Breakthrough Capacity Research Articles

Effective adsorption of hydrogen sulfide by intercalation of TiO2 and N-doped TiO2 in graphene oxide

In this research, hydrogen sulfide was adsorbed onto the TiO2/graphene oxide (TiO2/GO) nanohybrids. In this regard, the band gap energy of the TiO2 nanoparticles was altered through nitrogen doping which influence the chemical properties of the metal oxides. The nanoadsorbents were characterized before and after adsorption of H2S. The effect of the temperature (200−220 °C) on the H2S adsorption capacity was examined. The results showed that the increase in the temperature had a positive effect on the adsorption of H2S for all of TiO2/GO hybrid nanoadsorbents. The optimum breakthrough capacities for 5%TiO2/GO, 10 %TiO/GO and 5%N-TiO2/GO was obtained at 220 °C as 0.25, 0.20 and 0.17 gS/g sorbent, respectively. The 5%N-TiO2/GO was found to be the best nanoadsorbent due to its lower band gap, higher surface area, synergic effects and presence of active sites of N-TiO2 over the nanoadsorbents. The H2S uptake capability of the 5%N-TiO2/GO nanoadsorbent was reduced to about 30–60 % after 2 regeneration cycles due to the chemisorption.

Impact of the saturation level on the electrochemical regeneration of activated carbon in a single sequential reactor

The removal of non-biodegradable organics from industrial wastewater through adsorption onto activated carbon (AC) is a simple, effective and inexpensive process; however, as with any separation technology there is a need to regenerate the exhausted material. Here, electrochemical regeneration of AC was carried out in a single reactor alternating sequences of adsorption and regeneration. A key finding was that the contaminant (phenol here, as an industrially-relevant pollutant) saturation level of AC in the reactor directly impacts the efficiency of electrochemical regeneration. The regeneration efficiency was 20% lower and unstable with fully saturated AC, which could be explained by different phenol degradation pathways; upon reaching the exhaustion capacity of the reactor, electrochemical regeneration yielded recalcitrant polymers, whereas full mineralization could take place as long as the breakthrough capacity was not exceeded, even removing impurities originally present in the material. This cleaning effect further led to a change of porosity towards mesopores, which further improved mass transfers and resulted in sustained regeneration efficiencies close to 100%, sustained over 10 consecutive cycles. Under optimal conditions, it was thus possible to achieve over 97% phenol removal with energy consumption below 1 kWh kg−1 of AC, outcompeting traditional regeneration processes.

Treatment of Gaseous Ammonia Emissions Using Date Palm Pits Based Granular Activated Carbon.

The present work investigated the application of granular activated carbon (GAC) derived from date palm pits (DPP) agricultural waste for treating gaseous ammonia. Respective findings indicate increased breakthrough time (run time at which 5% of influent ammonia is exiting with the effluent gas) with a decrease in influent ammonia and increase in GAC bed depth. At a gas flow rate of 1.1 L/min and GAC column length of 8 cm, the following breakthrough trend was noted: 1295 min (2.5 ppmv) > 712 min (5 ppmv) > 532 min (7.5 ppmv). A qualitatively similar trend was also noted for the exhaustion time results (run time at which 95% of influent ammonia is exiting with the effluent gas). The Fourier Transform Infrared Spectroscopy (FTIR) findings for the produced GAC indicated some salient functional groups at the produced GAC surface including O–H, C–H, C–O, and S=O groups. Ammonia adsorption was suggested to result from its interaction with the respective surface functional groups via different mechanisms. Comparison with a commercial GAC showed the date palm pits based GAC to be having slightly higher breakthrough and exhaustion capacity.

Column Separation of Am(III) and Eu(III) by α-Zirconium Phosphate Ion Exchanger in Nitric Acid

