Process parameters methanol selectivity

The detailed parameter study of the methanol carbonylation reaction led to optimal reaction conditions and to the experimental establishment of the kinetic equation. Taking into account, the influence of all parameters on the reaction rates, a well-controlled process can be designed for the synthesis of acetic acid in two-phase (vapor-solid) reaction. By using properly chosen parameters, the selectivity towards acetic acid and the concentration of the highly corrosive hydrogen iodide in the reaction product mixture can be kept under control as well. 

However, with increasing duration of the process, accompanied by the growth of the conversion of reactants and the concentration of the products in the reactor, the methanol selectivity dropped to 22%, i.e., a value typical for this pressure range ( 40 atm). After decreasing the pressure from 40 to 5 atm, the selectivity of methanol formation in this initiated radical—chain reaction decreases sharply to 2%, thereby confirming the importance of this parameter for the formation of methanol. Thus, reducing the process temperature by more than 200 °C due to its initiation does not show any advantage in terms of selectivity of methanol. 

Two distinct classes of promoters have been identified for the reaction simple iodide complexes of zinc, cadmium, mercury, indium and gallium, and carbonyl complexes of tungsten, rhenium, ruthenium and osmium. The promoters exhibit a unique synergy with iodide salts, such as hthium iodide, under low water conditions. Both main group and transition metal salts can influence the equilibria of the iodide species involved. A rate maximum exists under low water conditions and optimization of the process parameters gives acetic acid with a selectivity in excess of 99% based upon methanol. IR spectroscopic studies have shown that the salts abstract iodide from the ionic methyl iridium species and that in the resulting neutral species the migration is 800 times faster [127]. 

This was initiated by first choosing a simple test bed chemical reaction to evaluate and understand the functionality, flexibility and limitations of the microreactor platform. The reaction of acetic acid and methanol to form methyl ester was selected because the reaction was temperature sensitive and of minimal toxicity. This chemistry has been extensively studied in the author s laboratory previously by Raman spectroscopy in a typical batch reactor. The batch reactor results were a very useful foundation when trying to understand the reaction processes in the microreactor. The microreactor experiments were structured to study reaction response to reactor parameter changes (temperature and flow rate) using Raman spectroscopy. 

In a subsequent simulation study, two important industrial selective oxidation processes were addressed in detail, namely the partial oxidation of methanol to formaldehyde and the epoxidation of ethylene to ethylene oxide. In both cases secondary undesired reactions play a significant role, i.e. the combustion of the primary product in the formaldehyde process and the combustion of the ethylene reactant in the ethylene oxide process, so that the study also provided information on how the adoption of high conductivity monolith catalysts would alfect the selectivity of industrial partial oxidation processes for both a consecutive and a parallel reaction scheme. For both processes intrinsic kinetics applicable to industrial catalysts as well as design and operational parameters for commercial reactors were derived from simulation studies and experimental investigations collected in the literature. 

In [101], a cylindrical CSTR with an inner Pyrex liner was used (Fig. 3.56). Experiments in this reactor showed that the reaction has a thermal hysteresis, the parameters of which are in qualitative agreement with estimates obtained in [104] within the framework of a nonisother-mal kinetic model of the process. It was demonstrated that the residence time of the mixture in the CSTR after complete oxygen conversion does not affect the selectivity and yield of methanol. As in flow reactors, at a constant rate of reagents consumption, the selectivity and yield of methanol increase with the pressure, in agreement with the simulation results. Generally, the results obtained in CSTRs are consistent with the results obtained in flow reactors. 

The works [158,185—188] investigated the effect of various parameters on the reaction onset temperature and the yield of the products. At pressures of 1 and 5 atm, the increase of the initial concentration of NO to 1% significantly, by 100 °C, decreased the temperature of the process, although the maximum obtainable conversion of methane was almost the same. However, the increase of the NO concentrations to 1.5% produced practically no effect. At these pressures, the selectivity of formation of oxygenates (methanol, formaldehyde, and nitromethane) reached a maximum at an NO concentration of 0.5%, so this concentration was adopted as optimal. The ethane formation selectivity decreased rapidly with increasing NO concentration, nearly to zero. Diluting the mixture with helium, at least up to 60%, had a moderate effect on the process. Even the CH4/O2 ratio, a key parameter of the... 

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