1. |
- Ahlstrom-Silversand, AF, et al.
(författare)
-
Modelling catalytic combustion of carbon monoxide and hydrocarbons over catalytically active wire meshes
- 1999
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Ingår i: Chemical Engineering Journal. - 1385-8947. ; 73:3, s. 205-216
-
Tidskriftsartikel (refereegranskat)abstract
- A new way of preparing catalytically active wire meshes through a thermal-spray technique is described. A metal substrate (e.g. Kanthal AF) was plasma-sprayed with a composite ceramic/polymer-powder. The polymer content of the sprayed layer was burnt off whereupon a well-defined macro-porosity was created. By treating the so obtained material with an alumina-sol the specific surface area could be increased by a factor of 50 or more. The ceramic layer was finally activated with precious metals through an impregnation step. A numerical model was developed to compare the performance of wire-mesh-, monolith- and pellets catalysts. The model describes the resistance to internal and external mass- and heat transfer and the effects of axial dispersion. The wire-mesh model was verified through experiments. Different evaluation parameters were derived to compare the catalyst performance relative to the catalyst volume, the geometric weight, the catalyst weight, the pressure drop and the temperature response. Wire-mesh catalysts offer the following advantages: high mass and heat transfer numbers, moderate pressure drop, insignificant effects of pore diffusion and axial dispersion, thermal and mechanical strength, geometric flexibility, excellent thermal response, simplicity in the catalyst recovery. The cost of a wire-mesh catalyst is expected to be competitive to other alternatives. (C) 1999 Elsevier Science S.A. All rights reserved.
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2. |
- Lipnizki, Frank, et al.
(författare)
-
Organophilic pervaporation : Prospects and performance
- 1999
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Ingår i: Chemical Engineering Journal. - 1385-8947. ; 73:2, s. 113-129
-
Tidskriftsartikel (refereegranskat)abstract
- Among the different membrane processes, organophilic pervaporation is one of the most promising technologies for environmental applications. The aim of this paper is to give a thorough introduction to organophilic pervaporation in the context of wastewater treatment. The emerging process of organophilic pervaporation is introduced together with other membrane processes relevant for environmental applications. With regard to the performance of pervaporation, an engineering model is presented which will enable ready assessment of process and module design. Sorption and coupled diffusion are covered in the model. Selection criteria for membranes and transport resistances for the mass transport as key process engineering parameters are included. The influences of permeate pressure and temperature upon performance are discussed and a description of commercial pervaporation modules given. Following a brief description of the hierarchy of waste management practice, guidelines for applying and integrating pervaporation into a process are proposed. The importance of considering hybrid processes is highlighted. A case study for phenol recovery with water treatment to 5 ppm is considered. Finally, present restrictions on the use of pervaporation in wastewater treatment such as (a) the unavailability of appropriate membranes and (b) fouling of the membrane are discussed and approaches to overcome the restrictions are presented.
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3. |
- Westerberg, Björn, et al.
(författare)
-
Optimisation of a dosing strategy for an HC-SCR diesel exhaust after-treatment system
- 2002
-
Ingår i: Chemical Engineering Journal. - 1385-8947 .- 1873-3212. ; 87:2, s. 207-217
-
Tidskriftsartikel (refereegranskat)abstract
- Several principal aspects and components of an advanced catalytic exhaust after-treatment system for NO, reduction on a heavy-duty diesel truck engine have been systematically examined and evaluated. The after-treatment system consists of de-NO, catalysts, injection of a reducing agent (diesel fuel), and computer programs to model the engine and catalysts in real time. These models are combined with a third program, a strategy, to control the injection of reducing agent during transient operation. Evaluation of the system was performed using the standard European transient cycle (ETC). The benefits and disadvantages of an oxidation catalyst upstream the reductant injection are clarified. Whereas an increased NO2/NO ratio is beneficial at larger reductant dosages, the effects of temperature levelling and delay are detrimental for system performance. The dynamic effect of introducing a strategy for distributing the reducing agent in time is elucidated. The strategy itself is presented and the process of its systematic optimisation is closely followed. Implications of the optimisation are that catalyst temperature is the most important variable in the strategy. Also, a considerable part of the reducing agent should be distributed at low and intermediate temperatures, for utilising an increased NO2/NO ratio. Furthermore, results suggest that a smooth, rather than instantaneous, adjustment of reductant dosage to driving conditions is necessary. Finally, a set-up with two injectors is examined for its potential in the application. It is shown to be of disadvantage for the ETC as a whole, but may not be so at lower exhaust gas flows.
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4. |
- Westerberg, Björn, et al.
