Total Residence Time Research Articles

Understanding oscillatory behaviour of gibbsite precipitation circuits

Gibbsite precipitation plays a central role in the production of alumina, the feedstock for aluminium smelters. A mathematical model of a simplified precipitation circuit is used in this work to investigate the main process parameters affecting the operating stability of gibbsite precipitation circuits incorporating solids classification and seed recycle. The crystallization process in continuous precipitation tanks is modelled using a dynamic crystallization population balance equation incorporating crystal growth, nucleation, and agglomeration kinetics. The precipitation circuit model provides a detailed particle size distribution response, which is crucial for evaluating the circuit's precipitation yield and product properties. Transient responses of the precipitation circuit model were investigated for key process parameters. It is shown that a rectangular pulse disturbance in the feed flow rate can generate an oscillatory response of the precipitation circuit if the solids residence time in the classification section is comparable in magnitude to the total slurry residence time in the precipitation section. An oscillatory circuit response has a detrimental effect on the product particle size distribution, but only slightly affects the production rate. Oscillations in the product mean size are believed to be a result of the impact of the main precipitation process variables on the gibbsite agglomeration rate.

Continuous-Flow Process for the Synthesis of 2-Ethylphenylhydrazine Hydrochloride

An expeditious process for the synthesis of 2-ethylphenylhydrazine hydrochloride via a continuous-flow reactor from 2-ethylaniline in 94% yield was described. The main steps in this synthesis involved not only the generation of diazonium salt intermediate in situ but also the temperature-programmed reduction by sodium sulfite in the tandem loop reactor. Total residence time was reduced to less than 31 min by increasing the reaction temperature and thereby taking advantage of improved mass and heat transfer of a continuous-flow system. The purification process was simplified by extraction of impurities in situ.

Designing Robust Crystallization Processes in the Presence of Parameter Uncertainty Using Attainable Regions

We consider the influence of uncertainty in crystallization kinetics (i.e., in the nucleation and growth rates) in the context of process design. Specifically, we model continuous and batch crystallization processes using population balance equation models and investigate how the inherent uncertainty in kinetic parameters propagates through the crystallization processes and how it ultimately affects the distribution of process outcomes (yield and mean particle size). We incorporate the effect of uncertainty into the concept of attainable regions, i.e., we exhaustively investigate which combinations of particle size and total residence time (or batch time) can be attained with a certain probability. Avoiding regions of low probability allows the design of robust crystallization processes that can deliver a product with desired specifications, even when the original process was designed using inadequately characterized crystallization kinetics. The concepts presented in this article are illustrated by a cas...

Residency and abundance of sperm whales (Physeter macrocephalus) in the Bleik Canyon, Norway

Sperm whales (Physeter macrocephalus) are widely distributed in the Norwegian Sea and feeding aggregations occur. One of these aggregations is in the Bleik Canyon, close to shore in Norway, where the present study was performed. The study used a whale safari company as a platform from which to conduct a photo-identification study of male sperm whales. Data for this study was comprised of a total of 3856 images from 22 seasons (1987–2010) of whale-watching tours. In total, 411 individuals were identified. This study supports the results from previous photo-identification studies in the Bleik Canyon and confirms the presence of both transient and resident male sperm whales in the Bleik Canyon. These results suggest that the sperm whale group(s) found there are a loose feeding aggregation and not a closed population. Total residence time varied between one day and 14 years, although most individuals were only seen in one or two years. The number of sighted whales fluctuated between years, from eight to 77 individuals. No trend in the number of sighted whales was found. The estimated size of the feeding aggregation in the Bleik Canyon also fluctuated between years, from 11 to 116 individuals, with no trend evident.

Modeling the Total Residence Time in a Rotary Dryer

Abstract A mathematical model for the rotary dryer that determines the total residence time is developed. Experiments were performed in a laboratory-scale direct contact rotary dryer with the gas flowing concurrently with the solids. The model predictions depicted that the total residence time decreases with increasing the inclination of the rotary drum, the speed of rotation and the radius of rotary drum. The validation of the model was carried out experimentally for maize while varying the inclination of the rotary drum and the speed of rotation. The experimental results were observed to be in good agreement with the model predictions.

