Development and application of a novel swirl cyclone scrubber—(1) Experimental

Conventional cyclones have a lower collection efficiency for smaller particles and conventional wet scrubbers have significant clogging and fouling problems by salt formation at the tip, the inside and outside of the nozzles, the tubes and the walls of scrubbers. Also, many companies and manufacturing sites have been in trouble for collecting their adhesive particulates. The novel swirl scrubber that we have developed consists mainly of a cyclone and a swirl scrubber with an impact cone and plates. This study reports the collection efficiency of particulates and the application of the novel swirl scrubber. The particle collection efficiency as a function of particle size was investigated with changes of plate angles, nozzle size and pressure, and volumetric flow rate of scrubbing medium. The particle collection efficiency increased with a decrease in plate angle, an increase in pressure of scrubbing medium at the nozzle tip, and an increase in volumetric flow rate of the scrubbing medium. The collection efficiency of PM₁₀ by scrubbing effect was much higher than that by cyclonic effect. In particular, the total increase in particle collection efficiency by scrubbing effect was significant (around 2.5 μm) in particle aerodynamic diameter. The developed novel swirl scrubber can be used for significantly increasing the collection efficiency of TSP, PM₁₀, and PM_2.5, in particular, which have adhesive characteristics. The costs for installation, operation and maintenance of the scrubber system are much cheaper than those of cyclones and scrubbers or other particulate collecting devices.     

Mercury Speciation in Flue Gases after an Oxidative Acid Wet Scrubber

Flue gases from a hazardous waste incinerator have been sampled in three campaigns, before and after, an oxidative acid wet scrubber working with the MercOx‐process. A continuous emission monitor for mercury speciation was used before the scrubber in the first campaign. In all campaigns, impingers with KCl and KMnO₄ were used. A solid adsorption method was used in the last campaign. The mercury leaving the scrubber is oxidized at > 90 % efficiency (independent of the inlet speciation). A substantial decrease in the redox potential of the scrubber liquid caused an increased fraction of elemental gaseous mercury to be present in the clean gas. The measurements also show that the scrubber has the ability to readily absorb mercury peaks. During one extreme peak of 3,600 μg/m³ (dry gas) in the raw gas, the removal efficiency was above 99.9 %.     

Downstream Processing of Lactic Acid by Membrane-Based Solvent Extraction∗

Abstract

Lactic acid has extensive use in the food and chemical industry. About half the lactic acid used in the world is produced by fermentation of carbohydrates using lactic acid bacteria. The recovery of lactic acid from the fermentation broth is more difficult than the fermentation itself. In the present work a study of membrane-based solvent extraction as a separation unit for the continuous downstream processing of lactic acid from fermentation broth was carried out. The experiments were performed using simulated fermentation broths made of lactic acid in acetate buffer or distilled water as the feed solution. The effects of membrane material, organic carrier, and pH of the feed solution on membrane extraction efficiency were investigated. A separation degree of 35% was obtained by using a polyether-etherketone (PEEK-WC 14%) membrane with 5% trioctylamine as the organic carrier in n-heptane. The experimental results obtained with the simulated system encourage the use of membrane-based solvent extraction with a real fermentation broth.

     

Designing Wet Scrubbers for SO2 Absorption into Fairly Concentrated Sulfuric Acid Solutions Containing Hydrogen Peroxide

Absorption of SO₂, diluted with nitrogen up to concentrations of 500 Pa, was performed at 20 °C and 1 atm, with water and sulfuric acid solutions containing hydrogen peroxide in two different contactors: a packed column and a cable scrubber. The absorption rate was determined for various SO₂ partial pressures, as well as different concentrations of sulfuric acid (up to 40 wt %) and of hydrogen peroxide in the scrubbing liquid. It was found that the SO₂ absorption rate increases with the hydrogen peroxide concentration, and decreases as the acidity of the scrubbing liquid increases. Taking into account hydrodynamic and mass transfer characteristics of the packing for both scrubbers, a practical enhancement factor depending on the liquid phase H₂SO₄ and H₂O₂ contents, was deduced from semi‐continuous tests. As a good concordance was observed between results determined for both contactors, a single correlation is proposed, allowing the computation of this kinetic factor for quite simple simulation or design of SO₂ scrubbers, provided the gas and liquid phase mass transfer coefficients k_Ga and k_La are known.     

Transport of Palladium(II) through Trioctylamine Liquid Membrane

Abstract

The permeation behavior of palladium(II) through a supported liquid membrane (SLM) impregnated with trioctylamine (TOA) in kerosene has been investigated. By selecting perchloric or nitric acid as a stripping agent, Pd(II) was transported through the SLM containing 0.5 M TOA and 20% 1-octanol without remaining in the liquid membrane. The permeation rate (k _{f. obs}) of Pd(II) for HNO₃ was faster than that for HClO₄. Palladium(II) was concentrated across the SLM from the 0.5 M CHI solution into the HClO₄ or HNO₃ solution.     