(författare)
-
Transient modelling of a HC-SCR catalyst for diesel exhaust aftertreatment
- 2003
-
Ingår i: Chemical Engineering Journal. - 1385-8947 .- 1873-3212. ; 92:1-3, s. 27-39
-
Tidskriftsartikel (refereegranskat)abstract
- The kinetics of a catalyst for hydrocarbon-selective catalytic reduction (HC-SCR) exhaust aftertreatment has been examined by means of transient experiments on a heavy-duty diesel engine rig. The influences of temperature, NO2 concentration, and the transient injection of hydrocarbon on the conversion of NO,, CO, and hydrocarbon were studied in a systematic manner. Hydrocarbon conversion was high and NO, conversion was related to the amount of injected hydrocarbon at high temperatures. At lower temperatures hydrocarbon conversion was low and NOx conversion was not directly related to hydrocarbon injection rate. Increased exhaust NO2/NO ratio resulted in NOx conversion at lower temperatures and also in accumulation of NO., on the catalyst surface. The findings are in agreement with results from recent studies of the selective catalytic reduction of NO by propene. A catalyst model was designed in accordance to these studies and fitted to results from tailored and standard European transient cycles (ETC). The model shows reasonable agreement with experimental CO, NO, and NO2) data. Experimental hydrocarbon data are not as well reproduced, presumably due to the model approximation of hydrocarbons to one species. The full catalyst model used in the study is presented, including reaction kinetics and equations for mass and heat transfer. Mechanistic aspects are discussed and related to other studies. (C) 2002 Elsevier Science B.V. All rights reserved.
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5. |
- Elustondo, Diego, et al.
(författare)
-
Drying with superheated steam : Maximum drying rate as a linear function of pressure
- 2002
-
Ingår i: Chemical Engineering Journal. - 1385-8947 .- 1873-3212. ; 86:1-2, s. 69-74
-
Tidskriftsartikel (refereegranskat)abstract
- Drying with superheated steam (SS) as heating agent is controlled through three operative variables, the steam temperature, the recycle velocity, and the system pressure. Once the other conditions are fixed, there is an optimum pressure at which drying rate reaches its maximum value. The exact optimum conditions can be found through a differential mass and energy balance over the heat exchange area, resulting in two equations. The first one to calculate the drying rate as function of the operating conditions and the second one to find the values of those conditions which make the operation optimum. Then, using these equations, this paper shows that the relationship between maximum drying rate and pressure can be rewritten in a unique linear equation. Experiments were performed in a model system to obtain a family of drying rates versus pressure curves, and in accordance with the predicted behaviour, it was observed that all maximum drying rates lay on a straight line
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6. |
- Lindström, B., et al.
(författare)
-
Combined methanol reforming for hydrogen generation over monolithic catalysts
- 2003
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Ingår i: Chemical Engineering Journal. - 1385-8947 .- 1873-3212. ; 93:1, s. 91-101
-
Tidskriftsartikel (refereegranskat)abstract
- An experimental investigation on hydrogen generation from methanol using monolithic catalysts is presented in this paper. The activity and carbon dioxide selectivity for the reforming of methanol over various binary copper-based materials, Cu/Cr, Cu/Zn and Cu/Zr, have been evaluated. The methanol reforming was performed using steam reforming and combined reforming (CMR, a combination of steam reforming and partial oxidation). The CMR process was carried out at two modes of operation: near auto-thermal and at slightly exothermal conditions. The catalysts have been characterized using BET surface area measurement, X-ray diffraction (XRD), temperature programmed reduction (TPR) and scanning electron microscopy (SEM-EDS). The results show that the choice of catalytic material has a great influence on the methanol conversion and carbon dioxide selectivity of the reforming reaction. The zinc-containing catalyst showed the highest activity for the steam reforming process, whereas the copper/chromium catalyst had the highest activity for the CMR process. The copper/zirconium catalyst had the highest CO2 selectivity for all the investigated process alternatives.
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7. |
- Vrabel, P., et al.
(författare)
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CMA : integration of fluid dynamics and microbial kinetics in modelling of large-scale fermentations
- 2001
-
Ingår i: Chemical Engineering Journal. - 1385-8947 .- 1873-3212. ; 84:3, s. 463-474
-
Tidskriftsartikel (refereegranskat)abstract
- Transport limitation is regarded as one of the major phenomena leading to process yield reduction in large-scale fermentations. Knowledge of both the fluid dynamics and the microbial kinetics is needed for understanding and describing situations in large-scale production bioreactors. Microbial kinetics of Escherichia coli including flow metabolism was determined in lab-scale batch and fed-batch experiments. The effect of high substrate fluctuations on metabolism was quantified in scale-down experiments. This knowledge was incorporated into a flow model based on the compartment model approach (CMA). The flow model was verified by mixing time experiments on aerated reactors mixed with multiple impellers at different regimes with liquid volumes 8-22 m(3). The integral model, predicting local glucose, acetate and biomass concentrations in different parts of the reactor, was compared to three large-scale fermentations performed in two different reactors. If lab-scale kinetics was used, the biomass prediction overestimated the biomass concentration. Lab-scale kinetics modified by the results of scale-down experiments incorporating the effect of substrate fluctuations gave a rather satisfying description of biomass concentration. Glucose gradients in different parts of the reactor and acetate produced as a result of overflow metabolism were predicted on a qualitative level. The simulations show that at present the decisive factor for a successful integration of fluid dynamics and microbial kinetics is the kinetics.
