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Operation Pressure (operation + pressure)

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Chemistry100%

Selected Abstracts

Dryout phenomena in a three-phase fixed-bed reactor

AICHE JOURNAL, Issue 1 2003
Zhen-Min Cheng
Understanding the mechanism of liquid-phase evaporation in a three-phase fixed-bed reactor is of practical importance, because the reaction heat is usually 7,10 times the vaporization heat of the liquid components. Evaporation, especially the liquid dryout, can largely influence the reactor performance and even safety. To predict the vanishing condition of the liquid phase, Raoult's law was applied as a preliminary approach, with the liquid vanishing temperature defined based on a liquid flow rate of zero. While providing correct trends, Raoult's law exhibits some limitation in explaining the temperature profile in the reactor. To comprehensively understand the whole process of liquid evaporation, a set of experiments on inlet temperature, catalyst activity, liquid flow rate, gas flow rate, and operation pressure were carried out. A liquid-region length-predicting equation is suggested based on these experiments and the principle of heat balance. [source]

Gating Characteristics of Thermo-Responsive Membranes with Grafted Linear and Crosslinked Poly(N -isopropylacrylamide) Gates

CHEMICAL ENGINEERING & TECHNOLOGY (CET), Issue 4 2009
Y.-C. Chen
Abstract Thermo-responsive porous membranes with grafted linear and crosslinked poly(N -isopropylacrylamide) (PNIPAM) gates are successfully prepared at temperatures above and below the lower critical solution temperature (LCST) of PNIPAM by using a plasma-induced grafting polymerization method, and the effects of operation pressure and grafting temperature on the thermo-responsive gating characteristics of the prepared membranes are investigated systematically. The fluxes of water through the grafted membranes increase simply with increasing the operation pressure no matter whether the environmental temperature is 40,°C or 25,°C. Under high operation pressure (e.g., higher than 0.14,MPa), the grafted linear PNIPAM gates deform to a certain extent, whereas the grafted crosslinked PNIPAM gates do not deform. For both membranes with grafted linear and crosslinked PNIPAM gates, the membranes prepared at 25,°C (below the LCST of PNIPAM) show larger thermo-responsive gating coefficients than those prepared at 40,°C (above the LCST of PNIPAM), which results from different distributions of grafted PNIPAM gates in the membrane pores. When the PNIPAM gates are grafted at 25,°C, the grafted layer near the membrane surface is much thicker than that inside the membrane pores; on the other hand, when the PNIPAM gates are grafted at 40,°C, the grafted layer is homogeneously formed throughout the whole pore length. Both linear and crosslinked grafted PNIPAM gates in the membrane pores exhibit stable and repeatable thermo-responsive "open-close" switch performances under the operation pressure of 0.26,MPa. The results in this study provide valuable guidance for designing, fabricating, and operating thermo-responsive gating membranes with desirable performances. [source]

Hydrogen in Porous Tetrahydrofuran Clathrate Hydrate

CHEMPHYSCHEM, Issue 9 2008
Fokko M. Mulder Dr.
Abstract The lack of practical methods for hydrogen storage is still a major bottleneck in the realization of an energy economy based on hydrogen as energy carrier.1 Storage within solid-state clathrate hydrates,2,4 and in the clathrate hydrate of tetrahydrofuran (THF), has been recently reported.5,,6 In the latter case, stabilization by THF is claimed to reduce the operation pressure by several orders of magnitude close to room temperature. Here, we apply in situ neutron diffraction to show that,in contrast to previous reports[5,,6],hydrogen (deuterium) occupies the small cages of the clathrate hydrate only to 30,% (at 274 K and 90.5 bar). Such a D2 load is equivalent to 0.27 wt.,% of stored H2. In addition, we show that a surplus of D2O results in the formation of additional D2O ice Ih instead of in the production of sub-stoichiometric clathrate that is stabilized by loaded hydrogen (as was reported in ref. 6). Structure-refinement studies show that [D8]THF is dynamically disordered, while it fills each of the large cages of [D8]THF,17D2O stoichiometrically. Our results show that the clathrate hydrate takes up hydrogen rapidly at pressures between 60 and 90 bar (at about 270 K). At temperatures above ,220 K, the H-storage characteristics of the clathrate hydrate have similarities with those of surface-adsorption materials, such as nanoporous zeolites and metal,organic frameworks,7,,8 but at lower temperatures, the adsorption rates slow down because of reduced D2 diffusion between the small cages. [source]