Search

A Ranque-Hilsch Vortex Tube (RHVT) is a device that can cause simultaneous thermal and species separation in a compressible fluid mixture. The binary mixture is compressed and tangentially introduced into the vortex chamber of the RHVT, and two streams are withdrawn at opposite ends of the device. The RHVT acts as a centrifugal separator that separates the mixture into two streams, one enriched and the other depleted of the component with higher molecular weight. The extent of separation depends on the magnitude of swirl velocity of gas mixture inside the RHVT. Now a new combined heat and mass transfer model using heat and mass transfer analogy has been proposed by the authors to predict the species separation in a RHVT. The aim of this paper is to use this model to estimate the magnitude of swirl velocity of gas mixture inside the RHVT. The estimated values have been compared with range of experimentally as well as numerically obtained values reported in the literature. For a given configuration in published literature and values of cold mass fraction the average swirl velocity inside the RHVT was found to vary between 90 m/s and 130 m/s. It is found that for a fixed value of inlet pressure, average swirl velocity is a function of cold mass fraction. The value of average swirl velocity minimizes near cold mass fraction = 0.3 and maximizes near cold mass fraction = 0.8. Parametric studies have been carried out to understand the effect of important RHVT parameters on swirl velocity. Also relation between swirl velocity and species separation has been explored. [ABSTRACT FROM AUTHOR]

90Sr (T1/2 = 28 y) is always in equilibrium with 90Y in High Level Liquid waste (HLLW) and hence 90Sr is a suitable long lasting source of 90Y, if it is purified suitably for therapeutic applications. A combination of CMPO & TBP was found to be the most suitable solvent system for alpha activity removal. CMPO has high selectivity for alpha contaminants (Pu/Am) w.r.t. 90Sr. For regeneration of spent organic, 3 M Phosphoric acid was most suitable with the ability to strip back more than 98% of gross alpha activity in single contact and thus solvent system was qualified for recycling. [ABSTRACT FROM AUTHOR]

The hydrogen in the vent gas stream of the hydrocracker (used to produce bio-jet fuel) cannot be reused since it has many impurities. The metal membrane can be a potential candidate for recovering hydrogen from this vent gas. In this work, the authors report the development of a composite palladium membrane and its application, for the first time, in the recovery of hydrogen from a simulated vent gas environment. A dense thin film (thickness ~3 µm) of Pd metal was coated on a ceramic support tube by the sputter deposition technique. The hydrogen permeance of the Pd membrane was found to be 18.75 × 10-6 mol·m-2·h-1·Pa-1, which was reduced to 3.25 × 10-6 mol·m-2·h-1·Pa-1, with an exposure of 100 h in the simulated bio-jet fuel environment. To avoid the loss of permeability, a thin layer of Pt can be coated over the Pd membrane. The present study used MATLAB software to simulate the Pt-coated Pd composite membrane performance in the bio-jet fuel production environment. Simulation studies confirmed that a membrane area of ~95 cm² (250 mm length and 12 mm OD) is sufficient for the complete recovery of hydrogen from the vent gas stream of hydrocracker at a feed velocity of 0.075 m/s. [ABSTRACT FROM AUTHOR]

Use of emulsion liquid membrane (ELM) extraction of uranium(VI) from lean streams containing nitric acid using tri- n -butyl phosphate (TBP) suffers from major drawback that TBP transports nitric acid to the strip phase, thereby reducing the driving force for extraction. This problem is completely eliminated by using near neutral sodium nitrate solution as the feed. The membrane phase is light liquid paraffin, containing TBP and the strip phase is aqueous sodium carbonate. Emulsion is stabilized using polymeric surfactant system, which exhibits low rate of leakage of the strip phase and no noticeable swelling of the emulsion. The key step is pH control of the continuous phase between 4.0 and 4.5 in order to neutralize sodium carbonate leaking from the emulsion phase. Effect of concentration of NaNO 3 in the feed phase, Na 2 CO 3 in the strip phase and volume ratio of the feed to the strip phase, on the rate of extraction of uranium(VI) and its enrichment, is studied. Using this process, it is possible to achieve nearly quantitative extraction of uranium(VI) with enrichment factor greater than 60. The superiority of the present process is established by comparing its performance with ELM extraction of uranium(VI) from nitric acid. [ABSTRACT FROM AUTHOR]