Gas Separation by a Continuous Membrane Column

Abstract

The continuous membrane column provides a revolutionary new separation technique. In gaseous diffusion the continuous membrane column is used to separate as highly concentrated products both the most permeable and least permeable gases from a feed mixture of any composition. The main features of the column are countercurrent enrichment, high reflux and minimal backmixing. The new method eliminates the need for numerous interstage compressors and extensive product stream recycling found in conventional gaseous diffusion cascades.

Experiments are carried out for systems of C0₂-O₂, O₂2-N₂ (air), and CO₂-N₂ mixtures using continuous membrane columns made out of silicone rubber membrane. Also, a theoretical model is developed to interpret the experimental data. The agreement between theory and experiment is excellent. The maximum degree of separation can be achieved at total reflux. It is experimentally verified that the maximum degree of enrichment attainable by a conventional method can easily be exceeded without limit when a continuous membrane column is employed.

Finally, a comparative study has been conducted for a conventional gas permeator and a continuous membrane column.     

Characterization of a Macrocycle-Mediated Dual Module Hollow Fiber Membrane Contactor for Making Cation Separations

Abstract

Separation of metal cations in aqueous solution by a macrocyclemediated Dual Hollow Fiber Membrane Contactor is described. The advantages of this type of supported liquid membrane configuration include easily accessible source, receiving and membrane phases; transport rates competitive with those of other types of membranes; and the potential for continuous operation. The new system was investigated to determine the effect of aqueous solution flow rate and membrane solvent stirring rate on Na⁺ and K⁺ transport using dicyclohexano-18-crown-6 as the carrier. The results demonstrated that transport increases with increasing stirring speed, but remains constant with increased aqueous flow rate through the fibers within the range of four to twelve m1/min. The membrane solvents hexane, toluene, octane, 1-octanol, 4-methyl-2-pentanone, octanal, and 2-octanone were tested for their ability to preserve membrane integrity in the presence of aqueous solutions of low pH, and to maximize transport. Of these solvents, 2-octanone was found to be most effective in minimizing acid diffusion across the membrane, while giving the highest facilitated K⁺ transport rate. Quantitative transport using 18-crown-6 was observed for K⁺ over Na⁺ (all solvents studied) and Ba²⁺ and Sr²⁺ over Ca²⁺ (only octanol was studied).     

CO2 Capture Using Monoethanolamine in a Bubble‐Column Scrubber

A continuous bubble‐column scrubber, capturing CO₂ gas by monoethanolamine (MEA) solution in a pH‐stat operation, is used to search for optimum process parameters by means of the Taguchi method. The process variables are the pH of the solution, gas flow rate, concentration of CO₂ gas, and temperature. From the measured outlet CO₂ gas concentrations, the absorption rate and overall mass transfer coefficient can be determined with the support of a steady‐state material balance equation as well as a two‐film model. According to the signal‐to‐noise ratio, the significance sequence influencing the parameters and optimum conditions can be determined. CO₂ concentration and pH value proved to be decisive parameters, while temperature and gas flow rate were minor. Five sets of optimum conditions were obtained and could be further verified by empirical equations.     

Separation of Fermentation Products by Membrane Techniques. II. Conversion of Lactate to Lactic Acid by Electrodialysis

ABSTRACT

The yield of an electrodialysis unit operating for the conversion of lactate to lactic acid (LA) is depressed by low conductivity of the lactic acid solution. Experiments performed with a laboratory electrodialysis unit (ED) designed to establish the limiting current density i_lim for the whole unit and for each of the membrane/solution elements revealed high voltage drops for membranes in contact with the lactic acid solution. By filling the LA compartment with a cation-exchange resin as the conducting turbulence promoter, it was possible to increase i_lim from 2.7 ± 0.3 to 18.3 ± 2.0 mA/cm². With a resin suspension the rate of lactic acid formation was 6.0 mol^{â2 â1}, the current efficiency amounted to 92%, and the energy consumption was 3.3 kWg^â1. A hypothesis for the 7-fold increase of i_lim by filling the LA compartment with a grained conducting resin is presented.     

