Scrubber units, liquid phase

Aqueous solution processes and the properties of aqueous species are of prime interest in wet 1ime-limestone and other liquid phase scrubber units. Accordingly, thermodynamics properties of interest include, but are not limited to AH°, y, < ,... 

In the retention of volatile radioiodine species in a Venturi scrubber unit, two different stages have to be distinguished. The first one is the transfer from the venting flow to the liquid phase, the second one the prevention of revolatilization from the liquid phase even in the case of a continuing and long-lasting (up to 36 hours) venting flow. 

Carbon monoxide and methanol from the scrubber unit are fed to the reactor containing the catalyst and the solvent. The liquid product stream is depressurized in a flash vessel and divided in a gas and liquid phase. In this step the rhodium catalyst is separated from the crude acetic acid and is recycled to the reactor. It is critical for the process economics to avoid any rhodium metal loss in this step that could occur by precipitation and vaporization. The gas stream is scrubbed with methanol to recover the toxic and volatile methyl iodide and the off-gas of the scrubber system is flared. The liquid phase is sent to the light ends column (separation of light compounds, e.g., methyl iodide and methyl acetate). The bottom of this column (catalyst, water, and acetic acid) is recycled to the reactor. Wet acetic acid is sent to the drying column and dried acetic acid is obtained as bottom product. The overhead (mixture of acetic acid and water) is recycled back to the reactor. In the product column heavy by-products (major liquid by-product propionic acid) are removed from the dried acetic acid. The overhead is sent to the finishing column, where ultrapure acetic acid is obtained as a side-stream. 

There are several other types of apparata used for reactive absorption, though these are less widespread. In mechanically agitated bubble columns it can be assumed that both phases are ideally mixed, whereas in the jet absorber, the gas stream breaks on a liquid surface and is dispersed in the liquid. In spray towers and venturi scrubbers, liquid is sprayed as fine droplets. Thin-jilm contactors, in which liquid film is scrapped from the walls by impellers, are applied for reactive absorption in viscous liquids. Some units, such as wetted-wall columns, contactor, laminar jet absorber and disc (sphere) column are used mainly in laboratory. 

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