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The biocatalytic performance of immobilized enzyme systems depends mostly on the intrinsic properties of both biomolecule and support, immobilization technique and immobilization ...conditions. Multi-walled carbon nanotubes (MWCNTs) possess unique features for enzyme immobilization by adsorption. Enhanced catalytic activity and stability can be achieved by optimization of the immobilization conditions and by investigating the effect of operational parameters.
Laccase was immobilized over MWCNTs by adsorption. The hybrid material was characterized by Fourier transformed infrared (FTIR) spectroscopy, scanning and transmission electron microscopy (SEM and TEM, respectively). The effect of different operational conditions (contact time, enzyme concentration and pH) on laccase immobilization was investigated. Optimized conditions were used for thermal stability, kinetic, and storage and operational stability studies.
The optimal immobilization conditions for a laccase concentration of 3.75μL/mL were a pH of 9.0 and a contact time of 30min (522 Ulac/gcarrier). A decrease in the thermal stability of laccase was observed after immobilization. Changes in ΔS and ΔH of deactivation were found for the immobilized enzyme. The Michaelis–Menten kinetic constant was higher for laccase/MWCNT system than for free laccase. Immobilized laccase maintained (or even increased) its catalytic performance up to nine cycles of utilization and revealed long-term storage stability.
The production of high purity hydrogen (99.99+%) at reduced cost is an important and sought target. This work is focused on the separation of hydrogen from a five component mixture (H
2/CO
2/CH
...4/CO/N
2) by pressure swing adsorption. A complete mathematical model that describes the dynamic behaviour of a PSA unit is presented. This model is applied in the study of the behaviour of both single column and four columns PSA processes with layered activated carbon/zeolite beds and with an eight steps cycle. In the single column simulation, a 99.9994% purity hydrogen stream is attained at the end of the feed step for a process hydrogen recovery of 51.84% and a productivity of
59.6
mol
H
2
/
kg
ads
/
day
. The multicolumn simulation predicts a hydrogen recovery and purity, respectively, of 52.11% and 99.9958%. The influence of feed flow rate, purge to feed ratio and lengths of both adsorbent layers on the system performance is assessed. It is shown that the introduction of the zeolite layer improves both the purity and recovery of the process. Reduced models are formulated based on the sequential identification of controlling resistances in the complete model. The predictions of the reduced models are evaluated by comparing their results with those obtained from the complete model. It is shown that the model that merely takes into account the micropore resistance (described by the LDF model) and assumes thermal equilibrium only between the gas and solid phases satisfactorily predicts the behaviour of the pressure swing adsorption unit.
Powder, agglomerates, and tablets of the microporous zirconium(IV) terephthalate metal–organic framework UiO-66 were evaluated for the selective adsorption and separation of xylene isomers in the ...liquid phase using n-heptane as the eluent. Pulse experiments, performed at 313 K in the presence of n-heptane, revealed the o-xylene preference of this material, which was further confirmed by binary and multicomponent breakthrough experiments in the presence of m- and p-xylene, resulting in selectivities at 313 K of 1.8 and 2.4 with regards to m-xylene and p-xylene, respectively. Additionally, because p-xylene is the less retained isomer, UiO-66 presents a selectivity pattern that is reverse of that of the xylenes' molecular dimension with respect to shape selectivity. The shaping of the material as tablets did not significantly change its selectivity toward the o-xylene isomer or toward p-xylene, which was the less retained isomer, despite a loss in capacity. Finally, the selectivity behavior of UiO-66 in the liquid n-heptane phase makes it a suitable material for o-xylene separation in the extract (heavy product) or p-xylene separation in the raffinate (light product) by simulated moving bed technology.
The valorization of wastewaters from the fish canning industry is of great concern, not only because of the high quantities generated, but also economic and environmental benefits may result from a ...proper treatment approach of the waste generated while reducing costs related to wastewater discharge.
