Oxygen-to-hydrocarbon ratio

Thermodynamically, the oxidation of hydrocarbons to carbon dioxide and water is preferred to any partial oxidation reaction. The possibility of forming partial oxidation products is thus entirely dependent on the kinetics of the oxidation process. The oxidation of hydrocarbons, is in general, a stepwise process. One way to confine the depth of oxidation, therefore, is to apply a low oxygen to hydrocarbon ratio and a short reaction time. However, to avoid a multitude of products with different oxidation depths, the use of a catalyst is obviously required. In that case, the above two factors (oxygen deficient conditions and short reaction time) may loose their importance. 

The hydrocarbon (methane or naphtha) and oxygen are preheated before introduction into a combustion chamber where, after passing through a venturi, they enter the burner block fitted with a hundred or so channels. Small amounts of oxygen introduced in countercurrent flow enhance the stability of the flame. The oxygen to hydrocarbon ratio is regulated s o that pan (about one-third) of the hydrocarbon is burned, mid the remainder cracked. The gas formed is quenched with water at a level of the combustion chamber corresponding to the maximum acetylene production- The coke formed is withdrawn and separated. 

Hydrocarbon-rich conditions imply that oxygen is the limiting reactant, due to the high oxygen-to-hydrocarbon stoichiometric ratio in n-hexane ammoxidation. Therefore, the conversion of the hydrocarbon is low this should favour, in principle, the selectivity to products of partial (amm)oxidation instead of that to combustion products. 

Abstract In this paper, we discuss the results of a preliminary systematic process simulation study the effect of operating parameters on the product distribution and conversion efficiency of hydrocarbon fuels in a reforming reactor. The ASPEN One HYSYS-2004 simulation software has been utilized for the simulations and calculations of the fuel-processing reactions. It is desired to produce hydrogen rich reformed gas with as low as possible carbon monoxide (CO) formation, which requires different combinations of reformer, steam to carbon and oxygen to carbon ratios. Fuel properties only slightly affect the general trends. 

The experiments were carried out at ambient pressure. All hydrocarbons were tested at a S/C ratio of three and all alcohols at a corresponding oxygen to carbon ratio. Decreasing conversion was found for the various fuels with increasing feed rates except for methanol owing to the very high reaction temperature of 725 °C. Table 2.9 summarizes some of the results presented for the various fuels. The proprietary catalyst showed only minor deactivation after 70 h TOS. It was deactivated reversibly by sulfur. Load changes of the liquid input from 100 to 10% resulted in a system response after 5-10 s. 

Theoretically, cellulose has the gross formula QHioCfe, and thus the oxygen-to-carbon ratio should be 0.83. The ESCA experimental data obtained in this study gave an oxygen-to-carbon ratio of 0.78. This result can be due to the deposition of impurities of hydrocarbon nature at the cellulosic surface. 

The favorable replacement ratio of oxygen to hydrocarbon fuels generally ensures a cost reduction to the smelter when the best possible oxygen supply mode is selected. One reference23 shows typical North American unit costs which have been applied to published data for three types of smelting furnace. The reference shows a reduction in power and fuel costs, with increased oxygen enrichment. 

An alternative route to produce synthesis gas starting from hydrocarbon feedstock is the partial oxidation reaction (POX) [16]. This reaction utilizes the oxygen in the air as oxidant and results moderately exothermic. The oxygen to carbon ratio is lower than that required by stoichiometric complete combustion. 

The ratio of adsorbed oxygen to hydrocarbon on p-type semiconductor oxides is generally high and is difficult to control even at low partial pressures of oxygen. The result is often complete combustion of the hydrocarbon. In contrast the amount of adsorbed oxygen on n-type semiconductors is generally small and can readily be controlled by means of the nature and amount of dopant, making selective hydrocarbon oxidation possible. 

The primary function of methyl tert-butyl ether (MTBE) as an additive in gasoline is to enhance the octane level of unleaded gasoline. By virtue of the oxygen atom it contains, it increases the oxygen-to-fuel ratio in gasoline. It has also been shown that adding MTBE results in lower emissions of carbon monoxide and hydrocarbon as well as polycychc aromatic hydrocarbons (PAHs). MTBE oxidation, initiated by hydroxyl radicals, can yield a number of products such as tert-butyl formate, formaldehyde, methyl acetate, and acetone, depending on the pathway. 

Figure 4. Percent propane converted to products with oxygen present. Homogeneous temperature, 718°C time, 0.227 sec. 0.4% Og is roughly 1 1 Og-to-hydrocarbon ratio.

Additionally, NO is reduced by H2 and by hydrocarbons. To enable the three reactions to proceed simultaneously - notice that the two first are oxidation reactions while the last is a reduction - the composition of the exhaust gas needs to be properly adjusted to an air-to-fuel ratio of 14.7 (Fig. 10.1). At higher oxygen content, the CO oxidation reaction consumes too much CO and hence NO conversion fails. If however, the oxygen content is too low, all of the NO is converted, but hydrocarbons and CO are not completely oxidized. An oxygen sensor (l-probe) is mounted in front of the catalyst to ensure the proper balance of fuel and air via a microprocessor-controlled injection system. 

---