Avoidance carbon

The properties required by jet engines are linked to the combustion process particular to aviation engines. They must have an excellent cold behavior down to -50°C, a chemical composition which results in a low radiation flame that avoids carbon deposition on the walls, a low level of contaminants such as sediment, water and gums, in order to avoid problems during the airport storage and handling phase. 

Naphtha desulfurization is conducted in the vapor phase as described for natural gas. Raw naphtha is preheated and vaporized in a separate furnace. If the sulfur content of the naphtha is very high, after Co—Mo hydrotreating, the naphtha is condensed, H2S is stripped out, and the residual H2S is adsorbed on ZnO. The primary reformer operates at conditions similar to those used with natural gas feed. The nickel catalyst, however, requires a promoter such as potassium in order to avoid carbon deposition at the practical levels of steam-to-carbon ratios of 3.5—5.0. Deposition of carbon from hydrocarbons cracking on the particles of the catalyst reduces the activity of the catalyst for the reforming and results in local uneven heating of the reformer tubes because the firing heat is not removed by the reforming reaction. 

Shipment and Storage, Specifications. A/-Vinyl-2-pyrrohdinone is available in tank cars and tank trailers and in dmms of various sizes. Shipping containers are normally steel or stainless steel. Tank cars are provided with heating coils to facihtate unloading in cold weather. Rubber, epoxy, and epoxy—phenohc coatings are attacked and must be avoided. Carbon steel has been successfully used for storage tanks, but stainless steel preserves product quahty better. Aluminum and certain phenohc coatings are also satisfactory. 

Carbon disulfide is normally stored and handled in mild steel equipment. Tanks and pipes are usually made from steel. Valves are typically cast-steel bodies with chrome steel trim. Lead is sometimes used, particularly for pressure reUef disks. Copper and copper alloys are attacked by carbon disulfide and must be avoided. Carbon disulfide Hquid and vapor become very corrosive to iron and steel at temperatures above about 250°C. High chromium stainless steels, glass, and ceramics maybe suitable at elevated temperatures. 

Typical reactions using either 1,2-dichloroethane or 1,2-dichloropropane to produce carbon tetrachloride and tetrachloroethylene by the chlorinolysis reaction are shown in equations 21—23. Continued removal of tetrachloroethylene and recycling of carbon tetrachloride can result in a net zero production of carbon tetrachloride. Most chemical producers using chlorinolysis for the production of perchloroethylene in the future will take advantage of the per/tet equiUbrium to maximize perchloroethylene to avoid carbon tetrachloride ipiod.uction.From 1,2-dichloroethane ... 

Tn the synthesis of methane from carbon monoxide and hydrogen, it is desired to operate the reactor or reactors in such a way as to avoid carbon deposition on catalyst surfaces and to produce high quality product gas. Since gas compositions entering the reactor may vary considerably because of the use of diluents and recycle gas in a technical operation, it is desirable to estimate the effects of initial gas composition on the subsequent operation. Pressure and temperature are additional variables. 

There is no separate shift conversion system and no recycle of product gas for temperature control (see Figure 1). Rather, this system is designed to operate adiabatically at elevated temperatures with sufficient steam addition to cause the shift reaction to occur over a nickel catalyst while avoiding carbon formation. The refractory lined reactors contain fixed catalyst beds and are of conventional design. The reactors can be of the minimum diameter for a given plant capacity since the process gas passes through once only with no recycle. Less steam is used than is conventional for shift conversion alone, and the catalyst is of standard ring size (% X %= in). 

In some catalytic processes, it is necessary to avoid carbon-carbon bond cleavage. For example, isobutane is mainly transformed into its lower alkane homologues (hydrogenolysis products) on metal surfaces, while it can be converted more and more selectively into isobutene when the Pt catalysts contain an increasing amount of Sn (selective dehydrogenation process) [131]. 

It is important to note that we have tried to avoid carbon-rich stars, because they have a rich molecular line spectrum, mostly CN, CH and C2, obliterating many interesting atomic lines of rare elements. This is why we had in our sample a star, CS 31082-001, in which we were able to measure the 385.97 nm line of U II, whereas in the similar r-process element enriched star CS 22892-052, but carbon rich, a CN line obliterates the U II line. 

The hydrocarbon feed must contain sufficient steam to avoid carbon formation on the catalyst. The steam-to-carbon ratio is defined as moles of steam per mole of carbon in the hydrocarbon. The steam-to-carbon ratios are about 3.0 for hydrocarbon feedstocks but lower values can be used for some feedstocks. Carbon formation is more likely with heavier feedstocks. An alkali-based catalyst can be used to repress carbon formation. 

Finally, an additional approach to using hydrocarbon fuels with Ni-based anodes involves using methanol and ethanol, molecules that carry sufficient oxygen to avoid carbon formation.Unlike the case with low-temperature fuel cells, methanol crossover is not an issue with ceramic membranes. Since methanol decomposes very readily to CO and H2. SOFC can operate with a very high performance using this fuel. ° ° In addition, recent work has shown promising performance levels with limited carbon deposition using dimethyl ether as fuel. ° ° ... 

Finally, with some precursors, complete removal of contaminants can sometimes be troublesome. Consequently, some authors have chosen to use dioxygen as the reactive gas to avoid carbon contamination [62-64]. Thus, pure platinum films have been obtained on thermally oxidized silicon substrate by decomposition of [Pt(CH3)3(CpCH3)j or [Pt(K -acac)2] in ArjOj mixtures at 623 K. Pt films produced from [Pt(K -acac)2] contained less than lat% carbon, while oxygen contamination was not detectable [64]. Similarly, a significative reduction of carbon incorporation into Ru films was evidenced when oxygen was used as a reactive gas during CVD from [RuCp(CO)2]2 [62]. 

