Pass Conversion Research Articles

Numerical simulation and optimisation of unconventional three‐section simulated countercurrent moving bed chromatographic reactor for oxidative coupling of methane reaction

AbstractThe simulated countercurrent moving‐bed chromatographic reactor (SCMCR) has been reported to significantly enhance methane conversion and C2 product yield for oxidative coupling of methane (OCM) reaction, which is otherwise a low per pass conversion reaction. A mathematical model of an unconventional three‐section SCMCR for OCM was first developed and solved using numerically tuned kinetic and adsorption parameters. The model predictions showed good agreement with available experimental results of SCMCR for OCM. Effects of several process parameters on the performance of SCMCR were investigated. A multi‐objective optimisation problem was solved at the operating stage using state‐of‐the‐art AI‐based non‐dominated sorting genetic algorithm with jumping genes adaptations (NSGA‐II‐JG), which resulted in Pareto Optimal solutions. It was found that the performance of the SCMCR could be significantly improved under optimal operating conditions. © 2011 Canadian Society for Chemical Engineering

Driver Design of the Piezoelectric Ultrasonic Transducer for Wire Bonding Based on Direct Digital Synthesis Technology

In order to design a driver of piezoelectric ultrasonic transducer which can provide high quality ultrasonic signal and be able to realize the frequency tracking rapidly, accurately and intelligently during the bonding process, the ATmega128 microcontroller and AD9851 synthesizer are selected as core components to build an ultrasonic generator and frequency tracking system. The basic circuit units including low pass filter, power amplifier, signal detection and conversion circuits are also established. The test results of the system shows that, based on DDS technology, high quality ultrasonic signal for transducer can be achieved. By combining the two kinds of frequency tracking methods, the system can realize the frequency tracking during the bonding process. It also indicates that the design significantly improve the precision and flexibility of the ultrasonic generator system.

Dehydrogenation of ethylbenzene using CO2 - A process design study

The scope in this project is the design of a dehydrogenation process for ethylbenzene using CO2 as mild oxidant including a technical and economical evaluation. Compared to the conventional process this process has a more favorable equilibrium and can therefore be operated at a lower temperature and lower energy consumption. The design is based on the data of the most promising catalyst investigated which is Fe/Al/Zn (1/2/6) reported by Mimura (2002). Laboratory results show a single pass conversion of 26% with a selectivity to styrene of 91% for a CO2/ethylbenzene ratio of 11. The process is designed according to the systematic process synthesis techniques. Results show that the low conversion and especially the high CO 2/ethylbenzene ratio results in an unfeasible recycle flow. It is decided to reduce the CO2/ethylbenzene ratio to 2. The economic evaluation shows that the current margin of $200 between the product and raw material is too low and should be minimal $250. An alternative would be to increase the selectivity to minimal 93%. The available catalyst data such as selectivity, conversion and lifetime is limited and should be subject of further research especially at low CO2/ethylbenzene ratios.

Tissue-Specific Increases in 11β-Hydroxysteroid Dehydrogenase Type 1 in Normal Weight Postmenopausal Women

With age and menopause there is a shift in adipose distribution from gluteo-femoral to abdominal depots in women. Associated with this redistribution of fat are increased risks of type 2 diabetes and cardiovascular disease. Glucocorticoids influence body composition, and 11β-hydroxysteroid dehydrogenase type 1 (11βHSD1) which converts inert cortisone to active cortisol is a putative key mediator of metabolic complications in obesity. Increased 11βHSD1 in adipose tissue may contribute to postmenopausal central obesity. We hypothesized that tissue-specific 11βHSD1 gene expression and activity are up-regulated in the older, postmenopausal women compared to young, premenopausal women. Twenty-three pre- and 23 postmenopausal, healthy, normal weight women were recruited. The participants underwent a urine collection, a subcutaneous adipose tissue biopsy and the hepatic 11βHSD1 activity was estimated by the serum cortisol response after an oral dose of cortisone. Urinary (5α-tetrahydrocortisol+5β-tetrahydrocortisol)/tetrahydrocortisone ratios were higher in postmenopausal women versus premenopausal women in luteal phase (P<0.05), indicating an increased whole-body 11βHSD1 activity. Postmenopausal women had higher 11βHSD1 gene expression in subcutaneous fat (P<0.05). Hepatic first pass conversion of oral cortisone to cortisol was also increased in postmenopausal women versus premenopausal women in follicular phase of the menstrual cycle (P<0.01, at 30 min post cortisone ingestion), suggesting higher hepatic 11βHSD1 activity. In conclusion, our results indicate that postmenopausal normal weight women have increased 11βHSD1 activity in adipose tissue and liver. This may contribute to metabolic dysfunctions with menopause and ageing in women.

