Prof. Subrata Kumar Majumder
Professor
HAG, FCET(I), FISRD (London), FERC (USA), FIIChE
Key Research Areas :Applied multiphase flow process system, Process intensifications in Chemical and environmental Processes, Micro-nanobubble technology and its applications in wastewater treatment, and enhanced oil recovery, Mineral and coal beneficiation by flotation and extraction, Fluidization and its application.
- Phone No: + 91 361 258 2265
- Email: skmaju@iitg.ac.in
- Room No: 0107
Mailing Address:
Prof. Subrata Kumar Majumder, Department of Chemical Engineering,
Indian Institute of Technology Guwahati,
Guwahati-781039, Assam, India.
Phone: +91-361-2582265; +91-361-2582300; Fax: +91-361-2582291
Email: skmaju@iitg.ac.in ; skmaju@gmail.com
Research
Research Group and Research
| Slurry reactors have attracted the attention of researchers over the years due to its widespread applications and importance in various processes in chemical and biochemical industries. Recently downflow slurry bubble column columns are gaining importance as a simple and inexpensive of means of achieving multiphase process yield due to its several advantages.From the literature it is found that a very few studies on hydrodynamics and transport processes in the downflow slurry bubble column reactor are available though it has several industrial applications. The present study reports on the hydrodynamic and mass transfer characteristics in an ejector induced modified slurry bubble column reactor. The completed work includes the gas holdup, bubble size distribution, the three-phase friction factor, bubble generated turbulent energy, the dispersion coefficient of bubble motion, velocity characteristic factor and mass transfer phenomena by current density method. A functional relationship between three-phase friction factor and energy loss due to wettability of liquid with the solid surface also developed. The gas holdup has been analyzed by the drift flux model and interpreted the same based on different significant dimensionless groups. The mass transfer coefficient is evaluated by using the electro-reductionof ferricyanide ions as the model reaction. | ||
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| The effects of superficial slurry velocity, gas velocity, slurry viscosity and gas holdup on mass transfer coefficient are analyzed. Empirical correlations have been developed for the downflow slurry system with the different variables to interpret the mass transfer phenomena. The developed correlation for mass transfer efficiency as a function of quality of mixedness is also interpreted by the information entropy theory. The present study in the modified downflow system may give insight into a further understanding and modeling of flow characteristics in industrial applications. | ||
| Ozone is applied to remove the organic and inorganic compounds present in the wastewater due to its various advantages. Many organic and inorganic compounds react with ozone or hydroxyl radicals directly or indirectly. However, it has a few disadvantages, which limit its application in water treatment. The main drawbacks of ozone are its relatively low solubility and stability in water. To alleviate some of the drawbacks of conventional ozonation processes, microbubble-aided ozonation has been successfully attempted by several scientists. Various wonderful properties of microbubbles such as large gas−liquid interfacial area, slow rising velocity with long lifetime, and small ozone requirement increase the ozonation efficiency. In addition, ozone microbubbles are also capable of generating hydroxyl radicals under certain conditions. | ||
| This work presents oxidation of some pollutants (e.g. ammonia, arsenic and dyestuffs) by ozone microbubbles in a pilot-plant. In-depth studies have been carried out on the change of concentration of pollutant in the reactor with time, mass transfer of ozone in water, reaction kinetics, and the effect of pH on the reactions. Adsorbents have been developed for adsorption of arsenic. Concentration of hydroxyl radicals has been measured. A mechanism has been proposed for the generation of hydroxyl radicals by ozone microbubbles. |
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In the present scenario microbubble has got much popularity as they are being used in many chemical, biochemical, metallurgical and petrochemical industries to increase the efficiency of the process (Devatine et al., 2007). They have been used as diagnostic aids to scan the various organs of body and they are being proposed to use as a drug or gene carrier and treatment in cancer therapy (Lindner, 2004). The microbubble-aided extraction process is becoming a highly promising direction in chemical engineering (Tan et al., 2011). Microbubble aided flotation has been widely employed in the various fields for the process intensification. They have been used for recovery of proteins (Amiri and Valsaraj, 2004), recovery of microorganism (Hanotu et al., 2012), removal of heavy metal ions from water (Ciriello et al., 1982), removal of dye and pigment (Alves et al., 2006). This work aimed to explore the rheology, dispersion