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A critical analysis of various reported experimental methods utilized for preparation of activated carbon using phosphoric acid was attempted to identify the right choice of experimental method. The various experimental methods were grouped into three major categories; of these, a two-stage activation process with the precursor exposed to preset furnace temperature in a self-generated atmosphere was identified to be a suitable method. Accordingly, activated carbon powders were prepared utilizing a two-stage activation process, covering the effect of activation time at 500°C with an impregnation ratio of 1.5. The samples were subjected to adsorption using methylene blue dye, and the adsorption capacity was found to increase with increase in activation time. An adsorption capacity greater than 400 mg/g of activated carbon shows highly developed pores, with pore size higher than 1.5 nm signifying its economical application to commercial liquid-phase adsorption processes. The adsorption isotherms were found to match well with the Langmuir isotherm model with correlation coefficient (r2) greater than 0.95 as compared to the Freundlich isotherm model with r2 less than 0.8. [ABSTRACT FROM AUTHOR]

The present study attempts to understand drying characteristics of rubber wood sawdust in a tray dryer as it is the simplest and oldest of the dryers known commercially. An increase in temperature, flow rate of the heating medium, and initial moisture content was found to increase the drying rate. However, an increase in the particle diameter and bed height was found to reduce the drying rate. The increase in drying rate with temperature and moisture content was attributed to increase in the diffusion coefficient, while the increase due to the flow rate is attributed to reduction in the external mass transfer resistance during early stages of drying while the drying rate was high. An increase in bed height as well as particle size increases the diffusion path length for moisture, which contributes to the reduction in drying rate. The experimental data were modeled using Fick's diffusion equation, and the effective diffusivity coefficient was evaluated by minimizing the error between the experimental data and the prediction using the model equation. The effective diffusion coefficient was found to increase with increase in temperature, initial moisture content, and the flow rate of the heating medium, while it was found to decrease with increase in particle size. The diffusion coefficient was not found to vary with the bed height/solid loading. The effective diffusion coefficient was found to vary within 9.1 × 10-9to 22 × 10-9 m2/min. The standard deviation of error between the experimental data and prediction using the model, using the estimated effective diffusivity coefficient, was found to be less than 0.07 for the entire set of data, indicating the appropriateness of the model in predicting drying kinetics. [ABSTRACT FROM AUTHOR]

The effects of various cooling modes such as natural cooling mode, linear cooling mode, and controlled cooling modes type A and B in a batch cooling crystallizer on crystal size distribution (CSD) as well as the mean crystal size have been studied for DL-malic acid. The natural cooling mode was found to yield crystals in the range of 250 to 1000 µm, whereas the linear cooling mode was found to yield larger crystals, in the range of 800 to 1600 µm. The mean crystal size was found to increase in the order of natural cooling mode, controlled cooling mode A, controlled cooling mode B, and linear cooling mode. Since linear cooling mode was found to yield larger mean crystal size, the effect of operating parameters such as the seed concentration and agitation rates on CSD was assessed using the linear cooling mode. The increase in seed concentration from 0.5 to 1% resulted in a larger mean crystal size; while an increase from 1 to 2% reduced the mean crystal size. An agitator rate of 90 rpm was found to yield larger mean crystal size than agitation rates of 60 and 120 rpm. [ABSTRACT FROM AUTHOR]