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8. |
- Abdelhamid, Hani Nasser, 1986-, et al.
(författare)
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Binder-free Three-dimensional (3D) printing of Cellulose-ZIF8 (CelloZIF-8) for water treatment and carbon dioxide (CO2) adsorption
- 2023
-
Ingår i: Chemical Engineering Journal. - 1385-8947 .- 1873-3212. ; 468
-
Tidskriftsartikel (refereegranskat)abstract
- Metal-organic frameworks (MOFs) have advanced several applications, including energy, biomedical and envi-ronmental remediation. However, most of the reported MOF materials are in powder form limiting their ap-plications. This study reported the processing of MOF via three-dimensional (3D) printing of cellulose-MOFs (denoted as CelloMOFs). The 3D printing procedure involved a one-pot method including three steps: gel for-mation, 3D printing, and in-situ growth of MOF crystals. This procedure offered 3D printing of CelloMOF via a binder-free method with high loading of 67.5 wt%. The 3D-printed porous structures were used as adsorbents for carbon dioxide (CO2), dye, and heavy metal ions. They can be also used as catalysts for the degradation of water pollutants such as organic dyes. The materials can be separated easily without requiring extra procedures such as centrifugation or filtration. The materials offered complete (>99%) removal of organic dyes within 10 min with high selectivity toward anionic dyes e.g, methyl blue (MeB). The materials exhibited CO2 and heavy metal ions adsorption capacities of 0.63 mmol/g (27.7 mg/g) and 8-328 mg/g, respectively, with good recyclability. Our methodology will open new venues for advanced 3D printing of CelloMOF and its applications for water treatment and air purification.
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9. |
- Abdelhamid, Hani Nasser, et al.
(författare)
-
CelloZIFPaper : Cellulose-ZIF hybrid paper for heavy metal removal and electrochemical sensing
- 2022
-
Ingår i: Chemical Engineering Journal. - : Elsevier BV. - 1385-8947 .- 1873-3212. ; 446
-
Tidskriftsartikel (refereegranskat)abstract
- The processing of hierarchical porous zeolitic imidazolate frameworks (ZIF-8) into a cellulose paper using sheet former Rapid-Kothen (R.K.) is reported. The procedure is a promising route to overcome a significant bottleneck towards applying metal-organic frameworks (MOFs) in commercial products. ZIF-8 crystals were integrated into cellulose pulp (CP) or TEMPO (2,2,6,6-tetramethylpiperidine-1-oxyl radical)-oxidized cellulose nanofibrils (TOCNF) following an in-situ or ex-situ process; the materials were denoted as CelloZIFPaper_In Situ and CelloZIFPaper_Ex Situ, respectively. The materials were applied as adsorbents to remove heavy metals from water, with adsorption capacities of 66.2-354.0 mg/g. CelloZIFPaper can also be used as a stand-alone working electrode for the selective sensing of toxic heavy metals, for instance, lead ions (Pb2+), using electrochemical-based methods with a limit of detection (LOD) of 8 mu M. The electrochemical measurements may advance 'Lab-onCelloZIFPaper' technologies for label-free detection of heavy metal ions.
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10. |
- Abdelhamid, Hani Nasser, et al.
(författare)
-
Cellulose-zeolitic imidazolate frameworks (CelloZIFs) for multifunctional environmental remediation : Adsorption and catalytic degradation
- 2021
-
Ingår i: Chemical Engineering Journal. - : Elsevier BV. - 1385-8947 .- 1873-3212. ; 426
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Tidskriftsartikel (refereegranskat)abstract
- The crystal growth of zeolitic imidazolate frameworks (ZIFs) on biopolymers such as cellulose is a promising method for obtaining hybrid materials that combinenatural and synthetic materials. Cellulose derivative viz. 2,2,6,6-tetramethylpiperidine-1-oxylradical (TEMPO)-mediated oxidized nanocellulose (TOCNF) was used to modulate the crystal growth of ZIF-8 (denoted as CelloZIF-8) and ZIF-L (CelloZIF-L). The synthesis procedure occurred in water at room temperature with and without NaOH. The reaction parameters such as the sequence of the chemical's addition and reactant molar ratio were investigated. The phases formed during the crystal growth were monitored. The data analysis ensured the presence of zinc hydroxide nitrate nanosheets modified TOCNF during the crystallization of CelloZIFs. These phases were converted to pure phases ofCelloZIF-8 and CelloZIF-L. The resultant CelloZIFs materials were used for the adsorption ofcarbon dioxide (CO2), metal ions, and dyes. The materials exhibited high selectivity with reasonable efficiency (100%) toward the adsorption of anionic dyes such as methyl blue (MeB). They can also be used as a catalyst for dye degradation via hydrogenation with an efficiency of 100%. CelloZIF crystals can be loaded into a filter paper for simple, fast, and selective adsorption of MeB from a dye mixture. The materials are recyclable for five cycles without significant loss of their performance. The mechanisms of adsorption and catalysis were also investigated.
