Yield losses

In general terms, there are two sources of yield loss in the process ... 

In this case, because there are no raw materials losses in the separation and recycle system, the only yield loss is in the reactor, and the process yield equals the reactor selectivity. 

Yield Losses. The numerous steps incur a built-in yield loss. For example, if only 2% yield loss were to be associated with each step, the overall yield for a purification sequence of 10 steps would be as in equation 1 ... 

Packaging (qv) represents the largest market area for film and sheeting materials (15). It is a complex market with so many categories that it is difficult to get an accurate measure of end usage for specific materials (16). The stmcture of the marketplace which uses both monolayers of film, as well as converted composite stmctures and laminates, adds to the complexity. The ultimate user or packager may purchase raw film direcdy from a manufacturer, or use the same film laminated to one or more other films or substrates through a converter. The converter may buy film or extmde his own supply. Resin sales to film producers do not always correlate with their film sales, because of scrap and yield losses. 

Silica. Sihca, which has the greatest impact on yield losses, reacts with HF and is discharged from the manufacturing process as H2SiFg. Yield losses can be calculated based on the chemical stoichiometry ... 

Calcium C rbon te. Calcium carbonate, like R2O2, affects sulfuric and oleum consumption in the HF process. Sulfuric acid loss is approximately 0.98% H2SO4 for each percentage of CaCO. The carbon dioxide evolved by the reaction increases the noncondensable gas flow, and because it carries HF, contributes to yield losses in the vent stream. 

Ma.gnesium Oxide. Magnesium oxide behaves in a similar manner to other metal oxides. However, most spars contain practically no magnesium oxide, so it does not affect yield loss or plant operation. 

Chemical, cultural, and mechanical weed control practices have been relatively successful ia reducing yield losses from weeds (448). However, herbicide-resistant weed populations, soil erosion, pesticide persistence ia the environment, and other problems associated with technologies used (ca 1993) to control weeds have raised concerns for the long-term efficacy and sustainability of herbicide-dependent crop production practices (449). These concerns, coupled with ever-increasing demands for food and fiber, contribute to the need for innovative weed management strategies (450). 

Dioxetanones decompose near or below room temperature to aldehydes or ketones (56). The decomposition reactions are weakly chemiluminescent Qc ca 10 ein/mol) because the products are poorly fluorescent. However, addition of 10 M mbrene provides 2iQc ca 10 ein/mol, and 2iQc on the order of was calculated at mbrene concentrations above 10 M after correcting for yield loss factors (57). The decomposition rates are first order ia... 

A multistep synthesis is strategically designed such that the labeled species is introduced as close to the last synthetic step as possible in order to minimize yield losses and cost. Use of indirect reaction sequences frequently maximizes the yield of the radioactive species at the expense of time and labor. 

The main by-products ia the dehydrogenation reactor are toluene and benzene. The formation of toluene accounts for the biggest yield loss, ie, approximately 2% of the styrene produced when a high selectivity catalyst is used. Toluene is formed mostly from styrene by catalytic reactions such as the foUowiag ... 

A small fraction of the hydrocarbons decompose and deposit on the catalyst as carbon. Although the effect is minute ia terms of yield losses, this carbon can stiU significantly reduce the activity of the catalyst. The carbon is formed from cracking of alkyl groups on the aromatic ring and of nonaromatics present ia certain ethylbenzene feedstocks. It can be removed by the water gas reaction, which is catalyzed by potassium compounds ia the catalyst. Steam, which is... 

In the reaction of ethylene with sulfuric acid, several side reactions can lead to yield losses. These involve oxidation, hydrolysis—dehydration, and polymerization, especially at sulfuric acid concentrations >98 wt % the sulfur thoxide can oxidize by cycHc addition processes (99). 

The feed streams should be reasonably pure to limit yield losses and protect the purity of the final products. Typically, polymer-grade propylene with 99.5% purity is employed propane impurity can react to undesirable 1-chloropropane (bp 46.6°C), which is very difficult to separate from aHyl chloride (bp 45°C). Both propylene and chlorine should be dry to prevent corrosion in downstream equipment where mixtures with HCl occur. 

Yields of propylene chlorohydrin range from 87—90% with dichloropropane yields of 6—9%. The dichloropropane is not only a yield loss but also represents a disposal problem as few uses are known for this material. Since almost all the propylene chlorohydrin is dehydrochlorinated to propylene oxide with lime or sodium hydroxide, none of the chlorine appears in the final product. Instead, it ends up as dilute calcium or sodium chloride solutions, which usually contain small amounts of propylene glycol and other organic compounds that can present significant disposal problems. 

As a result of these mechanisms, most process streams contain enough foreign nuclei to cause some fogging. While fogging has been reported in only a relatively low percent of process parti condensers, it is rarely looked for and volunteers its presence only when yield losses or pollution is intolerable. 

Practical separation techniques for hquid particles in gases are discussed. Since gas-borne particulates include both hquid and sohd particles, many devices used for dry-dust collection (discussed in Sec. 17 under Gas-Sohds Separation ) can be adapted to liquid-particle separation. Also, the basic subject of particle mechanics is covered in Sec. 6. Separation of liquid particulates is frequently desirable in chemical processes such as in countercurrent-stage contacting because hquid entrainment with the gas partially reduces true countercurrency. Separation before entering another process step may be needed to prevent corrosion, to prevent yield loss, or to prevent equipment damage or malfunc tion. Separation before the atmospheric release of gases may be necessaiy to prevent environmental problems and for regula-toiy compliance. 

Hydrofining has all the advantages of acid treating without the disadvantages. For example, acid treating does not readily remove refractory sulfur compounds such as thiophene the treated products must be rerun to remove polymers with a consequent yield loss and disposal of the acid sludges is a serious problem. 

Various materials, present by accident or design, can alter the course of reduction by arresting the reaction at an intermediate product or by causing the formation of coupled products (94,95). These deviations can range from only a small yield loss to the formation of a major product. The work of Kosak (56) on o-nitroanisole is instructive in this regard, where small amounts of... 

The main difficulties connected with this hydrogenation arise from over-reduction to the alcohol, which is a yield loss per se... 

If the resulting alcohol is susceptible to hydrogenolysis, still further yield loss occurs through formation of water. 

Moore, P.H. Osgood, R.V. (1985). Assessment of sugarcane crop damage and yield loss by high winds of hurricanes. Agricultural and Forest Meteorology, 35, 267-79. 

Halberg, N. Kristensen, I.S. (1997) Expected Crop Yield Loss when converting to Organic Dairy Farming in Denmark. Biological Agriculture and Horticulture, 14, 25-41. 

Yield loss due to modest chemical conversion and ee, and the need to remove both residual starting material and enantiomer from API. 

To allow for unaccounted physical yield losses, round off to 0.43... 

All the reaction yield losses were taken as caused by reaction 2. 

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