CVD starting from zerovalent complexes such as [Fe(CO)s] and [Mo(CO)6] can be attained over a quite broad temperature range (373-673 K), but the final deposits are significantly contaminated by carbon [65, 66], presumably generated by the Boudouart reaction involving two CO and affording CO2 and C. To avoid carbon deposition oxygen can be introduced into the gas phase [67], but metal oxides are produced instead. 

Avoid carbonated beverages during simethicone therapy... 

Obviously, equation 8 suggests that the ideal synthesis gas reactor should operate at a CH4 02 mole ratio of 2 1 (29.6% CH4 in air) if total conversion of the reactants occurs. At high enough temperatures, this mixture is completely converted to H2 and CO at thermodynamic equilibrium. Below about 1270 K, the equilibrium mole fraction of carbon becomes significant. Hence, a reactor must be maintained above 1270 K to avoid carbon formation. 

In a first reactor (Rl), the oxidized material is put in contact with 100% methane, to reduce hematite to wustite the formation of metallic iron has to be preferentially avoided. Carbon dioxide and water are the reaction products. This reaction is endothermic. 

To avoid carbon formation [as indicated by Eqs. (5.3) and (5.4)], the steam-to-gas ratio must be kept high enough to favor the reforming reaction [Eq. (5.1)] and the water gas shift reaction [Eq. (5.2)] over the reactions that form carbon. 

To avoid carbon deposition, the steam-to-carbon ratio is normally kept between 2.5 -3.0, but processes exist too where a steam to methane ratio is used, as high as 4.0 [6],... 

Steam reforming of hydrocarbons has become the most widely used process for producing hydrogen. One of the chief problems In the process Is the deposition of coke on the catalyst. To control coke deposition, high steam to hydrocarbon ratios, n, are used. However, excess steam must be recycled and It Is desirable to minimize the magnitude of the recycle stream for economy. Most of the research on this reaction has focused mainly on kinetic and mechanistic considerations of the steam-methane reaction at high values of n to avoid carbon deposition ( L 4). Therefore, the primary objective of this studyis to determine experimentally the minimum value of n for the coke-free operation at various temperatures for a commercial catalyst. 

Ki. The pH of the solutions in the present study was determined by using a "high-alkalinity" glass electrode, taking due precautions to avoid carbonation of the solutions. 

Avoiding carbon deposition on the catalyst is a major challenge [2, 3]. Carbon can be present as graphite-like coke and in the form of whiskers, or carbon nanofibers. The latter lead to detachment of the nickel crystallites from the support and breaking of the catalyst pellets. This may cause blockage of the reformer reactor tubes and the formation of hot spots. Higher hydrocarbons exhibit a larger tendency to form... 

Coal can supply U.S. needs for the next several hundred years, but there is increasing concern regarding pollution from both coal and petroleum. Unfortunately for the developed nations, using pollution-free energy sources such as nuclear and solar will do comparatively little to reduce worldwide atmospheric pollution. The sources of such pollution are worldwide. About 6 billion tons of C02 was generated in 1985, and this pollution source is expected to increase to 30 billion tons/year by 2060. In the 1980s only 10 percent of the 6 billion tons/year came from the United States. In 2002, this increased to about 5.7 billion tons (Annual Energy Review 2003, DOE) or about 23 percent of the world s total. In 2002, about 210 million tons of avoided carbon emission was achieved by nuclear (140 million) and renewables (mainly hydro).17... 

The equilibrium composition of the synthesis gas depends on the steam-to-gas ratio entering the reactor, the reaction temperature, the reaction pressure, and the quantity of inerts in the reaction mixture. To avoid carbon formation as indicated by reactions 22-3 and 22-4, the steam-to-gas ratio must be kept high... 

There are parallel achievements at the University of Pennsylvania, (Park etai, 1999 2000 2001 Gorte etai, 2000), using anodes with copper substituted for nickel to avoid carbon formation. The last two papers include the electrochemical oxidation of dry fuels other than methane, for example gasoline and diesel, the chemical exergy of which is difficult to calculate, since they are mixtures requiring separative work. 

All of these complexes decompose cleanly at low temperature to produce acetonitrile, carbon dioxide, and initially, the metal hydroxide (equation 45). The decomposition temperatures are 144,176, and 198 °C for Ba, Cu, and Y, respectively. In the case of copper and yttrium, the final product is the metal oxide produced by the dehydration of the hydroxide, while barium hydroxide recombines with carbon dioxide to yield the carbonate. Barium carbonate formation can be avoided, however, by use of a different ligand that avoids carbon dioxide formation. Benzoin a-oxime (Hbo) (13) has been found to be a quite suitable diprotic ligand for this purpose. The barium salt is easily prepared by reaction of the oxime with the metal dihydride (equation 46), and it decomposes cleanly to barium oxide by loss of benzaldehyde and benzonitrile at 250 °C (equation 47). 

CH4 gas was fed at a rate of 150 seem to the reformer at 780 °C. To avoid carbon deposition on the reforming catalyst and cool down the membrane throngh endothermic reaction of steam refonning of methane (SMR), steam was also fed to be a steam/carbon (S/C) ratio of 0.88. CH4 conversion, CO and H2 selectivity were calculated as follows, respectively ... 

---