Unstirred Batch Reactor Research Articles

Antiviral application of colloidal and immobilized silver nanoparticles

This study explored the application of colloidal and immobilized silver nanoparticles (AgNPs) for inactivation of bacteriophages. Coliphages that are commonly used as indicators for enteric viruses, were used in this study. Colloidal AgNPs were synthesized via a chemical reduction approach using sodium borohydride as reducing agent and trisodium citrate as stabilizing agent. AgNP-immobilized glass substrate was prepared by immobilizing AgNPs on amine-functionalized glass substrate by post-immobilization method. The AgNP-immobilized glass substrate was also tested so as to minimize the release of AgNPs in the treated water. The characterization of AgNPs and the AgNP-immobilized glass surface was done using field emission gun-transmission electron microscopy and scanning electron microscopy. Studies conducted with varying concentrations of colloidal AgNPs displayed good antiviral activity for MS2 and T4 bacteriophage. Colloidal AgNPs at a dose of 60 μg ml−1 could completely inactivate MS2 and T4 bacteriophage within 30 and 50 min with an initial concentration of 103 PFU ml−1. Contaminated water (100 ml) in an unstirred batch reactor with an initial bacteriophage concentration of 103 PFU ml−1 could be inactivated by the AgNP-immobilized glass substrate (1 cm × 1 cm, containing 3.7 μg cm−2 silver) suspended centrally in the batch reactor. Complete 3-Log bacteriophage inactivation was achieved within 70 and 80 min for MS2 and T4 bacteriophage, respectively, while the aqueous silver concentration was less than 25 μg l−1. This is significantly lower than the recommended standard for silver in drinking water (i.e. 100 μg l−1, US EPA). Thus, AgNP-immobilized glass may have good potential for generating virus-free drinking water.

Model-based prediction of the hydrodynamic radius of collapsed microgels and experimental validation

Microgels are functional colloidal polymer networks with diverse applications. Various applications require microgels of different sizes. The microgel size is determined during the synthesis and depends among other conditions on the reactor type, reactor temperature, monomer-to-initiator ratio, cross-linker concentration, and surfactant concentration. While experimental data covering these synthesis conditions are available in literature, a model taking into account all of the above factors has not yet been proposed. We present a mechanistic model considering all of the above conditions that agrees with experimental data from various literature sources. The effect of surfactant type and concentration is included by addition of a term in the coagulation kinetics. The reactor type and Reynolds number in the reactor is accounted for with a semi-empirical parameter describing the kinetics of particle coagulation. This parameter is fitted to the data of one of the available experiments, while all other experiments are used for validation. The model predictions quantitatively match the experimental data for stirred batch reactors. For unstirred batch reactors, the agreement with the experimental data is only qualitative. The mechanistic model enables model-based design of functional microgels for new applications.

Hydrothermal Oxidation of Fecal Sludge: Experimental Investigations and Kinetic Modeling.

Hydrothermal oxidation (HTO) provides an efficient technique to completely destroy wet organic wastes. In this study, HTO was applied to treat fecal sludge at well-defined experimental conditions. Four different kinetic models were adjusted to the obtained data. Among others, a distributed activation energy model (DAEM) was applied. A total of 33 experiments were carried out in an unstirred batch reactor with pressurized air as the oxidant at temperatures of <470 °C, oxygen-to-fuel equivalence ratios between 0 and 1.9, feed concentrations between 3.9 and 9.8 molTOC L–1 (TOC = total organic carbon), and reaction times between 86 and 1572 s. Decomposition of the fecal sludge was monitored by means of the conversion of TOC to CO2 and CO. In the presence of oxygen, ignition of the reaction was observed around 300 °C, followed by further rapid decomposition of the organic material. The TOC was completely decomposed to CO2 within 25 min at 470 °C and an oxygen-to-fuel equivalence ratio of 1.2. CO was formed as an intermediate product, and no other combustible products were found in the gas. At certain reaction conditions, the formation of unwanted coke and tarlike products occurred. The reaction temperature and oxygen-to-fuel equivalence ratio showed a significant influence on TOC conversion, while the initial TOC concentration did not. Conversion of TOC to CO2 could be well described with a first-order rate law and an activation energy of 39 kJ mol–1.

