Processing Yield

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

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. 

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. 

Increasing process yields of raw materials through improved selectivity in the reactor. 

Increasing process yields through improved separation and recycling. 

Increasing process yields through feed purification to reduce losses in the reactor and separation and recycle system. 

Polymerization processes yielding polymers, whose mers are constitutionally identical to the reacting monomers are now classified as addition polymerizations. Thus styrene can be converted, by addition polymerization, to polystyrene ... 

This construction requires one matrix-vector multiplication with S and two inner products in each recursive step. Therefore, it is not necessary to store S explicitly as a matrix. The Lanczos process yields the approximation [21, 7, 12]... 

Step 6 Proton transfer processes yielding ammonium ion and the carboxylic acid ... 

This process yields satisfactory monomer, either as crystals or in solution, but it also produces unwanted sulfates and waste streams. The reaction was usually mn in glass-lined equipment at 90—100°C with a residence time of 1 h. Long residence time and high reaction temperatures increase the selectivity to impurities, especially polymers and acrylic acid, which controls the properties of subsequent polymer products. 

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. 

Although each production process yields ash that is essentially chemically equivalent, the various products differ ia physical properties and ia contaminants as shown ia Table 6. Hopper cars, pneumatic tmcks, supersacks, and multiwaH kraft bags with polyethylene liners are the usual shipping containers. 

This process yields a purely straight-chain acid of even carbon number. Typically, the value of n varies from two to six, and distillation yields the pure components. Du Pont pioneered the development of this technology. Allied has used hexafluoroacetone to produce telomer iodides containing the... 

Biological—Biochemical Processes. Fermentation is a biological process in which a water slurry or solution of raw material interacts with microorganisms and is enzymatically converted to other products. Biomass can be subjected to fermentation conditions to form a variety of products. Two of the most common fermentation processes yield methane and ethanol. Biochemical processes include those that occur naturally within the biomass. 

Properties. Pilot-unit data indicate the EDS process may accommodate a wide variety of coal types. Overall process yields from bituminous, subbituminous, and lignite coals, which include Hquids from both Hquefaction and Flexicoking, are shown in Figure 14. The Hquids produced have higher nitrogen contents than are found in similar petroleum fractions. Sulfur contents reflect the sulfur levels of the starting coals ca 4.0 wt % sulfur in the dry bituminous coal 0.5 wt % in the subbituminous and 1.2 wt % sulfur in the dry lignite. 

Table 11. High Temperature Pyrolysis Process Yields...

Refining Processes. AH the reduction processes yield an impure metal containing some of the minor elements present in the concentrate, eg, cadmium in 2inc, or some elements introduced during the smelting process, eg, carbon in pig iron. These impurities must be removed from the cmde metal in order to meet specifications for use. Refining operations may be classified according to the kind of phases involved in the process, ie, separation of a vapor from a Hquid or soHd, separation of a soHd from a Hquid, or transfer between two Hquid phases. In addition, they may be characterized by whether or not they involve oxidation—reduction reactions. 

In the carbonyl process, the Hquid is purified, vaporized, and rapidly heated to ca 300°C which results in the decomposition of the vapor to carbon monoxide and a fine high purity nickel powder of particle sizes <10 fim. This product is useflil for powder metallurgical appHcations (see Metallurgy, powder). Nickel carbonyl can also be decomposed in the presence of nickel powder, upon which the nickel is deposited. This process yields nickel pellets, typically about 0.8 cm dia and of >99.9 wt% purity. 

In this representation the FeCl2 which takes part in the first step of the reaction is not a tme catalyst, but is continuously formed from HQ. and iron. This is a highly exothermic process with a heat of reaction of 546 kj /mol (130 kcal/mol) for the combined charging and reaction steps (50). Despite the complexity of the Bnchamp process, yields of 90—98% are often obtained. One of the major advantages of the Bnchamp process over catalytic hydrogenation is that it can be mn at atmospheric pressure. This eliminates the need for expensive high pressure equipment and makes it practical for use in small batch operations. The Bnchamp process can also be used in the laboratory for the synthesis of amines when catalytic hydrogenation caimot be used (51). 

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. 

The manufacture of polydimethylsiloxane polymers is a multistep process. The hydrolysis of the chlorosilanes obtained from the direction process yields a mixture of cycHc and linear sdanol-stopped oligomers, called hydrolysate (eq. 7) (21). In some cases, chloro-stopped polymers can also be obtained (59). 

Hydrogen sulfide has been produced in commercial quantities by the direct combination of the elements. The reaction of hydrogen and sulfur vapor proceeds at ca 500°C in the presence of a catalyst, eg, bauxite, an aluminosihcate, or cobalt molybdate. This process yields hydrogen sulfide that is of good purity and is suitable for preparation of sodium sulfide and sodium hydrosulfide (see Sodium compounds). Most hydrogen sulfide used commercially is either a by-product or is obtained from sour natural gas. 

The popularity of MSA as an electrolyte in electrochemical appHcations has developed as a result of the following unique physical and chemical properties (/) exhibits low corrosivity and is easy to handle, (2) nonoxidizing, (7) manufacturing process yields a high purity acid, (4) exceptional electrical conductivity, (3) high solubiHty of metal salts permits broad appHcations, (6) MSA-based formulations are simpler, (7) biodegradable, and (8) highly stable to heat and electrical current. 

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