The trivalent lanthanide-actinide separations are a major challenge in reprocessing of nuclear fuels. To achieve this, commonly organic extractants and solvents are utilized in elaborate processes. Here we report a simple new method that can perform a supportive or alternative role. A nanocrystalline α-zirconium phosphate ion exchanger was utilized for Eu(III)/Am(III) column separation. Comprehensive preliminary studies were done using batch experiments to optimize the final separation conditions. The distribution coefficients for Eu were determined as a function of pH (from 0 to 3) and salinity (Na, Sr). The distribution coefficients for Am were determined as a function of pH, and Eu concentration, from 1:40 to 10,000:1 Eu:Am molar ratio. The exchanger always preferred Eu over Am in our experimental conditions. Separation factors (Eu:Am) of up to 400 were achieved in binary Eu-Am solution in pH 1. The breakthrough capacity was determined in dynamic column conditions using Eu: 0.3 meq∙g−1, which is approximately 4% of the theoretical maximum capacity. Two types of hot column separation tests were conducted: (i) binary load (selective Am elution), and (ii) continuous equimolar binary feed. In both cases separation was achieved. In (i), the majority (82% of the recovered 93%) of Am could be purified from Eu with extremely high 99.999% molar purity, while alternatively even more (95% of the recovered 93%) at a lower purity of 99.7 mol %. In (ii), up to 330 L∙kg−1 of the equimolar solution per mass of the exchanger could be treated with Am purity above 99.5 mol % in the total eluate. Alternatively, up to 630 L∙kg−1 above 95 mol %, or up to 800 L∙kg−1 above 90 mol % purities.

H2S adsorption on nanostructured iron oxide at room temperature for biogas purification: Application of renewable energy

The energetic use of biogas is limited by the presence of contaminants which hinder the process and generate excessive maintenance costs. This study aims to evaluate the H2S adsorption on nanostructured iron oxide (NIO), towards applications for landfill gas cleaning. The iron oxide utilized in this study is obtained from mining residues, which provides economic and environmental advantages compared to other recognized adsorbents. In order to determine the performance of NIO, adsorption tests were performed in a lab scale with the use of synthetic gas (H2S + N2) and a continuous up-flow reactor. Experiments produced data regarding the process efficiency as a function of different operating conditions including gas hourly space velocity, H2S inlet concentration and gas humidity. Fresh and sulfided samples were characterized by SEM, TEM, BET, EDX and XRD techniques. The characterization results suggest that under lower GHSV (1,250 h-1), lower H2S inlet concentrations (200 ppm) and dry gas, the highest breakthrough capacity was recorded at 2.5 mg H2S per gram of NIO. Due to the good efficiency in removing H2S under ambient conditions, NIO can be considered a cost-effective promising alternative for biogas desulfurization.

Cyclic performance evaluation of a polyethylenimine/silica adsorbent with steam regeneration using simulated NGCC flue gas and actual flue gas of a gas-fired boiler in a bubbling fluidized bed reactor

To accelerate the deployment of Carbon Capture and Storage (CCS) based on the solid amine adsorbents towards a practical scale application relevant to Natural Gas Combined Cycle (NGCC) power plants, this study has evaluated the cyclic performance of a polyethylenimine/silica adsorbent of kg scale in a laboratory scale bubbling fluidized bed reactor. A high volumetric concentration 80−90 vol% of steam mixed with N2 and CO2 has been used as the stripping gas during a typical temperature swing adsorption (TSA) cycle. Both the simulated NGCC flue gas and the actual flue gas from a domestic gas boiler have been used as the feed gas of the CO2 capture tests with the solid adsorbent. Various characterization has been carried out to elucidate the possible reasons for the initial capacity decline under the steam regeneration conditions. The effect of presence of CO2 in the stripping gas has also been studied by comparing the working capacities using different regeneration strategies. It has been demonstrated that the breakthrough and equilibrium CO2 adsorption capacities can be stabilized at approximately 5.9 wt% and 8.6 wt%, respectively, using steam regeneration for both the simulated and actual natural gas boiler flue gases. However, using a concentration of 15 vol% CO2 in the stripping gas has resulted in a significantly low working capacity at a level of 1.5 wt%, most likely due to the incomplete CO2 desorption and degradation in a CO2 containing environment.