A limiting factor for reuse and recycling treated fish canning wastewater into an industrial plant and also for other uses is the high salt content, which persists even after conventional treatment. So, the reuse of fish canning industrial wastewater was assessed by combining conventional treatments, such as sedimentation, chemical coagulation-flocculation and aerobic biological degradation (activated sludge process) followed by a polishing step by reverse osmosis (RO) and ultraviolet (UV) disinfection.
In this investigation all these processes were optimized in order to remove essentially the effluent suspended particles (primary treatment), the organic matter content in the biological aerated reactor (secondary treatment) and, finally, the remaining salts and microorganisms (tertiary treatment).
The overall removal efficiencies obtained were: 99.9% for dissolved organic carbon (DOC), 99.8% for oil and grease (O&G), 98.4% for total suspended solids (TSS), above 96% for anions and cations and 100% for heterotrophic bacteria expressed as colony-forming units (CFU). The final clarified effluent was found to have the quality requirements to be recycled or reused in the industrial plant, allowing the reduction of the effluent to be discharged, the water use and the costs of tap water for industrial use.
As regards the energy and chemicals costs, to obtain a treated effluent to be reused in the process costs 0.85 €/m3. This value can be reduced by about 60% if the goal is only to meet the legislated standards for the effluent discharge into water bodies. Tap water for the industrial plant costs about 2.1 €/m3.
•Valorization of wastewaters from the fish canning industry.•Fish canning wastewater treatment for reuse or recycling into the industrial unit.•Reverse osmosis and UV disinfection were combined for effluent clarification.•The proposed sequential system attained removal efficiencies above 96%.•Reduction of effluents discharge, water use and its associated cost.
In this work, we investigate the potential of a MOF porous material, Cu-BTC in combination with cyclic adsorption processes (vacuum swing adsorption, VSA, and simulated moving bed, SMB) for the ...separation of propylene/propane mixture. A gravimetric method has been used to measure the adsorption isotherms of propylene, propane and isobutane onto Cu-BTC extrudates over a temperature range from 323 to 373
K and pressures up to 500
kPa. These were complemented by experimental characterization of the Cu-BTC material using XRD and SEM-EDS techniques. Whereas the separation and its kinetics were studied by breakthrough experiments on a column packed with the Cu-BTC material in the extruded form at 373
K. The Cu-BTC extrudates are selective towards propylene, highlighting the potential of this material for the separation of propane and propylene mixtures by PSA process. Furthermore, in a range of temperatures and pressures, the affinity of Cu-BTC for isobutane was observed to be intermediate to that of propane and propylene which suggest that isobutane is a promising desorbent in SMB processes for propane/propylene separations.
•An innovative micro–meso-structured-reactor for Cr(VI) photocatalytic reduction.•Cellulose acetate sheet coated with a TiO2 thin film was used in the micro-reactor.•The presence of tartaric acid ...enhanced Cr(VI) reduction by TiO2/UVA–Vis system.•Reynolds number of 830 provided the mixing degree needed to intensify the process.•The immobilized TiO2 proved to be suitable to the continuous Cr(VI) reduction.