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11. |
- Abromaitis, V., et al.
(författare)
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Effect of shear stress and carbon surface roughness on bioregeneration and performance of suspended versus attached biomass in metoprolol-loaded biological activated carbon systems
- 2017
-
Ingår i: Chemical Engineering Journal. - : Elsevier. - 1385-8947 .- 1873-3212. ; 317, s. 503-511
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Tidskriftsartikel (refereegranskat)abstract
- The bioregeneration of activated carbon (AC) in biological activated carbon (BAC) systems is limited by sorption-desorption hysteresis and transport between the adsorbent and biomass. In this study, we investigated these limitations and whether a biofilm covering the AC surface is required. Consequently, BAC reactors were operated at different shear stress and AC surface smoothness, since this may affect biofilm formation. The experiments were carried out in BAC and blank reactors treating synthetic wastewater containing the pharmaceutical metoprolol. After start-up, all reactors removed metoprolol completely; however, after 840 h the removal dropped due to saturation of the AC. In the blank reactors, the removal dropped to 0% while in the BAC reactors removal recovered to >99%, due to increased biological activity. During the initial phase, the metoprolol was adsorbed, rather than biodegraded. At the end, the AC from the BAC reactors had higher pore volume and sorption capacity than from the blank reactors, showing that the AC had been bioregenerated. At high shear (G = 25 s(-1)), the rough AC granules (R-a = 13 mu m) were covered with a 50-400 gm thick biofilm and the total protein content of the biofilm was 2.6 mg/gAC, while at lower shear (G = 8.8 s(-1)) the rough AC granules were only partly covered. The biofilm formation at lower shear (G = 8.8 s(-1)) on smooth AC granules (R-a = 1.6 mu m) was negligible. However, due to the presence of suspended biomass the reactor performance or bioregeneration were not reduced. This showed that direct contact between the AC and biomass was not essential in mixed BAC systems. The microbial analyses of the suspended biomass and the biofilm on AC surface indicated that metoprolol was mainly biodegraded in suspension. (C) 2017 Elsevier B.V. All rights reserved.
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12. |
- Achour, Abdenour, 1980, et al.
(författare)
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Evaluation of kraft and hydrolysis lignin hydroconversion over unsupported NiMoS catalyst
- 2023
-
Ingår i: Chemical Engineering Journal. - : Elsevier BV. - 1385-8947. ; 453
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Tidskriftsartikel (refereegranskat)abstract
- Catalytic hydroconversion of Kraft and hydrolysis lignins was for the first time compared in a batch reactor over an unsupported NiMoS-SBA catalyst. We also report the effect of key reaction parameters on the yields and properties of the products. The results obtained at 20 wt% catalyst loading for hydrolysis lignin showed the highest monomer yield of 76.0 wt%, which consisted of 39 wt% aromatics with the lowest alkylphenolics yield of 10.1 wt%. Identical operating conditions, 400 °C, 80 bar, 5 h at 10 wt% catalyst loading, were used to compare both lignins and the highest monomer yield (64.3 wt%) was found for the hydrolysis lignin, consisting of 16.0 wt% alkylphenolics and 20.1 wt% aromatic compounds. These values are considerably higher than those for Kraft lignin with its 47.0 wt% monomer yield. We suggest that the reason for high yields of monomeric units from hydrolysis lignin is that it is more reactive due to its lower ash and sulfur contents and the chemical structural differences compared to the Kraft lignin. More precisely, the bio-oil from hydrolysis lignin contained higher yields of small molecules, sourced from ring-opening of cellulose in the hydrolysis lignin, which could stabilize the reactive oligomeric groups. These yields were two to seven times higher from kraft and hydrolysis lignin, respectively, compared to those obtained without catalyst. The results showed that the NiMoS-SBA catalyst is a promising catalyst for reductive depolymerization of lignin and in addition that the regenerated catalyst had good stability for multiple reaction cycles.
