| 1. |
- Ademuyiwa, Adesoji O., et al.
(författare)
-
Determinants of morbidity and mortality following emergency abdominal surgery in children in low-income and middle-income countries
- 2016
-
Ingår i: BMJ Global Health. - : BMJ Publishing Group Ltd. - 2059-7908. ; 1:4
-
Tidskriftsartikel (refereegranskat)abstract
- Background: Child health is a key priority on the global health agenda, yet the provision of essential and emergency surgery in children is patchy in resource-poor regions. This study was aimed to determine the mortality risk for emergency abdominal paediatric surgery in low-income countries globally.Methods: Multicentre, international, prospective, cohort study. Self-selected surgical units performing emergency abdominal surgery submitted prespecified data for consecutive children aged <16 years during a 2-week period between July and December 2014. The United Nation's Human Development Index (HDI) was used to stratify countries. The main outcome measure was 30-day postoperative mortality, analysed by multilevel logistic regression.Results: This study included 1409 patients from 253 centres in 43 countries; 282 children were under 2 years of age. Among them, 265 (18.8%) were from low-HDI, 450 (31.9%) from middle-HDI and 694 (49.3%) from high-HDI countries. The most common operations performed were appendectomy, small bowel resection, pyloromyotomy and correction of intussusception. After adjustment for patient and hospital risk factors, child mortality at 30 days was significantly higher in low-HDI (adjusted OR 7.14 (95% CI 2.52 to 20.23), p<0.001) and middle-HDI (4.42 (1.44 to 13.56), p=0.009) countries compared with high-HDI countries, translating to 40 excess deaths per 1000 procedures performed.Conclusions: Adjusted mortality in children following emergency abdominal surgery may be as high as 7 times greater in low-HDI and middle-HDI countries compared with high-HDI countries. Effective provision of emergency essential surgery should be a key priority for global child health agendas.
|
|
| 2. |
- Amjad, Um-e-Salma, et al.
(författare)
-
Catalytic cracking of polystyrene pyrolysis oil: Effect of Nb2O5 and NiO/Nb2O5 catalyst on the liquid product composition
- 2022
-
Ingår i: Waste Management. - : Elsevier. - 0956-053X .- 1879-2456. ; 141, s. 240-250
-
Tidskriftsartikel (refereegranskat)abstract
- The catalytic cracking of polystyrene pyrolysis oil was investigated over a Nb2O5 and a NiO/Nb2O5 catalyst in a fixed bed reactor. First, the pyrolysis of two different polystyrene feedstock (polystyrene foam and polystyrene pellet) was carried out in a semi-batch reactor, and the resulting polystyrene pellets pyrolysis oil was selected for catalytic cracking reaction because of its high liquid yield (85%). Catalytic cracking experiments were then performed at different temperatures (350–500 °C) using Nb2O5 or NiO/Nb2O5 catalyst. Gas chromatography–mass spectrometry analysis of liquid product obtained from the catalytic cracking process showed that the dimers in the pyrolysis oil were converted to monomers during the catalytic cracking process. The catalytic cracking results also showed that the NiO/Nb2O5 catalyst (having slightly higher acidic sites) had slightly higher activity for monomer conversion than the Nb2O5 catalyst (having less acidic sites). X-ray diffraction, transmission electron microscopy, pyridine Fourier transform infrared spectroscopy, NH3 Temperature Programmed Desorption and X-ray photoelectron spectroscopy were used to characterize the catalyst. The highest catalytic cracking activity was observed at 400 °C with the Nb2O5 catalyst with 4% toluene, 6% ethylbenzene, approximately 50% styrene, 13% α-methyl styrene, and only 6% of dimers in the liquid oil. The increase in temperature positively affected the yield of gases during catalytic cracking process.
|
|
| 3. |
- Faisal, Abrar, et al.
