Closed-loop Reactor Research Articles

Spatiotemporal characteristics of microplastics in a university wastewater treatment plant: Influence of sudden on-campus population swings

We studied the occurrence and characteristics (sizes, shapes, and polymer compositions) of microplastics (MPs) in a secondary wastewater treatment plant (WWTP) at the University of Mississippi both spatially and temporally. Putative MPs were isolated by sieving, matrix digestion, and density separation, and quantified using stereomicroscopy, with a subset of samples analyzed by Focal Plane Array (FPA) µ-FTIR imaging. In the influent, the highest MP concentration (particles/L ± 1 SD, n = 3) occurred after a football game on campus (62.3 ± 7.6) and the lowest (19.7 ± 2.1) during the summer with little activity on campus. Over 90% of the MPs were removed in the primary treatment. Downstream, MPs were most abundant in the closed loop reactor with concentrations as high as 1962 particles/L. Concentrations in secondary clarifier and final treated effluent were both < 4 particles/L during both normal flow (∼2000 m3/d) and high-flow (>2500 m3/d) periods, and between 16 and 39 particles/L during a low-flow (<1500 m3/d) period. This difference likely stems from changes in plant operations during the low-flow period to support the activated sludge, including longer process times. MPs were mainly composed of polyester, polyethylene, acrylates, polypropylene, polyurethane, polyvinyl chloride, and polystyrene. Fibers were most abundant throughout the system, averaging 61%, followed by fragments (21%), films (13%), and beads and foams (∼5%). Overall, we show that flow rates and treatment times can profoundly influence MPs concentrations in the treated effluent, and that the optimal wastewater treatment conditions also yield the best MP removal efficiency.

Auto-Aspirated DAF Sparger Study on Flow Hydrodynamics, Bubble Generation and Aeration Efficiency

A novel auto-aspirated sparger is examined experimentally in a closed-loop reactor (CLR) at lab scale using particle image velocimetry, high-speed camera and oxygen mass transfer rate measurements. State-of-the-art 3D printing technology was utilized to develop the sparger design in stainless steel. An insignificant change in the bubble size distribution was observed along the aerated flow, proving the existence of a low coalescence rate in the constraint domain of the CLR pipeline. The studied sparger created macrobubbles evenly dispersed in space. In pure water, the produced bubble size distribution from 190 to 2500 μm is controlled by liquid flow rate. The bubble size dynamics exhibited a power-law function of water flow rate approaching a stable minimum bubble size, which was attributed to the ratio of the fast-growing energy of the bubble surface tension over the kinetic energy of the stream. Potentially, the stream energy can efficiently disperse higher gas flow rates. The oxygen transfer rate was rapid and depended on the water flow rate. The aeration efficiency below 0.4 kW/m3 was superior to the commonly used aerating apparatuses tested at lab scale. The efficient gas dissolution technology has potential in water treatment and carbon capture processes applications.

Reaction kinetic study of nonthermal plasma continuous degradation of acetone in a closed-loop reactor

Nonthermal plasma (NTP) degradation has been shown to be a promising method for volatile organic compounds (VOCs) removal from air. However, there have been few studies on the degradation of indoor VOCs using NTP, and even less on their reaction kinetics. In this study, NTP degradation of acetone, a representative of oxygenated VOCs, in a closed-loop reactor operating in recirculation mode was investigated. Acetone and organic by-products were characterized in real-time by proton transfer reaction time-of-flight mass spectrometry. The results showed that approximately 85.7% of the acetone degraded within 7.5 h with dielectric barrier discharge treatment at 4.3 W. Methanol, acetaldehyde, formic acid, and acetic acid were observed to be the main organic byproducts with concentrations time-dependent on the order of ppb/ppm. The concentrations of the inorganic by-products O3 and NO2 are also time-dependent and can decrease to nearly 0 after a sufficient degradation time. Based on the concentration measurement in real-time, several rate laws were used to fit the concentration variations of acetone and the organic by-products, and it was observed that they strictly followed the simple kinetic reaction rate laws: acetone followed the first-order rate law, and formic acid formation followed the one-half-order rate law, etc. This study provides a good example of characterizing NTP removal of VOCs in airtight spaces and has important theoretical and practical significance in designing a better NTP device, predicting NTP degradation reaction rate, and accelerating the practical application of NTP technology for indoor air treatment.

