Amar Nath Samanta

Zeolite from fly ash: synthesis and characterization

Coal fly ash was used to synthesize X-type zeolite by alkali fusion followed by hydrothermal treatment. The synthesized zeolite was characterized using various techniques such as X-ray diffraction, scanning electron microscopy, Fourier transform infrared spectroscopy, BET method for surface area measurement etc. The synthesis conditions were optimized to obtain highly crystalline zeolite with maximum BET surface area. The maximum surface area of the product was found to be 383 m2/g with high purity. The crystallinity of the prepared zeolite was found to change with fusion temperature and a maximum value was obtained at 823 K. The cost of synthesized zeolite was estimated to be almost one-fifth of that of commercial 13X zeolite available in the market.

Removal of Cr(VI) from Aqueous Solution: Electrocoagulation vs Chemical Coagulation

Abstract Hydrolyzed products of Al(III) have affinity below pHzpc for oppositely charged mono and bi‐nuclear species of hexavalent chromium. This study investigates the comparative performance of electrocoagulation (EC) and chemical coagulation (CC) for the removal of Cr(VI) from aqueous solution. The highest removal of Cr(VI) achieved with EC was about 42% with 4.36 mA/cm2 current density. Cathodic adsorption of chromium boosted up Cr(VI) removal during EC. Simultaneous electro‐ and chemical‐dissolution lead to high current efficiency of about 178%. Both the pH and the coagulant dosage have a significant impact on Cr(VI) removal in the pH ranges from 4.9 to 7.0. CC with alum and aluminum sulfate (AS) removed about 11% and 12% of Cr(VI). Co‐adsorption of divalent SO4 2− ions with Cr(VI) is responsible for the lower removal observed with chemical coagulants. About 0.061 and 0.099 mole of SO4 2− was adsorbed per mole Al in the precipitate in the pH range 4.9 to 7.0 with AS and alum. A higher coagulant dosage increases the removal of Cr(VI) but adversely affects the removal efficiency (Cr(VI) removed per unit of Al dosing). Cell current density (CD) has shown little effect on Cr(VI) removal and the pH elevation at the same charge density. Higher initial Cr(VI) concentration improves the removal efficiency as the species of Cr(VI) is acidic in solution and decreases the pH elevation rate.

Electro-Fenton treatment of synthetic organic dyes: Influence of operational parameters and kinetic study

This work investigates oxidative decolorization of two different dyes, Methylene blue and Titan yellow in aqueous solution using an environmentally friendly advanced electro-chemical oxidation (electro-Fenton) process. The effect of operating conditions like H2O2 concentration, current density, initial dye concentration was studied in a batch stirred cell. Individual decolorization decay kinetics for both dyes was investigated. The second-order absolute rate constants (L mol−1 s−1) between hydroxyl radical and dye have been calculated from experimental data by fitting it to the decolorization model. The apparent kinetic constants, kapp (s−1) for Methylene blue and Titan yellow dye decolorization were also determined. The experimental data showed a good fit to the theoretical model, which can predict data in a wide range of % dye decolorization. This process also reduces COD of the dye solution, and the unit energy demand (UED) in kWh/kg COD removed for different electrical current has been reported.

Nonlinear model-based control algorithm for a distillation column using software sensor

This paper presents the design of model-based globally linearizing control (GLC) structure for a distillation process within the differential geometric framework. The model of a nonideal binary distillation column, whose characteristics were highly nonlinear and strongly interactive, is used as a real process. The classical GLC law is comprised of a transformer (input-output linearizing state feedback), a nonlinear state observer, and an external PI controller. The tray temperature based short-cut observer (TTBSCO) has been used as a state estimator within the control structure, in which all tray temperatures were considered to be measured. Accordingly, the liquid phase composition of each tray was calculated online using the derived temperature-composition correlation. In the simulation experiment, the proposed GLC coupled with TTBSCO (GLC-TTBSCO) outperformed a conventional PI controller based on servo performances with and without measurement noise as well as on regulatory behaviors. In the subsequent part, the GLC law has been synthesized in conjunction with tray temperature based reduced-order observer (GLC-TTBROO) where the distillate and bottom compositions of the distillation process have been inferred from top and bottom product temperatures respectively, which were measured online. Finally, the comparative performance of the GLC-TTBSCO and the GLC-TTBROO has been addressed under parametric uncertainty and the GLC-TTBSCO algorithm provided slightly better performance than the GLC-TTBROO. The resulting control laws are rather general and can be easily adopted for other binary distillation columns.

Oxidation kinetics of degradation of 1,4-dioxane in aqueous solution by H2O2/Fe(II) system

Kinetic studies of oxidative degradation of 1,4-dioxane present in aqueous solutions in the concentration range between 2.27 × 10−3 mol/L (200 ppm) and 5.68 × 10−3 mol/L (500 ppm) were conducted in batch rector. This analysis considers the hydroxyl radicals (·OH) produced by Fenton reagent as the main species responsible for the degradation process. 1,4-dioxane was degraded to the extent of 97 to 99% after 30 min of reaction time. The pH of the reaction medium decreased substantially during the experiment. In all cases, most of 1,4-dixane degradation occurred during the initial 5 min of reaction. A kinetic model is proposed for the oxidation of 1,4-dioxane by Fenton reagent and this model is applied to calculate the kinetic rate constant for the reaction between hydroxyl radicals and 1,4 dioxane. The reaction rate constant for the reaction of 1,4-dioxane with ·OH radicals was evaluated and the value is 2.25 × 108/M-s.

