The Adsorption and Separation of Ethylene, Oxygen and Carbon Dioxide Gases on Molecular Sieves

The equilibrium adsorption and diffusion properties of ethylene, oxygen and carbon dioxide gases on two kinds of molecular sieve at 25°C were measured by gravimetric methods using a Cahn-2000 electrobalance. On both molecular sieves, the equilibrium adsorption capacity of ethylene was larger than that of oxygen and close to that of carbon dioxide, indicating that it would not be possible to remove oxygen and carbon dioxide gases from their mixture with ethylene in order to effect recovery of the latter via equilibrium separation methods. However, during the early stages of adsorption, the adsorption rates of carbon dioxide and oxygen were faster than that of ethylene thereby suggesting recovery of the latter from the gaseous mixture via kinetic separation based on the difference in adsorption diffusivity. Such separation was conducted using a two-bed column pressure swing adsorption arrangement with the effects of the experimental conditions on the separation being investigated. Oxygen and carbon dioxide may be adsorbed and removed from the gaseous mixture, leaving the output gases rich in ethylene

Study of the Relationships between the Spatial Extent of Surface Urban Heat Islands and Urban Characteristic Factors Based on Landsat ETM+ Data

Ten cities with different population and urban sizes located in the Pearl River Delta, Guangdong Province, P.R. China were selected to study the relationships between the spatial extent of surface urban heat islands (SUHI) and five urban characteristic factors such as urban size, development area, water proportion, mean NDVI (Normalized Vegetation Index) and population density, etc. The spatial extent of SUHI was quantified by using the hot island area (HIA). All the cities are almost at the same latitude, showing similar climate and solar radiation, the influence of which could thus be eliminated during our computation and comparative study. The land surface temperatures (LST) were retrieved from the data of Landsat 7 Enhanced Thematic Mapper Plus (ETM+) band 6 using a mono-window algorithm. A variance-segmenting method was proposed to compute HIA for each city from the retrieved LST. Factors like urban size, development area and water proportion were extracted directly from the classification images of the same ETM+ data and the population density factor is from the official census. Correlation and regression analyses were performed to study the relationships between the HIA and the related factors, and the results show that HIA is highly correlated to urban size (r=0.95), population density (r=0.97) and development area (r=0.83) in this area. It was also proved that a weak negative correlation existed between HIA and both mean NDVI and water proportion for each city. Linear functions between HIA and its related factors were established, respectively. The HIA can reflect the spatial extent and magnitude of the surface urban heat island effect, and can be used as reference in the urban planning

Study of the Relationships between the Spatial Extent of Surface Urban Heat Islands and Urban Characteristic Factors Based on Landsat ETM+ Data

Ten cities with different population and urban sizes located in the Pearl River Delta, Guangdong Province, P.R. China were selected to study the relationships between the spatial extent of surface urban heat islands (SUHI) and five urban characteristic factors such as urban size, development area, water proportion, mean NDVI (Normalized Vegetation Index) and population density, etc. The spatial extent of SUHI was quantified by using the hot island area (HIA). All the cities are almost at the same latitude, showing similar climate and solar radiation, the influence of which could thus be eliminated during our computation and comparative study. The land surface temperatures (LST) were retrieved from the data of Landsat 7 Enhanced Thematic Mapper Plus (ETM+) band 6 using a mono-window algorithm. A variance-segmenting method was proposed to compute HIA for each city from the retrieved LST. Factors like urban size, development area and water proportion were extracted directly from the classification images of the same ETM+ data and the population density factor is from the official census. Correlation and regression analyses were performed to study the relationships between the HIA and the related factors, and the results show that HIA is highly correlated to urban size (r=0.95), population density (r=0.97) and development area (r=0.83) in this area. It was also proved that a weak negative correlation existed between HIA and both mean NDVI and water proportion for each city. Linear functions between HIA and its related factors were established, respectively. The HIA can reflect the spatial extent and magnitude of the surface urban heat island effect, and can be used as reference in the urban planning

Evaluation and analysis method for natural gas hydrate storage and transportation processes

