Gas-liquid Mass Transfer Of Oxygen Research Articles

From understanding the rate limitations of bioleaching mechanisms to improved bioleach process design

While bioleaching has become established technology for the leaching of refractory gold concentrates and in the heap leaching of copper sulfide minerals, many other applications, although demonstrated at the laboratory scale, have not found significant uptake in industrial biomining. The reasons for this are manifold, but generally relate back to engineering constraints in operating processes at large scale while remaining economically viable.The paper unpacks acidophile sulfide bioleaching mechanisms within bioreactors into various sub-processes and analyses them in terms of their rate limitations, such as gas-liquid mass transfer of oxygen and CO2, diffusion constraints between and within mineral particles, competing side reactions etc. It becomes clear that microbial metabolic reactions are generally not what limits the kinetics of bioleaching reactions overall but rather the reaction environment. Improved process design to enhance the economic performance of bioleaching therefore needs to target the slowest sub-process in the bioleaching mechanism, which is rarely the biological one.Conventional tank and heap bioleaching processes are discussed in this context and routes taken towards their improvement discussed. Further, various promising novel concepts in biomining, such as leaching with biogenic lixiviants, phytomining and tailings leaching are evaluated within this framework, in each case identifying the potentially limiting sub-processes. It becomes clear that the relative ‘slowness’ of these sub-processes prohibits exploitation through designed active industrial processes; they can, however, still be facilitated through suitably designed ‘passive’ processes in which the time taken for slow processes is less of an economic constraint. While this is an obvious approach in bioremediation, it can also be employed for the economic recovery of value from otherwise sub-economic mineral deposits and waste materials through heap bioleaching. This way it can also play a role in the drive towards a circular economy.

Corrigendum to “Effect of surfactant lengths on gas–liquid oxygen mass transfer from a single rising bubble” [Chem. Eng. Sci. 247 (2022) 117102

Corrigendum to “Effect of surfactant lengths on gas–liquid oxygen mass transfer from a single rising bubble” [Chem. Eng. Sci. 247 (2022) 117102

Effect of surfactant lengths on gas-liquid oxygen mass transfer from a single rising bubble

This work is an experimental investigation of the effect of the nature of surfactants on oxygen mass transfer. The study focuses on three cationic surfactants with different hydrophobic chain lengths, and four nonionic surfactants with different hydrophilic chain lengths. Equilibrium adsorption isotherms are calculated for each surfactant from experimental values of surface tension in static conditions. Surfactant solutions at concentrations between 2.5 × 10-8 and 5 × 10-3 mol/L were prepared and oxygen transfer from millimetric air bubbles (between 0.82 and 1.08 mm) was measured by Planar Laser Induced Fluorescence with Inhibition (PLIF-I). When the bulk concentration of surfactant was increased, results showed a sharp decrease of bubble velocity, in the range of 283–75 mm/s, and of liquid-side mass transfer coefficient, in the range of 5.6 × 10-4–0.4 × 10-4 m/s. This effect was observed for all surfactants studied. However, the length of the hydrophilic chain did not appear to affect the hydrodynamics of the rising bubble or the oxygen transfer at the same bulk concentration. Furthermore, for the same bulk concentration, increasing the hydrophobic chain length had an impact on the velocity and the mass transfer coefficient of oxygen. Finally, the Sherwood number was calculated in each medium and compared with classical correlations for gas–liquid mass transfer prediction. Those correlations seemed to reach a limit for a very concentrated medium.

Characterization of power input and its impact on mass transfer in a rocking disposable bioreactor

The impact of specific power input on gas-liquid mass transfer and mixing has not been extensively reported for rocking disposable bioreactors. An electrical method was applied for measuring the specific power input into a disposable rocking (Wave) bioreactor at benchtop scales. The peak power input was shown to be suitable for characterizing the impact of operational parameters including rocking frequency, rocking angle and liquid volume. The average power inputs ranged from 66.5 W/m3 to 680.1 W/m3 which were comparable to those for stirred tank and orbitally-shaken disposable bioreactors. The gas-liquid oxygen mass transfer coefficient was shown to correlate with the peak power input in a power law model, confirming that the mass transfer capacity rapidly increased with power input, especially at 600 W/m3 and greater. The correlation between mixing time and power input indicated that power input at higher than 400 W/m3 was sufficient to induce relatively rapid mixing.

