Modeling of Fixed Adsorptive Distillation in Batch Operation

Abstract

This paper presents the modeling of fixed adsorptive distillation in batch operation. A combination of theoretical and empirical approaches is used to derive the model with the following procedures:

• (i)?modeling through each sub‐unit based on ideal concepts and assumptions,

• (ii)?addition of empirical correction factors into the model to eliminate assumptions.

The model is designated to predict the model parameter, which is the composition of the second column product, as a function of three process variables (i.e. time, feed composition, and flow ratio). It is found that the two above–mentioned approaches result in a representative model with an average error percentage of 5.46%.     

重力出流式膜生物反应器污泥浓度的优化控制

采用重力出流式膜生物反应器(Membrane Bioreactor, MBR)工艺对生活污水进行了实验研究. 重力出流式MBR是利用液位水头重力驱动出水,整个系统结构紧凑,操作简便. 结果表明,随着污泥浓度增大(3.9~18.4 g/L),同样的曝气强度对膜表面滤饼层的剪切能力降低,膜通量下降;污泥粘度从5.4 mPa×s上升到680 mPa×s,相应的污泥中的传氧系数与清水中的传氧系数之比a从0.89降到0.10. 因此,从提高膜通量、氧传递速率和降低能耗的角度出发,将MBR的污泥浓度控制在适当范围是非常必要的. 此外,当污泥浓度大于4.8 g/L,污泥浓度的提高对有机物的去除、硝化以及反硝化速率的提高没有明显的贡献. 因此,从MBR的处理能力和运行能耗的双重影响确定MBR的最佳处理污泥浓度值为4~6 g/L,在该浓度区间,生物反应器系统对冲击负荷有较好的抵御能力,同时系统的运行能耗也较低.     

Cysteine-Functionalized Chitosan Magnetic Nano-Based Particles for the Recovery of Uranium(VI): Uptake Kinetics and Sorption Isotherms

Magnetic-chitosan nanoparticles, functionalized with cysteine, were synthesized and characterized by element analysis, FT-IR, XRD, TEM, and vibrating sample magnetometry. The sorbent was tested for U(VI) recovery, considering:

• a. pH effect,

• b. sorption isotherms (fitted by Langmuir equation), and

• c. uptake kinetics (modeled using the PSORE).

Maximum sorption capacity approached 100 mg U g^?1. The nanometric size of sorbent reduces the impact of resistance to intraparticle diffusion; this may explain the fast kinetics (equilibrium within 50 min). The reaction is exothermic, spontaneous. The metal could be desorbed using acidified urea solution and the sorbent could be recycled for 5 cycles.     

Determination of the Mass Diffusion Coefficient Based on the Relative Humidity Measured at the Back Face of the Sample During Unsteady Regimes

This work proposes a new method for the determination of the mass diffusion coefficient in hygroscopic materials. The experiment consisted of submitting one face of the sample to a variation in time of the relative humidity (RH) and measuring the RH on its back face. The imposed RH and temperature were measured during the test and served as boundary conditions in a comprehensive computational code to solve heat and mass transfer in porous media. This model uses a physical engine embedded in the inverse procedure to determine the mass diffusion coefficient. Compared with classical methods, this new method has several advantages:

• It allows several samples to be measured simultaneously, simply by multiplexing the RH sensors.

• Accurate values can be obtained even when starting and ending out of equilibrium, which allows the characterization time to be drastically reduced.

• The external mass transfer coefficient has a negligible effect on the identified value.

• Nonstandard Fickian behaviors can be detected by the disagreement between the measured and simulated curves.

The results show that the diffusivity obtained for spruce wood is in good agreement with those found with classical methods. In contrast, the fiber board results differed between the experiment and model, or yielded unrealistic values, which confirms the dual-scale nature of mass transfer that occurs in this kind of material.     

