Interfacial area and mass transfer coefficients in liquid-gas ejectors

Measurements and correlations are reported for the interfacial area and mass transfer coefficients as a function of energy dissipation in a liquid-gas ejector. The correlations for interfacial area and mass transfer coefficients have been developed using Kolmogorov’s theory and Levich’s hydrodynamic derivations. The present developed correlations are validated using experimental results.     

An optimization study on microwave irradiated decomposition of phenol in the presence of H2O2

BACKGROUND Removal of phenol from industrial waste waters involves basic techniques namely extraction, biodegradation, photocatalytic degradation, etc. Among the available processes, the oxidation of phenols using H₂O₂ is a suitable alternative because of low cost and high oxidizing power. The application of an oxidation process for the decomposition of stable organic compounds in waste water leads to the total degradation of the compounds rather than transferring from one form to another. Since oxidation using Fenton's reagent is more dependent on pH, in this present work it was proposed to use H₂O₂ coupled with microwave irradiation. The effects of initial phenol concentration, microwave power and the irradiation time on the amount of decomposition were studied. RESULTS: In the present work experiments were conducted to estimate the percentage degradation of phenol for different initial concentrations of phenol (100, 200, 300, 400 and 500 mg L^?1), microwave power input (180, 360, 540, 720 and 900 W) for different irradiation times. The kinetics of the degradation process were examined through experimental data and the decomposition rate follows first‐order kinetics. Response surface methodology (RSM) was employed to optimize the design parameters for the present process. The interaction effect between the variables and the effect of interaction on to the responses (percentage decomposition of phenol) of the process was analysed and discussed in detail. The optimum values for the design parameters of the process were evaluated (initial phenol concentration 300 mg L^?1, microwave power output 668 W, and microwave irradiation time 60 s, giving phenol degradation 82.39%) through RSM by differential approximation, and were confirmed by experiment. CONCLUSION: The decomposition of phenol was carried out using H₂O₂ coupled with microwave irradiation for different initial phenol concentrations, microwave power input and irradiation times. The phenol degradation process follows first‐order kinetics. Optimization of the process was carried out through RSM by forming a design matrix using CCD. The optimized conditions were validated using experiments. The information is of value for the scale up of the oxidation process for the removal of phenol from wastewater. Copyright © 2008 Society of Chemical Industry     

A correlation for dispersed phase axial mixing coefficients in rotating disc contactors

A correlation for the estimation of dispersed phase axial mixing coefficients in terms of all the operating and fundamental variables was established. The proposed correlations are found to be a good representation of the present data (260 data points) obtained using four liquid‐liquid systems from two different sources. Copyright © 2005 Society of Chemical Industry     

Use of antioxidants for enhancing oxidative stability of bulk edible oils: a review

Edible oils industry is using synthetic and natural antioxidants to enhance the oxidative stability of bulk edible oils. Due to safety concerns of BHA, BHT and TBHQ, there is an ongoing effort to find an effective and safe replacement. Finding a safe antioxidant or its synergistic mixture, which delays, retard or prevent the oxidation of bulk oil without changing the colour or flavour upon addition is a challenge. In this review, a brief account of chemical basis of oxidative deterioration of the stored oil is given. The effectiveness of most widely experimented antioxidants such as tocopherols, carotenoids, ascorbic acid and its derivatives, lignan compounds, flavonoids, polyphenols and phenolic acids in various edible oils have been reviewed. Further, the synergistic and antagonistic combination of these antioxidants in controlling oxidative degradation of edible oils has been discussed.     

Drag reduction in co-current down flow packed column using xanthan gum

Drag reduction is one of the most important techniques for reducing energy consumption in a packed bed contactor. The present work involves an experimental investigation on flow regime transition for air-water system with and without drag reducing agent (DRA), two-phase pressure drop, friction factor and drag reduction using xanthan gum as DRA. Drag reduction was quantified from the two-phase pressure drop data. Based on the present observations it was found that the percentage drag reduction increases with an increase in the concentration of DRA and it is only effective in the range of 300 ppm to 800 ppm. The experimental results indicate that a maximum of 80% drag reduction was achievable using xanthan gum (800 ppm) as DRA. Furthermore, the experimental data were validated with the available literature correlations.     

