Low Feed Concentration Research Articles

Investigation of polyvinylchloride and cellulose acetate blend membranes for desalination

The pollution of water resources, severe climate changes, rapid population growth, increasing agricultural demands, and rapid industrialization insist the development of innovative technologies for generating potable water. Polyvinylchloride/cellulose acetate (PVC/CA) membranes were prepared using phase inversion technique for seawater reverse osmosis (SWRO). The membrane performance was investigated using Red Sea water (El-Ein El-Sokhna-Egypt). The membrane performance indicated that the prepared membranes were endowed to work under high pressure; increasing in feeding operating pressure led to increase permeate flux and rejection. Increasing feed operating pressure from zero to 40 bar led to increase in the salt rejection percent. Salt rejection percent reached to 99.99% at low feed concentration 5120 ppm and 99.95% for Red Sea water (38,528 ppm). The prepared membranes were characterized using scanning electron microscopy (SEM), Fourier transform infrared (FTIR) spectrophotometry, and mechanical properties. SEM, FTIR and mechanical results were used to distinguish the best membrane for desalination. According to characterization results, one prepared membrane was selected to run performance test in desalination testing unit. The membrane (M3) showed excellent performance and stability under different operating conditions and during the durability test for 36 days.

Ultrafiltration membrane for effective removal of chromium ions from potable water

The objective of the present work was to investigate the efficacy of indigenously developed polyacrylonitrile (PAN) based ultrafiltration (UF) membrane for chromium ions removal from potable water. The hydrolyzed PAN membranes effectively rejected chromium anions in the feed ranging from 250 ppb to 400 ppm and a rejection of ≥90% was achieved for pH ≥ 7 at low chromate concentration (≤25 ppm) in feed. The rejection mechanism of chromium ions was strongly dependent on Donnan exclusion principle, while size exclusion principle for UF did not play a major role on ions rejection. Feed pH played a vital role in changing porosity of membrane, which influenced the retention behavior of chromate ions. Cross-flow velocity, pressure did not play significant role for ions rejection at low feed concentration. However, at higher feed concentration (≥400 ppm), concentration polarization became important and it reduced the chromate rejection to 32% at low cross flow and high pressure. Donnan steric-partitioning pore and dielectric exclusion model (DSPM-DE) was applied to evaluate the chromate ions transport through PAN UF membrane as a function of flux by using optimized model parameters and the simulated data matched well with experimental results.

Contribution to the production of lactulose-rich whey by in situ electro-isomerization of lactose and effect on whey proteins after electro-activation as confirmed by matrix-assisted laser desorption/ionization time-of-flight-mass spectrometry and sodium dodecyl sulfate-polyacrylamide gel electrophoresis

Cheese-whey, a major co-product of the dairy industry, has recently been the subject of many technological applications. We studied the bioconversion of whey into valuable bio-products such as a potential lactulose prebiotic and compounds with antioxidant properties. This paper examines efficiency, safety, and economics of electro-activation as an eco-friendly technology for a maximum valorization of whey. Thus, a bottom-up approach was therefore addressed. The effect of 4 experimental parameters—low working temperatures (0, 10, and 25°C), current intensities (400, 600, and 800mA), volume conditions (100, 200, and 300mL), and feed concentrations [7, 14, and 28% (wt/vol)]—on lactose-whey isomerization to lactulose under electro-activation process were studied. Structural characteristics of whey proteins and antioxidant functionality were also investigated. The results showed a compromise to be reached between both parameters. Therefore, the maximum yield of 35% of lactulose was achieved after 40min of reaction at the working temperature of 10°C under 400mA electric current field and 100-mL volume conditions with using feed solution at 7% (wt/vol). The isomerization of lactose to lactulose is accomplished by subsequent degradation to galactose, but only at a very small amount. Additionally, whey electro-activation showed significantly elevated antioxidant capacity compared with the untreated samples. The enhancement of antioxidant functionality of whey electro-activation resulted from the synergistic effect of its partial hydrolysis and the formation of antioxidant components that were able to scavenge free radicals. In conclusion, the findings of this study reveal that the whey treated by the safety electro-activation technology has both lactulose-prebiotic and antioxidant properties and could have a substantial application in the manufacture of pharmaceutical and functional foods.

