Dewaxing Filters

The naphtha is recovered from the dewaxed oil solution in conventional distillation equipment. The wax cake containing the filter aid is discharged from the dewaxing filter into a heated vessel, where the wax is taken into solution and the inert filter aid settles to the bottom in the form of a concentrated slurry. The aid separated from the wax solution is slurried with kerosene and this slurry is filtered on a continuous filter at a temperature sufficiently high to flash off water adsorbed on the aid. The dried and recovered aid on the filter is subjected to a chilled naphtha wash to displace the kerosene and cool the aid, which is then recycled to the chilled oil-naphtha mixture. Recovery of the aid in this manner permits its re-use indefinitely. 

Figure 18.12 Dewaxing filter with zero solvent loss and zero emission (with gas tight hood).

Refers to the addition of solvent, in increments to the waxy raffinate feed as it flows through the heat exchanger equipment leading to the solvent dewaxing filters. 

Segment Each solvent dewaxing filter drum segment is made up... 

Insofar as they are used to purify other products, several processes used in the refinery fall under the classification of dewaxing processes however, such processes must also be classified as wax production processes (2). Most commercial dewaxing processes utilize solvent dilution, chilling to crystallize the wax, and filtration (28). The MEK process (methyl ethyl ketone—toluene solvent) is widely used. Wax crystals are formed by chilling through the walls of scraped surface chillers, and wax is separated from the resultant wax—oil—solvent slurry by using fliUy enclosed rotary vacuum filters. 

In the propane process, part of the propane diluent is allowed to evaporate by reducing pressure so as to chill the slurry to the desired filtration temperature, and rotary pressure filters are employed. Complex dewaxing requires no refrigeration, but depends on the formation of a soHd urea—/ -paraffin complex which is separated by filtration and then decomposed. This process is used to make low viscosity lubricants which must remain fluid at low temperatures (refrigeration, transformer, and hydraulic oils) (28). 

Solvent dewaxing Treatment Cool/filter Remove wax from Inbe stocks Vacuum tower lube oils Dewaxed lube base stock... 

The problem received concentrated attention. One method (87) introduced used naphtha as a diluent, with an inert material, such as diatomaceous earth, to build up the wax crystal structure artificially, so that relatively good filtration rates were obtained and a wash could be applied to the wax cake on the filter to displace the retained oil.. This method was identified as the Weir process or filter-aid dewaxing process and was placed in commercial operation about 1928 (30). It was the first commercial process capable of successfully dewaxing the intermediate distillates, as well as paraffin distillates of lowest viscosity and residual stocks of highest viscosity. 

In operation of the filter-aid dewaxing process, the waxy stock is diluted with naph-... 

The chilled oil-naphtha solution containing crystallized wax and the filter aid is then filtered by means of a continuous vacuum filter or an intermittent pressure leaf filter. Increased dewaxed oil yields are realized by applying a cold naphtha displacement wash to the wax cake on the filter. The pour point of the dewaxed oil is usually 25° to 35° F. higher than the filtering temperature. 

Basically, the process employs a selective solvent or mixture of solvents which have adequate oil solubility to permit operation at reduced temperatures without the separation of a second liquid or oil phase and in which the wax solubility is so low that the resulting dewaxed oil pour point is substantially the same as or within a few degrees of the dewaxing temperature. Generally, the solvent employed is a mixture of an aromatic solvent to obtain the required oil solubility and a polar solvent—for example, a ketone— to produce highly crystalline, easily filterable wax. 

In present-day commercial practice, waxy oil charge is blended with 1 to 3 volumes of liquid propane at a temperature sufficiently high (120° to 160° F.) to ensure complete solution of the wax. The mixture is first cooled by exchange with cold filtrate and then charged to a batch chilling vessel, in which temperature is reduced to that required to obtain the desired pour point of the dewaxed oil, by evaporation of propane from the solution. Cold propane is injected into the vessel in order to maintain the propane-oil ratio approximately constant. The crystallized wax is removed by filtration on a continuous rotary filter (59) under a pressure of about 4 to 8 pounds per square inch. 

In commercial operations of the dewaxing step, the mixture of wax-bearing oil and solvent is heated to ensure complete solution of the wax and is then passed through exchangers and chillers to totally enclosed rotary drum filters at a temperature about 10° to 15° F. below the desired pour point of the dewaxed oil. Vacuum for filtration is applied to the filtrate receiving vessel. The wax cake on the filter is washed with cold solvent, to remove the occluded oil-solvent solution. Sulfur dioxide superheated gas is used for stripping the solvent from the oil-solution and the wax phase, and the last traces of solvent are removed under vacuum. 

Consideration of installation costs cannot be restricted to the solvent refining step. A residuum of 460° F. flash point usually will contain all usable lubricating oil. In addition to the cost of solvent extraction facilities, the expense of equipment to fractionate the oil into usable cuts, to deasphalt, to dewax, and to clay filter, all must be... 

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... 

In solvent dewaxing, the oil is diluted with a solvent that has a high affinity for oil, chilled to precipitate the wax, filtered to remove the wax, stripped of solvent, and dried. The solvents (principally propane, naphtha, methyl ethyl ketone-MEK) act as diluents for the high molecular weight oil fractions to reduce the viscosity of the mixture and provide sufficient liquid volume to permit pumping and filtering. Wax produced by the solvent dewaxing process is used to make (1) paraffins for candle wax, (2) microwax for cosmetics, and (3) wax for petroleum jelly. 

Attempts have been made to recover the wax using cold and hot extraction (2). Wax yields of 1.29-1.82% of the crade oU are obtained. Continuous dewaxing of rice bran oil by chilling the oil or miscella to less than 20°C followed by filtration through plate and frame filters is practiced. Kinsey and Hummell (44) reported on the use of sodium silicate as an aid for dewaxing. The characteristics and physical properties of a purified rice bran wax are similar to carnauba wax (45). 

One method used to assure clear oil is to add a polish filtration step after the centrifuge dewaxing operation, as shown in Figure 9c With this system, a shp stream of oil is cooled and analyzed through a highly sensitive turbidity meter immediately after the deodorizer. When a haze is detected, the flow of oil is diverted through a chiller, filter aid added, and the mixture sent to a crystallizing tank. After... 

P6 Cylinder stock 615-830 Unfinished heavy-oil stocks used directly as lubricants for steam engine cylinders usually filtered but not dewaxed... 

Derivation A natural resin secreted by the insect Laccifer lacca (Coccus lacca) and deposited on the twigs of trees in India. After collection, washing, and purification by melting and filtering, it is formed into thin sheets, that are later fragmented into flakes of orange shellac. This may be dewaxed and bleached to a transparent product. Soluble in alcohol insoluble in water. 

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