Liquid-solid Mass Transfer Rates Research Articles

Intensification of the rate of heat and mass transfer at the wall of a stirred tank reactor by integrating a helical coil turbulence promoter with the tank wall

ABSTRACT The influence of a helical coil turbulence promoter on liquid-solid mass transfer rates in a stirred tank was investigated using a technique that involved measuring the rate of diffusion-controlled copper dissolution in acidified dichromate. The study examined the effects of helical coil tube diameter (d), helical coil pitch (p), impeller rotation speed, impeller geometry (axial and radial), the presence of baffles, and solution physical properties. The presence of the helical coil near the reactor wall significantly enhanced mass transfer rates, with a factor ranging from 1.01 to 2.48. This improvement was accompanied by a corresponding increase in the volumetric mass transfer coefficient (kA), ranging from 2.68 to 4.55, depending on operating conditions. Further analysis revealed that the average mass transfer coefficient increased with decreasing coil tube diameter, while coil pitch had a minimal impact. Additionally, radial flow turbines demonstrated superior mass transfer performance compared to axial flow turbines. The presence of baffles also promoted higher mass transfer rates compared to unbaffled reactors. The experimental data were successfully correlated using dimensionless correlations, emphasizing the significance of these correlations in scaleup and design optimization of catalytic stirred tank reactors with efficient cooling systems.

Turbulent flow-driven liquid-solid mass transfer in serpentine tube heat exchanger/reactors: applications and implications

ABSTRACT This study examines liquid-solid mass and heat transfer rates in serpentine tube heat exchangers/reactors under turbulent flow using the copper dissolution technique. Key factors include solution flow rate, properties, tube diameter, U-bend curvature, and drag-reducing polymers. An empirical correlation predicts mass transfer coefficients, which are 4.12–5.36 times higher than straight tubes. Serpentine tubes show potential for economically viable diffusion-controlled reactions. Drag-reducing polymer (Polyox WSR-301) reduces corrosion rates by up to 23.3%. The study highlights serpentine tubes’ applicability in catalytic continuous reactors and membrane processes, emphasizing their significance in heat exchanger design and corrosion allowance prediction.

Kinetics and mass transfer studies on the biosorption of organic matter from palm oil mill effluent by aerobic granules before and after the addition of Serratia marcescens SA30 in a sequencing batch reactor

Kinetic and mass transfer aspects of biosorption of oxidisable organic matter (OOM) from wastewater are important for better understanding of the mechanisms of granules initiation and development. The modified mass transfer factor models were used to predict the liquid–solid mass transfer rates of OOM biosorption from palm oil mill effluent (POME) attached to aerobic granular sludge (AGS) in a sequencing batch reactor (SBR). The variations of [kLa]g, [kLa]f and [kLa]d pursuant to time were verified to have a zigzag pattern due to the organic loading rate varies with a change in the quality of POME feeding the SBR. The influence of added Serratia marcescens SA30 on the rates of mass transfer would be very remarkable due to the effects of metabolites and biomass growth this can lead to a rapid utilisation of OOM accumulated into AGS. The maximum efficiencies of SBR reaching 48% for CODt removal at [kLa]g value of 3.054 h−1 and 68% for CODs removal at [kLa]g value of 21.012 h−1 were verified before the addition of S. marcescens SA30 and those reaching 68% for CODt removal at [kLa]g value of 1.229 × 1063 h−1 and 94% for CODs removal at [kLa]g value of 7.152 × 1064 h−1 were verified after the addition of S. marcescens SA30. The resistance of mass transfer could be dependent on external mass transfer, which controls the movement of organic molecules along the experimental period of POME fed the SBR without and with added S. marcescens SA30. The performance of SBR would increase with increase of [kLa]g value, and this provides new insight into dynamic response of the aerobic digestion to AGS development.

