Methanol limiting oxygen concentrations

The synthesis of methanol from C0(+C02) and H2 was also attempted by Campbell and co-workers (102) over a Cu(l 11) surface and over well-defined Cu overlayers on a ZnO(OOOl) single-crystal surface. They could set an upper limit of < 2 x 1012 molecules/cm2/s on the methanol production rate at temperatures up to 600 K and pressures up to 1500 torr. These limits are consistent with expectations based on (extrapolated) kinetics for high-surface-area Cu/ZnO catalysts. Their results also showed that C02 has extremely low reactivity for oxidation of the clean Cu(l 11) surface (102), and they argue that it is very unlikely that significant oxygen concentrations exist on the Cu(lll)-like surfaces of practical catalysts under methanol synthesis conditions (102, 103). 

This oxide-catalyzed process operates at a much lower temperature of 270400°C than the silver-catalyzed process, and its feed has a lower methanol-air ratio, which is below the lower flammability limit (6.7 vol% methanol in air). The methanol concentration can be increased without danger of explosion if the oxygen concentration is reduced to below 10 mol% by diluting with recycled off-gas [24]. The amount of air used is in excess of the stoichiometric ratio. Methanol is produced by the highly exothermic oxidative dehydrogenation reaction [Eq. 

The behaviour depends on the type of LCP and can be limited or unsatisfactory with certain concentrated acids, antifreezes, bases, oxygenated gasolines, very hot water and steam, amines, methanol, and phenol. 

The initial dehydration reaction is sufficiently fast to form an equilibrium mixture of methanol, dimethyl ether, and water. These oxygenates dehydrate further to give light olefins. They in turn polymerize and cyclize to form a variety of paraffins, aromatics, and cycloparaffins. The above reaction path is illustrated further by Figure 3 in terms of product selectivity measured in an isothermal laboratory reactor over a wide range of space velocities. ( 3) The rate limiting step is the conversion of oxygenates to olefins, a reaction step that appears to be autocatalytic. In the absence of olefins, this rate is slow but it is accelerated as the concentration of olefins increases. 

The basic setup of a NCD system is shown in Fig. 1. In almost all cases, only a portion of the entire SFC mobile phase is diverted to the CLND detector using a fused-silica capillary or restrictor [6-8,10,11]. Use of a restrictor minimizes the effects of the SFC decompressed carbon dioxide (CO2) and solvent composition on the pyrolysis reaction and chemiluminescence. The CO2 flow rate, dictated largely by the SFC outlet pressure, can affect the residence time of the solute in the pyrolysis chamber and the efficiency of the ozone reaction. The addition of modifiers to the SFC mobile phase (e.g., methanol) can compete for the available pyrolysis oxygen and can reduce signal response. High concentrations of modifier can dramatically affect the detection limits of some compounds [7]. Moreover, the sample concentration also appears to be limited by competition for oxygen, resulting in incomplete combustion. 

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