Short-contact-time properties

Due to the severe operating conditions (high temperature and high flow rates), typical of short contact time reactions, heat and mass transfer properties are expected to play a decisive role in the behavior of the reactor. Thus, in principle, the choice of catalyst support can greatly affect the reactor performance [69]. 

Cross-Polarization Kinetics. Knowledge of the CP kinetics (dependence of the intensity of the peaks versus contact time) is essential for quantification of the CP-spectra. The CP-kinetics parameters can also provide information on the dynamic properties of the materials under study. A typical CP-kinetics curve consists of two distinct parts at short contact times the magnetization is increased followed by the decrease... 

Cracking properties of a Si-VPl-5 (Si/Al=0.4 in the gel) and the reference catalyst were also investigated by Micro Activity Tests (MAT), using a short contact time MAT (SCT-MAT) which is a modified version of the ASTM MAT with better correlation to a commercial unit 1 g of atmospheric residue was fed to the reactor during 30 seconds at 524°C. Liquid products were collected at 0°C and analyzed on a HP 5880 Sim Dist GC, while gas products were collected over a saturated KCl-solution and injected on a HP 5880 Refinery Gas Analyzer. 

The importance of diffusion restrictions in FCC catalysis is often questioned. Short-contact-time pilot riser experiments confirm that combining zeolites with diffusion-enhancing matrices can result in significant product selectivity and product property improvements. The industrial benefits of a nonzeolite matrix on bottoms cracking in heavy vacuum gas oil (VGO) and resid FCC (RFCC) have also been confirmed in practice. Recently, some new methods have been used to measure the accessibility of FCC catalysts. 

The polymer is prepared by homo- or copolymerising a vinyl phosphonium salt monomer, such as 2-methacryloxyethyltri-n-octylphosphonium chloride and has a wide antimierobial spectram and a sufficient antimicrobial effect, even with a short contact time. The lens and lens care products exhibit excellent optical properties and processabihty. 

The dialysis membrane is a critical factor contributing to the efficiency of the dialysis separation system. In addition to their specificity on allowing the passage of a certain species of analyte while obstructing interfering components, which is a common requirement for all dialysis systems, on-line systems demand better mechanical and kinetic properties. Dialysis membranes of FI systems are expected to allow the achievement of high transfer factors within very short contact times of usually less than 30 seconds, while the membranes should be able to withstand hundreds of analytical cycles without significant deterioration in their performance. 

Modelling diffusion, reaction and deactivation in FCC catalysts becomes important as new trends in vacuum gas oil processing point to short catalyst/oil contact times (less than 1 sec) in industrial riser reactors. Under short contact times catalysts particles may experience diffusion limitations [6], and thus catalyst pore dimensions become very important in determining conversion and selectivity. FCC catalysts are made of several different components to produce the necessary activity and mechanical properties. As the accessibility of large molecules to the active sites within the catalyst might be constrained,... 

Activated carbon cloth (ACC) is used for the removal of volatile organic compounds fix)m effluent gas streams [1], Specific micropore structures in ACCs make them real candidates for use in adsorption processes where a high rate of adsorption is accompanied with short contact time between adsorbent and adsorbate. It is very important for manufacturers to produce ACC with desirable pore size distributions, and be able to control the development of various pores from primary micropores to mesopores during activation processes. Adsorption selectivity towards various gases is another very important property, which can be achieved by introducing oxygen complexes onto the surface during activation [2-4]. 

In the case of short-term catalysis, the basic processes of formation of the products occur in the gas phase after the interaction with the catalyst, which removes many of the issues related to changes in its properties under the influence of the products, for example, because of their deposition on the surface. High gas flow rates ( 1 m/s) and short contact times ( 1 ms) enable to produce a few kilograms of products per day per less than 1 g of catalyst [155]. Short-term catalysis makes it possible to realize complex combinations of temperature and concentration profiles during the reaction, as well as various versions of the relationship between the areas of catalytic and gas phase processes. 

The effect of carboxylate and/or sulfonate ion incorporation on the physical and blood contacting properties of polyurethanes was studied by Cooper and collaborators [476-478]. Specifically, propyl sulfonate and ethyl carboxylate groups were grafted onto polytetramethylene oxide-based polyurethanes. Carboxylate polymers had no statistically significant effect on canine ex vivo blood contact response, but propyl sulfonate incorporation significantly reduced platelet deposition for very short blood contact times. 

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