Experiments are carried out to study liquid-liquid two-phase flow patterns in Y-junction microchannels etched in glass chips. The liquid-liquid test systems used in the experiments are the three standard test systems recommended by the European Federation of Chemical Engineering (EFCE) for extraction studies. Four different flow patterns--slug flow, slug and droplet flow, droplet flow, and parallel flow--are observed. Effects of microchannel diameter, flow rate, interfacial tension of the liquids, and hydrophobicity of channel wall on two-phase flow patterns have been studied, and flow regime maps are presented and discussed. [ABSTRACT FROM AUTHOR]

90Y, a beta emitting radionuclide (T1/2 ~ 64 h, Emax= 2.3 MeV), the daughter product of 90Sr is used for radio therapeutic applications. Non dispersive solvent extraction in hollow fibre membrane contactor (HFMC) with CMPO solvent studies were done to achieve the desired purification of 90Sr nitrate solution with respect to gross alpha activity. This purified solution is promising feed for 90Sr–90Y generator to achieve the clinical grade product of 90Y. In HFMC recirculations, around 99.97% alpha impurities were extracted in two recirculations from the feed solution with 0.2 M CMPO while only two recirculations were required with 0.4 M CMPO. A simplified mathematical model has also been developed to model the extraction of alpha impurities through the HFMC using CMPO as a solvent. [ABSTRACT FROM AUTHOR]

The synthesis of a new alkylmethylimidazolium ionic liquid wherein the alkyl group is functionalized with dihexylphosphine oxide moiety at the terminal position has been achieved in four steps from 1-methylimidazole. This hybrid ionic liquid effectively catalyzed the nucleophilic fluorination of primary alkyl mesylates under mild conditions using CsF as the fluoride source with a faster rate compared to butylmethylimidazolium mesylate. The hybrid catalyst was recycled 5 times without compromising the yield and purity of the product. The nucleophilic fluorination has been used for the synthesis of diethyl 2-(5-fluoropentyl)-2-methyl malonate, a precursor of 18 F isotopomer of an apoptosis imaging agent and the protected form of O -(2′-fluoroethyl)- l -tyrosine, a 18 F isotopomer of a tumor imaging agent. [ABSTRACT FROM AUTHOR]

This manuscript presents a discussion on the algebraic state update step performed during recursive filtering of the differential–algebraic equation (DAE) systems. Existing DAE state estimation approaches follow a two-step state update procedure at each sampling instant. In particular, they first estimate the differential states using the Kalman update, and then update algebraic states by explicitly solving the algebraic equations. Specifically, for the case of DAE systems involving linear algebraic equations though the differential equations are nonlinear, we show that when appropriately initialized, this two-step state update procedure is not needed. It can instead be replaced with a one-step state update procedure that computes the differential and algebraic state estimates simultaneously through the Kalman update. The satisfaction of algebraic equations is guaranteed by this one-step update without it being explicitly enforced. Towards this end, we show that the error covariance matrix of augmented states, when properly initialized, satisfies a null-space property after prediction and update step at each sampling instant. This property ensures that the state estimates obtained using the proposed one-step update approach, satisfy the algebraic equations. This holds for both analytical linearization based extended Kalman filtering and statistical linearization based sigma-point filtering approaches. We also propose a heuristic-based update procedure for state estimation of DAE systems that involve nonlinear algebraic equations. This procedure draws out inferences from the case of DAE systems involving linear algebraic equations and is based on the analysis of algebraic equations residuals obtained from the updated differential and algebraic state estimates with a one-step state update. The efficacy of the proposed state update procedures is demonstrated by performing simulation studies on a benchmark drum boiler system case study. Results demonstrate that the proposed update procedures satisfactorily estimate the differential and algebraic states of a DAE system when compared to the traditional two-step update procedure. • One-step state update proposed for DAE state estimation. • Approach exact for linear algebraic equations coupled with nonlinear differential equations. • Null-space property satisfaction by augmented prediction-error covariance matrix established. • Valid for both analytical linearization, and statistical linearization based approaches. • Heuristic one-step state update for DAEs comprising nonlinear algebraic equations proposed. [ABSTRACT FROM AUTHOR]

