The Process Yield

Raw materials costs dominate the operating costs of most processes (see Chapter 2). Also, if raw materials are not used efficiently, this creates waste that becomes an environmental problem. It is therefore important to have a measure of the efficiency of raw materials usage. The process yield is defined as  

Stoichiometric factor = stoichiometric moles of toluene required per mole of benzene produced = 1 

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. 

Can byproduct formation be avoided or reduced by recycling This is often possible when the byproduct is formed by secondary reversible reactions. 

If a byproduct is formed by reaction involving feed impurities, can this be avoided or reduced by purification of the feed  

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

14 Time-event chart for a repeated batch cycle for Example 4.5. 

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Batch processes can be synthesized by first synthesizing a continuous process and then converting it to batch operation. The process yield is an important measure of both raw materials efficiency and environmental impact. 

If a linear mbber is used as a feedstock for the mass process (85), the mbber becomes insoluble in the mixture of monomers and SAN polymer which is formed in the reactors, and discrete mbber particles are formed. This is referred to as phase inversion since the continuous phase shifts from mbber to SAN. Grafting of some of the SAN onto the mbber particles occurs as in the emulsion process. Typically, the mass-produced mbber particles are larger (0.5 to 5 llm) than those of emulsion-based ABS (0.1 to 1 llm) and contain much larger internal occlusions of SAN polymer. The reaction recipe can include polymerization initiators, chain-transfer agents, and other additives. Diluents are sometimes used to reduce the viscosity of the monomer and polymer mixture to faciUtate processing at high conversion. The product from the reactor system is devolatilized to remove the unreacted monomers and is then pelletized. Equipment used for devolatilization includes single- and twin-screw extmders, and flash and thin film evaporators. Unreacted monomers are recovered for recycle to the reactors to improve the process yield. 

Isopropyl alcohol can be oxidized by reaction of an a,P-unsaturated aldehyde or ketone at high temperature over metal oxide catalysts (28). In one Shell process for the manufacture of aHyl alcohol, a vapor mixture of isopropyl alcohol and acrolein, which contains two to three moles of alcohol per mole of aldehyde, is passed over a bed of uncalcined magnesium oxide [1309-48-4] and zinc oxide [1314-13-2] at 400°C. The process yields about 77% aHyl alcohol based on acrolein. 

Release by Silver-Assisted Cleavag e. A soluble silver complex formed imagewise in the undeveloped areas of the silver haUde layer may be used to effect a cleavage reaction that releases a dye or a dye precursor. The process yields positive dye transfer images directiy with negative-working emulsions (46). An example is the silver-assisted cleavage of a dye-substituted thiazolidine compound, as shown in equation 7. 

The process yields a random, completely soluble polymer that shows no evidence of crystallinity of the polyethylene type down to —60°C. The polymer backbone is fully saturated, making it highly resistant to ozone attack even in the absence of antiozonant additives. The fluid resistance and low temperature properties of ethylene—acryUc elastomers are largely a function of the methyl acrylate to ethylene ratio. At higher methyl acrylate levels, the increased polarity augments resistance to hydrocarbon oils. However, the decreased chain mobiUty associated with this change results in less fiexibihty at low temperatures. 

It has been a persistent characteristic of shock-compression science that the first-order picture of the processes yields readily to solution whereas second-order descriptions fail to confirm material models. For example, the high-pressure, pressure-volume relations and equation-of-state data yield pressure values close to that expected at a given volume compression. Mechanical yielding behavior is observed to follow behaviors that can be modeled on concepts developed to describe solids under less severe loadings. Phase transformations are observed to occur at pressures reasonably close to those obtained in static compression. 

You should review the contract and the detail specifications to identify whether your existing controls will regulate quality within the limits required. You may need to change the limits, the standards, the techniques, the methods, the environment, and the instruments used to measure quality characteristics. One technique may be to introduce Just-in-time as a means of overcoming storage problems and eliminating receipt inspection. Another technique may be Statistical Process Control as a means of increasing the process yield. The introduction of these techniques needs to be planned and carefully implemented. 

Reversing the process yields an efficient method of energy storage. The process inputs combustion products such as carbon dioxide and water, and energy in tlie form of electricity or shaft power, and outputs oxygen and fuel (typically hydrogen or hydrocarbons). 

