Length Of Unused Bed Research Articles

Design and Construction of Equipment to Make Adsorption at Pilot Plant Scale of Heavy Metals

The purpose of this paper was to illustrate the procedure to obtain activated carbon from lignocellulosic residues through chemical and physical paths. A general surface characterization was made and aqueous solution isotherms were obtained in order to evaluate the behaviour of each carbon atom in solutions contaminated with selective ions. The other purpose was to show a simple way to perform a scale-up process of an absorber from the laboratory level to an industrial level, using the breaking curves in fixed beds developed through the continuous pursuit of the Pb(II) and Cr(VI) ions concentration in the effluent of the bed. Activated carbon was used to study the adsorption of Pb(II) and Cr(VI). Isotherms of aqueous adsorption were determined. This model was developed in order to examine its efficiency and to compare it with an experimental model made in the laboratory, which rendered very similar results. The main characteristic of the feasibility of the application of this design is the fact that neither tedious calculations nor mass transfer coefficients are required in order to construct the above-mentioned curves. The model was developed by applying concepts such as mass transfer zone (MTZ) and length of unused bed (LUB), which are the dynamical basis understanding for the adsorption process in fixed beds. As a complementary item of the experiment, within a pilot plant scale, a filter was developed in order to achieve flexibility when manipulating the most important adsorption parameters and to enable the control of the variables involved in the process that change the operating conditions.

Troca iônica em equilíbrio e dinâmica de Cr 3+ em zeólitas NaA e NaX

In this paper, the chromium uptake in zeolites NaA and NaX was investigated in equilibrium condition and in dynamic systems at 30 o C. The separation factors, obtained from the equilibrium data, were very similar to the isotherms Cr-NaA e Cr-NaX, which indicates that, in equilibrium conditions both zeolites remove similar quantities of chromium ions. For the dynamic runs, it was observed that the large size of hydrated chromium ion inhibited its exchange in all zeolite sites causing huge differences in the breakthrough curves. The dynamic data were used to estimate some mass transfer parameters such as the length of unused bed, operational ratio and dimensionless variance for various flow rates. Based on the breakthrough results, the optimal condition for column operation was 11 mL/min for zeolite NaA and 9 mL/min for zeolite NaX. Moreover, through the dynamic capacity of the column, it was concluded that the zeolite NaX has been more efficient for dynamic chromium uptake due to the larger aperture of its cages.

Comparison of adsorption characteristics according to polarity difference of acetone vapor and toluene vapor on silica–alumina fixed-bed reactor

Adsorption characteristics of acetone vapor and toluene vapor on silica–alumina were investigated using a fixed-bed reactor. The equilibrium adsorption capacity of acetone vapor on silica–alumina was about four times higher than that of toluene vapor because of polarity difference between adsorbent and adsorbate. As inlet concentration and linear velocity were increased, MTZ (mass transfer zone) and LUB (length of unused bed) were increased. In binary vapor systems, the phenomenon of “roll-up” was observed in the breakthrough curves. Thus the more strongly adsorbed adsorbate (acetone) displaces the weaker adsorbate (toluene), leading to a rise in the effluent concentration of the less strongly adsorbed adsorbate above the inlet concentration. Temperature changes in silica–alumina bed during adsorption of acetone vapor and toluene vapor were occurred near 30 min and the increase of temperature by adsorption heat was in the range of 6–7 °C.

Chromium uptake from tricomponent solution in zeolite fixed bed

Removal of Cr3+,Ca2+,Mg2+ and K+ in equilibrium isotherms and in tricomponent solutions (Cr/Ca/K, Cr/Ca/Mg and Cr/Mg/K) were investigated in NaX and NaY packed beds at 30∘C. The equilibrium selectivity was obtained as Cr+3 > Mg2+ > Ca2+≈K+ for zeolite NaY and Ca2 +≫Cr3 + > Mg2 +≈K+ for zeolite NaX. The breakthrough curves showed sequential ion exchange where chromium ions are able to replace the competing cations. Some mass transfer parameters, such as length of unused bed and overall mass transfer coefficient, were investigated. Chromium retention was also investigated through a mass balance. Based on the breakthrough results, it was concluded that chromium-uptake mechanism was hardly influenced by the competition and interaction between the entering ions. NaY showed a higher affinity towards Cr3+ for both equilibrium and dynamic systems and its sites were more efficiently used in the ion exchange process. Chromium was less retained in NaX due to the high selectivity towards calcium ions.

