Cracking chevron

Solvent, product aldehyde pressure, 500 psi temperature, 107°C catalyst, 3/1 weight ratio of PPh3 to HRh(CO)(PPh3)3. b Chevron cracked-wax o-olefin. c Gulf a-olefin from ethylene polymerization. 

Fig. 6.2.7 (a). Diagram of parameters of chevron cracks associated with spherical indenter action and (b) crack mechanism seen in cross-section of Hertz s cone (C—C crack plane). Crack growth tends to enlarge in (r, 0) in relation to the initiation of the crack peak, which optimizes the conditions for energy liberation. (After Lawn et at., 1975)... 

Misra and Finnie (1970) investigating the scribing process used for segmentation of semiconducting silicon wafers established the formation of three-crack systems (Fig. 6.2.6) on the lateral surfaces of the plate, chevron cracks develop along the scratch, whereas beneath the scratch,... 

Fig. 6.2.6. Diagrammatic representation of median, lateral and chevron cracks formed by scribing with a sharp indenter. (After Misra and Finnie, 1979)...

Zone 2B - River-hke chevron cracks are seen, appecffcuice is less brittle. 

The cracks observed around the groove were mainly surface chips or radial(chevron) cracks. There was no median crack beneath the groove. Figure 12 shows the cross section of the scratch groove in soda-lime glass. For the other glasses, no median crack can be also observed in the cross sections. 

Wax Cracking. One or more wax-cracked a-olefin plants were operated from 1962 to 1985 Chevron had two such plants at Richmond, California, and Shell had three in Europe. The wax-cracked olefins were of limited commercial value because they contained internal olefins, branched olefins, diolefins, aromatics, and paraffins. These were satisfactory for feed to alkyl benzene plants and for certain markets, but unsatisfactory for polyethylene comonomers and several other markets. Typical distributions were C 33% C q, 7% 25% and 35%. Since both odd and... 

During the 1980s, antimony was widely used in FCCUs that had a problem with contaminant metals. In the late 1980s, other additives were introduced to combat the contaminant metals, eg. Chevron introduced a bismuth-based additive, which is claimed to provide performance similar to antimony (18). Also in the late 1980s, cracking catalysts were developed with metals traps that appear to be so effective in containing the adverse effects of contaminant metals that additive-type inhibitors are no longer needed (19). 

Theories of the oxidation of tantalum in the presence of suboxide have been developed by Stringer. By means of single-crystal studies he has been able to show that a rate anisotropy stems from the orientation of the suboxide which is precipitated in the form of thin plates. Their influence on the oxidation rate is least when they lie parallel to the metal interface, since the stresses set up by their oxidation to the pentoxide are most easily accommodated. By contrast, when the plates are at 45° to the surface, complex stresses are established which create characteristic chevron markings and cracks in the oxide. The cracks in this case follow lines of pores generated by oxidation of the plates. This behaviour is also found with niobium, but surprisingly, these pores are not formed when Ta-Nb alloys are oxidised, and the rate anisotropy disappears. However, the rate remains linear it seems that this is another case in which molecular oxygen travels by sub-microscopic routes. 

Apart from the UOP Pacol process, today s only other meaningful economic process is the Shell higher olefin process (SHOP) in which /z-olefins are produced by ethylene oligomerization. Until 1992 Hiils AG used its own technology to produce -60,000 t/year of /z-olefins by the chlorination of /z-paraffins (from Molex plant) and subsequent dehydrochlorination [13]. In the past, the wax cracking process (Shell, Chevron) played a certain role. In the Pacol and Hiils processes, olefins are obtained as diluted solutions in paraffin (Pacol to max. 20%, Hiils about 30%) without further processing these are then used for alkylation. In contrast, the SHOP process produces pure olefins. 

Isodewaxing A catalytic dewaxing process developed by Chevron Research Technology. It incorporates catalysts that achieve both wax isomerization and shape-selective cracking. 

Until the recent discovery of UTD-1 and CIT-5, the largest pore zeolites known were composed of pore structures having 12-MRs or less. Many of these materials such as zeolite Y have enjoyed immense commercial success as catalysts (2). There is some evidence from catalytic cracking data that suggests the inverse selectivity found with the 12-MR pore ( 7.5 A) structure such as for SSZ-24 (Chevron) might be used to enhance octane values of fuel (3). However, small increases in pore size as well as variations in pore shape and dimensionality could further improve the catalysts. Pores with greater than a 12-MR structure might allow the conversion of... 

There are two main techniques used to measure the fracture toughness of ceramics fracture stress and hardness indentation. The former measures the load to fracture of a pre-cracked specimen using a single edge notched beam (SENB) or a chevron notched beam (CNB) sample. The main drawback of this technique is ensuring that the crack tip is atomically sharp. The second method uses the crack formed at the corners of the indentation produced during a Vickers indentation hardness test. This technique is rapid and relatively inexpensive. However, the toughness values measured are those of the surface, unlike the values obtained by fracture of the pre-cracked beams which are a measure of the bulk material properties. 

Isocracking A hydrocracking process, developed by Chevron and now licensed by Chevron Lummus Global. The catalyst contains a mixture of hydrous oxides for cracking, plus heavy metal sulfides for hydrogenation. First commercialized in 1962 and now widely licensed worldwide. See also Isomax. 

Sulfur s coefficient of thermal expansion can be reduced significantly when modified with plasticizers and fillers. Most Chevron composites have coefficients of expansion about one-half that of elemental sulfur. Even lower coefficients are possible with very high levels of filler. These lower coefficients contribute to the improved thermal shock resistance of sulfur composites and to their reduced tendency to crack or craze. 

The approximately 40 cracking operations are owned by various corporate entities. Some have several plants across the US. As well as US majors (Chevron-Phillips, Exxon-Mobil, Dow Chemical, Equistar), several foreign organisations operate crackers in order to have better access to the US market. Notables amongst these are BASE-Eina (EU), Formosa Petrochemical (Taiwan) and Sasol (South Africa). 

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