Centrifugal absorber selection

The per pass ethylene conversion in the primary reactors is maintained at 20—30% in order to ensure catalyst selectivities of 70—80%. Vapor-phase oxidation inhibitors such as ethylene dichloride or vinyl chloride or other halogenated compounds are added to the inlet of the reactors in ppm concentrations to retard carbon dioxide formation (107,120,121). The process stream exiting the reactor may contain 1—3 mol % ethylene oxide. This hot effluent gas is then cooled ia a shell-and-tube heat exchanger to around 35—40°C by usiag the cold recycle reactor feed stream gas from the primary absorber. The cooled cmde product gas is then compressed ia a centrifugal blower before entering the primary absorber. 

Acrylic Acid Recovery. The process flow sheet (Fig. 3) shows equipment and conditions for the separations step. The acrylic acid is extracted from the absorber effluent with a solvent, such as butyl acetate, xylene, diisobutyl ketone, or mixtures, chosen for high selectivity for acrylic acid and low solubility for water and by-products. The extraction is performed using 5—10 theoretical stages in a tower or centrifugal extractor (46,61—65). 

The effect of contactor design on the selectivity of amine solutions for absorbing H2S in tire presence of CO2 has been smdied by Darton et al. (1987). They conclude that selectirity, as represented by the ratio of overall mass transfer coefficients for H2S and CO2, is about the same (100) for trays and 2-in. Pall rings in a MDEA contactor operating at atmospheric pressure. Their work indicates that even higher selectivities should be possible with alternative contactor designs, such as cyclones, centrifuges, and cocunent gas/hquid flow tubes. 

---