Solvent recovery with activated carbon

Since several companies provide package units for activated carbon solvent recovery, new engineers are more likely to be involved in the purchase and installation of a unit than in designing a new unit. The more you know about solvent recovery with activated carbon, the better choice of unit and better bargain you will be able to make for your conpany. 

Adsorption Adsorption of the solvents by passing the waste air through an adsorber filled with activated carbon. Solvent recovery by steam or hot gas desorption By steam desorption the resulting desorbate has to be separated in a water and an organic phase using a gravity separator (or a rectification step)... 

Solvent recovery with adsorption is most feasible when the reusable solvent is valuable and is readily separated from the regeneration agent. When steam-regenerated activated-carbon adsorption is employed, the solvent should be immiscible with water. If more than one compound is to be recycled, the compounds should be easily separated or reused as a mixture. Only very large solvent users can afford the cost of solvent purification by distillation. ... 

This contribution deals with adsorptive solvent removal and recovery and some other hybrid processes using activated carbon in combination with other purification steps. 

Figure 18-9. Solvent recovery with activated carbon and steam regeneration...

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... 

VOC Removal and Solvent Recovery with Active Carbon... 

This contribution deals with adsorptive solvent removal,recovery, and some other hybrid proeesses using activated carbon in combination with other purification steps. Due to more stringent environmental protection requirements, further increases in die number of adsorption plants for exhaust air pmification may be expected. 

The volatile solvents recoverable by the activated carbon system or any other system are nearly all organic, and many of them form flammable or explosive mixtures with air. Such mixtures may lie between upper and lower explosive limits. The activated carbon system can avoid the explosive range by staying well below the lowest percentage of vapor which is still explosive it functions well at very low concentrations. The system also recovers solvents efficiently even in the presence of water the recovery efficiency is high (98 percent and 99 percent are not unusual) it may be fully automatic. The annual maintenance charge rarely exceeds 5 percent of the cost of equipment. The recovery expense may be as low as 0.2 cent per pound in some installations it rarely exceeds 1 cent per pound. 

Whenever activated carbons can be used for the recovery of valuable chemicals from aqueous streams, these are preferred as they are cheap, can often be conveniently regenerated, and their final disposal, by combustion, is easy. The disposal of activated carbons is usually undertaken by vendors. Regeneration can be done, as pointed out in Section 6.4.3, with steam or another solvent, and sometimes chemically, e.g. using NaOH from phenolic substances. 

The binding energies of the resin are normally lower than those of activated carbon for the same organic molecules, which permits solvent and chemical regeneration and recovery. Regeneration can be conducted with caustic or formaldehyde or in solvents such as methanol, isopropanol, and acetone. Batch distillation of regenerant solutions can be used to separate and return products to the process. 

---