Studies on the Recovery of Uranium from Phosphoric Acid Medium by D2EHPA/n-Dodecane Supported Liquid Membrane

Abstract

Present studies deal with the application of supported liquid membrane (SLM) technique for the separation of uranium (VI) from phosphoric acid medium using Di-2 ethyl hexyl phosphoric acid (D2EHPA)/n-dodecane as a carrier and ammonium carbonate as a receiving phase. The studies involve the investigation of process controlling parameters like feed acidity of phosphoric acid, carrier concentration, stripping agents, and the effect of thickness and the pore size of the membrane. The transport of uranium decreases with increase in the concentration of phosphoric acid in feed solution whereas it increases with increase in carrier concentration in supported liquid membrane. More than 90% uranium (VI) is recovered in 360 minutes using 0.5 M D2EHPA/dodecane as carrier and 0.5 M ammonium carbonate as stripping phase from the 0.001 M H₃PO₄ feed. Lower concentration of phosphoric acid and higher carrier concentration is found to be the most suitable condition for maximum transport of uranium (VI) from its lean sources like commercial phosphoric acid and analytical wastes generated from the analysis of uranium by Volumetric (Davis-Gray) method.     

Predictive Model of Hydrogen Sulfide Absorption by Chelate Solution in a Venturi Scrubber

In the present study, a simple model was used to predict the removal efficiency of a venturi scrubber for H₂S absorption into a ferric chelate solution. From momentum and mass balances in the scrubber, a set of first‐order, nonlinear ordinary differential equations relating predominantly the liquid velocity with the H₂S concentration in the liquid along the axial direction in the scrubber were formulated. These relationships were numerically solved to give performance profiles. The validity of the model was examined by comparing the results of the model with experimental data from the working laboratory scale. The results predicted from the model are in good agreement with the experimental data obtained in different sizes of the venturi scrubber and operating variables.     

Reverse osmosis of wash waters from simultaneous SO2/NOx wet removal technique of flue gas

A promising for simultaneous SO₂/NO_x removal from flue gas consists in using Fe (II)—EDTA solutions as absorbing substrate for a coordinative bonding of NO. Its reduction to molecular nitrogen occurs by bisulfite which results from SO₂ absorption. Economic and environmental requirements imply a need for a nearly complete recovery of the complexing agent EDTA. For this purpose reverse osmosis can be used. With porous cellulose acetate membranes, a high enough rejection of EDTA can be achieved as well as the regulation of the concentration of the accompanying chlorides within the scrubber solution. The relevant selectivity of the membranes increases with rising working pressure. The required removal of the accompanying salts can be adjusted by different membrane annealing and by varying the concentration.     

A Double Liquid Membrane System for the Removal of Actinides and Lanthanides from Acidic Nuclear Wastes

Abstract

Supported liquid membranes (SLM), consisting of an organic solution of n-octyl(phenyl)-N, N-diisobutylcar-bamoylmethylphosphine oxide (CMPO) and tributyl-phos-phate (TBP) in decalin are able to perform selective separation and concentration of actinide and lantha-nide ions from aqueous nitrate feed solutions and synthetic nuclear wastes.

In the membrane process a possible strip solution is a mixture of formic acid and hydroxylammonium formate (HAF). The effectiveness of this strip solution is reduced and eventually nullified by the simultaneous transfer through the SLM of HNOs which accumulates in the strip solution. A possible way to overcome this drawback is to make use of a second SLM consisting of a primary amine which is able to extract only HNO₃ from the strip solution.

In this work the results obtained by experimentally studying the membrane system: synthetic nuclear waste/CMPO-TBP membrane/HCOOH-HAF strip solution/ primary amine membrane/NaOH solution, are reported. They show that the use of a second liquid membrane is effective in controlling the HN0₃ concentration in the strip solution, thus allowing the actinide and lanthanide ions removal from the feed solution to proceed to completion.     

Separation of Zinc Ions from an Acidic Mine Drainage using a Stirred Transfer Cell–Type Emulsion Liquid Membrane Contactor

Abstract

This is a report on the separation and recovery of zinc ions from an acidic mine drainage using a stirred transfer cell‐type emulsion liquid membrane contactor. Di(2‐ethylhexyl) phosphoric acid was used as a highly selective carrier for the transport of zinc ions through the emulsified liquid membrane. A study was made of the effect on the extraction extent and initial extraction rate of the following variables: pH and initial metal concentration of the feed phase, carrier content in the organic solution, a stripping agent concentration in the receiving phase, and stirring speed in the transfer cell. The content of sulfuric acid as a stripping agent did not show in the studied range any significant influence on metal permeation through the SLM, although a minimum hydrogen ion concentration of 100 g/L is suggested in the internal aqueous solution to ensure an acidity gradient between both aqueous phases to promote the permeation of metal ions toward the strip liquor. Results show that using a pH of 4.0 in the feed acid solution, a concentration of 3% w/w_o of phosphoric carrier in the organic phase and a H₂SO₄ content of 100 g/L in the strip liquor, the extent and rate of extraction through the liquid membrane can be highly favored, pointing to the potential of this method for extracting heavy metals from many kinds of dilute aqueous solutions.     