Gasification of fruit wastes and agro-food residues in supercritical water

Considerable amounts of fruit wastes and agro-food residues are generated worldwide as a result of food processing. Converting the bioactive components (e.g., carbohydrates, lipids, fats, cellulose, hemicellulose and lignin) in food wastes to biofuels is a potential remediation approach. This study highlights the characterization and hydrothermal conversion of several fruit wastes and agro-food residues such as aloe vera rind, banana peel, coconut shell, lemon peel, orange peel, pineapple peel and sugarcane bagasse to hydrogen-rich syngas through supercritical water gasification. The agro-food wastes were gasified in supercritical water to study the impacts of temperature (400–600°C), biomass-to-water ratio (1:5 and 1:10) and reaction time (15–45min) at a pressure range of 23–25MPa. The catalytic effects of NaOH and K2CO3 were also investigated to maximize the hydrogen yields and selectivity. The elevated temperature (600°C), longer reaction time (45min) and lower feed concentration (1:10 biomass-to-water ratio) were optimal for higher hydrogen yield (0.91mmol/g) and total gas yield (5.5mmol/g) from orange peel. However, coconut shell with 2wt% K2CO3 at 600°C and 1:10 biomass-to-water ratio for 45min revealed superior hydrogen yield (4.8mmol/g), hydrogen selectivity (45.8%) and total gas yield (15mmol/g) with enhanced lower heating value of the gas product (1595kJ/Nm3). The overall findings suggest that supercritical water gasification of fruit wastes and agro-food residues could serve as an effective organic waste management technology with regards to bioenergy production.

Nanofiltration separation of highly concentrated multivalent electrolyte draw solution; a pilot plant study

Nanofiltration membrane system is proposed for the regeneration of draw solution in a two-stage forward osmosis (FO) process. Pilot plant experiments were carried out on two types of multivalent electrolyte draw solutions, MgSO4 and MgCl2. Two commercial size NF90-4040 Filmtec Nanofiltration (NF) membranes were packed in a high-pressure vessel for the regeneration of draw solution. The concentrations of the draw solution used were between 20 and 118 g/L. The impact of feed concentration, flow rate and feed pressure on the performance of NF membrane was investigated. Both metal salts have shown a high rejection rate by the NF membrane. The rejection rate to the MgSO4 was slightly higher than that to the MgCl2. Experimental results showed that NF rejection rate and permeate flow rate increased with increasing the feed pressure and flow rate but decreased with increasing the concentration of feed solution. However, this was achieved at the expense of higher power consumption. In general, the efficiency of NF system for the regeneration of draw solution was higher at lower feed concentration. This suggests that NF separation method is probably more suitable for the regeneration of low concentration draw solution which is generated from brackish water FO treatment plants. Furthermore, NF application in the regeneration of high-concentration draw solution is not yet feasible due to the limitations in the NF process such operating feed pressure and rejection rate.

Work of separation in CO2 capture: Applicability of the value function

The energy requirements for two CO2 separation processes (VSA and membrane), calculated from detailed numerical simulations, are shown to be qualitatively consistent with the trends predicted from value function theory. At low feed concentrations the work of separation increases strongly, in contrast to the thermodynamic minimum work which shows only a very gradual increase. This has important implications in relation to processes such as direct air capture of CO2 in which a concentrated product is separated from a very dilute feed. The present results suggest that the energy requirements for such processes may be much greater than that has been generally assumed.

Removal of amoxicillin from wastewater by self-made Polyethersulfone membrane using nanofiltration.

The present study investigated the performance of a self-made nanofiltration (NF) membrane for the removal of antibiotics from wastewater under changing operating conditions such as pH, initial feed concentration, operating pressure, and temperature. Amoxicillin (AMX) was used as one of the commonly prescribed antibiotics. A self-made NF membrane containing Polyethersulfone (PES), and Polyvinylpyrrolidone (PVP) was modified with Polyethylene glycol hexadecyl ether (Brij®58) surfactant. The self-made membrane was characterized by water contact angle, zeta potential, ATR-FTIR spectroscopy, and scanning electronic microscope (SEM). The obtained results showed that the AMX rejection and permeation flux by the self-made membrane varied from 56.49% to 99.09% and from 15.14 L/m2h to 110.29 L/m2h, respectively. The AMX rejection decreased at a higher level of initial feed concentration while other operating parameters such as pH, operating pressure, and temperature had a negligible effect on the removal of AMX from wastewater by the self-made NF membrane. The highest removal rate was achieved under conditions of pH 9.0, a temperature of 298 K, an operating pressure of 2 MPa, and an initial feed concentration of 20 ppm. According to the research findings, the self-made NF membrane is recommended for the removal of AMX to a considerable extent at low initial feed concentrations.

