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Through systematical experiment design, the physical blowing agent (PBA) mass loss of bio-based polyurethane rigid foam (PURF) in the foaming process was measured and calculated in this study, and different eco-friendly PBA mass losses were measured quantitatively for the first time. The core of the proposed method is to add water to replace the difference, and this method has a high fault tolerance rate for different foaming forms of foams. The method was proved to be stable and reliable through the standard deviations σ1 and σ2 for R1 (ratio of the PBA mass loss to the material total mass except the PBA) and R2 (ratio of the PBA mass loss to the PBA mass in the material total mass) in parallel experiments. It can be used to measure and calculate the actual PBA mass loss in the foaming process of both bio-based and petroleum-based PURF. The results show that the PBA mass loss in PURF with different PBA systems is controlled by its initial mass content of PBA in PU materials ω. The main way for PBA to dissipate into the air is evaporation/escape along the upper surface of foam. This study further reveals the mechanism of PBA mass loss: the evaporation/escape of PBA along the upper surface of foam is a typical diffusion behavior. Its spread power comes from the difference between the chemical potential of PBA in the interface layer and that in the outside air. For a certain PURF system, R1 has approximately linear relationship with the initial mass content of PBA in PU materials ω, which can be expressed by the functional relationship R1 = kω, where k is a variable related to PBA's own attributes. [ABSTRACT FROM AUTHOR]

The effects of operating temperature on the performance of small scale oxygen concentrator were experimentally investigated using a rotary valve multi-column rapid cycle pressure swing adsorption (PSA) unit which produced a continuous stream of ≥ 90% O2 from compressed air. Simple cooling fans and air cylinder were used for controlling the temperature of compressed air. The change of column midpoint gas temperature inside adsorption column was relatively small and approximately 3–5 K with a low pressure ratio of ~ 250:101 kPa during each cycle. The oxygen recovery could be improved by increasing the operating temperature and the bed size factor (BSF) could be reduced by decreasing the operating temperature. However, the adverse thermal effects on oxygen recovery and BSF became more dominant at very low and high operating temperatures. A similar trend between unit power and BSF at different operating temperature was emerged. There was an appropriate temperature range for achieving favorable performance. [ABSTRACT FROM AUTHOR]

The rapid pressure swing adsorption (RPSA) technology has been widely used for applications including portable oxygen generators due to high O2 productivities and low bed size factors (BSF, total amount of adsorbent per ton of O2 produced per day, kg/TPDO2). The improvement of RPSA process has been a key issue for efficient O2 production in terms of its generally lower O2 recovery as compared to other processes. In this work, a dual-column RPSA oxygen production system with an intermittent purge step (intermittently switching between purge and interruption) was designed to investigate the effects of interruption frequency (the number of interruptions during a purge step) and times on the O2 recovery, purity, productivity and BSF. Experimental results show the improvement on O2 production performance using the intermittent purge step in comparison to conventional continuous purge step. Under the optimized interruption frequency of 2 and time of 0.3 s, the O2 recovery, purity and productivity were increased from 36 to 39.2%, 89.5 to 93%, and 6.24 to 6.49 mmol/kg/s, respectively, while the BSF was decreased from 57.94 to 55.75 kg/TPDO2. [ABSTRACT FROM AUTHOR]