Process intensification of heterogeneous TiO2 photocatalysis using a new type of static mixer micro–meso-structured-reactor, based on the NETmix reactor, was evaluated to promote the hexavalent chromium reduction to its trivalent state, in the presence of sacrificial agents. The photocatalytic micro–meso-structured reactor comprises a back acrylic slab where chambers and channels are imprinted and a frontal borosilicate slab with especially high UV transparency, irradiated by simulated solar light. An UV transparent cellulose acetate (CA) sheet coated with TiO2-P25 by a simple spray method was assembled between the two slabs of the photoreactor. The reactor geometry provides an efficient exposure of TiO2-P25 CA sheets to radiation, with an illuminated surface per unit of volume inside the reactor of 470m2m−3 and 1.36g TiO2 per liter of liquid inside the reactor. Beyond that, it provides a good degree of mixing using a laminar flow, maximizing heterogeneous and homogeneous Cr(VI) reduction reactions. Firstly, different organic species were tested as hole scavengers in order to avoid the Cr(III) re-oxidation. The effect of the degree of mixing inside the photoreactor, according to the Reynolds number, on the Cr(VI) photocatalytic reduction was then evaluated. Following, operating conditions such as TiO2 mass, tartaric acid concentration, pH value, temperature and initial Cr(VI) concentration were analyzed. Results indicate high reduction rates (1mmolCr(VI)m−3illuminated volumes−1) and a photonic efficiency of 3.96% for Re=830, 30mg TiO2 and a Cr(VI):tartaric acid molar ratio of 1:90 at pH 3.0 and 25°C. Finally, the CA sheets coated with thin films of TiO2-P25 showed to be suitable for continuous Cr(VI) reduction, without losing efficiency during 3 consecutive photocatalytic cycles.
The potential of the porous crystalline titanium dicarboxylate MIL-125(Ti) in powder form was studied for the separation in liquid phase of xylene isomers and ethylbenzene (MIL stands for Materials ...from Institut Lavoisier). We report here a detailed experimental study consisting of binary and multi-component adsorption equilibrium of xylene isomers in MIL-125(Ti) powder at low (≤0.8 M) and bulk (≥0.8 M) concentrations. A series of multi-component breakthrough experiments was first performed using n-heptane as the eluent at 313 K, and the obtained selectivities were compared, followed by binary breakthrough experiments to determine the adsorption isotherms at 313 K, using n-heptane as the eluent. MIL-125(Ti) is a para-selective material suitable at low concentrations to separate p-xylene from the other xylene isomers. Pulse experiments indicate a separation factor of 1.3 for p-xylene over o-xylene and m-xylene, while breakthrough experiments using a diluted ternary mixture lead to selectivity values of 1.5 and 1.6 for p-xylene over m-xylene and o-xylene, respectively. Introduction of ethylbenzene in the mixture results however in a decrease of the selectivity.
The adsorption equilibrium of carbon dioxide (CO2), carbon monoxide (CO), nitrogen (N2), methane (CH4), and hydrogen (H2) was studied at 303, 323, and 343 K and pressures up to 7 bar in ...titanium-based metal–organic framework (MOF) granulates, amino-functionalized titanium terephthalate MIL-125(Ti)_NH2. The affinity of the different adsorbates toward the adsorbent presented the following order: CO2 > CH4 > CO > N2 > H2, from the most adsorbed to the least adsorbed component. Subsequently, adsorption kinetics and multicomponent adsorption equilibrium were studied by means of single, binary, and ternary breakthrough curves at 323 K and 4.5 bar with different feed mixtures. Both studies are complementary and aim the syngas purification for two different applications, hydrogen production and H2/CO composition adjustment, to be used as feed in the Fischer–Tropsch processes. The isosteric heats were calculated from the adsorption equilibrium isotherms and are 21.9 kJ mol–1 for CO2, 14.6 kJ mol–1 for CH4, 13.4 kJ mol–1 for CO, and 11.7 kJ mol–1 for N2. In the overall pressure and temperature range, the adsorption equilibrium isotherms were well-regressed against the Langmuir model. The multicomponent breakthrough experimental results allowed for validation of the adsorption equilibrium predicted by the multicomponent extension of the Langmuir isotherm and validation of the fixed-bed mathematical model. To conclude, two pressure swing adsorption (PSA) cycles were designed and performed experimentally, one for hydrogen purification from a 30/70% CO2/H2 mixture (hydrogen purity was 100% with a recovery of 23.5%) and a second PSA cycle to obtain a light product with a H2/CO ratio between 2.2 and 2.4 to feed to Fischer–Tropsch processes. The experimental cycle produced a light stream with a H2/CO ratio of 2.3 and a CO2-enriched stream with 86.6% purity as a heavy product. The CO2 recovery was 93.5%.
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