Ethylene synthesis from the oxidative bromination of ethane

Ethylene was prepared from HBr-mediated ethane oxidation. The process includes two catalytic reactions: the oxidative bromination reaction of ethane and the dehydrobromination reaction of bromoethane. In the oxidative bromination reaction of ethane, bromoethane was synthesized by oxidizing ethane in the presence of oxygen and HBr over a catalyst. The second reaction is the dehydrobromination reaction of bromoethane to form ethylene and HBr over a catalyst. An ethane single pass conversion of 33.9% with a bromoethane selectivity of 86.7% was obtained in the oxidative bromination reaction of ethane over catalyst 1.0%LaCl 3/5.9%KCl/5.9%FeCl 3/SiO 2. In the dehydrobromination reaction of bromoethane, a bromoethane conversion of 99.6% with almost 100% of ethylene selectivity was obtained over 12.0 wt%ZnO–SiO 2 catalyst.

Simulation of Reduction of Cr(VI) by Fe(II) Produced Electrochemically in a Parallel-Plate Electrochemical Reactor

A model is presented for the reduction of hexavalent chromium in a parallel-plate electrochemical reactor via a homogenous reaction between Cr(VI) and Fe(II) generated at the iron anode. The effects of the space velocity of the feed solution, the concentration of supporting electrolyte, the distance between the electrodes, and the cell potential on conversion of Cr(VI) to Cr(III), are discussed. This study indicates that for reduction of Cr(VI) using Fe(II), the space velocity must be maintained below or the system becomes limited by the rate of reduction of Cr(VI) by Fe(II). Increasing the current density by increasing the cell potential, increasing the amount of supporting electrolyte, and decreasing the distance between the electrodes increases single pass conversion of Cr(VI) to Cr(III); however, increasing the current density also increases the specific energy required by the system.

Continuous reaction performances of benzene alkylation with long chain olefins catalyzed by ionic liquid

Based on a compulsive mixing-reacting-separating-recycling small experimental setup,the continuous reaction performances of benzene alkylation with long chain olefins catalyzed by [BMIM]Cl-AlCl3 ionic liquid were investigated. Three different situations including normal continuous operation mode (reagent materials), sidetrack feeding from different axial positions along the static mixing reactor (reagent materials) and normal continuous alkylation using industrial paraffin and olefins materials were examined. Even under the relatively hypecritical reaction conditions, the single pass conversion of pure 1-dodecene could reach to nearly 100.0%, and the selectivity of 2-phenyl isomer was higher than 37.7%. Although the positions along the reactor for sidetrack feeding were different, the 100.0% single pass conversion of 1-dodecene was also attained before the outlet of the reactor. The refined industrial olefins as raw material could meet with the requirements of continuous alkylation. The influences of impurities such as di-olefins and non-benzene aromatics on the catalytic activity and stability should be studied further.

Models of Hypochlorite production in electrochemical reactors with plate and porous anodes

Pseudo two-dimensional finite element models were developed to predict the hypochlorite (chloric(I)) (HOCl + OCl−) production by electrolysis of near-neutral aqueous sodium chloride solution, in reactors with (a) an anode and cathode in the form of plates, and (b) a lead dioxide-coated graphite felt anode and titanium plate cathode. The model was used to investigate the feasibility of using a porous anode to achieve high single pass conversions in oxidising chloride ions. For the model reactor with planar anode, the effects of diffusion, migration and convection on the mass transport of the reacting species were considered, whereas with the porous anode, a supporting electrolyte (Na2SO4) was notionally present to eliminate the migrational contribution to reactant transport. For an electrolyte flow rate of 10−6 m3 s−1 (Re = 10 for plate electrodes, Re porous = 0.76 for porous anode), a cell voltage of 3.0 V and an inlet NaCl of 100 mol m−3, the single-pass conversion of Cl− was predicted to increase from 0.45 for the reactor with a planar anode to 0.81 for the reactor with a porous anode. For the same operating conditions, the overall current efficiency was also predicted to increase from 0.71 to 0.77 by replacing the plate with the porous anode.

100 mW high efficient single pass SHG at 488 nm of a single broad area laser diode with external cavity using a PPLN waveguide crystal

A frequency stabilized single broad area laser in a V-shaped external cavity is used for Second Harmonic Generation (SHG) in a waveguide channel with dimensions of 3 mum x 5 mum x 10 mm of a PPMgO: LN crystal. A maximum coupling efficiency of 63% could be obtained. An optical output power of 100.4 mW of visible light at 488 nm could be generated with 265 mW of coupled infrared light. This results in a single pass conversion efficiency of 37.8%. No photorefractive damage or saturation effects were observed.