Bifunctional ZnO-MgO/activated carbon adsorbents boost H2S room temperature adsorption and catalytic oxidation

A series of bifunctional ZnO-MgO/activated carbon adsorbents (denoted as MgxZn1-x/AC) were synthesized. The molar ratio of Mg/(Mg + Zn) was optimized maintaining a 20 wt. % total content of oxides. The materials were characterized using adsorption of nitrogen, TEM-EDS, XPS, XRD, FT-IR, TG and CO2-TPD. On them an H2S breakthrough capacity was measured in moist and dry conditions in the absence of oxygen in a gas stream. The best adsorbent retained 113.4 mg/g at moist conditions and 96.5 mg/g at dry conditions. Besides a large surface area and pore volume, and a high dispersion of ZnO, the high H2S removal capacity was attributed to MgO, which, owing to its basicity and limited solubility in water, continuously promoted the formation of HS− important for reactive adsorption and then for catalytic oxidation. The detected surface reaction/catalytic oxidation products were ZnS, elemental sulfur and sulfates. Based on the results obtained, plausible desulfurization mechanisms were proposed.

Preparation of a Solid Amine Microspherical Adsorbent with High CO2 Adsorption Capacity.

Amine-skeleton solid-amine materials are promising adsorbents for CO2 capture from flue gas. Here, a novel solid-amine microsphere was synthesized by cross-linking the skeleton poly(ethylenimine) (PEI) with ethylene glycol diglycidyl ether in a facile one-pot W/O emulsion system. The material had a remarkable CO2 adsorption capacity of 7.28 mmol/g in the presence of moisture at 20 °C, 0.1 bar. The highest ratio of breakthrough capacity to saturation capacity was ca. 84%. According to kinetic simulation, the Avrami kinetic model could better describe the adsorption process of CO2 under different temperatures, in which the value of R2 was above 0.99 and n was between 1 and 2, indicating that both physical and chemical adsorption mechanisms were performed during adsorption. Moreover, the material had a high swelling speed. Equilibrium was established within 30 s, and the swelling ratio was 271% at equilibrium. The saturated adsorbent could be easily regenerated with a regeneration efficiency of 94.63% after six cycles. The PEI microsphere appears to be a promising candidate material for CO2 capture from flue gas.

Kinetic characterization of adsorbed toluene removal involving hybrid material catalysts— [M/13X-γ-Al2O3 (M: Ag, Ce, Mn, and Co)] in a sequential non-thermal plasma system

This study was designed to evaluate the effectiveness of adsorbed toluene removal using a coaxial cylindrical dielectric barrier discharge (DBD) reactor packed with a hybrid material catalyst [M/13X-γ-Al2O3 (M: Ag, Ce, Mn, and Co)]. All experiments were conducted at atmosphere pressure and room temperature. Results showed that Ag/13X-γ-Al2O3 (Ag/13X-Al) exhibited the highest breakthrough capacity (˜2.14 mmol) and the highest mineralization rate (MR) for toluene decomposition (˜68%) at 20 kV. The kinetic model on adsorbed toluene mineralization showed a good fit with the pseudo-second-order kinetic model for all catalysts. The model determined by discharge power (P) and initial amount of adsorbed toluene (n0) is expressed as: 0.0009n0-2.402⋅P⋅t=1/n-1/n0, where t and n denote the reaction time and the amount of adsorbed toluene, respectively. Finally, the model reliability was verified by comparing the experimental values of MR with the calculated values.

Adsorptive removal of crystal violet from aqueous solution by cross-linked chitosan coated bentonite

Crystal violet has been reported as a recalcitrant dye molecule that persists in environment for long period and poses toxic effects in environment. The objective of this work is the study of adsorption of crystal violet dye solution using cross-linked Chitosan Coated Bentonite (CCB) Beads. The adsorptive removal of crystal violet from aqueous solution CCB beads was investigated. CCB beads were prepared by cross-linking reaction between chitosan and bentonite under acidic condition. CCB beads were characterized by Fourier Infrared (FTIR) spectroscopy, scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDX) and X-ray diffraction (XRD) analysis. Batch adsorption studies were carried out by observing the effect of experimental parameters such as pH, amount of adsorbent, contact time, concentration of adsorbate, temperature, etc. The optimized working conditions were found to be the solution pH of 5.0, adsorbent dose 50 mg, contact time 30 min and dye concentration 100 mg L−1. Fixed bed column studies were also conducted with inlet dye concentrations of 10 and 20 mg L−1, feed flow rate 5 mL min−1 and bed height 4 cm. The column type continuous flow operations were used to obtain the breakthrough curves. The breakthrough capacity, exhaustion capacity and degree of column utilization were evaluated from the plots. The material was found to have high adsorption capacity towards crystal violet in column mode.