Nonlinear state estimation and control of a refinery debutanizer column

Abstract This article concerns the issue of designing a nonlinear model-based controller for a refinery debutanizer column. First, a nonlinear adaptive state estimator/observer (ASE/ASO) was developed based on a simple observer model structure that mainly consists of only two component balance equations around the condenser-cum-reflux drum and the reboiler-cum-column base. In this observation approach, vapor flow rate of component nC5 (heavy key) leaving top tray, liquid flow rate of component nC4 (light key) leaving bottom tray and distribution coefficient of component n C4 in the reboiler were considered as extra states with no dynamics. Despite process/model mismatch, the proposed state observer estimated the required states of a simulated debutanizer column precisely. Mainly due to the design simplicity, negligible computational effort and fast convergence, the observer is recommended for online implementation. In the subsequent part, the globally linearizing control (GLC) structure, which was consisted of a nonlinear transformer (input–output linearizing state feedback), a linear external controller and an adaptive state observer, has been synthesized. The hybrid GLC–ASO control algorithm provided promising performance compared to the proportional integral (PI) controller that has been thoroughly investigated on the complex refinery debutanizer column.

Colour diminution and COD reduction in treatment of coloured effluent by Electrocoagulation

This work experimentally investigates the colour and Chemical Oxygen Demand (COD) removal of effluents containing: Trypan Blue (TB); Orange G (OG) dye using the two most common electrode materials – Mild Steel (MS) and Aluminium (Al). Effects of the time of electrotreatment, solution pH, electrode material, current density and initial dye concentration on decolourisation and COD reduction are reported. MS electrodes show better colour removal efficiency event at lower cell current efficiency compared with Al electrodes and are able to achieve up to 90–98% removal in less than 60 min. Removal efficiency is higher in the case of TB compared with OG irrespective of electrode material due to higher electrostatic attraction between TB molecules and metal hydroxide sludge. Higher current density enhances colour removal even though pH elevation (approaching close to zero point charge) rate is higher. COD reduction is found to be about 10-20% lower than colour diminution measured spectrophotometrically suggesting different mechanisms of dye removal involved during EC.

Non-linear control of a distillation column coupled with MPC and state observer

The synthesis of multivariable Globally Linearising Control (GLC) structure coupled with non-linear Reduced-Order Observer (ROO) and external linear controller has been studied for a distillation column. Two different linear controllers, namely Dynamic Matrix Controller (DMC) and conventional Proportional Integral (PI) controller, have been used as external controller within the control structure. The proposed control strategies outperformed a dual-loop PI controller. Simulation results of GLC-DMC combined structure indicated better set point tracking performance under modelling uncertainty than GLC-PI control algorithm. The effects of measurement noise on the controller performance also have been investigated through simulation experiment. A new state reconstruction technique, namely Short-cut Process Model-Based Observer (SPMBO), has been developed. The proposed observation scheme provided superior performance under uncertainty over the ROO within the GLC-DMC and GLC-PI control frameworks.

A hybrid feedback linearizing-Kalman filtering control algorithm for a distillation column

This paper studies the design of a discrete-time multivariable feedback linearizing control (FLC) structure. The control scheme included (i) a transformer [also called the input/output (I/O) linearizing state feedback law] that transformed the nonlinear u-y to a linearized v-y system, (ii) a closed-loop observer [extended Kalman filter (EKF)], which estimated the unmeasured states, and (iii) a conventional proportional integral (PI) controller that was employed around the v-y system as an external controller. To avoid the estimator design complexity, the design of EKF for a binary distillation column has been performed based on a reduced-order compartmental distillation model. Consequently, there is a significant process/predictor mismatch, and despite this discrepancy, the EKF estimated the required states of the simulated distillation column precisely. The FLC in conjunction with EKF (FLC-EKF) and that coupled with a measured composition-based reduced-order open-loop observer (FLC-MCROOLO) have been synthesized. The FLC structures showed better performance than the traditional proportional integral derivative controller. In practice, the presence of uncertainties and unknown disturbances are common, and in such situations, the proposed FLC-EKF control scheme ensured the superiority over the FLC-MCROOLO law.

Post-Combustion CO2 Capture with Sulfolane Based Activated Alkanolamine Solvent

Abstract In this work, new experimental data on vapour-liquid equilibrium (VLE) of CO 2 in piperazine (PZ) activated aqueous solutions of n-methyldiethylamine (MDEA) and hybrid solvents containing sulfolane as physical solvent along with aqueous (MDEA+PZ) have been reported over the temperature range of (313-333) K and CO 2 partial pressure range of (1-1400) kPa. PZ is used as a rate activator with a concentration range of 2 to 8 mass% and the total amine concentration in the aqueous solution of (MDEA+PZ) has been kept within 50 mass%, while the concentration of physical solvent sulfolane has been maintained at 10 mass%. Electrolyte non random two-liquid (ENRTL) theory has been used to model the VLE. A simulation work has been carried out using Aspen Plus (V7.1) to evaluate the energy requirements on % CO 2 removal. The hybrid solvent showed higher % CO 2 removal when compared with those of PZ-activated aqueous MDEA.