characteristics, and the stability of microbubble and efficiency of mineral beneficiation based on the physicochemical properties. The terminal rise velocity of carbon dioxide microbubble is found to higher than air and lower than nitrogen microbubble. From drainage curve analysis it is observed that the stability of the microbubble can be increased by increasing surface tension The results showed that the charge on the surface of microbubble is highly promising in separating opposite charged particles. The recovery of mineral particle are found to be dependent on surfactant concentration, size of microbubble and particles, zeta potential of microbubble, nature of surface potential of bubble and microbubble-particle mixture circulation velocity. The separation efficiency of microbubble increases with increase in mixture circulation velocity and surfactant concentration. The recoveries of ZnO and Al2O3 particles are maximum with CTAB. In case of CuO particles, the SDS and Tween-20 are found to be more effective than CTAB. The rate constant found to be significantly influenced by the physicochemical properties of the liquid and particles. These results clearly indicate that presence of a hydrophobic surface forces necessarily results in particle collection by a microbubble but other surface forces also contribute to fine particle separation. |
| Pattern formation resulting from evaporation of sessile droplets containing solute particles is encountered in various applications in microfluidic devices. In this study it is observed that by controlling the heating of the substrate one can modify the convection cells and hence finally the deposition pattern of solute particles. The fluid velocity and particle concentration inside the evaporating droplet was measured using the Particle Image Velocimetry (PIV) technique. Experiments were conducted for the case of symmetric as well as asymmetric heating of the substrate from the bottom. It was observed that the flow pattern inside the droplet results from the combined effect of buoyancy driven flow and Marangoni convection. At low temperature and symmetric heating, two counter rotating vortices were observed whose direction is such that the particle deposition occurs at the pinned contact line. However, at high temperature the flow is reserved and the particles are deposited at the center of the dried droplet. In case of asymmetric heating only one convection cell was observed with asymmetric particle deposition. Analysis of various dimensionless numbers associated with convective flow showed that Marangoni convection dominated in all our experiments. Also numerical simulations carried out to solve the fluid flow and energy transport equation inside the evaporating droplets for similar conditions as the experiments. The results from the simulations are found to be in qualitative agreement with the experiments. |
| The helical coil system is important as a compact helical reactor to execute the gas-liquid reaction with intense mixing. The reaction performance may be significant in the helical coil due to its absence of back mixing. Now-a-days, helical coil is hence gaining importance as a simple intensified and inexpensive gas-liquid or gas-liquid-solid reactor. In literature, significant research has been reported to understand the properties of Newtonian fluids like thermodynamics, stability, thermal conductivity, thermal diffusively, viscosity and convective heat transfer coefficient in helical coil system. | ||
| Apart from gas-Newtonian liquid reaction, there are lots of reactions with gas-non-Newtonian liquid are executed in the chemical and biochemical industries. Literature shows that there are limited works on air-non-Newtonian liquid two-phase flow through helical coils as compared to air-Newtonian fluids. This work aimed to investigate the flow characteristics and transport process of gas-non-Newtonian liquid flow through helical coil. The attention has been focused on flow patterns, hold-up, frictional two-phase pressure drop, mixing characteristics, heat transfer and mass transfer characteristics and effect of various geometrical parameters like tube diameter, coil diameter, pitch difference, particle diameter and physical properties of liquid on them. |
| The using of gas into the liquid-liquid mixing gives the emulsion of the mixture with fine drops by which the large interfacial area is developed for the mass transfer. The most of the extraction experiments were conducted in countercurrent flow of the liquids, there is less work done on the gas-aided concurrent liquid-liquid extraction system. Based on this, the present research work focussed on:
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Studies on objectives:
- Flow regime of areation in flotation column
- Phase holdup and particle interaction to contribute hydrodynamics in flotation column
- Bubble size distribution and its significance in the recovery of fine particles in a flotation column
- Mixing characteristics in a flotation column and model development
- Recovery efficiency based on mixing chaaracteristics and its kinetics of flotation
The objective of the study:
