Pervaporation technique that operates on the principle of selective permeation of a liquid component through a membrane is used to recover organic compounds from water. The prime requirement of this operation is a stable membrane. The suitability of the membrane is tested by the removal of water esterification of ethanol and acetic acid by pervaporation. Commercially, esterification reactions are typically carried out using either large excess of one of the reactants or by removing one of the products through reactive distillation. By virtue of the requirement of larger reactor volume, the latter method—reactive distillation—is becoming common in plant scale operation. Here again, as it is high-energy demanding operation, it is not being preferred while handling temperature sensitive chemicals. In this regard, pervaporation reactors are gaining attention.

Against this backdrop the authors, N Sirisha, S V Naidu, S Subba Rao and P Mohan Kumar Yadav, of the first paper of the issue, “Modeling of Esterification of Acetic Acid with Ethanol Coupled with Pervaporation Using Cross Linked PVA Membranes”, have made an attempt to develop theoretical models for both esterification and pervaporation-aided esterification of acetic acid with ethanol. The model results are compared with the available experimental data and were found to be in good agreement. Polyvinyl alcohol cross linked with maleic acid and citric acid showed good separation capability. They have obtained maximum conversion to ethyl acetate using PVACA membrane. By studying the impact of several process variables such as temperature, initial mole ratio of ethanol over acetic acid and the ratio of effective membrane area over volume of the reacting mixture on water concentration, the authors have obtained optimum conditions for esterification of acetic acid with ethanol in PV: reaction temperature of 80 °C, initial mole ratio of reactants 2.0, and the ratio of effective membrane area over volume of the reacting mixture of 3.0 m–1.

The next paper, “Mass Transfer at the Confining Wall of an Electrochemical Cell in the Presence of Twisted Tapes”, by B S Subramanyam, M S N Murty, B Surendra Babu and K V Ramesh, deals with augmentative methods for enhancement of heat and mass transfer rate for improved performance coupled with reduction in capital investment. The authors have investigated the effect of liquid velocity and the geometric variables of the experimental system on mass transfer coefficient in the presence of twisted tape promoter. They have also obtained mass transfer coefficient data by varying the viscosity of the liquid that is important by addition of carboxymethyl cellulose sodium sulphate in varied concentrations. Analysis of data revealed that with an increase in tape width, the mass transfer coefficient also increased, while with an increase in tape pitch, it decreased. An increase in CMC concentration resulted in a decrease in mass transfer coefficient value.

In the next paper, “Momentum Transfer in Circular Conduit with Coaxially Placed Entry Region Twisted Tape as Swirl Promoter”, the authors, V Nageswara Rao, P Rajendra Prasad and N Chitti Babu, have presented the results of the study carried out to assess the effect of coaxially placed entry region twisted tape as turbulence promoter on momentum transfer rates convection flow of electrolyte. The authors have used a wide range of variables: flow rate of electrolyte, pitch of the tape, length of the tape and width of the tape. The experimental results indicated that the friction factor increased with the increase in length and width of the tape, while it decreased with increase in the pitch of the tape. The authors have also analyzed momentum transfer rates with momentum transfer roughness function and roughness Reynolds number. They have developed correlation through empirical approach and opine that the correlation developed by them is useful in the design of efficient electrolytic cells without impairing the quality of products.

The authors, P Kalpana, K China Malakondaiah, D A Naidu, P King and V S R K Prasad, of the next paper, “Comparative Study on the Adsorption Kinetics of Cd (II) and Cu (II) Metal Ions Onto Eggshell Powder”, have investigated the biosorption potential of eggshells for the removal of cadmium and copper ions from aqueous solutions. They have also assessed the effect of pH, contact time, biomass dosage and temperature on biosorption process. They have evaluated the equilibrium biosorption data using Langmuir, Freundlich and Redlich Peterson isotherm models. The biosorption mechanism was also investigated in terms of kinetics. The experimental results indicate that eggshells can be used as efficient biosorbent for the removal of Cd (II) and Cu (II) ions from aqueous solution.

The last paper of the issue, “Liquefied Petroleum Gas: Fire and Explosion Hazards, Mathematical Models and Safe Storage”, by Kailas L Wasewar and M Siva Kumar, reviews the various hazards associated with chemical processing of the highly inflammable substance, liquefied petroleum gas, using appropriate mathematical models along with safe storage options for avoiding such mishaps.

-- GRK Murty
Consulting Editor