(författare)
-
MFI zeolite as adsorbent for selective recovery of hydrocarbons from ABE fermentation broths
- 2014
-
Ingår i: Adsorption. - : Springer Science and Business Media LLC. - 0929-5607 .- 1572-8757. ; 20:2-3, s. 465-470
-
Tidskriftsartikel (refereegranskat)abstract
- 1-Butanol and butyric acid are two interesting compounds that may be produced by acetone, butanol, and ethanol fermentation using e.g. Clostridium acetobutylicum. The main drawback, restricting the commercialization potential of this process, is the toxicity of butanol for the cell culture resulting in low concentrations of this compound in the broth. To make this process economically viable, an efficient recovery process has to be developed. In this work, a hydrophobic MFI type zeolite with high silica to alumina ratio was evaluated as adsorbent for the recovery of butanol and butyric acid from model solutions. Dual component adsorption experiments revealed that both butanol and butyric acid showed a high affinity for the hydrophobic MFI zeolite when adsorbed from aqueous model solutions. Multicomponent adsorption experiments using model solutions, mimicking real fermentation broths, revealed that the adsorbent was very selective to the target compounds. Further, the adsorption of butyric and acetic acid was found to be pH dependent with high adsorption below, and low adsorption above, the respective pKa values of the acids. Thermal desorption of butanol from MFI type zeolite was also studied and a suitable desorption temperature was identified.
|
|
| 4. |
- Faisal, Abrar
(författare)
-
Recovery of biochemicals from ABE fermentation broths using MFI adsorbents: A comparison between traditional beads and a structured adsorbent
- 2014
-
Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Energy demands of the world are ever increasing in this industrial era. Over reliance on petroleum-based fuels has a negative impact on the environment. In addition, with depleting reservoirs of fossil fuels, the need for new, sustainable fuels and chemicals is more urgent than ever. One such chemical is 1-butanol (or simply butanol), which has great potential as a gasoline substitute because of its favorable fuel properties. Butanol can be produced from acetone, butanol and ethanol (ABE) fermentation using e.g. Clostridium acetobutylicum. However, the concentration of butanol in fermentation in the resulting broth is limited to ca. 20 g/L due to its toxicity for microorganisms. Butyric acid is a precursor to butanol, which is produced prior to butanol in ABE fermentation. Butyric acid is an important industrial chemical, which can be further derived into a number of commercial compounds e.g. acetate butyrate, butyl acetate and butanol. In this study, hydrophobic MFI zeolite was evaluated for the recovery of butanol and butyric acid from both model and real fermentation broths. Adsorption isotherms of the main components viz. butanol, butyric acid, acetone, ethanol and acetic acid were determined at room temperature. The experimentally determined isotherms were than fitted to the Langmuir adsorption model with good fit. Butyric acid and butanol showed high affinity for the hydrophobic MFI zeolite. The butanol saturation loading was determined to be 0.11 g-butanol/g-zeolite for both binary (water-butanol) and multicomponent (ABE) model solutions in concert to previous findings. However, adsorption of butyric acid was found to be strongly pH dependent, with high adsorption below and little adsorption above the pKa value of the acid. Thermal desorption experiments showed that adsorbed water and butanol starts to desorb at 100 °C and 118 °C respectively. The hydrophobic MFI zeolite was also evaluated for the recovery of bio-butanol from real fermentation broth produced by Clostridium acetobutylicum using xylose recovered from birch Kraft black liquor. The results showed that even in the presence of phenolic compounds, which may interfere with the adsorption of butanol, the zeolite was very selective towards the targeted molecules i.e. butyric acid and butanol. In addition, butyric acid adsorption could be suppressed by increasing the pH of the solution to facilitate better selectivity towards butanol. The selectivity of butanol over acetone and ethanol was found to be 25 and 250 respectively at pH 8 and room temperature for batch adsorption experiments. A structured adsorbent in the form of steel monolith coated with a silicalite-1 film was prepared. X-ray diffractometry and scanning electron microscopy was used to characterize the adsorbent. The performance of the structured adsorbent was evaluated by performing breakthrough experiments at room temperature using model ABE fermentation broths and the performance was compared with that of traditional adsorbents in the form of beads. The structured silicalite-1 adsorbent required less amount of solution to achieve saturation as compared to the commercial ZSM-5 beads. Desorption studies showed that a high quality butanol product with purity up to 97% for butanol-water system and 89% for the ABE system can be recovered with the structured silicalite-1 adsorbent. The commercial ZSM-5 beads also showed good selectivity but the concentration of butanol in the desorbed product was limited to 71% for the butanol-water system and 61% for ABE system, probably as a result of entrained liquid between the beads.
|
|
| 5. |
- Faisal, Abrar, et al.