Accelerated desulphurization of waste lead battery paste in a high-gravity rotating packed bed

Pb-paste as the major composition in waste lead acid battery has an important role in the process of lead recycling. However, low liquid-solid mass transfer rates in conventional reactors have a significant limitation for the industrial application of Pb-paste desulphurization using hydrometallurgical process. In this paper, a cost-effective mass-transfer intensified approach for Pb-paste desulphurization with Na2CO3 solution in a rotating packed bed (RPB) reactor was presented. The effects of various variables on the desulphurization degree of PbSO4 were firstly explored. The results indicated that the increases in rotating speed, Na2CO3 concentration and Na2CO3/PbSO4 molar ratio were beneficial to the process. Temperature and reactant flow rate had obvious effects on the desulphurization degree only at a low reactant concentration. Further, the desulphurization processes of the simulated Pb-pastes were comparatively investigated. It was found that the RPB reactor markedly intensified the process in a very short contact time (about 1s), thereby achieving a continuous desulphurization process. Only one cycle liquid-solid contact could make the desulphurization degrees of PbSO4, anode powder and cathode powder reach 99.7%, 98.9% and 97.2%, respectively. Compared to a stirred tank reactor, the desulphurization time was greatly shortened by at least 2 orders of magnitude.

Effect of foam stirrer design on the catalytic performance of rotating foam stirrer reactors

The liquid–solid mass transfer rate in a rotating foam stirrer reactor and in a slurry reactor is studied using the hydrogenation of styrene as a model reaction. The rotating foam stirrer reactor is a novel type of multi-phase reactor where highly open-celled materials, solid foams, are used as a catalyst support and as a stirrer. The design of the foam stirrer has a strong influence on the liquid–solid mass transfer rate. Using a donut-shaped foam block configuration, the liquid solid mass transfer coefficient, kLS, is five times lower than in a blade configuration. The reduced liquid circulation through the foam block structure is explained by a higher frictional pressure drop. The pore Reynolds number indicates that the flow is in the laminar regime for the foam block stirrer while it is turbulent for the blade stirrer. Local measurements of kLS indicate a mass transfer profile along the height of the foam block structure, allowing a pertinent choice of the catalyst location within the foam block and/or suggesting changes of the foam block design to avoid the bottom effects, for instance, using a conical foam block shape. However, the foam block stirrer offers higher liquid–solid interfacial area than a blade stirrer, resulting in higher kLSaLS. At a power input above 1000W/mL3 and using a 20ppi foam block with the top part catalytically active, the reaction rate is not liquid–solid mass transfer limited. Compared to a Rushton stirrer, the liquid–solid mass transfer rate is enhanced because of a high liquid–solid interfacial area and a fast refreshment of the catalyst surface. kLSaLS values of 0.5s−1 are obtained compared to 0.04s−1 for the slurry system. The same production rate as in the slurry reactor is achieved using 62% less catalyst. As the catalyst is immobilized on the stirrer, an additional advantage of the rotating foam stirrer reactor is the absence of a catalyst separation step. Attrition and agglomeration of the catalyst do not occur and the foam catalyst can be reused.

Glucose Oxidation in Slurry Reactors and Rotating Foam Reactors

Glucose oxidation using platinum promoted by bismuth was studied as a three-phase model reaction. Using catalyst nanoparticles and measuring the oxygen concentration in the bulk liquid, the kinetic parameters and mass transfer characteristics were determined at a temperature of 333 K. The overall reaction rate was studied experimentally using three different support types: slurry catalysts, pellets, and a solid foam stirrer. The glucose conversion rate and the deactivation rate of the catalyst depend strongly on the ratio between mass transfer and reaction rate. At low catalyst concentrations, the glucose oxidation process is liquid–solid mass-transfer-limited. The block stirrer shows a superior performance over the slurry catalysts due to the high liquid–solid volumetric mass transfer coefficient. The bimodal pore size distribution of the catalyst layer further increases the conversion rate. Using slurry catalysts, a loading of 1 wt % in combination with pure oxygen feed is required to achieve acceptable conversion rates. Under these conditions, the gas–liquid mass transfer and partially the liquid–solid mass transfer are the rate-limiting steps. The foam block stirrer shows good gas–liquid mass transfer rates and high liquid–solid mass transfer rates, which still increase at high power input. Working under external mass transfer control and using this stirrer type, the catalyst loading can be strongly reduced to loadings less than 0.4 wt %, while the conversion rate remains comparable to slurry particles with loadings of 1 wt %. As the catalyst is fixed, attrition and agglomeration in high viscosity liquids are circumvented. There is further no need for filtration, and the catalyst can simply be reused.