Toward the implementation of self-powered, wireless, real-time reactor power sensing

The successful development of real-time, self-powered, wireless reactor power sensing technology would enable key operating parameters of every fuel assembly in a commercial reactor core to be continuously monitored, and potentially be utilized for applications such as closed-loop reactor control. This paper discusses the expansion of successful work on the application of Self Powered Neutron Detectors (SPND) for reactor power monitoring and the wireless transmission of these detector signals using advanced vacuum micro-electronic (VME) transmitter technology developed by Westinghouse in collaboration with the Penn State University Radiation Science and Engineering Center. Results demonstrate that this technology may be successfully applied via long-term testing in the Penn State TRIGA reactor. SPND are inherently slower than, for example, ion chambers due to their dependence on radioactive decay to generate a signal. Additional research developed delay compensation algorithms to accelerate the response of these detectors for use in near-real-time closed-loop reactor control. Initial results indicate that practical signal acceleration can be obtained digitally or with an equivalent analog circuit. Future research will apply an inverse model of the sensor’s balance differential equations to more-effectively accelerate the SPND signal. Use of inverse models will also prove to be adaptive in the sense that time-dependent burn-up of these detectors, due to neutron activation of the detector material, can be modeled and applied in the acceleration algorithm.

Gasification and catalytic reforming of corn straw in closed-loop reactor

A closed-loop gasification and catalytic reforming apparatus was applied for producing syngas from corn straw with upgraded syngas quality. Four nickel based catalysts at 10% and that at 5–15% loadings on γ-A12O3 were synthesized and tested. Effects of reforming temperature (700–900 °C), steam to biomass ratio (S/B, 0.5–2.5), catalyst to biomass ratio (C/B, 0.2–0.6) on the syngas quality and the carbon conversion and gasification efficiency were investigated. Incorporation of reforming reaction with 10% Ni/γ-A12O3 catalyst leads to the highest CO content (50.2%) and lowest CO2 content (7.5%) amongst the four tested catalysts and amongst the Ni/γ-A12O3 catalysts at different Ni loading. The syngas was upgraded by both the decoking reaction in the pyrolytic chamber and the steam reforming and water shift reactions in the reforming chamber.

Modelling photocatalytic detoxification of aflatoxin B1 in peanut oil on TiO2 layer in a closed-loop reactor

Aflatoxin B1 (AFB1) is the most common and toxic among the aflatoxin group. Improper storage of both raw and processed peanut oil makes it susceptible to AFB1 production. Here, a closed-loop photocatalytic reactor consisting of a glass tube coated with TiO2 as a catalyst has been developed to study the photocatalytic detoxification of AFB1 in peanut oil. The removal rates of AFB1 in the photocatalytic process were apparently higher than that of the photolysis process. It is inappropriate to approximate Langmuir–Hinshelwood kinetics by a first-order kinetic expression based on the experimental kinetic data for the photocatalytic process. The newly proposed Weibull distribution model provides a good description of the kinetics of the photocatalytic process over the ranges of initial AFB1 concentrations and light intensities studied. The key parameters affecting the detoxification efficiency in terms of the reliable life of this model are described.

Comparative study and simulation of tumor cell inactivation by microwave and conventional heating

PurposeThis paper aims to investigate in a self-designed closed loop reactor process conditions for thermal inactivation of B16 melanoma cells by microwave and conventional heating.Design/methodology/approachBesides control experiments (37°C), inactivation rate was determined in the range from 42°C to 46°C. Heating was achieved either by microwave radiation at 2.45 GHz or by warm water. To distinguish viable from dead cells, AnnexinV staining method was used and supported by field effect scanning electron microscopy (FE-SEM) imaging. Furthermore, numerical simulations were done to get a closer look into both heating devices. To investigate the thermal influence on cell inactivation and the differences between heating methods, a reaction kinetics approach was added as well.FindingsControl experiments and heating at 42°C resulted in low inactivation rates. Inactivation rate at 44°C remained below 12% under conventional, whereas it increased to >70% under microwave heating. At 46°C, inactivation rate attained 68% under conventional heating; meanwhile, even 88% were determined under microwave heating. FE-SEM images showed a porous membrane structure under microwave heating in contrast to mostly intact conventional heated cells. Numerical simulations of both heating devices and a macroscopic Arrhenius approach could not sufficiently explain the observed differences in inactivation.Originality/valueA combination of thermal and electrical effects owing to microwave heating results in higher inactivation rates than conventional heating achieves. Nevertheless, it was not possible to determine the exact mechanisms of inactivation under microwave radiation.