Investigation of petroleum-contaminated groundwater remediation using multi-stage pilot system: physical and biological approach

In this paper, a pilot-scale system including various process steps was investigated in order to treat contaminated groundwater supplies which have been exposed to oil pollutants for a long time as they are located near the Tehran oil refinery company (TORC). For achieving this goal, a combination of dissolved air flotation unit that is followed by activated sludge bioreactors (ASBRs) and an activated carbon filter was chosen. The crude oil combined with tap water was applied to synthesize contaminated groundwater. Activated sludge taken from wastewater treatment plant at TORC was used to supply oil-degrading bacteria. Besides, the solution of mineral salts was added to the bioreactor as nutrients amendment. The optimum design parameters such as hydraulic retention time, return activated sludge rate of the ASBRs, and total residence time for all steps were 14 h, 100%, and 21 h, respectively. The operation of the pilot system which was implemented in different initial crude oil concentrations (206 ± 1,412 ± 3,1590 ± 10 mg l−1) finally led to total petroleum hydrocarbons removal of 97, 97.25, and 98.57%, respectively. The reduction efficiency of chemical oxygen demand during the experiment was more than 97%. Furthermore, the quality of the treated groundwater was clearly improved, as the turbidity reduction through the experiment exceeded 90%. According to the results of the study, this treatment system can be considered as a reliable and efficient approach that is recommended to be used in case of extremely contaminated groundwater.

ПІДХОДИ ДО ОБСЛУГОВУВАННЯ ЗАЯВОК В ІНТЕЛЕКТУАЛЬНІЙ НАДБУДОВІ У МЕРЕЖАХ НАСТУПНОГО ПОКОЛІННЯ

У статті розглянуті особливості обслуговування заявок в системі управління інтелектуальними послугами в умовах зростаючого спектра послуг, що надаються телекомунікаційною мережею. Метою даної статті є розробка архітектури інтелектуальної надбудови (ІН) мереж наступного покоління з різними принципами управління послугами (централізоване, децентралізоване і змішане управління) та представлення можливих підходів до виконання послуг при архітектурі ІН зі змішаним принципом управління.

Design and optimization of a multistage continuous cooling mixed suspension, mixed product removal crystallizer

Continuously operated single and multistage MSMPR crystallizers using intermittent withdrawal through use of an automated pressure supply were developed for the cooling crystallization of Paracetamol from an aqueous isopropanol mixture. The onset of steady state was detected through analysis of the solid phase by means of Focused Beam Reflectance Measurement (FBRM). Simple extraction of the growth and nucleation parameters from the single stage reactor operating at steady state was performed though use of the population balance model. The kinetic data was then used with the two stage MSMPR models to predict the performance of the cascade under various operating conditions. A diagram of the mean particle size vs. total residence time in the MSMPR Cascade was obtained by incorporating the energy balance as a constraint. This affords a means to determine whether a desired product specification can be achieved in the chosen configuration. A multi-objective optimization is proposed to determine a Pareto optimal with respect to multiple attributes of the particle size distribution attained from the two stage MSMPR cascade. The optimal conditions were implemented experimentally and the crystal size distributions (CSDs) at steady state were compared to those predicted by the model.

Phase I Study of 131-I-Tositumomab Radioimmunotherapy (RIT) in Patients with Relapsed or Residual CD20 Antigen-Expressing B Cell Lymphomas Following Autologous Hematopoietic Stem Cell Transplantation

