Dewaxing is an important separation process whereby wax is removed from DAO feed stocks coming from deasphaulting. Furthermore, wax is a marketable by-product making the process much more useful. In addition, the process is optimized to produce lubricating oil base stock with important properties such as low pour points, low volatility, high viscosity index and high thermal stability. There are two main methods for dewaxing: solvent dewaxing and catalytic dewaxing. The first method is solvent dewaxing; solvent dewaxing is a physical process that uses stage-wise refrigeration of the feedstock after mixing it with the solvent. Wax crystals are formed and are then separated no a filter cloth by a rotating drum. the wax is scraped off the filter cloth and is taken to a steam stripping unit to recover and reuse the solvent. The final wax product, known as slack wax, has many uses such as producing candle wax, micro wax for the cosmetics industry, and petroleum jelly. Also, the dewaxed oil is taken to a steam stripping unit to recover the solvent and use it to produce more lube oil base stock. The second dewaxing method is catalytic dewaxing; catalytic dewaxing is a chemical process whereby wax is removed by selective cracking of n-paraffins. The selective cracking of the n-paraffins occurs in the pores of molecular sieve catalysts, known as zeolites, with pore openings on the order of 0.6 nm. This separates the i-paraffins  from the rest of product because of their larger size caused by their molecules’ branching. Thus, the process lowers the pour point and increases the ratio of i-paraffins to n-paraffins in the product. Hydrogen is also fed into the reactor to prevent coking from occurring on the catalyst beds. Furthermore, distillate fuels are produced as a by-product of the cracking process. Advantages of catalytic dewaxing include a lower capital investment and a better product stability.

Sources:

Course Webpage

Wikipedia: Solvent Dewaxing, Catalytic Dewaxing