Showing papers by "Jyeshtharaj B. Joshi published in 1995"

Wet air oxidation

Abstract: Wet air oxidation (WAO), involving oxidation at high temperature (125--320 C) and pressure (0.5--20 MPa) conditions, is useful for the treatment of hazardous, toxic, and nonbiodegradable waste streams. The process becomes self-sustaining when the feed chemical oxygen demand (COD) is about 20,000 mg/l and can be a net energy producer at sufficient higher feed COD's. All the published information on WAO has been analyzed and presented in a coherent manner. Wet air oxidation studies on pure compounds have been critically reviewed. Mechanism, kinetics, and structure-oxidizability correlation for WAO of carboxylic acids, phenols, cyanides, and nitriles have been described. The industrial applications discussed include municipal sewage sludge treatment, distillery waste treatment, black liquor treatment, cyanide and nitrile wastewater treatment, spent carbon regeneration, and energy and resource regeneration. Waste streams from other sources and some miscellaneous applications of WAO have also been included. Special emphasis is given to WAO under supercritical conditions (above the critical temperature of water) and oxydesulfurization of coal. In addition to the industrial applications, some other aspects (like various catalysts and oxidizing agents) of WAO have also been discussed. Recommendations and suggestions for further investigations have been made. 560 refs.

Studies on the lipozyme-catalyzed synthesis of butyl laurate.

Abstract: The effects of temperature, speed of agitation, enzyme concentration, etc., on butyl laurate synthessis using Mucor miehei lipase (Lipozyme™) have been studied. Although the soluble enzyme was quite thermcstable in aqeous solution, it deactivated rapidly at and above 40°C in the presence of butanol. This enzyme immobilized on an anion-exchange resin (Lipozyme™) showed enhanced stability (as compared to the soluble form) to denaturation by butanol under the same conditions. The denaturation of M. miehei lipase was found to be a function of the butanol concentration in the aqueous phase, and rapid denaturation takes place at the concentration corresponding to its saturation at that temperature. © 1995 John Wiley & Sons, Inc.

Specificity of a Lipase in Ester Synthesis: Effect of Alcohol

Abstract: Ester synthesis by the Mucor miehei lipase has been studied for various alcohol substrates: n-propanol, n-butanol, isoamyl alcohol, n-hexanol, n-octanol, 2-ethylhex-anol, n-decanol, and lauryl alcohol. The effects of temperature, the nature of the acid, and immobilization of the lipase on its substrate specficity have been elucidated by carrying out esterifications at 29 and 50 °C with lauric and oleic acids and by using both the soluble and immobilized (resin-adsorbed) forms of the lipase as catalysts. Higher synthesis rates were obtained with oleic acid than with lauric acid. A bimodal distribution pattern was observed for the reaction rate as a function of alcohol chain length. Two superimposed "bells" were obtained with maxima at C4 (butanol) and C10 (decanol) at 29 °C. Whereas immobilization of the lipase did not influence this substrate specificity, an increase in temperature to 50 °C caused a shift in the first peak from C4 to C6 (hexanol), while the second peak position was not affected. The minimum, in all cases, was found to be at C8 (octanol).

Simulation of Flow in Stirred Vessels with Axial Flow Impellers: Effects of Various Numerical Schemes and Turbulence Model Parameters

Abstract: The standard two-equation (k-e) turbulence model has been used to numerically simulate the flow in an agitated baffled cylindrical vessel with axial flow impellers. Three numerical schemes, namely, upwind scheme, hybrid scheme, and power-law scheme, were used to evaluate the competitiveness of the various schemes. The solutions were obtained by using the SIMPLE algorithm. The effects of initial guess values of the flow variables, the underrelaxation parameters, internal iterations, etc., on the rate of convergence were analyzed. The sensitivity of the model parameters on the flow characteristics was investigated thoroughly. Further, the effects of global grid sizes and near-wall grid sizes on the solution were also investigated. The boundary conditions in the impeller region for the velocities and turbulent kinetic energy were provided from the experimental data. However, for the energy dissipation rate, as iterative process was adopted taking the local information into account. Computations were carried out for six different impeller designs. It was found that the predicted values were qualitatively in good agreement with the experimental data.

Gas-inducing-type mechanically agitated contactors : hydrodynamic characteristics of multiple impellers

Abstract: The rate of gas induction was measured in gas-inducing-type mechanically agitated contactors (GIMAC) provided with two impellers. Three vessels of 0.57, 1.0, and 1.5 m i.d. were used. Tap water was used as the liquid phase, and air was used as the gas phase. Six different impeller designs (pitched-blade downflow and upflow turbines straight-blade turbine, disk turbine, and upflow and downflow propellers) were employed. From these designs, six different impeller combinations were made and an optimum combination has been proposed. The impeller speed was varied in the range of 0.30 to 15.45 rev/s. The ratio of impeller diameter to tank diameter (D/T) and the submergence (S) of upper impeller from the top were varied. The effects of clearance of lower impeller from the tank bottom (C 1 ) and the impeller spacing (C 3 , distance between the two impellers) were also varied over a wide range. The design of the lower impeller was optimized in terms of diameter (D), blade width (W), blade angle (B Φ ), number of blades (n b ), and the blade thickness (t b ). Rational correlations have been developed for the critical impeller speed for gas induction and the rate of gas induction.

Optimization of impeller design for gas inducing type mechanically agitated contactors

Abstract: Rates of gas induction and fractional gas hold-up were measured in a 0.57 m i.d. gas inducing type mechanically agitated contactor. Several designs of the impeller were employed for optimizing the rate of gas induction with respect to power consumption. The effect of blade width blade, angle, blade thickness, blade curvature, number of blades, etc. on gas induction, has been investigated in detail. An optimum design has been proposed. Hysteresis in the gas induction rate and power consumption was observed for a wider impeller projecting out of stator.

Affinity partitioning of enzymes using unbound triazine dyes in peg/phosphate system

Abstract: The partitioning of alcohol dehydrogenase glucose-6-phosphate dehydrogenase and hexokinase from pressed bakers' yeast was studied in polyethylene glycol (PEG)/potassium phosphate aqueous two-phase system using unbound reactive triazine dyes as affinity ligands. The various parameters investigated were ligand type and concentration, pH of the system, phase composition of the system, and molecular weight of PEG. It was found that the best ligands gave an increase in partition coefficient of 2 to 3 times over that in the absence of the ligand.