Ethyl tert-butyl ether (ETBE) is an alternative gasoline oxygenate that combines the blending properties of methyl tert-butyl ether (MTBE) and the renewability of ethanol. Technologically, the best means of synthesis utilizes reactive (or catalytic) distillation to maximize hydrocarbon conversion and energy efficiency while simultaneously producing a high-purity ether product. Mathematical models of reactive distillation are based on the conventional distillation process with supplementary equations added to model the reactions present. Ether-alkene-alcohol systems are highly nonideal in the liquid phase so that careful selection of physical property routines is required to ensure satisfactory simulation results. Column simulations performed here using both Pro/II and SpeedUp show excellent agreement with previously published experimental data for a MTBE system and also agree well with each other for both MTBE and ETBE systems. A homotopy analysis was performed on the tuned simulation models to determine the effects of key design and operating variables on column performance and, subsequently, to develop a design method for reactive distillation columns. Some unusual behavior was identified in ETBE reactive distillation columns compared with either MTBE columns or conventional distillation.

There i s current interest in the utilization of homogeneous suspensions of fine sized solids in the fluid transport of heterogeneous mixtures of coarse solid particles. It has been established that the introduction of the fines beneficially affects the transport of coarse solids (1, 2 ) . Although the homogeneous suspensions have been identified as non-Newtonians, there have not as yet been satisfactory solids pipelining design criteria for the transport of coarse particles based on the rheological properties of fines suspensions. A recent investigation (3) has shown that the use of existing design formulas, all of which include the coarse solids settling characteristics a s parameters, can result in significantly erroneous design unless these parameters are determined in the fluid actually used to transport these solids. This conclusion, based on limited experimental evidence, prompted a more detailed study of settling in nowNewtonian suspensions, particularly in the Stokes and intermediate settling regimes. EXPERIMENTAL PROCEDUREConsiderable preliminary work was necessary to find a fluid with stable Bingham properties, suitable for the settling tests. Although there have been numerous investigations of homogeneous suspensions in both pipelines and viscometers in which it has been suggested that the rheological behavior of these suspensions can be approximated by the idealized Bingham model (4 to6), most suspensions develop a density gradient after standing in a column and exhibit a nonlinear relation between shear stress and rate of shear at rates of shear approaching zero. Furthermore, to extend the range of variables, it was desirable to choose a plastic material with properties distinctly different from those used by others ( 3 , 7). Tomato sauce (catsup), which had been suggested (8) a s a Bingham plastic, was investigated; it was found suitable and used in the tests. The rheological properties of a Bingham plastic fluid are defined byThe Bingham plastic properties of the tomato sauce were substantiated by a series of flow t e s t s in tubes. Testing with a rotary viscometer was discontinued when the sauce showed a tendency to bleed after continuous shear of the material in contact with the viscometer. The tube viscometer offered much greater similarity to the subsequent settling tests in which the spheres continuously encountered material which had not recently undergone shear. Flow rates of the material under gravitational acceleration and under applied pressures were measured in stainless steel tubes ranging in internal diameter from 0.366 to 1.709 cm. to provide a similar scale to the subsequent drop tests. For the settling tests, silver balls were cast in various sizes and then neutron-irradiated to give a gamma activity of about 1 mC. of Ag 110 per sphere. The tests were made in a 6 in. x 6 in. x 54 in. high acrylic column. Spheres were dropped by hand a t the surface of the fluid in the column and were recovered from the conical bottom by permitting them to flow out with some fluid via a 3/4-in. dis...

Ethyl tert-butyl ether (ETBE) is growing in importance as a gasoline oxygenate and octane enhancer. Its gasoline blending properties are superior to methyl tert-butyl ether (MTBE), and its semirenewability is attracting subsidies from many governments. Synthesis of ETBE via reactive distillation offers advantages of higher conversion, improved energy efficiency, and lower capital costs. A dynamic simulation, based on the MESH equations with supplementary equations to model the main chemical reaction, was developed using SpeedUp. The simulations were then utilized for the study of transient open-loop responses and for control system design. The control of a reactive distillation column presents several difficulties not normally associated with distillation, and dynamic simulation proved to be the ideal tool for the study and resolution of these problems. Some general recommendations for the control of reactive ETBE columns are made, including the need to address control issues early in the design process to recognize implications on process equipment design.