Introduction: I-131-Tositumomab is a radiolabeled murine monoclonal antibody that binds to the CD20 antigen on the surface of malignant and normal B lymphocytes, targeting radiation to B cells. I-131-Tositumomab has been studied with chemotherapy and in high-doses as part of conditioning regimens for autologous stem cell transplant (ASCT) in relapsed/refractory B cell lymphoma patients (pts). Non-myeloablative I-131-tositumomab was approved in the US and Canada for treatment of CD20 antigen-expressing relapsed or refractory low-grade follicular or transformed non-Hodgkin lymphomas (NHL). Since February 2014, tositumomab and I-131-tositumomab, the Bexxar¨ therapeutic regimen, is no longer commercially available.Methods: We conducted a single-center, phase I trial of I-131-tositumomab in pts with CD20+ B cell NHL with relapsed or progressive lymphoma after ASCT. Eligibility criteria included creatinine <1.5; total bilirubin, AST and ALT <1.5 upper limit of normal; and no bone marrow involvement by lymphoma. Eligible pts had stored autologous stem cell products (> 2 x106 CD34+ cells/kg). Pts with active infection, ANC < 1,500/uL, platelet count <100,000/uL, prior anti-B cell RIT, or previous total body radiation were excluded from the study. After thyroid blockade, pts received a dosimetric dose of I-131-tositumomab to determine biodistribution and total body residence time for calculation of the therapeutic dose. Pts with expected biodistribution then received the calculated therapeutic dose 7 - 14 days later, according to a dose escalating 3+3 design based on platelet count (Table 1). Dose limiting toxicity (DLT) was defined as any >grade 3 adverse event according to the CTCAE v.3. All pts in each cohort had to be evaluable for response and toxicity before escalation to the next dose level. After enrollment of the first cohort, DLT was re-defined as any >grade 3 non-hematologic adverse event. After treatment, pts were monitored weekly for 13 weeks for hematological and other toxicities with response assessments at weeks 7 and 13, and then evaluated at weeks 26, 39, and 52, then every 3 months during year 2, every 4 months during year 3, every 6 months during year 4, and yearly thereafter.Results: 12 pts were enrolled and received both dosimetric and therapeutic doses of I-131-tositumomab; 6 pts (50%) were men. Median age was 58.5 years (range: 49-66). 5 of 12 (41.6%) pts had diffuse large B cell lymphoma (DLCBL), 4/12 (33.3%) follicular lymphoma (FL), and 3/12 (25.0%) FL transformed to DLBCL. Median number of prior therapies was 4 (range: 3 - 8); median time from ASCT was 1.6 years (range: 0.3 - 6.8). 2 pts had progressive disease after ASCT (1 transformed FL; 1 DLBCL); 10 pts had relapsed from complete remission (CR) after ASCT. 7 pts received 25cGy I-131-tositumomab. The cohort receiving 25cGy was expanded to 6 due to grade 4 neutropenia (1 pt), and then expanded to 7 because 1 pt progressed prior to week 7 response assessment. 3 pts received 50cGy and 1 pt each received 65cGy and 75cGy. At all doses, I-131-tositumomab was well-tolerated. Treatment-related toxicities > grade 3 were exclusively hematological and not dose dependent, including thrombocytopenia (2/12: 1 grade 3, 1 grade 4), neutropenia (2/12: 1 grade 3, 1 grade 4) and anemia (2/12: 2 grade 3). Hematologic toxicities were reversible in all cases, with median time to recovery to < grade 3 toxicity 7 days. Non-hematological adverse events were mild and < grade 2. The most commonly reported non-hematological adverse event was fatigue. Overall response rate at week 7 was 41.6% (5/12) with 33.3% (4/12) pts achieving CR (2 pts with FL; 2 pts with DLBCL). Median duration of response was 13.8 months. As of May 2014, 2 pts are still in CR, including 1 pt with FL at 10.3 months and 1 pt with DLBCL at 5.5 years. Median progression free survival is 6.5 months; median time to treatment failure is 4.4 months. At the median follow-up of 21.9 months (range: 10.3 – 66.3), overall survival is 68.7%; no secondary hematologic malignancies have been observed.Conclusion: This is the first study of I-131-tositumomab RIT in pts with relapsed or progressive NHL after ASCT. In pts with CD20+ DLBCL, FL, or transformed FL following ASCT, non-myeloablative I-131-tositumomab is well-tolerated and can achieve sustained complete remissions. Table 1:Dose Escalation SchemaPlatelet count>100,000, </=150,000>150,000Dose level 120 cGy25 cGyDose level 240 cGy50 cGyDose level 355 cGy65 cGy DisclosuresSchuster:GlaxoSmithKline: Research Funding.