Headspace diffusion limitations on heterogeneous catalysis in unstirred batch reactors

Headspace gas diffusion can affect measurements of catalytic rate constants in unstirred batch reactors when the reaction occurs in a small pile of catalyst within the reactor. To quantify these effects, the governing equations for catalysis in a round-bottom flask were solved numerically in a toroidal coordinate system. We also introduce a simpler model reactor geometry that preserves the essential characteristics of a typical bench-scale flask-reactor. The preserved characteristics include the reactor volume, an averaged diffusion length scale, and the area of the catalyst pile. An eigenfunction expansion solution for the model reactor closely parallels the full numerical solutions in the round-bottom flask reactor, thus confirming the validity of the simplified model reactor. Solutions for the model reactor show that concentrations measured above the catalyst pile decay exponentially to equilibrium even when transport limitations are important. Therefore, exponential decay rates in these reactors should not be equated to first order (or pseudo-first order) reaction rate constants without first checking carefully for diffusion limitations. Two dimensionless parameters govern the reactor performance. Effectiveness factors are computed for unstirred catalytic batch reactors over a wide range of the two dimensionless parameters. Our findings show quantitatively when headspace stirring is and is not necessary. When stirring is inconvenient or impossible, the tabulated effectiveness factors can be used to design reactors that are small enough, with kinetics that are slow enough, and with the catalyst dispersed over a large enough area to avoid headspace diffusion limitations.

Kinetics of Microbial Production of 2, 3-Butanediol from Cheese Whey Using Klebsiella pneumonia

 Abstract—In the light of limitation arising from the expensive nature of the production of 2,3-Butanediol (2,3-BD) from competitive petrochemical products and treatment of cheese whey based on biochemical oxygen demand (BOD) posed to the environment. The effect of aerated condition, pH, initial concentration of the cheese whey was studied with an aim to provide insight into optimal conditions for maximum bioremediation as an attractive alternative for cheese whey treatment and production of 2,3-BD using Klebsiella pneumonia (KP) at room temperature of 28 0 C for 96 h and kinetics parameters were evaluated from the experimental result. Based on the result of the proximate analysis, lactose content in 40g/l of cheese whey produced 61.3 percent of 2,3-BD at an optimum pH value of 6.40 and 36.6 percent of 2,3-BD at an optimum pH value of 6.46 in an air-stirred batch reactor and unstirred batch reactor respectively while lactose content in 20g/l of cheese whey produced 60.9 percent 2,3-BD at an optimum pH value of 5.92 and 29.2 percent of 2,3-BD at an optimum pH value of 6.14 in an air-stirred batch reactor and unstirred batch reactor respectively. The result shows that Klebsiella pneumonia has good bioremediation potential and production of 2,3-BD in air-stirred batch reactor compared to unstirred batch reactor at room temperature of 28 0 C under

Importance of co-captured gases in the underground storage of CO2 : Quantification of mineral alterations in chemical experiments

