Dewaxing Ketone

Comparison of Molecular Sieve and Ketone Dewaxing. To serve as a basis for comparison, a sample of the C16-C32 wax distillate was dewaxed using conventional procedures. The oil feed was dissolved in ketone solvent and cooled at a rate of 1.3 K per minute with stirring to 260 K. The slurry was filtered with a 20-35 pm cloth filter and the cake was washed with additional solvent to... 

Figure 12. Theoretical yield curves for solvent (ketone) dewaxing (O) Morales, (+) this work and supercritical-fluid-molecular-sieve extraction of Cie-C wax distillate (X) supercritical sieve extraction...

FIGURE 9.11 Urea and methyl isobutyl ketone dewaxing of waxy lube distillate dependence of pour point on distillation range and dewaxing method. 

Incremental ketone dewaxing plants (see Figure 20) use a combination of Scraped Surface Exchangers that use cold filtrate for cooling the slurry followed by Scraped Surface Chillers, which use a refrigerant (propane, propylene, ammonia) to cool the slurry to the filtration temperature. Solvent may be added at the beginning or along the train in increments . 

Rotary vacuum filters are used in ketone dewaxers and rotary pressure filters are used in propane plants. The principles of operation are the same. A typical filter is shown in Figure 30. 

The filter drums used in ketone dewaxing (rotary vacuum) and in propane dewaxing (Rotary pressure) have filter cloths secured to the drum surface. The filter cloth retains the wax crystals while allowing the filtrate to pass through the filter cake, through the filter cloth and into the internals of the filter drum and eventually to the filtrate receiver drum. 

Propane dewaxing uses liquid propane as the solvent. Propane is normally a gas at ambient temperature and the vessels in the unit must be pressure vessels. This also ineludes the filter. Filtration in propane dewaxing is pressure filtration vs. ketone dewaxing which uses vacuum filtration. The propane temperature depends on the pressure, so that it is of paramount importance that the pressure be controlled. It is often said that in propane dewaxing propane is always either flashing or condensing. This adds an additional level of complexity that is not present in ketone dewaxing. 

Warm liquid propane is added to waxy raffinate and the slurry is prechilled in a shell and tube prechiller, with the slurry in the tube side. The Warm Dilution Ratio is controlled by the operator. Like the feed precooler in ketone dewaxing the outlet temperature of the prechillers is maintained just above the cloud point of the slurry to avoid fouling in the prechiller. Some newer designs use a preehiller tower. 

Make-up propane is added to replace the vented propane so that at the end of the cycle the dilution in the slurry, the cold dilution ratio (CDR) is at the desired target. Similar to ketone dewaxing where the filtration rate depends on the solvent dilution to the filters, the filtration rate in propane dewaxing is dependent on the CDR that is also the dilution that will be seen at the filters. The CDR also has a big influence on the Pour point. Wax molecules are highly soluble in propane, more than Toluene. Increasing the CDR will carry more wax molecules into the filtrate and increase the pour point of the dewaxed oil. This requires the manufacturer to reduce the filtration... 

DeWaxing Aids (DWA) may be used in ketone dewaxing but are always used in propane dewaxing. Typically the DWA doses used in propane plants are 2-3 times higher than in ketone plants. While DWAs are economically justified for use on all grades in the propane plant, performance on light neutrals in ketone plants has typically not been economically justified. 

Methyl Ethyl Ketone or loose term for ketone dewaxing unit... 

Ketone Dewaxing. This process is a dev opment of the benzene-acetone process by the use of various mixed solvents consisting of benzene, toluene, methyl ethyl ketone, methyl n-propyl ketone, methyl n-butyl ketone, or mixtures of these ketones. The advantages of the lower molecular-weight ketones are high filter rates and low solubility of wax, but they have higher vapor pressures and are somewhat soluble in water. 

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