Optimization of two step karanja biodiesel synthesis under microwave irradiation

The free fatty acid of crude karanja oil (Pongamia pinnata) was reduced and biodiesel was synthesized from pretreated oil under microwave irradiation. The process variables such as irradiation time, methanol-oil ratio and sulfuric acid concentration for pretreatment step; irradiation time, methanol-oil ratio and KOH concentration were optimized through the Box-Behnken experimental design. The free fatty acid of crude karanja oil was reduced to 1.11 ± 0.07% with an optimal combination of 190 s irradiation time (180 W), 33.83 (w/w)% methanol-oil ratio and 3.73 (w/w)% sulfuric acid concentration. An optimal combination of 150 s irradiation time, 33.4 (w/w)% methanol-oil ratio and 1.33 (w/w)% KOH concentration yielded 89.9 ± 0.3% biodiesel. The model was validated by conducting experiments at optimal design conditions. The present work confirmed that the microwave energy has a significant effect on esterification and transesterification reaction.     

An Empirical Model for the Estimation of Moisture Ratio During Microwave Drying of Plaster of Paris

The drying characteristics of plaster of Paris (POP) under microwave irradiation were studied for different shapes of materials through various drying parameters like microwave power, initial moisture content, and drying time. An empirical model for the estimation of moisture ratio was developed using the drying kinetic data of POP. Further, the experimental data on moisture ratio of POP for different operating conditions were fitted with the nine basic drying model equations. Based on the observations, the constants and coefficients of the literature models were rewritten in the form of Arrhenius and logarithmic expressions considering microwave power as input variable. Fifty-eight new model expressions were derived by changing the constants and coefficients and tested using the present experimental data. From the analysis of RMSE, χ², and EF parameters for the derived models, a suitable empirical model (Model No. 55, RMSE = 0.0874; χ² = 0.0020; EF = 0.9999) was established to represent the present experimental data on microwave drying of POP.     

Optimization and analysis of nickel adsorption on microwave irradiated rice husk using response surface methodology (RSM)

BACKGROUND: The removal of heavy metals using adsorption techniques with low cost biosorbents is being extensively investigated. The improved adsorption is essentially due to the pores present in the adsorbent. One way of improving the porosity of the material is by irradiation of the precursor using microwaves. In the present study, the adsorption characteristics of nickel onto microwave‐irradiated rice husks were studied and the process variables were optimized through response surface methodology (RSM). RESULT: The adsorption of nickel onto microwave‐irradiated rice husk (MIRH) was found to be better than that of the raw rice husk (RRH). The kinetics of the adsorption of Ni(II) from aqueous solution onto MIRH was found to follow a pseudo‐second‐order model. Thermodynamic parameters such as standard Gibbs free energy (ΔG°), standard enthalpy (ΔH°), and standard entropy (ΔS°) were also evaluated. The thermodynamics of Ni(II) adsorption onto MIRH indicates that it is spontaneous and endothermic in nature. The response surface methodology (RSM) was employed to optimize the design parameters for the present process. CONCLUSION: Microwave‐irradiated rice husk was found to be a suitable adsorbent for the removal of nickel(II) ions from aqueous solutions. The adsorption capacity of the rice husk was found to be 1.17 mg g^?1. The optimized parameters for the current process were found as follows: adsorbent loading 2.8 g (100 mL)^?1; Initial adsorbate concentration 6 mg L^?1; adsorption time 210 min.; and adsorption temperature 35 °C. Copyright © 2008 Society of Chemical Industry     

Effectiveness of rutin and its lipophilic ester in improving oxidative stability of sardine oil containing trace water

Poor oxidative stability exhibited by n‐3 polyunsaturated fatty acid rich sardine oil is a major challenge for its utilisation in industry. Considering the fact that water is always present in bulk oil in trace amounts during storage, an effort was made to understand and compare the effectiveness of rutin and its corresponding lipophilic ester in enhancing oxidative stability of refined sardine oil containing trace water (0.16% w/w). Peroxide value, conjugated diene value, p‐anisidine value and thiobarbituric acid reactive substances (TBARS) value were determined during 20 days storage. Rutin fatty ester showed 50% reduction in primary oxidation and 42.46% reduction in secondary oxidation, whereas rutin showed 20.6% and 20.43% reduction in primary and secondary oxidation, respectively, by the end of 20 days storage. Thus, it is clearly established that rutin fatty ester is more effective than hydrophilic rutin in sardine oil containing trace water, which contradicts the polar paradox theory.