Paraffin Waxes from Petroleum
Crude oils and their products contain a large number of individual paraffin. The main physical characteristics of the most frequently occurring alkanes are listed in Table, indicating that n-pentane is already liquid and n-hexadecane solid at ambient temperature.
Classification: Aliphatic organic compd.; hydrocarbon
Definition: Solid mixture of hydrocarbons obtained from petroleum fractions by solvent crystallization or by the sweating process; consists predominantly of straight-chain hydrocarbons > C20; characterized by relatively large crystals
Properties: Colorless to wh. cyst. solid; odorless; tasteless; greasy feel; sol. in benzene, gasoline. chloroform. ether, carbon disulfide. oils; misc. with fats; insole. in water, alcohol; dens. – 0.9; m.p. 50-57 C; flash pt. (CC) 190 C
Toxicology: ACGIH TLV/TWA 2 mg/m3 (fume); TDLo (implant, rat) 120 mg/kg; primary Uses irritant; skin and eye irritant; anesthetic effect; chronic skin exposure can cause dermatitis. abnormal pigmentation. etc.; fumes cause lung damage; questionable carcinogen; experimental tumorigenic by implantation; many paraffin waxes contain carcinogens; TSCA listed
Precaution: Dangerous fire hazard; will burn above 198 C; burns with luminous flame; when heated, produces irritating fumes NFPA: Health 0, Flammability 1, Reactivity 0 Storage: Store away from heat; store in cool, dry place; refrigerate
Uses Candles; paper coating; glazing agent, protective sealant for foods; food coatings; plastics lubricant; hot-melt carpet backing; floor polishes; the masticatory substance in chewing gum; raising m.p. of ointments; antiozonant for rubber; Mfg. of varnishes: in elec. insulators: perfume extraction (from flowers); paper sizing agent; waterproofing agent for textiles, leather, paper, cork, wood: solvent for inks; emollient, visit. control agent, moisturizer, the stabilizer for cosmetics; pharmaceuticals (stiffener, tablet coating); defoamer, surf. lubricant in food-contact coatings; in cellophane for food pkg.; wood preservative for Agric. Prods. pkg.; pkg. material for irradiated foods.
is of two general types: (i) paraffin wax in petroleum distillates and (ii) microcrystalline wax in petroleum residua.
Paraffin wax is a solid crystalline mixture of straight-chain (normal) hydrocarbons ranging from C20 to C34 and possibly higher, that is, CH3(CH2) CH3, where n218. It is distinguished by its solid state at ordinary temperatures (25°C, 77°F) and low viscosity (35-45 SUS at 99°C, 210°F) when melted. However, in contrast to petroleum wax, petrolatum (petroleum jelly), although solid at ordinary temperatures, does, in fact, contain both solid and liquid hydrocarbons. It is essentially a low-melting, ductile, microcrystalline wax.
Microcrystalline waxes f0rm approximately 1-2% w/w of crude oil and arc valuable products having numerous applications. These waxes are usually obtained from heavy lube distillates by solvent dewaxing and from tank bottom sludge by acid clay treatment. However, these crude wax products usually contain appreciable quantity (10-20% w/w) of residual oil and, as such, are not suitable for many applications such as paper coating, electrical insulation, textile printing, and polishes.
Paraffin wax from a solvent dewaxing operation (Speight. 2014) is commonly known as slack was, and the processes employed for the production of waxes arc aimed at de-oiling the slack wax (petroleum wax concentrate).
Was “waling was originally used to separate wax fractions with various melting points from the wax obtained from shale oils. Wax sweating is Still used to some extent but is being replaced by the more convenient crystallization process. In wax sweating, a cake of slack wax is slowly warmed to a temperature at which the oil in the wax and the lower-melting waxes become fluid and drip (or sweat) from the bottom of the cake. leaving a residue of higher-melting wax. Sweated waxes generally contain small amounts of unsaturated aromatic and sulfur compounds, which are the source of unwanted color, odor, and the aisle that reduce the ability of the wax to resist oxidation; the commonly used method of removing these impurities is clay treatment of the molten wax.
