Zeolite Layer Research Articles

Optimizing the dual-layer Pt/Al2O3 + Cu/SSZ-13 washcoated monolith: Selective oxidation of NH3 to N2

The state-of-the-art Ammonia Slip Catalyst (ASC) has a dual-layer washcoat architecture with a bottom layer of Pt/Al2O3 and a top layer of Cu/SSZ-13. A trade-off between the NH3 conversion and N2 selectivity presents a challenge in the ASC design. While a sufficiently thick and active zeolitic top layer increases the N2 selectivity, it also imposes a diffusion barrier to the reacting species in reaching the bottom Pt layer, lowering NH3 conversion. Here we describe a systematic study to identify the ASC architecture and composition that optimizes the trade-off. The in-house synthesized ASC samples span the single layer Pt/Al2O3, conventional dual-layer Pt/Al2O3 + Cu/SSZ-13, uniform single layer of mixed Pt/Al2O3 + Cu/SSZ-13, and a hybrid design comprising a bottom layer of mixed Pt/Al2O3 + Cu/SSZ-13 and a thin top layer of Cu/SSZ-13. The overall Pt and Cu loadings are fixed across the series of samples with the Cu distributed between the two layers. The best results are obtained with the combination of a base mixed layer that provides for effective coupling between Pt and Cu active sites and a top Cu/SSZ-13 layer of an intermediate thickness and nominally half of the total Cu loading. This design has sufficient oxidation activity to convert the NH3 and reduction activity to limit NOx slippage. A 1 + 1 dimensional model which follows from our recent work [3] is effective in predicting most of the data and assists in converging on the best composition and architecture. The hybrid design exhibits a linearly decreasing dependence of the NH3 conversion and logarithmically increasing dependence of the N2 selectivity on the top layer Cu loading. The intersection of the two functions is shown to provide a good balance between the two opposing performance variables. The model is used to identify the combination of Pt loading and Cu loading distribution giving the maximum N2 yield for a specified temperature and space velocity.

Spectroscopic studies of MFI and USY zeolite layers over stainless steel 316L wire gauze meshes.

The objective of our study was to develop and optimize the in situ synthesis of zeolitic thin coatings with USY (ultrastabilised form of faujasite) and MFI (Model Five) type structure on metallic structured catalysts supports using the hydrothermal method. Thus, obtained zeolitic materials were studied in terms of their prospective activity in selective catalytic reduction of nitrogen oxides (SCR of NOx) with ammonia. Optimization of the preparation method consisted of several steps including: the pretreatment of steel carrier to obtain an adhesive surface, hydrothermal synthesis of zeolites at different conditions and adjustment of the zeolite structure type (MFI vs. USY). As a result, uniform zeolitic layers were deposited on steel supports. Prepared structured supports were ion-exchanged with copper or cobalt precursors to obtain active catalysts and then characterised by various physicochemical methods with a particular reference to the in situ Fourier-Transform Infrared Spectroscopy (FTIR), Ultraviolet-Visible Diffusion Reflectance Spectroscopy (DRS-UV/VIS) and Raman spectroscopy. For CuUSY sample, slightly better catalytic properties are related to higher copper content. In the case of Co-samples, worse catalytic properties in comparison with Cu counterparts might imply from higher concentration of Brønsted acid sites, lower cobalt loading (thus concentration of Lewis acid sites) and the presence of cobalt cation significantly in oxide form (evidenced by Raman, DRS-UV/VIS spectroscopy and by in situ FT-IR sorption studies).