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13. |
- Ahrens, Lutz
(författare)
-
A recent overview of per- and polyfluoroalkyl substances (PFAS) removal by functional framework materials
- 2023
-
Ingår i: Chemical Engineering Journal. - : Elsevier BV. - 1385-8947. ; 452
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Tidskriftsartikel (refereegranskat)abstract
- Per-and polyfluoroalkyl substances (PFAS) are a class of toxic and bioaccumulative compounds affecting environmental and human health. Conventional wastewater treatment processes are ineffective at remediating these persistent chemicals. While functional framework materials have been shown to remove PFAS via adsorption and catalytic degradation, there is an on-going debate about their practical use in water purification. Inspired by recent research on typical functional framework materials, including zeolites, metal-organic frameworks (MOFs), and covalent organic frameworks (COFs), our review summarizes the principles of their design, properties, and applications with a special emphasis on PFAS removal. The potential of framework material for catalytic degradation of PFAS is constructively discussed, based on limited studies thus far. Finally, the challenges of using framework materials to remove and degrade PFAS in wastewater are presented along with sustainable design prospects to improve the technology. The current review provides new insights in advancing framework materials for PFAS elimination from contaminated waters.
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14. |
- Al-Sabahi, J., et al.
(författare)
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Visible light photocatalytic degradation of HPAM polymer in oil produced water using supported zinc oxide nanorods
- 2018
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Ingår i: Chemical Engineering Journal. - : Elsevier B.V.. - 1385-8947 .- 1873-3212. ; 351, s. 56-64
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Tidskriftsartikel (refereegranskat)abstract
- Polymer flooding displacement ability during petroleum extraction from the earth's crust plays an important role in enhanced oil recovery processes. Produced water, as a byproduct, still contain high concentrations of petroleum hydrocarbons and partially hydrolyzed polyacrylamide (HPAM) which is a serious environmental concern. Remediating produced water economically is a big challenge for meeting the permissible discharge limits leading to failure in the effectiveness of the conventional water treatment technologies. Advanced oxidation processes (AOPs) are playing increasing role in the treatment of polluted water and is receiving much attention in recent times as a green and safer water treatment technology. Here we report a new approach to use vertically aligned zinc oxide nanorods (ZnO NRs) supported on substrates engineered for improving their visible light harvesting capacity for effective solar photocatalytic degradation of HPAM. The viscosity of collected oilfield produced water containing HPAM were found to be reduced dramatically when the samples are photocatalytically degraded using ZnO nanorod catalysts irradiated with simulated solar light showing a reduction of 51% within 6 h. With high pressure liquid chromatography 68, 62, 56 and 45% removal of 25, 50, 100 and 150 ppm HPAM, respectively, was demonstrated. The pH of the solution was observed to move to acidic region due to acetamide, nitrate, propionamide and acetic acid which are the intermediate byproducts formed during degradation as determined by mass spectrometry. Zinc oxide nanorod coatings showed about 74% removal efficiency over 5 cycles with less than 1.2% removal of zinc ions after 6 h of light irradiation.
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15. |
- Al-Soubaihi, Rola, et al.
(författare)
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Low-temperature CO oxidation by silver nanoparticles in silica aerogel mesoreactors
- 2023
-
Ingår i: Chemical Engineering Journal. - : Elsevier BV. - 1385-8947 .- 1873-3212. ; 455, s. 140576-
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Tidskriftsartikel (refereegranskat)abstract
- Low-temperature carbon monoxide (CO) oxidation on silver/silica aerogel (Ag/SiO2 AG) catalyst prepared by one-pot sol-gel synthesis followed by supercritical ethanol drying method is reported. Highly stable and sinterproof catalyst led to easy reactant diffusion to the active sites. The Ag/SiO2 AG catalyst showed enhanced catalytic activity toward low-temperature CO oxidation by preventing agglomeration of silver nanoparticles inside pores and facilitating well-dispersed active sites to enhance the mass heat transfer in the mesopores. Catalyst pretreatment conditions were found to play a crucial role in achieving high CO conversion efficiency at low light-off temperatures. Inverse counter-clockwise CO oxidation hysteresis was found to occur after the first run. The active sites contributing to this enhanced catalytic behavior were confirmed to be Ag0 from XPS, XRD, and TEM analysis. The catalyst exhibited good thermal stability up to 450 degrees C over repeated number of cycles.
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16. |
- Alzahrani, Faris, et al.
