed development of a route to polyester from purified terephthalic acid (PTA) by direct esterification, which has since become more widely used than the process using DMT. 

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. 

Fixed-bed reactors Trickle-flow reactor (TFR) This is a tubular flow reactor with a concurrent down-flow of gas and liquid over a fixed-bed of catalyst (Figure 3.10). Liquid trickles down whereas the gas phase is continuous. This reactor is mainly used in catalytic applications. Typical application examples of this reactor type are the following HDS of heavy oil fractions and catalytic hydrogenation of aqueous nitrate solutions. 

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