Abstract Carbon dioxide capture and geological storage (CCS) is being developed to reduce the carbon dioxide (CO 2 ) emissions from anthropogenic point sources, e.g. fossil-fuel power plants, to the atmosphere. To establish CCS technology, it is indispensable to develop a reliable database and geochemical models concerning the geological storage of CO 2 , e.g. in saline aquifers, which are to be filled with “overwhelmingly CO 2 ” (Directive 2009/31/EC). To establish reliable models it is essential to have applicable thermodynamic properties, kinetic data, and a good understanding of the occurring chemical reactions. So far most experiments and existing data apply to pure CO 2 gas instead of the captured CO 2 waste gas that will contain minor amounts of co-captured gases, e.g. O 2 , N 2 , NO x , SO x , CO, H 2 , H 2 S. Quantitative measures of the chemical alterations due to these accessory gases are scarce. In the national COORAL project “ CO 2 Purity for Separation and Storage”, a number of institutions work towards a better understanding of environmentally and economically feasible concentrations of the accessory gases during capture, transport, injection and storage. The sub-project at BGR focuses on high-pressure and high-temperature (HPHT) experiments to elucidate mineral and fluid alterations and quantify kinetic rates for the mineral-fluid- CO 2 -co-injected gas system. An unstirred batch-reactor system allows for four contemporaneous experiments at precisely defined p-T conditions of up to p≤590 bar T≤350 °C. Runs are conducted using three components: (1) natural mono-minerals, (2) salt solutions representing brines of deep saline aquifers in Northern Germany and (3) binary gas mixtures of CO 2 plus one accessory gas. All experiments take place in an inert environment, using gold reaction cells with volumes of up to 130 ml, which allow the addition or removal of fluids throughout the experiment without altering the experimental conditions. Further experiments comprise experiments using (1) multi-mineral set-ups in a batch experiment and (2) up to 45-cm-long sedimentary rock cores in flow-through reactors. The latter system is currently under construction, while batch - and capsular - experiments run successfully. To further optimize the experimental design and to evaluate the experiments the project combines laboratory experiments and numerical simulations, applying the geochemical simulators PHREEQC and ChemApp which will be coupled to OpenGeoSys (OGS) for thermo-hydro-mechanical-chemical (THMC) process simulations.

Effect of Secondary Phase Formation on the Carbonation of Olivine

Large-scale olivine carbonation has been proposed as a potential method for sequestering CO(2) emissions. For in situ carbonation techniques, understanding the relationship between the formation of carbonate and other phases is important to predict the impact of possible passivating layers on the reaction. Therefore, we have conducted reactions of olivine with carbonated saline solutions in unstirred batch reactors. Altering the reaction conditions changed the Mg-carbonate morphology. We propose that this corresponded to changes in the ability of the system to precipitate hydromagnesite or magnesite. During high-temperature reactions (200 degrees C), an amorphous silica-enriched phase was precipitated that was transformed to lizardite as the reaction progressed. Hematite was also precipitated in the initial stages of these reactions but dissolved as the reaction proceeded. Comparison of the experimental observations with reaction models indicates that the reactions are governed by the interfacial fluid composition. The presence of a new Mg-silicate phase and the formation of secondary products at the olivine surface are likely to limit the extent of olivine to carbonate conversion.

Inhibition Effect of Surfactants on CO2 Enclathration with Cyclopentane in an Unstirred Batch Reactor

The effect of sodium dodecyl sulfate (SDS), cetyl trimethylammonium bromide (CTAB), and fatty alcohol EO/PO derivative (LS54) on unsteady-state CO2 absorption in the metastable region of CO2 hydrates and CO2 enclathration with cyclopentane (CP) was investigated in an unstirred batch reactor. These surfactants have no measurable effect on the mass transfer of CO2 across the gas−liquid interface into water. However, they retard CO2 enclathration, and this inhibition effect becomes significant at 200 ppm of SDS and 100 ppm of LS54 or CTAB. A layer of clathrate hydrates is visually observed if charging CO2 and CP sequentially. Even though this layer cannot be macroscopically detected when swapping the order of CO2 and CP charge, the existence of this layer can be inferred from the unchanged pressure profile. This layer prevents CO2 from contacting with water and thus delays CO2 enclathration. The habit of clathrate hydrates growing along the reactor wall without agitation is discussed based on the magnitude o...

Transition Scenarios during the Evolution of the Belousov−Zhabotinsky Reaction in an Unstirred Batch Reactor

We report experimental evidence of transition scenarios during the chemical evolution in an unstirred closed Belousov−Zhabotinsky (BZ) system. We demonstrate that during its chemical evolution the system spontaneously gives the following sequence of dynamic behavior before reaching equilibrium: period-1 → quasiperiodicity → chaos → quasiperiodicity → period-1. Two transition scenarios are observed: at the onset of chaos and at its end. One appears as the mirror image of the other. Our observations support the view that closed chemical systems also are able to show chaotic behavior and the corresponding transition scenarios.