Application of nanofiltration to separate salts from a hydrogen-sulphide scrubber solution

Experiments were carried out using nanofiltration to separate salts from a hydrogen sulphide scrubber solution taken from an iron-based liquid-redox process. The scrubber solution used in these experiments contained organic chelating agents, iron, and various alkali metal inorganic salts (i.e., sulphates, thiosulphates, carbonates, and bicarbonates). The nanofiltration unit was equipped with monovalent ion-selective membranes. Results indicated that the nanofiltration membranes retained organic materials and iron and allowed ionic species (e.g., SO₄^2-, S₂^3-, CO₃^2-, HCO₃^-) to permeate. Results also indicated that the nanofiltration membranes used in these experiments preferentially removed CO₃^2- and HCO₃^- over SO₄^2- and S₂O₃^2-. The nanofiltration tests did not show any sign of membrane degradation in terms of ion selectivity; however, at high total-dissolved solids concentrations, the permeate flow rate was reduced.     

Absorption of NOx in packed column (II)

An absorption efficiency of packed column removing nitrogen oxides with water and NaOH solution under atmospheric pressure was studied. The efficiency and the acidity produced by absorption of NO, were measured in a packed column. The model developed that was based on the mass-transfer information for packed column and absorption mechanism accompanying the chemical reaction was compared with experimental results. Predictions using the model presented by the previous paper (part 1) was shown well to agree with from the experimental results (part II). The efficiency of NO_x, absorption is largely dependent on the height of packing material and the partial pressure of NO_x in the feed gas. The efficiency of NO_x absorption decreases with the increase of the acidity produced by recycling of water as a scrubber liquid. For the recycle mode with an aqueous NaOH solution as a scrubber liquid, NO_x absorption efficiency is shown to be constant until all of the C_OH- in the scrubber liquid are converted into C_H+.     

Study of Nonsteady-State Continuous Membrane Column for Gas Separation

Abstract

The permeation and transport processes occurring in a continuous membrane column (CMC) are quite complex, and the system will exhibit inverse response behavior in a certain operating regime. To understand the complex interaction of system variables, this work developed a mathematical model for the CMC and solved the model equations. Dynamic responses of a CMC for the separation of N₂-CO₂, CO₂-O₂, and O₂-N₂ gas mixtures with capillary silicone rubber membranes are presented. The effect of the membrane permeabilities on the CMC dynamics is examined. Responses of system variables to various disturbances, together with the start-up transient of the system, are discussed. The knowledge of the unsteady-state behavior of the CMC will enable us to predict the performance of the CMC and to control the CMC in a dynamic environment.     

Bibliography

ABSTRACT

This paper reports the results obtained by studying the transport properties of novel highly stable activated composite membranes (ACM) containing di-2-ethylhexyl phosphoric acid as a carrier. ACM samples containing different amount of DEHPA have been prepared by varying the DEHPA concentration in the casting solution. The selectivity of Ho and Pr transport through ACMs has been shown to depend on pH of the feed solution and DEHPA concentration in the membrane. ACM samples with a relatively low carrier content exhibit a higher selectivity for Ho, while an increase of DEHPA concentration in ACM results in the reversal of membrane selectivities. The transport properties of ACM do not change within a week of continuous operation.     

Experimental and modeling study on CO<Subscript>2</Subscript> absorption in a cyclone scrubber by phenomenological model and neural networks

Experimental and modeling studies have been conducted on CO₂ absorption in a cyclone scrubber operated at room temperature. The effects of parameters such as the initial concentration of alkali in the solution and the liquid - gas ratio on the CO₂ absorbed flux were experimentally and theoretically investigated. A phenomenological model and three-layer feed-forward neural networks have been applied to estimate the CO₂ absorbed flux in the cyclone scrubber. It was shown that the neural networks’ values agreed well with the experimental data, while the values by phenomenological model partly agreed with the experimental data around the initial concentration of alkali in the solution, C_Bo≤0.001 kmol/m³ (pH≤11).     

Transport of Europium through Supported Liquid Membrane Containing Dihexyl-N,N-diethylcarbamoylmethylphosphonate

Abstract

The transport of europium has been studied through a supported liquid membrane (SLM) impregnated with dihexy-N,N-diethylcarbamoylmethylphosphonate (CMP). Europium was effectively extracted from the perchlorate solution into SLM, but was insufficiently stripped to a dilute acid solution. The addition of 1-decanol improved the stripping process, and quantitative transport of europium was achieved. By the combination of two SLM systems consisting of diiso-decylphosphoric acid and CMP, europium was transported from the feed solution (0.1 M HNO₃) through the intermediate solution (1 M HclO₄ + 4 M NaClO₄) to the product solution (0.1 M HNO₃) and effectively concentrated by a factor of about 20.