Optical determination of oxygen mass transfer in a helically-coiled pipe compared to a straight horizontal tube

The gas-liquid mass transfer of oxygen has been examined experimentally in a helically-coiled pipe using an optical colorimetric method. Two tracer redox-reactions have been used for this purpose: (i) methylene blue and (ii) resazurin. The gas hold-up has been varied from 0.1 to 0.6, and liquid flow rate from 0.37 to 0.68 l/min, both leading to plug-flow conditions in the helix for all parameter combinations. A progress variable has been defined to measure the advancement of the reaction and thus, oxygen transfer to the liquid. The resazurin reaction turned out to be more appropriate for mass transfer studies, due to the bigger time constant difference of oxidation and reduction. Therefore, it can be adapted more easily to the specific conditions of the set-up. It also possesses more intense colours and higher fluorescence intensity, which might be useful for other mass transfer studies. As expected, the oxygen mass transfer increases with gas hold up, but liquid flow rate has little influence. A comparison with a horizontal tube of the same diameter shows the drastically increased mass transfer in the helix, due to better radial mixing and different flow pattern. Depending on the experimental conditions, oxygen concentration in the helix was up to twice that of the horizontal tube. This can be explained by the much higher liquid side mass transfer velocity, which is determined in this study from the experimental kla-values and specific bubble surface per turn of the helix. For this purpose, bubble dimensions and gas-liquid cell volumes have been determined from the experimental images. The paper thus presents a locally resolved characterization of gas-liquid mass transfer in a helically coiled reactor. The high mass transfer especially during the first turns of the helix shows its advantages compared to a straight tube.

Gas-liquid oxygen transfer in aerated and agitated slurry systems with high solid volume fractions

Oxygen transfer can be a limiting step in aerobic biodegradation processes. Therefore, this process has been widely investigated for wastewater treatment, but only few research works have been done on soil slurry systems. This study focuses on the gas-liquid oxygen mass transfer in clay slurry conditions in an aerated and agitated reactor using a marine propeller. Conversely to most studies on oxygen transfer, pneumatic power input is not negligible compared to mechanical power input. Clay presence has a negative impact on the oxygen transfer. However, the effect of agitation and aeration on this process remains unaffected at the clay concentrations tested. Three different phases explaining the depletion in the oxygen transfer rate are hypothesized. A model to predict the oxygen transfer coefficient in slurry reactors, including the three operational parameters tested within their respective ranges, is proposed.

Overcoming the Gas-Liquid Mass Transfer of Oxygen by Coupling Photosynthetic Water Oxidation with Biocatalytic Oxyfunctionalization.

Gas–liquid mass transfer of gaseous reactants is a major limitation for high space–time yields, especially for O2‐dependent (bio)catalytic reactions in aqueous solutions. Herein, oxygenic photosynthesis was used for homogeneous O2 supply via in situ generation in the liquid phase to overcome this limitation. The phototrophic cyanobacterium Synechocystis sp. PCC6803 was engineered to synthesize the alkane monooxygenase AlkBGT from Pseudomonas putida GPo1. With light, but without external addition of O2, the chemo‐ and regioselective hydroxylation of nonanoic acid methyl ester to ω‐hydroxynonanoic acid methyl ester was driven by O2 generated through photosynthetic water oxidation. Photosynthesis also delivered the necessary reduction equivalents to regenerate the Fe2+ center in AlkB for oxygen transfer to the terminal methyl group. The in situ coupling of oxygenic photosynthesis to O2‐transferring enzymes now enables the design of fast hydrocarbon oxyfunctionalization reactions.

Investigating the effects of hydrodynamics and mixing on mass transfer through the free-surface in stirred tank bioreactors

In stirred-tank bioreactors, flow structures of various length and time scales are implied in scalar transport phenomena, such as gas species transfer through the liquid free-surface and their homogenization in the bulk. A proper understanding of the underlying mechanisms, i.e. hydrodynamics, mixing and mass transfer, and of their interactions is required to design and develop reliable and efficient production-scale bioprocesses. The objective of the present work is to experimentally investigate the coupling between gas-liquid mass transfer of oxygen with mixing efficiency and circulation patterns inside an arbitrarily chosen stirred-tank configuration aerated through the liquid free-surface, a baffled 20L-vessel agitated by two Rushton turbines. Based on global parameter values, the most appropriate rotating speed, N=300rpm, is selected in order to further study local hydrodynamic quantities using Particle Image Velocimetry (PIV), as well as mixing and mass transfer dynamics using Planar Laser-Induced Fluorescence (PLIF). The results obtained with these local experimental methods are analyzed in detail. Their averages are first successfully compared to global data. Statistical analysis of their spatial distributions show that large-scale flow patterns significantly influence mass transfer through the free-surface of the stirred tank. Even if global measurements show that global characteristic times for mixing and mass transfer differ by two orders of magnitude, local experimental characterization shows persistent vertical gradients of dissolved gas concentrations. So the dissolved gas concentration is not as perfectly uniform as one might expect.