An evaluation and analysis method is presented to investigate an approach to scale-up a hydration reactor and to solve some economic problems by looking at the natural gas hydrate storage and transportation process as a whole. Experiments with the methane hydration process are used to evaluate the whole natural gas hydrate storage and transportation process. The specific contents and conclusions are as follows: first, batch stirring effects and load coefficients are studied in a semi-continuous stirred-tank reactor. Results indicate that batch stirring and appropriate load coefficients are effective in improving hydrate storage capacity. in the experiments, appropriate values for stirring velocity, stirring time and load coefficient were found to be 320 rpm, 30 min and 0.289, respectively. Second, throughput and energy consumption of the reactor for producing methane hydrates are calculated by mass and energy balance. Results show that throughput of this is 1.06 kg/d, with a product containing 12.4% methane gas. Energy consumption is 0.19 kJ, while methane hydrates containing 1 kJ heat are produced. Third, an energy consumption evaluation parameter is introduced to provide a single energy consumption evaluation rule for different hydration reactors. Parameter analyses indicate that process simplicity or process integration can decrease energy consumption. If experimental gas comes from a small-scale natural gas field and the energy consumption is 0.02 kJ when methane hydrates containing I kJ heat are produced, then the decrease is 87.9%. Moreover, the energy consumption evaluation parameter used as an economic criterion is converted into a process evaluation parameter. Analyses indicate that the process evaluation parameter is relevant to technology level and resource consumption for a system, which can make it applicable to economic analysis and venture forecasting for optimal capital utilization. (C) 2008 Elsevier Ltd. All rights reserved

Study on methane hydration process in a semi-continuous stirred tank reactor

The methane hydration process is investigated in a semi-continuous stirred tank reactor. Liquid temperatures and reaction rates without stirrer are compared with those occurring with stirrer, while at the same time better stirring conditions of the methane hydration process are given by the experiments. Some basic data of fluid mechanics, for example, stirring Reynolds number, Froucle number and stirrer power, are calculated during the methane hydration process, which can be applied to evaluate stirrer capacity and provide some basic data for a scaled up reactor. Based on experiment and calculations in this work, some conclusions are drawn. First, the stirrer has great influence on the methane hydration process. Batch stirring is helpful to improve the mass transfer and heat transfer performances of the methane hydration process. Second, induction time can be shortened effectively by use of the stirrer. Third, in this paper, the appropriate stirring velocity and stirring time were 320 rpm and 30 min, respectively, at 5.0 MPa, for which the storage capacity and reaction time were 159.1 V/V and 370 min, respectively. Under the condition of the on-flow state, the initial stirring Reynolds number of the fluid and the stirring power were 12,150 and 0.54 W, respectively. Fourth, some suggestions, for example, the use of another type of stirrer or some baffles, are proposed to accelerate the methane hydration process. Comparing with literature data, higher storage capacity and hydration rate are achieved in this work. Moreover, some fluid mechanics parameters are calculated, which can provide some references to engineering application. (c) 2006 Elsevier Ltd. All rights reserved

Preparation of titanium silicalite-1 catalytic films and application as catalytic membrane reactors

Titanium silicalite-1 (TS-1) films were prepared on porous alpha-Al2O3 tubes using nanosized silicalite-1 (Sil-1) particles as seeds by hydrothermal treatment and a TS-1 catalytic membrane reactors (CMR) was reasonably designed and evaluated by phenol hydroxylation with hydrogen peroxide as oxidant. Some factors on influencing TS-1 film formation and catalytic properties were investigated and the TS-1 films were characterized by scanning electron microscope (SEM), transmission electron micrograph (TEM), X-ray diffractometer (XRD), FTIR, UV-vis and X-ray fluorescence (XRF). It was indicated that TS-1 films prepared from Sil-1 and TS-1 seeds were comparable in structure, morphology and reaction behavior. The crystallization time and times of TS-1 film had a strong effect on its morphology, thickness and orientation. However, the film thickness could be easily controlled by crystallization time and times. The Ti/Si ratio in synthesis solution intensely influenced the content of the titanium atoms incorporated as framework Ti that was correlated well with the activity. The maximum Ti (IV) incorporated corresponds to a Ti/Si ratio of approximately 0.02-0.03. A constant conversion for phenol hydroxylation was obtained with the film thickness of over 7.5 mu m. It is demonstrated that most of the reaction occurred in a shallow layer near the film due to the mass transfer effects in the TS-1 films. (C) 2009 Elsevier B.V. All rights reserved