(författare)
-
Recovery of butanol from model ABE fermentation broths using MFI adsorbent: a comparison between traditional beads and a structured adsorbent in the form of a film
- 2016
-
Ingår i: Adsorption. - : Springer Science and Business Media LLC. - 0929-5607 .- 1572-8757. ; 22:2, s. 205-214
-
Tidskriftsartikel (refereegranskat)abstract
- Butanol, a promising biofuel, can be produced by ABE (acetone, butanol and ethanol) fermentation using e.g. Clostridium acetobutylicum. However, the butanol concentration in the resulting broth is limited to only ca. 20 g/L due to the toxicity for the microorganisms. This low product concentration demands an efficient recovery process for successful commercialization of this process. In this study, a structured adsorbent in the form of steel monolith coated with a silicalite-1 film was prepared using the in situ growth method. The adsorbent was carefully characterized by SEM and XRD. The performance of the adsorbent was evaluated by performing breakthrough experiments at room temperature using model ABE fermentation broths and the performance was compared with that of traditional adsorbents in the form of beads. The structured silicalite-1 adsorbent showed less saturation loading time as compared to commercial binder free silicalite-1 beads, reflecting the different dimensions of the columns used, set by experimental constraints. Studies of the desorption process showed that by operating at appropriate conditions, butanol with high concentration i.e. up to 95.2 wt% for butanol–water model system and 88.5 wt% for ABE fermentation broth can be obtained using the structured silicalite-1 adsorbent. Commercial silicalite-1 beads also showed good selectivity but the concentration of butanol in the desorbed product was limited to 70 % for the butanol–water model system and 69 % for ABE fermentation broth, probably as a result of entrained liquid between the beads.
|
|
| 6. |
- Faisal, Abrar, et al.
(författare)
-
Recovery of l-Arginine from Model Solutions and Fermentation Broth Using Zeolite-Y Adsorbent
- 2019
-
Ingår i: ACS Sustainable Chemistry and Engineering. - : American Chemical Society (ACS). - 2168-0485. ; 7:9, s. 8900-8907
-
Tidskriftsartikel (refereegranskat)abstract
- Arginine was produced via fermentation of sugars using the engineered microorganism Escherichia coli. Zeolite-Y adsorbents in the form of powder and extrudates were used to recover arginine from both a real fermentation broth and aqueous model solutions. An adsorption isotherm was determined using model solutions and zeolite-Y powder. The saturation loading was determined to be 0.2 g/g using the Sips model. Arginine adsorbed from a real fermentation broth using either zeolite-Y powder or extrudates both showed a maximum loading of 0.15 g/g at pH 11. This adsorbed loading is very close to the corresponding value obtained from the model solution showing that under the experimental conditions the presence of additional components in the broth did not have a significant effect on the adsorption of arginine. Furthermore, a breakthrough curve was determined for extrudates using a 1 wt % arginine model solution. The selectivity for arginine over ammonia and alanine from the real fermentation broth at pH 11 was 1.9 and 8.3, respectively, for powder, and 1.0, and 4.1, respectively, for extrudates. To the best of our knowledge, this is the first time recovery of arginine from real fermentation broths using any type of adsorbent has been reported.
|
|
| 7. |
- Faisal, Abrar, 1983-
(författare)
-
Zeolite adsorbents and catalysts for the recovery and production of biochemicals
- 2016
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Fossil based energy resources are dominating the world’s primary energy consumption for the last century. However, with decreasing crude oil reservoirs and the role they play in global warming by emitting greenhouse gases, the focus has been turned towards improved utilization of renewable resources and the need for new, sustainable fuels and chemicals is more urgent than ever. Biomass is a carbon neutral resource that can be used to produce biofuels and other useful chemicals. One such chemical is 1-butanol (or simply butanol), which has great potential as a gasoline substitute because of its favorable fuel properties. Butanol can be produced from acetone, butanol and ethanol (ABE) fermentation using e.g. Clostridium acetobutylicum. However, the concentration of butanol in fermentation in the resulting broth is limited to ca. 20 g/L due to its toxicity for microorganisms. Butyric acid is a precursor to butanol, which is produced prior to butanol in ABE fermentation. Butyric acid is an important industrial chemical, which can be further converted into a number of commercial compounds e.g. acetate butyrate, butyl acetate and butanol. Arginine is a semi-essential amino acid that has vast