Gas–liquid dynamics at low Reynolds numbers in pillared rectangular micro channels

Most heterogeneously catalyzed gas–liquid reactions in micro channels are chemically/kinetically limited because of the high gas–liquid and liquid–solid mass transfer rates that can be achieved. This motivates the design of systems with a larger surface area, which can be expected to offer higher reaction rates per unit volume of reactor. This increase in surface area can be realized by using structured micro channels. In this work, rectangular micro channels containing round pillars of 3 μm in diameter and 50 μm in height are studied. The flow regimes, gas hold-up, and pressure drop are determined for pillar pitches of 7, 12, 17, and 27 μm. Flow maps are presented and compared with flow maps of rectangular and round micro channels without pillars. The Armand correlation predicts the gas hold-up in the pillared micro channel within 3% error. Three models are derived which give the single-phase and the two-phase pressure drop as a function of the gas and liquid superficial velocities and the pillar pitches. For a pillar pitch of 27 μm, the Darcy-Brinkman equation predicts the single-phase pressure drop within 2% error. For pillar pitches of 7, 12, and 17 μm, the Blake-Kozeny equation predicts the single-phase pressure drop within 20%. The two-phase pressure drop model predicts the experimental data within 30% error for channels containing pillars with a pitch of 17 μm, whereas the Lockhart–Martinelli correlation is proven to be non-applicable for the system used in this work. The open structure and the higher production rate per unit of reactor volume make the pillared micro channel an efficient system for performing heterogeneously catalyzed gas–liquid reactions.

Enhanced liquid–solid mass transfer by carbon nanofibers on solid foam as catalyst support

This paper presents the liquid–solid mass transfer characteristics for Pd-catalyst on carbon nanofiber (CNF) covered reticulated vitreous carbon (RVC) foam (hairy foam). RVC foam was used with 20, 45, and 60 pores per linear inch (PPI), covered with CNFs synthesized at 773, 873, and 973 K. The effects of superficial liquid velocity ( u l = 4.3 × 10 - 3 to 77 × 10 - 3 m l 3 m r - 2 s - 1 ) and reaction temperature (323 and 343 K) are studied using the fast liquid phase oxidation of sodium formate. The overall reaction rate coefficient ( k ov ) increases with decreasing PPI number. k ov for 20 PPI CNF/RVC foam is significantly higher than for regular foam packings and random packings, ranging from 0.15 to 0.90 m l 3 m r - 3 s - 1 . k ov 's for 45 and 60 PPI CNF/RVC foams are higher than for regular foam packings and approximately equal to random packings, ranging from 0.075 to 0.36 m l 3 m r - 3 s - 1 . k ov 's for CNF/RVC foam with CNFs synthesized at 773 and 873 K are approximately equal, ranging from 0.07 to 0.4 m l 3 m r - 3 s - 1 . For CNFs synthesized at 973 K, k ov is significantly higher, ranging from 0.18 to 0.57 m l 3 m r - 3 s - 1 . The high liquid–solid mass transfer rates of CNFs on solid foam with respect to regular foam is attributed to the hydrodynamic accessibility of the CNFs. The pressure drop of the CNF/RVC foam ( < 4000 Pa m - 1 ) is significantly lower than for random packings ( 5.2 × 10 3 to 1.2 × 10 6 Pa m - 1 ). This shows that higher or at least equivalent mass transfer rates can be obtained, but at a considerably lower pressure drop than for random packings.

Simulation of an industrial trickle bed hydrogenation reactor in the pulsing flow regime

An industrial trickle bed reactor was simulated for pyrolysis gasoline selective hydrogenation. The operation was recognised in the upper limit of pulsing flow regime by the Charpentier-Tosun flow pattern diagram at a very low hydrogen to oil volumetric ratio. Hydrodynamic parameters in the pulsing flow regime were calculated from the literature correlations which apply to the hydrogen-paraffin system. The external wetting efficiency which should be no higher than 100% was found to be 147% according to the correlation of Al-Dahhan and Dudukovic (1995), due to the undefined upper limit of their equation. The reactor simulation shows the gas-liquid and liquid-solid mass transfer rates were large enough for the active Pd hydrogenation catalyst. By comparing with the mass transfer rate in the Taylor flow regime in a monolithic structure, it shows the hydrogen concentration in the liquid phase in an industrial trickle reactor is more than two times of that in the monolith, which implies the substitution of the conventional catalyst pellet by the monolith is not required.