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Separation technique is used in the industries for purification of some materials or removal of some unwanted materials from the others present in a solution. Solvent extraction and adsorption are attractive separation technique in separation of non-volatile solutes from aqueous solutions, separation of heat sensitive materials such as antibiotics (e.g., penicillin which is recovered from fermentation broth by using the solvent butyl acetate), separation of the close boiling component mixtures. The other most important use of separation for most of the chemicals, petrochemicals, refineries and other industries is the removal of organics from their waste effluent. In two-phase flow the in-situ composition is different from the inlet composition since the two fluids have different density. The lighter fluid tends to slip past the heavier one. So, in any two phase flow study, it is important to understand the flow patterns i.e., the phase distribution which occurs under specific flow conditions since the hydrodynamics and heat and mass transfer characteristics are governed by the existing flow distribution. The contact area of the extract and the raffinate phase is also different for different flow patterns. More area of contact between the extract and the raffinate phase results more mass transfer between the phases. An accurate estimation of pressure drop is also of considerable interest to estimate the required pumping power in petrochemical, chemical and other industries where two-phase mixture co-exists for different transport processes. In present, researchers and engineers are interested in miniaturization for process intensification of chemical processes or scaling out or numbering up approach. For such processes surface to volume ratio becomes significant and an increase in this ratio increases the transport rate specially in extraction and adsorption. The objectives of the present study are to develop a millichanel based packed device by assesing the followings: |
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Over the years, the research on the liquid-liquid plunging jet extraction column has drawn significant interest among the scientific fraternity because of its numerous applications, including fine chemical synthesis, recovery of fuel in nuclear plants, acid mixing, ink-jet, and liquid metal transfer (Asadollahzadeh et al., 2016; Gao et al., 2016; Hu et al., 2009; Tadrist et al., 1991). Various researchers have used different columns for the liquid-liquid extraction process such as Kühni column, rotating disc contactor, static mixer, and jet extraction column. Jet mixers have several advantages compared to mechanical mixers because they have low maintenance, low cost, low energy consumption, and shorter mixing time. The jet system has a higher liquid mixing and mass-transfer operation for mixing the liquid-liquid phase. For the past years, the jet device has been employed for wastewater treatment and acid extraction, but the studies were found to be limited. The jet device was used to extract copper ions, and it was discovered that the rate of copper extraction was 7 to 8 times higher than in the CSTR (Dehkordi, 2002a). Suresh et al. (2005) used liquid-liquid jet extraction system and separated uranium and thorium. They have stated that the ejector-type jet device can provide a high extraction efficiency. The various parameters such as liquid-liquid entrainment, drop size and its distribution, axial dispersion coefficient, extraction efficiency, and overall mass transfer play a significant role in designing and modeling of liquid-liquid extraction column. These parameters have an immense impact on selectivity and conversion in chemical engineering applications. Based on the literature, the jet-driven extraction column is gaining popularity for generating interfacial area, intense mass-transfer operations such as gas adsorption, liquid-liquid extraction, etc. However, there is a scarcity of studies on hydrodynamics and mass transfer for specific applications correlating the hydrodynamics in the jet-driven mixing column. The work afocusses on the study of:
- Entrainment characteristics of liquid-liquid dispersion
- Drop size distribution and drop aspect ratio
- Dispersion characteristics and its analysis
- Extraction efficiency and overall mass transfer in jet-driven extraction column
A significant amount of oil (i.e., 60-70%) remains trapped in the reservoirs after the conventional primary and secondary methods of oil recovery. Enhanced oil recovery (EOR) is, therefore, necessary to recover the major fraction of unrecovered trapped oil from the reservoir to meet the present-day energy demands. The chemical method of EOR involves the injection of alkali, surfactant, polymer, and a combination of alkali–surfactants–polymer solution in the reservoir with the objective of achieving a reduction in interfacial tension and matching the mobility between oil and water for more recovery of oil. Every oil field has different conditions, which imposes new challenges towards an alternative but more effective EOR techniques.