고정층 활성탄 흡착반응기에서 기상 톨루엔의 흡착특성

Adsorption characteristics of toluene vapor, which is one of important source of volatile organic compounds (VOCs), by activated carbon were investigated using a fixed bed adsorption column. The operating parameters such as breakthrough curve, adsorption capacity, mass transfer zone (MTZ), and length of unused bed (LUB) were studied. The experimental results showed that the breakthrough time decreased with increasing inlet toluene concentration and gas flow rate. MTZ and LUB increased with the increase of inlet concentration, gas flow rate, and particle size of activated carbon. The adsorption capacity increased with the increase of inlet toluene concentration, while it decreased with increasing particle size. However, it was kept at constant value regardless of the increase of gas flow rate. Adsorption isotherm of toluene vapor could be represented by the Freundlich adsorption equation fairly well. From the adsorption experiments using some VOC gases such as toluene, xylene, butyl acetate. butanol and acetone, it was also found that the adsorption capacity was higher in the case of gas with higher boiling point and lower vapor pressure.

H 2S retention with Ca-based sorbents in a pressurized fixed-bed reactor: application to moving-bed design

The H 2S retention with Ca-based sorbents in a pressurized fixed-bed reactor (1 MPa) has been analyzed, obtaining the breakthrough curves with a dolomite and two different limestones, different particle size (+0.8–1.0, +1.25–1.6, and +1.6–2.0 mm), and both at calcining (1173 K) and non-calcining conditions (1123 K). The effect of the stoichiometric time in the breakthrough curves has been analyzed varying the bed length, the gas velocity and the sorbent fraction in the bed. From these results, the conversion and H 2S concentration profiles in the transition zone and the length of unused bed (LUB) have been determined. H 2S retention in fixed-bed until concentration close to the given by the thermodynamic equilibrium was obtained using dolomite or limestone at calcining conditions, and dolomite at non-calcining conditions. The results of H 2S retention in a fixed-bed reactor has been applied to the calculus of the minimum height of a countercurrent moving-bed reactor to obtain the maximum H 2S retention with the minimum amount of sorbent. A mathematical model was developed to predict the experimental results obtained in the fixed-bed reactor, which was also valid for the design of countercurrent moving-bed reactors for gas desulphurization.

New method for monitoring of adsorption column saturation and regeneration II: on-line measurement

A new method suitable for the on-line monitoring of adsorption column saturation/regeneration cycles was developed based on the discovery that the electrical resistance of packed bed adsorbents changes dramatically upon adsorption and returns to its original value upon desorption. This change can be measured reliably and reproducibly. The two systems studied on-line in real time were methyl chloride (MeCl) adsorption on zeolite molecular sieve (HISIV 3000) and water vapour adsorption on basic alumina (RF-200). The sequential change in electrical readings at localized points within the column indicated the movement of the adsorption front, tracking the onset of breakthrough. The electrical readings returned to their original values upon desorption and the results were reproducible. Concurrently with the electrical measurements, the effluent gas of the MeCl/HISIV system was monitored for MeCl using an on-line gas chromatograph. An adsorption isotherm was created using the “length of unused bed” concept. The resistance change of the HISIV was found to be proportional to the square root of the amount of MeCl adsorbed, similarly to the C/CO 2 system discovered recently by our group. The universality of this correlation is being investigated. The simple measurement technique introduced here has the potential to improve the operating efficiency of industrial adsorption towers.