(författare)
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Deactivation of the preferential oxidation of CO in packed bed reactor by 3D modelling and near-infrared tomography
- 2019
-
Ingår i: Chemical Engineering Journal. - : ELSEVIER SCIENCE SA. - 1385-8947 .- 1873-3212. ; 378
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Tidskriftsartikel (refereegranskat)abstract
- Scaling up the results on catalyst deactivation to industrial operations, where transport phenomena are of significance, is often not straightforward. The operations of industrial reactors are judiciously focused on the dynamics of the deactivation along the axial length of the reactors, which are generally known approximately. Processes of strong energy release or fast chemical kinetics, such as oxidation reactions, cracking, etc., are associated with a deactivation where the time characteristics of the flow and transports are of magnitudes of the deactivation time-on-stream. Local deactivation of the preferential oxidation of CO was investigated by three-dimensional modelling of flow, mass and heat transfers inside a packed-bed reactor and validated by near-infrared tomography. The profiles of deactivation were sensitive to the rates of deactivation, heat transfer by dispersion and intra-particle mass transfer. At pore scale of the packing, pronounced deactivation was revealed near the wall due to a preferential flow circulation. The deactivation progressed at the exteriors of the catalytic particles, particularly over the regions in contact with the convective flow. Unlike the mass dispersion, the heat dispersion promoted the deactivation by shifting the moving waves of deactivation upstream, leading to asymmetrical maps inside the catalytic particles.
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17. |
- Anugwom, Ikenna, et al.
(författare)
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In quest for the optimal delignification of lignocellulosic biomass using hydrated, SO2 switched DBU MEASIL switchable ionic liquid
- 2016
-
Ingår i: Chemical Engineering Journal. - : Elsevier. - 1385-8947 .- 1873-3212. ; 297, s. 256-264
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Tidskriftsartikel (refereegranskat)abstract
- In this paper, various process parameters aiming at optimal short-time-high-temperature (STHT) process were studied upon fractionation of Nordic woody biomass into its primary constituents. Highly diluted, aqueous 'SO2-switched' switchable ionic liquid (SIL) based on an alkanol amine (monoethanol amine, MEA) and an organic superbase (1,8-diazabicyclo-[5.4.0]-undec-7-ene, DBU) was applied. The ultimate goal was to develop a more sustainable, environmentally friendly and cost efficient systems for efficient separation of the lignocellulosic fractions. One of the main products from the SIL fractionation is cellulose-rich pulp with very low lignin content, complemented with hemicelluloses. The NMR results reveal that substantial removal of lignin occurs even when relatively low amount of SIL was used. Further, a simple mathematical model describing the dissolution of the lignocellulose components (hemicellulose and lignin) and weight loss of wood as a function of time is described. Moreover, the most efficient process involved the use of SpinChem (R) rotating bed reactor while upon use of a flow through (loop) reactor, promising results were obtained at a treatment time of 4 h. Still, all the reactor systems studied gave rise to a rather low removal of hemicelluloses which mean that the solvent system is primary selective towards lignin dissolution.
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18. |
- Arif, Muhammad, et al.
(författare)
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Unraveling the synergy of interface engineering α-MnO2/Bi2WO6 heterostructures and defective active sites for superdurable photocatalysis: Mechanistic insights into charge separation/transfer
- 2023
-
Ingår i: Chemical Engineering Journal. - : ELSEVIER SCIENCE SA. - 1385-8947 .- 1873-3212. ; 475
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Tidskriftsartikel (refereegranskat)abstract
- The construction of visible-light-driven hybrid heterostructure photocatalysts is of great significance for environmental remediation, although the utilization of strong visible-light response photocatalysts with high efficiency and stability remains a major challenge. Defect engineering is an excellent way to introduce metal cation vacancies in materials, thereby ensuing in highly enhanced catalytic performance. Inspired by this, we effectively constructed a built-in interface alpha-MnO2/Bi2WO6 heterostructure with abundant intimate interfaces and defective Mn3+/Mn4+ active sites for photocatalytic tetracycline hydrochloride (TC-HCl), hexavalent chromium Cr6+ reduction, and Escherichia coli (E. coli) inactivation. The experimental results, such as the active species test and X-ray photoelectron spectroscopy, indicated that the defective sites Mn3+/Mn4+, surface oxygen vacancies, and Bi(3+x)+ boosted the visible light absorption, and highly enhanced the photoinduced charge separation/transfer. Furthermore, experimental and DFT calculations reveal the high charge density at the built-in interface heterostructure and the Z-scheme charge transfer mechanism during the photocatalytic process. The results further reveal that O-2(-) and O-1(2) are the main reactive active species contributing to the photocatalytic reaction. The exceptional TC-HCl decomposition activity of the alpha-MnO2/Bi2WO6 heterostructure (97.56%, 2.31, and 2.04 times higher than bulk), enhanced reaction kinetics (K-app = 0.041 min(-1), 6.4, and 5.2 times higher than bulk), removal rate of 80.3%, Cr6+ reduction to Cr3+ (98.56%, K-app = 0.0599 min(-1)), and almost 100% bacterial inactivation compared to bulk alpha-MnO2 (42.22%) and Bi2WO6 (47.76%), were mainly due to the enhanced charge separation/transfer at the built-in interface and high charge density. This study opens new horizons for constructing Z-scheme MnO-based interface heterostructures with abundant defect sites for exceptional photocatalytic applications.
