Write a post comparing the solvent dewaxing and catalytic dewaxing processes.

Wax is made up of long-chain paraffins and it is a desirable by-product, particularly lube oil base stock. Dewaxing is the process of removing wax from feedstocks that would otherwise readily solidify, such as DAO from deasphalting and HVGO from vacuum distillation. There are two commercial methods of dewaxing. On utilizes a physical process known as solvent dewaxing, while the other method of catalytic dewaxing involves a chemical process.

Solvent dewaxing is a physical process which separates the wax with respect to freezing and solvent transport. This method uses stage-wise refrigeration of the feedstock after being mixed with the solvent. Wax crystals are then carried to a rotary filter via the solvent to be separated on a filter cloth. This layer of wax is collected and taken to a steam-stripping unit to recycle the solvent separated from the wax product, known as slack wax. This product has several marketable uses, such as paraffin wax for candles, microwax for cosmetics, and for petroleum jelly. The refrigerator’s temperature can be manipulated to control the desired pour point of the resulting lube oil base stock product.

Catalytic dewaxing is a chemical process, which removes the wax by means of selective reactions of long chain n-alkanes. This method is technically a low-severity conversion process, which involves a selective catalytic cracking of n-paraffins. Molecular sieve catalysts, known as zeolites, host selective cracking of n-alkanes while simultaneously keeping out bulky i-paraffins. Therefore, this process increases the ratio of i-paraffins to n-paraffins in the product, in turn lowering its pour point.

In comparison, catalytic dewaxing has an advantage over solvent dewaxing in the fact that it yields a lube oil base stock with a lower pour point as well as a higher yield of this product. Catalytic dewaxing also poses the flexibility to produce both lube oil base stock along with light distillates such as gasoline.