Manufacturing processes, percent yield

All manufacturers of butynediol use this formaldehyde ethynylation process, and yields of butynediol may be in excess of 90 percent, in addition to 4 to 5% propargyl alcohol. 

The most common commercial process for the manufacture of vinylidene chloride is the dehydrochlorination of 1,1,2-trichloroethane with lime or caustic in slight excess (2 to 10%). A continuous liquid-phase reaction at 98 to 99°C gives a 90 percent yield of vinylidene. 

The key reaction in this manufacturing process is the hot chlorination of propylene, which fairly selectively gives substitution to methyl group rather than the addition to the double bond. In this chlorination step, fresh propylene is first mixed with recycle propylene. This mixture is dried over a desiccant, heated to 650-700°F, and then mixed with chlorine (C3H6 to Cl2 ratio is 4 1) and fed to a simple steel tube adiabatic reactor. The effluent gases (950°F) are cooled quickly to 120°F and fractionated. The yield of allyl chloride is 80-85 percent. 

A modification of the Bachmann process used to make RDX with the same starting materials and in similar equipment is employed for the manufacture of HMX. The reaction temperature is lower (44 1°C as compared to 68°C for RDX) and the raw materials are mixed in a two-step process. The yield of HMX per mole of hexamine is about 55 to 60 percent, as compared to 80 to 85 percent in the manufacture of RDX. 

LAB that in order to compete, manufacturers must reduce the cost of making their products to the lowest level possible. Percent yield is important in the calculation of overall cost effectiveness in industrial processes. For example, sulfuric acid (H2SO4) is made using mined sulfur. Figure 12-8. Sulfuric acid is an important chemical because it is a raw material for products such as fertilizers, detergents, pigments, and textiles. The cost of sulfuric acid affects the cost of many of the consumer items you use every day. 

The first industrial method, the lead-chamber process, is not commonly used now because its purity is low and its percent yield is only 60 to 80 percent. But it is much cheaper than the later and more productive contact process. The lead-chamber process is used for manufacturing sulfuric acid for applications that do not demand high purity. 

It is important to differentiate test yield from defect coverage of a test. The yield of the manufacturing process before test might be (say) 50 percent, and the yield after test may be 97 percent. This may be accomplished with a test that detects (covers) 90 percent of the important defects. 

If you know the percent yield, you can use it as a dimensional analysis conversion factor. Percent yield is grams actual yield per 100 grams theoretical yield. For example, assume that a manufacturer of magnesium hydroxide knows from experience that the percent yield is 81.3% from the production process. This can be used as either of 81.3 g (act) 100 g (theo)... 

Percent yields may range from a tiny fiaction to 100 percent. (They cannot exceed 1(X) percent.) Chemists try to maximize percent yield in a variety of ways. Factors that can affect percent yield, including temperature and pressure, are discussed in Chapter 15. Sample Problem 3.13 shows how to calculate the percent yield of a pharmaceutical manufacturing process. 

Cumene manufacture consumed about 10 percent (2.2 billion lb) of the propylene used for chemicals in the United States in 1998. It is prepared in near stoichiometric yield from propylene and benzene with acidic catalysts (scheme below). Many catalysts have been used commercially, but most cumene is made using a solid phosphoric acid catalyst. Recently, there has been a major industry shift to zeolite-based catalyst. The new process has better catalyst productivity and also eliminates the environmental waste from spent phosphoric acid catalyst. It significantly improves the product yield and lowers the production cost. Cumene is used almost exclusively as feed to the cumene oxidation process, which has phenol and acetone as its coproducts. 

The recovery of whole cells is best explained by the manufacturing procedure for baker s yeast. This process is almost identical to the early stage of protein recovery, except that the final product is the cell instead of the filtrate. After fermentation, the cells are spun out with a centrifuge, washed with water, and recentrifuged to yield a yeast cream with a solids concentration of approximately 18 percent. Cream yeast can be loaded directly into tanker trucks and delivered to customers equipped with an appropriate cream yeast handling system. Alternatively, the yeast cream can be pumped to a plate and frame filter press or an RDVF and dewatered to a cakelike consistency with 30-32 percent yeast solids content. The press cake yeast is crumbled into pieces and packed or spray-dried for dry products. After packaging, the yeast is ready for shipping to retail. 

S)-Naproxen, 18, and S-ibuprofen, 19, are important and widely used analgesics with annual sales of about US 1.4 billion and a production volume of about 8000 tons. A technical feasible use of R,R-tartaric acid as chiral auxiliary was demonstrated in the Zambon Process for S-naproxen manufacture [3]. The diastereoselective bromination is followed by bromine hydrogenolysis and hydrolysis to produce S-naproxen in 75 percent overall yield. 

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