Influence of trickling liquid velocity and flow pattern in the improvement of oxygen transport in aerobic biotrickling filters for biogas desulfurization

AbstractBACKGROUNDBiological oxidation in biotrickling filters of high H2S loads contained in biogas streams still requires further study to reduce elemental sulfur accumulation due to limited gas–liquid oxygen mass transfer inside biotrickling filter beds. Reduction of elemental sulfur accumulation may be improved by regulating the main manipulated variables related to oxygen mass transfer efficiency during biological hydrogen sulfide removal in biotrickling filters.RESULTSTrickling liquid velocity and co‐current flow were selected as the most appropriate manipulated variable and flow pattern configuration compared with manipulating the air supply flow rate and a counter‐current flow pattern in order to improve gas–liquid oxygen mass transfer in abiotic conditions. The influence of trickling liquid velocity on the performance of a lab‐scale biotrickling filter treating high loads of H2S in a biogas mimic and operating in co‐current flow at neutral pH and packed with plastic pall rings was investigated.CONCLUSIONSThe effect of trickling liquid velocity modulation between 4.4 and 18.9 m h−1 in biotrickling filter performance was compared with operation without trickling liquid velocity regulation. Velocity regulation resulted in an improvement of 10% in the elimination capacity and, most importantly, a 9% increase in product selectivity to sulfate at a loading rate of 283.8 g S‐H2S m−3 h−1. Concentration profiles along the biotrickling filter height evidenced that trickling liquid velocity regulation progressively led to better dissolved oxygen distribution and, thus, enhanced overall biotrickling filter performance. © 2015 Society of Chemical Industry

Enhancement of Oxygen Mass Transfer Using Functionalized Magnetic Nanoparticles

Venue, Cambridge, Massachusetts 02139 Oxygen-transfer enhancement has been observed in the presence of colloidal dispersions of magnetite (Fe3O4) nanoparticles coated with oleic acid and a polymerizable surfactant. These fluids improve gas-liquid oxygen mass transfer up to 6-fold (600%) at nanoparticle volume fractions below 1% in an agitated, sparged reactor and show remarkable stability in high-ionic strength media over a wide pH range. Through a combination of experiments using physical and chemical methods to characterize mass transfer, it is shown that (i) both the mass transfer coefficient (kL) and the gas-liquid interfacial area ( a) are enhanced in the presence of nanoparticles, the latter accounting for a large fraction of the total enhancement (80% or more), (ii) the enhancement in kL measured by physical and chemical methods is similar and ranges from 20 to 60% approximately, (iii) the enhancement in kL levels off at a nanoparticle volume fraction of approximately 1% v/v, and (iv) the enhancement in kLa shows a strong temperature dependence. These results are relevant to a wide range of processes limited by the mass transfer of a solute between a gas phase and a liquid phase, such as fermentation, waste treatment, and hydrogenation reactions.

Gas–Liquid Oxygen Mass-transfer; from Fundamentals to Applications in Hydrometallurgical Systems

Oxygen gas is used as a reactant in many hydrometallurgical processes. However, oxygen is sparingly soluble in aqueous electrolyte solutions, and the driving force for its masstransfer from the gas to the aqueous phase is also very low. Hence, the mass-transfer of oxygen depends significantly on the interfacial area between the gas and the liquid phase, which in turn depends on the mixing conditions inside the reactor. A change in the solution composition or the presence of solids can further alter the rate of oxygen masstransfer. All such phenomena related to the gas-liquid oxygen mass-transfer in hydrometallurgical unit operations are critically reviewed in the present article – from the basic thermodynamics and kinetics of oxygen dissolution in aqueous solutions to the most recent advances in oxygen mass-transfer systems.

Gas-Liquid Oxygen Mass-transfer; from Fundamentals to Applications in Hydrometallurgical Systems

Oxygen gas is used as a reactant in many hydrometallurgical processes. However, oxygen is sparingly soluble in aqueous electrolyte solutions, and the driving force for its mass-transfer from the gas to the aqueous phase is also very low. Hence, the mass-transfer of oxygen depends significantly on the interfacial area between the gas and the liquid phase, which in turn depends on the mixing conditions inside the reactor. A change in the solution composition or the presence of solids can further alter the rate of oxygen mass-transfer. All such phenomena related to the gas-liquid oxygen mass-transfer in hydro-metallurgical unit operations are critically reviewed in the present article - from the basic thermodynamics and kinetics of oxygen dissolution in aqueous solutions to the most recent advances in oxygen mass-transfer systems.