Optimization of the Production of Hydrogen From Syngas Using a 1∶7 Mass Ratio of Hematite to Calcium Oxide in a Pressurized Fluidized Bed

Abstract

A set of response surface experiments were designed to determine the optimum conditions for the production of high‐purity hydrogen from wet syngas of composition (44% CO, 23% steam, and 33% hydrogen) using 50 grams of a 1∶7 mass ratio of Fe₂O₃: CaO loaded into the fluidized bed reactor. Pressure was varied between 50 psi and 515 psi and temperature between 725°C and 800°C. Results indicated:

• High purity hydrogen production is possible at reactor conditions of 725°C & 50 psi, as well as 725°C & 250 psi;

• Optimum high purity hydrogen production (largest mass in 15 minutes with no CO_x) occurred near conditions of 725°C and 250 psi;

• Mass of produced high‐purity hydrogen increased most significantly with pressure;

• Methane production increased linearly with pressure due to the catalytic effect of the high nickel content of the reactor walls;

• The chemical reaction rate is predicted to be a controlling factor in the percentage of CO and CO₂ in the outlet at lower pressures.

     

Comparison of Efficiency between Poly‐aluminium Chloride and Aluminium Sulphate Coagulants during Full‐scale Experiments in a Drinking Water Treatment Plant

Abstract

The efficiency of poly‐aluminium chloride (PACl) and of aluminium sulphate (alum), two commonly applied coagulant agents, was studied comparatively in this work, during full‐scale experiments in a drinking water treatment plant. The removal of suspended solids (turbidity) and the residual aluminium concentrations were carefully monitored and they were used for the evaluation of effectiveness for each coagulant, as well as for the determination of optimal operative conditions. Two alternative treatment processes were examined:

• (a) the conventional coagulation‐flocculation‐sedimentation process, followed by gravity filtration through sand filter beds, and

• (b) the direct filtration process, i.e., coagulation‐flocculation and sand filtration, but without the intermediate sedimentation step.

PACl proved to be a more efficient coagulant than alum, as lower dosages of PACl, about 1.35 mg Al/L in this case, resulted to the production of treated water with low turbidity and residual aluminium content. In addition, the direct filtration process through dual sand‐anthracite filter beds was found to be equally sufficient, as the conventional one, i.e., when applying the sedimentation step; in this case, 0.70 mg Al/L of PACl resulted in low turbidity water (around 0.1 NTU) and residual aluminium content (lower than 150 µg/L). In addition, the operation time of filters was extended to more than 24 hours.     

Full-Scale Testing of a Caustic Side Solvent Extraction System to Remove Cesium from Savannah River Site Radioactive Waste

Abstract

Savannah River Site (SRS) personnel have completed construction and assembly of the Modular Caustic Side Solvent Extraction Unit (MCU) facility. Following assembly, they conducted testing to evaluate the ability of the process to remove non-radioactive cesium and to separate the aqueous and organic phases. They conducted tests at salt solution flow rates of 3.5, 6.0, and 8.5 gpm.

During testing, the MCU Facility collected samples and submitted them to Savannah River National Laboratory (SRNL) personnel for analysis of cesium, Isopar® L, and modifier [1-(2,2,3,3-tetrafluoropropoxy)-3-(4-sec-butylphenoxy)-2-propanol]. SRNL personnel analyzed the aqueous samples for cesium by Inductively-Coupled Plasma Mass Spectroscopy (ICP-MS) and the solvent samples for cesium using a Parr Bomb digestion followed by ICP-MS. They analyzed aqueous samples for Isopar® L and modifier by gas chromatography (GC).

The conclusions from the cesium analyses follow.

• The cesium in the feed samples measured 15.8 mg/L, in agreement with expectations.

• The decontamination factor measured 181–1580 at a salt solution flow rate of 3.5 gpm, 211–252 at a salt solution flow rate of 6.0 gpm, and 275–878 at a salt solution flow rate of 8.5 gpm.

• The concentration factor measured 11.0–11.1 at 3.5 gpm salt solution flow rate, 12.8–13.2 at 6.0 gpm salt solution flow rate, and 12.0–13.2 at 8.5 gpm salt solution flow rate.

• The organic carryover from the final extraction contactor (#7) varied between 22 and 710 mg/L Isopar® L. The organic carryover was less at the lowest flow rate.

• The organic carryover from the final strip contactor (#7) varied between 80 and 180 mg/L Isopar® L.

• The organic carryover in the Decontaminated Salt Solution Hold Tank (DSSHT) and the Strip Effluent Hold Tank (SEHT) was less than 10 mg/L Isopar® L, indicating good recovery of the solvent by the coalescers and decanters.