Surfactant plays a major role in EOR. It helps to achieve ultralow interfacial tension, which significantly increases the mobility of the trapped oil and also helps to improve wettability between oil and rock. Anionic surfactants such as the alkyl aryl sulfonates, sodium dodecyl sulfate, sodium octyl sulfate, alpha-olefin sulfonate, and N-ethoxy sulfonate are extensively being used in EOR due to their less adsorption on sandstones and clays. However, most of these surfactants are toxic, non-biodegradable, and can adsorb on the surface of the porous rocks.
This work is focused on the development of an alternative cost-effective and sustainable natural surfactant derived from the weed Eichhornia crassipes, and study its beneficial effects on EOR. The surfactant has been characterized by the FTIR, GC-MS, 1H NMR, FESEM, and FETEM analyses. The surface and interfacial tension have been measured. The influence of the synthesized surfactant on the rheological properties of xanthan gum (a polysaccharide) has been studied and compared with that of a commercially used surfactant (i.e., sodium dodecyl sulfate). The experimental data acquired from the rheological analysis of the surfactant–polymer solutions under varying shear rate were fitted by several non-Newtonian fluid models. An effective reduction in the interfacial properties, improvement in the rheological properties, and stability against heat and salinity suggest its potential application in EOR.
Loss of surfactant by adsorption on porous media is one of the most critical concerns of the surfactant flooding method of EOR. Hence, the present study is also dedicated to analyze the adsorption of the synthesized surfactant on sandstone and sand surfaces under reservoir-like conditions. The mechanism, equilibrium, and kinetics of adsorption of the synthesized natural surfactant on sandstone and sand surfaces have been investigated through batch experiments at different concentrations (i.e., 1000–5000 mg dm–3), temperatures (i.e., 298–333 K), and a fixed salinity. The mineralogy and morphology of the adsorbent samples were examined by the XRD and FESEM analyses. The mechanism of surfactant adsorption and maximum adsorption were determined by various isotherms and kinetic models. The standard Gibbs free energy changes (i.e., 
) for adsorption on sandstone and sand were found to be –21.48 and –20.80 kJ mol–1, respectively.
The interfacial phenomena are associated with the adsorption of the surfactant at the oil–rock and oil–water interfaces. Therefore, it is essential to understand the mechanism of adsorption of surfactant at the oil–water interface for better implementation of surfactant flooding. The adsorption of the synthesized surfactant on the oil–water interface was investigated using small-angle X-ray scattering, interfacial rheology, zeta potential, and phase behavior analyses. A noteworthy improvement in the stability of the oil-in-water emulsion was observed in the presence of the surfactant. An effective 27% increase in the zeta potential and ~26.9 times increase in the film elasticity signify the substantial adsorption of the surfactant at the oil–water interface.
Moreover, the feasibility of the use of the synthesized surfactant for EOR was studied based on the wettability alteration and IFT measurements under reservoir-like conditions (i.e., high temperature and pressure). Further, core flooding experiments were carried out by injecting the surfactant–polymer slugs of different concentration into the sandstone core sample under reservoir-like conditions. An effective reduction of ~37–41% in the IFT and ~43% in wettability was observed with increasing surfactant concentration. Based on the core flooding experiments, 13.3–22.4% additional oil recovery was achieved. Based on the aforesaid studies, the performance of the synthesized surfactant is promising for EOR applications.
