The factors affecting the adsorption and desorption kinetics in a TEOM are reviewed in detail with particular attention given to the assumptions required to obtain physical transport parameters from the data. Two models are presented to simulate TEOM adsorption data in the case that concentration differences down the catalyst bed can be neglected, as is appropriate when the amount of catalyst used is small, the carrier gas flowrate is large, and/or the adsorbate partial pressure is low. In the first model, the effective diffusion coefficient, De, is taken to be constant. In the second model, the effective diffusion coefficient is assumed to obey the Darken equation, De=D0/(1−θ). The TEOM results obtained on n-hexane, n heptane, n-octane, toluene and p-xylene on a commercial FCC catalyst and on pure rare-earth exchanged zeolite Y under non-reacting conditions (373-) are analysed in detail. It is found that intracrystalline diffusion is not the limiting factor affecting the overall rates of adsorption and desorption for the systems studied. Instead, it is the transport of molecules between the adsorbed and vapour phases at the edge of zeolite crystallites that is the limiting transport step affecting the overall kinetics. For the FCC catalyst, the limiting step is the transport of molecules at the zeolite-matrix interface rather than, say, the matrix-vapour interface. Local rate constants for the desorption of the hydrocarbons at the rate-controlling interface have been obtained. 相似文献
An experimental procedure to measure the adsorption and desorption kinetics of hydrocarbons in fluid catalytic cracking (FCC) catalysts using a tapered element oscillating microbalance is described. It enables adsorption rates to be measured on a timescale of about . Experiments using n-hexane, n-heptane, n-octane, toluene and p-xylene were performed on both a commercial FCC catalyst and a pure rare-earth exchanged zeolite Y sample under non-reacting conditions (temperatures of 373-). Heats of adsorption for these hydrocarbons are reported. The overall adsorption and desorption kinetics are found to depend on carrier gas flowrate in cases when adsorption is strong indicating that the length of the catalyst bed can have a significant influence on the observed kinetics. However, at high carrier gas flowrates the overall adsorption and desorption kinetics do not depend on the amount of catalyst present. It is found that the rates of adsorption and desorption of the hydrocarbons studied are the same for the FCC catalyst as for the pure zeolite Y sample. This means that mass transport in the matrix component of the FCC catalyst is rapid and not a limiting step in the adsorption process for the hydrocarbons studied in this work. 相似文献
A series of montmorillonite‐poly(ε‐caprolactone) nanocomposites were prepared according to a two‐stage procedure. In the first step Na‐type silicate clay was cation exchanged with protonated 12‐aminolauric acid. In the second step ε‐caprolactone was intercalated in the modified clay and ring‐opening polymerized. The clay content was varied regularly from 0 to 44 wt.‐%, with exfoliation of the silicate layers being detected by X‐ray diffraction in the nanocomposites dispersing up to at least 16 wt.‐% clay. Crystallization of poly(ε‐caprolactone) was not prevented in the nanocomposites, although it proceeded to a lower extent/order than in a homopolymer sample. The transport properties were investigated using water or dichloromethane as vapor permeants. In each case, a dual sorption behavior was observed as a function of the vapor activity because of the occurrence of different sorption mechanisms. The permeability of the nanocomposites to either permeant decreased with increasing clay content. In particular, the permeability behavior to water was largely dominated by the diffusion parameter. 相似文献
The simultaneous adsorption of SO2, NO, and CO2 on K2CO3‐modified γ‐alumina under different operating conditions was studied in a fixed‐bed reactor. The experimental results showed that the influence of a temperature increase on the simultaneous adsorption of the three gases was complex and different from the effects seen when both chemical adsorption and competitive adsorption existed. An increase in O2 concentration and small amounts of water could enhance the adsorption of SO2 and NO while the adsorption of CO2 was not influenced. The breakthrough curves of the simultaneous adsorption experiments suggested that the investigated adsorbent may be a good candidate for the simultaneous adsorption of SO2, NO, and part of the CO2 while the adsorption capacity for CO2 still needs to be enhanced. 相似文献
Efficient one‐step syntheses of α,β‐ and β,β‐dihaloenones were achieved by ruthenium(II)‐catalyzed reactions between cyclic or acyclic diazodicarbonyl compounds and oxalyl chloride or oxalyl bromide in moderate to good yields. This methodology offers several significant advantages, which include ease of handling, mild reaction conditions, one‐step reaction, and the use of an effective and non‐toxic catalyst. The synthesized compounds were further transformed into highly functionalized novel molecules bearing aromatic rings on the enone moiety using the Suzuki reaction.
A new synthetic method for α‐alkynyl‐α,β‐unsaturated esters is presented herein. The method is based on a copper(I)‐catalyzed three‐component reaction of a terminal alkyne, diazoesters and aldehydes. The reaction is featured by mild conditions, high yields and excellent stereoselectivity. Cu(I) carbene migratory insertion is proposed as the key step in the transformation.