     

单一反应体系曝气量与污泥质量浓度对同步硝化反硝化的影响

利用自培养硝化污泥与实验室筛选的1株反硝化细菌共培养形成共生污泥,构建膜生物反应器(MBR)单一反应体系同步硝化反硝化系统,得到系统良好同步硝化反硝化曝气量和污泥浓度的最优条件。由试验结果可知:在混合污泥质量浓度(MLSS)6.0~10.0 g/L时,调节曝气量,可以使单污泥同步硝化反硝化总氮(TN)去除率达到85%以上。不同MLSS下,达到最高TN去除率的最佳曝气量随着MLSS增高而向高曝气量偏移。随着MLSS增高,响应因子F变小,由曝气量的变化而引起的TN去除率变化明显变缓,表示MLSS对O2传递的缓冲能力越强。在MLSS为8 g/L条件下,低负荷比较容易达到较高的TN去除率,而高负荷下需要更高的曝气量以获得高的TN去除率,系统适合的NH4+-N负荷范围0~0.30 kg/(m3.d)。MLSS≥3.0 g/L,出水化学需氧量(COD)低于50 mg/L,COD大部分贡献于反硝化所需C源。单一反应体系同步硝化反硝化系统能对负荷的改变作出及时的回应,整体上运行比较稳定。     

Inverse vulcanization of sulfur with vinylic POSS

ABSTRACT

Novel sulfur-silsesquioxane random copolymer (poly(S-r-POSS)) was synthesized via the radical reaction between liquid sulfur and octavinyl silsesquioxane. Particulate solid POSS was dispersed in molten sulfur and heated in order to initiate the free radical reaction (inverse vulcanization). The appearance of new C–S bonds along with the disappearance of C=C bonds from vinyl groups was confirmed by Raman and FTIR spectroscopy. Moreover, the formation of saturated single C–C bonds from the reacting vinyl groups was revealed by FTIR. Microhomogenity of the copolymer was analyzed by means of SEM-EDS mapping and its thermal properties were studied using the TG-DSC method. After the extraction of free unreacted sulfur and POSS the copolymer exhibits porous micromorphology promising for application in lithium–sulfur batteries or heavy metals ion capturing.

Highlights

• Synthesis of silsesquioxane-sulfur hybrid copolymer via inversed vulcanization

• Highly porous cross-linked morphology

• Potential utilization for lithium–sulfur batteries or heavy metals ion capturing

     

Potential Ozone Applications for Water/Wastewater Treatment

Abstract

Several applications of ozonation were examined in this study for:

1. the treatment of stabilized high strength municipal landfill leachates,

2. the reclamation potential and toxicity reduction of municipal secondary effluents, and

3. the removal potential of phytoplanktons from surface waters.

The major parameters examined were the applied ozone dosage and the respective contact time. The application of single ozonation on leachates resulted in the efficient removal of color and organic loading, due to the respective oxidation, induced by ozonation. In addition, ozonation was found to be effective for the removal of the residual organic content of secondary municipal effluents. However, acute toxic effects after ozonation were observed on V. fischeri and were related to ozone concentration and contact time. Furthermore, the surface water used for drinking water production, was subjected to ozonation treatment for the removal of harmful cyanobacteria. Ozonation resulted in the reduction of the number of cyanobacteria species and in the breakage of the chain‐type species to cells with a lower number of atoms.     

Profile of Chemical Potential in Pressure-Driven Membrane Processes Accompanied by Gel-Enhanced Concentration Polarization

Abstract

A model for distribution of chemical potential and concentration polarization enhanced by gel accumulated on membrane surface has been proposed. It provides distribution of chemical potential and concentration in the liquid phase and within the gel layer. The model allows analyzing the influence of thickness of fouling gel layer on the CP degree, surface concentration and chemical potential.

The model is based on the following assumptions:

1. process is accompanied by accumulation of gel layer at membrane surface along with concentration polarization;

2. diffusion layer and deposited gel consist of different components and these layers are characterized by different values of diffusivity coefficients;

3. correlation for effective hindered back diffusion coefficient within deposited layer is adopted from [Boudreau, Geochim. Cosmochim. Acta, 60, 1996];

4. transverse transport is based on the following mechanisms: convection due to pressure difference and back diffusion owing to concentration gradient.