Investigation of fixed-bed photocatalytic membrane reactors based on submerged ceramic membranes

Though having been studied for more than four decades, photocatalysis is still hardly applied in large-scale water and wastewater treatment. This is mainly due to the low energy efficiency of conventional photocatalytic reactors. A recently introduced reactor concept, the fixed-bed photocatalytic membrane reactor (FPMR), can potentially overcome this shortcoming. Its performance for the degradation of organic compounds is examined for different modes of operation. For this purpose, FPMRs based on commercial submerged ceramic membranes were used, which are covered by a photocatalytic layer of pyrogenic titania. The FPMRs were performed in two operational modes: closed-loop reactor and continuous-flow reactor. Oxalic acid was used as a model organic compound to conduct photocatalysis. The influence of light intensity and catalyst layer thickness as well as mass transfer inside the layer were thoroughly studied. The evaluation of the reactors was based on the apparent quantum yield, the photocatalytic space–time yield and specific energy consumption. The results demonstrate that the FPMRs are considerably more efficient than other reported reactor concepts. Its apparent quantum yield can reach up to 11.1%. Furthermore, its specific light energy consumption is merely around 0.1 kWh/g (TOC). The results also reveal that closed-loop FPMRs achieve higher efficiencies than continuous-flow FPMRs. Last but not least, a quantitative model for calculating the reaction rate constant of a photocatalytic membrane from observed reaction rate constant of a photocatalytic membrane reactor was developed and experimentally verified.

Photocatalytic oxidation of VOCs at ppb level using a closed-loop reactor: The mixture effect

An investigation of the photocatalytic degradation of indoor air model pollutants: toluene, n-decane and trichloroethylene (TCE), as single contaminants and in a mixture is proposed. The degradation of these contaminants was performed in a continuous closed-loop reactor operating in recirculation mode. Degradations were conducted at ppb level concentrations and under humid conditions (RH = 50%) in order to be closer to real applications of photocatalytic oxidation (PCO) systems developed for indoor air quality improvement. Accurate analytical methods were developed to identify and quantify the majority of the potential formed intermediates. Kinetic constants and the time constant of degradation were obtained for the model pollutants. Under these conditions, the degradation of the three VOCs in a mixture did not really show a decrease in the kinetic rates. Toluene and decane degradations were slightly slowed down when they were in a mixture but no significant interference was demonstrated with TCE. The intermediates formed during the PCO of the mixture of VOCs were the same as those identified during single degradation, leading to the hypothesis of few interactions between them. Only the formation and degradation of secondary intermediates, mostly composed of aldehydes, were time delayed. The total VOC concentration may lead to a competitive adsorption that seemed more sensitive for the last formed oxygenated intermediates. This investigation points out the need to always monitor the last formed aldehyde intermediates. Monitoring acetaldehyde and formaldehyde enables an evaluation of the efficiency and a better design of future PCO systems for indoor applications.

Closed-loop reactor network synthesis with guaranteed robustness

This paper presents a systematic methodology to design closed-loop reactor networks with guaranteed robustness. The methodology is based on the superstructure approach for reactor network synthesis and extends our previous work (Zhao and Marquardt, 2016) to simultaneously design the process and the control system structure. The spectral abscissa of the Jacobian matrix of the closed-loop reactor network is chosen to measure the response speed of the designed process. A mixed-integer nonlinear program (MINLP) with complementarity constraints and a robust eigenvalue constraint is formulated and solved sequentially by a two-step solution strategy. Structural alternatives of the process and the control system as well as parametric uncertainties are considered in an integrated framework. A case study involving continuous stirred-tank (CSTR) and plug flow (PFR) reactors is presented to illustrate the novel approach and compared with an established two-step design approach.

Determination of the Clean Air Delivery Rate (CADR) of Photocatalytic Oxidation (PCO) Purifiers for Indoor Air Pollutants Using a Closed-Loop Reactor. Part II: Experimental Results.

The performances of a laboratory PhotoCatalytic Oxidation (PCO) device were determined using a recirculation closed-loop pilot reactor. The closed-loop system was modeled by associating equations related to two ideal reactors: a perfectly mixed reservoir with a volume of VR = 0.42 m3 and a plug flow system corresponding to the PCO device with a volume of VP = 5.6 × 10−3 m3. The PCO device was composed of a pleated photocatalytic filter (1100 cm2) and two 18-W UVA fluorescent tubes. The Clean Air Delivery Rate (CADR) of the apparatus was measured under different operating conditions. The influence of three operating parameters was investigated: (i) light irradiance I from 0.10 to 2.0 mW·cm−2; (ii) air velocity v from 0.2 to 1.9 m·s−1; and (iii) initial toluene concentration C0 (200, 600, 1000 and 4700 ppbv). The results showed that the conditions needed to apply a first-order decay model to the experimental data (described in Part I) were fulfilled. The CADR values, ranging from 0.35 to 3.95 m3·h−1, were mainly dependent on the light irradiance intensity. A square root influence of the light irradiance was observed. Although the CADR of the PCO device inserted in the closed-loop reactor did not theoretically depend on the flow rate (see Part I), the experimental results did not enable the confirmation of this prediction. The initial concentration was also a parameter influencing the CADR, as well as the toluene degradation rate. The maximum degradation rate rmax ranged from 342 to 4894 ppbv/h. Finally, this study evidenced that a recirculation closed-loop pilot could be used to develop a reliable standard test method to assess the effectiveness of PCO devices.