applications in the field of pharmaceutical and food industry. In addition, arginine can replace inorganic nitrogen as nitrogen source in fertilizers. It can be produced via fermentation of sugars using engineered microorganism like E. Coli, but like butanol its concentration is restricted to approximately 12 g/L. Due to low concentration of these useful chemicals in the resulting fermentation broths recovery of these chemicals remain challenging with today’s options and therefore novel recovery process should be developed.In this study, zeolite adsorbents were used to recover butanol, butyric acid and arginine from model and real fermentation broths. Zeolite MFI adsorbent efficiently adsorbed butanol from model solutions with a saturation loading of 0.11 g/g- zeolite. On the other hand, adsorption of butyric acid was found to be strongly pH dependent, with high adsorption below and little adsorption above the pKa value of the acid. A structured adsorbent in the form of steel monolith coated with a silicalite-1 film was also used and performance was evaluated by performing breakthrough experiments at room temperature using model ABE fermentation broths and the results were compared with those obtained using traditional adsorbent sin the form of beads. Desorption studies showed that a high quality butanol product with purity up to 95.2% for butanol-water system and 88.5% for the ABE system can be recovered with the structured silicalite-1 adsorbent. Further, zeolite X adsorbents in the form of powder and extrudates was used to recover arginine from a real fermentation broth and also from aqueous model solutions. To the best of our knowledge, this is the first time recovery of arginine from real fermentation broths using any type of adsorbent is reported. Arginine loading of 0.15 g/g was observed at pH 11 using zeolite X powder. The selectivity for arginine over ammonia and alanine from the fermentation broth at pH 11 was 1.9 and 8.3, respectively, for powder and 1.0 and 4.1, respectively, for extrudates. Synthesis gas (CO + H2) can be produced e.g.by gasification of lignocellulose biomass. This synthesis gas can be used to produce methanol, which subsequently may be converted into gasoline using zeolite ZSM-5 catalyst. However, during Methanol to Gasoline (MTG) process, undesirable carbon residue (coke) is formed that gradually reduces the activity of catalyst. It was hypothesized that intracrystalline defects in the zeolite formed during conventional synthesis may accelerate the deactivation rate by coke formation. In this work, a novel ZSM-5 zeolite catalyst essentially free of intracrystalline defects was synthesized and evaluated in the MTG reaction,. The novel catalyst showed significantly higher resistance towards deactivation by coke formation as compared to a reference catalyst containing defects.
|
|
| 8. |
- Faisal, Abrar, et al.
(författare)
-
Zeolite MFI adsorbent for recovery of butanol from ABE fermentation broths produced from an inexpensive black liquor-derived hydrolyzate
- 2018
-
Ingår i: Biomass Conversion and Biorefinery. - : Springer. - 2190-6815 .- 2190-6823. ; 8:3, s. 679-687
-
Tidskriftsartikel (refereegranskat)abstract
- In this work, high-silica MFI zeolite adsorbent was evaluated for selective recovery of butanol from a real ABE (acetone, butanol, and ethanol) fermentation broth by batch adsorption measurements. The fermentation broth was produced using a hydrolyzate originating from Kraft black liquor, an internal stream in pulp mills, i.e., a low-cost substrate. The adsorbent was very selective towards butanol and butyric acid and became nearly saturated with a mixture of butanol and butyric acid with relative amounts of butanol and butyric acid depending on the pH. The presence of phenolic compounds in significant amounts in the fermentation broths, originating from the black liquor hydrolyzate, did not affect the adsorption of butanol and butyric acid.
|
|
| 9. |
- Ghauri, Moinuddin, et al.
(författare)
-
A comparative study on meeting the energy demand from biogas in Pakistan
- 2011
-
Ingår i: International Journal of Chemical and Environmental Engineering. - 2078-0737. ; 2:6, s. 410-413
-
Tidskriftsartikel (refereegranskat)abstract
- Pakistan is facing energy crises from past decade due to experiencing increase in energy demands. This current work is a comparative study to meet the energy demand from production of biogas from waste solid materials. The main emphasis is to treat biomass, manure, municipal waste, sewage and green waste to produce biogas using different technologies. At the ends there are some suggestions for effective planning of sustainable energy exploitation and facilitate for technology solution of further research. These suggestions are very useful for meeting the energy demand in Pakistan as well as for third world countries.
|
|
| 10. |
- Grahn, Mattias, et al.