The following conclusions have been drawn: (A) diffusion resistance within the gel layer is getting dominant and cannot be ignored; (B) In the presence of a gel layer the membrane surface concentration, C_1M, is enhanced due to hindered back diffusion of salt ions that in turn, results in growth of osmotic pressure and chemical potential at the membrane surface. It provides elevated salt concentration in permeate and decreases the net driving force; (C) Analysis of calculated data indicates high sensitivity of CP degree to coefficient of hindered back diffusion within gel layer.     

Poly(glycerol pimelate) polyester as moderate mild steel protector in 0.5 M H2SO4: justified from electrochemical approach and XPS investigation

This work reports a facile synthesis of linear long chain aliphatic polyester, namely poly(glycerol pimelate) polyester (PGP) characterised by Fourier transform infrared spectroscopy (FTIR) and Nuclear magnetic resonance spectroscopy (¹H and ¹³C NMR). Thermal response of PGP was studied using Thermo gravimetric analysis (TGA) and Differential scanning calorimetry (DSC). Glass transition temperature (T_g) of 117?°C and thermal stability up to 290?°C was noticed from DSC and TGA analysis. As a potential application, the capability and extent of retarding the mild steel dissolution in 0.5?M H₂SO₄ medium rendered by the synthesised PGP was analysed by electrochemical and non-electrochemical methods. Weight loss measurements carried out at room temperature showed decreased corrosion rate with concentration (10, 50, 100, 500 and 1000?ppm) resulting in a moderate inhibition efficiency of 61.60% at 1000?ppm. Decreased inhibition efficiency was noticed on increasing the temperature from 303?K-333K. Various parameters were derived to understand the mode of adsorption. Increased charge transfer resistance (R_ct) from electrochemical impedance method (EIS) and decreased corrosion current density (I_corr) from potentiodynamic polarisation technique on increasing the concentration was in good agreement with weight loss measurements. Suppression of metal dissolution by the formation of film on the metal surface was additionally supported by X-ray diffraction studies (XRD), scanning electron microscopy (SEM) and Energy dispersive spectroscopy (EDS) followed by Atomic force microscopy (AFM). X-ray photoelectron spectroscopy (XPS) revealed the same with a detailed insight of adsorption of inhibitor on the metal surface.

• Highlights

• This paper explores the following highlights:

• Low cost and facile synthesis of polyester.

• Controversy result of moderate inhibition efficiency has been justified.

• Potentiodynamic polarisation studies revealed mixed type of inhibition.

• Morphological studies like XPS predicted detailed insight of adsorption.

     

Inhibitive effect of 4-amino-N-benzylidene-benzamide Schiff base on mild steel corrosion in HCl solution

Abstract

A newly Schiff base, 4-amino-N-benzylidene-benzamide (4-BAB) protection ability was synthesised from a condensation reaction of 4-aminobenzamide (4-AB) and benzaldehyde (BA). Adsorption and corrosion inhibition effect of this compound on mild steel (MS) in 1.0?M HCl solution were studied. The data obtained from measurments of this compound were compared with that of 4-AB and BA using many electrochemical, microscopic and hydrogen gas evolution techniques to clarify superiority of the Schiff base. Some thermodynamic parameters were calculated from experimental results and discussed. The value of ΔG_ads showed that adsorption of 4-BAB on MS from acidic solution obeys the Langmuir adsorption isotherm model. Surface SEM images of the MS specimens which were exposed to 1.0?M HCl solution in the absence and presence of the inhibitors showed that a homogeneous and protective inhibitor film forms on the metal surface, which hinder corrosive attack. It was concluded that synthesising the Schiff base improves protection ability with respect to related amine and aldehyde and the inhibitive action is in the order of 4-BAB > 4-AB?>?BA.