05/02479 Process analysis for hydrogen production by reaction integrated novel gasification (HyPr-RING)

The IS process to produce hydrogen from water requires efficient separation procedures. Effects of three typical membrane techniques (an electro-electrodialysis (EED), an electrochemical cell (EC), a hydrogen permselective membrane reactor (HPMR)) on total thermal efficiency were evaluated by heat/mass balance calculations based on the experimental data. The EED to concentrate HI solution is the most important membrane technique to obtain high thermal efficiency among the three techniques. The maximum thermal efficiency was 40.8% at 12.5molkg-H2O-1 of HI molality after the EED. The second important technique is the EC at the reaction of H2O, SO2 and I2. The maximum thermal efficiency was 38.9% at 15.3molkg-H2O-1 of H2SO4 molality after the EC. The HPMR at the decomposition reaction of HI was effective to improve one pass conversion of HI to 76.4%, and the amounts of recycled HI was reduced by 91.5% using this membrane technique. The required heat at the reactor was small compared with that at the EED or at the EC. Total thermal efficiency was improved only 0.7% by the application of the HPMR.

A Study on the Photodecomposition of Active Dye in a Baffled Fixed-Bed Reactor

The influence of dynamic parameters on the photodecomposition of active brilliant red X-3B in aqueous solution was studied using a baffled fixed-bed photoreactor. The results indicated that the per pass conversion (x) increased linearly with increasing light intensity (I 0), packed density of supported photocatalyst (N), and flow rate (Q). The slopes of the x–I0, x–N, and x–Q curves were 0.0288, 0.0392, and 0.00825 respectively. The different slopes of the x–I0, x–N, and x–Q curves suggestted that the photocatalytic decomposition rate of the active brilliant red X-3B in aqueous solution was largely dependent on the light intensity and catalyst packing density and less dependent on the flow rate.

Highly efficient conversion of propane to maleic anhydride and acetic acid by partial oxidation

Propane-selective oxidation was investigated over VMoO alone or over VMoO catalysts promoted by metal ions. Through this reaction, propane was efficiently converted to maleic anhydride, and acetic acid over VMoO itself and over metal-ion-doped VMoO catalysts. Over 70%Mo20%V10%AgO catalyst, 37.4% of propane single pass conversion was obtained at 300 °C with maleic anhydride selectivity of 53.6% and acetic acid selectivity of 38.9%. The studies on propylene oxidation indicated that propylene might not be a reaction intermediate for maleic anhydride formation in propane oxidation. A typical carbon–carbon bond cracking and reformation reaction occurred in propane oxidation by using molecular oxygen as oxidant.

Role of dehydration catalyst acid properties on one-step DME synthesis over physical mixtures

The direct synthesis of dimethyl ether (DME) was studied in a continuous high-pressure unit composed basically of a Berty reactor and on-line gas chromatograph. A commercial methanol synthesis catalyst and some solid-acid catalysts (alumina, HZSM-5, tungsten–zirconia and sulfated-zirconia) were used as physical mixtures. The dehydration catalysts were characterised by pyridine adsorption followed by IR spectroscopy and tested in the methanol dehydration reaction itself. All samples were active regardless of the differences in their acidity and a relationship between catalytic activity for methanol-to-DME and acidity could be envisaged; the activity of a solid acid on this reaction was found to be determined mainly by the number of its more acidic sites. On the one-step DME synthesis from syngas the addition of an acid catalyst to the catalytic system strongly shifted the methanol synthesis reaction, increasing significantly the pass conversion of CO. As a general rule, it could be concluded that the determining rate of DME direct synthesis is determined by the acid properties of the dehydrating catalyst, i.e., its acid strength and number of acid sites.

Singly-resonant optical parametric oscillator based on KTA crystal

Tunable mid-infra-red radiation by singly resonant optical parametric oscillation based on KTA crystal pumped by multi-axial Gaussian shape beam from Q-switched Nd:YAG laser has been demonstrated. Threshold energy of oscillation at different idler wavelengths for different cavity length has been demonstrated. Single pass conversion efficiency of incident pump energy to infra-red wavelength has also been measured.

Evaluation of the IS process featuring membrane techniques by total thermal efficiency

The IS process to produce hydrogen from water requires efficient separation procedures. Effects of three typical membrane techniques (an electro-electrodialysis (EED), an electrochemical cell (EC), a hydrogen permselective membrane reactor (HPMR)) on total thermal efficiency were evaluated by heat/mass balance calculations based on the experimental data. The EED to concentrate HI solution is the most important membrane technique to obtain high thermal efficiency among the three techniques. The maximum thermal efficiency was 40.8% at 12.5 mol kg - H 2 O - 1 of HI molality after the EED. The second important technique is the EC at the reaction of H 2O, SO 2 and I 2. The maximum thermal efficiency was 38.9% at 15.3 mol kg - H 2 O - 1 of H 2SO 4 molality after the EC. The HPMR at the decomposition reaction of HI was effective to improve one pass conversion of HI to 76.4%, and the amounts of recycled HI was reduced by 91.5% using this membrane technique. The required heat at the reactor was small compared with that at the EED or at the EC. Total thermal efficiency was improved only 0.7% by the application of the HPMR.