(författare)
-
Small ZSM-5 crystals with low defect density as an effective catalyst for conversion of methanol to hydrocarbons
- 2020
-
Ingår i: Catalysis Today. - : Elsevier B.V.. - 0920-5861 .- 1873-4308. ; 345, s. 136-146
-
Tidskriftsartikel (refereegranskat)abstract
- This work presents the synthesis of nearly defect-free ZSM-5 nanosized crystals, prepared in fluoride medium by seeding with silicalite-1. This material was carefully characterized and its catalytic performances in the methanol to hydrocarbons (MTH) reaction were assessed. Such fluoride-based material was compared to a reference ZSM-5, produced through a conventional alkaline synthesis but from the same seeding. Despite both the materials show closely identical morphology and they have a comparable acid site population, the catalyst prepared using the fluoride route showed significantly longer lifetime in MTH compared to the catalyst prepared using conventional synthesis at high pH. The slower deactivation for the samples prepared using the fluoride route was ascribed, thanks to a thorough in situ IR spectroscopy study, to its lower density of internal defects. According to the UV-Raman characterization of coke on the spent catalyst, the fluoride-based ZSM-5 catalyst produces less molecular coke species, most probably because of the absence of enlarged cavities/channels as due to the presence of internal defects. On the basis of these observations, the deactivation mechanism in the ZSM-5 synthesized by fluoride medium could be mostly related to the deposition of an external layer of bulk coke, whereas in the alkali-synthesized catalyst an additional effect from molecular coke accumulating within the porous network accelerates the deactivation process.
|
|
| 11. |
- Hassan, Mohsan, et al.
(författare)
-
Effects of Cu–Ag hybrid nanoparticles on the momentum and thermal boundary layer flow over the wedge
- 2019
-
Ingår i: Proceedings of the Institution of mechanical engineers. Part E, journal of process mechanical engineering. - : Sage Publications. - 0954-4089 .- 2041-3009. ; 233:5, s. 1128-1136
-
Tidskriftsartikel (refereegranskat)abstract
- In this work, the effects of hybrid nanoparticles on the momentum and thermal boundary layers as well as flow characteristics and thermal performance of the hybrid nanofluid are investigated over the wedge. The fluid in the enclosure is water containing hybrid nanoparticles Cu–Ag. The physical model of homogenous hybrid nanofluid is derived using the elementary equations of thermo-hydrodynamic and co-relation's model of a mixture that supports the effective physical features. The results are calculated to measure the effects of nanoparticle concentration on thermal and momentum boundary layers and displayed in graphs for discussions. In addition, the effects of nanoparticles concentration and different compositions of hybrid nanoparticles on temperature and velocity profiles, physical properties, skin friction, and convective heat transfer coefficient are deliberated through graphs and tables. To check its heat transfer performance, a comparison of hybrid nanofluid is made between the base fluid and single material nanofluids. It is found that the efficiency of hybrid nanofluids as a heat transfer fluid is much more than conventional fluids or single nanoparticles-based nanofluids. These results in terms of boundary layers phenomena, heat transfer performance, and temperature and velocity profiles under hybrid nanomaterial could help chemical engineers to design the critical equipment in a process industry such as heat exchangers and pumps and others.
|
|
| 12. |
- Hassan, Mohsan, et al.
(författare)
-
Interaction of aluminum oxide nanoparticles with flow of polyvinyl alcohol solutions base nanofluids over a wedge
- 2018
-
Ingår i: Applied Nanoscience. - : Springer. - 2190-5509 .- 2190-5517. ; 8:1-2, s. 53-60
-
Tidskriftsartikel (refereegranskat)abstract
- Polyvinyl alcohol (PVA) is an important industrial chemical, which is used in numerous chemical engineering applications. It is important to study and predict the flow behavior of PVA solutions and the role of nanoparticles in heat transfer applications to be used in chemical processes on industrial scale. Therefore, the present study deals with the PVA solution-based non-Newtonian Al2O3-nanofluid flow along with heat transfer over wedge. The power-law model is used for this non-Newtonian nanofluid which exhibited shear-thinning behavior. The influences of PVA and nanoparticles concentrations on the characteristics of velocity and temperature profiles are examined graphically. The impacts of these parameters on wall shear stress and convective heat transfer coefficient are also studied through tabular form. During the numerical computations, the impacts of these parameters on flow index and consistency index along with other physical properties of nanofluid are also considered. In this study, we found an improvement in heat transfer and temperature profile of fluid by distribution of Al2O3 nanoparticles. It is also noticed that resistance between adjacent layers of moving fluid is enhanced due to these nanoparticles which leads to decline in velocity profile and increases in shear stress at wall.
|
|
| 13. |
- Hassan, Mohsan, et al.