• Highlights

• 4-Amino-N-benzylidene-benzamide (4-BAB) is synthesized by condensation reaction between 4-aminobenzamide (4-AB) and benzaldehyde (BA)

• The inhibitor efficiencies calculated from all the applied methods are in agreement and are found to be in the order: 4-BAB >4-AB?>?BA

• The adsorption process of inhibitors on mild steel surface obeys the Langmuir adsorption isotherm

     

Thioxoquinazolines: synthesis,reactions and biological activities

ABSTRACT

Based on the results of quantum mechanical calculation extracted with the B3LYP functional at the density functional theory level, the impact of replacement of thiophene with thiazole rings in anthratetrathiophene (ATT) molecule was evaluated. Furthermore, to study the effect of substitution in the central benzene ring of anthracene, cyclic rings with heteroatoms were introduced. The optical and charge transport characteristics were also examined when the position of sulphur and nitrogen at the periphery of anthracene were interchanged. To analyze the electronic transitions in these molecules, TD-DFT calculations were performed. The outcome of the calculations suggest that swapping of the central benzene with hetero-cyclic rings and the change in positions of the sulphur and nitrogen have considerable influence on various properties, i.e. energies of HOMO &; LUMO, HOMO-LUMO energy gap, ionization potential (IP), electron affinity (EA), hole extraction potential (HEP), electron extraction potential (EEP) and reorganization energies (λ). Moreover, all the studied molecules posed better hole and electron transport characteristics than standard materials. The smaller values of hole and electron reorganization energies suggest that this analysis offers a supportive background for prospective design and fabrication of high-performance charge-transport materials.

Highlights

• On interchanging position of S and N at the periphery of ATTz results, a small change in absorption maxima.

• Replacement of central six-member ring of anthracene with a five-member ring in ATTz molecule results in blue-shifted absorption.

• Molecules where sulphur facing outward at the periphery of ATTz are better for hole transporting materials.

• On changing the position of S-atom (inward to outward position) at the periphery of ATTz lead to destabilization of both HOMO and LUMO levels.

     

Investigations with Electrodialysis Reversal for the Treatment of Surface Water to Make-Up Water

Abstract

In the Dutch power stations, boiler make-up water is nowadays prepared by treating drinking water with ion exchangers. A problem, however, is that drinking water is expensive in certain areas of the Netherlands. Therefore it seems to be attractive to prepare make-up water out of surface water with aid of electrodialysis reversal (EDR). The experiments with an EDR installation were carried out with different types of surface water.

The process consists of three main stages:

• pretreatment of the surface water to meet the requirements set for feed water for the EDR unit

• desalination in the EDR unit

• post-treatment of product water (with ion exchangers) from the EDR unit to comply with the guidelines for make-up water.

From experiments on pilot plant scale it could be concluded that a simple filtration step to remove suspended matter was sufficient to comply with the requirements set for feed water for the EDR unit. Further it was possible to desalt the surface water to a large extend (about 90% or more) at a low energy consumption. By means of ion exchangers installed downstream the EDR unit water could be produced that met all the guidelines for make-up water. Finally it was noted that during all experiments with different types of surface water no membrane fouling did occur. From an economical evaluation it appeared that the pay out time for a commercial EDR installation, including a pretreatment step, with a production capacity of 20 m³/h amounted to about 6.5 years.     

Kinetic and Equilibrium Studies on the Adsorption of Crystal Violet Dye using Kaolin as an Adsorbent

Abstract

Experimental investigations are carried out to adsorb toxic crystal violet dye from aqueous medium using kaolin as an adsorbent. Characterization of kaolin is done by measuring

1. particle size distribution using particle size analyzer,

2. BET surface area using BET surface analyzer,

3. structural analysis using X ray diffractometer, and

4. microscopic analysis using scanning electron microscope.

The effects of initial dye concentration, contact time, kaolin dose, stirring speed, pH, and temperature are studied for the adsorption of crystal violet in batch mode. Adsorption experiments indicate that the extent of adsorption is strongly dependent on the pH of the solution. Free energy of adsorption (ΔG ^o ), enthalpy (ΔH ^o ), and entropy (ΔS ^o ) changes are calculated to know the nature of adsorption. The calculated values of ΔG ^o are ?4.11 and ?4.48 kJ/mol at 295 K and 323 K, respectively, for 20 mg/L of dye concentration, which indicates that the adsorption process is spontaneous. The estimated values of ΔH ^o and ΔS ^o show the negative and positive sign, respectively, which indicate that the adsorption process is exothermic and the dye molecules are organized on the kaolin surface in more random fashion than in solution. The adsorption kinetic has been described by pseudo first order, pseudo second order and intra‐particle diffusion models. It is observed that the rate of dye adsorption follows pseudo second order model for the dye concentration range studied in the present case. Standard adsorption isotherms are used to fit the experimental equilibrium data. It is found that the adsorption of crystal violet on kaolin follows the Langmuir adsorption isotherm.     