Determination of the Clean Air Delivery Rate (CADR) of Photocatalytic Oxidation (PCO) Purifiers for Indoor Air Pollutants Using a Closed-Loop Reactor. Part I: Theoretical Considerations.

This study demonstrated that a laboratory-scale recirculation closed-loop reactor can be an efficient technique for the determination of the Clean Air Delivery Rate (CADR) of PhotoCatalytic Oxidation (PCO) air purification devices. The recirculation closed-loop reactor was modeled by associating equations related to two ideal reactors: one is a perfectly mixed reservoir and the other is a plug flow system corresponding to the PCO device itself. Based on the assumption that the ratio between the residence time in the PCO device and the residence time in the reservoir τP/τR tends to 0, the model highlights that a lab closed-loop reactor can be a suitable technique for the determination of the efficiency of PCO devices. Moreover, if the single-pass removal efficiency is lower than 5% of the treated flow rate, the decrease in the pollutant concentration over time can be characterized by a first-order decay model in which the time constant is proportional to the CADR. The limits of the model are examined and reported in terms of operating conditions (experiment duration, ratio of residence times, and flow rate ranges).

Synthesis of nano precipitated calcium carbonate by using a carbonation process through a closed loop reactor

Nano calcium carbonate particles have a wide range of industrial applications due to their beneficial properties such as high porosity and high surface area to volume ratio and due to their strengthening the mechanical properties of plastics and paper. Consequently, significant research has been done to deliver a new approach for the synthesis of precipitated nano calcium carbonate by using a carbonation process through a closed loop reactor. Both the experimental and the instrumental parameters, i.e. the CO2 flow rate, the concentration of the starting materials (Ca(OH)2 and CaO), the pH, the orifice diameter, etc., were investigated. The carbonation efficiency was increased due to the diffusion process involved in the loop reactor. The particle size was affected by the CO2 flow rate, reaction time, and orifice diameter. Finally, precipitated nano calcite calcium carbonate (50 to 100 nm) was synthesized by optimizing all the experimental and the instrumental parameters. The synthesized precipitated nano calcium carbonate was characterized by using scanning electron microscopy (SEM), X-ray diffraction (XRD), and Fourier transform infrared (FTIR) spectroscopy. This study has proved that the carbonation efficiency can be enhanced for a short time by using a loop reactor and that the carbonation process was more energy efficient and cost effective than other conventional methods.

Power probability density function control and performance assessment of a nuclear research reactor

One of the main issues in controlling a system is to keep track of the conditions of the system function. The performance condition of the system should be inspected continuously, to keep the system in reliable working condition. In this study, the nuclear reactor is considered as a complicated system and a principle of performance assessment is used for analyzing the performance of the power probability density function (PDF) of the nuclear research reactor control.First, the model of the power PDF is set up, then the controller is designed to make the power PDF for tracing the given shape, that make the reactor to be a closed-loop system. The operating data of the closed-loop reactor are used to assess the control performance with the performance assessment criteria. The modeling, controller design and the performance assessment of the power PDF are all applied to the control of Tehran Research Reactor (TRR) power in a nuclear process. In this paper, the performance assessment of the static PDF control system is discussed, the efficacy and efficiency of the proposed method are investigated, and finally its reliability is proven.

Photocatalytic degradation of several VOCs (n-hexane, n-butyl acetate and toluene) on TiO2 layer in a closed-loop reactor

This paper deals with photocatalytic degradation of three VOCs differing in chemical structure (n-hexane, n-butyl acetate and toluene) in a closed-loop reactor. Degradation tests were performed on particulate layers prepared from TiO2 VLP7000 (Kronos). Concentration dependencies of VOCs were simulated and initial degradation rates calculated. Dependence of the latter on initial concentrations confirms single-site Langmuir–Hinshelwood kinetics with value of hexane adsorption constant 0.023m3mmol−1. It was shown that butyl acetate is oxidized preferably to hexane when they react in a mixture, while their individual degradation seems to be kinetically similar. Toluene deactivates the photocatalyst and its degradation is thus very slow but the catalyst can be renewed by thermal treatment. The found selectivity or inhibitive ability of investigated VOCs in mixture is important for the proper choice of a suitable purification method of industrial exhaust fumes.