Predicting packed‐bed breakthrough behavior from PFG NMR diffusion data

AbstractPulsed field gradient (PFG) NMR measurements have been conducted to measure self‐diffusion coefficients of gases within porous media. Analysis of these microscopic data with the use of a previously developed long‐range diffusion model has enabled us to accurately predict breakthrough curves for transport through packed‐bed adsorption columns, and the length of unused bed (LUB). This methodology enables the evaluation of mass‐transfer coefficients without the complications associated with transient sorption experiments, that is, heat effects, and thereby offers a reasonable alternative to conventional breakthrough experimentation for the evaluation of mass‐transfer coefficients, and LUB for large‐scale unit operations. 2004 American Institute of Chemical Engineers AIChE J, 50:589–595, 2004)

Organic Vapor Recovery and Energy Efficiency during Electric Regeneration of an Activated Carbon Fiber Cloth Adsorber

An electrothermal-swing adsorption system was demonstrated on the bench scale for capture and recovery of organic vapors from air streams. Methyl propyl ketone (MPK), methyl ethyl ketone, \in-hexane, acetone, and methylene chloride were removed and recovered at 200–1,020 ppm\dv in a 40.0 slpm air stream while using activated carbon fiber cloth (ACFC) adsorbent. Removal efficiencies were greater than 99.9%. Liquid recovery fractions increased with increasing relative pressure, ranging from 0.11 for methylene chloride (\IP/P\Nsat = 2.1×10\U-3\N) to greater than 0.80 for MPK (\IP/P\Nsat = 2.2×10\U-2\N). The electrical energy consumed during regeneration per mol of liquid organic compound recovered decreased with increasing relative pressure of the inlet gas stream, ranging from 4,698 kJ/mol for methylene chloride to 327 kJ/mol for MPK. Equilibrium ACFC adsorption capacity, throughput ratio, and length of unused bed were also evaluated. These results are encouraging for the development of a new technology to capture and readily recover a wide range of organic vapors from air streams.

Binary ion exchange of metal ions in Y and X zeolites

The ion exchange of Na for Cr/K, Cr/Mg and Cr/Ca in Y and X zeolites was studied using breakthrough curves. It was observed that Cr3+ ions were able to remove some competitive ions that had already been exchanged at the zeolitic sites, producing a sequential ion exchange. Some mass transfer parameters such as length of unused bed, overall mass transfer coefficient, operational ratio and dimensionless variance were studied. Chromium uptake was influenced much more by the competing ion in the NaX zeolite columns. The dimensionless variance indicated that Cr/K solution produced a greater axial dispersion than the Cr/Mg and Cr/Ca systems, probably due to some interaction between Cr3+ and K+ ions. The order of dynamic selectivity, provided by the cation uptake, was Cr3+ > Ca2+, Cr3+ > Mg2+ and Cr3+ > K+ for NaY zeolite and Ca2+ »Cr3+, Mg2+ > Cr3+ and Cr3+ > K+ for NaX zeolite. Due to the more favorable mass transfer parameters and higher affinity for Cr3+, it was concluded that NaY zeolite was more efficient at chromium uptake in competitive systems.

Removal and recovery of lead fixed-bed biosorption with immobilized bacterial biomass

Fixed-bed columns packed with immobilized biomass of Pseudomonas aeruginosa PU21 were utilized to remove lead (Pb) from the contaminated water. Effects of the immobilization method, bed length, flow rate, and the particle size on the performance of Pb removal by the biosorption columns were systematically investigated. Calcium alginate-immobilized cells were found to hold better Pb capacity than polyacrylamide (PAA)-entrapped cells. Typical saturation capacity of calcium alginate (CA)-immobilized cells was 280 mg Pb/g, and 31 mg Pb/g for PAA-immobilized cells. Results of fixed-bed biosorption showed that the breakthrough time (tb) appeared to increase with the bed length, but decreased with the flow rate. The typical overall adsorption efficiency (Q) was within 50-60%, and did not appreciably fluctuate with changes in the operation conditions or the particle size. The initial rate of adsorption was facilitated nearly 40% as the size of immobilized cells was reduced from 3.5 mm to 2 mm, whereas the particle size did not affect the equilibrium adsorption of the immobilized biomass. The length of unused bed (LUB) remained constant with different bed length, while it slightly increased with the raising of the Pb loading rate. The metal-laden column was regenerated by elution of HCl solution (pH 2.0). For up to four adsorption/desorption (A/D) cycles, the metal recovery efficiency of each cycle was over 98%, and the recovery ratio was 8:1 and 27:1 for PAA and CA-immobilized cells, respectively. The regenerated beds were able to restore over 66% of their original adsorption capacity after four successive A/D cycles.