Wax crystallization, like wax sweating, separates slack wax into Inactions. but instead of using the differences in melting points, it makes use of the different solubility of the wax fractions in a solvent. such as the ketone used in the dewaxing process.When a mixture of ketone and slack wax is heated, the slack wax usually dissolves completely. and it’ the solution is cooled slowly, a temperature is reached at which a crop of wax crystals is formed. These crystals will all be of the same melting point. and if they arc removed by filtration, a wax fraction with a specific melting point is obtained. If the clear filtrate is further cooled, the second crop of wax crystals with a lower melting point is obtained. Thus, by alternate cooling and filtration, the slack wax can be subdivided into a large number of wax fractions, each with different melting points.
Chemically. paraffin wax is a mixture of saturated aliphatic hydrocarbons (with the general formula.Wax is the residue extracted when dewaxing lubricant oils and they have a crystalline structure with canton number greater than 12. The main characteristics of wax are (i) colorless. (ii) Odorless. (iii) translucent, and (iv) a melting point above 45°C (113°F).
The melting point of paraffin was (ASTM D87. IP 55) has both direct and indirect significance in most wax utilization. All wax grades are commercially indicated in a range of melting temperatures rather than at a single value, and a range of I °C (2°F) usually indicates a good degree of refinement. Other common physical properties that help to illustrate the degree of refinement of the wax are color (ASTM D156), oil content (ASTM D721, IP 158), and viscosity (ASTM D88, ASTM D445, IP 71).
Fully refined paraffin waxes are a hard, white crystalline material derived from petroleum. Paraffin waxes are predominately composed of normal, straight-chain hydrocarbons. The water-repellent and thermoplastic properties of paraffin waxes make them ideal for many applications. Typical end uses include cereal, delicatessen, and household wrap, corrugated containers, candles, cheese and vegetable coatings, and hot melt adhesives.
Paraffin wax is mostly found as a white, odorless, tasteless, waxy solid, with a typical melting point between about 46 and 68°C (115 and 154°F) and a density of approximately 900, is insoluble in water, but soluble in ether, benzene, and certain esters. Paraffin wax is often classed as a stable chemical since it is unaffected by most common chemical reagents but burns readily.
Microcrystalline waxes are a type of wax produced by de-oiling petrolatum, as part of the petroleum refining process. In contrast to the more familiar paraffin wax, which contains mostly unbranched alkanes, microcrystalline wax contains a higher percentage of iso-paraffin (branched) and naphthene hydrocarbons. It is characterized by the fineness of its crystals in contrast to the larger crystal of paraffin wax. It consists of high-molecular-weight saturated aliphatic hydrocarbons. It is generally darker, more viscous, denser, tackier, and more elastic than paraffin waxes, and has a higher molecular weight and melting point. The elastic and adhesive characteristics of microcrystalline waxes are related to the non-straight-chain components that they contain. The typical microcrystalline wax crystal structure is small and thin, making them more flexible than paraffin wax.
ASTM test method comment
ASTM D87 Used for paraffin wax only
Paraffin wax is generally white in color, whereas microcrystalline wax and petrolatum range from white to almost black. A fully refined wax should be virtually colorless (water-white) when examined in the molten state. The absence of color is of particular importance in wax used for pharmaceutical purposes or for the manufacture of food wrappings. The significance of the color of microcrystalline wax and petrolatum depends on the use for which they are intended. In some applications (e.g., the manufacture of corrosion preventives), color may be of little importance.
The Saybolt color test method (ASTM D156) is used for nearly colorless waxes, and in this method, a melted sample is placed in a heated vertical tube mounted alongside a second tube containing standard color disks. An optical viewer allows simultaneous viewing of both tubes. The level of the sample is decreased until its color is lighter than that of the standard, and the color number above this level is the Saybolt color.
The test method for the color of petroleum products (ASTM DI500, IP 196) is for wax and petrolatum that are too dark for the Saybolt colorimeter. A liquid sample is placed in the test container, a glass cylinder of 30-35 min ID, and compared with colored glass disks ranging in value from 0-5 to 8-0, using a standard light source. If an exact match is not found, and the sample color falls between two standard colors, the higher of the two colors is reported.
The Lovibond Tintometer (IP 17) is used to measure the tint and depth of color by comparison with a series of red, yellow, and blue standard glasses. Waxes and petrolatum are tested in the molten state, and a wide range of cell sizes is available for different types.
February 17, 2016