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19. |
- Arora, Prakhar, 1987, et al.
(författare)
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Kinetic study of hydrodeoxygenation of stearic acid as model compound for renewable oils
- 2019
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Ingår i: Chemical Engineering Journal. - : Elsevier BV. - 1385-8947. ; 364, s. 376-389
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Tidskriftsartikel (refereegranskat)abstract
- The kinetics during hydrodeoxygenation (HDO) of stearic acid (SA) was investigated to explore the fundamental chemistry and the reaction scheme involved for the reaction with a sulfide NiMo/Al2O3catalyst. Intermediates like octadecanal (C18 O) and octadecanol (C18 OH) were used to resolve the reaction scheme and explain the selectivity for the three major reaction routes (decarboxylation, decarbonylation and direct-HDO). Several reaction parameters, like temperature, pressure, feed concentration and batch-reactor stirring rate, were explored for their effect on changes in rate of conversion and selectivity. A weaker dependence on pressure (40–70 bar) and strong dependence on temperature (275–325 °C) was found for the product distribution during HDO of SA. A model based on Langmuir–Hinshelwood type kinetics was developed to correlate the experimental data. The model well predicted trends in variation of selectivities with the reaction conditions, in part by including intermediates like octadecanol and octadecanal and it predicted phenomenon like inhibiting effects of the fatty acid. The proposed kinetic model is expected to be applicable to liquid phase HDO of different renewable feeds containing long chain fatty acids, methyl esters and triglycerides etc.
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20. |
- Ashour, Radwa M., et al.
(författare)
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Selective separation of rare earth ions from aqueous solution using functionalized magnetite nanoparticles : kinetic and thermodynamic studies
- 2017
-
Ingår i: Chemical Engineering Journal. - : Elsevier. - 1385-8947 .- 1873-3212. ; 327, s. 286-296
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Tidskriftsartikel (refereegranskat)abstract
- Separation of rare earth ions (RE3+) from aqueous solution is a tricky problem due to their physico-chemical similarities of properties. In this study, we investigate the influence of the functionalized ligands on the adsorption efficiency and selective adsorption of La3+, Nd3+, Gd3+ and Y3+ from aqueous solution using Magnetite (Fe3O4) nanoparticles (NPs) functionalized with citric acid (CA@Fe3O4 NPs) or L-cysteine (Cys@Fe3O4 NPs). The microstructure, thermal behavior and surface functionalization of the synthesized nanoparticles were studied. The general adsorption capacity of Cys@Fe3O4 NPs was found to be high (98 mg g−1) in comparison to CA@Fe3O4 NPs (52 mg g−1) at neutral pH 7.0. The adsorption kinetic studies revealed that the adsorption of RE3+ ions follows a pseudo second-order model and the adsorption equilibrium data fits well to the Langmuir isotherm. Thermodynamic studies imply that the adsorption process was endothermic and spontaneous in nature. Controlled desorption within 30 min of the adsorbed RE3+ ions from both Cys@Fe3O4 NPs and CA@Fe3O4 NPs was achieved with 0.5 M HNO3. Furthermore, Cys@Fe3O4 NPs exhibited a higher separation factor (SF) in the separation of Gd3+/La3+, Gd3+/Nd3+, Gd3+/Y3+ ions compared to CA@Fe3O4 NPs.
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21. |
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22. |
- Avila, Marta, et al.
(författare)
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Surface functionalized nanofibers for the removal of chromium(VI) from aqueous solutions
- 2014
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Ingår i: Chemical Engineering Journal. - : Elsevier BV. - 1385-8947 .- 1873-3212. ; 245, s. 201-209
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Tidskriftsartikel (refereegranskat)abstract
- Polyacrylonitrile (PAN) nanofibers functionalized with amine groups (PAN-NH2) were prepared using a simple one-step reaction route. The PAN-NH2 nanofibers were investigated for the removal of chromium(VI) from aqueous solutions. The adsorption and the kinetic characteristics were evaluated in batch process. The adsorption process showed pH dependence and the maximum Cr(VI) adsorption occurred at pH = 2. The Langmuir adsorption model described well the experimental adsorption data and estimated a maximum loading capacity of 156 mg/g, which is a markedly high value compared to other adsorbents reported. The kinetics studies indicated that the equilibrium was attained after 90 min and the experimental data followed a pseudo-second order model suggesting a chemisorption process as the rate limiting step. X-ray Photoelectron Spectroscopy (XPS) and Fourier transform infrared spectroscopy (FT-IR) revealed that the adsorption of Cr(VI) species on PAN-NH2 was facilitated through both electrostatic attraction and surface complexation. High desorption efficiency (> 90%) of Cr(VI) was achieved using diluted base solutions that may allow the reuse of PAN-NH2 nanofibers.