Steady-State Multiplicity Behavior Analysis of a High-Impact Polystyrene Continuous Stirred Tank Reactor Using a Bifunctional Initiator

In this work, the steady-state multiplicity analysis of a complete and detailed high-impact polymerization system that has been performed in a nonisothermal continuous stirred tank reactor is addressed. The potential effect of manipulated disturbance and design variables on the reactor control is discussed. Through proper combination of certain bifurcation parameters, some ways of increasing monomer conversion without encountering problems related to the gel effect are proposed. It is shown that high-sensitivity dependence problems cannot be removed by making changes in the analyzed design parameters. Some of the best ways of conducting closed-loop reactor temperature control are identified.

An integrated strategy for early detection of hazardous states in chemical reactors

To detect possible hazardous states occurring in a chemical reactor, the off-line parameter sensitivity analysis can be applied to ascertain whether the reactor system is operated in a parameter sensitive region. However, as the reactor is usually operated under closed-loop control in a real application, the off-line parameter sensitivity analysis was extended to the closed-loop operation of a batch reactor. It was found that if a closed-loop reactor system was operated in the parameter sensitive region, the maximal sensitivities of all state variables appeared at the same time. To avoid any possible measurement error of the initial concentration, a state observer was applied to provide correct states for the parameter sensitivity analysis under closed-loop operation. For the on-line detection of hazardous states, a neural network was built and applied to evaluate whether the operation conditions were located in the parameter sensitive region in the least computation time. Applicability of the developed integrated strategy for the early detection of hazardous states was demonstrated in batch reactors or continuously stirred tank reactors (CSTRs) using the acetic anhydride reaction catalyzed by sulfuric acid as the model reaction. Based on the prediction, in-time adjustments of operation conditions can be made to prevent any hazardous condition that might ensue in either a batch reactor or a continuously stirred tank reactor.

The pattern of methylcyclopentane and n-hexane reactions on Rh/Al2O3 in catalytic runs of various length

Methylcyclopentane and n-hexane were reacted on a Rh/alumina catalyst in a closed-loop reactor. The product composition was analyzed at different moments of the run. In spite of a slow self-deactivation, the distribution of primary products and the depth of hydrogenolysis showed hardly any dependence on the sampling time in the conversion range of 1.5% and 50%. This is discussed in terms of accumulation of hydrocarbonaceous residues and the low readsorption probability of primary products on rhodium surface.

Kinetic study of the photocatalytic recovery of Pt from aqueous solution by TiO 2, in a closed-loop reactor

The photocatalytic recovery of platinum PtCl 2− 6 ions from aqueous solution by TiO 2 (anatase) at conditions met in hydrometallurgical practice (low platinum concentration, low pH values and high chloride concentration) was studied. A continuous flow system with recirculation of the TiO 2 suspension through an illuminated column was applied. The addition of methanol as a “hole scavenger” was proved essential for the reaction to proceed. The influence of various parameters, such as initial platinum and methanol concentration, TiO 2 concentration, pH and flow rate, on the recovery rate was studied. The rate determining stage was found to be the adsorption of methanol molecules on the particles surface. The process seems to be effective and recovery yields up to 95% were achieved.

Skeletal Reactions of n-Hexane over Pt-NaY, Pt/SiO 2, Hy, and Mixed Pt/Sio 2 + HY Catalysts

The activity and selectivity of three samples of 8% Pt-NaY calcined at 633, 723, and 823 K, respectively, have been probed with n-hexane as the model reactant at 603 K and subatmospheric pressures in a glass closed-loop reactor. These catalysts were compared with 6.3% Pt/SiO 2 (EUROPT-1), HY, and a physical mixture of the latter two. The activity of all Pt-NaY catalysts is superior to EUROPT-1 and they deactivate more slowly. The selectivity pattern of all Pt-NaY samples is closer to that characteristic of monofunctional Pt catalysts, as opposed to the pronounced acidic character of pure HY and the mechanical mixtures. The sample calcined at 633 K, which has the highest dispersion and probably contains Pt particles anchored to the support as [Pt n - H x] x+ entities, shows the highest aromatization selectivity. The sample precalcined at 823 K with the lowest dispersion has a pronouncedly high skeletal isomerization selectivity. The isomerization pathway may be related to the C 5 cyclic route on metal sites that are more abundant on the larger crystallites of this catalyst and are more easily accessible with its partially collapsed zeolite framework. Characteristic differences between samples in the response of their catalytic performance to changes in hydrogen and hydrocarbon pressure are discussed.