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. The kinetics of the absorption of carbon monoxide by basic solutions was studied at 80°C and carbon monoxide pressures up to 30 atmospheres. The reaction was followed by the rate of decrease of carbon monoxide pressure in a closed system. The observed kinetics in potassium hydroxide solutions yield a rate law of the form (formula omitted) No influence from Li⁺, Na⁺, K⁺ ions was detected and no catalytic effect from Ag(I),- Cu(II), T1(I), N0₃⁻, Mn0₄⁻ was observed. The kinetics are consistent with a mechanism which includes the insertion of a carbon monoxide molecule into the hydroxyl bond,viz. (formula omitted) The rate-controlling step above 90°C was found to be the mass transfer of carbon monoxide from the gas phase into the liquid phase under the conditions involved in this study. / Applied Science, Faculty of / Materials Engineering, Department of / Graduate

Gas absorption with chemical reaction is an important unit operation in the chemical and petroleum industries for the selective removal of components from industrial gas streams. Apart from choosing absorption media, the most difficult problems facing the design engineer are the sizing and performance prediction of the absorption tower due to the scarcity of fundamental design data, especially when novel absorption media and/or packings are used. The solubility of carbon dioxide in 2 and 3 M solutions of 2-amino-2-methyl-1-propanol (AMP), which is a newly introduced absorbent, was determined at 20, 40, 60 and 80 °C and for CO₂ partial pressures ranging from approximately 1 to 100 kPa. The results were interpreted with a modified Kent-Eisenberg model which predicted the present and previous experimental results well. The absorption capacities of AMP and monoethanolamine (MEA) solutions were also compared. Detailed concentration and temperature measurements were reported for the absorption of carbon dioxide from air into NaOH, MEA and AMP solutions. A full-length absorber (0.1 m ID, packed with 12.7 mm Berl Saddles up to heights of 6.55 m) was used. It was operated in countercurrent mode and at 30 to 75 % flooding velocities which are typical for gas absorber operations. The following ranges of operating conditions were employed: superficial gas flow rate 11.1 to 14.8 mol/m² s; superficial liquid flow rate 9.5 to 13.5 m³/m² h; feed CO₂ concentration 11.5 to 19.8 %; total absorbent concentration 1.2 to 3.8 kmol/m³; liquid feed temperature 14 to 20 °C; total pressure 103 kPa. The measurements for the CO₂-NaOH and CO₂-MEA systems were compared with predictions from a previously developed mathematical model. Generally good agreement was obtained except at high CO₂ loadings of MEA solutions. Compared with MEA, AMP was found to have superior CO₂ absorption capacities and inferior mass transfer rates. A new procedure, called the Pilot Plant Technique (PPT), for designing gas absorbers with chemical reactions has been developed. The PPT is primarily intended for designing absorbers for which fundamental design information is lacking. It is based on the premise that full-length absorption columns can be sized by making a minimum number of tests using a small-scale pilot plant. Two special features of the PPT are (i) the details of hydrodynamic parameters (i.e. mass transfer coefficients, effective interfacial area and liquid hold-up) and the physico-chemical information of the system (e.g. reaction mechanism, reaction rate constants) need not be known and (ii) complex calculations are avoided. Using the PPT to size the height or to predict the performance of a given full-length absorber, the specific absorption rate, which is the essential information, can be measured directly using the pilot plant model (PPM) column if both columns have the same hydrodynamic conditions. This can be achieved by using the same type and size of packing in the PPM and the full-length columns and ensuring that the end and wall effects are negligible. The PPM column must also be operated at the same superficial fluid velocities as those of the full-length column. The specific absorption rate was then obtained from the gradient of the fluid composition profile along the PPM column. The validity of the PPT was demonstrated by determining the height and predicting the performance of the full-length column in which carbon dioxide was absorbed from air by aqueous solutions of NaOH and AMP at various operating conditions; good agreement was obtained. / Applied Science, Faculty of / Chemical and Biological Engineering, Department of / Graduate

Mass transfer rates have been measured for streams of CO₂ bubbles of controlled frequency being absorbed into water in cocurrent pipeline flow. Superficial liquid Reynolds number varied from 1810 to 24000. Mass transfer coefficients based on equivalent spherical areas were between 0.6 and 4.5 cm/min. For 5/16- and 5/8 inch I.D. tubes oriented both horizontally and vertically, the mass transfer coefficients were proportional to (Reynolds number)⁰•⁵² and (tube diameter) ⁻⁰•⁸⁵ at high Reynolds number. Bubble velocities were measured for all test sections and flow conditions. Photographs of bubbles in turbulent flow were obtained by a high speed flash technique. The mass transfer results support a postulated mechanism of surface renewal by turbulent eddies which result from the mean flow of liquid through the tube. Two theoretical approaches have been described in an attempt to relate the surface renewal rate to the pipe flow turbulence. A model based on mixing length theory gives good agreement with the experimental results. In this model the larger scales of motion dominate. A second model was based on the assumption that the very small scales dominate. The flow and convective diffusion equations were solved for idealized viscous eddy cells which represent the small motions. The size, velocity and mass transfer rate of these cells were linked to the turbulent energy spectrum for both solid/liquid and gas/liquid interfaces. The predicted dependence of mass transfer coefficient on Schmidt number and energy dissipation is identical with experimental results for solid surfaces. However, the Reynolds number dependence (Re•⁶⁹) is higher than for the present experiments. Nevertheless, the eddy cell model maybe valid for bubbles and solids in sufficiently highly developed turbulence. / Applied Science, Faculty of / Chemical and Biological Engineering, Department of / Graduate

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