Performances of mesoporous materials in removal of polycyclic aromatic hydrocarbons (PAHs) from hot gases were evaluated systematically. The adsorption and desorption natures for PAHs with different aromatic rings, naphthalene (Nap), phenanthrene (Phe) and pyrene (Pyr) on mesosilicas MCM-41 and SBA-15, and mesocarbon CMK-3, were studied. Adsorption equilibria were well described by Langmuir or Freundlich model, giving the order of adsorption capacity of CMK-3 > SBA-15 > MCM-41 and Pry > Phe > Nap. Temperature programmed desorption exhibited the order of ease of desorption of SBA-15 > MCM-41 > CMK-3, along with desorption kinetic triplet determined by combined model fitting analysis. The Johnson-Mehl-Avrami (JMA) rate equation was found to well describe PAH desorption kinetics, except for Phe/SBA-15 and Pyr/CMK-3 due to potential blockage and strong binding, respectively. MCM-41 with simple 1-D mesoporous structure provided smooth diffusion and consistent behavior but very low adsorption capacity for each PAH. SBA-15 with micropores/small mesopores as interconnectivity between primary mesopores not only showed high sorption capacities but also diffusion advantages in desorption. CMK-3 with great microporosity facilitated the adsorption at low concentrations due to micropore-filling, and with surface hydrophobicity rendered high affinities especially for the bulkier Pyr. [ABSTRACT FROM AUTHOR]

A novel rapid vacuum pressure swing adsorption process with intermediate gas pressurization for producing oxygen is proposed to improve the performance of miniature oxygen concentrator based rapid pressure swing adsorption technology. The effects of intermediate gas pressurization and desorption pressure on the performance of the process are evaluated by experiments and simulations. Results showed that pressurization with intermediate gas from product end can effectively improve the oxygen purity of the product. The pressure and oxygen purity of intermediate gas before pressurization were key parameters that affected the oxygen purity of the product. When the adsorption pressure was 240 kPa and the desorption pressure was 60 kPa, the test unit for the process produced 0.75 L min of ~90% O with 29.45% of oxygen recovery from compressed air. The minimum bed size factor (BSF) for ~90% O product was 82.84 kg TPD. The BSF could be effectively reduced by lowering the desorption pressure. Moreover, oxygen recovery could be improved by lowering the desorption pressure. [ABSTRACT FROM AUTHOR]

Flow maldistribution and local high velocity in an axial adsorber is numerically studied to investigate the potential occurrence of sorbent pulverization and uneven utility. A considerable maldistribution induced by the entrance effect and local high velocity caused by rapid gas discharge during depressurization is observed. Three types of gas distributors and different depressurization strategies are then proposed and studied to determine their capabilities to create uniform velocity profiles. Results show that locating the predistributor in the dead zone is critical to flow distribution. The maldistribution factor ( Mf) can decrease to a minimum of 0.055 when a perforated inlet plenum is used with a conventional distributor. In addition, the internal ring can effectively reduce wall effects. Moreover, both gas expansion and desorption have a significant influence on the evolution of local velocity during depressurization. In this step, local high velocity can possibly exceed incipient fluidization velocity and cause attrition and pulverization of the sorbent. To a certain extent, employing methods to control the depressurization rate is necessary. Applying linear depressurization ( $$p = 101,325 - p_{AD} /t_{DP} \times t + p_{AD}$$ ) or downward convex conic depressurization ( $$p = p_{AD} - \sqrt {\left( {p_{AD} - 101,325} \right)^{2} /t_{DP} \times t}$$ ) can reduce local high velocity, and thus, improve flow conditions. [ABSTRACT FROM AUTHOR]

This study characterized the process by-product particles (mostly nanoparticles) released during the preventive maintenance of semiconductor fabrication facilities, such as chemical mechanical planarization (CMP), plasma-enhanced chemical vapor deposition (PECVD), and ion implantation. Manual sampling and real-time measurements with direct reading instruments were conducted to assess the exposure levels of nanoparticles and their physical and chemical properties. Significant amount of nanoparticles were observed in the breathing zone of the workers during the maintenance of the PECVD and ion implanters with the peak number concentrations as high as 6,470,000 and 65,444 #/cm3, respectively, indicating that the deposited residual chemicals in the reaction chambers were released as airborne nanoparticles by the maintenance activities. In contrast, nanoparticles released during the maintenance of the local scrubber, CMP, and replacing CMP slurry drums were insignificant. Causes of the particle release were discussed and suggestions were made to mitigate the nanoparticle release and reduce the exposure levels. [ABSTRACT FROM AUTHOR]