ADSORPTION PROCESS

  Adsorption processes use a solid material (adsorbent) possessing a large surface area and the ability to selectively adsorb a gas or a liquid on its surface. Examples of adsorbents are silica (SiO₂), anhydrous alumina (Al₂O₃), and molecular sieves (crystalline silica/alumina). Adsorptionprocesses may be used to remove acid gases from natural gas and gas streams. For example, molecular sieves are used to dehydrate natural gas and to reduce its acid gases. Adsorption processes are also used to separate liquid mixtures. For example, molecular sieve 5A selectively adsorbs n-paraffins from a lowoctane naphtha fraction.    

  Branched paraffins and aromatics in the mixture are not adsorbed on the solid surface. The collected fraction containing mainly aromatics and branched paraffins have a higher octane number than the feed. Desorbing n-paraffins is effected by displacement with another solvent or by using heat. The recovered n-paraffins in this range are good steam cracking feedstocks for olefin production.

  Adsorption of n-paraffins (C₁₀-C₁₄) from a kerosine or a gas oil fraction can be achieved in a liquid or a vapor phase adsorption process.  Normal paraffins in this range are important intermediates for alkylating benzene for synthetic detergents production. They are also good feedstocks for single-cell protein (SCP).

  The IsoSiv process is an isobaric, isothermal adsorption technique used to separate n-paraffins from gas oils. The operation conditions are approximately 370°C and 100 psi. Desorption is achieved using npentane or n-hexane. The solvent is easily distilled from the heavier n-paraffins and then recycled.