Hydrocarbon recovery with active carbon

Properties of Gas Adsorption Carbons, 1088 VOC Removal and Solvent Recovery with Active Carbon, 1093 Hydrocarbon Recovery with Active Carbon, 1109 Fluidized, Moving, and Rotating Bed Processes, 1109 Canister and Panel Systems for Air Purification, 1117... 

C02 is recoverable by physical adsorptions of active carbons or zeolites, or a chemical sorption by carbonation of calcium oxide (CaO) at the C02 recovery and separation process. CaO is absorbable chemically C02 at temperatures of 500-800°C [Eq. (5)]. CaO can remove C02 from hydrocarbon reaction system at the reaction temperature for C02 production with small sensible heat loss, and also enhance reaction rate and yield of the C02 production reaction (Kato, 2003). 

Interactions with the carbon surface can make the recovery of certain solvents, such as ketones and chlorinated hydrocarbons, difficult. Ketones and aldehydes can polymerize, releasing large amounts of heat. When this happens in a part of the bed with poor heat transfer, the temperature can reach the ignition point of the solvent. Fires always start with hot-spots in parts of the bed where the airflow is reduced due to poor design. The susceptibility of the carbon bed to autoignition can be reduced by removing soluble alkali sodium and potassium salts, that may be present as impurities in the activated carbon and which can function as combustion and gasification catalysts [29]. 

Pressure swing adsorption processes are also designed to produce high-purity (99.95+ %) H2 products from refinery-off gases containing H2 (65-90%) and C1-C5 hydrocarbon impurities with high H2 recoveries ( 86+ %). Silica gel and activated carbons are used as adsorbents. 

The recovery plants include a desiccant to dry the gas and prevent the formation of hydrate in the transmission lines. The desiccant is used in the same adsorber with the carbon on the inlet side or two adsorbers are used in series, one containing the desiccant and the other, activated carbon. The desiccant also adsorbs the higher-boiling-point hydrocarbons so that the total adsorption is a combined effect of the two. Operating cycles are fairly fast, the adsorption period varying from 20 to 45 minutes. 

The removal of aromatics and relatively heavy hydrocarbons from gas streams with fixed beds of activated carbon is essentially the same process as. solvent recovery, and similar adsorbents and equipment are used. The principal differences are that in hydrocarbon recovery the feed is typically a natural gas or other combustible gas stream rather than air, and adsorption is usually (but not always) conducted at elevated pressure. The basic design approach for hydrocarbon recovery systems follows the same general logic as that described for solvent recovery systems. A brief outline of the key design steps is given in the Calgon Carbon Corporation bulletin, Heavy Hydrocarbon Removal or Recovery from Gas Streams (1987). 

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