Effect of hydrodynamic multiplicity on trickle bed reactor performance

AbstractMultiple hydrodynamic states in trickle bed reactors have been the subject of numerous hydrodynamic investigations. The extent of variation in the hydrodynamic parameters (like holdup and pressure drop) is large and this variation can be expected to have a significant impact on the conversion in a reaction system. This study presents reaction data for α‐methyl styrene hydrogenation in a trickle bed reactor over a range of conditions that include gas and liquid limitations. It is seen that liquid flow rate variation induced hysteresis has a large impact on the conversion. For gas‐limited reactions, the upper branch of the pressure drop hysteresis loop has a higher conversion than the lower branch at the same linear fluid velocities and catalyst weight, while for liquid‐limited reactions the lower branch has a higher conversion than the upper branch (the difference in productivity being up to 20%). These trends cannot be explained by differences in wetting efficiency. Instead, it is proposed that for this system the gas–liquid mass transfer rate is the limiting step in gas‐limited reactions, while the liquid–solid mass transfer rate is the limiting step in liquid‐limited reactions. © 2007 American Institute of Chemical Engineers AIChE J, 2008

Application of catalytic distillation for the aldol condensation of acetone: the effect of the mass transfer and kinetic rates on the yield and selectivity

We have recently developed a catalytic distillation (CD) process for the aldol condensation of acetone to produce diacetone alcohol (DAA) which undergoes subsequent dehydration to produce mesityl oxide (MO). A rate-based model consisting of mass, energy and component balances, rate expressions, equilibrium and summation (MECRES) equations has been proposed to predict the yield and selectivity for this CD process. In this paper, the Onda et al. mass transfer correlations previously used in the MECRES equations were replaced by a new overall vapour–liquid mass transfer correlation determined in our laboratory for the non-reactive section in our CD column. Good agreement between model predictions and experimental data for the yield of DAA, MO and the temperature profile in the CD column was obtained without using any scaling factor. The effect of the mass transfer and kinetic rates on the yield and selectivity of the CD process were also examined. It was concluded that an increase in the external liquid–solid mass transfer rate through the catalyst bags results in a higher production rate of DAA but has little influence on the MO production rate, while increasing the kinetic rate results in a significant increase in the MO production but essentially no effect on the DAA production. This indicates that the DAA productivity is limited by the external liquid–solid mass transfer through the catalyst bags while the MO productivity is controlled by the apparent kinetic rate. Thus, an improvement on the packing geometry for the catalytic reaction zone with less mass transfer resistance will be required in order to achieve a higher selectivity to DAA.

Hydrodynamics and liquid—solid mass transfer mechanisms in packed beds operating in cocurrent gas—liquid downflow: An experimental study using electrochemical shear rate sensors

Overall and local hydrodynamics and liquid—solid mass transfer mechanisms were investigated in a laboratory scale packed bed reactor operating in gas—liquid downflow. The mean liquid saturation and the liquid—solid mass transfer rate were determined using classical electrochemical techniques and the local instantaneous hydrodynamics were analyzed using electrochemical shear rate sensors. The experimental results as well as theoretical considerations enabled us to contribute to the elucidation of gas—liquid flow mechanisms, especially in high-interaction regimes. In pulse flow at low liquid flow rates ( L < 10kg m −2 s −1) the wall is, on average, not entirely wetted, this might explain hot spot occurence in industrial fixed-bed reactors. In dispersed bubble flow and in the liquid rich slugs of pulse flow, the local instantaneous liquid-wall shear rate is characterized by high-amplitude—high-frequency fluctuations. The comparison of the space averaged shear rate measurements with the overall mass transfer rate indicates that the liquid—solid mass transfer mechanism is laminar in nature and may be modelized by a succession of developing laminar boundary layers. An overall mechanical force balance on the liquid shows that the average drag of the liquid by the gas is very small, compared to the total energy dissipated by the gas in the reactor. All the experimental results obtained in this work as well as several literature data can be explained by a flow mechanism in dispersed bubble flow, where the liquid flow is dominated by viscous forces whereas the gas bubbles pass through the packed bed by pressure pulses.

Local liquid-solid mass transfer measurement in a trickle film flow model using an electrochemical technique

A two-dimensional trickle film flow model consisting of a vertical column of horizontal rods is used to provide the liquid-solid mass transfer characteristics of a gas-continuous and fully wetted film flow trickle bed reactor. Local and average liquid-solid mass transfer rates are determined with the limiting current technique. Local Sherwood number variation with angular position is measured for 400 < Re < 2000. With a unique method of manipulating electrochemical mass transfer measurements, the existence of two vortices behind a flow separation is revealed.

Liquid—solid mass transfer rate in liquid-gas upward cocurrent flow in packed beds

Liquid—solid mass transfer rate in liquid-gas upward cocurrent flow in packed beds