Coupling of erratic Belousov-Zhabotinsky oscillators observed by spectrophotometric measure.

One reason for the current interest in oscillating reactions is the numerous periodic phenomena that occur in spatial and temporal control of processes, including phenomena in living organisms such as reactions catalyzed by enzymes and reactions across membranes. The study of the interaction of two or more oscillating systems is directly connected with biological problems and with spatial pattern formation. For this reason, the coupling of chemical oscillators has been the subject of a number of studies. Experiments have been carried out using batch reactors, as well as CSTR reactors.The simplest system in which the coupling can be studied is a single solution. The coupling that occurs inside the same solution is very interesting; as in a closed reactor, the different parts of the solution are obviously physically coupled. We used the Belousov-Zhabotinsky (BZ) reaction, a metal ion–catalyzed oxidation and bromination of an organic substrate, this being the most frequently used reaction for experiments in chemical oscillations. In unstirred batch reactors, diffusion and convection may be as important for a system’s dynamics as for its local kinetics. In particular, the coupling between a temporal oscillation and a spatial dishomogeneity may produce chaotic behavior. Epstein and Showalter recently dedicated a review to nonlinear chemical dynamics, which contains an exhaustive discussion on coupled systems.The phenomenon most frequently observed in coupled systems is the adaptation of the oscillators of one to the other so that the frequencies are rationally related. In this paper the coupling of the chaotic or regular oscillating phenomena that occurs in different parts of the same well-premixed oscillating solution and the effect of splitting the solution into two different portions are investigated. In order to avoid ions transport resistance phenomena and other complications that are present in electrical coupling experiments, we used the spectrophotometric method instead of the electrochemical method.

Zeolite synthesis in unstirred batch reactors I. Nuclear magnetic resonance imaging of non-uniform pre-mixing

The application of nuclear magnetic resonance (NMR) imaging to the study of the design and performance of chemical reactors is introduced. NMR imaging is a non-invasive technique which can be utilized for the investigation of physical processes such as the mixing of reagents within a sealed reactor. A series of experiments is described on the mixing of aluminate solutions with silicate solutions or silica slurries within zeolite crystal growth reactors. Mixing was followed by the imaging of protons present in triethanolamine (a nucleation suppressant) or tetraethylammonium bromide (a structure-directing agent) in sodium aluminosilicate mixtures which were otherwise fully deuterated. Compositions suitable for the crystallization of zeolites A, X and mordenite, in four reactor designs, were studied. The reactors were designed specifically for the growth of large zeolite crystals in microgravity aboard the space shuttle. NMR imaging was shown to be a reliable indicator of the mixing process, provided the organic was present in sufficient concentration and that its distribution was representative of the distribution of the other reagents. The possibility of utilizing NMR imaging to study a wide range of reactors, where other (invasive) techniques are unsuitable, is realized.

Zeolite synthesis in unstirred batch reactors II. Effect of non-uniform pre-mixing on the crystallization of zeolites A and X

The effects of deliberate non-uniform pre-mixing of the aluminate and silicate solutions in the unstirred batch syntheses of zeolites A and X were studied. Poorly mixed hydrogels gave rise to impurity phases, with the amount of impurity decreasing with improved pre-mixing. Experiments were carried out in reactors specially designed for the growth of large zeolite crystals under microgravity conditions, and in a parallel study using high-density polyethylene bottles. Both studies evidenced the appearance of impurities if the hydrogel was not well mixed prior to heating. No consistent effect was observed on the particle size distributions of the zeolite products. These results underlined the importance of proper reactor design for unstirred syntheses, and the usefulness of a non-invasive diagnostic technique for mixing effectiveness, such as nuclear magnetic resonance (NMR) imaging. The applicability of NMR imaging to the systems studied here was demonstrated in Part I of this series.