Fabrication of titanosilicate pillared MFI zeolites with tailored catalytic activity

Titanosilicate pillared MFI zeolite nanosheets were successfully synthesized by infiltrating the mixed tetraethyl orthosilicate (TEOS)/tetrabutyl orthotitanate (TBOT) solvent into the gallery space between adjacent MFI zeolite layers. The obtained zeolite catalysts were characterized using powder X-ray diffraction, N2 adsorption/desorption isotherms, scanning electron microscopy, transmission electron microscopy, ultraviolet-visible spectroscopy, X-ray photoelectron spectroscopy, and Fourier-transform infrared spectroscopy techniques. The H2O2 oxidation of dibenzothiophene (DBT) was used to evaluate the catalytic performance of the obtained titanosilicate pillared MFI zeolites. The conversion of DBT and selectivity of dibenzothiophene sulfone (DBTS) were most affected by the textural properties of the zeolites. This was attributed to the DBT and DBTS molecules being larger than micropores of the MFI zeolites. The conversion of DBT and yield of DBTS could be systematically tailored by tuning the molar ratio of the TEOS/TBOT solvent. These results implied that a balance between the meso- and microporosity of zeolites and tetrahedrally coordinated Ti (IV) active sites of titanosilicate pillars can be achieved for the preparation of desired catalysts during the oxidation of bulk S compounds.

Formation of NaY zeolite membrane: influence of intermediate layer and its characterization

In the synthesis process of zeolite membranes, the zeolites crystals are crystallized and grow during crystallization period to form polycrystalline film.Secondary growth method is an effective method to synthesis high quality zeolite membranes which involves two main steps which are coating and hydrothermal treatment (HT) synthesis. There are several problems associated with the coating process in secondary growth method such as lack of good adherence of the seeds, rough surface of the support, and thermal mismatch between the zeolite seeds and supports during hydrothermal process. In order to solve these issues, an intermediate layer (buffer layer) could be applied between the support and the seeds layer hence to reduce the defects forms during the hydrothermal treatment (HT) synthesis process. In current study, two different types of intermediate layer were studied and results were compared in terms of zeolite seeds coverage on the surface of the support and zeolite layer formed during subsequent hydrothermal treatment (HT) to form zeolite membranes. The formed zeolite membranes were characterized with X-Ray diffraction (XRD) and scanning electron microscopy (SEM) and energy dispersive X-Ray spectroscopy (EDX).

Effective Inhibition of Ammonium Released from Heavily Contaminated Sediments through Selective Oxidation with Zeolite Layer

In order to study the remediation effect of heavily contaminated sediments, the experiments to repair heavily contaminated sediments were carried out under selective and nonselective oxidation conditions. Results showed that a lot of denitrifying bacteria was detected on the surface of modified zeolite by fluorescence in situ hybridization (FISH) after inoculating both nitrifying and denitrifying bacteria for 7 days. Up to 3.69 mg/g, in-situ regeneration of ammonium on zeolite loading with high ammonium (ammonium adsorption: 4.20 m/g) was obtained, which was 1.42 times that of nonselective oxidation (2.60 mg/g). This indicated that the in-situ regeneration rate of zeolite under high ammonium adsorption (5.0 mg/g) and high bacterial inoculum (80 mL/g) was enhanced. Moreover, only 1.50 mg/L total nitrogen with 84% inhibition in the overlying water under selective oxidation conditions was observed, which was 2.37 times the inhibition percentage of modified zeolite under nonselective oxidation conditions. The results illuminated that effective inhibition of ammonium released from heavily contaminated sediments can be achieved through selective oxidation with zeolite layer. At the same time, the in-situ service life of attached biofilm-modified zeolite under selective oxidation conditions was 5.87 years, which was extended by 3 years compared with nonselective oxidation conditions.

Improved performance of vacuum membrane distillation in desalination with zeolite membranes

A supported Mordenite Framework Inverted (MFI) zeolite membrane with a length of 30 cm was synthesized by the secondary growth method using a fast heating profile for the template removal (calcination) step. The presence of defects into the zeolite layer (before and after calcination) was assessed by means of single gas permeation tests. Afterwards, the membrane performance was evaluated in Vacuum Membrane Distillation (VMD) for desalination. Two cleaning procedures were applied between consecutive experiments on salty solutions and their efficiency compared. NaCl rejections of 99.9% were achieved for feeds ranging from 0.2 M to 0.9 M, dropping down to 97% for the 1.2 M feed. The highest trans-membrane flux (20.6 kg m−2 h−1) was measured for 0.2 M feed, by working at 70 °C and 120 L/h.