Use of Ozone for Disinfection and Taste and Odor Control at Proposed Membrane Facility

Zone 7 of Alameda County Flood Control and Water Conservation District, in coordination with Black & Veatch, conducted a 9-month pilot study to determine preliminary design parameters for a new water treatment plant (WTP). The pilot study was performed to verify the performance of membrane filters and to establish preliminary design parameters for the submerged membrane process, followed by ozonation and biological granular activated carbon filtration. The pilot testing was conducted using water from the Patterson Pass WTP reservoir. The process included coagulation with either ferric chloride or polyaluminum chloride, flocculation, sedimentation, membrane filtration, ozonation, and filtration using biological granular activated carbon (BAC). The goals of the study were as follows:

1. Determine the potential effectiveness of ozone and BAC for removing geosmin and MIB.

2. Determine the impacts of different levels of pathogen inactivation, i.e., 0.5-log Giardia and 2-log virus inactivation.

3. Monitor the formation of bromate under various conditions of ozone oxidation for different levels of pathogen inactivation as well as for taste and odor control, and evaluate bromate mitigation strategies, if necessary.

The results of the study showed that the use of ozone achieved 2.0-log virus inactivation and 0.5-log Giardia inactivation. It also decreased the disinfection by-product formation and effectively controlled geosmin and removed a significant fraction of the MIB during a taste and odor event. Because the raw water bromide concentrations were low, bromate formation remained below the regulated level of 0.010 mg/L. However, in one instance, bromate mitigation was utilized by applying sulfuric acid to lower the pH to less than 7.1, which reduced bromate formation to less than 0.010 mg/L.     

Operation of Membrane Bioreactor with Powdered Activated Carbon Addition

Abstract

The effect of powdered activated carbon (PAC) addition to the activated sludge (AS) in a membrane bioreactor (MBR) has been investigated. The long term nature of the tests allowed the PAC to gradually incorporate into the biofloc forming biologically activated carbon (BAC). One series of tests involved 4 bench scale (2 L) MBRs operated at sludge retention times (SRTs) of 30 days with PAC inventories of 0, 1, 3 and 5 g/L and steady state biomass concentrations of 12.0±1.0 g/L. The characteristics of the mixed liquors (MLSS) from the 4 reactors were compared. Short term filtration tests, including measurement of specific cake resistance (SCR), flux decline profile, and irreversible fouling resistance in an unstirred cell and “sustainable” flux (by monitoring transmembrane pressure (TMP) rise) in a crossflow cell all showed better filtration performance for the MLSS with BAC compared with the AS alone. In terms of SCR and flux decline profile the 1 g/L PAC addition performed best, but in terms of minimizing irreversible membrane fouling and maximizing “sustainable” flux the 5 g/L PAC was best. All 4 systems showed lower total organic carbon (TOC) in the permeate compared to the bioreactors, but the lowest permeate TOC (and the best removal) was for the highest PAC loading.

The benefit of PAC addition was confirmed in a second series of tests with two 20 L MBRs with submerged hollow fibers, one operated without PAC, the MBR(AS), and the other with 5 g/L PAC, the MBR(BAC). For an SRT of 30 days (which involved 3.3% sludge wastage per day and 3.3% new PAC addition per day) and a fixed flux of 21 L/m²hr the MBR(AS) showed a TMP rise of about 2.4 kPa/day whereas the MBR(BAC) showed a rise of only 0.8 kPa/day. However when the MBRs were operated without wastage the performance of the MBR(BAC) was worse than the MBR(AS). Thus the improved performance of the MBR(BAC) requires regular replenishment of aged BAC with fresh PAC.