Vijaykumar V. Mahajani

INVITED REVIEW ABSORPTION OF NOX GASES

Oxidation of nitric oxide is an important step in NOx absorption. Recent advances namely catalytic oxidation and the use of slrong oxidizing agents have been reviewed. The refinements which have been made in the kinetics of NO oxidation have been discussed. Several liquid phase absorbents have been suggested for the NO removal, particularly for the purpose of pollution abatement. Different models for NO oxidation using nitric acid have been analysed and the limitations of published information have been brought out. Absorption of tetravalent nitrogen oxide (NO2 and N2O4) has received considerable attention. The absorbents include water, nitric and sulfuric acids, sodium hydroxide, sodium sulfite and sodium chlorite. Absorption in water and nitric acid is important in the manufacture of nitric acid. The published information on the mechanism of NO2 and N2O4 absorption in water has been critically analysed. The problem of nitrous acid decomposition has been analysed on the basis of film theory. The predicti...

Insight into sub-critical wet oxidation of phenol

Abstract Low molecular weight organic acids, especially acetic acid, are often formed during wet oxidation. The role of mass transfer in the formation of acetic acid in wet oxidation was studied. For this purpose, phenol was considered as a model substrate. Acetic acid formed was maximum when mass transfer limitations existed. The waste may contain free radical initiators or scavengers. Therefore, the model compound hydroquinone was used as a free radical generator. It accelerated degradation but acetic acid formation increased. On the other hand, t -butanol as a free radical scavenger suppressed both phenol degradation and acetic acid formation. The strongly alkaline pH resulted in more acetic acid formation, though rates of phenol degradation increased. Wet oxidation of phenol was also studied in the presence of the homogeneous catalysts cupric sulfate and ferrous sulfate. The effects of these catalysts on the rates of oxidation and the acetic acid formation were studied. The amount of acetic acid formed in the presence of ferrous sulfate was relatively higher.

Membrane stability and enrichment of nickel in the liquid emulsion membrane process

The parameters affecting the stability of a liquid emulsion membrane (LEM) for enrichment of nickel were studied. The liquid membrane is made up of a carrier (di-2-ethylhexylphosphoric acid), organic diluent and an emulsifying agent (sorbitan monooleate). Swelling of the internal phase during extraction results in breakage of the emulsion. The role of pH is very important in the LEM process for extraction of nickel. A significant decrease in swelling was observed by maintaining the pH of the feed phase constant during extraction. A lower osmotic pressure difference between the external and internal phase brings about lower changes in the swelling and membrane breakdown.

Liquid‐Phase Hydrogenation of Benzene to Cyclohexene Using Ruthenium‐Based Heterogeneous Catalyst

Selective hydrogenation of benzene to cyclohexene has been studied in a high pressure slurry reactor using supported ruthenium catalysts. The organic base monoethanolamine (MEA) was found to give better selectivities than the conventional inorganic salt additive (zinc sulphate). Parameters studied were the effects of various supports such as alumina, silica, titania, zirconia, niobium oxide, etc., benzene to water ratio, catalyst weight, and presence of cyclohexane in the feed. Reusability of the catalyst was also studied.

RECOVERY OF NICKEL VIA LIQUID EMULSION MEMBRANE PROCESS USING METHANE SULFONIC ACID AS A STRIPPANT

A liquid emulsion membrane (LEM) process is considered for the enrichment of nickel ions from dilute aqueous solutions. The liquid emulsion membrane consisted of a carrier di-2 ethylhexyl phosphoric acid (D2EHPA), an organic diluent, an emulsifying agent, and an aqueous stripping agent thereby having water in oil emulsion. Various stripping agents (hydrochloric, sulfuric, nitric, and methane sulfonic acid) were tested for the stability of membrane. The swelling, breakage, osmotic pressure, and particle size of LEM containing various stripping acids were compared. Methane sulfonic acid (MSA) outperformed the other acids as a stripping agent. The recovery of nickel depends on pH of aqueous feed phase. The other important variables affecting the LEM process of nickel such as acid strength, speed of agitation, organic diluent, and treat ratio were systematically investigated by using methane sulfonic acid as a strippant. It was found that nickel extraction was maximum when concentration of MSA was 1M and treat ratio was 1:3. It was also observed that dodecane as a diluent resulted in better extraction of nickel as compared to other diluents such as heptane, toluene, and xylene.