MODELING OF A RECTANGULAR CHANNEL MONOLITH REACTOR FOR SORPTION-ENHANCED WATER-GAS SHIFT

As CO2 concentration levels in the atmosphere are steadily reaching a point of no return, it is paramount that actions are taken towards mitigating emissions by improving the efficiency of existing processes. Sorption-enhanced water-gas shift (SEWGS) combines the water-gas shift reaction with in-situ adsorption of CO2 on potassium-promoted hydrotalcite (K-HTC). This enables a direct conversion of syngas into separate hot streams of H2 at feed pressure and CO2 at regeneration pressure, making the process attractive for pre-combustion carbon capture and storage (CCS) and reduction of greenhouse gas emissions. The current work is evaluating the high-temperature, high-pressure adsorption step of the SEWGS process enhanced by a novel technology which replaces common packed bed reactors with 3D-printed monolithic structures. This approach would enable an overall increase in process productivity. To this extent, innovative dynamic models based on validated competitive adsorption isotherms were developed in this work. COMSOL Multiphysics was used to develop a 1D computational fluid dynamics (CFD) model of adsorption for a fixed bed reactor in order to verify the model accuracy against existing studies. Subsequently, 2D CFD simulations were developed to describe adsorption inside monolith structures, both free and porous regions. The multi-component adsorption isotherm used in the simulations was validated with published breakthrough capacities for CO2 and H2O at different pressures. Model predictions are in agreement with expected behavior, as monolith reactors provide a more efficient mass transfer, and will be used to enhance the performance of experimental monolith structures used in SEWGS.

Simultaneous capture of NH3 and H2S using TiO2 and ZnO nanoparticles - laboratory evaluation and application in a livestock facility

Simultaneous removal of ammonia (NH3) and hydrogen sulphide (H2S) from pre-mixed gases and stored swine manure gases were investigated in laboratory and semi-pilot scale systems and in a swine production facility, using TiO2 and ZnO nanoparticles. Increase of NH3 concentration in the mixture from 50 to 500 ppmv led to higher breakthrough and equilibrium adsorption capacities, while increase of temperature had an opposite effect. Equilibrium adsorption capacities at 22 °C were in the range 6.92–11.95 mg NH3 g−1 and 1.35–3.57 mg NH3 g−1 at 280 °C. Increase of H2S concentration up to a certain level led to higher equilibrium adsorption capacities but no dependency between breakthrough adsorption capacity and H2S concentration was observed. Both breakthrough and equilibrium adsorption capacities increased with the increase of temperature. The highest equilibrium adsorption capacity of 52.31 mg H2S g−1 was obtained with 550 ppmv H2S in the mixture at 140 °C, while the lowest value was 14.55 mg H2S g−1 with 50 ppmv H2S at 22 °C. At low temperature (22 °C) NH3 adsorption occurred through both physical adsorption and chemisorption, while at 280 °C chemisorption was the dominant mechanism. A sulfidation reaction involving ZnO and H2S that was favored by higher temperatures was evident. Treating gases emitted from stored swine manure in a semi-pilot scale adsorption system led to complete elimination of NH3 and H2S. Application of a nano-based air filtration-circulation system with ZnO and TiO2 nanoparticles in a swine production room during manure handling led to removal efficiencies of 67–100% for H2S and 50–100% for NH3.

The adsorptive removal of lead ions in aquatic media: Performance comparison between advanced functional materials and conventional materials

The low permissible concentration of lead ions (Pb2+) in potable water (15 ppb) makes it even more challenging to develop highly efficient water purification technologies. Adsorption has become one of the preferred water treatment techniques for removing various metal species including Pb2+ ions. However, assessment of adsorbent capacities between the tested materials was often made in a biased manner (e.g., derivation of the maximum capacities under unrealistically high initial feeding conditions). In this work, such comparison was made in terms of partition coefficient (PC) as a key metric for the least biased evaluation to explore the best sorbents among materials with a broad range of breakthrough capacities. Nanoscale sorbents derived from carbon-based nanomaterials and MOFs are highly advantageous, as they can offer highly sensitive and selective adsorption of Pb2+ ions. In general, advanced functional materials showcased better adsorption-desorption efficiency for Pb2+ when compared to conventional materials (e.g., over three regeneration cycles). Continuous research and development for the functional materials are further required to scale down the production cost so that cost-effective technologies may be applied for environmental remediation. The future scope for Pb2+ removal techniques is discussed further with respect to the development of novel functional materials.

