Processing improvement

Successive PCA and Wavelet analysis processes improve small flaw detection (figure 14), because small size involves linear physical processes, where PCA is efficient. 

The catalytic vapor-phase oxidation of propylene is generally carried out in a fixed-bed multitube reactor at near atmospheric pressures and elevated temperatures (ca 350°C) molten salt is used for temperature control. Air is commonly used as the oxygen source and steam is added to suppress the formation of flammable gas mixtures. Operation can be single pass or a recycle stream may be employed. Recent interest has focused on improving process efficiency and minimizing process wastes by defining process improvements that use recycle of process gas streams and/or use of new reaction diluents (20-24). 

Recent patents and pubHcations describe process improvements. Conversions can be followed by on-line hplc (93). The enzyme amidase can be used to reduce residual monomers (94—96). A hydrogenation process for reduction of acrylamide in emulsions containing more that 5% residual monomer has been patented (95). Biodegradable oils have been developed (97). 

Elimination of unreacted monomers can be accompHshed by two methods dual initiators to enhance conversion of monomers to product (73—75) and steam stripping (70,76). Several process improvements have been claimed for dewatering beads (77), to reduce ha2e (78—81), improve color (82—86), remove monomer (87,88), and maintain homogeneous copolymer compositions (71,72,89). 

High Tena.city Sta.ple Fibers. When stronger staple fibers became marketable, the tire yam processes were adapted to suit the high productivity staple fiber processes. Improved staple fibers use a variant of the mixed modifier approach to reach 0.26 N /tex (3 gf/den). The full 0.4 N /tex (4.5 gf/den) potential of the chemistry is uimecessary for the target end uses and difficult to achieve on the regular staple production systems. 

An analytical model of the process has been developed to expedite process improvements and to aid in scaling the reactor to larger capacities. The theoretical results compare favorably with the experimental data, thereby lending vahdity to the appHcation of the model to predicting directions for process improvement. The model can predict temperature and compositional changes within the reactor as functions of time, power, coal feed, gas flows, and reaction kinetics. It therefore can be used to project optimum residence time, reactor si2e, power level, gas and soHd flow rates, and the nature, composition, and position of the reactor quench stream. 

The economics of the arc-coal process is sensitive to the electric power consumed to produce a kilogram of acetylene. Early plant economic assessments indicated that the arc power consumption (SER = kwh/kgC2H2) must be below 13.2. The coal feedcoal quench experiments yielded a 9.0 SER with data that indicated a further reduction to below 6.0 with certain process improvements. In the propane quench experiment, ethylene as well as acetylene is produced. The combined process SER was 6.2 with a C2H2/C2H4 production ratio of 3 to 2. Economic analysis was completed uti1i2ing the achieved acetylene yields, and an acetylene price approximately 35% lower than the price of ethylene was projected. 

Uses. A soluble form of magnesium nitrate is used as a fertilizer ia states such as Florida where drainage through the porous, sandy soil depletes the magnesium (see Fertilizers). Magnesium nitrate is also used as a prilling aid in the manufacture of ammonium nitrate. A 0.25—0.50% addition of magnesium nitrate to the process improves the stabHity of the prills and also improves durabHity and abrasion resistance. 

Metal Treatment. After rolling, the oxide scale on sheet steel is removed by acid treatment (pickling) (see Metal surface treatments). Phosphoric acid, a good pickling agent, leaves the steel coated with a thin film of iron phosphates. This process improves mst resistance but presents a problem if the steel is to be electroplated. 

Process Hazards Analysis. Analysis of processes for unrecogni2ed or inadequately controUed ha2ards (see Hazard analysis and risk assessment) is required by OSHA (36). The principal methods of analysis, in an approximate ascending order of intensity, are what-if checklist failure modes and effects ha2ard and operabiHty (HAZOP) and fault-tree analysis. Other complementary methods include human error prediction and cost/benefit analysis. The HAZOP method is the most popular as of 1995 because it can be used to identify ha2ards, pinpoint their causes and consequences, and disclose the need for protective systems. Fault-tree analysis is the method to be used if a quantitative evaluation of operational safety is needed to justify the implementation of process improvements. 

Several process improvements using aqueous solution at elevated temperatures (350 °C) and pressure (16) or using an organic solvent and an acid at milder temperatures (<80 C) have been described for o-l L) (17). 

The original hot carbonate process developed by the U.S. Bureau of Mines was found to be corrosive to carbon steel (55). Various additives have been used in order to improve the mass transfer rate as well as to inhibit corrosion. Vetrocoke, Carsol, Catacarb, Benfteld, and Lurgi processes are all activated carbonate processes. Improvements in additives and optimization of operation have made activated carbonate processes competitive with activated MDEA and nonaqueous solvent based systems. Typical energy requirements are given in Table 9. 