(författare)
-
The Impact of Different Arrangements of Molecular Chains in Terms of Low and High Shear Rate’s Viscosities on Heat and Mass Flow of Nonnewtonian Shear thinning Fluids
- 2022
-
Ingår i: Combinatorial chemistry & high throughput screening. - : Bentham Science Publishers. - 1386-2073 .- 1875-5402. ; 25:7, s. 1115-1126
-
Tidskriftsartikel (refereegranskat)abstract
- Background: Non-newtonian fluids, especially shear thinning fluids, have several applications in the polymer industry, food industry, and even everyday life. The viscosity of shear thinning fluids is decreased by two or three orders of magnitude due to the alignment of the molecules in order when the shear rate is increased, and it cannot be ignored in the case of polymer processing and lubrication problems.Objective: So, the effects of viscosities at the low and high shear rates on the heat and mass boundary layer flow of shear thinning fluid over moving belts are investigated in this study. For this purpose the generalized Carreau model of viscosity relate to shear rate is used in the momentum equation. The Carreau model contains the five parameters: low shear rate viscosity, high shear rate viscosity, viscosity curvature, consistency index, and flow behavior index. For the heat flow, the expression of the thermal conductivity model similar to the viscosity equation due to the non-Newtonian nature of the fluid is used in the energy equation.Methods: On the mathematical model of the problem, boundary layer approximations are applied and then simplified by applying the similarity transformations to get the solution. The solution of the simplified equations is obtained by numerical technique RK-shooting method. The results are compared with existing results for limited cases and found good agreement.Results: The results in the form of velocity and temperature profiles under the impact of all the viscosity’s parameters are obtained and displayed in graphical form. Moreover, the boundary layer parameters such as the thickness of the regions, momentum thickness, and displacement thickness are calculated to understand the structure of the boundary layer flow of fluid.Conclusion: The velocity and temperature of the fluid are decreased and increased respectively by all viscosity’s parameters of the model. So, the results of the boundary layer fluid flow under rheological parameters will not only help engineers to design superior chemical equipment but also help improve the economy and efficiency of the overall process.
|
|
| 14. |
- Hassan, M., et al.
(författare)
-
Thermal Energy and Mass Transport of Shear Thinning Fluid under Effects of Low to High Shear Rate Viscosity
- 2022
-
Ingår i: International Journal of Thermofluids. - : Elsevier. - 2666-2027. ; 15
-
Tidskriftsartikel (refereegranskat)abstract
- The current investigation is deliberated the flow and heat transfer of a shear thinning fluid over a non-linear stretching sheet has variable thickness. All rheological aspects at low to high shear rates are accounted theoretical by using generalized Carreau model of viscosity. Theoretical flow model is formulated for boundary layer phenomena by applying boundary layer approximations and then convert it from partial differential equations to ordinary differential equations with the help of similarity transformations. The solution is obtained by numerical method and the result are displayed in the form of velocity and temperature profiles under impact of rheological and geometrical governing parameters. In addition, the results of skin friction coefficient and Nusselt number are obtained under effects of these parameters. It is found that Nusselt number is significantly decreased when stretching is increased by velocity index parameter.
|
|
| 15. |
- Hedlund, Jonas, et al.
(författare)
-
Controlling diffusion resistance, selectivity and deactivation of ZSM-5 catalysts by crystal thickness and defects
- 2022
-
Ingår i: Journal of Catalysis. - : Elsevier. - 0021-9517 .- 1090-2694. ; 410, s. 320-332
-
Tidskriftsartikel (refereegranskat)abstract
- A systematic investigation of two sets of defect free and defective ZSM-5 crystals with controlled thickness (T) between 30 and 400 nm and of their performances in methanol conversion was reported for the first time in the present work. The defect free ZSM-5 crystals with a thickness of 35 nm are by far the smallest ever reported and displayed superior activity, stability and selectivity to slower diffusing compounds, which resulted in high yield of e.g. gasoline and the 1,2,4-trimethylbenzene isomer with high octane number, as compared to the other studied catalysts. Almost only products forming in the zeolite pores were detected and consequently, the external surface must be nearly inactive. Strong correlations between T and deactivation rate were observed. Thick crystals deactivated much faster than thin crystals, probably due to formation of carbon species in the zeolite pores, which results in pronounced percolation effects and faster deactivation of the former. At comparable thickness, crystals with defects deactivated much faster than defect free crystals, due to formation of additional small molecular coke species in the former. Strong correlations between T and selectivity were also observed and assigned to control of diffusion resistance by crystal thickness.
|
|