Adsorption Kinetics and Breakthrough Behaviour of Tri-n-butyl Phosphate on Amberlite XAD-4 Resin

Adsorption behaviour of tri-n-butyl phosphate (TBP) from aqueous solution (dilute HNO3) on Amberlite XAD-4 has been investigated experimentally. Factors affecting the adsorption rates and breakthrough curves have been studied in batchwise and semicontinuous fixed bed adsorber. The adsorption isotherm of TBP on Amberlite XAD-4 resin have also been determined and the Freundlich model of adsorption is used to describe adsorption equilibrium. For the case of nonlinear equilibrium a simplified method proposed by Chi Tein is used to estimate intraparticle diffusion coefficient. The intraparticle diffusion coefficient is found to be in the range of 10−8 cm2·s−1. Results of fixed bed column are used to estimate mass transfer zone (MTZ) length, length of unused bed (LUB), breakthrough capacity corresponding to fixed value of effluent concentration (5 mg/l of TBP) and degree of saturation of bed at breakthrough. The MTZ length was found to vary from 21.8 cm to 37.3cm when flow rate changed from 13.5 ml/min to 52 ml/min, whereas column utilization ranged from 65.1% for the lowest flow rate to 43.5% for the highest flow rate.

Removal and recovery of lead fixed-bed biosorption with immobilized bacterial biomass

Fixed-bed columns packed with immobilized biomass of Pseudomonas aeruginosa PU21 were utilized to remove lead (Pb) from the contaminated water. Effects of the immobilization method, bed length, flow rate, and the particle size on the performance of Pb removal by the biosorption columns were systematically investigated. Calcium alginate-immobilized cells were found to hold better Pb capacity than Polyacrylamide (PAA)-entrapped cells. Typical saturation capacity of calcium alginate (CA)-immobilized cells was 280 mg Pb/g, and 31 mg Pb/g for PAA-immobilized cells. Results of fixed-bed biosorption showed that the breakthrough time (tb) appeared to increase with the bed length, but decreased with the flow rate. The typical overall adsorption efficiency (Q) was within 50–60%, and did not appreciably fluctuate with changes in the operation conditions or the particle size. The initial rate of adsorption was facilitated nearly 40% as the size of immobilized cells was reduced from 3.5 mm to 2 mm, whereas the particle size did not affect the equilibrium adsorption of the immobilized biomass. The length of unused bed (LUB) remained constant with different bed length, while it slightly increased with the raising of the Pb loading rate. The metal-laden column was regenerated by elution of HCl solution (pH 2.0). For up to four adsorption/desorption (A/D) cycles, the metal recovery efficiency of each cycle was over 98%, and the recovery ratio was 8:1 and 27:1 for PAA and CA-immobilized cells, respectively. The regenerated beds were able to restore over 66% of their original adsorption capacity after four successive A/O cycles.

Kinetics of removal of impurities from gases by high pressure adsorption

AbstractAmong other processes, adsorption is used for the removal of hydrogen sulphide from natural gases. Hereby, competitive adsorption of the different gas components plays an important role, e.g., that of carbon dioxide. Data of equilibrium loading and adsorption kinetics are required for the design of adsorbers, filled with molecular sieve. In order to obtain these data under the prevailing operating conditions, hydrogen sulphide was removed from gas mixtures H2S/CH4 and H2S/CO2/CH4, in a pilot plant, by adsorption on molecular sieve 5A. The equilibrium loading, the height of transfer zone, and the length of unused bed were determined from the measured breakthrough curves of H2S. With these data, the breakthrough time and the optimum process conditions were calculated for a practical example.