Acetic acid synthesis from methane by non-synthesis gas process

Acetic acid was synthesized from methane by non-syngas process. In the process, methane was brominated with hydrogen bromide (40 wt.% HBr/H2O) and oxygen to give CH3Br and CO over a Ru/SiO2 catalyst. The as-generated CO and CH3Br reacted with water under the catalysis of RhCl3 to produce acetic acid, methanol, and methyl acetate. In the first step oxidative bromination reaction, 30.1% of methane single pass conversion with 72.4% of CH3Br selectivity and 25.5% of CO selectivity was attained. In the second step, almost 100% CH3Br conversion was reached.

Attrition properties of precipitated iron Fischer–Tropsch catalysts

While precipitated iron catalysts provide optimal activity and selectivity for Fischer–Tropsch (F–T) synthesis with coal-derived synthesis gas, their attrition resistance under reaction conditions has been questioned. It is well known that iron oxides undergo phase transformations during activation and reaction, leading to changes in volume, which are a primary cause of catalyst break up (‘chemical attrition’). In this paper we report on attrition properties of precipitated Fe catalysts under both inert and reactive conditions in a stirred tank slurry reactor (STSR). Our results show that after 364 h of testing in the STSR, the particle size reduction due to fracture and erosion was moderate. The observed increase in fraction of particles smaller than 10 μm was small (7.8%). Catalytic performance was excellent, yielding low methane and high C 5 + selectivities of 2.6 and 82.5%, respectively, at 78.5% single pass conversion. We conclude therefore that iron catalysts used in this study have adequate attrition resistance and desirable F–T activity and selectivity for use in conversion of coal-derived syngas to liquid fuels in the slurry bubble column reactor.

Amplified spontaneous emission enhanced forward stimulated Raman scattering in dye solutions

We study forward stimulated Raman emission from weakly fluorescent dye 4'-diethylamino-N-methyl-4-stilbazolium tosylate (DEST) in 1,2,dichloroethane solution excited by a 28 ps, 532 nm Nd: YAG laser. Neat 1, 2, dichloroethane emits the first Stokes line at 631 nm with a spectral width of 1.6 nm corresponding to a Raman shift of 2956 per cm. We observe reduction of spectral width with the addition of DEST in 1, 2, dichloroethane solution. The single pass conversion efficiency for forward Raman emission is as high as 20 percent in a 1 cm path length sample. The pulse duration of forward stimulated Raman emission measured by a third order autocorrelation technique is 10 ps in neat 1, 2, dichloroethane, whereas it is nearly 3 ps for 0.04 mM of DEST solution.

Effect of Polymer Growth Rate and Diffusion Resistance on the Behavior of Industrial Polyethylene Fluidized Bed Reactor

The two-phase model developed for the UNIPOL polyethylene process is improved by introducing polymer diffusion resistance, this means modelling of polyethylene fluidized bed reactors has been examined on two levels, at small scale of individual polymer particle, and macroscale of the whole reactor. The model utilizes the multigrain model that accounts for the reaction rate at catalyst surface to explore the static and dynamic bifurcation behavior of the fluidized bed catalytic reactor. Detailed bifurcation diagrams are developed and analyzed for the effect of polymer growth factor and Thiele modulus (the significance of the porous medium transport resistance is characterized by Thiele modulus) on reactor dense phase monomer concentration and reactor temperature as well as polyethylene production rate and reactor single pass conversion for the safe temperature region. The observations reveal that significant diffusion resistance to monomer transport exists, and this can mask the intrinsic rate constants of the catalyst. The investigation of polymer growth factor indicates that, the nascent stage of polymerization is highly gas phase diffusion influenced. Intraparticle temperature gradients would appear to be negligible under most normal operating conditions.

A simple adsorber dynamics approach to simulated countercurrent moving bed reactor performance

The design and performance of a simulated countercurrent moving bed chromatographic reactor (SCMCR) for high temperature reactions are investigated for both reversible and irreversible reactions of a single reactant. From an analysis of the solid phase and gas phase flow ratios in each of the SCMCR sections, the flow conditions necessary for optimizing the conversion and yield are obtained. Reactor performance is not evaluated from typical material balance equations, but rather by considering the separation of reactant and product waves as they flow through the sections of the SCMCR, and as the feed point is cycled under the assumption of dispersionless plug flow. The additional assumptions of linear adsorption equilibria and infinite gas–solid mass transfer rates permit the expressions for exit molar flow profiles during the initial transient period, and of the ultimate periodic steady state, to be readily obtained. Simple algebraic expressions for the production rate of the reaction product as a function of the adsorption equilibrium constants, the per pass conversion, the number of switching periods, and the molar flow rate of the reactant, are presented.