Tag Archives: solvent

The removal of wax from feed stocks using solvents and catalytic dewaxing processing

Posted on by
Reply

After my one Penn State laboratory class where we chilled different hydrocarbons to measure the cloud point (temperature at initial wax formation) and pour point (temperature at which hydrocarbon became practically solidified) it was determined that the cold resistance of fuel from forming wax was an important property of a hydrocarbon. In a real life application hydrocarbons are enhanced by additives to resist the wax (long-chain paraffin) formation. Before any additives are blended into fuels they undergo a solvent or catalytic dewaxing processes.

The first method for dewaxing is by using the physical process of solvent dewaxing. The two main solvents that are used in the solvent dewaxing process are propane and ketones (either methyl ketone with methyl isobutyl ketone or methyl ketone with toluene.) The object of solvent dewaxing to mix the solvents with the deasphaling oil, which will dilute the feedstock reducing viscosity, and then the mixture is cooled down until wax is formed. [1] Once the wax was formed it is sent into a rotating drum that forces the wax crystals to the outside where I can be extracted. The most economical way to perform this process is by using Dilchill dewaxing. Dilchill dewaxing is a process that injects cold solvent into DAO stream where it is highly agitated forcing the formation of larger wax crystals.[1]

Another way to extract wax from DAO is by Catalytic Dewaxing. Catalytic dewaxing is the chemical process that uses hydrocracking, performed by zeolite catalysts, to break apart the long chained n-paraffins to form branched i-paraffins. As mentioned before, this will cause the cloud point and pour point to be reduced. Going one step further, catalytic cracking can use two enzymes for the reduction of pour point and to also improve on the oxygen stability of the DAO. [1] Catalytic dewaxing the the preferred process compared to solvent dewaxing because it has a better yield and is a cheaper overall process.

Sources:
1. Gary, J. H., & Handwerk, G. E. (2007). Petroleum refining: technology and economics. New York: M. Dekker.

Product removal from applying solvents and non-polar solvents to a feedstock

Posted on by
Reply

Solvent fractionation is the process in which solvents, such as n-heptane, n-pentane, and propane, are used to further separate the feedstock that comes from the initial distillation process. The most common application for solvent fractionation is performed on the vacuum distillation residue. The reason that this feedstock is distilled further is because it can create different marketable products such as asphalt (from asphaltene), resins, and oil (used for lubrication and other products). The way that these distillates are separated, from the aromatic solvents of benzene and toluene, occurs in three stages which blend the feedstock with increasingly lighter paraffinic solvents. The first stage is using n-heptane to separate the solid asphaltene product from the VDR feedstock. The portions, such as n-heptane maltenes, which are soluble in the heptane solvent, are introduced to n-pentane. N-pentane allows for hard resin to be separated from the feedstock, and allows for further separation of the soluble products to finally be treated with propane to separate the feedstock into soft resin and oil.
In order to further understand how asphaltenes are extracted from the feedstock, with the use of n-heptane, n-pentane, and propane, one would need to use the Hildebrand Solubility Parameters. These parameters are used to determine the solvent power of these non-polar solvents and how the different carbon numbers define the power of the solvent. The Hildebrand Solubility Parameters use the characteristics of surface tension, molar volume, and energy of vaporization to be able to decide which solvent is best for asphaltene and resid extraction. Ultimately, the goal for this process is to obtain the highly usable deasphalted oils so that they can be further processed to make lube oil base stock and distillate fuels. Most of the deasphalting process is conducted by propane and then is further processed by furfural, phenol, and N-methyl-2-pyrrolidone solvents to separate the high carbon aromatics from the naphthenic and paraffinic ones. [1]
Sources:
1. Gary, J. H., & Handwerk, G. E. (2007). Petroleum refining: technology and economics. New York: M. Dekker.