Ketone Dewaxing Processes

Solvent Treatment. Solvent processes can be divided into two main categories, solvent extraction and solvent dewaxing. The solvent used in the extraction processes include propane and cresyHc acid, 2,2 -dichlorodiethyl ether, phenol (qv), furfural, sulfur dioxide, benzene, and nitrobenzene. In the dewaxing process (28), the principal solvents are benzene, methyl ethyl ketone, methyl isobutyl ketone, propane, petroleum naphtha, ethylene dichloride, methylene chloride, sulfur dioxide, and iV-methylpyrroHdinone. 

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. 

The first commercial installation employing special organic solvents in dewaxing was made by the Indian Refining Co. in 1927 (32). The process as originally used employed a mixture of acetone and benzene as the special solvents, based on the inventions of F. X. Govers. The process as further developed employs a mixture of methyl ethyl ketone and aromatic solvents such as benzene and toluene. It is known as the solvent dewaxing process. 

MEK dewaxing a continuous solvent dewaxing process in which the solvent is generally a mixture of methyl ethyl ketone and toluene. 

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. 

Examples of proposed DCC coolants include liquid butane for the seawater desalination process (section 8.4.7) and methyl ethyl ketone for the Dilchill lubricating oil dewaxing process (Bushnell and Eagen, 1975). Chlorinated hydrocarbons, fluorocarbons and CO2 have also found application in specific cases. 

The majority of dewaxing processes today use Methyl Ethyl Ketone (MEK), Methyl IsoButyl Ketone (MIBK), mixtures of MEK and MIBK, or mixtures of MEK and Toluene or propane. There are advantages and disadvantages to each solvent system. 

The use of two dewaxing methods, i.e., pressing and centrifuging, has been a source of great expense to refiners. Almost all new plants employ solvents (Table 11-1). The Weir filter-aid process (patented in 1924) was the first commercial solvent dewaxing process. It involved the filtration of chilled naphtha oil solution mixed with about 15 per cent of filter aid (fuller s or diatomaceous earth). Modem solvent processes employ special solvents, such as acetone-benzene, trichlorethylene, ethylene dichloride-benzol (Barisol), smd particularly propane and methyl ethyl ketone-benzol. ... 

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. 

Methyl ethyl ketone may also he produced hy the catalyzed dehydrogenation of sec-hutanol over zinc oxide or brass at about 500°C. The yield from this process is approximately 95%. MEK is used mainly as a solvent in vinyl and acrylic coatings, in nitrocellulose lacquers, and in adhesives. It is a selective solvent in dewaxing lubricating oils where it dissolves the oil and leaves out the wax. MEK is also used to synthesize various compounds such as methyl ethyl ketone peroxide, a polymerization catalyst used to form acrylic and polyester polymers and methyl pentynol by reacting with acetylene ... 

Dewaxing (Figure 4.17) processes also produce heater stack gas (carbon monoxide, sulfur oxides, nitrogen oxides, and particulate matter) as well as hydrocarbon emission such as fugitive propane and fugitive solvents. Steam stripping wastewater (oil and solvents) and solvent recovery wastewater (oil and propane) are also produced. The fugitive solvent emissions may be toxic (toluene, methyl ethyl ketone, methyl isobutyl ketone). 

Solvent dewaxing removes wax from lubricating oil stocks, promoting crystallization of the wax. Solvents include furfural, phenol, cresylic acid-propane (DuoSol), liquid sulfur dioxide (Eleleanu process), B,B-dichloroethyl ether, methyl ethyl ketone, nitrobenzene, and sulfur-benzene. The process yields de-oiled waxes, wax-free lubricating oils, aromatics, and recovered solvents. 

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. 

Solvents in use for wax removal include propane, which also serves as an autorefrigerant for the process by solvent evaporation, methyl ethyl ketone (MEK)-toluene mixtures, and methyl isobutyl ketone (MIBK). The last two systems are in widest use at present. MEK-benzene was once a common solvent combination for dewaxing but has now been abandoned from benzene toxicity considerations. 

The waxy raffinate from the solvent-extraction process is mixed with methyl ethyl, ketone, chilled, and filtered to remove the precipitated wax, after which the ketone is distilled away from the dewaxed oil. 

Solvent dewaxing removes wax (normal paraffins) from deasphalted lube base stocks. The main process steps include mixing the feedstock with the solvent, chilling the mixture to crystallize wax, and recovering the solvent. Commonly used solvents include toluene and methyl ethyl ketone (MEK). Methyl isobutyl ketone (MIBK) is used in a wax deoiling process to prepare food-grade wax. 

The largest industrial SRNF plant is installed in the petrochemical industry (Bhore et al., 1999). Wax is a monoester of fatty acids that severely modifies the properties of lube oil and must therefore be removed (Hart et al., 1995). The traditional process of dewaxing involved the cooling of a hydrocarbon mixture in solvent or solvent mixtures (methyl ethyl keton, acetone) to temperatures typically ranging from —5 to — 18°C. In this chilling section, waxy components coagulated and were precipitated or filtered the solvent in the filtrate was removed by evaporation and reused in the process (Cuperus and Ebert, 2002). 

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