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23. |
- Azis, Muhammad Mufti, 1983, et al.
(författare)
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Kinetic modeling of H2-assisted C3H6 selective catalytic reduction of NO over silver alumina catalyst
- 2015
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Ingår i: Chemical Engineering Journal. - : Elsevier BV. - 1385-8947. ; 278, s. 394-406
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Tidskriftsartikel (refereegranskat)abstract
- A global kinetic model was developed for C3H6-SCR consisting of NO oxidation, C3H6 oxidation and C3H6-SCR reactions with and without H-2 over Ag-Al2O3. The model is based on a dual role of H-2 to remove inhibiting nitrates from the active sites as well as to modify/form new active Ag sites. For model development, a range of temperature programmed reaction (TPR) and transient feed experimental conditions were used. The proposed model was eventually also validated with additional transient experimental data. The kinetic model proposed in this study predicts the experimental data well for a wide-range of feed conditions. Evaluation of mass transfer resistance in the washcoat indicated that during H-2-assisted C3H6-SCR, mild internal mass transfer resistance for NO was predicted to be important already at 250 degrees C.
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24. |
- Azis, Muhammad Mufti, 1983, et al.
(författare)
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Microkinetic modeling of H2-assisted NO oxidation over Ag-Al2O3
- 2013
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Ingår i: Chemical Engineering Journal. - : Elsevier BV. - 1385-8947. ; 221, s. 382-397
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Tidskriftsartikel (refereegranskat)abstract
- A microkinetic model has been assembled to investigate the mechanism for NO oxidation over a monolith-supported Ag–Al2O3 catalyst both in the presence and absence of H2. The effect of H2 examined in the kinetic model was to reduce self inhibiting surface nitrate species on active silver sites. A reduced factorial design of inlet experimental conditions was used to generate transient experimental data. The kinetic model was developed based on a single channel reactor model which accounted for mass and heat transfer between gas and catalyst washcoat as well as mass transport resistance in the washcoat. In general, the modeling results could reproduce the transient experimental data well with correct levels of outlet concentrations and time scales for transient responses. It was found that the effect of increased NO and NO2 inlet concentration had a negative correlation with the NO oxidation conversion, which in the model was considered related to the formation of nitrate surface species. In addition, the model in agreement with experiments, clearly showed that H2 promoted the NO oxidation mainly at low temperature and this effect tended to decrease at elevated temperatures. When H2 was present in the feed, the kinetic model showed that H2 was consumed rapidly in the front part of the monolith. This was also seen in the experiments where in all cases H2 was entirely consumed. The rapid reaction of H2 along with resulting transport limitations indicated that the H2 promotion of the NO oxidation reaction may have been isolated to only a portion of the catalyst.
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25. |
- Bai, Xue, et al.
(författare)
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D35-TiO2 nano-crystalline film as a high performance visible-light photocatalyst towards the degradation of bis-phenol A
- 2019
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Ingår i: Chemical Engineering Journal. - : ELSEVIER SCIENCE SA. - 1385-8947 .- 1873-3212. ; 355, s. 999-1010
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Tidskriftsartikel (refereegranskat)abstract
- Dye-sensitized photocatalytic suspension system for wastewater treatment is still limited in practice due to particle aggregation, fast charge carrier recombination, poor stability and recycling issue. In this study, we combine TiO2 nano-crystalline film with D35 organic dye to fabricate a new visible-light photocatalyst D35-TiO2, which exhibits excellent visible light absorption. Its transient photocurrent is almost 10 times higher than pure TiO2 under visible light illumination (lambda > 420 nm). Besides the well characterizations of the D35-TiO2 film, e.g., SEM, EDS, TEM, XRD, UV-Vis DRS, XPS, PL and I-T, degradation of bis-phenol A (BPA) is performed as the model reaction to test its photocatalytic activity. Meanwhile, we employ external bias in the reaction system to further enhance the photogenerated charge carrier separation, and improve the photocatalytic efficiency. Under the better experimental conditions of initial BPA concentration (5 mg/L), initial pH (pH 7), external bias (0.25 V) and sensitizer concentration (0.1 mM), BPA is almost completely degraded in 300 min, and the four intermediates are gradually mineralized. The ecotoxicity of BPA also decreases significantly after the photo-degradation. During the reaction, center dot O-2(-) plays a dominant role, meanwhile center dot OH and h(D35)(+) also contribute to the BPA degradation. After five cycles, the D35-TiO2 film still maintain the normal photocatalytic activity. Due to the high stability and recyclability, the D35-TiO2 nano-crystalline film provides a sustainable way for degrading micropollutants in wastewater.
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