Detection of pharmaceuticals in surface and ground water has become very frequent worldwide. The elevated concentration of pharmaceuticals is also raising concerns among researchers. These active organic compounds have become a major concern owing to their toxicity towards aquatic and human life. Excretion and improper disposal by the manufacturers are the main contributors. Most pharmaceuticals are found in the aquatic environment in their original or slightly modified form due to ineffective treatment in the urban wastewater treatment plants. Various processes have been applied for the degradation of pharmaceuticals. The formation of toxic metabolites and low mineralization were the main issues to be tackled.
The development of an efficient and economical technique to mineralize pharmaceutical compounds is the need of the hour. Over the last three decades, advanced oxidation processes (AOPs) have proven to be an excellent technique for removing refractory organic compounds from synthetic and real effluents. The hydroxyl radical is generated as the primary oxidant in most AOPs. The non-selective nature of the AOPs and the prospect of a high degree of mineralization have made them appealing. Ozone alone has been recognized as a strong oxidant, and it is capable of degrading recalcitrant organic compounds. Ozone selectively attacks organic compounds having a high electron density, whereas hydroxyl radical is a non-selective oxidant, and the latter reacts with a variety of organic compounds.
This work focuses on the degradation of pharmaceuticals synthetic and real industrial effluents by ozonation system. Three best-selling pharmaceuticals, naproxen, diclofenac, and ranitidine have been degraded by ozone in the presence of H2O2. To analyze the mass transfer of ozone from gas to a liquid, volumetric mass transfer coefficients were calculated in pure water for a pH range of 4-9. Concentration of pharmaceuticals was measured during and after ozonation by HPLC. Pseudo-first-order rate constants were calculated for all three pharmaceuticals. Effect of pH (i.e, 4 – 9), ozone dosage (i.e., 0.44 – 0.50 mg s-1), initial drug concentration (i.e., 50 – 125 mg dm-3), and hydroxyl radical generation were assessed for ozonation process. The contribution of hydroxyl radicals in the degradation process was analyzed in a scavenging agent. Metabolites formed after ozonation were identified with the help of HR-LCMS. Probable mechanisms of their formation were predicted for all drugs. At pH 9 and 48 – 50 mg s-1 ozone supply, all three drugs were completely removed in less than 10 min. Degradation follows the pseudo-first-order reaction rate for NPX, DCF, and RNT, with rate constants ranging from 0.043 to 0.0979 min-1. A model had been developed to analyze the effect of operation parameters on the rate of degradation. Decarboxylation, dichlorination, and hydroxylation are the major mechanisms involved in the degradation process.
After achieving efficient degradation of NPX, DCF, and RNT in ultra-pure water, a separate set of experiments was conducted in wastewater to ensure the degradation of drugs in real systems. The present study focused on degrading real pharmaceutical industrial effluent efficiently and economically. Real pharmaceutical industrial effluents were procured from two leading drug manufacturers in India. Characterization of effluents revealed that it contains mainly anti-cancer, anti-psychotics, anti-depressants, painkillers, and antibiotics. Water quality parameters were estimated for raw effluents, i.e., COD, TSS, TDS, color, alkalinity, ammonia, phenolic contents, etc. In the case of the first effluent, ozonation was used as a pre-treatment followed by adsorption by activated char. COD removal efficiencies were in the range of 75 – 88.5% in 3 h by ozonation. The minimum value of COD for the hybrid process achieved was 190 mg dm-3. Recalcitrant metabolites were formed, which were removed by adsorption on activated char.
Ozonation was used as a post-treatment technique for the second effluent, and coagulation was used to remove TSS as pre-treatment. Coagulation with FeCl3.6H2O removed 10% COD and 63% TSS at optimum circumstances. At pH 11, O3 + H2O2 removes 91.6% of COD. After the treatments, no toxicity was discovered in any effluent.
In the present work, synthetic and real effluents pharmaceuticals were successfully degraded by ozonation techniques.
