Indirect processes

Direct conversion of natural gas to Hquids has been actively researched. Process economics are highly variable and it is unclear whether direct natural gas conversion technologies are competitive with the estabUshed indirect processes. Some emerging technologies in this area are presented herein. 

The indirect hydration, also called the sulfuric acid process, practiced by the three U.S. domestic producers, was the only process used worldwide until ICI started up the first commercial direct hydration process in 1951. Both processes use propylene and water as raw materials. Early problems of high corrosion, high energy costs, and air pollution using the indirect process led to the development of the direct hydration process in Europe. However, a high purity propylene feedstock is required. In the indirect hydration process, C -feedstock streams from refinery off-gases containing only 40—60 wt % propylene are often used in the United States. 

Isopropyl Alcohol. Propylene may be easily hydrolyzed to isopropyl alcohol. Eady commercial processes involved the use of sulfuric acid in an indirect process (100). The disadvantage was the need to reconcentrate the sulfuric acid after hydrolysis. Direct catalytic hydration of propylene to 2-propanol followed commercialization of the sulfuric acid process and eliniinated the need for acid reconcentration, thus reducing corrosion problems, energy use, and air pollution by SO2 and organic sulfur compounds. Gas-phase hydration takes place over supported oxides of tungsten at 540 K and 25... 

Note This indirect process proceeds by hydrolysis and subsequent decarboxylation. 

The use of microbial siderophores by dicotyledonous plants appears to involve uptake of the entire metallated chelate (42-44), or an indirect process in which the siderophore undergoes degradation to release iron (45). As demonstrated in initial studies examining this question, there was concern that iron uptake from microbial siderophores may be an artifact of microbial iron uptake in which radiolabeled iron is accumulated by root-colonizing microorganisms (46). Consequently, evidence for direct uptake of iron from microbial siderophores has required the use of axenic plants. In experiments with cucumber, it was shown that the microbial siderophore ferrioxamine B could be used as an iron source at concentrations as low as 5 pM and that the siderophore itself entered the plant (42). 

The particular sites to which the B[a]P becomes attached in the DNA will probably greatly influence its role. This may be especially important if the adduct functions directly rather than through a nonspecific, indirect process, such as induction of DNA repair. Efforts have been made to determine the specific sites to which BtalP becomes bound (92.94) and its distribution on chromatin (97,98). 

An activator in rubber compounds containing organic accelerators. In polychloroprene, zinc oxide is considered to be the accelerator rather than the activator. The use of zinc oxide as a reinforcing agent and as a white colouring agent is obsolescent. Zinc oxide is manufactured by either the French (or indirect) process or by the American (or direct) process. It can be used as a filler to impart high thermal conductivity. 

The gasifiers considered in this overview can be differentiated into direct (autothermal) and indirect (allothermal) processes. In the indirect processes, the heat needed to drive the endothermic heterogeneous reactions is provided by inert (circulating) solid material or by heat exchangers. The processes are... 

French Also known as the Indirect process. A process for making zinc oxide, in the form of a white pigment, from metallic zinc. The zinc is melted and vaporized in a current of carbon monoxide. The vapor is oxidized with air in a second chamber, forming zinc oxide and carbon dioxide. The fume passes through a settling chamber, where oversized particles settle out, and from there go to a bag house, where the product is collected. Confusingly, the French process has been operated by North American Oxide Company, at Clarksville, TN. See also American. 

Consequently, in the early 1990s, interest in the direct processes decreased markedly, and the emphasis in research on CH4 conversion returned to the indirect processes giving synthesis gas (13). In 1990, Ashcroft et al. (13) reported some effective noble metal catalysts for the reaction about 90% conversion of methane and more than 90% selectivity to CO and H2 were achieved with a lanthanide ruthenium oxide catalyst (L2Ru207, where L = Pr, Eu, Gd, Dy, Yb or Lu) at a temperature of about 1048 K, atmospheric pressure, and a GHSV of 4 X 104 mL (mL catalyst)-1 h-1. This space velocity is much higher than that employed by Prettre et al. (3). Schmidt et al. (14-16) and Choudhary et al. (17) used even higher space velocities (with reactor residence times close to 10-3 s). 