A Three‐Minute Synthesis and Purification of Ibuprofen: Pushing the Limits of Continuous‐Flow Processing

AbstractIn a total residence time of three minutes, ibuprofen was assembled from its elementary building blocks with an average yield of above 90 % for each step. A scale‐up of this five‐stage process (3 bond‐forming steps, one work‐up, and one in‐line liquid–liquid separation) provided ibuprofen at a rate of 8.09 g h−1 (equivalent to 70.8 kg y−1) using a system with an overall footprint of half the size of a standard laboratory fume hood. Aside from the high throughput, several other aspects of this synthesis expand the capabilities of continuous‐flow processing, including a Friedel–Crafts acylation run under neat conditions and promoted by AlCl3, an exothermic in‐line quench of high concentrations of precipitation‐prone AlCl3, liquid–liquid separations run at or above 200 psi to provide solvent‐free product, and the use of highly aggressive oxidants, such as iodine monochloride. The use of simple, inexpensive, and readily available reagents thus affords a practical synthesis of this important generic pharmaceutical.

A three-minute synthesis and purification of ibuprofen: pushing the limits of continuous-flow processing.

In a total residence time of three minutes, ibuprofen was assembled from its elementary building blocks with an average yield of above 90% for each step. A scale-up of this five-stage process (3 bond-forming steps, one work-up, and one in-line liquid-liquid separation) provided ibuprofen at a rate of 8.09 g h(-1) (equivalent to 70.8 kg y(-1)) using a system with an overall footprint of half the size of a standard laboratory fume hood. Aside from the high throughput, several other aspects of this synthesis expand the capabilities of continuous-flow processing, including a Friedel-Crafts acylation run under neat conditions and promoted by AlCl3, an exothermic in-line quench of high concentrations of precipitation-prone AlCl3, liquid-liquid separations run at or above 200 psi to provide solvent-free product, and the use of highly aggressive oxidants, such as iodine monochloride. The use of simple, inexpensive, and readily available reagents thus affords a practical synthesis of this important generic pharmaceutical.

Refiner optimization and control Part I: Fiber residence time and major dynamic fluctuations in TMP refining processes

The study focuses on dynamic considerations in a mill-wide perspective showing that mill economy is closely linked to optimization of TMP and power plant. Special attention is given to stability issues in the refining processes. Describing the dynamics in such nonlinear processes is difficult and tedious and requires significant knowledge about where in the operating window to run the refiners. Results show the dynamics in the internal states, temperature profiles and the plate gap sensors responses and how they correspond to the refiner motor load. Disturbances in production affect the plate gap sensors and the temperature profiles in the same direction, while deliberate changes in the plate gap result in a dynamic situation where the motor load and temperature profile change in opposite directions. It is shown that the total residence time and the ratio between the residence time before and after the maximum temperature will be important when formulating specifications for energy efficient refining. As an example of how the refining process affects the mill economy, the start-up procedures for two different types of refiners will be penetrated. It is shown that the start-ups are most often associated with an over shoot in the motor load, which is easy to overcome.

Conceptual design of a passively safe thorium breeder Pebble Bed Reactor

More sustainable nuclear power generation might be achieved by combining the passive safety and high temperature applications of the Pebble Bed Reactor (PBR) design with the resource availability and favourable waste characteristics of the thorium fuel cycle. It has already been known that breeding can be achieved with the thorium fuel cycle inside a Pebble Bed Reactor if reprocessing is performed. This is also demonstrated in this work for a cylindrical core with a central driver zone, with 3g heavy metal pebbles for enhanced fission, surrounded by a breeder zone containing 30g thorium pebbles, for enhanced conversion.The main question of the present work is whether it is also possible to combine passive safety and breeding, within a practical operating regime, inside a thorium Pebble Bed Reactor. Therefore, the influence of several fuel design, core design and operational parameters upon the conversion ratio and passive safety is evaluated. A Depressurized Loss of Forced Cooling (DLOFC) is considered the worst safety scenario that can occur within a PBR. So, the response to a DLOFC with and without scram is evaluated for several breeder PBR designs using a coupled DALTON/THERMIX code scheme. With scram it is purely a heat transfer problem (THERMIX) demonstrating the decay heat removal capability of the design. In case control rods cannot be inserted, the temperature feedback of the core should also be able to counterbalance the reactivity insertion by the decaying xenon without fuel temperatures exceeding 1600°C.Results show that high conversion ratios (CR >0.96) and passive safety can be combined in a thorium PBR within a practical operating regime, which means a thermal power of 100MW or higher, 1000days total residence time of the breeder pebbles and fuel pebble handling times longer than 14.5s, like in the HTR-PM. With an increased U-233 content of the fresh driver pebbles (18w%), breeding (CR=1.0135) can already be achieved for a 220cm core and 80cm driver zone radius. While the decay heat removal is sufficient in this design, the temperature feedback of the undermoderated driver pebbles is too weak to compensate the reactivity insertion due to the xenon decay during a DLOFC without scram. With a lower U-233 content per driver pebble (10w%) it was found possible to combine breeding(CR=1.0036) and passive safety for a 300cm core and 100cm driver zone radius, but this does require more than a doubling of the pebble handling speed and a high reprocessing rate of the fuel pebbles. The maximum fuel temperature during a DLOFC without scram was simulated to be 1481°C for this design, still quite a bit below the TRISO failure temperature. The maximum reactivity insertion due to an ingress of water vapour is also limited with a value of +1497pcm.