Exploring the options for the improvement of H2S adsorption on sludge derived adsorbents: Building the composite with porous carbons

With an objective to fully utilize a high catalytic capability of sludge-based adsorbents towards hydrogen sulfide oxidation, the composites consisting of a sewage sludge derived phase and coconut-carbon were synthesized with 10 and 30% of the latter phase. They were obtained by simple pyrolysis at 600, 800 and 950 °C. After an extensive surface characterization from the viewpoints of chemistry and porosity, their performance was tested in a hydrogen sulfide removal from a moist gas phase at ambient conditions. The results showed an improvement in the performance only for the samples obtained at 600 and 800 °C. These composites performed better than the hypothetical physical mixtures of the components and the highest hydrogen sulfide breakthrough capacity reached 22 mg/g, which was three times more than for only sludge derived samples. The improvement was linked to the availability of catalytic centers contributing to hydrogen sulfide oxidation and to an increase in the porosity from the carbon phase, where the products of reactive adsorption could be stored. On the other hand, pyrolysis of the composites at 950 °C decreased the performance in comparison with that of an only-sludge-based adsorbent (87 mg/g). It was linked to the high temperature effect of blocking the favorable chemistry of the sludge phase by the carbon particles and by blocking the pores of carbon by its sintering with the inorganic sludge-based phase.

8-Hydroxyquinoline Anchoring 3-D Networking Silica Gel Utilizing Its HOMO as a Metal Trapping Center for Selective Sample Cleanup of Cu(II), Cr(III), and Co(II) and Chemical Speciation of Sorbed Species

8-Hydroxyquinoline has been chemically anchored on three-dimensional networking silica gel (SG) for selective sample cleanup of Co(II), Cr(III), and Cu(II) amidst several other naturally occurring ions as matrix. The extractor, utilizing its frontier orbital makes a 1:1 “ion-pair complexation” with different aqua species of Co(II), Cr(III), and Cu(II), identified as {Co2(OH)(H2O)4}3+, {Cr3(OH)4(H2O)10}5+, and {Cu2(OH)2(H2O)3}2+, through first-order sorption kinetics. The chemically stable (4 M HNO3) reusable material (820 cycles) attains an appreciable breakthrough capacity (BTC) of 557, 835, and 552 μmol·g–1, respectively, for Co(II), Cr(III), and Cu(II). The process is endothermic and spontaneous and becomes more ordered upon an eventual consequence of sorption. After sorption, exploiting the differences in the stripping behavior, the analytes were sequentially resolved and retrieved with selective eluents (Co(II): 0.01 M HNO3, Cr(III): 0.05 M H2SO4 and Cu(II): 0.1 M HCl) of minimum volume (4 mL) to att...

Sorption of Lanthanum(III) and Neodymium(III) from Concentrated Phosphoric Acid by Strongly Acidic Cation Exchange Resin (SQS-6)

The feasibility of using a macroporous strongly acidic cation exchange resin (SQS-6) as an adsorbent for lanthanum(III) and neodymium(III) from phosphoric acid medium, >4.0 M, was administered using batch and column techniques. Different parameters affecting the sorption of these metal ions such as v/m ratio, acid concentration and the metal ion concentration were separately investigated. The results indicated that the sorption process is relatively fast, reaching equilibrium state within 10 min. Influence of temperature on the equilibrium distribution values was also studied to evaluate the changes in standard thermodynamic quantities where the results indicated that the sorption is endothermic and the process is spontaneous associated with increasing the randomness of the system. The adsorption results of the studied metal ions were found to obey Langmuir isotherm model over the entire studied concentration range. The recovery of La(III) and Nd(III) from the loaded resin was performed with 1.0 M citric acid at pH 4.0. The breakthrough capacity of La(III) and Nd(III) was found to be 33.55 and 17.30 mg/g, respectively. The experimental data resulting from column technique were followed Thomas and Yoon-Nelson models.