Most suitable redox couples for indirect processes are inorganic, including ... 

During the indirect process, a redox couple is used as catalyst or electron carrier for the oxidation or reduction of another species in the system. The redox reagent is continuously reconverted eleetrochemically. 

Electrochemical destruction of organics can be an economically viable alternative to incineration, carbon beds, bioremediation, deep well disposal and other methods as destruction to very low acceptable levels is possible [227a], Electrochemical techniques are in fact superior to incineration or deep well disposal as it is a final solution and not a transfer of a toxic material from one environment to another, e.g. to the groundwater or the atmosphere [285], Common destruction pathways include both direct and indirect electrolysis. Many electrochemical degradation pathways remain unclear and may be a mixture of direct and indirect processes depending on the pollutant and its intermediates [84,285a]. 

The Chemistry of Indigo Dyeing.—On account of its insolubility the dye itself cannot be applied directly to the fibre. Yet an indirect process of great antiquity is available, for Tyrian purple has been identified as 6 6 -dibromoindigo 1 by Friedlander. The indigo is made soluble... 

Calcitriol and parathyroid hormone, on the one hand, and calcitonin on the other, ensure a more or less constant level of Ca "" in the blood plasma and in the extracellular space (80-110 mg 2.0-2.6 mM). The peptide parathyroid hormone (PTH 84 AA) and the steroid calcitriol (see p. 374) promote direct or indirect processes that raise the Ca "" level in blood. Calcitriol increases Ca "" resorption in the intestines and kidneys by inducing transporters. Parathyroid hormone supports these processes by stimulating calcitriol biosynthesis in the kidneys (see p. 330). In addition, it directly promotes resorption of Ca "" in the kidneys (see p. 328) and Ca "" release from bone (see B). The PTH antagonist calcitonin (32 AA) counteracts these processes. 

Photooxygenation may take place eii.ter as (a) a direct process, where light is absorbed by A designated as the substrate or as (b) an indirect process or photosensitized process where light is absorbed by a molecule other thin that which reacts and is called a sensitizer. The reaction is said to occur from the triplet state of the excited molecule. 

About 1 -2% of zinc oxide is produced by the wet process, 10-20% by the direct process, and the remainder by the indirect process. 

Raw Materials. In the early days, the raw materials were mainly zinc ores or concentrates for the direct process, or metal from zinc producers for the indirect process. Nowadays, zinc oxide manufacturers mainly use residues and secondary zinc. This fact, combined with the demand for chemical purity imposed by the users, means that processes have had to be modified and a number of purification techniques are used. 

Indirect process Indirect process Direct process Wet process... 

The free-radicals are generated by discharge of proton, peroxides and easily reducible compounds at the cathode according to Eq. (1—4). The radial-anion of monomer is obtained by both direct and indirect electron transfer process [Eq. (5—6)]. The indirect process means that the active oxidizing species is formed from the electrolytes by electrode reaction, followed by interaction with the monomer. An unstable monomer like a,a -2-trichloro-p-xylene is formed and polymerizes instantaneously [Eq. (7)]. The regeneration of ferrous ion from the pool of used up ferric ion in a redox system is electrolytically successful [Eq. (8)] and an... 

We have considered direct electron tunneling from a donor to an acceptor under the influence of radiation. Along with this some indirect processes of electron tunneling with the participation of light are possible. For instance, the absorption of light may result in the excitation of the donor... 

The type of electron exchange, which can take place either by direct heterogeneous electron transfer between the electrode and the substrate or by using an indirect process, in which a redox catalyst mediates the exchange of redox equivalents between the electrode and the substrate... 

A direct conversion of santonin to Formula 31 is thus possible in addition to the indirect process involving lumisantonin. The... 

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