Continuous Flow Total Synthesis of Rufinamide

Small molecules bearing 1,2,3-triazole functionalities are important intermediates and pharmaceuticals. Common methods to access the triazole moiety generally require the generation and isolation of organic azide intermediates. Continuous flow synthesis provides the opportunity to synthesize and consume the energetic organoazides, without accumulation thereof. In this report, we described a continuous synthesis of the antiseizure medication rufinamide. This route is convergent and features copper tubing reactor-catalyzed cycloaddition reaction. Each of the three chemical steps enjoys significant benefits and has several advantages by being conducted in flow. The total average residence time of the synthesis is approximately 11 min, and rufinamide is obtained in 92% overall yield.

Rolling and bouncing dynamics of particles in the inclined rotating bowl for sago sizing mechanism

A novel mechanism for automatic sizing of sago granules is presented in this paper with analytical and experimental studies. This automation method would help to overcome the difficulties faced in the conventional labor which is the intensive process of sago sizing. This paper mainly discusses the data required to define the particle trajectory and behavioral movement in shaping the sago granules. Mathematical models are prepared and experimental studies are performed for the instant at which the flight of particles will occur due to centrifugal flee force and for the trajectory of the particle dynamics for various rotational speeds of the bowl and inclined rod that is coupled to the bowl. The prepared range of inclination angle of the rod is 60° to 64° with the horizontal plane. The maximum flight velocity of particle with a maximum height for models and experiments is 9.81m/s for the height of 46.43mm and 9.8m/s for the height of 43.12mm. The total residence time of the particle inside the bowl diameter of 200mm and height 50mm is also determined numerically as 6min 43s and experimentally as 7min 15s for the initial radial position of the particle of 20mm from the axis of rotation of the bowl. The results of analytical models are compared and validated with the experimental results and the analytical results coincide with experimental results with negligible amount of error.

Application of a slurry feeder to 1 and 3 stage continuous simultaneous saccharification and fermentation of dilute acid pretreated corn stover

Continuous operation is often chosen for conceptual designs of biological processing of cellulosic biomass to ethanol to achieve higher volumetric productivities. Furthermore, continuous stirred tank reactors (CSTR) can handle higher solids concentrations than possible in batch mode due to broth thinning at partial conversion in a continuous fermentor. However, experience and literature data are very limited for continuous simultaneous saccharification and fermentation (cSSF) processes. In this work, a slurry feed system was developed and applied to a 3-stage bench-scale cSSF train to convert pretreated corn stover to ethanol and determine the effects of dilution rate and number of fermentation vessels on overall volumetric productivity. The highest productivity of 0.4gL−1h−1 was achieved in a single cSSF vessel with an 8h residence time. Furthermore, productivity at identical total residence times was 12% higher for operation with 3 cSSF stages than for a single CSTR stage for pretreated corn stover.

Microfluidic remote loading for rapid single-step liposomal drug preparation.

Microfluidic-directed formation of liposomes is combined with in-line sample purification and remote drug loading for single step, continuous-flow synthesis of nanoscale vesicles containing high concentrations of stably loaded drug compounds. Using an on-chip microdialysis element, the system enables rapid formation of large transmembrane pH and ion gradients, followed by immediate introduction of amphipathic drug for real-time remote loading into the liposomes. The microfluidic process enables in-line formation of drug-laden liposomes with drug : lipid molar ratios of up to 1.3, and a total on-chip residence time of approximately 3 min, representing a significant improvement over conventional bulk-scale methods which require hours to days for combined liposome synthesis and remote drug loading. The microfluidic platform may be further optimized to support real-time generation of purified liposomal drug formulations with high concentrations of drugs and minimal reagent waste for effective liposomal drug preparation at or near the point of care.

