The air exiting a furniture manufacturing factory from a extractor fan needs to be treated. What...

The air exiting a furniture manufacturing factory from a extractor fan needs to be treated. What method could be used to
treat the organic gases in the air? Explain with the used of diagrams, how this would be done.

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Expert Solution

Gases may be reactive to other chemicals, which is an important chemical property that can be used to collect vapor-phase pollutants.

Four general methods of separating gaseous pollutants are currently in use. These are (1) absorption in a liquid, (2) adsorption on a solid surface, (3) condensation to a liquid, and (4) conversion into a less polluting or nonpolluting gas.

Absorption of pollutant gases is accomplished by using a selective liquid in a wet scrubber, packed tower, or bubble tower. Pollutant gases commonly controlled by absorption include sulfur dioxide, hydrogen sulfide, hydrogen chloride, chlorine, ammonia, oxides of nitrogen, and low-boiling hydrocarbons.

The scrubbing liquid must be chosen with specific reference to the gas being removed. The gas solubility in the liquid solvent should be high so that reasonable quantities of solvent are required. The solvent should have a low vapor pressure to reduce losses; be noncorrosive, inexpensive, nontoxic, nonflammable, and chemically stable; and have a low freezing point. It is no wonder that water is the most popular solvent used in absorption devices. The water may be treated with an acid or a base to enhance the removal of a specific gas. If carbon dioxide is present in the gaseous effluent and water is used as the scrubbing liquid, a solution of carbonic acid will gradually replace the water in the system.

In many cases, water is a poor scrubbing solvent. Sulfur dioxide, for example, is only slightly soluble in water, so a scrubber of very large liquid capacity would be required. SO2 is readily soluble in an alkaline solution, so scrubbing solutions containing ammonia or amines are used in commercial applications.

Chlorine, hydrogen chloride, and hydrogen fluoride are examples of gases that are readily soluble in water, so water scrubbing is very effective for their control. For years, hydrogen sulfide has been removed from refinery gases by scrubbing with diethanolamine. All the gases mentioned have economic importance when recovered and can be valuable raw materials or products when removed from the scrubbing solvent.

Adsorption of pollutant gases occurs when certain gases are selectively retained on the surface or in the pores or interstices of prepared solids. The process may be strictly a surface phenomenon with only molecular forces involved, or it may be combined with a chemical reaction occurring at the surface once the gas and adsorber are in intimate contact. The latter type of adsorption is known as chemisorption.

The solid materials used as adsorbents are usually very porous, with extremely large surface-to-volume ratios. Activated carbon, alumina, and silica gel are widely used as adsorbents depending on the gases to be removed. Activated carbon, for example, is excellent for removing light hydrocarbon molecules, which may be odorous. Silica gel, being a polar material, does an excellent job of adsorbing polar gases. Its characteristics for the removal of water vapor are well known.

Solid adsorbents must also be structurally capable of being packed into a tower, resistant to fracturing, and capable of being regenerated and reused after saturation with gas molecules.

The efficiency of most adsorbers is very near 100% at the beginning of operation and remains extremely high until a break point occurs when the adsorbent becomes saturated with adsorbate. It is at the break point that the adsorber should be renewed or regenerated.

Industrial adsorption systems are engineered so that they operate in the region before the break point and are continually regenerated by units.

Amanda K answered 4 months ago

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