Catalytic reforming of glycerol in supercritical water with nickel-based catalysts

The catalytic performance of nickel catalysts supported on La2O3, α-Al2O3, γ-Al2O3, ZrO2, and YSZ for supercritical water reforming of glycerol was investigated. Experiments were conducted in a tubular reactor made of Inconel-625 with the temperature range of 723–848 K under a pressure of 25 MPa. Carbon formation causing operation failure was observed for α-Al2O3, γ-Al2O3 and ZrO2 at temperatures higher than 748, 798 and 823 K, respectively. Ni/La2O3 exhibited the highest H2 yield where almost complete conversion was obtained at 798 K. Moderate space velocities (WHSV = 6.45 h−1) and glycerol feed concentration (5wt.%) favor high hydrogen selectivity and yield. Methanation is favored at a low WHSV or high glycerol feed concentration, resulting in a lower H2 yield. Increasing Ni loading on the Ni/La2O3 catalyst strongly promoted the reforming, water–gas shift, and methanation reactions, which contributed significantly to the product species distribution.

Nano-cerium vanadate: A novel inorganic ion exchanger for removal of americium and uranium from simulated aqueous nuclear waste

Cerium vanadate nanopowders were synthesized by a facile low temperature co-precipitation method. The product was characterized by X-ray diffraction and transmission electron microscopy and found to consist of ∼25nm spherical nanoparticles. The efficiency of these nanopowders for uptake of alpha-emitting radionuclides 233U (4.82MeV α) and 241Am (5.49MeV α, 60keV γ) has been investigated. Thermodynamically and kinetically favorable uptake of these radionuclides resulted in their complete removal within 3h from aqueous acidic feed solutions. The uptake capacity was observed to increase with increase in pH as the zeta potential value decreased with the increase in pH but effect of ionic strength was insignificant. Little influence of the ions like Sr2+, Ru3+, Fe3+, etc., in the uptake process indicated CeVO4 nanopowders to be amenable for practical applications. The isotherms indicated predominant uptake of the radioactive metal ions in the solid phase of the exchanger at lower feed concentrations and linear Kielland plots with positive slopes indicated favorable exchange of the metal ions with the nanopowder. Performance comparison with the other sorbents reported indicated excellent potential of nano-cerium vanadate for removing americium and uranium from large volumes of aqueous acidic solutions.

A real-time simulating non-isothermal mathematical model for the passive feed direct methanol fuel cell

ABSTRACTIn order to understand the complex transport phenomena in a passive direct methanol fuel cell (DMFC), a theoretical model is essential. The analytical model provides a computationally efficient framework with a clear physical meaning. For this, a non-isothermal, analytical model for the passive DMFC has been developed in this study. The model considers the coupled heat and mass transport along with electrochemical reactions. The model is successfully validated with the experimental data. The model accurately describes the various species transport phenomena including methanol crossover and water crossover, heat transport phenomena, and efficiencies related to the passive DMFC. It suggests that the maximum real efficiency can be achieved by running the cell at low methanol feed concentration and moderate current density. The model also accurately predicts the effect of various operating and geometrical parameters on the cell performance such as methanol feed concentration, surrounding temperature, and polymer electrolyte membrane thickness. The model predictions are in accordance with the findings of the other researchers. The model is rapidly implementable and can be used in real-time simulation and control of the passive DMFC. This comprehensive model can be used for diagnostic purpose as well.