The Tools of Quality. Quahty assurance also plays an important role in problem solving and process improvement. To do so, QA personnel must be knowledgeable in the many so-called tools of quahty (TOQ) and theh apphcation, so as to guide the efforts of process improvement. Many QA organizations are involved in training employees in these techniques to facihtate quahty improvement. 

Oxide and nonoxide refractory fibers have become essential materials for use in modem high temperature industrial processes and advanced commercial appHcations. Future process improvements, cost reductions, and performance enhancements are expected to expand the uses and markets for these specialized fibrous materials. 

Another important use of a-pinene is the hydrogenation to i j -pinane (21). One use of the i j -pinane is based on oxidation to cis- and /n j -pinane hydroperoxide and their subsequent catalytic reduction to cis- and /n j -pinanol (22 and 23) in about an 80 20 ratio (53,54). Pyrolysis of the i j -pinanol is an important route to linalool overall the yield of linalool (3) from a-pinene is about 30%. Linalool can be readily isomerized to nerol and geraniol using an ortho vanadate catalyst (55). Because the isomerization is an equiUbrium process, use of borate esters in the process improves the yield of nerol and geraniol to as high as 90% (56). 

In a novel approach to vitamin K, Hoffmann-La Roche has exploited the potential acidity at C-3 as a means to attach the side chain of vitamin (36). Menadione was reacted with cyclopentadiene to yield the Diels-Alder adduct. The adduct is treated with base and alkylated at C-3 with phytyl chloride. A retro Diels-Alder reaction yields vitamin K. Process improvements in this basic methodology have been claimed by Japanese workers (37). 

Although carbon electrode production has been regarded as a mature business, the steady growth in demand and the need for improved electrodes has prompted ongoing development efforts in these areas (/) cost containment through raw material substitutions and process improvements (2) higher purity electrodes for those processes such as siUcon production (J) improvements in thermal shock resistance to enhance electrode performance and (4) better joining systems for prebakes. 

The demand for cement was stimulated by the growth of canal systems ia United States duting the nineteenth century. Process improvements were made ia the calciaation of certain limestones for the manufacture of natural cements, which were gradually displaced by Pordand cement. This latter was named ia a 1824 patent because of its color and resemblance to a natural limestone quarried on the Isle of Pordand ia England. Research conducted siace that time has provided a clear picture of the composition, properties, and fields of stabiUty of the principal systems found ia Pordand cement. These results led to the widely used Bogue calculation of composition based on oxide analysis (1). Details beyond the scope of this article may be found ia the Hterature (2). 

When chlorine dioxide is used for pulp bleaching in conjunction with the Kraft (sulfide) process for chemical pulping, by-product sodium sulfate can be used as a source of makeup sulfur and sodium consumed in the chemical cycle. The demand for sodium and sulfur in pulp bleaching is related to the loss of these chemicals through carryover in unbleached pulp. As process improvements have sought to reduce pollution from pulp mills, less sodium sulfate makeup is required. The trends in pulp bleaching to increase substitution of chlorine with chlorine dioxide have caused an oversupply of sodium sulfate, so that this by-product is often regarded as waste (81). 

In the 1930s, the Raschig Co. in Germany developed a different chlorobenzene-phenol process in which steam with a calcium phosphate catalyst was used to hydrolyze chlorobenzene to produce phenol (qv) and HCl (6). The recovered HCl reacts with air and benzene over a copper catalyst (Deacon Catalyst) to produce chlorobenzene and water (7,8). In the United States, a similar process was developed by the BakeHte Division of Union Carbide Corp., which operated for many years. The Durez Co. Hcensed the Raschig process and built a plant in the United States which was later taken over by the Hooker Chemical Corp. who made significant process improvements. 

Enei y. In recent years the concern for energy conservation has resulted in many innovative process improvements to make the manufacture of citric acid more efficient. Eor example, heat produced by the exotherm of the neutralization of citric acid with lime is used in another part of the process where heat is requited, such as the evaporation/crystallization step. 

A number of process improvements have been described, and iaclude the use of white mineral oil having a boiling range of 300—400°C (60) or the use of a mixture of cresols (61). These materials act to reduce the reaction mixture s viscosity, thus improving mixing. Higher sebacic acid yields are claimed by the use of catalysts such as barium salts (62), cadmium salts (63), lead oxide, and salts (64). 

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