| 1. |
- Ahlstrom-Silversand, AF, et al.
(författare)
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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
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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)
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Organophilic pervaporation : Prospects and performance
- 1999
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Ingår i: Chemical Engineering Journal. - 1385-8947. ; 73:2, s. 113-129
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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)
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Optimisation of a dosing strategy for an HC-SCR diesel exhaust after-treatment system
- 2002
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Ingår i: Chemical Engineering Journal. - 1385-8947 .- 1873-3212. ; 87:2, s. 207-217
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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)
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Transient modelling of a HC-SCR catalyst for diesel exhaust aftertreatment
- 2003
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Ingår i: Chemical Engineering Journal. - 1385-8947 .- 1873-3212. ; 92:1-3, s. 27-39
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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)
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Drying with superheated steam : Maximum drying rate as a linear function of pressure
- 2002
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Ingår i: Chemical Engineering Journal. - 1385-8947 .- 1873-3212. ; 86:1-2, s. 69-74
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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)
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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
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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
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Ingår i: Chemical Engineering Journal. - 1385-8947 .- 1873-3212. ; 84:3, s. 463-474
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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, et al.
(författare)
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CelloZIFPaper : Cellulose-ZIF hybrid paper for heavy metal removal and electrochemical sensing
- 2022
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Ingår i: Chemical Engineering Journal. - : Elsevier BV. - 1385-8947 .- 1873-3212. ; 446
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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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| 9. |
- Abdelhamid, Hani Nasser, et al.
(författare)
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Cellulose-zeolitic imidazolate frameworks (CelloZIFs) for multifunctional environmental remediation : Adsorption and catalytic degradation
- 2021
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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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| 10. |
- 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
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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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