Effects of bubbles on the structure and performance of zeolite membranes

Defects in the zeolite layer restricts the applications of the zeolite membrane. In this study, we found that the bubbles in the synthesis solution and the interface between the support and the synthesis solution impeded the movement of the Si/Al active ingredients to the surface of the support during the membrane synthesis process, leading to the formation of defects. Accordingly, we pre-degassed the synthesis solution containing 170-mm-long ceramic tube supports under a vacuum of 0.1 MPa at room temperature before the membrane synthesis. The characterization results showed that the degassing pretreatment drove out the gases in the synthesis solution and the interface between the synthesis solution and the support, and thus eliminated pinhole defects in the zeolite layer. The permselectivity of H2 over C3H8 increased from 8.8 to 20.2 when the synthesis solution was degassing pretreated. In conclusion, the degassing pretreatment clearly eliminated the defects in the membrane.

Effect of temperature on capping efficiency of zeolite and activated carbon under fabric mats for interrupting nutrient release from sediments

We investigated the influence of temperature on the capping efficiency to interrupt the release of nutrients from lake sediments. A 3-cm layer of Zeolite (ZL) or activated carbon (AC) was placed on the contaminated sediments, and nonwoven fabric mats (NWFM) were placed on top of these capping materials. Laboratory incubation experiments were performed under three different temperatures, namely 4, 15, and 30 °C. Under the uncapped condition at 30 °C, dissolved oxygen (DO) was depleted after 30 days, while at 4 °C and 15 °C, DO was present until the end of this experiment. DO concentration in overlying water was more dependent on the temperature than capping condition. ZL/NWFM effectively blocked the release of N from the sediments, and the capping efficiencies of ZL/NWFM for NH4-N at 4, 15, and 30 °C were 98%, 96%, and 94%, respectively. For the interruption of P release, both ZL/NWFM and AC/NWFM were not effective at 4 and 15 °C. At 30 °C, however, AC/NWFM was effective, and its capping efficiencies at 30 °C for PO4-P and T-P were 74.0% and 79.9%, respectively. In summary, nutrient release from sediments was accelerated at higher temperatures, and the effect of capping was significant at high temperature.

Chromatographic Behaviour of Antibiotics on Thin Layers of Zeolite

Introduction: Antibiotics analysis is performed by many methods such as spectrophotometry, fluorimetry, polarography, and high-performance liquid chromatography. This analysis doesn't require derivatization but requires expensive equipment and extensive preparation. When more than one antibiotic is present in a formulation, interactions may occur between the drugs that must be separated before measurement. Thin-layer chromatography is a useful technique for identifying antibiotics because of the low cost, high speed, and low servicing. Silica gel adsorbents have often been used as adsorbents in all thin-layer chromatography studies. In this study, zeolite was used as an adsorbent in thin- layer chromatography with high selectivity.
 Materials and Methods: The chromatographic behaviour of amoxicillin, ampicillin, cefazolin, cefixime, ceftriaxone, cefalexin, and penicillin was studied for the first time on a thin layer of zeolite with mobile, organic, and organic- organic phases.
 Discussion: The best separation of ceftriaxone from amoxicillin, ampicillin, cefazolin, cefixolin, cefalexin, and penicillin on a thin layer of zeolite using methanol as the mobile phase. The distance and rise time are 12 cm and 110 minutes, respectively.
 Conclusion: The results of the present study showed that using the current method, the selectivity of one antibiotic from other components as well as two-component andthree-component adsorption was obtained. Quantitative identification of antibiotics was also performed in multicomponent mixtures after selection of appropriate isolates.

Performance of mesoporous HZSM-5 and Silicalite-1 coated mesoporous HZSM-5 catalysts for deoxygenation of straw fast pyrolysis vapors

