Recovery from the gas phase

The most common adsorbant used is granular or powdered activated carbon. This material, which is available from almost all forms of organic carbon-containing matter, is a microcrystalline nongraphite form of carbon. The production of activated carbon can be achieved by use of rotary kilns, hearth furnaces, or furnaces of the vertical shaft or fluidised bed type, and each is suitable for the generation of different pore size and the source of carbon. The pore volume and size are influenced by both the carbon source and method of production. The adsorption properties are directly related to the pore volume, pore size distribution and the nature of the functional groups on the surface of the carbon. Activation is achieved chemically, by treatment by dehydration with zinc chloride or phosphoric acid, or by treatment with steam, hot carbon dioxide or a mixture of both. The activated carbon is available in three basic forms, powder, granules or as cylindrical or spherical pellets. For solvent recovery systems the carbon is usually obtained from either wood charcoal, petroleum residues or coconut shells and is often used in the form of pellets. 

Activated carbon is capable of adsorption of a wide variety of chemicals. The source and pore size of the carbon directly influences the performance of the process and can be optimised for different solvents. A typical system operates with two horizontal or vertical containers or beds of activated carbon coupled to a 

Continuous process Limited capacity Large spacial requirements Mixtures processed Low cost 

Generates solvent and water mixture As above except  

Liberates mixture requiring further separation Well established 

---

Our experiments demonstrate that sulfuric acid can be produced over activated carbon in a trickle bed flushed continuously with a solvent. Catalyst activity in this system is very high so that trickle-bed heights and thus pressure drops will be reasonable. As expected, gas and loading liquid are important parameters governing SO2 recovery from the gas phase and productivity of the catalyst. Of the solvents investigated, acetone and ethyl ether qipear to be feasible, although vacuum distillation will be needed to separate acid and acetone and a pressurized process will be required if ethyl acid is the solvent. 

---