Modelling of ammoniacal oxygen leaching of metallic iron in a stirred slurry reactor

A new model for iron dissolution kinetics by oxidative ammoniacal leaching similar to that encountered in the Becher process for synthetic rutile manufacture is proposed. The model takes into account solid-liquid and gas-liquid oxygen mass transfer as well as oxidation of Fe 2+ to Fe 3+ ions as the controlling steps in the initial linear phase of the overall process. The model has been validated for the system containing metallic iron particles in a multiphase, sparged, agitated reactor under isothermal conditions. Along with kinetic measurements, the variation in pH and oxidation reduction potential were also monitored continuously. Both disc type turbines and axial flow turbines were used as the agitators. The model was found to be applicable over a modest range of process parameters (8 ≤ specific energy dissipation rate ≤ 15 kW/m 3, 8 × 10 −5 ≤ air flow rate ≤ 2 × 10 −4 m 3/s, iron particle size 230 μm, partial pressure of oxygen ≤2.03 × 10 4 Pa and 5 ≤ weight percentage of iron particles ≤ 40). The results indicate that Sano's correlation for solid-liquid mass transfer and Linek's correlation for gas-liquid mass transfer are adequate for describing the data. The rate of iron dissolution was insensitive to the loading of iron particles, which is explained as being due to the solid particles acting as oxygen sinks inside an encapsulated shell around the bubble. Variations in pH, oxidation reduction potential and Fe 2+ ion concentration with solid loading and oxygen partial pressure are consistent with the overall reaction mechanism proposed in this work.

On the attainment of stable autothermal operation in continuous pressure leaching reactors

The autothermal model of operation of a multi-stage oxidative pressure leaching reactor is analysed with the aid of a descriptive mathematical model. For this, the adiabatic heat balance equation of the reactor is solved along with the mass balance equations. The model considers the process system (pressure oxidation) to be controlled simultaneously by the kinetics of the two parallel exothermic leaching reactions (oxidation of FeS 2/FeAsS by O 2), and the gas-liquid mass transfer of oxygen. By maintaining the total pressure of the system constant, that is P tot(=P H 2 O + P O 2 ∗ )= constant , enhanced thermal and kinetic stability is achieved at the autothermal steady-state operating temperature. The combined S/As content of the feed is of crucial importance to the thermal economy of the process. Feeds with sulphur content above 5.5 wt% can be processed without any preheating with either a 4 stage autoclave (equal size compartments), or a 5 stage autoclave having the first double the size of the rest. The higher the sulphur content the lower the concentration of solids in the feed slurry has to be in order to attain autothermal operation. For feeds with low sulphur content (<5 wt%), autoclaves with the first compartment substantially larger than the rest have to be employed for optimum thermal balance results.

Oxygen Mass Transfer in an Airlift Bioreactor using Static Mixers

The influence of static mixers on volumetric gas—liquid oxygen mass transfer coefficient, kLa, was investigated in an external-loop airlift bioreactor (approximately 170 l volume, 4 m static liquid height, AD/AR = 0.1225). The study was conducted with water and viscous, non—Newtonian starch solutions. The presence of static mixers in the riser was found to enhance kLa relative to witness column by 1.3–3 times, depending on the gas superficial velocity, liquid viscosity and the manner of liquid circulation (gas-induced or forced by means of a pump). The kLa increase was associated with increased gas hold-up and gas-liquid interfacial area, due to bubble breakup accomplished by the static mixers.

A reassessment of mixing cost in fermentation processes

AbstractThe gas–liquid oxygen transfer rate is a key step in the production of antibiotics in submerged fermentation. If the gas–liquid oxygen mass transfer rate is not equal to the required liquid–solid oxygen mass transfer rate at a particular cell concentration, then productivity of the particular fermentation operation will not be the maximum possible value.One way to increase the productivity of a given fermentation tank installation is to increase the cell concentration and to increase the oxygen transfer by changing the mixer and air supply to match the new requirements. In order to evaluate the cost of making this change to the larger mixing equipment, a typical cost example is given which can easily be modified for other combinations of production cost and mixer cost. As an example, it is seen that a considerable savings can result from a given installation by primarily changing the oxygen transfer ability of the equipment to utilize a given fermentor more efficiently. Production cost savings of 8 to 25% are shown in the example cited.