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Citrus fruits contain sufficient citric acid which is a main tricarboxylic acid. The properties of citric acid make it an important additive in various process industries. The aim of this experimental study is to produce citric acid from orange and grape juices. The chemical route for synthesis of citric acid from citrus juices involves three steps: (i) Neutralization to adjust pH (9-11) with 2.8 M NaOH solution, (ii) Addition of CaCl2 solution (40.3-41.1% (w/v)), and (iii) Acidification with H2SO4 solution (1.5-2.3 M) to produce citric acid. In this study, the fruits were peeled, crushed, filtered, neutralized, added CaCl2 solution and acidified to obtain citric acid. The experiments were carried out by varying final pH of solution, concentrations of CaCl2 and H2SO4 solutions maintaining volume constant. A maximum yield of citric acid at 91.1 and 79.8% from orange and grape fruits at optimum final pH of solution, concentrations of CaCl2 and H2SO4 solutions at 10, 40.7% (w/v) and 1.9 M respectively were achieved. Finally, the purified citric acid crystals were characterized using FTIR and XRD. Thus, it could be concluded that orange fruit would be a promising source for the production of citric acid than grape.

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Adsorption is a unit operation of separating solute from solution using another solid material. Modelling of experimental adsorption isotherm data is an essential way for predicting the mechanisms of adsorption, which will lead to an improvement in adsorption science. The main aim of the present work is to analyse various forms of Langmuir isotherm for adsorption of copper from its aqueous solution using cucumber peel from the batch experimental data. The linearized and nonlinearized isotherm models were compared and discussed. In order to determine the best fit isotherm model, the determination coefficient (R2) and sum of square of error (SSE) for each model were used. The modelling results showed that nonlinear Langmuir model could fit the data better than other forms, with relatively higher R2 values (0.9879) and smaller SSE (0.013). The linear forms of Langmuir model had the maximum adsorption capacities deviated from the experimental data. The maximum adsorption achieved was 66.61 mg/g after validation with experimental results.