Kinetics of Absorption of Carbon Dioxide in Aqueous Solution of Ethylaminoethanol Modified with N-methyl-2-pyrolidone

In this paper, kinetics of absorption of CO2 in an aqueous ethylaminoethanol (EAE) and formulated solvent (aqueous blend of EAE and N-methyl-2-pyrrolidone (NMP)) was studied in a stirred cell reactor by using a fall in pressure technique. The reaction pathways for CO2–aqueous EAE system were comprehensively described using both zwitterion and termolecular mechanisms. The physico-chemical properties such as density (ρ) and viscosity (μ) of aqueous EAE and formulated solvent and the solubility ( ) and diffusivity of CO2 ( ) in these solvents were estimated experimentally. The reactive absorption of CO2 in an aqueous EAE was observed to be first order with respect to both CO2 and EAE concentrations. Addition of NMP in aqueous EAE enhances the by 40%, which ultimately results into higher CO2 absorption rates in formulated solvent (∼20% higher) compared to that of the aqueous EAE. Effect of concentration of EAE (0.5 to 2 kmol/m3) and temperature (303 to 318 K) on CO2 absorption kinetics was studied in detail and it was realized that the rate of absorption of CO2 in aqueous EAE and formulated solvent was significantly affected by the change in these parameters. The findings obtained during the temperature dependency study further indicates that the activation energy of the absorption of CO2 in aqueous EAE (80.2 kJ/mol) was relatively lower in comparison with the activation energy of the absorption of CO2 in formulated solvent (88.95 kJ/mol). The overall reaction of CO2 with the formulated solvent could be regarded as the reaction of CO2 with aqueous EAE in parallel with the reaction between CO2 and aqueous NMP.

Waste Treatment of an Aqueous Waste Stream from a Cyclohexane Oxidation Unit: A Case Study

Catalytic wet oxidation of an aqueous waste stream, obtained after recovery of Na2SO4 and butyric acid, valeric acid and caproic acid (BVC acids) from a cyclohe oxidation unit, was carried out at elevated temperature and pressure to detoxify the waste stream with regard to COD to meet local discharge standards. The possibilities for recovery of Na2SO4 and C2–C6 carboxylic acids were also explored.

Mass transfer in packed columns: Co-current (downflow) operation: 1 in. And 1.5 in. Metal pall rings and ceramic intalox saddles: Multifilament gauze packings in 20 cm and 38 cm i.d. columns

Abstract The theory of gas absorption accompanied by fast pseudo- m th order reaction was used to obtain values of effective interfacial area, a, in 20 and 38 cm i.d. packed columns which were operated co-currently (downflow). Values of a were obtained for 1 in. and 1.5 in. metal Pall rings; 1 in. stainless steel Pall rings, having length (height) to diameter ratio of 1.0, 0.75, and 0.5; 1 in and 1.5 in. ceramic Italox saddles; and stainless steel multifilament wire gauze type packing over a wide range of gas and liquid superficial velocities. The gas superficial velocity was varied from 30 to 255 cm/sec in the 20 cm i.d. column and 14 to 73 cm/sec in the 38 cm i.d. column. The liquid superficial velocity was varied from 0.2 to 3 cm/sec in the 20 cm i.d. column and 0.2 to 1 cm/sec in the 38 cm i.d. column. Different flow regimes, namely, trickle flow (film flow), pulse flow and transition from pulse to disperse flow, were covered. The values of a were found to be in the range of 0.6 to 2 cm 2 /cm 3 for the trickle flow (film flow) regime, and 2.4–5 cm 2 /cm 3 for the pulse flow regime. In the case of multifilament wire gauze packing (MFWGP) remarkably high values of a up to 16 cm 2 /cm 3 were obtained in the pulse to disperse flow regime.

Liquid Emulsion Membrane (LEM) Process for Vanadium (IV) Enrichment: Process Intensification

Abstract A liquid emulsion membrane (LEM) system for vanadium (IV) transport has been designed using di‐2‐ethylhexyl phosphoric acid (D2EHPA), dissolved in n‐dodecane as carrier. The selection of extractant, D2EHPA, was made on the basis of conventional liquid‐liquid extraction studies. The work has been undertaken by first carrying out liquid‐liquid extraction studies for vanadium (IV) to get stoichiometric constant (n), and equilibrium constant (Kex), which are important for process design. Transport experiments were carried out at low vanadium (IV) concentration (ppm level). The studies on liquid emulsion membrane included i) the influence of process parameters i.e. feed phase pH, speed of agitation, treat ratio, residence time and ii) emulsion preparation study i.e., organic solvent, extractant concentration, surfactant concentration, internal strip phase concentration. When the strip phase concentration was 2 mol/dm3 (H2SO4) and feed phase pH 3 better extraction of vanadium was obtained. Higher Vm/V1 gave higher extraction of vanadium (IV). A simplified, design engineer friendly model was developed.

Insight into spent caustic treatment: on wet oxidation of thiosulfate to sulfate

Oxidation of thiosulfate to sulfate is often the rate controlling step during wet air oxidation (WAO) of spent caustic from the refinery and petrochemical industry and exhibits high Biological Oxygen Demand (BOD) and Chemical Oxygen Demand (COD). The kinetics of WAO of thiosulfate was studied in the absence and presence of a heterogeneous copper catalyst. Wet oxidation of thiosulfate to sulfate is a free radical reaction exhibiting an induction period. In non-catalytic oxidation, almost complete conversion of thiosulfate to sulfate was observed in 12 min at 150 °C and in 8 min at 120 °C in the presence of a heterogeneous copper catalyst at 0.69 MPa oxygen partial pressure. The presence of phenol accelerated thiosulfate oxidation. © 1999 Society of Chemical Industry