Effect of recycle ratio on the cost of natural gas processing in countercurrent hollow fiber membrane system

The separation of the countercurrent hollow fiber membrane module has been characterized adapting a “Multi-component Progressive Cell Balance” approach and incorporated within the Aspen HYSYS process simulator. The simulated data is found to exhibit good accordance with published experimental result. The study of the double staged membrane module with permeate recycle system, which was proposed to be the optimum configuration in previous works, has been extended by altering the recycle ratio of the permeate stream to study the process economics. Parameter sensitivities of typical membrane selectivity and CO2 feed concentration adapted in industrial application have been conducted. The study of high CO2 content is highlighted since it represents the future expansion of natural gas extraction considering that most of the remaining fields contain high concentration. It is observed that the recycle ratio is an important parameter to be considered in the industrial design process since it affects the gas processing cost significantly. Increasing the recycle ratio is proposed to increase the membrane area and compressor power while improving the hydrocarbon recovery, with substantial impact observed at low selectivity membrane and high CO2 feed concentration. A tradeoff must be determined among these parameters for determination of the optimal recycle ratio configuration.

Artificial neural network model for turbulence promoter-assisted crossflow microfiltration of particulate suspensions

In this study, an artificial neural network (ANN) model for the turbulence promoter-assisted crossflow microfiltration (CFMF) process was successfully established, in which the inlet velocity, transmembrane pressure (TMP) and feed concentration were taken as inputs, and the flux improvement efficiency (FIE) by turbulence promoter was taken as output. Using the trained ANN model, the FIE can be predicted under CFMF operation conditions that are not included in the training database. It reveals that the FIE first increases and then decreases with increasing either TMP or inlet velocity, and increases with increasing feed concentration. Among three input variables, TMP has the most important effect on the FIE. The optimization of MF operation conditions was largely dependent on the feed concentration. The high FIE can be obtained by exerting both high inlet velocity (>0.7m/s) and low TMP (<30kPa) at a relatively low feed concentration (<1g/L), and both high inlet velocity (>0.7m/s) and high TMP (>70kPa) at a relatively high feed concentration (>8g/L). This study provides a useful guide for the applications of turbulence promoter in CFMF processes.

Retracted Article: Selective Uptake of Uranium,Plutonium and Americium on Hydrogen Titanate Nanotubes

Hydrogen titanate nanotubes (HTNT) were prepared by hydrothermal method and characterized by SEM, TEM, XRD. The sorption efficiencies for alpha-emitting radionuclides 239Pu, 233U and 241Am were investigated. All three radionuclides studied were completely taken up by the synthesized HTNT between pH 1.00 to 6.00 from their mCi/L or mg/L feed concentration. The sorption process was sufficiently fast (complete uptake within an hour) and the standard free energy change accompanying the reaction was having very large negative value indicating it to be both thermodynamically and kinetically favourable. The sorption isotherms indicated predominant uptake of the radioactive metal ions in the solid phase of the exchanger at lower feed concentrations and linear Kielland plots with positive slopes indicated favourable exchange of the metal ions by the H+ ions in HTNT with the progress of the reaction. The Kielland plots suggested selective sorption of 233U , 239Pu and 241Am when their equivalent fractions in the solid was greater than 0.02, 0.015 and 5.0 ×10-4 , respectively and it was confirmed for americium uptake with interference studies. Even 5.00 g/L concentration of hydrogen titanate yielded 86 % sorption of 241Am after 15 minute and quantitative sorption after one hour of equilibration. The high Kd values suggest that the nano-titanate is potentially capable of removing americium, plutonium and uranium from large volumes of aqueous solutions.

Processing of glycerol under sub and supercritical water conditions

Converting glycerol, a by-product from biodiesel production into useful products and energy could contribute to a positive life cycle for the biodiesel process. One kg of glycerol is produced for every 10 kg of biodiesel and has the potential to be used as a source of H2, syngas or CH4 by an appropriate conversion process. Catalytic Supercritical Water Gasification (CSCWG) processing of crude glycerol solutions is one such viable option. Above its critical point [>221 barg, >374 °C], the properties of water, such as the low relative permittivity and high ionic product make it capable of dissolving non-polar organic compounds, allowing for high reactivity, and the ability to act as an acid/base catalyst. In this work, the degradation of glycerol by CSCWG at temperatures [400–550 °C] and pressures [170–270 barg] was investigated using a packed bed reactor (PBR) containing a Fe2O3 + Cr2O3 catalyst. Glycerol feed concentrations were between 2 and 30 wt% at flow rates from [10–65 ml/min], which gave weight hourly space velocities (WHSV) of [38–125 h−1]. The results indicated that high temperature and low feed concentration tended to increase the gas yield and selectivity toward H2 production with some char (<2.7 wt%). Syngas of up to 64 mole% was obtained with minimum 4:1 mole ratio of H2:CO. High yields of volatile hydrocarbons were also obtained: 14 and 69 mole % for methane and ethylene, respectively, which could be used for energy generation in SOFCs or turbines, reformed to syngas or converted to chemicals by an appropriate route. Pressure had little effect on the gas yields in the subcritical water region, but had a positive effect on H2 and CO2 in the supercritical region where char formation also was increased resulting in loss of catalyst activity. Complete conversion of glycerol was achieved at high temperature (550 °C). A maximum of 11 wt% liquid products were obtained at 400 °C (mainly allyl alcohol, methanol and formaldehyde). Catalyst stability was also evaluated, which was found to reach relative stability in the supercritical water environment for up to 9 h of operation.