When crude oil is refined, some of the processes yield additional gaseous products. The C3 and C4 constituents differ from those released from crude oil or from NGLs, which are saturated hydrocarbons. Refinery gases are high in unsaturates, e.g. propane (propylene) and butane (butylenes). These unsaturated hydrocarbons are a valuable source of chemical process intermediates and enjoy a large market alongside naphtha. 

A number of other chemistries which involve C-O bond cleavage have been reported.226 22 Druliner226 has reported on systems where NCO, 112, 113 or related species is the persistent radical. Homolysis rates for these systems were stated to he suitable for MMA polymerization at ambient temperature. The use of NCO has also been studied by Grande et al. z most recently for AA polymerization.2 0 Although control during AA homopolymerization was poor the process yielded NCO- terminated PAA that could be used to make PAA-block-PMMA.230... 

The reactants are loaded in a magnesia crucible and heated by a resistance furnace to 800°C (Figure 3). Once the CaCl2 is molten, a tantalum stirrer and a Ta-Ni thermocouple sheath are lowered into the melt. While stirring, the reaction is monitored with a thermocouple. Once the reaction is complete, the stirrer and thermocouple well are retracted and the melt is allowed to cool. Figure 4 shows a typical DOR product and salt/crucible residue. A typical product button weighs 600 g and the process yield is >99%. Essentially no purification takes place in the reduction step, meaning that the product button is no purer than the feed. 

Principles and Characteristics The fastest growing area in elemental analysis is in the use of hyphenated techniques for speciation measurement. Elemental spe-ciation analysis, defined as the qualitative identification and quantitative determination of the individual chemical forms that comprise the total concentration of an element in a sample, has become an important field of research in analytical chemistry. Speciation or the process yielding evidence of the molecular form of an analyte, has relevance in the fields of food, the environment, and occupational health analysis, and involves analytical chemists as well as legislators. The environmental and toxicological effects of a metal often depend on its forms. The determination of the total metal content... 

Example 13.7 Calculate the process yield of benzene from toluene and benzene from hydrogen for the approximate phase split in Example 13.2. 

The process yield is an important measure of both raw materials efficiency and environmental impact. 

From the material balance in Exercise 8, calculate the process yield for the manufacture of B. 

Atmospheric sulfur emissions can be minimized at source by improving the process yields and desulfurization of fuels prior to combustion. The difficulty of fuel desulfurization is solid > liquid > gas. Sulfur can be removed from emissions either as S02 or H2S. Removal of the H2S can be by ... 

Suppose that a company has been using a certain supplier of raw materials in one of its chemical processes. A new supplier approaches the company and states that its material, at the same cost, will increase the process yield. If the new supplier has a good reputation, the company might be willing to run a limited test. On the basis of the test results it would then make a decision to change suppliers or not. Good management would dictate that an improvement must be demonstrated... 

In Australia one alumina producer has started to specify membrane-only caustic soda for consumption in the process. Yields of alumina production can be increased if membrane caustic soda is used. 

In the study by Thompson, et al. (11), the ml of gel released per 100 g emulsion for the reference emuTsion without soy, with soy isolate (SIF), soy concentrate (SCF) or soy flour (SF) was 6.07, 5.83, 5.49 and 3.08, respectively, when the hydration ratios were 1 4 (flourrwater) for SIF, 1 3 for SCF and 1 2 for SF. The ml gel released per 100 g emulsion containing 10, 15, 20, and 25% soy protein was 6.70, 5.01, 3.94 and 3.57, respectively. When soy protein concentrate was incorporated into an emulsion at the 3.5% level, the processing yields, textural profile and sensory textural attributes of frankfurters were not different among the products with and without added soy concentrate (13). An objective measure of compression and shear modulus indicated that soy protein concentrate incorporated into frankfurters at the 3.5% level had no effect on batter strength or texture ( M). The addition of a cottonseed protein to frankfurters to replace 5, 10 or 15% of the meat resulted in higher pH, less cured color, less firmness of skin, softer texture and reduced desirability as judged by a sensory panel (J5J. 

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