•Catalytic treating of biomass fast pyrolysis vapors offers a promising route to convert many different types of lignocellulosic biomass into biofuels. Considerable research efforts have focused on using zeolite catalysts, especially the microporous HZSM-5 zeolite. Unfortunately, the zeolite’s initial high activity in forming coke and light gases reduces the overall oil yield. In this contribution, we synthesized conventional HZSM-5 zeolite, mesoporous HZSM-5 zeolite, and a core-shell catalyst consisting of mesoporous HZSM-5 zeolite coated with a thin layer (<20 nm) of silicalite-1 zeolite. The catalysts were characterized by inductively coupled plasma optical emission spectroscopy (ICP-OES), X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), N2 and Ar physisorption, temperature programmed desorption of ammonia (NH3-TPD), diffuse reflectance infrared fourier transform spectroscopy (DRIFT) spectra, and 27Al nuclear magnetic resonance (NMR). The catalysts were tested in a tandem micro-pyrolyzer system for deoxygenation of wheat straw derived fast pyrolysis vapors in a downstream catalytic fixed bed reactor and the quantitative product analysis was performed with GC-MS/FID/TCD and TGA-MS. The change in yields of different product groups was monitored during catalyst deactivation for an increasing number of pyrolysis vapor pulses and the cumulative carbon recoveries of all product streams (char, vapors, gas, and coke) were compared at different biomass-to-catalyst ratios (∼4 and ∼1) for catalyst loadings of 2 and 8 mg, respectively. In addition, the yields were compared for the same number of zeolitic acid sites. Even though the coking propensity was highest for the mesoporous HZSM-5 (5.1% carbon recovery of fed biomass at B:C = 1), it showed improved conversion of oxygenates (wt% O of vapors = 15) and a higher tolerance towards deactivation by coking compared to the conventional HZSM-5 (wt% O of vapors = 20). Coating of mesoporous HZSM-5 with silicalite-1 reduced the number of acid sites per mass of catalyst by ∼20%, which is attributed to the addition of the inert silicalite-1 layer and passivation of the external acid sites of the mesoporous HZSM-5. Compared to mesoporous HZSM-5, the added silicalite-1 shell reduced the coke yield by 43% (from 5.1–2.9 wt% of fed biomass carbon) for the same catalyst mass and by 8% (4.7 wt% of fed biomass carbon) for the same total number of acid sites. Furthermore, the tolerance towards deactivation observed for the mesoporous HZSM-5 core was largely preserved—especially for conversion of small oxygenates like acids, alcohols and aldehydes, resulting in vapors with 14 wt% O.

Synthesis of least defect NaY membranes: Defining optimum heating and cooling rate of hydrothermal treatment (HT) and application of zeta potential measurement via different seeding methods

Zeolite membrane is one type of microporous inorganic membrane which has gained so much interests among researchers as an alternative especially for gas separation. Among major challenges to produce high quality zeolite membranes with less defects are to have a good seeding and hydrothermal treatment (HT) method. On this matter, a study on the colloidal stability of the zeolite NaY seeds in the seeds solution in order to obtain homogenous seeds layer on top of the alumina support via several seeding methods and pHs of the seeds solutions were investigated. Then, the seeded samples were taken into HT process in order to form zeolite NaY membranes. During this stage, heating and cooling rates ( o C/hr) were varied in order to study their effects towards formation of zeolite membrane with least defects. Characterizations were performed by using X-Ray Diffraction (XRD) in order to identify degree of crystallization and amount of impurities while Scanning Electron Microscopy (SEM) was used in order to study surface morphology of the samples. From this study, it was found that densification effect from different seeding methods played important factor in forming zeolite membranes with least defects. Accordingly, suitable heating and cooling rates were required in order to optimize the growths of zeolite NaY seeds to form zeolite layer on top of the alumina support. In this case, due to thermal mismatch between the substrate and zeolite material, it could form some cracks on top of the alumina support. Thus, by implementing optimum heating/cooling rate, a zeolite NaY membrane with least amount of defects i.e. cracks and pinholes could be achieved with less degree of impurities i.e. zeolite NaP during HT process.