Study on the Reaction of CCl2F2with CH4in a Dielectric Barrier Discharge Nonequilibrium Plasma

The reaction of CCl2F2 (CFC-12) with methane (in an argon bath gas) in a dielectric barrier discharge (DBD) non-thermal plasma reactor at atmospheric pressure has been investigated. The reaction (where oxygen and nitrogen are excluded from the feed gas) produced a range of gas phase products, including H2, HCl, HF, CHF3, CF3CH2F, CHClF2, CH3Cl, CH2ClF, CH2Cl2, CHCl2F and CHCl3 as well as solid products which were primarily non-crosslinked polymers. The conversion of CCl2F2 increased, from 44 to 71%, when the input energy density of the plasma was raised from 3 to 13 kJ · L−1 (applied voltage range is 13.4–14.8 kV, peak-peak). The relatively low input feed concentration of CCl2F2 and methane in the argon bath gas modifies the strong filamentary appearance of the pure argon discharge to a more diffuse appearance.

Experimental study of the supercritical water reforming of glycerol without the addition of a catalyst

Hydrogen production from the supercritical water reforming of glycerol was studied in a tubular reactor without adding a catalyst. Experiments were carried out at a pressure of 240bar, temperatures of 750–850°C, and glycerol feed concentrations of 5–30wt.%. Likewise, the residence time was changed from 12 to 160s, by handling the feed flow-rate. The dry gas is mainly consisted of H2, CO2, CO, CH4. In addition, small concentrations of glycerol were measured in the liquid phase analysis, but barely traces of others like glycolaldehyde, glyceraldehyde, dihydroxyacetone and lactic acid were detected. Thus, two probable reaction pathways are discussed, which makes it possible to explain the experimental results by using a method applicable to other similar processes. The results showed that the glycerol conversion was almost complete, except at the highest glycerol feed concentration, in which the conversion was of 88%. Hydrogen yields from 2 to 4molH2/molglycerol were obtained at high and low glycerol feed concentrations, respectively, when operating at high temperature and residence time. Besides, it was verified the catalytic effect of the reactor material (Inconel 625) from the trend of the gas product yields with time and the structured carbon nanotubes encountered. The catalytic activity of the reactor material was decreasing to reach a steady state after a few tens of operating hours. This study illustrates that the reforming of glycerol using supercritical water without added catalyst is feasible to achieve a high-yield hydrogen production, and it encourages to continue the research line, to obtain a process economically interesting.

Catalytic gasification of lignite with KOH in supercritical water

AbstractSupercritical water gasification of lignite with KOH was investigated in a batch autoclave on a wide range of conditions, that is residence time (5–30 min), mass ratio of H2O to lignite (0.5–10), temperature (400–600°C) and mass ratio of KOH to lignite (0–20%). Although lignite is difficult to be gasified in supercritical water, the results indicated that gasification efficiency about 47% was achieved at 30 min, 550°C with 10% KOH. Higher mass ratio of H2O to lignite and temperature can lead to higher gas yields and GE. It is also observed that the solid residue was dispersed at low feed concentration and consolidated at high concentration. Besides KOH's improvement of water–gas shift reaction, in this case, it is also observed that KOH also enhances the gasification of aromatics of lignite in supercritical water, which leads to higher gasification efficiency of lignite.

