Separations Technology最新文献

The experimental adsorption and desorption equilibrium data for propane, propylene, and propane-propylene mixtures on 13X molecular sieves are presented for different temperatures and compositions; these data were efficiently determined by using the differential sorption bed system described by Liapis et al. (Sep. Technol. 1992, 2, 141–154). The Toth equation was found to correlate with the experimental equilibrium single-component data very well. For the binary propane-propylene mixtures, propylene is the most preferentially adsorbed component. The feasibility of describing the experimental binary equilibrium data with the ideal adsorbed solution expressions, the heterogeneous ideal adsorbed solution expressions and the heterogeneous ideal adsorbed solution with specific gas-solid interactions expressions was examined. Comparison between these expressions and the experimental binary equilibrium data showed that none of the expressions could satisfactorily describe the experimental results for the binary mixtures for all temperatures and compositions studied in this work. For a given multicomponent adsorption system of interest, numerous sets of experimental equilibrium data of adsorption and desorption could be efficiently and accurately determined by using the differential sorption bed system and the experimental procedures described in this work; these results could be used in parameter estimation and model discrimination studies, as well as in process design.

An experimental study of the filtration and dewatering of fine coal with and without additives was carried out. Filtration and dewatering behavior were determined using a vacuum filtration cell. The variables studied included the driving force, solids concentration, filter area, particle size and slurry pH. The effects of several flocculants, surfactants and hydrophobing additives (oils) on final moisture content of the filter cakes were determined. The investigations included determination of the rates of filtration and dewatering, assessment of the effects of additive type (anionic, cationic and nonionic), and establishment of optimum dosage of additives. Overall, it was found that the filtration and dewatering behavior were enhanced by increased driving force, higher initial slurry concentration, larger filtration area, larger particle size and lower slurry pH. Among surfactants and flocculating additives the anionic types were found to do the best job of filtration enhancement. At optimum dosages, the final cake moisture contents were reduced by 3.6% and 5.8% by weight using the appropriate surfactant and flocculant, respectively. However, the best filtration enhancements were achieved by addition of oils, which yielded cake moisture reductions of approximately 10% by weight.

The Macro State Markov Chain Model (MSMCM) is useful in developing parallel Monte Carlo simulation schemes to dramatically reduce computer simulation time (Chen, A. Hirtzel, C. S. Molecular Physics 1993, submitted; Chen, A.; Ph.D. diss., 1993). In this article, some special issues are addressed to apply the MSMCM to multicomponent system. A fourth type of transition, “replacement,” in addition to the conventional “move,” “add” and “remove” transitions, is introduced to guarantee the reachability of all states in a macro state. Adsorption of a mixture of oxygen and nitrogen in zeolite 5A is studied using the MSMCM model

We propose a complementary pressure swing adsorption (CPSA) process consisting of four beds for separating air into enriched oxygen and nitrogen. Simulation results showed that the CPSA process performed better than either the oxygen process or the nitrogen process. Using zeolite 5A and 4A as adsorbents, the mole fraction of oxygen and argon in the enriched oxygen may be as high as 99.57% (at 34.44% recovery), and the purity of the enriched nitrogen about 98% (at 47.86% recovery). For producing enriched oxygen of 80–90% purity, a modified CPSA process is suggested. The relationships between production rate, purity, and oxygen and nitrogen recoveries are discussed.

A new modification of the Frazier-thermal-diffusion system in which column length varies by a constant increment is proposed. Equations for estimating the most optimal column-length increment and column number corresponding to a maximum degree of separation are derived. It is found that by adopting the present modification, substantial improvement in performance over the classical Frazier scheme may be achieved.

The two approximate uptake rate expressions of spherical adsorbent pellets developed previously (Yao, C. and Tien, C. Approximation of uptake rate of spherical adsorbent pellets and their application to batch adsorption calculations. Chem. Eng. Sci. 1993, 48, 187) were applied to continuous-flow stirred tank and fixed-bed adsorption processes. The results show that both approximations represent improvement over the conventional linear driving force model. Relative accuracy of these two approximations was found to vary from case to case and can be related to the type of driving force for interphase mass transfer present in the particular problem.

Particle collisions and filter cake collapse are observed through a microscope during the formation of filter cakes. Cake filtration is widely applied throughout industry for fluid-particle separations. Models and theories have been developed to describe and predict filter cake performance, but there is little literature on direct observation of particle packing and cake formation. A filter assembly the size of a microscope slide is placed on the microscope such that the slurry flow and cake formation is across the field of view. The cake formation is recorded on video tape. Photographs of the video image show particles in the slurry colliding with and sometimes adhering to other particles when forming the filter cake. The photographs also show the cake structure collapse as the cake compacts or compresses.