Preparation of Pd/SAPO-34/PSS composite membranes for hydrogen separation: Effect of crystallization time on the zeolite growth on PSS support

In this study, palladium composite membranes were fabricated on porous stainless steel (PSS) supports using silicoaluminophosphate (SAPO) zeolite (SAPO-34) as a diffusion barrier and substrate modifier. The vacuum-assisted seeding and secondary growth method was used to coat the SAPO-34 zeolite layer on the PSS substrates. The morphologies and microstructures of the membranes were analyzed by AFM, XRD, BET, ICP–AES, FESEM and EDX techniques. The effect of crystallization time (24, 48 and 72h) on the morphology and quality of SAPO-34 modified supports was studied. A continuous palladium layer with a thickness of about 9μm was deposited on the SAPO-34 modified PSS support (72h crystallization time) by electroless plating (ELP) route. The hydrogen permeation tests were carried out in the feed pressures range of 2–4bar and various temperatures (623, 673 and 723K). The values of the hydrogen permeance and ideal selectivity of H2/N2 for the PSM3 membrane were achieved 7.1×10–7molm–2s–1Pa–1 and 866, respectively a feed pressure of 2bar and 723K. In addition, the PSM3 membrane showed perfect stability during 260h hydrogen permeation experiment at a feed pressure of 2bar and 623K.

Fixation of Titanium Dioxide Nanoparticles on Glass Fiber Cloths for Photocatalytic Degradation of Organic Dyes.

Titanium dioxide nanoparticles were fixed on a glass fiber cloth using zeolite synthesis. This led to the formation of a photocatalytic zeolite cloth (PZC). Cloth samples were characterized by various diffraction and scanning electron microscopic techniques. The evoked results showed that zeolite X was synthesized on the PZC, while titanium dioxide was included within the PZC. Additional PZC analyses indicated that the fiber cross-section had three-layered structures. The outer layer (third layer) contained zeolite X. It was found that most of the titanium dioxide nanoparticles were present between the second (amorphous) and third layers (zeolite) but only a few existed in the zeolite layer. The photocatalytic activity of PZC was evaluated based on the degradation of methylene blue in the presence of ultraviolet irradiation. Findings showed that PZC exhibited increased adsorption and degradation activities compared to the glass fiber cloth on which only titanium dioxide nanoparticles were coated.

Constructed wetland modified by biochar/zeolite addition for enhanced wastewater treatment

Abstract Wastewater treatment for water reuse has received considerable attention owing to water resource shortage. One of the most effective wastewater treatment methods involves the use of constructed wetlands (CWs). In this study, synthetic wastewater was treated by using a biochar/zeolite CW. Phragmites australis (common reed) was translocated into two cylinders (lysimeters) that serve as vertical subsurface flow CWs. One CW (CW1) contained gravels as substrate layer, whereas the other CW (CW2) contained three substrate layers, namely, biochar, zeolite, and gravel layers. Response surface methodology was used for statistical analysis. In this study, CW2 performed better in removing pollutants from wastewater than CW1. At optimum pH (6.3) and retention time (57.4 h), 99.9% (1000 mg/L) COD, 99.9% (1000 mg/L) ammonia, 99.9% (50 mg/L) phenols, 99.9% (50 mg/L) Pb, and 99.9% (50 mg/L) Mn were removed by CW2. During this research, nitrous oxide emission was lower in CW2 than in CW1.

Enhanced denitrification by design modifications to the standard permeable pavement structure

Abstract In this study, six permeable pavement systems (PPS) with different subbase configurations were tested to evaluate their nitrogen attenuation capabilities from urban stormwater runoff. The PPS subbases were configured based on the following rationale for achieving enhanced physical, chemical and biological treatment of nitrogen compounds commonly found in urban stormwater: (i) a layer of natural zeolite to enhance nitrogen removal by ion exchange and adsorption; (ii) a layer of bark chips as a carbon donor to enhance biodegradation; (iii) a saturated zone to maintain required moisture content and reduced oxygen level for enhanced denitrification and (iv) thin sand layer(s) to limit oxygen transport for creating an anoxic zone within the PPS. A laboratory water sampling and testing program was undertaken from these PPS over a six-month period using synthetic stormwater with different pollutant concentrations while simulating varying rainfall intensities to represent typical design rainfall events considered in urban stormwater management. Our results demonstrate an improved denitrification in the PPS when a saturated zone is maintained and an organic carbon source is added in the PPS subbase. Compared with the traditional PPS, the new PPS is found to attenuate twice the amount of the total inorganic nitrogen in stormwater. Also, the attenuation of nitrogen compounds by the standard PPS is found to be reduced with rainfall duration (e.g., 54% attenuation during the first hour and only 3.5% during the 4th hour of the rainfall). The new PPS is found to attenuate 68% of total inorganic nitrogen even in the 4th hour of the rainfall event. The new PPS has the potential to become an effective stormwater quality improvement device that can contribute towards cleaner urban waterways.