Niobium and tantalum are valued for their uses in nuclear, steel, aviation and electronics industries. This paper elucidates the development of a multistage counter-current separation process for obtaining pure niobium and tantalum from the hydrofluoric acid solution of Coumbite-Tantalite ore (leach liquor), with trioctyl amine (TOA) as the extractant solvent. Contrary to the conventionally used multistage process this novel route does not use any other acid in addition to hydrofluoric acid, resulting in the elimination of the generation of mixed fluoride waste. Reaction equilibrium constants for the reactions involving the extraction of hydrofluoric acid, niobium and tantalum have been determined and were used to generate equilibrium distribution curve of niobium and tantalum in the organic and aqueous phase. The number of counter-current stages required for an appropriate organic to aqueous phase volume (O/A) ratio was determined using McCabe-Thiele calculations. Selective extraction of 99% of tantalum from the leach liquor was achieved using 5 v / v % TOA and two counter-current stages for an O/A ratio of four. The tantalum lean raffinate was treated with commercial grade hydrofluoric acid to form the niobium feed solution having 16 M free acidity. Near complete extraction of niobium was achieved using a three stage counter-current process with O/A ratio of two and 10 v /v% TOA as the organic extractant. The calculations for the stage-wise variation of concentrations were validated by batch experimental simulation of counter-current processes. • A trioctyl-amine based continuous multistage counter-current process for niobium-tantalum separation has been developed. • Multiple numbers of HF molecules combines with one molecule TOA depending on the free acidity of the aqueous phase. • Selective extraction of tantalum from the leach liquor is achieved with low TOA concentration in the organic phase. • The stage-wise variation of metal concentrations was elucidated by batch experimental studies. [ABSTRACT FROM AUTHOR]

Deuterium-labeled biologically active compounds are gaining importance because they can be utilized as tracers or surrogate compounds to understand the mechanism of action, absorption, distribution, metabolism, and excretion. Deuterated drug molecules (heavy drugs) become novel as well as popular because of better stability and bioavailability compared with their hydrogen analogs. Labeling of organic molecules with deuterium at specific positions is thus gaining popularity. In this work, we have exploited a highly regioselective and enantioselective direct Michael addition of methyl- d3 alkyl ketones to dimethyl(phenyl)silylmethylene malonate that was catalyzed by ( S)- N-(2-pyrrolidinylmethyl)pyrrolidine/trifluoroacetic acid/ D2O combination with high yield and isotopic purity. The 5,5-dideutero-4-dimethyl(phenyl)silyl-6-undecyl-tetrahydropyran-2-one was obtained from the adduct of methyl- d3 undecanyl ketone and dimethyl(phenyl)silylmethylene malonate by a silicon controlled diastereoselective ketone reduction, lactonization, and deethoxycarbonylation. The dideuterated silylated tetrahydropyran-2-one is the precursor for geminal 2H2-labeled (+)-4-hydroxy-6-undecyl-tetrahydropyran-2-one, an advanced intermediate for gem-dideutero (-)-tetrahydrolipstatin and (+)-δ-hexadecanolide syntheses. [ABSTRACT FROM AUTHOR]

Ruthenium-palladium (Ru-Pd) and ruthenium-nickel (Ru-Ni) bimetallic nanoalloy particles with various metal compositions were synthesized by microwave irradiated (MWI) solvothermal technique using PVP (poly-N-vinyl-2-pyrrolidone) as capping agent and ethylene glycol as a solvent as well as reducing agent. Synthesized bimetallic nanoalloy particles were subsequently impregenated onto γ-Al2O3 support to obtain supported nanoalloy catalysts. Agglomeration of nanoalloyparticles were restricted by using excess solvent during synthesis, then distilled and recovered after completion of reaction. Hydrogenation of Dibenzo-18-crown-6 ether (DB18C6) was carried out at 9 MPa, 120°C and 3.5 h using synthesized bimetallic nanoalloy catalysts. It was observed that bimetallic nanolloycatalyst synthesized by MWI using Ru:Pd 3:1 % (w/w), exhibited higher catalytic activity and resulted 98.9 % conversion of DB18C6 with 100 % selectivity towards cis-syn-cis dicyclohexano-18-crown-6 ether (CSC DCH18C6). [ABSTRACT FROM AUTHOR]

Rh/γ-Al2O3 nanocatalysts with different metal loading were synthesized by two different techniques i. e. microemulsion and microwave irradiated solvothermal technique. Synthesized nanocatalysts were then successfully implemented for the hydrogenation of 4',4'(5')-di-tert-butyldibenzo-18-crown-6 ether (DTBuB18C6) at 70 bar, 353-393 K temperature and 5 h. It was observed that 3 wt% nanocatalyst obtained by microemulsion technique exhibited higher catalytic activity and resulted 40 % conversion with high selectivity towards cis-syn-cis di-tert-dicyclohexano-18-crown-6ether (CSC DTBuCH18C6). [ABSTRACT FROM AUTHOR]

A series of different fluorine-substituted compounds is synthesized by fluorination of primary alkyl mesylates using a new alkylmethylimidazolium ionic liquid as effective catalyst. [ABSTRACT FROM AUTHOR]