Kinetic modeling of atom transfer radical copolymerization of methyl methacrylate and 2‐(trimethylsilyl) ethyl methacrylate in a train of continuous stirred‐tank reactors

A comprehensive model was developed using the method of moments to describe the atom transfer radical copolymerization (ATRcoP) of methyl methacrylate and 2‐(trimethylsilyl) ethyl methacrylate in a train of continuous stirred‐tank reactors (CSTRs). The use of a train of CSTRs effectively decreases the residence time distribution and molecular weight distribution. Two different constraint conditions (i.e., constant feeding flow rate and constant total average residence time) were simulated. At constant feeding flow rate, the monomer conversion and average molecular weight are significantly improved by increasing the number of CSTRs in the train. Moreover, a constant total average residence time increases the productivity of copolymers with the increase in the number of CSTRs in the series. Thus, a train of CSTRs can be used to produce copolymers continuously with consistent quality. This method is important in obtaining a balance between the quality and quantity of the copolymer production for ATRcoP. POLYM. ENG. SCI., 55:1030–1038, 2015. © 2014 Society of Plastics Engineers

Age determination of coarse woody debris with radiocarbon analysis and dendrochronological cross-dating

To study the decay of coarse woody debris (CWD) in forest ecosystems, it is necessary to determine the time elapsed since tree death, which is difficult at advanced decay stages. Here, we compare two methods for age determination of CWD logs, dendrochronological cross-dating and radiocarbon analysis of the outermost tree ring. The methods were compared using samples from logs of European beech, Norway spruce and Sessile oak decomposing in situ at three different forest sites. For dendrochronological cross-dating, we prepared wood discs with diameters of 10–80 cm. For radiocarbon analysis, cellulose was isolated from shavings of the outermost tree rings. There was an overall good agreement between time of death determined by the two methods with median difference of 1 year. The uncertainty of age determination by the radiocarbon approach did not increase with decreasing carbon density, despite incomplete separation of chitin from the extracted cellulose. Fungal chitin has the potential to alter the radiocarbon signature of tree rings as the carbon for chitin synthesis originates from different sources. Significant correlations between year of tree death and carbon density of wood were found for beech and spruce, but not for oak due to relatively small decreases in carbon density within 50–60 years. Total residence times of CWD were calculated from these correlations and revealed 24 years for beech and 62 years for spruce. The uncertainty of total residence times results mainly from huge natural variability in carbon density of CWD rather than uncertainty in the age determination. The results suggest that both methods are suitable for age determination of CWD.

Residence time and axial dispersion of liquids in Trickle Bed Reactors at laboratory scale

Abstract Hydrodynamic behavior in a lab-scale Trickle Bed Reactor (I.D. 1.15 cm, L = 30 cm, filled with silica particles of 0.2–0.8 mm) has been investigated. Residence time distribution curves were determined using a step transient response via conductivity measurement varying gas flowrate (0–12 mL/min CO2–H2–O2 at 78–4.0–18 mol.%) and liquid flowrates (methanol 0.5–2.0 mL/min) at −10 °C and atmospheric pressure. We demonstrate that this reactor can be accurately modelled using a combined model of axial dispersion followed by one mixed tank reactor with absolute average deviations lower than 2.6% (maximum deviation of 6.50%). The best results were obtained for a model combining 1-tank reactor with 1.20–6.15 min of residence time in series with a plug flow with residence times from 8.1 to 38.1 min. These values highlight the prevalence of the axial dispersion over the backmixing (exemplified by the mixed tank reactor) with a contribution between 80.3% and 90.1% of the total residence time. The Peclet numbers determined were in the interval of 248.3–699.3, the highest values of Pe were obtained at the highest liquid flowrate indicating the lowest axial dispersion. Correlations with the fraction of liquid flow, gas and liquid Reynolds numbers and the Galilei number are given.