Efisiensi Sistem Multi Soil Layering Pada Pengolahan Air Limbah Domestik Pada Daerah Perkotaan Padat Penduduk

The discharge of domestic wastewater in urban areas without effective treatment may result in contamination of surrounding surface water. This study explored the wastewater treatment performance of multi-soil-layering (MSL) on domestic wastewater. Domestic wastewater parameter was use are Total Suspended Solids (TSS), Total Dissolved Solids (TDS), pH, Dissolved Oxygen (DO), Turbidity and Electrical conductivity (DHL). The experiment consisted of two stages, in stage 1, three partition in the reaktor was filled with layers of rock consisting of gravel, zeolite, and mix between gravel and zeolite. In stage 2, from the best results in stage 1, then added with stuffing mixture of andosol soil and coconut shell charcoal, mixture of andosol soil and sawdust and also mixture of andosol soil and rice straw charcoal. From the result it can be concluded that MSL with zeolite layer and mixture of andosol soil and coconut shell charcoal are the best result to purify the domestic wastewater. The efficiency for TSS, TDS, pH, DO, Turbidity and EC was 64.55%; 24.52%; 4.89%; 81.88%; 76.69% and 31,77% respectively.

High performance of integrated vertical-flow constructed wetland for polishing low C/N ratio river based on a pilot-scale study in Hangzhou, China.

We investigated the treatment efficiency of micro-polluted NO3--dominated river water with low C/N ratio by five parallel pilot-scale IVCWs with different plant and substrate collocation. When the mean concentration was 2.24 and 0.193mgL-1 in influent, IVCWs achieved an average (mass) removal rate of (0.09gm-2day-1) 46.8% and (0.77gm-2day-1) 62.3% for TN and TP, respectively, during 1year of operation. Water quality was significantly improved from grade V to meet the criterion of grade IV of surface water. Through the comparison of removal rate by different IVCWs, we found that lack of carbon sources in influent limited the denitrification in the middle and bottom layers (ML, BL) of IVCW. Zeolites deployed in the upper layer (UL) of IVCW reduced the overall N removal efficiency compared with gravels, due to a stronger nitrification but weaker denitrification. Canna indica (C. indica) was superior to Arundo donax (A. donax) and Thalia dealbata (T. dealbata) for N removal in the UL of IVCW due to higher aboveground biomass accumulation and microbial removal during the first 10months. Stronger nitrification and denitrification were simultaneously facilitated near the rhizosphere of C. indica. When entered into Dec., A. donax performed higher N removal efficiency than the other two species. The internal replenishment of peats in the ML as carbon sources significantly improved N and P removal efficiency. Zeolites with stronger capacity of ammonium (NH4+) adsorption was more in favor of anammox in the BL, when compared with roseites, but both of them were not conducive to the growth of denitrifiers. However, the deployment of shale ceramisites obtained an opposite result. Gemmata and Pirellula as anammox bacteria were more enriched in the zeolite layer, whereas some anaerobic denitrifiers (Corynebacterium and Paludibacter) and heterotrophic denitrifiers including Bacillus, Geobacter, Pseudomonas, and Lactococcus were more found in shale ceramisite. Supply of peats as carbon sources in the ML was beneficial for the adhesion of anammox bacteria and denitrifiers in the BL of shale ceramisites. An ideal model composed of C. indica + A. donax (DFU)-gravel (UL)-anthracite+peat (ML)-zeolite+shale ceramsite (BL)-Acorus calamus (UFU) was proposed for treating this type of river water to achieve high efficiency.

