Carbon dioxide residence time

Since many different gas/liquid contactors were used, the experimental conditions differed for each device and the reader is referred to the listing in the original reference [5], The liquid flows range from 10 to 1042 ml h and the gas volume flows from 180 to 25 020 ml h. The corresponding residence times were 0.01-19.58 s. The ratio of carbon dioxide to sodium hydroxide was fixed at 0.4. 

The carbon dioxide volume content was varied from 0.8 to 100 vol.-% the gas velocity changes from 0.1 to 42.9 mm s [5]. The residence time varied from 0.1 to 9.7 min 64 single streams of a liquid film thickness of 65 pm were used at a total volume flow of 50 ml h . The ratio of carbon dioxide to sodium hydroxide was fixed at 0.4. 

The reactor residence time is about 45 minutes, a 95 per cent approach to equilibrium being achieved in this time. The ammonia is fed directly to the reactor, but the carbon dioxide is fed to the reactor upwardly through a stripper, down which flows the product stream from the reactor. The carbon dioxide decomposes some of the carbamate in the product stream, and takes ammonia and water to a high-pressure condenser. The stripper is steam heated and operates at 180°C, whilst the high-pressure condenser is at 170°C and the heat released in it by recombination of ammonia and carbon dioxide to carbamate is used to raise steam. Additional recycled carbamate solution is added to the stream in the high-pressure condenser, and the combined flow goes to the reactor. 

These workers found that the efficiency of oxidation was a function of the residence time of the sample in the reactor and the flow rate of the carrier gas. A high precision of carbon dioxide determination was achieved at a sample flow rate of 50 ml/h and a carrier gas flow rate of 621/h, of which 401/h passes through the shielded zone. 

The results are shown in Figure 2-3, in which the solid line is the exact solution. This numerical approach shows no sign of instability even for a time step of 40 years, nearly five times larger than the residence time of atmospheric carbon dioxide (distime). In fact, the reverse Euler method is nearly always stable, and so I shall use it from now on. 

When coal or biomass is heated, many reactions including dehydration, cracking, isomerization, dehydrogenation, aromatization, and condensations take place. Products are water, carbon dioxide, hydrogen, other gases, oils, tars, and char. The product yields vary, depending on the particular feedstock composition, particle size, heating rate, solids and gas residence times, and the reactor temperature. 

Figure 4.2 presents a simplified flow diagram of the ENCOAL Liquid from Coal (LFC) process. The process upgrades low-rank coals to two fuels, Process-Derived Coal (PDF ) and Coal-Derived Liquid (CDL ). Coal is first crushed and screened to about 50 mm by 3 mm and conveyed to a rotary grate dryer, where it is heated and dried by a hot gas stream under controlled conditions. The gas temperature and solids residence time are controlled so that the moisture content of the coal is reduced but pyrolysis reactions are not initiated. Under the drier operating conditions most of the coal moisture content is released however, releases of methane, carbon dioxide, and monoxide are minimal. The dried coal is then transferred to a pyrolysis reactor, where hot recycled gas heats the coal to about 540°C. The solids residence time... 

POM composed of (NH4)3PMoi204o data were collected at a reaction temperature of 380°C, with an isobutane-rich feedstock (26 mol % isobutane, 13% oxygen, 12% steam, remainder helium), and a residence time of 3.6 s. At the very beginning of its lifetime, the fresh POM was completely unselective and inactive. After approximately 100 hours reaction time, it was 6.5% converted, with a selectivity to methacrylic acid of 42% and to methacrolein of 13%. The main by-product was carbon dioxide. Therefore, the equilibration time was necessary for the generation of the active and selective sites. 

Jacoby et al. (1994) studied the photocatalytic reaction of gaseous trichloroethylene in air in contact with UV-irradiated titanium dioxide catalyst. The UV radiation was kept less than the maximum wavelength so that the catalyst could be excited by photons, i.e., X <356 nm. Two reaction pathways were proposed. The first pathway includes the formation of the intermediate dichloroacetyl chloride. This compound has a very short residence time and is quickly converted to the following compounds phosgene, carbon dioxide, carbon monoxide, carbon dioxide, and hydrogen chloride. The second pathway involves the formation of the final products without the formation of the intermediate. 

Thermal decomposition of iron pentacarbonyl. Very finely divided red iron oxide is obtained by atomizing iron pentacarbonyl, Fe(CO)5, and burning it in excess of air. The size of the particles depends on the temperature (580-800 °C) and the residence time in the reactor. The smallest particles are transparent and consist of 2-line ferri-hydrite, whereas the larger, semi-transparent particles consist of hematite (see Chap. 19). The only byproduct of the reaction is carbon dioxide, hence, the process has no undesirable environmental side effects. Magnetite can be produced by the same process if it is carried out at 100-400 °C. Thermal decomposition of iron pentacarbonyl is also used to coat aluminium powder (in a fluidized bed) and also mica platelets with iron oxides to produce interference or nacreous pigments. 

Catalytic tests of n-pentane oxidation were carried out in a laboratory glass flow-reactor, operating at atmospheric pressure, and loading 3 g of catalyst diluted with inert material. Feed composition was 1 mol% n-pentane in air residence time was 2 g s/ml. The temperature of reaction was varied from 340 to 420°C. The products were collected and analyzed by means of gas chromatography. A FlP-l column (FID) was used for the separation of C5 hydrocarbons, MA and PA. A Carbosieve Sll column (TCD) was used for the separation of oxygen, carbon monoxide and carbon dioxide. 

Figure 2.10 Carbon dioxide yield from methanol steam reforming vs. temperature at a constant residence time of 125 ms and different channel geometries, from Pfeifer etal. [22] (by courtesy of Springer Verlag).

For the standard experiments a 2 1 molar water/mefhanol mixture was fed together with 60 vol.% helium at a pressure of 3 bar into the reactor with a hydrodynamic residence time of250 ms. The reaction started at 230 °C and showed maximum carbon dioxide yields between 235 and 250 °C. The best carbon dioxide yields were found for the catalyst based on TiOz impregnated with CuO/ZnO. 

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