Showing papers in "Industrial & Engineering Chemistry Process Design and Development in 1970"

Gas Separations with High-Flux Cellulose Acetate Membranes

Abstract: The high-flux cellulose acetate membranes used in desalination by reverse osmosis have been shown to consist of a dense layer, perhaps 0.2 mu m thick, supported on a highly porous substructure. Because they have a very thin diffusion barrier, high-flux cellulose acetate membranes permit a high gas permeation rate through a highly selective amorphous polymer. To examine the trade-off between high flow rates and separating efficiency, the data for cellulose acetate are compared in tabular form with data for other materials previously tabulated by Stern et al. According to Stern, Teflon FEP is available in 25-mu m thickness without pinholes. Such a membrane would give a helium flow rate only one-fiftieth that of the better of the high-flux cellulose acetates if both were operated at 80/sup 0/C. This temperature appears to be satisfactory for Teflon FEP but may be near the upper limit for cellulose acetate. The separation factors obtained with the cellulose acetate samples used were comparable to those reported for Teflon FEP.

Optimal Thermal Design of an Autothermal Ammonia Synthesis Reactor

Abstract: T h e treatment of variational problems has received considerable attention in the chemical engineering literature in the past decade. These can be classified as control or design problems. In chemical engineering, one would expect the most useful results to come from the solution of the design rather than the control problems, because in controlling a process one can, through feedback, correct and control by specifying the control algorithm (the functional relationship between corrective action and error) and not the control action function-e.g., valve stem position us. time. The solution to the variational control problem would yield the control action function, and while there are cases-e.g., batch processes-in which this would be useful, in most process control problems we are free to exert corrective action after the process has started and error has been measured. This is obviously not true in design problems; the configuration is first set and then the process is operated. This situation is more compatible to the nature of variational problem solutions. Thus it was decided to study variational problems that arise in design. Beginning with Temkin and Pyzhev (1960) and Denbigh (1944, there has developed a considerable literature (Aris, 1961) on the processing conditions under which a chemical reaction should be carried out in order to obtain maximum yield or selectivity. Although this work is of great value, there are two shortcomings: The process variables such as temperature, pressure, and concentration are not under direct control of the designer-for example, the designer

Catalytic dehydrogenation of 2-propanol to acetone

Abstract: Catalytic dehydrogenation of 2-propanol over Cu-SiO2 catalyst was investigated. The undesired side reaction of dehydration can be controlled by a selective catalyst and choice of proper operating conditions. The kinetics of the heterogeneous catalytic reaction can be adequately expressed by a forward first-order and reverse second-order mechanism. The rate-controlling step with chemically pure 2-propanol is single-site surface reaction, while for the technical grade alcohol the adsorption of alcohol is rate-controlling. The static bed data are compared with the fluidized bed dat