Catalytic pyrolysis of biomass with potassium compounds for Co-production of high-quality biofuels and porous carbons

This paper studied the catalytic pyrolysis of rice husk (RH) with different K-compounds (i.e., KOH, K2CO3, and K2C2O4) for co-production of biofuels and porous carbons. The decomposition of biomass occurred at lower temperature ranges due to the catalytic performance of K-compounds, following the order of KOH > K2CO3 > K2C2O4. By fast pyrolysis of RH with the K-compounds, the number of organic compounds was significantly reduced. More hydrocarbons (e.g., benzene, long-chain alkanes) were generated due to the in-situ catalytic upgrading (e.g., deoxygenation) of bio-oil. Pyrolysis of biomass with K-compounds could also accelerate the generation of unsaturated aliphatic hydrocarbons. In particular, pyrolysis of RH with K2C2O4 could result in the bio-oil with high-content of hydrocarbons and with low-content of oxygenated compounds (e.g., acids, phenols). Furthermore, the activated char with hierarchically micro-mesoporous structure was applied for toluene sorption. The pristine biochar had a relatively low adsorption time and capacity. By the chemical activation followed by the washing process, the specific surface area (SBET) of the RH-derived chars was significantly increased. The RHC-K2C2O4 had a maximum SBET of 1347 m2/g due to its mild activation process, which further contributed to a highest breakthrough time (1230 min) and capacity (609.38 mg/g) on toluene adsorption.

Probing the room-temperature oxidative desulfurization activity of three-dimensional alkaline graphene aerogel

Room-temperature catalytic oxidation of H2S has emerged as an intriguing solution to the H2S elimination, but is currently challenged by desulfurizers’ low capacity. Herein, three-dimensional alkaline graphene aerogels are prepared and demonstrated to be highly efficient catalysts for H2S oxidation, achieving 3.19 g/g of breakthrough capacity. Such high sulfur capacity is attributed to the interconnected graphene network consisting of graphene sheets, providing more product storehouse compared with traditional porous carbons. Further, a radical-induced reaction pathway of H2S oxidation is proposed that oxygen molecules could be activated to form superoxide radicals merely on graphene, which induces the dissociated HS− oxidation to sulfur. The characterization results also uncover that the formed sulfur goes through a process of nucleation and growth on graphene sheets. The current work could provide critical insights into the behavior of H2S oxidation and therefore offers a novel route of developing catalysts with large sulfur capacity at room temperature.

Nanocomposite of polyaniline functionalized Tafla: synthesis, characterization, and application as a novel sorbent for selective removal of Fe(III)

A novel PAn/Tafla nanocomposite was fabricated by the polymerization of aniline in a suspension of nano-sized Tafla using ployvinyl alcohol as a surfactant. The physicochemical characteristics including pH titration, chemical stability, and thermal stability of nanocomposite were examined. Sorption behavior of PAn/Tafla nanocomposite towards Fe(III), U(VI), Th(IV), La(III), and Ce(III) from aqueous solutions has been studied. This study revealed that the new nanocomposite is highly selective for Fe(III) ions rather than U(VI), Th(IV), La(III), and Ce(III) ions. The breakthrough capacity obtained from column study was equal to 190.0 mg/g. The new nanocomposite was applied successfully for purification of lanthanides leachate liquor.

Column adsorption of Cr (VI) from dilute aqueous solution on tailored micro-mesoporous low-cost activated carbon: performance indicators and breakthrough modeling

The adsorption technology based on low-cost adsorbents is of great interest for alternative sustainable abatement of toxic heavy metals from dilute industrial wastewaters. In this study, the performance of tailored low-cost activated carbon (AC) in column adsorption of Cr (VI) from dilute aqueous solution is evaluated using the rapid small scale column tests procedure. At solutions pH 2, the response of column performance indicators such as number of bed volumes, carbon usage rate, breakthrough capacity and column utilization for achieving effluent discharge limit of 0.5 mg L−1 Cr (VI) to changes in flow rate and bed height are studied. At breakpoints, the low-cost AC showed number of bed volumes (38–259) and column utilization (10–72%) for empty bed contact time (0.8–6.13 min). The bed regeneration efficiency was low at 48%. Also, the low-cost AC exhibited total dynamic selectivity for Cr (VI) from simulated electroplating wastewater. The breakthrough data were correlated using a mass transfer model of Michael’s constant-pattern behavior. The results of this study demonstrate the possible application of the tailored low-cost AC for efficient column adsorption of Cr (VI) from dilute wastewaters.