Optimized Preparation of Nanosized Hollow SSZ-13 Molecular Sieves with Ultrasonic Assistance

Because of its unique eight-membered ring pore structure and the arrangement of cations in its structure, the SSZ-13 molecular sieve has a higher affinity for CO2 than other gases, meaning it has attracted more attention than other porous materials for CO2 adsorption. However, the expensive template and long preparation time limits the industrial production of SSZ-13. In this work, a hollow structure was successfully introduced into the nanosized SSZ-13 molecular sieve with ultrasonic treatment. The effects of the amount of seed added and the ultrasonic time on the structure were investigated. When the amount of seed added was 0.5 wt.% and the ultrasonic time was 60 min, the sample showed a hollow cubic crystal with a diameter of about 50 nm. The specific surface area reached 791.50 m2/g, and the mesoporous ratio was 66.3%. The samples were tested for CO2 adsorption performance at 298 K. It was found that the hollow sample prepared in this work has higher CO2 adsorption capacity compared with the SSZ-13 zeolite prepared with conventional methods. When the adsorption pressure was 0.27 bar, the adsorption amount reached 2.53 mmol/g. The hollow SSZ-13 molecular sieve reached a CO2 adsorption capacity of 4.24 mmol/g at 1 bar

A novel method for the assembly of nano-zeolite crystals on porous stainless steel microchannel and then zeolite film growth

A new method that is simple, efficient, and clean was developed for seeding surfaces with a monolayer of covalently bonded zeolite seeds. This method was used to seed the microchannels fabricated on porous stainless steel with NaA nano-zeolites enabling the deposition and growth of defect-free zeolite film. The NaA nano-zeolites were attached to the surface of the stainless steel via alkoxysilane linkers (e.g., 3-chloropropyltrimethoxysilane and 3-aminopropyltrimethoxysilane) grafted on the stainless steel. The NaA zeolite grown on the microchannel by hydrothermal synthesis consists of intergrown, (111)-oriented pyramidal NaA crystals that completely clad the stainless steel grains. The zeolite cladding the grains grew uniformly until the zeolite layers of neighboring grain impinges, then intergrew to fully bridge the gaps between the grains forming a defect-free film layer. A separation factor of 10,000 and a flux of 0.04 kg m(-2) h(-1) were obtained for water pervaporation from a 3 wt\% water-benzaldehyde solution at room temperature. (c) 2006 Elsevier Ltd. All rights reserved

Investigating the Role of Zeolite Nanocrystal Seeds in the Synthesis of Mesoporous Catalysts with Zeolite Wall Structure

Mesoporous titania-silica catalysts were prepared by hydrothermal conversion from synthesis solutions containing a zeolite structure directing agent (TPA(+)) and a porogen (CTA(+)). Syntheses were carried out with and without addition of zeolite seeds (i.e., TS-1 and Sil-1 nanocrystals). Catalysts prepared in the presence of zeolite nanocrystal seeds have greater proportions of tetrahedrally coordinated titanium, which correlate well with the detection of zeolite SBU fragments and ring-structure by TOF-SIMS and FTIR The incorporation of titano-silicates and zeolite structural units in the mesopore walls could explain the better activity and stability of these catalysts (Ti-MT1 and Ti-MS1) compared to the catalyst prepared by the conventional method (Ti-MCM-41). The similarity in the reactivity of catalysts prepared from TS-1 and Sil-1 nanocrystal seeds dispels the idea that the seeds are merely a source of the zeolite fragments incorporated in the pore walls but instead suggests that the seeds play an active role to stabilize and promote the incorporation of SBU from the solution