Kinetic and equilibrium modeling for adsorption of textile dyes in aqueous solutions by carboxymethyl cellulose/poly(acrylamide‐co‐hydroxyethyl methacrylate) semi‐interpenetrating network hydrogel

Semi‐interpenetrating network (IPN) hydrogels were synthesized by free radical copolymerization of acrylamide (AM) and hydroxyethyl methacrylate (HEMA) in aqueous solution of sodium carboxy methyl cellulose (CMC). The hydrogels were crosslinked with N,N′‐methylene bisacrylamide (NMBA). Hydrogel was also synthesized from copolymerisation of AM and HEMA. This was designated as PAMHEMA. All of these hydrogels were characterized by Fourier transforms infrared (FTIR) spectroscopy, scanning electron microscopy (SEM), X‐ray diffraction (XRD), mechanical properties, and equilibrium swelling in deionized water. These hydrogels were used for adsorption of two important textile dyes, i.e., basic fuchsin and methyl violet from water at different experimental conditions. These hydrogels were found to show high removal% and adsorption of these two dyes from water for both low and high feed concentration range. Experimental dye adsorption data were fitted to five kinetic and seven adsorption model equations with non‐linear fittings. The experimental data were observed to fit well to most of these model equations because of non‐linear fitting. POLYM. ENG. SCI., 53:2439–2453, 2013. ©2013 Society of Plastics Engineers

Potential of nanofiltration and low pressure reverse osmosis in the removal of phosphorus for aquaculture

Aquaculture activities in developing countries have raised deep concern about nutrient pollution, especially excess phosphorus in wastewater, which leads to eutrophication. NF, NF90, NF450 and XLE membranes were studied to forecast the potential of nanofiltration and low pressure reverse osmosis in the removal of phosphorus from aquaculture wastewater. Cross-sectional morphology, water contact angle, water permeability and zeta potential of these membranes were first examined. Membrane with higher porosity and greater hydrophilicity showed better permeability. Membrane samples also commonly exhibited high zeta potential value in the polyphosphate-rich solution. All the selected membranes removed more than 90% of polyphosphate from the concentrated feed (75 mg/L) at 12 bar. The separation performance of XLE membrane was well maintained at 94.6% even at low pressure. At low feed concentration, more than 70.0% of phosphorus rejection was achieved using XLE membrane. The formation of intermolecular bonds between polyphosphate and the acquired membranes probably had improved the removal of polyphosphate at high feed concentration. XLE membrane was further tested and its rejection of polyphosphate reduced with the decline of pH and the addition of ammonium nitrate.

Catalyst screening for the hydrothermal gasification of aqueous phase of bio-oil

The catalytic gasification in supercritical water of the water soluble fraction of bio-oil, either obtained directly by phase-separated pyrolysis-oil from ligno-cellulosic biomass or by hydrotreatment of that oil, is reported in this study. Several heterogeneous metal catalysts Pt, Pd, Ru, Rh, and Ni supported on alumina were tested for their gasification efficiency (GE). The GE for the metals is decreasing in the order Ru>Pt>Rh∼Pd>Ni. For optimum H2 selectivity the order of the catalysts is Pd>Ru∼Rh>Pt>Ni. Pd catalysts with different supports have been screened and no significant changes in the GE were found for the different supports. However, the composition of the product gas differed significantly with the support type. High H2 selectivity was obtained with Al2O3 and Ce–ZrO2 supports. With increasing the organic concentration from 5 to 50wt% the GE as well as the H2 and CO2 selectivities dropped significantly. High reaction temperatures, long residence time, low feed stock concentrations and high catalyst loadings favored the high carbon to gas conversion. The aqueous wastes streams obtained from the hydrodeoxygenation process for the pyrolysis oil are easier to reform in supercritical in comparison to the feedstocks obtained directly as pyrolysis condenser fraction or as phase-separated aqueous fraction. Complete conversion of the made-up and the fast pyrolysis condenser fraction was obtained at low feed concentrations (5wt%) using a continuous flow reactor in the presence of Ru/Ce–ZrO2 catalyst. However, the catalyst quickly deactivated with the made-up fraction but the same catalyst retained its stability and activity with the pyrolysis condenser fraction during the 3h test run. The supercritical water gasification seems therefore a very suitable step for treating the aqueous phase obtained after hydrotreatment of pyrolysis oil in a (biomass) refinery concept.