Defect-free high-silica CHA zeolite membranes with high selectivity for light gas separation

A systematic approach is described for the fabrication of defect-free high-silica zeolite membranes with CHA (SSZ-13) topology. Home-made hydrothermally-synthesized CHA seeds were coated on porous α-alumina substrates with a pore diameter of 80 nm and by means of a further hydrothermal treatment a zeolite membrane layer was formed. In order to obtain a thin and defect-free zeolite layer, the influence on the final microstructure of seed concentration during coating, coating method (rubbing, dip- or spin-coating) and crystal growth time was investigated. The template removal procedure was optimized to avoid the formation of cracks or defects. For an optimal thermal treatment, using a step-wise temperature increase to 500 °C, the membranes exhibit CO2/CH4 permselectivities of 25–30 with CO2 permeances of around 2 x 10−7 mol m−2 s−1 Pa−1 at 22 °C and 2 bar of pressure difference. O2 plasma pre-treatment prior to template removal increased the CO2/CH4 permselectivity to 176, while maintaining the same CO2 permeance values when no pre-treatment was used. The SF6 permeances, both at low (22 °C) and high (200 °C) temperatures, were below the detection limit (2 x 10−10 mol m−2 s−1 Pa−1), which in return results in very high N2/SF6 permselectivities of more than 700.

Improved CO2 recovery from flue gas by layered bed Vacuum Swing Adsorption (VSA)

Performance of a two column five-step vacuum swing adsorption cycle is tested for CO2 enrichment and recovery from a simulated ternary flue gas mixture containing 13% CO2, 82% N2, and balance O2. The results are compared when a layered bed of commercial activated carbon (AC) (F-400, Calgon) and 13X zeolite (Z10-04, Zeochem) is employed with reference to an only single layer of AC and 13X adsorbent. With the layered bed, in which the first layer at the feed entry end is AC followed by 13X, the CO2 recovery obtained is 84% which is 42% more than that of pure 13X bed and the purity of CO2 is almost at the same level as that with 13X bed (∼90 mol%). The VSA is compared at same adsorption time, set as a 70% of CO2 breakthrough time. The CO2 purity obtained with the activated carbon bed was 76 mol% which is considerably lower compared to the bed with only zeolite 13X layer (90 mol%). The result can be explained due to higher CO2/N2 selectivity of the zeolite than activated carbon. The recovery of CO2 with activated carbon is, however, higher (97%) than zeolite (59%) due to its lower heat of CO2 adsorption compared to that with 13X. The lower heat of CO2 adsorption on the activated carbon surface implies weaker interaction and thus better desorption characteristics than 13X. VSA performance of the layered bed are also compared under different adsorption/evacuation time, bed temperature and evacuation level.

Enhanced nitrogen removal and microbial analysis in partially saturated constructed wetland for treating anaerobically digested swine wastewater

Nitrogen removal of wastewater containing high-strength ammonium by the constructed wetlands (CWs) has been paid much attention. In this study, the ability of a partially saturated CW to treat anaerobically-digested decentralized swine wastewater under varying operating parameters from summer to winter was investigated. The partially saturated CW achieved better NH4+-N and TN removal by tidal flow than intermittent flow. With surface loading rates of 0.108, 0.027, and 0.029 kg/(m2 ·d) for COD, NH4+-N, and TN, the partially saturated CW by tidal operation achieved corresponding removal efficiencies of 85.94%, 61.20%, and 57.41%, respectively, even at 10°C. When the rapid-adsorption of NH4+-N and the bioregeneration of zeolites reached dynamically stable, the simultaneous nitrification and denitrification in the aerobic zeolite layer was observed and accounted for 58.82% of the total denitrification of CW. The results of Illumina high-throughput sequencing also indicated that nitrifiers (Nitrospira and Rhizomicrobium) and denitrifiers (Rhodanobacter and Thauera) simultaneously existed in the zeolite layer. The dominant existence of versatile organic degraders and nitrifiers/denitrifiers in the zeolite layer was related to the removal of most COD and nitrogen in this zone. The contribution of the possible nitrogen removal pathways in the CW was as follows: nitrification-denitrification (86.55%)>substrate adsorption (11.70%)>plant uptake (1.15%) >microbial assimilation (0.60%).